Modified electrical survey for effective leakage detection at concrete hydraulic facilities

NASA Astrophysics Data System (ADS)

Lee, Bomi; Oh, Seokhoon

2018-02-01

Three original electrode arrays for the effective leakage detection of concrete hydraulic facilities through electrical resistivity surveys are proposed: 'cross-potential', 'direct-potential' and modified tomography-like arrays. The main differences with respect to the commonly used arrays are that the current line-sources are separated from potential pole lines and floated upon the water. The potential pole lines are located directly next to the facility in order to obtain intuitive data and useful interpretations of the internal conditions of the hydraulic facility. This modified configuration of the array clearly displays the horizontal variation of the electrical field around the damaged zones of the concrete hydraulic facility, and any anomalous regions that might be found between potential poles placed across the facilities. In order to facilitate the interpretation of these modified electrical surveys, a new and creative way of presenting the measurements is also proposed and an inversion approach is provided for the modified tomography-like array. A numerical modeling and two field tests were performed to verify these new arrays and interpretation methods. The cross and direct potential array implied an ability to detect small variations of the potential field near the measurement poles. The proposed array showed the overall potential distribution across the hydraulic facility which may be used to assist in the search of trouble zones within the structure, in combination with the traditional electrical resistivity array.

Integrated geophysical characterisation of Sunyani municipal solid waste disposal site using magnetic gradiometry, magnetic susceptibility survey and electrical resistivity tomography

NASA Astrophysics Data System (ADS)

Appiah, Isaac; Wemegah, David Dotse; Asare, Van-Dycke Sarpong; Danuor, Sylvester K.; Forson, Eric Dominic

2018-06-01

Non-invasive geophysical investigation using magnetic gradiometry, magnetic susceptibility survey and electrical resistivity tomography (ERT) was carried out on the Sunyani Municipal Assembly (SMA) solid waste disposal (SWD) site. The study was aimed at delineating the physical boundaries and the area extent of the waste deposit, mapping the distribution of the waste at the site, detecting and delineating zones of leachate contamination and its preferential migration pathways beneath the waste deposit and its surroundings. The results of both magnetic susceptibility and gradiometric methods displayed in anomaly maps clearly delineated the physical boundaries of the waste deposit with an approximate area extent of 82,650 m2 that are characterised by high magnetic susceptibilities between 426 × 10-5 SI and 9890 × 10-5 SI. They also revealed high magnetic anomalies erratically distributed within the waste deposit attributable to its heterogeneous and uncontrolled nature. The high magnetic anomalies outside the designated waste boundaries were also attributed to indiscriminate deposition of the waste. Similarly, the ERT sections delineated and characterised zones of leachate contamination beneath the waste body and its close surroundings as well as pathways for leachate migration with low resistivity signatures up to 43.9 Ωm. In spite of the successes reported herein using the ERT, this research also revealed that the ERT is less effective in estimating the thickness of the waste deposit in unlined SWD sites due to leachate infiltration into the ground beneath it that masks the resistivities of the top level ground and makes it indistinguishable from the waste body.

Monitoring of olive oil mills' wastes using electrical resistivity tomography techniques

NASA Astrophysics Data System (ADS)

Simyrdanis, Kleanthis; Papadopoulos, Nikos; Kirkou, Stella; Sarris, Apostolos; Tsourlos, Panagiotis

2014-08-01

Olive oil mills' wastes (OOMW) are one of the byproducts of the oil production that can lead to serious environmental pollution when they are deposited in ponds dug on the ground surface. Electrical Resistivity Tomography (ERT) method can provide a valuable tool in order to monitor through time the physical flow of the wastes into the subsurface. ERT could potentially locate the electrical signature due to lower resistivity values resulting from the leakage of OOMW to the subsurface. For this purpose, two vertical boreholes were installed (12m depth, 9 m apart) in the vicinity of an existing pond which is filled with OOMW during the oil production period. The test site is situated in Saint Andreas village about 15km south of the city of Rethymno (Crete, Greece). Surface ERT measurements were collected along multiple lines in order to reconstruct the subsurface resistivity models. Data acquisition was performed with standard and optimized electrode configuration protocols. The monitoring survey includes the ERT data collection for a period of time. The study was initiated before the OOMW were deposited in the pond, so resistivity fluctuations are expected due to the flow of OOMW in the porous subsurface media through time. Preliminary results show the good correlation of the ERT images with the drilled geological formations and the identification of low resistivity subsurface zone that could be attributed to the flow of the wastes within the porous layers.

Imaging of Ground Ice with Surface-Based Geophysics

DTIC Science & Technology

2015-10-01

terrains. Electrical Resistivity Tomography (ERT), in particular, has been effective for imaging ground ice. ERT measures the ability of materials to...13 2.2.1 Electrical resistivity tomography (ERT...Engineer Research and Development Center ERT Electrical Resistivity Tomography GPS Global Positioning System LiDAR Light Detection and Ranging SIPRE

Application of electrical resistivity tomography techniques for mapping man-made sinkholes

NASA Astrophysics Data System (ADS)

Rey, J.; Martínez, J.; Hidalgo, C.; Dueñas, J.

2012-04-01

The suitability of the geophysical prospecting by electrical resistivity tomography to detect and map man-made subsurface cavities and related sinkholes has been studied in the Linares abandoned mining district (Spain). We have selected for this study four mined sectors constituted of different lithologies: granite and phyllites of Paleozoic age, and Triassic shales and sandstones. In three of these sectors, detail underground topographic surveys were carried out to chart the position and dimensions of the mining voids (galleries and chamber), in order to analyze the resolution of this methodology to characterize these cavities by using different electrode arrays. The results are variable, depending on the depth and diameter of the void, the selected electrode array, the spacing between electrodes, geological complexity and data density. These results also indicate that when the cavity is empty, an anomaly with a steep gradient and high resistivity values is registered, because the air that fills the mining void is dielectric, while when the cavities are filled with fine grain sediments, frequently saturated in water, the electrical resistance is lower. In relation with the three different multi-electrode arrays tested, the Wenner-Schlumberger array has resulted to offer the maximum resolution in all these cases, with lower and more stable values for the RMS than the other arrays. Therefore, this electrode array has been applied in the fourth studied sector, a former mine near the city centre of Linares, in an area of urban expansion in which there are problems of subsidence. Two sets of four electrical tomography profiles have been carried out, perpendicular to each other, and which have allowed reaching depths of research between 30-35 m. This net-array allowed the identification of two shallow anomalies of low resistivity values, interpreted as old mining galleries filled with fine material saturated in water. It also allows detecting two fractures, correlated in the profiles and which can be mapped to more than 25 m in depth. As showed by this case study, electrical resistivity tomography can be a suitable tool in sub-surface cavities detection and man-made sinkhole investigations.

Seismics-electrics Joint Interpretation in a gypsiferous context.

NASA Astrophysics Data System (ADS)

Marzan, Ignacio; Marti, David; Lobo, Agustin; Alvarez-Marron, Joaquina; Carbonell, Ramon

2016-04-01

The main objective of this study is to improve the geophysical characterization resulting from a shallow 3D high resolution travel-time tomography survey (500x500m). This survey was acquired in Villar de Cañas (Cuenca, Spain) in late 2013 and early 2014. Lithology down to 150 m depth in this site is characterized by endorheic sediments, mainly siltstone and gypsum. After processing the tomography data, the velocity model showed a good correlation with geology models and borehole data except for the siltstone-gypsum transition. The model involves two lithological limits: the "transition layer - massive gypsum layer" (well resolved by a relatively high velocity contrast) and the "siltstone layer - transition layer" (constrained only in the central part of the model by a relatively low velocity contrast). As electrical resistivity is able to characterize shale-gypsum transitions, we complemented the seismic data with results from a collection of 2D ERT surveys, for which we build a new 3D grid with 2 parameters by node: velocity and resistivity. In order to derive a geological interpretation, we apply a statistical classification method (Linear Discriminant Analysis) to the new bi-parametric grid, using reference classes from well logs. This process results on a final 3D lithological model with less ambiguity and thus with a better definition of the two limits under discussion. Our study shows that the integration of seismic and electric methods significantly improves geological characterization in a gypsiferous context.

Joint Interpretation of Geological, Magnetic, AMT, and ERT Data for Mineral Exploration in the Northeast of Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Zhang, Gang; Lü, Qing-Tian; Zhang, Gui-Bin; Lin, Ping-Rong; Jia, Zheng-Yuan; Suo, Kui

2018-03-01

The integrated interpretation of data from various technologies has the potential to obtain a more accurate estimate of subterranean earth properties. In this paper, we implement the joint interpretation of geological and geophysical data for mineral exploration in the northeastern region of Inner Mongolia, China. The joint application of several methodologies reduces the exploration risk. We first determined an approximate and large potential area for mineral exploration with geological data and magnetic data interpretation in Gaoerqi. Results from the two types of data analysis show that the ore deposit strikes roughly east in the northern part of the Gaoerqi mining area. Next, we employed the audio-magnetotelluric (AMT) method to study the subterranean electrical resistivity distribution and divide the earth into four layers. Inverted resistivity sections from the AMT data illustrate that the ore deposits are likely developed in the low-resistivity zone of the survey area from the land surface to 300-m depth. Finally, the high-resolution borehole-to-surface electrical resistivity tomography (ERT) method was employed for further investigation of the location and attitude of the potential ore deposits. Inverted resistivity sections from the ERT data show that two prospective areas for mineral exploration were observed in the west of the survey area and that the eastern portion of the survey area warrants further investigation.

Combined GPR and ERT exploratory geophysical survey of the Medieval Village of Pancorbo Castle (Burgos, Spain)

NASA Astrophysics Data System (ADS)

Fernández-Álvarez, José-Paulino; Rubio-Melendi, David; Quirós Castillo, Juan Antonio; González-Quirós, Andrés; Cimadevilla-Fuente, David

2017-09-01

Ground-penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) have been fruitfully employed for archaeological purposes. An area at the Pancorbo medieval site in Burgos (Spain) has been jointly explored by GPR and ERT in the search for the buried remains of the Pancorbo medieval village. After data collection, quality control and merging, a shallow depth of interest was identified and studied in detail. 3D resistivity simulation, considering sensible geometrical structures of the targets helped discover anomalies present in the area. On the other hand, visual GPR inspection was considerably enhanced by trace energy attribute analysis which provided a plan view of the existing anomalies. Two posterior archaeological excavations have a very good correlation between the identified anomalies and the excavated remains. The survey also provides hints for the continuation of the excavation.

2-D Electrical Resistivity Tomography (ERT) Assessment of Ground Failure in Urban Area

NASA Astrophysics Data System (ADS)

Nordiana, M. M.; Bery, A. A.; Taqiuddin, Z. M.; Jinmin, M.; Abir, I. A.

2018-04-01

This study was carried out to assess the foundation defects around an urban area in Selangor, Malaysia using 2-D electrical resistivity tomography (ERT). The affected structure is a three storey houses and having severe foundation-based cracks. Six 2-D ERT survey lines with 5 m minimum electrode spacing using Pole-dipole array were executed parallel to building’s wall. Four boreholes were conducted to identify the depth to competent layer to verify the 2-D ERT results. Inversion model of 2-D resistivity show that the study area consists of two main zones. The first zone is a low resistivity value (<100 Ωm), which appears to be a zone that is fully saturated with sandy silt and this could be an influence factor the increasing water level because sandy silt is highly permeable in nature and alluvium (silt, sand and clay), boulder (1200-3500 Ωm) or highly weathered with the resistivity values of 100-1000 Ωm at 20-70 m depth. The second zone is the granite bedrock of more than 3500 Ωm with depth greater than 70 m. These results were complimented and confirmed by borehole records. The ERT and borehole record suggest that the clay, sand, saturated zone, highly weathered zone and boulders at foundation depths may lead to ground movements which affected the stability of the building.

Improving resistivity survey resolution at sites with limited spatial extent using buried electrode arrays

NASA Astrophysics Data System (ADS)

Kiflu, H.; Kruse, S.; Loke, M. H.; Wilkinson, P. B.; Harro, D.

2016-12-01

Electrical resistivity tomography (ERT) surveys are widely used in geological, environmental and engineering studies. However, the effectiveness of surface ERT surveys is limited by decreasing resolution with depth and near the ends of the survey line. Increasing the array length will increase depth of investigation, but may not be possible at urban sites where access is limited. One novel method of addressing these limitations while maintaining lateral coverage is to install an array of deep electrodes. Referred to here as the Multi-Electrode Resistivity Implant Technique (MERIT), self-driving pointed electrodes are implanted at depth below each surface electrode in an array, using direct-push technology. Optimal sequences of readings have been identified with the "Compare R" method of Wilkinson. Numerical, laboratory, and field case studies are applied to examine the effectiveness of the MERIT method, particularly for use in covered karst terrain. In the field case studies, resistivity images are compared against subsurface structure defined from borings, GPR surveys, and knowledge of prior land use. In karst terrain where limestone has a clay overburden, traditional surface resistivity methods suffer from lack of current penetration through the shallow clay layer. In these settings, the MERIT method is found to improve resolution of features between the surface and buried array, as well as increasing depth of penetration and enhancing imaging capabilities at the array ends. The method functions similar to a cross-borehole array between horizontal boreholes, and suffers from limitations common to borehole arrays. Inversion artifacts are common at depths close to the buried array, and because some readings involve high geometric factors, inversions are more susceptible to noise than traditional surface arrays. Results are improved by using errors from reciprocal measurements to weight the data during the inversion.

Anatomy of terminal moraine segments and implied lake stability on Ngozumpa Glacier, Nepal, from electrical resistivity tomography (ERT).

PubMed

Thompson, Sarah S; Kulessa, Bernd; Benn, Douglas I; Mertes, Jordan R

2017-04-20

Moraine-dammed lakes at debris-covered glaciers are becoming increasingly common and pose significant outburst flood hazards if the dam is breached. While moraine subsurface structure and internal processes are likely to influence dam stability, only few sites have so far been investigated. We conducted electrical resistivity tomography (ERT) surveys at two sites on the terminal moraine complex of the Ngozumpa Glacier, Nepal, to aid assessment of future terminus stability. The resistivity signature of glacier ice at the site (100-15 kΩ m) is more consistent with values measured from cold glacier ice and while this may be feasible, uncertainties in the data inversion introduce ambiguity to this thermal interpretation. However, the ERT data does provide a significant improvement to our knowledge of the subsurface characteristics at these sites, clearly showing the presence (or absence) of glacier ice. Our interpretation is that of a highly complex latero-terminal moraine, resulting from interaction between previous glacier advance, recession and outburst flooding. If the base-level Spillway Lake continues to expand to a fully formed moraine-dammed glacial lake, the degradation of the ice core could have implications for glacial lake outburst risk.

Anatomy of terminal moraine segments and implied lake stability on Ngozumpa Glacier, Nepal, from electrical resistivity tomography (ERT)

NASA Astrophysics Data System (ADS)

Thompson, Sarah S.; Kulessa, Bernd; Benn, Douglas I.; Mertes, Jordan R.

2017-04-01

Moraine-dammed lakes at debris-covered glaciers are becoming increasingly common and pose significant outburst flood hazards if the dam is breached. While moraine subsurface structure and internal processes are likely to influence dam stability, only few sites have so far been investigated. We conducted electrical resistivity tomography (ERT) surveys at two sites on the terminal moraine complex of the Ngozumpa Glacier, Nepal, to aid assessment of future terminus stability. The resistivity signature of glacier ice at the site (100-15 kΩ m) is more consistent with values measured from cold glacier ice and while this may be feasible, uncertainties in the data inversion introduce ambiguity to this thermal interpretation. However, the ERT data does provide a significant improvement to our knowledge of the subsurface characteristics at these sites, clearly showing the presence (or absence) of glacier ice. Our interpretation is that of a highly complex latero-terminal moraine, resulting from interaction between previous glacier advance, recession and outburst flooding. If the base-level Spillway Lake continues to expand to a fully formed moraine-dammed glacial lake, the degradation of the ice core could have implications for glacial lake outburst risk.

Anatomy of terminal moraine segments and implied lake stability on Ngozumpa Glacier, Nepal, from electrical resistivity tomography (ERT)

PubMed Central

Thompson, Sarah S.; Kulessa, Bernd; Benn, Douglas I.; Mertes, Jordan R.

2017-01-01

Moraine-dammed lakes at debris-covered glaciers are becoming increasingly common and pose significant outburst flood hazards if the dam is breached. While moraine subsurface structure and internal processes are likely to influence dam stability, only few sites have so far been investigated. We conducted electrical resistivity tomography (ERT) surveys at two sites on the terminal moraine complex of the Ngozumpa Glacier, Nepal, to aid assessment of future terminus stability. The resistivity signature of glacier ice at the site (100–15 kΩ m) is more consistent with values measured from cold glacier ice and while this may be feasible, uncertainties in the data inversion introduce ambiguity to this thermal interpretation. However, the ERT data does provide a significant improvement to our knowledge of the subsurface characteristics at these sites, clearly showing the presence (or absence) of glacier ice. Our interpretation is that of a highly complex latero-terminal moraine, resulting from interaction between previous glacier advance, recession and outburst flooding. If the base-level Spillway Lake continues to expand to a fully formed moraine-dammed glacial lake, the degradation of the ice core could have implications for glacial lake outburst risk. PMID:28425458

Assessment of correlation between geophysical and hydrogeological parameters of volcanic deposits at Bandama Caldera (Gran Canaria, Canary Islands, Spain)

NASA Astrophysics Data System (ADS)

Casas, Albert; Himi, Mahjoub; Estévez, Esmeralda; Lovera, Raúl; Sendrós, Alexandre; Palacios-Díaz, M. Pino; Tapias, Josefina C.; Cabrera, M. Carmen

2015-04-01

The characterization of the preferential areas of water infiltration through the vadose zone is of paramount importance to assess the pollution vulnerability of the underlying aquifers. Nevertheless, geometry and the hydraulic conductivity of each geological unit which constitute the unsaturated zone are difficult to study from traditional techniques (samples from trenches) and normally do not go beyond a meter depth from of the surface. On the other hand, boreholes are expensive and provide only local information not always representative of the whole unsaturated zone. For this reason, geophysical techniques and among them the electrical resistivity tomography method can be applicable in volcanic areas, where basaltic rocks, pyroclastic and volcanic ash-fall deposits have a wide range of values. In order to characterize the subsurface geology below the golf course of Bandama (Gran Canaria Island), irrigated with reclaimed wastewater, a detailed electrical resistivity tomography survey has been carried out. This technique has allowed to define the geometry of the existing geological formations by their high electrical resistivity contrast. Subsequently, in representative outcrops the value of resistivity of each of these lithologies has been measured and simultaneously undisturbed samples have been taken measuring the hydraulic conductivity in the laboratory. Finally a statistical correlation between both variables has been established for evaluating the vulnerability to groundwater pollution at different zones of the golf course.

Reconstructing former urban environments by combining geophysical electrical methods and geotechnical investigations—an example from Chania, Greece

NASA Astrophysics Data System (ADS)

Soupios, P. M.; Loupasakis, C.; Vallianatos, F.

2008-06-01

Nowadays, geophysical prospecting is implemented in order to resolve a diversity of geological, hydrogeological, environmental and geotechnical problems. Although plenty of applications and a lot of research have been conducted in the countryside, only a few cases have been reported in the literature concerning urban areas, mainly due to high levels of noise present that aggravate most of the geophysical methods or due to spatial limitations that hinder normal method implementation. Among all geophysical methods, electrical resistivity tomography has proven to be a rapid technique and the most robust with regard to urban noise. This work presents a case study in the urban area of Chania (Crete Island, Greece), where electrical resistivity tomography (ERT) has been applied for the detection and identification of possible buried ancient ruins or other man-made structures, prior to the construction of a building. The results of the detailed geophysical survey indicated eight areas of interest providing resistivity anomalies. Those anomalies were analysed and interpreted combining the resistivity readings with the geotechnical borehole data and the historical bibliographic reports—referring to the 1940s (Xalkiadakis 1997 Industrial Archaeology in Chania Territory pp 51-62). The collected ERT-data were processed by applying advanced algorithms in order to obtain a 3D-model of the study area that depicts the interesting subsurface structures more clearly and accurately.

Identification of different geologic units using fuzzy constrained resistivity tomography

NASA Astrophysics Data System (ADS)

Singh, Anand; Sharma, S. P.

2018-01-01

Different geophysical inversion strategies are utilized as a component of an interpretation process that tries to separate geologic units based on the resistivity distribution. In the present study, we present the results of separating different geologic units using fuzzy constrained resistivity tomography. This was accomplished using fuzzy c means, a clustering procedure to improve the 2D resistivity image and geologic separation within the iterative minimization through inversion. First, we developed a Matlab-based inversion technique to obtain a reliable resistivity image using different geophysical data sets (electrical resistivity and electromagnetic data). Following this, the recovered resistivity model was converted into a fuzzy constrained resistivity model by assigning the highest probability value of each model cell to the cluster utilizing fuzzy c means clustering procedure during the iterative process. The efficacy of the algorithm is demonstrated using three synthetic plane wave electromagnetic data sets and one electrical resistivity field dataset. The presented approach shows improvement on the conventional inversion approach to differentiate between different geologic units if the correct number of geologic units will be identified. Further, fuzzy constrained resistivity tomography was performed to examine the augmentation of uranium mineralization in the Beldih open cast mine as a case study. We also compared geologic units identified by fuzzy constrained resistivity tomography with geologic units interpreted from the borehole information.

Electrical Resistivity Tomography for coal fire mapping over Jharia coal field, India

NASA Astrophysics Data System (ADS)

Pal, S. K.; Kumar, S.; Bharti, A. K.; Pathak, V. K.; Kumar, R.

2016-12-01

Over the decades, coal fires are serious global concern posing grievous hazards to the valuable energy resources, local environments and human life. The coal seam and coal mine fires may be initiated due to improper mining activities, exothermic reactions, lighting, forest fire and other anthropic activities, which burn the coal and may continue underground for decades. The burning of concealed coal seams is a complex process involving numerous ill-defined parameters. Generally, the coal exhibits resistivity of 100 to 500Ωm at normal temperature conditions. During the pyrolysis process, at temperatures greater than 6500C coal became a good conductor with a resistivity of approximately 1 Ωm. The present study deals with the mapping of coal fire over Jharia coal field, India using Electrical Resistivity Tomography (ERT). A state-of-the-art 61-channel 64 electrode FlashRES-Universal ERT data acquisition system has been used for data acquisition in the field. The ERT data have been collected using Gradient array and processed in FlashRES Universal survey data checking program for removing noisy data. Then, filtered output data have been inverted using a 2.5D resistivity inversion program. Low resistivity anomalies over 80m-125m and 320m-390m along the profile are inferred to be active coal fire in seam- XVI at a depth of 25m -35m(Figure 1). High resistivity anomaly over 445m - 510m at a depth of 25m -35m has been delineated, due to void associated with complete combustion of seam- XVI coal, followed by char and ash formation resulting from the coal seam fire. Results prove the efficacy of the ERT study comprising Gradient array for coal fire mapping over, Jharia coal field, India.

Electrical Resistivity Tomography using a finite element based BFGS algorithm with algebraic multigrid preconditioning

NASA Astrophysics Data System (ADS)

Codd, A. L.; Gross, L.

2018-03-01

We present a new inversion method for Electrical Resistivity Tomography which, in contrast to established approaches, minimizes the cost function prior to finite element discretization for the unknown electric conductivity and electric potential. Minimization is performed with the Broyden-Fletcher-Goldfarb-Shanno method (BFGS) in an appropriate function space. BFGS is self-preconditioning and avoids construction of the dense Hessian which is the major obstacle to solving large 3-D problems using parallel computers. In addition to the forward problem predicting the measurement from the injected current, the so-called adjoint problem also needs to be solved. For this problem a virtual current is injected through the measurement electrodes and an adjoint electric potential is obtained. The magnitude of the injected virtual current is equal to the misfit at the measurement electrodes. This new approach has the advantage that the solution process of the optimization problem remains independent to the meshes used for discretization and allows for mesh adaptation during inversion. Computation time is reduced by using superposition of pole loads for the forward and adjoint problems. A smoothed aggregation algebraic multigrid (AMG) preconditioned conjugate gradient is applied to construct the potentials for a given electric conductivity estimate and for constructing a first level BFGS preconditioner. Through the additional reuse of AMG operators and coarse grid solvers inversion time for large 3-D problems can be reduced further. We apply our new inversion method to synthetic survey data created by the resistivity profile representing the characteristics of subsurface fluid injection. We further test it on data obtained from a 2-D surface electrode survey on Heron Island, a small tropical island off the east coast of central Queensland, Australia.

Improved characterisation of measurement errors in electrical resistivity tomography (ERT) surveys

NASA Astrophysics Data System (ADS)

Tso, C. H. M.; Binley, A. M.; Kuras, O.; Graham, J.

2016-12-01

Measurement errors can play a pivotal role in geophysical inversion. Most inverse models require users to prescribe a statistical model of data errors before inversion. Wrongly prescribed error levels can lead to over- or under-fitting of data, yet commonly used models of measurement error are relatively simplistic. With the heightening interests in uncertainty estimation across hydrogeophysics, better characterisation and treatment of measurement errors is needed to provide more reliable estimates of uncertainty. We have analysed two time-lapse electrical resistivity tomography (ERT) datasets; one contains 96 sets of direct and reciprocal data collected from a surface ERT line within a 24h timeframe, while the other is a year-long cross-borehole survey at a UK nuclear site with over 50,000 daily measurements. Our study included the characterisation of the spatial and temporal behaviour of measurement errors using autocorrelation and covariance analysis. We find that, in addition to well-known proportionality effects, ERT measurements can also be sensitive to the combination of electrodes used. This agrees with reported speculation in previous literature that ERT errors could be somewhat correlated. Based on these findings, we develop a new error model that allows grouping based on electrode number in additional to fitting a linear model to transfer resistance. The new model fits the observed measurement errors better and shows superior inversion and uncertainty estimates in synthetic examples. It is robust, because it groups errors together based on the number of the four electrodes used to make each measurement. The new model can be readily applied to the diagonal data weighting matrix commonly used in classical inversion methods, as well as to the data covariance matrix in the Bayesian inversion framework. We demonstrate its application using extensive ERT monitoring datasets from the two aforementioned sites.

Joint geophysical investigation of a small scale magnetic anomaly near Gotha, Germany

NASA Astrophysics Data System (ADS)

Queitsch, Matthias; Schiffler, Markus; Goepel, Andreas; Stolz, Ronny; Guenther, Thomas; Malz, Alexander; Meyer, Matthias; Meyer, Hans-Georg; Kukowski, Nina

2014-05-01

In the framework of the multidisciplinary project INFLUINS (INtegrated FLUid Dynamics IN Sedimentary Basins) several airborne surveys using a full tensor magnetic gradiometer (FTMG) system were conducted in and around the Thuringian basin (central Germany). These sensors are based on highly sensitive superconducting quantum interference devices (SQUIDs) with a planar-type gradiometer setup. One of the main goals was to map magnetic anomalies along major fault zones in this sedimentary basin. In most survey areas low signal amplitudes were observed caused by very low magnetization of subsurface rocks. Due to the high lateral resolution of a magnetic gradiometer system and a flight line spacing of only 50m, however, we were able to detect even small magnetic lineaments. Especially close to Gotha a NW-SE striking strong magnetic anomaly with a length of 1.5 km was detected, which cannot be explained by the structure of the Eichenberg-Gotha-Saalfeld (EGS) fault zone and the rock-physical properties (low susceptibilities). Therefore, we hypothesize that the source of the anomaly must be related to an anomalous magnetization in the fault plane. To test this hypothesis, here we focus on the results of the 3D inversion of the airborne magnetic data set and compare them with existing structural geological models. In addition, we conducted several ground based measurements such as electrical resistivity tomography (ERT) and frequency domain electromagnetics (FDEM) to locate the fault. Especially, the geoelectrical measurements were able to image the fault zone. The result of the 2D electrical resistivity tomography shows a lower resistivity in the fault zone. Joint interpretation of airborne magnetics, geoelectrical and geological information let us propose that the source of the magnetization may be a fluid-flow induced impregnation with iron-oxide bearing minerals in the vicinity of the EGS fault plane.

Sandbox experiments on Uraninite Ore: ERT and SP measurments.

NASA Astrophysics Data System (ADS)

Singh, R. K.

2015-12-01

Nuclear energy, considering its own intrinsic merits, would be a leading source for meeting the energy requirement in present and future scenario. Concealed Uranium deposits under sedimentary cover, with poor surface indications calls for reorientation of survey with large inputs involving integrated geophysical approach. Sand Box experiments have been carried out over Uraninite ore. The tank is a glass fish tank (height 39 cm, length 75 cm, width 30 cm). It was filled with sand up to 35 cm high. The sand was saturated from below to minimize the entrapment of the gas bubbles. The average size for sand grains is ~ 0.295mm. The formation factor of the sand is 3.5, with a negligible surface conductivity because of the coarse nature of the sand grains. The dimension of considered Uraninite ore sample is 4cm x 4cm x 4cm. The depth of top of the ore sample is kept at 3cm. In this paper both resistivity and self-potential measurements were carried out for possible detection of Uraninite. The resistivity measurements were made with 64 non-polarizable electrodes using Electrical Resistivity Tomography (ERT) equipment of FlashRes Universal developed by ZZ Resistivity Imaging Pty. Ltd. We have used screws of length 3cm as electrodes. The separation between these electrodes are ~ 1cm. The resistivity tomography results clearly outlines the target Uraninite body. The resistivity tomography results also detects small heterogeneities associated with air bubbles possibly due to unsaturated pore spaces. SP measurements were made using two non-polarizing Pb/PbCl2 electrodes and a Fluke 289 voltmeter (sensitivity 0.001 mV, internal impedance 100 MOhm). The reference electrode was located on the corner of the sandbox. The other electrode was used to scan the electrical potential at the surface of the sand. SP measurements were made with a spacing of 3 cm over the same ERT profile. The SP results also shows a dip (or a low SP anomaly) over the target ore body sample. Thus, both SP and ERT results show the presence of Uraninite and could be used on the routine basis for possible detection of Uraninite.

Why 1D electrical resistivity techniques can result in inaccurate siting of boreholes in hard rock aquifers and why electrical resistivity tomography must be preferred: the example of Benin, West Africa

NASA Astrophysics Data System (ADS)

Alle, Iboukoun Christian; Descloitres, Marc; Vouillamoz, Jean-Michel; Yalo, Nicaise; Lawson, Fabrice Messan Amen; Adihou, Akonfa Consolas

2018-03-01

Hard rock aquifers are of particular importance for supplying people with drinking water in Africa and in the world. Although the common use of one-dimensional (1D) electrical resistivity techniques to locate drilling site, the failure rate of boreholes is usually high. For instance, about 40% of boreholes drilled in hard rock aquifers in Benin are unsuccessful. This study investigates why the current use of 1D techniques (e.g. electrical profiling and electrical sounding) can result in inaccurate siting of boreholes, and checks the interest and the limitations of the use of two-dimensional (2D) Electrical Resistivity Tomography (ERT). Geophysical numerical modeling and comprehensive 1D and 2D resistivity surveys were carried out in hard rock aquifers in Benin. The experiments carried out at 7 sites located in different hard rock groups confirmed the results of the numerical modeling: the current use of 1D techniques can frequently leads to inaccurate siting, and ERT better reveals hydrogeological targets such as thick weathered zone (e.g. stratiform fractured layer and preferential weathering associated with subvertical fractured zone). Moreover, a cost analysis demonstrates that the use of ERT can save money at the scale of a drilling programme if ERT improves the success rate by only 5% as compared to the success rate obtained with 1D techniques. Finally, this study demonstrates, using the example of Benin, that the use of electrical resistivity profiling and sounding for siting boreholes in weathered hard rocks of western Africa should be discarded and replaced by the use of ERT technique, more efficient.

Using electrical resistivity tomography to assess the effectiveness of managed aquifer recharge in a salinized coastal aquifer.

PubMed

García-Menéndez, Olga; Ballesteros, Bruno J; Renau-Pruñonosa, Arianna; Morell, Ignacio; Mochales, Tania; Ibarra, Pedro I; Rubio, Félix M

2018-01-27

Over 40 years, the detrital aquifer of the Plana de Castellón (Spanish Mediterranean coast) has been subjected to seawater intrusion because of long dry periods combined with intensive groundwater exploitation. Against this backdrop, a managed artificial recharge (MAR) scheme was implemented to improve the groundwater quality. The large difference between the electrical conductivity (EC) of the ambient groundwater (brackish water due to marine intrusion) and the recharge water (freshwater) meant that there was a strong contrast between the resistivities of the brackish water saturated zone and the freshwater saturated zone. Electrical resistivity tomography (ERT) can be used for surveying similar settings to evaluate the effectiveness of artificial recharge schemes. By integrating geophysical data with lithological information, EC logs from boreholes, and hydrochemical data, we can interpret electrical resistivity (ER) with groundwater EC values and so identify freshwater saturated zones. Using this approach, ERT images provided a high-resolution spatial characterization and an accurate picture of the shape and extent of the recharge plume of the MAR site. After 5 months of injection, a freshwater plume with an EC of 400-600 μS/cm had formed that extended 400 m in the W-E direction, 250 m in the N-S direction, and to a depth of 40 m below piezometric level. This study also provides correlations between ER values with different lithologies and groundwater EC values that can be used to support other studies.

Imaging voids beneath bridge bent using electrical resistivity tomography.

DOT National Transportation Integrated Search

2014-02-01

Five electrical resistivity tomography (ERT) profiles and borehole control were acquired beneath two bridges on the bank of the : Gasconade River in order to determine extension of the underground water-filled openings in rock encountered during a dr...

Combining indoors thermo-hygric survey, thermal imaging and Electrical Resistivity Tomography through GIS for the characterization of moisture in historic buildings

NASA Astrophysics Data System (ADS)

Gomez-Heras, Miguel; Garcia-Morales, Soledad; Lopez-Gonzalez, Laura; Ortiz de Cosca, Raquel Otero

2015-04-01

This paper presents the results of the combination, through a GIS, of environmental indoors thermo-hygric parameters and Electrical Resistivity Tomography in the hermit of "Humilladero", a small historic building in the city of Avila (Spain). The Hermit of "humilladero" was built 1548 - 1550 and it underwent several refurbishment works throughout its history until the present day. The hermit is formed by two rooms and a basement: The hermit per se, a sacristy which was added at a later stage towards the east of the hermit and the basement excavated under the sacristy in 1990. The south wall is nowadays half buried by the adjacent street pavement and a staircase attached to the east wall. The walls are built with granite ashlars and the whole building displays severe moisture-related damage, including granular disaggregation of mortars and some ashlars. The most affected areas are the ones buried under the street towards the south and the staircase towards the east where liquid water appears from time to time due to infiltrations through the ground. A mesh of thermo-hygric measurements of the indoors environment of the hermit was carried out to detect the humidity focal points, in addition to Electrical Resistivity Tomography and Infrared thermography on the walls. All these data was uploaded to a GIS (ArcGIS) together with a photogrammetric model of the decayed areas. The combination of the information in the GIS improved decay maps and allowed a better diagnosis of the building moisture distribution and causes. Research funded by Geomateriales 2 S2013/MIT-2914 and CEI Moncloa (UPM, UCM, CSIC) through a PICATA contract and the equipment from RedLAbPAt Network

Geophysical anatomy of counter-slope scarps in sedimentary flysch rocks (Outer Western Carpathians)

NASA Astrophysics Data System (ADS)

Tábořík, P.; Lenart, J.; Blecha, V.; Vilhelm, J.; Turský, O.

2017-01-01

A multidisciplinary geophysical survey, consisting of electrical resistivity tomography (ERT), ground penetrating radar (GPR), shallow seismic refraction (SSR) and gravity survey (GS), was used to investigate the counter-slope scarps, one of the typical manifestations of the relaxed zones of rock massifs, and the possible initial stages of deep-seated landslides (DSLs). Two upper parts of the extensive DSLs within the Moravskoslezské Beskydy Mountains (Outer Western Carpathians - OWC) built by the sedimentary flysch rock were chosen as the testing sites. A combined geophysical survey on the flysch rocks was performed on both localities to enhance our present findings. The survey revealed that the ERT is able to reliably detect underground discontinuities, which are manifested at the ground surface by one of the typical landforms (tension cracks, trenches, pseudokarst sinkholes, double-crested ridges and counter-slope scarps). Previous studies suggested that bedrock discontinuities should be depicted by high-resistivity features within ERT surveying. According to SSR and GS, expected zones of weakened rock massif were not confirmed directly underneath the superficial landforms, but they were shifted. Based on the SSR and GS measurements, the depicted high-contrast transitions between high- and low-resistivity domains within the ERT profiles were newly identified as possible manifestation of bedrock discontinuities. The results of GPR measurements give only limited information on the sedimentary flysch rocks, due to shallow penetrating depth and locally strong signal attenuation. The combined results of multidisciplinary geophysical surveying confirmed an importance of employing more than one geophysical technique for integrated interpretations of measured data. Integrated interpretations of the measured geophysical data provided a new insight into massif disintegration and the geomorphic origin of the landforms related to the DSL.

Electrical Tomography for seismic hazard monitoring: state-of-the-art and future challenges.

NASA Astrophysics Data System (ADS)

Lapenna, Vincenzo; Piscitelli, Sabatino

2010-05-01

The Self-Potential (passive) and DC resistivity (active) methods have been considered for a long period as ancillary and/or secondary tools in geophysical exploration, simplified procedures for data processing and purely qualitative techniques for data inversion were the main drawbacks. Recently, innovative algorithms for tomographic data inversion, new models for describing the electrokinetic phenomena associated to the subsurface fluid migration and modern technologies for the field surveying have rapidly transformed these geoelectrical methods in powerful tools for geo-hazard monitoring. These technological and methodological improvements disclose the way for a wide spectra of interesting and challenging applications: mapping of the water content in landslide bodies; identification of fluid and gas emissions in volcanic areas; search of earthquake precursors. In this work we briefly resume the current start-of-the-art and analyse the new applications of the Electrical Tomography in the seismic hazard monitoring. An overview of the more interesting results obtained in different worldwide areas (i.e. Mediterranean Basin, California, Japan) is presented and discussed. To-date, combining novel techniques for data inversion and new strategies for the field data acquisition is possible to obtain high-resolution electrical images of complex geological structures. One of the key challenges for the near-future will be the integration of active (DC resistivity) and passive (Self-Potential) measurements for obtaining 2D, 3D and 4D electrical tomographies able to follow the spatial and temporal dynamics of electrical parameters (i.e. resistivity, self-potential). This approach could reduce the ambiguities related to the interpretation of anomalous SP signals in seismic active areas and their applicability for short-term earthquake prediction. The resistivity imaging can be applied for illuminating the fault geometry, while the SP imaging is the key instrument for capturing the fingerprints of the electrokinetic phenomena potentially generated in focal regions.

Seasonal electrical resistivity surveys of a coastal bluff, Barter Island, North Slope Alaska

USGS Publications Warehouse

Swarzenski, Peter W.; Johnson, Cordell; Lorenson, Thomas; Conaway, Christopher H.; Gibbs, Ann E.; Erikson, Li; Richmond, Bruce M.; Waldrop, Mark P.

2016-01-01

Select coastal regions of the North Slope of Alaska are experiencing high erosion rates that can be attributed in part to recent warming trends and associated increased storm intensity and frequency. The upper sediment column of the coastal North Slope of Alaska can be described as continuous permafrost underlying a thin (typically less than 1–2 m) active layer that responds variably to seasonal thaw cycles. Assessing the temporal and spatial variability of the active layer and underlying permafrost is essential to better constrain how heightened erosion may impact material fluxes to the atmosphere and the coastal ocean, and how enhanced thaw cycles may impact the stability of the coastal bluffs. In this study, multi-channel electrical resistivity tomography (ERT) was used to image shallow subsurface features of a coastal bluff west of Kaktovik, on Barter Island, northeast Alaska. A comparison of a suite of paired resistivity surveys conducted in early and late summer 2014 provided detailed information on how the active layer and permafrost are impacted during the short Arctic summer. Such results are useful in the development of coastal resilience models that tie together fluvial, terrestrial, climatic, geologic, and oceanographic forcings on shoreline stability.

Coastal Permafrost Bluff Response to Summer Warming, Barter Island, NE Alaska

NASA Astrophysics Data System (ADS)

Richmond, B. M.; Gibbs, A.; Johnson, C. D.; Swarzenski, P. W.; Oberle, F. J.; Tulaczyk, S. M.; Lorenson, T. D.

2016-12-01

Observations of warming air and sea temperatures in the Arctic are leading to longer periods of permafrost thaw and ice-free conditions during summer, which lead to increased exposure to coastal storm surge, wave impacts, and heightened erosion. Recently collected air and soil (bluff) temperatures, atmospheric pressure, water levels, time-lapse photography, aerial photography and satellite imagery, and electrical resistivity tomography (ERT) surveys were used to document coastal bluff morphological response to seasonal warming. Data collection instruments and time-lapse cameras installed overlooking a bluff face on the exposed open ocean coast and within an erosional gully were used to create an archive of hourly air temperature, pressure, bluff morphology, and sea-state conditions allowing for documentation of individual bluff failure events and coincident meteorology. Permafrost boreholes as deep as 6 m from the upper bluff tundra surface were fitted with thermistor arrays to record a high resolution temperature record that spanned an initial frozen state, a summer thaw cycle, and subsequent re-freezing. Late summer ERT surveys were used to link temperature observations to subsurface electrical resistivities and active-layer dynamics. Preliminary observations suggest surface warming and active layer growth are responsible for a significant amount of bluff face failures that are exacerbated in the shore perpendicular gullies and along the exposed ocean coast. Electrical resistivity surveys and geochemical data reveal concentrated brines at depth, which likely contribute to enhanced, localized erosion in weakened strata.

Distribution-based fuzzy clustering of electrical resistivity tomography images for interface detection

NASA Astrophysics Data System (ADS)

Ward, W. O. C.; Wilkinson, P. B.; Chambers, J. E.; Oxby, L. S.; Bai, L.

2014-04-01

A novel method for the effective identification of bedrock subsurface elevation from electrical resistivity tomography images is described. Identifying subsurface boundaries in the topographic data can be difficult due to smoothness constraints used in inversion, so a statistical population-based approach is used that extends previous work in calculating isoresistivity surfaces. The analysis framework involves a procedure for guiding a clustering approach based on the fuzzy c-means algorithm. An approximation of resistivity distributions, found using kernel density estimation, was utilized as a means of guiding the cluster centroids used to classify data. A fuzzy method was chosen over hard clustering due to uncertainty in hard edges in the topography data, and a measure of clustering uncertainty was identified based on the reciprocal of cluster membership. The algorithm was validated using a direct comparison of known observed bedrock depths at two 3-D survey sites, using real-time GPS information of exposed bedrock by quarrying on one site, and borehole logs at the other. Results show similarly accurate detection as a leading isosurface estimation method, and the proposed algorithm requires significantly less user input and prior site knowledge. Furthermore, the method is effectively dimension-independent and will scale to data of increased spatial dimensions without a significant effect on the runtime. A discussion on the results by automated versus supervised analysis is also presented.

Horizontal-to-vertical spectral ratio variability in the presence of permafrost

NASA Astrophysics Data System (ADS)

Kula, Damian; Olszewska, Dorota; Dobiński, Wojciech; Glazer, Michał

2018-07-01

Due to fluctuations in the thickness of the permafrost active layer, there exists a seasonal seismic impedance contrast in the permafrost table. The horizontal-to-vertical spectral ratio (HVSR) method is commonly used to estimate the resonant frequency of sedimentary layers on top of bedrock. Results obtained using this method are thought to be stable in time. The aim of the study is to verify whether seasonal variability in the permafrost active layer influences the results of the HVSR method. The research area lies in the direct vicinity of the Polish Polar Station, Hornsund, which is located in Southern Spitsbergen, Svalbard. Velocity models of the subsurface are obtained using the HVSR method, which are juxtaposed with electrical resistivity tomography profiles conducted near the seismic station. Survey results indicate that the active layer of permafrost has a major influence on the high-frequency section of the HVSR results. In addition, the depth of the permafrost table inferred using the HVSR method is comparable to the depth visible in electrical resistivity tomography results. This study proves that, in certain conditions, the HVSR method results vary seasonally, which must be taken into account in their interpretation.

Attenuation-difference radar tomography: results of a multiple-plane experiment at the U.S. Geological Survey Fractured-Rock Research Site, Mirror Lake, New Hampshire

USGS Publications Warehouse

Lane, J.W.; Day-Lewis, F. D.; Harris, J.M.; Haeni, F.P.; Gorelick, S.M.

2000-01-01

Attenuation-difference, borehole-radar tomography was used to monitor a series of sodium chloride tracer injection tests conducted within the FSE, wellfield at the U.S. Geological Survey Fractured-Rock Hydrology Research Site in Grafton County, New Hampshire, USA. Borehole-radar tomography surveys were conducted using the sequential-scanning and injection method in three boreholes that form a triangular prism of adjoining tomographic image planes. Results indicate that time-lapse tomography methods provide high-resolution images of tracer distribution in permeable zones.

Electronic resistance tomography imaging of spatial moisture distribution, moisture distribution and movement in pavements

DOT National Transportation Integrated Search

1997-07-01

Electronic resistance tomography (ERT) was used to follow the infiltration of water into a pavement section at the UC Berkeley Richmond Field Station. A volume of pavement 1 m square and 1.29 m in depth was sampled by an ERT array consisting of elect...

Shallow subsurface imaging of the Piano di Pezza active normal fault (central Italy) by high-resolution refraction and electrical resistivity tomography coupled with time domain electromagnetic data

NASA Astrophysics Data System (ADS)

Villani, Fabio; Tulliani, Valerio; Fierro, Elisa; Sapia, Vincenzo; Civico, Riccardo

2015-04-01

The Piano di Pezza fault is the north-westernmost segment of the >20 km long Ovindoli-Pezza active normal fault-system (central Italy). Although existing paleoseismic data document high vertical Holocene slip rates (~1 mm/yr) and a remarkable seismogenic potential of this fault, its subsurface setting and Pleistocene cumulative displacement are still poorly known. We investigated for the first time by means of high-resolution seismic and electrical resistivity tomography coupled with time domain electromagnetic (TDEM) measurements the shallow subsurface of a key section of the Piano di Pezza fault. Our surveys cross a ~5 m-high fault scarp that was generated by repeated surface-rupturing earthquakes displacing some Late Holocene alluvial fans. We provide 2-D Vp and resistivity images which clearly show significant details of the fault structure and the geometry of the shallow basin infill material down to 50 m depth. We can estimate the dip (~50°) and the Holocene vertical displacement of the master fault (~10 m). We also recognize in the hangingwall some low-velocity/low-resistivity regions that we relate to packages of colluvial wedges derived from scarp degradation, which may represent the record of several paleo-earthquakes older than the Late Holocene events previously recognized by paleoseismic trenching. Conversely, due to the limited investigation depth of seismic and electrical tomography, the estimation of the cumulative amount of Pleistocene throw is hampered. Therefore, to increase the depth of investigation, we performed 7 TDEM measurements along the electrical profile using a 50 m loop size both in central and offset configuration. The recovered 1-D resistivity models show a good match with 2-D resistivity images in the near surface. Moreover, TDEM inversion results indicate that in the hangingwall, ~200 m away from the surface fault trace, the carbonate pre-Quaternary basement may be found at ~90-100 m depth. The combined approach of electrical and seismic data coupled with TDEM measurements provides a robust constraint to the Piano di Pezza fault cumulative offset. Our data are useful for better reconstructing the deep structural setting of the Piano di Pezza basin and assessing the role played by extensional tectonics in its Quaternary evolution.

High resolution electrical resistivity tomography of golf course greens irrigated with reclaimed wastewater: Hydrological approach

NASA Astrophysics Data System (ADS)

Tapias, Josefina C.; Lovera, Raúl; Himi, Mahjoub; Gallardo, Helena; Sendrós, Alexandre; Marguí, Eva; Queralt, Ignasi; Casas, Albert

2014-05-01

Actually, there are over 300 golf courses and more than three thousand licensed players in Spain. For this reason golf cannot be considered simply a hobby or a sport, but a very significant economic activity. Considered as one of the most rapidly expanding land-use and water demanding business in the Mediterranean, golf course development generates controversy. In the recent years there has been a considerable demand for golf courses to adopt environmentally sustainable strategies and particularly water authorities are forcing by law golf managers to irrigate with alternative water resources, mainly reclaimed wastewater. Watering practices must be based on soil properties that are characterized by samples removed from the different zones of the golf course and submitted to an accredited physical soil testing laboratory. Watering schedules are critical on greens with poor drainage or on greens with excessively high infiltration rates. The geophysical survey was conducted over the greens of the Girona Golf Club. Eighteen electrical resistivity tomographies were acquired using a mixed Wenner-Schlumberger configuration with electrodes placed 0.5 meter apart. Small stainless-steel nails were used as electrodes to avoid any damage in the fine turfgrass of greens The resistivity meter was set for systematically and automatically selects current electrodes and measurement electrodes to sample apparent resistivity values. Particle size analysis (PSA) has been performed on soil materials of any putting green. The PSA analysis has been composed of two distinct phases. The first has been the textural analysis of the soils for determining the content of sand, silt, and clay fraction via the use of a stack of sieves with decreasing sized openings from the top sieve to the bottom. Subsequently, the hydraulic conductivity of the substrates has been evaluated by means of Bredding and Hazen empirical relationships. The results of this research show that the electrical resistivity tomography is a non-invasive and cost-effective technique for high resolution characterizing the subsurface below golf course greens. The obtained models have provided detailed information on the lateral and vertical variability of each the subsurface and from an empirical correlation between the values of electrical resistivity and hydraulic permeability to assess the preferred areas of drainage that could pose in risk to the vulnerability of the underlying aquifers.

Geo Techno Park potential at Arjuno-Welirang Volcano hosted geothermal area, Batu, East Java, Indonesia (Multi geophysical approach)

NASA Astrophysics Data System (ADS)

Maryanto, Sukir

2017-11-01

Arjuno Welirang Volcano Geothermal (AWVG) is located around Arjuno-Welirang Volcano in Malang, East Java, about 100 km southwest of Surabaya, the capital city of East Java province, and is still an undeveloped area of the geothermal field. The occurrence of solfatara and fumaroles with magmatic gasses indicated the existence of a volcanic geothermal system in the subsurface. A few hot springs are found in the Arjuno-Welirang volcanic complex, such as Padusan hot spring, Songgoriti hot spring, Kasinan hot spring, and Cangar hot spring. Multi geophysical observations in AWVG complex was carried out in order to explore the subsurface structure in supporting the plan of Geo Techno Park at the location. Gravity, Magnetic, Microearthquake, and Electrical Resistivity Tomography (ERT) methods were used to investigate the major and minor active faulting zones whether hot springs circulation occurs in these zones. The gravity methods allowed us to locate the subsurface structure and to evaluate their geometrical relationship base on density anomaly. Magnetic methods allow us to discriminate conductive areas which could correspond to an increase in thermal fluid circulation in the investigated sites. Micro-earthquakes using particle motion analysis to locate the focal depth related with hydrothermal activity and electrical resistivity tomography survey offers methods to locate more detail subsurface structure and geothermal fluids near the surface by identifying areas affected by the geothermal fluid. The magnetic and gravity anomaly indicates the subsurface structure of AWVG is composed of basalt rock, sulfide minerals, sandstone, and volcanic rock with high minor active fault structure as a medium for fluid circulation. While using micro-earthquake data in AWVG shown shallow focal depth range approximate 60 meters which indicates shallow hydrothermal circulation in AWVG. The geothermal fluid circulation zones along the fault structure resulted in some hot springs in a central and north-western part of AWVG detected by the Electrical Resistivity Tomography, appear to be well correlated with corresponding features derived from the gravity, magnetic, and micro-earthquake survey. We just ongoing process to develop Arjuno Welirang Volcano & Geothermal Research Center (AWVGRC) located at Universitas Brawijaya Agro Techno Park, Cangar in the flank of Arjuno Welirang volcano complex. Due to our initial observations, AWVG has a great potential for a pilot project of an educational geo technopark development area.

Optimized survey design for electrical resistivity tomography: combined optimization of measurement configuration and electrode placement

NASA Astrophysics Data System (ADS)

Uhlemann, Sebastian; Wilkinson, Paul B.; Maurer, Hansruedi; Wagner, Florian M.; Johnson, Timothy C.; Chambers, Jonathan E.

2018-07-01

Within geoelectrical imaging, the choice of measurement configurations and electrode locations is known to control the image resolution. Previous work has shown that optimized survey designs can provide a model resolution that is superior to standard survey designs. This paper demonstrates a methodology to optimize resolution within a target area, while limiting the number of required electrodes, thereby selecting optimal electrode locations. This is achieved by extending previous work on the `Compare-R' algorithm, which by calculating updates to the resolution matrix optimizes the model resolution in a target area. Here, an additional weighting factor is introduced that allows to preferentially adding measurement configurations that can be acquired on a given set of electrodes. The performance of the optimization is tested on two synthetic examples and verified with a laboratory study. The effect of the weighting factor is investigated using an acquisition layout comprising a single line of electrodes. The results show that an increasing weight decreases the area of improved resolution, but leads to a smaller number of electrode positions. Imaging results superior to a standard survey design were achieved using 56 per cent fewer electrodes. The performance was also tested on a 3-D acquisition grid, where superior resolution within a target at the base of an embankment was achieved using 22 per cent fewer electrodes than a comparable standard survey. The effect of the underlying resistivity distribution on the performance of the optimization was investigated and it was shown that even strong resistivity contrasts only have minor impact. The synthetic results were verified in a laboratory tank experiment, where notable image improvements were achieved. This work shows that optimized surveys can be designed that have a resolution superior to standard survey designs, while requiring significantly fewer electrodes. This methodology thereby provides a means for improving the efficiency of geoelectrical imaging.

Optimized survey design for Electrical Resistivity Tomography: combined optimization of measurement configuration and electrode placement

NASA Astrophysics Data System (ADS)

Uhlemann, Sebastian; Wilkinson, Paul B.; Maurer, Hansruedi; Wagner, Florian M.; Johnson, Timothy C.; Chambers, Jonathan E.

2018-03-01

Within geoelectrical imaging, the choice of measurement configurations and electrode locations is known to control the image resolution. Previous work has shown that optimized survey designs can provide a model resolution that is superior to standard survey designs. This paper demonstrates a methodology to optimize resolution within a target area, while limiting the number of required electrodes, thereby selecting optimal electrode locations. This is achieved by extending previous work on the `Compare-R' algorithm, which by calculating updates to the resolution matrix optimizes the model resolution in a target area. Here, an additional weighting factor is introduced that allows to preferentially adding measurement configurations that can be acquired on a given set of electrodes. The performance of the optimization is tested on two synthetic examples and verified with a laboratory study. The effect of the weighting factor is investigated using an acquisition layout comprising a single line of electrodes. The results show that an increasing weight decreases the area of improved resolution, but leads to a smaller number of electrode positions. Imaging results superior to a standard survey design were achieved using 56 per cent fewer electrodes. The performance was also tested on a 3D acquisition grid, where superior resolution within a target at the base of an embankment was achieved using 22 per cent fewer electrodes than a comparable standard survey. The effect of the underlying resistivity distribution on the performance of the optimization was investigated and it was shown that even strong resistivity contrasts only have minor impact. The synthetic results were verified in a laboratory tank experiment, where notable image improvements were achieved. This work shows that optimized surveys can be designed that have a resolution superior to standard survey designs, while requiring significantly fewer electrodes. This methodology thereby provides a means for improving the efficiency of geoelectrical imaging.

Improved characterisation and modelling of measurement errors in electrical resistivity tomography (ERT) surveys

NASA Astrophysics Data System (ADS)

Tso, Chak-Hau Michael; Kuras, Oliver; Wilkinson, Paul B.; Uhlemann, Sebastian; Chambers, Jonathan E.; Meldrum, Philip I.; Graham, James; Sherlock, Emma F.; Binley, Andrew

2017-11-01

Measurement errors can play a pivotal role in geophysical inversion. Most inverse models require users to prescribe or assume a statistical model of data errors before inversion. Wrongly prescribed errors can lead to over- or under-fitting of data; however, the derivation of models of data errors is often neglected. With the heightening interest in uncertainty estimation within hydrogeophysics, better characterisation and treatment of measurement errors is needed to provide improved image appraisal. Here we focus on the role of measurement errors in electrical resistivity tomography (ERT). We have analysed two time-lapse ERT datasets: one contains 96 sets of direct and reciprocal data collected from a surface ERT line within a 24 h timeframe; the other is a two-year-long cross-borehole survey at a UK nuclear site with 246 sets of over 50,000 measurements. Our study includes the characterisation of the spatial and temporal behaviour of measurement errors using autocorrelation and correlation coefficient analysis. We find that, in addition to well-known proportionality effects, ERT measurements can also be sensitive to the combination of electrodes used, i.e. errors may not be uncorrelated as often assumed. Based on these findings, we develop a new error model that allows grouping based on electrode number in addition to fitting a linear model to transfer resistance. The new model explains the observed measurement errors better and shows superior inversion results and uncertainty estimates in synthetic examples. It is robust, because it groups errors together based on the electrodes used to make the measurements. The new model can be readily applied to the diagonal data weighting matrix widely used in common inversion methods, as well as to the data covariance matrix in a Bayesian inversion framework. We demonstrate its application using extensive ERT monitoring datasets from the two aforementioned sites.

Electrical Resistivity Tomography Reveals Upward Redistribution of Soil-Water by Coyote Brush in a Shrub-Grassland Ecotone

NASA Astrophysics Data System (ADS)

Manning, J. E.; Schulz, M. S.; Lambrecht, D. S.

2016-12-01

Species imbalance within many California plant assemblages may arise due to more intense wildfires as well as climate warming. Given this, coyote brush (Baccharis pilularis DC), a native evergreen shrub known as a ready colonizer of disturbed soil, may become more dominant. While prolonged spring soil moisture is required for seedling establishment, 1+ year-old coyote brush can withstand low soil water potentials (-1.2 MPa). Beyond this, little is known about its soil-water dynamics. Hydraulic redistribution of water within the soil profile by plant roots has been established in numerous species in the past 20 years. Recent quantification of the water quantity re-distributed by root systems are beginning to provide detail that could inform ET, weathering, and carbon cycling models. Electrical resistivity tomography (ERT) has been used to study soil hydraulics in natural as well as cropland settings. This study is the first known to use ERT to investigate hydraulic redistribution in coyote brush. One mid-size shrub surrounded by open grassland was selected at the study site, located on a coastal marine terrace west of Santa Cruz, CA. The soil profile, previously characterized with ERT and auger-based soil-water sampling, includes a clay-rich B horizon and is texturally non-uniform due to bioturbation to 0.6 meter. The 12-m ERT survey transect had 48 semi-permanent electrodes, with the 4-m wide shrub canopy at probes 16 to 32. Five repeats of evening and morning surveys were conducted. Heterogeneous texture and severe soil drying necessitated qualitative comparison across time. Overnight resistivity changes using differences plots of the modelled data revealed increased moisture beneath the shrub canopy during the night. Areas beyond the canopy—presumably outside the root zone—experienced variable overnight changes, with moisture increasing in the clay-rich horizon. Preliminary analysis suggests that coyote brush roots redistribute water upward within the soil profile.

Electric resistivity and seismic refraction tomography: a challenging joint underwater survey at Äspö Hard Rock Laboratory

NASA Astrophysics Data System (ADS)

Ronczka, Mathias; Hellman, Kristofer; Günther, Thomas; Wisén, Roger; Dahlin, Torleif

2017-06-01

Tunnelling below water passages is a challenging task in terms of planning, pre-investigation and construction. Fracture zones in the underlying bedrock lead to low rock quality and thus reduced stability. For natural reasons, they tend to be more frequent at water passages. Ground investigations that provide information on the subsurface are necessary prior to the construction phase, but these can be logistically difficult. Geophysics can help close the gaps between local point information by producing subsurface images. An approach that combines seismic refraction tomography and electrical resistivity tomography has been tested at the Äspö Hard Rock Laboratory (HRL). The aim was to detect fracture zones in a well-known but logistically challenging area from a measuring perspective. The presented surveys cover a water passage along part of a tunnel that connects surface facilities with an underground test laboratory. The tunnel is approximately 100 m below and 20 m east of the survey line and gives evidence for one major and several minor fracture zones. The geological and general test site conditions, e.g. with strong power line noise from the nearby nuclear power plant, are challenging for geophysical measurements. Co-located positions for seismic and ERT sensors and source positions are used on the 450 m underwater section of the 700 m profile. Because of a large transition zone that appeared in the ERT result and the missing coverage of the seismic data, fracture zones at the southern and northern parts of the underwater passage cannot be detected by separated inversion. Synthetic studies show that significant three-dimensional (3-D) artefacts occur in the ERT model that even exceed the positioning errors of underwater electrodes. The model coverage is closely connected to the resolution and can be used to display the model uncertainty by introducing thresholds to fade-out regions of medium and low resolution. A structural coupling cooperative inversion approach is able to image the northern fracture zone successfully. In addition, previously unknown sedimentary deposits with a significantly large thickness are detected in the otherwise unusually well-documented geological environment. The results significantly improve the imaging of some geologic features, which would have been undetected or misinterpreted otherwise, and combines the images by means of cluster analysis into a conceptual subsurface model.

Nonmetastatic Castration-resistant Prostate Cancer: A Modern Perspective.

PubMed

Cancian, Madeline; Renzulli, Joseph F

2018-06-01

Nonmetastatic castration-resistant prostate cancer (nmCRPC) presents a challenge to urologists as currently there are no Food and Drug Administration-approved therapies. However, there are new imaging modalities, including fluciclovine positron emission tomography-computed tomography and Ga-PSMA (prostate specific membrane antigent) positron emission tomography-computed tomography, which are improving accuracy of diagnosis. With improved imaging, we are better able to target therapy. Today there are 3 ongoing clinical trials studying second-generation antiandrogens in nmCRPC, which hold the promise of a new treatment paradigm. In this article, we will review the new imaging techniques and the rationale behind novel treatment modalities in nmCRPC. Copyright © 2018 Elsevier Inc. All rights reserved.

Extremely high resolution 3D electrical resistivity tomography to depict archaeological subsurface structures

NASA Astrophysics Data System (ADS)

Al-Saadi, Osamah; Schmidt, Volkmar; Becken, Michael; Fritsch, Thomas

2017-04-01

Electrical resistivity tomography (ERT) methods have been increasingly used in various shallow depth archaeological prospections in the last few decades. These non-invasive techniques are very useful in saving time, costs, and efforts. Both 2D and 3D ERT techniques are used to obtain detailed images of subsurface anomalies. In two surveyed areas near Nonnweiler (Germany), we present the results of the full 3D setup with a roll-along technique and of the quasi-3D setup (parallel and orthogonal profiles in dipole-dipole configuration). In area A, a dipole-dipole array with 96 electrodes in a uniform rectangular survey grid has been used in full 3D to investigate a presumed Roman building. A roll-along technique has been utilized to cover a large part of the archaeological site with an electrode spacing of 1 meter and with 0.5 meter for a more detailed image. Additional dense parallel 2D profiles have been carried out in dipole-dipole array with 0.25 meter electrode spacing and 0.25 meter between adjacent profiles in both direction for higher- resolution subsurface images. We have designed a new field procedure, which used an electrode array fixed in a frame. This facilitates efficient field operation, which comprised 2376 electrode positions. With the quasi 3D imaging, we confirmed the full 3D inversion model but at a much better resolution. In area B, dense parallel 2D profiles were directly used to survey the second target with also 0.25 meter electrode spacing and profiles separation respectively. The same field measurement design has been utilized and comprised 9648 electrode positions in total. The quasi-3D inversion results clearly revealed the main structures of the Roman construction. These ERT inversion results coincided well with the archaeological excavation, which has been done in some parts of this area. The ERT result successfully images parts from the walls and also smaller internal structures of the Roman building.

An observational study of the association among interatrial adiposity by computed tomography measure, insulin resistance, and left atrial electromechanical disturbances in heart failure.

PubMed

Hung, Chung-Lieh; Yun, Chun-Ho; Lai, Yau-Huei; Sung, Kuo-Tzu; Bezerra, Hiram G; Kuo, Jen-Yuan; Hou, Charles Jia-Yin; Chao, Tze-Fan; Bulwer, Bernard E; Yeh, Hung-I; Shih, Shou-Chuan; Lin, Shing-Jong; Cury, Ricardo C

2016-06-01

Excessive visceral adiposity, hypothesized to be a key mediator in metabolic derangements, has recently been shown to exert toxic effects on cardiac structure and function. Data regarding the mechanistic link between regional adiposity, left atrial (LA) electromechanical remodeling, and heart failure with preserved ejection fraction (HFpEF) have been lacking.Various visceral adiposity measures, including pericardial fat (PCF), thoracic periaortic (TAT) fat, regional inter-atrial fat (IAF), and atrioventricular groove fat (AV Groove Fat), were assessed by multidetector computed tomography in 2 study cohorts (an annual health survey cohort and an outpatient cohort). We related such measures to cardiometabolic profiles in health survey cohort and LA electromechanical indices in our outpatient cohort, with Cox proportional hazards performed to examine the temporal trends of heart failure (HF).In our annual health survey cohort (n = 362), all 4 adiposity measures were positively related to unfavorable anthropometrics and systemic inflammation (high-sensitivity C-reactive protein) (all P < 0.05). In addition, both greater IAF and AV Groove Fat were positively associated with higher fasting glucose, HbA1c levels, and insulin resistance (all P < 0.05). In the outpatient cohort, the HFpEF group demonstrated the greatest adiposity measures, with greater IAF (≥8.2 mm, hazard ratio: 4.11, 95% confidence interval: 1.50-11.32) associated with reduced LA strain (ß-coef: -0.28), higher LA stiffness (ß-coef: 0.23), and longer P wave duration (ß-coef: 0.23) in multivariate models (all P < 0.05), and further related to higher HF hospitalization during follow-up.We therefore propose a possible pathophysiologic link among greater visceral adiposity, systemic inflammation, cardiometabolic risks, and HFpEF. Regional adiposity, especially IAF, was tightly linked to altered LA electromechanical properties and likely plays a key role in HF prognosis.

Waste disposal mapping with electrical resistivity tomography case: Leuwigajah landfill

NASA Astrophysics Data System (ADS)

Aryanti, Erisha; Ardi, Ahmad Puji; Almunziri, Muaz; Xanggam, Zael Yahd; Eleazar, Adino; Widodo

2017-07-01

Leuwigajah landfill as administrative is located between district of Bandung and Cimahi citythat has an environmental and social problem that caused aquifer contamination due to the big amount of waste from Bandung city, Cimahi and Bandung regency. It is occupied in abandoned andesite mine site with an area of about 25 hectare. The aim of this research is to map the geology structure and to study the leachate towards aquifer layer below Leuwigajah landfill. Here, we present the study of Leuwigajah landfill subsurface using Electrical Resistivity Tomography (ERT). ERT is one of the most promising prospecting techniques mainly concerning its effective contribution to resolve several environmental problems, was applied for the geophysical modeling. ERT is a robust imaging method the theory and implementation of which are well documented in geophysical research literature. The geological setting comprises clayed weathered layer, fractured andesitic dike. Due to the above-mentioned geological singularity and in the light of the requirement for an environmentally safe construction of the landfill, an ERT survey was carried out with dipole-dipole array, 78 m of acquisition line and 6 m of electrode spacing. The model consists of 4 layers below the Leuwigajah landfill and andesitic fracture until depth of 18.7 m below the surface.

Characterization of focused seepage through an earthfill dam using geoelectrical methods.

PubMed

Ikard, S J; Revil, A; Schmutz, M; Karaoulis, M; Jardani, A; Mooney, M

2014-01-01

Resistivity and self-potential tomography can be used to investigate anomalous seepage inside heterogeneous earthen dams. The self-potential (SP) signals provide a unique signature to groundwater flow because the source current density responsible for the SP signals is proportional to the Darcy velocity. The distribution of the SP signals is also influenced by the distribution of the resistivity; therefore, resistivity and SP need to be used in concert to elucidate groundwater flow pathways. In this study, a survey is conducted at a small earthen dam in Colorado where anomalous seepage is observed on the downstream face at the dam toe. The data reveal SP and direct current resistivity anomalies that are used to delineate three anomalous seepage zones within the dam and to estimate the source of the localized seepage discharge. The SP data are inverted in two dimensions using the resistivity distribution to determine the distribution of the Darcy velocity responsible for the observed seepage. The inverted Darcy velocity agrees with an estimation of the Darcy velocity from the hydraulic conductivity obtained from a slug test and the observed head gradient. © 2013, National Ground Water Association.

Characterizing hydrological processes on loess slopes using electrical resistivity tomography - A case study of the Heifangtai Terrace, Northwest China

NASA Astrophysics Data System (ADS)

Zeng, R. Q.; Meng, X. M.; Zhang, F. Y.; Wang, S. Y.; Cui, Z. J.; Zhang, M. S.; Zhang, Y.; Chen, G.

2016-10-01

From the perspective of engineering geology, loess has long been considered as a homogeneous and porous material. It is commonly believed that water penetrates loess via pores and in some cases causing mass movements. However, several researchers have expressed doubts about this mechanism as a cause of slope failures in loess, and moreover the actual hydrological processes operating in loess deposits and their effect on slope failures have not been fully investigated. Here we present the results of an electrical resistivity survey of the Heifangtai loess terrace in northwestern China, designed to characterize the hydrological processes in loess slopes and their relationship with slope failures. The Heifangtai loess terrace is located on the fourth terrace of the Yellow River and consists of 57-m-thickness of aeolian loess. 2D and 3D electrical resistivity tomography (ERT) was used to monitor the movement of ground water before and after irrigation and rainfall events and the evolution of a sink hole in the toe of the landslide deposits. Our main findings are as follows: (1) Based on the 2D ERT results, the depth of infiltration into the thick unsaturated loess is not more than 5 m in the profile at the top of the landslide. (2) Electrical resistivity decreased as a result of water infiltration through sinkholes, and this process can increase the soil water content and induce soil liquefaction which can eventually result in land sliding. (3) Landslide deposits block the groundwater drainage channels through the loess, which results in the concentration of water in the toe of the landslide. Consequently, groundwater together with rainfall, triggers the failure of sinkholes or cracks, which may induce a continuing process of new slope failures at the sites of past landslide.

Electrical resistance tomography from measurements inside a steel cased borehole

DOEpatents

Daily, William D.; Schenkel, Clifford; Ramirez, Abelardo L.

2000-01-01

Electrical resistance tomography (ERT) produced from measurements taken inside a steel cased borehole. A tomographic inversion of electrical resistance measurements made within a steel casing was then made for the purpose of imaging the electrical resistivity distribution in the formation remotely from the borehole. The ERT method involves combining electrical resistance measurements made inside a steel casing of a borehole to determine the electrical resistivity in the formation adjacent to the borehole; and the inversion of electrical resistance measurements made from a borehole not cased with an electrically conducting casing to determine the electrical resistivity distribution remotely from a borehole. It has been demonstrated that by using these combined techniques, highly accurate current injection and voltage measurements, made at appropriate points within the casing, can be tomographically inverted to yield useful information outside the borehole casing.

Single photon emission computed tomography and positron emission tomography imaging of multi-drug resistant P-glycoprotein--monitoring a transport activity important in cancer, blood-brain barrier function and Alzheimer's disease.

PubMed

Piwnica-Worms, David; Kesarwala, Aparna H; Pichler, Andrea; Prior, Julie L; Sharma, Vijay

2006-11-01

Overexpression of multi-drug resistant P-glycoprotein (Pgp) remains an important barrier to successful chemotherapy in cancer patients and impacts the pharmacokinetics of many important drugs. Pgp is also expressed on the luminal surface of brain capillary endothelial cells wherein Pgp functionally comprises a major component of the blood-brain barrier by limiting central nervous system penetration of various therapeutic agents. In addition, Pgp in brain capillary endothelial cells removes amyloid-beta from the brain. Several single photon emission computed tomography and positron emission tomography radiopharmaceutical have been shown to be transported by Pgp, thereby enabling the noninvasive interrogation of Pgp-mediated transport activity in vivo. Therefore, molecular imaging of Pgp activity may enable noninvasive dynamic monitoring of multi-drug resistance in cancer, guide therapeutic choices in cancer chemotherapy, and identify transporter deficiencies of the blood-brain barrier in Alzheimer's disease.

An Integration of Geophysical Methods to Explore Buried Structures on the Bench and in the Field

NASA Astrophysics Data System (ADS)

Booterbaugh, A. P.; Lachhab, A.

2011-12-01

In the following study, an integration of geophysical methods and devices were implemented on the bench and in the field to accurately identify buried structures. Electrical resistivity and ground penetrating radar methods, including both a fabricated electrical resistivity apparatus and an electrical resistivity device were all used in this study. The primary goal of the study was to test the accuracy and reliability of the apparatus which costs a fraction of the price of a commercially sold resistivity instrument. The apparatus consists of four electrodes, two multimeters, a 12-volt battery, a DC to AC inverter and wires. Using this apparatus, an electrical current, is injected into earth material through the outer electrodes and the potential voltage is measured across the inner electrodes using a multimeter. The recorded potential and the intensity of the current can then be used to calculate the apparent resistivity of a given material. In this study the Wenner array, which consists of four equally spaced electrodes, was used due to its higher accuracy and greater resolution when investigating lateral variations of resistivity in shallow depths. In addition, the apparatus was used with an electrical resistivity device and a ground penetrating radar unit to explore the buried building foundation of Gustavus Adolphus Hall located on Susquehanna University Campus, Selinsgrove, PA. The apparatus successfully produced consistent results on the bench level revealing the location of small bricks buried under a soil material. In the summer of 2010, seventeen electrical resistivity transects were conducted on the Gustavus Adolphus site where and revealed remnants of the foundation. In the summer of 2011, a ground penetrating radar survey and an electrical resistivity tomography survey were conducted to further explore the site. Together these methods identified the location of the foundation and proved that the apparatus was a reliable tool for regular use on the bench and in the field.

Towards a Global Permafrost Electrical Resistivity Survey (GPERS) database

NASA Astrophysics Data System (ADS)

Lewkowicz, Antoni G.; Douglas, Thomas; Hauck, Christian

2017-04-01

Hundreds, and perhaps thousands, of Electrical Resistivity Tomography (ERT) surveys have been undertaken over the past two decades in permafrost areas in North America, Europe, and Asia. Two main types of ERT configurations have been conducted: galvanic surveys using metallic rods as conductors and capacitive-coupled surveys using towed cable arrays. ERT surveys have been carried out in regions with mountain permafrost, lowland permafrost, and coastal saline permafrost, and in undisturbed, naturally-disturbed (e.g. fire-affected), and anthropogenically-affected sites (e.g. around buildings and infrastructure). Some surveys are associated with local validation of frozen ground conditions, through borehole temperatures, frost probing or creep phenomena. Others are in locations without boreholes or with clast-rich or bedrock active layers which preclude this direct confirmation. Most surveys have been carried out individually on particular dates but there are increasing numbers of repeated ERT measurements being made to detect change, either at intervals using a fixed array of electrodes, or at high frequency with a fixed and automated measurement apparatus. Taken as a group, ERT profiles represent an untapped knowledge base relating to permafrost presence, absence, or partial presence (i.e. discontinuous permafrost), and in some cases to the thickness of permafrost and ice content. When combined with borehole information, ERT measurements can identify massive ice features and provides information on soil stratigraphy. The Global Permafrost Electrical Resistivity Survey (GPERS) database is planned as a freely available on-line repository of data from two-dimensional electrical resistivity surveys undertaken in permafrost regions. Its development is supported by the Permafrost Carbon Network and an application for an International Permafrost Association (IPA) Action Group is also underway. When the future GPERS records are compared with the GTN-P database it will be possible to see which boreholes or CALM sites are associated with ERT surveys and which are not. This can be used to target particular sites for ERT surveys to provide a more holistic view of what GTN-P measurements represent. GPERS data will permit empirical analyses of relationships between measured resistivities and permafrost conditions, including ground temperature, ice and liquid water content, and sediment type. These analyses will assist researchers in interpreting their local surveys. The spatial coordinates of the surveys in the database will also permit reacquisition of data in the future to examine changes over years or decades. The purpose of this presentation is to communicate the initiation of GPERS, to explore the level of interest in its development, and to help guide its maturation. In particular, we wish to discuss whether the database should initially focus on meta-data, including site location, vegetation type, and frozen ground conditions, or whether researchers would be willing to supply measurement data immediately which would lead to a more rapid development of GPERS but would also require more resources.

Application Of Two Dimensional Electrical Resistivity Tomography Method For Delineating Cavities And Flowpath In Sinkhole Prone Area Of Armala Valley, Pokhara, Western Nepal

NASA Astrophysics Data System (ADS)

Bhusal, U. C.; Dwivedi, S.; Ghimire, H.; Ulak, P. D.; Khatiwada, B.; Rijal, M. L.; Neupane, Y.; Aryal, S.; Pandey, D.; Gautam, A.; Mishra, S.

2017-12-01

Sudden release of turbid groundwater through piping in the Kali Khola and subsequent formation of over one hundred twenty sinkholes since 18 November, 2013 to May, 2014 in Armala Valley in northern part of Pokhara created havoc to the local residents. The main objective of the work is to investigate subsurface anomalies so as to locate the subsurface cavities, groundwater movement and areas prone to sinkholes formation in the area. Findings of the several studies and observations carried out in area by the authors and preventive measures carried out by Department of Water Induced Disaster Management are presented in the paper. To fulfill the objective 2D-Electrical Resistivity Tomography Survey was carried out at sixty five profiles with minimum electrode spacing from 1 m to 5 m on different profiles using WDJD-4 Resistivity meter. Res2Dinv Software was used for processing and interpretation of the acquired data. Geological mapping, preparation of columnar section of the sinkholes and river bank were conducted. Hand auguring, tracer test and topography survey were also carried out in the area. Different geophysical anomalies were identified in 2D-ERT survey which indicates the presence of compositional difference in layered sediments, undulations in depositional pattern with top humus layer of thickness 0.5 m, loose unconsolidated gravel layer 0.5 m - 4 m and clayey silt/silty clay layer upto 75 m depth. The cavities were found both in clayey silt layer and gravel layer with size ranging from 1-2 m to 10-12 m in depth and 2 m-10 m in diameter either empty or water filled depending on locations. Fifteen cavities that were detected during survey were excavated and immediately filled up. Three major and four minor groundwater flow paths were detected which has been later confirmed by tracer test, formation of new sinkholes along the path and during excavation for construction of underground structures for blocking the underground flow. Major flow path was detected at a depth of 7 m. Undulations in the interface between gravel layer and underlying clayey silt layer, infiltration of acidic fluid, formation of fissures, cracks and dissolution, piping in the clayey silt layer increased the size of cavity, encroachment of Duhani Khola channel, rapid deepening of the Kali Khola are major causes for formation of sinkholes in Armala Valley.

Magnetic resonance electrical impedance tomography (MREIT): simulation study of J-substitution algorithm.

PubMed

Kwon, Ohin; Woo, Eung Je; Yoon, Jeong-Rock; Seo, Jin Keun

2002-02-01

We developed a new image reconstruction algorithm for magnetic resonance electrical impedance tomography (MREIT). MREIT is a new EIT imaging technique integrated into magnetic resonance imaging (MRI) system. Based on the assumption that internal current density distribution is obtained using magnetic resonance imaging (MRI) technique, the new image reconstruction algorithm called J-substitution algorithm produces cross-sectional static images of resistivity (or conductivity) distributions. Computer simulations show that the spatial resolution of resistivity image is comparable to that of MRI. MREIT provides accurate high-resolution cross-sectional resistivity images making resistivity values of various human tissues available for many biomedical applications.

Development of the EM tomography system by the vertical electromagnetic profiling (VEMP) method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miura, Y.; Osato, K.; Takasugi, S.

1995-12-31

As a part of the {open_quotes}Deep-Seated Geothermal Resources Survey{close_quotes} project being undertaken by the NEDO, the Vertical ElectroMagnetic Profiling (VEMP) method is being developed to accurately obtain deep resistivity structure. The VEMP method acquires multi-frequency three-component magnetic field data in an open hole well using controlled sources (loop sources or grounded-wire sources) emitted at the surface. Numerical simulation using EM3D demonstrated that phase data of the VEMP method is very sensitive to resistivity structure and the phase data will also indicate presence of deep anomalies. Forward modelling was also used to determine required transmitter moments for various grounded-wire and loopmore » sources for a field test using the WD-1 well in the Kakkonda geothermal area. Field logging of the well was carried out in May 1994 and the processed field data matches well the simulated data.« less

Applying geophysical surveys for studying subsurface geology of monogenetic volcanic fields: the example of La Garrotxa Volcanic Field (NE of Iberian Peninsula)

NASA Astrophysics Data System (ADS)

Bolós, Xavier; Barde-Cabusson, Stéphanie; Pedrazzi, Dario; Martí, Joan; Casas, Albert; Lovera, Raúl; Nadal-Sala, Daniel

2014-05-01

Improving knowledge of the shallowest part of the feeding system of monogenetic volcanoes and the relationship with the subsurface geology is an important task. We applied high-precision geophysical techniques that are self-potential and electrical resistivity tomography, for the exploration of the uppermost part of the substrate of La Garrotxa Volcanic Field, which is part of the European Cenozoic Rift System. Previous geophysical studies carried out in the same area at a less detailed scale were aimed at identifying deeper structures, and together constitute the basis to establish volcanic susceptibility in La Garrotxa. Self-potential study allowed identifying key areas where electrical resistivity tomography could be conducted. Dykes and faults associated with several monogenetic cones were identified through the generation of resistivity models. The combined results confirm that shallow tectonics controlling the distribution of the foci of eruptive activity in this volcanic zone mainly correspond to NNW-SSE and accessorily by NNE-SSW Neogene extensional fissures and faults and concretely show the associated magmatic intrusions. These studies show that previous alpine tectonic structures played no apparent role in controlling the loci of this volcanism. Furthermore, the results obtained show that the changes in eruption dynamics occurring at different vents located at relatively short distances in this volcanic area can be controlled by shallow stratigraphical, structural, and hydrogeological features underneath these monogenetic volcanoes. This study was partially funded by the Beca Ciutat d'Olot en Ciències Naturals and the European Commission (FT7 Theme: ENV.2011.1.3.3-1; Grant 282759: "VUELCO").

Emplacement of Zebín Hill, Jičín Volcanic Field, Bohemian Paradise, Czech Republic: Anisotropy of Magnetic Susceptibility, Ground Magnetometry, Electric Resistivity Tomography, and Paleomagnetic Data

NASA Astrophysics Data System (ADS)

Petronis, M. S.; Rapprich, , V.; Valenta, J.; Leman, J.; Brister, A. R.; van Wyk de Vries, B.

2014-12-01

A well-preserved set of mid-Miocene tuff-cones and their feeders outcrop in the Jičín Volcanic Field, Czech Republic. Zebín Hill is a tuff cone that has been quarried to reveal the volcanoes feeder system. This edifice offers the opportunity to understand how magma is transported through a monogenetic pyroclastic cone. Rock types include a coarse-grained basal phreatomagmatic layer and a stratified upper wall facies both of which are penetrated by feeder dikes. Anisotropy of magnetic susceptibility (AMS) and paleomagnetic data were collected at twenty-one sites from feeder dikes and the main conduit of the volcano. A high-resolution ground magnetometry survey, electric resistivity tomography and seismic tomography were also conducted. Magnetic susceptibility intensity indicates that the dominant magnetic mineral is a ferromagnetic phase with little contribution from paramagnetic minerals. AMS ellipsoids shapes are both oblate and prolate and inferred magma flow directions indicate magma flow away from the central vent area and subhorizontal flow towards and away from the axial conduit; both upward and downward magma flow is evident at some sites. Curie point estimates yield a spectrum of results indicating a mixture of high-Ti titanomagnetite, iron sulfide, and low-Ti titanomagnetite. Ground magnetometry data indicate that both normal and reverse polarity rocks are present at Zebín Hill. Paleomagnetic data confirm the ground magnetic data in that both normal and reverse polarity rocks are present. Most sites yield a single component magnetization that is well grouped at the site level and carried by pseudosingle domain titanomagnetite. The presence of both normal and reverse polarity magnetizations from the volcano indicate that significant time passed during the growth of this monogenic system. Complex system of branching dikes has been also observed from electric resistivity tomography. The simple external structure of monogenetic volcanoes hides a rather complex magmatic plumbing system that dynamically evolves during the life of the volcano. As we show, the well-exposed roots of Zebín Hill reveals that the growth of a volcano occurs not due to simple central axis feeder systems but rather through interplay of local structures, magmatic effects, and construct evolution during the life of the volcano

A method to improve tree water use estimates by distinguishing sapwood from heartwood using Electrical Resistivity Tomography

NASA Astrophysics Data System (ADS)

Guyot, A.; Ostergaard, K.; Lenkopane, M.; Fan, J.; Lockington, D. A.

2011-12-01

Estimating whole-plant water use in trees requires reliable and accurate methods. Measuring sap velocity and extrapolating to tree water use is seen as the most commonly used. However, deducing the tree water use from sap velocity requires an estimate of the sapwood area. This estimate is the highest cause of uncertainty, and can reach more than 50 % of the uncertainty in the estimate of water use per day. Here, we investigate the possibility of using Electrical Resistivity Tomography to evaluate the sapwood area distribution in a plantation of Pinus elliottii. Electric resistivity tomographs of Pinus elliottii show a very typical pattern of electrical resistivity, which is highly correlated to sapwood and heartwood distribution. To identify the key factors controlling the variation of electrical resistivity, cross sections at breast height for ten trees have been monitored with electrical resistivity tomography. Trees have been cut down after the experiment to identify the heartwood/sapwood boundaries and to extract wood and sap samples. pH, electrolyte concentration and wood moisture content have then been analysed for these samples. Results show that the heartwood/sapwood patterns are highly correlated with electrical resistivity, and that the wood moisture content is the most influencing factor controlling the variability of the patterns. These results show that electric resistivity tomography could be used as a powerful tool to identify the sapwood area, and thus be used in combination with sapflow sensors to map tree water use at stand scale. However, if Pinus elliottii shows typical patterns, further work is needed to identify to see if there are species - specific characterictics as shown in previous works (, electrolyte gradients from the bark to the heartwood). Also, patterns of high resistivity in between needles positions, which are not correlated with either wood moisture content or sapwood, appear to be artifacts. Thus, inversion methods have also to be improved to take into account these measurements issues.

Inner structure of the Puy de Dôme volcano: cross-comparison of geophysical models (ERT, Gravimetry, Muonic Imagery)

NASA Astrophysics Data System (ADS)

Portal, A.; Béné, S.; Boivin, P.; Busato, E.; Cârloganu, C.; Combaret, C.; Dupieux, P.; Fehr, F.; Gay, P.; Labazuy, P.; Laktineh, I.; Lénat, J.-F.; Miallier, D.; Mirabito, L.; Niess, V.; Vulpescu, B.

2012-09-01

Muon imagery of volcanoes and geological structures are presently and actively developed by several groups in the world. It has the potential to provide a 2-D or 3-D density distribution with an accuracy of a few percent. However, at this stage of the development of the method, comparisons with the results from established geophysical methods are necessary to validate its results. An experiment is currently carried out at the Puy de Dôme volcano involving the concurrent acquisition of muon imagery, electrical resistivity (2-D tomography) and gravity survey. Here, we present the preliminary results for the last two methods. North-south and east-west resistivity sections have been obtained in June 2011 and May 2012. These electric data allow to model of the distribution of the resistivity values down to the base of the dome. The dome and its surroundings are now mapped with more than 300 gravity stations measured during a detailed gravity survey carried out in March and May 2012. The computed Bouguer anomaly can be interpreted by models of the density distribution within the dome. This will be directly comparable with the results from the muon imagery. Our ultimate goal is to derive a model of the dome using the joint interpretation of all the sets of data.

Mapping a Pristine Glaciofluvial Aquifer on the Canadian Shield Using Ground-Penetrating Radar and Electrical Resistivity Tomography

NASA Astrophysics Data System (ADS)

Graves, L. W.; Shirokova, V.; Bank, C.

2013-12-01

Our study aims to construct a 3D structural model of an unconfined pristine aquifer in Laurentian Hills, Ontario, Canada. The stratigraphy of the study site, which covers about 5400 square meters, features reworked glaciofluvial sands and glacial till on top of Canadian Shield bedrock. A network of 25 existing piezometers provides ground-truth. We used two types of geophysical surveys to map the water table and the aquifer basin. Ground-penetrating radar (GPR) collected 40 profiles over distances up to 140 meters using 200MHz and 400MHz antennas with a survey wheel. The collected radargrams show a distinct reflective layer, which can be mapped to outcrops of glacial till within the area. This impermeable interface forms the aquitard. Depths of the subsurface features were calculated using hyperbolic fits on the radargrams in Matlab by determining wave velocity then converting measured two-way-time to depth. Electrical resistivity was used to determine the water table elevations because the unconfined water table did not reflect the radar waves. 20 resistivity profiles were collected in the same area using Wenner-Alpha and dipole-dipole arrays with both 24 and 48 electrodes and for 0.5, 0.75, 1.0 and 2.0 meter spacing. The inverted resistivity models show low resistivity values (<1000 Ohm.m) below 2 to 5 meter depths and higher resistivity values (2000-6000 Ohm.m) above 1 to 2 meter depths. These contrasting resistivity values correspond to saturated and wet sand (lower resistivity) to dry sand (higher resistivity); a correlation we could verify with several bore-hole logs. The water table is marked on the resistivity profiles as a steep resistivity gradient, and the depth can be added to the comprehensive 3D model. This model also incorporates hydrogeological characteristics and geochemical anomalies found within the aquifer. Ongoing seasonal and annual monitoring of the aquifer using geophysical methods will bring a fourth dimension to our understanding of this dynamic system. GPR Profile with Glacial Till Interface.

Large 3D resistivity and induced polarization acquisition using the Fullwaver system: towards an adapted processing methodology

NASA Astrophysics Data System (ADS)

Leite, Orlando; Gance, Julien; Texier, Benoît; Bernard, Jean; Truffert, Catherine

2017-04-01

Driven by needs in the mineral exploration market for ever faster and ever easier set-up of large 3D resistivity and induced polarization, autonomous and cableless recorded systems come to the forefront. Opposite to the traditional centralized acquisition, this new system permits a complete random distribution of receivers on the survey area allowing to obtain a real 3D imaging. This work presents the results of a 3 km2 large experiment up to 600m of depth performed with a new type of autonomous distributed receivers: the I&V-Fullwaver. With such system, all usual drawbacks induced by long cable set up over large 3D areas - time consuming, lack of accessibility, heavy weight, electromagnetic induction, etc. - disappear. The V-Fullwavers record the entire time series of voltage on two perpendicular axes, for a good determination of the data quality although I-Fullwaver records injected current simultaneously. For this survey, despite good assessment of each individual signal quality, on each channel of the set of Fullwaver systems, a significant number of negative apparent resistivity and chargeability remains present in the dataset (around 15%). These values are commonly not taken into account in the inversion software although they may be due to complex geological structure of interest (e.g. linked to the presence of sulfides in the earth). Taking into account that such distributed recording system aims to restitute the best 3D resistivity and IP tomography, how can 3D inversion be improved? In this work, we present the dataset, the processing chain and quality control of a large 3D survey. We show that the quality of the data selected is good enough to include it into the inversion processing. We propose a second way of processing based on the modulus of the apparent resistivity that stabilizes the inversion. We then discuss the results of both processing. We conclude that an effort could be made on the inclusion of negative apparent resistivity in the inversion code.

Three-dimensional resistivity tomography in extreme coastal terrain amidst dense cultural signals: application to cliff stability assessment at the historic D-Day site

NASA Astrophysics Data System (ADS)

Udphuay, Suwimon; Günther, Thomas; Everett, Mark E.; Warden, Robert R.; Briaud, Jean-Louis

2011-04-01

Pointe du Hoc overlooking the English Channel in Normandy, France was host to one of the most important military engagements of World War II but is vulnerable to cliff collapses that threaten important German fortifications including the forward observation post (OP) and Rudder's command post. The objective of this study is to apply advanced 3-D resistivity tomography towards a detailed site stability assessment with special attention to the two at-risk buildings. 3-D resistivity tomography data sets at Pointe du Hoc in the presence of extreme topography and dense cultural clutter have been successfully acquired, inverted and interpreted. A cliff stability hazard assessment scheme has been designed in which regions of high resistivity are interpreted as zones of open, dry fractures with a moderate mass movement potential. Regions of low resistivity are zones of wet, clay-filled fractures with a high mass movement potential. The OP tomography results indicate that the highest mass movement hazard appears to be associated with the marine caverns at the base of the cliff that are positioned at the point of strongest wave attack. These caverns likely occupy the future site of development of a sea arch that will threaten the OP building. The mass movement potential at the Rudder's command post area is low to moderate. The greatest risk there is associated with soil wedge failures at the top of the cliffs.

Improving the delineation of hydrocarbon-impacted soils and water through induced polarization (IP) tomographies: a field study at an industrial waste land.

PubMed

Deceuster, John; Kaufmann, Olivier

2012-08-01

Without a good estimation of samples representativeness, the delineation of the contaminated plume extent and the evaluation of volumes of hydrocarbon-impacted soils may remain difficult. To contribute to this question, a time domain induced polarization (IP) field experiment was conducted on an industrial waste land. Boreholes were drilled to specify the local geological context. Cross-hole seismic tomographies were performed to extend borehole logs and to draw an interpreted geological cross-section. Soil samples taken during drillings were analysed in laboratory. A preliminary survey was conducted to locate the IP profile. The polarization signatures linked to the presence of clayey sediments were filtered out from the data set. Chargeability and resistivity depth soundings were computed and compared to mean concentrations of total organic products to overcome the data support issue between the geophysical models and the spot samples of soils. A logarithmic relation between chargeabilities and smoothed hydrocarbon concentrations in soils was found. Taking into account contaminant's concentration thresholds defined in local codes and regulations allows defining chargeability classes to delineate hotspots on this site. This showed that IP tomography can be an accurate screening methodology. A statistical methodology is proposed to assess the efficiency of the investigation strategy. Copyright © 2012 Elsevier B.V. All rights reserved.

Electrical Resistivity Tomography monitoring reveals groundwater storage in a karst vadose zone

NASA Astrophysics Data System (ADS)

Watlet, A.; Kaufmann, O.; Van Camp, M. J.; Triantafyllou, A.; Cisse, M. F.; Quinif, Y.; Meldrum, P.; Wilkinson, P. B.; Chambers, J. E.

2016-12-01

Karst systems are among the most difficult aquifers to characterize, due to their high heterogeneity. In particular, temporary groundwater storage that occurs in the unsaturated zone and the discharge to deeper layers are difficult processes to identify and estimate with in-situ measurements. Electrical Resistivity Tomography (ERT) monitoring is meant to track changes in the electrical properties of the subsurface and has proved to be applicable to evidence and quantify hydrological processes in several types of environments. Applied to karst systems, it has particularly highlighted the challenges in linking electrical resistivity changes to groundwater content with usual approaches of petrophysical relationships, given the high heterogeneity of the subsurface. However, taking up the challenge, we undertook an ERT monitoring at the Rochefort Cave Laboratory (Belgium) lasting from Spring 2014 to Winter 2016. This includes 3 main periods of several months with daily measurements, from which seasonal groundwater content changes in the first meters of the vadose zone were successfully imaged. The monitoring concentrates on a 48 electrodes profile that goes from a limestone plateau to the bottom of a sinkhole. 3D UAV photoscans of the surveyed sinkhole and of the main chamber of the nearby cave were performed. Combined with lithological observations from a borehole drilled next to the ERT profile, the 3D information made it possible to project karstified layers visible in the cave to the surface and assess their potential locations along the ERT profile. Overall, this helped determining more realistic local petrophysical properties in the surveyed area, and improving the ERT data inversion by adding structural constraints. Given a strong air temperature gradient in the sinkhole, we also developed a new approach of temperature correction of the raw ERT data. This goes through the solving (using pyGIMLI package) of the 2D ground temperature field and its temporal evolution, calibrated with data from in-situ temperature probes installed along the ERT profile. Results from a 3D ERT monitoring of a sprinkling experiment, those of a gravimetric monitoring and an in-cave flow discharges monitoring were also of interest to verify interpretations of the permanent ERT monitoring in terms of groundwater content changes.

Electrical resistivity tomography to delineate greenhouse soil variability

NASA Astrophysics Data System (ADS)

Rossi, R.; Amato, M.; Bitella, G.; Bochicchio, R.

2013-03-01

Appropriate management of soil spatial variability is an important tool for optimizing farming inputs, with the result of yield increase and reduction of the environmental impact in field crops. Under greenhouses, several factors such as non-uniform irrigation and localized soil compaction can severely affect yield and quality. Additionally, if soil spatial variability is not taken into account, yield deficiencies are often compensated by extra-volumes of crop inputs; as a result, over-irrigation and overfertilization in some parts of the field may occur. Technology for spatially sound management of greenhouse crops is therefore needed to increase yield and quality and to address sustainability. In this experiment, 2D-electrical resistivity tomography was used as an exploratory tool to characterize greenhouse soil variability and its relations to wild rocket yield. Soil resistivity well matched biomass variation (R2=0.70), and was linked to differences in soil bulk density (R2=0.90), and clay content (R2=0.77). Electrical resistivity tomography shows a great potential in horticulture where there is a growing demand of sustainability coupled with the necessity of stabilizing yield and product quality.

Non-invasive Geophysical Surveys in Search of the Roman Temple of Augustus Under the Cathedral of Tarragona (Catalonia, Spain): A Case Study

NASA Astrophysics Data System (ADS)

Casas, Albert; Cosentino, Pietro L.; Fiandaca, Gianluca; Himi, Mahjoub; Macias, Josep M.; Martorana, Raffaele; Muñoz, Andreu; Rivero, Lluís; Sala, Roger; Teixell, Imma

2018-04-01

An integrated geophysical survey has been conducted at the Tarragona's Cathedral (Catalonia, NE Spain) with the aim to confirm the potential occurrence of archaeological remains of the Roman Temple dedicated to the Emperor Augustus. Many hypotheses have been proposed about its possible location, the last ones regarding the inner part of the Cathedral, which is one of the most renowned temples of Spain (twelfth century) evolving from Romanesque to Gothic styles. A geophysical project including electrical resistivity tomography (ERT) and ground probing radar (GPR) was planned over 1 year considering the administrative and logistic difficulties of such a project inside a cathedral of religious veneration. Finally, both ERT and GPR have been conducted during a week of intensive overnight surveys that provided detailed information on subsurface existing structures. The ERT method has been applied using different techniques and arrays, ranging from standard Wenner-Schlumberger 2D sections to full 3D electrical imaging with the advanced Maximum Yield Grid array. Electrical resistivity data were recorded extensively, making available many thousands of apparent resistivity data to obtain a complete 3D image after a full inversion. In conclusion, some significant buried structures have been revealed providing conclusive information for archaeologists. GPR results provided additional information about shallowest structures. The geophysical results were clear enough to persuade religious authorities and archaeologists to conduct selected excavations in the most promising areas that confirmed the interpretation of geophysical data. In conclusion, the significant buried structures revealed by geophysical methods under the cathedral were confirmed by archaeological digging as the basement of the impressive Roman Temple that headed the Provincial Forum of Tarraco, seat of the Concilium of Hispania Citerior Province.

Tailings Pond Characterization And Designing Through Geophysical Surveys In Dipping Sedimentary Formations

NASA Astrophysics Data System (ADS)

Muralidharan, D.; Andrade, R.; Anand, K.; Sathish, R.; Goud, K.

2009-12-01

Mining activities results into generation of disintegrated waste materials attaining increased mobilization status and requires a safe disposal mechanism through back filling process or secluded storage on surface with prevention of its interaction with environment cycle. The surface disposal of waste materials will become more critical in case of mined minerals having toxic or radioactive elements. In such cases, the surface disposal site is to be characterized for its sub-surface nature to understand its role in environmental impact due to the loading of waste materials. Near surface geophysics plays a major role in mapping the geophysical characters of the sub-surface formations in and around the disposal site and even to certain extent helps in designing of the storage structure. Integrated geophysical methods involving resistivity tomography, ground magnetic and shallow seismic studies were carried out over proposed tailings pond area of 0.3 sq. kms underlined by dipping sedimentary rocks consisting of ferruginous shales and dolomitic to siliceous limestone with varying thicknesses. The investigated site being located in tectonically disturbed area, geophysical investigations were carried out with number of profiles to visualize the sub-surface nature with clarity. The integration of results of twenty profiles of resistivity tomography with 2 m (shallow) and 10 m (moderate depth) electrode spacing’s enabled in preparing probable sub-surface geological section along the strike direction of the formation under the tailings pond with some geo-tectonic structure inferred to be a fault. Similarly, two resistivity tomography profiles perpendicular to the strike direction of the formations brought out the existence of buried basic intrusive body on the northern boundary of the proposed tailings pond. Two resistivity tomography profiles in criss-cross direction over the suspected fault zone confirmed fault existence on the north-eastern part of tailings pond. Thirty two magnetic profiles inside the tailings pond and surrounding areas on the southern part of the tailings pond enabled in identifying two parallel east-west intrusive bodies forming the impermeable boundary for the tailings pond. The shallow seismic refraction and the geophysical studies in and around the proposed tailings pond brought out the suitability of the site, even when the toxic elements percolates through the subsurface formations in to the groundwater system, the existence of dykes on either side of the proposed ponding area won’t allow the water to move across them thus by restricting the contamination within the tailings pond area. Similarly, the delineation of a fault zone within the tailings pond area helped in shifting the proposed dam axis of the pond to avoid leakage through the fault zone causing concern to environment pollution.

Permafrost Changes along the Alaska Highway Corridor, Southern Yukon, from Ground Temperature Measurements and DC Electrical Resistivity Tomography

NASA Astrophysics Data System (ADS)

Duguay, M. A.; Lewkowicz, A. G.; Smith, S.

2011-12-01

A natural gas pipeline running across permafrost terrain from Prudhoe Bay, Alaska, through Canada to US markets was first proposed more than 30 years ago. In the intervening period, mean annual air temperatures in the region have risen by 0.5-1.0°C and it is probable that the ground has also warmed. Renewed interest in the pipeline has meant that information on permafrost and geotechnical conditions within the Alaska Highway Corridor of the southern Yukon must be updated for engineering design and the assessment of environmental impacts. To accomplish this goal, results from 1977-1981 drilling and ground temperature monitoring programs within the proposed pipeline corridor were used in combination with air photo analysis to select sites potentially sensitive to climate change. The sites are distributed across the extensive and sporadic discontinuous permafrost zones over a distance of 475 km between Beaver Creek and Whitehorse. To date, 11 targeted boreholes with permafrost have been found and cased to permit renewed ground temperature monitoring. By the end of summer 2011, it is expected that another 7 will have been instrumented. Measurable temperature increases relative to the 1970s are expected, except where values were previously just below 0°C. In the latter case, if the sites are still in permafrost, latent heat effects may have substantially moderated the temperature increase. Electrical resistivity tomography surveys are also being conducted to characterize the local permafrost distribution and geotechnical conditions. These 2D resistivity profiles will be used with the ground temperatures to examine current conditions and response to climate change and vegetation disturbance.

Resistivity and self-potential tomography applied to groundwater remediation and contaminant plumes: Sandbox and field experiments

NASA Astrophysics Data System (ADS)

Mao, D.; Revil, A.; Hort, R. D.; Munakata-Marr, J.; Atekwana, E. A.; Kulessa, B.

2015-11-01

Geophysical methods can be used to remotely characterize contaminated sites and monitor in situ enhanced remediation processes. We have conducted one sandbox experiment and one contaminated field investigation to show the robustness of electrical resistivity tomography and self-potential (SP) tomography for these applications. In the sandbox experiment, we injected permanganate in a trichloroethylene (TCE)-contaminated environment under a constant hydraulic gradient. Inverted resistivity tomograms are able to track the evolution of the permanganate plume in agreement with visual observations made on the side of the tank. Self-potential measurements were also performed at the surface of the sandbox using non-polarizing Ag-AgCl electrodes. These data were inverted to obtain the source density distribution with and without the resistivity information. A compact horizontal dipole source located at the front of the plume was obtained from the inversion of these self-potential data. This current dipole may be related to the redox reaction occurring between TCE and permanganate and the strong concentration gradient at the front of the plume. We demonstrate that time-lapse self-potential signals can be used to track the kinetics of an advecting oxidizer plume with acceptable accuracy and, if needed, in real time, but are unable to completely resolve the shape of the plume. In the field investigation, a 3D resistivity tomography is used to characterize an organic contaminant plume (resistive domain) and an overlying zone of solid waste materials (conductive domain). After removing the influence of the streaming potential, the identified source current density had a magnitude of 0.5 A m-2. The strong source current density may be attributed to charge movement between the neighboring zones that encourage abiotic and microbially enhanced reduction and oxidation reactions. In both cases, the self-potential source current density is located in the area of strong resistivity gradient.

Delineating Potential Karst Water-Bearing Structures based on Resistivity Anomalies and Microtremor Analyses-A Case Study in Yunnan Province, China

NASA Astrophysics Data System (ADS)

Gan, F.; Su, C.; Liu, W.; Zhao, W.

2016-12-01

Heterogeneity, anisotropy and rugged landforms become challenges for geophysicists to locate drilling site by water-bearing structure profiling in Karst region. If only one geophysical method is used to achieve this objective, low resistivity anomalies deduced to be water-rich zones could actually be zones rich in marl and shale. In this study, integrated geophysical methods were used to locate a favorable drilling position for the provision of karst water to Juede village, which had been experiencing severe water shortages over a prolonged period. According to site conditions and hydrogeological data, appropriate geophysical profiles were conducted, approximately perpendicular to the direction of groundwater flow. In general, significant changes in resistivity occur between water-filled caves/ fractures and competent rocks. Thus, electrical and electromagnetic methods have been widely applied to search for karst groundwater indirectly. First, electrical resistivity tomography was carried out to discern shallow resistivity distributions within the profile where the low resistivity anomalies were of most interest. Second, one short profile of audio-frequency magnetotelluric survey was used to ascertain the vertical and horizontal extent of these low resistivity anomalies. Third, the microtremor H/V spectral ratio method was applied to identify potential water-bearing structures from low resistivity anomalies and to differentiate these from the interference of marl and shale with low resistivity. Finally, anomalous depths were estimated by interpreting Schlumberger sounding data to determine an optimal drilling site. The study shows that karst hydrogeology and geophysical methods can be effectively integrated for the purposes of karst groundwater exploration.

Geophysical Signitures From Hydrocarbon Contaminated Aquifers

NASA Astrophysics Data System (ADS)

Abbas, M.; Jardani, A.

2015-12-01

The task of delineating the contamination plumes as well as studying their impact on the soil and groundwater biogeochemical properties is needed to support the remediation efforts and plans. Geophysical methods including electrical resistivity tomography (ERT), induced polarization (IP), ground penetrating radar (GPR), and self-potential (SP) have been previously used to characterize contaminant plumes and investigate their impact on soil and groundwater properties (Atekwana et al., 2002, 2004; Benson et al., 1997; Campbell et al., 1996; Cassidy et al., 2001; Revil et al., 2003; Werkema et al., 2000). Our objective was to: estimate the hydrocarbon contamination extent in a contaminated site in northern France, and to adverse the effects of the oil spill on the groundwater properties. We aim to find a good combination of non-intrusive and low cost methods which we can use to follow the bio-remediation process, which is planned to proceed next year. We used four geophysical methods including electrical resistivity tomography, IP, GPR, and SP. The geophysical data was compared to geochemical ones obtained from 30 boreholes installed in the site during the geophysical surveys. Our results have shown: low electrical resistivity values; high chargeability values; negative SP anomalies; and attenuated GPR reflections coincident with groundwater contamination. Laboratory and field geochemical measurements have demonstrated increased groundwater electrical conductivity and increased microbial activity associated with hydrocarbon contamination of groundwater. Our study results support the conductive model suggested by studies such as Sauck (2000) and Atekwana et al., (2004), who suggest that biological alterations of hydrocarbon contamination can substantially modify the chemical and physical properties of the subsurface, producing a dramatic shift in the geo-electrical signature from resistive to conductive. The next stage of the research will include time lapse borehole and 3D geophysical measurements coupled to biological and chemical surface phase experiments in order to monitor the bioremediation processes.

Mapping Site Remediation with Electrical Resistivity Tomography Explored via Coupled-Model Simulations

NASA Astrophysics Data System (ADS)

Power, C.; Gerhard, J. I.; Tsourlos, P.; Giannopoulos, A.

2011-12-01

Remediation programs for sites contaminated with dense non-aqueous phase liquids (DNAPLs) would benefit from an ability to non-intrusively map the evolving volume and extent of the DNAPL source zone. Electrical resistivity tomography (ERT) is a well-established geophysical tool, widely used outside the remediation industry, that has significant potential for mapping DNAPL source zones. However, that potential has not been realized due to challenges in data interpretation from contaminated sites - in either a qualitative or quantitative way. The objective of this study is to evaluate the potential of ERT to map realistic, evolving DNAPL source zones within complex subsurface environments during remedial efforts. For this purpose, a novel coupled model was developed that integrates a multiphase flow model (DNAPL3D-MT), which generates realistic DNAPL release scenarios, with 3DINV, an ERT model which calculates the corresponding resistivity response. This presentation will describe the developed model coupling methodology, which integrates published petrophysical relationships to generate an electrical resistivity field that accounts for both the spatial heterogeneity of subsurface soils and the evolving spatial distribution of fluids (including permeability, porosity, clay content and air/water/DNAPL saturation). It will also present an example in which the coupled model was employed to explore the ability of ERT to track the remediation of a DNAPL source zone. A field-scale, three-dimensional release of chlorinated solvent DNAPL into heterogeneous clayey sand was simulated, including the subsurface migration and subsequent removal of the DNAPL source zone via dissolution in groundwater. Periodic surveys of this site via ERT applied at the surface were then simulated and inversion programs were used to calculate the subsurface distribution of electrical properties. This presentation will summarize this approach and its potential as a research tool exploring the range of site conditions under which ERT may prove useful in aiding DNAPL site remediation. Moreover, it is expected to provide a cost-effective avenue to test optimum ERT data acquisition, inversion and interpretative tools at contaminated sites.

Joint interpretation of seismic tomography and new magnetotelluric results provide evidence for support of high topography in the Southern Rocky Mountains and High Plains of eastern Colorado, USA

NASA Astrophysics Data System (ADS)

Feucht, D. W.; Sheehan, A. F.; Bedrosian, P.

2015-12-01

A recent magnetotelluric (MT) survey in central Colorado, USA, when interpreted alongside existing seismic tomography, reveals potential mechanisms of support for high topography both regionally and locally. Broadband and long period magnetotelluric data were collected at twenty-three sites along a 330 km E-W profile across the Southern Rocky Mountains and High Plains of central North America as part of the Deep RIFT Electrical Resistivity (DRIFTER) experiment. Remote-reference data processing yielded high quality MT data over a period range of 100 Hz to 10,000 seconds. A prominent feature of the regional geo-electric structure is the Denver Basin, which contains a thick package of highly conductive shales and porous sandstone aquifers. One-dimensional forward modeling was performed on stations within the Denver Basin to estimate depth to the base of this shallow conductor. Those estimates were then used to place a horizontal penalty cut in the model mesh of a regularized two-dimensional inversion. Two-dimensional modeling of the resistivity structure reveals two major anomalous regions in the lithosphere: 1) a high conductivity region in the crust under the tallest peaks of the Rocky Mountains and 2) a lateral step increase in lithospheric resistivity beneath the plains. The Rocky Mountain crustal anomaly coincides with low seismic wave speeds and enhanced heat flow and is thus interpreted as evidence of partial melt and/or high temperature fluids emplaced in the crust by tectonic activity along the Rio Grande Rift. The lateral variation in the mantle lithosphere, while co-located with a pronounced step increase in seismic velocity, appears to be a gradational boundary in resistivity across eastern Colorado and could indicate a small degree of compositional modification at the edge of the North American craton. These inferred conductivity mechanisms, namely crustal melt and modification of mantle lithosphere, likely contribute to high topography locally in the Rocky Mountains and regionally in the High Plains.

Using electrical resistivity tomography to differentiate sapwood from heartwood: application to conifers.

PubMed

Guyot, Adrien; Ostergaard, Kasper T; Lenkopane, Mothei; Fan, Junliang; Lockington, David A

2013-02-01

Estimating sapwood area is one of the main sources of error when upscaling point scale sap flow measurements to whole-tree water use. In this study, the potential use of electrical resistivity tomography (ERT) to determine the sapwood-heartwood (SW-HW) boundary is investigated for Pinus elliottii Engelm var. elliottii × Pinus caribaea Morelet var. hondurensis growing in a subtropical climate. Specifically, this study investigates: (i) how electrical resistivity is correlated to either wood moisture content, or electrolyte concentration, or both, and (ii) how the SW-HW boundary is defined in terms of electrical resistivity. Tree cross-sections at breast height are analysed using ERT before being felled and the cross-section surface sampled for analysis of major electrolyte concentrations, wood moisture content and density. Electrical resistivity tomography results show patterns with high resistivities occurring in the inner part of the cross-section, with much lower values towards the outside. The high-resistivity areas were generally smaller than the low-resistivity areas. A comparison between ERT and actual SW area measured after felling shows a slope of the linear regression close to unity (=0.96) with a large spread of values (R(2) = 0.56) mostly due to uncertainties in ERT. Electrolyte concentrations along sampled radial transects (cardinal directions) generally showed no trend from the centre of the tree to the bark. Wood moisture content and density show comparable trends that could explain the resistivity patterns. While this study indicates the potential for application of ERT for estimating SW area, it shows that there remains a need for refinement in locating the SW-HW boundary (e.g., by improvement of the inversion method, or perhaps electrode density) in order to increase the robustness of the method.

Real-time 4D electrical resistivity imaging of tracer transport within an energically stimulated fracture zone

NASA Astrophysics Data System (ADS)

Johnson, T. C.

2016-12-01

Hydraulic fracture stimulation is used extensively in the subsurface energy sector to improve access between energy bearing formations and production boreholes. However, large uncertainties exist concerning the location and extent of stimulated fractures, and concerning the behavior of flow within those fractures. This uncertainty often results in significant risks, including induced seismicity and contamination of potable groundwater aquifers. Time-lapse electrical resistivity tomography (ERT) is a proven method of imaging fluid flow within fracture networks, by imaging the change in bulk conductivity induced by the presence of an electrically anomalous tracer within the fracture. In this work we demonstrate characterization and flow monitoring of a stimulated fracture using real-time four-dimensional ERT imaging within an unsaturated rhyolite formation. After stimulation, a conductive tracer was injected into the fracture zone. ERT survey data were continuously and autonomously collected, pre-processed on site, submitted to an off-site high performance computing system for inversion, and returned to the field for inspection. Surveys were collected at approximately 12 minute intervals. Data transmission and inversion required approximately 2 minutes per survey. The time-lapse imaging results show the dominant flow-paths within the stimulated fracture zone, thereby revealing the location and extent of the fracture, and the behavior of tracer flow within the fracture. Ultimately real-time imaging will enable site operators to better understand stimulation operations, and control post-stimulation reservoir operations for optimal performance and environmental protection.

Contribution of 3D inversion of Electrical Resistivity Tomography data applied to volcanic structures

NASA Astrophysics Data System (ADS)

Portal, Angélie; Fargier, Yannick; Lénat, Jean-François; Labazuy, Philippe

2016-04-01

The electrical resistivity tomography (ERT) method, initially developed for environmental and engineering exploration, is now commonly used for geological structures imaging. Such structures can present complex characteristics that conventional 2D inversion processes cannot perfectly integrate. Here we present a new 3D inversion algorithm named EResI, firstly developed for levee investigation, and presently applied to the study of a complex lava dome (the Puy de Dôme volcano, France). EResI algorithm is based on a conventional regularized Gauss-Newton inversion scheme and a 3D non-structured discretization of the model (double grid method based on tetrahedrons). This discretization allows to accurately model the topography of investigated structure (without a mesh deformation procedure) and also permits a precise location of the electrodes. Moreover, we demonstrate that a complete 3D unstructured discretization limits the number of inversion cells and is better adapted to the resolution capacity of tomography than a structured discretization. This study shows that a 3D inversion with a non-structured parametrization has some advantages compared to classical 2D inversions. The first advantage comes from the fact that a 2D inversion leads to artefacts due to 3D effects (3D topography, 3D internal resistivity). The second advantage comes from the fact that the capacity to experimentally align electrodes along an axis (for 2D surveys) depends on the constrains on the field (topography...). In this case, a 2D assumption induced by 2.5D inversion software prevents its capacity to model electrodes outside this axis leading to artefacts in the inversion result. The last limitation comes from the use of mesh deformation techniques used to accurately model the topography in 2D softwares. This technique used for structured discretization (Res2dinv) is prohibed for strong topography (>60 %) and leads to a small computational errors. A wide geophysical survey was carried out on the Puy de Dôme volcano resulting in 12 ERT profiles with approximatively 800 electrodes. We performed two processing stages by inverting independently each profiles in 2D (RES2DINV software) and the complete data set in 3D (EResI). The comparison of the 3D inversion results with those obtained through a conventional 2D inversion process underlined that EResI allows to accurately take into account the random electrodes positioning and reduce out-line artefacts into the inversion models due to positioning errors out of the profile axis. This comparison also highlighted the advantages to integrate several ERT lines to compute the 3D models of complex volcanic structures. Finally, the resulting 3D model allows a better interpretation of the Puy de Dome Volcano.

Electrical resistivity tomography to quantify in situ liquid content in a full-scale dry anaerobic digestion reactor.

PubMed

André, L; Lamy, E; Lutz, P; Pernier, M; Lespinard, O; Pauss, A; Ribeiro, T

2016-02-01

The electrical resistivity tomography (ERT) method is a non-intrusive method widely used in landfills to detect and locate liquid content. An experimental set-up was performed on a dry batch anaerobic digestion reactor to investigate liquid repartition in process and to map spatial distribution of inoculum. Two array electrodes were used: pole-dipole and gradient arrays. A technical adaptation of ERT method was necessary. Measured resistivity data were inverted and modeled by RES2DINV software to get resistivity sections. Continuous calibration along resistivity section was necessary to understand data involving sampling and physicochemical analysis. Samples were analyzed performing both biochemical methane potential and fiber quantification. Correlations were established between the protocol of reactor preparation, resistivity values, liquid content, methane potential and fiber content representing liquid repartition, high methane potential zones and degradations zones. ERT method showed a strong relevance to monitor and to optimize the dry batch anaerobic digestion process. Copyright © 2015 Elsevier Ltd. All rights reserved.

A non-linear induced polarization effect on transient electromagnetic soundings

NASA Astrophysics Data System (ADS)

Hallbauer-Zadorozhnaya, Valeriya Yu.; Santarato, Giovanni; Abu Zeid, Nasser; Bignardi, Samuel

2016-10-01

In a TEM survey conducted for characterizing the subsurface for geothermal purposes, a strong induced polarization effect was recorded in all collected data. Surprisingly, anomalous decay curves were obtained in part of the sites, whose shape depended on the repetition frequency of the exciting square waveform, i.e. on current pulse length. The Cole-Cole model, besides being not directly related to physical parameters of rocks, was found inappropriate to model the observed distortion, due to induced polarization, because this model is linear, i.e. it cannot fit any dependence on current pulse. This phenomenon was investigated and explained as due to the presence of membrane polarization linked to constrictivity of (fresh) water-saturated pores. An algorithm for mathematical modeling of TEM data was then developed to fit this behavior. The case history is then discussed: 1D inversion, which accommodates non-linear effects, produced models that agree quite satisfactorily with resistivity and chargeability models obtained by an electrical resistivity tomography carried out for comparison.

Electrical resistance tomography using steel cased boreholes as electrodes

DOEpatents

Daily, W.D.; Ramirez, A.L.

1999-06-22

An electrical resistance tomography method is described which uses steel cased boreholes as electrodes. The method enables mapping the electrical resistivity distribution in the subsurface from measurements of electrical potential caused by electrical currents injected into an array of electrodes in the subsurface. By use of current injection and potential measurement electrodes to generate data about the subsurface resistivity distribution, which data is then used in an inverse calculation, a model of the electrical resistivity distribution can be obtained. The inverse model may be constrained by independent data to better define an inverse solution. The method utilizes pairs of electrically conductive (steel) borehole casings as current injection electrodes and as potential measurement electrodes. The greater the number of steel cased boreholes in an array, the greater the amount of data is obtained. The steel cased boreholes may be utilized for either current injection or potential measurement electrodes. The subsurface model produced by this method can be 2 or 3 dimensional in resistivity depending on the detail desired in the calculated resistivity distribution and the amount of data to constrain the models. 2 figs.

Electrical resistance tomography using steel cased boreholes as electrodes

DOEpatents

Daily, William D.; Ramirez, Abelardo L.

1999-01-01

An electrical resistance tomography method using steel cased boreholes as electrodes. The method enables mapping the electrical resistivity distribution in the subsurface from measurements of electrical potential caused by electrical currents injected into an array of electrodes in the subsurface. By use of current injection and potential measurement electrodes to generate data about the subsurface resistivity distribution, which data is then used in an inverse calculation, a model of the electrical resistivity distribution can be obtained. The inverse model may be constrained by independent data to better define an inverse solution. The method utilizes pairs of electrically conductive (steel) borehole casings as current injection electrodes and as potential measurement electrodes. The greater the number of steel cased boreholes in an array, the greater the amount of data is obtained. The steel cased boreholes may be utilized for either current injection or potential measurement electrodes. The subsurface model produced by this method can be 2 or 3 dimensional in resistivity depending on the detail desired in the calculated resistivity distribution and the amount of data to constain the models.

Resistivity and Seismic Surface Wave Tomography Results for the Nevşehir Kale Region: Cappadocia, Turkey

NASA Astrophysics Data System (ADS)

Coşkun, Nart; Çakır, Özcan; Erduran, Murat; Arif Kutlu, Yusuf

2014-05-01

The Nevşehir Kale region located in the middle of Cappadocia with approximately cone shape is investigated for existence of an underground city using the geophysical methods of electrical resistivity and seismic surface wave tomography together. Underground cities are generally known to exist in Cappadocia. The current study has obtained important clues that there may be another one under the Nevşehir Kale region. Two-dimensional resistivity and seismic profiles approximately 4-km long surrounding the Nevşehir Kale are measured to determine the distribution of electrical resistivities and seismic velocities under the profiles. Several high resistivity anomalies with a depth range 8-20 m are discovered to associate with a systematic void structure beneath the region. Because of the high resolution resistivity measurement system currently employed we were able to isolate the void structure from the embedding structure. Low seismic velocity zones associated with the high resistivity depths are also discovered. Using three-dimensional visualization techniques we show the extension of the void structure under the measured profiles.

An encoding readout method used for Multi-gap Resistive Plate Chambers (MRPCs) for muon tomography

NASA Astrophysics Data System (ADS)

Yue, X.; Zeng, M.; Wang, Y.; Wang, X.; Zeng, Z.; Zhao, Z.; Cheng, J.

2014-09-01

A muon tomography facility has been built in Tsinghua University. Because of the low flux of cosmic muon, an encoding readout method, based on the fine-fine configuration, was implemented for the 2880 channels induced signals from the Multi-gap Resistive Plate Chamber (MRPC) detectors. With the encoding method, the number of the readout electronics was dramatically reduced and thus the complexity and the cost of the facility was reduced, too. In this paper, the details of the encoding method, and the overall readout system setup in the muon tomography facility are described. With the commissioning of the facility, the readout method works well. The spatial resolution of all MRPC detectors are measured with cosmic muon and the preliminary imaging result are also given.

The role of integrated high resolution stratigraphic and geophysic surveys for groundwater modelling

NASA Astrophysics Data System (ADS)

Margiotta, S.; Mazzone, F.; Negri, S.; Calora, M.

2008-10-01

This work sets out a methodology of integrated geological, hydrogeological and geophysical surveys for the characterization of contaminated sites. The flow model of the shallow aquifer in the Brindisi area (recognized to be at significant environmental risk by the Italian government) and the impact of an antrophic structure on the groundwater flow have been evaluated. The stratigraphic and hydrogeological targets used for the calibration phase of the flow model provide a means of assessing calibration quality. The good calibration of the model point out the key role of a detailed knowledge of the physical-stratigraphycal attributes of the area to be studied and field data collection. Geoelectrical tomography focus the attention on an area resulted of particular interest by the flow model obtained. This method permit to reconstruct in detail the lateral and vertical lithological variations in the geological formations improving the spatial resolution of the data and consequently the scale of observation. Besides, anomaly resistivity values have been correlated with pollution. Chemical analysis have confirmed this correlation.

Study of Shallow Low-Enthalpy Geothermal Resources Using Integrated Geophysical Methods

NASA Astrophysics Data System (ADS)

De Giorgi, Lara; Leucci, Giovanni

2015-02-01

The paper is focused on low enthalpy geothermal exploration performed in south Italy and provides an integrated presentation of geological, hydrogeological, and geophysical surveys carried out in the area of municipality of Lecce. Geological and hydrogeological models were performed using the stratigraphical data from 51 wells. A ground-water flow (direction and velocity) model was obtained. Using the same wells data, the ground-water annual temperature was modeled. Furthermore, the ground surface temperature records from ten meteorological stations were studied. This allowed us to obtain a model related to the variations of the temperature at different depths in the subsoil. Integrated geophysical surveys were carried out in order to explore the low-enthalpy geothermal fluids and to evaluate the results of the model. Electrical resistivity tomography (ERT) and self-potential (SP) methods were used. The results obtained upon integrating the geophysical data with the models show a low-enthalpy geothermal resource constituted by a shallow ground-water system.

Determination of anisotropic karst features in the Biscayne Aquifer using multi electrical resistivity imaging techniques

NASA Astrophysics Data System (ADS)

Yeboah-Forson, A.; Whitman, D.

2012-12-01

The Biscayne Aquifer of Southeast Florida is characterized by limestone cavities and solution hole features that are often beneath the surface and are difficult to detect and quantify accurately. Electrical resistivity imaging (ERI) is often used to image the subsurface for detection of cavities and other karst features. A recent regional study of electrical anisotropy derived from rotated square array measurements measured coefficients of anisotropy of 1.12 or less. At one particular site however, the coefficient of anisotropy was found to be as high as 1.36 with the average minimum resistivity direction trending 105°. The highest values of anisotropy are found at squares array sizes equivalent to effective depths of 4-9m. The cause of this higher anisotropy and its associated orientation was investigated using a combination of azimuthal 2-D profiles and a 3-D tomography survey using a mixed dipole gradient array. Results indicate a low resistivity zone at a depth of 5-10 m in the saturated zone (10-40Ωm) trending 109° in the 2-D profiles and the presence of low resistivity zone (14-43Ωm) trending 90-105° in the 3-D model. This observed lower resistivity zone is at least 50% lower than the surrounding resistivity. Although further geophysical studies are planned at the site, the primary analysis from these three contrasting ERI techniques indicates that the cause of higher anisotropy might be due to the presence of a solution cavity oriented in the E-SE direction.

Cosmology with photometric weak lensing surveys: Constraints with redshift tomography of convergence peaks and moments

NASA Astrophysics Data System (ADS)

Petri, Andrea; May, Morgan; Haiman, Zoltán

2016-09-01

Weak gravitational lensing is becoming a mature technique for constraining cosmological parameters, and future surveys will be able to constrain the dark energy equation of state w . When analyzing galaxy surveys, redshift information has proven to be a valuable addition to angular shear correlations. We forecast parameter constraints on the triplet (Ωm,w ,σ8) for a LSST-like photometric galaxy survey, using tomography of the shear-shear power spectrum, convergence peak counts and higher convergence moments. We find that redshift tomography with the power spectrum reduces the area of the 1 σ confidence interval in (Ωm,w ) space by a factor of 8 with respect to the case of the single highest redshift bin. We also find that adding non-Gaussian information from the peak counts and higher-order moments of the convergence field and its spatial derivatives further reduces the constrained area in (Ωm,w ) by factors of 3 and 4, respectively. When we add cosmic microwave background parameter priors from Planck to our analysis, tomography improves power spectrum constraints by a factor of 3. Adding moments yields an improvement by an additional factor of 2, and adding both moments and peaks improves by almost a factor of 3 over power spectrum tomography alone. We evaluate the effect of uncorrected systematic photometric redshift errors on the parameter constraints. We find that different statistics lead to different bias directions in parameter space, suggesting the possibility of eliminating this bias via self-calibration.

Pseudo-polar drive patterns for brain electrical impedance tomography.

PubMed

Shi, Xuetao; Dong, Xiuzhen; Shuai, Wanjun; You, Fusheng; Fu, Feng; Liu, Ruigang

2006-11-01

Brain electrical impedance tomography (EIT) is a difficult task as brain tissues are enclosed by the skull of high resistance and cerebrospinal fluid (CSF) of low resistance, which makes internal resistivity information more difficult to extract. In order to seek a single source drive pattern that is more suitable for brain EIT, we built a more realistic experimental setting that simulates a head with the resistivity of the scalp, skull, CSF and brain, and compared the performance of adjacent, cross, polar and pseudo-polar drive patterns in terms of the boundary voltage dynamic range, independent measurement number, total boundary voltage changes and anti-noise performance based on it. The results demonstrate that the pseudo-polar drive pattern is optimal in all the aspects except for the dynamic range. The polar and cross drive patterns come next, and the adjacent drive pattern is the worst. Therefore, the pseudo-polar drive pattern should be chosen for brain EIT.

Using electrical resistance tomography to map subsurface temperatures

DOEpatents

Ramirez, A.L.; Chesnut, D.A.; Daily, W.D.

1994-09-13

A method is provided for measuring subsurface soil or rock temperatures remotely using electrical resistivity tomography (ERT). Electrical resistivity measurements are made using electrodes implanted in boreholes driven into the soil and/or at the ground surface. The measurements are repeated as some process changes the temperatures of the soil mass/rock mass. Tomographs of electrical resistivity are calculated based on the measurements using Poisson's equation. Changes in the soil/rock resistivity can be related to changes in soil/rock temperatures when: (1) the electrical conductivity of the fluid trapped in the soil's pore space is low, (2) the soil/rock has a high cation exchange capacity and (3) the temperature changes are sufficiently high. When these three conditions exist the resistivity changes observed in the ERT tomographs can be directly attributed to changes in soil/rock temperatures. This method provides a way of mapping temperature changes in subsurface soils remotely. Distances over which the ERT method can be used to monitor changes in soil temperature range from tens to hundreds of meters from the electrode locations. 1 fig.

Using electrical resistance tomography to map subsurface temperatures

DOEpatents

Ramirez, Abelardo L.; Chesnut, Dwayne A.; Daily, William D.

1994-01-01

A method is provided for measuring subsurface soil or rock temperatures remotely using electrical resistivity tomography (ERT). Electrical resistivity measurements are made using electrodes implanted in boreholes driven into the soil and/or at the ground surface. The measurements are repeated as some process changes the temperatures of the soil mass/rock mass. Tomographs of electrical resistivity are calculated based on the measurements using Poisson's equation. Changes in the soil/rock resistivity can be related to changes in soil/rock temperatures when: (1) the electrical conductivity of the fluid trapped in the soil's pore space is low, (2) the soil/rock has a high cation exchange capacity and (3) the temperature changes are sufficiently high. When these three conditions exist the resistivity changes observed in the ERT tomographs can be directly attributed to changes in soil/rock temperatures. This method provides a way of mapping temperature changes in subsurface soils remotely. Distances over which the ERT method can be used to monitor changes in soil temperature range from tens to hundreds of meters from the electrode locations.

New Electrical Resistivity Tomography approach for karst cave characterization: Castello di Lepre karst cave (Marsico Nuovo, Southern Italy).

NASA Astrophysics Data System (ADS)

Guerriero, Merilisa; Capozzoli, Luigi; De Martino, Gregory; Perciante, Felice; Gueguen, Erwan; Rizzo, Enzo

2017-04-01

Geophysical methods are commonly applied to characterize karst cave. Several geophysical method are used such as electrical resistivity tomography (ERT), gravimetric prospecting (G), ground penetrating radar (GPR) and seismic methods (S), in order to provide information on cave geometry and subsurface geological structure. In detail, in some complex karst systems, each geophysical method can only give partial information if used in normal way due to a low resolution for deep target. In order to reduce uncertainty and avoid misinterpretations based on a normal use of the electrical resistivity tomography method, a new ERT approach has been applied in karst cave Castello di Lepre (Marsico Nuovo, Basilicata region, Italy) located in the Mezo-Cenozoic carbonate substratum of the Monti della Maddalena ridge (Southern Appenines). In detail, a cross-ERT acquisition system was applied in order to improve the resolution on the electrical resistivity distribution on the surrounding geological structure of a karst cave. The cross-ERT system provides a more uniform model resolution vertically, increasing the resolution of the surface resistivity imaging. The usual cross-ERT is made by electrode setting in two or more borehole in order to acquire the resistivity data distribution. In this work the cross-ERT was made between the electrodes located on surface and along a karst cave, in order to obtain an high resolution of the electrical resistivity distributed between the cave and the surface topography. Finally, the acquired cross-ERT is potentially well-suited for imaging fracture zones since electrical current flow in fractured rock is primarily electrolytic via the secondary porosity associated with the fractures.

Method of imaging the electrical conductivity distribution of a subsurface

DOEpatents

Johnson, Timothy C.

2017-09-26

A method of imaging electrical conductivity distribution of a subsurface containing metallic structures with known locations and dimensions is disclosed. Current is injected into the subsurface to measure electrical potentials using multiple sets of electrodes, thus generating electrical resistivity tomography measurements. A numeric code is applied to simulate the measured potentials in the presence of the metallic structures. An inversion code is applied that utilizes the electrical resistivity tomography measurements and the simulated measured potentials to image the subsurface electrical conductivity distribution and remove effects of the subsurface metallic structures with known locations and dimensions.

Very-low-frequency resistivity, self-potential and ground temperature surveys on Taal volcano (Philippines): Implications for future activity

NASA Astrophysics Data System (ADS)

Zlotnicki, J.; Vargemezis, G.; Johnston, M. J. S.; Sasai, Y.; Reniva, P.; Alanis, P.

2017-06-01

Taal volcano is one of the most dangerous volcanoes in the Philippines. Thirty-three eruptions have occurred through historical time with several exhibiting cataclysmic phases. Most recent eruptions are confined to Volcano Island located within the prehistoric Taal collapse caldera that is now filled by Taal Lake. The last eruptive activity from 1965 to 1977 took place from Mt. Tabaro, about 2 km to the southwest of the Main Crater center. Since this time, episodes of seismic activity, ground deformation, gas release, surface fissuring, fumarole activity and temperature changes are recorded periodically around the main crater, but no major eruption has occurred. This period of quiescence is the third longest period without eruptive activity since 1572. In March 2010, a campaign based on Very-Low-Frequency (VLF) resistivity surveys together with repeated surveys of self-potential, ground temperature and fissure activity was intensified and the results compared to a large-scale Electrical Resistivity Tomography experiment. This work fortunately occurred before, within and after a new seismovolcanic crisis from late April 2010 to March 2011. The joint analysis of these new data, together with results from previous magnetotelluric soundings, allows a better description of the electrical resistivity and crustal structure beneath the Main Crater down to a depth of several kilometers. No indication of growth of the two geothermal areas located on both sides of the northern crater rim was apparent from 2005 to March 2010. These areas appear controlled by active fissures, opened during the 1992 and 1994 crises, that dip downward towards the core of the hydrothermal system located at about 2.5 km depth beneath the crater. Older mineralized fissures at lower elevations to the North of the geothermal areas also dip downward under the crater. Repeated self-potential and ground temperature surveys completed between 2005 and 2015 show new geothermal and hydrothermal activity in the areas of these older mineralized fissures that occurred during the April 2010 to March 2011 seismovolcanic crisis. This dramatically extends the geothermal activity further to the North on the volcano. The occurrence of these newly activated fissures after a long period of quiescence and indications of inflation in mid-2010 under the North rim of the Main Crater suggests that new eruptive activity near the North rim of the crater could occur in the future.

Combined geophysical methods for mapping infiltration pathways at the Aurora Water Aquifer recharge and recovery site

NASA Astrophysics Data System (ADS)

Jasper, Cameron A.

Although aquifer recharge and recovery systems are a sustainable, decentralized, low cost, and low energy approach for the reclamation, treatment, and storage of post- treatment wastewater, they can suffer from poor infiltration rates and the development of a near-surface clogging layer within infiltration ponds. One such aquifer recharge and recovery system, the Aurora Water site in Colorado, U.S.A, functions at about 25% of its predicted capacity to recharge floodplain deposits by flooding infiltration ponds with post-treatment wastewater extracted from river bank aquifers along the South Platte River. The underwater self-potential method was developed to survey self-potential signals at the ground surface in a flooded infiltration pond for mapping infiltration pathways. A method for using heat as a groundwater tracer within the infiltration pond used an array of in situ high-resolution temperature sensing probes. Both relatively positive and negative underwater self-potential anomalies are consistent with observed recovery well pumping rates and specific discharge estimates from temperature data. Results from electrical resistivity tomography and electromagnetics surveys provide consistent electrical conductivity distributions associated with sediment textures. A lab method was developed for resistivity tests of near-surface sediment samples. Forward numerical modeling synthesizes the geophysical information to best match observed self- potential anomalies and provide permeability distributions, which is important for effective aquifer recharge and recovery system design, and optimization strategy development.

Hydrothermal system of the Papandayan Volcano from temperature, self-potential (SP) and geochemical measurements

NASA Astrophysics Data System (ADS)

Byrdina, Svetlana; Revil, André; Gunawan, Hendra; Saing, Ugan B.; Grandis, Hendra

2017-07-01

Papandayan volcano in West Java, Indonesia, is characterized by intense hydrothermal activities manifested by numerous fumaroles at three craters or kawah, i.e. Mas, Manuk and Baru. The latter was created after November 2002 phreatic eruption. Since 2011, numerous volcano-tectonic B events are encountered and the volcano was set on alert status on several occasions. The purpose of the present study is to delineate the structure of the summital hydrothermal system from Self-Potential (SP), soil temperature and gas concentrations in the soil (CO2, SO2 and H2S) data. This combination of geophysical and geochemical methods allows identification of the weak permeable zones serving as preferential pathways for hydrothermal circulation and potential candidates to future landslides or flank collapses. This study is an on-going collaborative research project and we plan to conduct electrical resistivity tomography (ERT) and also Induced-Polarization (IP) surveys. Additional data would allow the 3D imaging of the studied area. The IP parameters will be used to characterise and to quantify the degree of alteration of the volcanic rocks as has been shown very recently in the laboratory studies. There are also rocks and soil samples that will undergo laboratory analyses at ISTerre for IP and complex resistivity parameters at the sample scale that will help to interpret the survey results.

Finding buried metallic pipes using a non-destructive approach based on 3D time-domain induced polarization data

NASA Astrophysics Data System (ADS)

Shao, Zhenlu; Revil, André; Mao, Deqiang; Wang, Deming

2018-04-01

The location of buried utility pipes is often unknown. We use the time-domain induced polarization method to non-intrusively localize metallic pipes. A new approach, based on injecting a primary electrical current between a pair of electrodes and measuring the time-lapse voltage response on a set of potential electrodes after shutting down this primary current is used. The secondary voltage is measured on all the electrodes with respect to a single electrode used as a reference for the electrical potential, in a way similar to a self-potential time lapse survey. This secondary voltage is due to the formation of a secondary current density in the ground associated with the polarization of the metallic pipes. An algorithm is designed to localize the metallic object using the secondary voltage distribution by performing a tomography of the secondary source current density associated with the polarization of the pipes. This algorithm is first benchmarked on a synthetic case. Then, two laboratory sandbox experiments are performed with buried metallic pipes located in a sandbox filled with some clean sand. In Experiment #1, we use a horizontal copper pipe while in Experiment #2 we use an inclined stainless steel pipe. The result shows that the method is effective in localizing these two pipes. At the opposite, electrical resistivity tomography is not effective in localizing the pipes because they may appear resistive at low frequencies. This is due to the polarization of the metallic pipes which blocks the charge carriers at its external boundaries.

Comparison of measuring strategies for the 3-D electrical resistivity imaging of tumuli

NASA Astrophysics Data System (ADS)

Tsourlos, Panagiotis; Papadopoulos, Nikos; Yi, Myeong-Jong; Kim, Jung-Ho; Tsokas, Gregory

2014-02-01

Artificial erected hills like tumuli, mounds, barrows and kurgans comprise monuments of the past human activity and offer opportunities to reconstruct habitation models regarding the life and customs during their building period. These structures also host features of archeological significance like architectural relics, graves or chamber tombs. Tumulus exploration is a challenging geophysical problem due to the complex distribution of the subsurface physical properties, the size and burial depth of potential relics and the uneven topographical terrain. Geoelectrical methods by means of three-dimensional (3-D) inversion are increasingly popular for tumulus investigation. Typically data are obtained by establishing a regular rectangular grid and assembling the data collected by parallel two-dimensional (2-D) tomographies. In this work the application of radial 3-D mode is studied, which is considered as the assembly of data collected by radially positioned Electrical Resistivity Tomography (ERT) lines. The relative advantages and disadvantages of this measuring mode over the regular grid measurements were investigated and optimum ways to perform 3-D ERT surveys for tumuli investigations were proposed. Comparative test was performed by means of synthetic examples as well as by tests with field data. Overall all tested models verified the superiority of the radial mode in delineating bodies positioned at the central part of the tumulus while regular measuring mode proved superior in recovering bodies positioned away from the center of the tumulus. The combined use of radial and regular modes seems to produce superior results in the expense of time required for data acquisition and processing.

Assessment of integrated electrical resistivity data on complex aquifer structures in NE Nuba Mountains - Sudan

NASA Astrophysics Data System (ADS)

Mohamed, N. E.; Yaramanci, U.; Kheiralla, K. M.; Abdelgalil, M. Y.

2011-07-01

Two geophysical techniques were integrated to map the groundwater aquifers on complex geological settings, in the crystalline basement terrain in northeast Nuba Mountains. The water flow is structurally controlled by the northwest-southeast extensional faults as one of several in-situ deformational patterns that are attributed to the collision of the Pan-African oceanic assemblage of the Nubian shield against the pre-Pan African continental crust to the west. The structural lineaments and drainage systems have been enhanced by the remote sensing technique. The geophysical techniques used are: vertical electrical soundings (VES) and electrical resistivity tomography (ERT), in addition to hydraulic conductivity measurements. These measurements were designed to overlap in order to improve the producibility of the geophysical data and to provide a better interpretation of the hydrogeological setting of the aquifer complex structure. Smooth and Block inversion schemes were attempted for the observed ERT data to study their reliability in mapping the different geometries in the complex subsurface. The VES data was conducted where ERT survey was not accessible, and inverted smoothly and merged with the ERT in the 3D resistivity grid. The hydraulic conductivity was measured for 42 water samples collected from the distributed dug wells in the study area; where extremely high saline zones were recorded and have been compared to the resistivity values in the 3D model.

Cosmology with photometric weak lensing surveys: Constraints with redshift tomography of convergence peaks and moments

DOE PAGES

Petri, Andrea; May, Morgan; Haiman, Zoltán

2016-09-30

Weak gravitational lensing is becoming a mature technique for constraining cosmological parameters, and future surveys will be able to constrain the dark energy equation of state w. When analyzing galaxy surveys, redshift information has proven to be a valuable addition to angular shear correlations. We forecast parameter constraints on the triplet (Ω m,w,σ 8) for a LSST-like photometric galaxy survey, using tomography of the shear-shear power spectrum, convergence peak counts and higher convergence moments. Here we find that redshift tomography with the power spectrum reduces the area of the 1σ confidence interval in (Ω m,w) space by a factor ofmore » 8 with respect to the case of the single highest redshift bin. We also find that adding non-Gaussian information from the peak counts and higher-order moments of the convergence field and its spatial derivatives further reduces the constrained area in (Ω m,w) by factors of 3 and 4, respectively. When we add cosmic microwave background parameter priors from Planck to our analysis, tomography improves power spectrum constraints by a factor of 3. Adding moments yields an improvement by an additional factor of 2, and adding both moments and peaks improves by almost a factor of 3 over power spectrum tomography alone. We evaluate the effect of uncorrected systematic photometric redshift errors on the parameter constraints. In conclusion, we find that different statistics lead to different bias directions in parameter space, suggesting the possibility of eliminating this bias via self-calibration.« less

Monitoring water flows with time-lapse Electrical Resistivity Tomography on the Super-Sauze landslide

NASA Astrophysics Data System (ADS)

Gance, J.; Sailhac, P.; Malet, J.-P.; Grandjean, G.; Supper, R.; Jochum, B.; Ottowitz, D.

2012-04-01

This work presents results of a permanent hydro-geophysical monitoring of an active landslide developed in clay-shales. Hydrology has been proved to be a major factor controlling the Super-Sauze earthflow behavior, but it knowledge still limited mainly because of the importance of spatial heterogeneities. The geometry of the bedrock creates internal crests and gullies that can guide waterflows or create a lock and engender an excess of pore water pressure; the soil surface characteristics plays also a large role in the surface hydraulic conductivity, and therefore, on the infiltration pattern. To understand in detail these processes, it is therefore important to monitor spatially at large scale (with high resolution) those phenomena and to overcome the monitoring difficulties inherent to a fast-moving clayey earthflow. The objectives of the survey are to identify and characterize spatially and temporarily the water flow circulation within the landslide body over a period of one year. The studied profile measures 114 m long and is surveyed with 93 electrodes spaced from 0.5, 1 or 2 meter according the soil surface cracking. Four resistivity datasets of 4300 measurements are acquired each day using a gradient array since May 2011. The monitoring is performed with the GEOMON4D system, developed by the Geological Survey of Austria. To facilitate the interpretation, humidity, conductivity, temperature, and piezometer sensors are placed along the profile. Two dGPS antenna placed upstream and downstream the profile allow to correlate the results with soil displacement. Lefranc tests and granulometry results realized on several samples have shown the important heterogeneities of the near surface. The objective of this work is to present the data processing strategy for the analysis of long periods time-lapse ERT survey of natural rain events taking into account changes through time of the position of the electrodes, changes in the soil surface state and important changes in sub-surface soil temperature. Two high-resolution optical cameras are installed on stable crests on the side of the cross-sections and time-lapse stereoscopy is used to reconstruct the displacement field to locate the electrodes in space and time (in order to take into account changes in the dipole geometry). The apparent electrical resistivity values were inverted with a time-lapse approach using an initial model constructed from statistical analysis of resistivity data and a priori knowledge on the landslide structure from a previous geotechnical model. The near surface apparent resistivity can vary of ten percent without any input of water. This shows the importance of temperature effect on the measurement. The temperature correction is handled from a complete study of the soil temperature propagation solving the heat equation with several temperature probes placed at different depths in soil and in the water table. The results are interpreted in combination to hydrological data (rain, water table level). The acquisition of 8 ERT all over the studied area, in different directions permits to create by interpolation a 3D electrical resistivity model of the area. This model shows the importance of the bedrock topography because high water content areas are visible at the theoretical hydrological network computed from the 3D geotechnical model of Travelletti and Malet (2011). Transversal waterflow circulation not predicted are also visible and permit to interpret the results taking into account the 3D structure of the landslide. A 250 m long P-wave tomography acquired on the studied profile and inversed with a quasi-Newton algorithm that uses Fresnel wavepaths and the finite bandwidth of the source signal, specially developed for the study of very heterogeneous soils, shows a very good correlation with electrical resistivity and permits to propose a geotechnical model of the profile. Spatially heterogeneous water flow patterns are identified and the presence of a deep water supply is hypothesized downstream of the investigated profile. The presentation will focus on some key factors and parameters to take into account for the analysis of time-lapse resistivity data. This work was supported by the Austrian Science Fund (FWF) (contract TRP 175-N21) and the French National Research Agency (ANR).

Solfatara volcano subsurface imaging: two different approaches to process and interpret multi-variate data sets

NASA Astrophysics Data System (ADS)

Bernardinetti, Stefano; Bruno, Pier Paolo; Lavoué, François; Gresse, Marceau; Vandemeulebrouck, Jean; Revil, André

2017-04-01

The need to reduce model uncertainty and produce a more reliable geophysical imaging and interpretations is nowadays a fundamental task required to geophysics techniques applied in complex environments such as Solfatara Volcano. The use of independent geophysical methods allows to obtain many information on the subsurface due to the different sensitivities of the data towards parameters such as compressional and shearing wave velocities, bulk electrical conductivity, or density. The joint processing of these multiple physical properties can lead to a very detailed characterization of the subsurface and therefore enhance our imaging and our interpretation. In this work, we develop two different processing approaches based on reflection seismology and seismic P-wave tomography on one hand, and electrical data acquired over the same line, on the other hand. From these data, we obtain an image-guided electrical resistivity tomography and a post processing integration of tomographic results. The image-guided electrical resistivity tomography is obtained by regularizing the inversion of the electrical data with structural constraints extracted from a migrated seismic section using image processing tools. This approach enables to focus the reconstruction of electrical resistivity anomalies along the features visible in the seismic section, and acts as a guide for interpretation in terms of subsurface structures and processes. To integrate co-registrated P-wave velocity and electrical resistivity values, we apply a data mining tool, the k-means algorithm, to individuate relationships between the two set of variables. This algorithm permits to individuate different clusters with the objective to minimize the sum of squared Euclidean distances within each cluster and maximize it between clusters for the multivariate data set. We obtain a partitioning of the multivariate data set in a finite number of well-correlated clusters, representative of the optimum clustering of our geophysical variables (P-wave velocities and electrical resistivities). The result is an integrated tomography that shows a finite number of homogeneous geophysical facies, and therefore permits to highlight the main geological features of the subsurface.

Comprehensive surface geophysical investigation of karst caves ahead of the tunnel face: A case study in the Xiaoheyan section of the water supply project from Songhua River, Jilin, China

NASA Astrophysics Data System (ADS)

Bin, Liu; Zhengyu, Liu; Shucai, Li; Lichao, Nie; Maoxin, Su; Huaifeng, Sun; Kerui, Fan; Xinxin, Zhang; Yonghao, Pang

2017-09-01

This paper describes the application of a comprehensive surface geophysical investigation of underground karst systems ahead of the tunnel face in the Xiaoheyan section in the main line of the water supply project from Songhua River, located in Jilin, China. To make an accurate investigation, Surface Electrical Resistivity Tomography (S-ERT), Transient Electromagnetic Method (TEM), Geological Drilling (Geo-D) and Three-dimensional Cross-hole Electrical Resistivity Tomography (3D cross-hole ERT) were applied to gain a comprehensive interpretation. To begin with, S-ERT and TEM are adopted to detect and delineate the underground karst zone. Based on the detection results, surface and in-tunnel Geo-D are placed in major areas with more specific and accurate information gained. After that, survey lines of 3D cross-hole ERT are used to conduct detailed exploration towards underground karst system. In the comprehensive investigation, it is the major question to make the best of prior information so as to promote the quality of detection. The paper has put forward strategies to make the full use of effective information in data processing and the main ideas of those strategies include: (1) Take the resistivity distribution of the subsurface stratum gained by S-ERT inversion as the initial model of TEM inversion; (2) Arrange borehole positions with the results of S-ERT and TEM. After that, gain more accurate information about resistivity of subsurface stratum using those boreholes located; (3) Through the comprehensive analysis of the information about S-ERT, TEM and Geo-D, set the initial model of 3D cross-hole resistivity inversion and meanwhile, gain the variation range of stratum resistivity. At last, a 3D cross-hole resistivity inversion based on the incorporated initial model and inequality constraint is conducted. Constrained inversion and joint interpretation are realized by the effective use of prior information in comprehensive investigation, helping to suppress the non-uniqueness problem of inversion so as to raise its reliability. In this way, a 3D detailed model of underground karst system which is 30 m ahead of tunnel face is finally formed. At the end of the paper, there is a geological sketch of the revealed karst caves, which illustrates the effectiveness of the presented strategy. To sum up, in the comprehensive investigation of underground karst caves, the integrated use of prior information can help to yield more accurate and detailed results.

Forward problem studies of electrical resistance tomography system on concrete materials

NASA Astrophysics Data System (ADS)

Ang, Vernoon; Rahiman, M. H. F.; Rahim, R. A.; Aw, S. R.; Wahab, Y. A.; Thomas W. K., T.; Siow, L. T.

2017-03-01

Electrical resistance tomography (ERT) is well known as non-invasive imaging technique, inexpensive, radiation free, visualization measurements of the multiphase flows and frequently applied in geophysical, medical and Industrial Process Tomography (IPT) applications. Application of ERT in concrete is a new exploration field, which can be used in monitoring and detecting the health and condition of concrete without destroying it. In this paper, ERT model under the condition of concrete is studied in which the sensitivity field model is produced and simulated by using COMSOL software. The affects brought by different current injection values with different concrete conductivity are studied in detail. This study able to provide the important direction for the further study of inverse problem in ERT system. Besides, the results of this technique hopefully can open a new exploration in inspection method of concrete structures in order to maintain the health of the concrete structure for civilian safety.

Using repeat electrical resistivity surveys to assess heterogeneity in soil moisture dynamics under contrasting vegetation types

NASA Astrophysics Data System (ADS)

Dick, Jonathan; Tetzlaff, Doerthe; Bradford, John; Soulsby, Chris

2018-04-01

As the relationship between vegetation and soil moisture is complex and reciprocal, there is a need to understand how spatial patterns in soil moisture influence the distribution of vegetation, and how the structure of vegetation canopies and root networks regulates the partitioning of precipitation. Spatial patterns of soil moisture are often difficult to visualise as usually, soil moisture is measured at point scales, and often difficult to extrapolate. Here, we address the difficulties in collecting large amounts of spatial soil moisture data through a study combining plot- and transect-scale electrical resistivity tomography (ERT) surveys to estimate soil moisture in a 3.2 km2 upland catchment in the Scottish Highlands. The aim was to assess the spatio-temporal variability in soil moisture under Scots pine forest (Pinus sylvestris) and heather moorland shrubs (Calluna vulgaris); the two dominant vegetation types in the Scottish Highlands. The study focussed on one year of fortnightly ERT surveys. The surveyed resistivity data was inverted and Archie's law was used to calculate volumetric soil moisture by estimating parameters and comparing against field measured data. Results showed that spatial soil moisture patterns were more heterogeneous in the forest site, as were patterns of wetting and drying, which can be linked to vegetation distribution and canopy structure. The heather site showed a less heterogeneous response to wetting and drying, reflecting the more uniform vegetation cover of the shrubs. Comparing soil moisture temporal variability during growing and non-growing seasons revealed further contrasts: under the heather there was little change in soil moisture during the growing season. Greatest changes in the forest were in areas where the trees were concentrated reflecting water uptake and canopy partitioning. Such differences have implications for climate and land use changes; increased forest cover can lead to greater spatial variability, greater growing season temporal variability, and reduced levels of soil moisture, whilst projected decreasing summer precipitation may alter the feedbacks between soil moisture and vegetation water use and increase growing season soil moisture deficits.

Sinop Province, Şahintepesi Region, Bayraktepe Tumulus' Display With Electrical Resistivity Tomography

NASA Astrophysics Data System (ADS)

Yıldırım, Şahin; Ahmet Yüksel, Fethi; Avcı, Kerim; Ziya Görücü, Mahmut

2017-04-01

Paphlagonia is located on the Boztepe Foreland (Sinop Foreland) and its peninsula, which extends northwards along the coastal lane of the Black Sea. Sinop is at the northernmost tip of Turkey, in the middle of the Black Sea region. Archaeological excavations of the entire Sinop province have uncovered artifacts from the Bronze Age dating back to 3000 BC. Most ancient sources indicate that Mithridates is buried in Sinop. It is alleged that the Tumuli on the crest of the historical peninsula, called Boztepe in Sinop, could be the resting spot of Mithridates. There are three tumuli in this area known as Şahin Tepesi Mevkii (Şahin Hill Site). In order to determine the location of the burial chamber of the tomb, Electrical Resistivity Tomography (ERT) measurement methods were used, which is a geophysical method capable of three dimensional (3D) measurement and evaluation. In the area of the tumulus, measurements were made in a 57 electrode array using a 42 x 36 m (total 1512 m2) spread electrode pattern with 6m spacing. In the study, an AGI brand SuperString R1 Resistivity device and equipment were used. Resistivity data were interpreted using AGI Earthimag 3D software. From the geoelectric resistivity data, 2D and 3D images were obtained as a result of data processing. In the tumulus area smooth geometrical forms and individual high-amplitude anomalies were visualized, that could be attributed to structural remains and the presence of archaeological materials. These anomalies were plotted on the gridded location plan of the excavation area. Within the artificial hill forming the tumulus, with regards to the natural geological units, anomalies such as very high resistivity, linear elongations, angular rotations, curves, etc. (stone wall, hollow room) that are caused by architectural elements were observed. These geometrically shaped, very highly resistive, anomalies should be checked. Keywords: Sinope, Tumulus, Electrical Resistivity Tomography, Archaeo-geophysics

Electrical resistance tomography during in-situ trichloroethylene remediation at the Savannah River Site

NASA Astrophysics Data System (ADS)

Daily, W.; Ramirez, A.

1995-04-01

Electrical resistance tomography was used to monitor in-situ remediation processes for removal of volatile organic compounds from subsurface water and soil at the Savannah River Site near Aiken, South Carolina. This work was designed to test the feasibility of injecting a weak mixture of methane in air as a metabolic carbon source for natural microbial populations which are capable of trichloroethylene degradation. Electrical resistance tomograms were constructed of the subsurface during the test to provide detailed images of the process. These images were made using an iterative reconstruction algorithm based on a finite element forward model and Newton-type least-squares minimization. Changes in the subsurface resistivity distribution were imaged by a pixel-by-pixel subtraction of images taken before and during the process. This differential tomography removed all static features of formation resistivity but clearly delineated dynamic features induced by remediation processes. The air-methane mixture was injected into the saturated zone and the intrained air migration paths were tomographically imaged by the increased resistivity of the path as air displaced formation water. We found the flow paths to be confined to a complex three-dimensional network of channels, some of which extended as far as 30 m from the injection well. These channels were not entirely stable over a period of months since new channels appeared to form with time. Also, the resistivity of the air injection paths increased with time. In another series of tests, resistivity images of water infiltration from the surface support similar conclusions about the preferential permeability paths in the vadose zone. In this case, the water infiltration front is confined to narrow channels which have a three-dimensional structure. Here, similar to air injection in the saturated zone, the water flow is controlled by local variations in formation permeability. However, temporal changes in these channels are minor, indicating that the permeable paths do not seem to be modified by continued infiltration.

Audiomagnetotellurics-Magnetotelluric (AMT-MT) survey of the Campi Flegrei inner caldera

NASA Astrophysics Data System (ADS)

Siniscalchi, Agata; Tripaldi, Simona; Romano, Gerardo; D'Auria, Luca; Improta, Luigi; Petrillo, Zaccaria

2017-04-01

In the framework of the EU project MED-SUV, an audiomagnetotellurics-magnetotelluric (AMT-MT) survey in the frequency band 0.1-100kHz was performed in the eastern border of the Campi Flegrei inner caldera comprising the area where seismicity is concentred in the last decade. This survey was aimed to provide new insights on the electrical resistivity structure of the subsoil. Among all the collected MT soundings, twenty-two, on a total of forty-three, were selected along a WSW-ENE alignment that crosses the main fumarole emissions (Solfatara, Pisciarelli and Agnano) and used for 2D regularized inversion. The obtained model is characterized by a quite narrow resistivity range that well matches typical range of enhanced geothermal environment as largely documented in the international literature. In particular focusing on the Solfatara and Pisciarelli districts the resistivity distribution clearly calls to mind the behavior of a high temperature geothermal system with a very conductive cap in the shallower part. Here the presence of gaps in this conductor just in correspondence of the main superficial emissions describes the inflow and outflow pathway of the shallow fluids circulation. A high resistive reservoir appearing at a depth of about 500 m b.s.l.. WithinWithin this region we selected a vertical resistivity profile just in correspondence of a Vp/Vs profile versus depth coming from a passive seismic tomography (Vanorio et al., 2005). The comparison of the two behaviors shows a clear anti-correlation between the two physical parameters (high resistivity and low Vp/Vs) in the depth range 500-1000 m supporting the interpretation that an over-pressurized gas bearing rocks under supercritical conditions constituting the reservoir of the enhanced geothermal system. On the eastern side of this resistive plume up to 2.5 km of depth is present a local relative conductive unit underneath the Pisciarelli area. In the same volume most of the recent (from 2005 up to date) micro-earthquake hypocenters are confined suggesting that in this volume geothermal fluid, pushed by the reservoir pressure and mixed with the powerful aquifer (testified in the well CF23), propagates in widespread pores and cracks triggering microseismicity. The present resistivity model is limited to 3 km of depth due to the adopted frequency range, thus does not investigate the magma feeding system of the Plegrean Field caldera that seismic imaging suggest to be a large magmatic sill within the basement formations at about 7.5 km of depth (Zollo et al., 2008). On the contrary it well image for the first time with higher resolution than in the past the geothermal system underneath Solfatara-Pisciarelli districts giving insights of the whole hydro-geothermal circulation.

Optimal surveys for weak-lensing tomography

NASA Astrophysics Data System (ADS)

Amara, Adam; Réfrégier, Alexandre

2007-11-01

Weak-lensing surveys provide a powerful probe of dark energy through the measurement of the mass distribution of the local Universe. A number of ground-based and space-based surveys are being planned for this purpose. Here, we study the optimal strategy for these future surveys using the joint constraints on the equation-of-state parameter wn and its evolution wa as a figure of merit by considering power spectrum tomography. For this purpose, we first consider an `ideal' survey which is both wide and deep and exempt from systematics. We find that such a survey has great potential for dark energy studies, reaching 1σ precisions of 1 and 10 per cent on the two parameters, respectively. We then study the relative impact of various limitations by degrading this ideal survey. In particular, we consider the effect of sky coverage, survey depth, shape measurement systematics, photometric redshift systematics and uncertainties in the non-linear power spectrum predictions. We find that, for a given observing time, it is always advantageous to choose a wide rather than a deep survey geometry. We also find that the dark energy constraints from power spectrum tomography are robust to photometric redshift errors and catastrophic failures, if a spectroscopic calibration sample of 104-105 galaxies are available. The impact of these systematics is small compared to the limitations that come from potential uncertainties in the power spectrum, due to shear measurement and theoretical errors. To help the planning of future surveys, we summarize our results with comprehensive scaling relations which avoid the need for full Fisher matrix calculations.

Leachate pollution management to overcome global climate change impact in Piyungan Landfill, Indonesia

NASA Astrophysics Data System (ADS)

Harjito; Suntoro; Gunawan, T.; Maskuri, M.

2018-03-01

Environmental problems associated with the landfill system are generated by domestic waste landfills, especially those with open dumping systems. In these systems, waste degrades and produces some gases, namely methane gas (CH4) and carbon dioxide (CO2), which can cause global climate change. This research aimed at identifying the areas that experience groundwater pollution and the spread pattern of leachate movement to the vicinity as well as to develop a leachate management model. The Electricity Resistivity Tomography (ERT) survey is deployed to assess the distribution of electrical resistivity in the polluted areas. In this study, the groundwater contamination is at a very low in the aquifer zone, i.e., 3-9 Ωm. It is caused by the downward migration of leachate to water table that raises the ion concentration of groundwater. These ions will increase the electrical conductivity (EC), i.e., up to 1,284 μmhos/cm, and decrease the electrical resistivity. The leachate spreads westward and northward at a depth of 6-17 m (aquifer) with a thickness of pollution between 4 and11 m.The recommended landfill management model involves the installation of rainwater drainage, use of cover and baseliner made of waterproof materials, and massive waste treatment.

Resolution capacity of geophysical monitoring regarding permafrost degradation induced by hydrological processes

NASA Astrophysics Data System (ADS)

Mewes, Benjamin; Hilbich, Christin; Delaloye, Reynald; Hauck, Christian

2017-12-01

Geophysical methods are often used to characterize and monitor the subsurface composition of permafrost. The resolution capacity of standard methods, i.e. electrical resistivity tomography and refraction seismic tomography, depends not only on static parameters such as measurement geometry, but also on the temporal variability in the contrast of the geophysical target variables (electrical resistivity and P-wave velocity). Our study analyses the resolution capacity of electrical resistivity tomography and refraction seismic tomography for typical processes in the context of permafrost degradation using synthetic and field data sets of mountain permafrost terrain. In addition, we tested the resolution capacity of a petrophysically based quantitative combination of both methods, the so-called 4-phase model, and through this analysed the expected changes in water and ice content upon permafrost thaw. The results from the synthetic data experiments suggest a higher sensitivity regarding an increase in water content compared to a decrease in ice content. A potentially larger uncertainty originates from the individual geophysical methods than from the combined evaluation with the 4-phase model. In the latter, a loss of ground ice can be detected quite reliably, whereas artefacts occur in the case of increased horizontal or vertical water flow. Analysis of field data from a well-investigated rock glacier in the Swiss Alps successfully visualized the seasonal ice loss in summer and the complex spatially variable ice, water and air content changes in an interannual comparison.

J-substitution algorithm in magnetic resonance electrical impedance tomography (MREIT): phantom experiments for static resistivity images.

PubMed

Khang, Hyun Soo; Lee, Byung Il; Oh, Suk Hoon; Woo, Eung Je; Lee, Soo Yeol; Cho, Min Hyoung; Kwon, Ohin; Yoon, Jeong Rock; Seo, Jin Keun

2002-06-01

Recently, a new static resistivity image reconstruction algorithm is proposed utilizing internal current density data obtained by magnetic resonance current density imaging technique. This new imaging method is called magnetic resonance electrical impedance tomography (MREIT). The derivation and performance of J-substitution algorithm in MREIT have been reported as a new accurate and high-resolution static impedance imaging technique via computer simulation methods. In this paper, we present experimental procedures, denoising techniques, and image reconstructions using a 0.3-tesla (T) experimental MREIT system and saline phantoms. MREIT using J-substitution algorithm effectively utilizes the internal current density information resolving the problem inherent in a conventional EIT, that is, the low sensitivity of boundary measurements to any changes of internal tissue resistivity values. Resistivity images of saline phantoms show an accuracy of 6.8%-47.2% and spatial resolution of 64 x 64. Both of them can be significantly improved by using an MRI system with a better signal-to-noise ratio.

An electric and electromagnetic geophysical approach for subsurface investigation of anthropogenic mounds in an urban environment

NASA Astrophysics Data System (ADS)

Pazzi, Veronica; Tapete, Deodato; Cappuccini, Luca; Fanti, Riccardo

2016-11-01

Scientific interest in mounds as geomorphological features that currently represent topographic anomalies in flat urban landscapes mainly lies on the understanding of their origin, either purely natural or anthropogenic. In this second circumstance, another question is whether traces of lost buildings are preserved within the mound subsurface and can be mapped as remnants testifying past settlement. When these landforms have been modified in centuries for civilian use, structural stability is a further element of concern. To address these issues we applied a geophysical approach based on a very low frequency electromagnetic (VLF-EM) technique and two-dimensional electrical resistivity tomography (2D-ERT) and integrated it with well-established surface survey methods within a diagnostic workflow of structural assessment. We demonstrate the practical benefits of this method in the English Cemetery of Florence, Italy, whose mixed nature and history of morphological changes are suggested by archival records. The combination of the two selected geophysical techniques allowed us to overcome the physical obstacles caused by tomb density and to prevent interference from the urban vehicular traffic on the geophysical signals. Eighty-two VLF-EM profiles and five 2D-ERTs were collected to maximise the spatial coverage of the subsurface prospection, while surface indicators of instability (e.g., tomb tilt, location, and direction of ground fractures and wall cracks) were mapped by standard metric survey. High resistive anomalies (> 300 and 400 Ωm) observed in VLF-EM tomographies are attributed to remnants of the ancient perimeter wall that are still buried along the southern side of the mound. While no apparent correlation is found between the causes of tomb and ground movements, the crack pattern map supplements the overall structural assessment. The main outcome is that the northern portion of the retaining wall is classed with the highest hazard rate. The impact of this cost-effective approach is to inform the design of maintenance and restoration measures based on improved geognostic knowledge. The geophysical and surface evidence informs decisions on where interventions are to be prioritised and whether costly invasive investigations are needed.

Geophysical evaluation of the Success Dam foundation, Porterville, California

USGS Publications Warehouse

Hunter, L.E.; Powers, M.H.; Haines, S.; Asch, T.; Burton, B.L.; Serafini, D.C.

2006-01-01

Success Dam is a zonedearth fill embankment located near Porterville, CA. Studies of Success Dam by the recent Dam Safety Assurance Program (DSAP) have demonstrated the potential for seismic instability and large deformation of the dam due to relatively low levels of earthquake shaking. The U.S. Army Corps of Engineers conducted several phases of investigations to determine the properties of the dam and its underlying foundation. Detailed engineering studies have been applied using a large number of analytical techniques to estimate the response of the dam and foundation system when subjected to earthquake loading. Although a large amount of data have been acquired, most are 'point' data from borings and results have to be extrapolated between the borings. Geophysical techniques were applied to image the subsurface to provide a better understanding of the spatial distribution of key units that potentially impact the stability. Geophysical investigations employing seismic refraction tomography, direct current (DC) resistivity, audio magnetotellurics (AMT) and self-potential (SP) were conducted across the location of the foundation of a new dam proposed to replace the existing one. Depth to bedrock and the occurrence of beds potentially susceptible to liquefaction were the focus of the investigations. Seismic refraction tomography offers a deep investigation of the foundation region and looks at compressional and shear properties of the material. Whereas resistivity surveys determines conductivity relationships in the shallow subsurface and can produce a relatively high-resolution image of geological units with different electrical properties. AMT was applied because it has the potential to look considerably deeper than the other methods, is useful for confirming depth to bedrock, and can be useful in identifying deep seated faults. SP is a passive electrical method that measures the electrical streaming potential in the subsurface that responds to the movement of ground water. SP surveys were conducted at low pool and high pool conditions in order to look for evidence of seepage below the existing dam. In this paper, we summarize these techniques, present their results at Success Dam, and discuss general application of these techniques for investigating dams and their foundations.

Geophysical Characterization of in situ Serpentinization Processes at the Coast Range Ophiolite Microbial Observatory (CROMO)

NASA Astrophysics Data System (ADS)

Ortiz, E.; Tominaga, M.; Cardace, D.; Schrenk, M. O.; Hoehler, T. M.; Kubo, M. D.

2016-12-01

Electrical and magnetic remote sensing both on land and at sea have emerged as a powerful approach to characterize in situ serpentinization and carbonation processes in time and space. We conducted 2D Electrical Resistivity Tomography (ERT) surveys to investigate in situ geological and hydrogeological architecture within the rock formation of the Jurassic age tectonic mélange portion of the Coast Range Ophiolite Microbiological Observatory (CROMO) where serpentinization processes are thought to facilitate an active deep biosphere. We acquired ERT imagery during both wet and dry seasons, along 9 survey tracks traversing two previously drilled wells, CSW1.1 and QV1.1, at different lateral and horizontal resolutions, yielding imagery with depth of 6.9 - 41m. Integrating ERT inversion models with wire-line and core data, we successfully documented temporal changes in the in situ hydrological properties at CROMO, i.e. the lateral and vertical water table boundaries (unconfined aquifer), non-permeable zones (confining bed), and possible confined aquifers that are juxtaposed within three dominant lithological units of serpentinite top soil, serpentinite gravel with clay, and serpentinite basement formation. We conducted rock magnetic experiments on core samples from drilled sites, including Magnetic Property Measurement System (MPMS) measurements, to better understand the connection between these hydrogeological properties and in situ serpentinization processes. Based on the observed downhole distribution of magnetite in correlation with ERT results and lithostratigraphy, we proposed that, at CROMO: (i) zones enriched in ferromagnetic minerals, correspond to in situ serpentinite formation with both high and low resistivity, suggesting that resistivity zones represent in situ architecture of consolidated serpentinite confining beds and possible fractured serpentinite aquifers, respectively; and (ii) zones (e.g. 14 - 31m at CSW site) enriched in superparamagnetic size magnetites (i.e. "pepper flake" magnetites that are observed in serpentine veins) are present in permeable serpentinite gravel aquifer formations (i.e. low resistivity, possible fractured serpentinite aquifers) suggesting groundwater available around the drilled sites is driving present-day serpentinization.

Publications - IC 52 | Alaska Division of Geological & Geophysical Surveys

Science.gov Websites

Mapping Advisory Board STATEMAP Publications Geophysics Program Information Geophysical Survey ; Aerial Photography; Aeromagnetic; Aeromagnetic Data; Aeromagnetic Survey; Airborne Geophysical Survey Resistivity Data; Apparent Resistivity Map; Apparent Resistivity Survey; Arctic Deposit; Arsenic; Arsenopyrite

Assessing clogging processes caused by biofilm growth and organic particle accumulation in constructed wetlands using time-lapse electrical resistivity tomography method

NASA Astrophysics Data System (ADS)

Mahjoub, Himi; Tapias, Josefina C.; Lovera, Raúl; Rivero, Lluís; Font, Xavier; Casas, Albert

2016-04-01

Constructed wetlands for removing pollutants from wastewater in small communities are growing rapidly in many regions of the world. The advantages over conventional mechanical sanitation systems, where land availability is not a limiting factor, are low energy requirements, easy operation and maintenance, low sludge production and cost-effectivity. Nevertheless, with time the cleaning process can result in gradual clogging of the porous layer by suspended solids, bacterial film, chemical precipitates and compaction. The clogging development causes decrease of hydraulic conductivity, reduced oxygen supply and further leads to a rapid decrease of the treatment performance. As the investment involved in reversing clogging can represent a substantial fraction of the cost of a new system it is essential to assess in advance the evolution of clogging process and detect potential failures in the system. Since there is a lack of experiences for monitoring the functionality of constructed wetlands time-lapse electrical resistivity tomography studies have been conducted at horizontal sub-surface flow municipal wastewater treatment wetlands of Catalonia (Spain). The results of this research show that electrical resistivity tomography can be a very useful technique for assessing the extent of silting up processes that clog the subsurface flow constructed wetlands through the gravel layer. In the unsaturated zone, the electrical resistivity is greater at the end of the filter, since the pores contains air which is dielectric, while at the beginning of the filter the resistivity is lower because the electrical conduction of organic matter around the mineral grains. Conversely, in the saturated zone, the electrical resistivity is lower at the end of the filter, since pores contain a higher proportion of high ionic conductivity wastewater, while at the beginning of the filter the electrical resistivity is higher because of the lower porosity due to the clogging process.

Applied potential tomography. A new noninvasive technique for measuring gastric emptying

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avill, R.; Mangnall, Y.F.; Bird, N.C.

1987-04-01

Applied potential tomography is a new, noninvasive technique that yields sequential images of the resistivity of gastric contents after subjects have ingested a liquid or semisolid meal. This study validates the technique as a means of measuring gastric emptying. Experiments in vitro showed an excellent correlation between measurements of resistivity and either the square of the radius of a glass rod or the volume of water in a spherical balloon when both were placed in an oval tank containing saline. Altering the lateral position of the rod in the tank did not alter the values obtained. Images of abdominal resistivitymore » were also directly correlated with the volume of air in a gastric balloon. Profiles of gastric emptying of liquid meals obtained using applied potential tomography were very similar to those obtained using scintigraphy or dye dilution techniques, provided that acid secretion was inhibited by cimetidine. Profiles of emptying of a mashed potato meal using applied potential tomography were also very similar to those obtained by scintigraphy. Measurements of the emptying of a liquid meal from the stomach were reproducible if acid secretion was inhibited by cimetidine. Thus, applied potential tomography is an accurate and reproducible method of measuring gastric emptying of liquids and particulate food. It is inexpensive, well tolerated, easy to use, and ideally suited for multiple studies in patients, even those who are pregnant.« less

Shallow subsurface imaging of the Piano di Pezza active normal fault (central Italy) by high-resolution refraction and electrical resistivity tomography coupled with time-domain electromagnetic data

NASA Astrophysics Data System (ADS)

Villani, Fabio; Tulliani, Valerio; Sapia, Vincenzo; Fierro, Elisa; Civico, Riccardo; Pantosti, Daniela

2015-12-01

The Piano di Pezza fault is the central section of the 35 km long L'Aquila-Celano active normal fault-system in the central Apennines of Italy. Although palaeoseismic data document high Holocene vertical slip rates (˜1 mm yr-1) and a remarkable seismogenic potential of this fault, its subsurface setting and Pleistocene cumulative displacement are still poorly known. We investigated for the first time the shallow subsurface of a key section of the main Piano di Pezza fault splay by means of high-resolution seismic and electrical resistivity tomography coupled with time-domain electromagnetic soundings (TDEM). Our surveys cross a ˜5-m-high fault scarp that was generated by repeated surface-rupturing earthquakes displacing Holocene alluvial fans. We provide 2-D Vp and resistivity images, which show significant details of the fault structure and the geometry of the shallow basin infill material down to 50 m depth. Our data indicate that the upper fault termination has a sub-vertical attitude, in agreement with palaeoseismological trench evidence, whereas it dips ˜50° to the southwest in the deeper part. We recognize some low-velocity/low-resistivity regions in the fault hangingwall that we relate to packages of colluvial wedges derived from scarp degradation, which may represent the record of some Holocene palaeo-earthquakes. We estimate a ˜13-15 m throw of this fault splay since the end of the Last Glacial Maximum (˜18 ka), leading to a 0.7-0.8 mm yr-1 throw rate that is quite in accordance with previous palaeoseismic estimation of Holocene vertical slip rates. The 1-D resistivity models from TDEM soundings collected along the trace of the electrical profile significantly match with 2-D resistivity images. Moreover, they indicate that in the fault hangingwall, ˜200 m away from the surface fault trace, the pre-Quaternary carbonate basement is at ˜90-100 m depth. We therefore provide a minimal ˜150-160 m estimate of the cumulative throw of the Piano di Pezza fault system in the investigated section. We further hypothesize that the onset of the Piano di Pezza fault activity may date back to the Middle Pleistocene (˜0.5 Ma), so this is a quite young active normal fault if compared to other mature normal fault systems active since 2-3 Ma in this portion of the central Apennines.

On the Salt Water Intrusion into the Durusu Lake, Istanbul: A Joint Central Loop TEM And Multi-Electrode ERT Field Survey

NASA Astrophysics Data System (ADS)

Ardali, Ayça Sultan; Tezkan, Bülent; Gürer, Aysan

2018-02-01

Durusu Lake is the biggest and most important freshwater source supplying drinking water to the European side of Istanbul. In this study, electrical resistivity tomography (ERT) and transient electromagnetic (TEM) measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of Durusu Lake. The ERT and TEM measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier. TEM data were interpreted using different 1-D inversion methods such as Occam, Marquardt, and laterally constrained inversion (LCI). ERT data were interpreted using 2-D inversion techniques. The inversion results of ERT and TEM data were shown as resistivity depth sections including topography. The sand layer spreading over the basin has a resistivity of 150-400 Ωm with a thickness of 5-10 m. The sandy layer with clay, silt, and gravel has a resistivity of 15-100 Ωm and a thickness of 10-40 m followed by a clay layer of a resistivity below 10 Ωm. When the inversion of these data is interpreted along with the hydrogeology of the area, it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close. Using information from boreholes around the lake, it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses.

Gravimetric water distribution assessment from geoelectrical methods (ERT and EMI) in municipal solid waste landfill.

PubMed

Dumont, Gaël; Pilawski, Tamara; Dzaomuho-Lenieregue, Phidias; Hiligsmann, Serge; Delvigne, Frank; Thonart, Philippe; Robert, Tanguy; Nguyen, Frédéric; Hermans, Thomas

2016-09-01

The gravimetric water content of the waste material is a key parameter in waste biodegradation. Previous studies suggest a correlation between changes in water content and modification of electrical resistivity. This study, based on field work in Mont-Saint-Guibert landfill (Belgium), aimed, on one hand, at characterizing the relationship between gravimetric water content and electrical resistivity and on the other hand, at assessing geoelectrical methods as tools to characterize the gravimetric water distribution in a landfill. Using excavated waste samples obtained after drilling, we investigated the influences of the temperature, the liquid phase conductivity, the compaction and the water content on the electrical resistivity. Our results demonstrate that Archie's law and Campbell's law accurately describe these relationships in municipal solid waste (MSW). Next, we conducted a geophysical survey in situ using two techniques: borehole electromagnetics (EM) and electrical resistivity tomography (ERT). First, in order to validate the use of EM, EM values obtained in situ were compared to electrical resistivity of excavated waste samples from corresponding depths. The petrophysical laws were used to account for the change of environmental parameters (temperature and compaction). A rather good correlation was obtained between direct measurement on waste samples and borehole electromagnetic data. Second, ERT and EM were used to acquire a spatial distribution of the electrical resistivity. Then, using the petrophysical laws, this information was used to estimate the water content distribution. In summary, our results demonstrate that geoelectrical methods represent a pertinent approach to characterize spatial distribution of water content in municipal landfills when properly interpreted using ground truth data. These methods might therefore prove to be valuable tools in waste biodegradation optimization projects. Copyright © 2016 Elsevier Ltd. All rights reserved.

Geophysical Images of the Shallow Hydrothermal Degassing at Solfatara (Phlegrean Fields, Italy)

NASA Astrophysics Data System (ADS)

Byrdina, S.; Vandemeulebrouck, J.; Cardellini, C.; Chiodini, G.; Legaz, A.; Camerlynck, C.; Lebourg, T.

2014-12-01

We present the results of an electric resistivity tomography (ERT) survey, combined with mappings of diffuse carbon dioxide flux, ground temperature and self-potential (SP) at Solfatara, the most active crater of Phlegrean Fields. Solfatara is characterized by an intense carbon dioxide degassing, fumarole activity, and ground deformation. This ensemble of methods is applied to image the hydrothermal system of Solfatara, to understand the geometry of the fluid circulation, and to define the extension of the hydrothermal plume at a high enough resolution for a quantitative modeling. ERT inversion results show Solfatara as a globally conductive structure, with resistivity in the range 1-200 Ohmm. Broad negative anomaly of self-potential in the inner part of Solfatara with a minimum in the area of Bocca Grande suggests a significant downward flow of condensing liquid water. Comparison between spatial variations of resistivity and gas flux indicates that resistivity changes at depth are related to gas saturation and fluid temperature. These variations delineate two plume structures: a liquid-dominated conductive plume below Fangaia mud-pool and a gas-dominated plume below Bocca Grande fumarole. The geometry of the Fangaia liquid-saturated plume is also imaged by a high resolution 3-D resistivity model. In order to estimate the permeability, we propose a 2-D axis-symmetric numerical model coupling Richards's equation for fluid flow in conditions of partial saturation with the resistivity calculation as function of saturation only. Alternatively, we apply the Dupuit equation to estimate the permeability of the shallow layer. Using these two approaches, we obtain the permeability of the shallow layer below Fangaia which ranges between (2 - 4) 10-14 m 2.

The Nature and Subsurface Geometry of Late Holocene Coquina Rocks, Karaburun-Istanbul, NW Turkey

NASA Astrophysics Data System (ADS)

Ekinci, Y. L.; Demirci, A.; Erginal, A. E.; Kaya, H.; Ekinci, R.

2012-04-01

The so-called coquina defines moderately to hardly amalgamated shell debris by calcium carbonate cement. Even though its some depositional features are similar to intertidal beachrocks and carbonate-cemented dune rocks or eolianites, coquina occurs in shoal environments and is, in some cases, representative of tectonically uplifted coasts when it exposes remarkably above sea-level. In this study (supported financially by the Research Foundation of Çanakkale Onsekiz Mart University under project number COMUBAP: 2011/41), we discuss diagenetic features, radiocarbon age and subsurface geometry of coquina on Black Sea coast of Istanbul, NW Turkey, where such a Late Holocene occurrence has not been recorded so far. Having a visible thickness of 1 m, the coquina beds crop out on a slightly inclined wide beach formed mostly of shell fragments less than 5 cm in size. It contains calcite and aragonite as connective cement and broken or unbroken shells of Donacilla sp., Pecten glaucum and Ostrea edulis together with various foraminifera such as Elphidium macellum Ammonia compacta and coccolithophore Emiliania huxleyi. Radiocarbon ages from four bulk samples yielded calibrated ages ranging between 3.7 and 2.8 ka BP. Electrical resistivity tomography survey along three distinct transects perpendicular to the coastline were carried out in order to understand the thickness of coquina and its subsurface extensions along the beach. The apparent resistivity data were acquired along the survey lines of 21 electrodes with electrode spacing of 2 m, to give a total length of the line of 40 m. Dipole-dipole electrode configuration was used for 9 data levels. Topographic changes at the locations of each electrode points were determined by means of optical leveling technique for a more accurate calculation and interpretation. Apparent resistivity data were inverted by using 2D smoothness-constrained least squares algorithm. Similar electrical resistivity tomograms were obtained for three lines after the inversion process. The 2D resistivity images displayed a depth range of ~ 4.5 m and showed a strong resistivity contrast between coquina beach material (composed of shell fragments) and coquina rocks. Low resistivity values located at the northern lowermost part of tomograms point to seawater saturated material whilst the highest resistivity values indicate coquina beach material, having larger pore spaces between the grains. The northern uppermost parts of the tomograms, having a moderate resistivity range, mark the coquina rocks with a thickness of ~ 1-1.5 m. Additionally, the images also showed that the landward extension of the coquina rocks reaches ~ 22 m. Keywords: Coquina rocks, diagenetic features, radiocarbon age, subsurface geometry, İstanbul-Turkey

Brine delineation and monitoring with electrical resistivity tomography and electromagnetic borehole logging at the Fort Knox well field near West Point, Kentucky

USGS Publications Warehouse

Henderson, Rory; Unthank, Michael D.; Zettwoch, Douglas D.; Lane, John W.

2010-01-01

The potable water system at Fort Knox is threatened by brine contamination from improperly abandoned natural gas exploration wells. The Fort Knox well field is located near the town of West Point, Kentucky, in the flood plain of the Ohio River. At the site, unconsolidated sediments approximately 30 – 40 m thick, overlie shale and porous limestone. Brine is believed to flow vertically from the underlying formations to the unconsolidated aquifer through damaged or leaky well casings under a high hydraulic gradient from the artificially pressurized porous limestone, which is utilized for natural gas storage by a regional energy company. Upon reaching the unconsolidated aquifer, brinecontaminated groundwater enters water supply production wells under the pumping‐induced gradient. As part of the Fort Knox remediation strategy to reduce the impact of brine contamination, electrical resistivity tomography (ERT) and borehole electromagnetic (EM) logs are being collected annually to detect gross changes in subsurface conductivity. The 2009 ERT data show areas of high conductivity on the western (contaminated) side of the site with conductivities more than an order of magnitude higher than on the eastern (uncontaminated) side of the site. The areas of high conductivity are interpreted as brine contamination, consistent with known regions of brine contamination. Conductivities from the EM logs are consistent with the results from the ERT inversions. The EM logs show little change between 2008 and 2009, except for some small changes in the brine distribution in well PZ1. Yearly ERT surveys will be continued to detect new areas of brine contamination and monitor the remediation effort.

Geophysical and geomorphological investigations of a Quaternary karstic paleolake and its underground marine connection in Cassis (Bestouan, Cassis, SE France)

NASA Astrophysics Data System (ADS)

Romey, Carole; Rochette, Pierre; Vella, Claude; Arfib, Bruno; Andrieu-Ponel, Valérie; Braucher, Régis; Champollion, Cédric; Douchet, Marc; Dussouillez, Philippe; Hermitte, Daniel; Mattioli, Emanuela; Parisot, Jean-Claude; Schwenninger, Jean-Luc

2014-06-01

An original karstic system in a coastal alluvial plain located in a carbonate environment (Cassis, Provence - SE France) was studied using a multi-method approach (electrical resistivity tomography, gravimetric, passive seismic survey), combined with geomorphologic methods, surface observations and drilling. Limestone dissolution and/or cavity collapse led to the development of a polje, which was filled rapidly by erosion of Aptian marls. The combination of several dating and paleoenvironmental proxies indicates that the polje was filled during a glacial period (MIS 6, 8 or 10, i.e. in the 130-360 ka age range). This discovery has implications for the understanding of karst processes. The connection between the polje and the three km-long Bestouan underwater karstic conduit with submarine outlet is strongly suggested by sedimentological studies and geophysical prospections.

Time-lapse electrical surveys to locate infiltration zones in weathered hard rock tropical areas

NASA Astrophysics Data System (ADS)

Wubda, M.; Descloitres, M.; Yalo, N.; Ribolzi, O.; Vouillamoz, J. M.; Boukari, M.; Hector, B.; Séguis, L.

2017-07-01

In West Africa, infiltration and groundwater recharge processes in hard rock areas are depending on climatic, surface and subsurface conditions, and are poorly documented. Part of the reason is that identification, location and monitoring of these processes is still a challenge. Here, we explore the potential for time-lapse electrical surveys to bring additional information on these processes for two different climate situations: a semi-arid Sahelian site (north of Burkina and a humid Sudanian site (north of Benin), respectively focusing on indirect (localized) and direct (diffuse) recharge processes. The methodology is based on surveys in dry season and rainy season on typical pond or gully using Electrical Resistivity Tomography (ERT) and frequency electromagnetic (FEM) apparent conductivity mapping. The results show that in the Sahelian zone an indirect recharge occurs as expected, but infiltration doesn't takes place at the center of the pond to the aquifer, but occurs laterally in the banks. In Sudanian zone, the ERT survey shows a direct recharge process as expected, but also a complicated behavior of groundwater dilution, as well as the role of hardpans for fast infiltration. These processes are ascertained by groundwater monitoring in adjacent observing wells. At last, FEM time lapse mapping is found to be difficult to quantitatively interpreted due to the non-uniqueness of the model, clearly evidenced comparing FEM result to auger holes monitoring. Finally, we found that time-lapse ERT can be an efficient way to track infiltration processes across ponds and gullies in both climatic conditions, the Sahelian setting providing results easier to interpret, due to significant resistivity contrasts between dry and rain seasons. Both methods can be used for efficient implementation of punctual sensors for complementary studies. However, FEM time-lapse mapping remains difficult to practice without external information that renders this method less attractive for quantitative interpretation purposes.

Non-invasive determination of absolute lung resistivity in adults using electrical impedance tomography.

PubMed

Zhang, Jie; Patterson, Robert

2010-08-01

Lung resistivity is a physiological parameter that describes the electrical characteristics of the lungs. Lung composition changes due to changes in the lung tissues, fluid and air volume. Various diseases that can cause a change in lung composition may be monitored by measuring lung resistivity. Currently, there is no accepted non-invasive method to measure lung resistivity. In this study, we presented a method and framework to non-invasively determine lung resistivity using electrical impedance tomography (EIT). By comparing actual measurements from subjects with data from a 3D human thorax model, an EIT image can be reconstructed to show a resistivity difference between the model and the subject. By adjusting the lung resistivity in the model, the resistivity difference in the lung regions can be reduced to near zero. This resistivity value then is the estimation of the lung resistivity of the subject. Using the proposed method, the lung resistivities of four normal adult males (43 +/- 13 years, 78 +/- 10 kg) in the supine position at air volumes starting at functional residual capacity (FRC--end expiration) and increasing in 0.5 l steps to 1.5 l were studied. The averaged lung resistivity changes 12.59%, from 1406 Omega cm to 1583 Omega cm, following the inspiration of 1.5 l air from FRC. The coefficients of variation (CV) of precision for the four subjects are less than 10%. The experiment was repeated five times at each air volume on a subject to test the reproducibility. The CVs are less than 3%. The results show that it is feasible to determine absolute lung resistivity using an EIT-based method.

A field assessment of the value of steady shape hydraulic tomography for characterization of aquifer heterogeneities

USGS Publications Warehouse

Bohling, Geoffrey C.; Butler, James J.; Zhan, Xiaoyong; Knoll, Michael D.

2007-01-01

Hydraulic tomography is a promising approach for obtaining information on variations in hydraulic conductivity on the scale of relevance for contaminant transport investigations. This approach involves performing a series of pumping tests in a format similar to tomography. We present a field‐scale assessment of hydraulic tomography in a porous aquifer, with an emphasis on the steady shape analysis methodology. The hydraulic conductivity (K) estimates from steady shape and transient analyses of the tomographic data compare well with those from a tracer test and direct‐push permeameter tests, providing a field validation of the method. Zonations based on equal‐thickness layers and cross‐hole radar surveys are used to regularize the inverse problem. The results indicate that the radar surveys provide some useful information regarding the geometry of the K field. The steady shape analysis provides results similar to the transient analysis at a fraction of the computational burden. This study clearly demonstrates the advantages of hydraulic tomography over conventional pumping tests, which provide only large‐scale averages, and small‐scale hydraulic tests (e.g., slug tests), which cannot assess strata connectivity and may fail to sample the most important pathways or barriers to flow.

Electric field tomography for contactless imaging of resistivity in biomedical applications.

PubMed

Korjenevsky, A V

2004-02-01

The technique of contactless imaging of resistivity distribution inside conductive objects, which can be applied in medical diagnostics, has been suggested and analyzed. The method exploits the interaction of a high-frequency electric field with a conductive medium. Unlike electrical impedance tomography, no electric current is injected into the medium from outside. The interaction is accompanied with excitation of high-frequency currents and redistribution of free charges inside the medium leading to strong and irregular perturbation of the field's magnitude outside and inside the object. Along with this the considered interaction also leads to small and regular phase shifts of the field in the area surrounding the object. Measuring these phase shifts using a set of electrodes placed around the object enables us to reconstruct the internal structure of the medium. The basics of this technique, which we name electric field tomography (EFT), are described, simple analytical estimations are made and requirements for measuring equipment are formulated. The realizability of the technique is verified by numerical simulations based on the finite elements method. Results of simulation have confirmed initial estimations and show that in the case of EFT even a comparatively simple filtered backprojection algorithm can be used for reconstructing the static resistivity distribution in biological tissues.

Integrated geoelectrical survey for groundwater and shallow subsurface evaluation: case study at Siliyin spring, El-Fayoum, Egypt

NASA Astrophysics Data System (ADS)

Metwaly, Mohamed; El-Qady, Gad; Massoud, Usama; El-Kenawy, Abeer; Matsushima, Jun; Al-Arifi, Nasser

2010-09-01

Siliyin spring is one of the many natural fresh water springs in the Western Desert of Egypt. It is located at the central part of El-Fayoum Delta, which is a potential place for urban developments and touristic activities. Integrated geoelectrical survey was conducted to facilitate mapping the groundwater resources and the shallow subsurface structures in the area. Twenty-eight transient electromagnetic (TEM) soundings, three vertical electrical soundings (VES) and three electrical resistivity tomography (ERT) profiles were carried out around the Siliyin spring location. The dense cultivation, the rugged topography and the existence of infra structure in the area hindered acquiring more data. The TEM data were inverted jointly with the VES and ERT, and constrained by available geological information. Based on the inversion results, a set of geoelectrical cross-sections have been constructed. The shallow sand to sandy clay layer that forms the shallow aquifer has been completely mapped underneath and around the spring area. Flowing of water from the Siliyin spring is interconnected with the lateral lithological changes from clay to sand soil. Exploration of the extension of Siliyin spring zone is recommended. The interpretation emphasizes the importance of integrating the geoelectrical survey with the available geological information to obtain useful, cheap and fast lithological and structural subsurface information.

Evaluation of fouling in nanofiltration for desalination using a resistance-in-series model and optical coherence tomography.

PubMed

Park, Jongkwan; Lee, Sungyun; You, Jeongyeop; Park, Sanghun; Ahn, Yujin; Jung, Woonggyu; Cho, Kyung Hwa

2018-06-12

Resistance-in-series models have been applied to investigate fouling behavior. However, it is difficult to model the influence of morphology on fouling behavior because resistance is indirectly calculated from the water flux and transmembrane pressure. In this study, optical coherence tomography (OCT) was applied to evaluate the resistance of the fouling layer based on fouling morphology. Sodium alginate, humic acid, and bovine serum albumin (BSA) with high salts concentrations (conductivity: 23 mS/cm) were used as model foulants. At the same total fouling resistance, BSA showed the highest cake layer thickness (BSA (114.5 μm) > humic acid (53.5 μm) > sodium alginate (20.0 μm)). However, a different order was found for the cake layer resistance (BSA > sodium alginate > humic acid). This indicates that fouling thickness is not correlated with cake layer resistance. According to the Carman-Kozeny equation, fouling layer porosity decreased in the following order: humic acid (0.30) > BSA (0.21) > sodium alginate (0.20). In addition, we provided a specific value that was calculated using the ratio between the fouling thickness and cake layer resistance. The results show that alginic acid induced a stronger cake layer resistance, despite its thin fouling layer, whereas BSA showed a relatively low potential for inducing cake layer resistance. The results obtained in this study could be used for estimating and predicting fouling behavior. Copyright © 2018 Elsevier B.V. All rights reserved.

Electrical Resistance Tomography to Monitor Mitigation of Metal-Toxic Acid-Leachates Ruby Gulch Waste Rock Repository Gilt Edge Mine Superfund Site, South Dakota USA

NASA Astrophysics Data System (ADS)

Versteeg, R.; Heath, G.; Richardson, A.; Paul, D.; Wangerud, K.

2003-12-01

At a cyanide heap-leach open-pit mine, 15-million cubic yards of acid-generating sulfides were dumped at the head of a steep-walled mountain valley, with 30 inches/year precipitation generating 60- gallons/minute ARD leachate. Remediation has reshaped the dump to a 70-acre, 3.5:1-sloped geometry, installed drainage benches and runoff diversions, and capped the repository and lined diversions with a polyethylene geomembrane and cover system. Monitoring was needed to evaluate (a) long-term geomembrane integrity, (b) diversion liner integrity and long-term effectiveness, (c) ARD geochemistry, kinetics and pore-gas dynamics within the repository mass, and (d) groundwater interactions. Observation wells were paired with a 600-electrode resistivity survey system. Using near-surface and down-hole electrodes and automated data collection and post-processing, periodic two- and three-dimensional resistivity images are developed to reflect current and changed-conditions in moisture, temperature, geochemical components, and flow-direction analysis. Examination of total resistivity values and time variances between images allows direct observation of liner and cap integrity with precise identification and location of leaks; likewise, if runoff migrates from degraded diversion ditches into the repository zone, there is an accompanying and noticeable change in resistivity values. Used in combination with monitoring wells containing borehole resistivity electrodes (calibrated with direct sampling of dump water/moisture, temperature and pore-gas composition), the resistivity arrays allow at-depth imaging of geochemical conditions within the repository mass. The information provides early indications of progress or deficiencies in de-watering and ARD- mitigation that is the remedy intent. If emerging technologies present opportunities for secondary treatment, deep resistivity images may assist in developing application methods and evaluating the effectiveness of any reagents introduced into the repository mass to further effect changes in oxidation/reduction reactions.

Improved 2-D resistivity imaging of features in covered karst terrain with arrays of implanted electrodes

NASA Astrophysics Data System (ADS)

Kiflu, H. G.; Kruse, S. E.; Harro, D.; Loke, M. H.; Wilkinson, P. B.

2013-12-01

Electrical resistivity tomography is commonly used to identify geologic features associated with sinkhole formation. In covered karst terrain, however, it can be difficult to resolve the depth to top of limestone with this method. This is due to the fact that array lengths, and hence depth of resolution, are often limited by residential or commercial lot dimensions in urban environments. Furthermore, the sediments mantling the limestone are often clay-rich and highly conductive. The resistivity method has limited sensitivity to resistive zones beneath conductive zones. This sensitivity can be improved significantly with electrodes implanted at depth in the cover sediments near the top of limestone. An array of deep electrodes is installed with direct push technology in the karst cover. When combined with a surface array in which each surface electrode is underlain by a deep electrode, the array geometry is similar to a borehole array turned on its side. This method, called the Multi-Electrode Resistivity Implant Technique (MERIT), offers the promise of significantly improved resolution of epikarst and cover collapse development zones in the overlying sediment, the limestone or at the sediment-bedrock interface in heterogeneous karst environments. With a non-traditional array design, the question of optimal array geometries arises. Optimizing array geometries is complicated by the fact that many plausible 4-electrode readings will produce negative apparent resistivity values, even in homogeneous terrain. Negative apparent resistivities cannot be used in inversions based on the logarithm of the apparent resistivity. New algorithms for seeking optimal array geometries have been developed by modifying the 'Compare R' method of Wilkinson and Loke. The optimized arrays show significantly improved resolution over basic arrays adapted from traditional 2D surface geometries. Several MERIT case study surveys have been conducted in covered karst in west-central Florida, with 28-electrode arrays with electrodes 2-5 meters apart, and the deep arrays buried at 4-8 meters depth. Ground penetrating radar surveys, SPT borings and coring data provide selected 'ground truthing'. The case studies show that inclusion of the deep electrode array permits karst features such as undulations at the top of limestone and raveling zones within surficial sediments to be imaged. These features are not accessible from surface arrays with equivalent surface footprints. The method also has better resolution at depth at the ends of the lines, where surface arrays are typically plotted with a trapezoidal truncation due to poor resolution at the lower corners of the profile.

Direct Test for Neuroinflammation with [11C]DAP-713-PET Scanning

DTIC Science & Technology

2015-10-01

individuals suffering from the Gulf War Illness (GWI). We are using quantitative positron emission tomography (PET) using [11C]DPA-713 (DPA). DPA...suffering from the Gulf War Illness (GWI). We are using quantitative positron emission tomography (PET) using [11C]DPA-713 (DPA). DPA binds to the... Resistant Prostate Cancer Time commitments: 0.12 calendar months Supporting Agency: CDMRP Grants Contact: TBD PI: Denmeade Co-Investigator

Integrating hydrogeophysics and hydrological tracers to characterise the spatial structure of groundwater storage in the critical zone of montane environments

NASA Astrophysics Data System (ADS)

Dick, J.; Tetzlaff, D.; Bradford, J.; Soulsby, C.

2015-12-01

It is increasingly recognised that groundwater (GW) in montane watersheds has a major influence on the distribution of vegetation communities and ecosystem function, as well as sustaining downstream river flows. In glaciated landscapes, complex and heterogenous drift deposits can have a dominant influence on GW stores and fluxes, and form a poorly understood component of the critical zone. Given the logistical problems and limitations of drilling observation wells in such terrain, hydrogeophysics has outstanding potential to help characterise aquifer structure and understand shallow GW in the critical zone of montane environments. We present the results of electrical resistivity tomography (ERT) surveys in an intensively monitored 3.2km2 watershed in the Scottish Highlands with a strong glacial past. We sought to characterise the structure and spatial organisation of GW stores in diverse quaternary drift deposits. This utilized distributed ERT transects that provided a basis for spatial interpolation using geostatistical methods and high resolution LiDAR surveys. Some transects coincided with shallow observation wells that were used to "ground-truth" the inversion of resistivity data. The surveys showed that the drifts covered around 70% of the catchment and varied from 5m deep on the hillslopes to 40m in the valleys. The water table was within 0.2m of the soil surface in the valley bottom areas and about 1.5m deep on steeper hillslopes. The water content of drifts inferred by the ERT surveys and characterisation of the aquifer properties showed highest water content in the peat (~80%) and basal till (20-30%), and low storage in moraine deposits (10%). Upscaling these estimates of inferred storage to the catchment scale indicated around ~2-3 m of GW storage, equivalent to around 4-6 years of effective precipitation. This generally compared well with independent storage estimates inferred from long-term stable isotope time series collected from the aquifers. Elucidating the importance of the critical zone for water storage in montane environments using ERT provides a basis for predicting their likely resistance and resilience to environmental change. This is of practical importance in the Scottish uplands where both climate and land use change are likely to have implications for water availability.

The impact of periglacial cover beds on runoff generation in a small spring catchment, Ore Mountains

NASA Astrophysics Data System (ADS)

Heller, Katja; Hübner, Rico; Kleber, Arno

2010-05-01

The knowledge of hillslope processes is essential to improve pollutant research and flood prediction. Relic periglacial covers are widespread on slopes of the central European low mountain ranges. Cover beds are assumed to be an important control factor for subcutaneous water flow paths. Periglacial cover beds originated by solifluction, kryoturbation and accumulation of loess during Pleistocene times. Differences in bulk density, sediment type, as well as structure and rate of coarse clasts in the layers result in vertical disparity in hydraulic conductivity (anisotropy), leading to interflow. This hypothesis has been testing in an ongoing study in a small spring catchment (6 ha) in the eastern Ore Mountains, south-eastern Germany, since November 2007. The study area is underlain by gneiss and is formed as a slope hollow. The cover beds consist of a 3-layer complex with upper layer, intermediate layer and basal layer. Soil water tension within the layers is measured with 76 recording tensiometers. Electrical resistivity tomography was used to monitor the spatial dispersal of soil moisture. Results of hydrometrical measurements and of electrical resistivity surveys will be described and new findings on slope water dynamics will be presented.

Geoelectrical monitoring of simulated subsurface leakage to support high-hazard nuclear decommissioning at the Sellafield Site, UK.

PubMed

Kuras, Oliver; Wilkinson, Paul B; Meldrum, Philip I; Oxby, Lucy S; Uhlemann, Sebastian; Chambers, Jonathan E; Binley, Andrew; Graham, James; Smith, Nicholas T; Atherton, Nick

2016-10-01

A full-scale field experiment applying 4D (3D time-lapse) cross-borehole Electrical Resistivity Tomography (ERT) to the monitoring of simulated subsurface leakage was undertaken at a legacy nuclear waste silo at the Sellafield Site, UK. The experiment constituted the first application of geoelectrical monitoring in support of decommissioning work at a UK nuclear licensed site. Images of resistivity changes occurring since a baseline date prior to the simulated leaks revealed likely preferential pathways of silo liquor simulant flow in the vadose zone and upper groundwater system. Geophysical evidence was found to be compatible with historic contamination detected in permeable facies in sediment cores retrieved from the ERT boreholes. Results indicate that laterally discontinuous till units forming localized hydraulic barriers substantially affect flow patterns and contaminant transport in the shallow subsurface at Sellafield. We conclude that only geophysical imaging of the kind presented here has the potential to provide the detailed spatial and temporal information at the (sub-)meter scale needed to reduce the uncertainty in models of subsurface processes at nuclear sites. Copyright © 2016 British Geological Survey, NERC. Published by Elsevier B.V. All rights reserved.

Nonlinear inversion of borehole-radar tomography data to reconstruct velocity and attenuation distribution in earth materials

USGS Publications Warehouse

Zhou, C.; Liu, L.; Lane, J.W.

2001-01-01

A nonlinear tomographic inversion method that uses first-arrival travel-time and amplitude-spectra information from cross-hole radar measurements was developed to simultaneously reconstruct electromagnetic velocity and attenuation distribution in earth materials. Inversion methods were developed to analyze single cross-hole tomography surveys and differential tomography surveys. Assuming the earth behaves as a linear system, the inversion methods do not require estimation of source radiation pattern, receiver coupling, or geometrical spreading. The data analysis and tomographic inversion algorithm were applied to synthetic test data and to cross-hole radar field data provided by the US Geological Survey (USGS). The cross-hole radar field data were acquired at the USGS fractured-rock field research site at Mirror Lake near Thornton, New Hampshire, before and after injection of a saline tracer, to monitor the transport of electrically conductive fluids in the image plane. Results from the synthetic data test demonstrate the algorithm computational efficiency and indicate that the method robustly can reconstruct electromagnetic (EM) wave velocity and attenuation distribution in earth materials. The field test results outline zones of velocity and attenuation anomalies consistent with the finding of previous investigators; however, the tomograms appear to be quite smooth. Further work is needed to effectively find the optimal smoothness criterion in applying the Tikhonov regularization in the nonlinear inversion algorithms for cross-hole radar tomography. ?? 2001 Elsevier Science B.V. All rights reserved.

Ocean acoustic reverberation tomography.

PubMed

Dunn, Robert A

2015-12-01

Seismic wide-angle imaging using ship-towed acoustic sources and networks of ocean bottom seismographs is a common technique for exploring earth structure beneath the oceans. In these studies, the recorded data are dominated by acoustic waves propagating as reverberations in the water column. For surveys with a small receiver spacing (e.g., <10 km), the acoustic wave field densely samples properties of the water column over the width of the receiver array. A method, referred to as ocean acoustic reverberation tomography, is developed that uses the travel times of direct and reflected waves to image ocean acoustic structure. Reverberation tomography offers an alternative approach for determining the structure of the oceans and advancing the understanding of ocean heat content and mixing processes. The technique has the potential for revealing small-scale ocean thermal structure over the entire vertical height of the water column and along long survey profiles or across three-dimensional volumes of the ocean. For realistic experimental geometries and data noise levels, the method can produce images of ocean sound speed on a smaller scale than traditional acoustic tomography.

Moment inference from tomograms

USGS Publications Warehouse

Day-Lewis, F. D.; Chen, Y.; Singha, K.

2007-01-01

Time-lapse geophysical tomography can provide valuable qualitative insights into hydrologic transport phenomena associated with aquifer dynamics, tracer experiments, and engineered remediation. Increasingly, tomograms are used to infer the spatial and/or temporal moments of solute plumes; these moments provide quantitative information about transport processes (e.g., advection, dispersion, and rate-limited mass transfer) and controlling parameters (e.g., permeability, dispersivity, and rate coefficients). The reliability of moments calculated from tomograms is, however, poorly understood because classic approaches to image appraisal (e.g., the model resolution matrix) are not directly applicable to moment inference. Here, we present a semi-analytical approach to construct a moment resolution matrix based on (1) the classic model resolution matrix and (2) image reconstruction from orthogonal moments. Numerical results for radar and electrical-resistivity imaging of solute plumes demonstrate that moment values calculated from tomograms depend strongly on plume location within the tomogram, survey geometry, regularization criteria, and measurement error. Copyright 2007 by the American Geophysical Union.

Moment inference from tomograms

USGS Publications Warehouse

Day-Lewis, Frederick D.; Chen, Yongping; Singha, Kamini

2007-01-01

Time-lapse geophysical tomography can provide valuable qualitative insights into hydrologic transport phenomena associated with aquifer dynamics, tracer experiments, and engineered remediation. Increasingly, tomograms are used to infer the spatial and/or temporal moments of solute plumes; these moments provide quantitative information about transport processes (e.g., advection, dispersion, and rate-limited mass transfer) and controlling parameters (e.g., permeability, dispersivity, and rate coefficients). The reliability of moments calculated from tomograms is, however, poorly understood because classic approaches to image appraisal (e.g., the model resolution matrix) are not directly applicable to moment inference. Here, we present a semi-analytical approach to construct a moment resolution matrix based on (1) the classic model resolution matrix and (2) image reconstruction from orthogonal moments. Numerical results for radar and electrical-resistivity imaging of solute plumes demonstrate that moment values calculated from tomograms depend strongly on plume location within the tomogram, survey geometry, regularization criteria, and measurement error.

Optimal Electrode Selection for Electrical Resistance Tomography in Carbon Fiber Reinforced Polymer Composites

PubMed Central

Escalona Galvis, Luis Waldo; Diaz-Montiel, Paulina; Venkataraman, Satchi

2017-01-01

Electrical Resistance Tomography (ERT) offers a non-destructive evaluation (NDE) technique that takes advantage of the inherent electrical properties in carbon fiber reinforced polymer (CFRP) composites for internal damage characterization. This paper investigates a method of optimum selection of sensing configurations for delamination detection in thick cross-ply laminates using ERT. Reduction in the number of sensing locations and measurements is necessary to minimize hardware and computational effort. The present work explores the use of an effective independence (EI) measure originally proposed for sensor location optimization in experimental vibration modal analysis. The EI measure is used for selecting the minimum set of resistance measurements among all possible combinations resulting from selecting sensing electrode pairs. Singular Value Decomposition (SVD) is applied to obtain a spectral representation of the resistance measurements in the laminate for subsequent EI based reduction to take place. The electrical potential field in a CFRP laminate is calculated using finite element analysis (FEA) applied on models for two different laminate layouts considering a set of specified delamination sizes and locations with two different sensing arrangements. The effectiveness of the EI measure in eliminating redundant electrode pairs is demonstrated by performing inverse identification of damage using the full set and the reduced set of resistance measurements. This investigation shows that the EI measure is effective for optimally selecting the electrode pairs needed for resistance measurements in ERT based damage detection. PMID:28772485

Optimal Electrode Selection for Electrical Resistance Tomography in Carbon Fiber Reinforced Polymer Composites.

PubMed

Escalona Galvis, Luis Waldo; Diaz-Montiel, Paulina; Venkataraman, Satchi

2017-02-04

Electrical Resistance Tomography (ERT) offers a non-destructive evaluation (NDE) technique that takes advantage of the inherent electrical properties in carbon fiber reinforced polymer (CFRP) composites for internal damage characterization. This paper investigates a method of optimum selection of sensing configurations for delamination detection in thick cross-ply laminates using ERT. Reduction in the number of sensing locations and measurements is necessary to minimize hardware and computational effort. The present work explores the use of an effective independence (EI) measure originally proposed for sensor location optimization in experimental vibration modal analysis. The EI measure is used for selecting the minimum set of resistance measurements among all possible combinations resulting from selecting sensing electrode pairs. Singular Value Decomposition (SVD) is applied to obtain a spectral representation of the resistance measurements in the laminate for subsequent EI based reduction to take place. The electrical potential field in a CFRP laminate is calculated using finite element analysis (FEA) applied on models for two different laminate layouts considering a set of specified delamination sizes and locations with two different sensing arrangements. The effectiveness of the EI measure in eliminating redundant electrode pairs is demonstrated by performing inverse identification of damage using the full set and the reduced set of resistance measurements. This investigation shows that the EI measure is effective for optimally selecting the electrode pairs needed for resistance measurements in ERT based damage detection.

3-D Resistivity Tomography for Cliff Stability Study at the D-Day Pointe du Hoc Historic Site in Normandy, France

NASA Astrophysics Data System (ADS)

Udphuay, S.; Everett, M. E.; Guenther, T.; Warden, R. R.

2007-12-01

The D-Day invasion site at Pointe du Hoc in Normandy, France is one of the most important World War II battlefields. The site remains today a valuable historic cultural resource. However the site is vulnerable to cliff collapses that could endanger the observation post building and U.S. Ranger memorial located just landward of the sea stack, and an anti-aircraft gun emplacement, Col. Rudder's command post, located on the cliff edge about 200 m east of the observation post. A 3-D resistivity tomography incorporating extreme topography is used in this study to provide a detailed site stability assessment with special attention to these two buildings. Multi-electrode resistivity measurements were made across the cliff face and along the top of the cliff around the two at-risk buildings to map major subsurface fracture zones and void spaces that could indicate possible accumulations and pathways of groundwater. The ingress of acidic groundwater through the underlying carbonate formations enlarges pre-existing tectonic fractures via limestone dissolution and weakens the overall structural integrity of the cliff. The achieved 3-D resistivity tomograms provide diagnostic subsurface resistivity distributions. Resistive zones associated with subsurface void spaces have been located. These void spaces constitute a stability geohazard as they become significant drainage routes during and after periods of heavy rainfalls.

Assessment of the Efficiency of Consolidation Treatment through Injections of Expanding Resins by Geotechnical Tests and 3D Electrical Resistivity Tomography

PubMed Central

2015-01-01

The design and execution of consolidation treatment of settled foundations by means of injection of polyurethane expanding resins require a proper investigation of the state of the foundation soil, in order to better identify anomalies responsible for the instability. To monitor the injection process, a procedure has been developed, which involves, in combination with traditional geotechnical tests, the application of a noninvasive, geophysical technique based on the electrical resistivity, which is strongly sensitive to presence of water or voids. Three-dimensional electrical resistivity tomography is a useful tool to produce effective 3D images of the foundation soils before, during, and after the injections. The achieved information allows designing the consolidation scheme and monitoring its effects on the treated volumes in real time. To better understand the complex processes induced by the treatment and to learn how variations of resistivity accompany increase of stiffness, an experiment was carried out in a full-scale test site. Injections of polyurethane expanding resin were performed as in real worksite conditions. Results confirm that the experimented approach by means of 3D resistivity imaging allows a reliable procedure of consolidation, and geotechnical tests demonstrate the increase of mechanical stiffness. PMID:26167521

Electrical resistivity tomography determines the spatial distribution of clay layer thickness and aquifer vulnerability, Kandal Province, Cambodia

NASA Astrophysics Data System (ADS)

Uhlemann, Sebastian; Kuras, Oliver; Richards, Laura A.; Naden, Emma; Polya, David A.

2017-10-01

Despite being rich in water resources, many areas of South East Asia face difficulties in securing clean water supply. This is particularly problematic in regions with a rapidly growing population. In this study, the spatial variability of the thickness of a clay layer, controlling surface - groundwater interactions that affect aquifer vulnerability, was investigated using electrical resistivity tomography (ERT). Data were acquired along two transects, showing significant differences in the imaged resistivities. Borehole samples were analyzed regarding particle density and composition, and linked to their resistivity. The obtained relationships were used to translate the field electrical resistivities into lithologies. Those revealed considerable variations in the thickness of the clay layer, ranging from 0 m up to 25 m. Geochemical data, highlighting zones of increased ingress of surface water into the groundwater, confirmed areas of discontinuities in the clay layer, which act as preferential flow paths. The results may guide urban planning of the Phnom Penh city expansion, in order to supply the growing population with safe water. The presented approach of using geophysics to estimate groundwater availability, accessibility, and vulnerability is not only applicable to Kandal Province, Cambodia, but also to many other areas of fast urbanization in South East Asia and beyond.

Characterization of a dismissed landfill via electrical resistivity tomography and mise-à-la-masse method

NASA Astrophysics Data System (ADS)

De Carlo, Lorenzo; Perri, Maria Teresa; Caputo, Maria Clementina; Deiana, Rita; Vurro, Michele; Cassiani, Giorgio

2013-11-01

Electrical resistivity methods are widely used for environmental applications, and they are particularly useful for the characterization and monitoring of sites where the presence of contamination requires a thorough understanding of the location and movement of water, that can act as a carrier of solutes. One such application is landfill studies, where the strong electrical contrasts between waste, leachate and surrounding formations make electrical methods a nearly ideal tool for investigation. In spite of the advantages, however, electrical investigation of landfills poses also challenges, both logistical and interpretational. This paper presents the results of a study conducted on a dismissed landfill, close to the city of Corigliano d'Otranto, in the Apulia region (Southern Italy). The landfill is located in an abandoned quarry, that was subsequently re-utilized about thirty years ago as a site for urban waste disposal. The waste was thought to be more than 20 m thick, and the landfill bottom was expected to be confined with an HDPE (high-density poli-ethylene) liner. During the digging operations performed to build a nearby new landfill, leachate was found, triggering an in-depth investigation including also non-invasive methods. The principal goal was to verify whether the leachate is indeed confined, and to what extent, by the HDPE liner. We performed both surface electrical resistivity tomography (ERT) and mise-à-la-masse (MALM) surveys, facing the severe challenges posed by the rugged terrain of the abandoned quarry complex. A conductive body, probably associated with leachate, was found as deep as 40 m below the current landfill surface i.e. at a depth much larger than the expected 20 m thickness of waste. Given the logistical difficulties that limit the geometry of acquisition, we utilized synthetic forward modeling in order to confirm/dismiss interpretational hypotheses emerging from the ERT and MALM results. This integration between measurements and modeling helped narrow the alternative interpretations and strengthened the confidence in results, confirming the effectiveness of non-invasive methods in landfill investigation and the importance of modeling in the interpretation of geophysical results.

Multidisciplinary approach for the characterization of landslides in volcanic areas - a case study from the Palma Sola-Chiconquiaco Mountain Range, Mexico

NASA Astrophysics Data System (ADS)

Wilde, Martina; Rodríguez Elizarrarás, Sergio R.; Morales Barrera, Wendy V.; Schwindt, Daniel; Bücker, Matthias; Flores Orozco, Adrián; García García, Emilio; Pita de la Paz, Carlos; Terhorst, Birgit

2017-04-01

The Palma Sola-Chiconquiaco mountain range, situated in the State of Veracruz, Mexico, is highly susceptible to landslides, which is evidenced by the high frequency of landslide events of different sizes. The study area is located near the Gulf of Mexico coastline in the eastern sector of the Trans Mexican Volcanic Belt. There, landslide triggers are intense rainfalls related to tropical storms and hurricanes. Steeper slopes are commonly affected by rockfalls, whereas moderate slopes, covered by massive slope deposits, are affected by shallow as well as deep seated landslides. Some of the landslides in the slope deposits reach dimensions of more than 1000 m in length and depths of over 30 m. The heterogeneous parent material as well as older slide masses hamper the detailed characterization of the involved materials. Therefore, in this study, a multidisciplinary approach is applied that integrates geomorphological, geological, and geophysical data. The aim is the reconstruction of process dynamics by analyzing the geomorphological situation and subsurface conditions before and after the event. The focus lies on the identification of past landslide areas, which represent areas with high susceptibility for the reactivation of old slide masses. Furthermore, the analysis of digital terrain models, generated before the landslide event, indicate initial movements like extension cracks, which are located close to the current scarp area. In order to characterize the subsurface of slide masses geophysical investigations are applied. The geophysical survey consists of a total of nine profiles covering relevant key features of the large affected area. Along these profiles, electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) data were collected. Both, electrical and seismic images reveal a sharp contrast between relatively loose and dry material of the slide mass (high resistivities and low seismic velocities) and the former land surface that is characterized by significantly reduced resistivities and higher seismic velocities. This contrast allows to establish the thicknesses of slope deposits and geological layers along all geophysical profiles. Furthermore, the investigations are complemented by a high resolution digital terrain model of the landslide and its surroundings, which was reconstructed from orthophotos derived from unmanned aerial vehicle photogrammetry.

Port Site Metastases: A Survey of the Society of Gynecologic Oncology and Commentary on the Clinical Workup and Management of Port Site Metastases.

PubMed

Baptiste, Caitlin D; Buckley de Meritens, Alexandre; Jones, Nathaniel L; Chatterjee Paer, Sudeshna; Tergas, Ana I; Hou, June Y; Wright, Jason D; Burke, William M

Laparoscopic port site metastases (PSMs) have an incidence of .5% to 2%. The management of an isolated PSM (iPSM), without evidence of recurrence elsewhere, remains unclear. The aim of this study was to elucidate practices regarding iPSMs. A 23-item survey was created using commercially available survey software. Over the course of January 2016 the survey was e-mailed to the members of the Society of Gynecologic Oncology with 2 follow-up reminder e-mails. (Canadian Task Force classification III.) SETTING: Online survey. Of the 709 surveys sent, 132 were returned. Providers practicing for <5 years saw fewer PSMs and those who performed more minimally invasive surgeries (MISs) saw more PSMs. Comparing providers who have or have not seen PSMs, no differences in pneumoinsufflation pressure, the mode of delivery of the specimen, the use of local anesthesia at port site incisions, or the method of deflation were seen. If an iPSM was suspected, most providers indicated they would obtain imaging (computed tomography, 51%, or positron emission tomography/computed tomography, 43%) followed by an interventional radiology-guided biopsy (29%) or resection of the mass. Tendency for treatment is to surgically resect the lesion followed by adjuvant therapy. After controlling for time in practice, we did not find a strong risk factor for iPSMs other than performing >75% of oncologic surgeries by MIS. Most respondents performed imaging when suspecting iPSMs and use systemic adjuvant therapy after confirming iPSMs. Copyright © 2017 AAGL. Published by Elsevier Inc. All rights reserved.

Seismic Velocity Structure of the Pacific Upper Mantle in the NoMelt Region from Finite-Frequency Traveltime Tomography

NASA Astrophysics Data System (ADS)

Hung, S. H.; Lin, P. Y.; Gaherty, J. B.; Russell, J. B.; Jin, G.; Collins, J. A.; Lizarralde, D.; Evans, R. L.; Hirth, G.

2017-12-01

Surface wave dispersion and magnetotelluric survey from the NoMelt Experiment conducted on 70 Ma central Pacific seafloor revealed an electrically resistive, high shear wave velocity lid of 80 km thick underlain by a non-highly conductive, low-velocity layer [Sarafian et al., 2015; Lin et al., 2016]. The vertical structure of the upper mantle consistent with these observational constraints suggests a plausible convection scenario, where the seismically fast, dehydrated lithosphere preserving very strong fossil spreading fabric moves at a constant plate speed over the hydrated, melt-free athenospheric mantle with the presence of either pressure-driven return flow or thermally-driven small scale circulation. To explore 3-D variations in compressional shear wave velocities related to the lithospheric and asthenospheric mantle dynamics, we employ a multichannel cross correlation method to measure relative traveltime residuals based on the vertical P and traverse S waveforms filtered at 10-33 s from telseismic earthquakes at epicentral distance between 30 and 98 degrees. The obtained P and S residuals show on average peak-to-peak variations of ±0.5 s and ±1 s, respectively, across the NoMelt OBS array. Particularly, the P residuals for most of the events display an asymmetrical pattern with respect to an axis oriented nearly N-S to NE-SW through the array. Preliminary ray-based P tomography results reveal similar asymmetric variations in the uppermost 100 km mantle. To verify the resulting structural features, we will further perform both the P and S traveltime tomography and resolution tests based on a multiscale finite-frequency approach which properly takes into account both the 3D off-path sensitivities of the measured residuals and data-adaptive resolution of the model.

Quantification of blood volume by electrical impedance tomography using a tissue-equivalent phantom.

PubMed

Sadleir, R; Fox, R

1998-11-01

An in vivo electrical impedance tomography (EIT) system was designed to accurately estimate quantities of intra-peritoneal blood in the abdominal cavity. For this it is essential that the response is relatively independent of the position of the high conductivity anomaly (blood) in the body. The sensitivity of the system to the introduction of blood-equivalent resistivity anomalies was assessed by using a cylindrical tissue-equivalent phantom. It was found that a satisfactorily uniform response of the system in both radial (transverse) and axial (longitudinal) directions in the phantom could be achieved by filtering resistivity profile images obtained by EIT measurement, and by using extended electrodes to collect data. Post-processing of single impedance images gave rise to a quantity denoted the resistivity index. A filter was then used to remove the remaining radial variation of the resistivity index. It was calculated by evaluating the resistivity index of a number of theoretically calculated images, and constructing a correction filter similar to those used to remove lens imperfections, such as coma, in optical components. The 30% increase in the resistivity index observed when an anomaly was moved to the maximum extent allowed by the filter calculation (0.75 of the phantom radius) was reduced by the filter to 6%. A study of the axial dependence observed in the resistivity index using electrodes extended in the axial direction by +/-5 cm found that the variation in resistivity index with axial position was about half of that observed using small circular electrodes similar to those used in the Sheffield mark I system.

Implementation of a national anti-tuberculosis drug resistance survey in Tanzania.

PubMed

Chonde, Timothy M; Doulla, Basra; van Leth, Frank; Mfinanga, Sayoki G M; Range, Nyagosya; Lwilla, Fred; Mfaume, Saidi M; van Deun, Armand; Zignol, Matteo; Cobelens, Frank G; Egwaga, Saidi M

2008-12-30

A drug resistance survey is an essential public health management tool for evaluating and improving the performance of National Tuberculosis control programmes. The current manuscript describes the implementation of the first national drug resistance survey in Tanzania. Description of the implementation process of a national anti-tuberculosis drug resistance survey in Tanzania, in relation to the study protocol and Standard Operating Procedures. Factors contributing positively to the implementation of the survey were a continuous commitment of the key stakeholders, the existence of a well organized National Tuberculosis Programme, and a detailed design of cluster-specific arrangements for rapid sputum transportation. Factors contributing negatively to the implementation were a long delay between training and actual survey activities, limited monitoring of activities, and an unclear design of the data capture forms leading to difficulties in form-filling. Careful preparation of the survey, timing of planned activities, a strong emphasis on data capture tools and data management, and timely supervision are essential for a proper implementation of a national drug resistance survey.

Assessment of errors in static electrical impedance tomography with adjacent and trigonometric current patterns.

PubMed

Kolehmainen, V; Vauhkonen, M; Karjalainen, P A; Kaipio, J P

1997-11-01

In electrical impedance tomography (EIT), difference imaging is often preferred over static imaging. This is because of the many unknowns in the forward modelling which make it difficult to obtain reliable absolute resistivity estimates. However, static imaging and absolute resistivity values are needed in some potential applications of EIT. In this paper we demonstrate by simulation the effects of different error components that are included in the reconstruction of static EIT images. All simulations are carried out in two dimensions with the so-called complete electrode model. Errors that are considered are the modelling error in the boundary shape of an object, errors in the electrode sizes and localizations and errors in the contact impedances under the electrodes. Results using both adjacent and trigonometric current patterns are given.

[Research on respiration course of human at different postures by electrical impedance tomography].

PubMed

Chen, Xiaoyan; Wu, Jun; Wang, Huaxiang; Li, Da

2010-10-01

In this paper, the respiration courses of human at different postures are reconstructed by electrical impedance tomography (EIT). Conjugate gradient least squares (CGLS) algorithm is applied to reconstruct the resistivity distribution during respiration courses, and the EIT images taken from human at flat lying, left lying, right lying, sitting and prone postures are reconstructed and compared. The relative changes of the resistivity in region of interest (ROI) are analyzed to evidence the influences caused by different postures. Results show that the changes in postures are the most influential factors for the reconstructions, and the EIT images vary with the postures. In human at flat-lying posture, the left and right lungs have larger pulmonary ventilation volume simultaneously, and the EIT-measured data are of lower variability.

Electrical resistance tomography to monitor unsaturated moisture flow in cementitious materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hallaji, Milad; Seppänen, Aku; Pour-Ghaz, Mohammad, E-mail: mpourghaz@ncsu.edu

2015-03-15

Traditionally the electrically-based assessment of the moisture flow in cement-based materials relies on two- or four-point measurements. In this paper, imaging of moisture distribution with electrical resistance tomography (ERT) is considered. Especially, the aim is to study whether ERT could give information on unsaturated moisture flows in cases where the flow is non-uniform. In the experiment, the specimens are monitored with ERT during the water ingress. The ERT reconstructions are compared with neutron radiographs, which provide high resolution information on the 2D distribution of the moisture. The results indicate that ERT is able to detect the moisture movement and tomore » show approximately the shape and position of the water front even if the flow is nonuniform.« less

Assessment of multiple geophysical techniques for the characterization of municipal waste deposit sites

NASA Astrophysics Data System (ADS)

Gaël, Dumont; Tanguy, Robert; Nicolas, Marck; Frédéric, Nguyen

2017-10-01

In this study, we tested the ability of geophysical methods to characterize a large technical landfill installed in a former sand quarry. The geophysical surveys specifically aimed at delimitating the deposit site horizontal extension, at estimating its thickness and at characterizing the waste material composition (the moisture content in the present case). The site delimitation was conducted with electromagnetic (in-phase and out-of-phase) and magnetic (vertical gradient and total field) methods that clearly showed the transition between the waste deposit and the host formation. Regarding waste deposit thickness evaluation, electrical resistivity tomography appeared inefficient on this particularly thick deposit site. Thus, we propose a combination of horizontal to vertical noise spectral ratio (HVNSR) and multichannel analysis of the surface waves (MASW), which successfully determined the approximate waste deposit thickness in our test landfill. However, ERT appeared to be an appropriate tool to characterize the moisture content of the waste, which is of prior information for the organic waste biodegradation process. The global multi-scale and multi-method geophysical survey offers precious information for site rehabilitation studies, water content mitigation processes for enhanced biodegradation or landfill mining operation planning.

Decay detection in red oak trees using a combination of visual inspection, acoustic testing, and resistance microdrilling

Treesearch

Xiping Wang; R. Bruce Allison

2008-01-01

Arborists are often challenged to identify internal structural defects hidden from view within tree trunks. This article reports the results of a study using a trunk inspection protocol combining visual observation, single-path stress wave testing, acoustic tomography, and resistance microdrilling to detect internal defects. Two century-old red oak (Quercus rubra)...

Small scale monitoring of a bioremediation barrier using miniature electrical resistivity tomography

NASA Astrophysics Data System (ADS)

Sentenac, Philippe; Hogson, Tom; Keenan, Helen; Kulessa, Bernd

2015-04-01

The aim of this study was to assess, in the laboratory, the efficiency of a barrier of oxygen release compound (ORC) to block and divert a diesel plume migration in a scaled aquifer model using miniature electrical resistivity tomography (ERT) as the monitoring system. Two plumes of contaminant (diesel) were injected in a soil model made of local sand and clay. The diesel plumes migration was imaged and monitored using a miniature resistivity array system that has proved to be accurate in soil resistivity variations in small-scaled models of soil. ERT results reflected the lateral spreading and diversion of the diesel plumes in the unsaturated zone. One of the contaminant plumes was partially blocked by the ORC barrier and a diversion and reorganisation of the diesel in the soil matrix was observed. The technique of time-lapse ERT imaging showed that a dense non-aqueous phase liquid (DNAPL) contaminant like diesel can be monitored through a bioremediation barrier and the technique is well suited to monitor the efficiency of the barrier. Therefore, miniature ERT as a small-scale modelling tool could complement conventional techniques, which require more expensive and intrusive site investigation prior to remediation.

Hydrologic Process-oriented Optimization of Electrical Resistivity Tomography

NASA Astrophysics Data System (ADS)

Hinnell, A.; Bechtold, M.; Ferre, T. A.; van der Kruk, J.

2010-12-01

Electrical resistivity tomography (ERT) is commonly used in hydrologic investigations. Advances in joint and coupled hydrogeophysical inversion have enhanced the quantitative use of ERT to construct and condition hydrologic models (i.e. identify hydrologic structure and estimate hydrologic parameters). However the selection of which electrical resistivity data to collect and use is often determined by a combination of data requirements for geophysical analysis, intuition on the part of the hydrogeophysicist and logistical constraints of the laboratory or field site. One of the advantages of coupled hydrogeophysical inversion is the direct link between the hydrologic model and the individual geophysical data used to condition the model. That is, there is no requirement to collect geophysical data suitable for independent geophysical inversion. The geophysical measurements collected can be optimized for estimation of hydrologic model parameters rather than to develop a geophysical model. Using a synthetic model of drip irrigation we evaluate the value of individual resistivity measurements to describe the soil hydraulic properties and then use this information to build a data set optimized for characterizing hydrologic processes. We then compare the information content in the optimized data set with the information content in a data set optimized using a Jacobian sensitivity analysis.

Use of electrical resistivity to detect underground mine voids in Ohio

USGS Publications Warehouse

Sheets, Rodney A.

2002-01-01

Electrical resistivity surveys were completed at two sites along State Route 32 in Jackson and Vinton Counties, Ohio. The surveys were done to determine whether the electrical resistivity method could identify areas where coal was mined, leaving air- or water-filled voids. These voids can be local sources of potable water or acid mine drainage. They could also result in potentially dangerous collapse of roads or buildings that overlie the voids. The resistivity response of air- or water-filled voids compared to the surrounding bedrock may allow electrical resistivity surveys to delineate areas underlain by such voids. Surface deformation along State Route 32 in Jackson County led to a site investigation, which included electrical resistivity surveys. Several highly resistive areas were identified using axial dipole-dipole and Wenner resistivity surveys. Subsequent drilling and excavation led to the discovery of several air-filled abandoned underground mine tunnels. A site along State Route 32 in Vinton County, Ohio, was drilled as part of a mining permit application process. A mine void under the highway was instrumented with a pressure transducer to monitor water levels. During a period of high water level, electrical resistivity surveys were completed. The electrical response was dominated by a thin, low-resistivity layer of iron ore above where the coal was mined out. Nearby overhead powerlines also affected the results.

Small-scale electrical resistivity tomography of wet fractured rocks.

PubMed

LaBrecque, Douglas J; Sharpe, Roger; Wood, Thomas; Heath, Gail

2004-01-01

This paper describes a series of experiments that tested the ability of the electrical resistivity tomography (ERT) method to locate correctly wet and dry fractures in a meso-scale model. The goal was to develop a method of monitoring the flow of water through a fractured rock matrix. The model was a four by six array of limestone blocks equipped with 28 stainless steel electrodes. Dry fractures were created by placing pieces of vinyl between one or more blocks. Wet fractures were created by injecting tap water into a joint between blocks. In electrical terms, the dry fractures are resistive and the wet fractures are conductive. The quantities measured by the ERT system are current and voltage around the outside edge of the model. The raw ERT data were translated to resistivity values inside the model using a three-dimensional Occam's inversion routine. This routine was one of the key components of ERT being tested. The model presented several challenges. First, the resistivity of both the blocks and the joints was highly variable. Second, the resistive targets introduced extreme changes the software could not precisely quantify. Third, the abrupt changes inherent in a fracture system were contrary to the smoothly varying changes expected by the Occam's inversion routine. Fourth, the response of the conductive fractures was small compared to the background variability. In general, ERT was able to locate correctly resistive fractures. Problems occurred, however, when the resistive fracture was near the edges of the model or when multiple fractures were close together. In particular, ERT tended to position the fracture closer to the model center than its true location. Conductive fractures yielded much smaller responses than the resistive case. A difference-inversion method was able to correctly locate these targets.

Publications - IC 51 | Alaska Division of Geological & Geophysical Surveys

Science.gov Websites

Mapping Advisory Board STATEMAP Publications Geophysics Program Information Geophysical Survey Photography; Aeromagnetic; Aeromagnetic Data; Aeromagnetic Survey; Airborne Geophysical Survey; Alaska Data; Apparent Resistivity Map; Apparent Resistivity Survey; Arctic Deposit; Arsenic; Arsenopyrite

Permafrost investigations at the Lake Hövsgöl, northern Mongolia, using DC resistivity tomography and DEM-analyses

NASA Astrophysics Data System (ADS)

Etzelmuller, B.; Heggem, E. S. F.; Frauenfelder, R.; Romanovsky, V.; Sharkhuu, N.; Jambaljav, Y.; Tumensetseg, S.; Kääb, A.; Goulden, C.

2003-04-01

The region of Lake Hövsgöl, northern Mongolia, lies at the southern edge of Siberia and forms the southern-most fringe of the Siberian continuous permafrost zone. Analysis of long-term temperature data from the area indicates that annual temperatures have warmed by about 1.5^oC over the last 40 years. Being at the southern fringe of permafrost existence, temperature changes are supposed to have a major impact on permafrost degradation and thus on the environment, in interaction with human activities like nomadic pasture use. The objective of this study is to define the distribution of permafrost and the depth of the active zones in detail, and to begin a monitoring program of soil and permafrost temperatures in the study area. During these studies (a) field measurements of ground temperature, (b) analyses of geophysical parameters (mainly ground resistivities), and (c) the generation and analyses of digital elevation models and satellite imagery were carried out. The field measurements provided the basis for the later development of statistical/empirical and physical models of the permafrost distribution in the Hövsgöl area. This presentation will focus on the DC-resistivity tomography mapping of permafrost and digital elevation model analyses. The study showed that DC resistivity tomography was useful to distinguish the active layer and permafrost thickness under different types of surface cover. The project is funded by a five-year grant from the Global Environment Facility to the Mongolian Academy of Sciences (MAS), implemented by the World Bank and a foundation of the Mongolian Long Term Ecological Research Program at Lake Hövsgöl.

The implementation of multi-task geophysical survey to locate Cleopatra Tomb at Tap-Osiris Magna, Borg El-Arab, Alexandria, Egypt “Phase II”

NASA Astrophysics Data System (ADS)

Abbas, Abbas M.; Khalil, Mohamed A.; Massoud, Usama; Santos, Fernando M.; Mesbah, Hany A.; Lethy, Ahmed; Soliman, Mamdouh; Ragab, El Said A.

2012-06-01

According to some new discoveries at Tap-Osiris Magna temple (West of Alexandria), there is potentiality to uncover a remarkable archeological finding at this site. Three years ago many significant archeological evidences have been discovered sustaining the idea that the tomb of Cleopatra and Anthony may be found in the Osiris temple inside Tap-Osiris Magna temple at a depth from 20 to 30 m. To confirm this idea, PHASE I was conducted in by joint application of Ground Penetrating Radar “GPR”, Electrical Resistivity Tomography “ERT” and Magnetometry. The results obtained from PHASE I could not confirm the existence of major tombs at this site. However, small possible cavities were strongly indicated which encouraged us to proceed in investigation of this site by using another geophysical approach including Very Low Frequency Electro Magnetic (VLF-EM) technique. VLF-EM data were collected along parallel lines covering the investigated site with a line-to-line spacing of 1 m. The point-to-point distance of 1 m along the same line was employed. The data were qualitatively interpreted by Fraser filtering process and quantitatively by 2-D VLF inversion of tipper data and forward modeling. Results obtained from VLF-EM interpretation are correlated with 2-D resistivity imaging and drilling information. Findings showed a highly resistive zone at a depth extended from about 25-45 m buried beneath Osiris temple, which could be indicated as the tomb of Cleopatra and Anthony. This result is supported by Fraser filtering and forward modeling results. The depth of archeological findings as indicated from the geophysical survey is correlated well with the depth expected by archeologists, as well as, the depth of discovered tombs outside Tap-Osiris Magna temple. This depth level has not been reached by drilling in this site. We hope that the site can be excavated in the future based on these geophysical results.

Resistivity sections, upper Arkansas River basin, Colorado

USGS Publications Warehouse

Zohdy, Adel A.R.; Hershey, Lloyd A.; Emery, Philip A.; Stanley, William D.

1971-01-01

A reconnaissance investigation of ground-water resources in the upper Arkansas River basin from Pueblo to Leadville is being made by the U.S. Geological Survey in cooperation with the Southeastern Colorado Water Conservancy District, and the Colorado Division of Water Resources, Colorado State Engineer. As part of the investigation, surface geophysical electrical resistivity surveys were made during the summer and fall of 1970 near Buena Vista and Westcliffe, Colo. (p1.1). The resistivity surveys were made to verify a previous gravity survey and to help locate areas where ground-water supplies might be developed. This report presents the results of the surveys in the form of two resistivity sections.

Recognition of Earthquake-Induced Damage in the Abakainon Necropolis (NE Sicily): Results From Geomorphological, Geophysical and Numerical Analyses

NASA Astrophysics Data System (ADS)

Bottari, C.; Albano, M.; Capizzi, P.; D'Alessandro, A.; Doumaz, F.; Martorana, R.; Moro, M.; Saroli, M.

2018-01-01

Seismotectonic activity and slope instability are a permanent threat in the archaeological site of Abakainon and in the nearby village of Tripi in NE Sicily. In recent times, signs of an ancient earthquake have been identified in the necropolis of Abakainon which dating was ascertained to the first century AD earthquake. The site is located on a slope of Peloritani Mts. along the Tindari Fault Line and contains evidence for earthquake-induced landslide, including fallen columns and blocks, horizontal shift and counter slope tilting of the tomb basements. In this paper, we used an integrated geomorphological and geophysical analysis to constrain the landslide. The research was directed to the acquisition of deep geological data for the reconstruction of slope process and the thickness of mobilized materials. The applied geophysical techniques included seismic refraction tomography and electrical resistivity tomography. The surveys were performed to delineate the sliding surface and to assess approximately the thickness of mobilized materials. The geophysical and geomorphologic data confirmed the presence of different overlapped landslides in the studied area. Moreover, a numerical simulation of the slope under seismic loads supports the hypothesis of a mobilization of the landslide mass in case of strong earthquakes (PGA > 0.3 g). However, numerical results highlight that the main cause of destruction for the Abakainon necropolis is the amplification of the seismic waves, occasionally accompanied by surficial sliding.

GEOELECTRICAL TOMOGRAPHY AS AN OPERATIVE TOOL FOR THE EMERGENCY MANAGEMENT OF LANDSLIDE: AN APPLICATION IN BASILICATA REGION, ITALY

NASA Astrophysics Data System (ADS)

Gerardo, C.; Lapenna, V.; Loperte, A.; Perrone, A.

2009-12-01

A new approach has been applied for investigating some landslides of recent genesis in Basilicata region (southern Italy), in particular a geophysical technique has been used to study a landslide bodies. Electrical resistivity tomography method has been applied to obtain information about the deep characteristics of the landslide bodies. The high resolution of the 2D ERTs allowed to locate the possible sliding surfaces of the landslide body. They also highlighted areas characterized by high water content, the increase of the saturation degree and pore pressures in these areas could have caused a weakening of the slopes. The information obtained by the application of indirect surveys appeared to be particularly useful for the end users involved in the risks management. In particular, taking into account the cycle of landslides emergency, the obtained data could give a valid contribution during the post-event phase which mainly regards the damage valuation. Indeed, only a corrected assessment of the damage and a precise geometric reconstruction of the landslide body, can direct the intervention actions of the end users. The results represent a valid cognitive support to choose the most appropriate technical solution for strengthening of the slopes and an example of best practice for the cooperation between the research activity (IMAA-CNR) and field emergency (Basilicata Civil Protection).

Surface-downhole and crosshole geoelectrics for monitoring of brine injection at the Ketzin CO2 storage site

NASA Astrophysics Data System (ADS)

Rippe, Dennis; Bergmann, Peter; Labitzke, Tim; Wagner, Florian; Schmidt-Hattenberger, Cornelia

2016-04-01

The Ketzin pilot site in Germany is the longest operating on-shore CO2 storage site in Europe. From June 2008 till August 2013, a total of ˜67,000 tonnes of CO2 were safely stored in a saline aquifer at depths of 630 m to 650 m. The storage site has now entered the abandonment phase, and continuation of the multi-disciplinary monitoring as part of the national project "CO2 post-injection monitoring and post-closure phase at the Ketzin pilot site" (COMPLETE) provides the unique chance to participate in the conclusion of the complete life cycle of a CO2 storage site. As part of the continuous evaluation of the functionality and integrity of the CO2 storage in Ketzin, from October 12, 2015 till January 6, 2015 a total of ˜2,900 tonnes of brine were successfully injected into the CO2 reservoir, hereby simulating in time-lapse the natural backflow of brine and the associated displacement of CO2. The main objectives of this brine injection experiment include investigation of how much of the CO2 in the pore space can be displaced by brine and if this displacement of CO2 during the brine injection differs from the displacement of formation fluid during the initial CO2 injection. Geophysical monitoring of the brine injection included continuous geoelectric measurements accompanied by monitoring of pressure and temperature conditions in the injection well and two adjacent observation wells. During the previous CO2 injection, the geoelectrical monitoring concept at the Ketzin pilot site consisted of permanent crosshole measurements and non-permanent large-scale surveys (Kiessling et al., 2010). Time-lapse geoelectrical tomographies derived from the weekly crosshole data at near-wellbore scale complemented by six surface-downhole surveys at a scale of 1.5 km showed a noticeable resistivity signature within the target storage zone, which was attributed to the CO2 plume (Schmidt-Hattenberger et al., 2011) and interpreted in terms of relative CO2 and brine saturations (Bergmann et al., 2012). During the brine injection, usage of a new data acquisition unit allowed the daily collection of an extended crosshole data set. This data set was complemented by an alternative surface-downhole acquisition geometry, which for the first time allowed for regular current injections from three permanent surface electrodes into the existing electrical resistivity downhole array without the demand of an extensive field survey. This alternative surface-downhole acquisition geometry is expected to be characterized by good data quality and well confined sensitivity to the target storage zone. Time-lapse geoelectrical tomographies have been derived from both surface-downhole and crosshole data and show a conductive signature around the injection well associated with the displacement of CO2 by the injected brine. In addition to the above mentioned objectives of this brine injection experiment, comparative analysis of the surface-downhole and crosshole data provides the opportunity to evaluate the alternative surface-downhole acquisition geometry with respect to its resolution within the target storage zone and its ability to quantitatively constrain the displacement of CO2 during the brine injection. These results will allow for further improvement of the deployed alternative surface-downhole acquisition geometries. References Bergmann, P., Schmidt-Hattenberger, C., Kiessling, D., Rücker, C., Labitzke, T., Henninges, J., Baumann, G., Schütt, H. (2012). Surface-Downhole Electrical Resistivity Tomography applied to Monitoring of the CO2 Storage Ketzin (Germany). Geophysics, 77, B253-B267. Kiessling, D., Schmidt-Hattenberger, C., Schuett, H., Schilling, F., Krueger, K., Schoebel, B., Danckwardt, E., Kummerow, J., CO2SINK Group (2010). Geoelectrical methods for monitoring geological CO2 storage: First results from cross-hole and surface-downhole measurements from the CO2SINK test site at Ketzin (Germany). International Journal of Greenhouse Gas Control, 4(5), 816-826. Schmidt-Hattenberger, C., Bergmann, P., Kießling, D., Krüger, K., Rücker, C., Schütt, H., Ketzin Group (2011). Application of a Vertical Electrical Resistivity Array (VERA) for monitoring CO2 migration at the Ketzin site: First performance evaluation. Energy Procedia, 4, 3363-3370.

Electrical resistivity tomography applied to a complex lava dome: 2D and 3D models comparison

NASA Astrophysics Data System (ADS)

Portal, Angélie; Fargier, Yannick; Lénat, Jean-François; Labazuy, Philippe

2015-04-01

The study of volcanic domes growth (e.g. St. Helens, Unzen, Montserrat) shows that it is often characterized by a succession of extrusion phases, dome explosions and collapse events. Lava dome eruptive activity may last from days to decades. Therefore, their internal structure, at the end of the eruption, is complex and includes massive extrusions and lava lobes, talus and pyroclastic deposits as well as hydrothermal alteration. The electrical resistivity tomography (ERT) method, initially developed for environmental and engineering exploration, is now commonly used for volcano structure imaging. Because a large range of resistivity values is often observed in volcanic environments, the method is well suited to study the internal structure of volcanic edifices. We performed an ERT survey on an 11ka years old trachytic lava dome, the Puy de Dôme volcano (French Massif Central). The analysis of a recent high resolution DEM (LiDAR 0.5 m), as well as other geophysical data, strongly suggest that the Puy de Dôme is a composite dome. 11 ERT profiles have been carried out, both at the scale of the entire dome (base diameter of ~2 km and height of 400 m) on the one hand, and at a smaller scale on the summit part on the other hand. Each profile is composed of 64 electrodes. Three different electrode spacing have been used depending on the study area (35 m for the entire dome, 10 m and 5 m for its summit part). Some profiles were performed with half-length roll-along acquisitions, in order to keep a good trade-off between depth of investigation and resolution. Both Wenner-alpha and Wenner-Schlumberger protocols were used. 2-D models of the electrical resistivity distribution were computed using RES2DINV software. In order to constrain inversion models interpretation, the depth of investigation (DOI) method was applied to those results. It aims to compute a sensitivity index on inversion results, illustrating how the data influence the model and constraining models interpretation. Geometry and location of ERT profiles on the Puy de Dôme volcano allow to compute 3D inversion models of the electrical resistivity distribution with a new inversion code. This code uses tetrahedrons to discretize the 3D model and uses also a conventional Gauss-Newton inversion scheme combined to an Occam regularisation to process the data. It allows to take into account all the data information and prevents the construction of 3D artefacts present in conventional 2D inversion results. Inversion results show a strong electrical resistivity heterogeneity of the entire dome. Underlying volcanic edifices are clearly identified below the lava dome. Generally speaking, the flanks of the volcano show high resistivity values, and the summit part is more conductive but also very heterogeneous.

Three-dimensional internal structure of an entire alpine rockglacier, detected by Electrical Resistivity Imaging

NASA Astrophysics Data System (ADS)

Emmert, Adrian; Kneisel, Christof

2017-04-01

Uertsch rockglacier (46.61° N, 9.84°E, ca. 2500m asl.) is a tongue-shaped 300m x 100m landform at the head of a small high mountain valley in the Eastern Swiss Alps. Located at the lower end of possible permafrost existence, the rockglacier shows indications of permafrost decay although borehole temperature measurements exhibit an at least partly occurrence of permanently frozen subsurface conditions. To delimit the extent of the frozen area and to characterize subsurface structures, we performed three adjacent 3-D Electrical Resistivity Imaging (ERI) surveys consisting of data from altogether 138 merged 2-D profiles, covering nearly the entire rockglacier by an investigation area of more than 2.5 ha. More than 47000 data points of Wenner-Schlumberger and Dipol-Dipol electrode arrays grant sufficient data coverage. Ground-truthing was achieved through borehole temperature measurements and multiple comparative ground-penetrating radar (GPR) and seismic refraction tomography (SRT) surveys. Results show that the rockglacier today lacks a consistent permafrost table and only shows a patchy permafrost distribution. Several structures differing in geometry and electric resistivity show a complex pattern of ice-rich, ice-poor and ice-free areas. We could identify glacial influence in the root zone of the rockglacier, where a 3200m2 perennial surface ice field is visible. In a downslope direction, a shallow layer of high resistivity values, which is limited to the shallow subsurface, follows the ice field and indicates a genesis by refreezing meltwater. The central part of the rockglacier also shows traces of glacial interaction by the occurrence of a several meters thick buried ice patch in the shallow subsurface at a marginal position. Next to this position, in an area where longitudinal surface ridges are exposed, modelled resistivity values indicate frozen conditions with relatively low ice content, limited to the shallow subsurface. We assume that these structures are likely connected to permafrost creep processes. The frontal part of the rockglacier is affected by a strong ridge-and-furrow topography with arcuate ridge structures. Frozen conditions within these structures indicate an increase of ice content by thickening through compressive flow. Our study reflects the complexity of landform evolution for Uertsch rockglacier, where glacial and periglacial processes occur in close proximity. This emphasize the value of comprehensive 3-D investigations to assess the geometry and characteristics of larger subsurface structures.

Implementation of a national anti-tuberculosis drug resistance survey in Tanzania

PubMed Central

Chonde, Timothy M; Doulla, Basra; van Leth, Frank; Mfinanga, Sayoki GM; Range, Nyagosya; Lwilla, Fred; Mfaume, Saidi M; van Deun, Armand; Zignol, Matteo; Cobelens, Frank G; Egwaga, Saidi M

2008-01-01

Background A drug resistance survey is an essential public health management tool for evaluating and improving the performance of National Tuberculosis control programmes. The current manuscript describes the implementation of the first national drug resistance survey in Tanzania. Methods Description of the implementation process of a national anti-tuberculosis drug resistance survey in Tanzania, in relation to the study protocol and Standard Operating Procedures. Results Factors contributing positively to the implementation of the survey were a continuous commitment of the key stakeholders, the existence of a well organized National Tuberculosis Programme, and a detailed design of cluster-specific arrangements for rapid sputum transportation. Factors contributing negatively to the implementation were a long delay between training and actual survey activities, limited monitoring of activities, and an unclear design of the data capture forms leading to difficulties in form-filling. Conclusion Careful preparation of the survey, timing of planned activities, a strong emphasis on data capture tools and data management, and timely supervision are essential for a proper implementation of a national drug resistance survey. PMID:19116022

Utilizing 2D Electrical Resistivity Tomography and Very Low Frequency Electromagnetics to Investigate the Hydrogeology of Natural Cold Springs Near Virginia City, Southwest Montana

NASA Astrophysics Data System (ADS)

Khalil, Mohamed A.; Bobst, Andrew; Mosolf, Jesse

2018-04-01

Virginia City, Montana, is located in the northern Rocky Mountains of the United States. Two natural springs supply the city's water; however, the source of that water is poorly understood. The springs are located on the east side of the city, on the edge of an area affected by landslides. 2D electric resistivity tomography (ERT) and very low frequency electromagnetics (VLF-EM) were used to explore the springs and landslides. Two intersecting 2D resistivity profiles were measured at each spring, and two VLF profiles were measured in a landslide zone. The inverted 2D resistivity profiles at the springs reveal high resistivity basalt flows juxtaposed with low resistivity volcanic ash. The VLF profiles within the landslide show a series of fracture zones in the basalt, which are interpreted to be a series of landslide scarps. Results show a strong correlation between the inferred scarps and local topography. This study provides valuable geological information to help understand the source of water to the springs. The contact between the fractured basalt and the ash provides a sharp contrast in permeability, which causes water to flow along the contact and discharge at outcrop. The fracture zones along the scarps in the landslide deposits provide conduits of high secondary permeability to transmit water to the springs. The fracture zones near the scarps may also provide targets for municipal supply wells.

Adjoint-state inversion of electric resistivity tomography data of seawater intrusion at the Argentona coastal aquifer (Spain)

NASA Astrophysics Data System (ADS)

Fernández-López, Sheila; Carrera, Jesús; Ledo, Juanjo; Queralt, Pilar; Luquot, Linda; Martínez, Laura; Bellmunt, Fabián

2016-04-01

Seawater intrusion in aquifers is a complex phenomenon that can be characterized with the help of electric resistivity tomography (ERT) because of the low resistivity of seawater, which underlies the freshwater floating on top. The problem is complex because of the need for joint inversion of electrical and hydraulic (density dependent flow) data. Here we present an adjoint-state algorithm to treat electrical data. This method is a common technique to obtain derivatives of an objective function, depending on potentials with respect to model parameters. The main advantages of it are its simplicity in stationary problems and the reduction of computational cost respect others methodologies. The relationship between the concentration of chlorides and the resistivity values of the field is well known. Also, these resistivities are related to the values of potentials measured using ERT. Taking this into account, it will be possible to define the different resistivities zones from the field data of potential distribution using the basis of inverse problem. In this case, the studied zone is situated in Argentona (Baix Maresme, Catalonia), where the values of chlorides obtained in some wells of the zone are too high. The adjoint-state method will be used to invert the measured data using a new finite element code in C ++ language developed in an open-source framework called Kratos. Finally, the information obtained numerically with our code will be checked with the information obtained with other codes.

Static resistivity image of a cubic saline phantom in magnetic resonance electrical impedance tomography (MREIT).

PubMed

Lee, Byung Il; Oh, Suk Hoon; Woo, Eung Je; Lee, Soo Yeol; Cho, Min Hyeong; Kwon, Ohin; Seo, Jin Keun; Baek, Woon Sik

2003-05-01

In magnetic resonance electrical impedance tomography (MREIT) we inject currents through electrodes placed on the surface of a subject and try to reconstruct cross-sectional resistivity (or conductivity) images using internal magnetic flux density as well as boundary voltage measurements. In this paper we present a static resistivity image of a cubic saline phantom (50 x 50 x 50 mm3) containing a cylindrical sausage object with an average resistivity value of 123.7 ohms cm. Our current MREIT system is based on an experimental 0.3 T MRI scanner and a current injection apparatus. We captured MR phase images of the phantom while injecting currents of 28 mA through two pairs of surface electrodes. We computed current density images from magnetic flux density images that are proportional to the MR phase images. From the current density images and boundary voltage data we reconstructed a cross-sectional resistivity image within a central region of 38.5 x 38.5 mm2 at the middle of the phantom using the J-substitution algorithm. The spatial resolution of the reconstructed image was 64 x 64 and the reconstructed average resistivity of the sausage was 117.7 ohms cm. Even though the error in the reconstructed average resistivity value was small, the relative L2-error of the reconstructed image was 25.5% due to the noise in measured MR phase images. We expect improvements in the accuracy by utilizing an MRI scanner with higher SNR and increasing the size of voxels scarifying the spatial resolution.

Seismic site survey investigations in urban environments: The case of the underground metro project in Copenhagen, Denmark.

NASA Astrophysics Data System (ADS)

Martínez, K.; Mendoza, J. A.; Colberg-Larsen, J.; Ploug, C.

2009-05-01

Near surface geophysics applications are gaining more widespread use in geotechnical and engineering projects. The development of data acquisition, processing tools and interpretation methods have optimized survey time, reduced logistics costs and increase results reliability of seismic surveys during the last decades. However, the use of wide-scale geophysical methods under urban environments continues to face great challenges due to multiple noise sources and obstacles inherent to cities. A seismic pre-investigation was conducted to investigate the feasibility of using seismic methods to obtain information about the subsurface layer locations and media properties in Copenhagen. Such information is needed for hydrological, geotechnical and groundwater modeling related to the Cityringen underground metro project. The pre-investigation objectives were to validate methods in an urban environment and optimize field survey procedures, processing and interpretation methods in urban settings in the event of further seismic investigations. The geological setting at the survey site is characterized by several interlaced layers of clay, till and sand. These layers are found unevenly distributed throughout the city and present varying thickness, overlaying several different unit types of limestone at shallow depths. Specific results objectives were to map the bedrock surface, ascertain a structural geological framework and investigate bedrock media properties relevant to the construction design. The seismic test consisted of a combined seismic reflection and refraction analyses of a profile line conducted along an approximately 1400 m section in the northern part of Copenhagen, along the projected metro city line. The data acquisition was carried out using a 192 channels array, receiver groups with 5 m spacing and a Vibroseis as a source at 10 m spacing. Complementarily, six vertical seismic profiles (VSP) were performed at boreholes located along the line. The reflection data underwent standard interpretation and the refraction included wavepath Eikonal traveltime tomography. The reflection results indicate the presence of horizontal reflectors with discontinuities likely related to deep lying structural features in deeper lying chalk layers. The refraction interpretation allowed the identification of the upper limestone surface, relevant to map for tunneling design. The VSP provided additional information regarding limestone quality and provided correlation data for improved refraction interpretation. In general, the pre-investigation results demonstrated that it is possible to image the limestone surface using the seismic method. The satisfactory results lead to the implementation of a 15 km survey planned during the spring 2009. The survey will combine reflection, refraction, walkaway-VSP and electrical resistivity tomography (ERT). The authors wish to acknowledge Metroselskabet I/S for permission in presenting the preliminary results and the Cityringen Joint Venture partners Arup and Systra.

Development of a large-area Multigap RPC with adequate spatial resolution for muon tomography

NASA Astrophysics Data System (ADS)

Wang, J.; Wang, Y.; Wang, X.; Zeng, M.; Xie, B.; Han, D.; Lyu, P.; Wang, F.; Li, Y.

2016-11-01

We study the performance of a large-area 2-D Multigap Resistive Plate Chamber (MRPC) designed for muon tomography with high spatial resolution. An efficiency up to 98% and a spatial resolution of around 270 μ m are obtained in cosmic ray and X-ray tests. The performance of the MRPC is also investigated for two working gases: standard gas and pure Freon. The result shows that the MRPC working in pure Freon can provide higher efficiency and better spatial resolution.

Simulation of a current source with a Cole-Cole load for multi-frequency electrical impedance tomography.

PubMed

Aguiar Santos, Susana; Schlebusch, Thomas; Leonhardt, Steffen

2013-01-01

An accurate current source is one of the keys in the hardware of Electrical impedance Tomography systems. Limitations appear mainly at higher frequencies and for non-simple resistive loads. In this paper, we simulate an improved Howland current source with a Cole-Cole load. Simulations comparing two different op-amps (THS4021 and OPA843) were performed at 1 kHz to 1 MHz. Results show that the THS4021 performed better than the OPA843. The current source with THS4021 reaches an output impedance of 20 MΩ at 1 kHz and above 320 kΩ at 1 MHz, it provides a constant and stable output current up to 4 mA, in the complete range of frequencies, and for Cole-Cole (resistive and capacitive) load.

Electrical resistivity tomography as monitoring tool for unsaturated zone transport: an example of preferential transport of deicing chemicals.

PubMed

Wehrer, Markus; Lissner, Heidi; Bloem, Esther; French, Helen; Totsche, Kai Uwe

2014-01-01

Non-invasive spatially resolved monitoring techniques may hold the key to observe heterogeneous flow and transport behavior of contaminants in soils. In this study, time-lapse electrical resistivity tomography (ERT) was employed during an infiltration experiment with deicing chemical in a small field lysimeter. Deicing chemicals like potassium formate, which frequently impact soils on airport sites, were infiltrated during snow melt. Chemical composition of seepage water and the electrical response was recorded over the spring period 2010. Time-lapse electrical resistivity tomographs are able to show the infiltration of the melt water loaded with ionic constituents of deicing chemicals and their degradation product hydrogen carbonate. The tomographs indicate early breakthrough behavior in parts of the profile. Groundtruthing with pore fluid conductivity and water content variations shows disagreement between expected and observed bulk conductivity. This was attributed to the different sampling volume of traditional methods and ERT due to a considerable fraction of immobile water in the soil. The results show that ERT can be used as a soil monitoring tool on airport sites if assisted by common soil monitoring techniques.

Real-time imaging of cerebral infarction in rabbits using electrical impedance tomography.

PubMed

Yang, Bin; Shi, Xuetao; Dai, Meng; Xu, Canhua; You, Fushen; Fu, Feng; Liu, Ruigang; Dong, Xiuzhen

2014-02-01

To investigate the possible use of electrical impedance tomography (EIT) in monitoring focal cerebral infarction in a rabbit model. A model of focal cerebral infarction was established in eight New Zealand rabbits using a photochemical method without craniectomy. Focal cerebral infarction was confirmed by histopathological examination. Intracranial impedance variation was measured using 16 electrodes placed in a circle on the scalp. EIT images were obtained using a damped least-squares reconstruction algorithm. The average resistivity value (ARV) of the infarct region on EIT images was calculated to quantify relative resistivity changes. A symmetry index was calculated to evaluate the relative difference in resistivity between the two sides of the cerebrum. EIT images and ARV curves showed that impedance changes caused by cerebral infarction increased linearly with irradiation time. A difference in ARV was found between measurements taken before and after infarct induction. Focal cerebral infarction can be monitored by EIT in the proposed animal model. The results are sufficiently encouraging that the authors plan to extend this study to humans, after further technical improvements.

Inner structure of the Puy de Dôme volcano: cross-comparison of geophysical models (ERT, gravimetry, muon imaging)

NASA Astrophysics Data System (ADS)

Portal, A.; Labazuy, P.; Lénat, J.-F.; Béné, S.; Boivin, P.; Busato, E.; Cârloganu, C.; Combaret, C.; Dupieux, P.; Fehr, F.; Gay, P.; Laktineh, I.; Miallier, D.; Mirabito, L.; Niess, V.; Vulpescu, B.

2013-01-01

Muon imaging of volcanoes and of geological structures in general is actively being developed by several groups in the world. It has the potential to provide 3-D density distributions with an accuracy of a few percent. At this stage of development, comparisons with established geophysical methods are useful to validate the method. An experiment has been carried out in 2011 and 2012 on a large trachytic dome, the Puy de Dôme volcano, to perform such a comparison of muon imaging with gravimetric tomography and 2-D electrical resistivity tomography. Here, we present the preliminary results for the last two methods. North-south and east-west resistivity profiles allow us to model the resistivity distribution down to the base of the dome. The modelling of the Bouguer anomaly provides models for the density distribution within the dome that are directly comparable with the results from the muon imaging. Our ultimate goal is to derive a model of the dome using the joint interpretation of all sets of data.

Geophysical Monitoring at the CO2SINK Site: Combining Seismic and Geoelectric Data

NASA Astrophysics Data System (ADS)

Giese, R.; Lüth, S.; Cosma, C.; Juhlin, C.; Kiessling, D.; Schütt, H.; Schöbel, B.; Schmidt-Hattenberger, C.; Schilling, F.; Co2SINK Group

2009-04-01

The CO2SINK project at the German town of Ketzin (near Berlin), is aimed at a pilot storage of CO2, and at developing and testing efficient integrated monitoring procedures (physical, chemical, and biological observations) for assessing the processes triggered within the reservoir by a long term injection operation. In particular, geophysical methods as seismic and geoelectric measurements have delivered the structural framework, and they enable to observe the reaction of the reservoir and the caprock to CO2 propagation at locations which are not accessible for direct observations. We report on the seismic monitoring program of the CO2SINK project which comprises baseline and repeat observations at different scales in time and space, combined with comprehensive geoelectrical monitoring performed in the Ketzin wells and on the surface. The main objectives of the 3D seismic survey (carried out in spring 2005) were to provide the structural model around the location of the Ketzin wells, to verify earlier geologic interpretations of structure based on vintage 2D seismic and borehole data, as well as providing a baseline for future seismic surveys. The uppermost 1000 m are well imaged and show an anticlinal structure with an east-west striking central graben on its top. The 3D baseline survey was extended by VSP (vertical seismic profiling), MSP (moving source profiling) on 7 profiles, and crosshole tomographic measurements. 2D "star" measurements were carried out on the 7 MSP profiles in order to tie-in the down-hole surveys with the 3D baseline survey. These measurements provide enhanced resolution in time (faster and more cost effective than a full 3D survey) and space (higher source and receiver frequencies). Three crosshole measurements were performed, one baseline survey in May 2008, and two repeats in July and August 2008, respectively. A third crosshole repeat is planned for a later stage in the project when a steady state situation has been reached in the reservoir between the two observation boreholes Ktzi 200 and Ktzi 202. The interpretation of the time lapse crosshole seismic measurements is still work in progress. A time lapse effect can be recognized on cross correlations of baseline and repeat data indicating that considering the full wave form of the recordings does have the potential to locate subtle changes in the seismic properties of the reservoir due to CO2 injection. In addition, we show the results of the site-specific geoelectrical monitoring concept VERA (Vertical Electrical Resistivity Array), which covers electrical resistivity measurements in all three Ketzin wells. The array consists of 45 permanent electrodes (15 in each well), placed on the electrically insulated casings of the wells in the 600 m to 750 m depth range with a spacing of 10 m. This layout has been designed according to numerical forward modeling assuming electrical properties of pre- and post-injection scenarios. In addition to the geoelectric downhole measurement setup, surface to surface, and surface to downhole measurements are added in order to enlarge the area of observation between the three Ketzin wells to a hemispherical area (with a radius of about 1.5 km) around the wells. First results of the Electrical Resistivity Tomography (ERT) fit the expected reservoir behaviour. Higher resistivity values (presently up to factor 3 compared to other horizons) represent the intervals of the sandstone reservoir as preferred pathways of the CO2 propagation.

Subsurface Resistivity Structures in and Around Strike-Slip Faults - Electromagnetic Surveys and Drillings Across Active Faults in Central Japan -

NASA Astrophysics Data System (ADS)

Omura, K.; Ikeda, R.; Iio, Y.; Matsuda, T.

2005-12-01

Electrical resistivity is important property to investigate the structure of active faults. Pore fluid affect seriously the electrical properties of rocks, subsurface electrical resistivity can be an indicator of the existence of fluid and distribution of pores. Fracture zone of fault is expected to have low resistivity due to high porosity and small gain size. Especially, strike-slip type fault has nearly vertical fracture zone and the fracture zone would be detected by an electrical survey across the fault. We performed electromagnetic survey across the strike-slip active faults in central Japan. At the same faults, we also drilled borehole into the fault and did downhole logging in the borehole. We applied MT or CSAMT methods onto 5 faults: Nojima fault which appeared on the surface by the 1995 Great Kobe earthquake (M=7.2), western Nagano Ohtaki area(1984 Nagano-ken seibu earthquake (M=6.8), the fault did not appeared on the surface), Neodani fault which appeared by the 1891 Nobi earthquake (M=8.0), Atera fault which seemed to be dislocated by the 1586 Tensyo earthquake (M=7.9), Gofukuji fault that is considered to have activated about 1200 years ago. The sampling frequencies of electrical and magnetic field were 2 - 1024Hz (10 frequencies) for CSAMT survey and 0.00055 - 384Hz (40 frequencies) for MT survey. The electromagnetic data were processed by standard method and inverted to 2-D resistivity structure along transects of the faults. Results of the survey were compared with downhole electrical logging data and observational descriptions of drilled cores. Fault plane of each fault were recognized as low resistivity region or boundary between relatively low and high resistivity region, except for Gofukuji fault. As for Gofukuji fault, fault was located in relatively high resistivity region. During very long elapsed time from the last earthquake, the properties of fracture zone of Gofukuji fault might changed from low resistivity properties as observed for other faults. Downhole electrical logging data were consistent to values of resistivity estimated by electromagnetic survey for each fault. The existence of relatively low and high resistivity regions in 2-D structure from electromagnetic survey was observed again by downhole logging at the correspondent portion in the borehole. Cores recovered from depthes where the electrical logging showed low resistivity were hardly fractured and altered from host rock which showed high resistivity. Results of electromagnetic survey, downhole electrical logging and observation of drilled cores were consistent to each other. In present case, electromagnetic survey is useful to explore the properties of fault fracture zone. In the further investigations, it is important to explore relationships among features of resistivity structure and geological and geophysical situations of the faults.

Drug resistance in Mexico: results from the National Survey on Drug-Resistant Tuberculosis.

PubMed

Bojorquez-Chapela, I; Bäcker, C E; Orejel, I; López, A; Díaz-Quiñonez, A; Hernández-Serrato, M I; Balandrano, S; Romero, M; Téllez-Rojo Solís, M M; Castellanos, M; Alpuche, C; Hernández-Ávila, M; López-Gatell, H

2013-04-01

To present estimations obtained from a population-level survey conducted in Mexico of prevalence rates of mono-, poly- and multidrug-resistant strains among newly diagnosed cases of pulmonary tuberculosis (TB), as well as the main factors associated with multidrug resistance (combined resistance to isoniazid and rifampicin). Study data came from the National Survey on TB Drug Resistance (ENTB-2008), a nationally representative survey conducted during 2008-2009 in nine states with a stratified cluster sampling design. Samples were obtained for all newly diagnosed cases of pulmonary TB in selected sites. Drug susceptibility testing (DST) was performed for anti-tuberculosis drugs. DST results were obtained for 75% of the cases. Of these, 82.2% (95%CI 79.5-84.7) were susceptible to all drugs. The prevalence of multidrug-resistant TB (MDR-TB) was estimated at 2.8% (95%CI 1.9-4.0). MDR-TB was associated with previous treatment (OR 3.3, 95%CI 1.1-9.4). The prevalence of drug resistance is relatively low in Mexico. ENTB-2008 can be used as a baseline for future follow-up of drug resistance.

Dipole-dipole resistivity survey of a portion of the Coso Hot Springs KGRA, Inyo County, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fox, R.C.

1978-05-01

A detailed electrical resistivity survey of 54 line-km was completed at the Coso Hot Springs KGRA in September 1977. This survey has defined a bedrock resistivity low at least 4 sq mi (10 sq km) in extent associated with the geothermal system at Coso. The boundaries of this low are generally well defined to the north and west but not as well to the south where an approximate southern limit has been determined. The bedrock resistivity low merges with an observed resistivity low over gravel fill east of Coso Hot Springs. A complex horizontal and vertical resistivity structure of themore » surveyed area has been defined which precludes the use of layered-earth or two-dimensional interpretive models for much of the surveyed area. In general the survey data indicate that a 10 to 20 ohm-meter zone extends from near surface to a depth greater than 750 meters within the geothermal system. This zone is bordered to the north and west by bedrock resistivities greater than 200 ohm-meters and to the south by bedrock resistivities greater than 50 ohm-meters. A combination of observed increases in: (1) fracture density (higher permeability), (2) alteration (high clay content), and (3) temperatures (higher dissolved solid content of ground water) within the bedrock low explain its presence.« less

Structure-from-Motion (SfM) and Electrical Resistivity Tomography (ERT) evaluation of the Ohuka landslide, North Island, New Zealand

NASA Astrophysics Data System (ADS)

Brook, Martin; Bevan, David; Prebble, Warwick; Tunnicliffe, Jon; Richards, Nick

2017-04-01

Globally, slope failures cause many thousands of deaths per year and damage infrastructure, costing billions of dollars to repair. There is a clear need for efficient and affordable techniques that can assess and evaluate ongoing slope instability. Of particular importance when assessing and evaluating ongoing landslide deformation is the availability of high-resolution Digital Surface Models (DSMs). Here, we applied the Structure-from-Motion (SfM) approach to low-altitude aerial images collected by an unmanned aerial vehicle (UAV) at the Ohuka coastal landslide on the North Island of New Zealand. The SfM image-based approach was selected as a mapping tool in order to provide a rapid, cost-effective, and highly automated method, generating high-resolution topography and coregistered texture (colour) from an unstructured set of overlapping photographs taken from varying viewpoints. This overcomes many of the cost, time, and logistical limitations of LiDAR and other topographic surveying methods. The SfM photogrammetry was undertaken in conjunction with Electrical Resistivity Tomography (ERT) to image the subsurface and provide an interpretation of the hydrogeology, due to the technique's high sensitivity to lateral and vertical changes in moisture content. Landslide features include a large arcuate scarp, flanked by gullies, which indicate the lateral boundaries of initial slope failure. Other topographic features include a 200 m wide bench with uphill-facing scarps, pull-apart zones, and surface flows from ongoing reactivation. ERT has proved useful in imaging the near-surface moisture movement driving the landsliding processes. Failure mechanisms include block-sliding along a clay seam in the early-Miocene Koheroa siltstone, and weathered deposits of the c. 1 Ma Kidnappers tephra. Cyclic variation in moisture content and formation of perched water tables above clay and tephra seam aquitards plays a key role in reactivation.

Evaluating four-dimensional time-lapse electrical resistivity tomography for monitoring DNAPL source zone remediation.

PubMed

Power, Christopher; Gerhard, Jason I; Karaoulis, Marios; Tsourlos, Panagiotis; Giannopoulos, Antonios

2014-07-01

Practical, non-invasive tools do not currently exist for mapping the remediation of dense non-aqueous phase liquids (DNAPLs). Electrical resistivity tomography (ERT) exhibits significant potential but has not yet become a practitioner's tool due to challenges in interpreting the survey results at real sites. This study explores the effectiveness of recently developed four-dimensional (4D, i.e., 3D space plus time) time-lapse surface ERT to monitor DNAPL source zone remediation. A laboratory experiment demonstrated the approach for mapping a changing NAPL distribution over time. A recently developed DNAPL-ERT numerical model was then employed to independently simulate the experiment, providing confidence that the DNAPL-ERT model is a reliable tool for simulating real systems. The numerical model was then used to evaluate the potential for this approach at the field scale. Four DNAPL source zones, exhibiting a range of complexity, were initially simulated, followed by modeled time-lapse ERT monitoring of complete DNAPL remediation by enhanced dissolution. 4D ERT inversion provided estimates of the regions of the source zone experiencing mass reduction with time. Results show that 4D time-lapse ERT has significant potential to map both the outline and the center of mass of the evolving treated portion of the source zone to within a few meters in each direction. In addition, the technique can provide a reasonable, albeit conservative, estimate of the DNAPL volume remediated with time: 25% underestimation in the upper 2m and up to 50% underestimation at late time between 2 and 4m depth. The technique is less reliable for identifying cleanup of DNAPL stringers outside the main DNAPL body. Overall, this study demonstrates that 4D time-lapse ERT has potential for mapping where and how quickly DNAPL mass changes in real time during site remediation. Copyright © 2014 Elsevier B.V. All rights reserved.

The DAFT/FADA Survey status and latest results

NASA Astrophysics Data System (ADS)

Guennou, L.

2011-12-01

We present here the latest results obtained from the American French collaboration called the Dark energy American French Team/French American DArk energy Team (DAFT/FADA). The goal of the DAFT/FADA collaboration is to carry out a weak lensing tomography survey of z = 0.4-0.9 rich clusters of galaxies. Unlike supernovae or other methods such as cluster of galaxy counts, weak lensing tomography is purely based on geometry and does not depend on knowledge of the physics of the objects used as distance indicators. In addition, the reason for analyzing observations in the direction of clusters is that the shear signal is enhanced by about 10 over the field. Our work will eventually contain results obtained on 91 rich clusters from the HST archive combined with ground based work to obtain photo-zs. This combination of photo-z and weak lensing tomography will enable us to constrain the equation of state of dark energy. We present here the latest results obtained so far in this study.

Dynamic imaging in electrical impedance tomography of the human chest with online transition matrix identification.

PubMed

Moura, Fernando Silva; Aya, Julio Cesar Ceballos; Fleury, Agenor Toledo; Amato, Marcelo Britto Passos; Lima, Raul Gonzalez

2010-02-01

One of the electrical impedance tomography objectives is to estimate the electrical resistivity distribution in a domain based only on electrical potential measurements at its boundary generated by an imposed electrical current distribution into the boundary. One of the methods used in dynamic estimation is the Kalman filter. In biomedical applications, the random walk model is frequently used as evolution model and, under this conditions, poor tracking ability of the extended Kalman filter (EKF) is achieved. An analytically developed evolution model is not feasible at this moment. The paper investigates the identification of the evolution model in parallel to the EKF and updating the evolution model with certain periodicity. The evolution model transition matrix is identified using the history of the estimated resistivity distribution obtained by a sensitivity matrix based algorithm and a Newton-Raphson algorithm. To numerically identify the linear evolution model, the Ibrahim time-domain method is used. The investigation is performed by numerical simulations of a domain with time-varying resistivity and by experimental data collected from the boundary of a human chest during normal breathing. The obtained dynamic resistivity values lie within the expected values for the tissues of a human chest. The EKF results suggest that the tracking ability is significantly improved with this approach.

Hyperbaric therapy for a postpartum patient with prolonged epidural blockade and tomographic evidence of epidural air.

PubMed

Panni, Moeen K; Camann, William; Bhavani Shankar, Kodali

2003-12-01

We used the epidural technique "loss of resistance to air" to provide labor analgesia in a healthy parturient. Inadequate analgesia required epidural catheter replacement using the same technique. Delayed recovery of sensory and motor blockade postpartum necessitated computed tomography and magnetic resonance imaging studies. These revealed 4-6 mL of air in the epidural space with no evidence of thecal compression. On the advice of the neurologist, this patient underwent hyperbaric therapy 14 h after the discontinuation of the epidural infusion. The patient made a complete recovery and was discharged without neurologic sequelae. It is possible that epidural air delayed the absorption of local anesthetics as a result of a reduction in the vascular surface area. Although a cause and effect relationship between epidural air and prolonged neurological block cannot be categorically established, the use of "loss of resistance to air" technique complicated the differential diagnosis. We report a case of prolonged motor and sensory block after labor analgesia using "loss of resistance to air" technique. The presence of epidural air on tomography resulted in the patient undergoing hyperbaric therapy. The use of loss of resistance to air technique complicated the differential diagnosis of prolonged sensory and motor block.

Dalton Highway 9 to 11 Mile expedient resistivity permafrost investigation.

DOT National Transportation Integrated Search

2014-01-01

This project performed capacitive coupled resistivity surveys over a roadway reconstruction project in Interior Alaska, for the determination of permafrost extent. The : objective was to ascertain the ability of an expedient earth resistivity survey ...

Joint project of the international network of agencies for health technology assessment--Part 1: Survey results on diffusion, assessment, and clinical use of positron emission tomography.

PubMed

Hastings, John; Adams, Elizabeth J

2006-01-01

The International Network of Agencies for Health Technology Assessment (INAHTA) has been tracking activities associated with the clinical use of positron emission tomography (PET) in its members' healthcare systems since 1997 and published its first Joint Project report on PET in 1999. Part 1 of this Joint Project report presents survey results on diffusion, assessment activities, and policy for clinical use related to PET among INAHTA members since 1999. INAHTA members were surveyed in 2003-2004. Twenty-seven INAHTA agencies (69 percent response rate) from nineteen countries responded to the survey. Dedicated PET systems are the most universally installed systems to date. Mobile scanners and modified gamma cameras are used occasionally as lower cost alternatives, and interest in PET-computed tomography hybrid models is rising despite limited assessment of impact on service planning. PET was used and assessed most commonly for managing patients with cancer. All respondents reported having some form of public funding for clinical PET frequently linked to data collection for the purpose of gathering evidence to refine clinical use and guide resource allocation toward indications that maximize clinical and cost-effectiveness. The use of HTA within a continuous quality improvement framework can help optimize scarce resources for evaluation and use of high cost diagnostic technologies such as PET, particularly where potential clinical or cost-effectiveness is considerable but conclusive evidence is lacking.

Identifying Resistivity Anomalies of Sungai Batu Ancient River using 3D Contour Map

NASA Astrophysics Data System (ADS)

Yusoh, R.; Saad, R.; Saidin, M.; Muhammad, S. B.; Anda, S. T.; Ismail, M. A. M.; Hazreek, Z. A. M.

2018-04-01

Electrical resistivity method was undertaken at archeological site at Sungai Batu in Lembah Bujang, located at Sungai Merbok in northwestern of Malaysia. The survey was implemented near the excavation site. This paper shows the results of 5 ground resistivity survey line was carry out using SAS4000 equipment. The wenner-schlumberger array was applied for measurement. Resistivity data are used to obtain valuable information to identify the remain buried archeology. The ground resistivity data were presented in contour map for various depth by using Surfer 13 software visualized clearly the anomalies evidenced for every single depth section. The results from the survey has found the appearance of sedimentation formation that believe happen long time ago after ancient river was buried by sediment from weathering process due to increasing sea level. Otherwise, another anomaly was found in the middle of the survey area which shows high resistivity value about 1000 – 2000 ohm.m

Subsurface architecture of two tropical alpine desert cinder cones that hold water

NASA Astrophysics Data System (ADS)

Leopold, Matthias; Morelli, Amanda; Schorghofer, Norbert

2016-06-01

Basaltic lava is generally porous and cannot hold water to form lakes. Here we investigate two impermeable cinder cones in the alpine desert of Maunakea volcano, Hawaii. We present the results of the first ever geophysical survey of the area around Lake Waiau, the highest lake on the Hawaiian Islands, and establish the existence of a second body of standing water in a nearby cinder cone, Pu`upōhaku (~4000 m above sea level), which has a sporadic pond of water. Based on unpublished field notes from Alfred Woodcock (*1905-†2005) spanning the years 1966-1977, more recent observations, and our own geophysical survey using electric resistivity tomography, we find that perched groundwater resides in the crater perennially to a depth of 2.5 m below the surface. Hence, Pu`upōhaku crater hosts a previously unrecognized permanent body of water, the highest on the Hawaiian Islands. Nearby Lake Waiau is also perched within a cinder cone known as Pu`uwaiau. Among other hypotheses, permafrost or a massive block of lava were discussed as a possible cause for perching the water table. Based on our results, ground temperatures are too high and specific electric resistivity values too low to be consistent with either ice-rich permafrost or massive rock. Fine-grained material such as ash and its clay-rich weathering products are likely the impermeable material that explains the perched water table at both study sites. At Pu`uwaiau we discovered a layer of high conductivity that may constitute a significant water reservoir outside of the lake and further be responsible for perching the water toward the lake.

Geophysical Investigations Over the Archaeological site of Rirha (Morocco)

NASA Astrophysics Data System (ADS)

Senechal, G.; Rousset, D.; Callegarin, L.; Kbiri Alaoui, M.

2007-05-01

The roman site of Rirha has been evidenced in the 1920's and loosely studied until nowadays. Archeaological evidences show a pre-roman to medieval occupation of the site. Excavations have revealed thermae and other buildings while their context, rural villa or urban domus was still unknown. A new survey began in 2004, focusing on the pre-roman occupation of the site, as well as the characterization of the roman occupation. The zone of interest, a hill in a river loop, is about 11hectares. A comprehensive geophysical survey was out of reach, so geophysical tests have been carried on with two goals. The first one was to identify the suitable methods adapted to this, the second one was to use these preliminary results to distinguish between rural or urban settings for the roman site. The first survey has been conducted in April 2005, using conductivitymeter (Geonics EM38) in order to get informations about the spatial organization of the site. The selected zone was located in an unsurveyed part of the site. Resistivity maps show orthogonal structures, far from the known roman remains. This result supports the hypothesis of the site being a roman town and not a large farm or a villa. The second survey has been carried on in February 2006 and involved GPR and DC tomography, in very wet conditions. DC survey aimed at constraining the geological context of the site and at finding the remains of a large wall described by early authors. GPR experiment was primarily a test of the tool there and has been conducted on the previously studied area to get some depth information. The geological context has been studied by carrying on a 2D vertical section, 330 m long and 25 meters deep. showing a substratum of river deposit (sand, gravel, pebbles with possible clay layers) located at 8 to 10 m deep. Above this formation, we observe a very conductive layer interpreted as a clay formation (3 to 6 m thick) and finally, just below the surface, a laterally heterogeneous formation with rocks and adobe masonry. 2D DC sections succesfully located the remains of the surrounding wall of the site supporting even more the town hypothesis. GPR 3D results (250 MHz) are in agreement with conductivity maps but are of poor quality due to the very low resistivity of the soil.

Model study of imaging myocardial infarction by intracardiac electrical impedance tomography.

PubMed

Li, Ying; Rao, Liyun; Ling, Yuesheng; He, Renjie; Khoury, Dirar S

2008-01-01

Electrical impedance tomography (EIT) detects tissue composition inside a medium by determining its resistive properties, and uses various electrode configurations to pass a small electric current and measure corresponding potential. We investigated the feasibility of reconstructing scarred tissue inside the heart wall by employing EIT on the basis of a catheter carrying a plurality of electrodes and placed inside the blood-filled heart cavity. We built a computer model of the biological medium, and reconstructed the resistivity distribution using the finite element method and Tikhonov regularization. The results established the successful implementation of the numeric methods and the possibility of localizing and quantifying scarred myocardium. Novel application of EIT from inside the heart cavity could be useful during catheterization and may complement other diagnostic modalities. Further research is necessary to assess the impact of several factors on the accuracy of the reconstruction and include number of electrodes, catheter location, and scar size.

Likelihood of Brine and CO 2 Leak Detection using Magnetotellurics and Electrical Resistivity Tomography Methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, X.; Buscheck, T. A.; Mansoor, K.

The US DOE National Risk Assessment Partnership (NRAP), funded through the Office of Fossil Energy and NETL, is developing methods to evaluate the effectiveness of monitoring techniques to detect brine and CO 2 leakage from legacy wells into underground sources of drinking water (USDW) overlying a CO 2 storage reservoir. As part of the NRAP Strategic Monitoring group, we have generated 140 simulations of aquifer impact data based on the Kimberlina site in California’s southern San Joaquin Basin, Kimberlina Rev. 1.1. CO 2 buoyancy allows some of the stored CO 2 to reach shallower permeable zones and is detectable withmore » surface geophysical sensors. We are using this simulated data set to evaluate effectiveness of electrical resistivity tomography (ERT) and magnetotellurics (MT) for leak detection. The evaluation of additional monitoring methods such as pressure, seismic and gravity is underway through a multi-lab collaboration.« less

Gas-water two-phase flow characterization with Electrical Resistance Tomography and Multivariate Multiscale Entropy analysis.

PubMed

Tan, Chao; Zhao, Jia; Dong, Feng

2015-03-01

Flow behavior characterization is important to understand gas-liquid two-phase flow mechanics and further establish its description model. An Electrical Resistance Tomography (ERT) provides information regarding flow conditions at different directions where the sensing electrodes implemented. We extracted the multivariate sample entropy (MSampEn) by treating ERT data as a multivariate time series. The dynamic experimental results indicate that the MSampEn is sensitive to complexity change of flow patterns including bubbly flow, stratified flow, plug flow and slug flow. MSampEn can characterize the flow behavior at different direction of two-phase flow, and reveal the transition between flow patterns when flow velocity changes. The proposed method is effective to analyze two-phase flow pattern transition by incorporating information of different scales and different spatial directions. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.

Contribution of electromagnetic and tomographic technique to the study of the impact of salinity in soils of the experimental station of Al Ain Atti (Errachidia, Morocco)

NASA Astrophysics Data System (ADS)

Benamara, A.; El Harnafi, M.; Ammar, A.

2017-03-01

Soil salinity is widespread particularly in arid areas. Much work has been done to remedy this natural contamination and make them more favorable to receive experimental soil of vegetation adapted to grow in these contrasting environments of scarce water resources. Over the 80 years, Morocco has experienced excessive dryness whose effects have been severely felt in the region of Errachidia. The depletion of the Quaternary alluvial aquifer has required the exploitation of deep reservoirs. In order to optimize the use of salt water in arid, the Institute of Agricultural Research tested soil experimenting three plant species; the Triplex, Acacia and Cypress. This experiment was not only economic objectives; increasing agricultural yields and production, but also reduce the impact of desertification in this region. So these are environmental reasons which have led researchers to realize this experiment whose purpose is to examine the ability of these plants to grow and adapt to irrigation by saline water from the deep aquifer in place. The experimental site is located on the left bank of the national road to Erfoud (Errachidia). In its entirety, the redesigned covering about 10 hectares. The studies that have been conducted mainly concerned pedogenetic analyzes and observations the development height of the plantation tested, regardless of the experimental ground heterogeneity. This is why we undertook a geophysical survey which aims to provide information on the quality of the tested soils and accumulation of salinity at different depths of the experimental ground. To achieve our goal, we used the technique of electrical and electromagnetic investigation in order to identify the main lines of a possible spatial heterogeneity. Recall that the work of OKAY (2010) on an experiment coring by examining the evolution of the newly formed fracturing have proved that the result of resistivity measurement is correlated with that of the chargeability. The electrical resistivity is closely related to the concentration of mineral particles. Characterization studies at the La Ronde tailings mine (Agnico-Eagle Ltd, in Abitibi), showed quite encouraging results (Campos, 2004; Anterrieu, 2006). Since it is a salt-bearing areas (highly conductive) and given that the induced polarization is very sensitive to the ground conductivity; by measurement of residual potential, so we took measures chargeability tomography, the result is compared to the resistivity measured at different soils (control and irrigated), which will better clarify the impact of salinity on the quality of the disturbed soil. Indeed, the chargeability response it possible to characterize the different irrigated soils and its variation is attributed not only to the effect of saline irrigation but also the existence of an heterogeneity of the original ground. Prospecting in electrical tomography has displayed vertically and horizontally anomalies existing within the experimental site of the station of Ain Al Atti, it showed that: - accumulation of salinity becomes wider going from the control ground to that of Acacias. - surveyed the ground at least appear more homogeneous in surface, but their conductivity varies in depth. - salinity origin and the concretion formed on the surface greatly influenced chargeability and resistivity measured on the different experimental soils.

Three-Dimensional Electrical Resistivity Tomography of the Solfatara Crater (Italy): Implication for the Multiphase Flow Structure of the Shallow Hydrothermal System

NASA Astrophysics Data System (ADS)

Gresse, Marceau; Vandemeulebrouck, Jean; Byrdina, Svetlana; Chiodini, Giovanni; Revil, André; Johnson, Timothy C.; Ricci, Tullio; Vilardo, Giuseppe; Mangiacapra, Annarita; Lebourg, Thomas; Grangeon, Jacques; Bascou, Pascale; Metral, Laurent

2017-11-01

The Solfatara volcano is the main degassing area of the Campi Flegrei caldera, characterized by 60 years of unrest. Assessing such renewal activity is a challenging task because hydrothermal interactions with magmatic gases remain poorly understood. In this study, we decipher the complex structure of the shallow Solfatara hydrothermal system by performing the first 3-D, high-resolution, electrical resistivity tomography of the volcano. The 3-D resistivity model was obtained from the inversion of 43,432 resistance measurements performed on an area of 0.68 km2. The proposed interpretation of the multiphase hydrothermal structures is based on the resistivity model, a high-resolution infrared surface temperature image, and 1,136 soil CO2 flux measurements. In addition, we realized 27 soil cation exchange capacity and pH measurements demonstrating a negligible contribution of surface conductivity to the shallow bulk electrical conductivity. Hence, we show that the resistivity changes are mainly controlled by fluid content and temperature. The high-resolution tomograms identify for the first time the structure of the gas-dominated reservoir at 60 m depth that feeds the Bocca Grande fumarole through a 10 m thick channel. In addition, the resistivity model reveals a channel-like conductive structure where the liquid produced by steam condensation around the main fumaroles flows down to the Fangaia area within a buried fault. The model delineates the emplacement of the main geological structures: Mount Olibano, Solfatara cryptodome, and tephra deposits. It also reveals the anatomy of the hydrothermal system, especially two liquid-dominated plumes, the Fangaia mud pool and the Pisciarelli fumarole, respectively.

Weight-adjusted lean body mass and calf circumference are protective against obesity-associated insulin resistance and metabolic abnormalities.

PubMed

Takamura, Toshinari; Kita, Yuki; Nakagen, Masatoshi; Sakurai, Masaru; Isobe, Yuki; Takeshita, Yumie; Kawai, Kohzo; Urabe, Takeshi; Kaneko, Shuichi

2017-07-01

To test the hypothesis that preserved muscle mass is protective against obesity-associated insulin resistance and metabolic abnormalities, we analyzed the relationship of lean body mass and computed tomography-assessed sectional areas of specific skeletal muscles with insulin resistance and metabolic abnormalities in a healthy cohort. A total of 195 subjects without diabetes who had completed a medical examination were included in this study. Various anthropometric indices such as circumferences of the arm, waist, hip, thigh, and calf were measured. Body composition (fat and lean body mass) was determined by bioelectrical impedance analysis. Sectional areas of specific skeletal muscles (iliopsoas, erector spinae, gluteus, femoris, and rectus abdominis muscles) were measured using computed tomography. Fat and lean body mass were significantly correlated with metabolic abnormalities and insulin resistance indices. When adjusted by weight, relationships of fat and lean body mass with metabolic parameters were mirror images of each other. The weight-adjusted lean body mass negatively correlated with systolic and diastolic blood pressures; fasting plasma glucose, HbA1c, alanine aminotransferase, and triglyceride, and insulin levels; and hepatic insulin resistance indices, and positively correlated with HDL-cholesterol levels and muscle insulin sensitivity indices. Compared with weight-adjusted lean body mass, weight-adjusted sectional areas of specific skeletal muscles showed similar, but not as strong, correlations with metabolic parameters. Among anthropometric measures, the calf circumference best reflected lean body mass, and weight-adjusted calf circumference negatively correlated with metabolic abnormalities and insulin resistance indices. Weight-adjusted lean body mass and skeletal muscle area are protective against weight-associated insulin resistance and metabolic abnormalities. The calf circumference reflects lean body mass and may be useful as a protective marker against obesity-associated metabolic abnormalities.

Geophysical investigations at the Paleolitic site Grotta delle Veneri near Parabita (Lecce, Italy)

NASA Astrophysics Data System (ADS)

Carrozzo, M. T.; Leucci, G.; Negri, S.; Nuzzo, L.

2003-04-01

The human presence in Apulia (southern Italy) is documented since 80.000 years before present. In 1966 near Parabita (Lecce, Italy) in a cave subsequently named "Grotta delle Veneri" human remains belonging to Homo Sapiens Neanderthalensis (Neanderthal) and Homo Sapiens-Sapiens (Cro-Magnon) were recovered together with two small statues of pregnant women ("Veneri") referable to 12.000--10.000 b.C. The local Archaeological Superintendence was interested in assessing the possibility to reconstruct by means of geophysical methods the planimetric position of the cave and further development of its burrows beyond those accessible to speleologists and reported in the underground topographic survey. Both electromagnetic (EM) and electric methods were tested using Ground Penetrating Radar (GPR) with 200 and 500 MHz antennas, GEM300 multi-frequency EM induction device and 2D Electrical Resistivity Tomography (ERT). Despite the rough surface and the presence of numerous obstacles (trees, stone walls and stone piles) limiting the accessible survey area and often preventing a good ground-coupling, the GPR survey successfully located the top of the karstic cave and identified zones of high density of diffraction hyperbolas, interpreted as highly fractured and karstified limestone, in a layer ranging from about 2 m to 6 m below ground. Zones characterised by high density of diffractions due to presence of voids were found also outside the known development of the cave. By means of the GEM 300, both in-phase and quadrature components of the induced EM signal were simultaneously collected at 8 frequencies, from 2025 to 19975 Hz, respectively related to the magnetic susceptibility and apparent conductivity of the soil down to a depth decreasing as the frequency increase. A presumable low contrast in the sought parameter between the highly fractured rock and karstic voids or refilled cavities as well as the presence of metallic debris on the ground allowed a difficult identification of only few anomalies in the EM map probably linked, by surface evidences, to underground interesting features. More interesting were the ETR results, revealing the presence of a high-resistive body (>2000 Ωm) in the same depth layer evidenced by GPR, with very high-resistive localised anomalies in good correspondence of known burrows and, more importantly, also in external zones, especially to the east of the cave.

Seismic tomography as a tool for measuring stress in mines

USGS Publications Warehouse

Scott, Douglas F.; Williams, T.J.; Denton, D.K.; Friedel, M.J.

1999-01-01

Spokane Research Center personnel have been investigating the use of seismic tomography to monitor the behavior of a rock mass, detect hazardous ground conditions and assess the mechanical integrity of a rock mass affected by mining. Seismic tomography can be a valuable tool for determining relative stress in deep, >1,220-m (>4,000-ft), underground pillars. If high-stress areas are detected, they can be destressed prior to development or they can be avoided. High-stress areas can be monitored with successive seismic surveys to determine if stress decreases to a level where development can be initiated safely. There are several benefits to using seismic tomography to identify high stress in deep underground pillars. The technique is reliable, cost-effective, efficient and noninvasive. Also, investigators can monitor large rock masses, as well as monitor pillars during the mining cycle. By identifying areas of high stress, engineers will be able to assure that miners are working in a safer environment.Spokane Research Center personnel have been investigating the use of seismic tomography to monitor the behavior of a rock mass, detect hazardous ground conditions and assess the mechanical integrity of a rock mass affected by mining. Seismic tomography can be a valuable tool for determining relative stress in deep, >1,200-m (>4,000-ft), underground pillars. If high-stress areas are detected, they can be destressed prior to development or they can be avoided. High-stress areas can be monitored with successive seismic surveys to determine if stress decreases to a level where development can be initiated safely. There are several benefits to using seismic tomography to identify high stress in deep underground pillars. The technique is reliable, cost-effective, efficient and noninvasive. Also, investigators can monitor large rock masses, as well as monitor pillars during the mining cycle. By identifying areas of high stress. engineers will be able to assure that miners are working in a safer environment.

Measuring Alignments between Galaxies and the Cosmic Web at z ˜ 2-3 Using IGM Tomography

NASA Astrophysics Data System (ADS)

Krolewski, Alex; Lee, Khee-Gan; Lukić, Zarija; White, Martin

2017-03-01

Many galaxy formation models predict alignments between galaxy spin and the cosmic web (I.e., directions of filaments and sheets), leading to an intrinsic alignment between galaxies that creates a systematic error in weak-lensing measurements. These effects are often predicted to be stronger at high redshifts (z ≳ 1) that are inaccessible to massive galaxy surveys on foreseeable instrumentation, but IGM tomography of the Lyα forest from closely spaced quasars and galaxies is starting to measure the z ˜ 2-3 cosmic web with requisite fidelity. Using mock surveys from hydrodynamical simulations, we examine the utility of this technique, in conjunction with coeval galaxy samples, to measure alignment between galaxies and the cosmic web at z ˜ 2.5. We show that IGM tomography surveys with ≲5 h -1 Mpc sightline spacing can accurately recover the eigenvectors of the tidal tensor, which we use to define the directions of the cosmic web. For galaxy spins and shapes, we use a model parameterized by the alignment strength, {{Δ }}< \\cos θ > , with respect to the tidal tensor eigenvectors from the underlying density field, and also consider observational effects such as errors in the galaxy position angle, inclination, and redshift. Measurements using the upcoming ˜1 deg2 CLAMATO tomographic survey and 600 coeval zCOSMOS-Deep galaxies should place 3σ limits on extreme alignment models with {{Δ }}< \\cos θ > ˜ 0.1, but much larger surveys encompassing >10,000 galaxies, such as Subaru PFS, will be required to constrain models with {{Δ }}< \\cos θ > ˜ 0.03. These measurements will constrain models of galaxy-cosmic web alignment and test tidal torque theory at z ˜ 2, improving our understanding of the physics of intrinsic alignments.

3D basin structure of the Santa Clara Valley constrained by ambient noise tomography

NASA Astrophysics Data System (ADS)

Cho, H.; Lee, S. J.; Rhie, J.; Kim, S.

2017-12-01

The basin structure is an important factor controls the intensity and duration of ground shaking due to earthquake. Thus it is important to study the basin structure for better understanding seismic hazard and also improving the earthquake preparedness. An active source seismic survey is the most appropriate method to determine the basin structure in detail but its applicability, especially in urban areas, is limited. In this study, we tested the potential of an ambient noise tomography, which can be a cheaper and more easily applicable method compared to a traditional active source survey, to construct the velocity model of the basin. Our testing region is the Santa Clara Valley, which is one of the major urban sedimentary basins in the States. We selected this region because continuous seismic recordings and well defined velocity models are available. Continuous seismic recordings of 6 months from short-period array of Santa Clara Valley Seismic Experiment are cross-correlated with 1 hour time window. And the fast marching method and the subspace method are jointly applied to construct 2-D group velocity maps between 0.2 - 4.0 Hz. Then, shear wave velocity model of the Santa Clara Valley is calculated up to 5 km depth using bayesian inversion technique. Although our model cannot depict the detailed structures, it is roughly comparable with the velocity model of the US Geological Survey, which is constrained by active seismic surveys and field researches. This result indicate that an ambient noise tomography can be a replacement, at least in part, of an active seismic survey to construct the velocity model of the basin.

Measuring Alignments between Galaxies and the Cosmic Web at z ~ 2–3 Using IGM Tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krolewski, Alex; Lee, Khee-Gan; Luki?, Zarija

Many galaxy formation models predict alignments between galaxy spin and the cosmic web (i.e., directions of filaments and sheets), leading to an intrinsic alignment between galaxies that creates a systematic error in weak-lensing measurements. These effects are often predicted to be stronger at high redshifts (z ≳ 1) that are inaccessible to massive galaxy surveys on foreseeable instrumentation, but IGM tomography of the Lyα forest from closely spaced quasars and galaxies is starting to measure the z ~ 2-3 cosmic web with requisite fidelity. Using mock surveys from hydrodynamical simulations, we examine the utility of this technique, in conjunction withmore » coeval galaxy samples, to measure alignment between galaxies and the cosmic web at z ~ 2.5. We show that IGM tomography surveys with ≲ 5 h -1 Mpc sightline spacing can accurately recover the eigenvectors of the tidal tensor, which we use to define the directions of the cosmic web. For galaxy spins and shapes, we use a model parameterized by the alignment strength, Δ (cos θ), with respect to the tidal tensor eigenvectors from the underlying density field, and also consider observational effects such as errors in the galaxy position angle, inclination, and redshift. Measurements using the upcoming ~ 1 deg 2 CLAMATO tomographic survey and 600 coeval zCOSMOS-Deep galaxies should place 3σ limits on extreme alignment models with Δ (cos θ) ~ 0.1, but much larger surveys encompassing > 10,000 galaxies, such as Subaru PFS, will be required to constrain models with Δ (cos θ) ~ 0.3. These measurements will constrain models of galaxy-cosmic web alignment and test tidal torque theory at z ~ 2, improving our understanding of the physics of intrinsic alignments.« less

Measuring Alignments between Galaxies and the Cosmic Web at z ~ 2–3 Using IGM Tomography

DOE PAGES

Krolewski, Alex; Lee, Khee-Gan; Luki?, Zarija; ...

2017-02-28

Many galaxy formation models predict alignments between galaxy spin and the cosmic web (i.e., directions of filaments and sheets), leading to an intrinsic alignment between galaxies that creates a systematic error in weak-lensing measurements. These effects are often predicted to be stronger at high redshifts (z ≳ 1) that are inaccessible to massive galaxy surveys on foreseeable instrumentation, but IGM tomography of the Lyα forest from closely spaced quasars and galaxies is starting to measure the z ~ 2-3 cosmic web with requisite fidelity. Using mock surveys from hydrodynamical simulations, we examine the utility of this technique, in conjunction withmore » coeval galaxy samples, to measure alignment between galaxies and the cosmic web at z ~ 2.5. We show that IGM tomography surveys with ≲ 5 h -1 Mpc sightline spacing can accurately recover the eigenvectors of the tidal tensor, which we use to define the directions of the cosmic web. For galaxy spins and shapes, we use a model parameterized by the alignment strength, Δ (cos θ), with respect to the tidal tensor eigenvectors from the underlying density field, and also consider observational effects such as errors in the galaxy position angle, inclination, and redshift. Measurements using the upcoming ~ 1 deg 2 CLAMATO tomographic survey and 600 coeval zCOSMOS-Deep galaxies should place 3σ limits on extreme alignment models with Δ (cos θ) ~ 0.1, but much larger surveys encompassing > 10,000 galaxies, such as Subaru PFS, will be required to constrain models with Δ (cos θ) ~ 0.3. These measurements will constrain models of galaxy-cosmic web alignment and test tidal torque theory at z ~ 2, improving our understanding of the physics of intrinsic alignments.« less

Imaging a Pyramid Interior by ERT-3D Methods, Preliminar Results at El Castillo Pyramid, Chichen Itza, Mexico

NASA Astrophysics Data System (ADS)

Chavez, R. E.; Tejero, A.; Cifuentes, G.; HernaNdez-Quintero, J. E.; Garcia-Serrano, A.

2016-12-01

The well known Pyramid El Castillo, located in the archaeological site of Chichen Itza, in the Yucatan Peninsula is the emblematic structure of this archaeological site and elected as one of the man-made world seven wonders. The archaeological team that restored this structure during the 1920's discovered a smaller pyramid inside this prehispanic body, which corresponded to an older Mayan period. The possibility of finding other constructive periods inside this edifice should be important to reconstruct the Mayan history. Previous geophysical studies carried out by us in 2014, employed novel Electrical Resistivity Tomography (ERT) arrays that surrounded the pyramids surface with flat electrodes to obtain a 3D image of the subsoil. At that time, a low resistivity body was found beneath the pyramid, which was associated to a sinkhole filled with sweet water. Employing the same technique, a series of flat electrodes were deployed on each body conforming the pyramid, a total of 10 bodies were covered, employing a different number of electrodes trying to keep the distance between each electrode constant ( 3 m). Each body was treated as a single observation cube, where the apparent resistivity data measured was later inverted. A precise topographic control for each electrode was realized and introduced in the inversion process. 45,000 observation points within the pyramid were obtained. Initially, each working cube corresponding to a given pyramid's body was inverted. A composition of each inversion was assembled to form the resistivity distribution within the pyramid using a smooth interpolation method. A high resistivity anomaly was found towards the northern portion of the model that could be associated to the main stairway of the inner pyramid. The cavity detected during the 2014 survey was observed as a low resistivity anomaly found at the pyramid's base. At the moment, we are assembling the full observed resistivity data as a single file to compute an integrated geophysical model that could be inverted. We expect to compute such final model soon.

Use of electrical resistivity to detect underground mine voids in Ohio.

DOT National Transportation Integrated Search

2002-01-01

Electrical resistivity surveys were completed at : two sites along State Route 32 in Jackson and Vinton : Counties, Ohio. The surveys were done to : determine whether the electrical resistivity method : could identify areas where coal was mined, leav...

Determination of Cenozoic sedimentary structures using integrated geophysical surveys: A case study in the Barkol Basin, Xinjiang, China

NASA Astrophysics Data System (ADS)

Sun, Kai; Chen, Chao; Du, Jinsong; Wang, Limin; Lei, Binhua

2018-01-01

Thickness estimation of sedimentary basin is a complex geological problem, especially in an orogenic environment. Intense and multiple tectonic movements and climate changes result in inhomogeneity of sedimentary layers and basement configurations, which making sedimentary structure modelling difficult. In this study, integrated geophysical methods, including gravity, magnetotelluric (MT) sounding and electrical resistivity tomography (ERT), were used to estimate basement relief to understand the geological structure and evolution of the eastern Barkol Basin in China. This basin formed with the uplift of the eastern Tianshan during the Cenozoic. Gravity anomaly map revealed the framework of the entire area, and ERT as well as MT sections reflected the geoelectric features of the Cenozoic two-layer distribution. Therefore, gravity data, constrained by MT, ERT and boreholes, were utilized to estimate the spatial distribution of the Quaternary layer. The gravity effect of the Quaternary layer related to the Tertiary layer was later subtracted to obtain the residual anomaly for inversion. For the Tertiary layer, the study area was divided into several parts because of lateral difference of density contrasts. Gravity data were interpreted to determine the density contrast constrained by the MT results. The basement relief can be verified by geological investigation, including the uplift process and regional tectonic setting. The agreement between geophysical survey and prior information from geology emphasizes the importance of integrated geophysical survey as a complementary means of geological studies in this region.

Mapping subsurface in proximity to newly-developed sinkhole along roadway.

DOT National Transportation Integrated Search

2013-02-01

MS&T acquired electrical resistivity tomography profiles in immediate proximity to a newly-developed sinkhole in Nixa Missouri : The sinkhole has closed a well-traveled municipal roadway and threatens proximal infrastructure. The intent of this inves...

Investigation of subsidence along segment of Missouri Route 65, Springfield, Missouri.

DOT National Transportation Integrated Search

2010-02-01

Electrical Resistivity Tomography (ERT) data were acquired on the ground surface across an underground limestone mine access tunnel in an effort to characterize the roof rock. This investigation was conducted because simultaneous localized failure oc...

Louisville Southern Indiana Ohio River bridges project, Kentucky east end approach tunnel.

DOT National Transportation Integrated Search

2010-07-01

Missouri S&T proposes to acquire electrical resistivity and refraction tomography at the KDOT tunnel site, Louisville, Kentucky. These geophysical data will be processed, analyzed and interpreted with the objective of mapping and characterizing soil ...

Helicopter electromagnetic and magnetic geophysical survey data, Swedeburg and Sprague study areas, eastern Nebraska, May 2009

USGS Publications Warehouse

Smith, B.D.; Abraham, J.D.; Cannia, J.C.; Minsley, B.J.; Ball, L.B.; Steele, G.V.; Deszcz-Pan, M.

2011-01-01

This report is a release of digital data from a helicopter electromagnetic and magnetic survey conducted by Fugro Airborne Surveys in areas of eastern Nebraska as part of a joint hydrologic study by the Lower Platte North and Lower Platte South Natural Resources Districts, and the U.S. Geological Survey. The survey flight lines covered 1,418.6 line km (882 line mile). The survey was flown from April 22 to May 2, 2009. The objective of the contracted survey was to improve the understanding of the relation between surface water and groundwater systems critical to developing groundwater models used in management programs for water resources. The electromagnetic equipment consisted of six different coil-pair orientations that measured resistivity at separate frequencies from about 400 hertz to about 140,000 hertz. The electromagnetic data were converted to georeferenced electrical resistivity grids and maps for each frequency that represent different approximate depths of investigation for each survey area. The electrical resistivity data were input into a numerical inversion to estimate resistivity variations with depth. In addition to the electromagnetic data, total field magnetic data and digital elevation data were collected. Data released in this report consist of flight line data, digital grids, digital databases of the inverted electrical resistivity with depth, and digital maps of the apparent resistivity and total magnetic field. The range of subsurface investigation is comparable to the depth of shallow aquifers. The survey areas, Swedeburg and Sprague, were chosen based on results from test flights in 2007 in eastern Nebraska and needs of local water managers. The geophysical and hydrologic information from U.S. Geological Survey studies are being used by resource managers to develop groundwater resource plans for the area.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorsey, Alison; Dudley, Colton; Louie, John

Linear deposits of calcium carbonate tufa columns mark recent faults that cut 11 ka Lake Lahontan sediments at Astor Pass, north of Pyramid Lake, Nevada. Throughout the Great Basin, faults appear to control the location of geothermal resources by providing pathways for fluid migration. Reservoir-depth (greater than 1 km) seismic imaging at Astor Pass reveals a fault that projects to one of the lines of tufa columns at the surface. The presence of the tufa deposits suggests this fault carried warm geothermal waters through the lakebed clay sediments in recent time. The warm fluids deposited the tufa when they hitmore » cold Lake Lahontan water at the lakebed. Lake Lahontan covered this location 11 ka to a depth of at least 60 m. In collaboration with the Pyramid Lake Paiute Tribe, an Applied Geophysics class at UNR investigated the near-surface geophysical characteristics of this fault. The survey at and near the tufa columns comprises near-surface Pwave seismic reflection and refraction, electrical resistivity tomography, nearsurface refraction microtremor arrays, nine near-surface direct-current resistivity soundings, magnetic surveys, and gravity surveys. The refraction microtremor results show shear velocities near tufa and faults to be marginally lower, compared to Vs away from the faults. Overall, the 30-m depth-averaged shear velocities are low, less than 300 m/s, consistent with the lakebed clay deposits. These results indicate that no seismically fast (> 500 m/s) tufa deposits are present below the surface at or near the tufa columns. Vs30 averages were for example 274 ± 13 m/s on the fault, 287 ± 2 m/s at 150 m east of the fault, and 290 ± 15 m/s at 150 m west of the fault. The P-velocity refraction optimization results similarly indicate a lack of high-velocity tufa buried below the surface in the Lahontan sediments, reinforcing the idea that all tufa was deposited above the lakebed surface. The seismic results provide a negative test of the hypothesis that deposition of the lakebeds in the Quaternary buried and preserved older tufa columns within the section. Near-surface Wenner arrays with a-spacings up to 30 m show a higher resistivity near the faults, and tufa, than away from the faults. Resistivity averages within a few meters of the surface were 33 ± 17 ohm-m on the fault, 13 ± 3 ohm-m east of the fault, and 9 ± 3 ohm-m west of the fault. It is possible that the geothermal waters are fresher, and more resistive, than waters held in the lakebed clays. Water samples from more than 1 km depth in exploration wells have a TDS of 2500 p.p.m., nearly drinking-water quality. The relatively resistive water, perhaps localized by greater permeability along the fault, could explain the higher resistivity measured near the fault. The results show that there is no high-velocity, high-resistivity tufa along the faults below the surface, so we are unable to use buried tufa to locate the faults that may promote geothermal upwelling in this area. We further hypothesize that as sedimentation buried the tufa during the Quaternary, warm geothermal waters re-dissolved it, and re-precipitated it in the cold lake-bottom water.« less

GPR survey, as one of the best geophysical methods for social and industrial needs

NASA Astrophysics Data System (ADS)

Chernov, Anatolii

2016-04-01

This paper is about ways and methods of applying non-invasive geophysical method - Ground penetrating radar (GPR) survey in different spheres of science, industry, social life and culture. Author would like to show that geological methods could be widely used for solving great variety of industrial, human safety and other problems. In that article, we take GPR survey as an example of such useful geophysical methods. It is a fact that investigation of near surface underground medium is important process, which influence on development of different spheres of science and social life: investigation of near surface geology (layering, spreading of rock types, identification of voids, etc.), hydrogeology (depth to water horizons, their thickness), preparation step for construction of roads and buildings (civil geology, engineering geology), investigation of cultural heritage (burial places, building remains,...), ecological investigations (land slides, variation in underground water level, etc.), glaciology. These tasks can be solved by geological methods, but as usual, geophysical survey takes a lot of time and energy (especially electric current and resistivity methods, seismic survey). Author claims that GPR survey can be performed faster than other geophysical surveys and results of GPR survey are informative enough to make proper conclusions. Some problems even cannot be solved without GPR. For example, identification of burial place (one of author's research objects): results of magnetic and electric resistivity tomography survey do not contain enough information to identify burial place, but according to anomalies on GPR survey radarograms, presence of burial place can be proven. Identification of voids and non-magnetic objects also hardly can be done by another non-invasive geophysics surveys and GPR is applicable for that purpose. GPR can be applied for monitoring of dangerous processes in geological medium under roads, buildings, parks and other places of human activity. Monitoring of such hazards as landslides, underground erosion, variation in ground water level can help prevent dangerous processes with destructive consequences, which can result in peoples' injuries and even death. Moreover, GPR can be used in other spheres of life, where investigation of hidden (under or behind conductive for electromagnetic wave material) objects is needed: rescue operations (finding of people after natural and human-made disasters under snow, under debris of building material); military purpose (security systems, identification of people presence through walls, doors, ground etc.). Author work on algorithms (first of all for VIY GPRs (http://viy.ua/)), which will help more precisely find objects of interest on radarograms and even solve inverse problem of geophysics. According to information in that article, geophysical methods can be widely used to solve great variety of tasks and help to investigate humans' past (researches of cultural heritage) and provide information to create safe and comfortable future (preventing of natural hazards and better planning of construction).

3D first-arrival traveltime tomography with modified total variation regularization

NASA Astrophysics Data System (ADS)

Jiang, Wenbin; Zhang, Jie

2018-02-01

Three-dimensional (3D) seismic surveys have become a major tool in the exploration and exploitation of hydrocarbons. 3D seismic first-arrival traveltime tomography is a robust method for near-surface velocity estimation. A common approach for stabilizing the ill-posed inverse problem is to apply Tikhonov regularization to the inversion. However, the Tikhonov regularization method recovers smooth local structures while blurring the sharp features in the model solution. We present a 3D first-arrival traveltime tomography method with modified total variation (MTV) regularization to preserve sharp velocity contrasts and improve the accuracy of velocity inversion. To solve the minimization problem of the new traveltime tomography method, we decouple the original optimization problem into two following subproblems: a standard traveltime tomography problem with the traditional Tikhonov regularization and a L2 total variation problem. We apply the conjugate gradient method and split-Bregman iterative method to solve these two subproblems, respectively. Our synthetic examples show that the new method produces higher resolution models than the conventional traveltime tomography with Tikhonov regularization. We apply the technique to field data. The stacking section shows significant improvements with static corrections from the MTV traveltime tomography.

4D ERT Monitoring of Subsurface Water Pipe Leakage During a Controlled Field Experiment

NASA Astrophysics Data System (ADS)

Inauen, C.; Chambers, J. E.; Wilkinson, P. B.; Meldrum, P.; Swift, R. T.; Uhlemann, S.; Gunn, D.; Dashwood, B.; Taxil, J.; Curioni, G.

2016-12-01

Locating and delineating leakage from subsurface pipelines is an important task for civil engineers. 4D Electrical Resistivity Tomography (ERT) allows changes in subsurface resistivity to be imaged at a high spatial and temporal resolution in a minimally invasive manner. It is therefore a promising tool to supplement conventional point-sensing techniques to monitor subsurface flow processes. To assess the efficacy of ERT for pipe leakage monitoring several controlled leak experiments were carried out at a test site in Blagdon, Bristol, UK. To simulate the leak, a plastic pipe with a hole was buried below a flat, grassed area at a depth of 0.7 m, representing a standard UK mains water pipe installation. The water table at the site lies well below the surface meaning that the experiment took entirely place in the vadose zone, where changes in resistivity are primarily sensitive to water content variations. The ERT array covered an area of 6.5m x 6.5m around the leak location. Data acquisition was carried out with the BGS PRIME (Proactive Infrastructure Monitoring and Evaluation) system, which facilitates remote scheduling and autonomous ERT data collection and transmission. To obtain the resistivity changes of the subsurface a 4D inversion was carried out using a Gauss-Newton approach with spatial and temporal smoothness constraints. We were able to reliably observe the onset, spread and cessation of the leakage. Measurements from in-situ soil sensors at several depths above and below the leak complemented the ERT data and allowed us to assess their reliability and directly relate them to hydrogeological processes. Moreover, through experimental tests with soil samples from the test area, a Waxman-Smits relation was obtained to directly convert the changes in electrical resistivity to gravimetric soil moisture content. With future experiments on the test site more work is planned towards survey optimization, automated processing and tracking of leakage plumes.

Microwave tomography enhanced GPR surveys in Centaur’s Domus, Regio VI of Pompeii, Italy

NASA Astrophysics Data System (ADS)

Catapano, I.; Crocco, L.; Di Napoli, R.; Soldovieri, F.; Brancaccio, A.; Pesando, F.; Aiello, A.

2012-08-01

The archaeological area of Pompeii (Naples, Italy) is known worldwide as one of the most remarkable examples of a Roman Empire town, but its origins are prior to the Roman age and there is a huge archeological interest in discovering the history of the forma urbis. With respect to this framework, the paper presents results from microwave tomography enhanced ground penetrating radar (GPR) surveys carried out in the Centaur’s Domus, Regio VI, one of the most ancient housing areas of Pompeii. The GPR prospections aimed at addressing and driving the archeological excavation campaign performed in this area in October 2010. The results of stratigraphic assays are used to assess the reliability of the tomographic images obtained.

Use of electrical resistivity to detect underground mine voids in Ohio : executive summary.

DOT National Transportation Integrated Search

2002-01-01

Electrical resistivity surveys were completed at two sites along State Route 32 in Jackson and Vinton Counties, Ohio. : The surveys were done to determine whether the electrical resistivity method could identify areas where coal was : mined, leaving ...

Evaluative studies in nuclear medicine research: emission computed tomography assessment. Final report, January 1-December 31, 1981

DOE Office of Scientific and Technical Information (OSTI.GOV)

Potchen, E.J.; Harris, G.I.; Gift, D.A.

The report provides information on an assessment of the potential short and long term benefits of emission computed tomography (ECT) in biomedical research and patient care. Work during the past year has been augmented by the development and use of an opinion survey instrument to reach a wider representation of knowledgeable investigators and users of this technology. This survey instrument is reproduced in an appendix. Information derived from analysis of the opinion survey, and used in conjunction with results of independent staff studies of available sources, provides the basis for the discussions given in following sections of PET applications inmore » the brain, of technical factors, and of economic implications. Projections of capital and operating costs on a per study basis were obtained from a computerized, pro forma accounting model and are compared with the survey cost estimates for both research and clinical modes of application. The results of a cash-flow model analysis of the relationship between projected economic benefit of PET research to disease management and the costs associated with such research are presented and discussed.« less

Temporal Dynamics and Spatial Variation of Azoxystrobin and Propiconazole Resistance in Zymoseptoria tritici: A Hierarchical Survey of Commercial Winter Wheat Fields in the Willamette Valley, Oregon.

PubMed

Hagerty, Christina H; Anderson, Nicole P; Mundt, Christopher C

2017-03-01

Fungicide resistance can cause disease control failure in agricultural systems, and is particularly concerning with Zymoseptoria tritici, the causal agent of Septoria tritici blotch of wheat. In North America, the first quinone outside inhibitor resistance in Z. tritici was discovered in the Willamette Valley of Oregon in 2012, which prompted this hierarchical survey of commercial winter wheat fields to monitor azoxystrobin- and propiconazole-resistant Z. tritici. Surveys were conducted in June 2014, January 2015, May 2015, and January 2016. The survey was organized in a hierarchical scheme: regions within the Willamette Valley, fields within the region, transects within the field, and samples within the transect. Overall, frequency of azoxystrobin-resistant isolates increased from 63 to 93% from June 2014 to January 2016. Resistance to azoxystrobin increased over time even within fields receiving no strobilurin applications. Propiconazole sensitivity varied over the course of the study but, overall, did not significantly change. Sensitivity to both fungicides showed no regional aggregation within the Willamette Valley. Greater than 80% of spatial variation in fungicide sensitivity was at the smallest hierarchical scale (within the transect) of the survey for both fungicides, and the resistance phenotypes were randomly distributed within sampled fields. Results suggest a need for a better understanding of the dynamics of fungicide resistance at the landscape level.

Electrical Resistivity and Ground Penetrating Radar Investigation of Presence and Extent of Hardpan Soil Layers

NASA Astrophysics Data System (ADS)

Thao, S. J.; Plattner, A.

2015-12-01

Farming in the San Joaquin Valley in central California is often impeded by a shallow rock-hard layer of consolidated soil commonly referred to as hardpan. To be able to successfully farm, this layer, if too shallow, needs to be removed either with explosives or heavy equipment. It is therefore of great value to obtain information about depth and presence of such a layer prior to agricultural operations. We tested the applicability of electrical resistivity tomography and ground penetrating radar in hardpan detection. On our test site of known hardpan depth (from trenching) and local absence (prior dynamiting to plant trees), we successfully recovered the known edge of a hardpan layer with both methods, ERT and GPR. The clay-rich soil significantly reduced the GPR penetration depth but we still managed to map the edges at a known gap where prior dynamiting had removed the hardpan. Electrical resistivity tomography with a dipole-dipole electrode configuration showed a clear conductive layer at expected depths with a clearly visible gap at the correct location. In our data analysis and representation we only used either freely available or in-house written software.

Constraints on the dark matter and dark energy interactions from weak lensing bispectrum tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

An, Rui; Feng, Chang; Wang, Bin, E-mail: an_rui@sjtu.edu.cn, E-mail: chang.feng@uci.edu, E-mail: wang_b@sjtu.edu.cn

We estimate uncertainties of cosmological parameters for phenomenological interacting dark energy models using weak lensing convergence power spectrum and bispectrum. We focus on the bispectrum tomography and examine how well the weak lensing bispectrum with tomography can constrain the interactions between dark sectors, as well as other cosmological parameters. Employing the Fisher matrix analysis, we forecast parameter uncertainties derived from weak lensing bispectra with a two-bin tomography and place upper bounds on strength of the interactions between the dark sectors. The cosmic shear will be measured from upcoming weak lensing surveys with high sensitivity, thus it enables us to usemore » the higher order correlation functions of weak lensing to constrain the interaction between dark sectors and will potentially provide more stringent results with other observations combined.« less

Optimal joule heating of the subsurface

DOEpatents

Berryman, James G.; Daily, William D.

1994-01-01

A method for simultaneously heating the subsurface and imaging the effects of the heating. This method combines the use of tomographic imaging (electrical resistance tomography or ERT) to image electrical resistivity distribution underground, with joule heating by electrical currents injected in the ground. A potential distribution is established on a series of buried electrodes resulting in energy deposition underground which is a function of the resistivity and injection current density. Measurement of the voltages and currents also permits a tomographic reconstruction of the resistivity distribution. Using this tomographic information, the current injection pattern on the driving electrodes can be adjusted to change the current density distribution and thus optimize the heating. As the heating changes conditions, the applied current pattern can be repeatedly adjusted (based on updated resistivity tomographs) to affect real time control of the heating.

Cytoplasmic GPER translocation in cancer-associated fibroblasts mediates cAMP/PKA/CREB/glycolytic axis to confer tumor cells with multidrug resistance.

PubMed

Yu, T; Yang, G; Hou, Y; Tang, X; Wu, C; Wu, X-A; Guo, L; Zhu, Q; Luo, H; Du, Y-E; Wen, S; Xu, L; Yin, J; Tu, G; Liu, M

2017-04-01

Multiple drug resistance is a challenging issue in the clinic. There is growing evidence that the G-protein-coupled estrogen receptor (GPER) is a novel mediator in the development of multidrug resistance in both estrogen receptor (ER)-positive and -negative breast cancers, and that cancer-associated fibroblasts (CAFs) in the tumor microenvironment may be a new agent that promotes drug resistance in tumor cells. However, the role of cytoplasmic GPER of CAFs on tumor therapy remains unclear. Here we first show that the breast tumor cell-activated PI3K/AKT (phosphoinositide 3-kinase/AKT) signaling pathway induces the cytoplasmic GPER translocation of CAFs in a CRM1-dependent pattern, and leads to the activation of a novel estrogen/GPER/cAMP/PKA/CREB signaling axis that triggers the aerobic glycolysis switch in CAFs. The glycolytic CAFs feed the extra pyruvate and lactate to tumor cells for augmentation of mitochondrial activity, and this energy metabolically coupled in a 'host-parasite relationship' between catabolic CAFs and anabolic cancer cells confers the tumor cells with multiple drug resistance to several conventional clinical treatments including endocrine therapy (tamoxifen), Her-2-targeted therapy (herceptin) and chemotherapy (epirubicin). Moreover, the clinical data from 18 F-fluorodeoxyglucose positron emission tomography/computed tomography further present a strong association between the GPER/cAMP/PKA/CREB pathway of stromal fibroblasts with tumor metabolic activity and clinical treatment, suggesting that targeting cytoplasmic GPER in CAFs may rescue the drug sensitivity in patients with breast cancer. Thus, our data define novel insights into the stromal GPER-mediated multiple drug resistance from the point of reprogramming of tumor energy metabolism and provide the rationale for CAFs as a promising target for clinical therapy.

Survey of computed tomography scanners in Taiwan: Dose descriptors, dose guidance levels, and effective doses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, H. Y.; Tung, C. J.; Yu, C. C.

2007-04-15

The IAEA and the ICRP recommended dose guidance levels for the most frequent computed tomography (CT) examinations to promote strategies for the optimization of radiation dose to CT patients. A national survey, including on-site measurements and questionnaires, was conducted in Taiwan in order to establish dose guidance levels and evaluate effective doses for CT. The beam quality and output and the phantom doses were measured for nine representative CT scanners. Questionnaire forms were completed by respondents from facilities of 146 CT scanners out of 285 total scanners. Information on patient, procedure, scanner, and technique for the head and body examinationsmore » was provided. The weighted computed tomography dose index (CTDI{sub w}), the dose length product (DLP), organ doses and effective dose were calculated using measured data, questionnaire information and Monte Carlo simulation results. A cost-effective analysis was applied to derive the dose guidance levels on CTDI{sub w} and DLP for several CT examinations. The mean effective dose{+-}standard deviation distributes from 1.6{+-}0.9 mSv for the routine head examination to 13{+-}11 mSv for the examination of liver, spleen, and pancreas. The surveyed results and the dose guidance levels were provided to the national authorities to develop quality control standards and protocols for CT examinations.« less

Direct-current resistivity profiling at the Pecos River Ecosystem Project study site near Mentone, Texas, 2006

USGS Publications Warehouse

Teeple, Andrew; McDonald, Alyson K.; Payne, Jason; Kress, Wade H.

2009-01-01

The U.S. Geological Survey, in cooperation with Texas A&M University AgriLife, did a surface geophysical investigation at the Pecos River Ecosystem Project study site near Mentone in West Texas intended to determine shallow (to about 14 meters below the water [river] surface) subsurface composition (lithology) in and near treated (eradicated of all saltcedar) and control (untreated) riparian zone sites during June-August 2006. Land-based direct-current resistivity profiling was applied in a 240-meter section of the riverbank at the control site, and waterborne direct-current continuous resistivity profiling (CRP) was applied along a 2.279-kilometer reach of the river adjacent to both sites to collect shallow subsurface resistivity data. Inverse modeling was used to obtain a nonunique estimate of the true subsurface resistivity from apparent resistivity calculated from the field measurements. The land-based survey showed that the sub-surface at the control site generally is of relatively low resis-tivity down to about 4 meters below the water surface. Most of the section from about 4 to 10 meters below the water surface is of relatively high resistivity. The waterborne CRP surveys convey essentially the same electrical representation of the lithology at the control site to 10 meters below the water surface; but the CRP surveys show considerably lower resistivity than the land-based survey in the subsection from about 4 to 10 meters below the water surface. The CRP surveys along the 2.279-kilometer reach of the river adjacent to both the treated and control sites show the same relatively low resistivity zone from the riverbed to about 4 meters below the water surface evident at the control site. A slightly higher resistivity zone is observed from about 4 to 14 meters below the water surface along the upstream approximately one-half of the profile than along the downstream one-half. The variations in resistivity could not be matched to variations in lithology because sufficient rock samples were not available.

An Integrated Hydrogeologic and Geophysical Investigation to Characterize the Hydrostratigraphy of the Edwards Aquifer in an Area of Northeastern Bexar County, Texas

USGS Publications Warehouse

Shah, Sachin D.; Smith, Bruce D.; Clark, Allan K.; Payne, Jason

2008-01-01

In August 2007, the U.S. Geological Survey, in cooperation with the San Antonio Water System, did a hydrogeologic and geophysical investigation to characterize the hydrostratigraphy (hydrostratigraphic zones) and also the hydrogeologic features (karst features such as sinkholes and caves) of the Edwards aquifer in a 16-square-kilometer area of northeastern Bexar County, Texas, undergoing urban development. Existing hydrostratigraphic information, enhanced by local-scale geologic mapping in the area, and surface geophysics were used to associate ranges of electrical resistivities obtained from capacitively coupled (CC) resistivity surveys, frequency-domain electromagnetic (FDEM) surveys, time-domain electromagnetic (TDEM) soundings, and two-dimensional direct-current (2D-DC) resistivity surveys with each of seven hydrostratigraphic zones (equivalent to members of the Kainer and Person Formations) of the Edwards aquifer. The principal finding of this investigation is the relation between electrical resistivity and the contacts between the hydrostratigraphic zones of the Edwards aquifer and the underlying Trinity aquifer in the area. In general, the TDEM data indicate a two-layer model in which an electrical conductor underlies an electrical resistor, which is consistent with the Trinity aquifer (conductor) underlying the Edwards aquifer (resistor). TDEM data also show the plane of Bat Cave fault, a well-known fault in the area, to be associated with a local, nearly vertical zone of low resistivity that provides evidence, although not definitive, for Bat Cave fault functioning as a flow barrier, at least locally. In general, the CC resistivity, FDEM survey, and 2D-DC resistivity survey data show a sharp electrical contrast from north to south, changing from high resistivity to low resistivity across Bat Cave fault as well as possible karst features in the study area. Interpreted karst features that show relatively low resistivity within a relatively high-resistivity area likely are attributable to clay or soil filling a sinkhole. In general, faults are inferred where lithologic incongruity indicates possible displacement. Along most inferred faults, displacement was not sufficient to place different members of the Kainer or Person Formations (hydrostratigraphic zones) adjacent across the inferred fault plane. In general, the Kainer Formation (hydrostratigraphic zones V through VIII) has a higher resistivity than the Person Formation (hydrostratigraphic zones II through IV). Although resistivity variations from the CC resistivity, FDEM, and 2D-DC resistivity surveys, with mapping information, were sufficient to allow surface mapping of the lateral extent of hydrostratigraphic zones in places, resistivity variations from TDEM data were not sufficient to allow vertical delineation of hydrostratigraphic zones; however, the Edwards aquifer-Trinity aquifer contact could be identified from the TDEM data.

Precision Medicine and PET/Computed Tomography: Challenges and Implementation.

PubMed

Subramaniam, Rathan M

2017-01-01

Precision Medicine is about selecting the right therapy for the right patient, at the right time, specific to the molecular targets expressed by disease or tumors, in the context of patient's environment and lifestyle. Some of the challenges for delivery of precision medicine in oncology include biomarkers for patient selection for enrichment-precision diagnostics, mapping out tumor heterogeneity that contributes to therapy failures, and early therapy assessment to identify resistance to therapies. PET/computed tomography offers solutions in these important areas of challenges and facilitates implementation of precision medicine. Copyright © 2016 Elsevier Inc. All rights reserved.

Effects of spatially variable resolution on field-scale estimates of tracer concentration from electrical inversions using Archie's law

USGS Publications Warehouse

Singha, Kamini; Gorelick, Steven M.

2006-01-01

Two important mechanisms affect our ability to estimate solute concentrations quantitatively from the inversion of field-scale electrical resistivity tomography (ERT) data: (1) the spatially variable physical processes that govern the flow of current as well as the variation of physical properties in space and (2) the overparameterization of inverse models, which requires the imposition of a smoothing constraint (regularization) to facilitate convergence of the inverse solution. Based on analyses of field and synthetic data, we find that the ability of ERT to recover the 3D shape and magnitudes of a migrating conductive target is spatially variable. Additionally, the application of Archie's law to tomograms from field ERT data produced solute concentrations that are consistently less than 10% of point measurements collected in the field and estimated from transport modeling. Estimates of concentration from ERT using Archie's law only fit measured solute concentrations if the apparent formation factor is varied with space and time and allowed to take on unreasonably high values. Our analysis suggests that the inability to find a single petrophysical relation in space and time between concentration and electrical resistivity is largely an effect of two properties of ERT surveys: (1) decreased sensitivity of ERT to detect the target plume with increasing distance from the electrodes and (2) the smoothing imprint of regularization used in inversion.

A high time and spatial resolution MRPC designed for muon tomography

NASA Astrophysics Data System (ADS)

Shi, L.; Wang, Y.; Huang, X.; Wang, X.; Zhu, W.; Li, Y.; Cheng, J.

2014-12-01

A prototype of cosmic muon scattering tomography system has been set up in Tsinghua University in Beijing. Multi-gap Resistive Plate Chamber (MRPC) is used in the system to get the muon tracks. Compared with other detectors, MRPC can not only provide the track but also the Time of Flight (ToF) between two detectors which can estimate the energy of particles. To get a more accurate track and higher efficiency of the tomography system, a new type of high time and two-dimensional spatial resolution MRPC has been developed. A series of experiments have been done to measure the efficiency, time resolution and spatial resolution. The results show that the efficiency can reach 95% and its time resolution is around 65 ps. The cluster size is around 4 and the spatial resolution can reach 200 μ m.

Using electrical impedance tomography to map subsurface hydraulic conductivity

DOEpatents

Berryman, James G.; Daily, William D.; Ramirez, Abelardo L.; Roberts, Jeffery J.

2000-01-01

The use of Electrical Impedance Tomography (EIT) to map subsurface hydraulic conductivity. EIT can be used to map hydraulic conductivity in the subsurface where measurements of both amplitude and phase are made. Hydraulic conductivity depends on at least two parameters: porosity and a length scale parameter. Electrical Resistance Tomography (ERT) measures and maps electrical conductivity (which can be related to porosity) in three dimensions. By introducing phase measurements along with amplitude, the desired additional measurement of a pertinent length scale can be achieved. Hydraulic conductivity controls the ability to flush unwanted fluid contaminants from the surface. Thus inexpensive maps of hydraulic conductivity would improve planning strategies for subsequent remediation efforts. Fluid permeability is also of importance for oil field exploitation and thus detailed knowledge of fluid permeability distribution in three-dimension (3-D) would be a great boon to petroleum reservoir analysts.

Non-cross talk multi-channel photomultiplier using guided electron multipliers

DOEpatents

Gomez, J.; Majewski, S.; Weisenberger, A.G.

1995-09-26

An improved multi-channel electron multiplier is provided that exhibits zero cross-talk and high rate operation. Resistive material input and output masks are employed to control divergence of electrons. Electron multiplication takes place in closed channels. Several embodiments are provided for these channels including a continuous resistive emissive multiplier and a discrete resistive multiplier with discrete dynode chains interspaced with resistive layers-masks. Both basic embodiments provide high gain multiplication of electrons without accumulating surface charges while containing electrons to their proper channels to eliminate cross-talk. The invention can be for example applied to improve the performance of ion mass spectrometers, positron emission tomography devices, in DNA sequencing and other beta radiography applications and in many applications in particle physics. 28 figs.

Non cross talk multi-channel photomultiplier using guided electron multipliers

DOEpatents

Gomez, Javier; Majewski, Stanislaw; Weisenberger, Andrew G.

1995-01-01

An improved multi-channel electron multiplier is provided that exhibits zero cross-talk and high rate operation. Resistive material input and output masks are employed to control divergence of electrons. Electron multiplication takes place in closed channels. Several embodiments are provided for these channels including a continuous resistive emissive multiplier and a discrete resistive multiplier with discrete dynode chains interspaced with resistive layers-masks. Both basic embodiments provide high gain multiplication of electrons without accumulating surface charges while containing electrons to their proper channels to eliminate cross-talk. The invention can be for example applied to improve the performance of ion mass spectrometers, positron emission tomography devices, in DNA sequencing and other beta radiography applications and in many applications in particle physics.

Simulation of variation of apparent resistivity in resistivity surveys using finite difference modelling with Monte Carlo analysis

NASA Astrophysics Data System (ADS)

Aguirre, E. E.; Karchewski, B.

2017-12-01

DC resistivity surveying is a geophysical method that quantifies the electrical properties of the subsurface of the earth by applying a source current between two electrodes and measuring potential differences between electrodes at known distances from the source. Analytical solutions for a homogeneous half-space and simple subsurface models are well known, as the former is used to define the concept of apparent resistivity. However, in situ properties are heterogeneous meaning that simple analytical models are only an approximation, and ignoring such heterogeneity can lead to misinterpretation of survey results costing time and money. The present study examines the extent to which random variations in electrical properties (i.e. electrical conductivity) affect potential difference readings and therefore apparent resistivities, relative to an assumed homogeneous subsurface model. We simulate the DC resistivity survey using a Finite Difference (FD) approximation of an appropriate simplification of Maxwell's equations implemented in Matlab. Electrical resistivity values at each node in the simulation were defined as random variables with a given mean and variance, and are assumed to follow a log-normal distribution. The Monte Carlo analysis for a given variance of electrical resistivity was performed until the mean and variance in potential difference measured at the surface converged. Finally, we used the simulation results to examine the relationship between variance in resistivity and variation in surface potential difference (or apparent resistivity) relative to a homogeneous half-space model. For relatively low values of standard deviation in the material properties (<10% of mean), we observed a linear correlation between variance of resistivity and variance in apparent resistivity.

Audio-magnetotelluric methods in reconnaissance geothermal exploration

USGS Publications Warehouse

Hoover, D.B.; Long, C.L.

1976-01-01

and 18 600 Hz where artificial VLF sources are available. As a reconnaissance technique we use AMT surveys in conjunction with regional gravity, magnetic, and telluric surveys. The exploration depth is a function of the resistivities of the lithologic section, but typically ranges from the surface to 0.2 km in low-resistivity areas and to greater than 2 km in high-resistivity regions. Results of the initial reconnaissance AMT surveys provide a rational basis for deciding on the extent of costlier follow-up surveys. As part of the U.S. Geological Survey geothermal program, surveys were conducted in Long Valley and Surprise Valley, California; the Vale, Ore-Weiser, Idaho region; and Bruneau-Grand View, Raft River, and Island Park regions of Idaho. AMT surveys in five additional known geothermal resource areas (KGRA's) have been scheduled for completion by May 1975. In the Raft River and Bruneau-Grand View regions and Long Valley, follow-up electrical surveys substantiated the effectiveness of the AMT technique for reconnaissance surveying.

Non-invasive imaging and assessment of active karst features in proximity to paved roadways.

DOT National Transportation Integrated Search

2014-02-01

In an effort to better understand and define the lateral and vertical extent of active karst features in immediate proximity to paved : MoDOT roadways in Springfield Missouri, MS&T will acquire electrical resistivity tomography (ERT) data. The intent...

External cervical resorption: an analysis using cone beam and microfocus computed tomography and scanning electron microscopy.

PubMed

Gunst, V; Mavridou, A; Huybrechts, B; Van Gorp, G; Bergmans, L; Lambrechts, P

2013-09-01

To provide a three-dimensional representation of external cervical resorption (ECR) with microscopy, stereo microscopy, cone beam computed tomography (CT), microfocus CT and scanning electron microscopy (SEM). External cervical resorption is an aggressive form of root resorption, leading to a loss of dental hard tissues. This is due to clastic action, activated by a damage of the covering cementum and stimulated probably by infection. Clinically, it is a challenging situation as it is characterized by a late symptomatology. This is due to the pericanalar protection from a resorption-resistant sheet, composed of pre-dentine and surrounding dentine. The clastic activity is often associated with an attempt to repair, seen by the formation of osteoid tissue. Cone beam CT is extremely useful in the diagnoses and treatment planning of ECR. SEM analyses provide a better insight into the activity of osteoclasts. The root canal is surrounded by a layer of dentine that is resistant to resorption. © 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd.

A 3D joint interpretation of magnetotelluric and seismic tomographic models: The case of the volcanic island of Tenerife

NASA Astrophysics Data System (ADS)

García-Yeguas, Araceli; Ledo, Juanjo; Piña-Varas, Perla; Prudencio, Janire; Queralt, Pilar; Marcuello, Alex; Ibañez, Jesús M.; Benjumea, Beatriz; Sánchez-Alzola, Alberto; Pérez, Nemesio

2017-12-01

In this work we have done a 3D joint interpretation of magnetotelluric and seismic tomography models. Previously we have described different techniques to infer the inner structure of the Earth. We have focused on volcanic regions, specifically on Tenerife Island volcano (Canary Islands, Spain). In this area, magnetotelluric and seismic tomography studies have been done separately. The novelty of the present work is the combination of both techniques in Tenerife Island. For this aim we have applied Fuzzy Clusters Method at different depths obtaining several clusters or classes. From the results, a geothermal system has been inferred below Teide volcano, in the center of Tenerife Island. An edifice hydrothermally altered and full of fluids is situated below Teide, ending at 600 m below sea level. From this depth the resistivity and VP values increase downwards. We also observe a clay cap structure, a typical feature in geothermal systems related with low resistivity and low VP values.

Using electrokinetic phenomena and electrical resistance tomography to characterize the movement of subsurface fluids

DOEpatents

Ramirez, Abelardo L.; Cooper, John F.; Daily, William D.

1996-01-01

This invention relates generally to the remote detections of subsurface liquid contaminants using in combination a geophysical technique known as ERT and an EKS. Electrokinetic transport is used to enhance the ability of electrical resistance tomography (ERT) to detect position and movement of subsurface contaminant liquids, particles or ions. ERT images alone are difficult to interpret because of natural inhomogeneities in soil composition and electrical properties. By subtracting two or more ERT images obtained before and after field induced movement, a high contrast image of a plume of distinct electrokinetic properties can be seen. The invention is applicable to important subsurface characterization problems including, as examples, (1) detection of liquid-saturated plumes of contaminants such as those associated with leaks from underground storage tanks containing hazardous concentrated electrolytes, (2) detection and characterization of soils contaminated with organic pollutants such as droplets of gasoline; and (3) monitoring the progress of electrokinetic containment or clean up of underground contamination.

Using electrokinetic phenomena and electrical resistance tomography to characterize the movement of subsurface fluids

DOEpatents

Ramirez, A.L.; Cooper, J.F.; Daily, W.D.

1996-02-27

This invention relates generally to the remote detections of subsurface liquid contaminants using in combination a geophysical technique known as ERT and an EKS. Electrokinetic transport is used to enhance the ability of electrical resistance tomography (ERT) to detect position and movement of subsurface contaminant liquids, particles or ions. ERT images alone are difficult to interpret because of natural inhomogeneities in soil composition and electrical properties. By subtracting two or more ERT images obtained before and after field induced movement, a high contrast image of a plume of distinct electrokinetic properties can be seen. The invention is applicable to important subsurface characterization problems including, as examples, (1) detection of liquid-saturated plumes of contaminants such as those associated with leaks from underground storage tanks containing hazardous concentrated electrolytes, (2) detection and characterization of soils contaminated with organic pollutants such as droplets of gasoline; and (3) monitoring the progress of electrokinetic containment or clean up of underground contamination. 1 fig.

Community Resistance to Survey Research and 1890 Colleges and Universities: The Case of Fort Valley State College.

ERIC Educational Resources Information Center

Walker, Melvin E., Jr.; Holik, John S.

In order to reduce community resistance to a multi-ethnic/cross-sectional survey by an 1890 institution and to identify those factors which influenced survey completion, 395 white and 335 black heads of households in 19 middle Georgia county areas were surveyed. Since a suit labeling Fort Valley a "diploma mill" had recently been filed…

Optimal joule heating of the subsurface

DOEpatents

Berryman, J.G.; Daily, W.D.

1994-07-05

A method for simultaneously heating the subsurface and imaging the effects of the heating is disclosed. This method combines the use of tomographic imaging (electrical resistance tomography or ERT) to image electrical resistivity distribution underground, with joule heating by electrical currents injected in the ground. A potential distribution is established on a series of buried electrodes resulting in energy deposition underground which is a function of the resistivity and injection current density. Measurement of the voltages and currents also permits a tomographic reconstruction of the resistivity distribution. Using this tomographic information, the current injection pattern on the driving electrodes can be adjusted to change the current density distribution and thus optimize the heating. As the heating changes conditions, the applied current pattern can be repeatedly adjusted (based on updated resistivity tomographs) to affect real time control of the heating.

Optical Coherence Tomography Angiography

PubMed Central

Gao, Simon S.; Jia, Yali; Zhang, Miao; Su, Johnny P.; Liu, Gangjun; Hwang, Thomas S.; Bailey, Steven T.; Huang, David

2016-01-01

Optical coherence tomography angiography (OCTA) is a noninvasive approach that can visualize blood vessels down to the capillary level. With the advent of high-speed OCT and efficient algorithms, practical OCTA of ocular circulation is now available to ophthalmologists. Clinical investigations that used OCTA have increased exponentially in the past few years. This review will cover the history of OCTA and survey its most important clinical applications. The salient problems in the interpretation and analysis of OCTA are described, and recent advances are highlighted. PMID:27409483

In vivo imaging of twist drill drainage for subdural hematoma: a clinical feasibility study on electrical impedance tomography for measuring intracranial bleeding in humans.

PubMed

Dai, Meng; Li, Bing; Hu, Shijie; Xu, Canhua; Yang, Bin; Li, Jianbo; Fu, Feng; Fei, Zhou; Dong, Xiuzhen

2013-01-01

Intracranial bleeding is one of the most severe medical emergencies in neurosurgery. Early detection or diagnosis would largely reduce the rate of disability and mortality, and improve the prognosis of the patients. Electrical Impedance Tomography (EIT) can non-invasively image the internal resistivity distribution within a human body using a ring of external electrodes, and is thus a promising technique to promptly detect the occurrence of intracranial bleedings because blood differs from other brain tissues in resistivity. However, so far there is no experimental study that has determined whether the intracranial resistivity changes in humans could be repeatedly detected and imaged by EIT. Hence, we for the first time attempt to clinically validate this by in vivo imaging the influx and efflux of irrigating fluid (5% dextrose in water, D5W) during the twist-drill drainage operation for the patients with subdural hematoma (SDH). In this study, six patients (four male, two female) with subacute or chronic SDH received the surgical operation in order to evacuate the hematoma around subdural region, and EIT measurements were performed simultaneously on each patient's head. The results showed that the resistivity significantly increased on the corresponding position of EIT images during the influx of D5W and gradually decreased back to baseline during the efflux. In the quantitative analysis, the average resistivity values demonstrated the similar results and had highly linear correlation (R(2) = 0.93 ± 0.06) with the injected D5W volumes, as well as the area of the resistivity gain(R(2) = 0.94 ± 0.05). In conclusion, it was clinically validated that intracranial resistivity changes in humans were detectable and quantifiable by the EIT method. After further technical improvements, EIT has the great potential of being a routine neuroimaging tool for early detection of intracranial bleedings.

In Vivo Imaging of Twist Drill Drainage for Subdural Hematoma: A Clinical Feasibility Study on Electrical Impedance Tomography for Measuring Intracranial Bleeding in Humans

PubMed Central

Xu, Canhua; Yang, Bin; Li, Jianbo; Fu, Feng; Fei, Zhou; Dong, Xiuzhen

2013-01-01

Intracranial bleeding is one of the most severe medical emergencies in neurosurgery. Early detection or diagnosis would largely reduce the rate of disability and mortality, and improve the prognosis of the patients. Electrical Impedance Tomography (EIT) can non-invasively image the internal resistivity distribution within a human body using a ring of external electrodes, and is thus a promising technique to promptly detect the occurrence of intracranial bleedings because blood differs from other brain tissues in resistivity. However, so far there is no experimental study that has determined whether the intracranial resistivity changes in humans could be repeatedly detected and imaged by EIT. Hence, we for the first time attempt to clinically validate this by in vivo imaging the influx and efflux of irrigating fluid (5% dextrose in water, D5W) during the twist-drill drainage operation for the patients with subdural hematoma (SDH). In this study, six patients (four male, two female) with subacute or chronic SDH received the surgical operation in order to evacuate the hematoma around subdural region, and EIT measurements were performed simultaneously on each patient’s head. The results showed that the resistivity significantly increased on the corresponding position of EIT images during the influx of D5W and gradually decreased back to baseline during the efflux. In the quantitative analysis, the average resistivity values demonstrated the similar results and had highly linear correlation (R2 = 0.93±0.06) with the injected D5W volumes, as well as the area of the resistivity gain(R2 = 0.94±0.05). In conclusion, it was clinically validated that intracranial resistivity changes in humans were detectable and quantifiable by the EIT method. After further technical improvements, EIT has the great potential of being a routine neuroimaging tool for early detection of intracranial bleedings. PMID:23372808

On the value of electrical resistivity tomography for monitoring leachate injection in solid state anaerobic digestion plants at farm scale.

PubMed

Degueurce, Axelle; Clément, Rémi; Moreau, Sylvain; Peu, Pascal

2016-10-01

Agricultural waste is a valuable resource for solid state anaerobic digestion (SSAD) thanks to its high solid content (>15%). Batch mode SSAD with leachate recirculation is particularly appropriate for such substrates. However, for successful degradation, the leachate must be evenly distributed through the substrate to improve its moisture content. To study the distribution of leachate in agricultural waste, electrical resistivity tomography (ERT) was performed. First, laboratory-scale experiments were conducted to check the reliability of this method to monitor infiltration of the leachate throughout the solid. Two representative mixtures of agricultural wastes were prepared: a "winter" mixture, with cattle manure, and a "summer" mixture, with cattle manure, wheat straw and hay. The influence of density and water content on electrical resistivity variations was assessed in the two mixtures. An increase in density was found to lead to a decrease in electrical resistivity: at the initial water content, resistivity decreased from 109.7 to 19.5Ω·m in the summer mixture and from 9.8 to 2.7Ω·m in the "winter" mixture with a respective increased in density of 0.134-0.269, and 0.311-0.577. Similarly, resistivity decreased with an increase in water content: for low densities, resistivity dropped from 109.7 to 7.1Ω·m and 9.8 to 4.0Ω·m with an increase in water content from 64 to 90w% and 74 to 93w% for "summer" and "winter" mixtures respectively. Second, a time-lapse ERT was performed in a farm-scale SSAD plant to monitor leachate infiltration. Results revealed very heterogeneous distribution of the leachate in the waste, with two particularly moist areas around the leachate injection holes. However, ERT was successfully applied in the SSAD plant, and produced a reliable 3D map of leachate infiltration. Copyright © 2016 Elsevier Ltd. All rights reserved.

KiDS-450 + 2dFLenS: Cosmological parameter constraints from weak gravitational lensing tomography and overlapping redshift-space galaxy clustering

NASA Astrophysics Data System (ADS)

Joudaki, Shahab; Blake, Chris; Johnson, Andrew; Amon, Alexandra; Asgari, Marika; Choi, Ami; Erben, Thomas; Glazebrook, Karl; Harnois-Déraps, Joachim; Heymans, Catherine; Hildebrandt, Hendrik; Hoekstra, Henk; Klaes, Dominik; Kuijken, Konrad; Lidman, Chris; Mead, Alexander; Miller, Lance; Parkinson, David; Poole, Gregory B.; Schneider, Peter; Viola, Massimo; Wolf, Christian

2018-03-01

We perform a combined analysis of cosmic shear tomography, galaxy-galaxy lensing tomography, and redshift-space multipole power spectra (monopole and quadrupole) using 450 deg2 of imaging data by the Kilo Degree Survey (KiDS-450) overlapping with two spectroscopic surveys: the 2-degree Field Lensing Survey (2dFLenS) and the Baryon Oscillation Spectroscopic Survey (BOSS). We restrict the galaxy-galaxy lensing and multipole power spectrum measurements to the overlapping regions with KiDS, and self-consistently compute the full covariance between the different observables using a large suite of N-body simulations. We methodically analyse different combinations of the observables, finding that the galaxy-galaxy lensing measurements are particularly useful in improving the constraint on the intrinsic alignment amplitude, while the multipole power spectra are useful in tightening the constraints along the lensing degeneracy direction. The fully combined constraint on S_8 ≡ σ _8 √{Ω _m/0.3}=0.742± 0.035, which is an improvement by 20 per cent compared to KiDS alone, corresponds to a 2.6σ discordance with Planck, and is not significantly affected by fitting to a more conservative set of scales. Given the tightening of the parameter space, we are unable to resolve the discordance with an extended cosmology that is simultaneously favoured in a model selection sense, including the sum of neutrino masses, curvature, evolving dark energy and modified gravity. The complementarity of our observables allows for constraints on modified gravity degrees of freedom that are not simultaneously bounded with either probe alone, and up to a factor of three improvement in the S8 constraint in the extended cosmology compared to KiDS alone.

Reconstruction of the water table from self-potential data: a bayesian approach.

PubMed

Jardani, A; Revil, A; Barrash, W; Crespy, A; Rizzo, E; Straface, S; Cardiff, M; Malama, B; Miller, C; Johnson, T

2009-01-01

Ground water flow associated with pumping and injection tests generates self-potential signals that can be measured at the ground surface and used to estimate the pattern of ground water flow at depth. We propose an inversion of the self-potential signals that accounts for the heterogeneous nature of the aquifer and a relationship between the electrical resistivity and the streaming current coupling coefficient. We recast the inversion of the self-potential data into a Bayesian framework. Synthetic tests are performed showing the advantage in using self-potential signals in addition to in situ measurements of the potentiometric levels to reconstruct the shape of the water table. This methodology is applied to a new data set from a series of coordinated hydraulic tomography, self-potential, and electrical resistivity tomography experiments performed at the Boise Hydrogeophysical Research Site, Idaho. In particular, we examine one of the dipole hydraulic tests and its reciprocal to show the sensitivity of the self-potential signals to variations of the potentiometric levels under steady-state conditions. However, because of the high pumping rate, the response was also influenced by the Reynolds number, especially near the pumping well for a given test. Ground water flow in the inertial laminar flow regime is responsible for nonlinearity that is not yet accounted for in self-potential tomography. Numerical modeling addresses the sensitivity of the self-potential response to this problem.

Hillslope characterization in terms of geophysical units based on the joint interpretation of electrical resistivity and seismic velocity data

NASA Astrophysics Data System (ADS)

Feskova, Tatiana; Dietrich, Peter

2015-04-01

Hydrological conditions in a catchment depend on many factors such as climatic, geological, geomorphological, biological and human, which interact with each other and influence water balance in a catchment. This interaction leads to the subordination in the landscape structure, namely the weak elements subordinate to the powerful elements. Thereby, geological and geomorphological factors play an essential role in catchment development and organization. A hillslope consequently can be allocated to one class of the representative units because the important flow processes run at the hillslope. Moreover, a hillslope can be subdivided into stratigraphic subsurface units and significant hillslope areas based on the lithological change of contrasting interfaces. The knowledge of subsurface structures is necessary to understand and predicate complex hydrological processes in a catchment. Geophysical techniques provide a good opportunity to explore the subsurface. A complete geophysical investigation of subsurface in a catchment with difficult environmental conditions never will be achieved because of large time effort in the field, equipment logistic, and ambiguity in the data interpretation. The case study demonstrates how a catchment can be investigated using geophysical methods in an effective manner in terms of characterization of representative units with respect to a functional role in the catchment. This case study aims to develop combined resistivity and seismic velocity hillslope subsurface models for the distinction of representative functional units. In order to identify the contrasting interfaces of the hillslope, to localize significant hillslope areas, and to address the ambiguity in the geophysical data interpretation, the case study combined resistivity surveys (vertical electrical soundings and electrical resistivity tomography) with refraction seismic method, and conducted these measurements at one single profile along the hillslope transect and perpendicular to this transect. The measurements along the hillslope transect deliver the two-dimensional hillslope section of resistivity and seismic velocity distribution with contrasting stratigraphic interfaces, whereas the measurements perpendicular to the hillslope transect obtained from vertical electrical soundings survey localize significant hillslope areas indicating existence of two-dimensional features in the subsurface. To demonstrate the suitability of the suggested approach, resistivity and refraction seismic measurements were carried out at the forested gently inclined hillslope in the Weierbach catchment, which belongs to the hydrological observatory Attert Basin locating in the mid-western part of the Grand-Duchy of Luxembourg. This hillslope is characterized by Pleistocene periglacial slope deposits, which plays an important role in the ecosystem functioning. The obtained resistivity and seismic hillslope models of the Weierbech catchment complement well one another. The hillslope models identify three significant hillslope areas along the hillslope called as elementary functional units, and four electrical vertical stratigraphic units and two seismic vertical stratigraphic units that agree with lithological stratigraphy of this study site. In conclusions, the suggested geophysical approach is suitable to characterise a hillslope as the representative unit only at a single transect in the efficient manner in contrast to the expensive 3D-measurements.

Imaging pathways in fractured rock using three-dimensional electrical resistivity tomography

USGS Publications Warehouse

Robinson, Judith; Slater, Lee; Johnson, Timothy B.; Shapiro, Allen M.; Tiedeman, Claire; Ntlargiannis, Dimitrios; Johnson, Carole D.; Day-Lewis, Frederick D.; Lacombe, Pierre; Imbrigiotta, Thomas; Lane, John W.

2016-01-01

Major challenges exist in delineating bedrock fracture zones because these cause abrupt changes in geological and hydrogeological properties over small distances. Borehole observations cannot sufficiently capture heterogeneity in these systems. Geophysical techniques offer the potential to image properties and processes in between boreholes. We used three-dimensional cross borehole electrical resistivity tomography (ERT) in a 9 m (diameter) × 15 m well field to capture high-resolution flow and transport processes in a fractured mudstone contaminated by chlorinated solvents, primarily trichloroethylene. Conductive (sodium bromide) and resistive (deionized water) injections were monitored in seven boreholes. Electrode arrays with isolation packers and fluid sampling ports were designed to enable acquisition of ERT measurements during pulsed tracer injections. Fracture zone locations and hydraulic pathways inferred from hydraulic head drawdown data were compared with electrical conductivity distributions from ERT measurements. Static ERT imaging has limited resolution to decipher individual fractures; however, these images showed alternating conductive and resistive zones, consistent with alternating laminated and massive mudstone units at the site. Tracer evolution and migration was clearly revealed in time-lapse ERT images and supported by in situ borehole vertical apparent conductivity profiles collected during the pulsed tracer test. While water samples provided important local information at the extraction borehole, ERT delineated tracer migration over spatial scales capturing the primary hydrogeological heterogeneity controlling flow and transport. The fate of these tracer injections at this scale could not have been quantified using borehole logging and/or borehole sampling methods alone.

Three-dimensional forward solver and its performance analysis for magnetic resonance electrical impedance tomography (MREIT) using recessed electrodes.

PubMed

Lee, Byung Il; Oh, Suk Hoon; Woo, Eung Je; Lee, Soo Yeol; Cho, Min Hyoung; Kwon, Ohin; Seo, Jin Keun; Lee, June-Yub; Baek, Woon Sik

2003-07-07

In magnetic resonance electrical impedance tomography (MREIT), we try to reconstruct a cross-sectional resistivity (or conductivity) image of a subject. When we inject a current through surface electrodes, it generates a magnetic field. Using a magnetic resonance imaging (MRI) scanner, we can obtain the induced magnetic flux density from MR phase images of the subject. We use recessed electrodes to avoid undesirable artefacts near electrodes in measuring magnetic flux densities. An MREIT image reconstruction algorithm produces cross-sectional resistivity images utilizing the measured internal magnetic flux density in addition to boundary voltage data. In order to develop such an image reconstruction algorithm, we need a three-dimensional forward solver. Given injection currents as boundary conditions, the forward solver described in this paper computes voltage and current density distributions using the finite element method (FEM). Then, it calculates the magnetic flux density within the subject using the Biot-Savart law and FEM. The performance of the forward solver is analysed and found to be enough for use in MREIT for resistivity image reconstructions and also experimental designs and validations. The forward solver may find other applications where one needs to compute voltage, current density and magnetic flux density distributions all within a volume conductor.

Integrated geophysical investigations in a fault zone located on southwestern part of İzmir city, Western Anatolia, Turkey

NASA Astrophysics Data System (ADS)

Drahor, Mahmut G.; Berge, Meriç A.

2017-01-01

Integrated geophysical investigations consisting of joint application of various geophysical techniques have become a major tool of active tectonic investigations. The choice of integrated techniques depends on geological features, tectonic and fault characteristics of the study area, required resolution and penetration depth of used techniques and also financial supports. Therefore, fault geometry and offsets, sediment thickness and properties, features of folded strata and tectonic characteristics of near-surface sections of the subsurface could be thoroughly determined using integrated geophysical approaches. Although Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT) methods are commonly used in active tectonic investigations, other geophysical techniques will also contribute in obtaining of different properties in the complex geological environments of tectonically active sites. In this study, six different geophysical methods used to define faulting locations and characterizations around the study area. These are GPR, ERT, SRT, Very Low Frequency electromagnetic (VLF), magnetics and self-potential (SP). Overall integrated geophysical approaches used in this study gave us commonly important results about the near surface geological properties and faulting characteristics in the investigation area. After integrated interpretations of geophysical surveys, we determined an optimal trench location for paleoseismological studies. The main geological properties associated with faulting process obtained after trenching studies. In addition, geophysical results pointed out some indications concerning the active faulting mechanism in the area investigated. Consequently, the trenching studies indicate that the integrated approach of geophysical techniques applied on the fault problem reveals very useful and interpretative results in description of various properties of faulting zone in the investigation site.

Mantle dynamics and seismic tomography

PubMed Central

Tanimoto, Toshiro; Lay, Thorne

2000-01-01

Three-dimensional imaging of the Earth's interior, called seismic tomography, has achieved breakthrough advances in the last two decades, revealing fundamental geodynamical processes throughout the Earth's mantle and core. Convective circulation of the entire mantle is taking place, with subducted oceanic lithosphere sinking into the lower mantle, overcoming the resistance to penetration provided by the phase boundary near 650-km depth that separates the upper and lower mantle. The boundary layer at the base of the mantle has been revealed to have complex structure, involving local stratification, extensive structural anisotropy, and massive regions of partial melt. The Earth's high Rayleigh number convective regime now is recognized to be much more interesting and complex than suggested by textbook cartoons, and continued advances in seismic tomography, geodynamical modeling, and high-pressure–high-temperature mineral physics will be needed to fully quantify the complex dynamics of our planet's interior. PMID:11035784

Generalized subcutaneous edema as a rare manifestation of dermatomyositis: clinical lesson from a rare feature.

PubMed

Haroon, Muhammad; Eltahir, Ahmed; Harney, Sinead

2011-04-01

Generalized subcutaneous edema is a very rare manifestation of inflammatory myopathies. A 61-year-old woman presented with classic signs and symptoms of dermatomyositis. She was also noted to have generalized edema that was so florid that an alternative diagnosis was considered. Her disease was resistant to corticosteroids, azathioprine, and mycophenolate mofetil. Intravenous administration of immunoglobulins was started because of marked worsening of her disease-muscle weakness, generalized anasarca, and involvement of her bulbar muscles. This led to dramatic resolution of her subcutaneous edema and significant improvement of her skin and muscle disease. As the initial screen for malignancy was negative, a positron emission tomography-computed tomography scan was requested, which interestingly showed a metabolically active cervical tumor. Anasarca is an unusual manifestation of dermatomyositis. In treatment-refractory cases, it seems reasonable to consider positron emission tomography scan in excluding underlying malignant disease.

Near surface geophysical techniques on subsoil contamination: laboratory experiments

NASA Astrophysics Data System (ADS)

Capozzoli, Luigi; Giampaolo, Valeria; Rizzo, Enzo

2016-04-01

Hydrocarbons contamination of soil and groundwater has become a serious environmental problem, because of the increasing number of accidental spills caused by human activities. The starting point of any studies is the reconstruction of the conceptual site model. To make valid predictions about the flow pathways following by hydrocarbons compound is necessary to make a correct reconstruction of their characteristics and the environment in which they move. Near-surface geophysical methods, based on the study of electrical and electromagnetic properties, are proved to be very useful in mapping spatial distribution of the organic contaminants in the subsurface. It is well known, in fact, that electrical properties of the porous media are significantly influenced by hydrocarbons because, when contaminants enter the rock matrix, surface reaction occur between the contaminant and the soil grain surface. The main aim of this work is to investigate the capability of near-surface geophysical methods in mapping and monitoring spatial distribution of contaminants in a controlled setting. A laboratory experiment has been performed at the Hydrogeosite Laboratory of CNR-IMAA (Marsico Nuovo, PZ) where a box-sand has been contaminated by diesel. The used contaminant is a LNAPL, added to the sand through a drilled pipe. Contaminant behaviour and its migration paths have been monitored for one year by Electrical Resistivity measurements. In details, a Cross Borehole Electrical Resistivity Tomography techniques were used to characterize the contamination dynamics after a controlled hydrocarbon spillage occurring in the vadose zone. The approach with cross-borehole resistivity imaging provide a great advantage compared to more conventional surface electrical resistivity tomography, due to the high resolution at high depth (obviously depending on the depth of the well instrumented for the acquisition). This method has been shown to provide good information on the distribution of electrical properties of the subsoil at high depths and, in some cases, a detailed assessment of dynamic processes in the subsurface environment (Binley et al., 2002). Our study confirms the link between hydrocarbons contamination and geoelectrical signal and the capability of cross-hole electrical resistivity tomographies to realize a non-invasive characterization of LNAPL contamination of the media. Although, the electrical behaviour is much more complex and the relation with the contaminants depends also by time of investigation.

LiDAR and 2D Electrical Resistivity Tomography as a Supplement of Geomorphological Investigations in Urban Areas: a Case Study from the City of Wrocław (SW Poland)

NASA Astrophysics Data System (ADS)

Kasprzak, Marek; Traczyk, Andrzej

2014-06-01

In urbanized areas, particularly in lowland terrains and floors of large river valleys, the natural land configuration is often hard to recognize due to a long history of human activity. Accordingly, archaeological works in cities, which supply knowledge on settlement conditions, are usually accompanied by geological and geomophological research. Lately, data from light detection and ranging (LiDAR) have become a valuable source of information on urban land configuration. Geophysical methods are also becoming increasingly popular in background studies. The paper presents a method of using and linking these sources of spatial information about landforms in such areas. The main aim is to identify to what extent these complementary sources of data and the proposed method can be used in such a specific environment to reconstruct natural, buried terrain morphology. The city of Wrocław in Central Europe serves as an example. To this end geomorphometric studies were conducted with the use of digital elevation models (DEMs) based on LiDAR scanning and derivated land-surface parameters—SAGA Wetness Index, Channel Network Base Level and Altitude above Channel Network. The study also involved determining morphological edges and measurements of the meanders of the Odra, as well as expanding information on the spatial distribution of alluvia and the structure of slope breaks. To this end, geophysical measurements were conducted using the Two-Dimensional Electrical Resistivity Tomography method. Additionally, five typical sequences of man-made ground present within the perimeter of the city were distinguished. As a result, a map of the main landforms of Wrocław is presented. Finally, we argue that although high resolution DEM and derivate land-surface parameters are very useful in terrain analysis, places with thick man-made ground or strongly levelled areas must be recognized by geoarchaeological excavations or geological bore holes. The geophysical survey is useful to identify buried morphological edges and older relief elements in open areas.

Water content estimated from point scale to plot scale

NASA Astrophysics Data System (ADS)

Akyurek, Z.; Binley, A. M.; Demir, G.; Abgarmi, B.

2017-12-01

Soil moisture controls the portioning of rainfall into infiltration and runoff. Here we investigate measurements of soil moisture using a range of techniques spanning different spatial scales. In order to understand soil water content in a test basin, 512 km2 in area, in the south of Turkey, a Cosmic Ray CRS200B soil moisture probe was installed at elevation of 1459 m and an ML3 ThetaProbe (CS 616) soil moisture sensor was established at 5cm depth used to get continuous soil moisture. Neutron count measurements were corrected for the changes in atmospheric pressure, atmospheric water vapour and intensity of incoming neutron flux. The calibration of the volumetric soil moisture was performed, from the laboratory analysis, the bulk density varies between 1.719 (g/cm3) -1.390 (g/cm3), and the dominant soil texture is silty clay loam and silt loamThe water content reflectometer was calibrated for soil-specific conditions and soil moisture estimates were also corrected with respect to soil temperature. In order to characterize the subsurface, soil electrical resistivity tomography was used. Wenner and Schlumberger array geometries were used with electrode spacing varied from 1m- 5 m along 40 m and 200 m profiles. From the inversions of ERT data it is apparent that within 50 m distance from the CRS200B, the soil is moderately resistive to a depth of 2m and more conductive at greater depths. At greater distances from the CRS200B, the ERT results indicate more resistive soils. In addition to the ERT surveys, ground penetrating radar surveys using a common mid-point configuration was used with 200MHz antennas. The volumetric soil moisture obtained from GPR appears to overestimate those based on TDR observations. The values obtained from CS616 (at a point scale) and CRS200B (at a mesoscale) are compared with the values obtained at a plot scale. For the field study dates (20-22.06.2017) the volumetric moisture content obtained from CS616 were 25.14%, 25.22% and 25.96% respectively. The values obtained from CRS200B were 23.23%, 22.81% and 23.26% for the same dates. Whereas the values obtained from GPR were between 32%-44%. Soil moisture observed by CRS200B is promising to monitor the water content in the soil at the mesoscale and ERT surveys help to understand the spatial variability of the soil water content within the footprint of CRS200B.

‘Double cortex’ sign on FDG-PET/CT in diffuse band heterotopia

PubMed Central

Tripathi, Madhavi; Tripathi, Manjari; Kumar, Ganesh; Malhotra, Arun; Bal, Chandra Sekhar

2013-01-01

F-18 Fluorodeoxyglucose (FDG) Positron emission tomography/Computed Tomography (PET/CT) has come to play an increasingly important role for the pre-surgical evaluation of drug resistant epilepsy and complements Magnetic Resonance Imaging (MRI) in the evaluation of grey matter heterotopias. This case illustrates the characteristic pattern of metabolic abnormality in diffuse band heterotopia (DBH) which is otherwise called double cortex syndrome. The presence of metabolic activity in the heterotopic inner cortical band and in the overlying true cortex gives rise to the ‘double cortex’ sign on FDG-PET, concurrent CT provides a good anato-metabolic coregistration. PMID:24379541

Acceptance and Resistance to Corporate E-Learning: A Case from the Retail Sector

ERIC Educational Resources Information Center

Rabak, Lynne; Cleveland-Innes, Martha

2006-01-01

The purpose of this study was to investigate what influences employees' acceptance and resistance to a corporate e-learning initiative provided by a large retail chain. The research used a survey design to gather interview and survey data to examine the factors affecting learner interest in, and resistance to, training and e-learning. The results…

Structure and tectonics of the northwestern United States from EarthScope USArray magnetotelluric data

USGS Publications Warehouse

Bedrosian, Paul A.; Feucht, Daniel W.

2014-01-01

The magnetotelluric component of the EarthScope USArray program has covered over 35% of the continental United States. Resistivity tomography models derived from these data image lithospheric structure and provide constraints on the distribution of fluids and melt within the lithosphere. We present a three-dimensional resistivity model of the northwestern United States which provides new insight into the tectonic assembly of western North America from the Archean to present. Comparison with seismic tomography models reveals regions of correlated and anti-correlated resistivity and velocity that help identify thermal and compositional variations within the lithosphere. Recent (Neogene) tectonic features reflected in the model include the subducting Juan de Fuca–Gorda plate which can be traced beneath the forearc to more than 100 km depth, high lithospheric conductivity along the Snake River Plain, and pronounced lower-crustal and upper-mantle conductivity beneath the Basin and Range. The latter is abruptly terminated to the northwest by the Klamath–Blue Mountains Lineament, which we interpret as an important structure during and since the Mesozoic assembly of the region. This boundary is interpreted to separate hot extended lithosphere from colder, less extended lithosphere. The western edge of Proterozoic North America, as indicated by the Cretaceous initial 87Sr/86Sr = 0.706 contour, is clearly reflected in the resistivity model. We further image an Archean crustal block (“Pend Oreille block”) straddling the Washington/Idaho border, which we speculate separated from the Archean Medicine Hat block in the Proterozoic. Finally, in the modern Cascades forearc, the geometry and internal structure of the Eocene Siletz terrane is reflected in the resistivity model. The apparent eastern edge of the Siletz terrane under the Cascades arc suggests that pre-Tertiary rocks fill the Washington and Oregon back-arc.

Evaluation of surface water and groundwater contamination in a MSW landfill area using hydrochemical analysis and electrical resistivity tomography: a case study in Sichuan province, Southwest China.

PubMed

Ling, Chengpeng; Zhang, Qiang

2017-04-01

As a primary disposal mean of municipal solid waste in China, the landfill has been recognized as one of the major threats to the surrounding surface water and groundwater environment due to the emission of leachate. The aim of this study was to determine the impact of leachate on the surface water and groundwater environment of the region of the Chang'an landfill, which is located in Sichuan province, China. The surface water and groundwater were sampled for hydrochemical analysis. Three electrical resistivity tomography profiles were conducted to evaluate the impact of leachate on the groundwater environment, and several laboratory tests were carried out to build the relationship between the soil bulk resistivity and the void fluid resistivity. The results showed that a seasonal creek named Longfeng creek, which crosses the landfill site, was contaminated by the leachate. The concentrations of COD, BOD5, and chlorides (Cl) of surface water samples increased by 12.3-105.7 times. The groundwater quality in the surface loose sediments along the valley deteriorated obviously from the landfill to 500 m downstream area. The laboratory tests of soil samples indicated that the resistivity value of 13 Ωm is a critical value whether the groundwater in the loose sediments is polluted. The groundwater at the site adjacent to the spillway in the landfill was partially contaminated by the emission of leachate. The groundwater contamination zones at 580 m downstream of the landfill were recognized at the shallow zones from 60 m left bank to 30 m right bank of Longfeng creek. The improved understanding of groundwater contamination around the landfill is beneficial for the landfill operation and groundwater environment remediation.

Post flooding damage assessment of earth dams and historical reservoirs using non-invasive geophysical techniques

NASA Astrophysics Data System (ADS)

Sentenac, Philippe; Benes, Vojtech; Budinsky, Vladimir; Keenan, Helen; Baron, Ron

2017-11-01

This paper describes the use of four geophysical techniques to map the structural integrity of historical earth reservoir embankments which are susceptible to natural decay with time. The four techniques that were used to assess the post flood damage were 1. A fast scanning technique using a dipole electromagnetic profile apparatus (GEM2), 2. Electrical Resistivity Tomography (ERT) in order to obtain a high resolution image of the shape of the damaged/seepage zone, 3. Self-Potential surveys were carried out to relate the detected seepage evolution and change of the water displacement inside the embankment, 4. The washed zone in the areas with piping was characterised with microgravimetry. The four geophysical techniques used were evaluated against the case studies of two reservoirs in South Bohemia, Czech Republic. A risk approach based on the Geophysical results was undertaken for the reservoir embankments. The four techniques together enabled a comprehensive non-invasive assessment whereby remedial action could be recommended where required. Conclusions were also drawn on the efficiency of the techniques to be applied for embankments with wood structures.

Patient grouping for dose surveys and establishment of diagnostic reference levels in paediatric computed tomography.

PubMed

Vassileva, J; Rehani, M

2015-07-01

There has been confusion in literature on whether paediatric patients should be grouped according to age, weight or other parameters when dealing with dose surveys. The present work aims to suggest a pragmatic approach to achieve reasonable accuracy for performing patient dose surveys in countries with limited resources. The analysis is based on a subset of data collected within the IAEA survey of paediatric computed tomography (CT) doses, involving 82 CT facilities from 32 countries in Asia, Europe, Africa and Latin America. Data for 6115 patients were collected, in 34.5 % of which data for weight were available. The present study suggests that using four age groups, <1, >1-5, >5-10 and >10-15 y, is realistic and pragmatic for dose surveys in less resourced countries and for the establishment of DRLs. To ensure relevant accuracy of results, data for >30 patients in a particular age group should be collected if patient weight is not known. If a smaller sample is used, patient weight should be recorded and the median weight in the sample should be within 5-10 % from the median weight of the sample for which the DRLs were established. Comparison of results from different surveys should always be performed with caution, taking into consideration the way of grouping of paediatric patients. Dose results can be corrected for differences in patient weight/age group. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Buried Man-made Structure Imaging using 2-D Resistivity Inversion

NASA Astrophysics Data System (ADS)

Anderson Bery, Andy; Nordiana, M. M.; El Hidayah Ismail, Noer; Jinmin, M.; Nur Amalina, M. K. A.

2018-04-01

This study is carried out with the objective to determine the suitable resistivity inversion method for buried man-made structure (bunker). This study was carried out with two stages. The first stage is suitable array determination using 2-D computerized modeling method. One suitable array is used for the infield resistivity survey to determine the dimension and location of the target. The 2-D resistivity inversion results showed that robust inversion method is suitable to resolve the top and bottom part of the buried bunker as target. In addition, the dimension of the buried bunker is successfully determined with height of 7 m and length of 20 m. The location of this target is located at -10 m until 10 m of the infield resistivity survey line. The 2-D resistivity inversion results obtained in this study showed that the parameters selection is important in order to give the optimum results. These parameters are array type, survey geometry and inversion method used in data processing.

Subsurface Investigation using 2D Resistivity and Ground Penetrating Radar at Teluk Kumbar, Penang

NASA Astrophysics Data System (ADS)

Teoh, YJ; Bruka, MA; Idris, NM; Ismail, NA; Muztaza, NM

2018-04-01

The objective of this study is to determine the structure and condition of the subsurface by using 2D resistivity and Ground Penetrating Radar (GPR) methods. The study was conducted at SK Sungai Batu, Teluk Kumbar, Penang Island. For 2D resistivity method, Wenner-Schlumberger array was used while for GPR, 250 MHz antenna was used at the site. The survey consists of 200m length survey line. GPR result shows that there is high intensity of EM. 2D resistivity result shows that the low resistivity region (200 Ωm to 340 Ωm) appears to be at the centre of the survey line from depth 7 m to 13 m. Meanwhile, the higher resistivity region (4000 Ωm to 6000 Ωm) may indicate the bedrock structure of the subsurface, which is the granitic rock. This region is bedrock which rested at depth 14 m and below. In conclusion, data obtained from GPR and 2D resistivity methods can be easily correlated to determine the features of the subsurface.

Source Repeatability of Time-Lapse Offset VSP Surveys for Monitoring CO2 Injection

NASA Astrophysics Data System (ADS)

Zhang, Z.; Huang, L.; Rutledge, J. T.; Denli, H.; Zhang, H.; McPherson, B. J.; Grigg, R.

2009-12-01

Time-lapse vertical seismic profiling (VSP) surveys have the potential to remotely track the migration of injected CO2 within a geologic formation. To accurately detect small changes due to CO2 injection, the sources of time-lapse VSP surveys must be located exactly at the same positions. However, in practice, the source locations can vary from one survey to another survey. Our numerical simulations demonstrate that a variation of a few meters in the VSP source locations can result in significant changes in time-lapse seismograms. To address the source repeatability issue, we apply double-difference tomography to downgoing waves of time-lapse offset VSP data to invert for the source locations and the velocity structures simultaneously. In collaboration with Resolute Natural Resources, Navajo National Oil and Gas Company, and the Southwest Regional Partnership on Carbon Sequestration under the support of the U.S. Department of Energy’s National Energy Technology Laboratory, one baseline and two repeat offset VSP datasets were acquired in 2007-2009 for monitoring CO2 injection at the Aneth oil field in Utah. A cemented geophone string was used to acquire the data for one zero-offset and seven offset source locations. During the data acquisition, there was some uncertainty in the repeatability of the source locations relative to the baseline survey. Our double-difference tomography results of the Aneth time-lapse VSP data show that the source locations for different surveys are separated up to a few meters. Accounting for these source location variations during VSP data analysis will improve reliability of time-lapse VSP monitoring.

The Feasibility of Xpert MTB/RIF Testing to Detect Rifampicin Resistance among Childhood Tuberculosis for Prevalence Surveys in Northern China.

PubMed

Lu, Jie; Li, Huimin; Dong, Fang; Shi, Jin; Yang, Hui; Han, Shujing; Chu, Ping; Zhao, Yanlin; Song, Wenqi; Guo, Yongli; Zhao, Shunying

2017-01-01

Drug resistance surveillance is crucial for control of drug-resistant tuberculosis (TB). However, limited data exists on the burden of drug-resistant TB in children. The goal of this work was to generate prevalence data regarding rifampicin- (RIF-) resistant childhood TB in northern China and to test the feasibility of Xpert for surveying pediatric TB drug resistance prevalence. We enrolled 362 clinically diagnosed childhood TB patients and collected sputum, gastric lavage aspirate (GLA), bronchoalveolar lavage fluid (BALF), and cerebral spinal fluid (CSF) samples. Xpert and solid culture were utilized to detect RIF resistance. The detection rate of Xpert-positive TB among new clinically diagnosed TB cases was 38.4% (139/362), significantly higher than that of solid culture-positive TB (16.3%, 59/362, P < 0.01). Notably, Xpert-positive rates differed significantly by sample type, with the highest positive rate for GLA (51.2%). The unit testing costs per RIF-resistant TB patient were $828.41 for solid culture and $761.86 for Xpert. Our data demonstrate that the prevalence of RIF resistance among childhood TB cases in our study (6.9%) is comparable to the national RIF resistance prevalence level of new cases (6.7%). In addition, Xpert is superior to the solid culture for RIF resistance survey in the childhood TB patients.

Jointly reconstructing ground motion and resistivity for ERT-based slope stability monitoring

NASA Astrophysics Data System (ADS)

Boyle, Alistair; Wilkinson, Paul B.; Chambers, Jonathan E.; Meldrum, Philip I.; Uhlemann, Sebastian; Adler, Andy

2018-02-01

Electrical resistivity tomography (ERT) is increasingly being used to investigate unstable slopes and monitor the hydrogeological processes within. But movement of electrodes or incorrect placement of electrodes with respect to an assumed model can introduce significant resistivity artefacts into the reconstruction. In this work, we demonstrate a joint resistivity and electrode movement reconstruction algorithm within an iterative Gauss-Newton framework. We apply this to ERT monitoring data from an active slow-moving landslide in the UK. Results show fewer resistivity artefacts and suggest that electrode movement and resistivity can be reconstructed at the same time under certain conditions. A new 2.5-D formulation for the electrode position Jacobian is developed and is shown to give accurate numerical solutions when compared to the adjoint method on 3-D models. On large finite element meshes, the calculation time of the newly developed approach was also proven to be orders of magnitude faster than the 3-D adjoint method and addressed modelling errors in the 2-D perturbation and adjoint electrode position Jacobian.

Risk analysis and detection of thrombosis by measurement of electrical resistivity of blood.

PubMed

Sapkota, Achyut; Asakura, Yuta; Maruyama, Osamu; Kosaka, Ryo; Yamane, Takashi; Takei, Masahiro

2013-01-01

Monitoring of thrombogenic process is very important in ventricular assistance devices (VADs) used as temporary or permanent measures in patients with advanced heart failure. Currently, there is a lack of a system which can perform a real-time monitoring of thrombogenic activity. Electrical signals vary according to the change in concentration of coagulation factors as well as the distribution of blood cells, and thus have potential to detect the thrombogenic process in an early stage. In the present work, we have made an assessment of an instrumentation system exploiting the electrical properties of blood. The experiments were conducted using bovine blood. Electrical resistance tomography with eight-electrode sensor was used to monitor the spatio-temporal change in electrical resistivity of blood in thrombogenic and non-thrombogenic condition. Under non-thrombogenic condition, the resistivity was uniform across the cross-section and average resistivity monotonically decreased with time before remaining almost flat. In contrary, under thrombogenic condition, there was non-uniform distribution across the cross-section, and average resistivity fluctuated with time.

Determination of slope failure using 2-D resistivity method

NASA Astrophysics Data System (ADS)

Muztaza, Nordiana Mohd; Saad, Rosli; Ismail, Nur Azwin; Bery, Andy Anderson

2017-07-01

Landslides and slope failure may give negative economic effects including the cost to repair structures, loss of property value and medical costs in the event of injury. To avoid landslide, slope failure and disturbance of the ecosystem, good and detailed planning must be done when developing hilly area. Slope failure classification and various factors contributing to the instability using 2-D resistivity survey conducted in Selangor, Malaysia are described. The study on landslide and slope failure was conducted at Site A and Site B, Selangor using 2-D resistivity method. The implications of the anticipated ground conditions as well as the field observation of the actual conditions are discussed. Nine 2-D resistivity survey lines were conducted in Site A and six 2-D resistivity survey lines with 5 m minimum electrode spacing using Pole-dipole array were performed in Site B. The data were processed using Res2Dinv and Surfer10 software to evaluate the subsurface characteristics. 2-D resistivity results from both locations show that the study areas consist of two main zones. The first zone is alluvium or highly weathered with the resistivity of 100-1000 Ωm at 20-70 m depth. This zone consists of saturated area (1-100 Ωm) and boulders with resistivity value of 1200-3000 Ωm. The second zone with resistivity values of > 3000 Ωm was interpreted as granitic bedrock. The study area was characterized by saturated zones, highly weathered zone, highly contain of sand and boulders that will trigger slope failure in the survey area. Based on the results obtained from the study findings, it can be concluded that 2-D resistivity method is useful method in determination of slope failure.

A study of the effect of seasonal climatic factors on the electrical resistivity response of three experimental graves

NASA Astrophysics Data System (ADS)

Jervis, John R.; Pringle, Jamie K.

2014-09-01

Electrical resistivity surveys have proven useful for locating clandestine graves in a number of forensic searches. However, some aspects of grave detection with resistivity surveys remain imperfectly understood. One such aspect is the effect of seasonal changes in climate on the resistivity response of graves. In this study, resistivity survey data collected over three years over three simulated graves were analysed in order to assess how the graves' resistivity anomalies varied seasonally and when they could most easily be detected. Thresholds were used to identify anomalies, and the ‘residual volume' of grave-related anomalies was calculated as the area bounded by the relevant thresholds multiplied by the anomaly's average value above the threshold. The residual volume of a resistivity anomaly associated with a buried pig cadaver showed evidence of repeating annual patterns and was moderately correlated with the soil moisture budget. This anomaly was easiest to detect between January and April each year, after prolonged periods of high net gain in soil moisture. The resistivity response of a wrapped cadaver was more complex, although it also showed evidence of seasonal variation during the third year after burial. We suggest that the observed variation in the graves' resistivity anomalies was caused by seasonal change in survey data noise levels, which was in turn influenced by the soil moisture budget. It is possible that similar variations occur elsewhere for sites with seasonal climate variations and this could affect successful detection of other subsurface features. Further research to investigate how different climates and soil types affect seasonal variation in grave-related resistivity anomalies would be useful.

Improvement of electrical resistivity tomography for leachate injection monitoring.

PubMed

Clément, R; Descloitres, M; Günther, T; Oxarango, L; Morra, C; Laurent, J-P; Gourc, J-P

2010-03-01

Leachate recirculation is a key process in the scope of operating municipal waste landfills as bioreactors, which aims to increase the moisture content to optimize the biodegradation in landfills. Given that liquid flows exhibit a complex behaviour in very heterogeneous porous media, in situ monitoring methods are required. Surface time-lapse electrical resistivity tomography (ERT) is usually proposed. Using numerical modelling with typical 2D and 3D injection plume patterns and 2D and 3D inversion codes, we show that wrong changes of resistivity can be calculated at depth if standard parameters are used for time-lapse ERT inversion. Major artefacts typically exhibit significant increases of resistivity (more than +30%) which can be misinterpreted as gas migration within the waste. In order to eliminate these artefacts, we tested an advanced time-lapse ERT procedure that includes (i) two advanced inversion tools and (ii) two alternative array geometries. The first advanced tool uses invariant regions in the model. The second advanced tool uses an inversion with a "minimum length" constraint. The alternative arrays focus on (i) a pole-dipole array (2D case), and (ii) a star array (3D case). The results show that these two advanced inversion tools and the two alternative arrays remove almost completely the artefacts within +/-5% both for 2D and 3D situations. As a field application, time-lapse ERT is applied using the star array during a 3D leachate injection in a non-hazardous municipal waste landfill. To evaluate the robustness of the two advanced tools, a synthetic model including both true decrease and increase of resistivity is built. The advanced time-lapse ERT procedure eliminates unwanted artefacts, while keeping a satisfactory image of true resistivity variations. This study demonstrates that significant and robust improvements can be obtained for time-lapse ERT monitoring of leachate recirculation in waste landfills. Copyright 2009 Elsevier Ltd. All rights reserved.

Improvement of electrical resistivity tomography for leachate injection monitoring

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clement, R., E-mail: remi.clement@hmg.inpg.f; Descloitres, M.; Guenther, T., E-mail: Thomas.Guenther@liag-hannover.d

2010-03-15

Leachate recirculation is a key process in the scope of operating municipal waste landfills as bioreactors, which aims to increase the moisture content to optimize the biodegradation in landfills. Given that liquid flows exhibit a complex behaviour in very heterogeneous porous media, in situ monitoring methods are required. Surface time-lapse electrical resistivity tomography (ERT) is usually proposed. Using numerical modelling with typical 2D and 3D injection plume patterns and 2D and 3D inversion codes, we show that wrong changes of resistivity can be calculated at depth if standard parameters are used for time-lapse ERT inversion. Major artefacts typically exhibit significantmore » increases of resistivity (more than +30%) which can be misinterpreted as gas migration within the waste. In order to eliminate these artefacts, we tested an advanced time-lapse ERT procedure that includes (i) two advanced inversion tools and (ii) two alternative array geometries. The first advanced tool uses invariant regions in the model. The second advanced tool uses an inversion with a 'minimum length' constraint. The alternative arrays focus on (i) a pole-dipole array (2D case), and (ii) a star array (3D case). The results show that these two advanced inversion tools and the two alternative arrays remove almost completely the artefacts within +/-5% both for 2D and 3D situations. As a field application, time-lapse ERT is applied using the star array during a 3D leachate injection in a non-hazardous municipal waste landfill. To evaluate the robustness of the two advanced tools, a synthetic model including both true decrease and increase of resistivity is built. The advanced time-lapse ERT procedure eliminates unwanted artefacts, while keeping a satisfactory image of true resistivity variations. This study demonstrates that significant and robust improvements can be obtained for time-lapse ERT monitoring of leachate recirculation in waste landfills.« less

Spatial and temporal variations of thaw layer thickness and its controlling factors identified using time-lapse electrical resistivity tomography and hydro-thermal modeling

NASA Astrophysics Data System (ADS)

Tran, Anh Phuong; Dafflon, Baptiste; Bisht, Gautam; Hubbard, Susan S.

2018-06-01

Quantitative understanding of controls on thaw layer thickness (TLT) dynamics in the Arctic peninsula is essential for predictive understanding of permafrost degradation feedbacks to global warming and hydrobiochemical processes. This study jointly interprets electrical resistivity tomography (ERT) measurements and hydro-thermal numerical simulation results to assess spatiotemporal variations of TLT and to determine its controlling factors in Barrow, Alaska. Time-lapse ERT measurements along a 35-m transect were autonomously collected from 2013 to 2015 and inverted to obtain soil electrical resistivity. Based on several probe-based TLT measurements and co-located soil electrical resistivity, we estimated the electrical resistivity thresholds associated with the boundary between the thaw layer and permafrost using a grid search optimization algorithm. Then, we used the obtained thresholds to derive the TLT from all soil electrical resistivity images. The spatiotemporal analysis of the ERT-derived TLT shows that the TLT at high-centered polygons (HCPs) is smaller than that at low-centered polygons (LCPs), and that both thawing and freezing occur earlier at the HCPs compared to the LCPs. In order to provide a physical explanation for dynamics in the thaw layer, we performed 1-D hydro-thermal simulations using the community land model (CLM). Simulation results showed that air temperature and precipitation jointly govern the temporal variations of TLT, while the topsoil organic content (SOC) and polygon morphology are responsible for its spatial variations. When the topsoil SOC and its thickness increase, TLT decreases. Meanwhile, at LCPs, a thicker snow layer and saturated soil contribute to a thicker TLT and extend the time needed for TLT to freeze and thaw. This research highlights the importance of combination of measurements and numerical modeling to improve our understanding spatiotemporal variations and key controls of TLT in cold regions.

Measurement of near-surface seismic compressional wave velocities using refraction tomography at a proposed construction site on the Presidio of Monterey, California

USGS Publications Warehouse

Powers, Michael H.; Burton, Bethany L.

2012-01-01

The U.S. Army Corps of Engineers is determining the feasibility of constructing a new barracks building on the U.S. Army Presidio of Monterey in Monterey, California. Due to the presence of an endangered orchid in the proposed area, invasive techniques such as exploratory drill holes are prohibited. To aid in determining the feasibility, budget, and design of this building, a compressional-wave seismic refraction survey was proposed by the U.S. Geological Survey as an alternative means of investigating the depth to competent bedrock. Two sub-parallel profiles were acquired along an existing foot path and a fence line to minimize impacts on the endangered flora. The compressional-wave seismic refraction tomography data for both profiles indicate that no competent rock classified as non-rippable or marginally rippable exists within the top 30 feet beneath the ground surface.

Preliminary Investigation of Paleochannels and Groundwater Specific Conductance using Direct-Current Resistivity and Surface-Wave Seismic Geophysical Surveys at the Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware, 2008

USGS Publications Warehouse

Degnan, James R.; Brayton, Michael J.

2010-01-01

The U.S. Geological Survey (USGS), in cooperation with Region III of the U.S. Environmental Protection Agency (USEPA) and the State of Delaware, is conducting an ongoing study of the water-quality and hydrogeologic properties of the Columbia and Potomac aquifers and the extent of cross-aquifer contamination with benzene; chlorobenzene; 1,2-dichlorobenzene; 1,4-dichlorobenzene; and hydrogen chloride (hydrochloric acid when dissolved in water) in the vicinity of the Standard Chlorine of Delaware, Inc. (SCD), Superfund Site, Delaware City, Delaware. Surface geophysical surveys and well data were used to identify and correlate low-permeability units (clays) across the site and to search for sand and gravel filled paleochannels that are potential conduits and receptors of contaminated groundwater and (or) Dense Non-Aqueous Phase Liquid (DNAPL) contaminants. The combined surveys and well data were also used to characterize areas of the site that have groundwater with elevated (greater than 1,000 microsiemens per centimeter) specific conductance (SC) as a result of contamination. The most electrically conductive features measured with direct-current (DC) resistivity at the SCD site are relatively impermeable clays and permeable sediment that are associated with elevated SC in groundwater. Many of the resistive features include paleochannel deposits consisting of coarse-grained sediments that are unsaturated, have low (less than 200 microsiemens per centimeter) SC pore water, or are cemented. Groundwater in uncontaminated parts of the Columbia aquifer and of the Potomac aquifer has a low SC. Specific-conductance data from monitoring wells at the site were used to corroborate the DC-resistivity survey results. For comparison with DC-resistivity surveys, multi-channel analysis of surface wave (MASW) surveys were used and were able to penetrate deep enough to measure the Columbia aquifer, which is known to have elevated SC in some places. MASW survey results respond to solid material stiffness; clays and cemented sediments will have a higher velocity than silts, sands, and gravels (in order of increasing hydraulic conductivity). Geophysical surveys detected elevated SC associated with contamination of the surficial Columbia aquifer. Groundwater with elevated SC over ambient (by an order of magnitude) produced a decrease in measured resistivity at the SCD site. Where SC data are not available from wells, it is not known if a low resistivity value measured with DC resistivity alone results from the geologic material (clay) or elevated SC in groundwater (in sand or gravel). Seismic surface waves used as part of the MASW technique are not affected by water content or quality and are used herein to distinguish between sand and clay when SC is high. Through concurrent interpretation of MASW and DC-resistivity surveys, information was gained about water quality and lithology over large areas at the SCD site.

WSJointInv2D-MT-DCR: An efficient joint two-dimensional magnetotelluric and direct current resistivity inversion

NASA Astrophysics Data System (ADS)

Amatyakul, Puwis; Vachiratienchai, Chatchai; Siripunvaraporn, Weerachai

2017-05-01

An efficient joint two-dimensional direct current resistivity (DCR) and magnetotelluric (MT) inversion, referred to as WSJointInv2D-MT-DCR, was developed with FORTRAN 95 based on the data space Occam's inversion algorithm. Our joint inversion software can be used to invert just the MT data or the DCR data, or invert both data sets simultaneously to get the electrical resistivity structures. Since both MT and DCR surveys yield the same resistivity structures, the two data types enhance each other leading to a better interpretation. Two synthetic and a real field survey are used here to demonstrate that the joint DCR and MT surveys can help constrain each other to reduce the ambiguities occurring when inverting the DCR or MT alone. The DCR data increases the lateral resolution of the near surface structures while the MT data reveals the deeper structures. When the MT apparent resistivity suffers from the static shift, the DCR apparent resistivity can serve as a replacement for the estimation of the static shift factor using the joint inversion. In addition, we also used these examples to show the efficiency of our joint inversion code. With the availability of our new joint inversion software, we expect the number of joint DCR and MT surveys to increase in the future.

The fourth national anti-tuberculosis drug resistance survey in Viet Nam.

PubMed

Nhung, N V; Hoa, N B; Sy, D N; Hennig, C M; Dean, A S

2015-06-01

Viet Nam's Fourth National Anti-Tuberculosis Drug Resistance Survey was conducted in 2011. To determine the prevalence of resistance to the four main first-line anti-tuberculosis drugs in Viet Nam. Eighty clusters were selected using a probability proportion to size approach. Drug susceptibility testing (DST) against the four main first-line anti-tuberculosis drugs was performed. A total of 1629 smear-positive tuberculosis (TB) patients were eligible for culture. Of these, DST results were available for 1312 patients, including 1105 new TB cases, 195 previously treated TB cases and 12 cases with an unknown treatment history. The proportion of cases with resistance to any drug was 32.7% (95%CI 29.1-36.5) among new cases and 54.2% (95%CI 44.3-63.7) among previously treated cases. The proportion of multidrug-resistant TB (MDR-TB) cases was 4.0% (95%CI 2.5-5.4) in new cases and 23.3 (95%CI 16.7-29.9) in previously treated cases. The fourth drug resistance survey in Viet Nam found that the proportion of MDR-TB among new and previously treated cases was not significantly different from that in the 2005 survey. The National TB Programme should prioritise the detection and treatment of MDR-TB to reduce transmission of MDR-TB in the community.

The Role of Functional Neuroimaging in Pre-Surgical Epilepsy Evaluation

PubMed Central

Pittau, Francesca; Grouiller, Frédéric; Spinelli, Laurent; Seeck, Margitta; Michel, Christoph M.; Vulliemoz, Serge

2014-01-01

The prevalence of epilepsy is about 1% and one-third of cases do not respond to medical treatment. In an eligible subset of patients with drug-resistant epilepsy, surgical resection of the epileptogenic zone is the only treatment that can possibly cure the disease. Non-invasive techniques provide information for the localization of the epileptic focus in the majority of cases, whereas in others invasive procedures are required. In the last years, non-invasive neuroimaging techniques, such as simultaneous recording of functional magnetic resonance imaging and electroencephalogram (EEG-fMRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), electric and magnetic source imaging (MSI, ESI), spectroscopy (MRS), have proved their usefulness in defining the epileptic focus. The combination of these functional techniques can yield complementary information and their concordance is crucial for guiding clinical decision, namely the planning of invasive EEG recordings or respective surgery. The aim of this review is to present these non-invasive neuroimaging techniques, their potential combination, and their role in the pre-surgical evaluation of patients with pharmaco-resistant epilepsy. PMID:24715886

Electrode Models for Electric Current Computed Tomography

PubMed Central

CHENG, KUO-SHENG; ISAACSON, DAVID; NEWELL, J. C.; GISSER, DAVID G.

2016-01-01

This paper develops a mathematical model for the physical properties of electrodes suitable for use in electric current computed tomography (ECCT). The model includes the effects of discretization, shunt, and contact impedance. The complete model was validated by experiment. Bath resistivities of 284.0, 139.7, 62.3, 29.5 Ω · cm were studied. Values of “effective” contact impedance z used in the numerical approximations were 58.0, 35.0, 15.0, and 7.5 Ω · cm2, respectively. Agreement between the calculated and experimentally measured values was excellent throughout the range of bath conductivities studied. It is desirable in electrical impedance imaging systems to model the observed voltages to the same precision as they are measured in order to be able to make the highest resolution reconstructions of the internal conductivity that the measurement precision allows. The complete electrode model, which includes the effects of discretization of the current pattern, the shunt effect due to the highly conductive electrode material, and the effect of an “effective” contact impedance, allows calculation of the voltages due to any current pattern applied to a homogeneous resistivity field. PMID:2777280

Electrode models for electric current computed tomography.

PubMed

Cheng, K S; Isaacson, D; Newell, J C; Gisser, D G

1989-09-01

This paper develops a mathematical model for the physical properties of electrodes suitable for use in electric current computed tomography (ECCT). The model includes the effects of discretization, shunt, and contact impedance. The complete model was validated by experiment. Bath resistivities of 284.0, 139.7, 62.3, 29.5 omega.cm were studied. Values of "effective" contact impedance zeta used in the numerical approximations were 58.0, 35.0, 15.0, and 7.5 omega.cm2, respectively. Agreement between the calculated and experimentally measured values was excellent throughout the range of bath conductivities studied. It is desirable in electrical impedance imaging systems to model the observed voltages to the same precision as they are measured in order to be able to make the highest resolution reconstructions of the internal conductivity that the measurement precision allows. The complete electrode model, which includes the effects of discretization of the current pattern, the shunt effect due to the highly conductive electrode material, and the effect of an "effective" contact impedance, allows calculation of the voltages due to any current pattern applied to a homogeneous resistivity field.

Three-dimensional electrical impedance tomography based on the complete electrode model.

PubMed

Vauhkonen, P J; Vauhkonen, M; Savolainen, T; Kaipio, J P

1999-09-01

In electrical impedance tomography an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. It is often assumed that the injected currents are confined to the two-dimensional (2-D) electrode plane and the reconstruction is based on 2-D assumptions. However, the currents spread out in three dimensions and, therefore, off-plane structures have significant effect on the reconstructed images. In this paper we propose a finite element-based method for the reconstruction of three-dimensional resistivity distributions. The proposed method is based on the so-called complete electrode model that takes into account the presence of the electrodes and the contact impedances. Both the forward and the inverse problems are discussed and results from static and dynamic (difference) reconstructions with real measurement data are given. It is shown that in phantom experiments with accurate finite element computations it is possible to obtain static images that are comparable with difference images that are reconstructed from the same object with the empty (saline filled) tank as a reference.

Implementation of ground penetrating radar and electrical resistivity tomography for inspecting the Greco-Roman Necropolis at Kilo 6 of the Golden Mummies Valley, Bahariya Oasis, Egypt

NASA Astrophysics Data System (ADS)

Abbas, Abbas M.; Ghazala, Hosni H.; Mesbah, Hany S.; Atya, Magdy A.; Radwan, Ali; Hamed, Diaa E.

2016-06-01

Bahariya Oasis is one of the lately inspected spots in Egypt and has a long historical record extending from the old kingdom till the emergence of Islam. Since June 1999, the Valley of the Golden Mummies near Bawiti (at kilometer 6 on the road leads to Farafra Oasis) became significant due to the discoveries of amazing mummies of gelded faces. The archeologists believe that the Valley has more valuable tombs that still unrevealed. Also, the possibility that the Greco-Roman Necropolis extends to areas other than Kilo-6 is sustainable. The ground penetrating radar and electrical resistivity tomography are two geophysical tools that have successful applications in archeological assessment. The two techniques were used in integration plan to assert the archeological potentiality of the studied site and to map the feasible tombs. Sum of 798 GPR profiles and 19 ERT cross sections was carried out over the study area. The results of them were analyzed to envisage these results in archeological terms.

Methods for monitoring erosion using optical coherence tomography

NASA Astrophysics Data System (ADS)

Chan, Kenneth H.; Chan, Andrew C.; Darling, Cynthia L.; Fried, Daniel

Since optical coherence tomography is well suited for measuring small dimensional changes on tooth surfaces it has great potential for monitoring tooth erosion. The purpose of this study was to explore different approaches for monitoring the erosion of enamel. Application of an acid resistant varnish to protect the tooth surface from erosion has proven effective for providing a reference surface for in vitro studies but has limited potential for in vivo studies. Two approaches which can potentially be used in vivo were investigated. The first approach is to measure the remaining enamel thickness, namely the distance from the tooth surface to the dentinal-enamel junction (DEJ). The second more novel approach is to irradiate the surface with a carbon dioxide laser to create a reference layer which resists erosion. Measuring the remaining enamel thickness proved challenging since the surface roughening and subsurface demineralization that commonly occurs during the erosion process can prevent resolution of the underlying DEJ. The areas irradiated by the laser manifested lower rates of erosion compared to the non-irradiated areas and this method appears promising but it is highly dependent on the severity of the acid challenge.

The plumbing system of the Pagosa thermal Springs, Colorado: Application of geologically constrained geophysical inversion and data fusion

NASA Astrophysics Data System (ADS)

Revil, A.; Cuttler, S.; Karaoulis, M.; Zhou, J.; Raynolds, B.; Batzle, M.

2015-06-01

Fault and fracture networks usually provide the plumbing for movement of hydrothermal fluids in geothermal fields. The Big Springs of Pagosa Springs in Colorado is known as the deepest geothermal hot springs in the world. However, little is known about the plumbing system of this hot spring, especially regarding the position of the reservoir (if any) or the position of the major tectonic faults controlling the flow of the thermal water in this area. The Mancos shale, a Cretaceous shale, dominates many of the surface expressions around the springs and impede an easy recognition of the fault network. We use three geophysical methods (DC resistivity, self-potential, and seismic) to image the faults in this area, most of which are not recognized in the geologic fault map of the region. Results from these surveys indicate that the hot Springs (the Big Spring and a warm spring located 1.8 km further south) are located at the intersection of the Victoire Fault, a major normal crustal fault, and two north-northeast trending faults (Fault A and B). Self-potential and DC resistivity tomographies can be combined and a set of joint attributes defined to determine the localization of the flow of hot water associated with the Eight Miles Mesa Fault, a second major tectonic feature responsible for the occurrence of warm springs further West and South from the Big Springs of Pagosa Springs.

Application of remote sensing analysis and MT method for identification geothermal prospect zone in Mt. Endut

NASA Astrophysics Data System (ADS)

Akbar, A. M.; Permadi, A. N.; Wildan, D.; Sobirin, R.; Supriyanto

2017-07-01

Mount Endut is located at Banten Province, 40 km southward Rangkasbitung City, with geographic UTM position between 9261000-9274000 N and 639000-652000 E. Preliminary survey at Mt. Endut was geological and geochemical survey in 2006, resistivity survey and MT survey in 2007 with 27 measurement point. All survey conducted by Pusat Sumber Daya Geologi (PSDG). According to result of premilinary survey, Mt. Endut is dominated by quartenary volcanic rock produced by Mt. Endut, which breakthrough tertiary sediment layer. NE to SW normal fault produced surface manifestation, namely Cikawah (CKW) hot spring and Handeleum (HDL) hot spring. According to SiO2 and NaK geothermometer, subsurface temperature of Mt Endut is ranging from 162 to 180 °C. Apparent resistivity maps show that thermal manifestation areas coincide with pronounced high anomaly due to resistive intrusion bodies contrast to conductive sedimentary basements. In order to delineate permeability zone, fracture fault density (FFD) analysis from remote sensing image is carry out. FFD analysis from lansdat 7 image shows the area on westward flank of Mt. Endut have high fracture fault density (162-276 m/km2), higher than it's surrounding area and can be assume that area is weak zone and have high permeability. That's structure density anomaly coincide with low resistivity from Magnetotelluric data. Resistivity structure from Magnetotelluric data shows western flank have low permeability layer (14-27 Ohmm) with average thickness 250 m. Below this layer there is layer with higher resistivity (37-100 Ohmm) with ±1000 m depth and interpreted as shallow reservoir. Massive resistif intrusive bodies act controlled the surface manifestation, and act as boundary and bounded the geothermal system in western part of Mt. Endut.

Resistant and sensitive strains of Mycobacterium tuberculosis found in repeated surveys among a South Indian rural population*

PubMed Central

Narain, Raj; Chandrasekhar, P.; Satyanarayanachar, R. A.; Lal, Pyare

1968-01-01

The findings in a highly selected group of patients, such as those attending clinics or sanatoria, cannot be used as the basis for assessing the true prevalence of strains of Mycobacterium tuberculosis with acquired or primary resistance or of sensitive strains in a community. The present report describes the prevalence of such strains as found in 3 successive surveys in a sizeable random sample of villages in a South Indian district. Changes in the status of cases with such strains from an earlier survey to a later one and the status at an earlier round of cases found at a later one are also described. The prevalence of tuberculous infection among household contacts of cases with acquired resistance to isoniazid was significantly higher than that among contacts of cases with primary resistance or of those with sensitive cultures. This is probably due to the longer duration of sputum positivity of the former at the time of diagnosis. But infectivity, as judged by the incidence of new infections among household contacts, was generally less for cases with acquired or primary resistance than for cases with sensitive cultures, though the difference was not statistically significant. A large number of culture-positive cases, especially those with primary resistance, had no radiological evidence of active pulmonary tuberculosis. The prevalence of primary resistance was very high among certain categories of cases, and the differences between cases with primary resistance and those with acquired resistance were many and large. It is suggested that this could be due to some of the primary resistant cultures being those of atypical mycobacteria, despite positivity in the niacin test. There was a significant increase in the number of cases with acquired resistance to isoniazid at the third survey round owing to irregular treatment with that drug after the second round. The prevalence of primary resistance at the 3 rounds was almost the same. PMID:4978410

Use of small scale electrical resistivity tomography to identify soil-root interactions during deficit irrigation

NASA Astrophysics Data System (ADS)

Vanella, D.; Cassiani, G.; Busato, L.; Boaga, J.; Barbagallo, S.; Binley, A.; Consoli, S.

2018-01-01

Plant roots activity affect the exchanges of mass and energy between the soil and atmosphere. However, it is challenging to monitor the activity of the root-zone because roots are not visible from the soil surface, and root systems undergo spatial and temporal variations in response to internal and external conditions. Therefore, measurements of the activity of root systems are interesting to ecohydrologists in general, and are especially important for specific applications, such as irrigation water management. This study demonstrates the use of small scale three-dimensional (3-D) electrical resistivity tomography (ERT) to monitor the root-zone of orange trees irrigated by two different regimes: (i) full rate, in which 100% of the crop evapotranspiration (ETc) is provided; and (ii) partial root-zone drying (PRD), in which 50% of ETc is supplied to alternate sides of the tree. We performed time-lapse 3-D ERT measurements on these trees from 5 June to 24 September 2015, and compared the long-term and short-term changes before, during, and after irrigation events. Given the small changes in soil temperature and pore water electrical conductivity, we interpreted changes of soil electrical resistivity from 3-D ERT data as proxies for changes in soil water content. The ERT results are consistent with measurements of transpiration flux and soil temperature. The changes in electrical resistivity obtained from ERT measurements in this case study indicate that root water uptake (RWU) processes occur at the 0.1 m scale, and highlight the impact of different irrigation schemes.

Imaging Pathways in Fractured Rock Using Three-Dimensional Electrical Resistivity Tomography.

PubMed

Robinson, Judith; Slater, Lee; Johnson, Timothy; Shapiro, Allen; Tiedeman, Claire; Ntarlagiannis, Dimitrios; Johnson, Carole; Day-Lewis, Frederick; Lacombe, Pierre; Imbrigiotta, Thomas; Lane, John

2016-03-01

Major challenges exist in delineating bedrock fracture zones because these cause abrupt changes in geological and hydrogeological properties over small distances. Borehole observations cannot sufficiently capture heterogeneity in these systems. Geophysical techniques offer the potential to image properties and processes in between boreholes. We used three-dimensional cross borehole electrical resistivity tomography (ERT) in a 9 m (diameter) × 15 m well field to capture high-resolution flow and transport processes in a fractured mudstone contaminated by chlorinated solvents, primarily trichloroethylene. Conductive (sodium bromide) and resistive (deionized water) injections were monitored in seven boreholes. Electrode arrays with isolation packers and fluid sampling ports were designed to enable acquisition of ERT measurements during pulsed tracer injections. Fracture zone locations and hydraulic pathways inferred from hydraulic head drawdown data were compared with electrical conductivity distributions from ERT measurements. Static ERT imaging has limited resolution to decipher individual fractures; however, these images showed alternating conductive and resistive zones, consistent with alternating laminated and massive mudstone units at the site. Tracer evolution and migration was clearly revealed in time-lapse ERT images and supported by in situ borehole vertical apparent conductivity profiles collected during the pulsed tracer test. While water samples provided important local information at the extraction borehole, ERT delineated tracer migration over spatial scales capturing the primary hydrogeological heterogeneity controlling flow and transport. The fate of these tracer injections at this scale could not have been quantified using borehole logging and/or borehole sampling methods alone. © 2015, National Ground Water Association.

PFLOTRAN-E4D: A parallel open source PFLOTRAN module for simulating time-lapse electrical resistivity data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Timothy C.; Hammond, Glenn E.; Chen, Xingyuan

Time-lapse electrical resistivity tomography (ERT) is finding increased application for remotely monitoring processes occurring in the near subsurface in three-dimensions (i.e. 4D monitoring). However, there are few codes capable of simulating the evolution of subsurface resistivity and corresponding tomographic measurements arising from a particular process, particularly in parallel and with an open source license. Herein we describe and demonstrate an electrical resistivity tomography module for the PFLOTRAN subsurface flow and reactive transport simulation code, named PFLOTRAN-E4D. The PFLOTRAN-E4D module operates in parallel using a dedicated set of compute cores in a master-slave configuration. At each time step, the master processesmore » receives subsurface states from PFLOTRAN, converts those states to bulk electrical conductivity, and instructs the slave processes to simulate a tomographic data set. The resulting multi-physics simulation capability enables accurate feasibility studies for ERT imaging, the identification of the ERT signatures that are unique to a given process, and facilitates the joint inversion of ERT data with hydrogeological data for subsurface characterization. PFLOTRAN-E4D is demonstrated herein using a field study of stage-driven groundwater/river water interaction ERT monitoring along the Columbia River, Washington, USA. Results demonstrate the complex nature of subsurface electrical conductivity changes, in both the saturated and unsaturated zones, arising from river stage fluctuations and associated river water intrusion into the aquifer. Furthermore, the results also demonstrate the sensitivity of surface based ERT measurements to those changes over time.« less

A method for recording resistance changes non-invasively during neuronal depolarization with a view to imaging brain activity with electrical impedance tomography.

PubMed

Gilad, Ori; Ghosh, Anthony; Oh, Dongin; Holder, David S

2009-05-30

Electrical impedance tomography (EIT) is a recently developed medical imaging method which has the potential to produce images of fast neuronal depolarization in the brain. The principle is that current remains in the extracellular space at rest but passes into the intracellular space during depolarization through open ion channels. As current passes into the intracellular space across the capacitance of cell membranes at higher frequencies, applied current needs to be below 100 Hz. A method is presented for its measurement with subtraction of the contemporaneous evoked potentials which occur in the same frequency band. Neuronal activity is evoked by stimulation and resistance is recorded from the potentials resulting from injection of a constant current square wave at 1 Hz with amplitude less than 25% of the threshold for stimulating neuronal activity. Potentials due to the evoked activity and the injected square wave are removed by subtraction. The method was validated with compound action potentials in crab walking leg nerve. Resistance changes of -0.85+/-0.4% (mean+/-SD) occurred which decreased from -0.97+/-0.43% to -0.46+/-0.16% with spacing of impedance current application electrodes from 2 to 8 mm but did not vary significantly with applied currents of 1-10 microA. These tallied with biophysical modelling, and so were consistent with a genuine physiological origin. This method appears to provide a reproducible and artefact free means for recording resistance changes during neuronal activity which could lead to the long-term goal of imaging of fast neural activity in the brain.

High-resolution proxies for wood density variations in Terminalia superba

PubMed Central

De Ridder, Maaike; Van den Bulcke, Jan; Vansteenkiste, Dries; Van Loo, Denis; Dierick, Manuel; Masschaele, Bert; De Witte, Yoni; Mannes, David; Lehmann, Eberhard; Beeckman, Hans; Van Hoorebeke, Luc; Van Acker, Joris

2011-01-01

Background and Aims Density is a crucial variable in forest and wood science and is evaluated by a multitude of methods. Direct gravimetric methods are mostly destructive and time-consuming. Therefore, faster and semi- to non-destructive indirect methods have been developed. Methods Profiles of wood density variations with a resolution of approx. 50 µm were derived from one-dimensional resistance drillings, two-dimensional neutron scans, and three-dimensional neutron and X-ray scans. All methods were applied on Terminalia superba Engl. & Diels, an African pioneer species which sometimes exhibits a brown heart (limba noir). Key Results The use of X-ray tomography combined with a reference material permitted direct estimates of wood density. These X-ray-derived densities overestimated gravimetrically determined densities non-significantly and showed high correlation (linear regression, R2 = 0·995). When comparing X-ray densities with the attenuation coefficients of neutron scans and the amplitude of drilling resistance, a significant linear relation was found with the neutron attenuation coefficient (R2 = 0·986) yet a weak relation with drilling resistance (R2 = 0·243). When density patterns are compared, all three methods are capable of revealing the same trends. Differences are mainly due to the orientation of tree rings and the different characteristics of the indirect methods. Conclusions High-resolution X-ray computed tomography is a promising technique for research on wood cores and will be explored further on other temperate and tropical species. Further study on limba noir is necessary to reveal the causes of density variations and to determine how resistance drillings can be further refined. PMID:21131386

PFLOTRAN-E4D: A parallel open source PFLOTRAN module for simulating time-lapse electrical resistivity data

DOE PAGES

Johnson, Timothy C.; Hammond, Glenn E.; Chen, Xingyuan

2016-09-22

Time-lapse electrical resistivity tomography (ERT) is finding increased application for remotely monitoring processes occurring in the near subsurface in three-dimensions (i.e. 4D monitoring). However, there are few codes capable of simulating the evolution of subsurface resistivity and corresponding tomographic measurements arising from a particular process, particularly in parallel and with an open source license. Herein we describe and demonstrate an electrical resistivity tomography module for the PFLOTRAN subsurface flow and reactive transport simulation code, named PFLOTRAN-E4D. The PFLOTRAN-E4D module operates in parallel using a dedicated set of compute cores in a master-slave configuration. At each time step, the master processesmore » receives subsurface states from PFLOTRAN, converts those states to bulk electrical conductivity, and instructs the slave processes to simulate a tomographic data set. The resulting multi-physics simulation capability enables accurate feasibility studies for ERT imaging, the identification of the ERT signatures that are unique to a given process, and facilitates the joint inversion of ERT data with hydrogeological data for subsurface characterization. PFLOTRAN-E4D is demonstrated herein using a field study of stage-driven groundwater/river water interaction ERT monitoring along the Columbia River, Washington, USA. Results demonstrate the complex nature of subsurface electrical conductivity changes, in both the saturated and unsaturated zones, arising from river stage fluctuations and associated river water intrusion into the aquifer. Furthermore, the results also demonstrate the sensitivity of surface based ERT measurements to those changes over time.« less

Contamination of the Clinical Microbiology Laboratory with Vancomycin-Resistant Enterococci and Multidrug- Resistant Enterobacteriaceae: Implications for Hospital and Laboratory Workers

PubMed Central

Collins, Susan M.; Hacek, Donna M.; Degen, Lisa A.; Wright, Marc O.; Noskin, Gary A.; Peterson, Lance R.

2001-01-01

We surveyed environmental surfaces in our clinical microbiology laboratory to determine the prevalence of vancomycin-resistant enterococci (VRE) and multidrug-resistant Enterobacteriaceae (MDRE) during a routine working day. From a total of 193 surfaces, VRE were present on 20 (10%) and MDRE were present on 4 (2%) of the surfaces tested. In a subsequent survey after routine cleaning, all of the 24 prior positive surfaces were found to be negative. Thus, those in the laboratory should recognize that many surfaces may be contaminated by resistant organisms during routine processing of patient specimens. PMID:11574615

Simulation of a small muon tomography station system based on RPCs

NASA Astrophysics Data System (ADS)

Chen, S.; Li, Q.; Ma, J.; Kong, H.; Ye, Y.; Gao, J.; Jiang, Y.

2014-10-01

In this work, Monte Carlo simulations were used to study the performance of a small muon Tomography Station based on four glass resistive plate chambers(RPCs) with a spatial resolution of approximately 1.0mm (FWHM). We developed a simulation code to generate cosmic ray muons with the appropriate distribution of energies and angles. PoCA and EM algorithm were used to rebuild the objects for comparison. We compared Z discrimination time with and without muon momentum measurement. The relation between Z discrimination time and spatial resolution was also studied. Simulation results suggest that mean scattering angle is a better Z indicator and upgrading to larger RPCs will improve reconstruction image quality.

2-D Fused Image Reconstruction approach for Microwave Tomography: a theoretical assessment using FDTD Model.

PubMed

Bindu, G; Semenov, S

2013-01-01

This paper describes an efficient two-dimensional fused image reconstruction approach for Microwave Tomography (MWT). Finite Difference Time Domain (FDTD) models were created for a viable MWT experimental system having the transceivers modelled using thin wire approximation with resistive voltage sources. Born Iterative and Distorted Born Iterative methods have been employed for image reconstruction with the extremity imaging being done using a differential imaging technique. The forward solver in the imaging algorithm employs the FDTD method of solving the time domain Maxwell's equations with the regularisation parameter computed using a stochastic approach. The algorithm is tested with 10% noise inclusion and successful image reconstruction has been shown implying its robustness.

On optimal current patterns for electrical impedance tomography.

PubMed

Demidenko, Eugene; Hartov, Alex; Soni, Nirmal; Paulsen, Keith D

2005-02-01

We develop a statistical criterion for optimal patterns in planar circular electrical impedance tomography. These patterns minimize the total variance of the estimation for the resistance or conductance matrix. It is shown that trigonometric patterns (Isaacson, 1986), originally derived from the concept of distinguishability, are a special case of our optimal statistical patterns. New optimal random patterns are introduced. Recovering the electrical properties of the measured body is greatly simplified when optimal patterns are used. The Neumann-to-Dirichlet map and the optimal patterns are derived for a homogeneous medium with an arbitrary distribution of the electrodes on the periphery. As a special case, optimal patterns are developed for a practical EIT system with a finite number of electrodes. For a general nonhomogeneous medium, with no a priori restriction, the optimal patterns for the resistance and conductance matrix are the same. However, for a homogeneous medium, the best current pattern is the worst voltage pattern and vice versa. We study the effect of the number and the width of the electrodes on the estimate of resistivity and conductivity in a homogeneous medium. We confirm experimentally that the optimal patterns produce minimum conductivity variance in a homogeneous medium. Our statistical model is able to discriminate between a homogenous agar phantom and one with a 2 mm air hole with error probability (p-value) 1/1000.

Railroad Classification Yard Technology Manual. Volume III. Freight Car Rollability

DOT National Transportation Integrated Search

1981-07-01

The report presents a survey of rolling resistance research, histograms of rolling resistance from five yards, a statistical regression analysis of causal factors affecting rolling resistance, procedures for constructing a rolling resistance histogra...

Multiscale tomography of buried magnetic structures: its use in the localization and characterization of archaeological structures

NASA Astrophysics Data System (ADS)

Saracco, Ginette; Moreau, Frédérique; Mathé, Pierre-Etienne; Hermitte, Daniel; Michel, Jean-Marie

2007-10-01

We have previously developed a method for characterizing and localizing `homogeneous' buried sources, from the measure of potential anomalies at a fixed height above ground (magnetic, electric and gravity). This method is based on potential theory and uses the properties of the Poisson kernel (real by definition) and the continuous wavelet theory. Here, we relax the assumption on sources and introduce a method that we call the `multiscale tomography'. Our approach is based on the harmonic extension of the observed magnetic field to produce a complex source by use of a complex Poisson kernel solution of the Laplace equation for complex potential field. A phase and modulus are defined. We show that the phase provides additional information on the total magnetic inclination and the structure of sources, while the modulus allows us to characterize its spatial location, depth and `effective degree'. This method is compared to the `complex dipolar tomography', extension of the Patella method that we previously developed. We applied both methods and a classical electrical resistivity tomography to detect and localize buried archaeological structures like antique ovens from magnetic measurements on the Fox-Amphoux site (France). The estimates are then compared with the results of excavations.

Feasibility study of archaeological structures scanning by muon tomography

NASA Astrophysics Data System (ADS)

Gómez, H.; Carloganu, C.; Gibert, D.; Marteau, J.; Niess, V.; Katsanevas, S.; Tonazzo, A.

2015-08-01

One of the main concerns in archaeology is to find of a method to study precisely archaeological structures in the least invasive way possible to avoid damage. The requirement of preserving the structures integrity prevents, in the case of pyramids or tumuli, the study of any internal structure (halls or tombs) which are not reachable by existing corridors. One non-invasive method is the muon tomography. By placing a detector which allows to register the muon direction after the structure, it is possible to have an idea of its composition based on the attenuation of the muon flux, which depends on the material length and density that muons have crossed. This technique, alone or together with other exploration techniques as seismic tomography or electrical resistivity tomography, can provide useful information about the internal structure of the archaeological form that can not be obtained by conventional archaeological methods. In this work, the time measurement necessary to obtain a significant result about the composition of an archaeological structure is estimated. To do that, a Monte Carlo simulation framework based on the MUSIC software, properly tuned for this study, has been developed. The particular case of the Kastas Amfipoli Macedonian tumulus has been considered to perform the simulations.

A New Dual-purpose Quality Control Dosimetry Protocol for Diagnostic Reference-level Determination in Computed Tomography.

PubMed

Sohrabi, Mehdi; Parsi, Masoumeh; Sina, Sedigheh

2018-05-17

A diagnostic reference level is an advisory dose level set by a regulatory authority in a country as an efficient criterion for protection of patients from unwanted medical exposure. In computed tomography, the direct dose measurement and data collection methods are commonly applied for determination of diagnostic reference levels. Recently, a new quality-control-based dose survey method was proposed by the authors to simplify the diagnostic reference-level determination using a retrospective quality control database usually available at a regulatory authority in a country. In line with such a development, a prospective dual-purpose quality control dosimetry protocol is proposed for determination of diagnostic reference levels in a country, which can be simply applied by quality control service providers. This new proposed method was applied to five computed tomography scanners in Shiraz, Iran, and diagnostic reference levels for head, abdomen/pelvis, sinus, chest, and lumbar spine examinations were determined. The results were compared to those obtained by the data collection and quality-control-based dose survey methods, carried out in parallel in this study, and were found to agree well within approximately 6%. This is highly acceptable for quality-control-based methods according to International Atomic Energy Agency tolerance levels (±20%).

Using Geophysics to Define Hydrostratigraphic Units in the Edwards and Trinity Aquifers, Texas

NASA Astrophysics Data System (ADS)

Smith, B. D.; Blome, C. D.; Clark, A. K.; Kress, W.; Smith, D. V.

2007-05-01

Airborne and ground geophysical surveys conducted in Uvalde, Medina, and northern Bexar counties, Texas, can be used to define and characterize hydrostratigraphic units of the Edwards and Trinity aquifers. Airborne magnetic surveys have defined numerous Cretaceous intrusive stocks and laccoliths, mainly in Uvalde County, that influence local hydrology and perhaps regional ground-water flow paths. Depositional environments in the aquifers can be classified as shallow water platforms (San Marcos Platform, Edwards Group), shoal and reef facies (Devils River Trend, Devils River Formation), and deeper water basins (Maverick Basin, West Nueces, McKnight, and Salmon Peak Formations). Detailed airborne and ground electromagnetic surveys have been conducted over the Edwards aquifer catchment zone (exposed Trinity aquifer rocks), recharge zone (exposed Edwards aquifer rocks), and artesian zone (confined Edwards) in the Seco Creek area (northeast Uvalde and Medina Counties; Devils River Trend). These geophysical survey data have been used to divide the Edwards exposed within the Balcones fault zone into upper and lower hydrostratigraphic units. Although both units are high electrical resistivity, the upper unit has slightly lower resistivity than the lower unit. The Georgetown Formation, at the top of the Edwards Group has a moderate resistivity. The formations that comprise the upper confining units to the Edwards aquifer rocks have varying resistivities. The Eagleford and Del Rio Groups (mainly clays) have very low resistivities and are excellent electrical marker beds in the Seco Creek area. The Buda Limestone is characterized by high resistivities. Moderate resistivities characterize the Austin Group rocks (mainly chalk). The older Trinity aquifer, underlying the Edwards aquifer rocks, is characterized by less limestone (electrically resistive or low conductivity units) and greater quantities of mudstones (electrically conductive or low resistivity units). In the western area (Devils River Trend and Maverick Basin) of the Trinity aquifer system there are well-defined collapse units and features that are marked by moderate resistivities bracketed by resistive limestone and conductive mudstone of the Glen Rose Limestone. In the central part of the aquifer (San Marcos Platform) the Trinity's lithologies are divided into upper and lower units with further subdivisions into hydrostratigraphic units. These hydrostratigraphic units are well mapped by an airborne electromagnetic survey in Bexar County. Electrical properties of the Edwards aquifer also vary across the fresh-saline water interface where ground and borehole electrical surveys have been conducted. The saline- saturated Edwards is predictably more conductive than the fresh-water saturated rocks. Similar fresh-saline water interfaces exist within the upper confining units of the Edwards aquifer (Carrizo-Wilcox aquifer) and the Trinity aquifer rocks.

Use of electromagnetic-terrain conductivity and DC-resistivity profiling techniques for bedrock characterization at the 15th-of-May City extension, Cairo, Egypt

NASA Astrophysics Data System (ADS)

Aly, Said A.; Farag, Karam S. I.; Atya, Magdy A.; Badr, Mohamed A. M.

2018-06-01

A joint multi-spacing electromagnetic-terrain conductivity meter and DC-resistivity horizontal profiling survey was conducted at the anticipated eastern extensional area of the 15th-of-May City, southeastern Cairo, Egypt. The main objective of the survey was to highlight the applicability, efficiency, and reliability of utilizing such non-invasive surface techniques in a field like geologic mapping, and hence to image both the vertical and lateral electrical resistivity structures of the subsurface bedrock. Consequently, a total of reliable 6 multi-spacing electromagnetic-terrain conductivity meter and 7 DC-resistivity horizontal profiles were carried out between August 2016 and February 2017. All data sets were transformed-inverted extensively and consistently in terms of two-dimensional (2D) electrical resistivity smoothed-earth models. They could be used effectively and inexpensively to interpret the area's bedrock geologic sequence using the encountered consecutive electrically resistive and conductive anomalies. Notably, the encountered subsurface electrical resistivity structures, below all surveying profiles, are correlated well with the mapped geological faults in the field. They even could provide a useful understanding of their faulting fashion. Absolute resistivity values were not necessarily diagnostic, but their vertical and lateral variations could provide more diagnostic information about the layer lateral extensions and thicknesses, and hence suggested reliable geo-electric earth models. The study demonstrated that a detailed multi-spacing electromagnetic-terrain conductivity meter and DC-resistivity horizontal profiling survey can help design an optimal geotechnical investigative program, not only for the whole eastern extensional area of the 15th-of-May City, but also for the other new urban communities within the Egyptian desert.

Scenario Evaluator for Electrical Resistivity survey pre-modeling tool

USGS Publications Warehouse

Terry, Neil; Day-Lewis, Frederick D.; Robinson, Judith L.; Slater, Lee D.; Halford, Keith J.; Binley, Andrew; Lane, John W.; Werkema, Dale D.

2017-01-01

Geophysical tools have much to offer users in environmental, water resource, and geotechnical fields; however, techniques such as electrical resistivity imaging (ERI) are often oversold and/or overinterpreted due to a lack of understanding of the limitations of the techniques, such as the appropriate depth intervals or resolution of the methods. The relationship between ERI data and resistivity is nonlinear; therefore, these limitations depend on site conditions and survey design and are best assessed through forward and inverse modeling exercises prior to field investigations. In this approach, proposed field surveys are first numerically simulated given the expected electrical properties of the site, and the resulting hypothetical data are then analyzed using inverse models. Performing ERI forward/inverse modeling, however, requires substantial expertise and can take many hours to implement. We present a new spreadsheet-based tool, the Scenario Evaluator for Electrical Resistivity (SEER), which features a graphical user interface that allows users to manipulate a resistivity model and instantly view how that model would likely be interpreted by an ERI survey. The SEER tool is intended for use by those who wish to determine the value of including ERI to achieve project goals, and is designed to have broad utility in industry, teaching, and research.

Full 3D Microwave Tomography enhanced GPR surveys: a case study

NASA Astrophysics Data System (ADS)

Catapano, Ilaria; Soldovieri, Francesco; Affinito, Antonio; Hugenschmidt, Johannes

2014-05-01

Ground Penetrating Radar (GPR) systems are well assessed non-invasive diagnostic tools capable of providing high resolution images of the inner structure of the probed spatial region. Owing to this capability, GPR systems are nowadays more and more considered in the frame of civil engineering surveys since they may give information on constructive details as well as on the aging and risk factors affecting the healthiness of an infrastructure. In this frame, accurate, reliable and easily interpretable images of the probed scenarios are mandatory in order to support the management of maintenance works and assure the safety of structures. Such a requirement motivates the use of different and sophisticated data processing approaches in order to compare more than one image of the same scene, thus improving the reliability and objectiveness of the GPR survey results. Among GPR data processing procedures, Microwave Tomography approaches based on the Born approximation face the imaging as the solution of a linear inverse problem, which is solved by using the Truncated Singular Value Decomposition as a regularized inversion scheme [1]. So far, an approach exploiting a 2D scalar model of the scattering phenomenon have been adopted to process GPR data gathered along a single scan. In this case, 3D images are obtained by interpolating 2D reconstructions (this is referred commonly as pseudo 3D imaging). Such an imaging approach have provided valuable results in several real cases dealing with not only surveys for civil engineering but also archeological prospection, subservice monitoring, security surveys and so on [1-4]. These encouraging results have motivated the development of a full 3D Microwave Tomography approach capable of accounting for the vectorial nature of the wave propagation. The reconstruction capabilities of this novel approach have been assessed mainly against experimental data collected in laboratory controlled conditions. The obtained results corroborate that, the use of a full 3D scattering model allows an improved estimation of the objects shape and size with respect to pseudo 3D imaging [5]. In this communication, the performance offered by the full 3D imaging approach is investigated by using a dataset from infrastructure inspection. Since the collapse of a car park in Switzerland killing 7 firemen, "punching", where a pile remains upright but the ceiling carried by the pile falls down, is considered a serious problem The 3D tomography approach was applied to a dataset acquired in a car park in the vicinity of piles. Such datasets can be used for an assessment of the safety of such structures and can therefore be considered as relevant test cases for innovative data processing and inversion strategies. REFERENCES [1] F. Soldovieri, J. Hugenschmidt, R. Persico and G. Leone, "A linear inverse scattering algorithm for realistic GPR applications, Near Surf. Geophys., vol. 5, pp.29-42, 2007. [2] I. Catapano, L. Crocco R. Di Napoli, F. Soldovieri, A. Brancaccio, F. Pesando, A. Aiello, "Microwave tomography enhanced GPR surveys in Centaur's Domus, Regio VI of Pompeii, Italy", J. Geophys. Eng., vol.9, S92-S99, 2012. [3] I. Catapano, R. Di Napoli, F. Soldovieri, M. Bavusi, A. Loperte, J. Dumoulin, Structural monitoring via microwave tomography-enhanced GPR: the Montagnole test site, J. Geophys. Eng., vol. 9, S100-S107, 2012 [4] J. Hugenschmidt, A. Kalogeropoulos, F. Soldovieri, G. Prisco (2010) Processing Strategies for high-resolution GPR Concrete Inspections, NDT & E International, Volume 43, Issue 4: 334-342. [5] I. Catapano, A. Affinito, G. Gennarelli, F. di Maio, A. Loperte, F. Soldovieri, Full three-dimensional imaging via ground penetrating radar: assessment in controlled conditions and on field for archaeological prospecting, Appl. Phys. A: Materials Science and Processing, pp. 1-8, Article in Press

Patterns of chloroquine use and resistance in sub-Saharan Africa: a systematic review of household survey and molecular data

PubMed Central

2011-01-01

Background As a result of widespread chloroquine and sulphadoxine-pyrimethamine (SP) resistance, 90% of sub-Saharan African countries had adopted policies of artemisinin-based combination therapy (ACT) for treatment of uncomplicated malaria by 2007. In Malawi, cessation of chloroquine use was followed by the re-emergence of chloroquine-susceptible malaria. It was expected that introduction of ACT would lead to a return in chloroquine susceptibility throughout Africa, but this has not yet widely occurred. This observation suggests that there is continuing use of ineffective anti-malarials in Africa and that persistent chloroquine-resistant malaria is due to ongoing drug pressure despite national policy changes. Methods To estimate drug use on a national level, 2006-2007 Demographic Health Survey and Multiple Indicator Cluster Survey data from 21 African countries were analysed. Resistance data were compiled by systematic review of the published literature on the prevalence of the Plasmodium falciparum chloroquine resistance transporter polymorphism at codon 76, which causes chloroquine resistance. Results Chloroquine was the most common anti-malarial used according to surveys from 14 of 21 countries analysed, predominantly in West Africa. SP was most commonly reported in two of 21 countries. Among eight countries with longitudinal molecular resistance data, the four countries where the highest proportion of children treated for fever received chloroquine (Uganda, Burkina Faso, Guinea Bissau, and Mali) also showed no significant declines in the prevalence of chloroquine-resistant infections. The three countries with low or decreasing chloroquine use among children who reported fever treatment (Malawi, Kenya, and Tanzania) had statistically significant declines in the prevalence of chloroquine resistance. Conclusions This study demonstrates that in 2006-2007, chloroquine and SP continued to be used at high rates in many African countries. In countries reporting sustained chloroquine use, chloroquine-resistant malaria persists. In contrast, a low level of estimated chloroquine use is associated with a declining prevalence of chloroquine resistance. PMID:21554692

A survey of the trichostrongylid nematode species present on UK sheep farms and associated anthelmintic control practices.

PubMed

Burgess, Charlotte G S; Bartley, Yvonne; Redman, Elizabeth; Skuce, Philip J; Nath, Mintu; Whitelaw, Fiona; Tait, Andrew; Gilleard, John S; Jackson, Frank

2012-10-26

A survey of sheep farms from across the UK was conducted to establish information on farming practices, the trichostrongylid nematode species present and anthelmintic usage. Questionnaires and faecal samples were returned from 118 farms. First stage larvae (L(1)) were cultured from faecal samples and used for PCR analysis to determine the presence/absence of selected trichostrongylid species. Teladorsagia circumcincta was the only species present on 100% of farms. Haemonchus contortus was found on ∼50% of farms and was widespread throughout the UK. The most common Trichostrongylus spp. was T. vitrinus, found on 95% of farms. Determining the anthelmintic dose rate based on the weight of the heaviest animal in the flock to avoid under dosing was carried out on 58% of farms and was associated with a significantly lower mean epg (p<0.001) in lambs. However, the weight of animals was only estimated (as opposed to animals weighed) on 32% of farms. Macrocyclic lactones (ML) were the most commonly used anthelmintic class for ewes, whilst benzimidazoles (BZ) were the most widely used in lambs. Twenty-two of the surveyed farms had confirmed anthelmintic resistance, of these, 18 had BZ resistance, one had levamisole (LEV) resistance and 3 had resistance to both BZ and LEV. No farms in this survey reported resistance to ML. Location had a significant effect on the incidence of anthelmintic resistance on the farms in this survey (p=0.002). There was evidence of a lower risk of anthelmintic resistance occurring on farms from Scotland compared to those in England (p(f)=0.047) and Wales (p(f)=0.012). Farm type, flock type and open or closed status did not have any significant effect on the incidence of anthelmintic resistance when all other factors were taken into consideration. Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.

Seeing a Mycobacterium-Infected Cell in Nanoscale 3D: Correlative Imaging by Light Microscopy and FIB/SEM Tomography

PubMed Central

Beckwith, Marianne Sandvold; Beckwith, Kai Sandvold; Sikorski, Pawel; Skogaker, Nan Tostrup

2015-01-01

Mycobacteria pose a threat to the world health today, with pathogenic and opportunistic bacteria causing tuberculosis and non-tuberculous disease in large parts of the population. Much is still unknown about the interplay between bacteria and host during infection and disease, and more research is needed to meet the challenge of drug resistance and inefficient vaccines. This work establishes a reliable and reproducible method for performing correlative imaging of human macrophages infected with mycobacteria at an ultra-high resolution and in 3D. Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) tomography is applied, together with confocal fluorescence microscopy for localization of appropriately infected cells. The method is based on an Aclar poly(chloro-tri-fluoro)ethylene substrate, micropatterned into an advantageous geometry by a simple thermomoulding process. The platform increases the throughput and quality of FIB/SEM tomography analyses, and was successfully applied to detail the intracellular environment of a whole mycobacterium-infected macrophage in 3D. PMID:26406896

Experimental measurement of oil-water two-phase flow by data fusion of electrical tomography sensors and venturi tube

NASA Astrophysics Data System (ADS)

Liu, Yinyan; Deng, Yuchi; Zhang, Maomao; Yu, Peining; Li, Yi

2017-09-01

Oil-water two-phase flows are commonly found in the production processes of the petroleum industry. Accurate online measurement of flow rates is crucial to ensure the safety and efficiency of oil exploration and production. A research team from Tsinghua University has developed an experimental apparatus for multiphase flow measurement based on an electrical capacitance tomography (ECT) sensor, an electrical resistance tomography (ERT) sensor, and a venturi tube. This work presents the phase fraction and flow rate measurements of oil-water two-phase flows based on the developed apparatus. Full-range phase fraction can be obtained by the combination of the ECT sensor and the ERT sensor. By data fusion of differential pressures measured by venturi tube and the phase fraction, the total flow rate and single-phase flow rate can be calculated. Dynamic experiments were conducted on the multiphase flow loop in horizontal and vertical pipelines and at various flow rates.

Determination of Sinkholes with Different Geophysical Techniques; A Case Study in Yarımburgaz, Küçükçekmece Lake NW Istanbul, Turkey

NASA Astrophysics Data System (ADS)

Karabulut, Savas; Cengiz Cinku, Mualla; Tezel, Okan; Dedecan, Hasan; Oygo, Azat

2016-04-01

The Yarımburgaz cave which is located in the city of Istanbul, NW Turkey plays an important host to the first human culture and preserve significant archaeological and paleontological resources. The cave was formed as a result of a subterranean stream erosion on the limestones of the Eocene Kırklareli formation. It has been reported that a double cave with upper and lower entrance chambers exist, although no geophysical research was conducted to detect the cave's trunk passages and the extend of the sediment fill inside the cave. The aim of this study was to test the preferred order for detection the response to different geophysical methods applied on the cave. We therefore carried out an a series of geophysical study to determine the size, position, and depth of sinkholes inside the caves. Integrated methodological approaches including multichannel analysis of surface wave (MASW) 2- microtremor array method, 3-single station microtremor measurements, 4- electrical tomography (ET) measuruments and 5-microgravity imaging showed that the geophysical response was succesfully applied. Based upon the flow-chart we concluded that the microgravity survey should be applied as a first step to detect the air-filled void and the geometry of the cave. The electric tomography method was well applied showing high resistivity values across the voids. The surface wave method showed that the low-velocity zones are detected in various locations of the cave. In addition we the results of MASW and ReMi methods showed clearly the density variation in the lateral direction. Fundamental frequency value above void decraese according the properties of geological units in lateral directional, especially when they are engineering rock like limestone.

Geoelectrical Tomographies for the study of some landslide areas in the Lucanian Apennine Chain (Southern Italy)

NASA Astrophysics Data System (ADS)

Perrone, A.; Lapenna, V.; Piscitelli, S.; Rizzo, E.; Sdao, F.

2003-04-01

In the frame of the two projects supported by the Italian Ministry of Research: "Design of geophysical monitoring network in areas of the Basilicata Region characterized by a high hydrogeological hazard" and "Geomorphological study and landslides control in some areas of the Basilicata region characterized by historical-cultural heritage", we developed a research activity focussed on a 2D electromagnetic monitoring and modelling of landslide bodies. Basilicata region (Southern Italy), being dissected by numerous and often significant rivers and characterized by the outcrop of terrains with bad mechanical properties, is one of the more exposed regions of the southern Apennine chain to hydrogeologic hazard and shows a complete panorama of mass movements. In order to study some landslide areas located in the Basilicata region, such as Varco Izzo, Latronico, Campomaggiore and Maratea, we carried out 2D electrical resistivity imaging (ERI), 2D-3D self-potential tomographies and maps, combining advanced technologies for data acquisition and new methods for data inversion (Loke and Barker, 1996; McCann and Forster, 1990; Patella, 1997). The geophysical results allowed us: to outline the discontinuity between landslide material and bedrock, to identify the possible reactivation surfaces, to obtain useful information about the thickness of the mobilised material and the main patterns of the underground fluid flow. Geophysical results were compared with the data coming from geological and hydrogeological surveys and from the analysis of aerial photo and boreholes. The good correlation between the main anomalous geoelectrical zones, the main structural lineaments and hydrogeological characteristics of the investigated areas, allowed us to consider the used geoelectrical methods as a possible powerful tool to investigate landslide areas characterised by very complex geology.

Joint inversion of hydraulic head and self-potential data associated with harmonic pumping tests

NASA Astrophysics Data System (ADS)

Soueid Ahmed, A.; Jardani, A.; Revil, A.; Dupont, J. P.

2016-09-01

Harmonic pumping tests consist in stimulating an aquifer by the means of hydraulic stimulations at some discrete frequencies. The inverse problem consisting in retrieving the hydraulic properties is inherently ill posed and is usually underdetermined when considering the number of well head data available in field conditions. To better constrain this inverse problem, we add self-potential data recorded at the ground surface to the head data. The self-potential method is a passive geophysical method. Its signals are generated by the groundwater flow through an electrokinetic coupling. We showed using a 3-D saturated unconfined synthetic aquifer that the self-potential method significantly improves the results of the harmonic hydraulic tomography. The hydroelectric forward problem is obtained by solving first the Richards equation, describing the groundwater flow, and then using the result in an electrical Poisson equation describing the self-potential problem. The joint inversion problem is solved using a reduction model based on the principal component geostatistical approach. In this method, the large prior covariance matrix is truncated and replaced by its low-rank approximation, allowing thus for notable computational time and storage savings. Three test cases are studied, to assess the validity of our approach. In the first test, we show that when the number of harmonic stimulations is low, combining the harmonic hydraulic and self-potential data does not improve the inversion results. In the second test where enough harmonic stimulations are performed, a significant improvement of the hydraulic parameters is observed. In the last synthetic test, we show that the electrical conductivity field required to invert the self-potential data can be determined with enough accuracy using an electrical resistivity tomography survey using the same electrodes configuration as used for the self-potential investigation.

Slope failures evaluation and landslides investigation using 2-D resistivity method

NASA Astrophysics Data System (ADS)

Nordiana, M. M.; Azwin, I. N.; Nawawi, M. N. M.; Khalil, A. E.

2018-06-01

Slope failure is a complex phenomenon that may caused to landslides. Buildings and infrastructure such as transportation facilities and pipelines located within the boundaries of a landslide can be damaged or destroyed. Slope failure classification and various factors contributing to the instability using 2-D resistivity survey conducted in Selangor, Malaysia are described. Six 2-D resistivity survey lines with 5 m minimum electrode spacing using Pole-dipole array were performed. The data were processed using Res2Dinv and surfer10 software to evaluate the subsurface characteristics. The 2-D resistivity results show that the subsurface consist of two main zones. The first zone was alluvium or highly weathered with resistivity value of 100-1000 Ω m and depth of >30 m. This zone consists of saturated area with resistivity value of 1-100 Ω m and boulders with resistivity value of 1200-7000 Ω m. The second zone with resistivity value of >7000 Ω m was interpreted as granitic bedrock. The study area was characterized by saturated zones, highly weathered zone, highly contain of sand and boulders that will trigger slope failure in the survey area. This will cause to low strength of soil, debris flow and movement of earth. On the basis of the case examples described, 2-D resistivity method is categorized into desirable and useful method in determination of slope failure and future assessments.

Insecticide resistance in house flies from the United States: Resistance levels and frequency of pyrethroid resistance alleles

USDA-ARS?s Scientific Manuscript database

Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein we report the first widespread survey of insecticide resistance ever undertaken for the house fly, Musca domestica, a major pest of a...

Evolving electrical SCLM models of the Australian continent - results of the South Australia AusLAMP deployment

NASA Astrophysics Data System (ADS)

Robertson, K. E.; Thiel, S.; Heinson, G. S.

2017-12-01

The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) is an Australian initiative to map the Australian continental lithosphere using magnetotelluric (MT) stations to obtain a resistivity model of the subsurface. It is a joint project between Geoscience Australia, state surveys, and Universities. We present new MT 3D inversion results of the largest coherent array of the AusLAMP MT deployments to date covering two-thirds of South Australia, funded largely by the Geological Survey of South Australia with additional funding by Geoscience Australia and The University of Adelaide. The model extends across the South Australian Gawler Craton, including the Eucla Basin to the west of the craton and the Flinders Ranges and Curnamona Province to the east. The MT array covers parts of the Australian lithosphere, which has been largely unexplored with seismic tomography methods and provide a unique insight into the tectonic evolution of the continent. We incorporate 284 long-period (10s-10,000s) MT stations separated roughly every half degree latitude and longitude across an area spanning 1200 km x 800 km, south of latitude -28.5 degrees and from longitude 129 degrees to 141 degrees. We invert 24 discrete periods of the impedance tenor between 7 s and 13,000 s, and 22 different periods of the tipper data between 7s-8000 s period. The results show a heterogeneous lower crust and mantle lithosphere with a primarily resistive mantle (>1000 Ωm) lithosphere in the central and western part of the Gawler Craton and Eucla Domain. The model shows a generally NS oriented electric LAB offset from deeper cratonic lithosphere in the west to a shallow lithosphere along the eastern margin of the Gawler Craton extending further east towards the Proterozoic and Phanerozoic eastern part of Australia. The lower crust is generally resistive with elongated lower crustal conductivity anomalies, which are associated with major translithospheric shear zones likely existent since the Archean/Proterozoic and coincident with the craton margins of the Gawler Craton. The geometry of the elongated shear zones follows major trends in the gravity field, isotope geochemistry and location of prospective mineral occurrences. Therefore, these zones reflect areas of enhanced fertility and metasomatism of the continental lithosphere.

Coincident Above- and Below-ground Autonomous Monitoring to Quantify Co-variability in Permafrost, Soil and Vegetation Properties in Arctic Tundra: Supporting Data

DOE Data Explorer

Baptiste Dafflon; Rusen Oktem; John Peterson; Craig Ulrich; Anh Phuong Tran; Vladimir Romanovsky; Susan Hubbard

2017-05-10

The dataset contains measurements obtained through electrical resistivity tomography (ERT) to monitor soil properties, pole-mounted optical cameras to monitor vegetation dynamics, point probes to measure soil temperature, and periodic manual measurements of thaw layer thickness, snow thickness and soil dielectric permittivity.

A new head phantom with realistic shape and spatially varying skull resistivity distribution.

PubMed

Li, Jian-Bo; Tang, Chi; Dai, Meng; Liu, Geng; Shi, Xue-Tao; Yang, Bin; Xu, Can-Hua; Fu, Feng; You, Fu-Sheng; Tang, Meng-Xing; Dong, Xiu-Zhen

2014-02-01

Brain electrical impedance tomography (EIT) is an emerging method for monitoring brain injuries. To effectively evaluate brain EIT systems and reconstruction algorithms, we have developed a novel head phantom that features realistic anatomy and spatially varying skull resistivity. The head phantom was created with three layers, representing scalp, skull, and brain tissues. The fabrication process entailed 3-D printing of the anatomical geometry for mold creation followed by casting to ensure high geometrical precision and accuracy of the resistivity distribution. We evaluated the accuracy and stability of the phantom. Results showed that the head phantom achieved high geometric accuracy, accurate skull resistivity values, and good stability over time and in the frequency domain. Experimental impedance reconstructions performed using the head phantom and computer simulations were found to be consistent for the same perturbation object. In conclusion, this new phantom could provide a more accurate test platform for brain EIT research.

Influence of microstructure on the fretting resistance of Al-Cu-Li alloys

NASA Astrophysics Data System (ADS)

Delacroix, Jessica; Cazottes, Sophie; Daniélou, Armelle; Fouvry, Siegfried; Buffiere, Jean-Yves

The resistance of two Al-Cu-Li alloys (2050 and 2196) to fretting has been investigated. For each material two heat treatments have been studied (T8 and low temperature ageing). Fretting tests with a cylinder-plane configuration have been performed in the partial slip regime. The results obtained show that the low temperature temper gives a better resistance to fretting crack initiation and propagation than the T8 temper for both alloys. The 3D shape of the fretting cracks has been observed by high resolution synchrotron X-ray tomography. Multiple initiation sites were observed below the contact. In their early stages of development, the fretting cracks grow approximately radially within the material leading to thumb nail cracks which eventually merge laterally. The difference in fretting resistance is analysed with respect to the 3D fracture surface of the fretting cracks in relation with the alloys precipitation state.

Comparison of magnetic resonance imaging and computed tomography in suspected lesions in the posterior cranial fossa.

PubMed Central

Teasdale, G. M.; Hadley, D. M.; Lawrence, A.; Bone, I.; Burton, H.; Grant, R.; Condon, B.; Macpherson, P.; Rowan, J.

1989-01-01

OBJECTIVE--To compare computed tomography and magnetic resonance imaging in investigating patients suspected of having a lesion in the posterior cranial fossa. DESIGN--Randomised allocation of newly referred patients to undergo either computed tomography or magnetic resonance imaging; the alternative investigation was performed subsequently only in response to a request from the referring doctor. SETTING--A regional neuroscience centre serving 2.7 million. PATIENTS--1020 Patients recruited between April 1986 and December 1987, all suspected by neurologists, neurosurgeons, or other specialists of having a lesion in the posterior fossa and referred for neuroradiology. The groups allocated to undergo computed tomography or magnetic resonance imaging were well matched in distributions of age, sex, specialty of referring doctor, investigation as an inpatient or an outpatient, suspected site of lesion, and presumed disease process; the referring doctor's confidence in the initial clinical diagnosis was also similar. INTERVENTIONS--After the patients had been imaged by either computed tomography or magnetic resonance (using a resistive magnet of 0.15 T) doctors were given the radiologist's report and a form asking if they considered that imaging with the alternative technique was necessary and, if so, why; it also asked for their current diagnoses and their confidence in them. MAIN OUTCOME MEASURES--Number of requests for the alternative method of investigation. Assessment of characteristics of patients for whom further imaging was requested and lesions that were suspected initially and how the results of the second imaging affected clinicians' and radiologists' opinions. RESULTS--Ninety three of the 501 patients who initially underwent computed tomography were referred subsequently for magnetic resonance imaging whereas only 28 of the 493 patients who initially underwent magnetic resonance imaging were referred subsequently for computed tomography. Over the study the number of patients referred for magnetic resonance imaging after computed tomography increased but requests for computed tomography after magnetic resonance imaging decreased. The reason that clinicians gave most commonly for requesting further imaging by magnetic resonance was that the results of the initial computed tomography failed to exclude their suspected diagnosis (64 patients). This was less common in patients investigated initially by magnetic resonance imaging (eight patients). Management of 28 patients (6%) imaged initially with computed tomography and 12 patients (2%) imaged initially with magnetic resonance was changed on the basis of the results of the alternative imaging. CONCLUSIONS--Magnetic resonance imaging provided doctors with the information required to manage patients suspected of having a lesion in the posterior fossa more commonly than computed tomography, but computed tomography alone was satisfactory in 80% of cases... PMID:2506965

Two-dimensional finite element modelling of the neonatal head.

PubMed

Gibson, A; Bayford, R H; Holder, D S

2000-02-01

Electrical impedance tomography (EIT) could allow the early diagnosis of infant brain injury following birth asphyxia. The purpose of this work was to determine the effect of variations in skull, scalp or cerebrospinal fluid (CSF) resistivity, as these vary in clinical conditions and could degrade image quality. These factors were investigated using finite element models of the adult and neonatal head. The results suggest that there is a wide range over which the resistivity of the neonatal skull has little effect on the sensitivity to a central impedance change. The scalp and CSF appear to shunt current away from the brain; when their resistivity was decreased from normal values, this shunting effect increased and caused a decrease in sensitivity to a central resistance change. The resistivity of neonatal skull has not, to our knowledge, been directly measured and will anyway vary within and between individuals; this work suggests that EIT will be relatively insensitive to variations in neonatal skull impedance.

A high-strength silicide phase in a stainless steel alloy designed for wear-resistant applications.

PubMed

Bowden, D; Krysiak, Y; Palatinus, L; Tsivoulas, D; Plana-Ruiz, S; Sarakinou, E; Kolb, U; Stewart, D; Preuss, M

2018-04-10

Hardfacing alloys provide strong, wear-resistant and corrosion-resistant coatings for extreme environments such as those within nuclear reactors. Here, we report an ultra-high-strength Fe-Cr-Ni silicide phase, named π-ferrosilicide, within a hardfacing Fe-based alloy. Electron diffraction tomography has allowed the determination of the atomic structure of this phase. Nanohardness testing indicates that the π-ferrosilicide phase is up to 2.5 times harder than the surrounding austenite and ferrite phases. The compressive strength of the π-ferrosilicide phase is exceptionally high and does not yield despite loading in excess of 1.6 GPa. Such a high-strength silicide phase could not only provide a new type of strong, wear-resistant and corrosion-resistant Fe-based coating, replacing more costly and hazardous Co-based alloys for nuclear applications, but also lead to the development of a new class of high-performance silicide-strengthened stainless steels, no longer reliant on carbon for strengthening.

A study of building the hydrogeological apparent model with geoelectrical measurements for the Chia-Nan Coastal Plain of SW Taiwan

NASA Astrophysics Data System (ADS)

Chang, P. Y.; Tsai, J. P.; Chang, L. C.

2016-12-01

In the study we used the resistivity measurements collected in the Chia-Nan coastal plain of SW Taiwan to establish a three-dimensional (3D) hydrogeological apparent model. The resistivity measurements include data from half-Schlumberger surveys conducted during the year of 1990-2000 across the entire area and from the recent two-dimensional resistivity surveys for characterizing the recharge zone boundaries. Core records from monitoring wells in the area were used for the training data to help determining the resistivity ranges of the gavel, sand, and muddy sediments in the coastal plain. These resistivity measurements were inverted and converted into 1-D data form and interpolated for rendering a three dimensional resistivity volume that represents the general resistivity distribution in the coastal-plain systems. In addition we used water resistivity data from the observation wells to calculating the formation factors (FI) and to render the FI model. We then compared the FIs with indexed core records near some of the resistivity surveys sites, and concluded the range of the FIs for different materials in a statistical sense. Lastly we transfer the FI model into the gravel-sand-clay apparent model with the classification criteria from previous petrophysical analysis. Because there are more resistivity measurements than the limited geological boreholes, the apparent model is better to represent the detailed sedimentary structures than the traditional over-simplified conceptual models.

Helicopter Electromagnetic and Magnetic Geophysical Survey Data for Portions of the North Platte River and Lodgepole Creek, Nebraska, June 2008

USGS Publications Warehouse

Smith, Bruce D.; Abraham, Jared D.; Cannia, James C.; Hill, Patricia

2009-01-01

This report is a release of digital data from a helicopter electromagnetic and magnetic survey that was conducted during June 2008 in areas of western Nebraska as part of a joint hydrologic study by the North Platte Natural Resource District, South Platte Natural Resource District, and U.S. Geological Survey. The objective of the contracted survey, conducted by Fugro Airborne, Ltd., was to improve the understanding of the relationship between surface water and groundwater systems critical to developing groundwater models used in management programs for water resources. The survey covered 1,375 line km (854 line mi). A unique aspect of this survey is the flight line layout. One set of flight lines were flown paralleling each side of the east-west trending North Platte River and Lodgepole Creek. The survey also included widely separated (10 km) perpendicular north-south lines. The success of this survey design depended on a well understood regional hydrogeologic framework and model developed by the Cooperative Hydrologic Study of the Platte River Basin. Resistivity variations along lines could be related to this framework. In addition to these lines, more traditional surveys consisting of parallel flight lines separated by about 270 m were carried out for one block in each of the drainages. These surveys helped to establish the spatial variations of the resistivity of hydrostratigraphic units. The electromagnetic equipment consisted of six different coil-pair orientations that measured resistivity at separated frequencies from about 400 Hz to about 140,000 Hz. The electromagnetic data along flight lines were converted to electrical resistivity. The resulting line data were converted to geo-referenced grids and maps which are included with this report. In addition to the electromagnetic data, total field magnetic data and digital elevation data were collected. Data released in this report consist of data along flight lines, digital grids, and digital maps of the apparent resistivity and total magnetic field. The depth range of the subsurface investigation for the electromagnetic survey (estimated as deep as 60 m) is comparable to the depth of shallow aquifers. The geophysical data and hydrologic information from U.S. Geological Survey and cooperator studies are being used by resource managers to develop groundwater resource plans for the area. In addition, data will be used to refine hydrologic models in western Nebraska.

Prevalence of drug-resistant tuberculosis and imputed burden in South Africa: a national and sub-national cross-sectional survey.

PubMed

Ismail, Nazir Ahmed; Mvusi, Lindiwe; Nanoo, Ananta; Dreyer, Andries; Omar, Shaheed V; Babatunde, Sanni; Molebatsi, Thabo; van der Walt, Martie; Adelekan, Adeboye; Deyde, Varough; Ihekweazu, Chikwe; Madhi, Shabir A

2018-04-20

Globally, per-capita, South Africa reports a disproportionately high number of cases of multidrug-resistant (MDR) tuberculosis and extensively drug-resistant (XDR) tuberculosis. We sought to estimate the prevalence of resistance to tuberculosis drugs in newly diagnosed and retreated patients with tuberculosis provincially and nationally, and compared these with the 2001-02 estimates. A cross-sectional survey was done between June 15, 2012-June 14, 2014, using population proportionate randomised cluster sampling in the nine provinces in South Africa. 343 clusters were included, ranging between 31 and 48 per province. A patient was eligible for inclusion in the survey if he or she presented as a presumptive case during the intake period at a drug resistance survey enrolling facility. Consenting participants (≥18 years old) completed a questionnaire and had a sputum sample tested for resistance to first-line and second-line drugs. Analysis was by logistic regression with robust SEs, inverse probability weighted against routine data, and estimates were derived using a random effects model. 101 422 participants were tested in 2012-14. Nationally, the prevalence of MDR tuberculosis was 2·1% (95% CI 1·5-2·7) among new tuberculosis cases and 4·6% (3·2-6·0) among retreatment cases. The provincial point prevalence of MDR tuberculosis ranged between 1·6% (95% CI 0·9-2·9) and 5·1% (3·7-7·0). Overall, the prevalence of rifampicin-resistant tuberculosis (4·6%, 95% CI 3·5-5·7) was higher than the prevalence of MDR tuberculosis (2·8%, 2·0-3·6; p=0·01). Comparing the current survey with the previous (2001-02) survey, the overall MDR tuberculosis prevalence was 2·8% versus 2·9% and prevalance of rifampicin-resistant tuberculosis was 3·4% versus 1·8%, respectively. The prevalence of isoniazid mono-resistant tuberculosis was above 5% in all provinces. The prevalence of ethionamide and pyrazinamide resistance among MDR tuberculosis cases was 44·7% (95% CI 25·9-63·6) and 59·1% (49·0-69·1), respectively. The prevalence of XDR tuberculosis was 4·9% (95% CI 1·0-8·8). Nationally, the estimated numbers of cases of rifampicin-resistant tuberculosis, MDR tuberculosis, and isoniazid mono-resistant tuberculosis for 2014 were 13 551, 8249, and 17 970, respectively. The overall prevalence of MDR tuberculosis in South Africa in 2012-14 was similar to that in 2001-02; however, prevalence of rifampicin-resistant tuberculosis almost doubled among new cases. Furthermore, the high prevalence of isoniazid mono-resistant tuberculosis, not routinely screened for, and resistance to second-line drugs has implications for empirical management. President's Emergency Plan for AIDS Relief through the Centers for Disease Control and Prevention under the terms of 1U19GH000571. Copyright © 2018 Elsevier Ltd. All rights reserved.

Imaging Saltwater Intrusion Along the Coast of Monterey Bay Using Long-Offset Electrical Resistivity Tomography

NASA Astrophysics Data System (ADS)

Goebel, M.; Knight, R. J.; Pidlisecky, A.

2016-12-01

Coastal regions represent a complex dynamic interface where saltwater intrusion moves seawater landward and groundwater discharge moves freshwater seaward. These processes can have a dramatic impact on water quality, affecting both humans and coastal ecosystems. The ability to map the subsurface distribution of fresh and salt water is a critical step in predicting and managing water quality in coastal regions. This is commonly accomplished using wells, which are expensive and provide point information, which may fail to capture the spatial complexity in subsurface conditions. We present an alternate method for acquiring data, long-offset Electrical Resistivity Tomography (ERT), which is non-invasive, cost effective, and can address the problem of poor spatial sampling. This geophysical method can produce continuous profiles of subsurface electrical resistivity to a depth of 300 m, with spatial resolution on the order of tens of meters. Our research focuses on the Monterey Bay region, where sustained groundwater extraction over the past century has led to significant saltwater intrusion. ERT was acquired along 40 kilometers of the coast using the roll along method, allowing for continuous overlap in data acquisition. Electrodes were spaced every 22.2 m, with a total of 81 electrodes along the 1.8 km active cable length. The data show a complex distribution of fresh and salt water, influenced by geology, groundwater pumping, recharge, and land-use. While the inverted ERT resistivity profiles correspond well with existing data sets and geologic interpretations in the region, the spatial complexity revealed through the ERT data goes beyond what is known from traditional data sources alone. This leads us to conclude that this form of data can be extremely useful in informing and calibrating groundwater flow models, making targeted management decisions, and monitoring changes in subsurface salinities over time.

PFLOTRAN-E4D: A parallel open source PFLOTRAN module for simulating time-lapse electrical resistivity data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Timothy C.; Hammond, Glenn E.; Chen, Xingyuan

Time-lapse electrical resistivity tomography (ERT) is finding increased application for remotely monitoring processes occurring in the near subsurface in three-dimensions (i.e. 4D monitoring). However, there are few codes capable of simulating the evolution of subsurface resistivity and corresponding tomographic measurements arising from a particular process, particularly in parallel and with an open source license. Herein we describe and demonstrate an electrical resistivity tomography module for the PFLOTRAN subsurface simulation code, named PFLOTRAN-E4D. The PFLOTRAN-E4D module operates in parallel using a dedicated set of compute cores in a master-slave configuration. At each time step, the master processes receives subsurface states frommore » PFLOTRAN, converts those states to bulk electrical conductivity, and instructs the slave processes to simulate a tomographic data set. The resulting multi-physics simulation capability enables accurate feasibility studies for ERT imaging, the identification of the ERT signatures that are unique to a given process, and facilitates the joint inversion of ERT data with hydrogeological data for subsurface characterization. PFLOTRAN-E4D is demonstrated herein using a field study of stage-driven groundwater/river water interaction ERT monitoring along the Columbia River, Washington, USA. Results demonstrate the complex nature of changes subsurface electrical conductivity, in both the saturated and unsaturated zones, arising from water table changes and from river water intrusion into the aquifer. The results also demonstrate the sensitivity of surface based ERT measurements to those changes over time. PFLOTRAN-E4D is available with the PFLOTRAN development version with an open-source license at https://bitbucket.org/pflotran/pflotran-dev .« less

Exploration of buried carbonate aquifers by the inverse and forward modelling of the Controlled Source Audio-Magnetotelluric data

NASA Astrophysics Data System (ADS)

Šumanovac, Franjo; Orešković, Jasna

2018-06-01

On the selected cases, Gotalovec in the area of Pannonian basin and Baška in the Dinaridic karst area, that are representing a common hydrogeological model in both regions of Croatia, CSAMT data together with data of other geophysical methods (electrical resistivity tomography, electrical sounding and seismic reflection) enabled the definition of a reliable prognostic geological model. The model consists of carbonate aquifer which underlies an impermeable thick package of clastic deposits. There are great variations of the dolomitic aquifer depths in the Gotalovec area due to strong tectonic activity, while in the Baška area depth changes are caused by the layer folding. The CSAMT method provides the most complete data on lithological and structural relationships in cases of hydrogeological targets deeper than 100 m. Based on the presented models we can conclude that the CSAMT method can provide greater exploration depth than electrical resistivity tomography (ERT) and can be considered as a fundamental geophysical method for exploration of buried carbonate aquifers, deeper than 100 m. But, the CSAMT research may demonstrate its advantages only in the case of very dense layout of CSAMT stations (25-50 m), due to the greater sensitivity to noise in relation to resistivity methods. Interpretation of CSAMT data is more complex in relation to resistivity methods, and a forward modelling method sometimes gives better results than an inversion due to possibility of the use of additional data acquired by other geophysical methods (ERT, electrical sounding and seismic reflection). At greater depths, the resolution of all electrical methods including the CSAMT method is significantly reduced, and seismic reflection can be very useful to resolve deeper lithological interfaces.

PFLOTRAN-E4D: A parallel open source PFLOTRAN module for simulating time-lapse electrical resistivity data

NASA Astrophysics Data System (ADS)

Johnson, Timothy C.; Hammond, Glenn E.; Chen, Xingyuan

2017-02-01

Time-lapse electrical resistivity tomography (ERT) is finding increased application for remotely monitoring processes occurring in the near subsurface in three-dimensions (i.e. 4D monitoring). However, there are few codes capable of simulating the evolution of subsurface resistivity and corresponding tomographic measurements arising from a particular process, particularly in parallel and with an open source license. Herein we describe and demonstrate an electrical resistivity tomography module for the PFLOTRAN subsurface flow and reactive transport simulation code, named PFLOTRAN-E4D. The PFLOTRAN-E4D module operates in parallel using a dedicated set of compute cores in a master-slave configuration. At each time step, the master processes receives subsurface states from PFLOTRAN, converts those states to bulk electrical conductivity, and instructs the slave processes to simulate a tomographic data set. The resulting multi-physics simulation capability enables accurate feasibility studies for ERT imaging, the identification of the ERT signatures that are unique to a given process, and facilitates the joint inversion of ERT data with hydrogeological data for subsurface characterization. PFLOTRAN-E4D is demonstrated herein using a field study of stage-driven groundwater/river water interaction ERT monitoring along the Columbia River, Washington, USA. Results demonstrate the complex nature of subsurface electrical conductivity changes, in both the saturated and unsaturated zones, arising from river stage fluctuations and associated river water intrusion into the aquifer. The results also demonstrate the sensitivity of surface based ERT measurements to those changes over time. PFLOTRAN-E4D is available with the PFLOTRAN development version with an open-source license at https://bitbucket.org/pflotran/pflotran-dev.

Assessment of central airway obstruction using impulse oscillometry before and after interventional bronchoscopy.

PubMed

Handa, Hiroshi; Huang, Jyongsu; Murgu, Septimiu D; Mineshita, Masamichi; Kurimoto, Noriaki; Colt, Henri G; Miyazawa, Teruomi

2014-02-01

Spirometry is used to physiologically assess patients with central airway obstruction (CAO) before and after interventional bronchoscopy, but is not always feasible in these patients, does not localize the anatomic site of obstruction, and may not correlate with the patient's functional impairment. Impulse oscillometry may overcome these limitations. We assessed the correlations between impulse oscillometry measurements, symptoms, and type of airway narrowing, before and after interventional bronchoscopy, and whether impulse oscillometry parameters can discriminate between fixed and dynamic CAO. Twenty consecutive patients with CAO underwent spirometry, impulse oscillometry, computed tomography, dyspnea assessment, and bronchoscopy, before and after interventional bronchoscopy. The collapsibility index (the percent difference in airway lumen diameter during expiration versus during inspiration) was calculated using morphometric bronchoscopic images during quiet breathing. Variable CAO was defined as a collapsibility index of > 50%. Fixed CAO was defined as a collapsibility index of < 50%. The degree of obstruction was analyzed with computed tomography measurements. After interventional bronchoscopy, all impulse oscillometry measurements significantly improved, especially resistance at 5 Hz, which decreased from 0.67 ± 0.29kPa/L/s to 0.38 ± 0.17kPa/L/s (P < .001), and reactance at 20 Hz, which increased from -0.09 ± 0.11 to 0.03 ± 0.08 (P < .001). Changes in dyspnea score correlated with resistance at 5 Hz, the difference between the resistance at 5 Hz and the resistance at 20 Hz, and the reactance at 5 Hz, but not with spirometry measurements. The type of obstruction also correlated with dyspnea score, and showed distinct impulse oscillometry measurements. Impulse oscillometry measurements correlate with symptom improvements after interventional bronchoscopy. Impulse oscillometry might be useful to discriminate variable from fixed central airway obstruction. (University Hospital Medical Information Network, http://www.umin.ac.jp/english, ID000005322).

Airborne electromagnetic data and processing within Leach Lake Basin, Fort Irwin, California: Chapter G in Geology and geophysics applied to groundwater hydrology at Fort Irwin, California

USGS Publications Warehouse

Bedrosian, Paul A.; Ball, Lyndsay B.; Bloss, Benjamin R.; Buesch, David C.

2014-01-01

From December 2010 to January 2011, the U.S. Geological Survey conducted airborne electromagnetic and magnetic surveys of Leach Lake Basin within the National Training Center, Fort Irwin, California. These data were collected to characterize the subsurface and provide information needed to understand and manage groundwater resources within Fort Irwin. A resistivity stratigraphy was developed using ground-based time-domain electromagnetic soundings together with laboratory resistivity measurements on hand samples and borehole geophysical logs from nearby basins. This report releases data associated with the airborne surveys, as well as resistivity cross-sections and depth slices derived from inversion of the airborne electromagnetic data. The resulting resistivity models confirm and add to the geologic framework, constrain the hydrostratigraphy and the depth to basement, and reveal the distribution of faults and folds within the basin.

Computerized tomography versus magnetic resonance imaging: a comparative study in hypothalamic-pituitary and parasellar pathology.

PubMed

Webb, S M; Ruscalleda, J; Schwarzstein, D; Calaf-Alsina, J; Rovira, A; Matos, G; Puig-Domingo, M; de Leiva, A

1992-05-01

We wished to analyse the relative value of computerized tomography and magnetic resonance in patients referred for evaluation of pituitary and parasellar lesions. We performed a separate evaluation by two independent neuroradiologists of computerized tomography and magnetic resonance images ordered numerically and anonymously, with no clinical data available. We studied 40 patients submitted for hypothalamic-pituitary study; 31 were carried out preoperatively, of which histological confirmation later became available in 14. The remaining nine patients were evaluated postoperatively. Over 40 parameters relating to the bony margins, cavernous sinuses, carotid arteries, optic chiasm, suprasellar cisterns, pituitary, pituitary stalk and extension of the lesion were evaluated. These reports were compared with the initial ones offered when the scans were ordered, and with the final diagnosis. Concordance between initial computerized tomography and magnetic resonance was observed in 27 cases (67.5%); among the discordant cases computerized tomography showed the lesion in two, magnetic resonance in 10, while in the remaining case reported to harbour a microadenoma on computerized tomography the differential diagnosis between a true TSH-secreting microadenoma and pituitary resistance to thyroid hormones is still unclear. Both neuroradiologists coincided in their reports in 32 patients (80%); when the initial report was compared with those of the neuroradiologists, concordance was observed with at least one of them in 34 instances (85%). Discordant results were observed principally in microadenomas secreting ACTH or PRL and in delayed puberty. In the eight patients with Cushing's disease (histologically confirmed in six) magnetic resonance was positive in five and computerized tomography in two; the abnormal image correctly identified the side of the lesion at surgery. In patients referred for evaluation of Cushing's syndrome or hyperprolactinaemia (due to microadenomas) or after surgery, magnetic resonance is clearly preferable to computerized tomography. In macroadenomas both scans are equally diagnostic but magnetic resonance offers more information on pituitary morphology and neighbouring structures. Nevertheless, there are cases in which the results of computerized tomography and magnetic resonance will complement each other, since different parameters are analysed with each examination and discordant results are encountered.

Optical study of the DAFT/FADA galaxy cluster survey

NASA Astrophysics Data System (ADS)

Martinet, N.; Durret, F.; Clowe, D.; Adami, C.

2013-11-01

DAFT/FADA (Dark energy American French Team) is a large survey of ˜90 high redshift (0.42×10^{14} M_{⊙}) clusters with HST weak lensing oriented data, plus BVRIZJ 4m ground based follow up to compute photometric redshifts. The main goals of this survey are to constrain dark energy parameters using weak lensing tomography and to study a large homogeneous sample of high redshift massive clusters. We will briefly review the latest results of this optical survey, focusing on two ongoing works: the calculation of galaxy luminosity functions from photometric redshift catalogs and the weak lensing analysis of ground based data.

Computerized Tomography Measures During and After Artificial Lengthening of the Vocal Tract in Subjects With Voice Disorders.

PubMed

Guzman, Marco; Miranda, Gonzalo; Olavarria, Christian; Madrid, Sofia; Muñoz, Daniel; Leiva, Miguel; Lopez, Lorena; Bortnem, Cori

2017-01-01

The present study aimed to observe the effect of two types of tubes on vocal tract bidimensional and tridimensional images. Ten participants with hyperfunctional dysphonia were included. Computerized tomography was performed during production of sustained [a:], followed by sustained phonation into a drinking straw, and then repetition of sustained [a:]. A similar procedure was performed with a stirring straw after 15 minutes of vocal rest. Anatomic distances and area measures were obtained from computerized tomography midsagittal and transversal images. Vocal tract total volume was also calculated. During tube phonation, increases were measured in the vertical length of the vocal tract, oropharyngeal area, hypopharyngeal area, outlet of the epilaryngeal tube, and inlet to the lower pharynx. Also, the larynx was lower, and more closure was noted between the velum and the nasal passage. Tube phonation causes an increased total vocal tract volume, mostly because of the increased cross-sectional areas in the pharyngeal region. This change is more prominent when the tube offers more airflow resistance (stirring straw) compared with less airflow resistance (drinking straw). Based on our data and previous studies, it seems that vocal tract changes are not dependent on the voice condition (vocally trained, untrained, or disordered voices), but on the exercise itself and the type of instructions given to subjects. Tube phonation is a good option to reach therapeutic goals (eg, wide pharynx and low larynx) without giving biomechanical instructions, but only asking patients to feel easy voice and vibratory sensations. Copyright © 2017 The Voice Foundation. Published by Elsevier Inc. All rights reserved.

Quantitative Electron Tomography of Rubber Composites

NASA Astrophysics Data System (ADS)

Staniewicz, Lech; Vaudey, Thomas; Degrandcourt, Christophe; Couty, Marc; Gaboriaud, Fabien; Midgley, Paul

2014-06-01

Rubber composite materials have many applications, one example being tyre manufacture. The presence of a filler material in the composite (such as carbon black or silica) causes its mechanical properties to differ in several ways when compared to pure rubber such as viscoelastic behaviour (the Payne effect), increased tensile strength and improved wear resistance. To fully understand these properties, it is necessary to characterise how the filler material is organised on the nanoscale. Using composite materials representative of those found in tyres, this work illustrates the use of electron tomography and machine learning methods as tools to describe the percolation behaviour of the filler; in this case, we focus on the largest proportion of particles absorbed into one single object as a function of particle spacing.

2-D Fused Image Reconstruction approach for Microwave Tomography: a theoretical assessment using FDTD Model

PubMed Central

Bindu, G.; Semenov, S.

2013-01-01

This paper describes an efficient two-dimensional fused image reconstruction approach for Microwave Tomography (MWT). Finite Difference Time Domain (FDTD) models were created for a viable MWT experimental system having the transceivers modelled using thin wire approximation with resistive voltage sources. Born Iterative and Distorted Born Iterative methods have been employed for image reconstruction with the extremity imaging being done using a differential imaging technique. The forward solver in the imaging algorithm employs the FDTD method of solving the time domain Maxwell’s equations with the regularisation parameter computed using a stochastic approach. The algorithm is tested with 10% noise inclusion and successful image reconstruction has been shown implying its robustness. PMID:24058889

Assessing the Knowledge, Attitudes and Behaviors of Human and Animal Health Students towards Antibiotic Use and Resistance: A Pilot Cross-Sectional Study in the UK.

PubMed

Dyar, Oliver James; Hills, Holly; Seitz, Lara-Turiya; Perry, Alex; Ashiru-Oredope, Diane

2018-01-30

The Global Action Plan on Antimicrobial Resistance highlights the importance of training all healthcare professionals. No study has assessed patterns of students' knowledge, attitudes and practices concerning antibiotic use simultaneously across different healthcare course types. We conducted a cross-sectional multi-center survey among UK students. The survey was advertised through local survey coordinators at 25 universities. The online survey was accessible from 10th October to 17th November 2016 (before European Antibiotic Awareness Day). A total of 255 students from 25 universities participated, including students on medicine, pharmacy, nursing, physician associate, dentistry and veterinary medicine courses. Antibiotic resistance was considered to be a more important global challenge than climate change, obesity or food security ( p < 0.001). Most students (95%) believed that antibiotic resistance will be a problem for their future practice, but fewer (69%) thought that the antibiotics they will prescribe, administer or dispense will contribute to the problem. A fifth of students felt they had sufficient knowledge of antibiotic use for their future work. Our exploratory study suggests that UK human and animal healthcare students are aware of the importance of antibiotic resistance, but many still have certain misconceptions. Campaigns and improved educational efforts applying behavioral insights methodology could address these.

Exchange bias and bistable magneto-resistance states in amorphous TbFeCo thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xiaopu, E-mail: xl6ba@virginia.edu; Ma, Chung T.; Poon, S. Joseph, E-mail: sjp9x@virginia.edu

2016-01-04

Amorphous TbFeCo thin films sputter deposited at room temperature on thermally oxidized Si substrate are found to exhibit strong perpendicular magnetic anisotropy. Atom probe tomography, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy mapping have revealed two nanoscale amorphous phases with different Tb atomic percentages distributed within the amorphous film. Exchange bias accompanied by bistable magneto-resistance states has been uncovered near room temperature by magnetization and magneto-transport measurements. The exchange anisotropy originates from the exchange interaction between the ferrimagnetic and ferromagnetic components corresponding to the two amorphous phases. This study provides a platform for exchange bias and magneto-resistance switchingmore » using single-layer amorphous ferrimagnetic thin films that require no epitaxial growth.« less

Comparison of DNQ/novolac resists for e-beam exposure

NASA Astrophysics Data System (ADS)

Fedynyshyn, Theodore H.; Doran, Scott P.; Lind, Michele L.; Lyszczarz, Theodore M.; DiNatale, William F.; Lennon, Donna; Sauer, Charles A.; Meute, Jeff

1999-12-01

We have surveyed the commercial resist market with the dual purpose of identifying diazoquinone/novolac based resists that have potential for use as e-beam mask making resists and baselining these resists for comparison against future mask making resist candidates. For completeness, this survey would require that each resist be compared with an optimized developer and development process. To accomplish this task in an acceptable time period, e-beam lithography modeling was employed to quickly identify the resist and developer combinations that lead to superior resist performance. We describe the verification of a method to quickly screen commercial i-line resists with different developers, by determining modeling parameters for i-line resists from e-beam exposures, modeling the resist performance, and comparing predicted performance versus actual performance. We determined the lithographic performance of several DNQ/novolac resists whose modeled performance suggests that sensitivities of less than 40 (mu) C/cm2 coupled with less than 10-nm CD change per percent change in dose are possible for target 600-nm features. This was accomplished by performing a series of statistically designed experiments on the leading resists candidates to optimize processing variables, followed by comparing experimentally determined resist sensitivities, latitudes, and profiles of the DNQ/novolac resists a their optimized process.

Characterization of subsurface stratigraphy along the lower American River floodplain using electrical resistivity, Sacramento, California, 2011

USGS Publications Warehouse

Burton, Bethany L.; Powers, Michael H.; Ball, Lyndsay B.

2014-01-01

In July 2011, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, completed a geophysical survey using electrical resistivity along an approximately 6-mile reach of the lower American River in Sacramento, California, to map near-surface lithological variations. This survey is a part of a manifold and comprehensive study of river-flow dynamics and geologic boundary-property knowledge necessary to estimate scour potential and levee erosion risk. Data were acquired on the left (south or west) bank between river mile 5 and 10.7 as well as a short section on the right bank from river mile 5.4 to 6. Thirteen direct-current resistivity profiles and approximately 8.3 miles of capacitively coupled resisistivity data were acquired along accessible areas of the floodplain between the levee and river bank. Capacitively coupled resistivity was used as a reconnaissance tool, because it allowed for greater spatial coverage of data but with lower resolution and depth of investigation than the DC resistivity method. The study area contains Pleistocene-age alluvial deposits, dominated by gravels, sands, silts, and clays, that vary in both lateral extent and depth. Several generations of lithologic logs were used to help interpret resistivity variations observed in the resistivity models.

Resistivity profiling for mapping gravel layers that may control contaminant migration at the Amargosa Desert Research Site, Nevada

USGS Publications Warehouse

Lucius, Jeffrey E.; Abraham, Jared D.; Burton, Bethany L.

2008-01-01

Gaseous contaminants, including CFC 113, chloroform, and tritiated compounds, move preferentially in unsaturated subsurface gravel layers away from disposal trenches at a closed low-level radioactive waste-disposal facility in the Amargosa Desert about 17 kilometers south of Beatty, Nevada. Two distinct gravel layers are involved in contaminant transport: a thin, shallow layer between about 0.5 and 2.2 meters below the surface and a layer of variable thickness between about 15 and 30 meters below land surface. From 2003 to 2005, the U.S. Geological Survey used multielectrode DC and AC resistivity surveys to map these gravel layers. Previous core sampling indicates the fine-grained sediments generally have higher water content than the gravel layers or the sediments near the surface. The relatively higher electrical resistivity of the dry gravel layers, compared to that of the surrounding finer sediments, makes the gravel readily mappable using electrical resistivity profiling. The upper gravel layer is not easily distinguished from the very dry, fine-grained deposits at the surface. Two-dimensional resistivity models, however, clearly identify the resistive lower gravel layer, which is continuous near the facility except to the southeast. Multielectrode resistivity surveys provide a practical noninvasive method to image hydrogeologic features in the arid environment of the Amargosa Desert.

Aquifer Characterization and Groundwater Potential Evaluation in Sedimentary Rock Formation

NASA Astrophysics Data System (ADS)

Ashraf, M. A. M.; Yusoh, R.; Sazalil, M. A.; Abidin, M. H. Z.

2018-04-01

This study was conducted to characterize the aquifer and evaluate the ground water potential in the formation of sedimentary rocks. Electrical resistivity and drilling methods were used to develop subsurface soil profile for determining suitable location for tube well construction. The electrical resistivity method was used to infer the subsurface soil layer by use of three types of arrays, namely, the pole–dipole, Wenner, and Schlumberger arrays. The surveys were conducted using ABEM Terrameter LS System, and the results were analyzed using 2D resistivity inversion program (RES2DINV) software. The survey alignments were performed with maximum electrode spreads of 400 and 800 m by employing two different resistivity survey lines at the targeted zone. The images were presented in the form of 2D resistivity profiles to provide a clear view of the distribution of interbedded sandstone, siltstone, and shale as well as the potential groundwater zones. The potential groundwater zones identified from the resistivity results were confirmed using pumping, step drawdown, and recovery tests. The combination among the three arrays and the correlation between the well log and pumping test are reliable and successful in identifying potential favorable zones for obtaining groundwater in the study area.

Localization of self-potential sources in volcano-electric effect with complex continuous wavelet transform and electrical tomography methods for an active volcano

NASA Astrophysics Data System (ADS)

Saracco, Ginette; Labazuy, Philippe; Moreau, Frédérique

2004-06-01

This study concerns the fluid flow circulation associated with magmatic intrusion during volcanic eruptions from electrical tomography studies. The objective is to localize and characterize the sources responsible for electrical disturbances during a time evolution survey between 1993 and 1999 of an active volcano, the Piton de la Fournaise. We have applied a dipolar probability tomography and a multi-scale analysis on synthetic and experimental SP data. We show the advantage of the complex continuous wavelet transform which allows to obtain directional information from the phase without a priori information on sources. In both cases, we point out a translation of potential sources through the upper depths during periods preceding a volcanic eruption around specific faults or structural features. The set of parameters obtained (vertical and horizontal localization, multipolar degree and inclination) could be taken into account as criteria to define volcanic precursors.

Electrical Methods: Resistivity Methods

EPA Pesticide Factsheets

Surface electrical resistivity surveying is based on the principle that the distribution of electrical potential in the ground around a current-carrying electrode depends on the electrical resistivities and distribution of the surrounding soils and rocks.

Multiple-Herbicide Resistance Is Widespread in Roadside Palmer Amaranth Populations.

PubMed

Bagavathiannan, Muthukumar V; Norsworthy, Jason K

2016-01-01

Herbicide-resistant Palmer amaranth is a widespread issue in row-crop production in the Midsouthern US. Palmer amaranth is commonly found on roadside habitats in this region, but little is known on the degree of herbicide resistance in these populations. Herbicide resistance in roadside Palmer amaranth populations can represent the spread of an adaptive trait across a selective landscape. A large-scale survey was carried out in the Mississippi Delta region of eastern Arkansas to document the level of resistance in roadside Palmer amaranth populations to pyrithiobac and glyphosate, two important herbicides with broad history of use in the region. A total of 215 Palmer amaranth populations collected across 500 random survey sites were used in the evaluations. About 89 and 73% of the surveyed populations showed >90% survival to pyrithiobac and glyphosate, respectively. Further, only 3% of the populations were completely susceptible to glyphosate, while none of the populations was completely controlled by pyrithiobac. Among the 215 populations evaluated, 209 populations showed multiple resistance to both pyrithiobac and glyphosate at varying degrees. Dose-response assays confirmed the presence of high levels of herbicide resistance in the five selected populations (≥ 25-fold compared to a susceptible standard). Results demonstrate the prevalence of multiple-herbicide resistance in roadside Palmer amaranth populations in this region. Growers should be vigilant of Palmer amaranth infestation in roadsides adjacent to their fields and implement appropriate control measures to prevent likely spread of herbicide resistance into their fields.

Use of the azimuthal resistivity technique for determination of regional azimuth of transmissivity

USGS Publications Warehouse

Carlson, D.

2010-01-01

Many bedrock units contain joint sets that commonly act as preferred paths for the movement of water, electrical charge, and possible contaminants associated with production or transit of crude oil or refined products. To facilitate the development of remediation programs, a need exists to reliably determine regional-scale properties of these joint sets: azimuth of transmissivity ellipse, dominant set, and trend(s). The surface azimuthal electrical resistivity survey method used for local in situ studies can be a noninvasive, reliable, efficient, and relatively cost-effective method for regional studies. The azimuthal resistivity survey method combines the use of standard resistivity equipment with a Wenner array rotated about a fixed center point, at selected degree intervals, which yields an apparent resistivity ellipse from which joint-set orientation can be determined. Regional application of the azimuthal survey method was tested at 17 sites in an approximately 500 km2 (193 mi2) area around Milwaukee, Wisconsin, with less than 15m (50 ft) overburden above the dolomite. Results of 26 azimuthal surveys were compared and determined to be consistent with the results of two other methods: direct observation of joint-set orientation and transmissivity ellipses from multiple-well-aquifer tests. The average of joint-set trend determined by azimuthal surveys is within 2.5?? of the average of joint-set trend determined by direct observation of major joint sets at 24 sites. The average of maximum of transmissivity trend determined by azimuthal surveys is within 5.7?? of the average of maximum of transmissivity trend determined for 14 multiple-well-aquifer tests. Copyright ?? 2010 The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.

Centrifuge technique consistently overestimates vulnerability to water-stress induced cavitation in grapevines as confirmed with high resolution computed tomography

USDA-ARS?s Scientific Manuscript database

Vulnerability to cavitation is a key variable defining the limits to drought resistance in woody plants (e.g. Kursar et al., 2009). This trait is typically assessed by a vulnerability curve, which can be generated by a range of methods including dehydration (Sperry et al., 1988) air injection (Cocha...

Modelling an induced thermal plume with data from electrical resistivity tomography and distributed temperature sensing: a case study in northeast Italy

NASA Astrophysics Data System (ADS)

Cultrera, Matteo; Boaga, Jacopo; Di Sipio, Eloisa; Dalla Santa, Giorgia; De Seta, Massimiliano; Galgaro, Antonio

2018-05-01

Groundwater tracer tests are often used to improve aquifer characterization, but they present several disadvantages, such as the need to pour solutions or dyes into the aquifer system and alteration of the water's chemical properties. Thus, tracers can affect the groundwater flow mechanics and data interpretation becomes more complex, hindering effective study of ground heat pumps for low enthalpy geothermal systems. This paper presents a preliminary methodology based on a multidisciplinary application of heat as a tracer for defining the main parameters of shallow aquifers. The field monitoring techniques electrical resistivity tomography (ERT) and distributed temperature sensing (DTS) are noninvasive and were applied to a shallow-aquifer test site in northeast Italy. The combination of these measurement techniques supports the definition of the main aquifer parameters and therefore the construction of a reliable conceptual model, which is then described through the numerical code FEFLOW. This model is calibrated with DTS and validated by ERT outcomes. The reliability of the numerical model in terms of fate and transport is thereby enhanced, leading to the potential for better environmental management and protection of groundwater resources through more cost-effective solutions.

Impedance computed tomography using an adaptive smoothing coefficient algorithm.

PubMed

Suzuki, A; Uchiyama, A

2001-01-01

In impedance computed tomography, a fixed coefficient regularization algorithm has been frequently used to improve the ill-conditioning problem of the Newton-Raphson algorithm. However, a lot of experimental data and a long period of computation time are needed to determine a good smoothing coefficient because a good smoothing coefficient has to be manually chosen from a number of coefficients and is a constant for each iteration calculation. Thus, sometimes the fixed coefficient regularization algorithm distorts the information or fails to obtain any effect. In this paper, a new adaptive smoothing coefficient algorithm is proposed. This algorithm automatically calculates the smoothing coefficient from the eigenvalue of the ill-conditioned matrix. Therefore, the effective images can be obtained within a short computation time. Also the smoothing coefficient is automatically adjusted by the information related to the real resistivity distribution and the data collection method. In our impedance system, we have reconstructed the resistivity distributions of two phantoms using this algorithm. As a result, this algorithm only needs one-fifth the computation time compared to the fixed coefficient regularization algorithm. When compared to the fixed coefficient regularization algorithm, it shows that the image is obtained more rapidly and applicable in real-time monitoring of the blood vessel.

Real-time imaging of subarachnoid hemorrhage in piglets with electrical impedance tomography.

PubMed

Dai, Meng; Wang, Liang; Xu, Canhua; Li, Lianfeng; Gao, Guodong; Dong, Xiuzhen

2010-09-01

Subarachnoid hemorrhage (SAH) is one of the most severe medical emergencies in neurosurgery. Early detection or diagnosis would significantly reduce the rate of disability and mortality, and improve the prognosis of the patients. Although the present medical imaging techniques generally have high sensitivity to identify bleeding, the use of an additional, non-invasive imaging technique capable of continuously monitoring SAH is required to prevent contingent bleeding or re-bleeding. In this study, electrical impedance tomography (EIT) was applied to detect the onset of SAH modeled on eight piglets in real time, with the subsequent process being monitored continuously. The experimental SAH model was introduced by one-time injection of 5 ml fresh autologous arterial blood into the cisterna magna. Results showed that resistivity variations within the brain caused by the added blood could be detected using the EIT method and may be associated not only with the resistivity difference among brain tissues, but also with variations of cerebrospinal fluid dynamics. In conclusion, EIT has unique potential for use in clinical practice to provide invaluable real-time neuroimaging data for SAH after the improvement of electrode design, anisotropic realistic modeling and instrumentation.

Detection and quantification of intraperitoneal fluid using electrical impedance tomography.

PubMed

Sadleir, R J; Fox, R A

2001-04-01

A prototype electrical impedance tomography system was evaluated prior to its use for the detection of intraperitoneal bleeding, with the assistance of patients undergoing continuous ambulatory peritoneal dialysis (CAPD). The system was sensitive enough to detect small amounts of dialysis fluid appearing in subtractive images over short time periods. Uniform sensitivity to blood appearing anywhere within the abdominal cavity was produced using a post-reconstructive filter that corrected for changes in apparent resistivity of anomalies with their radial position. The image parameter used as an indication of fluid quantity, the resistivity index, varied approximately linearly with the quantity of fluid added. A test of the system's response to the introduction of conductive fluid out of the electrode plane (when a blood-equivalent fluid was added to the stomach) found that the sensitivity of the system was about half that observed in the electrode plane. Breathing artifacts were found to upset quantitative monitoring of intraperitoneal bleeding, but only on time scales short compared with the fluid administration rate. Longer term breathing changes, such as those due to variations in the functional residual capacity of the lungs, should ultimately limit the sensitivity over long time periods.

Assessing the performance of a cold region evapotranspiration landfill cover using lysimetry and electrical resistivity tomography.

PubMed

Schnabel, William E; Munk, Jens; Abichou, Tarek; Barnes, David; Lee, William; Pape, Barbara

2012-01-01

In order to test the efficacy ofa cold-region evapotranspiration (ET) landfill cover against a conventional compacted clay (CCL) landfill cover, two pilot scale covers were constructed in side-by-side basin lysimeters (20m x 10m x 2m) at a site in Anchorage, Alaska. The primary basis of comparison between the two lysimeters was the percolation of moisture from the bottom of each lysimeter. Between 30 April 2005 and 16 May 2006, 51.5 mm of water percolated from the ET lysimeter, compared to 50.6 mm for the the CCL lysimeter. This difference was not found to be significant at the 95% confidence level. As part of the project, electrical resistivity tomography (ERT) was utilized to measure and map soil moisture in ET lysimeter cross sections. The ERT-generated cross sections were found to accurately predict the onset and duration of lysimeter percolation. Moreover, ERT-generated soil moisture values demonstrated a strong linear relationship to lysimeter percolation rates (R-Squared = 0.92). Consequently, ERT is proposed as a reliable tool for assessing the function of field scale ET covers in the absence of drainage measurement devices.

Buprofezin susceptibility survey, resistance selection and preliminary determination of the resistance mechanism in Nilaparvata lugens (Homoptera: Delphacidae).

PubMed

Wang, Yanhua; Gao, Congfen; Xu, Zhiping; Zhu, Yu Cheng; Zhang, Jiushuang; Li, Wenhong; Dai, Dejiang; Lin, Youwei; Zhou, Weijun; Shen, Jinliang

2008-10-01

Buprofezin has been used for many years to control Nilaparvata lugens (Stål). Assessment of susceptibility change in the insect is essential for maintaining control efficiency and resistance management. Eleven-year surveys showed that most field populations were susceptible before 2004. However, substantially higher levels of resistance (up to 28-fold) were found in most of the rice fields in China after 2004. A field population was collected and periodically selected for buprofezin resistance in the laboratory. After 65 generations (56 were selected), the colony successfully obtained 3599-fold resistance to buprofezin. Synergism tests showed that O,O-diethyl-O-phenyl phosphorothioate (SV1), piperonyl butoxide (PBO) and diethyl maleate (DEM) increased buprofezin toxicity in the resistant strain by only 1.5-1.6 fold, suggesting that esterases, P450-monooxygenases and glutathione S-transferases had no substantial effect on buprofezin resistance development. The results from this study indicate that N. lugens has the potential to develop high resistance to buprofezin. A resistance management program with rotation of buprofezin and other pesticides may efficiently delay or slow down resistance development in the insect. Further investigation is also necessary to understand the resistance mechanisms in N. lugens.

Comparison of Compressed Sensing Algorithms for Inversion of 3-D Electrical Resistivity Tomography.

NASA Astrophysics Data System (ADS)

Peddinti, S. R.; Ranjan, S.; Kbvn, D. P.

2016-12-01

Image reconstruction algorithms derived from electrical resistivity tomography (ERT) are highly non-linear, sparse, and ill-posed. The inverse problem is much severe, when dealing with 3-D datasets that result in large sized matrices. Conventional gradient based techniques using L2 norm minimization with some sort of regularization can impose smoothness constraint on the solution. Compressed sensing (CS) is relatively new technique that takes the advantage of inherent sparsity in parameter space in one or the other form. If favorable conditions are met, CS was proven to be an efficient image reconstruction technique that uses limited observations without losing edge sharpness. This paper deals with the development of an open source 3-D resistivity inversion tool using CS framework. The forward model was adopted from RESINVM3D (Pidlisecky et al., 2007) with CS as the inverse code. Discrete cosine transformation (DCT) function was used to induce model sparsity in orthogonal form. Two CS based algorithms viz., interior point method and two-step IST were evaluated on a synthetic layered model with surface electrode observations. The algorithms were tested (in terms of quality and convergence) under varying degrees of parameter heterogeneity, model refinement, and reduced observation data space. In comparison to conventional gradient algorithms, CS was proven to effectively reconstruct the sub-surface image with less computational cost. This was observed by a general increase in NRMSE from 0.5 in 10 iterations using gradient algorithm to 0.8 in 5 iterations using CS algorithms.

Dissolution-Enlarged Fractures Imaging Using Electrical Resistivity Tomography (ERT)

NASA Astrophysics Data System (ADS)

Siami-Irdemoosa, Elnaz

In recent years the electrical imaging techniques have been largely applied to geotechnical and environmental investigations. These techniques have proven to be the best geophysical methods for site investigations in karst terrain, particularly when the overburden soil is clay-dominated. Karst is terrain with a special landscape and distinctive hydrological system developed by dissolution of rocks, particularly carbonate rocks such as limestone and dolomite, made by enlarging fractures into underground conduits that can enlarge into caverns, and in some cases collapse to form sinkholes. Bedding planes, joints, and faults are the principal structural guides for underground flow and dissolution in almost all karstified rocks. Despite the important role of fractures in karst development, the geometry of dissolution-enlarged fractures remain poorly unknown. These features are characterized by an strong contrast with the surrounding formations in terms of physical properties, such as electrical resistivity. Electrical resistivity tomography (ERT) was used as the primary geophysical tool to image the subsurface in a karst terrain in Greene County, Missouri. Pattern, orientation and density of the joint sets were interpreted from ERT data in the investigation site. The Multi-channel Analysis of Surface Wave (MASW) method and coring were employed to validate the interpretation results. Two sets of orthogonal visually prominent joints have been identified in the investigation site: north-south trending joint sets and west-east trending joint sets. However, most of the visually prominent joint sets are associated with either cultural features that concentrate runoff, natural surface drainage features or natural surface drainage.

Comparing measurement response and inverted results of electrical resistivity tomography instruments

USGS Publications Warehouse

Parsekian, Andrew D.; Claes, Niels; Singha, Kamini; Minsley, Burke J.; Carr, Bradley; Voytek, Emily; Harmon, Ryan; Kass, Andy; Carey, Austin; Thayer, Drew; Flinchum, Brady

2017-01-01

In this investigation, we compare the results of electrical resistivity measurements made by six commercially available instruments on the same line of electrodes to determine if there are differences in the measured data or inverted results. These comparisons are important to determine whether measurements made between different instruments are consistent. We also degraded contact resistance on one quarter of the electrodes to study how each instrument responds to different electrical connection with the ground. We find that each instrument produced statistically similar apparent resistivity results, and that any conservative assessment of the final inverted resistivity models would result in a similar interpretation for each. We also note that inversions, as expected, are affected by measurement error weights. Increased measurement errors were most closely associated with degraded contact resistance in this set of experiments. In a separate test we recorded the full measured waveform for a single four-electrode array to show how poor electrode contact and instrument-specific recording settings can lead to systematic measurement errors. We find that it would be acceptable to use more than one instrument during an investigation with the expectation that the results would be comparable assuming contact resistance remained consistent.

A Survey and Analysis of the American Public's Perceptions and Knowledge About Antibiotic Resistance

PubMed Central

Carter, Rebecca R.; Sun, Jiayang; Jump, Robin L. P.

2016-01-01

Background. Little is known about the American public's perceptions or knowledge about antibiotic-resistant bacteria or antibiotic misuse. We hypothesized that although many people recognize antibiotic resistance as a problem, they may not understand the relationship between antibiotic consumption and selection of resistant bacteria. Methods. We developed and tested a survey asking respondents about their perceptions and knowledge regarding appropriate antibiotic use. Respondents were recruited with the Amazon Mechanical Turk crowdsourcing platform. The survey, carefully designed to assess a crowd-sourced population, asked respondents to explain “antibiotic resistance” in their own words. Subsequent questions were multiple choice. Results. Of 215 respondents, the vast majority agreed that inappropriate antibiotic use contributes to antibiotic resistance (92%), whereas a notable proportion (70%) responded neutrally or disagreed with the statement that antibiotic resistance is a problem. Over 40% of respondents indicated that antibiotics were the best choice to treat a fever or a runny nose and sore throat. Major themes from the free-text responses included that antibiotic resistance develops by bacteria, or by the infection, or the body (ie, an immune response). Minor themes included antibiotic overuse and antibiotic resistance caused by bacterial adaptation or an immune response. Conclusions. Our findings indicate that the public is aware that antibiotic misuse contributes to antibiotic resistance, but many do not consider it to be an important problem. The free-text responses suggest specific educational targets, including the difference between an immune response and bacterial adaptation, to increase awareness and understanding of antibiotic resistance. PMID:27382598

Antimicrobial resistance of Salmonella enterica isolated from bulk tank milk and milk filters in the United States

USDA-ARS?s Scientific Manuscript database

Salmonella isolates were recovered from bulk tank milk as part of the National Animal Health Monitoring System (NAHMS) Dairy 2002 and 2007 surveys. In-line milk filters were also tested in the 2007 survey. The objective of this study was to determine the prevalence of antimicrobial resistance among ...

Ambient noise tomography for characterize the subsoil structure below a collapsed mine. Integration with 3D models of electric resistivity tomography and micro-gravity data inversion

NASA Astrophysics Data System (ADS)

Cárdenas-Soto, M.; Tejero, A.; Nava-Flores, M.; Zenil, D. E.; Vidal-Garcia, M.; Garcia-Serrano, A.

2016-12-01

In this work we build 3D Vs models using seismic tomography of ambient noise. The goal is to characterize the subsurface structure in order to explore the causes of a sudden mine collapse in the 2nd section of Chapultepec park, Mexico City, near to a recreation lake whose subsoil is composed of vulcano-sedimentary materials that were economically exploited in the mid-20th century, leaving a series of underground mines that were rehabilitated for the construction of the Park. In this site we record ambient noise continuously at a 250 Hz sampling rate by intervals of 30 min in three arrays of quadrangular shape with 64 - 4.5 Hz vertical geophones separated 2m. In order to confront the seismic interferometry results, we also obtain 3D models derivated from Electrical Resistivity Tomography (ERT), and inverted surface micro-gravity data. The correlograms show a well defined pulse for those pairs of receivers whose backazimut is perpendicular to the beltway, which is the main source that generates ambient noise. We show that pulses had a dispersive character due to that define a dispersion curve (fundamental mode of Rayleigh wave) whose velocity values are close to 700 m/s at a frequency of 5 Hz, and tend to average values of 380 m/s in frequencies close to 16 Hz. Then, we build tomography images from the maximum time of the envelope pulse filtering in 18 center frequencies between 4 to 16 Hz. Through the relationship f=Vs/4z we create a 3D model in function of the seudo-depth (z). This model allows to distinguish the irregularity of the subsoil around the mine colapse (5m depth), which underlies a competent structure (Vs>450 m/s) surrounded by vulcano sedimentary material with low Vs values (200 m/s). ERT model show that the low velocity zones are associated with saturation areas, result that is corroborated by low-density values derived from micro-gravity model. The results indicate that the collapse was produced by the hydrostatic imbalance of the competent materials, which are the artificial filling that covers the different mined areas.

Hydrogeophysical investigation of Logan, MT using electrical techniques and diving wave refraction tomography

NASA Astrophysics Data System (ADS)

Stipe, T. D.

2014-12-01

Logan, Montana USA is located on the Gallatin river, one of the three rivers forming the headwaters of the Missouri river. Hydrogeological studies by the Montana Bureau of Mines and Geology have assumed that the location at Logan is a pinch-point for the local Gallatin watershed. Shallow groundwater is expected to discharge into the Gallatin river because depth to bedrock near the river is shallow (~5 meters). Groundwater monitoring wells indicate dry Tertiary sediments overlying bedrock, suggesting surface and groundwater systems are disconnected. We deployed shallow seismic refraction, electrical resistivity, spontaneous potential, and electromagnetic surveys to investigate the groundwater system in the study area. Geophysical measurements were preferentially obtained near the Gallatin river and close to shallow monitoring wells. Hand samples of Mississippian aged rocks of the Madison group were collected from local outcrops to help correlate geophysical results with properties of the carbonate rich bedrock. Preliminary interpretations of geophysical data confirm the shallow bedrock and dry sediments encountered in nearby wells. These results suggest that the pinch-point is located upstream or groundwater follows a network of preferential flow paths through limestone bedrock within the study area.

Discovery of ancient Roman "highway" reveals geomorphic changes in karst environments during historic times.

PubMed

Bernardini, Federico; Vinci, Giacomo; Forte, Emanuele; Furlani, Stefano; Pipan, Michele; Biolchi, Sara; De Min, Angelo; Fragiacomo, Andrea; Micheli, Roberto; Ventura, Paola; Tuniz, Claudio

2018-01-01

Sinkholes are a well-known geologic hazard but their past occurrence, useful for subsidence risk prediction, is difficult to define, especially for ancient historic times. Consequently, our knowledge about Holocene carbonate landscapes is often limited. A multidisciplinary study of Trieste Karst (Italy), close to early Roman military fortifications, led to the identification of possible ancient road tracks, cut by at least one sinkhole. Electrical Resistivity Tomography through the sinkhole has suggested the presence of a cave below its bottom, possibly responsible of the sinkhole formation, while Ground Penetrating Radar has detected no tectonic disturbances underneath the tracks. Additionally, archaeological surveys led to the discovery of over 200 Roman shoe hobnails within or close to the investigated route. According to these data, the tracks are interpreted as the remains of a main Roman road, whose itinerary has been reconstructed for more than 4 km together with other elements of ancient landscape. Our results provide the first known evidence of a Roman main road swallowed by sinkholes and suggest that Holocene karst landscapes could be much different from what previously believed. In fact, sinkholes visible nowadays in the investigated region could have been flat areas filled by sediments up to the Roman time.

Delineating the Groundwater Recharge Zone in the Pingtung Plan , Taiwan with Electrical Resistivity Surveys

NASA Astrophysics Data System (ADS)

Wu, C.; Chang, P.; Chang, L.; Chen, J.; Huang, C.

2012-12-01

In this study we used the two-dimensional electrical resistivity imaging (ERI) method, as well as the core records of monitoring wells to help determine the groundwater recharge zone in Pingtung plain in southwestern Taiwan. Pingtung fluvial plain is one of the major groundwater resources in Taiwan which is composed of several alluvial fans deriving from the uplifted mountain area to the east and north of the plain. The thick gravel layer constitutes the main recharge area of the upper alluvial fans and the conductive clay sediments dominate most of the lower fans. With the core records, we found that, the gravel layers have higher resistivity (mostly over 200 Ohm-m) and the resistivities of the clayey layers are low (about 1~10 Ohm-m). Therefore with the resistivity surveys we can have more confidences for determining the boundary of the groundwater recharge area in the area in-between the monitoring wells. In the past two years, we have finished 24 two-dimensional electrical resistivity imaging profile lines from Meinong to Fangliao, the lines are oriented in the east-west direction, and each line was about 400 meters long. With the inverted results, we are able to characterize two major alluvial systems and their recharge zones in the Pingtung fluvial plain. The resistivities we measured almost are consistent to the core records of monitoring wells except for the Wanluan site, which shows thick gravel layer in the drilling records but has low resistivity in the nearby resistivity survey. A reasonable explanation is that the electrical resistivity is sensitive to clayey materials with lower resistivities. The intercalated clay within the gravel layers is not shown in the churn drilling records.

Describing Soils: Calibration Tool for Teaching Soil Rupture Resistance

ERIC Educational Resources Information Center

Seybold, C. A.; Harms, D. S.; Grossman, R. B.

2009-01-01

Rupture resistance is a measure of the strength of a soil to withstand an applied stress or resist deformation. In soil survey, during routine soil descriptions, rupture resistance is described for each horizon or layer in the soil profile. The lower portion of the rupture resistance classes are assigned based on rupture between thumb and…

Inference of lithologic distributions in an alluvial aquifer using airborne transient electromagnetic surveys

USGS Publications Warehouse

Dickinson, Jesse; Pool, D.R.; Groom, R.W.; Davis, L.J.

2010-01-01

An airborne transient electromagnetic (TEM) survey was completed in the Upper San Pedro Basin in southeastern Arizona to map resistivity distributions within the alluvial aquifer. This investigation evaluated the utility of 1D vertical resistivity models of the TEM data to infer lithologic distributions in an alluvial aquifer. Comparisons of the resistivity values and layers in the 1D resistivity models of airborne TEM data to 1D resistivity models of ground TEM data, borehole resistivity logs, and lithologic descriptions in drill logs indicated that the airborne TEM identified thick conductive fine-grained sediments that result in semiconfined groundwater conditions. One-dimensional models of ground-based TEM surveys and subsurface lithology at three sites were used to determine starting models and constraints to invert airborne TEM data using a constrained Marquardt-styleunderparameterized method. A maximum structural resolution of six layers underlain by a half-space was determined from the resistivity structure of the 1D models of the ground TEM data. The 1D resistivity models of the airborne TEM data compared well with the control data to depths of approximately 100 m in areas of thick conductive silt and clay and to depths of 200 m in areas of resistive sand and gravel. Comparison of a 3D interpolation of the 1D resistivity models to drill logs indicated resistive (mean of 65 ohm-m ) coarse-grained sediments along basin margins and conductive (mean of 8 ohm-m ) fine-grained sediments at the basin center. Extents of hydrologically significant thick silt and clay were well mapped by the 1D resistivity models of airborne TEM data. Areas of uncertain lithology remain below conductive fine-grained sediments where the 1D resistivity structure is not resolved: in areas where multiple lithologies have similar resistivity values and in areas of high salinity.

Proglacial Hydrogeology of the Cordillera Blanca (Peru): Integrating Field Observations with Hydrogeophysical Inversions to Inform Groundwater Flow Simulations and Conceptual Models

NASA Astrophysics Data System (ADS)

Glas, R. L.; Lautz, L.; McKenzie, J. M.; Moucha, R.; Mark, B. G.

2017-12-01

Geological and depositional conditions of the glaciated Cordillera Blanca in Peru have given way to proglacial aquifer systems that contribute substantially to regional streams and rivers, particularly during the dry season. As glacial retreat accelerates, the dry season water budget will be increasingly dominated by groundwater inputs, although predictions of future groundwater quantities require estimations of groundwater storage capacity, aquifer extents, and groundwater residence time. We present a characterization of the sediment structure in a prototypical proglacial valley in the central portion of the range, the Quilcayhuanca Valley. Northern and Central valleys of the Cordillera Blanca feature ubiquitous talus deposits that line the steep granite walls, and have become partially buried beneath lacustrine sediments deposited in proglacial lake beds. The portion of the talus still exposed near the valley walls provides recharge to deeper portions of the valley aquifers that underlie lacustrine clay, resulting in a confined aquifer system that is connected to the surface via perennial springs. Seismic refraction surveys reveal an interface separating relatively slow ( 400-800 m/s) and fast ( 2500 m/s) p-wave velocities. The depth of this refractor coincides with the depth to buried talus observed in drilling records. Electrical resistivity tomography profiles of the same transect show depths near the buried talus to be relatively conductive (10-100 Ωm). At these depths, we hypothesize that electrical conductance is elevated by saturated clay particles in the sediment matrix of the talus deposit. The resistivity models all show a more resistive ( 700 Ω m) region at depth, likely corresponding to a more hydraulically conductive material. The resistive zone is interpreted to be a deeper portion of a buried talus deposit that did not accumulate clay in the matrix. Other possibilities include a thick deposit of gravelly glacial outwash, or a relatively clay-poor glacial till. We present a groundwater modeling framework to resolve the nature of the sediments in deeper layers, where geophysical data become less certain. Sediment permeability estimates will allow for more refined predictions of groundwater storage volume in buried talus aquifers, which are likely prevalent throughout the range.

EIT images of ventilation: what contributes to the resistivity changes?

PubMed

Zhang, Jie; Patterson, Robert P

2005-04-01

One promising application of electrical impedance tomography (EIT) is the monitoring of pulmonary ventilation and edema. Using three-dimensional (3D) finite difference human models as virtual phantoms, the factors that contribute to the observed lung resistivity changes in the EIT images were investigated. The results showed that the factors included not only tissue resistivity or vessel volume changes, but also chest expansion and tissue/organ movement. The chest expansion introduced artifacts in the center of the EIT images, ranging from -2% to 31% of the image magnitude. With the increase of simulated chest expansion, the percentage contribution of chest expansion relative to lung resistivity change in the EIT image remained relatively constant. The averaged resistivity changes in the lung regions caused by chest expansion ranged from 0.65% to 18.31%. Tissue/organ movement resulted in an increased resistivity in the lung region and in the center anterior region of EIT images. The increased resistivity with inspiration observed in the heart region was caused mainly by a drop in the heart position, which reduced the heart area at the electrode level and was replaced by the lung tissue with higher resistivity. This study indicates that for the analysis of EIT, data errors caused by chest expansion and tissue/organ movement need to be considered.

Geophysical and hydrologic studies of lake seepage variability

USGS Publications Warehouse

Toran, Laura; Nyquist, Jonathan E.; Rosenberry, Donald O.; Gagliano, Michael P.; Mitchell, Natasha; Mikochik, James

2014-01-01

Variations in lake seepage were studied along a 130 m shoreline of Mirror Lake NH. Seepage was downward from the lake to groundwater; rates measured from 28 seepage meters varied from 0 to −282 cm/d. Causes of this variation were investigated using electrical resistivity surveys and lakebed sediment characterization. Two-dimensional (2D) resistivity surveys showed a transition in lakebed sediments from outwash to till that correlated with high- and low-seepage zones, respectively. However, the 2D survey was not able to predict smaller scale variations within these facies. In the outwash, fast seepage was associated with permeability variations in a thin (2 cm) layer of sediments at the top of the lakebed. In the till, where seepage was slower than that in the outwash, a three-dimensional resistivity survey mapped a point of high seepage associated with heterogeneity (lower resistivity and likely higher permeability). Points of focused flow across the sediment–water interface are difficult to detect and can transmit a large percentage of total exchange. Using a series of electrical resistivity geophysical methods in combination with hydrologic data to locate heterogeneities that affect seepage rates can help guide seepage meter placement. Improving our understanding of the causes and types of heterogeneity in lake seepage will provide better data for lake budgets and prediction of mass transfer of solutes or contaminants between lakes and groundwater.

Assessing the Knowledge, Attitudes and Behaviors of Human and Animal Health Students towards Antibiotic Use and Resistance: A Pilot Cross-Sectional Study in the UK

PubMed Central

Hills, Holly; Seitz, Lara-Turiya; Perry, Alex

2018-01-01

The Global Action Plan on Antimicrobial Resistance highlights the importance of training all healthcare professionals. No study has assessed patterns of students’ knowledge, attitudes and practices concerning antibiotic use simultaneously across different healthcare course types. We conducted a cross-sectional multi-center survey among UK students. The survey was advertised through local survey coordinators at 25 universities. The online survey was accessible from 10th October to 17th November 2016 (before European Antibiotic Awareness Day). A total of 255 students from 25 universities participated, including students on medicine, pharmacy, nursing, physician associate, dentistry and veterinary medicine courses. Antibiotic resistance was considered to be a more important global challenge than climate change, obesity or food security (p < 0.001). Most students (95%) believed that antibiotic resistance will be a problem for their future practice, but fewer (69%) thought that the antibiotics they will prescribe, administer or dispense will contribute to the problem. A fifth of students felt they had sufficient knowledge of antibiotic use for their future work. Our exploratory study suggests that UK human and animal healthcare students are aware of the importance of antibiotic resistance, but many still have certain misconceptions. Campaigns and improved educational efforts applying behavioral insights methodology could address these. PMID:29385687

3D resistivity survey for shallow subsurface fault investigations

NASA Astrophysics Data System (ADS)

Petrit, Kraipat; Klamthim, Poonnapa; Duerrast, Helmut

2018-03-01

The shallow subsurface is subject to various human activities, and the place of occurrence of geohazards, e.g. shallow active faults. The identification of the location and orientation of such faults can be vital for infrastructure development. The aim of this study was to develop a low-cost 3D resistivity survey system, with reasonable survey time for shallow fault investigations. The study area in Songkhla Province, Thailand is located in an old quarry where faults could be identified in outcrops. The study area was designed to cover the expected fault with 100 electrodes arranged in a 10×10 square grid with an electrode spacing of 3 meters in x and y axis. Each electrode in turn was used as a current and potential electrode using a dipole-dipole array. Field data have been processed and interpreted using 3DResINV. Results, presented in horizontal depth slices and vertical xz- and yz-cross sections, revealed through differences in resistivity down to 8 m depths a complex structural setting with two shallow faults and dipping sedimentary rock layers. In conclusion, this study has shown that a 3D resistivity survey can imagine complex tectonic structures, thus providing a far more insight into the shallow subsurface.

The Use of Resistivity Methods in Terrestrial Forensic Searches

NASA Astrophysics Data System (ADS)

Wolf, R. C.; Raisuddin, I.; Bank, C.

2013-12-01

The increasing use of near-surface geophysical methods in forensic searches has demonstrated the need for further studies to identify the ideal physical, environmental and temporal settings for each geophysical method. Previous studies using resistivity methods have shown promising results, but additional work is required to more accurately interpret and analyze survey findings. The Ontario Provincial Police's UCRT (Urban Search and Rescue; Chemical, Biolgical, Radiological, Nuclear and Explosives; Response Team) is collaborating with the University of Toronto and two additional universities in a multi-year study investigating the applications of near-surface geophysical methods to terrestrial forensic searches. In the summer of 2012, on a test site near Bolton, Ontario, the OPP buried weapons, drums and pigs (naked, tarped, and clothed) to simulate clandestine graves and caches. Our study aims to conduct repeat surveys using an IRIS Syscal Junior with 48 electrode switching system resistivity-meter. These surveys will monitor changes in resistivity reflecting decomposition of the object since burial, and identify the strengths and weaknesses of resistivity when used in a rural, clandestine burial setting. Our initial findings indicate the usefulness of this method, as prominent resistivity changes have been observed. We anticipate our results will help to assist law enforcement agencies in determining the type of resistivity results to expect based on time since burial, depth of burial and state of dress of the body.

Interactions between Shrubs and Permafrost in the Torngat Mountains, Northern Labrador, Canada

NASA Astrophysics Data System (ADS)

Lewkowicz, A.; Way, R. G.; Hermanutz, L.; Trant, A.; Siegwart Collier, L.; Whitaker, D.

2017-12-01

Discontinuous permafrost is acutely sensitive to climate warming and vegetation dynamics. Shrub height is positively correlated with accumulation of snow in the tundra resulting in warming of the ground in winter, and greater shading and lower surface temperatures in summer. Rapid greening due to climate warming has been observed throughout northeastern Canada and particularly in the coastal mountainous terrain of the Torngat Mountains National Park. Our research examines how this shrubification in the Torngat Mountains is modifying permafrost characteristics using observations which extend over a 100 km south-north transect from the sporadic zone (Saglek, Torr Bay) to where permafrost is widespread (Nakvak Brook, Kangalaksiorvik Lake) and potentially continuous (Komaktorvik River). We use air and ground temperature monitoring, vegetation surveys, dendrochronology, frost probing and electrical resistivity tomography (ERT) to describe the complex interactions between shrub growth, geomorphology, climate and permafrost in a region where climate warming is rapidly altering the landscape. Preliminary analysis of field data shows low resistivity anomalies in the ERT profiles at some sites with thin permafrost, interpreted as unfrozen zones correlated with areas of tall shrubs (Alnus spp., Salix spp. and Betula glandulosa; ranging from prostrate to 2 m). Elsewhere, high resistivities extend to the base of the ERT profiles, indicating thicker permafrost, and no obvious impact of medium to low-prostrate shrubs (Salix spp., Betula glandulosa, Rhododendron spp., and Vaccinium spp.; up to 50 cm). Permafrost is interpreted to be present at most sites with low or prostrate shrubs, except where hydrological conditions favour warmer ground temperatures. We infer that the net impact of increasing shrub heights on the active layer and permafrost depends on antecedent ground temperatures and surficial geology. Increasing shrub heights may cause permafrost degradation at sites where mean ground temperatures are close to 0°C and rising due to climate warming. A deeper active layer or loss of permafrost in turn could affect hydrological conditions, potentially influencing shrub size and species composition.

Interactions between Shrubs and Permafrost in the Torngat Mountains, Northern Labrador, Canada

NASA Astrophysics Data System (ADS)

Lewkowicz, A.; Way, R. G.; Hermanutz, L.; Trant, A.; Siegwart Collier, L.; Whitaker, D.

2016-12-01

Discontinuous permafrost is acutely sensitive to climate warming and vegetation dynamics. Shrub height is positively correlated with accumulation of snow in the tundra resulting in warming of the ground in winter, and greater shading and lower surface temperatures in summer. Rapid greening due to climate warming has been observed throughout northeastern Canada and particularly in the coastal mountainous terrain of the Torngat Mountains National Park. Our research examines how this shrubification in the Torngat Mountains is modifying permafrost characteristics using observations which extend over a 100 km south-north transect from the sporadic zone (Saglek, Torr Bay) to where permafrost is widespread (Nakvak Brook, Kangalaksiorvik Lake) and potentially continuous (Komaktorvik River). We use air and ground temperature monitoring, vegetation surveys, dendrochronology, frost probing and electrical resistivity tomography (ERT) to describe the complex interactions between shrub growth, geomorphology, climate and permafrost in a region where climate warming is rapidly altering the landscape. Preliminary analysis of field data shows low resistivity anomalies in the ERT profiles at some sites with thin permafrost, interpreted as unfrozen zones correlated with areas of tall shrubs (Alnus spp., Salix spp. and Betula glandulosa; ranging from prostrate to 2 m). Elsewhere, high resistivities extend to the base of the ERT profiles, indicating thicker permafrost, and no obvious impact of medium to low-prostrate shrubs (Salix spp., Betula glandulosa, Rhododendron spp., and Vaccinium spp.; up to 50 cm). Permafrost is interpreted to be present at most sites with low or prostrate shrubs, except where hydrological conditions favour warmer ground temperatures. We infer that the net impact of increasing shrub heights on the active layer and permafrost depends on antecedent ground temperatures and surficial geology. Increasing shrub heights may cause permafrost degradation at sites where mean ground temperatures are close to 0°C and rising due to climate warming. A deeper active layer or loss of permafrost in turn could affect hydrological conditions, potentially influencing shrub size and species composition.

Magnetotelluric studies of the Caldas Novas geothermal reservoir, Brazil

NASA Astrophysics Data System (ADS)

de Lugão, Patricia Pastana; LaTerra, Emanuele Francesco; Kriegshäuser, Berthold; Fontes, Sergio L.

2002-01-01

A magnetotelluric (MT) survey was conducted on the Caldas Novas geothermal reservoir located in the state of Goiás, Central Brazil. The region of Caldas Novas is a popular tourist spot because of the occurrence of hot water springs. The purpose of the first MT survey in this area is to provide more information on the geoelectrical structure of this important geothermal reservoir. The MT method is a frequency domain technique that utilizes naturally occurring magnetic and electric signals as source to obtain a resistivity map of the subsurface. Since temperature and permeability are some of the factors controlling electrical resistivity, MT is widely utilized for surveying geothermal areas such as Caldas Novas. Data were acquired along two profiles crossing the Serra de Caldas (Caldas Mountains) with a total of 25 MT stations. Frequencies of acquisition were in the range from 0.008 to 176 Hz. Spacing between stations were usually around 5 km. Apparent resistivity and phase data from the transverse electric (TE) and transverse magnetic (TM) modes were computed for both profiles. Very high (100,000 Ω m) apparent resistivity values in the TM mode indicate distortion, possibly caused by 3-D resistive structures. In this work, we focus on Profile 2, which was acquired aligned at N40°E, approximately following the direction of weakness N50°E. Two-dimensional (2-D) inversion suggests a basin-like model with very high-resistivity block structures associated with concentric faulting below the Caldas Mountains inside a resistive basin that extends to depths of approximately 25-30 km. This model is in good agreement with gravity data and the available geological information in the area and can help delineate areas of new geothermal reservoirs. The high resistivity associated with the depression in the MT model can be interpreted as caused by the low-permeability quartzites that form the Caldas Mountains. Although the survey configuration does not allow for a full three-dimensional (3-D) interpretation, a 3-D resistivity model was constructed and the MT responses computed. The 3-D synthetic data explains the behavior of both the TE and TM modes in this faulted resistive environment.

Subsurface evaluation of the west parking lot and landfill 3 areas of Air Force Plant 4, Fort Worth, Texas, using two-dimensional direct-current resistivity profiling

USGS Publications Warehouse

Braun, Christopher L.; Jones, Sonya A.

2002-01-01

During September 1999, the U.S. Geological Survey made 10 two-dimensional direct-current resistivity profile surveys in the west parking lot and landfill 3 areas of Air Force Plant 4, Fort Worth, Texas, to identify subsurface areas of anomalously high or low resistivity that could indicate potential contamination, contaminant pathways, or anthropogenic structures. Six of the 10 surveys (transects) were in the west parking lot. Each of the inverted sections of these transects had anomalously high resistivities in the terrace alluvium/fill (the surficial subsurface layer) that probably were caused by highly resistive fill material. In addition, each of these transects had anomalously low resistivities in the Walnut Formation (a bedrock layer immediately beneath the alluvium/fill) that could have been caused by saturation of fractures within the Walnut Formation. A high-resistivity anomaly in the central part of the study area probably is associated with pea gravel fill used in construction of a French drain. Another high resistivity anomaly in the west parking lot, slightly southeast of the French drain, could be caused by dense nonaqueous-phase liquid in the Walnut Formation. The inverted sections of the four transects in the landfill 3 area tended to have slightly higher resistivities in both the alluvium/fill and the Walnut Formation than the transects in the west parking lot. The higher resistivities in the alluvium/fill could have been caused by drier conditions in grassy areas relative to conditions in the west parking lot. Higher resistivities in parts of the Walnut Formation also could be a function of drier conditions or variations in the lithology of the Walnut Formation. In addition to the 10 vertical sections, four horizontal sections at 2-meteraltitude intervals show generally increasing resistivity with decreasing altitude that most likely results from the increased influence of the Walnut Formation, which has a higher resistivity than the terrace alluvium/fill.

Physically motivated global alignment method for electron tomography

DOE PAGES

Sanders, Toby; Prange, Micah; Akatay, Cem; ...

2015-04-08

Electron tomography is widely used for nanoscale determination of 3-D structures in many areas of science. Determining the 3-D structure of a sample from electron tomography involves three major steps: acquisition of sequence of 2-D projection images of the sample with the electron microscope, alignment of the images to a common coordinate system, and 3-D reconstruction and segmentation of the sample from the aligned image data. The resolution of the 3-D reconstruction is directly influenced by the accuracy of the alignment, and therefore, it is crucial to have a robust and dependable alignment method. In this paper, we develop amore » new alignment method which avoids the use of markers and instead traces the computed paths of many identifiable ‘local’ center-of-mass points as the sample is rotated. Compared with traditional correlation schemes, the alignment method presented here is resistant to cumulative error observed from correlation techniques, has very rigorous mathematical justification, and is very robust since many points and paths are used, all of which inevitably improves the quality of the reconstruction and confidence in the scientific results.« less

Cell culture imaging using microimpedance tomography.

PubMed

Linderholm, Pontus; Marescot, Laurent; Loke, Meng Heng; Renaud, Philippe

2008-01-01

We present a novel, inexpensive, and fast microimpedance tomography system for two-dimensional imaging of cell and tissue cultures. The system is based on four-electrode measurements using 16 planar microelectrodes (5 microm x 4 mm) integrated into a culture chamber. An Agilent 4294A impedance analyzer combined with a front-end amplifier is used for the impedance measurements. Two-dimensional images are obtained using a reconstruction algorithm. This system is capable of accurately resolving the shape and position of a human hair, yielding vertical cross sections of the object. Human epithelial stem cells (YF 29) are also grown directly on the device surface. Tissue growth can be followed over several days. A rapid resistivity decrease caused by permeabilized cell membranes is also monitored, suggesting that this technique can be used in electroporation studies.

Resistivity Surveys on the Mauna Kea Saddle: Implications for groundwater resources on the Island of Hawaii

NASA Astrophysics Data System (ADS)

Thomas, D. M.; Pierce, H. A.

2009-12-01

A sequence of Audiomagnetotelluric (AMT) and Magnetotelluric (MT) surveys was recently completed on the Island of Hawaii along a transect spanning the 2000 m high Humu'ula Saddle region bounded by Mauna Kea, Mauna Loa and Hualalai volcanoes. The surveys extended down to an elevation of ~600 m on the eastern flank of the island and to 1,100 m on the drier, western slope of Mauna Kea and were intended to define the depth to the local groundwater table across the interior of the island. The results of the surveys present a much more complicated picture of the interior structure, and associated hydrology, of the island than has generally been assumed. At the eastern end of the transect, where existing wells unequivocally define the depth to the water table, young Mauna Kea basalts saturated with freshwater yielded a resistivity of ~600 ohm-meters. At increasing elevations toward the west, where rainfall rates decline markedly, the resistivity/depth profiles are consistent with progressively drier, resistive rocks to depths approaching 1000 m below the surface. These are underlain by well-defined, moderately resistive zones consistent with freshwater saturated basalts. As the transect approaches an inferred southeasterly-trending rift zone near the crest of the Saddle, the moderately resistive intervals are underlain by less resistive rocks near sea level that fall into the range expected for either (cold) saltwater or heated freshwater. Near the center of the transect, freshwater resistivity values extend to elevations of ~1000 m above sea level and are, again, underlain by significantly less resistive intervals near sea level. We believe that the moderately resistive intervals reflect substantial quantities of freshwater that are bounded by rift systems of Mauna Kea and Hualalai and the northern flank of Mauna Loa. The unexpectedly low resistivity values near sea level are considered to more probably reflect leakage of thermal fluids from the interior of Mauna Kea rather than saltwater intrusion from below the freshwater system. Alternatively, the less resistive formations may be the result of hydrothermal alteration from now-extinct geothermal leakage from Mauna Kea. The presence of freshwater to 1000 m above sea level within the Mauna Kea flanks, if confirmed by planned drilling, will increase estimates of groundwater storage within the island by as much as a factor of ten above those projected by traditional ocean island groundwater models.

Characteristics of Rib Fractures in Child Abuse-The Role of Low-Dose Chest Computed Tomography.

PubMed

Sanchez, Thomas R; Grasparil, Angelo D; Chaudhari, Ruchir; Coulter, Kevin P; Wootton-Gorges, Sandra L

2018-02-01

Our aim is to describe the radiologic characteristics of rib fractures in clinically diagnosed cases of child abuse and suggest a complementary imaging for radiographically occult injuries in highly suspicious cases of child abuse. Retrospective analysis of initial and follow-up skeletal surveys and computed tomography (CT) scans of 16 patients younger than 12 months were reviewed after obtaining approval from our institutional review board. The number, location, displacement, and age of the rib fractures were recorded. Out of a total 105 rib fractures, 84% (87/105) were detected on the initial skeletal survey. Seventeen percent (18/105) were seen only after follow-up imaging, more than half of which (11/18) were detected on a subsequent CT. Majority of the fractures were posterior (43%) and anterior (30%) in location. An overwhelming majority (96%) of the fractures are nondisplaced. Seventeen percent of rib fractures analyzed in the study were not documented on the initial skeletal survey. Majority of fractures are nondisplaced and located posteriorly or anteriorly, areas that are often difficult to assess especially in the acute stage. The CT scan is more sensitive in evaluating these types of fractures. Low-dose chest CT can be an important imaging modality for suspicious cases of child abuse when initial radiographic findings are inconclusive.

Sci—Thur PM: Imaging — 06: Canada's National Computed Tomography (CT) Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wardlaw, GM; Martel, N; Blackler, W

2014-08-15

The value of computed tomography (CT) in medical imaging is reflected in its' increased use and availability since the early 1990's; however, given CT's relatively larger exposures (vs. planar x-ray) greater care must be taken to ensure that CT procedures are optimised in terms of providing the smallest dose possible while maintaining sufficient diagnostic image quality. The development of CT Diagnostic Reference Levels (DRLs) supports this process. DRLs have been suggested/supported by international/national bodies since the early 1990's and widely adopted elsewhere, but not on a national basis in Canada. Essentially, CT DRLs provide guidance on what is considered goodmore » practice for common CT exams, but require a representative sample of CT examination data to make any recommendations. Canada's National CT Survey project, in collaboration with provincial/territorial authorities, has collected a large national sample of CT practice data for 7 common examinations (with associated clinical indications) of both adult and pediatric patients. Following completion of data entry into a common database, a survey summary report and recommendations will be made on CT DRLs from this data. It is hoped that these can then be used by local regions to promote CT practice optimisation and support any dose reduction initiatives.« less

The summit part of Mount Etna revealed by High Resolution DC Electrical Resistivity Tomography coupled with complementary geophysical and soil gas techniques

NASA Astrophysics Data System (ADS)

Finizola, Anthony; Ricci, Tullio; Antoine, Raphael; Delcher, Eric; Peltier, Aline; Bernard, Julien; Brothelande, Elodie; Fargier, Yannick; Fauchard, Cyrille; Foucart, Brice; Gailler, Lydie; Gusset, Rachel; Lazarte, Ivonne; Martin, Erwan; Mézon, Cécile; Portal, Angélie; Poret, Matthieu; Rossi, Matteo

2016-04-01

In the framework of the EC FP7 project "MEDiterranean SUpersite Volcanoes", one profile coupling DC electrical resistivity tomography (Pole-Dipole configuration with a remote electrode located between 8-10 km from the middle of the different acquisitions, 64 electrodes and 40 m spacing between the electrodes), self-potential, soil CO2 degassing, Radon measurements and sub-surface (30cm depth) temperature have been performed between June 25th and July 13th 2015. This profile, NE-SW direction, crossed the summit part of Mount Etna. A total 5720m of profile was performed, with a roll along protocol of 1/4 of the dispositive, for each new acquisitions. A total of 6 acquisitions was made to complete the entire profile. For the first time in the world, a multi-electrodes DC ERT profile, of high resolution (40 m of spacing between the electrodes) reached, thanks to a pole-dipole configuration, 900m for the depth of investigation. The ERT profile clearly evidences the hydrothermal system of Mount Etna: the lowest resistivity values are associated with a large scale positive self-potential anomaly, and smaller wavelength anomalies for temperature, CO2 concentration and Radon, in the area where the electrical conductor reach the surface. Structural discontinuities such as the Elliptic crater, was clearly evidenced by a sharp decrease of the self-potential values in the inner part of this crater. The striking result of this profile is the presence of a resistive body located just below the NE crater. This structure displays the highest degassing values of the entire profile. We interpret this resistive body as a consequence of the thermic over-heated plume rising from the top of the shallow feeding system. Indeed, above several hundred of degrees Celsuis, it is impossible to consider rain water infiltration and the presence of a wet hydrothermal system. The consequence would be therefore to obtain this resistive body, centred on the area of main heat transfer. Above this resistive body, we clearly note a preferential hydrothermal fluid flow, associated with maximum of self-potential anomaly, temperature and radon, and reaching the surface on the highest elevation area along the profile.

Investigation of Submarine Groundwater Discharge and Preferential Groundwater Flow-paths in a Coastal Karst Area using towed Marine and Terrestrial Electrical Resistivity

NASA Astrophysics Data System (ADS)

O'connell, Y.; Daly, E.; Duffy, G.; Henry, T.

2012-12-01

Large volumes of groundwater, containing nutrients and contaminants enter the coastal waters of southern Galway Bay on the west coast of Ireland through submarine groundwater discharge (SGD). The SGD occurs through karstified Carboniferous limestone in a major karst region comprising the Burren and Gort Lowlands. The Carboniferous limestones have experienced extensive dissolution resulting in the development of an underground network of conduits and fissures that define a trimodal groundwater flow pattern across the region. Groundwater discharge to the sea in this area is exclusively intertidal and submarine. Storage in the karst is limited and typical winter rainfall conditions result in the karst system becoming saturated. Temporary lakes (turloughs) form in lowlying areas and act as large reservoirs which provide storage to enable the transmission of the large volumes of water in the system to the sea. Between 2010 and 2012, terrestrial and shallow marine geophysical surveying has been undertaken to investigate preferential groundwater flow-paths and SGD locations in order to quantify the groundwater-seawater interactions in this coastal karst system. A report into the groundwater system of this karst region following a major flood event proposed a conceptual conduit model defined by extensive water tracing, water level monitoring, hydrochemical sampling, geological mapping and drilling. Limited information about the dimensions of the conduits was known. Electrical resistivity tomography (ERT) profiling to depths of 100m below ground level, with multiple array configurations, has been carried out to investigate the modes of groundwater flow in to and out of both temporary and permanent freshwater lakes in the system. Towed dipole-dipole profiles have been recorded to investigate conduits beneath a permanent lake exhibiting a tidal influence despite its location 5.5 km from the seashore. The ERT data indicates significant variations in subsurface resistivities including very low resistivity features which have been modeled as large diameter conduits. Ongoing analysis of the data will allow more accurate conduit dimensions to be incorporated in to future groundwater flow models. In the shallow marine bays along the coast, towed ERT employing dipole-dipole and non-conventional modified Wenner arrays has been coupled with high-resolution digital chirp sub-bottom profiling. Combining the two techniques allows the determination of sediment, structural and lithological variations beneath the sea floor, delineating saturated sediment layers, till and bedrock horizons. Incorporation of the water column thickness and conductivity, recorded simultaneously with the ERT survey, constrains the inversion process. In addition, multiple layer boundaries interpreted from the sub-bottom profiling are incorporated in to the model, further constraining the inversion process. The combined inversion allows improved data interpretation to facilitate more accurate assessment of SGD locations.

Slope monitoring by using 2-D resistivity method at Sungai Batu, Pulau Pinang, Malaysia

NASA Astrophysics Data System (ADS)

Azman, Muhamad Iqbal Mubarak Faharul; Yusof, Azim Hilmy Mohd; Ismail, Nur Azwin; Ismail, Noer El Hidayah

2017-07-01

Slope is a dynamic system of geo-environmental phenomena that related to the movement of the soil and rock masses. In Pulau Pinang, the occurrence of slope related phenomena such as landslide and rock fall has become a huge issue especially during rainy season as the government would have to invest more for the people safety. 2-D resistivity method is one of the geophysical methods that can be applied to overcome this issue thus prepare countermeasure actions. Monitoring is one of the common acquisition technique that has been used in solving such issue. This technique was applied to identify and monitor changes at the suspected area and thus, countermeasure steps can be taken accordingly and not blindfolded. Starting from August until November 2016, a 200 m survey line of 2-D resistivity survey had been conducted monthly at Sungai Batu, Pulau Pinang slope for monitoring purpose. Three resistivity ranges were able to detect within the subsurface. Resistivity value of 250 - 400 Ωm indicated the low resistivity value and interpreted as the weak zone located at distance of 90 - 120 m with depth of 10 m. Intermediate resistivity value was interpreted as weathered granite zone with resistivity value of 400 - 1500 Ωm was found at almost along survey line. High resistivity value was > 5000 Ωm and interpreted as granitic bedrock located at depth of > 20 m. Aside from weathered granite zone and weak zone, a fracture was found develop over time at distance of 130 - 140 m. The features found have the potential to be the cause for slope failure phenomena to occur. As a conclusion, monitoring slope using 2-D resistivity method is a success and indeed helpful in overcome landslide and rock fall issue as a pre-countermeasure action.

Monitoring subterraneous water regime at the new Ain Shams university campus in Al-Obour city (northeast of Cairo-Egypt) using both azimuthal very low frequency-electromagnetic and DC-resistivity sounding techniques

NASA Astrophysics Data System (ADS)

Farag, Karam S. I.; Abd El-Aal, Mohamed H.; Garamoon, Hassan K. F.

2018-07-01

A joint azimuthal very low frequency-electromagnetic (VLF-EM) and DC-resistivity sounding survey was conducted at the new Ain Shams university campus in Al-Obour city, northwest of Cairo, Egypt. The main objective of the survey was to highlight the applicability and reliability of such non-invasive surface techniques in mapping and monitoring both the vertical and lateral electrical conductivity structures of waterlogged areas, by subterraneous water accumulations, at the campus site. Consequently, a total of 743 azimuthal VLF-EM and 4 DC-resistivity soundings were carried out in June, 2011, 2012 and 2013. The data were interpreted extensively and consistently in terms of two-dimensional (2D) transformed EM equivalent current-density and stitched inverted electrical resistivity models, without using any geological a-priori information. They could be used effectively to image the local anomalous lower electrical resistivity (higher EM equivalent current-density) structures and their near-surface spreading with time, due to the excessive accumulations of subterraneous water at the campus site. The study demonstrated that a regional azimuthal VLF-EM and DC-resistivity sounding survey could help design an optimal dewatering program for the whole city, at greatly reduced execution time.

Dissolution rates of subsoil limestone in a doline on the Akiyoshi-dai Plateau, Japan: An approach from a weathering experiment, hydrological observations, and electrical resistivity tomography

NASA Astrophysics Data System (ADS)

Akiyama, Sanae; Hattanji, Tsuyoshi; Matsushi, Yuki; Matsukura, Yukinori

2015-10-01

This study aims at estimating the controlling factors for the denudation rates of limestone, which often forms solution dolines on karst tablelands. Our approaches include (1) electrical resistivity tomography (ERT) to reveal shallow subsurface structures and hydrological settings, (2) automated monitoring of volumetric water content in soil profiles and manual measurements of subsurface CO2 concentrations and soil water chemistry, and (3) a field weathering experiment using limestone tablets with the micro-weight loss technique for determining current denudation rates. The field experiment and monitoring were carried out over 768 days from 2009-2011 at four sites with varying topographic and hydrological conditions along the sideslope of a doline on the Akiyoshi-dai karst plateau in SW-Japan. The installation depths of the limestone tablets were 15 cm or 50 cm below the slope surface. The soil moisture conditions varied site by site. Water-saturated conditions continued for 40-50% of the whole experimental period at 50-cm depth of upper and middle sites, while only 0-10% of the experimental period was water-saturated at the other sites. Chemical analysis revealed that the soil water was chemically unsaturated with calcite for all the sites. Spatial differences in concentrations of CO2 in soil pore air were statistically less significant. The denudation rates of the buried limestone tablets were 17.7-21.9 mg cm- 2 a- 1 at the upper and middle slopes, where the soil was water-saturated for a long time after precipitation. The lowest denudation of 3.9 mg cm- 2 a- 1 was observed on lower slopes where soil was not capable of maintaining water at a near saturation level even after precipitation. Statistical analysis revealed that the denudation rates of the tablets were strongly controlled by the duration for which soil pores were saturated by water (the conditions defined here are degrees of water saturation greater than 97%). Electrical resistivity tomography indicated that areas with high soil moisture conditions were located at the deeper zone on the lower slopes and the bottom of the doline, where denudation would be faster.

Use of Airborne Electromagnetic Geophysical Survey to Map Discontinuous Permafrost in Goldstream Valley, Interior Alaska

NASA Astrophysics Data System (ADS)

Daanen, R. P.; Emond, A.; Liljedahl, A. K.; Walter Anthony, K. M.; Barnes, D. L.; Romanovsky, V. E.; Graham, G.

2016-12-01

An airborne electromagnetic (AEM) survey was conducted in Goldstream Valley, Alaska, to map the electrical resistivity of the ground by sending a magnetic field down from a transmitter flying 30m above the ground into the subsurface. The recorded electromagnetic data are a function of the resistivity structure in the ground. The RESOLVE system used in the survey records data for six frequencies, resulting in a depth of investigation from 1-3 meters and up to 150 meters, depending on resistivity of the ground. Recording six frequencies enables the use of inversion methods to find a solution for a discretized resistivity model providing resistivity as a function of depth below ground surface. Using the airborne RESOLVE system in a populated study area involved challenges related to signal noise, access, and public opinion. Noise issues were mainly the consequence of power lines, which produce varying levels and frequencies of noise. We were not permitted to fly directly over homes, cars, animals, or people because of safety concerns, which resulted in gaps in our dataset. Public outreach well in advance of the survey informed residents about the methods used, their benefits to understanding the environment, and their potential impacts on the environment. Inversion of the data provided resistivity models that were interpreted for frozen and thawed ground conditions; these interpretation were constrained by alternate data sources such as well logs, borehole data, ground-based geophysics, and temperature measurements. The resulting permafrost map will be used to interpret groundwater movement into the valley and methane release from thermokarst lakes.

In vitro corrosion resistance of porous NiTi intervertebral fusion devices

NASA Astrophysics Data System (ADS)

Schrooten, Jan; Assad, Michel; Van Humbeeck, Jan; Leroux, Michel A.

2007-02-01

Porous titanium-nickel (PTN) intervertebral fusion devices, produced by self-propagating high-temperature synthesis, represent an alternative to traditional long-term implants in the orthopaedic field. PTN promotes tissue ingrowth and has succeeded short-term and long-term biocompatibility in vivo testing. In this in vitro study, the PTN morphology was characterized using microfocus computer tomography (μCT) in order to calculate the active PTN surface. Potentiodynamic polarization testing was then performed to evaluate the in vitro corrosion resistance of PTN devices in Hanks' based salt solution. Direct coupling experiments of PTN with Ti6Al4V were also performed in order to establish the galvanic corrosion resistance of PTN intervertebral implants in the presence of potential Ti6Al4V supplemental fixation devices. Compared to the behaviour of other orthopaedic biomaterials and solid NiTi devices, PTN devices showed a level of corrosion resistance that is comparable to other NiTi devices and acceptable for the intended orthopaedic application. Further improvement of the corrosion resistance is still possible by specific electrochemical surface treatments.

Hydrostratigraphy of a Sand Aquifer from Combined ERT and GPR

NASA Astrophysics Data System (ADS)

Papadimitrios, K. S.; Ferris, G.; Bank, C.

2015-12-01

Overlapping resistivity and ground-penetrating radar transects were collected on a shallow sand aquifer. The study area covers about 150 by 150 m, and the water table depth in that area ranges from as shallow as 30 cm to over 2m. Electric resistivity tomography shows layers of resistances which we relate to the vadose zone (above 1200 Ohm.m), the saturated zone (approx. 300 Ohm.m), and underlying aquitard (above 1200 Ohm.m, made of glacial till). The resistivity sections fail to capture the topography of the sand-till boundary seen in collected radargrams (e.g., from 80 to 120 ns over a 30 m horizontal distance). Converting radar travel times to thickness of the aquifer requires knowledge of water table depth as well as radar velocity in both the saturated and unsaturated sands. Water table depth can be taken from resistivity pseudosections as well as local piezometers. Radar velocities can be estimated based on the properties of the local sand and assuming 100% saturation. In merging the results from the two datasets we are able to map local hydrostratigraphy and aquifer geometry.

Accounting for baryonic effects in cosmic shear tomography: Determining a minimal set of nuisance parameters using PCA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eifler, Tim; Krause, Elisabeth; Dodelson, Scott

2014-05-28

Systematic uncertainties that have been subdominant in past large-scale structure (LSS) surveys are likely to exceed statistical uncertainties of current and future LSS data sets, potentially limiting the extraction of cosmological information. Here we present a general framework (PCA marginalization) to consistently incorporate systematic effects into a likelihood analysis. This technique naturally accounts for degeneracies between nuisance parameters and can substantially reduce the dimension of the parameter space that needs to be sampled. As a practical application, we apply PCA marginalization to account for baryonic physics as an uncertainty in cosmic shear tomography. Specifically, we use CosmoLike to run simulatedmore » likelihood analyses on three independent sets of numerical simulations, each covering a wide range of baryonic scenarios differing in cooling, star formation, and feedback mechanisms. We simulate a Stage III (Dark Energy Survey) and Stage IV (Large Synoptic Survey Telescope/Euclid) survey and find a substantial bias in cosmological constraints if baryonic physics is not accounted for. We then show that PCA marginalization (employing at most 3 to 4 nuisance parameters) removes this bias. Our study demonstrates that it is possible to obtain robust, precise constraints on the dark energy equation of state even in the presence of large levels of systematic uncertainty in astrophysical processes. We conclude that the PCA marginalization technique is a powerful, general tool for addressing many of the challenges facing the precision cosmology program.« less

Survey of image-guided radiotherapy use in Australia.

PubMed

Batumalai, Vikneswary; Holloway, Lois Charlotte; Kumar, Shivani; Dundas, Kylie; Jameson, Michael Geoffrey; Vinod, Shalini Kavita; Delaney, Geoff P

2017-06-01

This study aimed to evaluate the current use of imaging technologies for planning and delivery of radiotherapy (RT) in Australia. An online survey was emailed to all Australian RT centres in August 2015. The survey inquired about imaging practices during planning and treatment delivery processes. Participants were asked about the types of image-guided RT (IGRT) technologies and the disease sites they were used for, reasons for implementation, frequency of imaging and future plans for IGRT use in their department. The survey was completed by 71% of Australian RT centres. All respondents had access to computed tomography (CT) simulators and regularly co-registered the following scans to the RT: diagnostic CT (50%), diagnostic magnetic resonance imaging (MRI) (95%), planning MRI (34%), planning positron emission tomography (PET) (26%) and diagnostic PET (97%) to aid in tumour delineation. The main reason for in-room IGRT implementation was the use of highly conformal techniques, while the most common reason for under-utilisation was lack of equipment capability. The most commonly used IGRT modalities were kilovoltage (kV) cone-beam CT (CBCT) (97%), kV electronic portal image (EPI) (89%) and megavoltage (MV) EPI (75%). Overall, participants planned to increase IGRT use in planning (33%) and treatment delivery (36%). IGRT is widely used among Australian RT centres. On the basis of future plans of respondents, the installation of new imaging modalities is expected to increase for both planning and treatment. © 2016 The Royal Australian and New Zealand College of Radiologists.

Combined 2-D Electrical Resistivity and Self Potential Survey to Investigate the Pattern of the Watukosek Fault System Around the Lusi Eruption Site, Indonesia.

NASA Astrophysics Data System (ADS)

Mazzini, A.; Husein, A.; Mauri, G.; Lupi, M.; Hadi, S.; Kemna, A.

2015-12-01

The Lusi mud eruption is located in the Sidoarjo area, Indonesia and is continuously erupting hot mud since its birth in May 2006. A comprehensive combined electrical resistivity and self-potential (SP) survey was performed in the 7 km2 area inside the Lusi embankment that had been built to contain the erupted mud and to prevent flooding of the surrounding roads and settlements. The goal of the geophysical survey is to map the near-surface occurrence of the Watukosek fault system, upon which LUSI resides, delineate its spatial pattern and monitor its development. We completed six lines of measurements combining resistivity measurement using Wenner configuration and SP measurements using roll-along technique. Three subparallel lines were located either to the north and to the south of the main crater. Each line was approximately W-E oriented extending for ~1.26 km. The surveyed regions consist of dried mud breccia (containing clayey-silty-sandy admixture with clast up to ~ 10 cm in size). The thickness of the dry walkable mud is approximately 2-3 m and the deeper layer consist of water saturated mud that could be vulnerable to a liquefaction scenario in case of significant seismic activity in the region. The resistivity data were inverted into 2-D resistivity images with a maximum exploration depth of almost 200 m. The resistivity images consistently reveal a region of about 300 m in width (between 30-90 m depth) characterized by anomalous resistivities, which are lower than the value observed in the surounding area. The position of these anomalies is also supported by the SP data, which suggests that their origin is related to fluid flow path in the subsurface. Thus the combined resistivity and SP results allow inference of an improved model of the Watukosek fault system.

Small scale characterization of vine plant root zone via 3D electrical resistivity tomography and Mise-à-la-Masse method: a case study in a Bordeaux Vineyard

NASA Astrophysics Data System (ADS)

Mary, Benjamin; Peruzzo, Luca; Boaga, Jacopo; Schmutz, Myriam; Wu, Yuxin; Hubbard, Susan S.; Cassiani, Giorgio

2017-04-01

Nowadays, best viticulture practices require the joint interpretation of climate and soils data. However, information about the soil structure and subsoil processes is often lacking, as point measurements, albeit precise, cannot ensure sufficient spatial coverage and resolution. Non-invasive methods can provide spatially extensive, high resolution information that, supported by traditional point-like data, help complete the complex picture of subsoil static and dynamic reality. So far very little emphasis has been given to investigating the role of soil properties and even less of roots activity on winegrapes. Vine plant's root systems play an important role in providing the minerals to the plants, but also control the water uptake and thus the water state of the vines, which is a key factor determining the grape quality potential. In this contribution we report about the measurements conducted since June 2016 in a vineyard near Bordeaux (France, Pessac Leognan Chateau). Two neighbor plants of different sizes have been selected. In order to spot small scale soil variations and root zone physical structure at the vicinity of the vine plants, we applied a methodology using longitudinal 2D tomography, 3D borehole-based electrical resistivity tomography and a variation of the mise-à-la-masse method (MALM) to assess the effect of plant roots on the current injection in the ground. Time-lapse measurements are particularly informative about the plant dynamics, and the focus is particularly applied on this approach. The time-lapse 3D ERT and MALM results are presented, and the potential to assimilate these data into a hydrological model that can account for the root water uptake as a function of atmospheric conditions is discussed.

Influence of 24-Nor-Ursodeoxycholic Acid on Hepatic Disposition of [(18)F]Ciprofloxacin, a Positron Emission Tomography Study in Mice.

PubMed

Wanek, Thomas; Halilbasic, Emina; Visentin, Michele; Mairinger, Severin; Römermann, Kerstin; Stieger, Bruno; Kuntner, Claudia; Müller, Markus; Langer, Oliver; Trauner, Michael

2016-01-01

24-nor-ursodeoxycholic acid (norUDCA) is a novel therapeutic approach to cholestatic liver diseases. In mouse models of cholestasis, norUDCA induces basolateral multidrug resistance-associated proteins 4 (Mrp4) and 3 in hepatocytes, which provide alternative escape routes for bile acids accumulating during cholestasis but could also result in altered hepatic disposition of concomitantly administered substrate drugs. We used positron emission tomography imaging to study the influence of norUDCA on hepatic disposition of the model Mrp4 substrate [(18)F]ciprofloxacin in wild-type and Mdr2((-/-)) mice, a model of cholestasis. Animals underwent [(18)F]ciprofloxacin positron emission tomography at baseline and after norUDCA treatment. After norUDCA treatment, liver-to-blood area under the curve ratio of [(18)F]ciprofloxacin was significantly decreased compared to baseline, both in wild-type (-34.0 ± 2.1%) and Mdr2((-/-)) mice (-20.5 ± 6.0%). [(18)F]Ciprofloxacin uptake clearance from blood into liver was reduced by -17.1 ± 9.0% in wild-type and by -20.1 ± 7.3% in Mdr2((-/-)) mice. Real-time PCR analysis showed significant increases in hepatic Mrp4 and multidrug resistance-associated protein 3 mRNA after norUDCA. Transport experiments in organic anion transporting polypeptide (OATP)1B1-, OATP1B3-, and OATP2B1-transfected cells revealed weak transport of [(14)C]ciprofloxacin by OATP1B3 and OATP2B1 and no inhibition by norUDCA. In conclusion, our data suggest that changes in hepatic [(18)F]ciprofloxacin disposition in mice after norUDCA treatment were caused by induction of basolateral Mrp4 in hepatocytes. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Variable Grid Traveltime Tomography for Near-surface Seismic Imaging

NASA Astrophysics Data System (ADS)

Cai, A.; Zhang, J.

2017-12-01

We present a new algorithm of traveltime tomography for imaging the subsurface with automated variable grids upon geological structures. The nonlinear traveltime tomography along with Tikhonov regularization using conjugate gradient method is a conventional method for near surface imaging. However, model regularization for any regular and even grids assumes uniform resolution. From geophysical point of view, long-wavelength and large scale structures can be reliably resolved, the details along geological boundaries are difficult to resolve. Therefore, we solve a traveltime tomography problem that automatically identifies large scale structures and aggregates grids within the structures for inversion. As a result, the number of velocity unknowns is reduced significantly, and inversion intends to resolve small-scale structures or the boundaries of large-scale structures. The approach is demonstrated by tests on both synthetic and field data. One synthetic model is a buried basalt model with one horizontal layer. Using the variable grid traveltime tomography, the resulted model is more accurate in top layer velocity, and basalt blocks, and leading to a less number of grids. The field data was collected in an oil field in China. The survey was performed in an area where the subsurface structures were predominantly layered. The data set includes 476 shots with a 10 meter spacing and 1735 receivers with a 10 meter spacing. The first-arrival traveltime of the seismogram is picked for tomography. The reciprocal errors of most shots are between 2ms and 6ms. The normal tomography results in fluctuations in layers and some artifacts in the velocity model. In comparison, the implementation of new method with proper threshold provides blocky model with resolved flat layer and less artifacts. Besides, the number of grids reduces from 205,656 to 4,930 and the inversion produces higher resolution due to less unknowns and relatively fine grids in small structures. The variable grid traveltime tomography provides an alternative imaging solution for blocky structures in the subsurface and builds a good starting model for waveform inversion and statics.

Inherent Limitations of Hydraulic Tomography

USGS Publications Warehouse

Bohling, Geoffrey C.; Butler, J.J.

2010-01-01

We offer a cautionary note in response to an increasing level of enthusiasm regarding high-resolution aquifer characterization with hydraulic tomography. We use synthetic examples based on two recent field experiments to demonstrate that a high degree of nonuniqueness remains in estimates of hydraulic parameter fields even when those estimates are based on simultaneous analysis of a number of carefully controlled hydraulic tests. We must, therefore, be careful not to oversell the technique to the community of practicing hydrogeologists, promising a degree of accuracy and resolution that, in many settings, will remain unattainable, regardless of the amount of effort invested in the field investigation. No practically feasible amount of hydraulic tomography data will ever remove the need to regularize or bias the inverse problem in some fashion in order to obtain a unique solution. Thus, along with improving the resolution of hydraulic tomography techniques, we must also strive to couple those techniques with procedures for experimental design and uncertainty assessment and with other more cost-effective field methods, such as geophysical surveying and, in unconsolidated formations, direct-push profiling, in order to develop methods for subsurface characterization with the resolution and accuracy needed for practical field applications. Copyright ?? 2010 The Author(s). Journal compilation ?? 2010 National Ground Water Association.

Survey of resistance to four insecticides and their associated mechanisms in different genotypes of the green peach aphid (Hemiptera: Aphididae) from Chile

USDA-ARS?s Scientific Manuscript database

The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) is a major pest of agriculture worldwide that is particularly adept at evolving insecticide resistance very frequently develop insecticide resistance. Seven mechanisms that confer resistance to many insecticide types have been des...

Evaluation of fall armyworm resistance in maize germplasm lines using visual leaf injury rating and predator survey

USDA-ARS?s Scientific Manuscript database

After examining ear-colonizing pest resistance, 20 maize lines from the USDA-ARS germplasm enhancement of Maize (GEM) Program were evaluated for whorl-feeding fall armyworm (FAW) (Spodoptera frugiperda) resistance using four maize inbred lines as the resistant and susceptible controls. Both FAW inju...

Epidemiology of 3rd generation cephalosporin-resistant Escherichia coli on dairy farms

USDA-ARS?s Scientific Manuscript database

Dairy cattle have been identified as a reservoir for 3rd generation cephalosporin (3GC)-resistant Escherichia coli. We previously identified 3GC-resistant E. coli from manure composite samples of calves and cows in a survey of 80 farms in Pennsylvania. Resistant strains were most frequently isolated...

Correlation of Resistivity Value with Geotechnical N-Value of Sedimentary Area in Nusajaya, Johor, Malaysia

NASA Astrophysics Data System (ADS)

Akip Tan, S. N. Mohd; Edy Tonnizam, M.; Saad, R.; Dan, M. F. Md; Nordiana, M. M.; Hazreek, Z. A. M.; Madun, A.

2018-04-01

Electrical resistivity survey and the geotechnical SPT blow counts (N-value) were carried out simultaneously on the tropically weathered sedimentary rock mass for an excavation project at Nusajaya, Johor, Malaysia. This study aims to determine subsurface profile by using 2D-resistivity methods and correlate with N-value derived from boring works. Four boreholes were investigated in five survey lines that revealed the site is underlain by moderately to completely weathered sandstone, clay, silt and shale. Data analysis from 2D-resistivity image shows that zones with high resistivity value generally have high N-value, and vice versa. Five zones have inversed the proportional relation between N-value and resistivity Ωm value due to different types of soil lithology. It indicates that 2D-resistivity is significance to detect bodies of anomalous materials or estimating the depth of bedrock. As a conclusion, the integration of geophysical and geotechnical analysis provides a promise approach to understand some relationship concerning the subsurface subsurface ground through the combination of 2D-resistivity and N-value.

Helicopter-borne geophysical survey over the areas struck by the tsunami of March 11, 2011, in northeast Japan

NASA Astrophysics Data System (ADS)

Okuma, S.; Ueda, T.; Mitsuhata, Y.; Uchida, T.

2012-12-01

The Geological Survey of Japan, AIST conducted a helicopter-borne EM and magnetic survey over tsunami invaded areas in northeast Japan 15 months after the 2011 off the Pacific coast of Tohoku Earthquake. The purpose of the survey is to map the electrical resistivity of the ground intruded by seawater during the tsunami on March 11, 2011 for its reutilization as farming lands and water assessment of the area. The survey was flown in June 2012 at an altitude of 60m above ground with a speed of 50km/h along survey and traverse lines spaced 100m and 1,000m apart, respectively. The airborne EM system (Fuguro Airborne Surveys' RESOLVE system) was installed in a bird and towed 30m below the helicopter. This is a frequency-domain system operated at five frequencies (340, 1,500, 6,900, 31,000, 140,000 Hz) in a horizontal coplanar configuration and at a frequency (3,300 Hz) in a coaxial configuration. The survey area is located at the border of Miyagi and Fukushima Prefectures along the Pacific coast in the southern part of the Sendai Plain and is divided into two sub-areas: Watari-Yamamoto-Shinchi area (area A) and Matsukawa-ura Bay area (area B). The area A is known for its production of high-quality strawberries on beach ridges and much fresh groundwater has been used for irrigation of strawberries and warming of strawberry greenhouses by water curtain. However, the salinity of groundwater from shallow irrigation wells in this area increased dramatically after the tsunami (Mori et al., 2012). Since it still remains at high level, there is an urgent need to find new water resources. Whereas, the area B is characterized by a beautiful lagoon called the Matsukawa-ura which is preserved as one of prefectural parks of Fukushima Prefecture. Rice fields occupy the areas west of the Matsukawa-ura and most of them were covered by seawater during the attack of the tsunami. Desalinization of the rice fields is being conducted intensively to resume rice farming in these fields. The observed electromagnetic data were processed and apparent resistivity maps were preliminary created for each frequencies. As for the apparent resistivity map at a frequency of 140,000Hz, very low resistivities less than 2 ohm-m are dominant over lagoons and river mouths along the coastline, indicating the existence of salt water wedge. Relatively low resistivities (8 - 22 ohm-m) range from close to the coastline up to 4km inland and are edged to the west by high resistivities (64 - 128 ohm-m), corresponding to the maximum flooded area as derived from aerial photos by the Geospatial Information Authority of Japan (2011). These low resistivities might be associated with the distribution of tsunami deposits with high salinity concentration. As the frequency becomes lower, low resistivities areas (< 8 ohm-m) extend to inland, indicating the existence of deep salt water wedges and/or fossil salt water. Further analyses such as a 1D inversion are being conducted and their results will be given at the presentation. Time-domain EM and high-density electrical surveys are also planned to be conducted on ground to verify the results by airborne surveys.

Geophysical Characterization of Serpentinite Hosted Hydrogeology at the McLaughlin Natural Reserve, Coast Range Ophiolite

NASA Astrophysics Data System (ADS)

Ortiz, Estefania; Tominaga, Masako; Cardace, Dawn; Schrenk, Matthew O.; Hoehler, Tori M.; Kubo, Michael D.; Rucker, Dale F.

2018-01-01

Geophysical remote sensing both on land and at sea has emerged as a powerful approach to characterize in situ water-rock interaction processes in time and space. We conducted 2-D Electrical Resistivity Tomography (ERT) surveys to investigate in situ hydrogeological architecture within the Jurassic age tectonic mélange portion of the Coast Range Ophiolite Microbial Observatory (CROMO) during wet and dry seasons, where water-rock interactive processes are thought to facilitate a subsurface biosphere. Integrating survey tracks traversing two previously drilled wells, QV1,1 and CSW1,1 at the CROMO site with wireline and core data, and the Serpentine Valley site, we successfully documented changes in hydrogeologic properties in the CROMO formation, i.e., lateral and vertical distribution of conductive zones and their temporal behavior that are dependent upon seasonal hydrology. Based on the core-log-ERT integration, we propose a hydrogeological architectural model, in which the formation is composed of three distinct aquifer systems: perched serpentinite aquifer without seasonal dependency (shallow system), well-cemented serpentine confining beds with seasonal dependency (intermediate system), serpentinite aquifer (deep system), and the ultramafic basement that acts as a quasi-aquiclude (below the deep system). The stunning contrast between the seasonality in the surface water availability and groundwater storativity in the formation allowed us to locate zones where serpentinite weathering and possibly deeper serpentinization processes might have taken place. We based our findings primarily on lithological composition and the distribution of the conductive formation, our work highlights the link between serpentinite weathering processes and possible sources of water in time and space.

Fluid circulation and structural system of Cerritos Colorados geothermal field in La Primavera volcanic caldera (Mexico) inferred from geophysical surveys

NASA Astrophysics Data System (ADS)

Bolós, X.; Cifuentes-Nava, G.; Macias, J. L.; Sosa-Ceballos, G.; García-Tenorio, F.; Albor, M., III; Juarez, M.; Gamez, V.

2017-12-01

Hydrothermal activity in volcanic calderas is the consequence of energy transfer between deep magmatic chambers and subsurface layers saturated in water. This hydrothermal system is generated by convection of the groundwater supplied by meteoric water recharged and the ascent of hot volcanic gasses exsolved from deep magma reservoirs. Calderas are heterogeneous geological structures that due to their formation and evolution produced a complex stratigraphy. All of these heterogeneities can be affected by deformation and also by the presence of fractures and faults which constitute the main pathways whereby hydrothermal fluids can move easily through the surface as spring discharges and fumarolic activity. Geophysical methods have been used in the last decades to investigate the relationship between structural geology and hydrothermal systems in different volcanic areas around the world. In this work, we have focused on the role of subsurface structures to understand and localize the pathways of fluids related to the hydrothermal system of the Cerritos Colorados geothermal field. We focused in the central area of the caldera (P12 well and Cerritos Colorados graben), where active hydrothermal activity is evidenced by fumaroles, thermal anomalies, CO2 diffuse emission, and sulfur precipitation. We have applied a self-potential method (SP) that combined with temperature measurements that allowed to identify the main infiltration and ascending fluid zones in the area, and their specific surface temperature coinciding with fumarolic activity. From this data we an applied Electrical Resistivity Tomography (ERT) survey in two selected places. One ERT profile (1.2 km in length) was located in the P12 well area. A 3D resistivity model used with the equatorial method was carried out on the Cerritos Colorados graben area. Combining the results of the SP, TºC, and ERT data with a detailed structural map we identified the main degassing zones (i.e. fumaroles) that correspond to higher permeability zones located along normal and strike-slip faults. In conclusion, a strong structural control of the surface manifestation of these hydrothermal systems is deduced from our new data. Then, our results emphasize the importance of old structural boundaries that are controlled by intra-caldera tectonic structures.

Initial Assessment of β3-Adrenoceptor-Activated Brown Adipose Tissue in Streptozotocin-Induced Type 1 Diabetes Rodent Model Using [18F]Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography.

PubMed

Baranwal, Aparna; Mirbolooki, M Reza; Mukherjee, Jogeshwar

2015-01-01

Metabolic activity of brown adipose tissue (BAT) is activated by β3-adrenoceptor agonists and norepinephrine transporter (NET) blockers and is measurable using [(18)F]fluorodeoxyglucose ([(18)F]FDG) positron emission tomography/computed tomography (PET/CT) in rats. Using the streptozotocin (STZ)-treated rat model of type 1 diabetes mellitus (T1DM), we investigated BAT activity in this rat model under fasting and nonfasting conditions using [(18)F]FDG PET/CT. Drugs that enhance BAT activity may have a potential for therapeutic development in lowering blood sugar in insulin-resistant diabetes. Rats were rendered diabetic by administration of STZ and confirmed by glucose measures. [(18)F]FDG was injected in the rats (fasted or nonfasted) pretreated with either saline or β3-adrenoceptor agonist CL316,243 or the NET blocker atomoxetine for PET/CT scans. [(18)F]FDG metabolic activity was computed as standard uptake values (SUVs) in interscapular brown adipose tissue (IBAT) and compared across the different drug treatment conditions. Blood glucose levels > 500 mg/dL were established for the STZ-treated diabetic rats. Under fasting conditions, average uptake of [(18)F]FDG in the IBAT of STZ-treated diabetic rats was approximately 70% lower compared to that of normal rats. Both CL316,243 and atomoxetine activated IBAT in normal rats had an SUV > 5, whereas activation in STZ-treated rats was significantly lower. The agonist CL316,243 activated IBAT up to threefold compared to saline in the fasted STZ-treated rat. In the nonfasted rat, the IBAT activation was up by twofold by CL316243. Atomoxetine had a greater effect on lowering blood sugar levels compared to CL316,243 in the nonfasted rats. A significant reduction in metabolic activity was observed in the STZ-treated diabetic rodent model. Increased IBAT activity in the STZ-treated diabetic rat under nonfasted conditions using the β3-adrenoceptor agonist CL316,243 suggests a potential role of BAT in modulating blood sugar levels. Further studies are needed to evaluate the therapeutic role of β3-adrenoceptor agonists in insulin-resistant T1DM.

Application of the surface azimuthal electrical resistivity survey method to determine patterns of regional joint orientation in glacial tills

USGS Publications Warehouse

Carlson, D.

2010-01-01

Joints within unconsolidated material such as glacial till can be primary avenues for the flow of electrical charge, water, and contaminants. To facilitate the siting and design of remediation programs, a need exists to map anisotropic distribution of such pathways within glacial tills by determining the azimuth of the dominant joint set. The azimuthal survey method uses standard resistivity equipment with a Wenner array rotated about a fixed center point at selected degree intervals that yields an apparent resistivity ellipse. From this ellipse, joint set orientation can be determined. Azimuthal surveys were conducted at 21 sites in a 500-km2 (193 mi2) area around Milwaukee, Wisconsin, and more specifically, at sites having more than 30 m (98 ft) of glacial till (to minimize the influence of underlying bedrock joints). The 26 azimuthal surveys revealed a systematic pattern to the trend of the dominant joint set within the tills, which is approximately parallel to ice flow direction during till deposition. The average orientation of the joint set parallel with the ice flow direction is N77??E and N37??E for the Oak Creek and Ozaukee tills, respectively. The mean difference between average direct observation of joint set orientations and average azimuthal resistivity results is 8??, which is one fifth of the difference of ice flow direction between the Ozaukee and Oak Creek tills. The results of this study suggest that the surface azimuthal electrical resistivity survey method used for local in situ studies can be a useful noninvasive method for delineating joint sets within shallow geologic material for regional studies. Copyright ?? 2010 The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.

Geoelectrical Tomography for landslide monitoring: state-of-the-art and future challenges.

NASA Astrophysics Data System (ADS)

Lapenna, V.; Perrone, A.; Piscitelli, S.

2011-12-01

Recently, novel algorithms for tomographic data inversion, robust models for describing the hydrogeophysical processes and new sensor networks for the field data acquisition have rapidly transformed the geoelectrical methods in a powerful and cost-effective tool for geo-hazard monitoring. These technological and methodological improvements disclose the way for a wide spectra of interesting and challenging applications in geo-hazards monitoring: reconstruction of landslide geometry; identification of fluid and gas uprising in volcanic areas; electrical imaging of seismic faults etc.. We briefly resume the current state-of-the-art of the geoelectrical methods in landslide monitoring and introduce new and emerging applications of the geoelectrical tomographic methods. An overview of the more interesting results obtained in different areas of Italian territory affected by wide and diffuse hydrogeological instability phenomena will be presented and discussed. We will focus the attention to some recent results obtained in the frame of national and international projects (Morfeo, Eurorisk/Preview, DORIS). One of the key challenges for the future will be the integration of active (Resistivity) and passive (Self-Potential) measurements for obtaining 2D, 3D and 4D (time-lapse) electrical tomographies able to follow the spatial and temporal dynamics of electrical parameters (i.e. resistivity, self-potential) inside the landslide body. The resistivity imaging can be applied for illuminating the sliding surfaces and for mapping the time-dependent changes of water content in vadose zones, while the Self Potential imaging could give a significant contribute for delineating the groundwater circulation patterns and to the early identification of triggering factors.

Indirect measurement of lung density and air volume from electrical impedance tomography (EIT) data.

PubMed

Nebuya, Satoru; Mills, Gary H; Milnes, Peter; Brown, Brian H

2011-12-01

This paper describes a method for estimating lung density, air volume and changes in fluid content from a non-invasive measurement of the electrical resistivity of the lungs. Resistivity in Ω m was found by fitting measured electrical impedance tomography (EIT) data to a finite difference model of the thorax. Lung density was determined by comparing the resistivity of the lungs, measured at a relatively high frequency, with values predicted from a published model of lung structure. Lung air volume can then be calculated if total lung weight is also known. Temporal changes in lung fluid content will produce proportional changes in lung density. The method was implemented on EIT data, collected using eight electrodes placed in a single plane around the thorax, from 46 adult male subjects and 36 adult female subjects. Mean lung densities (±SD) of 246 ± 67 and 239 ± 64 kg m(-3), respectively, were obtained. In seven adult male subjects estimates of 1.68 ± 0.30, 3.42 ± 0.49 and 4.40 ± 0.53 l in residual volume, functional residual capacity and vital capacity, respectively, were obtained. Sources of error are discussed. It is concluded that absolute differences in lung density of about 30% and changes over time of less than 30% should be detected using the current technology in normal subjects. These changes would result from approximately 300 ml increase in lung fluid. The method proposed could be used for non-invasive monitoring of total lung air and fluid content in normal subjects but needs to be assessed in patients with lung disease.

Study of material properties important for an optical property modulation-based radiation detection method for positron emission tomography.

PubMed

Tao, Li; Daghighian, Henry M; Levin, Craig S

2017-01-01

We compare the performance of two detector materials, cadmium telluride (CdTe) and bismuth silicon oxide (BSO), for optical property modulation-based radiation detection method for positron emission tomography (PET), which is a potential new direction to dramatically improve the annihilation photon pair coincidence time resolution. We have shown that the induced current flow in the detector crystal resulting from ionizing radiation determines the strength of optical modulation signal. A larger resistivity is favorable for reducing the dark current (noise) in the detector crystal, and thus the higher resistivity BSO crystal has a lower (50% lower on average) noise level than CdTe. The CdTe and BSO crystals can achieve the same sensitivity under laser diode illumination at the same crystal bias voltage condition while the BSO crystal is not as sensitive to 511-keV photons as the CdTe crystal under the same crystal bias voltage. The amplitude of the modulation signal induced by 511-keV photons in BSO crystal is around 30% of that induced in CdTe crystal under the same bias condition. In addition, we have found that the optical modulation strength increases linearly with crystal bias voltage before saturation. The modulation signal with CdTe tends to saturate at bias voltages higher than 1500 V due to its lower resistivity (thus larger dark current) while the modulation signal strength with BSO still increases after 3500 V. Further increasing the bias voltage for BSO could potentially further enhance the modulation strength and thus, the sensitivity.

Accuracy of arterial spin labeling magnetic resonance imaging (MRI) perfusion in detecting the epileptogenic zone in patients with drug-resistant neocortical epilepsy: comparison with electrophysiological data, structural MRI, SISCOM and FDG-PET.

PubMed

Sierra-Marcos, A; Carreño, M; Setoain, X; López-Rueda, A; Aparicio, J; Donaire, A; Bargalló, N

2016-01-01

Locating the epileptogenic zone (EZ) in patients with neocortical epilepsy presents major challenges. Our aim was to assess the accuracy of arterial spin labeling (ASL), an emerging non-invasive magnetic resonance imaging (MRI) perfusion technique, to locate the EZ in patients with drug-resistant neocortical epilepsy. Twenty-five consecutive patients with neocortical epilepsy referred to our epilepsy unit for pre-surgical evaluation underwent a standardized assessment including video-electroencephalography (EEG) monitoring, structural MRI, subtraction ictal single-photon emission computed tomography co-registered to MRI (SISCOM) and fluorodeoxyglucose positron emission tomography (FDG-PET) studies. An ASL sequence was included in the MRI studies. Areas of hypoperfusion or hyperperfusion on ASL were classified into 15 anatomic-functional cortical regions; these regional cerebral blood flow maps were compared with the EZ determined by the other tests and the strength of concordance was assessed with the kappa coefficient. Of the 25 patients [16 (64%) women; mean age 32.4 (±13.8) years], 18 (72%) had lesions on structural MRI. ASL abnormalities were seen in 15 (60%) patients (nine hypoperfusion, six hyperperfusion). ASL had a very good concordance with FDG-PET (k = 0.84), a good concordance with structural MRI (k = 0.76), a moderate concordance with video-EEG monitoring (k = 0.53) and a fair concordance with SISCOM (k = 0.28). Arterial spin labeling might help to confirm the location and extent of the EZ in the pre-surgical workup of patients with drug-resistant neocortical epilepsy. © 2015 EAN.

Saline tracer visualized with three-dimensional electrical resistivity tomography: Field-scale spatial moment analysis

USGS Publications Warehouse

Singha, Kamini; Gorelick, Steven M.

2005-01-01

Cross-well electrical resistivity tomography (ERT) was used to monitor the migration of a saline tracer in a two-well pumping-injection experiment conducted at the Massachusetts Military Reservation in Cape Cod, Massachusetts. After injecting 2200 mg/L of sodium chloride for 9 hours, ERT data sets were collected from four wells every 6 hours for 20 days. More than 180,000 resistance measurements were collected during the tracer test. Each ERT data set was inverted to produce a sequence of 3-D snapshot maps that track the plume. In addition to the ERT experiment a pumping test and an infiltration test were conducted to estimate horizontal and vertical hydraulic conductivity values. Using modified moment analysis of the electrical conductivity tomograms, the mass, center of mass, and spatial variance of the imaged tracer plume were estimated. Although the tomograms provide valuable insights into field-scale tracer migration behavior and aquifer heterogeneity, standard tomographic inversion and application of Archie's law to convert electrical conductivities to solute concentration results in underestimation of tracer mass. Such underestimation is attributed to (1) reduced measurement sensitivity to electrical conductivity values with distance from the electrodes and (2) spatial smoothing (regularization) from tomographic inversion. The center of mass estimated from the ERT inversions coincided with that given by migration of the tracer plume using 3-D advective-dispersion simulation. The 3-D plumes seen using ERT exhibit greater apparent dispersion than the simulated plumes and greater temporal spreading than observed in field data of concentration breakthrough at the pumping well.

Methicillin-resistant Staphylococcus aureus hepatic abscess in a patient with sickle-cell disease.

PubMed

Mancao, M; Estrada, B; Wilson, F; Figarola, M; Wesenberg, R

2007-12-01

We report a case of a 16-year-old female patient with sickle-cell disease with a liver abscess secondary to methicillin-resistant Staphylococcus aureus (MRSA). She had initially presented with jaundice and abdominal pain and subsequently underwent endoscopic retrograde cholangio-pancreaticography followed by laparoscopic cholecystectomy for removal of gallstones. However, post-cholecystectomy she presented with generalized abdominal pain and computed tomography scan of the abdomen revealed a liver abscess. A pigtail catheter was inserted into the abscess and culture of the aspirate yielded MRSA (susceptibility pattern of the organism was compatible with community-acquired MRSA). She was treated with intravenous clindamycin for 6 weeks with complete resolution of the abscess.

Flow-induced corrosion of absorbable magnesium alloy: In-situ and real-time electrochemical study

PubMed Central

Wang, Juan; Jang, Yongseok; Wan, Guojiang; Giridharan, Venkataraman; Song, Guang-Ling; Xu, Zhigang; Koo, Youngmi; Qi, Pengkai; Sankar, Jagannathan; Huang, Nan; Yun, Yeoheung

2016-01-01

An in-situ and real-time electrochemical study in a vascular bioreactor was designed to analyze corrosion mechanism of magnesium alloy (MgZnCa) under mimetic hydrodynamic conditions. Effect of hydrodynamics on corrosion kinetics, types, rates and products was analyzed. Flow-induced shear stress (FISS) accelerated mass and electron transfer, leading to an increase in uniform and localized corrosions. FISS increased the thickness of uniform corrosion layer, but filiform corrosion decreased this layer resistance at high FISS conditions. FISS also increased the removal rate of localized corrosion products. Impedance-estimated and linear polarization-measured polarization resistances provided a consistent correlation to corrosion rate calculated by computed tomography. PMID:28626241

Flow-induced corrosion of absorbable magnesium alloy: In-situ and real-time electrochemical study.

PubMed

Wang, Juan; Jang, Yongseok; Wan, Guojiang; Giridharan, Venkataraman; Song, Guang-Ling; Xu, Zhigang; Koo, Youngmi; Qi, Pengkai; Sankar, Jagannathan; Huang, Nan; Yun, Yeoheung

2016-03-01

An in-situ and real-time electrochemical study in a vascular bioreactor was designed to analyze corrosion mechanism of magnesium alloy (MgZnCa) under mimetic hydrodynamic conditions. Effect of hydrodynamics on corrosion kinetics, types, rates and products was analyzed. Flow-induced shear stress (FISS) accelerated mass and electron transfer, leading to an increase in uniform and localized corrosions. FISS increased the thickness of uniform corrosion layer, but filiform corrosion decreased this layer resistance at high FISS conditions. FISS also increased the removal rate of localized corrosion products. Impedance-estimated and linear polarization-measured polarization resistances provided a consistent correlation to corrosion rate calculated by computed tomography.

Monitoring of levees, bridges, pipelines, and other critical infrastructure during the 2011 flooding in the Mississippi River Basin: Chapter J in 2011 floods of the central United States

USGS Publications Warehouse

Densmore, Brenda K.; Burton, Bethany L.; Dietsch, Benjamin J.; Cannia, James C.; Huizinga, Richard J.

2014-01-01

During the 2011 Mississippi River Basin flood, the U.S. Geological Survey evaluated aspects of critical river infrastructure at the request of and in support of local, State, and Federal Agencies. Geotechnical and hydrographic data collected by the U.S. Geological Survey at numerous locations were able to provide needed information about 2011 flood effects to those managing the critical infrastructure. These data were collected and processed in a short time frame to provide managers the ability to make a timely evaluation of the safety of the infrastructure and, when needed, to take action to secure and protect critical infrastructure. Critical infrastructure surveyed by the U.S. Geological Survey included levees, bridges, pipeline crossings, power plant intakes and outlets, and an electrical transmission tower. Capacitively coupled resistivity data collected along the flood-protection levees surrounding the Omaha Public Power District Nebraska City power plant (Missouri River Levee Unit R573), mapped the near-subsurface electrical properties of the levee and the materials immediately below it. The near-subsurface maps provided a better understanding of the levee construction and the nature of the lithology beneath the levee. Comparison of the capacitively coupled resistivity surveys and soil borings indicated that low-resistivity value material composing the levee generally is associated with lean clay and silt to about 2 to 4 meters below the surface, overlying a more resistive layer associated with sand deposits. In general, the resistivity structure becomes more resistive to the south and the southern survey sections correlate well with the borehole data that indicate thinner clay and silt at the surface and thicker sand sequences at depth in these sections. With the resistivity data Omaha Public Power District could focus monitoring efforts on areas with higher resistivity values (coarser-grained deposits or more loosely compacted section), which typically are more prone to erosion or scour. Data collected from multibeam echosounder hydrographic surveys at selected bridges aided State agencies in evaluating the structural integrity of the bridges during the flood, by assessing the amount of scour present around piers and abutments. Hydrographic surveys of the riverbed detected scour depths ranging from zero (no scour) to approximately 5.8 meters in some areas adjacent to North Dakota bridge piers, zero to approximately 6 meters near bridge piers in Nebraska, and zero to approximately 10.4 meters near bridge piers in Missouri. Substructural support elements of some bridge piers in North Dakota, Nebraska, and Missouri that usually are buried were exposed to moving water and sediment. At five Missouri bridge piers the depth of scour left less than 1.8 meters of bed material between the bottom of the scour hole and bedrock. State agencies used this information along with bridge design and construction information to determine if reported scour depths would have a substantial effect on the stability of the structure. Multibeam echosounder hydrographic surveys of the riverbed near pipeline crossings did not detect exposed pipelines. However, analysis of the USGS survey data by pipeline companies aided in their evaluation of pipeline safety and led one company to further investigate the safety of their line and assisted another company in getting one offline pipeline back into operation. Multibeam echosounder hydrographic surveys of the banks, riverbed, and underwater infrastructure at Omaha Public Power District power plants documented the bed and scour conditions. These datasets were used by Omaha Public Power District to evaluate the effects that the flood had on operation, specifically to evaluate if scour during the peak of the flood or sediment deposition during the flood recession would affect the water intake structures. Hydrographic surveys at an Omaha Public Power District electrical transmission tower documented scour so that they could evaluate the structural integrity of the tower as well as have the information needed to make proper repairs after flood waters receded.

Cosmic shear results from the deep lens survey. II. Full cosmological parameter constraints from tomography

DOE PAGES

Jee, M. James; Tyson, J. Anthony; Hilbert, Stefan; ...

2016-06-15

Here, we present a tomographic cosmic shear study from the Deep Lens Survey (DLS), which, providing a limiting magnitudemore » $${r}_{\\mathrm{lim}}\\sim 27$$ ($$5\\sigma $$), is designed as a precursor Large Synoptic Survey Telescope (LSST) survey with an emphasis on depth. Using five tomographic redshift bins, we study their auto- and cross-correlations to constrain cosmological parameters. We use a luminosity-dependent nonlinear model to account for the astrophysical systematics originating from intrinsic alignments of galaxy shapes. We find that the cosmological leverage of the DLS is among the highest among existing $$\\gt 10$$ deg2 cosmic shear surveys. Combining the DLS tomography with the 9 yr results of the Wilkinson Microwave Anisotropy Probe (WMAP9) gives $${{\\rm{\\Omega }}}_{m}={0.293}_{-0.014}^{+0.012}$$, $${\\sigma }_{8}={0.833}_{-0.018}^{+0.011}$$, $${H}_{0}={68.6}_{-1.2}^{+1.4}\\;{\\text{km s}}^{-1}\\;{{\\rm{Mpc}}}^{-1}$$, and $${{\\rm{\\Omega }}}_{b}=0.0475\\pm 0.0012$$ for ΛCDM, reducing the uncertainties of the WMAP9-only constraints by ~50%. When we do not assume flatness for ΛCDM, we obtain the curvature constraint $${{\\rm{\\Omega }}}_{k}=-{0.010}_{-0.015}^{+0.013}$$ from the DLS+WMAP9 combination, which, however, is not well constrained when WMAP9 is used alone. The dark energy equation-of-state parameter w is tightly constrained when baryonic acoustic oscillation (BAO) data are added, yielding $$w=-{1.02}_{-0.09}^{+0.10}$$ with the DLS+WMAP9+BAO joint probe. The addition of supernova constraints further tightens the parameter to $$w=-1.03\\pm 0.03$$. Our joint constraints are fully consistent with the final Planck results and also with the predictions of a ΛCDM universe.« less

Sci-Thur PM – Colourful Interactions: Highlights 07: Canadian Computed Tomography Survey: National Diagnostic Reference Levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wardlaw, Graeme M; Martel, Narine

Purpose: The Canadian Computed (CT) Tomography Survey sought to collect CT technology and dose index data (CTDI and DLP) at the national level in order to establish national diagnostic reference levels (DRLs) for seven common CT examinations of standard-sized adults and pediatric patients. Methods: A single survey booklet (consisting of four sections) was mailed to and completed for each participating CT scanner. Survey sections collected data on (i) General facility and scanner information, (ii) routine protocols (as available), (iii) individual patient data (as applied) and (iv) manual CTDI measurements. Results: Dose index (CTDIvol and DLP) and associated patient data frommore » 24 280 individual patient exam sequences was analyzed for seven common CT examinations performed in Canada: Adult Head, Chest, Abdomen/Pelvis, and Chest/Abdomen/Pelvis, and Pediatric Head, Chest, and Abdomen. Pediatric examination data was sub-divided into three age ranges: 0–3, 3–7 and 7–13 years. DRLs (75th percentile of dose index distributions) were found for all thirteen groups. Further analysis also permitted segmentation of examination data into 8 sub-groups, whose dose index data was displayed along with group histograms – showing relative contribution of axial vs. helical, contrast use (C+ vs. C-), and application of fixed current vs. dose reduction (DR) – 75th percentiles of DR sub-groups were, in almost all cases, lower than whole group (examination) DRLs. Conclusions: The analysis and summaries presented in the pending survey report can serve to aid local CT imaging optimization efforts within Canada and also contribute further to international efforts in radiation protection of patients.« less

Survey of rice blast race identity for blast resistance gene identification in the USA and Puerto Rico

USDA-ARS?s Scientific Manuscript database

Rice blast disease is a significant threat to stable rice production in the USA and worldwide. The major resistance gene (Pi-ta) located within a cluster of resistance genes on rice chromosome 12 has been demonstrated to confer resistance to the rice blast disease. Katy, a rice cultivar released in ...

Structure and substructure analysis of DAFT/FADA galaxy clusters in the [0.4–0.9] redshift range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guennou, L.; et al.

2014-01-17

Context. The DAFT/FADA survey is based on the study of ~90 rich(masses found in the literature >2 x 10^14 M_⊙)and moderately distant clusters (redshifts 0.4 < z < 0.9), all withHST imaging data available. This survey has two main objectives: to constrain dark energy(DE) using weak lensing tomography on galaxy clusters and to build a database (deepmulti-band imaging allowing photometric redshift estimates, spectroscopic data, X-raydata) of rich distant clusters to study their properties.

Installation restoration research program: Assessment of geophysical methods for subsurface geologic mapping, cluster 13, Edgewood Area, Aberdeen Proving Ground, Maryland. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butler, D.K.; Sharp, M.K.; Sjostrom, K.J.

1996-10-01

Seismic refraction, electrical resistivity, and transient electromagnetic surveys were conducted at a portion of Cluster 13, Edgewood Area of Aberdeen Proving Ground, Maryland. Seismic refraction cross sections map the topsoil layer and the water table (saturated zone). The water table elevations from the seismic surveys correlate closely with water table elevations in nearby monitoring wells. Electrical resistivity cross sections reveal a very complicated distribution of sandy and clayey facies in the upper 10 - 15 m of the subsurface. A continuous surficial (topsoil) layer correlates with the surficial layer of the seismic section and nearby boring logs. The complexity andmore » details of the electrical resistivity cross section correlate well with boring and geophysical logs from nearby wells. The transient electromagnetic surveys map the Pleistocene-Cretaceous boundary, the saprolite, and the top of the Precambrian crystalline rocks. Conducting the transient electromagnetic surveys on a grid pattern allows the construction of a three-dimensional representation of subsurface geology (as represented by variations of electrical resistivity). Thickness and depth of the saprolitic layer and depth to top of the Precambrian rocks are consistent with generalized geologic cross sections for the Edgewood Area and depths projected from reported depths at the Aberdeen Proving Ground NW boundary using regional dips.« less

Connectivity in a Karst System Using Electrical Resistivity Tomography and Network Theory.

PubMed

Gómez-Nicolás, Mariana; Rebolledo-Vieyra, Mario; Canto-Lugo, Efrain; Huerta-Quintanilla, Rodrigo; Ochoa-Sandoval, Pablo

2017-11-29

The Ring of Cenotes (RC) is an alignment of numerous cenotes (sinkholes) in a semicircular form (with a radius of 100 km) located in northwestern Yucatán, México. The formation roughly coincides with a concentric ring that corresponds to a buried structure, which has been identified as the product of a meteor impact, known as the Chicxulub crater. Secondary permeability generated by the fracturing and faulting of the sedimentary sequence in the Chicxulub crater has favored the karstification process and therefore the development of underground rivers that transport water from the mainland to the sea. This study implements the network theory to study the hydrological connectivity between a group of 11 cenotes within the RC. Eight electrical resistivity tomography transects were used as an empirical basis. Each transect was acquired directly in the field using the SuperSting R1/IP equipment with a dipole-dipole configuration. An adapted version of the reliability algorithm for communication networks was used as a theoretical model. We found evidence of the existence of water cavities in the study area. We made a network from the data and assigned connection probabilities among cenotes as a function of the separation length and the number of water cavities, as well as their size. © 2017, National Ground Water Association.

EEG, PET, SPET and MRI in intractable childhood epilepsies: possible surgical correlations.

PubMed

Fois, A; Farnetani, M A; Balestri, P; Buoni, S; Di Cosmo, G; Vattimo, A; Guazzelli, M; Guzzardi, R; Salvadori, P A

1995-12-01

Magnetic resonance imaging (MRI), single photon emission tomography (SPET), and positron emission tomography (PET) using [18F]fluorodeoxyglucose were used in combination with scalp and scalp-video EEGs in a group of 30 pediatric patients with drug resistant epilepsy (DRE) in order to identify patients who could benefit from neurosurgical approach. Seizures were classified according to the consensus criteria of The International League Against Epilepsy. In three patients infantile spasms (IS) were diagnosed; 13 subjects were affected by different types of generalized seizures, associated with complex partial seizures (CPS) in three. In the other 14 patients partial seizures, either simple (SPS) or complex, were present. A localized abnormality was demonstrated in one patient with IS and in three patients with generalized seizures. Of the group of 14 subjects with CPS, MRI and CT were normal in 7, but SPET or PET indicated focal hypoperfusion or hypometabolism concordant with the localization of the EEG abnormalities. In 5 of the other 7 patients anatomical and functional imaging and EEG findings were concordant for a localized abnormality. It can be concluded that functional imaging combined with scalp EEGs appears to be superior to the use of only CT and MRI for selecting children with epilepsy in whom a surgical approach can be considered, in particular when CPS resistant to therapy are present.

Electrical resistivity tomography to monitor enhanced biodegradation of hydrocarbons with Rhodococcus erythropolis T902.1 at a pilot scale.

PubMed

Masy, Thibaut; Caterina, David; Tromme, Olivier; Lavigne, Benoît; Thonart, Philippe; Hiligsmann, Serge; Nguyen, Frédéric

2016-01-01

Petroleum hydrocarbons (HC) represent the most widespread contaminants and in-situ bioremediation remains a competitive treatment in terms of cost and environmental concerns. However, the efficiency of such a technique (by biostimulation or bioaugmentation) strongly depends on the environment affected and is still difficult to predict a priori. In order to overcome these uncertainties, Electrical Resistivity Tomography (ERT) appears as a valuable non-invasive tool to detect soil heterogeneities and to monitor biodegradation. The main objective of this study was to isolate an electrical signal linked to an enhanced bacterial activity with ERT, in an aged HC-contaminated clay loam soil. To achieve this, a pilot tank was built to mimic field conditions. Compared to a first insufficient biostimulation phase, bioaugmentation with Rhodococcus erythropolis T902.1 led to a HC depletion of almost 80% (6900 to 1600ppm) in 3months in the center of the contaminated zone, where pollutants were less bioavailable. In the meantime, lithological heterogeneities and microbial activities (growth and biosurfactant production) were successively discriminated by ERT images. In the future, this cost-effective technique should be more and more transferred to the field in order to monitor biodegradation processes and assist in selecting the most appropriate remediation technique. Copyright © 2015 Elsevier B.V. All rights reserved.

Characterizing Uncertainty In Electrical Resistivity Tomography Images Due To Subzero Temperature Variability

NASA Astrophysics Data System (ADS)

Herring, T.; Cey, E. E.; Pidlisecky, A.

2017-12-01

Time-lapse electrical resistivity tomography (ERT) is used to image changes in subsurface electrical conductivity (EC), e.g. due to a saline contaminant plume. Temperature variation also produces an EC response, which interferes with the signal of interest. Temperature compensation requires the temperature distribution and the relationship between EC and temperature, but this relationship at subzero temperatures is not well defined. The goal of this study is to examine how uncertainty in the subzero EC/temperature relationship manifests in temperature corrected ERT images, especially with respect to relevant plume parameters (location, contaminant mass, etc.). First, a lab experiment was performed to determine the EC of fine-grained glass beads over a range of temperatures (-20° to 20° C) and saturations. The measured EC/temperature relationship was then used to add temperature effects to a hypothetical EC model of a conductive plume. Forward simulations yielded synthetic field data to which temperature corrections were applied. Varying the temperature/EC relationship used in the temperature correction and comparing the temperature corrected ERT results to the synthetic model enabled a quantitative analysis of the error of plume parameters associated with temperature variability. Modeling possible scenarios in this way helps to establish the feasibility of different time-lapse ERT applications by quantifying the uncertainty associated with parameter(s) of interest.

Quantification of the degradation of Ni-YSZ anodes upon redox cycling

NASA Astrophysics Data System (ADS)

Song, Bowen; Ruiz-Trejo, Enrique; Bertei, Antonio; Brandon, Nigel P.

2018-01-01

Ni-YSZ anodes for Solid Oxide Fuel Cells are vulnerable to microstructural damage during redox cycling leading to a decrease in the electrochemical performance. This study quantifies the microstructural changes as a function of redox cycles at 800 °C and associates it to the deterioration of the mechanical properties and polarisation resistance. A physically-based model is used to estimate the triple-phase boundary (TPB) length from impedance spectra, and satisfactorily matches the TPB length quantified by FIB-SEM tomography: within 20 redox cycles, the TPB density decreases from 4.63 μm-2 to 1.06 μm-2. Although the polarisation resistance increases by an order of magnitude after 20 cycles, after each re-reduction the electrode polarisation improves consistently due to the transient generation of Ni nanoparticles around the TPBs. Nonetheless, the long-term degradation overshadows this transient improvement due to the nickel agglomeration. In addition, FIB-SEM tomography reveals fractures along YSZ grain boundaries, Ni-YSZ detachment and increased porosity in the composite that lead to irreversible mechanical damage: the elastic modulus diminishes from 36.4 GPa to 20.2 GPa and the hardness from 0.40 GPa to 0.15 GPa. These results suggest that microstructural, mechanical and electrochemical properties are strongly interdependent in determining the degradation caused by redox cycling.

Electrical resistivity tomography to monitor enhanced biodegradation of hydrocarbons with Rhodococcus erythropolis T902.1 at a pilot scale

NASA Astrophysics Data System (ADS)

Masy, Thibaut; Caterina, David; Tromme, Olivier; Lavigne, Benoît; Thonart, Philippe; Hiligsmann, Serge; Nguyen, Frédéric

2016-01-01

Petroleum hydrocarbons (HC) represent the most widespread contaminants and in-situ bioremediation remains a competitive treatment in terms of cost and environmental concerns. However, the efficiency of such a technique (by biostimulation or bioaugmentation) strongly depends on the environment affected and is still difficult to predict a priori. In order to overcome these uncertainties, Electrical Resistivity Tomography (ERT) appears as a valuable non-invasive tool to detect soil heterogeneities and to monitor biodegradation. The main objective of this study was to isolate an electrical signal linked to an enhanced bacterial activity with ERT, in an aged HC-contaminated clay loam soil. To achieve this, a pilot tank was built to mimic field conditions. Compared to a first insufficient biostimulation phase, bioaugmentation with Rhodococcus erythropolis T902.1 led to a HC depletion of almost 80% (6900 to 1600 ppm) in 3 months in the center of the contaminated zone, where pollutants were less bioavailable. In the meantime, lithological heterogeneities and microbial activities (growth and biosurfactant production) were successively discriminated by ERT images. In the future, this cost-effective technique should be more and more transferred to the field in order to monitor biodegradation processes and assist in selecting the most appropriate remediation technique.

Antimicrobial Resistance Control Strategies: A Coordinated Research Initiative Experience in the Asia Pacific Region.

PubMed

Lapierre, Lisette; Asenjo, Gabriela; Vergara, Constanza; Cornejo, Javiera

2017-05-01

The objective was to gather information on the status of antimicrobial surveillance in the Asia Pacific region and suggest control strategies. Twenty-one economies of the Asia Pacific region participated in this initiative. A survey was conducted on antimicrobial use and surveillance throughout the region. A workshop was carried out to create awareness about the issue and discuss the implementation of control strategies. Based on the survey results and workshop conclusions, it can be established that there is better understanding of the implications of antimicrobial resistance in the human medicine area. Only few economies take actions to control antimicrobial resistance on a veterinary/agricultural level. To confront antimicrobial resistance, it is critical to raise awareness; cooperation between all countries is needed to apply international standards, to be able to have harmonized public policies. Countries must align and improve their systems for surveillance and monitoring of antimicrobial resistance in human, animals, and the environment.

Groundwater Resources Evolution in Degrading Permafrost Environments: A Small Catchment-Scale Study in Northern Quebec, Canada

NASA Astrophysics Data System (ADS)

Molson, John; Lemieux, Jean-Michel; Fortier, Richard; Therrien, Rene; Ouellet, Michel; Barth, Johannes; van Geldern, Robert; Cochand, Marion; Sottas, Jonathan; Murray, Renaud; Banville, David

2015-04-01

A two square kilometre catchment in a discontinuous permafrost zone near the Inuit community of Umiujaq on the eastern shore of Hudson Bay in Northern Quebec, Canada, is being investigated to determine the impact of permafrost degradation on groundwater resources. The catchment, which became deglaciated about 7500 years ago, lies in a valley which includes about 30-40 m of glacial-fluvial and marine Quaternary sediments. Permafrost mounds at the site extend from a few meters below ground surface to depths of about 10-30 m. Instrumentation has been installed to measure groundwater levels and temperature, as well as groundwater and surface water geochemistry, isotope signatures (including δ18O and 3H) and stream flow. Preliminary groundwater isotope data reflect depleted δ18O signals that differ from expected values for local groundwater, possibly representing permafrost thaw. In addition, stable water isotopes indicate evaporation from shallow thermokarst lakes. Meteorological conditions including air temperatures, precipitation and snowpack are also being monitored. Near-surface geophysical surveys using electrical resistivity tomography (ERT), induced polarization tomography (IPT), georadar and seismic refraction tomography have been carried out to characterize the catchment and to build a 3D geological site model. A numerical model of coupled groundwater flow and heat transport, including thermal advection, conduction, freeze-thaw and latent heat, is being developed for the site to help develop the conceptual model and to assess future impacts of permafrost degradation due to climate warming. The model (Heatflow/3D) includes nonlinear functions for the temperature-dependent unfrozen moisture content and relative permeability, and has been tested against analytical solutions and using benchmarks developed by the INTERFROST modelling consortium. A conceptual 2D vertical-plane model including several permafrost mounds along a 1 km section shows dynamic seasonal behavior with preferential melting from below due to sub-permafrost horizontal groundwater flow and upward flow to surface water through taliks. Under current environmental conditions, the simulations suggest the remaining permafrost in the basin could completely thaw within 50 years. The long-term monitoring program in the catchment will help develop optimal investigative methods for monitoring hydrogeological systems and groundwater resources under permafrost-degrading conditions, and will help determine how new groundwater resources may become available for northern communities as permafrost thaws and recharge to aquifers increases.

A Coupled model for ERT monitoring of contaminated sites

NASA Astrophysics Data System (ADS)

Wang, Yuling; Zhang, Bo; Gong, Shulan; Xu, Ya

2018-02-01

The performance of electrical resistivity tomography (ERT) system is usually investigated using a fixed resistivity distribution model in numerical simulation study. In this paper, a method to construct a time-varying resistivity model by coupling water transport, solute transport and constant current field is proposed for ERT monitoring of contaminated sites. Using the proposed method, a monitoring model is constructed for a contaminated site with a pollution region on the surface and ERT monitoring results at different time is calculated by the finite element method. The results show that ERT monitoring profiles can effectively reflect the increase of the pollution area caused by the diffusion of pollutants, but the extent of the pollution is not exactly the same as the actual situation. The model can be extended to any other case and can be used to scheme design and results analysis for ERT monitoring.

Self Exchange Bias and Bi-stable Magneto-Resistance States in Amorphous TbFeCo and TbSmFeCo Thin Films

NASA Astrophysics Data System (ADS)

Ma, Chung; Li, Xiaopu; Lu, Jiwei; Poon, Joseph; Comes, Ryan; Devaraj, Arun; Spurgeon, Steven

Amorphous ferrimagetic TbFeCo and TbSmFeCo thin films are found to exhibit strong perpendicular magnetic anisotropy. Self exchange bias effect and bi-stable magneto-resistance states are observed near compensation temperature by magnetic hysteresis loop, anomalous Hall effect and transverse magneto-resistance measurements. Atom probe tomography, scanning transmission electron microscopy, and energy dispersive spectroscopy mapping have revealed two nanoscale amorphous phases with different Tb concentration distributed within the amorphous films. The observed exchange anisotropy originates from the exchange interaction between the two nanoscale amorphous phases. Exchange bias effect is used for increasing stability in spin valves and magnetic tunneling junctions. This study opens up a new platform for using amorphous ferrimagnetic thin films that require no epitaxial growth in nanodevices.. The work was supported by the Defense Threat Reduction Agency Grant and the U.S. Department of Energy.

Community-acquired methicillin-resistant Staphylococcus aureus (CAMRSA)--a rare cause of fulminant orbital cellulitis.

PubMed

Shome, Debraj; Jain, Vandana; Natarajan, Sundaram; Agrawal, Shyam; Shah, Kiran

2008-01-01

We report a 55-year-old female patient who developed a severe right-sided orbital cellulitis. Past history was significant for a boil on the right upper eyelid 2 days prior. Visual acuity at presentation was perception of light with inaccurate projection. Orbital computed tomography (CT) scan and routine blood investigations, including blood culture, urine examination, and urine culture, were performed. CT scan showed a superonasal orbital mass suggestive of an abscess. Abscess drainage followed by pus culture, sensitivity, and pulsed-field gel electrophoresis revealed community-acquired methicillin-resistant Staphylococcus aureus (CAMRSA) resistant to all antibiotics except vancomycin, cotrimoxazole, and amikacin. The condition completely resolved post antibiotic and steroid therapy. At 3 months follow-up, the vision in the right eye was 6/9. We report this case to highlight CAMRSA as a rare but virulent cause of orbital cellulitis; empiric antibiotic therapy should include coverage for CAMRSA until susceptibilities come back.

Antimicrobial multidrug resistance and coresistance patterns of Mannheimia haemolytica isolated from bovine respiratory disease cases--a three-year (2009-2011) retrospective analysis.

PubMed

Lubbers, Brian V; Hanzlicek, Gregg A

2013-05-01

Bovine respiratory disease continues to be the most important ailment of feed yard cattle. While the disease is multifactorial in nature, therapy continues to target the primary bacterial pathogens, Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. A survey of records from a single diagnostic laboratory was conducted to evaluate the percentage of M. haemolytica isolates that were resistant to multiple antimicrobials and if coresistance patterns could be detected. All susceptibility test results for M. haemolytica recovered from lung tissues of cattle were eligible for inclusion in the survey. There were no isolates over the course of the analysis that were resistant to all 6 antimicrobials, primarily due to a lack of resistance to ceftiofur. In 2009, just over 5% of isolates were resistant to 5 or more antimicrobials (pan-resistant). In 2011, more than 35% of the M. haemolytica isolates were characterized as pan-resistant. Significant antimicrobial coresistance patterns were only seen with oxytetracycline and tilmicosin; bacterial isolates that were resistant to either oxytetracycline or tilmicosin were more likely to be resistant to at least one other antimicrobial. The mechanisms by which M. haemolytica is developing multidrug resistance warrant investigation if antimicrobial utility in the therapy of bovine respiratory disease is to be preserved.

The micro-mechanics of strength, durability and damage tolerance in composites: new insights from high resolution computed tomography

NASA Astrophysics Data System (ADS)

Spearing, S. Mark; Sinclair, Ian

2016-07-01

Recent work, led by the authors, on impact damage resistance, particle toughening and tensile fibre failure is reviewed in order to illustrate the use of high-resolution X-ray tomography to observe and quantify damage mechanisms in carbon fibre composite laminates. Using synchrotron and micro-focus X-ray sources resolutions of less than 1 μm have been routinely achieved. This enables individual broken fibres and the micromechanisms of particle toughening to be observed and quantified. The data for fibre failure, cluster formation and overall tensile strength are compared with model predictions. This allows strategies for future model development to be identified. The overall implications for using such high-resolution 3-D measurements to inform a “data-rich mechanics” approach to materials evaluation and modeling is discussed.

Forward modeling to investigate inversion artifacts resulting from time-lapse electrical resistivity tomography during rainfall simulations

NASA Astrophysics Data System (ADS)

Carey, Austin M.; Paige, Ginger B.; Carr, Bradley J.; Dogan, Mine

2017-10-01

Time-lapse electrical resistivity tomography (ERT) is commonly used as a minimally invasive tool to study infiltration processes. In 2014, we conducted field studies coupling variable intensity rainfall simulation with high-resolution ERT to study the real-time partitioning of rainfall into surface and subsurface response. The significant contrast in resistivity in the subsurface from large changes in subsurface moisture resulted in artifacts during the inversion process of the time-lapse ERT data collected using a dipole-dipole electrode array. These artifacts, which are not representative of real subsurface moisture dynamics, have been shown to arise during time-lapse inversion of ERT data and may be subject to misinterpretation. Forward modeling of the infiltration process post field experiments using a two-layer system (saprolite overlain by a soil layer) was used to generate synthetic datasets. The synthetic data were used to investigate the influence of both changes in volumetric moisture content and electrode configuration on the development of the artifacts identified in the field datasets. For the dipole-dipole array, we found that a decrease in the resistivity of the bottom layer by 67% resulted in a 50% reduction in artifact development. Artifacts for the seven additional array configurations tested, ranged from a 19% increase in artifact development (using an extended dipole-dipole array) to as much as a 96% decrease in artifact development (using a wenner-alpha array), compared to that of the dipole-dipole array. Moreover, these arrays varied in their ability to accurately delineate the infiltration front. Model results showed that the modified pole-dipole array was able to accurately image the infiltration zone and presented fewer artifacts for our experiments. In this study, we identify an optimal array type for imaging rainfall-infiltration dynamics that reduces artifacts. The influence of moisture contrast between the infiltrating water and the bulk subsurface material was characterized and shown to be a major factor in contributing to artifact development. Through forward modeling, this study highlights the importance of considering array type and subsurface moisture conditions when using time-lapse resistivity to obtain reliable estimates of vadose zone flow processes during rainfall-infiltration events.

Seasonal Variations in Resistivity at a Police Forensic Site and the Effectiveness of Unconventional Array Types

NASA Astrophysics Data System (ADS)

Edwards, S.; Bank, C. G.

2016-12-01

Geophysical studies involving the detection of buried organic material can be affected by the passage of time and environmental changes such as temperature and, in more importantly, water content in the ground. These effects can be of particular concern for police forensic investigations. This study involved conducting multiple resistivity surveys across 4 months to determine how time and environmental variations affected the detection of porcine carcasses buried four years previous at a provincial police training and research site. Our research also explored survey results of non-conventional grid and square arrays versus traditional linear arrays. The study site is located in Bolton, Ontario, and measures 16 m by 30 m. It contains 18 graves plus other buried objects. Studies were conducted approximately every other week. The resistivity lines used Wenner arrays of 24 m (0.5 m electrode spacing) and 48 m (1 m spacing) in length. Environmental data was obtained from Environment Canada and through simple observations. Preliminary findings indicated that time and environmental changes affected the detection of the porcine bodies by either being too dry and having too high a resistivity to survey effectively, or too wet and having the site flushed with water making the surrounding ground similar in resistivity to the bodies. Future research is needed to further explore how best to minimize environmental changes from resistivity results to enable reliable detection of buried organic material such as human remains In regard to array configurations, the square array in particular shows promise in that it can be set up and executed in less time than running several linear arrays over the same area. The application of such unconventional arrays to police forensic work may prove valuable if the area of interest is off-limits for resistivity surveys due to physical obstructions.

Studies of electrical properties of low-resistivity sandstones based on digital rock technology

NASA Astrophysics Data System (ADS)

Yan, Weichao; Sun, Jianmeng; Zhang, Jinyan; Yuan, Weiguo; Zhang, Li; Cui, Likai; Dong, Huaimin

2018-02-01

Electrical properties are important parameters to quantitatively calculate water saturation in oil and gas reservoirs by well logging interpretation. It is usual that oil layers show high resistivity responses, while water layers show low-resistivity responses. However, there are low-resistivity oil zones that exist in many oilfields around the world, leading to difficulties for reservoir evaluation. In our research, we used digital rock technology to study different internal and external factors to account for low rock resistivity responses in oil layers. We first constructed three-dimensional digital rock models with five components based on micro-computed tomography technology and x-ray diffraction experimental results, and then oil and water distributions in pores were determined by the pore morphology method. When the resistivity of each component was assigned, rock resistivities were calculated by using the finite element method. We collected 20 sandstone samples to prove the effectiveness of our numerical simulation methods. Based on the control variate method, we studied the effects of different factors on the resistivity indexes and rock resistivities. After sensitivity analyses, we found the main factors which caused low rock resistivities in oil layers. For unfractured rocks, influential factors arranged in descending order of importance were porosity, clay content, temperature, water salinity, heavy mineral, clay type and wettability. In addition, we found that the resistivity index could not provide enough information to identify a low-resistivity oil zone by using laboratory rock-electric experimental results. These results can not only expand our understandings of the electrical properties of low-resistivity rocks from oil layers, but also help identify low-resistivity oil zones better.

Characterization of riverbed sediments hydraulic conductivity using slug tests and electrical resistivity tomography and induced polarization tomogrpahy.

NASA Astrophysics Data System (ADS)

Nguyen, F.; Benoit, S.; Gommers, K.; Ghysels, G.; Hermans, T.; Huysmans, M.

2017-12-01

Hydraulic conductivity of river sediments ranges from values smaller than 10-9 m/s to values higher than 10-2 m/s, with a dominance in values between 10-7 m/s and 10-3 m/s. Both horizontal hydraulic conductivity and vertical hydraulic conductivity show spatial variation in a riverbed. The spatial variation in hydraulic conductivity is due to the influence of the sedimentary and geomorphological environment as well as the method of determination, including scale, size and imprecision of the applied method. The characterization of the spatial variability of hydraulic conductivity in riverbeds is important because of its effect on the interaction between river and groundwater. These river - groundwater interactions influence water resource management, water quality and functioning of the riparian ecosystem. It is necessary in the simulation of 3D flow between river and aquifer near the interface and thus, it also determines contaminant transport and biogeochemical modelling in this riparian or hyporheic zone. Different processes occur in this specific zone such as transport, degradation, transformation, precipitation and sorption of substances, all dependent on hydraulic conductivity. Several methods exist to determine the hydraulic conductivity in river beds, both direct and indirect methods, from field to laboratory experiments or numerical modelling, but the uncertainty on obtained K values is often large because of the large variability of K. In the recent years, research has been performed on the usefulness of geophysical methods on rivers, in particular Electrical Resistivity Tomography (ERT) and Induced Polarization (IP). The implementation of ERT and IP in rivers provides a continuous image of the resistivity and chargeability of the subsurface, respectively, and can be used in several applications as proxies for hydraulic conductivity. This work reports and investigate a correlation between hydraulic conductivity measured by slug tests at an experimental site, and electrical resistivity, chargeability and normalized chargeability for riverbeds sediments.

Radiopaque Resists for Two-Photon Lithography To Enable Submicron 3D Imaging of Polymer Parts via X-ray Computed Tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, Sourabh K.; Oakdale, James S.; Cuadra, Jefferson A.

Two-photon lithography (TPL) is a high-resolution additive manufacturing (AM) technique capable of producing arbitrarily complex three-dimensional (3D) microstructures with features 2–3 orders of magnitude finer than human hair. This process finds numerous applications as a direct route toward the fabrication of novel optical and mechanical metamaterials, miniaturized optics, microfluidics, biological scaffolds, and various other intricate 3D parts. As TPL matures, metrology and inspection become a crucial step in the manufacturing process to ensure that the geometric form of the end product meets design specifications. X-ray-based computed tomography (CT) is a nondestructive technique that can provide this inspection capability for themore » evaluation of complex internal 3D structure. However, polymeric photoresists commonly used for TPL, as well as other forms of stereolithography, poorly attenuate X-rays due to the low atomic number (Z) of their constituent elements and therefore appear relatively transparent during imaging. We present the development of optically clear yet radiopaque photoresists for enhanced contrast under X-ray CT. We have synthesized iodinated acrylate monomers to formulate high-Z photoresist materials that are capable of forming 3D microstructures with sub-150 nm features. In addition, we have developed a formulation protocol to match the refractive index of the photoresists to the immersion medium of the objective lens so as to enable dip-in laser lithography, a direct laser writing technique for producing millimeter-tall structures. Our radiopaque photopolymer then resists increase X-ray attenuation by a factor of more than 10 times without sacrificing the sub-150 nm feature resolution or the millimeter-scale part height. Thus, our resists can successfully replace existing photopolymers to generate AM parts that are suitable for inspection via X-ray CT. By providing the “feedstock” for radiopaque AM parts, our resist formulation is expected to play a critical role in enabling fabrication of functional polymer parts to tight design tolerances.« less

Bone metastases in castration-resistant prostate cancer: associations between morphologic CT patterns, glycolytic activity, and androgen receptor expression on PET and overall survival.

PubMed

Vargas, Hebert Alberto; Wassberg, Cecilia; Fox, Josef J; Wibmer, Andreas; Goldman, Debra A; Kuk, Deborah; Gonen, Mithat; Larson, Steven M; Morris, Michael J; Scher, Howard I; Hricak, Hedvig

2014-04-01

To compare the features of bone metastases at computed tomography (CT) to tracer uptake at fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and fluorine 18 16β-fluoro-5-dihydrotestosterone (FDHT) PET and to determine associations between these imaging features and overall survival in men with castration-resistant prostate cancer. This is a retrospective study of 38 patients with castration-resistant prostate cancer. Two readers independently evaluated CT, FDG PET, and FDHT PET features of bone metastases. Associations between imaging findings and overall survival were determined by using univariate Cox proportional hazards regression. In 38 patients, reader 1 detected 881 lesions and reader 2 detected 867 lesions. Attenuation coefficients at CT correlated inversely with FDG (reader 1: r = -0.3007; P < .001; reader 2: r = -0.3147; P < .001) and FDHT (reader 1: r = -0.2680; P = .001; reader 2: r = -0.3656; P < .001) uptake. The number of lesions on CT scans was significantly associated with overall survival (reader 1: hazard ratio [HR], 1.025; P = .05; reader 2: HR, 1.021; P = .04). The numbers of lesions on FDG and FDHT PET scans were significantly associated with overall survival for reader 1 (HR, 1.051-1.109; P < .001) and reader 2 (HR, 1.026-1.082; P ≤ .009). Patients with higher FDHT uptake (lesion with the highest maximum standardized uptake value) had significantly shorter overall survival (reader 1: HR, 1.078; P = .02; reader 2: HR, 1.092; P = .02). FDG uptake intensity was not associated with overall survival (reader 1, P = .65; reader 2, P = .38). In patients with castration-resistant prostate cancer, numbers of bone lesions on CT, FDG PET, and FDHT PET scans and the intensity of FDHT uptake are significantly associated with overall survival. RSNA, 2013

Bone Metastases in Castration-Resistant Prostate Cancer: Associations between Morphologic CT Patterns, Glycolytic Activity, and Androgen Receptor Expression on PET and Overall Survival

PubMed Central

Wassberg, Cecilia; Fox, Josef J.; Wibmer, Andreas; Goldman, Debra A.; Kuk, Deborah; Gonen, Mithat; Larson, Steven M.; Morris, Michael J.; Scher, Howard I.; Hricak, Hedvig

2014-01-01

Purpose To compare the features of bone metastases at computed tomography (CT) to tracer uptake at fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and fluorine 18 16β-fluoro-5-dihydrotestosterone (FDHT) PET and to determine associations between these imaging features and overall survival in men with castration-resistant prostate cancer. Materials and Methods This is a retrospective study of 38 patients with castration-resistant prostate cancer. Two readers independently evaluated CT, FDG PET, and FDHT PET features of bone metastases. Associations between imaging findings and overall survival were determined by using univariate Cox proportional hazards regression. Results In 38 patients, reader 1 detected 881 lesions and reader 2 detected 867 lesions. Attenuation coefficients at CT correlated inversely with FDG (reader 1: r = −0.3007; P < .001; reader 2: r = −0.3147; P < .001) and FDHT (reader 1: r = −0.2680; P = .001; reader 2: r = −0.3656; P < .001) uptake. The number of lesions on CT scans was significantly associated with overall survival (reader 1: hazard ratio [HR], 1.025; P = .05; reader 2: HR, 1.021; P = .04). The numbers of lesions on FDG and FDHT PET scans were significantly associated with overall survival for reader 1 (HR, 1.051–1.109; P < .001) and reader 2 (HR, 1.026–1.082; P ≤ .009). Patients with higher FDHT uptake (lesion with the highest maximum standardized uptake value) had significantly shorter overall survival (reader 1: HR, 1.078; P = .02; reader 2: HR, 1.092; P = .02). FDG uptake intensity was not associated with overall survival (reader 1, P = .65; reader 2, P = .38). Conclusion In patients with castration-resistant prostate cancer, numbers of bone lesions on CT, FDG PET, and FDHT PET scans and the intensity of FDHT uptake are significantly associated with overall survival. © RSNA, 2013 PMID:24475817

Radiopaque Resists for Two-Photon Lithography To Enable Submicron 3D Imaging of Polymer Parts via X-ray Computed Tomography

DOE PAGES

Saha, Sourabh K.; Oakdale, James S.; Cuadra, Jefferson A.; ...

2017-11-24

Two-photon lithography (TPL) is a high-resolution additive manufacturing (AM) technique capable of producing arbitrarily complex three-dimensional (3D) microstructures with features 2–3 orders of magnitude finer than human hair. This process finds numerous applications as a direct route toward the fabrication of novel optical and mechanical metamaterials, miniaturized optics, microfluidics, biological scaffolds, and various other intricate 3D parts. As TPL matures, metrology and inspection become a crucial step in the manufacturing process to ensure that the geometric form of the end product meets design specifications. X-ray-based computed tomography (CT) is a nondestructive technique that can provide this inspection capability for themore » evaluation of complex internal 3D structure. However, polymeric photoresists commonly used for TPL, as well as other forms of stereolithography, poorly attenuate X-rays due to the low atomic number (Z) of their constituent elements and therefore appear relatively transparent during imaging. We present the development of optically clear yet radiopaque photoresists for enhanced contrast under X-ray CT. We have synthesized iodinated acrylate monomers to formulate high-Z photoresist materials that are capable of forming 3D microstructures with sub-150 nm features. In addition, we have developed a formulation protocol to match the refractive index of the photoresists to the immersion medium of the objective lens so as to enable dip-in laser lithography, a direct laser writing technique for producing millimeter-tall structures. Our radiopaque photopolymer then resists increase X-ray attenuation by a factor of more than 10 times without sacrificing the sub-150 nm feature resolution or the millimeter-scale part height. Thus, our resists can successfully replace existing photopolymers to generate AM parts that are suitable for inspection via X-ray CT. By providing the “feedstock” for radiopaque AM parts, our resist formulation is expected to play a critical role in enabling fabrication of functional polymer parts to tight design tolerances.« less

Research on a New Method of Estimating the Potential Depth of Slope Failure Using the Airborne Electromagnetic Survey

NASA Astrophysics Data System (ADS)

Seto, Shuji; Takahara, Teruyoshi; Kinoshita, Atsuhiko; Mizuno, Hideaki; Kawato, Katsushi; Okumura, Minoru; Kageura, Ryouta

2017-04-01

In Japan, at Ontake volcano in 1984 and Kurikoma volcano in 2008, parts of the volcanoes collapsed and large-scale sediment-related disasters occurred. These disasters were unrelated to volcanic eruption directly. We conducted the case studies by using the airborne electromagnetic surveys to investigate the slopes likely to induce landslides on such volcanoes. The airborne electromagnetic surveys are the effective exploration tool when we investigate in extreme environments that person can't enter and it's necessary to investigate with wide range by a short time. The surveys were conducted by using a helicopter carrying the survey instruments; this method of non-contact investigation acquires resistivity data by the electromagnetic induction. In Japan, the surveys were conducted of 15 active volcanoes where volcanic disasters could have serious social implications. These cases focused on the seeking for the possible slopes that landslides would occur. However, the depth of the slope failure was not evaluated. Therefore in the study, we proposed a new method to determine the potential depth of slope failure. First, we categorized the three characteristics as the cap rock type, the extended collapse type, and the landslide type on the basis of collapsed cases and paid attention to the slope of the cap rock type and also defined the collapse range based on the topography and geological properties. Second, we analyzed resistivity structure about collapsed cases with the differential filter and made clear that collapse occurred in the depth which resistivity suddenly changes. In other volcanoes, we could estimate failure depth by extracting the part which resistivity suddenly changes. In the study, we use the three volcanoes as the main cases, Hokkaido Komagatake, Asama Volcano, and Ontake volcano.

Evaluating time-lapse ERT for monitoring DNAPL remediation via numerical simulation

NASA Astrophysics Data System (ADS)

Power, C.; Karaoulis, M.; Gerhard, J.; Tsourlos, P.; Giannopoulos, A.

2012-12-01

Dense non-aqueous phase liquids (DNAPLs) remain a challenging geoenvironmental problem in the near subsurface. Numerous thermal, chemical, and biological treatment methods are being applied at sites but without a non-destructive, rapid technique to map the evolution of DNAPL mass in space and time, the degree of remedial success is difficult to quantify. Electrical resistivity tomography (ERT) has long been presented as highly promising in this context but has not yet become a practitioner's tool due to challenges in interpreting the survey results at real sites where the initial condition (DNAPL mass, DNAPL distribution, subsurface heterogeneity) is typically unknown. Recently, a new numerical model was presented that couples DNAPL and ERT simulation at the field scale, providing a tool for optimizing ERT application and interpretation at DNAPL sites (Power et al., 2011, Fall AGU, H31D-1191). The objective of this study is to employ this tool to evaluate the effectiveness of time-lapse ERT to monitor DNAPL source zone remediation, taking advantage of new inversion methodologies that exploit the differences in the target over time. Several three-dimensional releases of chlorinated solvent DNAPLs into heterogeneous clayey sand at the field scale were generated, varying in the depth and complexity of the source zone (target). Over time, dissolution of the DNAPL in groundwater was simulated with simultaneous mapping via periodic ERT surveys. Both surface and borehole ERT surveys were conducted for comparison purposes. The latest four-dimensional ERT inversion algorithms were employed to generate time-lapse isosurfaces of the DNAPL source zone for all cases. This methodology provided a qualitative assessment of the ability of ERT to track DNAPL mass removal for complex source zones in realistically heterogeneous environments. In addition, it provided a quantitative comparison between the actual DNAPL mass removed and that interpreted by ERT as a function of depth below the water table, as well as an estimate of the minimum DNAPL saturation changes necessary for an observable response from ERT.

High-resolution seismic survey for the characterization of planned PIER-ICDP fluid-monitoring sites in the Eger Rift zone

NASA Astrophysics Data System (ADS)

Simon, H.; Buske, S.

2017-12-01

The Eger Rift zone (Czech Republic) is a intra-continental non-volcanic region and is characterized by outstanding geodynamic activities, which result in earthquake swarms and significant CO2 emanations. Because fluid-induced stress can trigger earthquake swarms, both natural phenomena are probably related to each other. The epicentres of the earthquake swarms cluster at the northern edge of the Cheb Basin. Although the location of the cluster coincides with the major Mariánské-Lázně Fault Zone (MLFZ) the strike of the focal plane indicates another fault zone, the N-S trending Počátky-Plesná Zone (PPZ). Isotopic analysis of the CO2-rich fluids revealed a significant portion of upper mantle derived components, hence a magmatic fluid source in the upper mantle was postulated. Because of these phenomena, the Eger Rift area is a unique site for interdisciplinary drilling programs to study the fluid-earthquake interaction. The ICDP project PIER (Probing of Intra-continental magmatic activity: drilling the Eger Rift) will set up an observatory, consisting of five monitoring boreholes. In preparation for the drilling, the goal of the seismic survey is the characterization of the projected fluid-monitoring drill site at the CO2 degassing mofette field near Hartoušov. This will be achieved by a 6 km long profile with dense source and receiver spacing. The W-E trending profile will cross the proposed drill site and the surface traces of MLFZ and PPZ. The outcome of the seismic survey will be a high-resolution structural image of potential reflectors related to these fault zones. This will be achieved by the application of advanced pre-stack depth migration methods and a detailed P-wave velocity distribution of the area obtained from first arrival tomography. During interpretation of the seismic data, a geoelectrical resistivity model, acquired along the same profile line, will provide important constraints, especially with respect to fluid pathways.

Time-lapse Mise-á-la-Masse measurements and modeling for tracer test monitoring in a shallow aquifer

NASA Astrophysics Data System (ADS)

Perri, Maria Teresa; De Vita, Pantaleone; Masciale, Rita; Portoghese, Ivan; Chirico, Giovanni Battista; Cassiani, Giorgio

2018-06-01

The main goal of this study is to evaluate the reliability of the Mise-á-la-Masse (MALM) technique associated with saline tracer tests for the characterization of groundwater flow direction and velocity. The experimental site is located in the upper part of the Alento River alluvial plain (Campania Region, Southern Italy). In this paper we present the hydrogeological setting, the experimental setup and the relevant field results. Subsequently, we compare those data against the simulated results obtained with a 3D resistivity model of the test area, coupled with a model describing the Advection - Dispersion equation for continuous tracer injection. In particular, we calculate a series of 3D forward solutions starting from a reference model, all derived from electrical tomography results, but taking into consideration different values of mean flow velocity and directions. Each electrical resistivity 3D model is used to produce synthetic voltage maps for MALM surveys. Finally, the synthetic MALM voltage maps are compared with the ones measured in the field in order to assess the information content of the MALM dataset with respect to the groundwater field characteristics. The results demonstrate that the information content of the MALM data is sufficient to define important characteristics of the aquifer geometry and properties. This work shows how a combination of three-dimensional time-lapse modeling of flow, tracer transport and electrical current can substantially contribute towards a quantitative interpretation of MALM measurements during a saline tracer test. This approach can thus revive the use of MALM as a practical, low cost field technique for tracer test monitoring and aquifer hydrodynamic characterization.

A remote-control datalogger for large-scale resistivity surveys and robust processing of its signals using a software lock-in approach

NASA Astrophysics Data System (ADS)

Oppermann, Frank; Günther, Thomas

2018-02-01

We present a new versatile datalogger that can be used for a wide range of possible applications in geosciences. It is adjustable in signal strength and sampling frequency, battery saving and can remotely be controlled over a Global System for Mobile Communication (GSM) connection so that it saves running costs, particularly in monitoring experiments. The internet connection allows for checking functionality, controlling schedules and optimizing pre-amplification. We mainly use it for large-scale electrical resistivity tomography (ERT), where it independently registers voltage time series on three channels, while a square-wave current is injected. For the analysis of this time series we present a new approach that is based on the lock-in (LI) method, mainly known from electronic circuits. The method searches the working point (phase) using three different functions based on a mask signal, and determines the amplitude using a direct current (DC) correlation function. We use synthetic data with different types of noise to compare the new method with existing approaches, i.e. selective stacking and a modified fast Fourier transformation (FFT)-based approach that assumes a 1/f noise characteristics. All methods give comparable results, but the LI is better than the well-established stacking method. The FFT approach can be even better but only if the noise strictly follows the assumed characteristics. If overshoots are present in the data, which is typical in the field, FFT performs worse even with good data, which is why we conclude that the new LI approach is the most robust solution. This is also proved by a field data set from a long 2-D ERT profile.

Effects of small-scale hydrogeologic heterogeneity on submarine groundwater discharge (SGD) dynamics in river dominated estuaries: example of Mobile Bay, Alabama

NASA Astrophysics Data System (ADS)

Montiel, D.; Dimova, N.

2017-12-01

Submarine groundwater discharge (SGD) is known to be an important pathway for nutrients and dissolved constituents in estuarine environments worldwide. Despite its limited contribution to the total fresh water flux to the ocean (5 - 10 %), SGD-derived material loadings can rival riverine inputs. Therefore, a good understanding of the coastal hydrogeology and subsequent SGD dynamics is crucial to further investigate constituent fluxes and its implications on small and large scale coastal ecosystems. We evaluated SGD in Mobile Bay (Alabama), the fourth largest estuary in the US, using a combination of radiotracer techniques (223Ra, 226Ra, and 222Rn), stable isotopes (δ 18O and δ 2H), geophysical surveys (continuous resistivity profiling (CRP) and electrical resistivity tomography (ERT)), and seepage meters during three consecutive years. A detailed examination of the entire shoreline of Mobile Bay using CRP, ERT imaging, and multiple sediment cores collection unveiled a heterogeneous (horizontal and vertical) distribution of the surficial coastal aquifer. This was reflected and confirmed by groundwater tracer measurements and direct measurements of SGD in the coastal zone. We found that SGD occurs mainly in the northeast section of Mobile Bay with a total flux that ranged between 0.9 and 13 × 105 m3 d-1 during dry and wet periods, which represents 0.4 - 2 % of the total fresh water inputs into the Bay. While total SGD is insignificant when accounting the whole water budget of Mobile Bay, we found that small-scale geology variations produce groundwater flow preferential pathways in particular areas where SGD inputs play an important role in the water and nutrient budgets.

Cost-Effectiveness of Screening for Primary Aldosteronism and Subtype Diagnosis in the Resistant Hypertensive Patients.

PubMed

Lubitz, Carrie C; Economopoulos, Konstantinos P; Sy, Stephen; Johanson, Colden; Kunzel, Heike E; Reincke, Martin; Gazelle, G Scott; Weinstein, Milton C; Gaziano, Thomas A

2015-11-01

Primary aldosteronism (PA) is a common and underdiagnosed disease with significant morbidity potentially cured by surgery. We aim to assess if the long-term cardiovascular benefits of identifying and treating surgically correctable PA outweigh the upfront increased costs in patients at the time patients are diagnosed with resistant hypertension (RH). A decision-analytic model compares aggregate costs and systolic blood pressure changes of 6 recommended or implemented diagnostic strategies for PA in a simulated population of at-risk RH patients. We also evaluate a 7th "treat all" strategy wherein all patients with RH are treated with a mineralocorticoid-receptor antagonist without further testing at RH diagnosis. Changes in systolic blood pressure are subsequently converted into gains in quality-adjusted life years (QALYs) by applying National Health and Nutrition Examination Survey data on concomitant risk factors to an existing cardiovascular disease simulation model. QALYs and lifetime costs were then used to calculate incremental cost-effectiveness ratios for the competing strategies. The incremental cost-effectiveness ratio for the strategy of computerized tomography (CT) followed by adrenal venous sampling (AVS) was $82,000/QALY compared with treat all. Incremental cost-effectiveness ratios for CT alone and AVS alone were $200,000/QALY and $492,000/QALY; the other strategies were more costly and less effective. Integrating differential patient-reported health-related quality of life adjustments for patients with PA, and incremental cost-effectiveness ratios for screening patients with CT followed by AVS, CT alone, and AVS alone were $52,000/QALY, $114,000/QALY, and $269,000/QALY gained. CT scanning followed by AVS was a cost-effective strategy to screen for PA among patients with RH. © 2015 American Heart Association, Inc.

Current utilization of cardiac computed tomography in mainland China: A national survey.

PubMed

Liu, Kun; Hsieh, Christopher; Zhuang, Nan; Gao, Yang; Li, Zhennan; Ren, Xinshuang; Yang, Li; Zhang, Jiayin; Budoff, Matthew Jay; Lu, Bin

2016-01-01

Surveys that describe the utilization of cardiac CT are available for the United States, Germany, and Taiwan, but not mainland China. To analyze the clinical utilization of cardiac CT in mainland China. A 25-item questionnaire was created and 240 tertiary hospitals were randomly selected to participate. Survey data were collected and confirmed by email as well as phone interviews. In total, 237 (99%) hospitals consented to this survey, but 85 were excluded because of lack of cardiac CT patient volume or advanced technology. Finally, 152 (64%) questionnaires were available for analysis. Median patient volume was 1,037 patients (range: 150-8,072) annually. The most common clinical indications for coronary CT angiography were exclusion of coronary artery disease in patients with low to intermediate pretest likelihood, asymptomatic individuals with cardiovascular risk factors, and follow-up after coronary bypass grafting. The median heart rate threshold for beta blocker administration was >70 beats/min; most centers (86%) used sublingual nitroglycerin. Prospectively ECG triggered acquisition was the predominant technique in 44% of hospitals. Most (59%) providers adjusted the tube current to the body mass, but few (16%) adjusted the contrast injection rate. Per case, the mean examination duration was 14.2 min; post-processing time 13.6 min; and reporting time 18.0 min. Cardiac CT is widely established in clinical practice in mainland China but there is a need for more uniform standards regarding performance and clinical utilization. Copyright © 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.

Joint inversion of lake-floor electrical resistivity tomography and boat-towed radio-magnetotelluric data illustrated on synthetic data and an application from the Äspö Hard Rock Laboratory site, Sweden

NASA Astrophysics Data System (ADS)

Wang, Shunguo; Kalscheuer, Thomas; Bastani, Mehrdad; Malehmir, Alireza; Pedersen, Laust B.; Dahlin, Torleif; Meqbel, Naser

2018-04-01

The electrical resistivity tomography (ERT) method provides moderately good constraints for both conductive and resistive structures, while the radio-magnetotelluric (RMT) method is well suited to constrain conductive structures. Additionally, RMT and ERT data may have different target coverage and are differently affected by various types of noise. Hence, joint inversion of RMT and ERT data sets may provide a better constrained model as compared to individual inversions. In this study, joint inversion of boat-towed RMT and lake-floor ERT data has for the first time been formulated and implemented. The implementation was tested on both synthetic and field data sets incorporating RMT transverse electrical mode and ERT data. Results from synthetic data demonstrate that the joint inversion yields models with better resolution compared with individual inversions. A case study from an area adjacent to the Äspö Hard Rock Laboratory (HRL) in southeastern Sweden was used to demonstrate the implementation of the method. A 790-m-long profile comprising lake-floor ERT and boat-towed RMT data combined with partial land data was used for this purpose. Joint inversions with and without weighting (applied to different data sets, vertical and horizontal model smoothness) as well as constrained joint inversions incorporating bathymetry data and water resistivity measurements were performed. The resulting models delineate subsurface structures such as a major northeasterly directed fracture system, which is observed in the HRL facility underground and confirmed by boreholes. A previously uncertain weakness zone, likely a fracture system in the northern part of the profile, is inferred in this study. The fractures are highly saturated with saline water, which make them good targets of resistivity-based geophysical methods. Nevertheless, conductive sediments overlain by the lake water add further difficulty to resolve these deep fracture zones. Therefore, the joint inversion of RMT and ERT data particularly helps to improve the resolution of the resistivity models in areas where the profile traverses shallow water and land sections. Our modification of the joint inversion of RMT and ERT data improves the study of geological units underneath shallow water bodies where underground infrastructures are planned. Thus, it allows better planning and mitigating the risks and costs associated with conductive weakness zones.

Potential of electrical resistivity tomography and muon density imaging to study spatio-temporal variations in the sub-surface

NASA Astrophysics Data System (ADS)

Lesparre, Nolwenn; Cabrera, Justo; Courbet, Christelle

2015-04-01

We explore the capacity of electrical resistivity tomography and muon density imaging to detect spatio-temporal variations of the medium surrounding a regional fault crossing the underground platform of Tournemire (Aveyron, France). The studied Cernon fault is sub-vertical and intersects perpendicularly the tunnel of Tournemire and extends to surface. The fault separates clay and limestones layers of the Dogger from limestones layers of the Lias. The Cernon fault presents a thickness of a ten of meters and drives water from an aquifer circulating at the top of the Dogger clay layer to the tunnel. An experiment combining electrical resistivity imaging and muon density imaging was setup taking advantage of the tunnel presence. A specific array of electrodes were set up, adapted for the characterization of the fault. Electrodes were placed along the tunnel as well as at the surface above the tunnel on both sides of the fault in order to acquire data in transmission across the massif to better cover the sounded medium. Electrical resistivity is particularly sensitive to water presence in the medium and thus carry information on the main water flow paths and on the pore space saturation. At the same time a muon sensor was placed in the tunnel under the fault region to detect muons coming from the sky after their crossing of the rock medium. Since the muon flux is attenuated as function of the quantity of matter crossed, muons flux measurements supply information on the medium average density along muons paths. The sensor presents 961 angles of view so measurements performed from one station allows a comparison of the muon flux temporal variations along the fault as well as in the medium surrounding the fault. As the water saturation of the porous medium fluctuates through time the medium density might indeed present sensible variations as shown by gravimetric studies. During the experiment important rainfalls occurred leading variations of the medium properties affecting density and electrical resistivity physical parameters. We show with data sets acquired before and after an important rainfall event how muon density and electrical resistivity imaging may complementary characterize variations of the medium properties. The development of such innovative experiments for hydrogeophysical studies presents then the ability to supply new information on fluid dynamics in the sub-surface.

Reconstruction of the inner structure of small scale mining waste dumps by combining GPR and ERTdata.

NASA Astrophysics Data System (ADS)

Kniess, Rudolf; Martin, Tina

2015-04-01

Two abandoned small waste dumps in the west of the Harz mountains (Germany) were analysed using ground penetrating radar (GPR) and electrical resistivity tomography (ERT). Aim of the project (ROBEHA, funded by the German Federal Ministry of Education and Research (033R105)) is the assessment of the recycling potential of the mining residues taking into account environmental risks of reworking the dump site. One task of the geophysical prospection is the investigation of the inner structure of the mining dump. This is important for the estimation of the approximate volume of potentially reusable mining deposits within the waste dump. The two investigated dump sites are different in age and therefore differ in their structure. The older residues (< 1930) consist of ore processing waste from density separation (stamp mill sand). The younger dump site descends from comprises slag dump waste. The layer of fine grained residues at the first dump site is less than 6 m thick and the slag layer is less than 2 m thick. Both sites are partially overlain by forest or grassland vegetation and characterized by topographical irregularities. Due to the inhomogeneity of the sites we applied electrical resistivity tomography (ERT) and ground penetrating radar (GPR) for detailed investigation. Using ERT we could distinguish various layers within the mining dumps. The resistivities of the dumped material differ from the bedrock resistivities at both sites. The GPR measurements show near surface layer boundaries down to 3 - 4 m. In consecutive campaigns 100 MHz and 200 MHz antennas were used. The GPR results (layer boundaries) were included into the ERT inversion algorithm to enable more precise and stable resistivity models. This needs some special preprocessing steps. The 3D-Position of every electrode from ERT measurement and the GPR antenna position on the surface require an accuracy of less than 1cm. At some points, the layer boundaries and radar wave velocities can be calibrated with borehole stratigraphic data from a mineralogical drilling campaign. This is important for a precise time-depth conversion of reflectors from GPR measurement. This reflectors were taken from radargram and have been adopted as resistivity boundary in the start model of the geoelectric inversion algorithm.

Difficult Clients: Who Are They and How Do We Help Them?

ERIC Educational Resources Information Center

Seligman, Linda; Gaaserud, Lynn

1994-01-01

Reviewed literature on dealing with resistant clients and, based on review, developed survey to elicit counselors' reactions to and experiences with resistant clients. Responses from 215 American Mental Health Counselors Association members suggest that nearly all counselors have encountered resistant clients, but counselors' reactions to and…

Cone beam computed tomography in dental education: a survey of US, UK, and Australian dental schools.

PubMed

Parashar, Vijay; Whaites, Eric; Monsour, Paul; Chaudhry, Jahanzeb; Geist, James R

2012-11-01

Cone beam computed tomography (CBCT) is an excellent three-dimensional (3D) imaging modality. Traditional dental education has focused on teaching conventional (2D) imaging. The aims of this survey-based study were therefore to evaluate the incorporation of CBCT teaching in both the predoctoral/undergraduate (D.D.S./D.M.D./B.D.S.) and postgraduate/residency specialty training curricula in dental schools in the United States, the United Kingdom, and Australia. A nine-question survey form was electronically mailed to fifty-seven schools in the United States, sixteen schools in the United Kingdom, and seven schools in Australia. Fifty U.S. dental schools (89 percent), ten U.K. dental schools (62.5 percent), and one Australian dental school (14 percent) presently have CBCT equipment. The majority of responding schools do not include instruction in higher level use of this technology for undergraduate/predoctoral students, raising questions as to whether these students are adequately trained on qualification. Larger numbers of schools reported providing this training to residents in specialty programs. A similar trend was noticed in U.S., British, and Australian dental education. If general dentists are to be permitted to purchase and use CBCT equipment, inclusion of CBCT in dental education is an absolute requirement to prepare future dental practitioners to apply 3D imaging appropriately for diagnosis and treatment planning.

Airborne and Ground Electrical Surveys for Subsurface Mapping of the Arbuckle Aquifer, Central Oklahoma

NASA Astrophysics Data System (ADS)

Smith, D.; Smith, B. D.; Blome, C. D.; Osborn, N.

2008-12-01

Airborne and ground electrical surveys have been conducted to map the subsurface hydrogeologic character of the Arbuckle-Simpson aquifer in south central Oklahoma. An understanding of the geologic framework and hydrogeologic characteristics is necessary to evaluate groundwater flow through the highly faulted, structurally complex, carbonate aquifer. Results from this research will further understanding of the aquifer and will assist in managing the water resources of the region. The major issues include water quality, the allocation of water rights, and the potential impacts of pumping on springs and stream. Four areas in the Hunton anticline area, with distinctly different geology, were flown with a frequency domain helicopter electromagnetic system (HEM) in March, 2007. Ground electrical studies include dc resistivity imaging and natural field audiomagnetotelluric (AMT), and magnetotelluric (MT) surveys. The HEM resistivity and total field magnetic survey was flown in four blocks, A through D, mostly with a line spacing of 400 m. Block A extends from the Chickasaw National Recreational Area (CHIC) to Mill Creek on the west side of the anticline. The surface geology of this block is mostly dolomitic limestone of the Arbuckle Group that is in fault contact with younger Paleozoic clastic rocks. The flight line spacing was 800 meters in the western half of the block and 400 meters in the eastern part. Airborne magnetic data indicate that the Sulphur fault bends south to merge with the Mill Creek fault which substantiates an earlier hypothesis first made from interpretation of gravity data. Block B, located on the north side of the anticline consists of mostly of Arbuckle and Simpson Group rocks. Block C, covering most of the Clarita horst on the east side of the anticline, consists of the Upper Ordovician to the Lower Pennsylvanian shales. Block D, which was flown to include a deep test well site at Spears ranch, consisted of eight lines spaced at 400 meters. The HEM data are being used to more precisely locate faults, refine the lithostratigraphic units, and to map the depth and extent of shallow epikarst. The MT and AMT data revealed deep structural contacts and a transition between fresh and highly mineralized ground water between springs in the CHIC. The dc resistivity survey has greatly helped in mapping major faults both within dolomitic limestone and clastic units. Ground resistivity surveys also suggest that, in places, the faults within limestone are zones of lower resistivity and map low resistivity surficial epikarst a several meters thick. Ground penetrometer data also has been used to define the depth extent of epikarst in selected areas and the data correlate well with the dc resistivity and HEM resistivity depth sections.

Two-dimensional direct-current resistivity survey to supplement borehole data in ground-water models of the former Blaine Naval Ammunition Depot, Hastings, Nebraska, September 2003

USGS Publications Warehouse

Kress, Wade H.; Ball, Lyndsay B.; Teeple, Andrew; Turco, Michael J.

2006-01-01

The former Blaine Naval Ammunition Depot located immediately southeast of Hastings, Nebraska, was an ammunition facility during World War II and the Korean Conflict. Waste-management practices during operation and decommissioning of the former Depot resulted in soil and ground-water contamination. Ground-water models have been used by the U.S. Army Corps of Engineers to provide information on the fate and transport of contaminants on the former Depot site. During September 2003, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, Kansas City District, conducted a pilot study to collect two-dimensional direct-current resistivity data on the site along six profiles near existing monitoring wells. The inversion results of field data from five of the six two-dimensional direct-current resistivity profiles display distinct electrical stratigraphy consistent with three resistivity units (low resistivity, high resistivity, and low resistivity). These three resistivity units correlate with rock-stratigraphic or hydrogeologic units described prior to this study. To interpret the resistivity profiles, additional data extending through the lower confining unit into the underlying Niobrara Formation could be used with the existing data to construct forward models for data analysis and interpretation.

Challenges of using electrical resistivity method to locate karst conduits-A field case in the Inner Bluegrass Region, Kentucky

USGS Publications Warehouse

Zhu, J.; Currens, J.C.; Dinger, J.S.

2011-01-01

Conduits serve as major pathways for groundwater flow in karst aquifers. Locating them from the surface, however, is one of the most challenging tasks in karst research. Geophysical methods are often deployed to help locate voids by mapping variations of physical properties of the subsurface. Conduits can cause significant contrasts of some physical properties that can be detected; other subsurface features such as water-bearing fractures often yield similar contrasts, which are difficult to distinguish from the effects of the conduits. This study used electrical resistivity method to search for an unmapped karst conduit that recharges Royal Spring in the Inner Bluegrass karst region, Kentucky, USA. Three types of resistivity techniques (surface 2D survey, quasi-3D survey, and time-lapse survey) were used to map and characterize resistivity anomalies. Some of the major anomalies were selected as drilling targets to verify the existence of the conduits. Drilling near an anomaly identified by an electrical resistivity profile resulted in successful penetration of a major water-filled conduit. The drilling results also suggest that, in this study area, low resistivity anomalies in general are associated with water-bearing features. However, differences in the anomaly signals between the water-filled conduit and other water-bearing features such as water-filled fracture zones were undistinguishable. The electrical resistivity method is useful in conduit detection by providing potential drilling targets. Knowledge of geology and hydrogeology about the site and professional judgment also played important roles in locating the major conduit. ?? 2011 Elsevier B.V.

A Genetic Survey of Pyrethroid Insecticide Resistance in Aphids in New Brunswick, Canada, with Particular Emphasis on Aphids as Vectors of Potato virus Y.

PubMed

MacKenzie, Tyler D B; Arju, Irin; Poirier, René; Singh, Mathuresh

2018-05-28

Aphids are viral vectors in potatoes, most importantly of Potato virus Y (PVY), and insecticides are frequently used to reduce viral spread during the crop season. Aphids collected from the potato belt of New Brunswick, Canada, in 2015 and 2016 were surveyed for known and novel mutations in the Na-channel (para) gene, coding for the target of synthetic pyrethroid insecticides. Specific genetic mutations known to confer resistance (kdr and skdr) were found in great abundance in Myzus persicae (Sulzer) (Hemiptera: Aphididae), which rose from 76% in 2015 to 96% in 2016. Aphids other than M. persicae showed lower frequency of resistance. In 2015, 3% of individuals contained the resistance mutation skdr, rising to 13% in 2016 (of 45 species). Several novel resistance mutations or mutations not before reported in aphids were identified in this gene target. One of these mutations, I936V, is known to confer pyrethroid resistance in another unrelated insect, and three others occur immediately adjacent and prompt similar chemical shifts in the primary protein structure, to previously characterized mutations associated with pyrethroid resistance. Most novel mutations were found in species other than M. persicae or others currently tracked individually by the provincial aphid monitoring program, which were determined by cytochrome C oxidase I (cox1) sequencing. Through our cox1 DNA barcoding survey, at least 45 species of aphids were discovered in NB potato fields in 2015 and 2016, many of which are known carriers of PVY.

Epidemiology of multidrug resistant bacterial organisms and Clostridium difficile in German hospitals in 2014: Results from a nationwide one-day point prevalence of 329 German hospitals.

PubMed

Huebner, Nils-Olaf; Dittmann, Kathleen; Henck, Vivien; Wegner, Christian; Kramer, Axel

2016-09-02

One important aspect in combatting resistance to antibiotics is to increase the awareness and knowledge by epidemiological studies. We therefore conducted a German-wide point-prevalence survey for multidrug resistant bacterial organisms (MDROs) and Clostridium difficile (CD) to assess the epidemiology and structure quality of infection control in German hospitals. 1550 hospitals were asked to participate and to report surveillance data on the prevalence of Methicillin-resistant and Vancomycin resistant Staphylococcus aureus (MRSA, VRSA/GRSA), Vancomycin resistant Enterococcus faecalis/faecium (VRE), multiresistant strains of Escherichia coli (EC), Klebsiella spp. (KS), Enterobacter spp. (ES), Acinetobacter spp. (AB) and Pseudomonas spp. (PS). as well as CD infections. Surveys from 73,983 patients from 329 hospitals were eligible for analysis. MRSA was the most often reported pathogen (prevalence: 1.64 % [CI95: 1.46-1.82]), followed by 3 multidrug resistant EC (3MRGN-EC) (0.75 % [CI95: 0.60-0.89]), CD (0.74 % [CI95: 0.60-0.88]), VRE (0.25 % [CI95: 0.13-0.37]) und 3MRGN-KS (0.22 % [CI95: [0.15-0.29]). The majority of hospitals met the German recommendations for staffing with infection control personnel. The continuing increase in participating hospitals in this third survey in a row indicates a growing awareness to MDROs and our pragmatic approach. Our results confirm that MRSA, 3MRGN-EC, VRE and 3MRGN-KS remain the most prevalent MDROs in German hospitals.

A Phase 2 Study of 16α-[18F]-fluoro-17β-estradiol Positron Emission Tomography (FES-PET) as a Marker of Hormone Sensitivity in Metastatic Breast Cancer (MBC)

PubMed Central

Peterson, Lanell M.; Kurland, Brenda F.; Schubert, Erin K.; Link, Jeanne M.; Gadi, V.K.; Specht, Jennifer M.; Eary, Janet F.; Porter, Peggy; Shankar, Lalitha K.; Mankoff, David A.; Linden, Hannah M.

2014-01-01

Purpose 16α-[18F]-fluoro-17β-estradiol positron emission tomography (FES-PET) quantifies estrogen receptor (ER) expression in tumors and may provide diagnostic benefit. Procedures Women with newly diagnosed metastatic breast cancer (MBC) from an ER-positive primary tumor were imaged before starting endocrine therapy. FES uptake was evaluated qualitatively and quantitatively, and associated with response and with ER expression. Results Nineteen patients underwent FES imaging. Fifteen had a biopsy of a metastasis and 15 were evaluable for response. Five patients had quantitatively low FES uptake, six had at least one site of qualitatively FES-negative disease. All patients with an ER-negative biopsy had both low uptake and at least one site of FES-negative disease. Of response-evaluable patients, 2/2 with low FES standard uptake value tumors had progressive disease within 6 months, as did 2/3 with qualitatively FES-negative tumors. Conclusions Low/absent FES uptake correlates with lack of ER expression. FES-positron emission tomography can help identify patients with endocrine resistant disease and safely measures ER in MBC. PMID:24170452

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gómez, H.; Katsanevas, S.; Tonazzo, A.

One of the main concerns in archaeology is to find of a method to study precisely archaeological structures in the least invasive way possible to avoid damage. The requirement of preserving the structures integrity prevents, in the case of pyramids or tumuli, the study of any internal structure (halls or tombs) which are not reachable by existing corridors. One non-invasive method is the muon tomography. By placing a detector which allows to register the muon direction after the structure, it is possible to have an idea of its composition based on the attenuation of the muon flux, which depends onmore » the material length and density that muons have crossed. This technique, alone or together with other exploration techniques as seismic tomography or electrical resistivity tomography, can provide useful information about the internal structure of the archaeological form that can not be obtained by conventional archaeological methods. In this work, the time measurement necessary to obtain a significant result about the composition of an archaeological structure is estimated. To do that, a Monte Carlo simulation framework based on the MUSIC software, properly tuned for this study, has been developed. The particular case of the Kastas Amfipoli Macedonian tumulus has been considered to perform the simulations.« less

Tissue resistivity estimation in the presence of positional and geometrical uncertainties.

PubMed

Baysal, U; Eyüboğlu, B M

2000-08-01

Geometrical uncertainties (organ boundary variation and electrode position uncertainties) are the biggest sources of error in estimating electrical resistivity of tissues from body surface measurements. In this study, in order to decrease estimation errors, the statistically constrained minimum mean squared error estimation algorithm (MiMSEE) is constrained with a priori knowledge of the geometrical uncertainties in addition to the constraints based on geometry, resistivity range, linearization and instrumentation errors. The MiMSEE calculates an optimum inverse matrix, which maps the surface measurements to the unknown resistivity distribution. The required data are obtained from four-electrode impedance measurements, similar to injected-current electrical impedance tomography (EIT). In this study, the surface measurements are simulated by using a numerical thorax model. The data are perturbed with additive instrumentation noise. Simulated surface measurements are then used to estimate the tissue resistivities by using the proposed algorithm. The results are compared with the results of conventional least squares error estimator (LSEE). Depending on the region, the MiMSEE yields an estimation error between 0.42% and 31.3% compared with 7.12% to 2010% for the LSEE. It is shown that the MiMSEE is quite robust even in the case of geometrical uncertainties.

Geoelectrical and hydrochemical study for the assessment of seawater intrusion evolution in coastal aquifers of Oualidia, Morocco

NASA Astrophysics Data System (ADS)

Fadili, Ahmed; Najib, Saliha; Mehdi, Khalid; Riss, Joëlle; Malaurent, Philippe; Makan, Abdelhadi

2017-11-01

This study aims to assess the evolution of seawater intrusion between 1992 and 2011 periods in the coastal aquifers of Oualidia. To achieve this objective, the combination of geoelectrical and hydrochemical methods was adopted. Apparent resistivity maps, using 74 Vertical Electrical Sounding (VES) performed on 1992, allowed to distinguish two different zones. The conductive one, with apparent resistivity ranging between 4 and 86 Ω·m, is limited to 1 km with respect to the ocean. Meanwhile, the resistant one is much farther from the coastline. Besides, results of Electrical Resistivity Tomography (ERT) profiles performed during 2011 are in good agreement with those obtained by apparent resistivity maps. The ERT profiles show a conductive level characterized by low resistivity below 30 Ω·m assigned to seawater intrusion effect. Moreover, hydrochemical analysis, performed on 19 wells during three different periods, on June, December 2010 and May 2011, indicates that the most affected part with marine waters was at that time localized in the first kilometer from the ocean, with high amounts of Na+ and Cl- ions. Beyond this fringe, mineralization becomes very weak. Overall, the comparison of old VES with recent ERT coupled with hydrochemical results suggest no important evolution of the salt wedge since 1992.

Integrated geological-geophysical models of unstable slopes in seismogenic areas in NW and SE Europe

NASA Astrophysics Data System (ADS)

Mreyen, Anne-Sophie; Micu, Mihai; Onaca, Alexandru; Demoulin, Alain; Havenith, Hans-Balder

2017-04-01

We will present a series of new integrated 3D models of landslide sites that were investigated in distinctive seismotectonic and climatic contexts: (1) along the Hockai Fault Zone in Belgium, with the 1692 Verviers Earthquake (M 6 - 6.5) as most prominent earthquake that occurred in that fault zone and (2) in the seismic region of Vrancea, Romania, where four earthquakes with Mw > 7.4 have been recorded during the last two centuries. Both sites present deep-seated failures located in more or less seismically active areas. In such areas, slope stability analyses have to take into account the possible contributions to ground failure. Our investigation methods had to be adapted to capture the deep structure as well as the physico-mechanical characteristics that influence the dynamic behaviour of the landslide body. Field surveys included electrical resistivity tomography profiles, seismic refraction profiles (analysed in terms of both seismic P-wave tomography and surface waves), ambient noise measurements to determine the soil resonance frequencies through H/V analysis, complemented by geological and geomorphic mapping. The H/V method, in particular, is more and more used for landslide investigations or sites marked by topographic relief (in addition to the more classical applications on flat sites). Results of data interpretation were compiled in 3D geological-geophysical models supported by high resolution remote sensing data of the ground surface. Data and results were not only analysed in parallel or successively; to ensure full integration of all inputs-outputs, some data fusion and geostatistical techniques were applied to establish closer links between them. Inside the 3D models, material boundaries were defined in terms of surfaces and volumes. Those models were used as inputs for 2D dynamic numerical simulations completed with the UDEC (Itasca) software. For some sites, a full back-analysis was carried out to assess the possibility of a seismic triggering of the landslides.

Epicardial adipose tissue relating to anthropometrics, metabolic derangements and fatty liver disease independently contributes to serum high-sensitivity C-reactive protein beyond body fat composition: a study validated with computed tomography.

PubMed

Lai, Yau-Huei; Yun, Chun-Ho; Yang, Fei-Shih; Liu, Chuan-Chuan; Wu, Yih-Jer; Kuo, Jen-Yuan; Yeh, Hung-I; Lin, Tin-Yu; Bezerra, Hiram G; Shih, Shou-Chuan; Tsai, Cheng-Ho; Hung, Chung-Lieh

2012-02-01

Epicardial adipose tissue (EAT) measured by echocardiography has been proposed to be associated with metabolic syndrome and increased cardiovascular risks. However, its independent association with fatty liver disease and systemic inflammation beyond clinical variables and body fat remains less well known. The relationships between EAT and various factors of metabolic derangement were retrospectively examined in consecutive 359 asymptomatic subjects (mean age, 51.6 years; 31% women) who participated in a cardiovascular health survey. Echocardiography-derived regional EAT thickness from parasternal long-axis and short-axis views was quantified. A subset of data from 178 randomly chosen participants were validated using 16-slice multidetector computed tomography. Body fat composition was evaluated using bioelectrical impedance from foot-to-foot measurements. Increased EAT was associated with increased waist circumference, body weight, and body mass index (all P values for trend = .005). Graded increases in serum fasting glucose, insulin resistance, and alanine transaminase levels were observed across higher EAT tertiles as well as a graded decrease of high-density lipoprotein (all P values for trend <.05). The areas under the receiver operating characteristic curves for identifying metabolic syndrome and fatty liver disease were 0.8 and 0.77, with odds ratio estimated at 3.65 and 2.63, respectively. In a multivariate model, EAT remained independently associated with higher high-sensitivity C-reactive protein and fatty liver disease. These data suggested that echocardiography-based epicardial fat measurement can be clinically feasible and was related to several metabolic abnormalities and independently associated fatty liver disease. In addition, EAT amount may contribute to systemic inflammation beyond traditional cardiovascular risks and body fat composition. Copyright © 2012 American Society of Echocardiography. Published by Mosby, Inc. All rights reserved.

Pretreatment HIV-drug resistance in Mexico and its impact on the effectiveness of first-line antiretroviral therapy: a nationally representative 2015 WHO survey.

PubMed

Ávila-Ríos, Santiago; García-Morales, Claudia; Matías-Florentino, Margarita; Romero-Mora, Karla A; Tapia-Trejo, Daniela; Quiroz-Morales, Verónica S; Reyes-Gopar, Helena; Ji, Hezhao; Sandstrom, Paul; Casillas-Rodríguez, Jesús; Sierra-Madero, Juan; León-Juárez, Eddie A; Valenzuela-Lara, Marisol; Magis-Rodríguez, Carlos; Uribe-Zuñiga, Patricia; Reyes-Terán, Gustavo

2016-12-01

WHO has developed a global HIV-drug resistance surveillance strategy, including assessment of pretreatment HIV-drug resistance. We aimed to do a nationally representative survey of pretreatment HIV-drug resistance in Mexico using WHO-recommended methods. Among 161 Ministry of Health antiretroviral therapy (ART) clinics in Mexico, the largest, including 90% of ART initiators within the Ministry of Health (66 in total), were eligible for the survey. We used a probability-proportional-to-size design method to sample 25 clinics throughout the country. Consecutive ART-naive patients with HIV about to initiate treatment were invited to participate in the survey; individuals with previous exposure to ART were excluded. We assessed pretreatment HIV-drug resistance by Sanger sequencing and next-generation sequencing of viruses from plasma specimens from eligible participants with Stanford University HIV Drug Resistance Database methods. We obtained follow-up data for a median of 9·4 months (range 6-12) after enrolment. We investigated possible relations between demographic variables and pretreatment drug resistance with univariate and multivariate logistic regression. Between Feb 3 and July 30, 2015, we screened 288 patients in 25 clinics, from whom 264 provided successfully sequenced viruses with no evidence of current exposure to antiretroviral drugs. With the Sanger method, of these 264 participants, 41 (15·5%, 95% CI 11·4-20·5) had pretreatment resistance to any antiretroviral drug and 28 (10·6%, 7·2-15·0) had pretreatment resistance to non-nucleoside reverse transcriptase inhibitors (NNRTIs). At least low-level pretreatment resistance (Stanford penalty score ≥15) was noted in 13 (4 · 9%) of participants to efavirenz and in 23 (8·7%) to the combination tenofovir plus emtricitabine plus efavirenz. With next-generation sequencing, of 264 participants, 38 (14·4%, 95% CI 10·4-19·2) had pretreatment resistance to any antiretroviral drug and 26 (9·8%, 6·5-14·1) had pretreatment resistance to NNRTIs. After median follow-up of 8 months (IQR 6·5-9·4, range 5-11) after ART initiation, 97 (72%) of 135 NNRTI initiators achieved viral suppression (<50 copies per mL) compared with ten (40%) of 25 individuals who started with protease inhibitor-based regimens (p=0·0045). After multivariate regression considering pretreatment resistance and initial ART regimen as composite variables, people starting NNRTIs with pretreatment drug resistance achieved significantly lower viral suppression (odds ratio 0·24, 95% CI 0·07-0·74; p=0·014) than patients without NNRTI resistance. High levels of pretreatment drug resistance were noted in Mexico, and NNRTI pretreatment drug resistance significantly reduced the effectiveness of first-line ART regimens based on these drugs. Baseline HIV-drug resistance testing for initial ART follow-up and decision making should be considered. The Mexican Government and Consejo Nacional de Ciencia y Tecnología. Copyright © 2016 Elsevier Ltd. All rights reserved.

Metabolic profile and quality of life in class I sarcopenic overweight and obese postmenopausal women: a MONET study.

PubMed

Messier, Virginie; Karelis, Antony D; Lavoie, Marie-Eve; Brochu, Martin; Faraj, May; Strychar, Irene; Rabasa-Lhoret, Remi

2009-02-01

Sarcopenia is believed to be associated with disability and metabolic complications. The objective of this study was to examine the metabolic and quality-of-life profile of sarcopenic overweight and obese postmenopausal women. In this cross-sectional study of 136 healthy overweight and obese postmenopausal women, 9 class I sarcopenic women were identified. Class I sarcopenia was defined as an appendicular lean body mass index (ALBMI)

Permafrost on tropical Maunakea volcano, Hawaii

NASA Astrophysics Data System (ADS)

Leopold, Matthias; Schorghofer, Norbert; Yoshikawa, Kenji

2017-04-01

Maunakea volcano on Hawaii Island is known for one of the most unusual occurrences of sporadic permafrost. It was first documented in two cinder cone craters in the 1970's near the summit of the mountain where mean annual air temperatures are currently around +4 deg. Our study investigates the current state of this permafrost, by acquiring multi-year ground temperature data and by applying electrical resistivity tomography and ground penetrating radar techniques along several survey lines. Both of the previously known ice bodies still exist, but one of them has dramatically shrunken in volume. Based on current warming trends it might disappear soon. In addition insolation modelling, temperature probing, and geomorphological indicators were used to prospect for additional permafrost bodies on the wider summit region, however, none was found. It seems that permafrost preferentially appears in the interiors of cinder cones, even though there are exterior slopes that receive less sunlight annually. We hypothesis that snow cover with its high albedo, and a layer of coarse boulders where cold air settles in the pore space during calm nights, play a significant role in cooling the subsurface. Due to the relatively simple setting, the study site is an ideal model system and may also serve as an analogue to Mars.

An application of the geophysical methods and ALS DTM for the identification of the geological structure in the Kraśnik region - Lublin Upland, Poland

NASA Astrophysics Data System (ADS)

Kamiński, Mirosław

2017-11-01

The purpose of the study was the assessment of the viability of selected geophysical methods and the Airborne Laser Scanning (ALS) for the identification and interpretation of the geological structure. The studied area is covered with a dense forest. For this reason, the ALS numerical terrain model was applied for the analysis of the topography. Three geophysical methods were used: gravimetric, in the form of a semi-detailed gravimetric photograph, Vertical Electrical Sounding (VES), and Electrical Resistivity Tomography (ERT). The numerical terrain model enabled the identification of Jurassic limestone outcrops and interpretation of the directions of the faults network. The geological interpretation of the digitally processed gravimetric data enabled the determination of the spatial orientation of the synclines and anticlines axes and of the course directions of main faults. Vertical Electrical Sounding carried along the section line perpendicular to the Gościeradów anticline axis enabled the interpretation of the lithology of this structure and identification of its complex tectonic structure. The shallow geophysical surveys using the ERT method enabled the estimation of the thickness of Quaternary formations deposited unconformably on the highly eroded Jurassic limestone outcrop. The lithology of Quaternary, Cretaceous and Jurassic rocks was also interpreted.

Discovery of ancient Roman "highway" reveals geomorphic changes in karst environments during historic times

PubMed Central

Vinci, Giacomo; Forte, Emanuele; Furlani, Stefano; Pipan, Michele; Biolchi, Sara; De Min, Angelo; Fragiacomo, Andrea; Micheli, Roberto; Ventura, Paola; Tuniz, Claudio

2018-01-01

Sinkholes are a well-known geologic hazard but their past occurrence, useful for subsidence risk prediction, is difficult to define, especially for ancient historic times. Consequently, our knowledge about Holocene carbonate landscapes is often limited. A multidisciplinary study of Trieste Karst (Italy), close to early Roman military fortifications, led to the identification of possible ancient road tracks, cut by at least one sinkhole. Electrical Resistivity Tomography through the sinkhole has suggested the presence of a cave below its bottom, possibly responsible of the sinkhole formation, while Ground Penetrating Radar has detected no tectonic disturbances underneath the tracks. Additionally, archaeological surveys led to the discovery of over 200 Roman shoe hobnails within or close to the investigated route. According to these data, the tracks are interpreted as the remains of a main Roman road, whose itinerary has been reconstructed for more than 4 km together with other elements of ancient landscape. Our results provide the first known evidence of a Roman main road swallowed by sinkholes and suggest that Holocene karst landscapes could be much different from what previously believed. In fact, sinkholes visible nowadays in the investigated region could have been flat areas filled by sediments up to the Roman time. PMID:29570732

Regularized solution of a nonlinear problem in electromagnetic sounding

NASA Astrophysics Data System (ADS)

Piero Deidda, Gian; Fenu, Caterina; Rodriguez, Giuseppe

2014-12-01

Non destructive investigation of soil properties is crucial when trying to identify inhomogeneities in the ground or the presence of conductive substances. This kind of survey can be addressed with the aid of electromagnetic induction measurements taken with a ground conductivity meter. In this paper, starting from electromagnetic data collected by this device, we reconstruct the electrical conductivity of the soil with respect to depth, with the aid of a regularized damped Gauss-Newton method. We propose an inversion method based on the low-rank approximation of the Jacobian of the function to be inverted, for which we develop exact analytical formulae. The algorithm chooses a relaxation parameter in order to ensure the positivity of the solution and implements various methods for the automatic estimation of the regularization parameter. This leads to a fast and reliable algorithm, which is tested on numerical experiments both on synthetic data sets and on field data. The results show that the algorithm produces reasonable solutions in the case of synthetic data sets, even in the presence of a noise level consistent with real applications, and yields results that are compatible with those obtained by electrical resistivity tomography in the case of field data. Research supported in part by Regione Sardegna grant CRP2_686.

Lithostratigraphic interpretation from joint analysis of seismic tomography and magnetotelluric resistivity models using self-organizing map techniques

NASA Astrophysics Data System (ADS)

Bauer, K.; Muñoz, G.; Moeck, I.

2012-12-01

The combined interpretation of different models as derived from seismic tomography and magnetotelluric (MT) inversion represents a more efficient approach to determine the lithology of the subsurface compared with the separate treatment of each discipline. Such models can be developed independently or by application of joint inversion strategies. After the step of model generation using different geophysical methodologies, a joint interpretation work flow includes the following steps: (1) adjustment of a joint earth model based on the adapted, identical model geometry for the different methods, (2) classification of the model components (e.g. model blocks described by a set of geophysical parameters), and (3) re-mapping of the classified rock types to visualise their distribution within the earth model, and petrophysical characterization and interpretation. One possible approach for the classification of multi-parameter models is based on statistical pattern recognition, where different models are combined and translated into probability density functions. Classes of rock types are identified in these methods as isolated clusters with high probability density function values. Such techniques are well-established for the analysis of two-parameter models. Alternatively we apply self-organizing map (SOM) techniques, which have no limitations in the number of parameters to be analysed in the joint interpretation. Our SOM work flow includes (1) generation of a joint earth model described by so-called data vectors, (2) unsupervised learning or training, (3) analysis of the feature map by adopting image processing techniques, and (4) application of the knowledge to derive a lithological model which is based on the different geophysical parameters. We show the usage of the SOM work flow for a synthetic and a real data case study. Both tests rely on three geophysical properties: P velocity and vertical velocity gradient from seismic tomography, and electrical resistivity from MT inversion. The synthetic data are used as a benchmark test to demonstrate the performance of the SOM method. The real data were collected along a 40 km profile across parts of the NE German basin. The lithostratigraphic model from the joint SOM interpretation consists of eight litho-types and covers Cenozoic, Mesozoic and Paleozoic sediments down to 5 km depth. There is a remarkable agreement between the SOM based model and regional marker horizons interpolated from surrounding 2D industrial seismic data. The most interesting results include (1) distinct properties of the Jurassic (low P velocity gradients, low resistivities) interpreted as the signature of shaly clastics, and (2) a pattern within the Upper Permian Zechstein with decreased resistivities and increased P velocities within the salt depressions on the one hand, and increased resistivities and decreased P velocities in the salt pillows on the other hand. In our interpretation this pattern is related with flow of less dense salt matrix components into the pillows and remaining brittle evaporites within the depressions.

Assessing vulnerability to vegetation growth on earth dikes using geophysical investigation

NASA Astrophysics Data System (ADS)

Mary, Benjamin; Saracco, Ginette; Peyras, Laurent; Vennetier, Michel; Mériaux, Patrice

2015-04-01

The Mediterranean Basin is prone to a plethora of natural hazards including floods. Vegetation growth in hydraulic earth structures, such as flood protections or channel levees and dams, may induce several degradation mechanisms leading to a risk of failure. Typically, trees' rooting generates two types of risks: internal erosion from root development in earth embankments, and external erosion (slopes and crest) which is often related to trees uprooting. To better assess how woody vegetation can compromise levee integrity, we designed a methodology using acoustical and complex electrical tomography as non destructives methods to spot dangerous roots in the embankment. Our work has been first initiated during laboratory experiments; we performed soundings in controlled conditions to determine both acoustical and electrical intrinsic behavior of our root samples. By comparison with soil samples we expected to point out specific signatures that would be useful for the roots anomaly identification in real conditions. Measurements were repeated on several samples to ensure statistical interpretation. With help of an ultrasonic transmission device, we identified significant relative velocity differences of compressional waves propagation between soil and root samples. We also studied spectral properties using wavelet processing method as an additional parameter of root distinction with the surrounding soil. In the case of electrical soundings, complex resistivity was measured and we computed resistivity spectra. Amplitude of resistivity term showed us that root material behaves as an insulator compared to the soil. With the phase resistivity term information, root can also be seen as an electric power capacitance and reveals maximum polarization effect located around 1Hz. Then, as experimental device for the field measurements, we selected a 320 cm high poplar (Populus) planted in a homogeneous loamy-clayed soil, which is the same soil used in laboratory experiment to keep comparable conditions. Validity of geophysics data obtained was compared with results from excavation of the first decimeters of soil which allowed defining actual position, geometry and size of root system. For acoustical prospection, we reproduced RINNTECH® methodology on field. The technique relies on measuring the travel time between two sensors, respectively a mobile source defining a mesh all around the tree and fixed receivers on the tree stem. Our results showed that information provided by the amplitude of recorded wave seemed more relevant than the velocity term to discriminate roots from the soil. Unfortunately the signal at very low frequency was noisy which prevents an easy interpretation of spectral properties. From electrical tomography measurements, high resolution inverted images were obtained and showed correlation between roots direction and depth, and phase anomalies. This result was yet found with a too low resolution. Both complex resistivity tomography and acoustical prospection shows considerable promise to map tree roots. Considering a coupling approach is appreciable because each method is sensitive to a different physical parameter. This provides more information and facilitates the interpretation of variability observed in real conditions, where a lot of external parameters can disturb the information requested.

Carbon nanotube film interlayer for strain and damage sensing in composites during dynamic compressive loading

NASA Astrophysics Data System (ADS)

Wu, A. S.; Na, W.-J.; Yu, W.-R.; Byun, J.-H.; Chou, T.-W.

2012-11-01

A major challenge in the damage assessment of materials under dynamic, high strain rate loading lies in the inability to apply most health monitoring methodologies to the analysis and evaluation of damage incurred on short timescales. Here, we present a resistance-based sensing method utilizing an electrically conductive carbon nanotube film in a fiberglass/vinyl ester composite. This method reveals that applied strain and damage in the form of matrix cracking and delamination give rise to electrical resistance increases across the composite specimen; these can be measured in real-time during high strain rate loading. Damage within the composite specimens is confirmed through pre- and post-mortem x-ray micro computed tomography imaging.

Attitudes and perceptions regarding antimicrobial use and resistance among medical students in Central China.

PubMed

Yang, Kun; Wu, Dongfang; Tan, Fei; Shi, Shaojun; Guo, Xianxi; Min, Qing; Zhang, Xiaolian; Cheng, Hong

2016-01-01

Senior medical students, who are future doctors, should be prepared to use antimicrobials appropriately and will be important partners in antimicrobial stewardship. This survey was designed to investigate the attitudes and perceptions of senior medical students regarding antimicrobial use and resistance. We performed a multi-center survey involving a questionnaire handed out to all fourth year medical students from five representative teaching hospitals in Central China. The survey was completed within 1 month (October to November, 2015). Antimicrobial stewardship programs were taught in all of the teaching hospitals, yet only part of the respondents took part in it. A total of 611 out of 728 students completed our survey. The majority of the respondents (92 %) believed that inappropriate use of antimicrobials causes antimicrobial resistance and agreed with the importance of a strong knowledge of antimicrobials in their medical careers. Most students (67 %) rated their education concerning antimicrobial use and resistance as useful or very useful, but only 25 % recalled having courses on this subject. The overall mean number of correct answers on a section of 11 knowledge questions was 3.78 (standard deviation 1.57, P value for score between hospitals <0.001). We should make an effort to optimize curriculum system in Chinese institutions, and this may contribute to making our future doctors better prepared for antimicrobial stewardship and prudent antimicrobial prescribing.

Capacitively coupled and direct-current resistivity surveys of selected reaches of Cozad, Thirty-Mile, Orchard-Alfalfa, Kearney, and Outlet Canals in Nebraska, 2012-13

USGS Publications Warehouse

Hobza, Christopher M.; Burton, Bethany L.; Lucius, Jeffrey E.; Tompkins, Ryan E.

2014-01-01

Understanding the spatial characteristics of leakage from canals is critical to effectively managing and utilizing water resources for irrigation and hydroelectric purposes. Canal leakage in some parts of Nebraska is the primary source of water for groundwater recharge and helps maintain the base flow of streams. Because surface-water supplies depend on the streamflow of the Platte River and the available water stored in upstream reservoirs, water managers seek to minimize conveyance losses, which can include canal leakage. The U.S. Geological Survey, in cooperation with the Central Platte Natural Resources District and Nebraska Public Power District, used capacitively coupled (CC) and direct-current (DC) resistivity techniques for continuous resistivity profiling to map near-surface lithologies near and underlying the Cozad, Thirty-Mile, Orchard-Alfalfa, Kearney, and Outlet Canals. Approximately 84 kilometers (km) of CC-resistivity data were collected along the five canals. The CC-resistivity data were compared with results from continuous sediment cores and electrical conductivity logs. Generally, the highest resistivities were recorded at the upstream reaches of the Cozad, Thirty-Mile, and Orchard-Alfalfa canals where flood-plain deposits of silt and clay mantle coarser channel deposits of sand and gravel. The finer grained deposits gradually thicken with increasing distance away from the Platte River. Consequently, for many surveyed reaches the thickness of fine-grained deposits exceeded the 8-meter depth of investigation. A detailed geophysical investigation along a 5-km reach of the Outlet Canal southwest of North Platte, Nebraska, used CC and DC resistivity to examine the condition of a compacted-core bank structure and characterized other potential controls on areas of focused seepage. CC-resistivity data, collected along the 5-km study reach, were compared with continuous sediment cores and DC-resistivity data collected near a selected seep near Outlet Canal mile post 15.55 along 5 separate profiles. DC-resistivity results were compared to a schematic cross section of the Outlet Canal north embankment that include the original surfaces and modifications to the compacted-core bank structure. Along the canal road south line, there is a transition from high resistivity at land surface to much lower resistivity near the estimated depth of the northern slope of the original compacted-core bank; however, the surveyed elevation of the water surface in the canal also is at this elevation. Along the canal road north line, there is a transition from high resistivity near land surface to lower resistivity at depth. Although the transition is rapid near the estimated depth of the first-modified bank slope, it also is coincident with the groundwater level measured in piezometer PZ-4. Currently (2013), it is unknown if the indicated changes in resistivity at these elevations was the effect of saturation of the underlying sediments or caused by the compacted-core bank.

Multidrug-resistant Pulmonary Tuberculosis Among Young Korean Soldiers in a Communal Setting

PubMed Central

Lee, Sei Won; Kim, Kwang Hyun; Min, Kyung Hoon

2009-01-01

The goal of this study was to evaluate the prevalence of first-line anti-tuberculosis drug resistance and risk factors associated with multidrug-resistant tuberculosis (MDR TB) among young soldiers in the Korean military, which has a strict tuberculosis control program. All patients with culture-confirmed pulmonary tuberculosis during their service at the Armed Forces Capital Hospital from January 2001 to December 2006 were enrolled in the study. Drug resistant Mycobacterium tuberculosis was isolated from 18 patients (12.2%) and multidrug-resistant M. tuberculosis was isolated from 12 patients (8.1%). Previous treatment of tuberculosis and the presence of a cavity on the patient's chest computed tomography scan were associated with MDR TB; military rank, smoking habits, and positive acid-fast bacilli smears were not associated with MDR TB. In a multiple logistic regression analysis, previous treatment of tuberculosis was a significant independent risk factor for MDR TB (odds ratio 6.12, 95% confidence interval 1.53-24.46). The prevalence of drug resistant tuberculosis among young soldiers in the Korean military was moderately high and the majority of resistant cases were found in patients who had undergone previous treatment of tuberculosis. Based on our results, we suggest that relapsed tuberculosis cases within communal settings should be cautiously managed until the drug susceptibility tests report is completed, even if previous treatment results were satisfactory. PMID:19654938

Hydrologic interpretation of geophysical data from the southeastern Hueco Bolson, El Paso, and Hudspeth Counties, Texas

USGS Publications Warehouse

Gates, Joseph Spencer; Stanley, W.D.

1976-01-01

Airborne-electromagnetic and earth-resistivity surveys were used to explore for fresh ground water in the Hueco Bolson southeast of El Paso, Texas. Aerial surveys were made along about 500 miles (800 km) of flight line, and 67 resistivity soundings were made along 110 miles (180 km) of profile. The surveys did not indicate the presence of any large bodies of fresh ground water, but several areas may be underlain by small to moderate amounts of fresh to slightly saline water.The material underlying the flood plain of the Rio Grande is predominantly clay or sand of low resistivity. Along a band on the mesa next to and parallel to the flood plain, more resistive material composed partly of deposits of an ancient river channel extends to depths of about 400 to 1,700 feet (120 to 520 m). Locally, the lower part of this more resistive material is saturated with fresh to slightly saline water. The largest body of fresh to slightly saline ground water detected in this study is between Fabens and Tornillo, Texas, mostly in the sandhill area between the flood plain and the mesa. Under assumed conditions, the total amount of water in storage may be as much as 400,000 to 800,000 acre-feet (500 million to 1 billion m ).The resistivity data indicate that the deep artesian zone southwest of Fabens extends from a depth of about 1,200 feet (365 m) to about 2,800 feet (855 m).

Potential adoption and management of insect-resistant potato in Peru, and implications for genetically engineered potato.

PubMed

Buijs, Jasper; Martinet, Marianne; de Mendiburu, Felipe; Ghislain, Marc

2005-01-01

This paper analyzes some important issues surrounding possible deployment of genetically engineered (GE) insect-resistant potato in Peru, based on a large farmer survey held in Peru in 2003. We found that the formal seed system plays a limited role compared with the informal seed system, especially for smallholder farmers. Although 97% of smallholder farmers would buy seed of an insect-resistant variety, a majority would buy it only once every 2 to 4 years. Survey data show that farmers would be willing to pay a premium of 50% on seed cost for insect resistant varieties. Paying price premiums of 25% to 50%, farmers would still increase their net income, assuming insect resistance is high and pesticide use will be strongly reduced. Of all farmers, 55% indicated preference for insect-resistant potato in varieties other than their current varieties. The survey indicates that smallholder farmers are interested to experiment with new varieties and have a positive perception of improved varieties. Based on these findings, and considering the difficulties implementing existing biosafety regulatory systems such as those in place in the U.S. and E.U., we propose to develop a variety-based segregation system to separate GE from conventionally bred potatoes. In such a system, which would embrace the spread of GE potatoes through informal seed systems, only a limited number of sterile varieties would be introduced that are easily distinguishable from conventional varieties.

Kirchhoff and Ohm in action: solving electric currents in continuous extended media

NASA Astrophysics Data System (ADS)

Dolinko, A. E.

2018-03-01

In this paper we show a simple and versatile computational simulation method for determining electric currents and electric potential in 2D and 3D media with arbitrary distribution of resistivity. One of the highlights of the proposed method is that the simulation space containing the distribution of resistivity and the points of external applied voltage are introduced by means of digital images or bitmaps, which easily allows simulating any phenomena involving distributions of resistivity. The simulation is based on the Kirchhoff’s laws of electric currents and it is solved by means of an iterative procedure. The method is also generalised to account for media with distributions of reactive impedance. At the end of this work, we show an example of application of the simulation, consisting in reproducing the response obtained with the geophysical method of electric resistivity tomography in presence of soil cracks. This paper is aimed at undergraduate or graduated students interested in computational physics and electricity and also researchers involved in the area of continuous electric media, which could find a simple and powerful tool for investigation.

Inverse Tomo-Lithography for Making Microscopic 3D Parts

NASA Technical Reports Server (NTRS)

White, Victor; Wiberg, Dean

2003-01-01

According to a proposal, basic x-ray lithography would be extended to incorporate a technique, called inverse tomography, that would enable the fabrication of microscopic three-dimensional (3D) objects. The proposed inverse tomo-lithographic process would make it possible to produce complex shaped, submillimeter-sized parts that would be difficult or impossible to make in any other way. Examples of such shapes or parts include tapered helices, paraboloids with axes of different lengths, and even Archimedean screws that could serve as rotors in microturbines. The proposed inverse tomo-lithographic process would be based partly on a prior microfabrication process known by the German acronym LIGA (lithographie, galvanoformung, abformung, which means lithography, electroforming, molding). In LIGA, one generates a precise, high-aspect ratio pattern by exposing a thick, x-ray-sensitive resist material to an x-ray beam through a mask that contains the pattern. One can electrodeposit metal into the developed resist pattern to form a precise metal part, then dissolve the resist to free the metal. Aspect ratios of 100:1 and patterns into resist thicknesses of several millimeters are possible.

Identification of a novel mutation in a patient with pseudohypoparathyroidism type Ia

PubMed Central

Lee, Ye Seung; Kim, Hui Kwon; Kim, Hye Rim; Lee, Jong Yoon; Choi, Joong Wan; Bae, Eun Ju; Oh, Phil Soo; Park, Won Il; Ki, Chang Seok

2014-01-01

Pseudohypoparathyroidism type Ia (PHP Ia) is a disorder characterized by multiform hormonal resistance including parathyroid hormone (PTH) resistance and Albright hereditary osteodystrophy (AHO). It is caused by heterozygous inactivating mutations within the Gs alpha-encoding GNAS exons. A 9-year-old boy presented with clinical and laboratory abnormalities including hypocalcemia, hyperphosphatemia, PTH resistance, multihormone resistance and AHO (round face, short stature, obesity, brachydactyly and osteoma cutis) which were typical of PHP Ia. He had a history of repeated convulsive episodes that started from the age of 2 months. A cranial computed tomography scan showed bilateral calcifications in the basal ganglia and his intelligence quotient testing indicated mild mental retardation. Family history revealed that the patient's maternal relatives, including his grandmother and 2 of his mother's siblings, had features suggestive of AHO. Sequencing of the GNAS gene of the patient identified a heterozygous nonsense mutation within exon 11 (c.637 C>T). The C>T transversion results in an amino acid substitution from Gln to stop codon at codon 213 (p.Gln213*). To our knowledge, this is a novel mutation in GNAS. PMID:25045367

Large resistive 2D Micromegas with genetic multiplexing and some imaging applications

NASA Astrophysics Data System (ADS)

Bouteille, S.; Attié, D.; Baron, P.; Calvet, D.; Magnier, P.; Mandjavidze, I.; Procureur, S.; Riallot, M.

2016-10-01

The performance of the first large resistive Micromegas detectors with 2D readout and genetic multiplexing is presented. These detectors have a 50 × 50cm2 active area and are equipped with 1024 strips both in X- and Y-directions. The same genetic multiplexing pattern is applied on both coordinates, resulting in the compression of signals on 2 × 61 readout channels. Four such detectors have been built at CERN, and extensively tested with cosmics. The resistive strip film allows for very high gain operation, compensating for the charge spread on the 2 dimensions as well as the S / N loss due to the huge, 1 nF input capacitance. This film also creates a significantly different signal shape in the X- and Y-coordinates due to the charge evacuation along the resistive strips. All in all a detection efficiency above 95% is achieved with a 1 cm drift gap. Though not yet optimal, the measured 300 μm spatial resolution allows for very precise imaging in the field of muon tomography, and some applications of these detectors are presented.

The effect of obesity and insulin resistance on macular choroidal thickness in a pediatric population as assessed by enhanced depth imaging optical coherence tomography.

PubMed

Topcu-Yilmaz, Pinar; Akyurek, Nesibe; Erdogan, Erkan

2018-06-23

The purpose of this study was to evaluate the macular choroidal thickness in obese children with and without insulin resistance (IR). Thirty-six patients with obesity and 26 healthy volunteers were included in this cross-sectional study. The choroidal thickness was measured with enhanced depth imaging optical coherence tomography (EDI-OCT) at the fovea and at positions 500 μm, 1000 μm, 1500 μm nasal and temporal to the fovea. The choroidal thickness measurements of the groups were compared and the correlation between the homeostasis model assessment of insulin resistance (HOMA-IR) and choroidal thickness values was evaluated. The average choroidal thickness in the obese group was significantly lower than that of controls at locations 1000 μm (303.31±58.52 vs. 340.58±69.47, p=0.026) and 1500 μm (284.14±65.06 vs. 336.85±71.37, p=0.004) temporal to the fovea. A subgroup analysis depending on the presence of IR revealed that the choroidal thickness measurements at all positions were thinner in obese children without IR compared to children with IR and healthy controls. This thinning reached a statistical significance at locations 500 μm temporal, 1000 μm temporal and 1500 μm temporal to the fovea (p=0.03, p=0.009 and p=0.006; respectively). There was a moderate correlation between the choroidal thickness measurements and HOMA-IR values (r-values between 0.37 and 0.48; p<0.05). Our results suggest that obesity and IR may have an influence on the choroidal thickness in children. Longitudinal studies will clarify whether these choroidal changes are progressive and are a sign of microvascular dysfunction in childhood obesity.

Multidrug-resistant tuberculosis, Somalia, 2010-2011.

PubMed

Sindani, Ireneaus; Fitzpatrick, Christopher; Falzon, Dennis; Suleiman, Bashir; Arube, Peter; Adam, Ismail; Baghdadi, Samiha; Bassili, Amal; Zignol, Matteo

2013-03-01

In a nationwide survey in 2011, multidrug-resistant tuberculosis (MDR TB) was found in 5.2% and 40.8% of patients with new and previously treated TB, respectively. These levels of drug resistance are among the highest ever documented in Africa and the Middle East. This finding presents a serious challenge for TB control in Somalia.

Prevalence of drug-resistant tuberculosis in Nigeria: A systematic review and meta-analysis

PubMed Central

Onyedum, Cajetan C.; Alobu, Isaac

2017-01-01

Background Drug-resistant tuberculosis (TB) undermines control efforts and its burden is poorly understood in resource-limited settings. We performed a systematic review and meta-analysis to provide an up-to-date summary of the extent of drug-resistant TB in Nigeria. Methods We searched PubMed, Scopus, Embase, HINARI, AJOL, the Cochrane library, Web of Science, and Google Scholar for reports published before January 31 2017, that included any resistance, mono-resistance or multidrug resistance to anti-TB drugs in Nigeria. Summary estimates were calculated using random effects models. Results We identified 34 anti-TB drug resistance surveys with 8002 adult TB patients consisting of 2982 new and 5020 previously-treated cases. The prevalence rate of any drug resistance among new TB cases was 32.0% (95% CI 24.0–40.0%; 734/2892) and among previously-treated cases, the rate was 53.0% (95% CI 35.0–71.0%; 1467/5020). Furthermore, multidrug resistance among new and previously-treated cases was 6.0% (95% CI 4.0–8.0%;161/2502)and 32.0% (95%CI 20.0–44.0; 357/949), respectively. There was significant heterogeneity between the studies (p<0.001, I2 tests). The prevalence of drug-resistant TB varied according to methods of drug susceptibility testing and geographic region of Nigeria. Conclusion The burden of drug-resistant TB in Nigeria is high. We recommend that a national anti-TB drug resistance survey be carried out, and strategies for case detection and programmatic management of drug-resistant TB in Nigeria need to be strengthened. PMID:28704459