A model for the ∼ 1.10eV emission band in InP

A study of the emission band present in InP has been made at temperatures between 4.2 and 280 K. The emission spectrum has phonon-structure at lower temperatures. The observed band shape and band-peak position are well explained by the configuration coordinate model. The coupling strength S, a measure of the lattice-localized center interaction, ranges from 1.7 to 3.5. A nearest-neighbor molecular-like defect center (Fe)_In—(V)_p appears to be responsible for the 1.10eV emission band.     

A perturbation technique to model InGaAs/InP and GaAs FETs for millimeter-wave integrated circuits

A perturbation method is described to analytically model the electrical behavior of submicron FETs for millimeter-wave circuit applications. The approach includes the determination of the two-dimensional potential distribution in a non-rectangular depletion region. The result is used to derive analytical expressions for the threshold voltage and transconductance of FETs.     

An improved model for band tail states inn-type degenerate semiconductors

Summary Using two screened donor potential energy models and a wave vectork-positionr uncertainty relation, the results of the exponential band tail states, inn-type degenerate semiconductors, obtained in our previous paper, are improved. The second-order cumulant or the correlation functionW (ϱ,E) is expressed as a function of the total donor concentration ϱ and total carrier energyE. Near band edges, the conduction and valence band tails are, respectively, proportional to exp [E/E ₀(ϱ)] and exp [−E/E ₀(ϱ)], whereE ₀(ϱ) is the energy characteristic of the appropriate band tail, in good accordance with those experimentally obtained by Pankove. Far below the conduction band edge, our result of the conduction band tail is proportional to exp [−BE ² exp [A ]], whereA andB are the functions of ϱ, which is reduced to zero more rapidly in comparison with the corresponding result obtained by Halperin and Lax (i.e. exp [−|E| ⁿ , wheren varies between 1/2 and 2). To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

A performed model for band-gap narrowing of heavily doped semiconductors

The band-gap narrowing ΔE_g of n-type heavily doped crystals at an arbitrary temperature is investigated, basing on an extended Thomas-Fermi model given by Friedel and on our previous results.In highly degenerate semiconductors, the carrier-donor interaction contribution to ΔE_g is approximately proportional to the $\text{1}\text{6}$ power of electron concentration, in agreement with other theories.An exact expression for the inverse screening length is also obtained and compared with that given by Friedel.     

Experimental verification of an interpolation algorithm for improved estimates of animal position

This article presents experimental verification of an interpolation algorithm that was previously proposed in Jaffe [J. Acoust. Soc. Am. 105, 3168-3175 (1999)]. The goal of the algorithm is to improve estimates of both target position and target strength by minimizing a least-squares residual between noise-corrupted target measurement data and the output of a model of the sonar's amplitude response to a target at a set of known locations. Although this positional estimator was shown to be a maximum likelihood estimator, in principle, experimental verification was desired because of interest in understanding its true performance. Here, the accuracy of the algorithm is investigated by analyzing the correspondence between a target's true position and the algorithm's estimate. True target position was measured by precise translation of a small test target (bead) or from the analysis of images of fish from a coregistered optical imaging system. Results with the stationary spherical test bead in a high signal-to-noise environment indicate that a large increase in resolution is possible, while results with commercial aquarium fish indicate a smaller increase is obtainable. However, in both experiments the algorithm provides improved estimates of target position over those obtained by simply accepting the angular positions of the sonar beam with maximum output as target position. In addition, increased accuracy in target strength estimation is possible by considering the effects of the sonar beam patterns relative to the interpolated position. A benefit of the algorithm is that it can be applied "ex post facto" to existing data sets from commercial multibeam sonar systems when only the beam intensities have been stored after suitable calibration.     

基于期望响应内插技术的宽带波束优化设计

在以往窄带波束优化设计研究工作的基础上,提出了一种基于期望响应内插技术的宽带波束优化设计方法,目的在于避免宽带问题中由于频带划分过细带来的过重的设计负担,并使之可应用于稳健波束优化设计当中。该方法首先在设计频段内选取几个频率点,在每个频率点上设计得到相应的窄带波束优化权系数,并且根据每个阵元在不同频率点上的权系数构造一个宽带期望响应函数;然后用基于期望响应内插的FIR滤波器设计方法设计合适的FIR滤波器组,以使整个频段上的宽带波束优化得以实现。采用这种方法可以避免宽带波束优化设计中繁重的设计负担,并且在对实际声呐基阵进行宽带波束优化设计时只需少数几个频率点的测量值即可获得好的效果。仿真设计结果和实验研究表明了本文方法的有效性。     

Design of broadband beamformers based on an expected response interpolation technique

A method for designing broadband beamformers based on an expected response interpolation technique was proposed, with the aim of reducing the heavy optimization burden in the broadband beamformer design problem. In the method, some typical frequencies in the designing frequency band are selected and the optimal array weights are designed on these typical frequencies, based on which a broadband expected response function is constructed. Then, FIR filters are designed to realize the broadband beamforming over the whole designing frequency band, via the interpolation technique which is utilized to the expected responses of the FIR filters. Broadband beamforming can be fulfilled by applying these filters to each of the sensors in the array. By using the proposed method, designers need not to divide the whole designing frequency band into narrow subbands so as to make the narrow band assumption valid, which not only reduces the heavy designing burden, but also releases the requirement for measurements at fine frequency grids in the robust beamformer design. Results of both computer simulations and watertank experiments verify the effectiveness of the proposed method.     

A convenient technique for evaluating angular frequency in some nonlinear oscillations

In this paper, a convenient technique for evaluating angular frequency in some nonlinear oscillations is proposed. It is well known that once the restoring force function is given beforehand, the period of motion can be determined by an integral. The angular frequency has a relation with the period of motion as well as the integral. One makes a little modification for the integrand in the integral and a change of variable. It is found that if the three divisions are chosen on the integration interval and the trapezoid quadrature rule is used, a higher accurate result for the angular frequency can be achieved. For the restoring force being an odd function, three numerical examples are presented. The eardrum-type oscillation is studied as well. Higher accurate results for the angular frequency are obtained in all those examples.     

QWIP focal plane arrays on InP substrates for single and dual band thermal imagers

Alternative material systems on InP substrate provide certain advantages for mid-wavelength infrared (MWIR), long-wavelength infrared (LWIR) and dual band MWIR/LWIR quantum well infrared photodetector (QWIP) focal plane arrays (FPAs). While InP/InGaAs and InP/InGaAsP LWIR QWIPs provide much higher responsivity when compared to the AlGaAs/GaAs QWIPs, AlInAs/InGaAs system facilitates completely lattice matched single band MWIR and dual band MWIR/LWIR FPAs.We present an extensive review of the studies on InP based single and dual band QWIPs. While reviewing the characteristics of InP/InGaAs and InP/InGaAsP LWIR QWIPs at large format FPA level, we experimentally demonstrate that the cut-off wavelength of AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by only changing the quantum well (QW) width at the lattice matched composition. The cut-off wavelength can be shifted up to ～5.0 μm with a QW width of 22 Å in which case very broad spectral response (Δλ/λ_p = ～30%) and a reasonably high peak detectivity are achievable leading to a noise equivalent temperature difference as low as 14 mK (f/2) with 25 μm pitch in a 640 × 512 FPA. We also present the characteristics of InP based two-stack QWIPs with wavelengths properly tuned in the MWIR and LWIR bands for dual color detection. The results clearly demonstrate that InP based material systems display high potential for dual band MWIR/LWIR QWIP FPAs needed by third generation thermal imagers.     

On an interpolation model for the transition operator for Markov and non-Markov processes

A phenomenological interpolation model for the transition operator of a stationary Markov process is shown to be equivalent to the simplest difference approximation in the master equation for the conditional density. Comparison with the formal solution of the Fokker-Planck equation yields a criterion for the choice of the correlation time in the approximate solution. The interpolation model is shown to be form-invariant under an iteration-cum-rescaling scheme. Next, we go beyond Markov processes to find the effective time-development operator (the counterpart of the conditional density) in the following very general situation: the stochastic interruption of the systematic evolution of a variable by an arbitrary stationary sequence of randomizing pulses. Continuous-time random walk theory with a distinct first-waiting-time distribution is used, along with the interpolation model for the transition operator, to obtain the solution. Convenient closed-form expressions for the ‘averaged’ time-development operator and the autocorrelation function are presented in various special cases. These include (i) no systematic evolution, but correlated pulses; (ii) systematic evolution interrupted by an uncorrelated (Poisson) sequence of pulses.     

Motion estimation based on an improved block matching technique

An improved block-matching algorithm for fast motion estimation is proposed. The matching criterion is the sum of absolute difference. The basic idea is to obtain the best estimation of motion vectors by an optimization of the search process which can terminate the time-consuming computation of matching evaluation between the current block and the ineligible candidate block as early as possible and eliminate the search positions as many as possible in the search area. The performance of this algorithm is evaluated by theoretic analysis and compared with the full search algorithm (FSA). The simulation results demonstrate that the computation load of this algorithm is much less than that of FSA, and the motion vectors obtained by this algorithm are identical to those of FSA.     

Motion estimation based on an improved block matching technique

An improved block-matching algorithm for fast motion estimation is proposed. The matching criterion is the sum of absolute difference. The basic idea is to obtain the best estimation of motion vectors by an optimization of the search process which can terminate the time-consuming computation of matching evaluation between the current block and the ineligible candidate block as early as possible and eliminate the search positions as many as possible in the search area. The performance of this algorithm is evaluated by theoretic analysis and compared with the full search algorithm (FSA). The simulation results demonstrate that the computation load of this algorithm is much less than that of FSA, and the motion vectors obtained by this algorithm are identical to those of FSA.     

Vacancies and impurities in InP studied using positron lifetime and an improved Doppler-broadening spectrometer

In ^- in Zn-doped p-InP. The line-shape parameter measured by an improved Doppler-broadening spectrometer shows a significant difference between n-type and Fe-doped SI-InP materials: the S-parameter varies from 0.5203 in n-InP to 0.5184 in Fe-doped SI-InP by four times the standard deviation. A possible reason for this difference is discussed. Received: 7 January 1997/Accepted: 8 September 1997     

New interpolation technique for the CIP method on curvilinear coordinates

We propose a new interpolation technique for the CIP method applied to curvilinear coordinates. The CIP method can hardly maintain third-order accuracy on curvilinear coordinates. The reason for the degeneracy in accuracies has not been discussed in detail. This paper reveals the problems of the CIP method on curvilinear coordinates and presents an improved CIP method to solve the advection equation accurately. The features of the presented method are: (1) the metric computation on the upwind stencil is defined in the same manner as in the advection phase of the CIP method; and (2) gradient values in the physical domain in the computation on the curvilinear coordinates are used. Various test problems show that the improved CIP method has approximate third-order accuracy.     

A spatial filtering technique for improved holographic character recognition

Conventional holographic pattern recognition systems suffer from the disadvantage that, in dealing with highly ordered patterns such as Arabic numerals or the letters of the Roman alphabet it is sometimes impossible to distinguish between patterns with a high degree of similarity (eg the capital letters ‘E’ and ‘F’ or ‘B’ and ‘P’).The present paper analyzes a simple case and shows how the insertion of a suitable spatial filter in the Fourier transform plane can reduce the unwanted cross-correlation signal between dissimilar patterns to zero, without removing the desired auto-correlation signal between similar patterns. Although no attempt is made to generalize the analysis, it seems probable that in cases involving the recognition of a small number of patterns with a strong ‘family resemblance’ a compromise filtering arrangement could be developed which would lead to a substantially improved performance.     

A model for the electronic band structure of HMTSeF-TCNQ

An electronic band structure model is constructed for the organic charge- transfer complex HMTSeF-TCNQ, which is semi-metallic under pressure down to the lowest investigated temperatures. Some experimental data is used to estimate the various integrals involved. Admixture of molecular excited states of opposite parity to the ground state quenches the covalency gap and gives rise to a Fermi surface consisting of an ellipsoid of “electrons” and a more cylindrical FS of “holes” with long axes in the c-direction, and rather flat in the b-direction. Excellent agreement with all (independent) experimental observations is obtained.     

一种改进Nagel-Schreckenberg模型在开放边界条件下交通流的研究

研究了一种改进的Nagel-Schreckenberg模型在开放边界条件下交通流的性质，分析了边界条件，安全距离，刹车概率对交通流的影响. 关键词： 元胞自动机 交通流 安全距离 延迟起动     

A model for peak-gain coefficient in InGaAsP/InP semiconductor laser diodes

A parabolic model of the formg =n ² +n + has been suggested for long-wavelength InGaAsP laser diode peak-grain coefficient variations with the carrier density. The parameters, and, which are dependent on doping, bandgap-wavelength and temperature, have been calculated by applying the least-mean-square method to fit the results of the Lasher and Stern theory of the recombination in semiconductors. p ]This model is superior to the commonly used linear model in accuracy and range of applicability.     

A robust steganographic technique based on improved chaotic-range systems

This paper presents a novel chaos-based technique of steganography in spatial domain. In the last decade, chaos theory has gained utmost importance in multimedia security applications. Generally, 1-D chaotic maps are employed because of computational ease and structural simplicity but their limited chaotic range is an obstacle. In the proposed work, we model the nonlinear combinations of 1-D chaotic maps. These chaotic systems possess chaotic behavior throughout the domain. We, for the first time, propose an effective application of these improved chaotic systems in steganography. These newly synthesized systems are used to embed secret information in the least significant bits (LSBs) of the host image. By comparing with some recent models, we prove that involving improved chaotic systems in steganographic approach really produces extraordinary outcomes. We determine the strength of our steganographic algorithm through the most significant statistical analyses such as information entropy, correlation, contrast, energy, homogeneity, peak signal to noise ratio (PSNR) and mean square error (MSE). We further prove the robustness of the anticipated technique against several image processing attacks. The upshot of these analysis techniques shows that our algorithm is highly reliable and produces coherent results.     

Performance analysis of an improved burst-outputted model for an OBS core router

Differentiated probability outputted scheme (DPOS) is an improved burst-outputted paradigm in optical burst switching (OBS) core routers. In this paper, the blocking performance for multi-priority traffic in a DPOS applied OBS core router with limited buffers has been analyzed and discussed firstly. Several simulation results indicted that DPOS had a better performance in blocking than the outputted model presented in the previous work had. Besides, our proposed scheduling mechanism can supported the quality-of-service (QoS) efficiently for OBS networks.