A canonical space-time characterization of mobile wireless channels

A canonical space-time characterization of mobile wireless channels is introduced in terms of a fixed basis that is independent of the true channel parameters. The basis captures the essential degrees of freedom in the received signal using discrete multipath delays, Doppler shifts, and directions of arrival. This provides a robust representation of the propagation dynamics and dramatically reduces the number of channel parameters to be estimated. The resulting canonical space-time receivers deliver optimal performance at substantially reduced complexity compared to existing designs     

Probabilistic vector mapping with trajectory information fornoise-robust speech recognition

The authors propose a probabilistic vector mapping method with trajectory information for noise-robust speech recognition. The proposed method estimates a speech vector using not only the current noisy vector but also adjacent vectors in the form of a trajectory pattern. According to our isolated word recognition experiment, the new method yields a better recognition rate than the probabilistic vector mapping method previously proposed     

Wide-band network characterization by Fourier transformation of time-domain measurements

A novel method of measuring driving-point and transfer impedance over a wide spectrum rapidly and with good accuracy uses a digital computer to transform the pulse response of a network into the frequency domain. A sampling oscilloscope provides the time transformation needed for data acquisition. The method and laboratory technique are discussed. Experimental data show agreement within 12 percent between the data from a single pulse measurement and bridge measurements over a band of 40 harmonic frequencies, i.e., 25-1000 MHz. Fundamental accuracy and bandwidth are believed to be substantially greater than these figures.     

一种基于图像分割的几何变换映射色盲矫正方法

针对基于几何变换映射的色盲矫正方法进行色盲矫正时出现的映射计算量过高的问题,一种新型的几何变换映射色盲矫正方法被提出,这种矫正方法是基于图像分割原理的.首先研究了色盲图像的仿真方法,然后结合K-means和系统聚类算法对原始图像进行分割并计算各个区域在色盲图像下LAB颜色空间中的欧氏距离作为颜色相似性的度量,确定红绿色盲难以分辨的颜色区域.在这个区域内进行颜色映射区域的划分,这个划分主要包括根据领域内的颜色比例对空间内的几何平面进行相应变换,通过此类变换生成有利于色盲患者分辨的图案等步骤.     

A new characterization of canonical convolutional encoders (Corresp.)

A realization of a linear sequential circuit is called a canonical convolutional encoder if its state space has the smallest dimension among all realizations generating the same code. We give conditions for a realization to be a canonical oncoder and for two canonical encoders to generate the same code. The techniques used provide an enumeration of canonical encoders whose realizations are not isomorphic.     

Optimization of quantum circuit mapping using gate transformation and commutation

This paper addresses quantum circuit mapping for Noisy Intermediate-Scale Quantum (NISQ) computers. Since NISQ computers constrain two-qubit operations to limited couplings, an input circuit must be transformed into an equivalent output circuit obeying the constraints. The transformation often requires additional gates that can affect the accuracy of running the circuit. On the basis of a previous work on quantum circuit mapping that leverages gate commutation rules, this paper presents algorithms that utilize both transformation and commutation rules. Results of experiments on a standard benchmark dataset demonstrate the algorithms with more rules can find even better circuit mappings than the previously known best algorithms.     

Modified correlation theorem for the linear canonical transform with representation transformation in quantum mechanics

As generalization of the fractional Fourier transform, the linear canonical transform (LCT) has been used in several areas, including optics and signal processing. Many properties of the LCT are currently known including correlation theorem, but however, these do not generalize very nicely to the classical result for the FT. This paper presents a modified correlation theorem in the LCT domain with representation transformation in quantum mechanics. The derivation is direct and concise since the authors make full use of the Dirac’s representation theory. The proposed theorem is compared with the existing correlation theorem in the literature for the LCT and found to be better and befitting proposition. As an application, the proposed correlation theorem is used to determine the power spectral density of frequency-modulated (FM) signal, which shows that the same FM signal can be transmitted with less bandwidth requirement.     

Reduction of linear systems by canonical forms

A new companion-type realisation of a rational transfer function is introduced. This form is then used for obtaining a reduced-order model. It is possible, using this approach, to simultaneously match time moments, Markov parameters and to retain desired poles, thus combining the methods of partial realisation (Padé approximation) and aggregation.     

基于自适应方法的离散线性正则变换计算

线性正则变换(LCT)描述了光学变换上的平方相位系统的影响。提出了一种基于自适应最小均方(LMS)的离散线性正则变换(LCT)算法。文中导出了基于块和基于流的离散LCT算法,同时考虑了基于自适应滤波器的实现架构。提出的计算方法具有天生的并行结构,这使它适用于有效的超大规模集成电路(VLSI),并且对于传输过程中可能的计算误差呈现鲁棒性。     

Nanoscale characterization of the silicon dioxide-silicon carbide interface using elemental mapping by energy-filtered transmission electron microscopy

Energy-filtered transmission electron microscopy (EFTEM) was used to study 6H-SiC/SiO₂ interfaces produced by thermal oxidation as a function of the oxidation conditions. Elemental maps of C and Si were used to calculate C-to-Si concentration profiles across the interfaces. Enhanced C/Si concentrations (up to ∼ 35%) were observed at distinct regions in samples oxidized at 1100°C for 4 h in a wet ambient. The data from a number of randomly selected regions indicate that re-oxidation at 950°C for 3 h significantly reduced, but did not eliminate, the amount of excess interfacial carbon.     

Theory of sonogram characterization of optical pulses

We derive a formula for retrieving the amplitude and phase of an optical pulse from its sonogram. When the transfer function of the frequency filter is known, the pulse amplitude and phase are completely retrieved from the sonogram without iterative calculations by using the derived formula. Based on this formula, we find that the width of a sampling pulse, which is used for cross-correlation measurement of the sonogram, must be much shorter than the width of the pulse under test, and that it is not necessarily possible to reconstruct the pulse when we use the pulse under test itself as a sampling pulse. Finally, we discuss possible schemes for sonogram characterization of optical pulses     

Picosecond time-domain characterization of CPW bends using aphotoconductive near-field mapping probe

Propagation and reflection characteristics of right-angle coplanar waveguide (CPW) bends were measured using a novel photoconductive near-field probe with picosecond temporal resolution and pin spatial resolution. The probe can measure the transverse electric-field components existing over devices under test. Time-varying transverse electric field maps for different CPW bending structures were acquired by varying the probe position. The CSL mode generation and a difference in flight time of propagating pulses on two slots of the CPW bends were observed. Further, it was found that there exists a considerable unexpected pulse caused by the bent line structure, which has opposite polarity to the input pulse and exists only at the inner ground plane. The undesirable phenomena originated from the bend discontinuity were adequately reduced by bend smoothing techniques     

Theory of lossless reciprocal transformation of a reciprocal 2-state network

Properties of linear reciprocal 1- or 2-port variable networks with two states have been studied. Invariants and canonical forms of these networks under lossless reciprocal transformations have been found out. Optimum synthesis of these kinds of networks with respect to a newly defined `figure of merit? of a 2-state variable impedance is described.     

Amorphous selenium photodetector driven by diamond cold cathode

Amorphous selenium is one of the most promising candidates as photoconducting material for future imaging devices. It can exhibit ultra-high photosensitivity by using avalanche multiplication inside the solid. However, the requirement of high vacuum by the electron emitters prevents amorphous selenium from being a realistic imaging device in general. Diamond, with its outstanding properties of negative electron affinity and high chemical stability, can be an ultimate emitter with low extraction field and low vacuum operation, especially for imaging devices. This report presents the first successful operation of an amorphous selenium photodetector with low operational vacuum and extraction field using a diamond cold cathode.     

正则变量的量子隐形传态

利用位置和动量、相位和粒子数这两对正则共轭可观察量,研究了两种不同类型的量子隐形传态方案,把连续变量和分离变量的量子隐形传态统一到正则量子隐形传态的框架中.正则共轭可观察量在量子隐形传态中扮演了三重角色:首先,两个对易的正则可观察量,如相位差和粒子数和的共同本征态提供了一个两系统间的量子通道;其次,对另外两系统的一对正则可观察量进行了Bell基测量;最后,由单个系统的正则共轭观察量构成了两个局域的么正变换以恢复这个未知的量子态.     

Eigenfunctions of linear canonical transform

The linear canonical transform (the LCT) is a useful tool for optical system analysis and signal processing. It is parameterized by a 2×2 matrix {a, b, c, d}. Many operations, such as the Fourier transform (FT), fractional Fourier transform (FRFT), Fresnel transform, and scaling operations are all the special cases of the LCT. We discuss the eigenfunctions of the LCT. The eigenfunctions of the FT, FRFT, Fresnel transform, and scaling operations have been known, and we derive the eigenfunctions of the LCT based on the eigenfunctions of these operations. We find, for different cases, that the eigenfunctions of the LCT also have different forms. When |a+d|<2, the eigenfunctions are the scaling, chirp multiplication of Hermite functions, but when |a+d|=2, the eigenfunctions become the chirp multiplication, chirp convolution of almost-periodic functions, or impulse trains. In addition, when |a+d|>2, the eigenfunctions become the chirp multiplication and chirp convolution of self-similar functions (fractals). Besides, since many optical systems can be represented by the LCT, we can thus use the eigenfunctions of the LCT derived in this paper to discuss the self-imaging phenomena in optics. We show that there are usually varieties of input functions that can cause the self-imaging phenomena for an optical system     

基于极化变换的极化匹配滤波器及其通带理论

借助极化基变换思想,通过矩阵特征值与特征矢量的方法求取了部分极化情况下极化匹配滤波器的极化天线最优接收极化方式,即最优极化Jones矢量解。分析了极化白化滤波器与匹配滤波器的性能差异,提出了极化白化-匹配联合滤波方法。针对极化匹配滤波器,分析了其最优极化接收Jones矢量在极化复平面上的表征。并在极化复平面上分析了极化通带的特性,得出在poincaré球上的极化球冠的通带映射到极化复平面变化为极化圆的表征模式,给出了极化圆随通带大小变化的趋势,这是极化通带理论的一个新发展,为极化滤波创造了简便的判决方法,同时为极化滤波中的数据处理提供了新的途径。     

Field emission characteristics of nano-diamond cathode surface by graphitization pretreatment

Cathode samples of nano-diamond by graphitization pretreatment with different temperatures were fabricated by electrophoresis, then the structures and morphologies of the cathode samples were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), and the field emission tests were conducted. The effects of graphitization pretreatment on the field emission characteristics of nano-diamond cathode surface on titanium substrate are studied. The results indicate that the surface morphologies of nano-diamond cathode samples after graphitization pretreatment change a lot, and the field emission characteristics in low-voltage area are improved obviously. However, in high-voltage area, the curve distortion happens, and it doesn’t conform the mechanism of field emission characteristics.