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Computers RSS FeedsCapsule ReviewsThe Capsule Reviews are intended to provide a short succinct review of each paper in the issue in order to bring to a wider readership. The Capsule Reviews were compiled by Fairouz Kamareddine. Professor Kamareddine is an Associate Editor of The Computer Journal and is based in the Department of Mathematical and Computer Sciences at Heriot-Watt University, Edinburgh, UK. Reachability Analysis of Augmented Marked Graphs via Integer Linear Programming Augmented marked graphs (AMGs) are extensions of marked graphs that allow resource sharing. It has been shown that AMGs are useful for modeling and analyzing certain types of flexible manufacturing systems (FMSs). To our knowledge, the techniques developed for analyzing AMGs are mostly based upon checking certain Petri net structures such as siphons. This article exploits the integer linear programming approach for the analysis of a subclass of AMGs called decomposable AMGs. We show that reachability between two configurations of a decomposable AMG can be equated with solving an instance of integer linear programming. We further extend our technique to model checking a type of branching time temporal logics. Examples arisen in FMSs are used to demonstrate the application of our technique. General Tree k-Coteries to Reduce the Degradation of Quorums k-Coterie is a useful concept to solve the distributed k-mutual exclusion problem. The distributed k-mutual exclusion algorithms based on k-coteries have benefits of the high fault-tolerance and the low message cost. Harada and Yamashita proposed a basic tree structure to construct tree k-coteries. When the root fails, quorums are degraded and their sizes grow rapidly. In this paper, we propose the general tree structure to construct general tree 1-coteries to reduce the degradation of quorums. In the general tree 1-coterie, the responsibility of the root to construct small quorums could be adjusted. When the root fails, the degradation of quorums could be reduced. Then, we propose the coterie root-join operation to construct general tree k-coteries by root-joining k general tree 1-coteries at a common root. In the general tree k-coterie, the degradation of quorums and the quorum size could be reduced at same time. We show that general tree k-coteries could be complemental. Thus, general tree k-coteries are resilient when the network is 2-partitioned. Modeling DNA/RNA Strings Using Resistor--Capacitor (RC) Ladder Networks A passive ladder circuit employing resistors and capacitors has been used to model single-stranded DNA/RNA strings. A detailed examination of the circuit's behavior has revealed that a significant number of correspondences may be established between the behavior of such circuits and the biological/chemical properties of DNA/RNA strings. Amino acid classifications such as aromatic/aliphatic, hydrophobic/hydrophilic, alpha-helix former, beta sheet former, n-fold codon redundancy, etc. have been used in making the correspondences. The results of this study have applications in forensics, pharmacogenomics and single-nucleotide polymorphism-based linkage analysis. Also, the electrical model discussed in this paper can be the basis for creating a ‘DNA-chip’ of arbitrarily long genetic sequences using VLSI technology. Loopless Generation of Non-regular Trees with a Prescribed Branching Sequence An ordered tree is called a non-regular tree with a prescribed branching sequence (or non-regular tree for short) if its internal nodes have a prespecified degree sequence in preorder list. We define a concise representation, called right distance sequences to describe such trees. A coding tree helps us to systematically investigate the structural representation of non-regular trees. Consequently, we present a loopless algorithm to generate Gray-codes of non-regular trees using right distance sequences. The Bipancycle-Connectivity and the m-Pancycle-Connectivity of the k-ary n-cube The interconnection network considered in this paper is the k-ary n-cube that is an attractive variance of the well-known hypercube. Many interconnection networks that are desirable in both theoretical interests and practical systems, including the ring, torus and hypercube, may be regarded as the subclasses of k-ary n-cubes. In this paper, we investigate the pancycle-connected properties of the k-ary n-cube. We show that the k-ary n-cube is bipancycle-connected for k being even. That is, each pair of vertices x and y is contained by a cycle of each even length ranging from the length of the smallest even cycle that contains x and y to N, where N is the order of the network. We also show that the k-ary n-cube is strictly m-pancycle-connected for k being odd and n ≥ 2, where m = nk - n. That is, each pair of vertices is contained by a cycle of each length ranging from nk - n to N; and nk - n has reached the lower bound of the problem. An Abstract Interpretation Approach for Enhancing the Java Bytecode Verifier The Java virtual machine embodies a verifier that performs a set of checks on Java bytecode programs before their execution. The verifier carries out an efficient data-flow analysis applied to a type-level abstract interpretation of the code. The implementations of the bytecode verifier presented a significant problem with programs compiled with the Sun Java compiler (until version 1.4.1): there were legal Java programs which were correctly compiled into a bytecode that was rejected by the verifier. The problem was fixed by removing, in version 1.4.2 and following, some interesting features in the compilation of the On the Usefulness of Fibonacci Compression Codes Recent publications advocate the use of various variable length codes for which each codeword consists of an integral number of bytes in compression applications using large alphabets. This paper shows that another tradeoff with similar properties can be obtained by Fibonacci codes. These are fixed codeword sets, using binary representations of integers based on Fibonacci numbers of order m ≥ 2. Fibonacci codes have been used before, and this paper extends previous work presenting several novel features. In particular, the compression efficiency is analyzed and compared to that of dense codes, and various table-driven decoding routines are suggested. Fine-Grain Register Allocation and Instruction Scheduling in a Reference Flow This paper proposes a new register allocation technique in which register allocation is performed at every reference of a variable. For each reference, the costs of various possible register allocations are estimated by tracing a possible instruction sequence. A cost model is formulated to reduce the scope of tracing. With an extension of the cost model to the estimation of instruction execution time, a new technique for the integration of instruction scheduling and register allocation is also proposed. Experiments show that the proposed register allocation and the integration techniques achieve significant improvements when compared with widely used existing techniques. Hierarchical Radiosity for Multiresolution Systems Based on Normal Tests The hierarchical radiosity algorithm provides high-quality illumination and the view-independent results obtained can be re-employed for different camera positions. On the other hand, the utilization of multiresolution models is a common solution for the real-time rendering of complex scenes. In this case, the level of detail of each object depends on the specific camera position. Unfortunately, global illumination computations may present an important performance loss in this context. In this paper we present a new solution for hierarchical radiosity for multiresolution systems. Our proposal is based on the application of an enriched hierarchical radiosity algorithm to an input scene with low-resolution objects (represented by coarse meshes) and the efficient data management of the resulting values. The representation of the information we use permits the application of the radiosity values obtained for the coarse version of an object to finer resolution versions of that object. Results of our implementation show that our algorithm produces high-quality images with an important reduction in computational costs. NIPSOM: Parallel Architecture and Implementation of a Growing SOM This work describes a parallel implementation of a distinctly different concept in self-organizing maps (SOMs)—processing of the input as a whole, in parallel, via neurons attracted to cover regions of the input space rather than single input instances. The algorithm is analyzed from the perspective of its parallelism and a simple multi-machine concept is utilized to demonstrate the parallel nature of the neural network architecture. The nature of the classic SOM (Ozdzynski, P., Lin, A., Liljeholm, M. and Beatty, J. (2002) A parallel implementation of Kohonen's self-organizing map algorithm: performance and scalability. Neurocomputing, 44–46, 567–571) algorithm displays some parallel characteristics, but contains several bottlenecks, which prevent a true parallel execution. Most SOM parallel implementations either deal with expensive hardware that requires considerable algorithm adaptation, or run multiple instances of SOM on multiple machines and choose the most relevant, or adopt controller–worker architecture with the controller machine presenting a significant bottleneck in the parallelism. Our algorithm (Valova, I., Szer, D., Gueorguieva, G. and Buer, A. (2005) A parallel growing architecture for self-organizing maps with unsupervised learning. Neurocomputing, 68C, 177–195), which we eventually named ParaSOM, reveals no need for significant adaptation to be ported to parallelism and the analysis and implementations we discuss illustrate this quality. This work presents two designs for parallelizing our algorithm and analyzes both while demonstrating the easiness in the transition to a parallel paradigm. We have illustrated the performance gain of the proposed implementation and compared it with other similar methods, from the perspectives of both parallelism and nature of the mapping algorithm. Multi-criteria Scheduling of Precedence Task Graphs on Heterogeneous Platforms Latency, fault tolerance and reliability are important requirements for several applications that are time critical in nature: such applications require guarantees in terms of latency, even when processors are subject to failures. In this paper, we propose a fault-tolerant scheduling heuristic for mapping precedence task graphs on heterogeneous systems. Our approach is based on an active replication scheme, capable of supporting arbitrary fail-silent/fail-stop processor failures, and hence valid results will be provided even if processors fail. First we focus on a bi-criteria approach, where we aim at minimizing the latency given a fixed number of failures supported in the system, or the other way round. Next we derive a more complex algorithm in which we not only minimize latency and support a fixed number of failures, but also improve the overall reliability. Major achievements include low complexity of the new algorithms, and a drastic reduction of the number of additional communications induced by the replication mechanism. Experimental results demonstrate that our heuristics, despite their lower complexity, outperform their direct competitor, the fault-tolerance based active replication scheduling algorithm FTBAR. A Weighted Voting-Based Associative Classification Algorithm A new associative classification algorithm based on weighted voting (ACWV) is presented. ACWV takes advantage of two methods: the optimal rule method preferring high-quality rules and the voting method considering the majority of the rules. Moreover, the method takes into account both the length and convictions of rules to calculate their weights. First, ACWV builds a class-count FP-tree (called CCFP-tree) from the given historical data. After that, the weighted voting result for a new instance can be obtained from the CCFP-tree directly without storing, retrieving and sorting rules explicitly. The label of the class with maximal sum of weighted votes is then that of the new instance. Results of the experiments with 36 data sets selected from the UCI machine learning repository show that the proposed method has its advantages in comparison with previous methods in terms of classification accuracy. Resampling Halftone Images Using Interpolation and Error-Diffusion Halftoning schemes are developed for reserving the quality after transforming continuous tone images to binary images under human vision, and are widely used in printing and outputting. Modern halftoning schemes focus on transforming forward and backward the two kinds of images, but basic operations for halftone images like rescaling, blurring and sharpening are still insufficient. In this paper, a novel halftone image resampling scheme based on interpolation and error-diffusion is proposed. The proposed scheme can shrink and magnify halftone images to any desired scale and does not limit the source of the halftone images. To obtain the best performance, an evaluation tool is proposed to test various combinations of interpolation techniques and error-diffusion kernels. Due to the lack of evaluation research, the evaluation metric called light invariance is developed to evaluate the consistency before and after resampling. By the proposed scheme, resampling halftone images does not need transforming to and back from continuous-tone images anymore. Accelerating Multiple Sequence Alignment with the Cell BE Processor The Cell Broadband Engine (BE) Architecture is a new heterogeneous multi-core architecture targeted at compute-intensive workloads. The architecture of the Cell BE has several features that are unique in high-performance general-purpose processors, most notably the extensive support for vectorization, scratch pad memories and explicit programming of direct memory accesses (DMAs) and mailbox communication. While these features strongly increase programming complexity, it is generally claimed that significant speedups can be obtained by using Cell BE processors. This paper presents our experiences with using the Cell BE architecture to accelerate Clustal W, a bio-informatics program for multiple sequence alignment. We report on how we apply the unique features of the Cell BE to Clustal W and how important each is in obtaining high performance. By making extensive use of vectorization and by parallelizing the application across all cores, we demonstrate a speedup of 24.4 times when using 16 synergistic processor units on a QS21 Cell Blade compared to single-thread execution on the power processing unit. As the Cell BE exploits a large number of slim cores, our highly optimized implementation is just 3.8 times faster than a 3-thread version running on an Intel Core2 Duo, as the latter processor exploits a small number of fat cores. Area-Feature Boundary Labeling Boundary labeling is a relatively new labeling method. It can be useful in automating the production of technical drawings and medical drawings, where it is common to explain certain parts of the drawing with text labels, arranged on its boundary so that other parts of the drawing are not obscured. In boundary labeling, we are given a rectangle R which encloses a set of n sites. Each site s is associated with an axis-parallel rectangular label ls. The labels must be placed in distinct positions on the boundary of R and they must be connected to their corresponding sites with polygonal lines, called leaders, so that the labels are pairwise disjoint and the leaders do not intersect each other. In this paper, we study a version of the boundary labeling problem where the sites can ‘float’ within a polygonal region. We present a polynomial time algorithm, which runs in O(n3) time and produces a labeling of minimum total leader length for labels of uniform size placed in fixed positions on the boundary of rectangle R. In this paper, we present a case study on the development of interfaces for elderly and disabled users. The domain of the case study was situated in the home environment, where we focused on producing affordable technologies to enable users to interact with and to control home appliances. We have developed ambient user interfaces that are integrated in familiar home artefacts, such as televisions and digital picture frames. These interfaces are connected remotely to a home network and are adaptive to users’ expected increasing physical and cognitive needs. To support the development of the project, we created a novel methodology that is grounded in the ethical issues associated with a project of this nature. Our success with it has led to us presenting it here as a practical approach to developing user interfaces for a range of interactive applications, especially where there may be diverse user populations. This paper describes our journey through this project, how the methodology has been used throughout and the development of our user interfaces and their evaluation. Turning Back Time--What Impact on Performance? Consistent with the divide-and-conquer approach to problem solving, a recursive result is presented in the domain of stochastic modelling that derives product-form solutions for the steady state probabilities of certain networks composed from interacting Markov chains. Practical applications include multi-tasking operating systems, communication channels and multi-tiered storage systems. The approach is also applied to the computation of response time quantiles, which are vital in transaction processing, computer communication service level agreements and other operational systems. The joint probability distribution of the sojourn times of a tagged task at each node in a network is determined by noting that this is the same in both the forward and reversed processes. In this way, existing results for response time probability densities in tandem, tree-like, and overtake-free Markovian queueing networks are quickly and systematically obtained. We further show how to apply the method in more general networks. Program Analysis Probably Counts Semantics-based program analysis uses an abstract semantics of programs/systems to statically determine run-time properties. Classic examples from compiler technology include analyses to support constant propagation and constant folding transformations and estimation of pointer values to prevent buffer overruns. More recent examples include the estimation of information flows (to enforce security constraints) and estimation of non-functional properties such as timing (to determine worst case execution times in hard real-time applications). The classical approaches are based on semantics involving discrete mathematics. Paralleling trends in model-checking, there have been recent moves towards using probabilistic and quantitative methods in program analysis. In this paper we start by reviewing both classical and probabilistic/quantitative approaches to program analysis. We shall provide a comparison of the two approaches. We shall use a simple information flow analysis to exemplify the classical approach. The existence of covert information flows through timing channels are difficult to detect using classical techniques; we show how such problems can be addressed using probabilistic techniques. 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They say the technique, which is being used to create a database of DNA profiles of different marijuana plants, will help them to trace the source of any sample. 'It links everybody together: the user, the distributor, the grower,' says the database's creator, Heather Miller Coyle of the Connecticut State Forensic Science Laboratory in Meriden. 'That's the real intent of it, to show it's not just one guy with a little bag of marijuana, but it's a group of people.' A method for spotting the tiniest traces of marijuana, based on detecting DNA unique to cannabis chloroplasts, has already been developed in the UK (New Scientist print edition, 07 Aug 1999). But the profiling method, based on the same principles as DNA fingerprinting of people, can distinguish between closely related cannabis plants (Croatian Medical Journal, vol 44, p 315). In a case awaiting trial in Connecticut, prosecutors plan to use cannabis DNA profiles to show that two apparently separate cannabis growing operations were actually linked. The two operations, in different parts of the state appeared separate until analysis of the plants revealed that some had identical DNA fingerprints, showing that the growers were sharing material. [NewScientist.com] Mathematics: Does the Proof Stack Up? by George Szpiro 03 Jul 03 Just under five years ago, Thomas Hales made a startling claim. In an e-mail he sent to dozens of mathematicians, Hales declared that he had used a series of computers to prove an idea that has evaded certain confirmation for 400 years. The subject of his message was Kepler's conjecture, proposed by the German astronomer Johannes Kepler, which states that the densest arrangement of spheres is one in which they are stacked in a pyramid - much the same way as grocers arrange oranges. Soon after Hales made his announcement, reports of the breakthrough appeared on the front pages of newspapers around the world. But today, Hales's proof remains in limbo. It has been submitted to the prestigious Annals of Mathematics, but is yet to appear in print. Those charged with checking it say that they believe the proof is correct, but are so exhausted with the verification process that they cannot definitively rule out any errors. So when Hales's manuscript finally does appear in the Annals, probably during the next year, it will carry an unusual editorial note - a statement that parts of the paper have proved impossible to check. At the heart of this bizarre tale is the use of computers in mathematics, an issue that has split the field. [Nature] [Also see: Flyspeck Project, aka 'A Formal Proof of Kepler'] Scientists Discover Planetary System Similar to Our Own
by Josh Camot 03 Jul 03 ARLINGTON, Va. An international team of scientists has discovered a planet and star that may share the same relationship as Jupiter and our Sun, the closest comparison that researchers have found since they began their search for extra-solar planets nearly a decade ago. By analyzing light spectra collected with the 3.9-meter Anglo-Australian Telescope in Siding Spring, Australia, scientists from the United States, Australia, and Britain made precision measurements of the star HD 70642. The telescope data reveal a wobble in the star's position, an artifact from the gravitational tug of a planet roughly twice the size of Jupiter. The star is similar in size and structure to our Sun. From the wobble of HD 70642, the team has learned that the orbit of its planet is similar to the orbit of Jupiter in both shape and distance. The planet, a gas giant, is right where it should be if the solar system evolved like ours, suggesting that other planets may be found nearby and that the system could potentially harbor life. The researchers, supported by the National Science Foundation (NSF), conduct the Anglo-Australian Planet Search (AAPS), one of the leading extra-solar planet searches in the world. [National Science Foundation] Hacker How-To Good Summer Reading 27 Jun 03 Stealing the Network: How to Own the Box Stealing The Network: How to Own the Box, a compendium of tales written by well-known hackers, is a perfect summer read. The stories are fictional. The technology and techniques described are very real. A warning: Those who believe in the theory of 'security through obscurity' -- keeping information on hacking techniques under wraps so that fewer people might exploit them -- probably will be infuriated by this book. Each chapter details not only the methods used to hack and counterattack, but also explains the thought processes hackers use to carry out assaults on computer systems and people. The result is a fascinating look at the tedious and occasionally brilliant mental discipline of hacking. But it is a book that wanders close to what some might consider the ethical edge. [Wired News] Copyright © 2010, Jewelbeads. All Rights Reserved. |
