Einstein Relation in n-Channel Inversion Layers of Nonlinear Optical, Optoelectronic and Related Materials: Simplified Theory, Relative Comparison and Suggestion for an Experimental Determination

In this paper, we study the Einstein relation for the diffusivity to mobility ratio (DMR) in n-channel inversion layers of non-linear optical materials on the basis of a newly formulated electron dispersion relation by considering their special properties within the frame work of k.p formalism. The results for the n-channel inversion layers of III-V, ternary and quaternary materials form a special case of our generalized analysis. The DMR for n-channel inversion layers of II-VI, IV-VI and stressed materials has been investigated by formulating the respective 2D electron dispersion laws. It has been found, taking n-channel inversion layers of CdGeAs2, Cd(3)AS(2), InAs, InSb, Hg1-xCdxTe, In1-xGaxAsyP1-y lattice matched to InP, CdS, PbTe, PbSnTe, Pb1-xSnxSe and stressed InSb as examples, that the DMR increases with the increasing surface electric field with different numerical values and the nature of the variations are totally band structure dependent. The well-known expression of the DMR for wide gap materials has been obtained as a special case under certain limiting conditions and this compatibility is an indirect test for our generalized formalism. Besides, an experimental method of determining the 2D DMR for n-channel inversion layers having arbitrary dispersion laws has been suggested.

Energy-Efficient Decentralized Cooperative Routing in Wireless Networks

Wireless adhoc networks transmit information from a source to a destination via multiple hops in order to save energy and, thus, increase the lifetime of battery-operated nodes. The energy savings can be especially significant in cooperative transmission schemes, where several nodes cooperate during one hop to forward the information to the next node along a route to the destination. Finding the best multi-hop transmission policy in such a network which determines nodes that are involved in each hop, is a very important problem, but also a very difficult one especially when the physical wireless channel behavior is to be accounted for and exploited. We model the above optimization problem for randomly fading channels as a decentralized control problem - the channel observations available at each node define the information structure, while the control policy is defined by the power and phase of the signal transmitted by each node. In particular, we consider the problem of computing an energy-optimal cooperative transmission scheme in a wireless network for two different channel fading models: (i) slow fading channels, where the channel gains of the links remain the same for a large number of transmissions, and (ii) fast fading channels, where the channel gains of the links change quickly from one transmission to another. For slow fading, we consider a factored class of policies (corresponding to local cooperation between nodes), and show that the computation of an optimal policy in this class is equivalent to a shortest path computation on an induced graph, whose edge costs can be computed in a decentralized manner using only locally available channel state information (CSI). For fast fading, both CSI acquisition and data transmission consume energy. Hence, we need to jointly optimize over both these; we cast this optimization problem as a large stochastic optimization problem. We then jointly optimize over a set of CSI functions of the local channel states, and a c- - orresponding factored class of control poli.

Alamethicin, a Transmembrane Channel

Peptides possessing antibiotic activity, isolated from microbial sources, have been the subject of intensive structural and biological investigation over the past two decades.

Boundary-layer convective heat transfer in a convergent channel

In this paper the numerical solution of the heat transfer problem in a convergent channel with uniform and non-uniform wall temperatures under boundary-layer approximations has been presented. Also, a semi-analytical solution for uniform wall temperature has been obtained.

Alamethicin and related membrane channel forming polypeptides

Alamethicin and several related microbial polypeptides, which contain a high proportion of agr-aminoisobutyric acid (Aib) residues, possess the ability to modify the permeability properties of phospholipid bilayer membranes. Alamethicin induces excitability phenomena in model membranes and has served as an excellent model for the study of voltage sensitive transmembrane channels. This review summarizes various aspects of the structural chemistry and membrane modifying properties of alamethicin and related Alb containing peptides. The presence of Aib residues in these sequences, constrains the polypeptides to 310 or agr-helical conformations. Functional membrane channels are formed by aggregation of cylindrical peptide helices, which span the lipid bilayer, forming a scaffolding for an aqueous column across the membrane. After consideration of the available data on the conductance characteristics of alamethicin channels, a working, hypothesis for a channel model is outlined. Channel aggregates in the lipid phase may be stabilized by intermolecular hydrogen bonding, involving a central glutamine residue and also by interactions between the macro-dipoles of proximate peptide helices. Fluctuations between different conductance states are rationalized by transitions between states of different aggregation and hence altered dimensions of the aqueous core or by changes in net dipole moment of the aggregate. Ion fluxes through the channel may also be affected by the electric field within the aqueous core.

The helical conformations of 14- and 16-residue fragments of suzukacillin, a membrane channel-forming polypeptide

The suzukacillin fragments, Boc-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (14), Boc-Ala-Aib-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (16G) and the completely apolar 16-residue peptide in which the glutamine residue has been replaced by alanine (16A) have been studied by 270 MHz 1H-HMR, in C2HCl3 and (C2H3)2SO solution. Intramolecularly hydrogen-bonded NH groups have been identified by temperature and solvent dependence of chemical shifts. Peptides 14 and 16A adopt folded 310 helical conformations stabilized by 11 and 13 hydrogen bonds, respectively. In peptide 16G there are 12 intramolecular hydrogen bonds, with the glycine NH being solvent-exposed, in contrast to 14 and 16A.

Helical conformations of three crystalline pentapeptide fragments of suzukacillin, a membrane channel forming polypeptide

The crystal structures of three pentapeptide fragments of suzukacillin-A have been determined. Boc-Aib-Pro-Val-Aib-Val-OMe (peptide 1–5) adopts a distorted helical conformation, stabilized by three intramolecular hydrogen bonds (two 5→1, one 4→1). Boc-Ala-Aib-Ala-Aib-Aib-OMe (peptide 6–10) and Boc-Leu-Aib-Pro-Val-Aib-OMe (peptide 16–20) adopt 310 helical structures stabilized by three and two 4→1 intramolecular hydrogen bonds, respectively. These structures provide substantial support for a largely helical conformation for the suzukacillin membrane channel.

2 Algorithms For 3-Layer Channel Routing

A channel router is an important design aid in the design automation of VLSI circuit layout. Many algorithms have been developed based on various wiring models with routing done on two layers. With the recent advances in VLSI process technology, it is possible to have three independent layers for interconnection. In this paper two algorithms are presented for three-layer channel routing. The first assumes a very simple wiring model. This enables the routing problem to be solved optimally in a time of O(n log n). The second algorithm is for a different wiring model and has an upper bound of O(n2) for its execution time. It uses fewer horizontal tracks than the first algorithm. For the second model the channel width is not bounded by the channel density.

Non-Destructive Method to Estimate the Moisture Content in Bread using Multi-Channel Electrical Impedance Spectroscopy

Bread undergoes several physicochemical changes during storage that results in a rapid loss of freshness. These changes depend on moisture content present in bread product. An instrument based on electrical impedance spectroscopy technique is developed to estimate moisture content of bread at different zones using designed multi-channel ring electrodes. A dedicated AT89S52 microcontroller and associated peripherals are employed for hardware. A constant current is applied across bread loaf through central pair of electrodes and developed potential across different zones of bread loaf are measured using remaining four ring electrode pairs. These measured values of voltage and current are used to measure the impedance at each zone. Electrical impedance behavior of the bread loaf at crust and crumb is investigated during storage. A linear relationship is observed between the measured impedance and moisture content present in crust and crumb of bread loaf during storage of 120 hours.

Reverse Channel Training For Reciprocal Mimo Systems With Spatial Multiplexing

This paper investigates the problem of designing reverse channel training sequences for a TDD-MIMO spatial-multiplexing system. Assuming perfect channel state information at the receiver and spatial multiplexing at the transmitter with equal power allocation to them dominant modes of the estimated channel, the pilot is designed to ensure an stimate of the channel which improves the forward link capacity. Using perturbation techniques, a lower bound on the forward link capacity is derived with respect to which the training sequence is optimized. Thus, the reverse channel training sequence makes use of the channel knowledge at the receiver. The performance of orthogonal training sequence with MMSE estimation at the transmitter and the proposed training sequence are compared. Simulation results show a significant improvement in performance.

Evolution of texture during equal channel angular extrusion of commercially pure aluminum: Experiments and simulations

The evolution of crystallographic texture has been comprehensively studied for commercially pure Al as a function of amount of ECAE deformation for the three major routes of ECAE processing. It has been observed that processing through different routes leads to different type of texture, in both qualitative as well as quantitative sense. The results have been analyzed on the basis of existing concepts on ECAE deformation and simulations have been carried out using the simple shear model of ECAE implemented into the Viscoplastic Self Consistent model of polycrystal plasticity. The simulations revealed that non-octahedral slip is needed to reproduce the experimental texture development.

Inhibition of Human Two-Pore Domain K+ Channel TREK1 by Local Anesthetic Lidocaine: Negative Cooperativity and Half-of-Sites Saturation Kinetics

TWIK-related K+ channel TREK1, a background leak K+ channel, has been strongly implicated as the target of several general and local anesthetics. Here, using the whole-cell and single-channel patch-clamp technique, we investigated the effect of lidocaine, a local anesthetic, on the human (h) TREK1 channel heterologously expressed in human embryonic kidney 293 cells by an adenoviral-mediated expression system. Lidocaine, at clinical concentrations, produced reversible, concentration-dependent inhibition of hTREK1 current, with IC50 value of 180 mu M, by reducing the single-channel open probability and stabilizing the closed state. We have identified a strategically placed unique aromatic couplet (Tyr352 and Phe355) in the vicinity of the protein kinase A phosphorylation site, Ser348, in the C-terminal domain (CTD) of hTREK1, that is critical for the action of lidocaine. Furthermore, the phosphorylation state of Ser348 was found to have a regulatory role in lidocaine-mediated inhibition of hTREK1. It is interesting that we observed strong intersubunit negative cooperativity (Hill coefficient = 0.49) and half-of-sites saturation binding stoichiometry (half-reaction order) for the binding of lidocaine to hTREK1. Studies with the heterodimer of wild-type (wt)-hTREK1 and Delta 119 C-terminal deletion mutant (hTREK1(wt)-Delta 119) revealed that single CTD of hTREK1 was capable of mediating partial inhibition by lidocaine, but complete inhibition necessitates the cooperative interaction between both the CTDs upon binding of lidocaine. Based on our observations, we propose a model that explains the unique kinetics and provides a plausible paradigm for the inhibitory action of lidocaine on hTREK1.

Evolution of Grain-Boundary Microstructure and Texture in Interstitial-Free Steel Processed by Equal-Channel Angular Extrusion

The equal-channel angular extrusion (ECAE) of Ti-bearing interstitial-free (IF) steel was performed following two different routes, up to four passes, at a temperature of 300 degrees C. The ECAE led to a grain refinement to submicron size. After the second pass, the grain size attained saturation thereafter. The microstructural analysis indicated the presence of coincident-site lattice (CSL) boundaries in significant fraction, in addition to a high volume fraction of high-angle random boundaries and some low-angle boundaries after the deformation. Among the special boundaries, Sigma 3 and Sigma 13 were the most prominent ones and their fraction depended on the processing route followed. A deviation in the misorientation angle distribution from the Mackenzie distribution was noticed. The crystallographic texture after the first pass resembled that of simple shear, with the {112}, {110}, and {123} aligned to the macroscopic shear plane.

Kinetic characterization of rat brain type IIA sodium channel alpha-subunit stably expressed in a somatic cell line

1. The rat brain type IIA Na+ channel alpha-subunit was stably expressed in Chinese hamster ovary (CHO) cells. Current through the expressed Na+ channels was studied using the whole-cell configuration of the patch clamp technique. The transient Na+ current was sensitive to TTX and showed a bell-shaped peak current vs. membrane potential relation. 2. Na+ current inactivation was better described by the sum of two exponentials in the potential range -30 to +40 mV, with. a dominating fast component and a small slower component. 3. The steady-state inactivation, h(infinity), was related to potential by a Boltzmann distribution, underlying thr ee states of the inactivation gate. 4. Recovery of the channels from inactivation at different potentials in the range -70 to -120 mV were characterized by al? initial delay which decreased with hyperpolarization. The time course was well fitted by the sum of two exponentials. In this case the slower exponential was the major component, and both time constants decreased with hyperpolarization. 5. For a working description of the Na+ channel inactivation in this preparation, with a minimal deviation from the Hodgkin-Huxley model, a three-state scheme of the form O reversible arrow I-1 reversible arrow I-2 was proposed, replacing the original two-state scheme of the Hodgkin-Huxley model, and the rate constants are reported. 6. The instantaneous current-voltage relationship showed marked deviation from linearity and was satisfactorily fitted by the constant-field equation. 7. The time course of activation was described by an m(x) model. However, the best-fitted value of x varied with the membrane potential and had a mean value of 2. 8. Effective gating charge was determined to be 4.7e from the slope of the activation plot, plotted on a logarithmic scale. 9. The rate constants of activation, alpha(m) and beta(m), were determined. Their functional dependence on the membrane potential was investigated.