Nonstationary Currents Research Articles

Time-dependent theory of a double quantum well resonant interband tunnel transistor

A time-dependent theory of a double quantum well resonant interband tunnel transistor is presented. The theory is based on a system of three linear differential equations for time-dependent resonant currents and charges stored in the wells. First the stationary resonant current-voltage curve is investigated. then the general solution for the non-stationary tunnelling current is obtained by the perturbation method. The current is found to be an ultra-sensitive function of the time-dependent small external voltage which is applied between the emitter and the second quantum well for detuning the resonances of quantum levels. Two nonstationary cases are investigated. For a step-function impulse of external voltage the characteristics of the response current are found. For a harmonic external voltage the frequency dependence of the response current is found. Matched and unmatched systems of barriers are investigated and found to exhibit significantly different behaviours.

52] Analysis of nonstationary single-channel currents

This chapter discusses the procedures in the acquisition and analysis of single-channel activity that are specific to the nonstationary case. In many respects, the analysis of nonstationary single-channel recordings is the same as the analysis of stationary records. Many types of channels show changes in their gating behavior that occur on time scales of seconds to minutes. Ligand-gated channels, such as acetylcholine receptors, show long silent periods owing to desensitization. Switching among gating modes is particularly well characterized in long recordings from a voltage-gated Cl - channel. In patch-clamp recordings, the delay in the application of a voltage stimulus to the membrane is usually negligible. In some patch clamps, the stimulus input is passed through a filter to reduce the maximum rate of rise. When more than one channel is present in a patch, the interpretation of open and closed times becomes quite complicated.

The tides of the southern Weddell Sea

The tides of the Weddell Sea are described using all the available data. The primary data are a set of current meter and tide gauge records taken during the period of 1977 to 1979 in the southern Weddell Sea. These data show that the four major tidal constituents propagate from east to west along the coast of Queen Maud Land and around the Weddell Sea in a clockwise fashion. In the southern Weddell Sea the broad, deep continental shelf interacts with the tides and diurnal shelf waves are excited, mainly at the K 1 frequency. The preference of K 1 over O 1 might be due to the interaction of a variable shelf topography with a non-stationary mean current. The diurnal tidal currents are nearly barotropic while the semidiurnal tidal currents show distinct depth dependence. At 74°28'S the frequency of the M 2 tidal constituent equals the inertial frequency. Theory predicts that the M 2 velocity profile becomes strongly depth dependent at this latitude, and the observations support this prediction. The normalized variance associated with the cusps in the tidal spectra increases strongly towards the bottom for the semidiurnal constituents possibly due to the generation of internal waves at semidiurnal frequencies. The annual constituent, Sa, is quite large for tidal currents, probably due to environmental forcing.

Rapid singular value decomposition for time-domain analysis of magnetic resonance signals by use of the lanczos algorithm

Time-series analysis has become an integral part of signal interpretation in magnetic resonance and other experiments. As an example, linear prediction with singular value decomposition (LPSVD) (I, 2) and the related method, Hankel SVD (HSVD) (3)) have been recently applied to problems in NMR (2)) 2D NMR (4), 2D electron spin-echo spectroscopy (2D ESE) (5,6), Fourier transform ESR correlation spectroscopy ( 7)) time-resolved femtosecond spectroscopy (8)) and nonstationary neurological currents ( 9). The minimal goal of time-series analysis is to separate signal from noise. Spectral transform methods, such as FFT filtering (IO), maximum entropy ( MEM ) ( I I ) , and LPZ ( 12)) replace the original data with a new time series (or its spectrum) that has an enhanced signal-to-noise ratio. In contrast spectral decomposition methods, such as LPSVD or HSVD, which assume a certain functional form for the time series, provide both a recipe for separating signal from noise and a listing of the harmonic components contained in the original data. This harmonic list simplifies spectral analysis and can be used to (1) extend the noise-reduced time series, (2) selectively reconstruct certain regions of the harmonic spectrum, and (3) data-compress the signal. The substantial benefits of spectral decomposition are often offset by the requirements of considerable computational time and memory storage. For a time series of N data points spectral transform techniques usually require computational time of O(N logzN) to O(N’) and storage of O(N) whereas spectral decomposition, such as HSVD, requires computational time of 0( N3) and storage of O(N2). We have investigated a new approach for solving the spectral decomposition problem which is based on the Lanczos algorithm (LA) (13). In the past the LA has provided an effective means for solving slow-motional magnetic resonance spectra ( 14, 15) as well as other complicated problems in chemical physics ( 16, 17). The LA is an extremely fast method for solving large eigenelement problems when either (1)

The application of fully conservative difference schemes to the calculation of two-dimensional magnetohydrodynamic systems

A fully conservative difference schemes (FCDS) for calculating two-dimensional non-stationary MHD currents described in Eulerian variables is constructed. The conductivity of the medium is assumed to be ideal. The specific form of the difference schemes is implemented on a rectilinear lattice in Cartesian coordinates with two different orientations of the magnetic field induction vector. The general form of the description of the schemes we construct admits of the use of curvilinear lattices. The schemes considered enable us to calculate the currents for large and small values of the ratio of the matter pressure to the magnetic field. The quality of fully-conservative difference schemes and conservative difference schemes is compared using the example of the numerical solution of a model problem.

Fast charge translocations associated with partial reactions of the Na,K-pump: I. Current and voltage transients after photochemical release of ATP

Nonstationary electric currents are described which are generated by the Na,K-pump. Flat membrane sheets 0.2-1 micron in diameter containing a high density of oriented Na,K-ATPase molecules are bound to a planar lipid bilayer acting as a capacitive electrode. In the aqueous phase adjacent to the bound membrane sheets, ATP is released within milliseconds from an inactive, photolabile precursor ("caged" ATP) by an intense flash of light. After the ATP-concentration jump, transient current and voltage signals can be recorded in the external circuit corresponding to a translocation of positive charge across the pump protein from the cytoplasmic to the extracellular side. These electrical signals which can be suppressed by inhibitors of the Na,K-ATPase require the presence of Na+ but not of K+ in the aqueous medium. The intrinsic pump current Ip(t) can be evaluated from the recorded current signal, using estimated values of the circuit parameters of the compound membrane system. Ip(t) exhibits a biphasic behavior with a fast rising period, followed by a slower decline towards a small quasi-stationary current. The time constant of the rising phase of Ip(t) is found to depend on the rate of photochemical ATP release. Further information on the microscopic origin of the current transient can be obtained by double-flash experiments and by chymotrypsin modification of the protein. These and other experiments indicate that the observed charge-translocation is associated with early events in the normal transport cycle. After activation by ATP, the pump goes through the first steps of the cycle and then enters a long-lived state from which return to the initial state is slow.

Fast charge translocations associated with partial reactions of the Na,K-pump: II. Microscopic analysis of transient currents.

Nonstationary pump currents which have been observed in K+-free Na+ media after activation of the Na,K-ATPase by an ATP-concentration jump (see the preceding paper) are analyzed on the basis of microscopic reaction models. It is shown that the behavior of the current signal at short times is governed by electrically silent reactions preceding phosphorylation of the protein; accordingly, the main information on charge-translocating processes is contained in the declining phase of the pump current. The experimental results support the Albers-Post reaction scheme of the Na,K-pump, in which the translocation of Na+ precedes translocation of K+. The transient pump current is represented as the sum of contributions of the individual transitions in the reaction cycle. Each term in the sum is the product of a net transition rate times a "dielectric coefficient" describing the amount of charge translocated in a given reaction step. Charge translocation may result from the motion of ion-binding sites in the course of conformational changes, as well as from movement of ions in access channels connecting the binding sites to the aqueous media. A likely interpretation of the observed nonstationary currents consists in the assumption that the principal electrogenic step is the E1-P/P-E2 conformational transition of the protein, followed by a release of Na+ to the extracellular side. This conclusion is supported by kinetic data from the literature, as well as on the finding that chymotrypsin treatment which is known to block the E1-P/P-E2 transition abolishes the current transient. By numerical simulation of the Albers-Post reaction cycle, the proposed mechanism of charge translocation has been shown to reproduce the experimentally observed time behavior of pump currents.

Charge and current electrostatics. Nonstationary sources of static fields

The problem of determination of the sources of an electrostatic field within the framework of Maxwellian electrodynamics has two forms of solution: stationary charges and nonstationary rotational current. For example, an external current which depends on the time t according to a linear law and which flows along the surface of a toroidal solenoid creates in the external region a field identical to the field of an external charge dipole. From currents which increase as even powers of t it is possible to construct magnetostatic multipoles, and from currents which increase as odd powers oft it is possible to construct electrostatic multipoles. Following Ya. B. Zel'dovich one can call toroidal current sources anapoles, and therefore a system of static fields produced by nonstationary toroidal currents can be classified as anapole static fields (anapole-statics). Such current sources have certain strange features. For example, when the current charges are placed in an electrostatic field they do not experience the usual Coulomb forces, but obtain from the field or give it an electromagnetic momentum, experiencing thereby a corresponding recoil. Taking into account this recoil re-establishes the equivalence of current and charge multipoles for any interactions.

Covariance of nonstationary sodium current fluctuations at the node of Ranvier

A theory is presented which relates the nonstationary autocovariance (covariance) function to the kinetics of independently-gated ionic channels. The experimental covariance was calculated from ensembles of 256--504 current records elicited from single, voltage-clamped, frog myelinated nerve fibers. Analysis of the covariance shows that the decay of channels from conducting to nonconducting states proceeds more slowly late in a depolarization to near 0 mV, as compared with early in the same depolarization. This behavior is inconsistent with there being only one kinetic state corresponding to the open channel. The behavior can be explained by the existence of multiple kinetic states corresponding to the open channel, or, alternatively, by the existence of multiple, kinetically distinct populations of channels.

Beitrage zur instationaren korrosion des eisens in sauren und neutralen elektrolytlosungen—I. Potentiodynamische bestimmung der korrosions- und schichtbildungsanteile der instationaren passivstromdichte des eisens in 1 N H 2SO 4

Non-stationary partial currents of corrosion ( i k +) and passive layer formation ( i s +) in 1 N H 2SO 4 have been determined by comparing the potentiodynamic cd-potential measurements on Armco—Iron in 1 N H 2SO 4 and in borate-buffer-solutions, pH = 6.8. The following assumptions were made: (1) in borate-buffer-solution the non-stationary corrosion cd can be neglected compared with the cd of the layer formation; (2) Considering the same non-stationary total current ( p ) a definite increase of the oxide layer thickness is associated with nearly the same potential shift to more positive values in 1 N H 2SO 4 and also in borate-buffer-solution.

Time varying rotary spectra

A method for computing and displaying the temporal variation of rotary spectral estimates is described. The method is applied to time series measurements of highly nonstationary winds and currents. The results indicate approximately fortnightly modulation of diurnal wind energy and inertial current energy.

Some problems concerning nonstationary currents in dense plasma systems confined by walls

Nonstationary currents are examined in a dense magnetized plasma with β ≫ 1, in which energy release and heat loss by thermal conduction and radiation are possible. Solutions are found in two limiting cases: ¦f¦ ≫ ¦ div (η▽T)¦ and ¦f¦ ≪ ¦ div(η▽T)¦ (f is the radiation intensity, η is the coefficient of heat conduction, and T is the temperature). In the first case a solution was obtained of some problems of the cooling and heating of a plasma illustrated in part by the evolution in time of the temperature profile in the boundary layer. In the second case an isomorphic solution was found for an arbitrary dependence of the coefficient of heat conduction on the temperature, pressure, and magnetic field.

Electric field excited in air by a pulse of gamma rays

The characteristics of the electric field produced by air polarization during the passage of nonstationary Compton currents excited by a γ-ray pulse in low-density air are discussed. The influence of the field on the motion of the Compton electrons is taken into account. The amplitude and relaxation time of the field are evaluated. A polarization electric field is created through the action of a directed current of γ-rays in air because of the movement of the Compton electrons. This paper discusses the basic characteristics of the resultant field in low-density air. A similar problem was raised in [1], where the electromagnetic field excited by a nonstationary source of γ-radiation in the upper atmosphere was considered. In that case, the Compton-electron currents were specified and their magnitude was assumed to be proportional to the ratio between the gas kinetic ranges of Compton electron and γ-ray (this ratio is of the order of 0.01 and is indepenent of height). With an increase in electron range, however, the decelerating action of the resultant electric field on the motion of the Compton electron becomes important (eEι/ɛ is a criterion for the effect; E is the field intensity, and ι and ɛ are the range and energy of the Compton electron).

Adsorption and oxidation of organic compounds on a platinum electrode partly covered by adsorbed sulphur

The dependence of the non-stationary currents of formic acid, formaldehyde and methanol on the degree of coverage of the platinum electrode by adsorbed sulphur and the effect of adsorbed sulphur on the electrooxidation of methanol and formaldehyde have been studied. Non-stationary currents of formic acid for θHS < 0.6 are greater than the non-stationary currents on the electrode surface without adsorbed sulphur. Non-stationary currents of formaldehyde and of methanol are proportional to the amount of surface unoccupied by sulphur. The adsorbed sulphur increases the activity of the surface unoccupied by sulphur for the oxidation of methanol and formaldehyde. Methods of determination of the degree of coverage of the platinum electrode surface by adsorbed sulphur are also discussed.

Adsorption and oxidation of organic compounds on a platinum electrode partly covered by adsorbed sulphur

Summary The dependence of the non-stationary currents of formic acid, formaldehyde and methanol on the degree of coverage of the platinum electrode by adsorbed sulphur and the effect of adsorbed sulphur on the electrooxidation of methanol and formaldehyde have been studied. Non-stationary currents of formic acid for θHS

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