19,672 research outputs found
Extrapolation Method for the No-Core Shell Model
Nuclear many-body calculations are computationally demanding. An estimate of
their accuracy is often hampered by the limited amount of computational
resources even on present-day supercomputers. We provide an extrapolation
method based on perturbation theory, so that the binding energy of a large
basis-space calculation can be estimated without diagonalizing the Hamiltonian
in this space. The extrapolation method is tested for 3H and 6Li nuclei. It
will extend our computational abilities significantly and allow for reliable
error estimates.Comment: 8 pages, 7 figures, PRC accepte
Mesoscale assessments of cloud and rainfall over the British Isles
There are no author-identified significant results in this report
A study to define an in-flight dynamics measurement and data applications program for space shuttle payloads
Data measurement and interpretation techniques were defined for application to the first few space shuttle flights, so that the dynamic environment could be sufficiently well established to be used to reduce the cost of future payloads through more efficient design and environmental test techniques. It was concluded that: (1) initial payloads must be given comprehensive instrumentation coverage to obtain detailed definition of acoustics, vibration, and interface loads, (2) analytical models of selected initial payloads must be developed and verified by modal surveys and flight measurements, (3) acoustic tests should be performed on initial payloads to establish realistic test criteria for components and experiments in order to minimize unrealistic failures and retest requirements, (4) permanent data banks should be set up to establish statistical confidence in the data to be used, (5) a more unified design/test specification philosophy is needed, (6) additional work is needed to establish a practical testing technique for simulation of vehicle transients
Viking dynamics experience with application to future payload design
Analytical and test techniques are discussed. Areas in which hindsight indicated erroneous, redundant, or unnecessarily severe design and test specifications are identified. Recommendations are made for improvements in the dynamic design and criteria philosophy, aimed at reducing costs for payloads
Using microsimulation feedback for trip adaptation for realistic traffic in Dallas
This paper presents a day-to-day re-routing relaxation approach for traffic
simulations. Starting from an initial planset for the routes, the route-based
microsimulation is executed. The result of the microsimulation is fed into a
re-router, which re-routes a certain percentage of all trips. This approach
makes the traffic patterns in the microsimulation much more reasonable.
Further, it is shown that the method described in this paper can lead to strong
oscillations in the solutions.Comment: Accepted by International Journal of Modern Physics C. Complete
postscript version including figures in
http://www-transims.tsasa.lanl.gov/research_team/papers
Hybrid-parallel sparse matrix-vector multiplication with explicit communication overlap on current multicore-based systems
We evaluate optimized parallel sparse matrix-vector operations for several
representative application areas on widespread multicore-based cluster
configurations. First the single-socket baseline performance is analyzed and
modeled with respect to basic architectural properties of standard multicore
chips. Beyond the single node, the performance of parallel sparse matrix-vector
operations is often limited by communication overhead. Starting from the
observation that nonblocking MPI is not able to hide communication cost using
standard MPI implementations, we demonstrate that explicit overlap of
communication and computation can be achieved by using a dedicated
communication thread, which may run on a virtual core. Moreover we identify
performance benefits of hybrid MPI/OpenMP programming due to improved load
balancing even without explicit communication overlap. We compare performance
results for pure MPI, the widely used "vector-like" hybrid programming
strategies, and explicit overlap on a modern multicore-based cluster and a Cray
XE6 system.Comment: 16 pages, 10 figure
Analytical trade study of the STS payload environment
The current predicted acoustic environment for the shuttle orbiter payload bay will produce random vibration environments for payload components and subsystems which potentially will result in design, weight and cost penalties if means of protecting the payloads are not developed. Results are presented of a study to develop, through design and cost effectiveness trade studies, conceptual noise suppression device designs for space shuttle payloads. The impact of noise suppression on environmental levels and associated test costs, and on test philosophy for the various payload classes is considered with the ultimate goal of reducing payload test costs. Conclusions and recommendations are presented
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