Increase In Impedance Research Articles

Hypoxia increases expression of selected blood\u2013brain barrier transporters GLUT-1, P-gp, SLC7A5 and TFRC, while maintaining barrier integrity, in brain capillary endothelial monolayers

BackgroundBrain capillary endothelial cells (BCECs) experience hypoxic conditions during early brain development. The newly formed capillaries are tight and functional before astrocytes and pericytes join the capillaries and establish the neurovascular unit. Brain endothelial cell phenotype markers P-gp (ABCB1), LAT-1(SLC7A5), GLUT-1(SLC2A1), and TFR(TFRC) have all been described to be hypoxia sensitive. Therefore, we hypothesized that monolayers of BCECs, cultured under hypoxic conditions, would show an increase in LAT-1, GLUT-1 and TFR expression and display tight endothelial barriers.Methods and resultsPrimary bovine BCECs were cultured under normoxic and hypoxic conditions. Chronic hypoxia induced HIF-1α stabilization and translocation to the nucleus, as judged by immunocytochemistry and confocal laser scanning imaging. Endothelial cell morphology, claudin-5 and ZO-1 localization and barrier integrity were unaffected by hypoxia, indicating that the tight junctions in the BBB model were not compromised. SLC7A5, SLC2A1, and TFRC-mRNA levels were increased in hypoxic cultures, while ABCB1 remained unchanged as shown by real-time qPCR. P-gp, TfR and GLUT-1 were found to be significantly increased at protein levels. An increase in uptake of [3H]-glucose was demonstrated, while a non-significant increase in the efflux ratio of the P-gp substrate [3H]-digoxin was observed in hypoxic cells. No changes were observed in functional LAT-1 as judged by uptake studies of [3H]-leucine. Stabilization of HIF-1α under normoxic conditions with desferrioxamine (DFO) mimicked the effects of hypoxia on endothelial cells. Furthermore, low concentrations of DFO caused an increase in transendothelial electrical resistance (TEER), suggesting that a slight activation of the HIF-1α system may actually increase brain endothelial monolayer tightness. Moreover, exposure of confluent monolayers to hypoxia resulted in markedly increase in TEER after 24 and 48 h, which corresponded to a higher transcript level of CLDN5.ConclusionsOur findings collectively suggest that hypoxic conditions increase some BBB transporters' expression via HIF-1α stabilization, without compromising monolayer integrity. This may in part explain why brain capillaries show early maturation, in terms of barrier tightness and protein expression, during embryogenesis, and provides a novel methodological tool for optimal brain endothelial culture.

Enhanced Thermal Conducting Behavior of Pressurized Graphene-Silver Flake Composites.

Modern electronics continue to shrink down the sizes while becoming more and more powerful. To improve heat dissipation of electronics, fillers used in the semiconductor packaging process need to possess both high electrical and thermal conductivity. Graphene is known to improve thermal conductivity but suffers from van der Waals interactions and thus poor processibility. In this study, we wrapped silver microflakes with graphene sheets, which can enable intercoupling of phonon- and electron-based thermal transport, to improve the thermal conductivity. Using just 1.55 wt % graphene for wrapping can achieve a 2.64-times greater thermal diffusivity (equivalent to 254.196 ± 10.123 W/m·K) over pristine silver flakes. Graphene-wrapped silver flakes minimize the increase of electrical resistivity, which is one-order higher (1.4 × 10-3 Ω·cm) than the pristine flakes (5.7 × 10-4 Ω·cm). Trace contents of wrapped graphene (<1.55 wt %) were found to be enough to bridge the void between Ag flakes, and this enhances the thermal conductivity. Graphene loading at 3.76 wt % (beyond the threshold of 1.55 wt %) results in the significant graphene aggregation that decreases thermal diffusivity to as low as 16% of the pristine Ag filler. This work recognizes that suitable amounts of graphene wrapping can enhance heat dissipation, but too much graphene results in unwanted aggregation that hinders thermal conducting performance.

Smart behaviour of CNT modified adhesive films for carbon fiber composite repair

Epoxy adhesives films were doped by spraying an aqueous dispersion of carbon nanotubes. Sensing capability of carbon fiber reinforced composite coupons with bonded patch repairs was evaluated; several single lap shear and Mode-I fracture energy tests were conducted and their electrical responses were characterized. It was observed that electrical resistance increases with mechanical strain due to tunnelling effect on CNT percolating networks and increases of electrical resistance associated to crack propagations could be also detected. Once the smart behaviour if the adhesive joints was identified by means of mechanical tests in normalized adhesive joined specimens, panels (400 x 400mm) with square co-bonded patches, made using the same curing cycle based on the repaired material one, were prepared using CNT doped adhesive films. These panels were mechanical tested to determine the effect of the doping treatment on the mechanical behaviour of the repairs, at the same time that electric measurements were carried out to identified local failures during testing. Obtained results showed that structural film adhesives could be surface doped with CNT providing sensing capabilities to be used in structural health monitoring of adhesive repairs in composite structures.

The Impact of Matrix Cross-Linking Degree on Chemo-Resistive Properties of Natural Rubber-Carbon Nanostructure Composite

The aim of this work is to investigate chemo-resistivity properties of natural rubber-carbon nanostructure composite, that’s why a change of diffusion characteristics and reversibility of electro-chemical properties of the composite with different degree values of crosslinks have been analysed. The composites are made from natural rubber (polyisoprene) as matrix material and high structure carbon black as electro-conductive filler. In order to investigate diffusion characteristics of volatile organic compounds (VOC) in relation to chemo-resistive response of composites simultaneous mass, length and electrical resistance change measurements of the samples, when samples are held in VOC and after exposures to VOC were carried out. Electrical resistance increase mechanism in the composite advances with the composite structure development during vulcanization.

Surface characterisation of brass alloy in the correlation of hardness and electrical resistivity by carbon ion implantation

Material modification, as per demand of era, has been explored by several groups in different areas focusing its engineering prospect for better performance. Carbon ion implantation, using four different doses, has been done on α-brass (64% Cu; 36% Zn) to see its effects on hardness, microstructure and electrical resistivity. Carbon ions distorted the crystalline surface, increased defect density and hardened the surface by 13.2%. The crystallite size was found decreased by 41.15%, which in turn caused a significant increase in electrical resistivity, i.e. 234.8%. Overall, the lattice parameter found increased from 3.680 to 3.688 Å. SEM morphology exhibited nonuniform agglomerations in the form of pits, cracks, voids, cavities, craters, particulates, droplets and petals like structures at the surface by carbon ion implantation.

Disorder effect and thermoelectric properties of Bi1−xCaxCu1−ySeO with Cu vacancy

BiCuSeO exhibits remarkable low thermal conductivity among oxides. The lone pair of the Bi3+ and the point defects brought about by elemental doping are thought to be the origin of the low thermal conductivity. In a recent study, however, the Cu atoms in BiCuSeO play a more significant role in reducing the lattice thermal conductivity than the above two factors. In this work, two series of polycrystalline Bi1−xCaxCu0.975SeO (x = 0.025, 0.050, 0.075, 0.100, 0.125, 0.150) and Bi0.95Ca0.05Cu1−ySeO (y = 0.015, 0.025, 0.035) are synthesized by solid-state reaction. All the materials are of single phase. Point defects introduced by partial elemental substitution and atom vacancy are expected to reduce the lattice thermal conductivity, however, which is not followed by the prediction for Bi1−xCaxCu0.975SeO with 0.050 ≤ x ≤ 0.125 and Bi0.95Ca0.05Cu1−ySeO with y = 0.015, 0.025, and 0.035 in the temperature range where the resistivity decreases while the thermopower increases with temperature. This is in sharp contrast with those BiCuSeO with partial elemental substitution or Cu deficiency exhibiting either both the electrical resistivity and thermopower increase or decrease with increasing temperature. Our results support that the Cu atoms in BiCuSeO play a more significant role in reducing the lattice thermal conductivity than the lone pair of the Bi3+ and the point defects brought about by elemental doping.

3D Macroporous Oxidation‐Resistant Ti3C2Tx MXene Hybrid Hydrogels for Enhanced Supercapacitive Performances with Ultralong Cycle Life

AbstractAs a recently emerging group of 2D materials, MXene has attracted extensive attention in the energy storage field in recent years owing to their outstanding features. However, the notorious issues of inevitable oxidation stability and surface‐to‐surface self‐restacking for MXene significantly prevent its further wide‐ranging application. Herein, the 3D macroporous oxidation‐resistant Ti3C2Tx MXene/graphene/carbon nanotube (MRC) hybrid hydrogels are prepared by a simple gelation method assisted by l‐cysteine as crosslinker and l‐ascorbic acid (VC) as reductant. Benefitting from the effectively alleviated restacking, excellent electrical conductivity, and the 3D inter‐crosslinked macroporous architecture, as a supercapacitor electrode, the obtained MRC aerogel exhibits a superior specific capacitance of 349 F g−1, unparalleled rate capability (52.0% at 3000 mV s−1) and amazing cyclic stability (retention of 97.1% after 100 000 cycles). Moreover, the 3D MRC‐30 aerogel exhibits an impressive oxidation‐resistant performance with just a 9.3% increase in electrical resistance after storing in ambient condition for 60 days, effectively alleviating the oxidation problem of MXene. This work demonstrates a new method for construction of 3D oxidation‐resistant MXene hydrogel, shedding new light on the promising applications of MXene materials, especially in high humidity and oxygen environment.

Kinematic Viscosity and Electrical Resistivity of a Multicomponent Melt due to Liquid–Liquid Structure Transition

We investigated the kinematic viscosity and electrical resistivity of the multicomponent Fe74Cu1Nb1.5Mo1.5B8.5Si13.5 melt during three heating–cooling cycles. The temperature dependence of kinematic viscosity and electrical resistivity have the anomalous zones in the same temperature range and they are associated with the liquid–liquid structure transition (LLST). The anomalies were explained by changes in the activation energy and the cluster size. As the cluster size decreases, the activation energy decreases, but the viscosity and electrical resistance increase. LLST begins with the cluster dissolution, and as a result, the Arrhenius plot becomes nonlinear in the transition temperature range. After three cycles of heating–cooling, the temperature dependences of the kinematic viscosity and electrical resistance did not qualitatively change, and this allows us to conclude that LLST is thermoreversible. With an increase in the number of thermal cycles, the activation energy of viscous flow decreases, as well as the onset temperature and temperature range of LLST.

Multifunctional Electrically Conductive Copper Electroplated Fabrics Sensitizes by In-Situ Deposition of Copper and Silver Nanoparticles.

In this study, we developed multifunctional and durable textile sensors. The fabrics were coated with metal in two steps. At first, pretreatment of fabric was performed, and then copper and silver particles were coated by the chemical reduction method. Hence, the absorbance/adherence of metal was confirmed by the deposition of particles on microfibers. The particles filled the micro spaces between the fibers and made the continuous network to facilitate the electrical conduction. Secondly, further electroplating of the metal was performed to make the compact layer on the particle- coated fabric. The fabrics were analyzed against electrical resistivity and electromagnetic shielding over the frequency range of 200 MHz to 1500 MHz. The presence of metal coating was confirmed from the surface microstructure of coated fabric samples examined by scanning electron microscopy, EDS, and XRD tests. For optimized plating parameters, the minimum surface resistivity of 67 Ω, EMI shielding of 66 dB and Ohmic heating of 118 °C at 10 V was observed. It was found that EMI SH was increased with an increase in the deposition rate of the metal. Furthermore, towards the end, the durability of conductive textiles was observed against severe washing. It was observed that even after severe washing there was an insignificant increase in electrical resistivity and good retention of the metal coating, as was also proven with SEM images.

Modelling the correlation between the electrical resistance and stiffness degradation in conductive composite laminates with complex damage scenarios

The main aim of this work is to propose and validate an analytical strategy to correlate the electric and mechanical response of bi-directional laminates in the presence of both off-axis cracks and delamination. To this end, the attention is initially focused on the electrical problem, developing and validating against numerical results a new, fully analytical, model to properly assess the electrical resistance increase in the laminate as a function of the damage state.Subsequently, an analytical model to predict the laminate stiffness as a function of the damage scenario is derived and later combined with the electric one, thus establishing a direct correlation between the resistance change and the stiffness degradation.

Operation characteristics of open-cathode proton exchange membrane fuel cell with different cathode flow fields

Open-cathode proton exchange membrane fuel cell (PEMFC) is considered as a promising power source for unmanned aerial vehicles and portable applications due to its simple structure and low parasitic power. In this study, the operating condition effects of the open-cathode PEMFC with different cathode flow fields (parallel, pin-type, and metal foam) are investigated experimentally. Polarization curve and electrochemical impedance spectroscopy (EIS) are tested to characterize the cell performance and electrochemical impedance, respectively. The results show that the cell with the metal foam flow field has better performance than that with the other flow fields in the baseline conditions. Although increasing the fan voltage could provide adequate reactant gas and remove excess water, too large air flow rate could reduce membrane water content and decrease temperature that is bad for the cell performance. Increasing the operating temperature would improve the cell performance, but the increase of ohmic resistance caused by higher water evaporation rate cannot be neglected. The cell performance does not increase significantly with increasing the anode backpressure in the low current density region, but decreases with increasing the anode backpressure in the high current density region.

Evaluation of complexing agents in the gel electro-membrane extraction: An efficient approach for the quantification of zinc (II) ions in water samples

In this work, gel electro-membrane extraction (G-EME) combined with flame atomic absorption spectrometry (FAAS) was used for the determination of zinc ions (Zn2+) in water samples. For the first time, the effect of the presence of three types of complexing agents such as phenanthroline (Phen), crown ethers (12C4, 15C5, 18C6), and ethylene-diamine-tetra-acetic acid (EDTA) on the extraction efficiency of zinc ions was studied. In addition, the electroendosmosis (EEO) flow as an unwanted actuator was monitored in the presence and absence of complexing agents. By applying 50 V electrical potential across the membrane, the positive charged Zn2+ ions were migrated from a donor phase (pH 5.0) through the agarose gel membrane (pH 5.0, containing a complexing agent) into the acceptor phase (pH 3.0). The obtained results showed that the highest extraction recoveries were obtained when crown ethers, especially 1% (w/v) 18C6 was added to the gel membrane. In addition, EEO flow was decreased in the presence of all complexing agents (except EDTA), probably due to the increase in electrical resistance. Using the optimum conditions, the limit of detection (LOD), the limit of quantification (LOQ), and extraction recovery% (ER%) were 5.0 μg L−1, 15.0 μg L−1, and 92.5%, respectively. In the end, the applicability of the developed approach was successfully evaluated to determine Zn2+ in tap, mineral, and river water samples.

A Review on Ion-Exchange Membrane Fouling during the Electrodialysis Process in the Food Industry, Part 1: Types, Effects, Characterization Methods, Fouling Mechanisms and Interactions.

Electrodialysis (ED) was first established for water desalination and is still highly recommended in this field for its high water recovery, long lifetime and acceptable electricity consumption. Today, thanks to technological progress in ED processes and the emergence of new ion-exchange membranes (IEMs), ED has been extended to many other applications in the food industry. This expansion of uses has also generated several problems such as IEMs’ lifetime limitation due to different ageing phenomena (because of organic and/or mineral compounds). The current commercial IEMs show excellent performance in ED processes; however, organic foulants such as proteins, surfactants, polyphenols or other natural organic matters can adhere on their surface (especially when using anion-exchange membranes: AEMs) forming a colloid layer or can infiltrate the membrane matrix, which leads to the increase in electrical resistance, resulting in higher energy consumption, lower water recovery, loss of membrane permselectivity and current efficiency as well as lifetime limitation. If these aspects are not sufficiently controlled and mastered, the use and the efficiency of ED processes will be limited since, it will no longer be competitive or profitable compared to other separation methods. In this work we reviewed a significant amount of recent scientific publications, research and reviews studying the phenomena of IEM fouling during the ED process in food industry with a special focus on the last decade. We first classified the different types of fouling according to the most commonly used classifications. Then, the fouling effects, the characterization methods and techniques as well as the different fouling mechanisms and interactions as well as their influence on IEM matrix and fixed groups were presented, analyzed, discussed and illustrated.

Room-Temperature-Grown amorphous Indium-Tin-Silicon-Oxide thin film as a new electron transporting layer for perovskite solar cells

We report the amorphous quaternary oxide, indium-tin-silicon-oxide (ITSO), thin film as a new electron-transport layer (ETL) for perovskite solar cells (PSCs). ITSO thin films are grown by magnetron co-sputtering indium-tin-oxide (ITO) and silicon oxide (SiO2) on commercial transparent conducting oxide (TCO) thin films at room temperature. As Si content increases (0–53.8 at%) the optical bandgap increases by approximately 1.3 eV and the electrical resistivity increases by six orders mainly because of the carrier concentration decrease. Consequently, the ITSO electronic structure depends largely on Si content. PSCs employing ITSO thin films as ETLs were fabricated to evaluate the effect of Si content on device performances. Si content influenced the shunt and series resistance. The optimized device was obtained using an ITSO film with 33.0 at% Si content, exhibiting 14.50% power-conversion efficiency. These results demonstrate that ITSO films are promising for developing efficient PSCs by optimizing the growing process and/or In/Sn/Si/O compositions. This approach can reduce PSC manufacturing process time and costs if ITO and ITSO are grown together by continuous sequential sputtering in a dual gun (ITO and SiO2) chamber.

One-pot modified “grafting-welding” preparation of graphene/ polyimide carbon films for superior thermal management

Thermal management has attracted much recent attention due to the rapid development of 5G communication and electronic devices. Reduced GO/polyimide carbon (rGO/PI-carbon) films were prepared by a one-pot “grafting-welding” strategy, where GO was first grafted with amino groups using 1,3-bis(4-aminophenoxy) benzene, then polymerized with polyamic acid (PAA) and pyromellitic dianhydride to connect the GO sheets, before carbonization and graphitization. The rGO/PI film with a mass ratio of GO to PAA of 7% exhibits an increase in in-plane thermal conductivity (1102 W(m·K)−1) of 48.92% compared with the rGO film. It also has a superior bending performance and survives 2000 bend cycles with a small radius test while suffering an electrical resistance increase of less than 10%. Grafting-welding of rGO with PI carbon produces effective paths for phonon transport between the graphene sheets, reducing phonon scattering, which makes it a candidate for thermal interface materials for heat dissipation.

Experimental investigation of the failure mechanism of 18650 lithium-ion batteries due to shock and drop

This work presents an experimental investigation of the failure mechanism of 18650 lithium-ion batteries subject to dynamic mechanical loads and the implications of severe damages on the safety function of the current interruptive device (CID), as current literature offers no insight in this topic. First, a conducted shock test series with loads beyond automotive standards showed no distinct impact on various modern cell types in impedance and computed tomography (CT) analysis, while older cell types exhibited signs of damage such as mandrel displacement and increase of ohmic resistance, as had already been reported in literature. A following investigation with acceleration measurements of drops of power tool battery modules revealed that accelerations in some applications can exceed even high load-level standards significantly. In a subsequent test series with axial drop tests in both orientations with various cell types, impact surfaces and states of charge (SOC), multiple cell types exhibited high ohmic failure without a thermal event. Computed Tomography (CT) and Post Mortem analysis revealed that, among various observable damage mechanisms, the predominant failure mechanism is contact loss in the CID region. Even severe mechanical damages, although influencing electrical and thermal behavior, showed no impact on the functionality of the CID in overcharge tests

The effect of mineral admixtures on permeability, porosity and electrical resistivity of concrete

Evaluation of concrete durability is commonly performed by measuring its permeability, porosity and electrical resistivity. Moreover, using admixtures in concrete mix design is one of the methods of enhancing durability. For this reason, in this paper, the effect of pozzolanic admixtures (silica fume, fly ash and zeolite) and limestone powder on permeability, porosity and electrical resistivity of 28-day and 120-day cubic concrete specimens with 15cm dimension is investigated. For concrete preparation, 5, 10, 15 and 20 percent of cement mass were replaced by these admixtures. In this paper, the innovative method of “Cylindrical chamber” was used for measuring concrete permeability. The results obtained revealed that except the 28-day concrete specimen that 20 percent of its cement mass was replaced with limestone powder, other concrete specimens had lower permeability and porosity and higher electrical resistivity than the concrete specimen without any admixtures. In addition, volumetric porosity is a more accurate index for assessing concrete microstructure than surface porosity calculated from the images taken using scanning electron microscope. XRD test results also showed that pozzolanic material produce more calcium silicate hydrates by consuming calcium hydroxide which results in the reduction of permeability and porosity and increase of electrical resistivity, compared with the concrete specimen without any admixtures. Also, a slight reduction in calcium hydroxide and calcium silicate hydrate peaks was observed for the concrete containing limestone powder. This behavior showed that limestone powder decreases permeability and porosity and increase electrical resistivity of concrete, mainly due to the filler effect of its particles.

Degeneration of power output of a flexible and wearable thermoelectric module under bending fatigue

Strength and energy conversion efficiency of thermoelectric (TE) thin films upon cyclic mechanical loading are major concerns for flexible thermoelectric generator (TEG) applications. A comprehensively analysis model for the performance evaluation and fatigue failure of a TEG is constructed in this paper. The analytical solutions of temperature field, stress field, fatigue life, power output and energy conversion efficiency of the flexible TEG under cyclic loading are presented. A bending experiment is carried out to validate the analytical model and to fitting the model parameters. The results show that a continuing increase of electrical resistance and decrease of power output under the cyclic bending. The electrical resistance and power output of the TEG varies with the bending radius. The thickness ratio of the substrate to the TE film has a great influence on power output and energy conversion efficiency. A critical bending radius can be obtained from the model to provide a guideline for future flexible TEG design.

Electrical resistance changes of 3D carbon fiber/epoxy woven composites under short beam shear loading along different orientations

Electrical resistance under cyclic loading is important for designing intelligent structures of carbon-fiber reinforced composites. Here we report electrical resistance changes of 3D carbon fiber/epoxy woven composites under short beam shear loading along different orientations. The electric changes were measured in short beam shear tests combined with four-probe method and digital image correlation technology along five orientations, i.e., 0°, 30°, 45°, 60° and 90°. The on-axis (0° and 90°) samples have higher electrical conductivity, shear strength and resistance increase than other off-axis (30°, 45° and 60°) samples. Relative resistance changes become larger during monotonic loading and decrease under cyclic loading. The 45° and 60° samples show a higher relative resistance change compared with other samples under cyclic loading. Relationship between shear strength and relative resistance change was also revealed. This electric-mechanical coupling behavior provides a possible way for characterizing inner damages.

Operational parameters correlated with the long-term stability of anion exchange membrane water electrolyzers

In this study, we investigated the long-term stability of anion exchange membrane water electrolyzers (AEMWEs) under various bias conditions. The cell performance was relatively stable under conditions of voltage cycling in a narrow range, constant voltage and constant current. On the other hand, a relatively dynamic condition, voltage cycling, in a wide range detrimentally affected the cell stability. Abnormally high negative and positive currents were observed when the cell voltage was switched between 2.1 and 0 V. Impedance results and post-material analyses indicated that the performance degradation was mainly due to anode catalyst detachments, which increased non-ohmic resistance in the wide range voltage cycling. An increase in ohmic resistance was also observed, which was due to the membrane dehydration that occurred in the frequent rest times. Thus, it can be said that the voltage cycling range as well as the frequency of rest times are critical operational parameters in determining the long-term stability of AEMWEs.