8,078 research outputs found
An experimental investigation of the flow field for double-wedge configurations in a Mach 4.97 stream
The viscous-inviscid interactions which perturb the flow around the wing leading edge are discussed. The flow field perturbation results when the fuselage-generated shock wave interacts with the wing-generated shock wave. Three types of shock interference patterns are possible for the wing leading edge of the orbiter
Indirect Detection of CMSSM Neutralino Dark Matter with Neutrino Telescopes
We review the prospects of detecting supersymmetric dark matter in the
framework of the Constrained Minimal Supersymmetric Standard Model, and compare
indirect with direct detection capabilities.Comment: 6 pages, 4 figures, presented by J. Orloff at the York IDM02 workshop
(http://www.shef.ac.uk/~phys/idm2002
Neutrino Indirect Detection of Neutralino Dark Matter in the CMSSM
We study potential signals of neutralino dark matter indirect detection by
neutrino telescopes in a wide range of CMSSM parameters. We also compare with
direct detection potential signals taking into account in both cases present
and future experiment sensitivities. Only models with neutralino annihilation
into gauge bosons can satisfy cosmological constraints and current neutrino
indirect detection sensitivities. For both direct and indirect detection, only
next generation experiments will be able to really test this kind of models.Comment: 16 pages, 19 figures; v4: a few clarifications and significant
improvement of reference
Analysis of a two-dimensional type 6 shock-interference pattern using a perfect-gas code and a real-gas code
Numerical codes were developed to calculate the two dimensional flow field which results when supersonic flow encounters double wedge configurations whose angles are such that a type 4 pattern occurs. The flow field model included the shock interaction phenomena for a delta wing orbiter. Two numerical codes were developed, one which used the perfect gas relations and a second which incorporated a Mollier table to define equilibrium air properties. The two codes were used to generate theoretical surface pressure and heat transfer distributions for velocities from 3,821 feet per second to an entry condition of 25,000 feet per second
Relaxation of spherical systems with long-range interactions: a numerical investigation
The process of relaxation of a system of particles interacting with
long-range forces is relevant to many areas of Physics. For obvious reasons, in
Stellar Dynamics much attention has been paid to the case of 1/r^2 force law.
However, recently the interest in alternative gravities emerged, and
significant differences with respect to Newtonian gravity have been found in
relaxation phenomena. Here we begin to explore this matter further, by using a
numerical model of spherical shells interacting with an 1/r^alpha force law
obeying the superposition principle. We find that the virialization and
phase-mixing times depend on the exponent alpha, with small values of alpha
corresponding to longer relaxation times, similarly to what happens when
comparing for N-body simulations in classical gravity and in Modified Newtonian
Dynamics.Comment: 6 pages, 3 figures, accepted in the International Journal of
Bifurcation and Chao
Global fluctuations and Gumbel statistics
We explain how the statistics of global observables in correlated systems can
be related to extreme value problems and to Gumbel statistics. This
relationship then naturally leads to the emergence of the generalized Gumbel
distribution G_a(x), with a real index a, in the study of global fluctuations.
To illustrate these findings, we introduce an exactly solvable nonequilibrium
model describing an energy flux on a lattice, with local dissipation, in which
the fluctuations of the global energy are precisely described by the
generalized Gumbel distribution.Comment: 4 pages, 3 figures; final version with minor change
Shuttle orbiter boundary layer transition at flight and wind tunnel conditions
Hypersonic boundary layer transition data obtained on the windward centerline of the Shuttle orbiter during entry for the first five flights are presented and analyzed. Because the orbiter surface is composed of a large number of thermal protection tiles, the transition data include the effects of distributed roughness arising from tile misalignment and gaps. These data are used as a benchmark for assessing and improving the accuracy of boundary layer transition predictions based on correlations of wind tunnel data taken on both aerodynamically rough and smooth orbiter surfaces. By comparing these two data bases, the relative importance of tunnel free stream noise and surface roughness on orbiter boundary layer transition correlation parameters can be assessed. This assessment indicates that accurate predications of transition times can be made for the orbiter at hypersonic flight conditions by using roughness dominated wind tunnel data. Specifically, times of transition onset and completion is accurately predicted using a correlation based on critical and effective values of a roughness Reynolds number previously derived from wind tunnel data
Experimental and theoretical study of shuttle lee-side heat transfer rates
The experimental program which was conducted in the Calspan 96-inch hypersonic shock tunnel to investigate what effect the windward surface temperature had on the heat transfer to the leeward surface of the space shuttle orbiter is discussed. Heat-transfer distributions, surface-pressure distributions, and schlieren photographs were obtained for an 0.01-scale model of the 139 configuration space shuttle orbiter at angles-of-attack of 30 and 40 deg. Similar data were obtained for an 0.01 scale wingless model of the 139 configuration at angles-of-attack of 30 and 90 deg. Data were obtained for Mach numbers from Reynolds numbers, and surface temperatures and compared with theoretical results
Flow field for an underexpanded, supersonic nozzle exhausting into an expansive launch tube
Static pressure distributions along the launcher wall and pitot pressure measurements from the annular region between the rocket and the launcher were made as an underexpanded supersonic nozzle exhausted into an expansive launch tube. The flow remained supersonic along the entire length of the launcher for all nozzle locations studied
The Kovacs effect in model glasses
We discuss the `memory effect' discovered in the 60's by Kovacs in
temperature shift experiments on glassy polymers, where the volume (or energy)
displays a non monotonous time behaviour. This effect is generic and is
observed on a variety of different glassy systems (including granular
materials). The aim of this paper is to discuss whether some microscopic
information can be extracted from a quantitative analysis of the `Kovacs hump'.
We study analytically two families of theoretical models: domain growth and
traps, for which detailed predictions of the shape of the hump can be obtained.
Qualitatively, the Kovacs effect reflects the heterogeneity of the system: its
description requires to deal not only with averages but with a full probability
distribution (of domain sizes or of relaxation times). We end by some
suggestions for a quantitative analysis of experimental results.Comment: 17 pages, 6 figures; revised versio
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