953 research outputs found
Analysis of the project fire re-entry package flow field final technical report
Theoretical prediction of state of gas in flow field surrounding Apollo type vehicle in reentry at hypersonic speed
Twisted Rindler space-times
The (linearized) noncommutative Rindler space-times associated with
canonical, Lie-algebraic and quadratic twist-deformed Minkowski spaces are
provided. The corresponding deformed Hawking spectra detected by Rindler
observers are derived as well.Comment: 13 pages, no figures, keywords: quantum space-times, Hawking
radiatio
Singular Modes of the Electromagnetic Field
We show that the mode corresponding to the point of essential spectrum of the
electromagnetic scattering operator is a vector-valued distribution
representing the square root of the three-dimensional Dirac's delta function.
An explicit expression for this singular mode in terms of the Weyl sequence is
provided and analyzed. An essential resonance thus leads to a perfect
localization (confinement) of the electromagnetic field, which in practice,
however, may result in complete absorption.Comment: 14 pages, no figure
A conceptual design study of the reusable reentry satellite
Experimentation leading to an understanding of life processes under reduced and extremely low gravitational forces will profoundly contribute to the success of future space missions involving humans. In addition to research on gravitational biology, research on the effects of cosmic radiation and the interruption and change of circadian rhythms on life systems is also of prime importance. Research in space, however, is currently viewed by biological scientists as an arena that is essential, yet largely inaccessible to them for their experimentation. To fulfill this need, a project and spacecraft system described as the Reusuable Reentry Satellite or Lifesat has been proposed by NASA
Analytical model for laser-assisted recombination of hydrogenic atoms
We introduce a new method that allows one to obtain an analytical cross
section for the laser-assisted electron-ion collision in a closed form. As an
example we perform a calculation for the hydrogen laser-assisted recombination.
The -matrix element for the process is constructed from an exact electron
Coulomb-Volkov wave function and an approximate laser modified hydrogen state.
An explicit expression for the field-enhancement coefficient of the process is
expressed in terms of the dimensionless parameter , where and are the electron charge
and momentum respectively, and and are the
amplitude and frequency of the laser field respectively. The simplified version
of the cross section of the process is derived and analyzed within a soft
photon approximation.Comment: 10 page
Image method in the calculation of the van der Waals force between an atom and a conducting surface
Initially, we make a detailed historical survey of van der Waals forces,
collecting the main references on the subject. Then, we review a method
recently proposed by Eberlein and Zietal to compute the dispersion van der
Waals interaction between a neutral but polarizable atom and a perfectly
conducting surface of arbitrary shape. This method has the advantage of
relating the quantum problem to a corresponding classical one in electrostatics
so that all one needs is to compute an appropriate Green function. We show how
the image method of electrostatics can be conveniently used together with the
Eberlein and Zietal mehtod (when the problem admits an image solution). We then
illustrate this method in a couple of simple but important cases, including the
atom-sphere system. Particularly, in our last example, we present an original
result, namely, the van der Waals force between an atom and a boss hat made of
a grounded conducting material.Comment: This is a pedagogical and introductory paper on van der Waals forces
between an atom and a conducting surfac
Establishing the relationship between manufacturing and component performance in stretch formed thermoplastic composites
Flexible manufacturing methods are needed to reduce the cost of using advanced composites in structural applications. One method that allows for this is the stretch forming of long discontinuous fiber materials with thermoplastic matrices. In order to exploit this flexibility in an economical way, a thorough understanding of the relationship between manufacturing and component performance must be developed. This paper reviews some of the recent work geared toward establishing this understanding. Micromechanics models have been developed to predict the formability of the material during processing. The latest improvement of these models includes the viscoelastic nature of the matrix and comparison with experimental data. A finite element scheme is described which can be used to model the forming process. This model uses equivalent anisotropic viscosities from the micromechanics models and predicts the microstructure in the formed part. In addition, structural models have been built to account for the material property gradients that can result from the manufacturing procedures. Recent developments in this area include the analysis of stress concentrations and a failure model each accounting for the heterogeneous material fields
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