Frequency Switches at Transition Temperature in Voltage-Gated Ion Channel Dynamics of Neural Oscillators

Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big saddle homoclinic orbit type to the saddle node on an invariant circle type, and the saddle node on an invariant circle type to the small saddle homoclinic orbit type. The bifurcation transitions are accompanied by an increase in thermodynamic temperature that affects the voltage-gated ion channel in the neural oscillator. We show that nonlinear and thermodynamical mechanisms are responsible for different switches of the frequency in the neural oscillator. We report a dynamical role of the phase response curve in switches of the frequency, in terms of slopes of frequency-temperature curve at each bifurcation transition. Adopting the transition state theory of voltagegated ion channel dynamics, we confirm that switches of the frequency occur in the first-order phase transition temperature states and exhibit different features of their potential energy derivatives in the ion channel. Each bifurcation transition also creates a discontinuity in the Arrhenius plot used to compute the time constant of the ion channel.

Positive Bias Temperature Instability Degradation of Buried InGaAs Channel nMOSFETs with InGaP Barrier Layer and Al2O3 Dielectric

Positive bias temperature instability stress induced interface trap density in a buried InGaAs channel metaloxide-semiconductor field-effect transistor with a InCaP barrier layer and Al2O3 dielectric is investigated. Well behaved split C-V characteristics with small capacitance frequency dispersion are confirmed after the insertion of the InCaP barrier layer. The direct-current Id-Vg measurements show both degradations of positive gate voltage shift and sub-threshold swing in the sub-threshold region, and degradation of positive △Vg in the oncurrent region. The Id-Vg degradation during the positive bias temperature instability tests is mainly contributed by the generation of near interface acceptor traps under stress. Specifically, the stress induced aeceptor traps contain both permanent and recoverable traps. Compared with surface channel InCaAs devices, stress induced recoverable donor traps are negligible in the buried channel ones.

A back analysis of the temperature field in the combustion volume space during underground coal gasification

The exact shape and size of the gasification channel during underground coal gasification(UGC) are of vital importance for the safety and stability of the upper parts of the geological formation.In practice existing geological measurements are insufficient to obtain such information because the coal seam is typically deeply buried and the geological conditions are often complex.This paper introduces a cylindrical model for the gasification channel.The rock and soil masses are assumed to be homogeneous and isotropic and the effect of seepage on the temperature field was neglected.The theory of heat conduction was used to write the equation predicting the temperature field around the gasification channel.The idea of an excess temperature was introduced to solve the equations.Applying this model to UCG in the field for an influence radius,r,of 70 m gave the model parameters,u1,2,3...,of 2.4,5.5,8.7...By adjusting the radius(2,4,or 6 m) reasonable temperatures of the gasification channel were found for 4 m.The temperature distribution in the vertical direction,and the combustion volume,were also calculated.Comparison to field measurements shows that the results obtained from the proposed model are very close to practice.

Variations of temperature, salinity and current in the southern tidal passage of the Hangzhou Bay, China

Field surveys covering a spring-neap tidal period were conducted to investigate the characteristics of tidal dynamics within a curved channel in the southern Hangzhou Bay, China. The channel has a maximum depth of more than 100 m with an average tidal range of 2.5 m, serving as the main tidal passage in the southern part of the Hangzhou Bay. Water salinity, temperature and velocity data were collected from the ship-based transects and mooring measurements. During flood tide, the tidal current intrudes into the Hangzhou Bay through the northern side of the channel with a maximum velocity of about 2 m/s, while retreats through the southern side during ebb tide with a maximum velocity of 1.8 m/s. Due to the pressure, density gradients, the Coriolis force and centrifugal effect, a lateral exchange flow is generated as the tidal current relaxes from flood to ebb. Salinity and temperature data show that the water in the channel is weakly stratified during both spring and neap tides in summer time.However, mixing in the middle region will be enhanced by the lateral circulation. Mooring data indicate that the temperature and salinity are varying at a frequency similar to tidal current but higher than sea level oscillation.Our results support the hypothesis that the high frequency salinity and temperature variations could be generated by combination of the tidal current and the lateral exchanging flow.

Analytical model of non-uniform charge distribution within the gated region of GaN HEMTs

A physics-based analytical expression that predicts the charge,electrical field and potential distributions along the gated region of the GaN HEMT channel has been developed.Unlike the gradual channel approximation(GCA),the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied volt-ages.In addition,the model can capture the influence of mobility and channel temperature on the charge distribution trend.The comparison with the hydrodynamic(HD)numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration.The ana-lytical nature of the model allows us to reduce the computational and time cost of the simulation.Also,it can be used as a core expression to develop a complete physics-based transistorⅣmodel without GCA limitation.

Determination of channel temperature for AlGaN/GaN HEMTs by high spectral resolution micro-Raman spectroscopy

Channel temperature determinations of A1GaN/GaN high electron mobility transistors （HEMTs） by high spectral resolution microRaman spectroscopy are proposed. The temperature dependence of the E2 phonon fre quency of GaN material is calibrated by using a JYT64000 microRaman system. By using the Lorentz fitting method, the measurement uncertainty for the Raman phonon frequency of 40.035 cm1 is achieved, correspond ing to a temperature accuracy of 43.2 ~C for GaN material, which is the highest temperature resolution in the published works. The thermal resistance of the tested A1GaN/GaN HEMT sample is 22.8 °C/W, which is in rea sonably good agreement with a three dimensional heat conduction simulation. The difference among the channel temperatures obtained by microRaman spectroscopy, the pulsed electrical method and the infrared image method are also investigated quantificationally.

Myocardial protection with pinacidil induced hyperpolarized arrest during cardiopulmonary bypass

Objective To investigate the myocardial protective effects of pinacidil induced hyperpolarized arrest and compare with those afforded by conventional depolarized hyperkalemic arrestMethods Eighteen dogs were equally divided into three groups: normothermic hyperpolarized group (Group A), hypothermic hyperpolarized group (Group B), and hyperkalemic group (Group C) Pinacidil (50μmol/L) containing 37℃ St Thomas solution (K+5mmol/L, 10ml/kg), pinacidil (50μmol/L, Sigma, USA) containing 4℃ St Thomas solution (K+ 5mmol/L, 10ml/kg) and 4℃ standard St Thomas solution (K+ 16mmol/L, 10ml/kg) were infused respectively through the aortic root after aorticclamping Heart arrest and its recovery, ultrastructure of the myocardium, the level of serum myocardial enzymes, and lipid peroxide and adenine cleotide of the myocardium were measuredHemodynamics during ischemia and after reperfusion were observedResults The percentages of normal mitochondria and glycogen did not change much during ischemia (except at 60 min) and after reperfusion in B Group, but declined markedly in Group C 30 min and 60 min after ischemia and 20 min after reperfusion (P<0.01) In Group A,they were lower than those of Group B before ischemia, but higher than those of Group C The recoveries of CO, SV, CI, LVSW, RVSW and MAP in Group B were significantly better than those in other two groups 15 min and 30 min after reperfusion (P<0.05and0.01, respectively) However, they were still better in Group A than those in Group C(P<0.05 and 0.01, respectively)The onset of heart arrest was faster in Groups C and B than that in Group A Highly elevated serum myocardial enzymes were observed 60 min after ischemia and 20 min after reperfusion in Group C, while they were only mild in the hyperpolarized groups, especially in Group B, and their recoveries were rapid Adenine nucleotides of the myocardium were better preserved in Group B than in other two groups 30 min, 60 min after ischemia, and 20 min after reperfusion (P<0.05 and 0.01, respectively)They were also much better in Group A than in GroupC(P<0.05and0.01,respectively)Lipid peroxide of the myocardium were significantly lower in Group B than in other groups 20 min after reperfusion (P<0.01),and they were lower in Group A than in Group C(P<0.05) Conclusions Myocardial protection for global ischemia during cardiopulmonary bypass (CPB) could be achieved with hyperpolarized heart arrest induced by pinacidil, an ATP sensitive potassium channel opener,especially in the hypothermic state The protection is weaker in normothermia but is still superior to that with traditional depolarized hyperkalemic arrest

Self-heating and traps effects on the drain transient response of AlGaN/GaN HEMTs

The effects of self-heating and traps on the drain current transient responses of AlGaN/GaN HEMTs are studied by 2D numerical simulation. The variation of the drain current simulated by the drain turn-on pulses has been analyzed. Our results show that temperature is the main factor for the drain current lag. The time that the drain current takes to reach a steady state depends on the thermal time constant, which is 8μs in this case. The dynamics of the trapping of electron and channel electron density under drain turn-on pulse voltage are discussed in detail, which indicates that the accepter traps in the buffer are the major reason for the current collapse when the electric field significantly changes. The channel electron density has been shown to increase as the channel temperature rises.

A self-heating study on multi-finger AlGaN/GaN high electron mobility transistors

Self-heating in multi-finger AlGaN/GaN high-electron-mobility transistors（HEMTs） is investigated by measurements and modeling of device junction temperature under steady-state operation.Measurements are carried out using micro-Raman scattering to obtain the detailed and accurate temperature distribution of the device.The device peak temperature corresponds to the high field region at the drain side of gate edge.The channel temperature of the device is modeled using a combined electro-thermal model considering 2DEG transport characteristics and the Joule heating power distribution.The results reveal excellent correlation to the micro-Raman measurements, validating our model for the design of better cooled structures.Furthermore,the influence of layout design on the channel temperature of multi-finger AlGaN/GaN HEMTs is studied using the proposed electro-thermal model, allowing for device optimization.