构建一种安全的企业邮件服务器的考虑

当前,很多企业都建立了自己的邮件服务器。企业在建立邮件服务器时,希望该系统能价格相对便宜、管理简单,更能保证邮件安全的传送。针对企业的这种要求,论述了如何在Windows平台下运用COM技术和VPN技术构建安全的企业级邮件服务器。     

The Use Made of the Speedometer as an Aid to Driving

This note describes a study of the use which drivers of motor vehicles make of the speedometer when making changes of speed, particularly in circumstances where an appropriate speed is likely to be important to safety. By the combined use of behavioural observation and questionnaire techniques a comparison was also made between what drivers say they do, and what they actually do, on the road. The behaviour of 30 subjects was observed while they drove over a route chosen to include most situations where a speedometer might reasonably be considered helpful to safe driving.

The results showed that there were wide differences in the use made of the speed-ometer by different drivers and that the drivers thought they used a speedometer far more than they did. The only exceptions were on a motorway or in towns. Asked whether they thought they would drive loss safely without a speedometer, 22 drivers (70 per cent) said they thought not     

Editorial: Communication channels

"34. The objective of piloting superhighways in education, as with any other new technologies, is to establish whether they offer the potential to enrich the delivery and experience of education, are likely to help young people meet the challenges which they will face when they enter employment, and provide them with the skills which they will need for lifetime learning."*     

电视节目远程录制与点播系统的设计及应用

在当今社会,每天全国卫星电视网传送出近百套电视节目,覆盖了文化、教育、科技、体育等大量有价值的内容,能否让希望保存这些资源的人或由于某些原因无法及时看到并录制自己所关注节目的人方便快捷地获得这些电视资源?电视节目远程录制与点播系统就可以让使用者很容易地获得所需的电视资源,本文将介绍本系统的设计思想和编程技术。     

Thinking with external representations

Why do people create extra representations to help them make sense of situations, diagrams, illustrations, instructions and problems? The obvious explanation—external representations save internal memory and computation—is only part of the story. I discuss seven ways external representations enhance cognitive power: they change the cost structure of the inferential landscape; they provide a structure that can serve as a shareable object of thought; they create persistent referents; they facilitate re-representation; they are often a more natural representation of structure than mental representations; they facilitate the computation of more explicit encoding of information; they enable the construction of arbitrarily complex structure; and they lower the cost of controlling thought—they help coordinate thought. Jointly, these functions allow people to think more powerfully with external representations than without. They allow us to think the previously unthinkable.     

Convergence of recursive adaptive and identification procedures via weak convergence theory

Results and concepts in the theory of weak convergence of a sequence of probability measures are applied to convergence problems for a variety of recursive adaptive (stochastic approximation-like) methods. Similar techniques have had wide applicability in areas of operations research and in some other areas in stochastic control. It is quite likely that they will play a much more important role in control theory than they do at present, since they allow relatively simple and natural proofs for many types of convergence and approximation problems. Part of the aim of the paper is tutorial: to introduce the ideas and to show how they might be applied. Also, many of the results are new, and they can all be generalized in many directions.     

A survey on solutions and main free tools for privacy enhancing Web communications

Concern for privacy when users are surfing on the Web has increased recently. Nowadays, many users are aware that when they are accessing Web sites, these Web sites can track them and create profiles on the elements they access, the advertisements they see, the different links they visit, from which Web sites they come from and to which sites they exit, and so on. In order to maintain user privacy, several techniques, methods and solutions have appeared. In this paper we present an analysis of both these solutions and the main tools that are freely distributed or can be used freely and that implement some of these techniques and methods to preserve privacy when users and surfing on the Internet. This work, unlike previous reviews, shows in a comprehensive way, all the different risks when a user navigates on the Web, the different solutions proposed that finally have being implemented and being used to achieve Web privacy goal. Thus, users can decide which tools to use when they want navigate privately and what kind of risks they are assuming.     

German mathematicians and cryptology in WWII

Abstract

By now, a great deal is known about the contributions of Alan Turing, I. J. Good, Max Newman, and other mathematicians who worked at Bletchley Park during World War II. But what about the other side? Until recently, very little was known about the German mathematicians who aided the Nazi war effort: who were they, where did they work, and what did they do? But now, thanks to the release of a large number of TICOM documents in recent years, an initial picture is beginning to emerge. In this article, we identify the most important mathematicians who worked in the different German cryptologic organizations during the war: who they were, how they were recruited, which organizations they were in, and what they did (when this is known). Although their successes never rivaled those of Bletchley Park, they did have successes, and these were sometimes due to the efforts of mathematicians who went on to have distinguished careers after the war. One question that motivated this study was to understand the reasons for the German communications security meltdown during the war: how they got the Enigma and Tunny security assessments partly right but mostly wrong. As will be seen, this was not due to a lack of talent: some of the very best German mathematicians contributed to their war effort. The answer lies instead in how these potentially very useful assets were actually used (in striking contrast with what happened at Bletchley Park).     

Auditing NT — Part 2

This second article on NT auditing focuses on controlling users: whether or not they use the system, what they can do once they are in, and how to keep a record of what they have done. As with the operating system configuration that we looked at in the last article, you will need administrator access to review many of the security settings, and to review the security log. You will also be using tools supplied in the NT Resource kit to get listings of information that cannot be effectively scanned online.     

End-User Access Tools

A variety of end-user data access tools provide users and teams with access to the enterprise data they need—when they need it, from wherever it exists, and in a form they can use to improve the enterprise's performance.     

Using metrics to evaluate software system maintainability

Software metrics have been much criticized in the last few years, sometimes justly but more often unjustly, because critics misunderstand the intent behind the technology. Software complexity metrics, for example, rarely measure the “inherent complexity” embedded in software systems, but they do a very good job of comparing the relative complexity of one portion of a system with another. In essence, they are good modeling tools. Whether they are also good measuring tools depends on how consistently and appropriately they are applied     

Displays on Display

Color, resolution, and speed, though important factors in computer graphics, must be subordinate to the message the image must deliver. While many graphics designers and users have understood this, many others, bedazzled by the powerful hardware/software tools available to them, have been tempted to use all the techniques they can instead of the ones they should. If they had a system that could graph in eight colors and fifteen fonts, for example, they used them all-with confusion of the viewer the result.     

Modular type checking of anchored exception declarations

Checked exceptions improve the robustness of software, but they also decrease its adaptability because they must be propagated explicitly, and because they must often be handled even if they cannot be thrown. Anchored exception declarations solve both problems by allowing a method to declare its exceptional behavior in terms of other methods.The original type checking analyses for anchored exception declarations, however, are not modular. In this paper, we present algorithms for modular verification of soundness in an object-oriented language without parametric polymorphism.     

Progressive processing of subspace dominating queries

A top-k dominating query reports the k items with the highest domination score. Algorithms for efficient processing of this query have been recently proposed in the literature. Those methods, either index based or index free, apply a series of pruning criteria toward efficient processing. However, they are characterized by several limitations, such as (1) they lack progressiveness (they report the k best items at the end of the processing), (2) they require a multi-dimensional index or they build a grid-based index on-the-fly, which suffers from performance degradation, especially in high dimensionalities, and (3) they do not support vertically decomposed data. In this paper, we design efficient algorithms that can handle any subset of the dimensions in a progressive manner. Among the studied algorithms, the Differential Algorithm shows the best overall performance.     

Detection of Errors by Skilled Typists

Abstract

Skilled typists are able to detect and correct many errors which they make in copy text, even when they cannot see their copy; (Long 1976. West, 1967). The present investigation shows that they can also do this when they see neither their copy nor the keyboard they use; and that when they detect that they have made errors they arc usually also able to specify precisely what these have been. Typists sometimes make one, or even two additional correct keystrokes before pausing to signal that they have committed an error. They are nevertheless sometimes still able to report precisely what these errors were

When copy obtained from a typewriter using mechanical linkages is examined, the density of impressions of different characters may be taken to indicate how hard particular keys have been struck. A second experiment shows that errors, more frequently than correct responses, are executed with light keystrokes. This, in line with previous work by Megaw (1972). suggests that typists sometimes become aware that they are about to make an error before they complete the keystroke implementing it. They may then attempt to ‘pull back’ incorrect keystrokes, producing fainter impressions on copy

The probability that typists will subsequently signal detection of such ‘ faint’ (or‘ pulled’) errors was found to be significantly greater than the probability that they will subsequently signal their detection of other errors, made with ‘firm’ (i.e. ‘unpulled’) keystrokes

These data, related to earlier findings by Diehl and Seibel (1962), Klemmer (1971). Long (1975, 1976a,b) and Seibel (1972) offer little support for the assumption that skilled typists may monitor their emitted responses in ‘units’ of greater than one keystroke. They rather suggest that, even al very high response rates (e.g. 172ms or faster), typists read copy, programme and emit responses and evaluate each of their responses for accuracy as concurrent, or partially overlapping activities.     

Displays on Display

Color, resolution, and speed, though important factors in computer graphics, must be subordinate to the message the image must deliver. While many graphics designers and users have understood this, many others, bedazzled by the powerful hardware/software tools available to them, have been tempted to use all the techniques they can instead of the ones they should. If they had a system that could graph in eight colors and fifteen fonts, for example, they used them all-with confusion of the viewer the result.     

可重构计算机

本文主要介绍了可重构计算机的结构及发展现状。由于它可以实时改变硬件电路的结构 ,特别适用于模式识别、图象处理及密码学等领域