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Kinds of Shows Terms modified by Shows Selected AbstractsANTIMICROBIAL DEFENSE SHOWS AN ABRUPT EVOLUTIONARY TRANSITION IN THE FUNGUS-GROWING ANTSEVOLUTION, Issue 5 2008William O. H. Hughes Understanding the relative evolutionary importance of parasites to different host taxa is problematic because the expression of disease and resistance are often confounded by factors such as host age and condition. The antibiotic-producing metapleural glands of ants are a potentially useful exception to this rule because they are a key first-line defense that are fixed in size in adults. Here we conduct a comparative analysis of the size of the gland reservoir across the fungus-growing ants (tribe Attini). Most attines have singly mated queens, but in two derived genera, the leaf-cutting ants, the queens are multiply mated, which is hypothesized to have evolved to improve colony-level disease resistance. We found that, relative to body size, the gland reservoirs of most attines are similar in size but that those of the leaf-cutting ants are significantly larger. In contrast, the size of the reservoir did not relate with the evolutionary transition from lower to higher attines and correlated at most only slightly with colony size. The results thus suggest that the relationship between leaf-cutting ants and their parasites is distinctly different from that for other attine ants, in accord with the hypothesis that multiple mating by queens evolved to improve colony-level disease resistance. [source] Rethinking Substance Abuse: What the Science Shows, and What We Should Do About ItADDICTION, Issue 11 2007SARAH E. WOOLF No abstract is available for this article. [source] Experimental Manipulation of Intraclutch Variation in the Great Reed Warbler Shows No Effect on Rejection of Parasitic EggsETHOLOGY, Issue 1 2003Zsolt Karcza In the continuing arms race between hosts and brood parasites, hosts are expected to reduce variation in the appearance of their own eggs within clutches, as it facilitates recognition of parasitic eggs. At the same time, by increasing interclutch variation, hosts should make it more difficult for parasites to evolve perfectly mimetic eggs. In this study, we experimentally manipulated intraclutch variation in the great reed warbler, Acrocephalus arundinaceus, in Hungary, where this species is heavily (c. 64%) parasitized by the common cuckoo, Cuculus canorus. We placed artificial cuckoo eggs, which appeared moderately mimetic to humans, in two groups of nests; in one group we increased variability of egg appearance within clutches by exchanging host eggs among nests. These clutches showed a significantly higher intraclutch variability than natural clutches, which we used as a control group. Our results indicate that it has no effect on rejection behaviour in this species, neither when variation was increased experimentally, nor within the natural range of variation displayed by our population. We suggest that when parasitism is high, selection for reduced intraclutch variation may be less important than frequency-dependent selection for increased variation between individuals within a host population. [source] The Peritoneal Mesothelium Covering the Genital Tract and its Ligaments in the Female Pig Shows Signs of Active FunctionTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 7 2007Jesús Luis Yániz Abstract The aim of this study was to describe the surface features of the peritoneal mesothelium covering the genital tract and adjacent ligaments of the sow to find signs of biosynthetic activation of cells. Surface features of the serosa covering the genital tract and adjacent ligaments from 14 cyclic sows, 7 in the follicular phase and 7 in the luteal phase of the estrous cycle, were examined by histology and scanning electron microscopy. Five additional sows, three in the follicular phase and two in the luteal phase of the estrous cycle, were examined by transmission electron microscopy (TEM). In this study, the presence of cells of the oviductal epithelium in the serosa of the infundibulum and the ampulla, as well as indications of a high functional activity of the mesothelial cells in the areas studied were two aspects that differed from the findings of previous works. Presence of endosalpingeal cells was observed in the serosal surface, showing cyclical variations with a predominance of either ciliated cells during the follicular phase or secretory cells during the luteal phase. Signs of high functional activity of the mesothelial cells included the predominance of cuboidal over flattened cells, a cytoplasm richly supplied with organelles, a dense microvillous coat, numerous primary cilia, and many secretory structures on the surface of cells. These results indicate that the serosa covering the genital area and the adjacent ligaments in the sow has an active epithelium whose coordinating role between reproductive tissues may be far more significant than previously thought. Anat Rec, 2007. © 2007 Wiley-Liss, Inc. [source] A Genre Ŕ la Turque: Redefining Games Shows and the Turkish Version of Wheel Of FortuneTHE JOURNAL OF AMERICAN CULTURE, Issue 3-4 2002Asli Tunç No abstract is available for this article. [source] Prevention of pneumococcal disease in children.ACTA PAEDIATRICA, Issue 5 2001Pneumococcal conjugate vaccines: their use globally could have a major impact on public health Pneumococcal disease is a major cause of morbidity and mortality in infants and young children worldwide. New pneumococcal conjugate vaccines include 7 to 11 serotypes, which are the most common cause of paediatric disease in most parts of the world. The efficacy of a 7-valent conjugate vaccine was 97.4% (95% CI, 82.7,99.9) against invasive pneumococcal disease, and 57% (95% CI, 44,67) against otitis media, caused by vaccine serotypes. Evidence shows that the vaccine has the potential to prevent pneumonia. Pneumococcal conjugate vaccination has also been shown to reduce nasopharyngeal carriage of vaccine serotypes (particularly serotypes associated with antibiotic resistance). Thus widespread use of pneumococcal conjugate vaccine could substantially reduce the burden of invasive disease and would have the potential to control the global spread of antibiotic resistance in pneumococci. Conclusion: It is important that these highly effective vaccines should be made available to children in the developing countries. [source] ON SOCIAL LEARNING AND ROBUST EVOLUTIONARY ALGORITHM DESIGN IN THE COURNOT OLIGOPOLY GAMECOMPUTATIONAL INTELLIGENCE, Issue 2 2007Floortje Alkemade Agent-based computational economics (ACE) combines elements from economics and computer science. In this article, the focus is on the relation between the evolutionary technique that is used and the economic problem that is modeled. In the field of ACE, economic simulations often derive parameter settings for the genetic algorithm directly from the values of the economic model parameters. This article compares two important approaches that are dominating in ACE and shows that the above practice may hinder the performance of the genetic algorithm and thereby hinder agent learning. More specifically, it is shown that economic model parameters and evolutionary algorithm parameters should be treated separately by comparing the two widely used approaches to social learning with respect to their convergence properties and robustness. This leads to new considerations for the methodological aspects of evolutionary algorithm design within the field of ACE. [source] SORTAL ANAPHORA RESOLUTION IN MEDLINE ABSTRACTSCOMPUTATIONAL INTELLIGENCE, Issue 1 2007Manabu Torii This paper reports our investigation of machine learning methods applied to anaphora resolution for biology texts, particularly paper abstracts. Our primary concern is the investigation of features and their combinations for effective anaphora resolution. In this paper, we focus on the resolution of demonstrative phrases and definite determiner phrases, the two most prevalent forms of anaphoric expressions that we find in biology research articles. Different resolution models are developed for demonstrative and definite determiner phrases. Our work shows that models may be optimized differently for each of the phrase types. Also, because a significant number of definite determiner phrases are not anaphoric, we induce a model to detect anaphoricity, i.e., a model that classifies phrases as either anaphoric or nonanaphoric. We propose several novel features that we call highlighting features, and consider their utility particularly for processing paper abstracts. The system using the highlighting features achieved accuracies of 78% and 71% for demonstrative phrases and definite determiner phrases, respectively. The use of the highlighting features reduced the error rate by about 10%. [source] Detecting New Forms of Network Intrusion Using Genetic ProgrammingCOMPUTATIONAL INTELLIGENCE, Issue 3 2004Wei Lu How to find and detect novel or unknown network attacks is one of the most important objectives in current intrusion detection systems. In this paper, a rule evolution approach based on Genetic Programming (GP) for detecting novel attacks on networks is presented and four genetic operators, namely reproduction, mutation, crossover, and dropping condition operators, are used to evolve new rules. New rules are used to detect novel or known network attacks. A training and testing dataset proposed by DARPA is used to evolve and evaluate these new rules. The proof of concept implementation shows that a rule generated by GP has a low false positive rate (FPR), a low false negative rate and a high rate of detecting unknown attacks. Moreover, the rule base composed of new rules has high detection rate with low FPR. An alternative to the DARPA evaluation approach is also investigated. [source] THE DESIGN OF A STATISTICAL ALGORITHM FOR RESOLVING STRUCTURAL AMBIGUITY IN "V NP1 usde NP0"COMPUTATIONAL INTELLIGENCE, Issue 1 2003Wenjie Li The existence of structural ambiguity in modifying clauses renders noun phrase (NP) extraction from running Chinese texts complicated. It is shown from previous experiments that nearly 33% of the errors in an NP extractor were actually caused by the use of clause modifiers. For example, consider the sequence "V + NP1+ (of) + NP0." It can be interpreted as two alternatives, a verb phrase (i.e., [V[NP1++ NP0]NP]VP) or a noun phrase (i.e., [[V NP1]VP++ NP0]NP). To resolve this ambiguity, syntactical, contextual, and semantics-based approaches are investigated in this article. The conclusion is that the problem can be overcome only when the semantic knowledge about words is adopted. Therefore, a structural disambiguation algorithm based on lexical association is proposed. The algorithm uses the semantic class relation between a word pair derived from a standard Chinese thesaurus, , to work out whether a noun phrase or a verb phrase has a stronger lexical association within the collocation. This can, in turn, determine the intended phrase structure. With the proposed algorithm, the best accuracy and coverage are 79% and 100%, respectively. The experiment also shows that the backed-off model is more effective for this purpose. With this disambiguation algorithm, parsing performance can be significantly improved. [source] Review and Restore for Case-Base MaintenanceCOMPUTATIONAL INTELLIGENCE, Issue 2 2001Thomas Reinartz Case-base maintenance is one of the most important issues for current research in case-based reasoning (CBR). In this article we propose an extended six-step CBR cycle and discuss its two additional steps as part of the maintenance phase of the CBR process. The review step covers assessment and monitoring of the knowledge containers, whereas the restore step actually modifies the contents of the containers according to recommendations resulting from the review step in order to keep the knowledge containers in a usable state. Here we focus our attention on the case base. For the review step, we define several quality measures based on different case and case-base properties that describe specific characteristics of the case base such as correctness, consistency, uniqueness, minimality, and incoherence. Then we use these measures to realize monitoring capabilities for the case-base container that indicate when the restore step is necessary. Finally, we also describe several methods for modifications of the case base in the restore step and their relation to the review step. An initial experimental evaluation shows the appropriateness of the proposed concepts and methods before we conclude the article with a discussion of related work and an outline of future directions to extend these aspects of maintenance in CBR. [source] Modeling human affective postures: an information theoretic characterization of posture featuresCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2004P. Ravindra De Silva One of the challenging issues in affective computing is to give a machine the ability to recognize the mood of a person. Efforts in that direction have mainly focused on facial and oral cues. Gestures have been recently considered as well, but with less success. Our aim is to fill this gap by identifying and measuring the saliency of posture features that play a role in affective expression. As a case study, we collected affective gestures from human subjects using a motion capture system. We first described these gestures with spatial features, as suggested in studies on dance. Through standard statistical techniques, we verified that there was a statistically significant correlation between the emotion intended by the acting subjects, and the emotion perceived by the observers. We used Discriminant Analysis to build affective posture predictive models and to measure the saliency of the proposed set of posture features in discriminating between 4 basic emotional states: angry, fear, happy, and sad. An information theoretic characterization of the models shows that the set of features discriminates well between emotions, and also that the models built over-perform the human observers. Copyright © 2004 John Wiley & Sons, Ltd. [source] The application of spreadsheets to the analysis and optimization of systems and processes in the teaching of hydraulic and thermal engineeringCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 4 2006A. Rivas Abstract This article shows the capability of current spreadsheets to define, analyze and optimize models of systems and processes. Specifically, the Microsoft spreadsheet Excel is used, with its built-in solver, to analyze and to optimize systems and processes of medium complexity, whose mathematical models are expressed by means of nonlinear systems of equations. Two hydraulic and thermal engineering-based application examples are presented, respectively: the analysis and optimization of vapor power cycles, and the analysis and design of piping networks. The mathematical models of these examples have been implemented in Excel and have been solved with the solver. For the power cycles, the thermodynamic properties of water have been calculated by means of the add-in TPX (Thermodynamic Properties for Excel). Performance and optimum designs are presented in cases studies, according to the optimization criteria of maximum efficiency for the power cycle and minimum cost for the piping networks. © 2006 Wiley Periodicals, Inc. Comput Appl Eng Educ 14: 256,268, 2006; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20085 [source] The solution of fluid mechanics problems by probability methodsCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 2 2005Sergio E. Perez Abstract This study shows how fluid mechanics problems may be solved using probability methods. Problems solved include velocity distributions in steady and unsteady flow between parallel plates as well as steady flow through a constant diameter three-dimensional duct. We find that the results approach exact solutions as the number of random walks increases, and that the complexity of the flow equations precludes extension of the technique to three dimensions. We also find that these techniques are much easier for students to put into practice than others. © 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 133,136, 2005; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20038 [source] MATLAB based GUIs for linear controller design via convex optimizationCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 1 2003Wathanyoo Khaisongkram Abstract Owing to the current evolution of computational tools, a complicated parameter optimization problem could be effectively solved by a computer. In this paper, a CAD tool for multi-objective controller design based on MATLAB program is developed. In addition, we construct simple GUIs (using GUIDE tools within MATLAB) to provide a visual approach in specifying the constraints. The linear controller design problem can be cast as the convex optimization subjected to time domain and frequency domain constraints. This optimization problem is efficiently solved within a finite dimensional subspace by a practical ellipsoid algorithm. In the design process, we include a model reduction of the resulting controller to speed up the computational efficiency. Finally, a numerical example shows the capability of the program to design multi-objective controller for a one-link flexible robot arm. © 2003 Wiley Periodicals, Inc. Comput Appl Eng Educ 11: 13,24, 2003; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.10035 [source] Virtual reality simulations in Web-based science educationCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 1 2002Young-Suk Shin Abstract This article presents the educational possibilities of Web-based science education using a desktop virtual reality (VR) system. A Web site devoted to science education for middle school students has been designed and developed in the areas of earth sciences: meteorology, geophysics, geology, oceanography, and astronomy. Learners can establish by themselves the pace of their lessons using learning contents considered learner level and they can experiment in real time with the concepts they have learned, interacting with VR environments that we provide. A VR simulation program developed has been evaluated with a questionnaire from learners after learning freely on the Web. This study shows that Web-based science education using VR can be effectively used as a virtual class. When we consider the rapid development of VR technology and lowering of cost, the study can construct more immersive environments for the education in the near future. © 2002 Wiley Periodicals, Inc. Comput Appl Eng Educ 10: 18,25, 2002; Published online in Wiley InterScience (www.interscience.wiley.com.); DOI 10.1002/cae.10014 [source] Illustrative Hybrid Visualization and Exploration of Anatomical and Functional Brain DataCOMPUTER GRAPHICS FORUM, Issue 3 2008W. M. Jainek Abstract Common practice in brain research and brain surgery involves the multi-modal acquisition of brain anatomy and brain activation data. These highly complex three-dimensional data have to be displayed simultaneously in order to convey spatial relationships. Unique challenges in information and interaction design have to be solved in order to keep the visualization sufficiently complete and uncluttered at the same time. The visualization method presented in this paper addresses these issues by using a hybrid combination of polygonal rendering of brain structures and direct volume rendering of activation data. Advanced rendering techniques including illustrative display styles and ambient occlusion calculations enhance the clarity of the visual output. The presented rendering pipeline produces real-time frame rates and offers a high degree of configurability. Newly designed interaction and measurement tools are provided, which enable the user to explore the data at large, but also to inspect specific features closely. We demonstrate the system in the context of a cognitive neurosciences dataset. An initial informal evaluation shows that our visualization method is deemed useful for clinical research. [source] Failure Mechanism of Deformed Concrete Tunnels Subject to Diagonally Concentrated LoadsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2009Wei He Based on the experimental findings, an extended discussion is carried out to select a rational compressive model for concrete that represents the dominant failure modes of deformed concrete tunnels. Three main dominant final failure modes are described: structural failure due to the plastic rotation of softening hinges, tensile failure caused by localized cracks, and material failure due to concrete deterioration. A parametric analysis of the material properties of concrete shows that the compressive strength of concrete has a dominant effect on the load-carrying capacity, although the compressive fracture energy of concrete remarkably influences the post-peak deformation behavior of the tunnel. Moreover, the soil pressure, which is regarded as a distributed external load, plays an important role in controlling the final failure modes and the deformation behavior of concrete tunnels. The size effect on the load-carrying capacities of different-sized concrete tunnels is also discussed based on the numerical simulations. [source] Simulation of Accuracy Performance for Wireless Sensor-Based Construction Asset TrackingCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2009Miros, aw J. Skibniewski In particular, identifying the location of distributed mobile entities throughout wireless communications becomes the primary task to realize the remote tracking and monitoring of the construction assets. Even though several alternative solutions have been introduced by utilizing recent technologies, such as radio frequency identification (RFID) and the global positioning system (GPS), they could not provide a solid direction to accurate and scalable tracking frameworks in large-scale construction domains due to limited capability and inflexible networking architectures. This article introduces a new tracking architecture using wireless sensor modules and shows an accuracy performance using a numerical simulation approach based on the time-of-flight method. By combining radio frequency (RF) and ultrasound (US) signals, the simulation results showed an enhanced accuracy performance over the utilization of an RF signal only. The proposed approach can provide potential guidelines for further exploration of hardware/software design and for experimental analysis to implement the framework of tracking construction assets. [source] Algorithm for Spatial Clustering of Pavement SegmentsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 2 2009Chientai Yang This article formulates a new spatial search model for determining appropriate pavement preservation project termini. A spatial clustering algorithm using fuzzy c-mean clustering is developed to minimize the rating variation in each cluster (project) of pavement segments while considering minimal project scope (i.e., length) and cost, initial setup cost, and barriers, such as bridges. A case study using the actual roadway and pavement condition data in fiscal year 2005 on Georgia State Route 10 shows that the proposed algorithm can identify more appropriate segment clustering scheme, than the historical project termini. The benefits of using the developed algorithm are summarized, and recommendations for future research are discussed. [source] Performance of Buildings under Earthquakes in Barcelona, SpainCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 8 2006Alex H. Barbat The seismic hazard in the area of the city is described by means of the reduced 5% damped elastic response spectrum. Obtaining fragility curves for the most important building types of an urban center requires an important amount of information about the structures and the use of nonlinear structural analysis tools. The information on the buildings of Barcelona was obtained by collecting, arranging, improving, and completing the database of the housing and current buildings. The buildings existing in Barcelona are mainly of two types: unreinforced masonry structures and reinforced concrete buildings with waffled slab floors. In addition, the Arc-View software was used to create a GIS tool for managing the collected information to develop seismic risk scenarios. This study shows that the vulnerability of the buildings is significant and therefore, in spite of the medium to low seismic hazard in the area of the city, the expected seismic risk is considerable. [source] Robust Maintenance Policies for Markovian Systems under Model UncertaintyCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2006Kenneth D. Kuhn Many sources of error, some difficult to quantify, can limit the ability of asset management systems to accurately predict how built systems will deteriorate. This article introduces the use of robust optimization to deal with epistemic uncertainty. The Hurwicz criterion is employed to ensure management policies are never "too conservative." An efficient solution algorithm is developed to solve robust counterparts of the asset management problem. A case study demonstrates how the consideration of uncertainty alters optimal management policies and shows how the proposed approach may reduce maintenance and rehabilitation (M&R) expenditures. [source] Hybrid Meta-Heuristic Algorithm for the Simultaneous Optimization of the O,D Trip Matrix EstimationCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2004Antony Stathopoulos These include a genetic algorithm (GA), a simulated annealing (SA) algorithm, and a hybrid algorithm (GASA) based on the combination of GA and SA. The computational performance of the three algorithms is evaluated and compared by implementing them on a realistic urban road network. The results of the simulation tests demonstrate that SA and GASA produce a more accurate final solution than GA, whereas GASA shows a superior convergence rate, that is, faster improvement from the initial solution, in comparison to SA and GA. In addition, GASA produces a final solution that is more robust and less dependent on the initial demand pattern, in comparison to that obtained from a greedy search algorithm. [source] Foetal size to final heightACTA PAEDIATRICA, Issue 6 2000J Karlberg It is well known that some adult diseases, such as cardiovascular diseases, may be programmed during foetal life. It is not clear, however, whether final height may be predicted from foetal growth. A longitudinal cohort of full-term healthy Swedish babies (n = 3650) was followed up from birth to maturity in a population-based growth study. Length or height and its changes were analysed from birth to 18 y of age; 2807 children, with data available on birth length, final height and parental height, were included in this analysis. The result clearly shows that length at birth relates to final height. In terms of standard deviation scores (SDS), the mean difference in length at birth from the mean was greatly decreased in final height, but retained the same order as was seen at birth. In terms of centimeter difference from the reference mean values, the difference in length at birth remained roughly stable into final height. For instance, babies 5 cm above or below the mean birth length will end up approximately 5 cm above or below the mean in final height. Parental height,a surrogate value of the genetic final height potential of an individual,is shown to influence postnatal growth in height strongly. However, the difference from the mean in length at birth remained into adulthood within the same midparental height group. Conclusion: This study reveals that trends in foetal linear growth continue into maturity. Foetal growth is a significant predictor of postnatal growth. Final height is dependent on both the magnitude of foetal growth and the genetic potential in stature, and appears to some extent to be programmed from foetal growth. [source] A comparison of using Taverna and BPEL in building scientific workflows: the case of caGridCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 9 2010Wei Tan Abstract When the emergence of ,service-oriented science,' the need arises to orchestrate multiple services to facilitate scientific investigation,that is, to create ,science workflows.' We present here our findings in providing a workflow solution for the caGrid service-based grid infrastructure. We choose BPEL and Taverna as candidates, and compare their usability in the lifecycle of a scientific workflow, including workflow composition, execution, and result analysis. Our experience shows that BPEL as an imperative language offers a comprehensive set of modeling primitives for workflows of all flavors; whereas Taverna offers a dataflow model and a more compact set of primitives that facilitates dataflow modeling and pipelined execution. We hope that this comparison study not only helps researchers to select a language or tool that meets their specific needs, but also offers some insight into how a workflow language and tool can fulfill the requirement of the scientific community. Copyright © 2009 John Wiley & Sons, Ltd. [source] Exploring the performance of massively multithreaded architecturesCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 5 2010Shahid Bokhari Abstract We present a new scheme for evaluating the performance of multithreaded computers and demonstrate its application to the Cray MTA-2 and XMT supercomputers. Our scheme is based on the concept of clock cycles per element, , plotted against both problem size and the number of processors. This scheme clearly shows if an implementation has achieved its asymptotic efficiency and is more general than (but includes) the commonly used speedup metric. It permits the discovery of any imperfections in both the software as well as the hardware, and is expected to permit a unified comparison of many different parallel architectures. Measurements on a number of well-known parallel algorithms, ranging from matrix multiply to quicksort, are presented for the MTA-2 and XMT and highlight some interesting differences between these machines. The performance of sequence alignment using dynamic programming is evaluated on the MTA-2, XMT, IBM x3755 and SGI Altix 350 and provides a useful comparison of the capabilities of the Cray machines with more conventional shared memory architectures. Copyright © 2009 John Wiley & Sons, Ltd. [source] Multiversion concurrency control for the generalized search treeCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 12 2009Walter Binder Abstract Many read-intensive systems where fast access to data is more important than the rate at which data can change make use of multidimensional index structures, like the generalized search tree (GiST). Although in these systems the indexed data are rarely updated and read access is highly concurrent, the existing concurrency control mechanisms for multidimensional index structures are based on locking techniques, which cause significant overhead. In this article we present the multiversion-GiST (MVGiST), an in-memory mechanism that extends the GiST with multiversion concurrency control. The MVGiST enables lock-free read access and ensures a consistent view of the index structure throughout a reader's series of queries, by creating lightweight, read-only versions of the GiST that share unchanging nodes among themselves. An example of a system with high read to write ratio, where providing wait-free queries is of utmost importance, is a large-scale directory that indexes web services according to their input and output parameters. A performance evaluation shows that for low update rates, the MVGiST significantly improves scalability w.r.t. the number of concurrent read accesses when compared with a traditional, locking-based concurrency control mechanism. We propose a technique to control memory consumption and confirm through our evaluation that the MVGiST efficiently manages memory. Copyright © 2009 John Wiley & Sons, Ltd. [source] Coupling integrated Earth System Model components with BFG2CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 6 2009C. W. Armstrong Abstract GENIE is a suite of modular Earth System Model components coupled in a variety of configurations used to investigate climate phenomena. As part of the GENIEfy project, there is a desire to make the activity of coupling GENIE configurations more flexible in order to ease the integration of new components, permit experimentation with alternative model orderings and connectivity, and execute GENIE components in distributed environments. The current coupling framework is inflexible because models are run in a fixed order by a prescriptive main code. This paper shows how the BFG2 (Bespoke Framework Generator,version 2) coupling tool offers significantly more flexibility. Using BFG2, scientists describe GENIE configurations as metadata that can then be transformed automatically into the desired framework. It is demonstrated that BFG2 provides flexibility in composition and deployment, improvements that are brought without modification to the GENIE components, without loss of performance and in a such a manner that it is possible to produce exactly the same results as under the original framework. We also demonstrate how BFG2 may be used to improve the performance of future GENIE coupled models. Copyright © 2008 John Wiley & Sons, Ltd. [source] High-level distribution for the rapid production of robust telecoms software: comparing C++ and ERLANGCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 8 2008J. H. Nyström Abstract Currently most distributed telecoms software is engineered using low- and mid-level distributed technologies, but there is a drive to use high-level distribution. This paper reports the first systematic comparison of a high-level distributed programming language in the context of substantial commercial products. Our research strategy is to reengineer some C++/CORBA telecoms applications in ERLANG, a high-level distributed language, and make comparative measurements. Investigating the potential advantages of the high-level ERLANG technology shows that two significant benefits are realized. Firstly, robust configurable systems are easily developed using the high-level constructs for fault tolerance and distribution. The ERLANG code exhibits resilience: sustaining throughput at extreme loads and automatically recovering when load drops; availability: remaining available despite repeated and multiple failures; dynamic reconfigurability: with throughput scaling near-linearly when resources are added or removed. Secondly, ERLANG delivers significant productivity and maintainability benefits: the ERLANG components are less than one-third of the size of their C++ counterparts. The productivity gains are attributed to specific language features, for example, high-level communication saves 22%, and automatic memory management saves 11%,compared with the C++ implementation. Investigating the feasibility of the high-level ERLANG technology demonstrates that it fulfils several essential requirements. The requisite distributed functionality is readily specified, even although control of low-level distributed coordination aspects is abrogated to the ERLANG implementation. At the expense of additional memory residency, excellent time performance is achieved, e.g. three times faster than the C++ implementation, due to ERLANG's lightweight processes. ERLANG interoperates at low cost with conventional technologies, allowing incremental reengineering of large distributed systems. The technology is available on the required hardware/operating system platforms, and is well supported. Copyright © 2007 John Wiley & Sons, Ltd. [source] Using semantic links to support top- K join queries in peer-to-peer networksCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 15 2007Jie Liu Abstract An important issue raised in peer-to-peer (P2P) applications is how to accurately and efficiently retrieve a set of K best matching data objects from different sources while minimizing the number of objects that have to be accessed. The proposed solution is to organize peers by a semantic link network representing the semantic relationships between peers' data schemas. Queries are only routed to semantically relevant peers. A pruning-based local top- K ranking approach is proposed to reduce the transmitted data by pruning tuples that cannot produce the desired join results with a rank value at least equal to the lowest rank value generated. Experiments evaluate its performance in terms of the number of transmitted tuples and the miss rate. Comparison with the traditional threshold algorithm for centralized systems and other top- K ranking algorithms for P2P networks shows the features of the proposed approach. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||