Conductance

We present an experimental study of charge transport through single oligo(phenylene-ethynylene) (OPE3) molecules and anthracene substituted OPE3 (OPE3-AC) contacted with a mechanically controlled break junction. Both molecules are measured using two different methods. In the first approach, we measure the low-bias conductance, while the junction is repeatedly broken and fused. In the second approach, instead of applying a fixed bias, we record current-voltage characteristics. For both approaches the data is fitted to a model describing transport through a single level, and information about the level alignment and the electronic coupling to the electrodes is extracted. We find that the electronic coupling is similar for both molecules, but that the level alignment differs. The observed trends are confirmed by quantum chemistry calculations.

Polymers are important as materials for manufacturing microfluidic devices for electrodriven separations, in which Joule heating is an unavoidable phenomenon. Heating effects were investigated in polymer capillaries using a CE setup. This study is the first step toward the longer-term objective of the study of heating effects occurring in polymeric microfluidic devices. The thermal conductivity of polymers is much smaller than that of fused silica (FS), resulting in less efficient dissipation of heat in polymeric capillaries. This study used conductance measurements as a temperature probe to determine the mean electrolyte temperatures in CE capillaries of different materials. Values for mean electrolyte temperatures in capillaries made of New Generation FluoroPolymer (NGFP), poly-(methylmethacrylate) (PMMA), and poly(ether ether ketone) (PEEK) capillaries were compared with those obtained for FS capillaries. Extrapolation of plots of conductance versus power per unit length (P/L) to zero power was used to obtain conductance values free of Joule heating effects. The ratio of the measured conductance values at different power levels to the conductance at zero power was used to determine the mean temperature of the electrolyte. For each type of capillary material, it was found that the average increase in the mean temperature of the electrolyte (DT Mean ) was directly proportional to P/L and inversely proportional to the thermal conductivity (l) of the capillary material. At 7.5 W/m, values for DT Mean for NGFP, PMMA, and PEEK were determined to be 36.6, 33.8, and 30.77C, respectively. Under identical conditions, DT Mean for FS capillaries was 20.47C.

The electrical conductivity of blood is sufficiently higher than that of myocardium to make feasible the detection of cardiac volume changes by measurement of intraventricular fluid conductance. An eight-electrode catheter was used to inject an alternating current (100 microA or less, at 1500 Hz) via the two electrodes nearest the ventricular base and apex, then the resulting five voltage differences between adjacent pairs of the six intervening electrodes were measured. When current amplitude was held constant, the cross-sectional area of the ventricular cavity slice defined by planes perpendicular to the catheter through the relevant pair of electrodes was inversely proportional (to the first order) to the voltage difference. Measurement of multiple segments compensated for isovolumic cavity shape changes. The technique had previously been shown to measure left ventricular volume successfully, but the geometry of the right ventricle made this measurement more problematical. Using ...

A conductance study of the interaction between ammonium ion and 18-Crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6), ditertbutyl-dicyclohexano-18-crown-6 (t-bu) 2 DC18C6, diaza-15-crown-5 (DA15C5), dibenzo-21-crown-7 (DB21C7) and N-Phenylaza-15-crown-5 (NPA15C5) in acetonitril-dimethylsulfoxide mixture was carried out at various temperatures. The formation constants of the resultant 1:1 complexes were determined from the molar conductance-mole ratio data and found to vary in the order of DA15C5 > DC18C6 > 18C6 > (t-bu) 2 DC18C6 > DB21C7 > NPA15C5.

Based on nonpinned surface potential concept, in this paper we present a compact single-piece and complete I-V model for submicron lightly-doped drain (LDD) MOSFETs. The physics-based and analytical model was developed using the drift-diffusion equation and based on the quasi two-dimensional (2-D) Poisson equation. The important short-channel device features: drain-induced-barrier-lowering (DIBL), channel-length modulation (CLM), velocity saturation, and the parasitic series source and drain resistances have been included in the model in a physically consistent manner. In this model, the LDD region is treated as a bias-dependent series resistance, and the drain-voltage drop across the LDD region has been considered in modeling the DIBL effect. This model is smoothly-continuous, valid in all regions of operation and suitable for efficient circuit simulation. The accuracy of the model has been checked by comparing the calculated drain current, conductance and transconductance with the experimental data

The purpose of this study was to assess the roJeo/conductance catheter position within the right ventricle jn obfaining adequate indications 0/ phasic changes in ventricular volume. Possible appiicalions of this fechnology are in rate responsive pacemakers and impIantabJe de/ibrilJators. The conductance catheter ivas pJaced in the right ventricle by cannulation of a jugular or femoral vein or a branch of the pulmonary urtery. Position within the ventricle was documented from biplane/iuoroscopy. Stroke volume was perlurbed by: bolus injection of bJood, vagaJ stimulation, venous infusion of methylchoJine chJoride, or isoprenaiine. Four criteria were used to assess the quality 0/ volume signals: {1} volume signaJ phase j-eiative to the electrocardiogram; (2) magnitude parity of volume change from each electrode pair; (3) freedom/rom artifact; and (4) indication of stroke volume change during interventions. Greyhound dogs of eiliier sex (n = 33), weight 20-32 kg. A totaJ of 236 recordings from 14 distinct catheter positions were analyzed. Catheter positions originating from a femoral cannulation and one position from the pulmonary artery gave markedly superior volume transduction compared to those from the jugular route. Although right ventricular volume transduction was possible from all catheter trajectories, those resulting from the femoral approach were clearly superior. Jn the right ventricle, the inability to transduce a sufficient proportion of ventricular volume, in concert with the potential sensitivity of the catheter to atrial volume changes, may seriously limit the potential of the conductance technique in the applications envisaged. (PACE. Vol. 15, December, 1992] catheter, conductance, volumetry, right ventricle Address for reprints: CD. Bertram, D.Phil.

The effect of glycerol on both micellar formation and the structural evolution of the sodium dodecyl sulfate (SDS) aggregates in the context of the action mechanism of the cosolvent has been studied. The critical micelle concentration and the degree of counterion dissociation of the surfactant over a temperature range from 208 8 8 8 8C to 408 8 8 8 8C were obtained by the conductance method. The thermodynamic parameters of micellization were estimated by using the equilibrium model of micelle formation. The analysis of these parameters indicated that the lower aggregation of the surfactant is mainly due to a minor cohesive energy of the mixed solvent system in relation to the pure water. The effect of glycerol on the mean aggregation number of the micelles of SDS was analyzed by the static quenching method. It was found that the aggregation number decreased with the glycerol content. This reduction in the micellar size seems to be controlled by an increase in the surface area per headgroup, which was ascribed to a participation of glycerol in the micellar solvation layer. Studies on the micropolarity of the aggregates, as sensed by the probe pyrene, indicated that this microenvironmental parameter is almost unaffected by the presence of glycerol in the mixture. However, an increase in the micellar microviscosity at the surface region was observed from the photophysical behavior of two different probes, rhodamine B and auramine O. These results suggest a certain interaction of the cosolvent in the micellar solvation of SDS micelles.

The effect of isoproterenol on apical and basolateral membrane conductance in principal cells of short-circuited frog skin was analyzed using microelectrodes. Isoproterenol (10-6 mol/l) increased the apical membrane conductance in addition to stimulating CI-conductive pathways outside the principal cells. The effect on apical Na ÷ channels explains the increase in amiloride sensitive short-circuit current. Basolateral membrane conductance increased only slightly.

Physiological arousal is purportedly a key determinant in the development and maintenance of gambling behaviors, with problem gambling conceptualized in terms of abnormal autonomic responses. Theoretical conceptualizations of problem gambling are discordant regarding the nature of deficit in this disorder; some accounts posit that problem gamblers are hypersensitive to reward, and others that they are hyposensitive to reward and/or punishment. Previous research examining phasic electrodermal responses in gamblers has been limited to laboratory settings, and reactions to real gaming situations need to be examined. Skin conductance responses (SCRs) to losses, wins, and losses disguised as wins (LDWs) were recorded from 15 problem gamblers (PGs) and 15 nonproblem gamblers (NPGs) while they wagered their own money during electronic gaming machine play. PGs demonstrated significantly reduced SCRs to reward. SCRs to losses and LDWs did not differ for either PGs or NPGs. This hyposensitivity to wins may reflect abnormalities in incentive processing, and may represent a potential biological marker for problem gambling.

... Diatomsasindicatorsof environmentalchange inAntarcticand subantarcticfreshwaters SARAH A. SPAULDING, BART VAN DE VIJVER, DOMINIC A. HODGSON, DIANE M ... Accordingly, peatcoresobtained from Ile de la Possession (Crozet Archipelago) led to an envi-ronmental ...

The effect of a transverse electric field on Fano line shapes in electronic transport through a quantum wire is investigated via a Feshbach three-channel model. The coupling between channels is provided by an attractive short-range scatterer with lateral extent. It is shown that the resonance structure in a particular subband is sensitive on the electric field strength and direction. In particular, collapse of a Fano profile either in the first or the second subband may occur, depending on whether the electric field points in the negative or positive direction, respectively. This is due to the vanishing coupling between the bound states and the conduction ones which, in turn, is a consequence of the electric field-induced shift of the confining potential. This tunability of Fano resonances may prove experimentally useful in ballistic transport through narrow channels. The results in the first subband are compared with those obtained from a two-channel model. A detailed account of the transmission phase is also given, and the abrupt phase shift by is shown to occur whenever the energy of the transmitted electron crosses the energy of the transmission zero. Downloaded 31 Aug 2010 to 155.207.10.222. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 043710-2 Vargiamidis, Fessatidis, and Horing J. Appl. Phys. 106, 043710 ͑2009͒ Downloaded 31 Aug 2010 to 155.207.10.222. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 043710-6 Vargiamidis, Fessatidis, and Horing J. Appl. Phys. 106, 043710 ͑2009͒ Downloaded 31 Aug 2010 to 155.207.10.222. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 043710-8 Vargiamidis, Fessatidis, and Horing J. Appl. Phys. 106, 043710 ͑2009͒ Downloaded 31 Aug 2010 to 155.207.10.222. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions

In order to enhance thermal efficiency of a flat plate solar collector, the effects of thermo-physical properties of short Single Wall Carbon Nanotubes (SWCNTs) suspended in water was investigated in this study. Sodium dodecyl sulphate was used as a dispersant for preparing a stable nanofluid. Subsequently, the nanofluid was comprehensively characterized by particle size measurement and spectroscopic technique. Specific heat with the increase of particle loading and temperature was investigated. Thermal conductivity increment also showed a linear dependence on particle concentration and temperature. Viscosity of the nanofluids and water reduced with the increase of temperature and increased with the particle loading. Using improved thermo-physical properties of the nanofluid, the maximum energy and exergy efficiency of flat plate collector was enhanced up to 95.12% and 26.25% compared to water which was 42.07% and 8.77%, respectively. This low exergy efficiency shows that flat plate collectors still require substantial enhancement. To the authors' knowledge, SWCNTs-H 2 O was used as the functioning fluid for the first time to investigate both the thermos-physical properties as well as the increase in thermal efficiency of a flat plate solar collector.

A new module, SYNRAD, has been added to the MOLFLOW [l] software package, allowing the Montecarlo (MC) simulation of synchrotron radiation (SR) emission. The geometrical three-dimensional (3D) distribution of the photons, power and energy, and spectra can be calculated. A model of the vacuum chamber is generated, and the profiles of SR-induced desorption are obtained by means of SYNRAD. These desorption profiles are then embedded in the vacuum chamber model and the MC program for the calculation of UHV molecular flow is used for obtaining relevant quantities such as, among others, pressure profiles, pumping speed efficiencies and conductances. Results of the application of SYNRAD and MOLFLOW, and comparison with some published data will be given.

In order to enhance thermal efficiency of a flat plate solar collector, the effects of thermo-physical properties of short Single Wall Carbon Nanotubes (SWCNTs) suspended in water was investigated in this study. Sodium dodecyl sulphate was used as a dispersant for preparing a stable nanofluid. Subsequently, the nanofluid was comprehensively characterized by particle size measurement and spectroscopic technique. Specific heat with the increase of particle loading and temperature was investigated. Thermal conductivity increment also showed a linear dependence on particle concentration and temperature. Viscosity of the nanofluids and water reduced with the increase of temperature and increased with the particle loading. Using improved thermo-physical properties of the nanofluid, the maximum energy and exergy efficiency of flat plate collector was enhanced up to 95.12% and 26.25% compared to water which was 42.07% and 8.77%, respectively. This low exergy efficiency shows that flat plate collectors still require substantial enhancement. To the authors' knowledge, SWCNTs-H 2 O was used as the functioning fluid for the first time to investigate both the thermos-physical properties as well as the increase in thermal efficiency of a flat plate solar collector.

Precise measurements on the electrical conductivity of solutions of sodium polystyrenesulphonate in methanol–water mixed solvent media containing 8, 16, 25, and 34 wt.% of methanol at 308.15, 313.15, 318.15, and 323.15 K are reported. The degree of substitution of sodium polystyrenesulphonate used was 1, and the concentrations were varied from ∼2.0 × 10−4 to ∼4.0 × 10−3 monomol l−1. The results showed a slight and monotonous increase in the equivalent conductivity with decreasing polyelectrolyte concentration. The applicability of the Manning’s theory for salt-free polyelectrolyte solution was examined and a major discrepancy against the theory was observed. The calculated values of the equivalent conductivity deduced on the basis of this theory were found to be lower than the experimental ones. Possible reasons for this discrepancy have been discussed. The effects of the temperature and relative permittivity of the medium on the equivalent conductivity were also investigated. Estimation of the fractions of uncondensed counterions provides important insight regarding the solution behavior of the polyelectrolyte in methanol–water mixtures.

The accuracy of the open-ended waveguide technique for the determination of reflection coefficient of a sample is strongly affected by stray capacitance and conductance at the aperture end of the waveguide. The commercial waveguide calibration kit is quite expensive [1]. In this paper, we apply phase extension technique for determination of reflection coefficient of a sample using a HP 8720 vector network analyzer where the sample reference plane did not coincide with the calibration plane. The reference plane shown in labelled AA' was at waveguide's aperture. Calibration was only performed at the connector end of the coaxial cable labelled BB' in using standard HP 85052D 3.5 mm calibration kit. Measurements were carried out using WR-90 and WR 62 rectangular waveguides. The actual reflection coefficient, B B ′

The dynamic deformation upon stretching of Ni nanowires as those formed with mechanically controllable break junctions or with a scanning tunneling microscope is studied both experimentally and theoretically. Molecular dynamics simulations of the breaking process are performed. In addition, and in order to compare with experiments, we also compute the transport properties in the last stages before failure using the first-principles implementation of Landauer's formalism included in our transport package ALACANT.

A recent development trend for rechargeable lithium batteries is the use of ternary gel electrolytes. The main advantage of the gels is the mechanical rigidity, which improves as the polymer content is increased. However, the transport properties deteriorate with increasing polymer amount. This dualistic optimisation problem has caused an increased interest in understanding the transport processes in gels, however no full characterisation or modelling study could be found in the literature. In this paper, which is the first part of a study of the transport in the ternary gel system PMMA/PC/LiClO 4 , the liquid electrolyte PC/LiClO 4 is characterised and modelled for concentrations between 0.1 and 2 M according to a previously employed methodology, based on electrochemical measurements. A model using concentration dependent interaction parameters proved to describe the results in the whole concentration region well. The cationic transport number and salt diffusivity were determined to be approximately 0.3 and 1e−10 m 2 /s, respectively. The mean ionic activity factor variations prove to be substantial. Furthermore, it was demonstrated that the inter-ionic friction was important to consider at concentrations above 1 M. The fundamental friction parameters determined in this part will be used in the following part of the study to describe the friction between ions and solvent.

The effect of acylated homoserine lactones (AHLs) and autoinducer-2 (AI-2) signalling compounds present in the cell-free culture supernatants (CFS), of Pseudomonas aeruginosa, Yersinia enterocolitica-like GTE 112, Serratia proteamaculans 00612, Y. enterocolitica CITY650 and Y. enterocolitica CITY844, on the growth of two Salmonella Enteritidis and two S. Typhimurium strains was assessed though monitoring of changes in conductance of the medium. Detection times (T det), area and slope of conductance curves were recorded. Except for P. aeruginosa 108928, which was not found to produce AI-2, all other strains produced both AHLs and AI-2. Thereafter, aliquots (20% in the final volume) of these CFS were transferred into NZ Amine broth inoculated with ca. 10 3 CFU/ml of stationary phase cultures of each Salmonella strain. While the CFS of P. aeruginosa induced a shorter detection time, i.e. acceleration of the metabolic activity, the CFS of the other microorganisms increased the detection time of Salmonella strains compared to control samples (i.e. without CFS). Results indicate that the growth of Salmonella may be affected by the presence of Quorum sensing (QS) signalling compounds and/or other novel signals existing in CFS, produced by other bacterial species and confirm the complexity of bacterial communication. The luxCDABE-encoded luminescence response of the reporter strain V. harveyi BB170 was used as the basis for determining AI-2 activity in CFS of tester strains. The assay was performed as described by Lu et al. 2004, and Nychas et al. 2009 2.6. Monitoring the effect of the CFS on Salmonella strains metabolic activity Growth of Salmonella strains was indirectly monitored by conductance measurements using the Malthus 2000 instrument (Radiometer International, Copenhagen, Denmark). A typical Malthus conductivity cell contains platinum

In recent years, there is a tremendous interest and effort to control novel materials such as graphene to have desirable electric and magnetic properties via chemical, mechanical, and electrical manipulations . A particularly appealing approach is a dynamical engineering of materials, which offers a fascinating possibility to switch on and off properties at will . Here we propose a mechanism to dynamically control quantum transport in a class of semi-metals, such as graphene and topological insulators, via the application of light. In contrast to a conventional effect of light where photons induce current carriers by exciting electrons, we consider off-resonant, circularly polarized light which induces an effective gap in semi-metals. We analyze the transport properties of the resulting photo-induced non-equilibrium systems and show that graphene and surfaces of topological insulators exhibit insulating behaviors. Remarkably, these systems also exhibit quantum Hall effects in the absence of a magnetic field with a near quantization of the Hall conductance, realizing so-called quantum Hall systems without Landau levels . Our work opens new avenues for the study of quantum Hall effects in semi-metals and dynamical control of topological transport properties. arXiv:1104.4636v1 [cond-mat.mes-hall]

The terrestrial biosphere model Carbon Assimilation in the Biosphere (CARAIB) was improved by introducing two vegetation storeys and implementing a new module which simulates the equilibrium distribution of the vegetation inferred from physiological processes and climatic constraints. In this fourth version of CARAIB, we differentiate ground-level grasses from tree canopies, which allows us to determine the light available to grasses as a direct function of the leaf area index (LAI) of the forest canopy. Both of these storeys are potentially composed of several plant functional types (PFT). The cover fraction of each PFT within each storey is estimated according to its respective net primary productivity (NPP). A biome is assigned to each grid cell on the basis of three physiological criteria: (1) the cover fraction, (2) the NPP, and (3) the LAI; and two climatic constraints: (1) the growing degree-days (GDD) and (2) the lowest temperature reached during the cold season (T min ), which are well-known indices of vegetation expansion boundaries. Total biospheric carbon stocks (vegetation + soil) are reconstructed by forcing the model with eight climatic scenarios of the Last Glacial Maximum (LGM, 21 ka BP), which were obtained from the Paleo-Modelling Intercomparison Project (PMIP) from four general circulation models (MRI2, UGAMP, LMD4, and GEN2) using prescribed and computed sea surface temperatures (SSTs). The model was also forced with a current climate together with a preindustrial atmospheric CO 2 level of 280 ppm as reference simulation. To validate the model, current biome distribution is reconstructed and compared, for the modern climate, with two distributions of potential vegetation and, for the LGM, with pollen data. The model simulations are in good agreement with broad-scale patterns of vegetation distribution. The results indicate an increase in the total biospheric carbon stock of 827.8 -1106.1 Gt C since the LGM. Sensitivity analyses were performed to discriminate the relative effects of the atmospheric CO 2 level (''fertilization effect''), the climate (present or LGM), and the sea level. Our results suggest that the CO 2 fertilization effect is mostly responsible for the total increase in vegetation and soil carbon stocks. The four GCMs diverged in their predicted responses of continental climate to calculated SSTs. Only one of them, i.e., MRI2, predicted a marked decline of the continental temperatures in response to lower calculated SSTs. For this GCM, the effect of reduced SSTs on continental biospheric carbon stocks was a decrease of 544.1 Gt for the soil carbon stock and of 283.7 0921-8181/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 -8 1 8 1 ( 0 2 ) 0 0 0 6 6 -8 (D. Otto).

It has been observed that the degrees of the topologies of several communication networks follow heavy tailed statistics. What is the impact of such heavy tailed statistics on the performance of basic communication tasks that a network is presumed to support? How does performance scale with the size of the network? We study routing in families of sparse random graphs whose degrees follow heavy tailed distributions. Instantiations of such random graphs have been proposed as models for the topology of the Internet at the level of Autonomous Systems as well as at the level of routers. Let n be the number of nodes. Suppose that for each pair of nodes with degrees du and dv we have O(dudv) units of demand. Thus the total demand is O(n 2 ). We argue analytically and experimentally that in the considered random graph model such demand patterns can be routed so that the flow through each link is at most O n log 2 n . This is to be compared with a bound Ω n 2 that holds for arbitrary graphs. Similar results were previously known for sparse random regular graphs, a.k.a. "expander graphs." The significance is that Internet-like topologies, which grow in a dynamic, decentralized fashion and appear highly inhomogeneous, can support routing with performance characteristics comparable to those of their regular counterparts, at least under the assumption of uniform demand and capacities. Our proof uses approximation algorithms for multicommodity flow and establishes strong bounds of a generalization of "expansion," namely "conductance." Besides routing, our bounds on conductance have further implications, most notably on the gap between first and second eigenvalues of the stochastic normalization of the adjacency matrix of the graph.

We solve the Dirac equation, which describes charge massless chiral relativistic carriers in a twodimensional graphene. We have identified and analysed a novel pseudospin-dependent scattering effect. We compute the tunneling conductance and generalize the analytical result in the presence of the tunable atomic potential of a graphene strip. The absence of back scattering in graphene is shown to be due to Berry's phase which corresponds to a sign change of the wave function under a spin rotation of a particle. We use the transfer matrix approach and find that the electric conductance of doped graphene increases due to atomic potential fluctuations.

Aim: Ambulatory urodynamics has the potential to provide measurements of bladder function during activities of daily living; however, no method of real-time continuous bladder volume measurement exists. The present study was conducted to determine the feasibility of using fluid volume conductance to continuously assess bladder volume. Methods: Prototype devices consisted of four electrodes mounted on a polymer body. Each was tested in an in vitro organ bath system using latex vessels filled to 500 ml with saline matching the conductivity of urine. One device was selected and used to test the effects of fluid concentration (25%, 50%, 100%, 200%, and 400% physiological saline) in latex vessels as well as the effects of fluid concentration (25%, 50%, 100%, 200%, and 400% Tyrodes solution) and temperature (32, 37, and 42 C) in excised pig bladders. Results: Conductance demonstrated a linear increase at low volumes but approached an asymptotic value at high volumes. Conductivity increased with increased temperature or concentration. With the exception of the differences between 25% and 50% concentrations, 32 C and 37 C, and 37 C and 42 C temperatures, each concentration and temperature produced statistically different conductance measurements from all others. Conclusions: The conductance method is sensitive to changes in both concentration and temperature of the intravesical solution, likely due to changes in solution conductivity. Clinical application of conductance for measurement of bladder volume will require real-time conductivity compensation for the dynamically varying properties of urine. However, improved sensitivity at high volumes is necessary before this method has the potential to provide real-time bladder volume measurement for use in ambulatory urodynamics.

MESFET are used in circuitsof gigahertz frequencies as they are based on gallium arsenide (GaAs) having electron mobility six times higher than that of silicon. An analytical model simulating different device current-voltage characteristics, i.e., output conductance and output transconductance of a 0.3μm gate MESFET with temperature dependence is proposed. The model is validated by comparing the results of the proposed model and those of the numerical simulation. The parameter values are computed using an intrinsic MESFET of two-dimensional geometry. In this work, the distribution of different output loads for varied applied voltages is considered. Simulation results obtainedunder temperature variation effectsfor load distribution and applied driven voltage variation are considered. The RMS and average errors between the different models and GaAs MESFET simulations are calculated to evidence the proposed model accuracy. This was demonstrated by a good agreement between the proposed ...

Brain computation, in the early visual system, is often considered as a hierarchical process in which features extracted in a given sensory relay are not present in previous stages of integration. In particular, orientation preference and its fine tuning selectivity are functional properties shared by most cortical cells and they are not observed at the preceding geniculate stage. A classical problem is identifying the mechanisms and circuitry underlying these computations. Several organizational principles have been proposed, giving different weights to the feedforward thalamocortical drive or to intracortical recurrent architectures. Within this context, an important issue is whether intracortical inhibition is fundamental for the genesis of stimulus selectivity, or rather normalizes spike response tuning with respect to other features such as stimulus strength or contrast, without influencing the selectivity bias and preference expressed in the excitatory input alone. We review here experimental observations concerning the presence or absence of inhibitory input evoked by non-preferred orientation/directions. Intracellular current clamp and voltage clamp recordings are analyzed in the light of new methods allowing us (1) to increase the visibility of inhibitory input, and (2) to continuously measure the visually evoked dynamics of input conductances. We conclude that there exists a diversity of synaptic input combinations generating the same profile of spike-based orientation selectivity, and that this diversity most likely reflects anatomical non-homogeneities in input sampling provided by the local context of the columnar and lateral intracortical network in which the considered cortical cell is embedded.

Metabolic and body temperature (T b ) responses of star-nosed moles (Condylura cristata) exposed to air temperatures ranging from 0 to 33°C were investigated. The thermoneutral zone of this semi-aquatic mole extended from 24.5 to 33°C, over which its basal rate of metabolism averaged 2.25 ml O 2 g − 1 h − 1 (45.16 J g − 1 h − 1 ). This rate of metabolism is higher than predicted for terrestrial forms, and substantially higher than for other moles examined to date. Minimum thermal conductance was nearly identical to that predicted for similar-sized eutherians and may represent a compromise between the need to dissipate heat while digging and foraging in subterranean burrows, and the need to conserve heat and avoid hypothermia during exposure to cold. C. cristata precisely regulated T b (mean 9SE =37.790.05°C) over the entire range of test temperatures. Over three separate 24-h periods, T b of a radio-implanted mole varied from 36.6 to 38.8°C, and generally tracked level of activity. No obvious circadian variation in T b and activity was apparent, although cyclic 2 -4 h intervals of activity punctuated by periods of inactivity lasting 3-5 h were routinely observed. We suggest that the elevated basal metabolic rate and relatively high T b of star-nosed moles may reflect the semi-aquatic habits of this unique talpid.

Neste trabalho, foi investigada a interação entre substâncias húmicas e um polímero condutor (poli-(o-etoxianilina) -POEA), ambos em solução e filmes automontados. Os resultados mostram que as substâncias húmicas dopam a POEA por protonação, isto é evidenciado por espectroscopia UV-Vis e Raman. Os estudos de microscopia de força atômica (AFM) em filmes automontados mostram haver um aumento na rugosidade do filme polimérico quando este é exposto a substâncias húmicas (ácidos húmico e fúlvico), o que evidencia a existência de interação entre a POEA e as substâncias húmicas. Esta mudança na morfologia é reversível com a lavagem dos filmes com água, em concordância com as medidas elétricas, possibilitando a aplicação em sensores. Um sistema sensor formado por um arranjo de diferentes unidades sensoriais foi capaz de distinguir substâncias húmicas em solução aquosa, como é mostrado pela análise multivariada (análise da componente principal), o que é importante para controle da qualidade de água e solo.

The Au/polyvinyl alcohol (PVA) (Co, Zn‐doped)/n‐Si Schottky barrier diodes (SBDs) were exposed to various illumination intensities. Illumination effect on the dielectric properties has been investigated by using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics at 1 MHz and room temperature. The values of dielectric constant (ε′), dielectric loss (ε″), loss tangent (tanδ), electric modulus (M′ and M″), and AC electrical conductivity (σAC) were found strongly intensity dependent on both the illumination levels and applied bias voltage especially in depletion and accumulation regions. Such bias and illumination dependency of these parameters can be explained on the basis of Maxwell–Wagner interfacial polarization and restructuring and reordering of charges at interface states. In addition, the ε′–V plots also show an intersection feature at ∼ 2.8 V and such behavior of the ε′–V plots appears as an abnormality compared with the conventional behavior of an ideal SBD. The obtained results revealed that illumination intensity enhances the conductivity of Au/PVA(Co, Zn‐doped)/n‐Si SBD.

The critical levels for ozone effects on vegetation have been reviewed and revised by the LRTAP Convention. Eight new or revised critical levels based on the accumulated stomatal flux of ozone (POD Y , the Phytotoxic Ozone Dose above a threshold flux of Y nmol m À2 PLA s À1 , where PLA is the projected leaf area) have been agreed. For each receptor, data were combined from experiments conducted under naturally fluctuating environmental conditions in 2e4 countries, resulting in linear doseeresponse relationships with response variables specific to each receptor (r 2 ¼ 0.49e0.87, p < 0.001 for all). For crops, critical levels were derived for effects on wheat (grain yield, grain mass, and protein yield), potato (tuber yield) and tomato (fruit yield). For forest trees, critical levels were derived for effects on changes in annual increment in whole tree biomass for beech and birch, and Norway spruce. For (semi-)natural vegetation, the critical level for effects on productive and high conservation value perennial grasslands was based on effects on important component species of the genus Trifolium (clover species). These critical levels can be used to assess protection against the damaging effects of ozone on food security, important ecosystem services provided by forest trees (roundwood production, C sequestration, soil stability and flood prevention) and the vitality of pasture.

The influence of an intramolecular proton transfer reaction on the conductance of a molecular junction is investigated employing a generic model, which includes the effects of the electric field of the gate and leads electrodes and the coupling to a dissipative environment. Using a quantum master equation approach it is shown that, depending on the localization of the proton, the junction exhibits a high or low current state, which can be controlled by external electric fields. Considering different regimes, which range from weak to strong hydrogen bonds in the proton transfer complex and comprise situations with high and low barriers, necessary preconditions to achieve control are analyzed. The results show that systems with a weak hydrogen bond and a significant energy barrier for the proton transfer can be used as molecular transistors or diodes.

The literature dealing with the water conducting properties of sapwood xylem in trees is inconsistent in terminology, symbols and units. This has resulted from confusion in the use of either an analogy to Ohm's law or Darcy's law as the basis for nomenclature. Ohm's law describes movement of electricity through a conductor, whereas Darcy's law describes movement of a fluid (liquid or gas) through a porous medium. However, it is generally not realized that, in their full notation, these laws are mathematically equivalent. Despite this, plant physiologists have failed to agree on a convention for nomenclature. As a result, the study of water movement through sapwood xylem is confusing, especially for scientists entering the field. To improve clarity, we suggest the adoption of a single nomenclature that can be used by all plant physiologists when describing water movement in xylem. Darcy's law is an explicit hydraulic relationship and the basis for established theories that describe three-dimensional saturated and unsaturated flow in porous media. We suggest, therefore, that Darcy's law is the more appropriate theoretical framework on which to base nomenclature describing sapwood hydraulics. Our proposed nomenclature is summarized in a table that describes conventional terms, with their formulae, dimensions, units and symbols; the table also lists the many synonyms found in recent literature that describe the same concepts. Adoption of this proposal will require some changes in the use of terminology, but a common rigorous nomenclature is needed for efficient and clear communication among scientists.

Deciphering charge transport through multichannel pathwaysinsingle-molecule junctions is of high importance to construct nanoscale electronic devices and deepen insight into biological redoxp rocesses.H erein, we report two tailor-made folded single-molecule wires featuring intramolecular p-p stacking interactions.T he scanning tunneling microscope (STM) based break-junction technique and theoretical calculations showt hat through-bond and through-space conjugations are integrated into one single-molecule wire,allowing for two simultaneous conducting channels in as ingle-molecule junction. These folded molecules with stable p-p stacking interaction offer conceptual advances in single-molecule multichannel conductance,a nd are perfect models for conductance studies in biological systems,organic thin films,and p-stacked columnar aggregates.

K + depletion exerts dramatically variable effects on different potassium channels. Here we report that Shab channels are rather stable in the absence of either internal or external K + alone; however, its stability is greater with K + outside the cell. In contrast, with 0 K + (non-added) solutions on both sides of the membrane, the conductance (G K ) is rapidly and irreversibly lost. G K is lost with the channels closed and regardless of the composition of the 0 K + solutions. In comparison, it is known that the Shaker B G K collapses only if the channels are gated in 0 K + , Na + -containing solutions. In order to compare the behavior of Shab to that of Shaker, we show that after extensively gating the channels in 0 K + N-methyl-D-glucamine solutions, most Shaker channels remain stable, and in a conformation where G K collapses as soon as there is Na + in the solutions. Regarding ion conduction, in contrast to Kv2.1 and Shaker A463C that have a sizable G Na in 0 K + , Shab, which shares a 463-cysteine and an identical signature sequence with these channels, does not appreciably conduct Na + , although it presents a significant Cs + conductance. The observations suggest that there are at least two sites where K + binds and thus maintains Shab G K stable, one internal and the other(s) most likely located outside the selectivity filter.

The thermal dynamics induced by ultrashort laser pulses in nanoscale systems, i.e. all-optical time-resolved nanocalorimetry is theoretically investigated from 300 to 1.5 K. We report ab-initio calculations describing the temperature dependence of the electron-phonon interactions for Cu nanodisks supported on Si. The electrons and phonons temperatures are found to decouple on the ns time scale at ∼ 10 K, which is two orders of magnitude in excess with respect to that found for standard low-temperature transport experiments. By accounting for the physics behind our results we suggest an alternative route for overhauling the present knowledge of the electron-phonon decoupling mechanism in nanoscale systems by replacing the mK temperature requirements of conventional experiments with experiments in the time-domain.

Dense (n = 4 × 10 11 cm −2) arrays of Ge quantum dots in Si host were studied using attenuation of surface acoustic waves (SAWs) propagating along the surface of a piezoelectric crystal located near the sample. The SAW magneto-attenuation coefficient, ∆Γ = Γ(ω, H) − Γ(ω, 0), and change of velocity of SAW, ∆V /V = (V (H) − V (0))/V (0), were measured in the temperature interval T = 1.5-4.2 K as a function of magnetic field H up to 6 T for the waves in the frequency range f = 30-300 MHz. Basing on the dependences of ∆Γ on H, T and ω, as well as on its sign, we believe that the AC conduction mechanism is a combination of diffusion at the mobility edge with hopping between localized states at the Fermi level. The measured magnetic field dependence of the SAW attenuation is discussed basing on existing theoretical concepts.

The sodium channel saxitoxin binding component from rat sarcolemma was solubilized with medium chain length non-ionic detergents including NP-40, Brij-96 and Lubrol-PX. Phospholipid was required for stability of the binding component. Specific saxitoxin binding was significantly temperature sensitive even with optimal levels of phospholipid present. The solubilized saxitoxin binding component chromatographed on Sepharose 6B at a position corresponding to that of a globular protein of 95-100 .~ Stokes radius, but had an apparent S2O,w typical of a smaller molecule (S2o,w = 9.2-10). Column behavior and S2o,w were independent of the specific detergent used for solubilization. Anomalous column behavior may reflect molecular asymmetry, contribution from bound detergent or similar considerations.

In this paper we present a detailed analysis on how the critical charge (Qcrit) of a circuit node, usually employed to evaluate the probability of transient fault (TF) occurrence as a consequence of a particle hit, depends on transistors&#x27; sizing. We derive an analytical model allowing us to calculate a node&#x27;s Qcrit given the size of the node&#x27;s driving gate

In this paper, the network analog method is developed with a view to applying it to compute quasi-static electrical parameters (matrices of capacitance [Cij], inductance [Lij], conductance [Oij] and resistance [Rij]) of nlultilayer structures in CMOS technology. Finite-difference method with variable increments is applied to solve Laplace&#39;s equation. It involves constructing a network analog having complex or real branches. Hence, if any advantages can be obtained, one may solve a network problem using the network analog method instead of the corresponding Laplace&#39;s difference equations. Thus, the number of equations, the computational time and the memory space will be considerably reduced. Sample results are presented for conductor line sizes and spacing typical of multilevel VLSI structures.