Rebuttal of "Dispersion of Nonlinear Elements as a Source of Electromagnetic Shock Structure" (Letters)

lt is pointed out that if the classical method of weak solution is to be used for the solution of the problem, then it is necessary to include a resistive element of a sufficient magnitude. This also is a feature of Landauer's work. The solution so obtained is accurate under well-defined conditions, and among others, it can be shown that energy losses associated with the shock front can be accounted for by that resistance. However, it is inconsequential to assume that as the value of the resistive element is reduced to zero, the energy balance continues to hold. This requires a separate proof. An exact analysis based on a series of experimental results and computer modeling shows that the classical discrepancy can be accounted for in a different way.     

Enhancement of the accuracy of estimating a pulse’s instant of arrival

Estimation of a signal’s instant of arrival is considered. It is assumed that the arriving signal has a known shape and is distorted by a Gaussian white noise. An example is presented to show that application of the output matched-filter signal to this problem is inefficient. For solving such problems, a sufficient statistic is proposed. The components of this statistic are obtained from an orthogonal decomposition of observed data in the case when the Fisher information on the signal delay is retained. It is shown how to use this approach for synthesizing an estimation algorithm that ensures an accuracy better than the accuracy guaranteed by maximum-likelihood estimates.     

Evaluation of Level of Confidence and Optimization of Roll-back Recovery with Checkpointing for Real-Time Systems

Increasing soft error rates for semiconductor devices manufactured in later technologies enforce the usage of fault tolerant techniques such as Roll-back Recovery with Checkpointing (RRC). As RRC introduces time overhead that increases the completion (execution) time, time constraints (deadlines) might be violated. This is a drawback for a class of computer systems where the correct operation is defined not only by providing the correct outcome of an operation but also by ensuring that the deadlines are met. These computer systems are referred to as real-time systems (RTSs). In general RTSs are classified as soft and hard RTSs depending on the consequences of violating the deadlines. For soft RTSs, where consequences of violating the deadlines are not very severe, research have focused on optimizing RRC and shown that it is possible to find the optimal number of checkpoints such that the average execution time (AET) is minimal. While minimal AET is important for soft RTSs, it is more important to provide a high probability that deadlines are met for hard RTSs, where consequences of violating the deadlines may be catastrophic. Hence, there is a need of probabilistic guarantees that jobs employing RRC complete before a given deadline. Traditionally, AET analysis have been used for soft RTSs and worst case execution time (WCET) analysis along with schedule feasibility have been used for hard RTSs. In this paper we introduce a reliability metric, Level of Confidence (LoC), which is equally applicable to both soft and hard RTS. LoC is used as a metric to evaluate to what extent a deadline is met. The main contributions of this paper are as follows. First, we present a mathematical framework for the evaluation of LoC when RRC is employed. Second, we provide a proof to verify the correctness of the proposed expression. Third, in the context of hard RTSs, we provide a method to obtain the optimal number of checkpoints that maximizes the LoC. Fourth, in the context of soft RTSs where the maximal LoC may not be needed, but instead some LoC requirement is needed, we present an optimization method for RRC that finds the number of checkpoints that results in the minimal completion time while the minimal completion time satisfies a given LoC requirement. Fifth, we use the proposed framework to evaluate and compare probabilistic guarantees when RRC is optimized towards soft RTSs.     

Sequential detection of unknown frequency-hopped waveforms

The channelized receiver, which is optimal for the detection of unknown noncoherent frequency-hopped waveforms, bases its decisions on a fixed-length block of input data. A sequential method of interception is presented according to which whenever a new data element is collected, a decision is made as to the presence or nonpresence of a frequency-hopped waveform. If that decision is indeterminate, another data element is collected. An optimal sequential test is derived, under the assumption that the waveform signal-to-noise ratio (SNR) is known. It is shown that this sequential test requires less data, on average, than the fixed-length method to make a decision with the same reliability. A truncated sequential test is also derived where a decision is forced, if still indeterminate, after some fixed amount of data is collected. The truncated test is shown to improve the number of samples needed for a decision when the input SNR differs greatly from that assumed in the derivation of the test. Furthermore, it is shown that the truncated test yields a limited degree of robustness when the input SNR differs from that assumed.<>     

混频二极管及混频器的噪声分析

本文讨论了混频二极管在直流偏置和交流信号激励时的噪声温度比,提出了以“有效噪声温度比(tD)_(eff)”来表征二极管在交流激励下的噪声性能.文中还讨论了在信号及镜像频率的变频损耗不同时混频器输出噪声温度比和二极管噪声温度比的关系.根据分析结果对倒极性并联二极管对的噪声性能作了分析,表明这种复合管的(tD)_(eff)为一常数(0.5).这对降低混频器的系统噪声系数是十分有利的.可以相信:利用倒极性并联二极管对于研制优良性能的毫米波段混频器是一种很有希望的办法.     

虚拟设备在嵌入式LINUX系统中的使用

在Linux系统中，系统是把设备映射为一个特殊的设备文件，用户程序可以象对其它文件一样对此设备文件进行操作。我们可以根据这一点，构造一个不连接任何硬件的设备文件，即虚拟设备。利用这个设备，我们可以把一系列的底层操作转化为应用层操作，以减低上层工作量。     

Detection of the peak of an arbitrary spectrum

A new procedure is described for determining that frequency at which the spectrum of a signal has its absolute peak. The salient feature of the procedure is that it does not explicitly involve the estimation of the spectrum of the signal itself. Specifically, it is shown that the limit of the iterated normalized auto-correlation [see (8) and (9)] of a function,f(t), is a pure cosine wave whose frequency corresponds to the location of the peak of the spectrum off(t). Furthermore, if one is willing to accept an estimated peak frequency of maximum energy to within a given finite spectral resolution, then the procedure terminates after a specified finite number of iterations. Results from a computer simulation of the procedure are described. The areas of application of this procedure are discussed, and the results indicate that this method of detecting a signal (i.e., by the peak of its spectrum) merits further consideration. It is important to note that the consideration of random processes has not been undertaken in this initial study; the results apply to the spectral peak of a deterministic signal only.     

采用激光全息技术的实时指纹取像系统

所研制的实时指纹取像系统利用传统的光学全反射原理和激光全息光栅反射技术相结合的研究方法，解决了传统光学全反射指纹取像系统所存在的问题。给出了新型光学指纹取像系统的研究方法和光学设计的光路图。所研制的实时指纹取像系统图像具有无畸变、无失真、图像清晰的特点。     

非线性反馈移位寄存器串联分解唯一性探讨

非线性反馈移位寄存器(NFSR)是目前序列密码研究的热点问题之一。假定一个NFSR可以分解为更低级数NFSR的串联,该文讨论此分解是否唯一的问题。首先,对线性反馈移位寄存器(LFSR)而言,其串联分解等价于二元有限域F2上单变元多项式的分解,因而是唯一的。其次,针对给定NFSR可以分解为更低级数NFSR到LFSR串联的情形,该文给出了此NFSR具有这样分解的一个充分必要条件,并据此指出所有这样分解中级数最大的LFSR是唯一的。该文的最后构造了一类反例,此类反例表明对一般情形而言,NFSR的串联分解并不唯一。     

Theory of laser self-locking in the presence of host dispersion

A theory is developed of laser mode locking due to saturable absorbers when the dispersive property of the active material is taken into account. The electric field within the cavity is expanded in terms of cavity modes, the problem is treated under the rate-equation approximation, and only third-order nonlinear polarization terms of the dye are considered. The field is assumed to be made of2N + 1oscillating modes. It is shown that, owing to dispersion, the phase φlof the modes (lrunning from-Nto+N) has a term that is proportional to l²and a term (smaller than the previous one) that is proportional to l⁴. In agreement with the experimental results, the term proportional to l²increases the pulsewidth of the total electric field over the case of perfect mode-locking and it also gives a positive linear sweep of the field frequency. The pulsewidth increase is expressed by a factor γ that is proportional to the fourth power of the oscillating bandwidth, to the square of the relaxation time T1of the dye, and to the product of the length of the active material times a quantity ε that is related to dispersion of the material.     

Theory of lattice-based fine-coarse vector quantization

The performance of a lattice-based fast vector quantization (VQ) method, which yields rate-distortion performance to that of an optimal VQ, is analyzed. The method, which is a special case of fine-coarse vector quantization (FCVQ), uses the cascade of a fine lattice quantizer and a coarse optimal VQ to encode a given source vector. The second stage is implemented in the form of a lookup table, which needs to be stored at the encoder. The arithmetic complexity of this method is essentially that of lattice VQ. Its distortion can be made arbitrarily close to that of an optimal VQ, provided sufficient storage for the table is available. It is shown that the distortion of lattice-based FCVQ is larger than that of full search quantization by an amount that decreases as the square of the diameter of the lattice cells, and it provides exact formulas for the asymptotic constant of proportionality in terms of the properties of the lattice, coarse codebook, and source density. It is shown that the excess distortion asymptotically equals that of the fine quantizer. Simulation results indicate how small the lattice cells must be in order for the asymptotic formulas to be applicable     

Communication complexity of secure distributed computation in thepresence of noise

A simple model of distributed computation that requires information exchange over a noisy channel is considered. A communication protocol is utilized that requires alternate bit exchanges between two processors. First, the case of a single public channel is considered and the number of bits that need to be exchanged between the processors to permit δ-accuracy in their goal is compared. For this computation, an error-detection-and-retransmission mechanism of error control and an error-correction-and-retransmission mixture that are consistent with the logical protocol that governs this exchange are considered. Second, the case of the availability of an additional secret channel is considered and interest in determining the minimum number of bits that need to be exchanged over a secret channel in order to maintain ∈-uncertainty about the computation for an eavesdropper on the public channel is shown. Various subcases under this case are considered and an upper bound on the number of secret bits when no error-control scheme is used is obtained     

Characteristics of a crossed-wire scatterer without a junction point of an incident wave of circular polarization

A crossed-wire scatterer has the wires displaced in the backscattering direction, and is able to scatter an incident wave of circular polarization in such a way that the backscattering wave has the same rotational sense as that of the incident wave. The radiation performance of the scatterer is improved by bending the horizontal and the vertical wires. Arrays consisting of crossed-wire scatterers are constructed and the backscattering cross sections (BSCS's) are calculated. It is revealed that the increase in the current amplitude due to the mutual effects among the array elements contributes to enhancement in the BSCS. It is also shown that a maximum value of the BSCS of an array of3 times 3bent crossed-wire scatterers is 1.8 times as large as that of a dihedral corner reflector which has the same aperture area. The BSCS's as a function of the angle of incidence are presented with experimental results at a frequency of 9.375 GHz.     

Analysis of speckle noise contribution on wavelet decomposition ofSAR images

This paper describes the use of the wavelet transform for multiscale texture analysis. One of the basic problems is that texture measures have to adapt to the peculiarity of radar images that contain multiplicative speckle noise. In this paper, the focus is on the effect of speckle on the wavelet transform. The effect is first assessed analytically. It is shown that the wavelet coefficients are modulated by the multiplicative character of the speckle in a manner that is proportional to the target mean backscattering coefficient. The effect of speckle correlation is also demonstrated. Wavelet decomposition is then applied to a simulated radar image generated by a Monte Carlo approach and based on a statistical model. Modeling shows that the correlation properties of speckle have an effect up to a scale that corresponds to its granular size. The results also show that the main contribution to the wavelet transform for an homogeneous area is the first-order statistical distribution of speckle, which remains important even at large scales. The results are then compared to a ERS-1 synthetic aperture radar (SAR) image of a primary tropical forest region     

Parametric study of the crosspolarisation efficiency of parabolic reflectors

The crosspolarisation efficiency of a reflector antenna is the ratio between the peak crosspolarisation from the complete antenna to that from the feed. The results of a parametric study into this factor for parabolic reflectors fed by a mathematical model of a common class of feeds are presented, and it is concluded that the efficiency is typically ?4 to ?6 dB.     

Two-dimensional Bayesian estimate of images

A dynamic model for pictorial data that can be represented by a random field of an exponential autocorrelation function is developed. A partial difference equation describes the dynamic model and is used to realize a two-dimensional recursive filter that gives a Bayesian-estimate of the pictorial data from a noisy observation of the data. It is assumed that the noise is additive, white, and uncorrelated with the signal. Practical application of the estimation technique is illustrated by applying the results to enhance several pictures. A comparison of this technique and its one-dimensional counterpart (Kalman filter) is made, and generalization of the estimation technique to other autoregressive sources is considered.     

On Minimality of Convolutional Ring Encoders

Convolutional codes are considered with code sequences modeled as semi-infinite Laurent series. It is well known that a convolutional code C over a finite group G has a minimal trellis representation that can be derived from code sequences. It is also well known that, for the case that G is a finite field, any polynomial encoder of C can be algebraically manipulated to yield a minimal polynomial encoder whose controller canonical realization is a minimal trellis. In this paper we seek to extend this result to the finite ring case G = BBZpr by introducing a so-called ldquo p-encoderrdquo. We show how to manipulate a polynomial encoding scheme of a noncatastrophic convolutional code over BBZpr to produce a particular type of p-encoder (ldquominimal p -encoderrdquo) whose controller canonical realization is a minimal trellis with nonlinear features. The minimum number of trellis states is then expressed as p ^gamma, where gamma is the sum of the row degrees of the minimal p -encoder. In particular, we show that any convolutional code over BBZpr admits a delay-free p -encoder which implies the novel result that delay-freeness is not a property of the code but of the encoder, just as in the field case. We conjecture that a similar result holds with respect to catastrophicity, i.e., any catastrophic convolutional code over BBZpr admits a noncatastrophic p-encoder.     

The Unserviceable Probability of a Class of Telecommunications Networks

This paper discusses the use of computers in calculating the unserviceable probability of a class of telecommunication networks. The unserviceable probability for a pair of terminals in the network is derived and is so complicated that it is not feasible to calculate without the use of a computer. Under the condition that every junctor in the network has a small ratio of mean service time to mean time between failures, it is shown that the computer-aided methods available for calculating network unreliability and network blocking probability are also applicable to network unserviceable probability. For the general expression of the network unserviceable probability, no simple computer-aided method is yet known. However, no urgent need for a computer-aided method for the general expression of the network unserviceable probability is envisaged since practical networks usually have small ratios of mean service time to mean time between failures for each of its junctors.     

4-正则图着色的Kempe等价性

给定一个图G及它的一个正常顶点着色f, G中任意两种颜色的顶点导出子图称为G的一个2-色导出子图,该2-色导出子图的分支称为G的一个2-色分支。Kempe变换是指将图G的某个2-色分支实施颜色互换。若两个着色之间可通过若干次Kempe变换达到对方,则这两个着色是Kempe等价的。Mohar猜想当k3时,对于任意的连通k-正则图G,若G不是完全图,则G的所有k-着色是Kempe等价的。Feghali等人解决了k=3时的情况,当k4时,此猜想尚未解决。该文研究了k=4时的情况,证明了：(1)若G是一个连通度小于3的4-正则图,则G的所有4-着色是Kempe等价的;(2)若G是4-正则图,且含有与4-轮或近5-阶完全图同构的子图,则G的所有4-着色是Kempe等价的;(3)若G是一个3-连通4-正则图,且G存在一个顶点x和一个4-着色f,满足x的邻域中有3个或4个顶点在f下着相同颜色,则G的所有4-着色是Kempe等价的。