Conductivity Volume Research Articles

The effectiveness of a national security screening interview conducted by a computer-generated agent

To determine the feasibility of automating the process of interviewing applicants for Federal security clearances, the authors examined behavioral and physiological responses of individuals (n=120) to questions concerning their mental health, drug, alcohol, and criminal histories. The interviews were administered by a computer-generated (CG) agent. The results indicated that the number of relevant admissions during the CG interview exceeded the number of admissions made using a self-report questionnaire. In addition, significant blood volume and skin conductance amplitude differences were observed between individuals who made two or more relevant admissions and individuals who made less than two admissions. An interaction between perceived locus of interview control (either computer or human) and behavioral activation systems (BAS) on skin conductance (SC) responses was also observed.

Effect mechanism of mixing on improving conductivity of asphalt solar collector

This paper investigates the influence of different mixing parameters of 1 forced mixing on the conductivity of asphalt solar collector (ASC). Graphite powder and carbon fibers were used to improve the conductivity of asphalt concrete. The conductivity of ASC was measured with the same mix gradation, mixing procedure but different mixing parameters. The rational vibrating mixing parameters are obtained according to orthogonal experiments of the conductivity. A laboratory test of volume index and conductivity was performed after determining the rational mixing parameters. The effects of common forced mixing the on microstructure of ASC were investigated using scanning electron microscopy (SEM) and computed tomography (CT). The results obtained show that the mixing parameters have a major impact on the conductivity of asphalt concrete, among which the temperature have the strongest influence, while the revolutionary speed has less influence. The rational mixing parameters include: Bitumen temperature T1 160°C, aggregate temperature T2 180°C, mixing time t 90s and mixing revolution speed v 45r/min. ASC can obtain good conductivity and volume index with rational mixing parameters. The resistivity drops from insulation to 39.8ohmm and the thermal conductivity increases from 1.531W/mK to 2.120W/mK. The microstructure of ASC showed that the conductive fillers have uniform distributions in the sample. Conductive particles and carbon fibers promote the formation of conductive networks, because fibers may bridge up several isolated conductive particles.

Use of contact illumination for high-resistance semiconductor conductivity measurements

It is shown that illumination of ohmic contacts to high-resistance cadmium telluride and gallium arsenide samples affects not only the transient resistance of the contact, but the bulk conductivity of samples by increasing the concentration of free charge carriers. The model explaining the increase in the volume conductivity of the sample under the illumination of the contact region is presented. The procedure for separate determination of the transient resistances of the ohmic contact and the sample volume, suitable for highresistance semiconductors, is proposed.

Effect of carbon nanotubes shape on the properties of multiwall carbon nanotubes/polyethylene flexible transparent conductive films

Transparent conductive material is used in a wide range of applications and is particularly interesting. In the present work, a series of multiwall carbon nanotubes/low density polyethylene nanocomposites with different carbon nanotubes were prepared via solution casting method. The optical transparency, morphology, and resistivity of transparent conductive films have been characterized by using UV–Vis Spectrophotometer, Field emission scanning electron microscope and Multimeter, respectively. Their electrically conductive and optically transparent properties were studied and compared. The result showed that thinner and longer multiwall carbon nanotubes were more suitable for the fabrication of flexible transparent conductive nanocomposites. The sample filled with 1 wt% of T.1 (outside diameter <8 nm, length 10–30 μm) had good transparent conductive properties (volume conductivity of 3.12 × 10−3 S m−1 and optical transmittance of 62.8 % at the light wavelength of 600 nm). The high volume conductivity and optical transparency demonstrated that such kind of nanocomposite films had favorable potential in the applications from electromagnetic interference shielding to transparent electrodes.

Redundant dopaminergic activity may enable compensatory axonal sprouting in Parkinson disease

Neurodegenerative diseases become clinically apparent only after a substantial population of neurons is lost. This raises the possibility of compensatory mechanisms in the early phase of these diseases. The importance of understanding these mechanisms cannot be underestimated because it may guide future disease-modifying strategies. Because the anatomy and physiology of the nigrostriatal dopaminergic pathways have been well described, the study of Parkinson disease can offer insight into these early compensatory mechanisms. Collateral axonal sprouting of dopaminergic terminals into the denervated striatum is the most studied compensatory mechanism in animal (almost exclusively rodent) models of Parkinson disease and is correlated with behavioral recovery after partial lesions. This sprouting, however, does not respect the normal anatomy of the original nigrostriatal pathways and leads to aberrant neuronal networks. We suggest here that the unique physiologic property of the dopaminergic innervation of the striatum, namely redundancy of information encoding, is crucial to the efficacy of compensatory axonal sprouting in the presence of aberrant anatomical connections. Redundant information encoding results from the similarity of representation of salient and rewarding events by many dopaminergic neurons, from the wide axonal field of a single dopaminergic neuron in the striatum, and from the nonspecific spatial effect of dopamine on striatal neurons (volume conductance). Finally, we discuss the relevance of these findings in animal models to human patients with Parkinson disease.

Structural, AC conductivity and dielectric properties of vanado-tellurite glasses containing BaTiO3

Glasses with the composition, [(30−x)V2O5–xBaTiO3–70 TeO2] with x=5, 10 and 15 (in mol%) were prepared. The amorphous nature and glassy characteristics of the samples were established via X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) respectively. The nanocrystalline of BaTiO3 embedded in the network glass matrix at x=15mol% were established by DSC which is confirmed by infrared spectroscopy study. Properties such as density, molar volume, dielectric constant, dielectric loss and AC conductivity, as a function of frequency (120Hz–100kHz) and temperature (300–500K), have been investigated. The trends of these properties are attributed to changes in the glass network structure and presence of nanocrystalline of BaTiO3. The sample at x=15mol% exhibited dielectric anomaly and the Curie–Weiss law was found to be valid at a temperature above the transition temperature (Tc).

Physicochemical properties of bamboo leaf aerogels synthesized via different modes of gelation

Aerogels with ultralow silica concentration (3.5 %) was synthesized using bamboo leaf. The synthesis of aerogel was carried out in different pH to study the effect of gelation mechanisms on the properties of aerogel. Aerogel synthesized at acidic pH has generally exhibits more attractive properties, i.e. low shrinkage (24.3%), large specific surface area (547.2m2g−1), large pore volume (2.72cm3g−1) and low thermal conductivity (0.024Wm−1K−1). As comparison, the aerogel synthesized at basic condition has different properties, in which it has small pore volume (0.287cm3g−1) and pore size (11.44nm), large primary particles (6.69nm), small specific surface area (247.7m2g−1), low degree of fractality (6.69), strong absorption of water and relatively high thermal conductivity (0.0415Wm−1K−1). Properties of aerogels synthesized were also compared with aerogels synthesized using conventional TEOS precursor. The difference in the gelation mechanisms was discussed in detailed.

Transient field distribution in gas-solid insulation systems under DC voltages

The development of electric fields in gas-solid insulation systems under dc voltage stress goes hand in hand with the accumulation and decay of charges on dielectric interfaces. The charge transport through the solid insulator and the gas is determined by the electric properties of the involved insulating materials. Therefore, the nonlinearly field-dependent volume conductivity of a gas, resulting from a constant charge generation rate by natural ionization has to be considered. The transient field distribution on insulators under dc voltage is investigated theoretically, using a gas model, which takes into account the physical characteristics of insulating gases like air and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> as well as the effects resulting from electron emission from the electrodes. The influence of the ion pair generation rate in the gas, the electric field strength, and the volume and surface conductivity of the solid insulating material on the development of the electric field is investigated on cylindrical and conical insulators which are typical for gas insulated systems. Results of calculations using the gas model are compared to simulations assuming constant gas conductivity. The simulation results are verified by measurements of the surface potential on cylindrical epoxy resin insulators in air.

Transient field distribution in gas-solid insulation systems under DC voltages

The development of electric fields in gas-solid insulation systems under dc voltage stress goes hand in hand with the accumulation and decay of charges on dielectric interfaces. The charge transport through the solid insulator and the gas is determined by the electric properties of the involved insulating materials. Therefore, the nonlinearly field-dependent volume conductivity of a gas, resulting from a constant charge generation rate by natural ionization has to be considered. The transient field distribution on insulators under dc voltage is investigated theoretically, using a gas model, which takes into account the physical characteristics of insulating gases like air and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> as well as the effects resulting from electron emission from the electrodes. The influence of the ion pair generation rate in the gas, the electric field strength, and the volume and surface conductivity of the solid insulating material on the development of the electric field is investigated on cylindrical and conical insulators which are typical for gas insulated systems. Results of calculations using the gas model are compared to simulations assuming constant gas conductivity. The simulation results are verified by measurements of the surface potential on cylindrical epoxy resin insulators in air.

Hydrothermal synthesis and activation of graphene-incorporated nitrogen-rich carbon composite for high-performance supercapacitors

Graphene-incorporated nitrogen-rich carbon composite with nitrogen content of ca. 10wt.% has been synthesized by an effective yet simple hydrothermal reaction of glucosamine in the presence of graphene oxide (GO). The nitrogen content of carbon composite is nearly twice as high as that of hydrothermal carbon without graphene. GO is favorable for the high nitrogen doping in the carbon composite by the reaction between the glucosamine-released ammonia and GO. The hydrothermal carbon composite is further activated by KOH, and graphene in the activated carbon composite demonstrates a positive effect of increasing specific surface area, pore volume and electrical conductivity, resulting in superior electrochemical performance. The activated carbon composite with higher specific surface area and micropore volume possesses higher specific capacitance with a value of 300Fg−1 at 0.1Ag−1 in 6M KOH aqueous solution in the two electrode cell. Larger mesopore volume and higher conductivity of the activated carbon composite will provide fast ion and electron transfer, thus leading to higher rate capacity with a capacitance retention of 76% at 8Ag−1 in comparison to the activated hydrothermal carbon without graphene.

Single Polymer Composites of Poly(Butylene Terephthalate) Microfibrils Loaded with Carbon Nanotubes Exhibiting Electrical Conductivity and Improved Mechanical Properties

Applying the concept of microfibrillar composites, microfibrils of poly(butylene terephthalate) (PBT) loaded with 5 wt% multi-walled carbon nanotubes are prepared by extraction of polypropylene (PP) from drawn PP/PBT blends and shaped into single polymer composites (SPCs). SPCs show superior mechanical performance with up to 300–600% improvement in modulus and tensile strength as compared to neat isotropic PBT. In addition, the microfibrillar SPCs (MF-SPCs), as well as the single microfibrils, have electrical volume conductivity of 8 × 10−3 S cm−1 demonstrating electrical conductive behavior.

Porous Graphitic Carbon Loading Ultra High Sulfur as High-Performance Cathode of Rechargeable Lithium–Sulfur Batteries

Porous graphitic carbon of high specific surface area of 1416 m(2) g(-1) and high pore volume of 1.11 cm(3) g(-1) is prepared by using commercial CaCO3 nanoparticles as template and sucrose as carbon source followed by 1200 °C high-temperature calcination. Sulfur/porous graphitic carbon composites with ultra high sulfur loading of 88.9 wt % (88.9%S/PC) and lower sulfur loading of 60.8 wt % (60.8%S/PC) are both synthesized by a simple melt-diffusion strategy, and served as cathode of rechargeable lithium-sulfur batteries. In comparison with the 60.8%S/PC, the 88.9%S/PC exhibits higher overall discharge capacity of 649.4 mAh g(-1)(S-C), higher capacity retention of 84.6% and better coulombic efficiency of 97.4% after 50 cycles at a rate of 0.1C, which benefits from its remarkable specific capacity with such a high sulfur loading. Moreover, by using BP2000 to replace the conventional acetylene black conductive agent, the 88.9% S/PC can further improve its overall discharge capacity and high rate property. At a high rate of 4C, it can still deliver an overall discharge capacity of 387.2 mAh g(-1)(S-C). The porous structure, high specific surface area, high pore volume and high electronic conductivity that is originated from increased graphitization of the porous graphitic carbon can provide stable electronic and ionic transfer channel for sulfur/porous graphitic carbon composite with ultra high sulfur loading, and are ascribed to the excellent electrochemical performance of the 88.9%S/PC.

Synthesis of silver nanoparticles decorated MWCNTs and their application in antistatic polyetherimide matrix nanocomposite

A facile approach for fabricating antistatic polyetherimide (PEI) had been carried out by introducing poly(sodium acrylate) bonded multi-walled carbon nanotubes and silver nanoparticles (MWCNTs@PSA@Ag). The electrostatic discharge channel was well constructed through homogenously dispersed MWCNTs with polar PSA layer and enhanced by Ag nanoparticles. Chemical structures of MWCNTs@PSA@Ag were characterized by FTIR, XPS, Raman, TGA, UV–vis and TEM. Results revealed that PSA was covalently bonded onto the surface of MWCNTs. Thereby, the ester bond in PSA could improve the dispersion of MWCNT in PEI matrix, and assemble size controlled Ag nanoparticles through coordination bond. Thus, the percolation volume conductivity of MWCNTs@PSA@Ag/PEI nanocomposite was increased to 8.3×10−8S/cm at 0.75wt% concentration. Moreover, the percolation threshold was further declined to 0.5wt% concentration because ionic conduction of PSA could be formed after moisture absorption of MWCNTs@PSA@Ag/PEI nanocomposite in environment.

Equivalent surface conductivity of ice accumulated on insulators during development of AC and DC flashovers arcs

Surface conductivity of ice was investigated during the development of AC and DC arcs on ice-covered insulators. To determine this parameter, an approach based on fluid mechanics combined with experimental measurements of the water film flow rate and conductivity was used. In particular, the variation of the thickness and volume conductivity of the water film as well as the mechanisms of discharge initiation and arc development on the surface of an ice-covered post insulator were studied. The effect of ice surface conductivity on arc propagation velocity was evaluated for different freezing water conductivities using highspeed video camera techniques. Empirical models were proposed to account for equivalent surface conductivity dynamics during the flashover process. The derived equivalent surface conductivity was used to improve existing dynamic models to predict the minimum flashover voltage of the ice-covered insulator. The computed results from the models were in good agreement with those obtained experimentally.

Enhanced power output of an electrospun PVDF/MWCNTs-based nanogenerator by tuning its conductivity

PVDF nanofibre-based piezoelectric nanogenerators are directly prepared via electrospinning without any post-poling treatment. The effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the fibre diameter, mechanical properties, β-phase composition, surface and volume conductivities, output voltage and output power are investigated. Increased surface conductivity of the poly-vinylidene fluoride (PVDF) nanofibre mats, which plays an important role in the enhancement of output power, is first found by the addition of an appropriate amount of MWCNTs. The maximum generated piezo-voltage exhibited by PVDF nanofibre mats in the presence of 5 wt% MWCNTs is as high as 6 V, while the average capacitor charging power is 81.8 nW, increases of 200% and 44.8%, respectively, compared with bare PVDF nanofibre mats.

Arterial elastance and its impact on intrinsic right ventricular function in palliated hypoplastic left heart syndrome

BackgroundSystemic right ventricular (RV) function is a major determinant of long-term outcome in patients with palliated hypoplastic left heart syndrome (HLHS). Abnormal elastic properties of the reconstructed aorta may negatively impact on ventricular function. We therefore aimed to assess arterial elastance and its relationship to systemic RV function in these patients. MethodsFifty-six HLHS patients (median age 5.4years; range 2.9–14.2years) were studied at a median of 2.6years (range 0.8–12.7years) after completion of the Fontan circulation with the pressure–volume conductance system. ResultsArterial elastance (Ea) was abnormally high and correlated inversely with RV ejection fraction (r=−0.42, P=0.001). However, end systolic elastance (Ees) – a load independent measure of intrinsic systolic ventricular function – and more so end diastolic stiffness (Eed) were positively correlated with Ea (Ees vs. Ea: r=0.44, P=0.001: Eed vs. Ea: r=0.62, P<0.0001).Patients who were treated for significant aortic arch obstruction after surgical palliation showed higher Ea and Eed even four years after successful treatment compared to the remainder of the group (Ea: 3.4±1.2 vs. 2.8±1.0mmHg/ml, P=0.04 and Eed: 0.67±0.44 vs. 0.45±0.3mmHg/ml, P=0.04). ConclusionsArterial elastance is abnormally high in palliated HLHS patients and negatively impacts on ejection fraction but not on intrinsic systolic RV function early after completion of the Fontan circulation. Increased arterial elastance, however, is associated with increased RV diastolic stiffness with potential adverse effects on long-term outcome. Furthermore, arterial elastance and diastolic stiffness are particularly high in patients who needed treatment for aortic arch obstruction.

Foaming performance of aqueous albumin and mullite-albumin systems used in cellular ceramic processing

Abstract Bovine serum albumin (BSA) solutions (5, 10 and 15 vol%) and stabilized aqueous mullite (40 vol%)–BSA (5, 10 and 15 vol%) suspensions were foamed by mechanical stirring at 2300 rpm. The colloidal and rheological behaviors of suspensions were studied by measuring zeta potential and shear flow properties, respectively. The foaming performance of aqueous systems was evaluated by characterizing the foaming capacity and the foam stability by volume and electrical conductivity measurements. Overrun % was considered as a measure of the foaming capacity, while the variation of this parameter, the foam wetness ( Φ FW ) and the foam density stability ( FDS % ) with the stand time and the time to half collapse ( t 1/2 ) were evaluated in order to study the stability of foamed systems. Median bubble diameters, bubble size distribution widths and bubble shape factors as a function of time were determined by analyzing images captured by confocal laser-scanning microscopy (CLSM). The results related to the stability of foamed systems were used to evaluate the global destabilization mechanism of these systems, analyzing, in particular, the influence of the solid particles in the protein foam. The obtained results are useful for studying the shaping of cellular mullite green bodies from the thermogelation of foamed aqueous ceramic-protein suspensions.

Corrosion control in underground concrete structures using double waterproofing shield system (DWS)

High level of structural and waterproofing stability leads to long-term service life in underground infrastructures. Interaction between aggressive groundwater with tunnel causes corrosion and damage in concrete structure due to steel reinforcement corrosion and concrete cracks. This study introduces a double waterproofing shield system (DWS) as an innovative solution to waterproofing and structural failures in underground concrete structures. In this method, ordinary shotcrete mixture replaces by an organic polymer concrete (OPC) to construct a water-resistant temporary support right after each partial excavation. Two groups of specimens including reference concrete and OPC specimens were provided and tested in accordance with ASTM C 642. Waterproofing parameters including porosity, pore volume, permeability and hydraulic conductivity have been determined. Results show a remarkable reduction in mentioned parameters for OPC compared with ordinary concrete. Improvement in waterproofing performance of temporary support corresponds to a healthy final lining and increase in service life of the structure.

Investigation of microstructure and conducting mechanism of nanocomposite polymeric electrolytes with rectorite clay by PALS

Polymeric electrolytes with different modified organic nanoretorite (OREC) content have been prepared. Measurements of the structural transition, the positron annihilation lifetime, free volume and ionic conductivity as a function of the OREC content and the temperature have been performed. According to the variations of the ortho-positronium (o-Ps) lifetimes with temperature, the glass transition temperatures have been determined. A direct relationship between the ionic conductivity and the fractional free volume has been established using based on free volume theory Williams-Landel-Ferry (WLF)equations, implying a free-volume transport mechanism. Our experimental results indicated that the segmental chain motion and ionic migration and diffusion could be explained by the free volume theory.

Assessing the feasibility of CO2 storage in the New Albany Shale (Devonian–Mississippian) with potential enhanced gas recovery using reservoir simulation

The feasibility of storing carbon dioxide (CO2) in geologic formations as a means to mitigate global climate change is being evaluated around the globe. One option that has received limited attention is to store CO2 in shale formations that are currently productive unconventional shale gas plays. While CO2 trapping mechanisms in saline aquifers are primarily structural, capillary, solubility, and mineral trapping, the mechanisms are fundamentally different in gas shales, and CO2 adsorption onto organic materials and clay minerals plays a key role. Shale gas formations have a high content of organic matter that may store significant amounts of adsorbed natural gas, ranging from 20% to 80% of original-gas-in-place (OGIP). Laboratory and theoretical calculations suggest that CO2 is adsorbed preferentially over methane (CH4) onto the organics and could displace the methane (with up to a 5:1 ratio by molecule). This mechanism could be the basis of a new method of carbon capture, utilization, and storage (CCUS) that stores the CO2 in gas shales with the potential added benefit of enhanced gas recovery (EGR).This investigation evaluates the hypothesis of CO2 storage with EGR using reservoir modeling of the Devonian and Mississippian New Albany Shale gas play in the Illinois Basin, USA. The shale was evaluated in terms of CO2 injectivity, storage capacity, and effectiveness, as well as the impact of CO2 injection on methane recovery. The modeling technique employs a dual-porosity, dual-permeability approach, incorporating horizontal wells with multi-stage hydraulic fractures, Darcian and diffusive flow, gas sorption/desorption, hysteresis effects, and CO2 dissolution. Our simulation results demonstrate that CO2 storage in the New Albany Shale is feasible. Approximately 4×104metric tonnes of CO2 could be injected through one horizontal well (having four hydraulic fracture stages) within 5 years with minimal CO2 breakthrough (less than 1% of the injected CO2). Over 95% of the injected CO2 is effectively sequestered instantaneously with gas adsorption being the dominate storage mechanism. Residual trapping and solubility trapping sequester only ∼0.4% and ∼1.1%, respectively, of the injected CO2. Sensitivity tests were conducted on several key geological parameters (total organic carbon content, natural fracture conductivity, and matrix permeability) and engineering parameters (stimulated rock volume and hydraulic fracture conductivity). Among the evaluated factors, CO2 storage effectiveness appears to be dominated by changes in the stimulated rock volume and the total organic carbon content. Incremental CH4 recovery from CO2 injection was not substantial (∼1%) in either the CO2 flood or the huff-n-puff scenario under the simulated reservoir conditions and well designs, possibly because the unstimulated tight shale rock between the CO2 injector and CH4 producer impeded effective mass and pressure communication, which prerequisites for successful EGR. However, in the huff-n-puff scenario, with a similar amount of CH4 produced, a noticeable amount of CO2 was sequestered simultaneously. Assumptions, approximations, and compromises were made in the current modeling work because of gaps in the current knowledge base about various aspects of the gas shale reservoirs. These limitations are discussed in an effort to prioritize future research on this topic using experimental and observational methods, modeling tools, and field tests.