每次处理2个像素像素扩展度为1的(2,2)视觉密码方案

为了解决传统视觉密码像素扩展度高的问题及分存图像占用存储空间过大问题,提出每次处理2个像素像素扩展度为1的(2,2)视觉密码方案.方案中,秘密图像为黑白二值图像,每次处理2个像素,得到的2个分享份额图像为黑白噪声图像,叠加分享份额恢复秘密图像.该方案解密过程简单,恢复秘密图像无变形,像素扩展度为1.     

High contrast, low-voltage, symmetric-selfelectro-optic effect device (S-SEED)

A high contrast ( approximately 70:1), low voltage (4.2 V), asymmetric Fabry-Perot, multiquantum well, symmetric-selfelectro-optic effect device (S-SEED) is demonstrated.<>     

Network security (and the internet)

This article describes how organizations can fulfil their enterprise security requirements with the Cisco Internetwork Operating System.     

There is no (24, 12, 10) self-dual quaternary code

An attempt at directly constructing a (24, 12, 10) extremal quaternary code is reported. The attempt at directly constructing the generator matrix of the code is detailed. It was found that no such code exists     

浅谈内网的安全问题与对策(三)

市场上现有的大多数网络安全产品在防范内网安全问题上存在着或多或少的一些漏洞,我们结合自身多年来在实施大型网络项目上的经验,推出了自主研发的eCop系列产品,针对在内网监控方面的关键环节,提出了一整套的解决方案。1. 网络物理层安全应用网络拓扑发现工具发现内部网络的物理拓扑结构,显示当前路由器、交换机以及各主机之间的连接关系,并周期测试各网络节点之间的连通状态。网络设备监视器则通过SNMP协议实时监视各网络设备和关键主机的工作状态,一旦发现异常及时予以报警。使得网络管理员对内网的连接状况了如指掌,便于故障的快速定…     

浅谈内网的安全问题与对策(一)

随着计算机的应用和发展,网络安全问题越来越受到各行业、各部门领导的重视,投入了很大的精力和财力来解决计算机网络安全问题。上海宝信软件股份有限公司凭借多年来在实施大型网络项目上的经验,拥有一整套完整的解决方案,并开发了一些具有自主知识产权的网络安全产品。我们发表一系列的文章,主要讨论针对来自局域网内部的安全隐患的最新研究进展,并对这些安全问题进行分析,提出了完整的解决方案和对策。本文是第一部分,主要介绍内网的各种安全问题、发生形式和特点。内忧甚于外患2001年国家经贸委信息中心对国家重点企业和地方骨干企业的调…     

浅谈内网的安全问题与对策(二)

如何打造内网安全内网安全问题是我们在制定安全策略时必须要考虑的重点之一,只有这样才能事半功倍。要想从根本上杜绝恶性攻击事件的发生,必须首先强化企业内部网络的安全防范与安全管理。1. 安全管理与安全教育在协作及知识管理等新型业务手段中,信息共享是不可或缺的,有时企业间还需要进行信息交换。“这种可以自由交换信息的环境很容易导致计算机或网络的非法利用”(Gartner)。如果要明确规定业务伙伴与职员如何正当使用知识财产,就必须与相关人员达成有法律效力的协议,而不能仅仅依靠他们的道德约束力。但是,大部分企业没有制定有关共…     

Optimal (2, n) and (2, infinity) visual secret sharing by generalized random grids

Based on generalized random grids, this paper proposes two visual cryptography methods denoted as (2, n) GRG and (2, infinity) GRG. The (2, n) GRG is suitable for the pre-decided number of shares, and the (2, infinity) method is suitable for the adjustable number of shares. The proposed (2, n) GRG achieves better contrast on the stacking result, and the proposed (2, infinity) GRG enables extending the number of shares anytime. Based on the definition of contrast in Shyu’s work in 2007, we also demonstrate that the stacking result of (2, n) GRG is close to the theoretical bound of the contrast, and the stacking result of (2, infinity) GRG achieves the theoretical bound of the contrast.     

Two-channel perfect reconstruction (PR) quadrature mirror filter (QMF) bank design using logarithmic window function and spline function

In this work, two-channel perfect reconstruction quadrature mirror filter (QMF) bank has been proposed based on the prototype filter using windowing method. A novel window function based on logarithmic function along with the spline function is utilized for the design of prototype filter. The proposed window has a variable parameter ‘\(\alpha \)’, which varies the peak side lobe level and rate of fall-off side lobe level which in turn affects the peak reconstruction error (PRE) and amplitude distortion (\(e_{am}\)) of the QMF bank . The transition width of the prototype is controlled by the spline function using the parameter ‘\(\mu \)’. The perfect reconstruction condition is satisfied by setting the cutoff frequency (\(\omega _{c}\)) of the prototype low-pass filter at ‘\(\pi /2\)’. The performance of the proposed design method has been evaluated in terms of mean square error in the pass band, mean square error in the stop band, first side lobe attenuation (\(A_{1}\)), peak reconstruction error (PRE) and amplitude error (\(e_{am}\)) for different values of ‘\(\alpha \)’ and ‘\(\mu \)’. The results are provided and compared with the existing methods.     

IP协议的作用、安全性问题及其解决之道的战略思考(上)

本文从IP协议的内涵、作用与外延的一系列问题讨论出发。进一步以安全性为重点论述发展IP及NGN的理性战略思维。     

IP协议的作用、安全性问题及其解决之道的战略思考(下)

如上文所述，根据以TCP／IP协议为基础的INTERNET的发展历程可知，IP协议的最可取的内涵与作用即在于其充分的开放透明性与灵活有效的多业务增值能力。然而，要开放透明，往往便“充分暴露”，从而自然容易受到攻击。因此，INTERNET商用化后大量暴露出的一系列问题中最棘手、解决难度最大的问题即为安全性问题。     

Exponential spline perfect reconstruction,decomposition and reconstruction with applications in compression and denoising

B-splines caught interest of many engineering applications due to their merits of being flexible and provide a large degree of differentiability and cost/quality trade-off relationship. However, they have less impact with continuous-time applications as they are constructed from piecewise polynomials. On the other hand, exponential spline polynomials (E-splines) represent the best smooth transition between continuous and discrete domains as they are made of exponential segments. In this paper, we present a complete analysis for an E-spline-based subband coding (wavelet) perfect reconstruction (PR) system. Derivations for the scaling and wavelet functions are presented, along with application of the proposed system in image compression and image denoising. In image compression, a comparison of the proposed technique compared with the B-spline-based PR system as well as the basic wavelet subband system with the SPIHT image codec is presented. In image denoising, we report the enhancement achieved with the proposed E-spline-based denoising approach compared with B-spline-based denoising and another basic denoising technique. In both applications, E-splines show superior performance as will be illustrated.     

Effects of Heating Rate on Material Properties of Anisotropic Conductive Film (ACF) and Thermal Cycling Reliability of ACF Flip Chip Assembly

In this paper, the effects of heating rate during anisotropic conductive film (ACF) curing processes on ACF material properties such as thermomechanical and rheological properties were investigated. It was found that as the heating rate increased, the coefficient of thermal expansion (CTE) of the ACF increased, and the storage modulus and glass transition temperature $(T _{g})$ of the ACF decreased. Variation of the ACF material properties are attributed to cross-linking density, which is thought to be related with the ACF density. In addition, as the heating rate increased, the minimum viscosity of the ACF decreased and the curing onset temperature increased during the curing process. The similar phenomenon was also found in in-situ contact resistance measurement. As the heating rate increased, contact resistance establishing temperature increased and the contact resistances of the ACF flip chip assemblies decreased. The decrease in contact resistance was due to larger conductive particle deformation which leads to larger electrical contact area. The effect of the heating rate of ACFs on thermal cycling (T/C) reliability of flip chip assemblies was also investigated. As the heating rate increased, the contact resistances of the ACF flip chip assembly rapidly increased during the T/C test. The T/C reliability test result was analyzed by two terms of shear strain and conductive particle deformation. Reduced gap of joints due to reduced ACF viscosity resulted in larger shear strain. Moreover, many cracks were observed at metal-coated layers of conductive particles due to larger deformation.      

A visible watermarking algorithm based on the content and contrast aware (COCOA) technique

A novel visible watermarking algorithm based on the content and contrast aware (COCOA) technique with the consideration of Human Visual System (HVS) model is presented in this study. In order to determine the optimal watermark locations and strength at the watermark embedding stage, the COCOA visible watermarking utilizes the global and local characteristics of the host and watermark images in the discrete wavelet transform (DWT) domain. To achieve the best tradeoff between the embedding energy of watermark and the perceptual translucence, the utilization of contrast–sensitive function, noise visible function of perceptual model, and the basis function amplitudes of DWT coefficients are fine tuned, for the best quality of perceptual translucence and noise reduction of the COCOA algorithm. The experimental results demonstrate that COCOA technique not only provides high PSNR values for the watermarked images, but also preserves the watermark visibility under various signal processing operations, especially the watermark removal attack.     

Optoelectronic integrated circuit (OEIC) waveguide coupler for spotsize expansion and improved fibre coupling efficiency

An MOVPE vertical coupler structure is used to provide efficient coupling between InP/InGaAsP optoelectronic integrated circuit (OEIC) waveguides and cleaved monomode fibres. A 2 dB improvement in the coupling efficiency of TE polarised light of wavelength 1.55 μm is demonstrated. The structure does not require any additional growth steps, and is compatable with vertically integrated detector structures     

Thermal expansion and characteristic features of the strength of interatomic bonds in melts of III–V compounds (AlSb, GaSb, InSb, GaAs, InAs)

The temperature dependence of the specific volume of melts of III–V compounds has been studied thermometrically and with penetrating γ radiation. The thermal expansion of these melts has been estimated at various temperatures. Based on the similarity of the structure of the melts and the elastic continuum, the characteristic Debye temperatures and rms dynamic displacements of the atoms in the close-range-order structure of these melts have been calculated from the estimated thermal expansion. A considerable change in the indicated characteristics is observed at the transition from the solid state to the liquid state, indicating significant changes in the vibrational spectrum of III–V compounds upon melting. The thermal expansion of the melts is observed to increase upon heating, indicating a further loss of strength of the interatomic bonds in the melts with growth of temperature. Fiz. Tekh. Poluprovodn. 32, 429–431 (April 1998)     

2003国内外网络与信息安全年度报告(上)

国内的信息安全经过一年的发展变化,有许多问题值得回顾和总结。作者从战略全局的高度对2003年国内外信息安全的整体情况作了一个全面、深入的论述。本刊将分两期独家刊登。