PbS薄膜的激光敏化

为了解决敏化条件难掌握,重复性差等技术问题,我们采用激光在适当的情况下照射代替管式高温炉,取得了较好的敏化效果.本方法可直接通过观察颜色判断敏化情况,因而敏化过程中可直接控制条件.采用该方法敏化速度快,敏化后的器件性能好,成品率高,较稳定,为PbS多晶薄膜红外探测器的制造提供了较好的敏化手段.     

On comparisons of time-domain scattering schemes

The purpose of this paper is to offer a way to present comparative error data so that the true cost of the schemes are apparent. First, we review some common ways to present data, and illustrate why they are insufficient for cost comparison. Second, we offer a new way to present data, which is easy to generate, and which reveals additional valuable information about the schemes being compared. As an example, we present a comparison of some new and some old schemes. By facilitating comparisons, we hope to generate more beneficial dialog among different disciplines, such as electromagnetic scattering, acoustic scattering, and numerical analysis     

Communication and Telecommunication

In this paper we discuss the question of whether telecommunication experts are also experts in communication. Reviewing their profile of interest and their formal theories we are led to a rather negative conclusion. Further analysis shows that the knowledge of communication is rather inadequate anyhow: a long list of open questions can be presented. To find out more about these areas we find ourselves involved in sociotechnical research which is quite different from the technical research to which we are accustomed. This is illustrated by listing a number of weak points in the sociotechnical problem formulation. These characteristics reduce the possibility for early spectacular achievements as we are acquainted with in technical studies. The writer is not completely pessimistic however; he believes that an improved understanding of sociotechnical problems may be achieved by a close cooperation between telecommunication specialists and those trained in the humanities and social sciences. Three different strategies are discerned: basic research, field trials, and field work. The writer expresses some preference for the second approach. In conclusion, a reaction is given to the possible objection against sociotechnical studies, namely that divergencies in personal opinion about man and society might hamper agreement on objectives and interpretation. The writer gives a few considerations which he thinks are of general acceptance and sufficient for a common base of action.     

Approximations for characteristics of nomadic communications

In this paper we consider a mobile communication network in which users are moving along a road. It is desirable that each point of the road is in the range of at least one base‐station such that each user can communicate with a base‐station at any time. We model such a communication network with a Boolean model which we intersect with a line, the road on which the users are moving. Applying point process techniques we derive approximation formulae for the distribution of the covered and uncovered parts of the road. Furthermore, we examine for a rather general model the probability that exactly K users are communicating with a base station. Numerical examples illustrate how accurate the approximations are. This revised version was published online in June 2006 with corrections to the Cover Date.     

A metric for ARMA processes

Autoregressive-moving-average (ARMA) models seek to express a system function of a discretely sampled process as a rational function in the z-domain. Treating an ARMA model as a complex rational function, we discuss a metric defined on the set of complex rational functions. We give a natural measure of the “distance” between two ARMA processes. The paper concentrates on the mathematics behind the problem and shows that the various algebraic structures endow the choice of metric with some interesting and remarkable properties, which we discuss. We suggest that the metric can be used in at least two circumstances: (i) in which we have signals arising from various models that are unknown (so we construct the distance matrix and perform cluster analysis) and (ii) where there are several possible models M_i, all of which are known, and we wish to find which of these is closest to an observed data sequence modeled as M     

Optimal assignment of priorities for the machine interference problems

This paper investigates multiple machine repair problems with one repairman. Each machine is subject to two modes of failure, major and minor. The machines are identical, with times to repair and the times to failure assumed to be negative exponentially distributed. In this paper we consider the problem: when there are i and j failed machines in modes 1 and 2, respectively, which mode of failure should be selected for repair? A profit model is developed and then, to achieve the optimal profit, we derive the optimal repair policy for the single repairman. In addition, we describe a procedure to determine the optimal number of machines which should be assigned to a repairman. Numerical examples are provided in which the system characteristics are evaluated and profits are analyzed.     

Balanced multiwavelets theory and design

This article deals with multiwavelets, which are a generalization of wavelets in the context of time-varying filter banks and with their applications to signal processing and especially compression. By their inherent structure, multiwavelets are fit for processing multichannel signals. This is the main issue in which we are interested. First, we review material on multiwavelets and their links with multifilter banks and, especially, time-varying filter banks. Then, we have a close look at the problems encountered when using multiwavelets in applications, and we propose new solutions for the design of multiwavelets filter banks by introducing the so-called balanced multiwavelets     

P-Accountability: A Quantitative Study of Accountability in Networked Systems

Accountability in computing implies that an entity should be held responsible for its behaviors with verifiable evidence. In order to study accountability, quantitative methods would be very helpful. Even though there are some researches in accountability, there are no other works which study quantitative accountability in practical settings, while quantitative accountability is defined as using quantities or metrics to measure accountability. In this paper, we propose P-Accountability, which is a quantitative approach to assess the degree of accountability for practical systems. P-Accountability is defined with two versions, a flat model and a hierarchical one, which can be chosen to use depending on how complex the system is. We then provide a complete case study that applies P-Accountability to PeerReview, which provides Byzantine fault detection for distributed systems. In addition, we propose Traceable PeerReview, which is our effort to apply PeerReview to wireless multi-hop environments. In addition, through the system evaluation we can show that the simulation outcomes are aligned with the numeric results.     

Mean-Squared Error Sampling and Reconstruction in the Presence of Noise

One of the main goals of sampling theory is to represent a continuous-time function by a discrete set of samples. Here, we treat the class of sampling problems in which the underlying function can be specified by a finite set of samples. Our problem is to reconstruct the signal from nonideal, noisy samples, which are modeled as the inner products of the signal with a set of sampling vectors, contaminated by noise. To mitigate the effect of the noise and the mismatch between the sampling and reconstruction vectors, the samples are linearly processed prior to reconstruction. Considering a statistical reconstruction framework, we characterize the strategies that are mean-squared error (MSE) admissible, meaning that they are not dominated in terms of MSE by any other linear reconstruction. We also present explicit designs of admissible reconstructions that dominate a given inadmissible method. Adapting several classical estimation approaches to our particular sampling problem, we suggest concrete admissible reconstruction methods and compare their performance. The results are then specialized to the case in which the samples are processed by a digital correction filter     

Acousto-optic tunable filters (AOTFs) for multiwavelength opticalcross-connects: crosstalk considerations

Acousto-optic tunable filters (AOTF) have been investigated as a potential basis for multiwavelength cross-connects in optical networks. In this paper, we discuss crosstalk issues, some of which are common to other cross-connect technologies, and some of which are unique to the AOTF, which will determine the suitability of the AOTF technology for this application. In particular we show how the interactions between wavelength channels make the AOTF sensitive to switch architectures, we conclude that significant performance improvements will be required to diminish crosstalk if the AOTF is to be useful in any but small-size cross-connects, even when spare and wavelength dilation are used     

DroidEnemy: Battling adversarial example attacks for Android malware detection

In recent years, we have witnessed a surge in mobile devices such as smartphones, tablets, smart watches, etc., most of which are based on the Android operating system. However, because these Android-based mobile devices are becoming increasingly popular, they are now the primary target of mobile malware, which could lead to both privacy leakage and property loss. To address the rapidly deteriorating security issues caused by mobile malware, various research efforts have been made to develop novel and effective detection mechanisms to identify and combat them. Nevertheless, in order to avoid being caught by these malware detection mechanisms, malware authors are inclined to initiate adversarial example attacks by tampering with mobile applications. In this paper, several types of adversarial example attacks are investigated and a feasible approach is proposed to fight against them. First, we look at adversarial example attacks on the Android system and prior solutions that have been proposed to address these attacks. Then, we specifically focus on the data poisoning attack and evasion attack models, which may mutate various application features, such as API calls, permissions and the class label, to produce adversarial examples. Then, we propose and design a malware detection approach that is resistant to adversarial examples. To observe and investigate how the malware detection system is influenced by the adversarial example attacks, we conduct experiments on some real Android application datasets which are composed of both malware and benign applications. Experimental results clearly indicate that the performance of Android malware detection is severely degraded when facing adversarial example attacks.     

Statistical Pileup Correction Method for HPGe Detectors

We consider a nonlinear inversion problem occurring in gamma spectrometry. In that framework, photon energies are converted to electrical pulses which are susceptible to overlap, creating clusters of pulses, referred to as pileup. This phenomenon introduces a distortion that can be a nuisance for the correct identification of the radionuclides. In that application we are interested in the distribution of the individual photon energies, hence, it is necessary to estimate this distribution using the indirect observations of the piled-up electrical pulses. In this paper, we present a new method to correct the pileup phenomenon, based on a nonlinear formula, which is inverted to give a nonparametric estimator of the individual energy distribution. Since the proposed estimator depends on parameters to be chosen carefully by the user, we also detail data-driven selection methods for the associated algorithm. Applications on simulations and real datasets are presented, which shows the efficiency of the proposed method.     

Distributed source coding for satellite communications

Inspired by mobile satellite communications systems, we consider a source coding system which consists of multiple sources, multiple encoders, and multiple decoders. Each encoder has access to a certain subset of the sources, each decoder has access to certain subset of the encoders, and each decoder reconstructs a certain subset of the sources almost perfectly. The connectivity between the sources and the encoders, the connectivity between the encoders and the decoders, and the reconstruction requirements for the decoders are all arbitrary. Our goal is to characterize the admissible coding rate region. Despite the generality of the problem, we have developed an approach which enables us to study all cases on the same footing. We obtain inner and outer bounds of the admissible coding rate region in terms of Γ_N * and Γ¯_N*, respectively, which are fundamental regions in the entropy space defined by Yeung (1991). So far, there has not been a full characterization of Γ_N*, so these bounds cannot be evaluated explicitly except for some special cases. Nevertheless, we obtain an alternative outer bound which can be evaluated explicitly. We show that this bound is tight for all the special cases for which the admissible coding rate region is known. The model we study in this paper is more general than all previously reported models on multilevel diversity coding, and the tools we use are new in multiuser information theory     

Parity-check density versus performance of binary linear block codes over memoryless symmetric channels

We derive lower bounds on the density of parity-check matrices of binary linear codes which are used over memoryless binary-input output-symmetric (MBIOS) channels. The bounds are expressed in terms of the gap between the rate of these codes for which reliable communications is achievable and the channel capacity; they are valid for every sequence of binary linear block codes if there exists a decoding algorithm under which the average bit-error probability vanishes. For every MBIOS channel, we construct a sequence of ensembles of regular low-density parity-check (LDPC) codes, so that an upper bound on the asymptotic density of their parity-check matrices scales similarly to the lower bound. The tightness of the lower bound is demonstrated for the binary erasure channel by analyzing a sequence of ensembles of right-regular LDPC codes which was introduced by Shokrollahi, and which is known to achieve the capacity of this channel. Under iterative message-passing decoding, we show that this sequence of ensembles is asymptotically optimal (in a sense to be defined in this paper), strengthening a result of Shokrollahi. Finally, we derive lower bounds on the bit-error probability and on the gap to capacity for binary linear block codes which are represented by bipartite graphs, and study their performance limitations over MBIOS channels. The latter bounds provide a quantitative measure for the number of cycles of bipartite graphs which represent good error-correction codes.     

Access control for web data: models and policy languages

The web has made easily available an enormous amount of information in digital form and has facilitated the exchange of such information. In this environment, access control is a primary concern. The key issue is how to trade-off between maximizing the sharing of information and enforcing a controlled access to web data. In this paper we start by outlining which are the main access control requirements of web data. Then, we review researches carried on in the field, by mainly focusing on xml. Finally, we discuss policy languages for the semantic web, and outline which are the main research directions in this field.     

Compressed Sensing of Analog Signals in Shift-Invariant Spaces

A traditional assumption underlying most data converters is that the signal should be sampled at a rate exceeding twice the highest frequency. This statement is based on a worst-case scenario in which the signal occupies the entire available bandwidth. In practice, many signals are sparse so that only part of the bandwidth is used. In this paper, we develop methods for low-rate sampling of continuous-time sparse signals in shift-invariant (SI) spaces, generated by m kernels with period T . We model sparsity by treating the case in which only k out of the m generators are active, however, we do not know which k are chosen. We show how to sample such signals at a rate much lower than m/T, which is the minimal sampling rate without exploiting sparsity. Our approach combines ideas from analog sampling in a subspace with a recently developed block diagram that converts an infinite set of sparse equations to a finite counterpart. Using these two components we formulate our problem within the framework of finite compressed sensing (CS) and then rely on algorithms developed in that context. The distinguishing feature of our results is that in contrast to standard CS, which treats finite-length vectors, we consider sampling of analog signals for which no underlying finite-dimensional model exists. The proposed framework allows to extend much of the recent literature on CS to the analog domain.     

Modal analysis of semiconductor cylinder fibers

Semiconductor cylinder fibers (SCFs) are novel amplifying waveguide structures in which a semiconducting film is interlaid between conventional core and cladding fiber layers. We investigate the modal properties of SCFs by way of a comprehensive model which takes into account the wavelength-dependent refractive indexes of both the core and cladding glass layers and the semiconductor. Our semiconductor model also includes both thin-film effects and carrier-induced changes in the complex refractive index. We show that annular modes which are highly confined to the semiconductor are supported, and we calculate the corresponding modal effective indexes. Finally, we demonstrate that, depending on the pump-induced carrier concentration, a large gain is possible across a broad spectral region.     

基于高速单片机的GPS接收系统设计

为了得到满足工程需求的高精度GPS信息接收系统,文中提出了基于GPS接收模块的系统设计方案,利用功能强大的高速C8051F120单片机作为主控制器,对基于NMEA-0813协议的GPS数据信息进行解析、提取和LCD液晶显示以及利用GPS秒脉冲同步触发的串行通信;同时,利用EPM570T144型号CPLD（复杂可编程逻辑器件）实现基于GPS秒脉冲的同步时钟多路输出等功能。给出了硬件电路设计原理图和C语言的软件思想流程图、CPLD程序框图,通过设计成功实现了预期目标．     

A new framework for characterization of halftone textures.

Characterization of halftone texture is important for quantitative assessment of halftone quality. In this paper, we develop a new framework based on directional local sequency analysis and a filter bank structure. We decompose a halftone image into subband images, from which we can easily reconstruct the original halftone. Based on these subband images, we define the directional sequency spectrum which is analogous to the two-dimensional Fourier spectrum, and formulate several texture measures. Two test image sets are used to justify these measures.