Publications

Results 8576–8600 of 9,998

Search results

Jump to search filters

Qthreads: An API for programming with millions of lightweight threads

IPDPS Miami 2008 - Proceedings of the 22nd IEEE International Parallel and Distributed Processing Symposium, Program and CD-ROM

Wheeler, Kyle B.; Murphy, Richard C.; Thain, Douglas

Large scale hardware-supported multithreading, an attractive means of increasing computational power, benefits significantly from low per-thread costs. Hardware support for lightweight threads is a developing area of research. Each architecture with such support provides a unique interface, hindering development for them and comparisons between them. A portable abstraction that provides basic lightweight thread control and synchronization primitives is needed. Such an abstraction would assist in exploring both the architectural needs of large scale threading and the semantic power of existing languages. Managing thread resources is a problem that must be addressed if massive parallelism is to be popularized. The qthread abstraction enables development of large-scale multithreading applications on commodity architectures. This paper introduces the qthread API and its Unix implementation, discusses resource management, and presents performance results from the HPCCG benchmark. ©2008 IEEE.

More Details

LDRD final report for improving human effectiveness for extreme-scale problem solving : assessing the effectiveness of electronic brainstorming in an industrial setting

Dornburg, Courtney S.; Adams, Susan S.; Hendrickson, Stacey M.; Davidson, George S.

An experiment was conducted comparing the effectiveness of individual versus group electronic brainstorming in order to address difficult, real world challenges. While industrial reliance on electronic communications has become ubiquitous, empirical and theoretical understanding of the bounds of its effectiveness have been limited. Previous research using short-term, laboratory experiments have engaged small groups of students in answering questions irrelevant to an industrial setting. The present experiment extends current findings beyond the laboratory to larger groups of real-world employees addressing organization-relevant challenges over the course of four days. Employees and contractors at a national security laboratory participated, either in a group setting or individually, in an electronic brainstorm to pose solutions to a 'wickedly' difficult problem. The data demonstrate that (for this design) individuals perform at least as well as groups in producing quantity of electronic ideas, regardless of brainstorming duration. However, when judged with respect to quality along three dimensions (originality, feasibility, and effectiveness), the individuals significantly (p<0.05) out-performed the group working together. When idea quality is used as the benchmark of success, these data indicate that work-relevant challenges are better solved by aggregating electronic individual responses, rather than electronically convening a group. This research suggests that industrial reliance upon electronic problem solving groups should be tempered, and large nominal groups might be the more appropriate vehicle for solving wicked corporate issues.

More Details

Climate-derived tensions in Arctic security

Backus, George A.; Strickland, James H.

Globally, there is no lack of security threats. Many of them demand priority engagement and there can never be adequate resources to address all threats. In this context, climate is just another aspect of global security and the Arctic just another region. In light of physical and budgetary constraints, new security needs must be integrated and prioritized with existing ones. This discussion approaches the security impacts of climate from that perspective, starting with the broad security picture and establishing how climate may affect it. This method provides a different view from one that starts with climate and projects it, in isolation, as the source of a hypothetical security burden. That said, the Arctic does appear to present high-priority security challenges. Uncertainty in the timing of an ice-free Arctic affects how quickly it will become a security priority. Uncertainty in the emergent extreme and variable weather conditions will determine the difficulty (cost) of maintaining adequate security (order) in the area. The resolution of sovereignty boundaries affects the ability to enforce security measures, and the U.S. will most probably need a military presence to back-up negotiated sovereignty agreements. Without additional global warming, technology already allows the Arctic to become a strategic link in the global supply chain, possibly with northern Russia as its main hub. Additionally, the multinational corporations reaping the economic bounty may affect security tensions more than nation-states themselves. Countries will depend ever more heavily on the global supply chains. China has particular needs to protect its trade flows. In matters of security, nation-state and multinational-corporate interests will become heavily intertwined.

More Details

R&D for computational cognitive and social models : foundations for model evaluation through verification and validation (final LDRD report)

McNamara, Laura A.; Trucano, Timothy G.; Backus, George A.; Mitchell, Scott A.

Sandia National Laboratories is investing in projects that aim to develop computational modeling and simulation applications that explore human cognitive and social phenomena. While some of these modeling and simulation projects are explicitly research oriented, others are intended to support or provide insight for people involved in high consequence decision-making. This raises the issue of how to evaluate computational modeling and simulation applications in both research and applied settings where human behavior is the focus of the model: when is a simulation 'good enough' for the goals its designers want to achieve? In this report, we discuss two years' worth of review and assessment of the ASC program's approach to computational model verification and validation, uncertainty quantification, and decision making. We present a framework that extends the principles of the ASC approach into the area of computational social and cognitive modeling and simulation. In doing so, we argue that the potential for evaluation is a function of how the modeling and simulation software will be used in a particular setting. In making this argument, we move from strict, engineering and physics oriented approaches to V&V to a broader project of model evaluation, which asserts that the systematic, rigorous, and transparent accumulation of evidence about a model's performance under conditions of uncertainty is a reasonable and necessary goal for model evaluation, regardless of discipline. How to achieve the accumulation of evidence in areas outside physics and engineering is a significant research challenge, but one that requires addressing as modeling and simulation tools move out of research laboratories and into the hands of decision makers. This report provides an assessment of our thinking on ASC Verification and Validation, and argues for further extending V&V research in the physical and engineering sciences toward a broader program of model evaluation in situations of high consequence decision-making.

More Details

High-throughput proteomics : optical approaches

Davidson, George S.

Realistic cell models could greatly accelerate our ability to engineer biochemical pathways and the production of valuable organic products, which would be of great use in the development of biofuels, pharmaceuticals, and the crops for the next green revolution. However, this level of engineering will require a great deal more knowledge about the mechanisms of life than is currently available. In particular, we need to understand the interactome (which proteins interact) as it is situated in the three dimensional geometry of the cell (i.e., a situated interactome), and the regulation/dynamics of these interactions. Methods for optical proteomics have become available that allow the monitoring and even disruption/control of interacting proteins in living cells. Here, a range of these methods is reviewed with respect to their role in elucidating the interactome and the relevant spatial localizations. Development of these technologies and their integration into the core competencies of research organizations can position whole institutions and teams of researchers to lead in both the fundamental science and the engineering applications of cellular biology. That leadership could be particularly important with respect to problems of national urgency centered around security, biofuels, and healthcare.

More Details

Capabilities for Uncertainty in Predictive Science (LDRD Final Report)

Phipps, Eric T.; Eldred, Michael S.; Salinger, Andrew G.

Predictive simulation of systems comprised of numerous interconnected, tightly coupled components promises to help solve many problems of scientific and national interest. However predictive simulation of such systems is extremely challenging due to the coupling of a diverse set of physical and biological length and time scales. This report investigates un-certainty quantification methods for such systems that attempt to exploit their structure to gain computational efficiency. The traditional layering of uncertainty quantification around nonlinear solution processes is inverted to allow for heterogeneous uncertainty quantification methods to be applied to each component in a coupled system. Moreover this approach allows stochastic dimension reduction techniques to be applied at each coupling interface. The mathematical feasibility of these ideas is investigated in this report, and mathematical formulations for the resulting stochastically coupled nonlinear systems are developed.

More Details

Asymmetric cubature formulas for polynomial integration in the triangle and square

Journal of Computational and Applied Mathematics

Taylor, Mark A.

We present five new cubature formula in the triangle and square for exact integration of polynomials. The points were computed numerically with a cardinal function algorithm which does not impose any symmetry requirements on the points. Cubature formula are presented which integrate degrees 10, 11 and 12 in the triangle and degrees 10 and 12 in the square. They have positive weights, contain no points outside the domain, and have fewer points than previously known results. © 2007 Elsevier B.V. All rights reserved.

More Details

Computational modeling of analogy: Destined ever to only be metaphor?

Behavioral and Brain Sciences

Speed, Ann S.

The target article by Leech et al. presents a compelling computational theory of analogy-making. However, there is a key difficulty that persists in theoretical treatments of analogy-making, computational and otherwise: namely, the lack of a detailed account of the neurophysiological mechanisms that give rise to analogy behavior. My commentary explores this issue. © 2008 Cambridge University Press.

More Details
Results 8576–8600 of 9,998
Results 8576–8600 of 9,998