Computational modelling of internally cooled wet (ICW) electrodes for radiofrequency ablation: impact of rehydration, thermal convection and electrical conductivity.

PubMed

Trujillo, Macarena; Bon, Jose; Berjano, Enrique

2017-09-01

(1) To analyse rehydration, thermal convection and increased electrical conductivity as the three phenomena which distinguish the performance of internally cooled electrodes (IC) and internally cooled wet (ICW) electrodes during radiofrequency ablation (RFA), (2) Implement a RFA computer model with an ICW which includes these phenomena and (3) Assess their relative influence on the thermal and electrical tissue response and on the coagulation zone size. A 12-min RFA in liver was modelled using an ICW electrode (17 G, 3 cm tip) by an impedance-control pulsing protocol with a constant current of 1.5 A. A model of an IC electrode was used to compare the ICW electrode performance and the computational results with the experimental results. Rehydration and increased electrical conductivity were responsible for an increase in coagulation zone size and a delay (or absence) in the occurrence of abrupt increases in electrical impedance (roll-off). While the increased electrical conductivity had a remarkable effect on enlarging the coagulation zone (an increase of 0.74 cm for differences in electrical conductivity of 0.31 S/m), rehydration considerably affected the delay in roll-off, which, in fact, was absent with a sufficiently high rehydration level. In contrast, thermal convection had an insignificant effect for the flow rates considered (0.05 and 1 mL/min). Computer results suggest that rehydration and increased electrical conductivity were mainly responsible for the absence of roll-off and increased size of the coagulation zone, respectively, and in combination allow the thermal and electrical performance of ICW electrodes to be modelled during RFA.

Computational analysis of electrical conduction in hybrid nanomaterials with embedded non-penetrating conductive particles

NASA Astrophysics Data System (ADS)

Cai, Jizhe; Naraghi, Mohammad

2016-08-01

In this work, a comprehensive multi-resolution two-dimensional (2D) resistor network model is proposed to analyze the electrical conductivity of hybrid nanomaterials made of insulating matrix with conductive particles such as CNT reinforced nanocomposites and thick film resistors. Unlike existing approaches, our model takes into account the impenetrability of the particles and their random placement within the matrix. Moreover, our model presents a detailed description of intra-particle conductivity via finite element analysis, which to the authors’ best knowledge has not been addressed before. The inter-particle conductivity is assumed to be primarily due to electron tunneling. The model is then used to predict the electrical conductivity of electrospun carbon nanofibers as a function of microstructural parameters such as turbostratic domain alignment and aspect ratio. To simulate the microstructure of single CNF, randomly positioned nucleation sites were seeded and grown as turbostratic particles with anisotropic growth rates. Particle growth was in steps and growth of each particle in each direction was stopped upon contact with other particles. The study points to the significant contribution of both intra-particle and inter-particle conductivity to the overall conductivity of hybrid composites. Influence of particle alignment and anisotropic growth rate ratio on electrical conductivity is also discussed. The results show that partial alignment in contrast to complete alignment can result in maximum electrical conductivity of whole CNF. High degrees of alignment can adversely affect conductivity by lowering the probability of the formation of a conductive path. The results demonstrate approaches to enhance electrical conductivity of hybrid materials through controlling their microstructure which is applicable not only to carbon nanofibers, but also many other types of hybrid composites such as thick film resistors.

Nature of Dielectric Properties, Electric Modulus and AC Electrical Conductivity of Nanocrystalline ZnIn2Se4 Thin Films

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Attia, A. A.; Ali, H. A. M.; Salem, G. F.; Ismail, M. I.

2018-02-01

The structural characteristics of thermally deposited ZnIn2Se4 thin films were indexed utilizing x-ray diffraction as well as scanning electron microscopy techniques. Dielectric properties, electric modulus and AC electrical conductivity of ZnIn2Se4 thin films were examined in the frequency range from 42 Hz to 106 Hz. The capacitance, conductance and impedance were measured at different temperatures. The dielectric constant and dielectric loss decrease with an increase in frequency. The maximum barrier height was determined from the analysis of the dielectric loss depending on the Giuntini model. The real part of the electric modulus revealed a constant maximum value at higher frequencies and the imaginary part of the electric modulus was characterized by the appearance of dielectric relaxation peaks. The AC electrical conductivity obeyed the Jonscher universal power law. Correlated barrier hopping model was the appropriate mechanism for AC conduction in ZnIn2Se4 thin films. Estimation of the density of states at the Fermi level and activation energy, for AC conduction, was carried out based on the temperature dependence of AC electrical conductivity.

Laboratory-based electrical conductivity at Martian mantle conditions

NASA Astrophysics Data System (ADS)

Verhoeven, Olivier; Vacher, Pierre

2016-12-01

Information on temperature and composition of planetary mantles can be obtained from electrical conductivity profiles derived from induced magnetic field analysis. This requires a modeling of the conductivity for each mineral phase at conditions relevant to planetary interiors. Interpretation of iron-rich Martian mantle conductivity profile therefore requires a careful modeling of the conductivity of iron-bearing minerals. In this paper, we show that conduction mechanism called small polaron is the dominant conduction mechanism at temperature, water and iron content conditions relevant to Mars mantle. We then review the different measurements performed on mineral phases with various iron content. We show that, for all measurements of mineral conductivity reported so far, the effect of iron content on the activation energy governing the exponential decrease in the Arrhenius law can be modeled as the cubic square root of the iron content. We recast all laboratory results on a common generalized Arrhenius law for iron-bearing minerals, anchored on Earth's mantle values. We then use this modeling to compute a new synthetic profile of Martian mantle electrical conductivity. This new profile matches perfectly, in the depth range [100,1000] km, the electrical conductivity profile recently derived from the study of Mars Global Surveyor magnetic field measurements.

Salinity index determination of porous materials using open-ended probes

NASA Astrophysics Data System (ADS)

Szypłowska, Agnieszka; Kafarski, Marcin; Wilczek, Andrzej; Lewandowski, Arkadiusz; Skierucha, Wojciech

2017-01-01

The relations among soil water content, bulk electrical conductivity and electrical conductivity of soil solution can be described by a number of theoretical and empirical models. The aim of the paper is to examine the performance of open-ended coaxial probes with and without a short antenna in determination of complex dielectric permittivity spectra, moisture and salinity of porous materials using the salinity index approach. Glass beads of 0.26 and 1.24 mm average diameters moistened to various water contents with distilled water and KCl solutions were used to model the soil material. Due to the larger sensitivity zone, only the probe with the antenna enabled determination of bulk electrical conductivity and salinity index of the samples. The relations between bulk electrical conductivity and dielectric permittivity of the samples were highly linear, which was consistent with the salinity index model. The slope of the relation between salinity index and electrical conductivity of moistening solutions closely matched the value for 100 % sand presented in literature.

Penetration of Nonstationary Ionospheric Electric Fields into Lower Atmospheric Layers in the Global Electric Circuit Model

NASA Astrophysics Data System (ADS)

Morozov, V. N.

2018-01-01

The problem of the penetration of nonstationary ionospheric electric fields into the lower atmospheric layers is considered based on the model of the global electric circuit in the Earth's atmosphere. For the equation of the electric field potential, a solution that takes into account exponential variation in the electrical conductivity with height has been obtained. Analysis of the solution made it possible to reveal three cases of the dependence of the solution on height. The first case (the case of high frequencies) corresponds to the Coulomb approximation, when the electrical conductivity of the atmosphere can be neglected. In the case of low frequencies (when the frequency of changes in the ionosphere potential is less than the quantity reciprocal to the time of electric relaxation of the atmosphere), a quasi-stationary regime, in which the variation in the electric potential of the atmosphere is determined by the electric conduction currents, occurs. In the third case, due to the increase in the electrical conductivity of the atmosphere, two spherical regions appear: with the Coulomb approximation in the lower region and conduction currents in the upper one. For these three cases, formulas for estimating the electric field strength near the Earth's surface have been obtained.

Functional asymmetry and plasticity of electrical synapses interconnecting neurons through a 36-state model of gap junction channel gating

PubMed Central

Kraujalis, Tadas; Maciunas, Kestutis

2017-01-01

We combined the Hodgkin–Huxley equations and a 36-state model of gap junction channel gating to simulate electrical signal transfer through electrical synapses. Differently from most previous studies, our model can account for dynamic modulation of junctional conductance during the spread of electrical signal between coupled neurons. The model of electrical synapse is based on electrical properties of the gap junction channel encompassing two fast and two slow gates triggered by the transjunctional voltage. We quantified the influence of a difference in input resistances of electrically coupled neurons and instantaneous conductance–voltage rectification of gap junctions on an asymmetry of cell-to-cell signaling. We demonstrated that such asymmetry strongly depends on junctional conductance and can lead to the unidirectional transfer of action potentials. The simulation results also revealed that voltage spikes, which develop between neighboring cells during the spread of action potentials, can induce a rapid decay of junctional conductance, thus demonstrating spiking activity-dependent short-term plasticity of electrical synapses. This conclusion was supported by experimental data obtained in HeLa cells transfected with connexin45, which is among connexin isoforms expressed in neurons. Moreover, the model allowed us to replicate the kinetics of junctional conductance under different levels of intracellular concentration of free magnesium ([Mg2+]i), which was experimentally recorded in cells expressing connexin36, a major neuronal connexin. We demonstrated that such [Mg2+]i-dependent long-term plasticity of the electrical synapse can be adequately reproduced through the changes of slow gate parameters of the 36-state model. This suggests that some types of chemical modulation of gap junctions can be executed through the underlying mechanisms of voltage gating. Overall, the developed model accounts for direction-dependent asymmetry, as well as for short- and long-term plasticity of electrical synapses. Our modeling results demonstrate that such complex behavior of the electrical synapse is important in shaping the response of coupled neurons. PMID:28384220

Ohmic Heating of an Electrically Conductive Food Package.

PubMed

Kanogchaipramot, Kanyawee; Tongkhao, Kullanart; Sajjaanantakul, Tanaboon; Kamonpatana, Pitiya

2016-12-01

Ohmic heating through an electrically conductive food package is a new approach to heat the food and its package as a whole after packing to avoid post-process contamination and to serve consumer needs for convenience. This process has been successfully completed using polymer film integrated with an electrically conductive film to form a conductive package. Orange juice packed in the conductive package surrounded with a conductive medium was pasteurized in an ohmic heater. A mathematical model was developed to simulate the temperature distribution within the package and its surroundings. A 3-D thermal-electric model showed heating uniformity inside the food package while the hot zone appeared in the orange juice adjacent to the conductive film. The accuracy of the model was determined by comparing the experimental results with the simulated temperature and current drawn; the model showed good agreement between the actual and simulated results. An inoculated pack study using Escherichia coli O157:H7 indicated negative growth of viable microorganisms at the target and over target lethal process temperatures, whereas the microorganism was present in the under target temperature treatment. Consequently, our developed ohmic heating system with conductive packaging offers potential for producing safe food. © 2016 Institute of Food Technologists®.

A quasi-static model of global atmospheric electricity. II - Electrical coupling between the upper and lower atmosphere

NASA Technical Reports Server (NTRS)

Roble, R. G.; Hays, P. B.

1979-01-01

The paper presents a model of global atmospheric electricity used to examine the effect of upper atmospheric generators on the global electrical circuit. The model represents thunderstorms as dipole current generators randomly distributed in areas of known thunderstorm frequency; the electrical conductivity in the model increases with altitude, and electrical effects are coupled with a passive magnetosphere along geomagnetic field lines. The large horizontal-scale potential differences at ionospheric heights map downward into the lower atmosphere where the perturbations in the ground electric field are superimposed on the diurnal variation. Finally, changes in the upper atmospheric conductivity due to solar flares, polar cap absorptions, and Forbush decreases are shown to alter the downward mapping of the high-latitude potential pattern and the global distribution of fields and currents.

Electrical conductivity of metal powders under pressure

NASA Astrophysics Data System (ADS)

Montes, J. M.; Cuevas, F. G.; Cintas, J.; Urban, P.

2011-12-01

A model for calculating the electrical conductivity of a compressed powder mass consisting of oxide-coated metal particles has been derived. A theoretical tool previously developed by the authors, the so-called `equivalent simple cubic system', was used in the model deduction. This tool is based on relating the actual powder system to an equivalent one consisting of deforming spheres packed in a simple cubic lattice, which is much easier to examine. The proposed model relates the effective electrical conductivity of the powder mass under compression to its level of porosity. Other physically measurable parameters in the model are the conductivities of the metal and oxide constituting the powder particles, their radii, the mean thickness of the oxide layer and the tap porosity of the powder. Two additional parameters controlling the effect of the descaling of the particle oxide layer were empirically introduced. The proposed model was experimentally verified by measurements of the electrical conductivity of aluminium, bronze, iron, nickel and titanium powders under pressure. The consistency between theoretical predictions and experimental results was reasonably good in all cases.

Improved theory of time domain reflectometry with variable coaxial cable length for electrical conductivity measurements

USDA-ARS?s Scientific Manuscript database

Although empirical models have been developed previously, a mechanistic model is needed for estimating electrical conductivity (EC) using time domain reflectometry (TDR) with variable lengths of coaxial cable. The goals of this study are to: (1) derive a mechanistic model based on multisection tra...

3D modelling of the human thorax for ventilation distribution measured through electrical impedance tomography

NASA Astrophysics Data System (ADS)

Fan, W. R.; Wang, H. X.

2010-11-01

Thoracic electrical impedance tomography (EIT) aims to reconstruct a cross-sectional image of the internal spatial distribution of conductivity from electrical measurements made by injecting small alternating currents via an electrode array placed on the surface of the thorax. It is a non-invasive, radiation-free monitoring technique. In this paper, true 3D thorax models with conductivity distribution or complex conductivity distribution under different ARDS conditions are built up in comparison with the 2.5D ones, and EIT-derived numeric indices are also employed for evaluation of the lung ventilation. The purpose of this paper is to study different effects of different thorax models with either conductivity or complex conductivity on the reconstructed images and ventilation indices.

Anomalous electrical conductivity of nanoscale colloidal suspensions.

PubMed

Chakraborty, Suman; Padhy, Sourav

2008-10-28

The electrical conductivity of colloidal suspensions containing nanoscale conducting particles is nontrivially related to the particle volume fraction and the electrical double layer thickness. Classical electrochemical models, however, tend to grossly overpredict the pertinent effective electrical conductivity values, as compared to those obtained under experimental conditions. We attempt to address this discrepancy by appealing to the complex interconnection between the aggregation kinetics of the nanoscale particles and the electrodynamics within the double layer. In particular, we model the consequent alterations in the effective electrophoretic mobility values of the suspension by addressing the fundamentals of agglomeration-deagglomeration mechanisms through the pertinent variations in the effective particulate dimensions, solid fractions, as well as the equivalent suspension viscosity. The consequent alterations in the electrical conductivity values provide a substantially improved prediction of the corresponding experimental findings and explain the apparent anomalous behavior predicted by the classical theoretical postulates.

Simplified Calculation of the Electrical Conductivity of Composites with Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Ivanov, S. G.; Aniskevich, A.; Kulakov, V.

2018-03-01

The electrical conductivity of two groups of polymer nanocomposites filled with the same NC7000 carbon nanotubes (CNTs) beyond the percolation threshold is described with the help of simple formulas. Different manufacturing process of the nanocomposites led to different CNT network structures, and, as a consequence, their electrical conductivity, at the same CNT volume, differed by two orders of magnitude. The relation between the electrical conductivity and the volume content of CNTs of the first group of composites (with a higher electrical conductivity) is described assuming that the CNT network structure is close to a statistically homogeneous one. The formula for this case, derived on the basis of a self-consistent model, includes only two parameters: the effective longitudinal electrical conductivity of CNT and the percolation threshold (the critical value of CNT volume content). These parameters were determined from two experimental points of electrical conductivity as a function of the volume fraction of CNTs. The second group of nanocomposites had a pronounced agglomerative structure, which was confirmed by microscopy data. To describe the low electrical conductivity of this group of nanocomposites, a formula based on known models of micromechanics is proposed. Two parameters of this formula were determined from experimental data of the first group, but the other two — of the second group of nanocomposites. A comparison of calculation and experimental relations confirmed the practical expediency of using the approach described.

Enhancement of Electrical Conductivity in Multicomponent Nanocomposites.

NASA Astrophysics Data System (ADS)

Ni, Xiaojuan; Hui, Chao; Su, Ninghai; Liu, Feng

To date, very limited theoretical or numerical analyses have been carried out to understand the electrical percolation properties in multicomponent nanocomposite systems. In this work, a disk-stick percolation model was developed to investigate the electrical percolation behavior of an electrically insulating matrix reinforced with one-dimensional (1D) and two-dimensional (2D) conductors via Monte Carlo simulation. The effective electrical conductivity was evaluated through Kirchhoff's current law by transforming it into an equivalent resistor network. The percolation threshold, equivalent resistance and conductivity were obtained from the distribution of nodal voltages by solving a system of linear equations with Gaussian elimination method. The effects of size, aspect ratio, relative concentration and contact patterns of 1D/2D inclusions on conductivity performance were examined. Our model is able to predict the electrical percolation threshold and evaluate the conductivity for hybrid systems with multiple components. The results suggest that carbon-based nanocomposites can have a high potential for applications where favorable electrical properties and low specific weight are required. We acknowledge the financial support from DOE-BES (No. DE-FG02-04ER46148).

Electrical conductivity of a monolayer produced by random sequential adsorption of linear k -mers onto a square lattice

NASA Astrophysics Data System (ADS)

Tarasevich, Yuri Yu.; Goltseva, Valeria A.; Laptev, Valeri V.; Lebovka, Nikolai I.

2016-10-01

The electrical conductivity of a monolayer produced by the random sequential adsorption (RSA) of linear k -mers (particles occupying k adjacent adsorption sites) onto a square lattice was studied by means of computer simulation. Overlapping with predeposited k -mers and detachment from the surface were forbidden. The RSA process continued until the saturation jamming limit, pj. The isotropic (equiprobable orientations of k -mers along x and y axes) and anisotropic (all k -mers aligned along the y axis) depositions for two different models—of an insulating substrate and conducting k -mers (C model) and of a conducting substrate and insulating k -mers (I model)—were examined. The Frank-Lobb algorithm was applied to calculate the electrical conductivity in both the x and y directions for different lengths (k =1 - 128) and concentrations (p =0 - pj) of the k -mers. The "intrinsic electrical conductivity" and concentration dependence of the relative electrical conductivity Σ (p ) (Σ =σ /σm for the C model and Σ =σm/σ for the I model, where σm is the electrical conductivity of substrate) in different directions were analyzed. At large values of k the Σ (p ) curves became very similar and they almost coincided at k =128 . Moreover, for both models the greater the length of the k -mers the smoother the functions Σx y(p ) ,Σx(p ) and Σy(p ) . For the more practically important C model, the other interesting findings are (i) for large values of k (k =64 ,128 ), the values of Σx y and Σy increase rapidly with the initial increase of p from 0 to 0.1; (ii) for k ≥16 , all the Σx y(p ) and Σx(p ) curves intersect with each other at the same isoconductivity points; (iii) for anisotropic deposition, the percolation concentrations are the same in the x and y directions, whereas, at the percolation point the greater the length of the k -mers the larger the anisotropy of the electrical conductivity, i.e., the ratio σy/σx (>1 ).

Computer modeling of the combined effects of perfusion, electrical conductivity, and thermal conductivity on tissue heating patterns in radiofrequency tumor ablation.

PubMed

Ahmed, Muneeb; Liu, Zhengjun; Humphries, Stanley; Goldberg, S Nahum

2008-11-01

To use an established computer simulation model of radiofrequency (RF) ablation to characterize the combined effects of varying perfusion, and electrical and thermal conductivity on RF heating. Two-compartment computer simulation of RF heating using 2-D and 3-D finite element analysis (ETherm) was performed in three phases (n = 88 matrices, 144 data points each). In each phase, RF application was systematically modeled on a clinically relevant template of application parameters (i.e., varying tumor and surrounding tissue perfusion: 0-5 kg/m(3)-s) for internally cooled 3 cm single and 2.5 cm cluster electrodes for tumor diameters ranging from 2-5 cm, and RF application times (6-20 min). In the first phase, outer thermal conductivity was changed to reflect three common clinical scenarios: soft tissue, fat, and ascites (0.5, 0.23, and 0.7 W/m- degrees C, respectively). In the second phase, electrical conductivity was changed to reflect different tumor electrical conductivities (0.5 and 4.0 S/m, representing soft tissue and adjuvant saline injection, respectively) and background electrical conductivity representing soft tissue, lung, and kidney (0.5, 0.1, and 3.3 S/m, respectively). In the third phase, the best and worst combinations of electrical and thermal conductivity characteristics were modeled in combination. Tissue heating patterns and the time required to heat the entire tumor +/-a 5 mm margin to >50 degrees C were assessed. Increasing background tissue thermal conductivity increases the time required to achieve a 50 degrees C isotherm for all tumor sizes and electrode types, but enabled ablation of a given tumor size at higher tissue perfusions. An inner thermal conductivity equivalent to soft tissue (0.5 W/m- degrees C) surrounded by fat (0.23 W/m- degrees C) permitted the greatest degree of tumor heating in the shortest time, while soft tissue surrounded by ascites (0.7 W/m- degrees C) took longer to achieve the 50 degrees C isotherm, and complete ablation could not be achieved at higher inner/outer perfusions (>4 kg/m(3)-s). For varied electrical conductivities in the setting of varied perfusion, greatest RF heating occurred for inner electrical conductivities simulating injection of saline around the electrode with an outer electrical conductivity of soft tissue, and the least amount of heating occurring while simulating renal cell carcinoma in normal kidney. Characterization of these scenarios demonstrated the role of electrical and thermal conductivity interactions, with the greatest differences in effect seen in the 3-4 cm tumor range, as almost all 2 cm tumors and almost no 5 cm tumors could be treated. Optimal combinations of thermal and electrical conductivity can partially negate the effect of perfusion. For clinically relevant tumor sizes, thermal and electrical conductivity impact which tumors can be successfully ablated even in the setting of almost non-existent perfusion.

A review of anisotropic conductivity models of brain white matter based on diffusion tensor imaging.

PubMed

Wu, Zhanxiong; Liu, Yang; Hong, Ming; Yu, Xiaohui

2018-06-01

The conductivity of brain tissues is not only essential for electromagnetic source estimation (ESI), but also a key reflector of the brain functional changes. Different from the other brain tissues, the conductivity of whiter matter (WM) is highly anisotropic and a tensor is needed to describe it. The traditional electrical property imaging methods, such as electrical impedance tomography (EIT) and magnetic resonance electrical impedance tomography (MREIT), usually fail to image the anisotropic conductivity tensor of WM with high spatial resolution. The diffusion tensor imaging (DTI) is a newly developed technique that can fulfill this purpose. This paper reviews the existing anisotropic conductivity models of WM based on the DTI and discusses their advantages and disadvantages, as well as identifies opportunities for future research on this subject. It is crucial to obtain the linear conversion coefficient between the eigenvalues of anisotropic conductivity tensor and diffusion tensor, since they share the same eigenvectors. We conclude that the electrochemical model is suitable for ESI analysis because the conversion coefficient can be directly obtained from the concentration of ions in extracellular liquid and that the volume fraction model is appropriate to study the influence of WM structural changes on electrical conductivity. Graphical abstract ᅟ.

Improving the Ionospheric Auroral Conductance in a Global Ring Current Model and the Effects on the Ionospheric Electrodynamics

NASA Astrophysics Data System (ADS)

Yu, Y.; Jordanova, V. K.; McGranaghan, R. M.; Solomon, S. C.

2017-12-01

The ionospheric conductance, height-integrated electric conductivity, can regulate both the ionospheric electrodynamics and the magnetospheric dynamics because of its key role in determining the electric field within the coupled magnetosphere-ionosphere system. State-of-the-art global magnetosphere models commonly adopt empirical conductance calculators to obtain the auroral conductance. Such specification can bypass the complexity of the ionosphere-thermosphere chemistry but on the other hand breaks the self-consistent link within the coupled system. In this study, we couple a kinetic ring current model RAM-SCB-E that solves for anisotropic particle distributions with a two-stream electron transport code (GLOW) to more self-consistently compute the height-dependent electric conductivity, provided the auroral electron precipitation from the ring current model. Comparisons with the traditional empirical formula are carried out. It is found that the newly coupled modeling framework reveals smaller Hall and Pedersen conductance, resulting in a larger electric field. As a consequence, the subauroral polarization streams demonstrate a better agreement with observations from DMSP satellites. It is further found that the commonly assumed Maxwellian spectrum of the particle precipitation is not globally appropriate. Instead, a full precipitation spectrum resulted from wave particle interactions in the ring current accounts for a more comprehensive precipitation spectrum.

Determination of thermophysical characteristics of solid materials by electrical modelling of the solutions to the inverse problems in nonsteady heat conduction

NASA Technical Reports Server (NTRS)

Kozdoba, L. A.; Krivoshei, F. A.

1985-01-01

The solution of the inverse problem of nonsteady heat conduction is discussed, based on finding the coefficient of the heat conduction and the coefficient of specific volumetric heat capacity. These findings are included in the equation used for the electrical model of this phenomenon.

Integrating surface and borehole geophysics in ground water studies - an example using electromagnetic soundings in south Florida

USGS Publications Warehouse

Paillet, Frederick; Hite, Laura; Carlson, Matthew

1999-01-01

Time domain surface electromagnetic soundings, borehole induction logs, and other borehole logging techniques are used to construct a realistic model for the shallow subsurface hydraulic properties of unconsolidated sediments in south Florida. Induction logs are used to calibrate surface induction soundings in units of pore water salinity by correlating water sample specific electrical conductivity with the electrical conductivity of the formation over the sampled interval for a two‐layered aquifer model. Geophysical logs are also used to show that a constant conductivity layer model is appropriate for the south Florida study. Several physically independent log measurements are used to quantify the dependence of formation electrical conductivity on such parameters as salinity, permeability, and clay mineral fraction. The combined interpretation of electromagnetic soundings and induction logs was verified by logging three validation boreholes, confirming quantitative estimates of formation conductivity and thickness in the upper model layer, and qualitative estimates of conductivity in the lower model layer.

The Role of Electrical Anisotropy in Modeling and Interpreting Controlled-Source Electromagnetic Responses for Hydraulic Fracture Monitoring

NASA Astrophysics Data System (ADS)

Trevino, S., III; Hickey, M. S.; Everett, M. E.

2017-12-01

Controlled-Source Electromagnetics (CSEM) can be used to monitor the movement and extent of injection fluid during a hydraulic fracture. The response of the fluid to energization by a CSEM source is dependent upon the electrical conductivity difference between the fluid and background geological formation. An important property that must be taken into account when modeling and interpreting CSEM responses is that electrical conductivity may be anisotropic. We study the effect of electrical anisotropy in both the background formation and the fluid-injection zone. First, various properties of the background formation can affect anisotropy including variations in grain size, composition and bedding-plane orientation. In certain formations, such as shale, the horizontal component of the conductivity can be more than an order of magnitude larger than the vertical component. We study this effect by computing differences in surface CSEM responses using the analytic 1-D anisotropic primary solution of a horizontal electric dipole positioned at the surface. Second, during hydraulic fracturing, the injected fluid can create new fractures and infill existing natural fractures. To include the explicit fracture geometry in modeling, a large increase in the number of nodes and computational time is required which may not be feasible. An alternative is to instead model the large-scale fracture geometry as a uniform slab with an appropriate bulk conductivity. Micro-scale fracture geometry may cause preferential fluid propagation in a single direction or plane which can be represented by electrical anisotropy of the slab. To study such effects of bulk anisotropy on CSEM responses we present results from multiple scenarios of surface to surface hydraulic fracture monitoring using 3-D finite element modeling. The model uses Coulomb-gauged potentials to solve Maxwell's equations in the frequency domain and we have updated the code to allow a triaxial electrical conductivity tensor to be specified. By allowing for formation and target electrical anisotropy these modeling results contribute to a better understanding and faster interpretation of field data.

RF tumour ablation: computer simulation and mathematical modelling of the effects of electrical and thermal conductivity.

PubMed

Lobo, S M; Liu, Z-J; Yu, N C; Humphries, S; Ahmed, M; Cosman, E R; Lenkinski, R E; Goldberg, W; Goldberg, S N

2005-05-01

This study determined the effects of thermal conductivity on RF ablation tissue heating using mathematical modelling and computer simulations of RF heating coupled to thermal transport. Computer simulation of the Bio-Heat equation coupled with temperature-dependent solutions for RF electric fields (ETherm) was used to generate temperature profiles 2 cm away from a 3 cm internally-cooled electrode. Multiple conditions of clinically relevant electrical conductivities (0.07-12 S m-1) and 'tumour' radius (5-30 mm) at a given background electrical conductivity (0.12 S m-1) were studied. Temperature response surfaces were plotted for six thermal conductivities, ranging from 0.3-2 W m-1 degrees C (the range of anticipated clinical and experimental systems). A temperature response surface was obtained for each thermal conductivity at 25 electrical conductivities and 17 radii (n=425 temperature data points). The simulated temperature response was fit to a mathematical model derived from prior phantom data. This mathematical model is of the form (T=a+bRc exp(dR) s(f) exp(g)(s)) for RF generator-energy dependent situations and (T=h+k exp(mR)+n?exp(p)(s)) for RF generator-current limited situations, where T is the temperature (degrees C) 2 cm from the electrode and a, b, c, d, f, g, h, k, m, n and p are fitting parameters. For each of the thermal conductivity temperature profiles generated, the mathematical model fit the response surface to an r2 of 0.97-0.99. Parameters a, b, c, d, f, k and m were highly correlated to thermal conductivity (r2=0.96-0.99). The monotonic progression of fitting parameters permitted their mathematical expression using simple functions. Additionally, the effect of thermal conductivity simplified the above equation to the extent that g, h, n and p were found to be invariant. Thus, representation of the temperature response surface could be accurately expressed as a function of electrical conductivity, radius and thermal conductivity. As a result, the non-linear temperature response of RF induced heating can be adequately expressed mathematically as a function of electrical conductivity, radius and thermal conductivity. Hence, thermal conductivity accounts for some of the previously unexplained variance. Furthermore, the addition of this variable into the mathematical model substantially simplifies the equations and, as such, it is expected that this will permit improved prediction of RF ablation induced temperatures in clinical practice.

Modeling Geoelectric Fields and Geomagnetically Induced Currents Around New Zealand to Explore GIC in the South Island's Electrical Transmission Network

NASA Astrophysics Data System (ADS)

Divett, T.; Ingham, M.; Beggan, C. D.; Richardson, G. S.; Rodger, C. J.; Thomson, A. W. P.; Dalzell, M.

2017-10-01

Transformers in New Zealand's South Island electrical transmission network have been impacted by geomagnetically induced currents (GIC) during geomagnetic storms. We explore the impact of GIC on this network by developing a thin-sheet conductance (TSC) model for the region, a geoelectric field model, and a GIC network model. (The TSC is composed of a thin-sheet conductance map with underlying layered resistivity structure.) Using modeling approaches that have been successfully used in the United Kingdom and Ireland, we applied a thin-sheet model to calculate the electric field as a function of magnetic field and ground conductance. We developed a TSC model based on magnetotelluric surveys, geology, and bathymetry, modified to account for offshore sediments. Using this representation, the thin sheet model gave good agreement with measured impedance vectors. Driven by a spatially uniform magnetic field variation, the thin-sheet model results in electric fields dominated by the ocean-land boundary with effects due to the deep ocean and steep terrain. There is a strong tendency for the electric field to align northwest-southeast, irrespective of the direction of the magnetic field. Applying this electric field to a GIC network model, we show that modeled GIC are dominated by northwest-southeast transmission lines rather than east-west lines usually assumed to dominate.

Numerical simulation of electromagnetic fields and impedance of CERN LINAC4 H(-) source taking into account the effect of the plasma.

PubMed

Grudiev, A; Lettry, J; Mattei, S; Paoluzzi, M; Scrivens, R

2014-02-01

Numerical simulation of the CERN LINAC4 H(-) source 2 MHz RF system has been performed taking into account a realistic geometry from 3D Computer Aided Design model using commercial FEM high frequency simulation code. The effect of the plasma has been added to the model by the approximation of a homogenous electrically conducting medium. Electric and magnetic fields, RF power losses, and impedance of the circuit have been calculated for different values of the plasma conductivity. Three different regimes have been found depending on the plasma conductivity: (1) Zero or low plasma conductivity results in RF electric field induced by the RF antenna being mainly capacitive and has axial direction; (2) Intermediate conductivity results in the expulsion of capacitive electric field from plasma and the RF power coupling, which is increasing linearly with the plasma conductivity, is mainly dominated by the inductive azimuthal electric field; (3) High conductivity results in the shielding of both the electric and magnetic fields from plasma due to the skin effect, which reduces RF power coupling to plasma. From these simulations and measurements of the RF power coupling on the CERN source, a value of the plasma conductivity has been derived. It agrees well with an analytical estimate calculated from the measured plasma parameters. In addition, the simulated and measured impedances with and without plasma show very good agreement as well demonstrating validity of the plasma model used in the RF simulations.

Electrical conductivity anomaly beneath Mare Serenitatis detected by Lunokhod 2 and Apollo 16 magnetometers

NASA Technical Reports Server (NTRS)

Vanian, L. L.; Vnuchkova, T. A.; Egorov, I. V.; Basilevskii, A. T.; Eroshenko, E. G.; Fainberg, E. B.; Dyal, P.; Daily, W. D.

1979-01-01

Magnetic fluctuations measured by the Lunokhod 2 magnetometer in the Bay Le Monnier are distinctly anisotropic when compared to simultaneous Apollo 16 magnetometer data measured 1100 km away in the Descartes highlands. This anisotropy can be explained by an anomalous electrical conductivity of the upper mantle beneath Mare Serenitatis. A model is presented of anomalously lower electrical conductivity beneath Serenitatis and the simultaneous magnetic data from the Lunokhod 2 site at the mare edge and the Apollo 16 site are compared to the numerically calculated model solutions. This comparison indicates that the anisotropic fluctuations can be modeled by a nonconducting layer in the lunar lithosphere which is 150 km thick beneath the highlands and 300 km thick beneath Mare Serenitatis. A decreased electrical conductivity in the upper mantle beneath the mare may be due to a lower temperature resulting from heat carried out the magma source regions to the surface during mare flooding.

Multi-modality gellan gum-based tissue-mimicking phantom with targeted mechanical, electrical, and thermal properties.

PubMed

Chen, Roland K; Shih, A J

2013-08-21

This study develops a new class of gellan gum-based tissue-mimicking phantom material and a model to predict and control the elastic modulus, thermal conductivity, and electrical conductivity by adjusting the mass fractions of gellan gum, propylene glycol, and sodium chloride, respectively. One of the advantages of gellan gum is its gelling efficiency allowing highly regulable mechanical properties (elastic modulus, toughness, etc). An experiment was performed on 16 gellan gum-based tissue-mimicking phantoms and a regression model was fit to quantitatively predict three material properties (elastic modulus, thermal conductivity, and electrical conductivity) based on the phantom material's composition. Based on these material properties and the regression model developed, tissue-mimicking phantoms of porcine spinal cord and liver were formulated. These gellan gum tissue-mimicking phantoms have the mechanical, thermal, and electrical properties approximately equivalent to those of the spinal cord and the liver.

An effective medium approach to modelling the pressure-dependent electrical properties of porous rocks

NASA Astrophysics Data System (ADS)

Han, Tongcheng

2018-07-01

Understanding the electrical properties of rocks under varying pressure is important for a variety of geophysical applications. This study proposes an approach to modelling the pressure-dependent electrical properties of porous rocks based on an effective medium model. The so-named Textural model uses the aspect ratios and pressure-dependent volume fractions of the pores and the aspect ratio and electrical conductivity of the matrix grains. The pores were represented by randomly oriented stiff and compliant spheroidal shapes with constant aspect ratios, and their pressure-dependent volume fractions were inverted from the measured variation of total porosity with differential pressure using a dual porosity model. The unknown constant stiff and compliant pore aspect ratios and the aspect ratio and electrical conductivity of the matrix grains were inverted by best fitting the modelled electrical formation factor to the measured data. Application of the approach to three sandstone samples covering a broad porosity range showed that the pressure-dependent electrical properties can be satisfactorily modelled by the proposed approach. The results demonstrate that the dual porosity concept is sufficient to explain the electrical properties of porous rocks under pressure through the effective medium model scheme.

A Comparison of Peak Electric Fields and GICs in the Pacific Northwest Using 1-D and 3-D Conductivity

NASA Astrophysics Data System (ADS)

Gannon, J. L.; Birchfield, A. B.; Shetye, K. S.; Overbye, T. J.

2017-11-01

Geomagnetically induced currents (GICs) are a result of the changing magnetic fields during a geomagnetic disturbance interacting with the deep conductivity structures of the Earth. When assessing GIC hazard, it is a common practice to use layer-cake or one-dimensional conductivity models to approximate deep Earth conductivity. In this paper, we calculate the electric field and estimate GICs induced in the long lines of a realistic system model of the Pacific Northwest, using the traditional 1-D models, as well as 3-D models represented by Earthscope's Electromagnetic transfer functions. The results show that the peak electric field during a given event has considerable variation across the analysis region in the Pacific Northwest, but the 1-D physiographic approximations may accurately represent the average response of an area, although corrections are needed. Rotations caused by real deep Earth conductivity structures greatly affect the direction of the induced electric field. This effect may be just as, or more, important than peak intensity when estimating GICs induced in long bulk power system lines.

Investigation on magnetoacoustic signal generation with magnetic induction and its application to electrical conductivity reconstruction.

PubMed

Ma, Qingyu; He, Bin

2007-08-21

A theoretical study on the magnetoacoustic signal generation with magnetic induction and its applications to electrical conductivity reconstruction is conducted. An object with a concentric cylindrical geometry is located in a static magnetic field and a pulsed magnetic field. Driven by Lorentz force generated by the static magnetic field, the magnetically induced eddy current produces acoustic vibration and the propagated sound wave is received by a transducer around the object to reconstruct the corresponding electrical conductivity distribution of the object. A theory on the magnetoacoustic waveform generation for a circular symmetric model is provided as a forward problem. The explicit formulae and quantitative algorithm for the electrical conductivity reconstruction are then presented as an inverse problem. Computer simulations were conducted to test the proposed theory and assess the performance of the inverse algorithms for a multi-layer cylindrical model. The present simulation results confirm the validity of the proposed theory and suggest the feasibility of reconstructing electrical conductivity distribution based on the proposed theory on the magnetoacoustic signal generation with magnetic induction.

Atmospheric electric field and current configurations in the vicinity of mountains

NASA Technical Reports Server (NTRS)

Tzur, I.; Roble, R. G.; Adams, J. C.

1985-01-01

A number of investigations have been conducted regarding the electrical distortion produced by the earth's orography. Hays and Roble (1979) utilized their global model of atmospheric electricity to study the effect of large-scale orographic features on the currents and fields of the global circuit. The present paper is concerned with an extension of the previous work, taking into account an application of model calculations to orographic features with different configurations and an examination of the electric mapping of these features to ionospheric heights. A two-dimensional quasi-static numerical model of atmospheric electricity is employed. The model contains a detailed electrical conductivity profile. The model region extends from the surface to 100 km and includes the equalization layer located above approximately 70 km. The obtained results show that the electric field and current configurations above mountains depend upon the curvature of the mountain slopes, on the width of the mountain, and on the columnar resistance above the mountain (or mountain height).

Study of temperature dependent electrical properties of Se80-xTe20Bix (x = 0, 3, 6) glasses

NASA Astrophysics Data System (ADS)

Deepika, Singh, Hukum

2018-05-01

This paper reports the variation in electrical properties of Se80-xTe20Bix (x = 0, 3, 6) glasses studied at different temperatures. The amorphous samples were prepared using the melt quenching method and the electrical measurements were performed on Keithley Electrometer in the temperature ranging from 298-373 K. The I-V characteristics were noted at different temperatures and the data obtained was analysed to get dc electrical conductivity and activation energy of electrical conduction. Further, Mott's 3D VRH model has been applied to obtain density of states, hopping range and hopping energy at different temperatures. The obtained results show that dc electrical conductivity increases with increase in Bi composition in Se-Te system. These compositions also show close agreement to Mott's VRH model.

Accuracy testing of electric groundwater-level measurement tapes

USGS Publications Warehouse

Jelinski, Jim; Clayton, Christopher S.; Fulford, Janice M.

2015-01-01

The accuracy tests demonstrated that none of the electric-tape models tested consistently met the suggested USGS accuracy of ±0.01 ft. The test data show that the tape models in the study should give a water-level measurement that is accurate to roughly ±0.05 ft per 100 ft without additional calibration. To meet USGS accuracy guidelines, the electric-tape models tested will need to be individually calibrated. Specific conductance also plays a part in tape accuracy. The probes will not work in water with specific conductance values near zero, and the accuracy of one probe was unreliable in very high conductivity water (10,000 microsiemens per centimeter).

On the origin of electrical conductivity in the bio-electronic material melanin

NASA Astrophysics Data System (ADS)

Bernardus Mostert, A.; Powell, Ben J.; Gentle, Ian R.; Meredith, Paul

2012-02-01

The skin pigment melanin is one of a few bio-macromolecules that display electrical and photo-conductivity in the solid-state. A model for melanin charge transport based on amorphous semiconductivity has been widely accepted for 40 years. In this letter, we show that a central pillar in support of this hypothesis, namely experimental agreement with a hydrated dielectric model, is an artefact related to measurement geometry and non-equilibrium behaviour. Our results cast significant doubt on the validity of the amorphous semiconductor model and are a reminder of the difficulties of electrical measurements on low conductivity, disordered organic materials.

Electrical conductivity of nanocomposites based on carbon nanotubes: a 3D multiscale modeling approach

NASA Astrophysics Data System (ADS)

Grabowski, Krzysztof; Zbyrad, Paulina; Staszewski, Wieslaw J.; Uhl, Tadeusz; Wiatr, Kazimierz; Packo, Pawel

2016-04-01

Remarkable electrical properties of carbon nanotubes (CNT) have lead to increased interest in studying CNT- based devices. Many of current researches are devoted to using all kinds of carbon nanomaterials in the con- struction of sensory elements. One of the most common applications is the development of high performance, large scale sensors. Due to the remarkable conductivity of CNT's such devices represent very high sensitivity. However, there are no sufficient tools for studying and designing such sensors. The main objective of this paper is to develop and validate a multiscale numerical model for a carbon nanotubes based sensor. The device utilises the change of electrical conductivity of a nanocomposite material under applied deformation. The nanocomposite consists of a number of CNTs dispersed in polymer matrix. The paper is devoted to the analysis of the impact of spatial distribution of carbon nanotubes in polymer matrix on electrical conductivity of the sensor. One of key elements is also to examine the impact of strain on electric charge ow in such anisotropic composite structures. In the following work a multiscale electro-mechanical model for CNT - based nanocomposites is proposed. The model comprises of two length scales, namely the meso- and the macro-scale for mechanical and electrical domains. The approach allows for evaluation of macro-scale mechanical response of a strain sensor. Electrical properties of polymeric material with certain CNT fractions were derived considering electrical properties of CNTs, their contact and the tunnelling effect.

Concentration Dependent Electrical Transport Properties of Ni-Cr Binary Alloys

NASA Astrophysics Data System (ADS)

Suthar, P. H.; Khambholja, S. G.; Thakore, B. Y.; Gajjar, P. N.; Jani, A. R.

2011-07-01

The concentration dependent electrical transport properties viz. electrical resistivity and thermal conductivity of liquid Ni-Cr alloys are computed at 1400 K temperature. The electrical resistivity has been studied according to Faber-Ziman model in wide range of Cr concentration. In the present work, the electron-ion interaction is incorporated through our well tested local model potential with screening function due to Sarkar et al.. [S] along with the Hartree [H] dielectric function. Good agreement is achieved between the presently calculated results of resistivity as well as thermal conductivity with the experimental data found in the literature, confirming the applicability of model potential and Faber-Ziman model for such a study.

Analysis of the Diurnal Variation of the Global Electric Circuit Obtained From Different Numerical Models

NASA Astrophysics Data System (ADS)

Jánský, Jaroslav; Lucas, Greg M.; Kalb, Christina; Bayona, Victor; Peterson, Michael J.; Deierling, Wiebke; Flyer, Natasha; Pasko, Victor P.

2017-12-01

This work analyzes different current source and conductivity parameterizations and their influence on the diurnal variation of the global electric circuit (GEC). The diurnal variations of the current source parameterizations obtained using electric field and conductivity measurements from plane overflights combined with global Tropical Rainfall Measuring Mission satellite data give generally good agreement with measured diurnal variation of the electric field at Vostok, Antarctica, where reference experimental measurements are performed. An approach employing 85 GHz passive microwave observations to infer currents within the GEC is compared and shows the best agreement in amplitude and phase with experimental measurements. To study the conductivity influence, GEC models solving the continuity equation in 3-D are used to calculate atmospheric resistance using yearly averaged conductivity obtained from the global circulation model Community Earth System Model (CESM). Then, using current source parameterization combining mean currents and global counts of electrified clouds, if the exponential conductivity is substituted by the conductivity from CESM, the peak to peak diurnal variation of the ionospheric potential of the GEC decreases from 24% to 20%. The main reason for the change is the presence of clouds while effects of 222Rn ionization, aerosols, and topography are less pronounced. The simulated peak to peak diurnal variation of the electric field at Vostok is increased from 15% to 18% from the diurnal variation of the global current in the GEC if conductivity from CESM is used.

Electrical conductivity of a methane-air burning plasma under the action of weak electric fields

NASA Astrophysics Data System (ADS)

Colonna, G.; Pietanza, L. D.; D'Angola, A.; Laricchiuta, A.; Di Vita, A.

2017-02-01

This paper focuses on the calculation of the electrical conductivity of a methane-air flame in the presence of weak electric fields, solving the Boltzmann equation for free electrons self-consistently coupled with chemical kinetics. The chemical model GRI-Mech 3.0 has been completed with chemi-ionization reactions to model ionization in the absence of fields, and a database of cross sections for electron-impact-induced processes to account for reactions and transitions activated in the flame during discharge. The dependence of plasma properties on the frequency of an oscillating field has been studied under different pressure and gas temperature conditions. Fitting expressions of the electrical conductivity as a function of gas temperature and methane consumption are provided for different operational conditions in the Ansaldo Energia burner.

A model for the scattering of high-frequency electromagnetic fields from dielectrics exhibiting thermally-activated electrical losses

NASA Technical Reports Server (NTRS)

Hann, Raiford E.

1991-01-01

An equivalent circuit model (ECM) approach is used to predict the scattering behavior of temperature-activated, electrically lossy dielectric layers. The total electrical response of the dielectric (relaxation + conductive) is given by the ECM and used in combination with transmission line theory to compute reflectance spectra for a Dallenbach layer configuration. The effects of thermally-activated relaxation processes on the scattering properties is discussed. Also, the effect of relaxation and conduction activation energy on the electrical properties of the dielectric is described.

On the transport coefficients of hydrogen in the inertial confinement fusion regime

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

Lambert, Flavien; Recoules, Vanina; Decoster, Alain

2011-05-15

Ab initio molecular dynamics is used to compute the thermal and electrical conductivities of hydrogen from 10 to 160 g cm{sup -3} and temperatures up to 800 eV, i.e., thermodynamical conditions relevant to inertial confinement fusion (ICF). The ionic structure is obtained using molecular dynamics simulations based on an orbital-free treatment for the electrons. The transport properties were computed using ab initio simulations in the DFT/LDA approximation. The thermal and electrical conductivities are evaluated using Kubo-Greenwood formulation. Particular attention is paid to the convergence of electronic transport properties with respect to the number of bands and atoms. These calculations aremore » then used to check various analytical models (Hubbard's, Lee-More's and Ichimaru's) widely used in hydrodynamics simulations of ICF capsule implosions. The Lorenz number, which is the ratio between thermal and electrical conductivities, is also computed and compared to the well-known Wiedemann-Franz law in different regimes ranging from the highly degenerate to the kinetic one. This allows us to deduce electrical conductivity from thermal conductivity for analytical model. We find that the coupling of Hubbard and Spitzer models gives a correct description of the behavior of electrical and thermal conductivities in the whole thermodynamic regime.« less

Characterization and Physics-Based Modeling of Electrochemical Memristors

DTIC Science & Technology

2015-11-16

conducting films that result from electrical or optical stress. Model parameters and electrical characteristics were obtained from and validated...x- ray scattering, Conductive Bridge Random Access Memory 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME...Calculated DOS for GeSe2 in valence band and (b) conduction band .................. 43  Figure 45. DFT band structure for crystalline GeSe2

Using Rouse-Fowler model to describe radiation-induced electrical conductivity of nanocomposite materials

NASA Astrophysics Data System (ADS)

Dyuryagina, N. S.; Yalovets, A. P.

2017-05-01

Using the Rouse-Fowler (RF) model this work studies the radiation-induced electrical conductivity of a polymer nanocomposite material with spherical nanoparticles against the intensity and exposure time of gamma-ray, concentration and size of nanoparticles. The research has found the energy distribution of localized statesinduced by nanoparticles. The studies were conducted on polymethylmethacrylate (PMMA) with CdS nanoparticles.

Electric Conduction in Semiconductors: A Pedagogical Model Based on the Monte Carlo Method

ERIC Educational Resources Information Center

Capizzo, M. C.; Sperandeo-Mineo, R. M.; Zarcone, M.

2008-01-01

We present a pedagogic approach aimed at modelling electric conduction in semiconductors in order to describe and explain some macroscopic properties, such as the characteristic behaviour of resistance as a function of temperature. A simple model of the band structure is adopted for the generation of electron-hole pairs as well as for the carrier…

Modelling the effect of hydration on skin conductivity.

PubMed

Davies, L; Chappell, P; Melvin, T

2017-08-01

Electrical signals are recorded from and sent into the body via the skin in a number of applications. In practice, skin is often hydrated with liquids having different conductivities so a model was produced in order to determine the relationship between skin impedance and conductivity. A model representing the skin was subjected to a variety of electrical signals. The parts of the model representing the stratum corneum were given different conductivities to represent different levels of hydration. The overall impedance and conductivity of the cells did not vary at frequencies below 40 kHz. Above 40 kHz, levels of increased conductivity caused the overall impedance to decrease. The variation in impedance with conductivity between 5 and 50 mSm -1 can be modelled quadratically while variation in impedance with conductivity between 5 and 5000 mSm -1 can be modelled with a double exponential decay. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Electrical conductivity of hydrous andesitic melts pertinent to subduction zones

NASA Astrophysics Data System (ADS)

Guo, Xuan; Li, Bin; Ni, Huaiwei; Mao, Zhu

2017-03-01

Andesitic magmatism and rocks are widespread at convergent plate boundaries. Electrically conductive bodies beneath subduction zone arc volcanoes, such as the Uturuncu Volcano, Bolivia, may correspond to active reservoirs of H2O-bearing andesitic magma. Laboratory measurements of electrical conductivity of hydrous andesitic melts are required to constrain the physicochemical conditions of these magma reservoirs in combination with magnetotelluric data. This experimental study investigates electrical conductivity of andesitic melts with 0.01-5.9 wt % of H2O at 1164-1573 K and 0.5-1.0 GPa in a piston cylinder apparatus using sweeping-frequency impedance spectroscopy. Electrical conductivity of andesitic melt increases with increasing temperature and H2O concentration but decreases with pressure. Across the investigated range of H2O concentration, electrical conductivity varies by 1.2-2.4 log units, indicating stronger influence of H2O for andesitic melt than for rhyolitic and dacitic melts. Using the Nernst-Einstein equation, the principal charge carrier is inferred to be Na in anhydrous melt but divalent cations in hydrous andesitic melts. The experimental data are regressed into a general electrical conductivity model for andesitic melt accounting for the pressure-temperature-H2O dependences altogether. Modeling results show that the conductive layer at >20 km depths beneath the surface of the Uturuncu Volcano could be interpreted by the presence of less than 20 vol % of H2O-rich andesitic melt (with 6-9 wt % H2O).

ECON-KG: A Code for Computation of Electrical Conductivity Using Density Functional Theory

DTIC Science & Technology

2017-10-01

is presented. Details of the implementation and instructions for execution are presented, and an example calculation of the frequency- dependent ...shown to depend on carbon content,3 and electrical conductivity models have become a requirement for input into continuum-level simulations being... dependent electrical conductivity is computed as a weighted sum over k-points: () = ∑ () ∗ () , (2) where W(k) is

A novel approach to model hydraulic and electrical conductivity in fractal porous media

NASA Astrophysics Data System (ADS)

Ghanbarian, B.; Daigle, H.; Sahimi, M.

2014-12-01

Accurate prediction of conductivity in partially-saturated porous media has broad applications in various phenomena in porous media, and has been studied intensively since the 1940s by petroleum, chemical and civil engineers, and hydrologists. Many of the models developed in the past are based on the bundle of capillary tubes. In addition, pore network models have also been developed for simulating multiphase fluid flow in porous media and computing the conductivity in unsaturated porous media. In this study, we propose a novel approach using concepts from the effective-medium approximation (EMA) and percolation theory to model hydraulic and electrical conductivity in fractal porous media whose pore-size distributions exhibit power-law scaling. In our approach, the EMA, originally developed for predicting electrical conductivity of composite materials, is used to predict the effective conductivity, from complete saturation to some intermediate water content that represents a crossover point. Below the crossover water content, but still above a critical saturation (percolation threshold), a universal scaling predicted by percolation theory, a power law that expresses the dependence of the conductivity on the water content (less a critical water saturation) with an exponent of 2, is invoked to describe the effective conductivity. In order to evaluate the accuracy of the approach, experimental data were used from the literature. The predicted hydraulic conductivities for most cases are in excellent agreement with the data. In a few cases the theory underestimates the hydraulic conductivities, which correspond to porous media with very broad pore-size distribution in which the largest pore radius is more than 7 orders of magnitude greater than the smallest one. The approach is also used to predict the saturation dependence of the electrical conductivity for experiments in which capillary pressure data are available. The results indicate that the universal scaling of the electrical conductivity is valid from the percolation threshold all the way up to the complete saturation point. Our results confirm those reported previously by Ewing and Hunt (2006) who argued that the electrical conductivity should follow universal scaling over the entire range of saturation.

Bio-heat transfer model of electroconvulsive therapy: Effect of biological properties on induced temperature variation.

PubMed

de Oliveira, Marilia M; Wen, Paul; Ahfock, Tony

2016-08-01

A realistic human head model consisting of six tissue layers was modelled to investigate the behavior of temperature profile and magnitude when applying electroconvulsive therapy stimulation and different biological properties. The thermo-electrical model was constructed with the use of bio-heat transfer equation and Laplace equation. Three different electrode montages were analyzed as well as the influence of blood perfusion, metabolic heat and electric and thermal conductivity in the scalp. Also, the effect of including the fat layer was investigated. The results showed that temperature increase is inversely proportional to electrical and thermal conductivity increase. Furthermore, the inclusion of blood perfusion slightly drops the peak temperature. Finally, the inclusion of fat is highly recommended in order to acquire more realistic results from the thermo-electrical models.

Impurity effects on electrical conductivity of doped bilayer graphene in the presence of a bias voltage

NASA Astrophysics Data System (ADS)

E, Lotfi; H, Rezania; B, Arghavaninia; M, Yarmohammadi

2016-07-01

We address the electrical conductivity of bilayer graphene as a function of temperature, impurity concentration, and scattering strength in the presence of a finite bias voltage at finite doping, beginning with a description of the tight-binding model using the linear response theory and Green’s function approach. Our results show a linear behavior at high doping for the case of high bias voltage. The effects of electron doping on the electrical conductivity have been studied via changing the electronic chemical potential. We also discuss and analyze how the bias voltage affects the temperature behavior of the electrical conductivity. Finally, we study the behavior of the electrical conductivity as a function of the impurity concentration and scattering strength for different bias voltages and chemical potentials respectively. The electrical conductivity is found to be monotonically decreasing with impurity scattering strength due to the increased scattering among electrons at higher impurity scattering strength.

Prebreakdown characteristics of weakly ionized liquid and gaseous media in the strongly nonuniform electric field

NASA Astrophysics Data System (ADS)

Apfelbaum, M. S.; Syrovatka, R. A.; Vladimirov, V. I.

2018-01-01

A theoretical model of electrohydrodynamic prebreakdown phenomena in slightly ionized (weakly conductive) media is proposed. The electric high voltage conduction of weakly conductive liquids and slightly ionized gases in intense electric fields using this model is considered. The formula for the calculations of volt-ampere characteristics under high voltage spherical capacitor field is analytically obtained. The experimental corona discharge volt-ampere characteristics of air are presented. It was found that the size of the ionization region in the case of corona discharge in air increases monotonically with increasing discharge voltage.

Electrical Conductivity in Transition Metals

ERIC Educational Resources Information Center

Talbot, Christopher; Vickneson, Kishanda

2013-01-01

The aim of this "Science Note" is to describe how to test the electron-sea model to determine whether it accurately predicts relative electrical conductivity for first-row transition metals. In the electron-sea model, a metal crystal is viewed as a three-dimensional array of metal cations immersed in a sea of delocalised valence…

A Modeling Study of the Spatial Structure of Electric Fields Generated by Electrified Clouds with Screening Layers

NASA Astrophysics Data System (ADS)

Biagi, C. J.; Cummins, K. L.

2015-12-01

The growing possibility of inexpensive airborne observations of electric fields using one or more small UAVs increases the importance of understanding what can be determined about cloud electrification and associated electric fields outside cloud boundaries. If important information can be inferred from carefully selected flight paths outside of a cloud, then the aircraft and its instrumentation will be much cheaper to develop and much safer to operate. These facts have led us to revisit this long-standing topic using quasi-static, finite-element modeling inside and outside arbitrarily shaped clouds with a variety of internal charge distributions. In particular, we examine the effect of screening layers on electric fields outside of electrified clouds by comparing modeling results for charged clouds having electrical conductivities that are both equal to and lower than the surrounding clear air. The comparisons indicate that the spatial structure of the electric field is approximately the same regardless of the difference in the conductivities between the cloud and clear air and the formation of a screening layer, even for altitude-dependent electrical conductivities. This result is consistent with the numerical modeling results reported by Driscoll et al [1992]. The similarity of the spatial structure of the electric field outside of clouds with and without a screening layer suggests that "bulk" properties related to cloud electrification might be determined using measurements of the electric field at multiple locations in space outside the cloud, particularly at altitude. Finally, for this somewhat simplified model, the reduction in electric field magnitude outside the cloud due to the presence of a screening layer exhibits a simple dependence on the difference in conductivity between the cloud and clear air. These results are particularly relevant for studying clouds that are not producing lightning, such as developing thunderstorms and decaying anvils associated with mature storm systems.Driscoll K.T., R.J. Blakeslee, M.E. Baginski, 1992, A modeling study of the time-averaged electric currents in the vicinity of isolated thunderstorms, J. Geophys. Res., 97, D11, pp 11535-11551.

Differential and directional effects of perfusion on electrical and thermal conductivities in liver.

PubMed

Podhajsky, Ronald J; Yi, Ming; Mahajan, Roop L

2009-01-01

Two different measurement probes--an electrical probe and a thermal conductivity probe--were designed, fabricated, calibrated, and used in experimental studies on a pig liver model that was designed to control perfusion rates. These probes were fabricated by photolithography and mounted in 1.5-mm diameter catheters. We measured the local impedance and thermal conductivity, respectively, of the artificially perfused liver at different flow rates and, by rotating the probes, in different directions. The results show that both the local electrical conductivity and the thermal conductivity varied location to location, that thermal conductivity increased with decreased distance to large blood vessels, and that significant directional differences exist in both electrical and thermal conductivities. Measurements at different perfusion rates demonstrated that both the local electrical and local thermal conductivities increased linearly with the square root of perfusion rate. These correlations may be of great value to many energy-based biomedical applications.

An upper bound on the electrical conductivity of hydrated oceanic mantle at the onset of dehydration melting

NASA Astrophysics Data System (ADS)

Naif, Samer

2018-01-01

Electrical conductivity soundings provide important constraints on the thermal and hydration state of the mantle. Recent seafloor magnetotelluric surveys have imaged the electrical conductivity structure of the oceanic upper mantle over a variety of plate ages. All regions show high conductivity (0.02 to 0.2 S/m) at 50 to 150 km depths that cannot be explained with a sub-solidus dry mantle regime without unrealistic temperature gradients. Instead, the conductivity observations require either a small amount of water stored in nominally anhydrous minerals or the presence of interconnected partial melts. This ambiguity leads to dramatically different interpretations on the origin of the asthenosphere. Here, I apply the damp peridotite solidus together with plate cooling models to determine the amount of H2O needed to induce dehydration melting as a function of depth and plate age. Then, I use the temperature and water content estimates to calculate the electrical conductivity of the oceanic mantle with a two-phase mixture of olivine and pyroxene from several competing empirical conductivity models. This represents the maximum potential conductivity of sub-solidus oceanic mantle at the limit of hydration. The results show that partial melt is required to explain the subset of the high conductivity observations beneath young seafloor, irrespective of which empirical model is applied. In contrast, the end-member empirical models predict either nearly dry (<20 wt ppm H2O) or slightly damp (<200 wt ppm H2O) asthenosphere for observations of mature seafloor. Since the former estimate is too dry compared with geochemical constraints from mid-ocean ridge basalts, this suggests the effect of water on mantle conductivity is less pronounced than currently predicted by the conductive end-member empirical model.

Experimental Determination and Thermodynamic Modeling of Electrical Conductivity of SRS Waste Tank Supernate

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

Pike, J.; Reboul, S.

2015-06-01

SRS High Level Waste Tank Farm personnel rely on conductivity probes for detection of incipient overflow conditions in waste tanks. Minimal information is available concerning the sensitivity that must be achieved such that that liquid detection is assured. Overly sensitive electronics results in numerous nuisance alarms for these safety-related instruments. In order to determine the minimum sensitivity required of the probe, Tank Farm Engineering personnel need adequate conductivity data to improve the existing designs. Little or no measurements of liquid waste conductivity exist; however, the liquid phase of the waste consists of inorganic electrolytes for which the conductivity may bemore » calculated. Savannah River Remediation (SRR) Tank Farm Facility Engineering requested SRNL to determine the conductivity of the supernate resident in SRS waste Tank 40 experimentally as well as computationally. In addition, SRNL was requested to develop a correlation, if possible, that would be generally applicable to liquid waste resident in SRS waste tanks. A waste sample from Tank 40 was analyzed for composition and electrical conductivity as shown in Table 4-6, Table 4-7, and Table 4-9. The conductivity for undiluted Tank 40 sample was 0.087 S/cm. The accuracy of OLI Analyzer™ was determined using available literature data. Overall, 95% of computed estimates of electrical conductivity are within ±15% of literature values for component concentrations from 0 to 15 M and temperatures from 0 to 125 °C. Though the computational results are generally in good agreement with the measured data, a small portion of literature data deviates as much as ±76%. A simplified model was created that can be used readily to estimate electrical conductivity of waste solution in computer spreadsheets. The variability of this simplified approach deviates up to 140% from measured values. Generally, this model can be applied to estimate the conductivity within a factor of two. The comparison of the simplified model to pure component literature data suggests that the simplified model will tend to under estimate the electrical conductivity. Comparison of the computed Tank 40 conductivity with the measured conductivity shows good agreement within the range of deviation identified based on pure component literature data.« less

Ionosphere-magnetosphere coupling and convection

NASA Technical Reports Server (NTRS)

Wolf, R. A.; Spiro, R. W.

1984-01-01

The following international Magnetospheric Study quantitative models of observed ionosphere-magnetosphere events are reviewed: (1) a theoretical model of convection; (2) algorithms for deducing ionospheric current and electric-field patterns from sets of ground magnetograms and ionospheric conductivity information; and (3) empirical models of ionospheric conductances and polar cap potential drop. Research into magnetic-field-aligned electric fields is reviewed, particularly magnetic-mirror effects and double layers.

Lightning Strike Ablation Damage Influence Factors Analysis of Carbon Fiber/Epoxy Composite Based on Coupled Electrical-Thermal Simulation

NASA Astrophysics Data System (ADS)

Yin, J. J.; Chang, F.; Li, S. L.; Yao, X. L.; Sun, J. R.; Xiao, Y.

2017-10-01

According to the mathematical analysis model constructed on the basis of energy-balance relationship in lightning strike, and accompany with the simplified calculation strategy of composite resin pyrolysis degree dependent electrical conductivity, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate suffered from lightning current was established based on ABAQUS, to elucidate the effects of lighting current waveform parameters and thermal/electrical properties of composite laminate on the extent of ablation damage. Simulated predictions agree well with the composite lightning strike directed effect experimental data, illustrating the potential accuracy of the constructed model. The analytical results revealed that extent of composite lightning strike ablation damage can be characterized by action integral validly, there exist remarkable power function relationships between action integral and visual damage area, projected damage area, maximum damage depth and damage volume of ablation damage, and enhancing the electrical conductivity and specific heat of composite, ablation damage will be descended obviously, power function relationships also exist between electrical conductivity, specific heat and ablation damage, however, the impact of thermal conductivity on the extent of ablation damage is not notable. The conclusions obtained provide some guidance for composite anti-lightning strike structure-function integration design.

Experimental characterization of intrapulse tissue conductivity changes for electroporation.

PubMed

Neal, Robert E; Garcia, Paulo A; Robertson, John L; Davalos, Rafael V

2011-01-01

Cells exposed to short electric pulses experience a change in their transmembrane potential, which can lead to increased membrane permeability of the cell. When the energy of the pulses surpasses a threshold, the cell dies in a non-thermal manner known as irreversible electroporation (IRE). IRE has shown promise in the focal ablation of pathologic tissues. Its non-thermal mechanism spares sensitive structures and facilitates rapid lesion resolution. IRE effects depend on the electric field distribution, which can be predicted with numerical modeling. When the cells become permeabilized, the bulk tissue properties change, affecting this distribution. For IRE to become a reliable and successful treatment of diseased tissues, robust predictive treatment planning methods must be developed. It is vital to understand the changes in tissue properties undergoing the electric pulses to improve numerical models and predict treatment volumes. We report on the experimental characterization of these changes for kidney tissue. Tissue samples were pulsed between plate electrodes while intrapulse voltage and current data were measured to determine the conductivity of the tissue during the pulse. Conductivity was then established as a function of the electric field to which the tissue is exposed. This conductivity curve was used in a numerical model to demonstrate the impact of accounting for these changes when modeling electric field distributions to develop treatment plans.

Evaluation of electrical conductivity of Cu and Al through sub microsecond underwater electrical wire explosion

NASA Astrophysics Data System (ADS)

Sheftman, D.; Shafer, D.; Efimov, S.; Krasik, Ya. E.

2012-03-01

Sub-microsecond timescale underwater electrical wire explosions using Cu and Al materials have been conducted. Current and voltage waveforms and time-resolved streak images of the discharge channel, coupled to 1D magneto-hydrodynamic simulations, have been used to determine the electrical conductivity of the metals for the range of conditions between hot liquid metal and strongly coupled non-ideal plasma, in the temperature range of 10-60 KK. The results of these studies showed that the conductivity values obtained are typically lower than those corresponding to modern theoretical electrical conductivity models and provide a transition between the conductivity values obtained in microsecond time scale explosions and those obtained in nanosecond time scale wire explosions. In addition, the measured wire expansion shows good agreement with equation of state tables.

Anisotropy of synthetic quartz electrical conductivity at high pressure and temperature

NASA Astrophysics Data System (ADS)

Wang, Duojun; Li, Heping; Yi, Li; Matsuzaki, Takuya; Yoshino, Takashi

2010-09-01

AC measurements of the electrical conductivity of synthetic quartz along various orientations were made between 0.1 and 1 MHz, at ˜855˜1601 K and at 1.0 GPa. In addition, the electrical conductivity of quartz along the c axis has been studied at 1.0-3.0 GPa. The impedance arcs representing bulk conductivity occur in the frequency range of 103-106 Hz, and the electrical responses of the interface between the sample and the electrode occur in the 0.1˜103 Hz range. The pressure has a weak effect on the electrical conductivity. The electrical conductivity experiences no abrupt change near the α - β phase transition point. The electrical conductivity of quartz is highly anisotropic; the electrical conductivity along the c axis is strongest and several orders of magnitude larger than in other directions. The activation enthalpies along various orientations are determined to be 0.6 and 1.2 eV orders of magnitude, respectively. The interpretation of the former is based on the contribution of alkali ions, while the latter effect is attributed to additional unassociated aluminum ions. Comparison of determined anisotropic conductivity of quartz determined with those from field geophysical models shows that the quartz may potentially provide explanations for the behavior of electrical conductivity of anisotropy in the crust that are inferred from the transverse magnetic mode.

Temperature profiles in the earth of importance to deep electrical conductivity models

NASA Astrophysics Data System (ADS)

Čermák, Vladimír; Laštovičková, Marcela

1987-03-01

Deep in the Earth, the electrical conductivity of geological material is extremely dependent on temperature. The knowledge of temperature is thus essential for any interpretation of magnetotelluric data in projecting lithospheric structural models. The measured values of the terrestrial heat flow, radiogenic heat production and thermal conductivity of rocks allow the extrapolation of surface observations to a greater depth and the calculation of the temperature field within the lithosphere. Various methods of deep temperature calculations are presented and discussed. Characteristic geotherms are proposed for major tectonic provinces of Europe and it is shown that the existing temperatures on the crust-upper mantle boundary may vary in a broad interval of 350 1,000°C. The present work is completed with a survey of the temperature dependence of electrical conductivity for selected crustal and upper mantle rocks within the interval 200 1,000°C. It is shown how the knowledge of the temperature field can be used in the evaluation of the deep electrical conductivity pattern by converting the conductivity-versustemperature data into the conductivity-versus-depth data.

DNA in the material world: electrical properties and nano-applications.

PubMed

Triberis, Georgios P; Dimakogianni, Margarita

2009-01-01

Contradictory experimental findings and theoretical interpretations have spurred intense debate over the electrical properties of the DNA double helix. In the present review article the various factors responsible for these divergences are discussed. The enlightenment of this issue could improve long range chemistry of oxidative DNA damage and repair processes, monitoring protein-DNA interactions and possible applications in nano-electronic circuit technology. The update experimental situation concerning measurements of the electrical conductivity is given. The character of the carriers responsible for the electrical conductivity measured in DNA is investigated. A theoretical model for the temperature dependence of the electrical conductivity of DNA is presented, based on microscopic models and percolation theoretical arguments. The theoretical results, excluding or including correlation effects, are applied to recent experimental findings for DNA, considering it as a one dimensional molecular wire. The results indicate that correlation effects are probably responsible for large hopping distances in DNA samples. Other theoretical conductivity models proposed for the interpretation of the responsible transport mechanism are also reviewed. Some of the most known and pioneering works on DNA's nano-applications, future developments and perspectives along with current technological limitations and patents are presented and discussed.

Electrical conductivity modeling and experimental study of densely packed SWCNT networks.

PubMed

Jack, D A; Yeh, C-S; Liang, Z; Li, S; Park, J G; Fielding, J C

2010-05-14

Single-walled carbon nanotube (SWCNT) networks have become a subject of interest due to their ability to support structural, thermal and electrical loadings, but to date their application has been hindered due, in large part, to the inability to model macroscopic responses in an industrial product with any reasonable confidence. This paper seeks to address the relationship between macroscale electrical conductivity and the nanostructure of a dense network composed of SWCNTs and presents a uniquely formulated physics-based computational model for electrical conductivity predictions. The proposed model incorporates physics-based stochastic parameters for the individual nanotubes to construct the nanostructure such as: an experimentally obtained orientation distribution function, experimentally derived length and diameter distributions, and assumed distributions of chirality and registry of individual CNTs. Case studies are presented to investigate the relationship between macroscale conductivity and nanostructured variations in the bulk stochastic length, diameter and orientation distributions. Simulation results correspond nicely with those available in the literature for case studies of conductivity versus length and conductivity versus diameter. In addition, predictions for the increasing anisotropy of the bulk conductivity as a function of the tube orientation distribution are in reasonable agreement with our experimental results. Examples are presented to demonstrate the importance of incorporating various stochastic characteristics in bulk conductivity predictions. Finally, a design consideration for industrial applications is discussed based on localized network power emission considerations and may lend insight to the design engineer to better predict network failure under high current loading applications.

Variable Anisotropic Brain Electrical Conductivities in Epileptogenic Foci

PubMed Central

Mandelkern, M.; Bui, D.; Salamon, N.; Vinters, H. V.; Mathern, G. W.

2010-01-01

Source localization models assume brain electrical conductivities are isotropic at about 0.33 S/m. These assumptions have not been confirmed ex vivo in humans. This study determined bidirectional electrical conductivities from pediatric epilepsy surgery patients. Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables. Mean (±SD) electrical conductivities were 0.10 ± 0.01 S/m, and varied by 243% from patient to patient. Perpendicular and parallel conductivities differed by 45%, and the larger values were perpendicular to the pial surface in 47% and parallel in 40% of patients. A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI. Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies. The electrical conductivity values of freshly excised human brain tissues were approximately 30% of assumed values, varied by over 200% from patient to patient, and had erratic anisotropic and isotropic shapes if the MRI showed a lesion. Understanding brain electrical conductivity and ways to non-invasively measure them are probably necessary to enhance the ability to localize EEG sources from epilepsy surgery patients. PMID:20440549

Electrical conductivity and dielectric relaxation of 2-(antipyrin-4-ylhydrazono)-2-(4-nitrophenyl)acetonitrile

NASA Astrophysics Data System (ADS)

El-Menyawy, E. M.; Zedan, I. T.; Nawar, H. H.

2014-03-01

The electrical and dielectric properties of the synthesized 2-(antipyrin-4-ylhydrazono)-2-(4-nitrophenyl)acetonitrile (AHNA) have been studied. The direct and alternating current (DC and AC) conductivities and complex dielectric constant were investigated in temperature range 303-403 K. The AC conductivity and dielectric properties of AHNA were investigated over frequency range 100 Hz-5 MHz. From DC and AC measurements, electrical conduction is found to be a thermally activated process. The frequency-dependent AC conductivity obeys Jonscher's universal power law in which the frequency exponent decreases with increasing temperature. The correlated barrier hopping (CBH) is the predominant model for describing the charge carrier transport in which the electrical parameters are evaluated. The activation energy is found to decrease with increasing frequency. The behaviors of dielectric and dielectric loss are discussed in terms of a polarization mechanism. The dielectric loss shows frequency power law from which the maximum barrier height is determined as 0.19 eV in terms of the Guintini model.

Enhanced monitoring of hazardous waste site remediation: Electrical conductivity tomography and citizen monitoring of remediation through the EPA's community advisory group program

NASA Astrophysics Data System (ADS)

Hort, Ryan D.

In situ chemical oxidation using permanganate has become a common method for degrading trichloroethene (TCE) in contaminated aquifers. Its effectiveness, however, is dependent upon contact between the oxidant and contaminant. Monitoring permanganate movement after injection is often hampered by aquifer heterogeneity and insufficient well coverage. Time lapse electrical conductivity tomography increases the spatial extent of monitoring beyond well locations. This technique can create two- or three-dimensional images of the electrical conductivity within the aquifer to monitor aquifer chemistry changes caused by permanganate injection and oxidation reactions. In-phase and quadrature electrical conductivity were measured in homogeneous aqueous and porous media samples to determine the effects of TCE and humate oxidation by permanganate on both measures of conductivity. Further effects of clean sand, 10% kaolinite (v/v), and 10% smectite (v/v) on both types of conductivity were studied as well. Finally, in-phase electrical conductivity was measured over time after injecting permanganate solution into two-dimensional tanks containing artificial groundwater with and without TCE to observe the movement of the permanganate plume and its interaction with TCE and to examine the effectiveness of time-lapse conductivity tomography for monitoring the plume's movement. In-phase electrical conductivity after oxidation reactions involving permanganate, TCE, and humate could be accurately modeled in homogeneous batch samples. Use of forward modeling of in-phase conductivity from permanganate concentrations may be useful for improving recovery of conductivity values during survey inversion, but further work is needed combining the chemistry modeling with solute transport models. Small pH-related quadrature conductivity decreases were observed after TCE oxidation, and large quadrature conductivity increases were observed as a result of sodium ion addition; however, quadrature conductivity could not be related to concentrations of permanganate or reaction products. Additionally, EPA Superfund sites participating in the Community Advisory Group (CAG) program were examined to determine how communities may have benefitted from the program. While CAG participation was correlated with slower achievement of EPA cleanup milestones, many CAGs successfully achieved five standardized social goals. CAGs that achieved these social goals varied in composition but were similar in their focus on community outreach and ability to extend their influence beyond CAG meetings.

The Standard Hydrous Olivine (SHO) conductivity model: A new tool for probing water in the upper mantle

NASA Astrophysics Data System (ADS)

Gardés, Emmanuel; Gaillard, Fabrice; Tarits, Pascal

2014-05-01

It has long been assumed that the incorporation of water in olivine has dramatic effects on the physical properties of the mantle, affecting large scale geodynamic processesand triggering most electrical conductivity anomalies in the mantle. But the conductivity models for hydrous olivine based on experimental measurements predict contrasting effects of water (e.g. Wang et al. 2006; Yoshino et al. 2009), precluding any unequivocal interpretation of electrical conductivities in the mantle. Our thesis is that the uncertainties and biases in the water contents of the olivines used for experiments were inappropriately appreciated, resulting in apparent incompatibilities when analysing the different datasets and in significant biases in the models outside of their range of calibration. Here, we analyse all published experimental work and provide a new model, SHO, that settles these major inconstancies. SHO is calibrated on the largest database of raw conductivity measurements on oriented single crystals and polycrystals of hydrous olivine, with water concentrations and temperatures spreading over 0-2220 wt. ppm and 200-1440° C. Our model provides both oriented conductivities, allowing for calculating conductivity anisotropy, and isotropic conductivity, relevant for olivine aggregates without preferential orientation. SHO isotropic conductivity (S/m) is given by 2.93 - 157000 -1.54 - 87000-1820C1/H32O σ = 10 e RT + 10 CH2Oe RT , where CH2O is the water concentration in olivine (wt. ppm), T the temperature (K) and R = 8.314 J/K/mol. In the normally hot mantle, our model predicts a moderate effect of water on the conductivity of olivine. High conductivities (~ 0.1 S/m) are obtained at great depths and elevated water concentrations only (> 350 km and > 400 wt. ppm). The strongest effects are therefore expected in the coldest regions of the mantle, like cratonic lithospheres or subduction zones, where higher incorporation of water in olivine is allowed. Wang, D., Mookherjee, M., Xu, Y., Karato, S. The effect of water on the electrical conductivity of olivine. Nature 443, 977-980 (2006) Yoshino, T., Matsuzaki, T., Shatskiy, A., Katsura, T. The effect of water on the electrical conductivity of olivine aggregates and its implications for the electrical structure of the upper mantle. Earth Planet. Sc. Lett. 288, 291-300 (2009)

High Resolution Global Electrical Conductivity Variations in the Earth's Mantle

NASA Astrophysics Data System (ADS)

Kelbert, A.; Sun, J.; Egbert, G. D.

2013-12-01

Electrical conductivity of the Earth's mantle is a valuable constraint on the water content and melting processes. In Kelbert et al. (2009), we obtained the first global inverse model of electrical conductivity in the mantle capable of providing constraints on the lateral variations in mantle water content. However, in doing so we had to compromise on the problem complexity by using the historically very primitive ionospheric and magnetospheric source assumptions. In particular, possible model contamination by the auroral current systems had greatly restricted our use of available data. We have now addressed this problem by inverting for the external sources along with the electrical conductivity variations. In this study, we still focus primarily on long period data that are dominated by quasi-zonal source fields. The improved understanding of the ionospheric sources allows us to invert the magnetic fields directly, without a correction for the source and/or the use of transfer functions. It allows us to extend the period range of available data to 1.2 days - 102 days, achieving better sensitivity to the upper mantle and transition zone structures. Finally, once the source effects in the data are accounted for, a much larger subset of observatories may be used in the electrical conductivity inversion. Here, we use full magnetic fields at 207 geomagnetic observatories, which include mid-latitude, equatorial and high latitude data. Observatory hourly means from the years 1958-2010 are employed. The improved quality and spatial distribution of the data set, as well as the high resolution modeling and inversion using degree and order 40 spherical harmonics mapped to a 2x2 degree lateral grid, all contribute to the much improved resolution of our models, representing a conceptual step forward in global electromagnetic sounding. We present a fully three-dimensional, global electrical conductivity model of the Earth's mantle as inferred from ground geomagnetic observatory data, and use additional constraints to interpret these results in terms of mantle processes and compositional variations.

Nonlinear conductivity in silicon nitride

NASA Astrophysics Data System (ADS)

Tuncer, Enis

2017-08-01

To better comprehend electrical silicon-package interaction in high voltage applications requires full characterization of the electrical properties of dielectric materials employed in wafer and package level design. Not only the packaging but wafer level dielectrics, i.e. passivation layers, would experience high electric fields generated by the voltage applied pads. In addition the interface between the passivation layer and a mold compound might develop space charge because of the mismatch in electrical properties of the materials. In this contribution electrical properties of a thin silicon nitride (Si3N4) dielectric is reported as a function of temperature and electric field. The measured values later analyzed using different temperature dependent exponential expressions and found that the Mott variable range hopping conduction model was successful to express the data. A full temperature/electric field dependency of conductivity is generated. It was found that the conduction in Si3N4 could be expressed like a field ionization or Fowler-Nordheim mechanism.

Compliance of the Stokes-Einstein model and breakdown of the Stokes-Einstein-Debye model for a urea-based supramolecular polymer of high viscosity.

PubMed

Świergiel, Jolanta; Bouteiller, Laurent; Jadżyn, Jan

2014-11-14

Impedance spectroscopy was used for the study of the static and dynamic behavior of the electrical conductivity of a hydrogen-bonded supramolecular polymer of high viscosity. The experimental data are discussed in the frame of the Stokes-Einstein and Stokes-Einstein-Debye models. It was found that the translational movement of the ions is due to normal Brownian diffusion, which was revealed by a fulfillment of Ohm's law by the electric current and a strictly exponential decay of the current after removing the electric stimulus. The dependence of the dc conductivity on the viscosity of the medium fulfills the Stokes-Einstein model quite well. An extension of the model, by including in it the conductivity relaxation time, is proposed in this paper. A breakdown of the Stokes-Einstein-Debye model is revealed by the relations of the dipolar relaxation time to the viscosity and to the dc ionic conductivity. The importance of the C=O···H-N hydrogen bonds in that breakdown is discussed.

Electrical conductivity of the Earth's mantle from the first Swarm magnetic field measurements

NASA Astrophysics Data System (ADS)

Civet, F.; Thébault, E.; Verhoeven, O.; Langlais, B.; Saturnino, D.

2015-05-01

We present a 1-D electrical conductivity profile of the Earth's mantle down to 2000 km derived from L1b Swarm satellite magnetic field measurements from November 2013 to September 2014. We first derive a model for the main magnetic field, correct the data for a lithospheric field model, and additionally select the data to reduce the contributions of the ionospheric field. We then model the primary and induced magnetospheric fields for periods between 2 and 256 days and perform a Bayesian inversion to obtain the probability density function for the electrical conductivity as function of depth. The conductivity increases by 3 orders of magnitude in the 400-900 km depth range. Assuming a pyrolitic mantle composition, this profile is interpreted in terms of temperature variations leading to a temperature gradient in the lower mantle that is close to adiabatic.

Convective Electrokinetic Instability With Conductivity Gradients

NASA Astrophysics Data System (ADS)

Chen, Chuan-Hua; Lin, Hao; Lele, Sanjiva; Santiago, Juan

2003-11-01

Electrokinetic flow instability has been experimentally identified and quantified in a glass T-junction microchannel system with a cross section of 11 um x 155 um. In this system, buffers of different conductivities were electrokinetically driven into a common mixing channel by a DC electric field. A convective instability was observed with a threshold electric field of 0.45 kV/cm for a 10:1 conductivity ratio. A physical model has been developed which consists of a modified Ohmic model formulation for electrolyte solutions and the Navier-Stokes equations with an electric body force term. The model and experiments show that bulk charge accumulation in regions of conductivity gradients is the key mechanism of such instabilities. A linear stability analysis was performed in a convective framework, and Briggs-Bers criteria were applied to determine the nature of instability. The analysis shows the instability is governed by two key parameters: the ratio of molecular diffusion to electroviscous time scale which governs the onset of instability, and the ratio of electroviscous to electroosmotic velocity which governs whether the instability is convective or absolute. The model predicted critical electric field, growth rate, wavelength, and phase speed which were comparable to experimental data.

Ultrafast traveling wave dominates the electric organ discharge of Apteronotus leptorhynchus: an inverse modelling study.

PubMed

Shifman, Aaron R; Longtin, André; Lewis, John E

2015-10-30

Identifying and understanding the current sources that give rise to bioelectric fields is a fundamental problem in the biological sciences. It is very difficult, for example, to attribute the time-varying features of an electroencephalogram recorded from the head surface to the neural activity of specific brain areas; model systems can provide important insight into such problems. Some species of fish actively generate an oscillating (c. 1000 Hz) quasi-dipole electric field to communicate and sense their environment in the dark. A specialized electric organ comprises neuron-like cells whose collective signal underlies this electric field. As a step towards understanding the detailed biophysics of signal generation in these fish, we use an anatomically-detailed finite-element modelling approach to reverse-engineer the electric organ signal over one oscillation cycle. We find that the spatiotemporal profile of current along the electric organ constitutes a travelling wave that is well-described by two spatial Fourier components varying in time. The conduction velocity of this wave is faster than action potential conduction in any known neuronal axon (>200 m/s), suggesting that the spatiotemporal features of high-frequency electric organ discharges are not constrained by the conduction velocities of spinal neuron pathways.

Ultrafast traveling wave dominates the electric organ discharge of Apteronotus leptorhynchus: an inverse modelling study

PubMed Central

Shifman, Aaron R.; Longtin, André; Lewis, John E.

2015-01-01

Identifying and understanding the current sources that give rise to bioelectric fields is a fundamental problem in the biological sciences. It is very difficult, for example, to attribute the time-varying features of an electroencephalogram recorded from the head surface to the neural activity of specific brain areas; model systems can provide important insight into such problems. Some species of fish actively generate an oscillating (c. 1000 Hz) quasi-dipole electric field to communicate and sense their environment in the dark. A specialized electric organ comprises neuron-like cells whose collective signal underlies this electric field. As a step towards understanding the detailed biophysics of signal generation in these fish, we use an anatomically-detailed finite-element modelling approach to reverse-engineer the electric organ signal over one oscillation cycle. We find that the spatiotemporal profile of current along the electric organ constitutes a travelling wave that is well-described by two spatial Fourier components varying in time. The conduction velocity of this wave is faster than action potential conduction in any known neuronal axon (>200 m/s), suggesting that the spatiotemporal features of high-frequency electric organ discharges are not constrained by the conduction velocities of spinal neuron pathways. PMID:26514932

Macroscopic Modeling of In Vivo Drug Transport in Electroporated Tissue.

PubMed

Boyd, Bradley; Becker, Sid

2016-03-01

This study develops a macroscopic model of mass transport in electroporated biological tissue in order to predict the cellular drug uptake. The change in the macroscopic mass transport coefficient is related to the increase in electrical conductivity resulting from the applied electric field. Additionally, the model considers the influences of both irreversible electroporation (IRE) and the transient resealing of the cell membrane associated with reversible electroporation. Two case studies are conducted to illustrate the applicability of this model by comparing transport associated with two electrode arrangements: side-by-side arrangement and the clamp arrangement. The results show increased drug transmission to viable cells is possible using the clamp arrangement due to the more uniform electric field.

Electrical Transport Properties of Liquid Sn-Sb Binary Alloys

NASA Astrophysics Data System (ADS)

Thakore, B. Y.; Suthar, P. H.; Khambholja, S. G.; Jani, A. R.

2010-06-01

The study of electrical transport properties viz. electrical resistivity, thermo electrical power and thermal conductivity of liquid Sn-Sb binary alloys have been made by our well recognized single parametric model potential. In the present work, screening functions due to Hartree, Taylor, Ichimaru et al.. Farid et al.. and Sarkar et al.. have been employed to incorporate the exchange and correlation effects. The liquid alloy is studied as a function of its composition at temperature 823 K according to the Faber-Ziman model. Further, thermoelectric power and thermal conductivity have been predicted. The values of electrical resistivity of binary alloys computed with Ichimaru et al. and Farid et al.. screening function are in good agreement with the experimental data.

Model of the dust-loaded ionospheres of Mars and Titan

NASA Astrophysics Data System (ADS)

Witasse, Olivier; Cardnell, Sandy; Molina-Cuberos, Gregorio; Michael, Mary; Tripathi, Sachi; Deprez, Gregoire; Montmessin, Franck; O'Brien, Keran

2016-10-01

The ionization of lower atmospheres of celestial bodies and the presence of charged species are fundamental in the understanding of atmospheric electricity phenomena, such as electric discharges, large scale electric currents and Schumann resonances. On January 14, 2005, the Huygens Probe measured the electric conductivity of Titan's atmosphere from 140 km down to the surface. Micro-ARES, the electric field and conductivity sensor on board the ExoMars 2016 Schiaparelli lander, will conduct the very first measurement and characterization of Martian atmospheric electricity. The landing is scheduled for October 19, 2016 and the measurements will be performed over 2-4 sols.The present photochemical model is developed to compute the concentration of the most abundant charged species (cluster-ions, electrons and charged aerosols) and electric conductivity in the lower atmospheres of Mars (0-70 km) and Titan (0-145 km). For both cases, the main source of ionization is galactic cosmic rays. In addition, during daytime, photoionization of aerosols due to solar UV radiation is important at Mars. Ion and electron attachment to aerosols is another major source of aerosol charging, which can vary between -50 and +200 elementary charges for Mars and -55 and -25 for Titan. The steady state concentration of charged species is computed by solving the respective balance equations, which include the source and sink terms of the photochemical reactions. Since the amount of suspended dust in the Martian atmosphere can vary considerably and it has an important effect on the atmospheric properties, several dust scenarios, in addition to the day-night variations, are considered to characterize the variability of the concentration of charged species.The agreement between with the results of the model for Titan and the Huygens data suggests an improvement with respect to previous models. This gives confidence in the results of the model for Mars, which characterize the predicted electric environment in which Micro-ARES will operate, being essential to its data analysis and interpretation.

Influence of surface conductivity on the apparent zeta potential of calcite.

PubMed

Li, Shuai; Leroy, Philippe; Heberling, Frank; Devau, Nicolas; Jougnot, Damien; Chiaberge, Christophe

2016-04-15

Zeta potential is a physicochemical parameter of particular importance in describing the surface electrical properties of charged porous media. However, the zeta potential of calcite is still poorly known because of the difficulty to interpret streaming potential experiments. The Helmholtz-Smoluchowski (HS) equation is widely used to estimate the apparent zeta potential from these experiments. However, this equation neglects the influence of surface conductivity on streaming potential. We present streaming potential and electrical conductivity measurements on a calcite powder in contact with an aqueous NaCl electrolyte. Our streaming potential model corrects the apparent zeta potential of calcite by accounting for the influence of surface conductivity and flow regime. We show that the HS equation seriously underestimates the zeta potential of calcite, particularly when the electrolyte is diluted (ionic strength ⩽ 0.01 M) because of calcite surface conductivity. The basic Stern model successfully predicted the corrected zeta potential by assuming that the zeta potential is located at the outer Helmholtz plane, i.e. without considering a stagnant diffuse layer at the calcite-water interface. The surface conductivity of calcite crystals was inferred from electrical conductivity measurements and computed using our basic Stern model. Surface conductivity was also successfully predicted by our surface complexation model. Copyright © 2016 Elsevier Inc. All rights reserved.

A quasi-static model of global atmospheric electricity. I - The lower atmosphere

NASA Technical Reports Server (NTRS)

Hays, P. B.; Roble, R. G.

1979-01-01

A quasi-steady model of global lower atmospheric electricity is presented. The model considers thunderstorms as dipole electric generators that can be randomly distributed in various regions and that are the only source of atmospheric electricity and includes the effects of orography and electrical coupling along geomagnetic field lines in the ionosphere and magnetosphere. The model is used to calculate the global distribution of electric potential and current for model conductivities and assumed spatial distributions of thunderstorms. Results indicate that large positive electric potentials are generated over thunderstorms and penetrate to ionospheric heights and into the conjugate hemisphere along magnetic field lines. The perturbation of the calculated electric potential and current distributions during solar flares and subsequent Forbush decreases is discussed, and future measurements of atmospheric electrical parameters and modifications of the model which would improve the agreement between calculations and measurements are suggested.

The relation between temperature distribution for lung RFA and electromagnetic wave frequency dependence of electrical conductivity with changing a lung's internal air volumes.

PubMed

Yamazaki, Nozomu; Watanabe, Hiroki; Lu, Xiaowei; Isobe, Yosuke; Kobayashi, Yo; Miyashita, Tomoyuki; Fujie, Masakatsu G

2013-01-01

Radio frequency ablation (RFA) for lung cancer has increasingly been used over the past few years because it is a minimally invasive treatment. As a feature of RFA for lung cancer, lung contains air during operation. Air is low thermal and electrical conductivity. Therefore, RFA for this cancer has the advantage that only the cancer is coagulated, and it is difficult for operators to control the precise formation of coagulation lesion. In order to overcome this limitation, we previously proposed a model-based robotic ablation system using finite element method. Creating an accurate thermo physical model and constructing thermal control method were a challenging problem because the thermal properties of the organ are complex. In this study, we measured electromagnetic wave frequency dependence of lung's electrical conductivity that was based on lung's internal air volumes dependence with in vitro experiment. In addition, we validated the electromagnetic wave frequency dependence of lung's electrical conductivity using temperature distribution simulator. From the results of this study, it is confirmed that the electromagnetic wave frequency dependence of lung's electrical conductivity effects on heat generation of RFA.

3D imaging of soil apparent electrical conductivity from VERIS data using a 1D spatially constrained inversion algorithm

NASA Astrophysics Data System (ADS)

Jesús Moral García, Francisco; Rebollo Castillo, Francisco Javier; Monteiro Santos, Fernando

2016-04-01

Maps of apparent electrical conductivity of the soil are commonly used in precision agriculture to indirectly characterize some important properties like salinity, water, and clay content. Traditionally, these studies are made through an empirical relationship between apparent electrical conductivity and properties measured in soil samples collected at a few locations in the experimental area and at a few selected depths. Recently, some authors have used not the apparent conductivity values but the soil bulk conductivity (in 2D or 3D) calculated from measured apparent electrical conductivity through the application of an inversion method. All the published works used data collected with electromagnetic (EM) instruments. We present a new software to invert the apparent electrical conductivity data collected with VERIS 3100 and 3150 (or the more recent version with three pairs of electrodes) using the 1D spatially constrained inversion method (1D SCI). The software allows the calculation of the distribution of the bulk electrical conductivity in the survey area till a depth of 1 m. The algorithm is applied to experimental data and correlations with clay and water content have been established using soil samples collected at some boreholes. Keywords: Digital soil mapping; inversion modelling; VERIS; soil apparent electrical conductivity.

Electrical conduction mechanism of LaNi{sub x}Me{sub 1−x}O{sub 3−δ} (Me = Fe, Mn)

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

Niwa, Eiki, E-mail: e-niwa@phys.chs.nihon-u.ac.jp; Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, Setagaya-ku, Tokyo 156-8550; Maeda, Hiroki

Graphical abstract: Compositional dependence of (a) electrical conductivity and (b) E{sub a} for hopping conduction of LaNi{sub x}Me{sub 1−x}O{sub 3} (Me = Fe, Mn). - Highlights: • Electrical conduction mechanism of LaNi{sub x}Me{sub 1−x}O{sub 3} (Me = Fe, Mn) was investigated. • Hopping conduction model could be applied for conductivity of both specimens. • The difference of E{sub a} due to that of energy level of Fe and Mn was observed. • Hole concentration estimated by iodimetry increases with increasing Ni content. - Abstract: Electrical conduction mechanism of LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} and LaNi{sub x}Mn{sub 1−x}O{sub 3+δ} expected as Sr-freemore » new cathode material for solid oxide fuel cells was analyzed. Electrical conduction behaviors of both specimens could be well fitted by small polaron hopping conduction model. The electrical conductivity of LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} increased with increasing Ni content, showing agreement with decrease of activation energy for hopping conduction. The decrease of electrical conductivity and increase of activation energy of LaNi{sub x}Mn{sub 1−x}O{sub 3+δ} were observed with increasing Ni content for 0.0 ≤ x ≤ 0.4. Further Ni substitution increased electrical conductivity and decreased activation energy for 0.4 ≤ x ≤ 0.6. It was revealed using iodometry that the difference of hole carrier density between LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} and LaNi{sub x}Mn{sub 1−x}O{sub 3+δ} was small. It was suspected that the origin of the difference of electrical conduction behavior of LaNi{sub x}Fe{sub 1−x}O{sub 3−δ} and LaNi{sub x}Mn{sub 1-x}O{sub 3+δ} was difference of energy level of e{sub g} band composed of Fe 3d or Mn 3d orbitals and their overlapping quantity with O 2p and Ni 3d band.« less

External electric field driven modification of the anomalous and spin Hall conductivities in Fe thin films on MgO(001)

NASA Astrophysics Data System (ADS)

Pradipto, Abdul-Muizz; Akiyama, Toru; Ito, Tomonori; Nakamura, Kohji

2018-01-01

The effects of applying external electric fields to the anomalous and spin Hall conductivities in Fe thin-film models with different layer thicknesses on MgO(001) are investigated by using first-principles calculations. We observe that, for the considered systems, the application of positive electric field associated with the accumulation of negative charges on the Fe side generally decreases (increases) the anomalous (spin) Hall conductivities. The mapping of the Hall conductivities within the two-dimensional Brillouin zone shows that the electric-field-induced modifications are related to the modification of the band structures of the atoms at the interface with the MgO substrate. In particular, the external electric field affects the Hall conductivities via the modifications of the dx z,dy z orbitals, in which the application of positive electric field pushes the minority-spin states of the dx z,dy z bands closer to the Fermi level. Better agreement with the anomalous Hall conductivity for bulk Fe and a more realistic scenario for the electric field modification of Hall conductivities are obtained by using the thicker layers of Fe on MgO (Fe3/MgO and Fe5/MgO).

Electric Current Transmission Through Tissues of the Vestibular Labyrinth of a Patient: Perfection of the Vestibular Implant

NASA Astrophysics Data System (ADS)

Demkin, V. P.; Shchetinin, P. P.; Melnichuk, S. V.; Kingma, H.; Van de Berg, R.; Pleshkov, M. O.; Starkov, D. N.

2018-03-01

An electric model of current transmission through tissues of the vestibular labyrinth of a patient is suggested. To stimulate directly the vestibular nerve in surgical operation, terminations of the electrodes are implanted through the bone tissue of the labyrinth into the perilymph in the vicinity of the vestibular nerve. The biological tissue of the vestibular labyrinth surrounding the electrodes and having heterogeneous composition possesses conductive and dielectric properties. Thus, when a current pulse from the vestibular implant is applied to one of the electrodes, conductive disturbance currents may arise between the electrodes and the vestibular nerves that can significantly deteriorate the direct signal quality. To study such signals and to compensate for the conductive disturbance currents, an equivalent electric circuit with actual electric impedance properties of tissues of the vestibular system is suggested, and the time parameters of the conductive disturbance current transmission are calculated. It is demonstrated that these parameters can reach large values. The suggested electric model and the results of calculations can be used for perfection of the vestibular implant.

A global time-dependent model of thunderstorm electricity. I - Mathematical properties of the physical and numerical models

NASA Technical Reports Server (NTRS)

Browning, G. L.; Tzur, I.; Roble, R. G.

1987-01-01

A time-dependent model is introduced that can be used to simulate the interaction of a thunderstorm with its global electrical environment. The model solves the continuity equation of the Maxwell current, which is assumed to be composed of the conduction, displacement, and source currents. Boundary conditions which can be used in conjunction with the continuity equation to form a well-posed initial-boundary value problem are determined. Properties of various components of solutions of the initial-boundary value problem are analytically determined. The results indicate that the problem has two time scales, one determined by the background electrical conductivity and the other by the time variation of the source function. A numerical method for obtaining quantitative results is introduced, and its properties are studied. Some simulation results on the evolution of the displacement and conduction currents during the electrification of a storm are presented.

Conductance Effects on Inner Magnetospheric Plasma Morphology: Model Comparisons with IMAGE EUV, MENA, and HENA Data

NASA Technical Reports Server (NTRS)

Liemohn, M.; Ridley, A. J.; Kozyra, J. U.; Gallagher, D. L.; Brandt, P. C.; Henderson, M. G.; Denton, M. H.; Jahn, J. M.; Roelof, E. C.; DeMajistre, R. M.

2004-01-01

Modeling results of the inner magnetosphere showing the influence of the ionospheric conductance on the inner magnetospheric electric fields during the April 17, 2002 magnetic storm are presented. Kinetic plasma transport code results are analyzed in combination with observations of the inner magnetospheric plasma populations, in particular those from the IMAGE satellite. Qualitative and quantitative comparisons are made with the observations from EW, MENA, and HENA, covering the entire energy range simulated by the model (0 to 300 keV). The electric field description, and in particular the ionospheric conductance, is the only variable between the simulations. Results from the data-model comparisons are discussed, detailing the strengths and weaknesses of each conductance choice for each energy channel.

Analytical scanning evanescent microwave microscope and control stage

DOEpatents

Xiang, Xiao-Dong; Gao, Chen; Duewer, Fred; Yang, Hai Tao; Lu, Yalin

2013-01-22

A scanning evanescent microwave microscope (SEMM) that uses near-field evanescent electromagnetic waves to probe sample properties is disclosed. The SEMM is capable of high resolution imaging and quantitative measurements of the electrical properties of the sample. The SEMM has the ability to map dielectric constant, loss tangent, conductivity, electrical impedance, and other electrical parameters of materials. Such properties are then used to provide distance control over a wide range, from to microns to nanometers, over dielectric and conductive samples for a scanned evanescent microwave probe, which enable quantitative non-contact and submicron spatial resolution topographic and electrical impedance profiling of dielectric, nonlinear dielectric and conductive materials. The invention also allows quantitative estimation of microwave impedance using signals obtained by the scanned evanescent microwave probe and quasistatic approximation modeling. The SEMM can be used to measure electrical properties of both dielectric and electrically conducting materials.

Analytical scanning evanescent microwave microscope and control stage

DOEpatents

Xiang, Xiao-Dong; Gao, Chen; Duewer, Fred; Yang, Hai Tao; Lu, Yalin

2009-06-23

A scanning evanescent microwave microscope (SEMM) that uses near-field evanescent electromagnetic waves to probe sample properties is disclosed. The SEMM is capable of high resolution imaging and quantitative measurements of the electrical properties of the sample. The SEMM has the ability to map dielectric constant, loss tangent, conductivity, electrical impedance, and other electrical parameters of materials. Such properties are then used to provide distance control over a wide range, from to microns to nanometers, over dielectric and conductive samples for a scanned evanescent microwave probe, which enable quantitative non-contact and submicron spatial resolution topographic and electrical impedance profiling of dielectric, nonlinear dielectric and conductive materials. The invention also allows quantitative estimation of microwave impedance using signals obtained by the scanned evanescent microwave probe and quasistatic approximation modeling. The SEMM can be used to measure electrical properties of both dielectric and electrically conducting materials.

Effect of iron content on the electrical conductivity of perovskite and magnesiowuestite assemblages at lower mantle conditions

NASA Technical Reports Server (NTRS)

Li, Xiaoyuan; Jeanloz, Raymond

1991-01-01

The electrical conductivity of (Mg/0.76/Fe/0.24/)SiO3 perovskite and of an assemblage of (Mg/0.89/Fe/0.11/)SiO3 perovskite + (Mg/0.70/Fe/0.30/)O magnesiowiestite was measured at pressures of 45-80 GPa and temperatures from 295 to 3600 K. The apparent activation energy for electrical conduction is 0.24 (+ or - 0.10) eV for the perovskite and 0.20 (+ or - 0.08) eV for the perovskite + magnesiowuestite assemblage. Comparing present results with those derived previously for Fe-poor samples, it is found that the electrical conductivities of both the silicate perovskite and the perovskite + magnesiowuestite assemblage depend strongly on iron content. Thus, the electrical conductivity distribution inside the earth could provide an important constraint in modeling the composition of the lower mantle.

The effect of longitudinal conductance variations on the ionospheric prompt penetration electric fields

NASA Astrophysics Data System (ADS)

Sazykin, S.; Wolf, R.; Spiro, R.; Fejer, B.

Ionospheric prompt penetration electric fields of magnetospheric origin, together with the atmospheric disturbance dynamo, represent the most important parameters controlling the storm-time dynamics of the low and mid-latitude ionosphere. These prompt penetration fields result from the disruption of region-2 field-aligned shielding currents during geomagnetically disturbed conditions. Penetration electric fields con- trol, to a large extent, the generation and development of equatorial spread-F plasma instabilities as well as other dynamic space weather phenomena in the ionosphere equatorward of the auroral zone. While modeling studies typically agree with average patterns of prompt penetration fields, experimental results suggest that longitudinal variations of the ionospheric con- ductivities play a non-negligible role in controlling spread-F phenomena, an effect that has not previously been modeled. We present first results of modeling prompt pene- tration electric fields using a version of the Rice Convection Model (RCM) that allows for longitudinal variations in the ionospheric conductance tensor. The RCM is a first- principles numerical ionosphere-magnetosphere coupling model that solves for the electric fields, field-aligned currents, and particle distributions in the ionosphere and inner/middle magnetosphere. We compare these new theoretical results with electric field observations.

Some notes on hydrogen-related point defects and their role in the isotope exchange and electrical conductivity in olivine

NASA Astrophysics Data System (ADS)

Karato, Shun-ichiro

2015-11-01

Nominally anhydrous minerals such as olivine dissolve hydrogen in a variety of forms including free (or interstitial) proton (Hrad) and two protons trapped at the M-site ((2 H)M×). The strength of chemical bonding between protons and the surrounding atoms are different among different species, and consequently protons belonging to different species likely have different mobility (diffusion coefficients). I discuss the role of diffusion of protons in different species in the isotope exchange and hydrogen-assisted electrical conductivity adding a few notes to the previous work by Karato (2013) including a new way to test the model. I conclude that in the case of isotope exchange, the interaction among these species is strong because diffusion is heterogeneous, whereas there is no strong interaction among different species in electrical conduction where diffusion is homogeneous (in an infinite crystal). Consequently, the slowest diffusing species controls the rate of isotope exchange, whereas the fastest diffusing species controls electrical conductivity leading to a different temperature dependence of activation energy and anisotropy. This model explains the differences in the activation energy and anisotropy between isotope diffusion and electrical conductivity, and predicts that the mechanism of electrical conductivity changes with temperature providing an explanation for most of the discrepancies among different experimental observations at different temperatures except for those by Poe et al. (2010) who reported anomalously high water content dependence and highly anisotropic activation energy. When the results obtained at high temperatures are used, most of the geophysically observed high and highly anisotropic electrical conductivity in the asthenosphere can be explained without invoking partial melting.

[Modeling and analysis of volume conduction based on field-circuit coupling].

PubMed

Tang, Zhide; Liu, Hailong; Xie, Xiaohui; Chen, Xiufa; Hou, Deming

2012-08-01

Numerical simulations of volume conduction can be used to analyze the process of energy transfer and explore the effects of some physical factors on energy transfer efficiency. We analyzed the 3D quasi-static electric field by the finite element method, and developed A 3D coupled field-circuit model of volume conduction basing on the coupling between the circuit and the electric field. The model includes a circuit simulation of the volume conduction to provide direct theoretical guidance for energy transfer optimization design. A field-circuit coupling model with circular cylinder electrodes was established on the platform of the software FEM3.5. Based on this, the effects of electrode cross section area, electrode distance and circuit parameters on the performance of volume conduction system were obtained, which provided a basis for optimized design of energy transfer efficiency.

Note on heat conduction in liquid metals. A comparison of laminar and turbulent flow effects

NASA Astrophysics Data System (ADS)

Talmage, G.

1994-05-01

The difference between heat transfer in liquid metals with electric currents and magnetic fields on the one hand and heat transfer in electrically insulating fluids and in conducting solids on the other is pointed out. Laminar and turbulent flow effects in liquid metal sliding electric contacts for homopolar machines are considered. Large temperature gradients can develop within a small region of liquid metal. A model of a liquid-metal sliding electrical contact is developed and analyzed.

Evaluation of electrical conductivity and equations of state of non-ideal plasma through microsecond timescale underwater electrical wire explosion

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

Sheftman, D.; Krasik, Ya. E.

2011-09-15

Experimental and simulation results of underwater electrical Cu, Al, and W wire explosions in the microsecond timescale are presented. It was shown that the electrical conductivity results for Cu and Al agree well with modified Lee-More and quantum molecular dynamic models for temperatures above 10 kK. The equation of state (EOS) values based on SESAME tables for Cu and Al were slightly modified for intermediate temperatures in order to obtain fitting between experimental and simulated exploding wire radial expansion. Also, it was shown that the electrical conductivity results and the EOS evaluation differ significantly from the results obtained in nanosecondmore » timescale experiments. Finally, it was found that underwater electrical W wire explosion is characterized by the appearance of non-uniformities along the z-axis of the wire. This phenomena adds uncertainty to the possibility of applying this type of experiments for evaluation of the electrical conductivity and EOS of W.« less

Influence of uncertainties of the empirical models for inferring the E-region electric fields at the dip equator

NASA Astrophysics Data System (ADS)

Moro, Juliano; Denardini, Clezio Marcos; Resende, Laysa Cristina Araújo; Chen, Sony Su; Schuch, Nelson Jorge

2016-06-01

Daytime E-region electric fields play a crucial role in the ionospheric dynamics at the geomagnetic dip latitudes. Due to their importance, there is an interest in accurately measuring and modeling the electric fields for both climatological and near real-time studies. In this work, we present the daytime vertical ( Ez) and eastward ( Ey) electric fields for a reference quiet day (February 7, 2001) at the São Luís Space Observatory, Brazil (SLZ, 2.31°S, 44.16°W). The component Ez is inferred from Doppler shifts of type II echoes (gradient drift instability) and the anisotropic factor, which is computed from ion and electron gyro frequencies as well as ion and electron collision frequencies with neutral molecules. The component Ey depends on the ratio of Hall and Pedersen conductivities and Ez. A magnetic field-line-integrated conductivity model is used to obtain the anisotropic factor for calculating Ez and the ionospheric conductivities for calculating Ey. This model uses the NRLMSISE-00, IRI-2007, and IGRF-11 empirical models as input parameters for neutral atmosphere, ionosphere, and geomagnetic field, respectively. Consequently, it is worth determining the uncertainties (or errors) in Ey and Ez associated with these empirical model outputs in order to precisely define the confidence limit for the estimated electric field components. For this purpose, errors of ±10 % were artificially introduced in the magnitude of each empirical model output before estimating Ey and Ez. The corresponding uncertainties in the ionospheric conductivity and electric field are evaluated considering the individual and cumulative contribution of the artificial errors. The results show that the neutral densities and temperature may be responsible for the largest changes in Ey and Ez, followed by changes in the geomagnetic field intensity and electron and ions compositions.

Fibroblast proliferation alters cardiac excitation conduction and contraction: a computational study.

PubMed

Zhan, He-qing; Xia, Ling; Shou, Guo-fa; Zang, Yun-liang; Liu, Feng; Crozier, Stuart

2014-03-01

In this study, the effects of cardiac fibroblast proliferation on cardiac electric excitation conduction and mechanical contraction were investigated using a proposed integrated myocardial-fibroblastic electromechanical model. At the cellular level, models of the human ventricular myocyte and fibroblast were modified to incorporate a model of cardiac mechanical contraction and cooperativity mechanisms. Cellular electromechanical coupling was realized with a calcium buffer. At the tissue level, electrical excitation conduction was coupled to an elastic mechanics model in which the finite difference method (FDM) was used to solve electrical excitation equations, and the finite element method (FEM) was used to solve mechanics equations. The electromechanical properties of the proposed integrated model were investigated in one or two dimensions under normal and ischemic pathological conditions. Fibroblast proliferation slowed wave propagation, induced a conduction block, decreased strains in the fibroblast proliferous tissue, and increased dispersions in depolarization, repolarization, and action potential duration (APD). It also distorted the wave-front, leading to the initiation and maintenance of re-entry, and resulted in a sustained contraction in the proliferous areas. This study demonstrated the important role that fibroblast proliferation plays in modulating cardiac electromechanical behaviour and which should be considered in planning future heart-modeling studies.

Fibroblast proliferation alters cardiac excitation conduction and contraction: a computational study*

PubMed Central

Zhan, He-qing; Xia, Ling; Shou, Guo-fa; Zang, Yun-liang; Liu, Feng; Crozier, Stuart

2014-01-01

In this study, the effects of cardiac fibroblast proliferation on cardiac electric excitation conduction and mechanical contraction were investigated using a proposed integrated myocardial-fibroblastic electromechanical model. At the cellular level, models of the human ventricular myocyte and fibroblast were modified to incorporate a model of cardiac mechanical contraction and cooperativity mechanisms. Cellular electromechanical coupling was realized with a calcium buffer. At the tissue level, electrical excitation conduction was coupled to an elastic mechanics model in which the finite difference method (FDM) was used to solve electrical excitation equations, and the finite element method (FEM) was used to solve mechanics equations. The electromechanical properties of the proposed integrated model were investigated in one or two dimensions under normal and ischemic pathological conditions. Fibroblast proliferation slowed wave propagation, induced a conduction block, decreased strains in the fibroblast proliferous tissue, and increased dispersions in depolarization, repolarization, and action potential duration (APD). It also distorted the wave-front, leading to the initiation and maintenance of re-entry, and resulted in a sustained contraction in the proliferous areas. This study demonstrated the important role that fibroblast proliferation plays in modulating cardiac electromechanical behaviour and which should be considered in planning future heart-modeling studies. PMID:24599687

Gamma-Ray Light Curves from Pulsar Magnetospheres with Finite Conductivity

NASA Technical Reports Server (NTRS)

Harding, A. K.; Kalapotharakos, C.; Kazanas, D.; Contopoulos, I.

2012-01-01

The Fermi Large Area Telescope has provided an unprecedented database for pulsar emission studies that includes gamma-ray light curves for over 100 pulsars. Modeling these light curves can reveal and constrain the geometry of the particle accelerator, as well as the pulsar magnetic field structure. We have constructed 3D magnetosphere models with finite conductivity, that bridge the extreme vacuum and force-free solutions used in previous light curves modeling. We are investigating the shapes of pulsar gamma-ray light curves using these dissipative solutions with two different approaches: (l) assuming geometric emission patterns of the slot gap and outer gap, and (2) using the parallel electric field provided by the resistive models to compute the trajectories and . emission of the radiating particles. The light curves using geometric emission patterns show a systematic increase in gamma-ray peak phase with increasing conductivity, introducing a new diagnostic of these solutions. The light curves using the model electric fields are very sensitive to the conductivity but do not resemble the observed Fermi light curves, suggesting that some screening of the parallel electric field, by pair cascades not included in the models, is necessary

THE RELATIONSHIP OF TOTAL DISSOLVED SOLIDS MEASUREMENTS TO BULK ELECTRICAL CONDUCTIVITY IN AN AQUIFER CONTAMINATED WITH HYDROCARBON

EPA Science Inventory

A recent conceptual model links high bulk electrical conductivities at hydrocarbon impacted sites to higher total dissolved solids (TDS) resulting from enhanced mineral weathering due to acids produced during biodegradation. In this study, we investigated the vertical distributio...

Nonlinear dynamics in cardiac conduction

NASA Technical Reports Server (NTRS)

Kaplan, D. T.; Smith, J. M.; Saxberg, B. E.; Cohen, R. J.

1988-01-01

Electrical conduction in the heart shows many phenomena familiar from nonlinear dynamics. Among these phenomena are multiple basins of attraction, phase locking, and perhaps period-doubling bifurcations and chaos. We describe a simple cellular-automation model of electrical conduction which simulates normal conduction patterns in the heart as well as a wide range of disturbances of heart rhythm. In addition, we review the application of percolation theory to the analysis of the development of complex, self-sustaining conduction patterns.

Soil salinisation and irrigation management of date palms in a Saharan environment.

PubMed

Haj-Amor, Zied; Ibrahimi, Mohamed-Khaled; Feki, Nissma; Lhomme, Jean-Paul; Bouri, Salem

2016-08-01

The continuance of agricultural production in regions of the world with chronic water shortages depends upon understanding how soil salinity is impacted by irrigation practises such as water salinity, irrigation frequency and amount of irrigation. A two-year field study was conducted in a Saharan oasis of Tunisia (Lazala Oasis) to determine how the soil electrical conductivity was affected by irrigation of date palms with high saline water. The study area lacked a saline shallow water table. Field results indicate that, under current irrigation practises, soil electrical conductivity can build up to levels which exceed the salt tolerance of date palm trees. The effects of irrigation practises on the soil electrical conductivity were also evaluated using model simulations (HYDRUS-1D) of various irrigation regimes with different frequencies, different amounts of added water and different water salinities. The comparison between the simulated and observed results demonstrated that the model gave an acceptable estimation of water and salt dynamics in the soil profile, as indicated by the small values of root mean square error (RMSE) and the high values of the Nash-Sutcliffe model efficiency coefficient (NSE). The simulations demonstrated that, under field conditions without saline shallow groundwater, saline irrigation water can be used to maintain soil electrical conductivity and soil water content at safe levels (soil electrical conductivity <4 dS m(-1) and soil water content >0.04 cm(3) cm(-3)) if frequent irrigations with small amounts of water (90 % of the evapotranspiration requirements) were applied throughout the year.

Subsonic Ultra Green Aircraft Research: Phase 2. Volume 2; Hybrid Electric Design Exploration

NASA Technical Reports Server (NTRS)

Bradley, Marty K.; Droney, Christopher K.

2015-01-01

This report summarizes the hybrid electric concept design, analysis, and modeling work accomplished by the Boeing Subsonic Ultra Green Aircraft Research (SUGAR) team, consisting of Boeing Research and Technology, Boeing Commercial Airplanes, General Electric, and Georgia Tech.Performance and sizing tasks were conducted for hybrid electric versions of a conventional tube-and-wing aircraft and a hybrid wing body. The high wing Truss Braced Wing (TBW) SUGAR Volt was updated based on results from the TBW work (documented separately) and new engine performance models. Energy cost and acoustic analyses were conducted and technology roadmaps were updated for hybrid electric and battery technology. NOx emissions were calculated for landing and takeoff (LTO) and cruise. NPSS models were developed for hybrid electric components and tested using an integrated analysis of superconducting and non-superconducting hybrid electric engines. The hybrid electric SUGAR Volt was shown to produce significant emissions and fuel burn reductions beyond those achieved by the conventionally powered SUGAR High and was able to meet the NASA goals for fuel burn. Total energy utilization was not decreased but reduced energy cost can be achieved for some scenarios. The team was not able to identify a technology development path to meet NASA's noise goals

Electrical resistivity of CuAlMo thin films grown at room temperature by dc magnetron sputtering

NASA Astrophysics Data System (ADS)

Birkett, Martin; Penlington, Roger

2016-07-01

We report on the thickness dependence of electrical resistivity of CuAlMo films grown by dc magnetron sputtering on glass substrates at room temperature. The electrical resistance of the films was monitored in situ during their growth in the thickness range 10-1000 nm. By theoretically modelling the evolution of resistivity during growth we were able to gain an insight into the dominant electrical conduction mechanisms with increasing film thickness. For thicknesses in the range 10-25 nm the electrical resistivity is found to be a function of the film surface roughness and is well described by Namba’s model. For thicknesses of 25-40 nm the experimental data was most accurately fitted using the Mayadas and Shatkes model which accounts for grain boundary scattering of the conduction electrons. Beyond 40 nm, the thickness of the film was found to be the controlling factor and the Fuchs-Sonheimer (FS) model was used to fit the experimental data, with diffuse scattering of the conduction electrons at the two film surfaces. By combining the Fuchs and Namba (FN) models a suitable correlation between theoretical and experimental resistivity can be achieved across the full CuAlMo film thickness range of 10-1000 nm. The irreversibility of resistance for films of thickness >200 nm, which demonstrated bulk conductivity, was measured to be less than 0.03% following subjection to temperature cycles of -55 and +125 °C and the temperature co-efficient of resistance was less than ±15 ppm °C-1.

Relationship between anisotropies of permeability, electrical conductivity, and dielectric permittivity, with application to the Ellenburger dolomite reservoir analog

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.

The Measurement of Electrical Conductivity in Detonating Condensed Explosives

DTIC Science & Technology

1993-03-01

in the light of our existing understanding. DETONATION CONDUCTION MODELS Various models of conduction have been considered during the course of these...reduction, shock induced conduction in the reaction products, and conduction in coagulated carbon behind the reaction zone. The first model , due to...results below show. The second model was proposed by Griem. 3 For relative simplicity, he assumed that the reaction zone could be represented by a

Exploring electrical resistance: a novel kinesthetic model helps to resolve some misconceptions

NASA Astrophysics Data System (ADS)

Cottle, Dan; Marshall, Rick

2016-09-01

A simple ‘hands on’ physical model is described which displays analogous behaviour to some aspects of the free electron theory of metals. Using it students can get a real feel for what is going on inside a metallic conductor. Ohms Law, the temperature dependence of resistivity, the dependence of resistance on geometry, how the conduction electrons respond to a potential difference and the concepts of mean free path and drift speed of the conduction electrons can all be explored. Some quantitative results obtained by using the model are compared with the predictions of Drude’s free electron theory of electrical conduction.

Probability of conductive bond formation in a percolating network of nanowires with fusible tips

NASA Astrophysics Data System (ADS)

Rykaczewski, Konrad; Wang, Robert Y.

2018-03-01

Meeting the heat dissipation demands of microelectronic devices requires development of polymeric composites with high thermal conductivity. This property is drastically improved by percolation networks of metallic filler particles that have their particle-to-particle contact resistances reduced through thermal or electromagnetic fusing. However, composites with fused metallic fillers are electrically conductive, which prevents their application within the chip-board and the inter-chip gaps. Here, we propose that electrically insulating composites for these purposes can be achieved by the application of fusible metallic coatings to the tips of nanowires with thermally conductive but electrically insulating cores. We derive analytical models that relate the ratio of the coated and total nanowire lengths to the fraction of fused, and thus conductive, bonds within percolating networks of these structures. We consider two types of materials for these fusible coatings. First, we consider silver-like coatings, which form only conductive bonds when contacting the silver-like coating of another nanowire. Second, we consider liquid metal-like coatings, which form conductive bonds regardless of whether they contact a coated or an uncoated segment of another nanowire. These models were validated using Monte Carlo simulations, which also revealed that electrical short-circuiting is highly unlikely until most of the wire is coated. Furthermore, we demonstrate that switching the tip coating from silver- to liquid metal-like materials can double the fraction of conductive bonds. Consequently, this work provides motivation to develop scalable methods for fabrication of the hybrid liquid-coated nanowires, whose dispersion in a polymer matrix is predicted to yield highly thermally conductive but electrically insulating composites.

Geophysical monitoring of solute transport in dual-domain environments through laboratory experiments, field-scale solute tracer tests, and numerical simulation

NASA Astrophysics Data System (ADS)

Swanson, Ryan David

The advection-dispersion equation (ADE) fails to describe non-Fickian solute transport breakthrough curves (BTCs) in saturated porous media in both laboratory and field experiments, necessitating the use of other models. The dual-domain mass transfer (DDMT) model partitions the total porosity into mobile and less-mobile domains with an exchange of mass between the two domains, and this model can reproduce better fits to BTCs in many systems than ADE-based models. However, direct experimental estimation of DDMT model parameters remains elusive and model parameters are often calculated a posteriori by an optimization procedure. Here, we investigate the use of geophysical tools (direct-current resistivity, nuclear magnetic resonance, and complex conductivity) to estimate these model parameters directly. We use two different samples of the zeolite clinoptilolite, a material shown to demonstrate solute mass transfer due to a significant internal porosity, and provide the first evidence that direct-current electrical methods can track solute movement into and out of a less-mobile pore space in controlled laboratory experiments. We quantify the effects of assuming single-rate DDMT for multirate mass transfer systems. We analyze pore structures using material characterization methods (mercury porosimetry, scanning electron microscopy, and X-ray computer tomography), and compare these observations to geophysical measurements. Nuclear magnetic resonance in conjunction with direct-current resistivity measurements can constrain mobile and less-mobile porosities, but complex conductivity may have little value in relation to mass transfer despite the hypothesis that mass transfer and complex conductivity lengths scales are related. Finally, we conduct a geoelectrical monitored tracer test at the Macrodispersion Experiment (MADE) site in Columbus, MS. We relate hydraulic and electrical conductivity measurements to generate a 3D hydraulic conductivity field, and compare to hydraulic conductivity fields estimated through ordinary kriging and sequential Gaussian simulation. Time-lapse electrical measurements are used to verify or dismiss aspects of breakthrough curves for different hydraulic conductivity fields. Our results quantify the potential for geophysical measurements to infer on single-rate DDMT parameters, show site-specific relations between hydraulic and electrical conductivity, and track solute exchange into and out of less-mobile domains.

In vivo electric conductivity of cervical cancer patients based on B₁⁺ maps at 3T MRI.

PubMed

Balidemaj, E; de Boer, P; van Lier, A L H M W; Remis, R F; Stalpers, L J A; Westerveld, G H; Nederveen, A J; van den Berg, C A T; Crezee, J

2016-02-21

The in vivo electric conductivity (σ) values of tissue are essential for accurate electromagnetic simulations and specific absorption rate (SAR) assessment for applications such as thermal dose computations in hyperthermia. Currently used σ-values are mostly based on ex vivo measurements. In this study the conductivity of human muscle, bladder content and cervical tumors is acquired non-invasively in vivo using MRI. The conductivity of 20 cervical cancer patients was measured with the MR-based electric properties tomography method on a standard 3T MRI system. The average in vivo σ-value of muscle is 14% higher than currently used in human simulation models. The σ-value of bladder content is an order of magnitude higher than the value for bladder wall tissue that is used for the complete bladder in many models. Our findings are confirmed by various in vivo animal studies from the literature. In cervical tumors, the observed average conductivity was 13% higher than the literature value reported for cervical tissue. Considerable deviations were found for the electrical conductivity observed in this study and the commonly used values for SAR assessment, emphasizing the importance of acquiring in vivo conductivity for more accurate SAR assessment in various applications.

Ring discharge on the backsurface of a composite skin with ohmic anisotropy in response to frontal high current injection

NASA Astrophysics Data System (ADS)

Lee, T. S.; Robb, J. D.

The ring discharge hazard to a carbon-reinforced-composites fuel tank skin under lightning strike conditions is investigated. A model of anisotropy in electric conductivity is adopted whereby longitudinal conductivity and transverse conductivity are considered separately. It is concluded that the current flow pattern contains a stagnation-dominated near-field region and a geometry-dominated far-field decaying region. While this pattern is unaltered by anisotropy in conductivity, the accompanying nonliner electrical field pattern is greatly distorted. It is noted that conclusions applicable to the ignition hazard which were derived from the model of a uniform scalar conductivity for the skin still remain intact.

Electrode Models for Electric Current Computed Tomography

PubMed Central

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

2016-01-01

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

Electrode models for electric current computed tomography.

PubMed

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

1989-09-01

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

A modeling study of the time-averaged electric currents in the vicinity of isolated thunderstorms

NASA Technical Reports Server (NTRS)

Driscoll, Kevin T.; Blakeslee, Richard J.; Baginski, Michael E.

1992-01-01

A thorough examination of the results of a time-dependent computer model of a dipole thunderstorm revealed that there are numerous similarities between the time-averaged electrical properties and the steady-state properties of an active thunderstorm. Thus, the electrical behavior of the atmosphere in the vicinity of a thunderstorm can be determined with a formulation similar to what was first described by Holzer and Saxon (1952). From the Maxwell continuity equation of electric current, a simple analytical equation was derived that expresses a thunderstorm's average current contribution to the global electric circuit in terms of the generator current within the thundercloud, the intracloud lightning current, the cloud-to-ground lightning current, the altitudes of the charge centers, and the conductivity profile of the atmosphere. This equation was found to be nearly as accurate as the more computationally expensive numerical model, even when it is applied to a thunderstorm with a reduced conductivity thundercloud, a time-varying generator current, a varying flash rate, and a changing lightning mix.

Bioelectrical Impedance and The Frequency Dependent Current Conduction Through Biological Tissues: A Short Review

NASA Astrophysics Data System (ADS)

Kanti Bera, Tushar

2018-03-01

Biological tissues are developed with biological cells which exhibit complex electrical impedance called electrical bioimpedance. Under an alternating electrical excitation the bioimpedance varies with the tissue anatomy, composition and the signal frequency. The current penetration and conduction paths vary with frequency of the applied signal. Bioimpedance spectroscopy is used to study the frequency response of the electrical impedance of biological materials noninvasively. In bioimpedance spectroscopy, a low amplitude electrical signal is injected to the tissue sample or body parts to characterization the sample in terms of its bioimpedance. The electrical current conduction phenomena, which is highly influenced by the tissue impedance and the signal frequency, is an important phenomena which should be studied to understand the bioimpedance techniques like bioelectrical impedance analysis (BIA), EIS, or else. In this paper the origin of bioelectrical impedance and current conduction phenomena has been reviewed to present a brief summary of bioelectrical impedance and the frequency dependent current conduction through biological tissues. Simulation studies are conducted with alternation current injection through a two dimensional model of biological tissues containing finite number of biological cells suspended in extracellular fluid. The paper demonstrates the simulation of alternating current conduction through biological tissues conducted by COMSOL Multiphysics. Simulation studies also show the frequency response of the tissue impedance for different tissue compositions.

Leakage conduction behavior in electron-beam-cured nanoporous silicate films

NASA Astrophysics Data System (ADS)

Liu, Po-Tsun; Tsai, T. M.; Chang, T. C.

2005-05-01

This letter explores the application of electron-beam curing on nanoporous silicate films. The electrical conduction mechanism for the nanoporous silicate film cured by electron-beam radiation has been studied with metal-insulator-semiconductor capacitors. Electrical analyses over a varying temperature range from room temperature to 150°C provide evidence for space-charge-limited conduction in the electron-beam-cured thin film, while Schottky-emission-type leaky behavior is seen in the counterpart typically cured by a thermal furnace. A physical model consistent with electrical analyses is also proposed to deduce the origin of conduction behavior in the nanoporous silicate thin film.

Application of electrical and electromagnetic depth sounding in highly conductive sediments: The concept of vertical electrical anisotropy

NASA Astrophysics Data System (ADS)

Köhler, A.; Bahr, K.

2010-12-01

“Nördlinger Ries” is a meteorite crater in the Bavarian ‘Alb’ of Germany that was formed 15 million years ago, and subsequently filled with salty water. Evaporation resulted in an approximately 300 meter thick layer of young, highly conductive sediments. Audio-frequency Magnetotelluric (AMT) and geoelectric depth sounding (VES) techniques were used to analyze the electrical properties of these sediments. The apparent resistivities measured by the two methods are different, which can be explained by vertical electrical anisotropy (horizontal layering). Applying a joint forward modelling technique with resistivity variations found by a Monte Carlo method results in a best fit model containing a large number of layers, while separate inversions of the two data sets yield 3-layer models. Comparisons of the coefficient of anisotropy with drilling core samples demonstrate the reliability of the results. One difficulty of the AMT method is the low signal-to-noise ratio, because of the source’s deadband. Some suggestions for an “intelligent” processing are presented. Kerch (this session) is employing the result of the integrated conductivity as an input for 3D modelling of collected MT data.

The Charging of Composites in the Space Environment

NASA Technical Reports Server (NTRS)

Czepiela, Steven A.

1997-01-01

Deep dielectric charging and subsequent electrostatic discharge in composite materials used on spacecraft have become greater concerns since composite materials are being used more extensively as main structural components. Deep dielectric charging occurs when high energy particles penetrate and deposit themselves in the insulating material of spacecraft components. These deposited particles induce an electric field in the material, which causes the particles to move and thus changes the electric field. The electric field continues to change until a steady state is reached between the incoming particles from the space environment and the particles moving away due to the electric field. An electrostatic discharge occurs when the electric field is greater than the dielectric strength of the composite material. The goal of the current investigation is to investigate deep dielectric charging in composite materials and ascertain what modifications have to be made to the composite properties to alleviate any breakdown issues. A 1-D model was created. The space environment, which is calculated using the Environmental Workbench software, the composite material properties, and the electric field and voltage boundary conditions are input into the model. The output from the model is the charge density, electric field, and voltage distributions as functions of the depth into the material and time. Analysis using the model show that there should be no deep dielectric charging problem with conductive composites such as carbon fiber/epoxy. With insulating materials such as glass fiber/epoxy, Kevlar, and polymers, there is also no concern of deep dielectric charging problems with average day-to-day particle fluxes. However, problems can arise during geomagnetic substorms and solar particle events where particle flux levels increase by several orders of magnitude, and thus increase the electric field in the material by several orders of magnitude. Therefore, the second part of this investigation was an experimental attempt to measure the continuum electrical properties of a carbon fiber/epoxy composite, and to create a composite with tailorable conductivity without affecting its mechanical properties. The measurement of the conductivity and dielectric strength of carbon fiber/epoxy composites showed that these properties are surface layer dominated and difficult to measure. In the second experimental task, the conductivity of a glass fiber/epoxy composite was increased by 3 orders of magnitude, dielectric constant was increased approximately by a factor of 16, with minimal change to the mechanical properties, by adding conductive carbon black to the epoxy.

Dielectric and ac ionic conductivity investigation of Li2SrP2O7

NASA Astrophysics Data System (ADS)

Ajili, O.; Louati, B.; Guidara, K.

2018-07-01

The pyrophosphate Li2SrP2O7 compound has been synthesized by the classic ceramic method and characterized by X-ray diffraction, IR, Raman and electrical impedance spectroscopy. Detailed electrical properties of the compound were analyzed as a function of frequency (209 Hz-1 MHz) and temperature (519-628) K. Impedance analysis exhibits the grain and grain boundary contribution to the electrical response of the sample. The temperature dependence of these contribution obey the Arrhenius law with activation energies (1.03 ± 0.05) and (1.25 ± 0.05) eV, respectively. The ac conductivity for grain contribution was interpreted using the universal Jonscher's power law. The temperature dependence of frequency exponent s was investigated to understand the conduction mechanism. The correlated barrier hopping model was found to be the best model describing the conduction mechanism.

Dielectric and ac ionic conductivity investigation of Li2SrP2O7

NASA Astrophysics Data System (ADS)

Ajili, O.; Louati, B.; Guidara, K.

2018-02-01

The pyrophosphate Li2SrP2O7 compound has been synthesized by the classic ceramic method and characterized by X-ray diffraction, IR, Raman and electrical impedance spectroscopy. Detailed electrical properties of the compound were analyzed as a function of frequency (209 Hz-1 MHz) and temperature (519-628) K. Impedance analysis exhibits the grain and grain boundary contribution to the electrical response of the sample. The temperature dependence of these contribution obey the Arrhenius law with activation energies (1.03 ± 0.05) and (1.25 ± 0.05) eV, respectively. The ac conductivity for grain contribution was interpreted using the universal Jonscher's power law. The temperature dependence of frequency exponent s was investigated to understand the conduction mechanism. The correlated barrier hopping model was found to be the best model describing the conduction mechanism.

Electrical Investigation of Metal-Olivine Systems and Application to the Deep Interior of Mercury

NASA Astrophysics Data System (ADS)

Zhang, Zhou; Pommier, Anne

2017-12-01

We report electrical conductivity measurements on metal-olivine systems at about 5 and 6 GPa and up to 1,675°C in order to investigate the electrical properties of core-mantle boundary (CMB) systems. Electrical experiments were conducted in the multianvil apparatus using the impedance spectroscopy technique. The samples are composed of one metal layer (Fe, FeS, FeSi2, or Fe-Ni-S-Si) and one polycrystalline olivine layer, with the metal:olivine ratio ranging from 1:0.7 to 1:9.2. For all samples, we observe that the bulk electrical conductivity increases with temperature from 10-2.5 to 101.8 S/m, which is higher than the conductivity of polycrystalline olivine but lower than the conductivity of the pure metal phase at similar conditions. In some experiments, a conductivity jump is observed at the temperature corresponding to the melting temperature of the metallic phase. Both the metal:olivine ratio and the metal phase geometry control the electrical conductivity of the two-layer samples. By combining electrical results, textural analyses of the samples, and previous studies of the structure and composition of Mercury's interior, we propose an electrical profile of the deep interior of the planet that accounts for a layered CMB-outer core structure. The electrical model agrees with existing conductivity estimates of Mercury's lower mantle and CMB using magnetic observations and thermodynamic calculations, and thus, supports the hypothesis of a layered CMB-outermost core structure in the present-day interior of Mercury. We propose that the layered CMB-outer core structure is possibly electrically insulating, which may influence the planet's structure and cooling history.

Numerically simulated exposure of children and adults to pulsed gradient fields in MRI.

PubMed

Samoudi, Amine M; Vermeeren, Gunter; Tanghe, Emmeric; Van Holen, Roel; Martens, Luc; Josephs, Wout

2016-11-01

To determine exposure to gradient switching fields of adults and children in a magnetic resonance imaging (MRI) scanner by evaluating internal electric fields within realistic models of adult male, adult female, and child inside transverse and longitudinal gradient coils, and to compare these results with compliance guidelines. Patients inside x-, y-, and z-gradient coils were simulated using anatomically realistic models of adult male, adult female, and child. The induced electric fields were computed for 1 kHz sinusoidal current with a magnitude of 1 A in the gradient coils. Rheobase electric fields were then calculated and compared to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) 2004 and International Electrotechnical Commission (IEC) 2010 guidelines. The effect of the human body, coil type, and skin conductivity on the induced electric field was also investigated. The internal electric fields are within the first level controlled operating mode of the guidelines and range from 2.7V m -1 to 4.5V m -1 , except for the adult male inside the y-gradient coil (induced field reaches 5.4V m -1 ).The induced electric field is sensitive to the coil type (electric field in the skin of adult male: 4V m -1 , 4.6V m -1 , and 3.8V m -1 for x-, y-, and z-gradient coils, respectively), the human body model (electric field in the skin inside y-gradient coil: 4.6V m -1 , 4.2V m -1 , and 3V m -1 for adult male, adult female, and child, respectively), and the skin conductivity (electric field 2.35-4.29% higher for 0.1S m -1 skin conductivity compared to 0.2S m -1 ). The y-gradient coil induced the largest fields in the patients. The highest levels of internal electric fields occurred for the adult male model. J. Magn. Reson. Imaging 2016;44:1360-1367. © 2016 International Society for Magnetic Resonance in Medicine.

Modeling Percolation in Polymer Nanocomposites by Stochastic Microstructuring

PubMed Central

Soto, Matias; Esteva, Milton; Martínez-Romero, Oscar; Baez, Jesús; Elías-Zúñiga, Alex

2015-01-01

A methodology was developed for the prediction of the electrical properties of carbon nanotube-polymer nanocomposites via Monte Carlo computational simulations. A two-dimensional microstructure that takes into account waviness, fiber length and diameter distributions is used as a representative volume element. Fiber interactions in the microstructure are identified and then modeled as an equivalent electrical circuit, assuming one-third metallic and two-thirds semiconductor nanotubes. Tunneling paths in the microstructure are also modeled as electrical resistors, and crossing fibers are accounted for by assuming a contact resistance associated with them. The equivalent resistor network is then converted into a set of linear equations using nodal voltage analysis, which is then solved by means of the Gauss–Jordan elimination method. Nodal voltages are obtained for the microstructure, from which the percolation probability, equivalent resistance and conductivity are calculated. Percolation probability curves and electrical conductivity values are compared to those found in the literature. PMID:28793594

Numerical modeling of friction welding of bi-metal joints for electrical applications

NASA Astrophysics Data System (ADS)

Velu, P. Shenbaga; Hynes, N. Rajesh Jesudoss

2018-05-01

In the manufacturing industries, and more especially in electrical engineering applications, the usage of non-ferrous materials plays a vital role. Today's engineering applications relies upon some of the significant properties such as a good corrosion resistance, mechanical properties, good heat conductivity and higher electrical conductivity. Copper-aluminum bi-metal joint is one such combination that meets the demands requirements for electrical applications. In this work, the numerical simulation of AA 6061 T6 alloy/Copper was carried out under joining conditions. By using this developed model, the temperature distribution along the length of the dissimilar joint is predicted and the time-temperature profile has also been generated. Besides, a Finite Element Model has been developed by using the numerical simulation Tool "ABAQUS". This developed FEM is helpful in predicting various output parameters during friction welding of this dissimilar joint combination.

Spin- and valley-dependent electrical conductivity of ferromagnetic group-IV 2D sheets in the topological insulator phase

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Yarmohammadi, Mohsen; Mirabbaszadeh, Kavoos; Habibiyan, Hamidreza

2018-03-01

In this work, based on the Kubo-Greenwood formalism and the k . p Hamiltonian model, the impact of Rashba spin-orbit coupling on electronic band structure and electrical conductivity of spin-up and spin-down subbands in counterparts of graphene, including silicene, stanene, and germanene nanosheets has been studied. When Rashba coupling is considered, the effective mass of Dirac fermions decreases significantly and no significant change is caused by this coupling for the subband gaps. All these nanosheets are found to be in topological insulator quantum phase at low staggered on-site potentials due to the applied perpendicular external electric field. We point out that the electrical conductivity of germanene increases gradually with Rashab coupling, while silicene and stanene have some fluctuations due to their smaller Fermi velocity. Furthermore, some critical temperatures with the same electrical conductivity values for jumping to the higher energy levels are observed at various Rashba coupling strengths. For all structures, a broad peak appears at low temperatures in electrical conductivity curves corresponding to the large entropy of systems when the thermal energy reaches to the difference between the energy states. Finally, we have reported that silicene has the larger has the larger electrical conductivity than two others.

Mind the Gap: A Semicontinuum Model for Discrete Electrical Propagation in Cardiac Tissue.

PubMed

Costa, Caroline Mendonca; Silva, Pedro Andre Arroyo; dos Santos, Rodrigo Weber

2016-04-01

Electrical propagation in cardiac tissue is a discrete or discontinuous phenomenon that reflects the complexity of the anatomical structures and their organization in the heart, such as myocytes, gap junctions, microvessels, and extracellular matrix, just to name a few. Discrete models or microscopic and discontinuous models are, so far, the best options to accurately study how structural properties of cardiac tissue influence electrical propagation. These models are, however, inappropriate in the context of large scale simulations, which have been traditionally performed by the use of continuum and macroscopic models, such as the monodomain and the bidomain models. However, continuum models may fail to reproduce many important physiological and physiopathological aspects of cardiac electrophysiology, for instance, those related to slow conduction. In this study, we develop a new mathematical model that combines characteristics of both continuum and discrete models. The new model was evaluated in scenarios of low gap-junctional coupling, where slow conduction is observed, and was able to reproduce conduction block, increase of the maximum upstroke velocity and of the repolarization dispersion. None of these features can be captured by continuum models. In addition, the model overcomes a great disadvantage of discrete models, as it allows variation of the spatial resolution within a certain range.

A study of the influence of conductive paths and their directions in randomly generated conductor network.

NASA Astrophysics Data System (ADS)

Mandolesi, E.; Moorkamp, M.; Jones, A. G.

2014-12-01

Most electromagnetic (EM) geophysical methods focus on the electrical conductivity of rocks and sediments to determine the geological structure of the subsurface. Electric conductivity itself is measured in the laboratory with a wide range of instruments and techniques. These measurements seldom return a compatible result. The presence of partially-interconnected random pathways of electrically conductive materials in resistive hosts has been studied for decades, and recently with increasing interest. To comprehend which conductive mechanism scales from the microstructures up to field electrical conductivity measurements, two main branch of studies have been undertaken: statistical probability of having a conductive pathways and mixing laws. Several numerical approaches have been tested to understand the effects of interconnected pathways of conductors at field scale. Usually these studies were restricted in two ways: the sources are considered constant in time (i.e., DC) and the domain is, with few exception, two-dimensional. We simulated the effects of time-varying EM sources on the conductivity measured on the surface of a three-dimensional randomly generated body embedded in an uniform host by using electromagnetic induction equations. We modelled a two-phase mixture of resistive and conductive elements with the goal of comparing the conductivity measured on field scale with the one proper of the elements constituting the random rock, and to test how the internal structures influence the directionality of the responses. Moreover, we modelled data from randomly generated bodies characterized by coherent internal structures, to check the effect of the named structures on the anisotropy of the effective conductivity. We compared these values with the electrical conductivity limits predicted by Hashin-Shtrikman bounds and the effective conductivity predicted by the Archie's law, both cast in its classic form and in an updated that allow to take in account two materials. The same analysis was done for both the resistive and the conductive conductivity values for the anisotropic case.

Estimation of electrical conductivity distribution within the human head from magnetic flux density measurement.

PubMed

Gao, Nuo; Zhu, S A; He, Bin

2005-06-07

We have developed a new algorithm for magnetic resonance electrical impedance tomography (MREIT), which uses only one component of the magnetic flux density to reconstruct the electrical conductivity distribution within the body. The radial basis function (RBF) network and simplex method are used in the present approach to estimate the conductivity distribution by minimizing the errors between the 'measured' and model-predicted magnetic flux densities. Computer simulations were conducted in a realistic-geometry head model to test the feasibility of the proposed approach. Single-variable and three-variable simulations were performed to estimate the brain-skull conductivity ratio and the conductivity values of the brain, skull and scalp layers. When SNR = 15 for magnetic flux density measurements with the target skull-to-brain conductivity ratio being 1/15, the relative error (RE) between the target and estimated conductivity was 0.0737 +/- 0.0746 in the single-variable simulations. In the three-variable simulations, the RE was 0.1676 +/- 0.0317. Effects of electrode position uncertainty were also assessed by computer simulations. The present promising results suggest the feasibility of estimating important conductivity values within the head from noninvasive magnetic flux density measurements.

An Explosively Actuated Electrical Switch Using Kapton Insulation

DTIC Science & Technology

1993-03-01

ionization pin. This is consistent with a shock-induced conduction model because the conductivity is known to increase with pressure.5 The aluminum...34Shock Induced Electrical Activity in Polymeric Solids. A Mechanically Induced Bond Scission Model ," J. Phys. Chem., 83 (23), 1979, p. 3048. 9. Graham...NSWC, White Oak, MD. 6-2 NSWCDD/TR-92/124 DISTRIBUTION Copies Chief of Naval Research Attn: ONR1132P(R. Miller ) 1 ONT 20T (L. V. Schmidt) 1

A new theoretical formulation of coupling thermo-electric breakdown in LDPE film under dc high applied fields

NASA Astrophysics Data System (ADS)

Boughariou, F.; Chouikhi, S.; Kallel, A.; Belgaroui, E.

2015-12-01

In this paper, we present a new theoretical and numerical formulation for the electrical and thermal breakdown phenomena, induced by charge packet dynamics, in low-density polyethylene (LDPE) insulating film under dc high applied field. The theoretical physical formulation is composed by the equations of bipolar charge transport as well as by the thermo-electric coupled equation associated for the first time in modeling to the bipolar transport problem. This coupled equation is resolved by the finite-element numerical model. For the first time, all bipolar transport results are obtained under non-uniform temperature distributions in the sample bulk. The principal original results show the occurring of very sudden abrupt increase in local temperature associated to a very sharp increase in external and conduction current densities appearing during the steady state. The coupling between these electrical and thermal instabilities reflects physically the local coupling between electrical conduction and thermal joule effect. The results of non-uniform temperature distributions induced by non-uniform electrical conduction current are also presented for several times. According to our formulation, the strong injection current is the principal factor of the electrical and thermal breakdown of polymer insulating material. This result is shown in this work. Our formulation is also validated experimentally.

Induction signals from Callisto's ionosphere and their implications on a possible subsurface ocean

NASA Astrophysics Data System (ADS)

Hartkorn, Oliver; Saur, Joachim

2017-11-01

We investigate whether induction within Callisto's electrically conductive ionosphere can explain observed magnetic fields which have previously been interpreted as evidence of induction in a saline, electrically conductive subsurface ocean. Callisto's ionosphere is subject to the flow of time-periodic magnetized plasma of Jupiter's magnetosphere, which induces electric fields and electric currents in Callisto's electrically conductive ionosphere. We develop a simple analytic model for a first quantitative understanding of the effects of induction in Callisto's ionosphere caused by the interaction with a time-variable magnetic field environment. With this model, we also investigate how the associated ionospheric currents close in the ambient magnetospheric plasma. Based on our model, we find that the anisotropic nature of Callisto's ionospheric conductivity generates an enhancement effect on ionospheric loop currents which are driven by the time-variable magnetic field. This effect is similar to the Cowling channel effect known from Earth's ionosphere. Subsequently, we numerically calculate the expected induced magnetic fields due to Jupiter's time-variable magnetic field in an anisotropic conductive ionosphere and compare our results with the Galileo C-3 and C-9 flybys. We find that induction within Callisto's ionosphere is responsible for a significant part of the observed magnetic fields. Ionospheric induction creates induced magnetic fields to some extent similar as expected from a subsurface water ocean. Depending on currently unknown properties such as Callisto's nightside ionosphere, the existence of layers of "dirty ice" and the details of the plasma interaction, a water ocean might be located much deeper than previously thought or might not exist at all.

Modeling and Predicting the Electrical Conductivity of Composite Cathode for Solid Oxide Fuel Cell by Using Support Vector Regression

NASA Astrophysics Data System (ADS)

Tang, J. L.; Cai, C. Z.; Xiao, T. T.; Huang, S. J.

2012-07-01

The electrical conductivity of solid oxide fuel cell (SOFC) cathode is one of the most important indices affecting the efficiency of SOFC. In order to improve the performance of fuel cell system, it is advantageous to have accurate model with which one can predict the electrical conductivity. In this paper, a model utilizing support vector regression (SVR) approach combined with particle swarm optimization (PSO) algorithm for its parameter optimization was established to modeling and predicting the electrical conductivity of Ba0.5Sr0.5Co0.8Fe0.2 O3-δ-xSm0.5Sr0.5CoO3-δ (BSCF-xSSC) composite cathode under two influence factors, including operating temperature (T) and SSC content (x) in BSCF-xSSC composite cathode. The leave-one-out cross validation (LOOCV) test result by SVR strongly supports that the generalization ability of SVR model is high enough. The absolute percentage error (APE) of 27 samples does not exceed 0.05%. The mean absolute percentage error (MAPE) of all 30 samples is only 0.09% and the correlation coefficient (R2) as high as 0.999. This investigation suggests that the hybrid PSO-SVR approach may be not only a promising and practical methodology to simulate the properties of fuel cell system, but also a powerful tool to be used for optimal designing or controlling the operating process of a SOFC system.

Advanced computer techniques for inverse modeling of electric current in cardiac tissue

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

Hutchinson, S.A.; Romero, L.A.; Diegert, C.F.

1996-08-01

For many years, ECG`s and vector cardiograms have been the tools of choice for non-invasive diagnosis of cardiac conduction problems, such as found in reentrant tachycardia or Wolff-Parkinson-White (WPW) syndrome. Through skillful analysis of these skin-surface measurements of cardiac generated electric currents, a physician can deduce the general location of heart conduction irregularities. Using a combination of high-fidelity geometry modeling, advanced mathematical algorithms and massively parallel computing, Sandia`s approach would provide much more accurate information and thus allow the physician to pinpoint the source of an arrhythmia or abnormal conduction pathway.

[Image reconstruction of conductivity on magnetoacoustic tomography with magnetic induction].

PubMed

Li, Jingyu; Yin, Tao; Liu, Zhipeng; Xu, Guohui

2010-04-01

The electric characteristics such as impedance and conductivity of the organization will change in the case where pathological changes occurred in the biological tissue. The change in electric characteristics usually took place before the change in the density of tissues, and also, the difference in electric characteristics such as conductivity between normal tissue and pathological tissue is obvious. The method of magneto-acoustic tomography with magnetic induction is based on the theory of magnetic eddy current induction, the principle of vibration generation and acoustic transmission to get the boundary of the pathological tissue. The pathological change could be inspected by electricity characteristic imaging which is invasive to the tissue. In this study, a two-layer concentric spherical model is established to simulate the malignant tumor tissue surrounded by normal tissue mutual relations of the magneto-sound coupling effect and the coupling equations in the magnetic field are used to get the algorithms for reconstructing the conductivity. Simulation study is conducted to test the proposed model and validate the performance of the reconstructed algorithms. The result indicates that the use of signal processing method in this paper can image the conductivity boundaries of the sample in the scanning cross section. The computer simulating results validate the feasibility of applying the method of magneto-acoustic tomography with magnetic induction for malignant tumor imaging.

Metal-like electrical conductivity in LaxSr2-xTiMoO6 oxides for high temperature thermoelectric power generation.

PubMed

Saxena, Mandvi; Maiti, Tanmoy

2017-05-09

Increasing electrical conductivity in oxides, which are inherently insulators, can be a potential route in developing oxide-based thermoelectric power generators with higher energy conversion efficiency. In the present work, environmentally friendly non-toxic double perovskite La x Sr 2-x TiMoO 6 (LSTM) ceramics were synthesized using a solid-state reaction route by optimizing the sintering temperature and atmosphere for high temperature thermoelectric applications. Rietveld refinement of XRD data confirmed a single-phase solid solution with a cubic structure in these double perovskites with the space-group Pm3[combining macron]m. SEM studies showed a highly dense microstructure in these ceramics. High electrical conductivity on the order of 10 5 S m -1 and large carrier concentration (∼10 22 cm -3 ) were obtained in these materials. The temperature-dependent electrical conductivity measurement showed that the LSTM ceramics exhibit a semiconductor to metal transition. Thermopower (S) measurements demonstrated the conductivity switching from a p-type to n-type behavior at higher temperature. A temperature dependent Seebeck coefficient was further explained using a model for coexistence of both types of charge carriers in these oxides. A conductivity mechanism of these double perovskites was found to be governed by a small polaron hopping model.

Discretized modeling of beads-on-a-string morphology from electrically driven, conducting, and viscoelastic polymer jets

NASA Astrophysics Data System (ADS)

Divvela, Mounica Jyothi; Joo, Yong Lak

2017-04-01

In this paper, we provide a theoretical investigation of axisymmetric instabilities observed during electrospinning, which lead to beads-on-a-string morphology. We used a discretized method to model the instability phenomena observed in the jet. We considered the fluid to be analogous to a bead-spring model. The motion of these beads is governed by the electrical, viscoelastic, surface tension, aerodynamic drag, and gravitational forces. The bead is perturbed at the nozzle, and the growth of the instability is observed over time, and along the length of the jet. We considered both lower electrical conducting polyisobutylene (PIB)-based Boger fluids and highly electrical conducting, polyethylene oxide (PEO)/water systems. In PIB fluids, the onset of the axisymmetric instability is predominantly based on the capillary mode, and the growth rate of the instability is decreased with the viscoelasticity of the jet. However, in the PEO/water system, the instability is electrically driven, and a significant increase in the growth rate of the instability is observed with the increase in the voltage. Our predictions from the discretized model are in good agreement with the previous linear stability analysis and experimental results. Our results also revealed the non-stationary behavior of the disturbance, where the amplitude of the perturbation is observed to be oscillating. Furthermore, we showed that the discretized model is also used to observe the non-axisymmetric behavior of the jet, which can be further used to study the bending instability in electrospinning.

Project MANTIS: A MANTle Induction Simulator for coupling geodynamic and electromagnetic modeling

NASA Astrophysics Data System (ADS)

Weiss, C. J.

2009-12-01

A key component to testing geodynamic hypotheses resulting from the 3D mantle convection simulations is the ability to easily translate the predicted physiochemical state to the model space relevant for an independent geophysical observation, such as earth's seismic, geodetic or electromagnetic response. In this contribution a new parallel code for simulating low-frequency, global-scale electromagnetic induction phenomena is introduced that has the same Earth discretization as the popular CitcomS mantle convection code. Hence, projection of the CitcomS model into the model space of electrical conductivity is greatly simplified, and focuses solely on the node-to-node, physics-based relationship between these Earth parameters without the need for "upscaling", "downscaling", averaging or harmonizing with some other model basis such as spherical harmonics. Preliminary performance tests of the MANTIS code on shared and distributed memory parallel compute platforms shows favorable scaling (>70% efficiency) for up to 500 processors. As with CitcomS, an OpenDX visualization widget (VISMAN) is also provided for 3D rendering and interactive interrogation of model results. Details of the MANTIS code will be briefly discussed here, focusing on compatibility with CitcomS modeling, as will be preliminary results in which the electromagnetic response of a CitcomS model is evaluated. VISMAN rendering of electrical tomography-derived electrical conductivity model overlain by an a 1x1 deg crustal conductivity map. Grey scale represents the log_10 magnitude of conductivity [S/m]. Arrows are horiztonal components of a hypothetical magnetospheric source field used to electromagnetically excite the conductivity model.

Concentration and Mobility of Electrically-Conducting Defects in Olivine

NASA Astrophysics Data System (ADS)

Constable, S.; Roberts, J.; Duba, A.

2002-12-01

We have collected measurements of electrical conductivity and thermopower as a function of temperature and oxygen fugacity (f O2) on a sample of San Quintin dunite (95% olivine), and measurements of electrical conductivity equilibration after changes in f O2 on Mt.Porndon lherzolite (65% olivine). Both data sets have been analysed using nonlinear parameter inversion of mathematical models relating conductivity, thermopower, and diffusion kinetics to temperature, f O2, time, and defect concentration and mobility. From the dunite thermopower/conductivity data we are able to estimate the concentration and mobilities of electrically conducting defects. Our model allows electrons, small polarons (Fe+++ on Fe++ sites), and magnesium vacancies (V'' Mg) to contribute to conduction, but only polarons and V'' Mg are required by our data. Polarons dominate conduction below 1300°~C; at this temperature conduction, is equal for the two defects at all f O2 tested. Thermopower measurements allow us to estimate defect concentration independently from mobility, and so we can back out polaron mobility as 12.2x 10-6 exp(-1.05~eV/kT) m2V-1s-1 and magnesium vacancy mobility as 2.72x 10-6 exp(-1.09~eV/kT) m2V-1s-1. Electrical conductivity of the lherzolite, measured as a function of time after changes in the oxygen fugacity of the surrounding CO2/CO atmosphere, is used to infer the diffusivity of the point defects associated with the oxidation reactions. An observed f O2 dependence in the time constants associated with equilibration implies two species of fixed diffusivity, each with f O2-dependent concentrations. Although the rate-limiting step may not necessarily be associated with conducting defects, when time constants are converted to mobilities, the magnitudes and activation energies agree extremely well with the model presented above for the dunite, after one free parameter (effective grain size) is fit at a plausible 1.6~mm diameter. Not only does this study represent one of the few direct measurements of polaron mobility, but the very good agreement between two independent measurement techniques (thermopower versus equilibration kinetics) and two independent samples (dunite versus lherzolite) provides some level of confidence in the results. We are currently extending these modeling techniques to study olivine defect mobility anisotropy.

Air-stable electrical conduction in oxidized poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene] thin films

NASA Astrophysics Data System (ADS)

Hossein-Babaei, F.; Shabani, P.; Azadinia, M.

2013-11-01

Oxidation-caused electroluminescence and electrical conduction deteriorations in poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) have prevented the material from being used in applications requiring air exposure. Here, we report air-stable electrical conduction in oxidized MEH-PPV layers produced by room temperature annealing of MEH-PPV thin films in air. Oxidized layers exhibit lower, but stable, conductivities. As the process is irreversible, the final conductivity is retained in vacuum, inert gas, hydrogen, and oxygen. The oxidation rates recorded at different conditions for layers of varied thickness and electrode configuration are described by a surface oxidation model. Potentials of the oxidized MEH-PPV layers in sensor technology are demonstrated.

Effect of High Pressure Homogenization on the Physicochemical Properties of Natural Plant-based Model Emulsion Applicable for Dairy Products

PubMed Central

Park, Sung Hee; Min, Sang-Gi; Jo, Yeon-Ji; Chun, Ji-Yeon

2015-01-01

In the dairy industry, natural plant-based powders are widely used to develop flavor and functionality. However, most of these ingredients are water-insoluble; therefore, emulsification is essential. In this study, the efficacy of high pressure homogenization (HPH) on natural plant (chocolate or vanilla)-based model emulsions was investigated. The particle size, electrical conductivity, Brix, pH, and color were analyzed after HPH. HPH significantly decreased the particle size of chocolate-based emulsions as a function of elevated pressures (20-100 MPa). HPH decreased the mean particle size of chocolate-based emulsions from 29.01 μm to 5.12 μm, and that of vanilla-based emulsions from 4.18 μm to 2.44 μm. Electrical conductivity increased as a function of the elevated pressures after HPH, for both chocolate- and vanilla-based model emulsions. HPH at 100 MPa increased the electrical conductivity of chocolate-based model emulsions from 0.570 S/m to 0.680 S/m, and that of vanilla-based model emulsions from 0.573 S/m to 0.601 S/m. Increased electrical conductivity would be attributed to colloidal phase modification and dispersion of oil globules. Brix of both chocolate- and vanilla-based model emulsions gradually increased as a function of the HPH pressure. Thus, HPH increased the solubility of plant-based powders by decreasing the particle size. This study demonstrated the potential use of HPH for enhancing the emulsification process and stability of the natural plant powders for applications with dairy products. PMID:26761891

Lunar properties from transient and steady magnetic field measurements.

NASA Technical Reports Server (NTRS)

Dyal, P.; Parkin, C. W.

1972-01-01

The electrical conductivity of the lunar interior has been determined from magnetic field step transients measured on the lunar dark side. The simplest model which best fits the data is a spherically symmetric three layer model having a nonconducting outer crust, an intermediate layer with electrical conductivity of .00035 mhos/m, and an inner core with conductivity of .01 mhos/m. Temperatures calculated from these conductivities in the three regions for an example of an olivine moon are as follows: crust, below 440 K; intermediate layer, 890 K; and core, 1240 K. The whole-moon relative permeability has been calculated from the measurements to be 1.03 plus or minus 0.13.

Monitoring of In-Situ Remediation By Time Lapse 3D Geo-Electric Measurements

NASA Astrophysics Data System (ADS)

Kanli, A. I.; Tildy, P.; Neducza, B.; Nagy, P.; Hegymegi, C.

2017-12-01

Injection of chemical oxidant solution to degrade the subsurface contaminants can be used for hydrocarbon contamination remediation. In this study, we developed a non-destructive measurement strategy to monitor oxidative in-situ remediation processes. The difficulties of the presented study originate from the small volume of conductive solution that can be used due to environmental considerations. Due to the effect of conductive groundwater and the high clay content of the targeted layer and the small volume of conductive solution that can be used due to environmental considerations, a site specific synthetic modelling is necessary for measurement design involving the results of preliminary 2D ERT measurements, electrical conductivity measurements of different active agents and expected resistivity changes calculated by soil resistivity modelling. Because of chemical biodegradation, the results of soil resistivity modelling have suggested that the reagent have complex effects on contaminated soils. As a result the plume of resistivity changes caused by the injected agent was determined showing strong fracturing effect because of the high pressure of injection. 3D time-lapse geo-electric measurements were proven to provide a usable monitoring tool for in-situ remediation as a result of our sophisticated tests and synthetic modelling.

A cardiac electrical activity model based on a cellular automata system in comparison with neural network model.

PubMed

Khan, Muhammad Sadiq Ali; Yousuf, Sidrah

2016-03-01

Cardiac Electrical Activity is commonly distributed into three dimensions of Cardiac Tissue (Myocardium) and evolves with duration of time. The indicator of heart diseases can occur randomly at any time of a day. Heart rate, conduction and each electrical activity during cardiac cycle should be monitor non-invasively for the assessment of "Action Potential" (regular) and "Arrhythmia" (irregular) rhythms. Many heart diseases can easily be examined through Automata model like Cellular Automata concepts. This paper deals with the different states of cardiac rhythms using cellular automata with the comparison of neural network also provides fast and highly effective stimulation for the contraction of cardiac muscles on the Atria in the result of genesis of electrical spark or wave. The specific formulated model named as "States of automaton Proposed Model for CEA (Cardiac Electrical Activity)" by using Cellular Automata Methodology is commonly shows the three states of cardiac tissues conduction phenomena (i) Resting (Relax and Excitable state), (ii) ARP (Excited but Absolutely refractory Phase i.e. Excited but not able to excite neighboring cells) (iii) RRP (Excited but Relatively Refractory Phase i.e. Excited and able to excite neighboring cells). The result indicates most efficient modeling with few burden of computation and it is Action Potential during the pumping of blood in cardiac cycle.

Magnetically launched flyer plate technique for probing electrical conductivity of compressed copper

NASA Astrophysics Data System (ADS)

Cochrane, K. R.; Lemke, R. W.; Riford, Z.; Carpenter, J. H.

2016-03-01

The electrical conductivity of materials under extremes of temperature and pressure is of crucial importance for a wide variety of phenomena, including planetary modeling, inertial confinement fusion, and pulsed power based dynamic materials experiments. There is a dearth of experimental techniques and data for highly compressed materials, even at known states such as along the principal isentrope and Hugoniot, where many pulsed power experiments occur. We present a method for developing, calibrating, and validating material conductivity models as used in magnetohydrodynamic (MHD) simulations. The difficulty in calibrating a conductivity model is in knowing where the model should be modified. Our method isolates those regions that will have an impact. It also quantitatively prioritizes which regions will have the most beneficial impact. Finally, it tracks the quantitative improvements to the conductivity model during each incremental adjustment. In this paper, we use an experiment on Sandia National Laboratories Z-machine to isentropically launch multiple flyer plates and, with the MHD code ALEGRA and the optimization code DAKOTA, calibrated the conductivity such that we matched an experimental figure of merit to +/-1%.

Magnetically launched flyer plate technique for probing electrical conductivity of compressed copper

DOE PAGES

Cochrane, Kyle R.; Lemke, Raymond W.; Riford, Z.; ...

2016-03-11

The electrical conductivity of materials under extremes of temperature and pressure is of crucial importance for a wide variety of phenomena, including planetary modeling, inertial confinement fusion, and pulsed power based dynamic materialsexperiments. There is a dearth of experimental techniques and data for highly compressed materials, even at known states such as along the principal isentrope and Hugoniot, where many pulsed power experiments occur. We present a method for developing, calibrating, and validating material conductivity models as used in magnetohydrodynamic(MHD) simulations. The difficulty in calibrating a conductivity model is in knowing where the model should be modified. Our method isolatesmore » those regions that will have an impact. It also quantitatively prioritizes which regions will have the most beneficial impact. Finally, it tracks the quantitative improvements to the conductivity model during each incremental adjustment. In this study, we use an experiment on Sandia National Laboratories Z-machine to isentropically launch multiple flyer plates and, with the MHD code ALEGRA and the optimization code DAKOTA, calibrated the conductivity such that we matched an experimental figure of merit to +/–1%.« less

Electrical conduction of a XLPE nanocomposite

NASA Astrophysics Data System (ADS)

Park, Yong-Jun; Sim, Jae-Yong; Lim, Kee-Joe; Nam, Jin-Ho; Park, Wan-Gi

2014-07-01

The resistivity, breakdown strength, and formation of space charges are very important factors for insulation design of HVDC cable. It is known that a nano-sized metal-oxide inorganic filler reduces the formation of space charges in the polymer nanocomposite. Electrical conduction of cross-linked polyethylene(XLPE) nanocomposite insulating material is investigated in this paper. The conduction currents of two kinds of XLPE nanocomposites and XLPE without nano-filler were measured at temperature of 303 ~ 363 K under the applied electric fields of 10 ~ 50 kV/mm. The current of the nanocomposite specimen is smaller than that of XLPE specimen without nano-filler. The conduction mechanism may be explained in terms of Schottky emission and multi-core model.

Assembly of polythiophenes on responsive polymer microgels for the highly selective detection of ammonia gas

DOE PAGES

Chang, Aiping; Peng, Yahui; Li, Zezhou; ...

2016-04-05

For this study, a class of smart composite materials based on the assembly of conjugated polymers on responsive polymer microgels has been prepared. We have chosen poly(3-((2-(2-methoxyethoxy)ethoxy)methyl)-thiophene) as the model conjugated polymer and an ammonia-responsive microgel of phenoxazinium-functionalized poly(N-isopropylacrylamide-co-propargyl acrylate) as the model template. Under this design, the composite materials can combine the electrical conductivity of the conjugated polymers and the ammonia recognisability of the ammonia-responsive polymer microgels; the cooperation of these properties allows the reversible control of electrical conductivity by ammonia gas. Those composite materials can not only adapt to ammonia gas, but also convert changes in the concentrationmore » of ammonia into conductance, allowing the electrical detection of ammonia gas with high selectivity. This makes the composite materials different from the conductive polymer platforms reported previously, which may also respond to non-ammonia gases and the response induced by non-ammonia gases is close to that induced by ammonia gas. Using these composite materials as sensing materials for the electrical detection of ammonia gas, the detection limit can reach as low as 1.1 ppb. Finally, these features enable their use for the electrical detection of ammonia in breath.« less

Assembly of polythiophenes on responsive polymer microgels for the highly selective detection of ammonia gas

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

Chang, Aiping; Peng, Yahui; Li, Zezhou

For this study, a class of smart composite materials based on the assembly of conjugated polymers on responsive polymer microgels has been prepared. We have chosen poly(3-((2-(2-methoxyethoxy)ethoxy)methyl)-thiophene) as the model conjugated polymer and an ammonia-responsive microgel of phenoxazinium-functionalized poly(N-isopropylacrylamide-co-propargyl acrylate) as the model template. Under this design, the composite materials can combine the electrical conductivity of the conjugated polymers and the ammonia recognisability of the ammonia-responsive polymer microgels; the cooperation of these properties allows the reversible control of electrical conductivity by ammonia gas. Those composite materials can not only adapt to ammonia gas, but also convert changes in the concentrationmore » of ammonia into conductance, allowing the electrical detection of ammonia gas with high selectivity. This makes the composite materials different from the conductive polymer platforms reported previously, which may also respond to non-ammonia gases and the response induced by non-ammonia gases is close to that induced by ammonia gas. Using these composite materials as sensing materials for the electrical detection of ammonia gas, the detection limit can reach as low as 1.1 ppb. Finally, these features enable their use for the electrical detection of ammonia in breath.« less

A simple electrical-mechanical model of the heart applied to the study of electrical-mechanical alternans

NASA Technical Reports Server (NTRS)

Clancy, Edward A.; Smith, Joseph M.; Cohen, Richard J.

1991-01-01

Recent evidence has shown that a subtle alternation in the surface ECG (electrical alternans) may be correlated with the susceptibility to ventricular fibrillation. In the present work, the author presents evidence that a mechanical alternation in the heartbeat (mechanical alternans) generally accompanies electrical alternans. A simple finite-element computer model which emulates both the electrical and the mechanical activity of the heart is presented. A pilot animal study is also reported. The computer model and the animal study both found that (1) there exists a regime of combined electrical-mechanical alternans during the transition from a normal rhythm towards a fibrillatory rhythm, (2) the detected degree of alternation is correlated with the relative instability of the rhythm, and (3) the electrical and mechanical alternans may result from a dispersion in local electrical properties leading to a spatial-temporal alternation in the electrical conduction process.

Modeling thermoelectric transport in organic materials.

PubMed

Wang, Dong; Shi, Wen; Chen, Jianming; Xi, Jinyang; Shuai, Zhigang

2012-12-28

Thermoelectric energy converters can directly convert heat to electricity using semiconducting materials via the Seebeck effect and electricity to heat via the Peltier effect. Their efficiency depends on the dimensionless thermoelectric figure of merit of the material, which is defined as zT = S(2)σT/κ with S, σ, κ, and T being the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature respectively. Organic materials for thermoelectric applications have attracted great attention. In this review, we present our recent progress made in developing theories and computational schemes to predict the thermoelectric figure of merit at the first-principles level. The methods have been applied to model thermoelectric transport in closely-packed molecular crystals and one-dimensional conducting polymer chains. The physical insight gained in these studies will help in the design of efficient organic thermoelectric materials.

Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction.

PubMed

Johansson, Johannes D; Eriksson, Ola; Wren, Joakim; Loyd, Dan; Wårdell, Karin

2006-09-01

Radio-frequency brain lesioning is a method for reducing e.g. symptoms of movement disorders. A small electrode is used to thermally coagulate malfunctioning tissue. Influence on lesion size from thermal and electric conductivity of the tissue, microvascular perfusion and preset electrode temperature was investigated using a finite-element model. Perfusion was modelled as an increased thermal conductivity in non-coagulated tissue. The parameters were analysed using a 2(4)-factorial design (n=16) and quadratic regression analysis (n=47). Increased thermal conductivity of the tissue increased lesion volume, while increased perfusion decreased it since coagulation creates a thermally insulating layer due to the cessation of blood perfusion. These effects were strengthened with increased preset temperature. The electric conductivity had negligible effect. Simulations were found realistic compared to in vivo experimental lesions.

Electrical fatigue behaviour in lead zirconate titanate: an experimental and theoretical study

NASA Astrophysics Data System (ADS)

Bhattacharyya, Mainak; Arockiarajan, A.

2013-08-01

A systematic investigation on electrical fatigue in lead zirconate titanate (PZT) is carried out for different loading frequencies. Experiments are conducted up to 106 cycles to measure the electrical displacement and longitudinal strain on bulk ceramics in the bipolar mode with large electrical loading conditions. A simplified macroscopic model based on physical mechanisms of domain switching is developed to predict the non-linear behaviour. In this model, the volume fraction of a domain is used as the internal variable by considering the mechanisms of domain nucleation and propagation (domain wall movement). The measured material properties at different fatigue cycles are incorporated into the switching model as damage parameters and the classical strain versus electric field and electric displacement versus electric field curves are simulated. Comparison between the experiments and simulations shows that the proposed model can reproduce the characteristics of non-linear as well as fatigue responses.

A time dependent anatomically detailed model of cardiac conduction

NASA Technical Reports Server (NTRS)

Saxberg, B. E.; Grumbach, M. P.; Cohen, R. J.

1985-01-01

In order to understand the determinants of transitions in cardiac electrical activity from normal patterns to dysrhythmias such as ventricular fibrillation, we are constructing an anatomically and physiologically detailed finite element simulation of myocardial electrical propagation. A healthy human heart embedded in paraffin was sectioned to provide a detailed anatomical substrate for model calculations. The simulation of propagation includes anisotropy in conduction velocity due to fiber orientation as well as gradients in conduction velocities, absolute and relative refractory periods, action potential duration and electrotonic influence of nearest neighbors. The model also includes changes in the behaviour of myocardial tissue as a function of the past local activity. With this model, we can examine the significance of fiber orientation and time dependence of local propagation parameters on dysrhythmogenesis.

Electrical percolation in graphene–polymer composites

NASA Astrophysics Data System (ADS)

Marsden, A. J.; Papageorgiou, D. G.; Vallés, C.; Liscio, A.; Palermo, V.; Bissett, M. A.; Young, R. J.; Kinloch, I. A.

2018-07-01

Electrically conductive composites comprising polymers and graphene are extremely versatile and have a wide range of potential applications. The conductivity of these composites depends on the choice of polymer matrix, the type of graphene filler, the processing methodology, and any post-production treatments. In this review, we discuss the progress in graphene–polymer composites for electrical applications. Graphene filler types are reviewed, the progress in modelling these composites is outlined, the current optimal composites are presented, and the example of strain sensors is used to demonstrate their application.

Measured electric field in the vicinity of a thunderstorm system at an altitude of 37 km

NASA Technical Reports Server (NTRS)

Benbrook, J. R.; Kern, J. W.; Sheldon, W. R.

1974-01-01

A balloon-borne experiment to measure the atmospheric electric field was flown from the National Scientific Balloon Facility at Palestine, Texas, on July 10, 1973. The electric field and atmospheric conductivity were measured during ascent and for a 4-hour float period at 37-km altitude. Termination of the flight occurred near a thunderstorm line in west Texas. The perturbing influence of the thunderstorms on the electric field was observed at least 100 km from the storm line. The measured electric field is in reasonable agreement with calculations based on simple models of cloud structure and atmospheric conductivity. Large pulses in the measured electric field are interpreted as being the result of intracloud lightning.

Electrical Resistance Based Damage Modeling of Multifunctional Carbon Fiber Reinforced Polymer Matrix Composites

NASA Astrophysics Data System (ADS)

Hart, Robert James

In the current thesis, the 4-probe electrical resistance of carbon fiber-reinforced polymer (CFRP) composites is utilized as a metric for sensing low-velocity impact damage. A robust method has been developed for recovering the directionally dependent electrical resistivities using an experimental line-type 4-probe resistance method. Next, the concept of effective conducting thickness was uniquely applied in the development of a brand new point-type 4-probe method for applications with electrically anisotropic materials. An extensive experimental study was completed to characterize the 4-probe electrical resistance of CFRP specimens using both the traditional line-type and new point-type methods. Leveraging the concept of effective conducting thickness, a novel method was developed for building 4-probe electrical finite element (FE) models in COMSOL. The electrical models were validated against experimental resistance measurements and the FE models demonstrated predictive capabilities when applied to CFRP specimens with varying thickness and layup. These new models demonstrated a significant improvement in accuracy compared to previous literature and could provide a framework for future advancements in FE modeling of electrically anisotropic materials. FE models were then developed in ABAQUS for evaluating the influence of prescribed localized damage on the 4-probe resistance. Experimental data was compiled on the impact response of various CFRP laminates, and was used in the development of quasi- static FE models for predicting presence of impact-induced delamination. The simulation-based delamination predictions were then integrated into the electrical FE models for the purpose of studying the influence of realistic damage patterns on electrical resistance. When the size of the delamination damage was moderate compared to the electrode spacing, the electrical resistance increased by less than 1% due to the delamination damage. However, for a specimen with large delamination extending beyond the electrode locations, the oblique resistance increased by 30%. This result suggests that for damage sensing applications, the spacing of electrodes relative to the size of the delamination is important. Finally CT image data was used to model 3-D void distributions and the electrical response of such specimens were compared to models with no voids. As the void content increased, the electrical resistance increased non-linearly. The relationship between void content and electrical resistance was attributed to a combination of three factors: (i) size and shape, (ii) orientation, and (iii) distribution of voids. As a whole, the current thesis provides a comprehensive framework for developing predictive, resistance-based damage sensing models for CFRP laminates of various layup and thickness.

Synthesis and testing of a conducting polymeric composite material for lightning strike protection applications

NASA Astrophysics Data System (ADS)

Katunin, A.; Krukiewicz, K.; Turczyn, R.; Sul, P.; Łasica, A.; Catalanotti, G.; Bilewicz, M.

2017-02-01

Lightning strike protection is one of the important issues in the modern maintenance problems of aircraft. This is due to a fact that the most of exterior elements of modern aircraft is manufactured from polymeric composites which are characterized by isolating electrical properties, and thus cannot carry the giant electrical charge when the lightning strikes. This causes serious damage of an aircraft structure and necessity of repairs and tests before returning a vehicle to operation. In order to overcome this problem, usually metallic meshes are immersed in the polymeric elements. This approach is quite effective, but increases a mass of an aircraft and significantly complicates the manufacturing process. The approach proposed by the authors is based on a mixture of conducting and dielectric polymers. Numerous modeling studies which are based on percolation clustering using kinetic Monte Carlo methods, finite element modeling of electrical and mechanical properties, and preliminary experimental studies, allow achieving an optimal content of conducting particles in a dielectric matrix in order to achieve possibly the best electrical conductivity and mechanical properties, simultaneously. After manufacturing the samples with optimal content of a conducting polymer, mechanical and electrical characterization as well as high-voltage testing was performed. The application of such a material simplifies manufacturing process and ensures unique properties of aircraft structures, which allows for minimizing damage after lightning strike, as well as provide electrical bounding and grounding, interference shielding, etc. The proposed solution can minimize costs of repair, testing and certification of aircraft structures damaged by lightning strikes.

Temperature and frequency response of conductivity in Ag2S doped chalcogenide glassy semiconductor

NASA Astrophysics Data System (ADS)

Ojha, Swarupa; Das, Anindya Sundar; Roy, Madhab; Bhattacharya, Sanjib

2018-06-01

The electric conductivity of chalcogenide glassy semiconductor xAg2S-(1-x)(0.5S-0.5Te) has been presented here as a function of temperature and frequency. Formation of different nanocrystallites has been confirmed from X-ray diffraction study. It is also noteworthy that average size of nanocrystallites decreases with the increase of dislocation density. Dc conductivity data have been interpreted using Mott's model and Greaves's model in low and high temperature regions respectively. Ac conductivity above the room temperature has been analyzed using Meyer-Neldel (MN) conduction rule. It is interestingly noted that Correlated Barrier Hopping (CBH) model is the most appropriate conduction mechanism for x = 0.35, where pairs of charge carrier are considered to hop over the potential barrier between the sites via thermal activation. To interpret experimental data for x = 0.45, modified non-overlapping small polaron tunnelling (NSPT) model is supposed to be appropriate model due to tunnelling through grain boundary. The conductivity spectra at various temperatures have been analyzed using Almond-West Formalism (power law model). Scaling of conductivity spectra reveals that electrical relaxation process of charge carriers (polaron) is temperature independent but depends upon the composition of the present chalcogenide glassy system.

Evaluation of physico-mechanical properties of clayey soils using electrical resistivity imaging technique

NASA Astrophysics Data System (ADS)

Kibria, Golam

Resistivity imaging (RI) is a promising approach to obtaining continuous profile of soil subsurface. This method offers simple technique to identify moisture variation and heterogeneity of the investigated area. However, at present, only qualitative information of subsurface can be obtained using RI. A study on the quantification of geotechnical properties has become important for rigorous use of this method in the evaluation of geohazard potential and construction quality control of landfill liner system. Several studies have been performed to describe electrical resistivity of soil as a function of pore fluid conductivity and surface conductance. However, characterization tests on pore water and surface charge are not typically performed in a conventional geotechnical investigation. The overall objective of this study is to develop correlations between geotechnical parameters and electrical resistivity of soil, which would provide a mean to estimate geotechnical properties from RI. As a part of the study, multiple regression analyses were conducted to develop practically applicable models correlating resistivity with influential geotechnical parameters. The soil samples considered in this study were classified as highly plastic clay (CH) and low plasticity clay (CL) according to Unified Soil Classification System (USCS). Based on the physical tests, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) analysis, kaolinite was identified as the dominant mineral with some traces of magnesium, calcium, potassium, and iron. Electrical resistivity tests were conducted on compacted clays and undisturbed samples under varied geotechnical conditions. The experimental results indicated that the degree of saturation substantially influenced electrical resistivity. Electrical resistivity decreased as much as 11 times from initial value for the increase of degree of saturation from 23 to 100% in the laboratory tests on compacted clays. In case of undisturbed soil samples, resistivity decreased as much as sixteen fold (49.4 to 3.2 Ohm-m) for an increase of saturation from 31 to 100%. Furthermore, the resistivity results were different for the specimens at a specific degree of saturation because of varied surface activity and isomorphous substitution of clayey soils. In addition to physical properties, compressibility of clays was correlated with electrical conductivity. Based on the investigation, it was determined that the electrical conductivity vs. pressure curves followed similar trends as e vs. logp curves. Multiple linear regression (MLR) models were developed for compacted and undisturbed samples using statistical analysis software SAS (2009). During model development, degree of saturation and CEC were selected as independent variables. The proposed models were validated using experimental results on a different set of samples. Moreover, the applicability of the models in the determination of degrees of saturation was evaluated using field RI tests.

Inhomogeneity at the LaAlO3/SrTiO3 interface

NASA Astrophysics Data System (ADS)

Claeson, T.; Kalabukhov, A.; Gunnarsson, R.; Winkler, D.; Borjesson, J.; Ljustina, N.; Olsson, E.; Popok, V.; Boikov, Yu.; Serenkov, I.; Sakharov, V.

2010-03-01

High electrical conductivity has been reported for the interface between two wide-band gap insulators, LaAlO3 (LAO) and SrTiO3 (STO). It occurs above a critical thickness of LAO and can be tuned by an electric field. The conduction has been attributed to i) ``polar catastrophe'' , where the electrostatic charge at the interface is compensated by the transfer of half an electron per unit cell to the interface, ii) oxygen vacancies in the STO, and iii) cation intermixing, which may result in the formation of metallic La1-xSrxTiO3 layer. The relation between microstructure and electrical properties is crucial for understanding the origin of electrical conductivity. We have investigated the interface composition using medium-energy ion spectroscopy, high resolution electron microscopy, and Kelvin probe force microscopy. We find a correlation between cationic intermixing at the interface and electrical properties and inhomogeneities of the interface conductivity that may support a percolation model. Work supported by Swedish VR & KAW, Russian ISTC 3743, EC NANOXIDE

The role of acids in electrical conduction through ice

NASA Astrophysics Data System (ADS)

Stillman, David E.; MacGregor, Joseph A.; Grimm, Robert E.

2013-03-01

Electrical conduction through meteoric polar ice is controlled by soluble impurities that originate mostly from sea salt, biomass burning, and volcanic eruptions. The strongest conductivity response is to acids, yet the mechanism causing this response has been unclear. Here we elucidate conduction mechanisms in ice using broadband dielectric spectroscopy of meteoric polar ice cores. We find that conduction through polycrystalline polar ice is consistent with Jaccard theory for migration of charged protonic point defects through single ice crystals, except that bulk DC conduction is impeded by grain boundaries. Neither our observations nor modeling using Archie's Law support the hypothesis that grain-boundary networks of unfrozen acids cause significant electrolytic conduction. Common electrical logs of ice cores (by electrical conductivity measurement [ECM] or dielectric profiling [DEP]) and the attenuation of radio waves in ice sheets thus respond to protonic point defects only. This response implies that joint interpretation of electrical and chemical logs can determine impurity partitioning between the lattice and grain boundaries or inclusions. For example, in the Greenland Ice Core Project (GRIP) ice core from central Greenland, on average more than half of the available lattice-soluble impurities (H+, Cl-, NH4+) create defects. Understanding this partitioning could help further resolve the nature of past changes in atmospheric chemistry.

The Bulk Lunar Electrical Conductivity. Ph.D. Thesis. Final Report; [from Explorer 35 satellite and the Apollo 12 flight

NASA Technical Reports Server (NTRS)

Leavy, Donald Lucien

1975-01-01

The electrical conductivity structure was studied of a spherically layered moon consistent with the very low frequency magnetic data collected on the lunar surface and by Explorer 35. In order to obtain good agreement with the lunar surface magnetometer observations, the inclusion of a void cavity behind the moon requires a conductivity at shallow depths higher than that of models having the solar wind impinging on all sides. By varying only the source parameters, a conductivity model can be found that yields a good fit to both the tangential response upstream and the radial response downstream. This model also satisfies the dark side tangential response in the frequency range above 0.006 Hz, but the few data points presently available below this range do not seem to agree with the theory.

Medium-term electric power demand forecasting based on economic-electricity transmission model

NASA Astrophysics Data System (ADS)

Li, Wenfeng; Bao, Fangmin; Bai, Hongkun; Liu, Wei; Liu, Yongmin; Mao, Yubin; Wang, Jiangbo; Liu, Junhui

2018-06-01

Electric demand forecasting is a basic work to ensure the safe operation of power system. Based on the theories of experimental economics and econometrics, this paper introduces Prognoz Platform 7.2 intelligent adaptive modeling platform, and constructs the economic electricity transmission model that considers the economic development scenarios and the dynamic adjustment of industrial structure to predict the region's annual electricity demand, and the accurate prediction of the whole society's electricity consumption is realized. Firstly, based on the theories of experimental economics and econometrics, this dissertation attempts to find the economic indicator variables that drive the most economical growth of electricity consumption and availability, and build an annual regional macroeconomic forecast model that takes into account the dynamic adjustment of industrial structure. Secondly, it innovatively put forward the economic electricity directed conduction theory and constructed the economic power transfer function to realize the group forecast of the primary industry + rural residents living electricity consumption, urban residents living electricity, the second industry electricity consumption, the tertiary industry electricity consumption; By comparing with the actual value of economy and electricity in Henan province in 2016, the validity of EETM model is proved, and the electricity consumption of the whole province from 2017 to 2018 is predicted finally.

Accurate modeling and inversion of electrical resistivity data in the presence of metallic infrastructure with known location and dimension

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

Johnson, Timothy C.; Wellman, Dawn M.

2015-06-26

Electrical resistivity tomography (ERT) has been widely used in environmental applications to study processes associated with subsurface contaminants and contaminant remediation. Anthropogenic alterations in subsurface electrical conductivity associated with contamination often originate from highly industrialized areas with significant amounts of buried metallic infrastructure. The deleterious influence of such infrastructure on imaging results generally limits the utility of ERT where it might otherwise prove useful for subsurface investigation and monitoring. In this manuscript we present a method of accurately modeling the effects of buried conductive infrastructure within the forward modeling algorithm, thereby removing them from the inversion results. The method ismore » implemented in parallel using immersed interface boundary conditions, whereby the global solution is reconstructed from a series of well-conditioned partial solutions. Forward modeling accuracy is demonstrated by comparison with analytic solutions. Synthetic imaging examples are used to investigate imaging capabilities within a subsurface containing electrically conductive buried tanks, transfer piping, and well casing, using both well casings and vertical electrode arrays as current sources and potential measurement electrodes. Results show that, although accurate infrastructure modeling removes the dominating influence of buried metallic features, the presence of metallic infrastructure degrades imaging resolution compared to standard ERT imaging. However, accurate imaging results may be obtained if electrodes are appropriately located.« less

Estimation of electric fields and current from ground-based magnetometer data

NASA Technical Reports Server (NTRS)

Kamide, Y.; Richmond, A. D.

1984-01-01

Recent advances in numerical algorithms for estimating ionospheric electric fields and currents from groundbased magnetometer data are reviewed and evaluated. Tests of the adequacy of one such algorithm in reproducing large-scale patterns of electrodynamic parameters in the high-latitude ionosphere have yielded generally positive results, at least for some simple cases. Some encouraging advances in producing realistic conductivity models, which are a critical input, are pointed out. When the algorithms are applied to extensive data sets, such as the ones from meridian chain magnetometer networks during the IMS, together with refined conductivity models, unique information on instantaneous electric field and current patterns can be obtained. Examples of electric potentials, ionospheric currents, field-aligned currents, and Joule heating distributions derived from ground magnetic data are presented. Possible directions for future improvements are also pointed out.

Absence of Disorder-Driven Metal-Insulator Transitions in Simple Holographic Models

NASA Astrophysics Data System (ADS)

Grozdanov, Sašo; Lucas, Andrew; Sachdev, Subir; Schalm, Koenraad

2015-11-01

We study electrical transport in a strongly coupled strange metal in two spatial dimensions at finite temperature and charge density, holographically dual to the Einstein-Maxwell theory in an asymptotically four-dimensional anti-de Sitter space spacetime, with arbitrary spatial inhomogeneity, up to mild assumptions including emergent isotropy. In condensed matter, these are candidate models for exotic strange metals without long-lived quasiparticles. We prove that the electrical conductivity is bounded from below by a universal minimal conductance: the quantum critical conductivity of a clean, charge-neutral plasma. Beyond nonperturbatively justifying mean-field approximations to disorder, our work demonstrates the practicality of new hydrodynamic insight into holographic transport.

A methodology to investigate the intrinsic effect of the pulsed electric current during the spark plasma sintering of electrically conductive powders

PubMed Central

Locci, Antonio Mario; Cincotti, Alberto; Todde, Sara; Orrù, Roberto; Cao, Giacomo

2010-01-01

A novel methodology is proposed for investigating the effect of the pulsed electric current during the spark plasma sintering (SPS) of electrically conductive powders without potential misinterpretation of experimental results. First, ensemble configurations (geometry, size and material of the powder sample, die, plunger and spacers) are identified where the electric current is forced to flow only through either the sample or the die, so that the sample is heated either through the Joule effect or by thermal conduction, respectively. These ensemble configurations are selected using a recently proposed mathematical model of an SPS apparatus, which, once suitably modified, makes it possible to carry out detailed electrical and thermal analysis. Next, SPS experiments are conducted using the ensemble configurations theoretically identified. Using aluminum powders as a case study, we find that the temporal profiles of sample shrinkage, which indicate densification behavior, as well as the final density of the sample are clearly different when the electric current flows only through the sample or through the die containing it, whereas the temperature cycle and mechanical load are the same in both cases. PMID:27877354

Evaluation on expansive performance of the expansive soil using electrical responses

NASA Astrophysics Data System (ADS)

Chu, Ya; Liu, Songyu; Bate, Bate; Xu, Lei

2018-01-01

Light structures, such as highways and railroads, built on expansive soils are prone to damages from the swelling of their underlain soil layers. Considerable amount of research has been conducted to characterize the swelling properties of expansive soils. Current swell characterization models, however, are limited by lack of standardized tests. Electrical methods are non-destructive, and are faster and less expensive than the traditional geotechnical methods. Therefore, geo-electrical methods are attractive for defining soil characteristics, including the swelling behavior. In this study, comprehensive laboratory experiments were undertaken to measure the free swelling and electrical resistivity of the mixtures of commercial kaolinite and bentonite. The electrical conductivity of kaolinite-bentonite mixtures was measured by a self-developed four-electrode soil resistivity box. Increasing the free swelling rate of the kaolinite-bentonite mixtures (0.72 to 1 of porosity of soils samples) led to a reduction in the electrical resistivity and an increase in conductivity. A unique relationship between free swelling rate and normalized surface conductivity was constructed for expensive soils by eliminating influences of porosity and m exponent. Therefore, electrical response measurement can be used to characterize the free swelling rate of expensive soils.

Finite element simulation of thunderstorm electrodynamics in the proximity of the storm

NASA Technical Reports Server (NTRS)

Baginski, Michael Edward

1988-01-01

Observations of electric fields, Maxwell current density, and air conductivity over thunderstorms were presented. The measurements were obtained using electric field mils and conductivity probes installed on a U2 aircraft as the aircraft passed approximately directly over an active thunderstorm at an altitude of 18 to 20 km. Accurate electrical observations of this type are rare and provide important information to those involved in numerically modeling a thunderstorm. A preliminary set of computer simulations based on this data were conducted and are described. The simulations show good agreement with measurements and are used to infer the thundercloud's charging current and amount of charge exchanged per flash.

Electrical Conductivity Mechanism in Unconventional Lead Vanadate Glasses

NASA Astrophysics Data System (ADS)

Abdel-Wahab, F.; Merazga, A.; Montaser, A. A.

2017-03-01

Lead vanadate glasses of the system (V2O5)_{1-x}(PbO)x with x = 0.4, 0.45, 0.5, 0.55, 0.6 have been prepared by the press-quenching technique. The dc (σ (0)) and ac (σ (ω )) electrical conductivities were measured in the temperature range from 150 to 420 K and the frequency range from 102 to 106 Hz. The electrical properties are shown to be sensitive to composition. The experimental results have been analyzed within the framework of different models. The dc conductivity is found to be proportional to Tp with the exponent p ranging from 8.2 to 9.8, suggesting that the transport is determined by a multi-phonon process of weak electron-lattice coupling. The ac conductivity is explained by the percolation path approximation (PPA). In this model, σ (ω ) is closely related to the σ (0) and fitting the experimental data produces a dielectric relaxation time τ in good agreement with the expected value in both magnitude and temperature dependence.

Heat transfer due to electroconvulsive therapy: Influence of anisotropic thermal and electrical skull conductivity.

PubMed

Menezes de Oliveira, Marilia; Wen, Peng; Ahfock, Tony

2016-09-01

This paper focuses on electroconvulsive therapy (ECT) and head models to investigate temperature profiles arising when anisotropic thermal and electrical conductivities are considered in the skull layer. The aim was to numerically investigate the threshold for which this therapy operates safely to the brain, from the thermal point of view. A six-layer spherical head model consisting of scalp, fat, skull, cerebro-spinal fluid, grey matter and white matter was developed. Later on, a realistic human head model was also implemented. These models were built up using the packages from COMSOL Inc. and Simpleware Ltd. In these models, three of the most common electrode montages used in ECT were applied. Anisotropic conductivities were derived using volume constraint and included in both spherical and realistic head models. The bio-heat transferring problem governed by Laplace equation was solved numerically. The results show that both the tensor eigenvalues of electrical conductivity and the electrode montage affect the maximum temperature, but thermal anisotropy does not have a significant influence. Temperature increases occur mainly in the scalp and fat, and no harm is caused to the brain by the current applied during ECT. The work assures the thermal safety of ECT and also provides a numerical method to investigate other non-invasive therapies. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Thermally Stimulated Currents in Nanocrystalline Titania

PubMed Central

Bruzzi, Mara; Mori, Riccardo; Baldi, Andrea; Cavallaro, Alessandro; Scaringella, Monica

2018-01-01

A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO2. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5–630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 1014–1018 cm−3, associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies. PMID:29303976

Thermally Stimulated Currents in Nanocrystalline Titania.

PubMed

Bruzzi, Mara; Mori, Riccardo; Baldi, Andrea; Carnevale, Ennio Antonio; Cavallaro, Alessandro; Scaringella, Monica

2018-01-05

A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO₂. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5-630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 10 14 -10 18 cm -3 , associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies.

Thermal Conductivity in Soil: Theoretical Approach by 3D Infinite Resistance Grid Model

NASA Astrophysics Data System (ADS)

Changjan, A.; Intaravicha, N.

2018-05-01

Thermal conductivity in soil was elementary characteristic of soil that conduct heat, measured in terms of Fourier’s Law for heat conduction and useful application in many fields: such as Utilizing underground cable for transmission and distribution systems, the rate of cooling of the cable depends on the thermal properties of the soil surrounding the cable. In this paper, we investigated thermal conductivity in soil by infinite three dimensions (3D) electrical resistance circuit concept. Infinite resistance grid 3D was the grid of resistors that extends to infinity in all directions. Model of thermal conductivity in soil of this research was generated from this concept: comparison between electrical resistance and thermal resistance in soil. Finally, we investigated the analytical form of thermal conductivity in soil which helpful for engineering and science students that could exhibit education with a principle of physics that applied to real situations.

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

Aldridge, David F.; Bartel, Lewis C.

Program LETS calculates the electric current distribution (in space and time) along an electrically energized steel-cased geologic borehole situated within the subsurface earth. The borehole is modeled as an electrical transmission line that “leaks” current into the surrounding geology. Parameters pertinent to the transmission line current calculation (i.e., series resistance and inductance, shunt capacitance and conductance) are obtained by sampling the electromagnetic (EM) properties of a three-dimensional (3D) geologic earth model along a (possibly deviated) well track.

Alternating-current conductivity and dielectric relaxation of bulk iodoargentate

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

Duan, Hai-Bao, E-mail: duanhaibao4660@163.com; Yu, Shan-Shan; Zhou, Hong

Graphical abstract: The electric modulus shows single dielectric relaxation process in the measured frequency range. - Highlights: • The conduction mechanism is described by quantum mechanical tunneling model. • The applications of dielectric modulus give a simple method for evaluating the activation energy of the dielectric relaxation. • The [Ag{sub 2}I{sub 4}]{sup 2−}1-D chain and [Cu(en){sub 2}]{sup 2+} cation column form the layered stacks by hydrogen bond interactions. - Abstract: An inorganic-organic hybrid compound Cu(en){sub 2}Ag{sub 2}I{sub 4} (en = ethylenediamine) (1) was synthesized and single crystal structurally characterized. Along the [001] direction, the inorganic parts form an infinite 1-Dmore » chain and [Cu(en){sub 2}]{sup 2+} cations are separated by inorganic chain. The electrical conductivity and dielectric properties of 1 have been investigated over wide ranges of frequency. The alternating-current conductivities have been fitted to the Almond–West type power law expression with use of a single value of S. It is found that S values for 1 are nearly temperature-independent, which indicates that the conduction mechanism could be quantum mechanical tunneling (QMT) model. The dielectric loss and electric modulus show single dielectric relaxation process. The activation energy obtained from temperature-dependent electric modulus compare with the calculated from the dc conductivity plots.« less

Structure-property relationships in an Al matrix Ca nanofilamentary composite conductor with potential application in high-voltage power transmission

NASA Astrophysics Data System (ADS)

Tian, Liang

This study investigated the processing-structure-properties relationships in an Al/Ca composites using both experiments and modeling/simulation. A particular focus of the project was understanding how the strength and electrical conductivity of the composite are related to its microstructure in the hope that a conducting material with light weight, high strength, and high electrical conductivity can be developed to produce overhead high-voltage power transmission cables. The current power transmission cables (e.g., Aluminum Conductor Steel Reinforced (ACSR)) have acceptable performance for high-voltage AC transmission, but are less well suited for high-voltage DC transmission due to the poorly conducting core materials that support the cable weight. This Al/Ca composite was produced by powder metallurgy and severe plastic deformation by extrusion and swaging. The fine Ca metal powders have been produced by centrifugal atomization with rotating liquid oil quench bath, and a detailed study about the atomization process and powder characteristics has been conducted. The microstructure of Al/Ca composite was characterized by electron microscopy. Microstructure changes at elevated temperature were characterized by thermal analysis and indirect resistivity tests. The strength and electrical conductivity were measured by tensile tests and four-point probe resistivity tests. Predicting the strength and electrical conductivity of the composite was done by micro-mechanics-based analytical modeling. Microstructure evolution was studied by mesoscale-thermodynamics-based phase field modeling and a preliminary atomistic molecular dynamics simulation. The application prospects of this composite was studied by an economic analysis. This study suggests that the Al/Ca (20 vol. %) composite shows promise for use as overhead power transmission cables. Further studies are needed to measure the corrosion resistance, fatigue properties and energized field performance of this composite.

Effect of electrical coupling on ionic current and synaptic potential measurements.

PubMed

Rabbah, Pascale; Golowasch, Jorge; Nadim, Farzan

2005-07-01

Recent studies have found electrical coupling to be more ubiquitous than previously thought, and coupling through gap junctions is known to play a crucial role in neuronal function and network output. In particular, current spread through gap junctions may affect the activation of voltage-dependent conductances as well as chemical synaptic release. Using voltage-clamp recordings of two strongly electrically coupled neurons of the lobster stomatogastric ganglion and conductance-based models of these neurons, we identified effects of electrical coupling on the measurement of leak and voltage-gated outward currents, as well as synaptic potentials. Experimental measurements showed that both leak and voltage-gated outward currents are recruited by gap junctions from neurons coupled to the clamped cell. Nevertheless, in spite of the strong coupling between these neurons, the errors made in estimating voltage-gated conductance parameters were relatively minor (<10%). Thus in many cases isolation of coupled neurons may not be required if a small degree of measurement error of the voltage-gated currents or the synaptic potentials is acceptable. Modeling results show, however, that such errors may be as high as 20% if the gap-junction position is near the recording site or as high as 90% when measuring smaller voltage-gated ionic currents. Paradoxically, improved space clamp increases the errors arising from electrical coupling because voltage control across gap junctions is poor for even the highest realistic coupling conductances. Furthermore, the common procedure of leak subtraction can add an extra error to the conductance measurement, the sign of which depends on the maximal conductance.

In situ measurements of contributions to the global electrical circuit by a thunderstorm in southeastern Brazil

USGS Publications Warehouse

Thomas, J.N.; Holzworth, R.H.; McCarthy, M.P.

2009-01-01

The global electrical circuit, which maintains a potential of about 280??kV between the earth and the ionosphere, is thought to be driven mainly by thunderstorms and lightning. However, very few in situ measurements of electrical current above thunderstorms have been successfully obtained. In this paper, we present dc to very low frequency electric fields and atmospheric conductivity measured in the stratosphere (30-35??km altitude) above an active thunderstorm in southeastern Brazil. From these measurements, we estimate the mean quasi-static conduction current during the storm period to be 2.5 ?? 1.25??A. Additionally, we examine the transient conduction currents following a large positive cloud-to-ground (+ CG) lightning flash and typical - CG flashes. We find that the majority of the total current is attributed to the quasi-static thundercloud charge, rather than lightning, which supports the classical Wilson model for the global electrical circuit.

Electrical properties of methane hydrate + sediment mixtures

USGS Publications Warehouse

Du Frane, Wyatt L.; Stern, Laura A.; Constable, Steven; Weitemeyer, Karen A.; Smith, Megan M; Roberts, Jeffery J.

2015-01-01

Knowledge of the electrical properties of multicomponent systems with gas hydrate, sediments, and pore water is needed to help relate electromagnetic (EM) measurements to specific gas hydrate concentration and distribution patterns in nature. Toward this goal, we built a pressure cell capable of measuring in situ electrical properties of multicomponent systems such that the effects of individual components and mixing relations can be assessed. We first established the temperature-dependent electrical conductivity (σ) of pure, single-phase methane hydrate to be ~5 orders of magnitude lower than seawater, a substantial contrast that can help differentiate hydrate deposits from significantly more conductive water-saturated sediments in EM field surveys. Here we report σ measurements of two-component systems in which methane hydrate is mixed with variable amounts of quartz sand or glass beads. Sand by itself has low σ but is found to increase the overall σ of mixtures with well-connected methane hydrate. Alternatively, the overall σ decreases when sand concentrations are high enough to cause gas hydrate to be poorly connected, indicating that hydrate grains provide the primary conduction path. Our measurements suggest that impurities from sand induce chemical interactions and/or doping effects that result in higher electrical conductivity with lower temperature dependence. These results can be used in the modeling of massive or two-phase gas-hydrate-bearing systems devoid of conductive pore water. Further experiments that include a free water phase are the necessary next steps toward developing complex models relevant to most natural systems.

Comment on `Electrical conductance of a sandstone partially saturated with varying concentrations of NaCl solutions' by R. Umezawa, N. Nishiyama, M. Katsura and S. Nakashima

NASA Astrophysics Data System (ADS)

Revil, André; Soueid Ahmed, Abdellahi

2017-11-01

Umezawa et al. investigated the dependence of the electrical conductivity of rocks with respect to the saturation of the water phase. Four issues can be underlined in their work: (1) The conductivity model they used mixes bulk and surface tortuosities in the same linear equation (i.e., between the conductivity and the conductivity of the pore water). This conflicts with the fact that the conductivity is a concave down increasing function of the pore water conductivity and bulk tortuosity is defined only at high salinity while surface tortuosity is defined only at very low salinity. (2) The specific surface conductance obtained by Umezawa et al. is too low and conflicts with independent evaluations obtained with double layer models for aluminosilicates and silicates. (3) The expression given for the resistivity index conflicts with the inclusion of a surface conductivity term in the conductivity equation.

Electrical measurements in the atmosphere and the Ionosphere over an active thunderstorm. II - Direct current electric fields and conductivity

NASA Technical Reports Server (NTRS)

Holzworth, R. H.; Kelley, M. C.; Siefring, C. L.; Hale, L. C.; Mitchell, J. D.

1985-01-01

On August 9, 1981, a series of three rockets was launched over an air mass thunderstorm off the eastern seaboard of Virginia while simultaneous stratospheric and ground-based electric field measurements were made. The conductivity was substantially lower at most altitudes than the conductivity profiles used by theoretical models. Direct current electric fields over 80 mV/m were measured as far away as 96 km from the storm in the stratosphere at 23 km altitude. No dc electric fields above 75 km altitude could be identified with the thunderstorm, in agreement with theory. However, vertical current densities over 120 pA/sq m were seen well above the classical 'electrosphere' (at 50 or 60 km). Frequent dc shifts in the electric field following lightning transients were seen by both balloon and rocket payloads. These dc shifts are clearly identifiable with either cloud-to-ground (increases) or intercloud (decreases) lightning flashes.

Enhanced thermoelectric efficiency via orthogonal electrical and thermal conductances in phosphorene.

PubMed

Fei, Ruixiang; Faghaninia, Alireza; Soklaski, Ryan; Yan, Jia-An; Lo, Cynthia; Yang, Li

2014-11-12

Thermoelectric devices that utilize the Seebeck effect convert heat flow into electrical energy and are highly desirable for the development of portable, solid state, passively powered electronic systems. The conversion efficiencies of such devices are quantified by the dimensionless thermoelectric figure of merit (ZT), which is proportional to the ratio of a device's electrical conductance to its thermal conductance. In this paper, a recently fabricated two-dimensional (2D) semiconductor called phosphorene (monolayer black phosphorus) is assessed for its thermoelectric capabilities. First-principles and model calculations reveal not only that phosphorene possesses a spatially anisotropic electrical conductance, but that its lattice thermal conductance exhibits a pronounced spatial-anisotropy as well. The prominent electrical and thermal conducting directions are orthogonal to one another, enhancing the ratio of these conductances. As a result, ZT may reach the criterion for commercial deployment along the armchair direction of phosphorene at T = 500 K and is close to 1 even at room temperature given moderate doping (∼2 × 10(16) m(-2) or 2 × 10(12) cm(-2)). Ultimately, phosphorene hopefully stands out as an environmentally sound thermoelectric material with unprecedented qualities. Intrinsically, it is a mechanically flexible material that converts heat energy with high efficiency at low temperatures (∼300 K), one whose performance does not require any sophisticated engineering techniques.

Dielectric behavior of beef meat in the 1-1500kHz range: Simulation with the Fricke/Cole-Cole model.

PubMed

Damez, Jean-Louis; Clerjon, Sylvie; Abouelkaram, Saïd; Lepetit, Jacques

2007-12-01

The electrical properties of biological tissues have been researched for many years. Impedance measurements observed with increasing frequencies are mainly attributed to changes in membrane conductivity and ion and charged-molecule mobility (mainly Na(+), K(+), CL(-) ions). Equivalent circuits with passive electrical components are frequently used as a support model for presentation and analyses of the behavior of tissues submitted to electrical fields. Fricke proposed an electrical model where the elements are resistive and capacitive. The model is composed of a resistive element (Rp) representing extracellular fluids (ECF) placed in parallel with a capacitive element (Cs) representing insulating membranes in series and a resistive element (Rs) representing intracellular fluids (ICF). This model is able to describe impedance measurements: at lower frequencies, most of the current flows around the cells without being able to penetrate them, while at higher frequencies the membranes lose their insulating properties and the current flows through both the extracellular and intracellular compartments. Since meat ageing induces structural change, particularly in membrane integrity, the insulating properties of membranes decrease, and intracellular and extracellular electrolytes mix, thus driving changes in their electrical properties. We report a method combining the Fricke and Cole-Cole models that was developed to monitor and explain tissues conductivity changes in preferential directions during beef meat ageing.

Three Dimensional Distribution of Sensitive Field and Stress Field Inversion of Force Sensitive Materials under Constant Current Excitation.

PubMed

Zhao, Shuanfeng; Liu, Min; Guo, Wei; Zhang, Chuanwei

2018-02-28

Force sensitive conductive composite materials are functional materials which can be used as the sensitive material of force sensors. However, the existing sensors only use one-dimensional electrical properties of force sensitive conductive materials. Even in tactile sensors, the measurement of contact pressure is achieved by large-scale arrays and the units of a large-scale array are also based on the one-dimensional electrical properties of force sensitive materials. The main contribution of this work is to study the three-dimensional electrical properties and the inversion method of three-dimensional stress field of a force sensitive material (conductive rubber), which pushes the application of force sensitive material from one dimensional to three-dimensional. First, the mathematical model of the conductive rubber current field distribution under a constant force is established by the effective medium theory, and the current field distribution model of conductive rubber with different geometry, conductive rubber content and conductive rubber relaxation parameters is deduced. Secondly, the inversion method of the three-dimensional stress field of conductive rubber is established, which provides a theoretical basis for the design of a new tactile sensor, three-dimensional stress field and space force based on force sensitive materials.

Monte Carlo simulations of electrical percolation in multicomponent thin films with nanofillers

NASA Astrophysics Data System (ADS)

Ni, Xiaojuan; Hui, Chao; Su, Ninghai; Jiang, Wei; Liu, Feng

2018-02-01

We developed a 2D disk-stick percolation model to investigate the electrical percolation behavior of an insulating thin film reinforced with 1D and 2D conductive nanofillers via Monte Carlo simulation. Numerical predictions of the percolation threshold in single component thin films showed good agreement with the previous published work, validating our model for investigating the characteristics of the percolation phenomena. Parametric studies of size effect, i.e., length of 1D nanofiller and diameter of 2D nanofiller, were carried out to predict the electrical percolation threshold for hybrid systems. The relationships between the nanofillers in two hybrid systems was established, which showed differences from previous linear assumption. The effective electrical conductance was evaluated through Kirchhoff’s current law by transforming it into a resistor network. The equivalent resistance was obtained from the distribution of nodal voltages by solving a system of linear equations with a Gaussian elimination method. We examined the effects of stick length, relative concentration, and contact patterns of 1D/2D inclusions on electrical performance. One novel aspect of our study is its ability to investigate the effective conductance of nanocomposites as a function of relative concentrations, which shows there is a synergistic effect when nanofillers with different dimensionalities combine properly. Our work provides an important theoretical basis for designing the conductive networks and predicting the percolation properties of multicomponent nanocomposites.

Conductivity and power factor enhancement of n-type semiconducting polymers using sodium silica gel dopant

NASA Astrophysics Data System (ADS)

Madan, Deepa; Zhao, Xingang; Ireland, Robert M.; Xiao, Derek; Katz, Howard E.

2017-08-01

This work demonstrates the use of sodium silica gel (Na-SG) particles as a reducing agent for n-type conjugated polymers to improve the conductivity and thermoelectric properties. Substantial increase in the electrical conductivity (σ, from 10-7 to 10-3 S/cm in air) was observed in two naphthalenetetracarboxylic diimide solution-processable n-type polymers, one of which was designed and synthesized in our lab. Systematic investigations of electrical conductivity were done by varying the weight percentage of Na-SG in the polymers. Additional evidence for the reduction process was obtained from electron spin resonance spectroscopy and control experiments involving nonreducing silica particles and non-electron-accepting polystyrene. The Seebeck coefficient S of the highest conductivity sample was measured and found to be in agreement with an empirical model. All the electrical conductivity and Seebeck coefficients measurements were performed in ambient atmosphere.

Electrical properties of polycrystalline olivine: evidence for grain boundary transport

NASA Astrophysics Data System (ADS)

Ten Grotenhuis, S. M.; Drury, M. R.; Peach, C. J.; Spiers, C. J.

2003-12-01

The physical and chemical properties of grain boundaries are known to play an important role in determining the electrical properties of polycrystalline oxides. Grain boundaries can either enhance conductivity if the transport of charge carriers along the grain boundaries is faster than through the lattice, or grain boundaries can reduce conductivity if the grain boundaries block the transport of charge carriers. The purpose of the experiments presented here is to deduce the mechanisms responsible for electrical conductivity in fine-grained forsterite, the Mg-end member of olivine, in order to get a better understanding of the contribution of grain boundary transport, of the properties of the grain boundaries, and to determine any relation between grain size and conductivity. A relationship between grain size and conductivity at high temperature could potentially be used to interpret zones of anomalous conductivity in the upper mantle. The materials studied consist of fine-grained forsterite (Mg2SiO4) with a minor amount (5%) of enstatite (MgSiO3) added. The electrical conductivity of three melt-free synthetic polycrystalline samples, with grain sizes between 1.1 and 4.7 mm, was measured at temperatures up to 1470° C. The complex impedance plots display one clear arc, indicating a single dominant conduction mechanism. Bulk conductivity is inversely proportional to the grain size of the different samples. This relation suggests that grain boundary diffusion of the charge carriers is controlling the electrical conductivity of the samples. The activation energy for diffusion of the charge carriers lies between 315 and 323 kJ/mol. This resembles previous data on grain boundary diffusion of Mg in forsterite and grain boundary diffusion creep. A geometrical model of less conducting cubic grains and more conducting grain boundaries agrees well with the experimental data. This model is applied to a natural mantle shear zone to predict the conductivity contrast between fine-grained shear zones and less deformed regions in the lithosphere. Upper mantle shear zones are predicted to have 1.5 to 2 orders of magnitude higher conductivity than less deformed regions in the lithosphere. This may mean that fine-grained shear zones can be detected using magnetotelluric methods.

Electrical conduction in PVDF/ZnO-Ag nanocomposites

NASA Astrophysics Data System (ADS)

Singh, Utpal; Jha, Anal K.; Chandra, K. P.; Kolte, Jayant; Kulkarni, A. R.; Prasad, K.

2018-05-01

A hybrid combination of Ag and ZnO nanoparticles were utilized to fabricate PVDF/ZnO(90/10)-Ag nanocomposites (with Ag as filler: 0.5, 1 and 1.5%) utilizing melt-mixing technique. X-ray diffraction study confirmed the formations of nanocomposites. Electric modulus analysis indicated the dielectric relaxation in this system to be of non- Debye type. Correlated barrier hopping model successfully explained the charge conduction in PVDF/ZnO-Ag nanocomposites and ac conductivity data followed Jonscher's power law.

Measurements and models of electric fields in the in vivo human brain during transcranial electric stimulation

PubMed Central

Huang, Yu; Liu, Anli A; Lafon, Belen; Friedman, Daniel; Dayan, Michael; Wang, Xiuyuan; Bikson, Marom; Doyle, Werner K; Devinsky, Orrin; Parra, Lucas C

2017-01-01

Transcranial electric stimulation aims to stimulate the brain by applying weak electrical currents at the scalp. However, the magnitude and spatial distribution of electric fields in the human brain are unknown. We measured electric potentials intracranially in ten epilepsy patients and estimated electric fields across the entire brain by leveraging calibrated current-flow models. When stimulating at 2 mA, cortical electric fields reach 0.8 V/m, the lower limit of effectiveness in animal studies. When individual whole-head anatomy is considered, the predicted electric field magnitudes correlate with the recorded values in cortical (r = 0.86) and depth (r = 0.88) electrodes. Accurate models require adjustment of tissue conductivity values reported in the literature, but accuracy is not improved when incorporating white matter anisotropy or different skull compartments. This is the first study to validate and calibrate current-flow models with in vivo intracranial recordings in humans, providing a solid foundation to target stimulation and interpret clinical trials. DOI: http://dx.doi.org/10.7554/eLife.18834.001 PMID:28169833

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

Nishi, Shohei; Taguchi, Dai; Manaka, Takaaki

By using electric-field-induced optical second-harmonic generation measurement coupled with the conventional current-voltage (I-V) measurement, we studied the carrier transport of organic double-layer diodes with a Au/pentacene/fluorine polymer (FP)/indium zinc oxide (IZO) structure. The rectifying I-V characteristics were converted into the I-E characteristics of the FP and pentacene layers. Results suggest a model in which Schottky-type electron injection from the IZO electrode to the FP layer governs the forward electrical conduction (V > 0), where the space charge electric field produced in the FP layer by accumulated holes at the pentacene/FP interface makes a significant contribution. On the other hand, Schottky-type injection bymore » accumulated interface electrons from the pentacene layer to the FP layer governs the backward electrical conduction (V < 0). The electroluminescence generated from the pentacene layer in the region V > 0 verifies the electron transport across the FP layer, and supports the above suggested model.« less

Experimental investigations, modeling, and analyses of high-temperature devices for space applications: Part 1. Final report, June 1996--December 1998

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

Tournier, J.; El-Genk, M.S.; Huang, L.

1999-01-01

The Institute of Space and Nuclear Power Studies at the University of New Mexico has developed a computer simulation of cylindrical geometry alkali metal thermal-to-electric converter cells using a standard Fortran 77 computer code. The objective and use of this code was to compare the experimental measurements with computer simulations, upgrade the model as appropriate, and conduct investigations of various methods to improve the design and performance of the devices for improved efficiency, durability, and longer operational lifetime. The Institute of Space and Nuclear Power Studies participated in vacuum testing of PX series alkali metal thermal-to-electric converter cells and developedmore » the alkali metal thermal-to-electric converter Performance Evaluation and Analysis Model. This computer model consisted of a sodium pressure loss model, a cell electrochemical and electric model, and a radiation/conduction heat transfer model. The code closely predicted the operation and performance of a wide variety of PX series cells which led to suggestions for improvements to both lifetime and performance. The code provides valuable insight into the operation of the cell, predicts parameters of components within the cell, and is a useful tool for predicting both the transient and steady state performance of systems of cells.« less

Experimental investigations, modeling, and analyses of high-temperature devices for space applications: Part 2. Final report, June 1996--December 1998

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

Tournier, J.; El-Genk, M.S.; Huang, L.

1999-01-01

The Institute of Space and Nuclear Power Studies at the University of New Mexico has developed a computer simulation of cylindrical geometry alkali metal thermal-to-electric converter cells using a standard Fortran 77 computer code. The objective and use of this code was to compare the experimental measurements with computer simulations, upgrade the model as appropriate, and conduct investigations of various methods to improve the design and performance of the devices for improved efficiency, durability, and longer operational lifetime. The Institute of Space and Nuclear Power Studies participated in vacuum testing of PX series alkali metal thermal-to-electric converter cells and developedmore » the alkali metal thermal-to-electric converter Performance Evaluation and Analysis Model. This computer model consisted of a sodium pressure loss model, a cell electrochemical and electric model, and a radiation/conduction heat transfer model. The code closely predicted the operation and performance of a wide variety of PX series cells which led to suggestions for improvements to both lifetime and performance. The code provides valuable insight into the operation of the cell, predicts parameters of components within the cell, and is a useful tool for predicting both the transient and steady state performance of systems of cells.« less

Mathematical model of depolarization mechanism of conducted vasoreactivity

NASA Astrophysics Data System (ADS)

Neganova, Anastasiia Y.; Stiukhina, Elena S.; Postnov, Dmitry E.

2015-03-01

We address the problem of conducted vasodilation, the phenomenon which is also known as functional hyperemia. Specifically, we test the mechanism of nondecremental propagation of electric signals along endothelial cell layer recently hypothesized by Figueroa et al. By means of functional modeling we focus on possible nonlinear mechanisms that can underlie such regenerative pulse transmission (RPT). Since endothelial cells (EC) are generally known as electrically inexcitable, the possible role of ECs in RPT mechanisms is not evident. By means of mathematical modeling we check the dynamical self-consistency of Figueroa's hypothesis, as well as estimate the possible contribution of specific ionic currents to the suggested RPT mechanism.

Acoustic Source Analysis of Magnetoacoustic Tomography With Magnetic Induction for Conductivity Gradual-Varying Tissues.

PubMed

Wang, Jiawei; Zhou, Yuqi; Sun, Xiaodong; Ma, Qingyu; Zhang, Dong

2016-04-01

As a multiphysics imaging approach, magnetoacoustic tomography with magnetic induction (MAT-MI) works on the physical mechanism of magnetic excitation, acoustic vibration, and transmission. Based on the theoretical analysis of the source vibration, numerical studies are conducted to simulate the pathological changes of tissues for a single-layer cylindrical conductivity gradual-varying model and estimate the strengths of sources inside the model. The results suggest that the inner source is generated by the product of the conductivity and the curl of the induced electric intensity inside conductivity homogeneous medium, while the boundary source is produced by the cross product of the gradient of conductivity and the induced electric intensity at conductivity boundary. For a biological tissue with low conductivity, the strength of boundary source is much higher than that of the inner source only when the size of conductivity transition zone is small. In this case, the tissue can be treated as a conductivity abrupt-varying model, ignoring the influence of inner source. Otherwise, the contributions of inner and boundary sources should be evaluated together quantitatively. This study provide basis for further study of precise image reconstruction of MAT-MI for pathological tissues.

Physical Properties of Fractured Porous Media

NASA Astrophysics Data System (ADS)

Mohammed, T. E.; Schmitt, D. R.

2015-12-01

The effect of fractures on the physical properties of porous media is of considerable interest to oil and gas exploration as well as enhanced geothermal systems and carbon capture and storage. This work represents an attempt to study the effect fractures have on multiple physical properties of rocks. An experimental technique to make simultaneous electric and ultrasonic measurements on cylindrical core plugs is developed. Aluminum end caps are mounted with ultrasonic transducers to transmit pules along the axis of the cylinder while non-polarizing electrodes are mounted on the sides of the core to make complex conductivity measurements perpendicular to the cylinder axis. Electrical measurements are made by applying a sinusoidal voltage across the measurement circuit that consist of a resister and the sample in series. The magnitude and phase of the signal across the sample is recorded relative to the input signal across a range of frequencies. Synthetic rock analogs are constructed using sintered glass beads with fractures imbedded in them. The fracture location, size and orientation are controlled and each fractured specimen has an unfractured counterpart. Porosity, Permeability, electrical conductivity and ultrasonic velocity measurements are conducted on each sample with the complex electrical conductivities recorded at frequencies from 10hz to 1 Mhz. These measurements allow us to examine the changes induced by these mesoscale fractures on the embedding porous medium. Of particular interest is the effect of fracture orientation on electrical conductivity of the rock. Seismic anisotropy caused by fractures is a well understood phenomenon with many rock physics models dedicated to its understanding. The effect of fractures on electrical conductivity is less well understood with electrical anisotropy scarcely investigated in the literature. None the less, using electrical conductivity to characterize fractures can add an extra constraint to characterization based on seismic response. As well, the formal similarity between electrical conductivity and permeability can be utilized to help optimize injection and production strategies.

Polypyrrole-chitosan conductive biomaterial synchronizes cardiomyocyte contraction and improves myocardial electrical impulse propagation.

PubMed

Cui, Zhi; Ni, Nathan C; Wu, Jun; Du, Guo-Qing; He, Sheng; Yau, Terrence M; Weisel, Richard D; Sung, Hsing-Wen; Li, Ren-Ke

2018-01-01

Background: The post-myocardial infarction (MI) scar interrupts electrical impulse propagation and delays regional contraction, which contributes to ventricular dysfunction. We investigated the potential of an injectable conductive biomaterial to restore scar tissue conductivity and re-establish synchronous ventricular contraction. Methods: A conductive biomaterial was generated by conjugating conductive polypyrrole (PPY) onto chitosan (CHI) backbones. Trypan blue staining of neonatal rat cardiomyocytes (CMs) cultured on biomaterials was used to evaluate the biocompatibility of the conductive biomaterials. Ca 2+ imaging was used to visualize beating CMs. A cryoablation injury rat model was used to investigate the ability of PPY:CHI to improve cardiac electrical propagation in the injured heart in vivo . Electromyography was used to evaluate conductivity of scar tissue ex vivo . Results: Cell survival and morphology were similar between cells cultured on biomaterials-coated and uncoated-control dishes. PPY:CHI established synchronous contraction of two distinct clusters of spontaneously-beating CMs. Intramyocardial PPY:CHI injection into the cryoablation-induced injured region improved electrical impulse propagation across the scarred tissue and decreased the QRS interval, whereas saline- or CHI-injected hearts continued to have delayed propagation patterns and significantly reduced conduction velocity compared to healthy controls. Ex vivo evaluation found that scar tissue from PPY:CHI-treated rat hearts had higher signal amplitude compared to those from saline- or CHI-treated rat heart tissue. Conclusions: The PPY:CHI biomaterial is electrically conductive, biocompatible and injectable. It improved synchronous contraction between physically separated beating CM clusters in vitro . Intra-myocardial injection of PPY:CHI following cardiac injury improved electrical impulse propagation of scar tissue in vivo .

Influence of the ordering of impurities on the appearance of an energy gap and on the electrical conductance of graphene.

PubMed

Repetsky, S P; Vyshyvana, I G; Kruchinin, S P; Bellucci, Stefano

2018-06-14

In the one-band model of strong coupling, the influence of substitutional impurity atoms on the energy spectrum and electrical conductance of graphene is studied. It is established that the ordering of substitutional impurity atoms on nodes of the crystal lattice causes the appearance of a gap in the energy spectrum of graphene with width η|δ| centered at the point yδ, where η is the parameter of ordering, δ is the difference of the scattering potentials of impurity atoms and carbon atoms, and y is the impurity concentration. The maximum value of the parameter of ordering is [Formula: see text]. For the complete ordering of impurity atoms, the energy gap width equals [Formula: see text]. If the Fermi level falls in the region of the mentioned gap, then the electrical conductance [Formula: see text] at the ordering of graphene, i.e., the metal-dielectric transition arises. If the Fermi level is located outside the gap, then the electrical conductance increases with the parameter of order η by the relation [Formula: see text]. At the concentration [Formula: see text], as the ordering of impurity atoms η →1, the electrical conductance of graphene [Formula: see text], i.e., the transition of graphene in the state of ideal electrical conductance arises.

The role of skin conductivity in a low frequency exposure assessment for peripheral nerve tissue according to the ICNIRP 2010 guidelines

NASA Astrophysics Data System (ADS)

Schmid, Gernot; Cecil, Stefan; Überbacher, Richard

2013-07-01

Based on numerical computations using commercially available finite difference time domain code and a state-of-the art anatomical model of a 5-year old child, the influence of skin conductivity on the induced electric field strength inside the tissue for homogeneous front-to-back magnetic field exposure and homogeneous vertical electric field exposure was computed. Both ungrounded as well as grounded conditions of the body model were considered. For electric field strengths induced inside CNS tissue the impact of skin conductivity was found to be less than 15%. However, the results demonstrated that the use of skin conductivity values as obtainable from the most widely used data base of dielectric tissue properties and recommended by safety standards are not suitable for exposure assessment with respect to peripheral nerve tissue according to the ICNIRP 2010 guidelines in which the use of the induced electric field strengths inside the skin is suggested as a conservative surrogate for peripheral nerve exposure. This is due to the fact that the skin conductivity values derived from these data bases refer to the stratum corneum, the uppermost layer of the skin, which does not contain any nerve or receptor cells to be protected from stimulation effects. Using these skin conductivity values which are approximately a factor 250-500 lower than skin conductivity values used in studies on which the ICNIRP 2010 guidelines are based on, may lead to overestimations of the induced electric field strengths inside the skin by substantially more than a factor of 10. However, reliable conductivity data of deeper skin layers where nerve and preceptor cells are located is very limited. It is therefore recommended to include appropriate background information in the ICNIRP guidelines and the dielectric tissue property databases, and to put some emphasis on a detailed layer-specific characterization of skin conductivity in near future.

Formulation of advanced consumables management models: Executive summary. [modeling spacecraft environmental control, life support, and electric power supply systems

NASA Technical Reports Server (NTRS)

Daly, J. K.; Torian, J. G.

1979-01-01

An overview of studies conducted to establish the requirements for advanced subsystem analytical tools is presented. Modifications are defined for updating current computer programs used to analyze environmental control, life support, and electric power supply systems so that consumables for future advanced spacecraft may be managed.

Streamer discharges as advancing imperfect conductors: inhomogeneities in long ionized channels

NASA Astrophysics Data System (ADS)

Luque, A.; González, M.; Gordillo-Vázquez, F. J.

2017-12-01

A major obstacle for the understanding of long electrical discharges is the complex dynamics of streamer coronas, formed by many thin conducting filaments. Building macroscopic models for these filaments is one approach to attain a deeper knowledge of the discharge corona. Here, we present a one-dimensional, macroscopic model of a propagating streamer channel with a finite and evolving internal conductivity. We represent the streamer as an advancing finite-conductivity channel with a surface charge density at its boundary. This charge evolves self-consistently due to the electric current that flows through the streamer body and within a thin layer at its surface. We couple this electrodynamic evolution with a field-dependent set of chemical reactions that determine the internal channel conductivity. With this one-dimensional model, we investigate the formation of persisting structures in the wake of a streamer head. In accordance with experimental observations, our model shows that a within a streamer channel some regions are driven towards high fields that can be maintaned for tens of nanoseconds.

Electrical Properties of Bismuth/Lithium-Cosubstituted Strontium Titanate Ceramics

NASA Astrophysics Data System (ADS)

Alkathy, Mahmoud. S.; James Raju, K. C.

2018-03-01

Sr(1-x)(Bi,Li) x TiO3 compound was prepared via a solid-state reaction route with microwave heating of the starting materials. X-ray diffraction analysis revealed pure perovskite phase without formation of any secondary phases. The electrical conductivity was studied as a function of temperature and frequency. The experimental results indicate that the alternating-current (AC) conductivity increased with frequency, following the Jonscher power law. To interpret the possible mechanism for electrical conduction, the correlated barrier hopping model was applied. The effect of temperature and the Bi/Li concentration on the electrical resistivity was studied. The results showed that the electrical resistivity decreased with increasing temperature, which could be due to increased thermal energy of electrons. Also, the electrical resistivity decreased with increase in the amount of Bi and Li, which could be due to increased concentration of structural defects, which could increase the number of either electrons or holes available for conduction. A single semicircular arc corresponding to a single relaxation process was observed for all the investigated ceramics, suggesting a grain contribution to the total resistance in these materials. Arrhenius plots were used to obtain the activation energy for the samples.

Electrical Properties of Bismuth/Lithium-Cosubstituted Strontium Titanate Ceramics

NASA Astrophysics Data System (ADS)

Alkathy, Mahmoud. S.; James Raju, K. C.

2018-07-01

Sr(1- x)(Bi,Li) x TiO3 compound was prepared via a solid-state reaction route with microwave heating of the starting materials. X-ray diffraction analysis revealed pure perovskite phase without formation of any secondary phases. The electrical conductivity was studied as a function of temperature and frequency. The experimental results indicate that the alternating-current (AC) conductivity increased with frequency, following the Jonscher power law. To interpret the possible mechanism for electrical conduction, the correlated barrier hopping model was applied. The effect of temperature and the Bi/Li concentration on the electrical resistivity was studied. The results showed that the electrical resistivity decreased with increasing temperature, which could be due to increased thermal energy of electrons. Also, the electrical resistivity decreased with increase in the amount of Bi and Li, which could be due to increased concentration of structural defects, which could increase the number of either electrons or holes available for conduction. A single semicircular arc corresponding to a single relaxation process was observed for all the investigated ceramics, suggesting a grain contribution to the total resistance in these materials. Arrhenius plots were used to obtain the activation energy for the samples.

Disordered Nuclear Pasta, Magnetic Field Decay, and Crust Cooling in Neutron Stars

NASA Astrophysics Data System (ADS)

Horowitz, C. J.; Berry, D. K.; Briggs, C. M.; Caplan, M. E.; Cumming, A.; Schneider, A. S.

2015-01-01

Nuclear pasta, with nonspherical shapes, is expected near the base of the crust in neutron stars. Large-scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low-conductivity pasta layer by increasing an impurity parameter Qimp . Predictions of light curves for the low-mass x-ray binary MXB 1659-29, assuming a large Qimp, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore, observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust).

Disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars.

PubMed

Horowitz, C J; Berry, D K; Briggs, C M; Caplan, M E; Cumming, A; Schneider, A S

2015-01-23

Nuclear pasta, with nonspherical shapes, is expected near the base of the crust in neutron stars. Large-scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low-conductivity pasta layer by increasing an impurity parameter Q_{imp}. Predictions of light curves for the low-mass x-ray binary MXB 1659-29, assuming a large Q_{imp}, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore, observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust).

Numerical modelling of processes that occur in the selective waste disassembly installation

NASA Astrophysics Data System (ADS)

Cherecheş, T.; Lixandru, P.; Dragnea, D.; Cherecheş, D. M.

2017-08-01

This paper is the result of the attempts of quantitative approach of some of the processes that are occurring in the selective fragmentation with high voltage pulses installation. It has been formulated a methodology which customizes the general methods for the issue of transient electric field in mixed environments. The electromagnetic processes inside the fragmentation installation, the initiation and formation of the discharge channels, the thermodynamic and mechanical effects in the process vessel are complex, transient and very quick. One of the underlying principles of the fragmentation process consists in the differentiated reaction of materials in an electric field. Generally in the process vessel there can be found together three types of materials: dielectrics, metal, electrolytes. The conductivity of dielectric materials is virtually zero. Metallic materials conduct very well through electronic conductivity. Electrolytes have a more modest conductivity since they conduct through electrochemical processes. The electrical current, in this case, is the movement of ions having sizes and the masses different from the electrons. Here, the electric current includes displacements of ions and molecules, collisions and chemical reactions. Part of the electrical field’s energy is absorbed by the electrolyte in the form of mechanical and chemical energy.

On the value of incorporating spatial statistics in large-scale geophysical inversions: the SABRe case

NASA Astrophysics Data System (ADS)

Kokkinaki, A.; Sleep, B. E.; Chambers, J. E.; Cirpka, O. A.; Nowak, W.

2010-12-01

Electrical Resistance Tomography (ERT) is a popular method for investigating subsurface heterogeneity. The method relies on measuring electrical potential differences and obtaining, through inverse modeling, the underlying electrical conductivity field, which can be related to hydraulic conductivities. The quality of site characterization strongly depends on the utilized inversion technique. Standard ERT inversion methods, though highly computationally efficient, do not consider spatial correlation of soil properties; as a result, they often underestimate the spatial variability observed in earth materials, thereby producing unrealistic subsurface models. Also, these methods do not quantify the uncertainty of the estimated properties, thus limiting their use in subsequent investigations. Geostatistical inverse methods can be used to overcome both these limitations; however, they are computationally expensive, which has hindered their wide use in practice. In this work, we compare a standard Gauss-Newton smoothness constrained least squares inversion method against the quasi-linear geostatistical approach using the three-dimensional ERT dataset of the SABRe (Source Area Bioremediation) project. The two methods are evaluated for their ability to: a) produce physically realistic electrical conductivity fields that agree with the wide range of data available for the SABRe site while being computationally efficient, and b) provide information on the spatial statistics of other parameters of interest, such as hydraulic conductivity. To explore the trade-off between inversion quality and computational efficiency, we also employ a 2.5-D forward model with corrections for boundary conditions and source singularities. The 2.5-D model accelerates the 3-D geostatistical inversion method. New adjoint equations are developed for the 2.5-D forward model for the efficient calculation of sensitivities. Our work shows that spatial statistics can be incorporated in large-scale ERT inversions to improve the inversion results without making them computationally prohibitive.

A Technique for Estimating the Surface Conductivity of Single Molecules

NASA Astrophysics Data System (ADS)

Bau, Haim; Arsenault, Mark; Zhao, Hui; Purohit, Prashant; Goldman, Yale

2007-11-01

When an AC electric field at 2MHz was applied across a small gap between two metal electrodes elevated above a surface, rhodamine-phalloidin-labeled actin filaments were attracted to the gap and became suspended between the two electrodes. The variance of each filament's horizontal, lateral displacement was measured as a function of electric field intensity and position along the filament. The variance significantly decreased as the electric field intensity increased. Hypothesizing that the electric field induces electroosmotic flow around the filament that, in turn, induces drag on the filament, which appears as effective tension, we estimated the tension using a linear, Brownian dynamic model. Based on the tension, we estimated the filament's surface conductivity. Our experimental method provides a novel means for trapping and manipulating biological filaments and for probing the surface conductance and mechanical properties of single polymers.

Changes in geophysical properties caused by fluid injection into porous rocks: analytical models: Geophysical changes in porous rocks

DOE PAGES

Pride, Steven R.; Berryman, James G.; Commer, Michael; ...

2016-08-30

Analytical models are provided that describe how the elastic compliance, electrical conductivity, and fluid-flow permeability of rocks depend on stress and fluid pressure. In order to explain published laboratory data on how seismic velocities and electrical conductivity vary in sandstones and granites, the models require a population of cracks to be present in a possibly porous host phase. The central objective is to obtain a consistent mean-field analytical model that shows how each modeled rock property depends on the nature of the crack population. We describe the crack populations by a crack density, a probability distribution for the crack aperturesmore » and radii, and the averaged orientation of the cracks. The possibly anisotropic nature of the elasticity, conductivity, and permeability tensors is allowed for; however, only the isotropic limit is used when comparing to laboratory data. For the transport properties of conductivity and permeability, the percolation effect of the crack population linking up to form a connected path across a sample is modeled. But, this effect is important only in crystalline rock where the host phase has very small conductivity and permeability. In general, the importance of the crack population to the transport properties increases as the host phase becomes less conductive and less permeable.« less

Changes in geophysical properties caused by fluid injection into porous rocks: analytical models: Geophysical changes in porous rocks

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

Pride, Steven R.; Berryman, James G.; Commer, Michael

Analytical models are provided that describe how the elastic compliance, electrical conductivity, and fluid-flow permeability of rocks depend on stress and fluid pressure. In order to explain published laboratory data on how seismic velocities and electrical conductivity vary in sandstones and granites, the models require a population of cracks to be present in a possibly porous host phase. The central objective is to obtain a consistent mean-field analytical model that shows how each modeled rock property depends on the nature of the crack population. We describe the crack populations by a crack density, a probability distribution for the crack aperturesmore » and radii, and the averaged orientation of the cracks. The possibly anisotropic nature of the elasticity, conductivity, and permeability tensors is allowed for; however, only the isotropic limit is used when comparing to laboratory data. For the transport properties of conductivity and permeability, the percolation effect of the crack population linking up to form a connected path across a sample is modeled. But, this effect is important only in crystalline rock where the host phase has very small conductivity and permeability. In general, the importance of the crack population to the transport properties increases as the host phase becomes less conductive and less permeable.« less

Implications of Using the CASTLE Model.

ERIC Educational Resources Information Center

Mosca, Eugene P.; De Jong, Marvin L.

1993-01-01

Critiques the Capacitor-Aided System for Teaching and Learning Electricity (CASTLE) curriculum. Criticism is made of the model's use of a compressible-fluid model to demonstrate charge conduction. An alternative model is proposed. (ZWH)

Subsurface imaging of water electrical conductivity, hydraulic permeability and lithology at contaminated sites by induced polarization

NASA Astrophysics Data System (ADS)

Maurya, P. K.; Balbarini, N.; Møller, I.; Rønde, V.; Christiansen, A. V.; Bjerg, P. L.; Auken, E.; Fiandaca, G.

2018-05-01

At contaminated sites, knowledge about geology and hydraulic properties of the subsurface and extent of the contamination is needed for assessing the risk and for designing potential site remediation. In this study, we have developed a new approach for characterizing contaminated sites through time-domain spectral induced polarization. The new approach is based on: (1) spectral inversion of the induced polarization data through a reparametrization of the Cole-Cole model, which disentangles the electrolytic bulk conductivity from the surface conductivity for delineating the contamination plume; (2) estimation of hydraulic permeability directly from the inverted parameters using a laboratory-derived empirical equation without any calibration; (3) the use of the geophysical imaging results for supporting the geological modelling and planning of drilling campaigns. The new approach was tested on a data set from the Grindsted stream (Denmark), where contaminated groundwater from a factory site discharges to the stream. Two overlapping areas were covered with seven parallel 2-D profiles each, one large area of 410 m × 90 m (5 m electrode spacing) and one detailed area of 126 m × 42 m (2 m electrode spacing). The geophysical results were complemented and validated by an extensive set of hydrologic and geologic information, including 94 estimates of hydraulic permeability obtained from slug tests and grain size analyses, 89 measurements of water electrical conductivity in groundwater, and four geological logs. On average the IP-derived and measured permeability values agreed within one order of magnitude, except for those close to boundaries between lithological layers (e.g. between sand and clay), where mismatches occurred due to the lack of vertical resolution in the geophysical imaging. An average formation factor was estimated from the correlation between the imaged bulk conductivity values and the water conductivity values measured in groundwater, in order to convert the imaging results from bulk conductivity to water conductivity. The geophysical models were actively used for supporting the geological modelling and the imaging of hydraulic permeability and water conductivity allowed for a better discrimination of the clay/lignite lithology from the pore water conductivity. Furthermore, high water electrical conductivity values were found in a deep confined aquifer, which is separated by a low-permeability clay layer from a shallow aquifer. No contamination was expected in this part of the confined aquifer, and confirmation wells were drilled in the zone of increased water electrical conductivity derived from the geophysical results. Water samples from the new wells showed elevated concentrations of inorganic compounds responsible for the increased water electrical conductivity in the confined aquifer and high concentrations of xenobiotic organic contaminants such as chlorinated ethenes, sulfonamides and barbiturates.

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

NASA Astrophysics Data System (ADS)

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

2018-06-01

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

Joint inversion of satellite-detected tidal and magnetospheric signals constrains electrical conductivity and water content of the upper mantle and transition zone.

PubMed

Grayver, A V; Munch, F D; Kuvshinov, A V; Khan, A; Sabaka, T J; Tøffner-Clausen, L

2017-06-28

We present a new global electrical conductivity model of Earth's mantle. The model was derived by using a novel methodology, which is based on inverting satellite magnetic field measurements from different sources simultaneously. Specifically, we estimated responses of magnetospheric origin and ocean tidal magnetic signals from the most recent Swarm and CHAMP data. The challenging task of properly accounting for the ocean effect in the data was addressed through full three-dimensional solution of Maxwell's equations. We show that simultaneous inversion of magnetospheric and tidal magnetic signals results in a model with much improved resolution. Comparison with laboratory-based conductivity profiles shows that obtained models are compatible with a pyrolytic composition and a water content of 0.01 wt% and 0.1 wt% in the upper mantle and transition zone, respectively.

Response of larval sea lampreys (Petromyzon marinus) to pulsed DC electrical stimuli in laboratory experiments

USGS Publications Warehouse

Bowen, Anjanette K.; Weisser, John W.; Bergstedt, Roger A.; Famoye, Felix

2003-01-01

Four electrical factors that are used in pulsed DC electrofishing for larval sea lampreys (Petromyzon marinus) were evaluated in two laboratory studies to determine the optimal values to induce larval emergence over a range of water temperatures and conductivities. Burrowed larvae were exposed to combinations of pulsed DC electrical factors including five pulse frequencies, three pulse patterns, and two levels of duty cycle over a range of seven voltage gradients in two separate studies conducted at water temperatures of 10, 15, and 20°C and water conductivities of 25, 200, and 900 μS/cm. A four-way analysis of variance was used to determine significant (α = 0.05) influences of each electrical factor on larval emergence. Multiple comparison tests with Bonferroni adjustments were used to determine which values of each factor resulted in significantly higher emergence at each temperature and conductivity. Voltage gradient and pulse frequency significantly affected emergence according to the ANOVA model at each temperature and conductivity tested. Duty cycle and pulse pattern generally did not significantly influence the model. Findings suggest that a setting of 2.0 V/cm, 3 pulses/sec, 10% duty, and 2:2 pulse pattern seems the most promising in waters of medium conductivity and across a variety of temperatures. This information provides a basis for understanding larval response to pulsed DC electrofishing gear factors and identifies electrofisher settings that show promise to increase the efficiency of the gear during assessments for burrowed sea lamprey larvae.

Nanosecond Plasma Enhanced H2/O2/N2 Premixed Flat Flames

DTIC Science & Technology

2014-01-01

Simulations are conducted with a one-dimensional, multi-scale, pulsed -discharge model with detailed plasma-combustion kinetics to develop additional insight... model framework. The reduced electric field, E/N, during each pulse varies inversely with number density. A significant portion of the input energy is...dimensional numerical model [4, 12] capable of resolving electric field transients over nanosecond timescales (during each discharge pulse ) and radical

Electrical properties of methane hydrate + sediment mixtures: The σ of CH 4 Hydrate + Sediment

DOE PAGES

Du Frane, Wyatt L.; Stern, Laura A.; Constable, Steven; ...

2015-07-30

Knowledge of the electrical properties of multicomponent systems with gas hydrate, sediments, and pore water is needed to help relate electromagnetic (EM) measurements to specific gas hydrate concentration and distribution patterns in nature. We built a pressure cell capable of measuring in situ electrical properties of multicomponent systems such that the effects of individual components and mixing relations can be assessed. We first established the temperature-dependent electrical conductivity (σ) of pure, single-phase methane hydrate to be ~5 orders of magnitude lower than seawater, a substantial contrast that can help differentiate hydrate deposits from significantly more conductive water-saturated sediments in EMmore » field surveys. We report σ measurements of two-component systems in which methane hydrate is mixed with variable amounts of quartz sand or glass beads. Sand by itself has low σ but is found to increase the overall σ of mixtures with well-connected methane hydrate. Alternatively, the overall σ decreases when sand concentrations are high enough to cause gas hydrate to be poorly connected, indicating that hydrate grains provide the primary conduction path. Our measurements suggest that impurities from sand induce chemical interactions and/or doping effects that result in higher electrical conductivity with lower temperature dependence. Finally, these results can be used in the modeling of massive or two-phase gas-hydrate-bearing systems devoid of conductive pore water. Further experiments that include a free water phase are the necessary next steps toward developing complex models relevant to most natural systems.« less

Electrical properties of methane hydrate + sediment mixtures: The σ of CH 4 Hydrate + Sediment

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

Du Frane, Wyatt L.; Stern, Laura A.; Constable, Steven

Knowledge of the electrical properties of multicomponent systems with gas hydrate, sediments, and pore water is needed to help relate electromagnetic (EM) measurements to specific gas hydrate concentration and distribution patterns in nature. We built a pressure cell capable of measuring in situ electrical properties of multicomponent systems such that the effects of individual components and mixing relations can be assessed. We first established the temperature-dependent electrical conductivity (σ) of pure, single-phase methane hydrate to be ~5 orders of magnitude lower than seawater, a substantial contrast that can help differentiate hydrate deposits from significantly more conductive water-saturated sediments in EMmore » field surveys. We report σ measurements of two-component systems in which methane hydrate is mixed with variable amounts of quartz sand or glass beads. Sand by itself has low σ but is found to increase the overall σ of mixtures with well-connected methane hydrate. Alternatively, the overall σ decreases when sand concentrations are high enough to cause gas hydrate to be poorly connected, indicating that hydrate grains provide the primary conduction path. Our measurements suggest that impurities from sand induce chemical interactions and/or doping effects that result in higher electrical conductivity with lower temperature dependence. Finally, these results can be used in the modeling of massive or two-phase gas-hydrate-bearing systems devoid of conductive pore water. Further experiments that include a free water phase are the necessary next steps toward developing complex models relevant to most natural systems.« less

Low-frequency electrical properties of peat

NASA Astrophysics Data System (ADS)

Comas, Xavier; Slater, Lee

2004-12-01

Electrical resistivity/induced polarization (0.1-1000 Hz) and vertical hydraulic conductivity (Kv) measurements of peat samples extracted from different depths (0-11 m) in a peatland in Maine were obtained as a function of pore fluid conductivity (σw) between 0.001 and 2 S/m. Hydraulic conductivity increased with σw (Kv ∝ σw0.3 between 0.001 and 2 S/m), indicating that pore dilation occurs due to the reaction of NaCl with organic functional groups as postulated by previous workers. Electrical measurements were modeled by assuming that "bulk" electrolytic conduction through the interconnected pore space and surface conduction in the electrical double layer (EDL) at the organic sediment-fluid interface act in parallel. This analysis suggests that pore space dilation causes a nonlinear relationship between the "bulk" electrolytic conductivity (σel) and σw (σel ∝ σw1.3). The Archie equation predicts a linear dependence of σel on σw and thus appears inappropriate for organic sediments. Induced polarization (IP) measurements of the imaginary part (σ″surf) of the surface conductivity (σ*surf) show that σ″surf is greater and more strongly σw-dependent (σ″surf ∝ σw0.5 between 0.001 and 2 S/m) than observed for inorganic sediments. By assuming a linear relationship between the real (σ'surf) and the imaginary part (σ″surf) of the surface conductivity, we develop an empirical model relating the resistivity and induced polarization measurements to σw in peat. We demonstrate the use of this model to predict (a) σw and (b) the change in Kv due to an incremental change in σw from resistivity and induced polarization measurements on organic sediments. Our study has implications for noninvasive geophysical characterization of σw and Kv with potential to benefit studies of carbon cycling and greenhouse gas fluxes as well as nutrient supply dynamics in peatlands.

Conductometry of electrolyte solutions

NASA Astrophysics Data System (ADS)

Safonova, Lyubov P.; Kolker, Arkadii M.

1992-09-01

A review is given of the theories of the electrical conductance of electrolyte solutions of different ionic strengths and concentrations, and of the models of ion association. An analysis is made of the methods for mathematical processing of experimental conductometric data. An account is provided of various theories describing the dependence of the limiting value of the ionic electrical conductance on the properties of the solute and solvent. The bibliography includes 115 references.

Rheological and electrical properties used to investigate the coagulation process during sludge treatment.

PubMed

Mortadi, A; El Melouky, A; Chahid, E; Nasrellah, H; Bakasse, M; Zradba, A; Cherkaoui, O; El Moznine, R

2018-01-01

Analyses of rheological properties and electrical conductivity (σ dc ) at direct current have been employed in order to investigate the effects of calcium oxide on the coagulation process during sludge treatment in the textile industry. In this context, rheological and electrical measurements were performed on five samples - one that contained raw sludge and the other four that were prepared from the raw sludge and different amounts of calcium oxide: 2, 3, 4, 5% (w/w). Rheological behavior of these samples was analyzed using the Herschel-Bulkley modified model. The influence of calcium oxide content on the rheological parameters such as infinite viscosity, the yield stress, the consistency coefficient, and the consistency index, are presented and discussed. The impact of the calcium oxide content on pH and conductivity were also examined. Similar behaviors have been seen in the evolution of conductivity and infinite viscosity as a function of the calcium oxide content. These latter characteristics were modeled by an equation using two power laws. This equation was able to fit very well the evolution of electrical conductivity and also the viscosity versus the percentage of calcium oxide to predict the optimal amount of calcium oxide (3%) to achieve the coagulation step during sludge treatment.

A Model of the Turbulent Electric Dynamo in Multi-Phase Media

NASA Astrophysics Data System (ADS)

Dementyeva, Svetlana; Mareev, Evgeny

2016-04-01

Many terrestrial and astrophysical phenomena witness the conversion of kinetic energy into electric energy (the energy of the quasi-stationary electric field) in conducting media, which is natural to treat as manifestations of electric dynamo by analogy with well-known theory of magnetic dynamo. Such phenomena include thunderstorms and lightning in the Earth's atmosphere and atmospheres of other planets, electric activity caused by dust storms in terrestrial and Martian atmospheres, snow storms, electrical discharges occurring in technological setups, connected with intense mixing of aerosol particles like in the milling industry. We have developed a model of the large-scale turbulent electric dynamo in a weakly conducting medium, containing two heavy-particle components. We have distinguished two main classes of charging mechanisms (inductive and non-inductive) in accordance with the dependence or independence of the electric charge, transferred during a particle collision, on the electric field intensity and considered the simplified models which demonstrate the possibility of dynamo realization and its specific peculiarities for these mechanisms. Dynamo (the large-scale electric field growth) appears due to the charge separation between the colliding and rebounding particles. This process is may be greatly intensified by the turbulent mixing of particles with different masses and, consequently, different inertia. The particle charge fluctuations themselves (small-scale dynamo), however, do not automatically mean growth of the large-scale electric field without a large-scale asymmetry. Such an asymmetry arises due to the dependence of the transferred charge magnitude on the electric field intensity in the case of the inductive mechanism of charge separation, or due to the gravity and convection for non-inductive mechanisms. We have found that in the case of the inductive mechanism the large-scale dynamo occurs if the medium conductivity is small enough while the electrification process determined by the turbulence intensity and particles sizes is strong enough. The electric field strength grows exponentially. For the non-inductive mechanism we have found the conditions when the electric field strength grows but linearly in time. Our results show that turbulent electric dynamo could play a substantial role in the electrification processes for different mechanisms of charge generation and separation. Thunderstorms and lightning are the most frequent and spectacular manifestations of electric dynamo in the atmosphere, but turbulent electric dynamo may also be the reason of electric discharges occurring in dust and snow storms or even in technological setups with intense mixing of small particles.

Electrical signatures of ethanol-liquid mixtures: implications for monitoring biofuels migration in the subsurface

USGS Publications Warehouse

Personna, Yves Robert; Slater, Lee; Ntarlagiannis, Dimitrios; Werkema, Dale D.; Szabo, Zoltan

2013-01-01

Ethanol (EtOH), an emerging contaminant with potential direct and indirect environmental effects, poses threats to water supplies when spilled in large volumes. A series of experiments was directed at understanding the electrical geophysical signatures arising from groundwater contamination by ethanol. Conductivity measurements were performed at the laboratory scale on EtOH–water mixtures (0 to 0.97 v/v EtOH) and EtOH–salt solution mixtures (0 to 0.99 v/v EtOH) with and without a sand matrix using a conductivity probe and a four-electrode electrical measurement over the low frequency range (1–1000 Hz). A Lichtenecker–Rother (L–R) type mixing model was used to simulate electrical conductivity as a function of EtOH concentration in the mixture. For all three experimental treatments increasing EtOH concentration resulted in a decrease in measured conductivity magnitude (|σ|). The applied L–R model fitted the experimental data at concentration ≤ 0.4 v/v EtOH, presumably due to predominant and symmetric intermolecular (EtOH–water) interaction in the mixture. The deviation of the experimental |σ| data from the model prediction at higher EtOH concentrations may be associated with hydrophobic effects of EtOH–EtOH interactions in the mixture. The |σ| data presumably reflected changes in relative strength of the three types of interactions (water–water, EtOH–water, and EtOH–EtOH) occurring simultaneously in EtOH–water mixtures as the ratio of EtOH to water changed. No evidence of measurable polarization effects at the EtOH–water and EtOH–water–mineral interfaces over the investigated frequency range was found. Our results indicate the potential for using electrical measurements to characterize and monitor EtOH spills in the subsurface.

Relationship between electrical conductivity anisotropy and fabric anisotropy in granular materials during drained triaxial compressive tests: a numerical approach

NASA Astrophysics Data System (ADS)

Niu, Qifei; Revil, André; Li, Zhaofeng; Wang, Yu-Hsing

2017-07-01

The anisotropy of granular media and its evolution during shearing are important aspects required in developing physics-based constitutive models in Earth sciences. The development of relationships between geoelectrical properties and the deformation of porous media has applications to the monitoring of faulting and landslides. However, such relationships are still poorly understood. In this study, we first investigate the definition of the electrical conductivity anisotropy tensor of granular materials in presence of surface conductivity of the grains. Fabric anisotropy is related to the components of the fabric tensor. We define an electrical anisotropy factor based on the Archie's exponent second-order symmetric tensor m of granular materials. We use numerical simulations to confirm a relationship between the evolution of electrical and fabric anisotropy factors during shearing. To realize the simulations, we build a virtual laboratory in which we can easily perform synthetic experiments. We first simulate drained compressive triaxial tests of loose and dense granular materials (porosity 0.45 and 0.38, respectively) using the discrete element method. Then, the electrical conductivity tensor of a set of deformed synthetic samples is computed using the finite-difference method. The numerical results show that shear strains are responsible for a measurable anisotropy in the bulk conductivity of granular media. The observed electrical anisotropy response, during shearing, is distinct for dense and loose synthetic samples. Electrical and fabric anisotropy factors exhibit however a unique linear correlation, regardless of the shear strain and the initial state (porosity) of the synthetic samples. The practical implication of this finding confirms the usefulness of the electrical conductivity method in studying the fabric tensor of granular media. This result opens the door in using time-lapse electrical resistivity to study non-intrusively the evolution of anisotropy of soils and granular rocks during deformation, for instance during landslides, and to use the evolution of the conductivity tensor to monitor mechanical properties.

Structural and electrical transport properties of La2Mo2O9 thin films prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Paul, T.; Ghosh, A.

2017-04-01

We have studied the structure and electrical properties of La2Mo2O9 thin films of different thicknesses prepared by the laser deposition technique at different substrate temperatures. The structural properties of the thin films have been investigated using XRD, XPS, AFM, TEM, SEM, and Raman spectroscopy. The electrical transport properties of the thin films have been investigated in wide temperature and frequency ranges. The cubic nature of the thin films has been confirmed from structural analysis. An enhancement of the oxygen ion conductivity of the films up to five orders of magnitude is obtained compared to that of the bulk La2Mo2O9, suggesting usefulness of the thin films as electrolytes in micro-solid oxide fuel cells. The enhanced dc ionic conductivity of the thin films has been interpreted using the rule of the mixture model, while a power law model has been used to investigate the frequency and temperature dependences of the conductivity. The analysis of the results predicts the three-dimensional oxygen ion conduction in the thin films.

Understanding electricity generation in osmotic microbial fuel cells through integrated experimental investigation and mathematical modeling.

PubMed

Qin, Mohan; Ping, Qingyun; Lu, Yaobin; Abu-Reesh, Ibrahim M; He, Zhen

2015-11-01

Osmotic microbial fuel cells (OsMFCs) are a new type of MFCs with integrating forward osmosis (FO). However, it is not well understood why electricity generation is improved in OsMFCs compared to regular MFCs. Herein, an approach integrating experimental investigation and mathematical model was adopted to address the question. Both an OsMFC and an MFC achieved similar organic removal efficiency, but the OsMFC generated higher current than the MFC with or without water flux, resulting from the lower resistance of FO membrane. Combining NaCl and glucose as a catholyte demonstrated that the catholyte conductivity affected the electricity generation in the OsMFC. A mathematical model of OsMFCs was developed and validated with the experimental data. The model predicated the variation of internal resistance with increasing water flux, and confirmed the importance of membrane resistance. Increasing water flux with higher catholyte conductivity could decrease the membrane resistance. Copyright © 2015 Elsevier Ltd. All rights reserved.

Anelastic spherical dynamos with radially variable electrical conductivity

NASA Astrophysics Data System (ADS)

Dietrich, W.; Jones, C. A.

2018-05-01

A series of numerical simulations of the dynamo process operating inside gas giant planets has been performed. We use an anelastic, fully nonlinear, three-dimensional, benchmarked MHD code to evolve the flow, entropy and magnetic field. Our models take into account the varying electrical conductivity, high in the ionised metallic hydrogen region, low in the molecular outer region. Our suite of electrical conductivity profiles ranges from Jupiter-like, where the outer hydrodynamic region is quite thin, to Saturn-like, where there is a thick non-conducting shell. The rapid rotation leads to the formation of two distinct dynamical regimes which are separated by a magnetic tangent cylinder - mTC. Outside the mTC there are strong zonal flows, where Reynolds stress balances turbulent viscosity, but inside the mTC Lorentz force reduces the zonal flow. The dynamic interaction between both regions induces meridional circulation. We find a rich diversity of magnetic field morphologies. There are Jupiter-like steady dipolar fields, and a belt of quadrupolar dominated dynamos spanning the range of models between Jupiter-like and Saturn-like conductivity profiles. This diversity may be linked to the appearance of reversed sign helicity in the metallic regions of our dynamos. With Saturn-like conductivity profiles we find models with dipolar magnetic fields, whose axisymmetric components resemble those of Saturn, and which oscillate on a very long time-scale. However, the non-axisymmetric field components of our models are at least ten times larger than those of Saturn, possibly due to the absence of any stably stratified layer.

Physics of a novel magnetic resonance and electrical impedance combination for breast cancer diagnosis

NASA Astrophysics Data System (ADS)

Kallergi, Maria; Heine, John J.; Wollin, Ernest

2015-03-01

A new technique is proposed and experimentally validated for breast cancer detection and diagnosis. The technique combines magnetic resonance with electrical impedance measurements and has the potential to increase the specificity of magnetic resonance mammography (MRM) thereby reducing false positive biopsy rates. The new magnetic resonance electrical impedance mammography (MREIM) adds a time varying electric field during a supplementary sequence to a standard MRM examination with an apparatus that is "invisible" to the patient. The applied electric field produces a current that creates an additional magnetic field with a component aligned with the bore magnetic field that can alter the native signal in areas of higher electrical conductivity. The justification for adding the electric field is that the electrical conductivity of cancerous breast tissue is approximately 3-40 times higher than normal breast tissue and, hence, conductivity of malignant tissue represents a known clinical disease biomarker. In a pilot study with custom-made phantoms and experimental protocols, it was demonstrated that MREIM can produce, as theoretically predicted, a detectable differential signal in areas of higher electrical conductivity (tumor surrogate regions); the evidence indicates that the differential signal is produced by the confluence of two different effects at full image resolution without gadolinium chelate contrast agent injection, without extraneous reconstruction techniques, and without cumbersome multi-positioned patient electrode configurations. This paper describes the theoretical model that predicts and explains the observed experimental results that were also confirmed by simulation studies.

The effect of silver (Ag) addition to mechanical and electrical properties of copper alloy (Cu) casting product

NASA Astrophysics Data System (ADS)

Felicia, Dian M.; Rochiem, R.; Laia, Standley M.

2018-04-01

Copper have good mechanical properties and good electrical conductivities. Therefore, copper usually used as electrical components. Silver have better electrical conductivities than copper. Female contact resistor is one of the electrical component used in circuit breaker. This study aims to analyze the effect of silver addition to hardness, strength, and electric conductivity properties of copper alloy. This study uses variation of 0; 0.035; 0.07; 0.1 wt. % Ag (silver) addition to determine the effect on mechanical properties and electrical properties of copper alloy through sand casting process. Modelling of thermal analysis and structural analysis was calculated to find the best design for the sand casting experiments. The result of Cu-Ag alloy as cast will be characterized by OES test, metallography test, Brinell hardness test, tensile test, and LCR meter test. The result of this study showed that the addition of silver increase mechanical properties of Cu-Ag. The maximum hardness value of this alloy is 83.1 HRB which is Cu-0.01 Ag and the lowest is 52.26 HRB which is pure Cu. The maximum strength value is 153.2 MPa which is Cu-0.07 Ag and the lowest is 94.6 MPa which is pure Cu. Silver addition decrease electrical properties of this alloy. The highest electric conductivity is 438.98 S/m which is pure Cu and the lowest is 52.61 S.m which is Cu-0.1 Ag.

Investigating the Martian Ionospheric Conductivity Using MAVEN Key Parameter Data

NASA Astrophysics Data System (ADS)

Aleryani, O.; Raftery, C. L.; Fillingim, M. O.; Fogle, A. L.; Dunn, P.; McFadden, J. P.; Connerney, J. E. P.; Mahaffy, P. R.; Ergun, R. E.; Andersson, L.

2015-12-01

Since the Viking orbiters and landers in 1976, the Martian atmospheric composition has scarcely been investigated. New data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, launched in 2013, allows for a thorough study of the electrically conductive nature of the Martian ionosphere. Determinations of the electrical conductivity will be made using in-situ atmospheric and ionospheric measurements, rather than scientific models for the first time. The objective of this project is to calculate the conductivity of the Martian atmosphere, whenever possible, throughout the trajectory of the MAVEN spacecraft. MAVEN instrumentation used includes the Neutral Gas and Ion Mass Spectrometer (NGIMS) for neutral species density, the Suprathermal and Thermal Ion Compositions (STATIC) for ion composition, temperature and density, the Magnetometer (MAG) for the magnetic field strength and the Langmuir Probe and Waves (LPW) for electron temperature and density. MAVEN key parameter data are used for these calculations. We compare our results with previous, model-based estimates of the conductivity. These results will allow us to quantify the flow of atmospheric electric currents which can be analyzed further for a deeper understanding of the Martian ionospheric electrodynamics, bringing us closer to understanding the mystery of the loss of the Martian atmosphere.

Method And Apparatus For Two Dimensional Surface Property Analysis Based On Boundary Measurement

DOEpatents

Richardson, John G.

2005-11-15

An apparatus and method for determining properties of a conductive film is disclosed. A plurality of probe locations selected around a periphery of the conductive film define a plurality of measurement lines between each probe location and all other probe locations. Electrical resistance may be measured along each of the measurement lines. A lumped parameter model may be developed based on the measured values of electrical resistance. The lumped parameter model may be used to estimate resistivity at one or more selected locations encompassed by the plurality of probe locations. The resistivity may be extrapolated to other physical properties if the conductive film includes a correlation between resistivity and the other physical properties. A profile of the conductive film may be developed by determining resistivity at a plurality of locations. The conductive film may be applied to a structure such that resistivity may be estimated and profiled for the structure's surface.

Equilibrium electrodeformation of a spheroidal vesicle in an ac electric field

NASA Astrophysics Data System (ADS)

Nganguia, H.; Young, Y.-N.

2013-11-01

In this work, we develop a theoretical model to explain the equilibrium spheroidal deformation of a giant unilamellar vesicle (GUV) under an alternating (ac) electric field. Suspended in a leaky dielectric fluid, the vesicle membrane is modeled as a thin capacitive spheroidal shell. The equilibrium vesicle shape results from the balance between mechanical forces from the viscous fluid, the restoring elastic membrane forces, and the externally imposed electric forces. Our spheroidal model predicts a deformation-dependent transmembrane potential, and is able to capture large deformation of a vesicle under an electric field. A detailed comparison against both experiments and small-deformation (quasispherical) theory showed that the spheroidal model gives better agreement with experiments in terms of the dependence on fluid conductivity ratio, permittivity ratio, vesicle size, electric field strength, and frequency. The spheroidal model also allows for an asymptotic analysis on the crossover frequency where the equilibrium vesicle shape crosses over between prolate and oblate shapes. Comparisons show that the spheroidal model gives better agreement with experimental observations.

Electrical Investigation of Metal-Olivine Systems and Application to the Deep Interior of Mercury

NASA Astrophysics Data System (ADS)

Zhang, Z.; Pommier, A.

2017-12-01

Transfers of mass, heat, and electric currents between a silicate mantle and an underlying metallic core characterize the Core-Mantle Boundary (CMB) region of terrestrial planets. In particular, constraining the structure and chemistry of the CMB region of Mercury is crucial to understand its thermal state and unique magnetic activity. To probe the physical and chemical processes of the Hermean CMB, we conducted an electrical study of metal-olivine systems at pressure, temperature, and chemistry conditions relevant to the mantle and CMB region of Mercury. Electrical measurements were performed at 5-7 GPa and up to 1675ºC during heating and cooling in the multi-anvil apparatus using impedance spectroscopy. Samples are made of one metal layer (Fe, FeS, FeSi2, or Fe-Ni-S-Si systems) and one polycrystalline olivine (Fo90) layer, with the metal:olivine ratio ranging from 1:0.7 to 1:9.2. For all samples, we observe that bulk electrical conductivity increases with temperature from 10-2.5 to 101.8 S/m, which is higher than the conductivity of polycrystalline olivine but lower than the one of the metal phase at similar conditions. In some experiments, a conductivity jump is observed at a temperature corresponding to the melting temperature of the metal phase. This conductivity increase cannot be explained by the electrical properties of liquid metal as metal is less conductive with increasing temperature. We observe that both the metal:olivine ratio and the change in metal phase geometry during heating best explain the bulk conductivity. By combining our electrical results, textural analyses of the samples and previous experimental and numerical works, we propose an electrical profile of the deep interior of Mercury. Comparison of our model with existing conductivity estimates of Mercury's lowermost mantle and CMB from magnetic field observations and thermodynamic calculations supports the hypothesis of a layered CMB-outermost core structure in present-day Mercury.

To Guide or Not to Guide: Issues in the Sequencing of Pedagogical Structure in Computational Model-Based Learning

ERIC Educational Resources Information Center

Jacobson, Michael J.; Kim, Beaumie; Pathak, Suneeta; Zhang, BaoHui

2015-01-01

This research explores issues related to the sequencing of structure that is provided as pedagogical guidance. A study was conducted that involved grade 10 students in Singapore as they learned concepts about electricity using four NetLogo Investigations of Electricity agent-based models. It was found that the low-to-high structure learning…

Electrical model of dielectric barrier discharge homogenous and filamentary modes

NASA Astrophysics Data System (ADS)

López-Fernandez, J. A.; Peña-Eguiluz, R.; López-Callejas, R.; Mercado-Cabrera, A.; Valencia-Alvarado, R.; Muñoz-Castro, A.; Rodríguez-Méndez, B. G.

2017-01-01

This work proposes an electrical model that combines homogeneous and filamentary modes of an atmospheric pressure dielectric barrier discharge cell. A voltage controlled electric current source has been utilized to implement the power law equation that represents the homogeneous discharge mode, which starts when the gas breakdown voltage is reached. The filamentary mode implies the emergence of electric current conducting channels (microdischarges), to add this phenomenon an RC circuit commutated by an ideal switch has been proposed. The switch activation occurs at a higher voltage level than the gas breakdown voltage because it is necessary to impose a huge electric field that contributes to the appearance of streamers. The model allows the estimation of several electric parameters inside the reactor that cannot be measured. Also, it is possible to appreciate the modes of the DBD depending on the applied voltage magnitude. Finally, it has been recognized a good agreement between simulation outcomes and experimental results.

Electric field variations measured continuously in free air over a conductive thin zone in the tilted Lias-epsilon black shales near Osnabrück, Northwest Germany

NASA Astrophysics Data System (ADS)

Gurk, M.; Bosch, F. P.; Tougiannidis, N.

2013-04-01

Common studies on the static electric field distribution over a conductivity anomaly use the self-potential method. However, this method is time consuming and requires nonpolarizable electrodes to be placed in the ground. Moreover, the information gained by this method is restricted to the horizontal variations of the electric field. To overcome the limitation in the self-potential technique, we conducted a field experiment using a non conventional technique to assess the static electric field over a conductivity anomaly. We use two metallic potential probes arranged on an insulated boom with a separation of 126 cm. When placed into the electric field of the free air, a surface charge will be induced on each probe trying to equalize with the potential of the surrounding atmosphere. The use of a plasma source at both probes facilitated continuous and quicker measurement of the electric field in the air. The present study shows first experimental measurements with a modified potential probe technique (MPP) along a 600-meter-long transect to demonstrate the general feasibility of this method for studying the static electric field distribution over shallow conductivity anomalies. Field measurements were carried out on a test site on top of the Bramsche Massif near Osnabrück (Northwest Germany) to benefit from a variety of available near surface data over an almost vertical conductivity anomaly. High resolution self-potential data served in a numerical analysis to estimate the expected individual components of the electric field vector. During the experiment we found more anomalies in the vertical and horizontal components of the electric field than self-potential anomalies. These contrasting findings are successfully cross-validated with conventional near surface geophysical methods. Among these methods, we used self-potential, radiomagnetotelluric, electric resistivity tomography and induced polarization data to derive 2D conductivity models of the subsurface in order to infer the geometrical properties and the origin of the conductivity anomaly in the survey area. The presented study demonstrates the feasibility of electric field measurements in free air to detect and study near surface conductivity anomalies. Variations in Ez correlate well with the conductivity distribution obtained from resistivity methods. Compared to the self-potential technique, continuously free air measurements of the electric field are more rapid and of better lateral resolution combined with the unique ability to analyze vertical components of the electric field which are of particular importance to detect lateral conductivity contrasts. Mapping Ez in free air is a good tool to precisely map lateral changes of the electric field distribution in areas where SP generation fails. MPP offers interesting application in other geophysical techniques e.g. in time domain electromagnetics, DC and IP. With this method we were able to reveal a ca. 150 m broad zone of enhanced electric field strength.

Decision Models for Conducting an Economic Analysis of Alternative Fuels for the Ice Engine.

DTIC Science & Technology

1983-03-01

p.cduc.d ICE vehicles. This analysis focusqs on electric vehicles d=.signed for commercial use. Electric hybrid vehicles which combine electric...ccntain -:he minimum gross veicle weight, engine size, and other characterist-ca of vehicles generally procured by the Federal governmen. The ir...Electric and Hybrid Vehicles, Energy Technology Review Nc. 44 published by Noyes Data Corpora’-ion. It summarizes data cn characteristics, cost, maints

Electrical, dielectric properties and study of AC electrical conduction mechanism of Li0.9□0.1NiV0.5P0.5O4

NASA Astrophysics Data System (ADS)

Rahal, A.; Borchani, S. Megdiche; Guidara, K.; Megdiche, M.

2018-02-01

In this paper, we report the measurements of impedance spectroscopy for a new olivine-type lithium deficiency Li0.9□0.1NiV0.5P0.5O4 compound. It was synthesized by the conventional solid-state technique. All the X-ray diffraction peaks of the compound are indexed, and it is found that the sample is well crystallized in orthorhombic olivine structure belonging to the space group Pnma. Conductivity and dielectric analyses of the sample are carried out at different temperatures and frequencies using the complex impedance spectroscopy technique. The electrical conductivity of Li0.9□0.1NiV0.5P0.5O4 is higher than that of parent compound LiNiV0.5P0.5O4. Temperature dependence of the DC conductivity and modulus was found to obey the Arrhenius law. The obtained values of activation energy are different which confirms that transport in the title compound is not due to a simple hopping mechanism. To determine the conduction mechanism, the AC conductivity and its frequency exponent have been analysed in this work by a theoretical model based on quantum mechanical tunnelling: the non-overlapping small polaron tunnelling model.

Consequences of electrical conductivity in an orb spider's capture web

NASA Astrophysics Data System (ADS)

Vollrath, Fritz; Edmonds, Donald

2013-12-01

The glue-coated and wet capture spiral of the orb web of the garden cross spider Araneus diadematus is suspended between the dry silk radial and web frame threads. Here, we experimentally demonstrate that the capture spiral is electrically conductive because of necks of liquid connecting the droplets even if the thread is stretched. We examine how this conductivity of the capture spiral may lead to entrapment of charged airborne particles such as pollen, spray droplets and even insects. We further describe and model how the conducting spiral will also locally distort the Earth's ambient electric field. Finally, we examine the hypothesis that such distortion could be used by potential prey to detect the presence of a web but conclude that any effect would probably be too small to allow an insect to take evasive action.

Characterization of Contact and Bulk Thermal Resistance of Laminations for Electric Machines

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

Cousineau, Emily; Bennion, Kevin; Devoto, Douglas

Thermal management for electric motors is important as the automotive industry continues to transition to more electrically dominant vehicle propulsion systems. The transition to more electrically dominant propulsion systems leads to higher-power duty cycles for electric-drive systems. Thermal constraints place significant limitations on how electric motors ultimately perform. As thermal management improves, there will be a direct trade-off among motor performance, efficiency, cost, and the sizing of electric motors to operate within the thermal constraints. During the development of thermal finite element analysis models and computational fluid dynamics models for electric motors, it was found that there was a lackmore » of open literature detailing the thermal properties of key materials common in electric motors that are significant in terms of heat removal. The lack of available literature, coupled with the strong interest from industry in the passive-stack thermal measurement results, led to experiments to characterize the thermal contact resistance between motor laminations. We examined four lamination materials, including the commonly used 26 gauge and 29 gauge M19 materials, the HF10 and Arnon 7 materials. These latter two materials are thinner and reduce eddy currents responsible for core losses. We measured the thermal conductivity of the lamination materials and the thermal contact resistance between laminations in a stack, as well as investigated factors affecting contact resistance between laminations such as the contact pressure and surface finish. Lamination property data will be provided and we also develop a model to estimate the through-stack thermal conductivity for materials beyond those that were directly tested in this work. For example, at a clamping pressure of 138 kPa, the 29 gauge M19 material has a through-stack thermal conductivity of 1.68 W/m-K, and the contact resistance between laminations was measured to be 193 mm^2-K/W. The measured bulk thermal conductivity for the M19 29 gauge material is 21.0 W/m-K. Density and specific heat were measured to be 7450 kg/m^3 and 463 J/kg-K, respectively. These results are helping, and will continue to help engineers and researchers in the design and development of motors.« less

Mitigating Space Weather Impacts on the Power Grid in Real-Time: Applying 3-D EarthScope Magnetotelluric Data to Forecasting Reactive Power Loss in Power Transformers

NASA Astrophysics Data System (ADS)

Schultz, A.; Bonner, L. R., IV

2017-12-01

Current efforts to assess risk to the power grid from geomagnetic disturbances (GMDs) that result in geomagnetically induced currents (GICs) seek to identify potential "hotspots," based on statistical models of GMD storm scenarios and power distribution grounding models that assume that the electrical conductivity of the Earth's crust and mantle varies only with depth. The NSF-supported EarthScope Magnetotelluric (MT) Program operated by Oregon State University has mapped 3-D ground electrical conductivity structure across more than half of the continental US. MT data, the naturally occurring time variations in the Earth's vector electric and magnetic fields at ground level, are used to determine the MT impedance tensor for each site (the ratio of horizontal vector electric and magnetic fields at ground level expressed as a complex-valued frequency domain quantity). The impedance provides information on the 3-D electrical conductivity structure of the Earth's crust and mantle. We demonstrate that use of 3-D ground conductivity information significantly improves the fidelity of GIC predictions over existing 1-D approaches. We project real-time magnetic field data streams from US Geological Survey magnetic observatories into a set of linear filters that employ the impedance data and that generate estimates of ground level electric fields at the locations of MT stations. The resulting ground electric fields are projected to and integrated along the path of power transmission lines. This serves as inputs to power flow models that represent the power transmission grid, yielding a time-varying set of quasi-real-time estimates of reactive power loss at the power transformers that are critical infrastructure for power distribution. We demonstrate that peak reactive power loss and hence peak risk for transformer damage from GICs does not necessarily occur during peak GMD storm times, but rather depends on the time-evolution of the polarization of the GMD's inducing fields and the complex ground (3-D) electric field response, and the resulting alignment of the ground electric fields with the power transmission line paths. This is informing our efforts to provide a set of real-time tools for power grid operators to use in mitigating damage from space weather events.

Schumann Resonances on Mars - a Two-layer Ground Case

NASA Astrophysics Data System (ADS)

Kozakiewicz, J.; Kulak, A.; Mlynarczyk, J.

2012-04-01

Schumann resonances (SR) are global resonances of electromagnetic waves in the range of extremely low frequencies (ELF) propagating in a cavity formed by a planetary surface and a lower ionosphere. SR are induced by electrical discharges, which on Earth are associated mainly with lightning. They were predicted by Winfried Otto Schumann in 1952. SR are supposed to occur on Mars, although many properties of the Martian environment are still unknown. One of the most important problems in modeling SR on Mars is to estimate electrical properties of the Martian ground and their influence on ELF waves propagation. The Martian crust is composed mainly of basaltic materials. Water, which causes significant increase in electrical conductivity of rocks, does not exist in liquid state at the surface of Mars. Therefore the Martian ground is believed to be a low conductive one. However, it is possible that some liquid water may be present at various depths below the surface. In our previous study we have developed an analytical model, based on the characteristic electric and magnetic altitudes' formalism, that has allowed us to take into consideration the Martian ground. Using this new model, we found that basaltic ground of low conductivity greatly influenced the SR parameters. In this work, we carried out simulations in order to characterize an influence of vertical changes in ground properties on the parameters of the Martian ground-ionosphere waveguide. We have considered several cases of a two-layer ground, in which the lower layer was of higher conductivity than the upper one. The obtained results indicate how the SR parameters depend on electrical conductivity, permittivity, and depth of the layers. The results also point out the importance of studying SR on Mars and the need for further research in propagation of ELF waves in the Martian environment. SR can be used as a remote sensing tool for exploration of the Martian crust. Furthermore, they can be especially useful for groundwater detection.

Modeling electrical double-layer effects for microfluidic impedance spectroscopy from 100 kHz to 110 GHz.

PubMed

Little, Charles A E; Orloff, Nathan D; Hanemann, Isaac E; Long, Christian J; Bright, Victor M; Booth, James C

2017-07-25

Broadband microfluidic-based impedance spectroscopy can be used to characterize complex fluids, with applications in medical diagnostics and in chemical and pharmacological manufacturing. Many relevant fluids are ionic; during impedance measurements ions migrate to the electrodes, forming an electrical double-layer. Effects from the electrical double-layer dominate over, and reduce sensitivity to, the intrinsic impedance of the fluid below a characteristic frequency. Here we use calibrated measurements of saline solution in microfluidic coplanar waveguide devices at frequencies between 100 kHz and 110 GHz to directly measure the double-layer admittance for solutions of varying ionic conductivity. We successfully model the double-layer admittance using a combination of a Cole-Cole response with a constant phase element contribution. Our analysis yields a double-layer relaxation time that decreases linearly with solution conductivity, and allows for double-layer effects to be separated from the intrinsic fluid response and quantified for a wide range of conducting fluids.

Investigations for Thermal and Electrical Conductivity of ABS-Graphene Blended Prototypes

PubMed Central

Singh, Rupinder; Sandhu, Gurleen S.; Penna, Rosa; Farina, Ilenia

2017-01-01

The thermoplastic materials such as acrylonitrile-butadiene-styrene (ABS) and Nylon have large applications in three-dimensional printing of functional/non-functional prototypes. Usually these polymer-based prototypes are lacking in thermal and electrical conductivity. Graphene (Gr) has attracted impressive enthusiasm in the recent past due to its natural mechanical, thermal, and electrical properties. This paper presents the step by step procedure (as a case study) for development of an in-house ABS-Gr blended composite feedstock filament for fused deposition modelling (FDM) applications. The feedstock filament has been prepared by two different methods (mechanical and chemical mixing). For mechanical mixing, a twin screw extrusion (TSE) process has been used, and for chemical mixing, the composite of Gr in an ABS matrix has been set by chemical dissolution, followed by mechanical blending through TSE. Finally, the electrical and thermal conductivity of functional prototypes prepared from composite feedstock filaments have been optimized. PMID:28773244

Improving our understanding of hydraulic-electrical relations: A case study of the surficial aquifer in Emirate Abu Dhabi

USGS Publications Warehouse

Ikard, Scott; Kress, Wade

2016-01-01

Transmissivity is a bulk hydraulic property that can be correlated with bulk electrical properties of an aquifer. In aquifers that are electrically-resistive relative to adjacent layers in a horizontally stratified sequence, transmissivity has been shown to correlate with bulk transverse resistance. Conversely, in aquifers that are electrically-conductive relative to adjacent layers, transmissivity has been shown to correlate with bulk longitudinal conductance. In both cases, previous investigations have relied on small datasets (on average less than eight observations) that have yielded coefficients of determination (R2) that are typically in the range of 0.6 to 0.7 to substantiate these relations. Compared to previous investigations, this paper explores hydraulic-electrical relations using a much larger dataset. Geophysical data collected from 26 boreholes in Emirate Abu Dhabi, United Arab Emirates, are used to correlate transmissivity modeled from neutron porosity logs to the bulk electrical properties of the surficial aquifer that are computed from deep-induction logs. Transmissivity is found to be highly correlated with longitudinal conductance. An R2 value of 0.853 is obtained when electrical effects caused by variations in pore-fluid salinity are taken into consideration.

Using Reactive Transport Modeling to Understand Changes in Electrical Conductivity Associated with Bacterial Growth and Respiration

NASA Astrophysics Data System (ADS)

Regberg, A. B.; Singha, K.; Picardal, F.; Brantley, S. L.

2011-12-01

Previous research has linked measured changes in the bulk electrical conductivity (σb) of water-saturated sediments to the respiration and growth of anaerobic bacteria. If the mechanism causing this signal is understood and characterized it could be used to identify and monitor zones of bacterial activity in the subsurface. The 1-D reactive transport model PHREEQC was used to understand σb signals by modeling chemical gradients within two column reactors and corresponding changes in effluent chemistry. The flow-through column reactors were packed with Fe(III)-bearing sediment from Oyster, VA and inoculated with an environmental consortia of microorganisms. Influent in the first reactor was amended with 1mM Na-acetate to encourage the growth of iron-reducing bacteria. Influent in the second reactor was amended with 0.1mM Na-Acetate and 2mM NaNO3 to encourage the growth of nitrate-reducing bacteria. While effluent concentrations of acetate, Fe(II), NO3-, NO2-, and NH4+ remained at steady state, we measured a 3-fold increase (0.055 S/m - 0.2 S/m) in σb in the iron-reducing column and a 10-fold increase in σb (0.07 S/m - 0.8 S/m) in the nitrate-reducing column over 198 days. The ionic strength in both reactors remained constant through time indicating that the measured increases in σb were not caused by changing effluent concentrations. PHREEQC successfully matched the measured changes in effluent concentrations for both columns when the reaction database was modified in the following manner. For the iron-reducing column, kinetic expressions governing the rate of iron reduction, the rate of bacterial growth, and the production of methane were added to the reaction database. Additionally, surface adsorption and cation exchange reactions were added so that the model was consistent with measured effluent chemistry. For the nitrate-reducing column, kinetic expressions governing nitrate reduction and bacterial growth were added to the reaction database. Additionally, immobile porosity was added along with adsorption and cation exchange reactions. Although the model revealed the existence of chemical and biological gradients within the columns that were not discernable as changes in effluent concentrations, none of the chemical reactions or gradients could explain the measured σb increases in either column. This result is not consistent with chemical gradients within the column reactor causing the measured changes in σb. To test the alternate hypothesis that microbial biofilms are electrically conductive, we used the output from PHREEQC to calculate the amount of biomass produced within the column reactors. If biofilm causes the σb changes, our model is consistent with an electrical conductivity for biomass in the iron-reducing column between 2.75 and 220 S/m. The model is also consistent with an electrical conductivity for biomass in the nitrate-reducing column between 350 and 35,000 S/m. These estimates of biomass electrical conductivity are poorly constrained but represent a first step towards understanding the electrical properties associated with respiring biofilms.

Pragmatic analysis of the electric submerged arc furnace continuum

NASA Astrophysics Data System (ADS)

Karalis, K.; Karkalos, N.; Antipas, G. S. E.; Xenidis, A.

2017-09-01

A transient mathematical model was developed for the description of fluid flow, heat transfer and electromagnetic phenomena involved in the production of ferronickel in electric arc furnaces. The key operating variables considered were the thermal and electrical conductivity of the slag and the shape, immersion depth and applied electric potential of the electrodes. It was established that the principal stimuli of the velocities in the slag bath were the electric potential and immersion depth of the electrodes and the thermal and electrical conductivities of the slag. Additionally, it was determined that, under the set of operating conditions examined, the maximum slag temperature ranged between 1756 and 1825 K, which is in accordance with industrial measurements. Moreover, it was affirmed that contributions to slag stirring due to Lorentz forces and momentum forces due to the release of carbon monoxide bubbles from the electrode surface were negligible.

Hybrid and plug-in hybrid electric vehicle performance testing by the US Department of Energy Advanced Vehicle Testing Activity

NASA Astrophysics Data System (ADS)

Karner, Donald; Francfort, James

The Advanced Vehicle Testing Activity (AVTA), part of the U.S. Department of Energy's FreedomCAR and Vehicle Technologies Program, has conducted testing of advanced technology vehicles since August 1995 in support of the AVTA goal to provide benchmark data for technology modeling, and vehicle development programs. The AVTA has tested full size electric vehicles, urban electric vehicles, neighborhood electric vehicles, and hydrogen internal combustion engine powered vehicles. Currently, the AVTA is conducting baseline performance, battery benchmark and fleet tests of hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV). Testing has included all HEVs produced by major automotive manufacturers and spans over 2.5 million test miles. Testing is currently incorporating PHEVs from four different vehicle converters. The results of all testing are posted on the AVTA web page maintained by the Idaho National Laboratory.

Pragmatic analysis of the electric submerged arc furnace continuum

PubMed Central

Karkalos, N.; Xenidis, A.

2017-01-01

A transient mathematical model was developed for the description of fluid flow, heat transfer and electromagnetic phenomena involved in the production of ferronickel in electric arc furnaces. The key operating variables considered were the thermal and electrical conductivity of the slag and the shape, immersion depth and applied electric potential of the electrodes. It was established that the principal stimuli of the velocities in the slag bath were the electric potential and immersion depth of the electrodes and the thermal and electrical conductivities of the slag. Additionally, it was determined that, under the set of operating conditions examined, the maximum slag temperature ranged between 1756 and 1825 K, which is in accordance with industrial measurements. Moreover, it was affirmed that contributions to slag stirring due to Lorentz forces and momentum forces due to the release of carbon monoxide bubbles from the electrode surface were negligible. PMID:28989738

Simulation of action potential propagation in plants.

PubMed

Sukhov, Vladimir; Nerush, Vladimir; Orlova, Lyubov; Vodeneev, Vladimir

2011-12-21

Action potential is considered to be one of the primary responses of a plant to action of various environmental factors. Understanding plant action potential propagation mechanisms requires experimental investigation and simulation; however, a detailed mathematical model of plant electrical signal transmission is absent. Here, the mathematical model of action potential propagation in plants has been worked out. The model is a two-dimensional system of excitable cells; each of them is electrically coupled with four neighboring ones. Ion diffusion between excitable cell apoplast areas is also taken into account. The action potential generation in a single cell has been described on the basis of our previous model. The model simulates active and passive signal transmission well enough. It has been used to analyze theoretically the influence of cell to cell electrical conductivity and H(+)-ATPase activity on the signal transmission in plants. An increase in cell to cell electrical conductivity has been shown to stimulate an increase in the length constant, the action potential propagation velocity and the temperature threshold, while the membrane potential threshold being weakly changed. The growth of H(+)-ATPase activity has been found to induce the increase of temperature and membrane potential thresholds and the reduction of the length constant and the action potential propagation velocity. Copyright © 2011 Elsevier Ltd. All rights reserved.

Electrical and thermal behavior of unsaturated soils: experimental results

NASA Astrophysics Data System (ADS)

Nouveau, Marie; Grandjean, Gilles; Leroy, Philippe; Philippe, Mickael; Hedri, Estelle; Boukcim, Hassan

2016-05-01

When soil is affected by a heat source, some of its properties are modified, and in particular, the electrical resistivity due to changes in water content. As a result, these changes affect the thermal properties of soil, i.e., its thermal conductivity and diffusivity. We experimentally examine the changes in electrical resistivity and thermal conductivity for four soils with different grain size distributions and clay content over a wide range of temperatures, from 20 to 100 °C. This temperature range corresponds to the thermal conditions in the vicinity of a buried high voltage cable or a geothermal system. Experiments were conducted at the field scale, at a geothermal test facility, and in the laboratory using geophysical devices and probing systems. The results show that the electrical resistivity decreases and the thermal conductivity increases with temperature up to a critical temperature depending on soil types. At this critical temperature, the air volume in the pore space increases with temperature, and the resulting electrical resistivity also increases. For higher temperatures , the thermal conductivity increases sharply with temperature up to a second temperature limit. Beyond it, the thermal conductivity drops drastically. This limit corresponds to the temperature at which most of the water evaporates from the soil pore space. Once the evaporation is completed, the thermal conductivity stabilizes. To explain these experimental results, we modeled the electrical resistivity variations with temperature and water content in the temperature range 20 - 100°C, showing that two critical temperatures influence the main processes occurring during heating at temperatures below 100 °C.

Effective conductivity and permittivity of unsaturated porous materials in the frequency range 1 mHz–1GHz

PubMed Central

Revil, A

2013-01-01

A model combining low-frequency complex conductivity and high-frequency permittivity is developed in the frequency range from 1 mHz to 1 GHz. The low-frequency conductivity depends on pore water and surface conductivities. Surface conductivity is controlled by the electrical diffuse layer, the outer component of the electrical double layer coating the surface of the minerals. The frequency dependence of the effective quadrature conductivity shows three domains. Below a critical frequency fp, which depends on the dynamic pore throat size Λ, the quadrature conductivity is frequency dependent. Between fp and a second critical frequency fd, the quadrature conductivity is generally well described by a plateau when clay minerals are present in the material. Clay-free porous materials with a narrow grain size distribution are described by a Cole-Cole model. The characteristic frequency fd controls the transition between double layer polarization and the effect of the high-frequency permittivity of the material. The Maxwell-Wagner polarization is found to be relatively negligible. For a broad range of frequencies below 1 MHz, the effective permittivity exhibits a strong dependence with the cation exchange capacity and the specific surface area. At high frequency, above the critical frequency fd, the effective permittivity reaches a high-frequency asymptotic limit that is controlled by the two Archie's exponents m and n like the low-frequency electrical conductivity. The unified model is compared with various data sets from the literature and is able to explain fairly well a broad number of observations with a very small number of textural and electrochemical parameters. It could be therefore used to interpret induced polarization, induction-based electromagnetic methods, and ground penetrating radar data to characterize the vadose zone. PMID:23576823

Radiation from lightning return strokes over a finitely conducting earth

NASA Technical Reports Server (NTRS)

Le Vine, D. M.; Gesell, L.; Kao, Michael

1986-01-01

The effects of the conductivity of the earth on radiation from lightning return strokes are examined theoretically using a piecewise linear transmission line model for the return stroke. First, calculations are made of the electric field radiated during the return stroke, and then this electric field is used to compute the response of conventional AM radio receivers and electric field change systems during the return stroke. The calculations apply to the entire transient waveform (they are not restricted to the initial portions of the return stroke) and yield fast field changes and RF radiation in agreement with measurements made during real lightning. This research was motivated by measurements indicating that a time delay exists between the time of arrival of the fast electric field change and the RF radiation from first return strokes. The time delay is on the order of 20 microsec for frequencies in the HF-UHF range for lightning in Florida. The time delay is obtained theoretically in this paper. It occurs when both the effects of attenuation due to conductivity of the earth, and the finite velocity of propagation of the current pulse up the return stroke channel, are taken into account in the model.

Discharge current distribution in stratified soil under impulse discharge

NASA Astrophysics Data System (ADS)

Eniola Fajingbesi, Fawwaz; Shahida Midi, Nur; Elsheikh, Elsheikh M. A.; Hajar Yusoff, Siti

2017-06-01

The mobility of charge particles traversing a material defines its electrical properties. Soil (earth) have long been the universal grounding before and after the inception of active ground systems for electrical appliance purpose due to it semi-conductive properties. The soil can thus be modelled as a single material exhibiting semi-complex inductive-reactive impedance. Under impulse discharge such as lightning strikes to soil this property of soil could result in electric potential level fluctuation ranging from ground potential rise/fall to electromagnetic pulse coupling that could ultimately fail connected electrical appliance. In this work we have experimentally model the soil and lightning discharge using point to plane electrode setup to observe the current distribution characteristics at different soil conductivity [mS/m] range. The result presented from this research indicate above 5% shift in conductivity before and after discharge which is significant for consideration when dealing with grounding designs. The current distribution in soil have also be successfully observed and analysed from experimental result using mean current magnitude in relation to electrode distance and location, current density variation with depth all showing strong correlation with theoretical assumptions of a semi-complex impedance material.

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study

NASA Astrophysics Data System (ADS)

Wenger, Cornelia; Salvador, Ricardo; Basser, Peter J.; Miranda, Pedro C.

2015-09-01

Tumor treating fields (TTFields) are a non-invasive, anti-mitotic and approved treatment for recurrent glioblastoma multiforme (GBM) patients. In vitro studies have shown that inhibition of cell division in glioma is achieved when the applied alternating electric field has a frequency in the range of 200 kHz and an amplitude of 1-3 V cm-1. Our aim is to calculate the electric field distribution in the brain during TTFields therapy and to investigate the dependence of these predictions on the heterogeneous, anisotropic dielectric properties used in the computational model. A realistic head model was developed by segmenting MR images and by incorporating anisotropic conductivity values for the brain tissues. The finite element method (FEM) was used to solve for the electric potential within a volume mesh that consisted of the head tissues, a virtual lesion with an active tumour shell surrounding a necrotic core, and the transducer arrays. The induced electric field distribution is highly non-uniform. Average field strength values are slightly higher in the tumour when incorporating anisotropy, by about 10% or less. A sensitivity analysis with respect to the conductivity and permittivity of head tissues shows a variation in field strength of less than 42% in brain parenchyma and in the tumour, for values within the ranges reported in the literature. Comparing results to a previously developed head model suggests significant inter-subject variability. This modelling study predicts that during treatment with TTFields the electric field in the tumour exceeds 1 V cm-1, independent of modelling assumptions. In the future, computational models may be useful to optimize delivery of TTFields.

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study.

PubMed

Wenger, Cornelia; Salvador, Ricardo; Basser, Peter J; Miranda, Pedro C

2015-09-21

Tumor treating fields (TTFields) are a non-invasive, anti-mitotic and approved treatment for recurrent glioblastoma multiforme (GBM) patients. In vitro studies have shown that inhibition of cell division in glioma is achieved when the applied alternating electric field has a frequency in the range of 200 kHz and an amplitude of 1-3 V cm(-1). Our aim is to calculate the electric field distribution in the brain during TTFields therapy and to investigate the dependence of these predictions on the heterogeneous, anisotropic dielectric properties used in the computational model. A realistic head model was developed by segmenting MR images and by incorporating anisotropic conductivity values for the brain tissues. The finite element method (FEM) was used to solve for the electric potential within a volume mesh that consisted of the head tissues, a virtual lesion with an active tumour shell surrounding a necrotic core, and the transducer arrays. The induced electric field distribution is highly non-uniform. Average field strength values are slightly higher in the tumour when incorporating anisotropy, by about 10% or less. A sensitivity analysis with respect to the conductivity and permittivity of head tissues shows a variation in field strength of less than 42% in brain parenchyma and in the tumour, for values within the ranges reported in the literature. Comparing results to a previously developed head model suggests significant inter-subject variability. This modelling study predicts that during treatment with TTFields the electric field in the tumour exceeds 1 V cm(-1), independent of modelling assumptions. In the future, computational models may be useful to optimize delivery of TTFields.

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study

PubMed Central

Wenger, Cornelia; Salvador, Ricardo; Basser, Peter J; Miranda, Pedro C

2015-01-01

Tumor Treating Fields (TTFields) are a non-invasive, anti-mitotic and approved treatment for recurrent glioblastoma multiforme (GBM) patients. In vitro studies have shown that inhibition of cell division in glioma is achieved when the applied alternating electric field has a frequency in the range of 200 kHz and an amplitude of 1 - 3 V/cm. Our aim is to calculate the electric field distribution in the brain during TTFields therapy and to investigate the dependence of these predictions on the heterogeneous, anisotropic dielectric properties used in the computational model. A realistic head model was developed by segmenting MR images and by incorporating anisotropic conductivity values for the brain tissues. The finite element method (FEM) was used to solve for the electric potential within a volume mesh that consisted of the head tissues, a virtual lesion with an active tumour shell surrounding a necrotic core, and the transducer arrays. The induced electric field distribution is highly non-uniform. Average field strength values are slightly higher in the tumour when incorporating anisotropy, by about 10% or less. A sensitivity analysis with respect to the conductivity and permittivity of head tissues shows a variation in field strength of less than 42% in brain parenchyma and in the tumour, for values within the ranges reported in the literature. Comparing results to a previously developed head model suggests significant inter-subject variability. This modelling study predicts that during treatment with TTFields the electric field in the tumour exceeds 1 V/cm, independent of modelling assumptions. In the future, computational models may be useful to optimize delivery of TTFields. PMID:26350296

Using independent component analysis for electrical impedance tomography

NASA Astrophysics Data System (ADS)

Yan, Peimin; Mo, Yulong

2004-05-01

Independent component analysis (ICA) is a way to resolve signals into independent components based on the statistical characteristics of the signals. It is a method for factoring probability densities of measured signals into a set of densities that are as statistically independent as possible under the assumptions of a linear model. Electrical impedance tomography (EIT) is used to detect variations of the electric conductivity of the human body. Because there are variations of the conductivity distributions inside the body, EIT presents multi-channel data. In order to get all information contained in different location of tissue it is necessary to image the individual conductivity distribution. In this paper we consider to apply ICA to EIT on the signal subspace (individual conductivity distribution). Using ICA the signal subspace will then be decomposed into statistically independent components. The individual conductivity distribution can be reconstructed by the sensitivity theorem in this paper. Compute simulations show that the full information contained in the multi-conductivity distribution will be obtained by this method.

Electrical resistance tomography using steel cased boreholes as electrodes

DOEpatents

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

1999-06-22

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

Electrical resistance tomography using steel cased boreholes as electrodes

DOEpatents

Daily, William D.; Ramirez, Abelardo L.

1999-01-01

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

DC electrical conductivity of Ag2O-TeO2-V2O5 glassy systems

NASA Astrophysics Data System (ADS)

Souri, D.; Tahan, Z. Esmaeili; Salehizadeh, S. A.

2016-04-01

In the present article, samples of xAg2O-40TeO2-(60 - x)V2O5 ternary tellurite glasses with 0 ≤ x ≤ 50 (in mol%) have been prepared using the melt-quenching technique. XRD analysis, density measurement by Archimedes' law, determination of reduced vanadium ions by titration method, and electrical conductivity measurement by using four-probe methods have been done for these glasses. The mixed electronic-ionic conduction of these glasses has been investigated over a wide temperature range of 150-380 K. The experimental results have been analyzed with different theoretical models of hopping conduction. The analysis shows that at high temperatures the conductivity data are consistent with Mott's model of phonon-assisted polaronic hopping, while Mott's variable-range hopping model and Greaves' hopping model are valid at low temperatures. The temperature dependence of the conductivity has been also interpreted in the framework of the percolation model proposed by Triberis and Friedman. The analysis of the conductivity data also indicates that the hopping in these tellurite glasses occurs in the non-adiabatic regime. In each sample, based upon the justified transport mechanism, carrier density and mobility have been determined at different temperatures. The values of oxygen molar volume indicate the effect of Ag2O concentration on the thermal stability or fragility of understudied samples.

Geophysical constraints on contaminant transport modeling in a heterogeneous fluvial aquifer.

PubMed

Bowling, Jerry C; Zheng, Chunmiao; Rodriguez, Antonio B; Harry, Dennis L

2006-05-05

Approximately 3000 measurements of hydraulic conductivity in over 50 flowmeter boreholes were available at the Macro-Dispersion Experiment (MADE) site in Columbus, Mississippi, USA to quantify the heterogeneity in hydraulic conductivity at the site scale. This high-density measurement approach is perhaps infeasible for time and expense in typical groundwater remediation sites. A natural-gradient tracer experiment from the MADE site was simulated by a groundwater flow and solute transport model incorporating direct-current (DC) resistivity data collected over the observed plume location. Hydraulic conductivity from one borehole collected during the original site characterization was used to calibrate the electrical resistivity data to hydraulic conductivity using a previously derived log-log relationship. Application of this relationship, using site-specific empirical constants determined from the data, transforms the 3D electrical resistivity data into a 3D description of hydraulic conductivity that can be used in groundwater models. The validity of this approach was tested by using the geophysically derived hydraulic conductivity representation in numerical simulations of the natural-gradient tracer experiment. The agreement between the simulated and observed tracer plumes was quantified to gauge the effectiveness of geophysically derived and flowmeter based representations of the hydraulic conductivity field. This study demonstrates that a highly heterogeneous aquifer can be modeled with minimal hydrological data supplemented with geophysical data at least as well as previous models of the site using purely hydrologic data.

Passive safety device and internal short tested method for energy storage cells and systems

DOEpatents

Keyser, Matthew; Darcy, Eric; Long, Dirk; Pesaran, Ahmad

2015-09-22

A passive safety device for an energy storage cell for positioning between two electrically conductive layers of the energy storage cell. The safety device also comprising a separator and a non-conductive layer. A first electrically conductive material is provided on the non-conductive layer. A first opening is formed through the separator between the first electrically conductive material and one of the electrically conductive layers of the energy storage device. A second electrically conductive material is provided adjacent the first electrically conductive material on the non-conductive layer, wherein a space is formed on the non-conductive layer between the first and second electrically conductive materials. A second opening is formed through the non-conductive layer between the second electrically conductive material and another of the electrically conductive layers of the energy storage device. The first and second electrically conductive materials combine and exit at least partially through the first and second openings to connect the two electrically conductive layers of the energy storage device at a predetermined temperature.

The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

NASA Astrophysics Data System (ADS)

Mardaani, Mohammad; Rabani, Hassan; Esmaili, Esmat; Shariati, Ashrafalsadat

2015-08-01

A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance.

Broadband EIT borehole measurements with high phase accuracy using numerical corrections of electromagnetic coupling effects

NASA Astrophysics Data System (ADS)

Zhao, Y.; Zimmermann, E.; Huisman, J. A.; Treichel, A.; Wolters, B.; van Waasen, S.; Kemna, A.

2013-08-01

Electrical impedance tomography (EIT) is gaining importance in the field of geophysics and there is increasing interest for accurate borehole EIT measurements in a broad frequency range (mHz to kHz) in order to study subsurface properties. To characterize weakly polarizable soils and sediments with EIT, high phase accuracy is required. Typically, long electrode cables are used for borehole measurements. However, this may lead to undesired electromagnetic coupling effects associated with the inductive coupling between the double wire pairs for current injection and potential measurement and the capacitive coupling between the electrically conductive shield of the cable and the electrically conductive environment surrounding the electrode cables. Depending on the electrical properties of the subsurface and the measured transfer impedances, both coupling effects can cause large phase errors that have typically limited the frequency bandwidth of field EIT measurements to the mHz to Hz range. The aim of this paper is to develop numerical corrections for these phase errors. To this end, the inductive coupling effect was modeled using electronic circuit models, and the capacitive coupling effect was modeled by integrating discrete capacitances in the electrical forward model describing the EIT measurement process. The correction methods were successfully verified with measurements under controlled conditions in a water-filled rain barrel, where a high phase accuracy of 0.8 mrad in the frequency range up to 10 kHz was achieved. The corrections were also applied to field EIT measurements made using a 25 m long EIT borehole chain with eight electrodes and an electrode separation of 1 m. The results of a 1D inversion of these measurements showed that the correction methods increased the measurement accuracy considerably. It was concluded that the proposed correction methods enlarge the bandwidth of the field EIT measurement system, and that accurate EIT measurements can now be made in the mHz to kHz frequency range. This increased accuracy in the kHz range will allow a more accurate field characterization of the complex electrical conductivity of soils and sediments, which may lead to the improved estimation of saturated hydraulic conductivity from electrical properties. Although the correction methods have been developed for a custom-made EIT system, they also have potential to improve the phase accuracy of EIT measurements made with commercial systems relying on multicore cables.

The Effect of Electric Current Teaching Based upon the 5E Model on Academic Achievement and Attitudes of Students

ERIC Educational Resources Information Center

Guzel, Hattice

2017-01-01

In this research, the purpose was to examine and compare the effect of teaching Electric Current, which is a topic of grade 11 physics lesson, on student achievement and attitude according to the 5E model belonging to the constructivist learning theory and the traditional teaching method. The research was conducted in the spring semester of…

Electrical Transport Properties of Liquid Al-Cu Alloys

NASA Astrophysics Data System (ADS)

Thakore, B. Y.; Khambholja, S. G.; Suthar, P. H.; Jani, A. R.

2010-06-01

Electrical transport properties viz. electrical resistivity, thermoelectric power and thermal conductivity of liquid Al-Cu alloys as a function of Cu concentration have been studied in the present paper. Ashcroft empty core model potential has been used to incorporate the ion-electron interaction. To incorporate the exchange and correlation effects, five different forms of local field correction functions viz. Hartree, Taylor, Ichimaru et al., Farid et al. and Sarkar et al. have been used. The transport properties of binary system have been studied using Faber-Ziman formulation combined with Ashcroft-Langreth (AL) partial structure factor. The computed values of electrical resistivity are compared with experimental data and for low Cu concentration, good agreement has been observed. Further, thermoelectric power and thermal conductivity have also been predicted.

Current density in a model of a human body with a conductive implant exposed to ELF electric and magnetic fields.

PubMed

Valic, Blaz; Gajsek, Peter; Miklavcic, Damijan

2009-10-01

A numerical model of a human body with an intramedullary nail in the femur was built to evaluate the effects of the implant on the current density distribution in extremely low frequency electric and magnetic fields. The intramedullary nail was chosen because it is one of the longest high conductive implants used in the human body. As such it is expected to alter the electric and magnetic fields significantly. The exposure was a simultaneous combination of inferior to superior electric field and posterior to anterior magnetic field both alternating at 50 Hz with the values corresponding to the ICNIRP reference levels: 5000 V m(-1) for electric field and 100 microT for magnetic flux density. The calculated current density distribution inside the model was compared to the ICNIRP basic restrictions for general public (2 mA m(-2)). The results show that the implant significantly increases the current density up to 9.5 mA m(-2) in the region where it is in contact with soft tissue in the model with the implant in comparison to 0.9 mA m(-2) in the model without the implant. As demonstrated the ICNIRP basic restrictions are exceeded in a limited volume of the tissue in spite of the compliance with the ICNIRP reference levels for general public, meaning that the existing safety limits do not necessarily protect implanted persons to the same extent as they protect people without implants.

Results of thermal modeling of Smart Energy Coating with phase-transition material for independent electricity generation

NASA Astrophysics Data System (ADS)

Pospelova, I. Y.; Pospelova, M. Y.; Bondarenko, A. S.; Kornilov, D. A.

2018-05-01

The modeling for Smart Energy Coating is presented. The coating is able to produce electricity on the surface of pipelines and structural elements. Along with electric output, Smart Energy Coating ensures the stable temperature conditions of work for structures, pipelines and regulating elements. The energy production scheme is based on the Peltier principle and the insulating layer with a phase transition. Thermally conductive inclusions of the inside layer with a phase transition material ensure the stable operation of the Peltier element.

Resolving the deep electrical resistivity structure at Central Pontides, Northern Turkey by three-dimensional magnetotelluric modeling

NASA Astrophysics Data System (ADS)

Özaydın, Sinan; Bülent Tank, Sabri; Karaş, Mustafa; Sandvol, Eric

2017-04-01

Wide-band magnetotelluric (MT) (360 Hz - 1860 sec) data were acquired at 25 sites along a north - south aligned profile cutting across the Central Pontides, which are made up of highly metamorphosed formations and their tectonic boundaries including: a Lower Cretaceous-aged turbidite sequence, Central Pontides Metamorphic Supercomplex (CPMS), North Anatolian Fault Zone (NAFZ) and Izmir-Ankara-Erzincan Suture Zone (IAESZ). Dimensionality analyses over all observation points demonstrated high electrical anisotropy, which indicates complex geological and tectonic structures. This dimensional complexity and presence of the electrically conductive Black Sea augmented the requirement for a three-dimensional analysis. Inverse modeling routines, ModEM (Egbert and Kelbert, 2012) and WSINV3DMT (Siripunvaraporn et al., 2005) were utilized to reveal the geo-electrical implications over this unusually complicated region. Interpretations of the resultant models are summarized as follows: (i) Çangaldaǧ and Domuzdaǧ complexes appear as highly resistive bodies bounded by north dipping faults. (ii) Highly conductive Tosya Basin sediments overlain the ophiolitic materials as a thin cover located at the south of the NAFZ. (iii) North Anatolian Fault and some auxiliary faults within the system exhibit conductive-resistive interfaces that reach to lower crustal levels. (iv) IAESZ is a clear feature marked by the resistivity contrast between NAFZ-related sedimentary basins and Neo-Tethyan ophiolites.

Radiation-induced microcrystal shape change as a mechanism of wasteform degradation

NASA Astrophysics Data System (ADS)

Ojovan, Michael I.; Burakov, Boris E.; Lee, William E.

2018-04-01

Experiments with actinide-containing insulating wasteforms such as devitrified glasses containing 244Cm, Ti-pyrochlore, single-phase La-monazite, Pu-monazite ceramics, Eu-monazite and zircon single crystals containing 238Pu indicate that mechanical self-irradiation-induced destruction may not reveal itself for many years (even decades). The mechanisms causing these slowly-occurring changes remain unknown therefore in addition to known mechanisms of wasteform degradation such as matrix swelling and loss of solid solution we have modelled the damaging effects of electrical fields induced by the decay of radionuclides in clusters embedded in a non-conducting matrix. Three effects were important: (i) electric breakdown; (ii) cluster shape change due to dipole interaction, and (iii) cluster shape change due to polarisation interaction. We reveal a critical size of radioactive clusters in non-conducting matrices so that the matrix material can be damaged if clusters are larger than this critical size. The most important parameters that control the matrix integrity are the radioactive cluster (inhomogeneity) size, specific radioactivity, and effective matrix electrical conductivity. We conclude that the wasteform should be as homogeneous as possible and even electrically conductive to avoid potential damage caused by electrical charges induced by radioactive decay.

Improving high-altitude emp modeling capabilities by using a non-equilibrium electron swarm model to monitor conduction electron evolution

NASA Astrophysics Data System (ADS)

Pusateri, Elise Noel

An Electromagnetic Pulse (EMP) can severely disrupt the use of electronic devices in its path causing a significant amount of infrastructural damage. EMP can also cause breakdown of the surrounding atmosphere during lightning discharges. This makes modeling EMP phenomenon an important research effort in many military and atmospheric physics applications. EMP events include high-energy Compton electrons or photoelectrons that ionize air and produce low energy conduction electrons. A sufficient number of conduction electrons will damp or alter the EMP through conduction current. Therefore, it is important to understand how conduction electrons interact with air in order to accurately predict the EMP evolution and propagation in the air. It is common for EMP simulation codes to use an equilibrium ohmic model for computing the conduction current. Equilibrium ohmic models assume the conduction electrons are always in equilibrium with the local instantaneous electric field, i.e. for a specific EMP electric field, the conduction electrons instantaneously reach steady state without a transient process. An equilibrium model will work well if the electrons have time to reach their equilibrium distribution with respect to the rise time or duration of the EMP. If the time to reach equilibrium is comparable or longer than the rise time or duration of the EMP then the equilibrium model would not accurately predict the conduction current necessary for the EMP simulation. This is because transport coefficients used in the conduction current calculation will be found based on equilibrium reactions rates which may differ significantly from their non-equilibrium values. We see this deficiency in Los Alamos National Laboratory's EMP code, CHAP-LA (Compton High Altitude Pulse-Los Alamos), when modeling certain EMP scenarios at high altitudes, such as upward EMP, where the ionization rate by secondary electrons is over predicted by the equilibrium model, causing the EMP to short abruptly. The objective of the PhD research is to mitigate this effect by integrating a conduction electron model into CHAP-LA which can calculate the conduction current based on a non-equilibrium electron distribution. We propose to use an electron swarm model to monitor the time evolution of conduction electrons in the EMP environment which is characterized by electric field and pressure. Swarm theory uses various collision frequencies and reaction rates to study how the electron distribution and the resultant transport coefficients change with time, ultimately reaching an equilibrium distribution. Validation of the swarm model we develop is a necessary step for completion of the thesis work. After validation, the swarm model is integrated in the air chemistry model CHAP-LA employs for conduction electron simulations. We test high altitude EMP simulations with the swarm model option in the air chemistry model to show improvements in the computational capability of CHAP-LA. A swarm model has been developed that is based on a previous swarm model developed by Higgins, Longmire and O'Dell 1973, hereinafter HLO. The code used for the swarm model calculation solves a system of coupled differential equations for electric field, electron temperature, electron number density, and drift velocity. Important swarm parameters, including the momentum transfer collision frequency, energy transfer collision frequency, and ionization rate, are recalculated and compared to the previously reported empirical results given by HLO. These swarm parameters are found using BOLSIG+, a two term Boltzmann solver developed by Hagelaar and Pitchford 2005. BOLSIG+ utilizes updated electron scattering cross sections that are defined over an expanded energy range found in the atomic and molecular cross section database published by Phelps in the Phelps Database 2014 on the LXcat website created by Pancheshnyi et al. 2012. The swarm model is also updated from the original HLO model by including additional physical parameters such as the O2 electron attachment rate, recombination rate, and mutual neutralization rate. This necessitates tracking the positive and negative ion densities in the swarm model. Adding these parameters, especially electron attachment, is important at lower EMP altitudes where atmospheric density is high. We compare swarm model equilibrium temperatures and times using the HLO and BOLSIG+ coefficients for a uniform electric field of 1 StatV/cm for a range of atmospheric heights. This is done in order to test sensitivity to the swarm parameters used in the swarm model. It is shown that the equilibrium temperature and time are sensitive to the modifications in the collision frequency and ionization rate based on the updated electron interaction cross sections. We validate the swarm model by comparing ionization coefficients and equilibrium drift velocities to experimental results over a wide range of reduced electric field values. The final part of the PhD thesis work includes integrating the swarm model into CHAP-LA. We discuss the physics included in the CHAP-LA EMP model and demonstrate EMP damping behavior caused by the ohmic model at high altitudes. We report on numerical techniques for incorporation of the swarm model into CHAP-LA's Maxwell solver. This includes a discussion of integration techniques for Maxwell's equations in CHAP-LA using the swarm model calculated conduction current. We show improvements on EMP parameter calculations when modeling a high altitude, upward EMP scenario. This provides a novel computational capability that will have an important impact on the atmospheric and EMP research community.

Bioelectrical Signals and Ion Channels in the Modeling of Multicellular Patterns and Cancer Biophysics.

PubMed

Cervera, Javier; Alcaraz, Antonio; Mafe, Salvador

2016-02-04

Bioelectrical signals and ion channels are central to spatial patterns in cell ensembles, a problem of fundamental interest in positional information and cancer processes. We propose a model for electrically connected cells based on simple biological concepts: i) the membrane potential of a single cell characterizes its electrical state; ii) the long-range electrical coupling of the multicellular ensemble is realized by a network of gap junction channels between neighboring cells; and iii) the spatial distribution of an external biochemical agent can modify the conductances of the ion channels in a cell membrane and the multicellular electrical state. We focus on electrical effects in small multicellular ensembles, ignoring slow diffusional processes. The spatio-temporal patterns obtained for the local map of cell electric potentials illustrate the normalization of regions with abnormal cell electrical states. The effects of intercellular coupling and blocking of specific channels on the electrical patterns are described. These patterns can regulate the electrically-induced redistribution of charged nanoparticles over small regions of a model tissue. The inclusion of bioelectrical signals provides new insights for the modeling of cancer biophysics because collective multicellular states show electrical coupling mechanisms that are not readily deduced from biochemical descriptions at the individual cell level.

Bioelectrical Signals and Ion Channels in the Modeling of Multicellular Patterns and Cancer Biophysics

PubMed Central

Cervera, Javier; Alcaraz, Antonio; Mafe, Salvador

2016-01-01

Bioelectrical signals and ion channels are central to spatial patterns in cell ensembles, a problem of fundamental interest in positional information and cancer processes. We propose a model for electrically connected cells based on simple biological concepts: i) the membrane potential of a single cell characterizes its electrical state; ii) the long-range electrical coupling of the multicellular ensemble is realized by a network of gap junction channels between neighboring cells; and iii) the spatial distribution of an external biochemical agent can modify the conductances of the ion channels in a cell membrane and the multicellular electrical state. We focus on electrical effects in small multicellular ensembles, ignoring slow diffusional processes. The spatio-temporal patterns obtained for the local map of cell electric potentials illustrate the normalization of regions with abnormal cell electrical states. The effects of intercellular coupling and blocking of specific channels on the electrical patterns are described. These patterns can regulate the electrically-induced redistribution of charged nanoparticles over small regions of a model tissue. The inclusion of bioelectrical signals provides new insights for the modeling of cancer biophysics because collective multicellular states show electrical coupling mechanisms that are not readily deduced from biochemical descriptions at the individual cell level. PMID:26841954

Bioelectrical Signals and Ion Channels in the Modeling of Multicellular Patterns and Cancer Biophysics

NASA Astrophysics Data System (ADS)

Cervera, Javier; Alcaraz, Antonio; Mafe, Salvador

2016-02-01

Bioelectrical signals and ion channels are central to spatial patterns in cell ensembles, a problem of fundamental interest in positional information and cancer processes. We propose a model for electrically connected cells based on simple biological concepts: i) the membrane potential of a single cell characterizes its electrical state; ii) the long-range electrical coupling of the multicellular ensemble is realized by a network of gap junction channels between neighboring cells; and iii) the spatial distribution of an external biochemical agent can modify the conductances of the ion channels in a cell membrane and the multicellular electrical state. We focus on electrical effects in small multicellular ensembles, ignoring slow diffusional processes. The spatio-temporal patterns obtained for the local map of cell electric potentials illustrate the normalization of regions with abnormal cell electrical states. The effects of intercellular coupling and blocking of specific channels on the electrical patterns are described. These patterns can regulate the electrically-induced redistribution of charged nanoparticles over small regions of a model tissue. The inclusion of bioelectrical signals provides new insights for the modeling of cancer biophysics because collective multicellular states show electrical coupling mechanisms that are not readily deduced from biochemical descriptions at the individual cell level.

Canonical decomposition of magnetotelluric responses: Experiment on 1D anisotropic structures

NASA Astrophysics Data System (ADS)

Guo, Ze-qiu; Wei, Wen-bo; Ye, Gao-feng; Jin, Sheng; Jing, Jian-en

2015-08-01

Horizontal electrical heterogeneity of subsurface earth is mostly originated from structural complexity and electrical anisotropy, and local near-surface electrical heterogeneity will severely distort regional electromagnetic responses. Conventional distortion analyses for magnetotelluric soundings are primarily physical decomposition methods with respect to isotropic models, which mostly presume that the geoelectric distribution of geological structures is of local and regional patterns represented by 3D/2D models. Due to the widespread anisotropy of earth media, the confusion between 1D anisotropic responses and 2D isotropic responses, and the defects of physical decomposition methods, we propose to conduct modeling experiments with canonical decomposition in terms of 1D layered anisotropic models, and the method is one of the mathematical decomposition methods based on eigenstate analyses differentiated from distortion analyses, which can be used to recover electrical information such as strike directions, and maximum and minimum conductivity. We tested this method with numerical simulation experiments on several 1D synthetic models, which turned out that canonical decomposition is quite effective to reveal geological anisotropic information. Finally, for the background of anisotropy from previous study by geological and seismological methods, canonical decomposition is applied to real data acquired in North China Craton for 1D anisotropy analyses, and the result shows that, with effective modeling and cautious interpretation, canonical decomposition could be another good method to detect anisotropy of geological media.

Downhole transmission system

DOEpatents

Hall, David R [Provo, UT; Fox, Joe [Spanish Fork, UT

2008-01-15

A transmission system in a downhole component comprises a data transmission element in both ends of the downhole component. Each data transmission element houses an electrically conducting coil in a MCEI circular trough. An electrical conductor connects both the transmission elements. The electrical conductor comprises at least three electrically conductive elements insulated from each other. In the preferred embodiment the electrical conductor comprises an electrically conducting outer shield, an electrically conducting inner shield and an electrical conducting core. In some embodiments of the present invention, the electrical conductor comprises an electrically insulating jacket. In other embodiments, the electrical conductor comprises a pair of twisted wires. In some embodiments, the electrical conductor comprises semi-conductive material.

Crustal-scale electrical conductivity anomaly beneath inflating Lazufre volcanic complex, Central Andes

NASA Astrophysics Data System (ADS)

Budach, Ingmar; Brasse, Heinrich; Díaz, Daniel

2013-03-01

Large-scale surface deformation was observed at Lazufre volcanic center in the Central Andes of Northern Chile/Northwestern Argentina by means of Interferometric Synthetic Aperture Radar (InSAR). Uplift started there after 1998 and increased dramatically in the following years up to a rate of 3 cm/a. Lazufre is now one of the largest deforming volcano systems on Earth, but the cause for uplift - likely influx of magmatic material into the crust - is still poorly understood. In the beginning of 2010 a magnetotelluric survey was conducted to delineate the electrical conductivity distribution in the area. Several long-period magnetotelluric (LMT) sites and two broadband magnetotelluric (BBMT) sites were set up on an EW trending profile crossing the volcanic center; furthermore some LMT sites were arranged circularly around Lazufre complex and adjacent Lastarria volcano. Data were processed using an algorithm for robust and remote reference transfer function estimation. Electrical strike directions were estimated and induction arrows were derived. Although electrical strike is rather ambiguous, in a first step a 2-D resistivity model was calculated. The most prominent feature of this model is a well conducting structure rising from the upper mantle to the shallow crust beneath the center of elevation. This can be interpreted as partial melts ascending from the asthenospheric wedge and feeding a potential magma reservoir beneath Lazufre volcanic center. An improved model is finally achieved by 3-D inversion, supporting this feature. We assume that these rising melts are the source of the observed uplift at Lazufre complex.

Electron doping effects on the electrical conductivity of zigzag carbon nanotubes and corresponding unzipped armchair graphene nanoribbons

NASA Astrophysics Data System (ADS)

Mousavi, Hamze; Jalilvand, Samira; Kurdestany, Jamshid Moradi; Grabowski, Marek

2017-10-01

The Kubo formula is used to extract the electrical conductivity (EC) of different diameters of doped zigzag carbon nanotubes and their corresponding unzipped armchair graphene nanoribbons, as a function of temperature and chemical potential, within the tight-binding Hamiltonian model and Green's functions approach. The results reveal more sensitivity to temperature for semiconducting systems in addition to a decrease in EC of all systems with increasing cross-sections.

Resolving electrical conductivities from collisionally damped plasmons in isochorically heated warm dense aluminum

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

Sperling, P.; Fletcher, L. B.; Chung, H. -K.

2016-03-29

We measure the highly-resolved inelastic x-ray scattering spectrum of isochorically ultrafast heated aluminum. In the x-ray forward scattering spectra the electron temperature could be measured from the down- and upshifted plasmon, where the electron density of ne = 1:8 1023 cm 3 is known a priori. We have studied the plasmon damping by applying electron-particle collision models beyond the Born approximation determining the electrical conductivity of warm dense aluminum.

Transcleral delivery of triamcinolone acetonide and ranibizumab to retinal tissues using macroesis.

PubMed

Singh, Rishi P; Mathews, Michael Ellen; Kaufman, Michael; Riga, Alan

2010-02-01

To determine the feasibility of macroesis for the delivery of ranibizumab and triamcinolone acetonide via a transcleral route. Macroesis is a non-invasive method of drug delivery that uses alternating current (AC) to deliver drugs to target tissues. Two preclinical models of drug delivery were used for feasibility studies of delivering ranibizumab and triamcinolone acetonide to ocular tissues. In the first model, full-thickness sections of rabbit ocular tissue (conjunctiva to retina) were placed on an interdigitated electrode platform, and the drug was placed on the surface of the tissue. A non-uniform electrical field was applied to the ocular tissue, and electrical conductivity, a measurement of drug delivery, was monitored during the course of the experiment. In a second model, termed a 'simulated vitreous model,' the same full-thickness sections of rabbit ocular tissue were mounted below the electrode device, and the test compounds were placed on the electrodes. The fluid below the tissue, which simulated the vitreous cavity, was analysed using UV spectroscopy at the end of the study for the presence of drug. In the electrical conductivity studies, the electric characteristics of the tissue-drug system clearly showed movement of the drug through the tissue to the dielectric sensor based on changes in the electrical conductivity of the tissue sample with triamcinolone. No change in tissue conductivity was observed when no drug was placed. No heat generation occurred during the course of the study; nor was any gross tissue destruction noted. In the simulated vitreous model, studies using triamcinolone yielded concentrations ranging from 0.280 to 0.970 mg/ml, depending on the voltage, frequency and time applied. In as little as 6.7 min, clinically efficacious doses could be obtained in the preclinical system. Studies using ranibizumab yielded concentrations of 0.070-0.171 mg/ml, depending on the voltage, frequency, and time applied. In as little at 6.7 min, 92.8% throughput could be achieved. Successful delivery of ranibizumab and triamcinolone acetonide can be achieved with macroesis in preclinical studies.

Electrodynamic properties and height of atmospheric convective boundary layer

NASA Astrophysics Data System (ADS)

Anisimov, S. V.; Galichenko, S. V.; Mareev, E. A.

2017-09-01

We consider the relations between the mixed layer height and atmospheric electric parameters affected by convective mixing. Vertical turbulent transport of radon, its progeny and electrically charged particles is described under Lagrangian stochastic framework, which is the next step to develop a consistent model for the formation of electrical conditions in the atmospheric boundary layer. Using the data from detailed and complex measurements of vertical profiles of the temperature and turbulence statistics as input, we calculated non-stationary vertical profiles of radon and its daughter products concentrations, atmospheric electric conductivity and intensity of electric field in the convective boundary layer from the morning transition through early afternoon quasi-stationary conditions. These profiles demonstrate substantial variability due to the changing turbulent regime in the evolving boundary layer. We obtained quantitative estimates of the atmospheric electric field variability range essentially related to the sunrise and convection development. It is shown that the local change in the electrical conductivity is the only factor that can change the intensity of electric field at the earth's surface more than twice during the transition from night to day. The established relations between electric and turbulent parameters of the boundary layer indicate that the effect of sunrise is more pronounced in the case when development of convection is accompanied by an increase in aerosol concentration and, hence, a decrease in local conductivity.

Advanced single permanent magnet axipolar ironless stator ac motor for electric passenger vehicles

NASA Technical Reports Server (NTRS)

Beauchamp, E. D.; Hadfield, J. R.; Wuertz, K. L.

1983-01-01

A program was conducted to design and develop an advanced-concept motor specifically created for propulsion of electric vehicles with increased range, reduced energy consumption, and reduced life-cycle costs in comparison with conventional systems. The motor developed is a brushless, dc, rare-earth cobalt, permanent magnet, axial air gap inductor machine that uses an ironless stator. Air cooling is inherent provided by the centrifugal-fan action of the rotor poles. An extensive design phase was conducted, which included analysis of the system performance versus the SAE J227a(D) driving cycle. A proof-of-principle model was developed and tested, and a functional model was developed and tested. Full generator-level testing was conducted on the functional model, recording electromagnetic, thermal, aerodynamic, and acoustic noise data. The machine demonstrated 20.3 kW output at 1466 rad/s and 160 dc. The novel ironless stator demonstated the capability to continuously operate at peak current. The projected system performance based on the use of a transistor inverter is 23.6 kW output power at 1466 rad/s and 83.3 percent efficiency. Design areas of concern regarding electric vehicle applications include the inherently high windage loss and rotor inertia.

Spin Transport in Electric-Barrier-Modulated Ferromagnetic/Normal/Ferromagnetic Monolayer Zigzag MoS2 Nanoribbon Junction

NASA Astrophysics Data System (ADS)

Xia, Y.-Y.; Yuan, R.-Y.; Yang, Q.-J.; Sun, Q.; Zheng, J.; Guo, Y.

In this paper, with the three-band tight-binding model and non-equilibrium Green’s function technique, we investigate spin transport in electric-barrier-modulated Ferromagnetic/Normal/Ferromagnetic (F/N/F) monolayer (ML) zigzag MoS2 nanoribbon junction. The results demonstrate that once the double electric barriers structure emerges, the oscillations of spin conductances become violent, especially for spin-down conductance, the numbers of resonant peaks increase obviously, thus we can obtain 100% spin polarization in the low energy region. It is also found that with the intensity of the exchange field enhancement, the resonant peaks of spin-up and spin-down conductances move in the opposite direction in a certain energy region. As a consequence, the spin-down conductance can be filtered out completely. The findings here indicate that the present structure may be considered as a good candidate for spin filter.

Thermo-structural analysis and electrical conductivity behavior of epoxy/metals composites

NASA Astrophysics Data System (ADS)

Boumedienne, N.; Faska, Y.; Maaroufi, A.; Pinto, G.; Vicente, L.; Benavente, R.

2017-05-01

This paper reports on the elaboration and characterization of epoxy resin filled with metallic particles powder (aluminum, tin and zinc) composites. The scanning electron microscopy (SEM) pictures, density measurements and x-ray diffraction analysis (DRX) showed a homogeneous phase of obtained composites. The differential scanning calorimetry revealed a good adherence at matrix-filler interfaces, confirming the SEM observations. The measured glass transition temperatures depend on composites fillers' nature. Afterwards, the electrical conductivity of composites versus their fillers' contents has been investigated. The obtained results depict a nonlinear behavior, indicating an insulator to conductor phase transition at a conduction threshold; with high contrast of ten decades. Hence, the elaborated materials give a possibility to obtain dielectric or electrically conducting phases, which can to be interesting in the choice of desired applications. Finally, the obtained results have been successfully simulated on the basis of different percolation models approach combined with structural characterization inferences.

Disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars

NASA Astrophysics Data System (ADS)

Horowitz, C. J.; Berry, D. K.; Briggs, C. M.; Caplan, M. E.; Cumming, A.; Schneider, A. S.

2015-04-01

Nuclear pasta, with non-spherical shapes, is expected near the base of the crust in neutron stars. Large scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low conductivity pasta layer by increasing an impurity parameter Qimp. Predictions of light curves for the low mass X-ray binary MXB 1659-29, assuming a large Qimp, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust). This research was supported in part by DOE Grants DE-FG02-87ER40365 (Indiana University) and DE-SC0008808 (NUCLEI SciDAC Collaboration).

Electronic transport coefficients in plasmas using an effective energy-dependent electron-ion collision-frequency

NASA Astrophysics Data System (ADS)

Faussurier, G.; Blancard, C.; Combis, P.; Decoster, A.; Videau, L.

2017-10-01

We present a model to calculate the electrical and thermal electronic conductivities in plasmas using the Chester-Thellung-Kubo-Greenwood approach coupled with the Kramers approximation. The divergence in photon energy at low values is eliminated using a regularization scheme with an effective energy-dependent electron-ion collision-frequency. Doing so, we interpolate smoothly between the Drude-like and the Spitzer-like regularizations. The model still satisfies the well-known sum rule over the electrical conductivity. Such kind of approximation is also naturally extended to the average-atom model. A particular attention is paid to the Lorenz number. Its nondegenerate and degenerate limits are given and the transition towards the Drude-like limit is proved in the Kramers approximation.

Nonequilibrium simulations of model ionomers in an oscillating electric field

DOE PAGES

Ting, Christina L.; Sorensen-Unruh, Karen E.; Stevens, Mark J.; ...

2016-07-25

Here, we perform molecular dynamics simulations of a coarse-grained model of ionomer melts in an applied oscillating electric field. The frequency-dependent conductivity and susceptibility are calculated directly from the current density and polarization density, respectively. At high frequencies, we find a peak in the real part of the conductivity due to plasma oscillations of the ions. At lower frequencies, the dynamic response of the ionomers depends on the ionic aggregate morphology in the system, which consists of either percolated or isolated aggregates. We show that the dynamic response of the model ionomers to the applied oscillating field can be understoodmore » by comparison with relevant time scales in the systems, obtained from independent calculations.« less

Nonequilibrium simulations of model ionomers in an oscillating electric field

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

Ting, Christina L.; Sorensen-Unruh, Karen E.; Stevens, Mark J.

Here, we perform molecular dynamics simulations of a coarse-grained model of ionomer melts in an applied oscillating electric field. The frequency-dependent conductivity and susceptibility are calculated directly from the current density and polarization density, respectively. At high frequencies, we find a peak in the real part of the conductivity due to plasma oscillations of the ions. At lower frequencies, the dynamic response of the ionomers depends on the ionic aggregate morphology in the system, which consists of either percolated or isolated aggregates. We show that the dynamic response of the model ionomers to the applied oscillating field can be understoodmore » by comparison with relevant time scales in the systems, obtained from independent calculations.« less

Electrical transport properties of individual WS2 nanotubes and their dependence on water and oxygen absorption

NASA Astrophysics Data System (ADS)

Zhang, Chaoying; Ning, Zhiyuan; Liu, Yang; Xu, Tingting; Guo, Yao; Zak, Alla; Zhang, Zhiyong; Wang, Sheng; Tenne, Reshef; Chen, Qing

2012-09-01

The electrical properties of WS2 nanotubes (NTs) were studied through measuring 59 devices. Important electrical parameters, such as the carrier concentration, mobility, and effective barrier height at the contacts, were obtained through fitting experimental non-linear I-V curves using a metal-semiconductor-metal model. The carrier mobility was found to be several orders of magnitude higher than that have been reported previously for WS2 NTs. Water absorption was found to decrease the conductivity and carrier mobility of the NTs, and could be removed when the sample was dried. Oxygen absorption also slightly decreased the conductivity of WS2 NTs.

Study of electrical conductivity and memory switching in the zinc-vanadium-phosphate glasses

NASA Astrophysics Data System (ADS)

Mirzayi, M.; Hekmatshoar, M. H.

2013-07-01

Vanadium zinc phosphate glasses were prepared by the conventional melt quenching technique and effect of V2O5 concentration on d.c. conductivity of prepared samples were investigated. X-ray diffraction patterns confirmed the glassy character of the samples. The d.c. conductivity increased with increase in V2O5 content. Results showed that activation energy has a single value in the investigated range of temperature, which can be explained in accordance with Mott small pollaron hopping model. I-V characteristics at high electric field showed that switching in these glasses was memory type. The threshold field of switching was found to decrease with increase in V2O5 content. Non-linear behavior and switching phenomenon was explained by Pool-Frenkel effect and thermal model.

Thermal constitutive matrix applied to asynchronous electrical machine using the cell method

NASA Astrophysics Data System (ADS)

Domínguez, Pablo Ignacio González; Monzón-Verona, José Miguel; Rodríguez, Leopoldo Simón; Sánchez, Adrián de Pablo

2018-03-01

This work demonstrates the equivalence of two constitutive equations. One is used in Fourier's law of the heat conduction equation, the other in electric conduction equation; both are based on the numerical Cell Method, using the Finite Formulation (FF-CM). A 3-D pure heat conduction model is proposed. The temperatures are in steady state and there are no internal heat sources. The obtained results are compared with an equivalent model developed using the Finite Elements Method (FEM). The particular case of 2-D was also studied. The errors produced are not significant at less than 0.2%. The number of nodes is the number of the unknowns and equations to resolve. There is no significant gain in precision with increasing density of the mesh.

In-Situ Wire Damage Detection System

NASA Technical Reports Server (NTRS)

Jolley, Scott T. (Inventor); Gibson, Tracy L. (Inventor); Medelius, Pedro J. (Inventor); Roberson, Luke B. (Inventor); Tate, Lanetra C. (Inventor); Smith, Trent M. (Inventor); Williams, Martha K. (Inventor)

2014-01-01

An in-situ system for detecting damage in an electrically conductive wire. The system includes a substrate at least partially covered by a layer of electrically conductive material forming a continuous or non-continuous electrically conductive layer connected to an electrical signal generator adapted to delivering electrical signals to the electrically conductive layer. Data is received and processed to identify damage to the substrate or electrically conductive layer. The electrically conductive material may include metalized carbon fibers, a thin metal coating, a conductive polymer, carbon nanotubes, metal nanoparticles or a combination thereof.

Optimizing amorphous indium zinc oxide film growth for low residual stress and high electrical conductivity

NASA Astrophysics Data System (ADS)

Kumar, Mukesh; Sigdel, A. K.; Gennett, T.; Berry, J. J.; Perkins, J. D.; Ginley, D. S.; Packard, C. E.

2013-10-01

With recent advances in flexible electronics, there is a growing need for transparent conductors with optimum conductivity tailored to the application and nearly zero residual stress to ensure mechanical reliability. Within amorphous transparent conducting oxide (TCO) systems, a variety of sputter growth parameters have been shown to separately impact film stress and optoelectronic properties due to the complex nature of the deposition process. We apply a statistical design of experiments (DOE) approach to identify growth parameter-material property relationships in amorphous indium zinc oxide (a-IZO) thin films and observed large, compressive residual stresses in films grown under conditions typically used for the deposition of highly conductive samples. Power, growth pressure, oxygen partial pressure, and RF power ratio (RF/(RF + DC)) were varied according to a full-factorial test matrix and each film was characterized. The resulting regression model and analysis of variance (ANOVA) revealed significant contributions to the residual stress from individual growth parameters as well as interactions of different growth parameters, but no conditions were found within the initial growth space that simultaneously produced low residual stress and high electrical conductivity. Extrapolation of the model results to lower oxygen partial pressures, combined with prior knowledge of conductivity-growth parameter relationships in the IZO system, allowed the selection of two promising growth conditions that were both empirically verified to achieve nearly zero residual stress and electrical conductivities >1480 S/cm. This work shows that a-IZO can be simultaneously optimized for high conductivity and low residual stress.

Organic/inorganic hybrid synaptic transistors gated by proton conducting methylcellulose films

NASA Astrophysics Data System (ADS)

Wan, Chang Jin; Zhu, Li Qiang; Wan, Xiang; Shi, Yi; Wan, Qing

2016-01-01

The idea of building a brain-inspired cognitive system has been around for several decades. Recently, electric-double-layer transistors gated by ion conducting electrolytes were reported as the promising candidates for synaptic electronics and neuromorphic system. In this letter, indium-zinc-oxide transistors gated by proton conducting methylcellulose electrolyte films were experimentally demonstrated with synaptic plasticity including paired-pulse facilitation and spatiotemporal-correlated dynamic logic. More importantly, a model based on proton-related electric-double-layer modulation and stretched-exponential decay function was proposed, and the theoretical results are in good agreement with the experimentally measured synaptic behaviors.

Organic/inorganic hybrid synaptic transistors gated by proton conducting methylcellulose films

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

Wan, Chang Jin; Wan, Qing, E-mail: wanqing@nju.edu.cn, E-mail: yshi@nju.edu.cn; Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201

The idea of building a brain-inspired cognitive system has been around for several decades. Recently, electric-double-layer transistors gated by ion conducting electrolytes were reported as the promising candidates for synaptic electronics and neuromorphic system. In this letter, indium-zinc-oxide transistors gated by proton conducting methylcellulose electrolyte films were experimentally demonstrated with synaptic plasticity including paired-pulse facilitation and spatiotemporal-correlated dynamic logic. More importantly, a model based on proton-related electric-double-layer modulation and stretched-exponential decay function was proposed, and the theoretical results are in good agreement with the experimentally measured synaptic behaviors.

Electrical conductivity of the crust in central Baja California, México, based on magnetotelluric observations

NASA Astrophysics Data System (ADS)

Romo, J. M.; Gómez-Treviño, E.; Flores-Luna, C.; García-Abdeslem, J.

2017-12-01

Crustal and sub-crustal structure of northwestern Mexico (peninsular California) resulted from major accretion episodes occurred during the long-lived subduction of the Farallon plate beneath the North American plate, since late Jurassic time. A magnetotelluric profile across central Baja California reveals several electrical conductivity anomalies probably associated to the crustal boundaries of distinct Mezosoic terranes juxtaposed in the current peninsular crust. It is known that electrical conductivity is significantly increased by the pervasive presence of conductive minerals generated during metamorphic processes in highly sheared zones. We interpret a striking sub-horizontal conductivity anomaly reveled in the model as explained by the presence of high-salinity fluids released after dehydration of the subducted Magdalena microplate (Farallon plate?). The presence of fluids at the base of the peninsular crust may produce a zone of weakness, which supports the idea that Baja California lithosphere has not been entirely coupled to the Pacific plate. In addition, crustal thickness is estimated in our model in about 35 km beneath the western Peninsular Ranges batholith (PRB) and 20 km beneath the eastern PRB. This crustal thickness is in good agreement with independent estimations of a thinner crust in the Gulf of California margin and a thicker crust along the axial PRB.

Quantifying Power Grid Risk from Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Homeier, N.; Wei, L. H.; Gannon, J. L.

2012-12-01

We are creating a statistical model of the geophysical environment that can be used to quantify the geomagnetic storm hazard to power grid infrastructure. Our model is developed using a database of surface electric fields for the continental United States during a set of historical geomagnetic storms. These electric fields are derived from the SUPERMAG compilation of worldwide magnetometer data and surface impedances from the United States Geological Survey. This electric field data can be combined with a power grid model to determine GICs per node and reactive MVARs at each minute during a storm. Using publicly available substation locations, we derive relative risk maps by location by combining magnetic latitude and ground conductivity. We also estimate the surface electric fields during the August 1972 geomagnetic storm that caused a telephone cable outage across the middle of the United States. This event produced the largest surface electric fields in the continental U.S. in at least the past 40 years.

Performance of a Fuel-Cell-Powered, Small Electric Airplane Assessed

NASA Technical Reports Server (NTRS)

Berton, Jeffrey J.

2004-01-01

Rapidly emerging fuel-cell-power technologies may be used to launch a new revolution of electric propulsion systems for light aircraft. Future small electric airplanes using fuel cell technologies hold the promise of high reliability, low maintenance, low noise, and - with the exception of water vapor - zero emissions. An analytical feasibility and performance assessment was conducted by NASA Glenn Research Center's Airbreathing Systems Analysis Office of a fuel-cell-powered, propeller-driven, small electric airplane based on a model of the MCR-01 two-place kitplane (Dyn'Aero, Darois, France). This assessment was conducted in parallel with an ongoing effort by the Advanced Technology Products Corporation and the Foundation for Advancing Science and Technology Education. Their project - partially funded by a NASA grant - is to design, build, and fly the first manned, continuously propelled, nongliding electric airplane. In our study, an analytical performance model of a proton exchange membrane (PEM) fuel cell propulsion system was developed and applied to a notional, two-place light airplane modeled after the MCR-01 kitplane. The PEM fuel cell stack was fed pure hydrogen fuel and humidified ambient air via a small automotive centrifugal supercharger. The fuel cell performance models were based on chemical reaction analyses calibrated with published data from the fledgling U.S. automotive fuel cell industry. Electric propeller motors, rated at two shaft power levels in separate assessments, were used to directly drive a two-bladed, variable-pitch propeller. Fuel sources considered were compressed hydrogen gas and cryogenic liquid hydrogen. Both of these fuel sources provided pure, contaminant-free hydrogen for the PEM cells.

On the modeling and characterization of an interlocked flexible electronic skin

NASA Astrophysics Data System (ADS)

Khalili, Nazanin; Shen, Xuechen; Naguib, Hani E.

2017-04-01

Development of an electronic skin with ultra-high pressure sensitivity is now of critical importance due its broad range of applications including prosthetic skins and biomimetic robotics. Microstructured conductive composite elastomers can acquire mechanical and electrical properties analogous to those of natural skin. One of the most prominent features of human skin is its tactile sensing property which can be mimicked in an electronic skin. Herein, an electrically conductive composite comprising polydimethylsiloxane and conductive fillers is used as a flexible and stretchable piezoresistive sensor. The electrical conductivity is induced within the elastomer matrix via carbon nanotubes whereas the piezoresistivity is obtained by means of microstructuring the surface of the substrate. An interlocked array of pyramids in micro-scale allows the change in the contact resistance between two thin layers of the composite upon application of an external load. Deformation of the interlocked arrays endows the sensor with an ultra-high sensitivity to the external pressures within the range of human skin perception. Moreover, using finite element analysis, the change in the contact are between the two layers was captured for different geometries. The structure of the sensor can be optimized through an optimization model in order to acquire maximum sensitivity.

FDTD Modeling of LEMP Propagation in the Earth-Ionosphere Waveguide With Emphasis on Realistic Representation of Lightning Source

NASA Astrophysics Data System (ADS)

Tran, Thang H.; Baba, Yoshihiro; Somu, Vijaya B.; Rakov, Vladimir A.

2017-12-01

The finite difference time domain (FDTD) method in the 2-D cylindrical coordinate system was used to compute the nearly full-frequency-bandwidth vertical electric field and azimuthal magnetic field waveforms produced on the ground surface by lightning return strokes. The lightning source was represented by the modified transmission-line model with linear current decay with height, which was implemented in the FDTD computations as an appropriate vertical phased-current-source array. The conductivity of atmosphere was assumed to increase exponentially with height, with different conductivity profiles being used for daytime and nighttime conditions. The fields were computed at distances ranging from 50 to 500 km. Sky waves (reflections from the ionosphere) were identified in computed waveforms and used for estimation of apparent ionospheric reflection heights. It was found that our model reproduces reasonably well the daytime electric field waveforms measured at different distances and simulated (using a more sophisticated propagation model) by Qin et al. (2017). Sensitivity of model predictions to changes in the parameters of atmospheric conductivity profile, as well as influences of the lightning source characteristics (current waveshape parameters, return-stroke speed, and channel length) and ground conductivity were examined.

Repulsion-based model for contact angle saturation in electrowetting

PubMed Central

2015-01-01

We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results. PMID:25759748

Repulsion-based model for contact angle saturation in electrowetting.

PubMed

Ali, Hassan Abdelmoumen Abdellah; Mohamed, Hany Ahmed; Abdelgawad, Mohamed

2015-01-01

We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results.

Quantitative assessment of passive electrical properties of the cardiac T-tubular system by FRAP microscopy

PubMed Central

Scardigli, M.; Ferrantini, C.; Gabbrielli, T.; Silvestri, L.; Coppini, R.; Tesi, C.; Rog-Zielinska, E. A.; Kohl, P.; Cerbai, E.; Poggesi, C.; Pavone, F. S.; Sacconi, L.

2017-01-01

Well-coordinated activation of all cardiomyocytes must occur on every heartbeat. At the cell level, a complex network of sarcolemmal invaginations, called the transverse-axial tubular system (TATS), propagates membrane potential changes to the cell core, ensuring synchronous and uniform excitation–contraction coupling. Although myocardial conduction of excitation has been widely described, the electrical properties of the TATS remain mostly unknown. Here, we exploit the formal analogy between diffusion and electrical conductivity to link the latter with the diffusional properties of TATS. Fluorescence recovery after photobleaching (FRAP) microscopy is used to probe the diffusion properties of TATS in isolated rat cardiomyocytes: A fluorescent dextran inside TATS lumen is photobleached, and signal recovery by diffusion of unbleached dextran from the extracellular space is monitored. We designed a mathematical model to correlate the time constant of fluorescence recovery with the apparent diffusion coefficient of the fluorescent molecules. Then, apparent diffusion is linked to electrical conductivity and used to evaluate the efficiency of the passive spread of membrane depolarization along TATS. The method is first validated in cells where most TATS elements are acutely detached by osmotic shock and then applied to probe TATS electrical conductivity in failing heart cells. We find that acute and pathological tubular remodeling significantly affect TATS electrical conductivity. This may explain the occurrence of defects in action potential propagation at the level of single T-tubules, recently observed in diseased cardiomyocytes. PMID:28507142

Large Enhancement of Thermal Conductivity and Lorenz Number in Topological Insulator Thin Films.

PubMed

Luo, Zhe; Tian, Jifa; Huang, Shouyuan; Srinivasan, Mithun; Maassen, Jesse; Chen, Yong P; Xu, Xianfan

2018-02-27

Topological insulators (TI) have attracted extensive research effort due to their insulating bulk states but conducting surface states. However, investigation and understanding of thermal transport in topological insulators, particularly the effect of surface states, are lacking. In this work, we studied thickness-dependent in-plane thermal and electrical conductivity of Bi 2 Te 2 Se TI thin films. A large enhancement in both thermal and electrical conductivity was observed for films with thicknesses below 20 nm, which is attributed to the surface states and bulk-insulating nature of these films. Moreover, a surface Lorenz number much larger than the Sommerfeld value was found. Systematic transport measurements indicated that the Fermi surface is located near the charge neutrality point (CNP) when the film thickness is below 20 nm. Possible reasons for the large Lorenz number include electrical and thermal current decoupling in the surface state Dirac fluid, and bipolar diffusion transport. A simple computational model indicates that the surface states and bipolar diffusion indeed can lead to enhanced electrical and thermal transport and a large Lorenz number.

The Kubo-Greenwood spin-dependent electrical conductivity of 2D transition-metal dichalcogenides and group-IV materials: A Green's function study

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Yarmohammadi, Mohsen

2018-04-01

The spin-dependent electrical conductivity of counterparts of graphene, transition-metal dichalcogenides (TMDs) and group-IV nanosheets, have investigated by a magnetic exchange field (MEF)-induction to gain the electronic transport properties of charge carriers. We have implemented a k.p Hamiltonian model through the Kubo-Greenwood formalism in order to address the dynamical behavior of correlated Dirac fermions. Tuning the MEF enables one to control the effective mass of carriers in group-IV and TMDs, differently. We have found the Dirac-like points in a new quantum anomalous Hall (QAH) state at strong MEFs for both structures. For both cases, a broad peak in electrical conductivity originated from the scattering rate and entropy is observed. Spin degeneracy at some critical MEFs is another remarkable point. We have found that in the limit of zero or uniform MEFs with respect to the spin-orbit interaction, the large resulting electrical conductivity depends on the spin sub-bands in group-IV and MLDs. Featuring spin-dependent electronic transport properties, one can provide a new scenario for future possible applications.

Performance characteristics of an electric vehicle lead-acid battery pack at elevated temperatures

NASA Technical Reports Server (NTRS)

Chapman, P.

1982-01-01

Discharge testing data electric car battery pack over initial electrolyte temperature variations between 27 and 55 C are presented. The tests were conducted under laboratory conditions and then compared to detailed electric vehicle simulation models. Battery discharge capacity increased with temperature for constant current discharges, and battery energy capacity increased with temperature for constant power discharges. Dynamometer tests of the electric test vehicle showed an increase in range of 25% for the higher electrolyte temperature.

An Analytical Performance Assessment of a Fuel Cell-powered, Small Electric Airplane

NASA Technical Reports Server (NTRS)

Berton, Jeffrey J.; Freeh, Joshua E.; Wickenheiser, Timothy J.

2003-01-01

Rapidly emerging fuel cell power technologies may be used to launch a new revolution of electric propulsion systems for light aircraft. Future small electric airplanes using fuel cell technologies hold the promise of high reliability, low maintenance, low noise, and with exception of water vapor zero emissions. This paper describes an analytical feasibility and performance assessment conducted by NASA's Glenn Research Center of a fuel cell-powered, propeller-driven, small electric airplane based on a model of the MCR 01 two-place kitplane.

Investigation of vibration characteristics of electric motors

NASA Technical Reports Server (NTRS)

Bakshis, A. K.; Tamoshyunas, Y. K.

1973-01-01

The vibration characteristics of electric motors were analyzed using mathematical statistics methods. The equipment used and the method of conducting the test are described. Curves are developed to show the visualization of the electric motor vibrations in the vertical direction. Additional curves are included to show the amplitude-phase frequency characteristic of dynamic rotor-housing vibrations at the first lug and the same data for the second lug of the electric motor. Mathematical models were created to show the transmission function of the dynamic rotor housing system.

The influence of sulcus width on simulated electric fields induced by transcranial magnetic stimulation

PubMed Central

Janssen, A M; Rampersad, S M; Lucka, F; Lanfer, B; Lew, S; Aydin, Ü; Wolters, C H; Stegeman, D F; Oostendorp, T F

2013-01-01

Volume conduction models can help in acquiring knowledge about the distribution of the electric field induced by transcranial magnetic stimulation (TMS). One aspect of a detailed model is an accurate description of the cortical surface geometry. Since its estimation is difficult, it is important to know how accurate the geometry has to be represented. Previous studies only looked at the differences caused by neglecting the complete boundary between the CSF and GM (Thielscher et al. 2011; Bijsterbosch et al. 2012), or by resizing the whole brain (Wagner et al. 2008). However, due to the high conductive properties of the CSF, it can be expected that alterations in sulcus width can already have a significant effect on the distribution of the electric field. To answer this question, the sulcus width of a highly realistic head model, based on T1-, T2- and diffusion-weighted magnetic resonance images (MRI), was altered systematically. This study shows that alterations in the sulcus width do not cause large differences in the majority of the electric field values. However, considerable overestimation of sulcus width produces an overestimation of the calculated field strength, also at locations distant from the target location. PMID:23787706

Evaluating the potential for quantitative monitoring of in situ chemical oxidation of aqueous-phase TCE using in-phase and quadrature electrical conductivity

NASA Astrophysics Data System (ADS)

Hort, R. D.; Revil, A.; Munakata-Marr, J.; Mao, D.

2015-07-01

Electrical resistivity measurements can potentially be used to remotely monitor fate and transport of ionic oxidants such as permanganate (MnO4-) during in situ chemical oxidation (ISCO) of contaminants like trichloroethene (TCE). Time-lapse two-dimensional bulk conductivity and induced polarization surveys conducted during a sand tank ISCO simulation demonstrated that MnO4- plume movement could be monitored in a qualitative manner using bulk conductivity tomograms, although chargeability was below sensitivity limits. We also examined changes to in-phase and quadrature electrical conductivity resulting from ion injection, MnO2 and Cl- production, and pH change during TCE and humate oxidation by MnO4- in homogeneous aqueous solutions and saturated porous media samples. Data from the homogeneous samples demonstrated that inversion of the sand tank resistivity data using a common Tikhonov regularization approach was insufficient to recover an accurate conductivity distribution within the tank. While changes to in-phase conductivity could be successfully modeled, quadrature conductivity values could not be directly related to TCE oxidation product or MnO4- concentrations at frequencies consistent with field induced polarization surveys, limiting the utility of quadrature conductivity for monitoring ISCO.

One-dimensional nonlinear instability study of a slightly viscoelastic, perfectly conducting liquid jet under a radial electric field

NASA Astrophysics Data System (ADS)

Li, Fang; Yin, Xie-Yuan; Yin, Xie-Zhen

2016-05-01

A one-dimensional electrified viscoelastic model is built to study the nonlinear behavior of a slightly viscoelastic, perfectly conducting liquid jet under a radial electric field. The equations are solved numerically using an implicit finite difference scheme together with a boundary element method. The electrified viscoelastic jet is found to evolve into a beads-on-string structure in the presence of the radial electric field. Although the radial electric field greatly enhances the linear instability of the jet, its influence on the decay of the filament thickness is limited during the nonlinear evolution of the jet. On the other hand, the radial electric field induces axial non-uniformity of the first normal stress difference within the filament. The first normal stress difference in the center region of the filament may be greatly decreased by the radial electric field. The regions with/without satellite droplets are illuminated on the χ (the electrical Bond number)-k (the dimensionless wave number) plane. Satellite droplets may be formed for larger wave numbers at larger radial electric fields.

Electrical Conductivity Distributions in Discrete Fluid-Filled Fractures

NASA Astrophysics Data System (ADS)

James, S. C.; Ahmmed, B.; Knox, H. A.; Johnson, T.; Dunbar, J. A.

2017-12-01

It is commonly asserted that hydraulic fracturing enhances permeability by generating new fractures in the reservoir. Furthermore, it is assumed that in the fractured system predominant flow occurs in these newly formed and pre-existing fractures. Among the phenomenology that remains enigmatic are fluid distributions inside fractures. Therefore, determining fluid distribution and their associated temporal and spatial evolution in fractures is critical for safe and efficient hydraulic fracturing. Previous studies have used both forward modeling and inversion of electrical data to show that a geologic system consisting of fluid filled fractures has a conductivity distribution, where fractures act as electrically conductive bodies when the fluids are more conductive than the host material. We will use electrical inversion for estimating electrical conductivity distribution within multiple fractures from synthetic and measured data. Specifically, we will use data and well geometries from an experiment performed at Blue Canyon Dome in Socorro, NM, which was used as a study site for subsurface technology, engineering, and research (SubTER) funded by DOE. This project used a central borehole for energetically stimulating the system and four monitoring boreholes, emplaced in the cardinal directions. The electrical data taken during this project used 16 temporary electrodes deployed in the stimulation borehole and 64 permanent electrodes in the monitoring wells (16 each). We present results derived using E4D from scenarios with two discrete fractures, thereby discovering the electric potential response of both spatially and temporarily variant fluid distribution and the resolution of fluid and fracture boundaries. These two fractures have dimensions of 3m × 0.01m × 7m and are separated by 1m. These results can be used to develop stimulation and flow tests at the meso-scale that will be important for model validation. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

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

Tooker, Angela C.; Felix, Sarah H.; Pannu, Satinderpall S.

A neural interface includes a first dielectric material having at least one first opening for a first electrical conducting material, a first electrical conducting material in the first opening, and at least one first interconnection trace electrical conducting material connected to the first electrical conducting material. A stiffening shank material is located adjacent the first dielectric material, the first electrical conducting material, and the first interconnection trace electrical conducting material.

Branching Patterns and Stepped Leaders in an Electric-Circuit Model for Creeping Discharge

NASA Astrophysics Data System (ADS)

Hidetsugu Sakaguchi,; Sahim M. Kourkouss,

2010-06-01

We construct a two-dimensional electric circuit model for creeping discharge. Two types of discharge, surface corona and surface leader, are modeled by a two-step function of conductance. Branched patterns of surface leaders surrounded by the surface corona appear in numerical simulation. The fractal dimension of branched discharge patterns is calculated by changing voltage and capacitance. We find that surface leaders often grow stepwise in time, as is observed in lightning leaders of thunder.

Influence of anisotropic conductivity in the skull and white matter on transcranial direct current stimulation via an anatomically realistic finite element head model

NASA Astrophysics Data System (ADS)

Suh, Hyun Sang; Lee, Won Hee; Kim, Tae-Seong

2012-11-01

To establish safe and efficient transcranial direct current stimulation (tDCS), it is of particular importance to understand the electrical effects of tDCS in the brain. Since the current density (CD) and electric field (EF) in the brain generated by tDCS depend on various factors including complex head geometries and electrical tissue properties, in this work, we investigated the influence of anisotropic conductivity in the skull and white matter (WM) on tDCS via a 3D anatomically realistic finite element head model. We systematically incorporated various anisotropic conductivity ratios into the skull and WM. The effects of anisotropic tissue conductivity on the CD and EF were subsequently assessed through comparisons to the conventional isotropic solutions. Our results show that the anisotropic skull conductivity significantly affects the CD and EF distribution: there is a significant reduction in the ratio of the target versus non-target total CD and EF on the order of 12-14%. In contrast, the WM anisotropy does not significantly influence the CD and EF on the targeted cortical surface, only on the order of 1-3%. However, the WM anisotropy highly alters the spatial distribution of both the CD and EF inside the brain. This study shows that it is critical to incorporate anisotropic conductivities in planning of tDCS for improved efficacy and safety.

Field-aligned current sources in the high-latitude ionosphere

NASA Technical Reports Server (NTRS)

Barbosa, D. D.

1979-01-01

The paper determines the electric potential in a plane which is fed current from a pair of field-aligned current sheets. The ionospheric conductivity is modelled as a constant with an enhanced conductivity annular ring. It is shown that field-aligned current distributions are arbitrary functions of azimuth angle (MLT) and thus allow for asymmetric potential configurations over the pole cap. In addition, ionospheric surface currents are computed by means of stream functions. Finally, the discussion relates these methods to the electrical characteristics of the magnetosphere.

Application of classical thermodynamics to the conductivity in non-polar media

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

Gourdin-Bertin, S.; Chassagne, C.

Electrical conductivity in non-polar media is a subject which recently regained interest. If most of experiments and theoretical developments were done more than 50 years ago, new experiments and theories have been recently published. As the electrical conductivity describes, at low field, the equilibrium state of a system, it is natural to apply theories based on equilibrium thermodynamics. In this article, well-established classical thermodynamics and solvations models are applied to recently published data. This enables to get a new insight in intriguing phenomena, such as the linear dependence of the conductivity on the concentration of ionic surfactant and the evaluationmore » of conductivity for the mixture of two miscible fluids, such as alcohol and alcane, which have very different conductivities.« less

High Performance Polymer Memory and Its Formation

DTIC Science & Technology

2007-04-26

the retention time of the device was performed to estimate the barrier height of the charge trap . The activation energy was approximated to be about...characteristics and presented a model to explain the mechanism of electrical switching in the device. By exploiting an electric-field induced charge transfer...electrical current in the high conductivity state would be due to some temperature-independent charge tunneling processes. The IV curves could be

Transport of water and ions in partially water-saturated porous media. Part 1. Constitutive equations

NASA Astrophysics Data System (ADS)

Revil, A.

2017-05-01

I developed a model of cross-coupled flow in partially saturated porous media based on electrokinetic coupling including the effect of ion filtration (normal and reverse osmosis) and the multi-component nature of the pore water (wetting) phase. The model also handles diffusion and membrane polarization but is valid only for saturations above the irreducible water saturation. I start with the local Nernst-Planck and Stokes equations and I use a volume-averaging procedure to obtain the generalized Ohm, Fick, and Darcy equations with cross-coupling terms at the scale of a representative elementary volume of the porous rock. These coupling terms obey Onsager's reciprocity, which is a required condition, at the macroscale, to keep the total dissipation function of the system positive. Rather than writing the electrokinetic terms in terms of zeta potential (the double layer electrical potential on the slipping plane located in the pore water), I developed the model in terms of an effective charge density dragged by the flow of the pore water. This effective charge density is found to be strongly controlled by the permeability and the water saturation. I also developed an electrical conductivity equation including the effect of saturation on both bulk and surface conductivities, the surface conductivity being associated with electromigration in the electrical diffuse layer coating the grains. This surface conductivity depends on the CEC of the porous material.

Multiscale properties of unconventional reservoir rocks

NASA Astrophysics Data System (ADS)

Woodruff, W. F.

A multidisciplinary study of unconventional reservoir rocks is presented, providing the theory, forward modeling and Bayesian inverse modeling approaches, and laboratory protocols to characterize clay-rich, low porosity and permeability shales and mudstones within an anisotropic framework. Several physical models characterizing oil and gas shales are developed across multiple length scales, ranging from microscale phenomena, e.g. the effect of the cation exchange capacity of reactive clay mineral surfaces on water adsorption isotherms, and the effects of infinitesimal porosity compaction on elastic and electrical properties, to meso-scale phenomena, e.g. the role of mineral foliations, tortuosity of conduction pathways and the effects of organic matter (kerogen and hydrocarbon fractions) on complex conductivity and their connections to intrinsic electrical anisotropy, as well as the macro-scale electrical and elastic properties including formulations for the complex conductivity tensor and undrained stiffness tensor within the context of effective stress and poroelasticity. Detailed laboratory protocols are described for sample preparation and measurement of these properties using spectral induced polarization (SIP) and ultrasonics for the anisotropic characterization of shales for both unjacketed samples under benchtop conditions and jacketed samples under differential loading. An ongoing study of the effects of kerogen maturation through hydrous pyrolysis on the complex conductivity is also provided in review. Experimental results are catalogued and presented for various unconventional formations in North America including the Haynesville, Bakken, and Woodford shales.

The Effect of Precipitating Electrons and Ions on Ionospheric Conductance and Inner Magnetospheric Electric Fields 142106

NASA Astrophysics Data System (ADS)

Chen, M.; Lemon, C.; Hecht, J. H.; Evans, J. S.; Boyd, A. J.

2016-12-01

We investigate how scattering of electrons by waves and of ions by field-line curvature in the inner magnetosphere affect precipitating energy flux distributions and how the precipitating particles modify the ionospheric conductivity and electric potentials during magnetic storms. We examine how particle precipitation in the evening sector affects the development of the Sub-Auroral Polarization Stream (SAPS) electric field that is observed at sub-auroral latitudes in that sector as well as the electric field in the morning sector. Our approach is to use the magnetically and electrically self-consistent Rice Convection Model - Equilibrium (RCM-E) of the inner magnetosphere to simulate the stormtime precipitating particle distributions and the electric field. We use parameterized rates of whistler-generated electron pitch-angle scattering from Orlova and Shprits [JGR, 2014] that depend on equatorial radial distance, magnetic activity (Kp), and magnetic local time (MLT) outside the simulated plasmasphere. Inside the plasmasphere, parameterized scattering rates due to hiss [Orlova et al., GRL, 2014] are employed. Our description for the rate of ion scattering is more simplistic. We assume that the ions are scattered at a fraction of strong pitch-angle scattering where the fraction is scaled by epsilon, the ratio of the gyroradius to the field-line radius of curvature, when epsilon is greater than 0.1. We compare simulated trapped and precipitating electron/ion flux distributions with measurements from Van Allen Probes/MagEIS, POES and DMSP, respectively, to validate the particle loss models. DMSP observations of electric fields are compared with the simulation results. We discuss the effect of precipitating electrons and ions on the SAPS and the inner magnetospheric electric field through the data-model comparisons.

Studies on the electrical transport properties of carbon nanotube composites

NASA Astrophysics Data System (ADS)

Tarlton, Taylor Warren

This work presents a probabilistic approach to model the electrical transport properties of carbon nanotube composite materials. A pseudo-random generation method is presented with the ability to generate 3-D samples with a variety of different configurations. Periodic boundary conditions are employed in the directions perpendicular to transport to minimize edge effects. Simulations produce values for drift velocity, carrier mobility, and conductivity in samples that account for geometrical features resembling those found in the lab. All results show an excellent agreement to the well-known power law characteristic of percolation processes, which is used to compare across simulations. The effect of sample morphology, like nanotube waviness and aspect ratio, and agglomeration on charge transport within CNT composites is evaluated within this model. This study determines the optimum simulation box-sizes that lead to minimize size-effects without rendering the simulation unaffordable. In addition, physical parameters within the model are characterized, involving various density functional theory calculations within Atomistix Toolkit. Finite element calculations have been performed to solve Maxwell's Equations for static fields in the COMSOL Multiphysics software package in order to better understand the behavior of the electric field within the composite material to further improve the model within this work. The types of composites studied within this work are often studied for use in electromagnetic shielding, electrostatic reduction, or even monitoring structural changes due to compression, stretching, or damage through their effect on the conductivity. However, experimental works have shown that based on various processing techniques the electrical properties of specific composites can vary widely. Therefore, the goal of this work has been to form a model with the ability to accurately predict the conductive properties as a function physical characteristics of the composite material in order to aid in the design of these composites.

Apparatus for detecting alpha radiation in difficult access areas

DOEpatents

Steadman, Peter; MacArthur, Duncan W.

1997-09-02

An electrostatic alpha radiation detector for measuring alpha radiation emitted from inside an enclosure comprising an electrically conductive expandable electrode for insertion into the enclosure. After insertion, the electrically conductive expandable electrode is insulated from the enclosure and defines a decay cavity between the electrically conductive expandable electrode and the enclosure so that air ions generated in the decay cavity are electrostatically captured by the electrically conductive expandable electrode and the enclosure when an electric potential is applied between the electrically conductive expandable electrode and the enclosure. Indicator means are attached to the electrically conductive expandable electrode for indicating an electrical current produced by generation of the air ions generated in the decay cavity by collisions between air molecules and the alpha particles emitted from the enclosure. A voltage source is connected between the indicator means and the electrically conductive enclosure for creating an electric field between the electrically conductive expandable electrode and the enclosure.

Simultaneous head tissue conductivity and EEG source location estimation.

PubMed

Akalin Acar, Zeynep; Acar, Can E; Makeig, Scott

2016-01-01

Accurate electroencephalographic (EEG) source localization requires an electrical head model incorporating accurate geometries and conductivity values for the major head tissues. While consistent conductivity values have been reported for scalp, brain, and cerebrospinal fluid, measured brain-to-skull conductivity ratio (BSCR) estimates have varied between 8 and 80, likely reflecting both inter-subject and measurement method differences. In simulations, mis-estimation of skull conductivity can produce source localization errors as large as 3cm. Here, we describe an iterative gradient-based approach to Simultaneous tissue Conductivity And source Location Estimation (SCALE). The scalp projection maps used by SCALE are obtained from near-dipolar effective EEG sources found by adequate independent component analysis (ICA) decomposition of sufficient high-density EEG data. We applied SCALE to simulated scalp projections of 15cm(2)-scale cortical patch sources in an MR image-based electrical head model with simulated BSCR of 30. Initialized either with a BSCR of 80 or 20, SCALE estimated BSCR as 32.6. In Adaptive Mixture ICA (AMICA) decompositions of (45-min, 128-channel) EEG data from two young adults we identified sets of 13 independent components having near-dipolar scalp maps compatible with a single cortical source patch. Again initialized with either BSCR 80 or 25, SCALE gave BSCR estimates of 34 and 54 for the two subjects respectively. The ability to accurately estimate skull conductivity non-invasively from any well-recorded EEG data in combination with a stable and non-invasively acquired MR imaging-derived electrical head model could remove a critical barrier to using EEG as a sub-cm(2)-scale accurate 3-D functional cortical imaging modality. Copyright © 2015 Elsevier Inc. All rights reserved.

Simultaneous head tissue conductivity and EEG source location estimation

PubMed Central

Acar, Can E.; Makeig, Scott

2015-01-01

Accurate electroencephalographic (EEG) source localization requires an electrical head model incorporating accurate geometries and conductivity values for the major head tissues. While consistent conductivity values have been reported for scalp, brain, and cerebrospinal fluid, measured brain-to-skull conductivity ratio (BSCR) estimates have varied between 8 and 80, likely reflecting both inter-subject and measurement method differences. In simulations, mis-estimation of skull conductivity can produce source localization errors as large as 3 cm. Here, we describe an iterative gradient-based approach to Simultaneous tissue Conductivity And source Location Estimation (SCALE). The scalp projection maps used by SCALE are obtained from near-dipolar effective EEG sources found by adequate independent component analysis (ICA) decomposition of sufficient high-density EEG data. We applied SCALE to simulated scalp projections of 15 cm2-scale cortical patch sources in an MR image-based electrical head model with simulated BSCR of 30. Initialized either with a BSCR of 80 or 20, SCALE estimated BSCR as 32.6. In Adaptive Mixture ICA (AMICA) decompositions of (45-min, 128-channel) EEG data from two young adults we identified sets of 13 independent components having near-dipolar scalp maps compatible with a single cortical source patch. Again initialized with either BSCR 80 or 25, SCALE gave BSCR estimates of 34 and 54 for the two subjects respectively. The ability to accurately estimate skull conductivity non-invasively from any well-recorded EEG data in combination with a stable and non-invasively acquired MR imaging-derived electrical head model could remove a critical barrier to using EEG as a sub-cm2-scale accurate 3-D functional cortical imaging modality. PMID:26302675

Joint inversion of crosshole GPR and temporal moments of tracer data for improved estimation of hydraulic conductivity at the aquifer scale

NASA Astrophysics Data System (ADS)

Lochbühler, T.; Linde, N.

2012-04-01

Geophysical methods are widely used for aquifer characterization, but they usually fail to directly provide models of hydraulic conductivity. Here, a method is presented to jointly invert crosshole ground-penetrating radar (GPR) travel times and hydrological data to estimate the 2-D distribution of both GPR velocities and hydraulic conductivities. The hydrological data are the first temporal moments of tracer breakthrough curves measured at different depths (i.e., the mean arrival times of the tracer at the given locations). Structural resemblance between the geophysical and the hydrological model is enforced by strongly penalizing models for which the cross products of the model gradients are non-zero. The proposed method was first tested on a synthetic categorical facies model. The high resolution of the GPR velocity model markedly improves the hydraulic conductivity model by adding small-scale structures that remain unresolved by the individual inversion of the hydrological data. The method was then applied to field data acquired within a gravel aquifer located close to the Thur River, northeastern Switzerland. The hydrological data used were derived from transfer functions obtained by deconvolving groundwater electrical conductivity time series with electrical conductivity variations of the river water. These data were recorded over several years at three depth levels in three boreholes aligned along the main groundwater flow direction. The transfer functions are interpreted as breakthrough curves of a pulse injection in the river from which we retrieve the first temporal moments. These data were complemented with crosshole GPR data acquired between the three boreholes. Both the individual and joint inversion models provide a smooth hydraulic conductivity model that retrieves the same general trend as EM flowmeter data, but does not resolve small-scale variability.

Spin current and second harmonic generation in non-collinear magnetic systems: the hydrodynamic model

NASA Astrophysics Data System (ADS)

Karashtin, E. A.; Fraerman, A. A.

2018-04-01

We report a theoretical study of the second harmonic generation in a noncollinearly magnetized conductive medium with equilibrium spin current. The hydrodynamic model is used to unravel the mechanism of a novel effect of the double frequency signal generation that is attributed to the spin current. According to our calculations, this second harmonic response appears due to the ‘non-adiabatic’ spin polarization of the conduction electrons induced by the oscillations in the non-uniform magnetization forced by the electric field of the electromagnetic wave. Together with the linear velocity response this leads to the generation of the double frequency spin current. This spin current is converted to the electric current via the inverse spin Hall effect, and the double-frequency electric current emits the second harmonic radiation. Possible experiment for detection of the new second harmonic effect is proposed.

Electrical Counting and Sizing of Mammalian Cells in Suspension

PubMed Central

Gregg, E. C.; Steidley, K. David

1965-01-01

A recently developed method of determining the number and size of particles suspended in a conducting solution is to pump the suspension through a small orifice having an immersed electrode on each side to supply electrical current. The current changes due to the passage of particles of resistivity different from that of the solution. Theoretical expressions are developed which relate the current change caused by such particles to their volume and shape. It is found that most biological cells may be treated as dielectric particles whose capacitive effects are negligible. Electrolytic tank measurements on models confirm the theoretical development, and electric field plots of model orifices are used to predict the observed pulse shapes. An equivalent circuit of the orifice-electrode system is analyzed and shows that the current pulse may be made conductivity-independent when observed with a zero input impedance amplifier. PMID:5861698

Determination of medium electrical properties through full-wave modelling of frequency domain reflectrometry data

NASA Astrophysics Data System (ADS)

André, Frédéric; Lambot, Sébastien

2015-04-01

Accurate knowledge of the shallow soil properties is of prime importance in agricultural, hydrological and environmental engineering. During the last decade, numerous geophysical techniques, either invasive or resorting to proximal or remote sensing, have been developed and applied for quantitative characterization of soil properties. Amongst them, time domain reflectrometry (TDR) and frequency domain reflectometry (FDR) are recognized as standard techniques for the determination of soil dielectric permittivity and electrical conductivity, based on the reflected electromagnetic waves from a probe inserted into the soil. TDR data were first commonly analyzed in the time domain using methods considering only a part of the waveform information. Later, advancements have led to the possibility of analyzing the TDR signal through full-wave inverse modeling either in the time or the frequency domains. A major advantage of FDR compared to TDR is the possibility to increase the bandwidth, thereby increasing the information content of the data and providing more detailed characterization of the medium. Amongst the recent works in this field, Minet et al. (2010) developed a modeling procedure for processing FDR data based on an exact solution of Maxwell's equations for wave propagation in one-dimensional multilayered media. In this approach, the probe head is decoupled from the medium and is fully described by characteristic transfer functions. The authors successfully validated the method for homogeneous sand subject to a range of water contents. In the present study, we further validated the modelling approach using reference liquids with well-characterized frequency-dependent electrical properties. In addition, the FDR model was coupled with a dielectric mixing model to investigate the ability of retrieving water content, pore water electrical conductivity and sand porosity from inversion of FDR data acquired in sand subject to different water content levels. Finally, the possibility of reconstructing the vertical profile of the properties by inversion of FDR data collected during progressive insertion of the probe into a vertically heterogeneous medium was also investigated. Index Terms: Frequency domain reflectrometry (FDR), frequency dependence, dielectric permittivity, electrical conductivity Reference: Minet J., Lambot S., Delaide G., Huisman J.A., Vereecken H., Vanclooster M., 2010. A generalized frequency domain reflectometry modeling technique for soil electrical properties determination. Vadose Zone Journal, 9: 1063-1072.

Visual images in Luigi Galvani's path to animal electricity.

PubMed

Piccolino, Marco

2008-01-01

The scientific endeavor that led Luigi Galvani to his hypothesis of "animal electricity," i.e., of an electricity present in a condition of disequilibrium between the interior and the exterior of excitable animal fibers, is reviewed here with particular emphasis to the role played by visual images in Galvani's path of discovery. In 1791 Galvani formulated his model of neuromuscular physiology on the base of the image of a muscle and a nerve fiber together as in a "minute animal Leyden jar." This was the last instance of a series of physical models that accompanied Galvani's experimental efforts in the search of a theory capable of accounting for the electric nature of nerve conduction in spite of the many objections formulated in the eighteenth century against a possible role of electricity in animal physiology.

Mathematical modeling of electrical activity of uterine muscle cells.

PubMed

Rihana, Sandy; Terrien, Jeremy; Germain, Guy; Marque, Catherine

2009-06-01

The uterine electrical activity is an efficient parameter to study the uterine contractility. In order to understand the ionic mechanisms responsible for its generation, we aimed at building a mathematical model of the uterine cell electrical activity based upon the physiological mechanisms. First, based on the voltage clamp experiments found in the literature, we focus on the principal ionic channels and their cognate currents involved in the generation of this electrical activity. Second, we provide the methodology of formulations of uterine ionic currents derived from a wide range of electrophysiological data. The model is validated step by step by comparing simulated voltage-clamp results with the experimental ones. The model reproduces successfully the generation of single spikes or trains of action potentials that fit with the experimental data. It allows analyzing ionic channels implications. Likewise, the calcium-dependent conductance influences significantly the cellular oscillatory behavior.

Cell death, perfusion and electrical parameters are critical in models of hepatic radiofrequency ablation

PubMed Central

Hall, Sheldon K.; Ooi, Ean H.; Payne, Stephen J.

2015-01-01

Abstract Purpose: A sensitivity analysis has been performed on a mathematical model of radiofrequency ablation (RFA) in the liver. The purpose of this is to identify the most important parameters in the model, defined as those that produce the largest changes in the prediction. This is important in understanding the role of uncertainty and when comparing the model predictions to experimental data. Materials and methods: The Morris method was chosen to perform the sensitivity analysis because it is ideal for models with many parameters or that take a significant length of time to obtain solutions. A comprehensive literature review was performed to obtain ranges over which the model parameters are expected to vary, crucial input information. Results: The most important parameters in predicting the ablation zone size in our model of RFA are those representing the blood perfusion, electrical conductivity and the cell death model. The size of the 50 °C isotherm is sensitive to the electrical properties of tissue while the heat source is active, and to the thermal parameters during cooling. Conclusions: The parameter ranges chosen for the sensitivity analysis are believed to represent all that is currently known about their values in combination. The Morris method is able to compute global parameter sensitivities taking into account the interaction of all parameters, something that has not been done before. Research is needed to better understand the uncertainties in the cell death, electrical conductivity and perfusion models, but the other parameters are only of second order, providing a significant simplification. PMID:26000972

Time Lapse Electrical Resistivity to Connect Evapotranspiration and Groundwater Fluxes in the Critical Zone

NASA Astrophysics Data System (ADS)

Jarvis, S. K.; Harmon, R. E.; Barnard, H. R.; Randall, J.; Singha, K.

2017-12-01

The critical zone (CZ)—an open system extending from canopy top to the base of groundwater—is a highly dynamic and heterogeneous environment. In forested terrain, trees make up a large component of the CZ. This work aims to quantify the connection between vegetation and subsurface water storage at a hillslope scale within a forested watershed in the H.J. Andrews Experimental Forest, Oregon. To identify the mechanism(s) controlling the connection at the hillslope scale, we observe patterns in electrical conductivity using 2D-time lapse-DC resistivity. To compare inversions through time a representative error model was determined using L-curve criterion. Inverted data show high spatial variability in ground electrical conductivity and variation at both diel and seasonal timescales. These changes are most pronounced in areas corresponding to dense vegetation. The diel pattern in electrical conductivity is also observed in monitored sap flow sensors, water-level gauges, tensiometers, and sediment thermal probes. To quantify the temporal connection between these data over the course of the growing season a cross correlation analysis was conducted. Preliminary data show that over the course of the growing season transpiration becomes decoupled from both groundwater and soil moisture. Further decomposition of the inverted time lapse data will highlight spatial variability in electrical conductivity providing insight into the where, when, and how(s) of tree-modified subsurface storage.

Final Report - IHLW PCT, Spinel T1%, Electrical Conductivity, and Viscosity Model Development, VSL-07R1240-4

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

Kruger, Albert A.; Piepel, Gregory F.; Landmesser, S. M.

2013-11-13

This report is the last in a series of currently scheduled reports that presents the results from the High Level Waste (HLW) glass formulation development and testing work performed at the Vitreous State Laboratory (VSL) of the Catholic University of America (CUA) and the development of IHLW property-composition models performed jointly by Pacific Northwest National Laboratory (PNNL) and VSL for the River Protection Project-Waste Treatment and Immobilization Plant (RPP-WTP). Specifically, this report presents results of glass testing at VSL and model development at PNNL for Product Consistency Test (PCT), one-percent crystal fraction temperature (T1%), electrical conductivity (EC), and viscosity ofmore » HLW glasses. The models presented in this report may be augmented and additional validation work performed during any future immobilized HLW (IHLW) model development work. Completion of the test objectives is addressed.« less

Measurements of wave velocity and electrical conductivity of an amphibolite from southwestern margin of the Tarim Basin at pressures to 1.0 GPa and temperatures to 700 °C: comparison with field observations

NASA Astrophysics Data System (ADS)

Zhou, Wenge; Fan, Dawei; Liu, Yonggang; Xie, Hongsen

2011-12-01

In situ measurements of elastic wave velocities and electrical conductivities in the three structural directions (normal to foliation Z, perpendicular to lineation in foliation Y and parallel to lineation X) for an amphibolite collected from southwestern margin of the Tarim Basin, northwest China, were carried out in the laboratory. The elastic wave velocity was measured with the combined transmission-reflection method at pressures up to 1.0 GPa (at room temperature) and temperatures up to 700 °C (at 1.0 GPa) and the electrical conductivity was measured with the impedance spectroscopy from 250 to 700 °C at 1.0 GPa. The experimentally determined data included compressional (Vp) and shear wave velocities (Vs), velocity anisotropy (Av), intrinsic pressure and temperature derivatives of Vp and Vs, electrical conductivity (σ), electrical conductivity anisotropy (Aσ) and the parameters of the Arrhenius relationship. Elastic wave velocities increase in the structural directions Z, Y, X, with Vp of 6.63, 6.78 and 6.95 km s-1 and Vs of 3.75, 3.82 and 3.96 km s-1 for Z, Y and X, respectively, at pressure of 1.0 GPa. Elastic wave velocities increase linearly with pressure at room temperature and pressures between 0.25 and 1.0 GPa and decrease linearly with increasing temperature at 1.0 GPa. The pressure coefficients of the sample are in the range of 0.1883-0.2308 km s-1 GPa-1 for Vp and 0.1149-0.1678 km s-1 GPa-1 for Vs. The temperature coefficients are in the range of 2.09-2.35 × 10-4 km s-1 GPa-1 for Vp and 1.28-1.68 × 10-4 km s-1 GPa-1 for Vs. The electrical conductivity increases with increasing temperature, consistent with the Arrhenius relationship. Activation energies for the three structural directions of the amphibolite are in the range of 0.71-0.75 eV. The amphibolite shows velocity anisotropy (4.15-4.86 per cent for Vp and 5.29-5.84 per cent for Vs at 0.25-1.0 GPa) and electrical conductivity anisotropy (11.1-25.2 per cent). Based on the regional crust model and geothermal gradient, velocity and electrical conductivity-depth profiles were calculated for the sample. These profiles were then compared with those derived from seismic reflection/refraction data and from electromagnetic data. Our results showed that the amphibolite sample has Vp and Vs in agreement with those of the middle and lower crust obtained from seismic reflection/refraction data, and σ in accord with that of the lower crust deduced from electromagnetic data. The lower crust of the electromagnetic crust model is roughly equivalent to the middle and lower crust layers of the seismic crust model. Therefore, it is suggest that the amphibolite may be one of the constituents of the present middle and lower crust in the Tarim Basin.

Characterization and electrical properties of V 2O 5-CuO-P 2O 5 glasses

NASA Astrophysics Data System (ADS)

Al-Assiri, M. S.

2008-08-01

Characterization and electrical properties of vanadium-copper-phosphate glasses of compositions xV 2O 5-(40- x)CuO-60P 2O 5 have been reported. X-ray diffraction (XRD) confirms the amorphous nature of these glasses. It was observed that, the density ( d) decreases gradually while the molar volume ( Vm) increases with the increase of the vanadium oxide content in such glasses. This may be due to the effect of the polarizing power strength, PPS, which is a measure of ratio of the cation valance to its diameter. The dc conductivity increases while the activation energy decreases with the increase of the V 2O 5 content. The dc conductivity in the present glasses is electronic and depends strongly upon the average distance, R, between the vanadium ions. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron.

Energy and cost analysis of residential refrigerators

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

Hoskins, R.A.; Hirst, E.

1977-01-01

A detailed computer model is developed to calculate energy flows and electricity use for residential refrigerators. Model equations are derived from applications of the first law of thermodynamics, analysis of manufacturers' literature, and related studies. The model is used to evaluate the energy (and associated initial cost) impacts of alternative designs to reduce refrigerator energy use. Model results show that 56 percent of the total heat gain in a typical 0.45 m/sup 3/ (16 ft/sup 3/) top-freezer refrigerator is due to conduction through cabinet walls and doors. The remaining 44 percent is from door openings, heaters, fans, food, gasket areamore » infiltration, and miscellaneous heat sources. Operation of the compressor to remove this heat and maintain the refrigerated spaces at constant temperatures accounts for 70 percent of the unit's electricity use. The remainder is for operation of heaters and fans. Several energy-saving design changes are examined using the energy model. These changes are: increased insulation thickness, improved insulation conductivity, removal of fan from cooled area, use of anti-sweat heater switch, improved compressor efficiency, increased condenser and evaporator surface areas, and elimination of the frost-free feature. Application of all these changes would reduce refrigerator electricity use 71 percent and increase initial cost 5 percent. Implementing all these changes except for elimination of the frost-free feature would reduce electricity use 52 percent and increase initial cost 19 percent. These results show that there are large opportunities for reducing refrigerator electricity use with only slight initial cost increases.« less

Comparison of effectiveness between cork-screw and peg-screw electrodes for transcranial motor evoked potential monitoring using the finite element method.

PubMed

Tomio, Ryosuke; Akiyama, Takenori; Ohira, Takayuki; Yoshida, Kazunari

2016-01-01

Intraoperative monitoring of motor evoked potentials by transcranial electric stimulation is popular in neurosurgery for monitoring motor function preservation. Some authors have reported that the peg-screw electrodes screwed into the skull can more effectively conduct current to the brain compared to subdermal cork-screw electrodes screwed into the skin. The aim of this study was to investigate the influence of electrode design on transcranial motor evoked potential monitoring. We estimated differences in effectiveness between the cork-screw electrode, peg-screw electrode, and cortical electrode to produce electric fields in the brain. We used the finite element method to visualize electric fields in the brain generated by transcranial electric stimulation using realistic three-dimensional head models developed from T1-weighted images. Surfaces from five layers of the head were separated as accurately as possible. We created the "cork-screws model," "1 peg-screw model," "peg-screws model," and "cortical electrode model". Electric fields in the brain radially diffused from the brain surface at a maximum just below the electrodes in coronal sections. The coronal sections and surface views of the brain showed higher electric field distributions under the peg-screw compared to the cork-screw. An extremely high electric field was observed under cortical electrodes. Our main finding was that the intensity of electric fields in the brain are higher in the peg-screw model than the cork-screw model.

Inferences about Membrane Properties from Electrical Noise Measurements

PubMed Central

Stevens, Charles F.

1972-01-01

Four sources of electrical noise in biological membranes, each with a different physical basis, are discussed; the analysis of each type of noise potentially yields a different sort of information about membrane properties. (a) From the thermal noise spectrum, the passive membrane impedance may be obtained, so that thermal noise measurements are essentially equivalent to the type of since wave analysis carried out by Cole and Curtis. (b) If adequately high frequency measurements could be made, the shot noise spectrum should give information about the average motion of a single ion within the membrane. (c) The number of charge carriers and single ion mobilities within the membrane can possibly be inferred from measurements of noise with a 1/f spectrum. Available data indicate, for example, that increases in axon membrane conductance are not achieved by modulations in the mobility of ions within the membrane. (d) Fluctuations arising from the mechanisms normally responsible for membrane conductance changes can produce a type of electrical noise. Analysis of such conductance fluctuations provides a way to assess the validity of various microscopic models for the behavior of individual channels. Two different probabilistic interpretations of the Hodgkin-Huxley equations are investigated here and shown to yield different predictions about the spectrum of conductance fluctuations; thus, appropriate noise measurements may serve to eliminate certain classes of microscopic models for membrane conductance changes. Further, it is shown how the analysis of conductance fluctuations can, in some circumstances, provide an estimate of the conductance of a single channel. PMID:5044577

Low resistance thin film organic solar cell electrodes

DOEpatents

Forrest, Stephen [Princeton, NJ; Xue, Jiangeng [Piscataway, NJ

2008-01-01

A method which lower the series resistance of photosensitive devices includes providing a transparent film of a first electrically conductive material arranged on a transparent substrate; depositing and patterning a mask over the first electrically conductive material, such that openings in the mask have sloping sides which narrow approaching the substrate; depositing a second electrically conductive material directly onto the first electrically conductive material exposed in the openings of the mask, at least partially filling the openings; stripping the mask, leaving behind reentrant structures of the second electrically conductive material which were formed by the deposits in the openings of the mask; after stripping the mask, depositing a first organic material onto the first electrically conductive material in between the reentrant structures; and directionally depositing a third electrically conductive material over the first organic material deposited in between the reentrant structures, edges of the reentrant structures aligning deposition so that the third electrically conductive material does not directly contact the first electrically conductive material, and does not directly contact the second electrically conductive material.

Determination of effective electromagnetic parameters of concentrated suspensions of ellipsoidal particles using Generalized Differential Effective Medium approximation

NASA Astrophysics Data System (ADS)

Markov, M.; Levin, V.; Markova, I.

2018-02-01

The paper presents an approach to determine the effective electromagnetic parameters of suspensions of ellipsoidal dielectric particles with surface conductivity. This approach takes into account the existence of critical porosity that corresponds to the maximum packing volume fraction of solid inclusions. The approach is based on the Generalized Differential Effective Medium (GDEM) method. We have introduced a model of suspensions containing ellipsoidal inclusions of two types. Inclusions of the first type (phase 1) represent solid grains, and inclusions of the second type (phase 2) contain material with the same physical properties as the host (phase 0). In this model, with increasing porosity the concentration of the host decreases, and it tends to zero near the critical porosity. The proposed model has been used to simulate the effective electromagnetic parameters of concentrated suspensions. We have compared the modeling results for electrical conductivity and dielectric permittivity with the empirical equations. The results obtained have shown that the GDEM model describes the effective electrical conductivity and dielectric permittivity of suspensions in a wide range of inclusion concentrations.

High-Power Piezoelectric Acoustic-Electric Power Feedthru for Metal Walls

NASA Technical Reports Server (NTRS)

Bao, Xiaoqi; Biederman, Will; Sherrit, Stewart; Badescu, Mircea; Bar-Cohen, Yoseph; Jones, Christopher; Aldrich, Jack; Chang, Zensheu

2008-01-01

Piezoelectric acoustic-electric power feed-through devices transfer electric power wirelessly through a solid wall by using acoustic waves. This approach allows for the removal of holes through structures. The technology is applicable to power supply for electric equipment inside sealed containers, vacuum or pressure vessels, etc where the holes on the wall are prohibitive or result in significant performance degrade or complex designs. In the author's previous work, 100-W electric power was transferred through a metal wall by a small, simple-structure piezoelectric device. To meet requirements of higher power applications, the feasibility to transfer kilowatts level power was investigated. Pre-stressed longitudinal piezoelectric feedthru devices were analyzed by finite element model. An equivalent circuit model was developed to predict the power transfer characteristics to different electric loads. Based on the analysis results, a prototype device was designed, fabricated and a demonstration of the transmission of electric power up to 1-kW was successfully conducted. The methods to minimize the plate wave excitation on the wall were also analyzed. Both model analysis and experimental results are presented in detail in this presentation.

Electrical properties of dispersions of graphene in mineral oil

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

Monteiro, O. R., E-mail: othon.monteiro@bakerhughes.com

2014-02-03

Dispersions of graphene in mineral oil have been prepared and electrical conductivity and permittivity have been measured. The direct current (DC) conductivity of the dispersions depends on the surface characteristics of the graphene platelets and followed a percolation model with a percolation threshold ranging from 0.05 to 0.1 wt. %. The difference in DC conductivities can be attributed to different states of aggregation of the graphene platelets and to the inter-particle electron transfer, which is affected by the surface radicals. The frequency-dependent conductivity (σ(ω)) and permittivity (ε(ω)) were also measured. The conductivity of dispersions with particle contents much greater than themore » percolation threshold remains constant and equal to the DC conductivity at low frequencies ω with and followed a power-law σ(ω)∝ ω{sup s} dependence at very high frequencies with s≈0.9. For dispersions with graphene concentration near the percolation threshold, a third regime was displayed at intermediate frequencies indicative of interfacial polarization consistent with Maxwell-Wagner effect typically observed in mixtures of two (or more) phases with very distinct electrical and dielectric properties.« less

Flexible neural interfaces with integrated stiffening shank

DOEpatents

Tooker, Angela C.; Felix, Sarah H.; Pannu, Satinderpall S.; Shah, Kedar G.; Sheth, Heeral; Tolosa, Vanessa

2016-07-26

A neural interface includes a first dielectric material having at least one first opening for a first electrical conducting material, a first electrical conducting material in the first opening, and at least one first interconnection trace electrical conducting material connected to the first electrical conducting material. A stiffening shank material is located adjacent the first dielectric material, the first electrical conducting material, and the first interconnection trace electrical conducting material.

Imagerie par modulation acoustique de conductivite electrique destinee au diagnostic du cancer du sein

NASA Astrophysics Data System (ADS)

Gendron, Mathieu

This thesis describes a new medical imaging technique for determining the electrical conductivity distribution of tissues in a body region with a resolution comparable to that of current ultrasound techniques. The new technique, henceforth referred to as "Acousto-Electric Conductivity Modulation" (AECM) imaging, is based on the interaction of a sound wave with an electrical field. In its simplest form, four electrodes located near the region to be imaged apply a low-amplitude electrical current and measure the potential difference arising from current flow in the tissues. A focused ultrasound transducer directs a pressure wave to a voxel of the region of interest, modifying its conductivity distribution and, as a result, the amplitude of the potential measured by the electrodes. An image of the conductivity distribution can thus be constructed point-by-point by moving the electrodes and transducer to scan the object. In this context, the acoustic wave acts as the localization agent while the electrical potential provides a measure of the local conductivity change that occurs in the voxel. The first model presented in the thesis is based on the use of bipolar acoustic waves for excitation. This waveform is generally used with narrow band transducers. Acoustic waves generated by an ultrasound transducer driven with a burst of sine waves consists of alternating compression and rarefaction phases which tend to cancel each other in terms of the conductivity changes they produce. However when the thickness of the target object is small compared to the wavelength of the acoustic wave, this cancelling effect will not occur and the AECM signals will have sufficiently high amplitude to achieve image reconstruction using successive transducer positions to scan the region of interest. By extracting from the spectra of the AECM signals the amplitude of the peak at the excitation frequency, a map of the acousto-electric sensitivity of the system can be obtained. This map is then used to reconstruct the electrical conductivity distribution. The second model presented in the thesis uses a unipolar acoustic wave to generate AECM signals of relatively large amplitude. There are two aspects related to this type of wave. The first aspect is that the acoustic modulation is unidirectional if the applied pressure is unidirectional. As a result, a positive pressure only produces an increase in electrical conductivity and this will result in a large AECM signal even when the thickness of the object is large. The second aspect concerns the shape of the acoustic field. Since the unipolar acoustic wave is not focused, it modulates the conductivity over a large area, and thus the associated AECM signals needs to be processed through a reconstruction algorithm so as to recover local conductivity. In this model, the data required for image reconstruction are acquired by rotating the transducer around the target object. An experimental setup has been developed during our project to get values of certain parameter that are required to define the numerical models. The setup comprises a large tank which is filled with water and in which are immersed the ultrasound transducer, a hydrophone and a measurement cell. The acousto-electric interaction takes place within this cell. A computer controlled positioning system allows precise displacements of the transducer relative to the hydrophone and the measurement cell. This cell comprises a cavity in which the object to be analyzed is placed and that is then filled with an electrolytic solution. The cavity is closed on two sides by an acoustic window to allow propagation of the ultrasound wave and on another side by six Ag/AgCl electrodes that are used to apply current and to measure the resulting electrical potential. Mammography is presently the most widely used medical imaging procedure for breast cancer screening. The average sensitivity of this technique is 80 % but it is less for younger women. According to recent studies, MRI offers a higher sensitivity and the possibility of detecting very small tumors, thus allowing earlier treatment. The operating costs of MRI systems are at the moment too high to consider using the modality for breast cancer screening on a large scale. AECM imaging could eventually provide an interesting compromise between operating costs and the sensitivity required for screening patients of all ages. (Abstract shortened by UMI.).

Exploring harmonization between integrated assessment and capacity expansion models

NASA Astrophysics Data System (ADS)

Iyer, G.; Brown, M.; Cohen, S.; Macknick, J.; Patel, P.; Wise, M. A.; Horing, J.

2017-12-01

Forward-looking quantitative models of the electric sector are extensively used to provide science-based strategic decision support to national, international and private-sector entities. Given that these models are used to inform a wide-range of stakeholders and influence policy decisions, it is vital to examine how the models' underlying data and structure influence their outcomes. We conduct several experiments harmonizing key model characteristics between ReEDS—an electric sector only model, and GCAM—an integrated assessment model—to understand how different degrees of harmonization impact model outcomes. ReEDS has high spatial, temporal, and process detail but lacks electricity demand elasticity and endogenous representations of other economic sectors, while GCAM has internally consistent representations of energy (including the electric sector), agriculture, and land-use systems but relatively aggregate representations of the factors influencing electric sector investments . We vary the degree of harmonization in electricity demand, fuel prices, technology costs and performance, and variable renewable energy resource characteristics. We then identify the prominent sources of divergence in key outputs (electricity capacity, generation, and price) across the models and study how the convergence between models can be improved with permutations of harmonized characteristics. The remaining inconsistencies help to establish how differences in the models' underlying data, construction, perspective, and methodology play into each model's outcome. There are three broad contributions of this work. First, our study provides a framework to link models with similar scope but different resolutions. Second, our work provides insight into how the harmonization of assumptions contributes to a unified and robust portrayal of the US electricity sector under various potential futures. Finally, our study enhances the understanding of the influence of structural uncertainty on consistency of outcomes.

Modeling an Excitable Biosynthetic Tissue with Inherent Variability for Paired Computational-Experimental Studies.

PubMed

Gokhale, Tanmay A; Kim, Jong M; Kirkton, Robert D; Bursac, Nenad; Henriquez, Craig S

2017-01-01

To understand how excitable tissues give rise to arrhythmias, it is crucially necessary to understand the electrical dynamics of cells in the context of their environment. Multicellular monolayer cultures have proven useful for investigating arrhythmias and other conduction anomalies, and because of their relatively simple structure, these constructs lend themselves to paired computational studies that often help elucidate mechanisms of the observed behavior. However, tissue cultures of cardiomyocyte monolayers currently require the use of neonatal cells with ionic properties that change rapidly during development and have thus been poorly characterized and modeled to date. Recently, Kirkton and Bursac demonstrated the ability to create biosynthetic excitable tissues from genetically engineered and immortalized HEK293 cells with well-characterized electrical properties and the ability to propagate action potentials. In this study, we developed and validated a computational model of these excitable HEK293 cells (called "Ex293" cells) using existing electrophysiological data and a genetic search algorithm. In order to reproduce not only the mean but also the variability of experimental observations, we examined what sources of variation were required in the computational model. Random cell-to-cell and inter-monolayer variation in both ionic conductances and tissue conductivity was necessary to explain the experimentally observed variability in action potential shape and macroscopic conduction, and the spatial organization of cell-to-cell conductance variation was found to not impact macroscopic behavior; the resulting model accurately reproduces both normal and drug-modified conduction behavior. The development of a computational Ex293 cell and tissue model provides a novel framework to perform paired computational-experimental studies to study normal and abnormal conduction in multidimensional excitable tissue, and the methodology of modeling variation can be applied to models of any excitable cell.

Electrical conductivity of quasi-two-dimensional foams.

PubMed

Yazhgur, Pavel; Honorez, Clément; Drenckhan, Wiebke; Langevin, Dominique; Salonen, Anniina

2015-04-01

Quasi-two-dimensional (quasi-2D) foams consist of monolayers of bubbles squeezed between two narrowly spaced plates. These simplified foams have served successfully in the past to shed light on numerous issues in foam physics. Here we consider the electrical conductivity of such model foams. We compare experiments to a model which we propose, and which successfully relates the structural and the conductive properties of the foam over the full range of the investigated liquid content. We show in particular that in the case of quasi-2D foams the liquid in the nodes needs to be taken into account even at low liquid content. We think that these results may provide different approaches for the characterization of foam properties and for the in situ characterization of the liquid content of foams in confining geometries, such as microfluidics.

Induced mitochondrial membrane potential for modeling solitonic conduction of electrotonic signals

PubMed Central

Poznanski, R. R.; Cacha, L. A.; Ali, J.; Rizvi, Z. H.; Yupapin, P.; Salleh, S. H.; Bandyopadhyay, A.

2017-01-01

A cable model that includes polarization-induced capacitive current is derived for modeling the solitonic conduction of electrotonic potentials in neuronal branchlets with microstructure containing endoplasmic membranes. A solution of the nonlinear cable equation modified for fissured intracellular medium with a source term representing charge ‘soakage’ is used to show how intracellular capacitive effects of bound electrical charges within mitochondrial membranes can influence electrotonic signals expressed as solitary waves. The elastic collision resulting from a head-on collision of two solitary waves results in localized and non-dispersing electrical solitons created by the nonlinearity of the source term. It has been shown that solitons in neurons with mitochondrial membrane and quasi-electrostatic interactions of charges held by the microstructure (i.e., charge ‘soakage’) have a slower velocity of propagation compared with solitons in neurons with microstructure, but without endoplasmic membranes. When the equilibrium potential is a small deviation from rest, the nonohmic conductance acts as a leaky channel and the solitons are small compared when the equilibrium potential is large and the outer mitochondrial membrane acts as an amplifier, boosting the amplitude of the endogenously generated solitons. These findings demonstrate a functional role of quasi-electrostatic interactions of bound electrical charges held by microstructure for sustaining solitons with robust self-regulation in their amplitude through changes in the mitochondrial membrane equilibrium potential. The implication of our results indicate that a phenomenological description of ionic current can be successfully modeled with displacement current in Maxwell’s equations as a conduction process involving quasi-electrostatic interactions without the inclusion of diffusive current. This is the first study in which solitonic conduction of electrotonic potentials are generated by polarization-induced capacitive current in microstructure and nonohmic mitochondrial membrane current. PMID:28880876

Induced mitochondrial membrane potential for modeling solitonic conduction of electrotonic signals.

PubMed

Poznanski, R R; Cacha, L A; Ali, J; Rizvi, Z H; Yupapin, P; Salleh, S H; Bandyopadhyay, A

2017-01-01

A cable model that includes polarization-induced capacitive current is derived for modeling the solitonic conduction of electrotonic potentials in neuronal branchlets with microstructure containing endoplasmic membranes. A solution of the nonlinear cable equation modified for fissured intracellular medium with a source term representing charge 'soakage' is used to show how intracellular capacitive effects of bound electrical charges within mitochondrial membranes can influence electrotonic signals expressed as solitary waves. The elastic collision resulting from a head-on collision of two solitary waves results in localized and non-dispersing electrical solitons created by the nonlinearity of the source term. It has been shown that solitons in neurons with mitochondrial membrane and quasi-electrostatic interactions of charges held by the microstructure (i.e., charge 'soakage') have a slower velocity of propagation compared with solitons in neurons with microstructure, but without endoplasmic membranes. When the equilibrium potential is a small deviation from rest, the nonohmic conductance acts as a leaky channel and the solitons are small compared when the equilibrium potential is large and the outer mitochondrial membrane acts as an amplifier, boosting the amplitude of the endogenously generated solitons. These findings demonstrate a functional role of quasi-electrostatic interactions of bound electrical charges held by microstructure for sustaining solitons with robust self-regulation in their amplitude through changes in the mitochondrial membrane equilibrium potential. The implication of our results indicate that a phenomenological description of ionic current can be successfully modeled with displacement current in Maxwell's equations as a conduction process involving quasi-electrostatic interactions without the inclusion of diffusive current. This is the first study in which solitonic conduction of electrotonic potentials are generated by polarization-induced capacitive current in microstructure and nonohmic mitochondrial membrane current.

Modeling conduction in host-graft interactions between stem cell grafts and cardiomyocytes.

PubMed

Chen, Michael Q; Yu, Jin; Whittington, R Hollis; Wu, Joseph C; Kovacs, Gregory T A; Giovangrandi, Laurent

2009-01-01

Cell therapy has recently made great strides towards aiding heart failure. However, while transplanted cells may electromechanically integrate into host tissue, there may not be a uniform propagation of a depolarization wave between the heterogeneous tissue boundaries. A model using microelectrode array technology that maps the electrical interactions between host and graft tissues in co-culture is presented and sheds light on the effects of having a mismatch of conduction properties at the boundary. Skeletal myoblasts co-cultured with cardiomyocytes demonstrated that conduction velocity significantly decreases at the boundary despite electromechanical coupling. In an attempt to improve the uniformity of conduction with host cells, differentiating human embryonic stem cells (hESC) were used in co-culture. Over the course of four to seven days, synchronous electrical activity was observed at the hESC boundary, implying differentiation and integration. Activity did not extend far past the boundary, and conduction velocity was significantly greater than that of the host tissue, implying the need for other external measures to properly match the conduction properties between host and graft tissue.

Petrologically-based Electrical Profiles vs. Geophysical Observations through the Upper Mantle (Invited)

NASA Astrophysics Data System (ADS)

Gaillard, F.; Massuyeau, M.; Sifre, D.; Tarits, P.

2013-12-01

Mineralogical transformations in the up-welling mantle play a critical role on the dynamics of mass and heat transfers at mid-ocean-ridgeS. The melting event producing ridge basalts occur at 60 km depth below the ridge axis, but because of small amounts of H2O and CO2 in the source region of MOR-basalts, incipient melting can initiate at much greater depth. Such incipient melts concentrate incompatible elements, and are particularly rich in volatile species. These juices evolve from carbonatites, carbonated basalts, to CO2-H2O-rich basalts as recently exposed by petrological surveys; the passage from carbonate to silicate melts is a complex pathway that is strongly non-linear. This picture has recently been complicated further by studies showing that oxygen increasingly partitions into garnet as pressure increases; this implies that incipient melting may be prevented at depth exceeding 200 km because not enough oxygen is available in the system to stabilize carbonate melts. The aim of this work is twofold: - We modelled the complex pathway of mantle melting in presence of C-O-H volatiles by adjusting the thermodynamic properties of mixing in the multi-component C-O-H-melt system. This allows us to calculate the change in melt composition vs. depth following any sortS of adiabat. - We modelled the continuous change in electrical properties from carbonatites, carbonated basalts, to CO2-H2O-rich basalts. We then successfully converted this petrological evolution along a ridge adiabat into electrical conductivity vs. depth signal. The discussion that follows is about comparison of this petrologically-based conductivity profile with the recent profiles obtained by inversion of the long-period electromagnetic signals from the East-Pacific-Rise. These geophysically-based profiles reveal the electrical conductivity structure down to 400 km depth and they show some intriguing highly conductive sections. We will discuss heterogeneity in electrical conductivity of the upper mantle underneath the ridge in terms of melting processes. Our prime conclusion is that the redox melting process, universally predicted by petrological models, might not be universal and that incipient melting can extend down to the transition zone.

Assessment of local hydraulic properties from electrical resistivity tomography monitoring of a three-dimensional synthetic tracer test experiment

NASA Astrophysics Data System (ADS)

Camporese, M.; Cassiani, G.; Deiana, R.; Salandin, P.

2011-12-01

In recent years geophysical methods have become increasingly popular for hydrological applications. Time-lapse electrical resistivity tomography (ERT) represents a potentially powerful tool for subsurface solute transport characterization since a full picture of the spatiotemporal evolution of the process can be obtained. However, the quantitative interpretation of tracer tests is difficult because of the uncertainty related to the geoelectrical inversion, the constitutive models linking geophysical and hydrological quantities, and the a priori unknown heterogeneous properties of natural formations. Here an approach based on the Lagrangian formulation of transport and the ensemble Kalman filter (EnKF) data assimilation technique is applied to assess the spatial distribution of hydraulic conductivity K by incorporating time-lapse cross-hole ERT data. Electrical data consist of three-dimensional cross-hole ERT images generated for a synthetic tracer test in a heterogeneous aquifer. Under the assumption that the solute spreads as a passive tracer, for high Peclet numbers the spatial moments of the evolving plume are dominated by the spatial distribution of the hydraulic conductivity. The assimilation of the electrical conductivity 4D images allows updating of the hydrological state as well as the spatial distribution of K. Thus, delineation of the tracer plume and estimation of the local aquifer heterogeneity can be achieved at the same time by means of this interpretation of time-lapse electrical images from tracer tests. We assess the impact on the performance of the hydrological inversion of (i) the uncertainty inherently affecting ERT inversions in terms of tracer concentration and (ii) the choice of the prior statistics of K. Our findings show that realistic ERT images can be integrated into a hydrological model even within an uncoupled inverse modeling framework. The reconstruction of the hydraulic conductivity spatial distribution is satisfactory in the portion of the domain directly covered by the passage of the tracer. Aside from the issues commonly affecting inverse models, the proposed approach is subject to the problem of the filter inbreeding and the retrieval performance is sensitive to the choice of K prior geostatistical parameters.

Apparatus for detecting alpha radiation in difficult access areas

DOEpatents

Steadman, P.; MacArthur, D.W.

1997-09-02

An electrostatic alpha radiation detector for measuring alpha radiation emitted from inside an enclosure comprising an electrically conductive expandable electrode for insertion into the enclosure is disclosed. After insertion, the electrically conductive expandable electrode is insulated from the enclosure and defines a decay cavity between the electrically conductive expandable electrode and the enclosure so that air ions generated in the decay cavity are electrostatically captured by the electrically conductive expandable electrode and the enclosure when an electric potential is applied between the electrically conductive expandable electrode and the enclosure. Indicator means are attached to the electrically conductive expandable electrode for indicating an electrical current produced by generation of the air ions generated in the decay cavity by collisions between air molecules and the alpha particles emitted from the enclosure. A voltage source is connected between the indicator means and the electrically conductive enclosure for creating an electric field between the electrically conductive expandable electrode and the enclosure. 4 figs.

Modeling of conductive particle motion in viscous medium affected by an electric field considering particle-electrode interactions and microdischarge phenomenon

NASA Astrophysics Data System (ADS)

Eslami, Ghiyam; Esmaeilzadeh, Esmaeil; Pérez, Alberto T.

2016-10-01

Up and down motion of a spherical conductive particle in dielectric viscous fluid driven by a DC electric field between two parallel electrodes was investigated. A nonlinear differential equation, governing the particle dynamics, was derived, based on Newton's second law of mechanics, and solved numerically. All the pertaining dimensionless groups were extracted. In contrast to similar previous works, hydrodynamic interaction between the particle and the electrodes, as well as image electric forces, has been taken into account. Furthermore, the influence of the microdischarge produced between the electrodes and the approaching particle on the particle dynamics has been included in the model. The model results were compared with experimental data available in the literature, as well as with some additional experimental data obtained through the present study showing very good agreement. The results indicate that the wall hydrodynamic effect and the dielectric liquid ionic conductivity are very dominant factors determining the particle trajectory. A lower bound is derived for the charge transferred to the particle while rebounding from an electrode. It is found that the time and length scales of the post-microdischarge motion of the particle can be as small as microsecond and micrometer, respectively. The model is able to predict the so called settling/dwelling time phenomenon for the first time.

Geoelectrical inference of mass transfer parameters using temporal moments

USGS Publications Warehouse

Day-Lewis, Frederick D.; Singha, Kamini

2008-01-01

We present an approach to infer mass transfer parameters based on (1) an analytical model that relates the temporal moments of mobile and bulk concentration and (2) a bicontinuum modification to Archie's law. Whereas conventional geochemical measurements preferentially sample from the mobile domain, electrical resistivity tomography (ERT) is sensitive to bulk electrical conductivity and, thus, electrolytic solute in both the mobile and immobile domains. We demonstrate the new approach, in which temporal moments of collocated mobile domain conductivity (i.e., conventional sampling) and ERT‐estimated bulk conductivity are used to calculate heterogeneous mass transfer rate and immobile porosity fractions in a series of numerical column experiments.

Simulation of the Electrical Field in Equine Larynx to Optimize Functional Electrical Stimulation in Denervated Musculus Cricoarythenoideus Dorsalis

PubMed Central

Martinek, Johannes

2014-01-01

Distribution of the electrical field is very important to activate muscle and nerve cells properly. One therapeutic method to treat Recurrent Laryngeal Neuropathy (RLN) in horses can be performed by Functional Electrical Stimulation (FES). Current method to optimize the stimulation effect is to use implanted quadripolar electrodes to the musculus cricoarythenoideus dorsalis (CAD) and testing electrode configuration until best possible optimum is reached. For better understanding and finding of maximum possible activation of CAD a simulation model of the actual entire setting is currently in development. Therefore the geometric model is built from CT-data of a dissected larynx containing the quadripolar electrodes as well as fiducials for later data registration. The geometric model is the basis for a finite difference method containing of voxels with corresponding electrical conductivity of the different types of tissue due to threshold segmentation of the CT-data. Model validation can be done by the measurement of the 3D electrical potential distribution of a larynx positioned in an electrolytic tray. Finally, measured and calculated results have to be compared as well as further investigated. Preliminary results show, that changes of electrode as well as conductivity configuration leads to significant different voltage distributions and can be well presented by equipotential lines superimposed CT-slices – a Matlab graphical user interface visualizes the results in freely selectable slices of the 3D geometry. Voltage distribution along theoretically estimated fiber paths could be calculated as well as visualized. For further calculation of nerve or denervated muscle fiber activation and its optimization, real fiber paths have to be defined and referenced to the potential- and the CT-data. PMID:26913137

Numerical Simulation of Electrical Properties of Carbonate Reservoir Rocks Using µCT Images

NASA Astrophysics Data System (ADS)

Colgin, J.; Niu, Q.; Zhang, C.; Zhang, F.

2017-12-01

Digital rock physics involves the modern microscopic imaging of geomaterials, digitalization of the microstructure, and numerical simulation of physical properties of rocks. This physics-based approach can give important insight into understanding properties of reservoir rocks, and help reveal the link between intrinsic rock properties and macroscopic geophysical responses. The focus of this study is the simulation of the complex conductivity of carbonate reservoir rocks using reconstructed 3D rock structures from high-resolution X-ray micro computed tomography (µCT). Carbonate core samples with varying lithofacies and pore structures from the Cambro-Ordovician Arbuckle Group and the Upper Pennsylvanian Lansing-Kansas City Group in Kansas are used in this study. The wide variations in pore geometry and connectivity of these samples were imaged using µCT. A two-phase segmentation method was used to reconstruct a digital rock of solid particles and pores. We then calculate the effective electrical conductivity of the digital rock volume using a pore-scale numerical approach. The complex conductivity of geomaterials is influenced by the electrical properties and geometry of each phase, i.e., the solid and fluid phases. In addition, the electrical double layer that forms between the solid and fluid phases can also affect the effective conductivity of the material. In the numerical modeling, the influence of the electrical double layer is quantified by a complex surface conductance and converted to an apparent volumetric complex conductivity of either solid particles or pore fluid. The effective complex conductivity resulting from numerical simulations based on µCT images will be compared to results from laboratory experiments on equivalent rock samples. The imaging and digital segmentation method, assumptions in the numerical simulation, and trends as compared to laboratory results will be discussed. This study will help us understand how microscale physics affects macroscale electrical conductivity in porous media.

Calculation of conductivities and currents in the ionosphere

NASA Technical Reports Server (NTRS)

Kirchhoff, V. W. J. H.; Carpenter, L. A.

1975-01-01

Formulas and procedures to calculate ionospheric conductivities are summarized. Ionospheric currents are calculated using a semidiurnal E-region neutral wind model and electric fields from measurements at Millstone Hill. The results agree well with ground based magnetogram records for magnetic quiet days.

Transient finite element modeling of functional electrical stimulation.

PubMed

Filipovic, Nenad D; Peulic, Aleksandar S; Zdravkovic, Nebojsa D; Grbovic-Markovic, Vesna M; Jurisic-Skevin, Aleksandra J

2011-03-01

Transcutaneous functional electrical stimulation is commonly used for strengthening muscle. However, transient effects during stimulation are not yet well explored. The effect of an amplitude change of the stimulation can be described by static model, but there is no differency for different pulse duration. The aim of this study is to present the finite element (FE) model of a transient electrical stimulation on the forearm. Discrete FE equations were derived by using a standard Galerkin procedure. Different tissue conductive and dielectric properties are fitted using least square method and trial and error analysis from experimental measurement. This study showed that FE modeling of electrical stimulation can give the spatial-temporal distribution of applied current in the forearm. Three different cases were modeled with the same geometry but with different input of the current pulse, in order to fit the tissue properties by using transient FE analysis. All three cases were compared with experimental measurements of intramuscular voltage on one volunteer.

Mechanism of the free charge carrier generation in the dielectric breakdown

NASA Astrophysics Data System (ADS)

Rahim, N. A. A.; Ranom, R.; Zainuddin, H.

2017-12-01

Many studies have been conducted to investigate the effect of environmental, mechanical and electrical stresses on insulator. However, studies on physical process of discharge phenomenon, leading to the breakdown of the insulator surface are lacking and difficult to comprehend. Therefore, this paper analysed charge carrier generation mechanism that can cause free charge carrier generation, leading toward surface discharge development. Besides, this paper developed a model of surface discharge based on the charge generation mechanism on the outdoor insulator. Nernst’s Planck theory was used in order to model the behaviour of the charge carriers while Poisson’s equation was used to determine the distribution of electric field on insulator surface. In the modelling of surface discharge on the outdoor insulator, electric field dependent molecular ionization was used as the charge generation mechanism. A mathematical model of the surface discharge was solved using method of line technique (MOL). The result from the mathematical model showed that the behaviour of net space charge density was correlated with the electric field distribution.

Preliminary Study of 2-D Time Domain Electromagnetic (TDEM) Modeling to Analyze Subsurface Resistivity Distribution and its Application to the Geothermal Systems

NASA Astrophysics Data System (ADS)

Aji Hapsoro, Cahyo; Purqon, Acep; Srigutomo, Wahyu

2017-07-01

2-D Time Domain Electromagnetic (TDEM) has been successfully conducted to illustrate the value of Electric field distribution under the Earth surface. Electric field compared by magnetic field is used to analyze resistivity and resistivity is one of physical properties which very important to determine the reservoir potential area of geothermal systems as one of renewable energy. In this modeling we used Time Domain Electromagnetic method because it can solve EM field interaction problem with complex geometry and to analyze transient problems. TDEM methods used to model the value of electric and magnetic fields as a function of the time combined with the function of distance and depth. The result of this modeling is Electric field intensity value which is capable to describe the structure of the Earth’s subsurface. The result of this modeling can be applied to describe the Earths subsurface resistivity values to determine the reservoir potential of geothermal systems.

Conductivity of Nanowire Arrays under Random and Ordered Orientation Configurations

PubMed Central

Jagota, Milind; Tansu, Nelson

2015-01-01

A computational model was developed to analyze electrical conductivity of random metal nanowire networks. It was demonstrated for the first time through use of this model that a performance gain in random metal nanowire networks can be achieved by slightly restricting nanowire orientation. It was furthermore shown that heavily ordered configurations do not outperform configurations with some degree of randomness; randomness in the case of metal nanowire orientations acts to increase conductivity. PMID:25976936

Determining anisotropic conductivity using diffusion tensor imaging data in magneto-acoustic tomography with magnetic induction

NASA Astrophysics Data System (ADS)

Ammari, Habib; Qiu, Lingyun; Santosa, Fadil; Zhang, Wenlong

2017-12-01

In this paper we present a mathematical and numerical framework for a procedure of imaging anisotropic electrical conductivity tensor by integrating magneto-acoutic tomography with data acquired from diffusion tensor imaging. Magneto-acoustic tomography with magnetic induction (MAT-MI) is a hybrid, non-invasive medical imaging technique to produce conductivity images with improved spatial resolution and accuracy. Diffusion tensor imaging (DTI) is also a non-invasive technique for characterizing the diffusion properties of water molecules in tissues. We propose a model for anisotropic conductivity in which the conductivity is proportional to the diffusion tensor. Under this assumption, we propose an optimal control approach for reconstructing the anisotropic electrical conductivity tensor. We prove convergence and Lipschitz type stability of the algorithm and present numerical examples to illustrate its accuracy and feasibility.

Response of ionospheric electric fields at mid-low latitudes during sudden commencements

NASA Astrophysics Data System (ADS)

Takahashi, N.; Kasaba, Y.; Shinbori, A.; Nishimura, Y.; Kikuchi, T.; Ebihara, Y.; Nagatsuma, T.

2015-06-01

Using in situ observations from the Republic of China Satellite-1 spacecraft, we investigated the time response and local time dependence of the ionospheric electric field at mid-low latitudes associated with geomagnetic sudden commencements (SCs) that occurred from 1999 to 2004. We found that the ionospheric electric field variation associated with SCs instantaneously responds to the preliminary impulse (PI) signature on the ground regardless of spacecraft local time. Our statistical analysis also supports the global instant transmission of electric field from the polar region. In contrast, the peak time detected in the ionospheric electric field is earlier than that of the equatorial geomagnetic field (~20 s before in the PI phase). Based on the ground-ionosphere waveguide model, this time lag can be attributed to the latitudinal difference of ionospheric conductivity. However, the local time distribution of the initial excursion of ionospheric electric field shows that dusk-to-dawn ionospheric electric fields develop during the PI phase. Moreover, the westward electric field in the ionosphere, which produces the preliminary reverse impulse of the geomagnetic field on the dayside feature, appears at 18-22 h LT where the ionospheric conductivity beyond the duskside terminator (18 h LT) is lower than on the dayside. The result of a magnetohydrodynamic simulation for an ideal SC shows that the electric potential distribution is asymmetric with respect to the noon-midnight meridian. This produces the local time distribution of ionospheric electric fields similar to the observed result, which can be explained by the divergence of the Hall current under nonuniform ionospheric conductivity.

Direct numerical simulations of three-dimensional electrokinetic flows

NASA Astrophysics Data System (ADS)

Chiam, Keng-Hwee

2006-11-01

We discuss direct numerical simulations of three-dimensional electrokinetic flows in microfluidic devices. In particular, we focus on the study of the electrokinetic instability that develops when two solutions with different electrical conductivities are coupled to an external electric field. We characterize this ``mixing'' instability as a function of the parameters of the model, namely the Reynolds number of the flow, the electric Peclet number of the electrolyte solution, and the ratio of the electroosmotic to the electroviscous time scales. Finally, we describe how this model breaks down when the length scale of the device approaches the nanoscale, where the width of the electric Debye layer is comparable to the width of the channel, and discuss solutions to overcome this.

Evaluation of Hepatoprotective Effect of Curcumin on Liver Cirrhosis Using a Combination of Biochemical Analysis and Magnetic Resonance-Based Electrical Conductivity Imaging

PubMed Central

Kyung, Eun Jung; Kim, Hyun Bum; Hwang, Eun Sang; Lee, Seok; Choi, Bup Kyung; Lim, Sang Moo; Kwon, Oh In

2018-01-01

In oriental medicine, curcumin is used to treat inflammatory diseases, and its anti-inflammatory effect has been reported in recent research. In this feasibility study, the hepatoprotective effect of curcumin was investigated using a rat liver cirrhosis model, which was induced with dimethylnitrosamine (DMN). Together with biochemical analysis, we used a magnetic resonance-based electrical conductivity imaging method to evaluate tissue conditions associated with a protective effect. The effects of curcumin treatment and lactulose treatment on liver cirrhosis were compared. Electrical conductivity images indicated that liver tissues damaged by DMN showed decreased conductivity compared with normal liver tissues. In contrast, cirrhotic liver tissues treated with curcumin or lactulose showed increased conductivity than tissues in the DMN-only group. Specifically, conductivity of cirrhotic liver after curcumin treatment was similar to that of normal liver tissues. Histological staining and immunohistochemical examination showed significant levels of attenuated fibrosis and decreased inflammatory response after both curcumin and lactulose treatments compared with damaged liver tissues by DMN. The conductivity imaging and biochemical examination results indicate that curcumin's anti-inflammatory effect can prevent the progression of irreversible liver dysfunction. PMID:29887757

Dispersive FDTD analysis of induced electric field in human models due to electrostatic discharge.

PubMed

Hirata, Akimasa; Nagai, Toshihiro; Koyama, Teruyoshi; Hattori, Junya; Chan, Kwok Hung; Kavet, Robert

2012-07-07

Contact currents flow from/into a charged human body when touching a grounded conductive object. An electrostatic discharge (ESD) or spark may occur just before contact or upon release. The current may stimulate muscles and peripheral nerves. In order to clarify the difference in the induced electric field between different sized human models, the in-situ electric fields were computed in anatomically based models of adults and a child for a contact current in a human body following ESD. A dispersive finite-difference time-domain method was used, in which biological tissue is assumed to obey a four-pole Debye model. From our computational results, the first peak of the discharge current was almost identical across adult and child models. The decay of the induced current in the child was also faster due mainly to its smaller body capacitance compared to the adult models. The induced electric fields in the forefingers were comparable across different models. However, the electric field induced in the arm of the child model was found to be greater than that in the adult models primarily because of its smaller cross-sectional area. The tendency for greater doses in the child has also been reported for power frequency sinusoidal contact current exposures as reported by other investigators.

[Identification of the cumulative eco-environment effect of coal-electricity integration based on interpretative structural model].

PubMed

Han, Lin Wei; Fu, Xiao; Yan, Yan; Wang, Chen Xing; Wu, Gang

2017-05-18

In order to determine the cumulative eco-environmental effect of coal-electricity integration, we selected 29 eco-environmental factors including different development and construction activities of coal-electricity integration, soil, water, atmospheric conditions, biology, landscape, and ecology. Literature survey, expert questionnaire and interview were conducted to analyze the interactive relationships between different factors. The structure and correlations between the eco-environmental factors influenced by coal-electricity integration activities were analyzed using interpretive structural modeling (ISM) and the cumulative eco-environment effect of development and construction activities was determined. A research and evaluation framework for the cumulative eco-environmental effect was introduced in addition to specific evaluation and management needs. The results of this study would provide a theoretical and technical basis for planning and management of coal-electricity integration development activities.

Hydrodynamic model for conductivity in graphene.

PubMed

Mendoza, M; Herrmann, H J; Succi, S

2013-01-01

Based on the recently developed picture of an electronic ideal relativistic fluid at the Dirac point, we present an analytical model for the conductivity in graphene that is able to describe the linear dependence on the carrier density and the existence of a minimum conductivity. The model treats impurities as submerged rigid obstacles, forming a disordered medium through which graphene electrons flow, in close analogy with classical fluid dynamics. To describe the minimum conductivity, we take into account the additional carrier density induced by the impurities in the sample. The model, which predicts the conductivity as a function of the impurity fraction of the sample, is supported by extensive simulations for different values of ε, the dimensionless strength of the electric field, and provides excellent agreement with experimental data.

Electrical Conduction of Ba(Ti0.99Fe0.01)O3-δ Ceramic at High Temperatures

NASA Astrophysics Data System (ADS)

Yu, Zi-De; Chen, Xiao-Ming

2018-03-01

BaTiO3 and Ba(Ti0.99Fe0.01)O3-δ ceramics with dense microstructure have been synthesized by a solid-state reaction method, and their electrical conduction investigated by broadband electrical impedance spectroscopy at frequencies from 0.05 Hz to 3 × 106 Hz and temperatures from 200°C to 400°C. Compared with BaTiO3, the real part of the permittivity and the phase-transition temperature of Ba(Ti0.99Fe0.01)O3-δ decreased. Relaxation peaks appeared in the curves of the imaginary part of the permittivity as a function of frequency. With increase in frequency, the peaks gradually shifted towards higher frequency and their height increased. Conductivity was closely related to frequency and temperature. Frequency-dependent conductivity was analyzed using the Jonscher double power law. Compared with BaTO3, Ba(Ti0.99Fe0.01)O3-δ exhibited high impedance at given frequency and temperature. Impedance Cole-Cole plots displayed two semicircles, which could be well fit using two parallel RC equivalent circuit models. The conductivity activation energy was found to be around 1 eV. For Ba(Ti0.99Fe0.01)O3-δ , the electrical modulus curve versus frequency displayed two peaks.

Electrical Conduction of Ba(Ti0.99Fe0.01)O3- δ Ceramic at High Temperatures

NASA Astrophysics Data System (ADS)

Yu, Zi-De; Chen, Xiao-Ming

2018-07-01

BaTiO3 and Ba(Ti0.99Fe0.01)O3- δ ceramics with dense microstructure have been synthesized by a solid-state reaction method, and their electrical conduction investigated by broadband electrical impedance spectroscopy at frequencies from 0.05 Hz to 3 × 106 Hz and temperatures from 200°C to 400°C. Compared with BaTiO3, the real part of the permittivity and the phase-transition temperature of Ba(Ti0.99Fe0.01)O3- δ decreased. Relaxation peaks appeared in the curves of the imaginary part of the permittivity as a function of frequency. With increase in frequency, the peaks gradually shifted towards higher frequency and their height increased. Conductivity was closely related to frequency and temperature. Frequency-dependent conductivity was analyzed using the Jonscher double power law. Compared with BaTO3, Ba(Ti0.99Fe0.01)O3- δ exhibited high impedance at given frequency and temperature. Impedance Cole-Cole plots displayed two semicircles, which could be well fit using two parallel RC equivalent circuit models. The conductivity activation energy was found to be around 1 eV. For Ba(Ti0.99Fe0.01)O3- δ , the electrical modulus curve versus frequency displayed two peaks.

First Studies for the Development of Computational Tools for the Design of Liquid Metal Electromagnetic Pumps

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

Maidana, Carlos O.; Nieminen, Juha E.

Liquid alloy systems have a high degree of thermal conductivity, far superior to ordinary nonmetallic liquids and inherent high densities and electrical conductivities. This results in the use of these materials for specific heat conducting and dissipation applications for the nuclear and space sectors. Uniquely, they can be used to conduct heat and electricity between nonmetallic and metallic surfaces. The motion of liquid metals in strong magnetic fields generally induces electric currents, which, while interacting with the magnetic field, produce electromagnetic forces. Electromagnetic pumps exploit the fact that liquid metals are conducting fluids capable of carrying currents, which is amore » source of electromagnetic fields useful for pumping and diagnostics. The coupling between the electromagnetics and thermo-fluid mechanical phenomena and the determination of its geometry and electrical configuration, gives rise to complex engineering magnetohydrodynamics problems. The development of tools to model, characterize, design, and build liquid metal thermomagnetic systems for space, nuclear, and industrial applications are of primordial importance and represent a cross-cutting technology that can provide unique design and development capabilities as well as a better understanding of the physics behind the magneto-hydrodynamics of liquid metals. Here, first studies for the development of computational tools for the design of liquid metal electromagnetic pumps are discussed.« less

First Studies for the Development of Computational Tools for the Design of Liquid Metal Electromagnetic Pumps

DOE PAGES

Maidana, Carlos O.; Nieminen, Juha E.

2017-02-01

Liquid alloy systems have a high degree of thermal conductivity, far superior to ordinary nonmetallic liquids and inherent high densities and electrical conductivities. This results in the use of these materials for specific heat conducting and dissipation applications for the nuclear and space sectors. Uniquely, they can be used to conduct heat and electricity between nonmetallic and metallic surfaces. The motion of liquid metals in strong magnetic fields generally induces electric currents, which, while interacting with the magnetic field, produce electromagnetic forces. Electromagnetic pumps exploit the fact that liquid metals are conducting fluids capable of carrying currents, which is amore » source of electromagnetic fields useful for pumping and diagnostics. The coupling between the electromagnetics and thermo-fluid mechanical phenomena and the determination of its geometry and electrical configuration, gives rise to complex engineering magnetohydrodynamics problems. The development of tools to model, characterize, design, and build liquid metal thermomagnetic systems for space, nuclear, and industrial applications are of primordial importance and represent a cross-cutting technology that can provide unique design and development capabilities as well as a better understanding of the physics behind the magneto-hydrodynamics of liquid metals. Here, first studies for the development of computational tools for the design of liquid metal electromagnetic pumps are discussed.« less

Switching of the electrical conductivity of plasticized PVC films under uniaxial pressure

NASA Astrophysics Data System (ADS)

Vlasov, D. V.; Apresyan, L. A.; Vlasova, T. V.; Kryshtob, V. I.

2011-11-01

The jumplike switching of the electrical conductivity in wide-band-gap polymer (antistatic plasticized polyvinylchloride) films under uniaxial pressure is studied. In various plasticized PVC materials, the uniaxial pressure inducing a conductivity jump by four orders of magnitude or higher changes from several to several hundreds of bars, and this effect is retained at a film thickness of several hundred microns, which is two orders of magnitude larger than the critical film thicknesses known for other wide-band-gap polymers. In addition to the earlier interpretation of the conductivity anomalies in plasticized PVC, we proposed a phenomenological electron-molecular dynamic nanotrap model, in which local charge transfer is provided by mobile molecule segments in a plasticized polymer.

Electrical conductivity studies on (1-x)[PVA/PVP]: x[MgCl2{6H2O}] blend polymer electrolytes

NASA Astrophysics Data System (ADS)

Basha, S. K. Shahenoor; Reddy, K. Veera Bhadra; Rao, M. C.

2018-05-01

Blend polymer electrolytes of polyvinyl alcohol and polyvinyl pyrrolidone were prepared with different molecular wt% ratios of MgCl2.6H2O by solution cast technique. Electrical conductivity measurements for the prepared films were performed using Keithley electrometer model 6514 and the maximum ionic conductivity was found to be 1.01x10-3 S/cm at 373 K for the prepared composition of 35PVA/35PVP:30MgCl2.6H2O. The maximum ionic conductivity of polymer electrolyte has been used in fabrication of electrochemical cell with the configuration of Mg+/(PVA/PVP+MgCl2.6H2O)/(I2+C+electrolyte).

An electrical circuit model for simulation of indoor radon concentration.

PubMed

Musavi Nasab, S M; Negarestani, A

2013-01-01

In this study, a new model based on electric circuit theory was introduced to simulate the behaviour of indoor radon concentration. In this model, a voltage source simulates radon generation in walls, conductivity simulates migration through walls and voltage across a capacitor simulates radon concentration in a room. This simulation considers migration of radon through walls by diffusion mechanism in one-dimensional geometry. Data reported in a typical Greek house were employed to examine the application of this technique of simulation to the behaviour of radon.

A novel application of ADC/K-foaming agent-loaded NBR rubber composites as pressure sensor

NASA Astrophysics Data System (ADS)

Mahmoud, W. E.; El-Eraki, M. H. I.; El-Lawindy, A. M. Y.; Hassan, H. H.

2006-02-01

Nitrile butadiene rubber (NBR) structure foam of different apparent densities was obtained by using different concentrations of foaming agent, azodicarbonamide, ADC/K. The true stress-strain characteristics, in case of compression, of foamed samples were measured. It was found that the theoretical values predicted from the simple blending model are in more agreement with the experimental results than those from the square-relationship model. The effect of cyclic loading-unloading and dissipation energy of rubber foams was studied. The results also indicated that foams with low density exhibited a small hysteresis. The electrical properties were found dependent on the foaming agent concentration. This study was assisted by Mott and Gurney equation. The effect of compressive strain on the electrical conductivity of rubber foams was studied. The free current carrier mobility and the equilibrium concentration of charge carrier in the conduction band were produced as functions of compressive strain. The results also indicate that there is a linear variation between pressure and conductivity for all samples, which means that these samples can be used as a pressure sensor. At a certain concentration of foaming agent (5 phr) a change of electrical conductivity by more than three orders is observed at 20% compression strain.

Normal Values for Heart Electrophysiology Parameters of Healthy Swine Determined on Electrophysiology Study.

PubMed

Noszczyk-Nowak, Agnieszka; Cepiel, Alicja; Janiszewski, Adrian; Pasławski, Robert; Gajek, Jacek; Pasławska, Urszula; Nicpoń, Józef

2016-01-01

Swine are a well-recognized animal model for human cardiovascular diseases. Despite the widespread use of porcine model in experimental electrophysiology, still no reference values for intracardiac electrical activity and conduction parameters determined during an invasive electrophysiology study (EPS) have been developed in this species thus far. The aim of the study was to develop a set of normal values for intracardiac electrical activity and conduction parameters determined during an invasive EPS of swine. The study included 36 healthy domestic swine (24-40 kg body weight). EPS was performed under a general anesthesia with midazolam, propofol and isoflurane. The reference values for intracardiac electrical activity and conduction parameters were calculated as arithmetic means ± 2 standard deviations. The reference values were determined for AH, HV and PA intervals, interatrial conduction time at its own and imposed rhythm, sinus node recovery time (SNRT), corrected sinus node recovery time (CSNRT), anterograde and retrograde Wenckebach points, atrial, atrioventricular node and ventricular refractory periods. No significant correlations were found between body weight and heart rate of the examined pigs and their electrophysiological parameters. The hereby presented reference values can be helpful in comparing the results of various studies, as well as in more accurately estimating the values of electrophysiological parameters that can be expected in a given experiment.

Global Electromagnetic Imaging of Lithosphere and Upper Mantle from Space and Ground. Recent Results and Challenges

NASA Astrophysics Data System (ADS)

Kuvshinov, A. V.

2016-12-01

Electrical conductivity is one of the characteristic physical parameters of materials making up Earth's interior which is sensitive to variations of temperature, chemical composition, water content, and partial melt. As a consequence, estimating lithosphere and upper mantle (LUM) electrical conductivity structure is a potentially strong tool for mapping their chemistry, mineralogy and physical structure thus presenting a complementary method to seismic studies that focus on LUM elastic properties. Global electromagnetic (EM) studies, which provide information on LUM electrical conductivity, have attracted increasing interest during the last decade, mainly for three reasons. A primary reason is the recent growth in the amount of EM data available, especially from low-Earth orbiting magnetic satellite missions (Oersted, CHAMP, SAC-C, and Swarm). A second reason is the great interest in the characterization of the three-dimensional properties of Earth's interior on a global scale. Finally, the interest has also resulted from the significant methodological progress made during the last years in EM data analysis, forward modelling and inversion. In this talk I will summarize advances and challenges in EM data interpretation, and present recent global and regional models of LUM conductivity derived from satellite and ground-based data. I will also discuss possible topics for future research.

Integrated electrokinetics-adsorption remediation of saline-sodic soils: effects of voltage gradient and contaminant concentration on soil electrical conductivity.

PubMed

Essa, Mohammed Hussain; Mu'azu, Nuhu Dalhat; Lukman, Salihu; Bukhari, Alaadin

2013-01-01

In this study, an integrated in situ remediation technique which couples electrokinetics with adsorption, using locally produced granular activated carbon from date palm pits in the treatment zones that are installed directly to bracket the contaminated soils at bench-scale, is investigated. Natural saline-sodic clay soil, spiked with contaminant mixture (kerosene, phenol, Cr, Cd, Cu, Zn, Pb, and Hg), was used in this study to investigate the effects of voltage gradient, initial contaminant concentration, and polarity reversal rate on the soil electrical conductivity. Box-Behnken Design (BBD) was used for the experimental design and response surface methodology (RSM) was employed to model, optimize, and interpret the results obtained using Design-Expert version 8 platform. The total number of experiments conducted was 15 with voltage gradient, polarity reversal rate, and initial contaminant concentration as variables. The main target response discussed in this paper is the soil electrical conductivity due to its importance in electrokinetic remediation process. Responses obtained were fitted to quadratic models whose R (2) ranges from 84.66% to 99.19% with insignificant lack of fit in each case. Among the investigated factors, voltage gradient and initial contaminant concentration were found to be the most significant influential factors.

High conductance surge cable

DOEpatents

Murray, M.M.; Wilfong, D.H.; Lomax, R.E.

1998-12-08

An electrical cable for connecting transient voltage surge suppressors to electrical power panels. A strip of electrically conductive foil defines a longitudinal axis, with a length of an electrical conductor electrically attached to the metallic foil along the longitudinal axis. The strip of electrically conductive foil and the length of an electrical conductor are covered by an insulating material. For impedance matching purposes, triangular sections can be removed from the ends of the electrically conductive foil at the time of installation. 6 figs.

Apparent isotropic electrical property for electrical brain stimulation (EBS) using magnetic resonance diffusion weighted imaging (MR-DWI)

NASA Astrophysics Data System (ADS)

Lee, Mun Bae; Kwon, Oh-In

2018-04-01

Electrical brain stimulation (EBS) is an invasive electrotherapy and technique used in brain neurological disorders through direct or indirect stimulation using a small electric current. EBS has relied on computational modeling to achieve optimal stimulation effects and investigate the internal activations. Magnetic resonance diffusion weighted imaging (DWI) is commonly useful for diagnosis and investigation of tissue functions in various organs. The apparent diffusion coefficient (ADC) measures the intensity of water diffusion within biological tissues using DWI. By measuring trace ADC and magnetic flux density induced by the EBS, we propose a method to extract electrical properties including the effective extracellular ion-concentration (EEIC) and the apparent isotropic conductivity without any auxiliary additional current injection. First, the internal current density due to EBS is recovered using the measured one component of magnetic flux density. We update the EEIC by introducing a repetitive scheme called the diffusion weighting J-substitution algorithm using the recovered current density and the trace ADC. To verify the proposed method, we study an anesthetized canine brain to visualize electrical properties including electrical current density, effective extracellular ion-concentration, and effective isotropic conductivity by applying electrical stimulation of the brain.

Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films.

PubMed

Yang, C-H; Seidel, J; Kim, S Y; Rossen, P B; Yu, P; Gajek, M; Chu, Y H; Martin, L W; Holcomb, M B; He, Q; Maksymovych, P; Balke, N; Kalinin, S V; Baddorf, A P; Basu, S R; Scullin, M L; Ramesh, R

2009-06-01

Many interesting materials phenomena such as the emergence of high-Tc superconductivity in the cuprates and colossal magnetoresistance in the manganites arise out of a doping-driven competition between energetically similar ground states. Doped multiferroics present a tantalizing evolution of this generic concept of phase competition. Here, we present the observation of an electronic conductor-insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO3 through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p-n junction can be created, erased and inverted in this material. A 'dome-like' feature in the doping dependence of the ferroelectric transition is observed around a Ca concentration of approximately 1/8, where a new pseudo-tetragonal phase appears and the electric modulation of conduction is optimized. Possible mechanisms for the observed effects are discussed on the basis of the interplay of ionic and electronic conduction. This observation opens the door to merging magnetoelectrics and magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom already present in the multiferroic BiFeO3.

Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films

NASA Astrophysics Data System (ADS)

Yang, C.-H.; Seidel, J.; Kim, S. Y.; Rossen, P. B.; Yu, P.; Gajek, M.; Chu, Y. H.; Martin, L. W.; Holcomb, M. B.; He, Q.; Maksymovych, P.; Balke, N.; Kalinin, S. V.; Baddorf, A. P.; Basu, S. R.; Scullin, M. L.; Ramesh, R.

2009-06-01

Many interesting materials phenomena such as the emergence of high-Tc superconductivity in the cuprates and colossal magnetoresistance in the manganites arise out of a doping-driven competition between energetically similar ground states. Doped multiferroics present a tantalizing evolution of this generic concept of phase competition. Here, we present the observation of an electronic conductor-insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO3 through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p-n junction can be created, erased and inverted in this material. A `dome-like' feature in the doping dependence of the ferroelectric transition is observed around a Ca concentration of ~1/8, where a new pseudo-tetragonal phase appears and the electric modulation of conduction is optimized. Possible mechanisms for the observed effects are discussed on the basis of the interplay of ionic and electronic conduction. This observation opens the door to merging magnetoelectrics and magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom already present in the multiferroic BiFeO3.

A new petrological and geophysical investigation of the present-day plumbing system of Mount Vesuvius

NASA Astrophysics Data System (ADS)

Pommier, A.; Tarits, P.; Hautot, S.; Pichavant, M.; Scaillet, B.; Gaillard, F.

2010-07-01

A model of the electrical resistivity of Mt. Vesuvius has been elaborated to investigate the present structure of the volcanic edifice. The model is based on electrical conductivity measurements in the laboratory, on geophysical information, in particular, magnetotelluric (MT) data, and on petrological and geochemical constraints. Both 1-D and 3-D simulations explored the effect of depth, volume and resistivity of either one or two reservoirs in the structure. For each configuration tested, modeled MT transfer functions were compared to field transfer functions from field magnetotelluric studies. The field electrical data are reproduced with a shallow and very conductive layer (˜0.5 km depth, 1.2 km thick, 5 ohm.m resistive) that most likely corresponds to a saline brine present beneath the volcano. Our results are also compatible with the presence of cooling magma batches at shallow depths (<3-4 km depth). The presence of a deeper body at ˜8 km depth, as suggested by seismic studies, is consistent with the observed field transfer functions if such a body has an electrical resistivity > ˜100 ohm.m. According to a petro-physical conductivity model, such a resistivity value is in agreement either with a low-temperature, crystal-rich magma chamber or with a small quantity of hotter magma interconnected in the resistive surrounding carbonates. However, the low quality of MT field data at long periods prevent from placing strong constraints on a potential deep magma reservoir. A comparison with seismic velocity values tends to support the second hypothesis. Our findings would be consistent with a deep structure (8-10 km depth) made of a tephriphonolitic magma at 1000°C, containing 3.5 wt%H2O, 30 vol.% crystals, and interconnected in carbonates in proportions ˜45% melt -55% carbonates.

Method of Fault Detection and Rerouting

NASA Technical Reports Server (NTRS)

Gibson, Tracy L. (Inventor); Medelius, Pedro J. (Inventor); Lewis, Mark E. (Inventor)

2013-01-01

A system and method for detecting damage in an electrical wire, including delivering at least one test electrical signal to an outer electrically conductive material in a continuous or non-continuous layer covering an electrically insulative material layer that covers an electrically conductive wire core. Detecting the test electrical signals in the outer conductive material layer to obtain data that is processed to identify damage in the outer electrically conductive material layer.

Method for the thermal characterization, visualization, and integrity evaluation of conducting material samples or complex structures

DOEpatents

Ortiz, Marcos G.

1992-01-01

A method for modeling a conducting material sample or structure (herein called a system) as at least two regions which comprise an electrical network of resistances, for measuring electric resistance between at least two selected pairs of external leads attached to the surface of the system, wherein at least one external lead is attached to the surface of each of the regions, and, using basic circuit theory, for translating measured resistances into temperatures or thermophysical properties in corresponding regions of the system.

Method for the thermal characterization, visualization, and integrity evaluation of conducting material samples or complex structures

DOEpatents

Ortiz, M.G.

1992-11-24

Disclosed is a method for modeling a conducting material sample or structure (herein called a system) as at least two regions which comprise an electrical network of resistances, for measuring electric resistance between at least two selected pairs of external leads attached to the surface of the system, wherein at least one external lead is attached to the surface of each of the regions, and, using basic circuit theory, for translating measured resistances into temperatures or thermophysical properties in corresponding regions of the system. 16 figs.

On effective holographic Mott insulators

NASA Astrophysics Data System (ADS)

Baggioli, Matteo; Pujolàs, Oriol

2016-12-01

We present a class of holographic models that behave effectively as prototypes of Mott insulators — materials where electron-electron interactions dominate transport phenomena. The main ingredient in the gravity dual is that the gauge-field dynamics contains self-interactions by way of a particular type of non-linear electrodynamics. The electrical response in these models exhibits typical features of Mott-like states: i) the low-temperature DC conductivity is unboundedly low; ii) metal-insulator transitions appear by varying various parameters; iii) for large enough self-interaction strength, the conductivity can even decrease with increasing doping (density of carriers) — which appears as a sharp manifestation of `traffic-jam'-like behaviour; iv) the insulating state becomes very unstable towards superconductivity at large enough doping. We exhibit some of the properties of the resulting insulator-superconductor transition, which is sensitive to the momentum dissipation rate in a specific way. These models imply a clear and generic correlation between Mott behaviour and significant effects in the nonlinear electrical response. We compute the nonlinear current-voltage curve in our model and find that indeed at large voltage the conductivity is largely reduced.

Numerical simulations of electric potential field for alternating current potential drop associated with surface cracks in low-alloy steel nuclear material

NASA Astrophysics Data System (ADS)

Yeh, Chun-Ping; Huang, Jiunn-Yuan

2018-04-01

Low-alloy steels used as structural materials in nuclear power plants are subjected to cyclic stresses during power plant operations. As a result, cracks may develop and propagate through the material. The alternating current potential drop technique is used to measure the lengths of cracks in metallic components. The depth of the penetration of the alternating current is assumed to be small compared to the crack length. This assumption allows the adoption of the unfolding technique to simplify the problem to a surface Laplacian field. The numerical modelling of the electric potential and current density distribution prediction model for a compact tension specimen and the unfolded crack model are presented in this paper. The goal of this work is to conduct numerical simulations to reduce deviations occurring in the crack length measurements. Numerical simulations were conducted on AISI 4340 low-alloy steel with different crack lengths to evaluate the electric potential distribution. From the simulated results, an optimised position for voltage measurements in the crack region was proposed.

A new method for electric impedance imaging using an eddy current with a tetrapolar circuit.

PubMed

Ahsan-Ul-Ambia; Toda, Shogo; Takemae, Tadashi; Kosugi, Yukio; Hongo, Minoru

2009-02-01

A new contactless technique for electrical impedance imaging, using an eddy current managed along with the tetrapolar circuit method, is proposed. The eddy current produced by a magnetic field is superimposed on a constant current that is normally used in the tetrapolar circuit method, and thus is used to control the current distribution in the body. By changing the current distribution, a set of voltage differences is measured with a pair of electrodes. This set of voltage differences is used in the image reconstruction of the resistivity distribution. The least square error minimization method is used in the reconstruction algorithm. The principle of this method is explained theoretically. A backprojection algorithm was used to get 2-D images. Based on this principle, a measurement system was developed and model experiments were conducted with a saline-filled phantom. The estimated shape of each model in the reconstructed image was similar to that of the corresponding model. From the results of these experiments, it is confirmed that the proposed method is applicable to the realization of electrical conductivity imaging.

The Effect of Variation in Permittivity of Different Tissues on Induced Electric Field in the Brain during Transcranial Magnetic Stimulation

NASA Astrophysics Data System (ADS)

Hadimani, Ravi; Porzig, Konstantin; Crowther, Lawrence; Brauer, Hartmut; Toepfer, Hannes; Jiles, David; Department of Electrical and Computer Engineering, Iowa State University Team; Department of Advanced Electromagnetics, Ilmenau University of Technology Team

2013-03-01

Estimation of electric field in the brain during Transcranial Magnetic Stimulation (TMS) requires knowledge of the electric property of brain tissue. Grey and white matters have unusually high relative permittivities of ~ 106 at low frequencies. However, relative permittivity of cerebrospinal fluid is ~ 102. With such a variation it is necessary to consider the effect of boundaries. A model consisting of 2 hemispheres was used in the model with the properties of one hemisphere kept constant at σ1 = 0.1Sm-1 and ɛr 1 = 10 while the properties of the second hemisphere were changed kept at σ2 = 0.1Sm-1 to 2Sm-1 and ɛr 2 = 102 to 105. A 70 mm diameter double coil was used as the source of the magnetic field. The amplitude of the current in the coil was 5488 A at a frequency of 2.9 kHz. The results show that the electric field, E induced during magnetic stimulation is independent of the relative permittivity, ɛr and varies with the conductivity. Thus the variation in E, calculated with homogeneous and heterogeneous head models was due to variation in conductivity of the tissues and not due to variation in permittivities.

The influence of sulcus width on simulated electric fields induced by transcranial magnetic stimulation

NASA Astrophysics Data System (ADS)

Janssen, A. M.; Rampersad, S. M.; Lucka, F.; Lanfer, B.; Lew, S.; Aydin, Ü.; Wolters, C. H.; Stegeman, D. F.; Oostendorp, T. F.

2013-07-01

Volume conduction models can help in acquiring knowledge about the distribution of the electric field induced by transcranial magnetic stimulation. One aspect of a detailed model is an accurate description of the cortical surface geometry. Since its estimation is difficult, it is important to know how accurate the geometry has to be represented. Previous studies only looked at the differences caused by neglecting the complete boundary between cerebrospinal fluid (CSF) and grey matter (Thielscher et al 2011 NeuroImage 54 234-43, Bijsterbosch et al 2012 Med. Biol. Eng. Comput. 50 671-81), or by resizing the whole brain (Wagner et al 2008 Exp. Brain Res. 186 539-50). However, due to the high conductive properties of the CSF, it can be expected that alterations in sulcus width can already have a significant effect on the distribution of the electric field. To answer this question, the sulcus width of a highly realistic head model, based on T1-, T2- and diffusion-weighted magnetic resonance images, was altered systematically. This study shows that alterations in the sulcus width do not cause large differences in the majority of the electric field values. However, considerable overestimation of sulcus width produces an overestimation of the calculated field strength, also at locations distant from the target location.

Theoretical Insight Into the Empirical Tortuosity-Connectivity Factor in the Burdine-Brooks-Corey Water Relative Permeability Model

NASA Astrophysics Data System (ADS)

Ghanbarian, Behzad; Ioannidis, Marios A.; Hunt, Allen G.

2017-12-01

A model commonly applied to the estimation of water relative permeability krw in porous media is the Burdine-Brooks-Corey model, which relies on a simplified picture of pores as a bundle of noninterconnected capillary tubes. In this model, the empirical tortuosity-connectivity factor is assumed to be a power law function of effective saturation with an exponent (μ) commonly set equal to 2 in the literature. Invoking critical path analysis and using percolation theory, we relate the tortuosity-connectivity exponent μ to the critical scaling exponent t of percolation that characterizes the power law behavior of the saturation-dependent electrical conductivity of porous media. We also discuss the cause of the nonuniversality of μ in terms of the nonuniversality of t and compare model estimations with water relative permeability from experiments. The comparison supports determining μ from the electrical conductivity scaling exponent t, but also highlights limitations of the model.

Electrically conductive proppant and methods for detecting, locating and characterizing the electrically conductive proppant

DOEpatents

Cannan, Chad; Bartel, Lewis; Palisch, Terrence; Aldridge, David

2015-01-13

Electrically conductive proppants and methods for detecting, locating, and characterizing same are provided. The electrically conductive proppant can include a substantially uniform coating of an electrically conductive material having a thickness of at least 500 nm. The method can include injecting a hydraulic fluid into a wellbore extending into a subterranean formation at a rate and pressure sufficient to open a fracture therein, injecting into the fracture a fluid containing the electrically conductive proppant, electrically energizing the earth at or near the fracture, and measuring three dimensional (x, y, and z) components of electric and magnetic field responses at a surface of the earth or in an adjacent wellbore.

Parallel Infrastructure Modeling and Inversion Module for E4D

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

2014-10-09

Electrical resistivity tomography ERT is a method of imaging the electrical conductivity of the subsurface. Electrical conductivity is a useful metric for understanding the subsurface because it is governed by geomechanical and geochemical properties that drive subsurface systems. ERT works by injecting current into the subsurface across a pair of electrodes, and measuring the corresponding electrical potential response across another pair of electrodes. Many such measurements are strategically taken across an array of electrodes to produce an ERT data set. These data are then processed through a computationally demanding process known as inversion to produce an image of the subsurfacemore » conductivity structure that gave rise to the measurements. Data can be inverted to provide 2D images, 3D images, or in the case of time-lapse 3D imaging, 4D images. ERT is generally not well suited for environments with buried electrically conductive infrastructure such as pipes, tanks, or well casings, because these features tend to dominate and degrade ERT images. This reduces or eliminates the utility of ERT imaging where it would otherwise be highly useful for, for example, imaging fluid migration from leaking pipes, imaging soil contamination beneath leaking subusurface tanks, and monitoring contaminant migration in locations with dense network of metal cased monitoring wells. The location and dimension of buried metallic infrastructure is often known. If so, then the effects of the infrastructure can be explicitly modeled within the ERT imaging algorithm, and thereby removed from the corresponding ERT image. However,there are a number of obstacles limiting this application. 1) Metallic infrastructure cannot be accurately modeled with standard codes because of the large contrast in conductivity between the metal and host material. 2) Modeling infrastructure in true dimension requires the computational mesh to be highly refined near the metal inclusions, which increases computational demands. 3) The ERT imaging algorithm requires specialized modifications to accomodate high conductivty inclusions within the computational mesh. The solution to each of these challenges was implemented within E4D (formerly FERM3D), which is a parallel ERT imaging code developed at PNNL (IPID #30249). The infrastructure modeling module implement in E4D uses a method of decoupling the model at the metallic interface(s) boundaries, into several well posed sub-problems (one for each distinct metallicinclusion) that are subsequently solved and recombined to form the global solution. The approach is based on the immersed interface method, with has been applied for similar problems in other fields (e.g. semiconductor industry). Comparisons to analytic solutions have shown the results to be very accurate, addressing item 1 above. The solution is implemented about an unstructured mesh, which enables arbitrary shapes to be efficiently modelled, thereby addressing item 2 above. In addition, the algorithm is written in parallel and shows excellent scalability, which also addresses equation 2 above. Finally, because only the boundaries of metallic inclusions are modeled, there are no high conductivity cells within the modeling mesh, and the problem described by item 3 above is no longer applicable.« less

Nuclear electric propulsion reactor control systems status

NASA Technical Reports Server (NTRS)

Ferg, D. A.

1973-01-01

The thermionic reactor control system design studies conducted over the past several years for a nuclear electric propulsion system are described and summarized. The relevant reactor control system studies are discussed in qualitative terms, pointing out the significant advantages and disadvantages including the impact that the various control systems would have on the nuclear electric propulsion system design. A recommendation for the reference control system is made, and a program for future work leading to an engineering model is described.

Crystal growth and electrical properties of CuFeO 2 single crystals

NASA Astrophysics Data System (ADS)

Dordor, P.; Chaminade, J. P.; Wichainchai, A.; Marquestaut, E.; Doumerc, J. P.; Pouchard, M.; Hagenmuller, P.; Ammar, A.

1988-07-01

Delafossite-type CuFeO 2 single crystals have been prepared by a flux method: crystals obtained in a Cu crucible with LiBO 2 as flux are n-type whereas those prepared in a Pt crucible with a Cu 2O flux are p-type. Electrical measurements have revealed that n-type crystals exhibit weak anisotropic conductivities with large activation energies and small mobilities (r.t. values perpendicular and parallel to the c-axis: μ⊥ = 5 × 10 -5 and μ‖ = 10 -7 cm -2 V -1 sec -1). p-type crystals, less anisotropic, are characterized by low activation energies and higher mobilities ( μ⊥ = 34 and μ‖ = 8.9 cm 2 V -1 sec -1). A two -conduction-band model is proposed to account for the difference observed between the energy gap value deduced from photoelectrochemical measurements and the activation energy of the electrical conductivity in the intrinsic domain.

Temperature Dependence of Density, Viscosity and Electrical Conductivity for Hg-Based II-VI Semiconductor Melts

NASA Technical Reports Server (NTRS)

Li, C.; Ban, H.; Lin, B.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

The relaxation phenomenon of semiconductor melts, or the change of melt structure with time, impacts the crystal growth process and the eventual quality of the crystal. The thermophysical properties of the melt are good indicators of such changes in melt structure. Also, thermophysical properties are essential to the accurate predication of the crystal growth process by computational modeling. Currently, the temperature dependent thermophysical property data for the Hg-based II-VI semiconductor melts are scarce. This paper reports the results on the temperature dependence of melt density, viscosity and electrical conductivity of Hg-based II-VI compounds. The melt density was measured using a pycnometric method, and the viscosity and electrical conductivity were measured by a transient torque method. Results were compared with available published data and showed good agreement. The implication of the structural changes at different temperature ranges was also studied and discussed.

Seismicity in the platform regions of Ukraine in the zones of anomalous electrical conductivity

NASA Astrophysics Data System (ADS)

Kushnir, A. N.; Kulik, S. N.; Burakhovich, T. K.

2013-05-01

It is established for the first time that there are several regions in Ukraine, in which the earthquakes occurring within platform territory are correlated to the anomalous conductive structures in the Earth's crust and upper mantle. These regions are identified as (1) Donbass and the eastern part of the Dnieper-Donetsk Depression (DDD); (2) eastern margin of the Ingulets-Krivoi Rog suture zone in the area of the Krivoi Rog-Kremenchug fault zone; (3) the western part of the Cis-Azov megablock; (4) the western boundary of the Ukrainian Shield and its slope; (5) North Dobruja and Pre-Dobrujan Depression. The reconstructed tree-dimensional (3D) geoelectrical models of the Earth's crust and upper mantle feature anomalously low values of electric resistivity. The earthquake sources in the platform areas of Ukraine are localized above the top and in the upper parts of the crustal anomalies of electrical conductivity.

Structure, Raman, dielectric behavior and electrical conduction mechanism of strontium titanate

NASA Astrophysics Data System (ADS)

Trabelsi, H.; Bejar, M.; Dhahri, E.; Graça, M. P. F.; Valente, M. A.; Khirouni, K.

2018-05-01

Strontium titanate was prepared by solid-state reaction method. According to the XRD, it was single phase and has a cubic perovskite structure. The Raman spectroscopic investigation was carried out at room-temperature, and the second-order Raman modes were observed. By employing impedance spectroscopy, the dielectric relaxation and electrical properties were investigated over the temperature range of 500-700 K at various frequencies. The activation energies evaluated from dielectric and modulus studies are in good agreement and these values are attributed to the bulk relaxation. The impedance data were well fitted to an (R1//C1)-(R2//CPE1) equivalent electrical circuit. It could be concluded that the grain boundaries are more resistive and capacitive than the grains. The ac conductivity was found to follow the Jonscher's universal dynamic law ωS and the correlated barrier hopping model (CBH) has been proposed to describe the conduction mechanism.

Mathematical modeling of photovoltaic thermal PV/T system with v-groove collector

NASA Astrophysics Data System (ADS)

Zohri, M.; Fudholi, A.; Ruslan, M. H.; Sopian, K.

2017-07-01

The use of v-groove in solar collector has a higher thermal efficiency in references. Dropping the working heat of photovoltaic panel was able to raise the electrical efficiency performance. Electrical and thermal efficiency were produced by photovoltaic thermal (PV/T) system concurrently. Mathematical modeling based on steady-state thermal analysis of PV/T system with v-groove was conducted. With matrix inversion method, the energy balance equations are explained by means of the investigative method. The comparison results show that in the PV/T system with the V-groove collector is higher temperature, thermal and electrical efficiency than other collectors.

Electric-field control of conductance in metal quantum point contacts by electric-double-layer gating

NASA Astrophysics Data System (ADS)

Shibata, K.; Yoshida, K.; Daiguji, K.; Sato, H.; , T., Ii; Hirakawa, K.

2017-10-01

An electric-field control of quantized conductance in metal (gold) quantum point contacts (QPCs) is demonstrated by adopting a liquid-gated electric-double-layer (EDL) transistor geometry. Atomic-scale gold QPCs were fabricated by applying the feedback-controlled electrical break junction method to the gold nanojunction. The electric conductance in gold QPCs shows quantized conductance plateaus and step-wise increase/decrease by the conductance quantum, G0 = 2e2/h, as EDL-gate voltage is swept, demonstrating a modulation of the conductance of gold QPCs by EDL gating. The electric-field control of conductance in metal QPCs may open a way for their application to local charge sensing at room temperature.

A Reconstruction Algorithm for Breast Cancer Imaging With Electrical Impedance Tomography in Mammography Geometry

PubMed Central

Kao, Tzu-Jen; Isaacson, David; Saulnier, Gary J.; Newell, Jonathan C.

2009-01-01

The conductivity and permittivity of breast tumors are known to differ significantly from those of normal breast tissues, and electrical impedance tomography (EIT) is being studied as a modality for breast cancer imaging to exploit these differences. At present, X-ray mammography is the primary standard imaging modality used for breast cancer screening in clinical practice, so it is desirable to study EIT in the geometry of mammography. This paper presents a forward model of a simplified mammography geometry and a reconstruction algorithm for breast tumor imaging using EIT techniques. The mammography geometry is modeled as a rectangular box with electrode arrays on the top and bottom planes. A forward model for the electrical impedance imaging problem is derived for a homogeneous conductivity distribution and is validated by experiment using a phantom tank. A reconstruction algorithm for breast tumor imaging based on a linearization approach and the proposed forward model is presented. It is found that the proposed reconstruction algorithm performs well in the phantom experiment, and that the locations of a 5-mm-cube metal target and a 6-mm-cube agar target could be recovered at a target depth of 15 mm using a 32 electrode system. PMID:17405377

An analytic solution for numerical modeling validation in electromagnetics: the resistive sphere

NASA Astrophysics Data System (ADS)

Swidinsky, Andrei; Liu, Lifei

2017-11-01

We derive the electromagnetic response of a resistive sphere to an electric dipole source buried in a conductive whole space. The solution consists of an infinite series of spherical Bessel functions and associated Legendre polynomials, and follows the well-studied problem of a conductive sphere buried in a resistive whole space in the presence of a magnetic dipole. Our result is particularly useful for controlled-source electromagnetic problems using a grounded electric dipole transmitter and can be used to check numerical methods of calculating the response of resistive targets (such as finite difference, finite volume, finite element and integral equation). While we elect to focus on the resistive sphere in our examples, the expressions in this paper are completely general and allow for arbitrary source frequency, sphere radius, transmitter position, receiver position and sphere/host conductivity contrast so that conductive target responses can also be checked. Commonly used mesh validation techniques consist of comparisons against other numerical codes, but such solutions may not always be reliable or readily available. Alternatively, the response of simple 1-D models can be tested against well-known whole space, half-space and layered earth solutions, but such an approach is inadequate for validating models with curved surfaces. We demonstrate that our theoretical results can be used as a complementary validation tool by comparing analytic electric fields to those calculated through a finite-element analysis; the software implementation of this infinite series solution is made available for direct and immediate application.

Finite element method (FEM) model of the mechanical stress on phospholipid membranes from shock waves produced in nanosecond electric pulses (nsEP)

NASA Astrophysics Data System (ADS)

Barnes, Ronald; Roth, Caleb C.; Shadaram, Mehdi; Beier, Hope; Ibey, Bennett L.

2015-03-01

The underlying mechanism(s) responsible for nanoporation of phospholipid membranes by nanosecond pulsed electric fields (nsEP) remains unknown. The passage of a high electric field through a conductive medium creates two primary contributing factors that may induce poration: the electric field interaction at the membrane and the shockwave produced from electrostriction of a polar submersion medium exposed to an electric field. Previous work has focused on the electric field interaction at the cell membrane, through such models as the transport lattice method. Our objective is to model the shock wave cell membrane interaction induced from the density perturbation formed at the rising edge of a high voltage pulse in a polar liquid resulting in a shock wave propagating away from the electrode toward the cell membrane. Utilizing previous data from cell membrane mechanical parameters, and nsEP generated shockwave parameters, an acoustic shock wave model based on the Helmholtz equation for sound pressure was developed and coupled to a cell membrane model with finite-element modeling in COMSOL. The acoustic structure interaction model was developed to illustrate the harmonic membrane displacements and stresses resulting from shockwave and membrane interaction based on Hooke's law. Poration is predicted by utilizing membrane mechanical breakdown parameters including cortical stress limits and hydrostatic pressure gradients.

The Electrical and Thermal Conductivity of Woven Pristine and Intercalated Graphite Fiber-Polymer Composites

NASA Technical Reports Server (NTRS)

Gaier, James R.; Vandenburg, Yvonne Yoder; Berkebile, Steven; Stueben, Heather; Balagadde, Frederick

2002-01-01

A series of woven fabric laminar composite plates and narrow strips were fabricated from a variety of pitch-based pristine and bromine intercalated graphite fibers in an attempt to determine the influence of the weave on the electrical and thermal conduction. It was found generally that these materials can be treated as if they are homogeneous plates. The rule of mixtures describes the resistivity of the composite fairly well if it is realized that only the component of the fibers normal to the equipotential surface will conduct current. When the composite is narrow with respect to the fiber weave, however, there is a marked angular dependence of the resistance which was well modeled by assuming that the current follows only along the fibers (and not across them in a transverse direction), and that the contact resistance among the fibers in the composite is negligible. The thermal conductivity of composites made from less conductive fibers more closely followed the rule of mixtures than that of the high conductivity fibers, though this is thought to be an artifact of the measurement technique. Electrical and thermal anisotropy could be induced in a particular region of the structure by weaving together high and low conductivity fibers in different directions, though this must be done throughout all of the layers of the structure as interlaminar conduction precludes having only the top layer carry the anisotropy. The anisotropy in the thermal conductivity is considerably less than either that predicted by the rule of mixtures or the electrical resistivity.

Torsional Vibration Analysis of Reciprocating Compressor Trains driven by Induction Motors

NASA Astrophysics Data System (ADS)

Brunelli, M.; Fusi, A.; Grasso, F.; Pasteur, F.; Ussi, A.

2015-08-01

The dynamic study of electric motor driven compressors, for Oil&Gas (O&G) applications, are traditionally performed in two steps separating the mechanical and the electrical systems. The packager conducts a Torsional Vibration Analysis (TVA) modeling the mechanical system with a lumped parameter scheme, without taking into account the electrical part. The electric motor supplier later performs a source current pulsation analysis on the electric motor system, based on the TVA results. The mechanical and the electrical systems are actually linked by the electromagnetic effect. The effect of the motor air-gap on TVA has only recently been taken into account by adding a spring and a damper between motor and ground in the model. This model is more accurate than the traditional one, but is applicable only to the steady-state condition and still fails to consider the reciprocal effects between the two parts of the system. In this paper the torsional natural frequencies calculated using both the traditional and the new model have been compared. Furthermore, simulation of the complete system has been achieved through the use of LMS AMESim, multi-physics, one-dimensional simulation software that simultaneously solves the shafts rotation and electric motor voltage equation. Finally, the transient phenomena that occur during start-up have been studied.

Subcellular Electrical Measurements as a Function of Wood Moisture Content

Treesearch

Samuel L. Zelinka; José L. Colon Quintana; Samuel V. Glass; Joseph E. Jakes; Alex C. Wiedenhoeft

2015-01-01

The percolation model developed by Zelinka et al. was based upon macroscale measurements of the electrical conductivity and implicitly treats the wood material as homogenous. The transport mechanism proposed by Jakes et al. depends upon a moisture induced glass transition occurring in the hemicelluloses. This theory suggests that there are likely differences in the...

Solving the forward problem of magnetoacoustic tomography with magnetic induction by means of the finite element method

NASA Astrophysics Data System (ADS)

Li, Xun; Li, Xu; Zhu, Shanan; He, Bin

2009-05-01

Magnetoacoustic tomography with magnetic induction (MAT-MI) is a recently proposed imaging modality to image the electrical impedance of biological tissue. It combines the good contrast of electrical impedance tomography with the high spatial resolution of sonography. In this paper, a three-dimensional MAT-MI forward problem was investigated using the finite element method (FEM). The corresponding FEM formulae describing the forward problem are introduced. In the finite element analysis, magnetic induction in an object with conductivity values close to biological tissues was first carried out. The stimulating magnetic field was simulated as that generated from a three-dimensional coil. The corresponding acoustic source and field were then simulated. Computer simulation studies were conducted using both concentric and eccentric spherical conductivity models with different geometric specifications. In addition, the grid size for finite element analysis was evaluated for the model calibration and evaluation of the corresponding acoustic field.

The time and temperature dependence of the thermoelectric properties of silicon-germanium alloy

NASA Technical Reports Server (NTRS)

Raag, V.

1975-01-01

Experimental data on the electrical resistivity and Seebeck coefficient of n-type and p-type silicon-germanium alloys are analyzed in terms of a solid-state dopant precipitation model proposed by Lifshitz and Slyozov (1961). Experimental findings on the time and temperature dependence of the thermal conductivity of these two types of alloy indicate that the thermal conductivity of silicon-germanium alloys changes with time, contrary to previous hypothesis. A preliminary model is presented which stipulates that the observed thermal conductivity decrease in silicon-germanium alloys is due partly to dopant precipitation underlying the electrical property changes and partly to enhanced alloying of the material. It is significant that all three properties asymptotically approach equilibrium values with time. Total characterization of these properties will enable the time change to be fully compensated in the design of a thermoelectric device employing silicon-germanium alloys.

Solving the Forward Problem of Magnetoacoustic Tomography with Magnetic Induction by Means of the Finite Element Method

PubMed Central

Li, Xun; Li, Xu; Zhu, Shanan; He, Bin

2010-01-01

Magnetoacoustic Tomography with Magnetic Induction (MAT-MI) is a recently proposed imaging modality to image the electrical impedance of biological tissue. It combines the good contrast of electrical impedance tomography with the high spatial resolution of sonography. In this paper, three-dimensional MAT-MI forward problem was investigated using the finite element method (FEM). The corresponding FEM formulas describing the forward problem are introduced. In the finite element analysis, magnetic induction in an object with conductivity values close to biological tissues was first carried out. The stimulating magnetic field was simulated as that generated from a three-dimensional coil. The corresponding acoustic source and field were then simulated. Computer simulation studies were conducted using both concentric and eccentric spherical conductivity models with different geometric specifications. In addition, the grid size for finite element analysis was evaluated for model calibration and evaluation of the corresponding acoustic field. PMID:19351978

Fabrication and modeling of stretchable conductors for traumatic brain injury research

NASA Astrophysics Data System (ADS)

Cao, Wenzhe

Stretchable electronics are an emergent class of electronics that can retain their electric functionality under large mechanical deformation, such as stretching, bending and compression. Like traditional electric circuits, stretchable electronics rely on electrical conductors, but in this specific instance the conductors must also be stretchable. This thesis research had three goals: (1) fabricate elastically stretchable conductors that retain their electrical conductance when stretched by tens of percent of strain; (2) understand the underlying stretching mechanism of gold conductors on polydimethylsiloxane (PDMS) substrates; (3) produce a special device---a stretchable microelectrode array, which contains a matrix of stretchable conductors that enables a new approach to studying traumatic brain injury. We first developed and optimized the micro-fabrication process to make elastically stretchable thin gold film conductors on PDMS substrates. The conductors can retain electrical conduction while being stretched reversibly to 140% uniaxially and 16% radially. We further developed a fabrication process to encapsulate the conductors with either a commercially available photopatternable silicone (PPS) or with PDMS. 100 microm by 100 microm vias were patterned in the encapsulation layer to expose electrical contacts. PPS encapsulated conductors can be stretched uniaxially to 80%, and the PDMS encapsulated conductor can be stretched to ˜15%, without losing electrical conduction. We also introduced acrylate-based shape memory polymers (SMPs) as a new type of substrate for stretchable conductors. Their stiffness can be tuned by varying the monomer composition or by changing the ambient temperature. Thin gold film conductors deposited on pre-strained SMPs remain conductive when first stretched and then relaxed to their pre-strain value. Moreover, an SMP can also serve as a stretchable carrier to make pre-strained conductors on an overlying PDMS membrane. The resistance of gold conductors made on pre-strained PDMS changes less during stretching than that made on non-pre-strained PDMS substrate. We built a model of the electrical resistance in function of strain. The model is based on the topography of the thin gold film on PDMS. This model is a first attempt at predicting electrical resistance of stretchable thin gold film conductors. Lastly, we fabricated stretchable microelectrode arrays (SMEAs). They were utilized at Columbia University to study traumatic brain injury (TBI). Tissues cultured on SMEA remained viable for 19 days, and the electrodes were able to both stimulate and record neural tissue activity before, during and after stretching. Therefore SMEAs are able to bring together mechanical injury, electrophysiological recording and pharmacological studies. The SMEAs could serve as in vitro platforms for high throughput therapeutic screening and discovery for traumatic injury. The ability to reproducibly fabricate stretchable conductors using micro-fabrication technology will facilitate adoption by industry. The ability to understand the stretching mechanism will enable us to design more robust material systems. The SMEA prototypes demonstrate that stretchable conductors are practical, and their mechanical compatibility with biological systems also makes them candidates for use in biomedical devices.

Tunneling Conductivity and Piezoresistivity of Composites Containing Randomly Dispersed Conductive Nano-Platelets

PubMed Central

Oskouyi, Amirhossein Biabangard; Sundararaj, Uttandaraman; Mertiny, Pierre

2014-01-01

In this study, a three-dimensional continuum percolation model was developed based on a Monte Carlo simulation approach to investigate the percolation behavior of an electrically insulating matrix reinforced with conductive nano-platelet fillers. The conductivity behavior of composites rendered conductive by randomly dispersed conductive platelets was modeled by developing a three-dimensional finite element resistor network. Parameters related to the percolation threshold and a power-low describing the conductivity behavior were determined. The piezoresistivity behavior of conductive composites was studied employing a reoriented resistor network emulating a conductive composite subjected to mechanical strain. The effects of the governing parameters, i.e., electron tunneling distance, conductive particle aspect ratio and size effects on conductivity behavior were examined. PMID:28788580

Analytical solution of electromagnetic radiation by a vertical electric dipole inside the earth and the effect of atmospheric electrical conductivity inhomogeneity

NASA Astrophysics Data System (ADS)

Mosayebidorcheh, Taha; Hosseinibalam, Fahimeh; Hassanzadeh, Smaeyl

2017-11-01

In this paper, the effect of atmospheric electrical conductivity on the electromagnetic waves radiated by a vertical electric dipole located in the earth, near the surface of the earth, is investigated. As far as electrical conductivity is concerned, the atmosphere is divided into three areas, in which the electrical conductivity changes with altitude. The Maxwell equations in these areas are investigated as well. Using the differential transform method, the differential equation is solved in a way that atmospheric electrical conductivity is variable. Solving the problem in these areas indicates that electrical conductivity in the middle and lower areas of atmosphere may be ignored. However, in the upper areas of atmosphere, the magnitude of the magnetic field in the ionosphere at a frequency of 10 kHz at night is five times smaller when electrical conductivity is considered compared to when it is neglected.

Electromagnetic interference of power conditioners for solar electric propulsion

NASA Technical Reports Server (NTRS)

Whittlesey, A. C.; Macie, T. W.

1973-01-01

Electrical, multikilowatt power conditioning (PC) equipment needed on board a spacecraft utilizing solar electric propulsion creates an electromagnetic environment that is potentially deterimental to the science, navigation, and radio communication hardware. Within the scope of the solar electric propulsion system technology program, three lightweight, 2.5-kW PCs were evaluated in terms of their electromagnetic characteristics. It was found that the levels of radiated and conducted interference exceeded the levels anticipated for a solar electric propulsion mission. These noise emissions, however, were the result of deficient interference design in these models, rather than a basic inability to control interference in this type of PC.

Atmosphere-Ionosphere Electrodynamic Coupling

NASA Astrophysics Data System (ADS)

Sorokin, V. M.; Chmyrev, V. M.

Numerous phenomena that occur in the mesosphere, ionosphere, and the magnetosphere of the Earth are caused by the sources located in the lower atmosphere and on the ground. We describe the effects produced by lightning activity and by ground-based transmitters operated in high frequency (HF) and very low frequency (VLF) ranges. Among these phenomena are the ionosphere heating and the formation of plasma density inhomogeneities, the excitation of gamma ray bursts and atmospheric emissions in different spectral bands, the generation of ULF/ELF/VLF electromagnetic waves and plasma turbulence in the ionosphere, the stimulation of radiation belt electron precipitations and the acceleration of ions in the upper ionosphere. The most interesting results of experimental and theoretical studies of these phenomena are discussed below. The ionosphere is subject to the action of the conductive electric current flowing in the atmosphere-ionosphere circuit. We present a physical model of DC electric field and current formation in this circuit. The key element of this model is an external current, which is formed with the occurrence of convective upward transport of charged aerosols and their gravitational sedimentation in the atmosphere. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization and change of electrical conductivity. Variation of conductivity and external current in the lower atmosphere leads to perturbation of the electric current flowing in the global atmosphere-ionosphere circuit and to the associated DC electric field perturbation both on the Earth's surface and in the ionosphere. Description of these processes and some results of the electric field and current calculations are presented below. The seismic-induced electric field perturbations produce noticeable effects in the ionosphere by generating the electromagnetic field and plasma disturbances. We describe the generation mechanisms of such experimentally observed effects as excitation of plasma density inhomogeneities, field-aligned currents, and ULF/ELF emissions and the modification of electron and ion altitude profiles in the upper ionosphere. The electrodynamic model of the ionosphere modification under the influence of some natural and man-made processes in the atmosphere is also discussed. The model is based on the satellite and ground measurements of electromagnetic field and plasma perturbations and on the data on atmospheric radioactivity and soil gas injection into the atmosphere.

Effect of Substitutional Pb Doping on Bipolar and Lattice Thermal Conductivity in p-Type Bi0.48Sb1.52Te₃.

PubMed

Kim, Hyun-Sik; Lee, Kyu Hyoung; Yoo, Joonyeon; Youn, Jehun; Roh, Jong Wook; Kim, Sang-Il; Kim, Sung Wng

2017-07-06

Cation substitutional doping is an effective approach to modifying the electronic and thermal transports in Bi₂Te₃-based thermoelectric alloys. Here we present a comprehensive analysis of the electrical and thermal conductivities of polycrystalline Pb-doped p-type bulk Bi 0.48 Sb 1.52 Te₃. Pb doping significantly increased the electrical conductivity up to ~2700 S/cm at x = 0.02 in Bi 0.48-x Pb x Sb 1.52 Te₃ due to the increase in hole carrier concentration. Even though the total thermal conductivity increased as Pb was added, due to the increased hole carrier concentration, the thermal conductivity was reduced by 14-22% if the contribution of the increased hole carrier concentration was excluded. To further understand the origin of reduction in the thermal conductivity, we first estimated the contribution of bipolar conduction to thermal conductivity from a two-parabolic band model, which is an extension of the single parabolic band model. Thereafter, the contribution of additional point defect scattering caused by Pb substitution (Pb in the cation site) was analyzed using the Debye-Callaway model. We found that Pb doping significantly suppressed both the bipolar thermal conduction and lattice thermal conductivity simultaneously, while the bipolar contribution to the total thermal conductivity reduction increased at high temperatures. At Pb doping of x = 0.02, the bipolar thermal conductivity decreased by ~30% from 0.47 W/mK to 0.33 W/mK at 480 K, which accounts for 70% of the total reduction.

Effect of Substitutional Pb Doping on Bipolar and Lattice Thermal Conductivity in p-Type Bi0.48Sb1.52Te3

PubMed Central

Kim, Hyun-sik; Lee, Kyu Hyoung; Yoo, Joonyeon; Youn, Jehun; Roh, Jong Wook; Kim, Sang-il; Kim, Sung Wng

2017-01-01

Cation substitutional doping is an effective approach to modifying the electronic and thermal transports in Bi2Te3-based thermoelectric alloys. Here we present a comprehensive analysis of the electrical and thermal conductivities of polycrystalline Pb-doped p-type bulk Bi0.48Sb1.52Te3. Pb doping significantly increased the electrical conductivity up to ~2700 S/cm at x = 0.02 in Bi0.48-xPbxSb1.52Te3 due to the increase in hole carrier concentration. Even though the total thermal conductivity increased as Pb was added, due to the increased hole carrier concentration, the thermal conductivity was reduced by 14–22% if the contribution of the increased hole carrier concentration was excluded. To further understand the origin of reduction in the thermal conductivity, we first estimated the contribution of bipolar conduction to thermal conductivity from a two-parabolic band model, which is an extension of the single parabolic band model. Thereafter, the contribution of additional point defect scattering caused by Pb substitution (Pb in the cation site) was analyzed using the Debye–Callaway model. We found that Pb doping significantly suppressed both the bipolar thermal conduction and lattice thermal conductivity simultaneously, while the bipolar contribution to the total thermal conductivity reduction increased at high temperatures. At Pb doping of x = 0.02, the bipolar thermal conductivity decreased by ~30% from 0.47 W/mK to 0.33 W/mK at 480 K, which accounts for 70% of the total reduction. PMID:28773118

MO-F-CAMPUS-I-01: EIT Imaging to Monitor Human Salivary Gland Functionality: A Feasibility Study

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

Kohli, K; Karvat, A; Liu, J

Purpose: Clinically, there exists a need to develop a non-invasive technique for monitoring salivary activity. In this study, we investigate the feasibility of a using the electrical conductivity information from Electrical Impedance Tomography (EIT) to monitor salivary flow activity. Methods: To acquire EIT data, eight Ag/AgCl ECG electrodes were placed around the mandible of the subject. An EIT scan was obtained by injecting current at 50 KHz, 0.4 mA through each pair of electrodes and recording voltage across other electrode pairs. The functional conductivity image was obtained through reconstruction of the voltage data, using Electrical Impedance Tomography and Diffuse Opticalmore » Tomography Reconstruction Software (EIDORS) in Matlab. In using EIDORS, forward solution was obtained using a user-defined finite element model shape and inverse solution was obtained using one-step Gaussian solver. EIT scans of volunteer research team members were acquired for three different physiological states: pre-stimulation, stimulation and post-stimulation. For pre-stimulation phase, data were collected in intervals of 5 minutes for 15 minutes. The salivary glands were then stimulated in the subject using lemon and the data were collected immediately. Post-stimulation data were collected at 4 different timings after stimulation. Results: Variations were observed in the electrical conductivity patterns near parotid regions between the pre- and post-stimulation stages. The three images acquired during the 15 minute pre-stimulation phase showed no major changes in the conductivity. Immediately after stimulation, electrical conductivity increased near parotid regions and 15 minutes later slowly returned to pre-stimulation level. Conclusion: In the present study involving human subjects, the change in electrical conductivity pattern shown in the EIT images, acquired at different times with and without stimulation of salivary glands, appeared to be consistent with the change in salivary gland activity. The conductivity changes imaged through EIT are potentially useful for the purpose of salivary monitoring.« less

Silver Nanoparticle-Deposited Boron Nitride Nanosheets as Fillers for Polymeric Composites with High Thermal Conductivity.

PubMed

Wang, Fangfang; Zeng, Xiaoliang; Yao, Yimin; Sun, Rong; Xu, Jianbin; Wong, Ching-Ping

2016-01-19

Polymer composites with high thermal conductivity have recently attracted much attention, along with the rapid development of the electronic devices toward higher speed and performance. However, a common method to enhance polymer thermal conductivity through an addition of high thermally conductive fillers usually cannot provide an expected value, especially for composites requiring electrical insulation. Here, we show that polymeric composites with silver nanoparticle-deposited boron nitride nanosheets as fillers could effectively enhance the thermal conductivity of polymer, thanks to the bridging connections of silver nanoparticles among boron nitride nanosheets. The thermal conductivity of the composite is significantly increased from 1.63 W/m-K for the composite filled with the silver nanoparticle-deposited boron nitride nanosheets to 3.06 W/m-K at the boron nitride nanosheets loading of 25.1 vol %. In addition, the electrically insulating properties of the composite are well preserved. Fitting the measured thermal conductivity of epoxy composite with one physical model indicates that the composite with silver nanoparticle-deposited boron nitride nanosheets outperforms the one with boron nitride nanosheets, owning to the lower thermal contact resistance among boron nitride nanosheets' interfaces. The finding sheds new light on enhancement of thermal conductivity of the polymeric composites which concurrently require the electrical insulation.

Silver Nanoparticle-Deposited Boron Nitride Nanosheets as Fillers for Polymeric Composites with High Thermal Conductivity

PubMed Central

Wang, Fangfang; Zeng, Xiaoliang; Yao, Yimin; Sun, Rong; Xu, Jianbin; Wong, Ching-Ping

2016-01-01

Polymer composites with high thermal conductivity have recently attracted much attention, along with the rapid development of the electronic devices toward higher speed and performance. However, a common method to enhance polymer thermal conductivity through an addition of high thermally conductive fillers usually cannot provide an expected value, especially for composites requiring electrical insulation. Here, we show that polymeric composites with silver nanoparticle-deposited boron nitride nanosheets as fillers could effectively enhance the thermal conductivity of polymer, thanks to the bridging connections of silver nanoparticles among boron nitride nanosheets. The thermal conductivity of the composite is significantly increased from 1.63 W/m-K for the composite filled with the silver nanoparticle-deposited boron nitride nanosheets to 3.06 W/m-K at the boron nitride nanosheets loading of 25.1 vol %. In addition, the electrically insulating properties of the composite are well preserved. Fitting the measured thermal conductivity of epoxy composite with one physical model indicates that the composite with silver nanoparticle-deposited boron nitride nanosheets outperforms the one with boron nitride nanosheets, owning to the lower thermal contact resistance among boron nitride nanosheets’ interfaces. The finding sheds new light on enhancement of thermal conductivity of the polymeric composites which concurrently require the electrical insulation. PMID:26783258

Conductive fabric seal

DOEpatents

Livesay, Ronald Jason; Mason, Brandon William; Kuhn, Michael Joseph; Rowe, Nathan Carl

2017-04-04

Disclosed are several examples of a system and method for detecting if an article is being tampered with. Included is a covering made of a substrate that is coated with a layer of an electrically conductive material that forms an electrically conductive surface having an electrical resistance. The covering is configured to at least partially encapsulate the article such that the article cannot be tampered with, without modifying the electrical resistance of the electrically conductive surface of the covering. A sensing device is affixed to the electrically conductive surface of the covering and the sensing device monitors the condition of the covering by producing a signal that is indicative of the electrical resistance of the electrically conductive surface of the covering. A measured electrical resistance that differs from a nominal electrical resistance is indicative of a covering that is being tampered with and an alert is communicated to an observer.

Conductive fabric seal

DOEpatents

Livesay, Ronald Jason; Mason, Brandon William; Kuhn, Michael Joseph; Rowe, Nathan Carl

2015-10-13

Disclosed are several examples of a system and method for detecting if an article is being tampered with. Included is a covering made of a substrate that is coated with a layer of an electrically conductive material that forms an electrically conductive surface having an electrical resistance. The covering is configured to at least partially encapsulate the article such that the article cannot be tampered with, without modifying the electrical resistance of the electrically conductive surface of the covering. A sensing device is affixed to the electrically conductive surface of the covering and the sensing device monitors the condition of the covering by producing a signal that is indicative of the electrical resistance of the electrically conductive surface of the covering. A measured electrical resistance that differs from a nominal electrical resistance is indicative of a covering that is being tampered with and an alert is communicated to an observer.

High conductance surge cable

DOEpatents

Murray, Matthew M.; Wilfong, Dennis H.; Lomax, Ralph E.

1998-01-01

An electrical cable for connecting transient voltage surge suppressers to ectrical power panels. A strip of electrically conductive foil defines a longitudinal axis, with a length of an electrical conductor electrically attached to the metallic foil along the longitudinal axis. The strip of electrically conductive foil and the length of an electrical conductor are covered by an insulating material. For impedance matching purposes, triangular sections can be removed from the ends of the electrically conductive foil at the time of installation.

Photovoltaic conversion of laser power to electrical power

NASA Technical Reports Server (NTRS)

Walker, G. H.; Heinbockel, J. H.

1986-01-01

Photovoltaic laser to electric converters are attractive for use with a space-based laser power station. This paper presents the results of modeling studies for a silicon vertical junction converter used with a Nd laser. A computer code was developed for the model and this code was used to conduct a parametric study for a Si vertical junction converter consisting of one p-n junction irradiated with a Nd laser. These calculations predict an efficiency over 50 percent for an optimized converter.

Modeling the response of small myelinated axons in a compound nerve to kilohertz frequency signals

NASA Astrophysics Data System (ADS)

Pelot, N. A.; Behrend, C. E.; Grill, W. M.

2017-08-01

Objective. There is growing interest in electrical neuromodulation of peripheral nerves, particularly autonomic nerves, to treat various diseases. Electrical signals in the kilohertz frequency (KHF) range can produce different responses, including conduction block. For example, EnteroMedics’ vBloc® therapy for obesity delivers 5 kHz stimulation to block the abdominal vagus nerves, but the mechanisms of action are unclear. Approach. We developed a two-part computational model, coupling a 3D finite element model of a cuff electrode around the human abdominal vagus nerve with biophysically-realistic electrical circuit equivalent (cable) model axons (1, 2, and 5.7 µm in diameter). We developed an automated algorithm to classify conduction responses as subthreshold (transmission), KHF-evoked activity (excitation), or block. We quantified neural responses across kilohertz frequencies (5-20 kHz), amplitudes (1-8 mA), and electrode designs. Main results. We found heterogeneous conduction responses across the modeled nerve trunk, both for a given parameter set and across parameter sets, although most suprathreshold responses were excitation, rather than block. The firing patterns were irregular near transmission and block boundaries, but otherwise regular, and mean firing rates varied with electrode-fibre distance. Further, we identified excitation responses at amplitudes above block threshold, termed ‘re-excitation’, arising from action potentials initiated at virtual cathodes. Excitation and block thresholds decreased with smaller electrode-fibre distances, larger fibre diameters, and lower kilohertz frequencies. A point source model predicted a larger fraction of blocked fibres and greater change of threshold with distance as compared to the realistic cuff and nerve model. Significance. Our findings of widespread asynchronous KHF-evoked activity suggest that conduction block in the abdominal vagus nerves is unlikely with current clinical parameters. Our results indicate that compound neural or downstream muscle force recordings may be unreliable as quantitative measures of neural activity for in vivo studies or as biomarkers in closed-loop clinical devices.

Modeling the response of small myelinated axons in a compound nerve to kilohertz frequency signals.

PubMed

Pelot, N A; Behrend, C E; Grill, W M

2017-08-01

There is growing interest in electrical neuromodulation of peripheral nerves, particularly autonomic nerves, to treat various diseases. Electrical signals in the kilohertz frequency (KHF) range can produce different responses, including conduction block. For example, EnteroMedics' vBloc ® therapy for obesity delivers 5 kHz stimulation to block the abdominal vagus nerves, but the mechanisms of action are unclear. We developed a two-part computational model, coupling a 3D finite element model of a cuff electrode around the human abdominal vagus nerve with biophysically-realistic electrical circuit equivalent (cable) model axons (1, 2, and 5.7 µm in diameter). We developed an automated algorithm to classify conduction responses as subthreshold (transmission), KHF-evoked activity (excitation), or block. We quantified neural responses across kilohertz frequencies (5-20 kHz), amplitudes (1-8 mA), and electrode designs. We found heterogeneous conduction responses across the modeled nerve trunk, both for a given parameter set and across parameter sets, although most suprathreshold responses were excitation, rather than block. The firing patterns were irregular near transmission and block boundaries, but otherwise regular, and mean firing rates varied with electrode-fibre distance. Further, we identified excitation responses at amplitudes above block threshold, termed 're-excitation', arising from action potentials initiated at virtual cathodes. Excitation and block thresholds decreased with smaller electrode-fibre distances, larger fibre diameters, and lower kilohertz frequencies. A point source model predicted a larger fraction of blocked fibres and greater change of threshold with distance as compared to the realistic cuff and nerve model. Our findings of widespread asynchronous KHF-evoked activity suggest that conduction block in the abdominal vagus nerves is unlikely with current clinical parameters. Our results indicate that compound neural or downstream muscle force recordings may be unreliable as quantitative measures of neural activity for in vivo studies or as biomarkers in closed-loop clinical devices.

Computational Fluid Dynamics Modeling of the Operation of a Flame Ionization Sensor

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

Huckaby, E.D.; Chorpening, B.T.; Thornton, J.D.

The sensors and controls research group at the United States Department of Energy (DOE) National Energy Technology Laboratory (NETL) is continuing to develop the Combustion Control and Diagnostics Sensor (CCADS) for gas turbine applications. CCADS uses the electrical conduction of the charged species generated during the combustion process to detect combustion instabilities and monitor equivalence ratio. As part of this effort, combustion models are being developed which include the interaction between the electric field and the transport of charged species. The primary combustion process is computed using a flame wrinkling model (Weller et. al. 1998) which is a component ofmore » the OpenFOAM toolkit (Jasak et. al. 2004). A sub-model for the transport of charged species is attached to this model. The formulation of the charged-species model similar that applied by Penderson and Brown (1993) for the simulation of laminar flames. The sub-model consists of an additional flux due to the electric field (drift flux) added to the equations for the charged species concentrations and the solution the electric potential from the resolved charge density. The subgrid interactions between the electric field and charged species transport have been neglected. Using the above procedure, numerical simulations are performed and the results compared with several recent CCADS experiments.« less

Drude conductivity exhibited by chemically synthesized reduced graphene oxide

NASA Astrophysics Data System (ADS)

Younas, Daniyal; Javed, Qurat-ul-Ain; Fatima, Sabeen; Kalsoom, Riffat; Abbas, Hussain; Khan, Yaqoob

2017-09-01

Electrical conductance in graphene layers having Drude like response due to massless Dirac fermions have been well explained theoretically as well as experimentally. In this paper Drude like electrical conductivity response of reduced graphene oxide synthesized by chemical route is presented. A method slightly different from conventional methods is used to synthesize graphene oxide which is then converted to reduced graphene oxide. Various analytic techniques were employed to verify the successful oxidation and reductions in the process and were also used to measure various parameters like thickness of layers and conductivity. Obtained reduced graphene oxide has very thin layers of thickness around 13 nm on average and reduced graphene oxide has average thickness below 20 nm. Conductivity of the reduced graphene was observed to have Drude like response which is explained on basis of Drude model for conductors.

Large transient fault current test of an electrical roll ring

NASA Technical Reports Server (NTRS)

Yenni, Edward J.; Birchenough, Arthur G.

1992-01-01

The space station uses precision rotary gimbals to provide for sun tracking of its photoelectric arrays. Electrical power, command signals and data are transferred across the gimbals by roll rings. Roll rings have been shown to be capable of highly efficient electrical transmission and long life, through tests conducted at the NASA Lewis Research Center and Honeywell's Satellite and Space Systems Division in Phoenix, AZ. Large potential fault currents inherent to the power system's DC distribution architecture, have brought about the need to evaluate the effects of large transient fault currents on roll rings. A test recently conducted at Lewis subjected a roll ring to a simulated worst case space station electrical fault. The system model used to obtain the fault profile is described, along with details of the reduced order circuit that was used to simulate the fault. Test results comparing roll ring performance before and after the fault are also presented.

Evaluation of critical nuclear power plant electrical cable response to severe thermal fire conditions

NASA Astrophysics Data System (ADS)

Taylor, Gabriel James

The failure of electrical cables exposed to severe thermal fire conditions are a safety concern for operating commercial nuclear power plants (NPPs). The Nuclear Regulatory Commission (NRC) has promoted the use of risk-informed and performance-based methods for fire protection which resulted in a need to develop realistic methods to quantify the risk of fire to NPP safety. Recent electrical cable testing has been conducted to provide empirical data on the failure modes and likelihood of fire-induced damage. This thesis evaluated numerous aspects of the data. Circuit characteristics affecting fire-induced electrical cable failure modes have been evaluated. In addition, thermal failure temperatures corresponding to cable functional failures have been evaluated to develop realistic single point thermal failure thresholds and probability distributions for specific cable insulation types. Finally, the data was used to evaluate the prediction capabilities of a one-dimension conductive heat transfer model used to predict cable failure.

Mechanical signaling coordinates the embryonic heartbeat.

PubMed

Chiou, Kevin K; Rocks, Jason W; Chen, Christina Yingxian; Cho, Sangkyun; Merkus, Koen E; Rajaratnam, Anjali; Robison, Patrick; Tewari, Manorama; Vogel, Kenneth; Majkut, Stephanie F; Prosser, Benjamin L; Discher, Dennis E; Liu, Andrea J

2016-08-09

In the beating heart, cardiac myocytes (CMs) contract in a coordinated fashion, generating contractile wave fronts that propagate through the heart with each beat. Coordinating this wave front requires fast and robust signaling mechanisms between CMs. The primary signaling mechanism has long been identified as electrical: gap junctions conduct ions between CMs, triggering membrane depolarization, intracellular calcium release, and actomyosin contraction. In contrast, we propose here that, in the early embryonic heart tube, the signaling mechanism coordinating beats is mechanical rather than electrical. We present a simple biophysical model in which CMs are mechanically excitable inclusions embedded within the extracellular matrix (ECM), modeled as an elastic-fluid biphasic material. Our model predicts strong stiffness dependence in both the heartbeat velocity and strain in isolated hearts, as well as the strain for a hydrogel-cultured CM, in quantitative agreement with recent experiments. We challenge our model with experiments disrupting electrical conduction by perfusing intact adult and embryonic hearts with a gap junction blocker, β-glycyrrhetinic acid (BGA). We find this treatment causes rapid failure in adult hearts but not embryonic hearts-consistent with our hypothesis. Last, our model predicts a minimum matrix stiffness necessary to propagate a mechanically coordinated wave front. The predicted value is in accord with our stiffness measurements at the onset of beating, suggesting that mechanical signaling may initiate the very first heartbeats.

Optimization and control of dynamic percolationin nanostructured silicon oils

NASA Astrophysics Data System (ADS)

Badard, Mathieu; Combessis, Anthony; Allais, Arnaud; Flandin, Lionel

2017-06-01

The addition of carbonaceous fillers in polymers allows the conception of composites with optimized electrical properties. The conductivity of such material depends of the fillers structuration in matrix, especially the presence of percolated network. The objective of this paper is to understand the main aggregation mechanisms of carbon nanotubes in different media. The structuration of these filler network is probed by the use of electrical and dielectrical measurements. The innovative part of our work lies in the use of liquid matrices, especially silicon oils, to overcome mechanical constraints present in polymers on the one hand and to simplify processing on the other hand. Our work has revealed a filler aggregation over time, well known as dynamic percolation. Conductivity has been modeled as a function of time and filler content from Kirkpatrick equation. The further use of an electrical field led to conductivity enhancement as well as a decrease in percolation threshold. Finally, a study of intrinsic parameters of matrix has shown a strong effect of viscosity and surface tension on nanotubes aggregation. Contribution to the topical issue "Electrical Engineering Symposium (SGE 2016)", edited by Adel Razek

Solar photolysis of ozone to singlet D oxygen atoms

NASA Technical Reports Server (NTRS)

Blackburn, Thomas E.; Bairai, Solomon T.; Stedman, Donald H.

1992-01-01

The ground-level photolysis frequency of ozone J(O3) to produce metastable singlet D oxygen atoms (O (D-1)) is measured using a novel instrumental technique involving electrical conductivity. The O(D-1) atoms produced react with nitrous oxide (N2O) carrier gas to form higher oxides of nitrogen (NO(x)). These oxides were detected by mixing with methanol and determining the increase in electrical conductivity with a continuous-flow dual conductivity cell. Over 70 days of data were collected under varying sky conditions. The effect of temperature on J(O3) was measured. The results agree with model predictions. The effects of atmospheric aerosols, changes in overhead ozone column, and local cloudiness are discussed.

A Parametric Study of the Cold Plasma Refilling Rate on the Plasmasphere and Inner Magnetosphere Dynamics during the 17-March-2013 and 28-June-2013 Magnetic Storms

NASA Astrophysics Data System (ADS)

Lemon, C.; Bishop, R. L.; Coster, A. J.; Nikoukar, R.; Chen, M.; Turner, D. L.; Roeder, J. L.; Shumko, M.; Payne, C.; Bhatt, R.

2017-12-01

Magnetosphere-ionosphere coupling is a complex process, and researchers must consider a number of factors: particle transport in the electric and magnetic fields drives plasma from the high latitude tail to the mid-latitude inner magnetosphere; particle precipitation into the ionosphere, which is frequently driven by wave-particle interactions, enhances the ionospheric conductivities; feedback of the ionospheric conductivities on the electric fields determines how well the convection electric field penetrates to the mid-latitude ionosphere; and the erosion and refilling of cold plasma in the plasmasphere substantially determines the mass of plasma on magnetospheric field lines and the subsequent wave environment that drives particle precipitation. While we model all of these processes, in this presentation we focus on the role of the plasmasphere and its role in M-I coupling. We present RCM-E simulations in which particle transport through self-consistent fields controls the drainage of the plasmasphere, an outflow model determines the plasmasphere refilling rate, and electron and ion precipitation influences the electric field by enhancing the ionospheric conductivity. The plasmasphere significantly affects the spatial structure of the wave environment and electron precipitation rates. This impacts the dynamics of the sub-auroral polarization stream (SAPS) in the pre-midnight region equatorward of the auroral boundary, which itself drives erosion of the plasmasphere through strong westward electric fields near the plasmapause. We present comparisons with Van Allen Probes, THEMIS, the Plasmasphere Data Assimilation (PDA) model, and line-of-sight observations from Millstone Hill ISR and space-based GPS receivers, showing how our modeled plasmasphere compares with observational data during the 17-March-2013 and 28-June-2013 magnetic storms. To better understand refilling, we focus particular attention on densities in the recently-depleted flux tubes in the plasmasphere trough. We compare several empirical models of the plasmasphere refilling rate to see which ones give the best agreement, and through parametric simulations we systematically investigate the effect of varying the local time and L dependence of the refilling rate.

Model 'zero-age' lunar thermal profiles resulting from electrical induction

NASA Technical Reports Server (NTRS)

Herbert, F.; Sonett, C. P.; Wiskerchen, M. J.

1977-01-01

Thermal profiles for the moon are calculated under the assumption that a pre-main-sequence T-Tauri-like solar wind excites both transverse magnetic and transverse electric induction while the moon is accreting. A substantial initial temperature rise occurs, possibly of sufficient magnitude to cause subsequent early extensive melting throughout the moon in conjunction with nominal long-lived radioactives. In these models, accretion is an unimportant direct source of thermal energy but is important because even small temperature rises from accretion cause significant changes in bulk electrical conductivity. Induction depends upon the radius of the moon, which we take to be accumulating while it is being heated electrically. The 'zero-age' profiles calculated in this paper are proposed as initial conditions for long-term thermal evolution of the moon.

Apparatus for Use in Determining Surface Conductivity at Microwave Frequencies

NASA Technical Reports Server (NTRS)

Hearn, Chase P. (Inventor)

1995-01-01

An apparatus is provided for use in determining surface conductivity of a flat or shaped conductive material at microwave frequencies. A plate has an electrically conductive surface with first and second holes passing through the plate. An electrically conductive material under test (MUT) is maintained in a spaced apart relationship with the electrically conductive surface of the plate by one or more nonconductive spacers. A first coupling loop is electrically shielded within the first hole while a second coupling loop is electrically shielded within the second hole. A dielectric resonator element is positioned between the first and second coupling loops, while also being positioned closer to the MUT than the electrically conductive surface of the plate. Microwave energy at an operating frequency f is supplied from a signal source to the first coupling loop while microwave energy received at the second coupling loop is measured. The apparatus is capable of measuring the Q-factor of the dielectric resonator situated in the 'cavity' existing between the electrically conductive surface of the plate and the MUT. Surface conductivity of the electrically conductive surface can be determined via interpolation using: 1 ) the measured Q-factor with the electrically conductive surface in place, and 2) the measured Q-factor when the MUT is replaced with reference standards having known surface conductivities.

MHD thrust vectoring of a rocket engine

NASA Astrophysics Data System (ADS)

Labaune, Julien; Packan, Denis; Tholin, Fabien; Chemartin, Laurent; Stillace, Thierry; Masson, Frederic

2016-09-01

In this work, the possibility to use MagnetoHydroDynamics (MHD) to vectorize the thrust of a solid propellant rocket engine exhaust is investigated. Using a magnetic field for vectoring offers a mass gain and a reusability advantage compared to standard gimbaled, elastomer-joint systems. Analytical and numerical models were used to evaluate the flow deviation with a 1 Tesla magnetic field inside the nozzle. The fluid flow in the resistive MHD approximation is calculated using the KRONOS code from ONERA, coupling the hypersonic CFD platform CEDRE and the electrical code SATURNE from EDF. A critical parameter of these simulations is the electrical conductivity, which was evaluated using a set of equilibrium calculations with 25 species. Two models were used: local thermodynamic equilibrium and frozen flow. In both cases, chlorine captures a large fraction of free electrons, limiting the electrical conductivity to a value inadequate for thrust vectoring applications. However, when using chlorine-free propergols with 1% in mass of alkali, an MHD thrust vectoring of several degrees was obtained.

Characterizing fiber-reinforced composite structures using AC-impedance spectroscopy (AC-IS)

NASA Astrophysics Data System (ADS)

Woo, Leta Y.

Property enhancement in composites depends largely on the reinforcement. For fiber-reinforced composites, the distribution of fibers is crucial in determining the electrical and mechanical performance. Image analysis methods for characterization can be time-consuming and/or destructive. This work explores the capability of AC-impedance spectroscopy (AC-IS), an electrical measurement technique, to serve as a rapid, non-destructive tool for characterizing composite microstructure. The composite requirements include a filler that is electrically conducting or semi-conducting with higher conductivity than the matrix, and a high-impedance interface or coating between the filler and the matrix. To establish an AC-IS characterization method, cement-matrix composites with steel reinforcement were employed as both a technologically important and a model system to investigate how fibers affect the electrical response. Beginning with spherical particulates and then fibers, composites were examined using composite theory and an "intrinsic conductivity" approach. The intrinsic conductivity approach applies to composites with low volume fractions of fibers (i.e., in the dilute regime) and relates how the composite conductivity varies relative to the matrix as a function of volume fraction. A universal equivalent circuit model was created to understand the AC-IS response of composites based on the geometry and volume fraction of the filler. Deviation from predicted behavior was assessed using a developed f-function, which quantifies how fibers contribute to the overall electrical response of the composite. Using the f-function, an AC-IS method for investigating fiber dispersion was established to characterize alignment, settling/segregation, and aggregation. Alignment was investigated using measurements made in three directions. A point-probe technique characterized settling and/or large-scale inhomogeneous mixing in samples. Aggregation was quantified using a "dispersion factor" that compared theoretical with measured values and served as an upper limit for how well the fibers were dispersed. The AC-IS method was then extended to two different cement-matrix composite systems, low resistivity fresh-paste cement composites (confirmed by time domain reflectometry) and high resistivity cement composites, both of which required additional analysis to apply the AC-IS characterization method.

A receding horizon sliding control approach for electric powertrains with backlash and flexible half-shafts

NASA Astrophysics Data System (ADS)

Li, Yutong; Hansen, Andreas; Karl Hedrick, J.; Zhang, Junzhi

2017-12-01

Active control of electric powertrains is challenging, due to the fact that backlash and structural flexibility in transmission components can cause severe performance degradation or even instability of the control system. Furthermore, high impact forces in transmissions reduce driving comfort and possibly lead to damage of the mechanical elements in contact. In this paper, a nonlinear electric powertrain is modelled as a piecewise affine (PWA) system. The novel receding horizon sliding control (RHSC) idea is extended to constrained PWA systems and utilised to systematically address the active control problem for electric powertrains. Simulations are conducted in Matlab/Simulink in conjunction with the high fidelity Carsim software. RHSC shows superior jerk suppression and target wheel speed tracking performance as well as reduced computational cost over classical model predictive control (MPC). This indicates the newly proposed RHSC is an effective method to address the active control problem for electric powertrains.

Fractional diffusion models of cardiac electrical propagation: role of structural heterogeneity in dispersion of repolarization

PubMed Central

Bueno-Orovio, Alfonso; Kay, David; Grau, Vicente; Rodriguez, Blanca; Burrage, Kevin

2014-01-01

Impulse propagation in biological tissues is known to be modulated by structural heterogeneity. In cardiac muscle, improved understanding on how this heterogeneity influences electrical spread is key to advancing our interpretation of dispersion of repolarization. We propose fractional diffusion models as a novel mathematical description of structurally heterogeneous excitable media, as a means of representing the modulation of the total electric field by the secondary electrical sources associated with tissue inhomogeneities. Our results, analysed against in vivo human recordings and experimental data of different animal species, indicate that structural heterogeneity underlies relevant characteristics of cardiac electrical propagation at tissue level. These include conduction effects on action potential (AP) morphology, the shortening of AP duration along the activation pathway and the progressive modulation by premature beats of spatial patterns of dispersion of repolarization. The proposed approach may also have important implications in other research fields involving excitable complex media. PMID:24920109

Small-scale electrical resistivity tomography of wet fractured rocks.

PubMed

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

2004-01-01

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

Runoff load estimation of particulate and dissolved nitrogen in Lake Inba watershed using continuous monitoring data on turbidity and electric conductivity.

PubMed

Kim, J; Nagano, Y; Furumai, H

2012-01-01

Easy-to-measure surrogate parameters for water quality indicators are needed for real time monitoring as well as for generating data for model calibration and validation. In this study, a novel linear regression model for estimating total nitrogen (TN) based on two surrogate parameters is proposed based on evaluation of pollutant loads flowing into a eutrophic lake. Based on their runoff characteristics during wet weather, electric conductivity (EC) and turbidity were selected as surrogates for particulate nitrogen (PN) and dissolved nitrogen (DN), respectively. Strong linear relationships were established between PN and turbidity and DN and EC, and both models subsequently combined for estimation of TN. This model was evaluated by comparison of estimated and observed TN runoff loads during rainfall events. This analysis showed that turbidity and EC are viable surrogates for PN and DN, respectively, and that the linear regression model for TN concentration was successful in estimating TN runoff loads during rainfall events and also under dry weather conditions.

Discrete element weld model, phase 2

NASA Technical Reports Server (NTRS)

Prakash, C.; Samonds, M.; Singhal, A. K.

1987-01-01

A numerical method was developed for analyzing the tungsten inert gas (TIG) welding process. The phenomena being modeled include melting under the arc and the flow in the melt under the action of buoyancy, surface tension, and electromagnetic forces. The latter entails the calculation of the electric potential and the computation of electric current and magnetic field therefrom. Melting may occur at a single temperature or over a temperature range, and the electrical and thermal conductivities can be a function of temperature. Results of sample calculations are presented and discussed at length. A major research contribution has been the development of numerical methodology for the calculation of phase change problems in a fixed grid framework. The model has been implemented on CHAM's general purpose computer code PHOENICS. The inputs to the computer model include: geometric parameters, material properties, and weld process parameters.

Hydrodynamic Model for Conductivity in Graphene

PubMed Central

Mendoza, M.; Herrmann, H. J.; Succi, S.

2013-01-01

Based on the recently developed picture of an electronic ideal relativistic fluid at the Dirac point, we present an analytical model for the conductivity in graphene that is able to describe the linear dependence on the carrier density and the existence of a minimum conductivity. The model treats impurities as submerged rigid obstacles, forming a disordered medium through which graphene electrons flow, in close analogy with classical fluid dynamics. To describe the minimum conductivity, we take into account the additional carrier density induced by the impurities in the sample. The model, which predicts the conductivity as a function of the impurity fraction of the sample, is supported by extensive simulations for different values of ε, the dimensionless strength of the electric field, and provides excellent agreement with experimental data. PMID:23316277

Modeling chlorophyll-a and dissolved oxygen concentration in tropical floodplain lakes (Paraná River, Brazil).

PubMed

Rocha, R R A; Thomaz, S M; Carvalho, P; Gomes, L C

2009-06-01

The need for prediction is widely recognized in limnology. In this study, data from 25 lakes of the Upper Paraná River floodplain were used to build models to predict chlorophyll-a and dissolved oxygen concentrations. Akaike's information criterion (AIC) was used as a criterion for model selection. Models were validated with independent data obtained in the same lakes in 2001. Predictor variables that significantly explained chlorophyll-a concentration were pH, electrical conductivity, total seston (positive correlation) and nitrate (negative correlation). This model explained 52% of chlorophyll variability. Variables that significantly explained dissolved oxygen concentration were pH, lake area and nitrate (all positive correlations); water temperature and electrical conductivity were negatively correlated with oxygen. This model explained 54% of oxygen variability. Validation with independent data showed that both models had the potential to predict algal biomass and dissolved oxygen concentration in these lakes. These findings suggest that multiple regression models are valuable and practical tools for understanding the dynamics of ecosystems and that predictive limnology may still be considered a powerful approach in aquatic ecology.

Electricity Load Forecasting Using Support Vector Regression with Memetic Algorithms

PubMed Central

Hu, Zhongyi; Xiong, Tao

2013-01-01

Electricity load forecasting is an important issue that is widely explored and examined in power systems operation literature and commercial transactions in electricity markets literature as well. Among the existing forecasting models, support vector regression (SVR) has gained much attention. Considering the performance of SVR highly depends on its parameters; this study proposed a firefly algorithm (FA) based memetic algorithm (FA-MA) to appropriately determine the parameters of SVR forecasting model. In the proposed FA-MA algorithm, the FA algorithm is applied to explore the solution space, and the pattern search is used to conduct individual learning and thus enhance the exploitation of FA. Experimental results confirm that the proposed FA-MA based SVR model can not only yield more accurate forecasting results than the other four evolutionary algorithms based SVR models and three well-known forecasting models but also outperform the hybrid algorithms in the related existing literature. PMID:24459425

Electricity load forecasting using support vector regression with memetic algorithms.

PubMed

Hu, Zhongyi; Bao, Yukun; Xiong, Tao

2013-01-01

Electricity load forecasting is an important issue that is widely explored and examined in power systems operation literature and commercial transactions in electricity markets literature as well. Among the existing forecasting models, support vector regression (SVR) has gained much attention. Considering the performance of SVR highly depends on its parameters; this study proposed a firefly algorithm (FA) based memetic algorithm (FA-MA) to appropriately determine the parameters of SVR forecasting model. In the proposed FA-MA algorithm, the FA algorithm is applied to explore the solution space, and the pattern search is used to conduct individual learning and thus enhance the exploitation of FA. Experimental results confirm that the proposed FA-MA based SVR model can not only yield more accurate forecasting results than the other four evolutionary algorithms based SVR models and three well-known forecasting models but also outperform the hybrid algorithms in the related existing literature.

Conductive network formation of carbon nanotubes in elastic polymer microfibers and its effect on the electrical conductance: Experiment and simulation

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

Cho, Hyun Woo; Kim, Jeongmin; Sung, Bong June, E-mail: jjpark@chonnam.ac.kr, E-mail: bjsung@sogang.ac.kr

We investigate how the electrical conductance of microfibers (made of polymers and conductive nanofillers) decreases upon uniaxial deformation by performing both experiments and simulations. Even though various elastic conductors have been developed due to promising applications for deformable electronic devices, the mechanism at a molecular level for electrical conductance change has remained elusive. Previous studies proposed that the decrease in electrical conductance would result from changes in either distances or contact numbers between conductive fillers. In this work, we prepare microfibers of single walled carbon nanotubes (SWCNTs)/polyvinyl alcohol composites and investigate the electrical conductance and the orientation of SWCNTs uponmore » uniaxial deformation. We also perform extensive Monte Carlo simulations, which reproduce experimental results for the relative decrease in conductance and the SWCNTs orientation. We investigate the electrical networks of SWCNTs in microfibers and find that the decrease in the electrical conductance upon uniaxial deformation should be attributed to a subtle change in the topological structure of the electrical network.« less

Study of electrical resistivity on the location and identification of contamination

NASA Astrophysics Data System (ADS)

McCarty, B. D.

1985-12-01

Electrical resistance studies were conducted in two laboratory models to determine electrical resistivity relationships and to use those defined relationships to identify contamination spikes. A good correlation was established between resistance data and the composition of leachate and copper spiked leachate gelatin blocks under study. The major variable that could not be eliminated from this study which had the greatest effect on data was moisture content. This thesis contains a review of the theory and field application of electrical resistivity, a description of the experimental approach used, and a summary of the data collected.

On the importance of body posture and skin modelling with respect to in situ electric field strengths in magnetic field exposure scenarios

NASA Astrophysics Data System (ADS)

Schmid, Gernot; Hirtl, Rene

2016-06-01

The reference levels and maximum permissible exposure values for magnetic fields that are currently used have been derived from basic restrictions under the assumption of upright standing body models in a standard posture, i.e. with arms laterally down and without contact with metallic objects. Moreover, if anatomical modelling of the body was used at all, the skin was represented as a single homogeneous tissue layer. In the present paper we addressed the possible impacts of posture and skin modelling in scenarios of exposure to a 50 Hz uniform magnetic field on the in situ electric field strength in peripheral tissues, which must be limited in order to avoid peripheral nerve stimulation. We considered different body postures including situations where body parts form large induction loops (e.g. clasped hands) with skin-to-skin and skin-to-metal contact spots and compared the results obtained with a homogeneous single-layer skin model to results obtained with a more realistic two-layer skin representation consisting of a low-conductivity stratum corneum layer on top of a combined layer for the cellular epidermis and dermis. Our results clearly indicated that postures with loops formed of body parts may lead to substantially higher maximum values of induced in situ electric field strengths than in the case of standard postures due to a highly concentrated current density and in situ electric field strength in the skin-to-skin and skin-to-metal contact regions. With a homogeneous single-layer skin, as is used for even the most recent anatomical body models in exposure assessment, the in situ electric field strength may exceed the basic restrictions in such situations, even when the reference levels and maximum permissible exposure values are not exceeded. However, when using the more realistic two-layer skin model the obtained in situ electric field strengths were substantially lower and no violations of the basic restrictions occurred, which can be explained by the current-limiting effect of the low-conductivity stratum corneum layer.

Assessment of critical path analyses of the relationship between permeability and electrical conductivity of pore networks

USDA-ARS?s Scientific Manuscript database

Critical path analysis (CPA) is a method for estimating macroscopic transport coefficients of heterogeneous materials that are highly disordered at the micro-scale. Developed originally to model conduction in semiconductors, numerous researchers have noted that CPA might also have relevance to flow ...

Power module assembly

DOEpatents

Campbell, Jeremy B [Torrance, CA; Newson, Steve [Redondo Beach, CA

2011-11-15

A power module assembly of the type suitable for deployment in a vehicular power inverter, wherein the power inverter has a grounded chassis, is provided. The power module assembly comprises a conductive base layer electrically coupled to the chassis, an insulating layer disposed on the conductive base layer, a first conductive node disposed on the insulating layer, a second conductive node disposed on the insulating layer, wherein the first and second conductive nodes are electrically isolated from each other. The power module assembly also comprises a first capacitor having a first electrode electrically connected to the conductive base layer, and a second electrode electrically connected to the first conductive node, and further comprises a second capacitor having a first electrode electrically connected to the conductive base layer, and a second electrode electrically connected to the second conductive node.

Electromagnetic studies of global geodynamic processes

NASA Astrophysics Data System (ADS)

Tarits, Pascal

1994-03-01

The deep electromagnetic sounding (DES) technique is one of the few geophysical methods, along with seismology, gravity, heat flow, which may be use to probe the structure of the Earth's mantle directly. The interpretation of the DESs may provide electrical conductivity profiles down to the upper part of the lower mantle. The electrical conductivity is extremely sensitive to most of the thermodynamic processes we believe are acting in the Earth's mantle (temperature increases, partial melting, phase transition and to a lesser extent pressure). Therefore, in principle, results from DES along with laboratory measurements could be used to constrain models of these processes. The DES technique is reviewed in the light of recent results obtained in a variety of domains: data acquisition and analysis, global induction modeling and data inversion and interpretation. The mechanisms and the importance of surface distortions of the DES data are reviewed and techniques to model them are discussed. The recent results in terms of the conductivity distribution in the mantle from local and global DES are presented and a tentative synthesis is proposed. The geodynamic interpretations of the deep conductivity structures are reviewed. The existence of mantle lateral heterogeneities in conductivity at all scales and depths for which electromagnetic data are available is now well documented. A comparison with global results from seismology is presented.

Electrohydrodynamic fibrillation governed enhanced thermal transport in dielectric colloids under a field stimulus.

PubMed

Dhar, Purbarun; Maganti, Lakshmi Sirisha; Harikrishnan, A R

2018-05-30

Electrorheological (ER) fluids are known to exhibit enhanced viscous effects under an electric field stimulus. The present article reports the hitherto unreported phenomenon of greatly enhanced thermal conductivity in such electro-active colloidal dispersions in the presence of an externally applied electric field. Typical ER fluids are synthesized employing dielectric fluids and nanoparticles and experiments are performed employing an in-house designed setup. Greatly augmented thermal conductivity under a field's influence was observed. Enhanced thermal conduction along the fibril structures under the field effect is theorized as the crux of the mechanism. The formation of fibril structures has also been experimentally verified employing microscopy. Based on classical models for ER fluids, a mathematical formalism has been developed to predict the propensity of chain formation and statistically feasible chain dynamics at given Mason numbers. Further, a thermal resistance network model is employed to computationally predict the enhanced thermal conduction across the fibrillary colloid microstructure. Good agreement between the mathematical model and the experimental observations is achieved. The domineering role of thermal conductivity over relative permittivity has been shown by proposing a modified Hashin-Shtrikman (HS) formalism. The findings have implications towards better physical understanding and design of ER fluids from both 'smart' viscoelastic as well as thermally active materials points of view.

Relationship of the interplanetary electric field to the high-latitude ionospheric electric field and currents Observations and model simulation

NASA Technical Reports Server (NTRS)

Clauer, C. R.; Banks, P. M.

1986-01-01

The electrical coupling between the solar wind, magnetosphere, and ionosphere is studied. The coupling is analyzed using observations of high-latitude ion convection measured by the Sondre Stromfjord radar in Greenland and a computer simulation. The computer simulation calculates the ionospheric electric potential distribution for a given configuration of field-aligned currents and conductivity distribution. The technique for measuring F-region in velocities at high time resolution over a large range of latitudes is described. Variations in the currents on ionospheric plasma convection are examined using a model of field-aligned currents linking the solar wind with the dayside, high-latitude ionosphere. The data reveal that high-latitude ionospheric convection patterns, electric fields, and field-aligned currents are dependent on IMF orientation; it is observed that the electric field, which drives the F-region plasma curve, responds within about 14 minutes to IMF variations in the magnetopause. Comparisons of the simulated plasma convection with the ion velocity measurements reveal good correlation between the data.

Symposium N: Materials and Devices for Thermal-to-Electric Energy Conversion

DTIC Science & Technology

2010-08-24

X - ray diffraction, transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. Thermal conductivity measurements...SEM), X - ray diffraction (XRD) measurements as well as Raman spectroscopy. The results from these techniques indicate a clear modification...was examined by using scanning electron microscope (SEM; HITACHI S-4500 model) attached with an energy dispersive x - ray spectroscopy. The electrical

Effective electromagnetic properties of microheterogeneous materials with surface phenomena

NASA Astrophysics Data System (ADS)

Levin, Valery; Markov, Mikhail; Mousatov, Aleksandr; Kazatchenko, Elena; Pervago, Evgeny

2017-10-01

In this paper, we present an approach to calculate the complex dielectric permittivity of a micro-heterogeneous medium composed of non-conductive solid inclusions embedded into the conductive liquid continuous host. To take into account the surface effects, we approximate the inclusion by a layered ellipsoid consisting of a dielectric core and an infinitesimally thin outer shell corresponding to an electrical double layer (EDL). To predict the effective complex dielectric permittivity of materials with a high concentration of inclusions, we have modified the Effective Field Method (EFM) for the layered ellipsoidal particles with complex electrical properties. We present the results of complex permittivity calculations for the composites with randomly and parallel oriented ellipsoidal inclusions. To analyze the influence of surface polarization, we have accomplished modeling in a wide frequency range for different existing physic-chemical models of double electrical layer. The results obtained show that the tensor of effective complex permittivity of a micro-heterogeneous medium with surface effects has complicate dependences on the component electrical properties, spatial material texture, and the inclusion shape (ellipsoid aspect ratio) and size. The dispersion of dielectric permittivity corresponds to the frequency dependence for individual inclusion of given size, and does not depend on the inclusion concentration.

High-resolution vertical profiles of groundwater electrical conductivity (EC) and chloride from direct-push EC logs

NASA Astrophysics Data System (ADS)

Bourke, Sarah A.; Hermann, Kristian J.; Hendry, M. Jim

2017-11-01

Elevated groundwater salinity associated with produced water, leaching from landfills or secondary salinity can degrade arable soils and potable water resources. Direct-push electrical conductivity (EC) profiling enables rapid, relatively inexpensive, high-resolution in-situ measurements of subsurface salinity, without requiring core collection or installation of groundwater wells. However, because the direct-push tool measures the bulk EC of both solid and liquid phases (ECa), incorporation of ECa data into regional or historical groundwater data sets requires the prediction of pore water EC (ECw) or chloride (Cl-) concentrations from measured ECa. Statistical linear regression and physically based models for predicting ECw and Cl- from ECa profiles were tested on a brine plume in central Saskatchewan, Canada. A linear relationship between ECa/ECw and porosity was more accurate for predicting ECw and Cl- concentrations than a power-law relationship (Archie's Law). Despite clay contents of up to 96%, the addition of terms to account for electrical conductance in the solid phase did not improve model predictions. In the absence of porosity data, statistical linear regression models adequately predicted ECw and Cl- concentrations from direct-push ECa profiles (ECw = 5.48 ECa + 0.78, R 2 = 0.87; Cl- = 1,978 ECa - 1,398, R 2 = 0.73). These statistical models can be used to predict ECw in the absence of lithologic data and will be particularly useful for initial site assessments. The more accurate linear physically based model can be used to predict ECw and Cl- as porosity data become available and the site-specific ECw-Cl- relationship is determined.

Assessment of critical path analyses of the relationship between permeability and electrical conductivity of pore networks

NASA Astrophysics Data System (ADS)

Skaggs, Todd H.

2011-10-01

Critical path analysis (CPA) is a method for estimating macroscopic transport coefficients of heterogeneous materials that are highly disordered at the micro-scale. Developed originally to model conduction in semiconductors, numerous researchers have noted that CPA might also have relevance to flow and transport processes in porous media. However, the results of several numerical investigations of critical path analysis on pore network models raise questions about the applicability of CPA to porous media. Among other things, these studies found that (i) in well-connected 3D networks, CPA predictions were inaccurate and became worse when heterogeneity was increased; and (ii) CPA could not fully explain the transport properties of 2D networks. To better understand the applicability of CPA to porous media, we made numerical computations of permeability and electrical conductivity on 2D and 3D networks with differing pore-size distributions and geometries. A new CPA model for the relationship between the permeability and electrical conductivity was found to be in good agreement with numerical data, and to be a significant improvement over a classical CPA model. In sufficiently disordered 3D networks, the new CPA prediction was within ±20% of the true value, and was nearly optimal in terms of minimizing the squared prediction errors across differing network configurations. The agreement of CPA predictions with 2D network computations was similarly good, although 2D networks are in general not well-suited for evaluating CPA. Numerical transport coefficients derived for regular 3D networks of slit-shaped pores were found to be in better agreement with experimental data from rock samples than were coefficients derived for networks of cylindrical pores.

Electrically-conductive proppant and methods for making and using same

DOEpatents

Cannan, Chad; Roper, Todd; Savoy, Steve; Mitchell, Daniel R.

2016-09-06

Electrically-conductive sintered, substantially round and spherical particles and methods for producing such electrically-conductive sintered, substantially round and spherical particles from an alumina-containing raw material. Methods for using such electrically-conductive sintered, substantially round and spherical particles in hydraulic fracturing operations.

Sensorless Modeling of Varying Pulse Width Modulator Resolutions in Three-Phase Induction Motors

PubMed Central

Marko, Matthew David; Shevach, Glenn

2017-01-01

A sensorless algorithm was developed to predict rotor speeds in an electric three-phase induction motor. This sensorless model requires a measurement of the stator currents and voltages, and the rotor speed is predicted accurately without any mechanical measurement of the rotor speed. A model of an electric vehicle undergoing acceleration was built, and the sensorless prediction of the simulation rotor speed was determined to be robust even in the presence of fluctuating motor parameters and significant sensor errors. Studies were conducted for varying pulse width modulator resolutions, and the sensorless model was accurate for all resolutions of sinusoidal voltage functions. PMID:28076418

Sensorless Modeling of Varying Pulse Width Modulator Resolutions in Three-Phase Induction Motors.

PubMed

Marko, Matthew David; Shevach, Glenn

2017-01-01

A sensorless algorithm was developed to predict rotor speeds in an electric three-phase induction motor. This sensorless model requires a measurement of the stator currents and voltages, and the rotor speed is predicted accurately without any mechanical measurement of the rotor speed. A model of an electric vehicle undergoing acceleration was built, and the sensorless prediction of the simulation rotor speed was determined to be robust even in the presence of fluctuating motor parameters and significant sensor errors. Studies were conducted for varying pulse width modulator resolutions, and the sensorless model was accurate for all resolutions of sinusoidal voltage functions.

Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

NASA Astrophysics Data System (ADS)

Baba, Kiyoshi; Tada, Noriko; Matsuno, Tetsuo; Liang, Pengfei; Li, Ruibai; Zhang, Luolei; Shimizu, Hisayoshi; Abe, Natsue; Hirano, Naoto; Ichiki, Masahiro; Utada, Hisashi

2017-08-01

Seafloor magnetotelluric (MT) experiments were recently conducted in two areas of the northwestern Pacific to investigate the nature of the old oceanic upper mantle. The areas are far from any tectonic activity, and "normal" mantle structure is therefore expected. The data were carefully analyzed to reduce the effects of coastlines and seafloor topographic changes, which are significant boundaries in electrical conductivity and thus distort seafloor MT data. An isotropic, one-dimensional electrical conductivity profile was estimated for each area. The profiles were compared with those obtained from two previous study areas in the northwestern Pacific. Between the four profiles, significant differences were observed in the thickness of the resistive layer beyond expectations based on cooling of homogeneous oceanic lithosphere over time. This surprising feature is now further clarified from what was suggested in a previous study. To explain the observed spatial variation, dynamic processes must be introduced, such as influence of the plume associated with the formation of the Shatsky Rise, or spatially non-uniform, small-scale convection in the asthenosphere. There is significant room of further investigation to determine a reasonable and comprehensive interpretation of the lithosphere-asthenosphere system beneath the northwestern Pacific. The present results demonstrate that electrical conductivity provides key information for such investigation.[Figure not available: see fulltext.

The influence of the breakdown electric field in the configuration of lightning corona sheath on charge distribution in the channel

NASA Astrophysics Data System (ADS)

Ignjatovic, Milan; Cvetic, Jovan; Heidler, Fridolin; Markovic, Slavoljub; Djuric, Radivoje

2014-11-01

A model of corona sheath that surrounds the thin core of the lightning channel has been investigated by using a generalized traveling current source return stroke model. The lightning channel is modeled by a charged corona sheath that stretches around a highly conductive central core through which the main current flows. The channel core with the negatively charged outer channel sheath forms a strong electric field, with an overall radial orientation. The return stroke process is modeled as the negative leader charge in the corona sheath being discharged by the positive charge coming from the channel core. Expressions that describe how the corona sheath radius evolves during the return stroke are obtained from the corona sheath model, which predicts charge motion within the sheath. The corona sheath model, set forth by Maslowski and Rakov (2006), Tausanovic et al. (2010), Marjanovic and Cvetic (2009), Cvetic et al. (2011) and Cvetic et al. (2012), divides the sheath onto three zones: zone 1 (surrounding the channel core with net positive charge), zone 2 (surrounding zone 1 with negative charge) and zone 3 (the outer zone, representing uncharged virgin air). In the present study, we have assumed a constant electric field inside zone 1, as suggested by experimental research of corona discharges in coaxial geometry conducted by Cooray (2000). The present investigation builds upon previous studies by Tausanovic et al. (2010) and Cvetic et al. (2012) in several ways. The value of the breakdown electric field has been varied for probing its effect on channel charge distribution prior and during the return stroke. With the aim of investigating initial space charge distribution along the channel, total electric field at the outer surface of the channel corona sheath, just before the return stroke, is calculated and compared for various return stroke models. A self-consistent algorithm is applied to the generalized traveling current source return stroke model, so that the boundary condition for total electric field is fulfilled. The new density of space charge and the new radius of channel corona envelope, immediately before the return stroke stage, are calculated. The obtained results indicate a strong dependence of channel charge distribution on the breakdown electric field value. Among the compared return stroke models, transmission-line-type models have exhibited a good agreement with the predictions of the Gauss' law regarding total breakdown electric field on the corona sheath's outer surface. The generalized lightning traveling current source return stroke model gives similar results if the adjustment of the space charge density inside the corona sheath is performed.

Simplified realistic human head model for simulating Tumor Treating Fields (TTFields).

PubMed

Wenger, Cornelia; Bomzon, Ze'ev; Salvador, Ricardo; Basser, Peter J; Miranda, Pedro C

2016-08-01

Tumor Treating Fields (TTFields) are alternating electric fields in the intermediate frequency range (100-300 kHz) of low-intensity (1-3 V/cm). TTFields are an anti-mitotic treatment against solid tumors, which are approved for Glioblastoma Multiforme (GBM) patients. These electric fields are induced non-invasively by transducer arrays placed directly on the patient's scalp. Cell culture experiments showed that treatment efficacy is dependent on the induced field intensity. In clinical practice, a software called NovoTalTM uses head measurements to estimate the optimal array placement to maximize the electric field delivery to the tumor. Computational studies predict an increase in the tumor's electric field strength when adapting transducer arrays to its location. Ideally, a personalized head model could be created for each patient, to calculate the electric field distribution for the specific situation. Thus, the optimal transducer layout could be inferred from field calculation rather than distance measurements. Nonetheless, creating realistic head models of patients is time-consuming and often needs user interaction, because automated image segmentation is prone to failure. This study presents a first approach to creating simplified head models consisting of convex hulls of the tissue layers. The model is able to account for anisotropic conductivity in the cortical tissues by using a tensor representation estimated from Diffusion Tensor Imaging. The induced electric field distribution is compared in the simplified and realistic head models. The average field intensities in the brain and tumor are generally slightly higher in the realistic head model, with a maximal ratio of 114% for a simplified model with reasonable layer thicknesses. Thus, the present pipeline is a fast and efficient means towards personalized head models with less complexity involved in characterizing tissue interfaces, while enabling accurate predictions of electric field distribution.

On the physics of frequency domain controlled source electromagnetics in shallow water, 2: transverse anisotropy

NASA Astrophysics Data System (ADS)

Chave, Alan D.; Mattsson, Johan; Everett, Mark E.

2017-11-01

In recent years, marine controlled source electromagnetics (CSEM) has found increasing use in hydrocarbon exploration due to its ability to detect thin resistive zones beneath the seafloor. It is the purpose of this paper to evaluate the physics of CSEM for an ocean whose electrical thickness is comparable to or much thinner than that of the overburden using the in-line configuration through examination of the elliptically-polarized seafloor electric field, the time-averaged energy flow depicted by the real part of the complex Poynting vector, energy dissipation through Joule heating and the Fréchet derivatives of the seafloor field with respect to the sub-seafloor conductivity that is assumed to be transversely anisotropic, with a vertical-to-horizontal resistivity ratio of 3:1. For an ocean whose electrical thickness is comparable to that of the overburden, the seafloor electromagnetic response for a model containing a resistive reservoir layer has a greater amplitude and reduced phase as a function of offset compared to that for a halfspace, or a stronger and faster response, and displays little to no evidence for the air interaction. For an ocean whose electrical thickness is much smaller than that of the overburden, the electric field displays a greater amplitude and reduced phase at small offsets, shifting to a stronger amplitude and increased phase at intermediate offsets, and a weaker amplitude and enhanced phase at long offsets, or a stronger and faster response that first changes to stronger and slower, and then transitions to weaker and slower. By comparison to the isotropic case with the same horizontal conductivity, transverse anisotropy stretches the Poynting vector and the electric field response from a thin resistive layer to much longer offsets. These phenomena can be understood by visualizing the energy flow throughout the structure caused by the competing influences of the dipole source and guided energy flow in the reservoir layer, and the air interaction caused by coupling of the entire sub-seafloor resistivity structure with the sea surface. The Fréchet derivatives are dominated by preferential sensitivity to the vertical conductivity in the reservoir layer and overburden at short offsets. The horizontal conductivity Fréchet derivatives are weaker than to comparable to the vertical derivatives at long offsets in the substrate. This means that the sensitivity to the horizontal conductivity is present in the shallow parts of the subsurface. In the presence of transverse anisotropy, it is necessary to go to higher frequencies to sense the horizontal conductivity in the overburden as compared to an isotropic model with the same horizontal conductivity. These observations in part explain the success of shallow towed CSEM using only measurements of the in-line component of the electric field.

New equivalent-electrical circuit model and a practical measurement method for human body impedance.

PubMed

Chinen, Koyu; Kinjo, Ichiko; Zamami, Aki; Irei, Kotoyo; Nagayama, Kanako

2015-01-01

Human body impedance analysis is an effective tool to extract electrical information from tissues in the human body. This paper presents a new measurement method of impedance using armpit electrode and a new equivalent circuit model for the human body. The lowest impedance was measured by using an LCR meter and six electrodes including armpit electrodes. The electrical equivalent circuit model for the cell consists of resistance R and capacitance C. The R represents electrical resistance of the liquid of the inside and outside of the cell, and the C represents high frequency conductance of the cell membrane. We propose an equivalent circuit model which consists of five parallel high frequency-passing CR circuits. The proposed equivalent circuit represents alpha distribution in the impedance measured at a lower frequency range due to ion current of the outside of the cell, and beta distribution at a high frequency range due to the cell membrane and the liquid inside cell. The calculated values by using the proposed equivalent circuit model were consistent with the measured values for the human body impedance.

Electrical conductivity and modulus formulation in zinc modified bismuth boro-tellurite glasses

NASA Astrophysics Data System (ADS)

Dhankhar, Sunil; Kundu, R. S.; Dult, Meenakshi; Murugavel, S.; Punia, R.; Kishore, N.

2016-09-01

The ac conductivity of zinc modified tellurium based quaternary glasses having composition 60 TeO2-10 B2O3-(30 - x) Bi2O3-x ZnO; x = 10, 15, 20, 25 and 30 has been investigated in the frequency range 10-1-105 Hz and in temperature range 483-593 K. Frequency and temperature dependent ac conductivity found to obey Jonscher power law modified by Almond-West. DC conductivity, crossover frequency and frequency exponent have been estimated from the fitting of the experimental data of conductivity with Jonscher power law modified by Almond-West. The ac conductivity and its frequency exponent have been analyzed by various theoretical models. In presently studied glasses ac conduction takes place via tunneling of overlapping large polaron tunneling. Activation energy is found to be increased with increase in zinc content and dc conduction takes place via variable range hopping proposed by Mott with some modification suggested by Punia et al. The value of the stretched exponent ( β) obtained by fitting of M^' ' }} reveals the presence of non-Debye type relaxation. Scaling spectra of ac conductivity and electric modulus collapse into a single master curve for all compositions and temperatures, reveals the presence of composition and temperature independent conduction and relaxation process in these glasses. Activation energy of conduction ( W) and electric modulus ( E R ) are nearly equal, indicating that polaron have to overcome the same energy barrier during conduction as well as relaxation processes.

Electric fields in the ionosphere

NASA Technical Reports Server (NTRS)

Kirchhoff, V. W. J. H.

1975-01-01

F-region drift velocities, measured by incoherent-scatter radar were analyzed in terms of diurnal, seasonal, magnetic activity, and solar cycle effects. A comprehensive electric field model was developed that includes the effects of the E and F-region dynamos, magnetospheric sources, and ionospheric conductivities, for both the local and conjugate regions. The E-region dynamo dominates during the day but at night the F-region and convection are more important. This model provides much better agreement with observations of the F-region drifts than previous models. Results indicate that larger magnitudes occur at night, and that daily variation is dominated by the diurnal mode. Seasonal variations in conductivities and thermospheric winds indicate a reversal in direction in the early morning during winter from south to northward. On magnetic perturbed days and the drifts deviate rather strongly from the quiet days average, especially around 13 L.T. for the northward and 18 L.T. for the westward component.

Robust Neurite Extension Following Exogenous Electrical Stimulation within Single Walled Carbon Nanotube-Composite Hydrogels

PubMed Central

Koppes, A. N.; Keating, K. W.; McGregor, A. L.; Koppes, R. A.; Kearns, K. R.; Ziemba, A. M.; McKay, C. A.; Zuidema, J. M.; Rivet, C. J.; Gilbert, R. J.; Thompson, D. M.

2016-01-01

The use of exogenous electrical stimulation to promote nerve regeneration has achieved only limited success. Conditions impeding optimized outgrowth may arise from inadequate stimulus presentation due to differences in injury geometry or signal attenuation. Implantation of an electrically-conductive biomaterial may mitigate this attenuation and provide a more reproducible signal. In this study, a conductive nanofiller (single-walled carbon nanotubes [SWCNT]) was selected as one possible material to manipulate the bulk electrical properties of a collagen type I-10% Matrigel™ composite hydrogel. Neurite outgrowth within hydrogels (SWCNT or nanofiller-free controls) was characterized to determine if: 1) nanofillers influence neurite extension and 2) electrical stimulation of the nanofiller composite hydrogel enhances neurite outgrowth. Increased SWCNT loading (10–100-μg/ml) resulted in greater bulk conductivity (up to 1.7-fold) with no significant changes to elastic modulus. Neurite outgrowth increased 3.3-fold in 20-μg/mL SWCNT loaded biomaterials relative to the nanofiller-free control. Electrical stimulation promoted greater outgrowth (2.9-fold) within SWCNT-free control. The concurrent presentation of electrical stimulation and SWCNT-loaded biomaterials resulted in a 7.0-fold increase in outgrowth relative to the unstimulated, nanofiller-free controls. Local glia residing within the DRG likely contribute, in part, to the observed increases in outgrowth; but it is unknown which specific nanofiller properties influence neurite extension. Characterization of neuronal behavior in model systems, such as those described here, will aid the rational development of biomaterials as well as the appropriate delivery of electrical stimuli to support nerve repair. PMID:27167609

Electrical Conductivity Model of the Mantle Lithosphere of the Slave Craton (NW Canada) and its tectonic interpretation in the context of Geochemical Results

NASA Astrophysics Data System (ADS)

Lezaeta, P.; Chave, A.; Evans, R.; Jones, A. G.; Ferguson, I.

2002-12-01

The Slave Craton, northwestern Canada, contains the oldest known rocks on Earth, with exposed outcrop over an area of about 600x400 km2. The discovery of economic diamondiferous kimberlite pipes during the early 1990s motivated extensive research in the region. Over the last six years, four types of deep-probing magnetotelluric (MT) surveys were conducted within the framework of diverse geoscientific programs, aimed at determining the regional-scale electrical structures of the craton. Two of the surveys involved novel acquisition; one through frozen lake ice along ice roads during winter, and the second deploying ocean-bottom instrumentation from float planes during summer. The latter surveys required one year of recording between summers, thus allowing long period transfer functions that lead to mantle penetration depths of over 300 km. Two-dimensional modeling of the MT data from along the winter road showed the existence of a high conductivity zone at depths of 80-120 km beneath the central Slave craton. This anomalous region is spatially coincident with an ultradepleted harzburgitic layer in the upper mantle that was interpreted by others to be related to a subducted slab emplaced during the mid-Archean. A 3-D electrical conductivity model of the Slave lithosphere has been obtained, by trial and error, to fit the magnetic transfer and MT response functions from the lake experiments. This 3-D model traces the central Slave conductor as a NE-SW oriented mantle structure. Its NE-SW orientation coincides with that of a late fold belt system, with the first phase of craton-wide plutonism at ca 2630-2590 Ma, three-part subdivision of the craton based on SKS results, and with a G10 (garnet) geochemical mantle boundaries. All of these highlight a NE-SW structural grain to the lithospheric mantle of the craton, in sharp contrast to the N-S grain of the crust. Constraints on the depth range and lateral extension of the electrical conductive structure are obtained through a sensitivity analysis to verify a recent hypothesis about tectonic imbrication of lithosphere emplaced at ca 2.6 Ga in which SE-NW subduction is proposed. If such subduction has taken place, and arc-related or oceanic lithosphere has been trapped in the system, then an enhanced conductivity in the mantle deepening to NW supports the tectonic model.

Picosecond Electric-Field-Induced Threshold Switching in Phase-Change Materials.

PubMed

Zalden, Peter; Shu, Michael J; Chen, Frank; Wu, Xiaoxi; Zhu, Yi; Wen, Haidan; Johnston, Scott; Shen, Zhi-Xun; Landreman, Patrick; Brongersma, Mark; Fong, Scott W; Wong, H-S Philip; Sher, Meng-Ju; Jost, Peter; Kaes, Matthias; Salinga, Martin; von Hoegen, Alexander; Wuttig, Matthias; Lindenberg, Aaron M

2016-08-05

Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag_{4}In_{3}Sb_{67}Te_{26}. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales-faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

Adapting Better Interpolation Methods to Model Amphibious MT Data Along the Cascadian Subduction Zone.

NASA Astrophysics Data System (ADS)

Parris, B. A.; Egbert, G. D.; Key, K.; Livelybrooks, D.

2016-12-01

Magnetotellurics (MT) is an electromagnetic technique used to model the inner Earth's electrical conductivity structure. MT data can be analyzed using iterative, linearized inversion techniques to generate models imaging, in particular, conductive partial melts and aqueous fluids that play critical roles in subduction zone processes and volcanism. For example, the Magnetotelluric Observations of Cascadia using a Huge Array (MOCHA) experiment provides amphibious data useful for imaging subducted fluids from trench to mantle wedge corner. When using MOD3DEM(Egbert et al. 2012), a finite difference inversion package, we have encountered problems inverting, particularly, sea floor stations due to the strong, nearby conductivity gradients. As a work-around, we have found that denser, finer model grids near the land-sea interface produce better inversions, as characterized by reduced data residuals. This is partly to be due to our ability to more accurately capture topography and bathymetry. We are experimenting with improved interpolation schemes that more accurately track EM fields across cell boundaries, with an eye to enhancing the accuracy of the simulated responses and, thus, inversion results. We are adapting how MOD3DEM interpolates EM fields in two ways. The first seeks to improve weighting functions for interpolants to better address current continuity across grid boundaries. Electric fields are interpolated using a tri-linear spline technique, where the eight nearest electrical field estimates are each given weights determined by the technique, a kind of weighted average. We are modifying these weights to include cross-boundary conductivity ratios to better model current continuity. We are also adapting some of the techniques discussed in Shantsev et al (2014) to enhance the accuracy of the interpolated fields calculated by our forward solver, as well as to better approximate the sensitivities passed to the software's Jacobian that are used to generate a new forward model during each iteration of the inversion.

Experimental Study on the Electrical Conductivity of Pyroxene Andesite at High Temperature and High Pressure

NASA Astrophysics Data System (ADS)

Hui, KeShi; Dai, LiDong; Li, HePing; Hu, HaiYing; Jiang, JianJun; Sun, WenQing; Zhang, Hui

2017-03-01

The electrical conductivity of pyroxene andesite was in situ measured under conditions of 1.0-2.0 GPa and 673-1073 K using a YJ-3000t multi-anvil press and Solartron-1260 Impedance/Gain-phase analyzer. Experimental results indicate that the electrical conductivities of pyroxene andesite increase with increasing temperature, and the electrical conductivities decrease with the rise of pressure, and the relationship between electrical conductivity ( σ) and temperature ( T) conforms to an Arrhenius relation within a given pressure and temperature range. When temperature rises up to 873-923 K, the electrical conductivities of pyroxene andesite abruptly increase, and the activation enthalpy increases at this range, which demonstrates that pyroxene andesite starts to dehydrate. By the virtue of the activation enthalpy (0.35-0.42 eV) and the activation volume (-6.75 ± 1.67 cm3/mole) which characterizes the electrical properties of sample after dehydration, we consider that the conduction mechanism is the small polaron conduction before and after dehydration, and that the rise of carrier concentration is the most important reason of increased electrical conductivity.

Nonlinear transport theory in the metal with tunnel barrier

NASA Astrophysics Data System (ADS)

Zubov, E. E.

2018-02-01

Within the framework of the scattering matrix formalism, the nonlinear Kubo theory for electron transport in the metal with a tunnel barrier has been considered. A general expression for the mean electrical current was obtained. It significantly simplifies the calculation of nonlinear contributions to the conductivity of various hybrid structures. In the model of the tunnel Hamiltonian, all linear and nonlinear contributions to a mean electrical current are evaluated. The linear approximation agrees with results of other theories. For effective barrier transmission ?, the ballistic transport is realised with a value of the Landauer conductivity equal to ?.

Variable-Resistivity Material For Memory Circuits

NASA Technical Reports Server (NTRS)

Nagasubramanian, Ganesan; Distefano, Salvador; Moacanin, Jovan

1989-01-01

Nonvolatile memory elements packed densely. Electrically-erasable, programmable, read-only memory matrices made with newly-synthesized organic material of variable electrical resistivity. Material, polypyrrole doped with tetracyanoquinhydrone (TCNQ), changes reversibly between insulating or higher-resistivity state and conducting or low-resistivity state. Thin film of conductive polymer separates layer of row conductors from layer of column conductors. Resistivity of film at each intersection and, therefore, resistance of memory element defined by row and column, increased or decreased by application of suitable switching voltage. Matrix circuits made with this material useful for experiments in associative electronic memories based on models of neural networks.

Electrically conductive cellulose composite

DOEpatents

Evans, Barbara R.; O'Neill, Hugh M.; Woodward, Jonathan

2010-05-04

An electrically conductive cellulose composite includes a cellulose matrix and an electrically conductive carbonaceous material incorporated into the cellulose matrix. The electrical conductivity of the cellulose composite is at least 10 .mu.S/cm at 25.degree. C. The composite can be made by incorporating the electrically conductive carbonaceous material into a culture medium with a cellulose-producing organism, such as Gluconoacetobacter hansenii. The composites can be used to form electrodes, such as for use in membrane electrode assemblies for fuel cells.