Best case lower bounds for Heapsort

The performance of Heapsort algorithms on arbitrary input is examined. It is proved that ann logn?O(n) lower bound on the number of comparisons holds for a set of Heapsort algorithms, including Williams-Floyd's algorithm, Carlsson's bottom-up linear or binary insertion algorithm, and all up-down algorithms, on any input.     

The linear landscape of external contextual languages

The class of external contextual languages isstrictly included in the class of linear languages. A reason for the strict inclusion in linear languages is that external contextual grammars generate languages in the exhaustive way: each sentential form belongs to the language of a grammar. In this paper we study the effect of adding various squeezing mechanisms to the basic classes of exhaustive contextual grammars. We obtain in this way a characterization of linear languages and a whole landscape of sublinear families. By restricting the contexts to be one-sided (only left-sided or only right-sided) we obtain a characterization of regular languages — here the subregular landscape reduces to two families.     

The mediation of external variables in the technology acceptance model

TAM specifies a pathway of technology acceptance, from external variables to beliefs, attitudes, and system usage. We tested one of its assumptions that the ‘perceived ease-of-use’ and ‘perceived usefulness’ constructs fully mediate the influence of external variables on usage behaviors. Using a survey of 125 employees of a U.S. Government agency we found, contrary to the normally accepted assumption, that external variables could have direct effects on usage behavior over and above their indirect effects. We also found that TAM is significantly and consistently better at predicting frequency than volume of usage.     

The external structure: Experience with an automated module interconnection language

To study the problems of modifiable software, the Software Technology project has investigated approaches and methodologies that could improve modifiability. To test our approaches tools based on data abstraction—a design and programming language and a module interconnection language—were built and used. The incorporation of the module interconnection language into design altered the traditional model of system building. Introducing novices to our approach led to the formalization of new models of program design, development, and evaluation.     

Speeding up external mergesort

External mergesort is normally implemented so that each run is stored continuously on disk and blocks of data are read exactly in the order they are needed during merging. We investigate two ideas for improving the performance of external mergesort: interleaved layout and a new reading strategy. Interleaved layout places blocks from different runs in consecutive disk addresses. This is done in the hope that interleaving will reduce seek overhead during merging. The new reading strategy precomputes the order in which data blocks are to be read according to where they are located on disk and when they are needed for merging. Extra buffer space makes it possible to read blocks in an order that reduces seek overhead, instead of reading them exactly in the order they are needed for merging. A detailed simulation model was used to compare the two layout strategies and three reading strategies. The effects of using multiple work disks were also investigated. We found that, in most cases, interleaved layout does not improve performance, but that the new reading strategy consistently performs better than double buffering and forecasting     

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.     

The impact of external facial features on the construction of facial composites

Witnesses may construct a composite face of a perpetrator using a computerised interface. Police practitioners guide witnesses through this unusual process, the goal being to produce an identifiable image. However, any changes a perpetrator makes to their external facial-features may interfere with this process. In Experiment 1, participants constructed a composite using a holistic interface one day after target encoding. Target faces were unaltered, or had altered external-features: (i) changed hair, (ii) external-features removed or (iii) naturally-concealed external-features (hair, ears, face-shape occluded by a hooded top). These manipulations produced composites with more error-prone internal-features: participants’ familiar with a target’s unaltered appearance less often provided a correct name. Experiment 2 applied external-feature alterations to composites of unaltered targets; although whole-face composites contained less error-prone internal-features, identification was impaired. Experiment 3 replicated negative effects of changing target hair on construction and tested a practical solution: selectively concealing hair and eyes improved identification.

Practitioner Summary: The research indicates that when a target identity disguises or changes hair, this can lead to a witness (or victim) constructing a composite that is less readily identified. We assess a practical method to overcome this forensic issue.

Abbreviation: GEE: Generalized Estimating Equations     

Task-driven learning: The antecedents and outcomes of internal and external knowledge sourcing

The degree to which individuals leverage knowledge resources influences their effectiveness and may shape their organizations’ competitive advantage. We examine the ways in which tasks with different characteristics affect individuals’ use of internal and external knowledge and the outcomes of such behaviors. Our analysis reveals that interdependent and non-routine tasks drive internal knowledge sourcing, while complex tasks motivate external knowledge sourcing. Internal and external knowledge sourcing activities contribute to individuals’ cognitive adaptation and innovation, with a negative interaction between them, while cognitive replication benefits only from internal knowledge sourcing. These findings can help managers better satisfy individuals’ knowledge needs and achieve intended organizational outcomes.     

Gateway connections in external computers

The software for the Prestel Gateway to third-party databases was originally developed for the Bildschirm-text market trial carried out by the FRG Post Office. Based on experience gained in the specification of this software, and in the coordination of the introduction of Bildschirmtext, it is possible to describe the software development required in a third-party database to a achieve a Gateway connection, and to give an indication of the costs.     

Blocking for external graph searching

In this paper we consider the problem of using disk blocks efficiently in searching graphs that are too large to fit in internal memory. Our model allows a vertex to be represented any number of times on the disk in order to take advantage of redundancy. We give matching upper and lower bounds for completed-ary trees andd-dimensional grid graphs, as well as for classes of general graphs that intuitively speaking have a close to uniform number of neighbors around each vertex. We also show that, for the special case of grid graphs blocked with isothetic hypercubes, there is a provably better speed-up if even a small amount of redundancy is permitted.Support was provided in part by an IBM Graduate Fellowship, by NSF Research Grants CCR-9007851 and IRI-9116451, and by Army Research Office Grant DAAL03-91-G-0035.Support was provided in part by NSF Grants CCR-9003299, CCR-9300079, and IRI-9116843, and by NSF/DARPA Grant CCR-8908092.Support was provided in part by a National Science Foundation Presidential Young Investigator Award CCR-9047466 with matching funds from IBM, by NSF Research Grant CCR-9007851, and by Army Research Office Grant DAAL03-91-G-0035.     

Securing systems against external programs

Internet users routinely and often unknowingly download and run programs, such as Java applets; and some Web servers let users upload external programs and run them on the server. Although the practice of executing these external programs has the sanction of widespread use, its security implications haven't yet been systematically addressed. In the brief, dynamic history of the Internet, such a situation is not unusual. New communication mechanisms and computing paradigms are often implemented before the security issues they engender have been rigorously analyzed. Our goal is to address this problem in the subdomain of external programs by systematically outlining security issues and classifying current solutions. Our focus is solely on protecting a host from external programs. We do not address the problem of protecting the communication medium or protecting an external program from runtime systems. Furthermore, we do not address the problem of correctly identifying the source of an external program (authentication). We start our inquiry by reviewing the relevant models of computation, followed by an overview of the security problems associated with them. We then classify both the problems and the existing solutions using a resource-centric model that distinguishes problems associated with resource access from those associated with resource consumption. Finally, we classify solutions to each problem according to how and when they are applied     

通用外挂式辅助数据库设计程序

针对目前数据库设计中可视化程度不高、数据库表字段难以管理以及数据库更改会导致程序改动较大的问题,以离散制造执行系统(Discrete Manufacturing Execution System,DMES)为软件设计背景,结合软件设计的通用性原则及目标,采用Delphi 6.0进行开发,并以ini文件方式保存系统配置,从而增加数据库链接的灵活性、统一各应用程序链接数据库的模式,实现通用外挂式辅助数据库设计程序. 在DMES中的应用实例表明,利用此程序可提高数据库设计过程中的可视化程度,灵活管理数据库资源,缩短软件开发周期,提高软件开发效率.     

虚拟外存管理技术研究

为解决多虚拟机环境中的外存管理问题,研究了基于虚拟机监控器的多虚拟机结构,总结出了多虚拟机环境所面临的3个主要外存管理问题,即外存空间的隔离与保护、外存空间的按需分配和外存空间的扩展.借鉴操作系统中成熟的虚拟内存管理思想,提出了一种虚拟外存管理器的设计方案,有效地解决了外存管理中的上述问题.实验结果表明,虚拟分区可以动态创建和撤销,分区的容量可以根据实际需要动态增长,并可实现基于分区的写保护,外存管理的灵活性大大增加,外存空间的利用率大大提高.     

The axisymmetric problem for a thick-walled spherical shell with an external edge crack

This paper considers the elasto-static axisymmetric problem for a thick-walled spherical shell containing a circumferential edge crack on the outer surface. Using the standard integral transform technique, the problem is formulated in terms of a singular integral equation of the first kind which has a generalized Cauchy kernel as the dominant part. As an example the axisymmetric load problem has been solved. The integral equation is solved numerically and the influences of the geometrical configurations on the stress intensity factors and crack opening displacements are shown graphically in detail.