Large Variations In Conductivity Research Articles

Crustal conductivity footprint of the Miocene porphyry copper polymetallic deposits in the Gangdese metallogenic belt, Tibetan Plateau

New evidence worldwide has linked the surface locations of mineral deposits and their crustal-scale electrical conductivity footprint. We examine the relationship between the Gangdese Miocene porphyry copper deposits, Tibetan Plateau, and the electrical conductivity signature from a three-dimensional model generated from 311 magnetotelluric measurements. The distribution of electrical resistivity throughout the crust and the conductance within the mid-lower crust (depth range of 25–70 km) is analyzed. The results clearly show that the large and ultra-large Miocene porphyry copper deposits coincide spatially with conductive zones and areas of very-high conductance (>10,000S) in the mid-lower crust. Computations are undertaken to determine the influence of water-bearing silicate melts and alkali-bearing (Na+ and K+) fluids on conductivity. Based on this, the bulk conductivity is interpretated to be caused by a system of alkali-rich volatile-rich partial melt. The alkali-rich volatile-rich magmatic-hydrothermal fluids facilitate the migration and concentration of metal ions originating in deep areas. The volumes necessary are much less than partial melt alone and can thus help to reconcile large conductivity variations with small seismic velocity variations. The electrical structure indicates the magma source area of anatexis in the lower crust, a multi-stage magmatic system with large mid-crustal and small upper-crustal magma reservoirs, and complex pathways related to rift zones. We determine that the conductive zones in the mid-lower crust have an influence on the development of the mineralization and the location of the mineral belt.

Synthesis, conductivity and sensitivity studies of polyaniline – iron oxide nanocomposites

ABSTRACTPolyaniline and polyaniline/Iron oxide nanocomposites were synthesized by in-situ polymerization technique. The formation of PANI/Iron oxide nanocomposites with regards to the structural properties of the materials were investigated by X-Ray diffraction (XRD), Scanning electron microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques.The crystallite size of iron oxide was found to be 36 nm as indicated by (XRD). The frequency dependent conductivity of these nanocomposites have been studied. Large variations in conductivity were observed may be due to lattice polarization around a charge in localized state and due to variation of distribution of Iron oxide in polymer matrix. Compare to all the composites 50 wt% shows highest Sensitivity. The results obtained for these composites are of scientific and technological interest.

Equilibrium and transient conductivity for gadolium-doped ceria under large perturbations: II. Modeling

A model-based approach is used to interpret equilibrium and transient conductivity measurements for 10% gadolinium-doped ceria: Ce0.9Gd0.1O1.95−δ (GDC10). The measurements were carried out by AC impedance spectroscopy on slender extruded GDC10 rods. Although equilibrium conductivity measurements provide sufficient information from which to derive material properties, it is found that uniquely establishing properties is difficult. Augmenting equilibrium measurements with conductivity relaxation significantly improves the evaluation of needed physical properties. This paper develops and applies the computational implementation of a Nernst–Planck–Poisson (NPP) model to represent and interpret conductivity-relaxation measurements. Defect surface chemistry is represented with both equilibrium and finite-rate kinetic models. The experiments and the models are capable of representing relaxations from strongly reducing to strongly oxidizing gas-phase environments, and vice versa. Compared to alternative models, such as ambipolar models, the NPP approach enables the direct study of large variations in conductivity that are associated with large variations in gas-phase environments.

Influence of ZnO on the Electrical Properties of YSZ

Impedance spectroscopy was performed on dense YSZ/ZnO composites with a ZnO content varying from 3 to 25 vol% and under different oxygen pressures. Raman spectroscopy showed that the cubic zirconia phase is not fully stable in contact with ZnO, under the selected sintering conditions (1300°C, 2h). The impedance diagrams reveal a peculiar blocking effect associated with the ZnO grains. Its magnitude is independent of the large variations in conductivity of ZnO, associated with changes in the equilibrium oxygen pressure. Its relaxation frequency markedly depends on this parameter. These peculiar properties are interpreted in terms of a pseudo-capacitive behavior of the electronically conducting ZnO in contact with the YSZ ionic conductor. This contact forms an electrode, the potential of which being determined by the predominant point defect concentration in ZnO.

Single Nanostructure Electrochemical Devices for Studying Electronic Properties and Structural Changes in Lithiated Si Nanowires

AbstractNanostructured Si is a promising anode material for the next generation of Li‐ion batteries, but few studies have focused on the electrical properties of the Li‐Si alloy phase, which are important for determining power capabilities and ensuring sufficient electrical conduction in the electrode structure. Here, we demonstrate an electrochemical device framework suitable for testing the electrical properties of single Si nanowires (NWs) at different lithiation states and correlating these properties with structural changes via transmission electron microscopy (TEM). We find that single Si NWs usually exhibit Ohmic I–V response in the lithiated state, with conductivities two to three orders of magnitude higher than in the delithiated state. After a number of sequential lithiation/delithiation cycles, the single NWs show similar conductivity after each lithiation step but show large variations in conductivity in the delithiated state. Finally, devices with groups of NWs in physical contact were fabricated, and structural changes in the NWs were observed after lithiation to investigate how the electrical resistance of NW junctions and the NWs themselves affect the lithiation behavior. The results suggest that electrical resistance of NW junctions can limit lithiation. Overall, this study shows the importance of investigating the electronic properties of individual components of a battery electrode (single nanostructures in this case) along with studying the nature of interactions within a collection of these component structures.

Printable organic electrochemical circuit to record time–temperature history

An electrochemical circuit to record time–temperature history has been realized by using the propagation of over-oxidation fronts in stripes of poly(3,4-ethylenedioxythiopehene) blended with poly(styrenesulfonate) (PEDOT:PSS). The over-oxidation front propagation has been characterized and related to the phase change of polyethylene glycol (PEG) electrolytes. The electrolytes were chosen to have a phase transition in the temperature interval to be monitored, resulting in large conductivity variations and thereby an easily interpreted output. A demonstrator has been fabricated and shown to detect a temperature increase and a following temperature decrease. This very simple device is cheap to produce and could be used to monitor the temperature of packages.

Community structure and diversity of cyanobacteria and green algae in the soils of Thar Desert (India)

Algal-cyanobacterial component of 51 soil samples collected from 27 locations, representing varied agroecological regions of Thar desert of India was analysed using enrichment culture technique in presence and absence of nitrate nitrogen fortification of BG 11 medium. The soils were alkaline, poor in nutrients and showed large variations in conductivity and water soluble cations Na + , K + and Ca 2 + ) . The samples harboured 79 morphotypes belonging to 21 genera of cyanobacteria and four morphotypes belonging to three genera of green algae. The unbranched cyanobacteria dominated the flora. Phormidium > Oscillatoria > Lyngbya exhibited maximum morphotypic diversity on N supplementation while Anabaena was the most diverse genus followed by Nostoc, Scytonema and Calothrix in the absence of N supplementation. Morphotype richness varied from 1 to 6 and the frequency was < 18 % for non-diazotrophs and < 51 % for diazotrophs. Non-repeatability of forms was as high as 66%. Shannon and Weaver's diversity index was very low for both + N and - N enrichments. Principle component analysis suggested that variation in chemical composition of the soil did not influence the algal-cyanobacterial diversity. The structure of community composition was found to be more homogeneous in non-sandy, crusted and vegetated soils than in sandy, non-crusted and barren soils, suggesting that the incidence and colonisation of desert soils by cyanobacteria is predominantly a function of agroecological conditions. On the contrary, vegetated and non-sandy soils showed presence of large number of infrequent morphotypes.

Critical roles of metal-molecule contacts in electron transport through molecular-wire junctions

We study the variation of electron transmission through Au-S-benzene-S-Au junctions and related systems as a function of the structure of the Au:S contacts. For junctions with semi-infinite flat Au(111) electrodes, the highly coordinated in-hollow and bridge positions are connected with broad transmission peaks around the Fermi level, due to a broad range of transmission angles from transverse motion, resulting in high conductivity and weak dependence on geometrical variations. In contrast, for (unstable) S-adsorption on top of an Au atom, or in the hollow of a 3-Au-atom island, the transmission peaks narrow up due to suppression of large transmission angles. Such more one-dimensional situations may describe more common types of contacts and junctions, resulting in large variations in conductivity and sensitivity to bonding sites, tilting and gating. In particular, if S is adsorbed in an Au vacancy, sharp spectral features appear near the Fermi level due to essential changes of the level structure and hybridization in the contacts, admitting order-of-magnitude variations of the conductivity. Possibly such a system, can it be fabricated, will show extremely strong non-linear effects and might work as uni- or bi-directional voltage-controlled 2-terminal switches and non-linear mixing elements. Finally, density-functional-theory (DFT) based transport calculations seem relevant, being capable of describing a wide range of transmission peak structures and conductivities. Prediction and interpretation of experimental results probably require more precise modeling of realistic experimental situations.

Multigrid Preconditioning for Krylov Methods for Time-Harmonic Maxwell's Equations in Three Dimensions

We consider the rapid simulation of three-dimensional electromagnetic problems in geophysical parameter regimes, where the conductivity may vary significantly and the range of frequencies is moderate. Toward developing a multigrid preconditioner, we present a Fourier analysis based on a finite-volume discretization of a vector potential formulation of time-harmonic Maxwell's equations on a staggered grid in three dimensions. We prove grid-independent bounds on the eigenvalue and singular value ranges of the system obtained using a preconditioner based on exact inversion of the dominant diagonal blocks of the non-Hermitian coefficient matrix. This result implies that a preconditioner that uses single multigrid cycles to effect inversion of the diagonal blocks also yields a preconditioned system with an $\ell_2$-condition number bounded independent of the grid size. We then present numerical examples for more realistic situations involving large variations in conductivity (i.e.,\ jump discontinuities). Block-preconditioning with one multigrid cycle using Dendy's BOXMG solver is found to yield convergence in very few iterations, apparently independent of the grid size. The experiments show that the somewhat restrictive assumptions of the Fourier analysis do not prohibit it from describing the essential local behavior of the preconditioned operator under consideration. A very efficient, practical solver is obtained.

Evaluation of conducting LB films based on ethylenedithio-tetrathiafulvalene (EDT-TTF) derivatives for phosphine sensing

We report the preliminary results obtained with new conducting LB films based on EDT-TTF derivatives used as sensing heads in conductivity phosphine sensors. This second generation of conducting materials for gas sensors derived from the phosphine sensing properties of the previous heads based on TCNQ derivatives: like TCNQ derivative films, EDT-TTF derivative films exhibit a stable and well-controlled conducting behaviour after iodine vapour exposure and large conductivity variations under phosphine exposure. The mean features of the new sensing head are a short response time (30 s) and a ppm range sensitivity, which is achieved without the need of cycling at high concentrations of gas.

Doping effects in off-stoichiometric glow discharge amorphous silicon nitride

The effects of boron and phosphorus doping on the electrical properties of a-SiNx:H films are studied. The material is obtained by the glow discharge of SiH4 and N2 mixtures. It is found that for Si-rich materials boron doping produces large conductivity variations while phosphorus appears to be a much less efficient dopant. A phenomenological explanation is given assuming that phosphorus prefers to form bonds in accordance with its own valence configuration; i.e., it will go substitutionally to threefold coordinated N sites. Experimental evidence of such behavior obtained from published IR transmission measurements confirms this assumption.

Determining the Volume of Sampled Soil When Using the Four‐Electrode Technique

AbstractA theoretical discussion of the ratio between apparent resistivity and real resistivity of a soil layer as a function of (i) layer thickness/electrode spacing ratio; (ii) the soil layer thickness and resistivity of an underlying layer; and (iii) horizontal distance of a different medium from the current electrode is presented. Laboratory experimental work was carried out in order to study the effects the electrode spacing and current density have on the determination of the electrical conductivity of soil solution. It was found out that the depth sensed by a Wenner Configuration would be deeper than the inner electrode spacing for most field situations and especially where there are large variations in conductivity (due to salinity or water content) with depth. The laboratory calibration of the salinity probe should be done in a volume of about 2.5 liters or greater. The volume sensed by this method is greater the lower is the water content. The implications in laboratory calibration‐field measurements relationships are discussed.

The predicted effects of red blood cells on electromagnetic flowmeter sensitivity

Non-uniformity and anisotropy of the conductivity of a liquid flowing through an electromagnetic flowmeter affects its sensitivity. This effect is analysed for a circular meter with small electrodes and rectilinear flow with an axisymmetric velocity profile. The magnetic field is assumed invariant in the flow direction. The conductivity tensor is assumed to have principal axes in the radial and azimuthal directions with the principal conductivities σr, σθ depending only on the radius. The sensitivity is found analytically for an arbitrary plane magnetic field in the case σrσθ=constant. When the field is uniform the condition on σr and σθ necessary to make the sensitivity independent of the shape of the velocity profile is found. The sensitivity change is deduced for small perturbations from this conductivity distribution, for an arbitrary axisymmetric velocity profile. The effect of blood vessel walls having large conductivity variations of a simple type is also found. The results agree well with the numerical calculations of Baker in 1970 and satisfactorily with deductions made from the experimental results of Phibbs in 1968 and Dennis and Wyatt in 1969.