Showing papers on "Conductance published in 1996"
TL;DR: It is observed that deformation occurs as a sequence of structural transformations involving elastic and yielding stages and that force and conductance before rupture have definite values which are likely to correspond to a single atom contact.
Abstract: Measuring simultaneously the force and the conductance during the formation and rupture of an atomic-sized gold contact at room temperature, we observe that deformation occurs as a sequence of structural transformations involving elastic and yielding stages and that force and conductance before rupture have definite values which are likely to correspond to a single atom contact. We measure the mechanical properties of contacts consisting of only a few atoms and show that the stepwise variation of the conductance is always due to the atomic rearrangements in the contact.
451 citations
TL;DR: The one-dimensional to two-dimensional crossover in these systems is examined and the existence of metallic tube junctions in which the conductance is suppressed for symmetry reasons is shown.
Abstract: We study the conductance of metallic carbon nanotubes with vacancies and pentagon-heptagon pair defects within the Landauer formalism. Using a tight-binding model and a Green's function technique to calculate the scattering matrix, we examine the one-dimensional to two-dimensional crossover in these systems and show the existence of metallic tube junctions in which the conductance is suppressed for symmetry reasons. \textcopyright{} 1996 The American Physical Society.
421 citations
TL;DR: Electrical resistance measurements of an individual carbon nanotube down to a temperature T = 20 mK find a global and coherent interpretation in terms of two-dimensional weak localization and universal conductance fluctuations in mesoscopic conductors.
Abstract: We report on electrical resistance measurements of an individual carbon nanotube down to a temperature T = 20 mK. The conductance exhibits a lnT dependence and saturates at low temperature. A magnetic field applied perpendicular to the tube axis increases the conductance and produces aperiodic fluctuations. The data find a global and coherent interpretation in terms of two-dimensional weak localization and universal conductance fluctuations in mesoscopic conductors. The dimensionality of the electronic system is discussed in terms of the peculiar structure of carbon nanotubes.
414 citations
TL;DR: The transport properties of high-quality quantum wires fabricated in GaAs-AlGaAs by using cleaved edge overgrowth are measured and several aspects of the data can be explained qualitatively using Luttinger liquid theory although there remain major inconsistencies with such an interpretation.
Abstract: We have measured the transport properties of high-quality quantum wires fabricated in GaAs-AlGaAs by using cleaved edge overgrowth. The low temperature conductance is quantized as the electron density in the wire is varied. While the values of the conductance plateaus are reproducible, they deviate from multiples of the universal value of ${2e}^{2}/h$ by as much as 25%. As the temperature or dc bias increases the conductance steps approach the universal value. Several aspects of the data can be explained qualitatively using Luttinger liquid theory although there remain major inconsistencies with such an interpretation.
328 citations
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01 Jan 1996
TL;DR: In this paper, thermal constriction resistance and solid spot thermal conductance of a joint are investigated. But they do not consider the effect of gas gap conductance on the performance of the joint.
Abstract: Contents: Introduction.- Thermal Constriction Resistance.- Solid Spot Thermal Conductance of a Joint.- Gas Gap Conductance.
325 citations
TL;DR: It is shown that the conductance spectra are a function not only of the amplitudes of pair potentials but also of their phases as well as the local density of states of superconductors.
Abstract: A theory for the tunneling spectroscopy of a normal-metal--insulator--anisotropic-superconductor (N-I-S) junction is presented. In anisotropic superconductors, the effective pair potential felt by the quasiparticles depends on their wave vectors in contrast to the case of isotropic s-wave superconductors. By introducing the effect into the Blonder-Tinkham-Klapwidjk formula, a conductance formula for N-I-S junctions is obtained. It is shown that the conductance spectra are a function not only of the amplitudes of pair potentials but also of their phases. Tunneling conductance spectra calculated for various symmetries strongly depend on the relation between the tunneling direction and crystalline axes. In some crystalline angle regions of d-wave superconductors, a zero-energy peak in the conductance spectra is calculated. This conductance peak reflects the existence of anomalous bound states around the insulator--anisotropic-superconductor interface. The relation between the tunneling conductance spectra and the local density of states of superconductors is discussed. \textcopyright{} 1996 The American Physical Society.
270 citations
TL;DR: The often held contention that channel conductance and ionic or molecular selectivity are inversely proportional is refuted by recent evidence from five distinct connexin channels.
Abstract: Gap junction channels have long been viewed as static structures containing a large-diameter, aqueous pore. This pore has a high permeability to hydrophilic molecules of approximately 900 daltons in molecular weight and a weak ionic selectivity. The evidence leading to these conclusions is reviewed in the context of more recent observations primarily coming from unitary channel recordings from transfected connexin channels expressed in communication-deficient cell lines. What is emerging is a more diverse view of connexin-specific gap junction channel structure and function where electrical conductance, ionic selectivity, and dye permeability vary by one full order of magnitude or more. furthermore, the often held contention that channel conductance and ionic or molecular selectivity are inversely proportional is refuted by recent evidence from five distinct connexin channels. The molecular basis for this diversity of channel function remains to be identified for the connexin family of gap junction proteins.
236 citations
TL;DR: The Coulomb blockade was used to determine the ground-state charge configuration within the “molecule” as a function of the total charge on the double dot and the interdot polarization induced by electrostatic gates.
Abstract: Individual quantum dots are often referred to as “artificial atoms.” Two tunnel-coupled quantum dots can be considered an “artificial molecule.” Low-temperature measurements were made on a series double quantum dot with adjustable interdot tunnel conductance that was fabricated in a gallium arsenide-aluminum gallium arsenide heterostructure. The Coulomb blockade was used to determine the ground-state charge configuration within the “molecule” as a function of the total charge on the double dot and the interdot polarization induced by electrostatic gates. As the tunnel conductance between the two dots is increased from near zero to 2 e 2 / h (where e is the electron charge and h is Planck9s constant), the measured conductance peaks of the double dot exhibit pronounced changes in agreement with many-body theory.
220 citations
TL;DR: It is concluded that the protonation site in L-type Ca2+ channels lies within the pore and is formed by a combination of conserved P-region glutamates in repeats I, II, and III, acting in concert.
Abstract: Hydrogen ions are important regulators of ion flux through voltage-gated Ca2+ channels but their site of action has been controversial. To identify molecular determinants of proton block of L-type Ca2+ channels, we combined site-directed mutagenesis and unitary current recordings from wild-type (WT) and mutant L-type Ca2+ channels expressed in Xenopus oocytes. WT channels in 150 mM K+ displayed two conductance states, deprotonated (140 pS) and protonated (45 pS), as found previously in native L-type Ca2+ channels. Proton block was altered in a unique fashion by mutation of each of the four P-region glutamates (EI-EIV) that form the locus of high affinity Ca2+ interaction. Glu(E)-->Gln(Q) substitution in either repeats I or III abolished the high-conductance state, as if the titration site had become permanently protonated. While the EIQ mutant displayed only an approximately 40 pS conductance, the EIIIQ mutant showed the approximately 40 pS conductance plus additional pH-sensitive transitions to an even lower conductance level. The EIVQ mutant exhibited the same deprotonated and protonated conductance states as WT, but with an accelerated rate of deprotonation. The EIIQ mutant was unusual in exhibiting three conductance states (approximately 145, 102, 50 pS, respectively). Occupancy of the low conductance state increased with external acidification, albeit much higher proton concentration was required than for WT. In contrast, the equilibrium between medium and high conductance levels was apparently pH-insensitive. We concluded that the protonation site in L-type Ca2+ channels lies within the pore and is formed by a combination of conserved P-region glutamates in repeats I, II, and III, acting in concert. EIV lies to the cytoplasmic side of the site but exerts an additional stabilizing influence on protonation, most likely via electrostatic interaction. These findings are likely to hold for all voltage-gated Ca2+ channels and provide a simple molecular explanation for the modulatory effect of H+ ions on open channel flux and the competition between H+ ions and permeant divalent cations. The characteristics of H+ interactions advanced our picture of the functional interplay between P-region glutamates, with important implications for the mechanism of Ca2+ selectivity and permeation.
145 citations
TL;DR: In this paper, the interplay between cell turgor pressure and electrical properties of the cell: membrane potential, conductance, cell-to-cell coupling, and input resistance was examined.
Abstract: Actively growing Arabidopsis thaliana L. (Columbia wild type) root hairs were used to examine the interplay between cell turgor pressure and electrical properties of the cell: membrane potential, conductance, cell-to-cell coupling, and input resistance. Pressure was directly modulated using a pressure probe or indirectly by changing the extracellular osmolarity. Direct modulation of pressure in the range of 0 to about 15 x 10(5) Pa (normal turgor pressure was 6.8 +/- 2.0 x 10(5) Pa, n = 29) did not affect the membrane potential, conductance, coupling, or input resistance. Indirect modulation of turgor pressure by adding (hyperosmotic) or removing (hypo-osmotic) 200 mM mannitol/sorbitol affected the potential and conductance but not cell-to-cell coupling. Hypo-osmotic treatment depolarized the potential about 40 mV from an initial potential of about -190 mV and increased membrane conductance, consistent with an increase in anion efflux from the cell. Hyperosmotic treatment hyperpolarized the cell about 25 mV from the same initial potential and decreased conductance, consistent with a decline in cation influx. The results are likely due to the presence of an "osmo-sensor," rather than a "turgor-sensor," regulating the cell's response to osmotic stress.
102 citations
TL;DR: In this paper, the thermal conductivity and thermal contact conductance of thermoplastic and thermosetting polymers have been studied over a range of interface pressures and temperatures, and it was shown that ultra high molecular weight (UHMW) polyethylene had the highest thermal conductivities through the range of temperatures and also had a higher interface temperature of 20°C (68°F).
Abstract: The thermal conductivity and thermal contact conductance of several thermoplastic and thermosetting polymers have been studied over a range of interface pressures and temperatures. The temperature range for the thermal conductivity study varied from 10 to 100°C (50 to 212°F). The study showed that ultra high molecular weight (UHMW) polyethylene had the highest thermal conductivity through the range of temperatures and also had the highest thermal conductance values at an interface temperature of 20°C (68°F). The thermal contact conductance study was conducted over a pressure range of 510-2760 kPa (75-400 psi) and a temperature range of 20-40°C (68-104°F). The conductance values for UHMW polyethylene ranged from 1095.3 to 1659.4 W/m2 K (192.9 to 292.2 Btu/h ft2 °F), whereas the thermal conductivity remained constant at 0.45 W/m K (0.26 Btu/h ft °F) throughout the range of temperatures. Polycarbonate and Teflon® had the next highest thermal conductance values at the same interface temperature. The thermal contact conductance values for polyethylene, Teflon, and phenolic polymers were measured at an elevated temperature of 40°C (104°F). The thermal contact conductance values for both Teflon and phenolic increased with increasing temperature, whereas the values for UHMW polyethylene decreased due to their unique chain structure at the higher temperature. The polymers were chosen because of their widespread engineering interest applications.
TL;DR: Single L‐type calcium channels in chick ciliary ganglion neurons were studied at high current resolution in cell‐attached patch recordings using quartz‐glass micropipettes to optimize the responsiveness of the cell to small changes in ambient calcium concentrations while limiting excess entry in the presence of abnormally high calcium levels.
Abstract: 1. Single L-type calcium channels in chick ciliary ganglion neurons were studied at high current resolution in cell-attached patch recordings using quartz-glass micropipettes. 2. A single open-channel current amplitude was observed when Ba2+ was the charge carrier with a conductance of 26 pS at 110 mM barium. However, with 110 mM calcium two current fluctuation amplitudes were observed. These were termed low and high fluctuation amplitudes, CaL and CaH, and had conductances of 8.8 and 12 pS, respectively. These two levels probably reflect two different channel species. CaL was identified as an L-type calcium channel on the basis of resistance to inactivation, conductance, and dihydropyridine sensitivity. 3. Single-channel current fluctuations could be detected with calcium concentrations as low as 1.0 mM. Although the unitary conductance (gamma) was much greater with barium than calcium at every concentration tested, the concentration dependence of conductance was similar for gamma Ba, gamma CaH and gamma CaL. Fitting the concentration dependencies of these conductances with a Langmuir isotherm gave KD estimates of 4.7, 5.6 and 5.0 mM for barium, CaL and CaH, respectively 4. The single-channel conductance of the L-type channel (gamma L) can be described by the relation: conductance (in pS) = 9.2/(1 + 5.6/[Ca]) where [Ca] is the external calcium concentration in the 1.0-110 mM range. Thus, at a physiological external calcium concentration of 2 mM the conductance is 2.4 pS. 5. Ca2+ transport through the L-type calcium channel is particularly sensitive to changes in external calcium concentration in the physiological range but approaches saturation at about 10 mM. this characteristic may optimize the responsiveness of the cell to small changes in ambient calcium concentrations while limiting excess entry in the presence of abnormally high calcium levels.
TL;DR: The whole-cell patch-clamp recording technique was used to measure volume-activated currents in K+-free solutions in RINm5F and HIT-T15 insulinoma cells and in dispersed rat islet cells, providing evidence for aVolume-activated anion conductance in insulin-secreting cells which could be involved in the RVD following osmotic stress.
Abstract: The whole-cell patch-clamp recording technique was used to measure volume-activated currents in K+-free solutions in RINm5F and HIT-T15 insulinoma cells and in dispersed rat islet cells. Cell swelling, induced by intracellular hypertonicity or extracellular hypotonicity, caused activation of an outwardly rectifying conductance which could be subsequently inactivated by hypertonic extracellular solutions. The conductance required adenosine 5′-triphosphate (ATP) in the pipette solution but was Ca2+ independent. Na+ and Cl− substitution studies suggested that the swelling-activated current is Cl− selective with a halide permeability sequence of Br > Cl > 1. The conductance was reversibly inhibited by the anion channel inhibitors 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS) and by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). Further evidence for a volume-activated anion conductance was provided by studies of volume regulation in insulin-secreting cells. When RINm5F cells were exposed to a hypotonic medium, the initial cell swelling was followed by a regulatory volume decrease (RVD). This RVD response was also inhibited by DIDS and by NPPB. These data therefore provide evidence for a volume-activated anion conductance in insulin-secreting cells which could be involved in the RVD following osmotic stress. A possible role for the conductance in hypotonically induced insulin release is also discussed.
TL;DR: GP64-mediated pores do not flicker, can have large, stable initial pore conductances lasting up to a minute, and have typical lag times of < 1 s, unlike previously measured fusion pores.
Abstract: The formation of the fusion pore is the first detectable event in membrane fusion (Zimmerberg, J., R. Blumenthal, D.P. Sarkar, M. Curran, and S.J. Morris. 1994. J. Cell Biol. 127:1885-1894). To date, fusion pores measured in exocytosis and viral fusion have shared features that include reversible closure (flickering), highly fluctuating semistable stages, and a lag time of at least several seconds between the triggering and the pore opening. We investigated baculovirus GP64-induced Sf9 cell-cell fusion, triggered by external acid solution, using two different electrophysiological techniques: double whole-cell recording (for high time resolution, model-independent measurements), and the more conventional time-resolved admittance recordings. Both methods gave essentially the same results, thus validating the use of the admittance measurements for fusion pore conductance calculations. Fusion was first detected by abrupt pore formation with a wide distribution of initial conductance, centered around 1 nS. Often the initial fusion pore conductance was stable for many seconds. Fluctuations in semistable conductances were much less than those of other fusion pores. The waiting time distribution, measured between pH onset and initial pore appearance, fits best to a model with many (approximately 19) independent elements. Thus, unlike previously measured fusion pores, GP64-mediated pores do not flicker, can have large, stable initial pore conductances lasting up to a minute, and have typical lag times of < 1 s. These findings are consistent with a barrel-shaped model of an initial fusion pore consisting of five to eight GP64 trimers that is lined with lipid.
TL;DR: Single-channel events produced by neurotransmitter transporters indicate the functional and structural similarities between transporter and ion channels and provide a new tool, at single-molecule resolution, for detailed structure-function studies of transporers.
TL;DR: It is found that the combined TappingMode atomic force microscope and scanning ion conductance microscope provided higher contrast and less apparent sample damage in the topographic and ionic conductance images in the tapping mode.
TL;DR: It is proposed that the main function of the outwardly rectifying anion channel is nonselective transport of organic solutes in mammalian cells, and increases in cell Cl- levels increase the volume set point of the channel.
Abstract: Cell swelling activates an outwardly rectifying anion conductance in mammalian cells. The channel responsible for this conductance mediates volume-regulatory efflux of organic osmolytes such as tau...
TL;DR: Differences between conductance steps for noble and transition metals are interpreted as being due to the d orbitals that, in transition metals, provide new channels to the electron conductance.
Abstract: Conductance steps for atomic point contacts of Au, Ni, and Pt have been measured. Jump-to-contact and jump-to-tunnel processes have been identified and their conductances measured. Differences between conductance steps for noble and transition metals are interpreted as being due to the d orbitals that, in transition metals, provide new channels to the electron conductance. This interpretation is supported by a theoretical analysis, which shows good agreement with the experimental data. @S0163-1829~96!03323-1#
TL;DR: In this article, the electrical properties of the Pb center have been measured using the conductance technique over the temperature range 130-290 K. A high concentration of Pb centers was created by vacuum annealing of 28nm-thick thermal oxides on (111) silicon surfaces.
Abstract: The electrical properties of the Pb center have been measured using the conductance technique over the temperature range 130–290 K. A high concentration of Pb centers was created by vacuum annealing of 28‐nm‐thick thermal oxides on (111) silicon surfaces. Fitting the conductance data allowed the contribution of the (0/−) Pb level to be separated from the U‐shaped background states. The (0/−) peak in the density of states was found to be asymmetrical with a broad shoulder on the conduction band side. The Pb levels were found to show a capture cross section which fell toward the band edges and which could be fitted by assuming an activated cross section with an activation energy which increased toward the band edges. By contrast, the background states showed a cross section which was temperature and band bending independent.
TL;DR: Using the planar lipid bilayer technique, it is demonstrated that the lipodepsipeptide antibiotic, syringomycin E, forms voltage-sensitive ion channels of weak anion selectivity, suggesting that at least six monomers are required for channel formation.
Abstract: Using the planar lipid bilayer technique we demonstrate that the lipodepsipeptide antibiotic, syringomycin E, forms voltage-sensitive ion channels of weak anion selectivity. The formation of channels in bilayers made from dioleoylglycerophosphatidylserine doped with syringomycin E at one side (1–40 μg/ml) was greatly affected by cis-positive voltage. A change of voltage from a positive to a negative value resulted in (i) an abrupt increase in the single channel conductance (the rate of increase was voltage dependent) simultaneous with (ii) a closing of these channels and an exponential decrease in macroscopic conductance over time. The strong voltage dependence of multichannel steady state conductance, the single channel conductance, the rate of opening of channels at positive voltages and closing them at negative voltages, as well as the observed abrupt increase of single channel conductance after voltage sign reversal suggest that the change of the transmembrane field induces a significant rearrangement of syringomycin E channels, including a change in the spacing of charged groups that function as voltage sensors. The conductance induced by syringomycin E increased with the sixth power of syringomycin E concentration suggesting that at least six monomers are required for channel formation.
TL;DR: A new algorithm is presented for idealizing single channel data containing any number of conductance levels and this "interpretation" allows a statistical analysis of individual (sub)conductance states.
TL;DR: In this article, the authors analyzed the conductance transient of a Taguchi TGS-822 sensor under a step change in the vapour concentration and found that a diffusion-limited range in the transient is observed, which can give useful information for gas/vapour recognition.
Abstract: In this paper, we analyse the conductance transient of a Taguchi TGS-822 sensor under a step change in the vapour concentration. A diffusion-limited range in the conductance transient is observed. Adjustments between the theoretical calculations based on a non-linear diffusion-reaction model and the experimental results alloy a constant, τ′, to be estimated, which is independent of the final conductance value and depends, among other parameters, on the effective diffusion coefficients of vapours in the porous tin oxide sensor. From transient measurements of organic solvents (benzene and o-xylene) we have obtained τ′ values that are independent of concentration and characteristic for each vapour. This new parameter can give useful information for gas/vapour recognition.
TL;DR: The shapes of the Coulomb blockade peaks in conductance as a function of gate voltage are found and this suppression is a manifestation of the Anderson orthogonality catastrophe associated with the charge redistribution between the dots.
Abstract: We study the Coulomb blockade of tunneling through a double quantum dot. The temperature dependence of the linear conductance is strongly affected by the interdot tunneling. As the tunneling grows, a crossover from temperature-independent peak conductance to a power-law suppression of conductance at low temperatures is predicted. This suppression is a manifestation of the Anderson orthogonality catastrophe associated with the charge redistribution between the dots, which accompanies the tunneling of an electron into a dot. We find analytically the shapes of the Coulomb blockade peaks in conductance as a function of gate voltage. \textcopyright{} 1996 The American Physical Society.
TL;DR: It is concluded that in the neuronal alpha 1E the charge movement is tightly coupled with the pore opening and that the beta 2a subunit coexpression further improves this coupling.
Abstract: 1. Neuronal alpha 1E Ca2+ channels were expressed alone and in combination with the beta 2a subunit in Xenopus laevis oocytes. 2. The properties of ionic and gating currents of alpha 1E were investigated: ionic currents were measured in 10 mM external Ba2+; gating currents were isolated in 2 mM external Co2+. 3. Charge movement preceded channel opening. The charge movement voltage curve (Q(V)) preceded the ionic conductance voltage dependence (G(V)) by approximately 20 mV. 4. Coexpression of alpha 1E with the beta 2a subunit did not modify the voltage dependence of charge movement but shifted the G(V) curve to more negative potentials. The voltage gap between Q(V) and G(V) curves was reduced by the beta 2a subunit and both curves overlapped at potentials near 0 mV. 5. The coupling efficiency between the charge movement and pore opening was estimated by the ration between limiting conductance and maximum charge movement (Gmax/Qmax). Coexpression of the beta 2a subunit increased the Gmax/Qmax ratio from 9.2 x 10(5) +/- 1.4 x 10(5) to 21.9 x 10(5) +/- 2.8 X 10(5) S C-1 for alpha 1E and alpha 1E + beta 2a, respectively. 6. We conclude that in the neuronal alpha 1E the charge movement is tightly coupled with the pore opening and that the beta 2a subunit coexpression further improves this coupling.
TL;DR: A simple model for the evolution of atomic-scale metallic contacts together with exact free-electron calculations of the conductance during an elongation-contraction process, inspired by the results of MD simulations as well as by the recent experiments on contact nanomechanics.
Abstract: We present a simple model for the evolution of atomic-scale metallic contacts together with exact free-electron calculations of the conductance during an elongation-contraction process. The critical pressure that the neck can sustain before yielding is constant. Shortly before the neck breaks the pressure gradually increases up to a maximum for a single-atom contact. In force microscopy experiments this maximum value also depends on the cantilever constant. Conductance histograms show clear peaks at integer multiples of ${2e}^{2}/h$ slightly shifted to lower values.
TL;DR: This work studies the relation between the barrier conductance and the Coulomb blockade peak splitting for two electrostatically equivalent dots connected by tunneling channels with bandwidths much larger than the dot charging energies.
Abstract: We study the relation between the barrier conductance and the Coulomb blockade peak splitting for two electrostatically equivalent dots connected by tunneling channels with bandwidths much larger than the dot charging energies. We find that this problem is equivalent to a well-known single-dot problem and present solutions for the relation between peak splitting and barrier conductance in both the weak- and strong-coupling limits. Results are in good qualitative agreement with the experimental findings of Waugh et al. \textcopyright{} 1996 The American Physical Society.
TL;DR: The NT response could be elicited after desensitizing the responses to these other neurotransmitters, indicating receptor specificity in the activation of the nonselective conductance.
Abstract: 1. A widespread mechanism of slow excitation throughout the nervous system involves overlapping changes in nonselective ion conductance and K+ conductance. We used whole cell patch-clamp recording to characterize such a nonselective conductance induced by neurotensin (NT) and other neurotransmitters in immunocytochemically identified dopaminergic neurons cultured from the rat ventral tegmental area (VTA). 2. The NT-induced inward current consisted of an initial peak and later "hump." The response was blocked reversibly by the nonpeptide NT-receptor antagonist SR48692, suggesting that it resulted from activation of NT receptors. 3. The channel was almost equally permeable to Na+ and K+, as determined from the reversal potential shift upon switching from Na+- to K(+)-containing external solution. The permeability of Cs+ was similar to that of Na+, as determined from the zero-current equation and average reversal potential in the 75 mM Na+ solution. Cl- was not significantly permeable. 4. In Ca(2+)-free external solution, the NT-induced current showed a fourfold increase in amplitude, and in high Mg2+ (20 mM) external solution, the NT-induced current showed an 80% decrease in amplitude, suggesting that external Ca2+ and Mg2+ could block the nonselective conductance. 5. The NT response was unaffected by loading the neurons with either the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or with 1 mM ca2+. The nonselective conductance was therefore not Ca2+ activated. 6. Loading the neurons with cyclic GMP or cyclic AMP (each with the phosphodiesterase inhibitor isobutyl-methylxanthine) did not affect the NT response. The NT-induced nonselective conductance was therefore not cyclic nucleotide-activated. 7. The latency of the NT response was long (> or = 185 ms, average 406 ms, 30 degrees C), indicating that NT did not induce the conductance through ligand-gated channels. Thus, NT activated a slow nonselective cation conductance. 8. Neurokinin B, a metabotropic glutamate agonist, and muscarine elicited responses similar to the NT response. The NT response could be elicited after desensitizing the responses to these other neurotransmitters, indicating receptor specificity in the activation of the nonselective conductance.
TL;DR: A nonsymmetrical two-site three-barrier model can qualitatively explain both the I-V relations and the [K+] dependence of conductance of open IRK1 (Kir2.1) channels.
TL;DR: In this paper, the pull off of a Au contact at a temperature of 1 K was simulated and the conductance and tensile force on the contact were calculated throughout the pull-off.
Abstract: We have performed dynamic simulations of the pull off of a Au contact at a temperature of 1 K The conductance and the tensile force on the contact are calculated throughout the pull off There are prominent jumps both in the conductance and in the force The force and conductance jumps generally coincide with each other, and correspond to abrupt atomic rearrangements in the contact The correlation between the force and conductance jumps and the effective spring constant of the contact during pull off are in agreement with recent experiments \textcopyright{} 1996 The American Physical Society
TL;DR: In this article, the nitrogen levels in 4H-SiC were determined using thermal admittance spectroscopy, and it was inferred from a comparison with 6H−SiC that the conductance peak b4 is due to excitation of electrons from the vanadium donor at Ec−1.73 eV.
Abstract: The nitrogen levels in 4H‐SiC have been determined using thermal admittance spectroscopy. The values of Ec−0.053 eV for nitrogen at the hexagonal site and Ec−0.10 eV for nitrogen at the quasicubic site agree with those reported using other techniques. The deep levels in 4H‐SiC were studied using optical admittance spectroscopy. The optical admittance spectrum showed, besides the conductance peak corresponding to band to band transitions, four other conductance peaks. These peaks correspond to photoexcitation of carriers from the defect levels to the conduction band. It is inferred from a comparison with 6H‐SiC that the conductance peak b4 is due to excitation of electrons from the vanadium donor at Ec−1.73 eV. The photoconductance build up transients of the Ec−1.73 eV level are described fully by one exponential term. This suggests that only one center contributed to the observed conductance. The decay kinetics of persistent photoconductance due to the Ec−1.73 eV level follow the stretched exponential for...