Carrier mobility in two-dimensional disordered hopping systems

A model of the equilibrium 2D hopping mobility in a disordered organic semiconductor is formulated for arbitrary charge carrier densities and arbitrary temperatures. The calculated dependence of the 2D mobility upon inverse temperature is compared with experimental data obtained on 2D carrier transport in poly(3-hexylthiophene) thin film field-effect transistors.     

On the effect of electron-phonon interaction on the temperature dependences of magnetotransport in quantum hall systems

The effect of electron-phonon interaction on the temperature dependences of conductivity is studied in the mode of the integer quantum Hall effect. It is shown that electron-phonon interaction leads to the possibility of transport in the region of localized states, thus forming the shape of magnetotransport curves at a given temperature. The relation between scaling indices in the power laws describing the dependences of the widths of transition regions between successive plateaus of the quantum Hall effect on the temperature and localization length is determined within an analytical model as a function of the energy measured from a certain Landau-level center. Direct numerical calculations of the magnetotransport curves are performed at various temperatures. The results are in good agreement with theory and experimental data on the integer quantum Hall effect.     

The hall effect in Fe submonolayer systems on n-and p-type Si(111)

The in situ Hall effect measurements at room temperature showed that formation of the atomically clean Si(111) 7×7 surface as a result of high-temperature annealing (T=1250°C, t=120–180 s) of n-Si reverses the majority carrier sign at the surface, and a hole-enriched layer is formed at the p-Si surface. The different dynamics of Hall and resistivity voltage variations within the first monolayer of iron adsorbed onto substrates with a p-n junction or with a hole-enriched layer is not related to conduction over the adsorbed layer. Conduction in the Fe layer of thickness exceeding three monolayers is caused in both cases by the transport of electrons with densities 2×10¹³–2×10¹⁴ cm^?2 and mobilities 65–90 cm²/(V s).     

Temperature- and potential-distributions determination method for hall plates,considering the effect of temperature-dependent conductivity and hall coefficient

An existing technique for determining the temperature distribution and the potential distribution of a Hall plate is extended to take into account the effect of the temperature-dependent conductivity and Hall coefficient. Equations to be used for that are presented. A practical example—the modeling of an intrinsic indium antimonide semiconductor-made Hall plate—is used to illustrate and evaluate the method using these equations.     

Anomalies of the fractional quantum hall effect in a wide ballistic wire

Magnetotransport in a ballistic wire under the conditions of integer and fractional quantization was studied experimentally. A nonlinear magnetic-field dependence of filling factor (ν) of the Landau level was observed; this dependence arises if the self-consistent electrostatic potential of the wire has a specific form. It is assumed that the observed effect results from the influence of interaction between electrons at the partially occupied Landau level on this potential, which brings about a decrease in the electron concentration in the wire as the magnetic field increases in the case of ν<1.     

Enhancement of the photovoltaic effect in a two-dimensionally disordered medium

The photogalvanic effect in a two-dimensional, weakly absorbing Dykhne medium without an inversion center is studied. It is shown that a giant enhancement of the effective photovoltaic coefficient occurs as a result of the divergence of the mean-square modulus of the electric field. Fiz. Tekh. Poluprovodn. 31, 973–975 (August 1997)     

Purcell effect in disordered one-dimensional photonic crystals

Semiconductors - The rate of spontaneous emission of an emitter placed in a disordered one-dimensional photonic crystal is analyzed. It is shown that the spontaneous emission of a dipole placed in...     

On the analysis of two-dimensional discrete singular systems

In contrast to 1-D systems, the 2-D systems have no natural notion of causality. An artificial restriction traditionally imposed to allow recursive solution of these systems is that of recursibility. In this paper we study 2-Dsingular systems, taking advantage of the nonoriented or noncausal nature of these systems to provide a solution even if the requirement of recursibility does not hold. It is shown thatnonrecursible masks may be described using singular 2-D systems. The analysis approach relies on thefundamental matrix.Research supported by the US Fulbright Foundation in Greece and NSF Grant ECS-8805932.     

Stability determination of two-dimensional discrete-time systems

In determining root distribution of univariate polynomials with real or complex-valued coefficients, the Bistritz tabular form offers a significant computational advantage. Stability studies of two-dimensional (2-D) discrete-time systems involve univariate polynomials possessing parameter-dependent coefficients, where the parameter takes values on the unit circle in the complex plane. This paper investigates the application of Bistritz tabular form in determining stability of 2-D discrete-time systems, and for this purpose we present two algorithms. Both algorithms utilize a recent result that has established the relationship between Schur-Cohn minors and the entries of the Bistritz tabular form corresponding to a given polynomial. A comparison between the use of the modified Jury table and the Bistritz table in stability checking of 2-D discrete-time systems is also presented.     

Symbolic time-series analysis for anomaly detection in mechanical systems

This paper examines the efficacy of a novel method for anomaly detection in mechanical systems, which makes use of a hidden Markov model, derived from the time-series data of pertinent measurement(s). The core concept of the anomaly detection method is symbolic time-series analysis that is built upon the principles of Automata Theory, Information Theory, and Pattern Recognition. The performance of this method is compared with that of other existing pattern-recognition techniques from the perspective of early detection of small fatigue cracks in ductile alloy structures. The experimental apparatus, on which the anomaly detection method is tested, is a multi-degree-of-freedom mass-beam structure excited by oscillatory motion of two electromagnetic shakers. The evolution of fatigue crack damage at one or more failure sites are detected from symbolic time-series analysis of displacement sensor signals.     

Spin hall effect in semiconductor structures with spatially inhomogeneous spin relaxation

The extrinsic spin Hall effect in samples with coordinate-dependent relaxation time of the spin was studied. It was shown that the spin Hall effect in this case results in not only spatial separation of electrons with different spin projections, but also in the generation of a certain spin; therefore, the total spin’s moment of a sample became nonzero under an electric current. A two-layer structure with different times of spin relaxation in layers and a homogeneous sample with linear behavior of the surface’s spin relaxation were considered. An expression for the effective spin’s relaxation time, which defines the spin polarization distribution in thin films, was derived. It was shown that the uniform spins polarization parallel to the film plane is possible, if the film thickness amounts to several diffusion lengths of the spin.     

Theoretical analysis of hall factor and hall mobility in p-type silicon

Using a two-band (i.e. heavy-hole and light-hole band) model and the relaxation time approximation, the Hall factor was calculated for the case of silicon doped with boron. Contributions from scattering by acoustical and optical phonons and by ionized and neutral impurities were considered. In addition, the effects of hole-hole scattering, as well as valence band nonparabolicity and anistropy were also taken into account. The scattering and anistropy factors were separately evaluated to emphasize their individual contributions to the Hall factor. Theoretical values of the Hall factor at 300 K vary between 0.882 and 0.714 over the dopant density ranges 10¹⁴ ≦ N_A ≦ 3 × 10¹⁸ cm^?3. Hall mobilities for p-type silicon were calculated and compared with published data 100 ≤ T ≤ 400 K and 10¹⁴ ≦ N_A ≦ 3 × 10¹⁸ cm^?3. The present model is limited to the case of uncompensated material and for the weak field in which μ_HB ? 1.     

Output feedback stabilization of two-dimensional fuzzy systems

Multidimensional Systems and Signal Processing - This paper is concerned with the output feedback stabilization of two-dimensional discrete fuzzy systems described by the Fornasini–Marchesini...     

骚动,发生在证券交易大厅

九江市是江西省的北大门，人口约40万。人口虽不多，但在市区内拥有国泰、君安等5家证券公司。前不久，5家证券公司接收上海证券所的卫星信号突然中断，致使上海股票不能交易。对这突如其来的情况，证券公司一时间拿不出解决办法，而股民们手中的股票不能交易，时间一长，就躁动不安，纷纷质询证券公司，并提出损失由证券公司承担。少数股民失去理智，冲进办公室，砸坏门窗、桌椅。在这种混乱的情况下，5家证券公司的老总们想到了九江市无线电管理处。管理处接到求援后，马上向省无线电监测站报告。省监测站立即携带卫星地球站测试设备赴九…     

Nondiffusive weak localization in two-dimensional systems with spin-orbit splitting of the spectrum

The effect of spin splitting caused by structural asymmetry (Rashba’s contribution) and bulk asymmetry (Dresselhaus’s contribution) on the magnetoconductance of two-dimensional structures with high mobility of charge carriers is studied. The theory of weak localization with regard to both of the contributions is developed. The theory is valid in the entire region of classically low magnetic fields for arbitrary relations between the frequencies of spin precession and elastic collisions. The suppression of the correction for antilocalization is demonstrated in the case of equal contributions of structural anisotropy and bulk anisotropy to the spin splitting. The effect of the contribution, cubic in the wave vector, to the spin splitting on the quantum magnetoresistance is studied.     

Synthesis filter bank optimization in two-dimensional separablesubband coding systems

Subband coding is a popular and well established technique used in visual communications, such as image and video transmission. In the absence of quantization and transmission errors, the analysis and synthesis filters in a subband coding scheme can be designed to obtain perfect reconstruction of the input signal, but this is no longer the optimal solution in the presence of quantization of the subband coefficients. We presuppose the use of a two-dimensional (2-D) separable subband scheme and we address the problem of designing, for a given analysis filter bank and assuming uniform quantization of the subband coefficients, the set of row and column synthesis filters that minimize the mean squared reconstruction error at the output of the subband system. Since the corresponding optimization problem is inherently nonlinear, we propose a suboptimal solution that extends a one-dimensional (l-D) optimal filter design procedure, already presented in the literature, to a 2-D separable synthesis filter bank. The separable 2-D extension is not trivial, since the processing in one direction, e.g., the rows, alters the statistics of the signals for the design of the filters in the other direction, e.g., the columns. To further simplify the filter design, we propose to model the input image as a 2-D separable Markov process plus an additive white component. Several design examples using both synthetic signals and real world images are presented, showing that the filters designed using the proposed technique can give a significant gain with respect to the perfect reconstruction solution, especially when the dither technique is used for quantization. The simulation results also show that the proposed image model can be conveniently used in the synthesis filter design procedure.     

Hierarchical and parallel processing structure of two-dimensional systems

Hierarchical and parallel processing structures are shown to exist in two-dimensional systems which could be exploited to develop fast algorithms.     

二维同步OCDMA系统的性能分析

构造了一种用于二维同步光码分多址(OCDMA)系统的修正素数跳频码(MPC/PC),分析了码字的自相关和互相关性能,研究了二维同步OCDMA系统的误码率和吞吐量性能.结果表明,与一维同步OCDMA系统相比,二维同步OCDMA系统的可接入用户数大大增加,误码率大大降低,吞吐量明显提高.     

On the effect of gate oxide thickness upon the hall mobility and other magneto-electrical characteristics in most structures

P-Channel silicon MOS Halltrons with a different thickness of the oxide under the gate are studied. The measurements are performed in steady-state conditions at room temperature and in a weak magnetic field. Some conclusions about the surface conductivity, Hall mobility and Hall coefficient of carriers in the channel are given. The magneto-electrical characteristics are presented as a function of space charge, surface potential and free charge at the surface of the semiconductor. An explanation of the decrease of the surface conductivity in the nonlinear part of the curve of surface conductivity vs gate voltage is proposed.