New hyperbolic function window family

A new window family is introduced, whose normalised half mainlobe width falls between those of rectangular and Hamming windows. The proposed window has two variable parameters by which the mainlobe width and the sidelobe levels can be controlled and used for many digital signal processing applications. This window is compared with a Kaiser-Bessel window, and a tanh window     

On characterization of the optimal biorthogonal window functionsfor Gabor transform

Gabor transforms have been recognized as useful tools in signal analysis. It is known that the solutions for the biorthogonal analysis window function γ(t) given a synthesis window function h(t) in Gabor transforms are not unique in general. Among these solutions, the minimum norm solution has already been given by Wexler and Raz (1990) in the discrete-time case and has been studied by Janssen, Ron and Shen, and Daubechies et al. (1995), in the continuous-time case. The minimum norm solution in the discrete-time case was also proved to be equal to the most orthogonal-like solution by Qian and Chen (1993). In this note, we consider a general optimal-solution problem, where the minimum norm and the most orthogonal-like solutions are two special cases. We prove that these optimal solutions in many cases are equal. We also prove that it remains true in the continuous-time case     

On acknowledgement schemes of sliding window flow control

An investigation is conducted of two acknowledgment schemes for sliding window flow control in packet communications: the delayed acknowledgment (D-ACK) scheme and the window acknowledgment (W-ACK) scheme. It is shown that the acknowledgment scheme of the link layer of the X.25 protocol can be modeled by the D-ACK scheme and that of the packet layer by the W-ACK scheme. The efficiencies of these acknowledgment schemes are shown by the mean number of acknowledgment control frames generated for the transmission of a single information frame, the transmission blocking probability, and the mean transmission time of data frames. Numerical and simulation results showing that the D-ACK scheme with an appropriately selected value of predetermined waiting time is better than the W-ACK scheme are presented     

气体激光器电子束窗口中的热传输问题

一、引言 近十年来,电子束激发气体激光器、电子束控制放电气体激光器与电子束引发气体激光器都有了迅速的发展。在这三类器件中,高能电子束的输出特性在很大程度上决定了激光器的某些输出特性,而电子束的输出窗口又是影响电子束特性并限制其输出的一个重要因素。 V.Blricikoglu讨论了连续输出电子束窗口由于吸收电子能量所发生的温度变化,     

On asymptotic optimality of a sliding window variation ofLempel-Ziv codes

The authors modify the algorithm of Z. Ziv and A. Lempel (1977), LZ77, restricting pointers to start only at the boundary of a previously parsed phrase in a window. Although the number of parsed phrases should increase more than those in LZ77, the number of bits needed to encoded pointers is considerably reduced since the number of possible positions to be encoded is much smaller. It is shown that, for any stationary finite state source, the modified LZ77 code is asymptotically optimal with the convergence rate O(log log M/log M), where M is the size of a sliding window     

Sum-cosine window

A simple window that yields 6 dB improvement in the first sidelobe gain, with almost no loss in the maximum sidclobe gain, compared with that of Kaiser's near optimum zeroth-order Bessel window, is developed. The main-lobe energy of Kaiser's window is about 0.00078% more than that of the new window. The distinct advantage of the window is its very simple form similar to that of a Hamming window.     

On the family of ML spectral estimates for mixed spectrumidentification

A recently developed point spectrum identification procedure based on a family of AR and ML spectral estimates is exploited to arrive at a mixed spectrum identification procedure. To this end, a variety of properties of the AR and ML estimates as a function of model order are described. These properties relate to amplitude convergence, resolution and a characterization of the AR spectral artifact which is used to arrive at improved continuous spectral estimates. A variety of examples are presented     

Thick metal-dielectric window

A three-quarters wavelength thick electromagnetic window is presented. The window is centrally loaded by a periodic array of sub-resonant conducting inclusions. Contrary to the classic half-wavelength thick window that displays isolated zeros in the reflection frequency response, the new window displays a double-zero reflection frequency response leading to a wider transmission curve     

Microstrip window array

The dichroic microstrip antenna concept is further exploited to create a microstrip antenna array which is also capable of functioning as an electromagnetic window at a higher frequency. Experiments on a planar structure comprised of an expanded polystyrene foam substrate, sandwiched between printed mesh conductors, demonstrate the feasibility for normal incidence. Possible ways of developing the technique further and possible applications are briefly mentioned     

Waveguide-sandwich electromagnetic window

The reflection and transmission properties of a new symmetrical radome-wall construction are obtained from a matrix representation. The structure consists of a sandwich of two layers of dielectric material enclosing a medium of artificial dielectric in the form of a 2-dimensional array of waveguides, as is used in waveguide lenses. Two important properties are disclosed: first, the possibility of creating a reflectionless radome with no insertion phase delay (i.p.d.), and, secondly, thin radomes with bandwidths of 10:1 for a power-reflection loss less than 10%, despite the cutoff effect of the centre medium.     

Optimality property of the Gaussian window spectrogram

It is shown that for any signal x(t) the minimum of ∫_-∞^∞∫_-∞ ^∞ [(t-t_x)²+(f-f _x)²] S_x^(w)(t , f) dt df over all normalized time-windows w(t) is achieved by the Gaussian window w(t)=2^1/4 exp (-πt²). Here (t_x, f _x) is the center of gravity of the signal x(t ), S_x^(w) (t, f) is the spectrogram of x(t) due to the window w( t), and the double integral is a measure of the spread of S _x^(w) (t, f) around (t _x, f_X) in the time-frequency plane     

Block acknowledgment: redesigning the window protocol

A window protocol based on the block acknowledgment method, in which acknowledgment message has two numbers, m and n, to acknowledge the reception of all data messages with sequence numbers ranging from m to n, is discussed. In the window protocol, message sequence numbers are taken from a finite domain and both message disorder and loss can be tolerated. An initial version of the protocol that uses a simplified timeout action and unbounded sequence numbers is presented, the simplified timeout action in the protocol is replaced by a sophisticated one without disturbing the protocol's correctness, and the unbounded sequence numbers are replaced by bounded ones while preserving the protocol's correctness. Remarks concerning other variations of the protocol are also presented     

光学窗口的抗振结构优化分析

作为航空侦察设备中的重要组成部分,光学窗口材料昂贵,加工周期长,而其工作环境非常恶劣,所以如何提高其环境适应性就显得尤为重要。据统计,振动是其失效的主要原因。本文以某工程项目中使用的试验窗口为例,以提高抗振能力为目的,通过理论分析,找出其改善措施,然后通过Ansys Workbench进行有限元仿真,最终得出的分析结果及半实物仿真试验均验证了此措施的可行性。     

New time domain window

A new window formula in the time domain is presented. It has mediate properties (figures of merit) into the Dolph-Chebyshev and Kaiser-Bessel windows, and its form is simple. The proposed window has four parameters, which allow its properties to be shaped for more applications     

Some high-power window failures

Two types of RF window failure in a high-power magnetron are investigated. Cracking is shown to depend on electrostatic charging of an evaporated metallic deposit on the window. Punctures were investigated by observation of X-ray stereo-autograms, and are shown to result from an internal multipactor discharge, which in turn is enabled to function at high voltages by the stray magnetic field. Methods for curing both types of defect are given, with evidence that they are successful. The methods are applicable to other high-power microwave tubes, both magnetrons and klystrons.     

An optimal sidelobeless window

A window is derived whose Fourier transform magnitude is unimodal and whose processing gain against white noise is maximized. As such, the spectral window does not exhibit sidelobes and is as narrow in frequency as possible. If should be useful for a variety of signal processing applications     

On some properties of the bathtub failure rate family of life distributions

In this paper, some of the basic issues concerning the bathtub failure rate (BFR) life distributions, thus far unresolved, have been investigated. Specifically, exponential bounds have been obtained for the survival function as well as the moments of a BFR distribution. Closure properties of the BFR family under the formation of coherent systems, convolutions and mixtures have been dealt with. Closure of the BFR class under the formation of limits in distribution and the equivalence of weak convergence and convergence of moment sequences have been established.     

一类低相关序列集的线性复杂度研究

在密码系统和通信系统中使用大线性复杂度的低相关序列能有效地提高数据的安全性,设计大线性复杂度的二元低相关序列是一个重要的研究问题.使用d-齐次函数是构造低相关序列集的一种有效途径,Key方法可以确定这些序列的线性复杂度.对正偶数n和与2n/2-1互素的任意正整数r,提出了一类周期为2n-1的2n条序列组成的二元序列集S(r).对某些适当选取的参数r,S(r)中序列的线性复杂度为n2n/2-3,或n2n.2-4.参数n可以取任意正偶数,所构造的具有大线性复杂度的序列具有广泛的使用范围.     

Understanding the process window for printing lead-free solderpastes

Solder paste is primarily used as a bonding medium for surface mount assemblies (SMA) in the electronics industry, and is typically deposited using the stencil printing process. Stencil printing is a very important and critical stage in the reflow soldering of surface mount devices, and a high proportion of all SMA defects are related to this process. This is likely to continue with the drive toward the introduction of lead-free solder pastes. Work is continuing on the metallurgical properties of these lead-free solders, including solder joint strength and material compatibility. However, the initial challenge for the new Pb-free formulations is in achieving repeatable solder deposit from print to print and from pad to pad. To meet this challenge, new flux formulations are being developed. For a smooth transition to Pb-free soldering formulations, a proper understanding of the solder paste printing performance is necessary. The key parameters that affect solder paste printing have been identified and are the subject of numerous studies. In lead-free solder paste, the replacement of lead with other elements (including Bi, Cu) changes the density of this dense suspension. In this paper, we investigate the effects of printer parameters, i.e. squeegee speed and pressure (defined as the process window) on the printing performance of a variety of lead-free solder pastes. A three-level design of experiment on these factors was used. Comparisons are presented with lead-rich solder pastes. The metal content of the lead-free solders had a significant effect on the process window