Large Increase In Conductivity Research Articles

Intraspinally mediated state‐dependent enhancement of motoneurone excitability during fictive scratch in the adult decerebrate cat

This is the first study to report on the increase in motoneurone excitability during fictive scratch in adult decerebrate cats. Intracellular recordings from antidromically identified motoneurones revealed a decrease in the voltage threshold for spike initiation (V(th)), a suppression of motoneurone afterhyperpolarization and activation of voltage-dependent excitation at the onset of scratch. These state-dependent changes recovered within 10-20 s after scratch and could be evoked after acute transection of the spinal cord at C1. Thus, there is a powerful intraspinal system that can quickly and reversibly re-configure neuronal excitability during spinal network activation. Fictive scratch was evoked in spinal intact and transected decerebrate preparations by stroking the pinnae following topical curare application to the dorsal cervical spinal cord and neuromuscular block. Hyperpolarization of V(th) occurred (mean 5.8 mV) in about 80% of ipsilateral flexor, extensor or bifunctional motoneurones during fictive scratch. The decrease in V(th) began before any scratch-evoked motoneurone activity as well as during the initial phase in which extensors are tonically hyperpolarized. The V(th) of contralateral extensors depolarized by a mean of +3.7 mV during the tonic contralateral extensor activity accompanying ipsilateral scratch. There was a consistent and substantial reduction of afterhyperpolarization amplitude without large increases in motoneurone conductance in both spinal intact and transected preparations. Depolarizing current injection increased, and hyperpolarization decreased the amplitude of rhythmic scratch drive potentials in acute spinal preparations indicating that the spinal scratch-generating network can activate voltage-dependent conductances in motoneurones. The enhanced excitability in spinal preparations associated with fictive scratch indicates the existence of previously unrecognized, intraspinal mechanisms increasing motoneurone excitability.

Improving Thermoelectric Properties of Chemically Synthesized Bi2Te3-Based Nanocrystals by Annealing

The power factors of chemically synthesized Bi2Te3 and Bi0.5Sb1.5Te3 nanocrystals (NCs) were improved up to 2.4 and 7.8 μW cm−1 K−2, respectively, which are significantly higher than previously reported values for chemically synthesized Bi2Te3 NCs and even comparable to the recently reported highest power factor of 5 μW cm−1 K−2 for Bi2Te3 NCs consolidated by spark plasma sintering. This improvement was achieved by annealing the NCs under argon protection, and the crystal structures and morphologies of these annealed NCs were characterized via XRD, SEM, and TEM measurements. The temperature-dependent thermoelectric properties of these modified NCs were explored on cold-pressed pellets of NCs. Improvement of the thermoelectric performances of the pellets resulted primarily from an increase in electrical conductivity (σ), while only weakly increasing the lattice thermal conductivity (κL), which was still kept lower than bulk values. Hall carrier concentration studies suggest that the improvement of the electrical conductivity is caused primarily by modification of the charge carrier mobility rather than the carrier concentration. A mechanism is proposed to explain a large increase of electrical conductivity by annealing related to a decrease of activation energy for the mobility after the removal of organic capping ligands through annealing.

Visual patch clamp recording of neurons in thick portions of the adult spinal cord

The study of visually identified neurons in slice preparations from the central nervous system offers considerable advantages over in vivo preparations including high mechanical stability in the absence of anaesthesia and full control of the extracellular medium. However, because of their relative thinness, slices are not appropriate for investigating how individual neurons integrate synaptic inputs generated by large numbers of neurons. Here we took advantage of the exceptional resistance of the turtle to anoxia to make slices of increasing thicknesses (from 300 to 3000μm) from the lumbar enlargement of the spinal cord. With a conventional upright microscope in which the light condenser was carefully adjusted, we could visualize neurons present at the surface of the slice and record them with the whole-cell patch clamp technique. We show that neurons present in the middle of the preparation remain alive and capable of generating action potentials. By stimulating the lateral funiculus we can evoke intense synaptic activity associated with large increases in conductance of the recorded neurons. The conductance increases substantially more in neurons recorded in thick slices suggesting that the size of the network recruited with the stimulation increases with the thickness of the slices. We also find that that the number of spontaneous excitatory postsynaptic currents (EPSCs) is higher in thick slices compared with thin slices while the number of spontaneous inhibitory postsynaptic currents (IPSCs) remains constant. These preliminary data suggest that inhibitory and excitatory synaptic connections are balanced locally while excitation dominates long-range connections in the spinal cord.

Variation of power generation at different buffer types and conductivities in single chamber microbial fuel cells

Microbial fuel cells (MFCs) are operated with solutions containing various chemical species required for the growth of electrochemically active microorganisms including nutrients and vitamins, substrates, and chemical buffers. Many different buffers are used in laboratory media, but the effects of these buffers and their inherent electrolyte conductivities have not been examined relative to current generation in MFCs. We investigated the effect of several common buffers (phosphate, MES, HEPES, and PIPES) on power production in single chambered MFCs compared to a non-buffered control. At the same concentrations the buffers produced different solution conductivities which resulted in different ohmic resistances and power densities. Increasing the solution conductivities to the same values using NaCl produced comparable power densities for all buffers. Very large increases in conductivity resulted in a rapid voltage drop at high current densities. Our results suggest that solution conductivity at a specific pH for each buffer is more important in MFC studies than the buffer itself given relatively constant pH conditions. Based on our analysis of internal resistance and a set neutral pH, phosphate and PIPES are the most useful buffers of those examined here because pH was maintained close to the p K a of the buffer, maximizing the ability of the buffer to contribute to increase current generation at high power densities.

Photoinduced conductivity in tin dioxide thin films

The effects of ultraviolet light irradiation on the conducting properties of SnO2−x thin films grown epitaxially on TiO2 or Al2O3 single-crystal substrates are studied at room temperature. A large increase in conductivity by two to four orders of magnitude is observed with light irradiation in an inert atmosphere and remains after the light is removed. The high-conducting state reverts to the original low-conducting state by exposing it to oxygen gas. These reversible phenomena are ascribed to the desorption and adsorption of negatively charged oxygen species at the grain boundaries, which critically change the mobility of electron carriers already present inside grains by changing the potential barrier height at the grain boundary. The UV light irradiation provides us with an easy and useful route to achieve a high-conducting state even at low carrier density in transparent conducting oxides and also to draw an invisible conducting wire or a specific pattern on an insulating film.

Correlation Between Ion Diffusional Motion and Ionic Conductivity for Different Electrolytes Based on Ionic Liquid

Room temperature ionic liquid 2,3-dimethyl-1-hexylimidazolium bis(trifluoromethane sulfonyl)imide (DMHxImTFSI) has been synthesized and used in the preparation of polymer gel electrolytes containing polymethylmethacrylate and propylene carbonate (PC). The onset of ion diffusional motion has been studied by (1)H and (19)F NMR spectroscopy and the results obtained for ionic liquid, liquid electrolytes, and polymer gel electrolytes have been correlated with the ionic conductivity results for these electrolytes in the 100-400 K temperature range. The temperature at which (1)H and (19)F NMR lines show motional narrowing and hence ion diffusional motion starts has been found to be closely related to the temperature at which a large increase in ionic conductivity has been observed for these electrolytes. Polymer gel electrolytes have high ionic conductivity over a wide range of temperatures. Thermogravimetric analysis/differential scanning calorimetry studies show that the ionic liquid (DMHxImTFSI) used in the present study is thermally stable up to 400 degrees C, whereas the addition of PC lowers the thermal stability of polymer gel electrolytes containing the ionic liquid. Different electrolytes have been observed to show high ionic conductivity in different range of temperatures, which can be helpful in the design of polymer gel electrolytes for specific applications.

Thermal conductivity of polymer composites with close-packed structure of nano and micro fillers

Thermal conductivity of polymer composites with nano and micro fillers has been investigated numerically and experimentally. The nano fillers used were multi-walled carbon nanotubes (MWNTs) and alumina nanoparticles, and the spherical alumina particles were selected as the micro fillers. A periodic unit cell with a random close-packed structure was created using a packing algorithm that treat the micro filler as spheres. Finite element analyses were also performed to predict the potential of nano fillers to enhance thermal conductivity of the composites and to analyze the effect of microstructure of micro fillers. Additionally, the polymer composites with nano and micro fillers were made and the thermal conductivity of the composites were measured. The results showed that the addition of MWNTs to the matrix lead to a large increase in thermal conductivity of the composites. The proposed thermal model predicted a thermal conductivity in good agreement with experiment.

Electrolyte effects on hydrogen evolution and solution resistance in microbial electrolysis cells

Protonated weak acids commonly used in microbial electrolysis cell (MEC) solutions can affect the hydrogen evolution reaction (HER) through weak acid catalysis, and by lowering solution resistance between the anode and the cathode. Weak acid catalysis of the HER with protonated phosphate, acetate, and carbonate electrolyte species improved MEC performance by lowering the cathode's overpotential by up to 0.30 V at pH 5, compared to sodium chloride electrolytes. Deprotonation of weak acids into charged species at higher pHs improved MEC performance primarily by increasing the electrolyte's conductivity and therefore decreasing the solution resistance between electrodes. The potential contributions from weak acid catalysis and solution resistance were compared to determine whether a reactor would operate more efficiently at lower pH because of the HER, or at higher pH because of solution resistance. Phosphate and acetate electrolytes allowed the MEC to operate more efficiently under more acidic conditions (pH 5). Carbonate electrolytes increased performance from pH 5 to 9 due to a relatively large increases in conductivity. These results demonstrate that specific buffers can substantially contribute to MEC performance through both reduction in cathode overpotential and solution resistance.

Relative Abundance of Monovalent and Divalent Cations and the Impact of Desiccation on Geosynthetic Clay Liners

Laboratory experiments were conducted on a geosynthetic clay liner (GCL) containing Na–bentonite to determine how the swell index and hydraulic conductivity of GCLs are affected by wet-dry cycling with solutions having different relative abundance of monovalent and multivalent cations. Relative abundance of monovalent and multivalent cations was characterized by the RMD of the test solution, which is defined as the ratio of the total molarity of monovalent cations to the square root of the total molarity of multivalent cations at a given ionic strength. RMD was found to control the final swell index, relative abundance of monovalent and divalent cations in the final exchange complex, and the final hydraulic conductivity of bentonite exposed to wet-dry cycling. Ionic strength affects the number of wet-dry cycles required for a change in hydraulic conductivity to occur and the rate of change in swell index. Large increases in hydraulic conductivity and loss of swelling capacity occurred for solutions having...

Increases in core body temperature precede hot flashes in a prostate cancer patient

An effective and safe alternative treatment to hormone replacement therapy for hot flashes is needed for cancer patients. Interventions targeting the triggering mechanisms of hot flashes hold promise. Increases in core body temperature are a precursor of most hot flashes in women, and similar findings in prostate cancer patients undergoing androgen deprivation therapy would support further research in this area. We present preliminary findings of physiological changes in a prostate cancer patient with frequent hot flashes. Physiological changes in sternal skin conductance, heart rate, and core body temperature were continuously measured during two 3.5 h laboratory sessions. Perceived characteristics of hot flashes were recorded in a diary. Five hot flashes were reported during laboratory sessions. Severity and bother ratings were low. All hot flashes were accompanied by large increases in sternal skin conductance and moderate increases in heart rate. Core body temperature increased 0.11-0.32 degrees C prior to and fell 0.23-0.44 degrees C following the peak increase in skin conductance. This case study suggests that hot flashes in men may be preceded by increases in core body temperature. Identification of behavioral factors that raise core body temperature may lead to specific treatment strategies to reduce the frequency of hot flashes.

Effect of Different Dopants on Polymer Cholesteric Liquid Crystal Flakes

Two types of dopants are incorporated into polymer cholesteric liquid crystal (PCLC) materials to change their dielectric properties. Conductive dopants consisting of either carbon-based or metallic particles show large increases in composite conductivity with percolation thresholds of from 0.4 vol% to 30 vol%, depending on the size and shape of the dopant particles. Inorganic insulating dopants change the dielectric constant from 2 (neat PCLC) to < 10 at dopant levels of ∼ 30 vol%, accompanied by an increase in density. These composites offer opportunities for use of PCLC's as particles or flakes in reflective displays.

Effect of structural anisotropy on electronic conduction in delafossite tin doped copper indium oxide thin films

Sn doped CuInO2 thin films having a single delafossite phase have been synthesized by magnetron sputtering technique. A gradual decrease in the activation energy from 0.43 to about 0.10 eV and a large increase in conductivity are observed in Sn doped samples with increasing fraction of crystallites having (006) orientation due to an increase in substrate temperature. Due to thermally activated carrier transport along O-A-O layers and activated carrier generation along BO6 layers, crystallite orientation becomes a crucial factor in controlling the conduction in delafossite thin films.

High Carrier Density and Capacitance in TiO2 Nanotube Arrays Induced by Electrochemical Doping

The paper describes the electronic charging and conducting properties of vertically oriented TiO 2 nanotube arrays formed by anodization of Ti foil samples. The resulting films, composed of vertically oriented nanotubes approximately 10 mum long, wall thickness 22 nm, and pore diameter 56 nm, are analyzed using impedance spectroscopy and cyclic voltammetry. Depending on the electrochemical conditions two rather different electronic behaviors are observed. Nanotube array samples in basic medium show behavior analogous to that of nanoparticulate TiO 2 films used in dye-sensitized solar cells: a chemical capacitance and electronic conductivity that increase exponentially with bias potential indicating a displacement of the Fermi level. Nanotube array samples in acidic medium, or samples in a basic medium submitted to a strong negative bias, exhibit a large increase in capacitance and conductivity indicating Fermi level pinning. The contrasting behaviors are ascribed to proton intercalation of the TiO 2. Our results suggest a route for controlling the electronic properties of the ordered metal-oxide nanostructures for their use in applications including supercapacitors, dye-sensitized solar cells, and gas sensing.

Conducting Polymer Memory Devices Based on Dynamic Doping

Molecular electronic junctions consisting of a 20 nm thick layer of polypyrrole (PPy) and 10 nm of TiO2 between conducting layers of carbon and gold were investigated as potential nonvolatile memory devices. By making the polymer layer much thinner than conventional polymer electronic devices, it is possible to dynamically oxidize and reduce the polypyrrole layer by an applied bias. When the electrode in contact with the PPy is biased positive, oxidation of the PPy occurs to yield a conducting polaron state. The junctions exhibit a large increase in conductance in response to the positive bias, which is reversed by a subsequent negatively biased pulse. Switching between the conducting and nonconducting state can occur for pulses at least as short as 10 micros, and the conducting state persists after a positive bias pulse for at least 1 week. The read/write/read/erase cycle may be repeated for at least 1700 cycles, although with an error rate of approximately 3% due mainly to an incomplete "erase" step. The speed and retention of the PPy/TiO2 junctions are far superior to those of the analogous fluorene/TiO2 devices lacking the polymer, and the conductance changes are absent if SiO2 is substituted for TiO2. The observations are consistent with "dynamic doping" of the solid-state polymer layer, with the possible involvement of adventitious mobile ions. Although the speed of the current polymer/TiO2 junctions is slower than commercial dynamic random access memory, their retention is approximately 5 orders of magnitude longer.

Electrical conductivity of thin-film composites containing silver nanoparticles embedded in a dielectric fluoropolymer matrix

Thin-film nanocomposites, consisting of silver nanoparticles embedded in a dielectric fluoropolymer matrix (poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene]), were synthesized using vapor-phase co-deposition. The electrical conductivity of these composites was measured in-situ as a function of film thickness at various metal concentrations. At low metal concentrations (< 30%), dielectric behavior and very little change with film thickness were observed. At moderate to high silver loadings (30–80%) a large increase in electrical conductivity was observed as the films grew thicker. As the thickness increased further, the conductivity flattened out. At very high silver content (> 90%), fragmented fractal nanoclusters were able to further interconnect to achieve the percolation process and eventually evolve into a metallic continuum with dielectric polymer inclusions.

Variations in tissue resistivity and in the extension of activated neuron domains shape the voltage signal during spreading depression in the CA1 in vivo

Spreading depression (SD), a wave of neuron activity related to migraine and the ischaemic penumbra, features a moving shell of extracellular negative potential shift (V(o)) whose generators are poorly understood. We investigated its subcellular correlates in the hippocampal CA1 in vivo by localizing the neuron domains that generate transmembrane current (I(m)) using field analysis, and the local changes of tissue resistivity, a major determinant of extracellular current flow. A large increase of tissue resistivity occurred in times and dendritic strata displaying large V(o), albeit with different rates. Typically, SD is composed of basal and apical dendritic components. The apical SD lasts much longer, while it becomes gradually restricted to a narrow dendritic region. Strikingly, pyramidal cells displayed a strong surge of inward current only when SD affected a small dendritic region. However, when the V(o) signal covered most of the main neuron axis, only smaller surges of inward current developed at the outer dendritic rims of a wide null current zone. Computational reconstruction showed that this effect was due to strong spatial cancellation of the inward and outward currents in SD-activated isopotential and shunted regions of individual neurons. Consequently, despite former accounts of large conductance increase, the net I(m) is small and the large DeltaV(o) amplitude mostly due to increased tissue resistivity. The particular subcellular evolution indicates an initial explosive opening of conductance along most of the pyramidal neuron followed by a wave-like centripetal closure towards the apical dendrites. The applicability of these mechanisms to SD in other brain regions is discussed.

Effect of carbon black concentration on electrical conductivity of epoxy resin–carbon black–silica nanocomposites

This work presents an insight into the conductivity-carbon black (CB) concentration relationship of nanocomposites. High conductivity is observed above 14% CB loading (% on mass of epoxy resin), indicating the generation of conductive networks throughout the nanocomposites. Observation of the relationship between the natural logarithm of conductivity values versus CB loading shows a remarkable increase in conductivity when the CB loading increases from 19 to 24%. In this region (percolation) a relatively small increase in CB loading produces a large increase in conductivity. When the quantity of CB is low ( 24%) causes marginal change in conductivity. The uniformity of the nanocomposites is evidenced by both microstructure (Si-mapping) and macro-property (resistance versus distance relationship) analyses.

Behavioral and Neural Responses of Toads to Salt Solutions Correlate with Basolateral Membrane Potential of Epidermal Cells of the Skin

Dehydrated toads initiated water absorption response (WR) behavior and absorbed water from dilute NaCl solutions. With 200-250 mM NaCl, WR behavior and water absorption were both suppressed. With 200-250 mM Na-gluconate, WR initiation was significantly greater than with NaCl but water loss was greater. Neural recordings from spinal nerve #6 showed a greater integrated response to 250 mM NaCl than to 250 mM Na-gluconate, whereas a larger rinse response was seen with Na-gluconate. Studies with isolated epithelium showed a large increase in conductance (G(t)) when 250 mM NaCl replaced NaCl Ringer's as the apical bathing solution that was accompanied by depolarization of the transepithelial potential (V(t)) and basolateral membrane potential (V(b)). Depolarization of V(b) corresponded with the neural response to 250 mM NaCl. When 250 mM Na-gluconate replaced Ringer's as the apical solution G(t) remained low, V(b) transiently hyperpolarized to values near the equilibrium potential for K(+) and corresponded with the reduced neural response. These results support the hypothesis that chemosensory function of the skin is analogous to that of mammalian taste cells but utilizes paracellular ion transport to a greater degree.

Palytoxin Acts on Na+,K+-ATPase but not Nongastric H+,K+-ATPase

Palytoxin (PTX) opens a pathway for ions to pass through Na,K-ATPase. We investigate here whether PTX also acts on nongastric H,K-ATPases. The following combinations of cRNA were expressed in Xenopus laevis oocytes: Bufo marinus bladder H,K-ATPase alpha(2)- and Na,K-ATPase beta(2)-subunits; Bufo Na,K-ATPase alpha(1)- and Na,K-ATPase beta(2)-subunits; and Bufo Na,K-ATPase beta(2)-subunit alone. The response to PTX was measured after blocking endogenous Xenopus Na,K-ATPase with 10 microM ouabain. Functional expression was confirmed by measuring (86)Rb uptake. PTX (5 nM: ) produced a large increase of membrane conductance in oocytes expressing Bufo Na,K-ATPase, but no significant increase occurred in oocytes expressing Bufo H,K-ATPase or in those injected with Bufo beta(2)-subunit alone. Expression of the following combinations of cDNA was investigated in HeLa cells: rat colonic H,K-ATPase alpha(1)-subunit and Na,K-ATPase beta(1)-subunit; rat Na,K-ATPase alpha(2)-subunit and Na,K-ATPase beta(2)-subunit; and rat Na,K-ATPase beta(1)- or Na,K-ATPase beta(2)-subunit alone. Measurement of increases in (86)Rb uptake confirmed that both rat Na,K and H,K pumps were functional in HeLa cells expressing rat colonic HKalpha(1)/NKbeta(1) and NKalpha(2)/NKbeta(2). Whole-cell patch-clamp measurements in HeLa cells expressing rat colonic HKalpha(1)/NKbeta(1) exposed to 100 nM PTX showed no significant increase of membrane current, and there was no membrane conductance increase in HeLa cells transfected with rat NKbeta(1)- or rat NKbeta(2)-subunit alone. However, in HeLa cells expressing rat NKalpha(2)/NKbeta(2), outward current was observed after pump activation by 20 mM K(+) and a large membrane conductance increase occurred after 100 nM PTX. We conclude that nongastric H,K-ATPases are not sensitive to PTX when expressed in these cells, whereas PTX does act on Na,K-ATPase.

Optical Switching of Porphyrin-Coated Silicon Nanowire Field Effect Transistors

We study porphyrin derivative coated silicon nanowire field effect transistors (SiNW-FETs), which display a large, stable, and reproducible conductance increase upon illumination. The efficiency and the kinetics of the optical switching are studied as a function of gate voltage, illumination wavelength, and temperature. The decay kinetics from the high- to the low-conductance state is governed by charge recombination via tunneling, with a rate depending on the state of the SiNW-FET. The comparison to porphyrin-sensitized carbon nanotube FETs allows the environment- and molecule-dependent photoconversion process to be distinguished from the charge-to-current transducing effect of the semiconducting channel.