Distributed simulation and the grid: Position statements

The Grid provides a new and unrivaled technology for large scale distributed simulation as it enables collaboration and the use of distributed computing resources. This panel paper presents the views of four researchers in the area of Distributed Simulation and the Grid. Together we try to identify the main research issues involved in applying Grid technology to distributed simulation and the key future challenges that need to be solved to achieve this goal. Such challenges include not only technical challenges, but also political ones such as management methodology for the Grid and the development of standards. The benefits of the Grid to end-user simulation modelers also are discussed

Height Measurements of OI (557.7 nm) Gravity Wave Structure Over the Hawaiian Islands During ALOHA-93

During the ALOHA‐93 campaign simultaneous observations of gravity wave structure in the OI(557.7 nm) nightglow emission were made using two all‐sky CCD imagers; one located near the summit of Haleakala Crater, Maui and the other at Mauna Loa Observatory, Hawaii. On 19 October a set of bright, planar, monochromatic waves was imaged by both systems as it progressed rapidly over the Hawaiian Islands. Triangulation on these wave forms indicates a mean altitude of 95±2 km in good agreement with previous rocket soundings at mid‐latitudes. Two methods of triangulation were employed, both achieving similar results

Rotational predissociation of extremely weakly bound atom-molecule complexes produced by Feshbach resonance association

We study the rotational predissociation of atom - molecule complexes with very small binding energy. Such complexes can be produced by Feshbach resonance association of ultracold molecules with ultracold atoms. Numerical calculations of the predissociation lifetimes based on the computation of the energy dependence of the scattering matrix elements become inaccurate when the binding energy is smaller than the energy width of the predissociating state. We derive expressions that represent accurately the predissociation lifetimes in terms of the real and imaginary parts of the scattering length and effective range for molecules in an excited rotational state. Our results show that the predissociation lifetimes are the longest when the binding energy is positive, i.e. when the predissociating state is just above the excited state threshold.Comment: 17 pages, 5 figure

The transition to irreversibility in sheared suspensions: An analysis based on a mesoscopic entropy production

We study the shear-induced diffusion effect and the transition to irreversibility in suspensions under oscillatory shear flow by performing an analysis of the entropy production associated to the motion of the particles. We show that the Onsager coupling between different contributions to the entropy production is responsible for the scaling of the mean square displacement on particle diameter and applied strain. We also show that the shear-induced effective diffusion coefficient depends on the volume fraction and use Lattice-Boltzmann simulations to characterize the effect through the power spectrum of particle positions for different Reynolds numbers and volume fractions. Our study gives a thermodynamic explanation of the the transition to irreversibility through a pertinent analysis of the second law of thermodynamics.Comment: 17 pages, 3 figures, paper submitted tp phys rev

Anomalous diffusion, clustering, and pinch of impurities in plasma edge turbulence

The turbulent transport of impurity particles in plasma edge turbulence is investigated. The impurities are modeled as a passive fluid advected by the electric and polarization drifts, while the ambient plasma turbulence is modeled using the two-dimensional Hasegawa--Wakatani paradigm for resistive drift-wave turbulence. The features of the turbulent transport of impurities are investigated by numerical simulations using a novel code that applies semi-Lagrangian pseudospectral schemes. The diffusive character of the turbulent transport of ideal impurities is demonstrated by relative-diffusion analysis of the evolution of impurity puffs. Additional effects appear for inertial impurities as a consequence of compressibility. First, the density of inertial impurities is found to correlate with the vorticity of the electric drift velocity, that is, impurities cluster in vortices of a precise orientation determined by the charge of the impurity particles. Second, a radial pinch scaling linearly with the mass--charge ratio of the impurities is discovered. Theoretical explanation for these observations is obtained by analysis of the model equations.Comment: This article has been submitted to Physics of Plasmas. After it is published, it will be found at http://pop.aip.org/pop

Aharonov-Casher oscillations of spin current through a multichannel mesoscopic ring

The Aharonov-Casher (AC) oscillations of spin current through a 2D ballistic ring in the presence of Rashba spin-orbit interaction and external magnetic field has been calculated using the semiclassical path integral method. For classically chaotic trajectories the Fokker-Planck equation determining dynamics of the particle spin polarization has been derived. On the basis of this equation an analytic expression for the spin conductance has been obtained taking into account a finite width of the ring arms carrying large number of conducting channels. It was shown that the finite width results in a broadening and damping of spin current AC oscillations. We found that an external magnetic field leads to appearance of new nondiagonal components of the spin conductance, allowing thus by applying a rather weak magnetic field to change a direction of the transmitted spin current polarization.Comment: 16 pages, 6 figure

Accretion Disk Instabilities, CDM models and their role in Quasar Evolution

We have developed a consistent analytical model to describe the observed evolution of the quasar luminosity function. Our model combines black hole mass distributions based on the Press - Schechter theory of the structure formation in the Universe with quasar luminosity functions resulting from a physics-based emission model that takes into account the time-dependent phenomena occurring in the accretion disks. Quasar evolution and CDM models are mutually constraining, therefore our model gives an estimation of the exponent, n, of the power spectrum, P(k), which is found to be -1.8 < n < -1.6. We were able to reject a generally assumed hypothesis of a constant ratio between Dark Matter Halo and the Black Hole mass, since the observed data could not be fitted under this assumption. We found that the relation between the Dark Matter Halos and Black Hole masses is better described by M_{BH}=M_{DMH}^{0.668}. This model provides a reasonable fit to the observed quasar luminosity function at redshifts higher than ~2.0. We suggest that the disagreement at lower redshift is due to mergers. Based on the agreement at high redshift, we estimated the merger rate at lower redshift, and argue that this rate should depend on the redshift, like (1+z)^3.Comment: 15 pages, 18 figures, Accepted for Publication in Ap

Advection of vector fields by chaotic flows

We have introduced a new transfer operator for chaotic flows whose leading eigenvalue yields the dynamo rate of the fast kinematic dynamo and applied cycle expansion of the Fredholm determinant of the new operator to evaluation of its spectrum. The theory hs been tested on a normal form model of the vector advecting dynamical flow. If the model is a simple map with constant time between two iterations, the dynamo rate is the same as the escape rate of scalar quantties. However, a spread in Poincar\'e section return times lifts the degeneracy of the vector and scalar advection rates, and leads to dynamo rates that dominate over the scalar advection rates. For sufficiently large time spreads we have even found repellers for which the magnetic field grows exponentially, even though the scalar densities are decaying exponentially.Comment: 12 pages, Latex. Ask for figures from [email protected]

The Bloch-Okounkov correlation functions, a classical half-integral case

Bloch and Okounkov's correlation function on the infinite wedge space has connections to Gromov-Witten theory, Hilbert schemes, symmetric groups, and certain character functions of \hgl_\infty-modules of level one. Recent works have calculated these character functions for higher levels for \hgl_\infty and its Lie subalgebras of classical type. Here we obtain these functions for the subalgebra of type $D$ of half-integral levels and as a byproduct, obtain $q$-dimension formulas for integral modules of type $D$ at half-integral level.Comment: v2: minor changes to the introduction; accepted for publication in Letters in Mathematical Physic