14105636
Experience with concurrent simulation
We have successfully implemented a concurrent simulator and we report initial speedup measurements for this technique. Our algorithm requires a shared-memory multiprocessor and is appropriate to any discrete-event simulation model. In addition, our algorithm places no constraints on minimum service times or the presence of cycles in the simulation model. Our experimental simulator runs on an Encore Multimax computer and is applicable to closed product-form queueing networks. We have observed speedups of 2.3 for a central-server queueing model using our simulator.
18506033
Evaluation of voting systems
T he recent spate of security issues and allegations of " lost votes " in the U.S. demonstrates the inadequacy of the standards used to evaluate our election systems. The current standards (the FEC Voting Systems Standards) along with the revision being developed by IEEE 1583 (see the article by Deutsch and Berger in last month's Communications) are poor from another perspective: they establish a single pass/fail threshold for all systems, thereby eliminating incentives for existing suppliers to improve their products and rendering the market unattractive to new entrants. Moreover, they fail to precisely define the properties that should be required of a voting system. Instead, the standards rely on specific designs that are more than 15 years old. These legacy designs handicap promising new approaches, such as the various voter-verified printing schemes. New systems are unnecessarily burdened, while their substantial advantages go unrecognized. A set of well-defined properties would encourage the development and commercialization of better voting systems, especially when combined with objective ways to measure performance with respect to those properties. The overall result would then resemble the quantitative federal ratings for automobiles , where features such as vehicle safety and fuel efficiency form a basis for Consumer Reports-style comparative tables. Similarly, specific performance rating guidelines for different aspects of voting systems would provide meaningful metrics upon which system developers could compete. Decision makers, both regulatory and purchasing, would then be free to establish their own minimums for these metrics. Such a rating system can thus cleanly disentangle the development of the technical evaluation process from the various political and regulatory processes. asked the technical community for assistance in determining a new standard. This community is no stranger to the area of voting system properties and standards: a number of authors have tried to characterize requirements , and, in 2002, the Workshop on Election Standards and Technology addressed similar issues. The performance properties for voting systems might include the following: integrity of the votes (both voter verification, " I can check that my vote was captured correctly " and public verification, " anyone can check that all recorded votes were counted correctly "); ballot secrecy (both voter privacy and resistance to vote selling and coercion); robustness (including resistance to denial of service attacks); usability and accuracy (including access for the disabled); and transparency (both of mechanism and election data). The inherent differences in system architectures can be characterized …
44497725
Simulation of information flow in organizations
The Icarus simulation system is the result of an experiment in embedding small rule-based expert systems into a discrete event simulation environment. The goal of this work is to allow the use of expert systems to model the intelligent behavior of people that are included in the system being simulated. The major problems we have encountered in building the Icarus system have resulted from unexpected and fundamental interactions between expert systems and our discrete event simulation framework. These interactions are the focus of this paper.
42995338
Assembly Language as Object Code
The set of meanings that may be encoded in most object languages is a subset of the meanings that may be encoded in most assembly languages. Careful exploitation of this fact in the design of the SMAL assembly and object language allows the SMAL assembler itself to be used as a linkage editor, thus eliminating the need for an expensive and often misunderstood system program. The SMAL assembler is no more complex than many assemblers in common use today, nor are the relevant aspects of the SMAL language particularly unique.
31768671
Protein fold recognition
SummaryAn important, yet seemingly unattainable, goal in structural molecular biology is to be able to predict the native three-dimensional structure of a protein entirely from its amino acid sequence. Prediction methods based on rigorous energy calculations have not yet been successful, and best results have been obtained from homology modelling and statistical secondary structure prediction. Homology modelling is limited to cases where significant sequence similarity is shared between a protein of known structure and the unknown. Secondary structure prediction methods are not only unreliable, but also do not offer any obvious route to the full tertiary structure. Recently, methods have been developed whereby entire protein folds are recognized from sequence, even where little or no sequence similarity is shared between the proteins under consideration. In this paper we review the current methods, including our own, and in particular offer a historical background to their development. In addition, we also discuss the future of these methods and outline the developments under investigation in our laboratory.
1963957
Fast and efficient searches for effective optimization-phase sequences
It has long been known that a fixed ordering of optimization phases will not produce the best code for every application. One approach for addressing this phase-ordering problem is to use an evolutionary algorithm to search for a specific sequence of phases for each module or function. While such searches have been shown to produce more efficient code, the approach can be extremely slow because the application is compiled and possibly executed to evaluate each sequence's effectiveness. Consequently, evolutionary or iterative compilation schemes have been promoted for compilation systems targeting embedded applications where meeting strict constraints on execution time, code size, and power consumption is paramount and longer compilation times may be tolerated in the final stage of development, when an application is compiled one last time and embedded in a product. Unfortunately, even for small embedded applications, the search process can take many hours or even days making the approach less attractive to developers. In this paper, we describe two complementary general approaches for achieving faster searches for effective optimization sequences when using a genetic algorithm. The first approach reduces the search time by avoiding unnecessary executions of the application when possible. Results indicate search time reductions of 62%, on average, often reducing searches from hours to minutes. The second approach modifies the search so fewer generations are required to achieve the same results. Measurements show this approach decreases the average number of required generations by 59%. These improvements have the potential for making evolutionary compilation a viable choice for tuning embedded applications.
12160909
An Architecture For A Universal Lexicon: A Case Study on Shared Syntactic Information in Japanese, Hindi, Bengali, Greek, and English
Naoyuki Nomura, Douglas A. Jones, Robert C. Berwick Massachusetts Institute of Technology, NE43-802 Artificial Intelligence Laboratory nomura@ai.mit.edu Introduction. Given the prominence of the lexicon in most current linguistic theories (LFG, HPSG, GB), the inventory of language particular information left in the lexicon deserves special attention. Constructing large computerized lexicons remains a difficult problem, building a large array of apparently arbitrary information. This paper shows that this arbitrariness can be constrained more than might have been previously thought. In particular, arbitrariness of argument structure, word sense, and paraphrasability will be shown not only to be constrained, but also to be integrally related. Our (radical) view is that variation of lexical behavior across languages is exactly like lexical variation within languages, specifically, the difference lies in the presence or absence of certain morphemes. For example, the fact that Japanese has richer possibilities in certain verbal patterns is derived solely from its morphological inventory.1 Put another way, language parameters simply are the presence or absence of lexical material in the morphological component. Observed language variation patterns reflect morphological systematicity. The generative machinery for producing argument structure positions is fixed across languages. Linguistic Motivation. A striking example underscoring universality of argument structure is the familiar Spray/Load alternation2, shown in (1). Despite the many surface differences in these data across languages, they share several essential properties. (1) a. b. John loaded the hay on the wagon. John loaded the wagon with the hay. Japanese (2) a. taroo-wa teepu-o boo-ni maita. Taro-NOM tape-ACC stick-DAT wrap-PRF 'Taro wrapped the tape around the stick.'
2547802
Online assignment management: an evolutionary tale
Due to the potential benefits there has been widespread interest in the use of online assignment submission and management (OASM). However, much of the reported work is limited to small-scale use usually in courses taught by innovative staff. This paper draws on experience with OASM in a growing number of courses taught by a number of different staff from different disciplines. It aims to investigate the process by which OASM is adopted across an organization and identify the factors that influence its growth, adoption, and adaptation. In particular the paper demonstrates that the introduction and successful use of OASM requires changes in practice, the ability to cater for a wide range of requirements, and a continual questioning of the appropriateness of the resulting changes to practice.
6177362
Line and boundary detection in speckle images
This paper considers the problem of detecting lines in speckle imagery, such as that produced by synthetic aperture radar (SAR) or ultrasound techniques. Using the physical principles that account for the speckle phenomenon, we derive the optimal detector for lines in fully developed speckle, and we compare the optimal detector to several suboptimal detection rules that are more computationally efficient. We show that when the noise is uncorrelated, a very simple suboptimal detection rule is nearly optimal, and that even in colored speckle, a related class of detectors can approach optimal performance. Finally, we also discuss the application of this technique to medical ultrasonic images, where the detection of tissue boundaries is considered as a problem of line detection.