In bacterial genomes composed of more than one chromosome, one replicon is typically larger, harbors more essential genes than the others, and is considered primary. The greater variability of secondary chromosomes among related taxa has led to the theory that they serve as an accessory genome for specific niches or conditions. By this rationale, purifying selection should be weaker on genes on secondary chromosomes because of their reduced necessity or usage. To test this hypothesis we selected bacterial genomes composed of multiple chromosomes from two genera, Burkholderia and Vibrio, and quantified the evolutionary rates (dN and dS) of all orthologs within each genus. Both evolutionary rate parameters were faster among orthologs found on secondary chromosomes than those on the primary chromosome. Further, in every bacterial genome with multiple chromosomes that we studied, genes on secondary chromosomes exhibited significantly weaker codon usage bias than those on primary chromosomes. Faster evolution and reduced codon bias could in turn result from global effects of chromosome position, as genes on secondary chromosomes experience reduced dosage and expression due to their delayed replication, or selection on specific gene attributes. These alternatives were evaluated using orthologs common to genomes with multiple chromosomes and genomes with single chromosomes. Analysis of these ortholog sets suggested that inherently fast-evolving genes tend to be sorted to secondary chromosomes when they arise; however, prolonged evolution on a secondary chromosome further accelerated substitution rates. In summary, secondary chromosomes in bacteria are evolutionary test beds where genes are weakly preserved and evolve more rapidly, likely because they are used less frequently.

The arrival of the P2P model has opened many new avenues for research within the field of distributed computing. This is mainly due to important practical features (such as support for volatility, high scalability). Several generic P2P libraries have been proposed for building higher-level services. In order to judge the appropriateness of using a generic P2P library for a given application type, an experimental performance evaluation of the provided functionalities is unavoidable. Very few analyses of this kind have been reported, as most evaluations are limited to complexity analyses and to simulations. Such experimental analyses are important, especially when using P2P software in a grid computing context, where applications may have precise efficiency requirements. In this paper, we focus on JXTA, which provides generic building blocks and protocols intended to serve as a basis for specialized P2P services and applications. We perform a performance evaluation of the three communication layers (endpoint, pipe and socket) over a fast Ethernet local-area network, for recent versions of the J2SE and C bindings of JXTA. We provide a detailed analysis explaining the behavior of these three layers and we give hints showing how to efficiently use them.

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article Free Access Share on A production-quality C* compiler for Hypercube multicomputers Authors: Philip J. Hatcher View Profile , Anthony J. Lapadula View Profile , Robert R. Jones View Profile , Michael J. Quinn View Profile , Ray J. Anderson View Profile Authors Info & Claims ACM SIGPLAN NoticesVolume 26Issue 7July 1991 pp 73–82https://doi.org/10.1145/109626.109634Online:01 April 1991Publication History 24citation249DownloadsMetricsTotal Citations24Total Downloads249Last 12 Months9Last 6 weeks1 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my Alerts New Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

DataparallelC is a SIMD programming language suitable for solving many problems arising in science and engineering, We have developed compilers that translate Dataparallel C programs into C code that can be compiled and executed on multicomputers and multiprocessors.We describe the Dataparallel C programming language, the implementation of three scienti$c programs in Dataparallel C, and the pe~ormance of the compiled programs on three MIMD computers: the Intel iPSC/2, the nCUBE 3200, and the Sequent Symmetry S81.These case studies-an ocean circulation model, the "shallow-water" atmospheric model, and the Sharks World model-illustrate that nontrivial SIMD programs can achieve good speedup on MIMD computers and still be portable.

The implementation of two compilers for the data-parallel programming language Dataparallel C is described. One compiler generates code for Intel and nCUBE hypercube multicomputers; the other generates code for Sequent multiprocessors. A suite of Dataparallel C programs has been compiled and executed, and their execution times and speedups on the Intel iPSC/2, the nCUBE 3200 and the Sequent Symmetry are presented.>

High-quality local code generation is one of the most difficult tasks the compiler-writer faces. Even if register allocation decisions are postponed and common subexpressions are ignored, instruction selection on machines with complex addressing can be quite difficult. Efficient and general algorithms have been developed to do instruction selection, but these algorithms fail to always find optimal solutions. Instruction selection algorithms based on dynamic programming or complete enumeration always find optimal solutions, but seem to be too costly to be practical. This paper describes a new instruction selection algorithm, and its prototype implementation, based on bottom-up tree pattern-matching. This algorithm is both time and space efficient, and is capable of doing optimal instruction selection for the DEC VAX-11 with its rich set of addressing modes.