Preliminary relative permeability estimates of methanehydrate-bearing sand
Seol, Yongkoo; Kneafsey, Timothy J.; Tomutsa, Liviu; Moridis,George J.
2006-05-08
The relative permeability to fluids in hydrate-bearing sediments is an important parameter for predicting natural gas production from gas hydrate reservoirs. We estimated the relative permeability parameters (van Genuchten alpha and m) in a hydrate-bearing sand by means of inverse modeling, which involved matching water saturation predictions with observations from a controlled waterflood experiment. We used x-ray computed tomography (CT) scanning to determine both the porosity and the hydrate and aqueous phase saturation distributions in the samples. X-ray CT images showed that hydrate and aqueous phase saturations are non-uniform, and that water flow focuses in regions of lower hydrate saturation. The relative permeability parameters were estimated at two locations in each sample. Differences between the estimated parameter sets at the two locations were attributed to heterogeneity in the hydrate saturation. Better estimates of the relative permeability parameters require further refinement of the experimental design, and better description of heterogeneity in the numerical inversions.
Two Relations to Estimate Membrane Permeability Using Milestoning
2016-01-01
Prediction of passive permeation rates of solutes across lipid bilayers is important to drug design, toxicology, and other biological processes such as signaling. The inhomogeneous solubility-diffusion (ISD) equation is traditionally used to relate the position-dependent potential of mean force and diffusivity to the permeability coefficient. The ISD equation is derived via the Smoluchowski equation and assumes overdamped system dynamics. It has been suggested that the complex membrane environment may exhibit more complicated damping conditions. Here we derive a variant of the inhomogeneous solubility diffusion equation as a function of the mean first passage time (MFPT) and show how milestoning, a method that can estimate kinetic quantities of interest, can be used to estimate the MFPT of membrane crossing and, by extension, the permeability coefficient. We further describe a second scheme, agnostic to the damping condition, to estimate the permeability coefficient from milestoning results or other methods that compute a probability of membrane crossing. The derived relationships are tested using a one-dimensional Langevin dynamics toy system confirming that the presented theoretical methods can be used to estimate permeabilities given simulation and milestoning results. PMID:27154639
Estimating three phase relative permeability based on realistic pore scale configurations
NASA Astrophysics Data System (ADS)
Verma, R.; Prodanovic, M.; Wildenschild, D.
2013-12-01
Multiphase (water, oil, gas) flow in porous media is commonly encountered in subsurface. Study of multiphase flows is important in applications such as hydrocarbon recovery, carbon capture and storage, groundwater flow modeling, flow of non-aqueous phase liquids (NAPL), and many others. The problem is notoriously difficult to study, and much effort has gone into understanding the physics of the multiphase flow on the pore scale. In particular, imaging techniques such as x-ray microtomography can now provide 3D microstructure as well as fluid phase configurations at a very high resolution. Using these images, one can validate simulations done by various techniques, such as pore network modeling, the Lattice-Boltzmann method or computational fluid dynamics to name a few. In this work, we present an analysis of several pore-scale images of multiphase flow as well as comparable multiphase flow simulations and show the distribution of various phases in three phase flow situations. We are particularly interested in quantifying spatial configurations, connectivity and relative permeability of the intermediate wetting phase. The rock wettability is one of the key parameters that determines positioning of the phases within the pore space. The wetting phase sticks closer to the wall, while the non-wetting phase is at the center of the pores. In three phase flow, the intermediate wetting phase exists as a layer between the two phases, and this is often the oil phase that we are trying to drain from the system. At the macro scale, this means that the relative permeability is a function of more than one saturation as well as its often complicated spatial configuration. One of the key observations from experiment is high oil relative permeability even at low oil saturations. It is hypothesized that the oil exists as a very thin layer throughout the core sample, and one of the goals of this work is to validate this hypothesis. This layer is rather difficult to observe even with
NASA Astrophysics Data System (ADS)
Jiang, F.; Tsuji, T.
2017-01-01
Given the world's growing demand for energy, a combination of geological CO2 sequestration and enhanced oil recovery (EOR) technologies is currently regarded as a promising solution, as it would provide a means of reducing carbon emissions into the atmosphere while also leading to the economic benefit of simultaneously recovering oil. The optimization of injection strategies to maximize CO2 storage and increase the oil recovery factors requires complicated pore-scale flow information within a reservoir system consisting of coexisting oil, water, and CO2 phases. In this study, an immiscible three-phase lattice-Boltzmann (LB) model was developed to investigate the complicated flow state with interaction between water, oil, and CO2 systems in porous media. The two main mechanisms of oil remobilization, namely, double-drainage and film flow, can be captured by our model. The estimation of three-phase relative permeability is proposed using the digital rock physics (DRP) simulations. The results indicate that the relative permeability of CO2 as calculated using our steady state method is not sensitive to the initial oil fraction if the oil distribution is originally uniform. Baker's (1988) empirical model was tested and found to be able to provide a good prediction of the three-phase relative permeability data. Our numerical method provides a new tool for accurately predicting three-phase relative permeability data directly based on micro-CT rock images.
NASA Astrophysics Data System (ADS)
Zhou, Kang; Hou, Jian; Fu, Hongfei; Wei, Bei; Liu, Yongge
2017-01-01
Relative permeability controls the flow of multiphase fluids in porous media. The estimation of relative permeability is generally solved by Levenberg-Marquardt method with finite difference Jacobian approximation (LM-FD). However, the method can hardly be used in large-scale reservoirs because of unbearably huge computational cost. To eliminate this problem, the paper introduces the idea of simultaneous perturbation to simplify the generation of the Jacobian matrix needed in the Levenberg-Marquardt procedure and denotes the improved method as LM-SP. It is verified by numerical experiments and then applied to laboratory experiments and a real commercial oilfield. Numerical experiment indicates that LM-SP uses only 16.1% computational cost to obtain similar estimation of relative permeability and prediction of production performance compared with LM-FD. Laboratory experiment also shows the LM-SP has a 60.4% decrease in simulation cost while a 68.5% increase in estimation accuracy compared with the earlier published results. This is mainly because LM-FD needs 2n (n is the number of controlling knots) simulations to approximate Jacobian in each iteration, while only 2 simulations are enough in basic LM-SP. The convergence rate and estimation accuracy of LM-SP can be improved by averaging several simultaneous perturbation Jacobian approximations but the computational cost of each iteration may be increased. Considering the estimation accuracy and computational cost, averaging two Jacobian approximations is recommended in this paper. As the number of unknown controlling knots increases from 7 to 15, the saved simulation runs by LM-SP than LM-FD increases from 114 to 1164. This indicates LM-SP is more suitable than LM-FD for multivariate problems. Field application further proves the applicability of LM-SP on large real field as well as small laboratory problems.
Relative permeability through fractures
Diomampo, Gracel, P.
2001-08-01
The mechanism of two-phase flow through fractures is of importance in understanding many geologic processes. Currently, two-phase flow through fractures is still poorly understood. In this study, nitrogen-water experiments were done on both smooth and rough parallel plates to determine the governing flow mechanism for fractures and the appropriate methodology for data analysis. The experiments were done using a glass plate to allow visualization of flow. Digital video recording allowed instantaneous measurement of pressure, flow rate and saturation. Saturation was computed using image analysis techniques. The experiments showed that gas and liquid phases flow through fractures in nonuniform separate channels. The localized channels change with time as each phase path undergoes continues breaking and reforming due to invasion of the other phase. The stability of the phase paths is dependent on liquid and gas flow rate ratio. This mechanism holds true for over a range of saturation for both smooth and rough fractures. In imbibition for rough-walled fractures, another mechanism similar to wave-like flow in pipes was also observed. The data from the experiments were analyzed using Darcy's law and using the concept of friction factor and equivalent Reynold's number for two-phase flow. For both smooth- and rough-walled fractures a clear relationship between relative permeability and saturation was seen. The calculated relative permeability curves follow Corey-type behavior and can be modeled using Honarpour expressions. The sum of the relative permeabilities is not equal one, indicating phase interference. The equivalent homogeneous single-phase approach did not give satisfactory representation of flow through fractures. The graphs of experimentally derived friction factor with the modified Reynolds number do not reveal a distinctive linear relationship.
NASA Astrophysics Data System (ADS)
Hiratsuka, Y.; Yamamoto, H.
2014-12-01
CCS (Carbon dioxide Capture and Storage) is a promising option for mitigating climate changes. To predict the behavior of injected CO2 in a deep reservoir, relative permeability of supercritical CO2 and water of the reservoir rock is one of the most fundamental and influential properties. For determining the relative permeability, we employed the unsteady state method, in which the relative permeability is determined based on history matching of transient monitoring data with a multi-phase flow model. The unsteady-state method is relatively simple and short, but obviously its accuracy strongly depends on the flow model assumed in the history matching. In this study, we conducted relative permeability measurements of supercritical CO2-water system for Berea sandstone with the unsteady-state method under a reservoir condition at a 1km depth (P= 9.5MPa, T = 44˚C). Automatic history matching was performed with an inversion simulator iTOUGH2/ECO2N for multi-phase flow system of supercritical CO2, NaCl, and water. A sensitivity analysis of relative permeability parameters for CO2 and water was carried out to better understand the uniqueness and the uncertainty of the optimum solution estimated by the history matching. Among the parameters of the Corey-type curve employed in this study, while the end-point permeability could be optimized in a limited range, the other parameters were correlated and their combinations were not unique. However it was found that any combination of these parameters results in nearly identical shapes of the curve in the range of CO2 saturation in this study (0 to 60%). The optimally estimated curve from the unsteady-method was well comparable with those from the steady-state method acquired in the previous studies. Our experiment also focuses on the impact of injection rate on the estimates of relative permeability, as it is known that the injection rate could have a significant effect on fluid distribution such as viscous fingering with
Relative Permeability of Fractured Rock
Mark D. Habana
2002-06-30
Contemporary understanding of multiphase flow through fractures is limited. Different studies using synthetic fractures and various fluids have yielded different relative permeability-saturation relations. This study aimed to extend the understanding of multiphase flow by conducting nitrogen-water relative permeability experiments on a naturally-fractured rock from The Geysers geothermal field. The steady-state approach was used. However, steady state was achieved only at the endpoint saturations. Several difficulties were encountered that are attributed to phase interference and changes in fracture aperture and surface roughness, along with fracture propagation/initiation. Absolute permeabilities were determined using nitrogen and water. The permeability values obtained change with the number of load cycles. Determining the absolute permeability of a core is especially important in a fractured rock. The rock may change as asperities are destroyed and fractures propagate or st rain harden as the net stresses vary. Pressure spikes occurred in water a solute permeability experiments. Conceptual models of an elastic fracture network can explain the pressure spike behavior. At the endpoint saturations the water relative permeabilities obtained are much less than the nitrogen gas relative permeabilities. Saturations were determined by weighing and by resistivity calculations. The resistivity-saturation relationship developed for the core gave saturation values that differ by 5% from the value determined by weighing. Further work is required to complete the relative permeability curve. The steady-state experimental approach encountered difficulties due to phase interference and fracture change. Steady state may not be reached until an impractical length of time. Thus, unsteady-state methods should be pursued. In unsteady-state experiments the challenge will be in quantifying rock fracture change in addition to fluid flow changes.
NASA Astrophysics Data System (ADS)
Sanford, Ward E.
2017-03-01
The trend of decreasing permeability with depth was estimated in the fractured-rock terrain of the upper Potomac River basin in the eastern USA using model calibration on 200 water-level observations in wells and 12 base-flow observations in subwatersheds. Results indicate that permeability at the 1-10 km scale (for groundwater flowpaths) decreases by several orders of magnitude within the top 100 m of land surface. This depth range represents the transition from the weathered, fractured regolith into unweathered bedrock. This rate of decline is substantially greater than has been observed by previous investigators that have plotted in situ wellbore measurements versus depth. The difference is that regional water levels give information on kilometer-scale connectivity of the regolith and adjacent fracture networks, whereas in situ measurements give information on near-hole fractures and fracture networks. The approach taken was to calibrate model layer-to-layer ratios of hydraulic conductivity (LLKs) for each major rock type. Most rock types gave optimal LLK values of 40-60, where each layer was twice a thick as the one overlying it. Previous estimates of permeability with depth from deeper data showed less of a decline at <300 m than the regional modeling results. There was less certainty in the modeling results deeper than 200 m and for certain rock types where fewer water-level observations were available. The results have implications for improved understanding of watershed-scale groundwater flow and transport, such as for the timing of the migration of pollutants from the water table to streams.
NASA Astrophysics Data System (ADS)
Sanford, Ward E.
2016-11-01
The trend of decreasing permeability with depth was estimated in the fractured-rock terrain of the upper Potomac River basin in the eastern USA using model calibration on 200 water-level observations in wells and 12 base-flow observations in subwatersheds. Results indicate that permeability at the 1-10 km scale (for groundwater flowpaths) decreases by several orders of magnitude within the top 100 m of land surface. This depth range represents the transition from the weathered, fractured regolith into unweathered bedrock. This rate of decline is substantially greater than has been observed by previous investigators that have plotted in situ wellbore measurements versus depth. The difference is that regional water levels give information on kilometer-scale connectivity of the regolith and adjacent fracture networks, whereas in situ measurements give information on near-hole fractures and fracture networks. The approach taken was to calibrate model layer-to-layer ratios of hydraulic conductivity (LLKs) for each major rock type. Most rock types gave optimal LLK values of 40-60, where each layer was twice a thick as the one overlying it. Previous estimates of permeability with depth from deeper data showed less of a decline at <300 m than the regional modeling results. There was less certainty in the modeling results deeper than 200 m and for certain rock types where fewer water-level observations were available. The results have implications for improved understanding of watershed-scale groundwater flow and transport, such as for the timing of the migration of pollutants from the water table to streams.
SINGLE-INTERVAL GAS PERMEABILITY ESTIMATION
Single-interval, steady-steady-state gas permeability testing requires estimation of pressure at a screened interval which in turn requires measurement of friction factors as a function of mass flow rate. Friction factors can be obtained by injecting air through a length of pipe...
SINGLE-INTERVAL GAS PERMEABILITY ESTIMATION
Single-interval, steady-steady-state gas permeability testing requires estimation of pressure at a screened interval which in turn requires measurement of friction factors as a function of mass flow rate. Friction factors can be obtained by injecting air through a length of pipe...
Steam-water relative permeability
Ambusso, W.; Satik, C.; Home, R.N.
1997-12-31
A set of relative permeability relations for simultaneous flow of steam and water in porous media have been measured in steady state experiments conducted under the conditions that eliminate most errors associated with saturation and pressure measurements. These relations show that the relative permeabilities for steam-water flow in porous media vary approximately linearly with saturation. This departure from the nitrogen/water behavior indicates that there are fundamental differences between steam/water and nitrogen/water flows. The saturations in these experiments were measured by using a high resolution X-ray computer tomography (CT) scanner. In addition the pressure gradients were obtained from the measurements of liquid phase pressure over the portions with flat saturation profiles. These two aspects constitute a major improvement in the experimental method compared to those used in the past. Comparison of the saturation profiles measured by the X-ray CT scanner during the experiments shows a good agreement with those predicted by numerical simulations. To obtain results that are applicable to general flow of steam and water in porous media similar experiments will be conducted at higher temperature and with porous rocks of different wetting characteristics and porosity distribution.
Characterization and estimation of permeability correlation structure from performance data
Ershaghi, I.; Al-Qahtani, M.
1997-08-01
In this study, the influence of permeability structure and correlation length on the system effective permeability and recovery factors of 2-D cross-sectional reservoir models, under waterflood, is investigated. Reservoirs with identical statistical representation of permeability attributes are shown to exhibit different system effective permeability and production characteristics which can be expressed by a mean and variance. The mean and variance are shown to be significantly influenced by the correlation length. Detailed quantification of the influence of horizontal and vertical correlation lengths for different permeability distributions is presented. The effect of capillary pressure, P{sub c1} on the production characteristics and saturation profiles at different correlation lengths is also investigated. It is observed that neglecting P{sub c} causes considerable error at large horizontal and short vertical correlation lengths. The effect of using constant as opposed to variable relative permeability attributes is also investigated at different correlation lengths. Next we studied the influence of correlation anisotropy in 2-D reservoir models. For a reservoir under five-spot waterflood pattern, it is shown that the ratios of breakthrough times and recovery factors of the wells in each direction of correlation are greatly influenced by the degree of anisotropy. In fully developed fields, performance data can aid in the recognition of reservoir anisotropy. Finally, a procedure for estimating the spatial correlation length from performance data is presented. Both the production performance data and the system`s effective permeability are required in estimating the correlation length.
IMPACT OF CAPILLARY AND BOND NUMBERS ON RELATIVE PERMEABILITY
Kishore K. Mohanty
2002-09-30
Recovery and recovery rate of oil, gas and condensates depend crucially on their relative permeability. Relative permeability in turn depends on the pore structure, wettability and flooding conditions, which can be represented by a set of dimensionless groups including capillary and bond numbers. The effect of flooding conditions on drainage relative permeabilities is not well understood and is the overall goal of this project. This project has three specific objectives: to improve the centrifuge relative permeability method, to measure capillary and bond number effects experimentally, and to develop a pore network model for multiphase flows. A centrifuge has been built that can accommodate high pressure core holders and x-ray saturation monitoring. The centrifuge core holders can operate at a pore pressure of 6.9 MPa (1000 psi) and an overburden pressure of 17 MPa (2500 psi). The effect of capillary number on residual saturation and relative permeability in drainage flow has been measured. A pore network model has been developed to study the effect of capillary numbers and viscosity ratio on drainage relative permeability. Capillary and Reynolds number dependence of gas-condensate flow has been studied during well testing. A method has been developed to estimate relative permeability parameters from gas-condensate well test data.
Relating tortuosity and permeability in microfractured and unfractured porous media
NASA Astrophysics Data System (ADS)
Tokan-Lawal, A.; Wang, W.; Prodanovic, M.
2012-12-01
Permeability estimates are key to any subsurface flow prediction. Several methods are available for estimating (relative) permeability either on Darcy scale (lab measurements) or on pore scale (numerical flow simulation, assuming pore space geometry is known). However, relative permeability measurements in particular can be time consuming, and there is a benefit in having a fast estimate. Thus, a number of permeability estimates are available based on the some known porous medium parameters. The famous Carman Kozeny (1937) model represents the pores as parallel tubes of length equal to the sample length and of a range of radii. This single phase permeability model developed for packings of equal spherical grains relates the absolute permeability to the tortuosity of the medium. Fractures or fracture networks, on the other hand, do not lend themselves to an analytical description akin to pores spaces in-between a packing of spheres. Thus far, the study of flow in fractures has for the most part been limited to fractures in rock with impermeable fractures. The simplest models, such as the cubic law, relate fracture permeability to its average aperture and model fracture as parallel planes which are insufficient to extend to multiphase displacement. In this study, we focus on correlating permeability with geometric tortuosity of both pore space and individual fluid phases for a wide variety of homogeneous as well as microfractured porous samples. We use a combination of lattice-Boltzmann simulation and the level set method based progressive-quasistatic (LSMPQS) algorithm to characterize the capillary dominated flow properties (capillary pressure-saturation and relative permeability-saturation relationships) of the matrix, and when present, the fracture, in samples of different compositions. At the same time, we use image analysis tools to characterize the connectivity and tortuosity of the pore space, as well as individual fluid phases at different saturations
Satiated Relative Permeability of Variable-Aperture Fractures
Detwiler, R L; Glass, R J; Rajaram, H; Nicholl, M J
2001-12-11
The relative permeability of a variable-aperture fracture under satiated conditions (wetting phase spans the fracture, non-wetting phase is completely entrapped) is controlled by the distribution of the entrapped phase within the fracture plane. We use simulations to investigate the combined influence of capillary forces and aperture variability on satiated relative permeability and demonstrate the effectiveness of a dimensionless perturbation curvature number (C') for predicting entrapped-phase structure. C' combines the relative influence of in-plane and out-of-plane interface curvature and the aperture coefficient of variation ({sigma}{sub a}/) on local capillary forces. Results suggest that C' provides a single parameter that can be used to estimate satiated relative permeability.
Estimation of sub-core permeability statistical properties from coreflooding data
NASA Astrophysics Data System (ADS)
Rabinovich, Avinoam
2017-10-01
Knowledge of sub-core permeability is necessary for accurate numerical modeling of coreflooding experiments and for investigation of sub-core flow phenomenon. A new method for estimating sub-core permeability geometric mean (kG) and log-permeability variance (σy2) is presented. The method is based on matching coreflooding experiment measurements of wetting phase relative permeability with semi-analytical calculations of effective relative permeability. The semi-analytical solution is formulated assuming log-normal permeability (k), steady state and capillary-limit conditions. It is based on the geometric mean and log-phase-permeability variance for isotropic k and power law averaging for anisotropic correlations. The solution is validated on synthetic k realizations by comparison with numerical calculations. Then, the estimation method is tested on synthetic data assuming various types of core capillary pressure relationships, relative permeability functions and k anisotropies. Results demonstrate high accuracy in almost all of the cases except for small anisotropy ratios lh/lv between horizontal (lh) and vertical (lv) dimensionless correlation lengths, where flow is in the horizontal direction, and when σy2 is large. The method is also validated using data from CO2-brine coreflooding experiments conducted on two different cores. It is found that the estimation method remains accurate in these realistic settings, however, accuracy of kG is reduced when the core permeability departs from a log-normal distribution.
Relating tortuosity and permeability in the Niobrara Formation
NASA Astrophysics Data System (ADS)
Tokan-Lawal, A.; Landry, C.; Prodanovic, M.; Eichhubl, P.
2013-12-01
Natural fractures are typically partially lined and/or filled with mineral cements, which can constrict fluid flow and create very rough fracture wall surfaces. In this study, we investigate fluid flow in the carbonate-rich, low-matrix permeability Niobrara formation. We focus on correlating fluid flow parameters (such as permeability) with the geometric tortuosity of the fracture (pore space) and the individual fluid phases for a fractured carbonate. We use x-ray microtomography imaging to provide information on fracture geometry. Image analysis is performed (via 3DMA Rock software), to characterize the connectivity and geometric tortuosity of the pore space and individual fluid phases at different saturations. We also use a combination of the level-set-method-based progressive-quasistatic algorithm (LSMPQS software), and lattice Boltzmann simulation (Palabos software) to characterize the capillary dominated displacement properties and the relative permeability of the naturally cemented fractures within. Finally, we numerically investigate the effect of (uniform) cementation on the fracture permeability as well as the tortuosity of the pore space and the capillary pressure-water saturation (Pc-Sw) relationship using two different methods. Permeability estimates in the Niobrara sample were consistent regardless of the method used. Pore space tortuosity and capillary pressure as a function of water saturation relationships both increase with cementation, and while the behavior is similar to that of cementation effects in sandstones, it is much more abrupt in fractures. This is likely because the fluid pathways are restricted to nearly planar spaces.
Permeability estimation from NMR diffusion measurements in reservoir rocks.
Balzarini, M; Brancolini, A; Gossenberg, P
1998-01-01
It is well known that in restricted geometries, such as in porous media, the apparent diffusion coefficient (D) of the fluid depends on the observation time. From the time dependence of D, interesting information can be derived to characterise geometrical features of the porous media that are relevant in oil industry applications. In particular, the permeability can be related to the surface-to-volume ratio (S/V), estimated from the short time behaviour of D(t), and to the connectivity of the pore space, which is probed by the long time behaviour of D(t). The stimulated spin-echo pulse sequence, with pulsed magnetic field gradients, has been used to measure the diffusion coefficients on various homogeneous and heterogeneous sandstone samples. It is shown that the petrophysical parameters obtained by our measurements are in good agreement with those yielded by conventional laboratory techniques (gas permeability and electrical conductivity). Although the diffusing time is limited by T1, eventually preventing an observation of the real asymptotic behaviour, and the surface-to-volume ratio measured by nuclear magnetic resonance is different from the value obtained by BET because of the different length scales probed, the measurement remains reliable and low-time consuming.
Perm-Fit: a new program to estimate permeability at high P-T conditions
NASA Astrophysics Data System (ADS)
Moulas, Evangelos; Madonna, Claudio
2016-04-01
Several geological processes are controlled by porous fluid flow. The circulation of porous fluids influences many physical phenomena and in turn it depends on the rock permeability. The permeability of rocks is a physical property that needs to be measured since it depends on many factors such as secondary porosity (fractures etc). We present a numerical approach to estimate permeability using the transient step method (Brace et al., 1968). When a non-reacting, compressible fluid is considered in a relative incompressible solid matrix, the only unknown parameter in the equations of porous flow is permeability. Porosity is assumed to be known and the physical properties of the fluid (compressibility, density, viscosity) are taken from the NIST database. Forward numerical calculations for different values of permeability are used and the results are compared to experimental measurements. The extracted permeability value is the one that minimizes the misfit between experimental and numerical results. The uncertainty on the value of permeability is estimated using a Monte Carlo method. REFERENCES Brace, W.F., Walsh J.B., & Frangos, W.T. 1968: Permeability of Granite under High Pressure, Journal of Geophysical Research, 73, 6, 2225-2236
NASA Astrophysics Data System (ADS)
Qin, Z.
2016-12-01
Permeability of fracture-matrix system is an important but difficult to estimate parameter in evaluation and production in fractured tight sandstone reservoirs. Because nuclear magnetic resonance (NMR) logs cannot indicate fracture permeability, NMR can be used to obtain accurate matrix permeability in fractured tight sandstones. Considering lateral logs can be used to identify and evaluate fracture, thus the fracture permeability can be estimated using lateral logs. In the interval without fracture, the permeability of fracture-matrix system is equal to the matrix permeability; while in the only fracture permeable interval, it is equal to the fracture permeability. Considering the obtained matrix permeability from NMR logs may include the contribution of fracture porosity in fractured tight sandstones, the estimated matrix permeability and estimated fracture permeability have overlap. Thus the permeability of fracture-matrix system is not a simple summation of the estimated fracture permeability and the estimated matrix permeability. A new method is proposed to obtain consecutive permeability in fractured tight sandstones. In the method, we believe that the obtained fracture permeability from lateral logs contains the actual fracture permeability and the fracture porosity permeability, which is contributed from the fracture porosity in rock. After calculating fracture width by using the Faivre-Sibbit (F-S) model, the fracture porosity can be estimated. Based on the hydraulic flow unit (HFU) approach, the fracture porosity permeability can be calculated, and then the actual fracture permeability can be obtained. Thus the Permeability of fracture-matrix system is the summation of actual fracture permeability and the estimated matrix permeability. Compared with the simple summation in the field example, the method can be used to obtain more reliable permeability of fracture-matrix system.
Estimation of bone permeability using accurate microstructural measurements.
Beno, Thoma; Yoon, Young-June; Cowin, Stephen C; Fritton, Susannah P
2006-01-01
While interstitial fluid flow is necessary for the viability of osteocytes, it is also believed to play a role in bone's mechanosensory system by shearing bone cell membranes or causing cytoskeleton deformation and thus activating biochemical responses that lead to the process of bone adaptation. However, the fluid flow properties that regulate bone's adaptive response are poorly understood. In this paper, we present an analytical approach to determine the degree of anisotropy of the permeability of the lacunar-canalicular porosity in bone. First, we estimate the total number of canaliculi emanating from each osteocyte lacuna based on published measurements from parallel-fibered shaft bones of several species (chick, rabbit, bovine, horse, dog, and human). Next, we determine the local three-dimensional permeability of the lacunar-canalicular porosity for these species using recent microstructural measurements and adapting a previously developed model. Results demonstrated that the number of canaliculi per osteocyte lacuna ranged from 41 for human to 115 for horse. Permeability coefficients were found to be different in three local principal directions, indicating local orthotropic symmetry of bone permeability in parallel-fibered cortical bone for all species examined. For the range of parameters investigated, the local lacunar-canalicular permeability varied more than three orders of magnitude, with the osteocyte lacunar shape and size along with the 3-D canalicular distribution determining the degree of anisotropy of the local permeability. This two-step theoretical approach to determine the degree of anisotropy of the permeability of the lacunar-canalicular porosity will be useful for accurate quantification of interstitial fluid movement in bone.
A Model Relating Root Permeability to Flux and Potentials
Michel, Burlyn E.
1977-01-01
A model that relates hydraulic permeability to water flux and to gradients in pressure potential and solute potential was tested using soybean (Glycine max) plants. Water flux was varied by additions of polyethylene glycol 6,000 around one portion of a divided root system and by changing the light intensity and CO2 concentration around the plants. The data are compatible with the model only if the hydraulic permeability varies with flux; however, the data were insufficient for rigorous testing. Three sets of published data fit the model only if hydraulic permeability varies. Evidence originally presented as involving constant hydraulic permeability is shown, rather, to require variable hydraulic permeability. PMID:16660071
Sensitivity of geothermal reservoir behavior to relative permeability parameters
Bodvarsson, G.S.; O'Sullivan, M.J.; Tsang, C.F.
1980-12-01
Three problems are considered: (1) the sensitivity of the total kinematic viscosity, ..nu..{sub t}, and the flowing enthalpy, h{sub f}, to variations in the relative permeability functions; (2) the determination of ..nu..{sub t} and h/sub f/ from well-test data, following which a method is suggested to use these results together with theoretical plots of the relative permeability functions versus h{sub f} to deduce the general shape of the relative permeability functions; and (3) the effect of the relative permeability functions on the pressure decline and flowing enthalpy build-up during a constant rate production test. (MHR)
Estimated bounds on rock permeability changes from THM Processes
Berge, P A; Blair, S C; Wang, H F
1998-08-01
We performed THM modeling to estimate bounds on permeability changes in the NFE. For our modeling, we used the TM three-dimensional (3-D) finite-difference code FLAC{sup 3D} version 2.0 (Itasca Consulting Group Inc. 1997) to compute changes in stress and displacement in an elastic model subjected to temperature changes over time. Output from TH modeling (Hardin et al., 1998, Chapter 3) using the code NUFT (Nitao 1993) provided the temperature changes for input to FLAC{sup 3D}. We then estimated how the stress changes could affect permeability. For this report, we chose to base our 3-D THM modeling on a coarser version of the 2-D model we ran for the work described in Chapter 4 of the Near-Field/Altered Zone Models Report (Hardin et al., 1998, Chapter 4). The grid and temperature field were based on those used by the TH code for 50 yr of heating for the reference Case 1 TH model calculated using Total System Performance Assessment-Viability Assessment (TSPA-VA) base-case properties, nominal infiltration, and a point-load repository design (Hardin et al., 1998, Chapter 3). The stress field rotated in the region between and below the drifts after 50 yr of heating. High vertical shear stresses were computed for these regions. The maximum computed displacement was about 7 cm, mainly vertical. Estimates of permeability changes were obtained by analyzing stresses, following a method we developed previously for 2-D models. In our 3-D modeling for this report, we only considered vertical and horizontal fractures. We extended our 2-D method to a simplified 3-D case. We conclude that widespread permeability enhancement is likely for fractures parallel to NS fracture set No.2, the vertical fractures that strike north-south, for regions above the drifts. In some regions just above the drifts, permeability may increase by a minimum of a factor of two and possibly more than a factor of four if slip also occurs along the vertical fractures in EW set No.1, the east-west fractures
NASA Astrophysics Data System (ADS)
Lee, M.; Keehm, Y.
2013-12-01
Direct numerical simulation on pore microstructures from X-ray microtomography is regarded as a good tool to determine and characterize the physical properties of rocks, especially for sandstone. When the same approach is considered for carbonate rocks, we face many difficulties mostly from the heterogeneous nature of carbonates. In this study, we report preliminary results on permeability estimation of carbonate rocks from X-ray tomographic pore microstructures. Since carbonate rocks have quite different types of pore geometry depending on depositional and diagenetic environments, we choose three rock samples with different porosity types: interparticle; vuggy/moldic; and fracture, and obtain high-resolution 3D pore microstructures using X-ray microtomography technique. From the original 3D pore geometry (typically 2,000^3 voxels), we choose various digital sub-blocks to determine local variation and length dependency, and calculate permeability using the Lattice-Boltzmann method. For the interparticle case, the calculated permeability values show very similar trends to clastic sediments, and we can determine a porosity-permeability relation for a given formation as we do with the Koneny-Carman relation. On the other hand, for vuggy or fracture cases, we cannot observe any significant dependence of permeability on porosity. Thus we focus more on the local variation and scale variation of permeability. We perform analyses on percolation probability; local porosity distribution; and direction/length/width of fractures. And we present preliminary conceptual models to determine permeability characteristics. Although the results are from a few limited samples and more detailed researches will be required, our approach will be helpful to estimate and characterize permeability of carbonate rocks, and to investigate scaling and representativeness issues. Acknowledgements: This research was supported by the Basic Research Project of the Korea Institute of Geoscience and
Estimation of Permeability Field via Ensemble Kalman Filter
NASA Astrophysics Data System (ADS)
Jafarpour, B.; McLaughlin, D. B.
2005-12-01
History matching, as commonly referred to in petroleum industry, is an inverse parameter estimation problem which uses sparse observations of the states of the reservoir/aquifer (e.g. pressure) to tune spatially distributed parameters such as permeability and porosity. Even though significant progress is made in improving history matching algorithms, current history matching techniques are not suitable for real-time updating of the reservoir models using the frequent observations obtained form smart/intelligent fields and time-lapsed seismic. Recursive data assimilation algorithms, such as those based on the Kalman filter, can update the reservoir model (by tuning unknown parameters) without including previously used data, thereby saving computational cost. They are very convenient to apply with reservoir simulators, do not require adjoint models, and can easily incorporate 4D seismic attributes as areal measurements. Further, these algorithms readily provide an estimate of the uncertainty of the updated parameters and the states as a byproduct of the estimation process. This fits very well into the uncertainty and risk analysis aspects of the reservoir management. Our research focuses on the application of Ensemble Kalman Filter (EnKF) technique in updating reservoir models by integrating static/dynamic point and areal measurements such as frequent production and 4D seismic data. We present our preliminary results from the application of the EnKF in updating reservoir models with and without tuning heterogeneous permeability fields. A discussion of the issues and challenges encountered in our preliminary work will be provided.
Extending Nuclear Magnetic Resonance Data for Permeability Estimation in Fine-Grained Sediments
NASA Astrophysics Data System (ADS)
Daigle, H.; Dugan, B.
2008-12-01
We developed a method for using nuclear magnetic resonance (NMR) T2 data and gamma ray data to estimate lithology-dependent permeability in silt- and clay-rich sediments. This model, based on the Schlumberger-Doll Research (SDR) model, allows for high resolution (<1 m) permeability estimates throughout a logged interval. Our model was calibrated using direct measurements on core samples from Keathley Canyon Lease Block 151 in the northern Gulf of Mexico. From NMR and gamma ray data we are able to determine permeability from 10-18 to 10-14 m2 (0.001 to 10 millidarcies). Thus from discrete core samples and log data we were able to develop a permeability model for the entire sedimentary column (425 m). Lithologic variation was incorporated into the model by varying the A coefficient based on the gamma ray response. This provides a more accurate permeability model than assigning a constant value to A as is typically done. The relationship between A and intrinsic lithologic properties is unclear; simple pore system models suggest that A may be related to specific surface, tortuosity, and pore structure; we investigate simple models to quantify how these properties vary with sediment consolidation and what their relationship is to A. A comprehensive understanding that links NMR data and A to pore-scale properties will provide new constraints on deformation and flow in porous systems, and will contribute to our understanding of sediment properties for fluid flow modeling at local and regional scales.
Blair, S.C.; Berge, P.A.; Berryman, J.G.
1993-08-01
We have developed an image-processing method for characterizing the microstructure of rock and other porous materials, and for providing a quantitative means for understanding the dependence of physical properties on the pore structure. This method is based upon the statistical properties of the microgeometry as observed in scanning electron micrograph (SEM) images of cross sections of porous materials. The method utilizes a simple statistical function, called the spatial correlation function, which can be used to predict bounds on permeability and other physical properties. We obtain estimates of the porosity and specific surface area of the material from the two-point correlation function. The specific surface area can be related to the permeability of porous materials using a Kozeny-Carman relation, and we show that the specific surface area measured on images of sandstones is consistent with the specific surface area used in a simple flow model for computation of permeability. In this paper, we discuss the two-point spatial correlation function and its use in characterizing microstructure features such as pore and grain sizes. We present estimates of permeabilities found using SEM images of several different synthetic and natural sandstones. Comparison of the estimates to laboratory measurements shows good agreement. Finally, we briefly discuss extension of this technique to two-phase flow.
Tight junction, selective permeability, and related diseases.
Krug, Susanne M; Schulzke, Jörg D; Fromm, Michael
2014-12-01
The tight junction forms a barrier against unlimited paracellular passage but some of the tight junction proteins just do the opposite, they form extracellular channels zigzagging between lateral membranes of neighboring cells. All of these channel-forming proteins and even some of the barrier formers exhibit selectivity, which means that they prefer certain substances over others. All channel formers exhibit at least one of the three types of selectivity: for cations (claudin-2, -10b, -15), for anions (claudin-10a, -17) or for water (claudin-2). Also some, but not all, barrier-forming claudins are charge-selective (claudin-4, -8, -14). Moreover, occludin and tricellulin turned out to be relevant for barrier formation against macromolecule passage. Tight junction proteins are dysregulated or can be genetically defective in numerous diseases, which may lead to three effects: (i) impaired paracellular transport e.g. causing magnesium loss in the kidney, (ii) increased paracellular transport of solutes and water e.g. causing leak-flux diarrhea in the intestine, and (iii) increased permeability to large molecules e.g. unwanted intestinal pathogen uptake fueling inflammatory processes. This review gives an overview on the properties of tight junction proteins featuring selective permeability, and in this context explains how these proteins induce or aggravate diseases. Copyright © 2014 Elsevier Ltd. All rights reserved.
Analytical approximations for effective relative permeability in the capillary limit
NASA Astrophysics Data System (ADS)
Rabinovich, Avinoam; Li, Boxiao; Durlofsky, Louis J.
2016-10-01
We present an analytical method for calculating two-phase effective relative permeability, krjeff, where j designates phase (here CO2 and water), under steady state and capillary-limit assumptions. These effective relative permeabilities may be applied in experimental settings and for upscaling in the context of numerical flow simulations, e.g., for CO2 storage. An exact solution for effective absolute permeability, keff, in two-dimensional log-normally distributed isotropic permeability (k) fields is the geometric mean. We show that this does not hold for krjeff since log normality is not maintained in the capillary-limit phase permeability field (Kj=k·krj) when capillary pressure, and thus the saturation field, is varied. Nevertheless, the geometric mean is still shown to be suitable for approximating krjeff when the variance of lnk is low. For high-variance cases, we apply a correction to the geometric average gas effective relative permeability using a Winsorized mean, which neglects large and small Kj values symmetrically. The analytical method is extended to anisotropically correlated log-normal permeability fields using power law averaging. In these cases, the Winsorized mean treatment is applied to the gas curves for cases described by negative power law exponents (flow across incomplete layers). The accuracy of our analytical expressions for krjeff is demonstrated through extensive numerical tests, using low-variance and high-variance permeability realizations with a range of correlation structures. We also present integral expressions for geometric-mean and power law average krjeff for the systems considered, which enable derivation of closed-form series solutions for krjeff without generating permeability realizations.
NASA Astrophysics Data System (ADS)
Honda, H.; Mitani, Y.; Ikemi, H.; Kitamura, K.
2014-12-01
Recently, it is generally believed that the increase of atmospheric carbon dioxide (CO2) emission has become a major contributing factor of a global warming. Carbon dioxide capture and storage (CCS) is an emerging technology and considered as the promising method to reduce greenhouse gas emissions in the atmosphere. Generally, CCS is intended to apply in oil or natural gas reservoir layers with overlying cap rock. However, in Japan, few proper sites are available for CCS. Therefore, low-permeable rock mass without cap rock is suggested as alternative option. It is required to clarify behavior of CO2 in rock for longitudinal and stable storage of CO2. In order to clarify the properties of permeability and storativity of low permeable rocks, Ainoura sandstone, saturated with water injected with a constant and appropriate flow rate of supercritical CO2, flow pump permeability test under the condition of temperature and pressure of in-situ CO2 reservoir has been conducted. In this experiment, the differential pressure between both ends of specimen changed in 4 stages and finally in stable condition. Furthermore, relative permeability of water and CO2, and specific storage of specimen during CO2 injection has been calculated with theoretical analysis of flow pump permeability test for two phase flow. Using the results of the experiment, 3D core-scale flow-simulation by using TOUGH2 (ECO2N module) has been conducted due to confirm the flow of fluid and CO2 distribution in the specimen. To compare the results of simulation and experimental results, the permeability and storativity properties of carbon dioxide in low permeable rock has been estimated. As a result, low permeable rocks could become an effective storage of supercritical CO2.
Effective Permeability and Miniaturization Estimation of Ferrite-loaded Microstrip Patch Antenna
NASA Astrophysics Data System (ADS)
Saini, Ashish; Thakur, Atul; Thakur, Preeti
2016-08-01
Miniaturization of a microstrip patch antenna using composite nanosized ferrite material is proposed in this paper. Detailed simulations were performed to analyze the effect of increase in relative permeability of substrate material on physical size and efficiency of a microstrip antenna. An analytical expression for estimation of the effective relative permeability is established here on the basis of the detailed simulation. Composite nano ferrite (Mn0.5Zn0.35Co0.15Fe2O4 + SrFe12O19) with an average crystallite size of 72 nm was synthesized and characterized for electromagnetic properties. The substrate material was prepared by the co-precipitation method. Matching values of complex permittivity ( ɛ* = 4.1-0.1j) and complex permeability ( μ* = 3.72-0.28j) up to 1 GHz were obtained from the electromagnetic characterization. Measurement of the resonant frequency of the fabricated antenna validates the derived expression of effective relative permeability. It reduces the error in calculation of resonant frequency from 10% to 1%. Simulation and measurement results also confirm that an antenna fabricated with the above parameters can reduce the patch size by almost 44% and increases -10 dB reflection loss bandwidth over a pure dielectric FR4 substrate. Therefore, we propose here an analytical expression for estimation of effective relative permeability and Mn0.5Zn0.35Co0.15Fe2O4 + SrFe12O19 composite nano ferrites as suitable candidate for a high-bandwidth miniaturized antenna in the microwave frequency range.
Tentative estimate of bulk permeability of basement rocks from heat discharges in a geothermal field
NASA Astrophysics Data System (ADS)
Sekioka, Mitsuru
1988-09-01
A simple, columnar model is applied to fissured basement rocks including a geothermal reservoir at depth in a geothermal system to derive a formula determining the bulk permeability of the rocks (the extended permeability averaged for the whole fissured basement rocks), under some assumptions and approximations. The bulk permeability is found to depend mainly upon the conductive and convective heat discharges and the thermal conductivity of the rock in steaming grounds. Tentative estimate of the bulk permeability is carried out for the eight geothermal fields in Japan where the above three variables are available. Finally, the field data are presented to support a part of the estimated bulk permeability.
NASA Astrophysics Data System (ADS)
Emanuele Rizzo, Roberto; Healy, David; De Siena, Luca
2016-04-01
The success of any predictive model is largely dependent on the accuracy with which its parameters are known. When characterising fracture networks in fractured rock, one of the main issues is accurately scaling the parameters governing the distribution of fracture attributes. Optimal characterisation and analysis of fracture attributes (lengths, apertures, orientations and densities) is fundamental to the estimation of permeability and fluid flow, which are of primary importance in a number of contexts including: hydrocarbon production from fractured reservoirs; geothermal energy extraction; and deeper Earth systems, such as earthquakes and ocean floor hydrothermal venting. Our work links outcrop fracture data to modelled fracture networks in order to numerically predict bulk permeability. We collected outcrop data from a highly fractured upper Miocene biosiliceous mudstone formation, cropping out along the coastline north of Santa Cruz (California, USA). Using outcrop fracture networks as analogues for subsurface fracture systems has several advantages, because key fracture attributes such as spatial arrangements and lengths can be effectively measured only on outcrops [1]. However, a limitation when dealing with outcrop data is the relative sparseness of natural data due to the intrinsic finite size of the outcrops. We make use of a statistical approach for the overall workflow, starting from data collection with the Circular Windows Method [2]. Then we analyse the data statistically using Maximum Likelihood Estimators, which provide greater accuracy compared to the more commonly used Least Squares linear regression when investigating distribution of fracture attributes. Finally, we estimate the bulk permeability of the fractured rock mass using Oda's tensorial approach [3]. The higher quality of this statistical analysis is fundamental: better statistics of the fracture attributes means more accurate permeability estimation, since the fracture attributes feed
Constant-pressure measurement of steam-water relative permeability
O'Connor, Peter A.
2001-06-01
A series of steady-state experiments have established relative permeability curves for two-phase flow of water in a porous medium. These experiments have minimized uncertainty in pressure, heat loss, and saturation. By attempting to maintain a constant pressure gradient, the experiments have provided a baseline from which to determine the effect of temperature on relative permeability. The use of a flexible heater with an automatic control system made it possible to assume negligible phase change for the mobile fluid. X-ray computer tomography (CT) aided by measuring in-situ steam saturation more directly. Mobile steam mass fraction was established by separate steam and water inlets or by correlating with previous results. The measured steam-water relative permeability curves assume a shape similar to those obtained by Corey (1954) for the simultaneous flow of nitrogen and water. Close agreement between the curves by Satik (1998), Mahiya (1999), and this study establishes the reliability of the experimental method and instrumentation adopted in these experiments, though some differences may bear further investigation. In particular, the steam phase relative permeability appears to vary much more linearly with saturation than does the water phase relative permeability.
Lenormand, R.; Thiele, M.R.
1997-08-01
The paper describes the method and presents preliminary results for the calculation of homogenized relative permeabilities
Water retention and gas relative permeability of two industrial concretes
Chen Wei; Liu Jian; Brue, Flore; Skoczylas, Frederic; Davy, C.A.; Bourbon, Xavier; Talandier, Jean
2012-07-15
This experimental study aims at identifying the water retention properties of two industrial concretes to be used for long term underground nuclear waste storage structures. Together with water retention, gas transfer properties are identified at varying water saturation level, i.e. relative gas permeability is assessed directly as a function of water saturation level S{sub w}. The influence of the initial de-sorption path and of the subsequent re-saturation are analysed both in terms of water retention and gas transfer properties. Also, the influence of concrete microstructure upon water retention and relative gas permeability is assessed, using porosity measurements, analysis of the BET theory from water retention properties, and MIP. Finally, a single relative gas permeability curve is proposed for each concrete, based on Van Genuchten-Mualem's statistical model, to be used for continuous modelling approaches of concrete structures, both during drying and imbibition.
The Interfacial-Area-Based Relative Permeability Function
Zhang, Z. F.; Khaleel, Raziuddin
2009-09-25
CH2M Hill Plateau Remediation Company (CHPRC) requested the services of the Pacific Northwest National Laboratory (PNNL) to provide technical support for the Remediation Decision Support (RDS) activity within the Soil & Groundwater Remediation Project. A portion of the support provided in FY2009, was to extend the soil unsaturated hydraulic conductivity using an alternative approach. This alternative approach incorporates the Brooks and Corey (1964), van Genuchten (1980), and a modified van Genuchten water-retention models into the interfacial-area-based relative permeability model presented by Embid (1997). The general performance of the incorporated models is shown using typical hydraulic parameters. The relative permeability models for the wetting phase were further examined using data from literature. Results indicate that the interfacial-area-based model can describe the relative permeability of the wetting phase reasonably well.
NASA Astrophysics Data System (ADS)
Rios, Edmilson Helton; Figueiredo, Irineu; Moss, Adam Keith; Pritchard, Timothy Neil; Glassborow, Brent Anthony; Guedes Domingues, Ana Beatriz; Bagueira de Vasconcellos Azeredo, Rodrigo
2016-07-01
The effect of the selection of different nuclear magnetic resonance (NMR) relaxation times for permeability estimation is investigated for a set of fully brine-saturated rocks acquired from Cretaceous carbonate reservoirs in the North Sea and Middle East. Estimators that are obtained from the relaxation times based on the Pythagorean means are compared with estimators that are obtained from the relaxation times based on the concept of a cumulative saturation cut-off. Select portions of the longitudinal (T1) and transverse (T2) relaxation-time distributions are systematically evaluated by applying various cut-offs, analogous to the Winland-Pittman approach for mercury injection capillary pressure (MICP) curves. Finally, different approaches to matching the NMR and MICP distributions using different mean-based scaling factors are validated based on the performance of the related size-scaled estimators. The good results that were obtained demonstrate possible alternatives to the commonly adopted logarithmic mean estimator and reinforce the importance of NMR-MICP integration to improving carbonate permeability estimates.
Tracer kinetic modelling in MRI: estimating perfusion and capillary permeability
NASA Astrophysics Data System (ADS)
Sourbron, S. P.; Buckley, D. L.
2012-01-01
The tracer-kinetic models developed in the early 1990s for dynamic contrast-enhanced MRI (DCE-MRI) have since become a standard in numerous applications. At the same time, the development of MRI hardware has led to increases in image quality and temporal resolution that reveal the limitations of the early models. This in turn has stimulated an interest in the development and application of a second generation of modelling approaches. They are designed to overcome these limitations and produce additional and more accurate information on tissue status. In particular, models of the second generation enable separate estimates of perfusion and capillary permeability rather than a single parameter Ktrans that represents a combination of the two. A variety of such models has been proposed in the literature, and development in the field has been constrained by a lack of transparency regarding terminology, notations and physiological assumptions. In this review, we provide an overview of these models in a manner that is both physically intuitive and mathematically rigourous. All are derived from common first principles, using concepts and notations from general tracer-kinetic theory. Explicit links to their historical origins are included to allow for a transfer of experience obtained in other fields (PET, SPECT, CT). A classification is presented that reveals the links between all models, and with the models of the first generation. Detailed formulae for all solutions are provided to facilitate implementation. Our aim is to encourage the application of these tools to DCE-MRI by offering researchers a clearer understanding of their assumptions and requirements.
Model-based Permeability Estimation of Shaly Sands Using Seismic Velocity and Resistivity Data
NASA Astrophysics Data System (ADS)
Takahashi, T.
2016-12-01
Permeability is an indispensable parameter for hydraulic characterization of soils and rocks in many applications. Permeability of soils and rocks is usually obtained with the in-situ permeability test in a borehole and/or laboratory permeability test of soil/rock core samples obtained in the borehole. Many boreholes are necessary for building a hydraulic model of a large soil/rock mass. It is, however, often difficult to drill many boreholes due to time and cost constraints. For such a case, geophysical methods can be effectively utilized for profiling permeability of a large soil/rock mass if geophysical properties such as seismic velocity and resistivity can be used for estimating permeability. We, therefore, propose an effective method for estimating permeability of shaly sands by applying a rock physics model to seismic velocity and resistivity data. Because consolidated shaly sand is a key rock for aquifers and oil/gas reservoirs, and unconsolidated shaly sand is very common soils whose hydraulic properties are often important for safety evaluation of river embankments and designing countermeasure of its liquefaction. The method first estimates the grain size distribution of the shaly sand by applying a shaly sand model to seismic velocity and resistivity data obtained with seismic and resistivity measurements. The grain size of the soil/rock thus obtained and porosity estimated from resistivity data by applying the Glover's equation are then input to the Kozeny-Carman equation for estimating permeability of the shaly sand. The proposed method is applied to P- and S-wave velocities and resistivity data measured in the laboratory, well logging and surface seismic and electric surveys for shaly sands. Comparison of estimated permeability with actual measurements reveals that permeability can be estimated in accuracy less than one order of magnitude and the method can be used for profiling permeability of a large shaly sand using geophysical data measured on it.
Comparative assessment of three-phase oil relative permeability models
NASA Astrophysics Data System (ADS)
Ranaee, Ehsan; Riva, Monica; Porta, Giovanni M.; Guadagnini, Alberto
2016-07-01
We assess the ability of 11 models to reproduce three-phase oil relative permeability (kro) laboratory data obtained in a water-wet sandstone sample. We do so by considering model performance when (i) solely two-phase data are employed to render predictions of kro and (ii) two and three-phase data are jointly used for model calibration. In the latter case, a Maximum Likelihood (ML) approach is used to estimate model parameters. The tested models are selected among (i) classical models routinely employed in practical applications and implemented in commercial reservoir software and (ii) relatively recent models which are considered to allow overcoming some drawbacks of the classical formulations. Among others, the latter set of models includes the formulation recently proposed by Ranaee et al., which has been shown to embed the critical effects of hysteresis, including the reproduction of oil remobilization induced by gas injection in water-wet media. We employ formal model discrimination criteria to rank models according to their skill to reproduce the observed data and use ML Bayesian model averaging to provide model-averaged estimates (and associated uncertainty bounds) of kro by taking advantage of the diverse interpretive abilities of all models analyzed. The occurrence of elliptic regions is also analyzed for selected models in the framework of the classical fractional flow theory of displacement. Our study confirms that model outcomes based on channel flow theory and classical saturation-weighted interpolation models do not generally yield accurate reproduction of kro data, especially in the regime associated with low oil saturations, where water alternating gas injection (WAG) techniques are usually employed for enhanced oil recovery. This negative feature is not observed in the model of Ranaee et al. (2015) due to its ability to embed key effects of pore-scale phase distributions, such as hysteresis effects and cycle dependency, for modeling kro observed
High-Throughput Evaluation of Relative Cell Permeability between Peptoids and Peptides
Tan, Niclas C.; Yu, Peng; Kwon, Yong-Uk; Kodadek, Thomas
2008-01-01
Peptides are limited in their use as drugs due to low cell permeability and vulnerability to proteases. In contrast, peptoids are immune to enzymatic degradation and some peptoids have been shown to be relatively cell permeable. In order to facilitate future design of peptoid libraries for screening experiments, it would be useful to have a high-throughput method to estimate the cell permeability of peptoids containing different residues. In this paper, we report the strengths and limitations of a high-throughput cell-based permeability assay that registers the relative ability of steroid-conjugated peptides and peptoids to enter a cell. A comparative investigation of the physicochemical properties and side chain composition of peptoids and peptides is described to explain the observed higher cell permeability of peptoids over peptides. These data suggest that the conversion of the monomeric residues in peptides to an N-alkylglycine moiety in peptoids reduced the hydrogen bonding potential of the molecules and is the main contributor to the observed permeability improvement. PMID:18490170
NASA Astrophysics Data System (ADS)
Nambi, I.; Mukunda, P.; Kumar N, S.
2009-12-01
Predicting Dissolution of Entrapped NAPL in Heterogeneous Aquifers Using New Relative Permeability Correlations Indumathi M. Nambi1, Pavitra,M2 and Sateesh Kumar N2 1Assistant Professor, 2 PhD Student, 3 Graduate Student Department of Civil Engineering, Indian Institute of Technology Madras, India Non-Aqueous Phase Liquids such as organic compounds are major sources of groundwater contamination throughout the world. The non-uniform distribution of these contaminants as NAPL pools and NAPL residuals introduce additional spatial heterogeneity in the hydrogeological parameters such as porosity and permeability. In addition to this, as the NAPL dissolve over time, the hydrogeological parameter such as relative permeability change as more and more pore space is available for water flow. There are no adequate studies conducted so far to predict the changes taking place in the permeability of a contaminated region. The existing models have repeatedly used models developed based on two phase flow experiments such as Corey’s and Wylie’s equations which relate relative permeability to effective water saturation. It is hypothesized that the pattern of changes in relative permeability as the NAPL pools or residuals dissolve is quite different from the relative permeability variations during two phase flow. Hence the use of these empirical relationships developed for relative permeabilities as a function of effective permeabilities for the case of dissolving NAPL pools is questionable. In this study, column dissolution experiments were conducted in a simplified heterogeneous system and the changes in relative permeabilities were quantified by measuring differential pressures at various time points. The NAPL saturations were also quantified as the NAPL dissolved by estimating aqueous phase concentrations and applying mass balance. These experimental data when compared to the existing correlation predictions proved our hypothesis that the relative permeability variations as
Estimation of In Situ Stress and Permeability from an Extended Leak-off Test
NASA Astrophysics Data System (ADS)
Nghiep Quach, Quoc; Jo, Yeonguk; Chang, Chandong; Song, Insun
2016-04-01
Among many parameters needed to analyze a variety of geomechanical problems related to subsurface CO2 storage projects, two important ones are in situ stress states and permeability of the storage reservoirs and cap rocks. In situ stress is needed for investigating potential risk of fault slip in the reservoir systems and permeability is needed for assessing reservoir flow characteristics and sealing capability of cap rocks. We used an extended leak-off test (XLOT), which is often routinely conducted to assess borehole/casing integrity as well as fracture gradient, to estimate both in situ least principal stress magnitude and in situ permeability in a CO2 storage test site, offshore southeast Korea. The XLOT was conducted at a casing shoe depth (700 m below seafloor) within the cap rock consisting of mudstone, approximately 50 m above the interface between cap rock and storage reservoir. The test depth was cement-grouted and remained for 4 days for curing. Then the hole was further drilled below the casing shoe to create a 4 m open-hole interval at the bottom. Water was injected using hydraulic pump at an approximately constant flowrate into the bottom interval through the casing, during which pressure and flowrate were recorded continuously at the surface. The interval pressure (P) was increased linearly with time (t) as water was injected. At some point, the slope of P-t curve deviated from the linear trend, which indicates leak-off. Pressure reached its peak upon formation breakdown, followed by a gradual pressure decrease. Soon after the formation breakdown, the hole was shut-in by pump shut-off, from which we determined the instantaneous shut-in pressure (ISIP). The ISIP was taken to be the magnitude of the in situ least principal stress (S3), which was determined to be 12.1 MPa. This value is lower than the lithostatic vertical stress, indicating that the S3 is the least horizontal principal stress. The determined S3 magnitude will be used to characterize the
NASA Astrophysics Data System (ADS)
Woith, Heiko; Chiodini, Giovanni; Mangiacapra, Annarita; Wang, Rongjiang
2016-04-01
The hydrothermal system beneath Campi Flegrei is strongly affected by sub-surface processes as manifested by a geothermal "plume" below Solfatara, associated with the formation of mud-pools (Fangaia), fumaroles (Bocca Grande, Pisciarelli), and thermal springs (Agnano). Within the frame of MED-SUV (The MED-SUV project has received funding from the European Union Seventh Framework Programme FP7 under Grant agreement no 308665), pressure transients in the hydrothermal system of Campi Flegrei are being continuously monitored at fumaroles, mudpools, hot springs, and geothermal wells. In total, waterlevel and temperature is recorded at 8 sites across the hydrothermal plume along a profile aligned between Agnano Termal in the East and Fangaia in the West. Autonomous devices are used to record the water level and water temperature at 10 minute intervals. At Fangaia mudpool water level and water temperature are dominantly controlled by rain water. Thus, the pool is refilled episodically. Contrary, the water level at a well producing hot water (82°C) for the Pisciarelli tennis club drops and recovers at nearly regular intervals. The induced water level changes are of the order of 1-2m and 3-4m in case of the mudpool and the hot-water-well, respectively. At first glance, both monitoring sites might seem to be fully useless to access natural changes in the Campi Flegrei fluid system. At a second thought, both timeseries provide a unique opportunity to monitor potential permeability changes in the aquifer system. A similar approach had been proposed to deduce earthquake-related permeability changes from Earth tide variations. Contrary to the indirect Earth tide approach, we have the chance to estimate the hydraulic aquifer properties from our monitoring data directly, since each time series contains a sequence of discrete hydraulic tests - namely drawdown tests and refill experiments. Although our Cooper-Jacob approach is really crude, we obtained reasonable permeability
Use of geophysical logs to estimate the quality of ground water and the permeability of aquifers
Hudson, J.D.
1996-01-01
The relation of formation factor to resistivity of formation water and intergranular permeability has often been investigated, and the general consensus is that this relation is closest when established in a clean-sand aquifer in which water quality does not vary substantially. When these restrictions are applied, the following standard equation is a useful tool in estimating the resistance of the formation water: F = Ro/Rw, where F is the formation factor, which is a function of the effective porosity; Ro is the resistivity of a formation that is 100 percent saturated with interstitial water; and Rw is the resistivity of the water in the saturated zone. However, arenaceous aquifers can have electrical resistivities that are not directly related to resistivity of water or porosity. Surface conductivity and ion exchange are significant factors when the sediments are clay bearing. The solid constituents are a major component of the parameters needed to solve the equation for formation-water resistivity and estimates of aquifer permeability. A correction process needs to be applied to adjust the variables, Ro and F, to the equivalent of clean sand. This report presents an empirical method of using the neutron log and the electrical-resistivity values from long- and short-normal resistivity logs to correct for fine-grained material and the subsequent effects of low impedance to electrical flow that are not related to the resistance of formation water.
PARAMETER ESTIMATION OF TWO-FLUID CAPILLARY PRESSURE-SATURATION AND PERMEABILITY FUNCTIONS
Capillary pressure and permeability functions are crucial to the quantitative description of subsurface flow and transport. Earlier work has demonstrated the feasibility of using the inverse parameter estimation approach in determining these functions if both capillary pressure ...
PARAMETER ESTIMATION OF TWO-FLUID CAPILLARY PRESSURE-SATURATION AND PERMEABILITY FUNCTIONS
Capillary pressure and permeability functions are crucial to the quantitative description of subsurface flow and transport. Earlier work has demonstrated the feasibility of using the inverse parameter estimation approach in determining these functions if both capillary pressure ...
NASA Astrophysics Data System (ADS)
Rizzo, R. E.; Healy, D.; De Siena, L.
2015-12-01
The success of any model prediction is largely dependent on the accuracy with which its parameters are known. In characterising fracture networks in naturally fractured rocks, the main issues are related with the difficulties in accurately up- and down-scaling the parameters governing the distribution of fracture attributes. Optimal characterisation and analysis of fracture attributes (fracture lengths, apertures, orientations and densities) represents a fundamental step which can aid the estimation of permeability and fluid flow, which are of primary importance in a number of contexts ranging from hydrocarbon production in fractured reservoirs and reservoir stimulation by hydrofracturing, to geothermal energy extraction and deeper Earth systems, such as earthquakes and ocean floor hydrothermal venting. This work focuses on linking fracture data collected directly from outcrops to permeability estimation and fracture network modelling. Outcrop studies can supplement the limited data inherent to natural fractured systems in the subsurface. The study area is a highly fractured upper Miocene biosiliceous mudstone formation cropping out along the coastline north of Santa Cruz (California, USA). These unique outcrops exposes a recently active bitumen-bearing formation representing a geological analogue of a fractured top seal. In order to validate field observations as useful analogues of subsurface reservoirs, we describe a methodology of statistical analysis for more accurate probability distribution of fracture attributes, using Maximum Likelihood Estimators. These procedures aim to understand whether the average permeability of a fracture network can be predicted reducing its uncertainties, and if outcrop measurements of fracture attributes can be used directly to generate statistically identical fracture network models.
A multiple fractal model for estimating permeability of dual-porosity media
NASA Astrophysics Data System (ADS)
Li, Bo; Liu, Richeng; Jiang, Yujing
2016-09-01
A multiple fractal model that considers the fractal properties of both porous matrices and fracture networks is proposed for the permeability of dual-porosity media embedded with randomly distributed fractures. In this model, the aperture distribution is verified to follow the fractal scaling law, and the porous matrix is assumed to comprise a bundle of tortuous capillaries that also follow the fractal scaling law. Analytical expressions for fractal aperture distribution, total flow rate, total equivalent permeability, and dimensionless permeability are established, where the dimensionless permeability is defined as the ratio of permeability of the porous matrices to that of the fracture networks. The dimensionless permeability is closely correlated to the structural parameters (i.e., α, θ, Dtf, Dtp, De, Dp, emax, λmax) of the dual-porosity media, and it is more sensitive to the fractal dimension for the size distribution of fracture aperture than to that for the size distribution of pore/capillary diameter. The maximum pore/capillary diameter has a greater impact on the dimensionless permeability than that of the maximum fracture aperture. The dimensionless permeability of fracture networks constructed by the fractal aperture distribution has close values with those of models with lognormal aperture distribution. The proposed multiple fractal model does not involve any empirical constants that do not have clear physical meanings, which could serve as a quick estimation method for assessing permeability of dual-porosity media.
NASA Astrophysics Data System (ADS)
Iturrarán-Viveros, Ursula; Parra, Jorge O.
2014-08-01
Permeability and porosity are two fundamental reservoir properties which relate to the amount of fluid contained in a reservoir and its ability to flow. The intrinsic attenuation is another important parameter since it is related to porosity, permeability, oil and gas saturation and these parameters significantly affect the seismic signature of a reservoir. We apply Artificial Neural Network (ANN) models to predict permeability (k) and porosity (ϕ) for a carbonate aquifer in southeastern Florida and to predict intrinsic attenuation (1/Q) for a sand-shale oil reservoir in northeast Texas. In this study, the Gamma test (a revolutionary estimator of the noise in a data set) has been used as a mathematically non-parametric nonlinear smooth modeling tool to choose the best input combination of seismic attributes to estimate k and ϕ, and the best combination of well-logs to estimate 1/Q. This saves time during the construction and training of ANN models and also sets a lower bound for the mean squared error to prevent over-training. The Neural Network method successfully delineates a highly permeable zone that corresponds to a high water production in the aquifer. The Gamma test found nonlinear relations that were not visible to linear regression allowing us to generalize the ANN estimations of k, ϕ and 1/Q for their respective sets of patterns that were not used during the learning phase.
Estimation of Permeability from NMR Logs Based on Formation Classification Method in Tight Gas Sands
NASA Astrophysics Data System (ADS)
Wei, Deng-Feng; Liu, Xiao-Peng; Hu, Xiao-Xin; Xu, Rui; Zhu, Ling-Ling
2015-10-01
The Schlumberger Doll Research (SDR) model and cross plot of porosity versus permeability cannot be directly used in tight gas sands. In this study, the HFU approach is introduced to classify rocks, and determine the involved parameters in the SDR model. Based on the difference of FZI, 87 core samples, drilled from tight gas sandstones reservoirs of E basin in northwest China and applied for laboratory NMR measurements, were classified into three types, and the involved parameters in the SDR model are calibrated separately. Meanwhile, relationships of porosity versus permeability are also established. The statistical model is used to calculate consecutive FZI from conventional logs. Field examples illustrate that the calibrated SDR models are applicable in permeability estimation; models established from routine core analyzed results are effective in reservoirs with permeability lower than 0.3 mD, while the unified SDR model is only valid in reservoirs with permeability ranges from 0.1 to 0.3 mD.
Frequency-Dependence of Relative Permeability in Steel
Bowler, N.
2006-03-06
A study to characterize metal plates by means of a model-based, broadband, four-point potential drop measurement technique has shown that the relative permeability of alloy 1018 low-carbon steel is complex and a function of frequency. A magnetic relaxation is observed at approximately 5 kHz. The relaxation can be described in terms of a parametric (Cole-Cole) model. Factors which influence the frequency, amplitude and breadth of the relaxation, such as applied current amplitude, sample geometry and disorder (e.g. percent carbon content and surface condition), are considered.
Paillet, Frederick L.
1988-01-01
Various conventional geophysical well logs were obtained in conjunction with acoustic tube-wave amplitude and experimental heat-pulse flowmeter measurements in two deep boreholes in granitic rocks on the Canadian shield in southeastern Manitoba. The objective of this study is the development of measurement techniques and data processing methods for characterization of rock volumes that might be suitable for hosting a nuclear waste repository. One borehole, WRA1, intersected several major fracture zones, and was suitable for testing quantitative permeability estimation methods. The other borehole, URL13, appeared to intersect almost no permeable fractures; it was suitable for testing methods for the characterization of rocks of very small permeability and uniform thermo-mechanical properties in a potential repository horizon. Epithermal neutron , acoustic transit time, and single-point resistance logs provided useful, qualitative indications of fractures in the extensively fractured borehole, WRA1. A single-point log indicates both weathering and the degree of opening of a fracture-borehole intersection. All logs indicate the large intervals of mechanically and geochemically uniform, unfractured granite below depths of 300 m in the relatively unfractured borehole, URL13. Some indications of minor fracturing were identified in that borehole, with one possible fracture at a depth of about 914 m, producing a major acoustic waveform anomaly. Comparison of acoustic tube-wave attenuation with models of tube-wave attenuation in infinite fractures of given aperture provide permeability estimates ranging from equivalent single-fractured apertures of less than 0.01 mm to apertures of > 0.5 mm. One possible fracture anomaly in borehole URL13 at a depth of about 914 m corresponds with a thin mafic dike on the core where unusually large acoustic contrast may have produced the observed waveform anomaly. No indications of naturally occurring flow existed in borehole URL13; however
The effective porosity and grain size relations in permeability functions
NASA Astrophysics Data System (ADS)
Urumović, K.; Urumović, K., Sr.
2014-06-01
Hydrogeological parameters of coherent and incoherent deposits are deeply dependent of their granulometric characteristics. These relations were shaped in formulas and defaultly used for calculation of hydraulic conductivity, and are valid only for uniform incoherent materials, mostly sands. In this paper, the results of analyses of permeability and specific surface area as a function of granulometric composition of various sediments - from siltey clays to very well graded gravels are presented. The effective porosity and the referential grain size are presented as fundamental granulometric parameters which express an effect of forces operating fluid movement through the saturated porous media. Suggested procedures for calculating referential grain size and determining effective (flow) porosity result with parameters that reliably determine specific surface area and permeability. These procedures ensure successful appliance of Kozeny-Carman model up to the limits of validity of Darcy's law. The value of an effective porosity in function of referential mean grain size has been calibrated within range from 1.5 μm to 6.0 mm. Reliability of these parameters application in KC model was confirmed by very high correlation between predicted and tested hydraulic conductivity - R2 = 0.99 for sandy and gravelly materials and R2 = 0.70 for clayey-siltey materials. Group representation of hydraulic conductivity (ranged from 10-12 m s-1 up to 10-2 m s-1) presents coefficient of correlation R2 = 0.97, for total sum of 175 samples of various deposits. These results present the new road to researches of porous material's effective porosity, permeability and specific surface area distribution, since these three parameters are critical conditions for successful groundwater flow modelling and contaminant transport. From the practical point of view, it is very important to be able to identify these parameters swiftly, cheaply and very accurately.
A new stylolite classification scheme to estimate compaction and local permeability variations
NASA Astrophysics Data System (ADS)
Koehn, D.; Rood, M. P.; Beaudoin, N.; Chung, P.; Bons, P. D.; Gomez-Rivas, E.
2016-12-01
We modeled the geometrical roughening of bedding-parallel, mainly layer-dominated stylolites in order to understand their structural evolution, to present an advanced classification of stylolite shapes and to relate this classification to chemical compaction and permeability variations at stylolites. Stylolites are rough dissolution seams that develop in sedimentary basins during chemical compaction. In the Zechstein 2 carbonate units, an important lean gas reservoir in the southern Permian Zechstein basin in Germany, stylolites influence local fluid flow, mineral replacement reactions and hence the permeability of the reservoir. Our simulations demonstrate that layer-dominated stylolites can grow in three distinct stages: an initial slow nucleation phase, a fast layer-pinning phase and a final freezing phase if the layer is completely dissolved during growth. Dissolution of the pinning layer and thus destruction of the stylolite's compaction tracking capabilities is a function of the background noise in the rock and the dissolution rate of the layer itself. Low background noise needs a slower dissolving layer for pinning to be successful but produces flatter teeth than higher background noise. We present an advanced classification based on our simulations and separate stylolites into four classes: (1) rectangular layer type, (2) seismogram pinning type, (3) suture/sharp peak type and (4) simple wave-like type. Rectangular layer type stylolites are the most appropriate for chemical compaction estimates because they grow linearly and record most of the actual compaction (up to 40 mm in the Zechstein example). Seismogram pinning type stylolites also provide good tracking capabilities, with the largest teeth tracking most of the compaction. Suture/sharp peak type stylolites grow in a non-linear fashion and thus do not record most of the actual compaction. However, when a non-linear growth law is used, the compaction estimates are similar to those making use of the
Relative Permeabilities: a pore-level model study of the capillary number dependence
Ferer, M.V.; Mason, G.; Bromhal, G.S.; Smith, D.H.
2008-03-01
Relative permeabilities are widely used by the petroleum industry in reservoir simulations of recovery strategies. In recent years, pore level modeling has been used to determine relative permeabilities at zero capillary number for a variety of more and more realistic model porous media. Unfortunately, these studies cannot address the issue of the observed capillary number dependence of the relative permeabilities. Several years ago, we presented a method for determining the relative permeabilities from pore-level modeling at general capillary number. We have used this method to determine the relative permeabilities at several capillary numbers and stable viscosity ratios. In addition, we have determined these relative permeabilities using one of the standard dynamic methods for determining relative permeabilities from core flood experiments. Our results from the two methods are compared with each other and with experimental results.
Effect of simulated intestinal fluid on drug permeability estimation across Caco-2 monolayers.
Ingels, F; Beck, B; Oth, M; Augustijns, P
2004-04-15
Presently, the Caco-2 cell culture model is widely used during drug discovery and development as a predictive tool for the oral absorption of drug candidates. For transport experiments in the Caco-2 system, HBSS-like buffered salt solutions are commonly used, although different shortcomings have been associated with the use of these buffers. In this paper, we investigated the effect of using fasted state simulated intestinal fluid (FaSSIF) as potential biorelevant medium for the drug permeability estimation across Caco-2 monolayers. The transport characteristics of 19 model compounds were determined in the Caco-2 cell culture model in the presence of FaSSIF as compared to classic transport medium. A sigmoidal relation was obtained when the estimated P(app), s of the apical to basolateral transport were plotted versus the reported values of the fraction absorbed in man. Although no effect of FaSSIF as compared to classic transport medium (TM) was observed on the total predictability of the model, an impact was demonstrated (1) on the bi-directional transport of actively transported drugs (including talinolol, digoxin and doxorubicin), (2) on recovery and (3) on the solubility and permeability estimation of poorly water-soluble drugs. The observed differences may be attributed to a P-gp inhibitory effect of sodium taurocholate (NaTC), micellar encapsulation by the NaTC/lecithin mixed micelles and/or an increase of the solubility of lipophilic drugs. As the experimental conditions should mimic the physiological in vivo conditions, the use of FaSSIF as medium during Caco-2 experiments may improve the biorelevance of the model.
A new method for permeability estimation from conventional well logs in glutenite reservoirs
NASA Astrophysics Data System (ADS)
Shen, Bo; Wu, Dong; Wang, Zhonghao
2017-10-01
Permeability is one of the most important petrophysical parameters in formation evaluation. In glutenite reservoirs, the traditional permeability estimation method from conventional well logs cannot provide satisfactory results due to the characteristic of strong heterogeneity resulting from the wide variety of clastic grains and the extremely complex percolation network. In this paper, a new method for estimating permeability from conventional well logs is developed. On the basis of previous research, a simple method for estimating the flowing porosity of the Maxwell conductive model via well logs is proposed and then a ‘flowing permeability’ equation is established by using the equivalent parameters of geometry and flowing porosity. The form is similar to that of the Kozeny–Carman model for characterizing permeability. Based on the Maxwell conductive model, threshold theory, conductive efficiency theory and core analysis data, a new method to calculate the permeability of glutenite reservoirs by using float porosity is built up through deduction and analysis of the Kozeny–Carman equation, and field application to a glutenite reservoir shows that the result of the proposed method in this paper is accurate and reasonable.
Permeability Estimation of Porous Rock by Means of Fluid Flow Simulation and Digital Image Analysis
NASA Astrophysics Data System (ADS)
Winardhi, C. W.; Maulana, F. I.; Latief, F. D. E.
2016-01-01
Permeability plays an important role to determine the characteristics of how fluids flow through a porous medium which can be estimated using various methods. Darcy's law and the Kozeny-Carman equation are two of the most utilized methods in estimating permeability. In Darcy's law, permeability can be calculated by applying a pressure gradient between opposing sides of inlet-outlet of a certain direction. The permeability then depends on the fluid viscosity and the flowrate. The Kozeny-Carman equation is an empirical equation which depends on several parameters such as shape factor of the pore, tortuosity, specific surface area, and porosity to determine the permeability. For both methods, digital image obtained by means of Micro CT-Scan is used. In this research, the permeability estimation using the Darcy's law was conducted by simulating fluid flow through the digital image using Lattice Boltzmann Method (LBM). As for the Kozeny-Carman equation, digital image analysis was used to obtain the required parameters. Two Kozeny-Carman equations were used to calculate the permeability of the samples. The first equation (KC1) depends on pore shape factor, porosity, tortuosity, and specific surface area while the second equation (KC2) only depends on pore radius, porosity, and tortuosity. We investigate the methods by first testing on three simple pipe models which vary in the radii. By using the result from Darcy's law as a reference, we compare the results from the Kozeny-Carman equations. From the calculation, KC2 yield smaller difference to the reference. The three methods were then applied to the Fontainebleau sandstone to verify the previous result.
Effects of phase transformation of steam-water relative permeabilities
Verma, A.K.
1986-03-01
A combined theoretical and experimental study of steam-water relative permeabilities (RPs) was carried out. First, an experimental study of two-phase concurrent flow of steam and water was conducted and a set of RP curves was obtained. These curves were compared with semi-empirical and experimental results obtained by other investigators for two-phase, two-component flow (oil/gas; gas/water; gas/oil). It was found that while the wetting phase RPs were in good agreement, RPs for the steam phase were considerably higher than the non-wetting phase RPs in two-component systems. This enhancement of steam RP is attributed to phase transformation effects at the pore level in flow channels. The effects of phase transformation were studied theoretically. This study indicates that there are two separate mechanisms by which phase transformation affects RP curves: (1) Phase transformation is converging-diverging flow channels can cause an enhancement of steam phase RP. In a channel dominated by steam a fraction of the flowing steam condenses upstream from the constriction, depositing its latent heat of condensation. This heat is conducted through the solid grains around the pore throat, and evaporation takes place downstream from it. Therefore, for a given bulk flow quality; a smaller fraction of steam actually flows through the throat segments. This pore-level effect manifests itself as relative permeability enhancement on a macroscopic level; and (2) phase transformation along the interface of a stagnant phase and the phase flowing around it controls the irreducible phase saturation. Therefore, the irreducible phase saturation in steam-water flow will depend, among other factors, on the boundary conditions of the flow.
NASA Astrophysics Data System (ADS)
Jia, W.; Pan, F.; McPherson, B. J. O. L.
2015-12-01
Due to the presence of multiple phases in a given system, CO2 sequestration with enhanced oil recovery (CO2-EOR) includes complex multiphase flow processes compared to CO2 sequestration in deep saline aquifers (no hydrocarbons). Two of the most important factors are three-phase relative permeability and hysteresis effects, both of which are difficult to measure and are usually represented by numerical interpolation models. The purposes of this study included quantification of impacts of different three-phase relative permeability models and hysteresis models on CO2 sequestration simulation results, and associated quantitative estimation of uncertainty. Four three-phase relative permeability models and three hysteresis models were applied to a model of an active CO2-EOR site, the SACROC unit located in western Texas. To eliminate possible bias of deterministic parameters on the evaluation, a sequential Gaussian simulation technique was utilized to generate 50 realizations to describe heterogeneity of porosity and permeability, initially obtained from well logs and seismic survey data. Simulation results of forecasted pressure distributions and CO2 storage suggest that (1) the choice of three-phase relative permeability model and hysteresis model have noticeable impacts on CO2 sequestration simulation results; (2) influences of both factors are observed in all 50 realizations; and (3) the specific choice of hysteresis model appears to be somewhat more important relative to the choice of three-phase relative permeability model in terms of model uncertainty.
NASA Astrophysics Data System (ADS)
Chen, X.; Kianinejad, A.; DiCarlo, D. A.
2014-12-01
CO2-brine relative permeability relations are important parameters in modeling scenarios such as CO2 sequestration in saline aquifers and CO2 enhanced recovery in oil reservoir. Many steady-state experimental studies on CO2-brine relative permeability showed that the CO2-brine relative permeability differs greatly from typical oil-brine relative permeability. Particularly, they reported a very small endpoint CO2 relative permeability of 0.1~0.2 at a relative high residual water saturation of 0.4~0.6. In this study, we hypothesize the measured low endpoint CO2 relative permeability in previous studies was an experimental artifact that is primary due to low CO2 viscosity. We conducted steady-state CO2 drainage experiments by co-injecting equlibrated CO2 and brine into a long (60.8 cm) and low permeability (116-mD) Berea sandstone core at 20 °C and 1500 psi. During every experiment, both the overall pressure drop across the core and the pressure drops of the five independent and continuous sections of the core were monitored. The in-situ saturation was measured with a medical X-ray Computed Tomography (CT) scanner. In the center three sections where saturation was uniform, we determined the relative permeability to both brine and CO2 phases. In the entrance and exit sections, both measured pressure gradients and saturation were non-uniform. To cope with this, we make several self-consistent assumptions that reveal the nature of capillary entrance and effect in steady-state two-phase core flooding experiments. Based on these assumptions we determined the relative permeability to CO2 and CO2-brine capillary pressure simultaneously using measured pressure drops. We found: (1) a much higher endpoint CO2 relative permeability of 0.58 at a water saturation of 48%, (2) the entrance region with non-uniform saturation expanded CO2 relative permeability data to much lower water saturation, (3) the determined CO2-brine capillary pressure curve is self-consistent and matches
Estimation of soil air permeability components at a laboratory-scale pilot.
Boudouch, Otmane; Esrael, Daoud; Kacem, Mariem; Benadda, Belkacem
2012-01-01
Soil air permeability is a key parameter in the design of soil vapour extraction. The purpose of this study is to verify the applicability of different analytical solutions, developed to determine soil characteristics in field conditions, to estimate soil air permeability in a small-scale pilot, since field testing may be expensive. A laboratory tridirectional pilot and a unidirectional column were designed in order to achieve the objectives of this work. Use of a steady-state unconfined analytical solution was found to be an appropriate method to determine soil air permeability components for the pilot conditions. Using pressure data collected under open, steady-state conditions, the average values of radial and vertical permeability were found to be, respectively, 9.97 x 10(-7) and 8.74 x 10(-7) cm2. The use of semi-confined analytical solutions may not be suitable to estimate soil parameters since a significant difference was observed between simulated and observed vacuums. Air permeability was underestimated when transient solutions were used, in comparison with methods based on steady-state solutions. The air radial and vertical permeability was found to be, respectively, 7.06 x 10(-7) and 4.93 x 10(-7) cm2, in the open scenario, and 2.30 x 10(-7) and 1.51 x 10(-7) cm2 in the semi-confined scenario. However, a good estimate of soil porosity was achieved using the two transient methods. The average values were predicted to be 0.482, in the open scenario, and 0.451 in the semi-confined scenario, which was in good agreement with the real value.
Experimental investigation the effect of nanoparticles on the oil-water relative permeability
NASA Astrophysics Data System (ADS)
Amedi, Hamidreza; Ahmadi, Mohammad-Ali
2016-05-01
This paper presents the effects of the nanosilica particles on the water and oil relative permeability curves at reservoir conditions. Real reservoir crude oil sample was employed as an oil phase in relative permeability measurements. In addition, real carbonate reservoir rock samples were employed as a porous media in core displacement experiments. To determine relative permeability curves, the unsteady-state approach was employed in which Toth et al. method was applied to the recovery data points. By increasing the nanosilica content of the aqueous phase the oil relative permeability increased while the residual oil saturation decreased; however, by increasing the nanosilica concentration in the aqueous solution the water relative permeability decreased. The outcomes of this paper can provide a better understanding regarding chemically enhanced oil recovery (EOR) by nanoparticles. Moreover, relative permeability curves help us in the history matching section of reservoir simulation for any further EOR scenarios.
NASA Astrophysics Data System (ADS)
Rezaei Niya, S. M.; Selvadurai, A. P. S.
2017-03-01
The paper presents an approach for estimating the permeability of a porous medium that is based on the characteristics of the porous structure. The pressure drop in different fluid flow passages is estimated and these are combined to evaluate the overall reduction. The theory employed is presented and the level of accuracy for different cases is discussed. The successive steps in the solution algorithm are described. The accuracy and computational efficiency of the approach are compared with results obtained from a finite-element-based multiphysics formulation. It is shown that for a comparable accuracy, the computational efficiency of the approach can be two orders of magnitude faster. Finally, the model predictions are examined with conventional relationships that have been reported in the literature and are based on permeability-porosity relationships. It is shown that estimating the permeability of a porous medium using porosity can lead to an order of magnitude error and the expected permeability range in different porosities is presented using 10 000 random structures.
A probabilistic approach for estimating water permeability in pressure-driven membranes.
Boateng, Linkel K; Madarshahian, Ramin; Yoon, Yeomin; Caicedo, Juan M; Flora, Joseph R V
2016-08-01
A probabilistic approach is proposed to estimate water permeability in a cellulose triacetate (CTA) membrane. Water transport across the membrane is simulated in reverse osmosis mode by means of non-equilibrium molecular dynamics (MD) simulations. Different membrane configurations obtained by an annealing MD simulation are considered and simulation results are analyzed by using a hierarchical Bayesian model to obtain the permeability of the different membranes. The estimated membrane permeability is used to predict full-scale water flux by means of a process-level Monte Carlo simulation. Based on the results, the parameters of the model are observed to converge within 5-ns total simulation time. The results also indicate that the use of unique structural configurations in MD simulations is essential to capture realistic membrane properties at the molecular scale. Furthermore, the predicted full-scale water flux based on the estimated permeability is within the same order of magnitude of bench-scale experimental measurement of 1.72×10(-5) m/s.
Estimating large-scale fracture permeability of unsaturatedrockusing barometric pressure data
Wu, Yu-Shu; Zhang, Keni; Liu, Hui-Hai
2005-05-17
We present a three-dimensional modeling study of gas flow inthe unsaturated fractured rock of Yucca Mountain. Our objective is toestimate large-scale fracture permeability, using the changes insubsurface pneumatic pressure in response to barometric pressure changesat the land surface. We incorporate the field-measured pneumatic datainto a multiphase flow model for describing the coupled processes ofliquid and gas flow under ambient geothermal conditions. Comparison offield-measured pneumatic data with model-predicted gas pressures is foundto be a powerful technique for estimating the fracture permeability ofthe unsaturated fractured rock, which is otherwise extremely difficult todetermine on the large scales of interest. In addition, this studydemonstrates that the multi-dimensional-flow effect on estimatedpermeability values is significant and should be included whendetermining fracture permeability in heterogeneous fracturedmedia.
Simulating gas-water relative permeabilities for nanoscale porous media with interfacial effects
NASA Astrophysics Data System (ADS)
Wang, Jiulong; Song, Hongqing; Li, Tianxin; Wang, Yuhe; Gao, Xuhua
2017-08-01
This paper presents a theoretical method to simulate gas-water relative permeability for nanoscale porous media utilizing fractal theory. The comparison between the calculation results and experimental data was performed to validate the present model. The result shows that the gas-water relative permeability would be underestimated significantly without interfacial effects. The thinner the liquid film thickness, the greater the liquid-phase relative permeability. In addition, both liquid surface diffusion and gas diffusion coefficient can promote gas-liquid two-phase flow. Increase of liquid surface diffusion prefer to increase liquid-phase permeability obviously as similar as increase of gas diffusion coefficient to increase gas-phase permeability. Moreover, the pore structure will become complicated with the increase of fractal dimension, which would reduce the gas-water relative permeability. This study has provided new insights for development of gas reservoirs with nanoscale pores such as shale.
NASA Astrophysics Data System (ADS)
Ge, Xinmin; Fan, Yiren; Deng, Shaogui; Han, Yujiao; Liu, Jiaxiong
2016-09-01
We present an improved fractal model for pore structure evaluation and permeability estimation based on the high pressure mercury porosimetry data. An accumulative fractal equation is introduced to characterize the piecewise nature of the capillary pressure and the mercury saturation. The iterative truncated singular value decomposition algorithm is developed to solve the accumulative fractal equation and obtain the fractal dimension distributions. Furthermore, the fractal dimension distributions and relevant parameters are used to characterize the pore structure and permeability. The results demonstrate that the proposed model provides better characterization of the mercury injection capillary pressure than conventional monofractal theory. In addition, there is a direct relationship between the pore structure types and the fractal dimension spectrums. What is more, the permeability is strongly correlated with the geometric and the arithmetic mean values of fractal dimensions, and the permeability estimated using these new fractal dimension parameters achieve excellent result. The improved model and solution give a fresh perspective of the conventional monofractal theory, which may be applied in many geological and geophysical fields.
Gap junctional conductance and permeability are linearly related.
Verselis, V; White, R L; Spray, D C; Bennett, M V
1986-10-24
The permeability of gap junctions to tetraethylammonium ions was measured in isolated pairs of blastomeres from Rana pipiens L. and compared to the junctional conductance. In this system, the junctional conductance is voltage-dependent and decreases with moderate transjunctional voltage of either sign. The permeability to tetraethylammonium ions was determined by injecting one cell of a pair with tetraethylammonium and monitoring its changing concentration in the prejunctional and postjunctional cells with ion-selective electrodes. Junctional conductance was determined by current-clamp and voltage-clamp techniques. For different cell pairs in which the transjunctional voltage was small and the junctional conductance at its maximum value, the permeability to tetraethylammonium ions was proportional to the junctional conductance. In individual cell pairs, a reduction in the junctional conductance induced by voltage was accompanied by a proportional reduction in the permeability of the gap junction over a wide range. The diameter of the tetraethylammonium ion (8.0 to 8.5 A, unhydrated) is larger than that of the potassium ion (4.6 A, hydrated), the predominant current-carrying species. The proportionality between the permeability to tetraethylammonium ions and the junctional conductance, measured here with exceptionally fine time resolution, indicates that a common gap junctional pathway mediates both electrical and chemical fluxes between cells, and that closure of single gap junction channels by voltage is all or none.
2010-04-01
Acronyms CCD Charge Couple Device CPT Cone Penetrometer Technology DOD U.S. Department of Defense DOE U.S. Department of Energy EPA U.S...commonly used to estimate permeability include pneumatic and hydraulic slug tests with permeameters deployed by cone penetrometer and hollow-stem...an area approximately 2 mm x 3 mm through a sapphire window on a cone penetrometer probe. The soil at the window is illuminated using LEDs mounted
Compositional effects on relative permeability and hysteresis for enhanced oil recovery
NASA Astrophysics Data System (ADS)
Khorsandi, S.; Li, L.; Johns, R. T.
2016-12-01
There are enormous efforts to develop relative permeability models that interpret pore scale flow mechanism into continuum scale observations. Relative permeabilities are complex functions of phase saturations, fluid compositions, pore structure, pore size distribution, interfacial properties, and distribution of phases. The current compositional reservoir simulators, however, are limited to use tuned correlations for relative permeabilities calculations. These correlations cannot quantify the more complex hysteresis, film drainage, capillary trapping or wettability alteration. Such processes are captured by adjusting the coefficients of relative permeability models based on capillary number, maximum non-wetting saturation, or phase compositions. Since the relative permeability models are not physical-based, the adjustments can result in inconsistency. The labeling of phases is another challenge for compositional floods, where phase properties can vary significantly such that phase inversion can happen. Therefore, common phase labeling techniques based on density or component tracking can fail. We proposed a novel compositional-dependent relative permeability model which calculates the phase flow rates based on pore structure, phase compositions, and phase distributions. This model can quantify many processes such as hysteresis, capillary trapping and film drainage, and does not require phase labeling. The effects of dissolution, vaporization and wettability alteration on relative permeabilities are also captured by the developed physical relative permeability model.
Gauden, Victoria; Hu, D-E; Kurokawa, T; Sarker, M H; Fraser, P A
2007-01-01
There has been some discussion as to whether the pial vasculature behaves in the same way as the blood-brain barrier as a whole. Recent studies have shown that capsazepine protects these vessels from the effects of ischemia-reperfusion. We have now used a new method to examine this protection in the whole brain. Horseradish peroxidase concentrations were measured in brain sections and plasma, following starch microsphere induced ischemia, which lasted from 20 to 60 minutes, with 30 minutes reperfusion. The PS product was calculated from the Crone-Renkin equation. Permeability increase, which depended on duration of ischemia, was considerably greater in the pia than the parenchyma. The increase was also greater in tissue surrounding large radial venules of the cortex. Single vessel studies showed that these differences mirror those between small and large pial venules. Capsazepine treatment protected the parenchymal blood-brain barrier by limiting the post-ischemic permeability increase to about one third, but had no effect on the pia or radial vessel permeability. Permeability has been estimated in tissue sections with good spatial resolution using this new technique, which has demonstrated that the TRPV1 receptor plays an important role in the whole brain, not confined to small pial venules.
Maloney, D.
1993-11-01
This report describes the results from special core analyses and relative permeability measurements conducted on Almond formation and Fontainebleu sandstone plugs. Almond formation plug tests were performed to evaluate multiphase, steady-state,reservoir-condition relative permeability measurement techniques and to examine the effect of temperature on relative permeability characteristics. Some conclusions from this project are as follows: An increase in temperature appeared to cause an increase in brine relative permeability results for an Almond formation plug compared to room temperature results. The plug was tested using steady-state oil/brine methods. The oil was a low-viscosity, isoparaffinic refined oil. Fontainebleu sandstone rock and fluid flow characteristics were measured and are reported. Most of the relative permeability versus saturation results could be represented by one of two trends -- either a k{sub rx} versus S{sub x} or k{sub rx} versus Sy trend where x and y are fluid phases (gas, oil, or brine). An oil/surfactant-brine steady-state relative permeability test was performed to examine changes in oil/brine relative permeability characteristics from changes in fluid IFTS. It appeared that, while low interfacial tension increased the aqueous phase relative permeability, it had no effect on the oil relative permeability. The BOAST simulator was modified for coreflood simulation. The simulator was useful for examining effects of variations in relative permeability and capillary pressure functions. Coreflood production monitoring and separator interface level measurement techniques were developed using X-ray absorption, weight methods, and RF admittance technologies. The three types of separators should be useful for routine and specialized core analysis applications.
Risk factor(s) related to high membrane permeability in peritoneal dialysis.
Unal, Aydin; Sipahioglu, Murat Hayri; Kocyigit, Ismail; Tunca, Onur; Tokgoz, Bulent; Oymak, Oktay
2016-01-01
Peritoneal dialysis (PD) patients have different peritoneal membrane permeability (transport) characteristics. High peritoneal membrane permeability is associated with increased mortality risk in the patient population. In this study, we aimed to investigate possible risk factor(s) related to high peritoneal membrane permeability. The study included 475 PD patients (46.1 ± 14.5 years of mean age; 198 female and 277 male). The patients were divided two groups according to peritoneal equilibration test (PET) result: high-permeability group (high and high-average) and low- permeability group (low-average and low). In both the univariate and multivariate logistic regression analyses, it was found that diabetes mellitus and hypoalbuminemia was significantly associated with high peritoneal membrane permeability [relative risk (RR): 1.90, 95% confidence interval (CI): 1.26-2.86, p: 0.002 and RR: 2.14, 95% CI: 1.44-3.18, p<0.001, respectively]. Diabetes mellitus and hypoalbuminemia were closely associated with high peritoneal membrane permeability. Diabetic patients had 1.9 times the likelihood of having high permeability. However, the relationship between hypoalbuminemia and high peritoneal permeability appears to be a result rather than cause.
The effect of the capillary number and its constituents on two-phase relative permeability curves
Fulcher, R.A.; Ertekin, T.; Stahl, C.D.
1983-10-01
The goal of this study is to determine the effect of the capillary number on two-phase (oil-water) relative permeability curves. Specifically, a series of steady-state relative permeability measurements were carried out to determine if the capillary number causes changes in the two-phase permeabilities or if any one of its constituents, such as flow velocity, fluid viscosity, or interfacial tension, are the controlling variables. For the core tests, run in fired Berea sandstone, a Soltrol 170 oil-calcium chloride brine-isopropyl alcohol-glycerin system was utilized. Alcohol was the interfacial tension reducer and glycerin was the wetting phase viscosifier. The non-wetting phase (oil) relative permeability showed little correlation with the capillary number. As the interfacial tension decreased below 2.0 dynes/cm, the oil permeability increased dramatically. However, as the wetting phase viscosity increased, the non-wetting phase demonstrated less ability to flow. For the wetting phase (water) relative permeability, the opposite capillary number effect was shown. For both the tension decrease and the viscosity increase, i.e., a capillary number rise, the water permeability increased, but not as much as with the oil curves. No velocity effects were noted for the range studied. A relative permeability model was then developed from the experimental data, based on fluid saturations, interfacial tension, fluid viscosities, and the residual saturations, using regression analysis. The applicability of these regression models were then tested with the aid of a two-phase reservoir simulator.
Review: Mathematical expressions for estimating equivalent permeability of rock fracture networks
NASA Astrophysics Data System (ADS)
Liu, Richeng; Li, Bo; Jiang, Yujing; Huang, Na
2016-11-01
Fracture networks play a more significant role in conducting fluid flow and solute transport in fractured rock masses, comparing with that of the rock matrix. Accurate estimation of the permeability of fracture networks would help researchers and engineers better assess the performance of projects associated with fluid flow in fractured rock masses. This study provides a review of previous works that have focused on the estimation of equivalent permeability of two-dimensional (2-D) discrete fracture networks (DFNs) considering the influences of geometric properties of fractured rock masses. Mathematical expressions for the effects of nine important parameters that significantly impact on the equivalent permeability of DFNs are summarized, including (1) fracture-length distribution, (2) aperture distribution, (3) fracture surface roughness, (4) fracture dead-end, (5) number of intersections, (6) hydraulic gradient, (7) boundary stress, (8) anisotropy, and (9) scale. Recent developments of 3-D fracture networks are briefly reviewed to underline the importance of utilizing 3-D models in future research.
Relative ion permeability of normal and cystic fibrosis nasal epithelium.
Knowles, M; Gatzy, J; Boucher, R
1983-01-01
The raised transepithelial electric potential difference (PD) across respiratory epithelia in cystic fibrosis (CF) has suggested an abnormality in ion permeation. We characterized this abnormality further by measuring in the nasal epithelia of CF and normal subjects the concentration-PD relationship for amiloride, an inhibitor of cell Na+ permeability, and PD responses to superfusion with solutions of different composition. Amiloride was more efficacious in the CF subjects but the ED50 was not different from that of normals (approximately 2 X 10(-6) M). Na+ replacement by choline induced effects similar to those of amiloride, i.e. a greater depolarization in CF subjects. A 10-fold increase in the K+ concentration of the perfusate induced a small (less than 10 mV) depolarization in both subject populations. When Cl- in the perfusate was replaced by gluconate or SO2-(4) the nasal PD of normal subjects hyperpolarized (lumen became more negative) by approximately 35 mV. A significantly smaller response (less than 17 mV) was induced in CF homozygotes but not in heterozygotes (38 mV). The smaller response of CF subjects appears to reflect an absolute decrease in luminal surface Cl- permeability because pretreatment with amiloride did not increase the response to Cl- free solution (7 mV). Accordingly, three abnormalities (decreased Cl- permeability, raised PD, greater amiloride efficacy) have been identified in CF respiratory epithelia. Whereas "excessive" active Na+ transport can account for these abnormalities and the dessication of airway surface liquid, it is possible that a lower lumenal cell membrane Cl- permeability and inhibition of a potential path of Cl- secretion can also explain the observations. PMID:6853720
Predicting relative permeability from water retention: A direct approach based on fractal geometry
NASA Astrophysics Data System (ADS)
Cihan, Abdullah; Tyner, John S.; Perfect, Edmund
2009-04-01
Commonly, a soil's relative permeability curve is predicted from its measured water retention curve by fitting equations that share parameters between the two curves (e.g., Brooks/Corey-Mualem and van Genuchten-Mualem). We present a new approach to predict relative permeability by direct application of measured soil water retention data without any fitting procedures. The new relative permeability model, derived from a probabilistic fractal approach, appears in series form as a function of suction and the incremental change in water content. This discrete approach describes the drained pore space and permeability at different suctions incorporating the effects of both pore size distribution and connectivity among water-filled pores. We compared the new model performance predicting relative permeability to that of the van Genuchten-Mualem (VG-M) model for 35 paired data sets from the Unsaturated Soil hydraulic Database (UNSODA) and five other previously published data sets. At the 5% level of significance, the new method predicts relative permeabilities from the UNSODA database significantly better (mean logarithmic root-mean-square error, LRMSE = 0.813) than the VG-M model (LRMSE = 1.555). Each prediction of relative permeability from the five other previously published data sets was also significantly better.
Effects of heterogeneities on capillary pressure-saturation-relative permeability relationships.
Ataie-Ashtiani, Behzad; Hassanizadeh, S Majid; Celia, Michael A
2002-06-01
In theories of multiphase flow through porous media, capillary pressure-saturation and relative permeability-saturation curves are assumed to be intrinsic properties of the medium. Moreover, relative permeability is assumed to be a scalar property. However, numerous theoretical and experimental works have shown that these basic assumptions may not be valid. For example, relative permeability is known to be affected by the flow velocity (or pressure gradient) at which the measurements are carried out. In this article, it is suggested that the nonuniqueness of capillary pressure-relative permeability-saturation relationships is due to the presence of microheterogeneities within a laboratory sample. In order to investigate this hypothesis, a large number of "numerical experiments" are carried out. A numerical multiphase flow model is used to simulate the procedures that are commonly used in the laboratory for the measurement of capillary pressure and relative permeability curves. The dimensions of the simulation domain are similar to those of a typical laboratory sample (a few centimeters in each direction). Various combinations of boundary conditions and soil heterogeneity are simulated and average capillary pressure, saturation, and relative permeability for the "soil sample" are obtained. It is found that the irreducible water saturation is a function of the capillary number; the smaller the capillary number, the larger the irreducible water saturation. Both drainage and imbibition capillary pressure curves are found to be strongly affected by heterogeneities and boundary conditions. Relative permeability is also found to be affected by the boundary conditions; this is especially true about the nonaqueous phase permeability. Our results reveal that there is much need for laboratory experiments aimed at investigating the interplay of boundary conditions and microheterogeneities and their effect on capillary pressure and relative permeability.
Obtaining permeability estimates from NMR logging data in an unconsolidated groundwater aquifer
NASA Astrophysics Data System (ADS)
Dlubac, K.; Knight, R. J.; Song, Y.; Bachman, N.; Grau, B.; Cannia, J. C.; Williams, J.
2011-12-01
There is growing interest in the use of proton nuclear magnetic resonance (NMR) logging for aquifer characterization because it provides information about water-filled porosity and pore space geometry that can be used to estimate permeability (k). Hydrologists estimate hydraulic conductivity, from which k can be calculated, using wellbore flow (WBF) logging. WBF logging data distributes the total hydraulic conductivity, determined from aquifer testing, throughout the aquifer. However, this method is time consuming and has relatively low vertical resolution. If reliable estimates of k can be obtained from NMR logging data, this would provide hydrologists with an efficient alternate method for characterizing aquifer properties. The Schlumberger Doll Research (SDR) and Timur-Coates (T-C) equations are widely used in petroleum applications to obtain k from NMR logging measurements of the relaxation time T2. In this abstract, we focus on the SDR equation which takes the form kSDR=aφ mT2MLn where a, m and n are empirical constants, T2ML is the mean log of the T2 distribution and φ is porosity. The constants have been empirically determined in consolidated materials and are typically assumed to have the following values: a=4, m=4 and n=2. The use of the SDR equation with these values has been found to yield reliable estimates of k in consolidated materials. However, this same equation underestimates k in unconsolidated materials. In this study, we collected NMR logging, aquifer-test, and WBF data from a 150-m deep well that penetrated the High Plains aquifer in central Nebraska. We then worked with a generalized form of the SDR equation: kSDR Generalized =aφ mT2AVG2, where we allowed T2AVG to be calculated as the mean log and arithmetic mean (T2AM) of the T2 distribution. We elected to set the exponent n on the T2 term equal to 2, which results in a k estimate that has the appropriate units of length squared. We used a semi-constrained least squares inversion to
NASA Astrophysics Data System (ADS)
Tichauer, Kenneth M.; Osswald, Christian R.; Dosmar, Emily; Guthrie, Micah J.; Hones, Logan; Sinha, Lagnojita; Xu, Xiaochun; Mieler, William F.; St. Lawrence, Keith; Kang-Mieler, Jennifer J.
2015-06-01
Clinical symptoms of diabetic retinopathy are not detectable until damage to the retina reaches an irreversible stage, at least by today's treatment standards. As a result, there is a push to develop new, "sub-clinical" methods of predicting the onset of diabetic retinopathy before the onset of irreversible damage. With diabetic retinopathy being associated with the accumulation of long-term mild damage to the retinal vasculature, retinal blood vessel permeability has been proposed as a key parameter for detecting preclinical stages of retinopathy. In this study, a kinetic modeling approach used to quantify vascular permeability in dynamic contrast-enhanced medical imaging was evaluated in noise simulations and then applied to retinal videoangiography data in a diabetic rat for the first time to determine the potential for this approach to be employed clinically as an early indicator of diabetic retinopathy. Experimental levels of noise were found to introduce errors of less than 15% in estimates of blood flow and extraction fraction (a marker of vascular permeability), and fitting of rat retinal fluorescein angiography data provided stable maps of both parameters.
Vasco, D.W.; Ferretti, Alessandro; Novali, Fabrizio
2008-05-01
Transient pressure variations within a reservoir can be treated as a propagating front and analyzed using an asymptotic formulation. From this perspective one can define a pressure 'arrival time' and formulate solutions along trajectories, in the manner of ray theory. We combine this methodology and a technique for mapping overburden deformation into reservoir volume change as a means to estimate reservoir flow properties, such as permeability. Given the entire 'travel time' or phase field, obtained from the deformation data, we can construct the trajectories directly, there-by linearizing the inverse problem. A numerical study indicates that, using this approach, we can infer large-scale variations in flow properties. In an application to Interferometric Synthetic Aperture (InSAR) observations associated with a CO{sub 2} injection at the Krechba field, Algeria, we image pressure propagation to the northwest. An inversion for flow properties indicates a linear trend of high permeability. The high permeability correlates with a northwest trending fault on the flank of the anticline which defines the field.
NASA Astrophysics Data System (ADS)
Rizzo, R. E.; Healy, D.; De Siena, L.
2017-02-01
The success of any predictive model is largely dependent on the accuracy with which its parameters are known. When characterising fracture networks in rocks, one of the main issues is accurately scaling the parameters governing the distribution of fracture attributes. Optimal characterisation and analysis of fracture lengths and apertures are fundamental to estimate bulk permeability and therefore fluid flow, especially for rocks with low primary porosity where most of the flow takes place within fractures. We collected outcrop data from a fractured upper Miocene biosiliceous mudstone formation (California, USA), which exhibits seepage of bitumen-rich fluids through the fractures. The dataset was analysed using Maximum Likelihood Estimators to extract the underlying scaling parameters, and we found a log-normal distribution to be the best representative statistic for both fracture lengths and apertures in the study area. By applying Maximum Likelihood Estimators on outcrop fracture data, we generate fracture network models with the same statistical attributes to the ones observed on outcrop, from which we can achieve more robust predictions of bulk permeability.
More general capillary pressure and relative permeability models from fractal geometry.
Li, Kewen
2010-01-15
More general capillary pressure and relative permeability models were derived theoretically from fractal modeling of a porous medium. It was found that the new capillary pressure model could be reduced to the frequently-used Brooks-Corey capillary pressure model and the Li-Horne imbibition model when the fractal dimension of a porous medium takes specific values. This also demonstrates that the Brooks-Corey model and the Li-Horne model have a further confirmed theoretical basis. Capillary pressure data measured using mercury intrusion techinque were used to verify the model. The results demonstrated that the new capillary pressure model could represent the capillary pressure curves in those rocks with fracures or with great heterogeneity while the existing models cannot. The new relative permeability models can be reduced to the Brooks-Corey relative permeability model in a specific case. It has been proved theoretically that the relative permeability of each phase in a smooth fracture is only a linear function of its own saturation. Relative permeability data were calculated using the new models and the model results were compared with experimental data measured using a steady-state technique. The comparison demonstrated that the relative permeability models and experimental results were consistent with each other.
Kumar, Niyanta N.; Gautam, Mohan; Lochhead, Jeffrey J.; Wolak, Daniel J.; Ithapu, Vamsi; Singh, Vikas; Thorne, Robert G.
2016-01-01
Intranasal administration provides a non-invasive drug delivery route that has been proposed to target macromolecules either to the brain via direct extracellular cranial nerve-associated pathways or to the periphery via absorption into the systemic circulation. Delivering drugs to nasal regions that have lower vascular density and/or permeability may allow more drug to access the extracellular cranial nerve-associated pathways and therefore favor delivery to the brain. However, relative vascular permeabilities of the different nasal mucosal sites have not yet been reported. Here, we determined that the relative capillary permeability to hydrophilic macromolecule tracers is significantly greater in nasal respiratory regions than in olfactory regions. Mean capillary density in the nasal mucosa was also approximately 5-fold higher in nasal respiratory regions than in olfactory regions. Applying capillary pore theory and normalization to our permeability data yielded mean pore diameter estimates ranging from 13–17 nm for the nasal respiratory vasculature compared to <10 nm for the vasculature in olfactory regions. The results suggest lymphatic drainage for CNS immune responses may be favored in olfactory regions due to relatively lower clearance to the bloodstream. Lower blood clearance may also provide a reason to target the olfactory area for drug delivery to the brain. PMID:27558973
NASA Astrophysics Data System (ADS)
Xie, Jian.-Fei.; He, S.; Zu, Y. Q.; Lamy-Chappuis, B.; Yardley, B. W. D.
2017-03-01
In this paper, the migration of supercritical carbon dioxide (CO2 ) in realistic sandstone rocks under conditions of saline aquifers, with applications to the carbon geological storage, has been investigated by a two-phase lattice Boltzmann method (LBM). Firstly the digital images of sandstone rocks were reproduced utilizing the X-ray computed microtomography (micro-CT), and high resolutions (up to 2.5 μm) were applied to the pore-scale LBM simulations. For the sake of numerical stability, the digital images were "cleaned" by closing the dead holes and removing the suspended particles in sandstone rocks. In addition, the effect of chemical reactions occurred in the carbonation process on the permeability was taken into account. For the wetting brine and non-wetting supercritical CO2 flows, they were treated as the immiscible fluids and were driven by pressure gradients in sandstone rocks. Relative permeabilities of brine and supercritical CO2 in sandstone rocks were estimated. Particularly the dynamic saturation was applied to improve the reliability of the calculations of the relative permeabilities. Moreover, the effects of the viscosity ratio of the two immiscible fluids and the resolution of digital images on the relative permeability were systematically investigated.
NASA Astrophysics Data System (ADS)
Xie, Jian.-Fei.; He, S.; Zu, Y. Q.; Lamy-Chappuis, B.; Yardley, B. W. D.
2017-08-01
In this paper, the migration of supercritical carbon dioxide (CO2) in realistic sandstone rocks under conditions of saline aquifers, with applications to the carbon geological storage, has been investigated by a two-phase lattice Boltzmann method (LBM). Firstly the digital images of sandstone rocks were reproduced utilizing the X-ray computed microtomography (micro-CT), and high resolutions (up to 2.5 μm) were applied to the pore-scale LBM simulations. For the sake of numerical stability, the digital images were "cleaned" by closing the dead holes and removing the suspended particles in sandstone rocks. In addition, the effect of chemical reactions occurred in the carbonation process on the permeability was taken into account. For the wetting brine and non-wetting supercritical CO2 flows, they were treated as the immiscible fluids and were driven by pressure gradients in sandstone rocks. Relative permeabilities of brine and supercritical CO2 in sandstone rocks were estimated. Particularly the dynamic saturation was applied to improve the reliability of the calculations of the relative permeabilities. Moreover, the effects of the viscosity ratio of the two immiscible fluids and the resolution of digital images on the relative permeability were systematically investigated.
Kumar, Niyanta N; Gautam, Mohan; Lochhead, Jeffrey J; Wolak, Daniel J; Ithapu, Vamsi; Singh, Vikas; Thorne, Robert G
2016-08-25
Intranasal administration provides a non-invasive drug delivery route that has been proposed to target macromolecules either to the brain via direct extracellular cranial nerve-associated pathways or to the periphery via absorption into the systemic circulation. Delivering drugs to nasal regions that have lower vascular density and/or permeability may allow more drug to access the extracellular cranial nerve-associated pathways and therefore favor delivery to the brain. However, relative vascular permeabilities of the different nasal mucosal sites have not yet been reported. Here, we determined that the relative capillary permeability to hydrophilic macromolecule tracers is significantly greater in nasal respiratory regions than in olfactory regions. Mean capillary density in the nasal mucosa was also approximately 5-fold higher in nasal respiratory regions than in olfactory regions. Applying capillary pore theory and normalization to our permeability data yielded mean pore diameter estimates ranging from 13-17 nm for the nasal respiratory vasculature compared to <10 nm for the vasculature in olfactory regions. The results suggest lymphatic drainage for CNS immune responses may be favored in olfactory regions due to relatively lower clearance to the bloodstream. Lower blood clearance may also provide a reason to target the olfactory area for drug delivery to the brain.
Use of geology in the interpretation of core-scale relative permeability data
Ringrose, P.S.; Jensen, J.L.; Sorbie, K.S.
1996-09-01
A number of factors, such as wettability, pore-size distribution, and core-scale heterogeneity, are known to affect the measured relative permeability in core plug samples. This paper focuses on the influence of geological structure at the laminaset scale on water-oil imbibition relative permeability curves. The endpoint positions and curve shapes vary as a function of the type of internal heterogeneity, the flow rate, and the assumptions on the pore-scale petrophysics (e.g. wettability). Interaction between the capillary forces and heterogeneity can occur at the cm-dm scale, which results in widely varying two-phase flow behavior for rocks with the same single-phase permeability. The geometry of heterogeneity as expressed in standard geological descriptions (e.g., cross-laminated, ripple-laminated, plane-laminated) can be translated into features of the expected relative permeability behavior for each rock type, thus aiding the interpretation of relative permeability data. The authors illustrate how their findings can help to interpret sets of relative permeability data from the field, using some examples from the Admire sand, El Dorado Field, Kansas.
Special core analyses and relative permeability measurement on Almond formation reservoir rocks
Maloney, D.; Doggett, K.; Brinkmeyer, A.
1993-02-01
This report describes the results from special core analyses and relative permeability measurements conducted on samples of rock from the Almond Formation in Greater Green River Basin of southwestern Wyoming. The core was from Arch Unit Well 121 of Patrick Draw field. Samples were taken from the 4,950 to 4,965 ft depth interval. Thin section evaluation, X-ray diffraction, routine permeability and porosity, capillary pressure and wettability tests were performed to characterize the samples. Fluid flow capacity characteristics were measured during two-phase unsteady- and steady-state and three-phase steady-state relative permeability tests. Test results are presented in tables and graphs. Relative permeability results are compared with those of a 260-mD, fired Berea sandstone sample which was previously subjected to similar tests. Brine relative permeabilities were similar for the two samples, whereas oil and gas relative permeabilities for the Almond formation rock were higher at equivalent saturation conditions compared to Berea results. Most of the tests described in this report were conducted at 74[degrees]F laboratory temperature. Additional tests are planned at 150[degrees]F temperature. Equipment and procedural modifications to perform the elevated temperature tests are described.
Special core analyses and relative permeability measurement on Almond formation reservoir rocks
Maloney, D.; Doggett, K.; Brinkmeyer, A.
1993-02-01
This report describes the results from special core analyses and relative permeability measurements conducted on samples of rock from the Almond Formation in Greater Green River Basin of southwestern Wyoming. The core was from Arch Unit Well 121 of Patrick Draw field. Samples were taken from the 4,950 to 4,965 ft depth interval. Thin section evaluation, X-ray diffraction, routine permeability and porosity, capillary pressure and wettability tests were performed to characterize the samples. Fluid flow capacity characteristics were measured during two-phase unsteady- and steady-state and three-phase steady-state relative permeability tests. Test results are presented in tables and graphs. Relative permeability results are compared with those of a 260-mD, fired Berea sandstone sample which was previously subjected to similar tests. Brine relative permeabilities were similar for the two samples, whereas oil and gas relative permeabilities for the Almond formation rock were higher at equivalent saturation conditions compared to Berea results. Most of the tests described in this report were conducted at 74{degrees}F laboratory temperature. Additional tests are planned at 150{degrees}F temperature. Equipment and procedural modifications to perform the elevated temperature tests are described.
Effect of the capillary number and its constituents on two-phase relative permeabilities
Fulcher, R.A. Jr.
1982-01-01
One of the primary goals of any enhanced recovery project is to maximize the ability of the fluids to flow through a porous medium, i.e., the reservoir. The topic of this study is the effect of the capillary number, a dimensionless group describing the ratio of viscous to capillary forces, on two-phase (oil-water) relative permeability curves. Specifically, a series of steady-state measurements were carried out to determine if the capillary number causes changes in the two-phase permeabilities or if any one of its constituents, such as flow velocity, fluid viscosity, or interfacial tension, are the controlling variables. For the core tests, run in fired Berea sandstone, a Soltrol 170 oil-calcium chloride brine-isopropyl alcohol-glycerin system was utilized. Alcohol was the tension reducer and glycerin was used as the wetting phase viscosifier. It was found that the non-wetting phase (oil) relative permeability shows no correlation with the capillary number. As the interfacial tension decreased below 2.0 dyne/cm, the oil permeability increased dramatically. However, as the wetting phase viscosity increased, the non-wetting phase demonstrated less ability to flow. For the wetting phase (water) relative permeability, the opposite effect was shown. For both the viscosity increase and the tension reduction, i.e., a capillary number rise, the water permeability increased, but not as pronounced as with the oil curves. No velocity effects were noted for the range studied. A relative permeability model was developed from the experimental data, based on fluid saturation, interfacial tension, fluid viscosities, and the residual saturations using regression analysis. Both phases were modeled for both the imbibition and drainage processes. These models demonstrated similar or better fits with experimental data, of other fluid and wetting systems, when compared with other existing relative permeability models.
NASA Astrophysics Data System (ADS)
Chen, Chih-Ying
2005-11-01
Two-phase flow through fractured media is important in petroleum, geothermal, and environmental applications. However, the actual physics and phenomena that occur inside fractures are poorly understood, and oversimplified relative permeability curves are commonly used in fractured reservoir simulations. In this work, an experimental apparatus equipped with a high-speed data acquisition system, real-time visualization, and automated image processing technology was constructed to study three transparent analog fractures with distinct surface roughnesses: smooth, homogeneously rough, and randomly rough. Air-water relative permeability measurements obtained in this study were compared with models suggested by earlier studies and analyzed by examining the flow structures. A method to evaluate the tortuosities induced by the blocking phase, namely the channel tortuosity, was proposed from observations of the flow structure images. The relationship between the coefficients of channel tortuosity and the relative permeabilities was studied with the aid of laboratory experiments and visualizations. Experimental data from these fractures were used to develop a broad approach for modeling two-phase flow behavior based on the flow structures. Finally, a general model deduced from these data was proposed to describe two-phase relative permeabilities in both smooth and rough fractures. For the theoretical analysis of liquid-vapor relative permeabilities, accounting for phase transformations, the inviscid bubble train models coupled with relative permeability concepts were developed. The phase transformation effects were evaluated by accounting for the molecular transport through liquid-vapor interfaces. For the steam-water relative permeabilities, we conducted steam-water flow experiments in the same fractures as used for air-water experiments. We compared the flow behavior and relative permeability differences between two-phase flow with and without phase transformation effects
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Sahimi, Muhammad; Daigle, Hugh
2016-07-01
Accurate prediction of the relative permeability to water under partially saturated condition has broad applications and has been studied intensively since the 1940s by petroleum, chemical, and civil engineers, as well as hydrologists and soil scientists. Many models have been developed for this purpose, ranging from those that represent the pore space as a bundle of capillary tubes, to those that utilize complex networks of interconnected pore bodies and pore throats with various cross-section shapes. In this paper, we propose an approach based on the effective-medium approximation (EMA) and percolation theory in order to predict the water relative permeability. The approach is general and applicable to any type of porous media. We use the method to compute the water relative permeability in porous media whose pore-size distribution follows a power law. The EMA is invoked to predict the relative permeability from the fully saturated pore space to some intermediate water saturation that represents a crossover from the EMA to what we refer to as the "critical region." In the critical region below the crossover water saturation Swx, but still above the critical water saturation Swc (the residual saturation or the percolation threshold of the water phase), the universal power law predicted by percolation theory is used to compute the relative permeability. To evaluate the accuracy of the approach, data for 21 sets of undisturbed laboratory samples were selected from the UNSODA database. For 14 cases, the predicted relative permeabilities are in good agreement with the data. For the remaining seven samples, however, the theory underestimates the relative permeabilities. Some plausible sources of the discrepancy are discussed.
Least Absolute Relative Error Estimation.
Chen, Kani; Guo, Shaojun; Lin, Yuanyuan; Ying, Zhiliang
2010-01-01
Multiplicative regression model or accelerated failure time model, which becomes linear regression model after logarithmic transformation, is useful in analyzing data with positive responses, such as stock prices or life times, that are particularly common in economic/financial or biomedical studies. Least squares or least absolute deviation are among the most widely used criterions in statistical estimation for linear regression model. However, in many practical applications, especially in treating, for example, stock price data, the size of relative error, rather than that of error itself, is the central concern of the practitioners. This paper offers an alternative to the traditional estimation methods by considering minimizing the least absolute relative errors for multiplicative regression models. We prove consistency and asymptotic normality and provide an inference approach via random weighting. We also specify the error distribution, with which the proposed least absolute relative errors estimation is efficient. Supportive evidence is shown in simulation studies. Application is illustrated in an analysis of stock returns in Hong Kong Stock Exchange.
NASA Astrophysics Data System (ADS)
Tsakiroglou, C. D.; Avraam, D. G.; Payatakes, A. C.
2007-09-01
The water krw and oil kro relative permeability curves of a glass-etched planar pore network are estimated with history matching from transient displacement experiments performed at varying values of the capillary number, Ca, for two fluid systems: one of intermediate and one of strong wettability. The transient k,k are compared to corresponding ones measured with the steady-state method on the same porous medium [Avraam DG, Payatakes AC. Flow regimes and relative permeabilities during steady-state two-phase flow in porous media. J Fluid Mech 1995;293:207-36; Avraam DG, Payatakes AC. Generalized relative permeability coefficients during steady-state two-phase flow in porous media and correlation with the flow mechanisms. Transport Porous Med 1995;20:135-68; Avraam DG, Payatakes AC. Flow mechanisms, relative permeabilities, and coupling effects in steady-state two-phase flow through porous media. The case of strong wettability. Ind Eng Chem Res 1999;38:778-86.], and potential differences from them are interpreted in the light of the differences between the transient growth pattern, and the steady-state two-phase flow regime. For intermediate wettability, the transient kro and krw exceed the corresponding steady-state functions at low Ca values and have the tendency to become smaller than the steady-state ones at high Ca values. For strong wettability, the transient kro and krw are increasing functions of Ca, the transient kro is higher than the steady-state one, whereas the transient krw decreases substantially and becomes lower than the steady-state one at low Ca values. The dynamic capillary pressure estimated from transient experiments is a decreasing function of Ca in agreement with previous theoretical and experimental studies.
Numerical-Simulation-Based Determination of Relative Permeability in Laminated Rocks
NASA Astrophysics Data System (ADS)
Sedaghat, Mohammad H.; Gerke, Kirill; Azizmohammadi, Siroos; Matthai, Stephan
2016-04-01
Reservoir simulation using the extended Darcy's law approach requires relative permeability curves derived either via analytic saturation functions (Corey models etc.) or from special core analysis (SCAL). Since such experimental exploration of the space of influential parameters (pore geometry and wettability) is costly and time consuming, establishing ways to extract ensemble relative permeability from numerical simulation, kri, over the entire range of water saturation is highly desirable. Recent work has highlighted that the shape of relative permeability strongly depends on the balance between viscous, gravitational, and capillary forces. Our work focuses on finding accurate ways to compute ensemble kri(sw) for layered rocks when both capillary and viscous forces are strong. Two methods are proposed: an unsteady state saturation variation (USSV) method and a steady state saturation variation (SSSV) technique. To evaluate these approaches, SCAL data was extracted numerically from a real mm-scale layered sample. Results obtained with a Finite Element-Centered Finite Volume (FECFM) simulator, suggest that either of the approaches work significantly better than conventional unsteady state and JBN (Johnson-Bossler-Naumann) methods. Also, investigating saturation and velocity profiles within the sample indicates that bed-by-bed variations in wettability influence the flow pattern along/across interfaces making equipermeable layers behave like zones with different flow velocity. This dramatically challenges conventional relative permeability models and is addressed in terms of a new variable called relative permeability index.
Liu, Qingjie; Shen, Pingping; Wu, Yu-Shu
2004-03-15
A dynamic pore-scale network model is presented for investigating the effects of interfacial tension and oil-water viscosity on relative permeability during chemical flooding. This model takes into account both viscous and capillary forces in analyzing the impact of chemical properties on flow behavior or displacement configuration, as opposed to the conventional or invasion percolation algorithm which incorporates capillary pressure only. The study results indicate that both water and oil relative-permeability curves are dependent strongly on interfacial tension as well as an oil-water viscosity ratio. In particular, water and oil relative-permeability curves are both found to shift upward as interfacial tension is reduced, and they both tend to become linear versus saturation once interfacial tension is at low values. In addition, the oil-water viscosity ratio appears to have only a small effect under conditions of high interfacial tension. When the interfacial tension is low, however, water relative permeability decreases more rapidly (with the increase in the aqueous-phase viscosity) than oil relative permeability. The breakthrough saturation of the aqueous phase during chemical flooding tends to decrease with the reduction of interfacial tension and may also be affected by the oil-water viscosity ratio.
NASA Astrophysics Data System (ADS)
Popov, Evgeny; Popov, Yury; Spasennykh, Mikhail; Kozlova, Elena; Chekhonin, Evgeny; Zagranovskaya, Dzhuliya; Belenkaya, Irina; Alekseev, Aleksey
2016-04-01
A practical method of organic-rich intervals identifying within the low-permeable dispersive rocks based on thermal conductivity measurements along the core is presented. Non-destructive non-contact thermal core logging was performed with optical scanning technique on 4 685 full size core samples from 7 wells drilled in four low-permeable zones of the Bazhen formation (B.fm.) in the Western Siberia (Russia). The method employs continuous simultaneous measurements of rock anisotropy, volumetric heat capacity, thermal anisotropy coefficient and thermal heterogeneity factor along the cores allowing the high vertical resolution (of up to 1-2 mm). B.fm. rock matrix thermal conductivity was observed to be essentially stable within the range of 2.5-2.7 W/(m*K). However, stable matrix thermal conductivity along with the high thermal anisotropy coefficient is characteristic for B.fm. sediments due to the low rock porosity values. It is shown experimentally that thermal parameters measured relate linearly to organic richness rather than to porosity coefficient deviations. Thus, a new technique employing the transformation of the thermal conductivity profiles into continuous profiles of total organic carbon (TOC) values along the core was developed. Comparison of TOC values, estimated from the thermal conductivity values, with experimental pyrolytic TOC estimations of 665 samples from the cores using the Rock-Eval and HAWK instruments demonstrated high efficiency of the new technique for the organic rich intervals separation. The data obtained with the new technique are essential for the SR hydrocarbon generation potential, for basin and petroleum system modeling application, and estimation of hydrocarbon reserves. The method allows for the TOC richness to be accurately assessed using the thermal well logs. The research work was done with financial support of the Russian Ministry of Education and Science (unique identification number RFMEFI58114X0008).
NASA Astrophysics Data System (ADS)
Wang, L.; Cardenas, M. B.
2015-12-01
The coupling between hydraulic and mechanical properties of porous and fractured geologic media are critical for many geophysical processes and practical applications. Thus, the prediction of linkage between these properties are broadly important. Here we present a parameterized model that links fracture permeability and specific stiffness with scaling coefficients dependent on fracture roughness and correlation length. The model was developed empirically from results of modeling the deformation and flow through synthetic fractures with aperture fields that follow a normal distribution. The fractures were subjected to increasing normal stress and deformed follow an elastic model. Specific stiffness was directly quantified from these numerical experiments with resultant displacement. Moreover, intrinsic permeability was estimated through calculation of the local flow field while considering effects of local fracture roughness and tortuosity through the modified Local Cubic Law. We found that fracture displacement increases non-linearly with applied normal stress, while specific stiffness is expectedly proportional to normal stress. Most importantly, permeability decreases exponentially with increasing specific stiffness following different deformation paths depending mainly on fracture roughness rather than correlation length. Based on the calculated permeability and specific stiffness, we propose an empirical model that predicts a clustered linkage between specific stiffness and permeability. The model can capture the transition from effective medium to percolation flow regimes with increasing specific stiffness.
Uncertainty Assessment of Interpolation-Based Three Phase Relative Permeability Models
NASA Astrophysics Data System (ADS)
Ranaee, Ehsan; Giovanni, Porta; Monica, Riva; Alberto, Guadagnini
2013-04-01
A major element affecting uncertainty associated with prediction of three-phase flow in reservoirs is the parameterization of relative permeability. The latter are typically obtained through interpolation of two phase relative permeability data because of intrinsic difficulties related to direct measurements. Here, we discuss and analyze the saturation history dependency of water, oil and gas relative permeabilities and distinguish key features of three- and two- phase flow configurations. We start by investigating the advantages and limitations of several methodologies available in the literature and widely adopted in three-phase flow simulation. This analysis is performed by comparing model outcomes against experimental data published in the literature. The results provided by considering Corey-type equations as input to the aforesaid models is compared against the use of linear interpolation of two-phase measurements from oil-water and oil-gas environment. Our results show that available models typically fail to reproduce the set of experimental results ever the full range of saturations. This analysis suggests that not only saturation history but also wettability, residual oil and trapping behavior of oil during drainage and imbibition are key elements distinguishing between the physics of two- and three-phase settings. These effects should be taken in account to predict three-phase relative permeability. We then propose an alternative formulation to compute oil relative permability under three-phase conditions. Our model takes into account (i) the dependence of three-phase oil relative permeability on the saturation path, and (ii) the effect of wettability observed for three-phase systems. The model is based on a sigmoid-type interpolation of the oil relative permeability-saturation data in a two-phase oil-water system. Three-phase oil relative permeability is then computed through an additional interpolation between the oil-water effective sigmoid curve and
NASA Astrophysics Data System (ADS)
Mirabolghasemi, M.; Prodanovic, M.
2012-12-01
The problem of fine particle infiltration is seen in fields from subsurface transport, to drug delivery to industrial slurry flows. Sediment filtration and pathogen retention are well-known subsurface engineering problems that have been extensively studied through different macroscopic, microscopic and experimental modeling techniques Due to heterogeneity, standard constitutive relationships and models yield poor predictions for flow (e.g. permeability) and rock properties (e.g. elastic moduli) of the invaded (damaged) porous media. This severely reduces our ability to, for instance, predict retention, pressure build-up, newly formed flow pathways or porous medium mechanical behavior. We chose a coupled computational fluid dynamics (CFD) - discrete element modeling (DEM) approach to simulate the particulate flow through porous media represented by sphere packings. In order to minimize the uncertainty involved in estimating the flow properties of porous media on Darcy scale and address the dynamic nature of filtration process, this microscopic approach is adapted as a robust method that can incorporate particle interaction physics as well as the heterogeneity of the porous medium.. The coupled simulation was done in open-source packages which has both CFD (openFOAM) and DEM components (LIGGGHTS). We ran several sensitivity analyses over different parameters such as particle/grain size ratio, fluid viscosity, flow rate and sphere packing porosity in order to investigate their effects on the depth of invasion and damaged porous medium permeability. The response of the system to the variation of different parameters is reflected through different clogging mechanism; for instance, bridging is the dominant mechanism of pore-throat clogging when larger particles penetrate into the packing, whereas, in case of fine particles which are much smaller than porous medium grains (1/20 in diameter), this mechanism is not very effective due to the frequent formation and
Impacts of relative permeability on CO2 phase behavior, phase distribution, and trapping mechanisms
NASA Astrophysics Data System (ADS)
Moodie, N.; McPherson, B. J. O. L.; Pan, F.
2015-12-01
A critical aspect of geologic carbon storage, a carbon-emissions reduction method under extensive review and testing, is effective multiphase CO2 flow and transport simulation. Relative permeability is a flow parameter particularly critical for accurate forecasting of multiphase behavior of CO2 in the subsurface. The relative permeability relationship assumed and especially the irreducible saturation of the gas phase greatly impacts predicted CO2 trapping mechanisms and long-term plume migration behavior. A primary goal of this study was to evaluate the impact of relative permeability on efficacy of regional-scale CO2 sequestration models. To accomplish this we built a 2-D vertical cross-section of the San Rafael Swell area of East-central Utah. This model simulated injection of CO2 into a brine aquifer for 30 years. The well was then shut-in and the CO2 plume behavior monitored for another 970 years. We evaluated five different relative permeability relationships to quantify their relative impacts on forecasted flow results of the model, with all other parameters maintained uniform and constant. Results of this analysis suggest that CO2 plume movement and behavior are significantly dependent on the specific relative permeability formulation assigned, including the assumed irreducible saturation values of CO2 and brine. More specifically, different relative permeability relationships translate to significant differences in CO2 plume behavior and corresponding trapping mechanisms.
An extended vascular model for less biased estimation of permeability parameters in DCE-T1 images.
Nejad-Davarani, Siamak P; Bagher-Ebadian, Hassan; Ewing, James R; Noll, Douglas C; Mikkelsen, Tom; Chopp, Michael; Jiang, Quan
2017-02-17
One of the key elements in dynamic contrast enhanced (DCE) image analysis is the arterial input function (AIF). Traditionally, in DCE studies a global AIF sampled from a major artery or vein is used to estimate the vascular permeability parameters; however, not addressing dispersion and delay of the AIF at the tissue level can lead to biased estimates of these parameters. To find less biased estimates of vascular permeability parameters, a vascular model of the cerebral vascular system is proposed that considers effects of dispersion of the AIF in the vessel branches, as well as extravasation of the contrast agent (CA) to the extravascular-extracellular space. Profiles of the CA concentration were simulated for different branching levels of the vascular structure, combined with the effects of vascular leakage. To estimate the permeability parameters, the extended model was applied to these simulated signals and also to DCE-T1 (dynamic contrast enhanced T1 ) images of patients with glioblastoma multiforme tumors. The simulation study showed that, compared with the case of solving the pharmacokinetic equation with a global AIF, using the local AIF that is corrected by the vascular model can give less biased estimates of the permeability parameters (K(trans) , vp and Kb ). Applying the extended model to signals sampled from different areas of the DCE-T1 image showed that it is able to explain the CA concentration profile in both the normal areas and the tumor area, where effects of vascular leakage exist. Differences in the values of the permeability parameters estimated in these images using the local and global AIFs followed the same trend as the simulation study. These results demonstrate that the vascular model can be a useful tool for obtaining more accurate estimation of parameters in DCE studies.
NASA Astrophysics Data System (ADS)
Osterman, Gordon; Keating, Kristina; Binley, Andrew; Slater, Lee
2016-06-01
We estimate parameters from the Katz and Thompson permeability model using laboratory complex electrical conductivity (CC) and nuclear magnetic resonance (NMR) data to build permeability models parameterized with geophysical measurements. We use the Katz and Thompson model based on the characteristic hydraulic length scale, determined from mercury injection capillary pressure estimates of pore throat size, and the intrinsic formation factor, determined from multisalinity conductivity measurements, for this purpose. Two new permeability models are tested, one based on CC data and another that incorporates CC and NMR data. From measurements made on forty-five sandstone cores collected from fifteen different formations, we evaluate how well the CC relaxation time and the NMR transverse relaxation times compare to the characteristic hydraulic length scale and how well the formation factor estimated from CC parameters compares to the intrinsic formation factor. We find: (1) the NMR transverse relaxation time models the characteristic hydraulic length scale more accurately than the CC relaxation time (R2 of 0.69 and 0.33 and normalized root mean square errors (NRMSE) of 0.16 and 0.21, respectively); (2) the CC estimated formation factor is well correlated with the intrinsic formation factor (NRMSE=0.23). We demonstrate that that permeability estimates from the joint-NMR-CC model (NRMSE=0.13) compare favorably to estimates from the Katz and Thompson model (NRMSE=0.074). This model advances the capability of the Katz and Thompson model by employing parameters measureable in the field giving it the potential to more accurately estimate permeability using geophysical measurements than are currently possible.
Effect of the capillary number and its constituents on two-phase relative permeabilities
Fulcher, R.A. Jr.
1983-03-01
One of the primary goals of any enhanced recovery project is to maximize the ability of the fluids to flow through a porous medium, i.e., the reservoir. The topic of this study is the effect of the capillary number, a dimensionless group describing the ratio of viscous to capillary forces, on 2-phase (oil-water) relative permeability curves. Specifically, a series of steady-state measurements were performed to determine if the capillary number causes changes in the 2-phase permeabilities or if any one of its constituents, such as flow velocity, fluid viscosity, or interfacial tension, are the controlling variables. For the core tests, run in fired Berea Sandstone, a Soltrol 170 oil-calcium chloride brine- isopropyl alcohol-glycerin system was utilized. Alcohol was the tension reducer and glycerin was used as the wetting phase viscosifier. It was found that the nonwetting phase (oil) relative permeability shows no correlation with the capillary number.
NASA Astrophysics Data System (ADS)
Osterman, G. K.; Keating, K.; Binley, A. M.; Slater, L. D.; McDonald, R.
2014-12-01
In spite of the importance of permeability in controlling numerous hydrogeological and biogeochemical processes, the property can be exceptionally difficult to measure directly in the field. Recently, nuclear magnetic resonance (NMR) has become an increasingly popular method, both in the lab and the field, for hydrogeophysical investigations due to its sensitivity to water content and pore surface area. Additionally, previous work has shown that the electrical formation factor can be used as a proxy for the tortuosity of the pore space—a parameter NMR is incapable of detecting—in permeability models. However, the formation factor is impossible to accurately measure in the field using DC electrical methods, as the measured conductivity cannot be decomposed into the fluid and surface conduction components. Therefore, our approach is to use induced polarization (IP) and spectral induced polarization (SIP) in the laboratory to correct for the influence of surface conductivity in the formation factor calculation. The corrected formation factor can then be used along with NMR parameters for more accurate permeability estimation. Laboratory SIP and NMR datasets were acquired on 40 sandstone cores with a range of permeabilities spanning six orders of magnitude as estimated from gas permeameter measurements. We examine how different estimates of the electrical formation factor can be combined with the NMR transverse relaxation time to estimate permeability. Specifically, we compare the electrical formation factor measured at high and low pore-fluid salinity with the formation factor derived using IP and SIP. Using both empirical and mechanistic petrophysical relationships, we explore the utility of IP- and SIP-corrected formation factors in tandem with NMR parameters for permeability prediction as compared to the low-salinity formation factor typically measured in the field. Furthermore, we develop our models using IP and SIP data that may be acquired in the field
Jiang, Fei; Tsuji, Takeshi
2014-11-01
The CO_{2} behavior within the reservoirs of carbon capture and storage projects is usually predicted from large-scale simulations of the reservoir. A key parameter in reservoir simulation is relative permeability. However, mineral precipitation alters the pore structure over time, and leads correspondingly to permeability changing with time. In this study, we numerically investigate the influence of carbonate precipitation on relative permeability during CO_{2} storage. The pore spaces in rock samples were extracted by high-resolution microcomputed tomography (CT) scanned images. The fluid velocity field within the three-dimensional pore spaces was calculated by the lattice Boltzmann method, while reactive transport with calcite deposition was modeled by an advection-reaction formulation solved by the finite volume method. To increase the computational efficiency and reduce the processing time, we adopted a graphics processing unit parallel computing technique. The relative permeability of the sample rock was then calculated by a highly optimized two-phase lattice Boltzmann model. We also proposed two pore clogging models. In the first model, the clogging processes are modeled by transforming fluid nodes to solid nodes based on their precipitated mass level. In the second model, the porosity is artificially reduced by adjusting the gray scale threshold of the CT images. The developed method accurately simulates the mineralization process observed in laboratory experiment. Precipitation-induced evolution of pore structure significantly influenced the absolute permeability. The relative permeability, however, was much more influenced by pore reduction in the nonwetting phase than in the wetting phase. The output of the structural changes in pore geometry by this model could be input to CO_{2} reservoir simulators to investigate the outcome of sequestered CO_{2}.
A study of relative permeability for steam-water flow in porous media
Ambusso, Willis; Satik, Cengiz; Horne, Roland
1996-01-24
We report on continuing experimental and numerical efforts to obtain steam-water relative permeability functions and to assess effect of heat transfer and phase change. To achieve these, two sets of steady-state flow experiments were conducted: one with nitrogen and water and another with steam and water. During these experiments, a mixture of nitrogen-water (or steam-water) was injected into a Berea sandstone core. At the onset of steady state conditions, three-dimensional saturation distributions were obtained by using a high resolution X-ray computer tomography scanner. By identifying a length of the core over which a flat saturation profile exists and measuring the pressure gradient associated with this length, we calculated relative permeabilities for nitrogen-water flow experiments. The relative permeability relations obtained in this case were in good agreement with those reported by other investigators. Another attempt was also made to conduct a steam-water flow experiment under adiabatic conditions. This experiment was completed with partial success due to the difficulties encountered during the experiment. The results of this experiment showed that a flat saturation profile actually developed over a substantial length of the core even at a comparatively modest injection rate (6 grams per minute) with low steam quality (4% by mass). The completion of this set of experiments should yield steam-water relative permeability relations in the near future.
NASA Astrophysics Data System (ADS)
Um, W.; Rod, K. A.; Strickland, C. E.
2016-12-01
Permeability is a critical parameter needed to understand flow in subsurface environments; it is particularly important in deep subsurface reservoirs where multiphase fluid flow is common, such as carbon sequestration and geothermal reservoirs. Cement is used in the annulus of wellbores due to its low permeable properties to seal aquifers, reducing leaks to adjacent strata. Extreme subsurface environments of CO2 storage and geothermal production conditions will eventually reduce the cement integrity, propagating fracture networks and increasing the permeability for air and/or water. To date, there have been no reproducible experimental investigations of relative permeability in fractured wellbore cement published. To address this gap, we conducted a series of experiments using fractured Portland cement monoliths with increasing fracture networks. The monolith cylinder sides were jacketed with heavy-duty moisture-seal heat-shrink tubing, then fractured using shear force applied via a hydraulic press. Fractures were generated with different severity for each of three monoliths. Stainless steel endcaps were fixed to the monoliths using the same shrink-wrapped jacket. Fracture characteristics were determined using X-ray microtomography and image analysis. Flow controllers were used to control flow of water and air to supply continuous water or water plus air, both of which were delivered through the influent end cap. Effluent air flow was monitored using a flow meter, and water flow was measured gravimetrically. To monitor the effective saturation of the fractures, a RCON2 concrete bulk electrical resistivity test device was attached across both endcaps and a 0.1M NaNO3 brine was used as the transport fluid to improve resistivity measurements. Water content correlated to resistivity measurements with a r2 > 0.96. Data from the experiments was evaluated using two relative permeability models, the Corey-curve, often used for modeling relative permeability in porous media
Investigating the Relative Permeability of Tight Porous Media Using a Multiscale Network Model
NASA Astrophysics Data System (ADS)
Mehmani, A.; Prodanovic, M.
2013-12-01
Tight reservoirs, such as tight gas sandstone and tight carbonates, are rich sources of oil and gas that can significantly benefit the high global energy demand. However, the petrophysical properties (such as permeability or capillary pressure) of these so called unconventional reservoirs is difficult to quantify in terms of only porosity or saturation. This is mainly due to the high heterogeneity in pore shape, pore configuration, pore interconnectivity and a lack of understanding of fluid physics within said porous media. One unorthodox petrophysical phenomenon that remains inexplicable via conventional models is what is coined as 'permeability jail' (Shanley et al, 2004). By definition, a permeability jail is a range of water saturation in which neither the wetting phase nor the nonwetting phase is capable of moving. We investigate the effects of fluid physics (snap-off, film flow and wettability) and pore connectivity (pore shape and pore connectivity due to cementation and existence of microporosity) on tight rock relative permeability curves. Pore level modeling has become an established approach in investigating the effects of various pore structure features and fluid behaviors in pore scale on macroscopic petrophysical properties. We construct multiscale pore network flow models that contain both macro- (primary) and microporosity (secondary porosity). We first build theoretical network models based on granular packings to isolate the effects of each pore structure feature as well as fluid physics on both drainage and imbibition relative permeability curves. We then extend our method to imaged media to predict the relative permeability curves of Estaillades limestone based on X-ray microtomography images with identified solid, microporous and pore spaces.
Quantifying Evaporation and Evaluating Runoff Estimation Methods in a Permeable Pavement System
The U.S. Environmental Protection Agency constructed a 0.4-ha parking lot in Edison, New Jersey, that incorporated permeable pavement in the parking lanes which were designed to receive run-on from the impervious hot-mix asphalt driving lanes. Twelve lined permeable pavement sec...
Quantifying Evaporation and Evaluating Runoff Estimation Methods in a Permeable Pavement System
The U.S. Environmental Protection Agency constructed a 0.4-ha parking lot in Edison, New Jersey, that incorporated permeable pavement in the parking lanes which were designed to receive run-on from the impervious hot-mix asphalt driving lanes. Twelve lined permeable pavement sec...
Daish, C; Blanchard, R; Gulati, K; Losic, D; Findlay, D; Harvie, D J E; Pivonka, P
2017-06-01
In this paper, a comprehensive framework is proposed to estimate the anisotropic permeability matrix in trabecular bone specimens based on micro-computed tomography (microCT) imaging combined with pore-scale fluid dynamics simulations. Two essential steps in the proposed methodology are the selection of (i) a representative volume element (RVE) for calculation of trabecular bone permeability and (ii) a converged mesh for accurate calculation of pore fluid flow properties. Accurate estimates of trabecular bone porosities are obtained using a microCT image resolution of approximately 10 μm. We show that a trabecular bone RVE in the order of 2 × 2 × 2 mm(3) is most suitable. Mesh convergence studies show that accurate fluid flow properties are obtained for a mesh size above 125,000 elements. Volume averaging of the pore-scale fluid flow properties allows calculation of the apparent permeability matrix of trabecular bone specimens. For the four specimens chosen, our numerical results show that the so obtained permeability coefficients are in excellent agreement with previously reported experimental data for both human and bovine trabecular bone samples. We also identified that bone samples taken from long bones generally exhibit a larger permeability in the longitudinal direction. The fact that all coefficients of the permeability matrix were different from zero indicates that bone samples are generally not harvested in the principal flow directions. The full permeability matrix was diagonalized by calculating the eigenvalues, while the eigenvectors showed how strongly the bone sample's orientations deviated from the principal flow directions. Porosity values of the four bone specimens range from 0.83 to 0.86, with a low standard deviation of ± 0.016, principal permeability values range from 0.22 to 1.45 ⋅ 10( -8) m(2), with a high standard deviation of ± 0.33. Also, the anisotropic ratio ranged from 0.27 to 0.83, with high standard deviation. These
Schlueter, E.M.; Cook, N.G.W. |; Witherspoon, P.A.; Myer, L.R.
1994-04-01
Experiments to study relative permeabilities of a partially saturated rock have been carried out in Berea sandstone using fluids that can be solidified in place. The effective permeability of the spaces not occupied by the wetting fluid (paraffin wax) or the nonwetting fluid (Wood`s metal), have been measured at various saturations after solidifying each of the phases. The tests were conducted on Berea sandstone samples that had an absolute permeability of about 600 md. The shape of the laboratory-derived relative permeability vs. saturation curves measured with the other phase solidified conforms well with typical curves obtained using conventional experimental methods. The corresponding wetting and nonwetting fluid distributions at different saturations are presented and analyzed in light of the role of the pore structure in the invasion process, and their impact on relative permeability and capillary pressure. Irreducible wetting and nonwetting phase fluid distributions are studied. The effect of clay minerals on permeability is also assessed.
Naderkhani, Elenaz; Isaksson, Johan; Ryzhakov, Alexey; Flaten, Gøril Eide
2014-06-01
Permeability is a crucial property of orally administered drugs. Therefore, in drug discovery, it is important to employ methods suitable for rapidly and reliably screening the permeability of large numbers of new drug candidates. The phospholipid vesicle-based permeation assay (PVPA), a model consisting of a tight layer of liposomes immobilized on a filter, offers potential advantages unmet by other methods and has been successfully used in permeability testing of novel active substances as well as formulations. In this study, the PVPA was developed into a more robust, biomimetic model by employing a lipid composition matching that of the intestinal permeation barrier and performing the experiments at the more biologically relevant pH 6.2. As expected, positively charged basic compounds demonstrated increased permeability through the negatively charged biomimetic barriers, and the degree of correct classification according to in vivo absorption was comparable between the original PVPA and the biomimetic PVPA. The biomimetic PVPA further proved to be tremendously more robust toward the presence of tensides compared with the original PVPA; this is a promising finding that renders the biomimetic PVPA an enhanced ability to estimate the permeability of poorly soluble compounds. Hence, the PVPA model developed in this study has evolved an important step forward.
NASA Astrophysics Data System (ADS)
Lamorski, Krzysztof; Sławiński, Cezary; Barna, Gyöngyi
2014-05-01
There are some important macroscopic properties of the soil porous media such as: saturated permeability and water retention characteristics. These soil characteristics are very important as they determine soil transport processes and are commonly used as a parameters of general models of soil transport processes used extensively for scientific developments and engineering practise. These characteristics are usually measured or estimated using some statistical or phenomenological modelling, i.e. pedotransfer functions. On the physical basis, saturated soil permeability arises from physical transport processes occurring at the pore level. Current progress in modelling techniques, computational methods and X-ray micro-tomographic technology gives opportunity to use direct methods of physical modelling for pore level transport processes. Physically valid description of transport processes at micro-scale based on Navier-Stokes type modelling approach gives chance to recover macroscopic porous medium characteristics from micro-flow modelling. Water microflow transport processes occurring at the pore level are dependent on the microstructure of porous body and interactions between the fluid and the medium. In case of soils, i.e. the medium there exist relatively big pores in which water can move easily but also finer pores are present in which water transport processes are dominated by strong interactions between the medium and the fluid - full physical description of these phenomena is a challenge. Ten samples of different soils were scanned using X-ray computational microtomograph. The diameter of samples was 5 mm. The voxel resolution of CT scan was 2.5 µm. Resulting 3D soil samples images were used for reconstruction of the pore space for further modelling. 3D image threshholding was made to determine the soil grain surface. This surface was triangulated and used for computational mesh construction for the pore space. Numerical modelling of water flow through the
Estimation of the differential stress from the stress rotation angle in low permeable rock
NASA Astrophysics Data System (ADS)
Ziegler, Moritz O.; Heidbach, Oliver; Zang, Arno; Martínez-Garzón, Patricia; Bohnhoff, Marco
2017-07-01
Rotations of the principal stress axes are observed as a result of fluid injection into reservoirs. We use a generic, fully coupled 3-D thermo-hydro-mechanical model to investigate systematically the dependence of this stress rotation on different reservoir properties and injection scenarios. We find that permeability, injection rate, and initial differential stress are the key factors, while other reservoir properties only play a negligible role. In particular, we find that thermal effects do not significantly contribute to stress rotations. For reservoir types with usual differential stress and reservoir treatment the occurrence of significant stress rotations is limited to reservoirs with a permeability of less than approximately 10-12 m2. Higher permeability effectively prevents stress rotations to occur. Thus, according to these general findings, the observed principal stress axes rotation can be used as a proxy of the initial differential stress provided that rock permeability and fluid injection rate are known a priori.
Keating, J; Bjarnason, I; Somasundaram, S; Macpherson, A; Francis, N; Price, A B; Sharpstone, D; Smithson, J; Menzies, I S; Gazzard, B G
1995-01-01
Intestinal function is poorly defined in patients with HIV infection. Absorptive capacity and intestinal permeability were assessed using 3-O-methyl-D-glucose, D-xylose, L-rhamnose, and lactulose in 88 HIV infected patients and the findings were correlated with the degree of immunosuppression (CD4 counts), diarrhoea, wasting, intestinal pathogen status, and histomorphometric analysis of jejunal biopsy samples. Malabsorption of 3-O-methyl-D-glucose and D-xylose was prevalent in all groups of patients with AIDS but not in asymptomatic, well patients with HIV. Malabsorption correlated significantly (r = 0.34-0.56, p < 0.005) with the degree of immune suppression and with body mass index. Increased intestinal permeability was found in all subgroups of patients. The changes in absorption-permeability were of comparable severity to those found in patients with untreated coeliac disease. Jejunal histology, however, showed only mild changes in the villus height/crypt depth ratio as compared with subtotal villus atrophy in coeliac disease. Malabsorption and increased intestinal permeability are common in AIDS patients. Malabsorption, which has nutritional implications, relates more to immune suppression than jejunal morphological changes. PMID:8549936
NASA Astrophysics Data System (ADS)
Lipsey, Lindsay; van Wees, Jan-Diederik; Pluymaekers, Maarten; Cloetingh, Sierd
2015-04-01
Thermal anomalies in deep sedimentary settings are largely controlled by fluid circulation within permeable zones. Convection is of particular interest in geothermal exploration, as it creates areas with anomalously high temperatures at shallow depths. Recent work on the temperature distribution in the Dutch subsurface revealed a thermal anomaly at the Luttelgeest-01 (LTG-01) at 4-5 km depth, which could be explained by thermal convection. Temperature measurements show a shift to higher temperatures at depths greater than 4000 m, corresponding the Dinantian carbonates. In order for convective heat transport to explain the anomaly, there must also be sufficient permeability. Rayleigh number calculations show that convection may be possible within the Dinantian carbonate layer, depending on its thickness, permeability and geothermal gradient. For example, an average permeability of 60 mD permits convection in a 600 m aquifer, given a geothermal gradient of 31°C/km. If the permeability is reduced to 20 mD, convection can only occur where the thickness of the aquifer is greater than 900 m. Interestingly, numerical simulations were able to come within 5-10 mD of the theoretical minimum permeability values calculated for each scenario. 3D numerical simulations provide insight on possible flow and thermal structures within the fractured carbonate interval, as well as illustrate the role of permeability on the timing of convection onset, convection cell structure development and the resulting temperature patterns. The development and number of convection cells is very much a time dependent process. Many cells may develop in the beginning of simulations, but they seem to gradually converge until steady state is reached. The shape of convective upwellings varies from roughly circular or hexagonal to more elongated upwellings and downwellings. Furthermore, the geometric aspects of the carbonate platform itself likely control the shape and location of upwellings, as well as
Levine, Jonathan S; Goldberg, David S; Lackner, Klaus S; Matter, Juerg M; Supp, Michael G; Ramakrishnan, T S
2014-01-01
To mitigate anthropogenically induced climate change and ocean acidification, net carbon dioxide emissions to the atmosphere must be reduced. One proposed option is underground CO2 disposal. Large-scale injection of CO2 into the Earth's crust requires an understanding of the multiphase flow properties of high-pressure CO2 displacing brine. We present laboratory-scale core flooding experiments designed to measure CO2 endpoint relative permeability for CO2 displacing brine at in situ pressures, salinities, and temperatures. Endpoint drainage CO2 relative permeabilities for liquid and supercritical CO2 were found to be clustered around 0.4 for both the synthetic and natural media studied. These values indicate that relative to CO2, water may not be strongly wetting the solid surface. Based on these results, CO2 injectivity will be reduced and pressure-limited reservoirs will have reduced disposal capacity, though area-limited reservoirs may have increased capacity. Future reservoir-scale modeling efforts should incorporate sensitivity to relative permeability. Assuming applicability of the experimental results to other lithologies and that the majority of reservoirs are pressure limited, geologic carbon sequestration would require approximately twice the number of wells for the same injectivity.
NASA Astrophysics Data System (ADS)
Daigle, H.; Rice, M. A.
2015-12-01
Relative permeabilities to water and gas are important parameters for accurate modeling of the formation of methane hydrate deposits and production of methane from hydrate reservoirs. Experimental measurements of gas and water permeability in the presence of hydrate are difficult to obtain. The few datasets that do exist suggest that relative permeability obeys a power law relationship with water or gas saturation with exponents ranging from around 2 to greater than 10. Critical path analysis and percolation theory provide a framework for interpreting the saturation-dependence of relative permeability based on percolation thresholds and the breadth of pore size distributions, which may be determined easily from 3-D images or gas adsorption-desorption hysteresis. We show that the exponent of the permeability-saturation relationship for relative permeability to water is related to the breadth of the pore size distribution, with broader pore size distributions corresponding to larger exponents. Relative permeability to water in well-sorted sediments with narrow pore size distributions, such as Berea sandstone or Toyoura sand, follows percolation scaling with an exponent of 2. On the other hand, pore-size distributions determined from argon adsorption measurements we performed on clays from the Nankai Trough suggest that relative permeability to water in fine-grained intervals may be characterized by exponents as large as 10 as determined from critical path analysis. We also show that relative permeability to the gas phase follows percolation scaling with a quadratic dependence on gas saturation, but the threshold gas saturation for percolation changes with hydrate saturation, which is an important consideration in systems in which both hydrate and gas are present, such as during production from a hydrate reservoir. Our work shows how measurements of pore size distributions from 3-D imaging or gas adsorption may be used to determine relative permeabilities.
Christiansen, R.L.; Kalbus, J.S.; Howarth, S.M.
1997-05-01
This report documents, demonstrates, evaluates, and provides theoretical justification for methods used to convert experimental data into relative permeability relationships. The report facilities accurate determination of relative permeabilities of anhydride rock samples from the Salado Formation at the Waste Isolation Pilot Plant (WIPP). Relative permeability characteristic curves are necessary for WIPP Performance Assessment (PA) predictions of the potential for flow of waste-generated gas from the repository and brine flow into repository. This report follows Christiansen and Howarth (1995), a comprehensive literature review of methods for measuring relative permeability. It focuses on unsteady-state experiments and describes five methods for obtaining relative permeability relationships from unsteady-state experiments. Unsteady-state experimental methods were recommended for relative permeability measurements of low-permeability anhydrite rock samples form the Salado Formation because these tests produce accurate relative permeability information and take significantly less time to complete than steady-state tests. Five methods for obtaining relative permeability relationships from unsteady-state experiments are described: the Welge method, the Johnson-Bossler-Naumann method, the Jones-Roszelle method, the Ramakrishnan-Cappiello method, and the Hagoort method. A summary, an example of the calculations, and a theoretical justification are provided for each of the five methods. Displacements in porous media are numerically simulated for the calculation examples. The simulated product data were processed using the methods, and the relative permeabilities obtained were compared with those input to the numerical model. A variety of operating conditions were simulated to show sensitivity of production behavior to rock-fluid properties.
Daigle, Hugh; Rice, Mary Anna; Daigle, Hugh
2015-12-14
Relative permeabilities to water and gas are important parameters for accurate modeling of the formation of methane hydrate deposits and production of methane from hydrate reservoirs. Experimental measurements of gas and water permeability in the presence of hydrate are difficult to obtain. The few datasets that do exist suggest that relative permeability obeys a power law relationship with water or gas saturation with exponents ranging from around 2 to greater than 10. Critical path analysis and percolation theory provide a framework for interpreting the saturation-dependence of relative permeability based on percolation thresholds and the breadth of pore size distributions, which may be determined easily from 3-D images or gas adsorption-desorption hysteresis. We show that the exponent of the permeability-saturation relationship for relative permeability to water is related to the breadth of the pore size distribution, with broader pore size distributions corresponding to larger exponents. Relative permeability to water in well-sorted sediments with narrow pore size distributions, such as Berea sandstone or Toyoura sand, follows percolation scaling with an exponent of 2. On the other hand, pore-size distributions determined from argon adsorption measurements we performed on clays from the Nankai Trough suggest that relative permeability to water in fine-grained intervals may be characterized by exponents as large as 10 as determined from critical path analysis. We also show that relative permeability to the gas phase follows percolation scaling with a quadratic dependence on gas saturation, but the threshold gas saturation for percolation changes with hydrate saturation, which is an important consideration in systems in which both hydrate and gas are present, such as during production from a hydrate reservoir. Our work shows how measurements of pore size distributions from 3-D imaging or gas adsorption may be used to determine relative permeabilities.
NASA Astrophysics Data System (ADS)
Wang, Hao; Li, Chang-sheng; Zhu, Tao
2014-11-01
The magnetic properties of highly grain-oriented electrical steel vary along different directions. In order to investigate these properties, standard Epstein samples were cut at different angles to the rolling direction. The hard magnetization direction was found at an angle of 60° to the rolling direction. To compare the measured and fitting curves, when the magnetic field intensity is higher than 7000 A/m, it is appropriate to simulate the relation of magnetic permeability and magnetization angle using the conventional elliptical model. When the magnetic field intensity is less than 3000 A/m, parabolic fitting models should be used; but when the magnetic field intensity is between 3000 and 7000 A/m, hybrid models with high accuracy, as proposed in this paper, should be applied. Piecewise relation models of magnetic permeability and magnetization angle are significant for improving the accuracy of electromagnetic engineering calculations of electrical steel, and these new models could be applied in further industrial applications.
NASA Astrophysics Data System (ADS)
Tarrahi, Mohammadali; Jafarpour, Behnam
2012-10-01
Hydraulic stimulation of subsurface rocks is performed in developing geothermal and hydrocarbon reservoirs to create permeable zones and enhance flow and transport in low-permeability formations. Borehole fluid injection often induces measurable microearthquakes (MEQs). While the nature and source of the processes that lead to triggering of these events is yet to be fully understood, a major hypothesis has linked these events to an increase in pore pressure that decreases the effective compressional stress and causes sliding along preexisting cracks. Based on this hypothesis, the distribution of the resulting microseismicity clouds can be viewed as monitoring data that carry important information about the spatial distribution of hydraulic rock properties. However, integration of fluid-induced microseismicity events into prior rock permeability distributions is complicated by the discrete nature of the MEQ events, which is not amenable to well-established inversion methods. We use kernel density estimation to first interpret the MEQ data events as continuous seismicity density measurements and, subsequently, assimilate them to estimate rock permeability distribution. We apply the ensemble Kalman filter (EnKF) for microseimic data integration where we update a prior ensemble of permeability distributions to obtain a new set of calibrated models for prediction. The EnKF offers several advantages for this application, including the ensemble formulation for uncertainty assessment, convenient gradient-free implementation, and the flexibility to incorporate various failure mechanisms and additional data types. Using several numerical experiments, we illustrate the suitability of the proposed approach for characterization of reservoir hydraulic properties from discrete MEQ monitoring measurements.
Three-phase flow in porous media: A review of experimental studies on relative permeability
NASA Astrophysics Data System (ADS)
Alizadeh, A. H.; Piri, M.
2014-09-01
We present a detailed, synthesized review of experimental studies on three-phase relative permeability published since 1980. We provide comprehensive, yet highly focused, analysis of critical aspects of the field and their evolution over the last three decades. In particular, we review the effects of saturation history, wettability, spreading, and layer drainage on the measured flow properties. We also list all the processes, rock types, fluid systems, and measurement techniques in order to provide a clear map for future studies. Behavior of the measured three-phase relative permeabilities with respect to fluid saturations, saturation histories, wettability of rock samples, spreading characteristics, interfacial tensions, and other pertinent properties are carefully discussed. Studies that use a diverse set of experimental techniques and data analysis to deduce relative permeability are included. The experimental techniques that should be utilized to reduce uncertainty are also explored. We interpret the measured properties and outcomes of different studies and compare them to substantiate distinct trends at various saturation ranges and provide ideas for new studies. This is intended to distill a clear image of where the field stands and to allow composition of possible paths for future investigations. The areas of critical relevance that have not been investigated or require further studies are highlighted.
NASA Astrophysics Data System (ADS)
Jiang, Lanlan; Liu, Yu; Teng, Ying; Zhao, Jiafei; Zhang, Yi; Yang, Mingjun; Song, Yongchen
2017-01-01
The purpose of this work is to develop a permeability estimation method for porous media. This method is based on an improved capillary bundle model by introducing some pore geometries. We firstly carried out micro-CT scans to extract the 3D digital model of porous media. Then we applied a maximum ball extraction method to the digital model to obtain the topological and geometrical pore parameters such as the pore radius, the throat radius and length and the average coordination number. We also applied a random walker method to calculate the tortuosity factors of porous media. We improved the capillary bundle model by introducing the pore geometries and tortuosity factors. Finally, we calculated the absolute permeabilities of four kinds of porous media formed of glass beads and compared the results with experiments and several other models to verify the improved model. We found that the calculated permeabilities using this improved capillary bundle model show better agreement with the measured permeabilities than the other methods.
Estimation of Michaelis-Menten constant of efflux transporter considering asymmetric permeability.
Sugano, Kiyohiko; Shirasaka, Yoshiyuki; Yamashita, Shinji
2011-10-14
It was previously reported that the apparent K(m) values of P-gp in apical to basal (A to B) and basal to apical (B to A) directions were different. The purpose of the present study was to derive a theoretical framework by which this asymmetric concentration-permeability profile can be explained using a single intrinsic K(m) value. A three compartment model was used to represent the apical, cytosol and basal compartments. The difference of passive permeability and the surface areas between the apical and basolateral membrane were explicitly taken into account. Applying the steady state approximation and considering the mass balance in the cytosol compartment, an open analytical solution was obtained. By using this equation, the asymmetric concentration-permeability profile was appropriately reproduced. In addition, the expression level dependency of apparent K(m) was also reproduced. Copyright © 2011 Elsevier B.V. All rights reserved.
NASA Astrophysics Data System (ADS)
Lee, S. H.; Efendiev, Y.
2016-10-01
Three-phase flow in a reservoir model has been a major challenge in simulation studies due to slowly convergent iterations in Newton solution of nonlinear transport equations. In this paper, we examine the numerical characteristics of three-phase flow and propose a consistent, "C1-continuous discretization" (to be clarified later) of transport equations that ensures a convergent solution in finite difference approximation. First, we examine three-phase relative permeabilities that are critical in solving nonlinear transport equations. Three-phase relative permeabilities are difficult to measure in the laboratory, and they are often correlated with two-phase relative permeabilities (e.g., oil-gas and water-oil systems). Numerical convergence of non-linear transport equations entails that three-phase relative permeability correlations are a monotonically increasing function of the phase saturation and the consistency conditions of phase transitions are satisfied. The Modified Stone's Method II and the Linear Interpolation Method for three-phase relative permeability are closely examined for their mathematical properties. We show that the Linear Interpolation Method yields C1-continuous three-phase relative permeabilities for smooth solutions if the two phase relative permeabilities are monotonic and continuously differentiable. In the second part of the paper, we extend a Hybrid-Upwinding (HU) method of two-phase flow (Lee, Efendiev and Tchelepi, ADWR 82 (2015) 27-38) to three phase flow. In the HU method, the phase flux is divided into two parts based on the driving forces (in general, it can be divided into several parts): viscous and buoyancy. The viscous-driven and buoyancy-driven fluxes are upwinded differently. Specifically, the viscous flux, which is always co-current, is upwinded based on the direction of the total velocity. The pure buoyancy-induced flux is shown to be only dependent on saturation distributions and counter-current. In three-phase flow, the
Studies on quantifying evaporation in permeable pavement systems are limited to few laboratory studies that used a scale to weigh evaporative losses and a field application with a tunnel-evaporation gauge. A primary objective of this research was to quantify evaporation for a la...
Studies on quantifying evaporation in permeable pavement systems are limited to few laboratory studies that used a scale to weigh evaporative losses and a field application with a tunnel-evaporation gauge. A primary objective of this research was to quantify evaporation for a la...
NASA Astrophysics Data System (ADS)
Hosa, Aleksandra; Curtis, Andrew; Wood, Rachel
2016-08-01
A common way to simulate fluid flow in porous media is to use Lattice Boltzmann (LB) methods. Permeability predictions from such flow simulations are controlled by parameters whose settings must be calibrated in order to produce realistic modelling results. Herein we focus on the simplest and most commonly used implementation of the LB method: the single-relaxation-time BGK model. A key parameter in the BGK model is the relaxation time τ which controls flow velocity and has a substantial influence on the permeability calculation. Currently there is no rigorous scheme to calibrate its value for models of real media. We show that the standard method of calibration, by matching the flow profile of the analytic Hagen-Poiseuille pipe-flow model, results in a BGK-LB model that is unable to accurately predict permeability even in simple realistic porous media (herein, Fontainebleau sandstone). In order to reconcile the differences between predicted permeability and experimental data, we propose a method to calibrate τ using an enhanced Transitional Markov Chain Monte Carlo method, which is suitable for parallel computer architectures. We also propose a porosity-dependent τ calibration that provides an excellent fit to experimental data and which creates an empirical model that can be used to choose τ for new samples of known porosity. Our Bayesian framework thus provides robust predictions of permeability of realistic porous media, herein demonstrated on the BGK-LB model, and should therefore replace the standard pipe-flow based methods of calibration for more complex media. The calibration methodology can also be extended to more advanced LB methods.
Katneni, Kasiram; Charman, Susan A; Porter, Christopher J H
2007-02-01
The effect of Cremophor-EL (Cr-EL) and polysorbate-80 (PS-80) on the transepithelial permeability of digoxin (DIG) has been evaluated using the reciprocal permeability approach to delineate thermodynamic and transporter related events. Permeability data were corrected for solubilization using the micellar association constant (Ka) obtained from Papp data generated in the presence of the nonspecific ATPase inhibitor sodium orthovanadate. In the presence of mucosal Cr-EL, a concentration dependent decrease in serosal-mucosal (S-M) and increase in M-S transport was observed. Whilst serosal Cr-EL resulted in a reduction in S-M DIG transport, no impact on M-S transport was apparent. For PS-80, the presence of either serosal or mucosal surfactant led to a decrease in secretory (S-M) DIG transport, however no effect on absorptive transport was evident. The data confirm the potential P-gp inhibitory effects of Cr-EL, but suggest that in contrast to Cr-EL, PS-80 is not a potent inhibitor of P-gp and is incapable of increasing absorptive drug transport, at least in excised rat intestinal tissue and at the concentrations tested. The data are also consistent with the involvement of additional transporters (both apical and basolateral) in the intestinal permeability of DIG, although more definitive data is required to confirm this possibility.
Larson, Judd; Kumar, Sendhil; Gale, S Adrian; Jain, Pradeep; Townsend, Timothy
2012-03-01
The measurement of vertical gas diffusivity and permeability of compacted municipal solid waste (MSW) using an analytical gas flow and transport model was evaluated. A series of pressure transducers were buried in a MSW landfill and in situ pressures were modelled using an algorithm that predicts soil-gas pressures based on field-measured barometric pressure data and vertical diffusivity. The vertical gas diffusivity that represented the best-fit of the measured pressures was estimated at 20 locations and ranged from 0.002 to 0.052 m2 s(-1). The vertical gas permeability ranged from 3.3 × 10(-14) to 4.5 × 10(-12) m2 for the upper-most 3 to 6 m of compacted MSW. The shortfalls of applying this method to landfill conditions are also discussed.
Air permeability of compost as related to bulk density and volumetric air content.
Poulsen, Tjalfe G; Moldrup, Per
2007-08-01
Compost air permeability controls air flow through compost during composting or when using compost as biofilter material. Air permeability is therefore an important characteristic of compost. The relationships between air permeability (k(a)) in compost and compost dry bulk density (rho b), gravimetric water content (omega), and volumetric air content (epsilon) was investigated for two types of composts. The composts used were produced from a digested sewage sludge-straw mixture and from garden waste and measurements were conducted on sieved and repacked 100 cm3 compost samples. Results showed a linear relation between log(k(a)) and rho b at constant values of omega for both composts, indicating an exponential relationship between k(a) and rho b. The slopes of these relationships generally became more negative with increasing rho b. The results further showed a linear relationship between log(k(a)) and log(epsilon) for both composts as also often observed for soils. It was observed that the log(k(a)) and log(epsilon) relationships for the garden waste compost all intercepted at the same location despite having very different slopes. This means that it is possible to predict the entire k(a)-epsilon relationship using only one measurement of corresponding (k(a), epsilon) for garden waste. It was not possible to determine whether this was also the case for the sewage sludge compost due to difficulties in sample preparation at low and high water content.
[Estimation of the Index Value of Dielectric Permeability inside the Membranes of Purple Bacteria].
Borisov, A Y; Kozlovsky, V S
2015-01-01
The joint application of the precise X-ray data for isolated bacteriochlorophyll complexes of reaction centers and the fundamental formulae for the energy of interaction between two equal dipoles enabled us to suggest a new methodical approach for determination of the values of the index of dielectric permeability in the micro volume enclosing special pairs in Rhodobacter sphaeroides reaction centers. The most probable value for this parameter was thus determined within 1.66-1.76. This approach was generalized for the inner layer of the membranes of purple bacteria and yielded the index value about 1.70-1.85. It is argued that this range of dielectric permeability is adequate for bacterial and plant membranes as well. Low magnitude of this parameter contributes to higher efficiency of energy migration from vast light-harvesting chlorophyll "antenna" to the energy converting reaction centers and hence to higher efficiency of the whole photosynthesis.
Diniz, Andréa; Escuder-Gilabert, Laura; Lopes, Norberto P; Gobbo-Neto, Leonardo; Villanueva-Camañas, Rosa María; Sagrado, Salvador; Medina-Hernández, María José
2007-10-17
This paper points out the usefulness of biopartitioning micellar chromatography (BMC) using capillary columns as a high-throughput primary screening tool providing key information about the oral absorption, skin permeability, and brain-blood distribution coefficients of 15 polyphenols (6 flavones, 2 flavonols, a flavanone, 2 flavan-3-ols, 3 phenolic acids, and a phloroglucinol) in a simple and economical way. For the compounds studied, except vicenin-2, rutin, chlorogenic acid, p-hydroxycinnamic acid, and 4-hydroxybenzoic acid, maximal oral absorption (>90%) can be expected, if there are not solubility problems or metabolic processes. On the other hand, the most retained compounds in BMC, that is, 5-hydroxyflavone, flavone, and flavanone, show the highest brain-blood distribution coefficients and skin permeability coefficients.
NASA Astrophysics Data System (ADS)
Zarivnyy, Ostap
CO2 flooding has gained increased interest in regard to both light and heavy oil reservoirs, as a means of combining improved oil recovery and geological storage of CO2 in partially depleted oil reservoirs. Distribution and movement of CO2 in oil reservoirs is a function of the relative permeability of three phases of water, oil, and CO2 in oil reservoirs. In general, three-phase relative permeability relations are required with respect to the design of CO2 field projects for accurate predictions via numerical reservoir simulation of CO 2 flood performance and to model production and injection problems. However, a two-phase relative permeability relation is used to generate the three-phase relative permeability relation for use in reservoir simulations. An overview of the available literature indicates few attempts have been made to experimentally determine the three-phase relative permeability relation for CO2-oil-water systems under practical reservoir conditions. This research attempts to investigate the two- and three-phase relative permeability relation of CO2-oil-water systems through a series of carefully designed laboratory experiments. Fourteen experiments in two-phase systems, and four experiments in three-phase systems with heavy and light oils, were conducted in order to study the effect of pressure, temperature, viscosity, and flow rate on the relative permeability relation. It was shown that relative permeability is temperature dependent and increases with an increase in temperature. Pressure and oil viscosity had similar effects, although higher pressure caused a decrease in relative permeability to water in water-oil and water-oil-gas systems. Investigating the effect of flow rate it was found that higher injection flow rate caused increase in relative permeability values. The effect of the injection flow rate on relative permeability behaviour can be explained by the formation of emulsion during the displacement process. A set of new correlations
Hyun Jo, Dong; Lee, Rimi; Hyoung Kim, Jin; Oh Jun, Hyoung; Geol Lee, Tae; Hun Kim, Jeong
2015-01-01
Vascular integrity is important in maintaining homeostasis of brain microenvironments. In various brain diseases including Alzheimer’s disease, stroke, and multiple sclerosis, increased paracellular permeability due to breakdown of blood-brain barrier is linked with initiation and progression of pathological conditions. We developed a capacitance sensor array to monitor dielectric responses of cerebral endothelial cell monolayer, which could be utilized to evaluate the integrity of brain microvasculature. Our system measured real-time capacitance values which demonstrated frequency- and time-dependent variations. With the measurement of capacitance at the frequency of 100 Hz, we could differentiate the effects of vascular endothelial growth factor (VEGF), a representative permeability-inducing factor, on endothelial cells and quantitatively analyse the normalized values. Interestingly, we showed differential capacitance values according to the status of endothelial cell monolayer, confluent or sparse, evidencing that the integrity of monolayer was associated with capacitance values. Another notable feature was that we could evaluate the expression of molecules in samples in our system with the reference of real-time capacitance values. We suggest that this dielectric spectroscopy system could be successfully implanted as a novel in vitro assay in the investigation of the roles of paracellular permeability in various brain diseases. PMID:26047027
NASA Astrophysics Data System (ADS)
Hyun Jo, Dong; Lee, Rimi; Hyoung Kim, Jin; Oh Jun, Hyoung; Geol Lee, Tae; Hun Kim, Jeong
2015-06-01
Vascular integrity is important in maintaining homeostasis of brain microenvironments. In various brain diseases including Alzheimer’s disease, stroke, and multiple sclerosis, increased paracellular permeability due to breakdown of blood-brain barrier is linked with initiation and progression of pathological conditions. We developed a capacitance sensor array to monitor dielectric responses of cerebral endothelial cell monolayer, which could be utilized to evaluate the integrity of brain microvasculature. Our system measured real-time capacitance values which demonstrated frequency- and time-dependent variations. With the measurement of capacitance at the frequency of 100 Hz, we could differentiate the effects of vascular endothelial growth factor (VEGF), a representative permeability-inducing factor, on endothelial cells and quantitatively analyse the normalized values. Interestingly, we showed differential capacitance values according to the status of endothelial cell monolayer, confluent or sparse, evidencing that the integrity of monolayer was associated with capacitance values. Another notable feature was that we could evaluate the expression of molecules in samples in our system with the reference of real-time capacitance values. We suggest that this dielectric spectroscopy system could be successfully implanted as a novel in vitro assay in the investigation of the roles of paracellular permeability in various brain diseases.
Verification of capillary pressure functions and relative permeability equations for gas production
Jang, Jaewon
2016-10-25
The understanding of multiphase fluid flow in porous media is of great importance in many fields such as enhanced oil recovery, hydrology, CO_{2} sequestration, contaminants cleanup and natural gas production from hydrate bearing sediments. However, there are many unanswered questions about the key parameters that characterize gas and water flows in porous media. The characteristics of multiphase fluid flow in porous media such as water retention curve, relative permeability, preferential fluid flow patterns and fluid-particle interaction should be taken into consideration for a fundamental understanding of the behavior of pore scale systems.
NASA Astrophysics Data System (ADS)
Peters, C. A.; Crandell, L. E.; Um, W.; Jones, K. W.; Lindquist, W. B.
2011-12-01
Geochemical reactions in the subsurface can alter the porosity and permeability of a porous medium through mineral precipitation and dissolution. While effects on porosity are relatively well understood, changes in permeability are more difficult to estimate. In this work, pore-network modeling is used to estimate the permeability of a porous medium using pore and throat size distributions. These distributions can be determined from 2D Scanning Electron Microscopy (SEM) images of thin sections or from 3D X-ray Computed Tomography (CT) images of small cores. Each method has unique advantages as well as unique sources of error. 3D CT imaging has the advantage of reconstructing a 3D pore network without the inherent geometry-based biases of 2D images but is limited by resolutions around 1 μm. 2D SEM imaging has the advantage of higher resolution, and the ability to examine sub-grain scale variations in porosity and mineralogy, but is limited by the small size of the sample of pores that are quantified. A pore network model was created to estimate flow permeability in a sand-packed experimental column investigating reaction of sediments with caustic radioactive tank wastes in the context of the Hanford, WA site. Before, periodically during, and after reaction, 3D images of the porous medium in the column were produced using the X2B beam line facility at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab. These images were interpreted using 3DMA-Rock to characterize the pore and throat size distributions. After completion of the experiment, the column was sectioned and imaged using 2D SEM in backscattered electron mode. The 2D images were interpreted using erosion-dilation to estimate the pore and throat size distributions. A bias correction was determined by comparison with the 3D image data. A special image processing method was developed to infer the pore space before reaction by digitally removing the precipitate. The different sets of pore
NASA Astrophysics Data System (ADS)
Hewett, Thomas A.; Yamada, Tomomi
A semi-analytical method has been developed for calculating oil recovery in two and three dimensions, and for calculating effective relative permeabilities for coarse grids. The calculations are based on the assumption that the effects of a changing mobility field can be accounted for by using fixed streamtube geometries with flowrates updated to account for the changing mobility distribution. The single-phase pressure distribution from a numerical solution of Laplace's equation is used to calculate the pressure distribution for a two-phase flow based on a mapping of the solution of the Buckley-Leverett equation onto the streamtubes derived from the single-phase solution. The displacement calculations for oil recovery are based on theory previously developed by Dykstra and Parsons, extended to include the effects of spatially varying permeability and continuously changing mobilities, as occurs in solutions of the Buckley-Leverett equation for typical values of the mobility ratio. This idea has also been extended to the calculation of effective relative permeabilities for coarse-grid simulation and finally establishes the proper rules for averaging the results of fine-grid numerical simulations of two-phase flow for the definition of effective two-phase flow properties on coarse grids. These calculations have been generalized to three-dimensional flows by the simple device of conceptually inserting a gridded plane across the flow and defining each streamtube at that location as those streamlines which pass through any one of the grid cells. When combined with time-of-flight calculations from the gridded plane to both the producer and injector, the distribution of pore volume along each streamtube can be calculated. This information, combined with a tabulation of the single-phase, steady-state pressure distribution along each streamtube, provides all of the information needed for the semi-analytical calculation of oil recovery and effective flow properties in three
NASA Astrophysics Data System (ADS)
Cherubini, Aurélien; Cerepi, Adrian; Garcia, Bruno; Deschamps, Hervé; Revil, André
2017-04-01
The seismoelectric method is showing promises to characterize both the vadose zone of the Earth and hydrocarbon reservoirs. That said, the dependence of a key parameter, the streaming coupling coefficient with the saturation remains highly debated. We explore here the relationship between the streaming potential coupling coefficient, resistivity, and permeability in saturated and unsaturated carbonate rocks together with the capillary pressure curves. Two rock samples, a limestone from the Paris basin (the Brauvilliers limestone) and a dolostone from the Aquitain basin (Sample labeled LS2), are characterized in terms of their porosity, specific surface area, and intrinsic formation factor. A new core flooding system is used to measure simultaneously and for the first time both the relative permeability, the resistivity, and the streaming potential coupling coefficient in steady-state two phase flow conditions as a function of the saturation. The results are compared with theoretical models predicting the relationship between the streaming potential coupling coefficient, the relative permeability, and the second Archie's exponent. A good agreement is found between the model based on the van Genuchten approach and experimental data but still we could not fit all the curves with the same van Genuchten exponent. Moreover, measurements of the streaming potential coupling coefficient in intact limestones samples saturated with NaCl brines at concentrations up to 100 g/L were realised. As brine salinity increases, the coupling coefficient decreases in magnitude, but is still measureable up to the saturated concentration limit. Our results suggest that streaming potential measurements may be used to monitor flow in saline subsurface environments such as deep saline aquifers and hydrocarbon reservoirs.
NASA Astrophysics Data System (ADS)
Gomila, Rodrigo; Arancibia, Gloria; Nehler, Mathias; Bracke, Rolf; Stöckhert, Ferdinand
2016-04-01
Fault zones and their related structural permeability play a leading role in the migration of fluids through the continental crust. A first approximation to understanding the structural permeability conditions, and the estimation of its hydraulic properties (i.e. palaeopermeability and fracture porosity conditions) of the fault-related fracture mesh is the 2D analysis of its veinlets, usually made in thin-section. Those estimations are based in the geometrical parameters of the veinlets, such as average fracture density, length and aperture, which can be statistically modelled assuming penny-shaped fractures of constant radius and aperture within an anisotropic fracture system. Thus, this model is related to fracture connectivity, its length and to the cube of the fracture apertures. In this way, the estimated values presents their own inaccuracies owing to the method used. Therefore, the study of the real spatial distribution of the veinlets of the fault-related fracture mesh (3D), feasible with the use of micro-CT analyses, is a first order factor to unravel both, the real structural permeability conditions of a fault-zone, together with the validation of previous estimations made in 2D analyses in thin-sections. This early contribution shows the preliminary results of a fault-related fracture mesh and its 3D spatial distribution in the damage zone of the Jorgillo Fault (JF), an ancient subvertical left-lateral strike-slip fault exposed in the Atacama Fault System in northern Chile. The JF is a ca. 20 km long NNW-striking strike-slip fault with sinistral displacement of ca. 4 km. The methodology consisted of the drilling of vertically oriented plugs of 5 mm in diameter located at different distances from the JF core - damage zone boundary. Each specimen was, then, scanned with an x-ray micro-CT scanner (ProCon X-Ray CTalpha) in order to assess the fracture mesh. X-rays were generated in a transmission target x-ray tube with acceleration voltages ranging from 90
Papiernik, Sharon K; Yates, Scott R; Chellemi, Daniel O
2011-01-01
Minimizing atmospheric emissions of soil fumigants is critical for protecting human and environmental health. Covering the soil surface with a plastic tarp is a common approach to restrict fumigant emissions. The mass transfer of the fumigant vapors through the tarp is often the rate-limiting factor in fumigant emissions. An approach for standardizing measurements of film permeability is proposed that is based on determining the resistance (R) of films to diffusion of fumigants. Using this approach, values were determined for more than 200 film-chemical combinations under a range of temperature, relative humidity, and film handling conditions. Resistance to diffusion was specific for each fumigant/film combination, with the largest range of values observed for the fumigant chloropicrin. For each fumigant, decreased with increasing temperature. Changes in film permeability due to increases in temperature or field installation were generally less than a factor of five. For one film, values determined under conditions of very high relative humidity (approximately 100%) were at least 100 times lower than when humidity was very low (approximately 2%). This approach simplifies the selection of appropriate films for soil fumigation by providing rapid, reproducible, and precise measurements of their permeability to specific fumigants and application conditions. by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.
NASA Astrophysics Data System (ADS)
Aizawa, Y.; Shimamoto, T.; Flemings, P. B.; Behrmann, J. H.; John, C. M.
2005-12-01
The Brazos-Trinity Basin #4 and Ursa Basin on the northern continental slope off Texas and Louisiana in the Gulf of Mexico are ideal locations for studying the sedimentation and fluid flow processes leading to the development of overpressure because of their contrasting sedimentation histories. The former is a small basin with a slow sedimentation rate and with no overpressure development. Whereas the sedimentation in the latter is high, resulting in the development of overpressure which is likely to have triggered a large-scale slope failure, slumping and faulting. The purposes of Expedition 308 are to document how pressure, stress and geology are coupled to control fluid migration on passive margins, through drilling at sites U1319 and U1320 in the Brazos-Trinity Basin #4 and at sites U1322 and U1324 in Ursa Basin. Quantitative basin analysis, i.e., analysis of sedimentation, fluid flow and compaction processes at least in two dimensions, is possible based on the measured hydraulic properties of those core samples at elevated effective pressures corresponding to various depths. We have just started systematic measurement of permeability, porosity and specific storage capacity of core samples, using an intravessel deformation and fluid-flow apparatus at Kyoto University. Samples were first dried at temperatures of 90-100°C for more than 3 days to evaporate pore water. Permeability and porosity have been measured with N2 gas flow method and with a picnometer, respectively, at confining pressures up to 200 MPa and pore pressures to 2 MPa. The age of drill cores range from the Pleistocene to the Quarternary, and we plan to evaluate the long-term cementation effect by measuring porosity for samples from all stratigraphic horizons. The complete data set will allow one to estimate permeability and porosity structures at depths even greater than 10 km. Our measurements show that permeability of silt in the shallow part of Brazos-Trinity Basin #4 ranges from 10-15 m2 at
Macmillan, Carolyn J; Starkey, Ryan J; Easton, Alexander S
2011-12-01
The regulation of angiogenesis was studied over the course of the animal model of multiple sclerosis, acute experimental autoimmune encephalomyelitis (EAE) in mice using immunohistochemistry. During EAE, angiogenesis peaked 21 days after disease induction, with significant increases in gray matter and adjacent to the leptomeninges. Angiogenesis correlated with clinical and pathologic scores. Spinal cord expression of angiopoietin 1 (Ang-1) by neurons and glia was reduced at Day 14, but expression by inflammatory cells restored earlier levels at Day 21. Angiopoietin 2 expression increased markedly at Day 21 and was mostly associated with inflammatory cells. Levels of the angiopoietin receptor Tie-2 were reduced at Day 14, but recovered by day D21. Double labeling demonstrated Ang-1 expression on infiltrating CD3-positive T cells; Ang-2 was expressed by monocytes/macrophages. During EAE, the expression of vascular endothelial growth factor peaked at Day 14 and began to decrease by Day 21. Double labeling showed expression of Tie-2 and vascular endothelial growth factor receptor 2 but not Ang-2 in blood vessels at Day 21. Vascular permeability increased early in EAE, but was reduced by Day 21. Although individual values did not correlate with angiogenesis, the volume of permeable tissue showed a weak positive correlation with angiogenesis. These temporal changes in angiogenic factors suggest an integral role during EAE-related angiogenesis.
Kelly, John R; Kennedy, Paul J; Cryan, John F; Dinan, Timothy G; Clarke, Gerard; Hyland, Niall P
2015-01-01
The emerging links between our gut microbiome and the central nervous system (CNS) are regarded as a paradigm shift in neuroscience with possible implications for not only understanding the pathophysiology of stress-related psychiatric disorders, but also their treatment. Thus the gut microbiome and its influence on host barrier function is positioned to be a critical node within the brain-gut axis. Mounting preclinical evidence broadly suggests that the gut microbiota can modulate brain development, function and behavior by immune, endocrine and neural pathways of the brain-gut-microbiota axis. Detailed mechanistic insights explaining these specific interactions are currently underdeveloped. However, the concept that a "leaky gut" may facilitate communication between the microbiota and these key signaling pathways has gained traction. Deficits in intestinal permeability may underpin the chronic low-grade inflammation observed in disorders such as depression and the gut microbiome plays a critical role in regulating intestinal permeability. In this review we will discuss the possible role played by the gut microbiota in maintaining intestinal barrier function and the CNS consequences when it becomes disrupted. We will draw on both clinical and preclinical evidence to support this concept as well as the key features of the gut microbiota which are necessary for normal intestinal barrier function.
Kelly, John R.; Kennedy, Paul J.; Cryan, John F.; Dinan, Timothy G.; Clarke, Gerard; Hyland, Niall P.
2015-01-01
The emerging links between our gut microbiome and the central nervous system (CNS) are regarded as a paradigm shift in neuroscience with possible implications for not only understanding the pathophysiology of stress-related psychiatric disorders, but also their treatment. Thus the gut microbiome and its influence on host barrier function is positioned to be a critical node within the brain-gut axis. Mounting preclinical evidence broadly suggests that the gut microbiota can modulate brain development, function and behavior by immune, endocrine and neural pathways of the brain-gut-microbiota axis. Detailed mechanistic insights explaining these specific interactions are currently underdeveloped. However, the concept that a “leaky gut” may facilitate communication between the microbiota and these key signaling pathways has gained traction. Deficits in intestinal permeability may underpin the chronic low-grade inflammation observed in disorders such as depression and the gut microbiome plays a critical role in regulating intestinal permeability. In this review we will discuss the possible role played by the gut microbiota in maintaining intestinal barrier function and the CNS consequences when it becomes disrupted. We will draw on both clinical and preclinical evidence to support this concept as well as the key features of the gut microbiota which are necessary for normal intestinal barrier function. PMID:26528128
Choi, Myung-Kyu; Son, Sangwon; Hong, Mingi; Choi, Min Sung; Kwon, Jae Young; Lee, Junho
2016-04-01
Membrane integrity is critical for cell survival, defects of which cause pathological symptoms such as metabolic diseases. In this study, we used ethanol sensitivity of the nematode Caenorhabditis elegans to identify genetic factors involved in membrane integrity. InC. elegans, acute exposure to a high concentration (7% v/v) of ethanol changes membrane permeability, as measured by propidium iodide staining, and causes paralysis. We used the timing of complete paralysis as an indicator for alteration of membrane integrity in our genetic screen, and identified ptr-6 as a gene that confers ethanol resistance when mutated. PTR-6 is a patched-related protein and contains a sterol sensing domain. Inhibition of two PTR-encoding genes,ptr-15 and ptr-23, and mboa-1, encoding an Acyl Co-A: cholesterol acyltransferase homolog, restored ethanol sensitivity of the ptr-6 mutant, suggesting that these ptr genes and mboa-1 are involved in the maintenance of membrane integrity and permeability. Our results suggest that C. elegans can be used as a model system to identify factors involved in metabolic diseases and to screen for therapeutic drugs. Copyright © 2016 by the Genetics Society of America.
NASA Astrophysics Data System (ADS)
Hale, V. Cody; McDonnell, Jeffrey J.
2016-02-01
The effect of bedrock permeability and underlying catchment boundaries on stream base flow mean transit time (MTT) and MTT scaling relationships in headwater catchments is poorly understood. Here we examine the effect of bedrock permeability on MTT and MTT scaling relations by comparing 15 nested research catchments in western Oregon; half within the HJ Andrews Experimental Forest and half at the site of the Alsea Watershed Study. The two sites share remarkably similar vegetation, topography, and climate and differ only in bedrock permeability (one poorly permeable volcanic rock and the other more permeable sandstone). We found longer MTTs in the catchments with more permeable fractured and weathered sandstone bedrock than in the catchments with tight, volcanic bedrock (on average, 6.2 versus 1.8 years, respectively). At the permeable bedrock site, 67% of the variance in MTT across catchments scales was explained by drainage area, with no significant correlation to topographic characteristics. The poorly permeable site had opposite scaling relations, where MTT showed no correlation to drainage area but the ratio of median flow path length to median flow path gradient explained 91% of the variance in MTT across seven catchment scales. Despite these differences, hydrometric analyses, including flow duration and recession analysis, and storm response analysis, show that the two sites share relatively indistinguishable hydrodynamic behavior. These results show that similar catchment forms and hydrologic regimes hide different subsurface routing, storage, and scaling behavior—a major issue if only hydrometric data are used to define hydrological similarity for assessing land use or climate change response.
Evaluating the relative air permeability of porous media from their water retention curves
NASA Astrophysics Data System (ADS)
Assouline, S.; Tuli, A.; Hopmans, J. W.
2016-05-01
Accurate modeling of water and air flow in porous media requires the definition of the relevant hydraulic properties, namely, the water retention curve (WRC) and the relative hydraulic conductivity function (RHC), as well as the definition of the relative air permeability function (RAP). Capitalizing on the approach developed previously to represent the RHC, a new model allowing the prediction of RAP based on information resulting from the WRC is proposed. The power value ηa in the model is a decreasing exponential function of the coefficient of variation, ɛ, characterizing the pore size distribution of the porous medium, and derived from its WRC. The model was calibrated using data from 22 disturbed and undisturbed soil samples and was validated using data from eight soil types ranging from quartz sand to silty clay loam. The proposed model provided accurate prediction of the soil RAP and performed in some cases (sandy loam and silty clay loam soils) better than available alternative models.
Escuder-Gilabert, L; Villanueva-Camañas, R M; Sagrado, S; Medina-Hernandez, M J
2009-04-01
This paper points out the usefulness of biopartitioning micellar chromatography (BMC) as a high-throughput primary screening tool providing key information about the oral absorption, skin permeability (K(p)), brain-blood distribution coefficient (BB) and ecotoxicological parameters such as median lethal concentration (LC(50)) and bioconcentration factors of 15 organochloride compounds. The retention data of compounds in BMC conditions were interpolated in previously developed quantitative-retention activity relationships by our research group. Results show that the compounds studied readily cross the intestinal barrier (oral absorption > 90%) and the blood-brain barrier (log BB > 0.4). In addition, the organochlorines DDE, chlorobenzene, 1,3-dichlorobenzene and 1,2-dichlorobenzene are the compounds which can more quickly cross the skin barrier (log K(p ) > -0.74 cm/h). From a ecotoxicological point of view, it can be concluded that the most retained compounds, DDE, DDD, hexachlorobenzene and dicofol, are the most toxic and bioacumulative.
NASA Astrophysics Data System (ADS)
Boles, J. R.; Horner, S.
2003-12-01
Methane has leaked from the offshore South Ellwood fault at least since discovery of the South Ellwood field at Platform Holly. The fault bounds the north side of the field and has 600 meters of normal offset. The reservoir, which is fractured Monterey shale at one kilometer depth, was initially 5% over hydrostatic pressure, but is currently at 25% below hydrostatic pressure. Production fluid in well tubing that connects the platform and reservoir is isolated from the ocean. New data indicate that the ocean is in direct hydraulic communication with the reservoir in the vicinity of the fault. Quartz pressure sensors were installed at about one km depth in five wells during a 15 day production shut down. A well that intersects the fault at reservoir depth (about one km subsea), shows a pressure variation that matches the frequency of the ocean tide. Within +/- 1 minute, there is no lag between the predicted tide signal and the pressure variation in the well. The pressure change is less than predicted from sea heights, which we attribute to compressibility of the gas in the fault zone. The other wells (160m-1 km from the fault) do not show the tidal signal, indicating that pressure change is not a general effect of the tide on the earth's crust. During testing, fluid pressures increased at a rate of 55 Pa/hr (0.008 psi/hr) in the well adjacent to the fault. We conclude that the pressure recovery from sub-hydrostatic conditions is due to sea water flowing down the fault into the under pressured reservoir. From this data we calculate the permeability of the South Ellwood Fault to be about 20 md, a value similar to the overall field permeability in the fractured Monterey reservoir.
Almost efficient estimation of relative risk regression
Fitzmaurice, Garrett M.; Lipsitz, Stuart R.; Arriaga, Alex; Sinha, Debajyoti; Greenberg, Caprice; Gawande, Atul A.
2014-01-01
Relative risks (RRs) are often considered the preferred measures of association in prospective studies, especially when the binary outcome of interest is common. In particular, many researchers regard RRs to be more intuitively interpretable than odds ratios. Although RR regression is a special case of generalized linear models, specifically with a log link function for the binomial (or Bernoulli) outcome, the resulting log-binomial regression does not respect the natural parameter constraints. Because log-binomial regression does not ensure that predicted probabilities are mapped to the [0,1] range, maximum likelihood (ML) estimation is often subject to numerical instability that leads to convergence problems. To circumvent these problems, a number of alternative approaches for estimating RR regression parameters have been proposed. One approach that has been widely studied is the use of Poisson regression estimating equations. The estimating equations for Poisson regression yield consistent, albeit inefficient, estimators of the RR regression parameters. We consider the relative efficiency of the Poisson regression estimator and develop an alternative, almost efficient estimator for the RR regression parameters. The proposed method uses near-optimal weights based on a Maclaurin series (Taylor series expanded around zero) approximation to the true Bernoulli or binomial weight function. This yields an almost efficient estimator while avoiding convergence problems. We examine the asymptotic relative efficiency of the proposed estimator for an increase in the number of terms in the series. Using simulations, we demonstrate the potential for convergence problems with standard ML estimation of the log-binomial regression model and illustrate how this is overcome using the proposed estimator. We apply the proposed estimator to a study of predictors of pre-operative use of beta blockers among patients undergoing colorectal surgery after diagnosis of colon cancer. PMID
Intestinal permeability in relation to birth weight and gestational and postnatal age
van Elburg, R M; Fetter, W; Bunkers, C; Heymans, H
2003-01-01
Objective: To determine the relation between intestinal permeability and birth weight, gestational age, postnatal age, and perinatal risk factors in neonates. Study design: Intestinal permeability was measured by the sugar absorption test within two days of birth and three to six days later in preterm and healthy term infants. In the sugar absorption test, the urinary lactulose/mannitol ratio is measured after oral ingestion of a solution (375 mosm) of lactulose and mannitol. Results: A first sugar absorption test was performed in 116 preterm (26–36 weeks gestation) and 16 term infants. A second test was performed in 102 preterm and nine term infants. In the preterm infants, the lactulose/mannitol ratio was not related to gestational age (r = -0.09, p = 0.32) or birth weight (r = 0.07, p = 0.43). The median lactulose/mannitol ratio was higher if measured less than two days after birth than when measured three to six days later (0.427 and 0.182 respectively, p<0.001). The lactulose/mannitol ratio was higher in preterm infants than term infants if measured within the first 2 days of life (0.404 and 0.170 respectively, p < 0.001), but not different three to six days later (0.182 and 0.123 respectively, p = 0.08). In multiple regression analysis of perinatal risk factors, only umbilical arterial pH correlated with the lactulose/mannitol ratio in preterm infants less than 2 days of age (T = -1.98, p = 0.05). Conclusions: In preterm infants (26–36 weeks gestation), intestinal permeability is not related to gestational age or birth weight but is higher during the first 2 days of life than three to six days later. It is higher in preterm infants than in healthy term infants only if measured within two days of birth. This suggests rapid postnatal adaptation of the small intestine in preterm infants. PMID:12496227
Laura J. Pyrak-Nolte; Nicholas J. Giordano; David D. Nolte
2004-03-01
The principal challenge of upscaling techniques for multi-phase fluid dynamics in porous media is to determine which properties on the micro-scale can be used to predict macroscopic flow and spatial distribution of phases at core- and field-scales. The most notable outcome of recent theories is the identification of interfacial areas per volume for multiple phases as a fundamental parameter that determines much of the multi-phase properties of the porous medium. A formal program of experimental research was begun to directly test upscaling theories in fluid flow through porous media by comparing measurements of relative permeability and capillary-saturation with measurements of interfacial area per volume. This project on the experimental investigation of relative permeability upscaling has produced a unique combination of three quite different technical approaches to the upscaling problem of obtaining pore-related microscopic properties and using them to predict macroscopic behavior. Several important ''firsts'' have been achieved during the course of the project. (1) Optical coherence imaging, a laser-based ranging and imaging technique, has produced the first images of grain and pore structure up to 1 mm beneath the surface of the sandstone and in a laboratory borehole. (2) Woods metal injection has connected for the first time microscopic pore-scale geometric measurements with macroscopic saturation in real sandstone cores. (3) The micro-model technique has produced the first invertible relationship between saturation and capillary pressure--showing that interfacial area per volume (IAV) provides the linking parameter. IAV is a key element in upscaling theories, so this experimental finding may represent the most important result of this project, with wide ramifications for predictions of fluid behavior in porous media.
NASA Astrophysics Data System (ADS)
Reynolds, C. A.; Krevor, S.
2015-12-01
We provide a comprehensive experimental study of steady state, drainage relative permeability curves with CO2-brine and N2-deionized water, on a single Bentheimer sandstone core with a simple two-layer heterogeneity. We demonstrate that, if measured in the viscous limit, relative permeability is invariant with changing reservoir conditions, and is consistent with the continuum-scale multiphase flow theory for water wet systems. Furthermore, we show that under capillary limited conditions, the CO2-brine system is very sensitive to heterogeneity in capillary pressure, and by performing core floods under capillary limited conditions, we produce effective relative permeability curves that are flow rate and fluid parameter dependent. We suggest that the major uncertainty in past observations of CO2-brine relative permeability curves is due to the interaction of CO2 flow with pore space heterogeneity under capillary limited conditions and is not due to the effects of changing reservoir conditions. We show that the appropriate conditions for measuring intrinsic or effective relative permeability curves can be selected simply by scaling the driving force for flow by a quantification of capillary heterogeneity. Measuring one or two effective curves on a core with capillary heterogeneity that is representative of the reservoir will be sufficient for reservoir simulation.
Tsai, Jui-Pin; Chang, Liang-Cheng; Hsu, Shao-Yiu; Shan, Hsin-Yu
2015-07-08
In the current study, we used micromodel experiments to study three-phase fluid flow in porous media. In contrast to previous studies, we simultaneously observed and measured pore-scale fluid behavior and three-phase constitutive relationships with digital image acquisition/analysis, fluid pressure control, and permeability assays. Our results showed that the fluid layers significantly influenced pore-scale, three-phase fluid displacement as well as water relative permeability. At low water saturation, water relative permeability not only depended on water saturation but also on the distributions of air and diesel. The results also indicate that the relative permeability-saturation model proposed by Parker et al. (1987) could not completely describe the experimental data from our three-phase flow experiments because these models ignore the effects of phase distribution. A simple bundle-of-tubes model shows that the water relative permeability was proportional to the number of apparently continuous water paths before the critical stage in which no apparently continuous water flow path could be found. Our findings constitute additional information about the essential constitutive relationships involved in both the understanding and the modeling of three-phase flows in porous media.
System response as a function of relative permeability in geologic CO2 sequestration
NASA Astrophysics Data System (ADS)
Pollyea, R.
2015-12-01
Within the portfolio of risk assessment strategies for carbon capture and sequestration projects, numerical modeling and simulation is frequently utilized for predicting CO2 storage capacity, leakage potential, and geomechanical reservoir integrity. In numerical CO2 injection models, one commonly used approach for simulating the effects of relative permeability (krel) is to apply the van Genuchten (1980) model to the wetting phase and the Corey (1954) model to the non-wetting phase. In this formulation, wetting phase permeability decay is controlled by a phase interference parameter (m), and non-wetting phase permeability decay is controlled by irreducible non-wetting phase saturation (Sgr). Although krel is a well-known phenomenon, there exists much uncertainty in parameterizing krel models and little is known about the influence of parameter space on reservoir performance. This work presents results from a numerical modeling experiment designed to isolate the effects of variability in krel parameters, m and Sgr. A series of CO2 injection simulations is performed for 399 unique combinations of m and Sgr, which vary systematically over a range of 0.1 - 0.99 and 0.01 - 0.50, respectively. CO2 is injected at modest 2.78 kg/s for 10 years into a radially symmetric grid using a beta version of TOUGH3/ECO2N, and all reservoir properties remain constant across the ensemble of 399 simulations. Results from this work show the injection pressure response ranging from ~10 MPa to >60 MPa, where the high end of this range is focused on a narrow portion of the parameter space corresponding to m < 0.3 for all Sgr. Additionally, the maximum CO2 plume radius (defined as CO2 saturation > 0.01) ranges from 550 m to 1250 m, where the high end of this range corresponds with low m and low Sgr. Although the model geometry is quite simple, these results demonstrate enormous variability in the both injection pressure and CO2 plume dimension solely as a function of krel.
NASA Astrophysics Data System (ADS)
Lipsey, Lindsay; Pluymaekers, Maarten; van Wees, Jan-Diederik; Limberger, Jon; Cloetingh, Sierd
2016-04-01
The presence of convective fluid flow in permeable layers can create zones of anomalously high temperature which can be exploited for geothermal energy. Temperature measurements from the Luttelgeest-01 (LTG-01) well in the northern onshore region of the Netherlands indicate variations in the thermal regime that could be indicative of convection. This thermal anomaly coincides with a 600 m interval (4600 - 5200 m) of Dinantian carbonates showing signs of increased fracture permeability of ~60 mD. For the purpose of geothermal energy exploration, it is of interest to know whether or not convection can occur in a particular reservoir, where convection cells are likely to develop and the temperature enhancements in convective upwellings. Three-dimensional numerical simulations provide insight on possible flow and thermal structures within the fractured carbonate interval. The development and number of convection cells is very much a time dependent process. First longitudinal rolls fill the domain, increasing in width until ultimately transforming into a more complex polyhedral structure. The model relaxes into a steady-state five-cell convection pattern. Furthermore, geometric aspects of the carbonate platform itself likely control the shape and location of upwellings. Convective upwellings can create significant temperature enhancements relative to the conductive profile and in agreement with the observations in the Luttelgeest carbonate platform. This enhancement is critically dependent on the aquifer thickness and geothermal gradient. Given a gradient of 39 °C/km and an aquifer thickness of 600 m, a temperature of 203 °C can be obtained at a depth of 4600 m directly above upwelling zones. Contrarily, downwelling zones result in a temperature of 185 °C at the same depth. This demonstrates the strong spatial variability of thermal anomalies in convective fractures aquifers at large depth, which can have a strong effect on exploration opportunity and risk of
Permeability of filter cakes of palm oil in relation to mechanical expression
Kamst, G.F.; Bruinsma, O.S.L.; Graauw, J. de
1997-03-01
Permeability and compressibility data are required for an adequate process model for compressible-cake filtration and mechanical expression. Experimental and modeling results of the permeability of palm-oil filter cakes (a highly compressible viscoelastic material) are combined with compressibility data, leading to a model for the expression step. Permeability measurements show that permeability depends strongly on the quantity of fine particles in the cake. Removal of fine particles from the slurry before expression significantly increases the solid-phase content during expression due to higher permeability. Modeling results of the expression step show that for palm-oil filter cakes there is a pressure above which the attainable mass fraction of solids becomes independent of pressure. Decrease in specific cake resistance has two effects: a higher mass fraction of solids at the same pressure and a higher pressure at which the mass fraction of solids is not affected further.
Li, Cheng-He; Chen, Fang-Hsin; Schellingerhout, Dawid; Lin, Yu-Shi; Hong, Ji-Hong; Liu, Ho-Ling
2017-02-01
To quantify the differential plasma flow- (Fp-) and permeability surface area product per unit mass of tissue- (PS-) weighting in forward volumetric transfer constant (K(trans)) estimates by using a low molecular (Gd-DTPA) versus high molecular (Gadomer) weight contrast agent in dynamic contrast enhanced (DCE) MRI. DCE MRI was performed using a 7T animal scanner in 14 C57BL/6J mice syngeneic for TRAMP tumors, by administering Gd-DTPA (0.9kD) in eight mice and Gadomer (35kD) in the remainder. The acquisition time was 10min with a sampling rate of one image every 2s. Pharmacokinetic modeling was performed to obtain K(trans) by using Extended Tofts model (ETM). In addition, the adiabatic approximation to the tissue homogeneity (AATH) model was employed to obtain the relative contributions of Fp and PS. The K(trans) values derived from DCE-MRI with Gd-DTPA showed significant correlations with both PS (r(2)=0.64, p=0.009) and Fp (r(2)=0.57, p=0.016), whereas those with Gadomer were found only significantly correlated with PS (r(2)=0.96, p=0.0003) but not with Fp (r(2)=0.34, p=0.111). A voxel-based analysis showed that K(trans) approximated PS (<30% difference) in 78.3% of perfused tumor volume for Gadomer, but only 37.3% for Gd-DTPA. The differential contributions of Fp and PS in estimating K(trans) values vary with the molecular weight of the contrast agent used. The macromolecular contrast agent resulted in K(trans) values that were much less dependent on flow. These findings support the use of macromolecular contrast agents for estimating tumor vessel permeability with DCE-MRI. Copyright © 2016 Elsevier Inc. All rights reserved.
Cox, B.L.; Pruess, K.; Persoff, P.
1990-01-01
A casting technique has been developed for making translucent replicas of the void space of natural rock fractures. Attenuation of light shined through the cast combined with digital image analysis provides a pointwise definition of fracture apertures. The technique has been applied to a fracture specimen from Dixie Valley, Nevada, and the measured void space geometry has been used to develop theoretical predictions of two-phase relative permeability. A strong anisotropy in relative permeabilities has been found, which is caused by highly anisotropic spatial correlations among fracture apertures. 16 refs., 6 figs.
Estimating the relative utility of screening mammography.
Abbey, Craig K; Eckstein, Miguel P; Boone, John M
2013-05-01
The concept of diagnostic utility is a fundamental component of signal detection theory, going back to some of its earliest works. Attaching utility values to the various possible outcomes of a diagnostic test should, in principle, lead to meaningful approaches to evaluating and comparing such systems. However, in many areas of medical imaging, utility is not used because it is presumed to be unknown. In this work, we estimate relative utility (the utility benefit of a detection relative to that of a correct rejection) for screening mammography using its known relation to the slope of a receiver operating characteristic (ROC) curve at the optimal operating point. The approach assumes that the clinical operating point is optimal for the goal of maximizing expected utility and therefore the slope at this point implies a value of relative utility for the diagnostic task, for known disease prevalence. We examine utility estimation in the context of screening mammography using the Digital Mammographic Imaging Screening Trials (DMIST) data. We show how various conditions can influence the estimated relative utility, including characteristics of the rating scale, verification time, probability model, and scope of the ROC curve fit. Relative utility estimates range from 66 to 227. We argue for one particular set of conditions that results in a relative utility estimate of 162 (±14%). This is broadly consistent with values in screening mammography determined previously by other means. At the disease prevalence found in the DMIST study (0.59% at 365-day verification), optimal ROC slopes are near unity, suggesting that utility-based assessments of screening mammography will be similar to those found using Youden's index.
Berge, P A; Blair, S C; Shaffer, R J; Wang, H F
1997-02-18
We provide in this report a methodology to estimate bounds on the changes in fracture permeability due to thermal-mechanical processes associated with excavation of drifts and emplacement of waste. This report is the first milestone associated with Task A of the LLNL initiative to evaluate available methods for estimating chamges in fracture permeability surrounding drifts in the Exploratory Studies Facility (ESF) and the potential repository at Yucca Mountain in response to (1) construction-induced stress changes and (2) subsequent thermal pulse effects due to waste emplacement. These results are needed for modeling changes in repository-level moisture movement and seepage.
NASA Astrophysics Data System (ADS)
Kosack, Christian; Vogt, Christian; Rath, Volker; Marquart, Gabriele
2010-05-01
The knowledge of the permeability distribution at depth is of primary concern for any geothermal reservoir engineering. However, permeability might change over orders of magnitude even for a single rock type and is additionally controlled by tectonic or engineered fracturing of the rocks. During reservoir exploration pumping tests are regularly performed where tracer marked water is pumped in one borehole and retrieved at one or a few others. At the European Enhanced Geothermal System (EGS) test site at Soultz-sous-Forêts three wells had been drilled in the granitic bedrock down to 4 to 5 km and were hydraulically stimulated to enhance the hydraulic connectivity between the wells. In July 2005, a tracer circulation test was carried out in order to estimate the changes of the hydraulic properties. Therefore a tracer was injected into the well GPK3 for 19 hours at a rate of 0.015 m3 s-1 and a concentration of 0.389 mol m-3. Tracer concentration was measured in the production wells over the following 5 months, while the produced water was re-injected into GPK3. This experiment demonstrated a good hydraulic connection between GPK3 and one of the production wells, GPK2, while a very low connectivity was observed in the other one, GPK4. We tested three different approaches simulating the pumping experiment with the numerical simulator shemat_suite in a simplified 3D model of the site in order to study their respective potential to estimate a reliable permeability distribution for the Soultz reservoir: A full-physics gradient-based Bayesian inversion, a massive Monte Carlo approach with geostatistic analysis, and an Ensemble-Kalman-Filter (EnKF) assimilation. A common feature in all models is a high permeability zone which acts as main flow area and transports most of the tracer. It is assumed to be associated with the fault zone cutting through the boreholes GPK2 and GPK3. With the Bayesian Inversion we were able to estimate a parameter set consisting of porosity
Paillet, Frederick L.
1998-01-01
A numerical model of flow in the vicinity of a borehole is used to analyze flowmeter data obtained with high-resolution flowmeters. The model is designed to (1) precisely compute flow in a borehole, (2) approximate the effects of flow in surrounding aquifers on the measured borehole flow, (3) allow for an arbitrary number (N) of entry/exit points connected to M < N far-field aquifers, and (4) be consistent with the practical limitations of flowmeter measurements such as limits of resolution, typical measurement error, and finite measurement periods. The model is used in three modes: (1) a quasi-steady pumping mode where there is no ambient flow, (2) a steady flow mode where ambient differences in far-field water levels drive flow between fracture zones in the borehole, and (3) a cross-borehole test mode where pumping in an adjacent borehole drives flow in the observation borehole. The model gives estimates of transmissivity for any number of fractures in steady or quasi-steady flow experiments that agree with straddle-packer test data. Field examples show how these cross-borehole-type curves can be used to estimate the storage coefficient of fractures and bedding planes and to determine whether fractures intersecting a borehole at different locations are hydraulically connected in the surrounding rock mass.
NASA Astrophysics Data System (ADS)
Riviere, J.; Madara, B.; Elsworth, D.; Johnson, P. A.; Marone, C.
2016-12-01
Dynamic stressing of rocks is known to transiently increase permeability, and has potential application to improve the efficiency of geothermal energy production and oil/gas recovery. At larger scale, teleseismic waves have been observed to transiently increase permeability of aquifer systems. Seismic waves are also known to transiently decrease elastic moduli near fault zones. However, it remains unclear which parameters control the magnitude of permeability increase and how this magnitude can be predicted. We report on laboratory studies that monitor both permeability evolution and elastic properties in fractured granite and shale. We use L-shaped samples that are loaded with triaxial stresses of order 10 MPa and fractured in a triaxial cell. Deionized water is forced to flow along the resulting fracture path by applying a differential pore pressure along the shear direction. Dynamic stressing is applied via pore pressure or normal stress oscillations (20 s-duration, up to 1 Hz-frequency and 1 MPa-amplitude), while measuring flow rates and elastic wave velocities. Our observations enable transient increases in permeability to be determined following dynamic stressing and constrained via measurements of ultrasonic velocity. In particular, these preliminary results are discussed with former results suggesting that permeability enhancement is dictated by flow rate.
NASA Astrophysics Data System (ADS)
Bianchi Janetti, Emanuela; Riva, Monica; Guadagnini, Alberto
2017-04-01
We study the relative role of the complex pore space geometry and wettability of the solid matrix on the quantification of relative permeabilities characterizing steady state immiscible two-phase flow in porous media. We do so by considering elementary cells, which are typically employed in upscaling frameworks based on, e.g., homogenization or volume averaging. In this context one typically relies on the solution of pore-scale physics at a scale which is much smaller than that of an investigated porous system. Pressure-driven two-phase flow following simultaneous co-current injection of water and oil is numerically solved for a suite of regular and stochastically generated two-dimensional explicit elementary cells with fixed porosity and sharing main topological/morphological features. We show that relative permeabilities of the randomly generated elementary cells are significantly influenced by the formation of preferential percolation paths (principal pathways), giving rise to a strongly nonuniform distribution of fluid fluxes. These pathways are a result of the spatially variable resistance that the random pore structures exert on the fluid. The overall effect on relative permeabilities of the diverse organization of principal pathways, as driven by a given random realization at the scale of the unit cell, is significantly larger than that of the wettability of the host rock. In contrast to what can be observed for the random cells analyzed, relative permeabilities of regular cells display a clear trend with contact angle at the investigated scale. Our findings suggest the need to perform systematic upscaling studies in a stochastic context, to propagate the effects of uncertain pore space geometries to a probabilistic description of relative permeability curves at the continuum scale.
Laura J. Pyrak-Nolte; Ping Yu; JiangTao Cheng; Daiquan Chen; Nicholas Giordano; Mirela Mustata; John Coy; Nathan Cooper; David D. Nolte
2002-12-01
The principal challenge of upscaling techniques for multi-phase fluid dynamics in porous media is to determine which properties on the micro-scale can be used to predict macroscopic flow and spatial distribution of phases at core- and field-scales. The most notable outcome of recent theories is the identification of interfacial areas per volume for multiple phases as a fundamental parameter that determines much of the multi-phase properties of the porous medium. A formal program of experimental research was begun to directly test upscaling theories in fluid flow through porous media by comparing measurements of relative permeability and capillary-saturation with measurements of interfacial area per volume. During this reporting period, we have shown experimentally that the coherence detection can be performed in a borescope. The measurement of interfacial area per volume (IAV), capillary pressure and saturation in two dimensional micro-models structures has shown the existence of a unique relationship among these hydraulic parameters for different pore geometry. The measurement of interfacial area per volume on a three-dimensional natural sample, i.e., sandstone, is essentially completed for imbibition conditions.
JiangTao Cheng; Ping Yu; William Headley; Nicholas Giordao; Mirela Mustata; Daiquan Chen; Nathan Cooper; David D. Nolte; Laura J. Pyrak-Nolte
2001-12-01
The principal challenge of upscaling techniques for multi-phase fluid dynamics in porous media is to determine which properties on the micro-scale can be used to predict macroscopic flow and spatial distribution of phases at core- and field-scales. The most notable outcome of recent theories is the identification of interfacial areas per volume for multiple phases as a fundamental parameter that determines much of the multi-phase properties of the porous medium. A formal program of experimental research was begun to directly test upscaling theories in fluid flow through porous media by comparing measurements of relative permeability and capillary-saturation with measurements of interfacial area per volume. During this reporting period, we have shown experimentally and theoretically that the optical coherence imaging system is optimized for sandstone. The measurement of interfacial area per volume (IAV), capillary pressure and saturation in two dimensional micro-models structures that are statistically similar to real porous media has shown the existence of a unique relationship among these hydraulic parameters. The measurement of interfacial area per volume on a three-dimensional natural sample, i.e., sandstone, has the same length-scale as the values of IAV determined for the two-dimensional micro-models.
Field-scale estimation of gas permeability and subsequent computation of pore-gas velocity profiles are critical elements of sound soil venting design. It has been our experience however in U.S. EPA's technical assistance program, provided by the Office of Research and Developme...
Field-scale estimation of gas permeability and subsequent computation of pore-gas velocity profiles are critical elements of sound soil venting design. It has been our experience however in U.S. EPA's technical assistance program, provided by the Office of Research and Developme...
NASA Astrophysics Data System (ADS)
Dalla Valle, Nicolas; Wutzler, Thomas; Meyer, Stefanie; Potthast, Karin; Michalzik, Beate
2017-04-01
Dual-permeability type models are widely used to simulate water fluxes and solute transport in structured soils. These models contain two spatially overlapping flow domains with different parameterizations or even entirely different conceptual descriptions of flow processes. They are usually able to capture preferential flow phenomena, but a large set of parameters is needed, which are very laborious to obtain or cannot be measured at all. Therefore, model inversions are often used to derive the necessary parameters. Although these require sufficient input data themselves, they can use measurements of state variables instead, which are often easier to obtain and can be monitored by automated measurement systems. In this work we show a method to estimate soil hydraulic parameters from high frequency soil moisture time series data gathered at two different measurement depths by inversion of a simple one dimensional dual-permeability model. The model uses an advection equation based on the kinematic wave theory to describe the flow in the fracture domain and a Richards equation for the flow in the matrix domain. The soil moisture time series data were measured in mesocosms during sprinkling experiments. The inversion consists of three consecutive steps: First, the parameters of the water retention function were assessed using vertical soil moisture profiles in hydraulic equilibrium. This was done using two different exponential retention functions and the Campbell function. Second, the soil sorptivity and diffusivity functions were estimated from Boltzmann-transformed soil moisture data, which allowed the calculation of the hydraulic conductivity function. Third, the parameters governing flow in the fracture domain were determined using the whole soil moisture time series. The resulting retention functions were within the range of values predicted by pedotransfer functions apart from very dry conditions, where all retention functions predicted lower matrix potentials
Salmachi, Alireza; Karacan, C Özgen
2017-03-01
Coalbed methane (CBM) wells tend to produce large volumes of water, especially when there is hydraulic connectivity between coalbed and nearby formations. Cross-formational flow between producing coal and adjacent formations can have significant production and environmental implications, affecting economic viability of production from these shallow reservoirs. Such flows can also affect how much gas can be removed from a coalbed prior to mining and thus can have implications for methane control in mining as well. The aim of this paper is to investigate the impact of water flow from an external source into coalbed on production performance and also on reservoir variables including cleat porosity and relative permeability curves derived from production data analysis. A reservoir model is constructed to investigate the production performance of a CBM well when cross-formational flow is present between the coalbed and the overlying formation. Results show that cleat porosity calculated by analysis of production data can be more than one order of magnitude higher than actual cleat porosity. Due to hydraulic connectivity, water saturation within coalbed does not considerably change for a period of time, and hence, the peak of gas production is delayed. Upon depletion of the overlying formation, water saturation in coalbed quickly decreases. Rapid decline of water saturation in the coalbed corresponds to a sharp increase in gas production. As an important consequence, when cross-flow is present, gas and water relative permeability curves, derived from simulated production data, have distinctive features compared to the initial relative permeability curves. In the case of cross-flow, signatures of relative permeability curves are concave downward and low gas permeability for a range of water saturation, followed by rapid increase afterward for water and gas, respectively. The results and analyses presented in this work can help to assess the impact of cross
Karacan, C. Özgen
2017-01-01
Coalbed methane (CBM) wells tend to produce large volumes of water, especially when there is hydraulic connectivity between coalbed and nearby formations. Cross-formational flow between producing coal and adjacent formations can have significant production and environmental implications, affecting economic viability of production from these shallow reservoirs. Such flows can also affect how much gas can be removed from a coalbed prior to mining and thus can have implications for methane control in mining as well. The aim of this paper is to investigate the impact of water flow from an external source into coalbed on production performance and also on reservoir variables including cleat porosity and relative permeability curves derived from production data analysis. A reservoir model is constructed to investigate the production performance of a CBM well when cross-formational flow is present between the coalbed and the overlying formation. Results show that cleat porosity calculated by analysis of production data can be more than one order of magnitude higher than actual cleat porosity. Due to hydraulic connectivity, water saturation within coalbed does not considerably change for a period of time, and hence, the peak of gas production is delayed. Upon depletion of the overlying formation, water saturation in coalbed quickly decreases. Rapid decline of water saturation in the coalbed corresponds to a sharp increase in gas production. As an important consequence, when cross-flow is present, gas and water relative permeability curves, derived from simulated production data, have distinctive features compared to the initial relative permeability curves. In the case of cross-flow, signatures of relative permeability curves are concave downward and low gas permeability for a range of water saturation, followed by rapid increase afterward for water and gas, respectively. The results and analyses presented in this work can help to assess the impact of cross
NASA Astrophysics Data System (ADS)
Launay, Gaetan; Sizaret, Stanislas; Guillou-Frottier, Laurent; Gloaguen, Eric; Melleton, Jérémie; Pichavant, Michel; Champallier, Rémi; Pinto, Filipe
2017-04-01
The Panasqueira Sn-W deposit occurs as a dense network of flat wolframite and cassiterite-bearing quartz veins concentrated in the vicinity of a hidden greisen cupola, and to a lesser extent as disseminated cassiterites in the greisen. Previous studies (Thadeu 1951; 1979) have suggested that the Panasqueira deposit is genetically related to magmatic activity for which the most part is unexposed, and being only represented by the greisen cupola. Hydrothermal fluid circulation during the final stages of granite crystallisation has probably led to the greisenisation of the cupola followed by the deposition of the mineralization in the veins system. Mineral replacement reactions that occurred during the greisenisation could affect rock properties (porosity, density and permeability) which control fluid circulation in the granite. This study aims to investigate effects of greisenisation reactions on the dynamic (time varying) permeability that ultimately leads to fluid circulation in the greisen cupola. To do so, petrological study and experimental determinations of hydrodynamic features (porosity and permeability) for different granite alteration levels and petrographic types (unaltered granite to greisen) are combined and then integrated in coupled numerical models of fluid circulation around the granitic intrusion. Greisen occurs in the apical part of the granitic body and results in the pervasive alteration of the granite along the granite-schist contact. This greisen consists mainly of quartz and muscovite formed by the replacement of feldspars and bleaching of biotites of the initial granite. Otherwise, greisen is generally vuggy which suggests a porosity increase of the granite during hydrothermal alteration processes. This porosity increase has a positive effect on the permeability of the granitic system. Indeed, experimental measurements of permeability with the Paterson press indicate that the initial granite is impermeable (10-20 m2) whereas the greisen is
Uncertainty relation based on unbiased parameter estimations
NASA Astrophysics Data System (ADS)
Sun, Liang-Liang; Song, Yong-Shun; Qiao, Cong-Feng; Yu, Sixia; Chen, Zeng-Bing
2017-02-01
Heisenberg's uncertainty relation has been extensively studied in spirit of its well-known original form, in which the inaccuracy measures used exhibit some controversial properties and don't conform with quantum metrology, where the measurement precision is well defined in terms of estimation theory. In this paper, we treat the joint measurement of incompatible observables as a parameter estimation problem, i.e., estimating the parameters characterizing the statistics of the incompatible observables. Our crucial observation is that, in a sequential measurement scenario, the bias induced by the first unbiased measurement in the subsequent measurement can be eradicated by the information acquired, allowing one to extract unbiased information of the second measurement of an incompatible observable. In terms of Fisher information we propose a kind of information comparison measure and explore various types of trade-offs between the information gains and measurement precisions, which interpret the uncertainty relation as surplus variance trade-off over individual perfect measurements instead of a constraint on extracting complete information of incompatible observables.
Estimating Relative Changes of Metabolic Fluxes
Huang, Lei; Kim, Dongsung; Liu, Xiaojing; Myers, Christopher R.; Locasale, Jason W.
2014-01-01
Fluxes are the central trait of metabolism and Kinetic Flux Profiling (KFP) is an effective method of measuring them. To generalize its applicability, we present an extension of the method that estimates the relative changes of fluxes using only relative quantitation of 13C-labeled metabolites. Such features are directly tailored to the more common experiment that performs only relative quantitation and compares fluxes between two conditions. We call our extension rKFP. Moreover, we examine the effects of common missing data and common modeling assumptions on (r)KFP, and provide practical suggestions. We also investigate the selection of measuring times for (r)KFP and provide a simple recipe. We then apply rKFP to 13C-labeled glucose time series data collected from cells under normal and glucose-deprived conditions, estimating the relative flux changes of glycolysis and its branching pathways. We identify an adaptive response in which de novo serine biosynthesis is compromised to maintain the glycolytic flux backbone. Together, these results greatly expand the capabilities of KFP and are suitable for broad biological applications. PMID:25412287
NASA Astrophysics Data System (ADS)
Pini, Ronny; Hingerl, Ferdinand; Benson, Sally
2013-04-01
Geological systems are complex and so are the processes that determine the distribution of two (or more) immiscible phases within their porous structure; nevertheless, an empirical relationship between the capillary pressure and saturation, the capillary pressure function, provides the foundation for the theory of multiphase flow in porous media. The simultaneous existence of at least two fluids in a porous rock further implies that the ability of each fluid to flow is reduced by the presence of the other and a so-called relative permeability function has been introduced and defined as the ratio between the effective permeability to the given phase and the absolute permeability of the rock. When coupled to the continuum-scale equations of motion, these two characteristic curves allow for a description of multiphase displacement processes in a variety of natural settings that are related to a wide range of applications, thus including the storage of carbon dioxide into deep saline aquifers. In this study, capillary pressure and relative permeability drainage curves are measured on a single Berea Sandstone core by using three different fluid pairs, namely gCO2/water, gN2/water and scCO2/brine. An important feature of this experimental investigation is that these two multiphase properties are obtained simultaneously during a core-flooding experiment. The applied technique possesses many of the characteristics of a conventional steady-state relative permeability experiment and consists of injecting the nonwetting fluid at increasingly higher flow rates in a core that is initially saturated with the wetting phase, while observing fluid saturations with a medical x-ray CT scanner [Pini et al. 2012]. Injection flow rates are varied so as to cover a sufficiently large range of capillary pressures, whereas fluid-pairs and experimental conditions are selected in order to move across a range interfacial tension values (40-65 mN/m), while maintaining a constant viscosity ratio
Factoring Algebraic Error for Relative Pose Estimation
Lindstrom, P; Duchaineau, M
2009-03-09
We address the problem of estimating the relative pose, i.e. translation and rotation, of two calibrated cameras from image point correspondences. Our approach is to factor the nonlinear algebraic pose error functional into translational and rotational components, and to optimize translation and rotation independently. This factorization admits subproblems that can be solved using direct methods with practical guarantees on global optimality. That is, for a given translation, the corresponding optimal rotation can directly be determined, and vice versa. We show that these subproblems are equivalent to computing the least eigenvector of second- and fourth-order symmetric tensors. When neither translation or rotation is known, alternating translation and rotation optimization leads to a simple, efficient, and robust algorithm for pose estimation that improves on the well-known 5- and 8-point methods.
Byrnes, Alan P.; Bhattacharya, Saibal; Victorine, John; Stalder, Ken
2007-09-30
Thin (3-40 ft thick), heterogeneous, limestone and dolomite reservoirs, deposited in shallow-shelf environments, represent a significant fraction of the reservoirs in the U.S. midcontinent and worldwide. In Kansas, reservoirs of the Arbuckle, Mississippian, and Lansing-Kansas City formations account for over 73% of the 6.3 BBO cumulative oil produced over the last century. For these reservoirs basic petrophysical properties (e.g., porosity, absolute permeability, capillary pressure, residual oil saturation to waterflood, resistivity, and relative permeability) vary significantly horizontally, vertically, and with scale of measurement. Many of these reservoirs produce from structures of less than 30-60 ft, and being located in the capillary pressure transition zone, exhibit vertically variable initial saturations and relative permeability properties. Rather than being simpler to model because of their small size, these reservoirs challenge characterization and simulation methodology and illustrate issues that are less apparent in larger reservoirs where transition zone effects are minor and most of the reservoir is at saturations near S{sub wirr}. These issues are further augmented by the presence of variable moldic porosity and possible intermediate to mixed wettability and the influence of these on capillary pressure and relative permeability. Understanding how capillary-pressure properties change with rock lithology and, in turn, within transition zones, and how relative permeability and residual oil saturation to waterflood change through the transition zone is critical to successful reservoir management and as advanced waterflood and improved and enhanced recovery methods are planned and implemented. Major aspects of the proposed study involve a series of tasks to measure data to reveal the nature of how wettability and drainage and imbibition oil-water relative permeability change with pore architecture and initial water saturation. Focus is placed on
Christiansen, R.L.; Howarth, S.M.
1995-08-01
This report documents a literature review of methods for measuring relative permeability as applied to low permeability anhydrite rock samples from the Salado Formation. About one hundred papers were reviewed, and four methods were identified as promising techniques for measuring the relative permeability of the Salado anhydrite: (1) the unsteady-state high-rate method, (2) the unsteady-state stationary-liquid method, (3) the unsteady-state centrifuge method, and (4) the unsteady-state low-rate method. Except for the centrifuge method, all have been used for low permeability rocks. The unsteady-state high-rate method is preferred for measuring relative permeability of Salado anhydrite, and the unsteady-state stationary-liquid method could be well suited for measuring gas relative permeability of Salado anhydrite. The unsteady-state low-rate method, which combines capillary pressure effects with relative permeability concepts may also prove effective. Likewise, the unsteady-state centrifuge method may be an efficient means for measuring brine relative permeability for Salado anhydrite, especially at high gas saturations.
Takeuchi, K.; Okada, M.; Niida, H.; Okabe, S.
1989-02-01
The relationship between gastric mucosal glutathione (GSH) levels, vascular permeability, gastric motility and mucosal injury caused by ethanol was investigated in rats. Oral administration of 50% ethanol (1 ml) produced elongated reddish bands of lesions in the mucosa with a significant reduction of GSH levels and increase of microvascular permeability. These lesions were significantly inhibited by pretreatment with s.c. administered diethylmaleate (DEM: 1 ml/kg), cysteamine (100 mg/kg) and 16, 16-dimethyl prostaglandin E2 (dmPGE2, 10 micrograms/kg) but worsened markedly by N-ethylmaleimide (NEM: 10 mg/kg). Irrespective of whether the animals were treated with 50% ethanol or not, the mucosal GSH levels were significantly decreased or increased, respectively, by DEM or cysteamine, and were not affected by both NEM and dmPGE2. NEM significantly enhanced the vascular permeability in the absence or presence of ethanol (greater than 10%), whereas other agents significantly inhibited only the increased vascular permeability caused by ethanol. On the other hand, gastric motility was potently and persistently inhibited by either DEM, cysteamine or dmPGE2 at the doses which prevented ethanol-induced mucosal injury, whereas NEM had no effect on the motility. These results suggest that 1) the mucosal GSH levels do not relate directly to either development or prevention of ethanol-induced gastric injury, 2) potentiation by NEM of the mucosal injury may be accounted for by its enhancement of the vascular permeability and 3) inhibition of gastric motility may be associated with prevention of mucosal lesions.
Udegbunam, E.O.
1991-01-01
This paper presents a FORTRAN program for the determination of two-phase relative permeabilities from unsteady-state displacement data with capillary pressure terms included. The interpretative model employed in this program combines the simultaneous solution of a variant of the fractional flow equation which includes a capillary pressure term and an integro-differential equation derived from Darcy's law without assuming the simplified Buckley-Leverett flow. The incorporation of capillary pressure in the governing equations dispenses with the high flowrate experimental requirements normally employed to overcome capillarity effects. An illustrative example is presented herein which implements this program for the determination of oil/water relative permeabilities from a sandstone core sample. Results obtained compares favorably with results previously given in the literature. ?? 1991.
Dehoff, Karl J.; Oostrom, Martinus; Zhang, Changyong; Grate, Jay W.
2012-10-29
A series of displacement experiments was conducted using five wetting-nonwetting immiscible fluid pairs in a homogenous and uniform pore network. The micromodel was initially saturated with either polyethylene glycol 200 (PEG) or water as a wetting fluid, which was subsequently displaced by a nonwetting fluid (dodecane, hexadecane, or mineral oil) at different flow rates. The experiments were designed to allow determinations of nonwetting fluid relative permeabilities ( ), fluid saturations ( ), and capillary pressure heads ( ). In the displacements, nonwetting fluid saturations increased with increasing flow rates for all five fluid pairs, and viscous fingering, capillary fingering, and stable displacement were observed. Viscous fingering occurred when PEG was displaced by either dodecane or hexadecane. For the water displacements, capillary fingers were observed at low capillary numbers. Due to unstable fingering phenomena, values for the PEG displacements were smaller than for the water displacements. A fitting exercise using the Brooks-Corey (1964) relationship showed that the fitted entry pressure heads are reasonably close to the computed entry pressure head. The fitted pore geometry factor, S_{n} values for the displacements are considerably lower than what is expected for displacements in homogeneous, highly uniform, porous systems, demonstrating the impact of unstable displacement on the apparent value of S_{n}. It was shown that a continuum-based multiphase model could be used to predict the average behavior for wetting fluid drainage in a pore network as long as independently fitted - and - relations are used. The use of a coupled approach through the Brooks-Corey pore geometry factor underpredicts observed values.
NASA Astrophysics Data System (ADS)
Hayek, Mohamed
2014-09-01
The paper presents certain exact solutions describing the vertical movement of a water pulse through a semi-infinite unsaturated porous column. The saturation-based form of the Richards' equation is used with special power law relative-permeability functions. Both capillary and gravity effects are taken into account. Three exact solutions are derived corresponding to three relative-permeability functions, linear, quadratic and cubic. The Richards' equation is nonlinear for the three cases. The solutions are obtained by applying a general similarity transformation. They are explicit in space and time variables and do not contain any approximation. They describe the evolution of the water saturation in the vertical column and they can be used to predict the post-infiltration movement of a finite quantity of water. Exact expressions of the masses of water leaving a given depth are also derived for the three cases. We analyze the effect of relative-permeability and capillary pressure. The proposed solutions are also useful for checking numerical schemes. One of the exact solutions is used to validate numerical solution obtained from an arbitrary initial condition. Results show that the numerical solution converges to the exact solution for large times.
Elimadi, A; Bouillot, L; Sapena, R; Tillement, J P; Morin, D
1998-05-01
We investigated the effects of cinnarizine and flunarizine on mitochondrial permeability transition, ATP synthesis, membrane potential and NAD(P)H oxidation. Both drugs were effective in inhibiting the mitochondrial permeability transition induced either by Ca2+ alone or in the presence of tert-butylhydroperoxide. This protective effect occurred at low concentrations (< 50 microM) of these drugs and was accompanied by the inhibition of NAD(P)H oxidation and the restoration of the mitochondrial membrane potential decreased by a high concentration of Ca2+ (25 microM). However, at higher concentrations (> 50 microM) of cinnarizine and flunarizine and in the absence of both tert-butylhydroperoxide and Ca2+, their effects on the mitochondria were reversed as follows: mitochondrial permeability transition was generated, mitochondrial NAD(P)H was oxidized and membrane potential collapsed. These deleterious effects were not antagonized by cyclosporine A, the most potent inhibitor of the mitochondrial permeability transition, but by 2,6-di-tert-butyl-4-methylphenol, a known antioxidant agent. This mitochondrial effect was neither accompanied by an increase in malondialdehyde production nor by an increase in H2O2 generation, which attested that the effect of both drugs was not due to an increase in reactive oxygen species production. The dual effects of both cinnarizine and flunarizine on mitochondrial functions is discussed with regard to both the protective effect afforded by these drugs against ischemia-reperfusion injury and their side effect observed in some therapeutic situations where an overdosage seems likely.
THE RELATION OF HYDROSTATIC PRESSURE TO THE GRADIENT OF CAPILLARY PERMEABILITY
McMaster, Philip D.; Hudack, Stephen; Rous, Peyton
1932-01-01
The gradient of permeability along the capillaries of voluntary muscle and the capillaries and venules of skin exists independently of the hydrostatic conditions, though influenced by them. Its presence cannot be explained by a graded tonic contraction of the capillaries. The evidence,—like that of previous papers,—points to local differences in the barrier offered by the wall of these vessels as responsible for the gradient. PMID:19869986
Ballelos, E.E.
1982-01-01
This study was designed to investigate the effects of wholebody X-irradiation on the fibrinolytic system, the causes of radiation-induced changes in plasmin (fibrinolytic) activity, and the contribution of increased plasmin activity to increased capillary (endothelial) permeability and hemorrhagic diathesis. The parameters evaluated using adult, male, Rochester ex-Wistar rats were: (1) plasmin, plasminogen, and plasminogen activator levels in plasma within one month after 425, 655, or 885 rad and at 3.5, 7 and 12 months after 425 rad, by a modified caseinolytic method; (2) tissue plasminogen activator activity (TPAA) in heart, kidneys, lungs, liver, pancreas and spleen, by a fibrin plate method (885 rad); (3) vascular permeability, by a radioisotopic method (885 rad); and (4) gross hemorrhagic response, scored for severity. The dose-dependent changes described in plasmin, plasminogen and plasminogen activator were multi-phasic. Epsilon-amino-caproic acid (0.3 gm/kg body weight) prevented the immediate and early radiation effects on these fibrinolytic components, and partially inhibited the later effects (within one month) whether administered only as a single injection before irradiation or maintained by daily water intake thereafter. The kidneys, spleen and pancreas were markedly susceptible to radiation-induced changes in TPAA. The lungs and liver showed significant changes in capillary permeability, which correlated positively with changes in vascular volume and blood plasmin and plasminogen activator levels. Increased plasmin (fibrinolytic) activity, superimposed on a hemostatic apparatus already impaired because of thrombocytopenia, contributed to hemorrhagic diathesis in acute radiation sickness.
Malykh, O V; Golub, A Yu; Teplyakov, V V
2011-05-11
Membrane gas separation technologies (air separation, hydrogen recovery from dehydrogenation processes, etc.) use traditionally the glassy polymer membranes with dominating permeability of "small" gas molecules. For this purposes the membranes based on the low free volume glassy polymers (e.g., polysulfone, tetrabromopolycarbonate and polyimides) are used. On the other hand, an application of membrane methods for VOCs and some toxic gas recovery from air, separation of the lower hydrocarbons containing mixtures (in petrochemistry and oil refining) needs the membranes with preferable penetration of components with relatively larger molecular sizes. In general, this kind of permeability is characterized for rubbers and for the high free volume glassy polymers. Data files accumulated (more than 1500 polymeric materials) represent the region of parameters "inside" of these "boundaries." Two main approaches to the prediction of gas permeability of polymers are considered in this paper: (1) the statistical treatment of published transport parameters of polymers and (2) the prediction using model of ≪diffusion jump≫ with consideration of the key properties of the diffusing molecule and polymeric matrix. In the frames of (1) the paper presents N-dimensional methods of the gas permeability estimation of polymers using the correlations "selectivity/permeability." It is found that the optimal accuracy of prediction is provided at n=4. In the frames of the solution-diffusion mechanism (2) the key properties include the effective molecular cross-section of penetrating species to be responsible for molecular transportation in polymeric matrix and the well known force constant (ε/k)(eff i) of {6-12} potential for gas-gas interaction. Set of corrected effective molecular cross-section of penetrant including noble gases (He, Ne, Ar, Kr, Xe), permanent gases (H(2), O(2), N(2), CO), ballast and toxic gases (CO(2), NO(,) NO(2), SO(2), H(2)S) and linear lower hydrocarbons (CH(4
Oláh, Gáspár; Herédi, Judit; Menyhárt, Ákos; Czinege, Zsolt; Nagy, Dávid; Fuzik, János; Kocsis, Kitti; Knapp, Levente; Krucsó, Erika; Gellért, Levente; Kis, Zsolt; Farkas, Tamás; Fülöp, Ferenc; Párdutz, Árpád; Tajti, János; Vécsei, László; Toldi, József
2013-01-01
Cortical spreading depression (CSD) involves a slowly-propagating depolarization wave in the cortex, which can appear in numerous pathophysiological conditions, such as migraine with aura, stroke, and traumatic brain injury. Neurons and glial cells are also depolarized transiently during the phenomena. CSD is followed by a massive increase in glutamate release and by changes in the brain microcirculation. The aim of this study was to investigate the effects of two N-methyl-D-aspartate receptor antagonists, endogenous kynurenic acid (KYNA) and dizocilpine, on CSD and the related blood–brain barrier (BBB) permeability in rats. In intact animals, KYNA hardly crosses the BBB but has some positive features as compared with its precursor L-Kynurenine, which is frequently used in animal studies (KYNA cannot be metabolized to excitotoxic agents such as 3-hydroxy-L-kynurenine and quinolinic acid). We therefore investigated the possible effects of peripherally administered KYNA. Repetitive CSD waves were elicited by the application of 1 M KCl solution to the cortex. Direct current-electrocorticograms were measured for 1 hour. Four parameters of the waves were compared. Evans blue dye and fluorescent microscopy were used to study the possible changes in the permeability of the BBB. The results demonstrated that N-methyl-D-aspartate receptor antagonists can reduce the number of CSD waves and decrease the permeability of the BBB during CSD. These results suggest that KYNA itself or its derivatives may offer a new approach in the therapy of migraines. PMID:24068867
Relating damage evolution of concrete cooled to cryogenic temperatures to permeability
NASA Astrophysics Data System (ADS)
Kogbara, Reginald B.; Iyengar, Srinath R.; Grasley, Zachary C.; Rahman, Syeda; Masad, Eyad A.; Zollinger, Dan G.
2014-11-01
Typically, 9% Ni steel is used for primary containment of liquefied natural gas (LNG). Utilization of concrete in place of 9% Ni steel for primary containment would lead to significant cost savings. Hence, this study investigates changes in the microstructure of concrete due to cryogenic freezing that would affect its relevant engineering properties for containment. The study also evaluates the effect of aggregate type on the damage potential of concrete subjected to cryogenic freezing. The aim is to investigate design methodologies to produce damage-resistant cryogenic concrete. The study employed four concrete mixture designs involving river sand as fine aggregate, and coarse aggregates with different coefficient of thermal expansion (CTE) values. Specifically, the coarse aggregates were limestone, sandstone, trap rock and lightweight aggregate. Concrete cubes were cured under water for at least 28 days and thereafter frozen from ambient (20 °C) to cryogenic temperature (-165 °C). Acoustic emission (AE) sensors were placed on the concrete cubes during freezing. X-ray computed tomography (XRCT) was employed to study the microstructure of concrete cores, before and after cryogenic freezing. The impact of the microstructural evolution thus obtained from AE and XRCT on relevant engineering properties was determined via water and chloride permeability tests. Microcrack propagation determined from AE correlated with changes in permeability. There were no observable cracks in majority of the concrete mixtures after freezing. This implies that microcracks detected via AE and increased permeability was very well distributed and smaller than the XRCT's resolution. Damage (microcracking) resistance of the concrete with different aggregates was in the order limestone ⩾ trap rock ≫ lightweight aggregate ⩾ sandstone.
Karande, Tejas S; Ong, Joo L; Agrawal, C Mauli
2004-12-01
The field of tissue engineering continues to advance with the discovery of new biomaterials, growth factors and scaffold fabrication techniques. However, for the ultimate success of a tissue engineered construct the issue of nutrient transport to the scaffold interior needs to be addressed. Often, the requirements for adequate nutrient supply are at odds with other scaffold design parameters such as mechanical properties as well as scaffold fabrication techniques, leading to incongruities in finding optimal solutions. The goal of this review article is to provide an overview of the various engineering design factors that promote movement of nutrients, waste and other biomolecules in scaffolds for musculoskeletal tissue engineering applications. The importance of diffusion in scaffolds and how it is influenced by porosity, permeability, architecture, and nutrient mixing has been emphasized. Methods for measuring porosity and permeability have also been outlined. The different types of biomaterials used, scaffold fabrication techniques implemented and the pore sizes/porosities obtained over the past 5 years have also been addressed.
Bouzerar, Roger; Chaarani, Bader; Gondry-Jouet, Catherine; Zmudka, Jadwiga; Balédent, Olivier
2013-12-01
The cerebrospinal fluid (CSF) plays a major role in the physiology of the central nervous system. The continuous turnover of CSF is mainly attributed to the highly vascularized choroid plexus (CP) located in the cerebral ventricles which represent a complex interface between blood and CSF. We propose a method for evaluating CP functionality in vivo using perfusion MR imaging and establish the age-related changes of associated parameters. Fifteen patients with small intracranial tumors were retrospectively studied. MR Imaging was performed on a 3T MR Scanner. Gradient-echo echo planar images were acquired after bolus injection of gadolinium-based contrast agent (CA). The software developed used the combined T1- and T2-effects. The decomposition of the relaxivity signals enables the calculation of the CP capillary permeability (K2). The relative cerebral blood volume (rCBV), mean transit time (MTT), and signal slope decrease (SSD) were also calculated. The mean permeability K2 of the extracted CP was 0.033+/-0.18 s(-1). K2 and SSD significantly decreased with subject's age whereas MTT significantly increased with subject's age. No significant correlation was found for age-related changes in rCBV and rCBF. The decrease in CP permeability is in line with the age-related changes in CSF secretion observed in animals. The MTT increase indicates significant structural changes corroborated by microscopy studies in animals or humans. Overall, DSC MR-perfusion enables an in vivo evaluation of the hemodynamic state of CP. Clinical applications such as neurodegenerative diseases could be considered thanks to specific functional studies of CP.
Naderkhani, Elenaz; Vasskog, Terje; Flaten, Gøril Eide
2015-06-20
A prerequisite for successful oral drug therapy is the drug's ability to cross the gastrointestinal barrier. Considering the increasing number of new chemical entities in modern drug discovery, reliable and fast in vitro models are required for early and efficient prediction of intestinal permeability. To mimic the intestinal environment, use of biorelevant media may provide valuable information on in vivo drug permeation. The present study aims at improving the novel biomimetic phospholipid vesicle-based permeation assay's (PVPAbiomimetic) biorelevance by investigating the applicability of the biorelevant media; fasted state simulated intestinal fluid (FaSSIF) and fed state simulated intestinal fluid (FeSSIF). The FaSSIF and FeSSIF's influence on the permeability of the model drugs acyclovir, indomethacin, griseofulvin and nadolol was then assessed. The barriers' robustness in terms of storage stability was also evaluated. The barriers were found to maintain their integrity in presence of FaSSIF and FeSSIF. The model drugs showed changes in permeability in presence of the different simulated intestinal fluids that were in agreement with previous reports. Moreover, the barrier showed improved storage stability by maintaining its integrity for 6months. Altogether, this study moves the PVPAbiomimetic an important step towards a better in vitro permeability model for use in drug development.
NASA Astrophysics Data System (ADS)
Dotsenko, O. A.; Suslyaev, V. I.; Frolov, K. O.; Zhuravlyova, E. V.
2017-01-01
The frequency dependences of the magnetic permeability of textured composite based on Ba3Co2,4Fe23,2O41 ferrite are given. The magnetic permeability spectra were obtained by coaxial method in the frequency range 0.01–18 GHz. The expert judgement on the spectra was made by using Cramers – Kronig relations. It was shown, that the Cramers – Kronig relations can be used to correct magnetic permeability measurements by reciprocal recalculation of the frequency dependences of the real and imaginary parts.
Dunn, T.L.
1996-03-01
This research is to provide improved strategies for enhanced oil recovery from the Tensleep Sandstone oil reservoirs in the Bighorn and Wind River basins, Wyoming. Because of the great range of API gravities of the oils produced from these reservoirs, the proposed study concentrates on understanding the spatial variation and anisotropy of relative permeability within the Tensleep Sandstone. This research will associate those spatial distributions and anisotropies with the depositional subfacies and zones of diagenetic alteration found within the sandstone. The associations of the above with pore geometry will link relative permeability with the dimensions of lithofacies and authigenic mineral facies. Hence, the study is to provide criteria for scaling this parameter on a range of scales, from the laboratory to the basin-wide scale of subfacies distribution. Effects of depositional processes and burial diagenesis will be investigated. Image analysis of pore systems will be done to produce algorithms for estimating relative permeability from petrographic analyses of core and well cuttings. In addition, these studies are being coupled with geochemical modeling and coreflood experiments to investigate the potential for wellbore scaling and formation damage anticipated during EOR, eg., CO{sub 2} flooding. This will provide a regional basis for EOR strategies for the largest potential target reservoir in Wyoming; results will have application to all eolian reservoirs through correlations of relative permeability variation and anisotropy with eolian depositional lithofacies.
Cancer Related-Knowledge - Small Area Estimates
These model-based estimates are produced using statistical models that combine data from the Health Information National Trends Survey, and auxiliary variables obtained from relevant sources and borrow strength from other areas with similar characteristics.
NASA Astrophysics Data System (ADS)
Konno, Y.; Jin, Y.; Nagao, J.
2012-04-01
Oceanic gas hydrate deposits at high saturations have been found within sandy sediments in areas such as the Eastern Nankai Trough and the Gulf of Mexico. The recent discovery of these deposits has stimulated research and development programs exploring the use of gas hydrates as energy resources. Depressurization is thought to be a promising method for gas recovery from gas hydrates deposits; however, considerable water production is expected when this method is applied for oceanic gas hydrate deposits. The prediction of water production is a critical problem for successful gas production from these deposits. The gas-water relative permeability of gas-hydrate-bearing sediments is a key parameter to predict gas-water-ratio (GWR) during gas production. However, the experimental measurement of gas-water relative permeability for gas-hydrate-bearing sediments is a challenging problem due to a phase change (gas hydrate formation/dissociation) during gas-water flooding test. We used X-ray computed tomography (CT) and a newly-developed core holder to measure gas-water relative permeability for gas-hydrate-bearing sediments. X-ray CT was used to image a displacement front and quantify density changes during water flooding test in methane-hydrate-bearing cores. We obtained CT images every two minutes during a water flooding test for a gas-saturated methane-hydrate-bearing core. The movement of displacement front was captured from these CT images. Quantitative analysis of density change was also done to analyze the change of gas/water saturations. We developed a multi-sensor-tap core holder to minimize capillary end effect on the pressure measurements. To be able to obtain CT images by X-ray, the core holder was made of aluminum alloy. We successfully measured pressure differences of the intermediate section of the core during water flooding test. The change of pressure differences during water flooding test showed strong correlation with the movement of displacement front
NASA Astrophysics Data System (ADS)
Vogt, C.; Marquart, G.; Kosack, C.; Wolf, A.; Clauser, C.
2012-08-01
We present an estimation of the permeability fields of the reservoir at the Enhanced Geothermal System (EGS) at Soultz-sous-Forêts, France, based on the data assimilation technique Ensemble Kalman Filter (EnKF). To this end, we assimilate data from a tracer circulation experiment performed in 2005. Using a 3-D numerical simulation of fluid transport and chemical tracer dispersion, we advance the tracer in time and control the concentration. With the EnKF we obtain reliable fits for concentration data recorded in both existing production boreholes, GPK2 and GPK4. As an alternative to discrete fracture networks, our heterogeneous equivalent porous medium approach thus can also characterize the hydraulically fractured zone of the engineered geothermal system. We present best estimates for permeabilities (10-14 m2-10-12 m2for the fracture zone) and the corresponding uncertainty which is about one order of magnitude. After comparing our results to results from a massive Monte Carlo and from a gradient-based Bayesian approach, it becomes clear that only the EnKF of this three approaches is able to fit concentrations at GPK2 and GPK4 simultaneously. Based on the EnKF estimates obtained, a long-term performance prediction including an uncertainty analysis for the reservoir (as it was in 2005) yields no thermal breakthrough in the system within at least 50 years of operation. Our study demonstrates the efficiency of the EnKF when estimating the permeability distribution in an EGS reservoir even with sparse data available.
Gleeson, Tom; Ingebritsen, Steven E.
2016-01-01
Permeability is the primary control on fluid flow in the Earth’s crust and is key to a surprisingly wide range of geological processes, because it controls the advection of heat and solutes and the generation of anomalous pore pressures. The practical importance of permeability – and the potential for large, dynamic changes in permeability – is highlighted by ongoing issues associated with hydraulic fracturing for hydrocarbon production (“fracking”), enhanced geothermal systems, and geologic carbon sequestration. Although there are thousands of research papers on crustal permeability, this is the first book-length treatment. This book bridges the historical dichotomy between the hydrogeologic perspective of permeability as a static material property and the perspective of other Earth scientists who have long recognized permeability as a dynamic parameter that changes in response to tectonism, fluid production, and geochemical reactions.
EXPOSURE RELATED DOSE ESTIMATING MODEL (ERDEM)
ERDEM is a physiologically-based pharmacokinetic (PBPK) model with a graphical user interface (GUI) front end. Such a mathematical model was needed to make reliable estimates of the chemical dose to organs of animals or humans because of uncertainties of making route-to route, lo...
EXPOSURE RELATED DOSE ESTIMATING MODEL (ERDEM)
ERDEM is a physiologically-based pharmacokinetic (PBPK) model with a graphical user interface (GUI) front end. Such a mathematical model was needed to make reliable estimates of the chemical dose to organs of animals or humans because of uncertainties of making route-to route, lo...
Powers, M.R.; Wallace, J.R.; Bell, D.R.
1986-03-05
The initial equilibration of /sup 125/I-labelled albumin between the vascular and extravascular compartments was studied in hindpaw heel skin of anesthetized rabbits. Bradykinin (0.3 ..mu..g/min) was infused into a small branch of the femoral artery. A second group of rabbits served as control. Following bradykinin, prenodal popliteal lymph flow was 4 times control flow. The lymph-to-plasma concentration ratios for total protein and albumin were, respectively, 60% and 50% larger than control. Tissue albumin concentration was twice control. After reaching a steady, elevated lymph flow, tracer albumin was infused to maintain plasma activity constant for 3 hrs. The plasma volume in tissue samples was measured using /sup 131/I-labeled albumin injected 10 min before ending the experiment. Endogenous albumin was measured in plasma, lymph, and tissue samples using rocket electroimmunoassay. After 3 hrs of tracer infusion, lymph specific activity was 3 times greater than control. In the control group, plasma albumin equilibrated more rapidly with lymph than with tissue (p < 0.05). Following bradykinin, extravascular specific activity was 4 times control, resulting in lymph and tissue equilibrating with plasma at similar rates. Thus, increasing capillary permeability causes the extravascular albumin mass to behave as if distributed in a single compartment.
NASA Astrophysics Data System (ADS)
Ishitsuka, Kazuya; Matsuoka, Toshifumi; Nishimura, Takuya; Tsuji, Takeshi; ElGharbawi, Tamer
2017-06-01
We investigated the post-seismic surface displacement of the 2011 Tohoku earthquake around the Kanto Plain (including the capital area of Japan), which is located approximately 400 km from the epicenter, using a global positioning system network during 2005-2015 and persistent scatterer interferometry of TerraSAR-X data from March 2011 to November 2012. Uniform uplift owing to viscoelastic relaxation and afterslip on the plain has been reported previously. In addition to the general trend, we identified areas where the surface displacement velocity was faster than the surrounding areas, as much as 7 mm/year for 3 years after the earthquake and with a velocity decay over time. Local uplift areas were 30 × 50 km2 and showed a complex spatial distribution with an irregular shape. Based on an observed groundwater level increase, we deduce that the local ground uplift was induced by a permeability enhancement and a pore pressure increase in the aquifer system, which is attributable to mainshock vibration.[Figure not available: see fulltext.
Farahmand, Sara; Maibach, Howard I
2009-06-22
This study evaluates the correlation of some widely used skin permeability predictive models with a recently proposed empirical model based on human in vivo dermatopharmacokinetic data. Drug fluxes through the skin have been calculated using in vitro- and in vivo-based models, and observed in vivo data, and the values compared. Most in vitro-based models underestimate the in vivo data by 1-100-fold. The discrepancy between observed data and prediction reaches the maximum (1000-10,000-fold underestimation) for nicotine (with the smallest molecular weight and logK(oct)), nitroglycerin (with the largest number of hydrogen bond acceptor groups), and for oxybutynin (with the largest molecular weight and logK(oct)) where there was a 1000-fold flux overestimation. However, most models correlated well with the in vivo data and the in vivo-based model (p<0.05). The vehicle effect and using non-steady state in vivo data in the flux calculations partly account for the observed discrepancies between predicted and observed values. Nevertheless, these results reveal the need for further refinement of skin permeability predictive equations, using the steady state in vivo data, and consideration of formulation effect.
Relating space radiation environments to risk estimates
NASA Technical Reports Server (NTRS)
Curtis, Stanley B.
1993-01-01
A number of considerations must go into the process of determining the risk of deleterious effects of space radiation to travelers. Among them are (1) determination of the components of the radiation environment (particle species, fluxes and energy spectra) which will encounter, (2) determination of the effects of shielding provided by the spacecraft and the bodies of the travelers which modify the incident particle spectra and mix of particles, and (3) determination of relevant biological effects of the radiation in the organs of interest. The latter can then lead to an estimation of risk from a given space scenario. Clearly, the process spans many scientific disciplines from solar and cosmic ray physics to radiation transport theeory to the multistage problem of the induction by radiation of initial lesions in living material and their evolution via physical, chemical, and biological processes at the molecular, cellular, and tissue levels to produce the end point of importance.
NASA Astrophysics Data System (ADS)
Cavé, Lisa; Al, Tom; Xiang, Yan; Vilks, Peter
2009-01-01
The measurement of diffusive properties of low-permeability rocks is of interest to the nuclear power industry, which is considering the option of deep geologic repositories for management of radioactive waste. We present a simple, non-destructive, constant source in-diffusion method for estimating one-dimensional pore diffusion coefficients ( Dp) in geologic materials based on X-ray radiography. Changes in X-ray absorption coefficient (Δ μ) are used to quantify changes in relative concentration ( C/ C0) of an X-ray attenuating iodide tracer as the tracer solution diffuses through the rock pores. Estimated values of Dp are then obtained by fitting an analytical solution to the measured concentration profiles over time. Measurements on samples before and after saturation with iodide can also be used to determine iodide-accessible porosity (ϕ I). To evaluate the radiography method, results were compared with traditional steady-state through-diffusion measurements on two rock types: shale and limestone. Values of Dp of (4.8 ± 2.5) × 10 - 11 m 2·s - 1 (mean ± standard deviation) were measured for samples of Queenston Formation shale and (2.6 ± 1.0) × 10 - 11 m 2·s - 1 for samples of Cobourg Formation limestone using the radiography method. The range of results for each rock type agree well with Dp values of (4.6 ± 2.0) × 10 - 11 m 2·s - 1 for shale and (3.5 ± 1.8) × 10 - 11 m 2·s - 1 for limestone, calculated from through-diffusion experiments on adjacent rock samples. Low porosity (0.01 to 0.03) and heterogeneous distribution of porosity in the Cobourg Formation may be responsible for the slightly poorer agreement between radiography and through-diffusion results for limestones. Mean values of ϕ I for shales (0.060) and limestones (0.028) were close to mean porosity measurements made on bulk samples by the independent water loss technique (0.062 and 0.020 for shales and limestones, respectively). Radiography measurements offer the advantage of time
Cavé, Lisa; Al, Tom; Xiang, Yan; Vilks, Peter
2009-01-07
The measurement of diffusive properties of low-permeability rocks is of interest to the nuclear power industry, which is considering the option of deep geologic repositories for management of radioactive waste. We present a simple, non-destructive, constant source in-diffusion method for estimating one-dimensional pore diffusion coefficients (D(p)) in geologic materials based on X-ray radiography. Changes in X-ray absorption coefficient (Deltamicro) are used to quantify changes in relative concentration (C/C(0)) of an X-ray attenuating iodide tracer as the tracer solution diffuses through the rock pores. Estimated values of D(p) are then obtained by fitting an analytical solution to the measured concentration profiles over time. Measurements on samples before and after saturation with iodide can also be used to determine iodide-accessible porosity (phi(I)). To evaluate the radiography method, results were compared with traditional steady-state through-diffusion measurements on two rock types: shale and limestone. Values of D(p) of (4.8+/-2.5)x10(-11) m(2).s(-1) (mean+/-standard deviation) were measured for samples of Queenston Formation shale and (2.6+/-1.0)x10(-11) m(2).s(-1) for samples of Cobourg Formation limestone using the radiography method. The range of results for each rock type agree well with D(p) values of (4.6+/-2.0)x10(-11) m(2).s(-1) for shale and (3.5+/-1.8)x10(-11) m(2).s(-1) for limestone, calculated from through-diffusion experiments on adjacent rock samples. Low porosity (0.01 to 0.03) and heterogeneous distribution of porosity in the Cobourg Formation may be responsible for the slightly poorer agreement between radiography and through-diffusion results for limestones. Mean values of phi(I) for shales (0.060) and limestones (0.028) were close to mean porosity measurements made on bulk samples by the independent water loss technique (0.062 and 0.020 for shales and limestones, respectively). Radiography measurements offer the advantage of time
NASA Astrophysics Data System (ADS)
Landry, C. J.; Karpyn, Z. T.; Ayala, O.
2014-05-01
We present a pore-scale study of two-phase relative permeability in homogenous-wet porous media, and porous media altered to a mixed-wet state. A Shan-Chen type multicomponent lattice Boltzmann (LB) model is employed to determine pore-scale fluid distributions and relative permeability. Mixed-wet states are created by altering the wettability of solid surfaces in contact with the nonwetting phase at the end of steady state simulation of initially homogenous-wet porous media. To ensure accurate representation of fluid-solid interfacial areas, we compare LB simulation results to experimental measurements of interfacial fluid-fluid and fluid-solid areas determined by X-ray computed microtomography imaging of water and oil distributions in bead packs. The LB simulations are found to match experimental trends observed for fluid-fluid and fluid-solid interfacial area-saturation relationships. The relative permeability of both fluids in the homogenous-wet porous media was found to decrease with a decreasing contact angle. The relative permeability of both fluids in the altered, mixed-wet porous media was found to decrease for all mixed-wet states in comparison to the initial homogenous-wet states. The nonwetting phase relative permeability decreased significantly, while the wetting phase experienced only a minor decrease. The significance of the decrease was found to be dependent on the distribution of the unaltered solid surfaces, with less dependence on the severity of alteration.
The quantitative estimation of IT-related risk probabilities.
Herrmann, Andrea
2013-08-01
How well can people estimate IT-related risk? Although estimating risk is a fundamental activity in software management and risk is the basis for many decisions, little is known about how well IT-related risk can be estimated at all. Therefore, we executed a risk estimation experiment with 36 participants. They estimated the probabilities of IT-related risks and we investigated the effect of the following factors on the quality of the risk estimation: the estimator's age, work experience in computing, (self-reported) safety awareness and previous experience with this risk, the absolute value of the risk's probability, and the effect of knowing the estimates of the other participants (see: Delphi method). Our main findings are: risk probabilities are difficult to estimate. Younger and inexperienced estimators were not significantly worse than older and more experienced estimators, but the older and more experienced subjects better used the knowledge gained by knowing the other estimators' results. Persons with higher safety awareness tend to overestimate risk probabilities, but can better estimate ordinal ranks of risk probabilities. Previous own experience with a risk leads to an overestimation of its probability (unlike in other fields like medicine or disasters, where experience with a disease leads to more realistic probability estimates and nonexperience to an underestimation).
NASA Astrophysics Data System (ADS)
Feldman, J.; Dewers, T. A.; Heath, J. E.; Cather, M.; Mozley, P.
2016-12-01
Multiphase flow in clay-bearing sandstones of the Morrow Sandstone governs the efficiency of CO2 storage and enhanced oil recovery at the Farnsworth Unit, Texas. This formation is the target for enhanced oil recovery and injection of one million metric ton of anthropogenically-sourced CO2. The sandstone hosts eight major flow units that exhibit distinct microstructural characteristics due to diagenesis, including: "clean" macro-porosity; quartz overgrowths constricting some pores; ghost grains; intergranular porosity filled by microporous authigenic clay; and feldspar dissolution. We examine the microstructural controls on macroscale (core scale) relative permeability and capillary pressure behavior through: X-ray computed tomography, Robomet.3d, and focused ion beam-scanning electron microscopy imaging of the pore structure of the major flow units of the Morrow Sandstone; relative permeability and capillary pressure in the laboratory using CO2, brine, and oil at reservoir pressure and effective stress conditions. The combined data sets inform links between patterns of diagenesis and multiphase flow. These data support multiphase reservoir simulation and performance assessment by the Southwest Regional Partnership on Carbon Sequestration (SWP). Funding for this project is provided by the U.S. Department of Energy's National Energy Technology Laboratory through the SWP under Award No. DE-FC26-05NT42591. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
NASA Astrophysics Data System (ADS)
Darwish, M. A.; Saafan, S. A.; El-Kony, D.; Salahuddin, N. A.
2015-07-01
Ferrite nanoparticles - having the compositions Li(x/2)(Ni0.5Zn0.5)(1-x)Fe(2+x/2)O4 (x=0, 0.2, 0.3) - have been prepared by the co-precipitation method. The prepared powders have been divided into groups and sintered at different temperatures (373 K, 1074 K and 1473 K). X-Ray diffraction analysis (XRD) for all samples has confirmed the formation of the desired ferrites with crystallite sizes within the nanoscale (<100 nm). The dc conductivity, the relative permeability and the magnetization of the ferrite samples have been investigated and according to the results, the sample Li0.15(Ni0.5Zn0.5)0.7 Fe2.15O4 sintered at 1473 K has been chosen to prepare the composites. The particle size of this sample has been recalculated by using JEOL JEM-100SX transmission electron microscope and it has been found about 64.7 nm. Then, a pure epoxy sample and four pristine epoxy resin /Li0.15(Ni0.5Zn0.5)0.7 Fe2.15O4 composites have been prepared using different ferrite contents (20%, 30%, 40%, and 50%) wt.%. These samples have been characterized by Fourier transform infrared (FTIR) spectroscopy and their dc conductivity, relative permeability and magnetization have also been investigated. The obtained results indicate that the investigated composites may be promising candidates for practical applications such as EMI suppressor and high frequency applications.
Prat, C; Bouvier, D; Comptour, A; Marceau, G; Belville, C; Clairefond, G; Blanc, P; Gallot, D; Blanchon, L; Sapin, V
2015-08-01
The aquaporins (AQP1, 3, 8, 9 and 11) are known to be expressed, and involved in the transport of water and small molecules through fetal membranes. To exert these crucial functions, these AQPs have to be finely regulated. All-trans-retinoic acid (atRA) was previously found to regulate some genes in this environment, raising the question of whether these AQPs were regulated by atRA. Explants, and primary and established amniotic cells were cultured to determine which AQP were transcriptionally modified by atRA, using the qRT-PCR strategy. Immunohistochemistry and glycerol uptake tests were used to determine the impact of atRA on AQP protein expression and function. Specific agonists of retinoic acid receptors were used to identify the molecular mechanisms of AQP promoter activation. A classical gene AQP promoter study was also used to identify DR5 retinoic acid receptor elements (RAREs). Beyond these AQPs, only one specific atRA-dependent increase in AQP3 transcripts and proteins level was established in amnion (not in chorion) and in related primary and established cells. We found three DR5-RAREs essential for inducing this transcriptional AQP3 through RARα. This transactivation of the AQP3 coding gene was functionally related to an increase of AQP3 permeability tests by a glycerol uptake assay. Our data support an atRA regulatory model of AQP3 expression leading to an increased cellular permeability in the epithelial amniotic environment. We cast new light on AF regulation in healthy pregnancy, and advance new hypotheses for obstetrical complications linked to impairment of the retinoic signaling pathway. Copyright © 2015 Elsevier Ltd. All rights reserved.
Schroeder, Hobe J.; Kanda, Eriko; Power, Gordon G.; Blood, Arlin B.
2016-01-01
Introduction Nitrite conveys NO-bioactivity that may contribute to the high-flow, low-resistance character of the fetal circulation. Fetal blood nitrite concentrations depend partly on placental permeability which has not been determined experimentally. We aimed to extract the placental permeability-surface (PS) product for nitrite in sheep from a computational model. Methods An eight-compartment computational model of the fetal-maternal unit was constructed (Matlab® (R2013b (8.2.0.701), MathWorks Inc., Natick, MA). Taking into account fetal and maternal body weights, four variables (PS, the rate of nitrite metabolism within red cells, and two nitrite distribution volumes, one with and one without nitrite metabolism), were varied to obtain optimal fits to the experimental plasma nitrite profiles observed following the infusion of nitrite into either the fetus (n=7) or the ewe (n=8). Results The model was able to replicate the average and individual nitrite-time profiles (r2 > 0.93) following both fetal and maternal nitrite infusions with reasonable variation of the four fitting parameters. Simulated transplacental nitrite fluxes were able to predict umbilical arterial-venous nitrite concentration differences that agreed with experimental values. The predicted PS values for a 3 kg sheep fetus were 0.024±0.005 l·min−1 in the fetal-maternal direction and 0.025±0.003 l·min−1 in the maternal-fetal direction (mean±SEM). These values are many-fold higher than the reported PS product for chloride anions across the sheep placenta. Conclusion The result suggests a transfer of nitrite across the sheep placenta that is not exclusively by simple diffusion through water-filled channels. PMID:26907384
Ozeki, Kazuhisa; Kato, Motohiro; Sakurai, Yuuji; Ishigai, Masaki; Kudo, Toshiyuki; Ito, Kiyomi
2015-11-30
In a transcellular transport study, the apparent permeability coefficient (Papp) of a compound is evaluated using the range by which the amount of compound accumulated on the receiver side is assumed to be proportional to time. However, the time profile of the concentration of the compound in receiver (C3) often shows a lag time before reaching the linear range and later changes from linear to steady state. In this study, the linear range needed to calculate Papp in the C3-time profile was evaluated by a 3-compartment model. C3 was described by an equation with two steady states (C3=A3(1-e(-αt))+B3(1-e(-βt)), α>β), and by a simple approximate line (C3=A3-A3×αt) in the time range of 3/α
Bogen, Kenneth T; Singhal, Ankur
2017-02-01
Estimates of dermal permeability (Kp), obtained by fitting an updated human PBPK model for malathion to previously reported data on excreted urinary metabolites after 29 volunteers were dermally exposed to measured values of [(14)C]malathion dermal load (L), were used to examine the empirical relationship between Kp and L. The PBPK model was adapted from previously reported human biokinetic and PBPK models for malathion, fit to previously reported urinary excretion data after oral [(14)C]malathion intake by volunteers, and then augmented to incorporate a standard Kp approach to modeling dermal-uptake kinetics. Good to excellent PBPK-model fits were obtained to all of 29 sets of cumulative urinary metabolite-excretion data (ave. [±1 SD] R(2) = 0.953 [±0.064]). Contrary to the assumption that Kp and L are independent typically applied for dermally administered liquids or solutions, the 29 PBPK-based estimates of Kp obtained for malathion exhibit a strong positive association with the 2/3rds power of L (log-log Pearson correlation = 0.925, p = ∼0). Possible explanations of this observation involving physico-chemical characteristics and/or in vivo cutaneous effects of malathion are discussed. The PBPK model presented, and our observation that Kp estimates obtained by fitting this model to human experimental urinary-excretion data correlate well with L(2/3), allow more realistic assessments of absorbed and metabolized dose during or after a variety of scenarios involving actual or potential dermal or multi-route malathion exposures, including for pesticide workers or farmers who apply malathion to crops.
Damms-Machado, Antje; Louis, Sandrine; Schnitzer, Anna; Volynets, Valentina; Rings, Andreas; Basrai, Maryam; Bischoff, Stephan C
2017-01-01
Obesity and associated metabolic disorders are related to impairments of the intestinal barrier. We examined lactulose:mannitol (Lac:Man) permeability in obese individuals with and without liver steatosis undergoing a weight-reduction program to test whether an effective weight-loss program improves gut barrier function and whether obese patients with or without liver steatosis differ in this function. Twenty-seven adult, nondiabetic individuals [mean ± SD body mass index (BMI; in kg/m(2)): 43.7 ± 5.2; 78% with moderate or severe liver steatosis] were included in the follow-up intervention study (n = 13 by month 12). All patients reduced their weight to a mean ± SD BMI of 36.4 ± 5.1 within 12 mo. We assessed barrier functions by the oral Lac:Man and the fecal zonulin tests. Insulin resistance was assessed by the homeostatic model assessment index (HOMA), and liver steatosis by sonography and the fatty liver index (FLI). The Lac:Man ratio and circulating interleukin (IL) 6 concentration decreased during intervention from 0.080 (95% CI: 0.073, 0.093) to 0.027 (95% CI: 0.024, 0.034; P < 0.001) and from 4.2 ± 1.4 to 2.8 ± 1.6 pg/mL (P < 0.01), respectively. At study start, the Lac:Man ratio was higher in patients with moderate or severe steatosis than in those without any steatosis (P < 0.001). The Lac:Man ratio tended to correlate with HOMA (ρ = 0.55, P = 0.052), which correlated with FLI (ρ = 0.75, P < 0.01). A multiple-regression analysis led to a final model explaining FLI best through BMI, waist circumference, and the Lac:Man ratio. Intestinal permeability is increased in obese patients with steatosis compared with obese patients without. The increased permeability fell to within the previously reported normal range after weight reduction. The data suggest that a leaky gut barrier is linked with liver steatosis and could be a new target for future steatosis therapies. This trial was registered at clinicaltrials.gov as NCT01344525. © 2017 American Society
Relating space radiation environments to risk estimates
Curtis, S.B.
1991-10-01
This lecture will provide a bridge from the physical energy or LET spectra as might be calculated in an organ to the risk of carcinogenesis, a particular concern for extended missions to the moon or beyond to Mars. Topics covered will include (1) LET spectra expected from galactic cosmic rays, (2) probabilities that individual cell nuclei in the body will be hit by heavy galactic cosmic ray particles, (3) the conventional methods of calculating risks from a mixed environment of high and low LET radiation, (4) an alternate method which provides certain advantages using fluence-related risk coefficients (risk cross sections), and (5) directions for future research and development of these ideas.
Relating space radiation environments to risk estimates
Curtis, S.B.
1991-10-01
This lecture will provide a bridge from the physical energy or LET spectra as might be calculated in an organ to the risk of carcinogenesis, a particular concern for extended missions to the moon or beyond to Mars. Topics covered will include (1) LET spectra expected from galactic cosmic rays, (2) probabilities that individual cell nuclei in the body will be hit by heavy galactic cosmic ray particles, (3) the conventional methods of calculating risks from a mixed environment of high and low LET radiation, (4) an alternate method which provides certain advantages using fluence-related risk coefficients (risk cross sections), and (5) directions for future research and development of these ideas.
X-ray aided permeability computations inside compaction bands in sandstones
NASA Astrophysics Data System (ADS)
Andrade, J.; Lenoir, N.; Sun, W.; Rudnicki, J. W.
2009-12-01
This work presents preliminary data on permeability calculations using 3D X-ray tomography images taken inside and outside compaction bands. Aztec sandstone samples are taken from the Valley of Fire in Nevada and are scanned using the synchrotron APS facility at Argonne National Laboratory. The 3D microstructures inside and outside the compaction bands, formed in situ, are then used to perform lattice Boltzmann computations to estimate the components of permeability in different principal directions. We show that i) the permeability component in the direction perpendicular to the compaction band is reduced by orders of magnitude in the presence of a compaction band, ii) inside the compaction band, there is a strong anisotropy manifested by the permeability tensor, and iii) the Kozeny-Carman relation does a pretty good job at estimating the permeability outside of the compaction band, but fails to estimate the reduction in permeability in the presence of compaction bands.
Wang, Yusong; Bradford, Scott A; Šimůnek, Jiří
2014-04-01
Dual-permeability models are increasingly used to quantify the transport of solutes and microorganisms in soils with preferential flow. An ability to accurately determine the model parameters and their variation with preferential pathway characteristics is crucial for predicting the transport of microorganisms in the field. The dual-permeability model with optimized parameters was able to accurately describe the transport of E. coli D21g in columns with artificial macropores of different configurations and lengths at two ionic strength levels (1 and 20mM NaCl). Correlations between the model parameters and the structural geometry of the preferential flow path were subsequently investigated. Decreasing the macropore length produced a decrease in the apparent saturated hydraulic conductivity of the macropore domain and an increase in the mass transfer between the macropore and matrix domains. The mass transfer coefficient was also found to be dependent on the configuration of the preferential flow pathway. A linear superposition approach was used to estimate field-scale preferential transport behavior for hypothetical fields with different amounts and configurations of macropores. Upscaling procedures were numerically investigated to predict this field-scale transport behavior from column-scale parameters. The upscaling method provided a satisfactory prediction of the field results under the tested scenarios. This information will be useful in assessing the risks of microbial transport due to preferential flow.
Soil Water Retention and Relative Permeability for Full Range of Saturation
Zhang, Z. F.
2010-09-28
Common conceptual models for unsaturated flow often rely on the oversimplified representation of medium pores as a bundle of cylindrical capillaries and assume that the matric potential is attributed to capillary forces only. The adsorptive surface forces are ignored. It is often assumed that aqueous flow is negligible when a soil is near or at the residual water content. These models are successful at high and medium water contents but often give poor results at low water contents. These models do not apply to conditions at which water content is less than the residual water content. We extend the lower bound of existing water-retention functions and conductivity models from residual water content to the oven-dry condition (i.e., zero water content) by defining a state-dependent, residual-water content for a soil drier than a critical value. Furthermore, a hydraulic conductivity model for smooth uniform spheres was modified by introducing a correction factor to describe the film flow-induced hydraulic conductivity for natural porous media. The total unsaturated hydraulic conductivity is the sum of those due to capillary and film flow. The extended retention and conductivity models were verified with six datasets from the literature. Results show that, when the soil is at high and intermediate water content, there is no difference between the un-extended and the extended models; when the soil is at low water content, the un-extended models overestimate the water content but under-estimate the conductivity while the extended models match the retention and conductivity measurements well.
Estimating relative bioavailability of soil lead in the mouse.
Bradham, Karen D; Green, William; Hayes, Hunter; Nelson, Clay; Alava, Pradeep; Misenheimer, John; Diamond, Gary L; Thayer, William C; Thomas, David J
2016-01-01
Lead (Pb) in soil is an important exposure source for children. Thus, determining bioavailability of Pb in soil is critical in evaluating risk and selecting appropriate strategies to minimize exposure. A mouse model was developed to estimate relative bioavailability of Pb in NIST SRM 2710a (Montana 1 Soil). Based on Pb levels in tissues, the mean relative bioavailability of this metal in this soil was 0.5. Estimates of relative bioavailabilities derived from mouse compared favorably with those obtained in juvenile swine. The mouse model is thus an efficient and inexpensive method to obtain estimates of relative bioavailability of soil Pb.
Soil permeability profiling using multiple geophysical data
NASA Astrophysics Data System (ADS)
Takahashi, Toru
2014-05-01
We propose a new method to estimate permeability of soils with multiple geophysical data based on rock physics. The method uses the unconsolidated sand model in rock physics to identify the soil type with seismic velocity and resistivity. The grain size representing each soil type thus derived and porosity estimated from resistivity by the modified Archie's law are input to the Kozeny-Carman equation for estimating permeability of the soil. The proposed method is applied to S-wave velocity and resistivity profiles obtained in well logging in saturated diluvial soils and acquired on an earthen levee to estimate soil permeability profiles. Comparison of estimated permeability with actual measurements by the in-situ permeability tests and laboratory tests shows that permeability can be estimated in accuracy less than one order of magnitude. This result indicates that the proposed method is promising for permeability profiling of soils using geophysical data.
NASA Astrophysics Data System (ADS)
Hsu, S. Y.; Tsai, J. P.; Chang, L. C.
2014-12-01
The flow of three immiscible fluids - water, NAPL, air - in porous media is important in many subsurface processes. To model the three-fluid flow, the relation of relative permeability-saturation-capillary pressure (k-S-P) of three fluids is of central importance. In this experimental study, we directly measure the k-S-P of the water (wetting phase) when three fluids are coexist in a micromodel during the water drainage and imbibition. The results show that the sequence of the non-wetting fluids (air and NAPL) entering into the micromodel affects the fluid distributions as well as the relative permeability of water. During the drainage process, the relative permeability of water dropped drastically when the pathway of water from inlet to outlet of the micromodel was visually blocked by the non-wetting fluids. At this stage, the relative permeability of water was low but not down to zero. The water was still able to move via corner flows or thin-film flows. During the imbibition process, the water displaced two non-wetting liquids via both "snap-off" and "piston-type" motions. The relative permeability of water jumped when the water pathway was formed again. In addition, we found that the well-known scaling format proposed by Parker et al. [1] might fail when the interfaces between the most non-wetting (air) and the most wetting (water) fluids occurs in the three-fluids system. References[1] J. C. Parker, R. J. Lenhard, and T. Kuppusamy, Water Resources Research, 23, 4, 618-624 (1987)
Why Might Relative Fit Indices Differ between Estimators?
ERIC Educational Resources Information Center
Weng, Li-Jen; Cheng, Chung-Ping
1997-01-01
Relative fit indices using the null model as the reference point in computation may differ across estimation methods, as this article illustrates by comparing maximum likelihood, ordinary least squares, and generalized least squares estimation in structural equation modeling. The illustration uses a covariance matrix for six observed variables…
Estimates of Preventability and Their Relation to Health Behavior.
ERIC Educational Resources Information Center
Poole, Gary D.
It was hypothesized that a person's estimates of the preventability of health problems would be related to health behaviors such that a person who engages in healthful behavior should make higher estimates of preventability. A study was conducted to investigate the relationship between causal attribution of health problems and health-related…
NASA Astrophysics Data System (ADS)
Chen, Xiongyu; DiCarlo, David A.
2016-10-01
This study presents a new unsteady-state method for measuring two-phase relative permeability by obtaining local values of the three key parameters (saturation, pressure drop, and phase flux) versus time during a displacement. These three parameters can be substituted to two-phase Darcy Buckingham equation to directly determine relative permeability. To obtain the first two, we use a medical X-ray Computed Tomography (CT) scanner to monitor saturation in time and space, and six differential pressure transducers to measure the overall pressure drop and the pressure drops of five individual sections (divided by four pressure taps on the core) continuously. At each scanning time, the local phase flux is obtained by spatially integrating the saturation profile and converting this to the flux using a fractional flow framework. One advantage of this local method over most previous methods is that the capillary end effect is experimentally avoided; this improvement is crucial for experiments using low viscosity fluids such as supercritical and gas phases. To illustrate the new method, we conduct five CO2-brine primary drainage experiments in a 60.8 cm long and 116 mD Berea sandstone core at 20 °C and 1500 psi. In return, we obtain hundreds of unsteady-state CO2 and brine relative permeability data points that are consistent with steady-state relative permeability data from the same experiments. Due to the large amount of relative permeability data obtained by the new unsteady-state method, the uncertainties of the exponents in the Corey-type fits decrease by up to 90% compared with the steady-state method.
Relative Camera Pose Estimation Method Using Optimization on the Manifold
NASA Astrophysics Data System (ADS)
Cheng, C.; Hao, X.; Li, J.
2017-05-01
To solve the problem of relative camera pose estimation, a method using optimization with respect to the manifold is proposed. Firstly from maximum-a-posteriori (MAP) model to nonlinear least squares (NLS) model, the general state estimation model using optimization is derived. Then the camera pose estimation model is applied to the general state estimation model, while the parameterization of rigid body transformation is represented by Lie group/algebra. The jacobian of point-pose model with respect to Lie group/algebra is derived in detail and thus the optimization model of rigid body transformation is established. Experimental results show that compared with the original algorithms, the approaches with optimization can obtain higher accuracy both in rotation and translation, while avoiding the singularity of Euler angle parameterization of rotation. Thus the proposed method can estimate relative camera pose with high accuracy and robustness.
NASA Astrophysics Data System (ADS)
Zuo, L.; Krevor, S. C.; Falta, R. W.; Benson, S. M.
2011-12-01
Saline aquifers and depleted oil and gas fields have been considered as preferred geological sequestration options for carbon dioxide to reduce greenhouse gas emissions. Given the high solubility of CO2 in water, over time, the fraction of CO2 in the subsurface may be dominated by dissolved CO2. CO2 laden brine may permeate cap rocks and carry dissolved CO2 to shallower depths, if there is an upward pressure gradient from the reservoir to the overlying groundwater aquifers. This kind of non-hydrostatic pressure gradients can be caused by gas injection in deeper formations, or groundwater depletion. Such upward flows will depressurize the brine and the dissolved CO2 will come out of solution as pressure drops. We present the results of an experimental investigation into the effects of CO2 exsolution on multiphase flow properties in a CO2-water system with various reservoir rocks and a risk assessment of CO2 leakage due to exsolution in carbon sequestration. The relative permeability of exsolved CO2 and water was measured in a core-flooding apparatus during depressurization with X-ray computed tomography. Very low relative permeabilities of CO2 and water are measured in the exsolution experiments, compared to the relative permeabilities derived from steady-state drainage measurements in the same cores, even when the CO2 saturation is as high as 40%. The large relative permeability reduction in both the CO2 and water phases is hypothesized to result from the presence of a disconnected exsolution gas phase in this flow system. After the CO2 was exsolved, a CO2-saturated water flooding experiment demonstrated the durability and the stability of the low water mobility in the presence of the exsolution gas phase, while the water mobility returned to normal after all of the exsolved CO2 dissolved by a fresh water. A large pressure drop across the core, which is 4~5 times higher than the pressure drop predicted by the drainage relative permeability, was maintained over 120
Non-parametric estimation of spatial variation in relative risk.
Kelsall, J E; Diggle, P J
We consider the problem of estimating the spatial variation in relative risks of two diseases, say, over a geographical region. Using an underlying Poisson point process model, we approach the problem as one of density ratio estimation implemented with a non-parametric kernel smoothing method. In order to assess the significance of any local peaks or troughs in the estimated risk surface, we introduce pointwise tolerance contours which can enhance a greyscale image plot of the estimate. We also propose a Monte Carlo test of the null hypothesis of constant risk over the whole region, to avoid possible over-interpretation of the estimated risk surface. We illustrate the capabilities of the methodology with two epidemiological examples.
Minimax Quantum Tomography: Estimators and Relative Entropy Bounds
Ferrie, Christopher; Blume-Kohout, Robin
2016-03-04
A minimax estimator has the minimum possible error (“risk”) in the worst case. Here we construct the first minimax estimators for quantum state tomography with relative entropy risk. The minimax risk of nonadaptive tomography scales as O (1/more » $$\\sqrt{N}$$ ) —in contrast to that of classical probability estimation, which is O (1/N) —where N is the number of copies of the quantum state used. We trace this deficiency to sampling mismatch: future observations that determine risk may come from a different sample space than the past data that determine the estimate. Lastly, this makes minimax estimators very biased, and we propose a computationally tractable alternative with similar behavior in the worst case, but superior accuracy on most states.« less
Minimax Quantum Tomography: Estimators and Relative Entropy Bounds
Ferrie, Christopher; Blume-Kohout, Robin
2016-03-04
A minimax estimator has the minimum possible error (“risk”) in the worst case. Here we construct the first minimax estimators for quantum state tomography with relative entropy risk. The minimax risk of nonadaptive tomography scales as O (1/$\\sqrt{N}$ ) —in contrast to that of classical probability estimation, which is O (1/N) —where N is the number of copies of the quantum state used. We trace this deficiency to sampling mismatch: future observations that determine risk may come from a different sample space than the past data that determine the estimate. Lastly, this makes minimax estimators very biased, and we propose a computationally tractable alternative with similar behavior in the worst case, but superior accuracy on most states.
Estimating Relative Positions of Outer-Space Structures
NASA Technical Reports Server (NTRS)
Balian, Harry; Breckenridge, William; Brugarolas, Paul
2009-01-01
A computer program estimates the relative position and orientation of two structures from measurements, made by use of electronic cameras and laser range finders on one structure, of distances and angular positions of fiducial objects on the other structure. The program was written specifically for use in determining errors in the alignment of large structures deployed in outer space from a space shuttle. The program is based partly on equations for transformations among the various coordinate systems involved in the measurements and on equations that account for errors in the transformation operators. It computes a least-squares estimate of the relative position and orientation. Sequential least-squares estimates, acquired at a measurement rate of 4 Hz, are averaged by passing them through a fourth-order Butterworth filter. The program is executed in a computer aboard the space shuttle, and its position and orientation estimates are displayed to astronauts on a graphical user interface.
Estimating maneuvers for precise relative orbit determination using GPS
NASA Astrophysics Data System (ADS)
Allende-Alba, Gerardo; Montenbruck, Oliver; Ardaens, Jean-Sébastien; Wermuth, Martin; Hugentobler, Urs
2017-01-01
Precise relative orbit determination is an essential element for the generation of science products from distributed instrumentation of formation flying satellites in low Earth orbit. According to the mission profile, the required formation is typically maintained and/or controlled by executing maneuvers. In order to generate consistent and precise orbit products, a strategy for maneuver handling is mandatory in order to avoid discontinuities or precision degradation before, after and during maneuver execution. Precise orbit determination offers the possibility of maneuver estimation in an adjustment of single-satellite trajectories using GPS measurements. However, a consistent formulation of a precise relative orbit determination scheme requires the implementation of a maneuver estimation strategy which can be used, in addition, to improve the precision of maneuver estimates by drawing upon the use of differential GPS measurements. The present study introduces a method for precise relative orbit determination based on a reduced-dynamic batch processing of differential GPS pseudorange and carrier phase measurements, which includes maneuver estimation as part of the relative orbit adjustment. The proposed method has been validated using flight data from space missions with different rates of maneuvering activity, including the GRACE, TanDEM-X and PRISMA missions. The results show the feasibility of obtaining precise relative orbits without degradation in the vicinity of maneuvers as well as improved maneuver estimates that can be used for better maneuver planning in flight dynamics operations.
Rough and partially-cemented fracture permeability
NASA Astrophysics Data System (ADS)
Landry, C. J.; Eichhubl, P.; Prodanovic, M.
2016-12-01
Numerical studies of mass transport in fractured rock, such as discrete fracture network models, use models to assign estimates of permeability to individual fractures. These fracture permeability models typically employ statistical moments of the fracture aperture distribution to estimate permeability. Although it is known that these fracture permeability models are in error, the quantification of this error is limited. We use a digital rock physics workflow to quantify this error in four fracture samples, a barren artificially-induced fracture in sandstone, a calcite-lined fracture sampled from outcrop, and two quartz-bridged fractures sampled from reservoir core. Each of the fracture samples is imaged using three-dimensional x-ray computed microtomography. The images are then processed, segmented and used in a lattice-Boltzmann-method-based flow simulation. We also vary the kinematic apertures of the barren and calcite-lined fractures through digital dilatation and closure in order to investigate sensitivity to the relative fracture roughness. We define the scalar error, F, between the actual permeability determined from simulation, kLB, and that predicted using the fracture permeability model of Zimmerman and Bodvarsson (1996), kZB, as, F±1=kZB/kLB. Although the pore space shape of the fractures appears quite different, the scalar error as a function of relative roughness is found to be similar for all fracture samples investigated, with a maximum of approximately 2. Considering two-dimensional cross-sections of fractures are more readily available than three-dimensional images we then plot the scalar error as a function of relative roughness and the number of observations measured from two-dimensional images (width of fracture analyzed). In general, the rougher the fracture, the greater the number of observations that are required to define the statistical moment inputs for the fracture permeability model. We use these results to approximate the width of the
NASA Astrophysics Data System (ADS)
Wassermann, Jérôme; Sabroux, Jean-Christophe; Richon, Patrick; Pontreau, Sébastien; Guillon, Sophie; Pili, Eric
2010-05-01
The Roselend tunnel was drilled in the fifties by blasting in the micashists, granites and gneisses of the Méraillet massif (French Alps). It is situated on the shore of the Roselend reservoir Lake near its dam. Several tectonic shear fractures related to the Alpine orogeny intersect the dead end tunnel (with length of 128 m and section about 2 m), indeed the fracture density varies from 0.45 to 1 fracture per meter along the tunnel (Dezayes and Villemin 2002). Some fractures are partially or totally filled with secondary minerals. The flow rates of percolating water through the fractured medium are seasonal dependent. Large fractures drain a large fluid volume unlike small ones that drain limited fluid volume (Patriarche et al. 2007). The Roselend underground laboratory allows the study of the geochemical and geophysical responses of a fractured rock mass to periodic sollicitations due to water level variations of the nearby Roselend reservoir Lake. The tunnel was instrumented in the nineties to understand the relationship between radon (Rn-222) concentration and water level variations of the Roselend reservoir Lake (Trique et al. 1999). In order to characterize the geometry and the extent of the EDZ, core drilling and permeability measurements through pneumatic testing are performed along the Roselend tunnel. Drilled core analysis consists of direct observations at a macroscopic scale of fractures (density of fractures from EDZ) and also at a microscopic scale via thin sections. Method of pressure build-up in wells (Jakubick and Franz 1993, Bossart et al. 2002) is used to determine permeability profile along each borehole and hence to precise the extent and geometry of the EDZ. A strong correlation is observed between permeability profiles and the density of fractures estimated from core analysis. The extent of the EDZ appears to be about one tunnel radius i.e. one meter around the tunnel corridor. Another experiment consisting of continuous differential
Seismic waves increase permeability.
Elkhoury, Jean E; Brodsky, Emily E; Agnew, Duncan C
2006-06-29
Earthquakes have been observed to affect hydrological systems in a variety of ways--water well levels can change dramatically, streams can become fuller and spring discharges can increase at the time of earthquakes. Distant earthquakes may even increase the permeability in faults. Most of these hydrological observations can be explained by some form of permeability increase. Here we use the response of water well levels to solid Earth tides to measure permeability over a 20-year period. At the time of each of seven earthquakes in Southern California, we observe transient changes of up to 24 degrees in the phase of the water level response to the dilatational volumetric strain of the semidiurnal tidal components of wells at the Piñon Flat Observatory in Southern California. After the earthquakes, the phase gradually returns to the background value at a rate of less than 0.1 degrees per day. We use a model of axisymmetric flow driven by an imposed head oscillation through a single, laterally extensive, confined, homogeneous and isotropic aquifer to relate the phase response to aquifer properties. We interpret the changes in phase response as due to changes in permeability. At the time of the earthquakes, the permeability at the site increases by a factor as high as three. The permeability increase depends roughly linearly on the amplitude of seismic-wave peak ground velocity in the range of 0.21-2.1 cm s(-1). Such permeability increases are of interest to hydrologists and oil reservoir engineers as they affect fluid flow and might determine long-term evolution of hydrological and oil-bearing systems. They may also be interesting to seismologists, as the resulting pore pressure changes can affect earthquakes by changing normal stresses on faults.
Ranathunge, Kosala; Schreiber, Lukas
2011-01-01
Although it is implied that suberized apoplastic barriers of roots negatively correlate with water and solute permeabilities, direct transport measurements across roots with altered amounts and compositions of aliphatic suberin are scarce. In the present study, hydroponically grown Arabidopsis wild types (Col8 and Col0) and different suberin mutants with altered amounts and/or compositions (horst, esb1-1, and esb1-2) were used to test this hypothesis. Detailed histochemical studies revealed late development of Casparian bands and suberin lamellae in the horst mutant compared with wild types and esb mutants. Suberin analysis with gas chromatography and mass spectrometry (GC-MS) showed that the horst mutant had ∼33% lower amounts of aliphatic monomers than Col8 and Col0. In contrast, enhanced suberin mutants (esb1-1 and esb1-2) had twice the amount of suberin as the wild types. Correlative permeability measurements, which were carried out for the first time with a root pressure probe for Arabidopsis, revealed that the hydraulic conductivity (Lpr) and NaCl permeability (Psr) of the whole root system of the horst mutant were markedly greater than in the respective wild types. This was reflected by the total amounts of aliphatic suberin determined in the roots. However, increased levels of aliphatic suberin in esb mutants failed to reduce either water or NaCl permeabilities below those of the wild types. It was concluded that the simple view and the conventional assumption that the amount of root suberin negatively correlates with permeability may not always be true. The aliphatic monomer arrangement in the suberin biopolymer and its microstructure also play a role in apoplastic barrier formation. PMID:21421706
NASA Astrophysics Data System (ADS)
Al-Amri, Meshal; Mahmoud, Mohamed; Elkatatny, Salaheldin; Al-Yousef, Hasan; Al-Ghamdi, Tariq
2017-07-01
Accurate estimation of permeability is essential in reservoir characterization and in determining fluid flow in porous media which greatly assists optimize the production of a field. Some of the permeability prediction techniques such as Porosity-Permeability transforms and recently artificial intelligence and neural networks are encouraging but still show moderate to good match to core data. This could be due to limitation to homogenous media while the knowledge about geology and heterogeneity is indirectly related or absent. The use of geological information from core description as in Lithofacies which includes digenetic information show a link to permeability when categorized into rock types exposed to similar depositional environment. The objective of this paper is to develop a robust combined workflow integrating geology and petrophysics and wireline logs in an extremely heterogeneous carbonate reservoir to accurately predict permeability. Permeability prediction is carried out using pattern recognition algorithm called multi-resolution graph-based clustering (MRGC). We will bench mark the prediction results with hard data from core and well test analysis. As a result, we showed how much better improvements are achieved in the permeability prediction when geology is integrated within the analysis. Finally, we use the predicted permeability as an input parameter in J-function and correct for uncertainties in saturation calculation produced by wireline logs using the classical Archie equation. Eventually, high level of confidence in hydrocarbon volumes estimation is reached when robust permeability and saturation height functions are estimated in presence of important geological details that are petrophysically meaningful.
Design of an Orbital Element Estimator Using Relative Motion Data.
1981-12-01
the semi-major axis and used to definethe total energy of the orbit. G is related to the eccentricity and is the total angular momentum of the orbit...errors 67 Compute 66 (changes to the relative element state vector) using least squares estimation Store ( TQ-I1K) as P 1 (-) for subsequent Bayes...A6i < Vii 68 68t convergence GO TO B NO Criteria Met? YES Estimation o elative lement - sta.e vector is E Store 3 as Z(-) for Bayes filter Sequential
Relative azimuth inversion by way of damped maximum correlation estimates
Ringler, A.T.; Edwards, J.D.; Hutt, C.R.; Shelly, F.
2012-01-01
Horizontal seismic data are utilized in a large number of Earth studies. Such work depends on the published orientations of the sensitive axes of seismic sensors relative to true North. These orientations can be estimated using a number of different techniques: SensOrLoc (Sensitivity, Orientation and Location), comparison to synthetics (Ekstrom and Busby, 2008), or by way of magnetic compass. Current methods for finding relative station azimuths are unable to do so with arbitrary precision quickly because of limitations in the algorithms (e.g. grid search methods). Furthermore, in order to determine instrument orientations during station visits, it is critical that any analysis software be easily run on a large number of different computer platforms and the results be obtained quickly while on site. We developed a new technique for estimating relative sensor azimuths by inverting for the orientation with the maximum correlation to a reference instrument, using a non-linear parameter estimation routine. By making use of overlapping windows, we are able to make multiple azimuth estimates, which helps to identify the confidence of our azimuth estimate, even when the signal-to-noise ratio (SNR) is low. Finally, our algorithm has been written as a stand-alone, platform independent, Java software package with a graphical user interface for reading and selecting data segments to be analyzed.
NASA Astrophysics Data System (ADS)
Liu, Hui-Hai
2014-05-01
In clay or other low-permeability media, water flow becomes non-Darcian and characterized by the non-linear relationship between water flux and hydraulic gradient. This work is devoted to addressing a number of key issues related to geological disposal of high-level nuclear waste in clay/shale formations. It is demonstrated that water flow velocity in the damaged zone (often considered as a potential preferential advection paths in a repository) surrounding the tunnel is extremely small, as a result of non-Darcian flow behavior, such that solute transport is dominated by diffusion, rather than advection. The finding is also consistent with the often-observed existence of persistent abnormal pressures in shale formations. While relative permeability is the key parameter for modeling the unsaturated flow process, without incorporating non-Darcian flow behavior, significant errors can occur in the determination of relative permeability values from traditional measurement methods. An approach for dealing with temperature impact on non-Darcian flow and a formulation to calculate non-Darcian water flux in an anisotropic medium are presented, taking into consideration that a geological repository is subject to temperature evolution in the near field as a result of heat generated by nuclear waste, and that shale formations are generally anisotropic.
Permeable Boundaries in Organizational Learning
NASA Astrophysics Data System (ADS)
Hazy, James K.; Tivnan, Brian F.; Schwandt, David R.
The nature of the organizational boundary is investigated in the context of organizational learning. Boundary permeability is defined and hypotheses relating it to performance are tested computationally using data from 5,500 artificial organizations. We find that matching boundary permeability to the environment predicts both agent and organization survival.
[Estimation of arterial oxygen saturation in relation to altitude].
Lorente-Aznar, Teófilo; Perez-Aguilar, Guillermo; García-Espot, Alma; Benabarre-Ciria, Sergio; Mendia-Gorostidi, Juan Luis; Dols-Alonso, Daniel; Blasco-Romero, Julia
2016-11-18
Arterial Oxygen Saturation (AOS) predicts altitude sickness. To estimate the AOS values with relation to altitude. Furthermore, make a graph to use during activity which assesses the AOS for each altitude and the normal range. Values of AOS were assessed during eight high mountain activities in the Alps, Himalaya, Caucasus and Andes; 53 mountaineers participated, 17 of them in more than one activity; 761 measurements of AOS were registered. A Logistic Regression Model was made to estimate the AOS values dependent on altitude, adjusted to possible related factors. A strong lineal relationship exists between altitude and AOS (R(2)=.83, P<.001); .7 points more in women. The AOS in a particular altitude is not related to age, weight, height, smoking, heart rate, or even with previous experiences in mountains. The calculation of the AOS responds to the follow equation: Blood Oxygen Saturation=103.3-(altitude × .0047)+(Z), being Z=.7 in men and 1.4 in women. A scatter plot was made to relate the estimated altitude with the AOS, with their normal limits values: percentiles 2.5 and 97.5. The simple calculation of the AOS estimated for a particular altitude with the proposed graphic can help in the early decision-making onsite. Copyright © 2016 Elsevier España, S.L.U. All rights reserved.
Numerical estimation of the relative entropy of entanglement
Zinchenko, Yuriy; Friedland, Shmuel; Gour, Gilad
2010-11-15
We propose a practical algorithm for the calculation of the relative entropy of entanglement (REE), defined as the minimum relative entropy between a state and the set of states with positive partial transpose. Our algorithm is based on a practical semidefinite cutting plane approach. In low dimensions the implementation of the algorithm in matlab provides an estimation for the REE with an absolute error smaller than 10{sup -3}.
Pedotransfer functions for permeability: A computational study at pore scales
NASA Astrophysics Data System (ADS)
Hyman, Jeffrey D.; Smolarkiewicz, Piotr K.; Larrabee Winter, C.
2013-04-01
Three phenomenological power law models for the permeability of porous media are derived from computational experiments with flow through explicit pore spaces. The pore spaces are represented by three-dimensional pore networks in 63 virtual porous media along with 15 physical pore networks. The power laws relate permeability to (i) porosity, (ii) squared mean hydraulic radius of pores, and (iii) their product. Their performance is compared to estimates derived via the Kozeny equation, which also uses the product of porosity with squared mean hydraulic pore radius to estimate permeability. The power laws provide tighter estimates than the Kozeny equation even after adjusting for the extra parameter they each require. The best fit is with the power law based on the Kozeny predictor, that is, the product of porosity with the square of mean hydraulic pore radius.
Accurate genome relative abundance estimation based on shotgun metagenomic reads.
Xia, Li C; Cram, Jacob A; Chen, Ting; Fuhrman, Jed A; Sun, Fengzhu
2011-01-01
Accurate estimation of microbial community composition based on metagenomic sequencing data is fundamental for subsequent metagenomics analysis. Prevalent estimation methods are mainly based on directly summarizing alignment results or its variants; often result in biased and/or unstable estimates. We have developed a unified probabilistic framework (named GRAMMy) by explicitly modeling read assignment ambiguities, genome size biases and read distributions along the genomes. Maximum likelihood method is employed to compute Genome Relative Abundance of microbial communities using the Mixture Model theory (GRAMMy). GRAMMy has been demonstrated to give estimates that are accurate and robust across both simulated and real read benchmark datasets. We applied GRAMMy to a collection of 34 metagenomic read sets from four metagenomics projects and identified 99 frequent species (minimally 0.5% abundant in at least 50% of the data-sets) in the human gut samples. Our results show substantial improvements over previous studies, such as adjusting the over-estimated abundance for Bacteroides species for human gut samples, by providing a new reference-based strategy for metagenomic sample comparisons. GRAMMy can be used flexibly with many read assignment tools (mapping, alignment or composition-based) even with low-sensitivity mapping results from huge short-read datasets. It will be increasingly useful as an accurate and robust tool for abundance estimation with the growing size of read sets and the expanding database of reference genomes.
Drug permeability prediction using PMF method.
Meng, Fancui; Xu, Weiren
2013-03-01
Drug permeability determines the oral availability of drugs via cellular membranes. Poor permeability makes a drug unsuitable for further development. The permeability may be estimated as the free energy change that the drug should overcome through crossing membrane. In this paper the drug permeability was simulated using molecular dynamics method and the potential energy profile was calculated with potential of mean force (PMF) method. The membrane was simulated using DPPC bilayer and three drugs with different permeability were tested. PMF studies on these three drugs show that doxorubicin (low permeability) should pass higher free energy barrier from water to DPPC bilayer center while ibuprofen (high permeability) has a lower energy barrier. Our calculation indicates that the simulation model we built is suitable to predict drug permeability.
Measuring Mudstone Permeability at Two Different (Borehole and Core) Scales
NASA Astrophysics Data System (ADS)
Quach, N. Q.; Chang, C.; Jo, Y.; Song, I.
2016-12-01
We had an opportunity to measure permeability of the same mudstone at borehole-scale and core-scale. The mudstone tested is located in offshore SE Korea, where a CO2 storage test project is underway. The mudstone is a part of cap rock formation overlying a potential CO2 storage reservoir, and thus its permeability is of great importance for the sealing purpose. We ran a leak-off test (LOT) at a 4 m open-hole interval below casing shoe in a cored borehole. Borehole-scale permeability estimation is based on the LOT, and core-scale estimation is based on laboratory tests in cores recovered from the same depth where the LOT was conducted. Although LOT is a pumping test mainly for checking borehole/casing integrity and assessing frac-gradient for further drilling, the pressure (P) and injected water volume (V) recorded during test enable us to estimate permeability. We derive an analytic equation that relates permeability to P-V curve based on Darcy's law, which suits for the LOT configuration. Based on the equation, the borehole-scale permeability is estimated to be 10-17 m2. For the core-scale estimation, we conduct laboratory tests, in which we inject argon gas to attain a constant pressure at one side of the cores (diameter: 38 mm) subjected to a constant confining pressure similar to the effective stress at the depth of the LOT. The core-scale permeability is estimated to be 10-19 m2, which is two order of magnitude lower than borehole-scale permeability. Although there may be other sources that contribute to the observed difference in permeability, one of the major factors is the scale-difference, more than 800 times larger scale in the borehole-scale than in the core-scale. Another possible sources of the difference are different flow direction (horizontal in LOT and vertical in core) and different fluids used for permeability measurements (water in LOT and gas in core).
Pricing Medicare's diagnosis-related groups: Charges versus estimated costs
Price, Kurt F.
1989-01-01
Hospital payments under Medicare's prospective payment system (PPS) are based on prices established for 474 diagnosis-related groups (DRG's). Previous analyses using 1981 data demonstrated that DRG prices based on charges alone were not that different from prices calculated from estimated costs. Data for 1986 were used in this study to show that the differences between the two sets of DRG prices are much larger than previously reported. If DRG prices were once again based on estimated costs instead of the current charge-based prices, payments would be significantly redistributed. PMID:10313356
Maximum Correntropy Unscented Kalman Filter for Spacecraft Relative State Estimation.
Liu, Xi; Qu, Hua; Zhao, Jihong; Yue, Pengcheng; Wang, Meng
2016-09-20
A new algorithm called maximum correntropy unscented Kalman filter (MCUKF) is proposed and applied to relative state estimation in space communication networks. As is well known, the unscented Kalman filter (UKF) provides an efficient tool to solve the non-linear state estimate problem. However, the UKF usually plays well in Gaussian noises. Its performance may deteriorate substantially in the presence of non-Gaussian noises, especially when the measurements are disturbed by some heavy-tailed impulsive noises. By making use of the maximum correntropy criterion (MCC), the proposed algorithm can enhance the robustness of UKF against impulsive noises. In the MCUKF, the unscented transformation (UT) is applied to obtain a predicted state estimation and covariance matrix, and a nonlinear regression method with the MCC cost is then used to reformulate the measurement information. Finally, the UT is adopted to the measurement equation to obtain the filter state and covariance matrix. Illustrative examples demonstrate the superior performance of the new algorithm.
Worldwide Estimates Relative to Five Continental-Scale Populations
Steele, Christopher D; Court, Denise Syndercombe; Balding, David J
2014-01-01
We estimate the population genetics parameter (also referred to as the fixation index) from short tandem repeat (STR) allele frequencies, comparing many worldwide human subpopulations at approximately the national level with continental-scale populations. is commonly used to measure population differentiation, and is important in forensic DNA analysis to account for remote shared ancestry between a suspect and an alternative source of the DNA. We estimate comparing subpopulations with a hypothetical ancestral population, which is the approach most widely used in population genetics, and also compare a subpopulation with a sampled reference population, which is more appropriate for forensic applications. Both estimation methods are likelihood-based, in which is related to the variance of the multinomial-Dirichlet distribution for allele counts. Overall, we find low values, with posterior 97.5 percentiles when comparing a subpopulation with the most appropriate population, and even for inter-population comparisons we find . These are much smaller than single nucleotide polymorphism-based inter-continental estimates, and are also about half the magnitude of STR-based estimates from population genetics surveys that focus on distinct ethnic groups rather than a general population. Our findings support the use of up to 3% in forensic calculations, which corresponds to some current practice. PMID:26460400
Multiple Component Event-Related Potential (mcERP) Estimation
NASA Technical Reports Server (NTRS)
Knuth, K. H.; Clanton, S. T.; Shah, A. S.; Truccolo, W. A.; Ding, M.; Bressler, S. L.; Trejo, L. J.; Schroeder, C. E.; Clancy, Daniel (Technical Monitor)
2002-01-01
We show how model-based estimation of the neural sources responsible for transient neuroelectric signals can be improved by the analysis of single trial data. Previously, we showed that a multiple component event-related potential (mcERP) algorithm can extract the responses of individual sources from recordings of a mixture of multiple, possibly interacting, neural ensembles. McERP also estimated single-trial amplitudes and onset latencies, thus allowing more accurate estimation of ongoing neural activity during an experimental trial. The mcERP algorithm is related to informax independent component analysis (ICA); however, the underlying signal model is more physiologically realistic in that a component is modeled as a stereotypic waveshape varying both in amplitude and onset latency from trial to trial. The result is a model that reflects quantities of interest to the neuroscientist. Here we demonstrate that the mcERP algorithm provides more accurate results than more traditional methods such as factor analysis and the more recent ICA. Whereas factor analysis assumes the sources are orthogonal and ICA assumes the sources are statistically independent, the mcERP algorithm makes no such assumptions thus allowing investigators to examine interactions among components by estimating the properties of single-trial responses.
Multiple Component Event-Related Potential (mcERP) Estimation
NASA Technical Reports Server (NTRS)
Knuth, K. H.; Clanton, S. T.; Shah, A. S.; Truccolo, W. A.; Ding, M.; Bressler, S. L.; Trejo, L. J.; Schroeder, C. E.; Clancy, Daniel (Technical Monitor)
2002-01-01
We show how model-based estimation of the neural sources responsible for transient neuroelectric signals can be improved by the analysis of single trial data. Previously, we showed that a multiple component event-related potential (mcERP) algorithm can extract the responses of individual sources from recordings of a mixture of multiple, possibly interacting, neural ensembles. McERP also estimated single-trial amplitudes and onset latencies, thus allowing more accurate estimation of ongoing neural activity during an experimental trial. The mcERP algorithm is related to informax independent component analysis (ICA); however, the underlying signal model is more physiologically realistic in that a component is modeled as a stereotypic waveshape varying both in amplitude and onset latency from trial to trial. The result is a model that reflects quantities of interest to the neuroscientist. Here we demonstrate that the mcERP algorithm provides more accurate results than more traditional methods such as factor analysis and the more recent ICA. Whereas factor analysis assumes the sources are orthogonal and ICA assumes the sources are statistically independent, the mcERP algorithm makes no such assumptions thus allowing investigators to examine interactions among components by estimating the properties of single-trial responses.
NASA Astrophysics Data System (ADS)
Diliberto, Iole Serena; Cangemi, Marianna; Gagliano, Antonina Lisa; Inguaggiato, Salvatore; Madonia, Paolo; Pedone, Maria; Fabio Pisciotta, Antonino
2016-04-01
Vulcano, the southernmost island of the Aeolian archipelago (Italy), is presently characterized by active fumarolic fields located along the rim of La Fossa cone and the shoreline of the Baia di Levante beach, in the northern portion of the island.The Baia di Levante fumarolic vents are fed by a shallow hydrothermal aquifer heated by magmatic gases rising from the deep down, with a spatial distribution strongly affected by the local fracture network. These fractures are the expression of a deformation field, dominated by a northward motion to Lipari, abruptly decaying to the Vulcanello peninsula, immediately northward of the Baia di Levante beach. Variable rates of fluid transfer to the surface, following permeability changes affecting the fracture network are among the results of stress field variations over time which induce fluctuations in the pressure state of the hydrothermal system. Under these conditions, increments in hydrothermal gas flow, able to cause an increase of gas hazard, could be determined by a rearrangement of the shallow permeability distribution induced by changes in the deformation field. In this case not associated to any variation in the volcanic activity state. Since 2009 an huge gas flow increment has been noticed in some undersea vents of the Baia di Levante area, leading to increase of gas hazard in their immediate surroundings. On the contrary, the acquired data from the INGV volcanic surveillance program didn't suggest any correlated increase of the magmatic fluid component in the degassing activity.In July 2015, we carried out multi-parametric geochemical surveys in this area, based on direct (thermocouple) and indirect (thermal infrared camera and pyrometer) soil temperature, soil CO2 flux, atmospheric concentration of CO2 and H2S measurements at low elevation (one meter a.s.l.). The chemical and isotopic composition of low temperature fumarole gases was determined too.The comparison of the new data with previous surveys carried out
Space-to-Space Based Relative Motion Estimation Using Direct Relative Orbit Parameters
NASA Astrophysics Data System (ADS)
Bennett, T.; Schaub, H.
There has been an increasing interest in space-based space situational awareness around satellite assets and the tracking of orbital debris. Of particular interest is the space-based tracking of objects near critical circular orbit regimes, for example near the Geostationary belt or the International Space Station. Relative orbit descriptions such as the Clohessy-Wiltshire equations describe the motion using time-varying Cartesian or curvilinear coordinates. Orbit element differences describe the unperturbed motion using constant variations of inertial orbit elements. With perturbations these only vary slowly, but can be challenging to estimate. Linearized Relative Orbit Elements (LROEs) employ invariants of the linearized relative motion, are thus constant for the unperturbed linear case, and share the benefit of the CW equations in that they directly related to space-based relative motion measurements. The variational LROE equations enable the relative orbit to be directly propagated including perturbation forces. Utilization of the invariant-inspired relative motion parameters exhibits exciting applications in relative motion sensing and control. Many methods of relative motion estimation involve the direct estimation of time-evolving position and velocity variables. Developed is an angles-only relative orbit Extended Kalman filter (EKF) navigation approach that directly estimates these nominally constant LROEs. The proposed variational equations and filtering scheme enables direct estimation of geometric parameters with clear geometric insight. Preliminary numerical simulation results demonstrate the relative orbit insight gained and speed of convergence. EKF implementations often exhibit significant sensitivity to initial conditions, however, initial results show that the LROE filter converges within fractions of an orbit with initialization errors that exceed 100 percent. The manuscript presents the invariants of motion, develops the variational equations for
Captive Ancestry Upwardly Biases Estimates of Relative Reproductive Success.
Willoughby, Janna R; Christie, Mark R
2017-07-01
Supplementation programs, which release captive-born individuals into the wild, are commonly used to demographically bolster declining populations. In order to evaluate the effectiveness of these programs, the reproductive success of captive-born individuals released into the wild is often compared to the reproductive success of wild-born individuals in the recipient population (relative reproductive success, RRS). However, if there are heritable reductions in fitness associated with captive breeding, gene flow from captive-born individuals into the wild population can reduce the fitness of the wild population. Here, we show that when captive ancestry in the wild population reduces mean population fitness, estimates of RRS are upwardly biased, meaning that the relative fitness of captive-born individuals is over-estimated. Furthermore, the magnitude of this bias increases with the length of time that a supplementation program has been releasing captive-born individuals. This phenomenon has long-term conservation impacts since management decisions regarding the design of a supplementation program and the number of individuals to release can be based, at least in part, on RRS estimates. Therefore, we urge caution in the interpretation of relative fitness measures when the captive ancestry of the wild population cannot be precisely measured. © The American Genetic Association 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
Relative CO₂/NH₃ permeabilities of human RhAG, RhBG and RhCG.
Geyer, R Ryan; Parker, Mark D; Toye, Ashley M; Boron, Walter F; Musa-Aziz, Raif
2013-12-01
Mammalian glycosylated rhesus (Rh) proteins include the erythroid RhAG and the nonerythroid RhBG and RhCG. RhBG and RhCG are expressed in multiple tissues, including hepatocytes and the collecting duct (CD) of the kidney. Here, we expressed human RhAG, RhBG and RhCG in Xenopus oocytes (vs. H2O-injected control oocytes) and used microelectrodes to monitor the maximum transient change in surface pH (DpHS) caused by exposing the same oocyte to 5 % CO₂/33 mM HCO₃⁻ (an increase) or 0.5 mM NH₃/NH₄⁺ (a decrease). Subtracting the respective values for day-matched, H₂O-injected control oocytes yielded channel-specific values (*). (ΔpH*(S))(CO₂) and (-ΔpH*(S))(NH₃) were each significantly >0 for all channels, indicating that RhBG and RhCG--like RhAG--can carry CO₂ and NH₃. We also investigated the role of a conserved aspartate residue, which was reported to inhibit NH₃ transport. However, surface biotinylation experiments indicate the mutants RhBG(D178N) and RhCG(D177N) have at most a very low abundance in the oocyte plasma membrane. We demonstrate for the first time that RhBG and RhCG--like RhAG--have significant CO₂ permeability, and we confirm that RhAG, RhBG and RhCG all have significant NH₃ permeability. However, as evidenced by (ΔpH*(S))(CO₂)/ (-ΔpH*(S))(NH₃) values, we could not distinguish among the CO₂/ NH₃ permeability ratios for RhAG, RhBG and RhCG. Finally, we propose a mechanism whereby RhBG and RhCG contribute to acid secretion in the CD by enhancing the transport of not only NH₃ but also CO₂ across the membranes of CD cells.
Buchenauer, Dean A.; Karnesky, Richard A.
2015-09-01
An understanding of the behavior of hydrogen isotopes in materials is critical to predicting tritium transport in structural metals (at high pressure), estimating tritium losses during production (fission environment), and predicting in-vessel inventory for future fusion devices (plasma driven permeation). Current models often assume equilibrium diffusivity and solubility for a class of materials (e.g. stainless steels or aluminum alloys), neglecting trapping effects or, at best, considering a single population of trapping sites. Permeation and trapping studies of the particular castings and forgings enable greater confidence and reduced margins in the models. For FY15, we have continued our investigation of the role of ferrite in permeation for steels of interest to GTS, through measurements of the duplex steel 2507. We also initiated an investigation of the permeability in work hardened materials, to follow up on earlier observations of unusual permeability in a particular region of 304L forgings. Samples were prepared and characterized for ferrite content and coated with palladium to prevent oxidation. Issues with the poor reproducibility of measurements at low permeability were overcome, although the techniques in use are tedious. Funding through TPBAR and GTS were secured for a research grade quadrupole mass spectrometer (QMS) and replacement turbo pumps, which should improve the fidelity and throughput of measurements in FY16.
Alvarez-Figueroa, M Javiera; Pessoa-Mahana, C David; Palavecino-González, M Elisa; Mella-Raipán, Jaime; Espinosa-Bustos, Cristián; Lagos-Muñoz, Manuel E
2011-06-01
The permeability of five benzimidazole derivates with potential cannabinoid activity was determined in two models of membranes, parallel artificial membrane permeability assay (PAMPA) and skin, in order to study the relationship of the physicochemical properties of the molecules and characteristics of the membranes with the permeability defined by the Biopharmaceutics Classification System. It was established that the PAMPA intestinal absorption method is a good predictor for classifying these molecules as very permeable, independent of their thermodynamic solubility, if and only if these have a Log P(oct) value <3.0. In contrast, transdermal permeability is conditioned on the solubility of the molecule so that it can only serve as a model for classifying the permeability of molecules that possess high solubility (class I: high solubility, high permeability; class III: high solubility, low permeability).
NASA Astrophysics Data System (ADS)
Li, Zhaoqi; Goldstein, Robert H.; Franseen, Evan K.
2017-03-01
A dolomitized Upper Miocene carbonate system in southeast Spain contains extensive upper and lower zones of calcite cementation that cut across the stratigraphy. Cement textures including isopachous and circumgranular, which are consistent with phreatic-zone cementation. Cements in the upper cemented zone are non-luminescent, whereas those in the lower cemented zone exhibit multiple bands of luminescent and non-luminescent cements. In the upper cemented zone, isotopic data show two meteoric calcite lines (MCL) with mean δ18O at - 5.1‰ and - 5.8‰ VPDB, whereas no clear MCL is defined in the lower cemented zone where mean δ18O for calcite cement is at - 6.7‰ VPDB. δ13C values in both cement zones are predominantly negative, ranging from - 10 to + 2‰ VPDB, suggestive of carbon from soil gas or decayed organics. Measurements of Tm ice in primary fluid inclusions yield a mode of 0.0 °C in both zones, indicating calcite cementation from fresh water. These two zones define the positions of two different paleo-water tables that formed during a relative sea-level fall and erosional downcutting during the Plio-Pleistocene. The upper cemented zone pre-dated the lower cemented zone on the basis of known relative sea-level history. Meteoric calcite cementation reduced porosity and permeability, but measured values are inconsistent with simple filling of open pore space. Each texture, boundstone, grainstone, packstone, wackestone, produces a different relationship between percent calcite cement and porosity/permeability. Distribution of cements may be predictable on the basis of known sea-level history, and the effect of the cementation can be incorporated into subsurface geomodels by defining surfaces of rock boundaries that separate cemented zones from uncemented zones, and applying texture-specific relationships among cementation, porosity and permeability.
Estimating the mission-related costs of teaching hospitals.
Koenig, Lane; Dobson, Allen; Ho, Silver; Siegel, Jonathan M; Blumenthal, David; Weissman, Joel S
2003-01-01
Academic health centers and other teaching hospitals face higher patient care costs than nonteaching community hospitals face, because of their missions of graduate medical education (GME), biomedical research, and the maintenance of standby capacity for medically complex patients. We estimate that total mission-related costs were dollar 27 billion in 2002 for all teaching hospitals, with GME (including indirect and direct GME) and standby capacity accounting for roughly 60 and 35 percent of these costs, respectively. To assure their continued ability to perform important social missions in a competitive environment, it may be necessary to reassess the way in which these activities are financed.
Prevalence Estimates of Combat-Related PTSD: A Critical Review
Richardson, Lisa K.; Frueh, B. Christopher; Acierno, Ronald
2010-01-01
Objective To provide a critical review of prevalence estimates of combat-related PTSD among military personnel and veterans, and of the relevant factors that may account for the variability of estimates within and across cohorts, including methodological and conceptual factors accounting for differences in prevalence rates across nations, conflicts/wars, and studies. Method We examined MEDLINE and PsycINFO databases for literature on combat-related PTSD. The following terms were used independently and in combinations in this search: PTSD, combat, veterans, military, epidemiology, prevalence. Results The point prevalence of combat-related PTSD in US military veterans since the Vietnam War ranges from about 2 – 17%. Studies of recent conflicts suggest that combat-related PTSD afflicts between 4 – 17% of US Iraq War veterans, but only 3 – 6% of returning UK Iraq War veterans. Thus, the prevalence range is narrower and tends to have a lower ceiling among combat veterans of non-US Western nations. Variability in prevalence is likely due to differences in sampling strategies; measurement strategies; inclusion and measurement of the DSM-IV clinically significant impairment criterion; timing and latency of assessment and potential for recall bias; and combat experiences. Prevalence rates are also likely affected by issues related to PTSD course, chronicity, and comorbidity; symptom overlap with other psychiatric disorders; and sociopolitical and cultural factors that may vary over time and by nation. Conclusions The disorder represents a significant and costly illness to veterans, their families, and society as a whole. However, further carefully conceptualized research is needed to advance our understanding of disorder prevalence, as well as associated information on course, phenomenology, protective factors, treatment, and economic costs. PMID:20073563
Maximum Correntropy Unscented Kalman Filter for Spacecraft Relative State Estimation
Liu, Xi; Qu, Hua; Zhao, Jihong; Yue, Pengcheng; Wang, Meng
2016-01-01
A new algorithm called maximum correntropy unscented Kalman filter (MCUKF) is proposed and applied to relative state estimation in space communication networks. As is well known, the unscented Kalman filter (UKF) provides an efficient tool to solve the non-linear state estimate problem. However, the UKF usually plays well in Gaussian noises. Its performance may deteriorate substantially in the presence of non-Gaussian noises, especially when the measurements are disturbed by some heavy-tailed impulsive noises. By making use of the maximum correntropy criterion (MCC), the proposed algorithm can enhance the robustness of UKF against impulsive noises. In the MCUKF, the unscented transformation (UT) is applied to obtain a predicted state estimation and covariance matrix, and a nonlinear regression method with the MCC cost is then used to reformulate the measurement information. Finally, the UT is adopted to the measurement equation to obtain the filter state and covariance matrix. Illustrative examples demonstrate the superior performance of the new algorithm. PMID:27657069
USDA-ARS?s Scientific Manuscript database
Dual-permeability models are increasingly used to quantify the transport of solutes and microorganisms in soils with preferential flow. An ability to accurately determine the model parameters and their variation with preferential pathway characteristics is crucial for predicting the transport of mi...
Relations for estimating unit-hydrograph parameters in New Mexico
Waltemeyer, Scott D.
2001-01-01
Data collected from 20 U.S. Geological Survey streamflow-gaging stations, most of which were operated in New Mexico between about 1969 and 1977, were used to define hydrograph characteristics for small New Mexico streams. Drainage areas for the gaging stations ranged from 0.23 to 18.2 square miles. Observed values for the hydrograph characteristics were determined for 87 of the most significant rainfall-runoff events at these gaging stations and were used to define regional regression relations with basin characteristics. Regional relations defined lag time (tl), time of concentration (tc), and time to peak (tp) as functions of stream length and basin shape. The regional equation developed for time of concentration for New Mexico agrees well with the Kirpich equation developed for Tennessee. The Kirpich equation is based on stream length and channel slope, whereas the New Mexico equation is based on stream length and basin shape. Both equations, however, underestimate tc when applied to larger basins where tc is greater than about 2 hours. The median ratio between tp and tc for the observed data was 0.66, which equals the value (0.67) recommended by the Natural Resources Conservation Service (formerly the Soil Conservation Service). However, the median ratio between tl and tc was only 0.42, whereas the commonly used ratio is 0.60. A relation also was developed between unit-peak discharge (qu) and time of concentration. The unit-peak discharge relation is similar in slope to the Natural Resources Conservation Service equation, but the equation developed for New Mexico in this study produces estimates of qu that range from two to three times as large as those estimated from the Natural Resources Conservation Service equation. An average value of 833 was determined for the empirical constant Kp. A default value of 484 has been used by the Natural Resources Conservation Service when site-specific data are not available. The use of a lower value of Kp in calculations
NASA Astrophysics Data System (ADS)
Niu, B.; Al-Menhali, A.; Krevor, S. C.
2014-12-01
Successful industrial scale carbon dioxide injection into deep saline aquifers will be dependent on the ability to model the flow of the fluid and to quantify the impact of various trapping mechanisms. The effectiveness of the models is in turn dependent on high quality laboratory measurements of basic multiphase flow properties such as relative permeability and residual trapping at reservoir conditions. Compared with typical oil-brine systems, however, a unique defining characteristic of the CO2-brine system is its combination of high viscosity ratio and low density ratio. This combination of properties results in unique complications for experiments with CO2 and brine and unique flow conditions must be used to achieve the combined goals of observations across a large saturation range and the avoidance of the effects of heterogeneity as well as capillary forces and gravity segregation. We have simulated the corefloods experiments at various conditions and calculated with different interpretation techniques: Steady state method, JBN-type method and history matching. As one of the essential mechanisms for CO2 storage underground, residual trapping refers to the trapping of CO2 through capillary forces within the pore space of a permeable aquifer. There are few studies that have observed the trapping characteristics for CO2-brine systems in permeable rocks, including the impact of reservoir conditions, and this remains a major uncertainty for geologic CO2 storage. This work presents results from a core-flooding laboratory that has been recently developed at Imperial College dedicated to observations of CO2-brine systems. The apparatus includes high precision pumps, accurate temperature control and a rotating X-ray CT scanner that allows experiments to be performed in both vertical and horizontal directions. The proper approach to measuring relative permeability for CO2-brine system is proposed and demonstrated. The changes in residual trapping correlated to pressure
Relate Watershed Erosion Estimation to Bankfull Channel Dimension
NASA Astrophysics Data System (ADS)
Zhou, H.; Chang, T. J.; Caballero, I.; Fang, Y.
2016-12-01
It is believed that a stream is of function properly to carry water and sediment by maintaining channel dimensions, pattern, and profile without degrading or aggrading them over time. The formation of channel dimensions is extremely complex. This study is to relate quantifiable and consistent channel dimensions at the bankfull stage to the corresponding watershed erosion estimation by the Revised Universal Soil Loss Equation (RUSLE). Twelve sites of which drainage areas range from 7 to 100 square miles in the Hocking River Basin of Ohio were selected for the bankfull geometry determinations including width, depth, cross-section area, bed slope, and drainage area. The twelve sub-watersheds were chosen to obtain a good overall representation of the Hocking River Basin. It is of interest to determine how these bankfull channel dimensions are related to the soil erosion of corresponding sub-watersheds. Soil erosion is a natural process that has occurred in a watershed over time. The RUSLE used to quantify watershed erosion is to estimate the erosions of the twelve selected sub-watersheds where the bankfull geometry measurements are conducted. These quantified erosions of sub-watersheds are used to investigate possible correlations with bankfull channel dimensions including discharge, channel width, channel depth, cross-sectional area, and pebble distribution.
The role of geology in the behavior and choice of permeability predictors
Ball, L.D.; Corbett, P.W.M.; Jensen, J.L.; Lewis, J.J.M.
1997-03-01
For effective flow-simulation models, it may be important to estimate permeability accurately over several scales of geological heterogeneity. Critical to the data analysis and permeability prediction are the volume of investigation and sampling interval of each petrophysical tool and how each relates to these geological scales. The authors examine these issues in the context of the As Sarah Field, Sirte Basin, Libya. A geological study of this braided fluvial reservoir has revealed heterogeneity at a series of scales. This geological hierarchy in turn possessed a corresponding hierarchy of permeability variation.The link between the geology and permeability was found to be very important in understanding well logs and core data and subsequent permeability upscaling. They found that the small scale (cm) permeability variability was better predicted using a flushed-zone resistivity, R{sub xo}, tool, rather than a wireline porosity measurement. The perm-resistivity correlation was strongest when the probe permeabilities were averaged to best match the window size of the wireline R{sub xo}. This behavior was explained by the geological variation present at this scale. For the larger scale geological heterogeneity, the production flowmeter highlighted discrepancies between flow data and averaged permeability. This yielded a layered sedimentological model interpretation and a change in averaging for permeability prediction at the bedset scale (ms-10 x ms).
Permeability of cork to gases.
Faria, David P; Fonseca, Ana L; Pereira, Helen; Teodoro, Orlando M N D
2011-04-27
The permeability of gases through uncompressed cork was investigated. More than 100 samples were assessed from different plank qualities to provide a picture of the permeability distribution. A novel technique based on a mass spectrometer leak detector was used to directly measure the helium flow through the central area of small disks 10 mm in diameter and 2 mm thick. The permeability for nitrogen, oxygen, and other gases was measured by the pressure rise technique. Boiled and nonboiled cork samples from different sections were evaluated. An asymmetric frequency distribution ranging 3 orders of magnitude (roughly from 1 to 1000 μmol/(cm·atm·day)) for selected samples without macroscopic defects was found, having a peak below 100 μmol/(cm·atm·day). Correlation was found between density and permeability: higher density samples tend to show lower permeability. However, boiled cork showed a mean lower permeability despite having a lower density. The transport mechanism of gases through cork was also examined. Calculations suggest that gases permeate uncompressed cork mainly through small channels between cells under a molecular flow regime. The diameter of such channels was estimated to be in the range of 100 nm, in agreement with the plasmodesmata size in the cork cell walls.
Mokkala, Kati; Röytiö, Henna; Munukka, Eveliina; Pietilä, Sami; Ekblad, Ulla; Rönnemaa, Tapani; Eerola, Erkki; Laiho, Asta; Laitinen, Kirsi
2016-09-01
Increased intestinal permeability may precede adverse metabolic conditions. The extent to which the composition of the gut microbiota and diet contribute to intestinal permeability during pregnancy is unknown. The aim was to investigate whether the gut microbiota and diet differ according to serum zonulin concentration, a marker of intestinal permeability, in overweight pregnant women. This cross-sectional study included 100 overweight women [mean age: 29 y; median body mass index (in kg/m(2)): 30] in early pregnancy (<17 wk of gestation; median: 13 wk). Serum zonulin (primary outcome) was determined by using ELISA, gut microbiota by 16S ribosomal RNA sequencing, and dietary intake of macro- and micronutrients from 3-d food diaries. The Mann-Whitney U test was used for pairwise comparisons and linear regression and Spearman's nonparametric correlations for relations between serum zonulin and other outcome variables. Women were divided into "low" (<46.4 ng/mL) and "high" (≥46.4 ng/mL) serum zonulin groups on the basis of the median concentration of zonulin (46.4 ng/mL). The richness of the gut microbiota (Chao 1, observed species and phylogenetic diversity) was higher in the low zonulin group than in the high zonulin group (P = 0.01). The abundances of Bacteroidaceae and Veillonellaceae, Bacteroides and Blautia, and Blautia sp. were lower and of Faecalibacterium and Faecalibacterium prausnitzii higher (P < 0.05) in the low zonulin group than in the high zonulin group. Dietary quantitative intakes of n-3 (ω-3) polyunsaturated fatty acids (PUFAs), fiber, and a range of vitamins and minerals were higher (P < 0.05) in women in the low zonulin group than those in the high zonulin group. The richness and composition of the gut microbiota and the intake of n-3 PUFAs, fiber, and a range of vitamins and minerals in overweight pregnant women are associated with serum zonulin concentration. Modification of the gut microbiota and diet may beneficially affect intestinal
Quantitation of small intestinal permeability during normal human drug absorption
2013-01-01
Background Understanding the quantitative relationship between a drug’s physical chemical properties and its rate of intestinal absorption (QSAR) is critical for selecting candidate drugs. Because of limited experimental human small intestinal permeability data, approximate surrogates such as the fraction absorbed or Caco-2 permeability are used, both of which have limitations. Methods Given the blood concentration following an oral and intravenous dose, the time course of intestinal absorption in humans was determined by deconvolution and related to the intestinal permeability by the use of a new 3 parameter model function (“Averaged Model” (AM)). The theoretical validity of this AM model was evaluated by comparing it to the standard diffusion-convection model (DC). This analysis was applied to 90 drugs using previously published data. Only drugs that were administered in oral solution form to fasting subjects were considered so that the rate of gastric emptying was approximately known. All the calculations are carried out using the freely available routine PKQuest Java (http://www.pkquest.com) which has an easy to use, simple interface. Results Theoretically, the AM permeability provides an accurate estimate of the intestinal DC permeability for solutes whose absorption ranges from 1% to 99%. The experimental human AM permeabilities determined by deconvolution are similar to those determined by direct human jejunal perfusion. The small intestinal pH varies with position and the results are interpreted in terms of the pH dependent octanol partition. The permeability versus partition relations are presented separately for the uncharged, basic, acidic and charged solutes. The small uncharged solutes caffeine, acetaminophen and antipyrine have very high permeabilities (about 20 x 10-4 cm/sec) corresponding to an unstirred layer of only 45 μm. The weak acid aspirin also has a large AM permeability despite its low octanol partition at pH 7.4, suggesting
Robust estimation of event-related potentials via particle filter.
Fukami, Tadanori; Watanabe, Jun; Ishikawa, Fumito
2016-03-01
In clinical examinations and brain-computer interface (BCI) research, a short electroencephalogram (EEG) measurement time is ideal. The use of event-related potentials (ERPs) relies on both estimation accuracy and processing time. We tested a particle filter that uses a large number of particles to construct a probability distribution. We constructed a simple model for recording EEG comprising three components: ERPs approximated via a trend model, background waves constructed via an autoregressive model, and noise. We evaluated the performance of the particle filter based on mean squared error (MSE), P300 peak amplitude, and latency. We then compared our filter with the Kalman filter and a conventional simple averaging method. To confirm the efficacy of the filter, we used it to estimate ERP elicited by a P300 BCI speller. A 400-particle filter produced the best MSE. We found that the merit of the filter increased when the original waveform already had a low signal-to-noise ratio (SNR) (i.e., the power ratio between ERP and background EEG). We calculated the amount of averaging necessary after applying a particle filter that produced a result equivalent to that associated with conventional averaging, and determined that the particle filter yielded a maximum 42.8% reduction in measurement time. The particle filter performed better than both the Kalman filter and conventional averaging for a low SNR in terms of both MSE and P300 peak amplitude and latency. For EEG data produced by the P300 speller, we were able to use our filter to obtain ERP waveforms that were stable compared with averages produced by a conventional averaging method, irrespective of the amount of averaging. We confirmed that particle filters are efficacious in reducing the measurement time required during simulations with a low SNR. Additionally, particle filters can perform robust ERP estimation for EEG data produced via a P300 speller. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
Fries, Walter; Renda, Maria C; Lo Presti, Maria A; Raso, Antonella; Orlando, Ambrogio; Oliva, Lorenzo; Giofré, Maria R; Maggio, Aurelio; Mattaliano, Anna; Macaluso, Alfredo; Cottone, Mario
2005-12-01
A defect of gastrointestinal barrier function is considered to represent an important step in the pathogenesis of Crohn's disease (CD) but the mechanisms leading to an increased intestinal permeability (IP) are poorly understood. Since IP is influenced by pro-inflammatory mediators, it seems likely that a genetically determined abnormal immune response may lead to a loss of barrier function. In a geographic area in Southern Italy with high incidence of CD we investigated IP (lactulose/mannitol testing) together with the three main mutations of the NOD2/CARD15 and the D299G polymorphism of the toll-like receptor (TLR)-4 gene in 23 families of CD patients (patients and first-degree relatives). Forty-eight percent of CD patients and 40% of their healthy relatives were found to have an abnormal IP compared to 5% of an appropriate control population (p < 0.0001). IP, however, was not associated with the L1007finsC mutation of the NOD2/CARD15 or the D299G variant of the TLR-4 gene. Allele frequency of the only L1007finsC mutation of CARD15 was significantly increased in patients (8.7%, p < 0.003) and in relatives (8.3%, p < 0.024) compared with controls (2.4%), whereas the D299G variant of the TLR-4 gene was found to be increased only in relatives (8.3%, p < 0.022), but not in patients (4.3%) compared with the control population (1.7%). There was no association between IP and genetic markers. Our findings showed a very high proportion of healthy first-degree relatives to bare alterations suggested to constitute determinants of CD. Mutations of NOD2/CARD15 or TLR-4, however, do not lead to permeability defects emphasizing the importance of additional environmental and/or genetic factors for pathogenesis.
Being surveyed can change later behavior and related parameter estimates
Zwane, Alix Peterson; Zinman, Jonathan; Van Dusen, Eric; Pariente, William; Null, Clair; Miguel, Edward; Kremer, Michael; Hornbeck, Richard; Giné, Xavier; Duflo, Esther; Devoto, Florencia; Crepon, Bruno; Banerjee, Abhijit
2011-01-01
Does completing a household survey change the later behavior of those surveyed? In three field studies of health and two of microlending, we randomly assigned subjects to be surveyed about health and/or household finances and then measured subsequent use of a related product with data that does not rely on subjects' self-reports. In the three health experiments, we find that being surveyed increases use of water treatment products and take-up of medical insurance. Frequent surveys on reported diarrhea also led to biased estimates of the impact of improved source water quality. In two microlending studies, we do not find an effect of being surveyed on borrowing behavior. The results suggest that limited attention could play an important but context-dependent role in consumer choice, with the implication that researchers should reconsider whether, how, and how much to survey their subjects. PMID:21245314
Estimation of Relative Elasticities of Substitution and Relative Compensation for Part-Time Faculty.
ERIC Educational Resources Information Center
Tuckman, Howard P.; Katz, David A.
1981-01-01
Using data from 881 higher education institutions and a mathematical model, researchers related the estimated compensation rates of part-time faculty members to their institutional types and sexes. Results indicate a growing compensation gap between part- and full-time faculty and increasing substitutability of part- for full-time teachers. (RW)
Dunn, T.L.
1993-12-14
This multidisciplinary study is designed to provide improvements in advanced reservoir characterization techniques. This goal is to be accomplished through: (1) an examination of the spatial variation and anisotropy of relative permeability in the Tensleep Sandstone reservoirs of Wyoming; (2) the placement of that variation and anisotropy into paleogeographic, depositional, and diagenetic frameworks; (3) the development of pore-system imagery techniques for the calculation of relative permeability; and (4) reservoir simulations testing the impact of relative permeability anisotropy and spatial variation on Tensleep Sandstone reservoir enhanced oil recovery. Concurrent efforts are aimed at understanding the spatial and dynamic alteration in sandstone reservoirs that is caused by rock-fluid interaction during CO{sub 2} enhanced oil recovery processes. The work focuses on quantifying the interrelationship of fluid-rock interaction with lithologic characterization in terms of changes in relative permeability, wettability, and pore structure, and with fluid characterization in terms of changes in chemical composition and fluid properties. This work will establish new criteria for the susceptibility of Tensleep Sandstone reservoirs to formation alteration that results in a change in relative permeability and wellbore scale damage. This task will be accomplished by flow experiments using core material; examination of regional trends in water chemistry; examination of local water chemistry trends on the scale of a field; and chemical modeling of the reservoir and experimental systems in order to scale-up the experiments to reservoir conditions.
Distribution Theory for Glass's Estimator of Effect Size and Related Estimators.
ERIC Educational Resources Information Center
Hedges, Larry V.
1981-01-01
Glass's estimator of effect size, the sample mean difference divided by the sample standard deviation, is studied in the context of an explicit statistical model. The exact distribution of Glass's estimator is obtained and the estimator is shown to have a small sample bias. Alternatives are proposed and discussed. (Author/JKS)
Relating the Hadamard Variance to MCS Kalman Filter Clock Estimation
NASA Technical Reports Server (NTRS)
Hutsell, Steven T.
1996-01-01
The Global Positioning System (GPS) Master Control Station (MCS) currently makes significant use of the Allan Variance. This two-sample variance equation has proven excellent as a handy, understandable tool, both for time domain analysis of GPS cesium frequency standards, and for fine tuning the MCS's state estimation of these atomic clocks. The Allan Variance does not explicitly converge for the nose types of alpha less than or equal to minus 3 and can be greatly affected by frequency drift. Because GPS rubidium frequency standards exhibit non-trivial aging and aging noise characteristics, the basic Allan Variance analysis must be augmented in order to (a) compensate for a dynamic frequency drift, and (b) characterize two additional noise types, specifically alpha = minus 3, and alpha = minus 4. As the GPS program progresses, we will utilize a larger percentage of rubidium frequency standards than ever before. Hence, GPS rubidium clock characterization will require more attention than ever before. The three sample variance, commonly referred to as a renormalized Hadamard Variance, is unaffected by linear frequency drift, converges for alpha is greater than minus 5, and thus has utility for modeling noise in GPS rubidium frequency standards. This paper demonstrates the potential of Hadamard Variance analysis in GPS operations, and presents an equation that relates the Hadamard Variance to the MCS's Kalman filter process noises.
Changes in airway permeability and responsiveness after exposure to ozone. [Sheep
Abraham, W.M.; Delehunt, J.C.; Yerger, L.; Marchette, B.; Oliver, W. Jr.
1984-06-01
The relationship between airway responsiveness and the permeability of histamine through the airways in conscious sheep after exposure to ozone (O/sub 3/ was examined). Airway responsiveness was assessed by measuring the change from baseline in mean pulmonary flow resistance following a controlled 2-min inhalation challenge with 1% histamine, containing 200 ..mu..Ci/ml of (/sup 3/H)histamine. The rate of appearance of the (/sup 3/H)histamine in the plasma during inhalation challenge was used to estimate airway permeability. To perturb the airways, conscious sheep were exposed to either 0.5 or 1.0 ppm O/sub 3/ for 2 hr via an endotracheal tube. Airway responsiveness and airway permeability were measured prior to and 1 day after exposure. In six sheep exposed to 0.5 ppm O/sub 3/, increased airway responsiveness and airway permeability were obseved 1 day after exposure. Four of seven sheep exposed to 1.0 ppm O/sub 3/ had enhanced airway responsiveness and airway permeability, while the remaining three sheep showed corresponding decreases in airway responsiveness and airway permeability. Since the O/sub 3/-induced directional changes in airway responsiveness paralleled the directional changes in airway permeability in both the positive and negative directions, it was concluded that changes in airway responsiveness to inhaled histamine following exposure to O/sub 3/ may be related to concomitant changes in airway permeability to this agent.
EPA Permeable Surface Research
EPA recognizes permeable surfaces as an effective post-construction infiltration-based Best Management Practice to mitigate the adverse effects of stormwater runoff. The professional user community conceptually embraces permeable surfaces as a tool for making runoff more closely...
EPA Permeable Surface Research
EPA recognizes permeable surfaces as an effective post-construction infiltration-based Best Management Practice to mitigate the adverse effects of stormwater runoff. The professional user community conceptually embraces permeable surfaces as a tool for making runoff more closely...
Permeability of Clay Concretes
NASA Astrophysics Data System (ADS)
Solomon, F.; Ekolu, S. O.
2015-11-01
This paper presents an investigation on the effect of clay addition on water permeability and air permeability of concretes. Clay concrete mixes consisted of 0 to 40% clay content incorporated as cement replacement. Flow methods using triaxial cells and air permeameters were used for measuring the injected water and air flows under pressure. It was found that the higher the clay content in the mixture, the greater the permeability. At higher water-cement ratios (w/c), the paste matrix is less dense and easily allows water to ingress into concrete. But at high clay contents of 30 to 40% clay, the variation in permeability was significantly diminished among different concrete mixtures. It was confirmed that air permeability results were higher than the corresponding water permeability values when all permeability coefficients were converted to intrinsic permeability values.
Estimating Defoliation of Hardwoods Using Blade-petiole Relations
Harry T. Valentine
1978-01-01
Prediction equations for estimating leaf blade area and dry weight from measurements of petiole thickness were used to estimate defoliation of Populus tremuloides, Acer rubrum, Quercus rubra, and Q. alba. On one tree of each species, a sample of leaves was artifically browsed in May and...
State Medicaid Pharmacy Payments and Their Relation to Estimated Costs
Adams, E. Kathleen; Kreling, David H.; Gondek, Kathleen
1994-01-01
Although prescription drugs do not appear to be a primary source of recent surges in Medicaid spending, their share of Medicaid expenditures has risen despite efforts to control costs. As part of a general concern with prescription drug policy, Congress mandated a study of the adequacy of Medicaid payments to pharmacies. In this study, several data sources were used to develop 1991 estimates of average pharmacy ingredient and dispensing costs. A simulation was used to estimate the amounts States pay. Nationally, simulated payments averaged 96 percent of estimated costs overall but were lower for dispensing costs (79 percent) and higher for ingredient costs (102 percent). PMID:10137796
Seismogenic Permeability and Fluid Flow in Crustal Rocks
NASA Astrophysics Data System (ADS)
Talwani, P.
2005-12-01
Pore fluids play both a chemical and a mechanical role in the onset of seismicity. The mechanical role is usually associated with time dependent increases in pore pressures. A study of the temporal and spatial pattern of reservoir and fluid injection induced seismicity, and aftershock patterns of large earthquakes suggest that these pore pressure increases occur by diffusion to hypocentral regions through suitably located fractures. The efficiency of this diffusion depends on the hydraulic diffusivity of the fractures, which in turn is related to their intrinsic permeability, k. I have estimated the permeability from the temporal and spatial pattern of these earthquakes. For 82/84 cases this fracture permeability was found to lie between 0.5x10-15 m2 and 50x10-15 m2 (0.5 to 50 mDarcy), a range that I have labeled seismogenic permeability, ks. Theoretical modeling shows that when the fracture permeability, k
Calabrò, P S; Moraci, N; Suraci, P
2012-03-15
This paper presents the results of laboratory column tests aimed at defining the optimum weight ratio of zero-valent iron (ZVI)/pumice granular mixtures to be used in permeable reactive barriers (PRBs) for the removal of nickel from contaminated groundwater. The tests were carried out feeding the columns with aqueous solutions of nickel nitrate at concentrations of 5 and 50 mg/l using three ZVI/pumice granular mixtures at various weight ratios (10/90, 30/70 and 50/50), for a total of six column tests; two additional tests were carried out using ZVI alone. The most successful compromise between reactivity (higher ZVI content) and long-term hydraulic performance (higher Pumice content) seems to be given by the ZVI/pumice granular mixture with a 30/70 weight ratio. Copyright Â© 2011 Elsevier B.V. All rights reserved.
Permeability structure and its influence on microbial activity at off-Shimokita basin, Japan
NASA Astrophysics Data System (ADS)
Tanikawa, W.; Yamada, Y.; Sanada, Y.; Kubo, Y.; Inagaki, F.
2016-12-01
The microbial populations and the limit of microbial life are probably limited by chemical, physical, and geological conditions, such as temperature, pore water chemistry, pH, and water activity; however, the key parameters affecting growth in deep subseafloor sediments remain unclarified (Hinrichs and Inagaki 2012). IODP expedition 337 was conducted near a continental margin basin off Shimokita Peninsula, Japan to investigate the microbial activity under deep marine coalbed sediments down to 2500 mbsf. Inagaki et al. (2015) discovered that microbial abundance decreased markedly with depth (the lowest cell density of <1 cell/cm3 was recorded below 2000 mbsf), and that the coal bed layers had relatively higher cell densities. In this study, permeability was measured on core samples from IODP Expedition 337 and Expedition CK06-06 in the D/V Chikyu shakedown cruise. Permeability was measured at in-situ effective pressure condition. Permeability was calculated by the steady state flow method by keeping differential pore pressure from 0.1 to 0.8 MPa.Our results show that the permeability for core samples decreases with depth from 10-16 m2 on the seafloor to 10-20 m2 at the bottom of hole. However, permeability is highly scattered within the coal bed unit (1900 to 2000 mbsf). Permeabilities for sandstone and coal is higher than those for siltstone and shale, therefore the scatter of the permeabilities at the same unit is due to the high variation of lithology. The highest permeability was observed in coal samples and this is probably due to formation of micro cracks (cleats). Permeability estimated from the NMR logging using the empirical parameters is around two orders of magnitude higher than permeability of core samples, even though the relative permeability variation at vertical direction is quite similar between core and logging data.The higher cell density is observed in the relatively permeable formation. On the other hand, the correlation between cell density
Chatterjee, Nabamita; Nagarajan, Shantha
2006-08-01
The relative binding of seed water and seed coat membrane stability were measured in two contrasting wheat (Triticum aestivum L) varieties, HDR 77 (drought-tolerant) and HD 2009 (susceptible) using seed water sorption isotherms, electrical conductivity (EC) of leachates and desorption-absorption isotherms. Analysis of sorption isotherm at 25 degrees C showed that the seeds of HDR 77 had significantly higher number of strong binding sites, with correspondingly greater amount of seed water as strongly bound water, as compared to HD 2009. Total number of binding sites was also higher in HDR 77 than HD 2009, which explained the better desiccation tolerance and higher capacity to bind water in seeds of HDR 77. EC of seed leachate in both varieties did not change with respect to change in equilibrium relative humidity (RII), indicating the general seed coat membrane stability of wheat seeds. However, absolute conductivity values were higher for HD 2009. showing its relatively porous seed coat membrane. Significantly lower area enclosed by the desorption-absorption isotherm loop in HDR 77, as compared to HD 2009 also indicated the greater membrane integrity of HDR 77. Germination and seedling vigour of HD 2009 were reduced when equilibrated over very low and very high RH. In contrast, germination and vigour in HDR 77 were maintained high, except at very high RH, indicating again its desiccation tolerance. Thus, the study demonstrated the relative drought tolerance of HDR 77, on the basis of seed water-binding characteristics and seed membrane stability. Seed membrane stability as measured by seed leachate conductivity or as area under dehydration-rehydration loop may be used as a preliminary screening test for drought tolerance in wheat.
Film Permeability Determination Using Static Permeability Cells
The permeability of tarps to soil fumigant pesticides varies depending on the active ingredient chemical: dimethyl disulfide (DMDS), methyl bromide, chloropicrin, or other. The diffusion rate can be represented by the mass transfer coefficient (MTC).
NASA Astrophysics Data System (ADS)
Austin Suthanthiraraj, Pearlson Prashanth
We present the results of an extensive experimental study on the effects of hysteresis on permanent capillary trapping and relative permeability of CO2/brine and supercritical (sc)CO2+SO2/brine systems. We performed numerous unsteady- and steady-state drainage and imbibition full-recirculation flow experiments in three different sandstone rock samples, i.e., low and high-permeability Berea, Nugget sandstones, and Madison limestone carbonate rock sample. A state-of-the-art reservoir conditions core-flooding system was used to perform the tests. The core-flooding apparatus included a medical CT scanner to measure in-situ saturations. The scanner was rotated to the horizontal orientation allowing flow tests through vertically-placed core samples with about 3.8 cm diameter and 15 cm length. Both scCO2 /brine and gaseous CO2 (gCO2)/brine fluid systems were studied. The gaseous and supercritical CO2/brine experiments were carried out at 3.46 and 11 MPa back pressures and 20 and 55°C temperatures, respectively. Under the above-mentioned conditions, the gCO2 and scCO2 have 0.081 and 0.393 gr/cm3 densities, respectively. During unsteady-state tests, the samples were first saturated with brine and then flooded with CO2 (drainage) at different maximum flow rates. The drainage process was then followed by a low flow rate (0.375 cm 3/min) imbibition until residual CO2 saturation was achieved. Wide flow rate ranges of 0.25 to 20 cm3/min for scCO2 and 0.125 to 120 cm3min for gCO2 were used to investigate the variation of initial brine saturation (Swi) with maximum CO2 flow rate and variation of trapped CO2 saturation (SCO2r) with Swi. For a given Swi, the trapped scCO2 saturation was less than that of gCO2 in the same sample. This was attributed to brine being less wetting in the presence of scCO2 than in the presence of gCO 2. During the steady-state experiments, after providing of fully-brine saturated core, scCO2 was injected along with brine to find the drainage curve and as
Theoretical studies of permeability inversion from seismoelectric logs
NASA Astrophysics Data System (ADS)
Hu, H.; Guan, W.; Zhao, W.
2012-04-01
Permeability is one of the most important parameters for evaluating the level of difficulty in oil and gas exploitation. A quick, continuous and accurate in-situ estimate of reservoir permeability is highly significant. Stoneley wave logs have been used to determine formation permeability (Tang and Cheng, 1996). However, the inversion errors of this method are too big in low-permeability formations, especially in high-porosity and low-permeability formations resulting from the high clay content in pores. In this study, we propose to invert permeability by using the full waveforms of seismoelectric logs with low frequencies. This method is based on the relationship of permeability with the ratio of the electric excitation intensity to the pressure field's (REP) with respect to the Stoneley wave in seismoelectric logs. By solving the governing equations for electrokinetic coupled wavefields in homogeneous fluid-saturated porous media (Pride, 1994), we calculate the full waveforms of the borehole seismoelectric wavefields excited by a point pressure source and investigate frequency-dependent excitation intensities of the mode waves and excitation intensities of the real branch points in seismoelectric logs. It is found that the REP's phase, which reflects the phase discrepancy between the Stoneley-wave-induced electric field and the acoustic pressure, is sensitive to formation permeability. To check the relation between permeability and REP's phase qualitatively, an approximate expression of the tangent of the REP's argument is derived theoretically as tan(θEP) ≈-ωc/ω = -φη/ (2πfα ∞ρfκ0), where θEPdenotes the arguments of the REP and their principal value is the REP's phase,ω is the angular frequency,ωc is a critical angular frequency that separates the low-frequency viscous flow from the high-frequency inertial flow, φ is the porosity, α∞ is the tortuosity, κ0 is the Darcy permeability, ρf and η are the density and the viscosity of the pore
Estimated Perennial Streams of Idaho and Related Geospatial Datasets
Rea, Alan; Skinner, Kenneth D.
2009-01-01
The perennial or intermittent status of a stream has bearing on many regulatory requirements. Because of changing technologies over time, cartographic representation of perennial/intermittent status of streams on U.S. Geological Survey (USGS) topographic maps is not always accurate and (or) consistent from one map sheet to another. Idaho Administrative Code defines an intermittent stream as one having a 7-day, 2-year low flow (7Q2) less than 0.1 cubic feet per second. To establish consistency with the Idaho Administrative Code, the USGS developed regional regression equations for Idaho streams for several low-flow statistics, including 7Q2. Using these regression equations, the 7Q2 streamflow may be estimated for naturally flowing streams anywhere in Idaho to help determine perennial/intermittent status of streams. Using these equations in conjunction with a Geographic Information System (GIS) technique known as weighted flow accumulation allows for an automated and continuous estimation of 7Q2 streamflow at all points along a stream, which in turn can be used to determine if a stream is intermittent or perennial according to the Idaho Administrative Code operational definition. The selected regression equations were applied to create continuous grids of 7Q2 estimates for the eight low-flow regression regions of Idaho. By applying the 0.1 ft3/s criterion, the perennial streams have been estimated in each low-flow region. Uncertainty in the estimates is shown by identifying a 'transitional' zone, corresponding to flow estimates of 0.1 ft3/s plus and minus one standard error. Considerable additional uncertainty exists in the model of perennial streams presented in this report. The regression models provide overall estimates based on general trends within each regression region. These models do not include local factors such as a large spring or a losing reach that may greatly affect flows at any given point. Site-specific flow data, assuming a sufficient period of
Clogging in permeable concrete: A review.
Kia, Alalea; Wong, Hong S; Cheeseman, Christopher R
2017-05-15
Permeable concrete (or "pervious concrete" in North America) is used to reduce local flooding in urban areas and is an important sustainable urban drainage system. However, permeable concrete exhibits reduction in permeability due to clogging by particulates, which severely limits service life. This paper reviews the clogging mechanism and current mitigating strategies in order to inform future research needs. The pore structure of permeable concrete and characteristics of flowing particulates influence clogging, which occurs when particles build-up and block connected porosity. Permeable concrete requires regular maintenance by vacuum sweeping and pressure washing, but the effectiveness and viability of these methods is questionable. The potential for clogging is related to the tortuosity of the connected porosity, with greater tortuosity resulting in increased potential for clogging. Research is required to develop permeable concrete that can be poured on-site, which produces a pore structure with significantly reduced tortuosity.
The HINTS is designed to produce reliable estimates at the national and regional levels. GIS maps using HINTS data have been used to provide a visual representation of possible geographic relationships in HINTS cancer-related variables.
Van As, Henk
2007-01-01
Water content and hydraulic conductivity, including transport within cells, over membranes, cell-to-cell, and long-distance xylem and phloem transport, are strongly affected by plant water stress. By being able to measure these transport processes non-invasely in the intact plant situation in relation to the plant (cell) water balance, it will be possible explicitly or implicitly to examine many aspects of plant function, plant performance, and stress responses. Nuclear magnetic resonance imaging (MRI) techniques are now available that allow studying plant hydraulics on different length scales within intact plants. The information within MRI images can be manipulated in such a way that cell compartment size, water membrane permeability, water cell-to-cell transport, and xylem and phloem flow hydraulics are obtained in addition to anatomical information. These techniques are non-destructive and non-invasive and can be used to study the dynamics of plant water relations and water transport, for example, as a function of environmental (stress) conditions. An overview of NMR and MRI methods to measure such information is presented and hardware solutions for minimal invasive intact plant MRI are discussed.
Pyrotechnic deflagration velocity and permeability
Begeal, D R; Stanton, P L
1982-01-01
Particle size, porosity, and permeability of the reactive material have long been considered to be important factors in propellant burning rates and the deflagration-to-detonation transition in explosives. It is reasonable to assume that these same parameters will also affect the deflagration velocity of pyrotechnics. This report describes an experimental program that addresses the permeability of porous solids (particulate beds), in terms of particle size and porosity, and the relationship between permeability and the behavior of pyrotechnics and explosives. The experimental techniques used to acquire permeability data and to characterize the pyrotechnic burning are discussed. Preliminary data have been obtained on the burning characteristics of titanium hydride/potassium perchlorate (THKP) and boron/calcium chromate (BCCR). With THKP, the velocity of a pressure wave (from hot product gases) in the unburned region shows unsteady behavior which is related to the initial porosity or permeability. Simultaneous measurements with pressure gauges and ion gauges reveal that the pressure wave precedes the burn front. Steady burning of BCCR was observed with pressure gauge diagnostics and with a microwave interferometry technique.
An Estimate Related to the Strong Maximum Principle.
1979-09-01
Some of the most useful and important tools in the study of elliptic boundary value problems are maximum principles . So called strong maximum... principles provide strict inequalities when appropriate conditions are fulfilled. In this work a strong maximum principle is improved by exhibiting an explicit estimate sharper than what follows from usual arguments. (Author)
Matching using estimated propensity scores: relating theory to practice.
Rubin, D B; Thomas, N
1996-03-01
Matched sampling is a standard technique in the evaluation of treatments in observational studies. Matching on estimated propensity scores comprises an important class of procedures when there are numerous matching variables. Recent theoretical work (Rubin, D. B. and Thomas, N., 1992, The Annals of Statistics 20, 1079-1093) on affinely invariant matching methods with ellipsoidal distributions provides a general framework for evaluating the operating characteristics of such methods. Moreover, Rubin and Thomas (1992, Biometrika 79, 797-809) uses this framework to derive several analytic approximations under normality for the distribution of the first two moments of the matching variables in samples obtained by matching on estimated linear propensity scores. Here we provide a bridge between these theoretical approximations and actual practice. First, we complete and refine the nomal-based analytic approximations, thereby making it possible to apply these results to practice. Second, we perform Monte Carlo evaluations of the analytic results under normal and nonnormal ellipsoidal distributions, which confirm the accuracy of the analytic approximations, and demonstrate the predictable ways in which the approximations deviate from simulation results when normal assumptions are violated within the ellipsoidal family. Third, we apply the analytic approximations to real data with clearly nonellipsoidal distributions, and show that the theoretical expressions, although derived under artificial distributional conditions, produce useful guidance for practice. Our results delineate the wide range of settings in which matching on estimated linear propensity scores performs well, thereby providing useful information for the design of matching studies. When matching with a particular data set, our theoretical approximations provide benchmarks for expected performance under favorable conditions, thereby identifying matching variables requiring special treatment. After matching is
Estimating Wartime Support Resource Requirements. Statistical and Related Policy Issues.
1984-07-01
Fitzgerald of Headquarters, Air Force Logistics Command explained the engine requirements Computation arid identified a body of past work that suggests that...C-5 and other aircraft, as well as the more general problem of * estimating wartime support resource requirements. 3 " Cannibalization " is the use of...service. The missing parts should eventually be replaced, but some TF39 engines have been * cannibalized so extensively that it might be cheaper to
Katneni, Kasiram; Charman, Susan A; Porter, Christopher J H
2006-10-01
The objective of this study was to develop a general method to assess the intestinal permeability of poorly water-soluble drugs where low-aqueous drug solubility requires conduct of experiments under solubilizing experimental conditions. The permeability (Papp) of diazepam (DIA) was assessed across excised rat jejunum in the absence (Pappcontrol) and presence (Pappuncorr) of polysorbate-80 (PS-80). The micellar association constant (Ka) of DIA, estimated via equilibrium solubility studies, was used to correct Pappuncorr data and obtain an estimate of the true permeability coefficient (Pappcorr). An alternate approach was also developed (the reciprocal permeability approach) to allow direct estimation of Pappcorr without the need for independent estimation of Ka. The approach was further examined experimentally using a range of model drugs. DIA Pappcorr values obtained using the Ka from equilibrium solubility studies deviated from Papp(control) values, especially at PS-80 concentrations above 0.1% w/v. In contrast, data obtained using the reciprocal permeability method were consistent with Pappcontrol across the PS-80 concentration range. Similar trends were observed with propranolol (PRO), antipyrine (ANT), naproxen (NAP), and cinnarizine (CIN). The reciprocal permeability approach therefore provides a simple and accurate method by which the permeability of poorly water-soluble compounds may be estimated under solubilizing conditions.
Crustal permeability: Introduction to the special issue
Ingebritsen, Steven E.; Gleeson, Tom
2015-01-01
The topic of crustal permeability is of broad interest in light of the controlling effect of permeability on diverse geologic processes and also timely in light of the practical challenges associated with emerging technologies such as hydraulic fracturing for oil and gas production (‘fracking’), enhanced geothermal systems, and geologic carbon sequestration. This special issue of Geofluids is also motivated by the historical dichotomy between the hydrogeologic concept of permeability as a static material property that exerts control on fluid flow and the perspective of economic geologists, geophysicists, and crustal petrologists who have long recognized permeability as a dynamic parameter that changes in response to tectonism, fluid production, and geochemical reactions. Issues associated with fracking, enhanced geothermal systems, and geologic carbon sequestration have already begun to promote a constructive dialog between the static and dynamic views of permeability, and here we have made a conscious effort to include both viewpoints. This special issue also focuses on the quantification of permeability, encompassing both direct measurement of permeability in the uppermost crust and inferential permeability estimates, mainly for the deeper crust.
Kanehiro, B.Y.; Lai, C.H.; Stow, S.H.
1987-05-01
Conceptual models for sedimentary rock settings that could be used in future evaluation and suitability studies are being examined through the DOE Repository Technology Program. One area of concern for the hydrologic aspects of these models is discrete fracture flow analysis as related to the estimation of the size of the representative elementary volume, evaluation of the appropriateness of continuum assumptions and estimation of the large-scale permeabilities of sedimentary rocks. A basis for preliminary analysis of flow in fracture systems of the types that might be expected to occur in low permeability sedimentary rocks is presented. The approach used involves numerical modeling of discrete fracture flow for the configuration of a large-scale hydrologic field test directed at estimation of the size of the representative elementary volume and large-scale permeability. Analysis of fracture data on the basis of this configuration is expected to provide a preliminary indication of the scale at which continuum assumptions can be made.
2D and 3D imaging resolution trade-offs in quantifying pore throats for prediction of permeability
Beckingham, Lauren E.; Peters, Catherine A.; Um, Wooyong; Jones, Keith W.; Lindquist, W.Brent
2013-09-03
Although the impact of subsurface geochemical reactions on porosity is relatively well understood, changes in permeability remain difficult to estimate. In this work, pore-network modeling was used to predict permeability based on pore- and pore-throat size distributions determined from analysis of 2D scanning electron microscopy (SEM) images of thin sections and 3D X-ray computed microtomography (CMT) data. The analyzed specimens were a Viking sandstone sample from the Alberta sedimentary basin and an experimental column of reacted Hanford sediments. For the column, a decrease in permeability due to mineral precipitation was estimated, but the permeability estimates were dependent on imaging technique and resolution. X-ray CT imaging has the advantage of reconstructing a 3D pore network while 2D SEM imaging can easily analyze sub-grain and intragranular variations in mineralogy. Pore network models informed by analyses of 2D and 3D images at comparable resolutions produced permeability esti- mates with relatively good agreement. Large discrepancies in predicted permeabilities resulted from small variations in image resolution. Images with resolutions 0.4 to 4 lm predicted permeabilities differ- ing by orders of magnitude. While lower-resolution scans can analyze larger specimens, small pore throats may be missed due to resolution limitations, which in turn overestimates permeability in a pore-network model in which pore-to-pore conductances are statistically assigned. Conversely, high-res- olution scans are capable of capturing small pore throats, but if they are not actually flow-conducting predicted permeabilities will be below expected values. In addition, permeability is underestimated due to misinterpreting surface-roughness features as small pore throats. Comparison of permeability pre- dictions with expected and measured permeability values showed that the largest discrepancies resulted from the highest resolution images and the best predictions of
A permeability and compliance contrast measured hydrogeologically on the San Andreas Fault
NASA Astrophysics Data System (ADS)
Xue, Lian; Brodsky, Emily E.; Erskine, Jon; Fulton, Patrick M.; Carter, Reed
2016-03-01
Hydrogeologic properties of fault zones are critical to faulting processes; however, they are not well understood and difficult to measure in situ, particularly in low-permeability fractured bedrock formations. Analysis of continuous water level response to Earth tides in monitoring wells provides a method to measure the in situ hydrogeologic properties. We utilize four monitoring wells within the San Andreas Fault zone near Logan Quarry to study the fault zone hydrogeologic architecture by measuring the water level tidal response. The specific storage and permeability inferred from the tidal response suggest that there is a difference in properties at different distances from the fault. The sites closer to the fault have higher specific storage and higher permeability than farther from the fault. This difference of properties might be related to the fault zone fracture distribution decreasing away from the fault. Although permeability channels near faults have been documented before, the difference in specific storage near the fault is a new observation. The inferred compliance contrast is consistent with prior estimates of elastic moduli in the near-fault environment, but the direct measurements are new. The combination of measured permeability and storage yields a diffusivity of about 10-2 m2/s at all the sites both near and far from the fault as a result of the competing effects of permeability and specific storage. This uniform diffusivity structure suggests that the permeability contrast might not efficiently trap fluids during the interseismic period.
Placental Permeability of Lead
Carpenter, Stanley J.
1974-01-01
The detection of lead in fetal tissues by chemical analysis has long been accepted as prima facie evidence for the permeability of the placenta to this nonessential trace metal. However, only a few investigations, all on lower mammalian species, have contributed any direct experimental data bearing on this physiological process. Recent radioactive tracer and radioautographic studies on rodents have shown that lead crosses the placental membranes rapidly and in significant amounts even at relatively low maternal blood levels. While it is not possible to extrapolate directly the results of these experiments to humans because of differences in placental structure and other factors, the results do serve as a warning of the possible hazard to the human embryo and fetus of even low levels of lead in the maternal system. PMID:4857497
Committee neural network model for rock permeability prediction
NASA Astrophysics Data System (ADS)
Bagheripour, Parisa
2014-05-01
Quantitative formulation between conventional well log data and rock permeability, undoubtedly the most critical parameter of hydrocarbon reservoir, could be a potent tool for solving problems associated with almost all tasks involved in petroleum engineering. The present study proposes a novel approach in charge of the quest for high-accuracy method of permeability prediction. At the first stage, overlapping of conventional well log data (inputs) was eliminated by means of principal component analysis (PCA). Subsequently, rock permeability was predicted from extracted PCs using multi-layer perceptron (MLP), radial basis function (RBF), and generalized regression neural network (GRNN). Eventually, a committee neural network (CNN) was constructed by virtue of genetic algorithm (GA) to enhance the precision of ultimate permeability prediction. The values of rock permeability, derived from the MPL, RBF, and GRNN models, were used as inputs of CNN. The proposed CNN combines results of different ANNs to reap beneficial advantages of all models and consequently producing more accurate estimations. The GA, embedded in the structure of the CNN assigns a weight factor to each ANN which shows relative involvement of each ANN in overall prediction of rock permeability from PCs of conventional well logs. The proposed methodology was applied in Kangan and Dalan Formations, which are the major carbonate reservoir rocks of South Pars Gas Field-Iran. A group of 350 data points was used to establish the CNN model, and a group of 245 data points was employed to assess the reliability of constructed CNN model. Results showed that the CNN method performed better than individual intelligent systems performing alone.
Katneni, Kasiram; Charman, Susan A; Porter, Christopher J H
2008-10-01
The roles of the unstirred water layer (UWL) and receptor sink on the in-vitro transmembrane permeability of an increasingly lipophilic series of compounds (mannitol (MAN), diazepam (DIA) and cinnarizine (CIN)) have been assessed. Altered carbogen bubbling rates were used as a means to change the UWL thickness and polysorbate-80 (PS-80), bovine serum albumin (BSA) and alpha-1-acid glycoprotein (AAG) were employed to alter sink conditions. After correction for solubilisation, Papp data for MAN, DIA and CIN were consistent across varying donor PS-80 concentrations suggesting that for the drugs examined here, the donor UWL did not limit in-vitro permeability. Similarly, altered bubbling rates and receptor sink conditions had no impact on the permeability of MAN. In contrast, decreasing the size of the receptor UWL or adding solubilising agents to the receptor sink resulted in modest enhancements to the permeability of the more lipophilic probe DIA. For the most lipophilic compound, CIN, very significant changes to measured permeability (>30 fold) were possible, but were most evident only after concomitant changes to both the UWL and sink conditions, suggesting that the effectiveness of enhanced sink conditions were dependent on a decrease in the width of the UWL.
Ghazali, Farid Bin Che
2003-01-01
This is an update on the present integrated knowledge regarding dentine permeability that assumed a role in dentine sensitivity and contribute clinically to the effective bonding properties of restorative dental materials. This paper will attempt to refer to in vivo and in vitro studies of dentine permeability and the various interrelated factors governing it. PMID:23365497
Ghazali, Farid Bin Che
2003-01-01
This is an update on the present integrated knowledge regarding dentine permeability that assumed a role in dentine sensitivity and contribute clinically to the effective bonding properties of restorative dental materials. This paper will attempt to refer to in vivo and in vitro studies of dentine permeability and the various interrelated factors governing it.
Nexal membrane permeability to anions
1978-01-01
The permeability of the septa of the earthworm in the median axon has been calculated for the anions fluorescein and its halogen derivatives. The values ranged from 5.4 X 10(-5) to 4 X 10(-6) cm/s. Previously, the septa had been shown to contain nexuses. By using freeze-fracture material, the surface area of nexus on the septal membranes was determined to be 4.5%, very similar to the percentage of nexus in the intercalated disk of mammalian myocardium. Plasma membrane permeability to these dyes was also calculated and shown to be much less than that of the septal membranes. In addition, an estimate of cytoplasmic binding for each dye was made, and most dyes showed little or no binding with the exception of aminofluorescein. PMID:702107
Acoustic method for permeability measurement of tissue-engineering scaffold
NASA Astrophysics Data System (ADS)
Schiavi, A.; Guglielmone, C.; Pennella, F.; Morbiducci, U.
2012-10-01
An accurate intrinsic permeability measurement system has been designed and realized in order to quantify the inter-pore connectivity structure of tissue-engineering scaffolds by using a single (pressure) transducer. The proposed method uses a slow alternating airflow as a fluid medium and allows at the same time a simple and accurate measurement procedure. The intrinsic permeability is determined in the linear Darcy's region, and deviation from linearity due to inertial losses is also quantified. The structural parameters of a scaffold, such as effective porosity, tortuosity and effective length of cylindrical pores, are estimated using the classical Ergun's equation recently modified by Wu et al. From this relation, it is possible to achieve a well-defined range of data and associated uncertainties for characterizing the structure/architecture of tissue-engineering scaffolds. This quantitative analysis is of paramount importance in tissue engineering, where scaffold topological features are strongly related to their biological performance.
Leaf Relative Water Content Estimated from Leaf Reflectance and Transmittance
NASA Technical Reports Server (NTRS)
Vanderbilt, Vern; Daughtry, Craig; Dahlgren, Robert
2016-01-01
Remotely sensing the water status of plants and the water content of canopies remain long term goals of remote sensing research. In the research we report here, we used optical polarization techniques to monitor the light reflected from the leaf interior, R, as well as the leaf transmittance, T, as the relative water content (RWC) of corn (Zea mays) leaves decreased. Our results show that R and T both change nonlinearly. The result show that the nonlinearities cancel in the ratio R/T, which appears linearly related to RWC for RWC less than 90%. The results suggest that potentially leaf water status and perhaps even canopy water status could be monitored starting from leaf and canopy optical measurements.
Improving Relative Combat Power Estimation: The Road to Victory
2014-06-13
that we shall be many to the enemy’s few.”7 Aristotle in his Rhetoric paid special attention to relative combat power and its importance for the...force employment. Ancient linear warfare hardly touched the complexity of modern war, but the principles of Sun Tzu and Aristotle , including their...8Aristotle, Rhetoric by Aristotle , trans. W. Rhys Roberts (The Pennsylvania State University, Electronic Classics Series, 2010), 20, http://www2
Calibrating NMR measured porosity/permeability relationships using µXRCT measurements
NASA Astrophysics Data System (ADS)
Mason, H. E.; Smith, M. M.; Hao, Y.; Carroll, S.
2015-12-01
Carbonate reservoirs have garnered interest for potential use in carbon capture and storage (CCS) activities. To be suitable for long term carbon dioxide (CO2) storage, they must possess sufficient permeability either through existing connected pore space, or due to reactivity with CO2-acidified fluids. Adequate assessment of the target formation permeability will rely on accurate downhole well-logging tools. Primary among these tools is nuclear magnetic resonance (NMR) well-logging. Application of this tool relies on our ability to relate the porosity and pore distributions measured by NMR to permeability. These methods are challenging to apply in carbonate reservoirs with complex mineralogies where pores sizes often span orders of magnitudes. We have assessed the ability of NMR methods to measure permeability using rocks from the Weyburn-Midale CO2 Monitoring and Storage Project Saskatchewan, Canada and the Arbuckle injection zone at the Wellington CO2 storage demonstration site, Kansas. Results of laboratory measured permeability values of these rocks indicate that the standard NMR methods for predicting permeability values can produce values off by orders of magnitude within the same flow units. In this presentation, we present the results of a combined NMR and micro X-ray computed tomography (μXRCT) study of these rock cores to better estimate downhole permeability values of carbonate rocks. The results of the study suggest that the dramatic differences in predicted permeability values derive from large differences in the matrix porosity, pore network tortuosities, and mineralogy of the various rock units. We will present new laboratory measurements, and methodologies aimed at producing a universal NMR calibration procedure for determining permeability in carbonate reservoirs. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Pressure sensitivity of low permeability sandstones
Kilmer, N.H.; Morrow, N.R.; Pitman, J.K.
1987-01-01
Detailed core analysis has been carried out on 32 tight sandstones with permeabilities ranging over four orders of magnitude (0.0002 to 4.8 mD at 5000 psi confining pressure). Relationships between gas permeability and net confining pressure were measured for cycles of loading and unloading. For some samples, permeabilities were measured both along and across bedding planes. Large variations in stress sensitivity of permeability were observed from one sample to another. The ratio of permeability at a nominal confining pressure of 500 psi to that at 5000 psi was used to define a stress sensitivity ratio. For a given sample, confining pressure vs permeability followed a linear log-log relationship, the slope of which provided an index of pressure sensitivity. This index, as obtained for first unloading data, was used in testing relationships between stress sensitivity and other measured rock properties. Pressure sensitivity tended to increase with increase in carbonate content and depth, and with decrease in porosity, permeability and sodium feldspar. However, scatter in these relationships increased as permeability decreased. Tests for correlations between pressure sensitivity and various linear combinations of variables are reported. Details of pore structure related to diagenetic changes appears to be of much greater significance to pressure sensitivity than mineral composition. ?? 1987.
On GPS Water Vapour estimation and related errors
NASA Astrophysics Data System (ADS)
Antonini, Andrea; Ortolani, Alberto; Rovai, Luca; Benedetti, Riccardo; Melani, Samantha
2010-05-01
Water vapour (WV) is one of the most important constituents of the atmosphere: it plays a crucial role in the earth's radiation budget in the absorption processes both of the incoming shortwave and the outgoing longwave radiation; it is one of the main greenhouse gases of the atmosphere, by far the one with higher concentration. In addition moisture and latent heat are transported through the WV phase, which is one of the driving factor of the weather dynamics, feeding the cloud systems evolution. An accurate, dense and frequent sampling of WV at different scales, is consequently of great importance for climatology and meteorology research as well as operational weather forecasting. Since the development of the satellite positioning systems, it has been clear that the troposphere and its WV content were a source of delay in the positioning signal, in other words a source of error in the positioning process or in turn a source of information in meteorology. The use of the GPS (Global Positioning System) signal for WV estimation has increased in recent years, starting from measurements collected from a ground-fixed dual frequency GPS geodetic station. This technique for processing the GPS data is based on measuring the signal travel time in the satellite-receiver path and then processing such signal to filter out all delay contributions except the tropospheric one. Once the troposheric delay is computed, the wet and dry part are decoupled under some hypotheses on the tropospheric structure and/or through ancillary information on pressure and temperature. The processing chain normally aims at producing a vertical Integrated Water Vapour (IWV) value. The other non troposheric delays are due to ionospheric free electrons, relativistic effects, multipath effects, transmitter and receiver instrumental biases, signal bending. The total effect is a delay in the signal travel time with respect to the geometrical straight path. The GPS signal has the advantage to be nearly
Fredlund, Linda; Winiwarter, Susanne; Hilgendorf, Constanze
2017-04-04
In vitro permeability data have a central place in absorption risk assessments in drug discovery and development. For compounds where active efflux impacts permeability in vitro, the inherent passive membrane permeability ("intrinsic permeability") gives a concentration-independent measure of the compound's permeability. This work describes the validation of an in vitro intrinsic permeability assay and application of the data in a predictive in silico model. Apparent intrinsic permeability (Papp) across Caco-2 cell monolayers is determined in the presence of an optimized cocktail of chemical inhibitors toward the three major efflux transporters ABCB1, ABCC2, and ABCG2. The intrinsic Papp value gives an estimate of passive permeability, which is independent of transporter expression levels and not limited by solubility or cell toxicity. An in silico model has been established to predict the Caco-2 intrinsic permeability and shown to consistently identify highly permeable compounds. The new intrinsic permeability assay is useful for early absorption estimates and suitable for absorption risk assessment in DMPK and pharmaceutical development.
Permeability of porour rhyolite
NASA Astrophysics Data System (ADS)
Cashman, K.; Rust, A.; Wright, H.; Roberge, J.
2003-04-01
The development of permeability in bubble-bearing magmas determines the efficiency of volatile escape during their ascent through volcanic conduits, which, in turn, controls their explosive potential. As permeability requires bubble connectivity, relationships between permeability and porosity in silicic magmas must be controlled by the formation, growth, deformation and coalescence of their constituent bubbles. Although permeability data on porous volcanic pyroclasts are limited, the database can be greatly extended by including data for ceramic and metallic foams1. Several studies indicate that a single number does not adequately describe the permeability of a foam because inertial effects, which predominate at high flow rates, cause deviations from Darcy's law. These studies suggest that permeability is best modeled using the Forschheimer equation to determine both the Darcy permeability (k1) and the non-Darcian (k2) permeability. Importantly, at the high porosities of ceramic foams (75-95%), both k1 and k2 are strongly dependent on pore size and geometry, suggesting that measurement of these parameters provides important information on foam structure. We determined both the connected porosity (by He-pycnometry) and the permeability (k1 and k2) of rhyolitic samples having a wide range in porosity (22-85%) and vesicle textures. In general, these data support previous observations of a power law relationship between connected porosity and Darcy permeability2. In detail, variations in k1 increase at higher porosities. Similarly, k2 generally increases in both mean and standard deviation with increasing porosity. Measurements made on three mutually perpendicular cores from individual pumice clasts suggest that some of the variability can be explained by anisotropy in the vesicle structure. By comparison with ceramic foams, we suggest that the remaining variability results from differences either in average vesicle size or, more likely, in the size of apertures
Permeability Barrier Generation in the Martian Lithosphere
NASA Astrophysics Data System (ADS)
Schools, Joe; Montési, Laurent
2015-11-01
Permeability barriers develop when a magma produced in the interior of a planet rises into the cooler lithosphere and crystallizes more rapidly than the lithosphere can deform (Sparks and Parmentier, 1991). Crystallization products may then clog the porous network in which melt is propagating, reducing the permeability to almost zero, i.e., forming a permeability barrier. Subsequent melts cannot cross the barrier. Permeability barriers have been useful to explain variations in crustal thickness at mid-ocean ridges on Earth (Magde et al., 1997; Hebert and Montési, 2011; Montési et al., 2011). We explore here under what conditions permeability barriers may form on Mars.We use the MELTS thermodynamic calculator (Ghiorso and Sack, 1995; Ghiorso et al., 2002; Asimow et al., 2004) in conjunction with estimated Martian mantle compositions (Morgan and Anders, 1979; Wänke and Dreibus, 1994; Lodders and Fegley, 1997; Sanloup et al., 1999; Taylor 2013) to model the formation of permeability barriers in the lithosphere of Mars. In order to represent potential past and present conditions of Mars, we vary the lithospheric thickness, mantle potential temperature (heat flux), oxygen fugacity, and water content.Our results show that permeability layers can develop in the thermal boundary layer of the simulated Martian lithosphere if the mantle potential temperature is higher than ~1500°C. The various Martian mantle compositions yield barriers in the same locations, under matching variable conditions. There is no significant difference in barrier location over the range of accepted Martian oxygen fugacity values. Water content is the most significant influence on barrier development as it reduces the temperature of crystallization, allowing melt to rise further into the lithosphere. Our lower temperature and thicker lithosphere model runs, which are likely the most similar to modern Mars, show no permeability barrier generation. Losing the possibility of having a permeability
Lunar electrical conductivity and magnetic permeability
NASA Technical Reports Server (NTRS)
Dyal, P.; Parkin, C. W.; Daily, W. D.
1975-01-01
Improved analytical techniques are applied to a large Apollo magnetometer data set to yield values of electroconductivity, temperature, magnetic permeability, and iron abundance. Average bulk electroconductivity of the moon is calculated to be .0007 mho/m; a rapid increase with depth to about .003 mho/m within 250 km is indicated. The temperature profile, obtained from the electroconductivity profile for olivine, indicates high lunar temperatures at relatively shallow depths. Magnetic permeability of the moon relative to its environment is calculated to be 1.008 plus or minus .005; a permeability relative to free space of 1.012 plus 0.011, minus 0.008 is obtained. Lunar iron abundances corresponding to this permeability value are 2.5 plus 2.3, minus 1.7 wt% free iron and 5.0-13.5 wt% total iron for a moon composed of a combination of free iron, olivine, and orthopyroxene.
Intestinal permeability, leaky gut, and intestinal disorders.
Hollander, D
1999-10-01
A major task of the intestine is to form a defensive barrier to prevent absorption of damaging substances from the external environment. This protective function of the intestinal mucosa is called permeability. Clinicians can use inert, nonmetabolized sugars such as mannitol, rhamnose, or lactulose to measure the permeability barrier or the degree of leakiness of the intestinal mucosa. Ample evidence indicates that permeability is increased in most patients with Crohn's disease and in 10% to 20% of their clinically healthy relatives. The abnormal leakiness of the mucosa in Crohn's patients and their relatives can be greatly amplified by aspirin preadministration. Permeability measurements in Crohn's patients reflect the activity, extent, and distribution of the disease and may allow us to predict the likelihood of recurrence after surgery or medically induced remission. Permeability is also increased in celiac disease and by trauma, burns, and nonsteroidal anti-inflammatory drugs. The major determinant of the rate of intestinal permeability is the opening or closure of the tight junctions between enterocytes in the paracellular space. As we broaden our understanding of the mechanisms and agents that control the degree of leakiness of the tight junctions, we will be increasingly able to use permeability measurements to study the etiology and pathogenesis of various disorders and to design or monitor therapies for their management.
Permeability of edible coatings.
Mishra, B; Khatkar, B S; Garg, M K; Wilson, L A
2010-01-01
The permeabilities of water vapour, O2 and CO2 were determined for 18 coating formulations. Water vapour transmission rate ranged from 98.8 g/m(2).day (6% beeswax) to 758.0 g/m(2).day (1.5% carboxymethyl cellulose with glycerol). O2 permeability at 14 ± 1°C and 55 ± 5% RH ranged from 1.50 to 7.95 cm(3)cm cm(-2)s(-1)Pa(-1), with CO2 permeability 2 to 6 times as high. Permeability to noncondensable gases (O2 and CO2) was higher for hydrophobic (peanut oil followed by beeswax) coatings as compared to hydrophilic (whey protein concentrate and carboxymethyl cellulose).
Dunn, T.L.
1996-10-01
This multidisciplinary study was designed to provide improvements in advanced reservoir characterization techniques. This goal was accomplished through: (1) an examination of the spatial variation and anisotropy of relative permeability in the Tensleep Sandstone reservoirs of Wyoming; (2) the placement of that variation and anisotropy into paleogeographic, and depositional regional frameworks; (3) the development of pore-system imagery techniques for the calculation of relative permeability; and (4) reservoir simulations testing the impact of relative permeability anisotropy and spatial variation on Tensleep Sandstone reservoir enhanced oil recovery. Concurrent efforts were aimed at understanding the spatial and dynamic alteration in sandstone reservoirs that is caused by rock-fluid interaction during CO{sub 2} enhanced oil recovery processes. The work focused on quantifying the interrelationship of fluid-rock interaction with lithologic characterization and with fluid characterization in terms of changes in chemical composition and fluid properties. This work establishes new criteria for the susceptibility of Tensleep Sandstone reservoirs to formation alteration that results in wellbore scale damage. This task was accomplished by flow experiments using core material; examination of regional trends in water chemistry; examination of local water chemistry trends the at field scale; and chemical modeling of both the experimental and reservoir systems.
Dunn, T.L.
1995-07-01
The principal focus of this project is to evaluate the importance of relative permeability anisotropy with respect to other known geologic and engineering production concepts. This research is to provide improved strategies for enhanced oil recovery from the Tensleep Sandstone oil reservoirs in the Bighorn and Wind River basins, Wyoming. The Tensleep Sandstone contains the largest potential reserves within reservoirs which are candidates for EOR processes in the State of Wyoming. Although this formation has produced billions of barrels of oil, in some fields, as little as one in seven barrels of discovered oil is recoverable by current primary and secondary techniques. Because of the great range of {degree}API gravities of the oils produced from the Tensleep Sandstone reservoirs, the proposed study concentrates on establishing an understanding of the spatial variation and anisotropy of relative permeability within the Tensleep Sandstone. This research is to associate those spatial distributions and anisotropies with the depositional subfacies and zones of diagenetic alteration found within the Tensleep Sandstone. In addition, these studies are being coupled with geochemical modeling and coreflood experiments to investigate the potential for wellbore scaling and formation damage anticipated during EOR processes (e.g., C0{sub 2} flooding). This multidisciplinary project will provide a regional basis for EOR strategies which can be clearly mapped and efficiently applied to the largest potential target reservoir in the State of Wyoming. Additionally, the results of this study have application to all eolian reservoirs through the correlations of relative permeability variation and anisotropy with eolian depositional lithofacies.
Permeability of displaced fractures
NASA Astrophysics Data System (ADS)
Kluge, Christian; Milsch, Harald; Blöcher, Guido
2017-04-01
Flow along fractures or in fissured systems becomes increasingly important in the context of Enhanced Geothermal Systems (EGS), shale gas recovery or nuclear waste deposit. Commonly, the permeability of fractures is approximated using the Hagen-Poiseuille solution of Navier Stokes equation. Furthermore, the flow in fractures is assumed to be laminar flow between two parallel plates and the cubic law for calculating the velocity field is applied. It is a well-known fact, that fracture flow is strongly influenced by the fracture surface roughness and the shear displacement along the fracture plane. Therefore, a numerical approach was developed which calculates the flow pattern within a fracture-matrix system. The flow in the fracture is described by a free fluid flow and the flow in the matrix is assumed to be laminar and therefore validates Darcy's law. The presented approach can be applied for artificially generated fractures or real fractures measured by surface scanning. Artificial fracture surfaces are generated using the power spectral density of the surface height random process with a spectral exponent to define roughness. For calculating the permeability of such fracture-matrix systems the mean fracture aperture, the shear displacement and the surface roughness are considered by use of a 3D numerical simulator. By use of this approach correlation between shear displacement and mean aperture, shear displacement and permeability, as well as surface roughness and permeability can be obtained. Furthermore, the intrinsic measured permeability presents a combination of matrix and fracture permeability. The presented approach allows the separation and quantification of the absolute magnitudes of the matrix and the fracture permeability and the permeability of displaced fractures can be calculated. The numerical approach which is a 3D numerical simulation of the fracture-matrix system can be applied for artificial as well as real systems.
Exploring the scale-dependent permeability of fractured andesite
NASA Astrophysics Data System (ADS)
Heap, Michael J.; Kennedy, Ben M.
2016-08-01
Extension fractures in volcanic systems exist on all scales, from microscopic fractures to large fissures. They play a fundamental role in the movement of fluids and distribution of pore pressure, and therefore exert considerable influence over volcanic eruption recurrence. We present here laboratory permeability measurements for porous (porosity = 0.03-0.6) andesites before (i.e., intact) and after failure in tension (i.e., the samples host a throughgoing tensile fracture). The permeability of the intact andesites increases with increasing porosity, from 2 ×10-17 to 5 ×10-11 m2. Following fracture formation, the permeability of the samples (the equivalent permeability) falls within a narrow range, 2- 6 ×10-11 m2, regardless of their initial porosity. However, laboratory measurements on fractured samples likely overestimate the equivalent permeability due to the inherent scale-dependence of permeability. To explore this scale-dependence, we first determined the permeability of the tensile fractures using a two-dimensional model that considers flow in parallel layers. Our calculations highlight that tensile fractures in low-porosity samples are more permeable (as high as 3.5 ×10-9 m2) than those in high-porosity samples (as low as 4.1 ×10-10 m2), a difference that can be explained by an increase in fracture tortuosity with porosity. We then use our fracture permeability data to model the equivalent permeability of fractured rock (with different host rock permeabilities, from 10-17 to 10-11 m2) with increasing lengthscale. We highlight that our modelling approach can be used to estimate the equivalent permeability of numerous scenarios at andesitic stratovolcanoes in which the fracture density and width and host rock porosity or permeability are known. The model shows that the equivalent permeability of fractured andesite depends heavily on the initial host rock permeability and the scale of interest. At a given lengthscale, the equivalent permeability of
Hüve, Katja; Bichele, Irina; Rasulov, Bahtijor; Niinemets, Ulo
2011-01-01
Photosynthesis rate (A(n)) becomes unstable above a threshold temperature, and the recovery upon return to low temperature varies because of reasons not fully understood. We investigated responses of A(n), dark respiration and chlorophyll fluorescence to supraoptimal temperatures of varying duration and kinetics in Phaseolus vulgaris asking whether the instability of photosynthesis under severe heat stress is associated with cellular damage. Cellular damage was assessed by Evans blue penetration (enhanced membrane permeability) and by H₂O₂ generation [3,3'-diaminobenzidine 4HCl (DAB)-staining]. Critical temperature for dark fluorescence (F(0) ) rise (T(F)) was at 46-48 °C, and a burst of respiration was observed near T(F). However, A(n) was strongly inhibited already before T(F) was reached. Membrane permeability increased with temperature according to a switch-type response, with enhanced permeability observed above 48 °C. Experiments with varying heat pulse lengths and intensities underscored the threshold-type loss of photosynthetic function, and indicated that the degree of photosynthetic deterioration and cellular damage depended on accumulated heat-dose. Beyond the 'point of no return', propagation of cellular damage and reduction of photosynthesis continued upon transfer to lower temperatures and photosynthetic recovery was slow or absent. We conclude that instability of photosynthesis under severe heat stress is associated with time-dependent propagation of cellular lesions.
Cross-Evaluation of Laboratory Permeability Tests by Dimensionless Analysis
NASA Astrophysics Data System (ADS)
Takeda, M.; Zhang, M.; Hiratsuka, T.
2007-12-01
Accurate estimations of transport parameters of engineered and natural barrier materials are indispensable for assessments of the safety of geological disposal of hazardous wastes including radioactive nuclear waste. In such projects, it is essential that the barrier materials be capable of retarding the migration of contaminants. When groundwater flow is dominant, the evaluation of hydraulic parameters, particularly the permeability and specific storage, is of fundamental importance in the safety assessment. The permeability and specific storage of synthetic and geological materials are measured using permeability tests; however, conventional test methods are routinely applied to barrier materials with relatively low-permeabilities with little knowledge about their applicabilities. In order to provide a theoretical basis for designing laboratory permeability tests, the applicabilites of currently available test methods were examined and cross-evaluated with emphases on the experimental time and the parameter sensitivity using a numerical approach. To allow for a general discussion, a series of examinations were conducted based on a dimensionless analysis using dimensionless parameters representing the hydraulic properties and dimensions of the specimen and the other experimental conditions. In the dimensionless-time scale, the experimental time and the parameter sensitivity of the individual test methods can be simulated and compared by varying a few dimensionless parameters representing the experimental conditions. From a series of examinations, it was found that the experimental time and the parameter sensitivity of the individual test methods can be ascertained and compared using a few dimensionless parameters. This research project has been conducted under the research contract with the Japan Nuclear Energy Safety Organization (JNES).
Fluid permeability of deformable fracture networks
Brown, S.R.; Bruhn, R.L.
1997-04-01
The authors consider the problem of defining the fracture permeability tensor for each grid lock in a rock mass from maps of natural fractures. For this purpose they implement a statistical model of cracked rock due to M. Oda [1985], where the permeability tensor is related to the crack geometry via a volume average of the contribution from each crack in the population. In this model tectonic stress is implicitly coupled to fluid flow through an assumed relationship between crack aperture and normal stress across the crack. The authors have included the following enhancements to the basic model: (1) a realistic model of crack closure under stress has been added along with the provision to apply tectonic stresses to the fracture system in any orientation, the application of stress results in fracture closure and consequently a reduction in permeability; (2) the fracture permeability can be superimposed onto an arbitrary anisotropic matrix permeability; (3) the fracture surfaces are allowed to slide under the application of shear stress, causing fractures to dilate and result in a permeability increase. Through an example, the authors demonstrate that significant changes in permeability magnitudes and orientations are possible when tectonic stress is applied to a fracture system.
Anisotropy of permeability in faulted porous sandstones
NASA Astrophysics Data System (ADS)
Farrell, N. J. C.; Healy, D.; Taylor, C. W.
2014-06-01
Studies of fault rock permeabilities advance the understanding of fluid migration patterns around faults and contribute to predictions of fault stability. In this study a new model is proposed combining brittle deformation structures formed during faulting, with fluid flow through pores. It assesses the impact of faulting on the permeability anisotropy of porous sandstone, hypothesising that the formation of fault related micro-scale deformation structures will alter the host rock porosity organisation and create new permeability pathways. Core plugs and thin sections were sampled around a normal fault and oriented with respect to the fault plane. Anisotropy of permeability was determined in three orientations to the fault plane at ambient and confining pressures. Results show that permeabilities measured parallel to fault dip were up to 10 times higher than along fault strike permeability. Analysis of corresponding thin sections shows elongate pores oriented at a low angle to the maximum principal palaeo-stress (σ1) and parallel to fault dip, indicating that permeability anisotropy is produced by grain scale deformation mechanisms associated with faulting. Using a soil mechanics 'void cell model' this study shows how elongate pores could be produced in faulted porous sandstone by compaction and reorganisation of grains through shearing and cataclasis.
Simulating perforation permeability damage and cleanup
Morris, J P; Lomov, I N; Glenn, L A
2000-12-15
Completion of cased and cemented wells by shaped charge perforation causes its own damage to the formation, potentially reducing well productivity. In practice it is found that underbalance conditions clean up the damaged zone to some extent, however, the mechanisms of these processes are poorly understood. Most hydrocodes typically used to simulate rock response to shaped charge penetration do not provide permeability estimates. Furthermore, the time scales for formation clean up are potentially much longer than the period of jet penetration. We have developed a simple, yet accurate model for the evolution of porosity and permeability which can easily be incorporated into existing hydrocodes using information from the history of each cell. In addition, we have developed a code that efficiently simulates fines migration during the post-shot surge period using initial conditions taken directly from hydrocode simulations of jet penetration. Results from a one-dimensional model simulation are in excellent agreement with measured permeability distributions. We also present two-dimensional numerical results which qualitatively reproduce experimentally obtained permeability maps for different values of underbalance. Although initial results have been promising, further comparison with experiment is essential to tune the coupling between the hydrocode and fines migration simulator. Currently the permeability model is most appropriate for high permeability sandstones (such as Berea), but with little effort, the model can be extended to other rock types, given sufficient experimental data.
Oxygen Evolution and the Permeability of the Outer Envelope of Isolated Whole Chloroplasts 1
Robinson, J. Michael; Stocking, C. R.
1968-01-01
A rapid oxygraph method of studying the permeability of the envelope of isolated chloroplasts was used. The outer envelope of aqueously isolated whole spinach (Spinacia oleracea L.) chloroplasts in buffer is readily permeable to 3-phosphoglyceric acid, which induces an immediate light dependent oxygen evolution. This light dependent oxygen evolution was completely eliminated by swelling these plastids in an osmotically dilute solution. Exogenous adenosine diphosphate, but not inorganic phosphate, strongly stimulated this oxygen evolution. This indicated that the chloroplast envelope is relatively permeable to adenosine diphosphate. Oxygen evolution and swelling studies indicated that the chloroplast envelope is relatively impermeable to NADP and to ferredoxin. A method is described whereby the percent of whole chloroplasts present in a chloroplast preparation may be rapidly estimated. PMID:16656943
Optical investigation of effective permeability of dilute magnetic dielectrics with magnetic field
Banerjee, Ananya Sarkar, A.
2016-05-06
The prime objective of this paper is to investigate the magnetic nature of dilute magnetic dielectrics (DMD) under variation of external magnetic field. The said variation is studied over developed nano-sized Gadolinium Oxide as a DMD system. The observed experimental field variation of the effective magnetic permeability is analyzed results of optical experiment. The experiment records the variation of Brewster angle of incident polarized LASER beam from the surface of developed DMD specimen with applied out of plane external magnetic field. The effective refractive index and hence relative magnetic permeability were estimated following electro-magnetic theory. The overall results obtained and agreement between theory and experiment are good.
NgsRelate: a software tool for estimating pairwise relatedness from next-generation sequencing data.
Korneliussen, Thorfinn Sand; Moltke, Ida
2015-12-15
Pairwise relatedness estimation is important in many contexts such as disease mapping and population genetics. However, all existing estimation methods are based on called genotypes, which is not ideal for next-generation sequencing (NGS) data of low depth from which genotypes cannot be called with high certainty. We present a software tool, NgsRelate, for estimating pairwise relatedness from NGS data. It provides maximum likelihood estimates that are based on genotype likelihoods instead of genotypes and thereby takes the inherent uncertainty of the genotypes into account. Using both simulated and real data, we show that NgsRelate provides markedly better estimates for low-depth NGS data than two state-of-the-art genotype-based methods. NgsRelate is implemented in C++ and is available under the GNU license at www.popgen.dk/software. © The Author 2015. Published by Oxford University Press.
NgsRelate: a software tool for estimating pairwise relatedness from next-generation sequencing data
Korneliussen, Thorfinn Sand; Moltke, Ida
2015-01-01
Motivation: Pairwise relatedness estimation is important in many contexts such as disease mapping and population genetics. However, all existing estimation methods are based on called genotypes, which is not ideal for next-generation sequencing (NGS) data of low depth from which genotypes cannot be called with high certainty. Results: We present a software tool, NgsRelate, for estimating pairwise relatedness from NGS data. It provides maximum likelihood estimates that are based on genotype likelihoods instead of genotypes and thereby takes the inherent uncertainty of the genotypes into account. Using both simulated and real data, we show that NgsRelate provides markedly better estimates for low-depth NGS data than two state-of-the-art genotype-based methods. Availability: NgsRelate is implemented in C++ and is available under the GNU license at www.popgen.dk/software. Contact: ida@binf.ku.dk Supplementary information: Supplementary data are available at Bioinformatics online. PMID:26323718
Rutqvist, J.
2014-09-19
The purpose of this paper is to (i) review field data on stress-induced permeability changes in fractured rock; (ii) describe estimation of fractured rock stress-permeability relationships through model calibration against such field data; and (iii) discuss observations of temperature and chemically mediated fracture closure and its effect on fractured rock permeability. The field data that are reviewed include in situ block experiments, excavation-induced changes in permeability around tunnels, borehole injection experiments, depth (and stress) dependent permeability, and permeability changes associated with a large-scale rock-mass heating experiment. Data show how the stress-permeability relationship of fractured rock very much depends on localmore » in situ conditions, such as fracture shear offset and fracture infilling by mineral precipitation. Field and laboratory experiments involving temperature have shown significant temperature-driven fracture closure even under constant stress. Such temperature-driven fracture closure has been described as thermal overclosure and relates to better fitting of opposing fracture surfaces at high temperatures, or is attributed to chemically mediated fracture closure related to pressure solution (and compaction) of stressed fracture surface asperities. Back-calculated stress-permeability relationships from field data may implicitly account for such effects, but the relative contribution of purely thermal-mechanical and chemically mediated changes is difficult to isolate. Therefore, it is concluded that further laboratory and in situ experiments are needed to increase the knowledge of the true mechanisms behind thermally driven fracture closure, and to further assess the importance of chemical-mechanical coupling for the long-term evolution of fractured rock permeability.« less
NASA Astrophysics Data System (ADS)
Boulin, P. F.; Bretonnier, P.; Gland, N.
2010-12-01
Very low permeability geomaterials (order of nanoDarcy (10-21 m2)), such as clays rocks, are studied for many industrial applications such as production from unconventional reserves of oil and gas, CO2 geological storage and deep geological disposal of high-level long-lived nuclear wastes. For these last two applications, clay efficiency as barrier relies mainly on their very low permeability. Laboratory measurement of low permeability to water (below 10-19 m2) remains a technical challenge. Some authors argue that steady state methods are irrelevant due to the time required to stabilize water fluxes in such low permeability media. Most of the authors measuring low permeabilities use a transient technique called pulse decay. This study aims to compare objectively these different types of permeability tests performed on a single clay sample. For the steady state method, a high precision pump was used to impose a pressure gradient and to measure the small resulting water flow rate at steady state. We show that with a suitable set-up, the steady state method enables to measure a very low permeability of 8 10-22 m2 in a period of three days. For a comparable duration, the pulse decay test, most commonly used for such low permeability measurements, provides only an average estimate of the permeability. Permeability measurements by pulse decay require to perform simulations to interpret the pressure relaxation signals. Many uncertainties remain such as the determination of the reservoirs storage factor, micro leakage effect, or the determination of the initial pulse pressure. All these uncertainties have a very significant impact on the determination of sample permeability and specific storage. Opposite to the wide-spread idea that transient techniques are required to measure very low permeability, we show that direct steady state measurement of water permeability with suitable equipments can be much faster and more accurate than measurement by pulse decay, especially in
Multiple imputation for handling missing outcome data when estimating the relative risk.
Sullivan, Thomas R; Lee, Katherine J; Ryan, Philip; Salter, Amy B
2017-09-06
Multiple imputation is a popular approach to handling missing data in medical research, yet little is known about its applicability for estimating the relative risk. Standard methods for imputing incomplete binary outcomes involve logistic regression or an assumption of multivariate normality, whereas relative risks are typically estimated using log binomial models. It is unclear whether misspecification of the imputation model in this setting could lead to biased parameter estimates. Using simulated data, we evaluated the performance of multiple imputation for handling missing data prior to estimating adjusted relative risks from a correctly specified multivariable log binomial model. We considered an arbitrary pattern of missing data in both outcome and exposure variables, with missing data induced under missing at random mechanisms. Focusing on standard model-based methods of multiple imputation, missing data were imputed using multivariate normal imputation or fully conditional specification with a logistic imputation model for the outcome. Multivariate normal imputation performed poorly in the simulation study, consistently producing estimates of the relative risk that were biased towards the null. Despite outperforming multivariate normal imputation, fully conditional specification also produced somewhat biased estimates, with greater bias observed for higher outcome prevalences and larger relative risks. Deleting imputed outcomes from analysis datasets did not improve the performance of fully conditional specification. Both multivariate normal imputation and fully conditional specification produced biased estimates of the relative risk, presumably since both use a misspecified imputation model. Based on simulation results, we recommend researchers use fully conditional specification rather than multivariate normal imputation and retain imputed outcomes in the analysis when estimating relative risks. However fully conditional specification is not without its
Permeable pavement study (Edison)
While permeable pavement is increasingly being used to control stormwater runoff, field-based, side-by-side investigations on the effects different pavement types have on nutrient concentrations present in stormwater runoff are limited. In 2009, the U.S. EPA constructed a 0.4-ha parking lot in Edison, New Jersey, that incorporated permeable interlocking concrete pavement (PICP), pervious concrete (PC), and porous asphalt (PA). Each permeable pavement type has four, 54.9-m2, lined sections that direct all infiltrate into 5.7-m3 tanks enabling complete volume collection and sampling. This paper highlights the results from a 12-month period when samples were collected from 13 rainfall/runoff events and analyzed for nitrogen species, orthophosphate, and organic carbon. Differences in infiltrate concentrations among the three permeable pavement types were assessed and compared with concentrations in rainwater samples and impervious asphalt runoff samples, which were collected as controls. Contrary to expectations based on the literature, the PA infiltrate had significantly larger total nitrogen (TN) concentrations than runoff and infiltrate from the other two permeable pavement types, indicating that nitrogen leached from materials in the PA strata. There was no significant difference in TN concentration between runoff and infiltrate from either PICP or PC, but TN in runoff was significantly larger than in the rainwater, suggesting meaningful inter-event dry de
An estimator for the relative entropy rate of path measures for stochastic differential equations
NASA Astrophysics Data System (ADS)
Opper, Manfred
2017-02-01
We address the problem of estimating the relative entropy rate (RER) for two stochastic processes described by stochastic differential equations. For the case where the drift of one process is known analytically, but one has only observations from the second process, we use a variational bound on the RER to construct an estimator.
Fracture and healing in magmas: a dual role on permeability evolution
NASA Astrophysics Data System (ADS)
Lamur, Anthony; Lavallée, Yan; Wall, Richard; Ashworth, James; Kendrick, Jackie; Wadsworth, Fabian
2016-04-01
The development of a permeable network in silicic volcanic conduits controls outgassing and plays a major role on the subsequent eruptive behaviour. Efficient outgassing, at higher permeabilities, is achieved through the coalescence of pores and fractures. Whilst the relationship between permeability and increasing connected porosity is now relatively well constrained, the effects of fractures have, on the other hand, rarely been investigated. Here, we present the results of an experimental study focusing on the impacts of tensile fracturing and healing on permeability. Permeability measurements have been performed on over 60 disk-shaped samples (26 mm diameter, 13 mm thickness) with connected porosities ranging from 2 to 45%. Our results for unfractured samples display the same porosity-permeability trend as previous studies and permeabilities span from 10-15 at low porosities to over 5x10-12 m2 at higher porosities. These samples were then broken via Brazilian tests and the resultant permeability of the rocks were then measured across the fracture zone. Whilst high porosity samples reached permeabilities of about 5x10-10 m2 (2 orders of magnitude higher than intact samples), low porosity samples, on the other hand, reached permeabilities around 5x10-12 m2 (more than 3 orders of magnitude above intact samples). Our results show that fracturing favours the development of a permeable network that adheres to a different permeability-porosity relationship than previously presented, and that this effect is emphasized in magmas with low connected porosities. The effect of fracture healing by diffusion on permeability has been investigated through a series of experiments on borosilicate standard glass (NIST 717a). These experiments were conducted at 560oC (viscosity of 1010.33 Pa.s) on pairs of columns pressed and held in contact at constant load for times varying between 0.5s and 15000 s before being pulled apart at a strain rate of 10-3s-1. Using Maxwell's theory of
Adachi, Yasuko; Hatano, Yutaka; Sakai, Takashi; Fujiwara, Sakuhei
2013-09-01
Previous studies have demonstrated that the activation of peroxisome proliferator-activated receptors (PPARs) not only has positive effects on permeability barrier homoeostasis but also has anti-inflammatory effects by an as yet unknown mechanism. Reduced expression of PPARα in lesion of human atopic dermatitis (AD) and in epidermis of murine AD-like dermatitis has been demonstrated. This study revealed that expression of PPARα alone among PPARs (α, β/δ and γ) was suppressed by both permeability barrier abrogation and additional existence of Th2 cytokine in cultured normal human keratinocytes. In addition, expressions of transglutaminase 1 and loricrin and those of thymus and activation-related chemokine and regulated on activation normal T-cell expressed in cultured human keratinocytes were reduced and enhanced, respectively, by transfection with siRNA for PPARα. In conclusion, depressed PPARα in keratinocytes might be involved in a relationship between permeability barrier abrogation and allergic inflammation and could be a therapeutic target which accounts for both the aspects in AD. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
The Relation between Factor Score Estimates, Image Scores, and Principal Component Scores
ERIC Educational Resources Information Center
Velicer, Wayne F.
1976-01-01
Investigates the relation between factor score estimates, principal component scores, and image scores. The three methods compared are maximum likelihood factor analysis, principal component analysis, and a variant of rescaled image analysis. (RC)
The Relation between Factor Score Estimates, Image Scores, and Principal Component Scores
ERIC Educational Resources Information Center
Velicer, Wayne F.
1976-01-01
Investigates the relation between factor score estimates, principal component scores, and image scores. The three methods compared are maximum likelihood factor analysis, principal component analysis, and a variant of rescaled image analysis. (RC)
Permeability of Two Parachute Fabrics: Measurements, Modeling, and Application
NASA Technical Reports Server (NTRS)
Cruz, Juan R.; O'Farrell, Clara; Hennings, Elsa; Runnells, Paul
2017-01-01
Two parachute fabrics, described by Parachute Industry Specifications PIA-C-7020D Type I and PIA-C-44378D Type I, were tested to obtain their permeabilities in air (i.e., flow-through volume of air per area per time) over the range of differential pressures from 0.146 psf (7 Pa) to 25 psf (1197 Pa). Both fabrics met their specification permeabilities at the standard differential pressure of 0.5 inch of water (2.60 psf, 124 Pa). The permeability results were transformed into an effective porosity for use in calculations related to parachutes. Models were created that related the effective porosity to the unit Reynolds number for each of the fabrics. As an application example, these models were used to calculate the total porosities for two geometrically-equivalent subscale Disk-Gap-Band (DGB) parachutes fabricated from each of the two fabrics, and tested at the same operating conditions in a wind tunnel. Using the calculated total porosities and the results of the wind tunnel tests, the drag coefficient of a geometrically-equivalent full-scale DGB operating on Mars was estimated.
Permeability of Two Parachute Fabrics - Measurements, Modeling, and Application
NASA Technical Reports Server (NTRS)
Cruz, Juan R.; O'Farrell, Clara; Hennings, Elsa; Runnells, Paul
2016-01-01
Two parachute fabrics, described by Parachute Industry Specifications PIA-C-7020D Type I and PIA-C-44378D Type I, were tested to obtain their permeabilities in air (i.e., flow-through volume of air per area per time) over the range of differential pressures from 0.146 psf (7 Pa) to 25 psf (1197 Pa). Both fabrics met their specification permeabilities at the standard differential pressure of 0.5 inch of water (2.60 psf, 124 Pa). The permeability results were transformed into an effective porosity for use in calculations related to parachutes. Models were created that related the effective porosity to the unit Reynolds number for each of the fabrics. As an application example, these models were used to calculate the total porosities for two geometrically-equivalent subscale Disk-Gap-Band (DGB) parachutes fabricated from each of the two fabrics, and tested at the same operating conditions in a wind tunnel. Using the calculated total porosities and the results of the wind tunnel tests, the drag coefficient of a geometrically-equivalent full-scale DGB operating on Mars was estimated.
Cárdenas-Rodríguez, Julio; Howison, Christine M.; Matsunaga, Terry O.; Pagel, Mark D.
2013-01-01
Dynamic Contrast Enhancement (DCE) MRI has been used to measure the kinetic transport constant, Ktrans, which is used to assess tumor angiogenesis and the effects of anti-angiogenic therapies. Standard DCE MRI methods must measure the pharmacokinetics of a contrast agent in the blood stream, known as the Arterial Input Function (AIF), which is then used as a reference for the pharmacokinetics of the agent in tumor tissue. However, the AIF is difficult to measure in pre-clinical tumor models and in patients. Moreover the AIF is dependent on the Fahraeus effect that causes a highly variable hematocrit (Hct) in tumor microvasculature, leading to erroneous estimates of Ktrans. To overcome these problems, we have developed the Reference Agent Model (RAM) for DCE MRI analyses, which determines the ratio of Ktrans values of two contrast agents that are simultaneously co-injected and detected during a single DCE-MRI scan session. The RAM obviates the need to monitor the AIF because one contrast agent effectively serves as an internal reference in the tumor tissue for the other agent, and it also eliminates the systematic errors in the estimated Ktrans caused by assuming an erroneous Hct. Simulations demonstrated that the RAM can accurately and precisely estimate the relative Ktrans (RKtrans) of two agents. To experimentally evaluate the utility of RAM for analyzing DCE MRI results, we optimized a previously reported multiecho 19F MRI method to detect two perfluorocarbon contrast agents that were co-injected during a single in vivo study and selectively detected in the same tumor location. The results demonstrated that RAM determined RKtrans with excellent accuracy and precision. PMID:23583323
NASA Astrophysics Data System (ADS)
Peng, Sheng; Marone, Federica; Dultz, Stefan
2014-03-01
Resolution selection when using X-ray microcomputed tomography should be made based on the compromise between accuracy and representativeness. The question is then how accurate is accurate enough, that is, how small a pore is small enough to be ignored without generating misleading results on pore representation and subsequent flow properties such as permeability. In this study, synchrotron X-ray microcomputed tomographic scans of a Berea sandstone sample were acquired for two resolutions (with 1.85 and 5.92 μm pixel width). Higher resolution images resolve more small pores, and have similar large pores as the lower resolution images. Pore characterization and permeability estimation were conducted based on these two sets of images. The pore parameters and permeability were also measured for another larger sample from the same rock fragment through laboratory experiments. The comparison between the different resolution image analyses and the laboratory measurement indicates that small pores contribute to larger porosity, smaller tortuosity, and larger surface area, but do not influence permeability significantly. Therefore, relatively low resolution (pixel width up to 5.92 μm) can be used for Berea sandstone when permeability is the focus. However, use of even lower resolution needs to be careful since lower resolution not only excludes more small pores, but also has the potential to overestimate the pore size and thereby the permeability. Kozeny-Carman equation was used to estimate the permeability with geometric and diffusional tortuosity. The results indicate that the latter tortuosity can serve better for the permeability estimation than the former.
NASA Astrophysics Data System (ADS)
Davis, M. A.; Walsh, S. D.; Saar, M. O.; Roberts, J. J.
2007-12-01
Understanding the processes that cause volcanic eruptions to be either effusive or explosive is vital to improve predictability and minimize hazards associated with volcanic eruptions. Explosivity appears to be linked to gas pressure build-up within magma, which is in turn affected by the degree of degassing of magmatic volatiles through permeable bubble networks or fractures in the magma. Magma permeability inside a volcano conduit is typically estimated experimentally by measuring the permeability of small pumice clasts (e.g., Klug and Cashman, Bull. Volcanol., 1996). However, permeability has been shown to be very scale-dependent (e.g., Hyun et al., Water Resor. Res., 2002), leaving substantial uncertainty in magma permeability-dependent calculations, such as magmatic volatile degassing rates. The objective of this study is to up-scale the permeability and microstructure (bubbles and crystals) of volcanic ejecta, and related magma degassing rates, to volcano-conduit scales. This is achieved by creating a numerical reconstruction method using X-ray tomography images of pumice clasts and two-point correlation functions. These numerical reconstructions reproduce the statistics of the spatial relationships of bubbles found in a given pumice clast. Once the bubble network is reconstructed, we are able to determine the porosity, tortuosity, and specific surface area of the bubble networks in the numerical reconstruction. In addition, lattice-Boltzmann simulations can be employed to numerically determine the bubble network's permeability.
Permeability of rayon based polymer composites
NASA Technical Reports Server (NTRS)
Stokes, E. H.
1992-01-01
Several types of anomalous rayon based phenolic behavior have been observed in post-fired nozzles and exit cones. Many of these events have been shown to be related to the development of internal gas pressure within the material. The development of internal gas pressure is a function of the amount of gas produced within the material and the rate at which that gas is allowed to escape. The latter property of the material is referred to as the material's permeability. The permeability of two dimensional carbonized rayon based phenolic composites is a function of material direction, temperature, and stress/strain state. Recently significant differences in the permeability of these materials has been uncovered which may explain their inconsistent performance. This paper summarizes what is known about the permeability of these materials to date and gives possible implications of these finding to the performance of these materials in an ablative environment.
Permeability-porosity relationships of subduction zone sediments
Gamage, Kusali; Screaton, Elizabeth; Bekins, B.; Aiello, I.
2011-01-01
Permeability-porosity relationships for sediments from the northern Barbados, Costa Rica, Nankai, and Peru subduction zones were examined based on sediment type, grain size distribution, and general mechanical and chemical compaction history. Greater correlation was observed between permeability and porosity in siliciclastic sediments, diatom oozes, and nannofossil chalks than in nannofossil oozes. For siliciclastic sediments, grouping of sediments by percentage of clay-sized material yields relationships that are generally consistent with results from other marine settings and suggests decreasing permeability as percentage of clay-sized material increases. Correction of measured porosities for smectite content improved the correlation of permeability-porosity relationships for siliciclastic sediments and diatom oozes. The relationship between permeability and porosity for diatom oozes is very similar to the relationship in siliciclastic sediments, and permeabilities of both sediment types are related to the amount of clay-size particles. In contrast, nannofossil oozes have higher permeability values by 1.5 orders of magnitude than siliciclastic sediments of the same porosity and show poor correlation between permeability and porosity. More indurated calcareous sediments, nannofossil chalks, overlap siliciclastic permeabilities at the lower end of their measured permeability range, suggesting similar consolidation patterns at depth. Thus, the lack of correlation between permeability and porosity for nannofossil oozes is likely related to variations in mechanical and chemical compaction at shallow depths. This study provides the foundation for a much-needed global database with fundamental properties that relate to permeability in marine settings. Further progress in delineating controls on permeability requires additional carefully documented permeability measurements on well-characterized samples. ?? 2010 Elsevier B.V.
A Robust Method for Relative Gravity Data Estimation with High Efficiency
NASA Astrophysics Data System (ADS)
Touati, F.; Idres, M.; Kahlouche, S.
2010-01-01
When gravimetric data observations have outliers, using standard least squares (LS) estimation will likely give poor accuracies and unreliable parameter estimates. One of the typical approaches to overcome this problem consists of using the robust estimation techniques. In this paper, we modified the robust estimator of Gervini and Yohai (2002) called REWLSE (Robust and Efficient Weighted Least Squares Estimator), which combines simultaneously high statistical efficiency and high breakdown point by replacing the weight function by a new weight function. This method allows reducing the outlier impacts and makes more use of the information provided by the data. In order to adapt this technique to the relative gravity data, weights are computed using the empirical distribution of the residuals obtained initially by the LTS (Least Trimmed Squares) estimator and by minimizing the mean distances relatively to the LS-estimator without outliers. The robustness of the initial estimator is maintained by adapted cut-off values as suggested by the REWLSE method which allows also a reasonable statistical efficiency. Hereafter we give the advantage and the pertinence of REWLSE procedure on real and semi-simulated gravity data by comparing it with conventional LS and other robust approaches like M- and MM-estimators.
Estimating the asbestos-related lung cancer burden from mesothelioma mortality
McCormack, V; Peto, J; Byrnes, G; Straif, K; Boffetta, P
2012-01-01
Background: Quantifying the asbestos-related lung cancer burden is difficult in the presence of this disease's multiple causes. We explore two methods to estimate this burden using mesothelioma deaths as a proxy for asbestos exposure. Methods: From the follow-up of 55 asbestos cohorts, we estimated ratios of (i) absolute number of asbestos-related lung cancers to mesothelioma deaths; (ii) excess lung cancer relative risk (%) to mesothelioma mortality per 1000 non-asbestos-related deaths. Results: Ratios varied by asbestos type; there were a mean 0.7 (95% confidence interval 0.5, 1.0) asbestos-related lung cancers per mesothelioma death in crocidolite cohorts (n=6 estimates), 6.1 (3.6, 10.5) in chrysotile (n=16), 4.0 (2.8, 5.9) in amosite (n=4) and 1.9 (1.4, 2.6) in mixed asbestos fibre cohorts (n=31). In a population with 2 mesothelioma deaths per 1000 deaths at ages 40–84 years (e.g., US men), the estimated lung cancer population attributable fraction due to mixed asbestos was estimated to be 4.0%. Conclusion: All types of asbestos fibres kill at least twice as many people through lung cancer than through mesothelioma, except for crocidolite. For chrysotile, widely consumed today, asbestos-related lung cancers cannot be robustly estimated from few mesothelioma deaths and the latter cannot be used to infer no excess risk of lung or other cancers. PMID:22233924
[Adaptive moving averaging based estimation of single event-related potentials].
Qi, C; Liang, D; Jiang, X
2001-03-01
Event-related potentials (ERP) is pertinent to medical research and clinical diagnosis. Estimation of single event-related potentials (sERP) is the objective of ERP processing. A new technique, adaptive moving averaging based method for estimation of sERP, is presented. After analysis of the properties of background noise by crossing zero, the window length of moving averaging is adaptively set according to the maximum width of the impulse noise for each recorded raw data. The experiments are made with real recorded data and the results demonstrate that the performance of sERP estimation is excellent. So the method proposed is suitable to sERP processing.
Development of a Digital Aquifer Permeability Map for the ...
Researchers at the U.S. Environmental Protection Agency’s Western Ecology Division have been developing hydrologic landscape maps for selected U.S. states in an effort to create a method to identify the intrinsic watershed attributes of landscapes in regions with little data. Each hydrologic landscape unit is assigned a categorical value from five key indices of macro-scale hydrologic behavior, including annual climate, climate seasonality, aquifer permeability, terrain, and soil permeability. The aquifer permeability index requires creation of a from-scratch dataset for each state. The permeability index for the Pacific Southwest (California, Nevada, and Arizona) expands and modifies the permeability index for the Pacific Northwest (Oregon, Washington, and Idaho), which preceded it. The permeability index was created by assigning geologic map units to one of 18 categories with presumed similar values of permeability to create a hydrolithologic map. The hydrolithologies were then further categorized into permeability index classifications of high, low, unknown and surface water. Unconsolidated, carbonate, volcanic, and undifferentiated units are classified more conservatively to better address uncertainty in source data. High vs. low permeability classifications are assigned qualitatively but follow a threshold guideline of 8.5x10-2 m/day hydraulic conductivity. Estimates of permeability from surface lithology is the current best practice for broad-sca
Development of a Digital Aquifer Permeability Map for the ...
Researchers at the U.S. Environmental Protection Agency’s Western Ecology Division have been developing hydrologic landscape maps for selected U.S. states in an effort to create a method to identify the intrinsic watershed attributes of landscapes in regions with little data. Each hydrologic landscape unit is assigned a categorical value from five key indices of macro-scale hydrologic behavior, including annual climate, climate seasonality, aquifer permeability, terrain, and soil permeability. The aquifer permeability index requires creation of a from-scratch dataset for each state. The permeability index for the Pacific Southwest (California, Nevada, and Arizona) expands and modifies the permeability index for the Pacific Northwest (Oregon, Washington, and Idaho), which preceded it. The permeability index was created by assigning geologic map units to one of 18 categories with presumed similar values of permeability to create a hydrolithologic map. The hydrolithologies were then further categorized into permeability index classifications of high, low, unknown and surface water. Unconsolidated, carbonate, volcanic, and undifferentiated units are classified more conservatively to better address uncertainty in source data. High vs. low permeability classifications are assigned qualitatively but follow a threshold guideline of 8.5x10-2 m/day hydraulic conductivity. Estimates of permeability from surface lithology is the current best practice for broad-sca
Peters, R.L.; van Kooten, O.; Vredenberg, W.J.
1985-08-01
The effect of dicyclohexylcarbodiimide (DCCD) on the kinetics of the flash-induced P515 response and on the activity of the ATPase was investigated in isolated spinach chloroplasts. It was found that after the addition of 5 X 10(-8)mol DCCD the rate of ATP hydrolysis induced by a period of 60 sec illumination was decreased to less than 5% of its original value. At this concentration, hardly any effect, if at all, could be detected on the kinetics of the flash-induced P515 response, neither in dark-adapted nor in light-activated chloroplasts. It was concluded that the presence of concentrations of DCCD, sufficiently high to affect the ATPase activity, does not affect the kinetics of the flash-induced P515 response. Since DCCD decreases the H+ permeability of the membrane-bound ATPase, it was concluded that this permeability coefficient for protons is not an important factor in the regulation of the flash-induced membrane potential and, therefore, does not affect the kinetics of the flash-induced P515 response.
Particle filter-based relative rolling estimation algorithm for non-cooperative infrared spacecraft
NASA Astrophysics Data System (ADS)
Li, Zhengzhou; Ge, Fengzeng; Chen, Wenhao; Shao, Wanxing; Liu, Bing; Cheng, Bei
2016-09-01
The issue of feature point mismatching among infrared image sequence would bring big challenge to estimating the relative motion of non-cooperative spacecraft for it couldn't provide the prior knowledge about its geometric structure and motion pattern. The paper introduces particle filter to precisely match the feature points within a desired region predicted by a kinetic equation, and presents a least square estimation-based algorithm to measure the relative rolling motion of non-cooperative spacecraft. The state transition equation and the measurement update equation of non-cooperative spacecraft are represented by establishing its kinetic equations, and then the relative pose measurement is converted to the maximum posteriori probability estimation via assuming the uncertainties about geometric structure and motion pattern as random and time-varying variables. These uncertainties would be interpreted and even solved through continuously measuring the image feature points of the rotating non-cooperative infrared spacecraft. Subsequently, the feature point is matched within a predicted region among sequence infrared image using particle filter algorithm to overcome the position estimation noise caused by the uncertainties of geometric structure and motion pattern. Finally, the position parameters including rotation motion are estimated by means of solving the minimum error of feature point mismatching using least square estimate theory. Both simulated and real infrared image sequences are induced in the experiment to evaluate the performance of the relative rolling estimation, and the experimental data show that the rolling motion estimated by the proposed algorithm is more robust to the feature extraction noise and various rotation speed. Meanwhile, the relative rolling estimation error would increase dramatically with distance and rotation speed increasing.
NASA Astrophysics Data System (ADS)
Geller, D.
2007-06-01
A key component of satellite inspection and orbital rendezvous missions is relative attitude estimation and control. This paper analyzes a specific angles-only relative attitude estimation concept where it is assumed that a chaser spacecraft is capable of processing onboard imagery of a resident space object (RSO) and identifying the pixel locations of preselected RSO features. The pixel measurements along with chaser gyro and star camera data are processed by an extended Kalman filter to provide continuous estimates of the relative position and attitude. A novel linear covariance program is used to evaluate the effects of feature-tracking camera errors, gyro errors, star camera errors, measurement rates, and translation and rotational disturbances on relative navigation performance. Linear covariance techniques are further employed to evaluate the closed-loop performance of a relative attitude and position control system.
Addition of Cleaved Tail Fragments during Lipid Oxidation Stabilizes Membrane Permeability Behavior.
Runas, Kristina A; Acharya, Shiv J; Schmidt, Jacob J; Malmstadt, Noah
2016-01-26
Lipid oxidation has been linked to plasma membrane damage leading to cell death. In previous work, we examined the effect of oxidation on bilayer permeability by replacing defined amounts of an unsaturated lipid species with the corresponding phospholipid product that would result from oxidative tail scission of that species. This study adds the cleaved tail fragment, better mimicking the chemical results of oxidation. Permeability of PEG12-NBD, a small, uncharged molecule, was measured for vesicles with oxidation concentration corresponding to between 0 and 18 mol % of total lipid content. Permeability was measured using a microfluidic trap to capture the vesicles and spinning disk confocal microscopy (SDCM) to measure the transport of fluorescent PEG12-NBD at the equatorial plane. The thicknesses of lipid bilayers containing oxidized species were estimated by measuring capacitance of a black lipid membrane while simultaneously measuring bilayer area. We found that relative to chemically modeled oxidized bilayers without tail fragments, bilayers containing cleaved tail groups were less permeable for the same degree of oxidation. Curiously, membrane capacitance measurements indicated that the addition of tail fragments to chemically modeled oxidized bilayers also thinned these bilayers relative to samples with no tail fragments; in other words, the more permeable membranes were thicker. Above 12.5% chemically modeled oxidation, compositions both with and without the cleaved tail groups showed pore formation. This work highlights the complexity of the relationship between chemically modeled lipid bilayer oxidation and cell membrane properties.
NASA Astrophysics Data System (ADS)
Ghezzehei, Teamrat A.
2012-04-01
Subsurface geochemical and biological transformations often influence fluid flow by altering the pore space morphology and related hydrologic properties such as porosity and permeability. In most coupled-processes models changes in porosity are inferred from geochemical and biological process models using mass-balance. The corresponding evolution of permeability is estimated using (semi-) empirical porosity-permeability functions such as the Kozeny-Carman equation or power-law functions. These equations typically do not account for the heterogeneous spatial distribution and morphological irregularities of the geochemical precipitates and biomass. As a result, predictions of permeability evolution are generally unsatisfactory. In this communication, we demonstrate the significance of pore-scale precipitate distribution on porosity-permeability relations using high resolution simulations of fluid flow through a single pore interspersed with crystals. Based on these simulations, we propose a modification to the Kozeny-Carman model that accounts for the shape of the deposits. Limited comparison with published experimental data suggests the plausibility of the proposed conceptual model.
NASA Astrophysics Data System (ADS)
Kutemi, Titilope F.
The steady-state flow technique was employed to measure the flow rate of clean dry air through thirty core plugs (approximately 1" diameter) of the Ellenburger dolomite, drilled normal and parallel to the dominant fractures. Porosity was estimated by the method of imbibition. Electrical parameters (electrical conductivity and dielectric permittivity) were calculated from electrical resistance and capacitance measured as a function of frequency (100 Hz, 120 Hz, 1 KHz, and 10 KHz) and saturation (dry/ambient and brine saturated conditions). Another set of permeability data obtained by the method of pressure decay on similar samples was used for correlation. Anisotropies of permeability and electromagnetic parameters were established. Empirical relations between porosity (phi), permeability (k), electrical conductivity (sigma), and dielectric permittivity (epsilon) were defined via cross-plots and linear regressions. Prediction of k from sigma and epsilon was attempted; k from sigma was modeled from a combination of the Archie's relation and the Carman-Kozeny relation. Anisotropic EM responses are sensitive to saturation. Anisotropies of conductivity and permeability were observed to be controlled by the pore micro-structure. Although the rock is fractured, the fracture density appears insufficient to dominate the effects of primary structures in these samples of the Ellenburger dolomite. Model-based prediction of permeability from conductivity is generally unreliable, and is attributed to the underlying assumptions of the models, which are not consistent with the properties of the samples used for this study. Permeability was not predictable from dielectric permittivity.
Reanalysis of in situ permeability measurements in the Barbados décollement
Bekins, B.A.; Matmon, D.; Screaton, E.J.; Brown, K.M.
2011-01-01
A cased and sealed borehole in the Northern Barbados accretionary complex was the site of the first attempts to measure permeability in situ along a plate boundary décollement. Three separate efforts at Hole 949C yielded permeability estimates for the décollement spanning four orders of magnitude. An analysis of problems encountered during installation of the casing and seals provides insights into how the borehole conditions may have led to the wide range of results. During the installation, sediments from the surrounding formation repeatedly intruded into the borehole and casing. Stress analysis shows that the weak sediments were deforming plastically and the radial and tangential stresses around the borehole were significantly lower than lithostatic. This perturbed stress state may explain why the test pressure records showed indications of hydrofracture at pressures below lithostatic, and permeabilities rose rapidly as the estimated effective stress dropped below 0.8 MPa. Even after the borehole was sealed, the plastic deformation of the formation and relatively large gap of the wire wrapped screen allowed sediment to flow into the casing. Force equilibrium calculations predict sediment would have filled the borehole to 10 cm above the top of the screen by the time slug tests were conducted 1.5 years after the borehole was sealed. Reanalysis of the slug test results with these conditions yields several orders of magnitude higher permeability estimates than the original analysis which assumed an open casing. Overall the results based on only the tests with no sign of hydrofracture yield a permeability range of 10−14–10−15 m2 and a rate of increase in permeability with decreasing effective stress consistent with laboratory tests on samples from the décollement zone.
NASA Astrophysics Data System (ADS)
Heiland, J.
- The influence of differential stress on the permeability of a Lower Permian sandstone was investigated. Rock cylinders of 50 mm in diameter and 100 mm length of a fine-grained (mean grain size 0.2 mm), low-porosity (6-9%) sandstone were used to study the relation between differential stress, rock deformation, rock failure and hydraulic properties, with a focus on the changes of hydraulic properties in the pre-failure and failure region of triaxial rock deformation. The experiments were conducted at confining pressures up to 20 MPa, and axial force was controlled by lateral strain with a rate ranging from 10-6 to 10-7 sec-1. While deforming the samples, permeability was determined by steady-state technique with a pressure gradient of 1 MPa over the specimen length and a fluid pressure level between 40 and 90% of the confining pressure. The results show that permeability of low-porosity sandstones under increasing triaxial stress firstly decreases due to compaction and starts to increase after the onset of dilatancy. This kind of permeability evolution is similar to that of crystalline rocks. A significant dependence of permeability evolution on strain rate was found. Comparison of permeability to volumetric strain demonstrates that the permeability increase after the onset of dilatancy is not sufficient to regain the initial permeability up to failure of the specimen. The initial permeability, which was determined in advance of the experiments, usually was regained in the post-failure region. After the onset of dilatancy, the permeability increase displays a linear dependence on volumetric strain.
Chromatographic demonstration of reversible changes in endothelial permeability
Haselton, F.R.; Mueller, S.N.; Howell, R.E.; Levine, E.M.; Fishman, A.P. )
1989-11-01
This report describes a new in vitro method for measuring the diffusional permeability of an endothelial monolayer and its use in investigating the modulation of permeability by various agents, e.g., isoproterenol, propranolol, dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP), and cytochalasin D. To determine permeability, tracers of different molecular weights were applied simultaneously on a chromatography column containing confluent endothelial cells cultured on porous microcarrier beads. The Sangren-Sheppard model was used to determine the permeability of the endothelial monolayer from the tracer elution profiles. For six radiolabeled tracers the mean (+/- SD) permeabilities (cm/s x 10(-5)) in order of increasing tracer molecular weight were (3H)water, 82.0 +/- 28.8; (14C)urea, 49.5 +/- 9.5; (14C)mannitol, 13.3 +/- 4.7; (14C)-sucrose, 14.1 +/- 2.5; (3H)polyethylene glycol (900 mol wt), 4.80 +/- 1.61; and (3H)polyethylene glycol (4,000 mol wt), 1.97 +/- 1.01. These permeabilities deviate less from in vivo values than those obtained in other in vitro systems and are 10 times higher than in vivo estimates. The values were reproducible for up to the 4 h tested. Modulation of endothelial monolayer permeability was studied in a separate series of experiments. The beta-adrenergic agonist isoproterenol (10(-6) M) decreased the permeability to mannitol by 36% and to polyethylene glycol (900 mol wt) by 49%; in both instances the decrease in permeability was reversed by propranolol. Propranolol alone had no effect. Dibutyryl cAMP (10(-3) M) decreased the permeability to mannitol by 40% and to polyethylene glycol by 47%; permeability returned to base line when dibutyryl cAMP was removed. Cytochalasin D increased permeability by 350% for mannitol and 380% for polyethylene glycol; the permeability change was reversed after removal of cytochalasin D.
Two scale analysis applied to low permeability sandstones
NASA Astrophysics Data System (ADS)
Davy, Catherine; Song, Yang; Nguyen Kim, Thang; Adler, Pierre
2015-04-01
Low permeability materials are often composed of several pore structures of various scales, which are superposed one to another. It is often impossible to measure and to determine the macroscopic properties in one step. In the low permeability sandstones that we consider, the pore space is essentially made of micro-cracks between grains. These fissures are two dimensional structures, which aperture is roughly on the order of one micron. On the grain scale, i.e., on the scale of 1 mm, the fissures form a network. These two structures can be measured by using two different tools [1]. The density of the fissure networks is estimated by trace measurements on the two dimensional images provided by classical 2D Scanning Electron Microscopy (SEM) with a pixel size of 2.2 micron. The three dimensional geometry of the fissures is measured by X-Ray micro-tomography (micro-CT) in the laboratory, with a voxel size of 0.6x0.6x0.6microns3. The macroscopic permeability is calculated in two steps. On the small scale, the fracture transmissivity is calculated by solving the Stokes equation on several portions of the measured fissures by micro-CT. On the large scale, the density of the fissures is estimated by three different means based on the number of intersections with scanlines, on the surface density of fissures and on the intersections between fissures per unit surface. These three means show that the network is relatively isotropic and they provide very close estimations of the density. Then, a general formula derived from systematic numerical computations [2] is used to derive the macroscopic dimensionless permeability which is proportional to the fracture transmissivity. The combination of the two previous results yields the dimensional macroscopic permeability which is found to be in acceptable agreement with the experimental measurements. Some extensions of these preliminary works will be presented as a tentative conclusion. References [1] Z. Duan, C. A. Davy, F
A falling-pressure method for measuring air permeability of asphalt in laboratory
NASA Astrophysics Data System (ADS)
Li, Hailong; Jiao, Jiu Jimmy; Luk, Mario
2004-01-01
This paper presents a simple analytical solution for estimating air permeability using the test data obtained by a falling-pressure method in laboratory. The perimeter of the column-shaped sample is fixed in a steel cylinder with the upper sample surface open to the atmosphere. The lower surface of the sample and the cylinder form an air chamber. A water manometer is connected to the air chamber to measure the air pressure inside after the chamber is pressurized. The data of pressure versus time in the air chamber are recorded and analyzed. An approximate analytical solution is derived to describe the pressure-time relationship in the air chamber. The air permeability can be easily estimated using the approximate analytical solution based on the linear least-squares fitting to the recorded pressure-time test data. This method is used to estimate the falling-pressure test data of 15 asphalt samples. The agreement between the test data and the analytical prediction is satisfactory for all the samples. To investigate the error caused by the approximate analytical solution, the air permeabilities are also estimated based on fully numerical solutions. The permeability values obtained from analytical and numerical solutions are very close. The maximum relative error is less than 6% for samples with more than five pressure-time records. A quantitative condition is given under which the analytical solution applies with negligible estimation error. Compared with the common, steady-state method for measuring air permeability, the falling-pressure method has its advantages such as simplicity and economy. The steady-state method has to measure the air flux through the sample, while the falling-pressure method does not.
Mohagheghi, Fatemeh; Bigdeli, Mohammad Reza; Rasoulian, Bahram; Hashemi, Payman; Pour, Marzyeh Rashidi
2011-01-15
Recent studies suggest that olive extracts suppress inflammation and reduce stress oxidative injury. We sought to extend these observations in an in vivo study of rat cerebral ischemia-reperfusion injury. Four groups, each of 18 Wister rats, were studied. One (control) group received distilled water, while three treatment groups received oral olive leaf extract (50, 75 and 100mg/kg/day respectively). After 30 days, blood lipid profiles were determined, before a 60 min period of middle cerebral artery occlusion (MCAO). After 24h reperfusion, neurological deficit scores, infarct volume, brain edema, and blood-brain barrier permeability were each assessed in subgroups of six animals drawn from each main group. Olive leaf extract reduced the LDL/HDL ratio in doses 50, 75, and 100mg/kg/day in comparison to the control group (P<0.001), and offered cerebroprotection from ischemia-reperfusion. For controls vs. doses of 50mg/kg/day vs. 75 mg/kg/day vs. 100mg/kg/day, attenuated corrected infarct volumes were 209.79 ± 33.05 mm(3) vs. 164.36 ± 13.44 mm(3) vs. 123.06 ± 28.83 mm(3) vs. 94.71 ± 33.03 mm(3); brain water content of the infarcted hemisphere 82.33 ± 0.33% vs. 81.33 ± 0.66% vs. 80.75 ± 0.6% vs. 80.16 ± 0.47%, and blood-brain barrier permeability of the infarcted hemisphere 11.22 ± 2.19 μg/g vs. 9.56 ± 1.74 μg/g vs. 6.99 ± 1.48 μg/g vs. 5.94 ± 1.73 μg/g tissue (P<0.05 and P<0.01 for measures in doses 75 and 100mg/kg/day vs. controls respectively). Oral administration of olive leaf extract reduces infarct volume, brain edema, blood-brain barrier permeability, and improves neurologic deficit scores after transient middle cerebral artery occlusion in rats.
Apical membrane permeability of MDCK cells.
Rivers, R L; McAteer, J A; Clendenon, J L; Connors, B A; Evan, A P; Williams, J C
1996-07-01
The osmotic water permeability (Pf) and permeability to nonelectrolytes were determined for the apical membrane of clonal strain Madin-Darby canine kidney (MDCK) C12 cells cultured as cysts with the apical membrane facing the surrounding medium. Pf and solute permeabilities were calculated from the rate of volume change of cysts by digitizing images at 1-s intervals after instantaneous osmotic challenge. Image measurement was fully automated with the use of a program that separated the image of the cyst from the background by using adaptive intensity thresholding and shape analysis. Pf, calculated by curve fitting to the volume loss data, averaged 2.4 +/- 0.1 micron/s and was increased by addition of amphotericin B. The energy of activation for Pf was high (16.3 kcal/mol), and forskolin (50 microM) had no effect on Pf. Two populations of MDCK cysts were studied: those with two to three cells and those that appeared to be composed of only one cell. The Pf of multicell cysts was the same as single cell cysts, suggesting that paracellular water flow is not significant. Solute permeability was measured using paired osmotic challenges (sucrose and test solute) on the same cyst. Urea permeability was not different from zero, whereas the permeabilities of acetamide and formamide were consistent with their relative oil-water partition coefficients. Our data are similar to values from studies on the permeability properties of vesicles of water-tight epithelial apical membrane. The combination of the unique model of MDCK apical-out cysts and fully automated data analysis enabled determination of apical membrane permeability in intact epithelial cells with high precision.
NASA Astrophysics Data System (ADS)
Gibbons, S. J.; Pabian, F.; Näsholm, S. P.; Kværna', T.; Mykkeltveit, S.
2016-10-01
Declared North Korean nuclear tests in 2006, 2009, 2013, and 2016 were observed seismically at regional and teleseismic distances. Waveform similarity allows the events to be located relatively with far greater accuracy than the absolute locations can be determined from seismic data alone. There is now significant redundancy in the data given the large number of regional and teleseismic stations that have recorded multiple events, and relative location estimates can be confirmed independently by performing calculations on many mutually exclusive sets of measurements. Using a 1-dimensional global velocity model, the distances between the events estimated using teleseismic P phases are found to be approximately 25% shorter than the distances between events estimated using regional Pn phases. The 2009, 2013, and 2016 events all take place within 1 km of each other and the discrepancy between the regional and teleseismic relative location estimates is no more than about 150 m. The discrepancy is much more significant when estimating the location of the more distant 2006 event relative to the later explosions with regional and teleseismic estimates varying by many hundreds of meters. The relative location of the 2006 event is challenging given the smaller number of observing stations, the lower signal-to-noise ratio, and significant waveform dissimilarity at some regional stations. The 2006 event is however highly significant in constraining the absolute locations in the terrain at the Punggye-ri test-site in relation to observed surface infrastructure. For each seismic arrival used to estimate the relative locations, we define a slowness scaling factor which multiplies the gradient of seismic traveltime versus distance, evaluated at the source, relative to the applied 1-d velocity model. A procedure for estimating correction terms which reduce the double-difference time residual vector norms is presented together with a discussion of the associated uncertainty. The
NASA Astrophysics Data System (ADS)
Gibbons, S. J.; Pabian, F.; Näsholm, S. P.; Kværna, T.; Mykkeltveit, S.
2017-01-01
Declared North Korean nuclear tests in 2006, 2009, 2013 and 2016 were observed seismically at regional and teleseismic distances. Waveform similarity allows the events to be located relatively with far greater accuracy than the absolute locations can be determined from seismic data alone. There is now significant redundancy in the data given the large number of regional and teleseismic stations that have recorded multiple events, and relative location estimates can be confirmed independently by performing calculations on many mutually exclusive sets of measurements. Using a 1-D global velocity model, the distances between the events estimated using teleseismic P phases are found to be approximately 25 per cent shorter than the distances between events estimated using regional Pn phases. The 2009, 2013 and 2016 events all take place within 1 km of each other and the discrepancy between the regional and teleseismic relative location estimates is no more than about 150 m. The discrepancy is much more significant when estimating the location of the more distant 2006 event relative to the later explosions with regional and teleseismic estimates varying by many hundreds of metres. The relative location of the 2006 event is challenging given the smaller number of observing stations, the lower signal-to-noise ratio and significant waveform dissimilarity at some regional stations. The 2006 event is however highly significant in constraining the absolute locations in the terrain at the Punggye-ri test-site in relation to observed surface infrastructure. For each seismic arrival used to estimate the relative locations, we define a slowness scaling factor which multiplies the gradient of seismic traveltime versus distance, evaluated at the source, relative to the applied 1-D velocity model. A procedure for estimating correction terms which reduce the double-difference time residual vector norms is presented together with a discussion of the associated uncertainty. The modified
Relative risk estimates from spatial and space-time scan statistics: Are they biased?
Prates, Marcos O.; Kulldorff, Martin; Assunção, Renato M.
2014-01-01
The purely spatial and space-time scan statistics have been successfully used by many scientists to detect and evaluate geographical disease clusters. Although the scan statistic has high power in correctly identifying a cluster, no study has considered the estimates of the cluster relative risk in the detected cluster. In this paper we evaluate whether there is any bias on these estimated relative risks. Intuitively, one may expect that the estimated relative risks has upward bias, since the scan statistic cherry picks high rate areas to include in the cluster. We show that this intuition is correct for clusters with low statistical power, but with medium to high power the bias becomes negligible. The same behaviour is not observed for the prospective space-time scan statistic, where there is an increasing conservative downward bias of the relative risk as the power to detect the cluster increases. PMID:24639031
Relative risk estimates from spatial and space-time scan statistics: are they biased?
Prates, Marcos O; Kulldorff, Martin; Assunção, Renato M
2014-07-10
The purely spatial and space-time scan statistics have been successfully used by many scientists to detect and evaluate geographical disease clusters. Although the scan statistic has high power in correctly identifying a cluster, no study has considered the estimates of the cluster relative risk in the detected cluster. In this paper, we evaluate whether there is any bias on these estimated relative risks. Intuitively, one may expect that the estimated relative risks has upward bias, because the scan statistic cherry picks high rate areas to include in the cluster. We show that this intuition is correct for clusters with low statistical power, but with medium to high power, the bias becomes negligible. The same behavior is not observed for the prospective space-time scan statistic, where there is an increasing conservative downward bias of the relative risk as the power to detect the cluster increases. Copyright © 2014 John Wiley & Sons, Ltd.
Colloid transport in dual-permeability media.
Leij, Feike J; Bradford, Scott A
2013-07-01
It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the increased risks for disease caused by microorganisms and colloid-associated contaminants. This study presents a model for colloid transport in dual-permeability media that includes reversible and irreversible retention of colloids and first-order exchange between the aqueous phases of the two regions. The model may also be used to describe transport of other reactive solutes in dual-permeability media. Analytical solutions for colloid concentrations in aqueous and solid phases were obtained using Laplace transformation and matrix decomposition. The solutions proved convenient to assess the effect of model parameters on the colloid distribution. The analytical model was used to describe effluent concentrations for a bromide tracer and 3.2- or 1-μm-colloids that were observed after transport through a composite 10-cm long porous medium made up of a cylindrical lens or core of sand and a surrounding matrix with sand of a different grain size. The tracer data were described very well and realistic estimates were obtained for the pore-water velocity in the two flow domains. An accurate description was also achieved for most colloid breakthrough curves. Dispersivity and retention parameters were typically greater for the larger 3.2-μm-colloids while both reversible and irreversible retention rates tended to be higher for the finer sands than the coarser sand. The relatively small sample size and the complex flow pattern in the composite medium made it difficult to reach definitive conclusions regarding transport parameters for colloid transport.
ERIC Educational Resources Information Center
Zippert, Erica L.; Ramani, Geetha B.
2017-01-01
According to Hunt's match hypothesis, the accuracy of parents' beliefs about their children's abilities can influence the nature of the early learning experiences they provide. The present study examined the accuracy of parents' beliefs about their preschoolers' number development and relations to parent-reported frequency of engaging children in…
Skewness of cloud droplet spectrum and an improved estimation for its relative dispersion
NASA Astrophysics Data System (ADS)
Liu, Yu; Lu, Chunsong; Li, Weiliang
2017-02-01
The relative dispersion of the cloud droplet spectrum is a very important parameter in describing and modeling cloud microphysical processes. Based on the definition of skewness as well as theoretical and data analyses, a linear fitting relationship ( α = 2.91 ɛ-0.59) between skewness ( α) and relative dispersion ( ɛ) is established and a new method is developed to estimate the relative dispersion of the cloud droplet spectrum. The new method does not depend on any assumption of a particular distribution for the cloud droplet spectrum and has broader applicability than the previous methods. Comparisons of the three methods for the relative dispersion with the observed data supported the following conclusions. (1) The skewness of the cloud droplet spectrum is asymmetrically distributed. An assumption of zero skewness in quantifying the relative dispersion inevitably results in relatively large deviations from the observations. Errors of the estimated relative dispersion due to the omission of the skewness term are not solely related to the skewness, but rather to the product of the skewness and relative dispersion. (2) The use of the assumption that the cloud droplet spectrum takes a gamma distribution is similar to the assumption that the skewness is twice the relative dispersion. This leads to a better accuracy in estimating the relative dispersion than that with zero skewness assumption. (3) Comparisons with observations show that the new method is more accurate than the one under gamma distribution assumption and is the best among all the three methods. (4) It is believed that finding a better correlation between the skewness and the relative dispersion would further reduce the deviations for the estimated relative dispersion.
EPA Permeable Surface Research - Poster
EPA recognizes permeable surfaces as an effective post-construction infiltration-based Best Management Practice to mitigate the adverse effects of stormwater runoff. The professional user community conceptually embraces permeable surfaces as a tool for making runoff more closely...
EPA Permeable Surface Research - Poster
EPA recognizes permeable surfaces as an effective post-construction infiltration-based Best Management Practice to mitigate the adverse effects of stormwater runoff. The professional user community conceptually embraces permeable surfaces as a tool for making runoff more closely...
The permeability of gabbro in oceanic core complexes
NASA Astrophysics Data System (ADS)
Titarenko, S.; McCaig, A. M.
2013-12-01
In IODP Expedition 340T, a thermal gradient of about 100 °C km-1 was measured in IODP Hole U1309D (Blackman et al. 2013), located in 1.2 My old gabbroic crust in the footwall of an oceanic detachment fault in the Atlantis Massif, just west of the mid-Atlantic Ridge at 30° N. The gradient is linear below 748 mbsf, indicating an essentially conductive regime, and slightly concave above that depth, suggesting slow, long-term downward flow of seawater in surrounding rocks. The lack of any vigorous hydrothermal circulation at this site is remarkable considering that the serpentinite-hosted Lost City Hydrothermal Field (LCHF) is located only 5 km to the south, and has been venting highly alkaline fluids at 40-90 °C for at least the last 140,000 years. We have created a 2-D topographic model of the Atlantis Massif using a N-S profile through the LCHF and the drillhole location, and modelled hydrothermal circulation using Comsol Multiphysics. A maximum permeability of 10-17 m2 below 750 mbsf, and a basal heatflow of 0.22 Wm-1 are required at the drillhole location to suppress hydrothermal circulation and preserve the observed conductive thermal gradient at depth. The concave gradient above this depth can be closely fitted over long time periods with a layer 750 m thick of higher permeability, ~3x 10-14 m2. Fluid vents at the site of the LCHF and in a small knoll north of the drill hole, and enters the seafloor everywhere else, including the drillhole location. Model vent temperatures are only about 20 °C however, much less that at the LCHF. A model with a deeper permeable zone beneath the LCHF, with a permeability of 10-15 m2 or more, is required to match simultaneously both observed vent temperatures and the drillhole gradient. This deep permeable zone is hosted in serpentinite but is most likely related to active faulting related to the Atlantis Transform Fault, not lithological control on permeability. Data from the flanks of both fast and intermediate spreading
NASA Technical Reports Server (NTRS)
Wahba, Grace; Deepak, A. (Editor)
1988-01-01
The problem of merging direct and remotely sensed (indirect) data with forecast data to get an estimate of the present state of the atmosphere for the purpose of numerical weather prediction is examined. To carry out this merging optimally, it is necessary to provide an estimate of the relative weights to be given to the observations and forecast. It is possible to do this dynamically from the information to be merged, if the correlation structure of the errors from the various sources is sufficiently different. Some new statistical approaches to doing this are described, and conditions quantified in which such estimates are likely to be good.
Masaki, Yoshiaki; Sekine, Mitsuo; Seio, Kohji
2017-03-02
Chemical modification of RNA duplexes alters their stability. We have attempted to develop a computational approach to estimate the thermal stability of chemically modified duplexes. These studies revealed that the deformability of chemically modified RNA duplexes, calculated from molecular dynamics simulations, could be used as a good indicator for estimating the effect of chemical modification on duplex thermal stability. This unit describes how deformability calculation can be applied to estimate the relative stability of chemically modified RNA duplexes. © 2017 by John Wiley & Sons, Inc.
Tunable permeability of magnetic wires at microwaves
NASA Astrophysics Data System (ADS)
Panina, L. V.; Makhnovskiy, D. P.; Morchenko, A. T.; Kostishin, V. G.
2015-06-01
This paper presents the analysis into microwave magnetic properties of magnetic microwires and their composites in the context of applications in wireless sensors and tunable microwave materials. It is demonstrated that the intrinsic permeability of wires has a wide frequency dispersion with relatively large values in the GHz band. In the case of a specific magnetic anisotropy this results in a tunable microwave impedance which could be used for distributed wireless sensing networks in functional composites. The other range of applications is related with developing the artificial magnetic dielectrics with large and tunable permeability. The composites with magnetic wires with a circumferential anisotropy have the effective permeability which differs substantially from unity for a relatively low concentration (less than 10%). This can make it possible to design the wire media with a negative and tunable index of refraction utilising natural magnetic properties of wires.
Wetting phase permeability in a partially saturated horizontal fracture
Nicholl, M.J.; Glass, R.J.
1993-12-31
A major obstacle to understanding of unsaturated fracture flow is the paucity of physical data on both fracture aperture structure and the effects of phase structure on permeability. An experimental procedure is developed for collecting detailed data on aperture and phase structure from a transparent analog fracture. Stable phase structures of varying complexity are creating within the horizontal analog fracture. Wetting phase permeability is measured under steady-state conditions. A process based model for wetting phase relative permeability is explored. Average distribution of the wetting phase is shown to provide insufficient information for modeling relative permeability; descriptive models must account for spatial structure of the phases.
Upscaling of permeability in Shale with Heterogeneous Kerogen Distribution
NASA Astrophysics Data System (ADS)
Cao, G.; Lin, M.
2016-12-01
Apparent permeability is a vital parameter for accurate estimation of exploitable gas reserve in shale. In this paper, we introduce a new model to investigate multi-scale gas-transport phenomena in organic-rich-shale with heterogeneous kerogen distribution. The formulation is decomposed into two subdomains: kerogen and inorganic matrix. On the one hand, considering the molecular phenomena (slip and diffusive transport) is significant in kerogen for its enrichment of nanopores, we use pore-scale network model (PNM) to represent it and apply Javadpour's apparent permeability formula(2009) to calculate flow in the nanoscale throats. On the other hand, inorganic matrix, with relatively large pores, micro natural fractures and manual hydraulic fracturing cracks, its flow is approximate to Darcy, so we model it as continuum-scale models FVM. The two subdomains are coupled using mortars. Mortars are finite-element spaces employed to couple independent subdomains by ensuring interfacial pressures and fluxes are matched. Considering the local heterogeneities, kerogen is treated as several nanoporous organic material blocks randomly dispersed within the inorganic matrix. We study on four factors: the distribution of kerogen, the permeability of inorganic matrix (Ki), the magnitude of pressure, and the TOC of coupling model. The results are shown intuitively by APF (apparent permeability function) graph. We conclude that: (1) when Ki is greater than the Darcy permeability of kerogen, the APF graphs with different TOC and distribution have an intersection point, and this point is only decided by permeability of Ki and the pore size distribution of kerogen; (2) when pressure is close to or higher than the pressure of intersection point, the influence of heterogeneous distribution can be ignored, and the complex coupling model can instead by a simple equivalent model. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB
Health-related lost productive time (LPT): recall interval and bias in LPT estimates.
Stewart, Walter F; Ricci, Judith A; Leotta, Carol
2004-06-01
We examined the effect of interview characteristics (ie, recall interval, interview version) on estimates of health-related lost productive work time (LPT). Three versions of a telephone interview were administered using 7-day and 4-week recall periods. In a population-based survey, 7674 workers randomly were assigned to one of six interviews at contact; 615 participants received a follow-up interview. We found strong evidence of under-reporting using a 4-week recall period and a not significant trend in over-reporting LPT using a 7-day recall period. Of the three interviews, version 3 could be administered most quickly, on average, and yielded the most discriminating estimates of LPT by health condition (ie, headache, allergic rhinitis, and cold/flu). Our data suggest that variation in relatively short recall periods influences estimates of health-related LPT. A 2-week recall period may be optimal for minimizing overall reporting error but requires additional research to verify.
Permeability of continental crust influenced by internal and external forcing
Rojstaczer, S.A.; Ingebritsen, S.E.; Hayba, D.O.
2008-01-01
The permeability of continental crust is so highly variable that it is often considered to defy systematic characterization. However, despite this variability, some order has been gleaned from globally compiled data. What accounts for the apparent coherence of mean permeability in the continental crust (and permeability-depth relations) on a very large scale? Here we argue that large-scale crustal permeability adjusts to accommodate rates of internal and external forcing. In the deeper crust, internal forcing - fluxes induced by metamorphism, magmatism, and mantle degassing - is dominant, whereas in the shallow crust, external forcing - the vigor of the hydrologic cycle - is a primary control. Crustal petrologists have long recognized the likelihood of a causal relation between fluid flux and permeability in the deep, ductile crust, where fluid pressures are typically near-lithostatic. It is less obvious that such a relation should pertain in the relatively cool, brittle upper crust, where near-hydrostatic fluid pressures are the norm. We use first-order calculations and numerical modeling to explore the hypothesis that upper-crustal permeability is influenced by the magnitude of external fluid sources, much as lower-crustal permeability is influenced by the magnitude of internal fluid sources. We compare model-generated permeability structures with various observations of crustal permeability. ?? 2008 The Authors Journal compilation ?? 2008 Blackwell Publishing Ltd.
Permeability and selectivity of reverse osmosis membranes: correlation to swelling revisited.
Dražević, Emil; Košutić, Krešimir; Freger, Viatcheslav
2014-02-01
Membrane swelling governs both rejection of solutes and permeability of polymeric membranes, however very few data have been available on swelling in water of salt-rejecting reverse osmosis (RO) membranes. This study assesses swelling, thickness and their relation to water permeability for four commercial polyamide (PA) RO membranes (SWC4+, ESPA1, XLE and BW30) using atomic force microscopy (AFM) and attenuated total reflection Fourier transform IR spectroscopy (ATR-FTIR). ATR-FTIR offered a significantly improved estimate of the actual barrier thickness of PA, given AFM is biased by porosity ("fluffy parts") or wiggling of the active layer or presence of a coating layer. Thus obtained intrinsic permeability (permeability times thickness) and selectivity of aromatic polyamides plotted versus swelling falls well on a general trend, along with previously reported data on several common materials showing RO and NF selectivity. The observed general trend may be rationalized by viewing the polymers as a random composite medium containing molecularly small pores. The results suggest that the combination of a rigid low dielectric matrix, limiting the pore size, with multiple hydrophilic H-bonding sites may be a common feature of RO/NF membranes, allowing both high permeability and selectivity.
Use of artifical neural nets to predict permeability in Hugoton Field
Thompson, K.A.; Franklin, M.H.; Olson, T.M. )
1996-01-01
One of the most difficult tasks in petrophysics is establishing a quantitative relationship between core permeability and wireline logs. This is a tough problem in Hugoton Field, where a complicated mix of carbonates and clastics further obscure the correlation. One can successfully model complex relationships such as permeability-to-logs using artificial neural networks. Mind and Vision, Inc.'s neural net software was used because of its orientation toward depth-related data (such as logs) and its ability to run on a variety of log analysis platforms. This type of neural net program allows the expert geologist to select a few (10-100) points of control to train the [open quotes]brainstate[close quotes] using logs as predicters and core permeability as [open quotes]truth[close quotes]. In Hugoton Field, the brainstate provides an estimate of permeability at each depth in 474 logged wells. These neural net-derived permeabilities are being used in reservoir characterization models for fluid saturations. Other applications of this artificial neural network technique include deterministic relationships of logs to: core lithology, core porosity, pore type, and other wireline logs (e.g., predicting a sonic log from a density log).
Use of artifical neural nets to predict permeability in Hugoton Field
Thompson, K.A.; Franklin, M.H.; Olson, T.M.
1996-12-31
One of the most difficult tasks in petrophysics is establishing a quantitative relationship between core permeability and wireline logs. This is a tough problem in Hugoton Field, where a complicated mix of carbonates and clastics further obscure the correlation. One can successfully model complex relationships such as permeability-to-logs using artificial neural networks. Mind and Vision, Inc.`s neural net software was used because of its orientation toward depth-related data (such as logs) and its ability to run on a variety of log analysis platforms. This type of neural net program allows the expert geologist to select a few (10-100) points of control to train the {open_quotes}brainstate{close_quotes} using logs as predicters and core permeability as {open_quotes}truth{close_quotes}. In Hugoton Field, the brainstate provides an estimate of permeability at each depth in 474 logged wells. These neural net-derived permeabilities are being used in reservoir characterization models for fluid saturations. Other applications of this artificial neural network technique include deterministic relationships of logs to: core lithology, core porosity, pore type, and other wireline logs (e.g., predicting a sonic log from a density log).
NASA Astrophysics Data System (ADS)
Patton, J. C.; Hornbuckle, B. K.
2013-12-01
Microwave radiation emitted by Earth's land surface is primarily determined by soil moisture and vegetation. One of the effects of vegetation on surface microwave emissions is often termed the "vegetation optical thickness" or "vegetation opacity" and is often abbreviated as tau. Retrievals of soil moisture from microwave radiometer measurements requires knowledge of tau. The Soil Moisture and Ocean Salinity (SMOS) satellite measures microwave radiation at multiple incidence angles, enabling the simultaneous retrieval of soil moisture and tau. Other soil moisture satellites, such as the upcoming Soil Moisture Active Passive (SMAP) satellite, only measure at single incidence angles and may need auxiliary sources of tau data in order to retrieve soil moisture. One proposed method for estimating tau for these satellites is by relating reflectance data, e.g. the normalized difference vegetation index, to vegetation water content (VWC), then relating VWC to tau. VWC and tau can be related through the b parameter, i.e. tau = b x VWC. Values of b for different land cover types have been estimated from tower (~1 m) and airplane (~10-100 m) data, but have not been measured at the satellite scale (~10 km). Estimating b at the satellite scale from measurements at smaller scales is difficult because the effective value of b in a satellite pixel may not be well represented by linear weighted average based on the fraction of each land cover type in the pixel. However, by relating county crop yields, estimated by the USDA National Agricultural Statistics Service, to measurements of SMOS tau, and by using certain allometric relationships, such as the ratio of water to dry matter and the harvest index of crops, we can estimate b at the satellite scale. We have used this method to estimate b for each Iowa county for the years 2010-2012. Initial results suggest that b may change year to year; our current estimates for b in Iowa range from 0.065 in 2010 to 0.100 in 2012. These
Folser, George R.
1980-01-01
Electrodes for use in an electrolytic cell, which are liquid-permeable and have low electrical resistance and high internal surface area are provided of a rigid, porous, carbonaceous matrix having activated carbon uniformly embedded throughout. The activated carbon may be catalyzed with platinum for improved electron transfer between electrode and electrolyte. Activated carbon is mixed with a powdered thermosetting phenolic resin and compacted to the desired shape in a heated mold to melt the resin and form the green electrode. The compact is then heated to a pyrolyzing temperature to carbonize and volatilize the resin, forming a rigid, porous structure. The permeable structure and high internal surface area are useful in electrolytic cells where it is necessary to continuously remove the products of the electrochemical reaction.
A new quasi-steady method to measure gas permeability of weakly permeable porous media
NASA Astrophysics Data System (ADS)
Jannot, Yves; Lasseux, Didier
2012-01-01
A new quasi-steady method for the determination of the apparent gas permeability of porous materials is presented in this paper along with the corresponding interpretative physical model derived from the unsteady flow equations. This method is mainly dedicated to the measurement of very low permeability of thin porous media, although thicker but more permeable samples may also be analyzed. The method relies on quasi-steady flow resulting from a (quasi) constant pressure maintained at the inlet face of the sample. Gas flow-rate, as low as 3 × 10-10 m3/s, is determined from the record of pressure increase in a reservoir connected to the outlet face of the sample. An estimate of the characteristic time, tc, to reach quasi-steady flow after imposing a constant pressure at the inlet is derived. It is validated by direct numerical simulations of the complete unsteady flow, clearly defining the required experimental duration for the method to apply. Experimental results obtained on rather permeable and thick rock samples are reported showing an excellent agreement of the measured permeability with that determined independently on the same sample whereas the experimental value of tc is also in very good agreement with the predicted one. The method is further employed on a composite material sheet allowing the identification of an apparent gas permeability of about 10-23 m2.
NASA Astrophysics Data System (ADS)
Massart, T. J.; Selvadurai, A. P.
2012-12-01
Poroelasticity is the most widely used geomechanics model for examining critical problems of current importance to environmental geosciences. A fundamental assumption in poroelasticity is that the material properties such as the deformability or the permeability remain unchanged during the coupled interaction between the porous skeleton and the saturating fluid. However, it is known that the porous fabric can experience micro-mechanical damage due to the application of stresses or to the transport of reactive fluids that can lead to changes in the deformability, strength and permeability characteristics. By far the most common action that can alter the properties of the porous geomaterials is the micromechanical damage resulting from the application of stresses. Experimental results conducted on granite and limestone indicate variations in permeability with an increase in deviatoric stress states well below the peak failure loads. This can in turn drastically influence the duration of transient processes involving pore fluid pressure dissipation. In this research, we present a multi-scale computational approach for investigating permeability evolution in a heterogeneous porous quasi-brittle geomaterial. Three-dimensional representative volume elements are produced to replicate the geomaterial with a heterogeneous fabric by means of different techniques (Voronoi tessellation, ...). Fine scale constitutive laws are used to model the progressive mechanical degradation under stress at the level of individual cracks. Interfacial cohesive laws are used for this purpose, which incorporate measurable mechanical parameters such as tensile strength, cohesion and related fracture energies. A fine-scale coupling is then used to translate the local crack features into evolving local permeability quantities, and a versatile computational homogenization technique is developed to upscale mechanical and transport properties corresponding to heterogeneous microstructures towards
Estimating Vehicle Pose Relative to Current Lane from Fisheye Camera System
NASA Astrophysics Data System (ADS)
Li, Shigang; Oshima, Hideki; Nakanishi, Isao
A fisheye camera system is usually used for eliminating the blind spot around a vehicle. In this paper we propose a method of estimating vehicle pose relative to current lane from the side fisheye cameras of such a fisheye camera system. The side fisheye camera with hemispherical field of view can observe the side boundary of the vehicle and the lane markings simultaneously. An algorithm of estimating the distance and the relative orientation between the vehicle and the current lane is presented based on the side boundary of the vehicle and the nearest lane marking. The experimental results are also presented to show the effectiveness of the proposed method.
Heritability estimates of endurance-related phenotypes: A systematic review and meta-analysis.
Miyamoto-Mikami, E; Zempo, H; Fuku, N; Kikuchi, N; Miyachi, M; Murakami, H
2017-08-12
The aim of this study was to clarify heritability estimates for endurance-related phenotypes and the underlying factors affecting these estimates. A systematic literature search was conducted for studies reporting heritability estimates of endurance-related phenotypes using the PubMed database (up to 30 September 2016). Studies that estimated the heritability of maximal oxygen uptake (V˙O2max), submaximal endurance phenotypes, and endurance performance were selected. The weighted mean heritability for endurance-related phenotypes was calculated using a random-effects model. A total of 15 studies were selected via a systematic review. Meta-analysis revealed that the weighted means of the heritability of V˙O2max absolute values and those adjusted for body weight and for fat-free mass were 0.68 (95% CI: 0.59-0.77), 0.56 (95% CI: 0.47-0.65), and 0.44 (95% CI: 0.13-0.75), respectively. There was a significant difference in the weighted means of the heritability of V˙O2max across these different adjustment methods (P < .05). Moreover, there was evidence of statistical heterogeneity in the heritability estimates among studies. Meta-regression analysis revealed that sex could partially explain the heterogeneity in the V˙O2max heritability estimates adjusted by body weight. For submaximal endurance phenotypes and endurance performance, the weighted mean heritabilities were 0.49 (95% CI: 0.33-0.65) and 0.53 (95% CI: 0.27-0.78), respectively. There was statistically significant heterogeneity in the heritability estimates reported among the studies, and we could not identify the specific factors explaining the heterogeneity. Although existing studies indicate that genetic factors account for 44%-68% of the variability in endurance-related phenotypes, further studies are necessary to clarify these values. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
Structural determinants of glomerular permeability.
Deen, W M; Lazzara, M J; Myers, B D
2001-10-01
Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular basement membrane (GBM), and epithelial filtration slits form a series arrangement in which the flow diverges as it enters the GBM from the fenestrae and converges again at the filtration slits. A hydrodynamic model that combines morphometric findings with water flow data in isolated GBM has predicted overall hydraulic permeabilities that are consistent with measurements in vivo. The resistance of the GBM to water flow, which accounts for roughly half that of the capillary wall, is strongly dependent on the extent to which the GBM surfaces are blocked by cells. The spatial frequency of filtration slits is predicted to be a very important determinant of the overall hydraulic permeability, in keeping with observations in several glomerular diseases in humans. Whereas the hydraulic resistances of the cell layers and GBM are additive, the overall sieving coefficient for a macromolecule (its concentration in Bowman's space divided by that in plasma) is the product of the sieving coefficients for the individual layers. Models for macromolecule filtration reveal that the individual sieving coefficients are influenced by one another and by the filtrate velocity, requiring great care in extrapolating in vitro observations to the living animal. The size selectivity of the glomerular capillary has been shown to be determined largely by the cellular layers, rather than the GBM. Controversial findings concerning glomerular charge selectivity are reviewed, and it is concluded that there is good evidence for a role of charge in restricting the transmural movement of albumin. Also discussed is an effect of albumin that has received little attention, namely, its tendency to increase the sieving coefficients of test macromolecules via steric interactions. Among the unresolved issues are the specific contributions of the
Secondary porosity and permeability of coal vs. gas composition and pressure
Mavor, M.J,; Gunter, W.D.
2006-04-15
We have been investigating the sequestration of atmospheric pollutants by injection into coal seams while at the same time enhancing hydrocarbon productivity by displacement of methane with pollutants. We found that changing the composition of the gas sorbed into the coal changes the porosity and permeability of the coal natural-fracture system owing to gas-content changes, which cause matrix swelling or shrinkage due to relative adsorption of different gases. We collected sufficient information to develop a method for predicting the permeability and porosity of a coalbed as a function of the secondary porosity system (SPS) pressure and the gas content and composition of the primary porosity system (PPS). The method uses data from injection/falloff tests with water and/or a weaker adsorbing gas (WAG) than CH{sub 4} and a stronger adsorbing gas (SAG) than CH{sub 4}. Estimates of effective permeability to gas and water obtained from these tests are used with an iterative computation procedure subject to constraints to solve for equivalent SPS porosity and absolute permeability at atmospheric pressure. Once calibrated, the model can be used to predict a coalbed's permeability and porosity as a function of injection pressure and injected-fluid composition, which in turn are used to predict injection performance. The model is applicable to production forecasts to account for SPS permeability and porosity changes as reservoir pressure declines with changes in gas composition. This paper describes the new model and discusses well-test procedures to obtain the data required for model calibration. Also included are coal property estimates resulting from Alberta Medicine River (Manville) coal core and test data and an example model calibration.
NASA Astrophysics Data System (ADS)
Allègre, V.; Brodsky, E. E.; Nale, S. M.; Johnson, N. M.
2014-12-01
The use of water level oscillations driven by earth tides is a technique which has been used to infer rock properties such as permeability and storage at the field scale. The tidal method is attractive because it provides passively estimated permeability time series, allows identification of dynamic changes over time, and measures a hard to access scale ranging from a meters to tens of meters. It consists of computing the phase shift between tidally induced water level changes measured in boreholes, and theoretical earth tide strains. This leads to an estimate of the transmissivity, from which permeability can be deduced. To our knowledge, it has not been compared to standard method, such as pumping test analysis.In this work, water level data monitored before, during, and after two constant rate pumping tests performed in a shallow fractured aquifer were used, at the Santa Susana Field Site in Southern California. The two tests were one to five months long, the recordings lasting approximately 6 months. Tidal frequency oscillations appearing in the measurements were used to get permeability at thirteen locations, some of the wells providing several isolated open screened intervals at depth. As a comparison, permeabilities were also estimated from the fit of two aquifer tests at both early and late stages, using Theis solution (Gringarten solution gives similar results). The simple Theis solution is selected because it includes assumptions consistent with the assumptions in the isotropic and homogeneous tidal solution. The values obtained from both methods are consistent. No significant relation between permeability and faults located in the vicinity of the wells was identified, however, we do observe some variations at depth. Furthermore, some variability is observed in permeability time series during the pumping phases. This study shows that tidal responses lead to a passive and accurate capture of the shallow aquifer properties.
Validation of an Algorithm for Semi-automated Estimation of Voice Relative Fundamental Frequency.
Lien, Yu-An S; Heller Murray, Elizabeth S; Calabrese, Carolyn R; Michener, Carolyn M; Van Stan, Jarrad H; Mehta, Daryush D; Hillman, Robert E; Noordzij, J Pieter; Stepp, Cara E
2017-10-01
Relative fundamental frequency (RFF) has shown promise as an acoustic measure of voice, but the subjective and time-consuming nature of its manual estimation has made clinical translation infeasible. Here, a faster, more objective algorithm for RFF estimation is evaluated in a large and diverse sample of individuals with and without voice disorders. Acoustic recordings were collected from 154 individuals with voice disorders and 36 age- and sex-matched controls with typical voices. These recordings were split into training and 2 testing sets. Using an algorithm tuned to the training set, semi-automated RFF estimates in the testing sets were compared to manual RFF estimates derived from 3 trained technicians. The semi-automated RFF estimations were highly correlated ( r = 0.82-0.91) with the manual RFF estimates. Fast and more objective estimation of RFF makes large-scale RFF analysis feasible. This algorithm allows for future work to optimize RFF measures and expand their potential for clinical voice assessment.
Time estimation during prolonged sleep deprivation and its relation to activation measures.
Miró, Elena; Cano, M Carmen; Espinosa-Fernández, Lourdes; Buela-Casal, Gualberto
2003-01-01
This is the first study to analyze variations in time estimation during 60 h of sleep deprivation and the relation between time estimation performance and the activation measures of skin resistance level, body temperature, and Stanford Sleepiness Scale (SSS) scores. Among 30 healthy participants 18 to 24 years of age, for a 10-s interval using the production method, we found a lengthening in time estimations that was modulated by circadian oscillations. No differences in gender were found in the time estimation task during sleep deprivation. The variations in time estimation correlated significantly with body temperature, skin resistance level, and SSS throughout the sleep deprivation period. When body temperature is elevated, indicating a high level of activation, the interval tends to be underestimated, and vice versa. When the skin resistance level or SSS is elevated (low activation), time estimation is lengthened, and vice versa. This lengthening is important because many everyday situations involve duration estimation under moderate to severe sleep loss. Actual or potential applications of this research include transportation systems, emergency response work, sporting activities, and industrial settings in which accuracy in anticipation or coincidence timing is important for safety or efficiency.
Avetisov, K S; Markosian, A G
2013-01-01
Results of combined ultrasound scanning for estimation of acoustic lens density and biometric relations of lens and other eye structures are presented. A group of 124 patients (189 eyes) was studied; they were subdivided depending on age and length of anteroposterior axis of the eye. Examination algorithm was developed that allows selective estimation of acoustic density of different lens zones and biometric measurements including volumetric. Age-related increase of acoustic density of different lens zones was revealed that indirectly shows method efficiency. Biometric studies showed almost concurring volumetric lens measurements in "normal" and "short" eyes in spite of significantly thicker central zone of the latter. Significantly lower correlation between anterior chamber volume and width of its angle was revealed in "short" eyes and "normal" and "long" eyes (correlation coefficients 0.37, 0.68 and 0.63 respectively).
Estimating one's own and one's relatives' multiple intelligence: a study from Argentina.
Furnham, Adrian; Chamorro-Premuzic, Tomas
2005-05-01
Participants from Argentina (N = 217) estimated their own, their partner's, their parents' and their grandparents' overall and multiple intelligences. The Argentinean data showed that men gave higher overall estimates than women (M = 110.4 vs. 105.1) as well as higher estimates on mathematical and spatial intelligence. Participants thought themselves slightly less bright than their fathers (2 IQ points) but brighter than their mothers (6 points), their grandfathers (8 points), but especially their grandmothers (11 points). Regressions showed that participants thought verbal and mathematical IQ to be the best predictors of overall IQ. Results were broadly in agreement with other studies in the area. A comparison was also made with British data using the same questionnaire. British participants tended to give significantly higher self-estimates than for relatives, though the pattern was generally similar. Results are discussed in terms of the studies in the field.
van Breukelen, Gerard Jp; Candel, Math Jjm; Berger, Martijn Pf
2008-08-01
Cluster randomized and multicentre trials evaluate the effect of a treatment on persons nested within clusters, for instance patients within clinics or pupils within schools. Although equal sample sizes per cluster are generally optimal for parameter estimation, they are rarely feasible. This paper addresses the relative efficiency (RE) of unequal versus equal cluster sizes for estimating variance components in cluster randomized trials and in multicentre trials with person randomization within centres, assuming a quantitative outcome. Starting from maximum likelihood estimation, the RE is investigated numerically for a range of cluster size distributions. An approximate formula is presented for computing the RE as a function of the mean and variance of cluster sizes and the intraclass correlation. The accuracy of this approximation is checked and found to be good. It is concluded that the loss of efficiency for variance component estimation due to variation of cluster sizes rarely exceeds 20% and can be compensated by sampling 25% more clusters.
Friedman, Alinda; Montello, Daniel R
2006-03-01
The authors examined whether absolute and relative judgments about global-scale locations and distances were generated from common representations. At the end of a 10-week class on the regional geography of the United States, participants estimated the latitudes of 16 North American cities and all possible pairwise distances between them. Although participants were relative experts, their latitude estimates revealed the presence of psychologically based regions with large gaps between them and a tendency to stretch North America southward toward the equator. The distance estimates revealed the same properties in the representation recovered via multidimensional scaling. Though the aggregated within- and between-regions distance estimates were fitted by Stevens's law (S. S. Stevens, 1957), this was an averaging artifact: The appropriateness of a power function to describe distance estimates depended on the regional membership of the cities. The authors conclude that plausible reasoning strategies, combined with regionalized representations and beliefs about the location of these relative to global landmarks, underlie global-scale latitude and distance judgments.
Using a pictorial timeline to assess age-related changes in time estimation of daily events.
Yu, Jing; Cheng, Heben; Peng, Peng
2016-02-01
How do older adults compare with younger adults in estimating the timing of daily events, such as heating a meal, keeping an appointment, or taking medication? In Experiment 1, we used a pictorial timeline method to examine age-related changes in how people estimate the time involved in daily events. We also conducted a spatial processing task to control for possible age-related bias in spatial processing. Findings showed that older adults projected smaller windows of time on the timeline to represent the duration of events than did younger adults, which indicates that older adults underestimate time duration. However, older adults also projected smaller windows in spatial task, which creates ambiguity in interpreting the reduced duration estimates among older adults. In Experiment 2, we administered an improved timeline task and spatial task that were comparable in difficulty between age groups and used defined endpoints of the reference line. Consistent with findings from Experiment 1, older adults projected a smaller time window than their younger counterparts, whereas the two age groups showed no differences in estimating spatial distances in the improved spatial experiment. Taken together, our findings suggest that older adults make shorter estimates of the duration of an event than younger adults, and that these age differences are due to age-related differences in orientation to time rather than to a general bias in spatial processing. Copyright © 2015 Elsevier B.V. All rights reserved.
Azarashvili, Tamara S; Tyynelä, Jaana; Odinokova, Irina V; Grigorjev, Pavel A; Baumann, Marc; Evtodienko, Yuri V; Saris, Nils-Erik L
2002-08-01
A phosphorylated polypeptide (ScIRP) from the inner membrane of rat liver mitochondria with an apparent molecular mass of 3.5 kDa was found to be immunoreactive with specific antibodies against subunit c of F0F1-ATPase/ATP synthase (Azarashvily, T. S., Tyynelä, J., Baumann, M., Evtodienko, Yu. V., and Saris, N.-E. L. (2000). Biochem. Biophys. Res. Commun. 270, 741-744. In the present paper we show that the dephosphorylation of ScIRP was promoted by the Ca2+-induced mitochondrial permeability transition (MPT) and prevented by cyclosporin A. Preincubation of ScIRP isolated in its dephosphorylated form with the mitochondrial suspension decreased the membrane potential (delta psiM) and the Ca2+-uptake capacity by promoting MPT. Incorporation of ScIRP into black-lipid membranes increased the membrane conductivity by inducing channel formation that was also suppressed by antibodies to subunit c. These data indicate that the phosphorylation level of ScIRP is influenced by the MPT pore state, presumably by stimulation of calcineurin phosphatase by the Ca2+ used to induce MPT. The possibility of ScIRP being part of the MPT pore assembly is discussed in view of its capability to induced channel activity.
Permeability reduction in granite under hydrothermal conditions
Morrow, C.A.; Moore, Diane E.; Lockner, D.A.
2001-01-01
The formation of impermeable fault seals between earthquake events is a feature of many models of earthquake generation, suggesting that earthquake recurrence may depend in part on the rate of permeability reduction of fault zone materials under hydrothermal conditions. In this study, permeability measurements were conducted on intact, fractured, and gouge-bearing Westerly granite at an effective pressure of 50 MPa and at temperatures from 150?? to 500??C, simulating conditions in the earthquake-generating portions of fault zones. Pore fluids were cycled back and forth under a 2 MPa pressure differential for periods of up to 40 days. Permeability of the granite decreased with time t, following the exponential relation k = c(10-rt). For intact samples run between 250?? and 500??C the time constant for permeability decrease r was proportional to temperature and ranged between 0.001 and 0.1 days-1 (i.e., between 0.4 and 40 decades year-1 loss of permeability). Values of r for the lower-temperature experiments differed little from the 250??C runs. In contrast, prefractured samples showed higher rates of permeability decrease at a given temperature. The surfaces of the fractured samples showed evidence of dissolution and mineral growth that increased in abundance with both temperature and time. The experimentally grown mineral assemblages varied with temperature and were consistent with a rock-dominated hydrothermal system. As such mineral deposits progressively seal the fractured samples, their rates of permeability decrease approach the rates for intact rocks at the same temperature. These results place constraints on models of precipitation sealing and suggest that fault rocks may seal at a rate consistent with earthquake recurrence intervals of typical fault zones.
Controlling DC permeability in cast steels
NASA Astrophysics Data System (ADS)
Sumner, Aaran; Gerada, Chris; Brown, Neil; Clare, Adam
2017-05-01
Annealing (at multiple cooling rates) and quenching (with tempering) was performed on specimens of cast steel of varying composition. The aim was to devise a method for selecting the steel with the highest permeability, from any given range of steels, and then increasing the permeability by heat treatment. Metallographic samples were imaged using optical microscopy to show the effect of the applied heat treatments on the microstructure. Commonly cast steels can have DC permeability altered by the careful selection of a heat treatment. Increases of up to 381% were achieved by annealing using a cooling rate of 6.0 °C/min. Annealing was found to cause the carbon present in the steel to migrate from grain boundaries and from within ferrite crystals into adjacent pearlite crystals. The migration of the carbon resulted in less carbon at grain boundaries and within ferrite crystals reducing the number of pinning sites between magnetic domains. This gives rise to a higher permeability. Quenching then tempering was found to cause the formation of small ferrite crystals with the carbon content of the steel predominately held in the martensitic crystal structures. The results show that with any given range of steel compositions the highest baseline DC permeability will be found with the steel that has the highest iron content and the lowest carbon content. For the samples tested in this paper a cooling rate of 4.5 °C/min resulted in the relative permeability of the sample with the highest baseline permeability, AS4, increasing from 783 to 1479 at 0.5 T. This paper shows how heat treatments commonly applied to hypoeutectoid cast steels, to improve their mechanical performance, can be used to also enhance electromagnetic properties of these alloys. The use of cast steels allows the creation of DC components for electrical machines not possible by the widely used method of stacking of electrical grade sheet steels.
Real time, high accuracy, relative state estimation for multiple vehicle systems
NASA Astrophysics Data System (ADS)
Williamson, Walton Ross
2000-10-01
This dissertation presents the development, implementation, and test results from a new instrumentation package for relative navigation between moving vehicles. The instrumentation package on each vehicle is composed of a GPS (Global Positioning System) receiver, an IMU (Inertial Measurement Unit), a wireless communication system, and a modular computer system. The GPS places all vehicles into the same inertial reference frame and provides a common clock allowing synchronization among all instrument packages. The IMU tracks the high frequency motion of the vehicle alleviating the need for a fixed base station. The wireless communication system communicates GPS code and carrier phase measurements and computed state estimates from each vehicle at a rate fast enough to capture the dynamic changes in the vehicles. This data representing both GPS and IMU measurements from each vehicle is fused together on each vehicle to produce position, velocity and attitude estimates relative to the other vehicles. This capability to estimate relative motion without a base station appears unique. Furthermore, the application of fusion algorithms to address this new estimation problem is unique. The use of carrier phase provides very accurate relative measurements. In constructing carrier phase measurement, the integer number of wave lengths between vehicles must be resolved. Although there exist integer resolution schemes, these algorithms are ad hoe. The scheme presented here is based on generating the conditional probability of the hypothesis of each integer given the measurement sequence. This nonlinear filter is an elegant and novel contribution. The entire system is tested in real time in an experiment intended to validate the measurement accuracy. The system built using the algorithms designed in this dissertation is capable of estimating relative range to less than 5 cm. RMS, relative roll and pitch to less than 0.2 degrees RMS, and relative yaw to less than 0.7 degrees RMS
NASA Astrophysics Data System (ADS)
Yousefi, Siavash; Wang, Ruikang K.
2014-11-01
In an optical coherence tomography (OCT) scan from a living tissue, red blood cells (RBCs) are the major source of backscattering signal from moving particles within microcirculatory system. Measuring the concentration and velocity of RBC particles allows assessment of RBC flux and flow, respectively, to assess tissue perfusion and oxygen/nutrition exchange rates within micro-structures. In this paper, we propose utilizing spectral estimation techniques to simultaneously quantify bi-directional particle flow and relative flux by spectral estimation of the received OCT signal from moving particles within capillary tubes embedded in tissue mimicking phantoms. The proposed method can be directly utilized for in vivo quantification of capillaries and microvessels. Compared to the existing methods in the literature that can either quantify flow direction or power, our proposed method allows simultaneous flow (velocity) direction and relative flux (power) estimation.
Using Passive Sensing to Estimate Relative Energy Expenditure for Eldercare Monitoring.
Wang, Shuang; Skubic, Marjorie; Zhu, Yingnan; Galambos, Colleen
2011-03-21
This paper describes ongoing work in analyzing sensor data logged in the homes of seniors. An estimation of relative energy expenditure is computed using motion density from passive infrared motion sensors mounted in the environment. We introduce a new algorithm for detecting visitors in the home using motion sensor data and a set of fuzzy rules. The visitor algorithm, as well as a previous algorithm for identifying time-away-from-home (TAFH), are used to filter the logged motion sensor data. Thus, the energy expenditure estimate uses data collected only when the resident is home alone. Case studies are included from TigerPlace, an Aging in Place community, to illustrate how the relative energy expenditure estimate can be used to track health conditions over time.
Non-parametric estimation of relative risk in survival and associated tests.
Wakounig, Samo; Heinze, Georg; Schemper, Michael
2015-12-01
We extend the Tarone and Ware scheme of weighted log-rank tests to cover the associated weighted Mantel-Haenszel estimators of relative risk. Weighting functions previously employed are critically reviewed. The notion of an average hazard ratio is defined and its connection to the effect size measure P(Y > X) is emphasized. The connection makes estimation of P(Y > X) possible also under censoring. Two members of the extended Tarone-Ware scheme accomplish the estimation of intuitively interpretable average hazard ratios, also under censoring and time-varying relative risk which is achieved by an inverse probability of censoring weighting. The empirical properties of the members of the extended Tarone-Ware scheme are demonstrated by a Monte Carlo study. The differential role of the weighting functions considered is illustrated by a comparative analysis of four real data sets.
Yousefi, Siavash; Wang, Ruikang K
2014-11-21
In an optical coherence tomography (OCT) scan from a living tissue, red blood cells (RBCs) are the major source of backscattering signal from moving particles within microcirculatory system. Measuring the concentration and velocity of RBC particles allows assessment of RBC flux and flow, respectively, to assess tissue perfusion and oxygen/nutrition exchange rates within micro-structures. In this paper, we propose utilizing spectral estimation techniques to simultaneously quantify bi-directional particle flow and relative flux by spectral estimation of the received OCT signal from moving particles within capillary tubes embedded in tissue mimicking phantoms. The proposed method can be directly utilized for in vivo quantification of capillaries and microvessels. Compared to the existing methods in the literature that can either quantify flow direction or power, our proposed method allows simultaneous flow (velocity) direction and relative flux (power) estimation.
Regression estimators for generic health-related quality of life and quality-adjusted life years.
Basu, Anirban; Manca, Andrea
2012-01-01
To develop regression models for outcomes with truncated supports, such as health-related quality of life (HRQoL) data, and account for features typical of such data such as a skewed distribution, spikes at 1 or 0, and heteroskedasticity. Regression estimators based on features of the Beta distribution. First, both a single equation and a 2-part model are presented, along with estimation algorithms based on maximum-likelihood, quasi-likelihood, and Bayesian Markov-chain Monte Carlo methods. A novel Bayesian quasi-likelihood estimator is proposed. Second, a simulation exercise is presented to assess the performance of the proposed estimators against ordinary least squares (OLS) regression for a variety of HRQoL distributions that are encountered in practice. Finally, the performance of the proposed estimators is assessed by using them to quantify the treatment effect on QALYs in the EVALUATE hysterectomy trial. Overall model fit is studied using several goodness-of-fit tests such as Pearson's correlation test, link and reset tests, and a modified Hosmer-Lemeshow test. The simulation results indicate that the proposed methods are more robust in estimating covariate effects than OLS, especially when the effects are large or the HRQoL distribution has a large spike at 1. Quasi-likelihood techniques are more robust than maximum likelihood estimators. When applied to the EVALUATE trial, all but the maximum likelihood estimators produce unbiased estimates of the treatment effect. One and 2-part Beta regression models provide flexible approaches to regress the outcomes with truncated supports, such as HRQoL, on covariates, after accounting for many idiosyncratic features of the outcomes distribution. This work will provide applied researchers with a practical set of tools to model outcomes in cost-effectiveness analysis.
Lee, Eugenia E; Stewart, Barclay; Zha, Yuanting A; Groen, Thomas A; Burkle, Frederick M; Kushner, Adam L
2016-08-10
Climate extremes will increase the frequency and severity of natural disasters worldwide. Climate-related natural disasters were anticipated to affect 375 million people in 2015, more than 50% greater than the yearly average in the previous decade. To inform surgical assistance preparedness, we estimated the number of surgical procedures needed. The numbers of people affected by climate-related disasters from 2004 to 2014 were obtained from the Centre for Research of the Epidemiology of Disasters database. Using 5,000 procedures per 100,000 persons as the minimum, baseline estimates were calculated. A linear regression of the number of surgical procedures performed annually and the estimated number of surgical procedures required for climate-related natural disasters was performed. Approximately 140 million people were affected by climate-related natural disasters annually requiring 7.0 million surgical procedures. The greatest need for surgical care was in the People's Republic of China, India, and the Philippines. Linear regression demonstrated a poor relationship between national surgical capacity and estimated need for surgical care resulting from natural disaster, but countries with the least surgical capacity will have the greatest need for surgical care for persons affected by climate-related natural disasters. As climate extremes increase the frequency and severity of natural disasters, millions will need surgical care beyond baseline needs. Countries with insufficient surgical capacity will have the most need for surgical care for persons affected by climate-related natural disasters. Estimates of surgical are particularly important for countries least equipped to meet surgical care demands given critical human and physical resource deficiencies.
Lee, Eugenia E.; Stewart, Barclay; Zha, Yuanting A.; Groen, Thomas A.; Burkle, Frederick M.; Kushner, Adam L.
2016-01-01
Background: Climate extremes will increase the frequency and severity of natural disasters worldwide. Climate-related natural disasters were anticipated to affect 375 million people in 2015, more than 50% greater than the yearly average in the previous decade. To inform surgical assistance preparedness, we estimated the number of surgical procedures needed. Methods: The numbers of people affected by climate-related disasters from 2004 to 2014 were obtained from the Centre for Research of the Epidemiology of Disasters database. Using 5,000 procedures per 100,000 persons as the minimum, baseline estimates were calculated. A linear regression of the number of surgical procedures performed annually and the estimated number of surgical procedures required for climate-related natural disasters was performed. Results: Approximately 140 million people were affected by climate-related natural disasters annually requiring 7.0 million surgical procedures. The greatest need for surgical care was in the People’s Republic of China, India, and the Philippines. Linear regression demonstrated a poor relationship between national surgical capacity and estimated need for surgical care resulting from natural disaster, but countries with the least surgical capacity will have the greatest need for surgical care for persons affected by climate-related natural disasters. Conclusion: As climate extremes increase the frequency and severity of natural disasters, millions will need surgical care beyond baseline needs. Countries with insufficient surgical capacity will have the most need for surgical care for persons affected by climate-related natural disasters. Estimates of surgical are particularly important for countries least equipped to meet surgical care demands given critical human and physical resource deficiencies. PMID:27617165
A non-orthogonal SVD-based decomposition for phase invariant error-related potential estimation.
Phlypo, Ronald; Jrad, Nisrine; Rousseau, Sandra; Congedo, Marco
2011-01-01
The estimation of the Error Related Potential from a set of trials is a challenging problem. Indeed, the Error Related Potential is of low amplitude compared to the ongoing electroencephalographic activity. In addition, simple summing over the different trials is prone to errors, since the waveform does not appear at an exact latency with respect to the trigger. In this work, we propose a method to cope with the discrepancy of these latencies of the Error Related Potential waveform and offer a framework in which the estimation of the Error Related Potential waveform reduces to a simple Singular Value Decomposition of an analytic waveform representation of the observed signal. The followed approach is promising, since we are able to explain a higher portion of the variance of the observed signal with fewer components in the expansion.
ERIC Educational Resources Information Center
Friedman, Alinda; Montello, Daniel R.
2006-01-01
The authors examined whether absolute and relative judgments about global-scale locations and distances were generated from common representations. At the end of a 10-week class on the regional geography of the United States, participants estimated the latitudes of 16 North American cities and all possible pairwise distances between them. Although…
ERIC Educational Resources Information Center
McKenna, Victoria S.; Heller Murray, Elizabeth S.; Lien, Yu-An S.; Stepp, Cara E.
2016-01-01
Purpose: This study examined the relationship between the acoustic measure relative fundamental frequency (RFF) and a kinematic estimate of laryngeal stiffness. Method: Twelve healthy adults (mean age = 22.7 years, SD = 4.4; 10 women, 2 men) produced repetitions of /ifi/ while varying their vocal effort during simultaneous acoustic and video…
ERIC Educational Resources Information Center
McKenna, Victoria S.; Heller Murray, Elizabeth S.; Lien, Yu-An S.; Stepp, Cara E.
2016-01-01
Purpose: This study examined the relationship between the acoustic measure relative fundamental frequency (RFF) and a kinematic estimate of laryngeal stiffness. Method: Twelve healthy adults (mean age = 22.7 years, SD = 4.4; 10 women, 2 men) produced repetitions of /ifi/ while varying their vocal effort during simultaneous acoustic and video…
A General and Flexible Approach to Estimating the Social Relations Model Using Bayesian Methods
ERIC Educational Resources Information Center
Ludtke, Oliver; Robitzsch, Alexander; Kenny, David A.; Trautwein, Ulrich
2013-01-01
The social relations model (SRM) is a conceptual, methodological, and analytical approach that is widely used to examine dyadic behaviors and interpersonal perception within groups. This article introduces a general and flexible approach to estimating the parameters of the SRM that is based on Bayesian methods using Markov chain Monte Carlo…
Martínez-Martínez, Víctor; Baladrón, Carlos; Gomez-Gil, Jaime; Ruiz-Ruiz, Gonzalo; Navas-Gracia, Luis M.; Aguiar, Javier M.; Carro, Belén
2012-01-01
This paper presents a system based on an Artificial Neural Network (ANN) for estimating and predicting environmental variables related to tobacco drying processes. This system has been validated with temperature and relative humidity data obtained from a real tobacco dryer with a Wireless Sensor Network (WSN). A fitting ANN was used to estimate temperature and relative humidity in different locations inside the tobacco dryer and to predict them with different time horizons. An error under 2% can be achieved when estimating temperature as a function of temperature and relative humidity in other locations. Moreover, an error around 1.5 times lower than that obtained with an interpolation method can be achieved when predicting the temperature inside the tobacco mass as a function of its present and past values with time horizons over 150 minutes. These results show that the tobacco drying process can be improved taking into account the predicted future value of the monitored variables and the estimated actual value of other variables using a fitting ANN as proposed. PMID:23202032
Estimation of short-time cross-correlation between frequency bands of event related EEG.
Zygierewicz, J; Mazurkiewicz, J; Durka, P J; Franaszczuk, P J; Crone, N E
2006-10-30
Simultaneous variations of the event-related power changes (ERD/ERS) are often observed in a number of frequency bands. ERD/ERS measures are usually based on the relative changes of power in a given single frequency band. Within such an approach one cannot answer questions concerning the mutual relations between the band-power variations observed in different frequency bands. This paper addresses the problem of estimating and assessing the significance of the average cross-correlation between ERD/ERS phenomena occurring in two frequency bands. The cross-correlation function in a natural way also provides estimation of the delay between ERD/ERS in those bands. The proposed method is based on estimating the short-time cross-correlation function between relative changes of power in two selected frequency bands. The cross-correlation function is estimated in each trial separately and then averaged across trials. The significance of those mean cross-correlation functions is evaluated by means of a nonparametric test. The basic properties of the method are presented on simulated signals, and an example application to real EEG and ECoG signals is given.
Frutiger, Jérôme; Marcarie, Camille; Abildskov, Jens; Sin, Gürkan
2016-11-15
This study presents new group contribution (GC) models for the prediction of Lower and Upper Flammability Limits (LFL and UFL), Flash Point (FP) and Auto Ignition Temperature (AIT) of organic chemicals applying the Marrero/Gani (MG) method. Advanced methods for parameter estimation using robust regression and outlier treatment have been applied to achieve high accuracy. Furthermore, linear error propagation based on covariance matrix of estimated parameters was performed. Therefore, every estimated property value of the flammability-related properties is reported together with its corresponding 95%-confidence interval of the prediction. Compared to existing models the developed ones have a higher accuracy, are simple to apply and provide uncertainty information on the calculated prediction. The average relative error and correlation coefficient are 11.5% and 0.99 for LFL, 15.9% and 0.91 for UFL, 2.0% and 0.99 for FP as well as 6.4% and 0.76 for AIT. Moreover, the temperature-dependence of LFL property was studied. A compound specific proportionality constant (K(LFL)) between LFL and temperature is introduced and an MG GC model to estimate K(LFL) is developed. Overall the ability to predict flammability-related properties including the corresponding uncertainty of the prediction can provide important information for a qualitative and quantitative safety-related risk assessment studies.
A General and Flexible Approach to Estimating the Social Relations Model Using Bayesian Methods
ERIC Educational Resources Information Center
Ludtke, Oliver; Robitzsch, Alexander; Kenny, David A.; Trautwein, Ulrich
2013-01-01
The social relations model (SRM) is a conceptual, methodological, and analytical approach that is widely used to examine dyadic behaviors and interpersonal perception within groups. This article introduces a general and flexible approach to estimating the parameters of the SRM that is based on Bayesian methods using Markov chain Monte Carlo…
Martínez-Martínez, Víctor; Baladrón, Carlos; Gomez-Gil, Jaime; Ruiz-Ruiz, Gonzalo; Navas-Gracia, Luis M; Aguiar, Javier M; Carro, Belén
2012-10-17
This paper presents a system based on an Artificial Neural Network (ANN) for estimating and predicting environmental variables related to tobacco drying processes. This system has been validated with temperature and relative humidity data obtained from a real tobacco dryer with a Wireless Sensor Network (WSN). A fitting ANN was used to estimate temperature and relative humidity in different locations inside the tobacco dryer and to predict them with different time horizons. An error under 2% can be achieved when estimating temperature as a function of temperature and relative humidity in other locations. Moreover, an error around 1.5 times lower than that obtained with an interpolation method can be achieved when predicting the temperature inside the tobacco mass as a function of its present and past values with time horizons over 150 minutes. These results show that the tobacco drying process can be improved taking into account the predicted future value of the monitored variables and the estimated actual value of other variables using a fitting ANN as proposed.
Effect of geocoding errors on traffic-related air pollutant exposure and concentration estimates
Exposure to traffic-related air pollutants is highest very near roads, and thus exposure estimates are sensitive to positional errors. This study evaluates positional and PM2.5 concentration errors that result from the use of automated geocoding methods and from linearized approx...
Effect of geocoding errors on traffic-related air pollutant exposure and concentration estimates
Exposure to traffic-related air pollutants is highest very near roads, and thus exposure estimates are sensitive to positional errors. This study evaluates positional and PM2.5 concentration errors that result from the use of automated geocoding methods and from linearized approx...
Non-parametric estimation of age-related centiles over wide age ranges.
Pan, H Q; Goldstein, H; Yang, Q
1990-01-01
A new method for estimating age-related centile curves has been developed, which is suitable for measurement covering a wide age range. The method was used to calculate weight centile curves of 8995 children from birth to 6 years obtained by the Collaborating Centre for Physical Growth and Psychosocial Development of Children in Shanghai, China.
Strain-dependent permeability of volcanic rocks.
NASA Astrophysics Data System (ADS)
Farquharson, Jamie; Heap, Michael; Baud, Patrick
2016-04-01
We explore permeability evolution during deformation of volcanic materials using a suite of rocks with varying compositions and physical properties (such as porosity ϕ). 40 mm × 20 mm cylindrical samples were made from a range of extrusive rocks, including andesites from Colima, Mexico (ϕ˜0.08; 0.18; 0.21), Kumamoto, Japan (ϕ˜0.13), and Ruapehu, New Zealand (ϕ˜0.15), and basalt from Mt Etna, Italy (ϕ˜0.04). Gas permeability of each sample was measured before and after triaxial deformation using a steady-state benchtop permeameter. To study the strain-dependence of permeability in volcanic rocks, we deformed samples to 2, 3, 4, 6, and 12 % axial strain at a constant strain rate of 10-5 s-1. Further, the influence of failure mode - dilatant or compactant - on permeability was assessed by repeating experiments at different confining pressures. During triaxial deformation, porosity change of the samples was monitored by a servo-controlled pore fluid pump. Below an initial porosity of ˜0.18, and at low confining pressures (≤ 20 MPa), we observe a dilatant failure mode (shear fracture formation). With increasing axial strain, stress is accommodated by fault sliding and the generation of ash-sized gouge between the fracture planes. In higher-porosity samples, or at relatively higher confining pressures (≥ 60 MPa), we observe compactant deformation characterised by a monotonous decrease in porosity with increasing axial strain. The relative permeability k' is given by the change in permeability divided by the initial reference state. When behaviour is dilatant, k' tends to be positive: permeability increases with progressive deformation. However, results suggest that after a threshold amount of strain, k' can decrease. k' always is negative (permeability decreases during deformation) when compaction is the dominant behaviour. Our results show that - in the absence of a sealing or healing process - the efficiency of a fault to transmit fluids is correlated to
Experimental water vapor permeability results for common wall materials
Sipes, J.M.; Hosni, M.H.
2000-07-01
This paper presents the experimental water vapor permeability results for gypsum board, latex paint, permeable vinyl wallpaper, vinyl wallpaper, and elastomeric stucco. For each material, a series of modified cup tests was conducted, and the material water vapor permeability was obtained as a function of relative humidity across the specimen. This test method was a modification of the ASTM Standard Test Method E 96-93. The permeability values for the materials tested in this study were compared to the limited available data from literature and were found to be in good agreement.
The nonelectrolyte permeability of planar lipid bilayer membranes
1980-01-01
The permeability of lecithin bilayer membranes to nonelectrolytes is in reasonable agreement with Overton's rule. The is, Pd alpha DKhc, where/Pd is the permeability coefficient of a solute through the bilayer, Khc is its hydrocarbon:water partition coefficient, and D is its diffusion coefficient in bulk hydrocarbon. The partition coefficients are by far the major determinants of the relative magnitudes of the permeability coefficients; the diffusion coefficients make only a minor contribution. We note that the recent emphasis on theoretically calculated intramembranous diffusion coefficients (Dm'S) has diverted attention from the experimentally measurable and physiologically relevant permeability coefficients (Pd'S) and has obscured the simplicity and usefulness of Overton's rule. PMID:7381427
Evaluation of air permeability in layered unsaturated materials.
Switzer, Christine; Kosson, David S
2007-03-20
Field estimation of air permeability is important in the design and operation of soil-vapor extraction systems. Previous models have examined airflow in homogenous soils, incorporating leakage through a low-permeability cap either as a correction to the airflow equation or as a boundary condition. The dual leakage model solution developed here improves upon the previous efforts by adding a leaky lower boundary condition, allowing for the examination of airflow in heterogeneous layered soils. The dual leakage model is applied to the evaluation of pump tests at a pilot soil-vapor extraction system at the Savannah River Site in South Carolina. A thick, low-permeability, stiff clay layer divides the stratigraphy at the site into two units for evaluation. A modified version of the previous model, using the water table as the impermeable lower boundary, is used t