ALAN TURING: THE ENIGMA – BOOK REVIEW

Abstract

Simple substitution ciphers are a class of puzzles often found in newspapers, in which each plaintext letter is mapped to a fixed ciphertext letter and spaces are preserved. In this article, a system for automatically solving them is described even when the ciphertext is too short for statistical analysis, and when the puzzle contains non-dictionary words. The approach is based around a dictionary attack; several important performance optimizations are described as well as effective techniques for dealing with non-dictionary words. Quantitative performance results for several variations of the approach and two other implementations are presented.     

CRYPTANALYSIS OF SHIFT STREAM GENERATED STREAM CIPHER SYSTEMS – BOOK REVIEW

A new method for realizing public-key cryptosystem is proposed in this paper. Three plaintext messages are transformed into three cryptograms in this method. Message authentication is easily realized by this method. Y≡A^x mod P is used as a one-way function, where P is prime.     

KONHEIM'S CRYPTOGRAPHY–A PRIMER: A BOOK REVIEW

In this paper, we present an approach to compute master keys for an M ³ public-key cryptoscfaeme. At first, the existence conditions of master keys are derived. Then an algorithm to compute master keys is given. Further, the security of our master key cryptosystem is also guaranteed, no matter what relations or key values are exposed.     

Revising Z: Part II – logical development

This is the second of two related papers. In “Revising Z: Part I - logic and semantics” (this journal) we introduced a simple specification logic Z _C comprising a logic and a semantics (in ZF set theory). We then provided an interpretation for (a rational reconstruction of) the specification language Z within Z _C . As a result we obtained a sound logic for Z, including the basic schema calculus. In this paper we extend the basic framework with more sophisticated features (including schema operations) and we mount a critique of a number of concepts used in Z. We further demonstrate that the complications and confusions which these concepts introduce can be avoided without compromising expressibility. Received March 1998 / Accepted in revised form April 1999     

On the Numerical Solution of Some Semilinear Elliptic Problems – II

In the earlier paper [6], a Galerkin method was proposed and analyzed for the numerical solution of a Dirichlet problem for a semi-linear elliptic boundary value problem of the form –U=F(·,U). This was converted to a problem on a standard domain and then converted to an equivalent integral equation. Galerkins method was used to solve the integral equation, with the eigenfunctions of the Laplacian operator on the standard domain D as the basis functions. In this paper we consider the implementing of this scheme, and we illustrate it for some standard domains D.     

腾龙AF3.5-6.3/18-270mm Di II VC PZD 万能旅伴

由于其非常广泛的焦距范围,腾龙的旅行变焦镜头几乎在所有情况下都能使用。我们的测试工程师带着它来到世界的另一端,对任何一天的拍摄都没有感到遗憾。     

CALPHAD-based alloy design for advanced automotive steels – Part II: Compositional and microstructural modification for advanced carburizing steels

The CALPHAD-based computational techniques established in the first part of this series [1] have been applied for the development of advanced carburizing steels used for gears in vehicle transmissions. To improve the strength and hardenability of a conventional carburizing steel, the alloying composition has been modified based on the calculation of phase equilibria and the prediction of mechanical properties such as the yield and tensile strengths, hardness, and volume fractions of martensite and bainite. The size and density of carbides precipitated with V, Nb or Ti microalloying elements as well as their austenite grain size have been predicted by thermo-kinetic simulation to optimize the microstructure. The reliability of the computational results has been experimentally confirmed by comparing the austenite grain size and the hardness of the newly developed carburizing steels with those of the conventional carburizing steels.     

A systems-level perspective of the biomechanics of the trunk flexion-extension movement: Part II – Fatigued low back conditions

Our companion paper demonstrated the importance of a systems-level perspective on spine biomechanics by showing the effects of lower extremity constraints during simple, trunk flexion-extension motions. This paper explores the impact of trunk muscle fatigue and stress-relaxation of lumbar passive tissues on this systems-level response. Twelve participants performed experimental protocols to achieve lumbar passive tissue stress-relaxation fatigue and lumbar muscle fatigue. Participants performed full range of sagittal-plane trunk flexion-extension under unconstrained stoop movement and pelvic/lower extremity constrained stoop movement. They performed these motions both before and after the fatigue protocols and trunk kinematics and muscle activities in trunk and lower extremity muscles were monitored. Under the condition of passive tissue fatigue, low back muscles and lower extremity muscles revealed significantly increased activation level (21% and 22%, respectively) in the free stoop condition but under the restricted stoop condition, there was no significant effect of the protocol. Under the lumbar muscle fatigue condition, a significant antagonistic and lower extremity activation effect (34% increase in abdominal muscles, 16% increase in lower extremity muscles) was observed in the free stooping condition while these variables were not affected by the protocol under the restricted stooping condition.Relevance to industryFatigue of the lumbar musculature and passive tissues is prevalent in jobs requiring full trunk flexion postures. Developing accurate biomechanical models of spinal stress in these full stooping postures can help in the development of appropriate interventions to reduce the prevalence of back injuries in these jobs.     

腾龙18-270mm F3.5-6.3 Di II VCPZD 一镜在手,拍摄不愁

春节刚过,我受命前往五台山做一期栏目,随身携带了腾龙的18-270mmF3.5-6.3Di II VC PZD镜头。这款号称全球最轻、最小的15倍变焦镜头,装配在佳能EOS60D上的35mm等效焦距为28-419mm。我想,作为一只全能型的旅变镜头,它的焦段范围应该能满足任何苛刻的拍摄题材了。此次出行,我不仅用它拍摄风景、建筑、人像和微距小品,甚至还抓拍了几张不错的鸟类照片。     

Topological optimization of continuum structures with design-dependent surface loading – Part II: algorithm and examples for 3D problems

The problem of topology optimization of 3D structures with design-dependent loading is considered. An algorithm for generating the valid loading surface of the 3D structure is presented, constituting an extension of the algorithm for 2D structures developed in Part I of this paper on the basis of a modified isoline technique. In this way the complicated calculation of the fit of the loading surface of a 3D structure may be avoided. Since the finite element mesh is fixed in the admissible 3D design domain during the period of topology evolution, the design-dependent loading surface may intersect the elements as the design changes. Independent interpolation functions are introduced along the loading surface so that the surface integral for generating the loading on the surface of the 3D structure can be performed more efficiently and simply. The bilinear 4-node serendipity surface element is constructed to describe the variable loading surface, and this matches well with the 8-node isoparametric 3D elements which have been used for the discretization of the 3D design domain. The validity of the algorithm is verified by numerical examples for 3D problems. Results of designing with design-dependent loads and with corresponding fixed loads are presented, and some important features of the computational results are discussed.     

腾龙SP AF17-50mm F2.8XR Di II LD 取代套头

腾龙旗下的镜头产品总数量虽然不算多,但每款产品都有着自己的特点。无论是以性价比、成像锐利度见长的SP90,或是以色彩赢得用户肯定的SP AF 28-75mm F2.8都属于能让用户铭记在心的好头。而这支SP AF 17-50mm F2.8XR Di II LD是否能延续腾龙的优良传统呢?     

A Review of: “PROBLEM - SOLVING METHODS IN ARTIFICIAL INTELLIGENCE”, by Nils J. Nilsson. McGraw-Hill,New York, 1971. 255 pp.

After defining systems that can be represented by scators it is shown that the merging of such systems is conveniently modelled by scator addition. It is shown that scator addition although not generally associative will be so if a certain function involved is solution of a functional equation whose general solution is found. Finally after defining scator derivatives it is shown that systems with continuous merging lead to differential equations in scators.     

腾龙16-300mm F3.5-6.3 Di II VC PZD(约3980元) 开启旅游摄影新时代

腾龙继续着自己探索的道路。凭借24mm~450mm(按1.5×焦距转换系数计算)的等效焦距,这支全新的超级变焦镜头在广角端和长焦端都取得了破纪录的评分。这支重量几乎与我随身携带的佳能EOS700D单反机身相仿的超级变焦镜头会不会成为轻装旅行摄影中的累赘?一些旅行摄影师可能会为此而担忧,但这支镜头的体积并不大,即使装上机身也能放置在小号的     

The TV-WEB project - combining internet and television – lessons learnt from the user experience studies

We present the results of the user experience studies conducted as part of the European SEE TV-WEB project activities. The SEE TV-WEB project aims to use the free digital terrestrial television (DTT) broadcasting frequency spectrum capacities for transmitting selected Internet content and ensuring at least some Internet experience via TV devices to the certain less advantaged segments of the population, or those in rural areas without broadband access. Five different test study cases are presented, four in Slovenia and one in Austria, each with different specific target user groups and their own dynamics. According to the project disposition goals the focus was on the elderly. Methods, such as think-aloud protocol in combination with a guided interview and observation of verbal as well as of non-verbal responses, were used. To ensure the repeatability of tests and to help guide the process, a special questionnaire was developed. The research questions focused on: the navigation and interaction concept, the content, the readability, and the overall acceptance and the perception of value of the TV-WEB service. More than 74 users participated in the user experience studies, 27 of them 65 years old or older. The results indicate that the presented navigation and interaction concept is indeed intuitive and simple enough to be used by most users with no or little effort. This is especially proven by the results from studies at both elderly citizens homes, where the majority of participants were 65 years old or older.