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Distributed Resources (distributed + resource)
Selected AbstractsEVOLUTION OF NICHE WIDTH AND ADAPTIVE DIVERSIFICATIONEVOLUTION, Issue 12 2004Martin Ackermann Abstract Theoretical models suggest that resource competition can lead to the adaptive splitting of consumer populations into diverging lineages, that is, to adaptive diversification. In general, diversification is likely if consumers use only a narrow range of resources and thus have a small niche width. Here we use analytical and numerical methods to study the consequences for diversification if the niche width itself evolves. We found that the evolutionary outcome depends on the inherent costs or benefits of widening the niche. If widening the niche did not have costs in terms of overall resource uptake, then the consumer evolved a niche that was wide enough for disruptive selection on the niche position to vanish; adaptive diversification was no longer observed. However, if widening the niche was costly, then the niche widths remained relatively narrow, allowing for adaptive diversification in niche position. Adaptive diversification and speciation resulting from competition for a broadly distributed resource is thus likely if the niche width is fixed and relatively narrow or free to evolve but subject to costs. These results refine the conditions for adaptive diversification due to competition and formulate them in a way that might be more amenable for experimental investigations. [source] Performance evaluation of an autonomic network-aware metascheduler for GridsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 13 2009A. Caminero Abstract Grid technologies have enabled the aggregation of geographically distributed resources in the context of a particular application. The network remains an important requirement for any Grid application, as entities involved in a Grid system (such as users, services, and data) need to communicate with each other over a network. The performance of the network must therefore be considered when carrying out tasks such as scheduling, migration or monitoring of jobs. Surprisingly, many existing quality of service efforts ignore the network and focus instead on processor workload and disk access time. Making use of the network in an efficient and fault-tolerant manner is challenging. In a previous contribution, we proposed an autonomic network-aware scheduling architecture that is capable of adapting its behavior to the current status of the environment. Now, we present a performance evaluation in which our proposal is compared with a conventional scheduling strategy. We present simulation results that show the benefits of our approach. Copyright © 2009 John Wiley & Sons, Ltd. [source] Cross-domain authorization for federated virtual organizations using the myVocs collaboration environmentCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 4 2009Jill Gemmill Abstract This paper describes our experiences building and working with the reference implementation of myVocs (my Virtual Organization Collaboration System). myVocs provides a flexible environment for exploring new approaches to security, application development, and access control built from Internet services without a central identity repository. The myVocs framework enables virtual organization (VO) self-management across unrelated security domains for multiple, unrelated VOs. By leveraging the emerging distributed identity management infrastructure. myVocs provides an accessible, secure collaborative environment using standards for federated identity management and open-source software developed through the National Science Foundation Middleware Initiative. The Shibboleth software, an early implementation of the Organization for the Advancement of Structured Information Standards Security Assertion Markup Language standard for browser single sign-on, provides the middleware needed to assert identity and attributes across domains so that access control decisions can be determined at each resource based on local policy. The eduPerson object class for lightweight directory access protocol (LDAP) provides standardized naming, format, and semantics for a global identifier. We have found that a Shibboleth deployment supporting VOs requires the addition of a new VO service component allowing VOs to manage their own membership and control access to their distributed resources. The myVocs system can be integrated with Grid authentication and authorization using GridShib. Copyright © 2008 John Wiley & Sons, Ltd. [source] Studying protein folding on the Grid: experiences using CHARMM on NPACI resources under LegionCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 4 2004Anand Natrajan Abstract One benefit of a computational Grid is the ability to run high-performance applications over distributed resources simply and securely. We demonstrated this benefit with an experiment in which we studied the protein-folding process with the CHARMM molecular simulation package over a Grid managed by Legion, a Grid operating system. High-performance applications can take advantage of Grid resources if the Grid operating system provides both low-level functionality as well as high-level services. We describe the nature of services provided by Legion for high-performance applications. Our experiences indicate that human factors continue to play a crucial role in the configuration of Grid resources, underlying resources can be problematic, Grid services must tolerate underlying problems or inform the user, and high-level services must continue to evolve to meet user requirements. Our experiment not only helped a scientist perform an important study, but also showed the viability of an integrated approach such as Legion's for managing a Grid. Copyright © 2004 John Wiley & Sons, Ltd. [source] The ASCI Computational Grid: initial deploymentCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 13-15 2002Randal Rheinheimer Abstract Grid Services, a Department of Energy Accelerated Strategic Computing Initiative program, has designed, implemented, and deployed a grid-based solution for customer access to large computing resources at DOE weapons labs and plants. Customers can access and monitor diverse, geographically distributed resources using the common Grid Services interfaces. This paper discusses the architecture, security, and user interfaces of the Grid Services infrastructure. Published in 2002 by John Wiley & Sons, Ltd. [source] Foraging on spatially distributed resources with sub-optimal movement, imperfect information, and travelling costs: departures from the ideal free distributionOIKOS, Issue 9 2010Shuichi Matsumura Ideal free distribution (IFD) theory offers an important baseline for predicting the distribution of foragers across resource patches. Yet it is well known that IFD theory relies on several over-simplifying assumptions that are unlikely to be met in reality. Here we relax three of the most critical assumptions: (1) optimal foraging moves among patches, (2) omniscience about the utility of resource patches, and (3) cost-free travelling between patches. Based on these generalizations, we investigate the distributions of a constant number of foragers in models with explicit resource dynamics of logistic type. We find that, first, when foragers do not always move to the patch offering maximum intake rate (optimal foraging), but instead move probabilistically according to differences in resource intake rates between patches (sub-optimal foraging), the distribution of foragers becomes less skewed than the IFD, so that high-quality patches attract fewer foragers. Second, this homogenization is strengthened when foragers have less than perfect knowledge about the utility of resource patches. Third, and perhaps most surprisingly, the introduction of travelling costs causes departures in the opposite direction: the distribution of sub-optimal foragers approaches the IFD as travelling costs increase. We demonstrate that these three findings are robust when considering patches that differ in the resource's carrying capacity or intrinsic growth rate, and when considering simple two-patch and more complex multiple-patch models. By overcoming three major over-simplifications of IFD theory, our analyses contribute to the systematic investigation of ecological factors influencing the spatial distribution of foragers, and thus help in deriving new hypotheses that are testable in empirical systems. A confluence of theoretical and empirical studies that go beyond classical IFD theory is essential for improving insights into how animal distributions across resource patches are determined in nature. [source] | ||||||||||