Efficient quantization for overcomplete expansions in /spl Ropf//sup N/

We study construction of structured regular quantizers for overcomplete expansions in /spl Ropf//sup N/. Our goal is to design structured quantizers which allow simple reconstruction algorithms with low complexity and which have good performance in terms of accuracy. Most related work to date in quantized redundant expansions has assumed that the same uniform scalar quantizer was used on all the expansion coefficients. Several approaches have been proposed to improve the reconstruction accuracy, with some of these methods having significant complexity. Instead, we consider the joint design of the overcomplete expansion and the scalar quantizers (allowing different step sizes) in such a way as to produce an equivalent vector quantizer (EVQ) with periodic structure. The construction of a periodic quantizer is based on lattices in /spl Ropf//sup N/ and the concept of geometrically scaled- similar sublattices. The periodicity makes it possible to achieve good accuracy using simple reconstruction algorithms (e.g., linear reconstruction or a small lookup table).     

Mathematical programming algorithms for regression-based nonlinearfiltering in RN

This paper is concerned with regression under a “sum” of partial order constraints. Examples include locally monotonic, piecewise monotonic, runlength constrained, and unimodal and oligomodal regression. These are of interest not only in nonlinear filtering but also in density estimation and chromatographic analysis. It is shown that under a least absolute error criterion, these problems can be transformed into appropriate finite problems, which can then be efficiently solved via dynamic programming techniques. Although the result does not carry over to least squares regression, hybrid programming algorithms can be developed to solve least squares counterparts of certain problems in the class     

Gain measurement and upconversion analysis in Tm3+, Ho3+ co-doped alumino-zirco-fluoride glass

The small signal gain coefficients were measured in Tm³⁺,Ho³⁺ co-doped alumino-zirco-fluoride glass. A gain of 15%/cm at 2.05 μm was obtained for pump power density of 42 kW/cm². The temperature increase of the glass was found to be more than 150 K with this pump power, which was estimated from a comparison between fluorescence intensities of Tm^{3+ 3} F₄-³H₆ and Ho^{3+ 5} I₇-⁵I₈. An upconversion rate constant of 12.5×10^-17 cm³ sec^-1 from a coupled (Tm^{3+ 3}F₄, Ho^{3+ 5}I₇) level to a coupled (Tm^{3+ 3}H₅, Ho^{3+ 5}I₆) level was determined by fitting the experimentally obtained gain coefficients to the calculated one which takes into consideration any temperature increase     

Energy-efficient bandwidth allocation in wireless networks: algorithms, analysis, and simulations

In this paper, we present a new energy-efficient bandwidth allocation scheme for wireless networks. First of all, we investigate the intrinsic relationship between the energy consumption and transmission rates of mobile terminals, in which transmission rate is determined through channel allocations. Then, we propose two schemes for connection admission control: victim selection algorithm (VSA) and beneficiary selection algorithm (BSA) with the intent to reduce energy consumption of each terminal. Moreover, we introduce an adjustment algorithm to statistically meet the demands for quality of service (QoS) during the resource allocation. The performance of the proposed schemes is evaluated with respect to energy consumption rate of each successfully transmitted bit, throughput and call blocking probabilities. An extensive analysis and simulation study is conducted for Poisson and self-similar, multi-class traffic.     

基于压力应变的放大电路实验

基于压力传感器的高阻抗小信号输出,分别通过单个运算放大器差分电路、三个运算放大器构成的仪用放大电路以及集成仪用放大电路来放大,应用零点与增益调整电路来实现重量与电压的一一对称,通过数字万用表的电压值来表示重量。该实验具有趣味性、实用性和不确定性有利于学生发现问题、分析问题、解决问题。     

Generalized Gabor expansions of discrete-time signals in l2(Z) via biorthogonal-like sequences

In this paper, a biorthogonal-like sequences (BLS) theory and its application to the generalized Gabor expansions (equivalently, the generalized short-time Fourier transform/filterbank summation) are presented. A pair of BLS's are defined to be two sequences satisfying a biorthogonal-like condition (BLC), which is a moment equation and equivalent to a linear difference equation. We show that two collections in a Hilbert space generated by a pair of BLS's in the joint time-frequency domain are complete, either can be used as an analysis filter, and the other can be used as a synthesis filter for a generalized Gabor expansion of discrete-time signals. A sufficient and necessary condition on the existence of BLS's based on the moment equation is presented, which is simpler to use than frame theory. Given a filter generating a frame, its BLS's also generate frames. The dual frame is one of them. Given a FIR analysis/synthesis filter, there is a FIR synthesis/analysis filter if BLS's exist. The algorithm to compute FIR analysis and synthesis filters based on the linear difference equation is presented in this paper, which is simpler than frame operator     

Effect of electron cyclotron resonance H+,Ne+, Ar+, and Xe+ plasma precleaning ontitanium silicide formation

A vacuum integrated cluster tool process incorporating electron cyclotron resonance plasma cleaning, Ti sputter deposition, and rapid thermal annealing in N₂ is used to form a TiN_x<1/TiSi_y bilayer on (100) Si where the film composition is controlled by the preclean chemistry. Chemical cleaning with nominal 10 eV H⁺ completely removes native Si oxide resulting in a hydrogen terminated surface that promotes silicidation compared to one cleaned with buffered-oxide-etching (BOE). If the native oxide is only partially reduced, viz., SiO_x<2 surface, for example by shortening the H⁺ exposure time, then silicidation is largely inhibited and a thicker nitride layer is formed. Sputter cleaning with 50 to 250 eV Ar⁺ results in a bilayer that is roughly equivalent to that formed with BOE, whereas 50 to 150 eV Xe⁺ bombardment favors nitridation. Precleaning with >150 eV Ne⁺ promotes silicidation, thereby minimizing nitride thickness. The effects of precleaning are significant as the activation energy for TiSi_y formation is reduced from 1.8 eV characteristic of a BOE cleaned surface to 1.2 eV on Si etched with 250 eV Ne⁺. Mechanistically, the silicide kinetics are shown to be inhibited by the presence of a thin amorphous layer that is formed only when cleaning Si with Ar⁺ and Xe⁺ with the effect that both knock-on oxygen atoms and implanted noble gas atoms trapped within the amorphous layer retard the requisite solid-phase epitaxial regrowth kinetics. Recrystallizing the amorphous Si surface prior to metallization appears to restore the near-normal silicide kinetics that is characteristic of Ne⁺ cleaning     

Turbo estimation algorithms: general principles, and applications to modal analysis

In this paper, a new class of parameter estimation algorithms, called turbo estimation algorithms (TEA), is introduced. The basic idea is that each estimation algorithm (EA) must perform a sort of intrinsic denoising of the input data in order to achieve reliable estimates. Optimum algorithms implement the best possible noise reduction, compatible with the problem definition and the related lower bounds to the estimation error variance; however, their computational complexity is often overwhelming, so that in real life one must often resort to suboptimal algorithms; in this case, some amount of noise could be still eliminated. The TEA methods reduce the residual noise by means of a closed loop configuration, in which an external denoising system, fed by the master estimator output, generates an enhanced signal to be input to the estimator for next iteration. The working principle of such schemes can be described in terms of a more general turbo principle, well known in an information theory context. In this paper, an example of turbo algorithm for modal analysis is described, which employs the Tufts and Kumaresan (TK) method as a master EA.     

Learning characteristics of stochastic-gradient-descent algorithms: A general study,analysis, and critique

A comprehensive analysis of the mean-square learning characteristics of stochastic-descent algorithms is presented. The approach is based on the commonly exploited simplifying assumption of stationary independent training vectors. Characteristics analyzed include stability, steady-state misadjustment, initial rate of convergence, optimum step size, and steady-state autocovariance and spectral characteristics of the weight-vector. Effects on these characteristics due to degree of randomness of stochastic gradient, particular data distribution, and data corruption are isolated and analyzed. An objective of the work is to keep the number of simplifying assumptions and approximations to a minimum. Comparison of results with previous more approximate analyses are made.     

Infrared cross-section measurements for crystals doped withEr3+, Tm3+, and Ho3+

The absorption and emission cross sections of the transition between the ground spin-orbit multiplet and the lowest excited multiplet were measured for Er³⁺, Tm³⁺, and Ho³⁺ ions in a variety of crystalline hosts. The materials that were investigated include LiYF₄, BaY₂F₈, Y ₃Al₅O₁₂, LaF₃, KCaF₃ , YAlO₃, and La₂Be₂O₅. The absolute magnitudes of the emission cross sections were determined from the absorption spectra, with the aid of the principle of reciprocity. The calculated radiative emission lifetimes derived from these measured cross sections agree well with the measured emission decay times for most materials. The potential use of these rare-earth-doped materials in pulsed laser applications requires that the ground state exhibit adequate splitting to minimize the detrimental effects of the ground state thermal population, and also that the emission cross section be sufficiently large to permit efficient extraction energy. The systems based on Ho³⁺ in the eightfold coordinated sites of LiYF₄, BaY₂F₈, and Y₃Al₅O₁₂ appear to be the most promising     

Image processing algorithms for retinal montage synthesis, mapping,and real-time location determination

Although laser retinal surgery is the best available treatment for choroidal neovascularization, the current procedure has a low success rate (50%). Challenges, such as motion-compensated beam steering, ensuring complete coverage and minimizing incidental photodamage, can be overcome with improved instrumentation. This paper presents core image processing algorithms for (1) rapid identification of branching and crossover points of the retinal vasculature; (2) automatic montaging of video retinal angiograms; (3) real-time location determination and tracking using a combination of feature-tagged point-matching and dynamic-pixel templates. These algorithms tradeoff conflicting needs for accuracy, robustness to image variations (due to movements and the difficulty of providing steady illumination) and noise, and operational speed in the context of available hardware. The algorithm for locating vasculature landmarks performed robustly at a speed of 16-30 video image frames/s depending upon the field on a Silicon Graphics workstation. The montaging algorithm performed at a speed of 1.6-4 s for merging 5-12 frames. The tracking algorithm was validated by manually locating six landmark points on an image sequence with 180 frames, demonstrating a mean-squared error of 1.35 pixels. It successfully detected and rejected instances when the image dimmed, faded, lost contrast, or lost focus     

Temperature dependence of pulsed laser threshold in YAG:Er3+, Tm3+, Ho +

The variation of pulsed laser threshold with temperature is graphically presented for YAG: Er³⁺, Tm³⁺, Ho³⁺over the range from 90 to 300°K. The active ion is Ho³⁺and threshold for the 2.13-micron line varies between 4 and 60 joules over this temperature range.     

Multi-path content delivery: Efficiency analysis and optimization algorithms

The paper studies the benefits of multi-path content delivery from a rate-distortion efficiency perspective. We develop an optimization framework for computing transmission schedules for streaming media packets over multiple network paths that maximize the end-to-end video quality, for the given bandwidth resources. We comprehensively address the two prospective scenarios of content delivery with packet path diversity. In the context of sender-driven systems, our framework enables the sender to compute at every transmission instance the mapping of packets to network paths that meets a rate constraint while minimizing the end-to-end distortion. In receiver-driven multi-path streaming, our framework enables the client to dynamically decide which packets, if any, to request for transmission and from which media servers, such that the end-to-end distortion is minimized for a given transmission rate constraint. Via simulation experiments, we carefully examine the performance of the scheduling framework in both multi-path delivery scenarios. We demonstrate that the optimization framework closely approaches the performance of an ideal streaming system working at channel capacity with an infinite play-out delay. We also show that the optimization leads to substantial gains in rate-distortion performance over a conventional content-agnostic scheduler. Through the concept of error-cost performance for streaming a single packet, we provide another useful insight into the operation of the optimization framework and the conventional scheduling system.     

Morphological grayscale reconstruction in image analysis:applications and efficient algorithms

Two different formal definitions of gray-scale reconstruction are presented. The use of gray-scale reconstruction in various image processing applications discussed to illustrate the usefulness of this transformation for image filtering and segmentation tasks. The standard parallel and sequential approaches to reconstruction are reviewed. It is shown that their common drawback is their inefficiency on conventional computers. To improve this situation, an algorithm that is based on the notion of regional maxima and makes use of breadth-first image scannings implemented using a queue of pixels is introduced. Its combination with the sequential technique results in a hybrid gray-scale reconstruction algorithm which is an order of magnitude faster than any previously known algorithm.     

Er3+,Yb3+:glass/Co2+:MgAl2O4复合材料LD泵浦被动调Q微型激光器

报道了一种应用于激光测距的Er³⁺,Yb³⁺:glass/Co²⁺:MgAl₂O₄复合材料LD泵浦的被动调Q微型激光器。 采用玻璃与晶体复合技术,将增益介质Er3＋/Yb3＋共掺 磷酸盐玻璃和被动调Q可饱和 Co²⁺:MgAl₂O₄晶体进行了光学热复合,复合材料会降低增益介质内部的温度梯度 ,使热焦距变长,模体积 增加,激光光束质量提高;另外,复合材料使腔内损耗减小,腔内的粒子数密度提高,脉宽 变窄,输出能 量增加,从而激光器性能得到提高。在重复频率为10Hz情况下,采 用中心波长为940nm的单管LD作为泵 浦源,获得单脉冲能量为210μJ、脉冲宽度为2.8ns,峰值功率大于70kW的波长为1.5 μm的被动调Q激光输出,光束质量为1.2     

Coding gain in paraunitary analysis/synthesis systems

A formal proof that bit allocation results hold for the entire class of paraunitary subband coders is presented. The problem of finding an optimal paraunitary subband coder, so as to maximize the coding gain of the system, is discussed. The bit allocation problem is analyzed for the case of the paraunitary tree-structured filter banks, such as those used for generating orthonormal wavelets. The even more general case of nonuniform filter banks is also considered. In all cases it is shown that under optimal bit allocation, the variances of the errors introduced by each of the quantizers have to be equal. Expressions for coding gains for these systems are derived     

磷酸盐玻璃中稀土离子Ce~(3 )、Tb~(3 )、Er~(3 )和Tm~(3 )的能量转移和敏化过程的研究

本文报道了磷酸盐玻璃中Tb~(3 )和Ce~(3 )的浓度猝灭效应。在KrF激光(248毫微米,10毫微秒)激发下,测出磷酸盐玻璃中不同浓度Ce~(3 )或Tb~(3 )离子的荧光寿命。着重讨论了磷酸盐玻璃中Ce~(3 )→Tb~(3 )、Er~(3 )和Tm~(3 )的能量转移和敏化过程。     

直流辉光放电HgX(X=Cl,Br,I)B~2∑~+→X~2∑~+发射光谱的研究

蓝绿色激光由于在水下通讯等方面的应用近年来颇受重视,溴化汞激光就是其中的一种,连同氯化汞、碘化汞激光,统称为HgX(X=Cl,Br,Il)激光,其波长在可见波段一定范围内可调(HgCl:552～559nm,HgBr:495～505nm,HgI:443～445nm).激光跃迁B~2∑~+→X~2∑~+的上能态激发可由HgX_2蒸气在紫外光或快放电作用下分解实现:HgX_2→HgX_2(b~1∑_u~+)→HgX(B~2∑~+)+X(~2P).用后一种方式可制成小型、封闭、长寿命器件,但至今只能得到短脉冲(几+ns)输出.本文目的是通过研     

YPO4:Ce3+，Tb3+反蛋白石光子晶体的制备及其发光性能的研究

本研究通过自组装法制备得到YPO₄:Ce³⁺ ,Tb³⁺ 反蛋白石光子晶体。对不同光子带隙的YPO₄:Ce³⁺,Tb³⁺的发光光谱进行研 究,可以明显的看出,反蛋白石光子晶体对⁵D₄-⁷F₅跃 迁相对于参考样品有了很明显的抑制。通过不同Tb³⁺离子掺杂浓度对发射光谱和浓度 淬 灭的研究,得出随着Tb³⁺离子浓度的不断增加其Tb³⁺离子的⁵D ₃－⁷FJ和⁵D₄－⁷FJ窄带发射强 度逐渐增大,但其⁵D₄－⁷F₅跃迁(546 nm)的 发光寿命则逐渐减少,光子晶体相对于参考样品 对Tb³⁺的浓度 淬灭抑制明显。这些发现对于进一步研究稀土发光特性以及制备新型发 光器件具有很大的指导 意义。