Home About us Contact
|
Home About us Contact | ||
|
|
||
Conductance
Kinds of Conductance Terms modified by Conductance Selected AbstractsElectrical Conductance in Biological MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 12 2010M. Waleed Shinwari Abstract Nucleic acids and proteins are not only biologically important polymers. They have recently been recognized as novel functional materials surpassing conventional materials in many aspects. Although Herculean efforts have been undertaken to unravel fine functioning mechanisms of the biopolymers in question, there is still much more to be done. Here the topic of biomolecular charge transport is presented with a particular focus on charge transfer/transport in DNA and protein molecules. The experimentally revealed details, as well as the presently available theories, of charge transfer/transport along these biopolymers are critically reviewed and analyzed. A summary of the active research in this field is also given, along with a number of practical recommendations. [source] Observation of a 2D Electron Gas and the Tuning of the Electrical Conductance of ZnO Nanowires by Controllable Surface Band-BendingADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Youfan Hu Abstract Direct experimental evidence for the existence of a 2D electron gas in devices based on ZnO nanowires (NWs) is presented. A two-channel core/shell model is proposed for the interpretation of the temperature-dependent current,voltage (I,V) characteristics of the ZnO NW, where a mixed metallic,semiconducting behavior is observed. The experimental results are quantitatively analyzed using a weak-localization theory, and suggest that the NW is composed of a "bulk" semiconducting core with a metallic surface accumulation layer, which is basically a 2D electron gas in which the electron,phonon inelastic scattering is much weaker than the electron,electron inelastic scattering. A series of I,V measurements on a single NW device are carried out by alternating the atmosphere (vacuum, H2, vacuum, O2), and a reversible change in the conductance from metallic to semiconducting is achieved, indicating the surface accumulation layer is likely hydroxide-induced. Such results strongly support the two-channel model and demonstrate the controllable tuning of the ZnO NW electrical behavior via surface band-bending. [source] Efficient Reduction of Graphite Oxide by Sodium Borohydride and Its Effect on Electrical ConductanceADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Hyeon-Jin Shin Abstract The conductivity of graphite oxide films is modulated using reducing agents. It is found that the sheet resistance of graphite oxide film reduced using sodium borohydride (NaBH4) is much lower than that of films reduced using hydrazine (N2H4). This is attributed to the formation of CN groups in the N2H4 case, which may act as donors compensating the hole carriers in reduced graphite oxide. In the case of NaBH4 reduction, the interlayer distance is first slightly expanded by the formation of intermediate boron oxide complexes and then contracted by the gradual removal of carbonyl and hydroxyl groups along with the boron oxide complexes. The fabricated conducting film comprising a NaBH4 -reduced graphite oxide reveals a sheet resistance comparable to that of dispersed graphene. [source] Thermal Conductance of Delamination Cracks in a Fiber-Reinforced Ceramic CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Kathleen R. McDonald The thermal conductance of delamination cracks in a unidirectionally reinforced ceramic composite is investigated. A phase-sensitive photothermal technique is used to measure the crack conductance in situ under load. Special emphasis is given to the effects of the local crack opening displacement (,). A crack conductance model that considers the contributions from both the air and the fibers within the crack is developed and compared with the measurements. Despite considerable scatter in the experimental data, the model adequately predicts the increased conductance that is associated with fiber bridging, as well as the overall trend that is observed with ,. [source] Antecedent Ethanol Attenuates Cerebral Ischemia/Reperfusion-Induced Leukocyte-Endothelial Adhesive Interactions and Delayed Neuronal Death: Role of Large Conductance, Ca2+ -activated K+ ChannelsMICROCIRCULATION, Issue 6 2010QUN WANG Please cite this paper as: Wang, Kalogeris, Wang, Jones and Korthuis (2010). Antecedent Ethanol Attenuates Cerebral Ischemia/Reperfusion-Induced Leukocyte-Endothelial Adhesive Interactions and Delayed Neuronal Death: Role of Large Conductance, Ca2+ -activated K+ Channels. Microcirculation17(6), 427,438. Abstract EtOH-PC reduces postischemic neuronal injury in response to cerebral (I/R). We examined the mechanism underlying this protective effect by determining (i) whether it was associated with a decrease in I/R-induced leukocyte-endothelial adhesive interactions in postcapillary venules, and (ii) whether the protective effects were mediated by activation of large conductance, calcium-activated potassium (BKCa) channels. Mice were administered ethanol by gavage or treated with the BKCa channel opener, NS1619, 24 hours prior to I/R with or without prior treatment with the BKCa channel blocker, PX. Both CCA were occluded for 20 minutes followed by two and three hours of reperfusion, and rolling (LR) and adherent (LA) leukocytes were quantified in pial venules using intravital microscopy. The extent of DND, apoptosis and glial activation in hippocampus were assessed four days after I/R. Compared with sham, I/R elicited increases in LR and LA in pial venules and DND and apoptosis as well as glial activation in the hippocampus. These effects were attenuated by EtOH-PC or antecedent NS1619 administration, and this protection was reversed by prior treatment with PX. Our results support a role for BKCa channel activation in the neuroprotective effects of EtOH-PC in cerebral I/R. [source] Conductance through a redox system in the Coulomb blockade regime: Many-particle effects and influence of electronic correlationsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1-2 2010Sabine Tornow Abstract We investigate the transport characteristics of a redox system weakly coupled to leads in the Coulomb blockade regime. The redox system comprises a donor and acceptor separated by an insulating bridge in a solution. It is modeled by a two-site extended Hubbard model which includes on-site and inter-site Coulomb interactions and the coupling to a bosonic bath. The current,voltage characteristics is calculated at high temperatures using a rate equation approach. For high voltages exceeding the Coulomb repulsion at the donor site the calculated transport characteristics exhibit pronounced deviations from the behavior expected from single-electron transport. Depending on the relative sizes of the effective on-site and inter-site Coulomb interactions on one side and the reorganization energy on the other side we find either negative differential resistance or current enhancement. Schematic view of the redox system with donor (D) and acceptor (A) coupled to the leads L and R. The electronic degrees of freedom of the DA system are coupled to the environment comprising internal vibrations and the solvent dynamics. The current is calculated as a function of the bias voltage Vb and gate voltage Vg. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic transport through large quantum dots in the Kondo regimePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003P. Stefa Abstract Conductance through a large two-level quantum dot is investigated theoretically in the strong coupling regime. In large quantum dots the separation between discrete levels becomes smaller than the level width due to strong hybridization with electrodes. In such circumstances, apart from strong electronic correlations in the quantum dot, the indirect interaction between both the spatial levels comes into play. It takes place in lateral quantum dots, where the spatial level index is not conserved during the hybridization process with electrodes. This interaction shifts the Kondo resonance peak in the density of states out of the Fermi surface and alters its intensity. This feature can be observed in the differential conductance dependence vs. bias voltage. The virtual inter-level mixing is suppressed for temperatures above the Kondo temperature of the system. The results of theoretical predictions are compared with the results of experimental conductance measurements performed on large quantum dots and some non-typical conductance features are clarified. [source] Diurnal and seasonal variations in stomatal conductance of rice at elevated atmospheric CO2 under fully open-air conditionsPLANT CELL & ENVIRONMENT, Issue 3 2010HIROYUKI SHIMONO ABSTRACT Understanding of leaf stomatal responses to the atmospheric CO2 concentration, [CO2], is essential for accurate prediction of plant water use under future climates. However, limited information is available for the diurnal and seasonal changes in stomatal conductance (gs) under elevated [CO2]. We examined the factors responsible for variations in gs under elevated [CO2] with three rice cultivars grown in an open-field environment under flooded conditions during two growing seasons (a total of 2140 individual measurements). Conductance of all cultivars was generally higher in the morning and around noon than in the afternoon, and elevated [CO2] decreased gs by up to 64% over the 2 years (significantly on 26 out of 38 measurement days), with a mean gs decrease of 23%. We plotted the gs variations against three parameters from the Ball-Berry model and two revised versions of the model, and all parameters explained the gs variations well at each [CO2] in the morning and around noon (R2 > 0.68), but could not explain these variations in the afternoon (R2 < 0.33). The present results provide an important basis for modelling future water use in rice production. [source] Calcium-dependent K current in plasma membranes of dermal cells of developing bean cotyledonsPLANT CELL & ENVIRONMENT, Issue 2 2004W.-H. ZHANG ABSTRACT In developing seeds of bean (Phaseolus vulgaris L.), phloem-imported assimilates (largely sucrose and potassium) are released from coats to seed apoplasm and subsequently retrieved by the dermal cell complexes of cotyledons. To investigate the mechanisms of K+ uptake by the cotyledons, protoplasts of dermal cell complexes were isolated and whole-cell currents across their plasma membranes were measured with the patch-clamp technique. A weakly rectified cation current displaying a voltage-dependent blockade by external Ca2+ and acidic pH, dominated the conductance of the protoplasts. The P haseolus v ulgaris Cotyledon Dermal-cell pH and Calcium-dependent Cation Conductance (Pv-CD-pHCaCC) was highly selective for K+ over Ca2+ and Cl,. For K+ current through Pv-CD-pHCaCC a sigmoid shaped current,voltage (I,V) curve was observed with negative conductance at voltages between ,200 and ,140 mV. This negative K+ conductance was Ca2+ dependent. With other univalent cations (Na+, Rb+, NH4+) the currents were smaller and were not Ca2+ dependent. Reversal potentials remained constant when external K+ was substituted with these cations, suggesting that Pv-CD-pHCaCC channels were non-selective. The Pv-CD-pHCaCC would provide a pathway for K+ and other univalent cation influx into developing cotyledons. These cation influxes could be co-ordinated with sucrose influx via pH and Ca2+dependence. [source] Conductance of inhomogeneous systems: Real-time dynamicsANNALEN DER PHYSIK, Issue 9 2010A. Branschädel Numerical time evolution of transport states using time dependent Density Matrix Renormalization Group (td-DMRG) methods has turned out to be a powerful tool to calculate the linear and finite bias conductance of interacting impurity systems coupled to non-interacting one-dimensional leads. Several models, including the Interacting Resonant Level Model (IRLM), the Single Impurity Anderson Model (SIAM), as well as models with different multi site structures, have been subject of investigations in this context. In this work we give an overview of the different numerical approaches that have been successfully applied to the problem and go into considerable detail when we comment on the techniques that have been used to obtain the full I,V-characteristics for the IRLM. Using a model of spinless fermions consisting of an extended interacting nanostructure attached to non-interacting leads, we explain the method we use to obtain the current,voltage characteristics and discuss the finite size effects that have to be taken into account. We report results for the linear and finite bias conductance through a seven site structure with weak and strong nearest-neighbor interactions. Comparison with exact diagonalisation results in the non-interacting limit serve as a verification of the accuracy of our approach. Finally we discuss the possibility of effectively enlarging the finite system by applying damped boundaries and give an estimate of the effective system size and accuracy that can be expected in this case. [source] Pulse Conductance and Flow-induced Hemolysis During Pulsatile Cardiopulmonary BypassARTIFICIAL ORGANS, Issue 4 2010Antoine P. Simons Abstract In this study, the hypothesis was tested that a low-resistant, high-compliant oxygenator provides better pulse conductance and less hemolysis than a high-resistant, low-compliant oxygenator during pulsatile cardiopulmonary bypass. Forty adults undergoing coronary artery bypass surgery were randomly divided into two groups using either an oxygenator with a relatively low hydraulic resistance (Quadrox BE-HMO 2000, Maquet Cardiopulmonary AG, Hirrlingen, Germany) or with a relatively high hydraulic resistance (Capiox SX18, Terumo Cardiovascular Systems, Tokyo, Japan). The phase shift between the flow signals measured at the inlet and outlet of the oxygenator was used to assess compliance. Pulse conductance in terms of pressure attenuation was calculated by dividing the outlet pulse pressure of the oxygenator by the inlet pulse pressure. A normalized index was used to assess hemolysis. The phase shifts in time of the flow pulses were 36 ± 6 ms in the low-resistant (high-compliant) oxygenator, and 14 ± 2 ms in the high-resistant (low-compliant) oxygenator group (P < 0.001). The low-resistant, high-compliant oxygenator provided 27% better pulse conductance compared with the high-resistant, low-compliant oxygenator (0.84 ± 0.02 and 0.66 ± 0.01, respectively, P < 0.001). Inlet pulse pressures were significantly higher (29%) in the high-resistant, low-compliant (Capiox) group than in the low-resistant, high-compliant (Quadrox) group (838 ± 38 mm Hg and 648 ± 25 mm Hg respectively, P < 0.001), but no significant difference in hemolysis was found. A low-resistant, high-compliant oxygenator provides better pulse conduction than a high-resistant, low-compliant oxygenator. However, the study data could not confirm the association of high pressures with increased hemolysis. [source] ,-Adrenergic and neuropeptide Y Y1 receptor control of collateral circuit conductance: influence of exercise trainingTHE JOURNAL OF PHYSIOLOGY, Issue 24 2008Jessica C. Taylor This study evaluated the role of ,-adrenergic receptor- and neuropeptide Y (NPY) Y1 receptor-mediated vasoconstriction in the collateral circuit of the hind limb. Animals were evaluated either the same day (Acute) or 3 weeks following occlusion of the femoral artery; the 3-week animals were in turn limited to cage activity (Sed) or given daily exercise (Trained). Collateral-dependent blood flows (BFs) were measured during exercise with microspheres before and after ,-receptor inhibition (phentolamine) and then NPY Y1 receptor inhibition (BIBP 3226) at the same running speed. Blood pressures (BPs) were measured above (caudal artery) and below (distal femoral artery) the collateral circuit. Arterial BPs were reduced by ,-inhibition (50,60 mmHg) to ,75 mmHg, but not further by NPY Y1 receptor inhibition. Effective experimental sympatholysis was verified by 50,100% increases (P < 0.001) in conductance of active muscles not affected by femoral occlusion with receptor inhibition. In the absence of receptor inhibition, vascular conductance of the collateral circuit was minimal in the Acute group (0.13 ± 0.02), increased over time in the Sed group (0.41 ± 0.03; P < 0.001), and increased further in the Trained group (0.53 ± 0.03; P < 0.02). Combined receptor inhibition increased collateral circuit conductances (P < 0.005), most in the Acute group (116 ± 37%; P < 0.02), as compared to the Sed (41 ± 6.6%; P < 0.001) and Trained (31 ± 5.6%; P < 0.001) groups. Thus, while the sympathetic influence of the collateral circuit remained in the Sed and Trained animals, it became less influential with time post-occlusion. Collateral conductances were collectively greater (P < 0.01) in the Trained as compared to Sed group, irrespective of the presence or absence of receptor inhibition. Conductances of the active ischaemic calf muscle, with combined receptor inhibition, were suboptimal in the Acute group, but increased in Sed and Trained animals to exceptionally high values (e.g. red fibre section of the gastrocnemius: ,7 ml min,1 (100 g),1 mmHg,1). Thus, occlusion of the femoral artery promulgated vascular adaptations, even in vessels that are not part of the collateral circuit. The presence of active sympathetic control of the collateral circuit, even with exercise training, raises the potential for reductions in collateral BF below that possible by the structure of the collateral circuit. However, even with release of this sympathetic vasoconstriction, conductance of the collateral circuit was significantly greater with exercise training, probably due to the network of structurally larger collateral vessels. [source] A role for the volume regulated anion channel in volume regulation in the murine CNS cell line, CADACTA PHYSIOLOGICA, Issue 2 2010V. L. Harvey Abstract Aim:, The role of the volume regulated anion channel (VRAC) in a model CNS neuronal cell line, CAD, was investigated. Methods:, Changes in cell volume following hypotonic challenges were measured using a video-imaging technique. The effect of the Cl, channel antagonists tamoxifen (10 ,m) and 4,4,-diisothiocyanatostilbene-2,2,-disulphonic acid (DIDS; 100 ,m) on regulatory volume decrease (RVD) were measured. The whole-cell voltage-clamp technique was used to characterize IClswell, the current underlying the VRAC. Results:, Using the video-imaging technique, CAD cells were found to swell and subsequently exhibit RVD when subjected to a sustained hypotonic challenge from 300 mOsmol kg,1 H2O to 210 mOsmol kg,1 H2O. In the presence of tamoxifen (10 ,m) or DIDS (100 ,m) RVD was abolished, suggesting a role for the VRAC. A hypotonic solution (230 mOsmol kg,1 H2O) evoked IClswell, an outwardly rectifying current displaying time-independent activation, which reversed upon return to isotonic conditions. The reversal potential (Erev) for IClswell was ,14.7 ± 1.4 mV, similar to the theoretical Erev for a selective Cl, conductance. IClswell was inhibited in the presence of DIDS (100 ,m) and tamoxifen (10 ,m), the DIDS inhibition being voltage dependent. Conclusions:, Osmotic swelling elicits an outwardly rectifying Cl, conductance in CAD cells. The IClswell observed in these cells is similar to that observed in other cells, and is likely to provide a pathway for the loss of Cl, which leads to water loss and RVD. As ischaemia, brain trauma, hypoxia and other brain pathologies can cause cell swelling, CAD cells represent a model cell line for the study of neuronal cell volume regulation. [source] Part 1: Kinetics and mechanism of the crystallization processCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006Oleg D. Linnikov Abstract The kinetics of spontaneous crystallization of sodium chloride from aqueous-ethanol solutions were studied. During the crystallization the electrical conductance and optical transmission of the supersaturated solutions were measured automatically. For monitoring of the total surface of growing potassium chloride crystals at the crystallization the turbidimetric method was used. The growth rate and activation energy were determined. The crystal growth rate was proportional to supersaturation. When the volume fraction of ethanol in solution increased from 14.85 to 29.72%, the activation energy of the growth process did not change and was about 50 kJ· mol -1. Aggregation of the crystals was found. The aggregation kinetics of the crystals may be described approximately by the famous Smoluchowski equation for coagulation of colloidal particles. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of semi-insulating InP co-doped with Ti and various acceptors for use in X-ray detectionCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005K. Zdansky Abstract Semi-insulating InP single crystals co-doped with Zn and Ti and co-doped with Ti and Mn were grown by Czochralski technique. Wafers of these crystals were annealed for a long time at a high temperature and cooled slowly. The samples were characterized by temperature dependent resistivity and Hall coefficient measurements. The binding energies of Ti in semi-insulating InP co-doped with Ti and Zn and co-doped with Ti and Mn were found to differ which shows that Ti may occupy different sites in InP. The curves of Hall coefficient vs. reciprocal temperature deviate from straight lines at low temperatures due to electron and hole mixed conductance. The value of resistivity of the annealed semi-insulating InP co-doped with Ti and Mn reaches high resistivity at a reduced temperature easily achievable by thermo-electric devices which could make this material useable in X-ray detection. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Responses of the bronchial and pulmonary circulations to short-term nitric oxide inhalation before and after endotoxaemia in the pigACTA PHYSIOLOGICA, Issue 1 2002R. J. M. Middelveld ABSTRACT The physiological responses of the bronchial circulation to acute lung injury and endotoxin shock are largely unexplored territory. This study was carried out to study the responsiveness of the bronchial circulation to nitric oxide (NO) inhalation before and after endotoxaemia, in comparison with the pulmonary circulation, as well as to study changes in bronchial blood flow during endotoxaemia. Six anaesthetized pigs (pre-treated with the cortisol-synthesis inhibitor metyrapone) received an infusion of 10 µg/kg endotoxin during 2 h. Absolute bronchial blood flow was measured via an ultrasonic flow probe around the bronchial artery. The pigs received increasing doses of inhaled NO over 5 min each (0, 0.2, 2 and 20 ppm) before and after 4 h of endotoxaemia. The increase in bronchial vascular conductance during 5 min of inhalation of 20 ppm NO before endotoxin shock was significantly higher (area under curve (AUC) 474.2 ± 84.5% change) than after endotoxin shock (AUC 118.2 ± 40.4%, P < 0.05 Mann,Whitney U -test). The reduction of the pulmonary arterial pressure by 20 ppm NO was not different. A short rebound effect of the pulmonary arterial pressure occurred after discontinuation of inhaled NO before endotoxaemia (AUC values above baseline 54.4 ± 19.7% change), and was virtually abolished after endotoxaemia (AUC 6.1 ± 4.0%, P = 0.052, Mann,Whitney U -test). Our results indicate that the responsiveness of the bronchial circulation to inhalation of increasing doses of inhaled NO during endotoxin shock clearly differ from the responsiveness of the pulmonary circulation. The reduced responsiveness of the bronchial circulation is probably related to decreased driving pressure for the bronchial blood flow. The absence of the short rebound effect on pulmonary arterial pressure (PAP) after induction of shock could be related to maximum constriction of the pulmonary vessels at 4 h. [source] Electrophysiological and morphological characterization of dentate astrocytes in the hippocampusDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2005Masako Isokawa Abstract We studied electrophysiological and morphological properties of astrocytes in the dentate gyrus of the rat hippocampus in slices. Intracellular application of Lucifer yellow revealed two types of morphology: one with a long process extruding from the cell body, and the other with numerous short processes surrounding the cell body. Their electrophysiological properties were either passive, that is, no detectable voltage-dependent conductance, or complex, with Na+/K+ currents similar to those reported in the Ammon's horn astrocytes. We did not find any morphological correlate to the types of electrophysiological profile or dye coupling. Chelation of cytoplasmic calcium ([Ca2+]i) by BAPTA increased the incidence of detecting a low Na+ conductance and transient outward K+ currents. However, an inwardly rectifying K+ current (Kir), a hallmark of differentiated CA1/3 astrocytes, was not a representative K+ -current in the complex dentate astrocytes, suggesting that these astrocytes could retain an immature form of K-currents. Dentate astrocytes may possess a distinct current profile that is different from those in CA1/3 Ammon's horn. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2005 [source] Transpiration and stomatal conductance across a steep climate gradient in the southern Rocky MountainsECOHYDROLOGY, Issue 3 2008Nate G. McDowell Abstract Transpiration (E) is regulated over short time periods by stomatal conductance (Gs) and over multi-year periods by tree- and stand-structural factors such as leaf area, height and density, with upper limits ultimately set by climate. We tested the hypothesis that tree structure, stand structure and Gs together regulate E per ground area (Eg) within climatic limits using three sites located across a steep climatic gradient: a low-elevation Juniperus woodland, a mid-elevation Pinus forest and a high-elevation Picea forest. We measured leaf area : sapwood area ratio (Al : As), height and ecosystem sapwood area : ground area ratio (As : Ag) to assess long-term structural adjustments, tree-ring carbon isotope ratios (,13C) to assess seasonal gas exchange, and whole-tree E and Gs to assess short-term regulation. We used a hydraulic model based on Darcy's law to interpret the interactive regulation of Gs and Eg. Common allometric dependencies were found only in the relationship of sapwood area to diameter for pine and spruce; there were strong site differences for allometric relationships of sapwood area to basal area, Al : As and As : Ag. On a sapwood area basis, E decreased with increasing elevation, but this pattern was reversed when E was scaled to the crown using Al : As. Eg was controlled largely by As : Ag, and both Eg and Gs declined from high- to low-elevation sites. Observation-model comparisons of Eg, Gs and ,13C were strongest using the hydraulic model parameterized with precipitation, vapour pressure deficit, Al : As, height, and As : Ag, supporting the concept that climate, Gs, tree- and stand-structure interact to regulate Eg. Copyright © 2008 John Wiley & Sons, Ltd. [source] Seasonal and spatial variation in a prairie stream-fish assemblageECOLOGY OF FRESHWATER FISH, Issue 3 2002K. G. Ostrand Abstract,,,Stream-fish assemblage and environmental data for 13 sites in the upper Brazos River, Texas, USA during 1997 and 1998 were used to assess the relationship between environmental conditions, and seasonal and spatial variation in fish species abundance and distribution patterns. There was considerable spatial variation in environmental conditions among sites. Spatial variation in species diversity and species composition was related to variation in conductance (salinity), depth and current velocity among sites and streams. Species diversity increased downstream and species composition shifted from primarily cyprinodontids upstream to cyprinids downstream. Among all dominant species, spatial components of variation in fish abundance were greater than seasonal components, suggesting that assemblage structure is determined more by average or persistent differences in environmental conditions among sites than by seasonal variation in environmental conditions. [source] The impact of cigarette deprivation and cigarette availability on cue,reactivity in smokersADDICTION, Issue 2 2010Steffani R. Bailey ABSTRACT Aims This experiment was conducted to determine the impact of cigarette deprivation and cigarette availability on reactivity measures to cigarette cues. Participants Smokers were recruited who were 18 years of age or older, not attempting to quit or cut down on their smoking, smoked at least 20 cigarettes daily, had been smoking regularly for past year and had an expired carbon monoxide level of at least 10 parts per million. Design Smokers were assigned randomly to abstain from smoking for 24 hours (n = 51) or continue smoking their regular amount (n = 50). Twenty-four hours later, they were exposed to trials of either a lit cigarette or a glass of water with a 0, 50 or 100% probability of being able to sample the cue on each trial. Craving, mood, heart rate, skin conductance, puff topography and latency to access door to sample the cue were measured. Findings Both exposure to cigarette cues and increasing availability of those cues produced higher levels of craving to smoke. Deprivation produced a generalized increase in craving. There was no consistent evidence, however, that even under conditions of high cigarette availability, deprived smokers were sensitized selectively to presentations of cigarette cues. Conclusions The data suggest that, even under conditions of immediate cigarette availability, deprivation and cue presentations have independent, additive effects on self-reported craving levels in smokers. [source] Organic solvents in CEELECTROPHORESIS, Issue S1 2009Ernst Kenndler Abstract In this contribution some fundamental aspects are discussed serving for a critical reflection and elucidation of the role of organic solvents in CE. The implications of the solvent on the parameters governing peak resolution are discussed based on the concepts describing migration and zone broadening in capillary zone electrophoresis. This discussion includes the solvent-dependent influence of the ionic strength on the mobility. The role of the solvent on the plate number in case of the inevitable diffusional peak dispersion is outlined, and its effect on other peak broadening contributions is briefly examined. This paper also deals with the problems of conductance, applicable voltage and analysis time upon application of organic solvents, and tries to clarify some misunderstandings common in the literature. [source] Effects of Stern layer conductance on electrokinetic energy conversion in nanofluidic channelsELECTROPHORESIS, Issue 5 2008Christian Davidson Abstract A thermo-electro-hydro-dynamic model is developed to analytically account for the effects of Stern layer conductance on electrokinetic energy conversion in nanofluidic channels. The optimum electrokinetic devices performance is dependent on a figure of merit, in which the Stern layer conductance appears as a nondimensional Dukhin number. Such surface conductance is found to significantly reduce the figure of merit and thus the efficiency and power output. This finding may explain why the recently measured electrokinetic devices performances are far below the theoretical predictions where the effects of Stern layer conductance have been ignored. [source] Internal electrolyte temperatures for polymer and fused-silica capillaries used in capillary electrophoresisELECTROPHORESIS, Issue 22 2005Christopher J. Evenhuis Abstract 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 (,TMean) was directly proportional to P/L and inversely proportional to the thermal conductivity (,) of the capillary material. At 7.5,W/m, values for ,TMean for NGFP, PMMA, and PEEK were determined to be 36.6, 33.8, and 30.7°C, respectively. Under identical conditions, ,TMean for FS capillaries was 20.4°C. [source] Effect of cotton nitrogen fertilization on Bemisia argentifolii populations and honeydew productionENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 1 2001J.L. Bi Abstract The impact of nitrogen fertilization on cotton plants, Gossypium hirsutum L., silverleaf whitefly, Bemisia argentifolii Bellows & Perring, population dynamics and honeydew production were investigated in the field at Riverside, California, USA. Treatments were soil applications of 0, 112, 168 and 224 kg nitrogen per hectare, and a soil application of 112 kg of nitrogen plus a foliar application of 17 kg nitrogen per hectare. Increased numbers of both adult and immature whiteflies occurred during population peaks with increasing amounts of applied nitrogen. Higher numbers of whiteflies resulted in increased levels of honeydew. Increasing plant nitrogen also enhanced cotton foliar photosynthetic rates and stomatal conductance, and altered concentrations of glucose, fructose and sucrose in cotton petioles. However, at our treatment levels nitrogen had no effect on seedcotton yield. Petiole glucose levels were significantly correlated with numbers of whitefly adults on leaves during their peak populations. Significant correlations between whitefly numbers and other cotton physiological parameters occurred on only a few sampling dates. [source] Excitatory actions of substance P in the rat lateral posterior nucleusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2010Kush Paul Abstract The lateral posterior nucleus (LP) receives inputs from both neocortex and superior colliculus (SC), and is involved with integration and processing of higher-level visual information. Relay neurons in LP contain tachykinin receptors and are innervated by substance P (SP)-containing SC neurons and by layer V neurons of the visual cortex. In this study, we investigated the actions of SP on LP relay neurons using whole-cell recording techniques. SP produced a graded depolarizing response in LP neurons along the rostro-caudal extent of the lateral subdivision of LP nuclei (LPl), with a significantly larger response in rostral LPl neurons compared with caudal LPl neurons. In rostral LPl, SP (5,2000 nm) depolarized nearly all relay neurons tested (> 98%) in a concentration-dependent manner. Voltage-clamp experiments revealed that SP produced an inward current associated with a decreased conductance. The inward current was mediated primarily by neurokinin receptor (NK)1 tachykinin receptors, although significantly smaller inward currents were produced by specific NK2 and NK3 receptor agonists. The selective NK1 receptor antagonist RP67580 attenuated the SP-mediated response by 71.5% and was significantly larger than the attenuation of the SP response obtained by NK2 and NK3 receptor antagonists, GR159897 and SB222200, respectively. The SP-mediated response showed voltage characteristics consistent with a K+ conductance, and was attenuated by Cs+, a K+ channel blocker. Our data suggest that SP may modulate visual information that is being processed and integrated in the LPl with inputs from collicular sources. [source] NCS-1 differentially regulates growth cone and somata calcium channels in Lymnaea neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2008Kwokyin Hui Abstract Local voltage-gated calcium channels, which regulate intracellular Ca2+ levels by allowing Ca2+ influx, play an important role in guiding and shaping growth cones, and in regulating the outgrowth and branching of neurites. Therefore, elucidating the mechanisms that regulate the biophysical properties of whole-cell calcium currents in the growth cones and somata of growing neurons is important to improving our understanding of neuronal development and regeneration. In this study, taking advantage of the large size of the pedal A (PeA) neurons in Lymnaea stagnalis, we compared the biophysical properties of somata and growth cone whole-cell calcium channel currents using Ba2+ and Ca2+ as current carriers. We found that somata and growth cone currents exhibit similar high-voltage activation properties. However, Ba2+ and Ca2+ currents in growth cones and somata are differentially affected by a dominant-negative peptide containing the C-terminal amino acid sequence of neuronal calcium sensor-1 (NCS-1). The peptide selectively reduces the peak and sustained components of current densities and the slope conductance in growth cones, and shifts the reversal potential of the growth cone currents to more hyperpolarized voltages. In contrast, the peptide had no significant effect on the somata calcium channels. Thus, we conclude that NCS-1 differentially modulates Ca2+ currents in the somata and growth cones of regenerating neurons, and may serve as a key regulator to facilitate the growth cone calcium channel activity. [source] Small-conductance Cl, channels contribute to volume regulation and phagocytosis in microgliaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2007Guillaume Ducharme Abstract The shape and volume of microglia (brain immune cells) change when they activate during brain inflammation and become migratory and phagocytic. Swollen rat microglia express a large Cl, current (IClswell), whose biophysical properties and functional roles are poorly understood and whose molecular identity is unknown. We constructed a fingerprint of useful biophysical properties for comparison with IClswell in other cell types and with cloned Cl, channels. The microglial IClswell was rapidly activated by cell swelling but not by voltage, and showed no time-dependence during voltage-clamp steps. Like IClswell in many cell types, the halide selectivity sequence was I, > Br, > Cl, > F,. However, it differed in lacking inactivation, even at +100 mV with high extracellular Mg2+, and in having a much lower single-channel conductance: 1,3 pS. Based on these fundamental differences, the microglia channel is apparently a different gene product than the more common intermediate-conductance IClswell. Microglia express several candidate genes, with relative mRNA expression levels of: CLIC1 > ClC3 > ICln , ClC2 > Best2 > Best1 , Best3 > Best4. Using a pharmacological toolbox, we show that all drugs that reduced the microglia current (NPPB, IAA-94, flufenamic acid and DIOA) increased the resting cell volume in isotonic solution and inhibited the regulatory volume decrease that followed cell swelling in hypotonic solution. Both channel blockers tested (NPPB and flufenamic acid) dose-dependently inhibited microglia phagocytosis of E. coli bacteria. Because IClswell is involved in microglia functions that involve shape and volume changes, it is potentially important for controlling their ability to migrate to damage sites and phagocytose dead cells and debris. [source] Diversity of GABAA receptor synaptic currents on individual pyramidal cortical neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2007Timothy Ing Abstract Miniature GABAA receptor-mediated inhibitory postsynaptic currents (mIPSCs) in cortical pyramidal neurons have previously been categorized into two types: small amplitude mIPSCs with a mono-exponential deactivation (mono-mIPSCs) and relatively larger mIPSCs with bi-exponential deactivation (bi-mIPSCs). The aim of this study was to determine if the GABAA channels that underlie these mIPSCSs are molecularly distinct. We found, using non-stationary noise analysis, that the difference in their amplitude could be not accounted for by their single channel conductance (both were 40 pS). Next, using , subunit selective GABAA receptor modulators, we examined the identity of the , subunits that may be expressed in the synapses that give rise to these mIPSCs. Zolpidem (100 and 500 nm, ,1 selective) affected the deactivation of a subset of the mono-mIPSCs, indicating that ,1 subunits are not highly expressed in these synapses. However, zolpidem (100 nm) prolonged the deactivation of all bi-mIPSCs, indicating a high abundance of ,1 subunits in these synapses. SB-205384 (,3 selective) had no effect on the mono-mIPSCs but the bi-mIPSCs were prolonged. Furosemide (,4 selective) reduced the amplitude of only the mono-mIPSCs. L655,708 (,5 selective) reduced the amplitude of both populations and shortened the duration of the mono-mIPSCs. Finally, we found that the neuroactive steroid pregesterone sulphate reduced the amplitude of both mIPSC types. These results provide pharmacological evidence that synapses on cortical pyramidal neurons are molecularly distinct. The purpose of these different types of synapses may be to provide different inhibitory timing patterns on these cells. [source] A population-based model of the nonlinear dynamics of the thalamocortical feedback network displays intrinsic oscillations in the spindling (7,14 Hz) rangeEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2005Nada A. B. Yousif Abstract The thalamocortical network is modelled using the Wilson,Cowan equations for neuronal population activity. We show that this population model with biologically derived parameters possesses intrinsic nonlinear oscillatory dynamics, and that the frequency of oscillation lies within the spindle range. Spindle oscillations are an early sleep oscillation characterized by high-frequency bursts of action potentials followed by a period of quiescence, at a frequency of 7,14 Hz. Spindles are generally regarded as being generated by intrathalamic circuitry, as decorticated thalamic slices and the isolated thalamic reticular nucleus exhibit spindles. However, the role of cortical feedback has been shown to regulate and synchronize the oscillation. Previous modelling studies have mainly used conductance-based models and hence the mechanism relied upon the inclusion of ionic currents, particularly the T-type calcium current. Here we demonstrate that spindle-frequency oscillatory activity can also arise from the nonlinear dynamics of the thalamocortical circuit, and we use bifurcation analysis to examine the robustness of this oscillation in terms of the functional range of the parameters used in the model. The results suggest that the thalamocortical circuit has intrinsic nonlinear population dynamics which are capable of providing robust support for oscillatory activity within the frequency range of spindle oscillations. [source] Auxiliary subunit regulation of high-voltage activated calcium channels expressed in mammalian cellsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2004Takahiro Yasuda Abstract The effects of auxiliary calcium channel subunits on the expression and functional properties of high-voltage activated (HVA) calcium channels have been studied extensively in the Xenopus oocyte expression system, but are less completely characterized in a mammalian cellular environment. Here, we provide the first systematic analysis of the effects of calcium channel , and ,2,, subunits on expression levels and biophysical properties of three different types (Cav1.2, Cav2.1 and Cav2.3) of HVA calcium channels expressed in tsA-201 cells. Our data show that Cav1.2 and Cav2.3 channels yield significant barium current in the absence of any auxiliary subunits. Although calcium channel , subunits were in principle capable of increasing whole cell conductance, this effect was dependent on the type of calcium channel ,1 subunit, and ,3 subunits altogether failed to enhance current amplitude irrespective of channel subtype. Moreover, the ,2,, subunit alone is capable of increasing current amplitude of each channel type examined, and at least for members of the Cav2 channel family, appears to act synergistically with , subunits. In general agreement with previous studies, channel activation and inactivation gating was regulated both by , and by ,2,, subunits. However, whereas pronounced regulation of inactivation characteristics was seen with the majority of the auxiliary subunits, effects on voltage dependence of activation were only small (< 5 mV). Overall, through a systematic approach, we have elucidated a previously underestimated role of the ,2,,1 subunit with regard to current enhancement and kinetics. Moreover, the effects of each auxiliary subunit on whole cell conductance and channel gating appear to be specifically tailored to subsets of calcium channel subtypes. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||