485,226 research outputs found
MPP parallel forth
Massively Parallel Processor (MPP) Parallel FORTH is a derivative of FORTH-83 and Unified Software Systems' Uni-FORTH. The extension of FORTH into the realm of parallel processing on the MPP is described. With few exceptions, Parallel FORTH was made to follow the description of Uni-FORTH as closely as possible. Likewise, the parallel FORTH extensions were designed as philosophically similar to serial FORTH as possible. The MPP hardware characteristics, as viewed by the FORTH programmer, is discussed. Then a description is presented of how parallel FORTH is implemented on the MPP
More Evidence for a Distribution of Tunnel Splittings in Mn-acetate
In magnetic fields applied parallel to the anisotropy axis, the magnetization
of Mn has been measured in response to a field that is swept back and
forth across the resonances corresponding to steps . The fraction
of molecules remaining in the metastable well after each sweep through the
resonance is inconsistent with expectations for an ensemble of identical
molecules. The data are consistent instead with the presence of a broad
distribution of tunnel splittings. A very good fit is obtained for a Gaussian
distribution of the second-order anisotropy tunneling parameter . We show that dipolar shuffling is a negligible effect which cannot
explain our data.Comment: minor corrections (PACS nos, signs in Fig. 2
Symmetry breaking and phase coexistence in a driven diffusive two-channel system
We consider classical hard-core particles moving on two parallel chains in
the same direction. An interaction between the channels is included via the
hopping rates. For a ring, the stationary state has a product form. For the
case of coupling to two reservoirs, it is investigated analytically and
numerically. In addition to the known one-channel phases, two new regions are
found, in particular the one, where the total density is fixed, but the filling
of the individual chains changes back and forth, with a preference for strongly
different densities. The corresponding probability distribution is determined
and shown to have an universal form. The phase diagram and general aspects of
the problem are discussed.Comment: 12 pages, 10 figures, to appear in Phys.Rev.
The Pioneer anomaly: the measure of a topological phase defect of light in cosmology
It is shown that a wave vector representing a light pulse in an adiabatically
evolving expanding space should develop, after a round trip (back and forth to
the emitter) a geometric phase for helicity states at a given fixed position
coordinate of this expanding space.In a section of the Hopf fibration of the
Poincare sphere that identifies a projection to the physically allowed states,
the evolution defines a parallel transported state that can be joined
continuously with the initial state by means of the associated
Berry-Pancharatnam connection. The connection allows to compute an anomaly in
the frequency for the vector modes in terms of the scale factor of the
space-time background being identical to the reported Pioneer Anomaly.Comment: 10 pages, some minor notation changes have been made. Some additional
remarks were writte
Restoration of the Broken D2-Symmetry in the Mean Field Description of Rotating Nuclei
Signature effects observed in rotational bands are a consequence of an
inherent D2-symmetry. This symmetry is naturally broken by the mean field
cranking approximation when a tilted (non-principal) axis orientation of the
nuclear spin becomes stable. The possible tunneling forth and back between the
two symmetry-related minima in the double-humped potential-energy surface
appears as a typical bifurcation of the rotational band. We describe this
many-body process in which all nucleons participate by diagonalizing the
nuclear Hamiltonian within a selected set of tilted and non-tilted cranking
quasiparticle states. This microscopic approach is able to restore the broken
D2 symmetry and reproduce the quantum fluctuations between symmetry- related
HFB states which emerge as splitting of the band energies and in parallel
staggering in intraband M1 transitions.Comment: 9 pages, 4 figure
21st Century Simulation: Exploiting High Performance Computing and Data Analysis
This paper identifies, defines, and analyzes the limitations imposed on Modeling and Simulation by outmoded
paradigms in computer utilization and data analysis. The authors then discuss two emerging capabilities to
overcome these limitations: High Performance Parallel Computing and Advanced Data Analysis. First, parallel
computing, in supercomputers and Linux clusters, has proven effective by providing users an advantage in
computing power. This has been characterized as a ten-year lead over the use of single-processor computers.
Second, advanced data analysis techniques are both necessitated and enabled by this leap in computing power.
JFCOM's JESPP project is one of the few simulation initiatives to effectively embrace these concepts. The
challenges facing the defense analyst today have grown to include the need to consider operations among non-combatant
populations, to focus on impacts to civilian infrastructure, to differentiate combatants from non-combatants,
and to understand non-linear, asymmetric warfare. These requirements stretch both current
computational techniques and data analysis methodologies. In this paper, documented examples and potential
solutions will be advanced. The authors discuss the paths to successful implementation based on their experience.
Reviewed technologies include parallel computing, cluster computing, grid computing, data logging, OpsResearch,
database advances, data mining, evolutionary computing, genetic algorithms, and Monte Carlo sensitivity analyses.
The modeling and simulation community has significant potential to provide more opportunities for training and
analysis. Simulations must include increasingly sophisticated environments, better emulations of foes, and more
realistic civilian populations. Overcoming the implementation challenges will produce dramatically better insights,
for trainees and analysts. High Performance Parallel Computing and Advanced Data Analysis promise increased
understanding of future vulnerabilities to help avoid unneeded mission failures and unacceptable personnel losses.
The authors set forth road maps for rapid prototyping and adoption of advanced capabilities. They discuss the
beneficial impact of embracing these technologies, as well as risk mitigation required to ensure success
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