Direct Current Resistivity Research Articles

Effect of Al Substitution on Structural and Electrical Properties of Bi1.6Pb0.4Sr2CaCu2−x M x O8+δ Superconducting Ceramics

In this work we study the effect on structural and electrical properties of superconducting compound Bi1.6Pb0.4Sr2CaCu2−yMyO8+δ were M=Al (with y=0–0.6). The samples were prepared by the solid-state reaction method. The samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), direct current (DC) resistivity versus temperature ρ(T) and alternative current (AC) susceptibility measurements. Structural analysis shows that the crystalline lattice structure of the prepared sample belongs, mainly, to the superconductive tetragonal phase Bi(Pb)2212. The SEM micrographs show that in the undoped sample the grain size has a random distribution with few grains greater than 5 μm. The grains are very dense and well connected. A quite different microstructure is obtained for the doped samples of which grains are more connected with a flat characteristic shape of Bi(Pb)2212 superconductors. All samples exhibit a superconducting character and Tc and the superconducting volume fraction decrease with increasing rate of aluminum.

Finite Element Resistivity Forward Modeling Using Algebraic Multigrid Preconditioned Conjugate Gradient Method

An algebraic multigrid by smoothed aggregation preconditioned conjugate gradient method is developed to solve the liner system arising from 3-D direct current finite element resistivity forward modeling. The algorithm combines the efficiency of algebraic multigrid method and the stability of conjugate gradient method. Algebraic multigrid by smoothed aggregation keep in high-efficiency while simulation using local quasi-uniform mesh and its convergence effect will reduce while numerical modeling using anisotropic stretched grids. However tensor product non-equidistant mesh, a kind of anisotropic stretched grids, is often used in 3-D direct current resistivity forward modeling. In order to improve this situation, a factor is added to guide correct aggregation. Consequently, a typical example is used to prove that the improvement is the right. Finally, it is natural to conclude that the algorithm suggested in this paper is efficient and robust whether simulation using local quasi-uniform mesh or tensor product non-equidistant mesh

Development of a multi-ring resistivity cell and multi-electrode resistivity probe for investigation of cover concrete condition

Direct Current (DC) electrical resistivity is a material property well known to be sensitive to various aspects of concrete condition related to corrosion risk. This paper describes the development of a multi-ring electrical resistivity cell for the evaluation of concrete. A multi-electrode surface resistivity probe for on-site applications is also presented. The multi-ring resistivity cell is capable of assessing the homogeneity of the investigated specimen, which is an important requirement for obtaining representative bulk resistivity results. The multi-electrode surface probe is used for depth investigation of cover concrete to identify moisture and chloride gradients by means of electrical resistivity tomography (ERT). The paper focuses on the development of these two resistivity devices, and the numerical modelisation, calibration, validation and cross-correlation thereof.The development of the resistivity cell will enable future work to establish master curves relating DC-resistivity to parameters indicative of concrete condition (particularly water content, chloride content and porosity). The final aim is then to estimate these state parameters for in situ concrete by means of the combination of electromagnetic non-destructive evaluation (NDE) techniques such as Electrical Resistivity Tomography (ERT), capacitive method and Ground Penetrating Radar (GPR).

An efficient inversion for two-dimensional direct current resistivity surveys based on the hybrid finite difference–finite element method

For efficient inversion code, the forward modeling routine, the sensitivity calculation, and the inversion algorithm must be efficient. Here, the hybrid finite difference–finite element algorithm, which is fast and accurate even when the slope of the topography is greater than 45°, is used as the forward modeling routine to calculate the responses. The sensitivity calculation is adapted from the most efficient adjoint Green’s function technique. Both of these algorithms are then driven with the data space Occam’s inversion. This combination of modules makes it possible to obtain an efficient inversion code based on MATLAB for two-dimensional direct current (DC) resistivity data. To demonstrate its efficiency, numerical experiments with our code and with commercial software are performed on synthetic data and real field data collected in the western part of Thailand where limestone and cavities dominate the region. In general, our code takes substantially longer than the commercial code to run but converges to a solution with a lower misfit. The result shows that the efficiency of our code makes it practical for real field surveys.

Inversion of electromagnetic geosoundings using coordinate descent optimization

A coordinate-descent inversion algorithm is tested for a non-separable regularization operator. The algorithm is based on a homotopy moving regularization operator from l2 to l1. Results are presented for both linear and nonlinear problems. The linear case corresponds to electromagnetic soundings typically used for prospecting down to a few tens of meters. The first nonlinear case corresponds to direct-current resistivity soundings, which are typically useful for prospecting down to hundreds of meters. The last application is to magnetotelluric soundings that can reach penetration depths of tens of kilometers. Developed models are comparable with the original for the synthetic cases and with those obtained by other researchers for field data.

Factors influencing cavity detection in Karst terrain on two-dimensional (2-D) direct current (DC) resistivity survey: A case study from the western part of Thailand

To create a three-dimensional (3-D) cave and cavity network model in Karst terrain from two-dimensional (2-D) direct current resistivity (DCR) profiles, we first need to recognize their effects on the inversion results from a number of special cases. 2-D and 3-D cavity models are created to demonstrate effects from (1) depth of the cavity, (2) size and shape, (3) distance to the edge of the cavity, (4) orientations (inclination and declination) of the cavity and (5) several smaller cavities lying in an array. For other complicated models, combinations of these factors can be used to infer the results. Two parallel DCR profiles from the western part of Thailand were first inverted with the 2-D inversion for interpretation. Knowledge gained from the numerical modeling on these special cases is helpful to constrain the interpretation and also to extend the interpretation to 3-D. This gives us a picture of the 3-D cave and cavity networks beneath the area of study. Two main connected cavities between these two profiles can be inferred from the data along with several local cavities near the surface.

Influence of Cr3+ substitution on the electrical and magnetic properties of Ni0.4Cu0.4Zn0.2Fe2O4 nanoparticles

AbstractThe Ni0.4Cu0.2Zn0.4ferrites with different concentrations of Cr3+were synthesized at a low temperature (450°C) using sol–gel auto-combustion method. The X-ray diffraction analysis of the samples confirms the formation of a single-phase cubic spinel structure. The lattice constant decreases from 8.331 to 8.253 Å with an increase in Cr3+substitution. Bulk density decreases from 4.95 to 4.71 gm/cm3whereas porosity increases from 9.34% to 14.76% with an increase in Cr3+substitution. Transmission electron microscopy was adopted to determine the particle size. Particle size decreases from 19 to 13 nm with the addition of Cr3+ions. Saturation magnetization, coercivity, and other hysteresis parameters were measured using a vibrating sample magnetometer at room temperature with a maximum magnetic field of 8 kOe. Magnetization decreases from 62 to 48 emu/g, whereas coercivity increases from 65 to 180 Oe. The direct current (DC) resistivity increases from 3.62 × 106to 4.21 × 106Ω cm with Cr3+contentx. The dielectric constant (ε′) decreases with increasing concentration of Cr3+ions.

Geo-electrical delineations within Kubanni basin, north-central Nigeria

The research site is the whole landmass of the Federal College of Education, Zaria, seated on basement complex of north-central Nigeria. Direct current resistivity geophysical method was employed to characterise parameters such as the basement depth and topography, aquifer depth and thickness, weathered basement distribution as well as mapping of orientations of fractures and faults present in the premises using radial sounding technique. The conventional vertical electrical sounding (VES) Schlumberger array was carried out at 40 stations, and eight of which were radial stations. Radial sounding was used to establish resistivity anisotropy which gives clue for the choice of consistent VES profile direction used throughout the fieldwork. Results from the resistivity interpretation suggest three layers in most parts of the premises with some minor occurrence of two and four layers. The first layer (topsoil) has its thickness ranging between 3.5 and 14.0 m; second layer (weathered basement) thickness ranges between 9.0 and 36.5 m, while the third layer (fresh basement) is deepest (40.1 m) towards the eastern corner of the area. The aquifer depth ranges from 1.5 to 4.0 m with a thickness range of 5.0 to 14.0 m. The thickest aquifer occurs around the centre to the west in the area. Results from radial sounding show presence of resistivity anisotropy, an insight to fracturing and faulting; this is more pronounced around the west-central part of the premises.

Stochastic joint inversion of hydrogeophysical data for salt tracer test monitoring and hydraulic conductivity imaging

The assessment of hydraulic conductivity of heterogeneous aquifers is a difficult task using traditional hydrogeological methods (e.g., steady state or transient pumping tests) due to their low spatial resolution. Geophysical measurements performed at the ground surface and in boreholes provide additional information for increasing the resolution and accuracy of the inverted hydraulic conductivity field. We used a stochastic joint inversion of Direct Current (DC) resistivity and self-potential (SP) data plus in situ measurement of the salinity in a downstream well during a synthetic salt tracer experiment to reconstruct the hydraulic conductivity field between two wells. The pilot point parameterization was used to avoid over-parameterization of the inverse problem. Bounds on the model parameters were used to promote a consistent Markov chain Monte Carlo sampling of the model parameters. To evaluate the effectiveness of the joint inversion process, we compared eight cases in which the geophysical data are coupled or not to the in situ sampling of the salinity to map the hydraulic conductivity. We first tested the effectiveness of the inversion of each type of data alone (concentration sampling, self-potential, and DC resistivity), and then we combined the data two by two. We finally combined all the data together to show the value of each type of geophysical data in the joint inversion process because of their different sensitivity map. We also investigated a case in which the data were contaminated with noise and the variogram unknown and inverted stochastically. The results of the inversion revealed that incorporating the self-potential data improves the estimate of hydraulic conductivity field especially when the self-potential data were combined to the salt concentration measurement in the second well or to the time-lapse cross-well electrical resistivity data. Various tests were also performed to quantify the uncertainty in the inverted hydraulic conductivity field.

Effect of the particle size of conductive inclusions on the structurization and resistivity of Si3N4–ZrC ceramics

Heating elements with a resistive layer composed of Si3N4 and 13.5 vol.% ZrC with an average grain size varying from 1 to 46 μm are produced by hot pressing. The phase and grain-size composition and morphology of zirconium carbide grains are examined with X-ray diffraction, sedimentation analysis, and scanning electron microscopy. Microstructural images of the hot-pressed composites are taken with an optical microscope. Direct current resistivity is studied by voltmeter–ammeter method in the temperature range between 20 and 600°C. Different types of structure may form at different dielectric–conductor diameter ratios. These structures considerably differ in resistivity. The resistivity of the composites depends on the specific surface area of the conductive particles and effective cross-sectional area of the conductive cluster (resistivity increases by one order of magnitude with transition from statistical to matrix structure). It is shown that the structure and resistivity can be controlled by introducing a bimodal mixture of coarse and fine conductive particles. The matricity of the composite is evaluated by measuring its resistivity.

Delineation of Fractured Zones in Crystalline Basement Rocks by Direct Current Electrical Resistivity Method in Oke-ila Area, Southwestern Nigeria

A dc-electrical resistivity investigation of Oke-Ila area was carried out with a view to delineating fractured zones within the crystalline basement rocks. The electrical resistivity survey involved vertical electrical soundings at twenty five locations using ABEM SAS 1000 terrameter. The results of the investigation revealed three distinct geoelectric layers: top soil, weathered layer and fractured/fresh crystalline basement rocks. Fractured zones with high aquifer potential were delineated as resistivity lows against the background resistivity highs of the fresh basement rocks. The study revealed that the fractured zones which constitute the productive water bearing zones are discontinuous (localized) and they occur at an average depth of 37.5m.

Delineation of fractured zones in crystalline basement rocks by direct current electrical resistivity method in Oke-Ila area, southwestern Nigeria

A dc-electrical resistivity investigation of Oke-Ila area was carried out with a view to delineating fractured zones within the crystalline basement rocks. The electrical resistivity survey involved vertical electrical soundings at twenty five locations using ABEM SAS 1000 terrameter. The results of the investigation revealed three distinct geoelectric layers: top soil, weathered layer and fractured/fresh crystalline basement rocks. Fractured zones with high aquifer potential were delineated as resistivity lows against the background resistivity highs of the fresh basement rocks. The study revealed that the fractured zones which constitute the productive water bearing zones are discontinuous (localized) and they occur at an average depth of 37.5m.

ANN based inversion of DC resistivity data for groundwater exploration in hard rock terrain of western Maharashtra (India)

Inversion of vertical electrical sounding (VES) data, especially from the crystalline hard rock area, assumes a special significance for groundwater exploration. Here we used a newly developed algorithm based on the Bayesian neural network (BNN) theory combined with Hybrid Monte Carlo (HMC)/Markov Chain Monte Carlo (MCMC) simulation scheme to invert the Direct Current (DC) VES measurements obtained from 30-locations around Tenduli-Vengurla, Sindhudurg district, Maharashtra, India. The inversion results suggest that the top layer is mostly comprised of laterites followed by mixture of clay/clayey sand and garnulites/granite as basement rocks. The source of groundwater appears to be accessible in weathered/semi-weathered layer of laterite/clayey sand that exists within the depth of 10–15 m from the surface. The NW–SE trending major lineaments and its criss-crosses are also identified from the apparent and true resistivity surface map. The pseudo-section at different depths in the western part of the area, near Nivti, shows extensive influence of saltwater intrusion and its impact reaching up to the depth of 30 m from the surface along the coastal area. Our results also show that intrusion of saline water decreases from the western part to the eastern part of the region. Two dimensional modeling of four resistivity profiles from the study region identified two potential groundwater reservoirs; one lying between Path-Tenduli and another in between Mat and Zaraph. The deduced true electrical resistivity section against depth correlates well with available borehole lithology in the area. The results presented here would be useful for interpreting the geological signatures like fractures, major joints and lineaments, which in turn will be helpful for identifying groundwater reservoirs and drainage pattern in the crystalline hard rock area. The newly developed HMC-based BNN method is robust and would provide insights for constraining the geophysical models and criteria for modeling resistivity data.

Aquifer Transmissivity from Surface Geo-electrical Data: A Case Study of Owerri and Environs, Southeastern Nigeria

Abstract The combination of layer resistivity and thickness in the so called Da-zarrouk parameters S (longitudinal conductance) and R (transverse resistance) have proved useful in the evaluation of the transmissivities of the aquifers around Owerri and environs. The area is underlain by the unconsolidated to semi-consolidated coastal Benin Formation. The surface direct current electrical resistivity method was used in the study. Seven Vertical Electrical Soundings (VES) data by the Schlumberger array was acquired in the area. A maximum current electrode spacing (AB) of 1000 m was used for data acquisition. Four of the soundings were carried out near existing boreholes. Computer modelled interpretative methods was utilized in processing the data. Results show that the depth to the water level is shallow around Ife and Egbu areas with a mean depth of 30 m. Semi-deep aquifers were encountered around Okpalla and AVU areas with a mean depth of 90 m while very deep aquifers were sensed around Owerri and Obinze areas with a mean depth of 125 m. Aquifer thicknesses in the study area range from 8 m at Ife and 117 m at Owerri. The diagnostic Kσ = constant value have proved so useful in calculating transmisivities and hydraulic conductivities of all the sounding locations including areas where no boreholes exist. Hydraulic conductivity varies between 6.19m/day at Ife and 24.7 m/day at Obinze. Transmissivity values also very between 51.39 m2/day at Ife and 1379.56 m2/day at Owerri. It is hoped that the results would help in long term planning of groundwater exploitation schemes within the study area.

Application of time domain induced polarization to the mapping of lithotypes in a landfill site

Abstract. A direct current (DC) resistivity and time domain induced polarization (TDIP) survey was undertaken at a decommissioned landfill site situated in Hørløkke, Denmark, for the purpose of mapping the waste deposits and to discriminate important geological units that control the hydrology of the surrounding area. It is known that both waste deposits and clay have clear signatures in TDIP data, making it possible to enhance the resolution of geological structures compared to DC surveys alone. Four DC/TDIP profiles were carried out crossing the landfill, and another seven profiles in the surroundings provide a sufficiently dense coverage of the entire area. The whole dataset was inverted using a 1-D laterally constrained inversion scheme, recently implemented for TDIP data, in order to use the entire decay curves for reconstructing the electrical parameters of the soil in terms of the Cole-Cole polarization model. Results show that it is possible to resolve both the geometry of the buried waste body and key geological structures. In particular, it was possible to find a silt/clay lens at depth that correlates with the flow direction of the pollution plume spreading out from the landfill and to map a shallow sandy layer rich in clay that likely has a strong influence on the hydrology of the site. This interpretation of the geophysical findings was constrained by borehole data, in terms of geology and gamma ray logging. The results of this study are important for the impact of the resolved geological units on the hydrology of the area, making it possible to construct more realistic scenarios of the variation of the pollution plume as a function of the climate change.

Pressure effects on grain boundary, electrical and vibrational properties of the polycrystalline BaTeO3

The evolutions of alternate current (AC) impedance spectra, direct current (DC) resistivity and Raman spectra in polycrystalline BaTeO3 have been investigated at high pressures. The abrupt changes observed in electrical transport measurements at 12.73 GPa indicated a kind of phase transition, which was confirmed to be related to the structural phase transition by high-pressure Raman scattering experiments. From the impedance spectra, both grain resistance and grain boundary resistance decreased with increasing pressure, and two clear discontinuities occurred at 12.73 GPa and 17.47 GPa, respectively. After the transition, the contribution to the total resistance by the grain boundary effect dramatically declined and the grain resistance began to play a dominant role. Besides, the electric polarization process was changed due to the phase transition, and it led to a significant rise of the relaxation frequency. From the decompression impedance spectra, it could be clearly seen that the phase transition was irreversible, and it was probably attributed to the irreversible change of the grain boundary for the two different crystal structures. By varying the temperature, the transport behaviour at high pressure was still of semiconductor type but with different slopes for the ambient and high-pressure phases. High-pressure Raman measurements revealed an irreversible structural phase transition occurring above 15 GPa, and the results were consistent with the observed changes of the electrical properties at high pressures.

Electrical conductivity and magnetic properties of core-shell silver-coated magnetite composite nanoparticles

Abstract

Influence of carbon nanofibers reinforcement on thermal and electrical behavior of polysulfone nanocomposites

AbstractCarbon nanofiber (CNF) based polysulfone (PSU) nanocomposites have been developed successfully by a innovative solution mixing technique to explore the effect of state of dispersion and wt% loading of CNFs on different properties of PSU. In order to enhance the interfacial adhesion between CNFs and PSU, CNFs were functionalized by air oxidation. Thermal properties were characterized by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and it was seen that thermal stability of PSU was increased with increase in CNFs loading. The state of dispersion of CNFs throughout the PSU matrix and PSU–CNFs interaction were confirmed using field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) study. The electrical properties of nanocomposites were studied from direct current (DC) and alternating current (AC) resistivity measurement. DC resistivity registered a very low percolation threshold in‐between 0.5–1 wt% of CNFs loading. DC resistivity of PSU was decreased by nine orders of magnitude with the addition of 1 wt% CNFs loading. Dielectric constant and dissipation factor of nanocomposites were significantly increased with increase in CNFs content in nanocomposites. The enhancement in these properties suggests a great potential application of the resulting nanocomposites as multifunctional materials in various electronics industries. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

VFSARES-a very fast simulated annealing FORTRAN program for interpretation of 1-D DC resistivity sounding data from various electrode arrays

Employing the very fast simulated annealing (VFSA) global optimization technique, a FORTRAN program is developed for the interpretation of one-dimensional direct current resistivity sounding data f...

Geoelectric observations of the degradation of nearshore submarine permafrost at Barrow (Alaskan Beaufort Sea)

Submarine permafrost degradation rates may be determined by a number of interacting processes, including rates of sea level rise and coastal erosion, sea bottom temperature and salinity regimes, geothermal heat flux and heat and mass diffusion within the sediment column. Observations of ice‐bearing permafrost in shelf sediments are necessary in order to determine its spatial distribution and to quantify its degradation rate. We tested the use of direct current electrical resistivity to ice‐bearing permafrost in Elson Lagoon northeast of Barrow, Alaska (Beaufort Sea). A sharp increase in electrical resistivity was observed in profiles collected perpendicular to and along the coastline and is interpreted to be the boundary between ice‐free sediment and underlying ice‐bearing submarine permafrost. The depth to the interpreted ice‐bearing permafrost increases from <2 m below sea level to over 12 m below sea level with increasing distance from the coastline. The dependence of the saline sediment electrical resistivity on temperature and freezing was measured in the laboratory to provide validation for the field measurements. Electrical resistivity was shown to be effective for detection of shallow ice‐bearing permafrost in the coastal zone. Historical coastal retreat rates were combined with the inclination of the top of the ice‐bearing permafrost to calculate mean vertical permafrost degradation rates of 1 to 4 cm yr−1.