12,992 research outputs found
On optical imaging through aircraft turbulent boundary layers
Optical resolution quality as affected by aircraft turbulent boundary layers is analyzed. Wind-tunnel data was analyzed to obtained the variation of boundary layer turbulence scale length and mass density rms fluctuations with Mach number. The data gave good agreement with a mass density fluctuation turbulence spectrum that is either isotropic of orthogonally anisotropic. The data did not match an isotropic turbulence velocity spectrum which causes an anisotropic non-orthogonal mass density fluctuation spectrum. The results indicate that the average mass density rms fluctuation is about 10% of the maximum mass density across the boundary layer and that the transverse turbulence scale size is about 10% of the boundary layer thickness. The results indicate that the effect of the turbulent boundary layer is large angle scattering which decreases contrast but not resolution. Using extinction as a criteria the range of acceptable aircraft operating conditions are given
A Photoelastic Study of Strain Waves Caused by Cavitation
Ultra-high-speed photoelastic techniques have been applied to a study of the transient stresses and strains in a photoelastic plastic when subject to cavitation. A photocell, used to detect the transient strains, indicated that the time duration of the strains was about 2
microseconds. Using an ultra-high-speed motion picture camera, ultrasonic cavitation bubbles have been photographed collapsing on the surface of a photoelastic specimen, and the resulting strain wave in
the solid has been photographed.
The dynamic properties of a photoelastic material have been
obtained in order to permit quantitative interpretation of the transients. This has indicated that the stresses due to cavitation may be as high as 2.8 x 10^5 psi.
The photoelastic plastic, CR-39, was found to exhibit strain
birefringence, and its strain-optic constant was found to be independent of the rate of loading
An Intermediate Theory of Longitudinal Stress Waves in Bars
The expressions for kinetic and strain energy for longitudinal stress waves in a bar are considered, first in a one-dimensional model in which cross sections are assumed to remain plane, and stresses in the radial and
circumferential direction are assumed to be zero. From this, an equation of motion is derived which is used to determine the speed of longitudinal sinusoidal stress waves as a function of wave length. Secondly, a simplified
three-dimensional model is considered where the axial motion is a parabolic function of the radius, from which the speed of sinusoidal stress waves is derived. The derived expressions are compared with previously
published solutions
A Mechanism for Ferrimagnetism and Incommensurability in One-Dimensional Systems
A mechanism for ferrimagnetism in
(1+1)-dimensions is discussed. The ferrimagnetism is cased by interactions
described by operators with non-zero conformal spin. Such interactions appear
in such problems as the problem of tunneling between Luttinger liquids and the
problem of frustrated spin ladder. I present exact solutions for a
representative class of models containing such interactions together with a
simple mean field analysis. It is shown that the interactions (i) dynamically
generate static oscillations with a wave vector dependent on the coupling
constant, (ii) give rise to a finite magnetic moment at accompanied by
the soft mode with a non-relativistic ({\it ferromagnetic}) dispersion , (iii) generate massive (roton) modes.Comment: replaced by the extended version, references adde
Josephson Coupling through a Quantum Dot
We derive, via fourth order perturbation theory, an expression for the
Josephson current through a gated interacting quantum dot. We analyze our
expression for two different models of the superconductor-dot-superconductor
(SDS) system. When the matrix elements connecting dot and leads are featureless
constants, we compute the Josephson coupling J_c as a function of the gate
voltage and Coulomb interaction. In the diffusive dot limit, we compute the
probability distribution P(J_c) of Josephson couplings. In both cases, pi
junction behavior (J_c < 0) is possible, and is not simply dependent on the
parity of the dot occupancy.Comment: 9 pages; 3 encapsulated PostScript figure
Temperature dependence of surface reconstructions of Au on Pd(110)
Surface reconstructions of Au film on Pd(110) substrate are studied using a
local Einstein approximation to quasiharmonic theory with the Sutton-Chen
interatomic potential. Temperature dependent surface free energies for
different coverages and surface structures are calculated. Experimentally
observed transformations from to and
structures can be explained in the framework of this model. Also conditions for
Stranski-Krastanov growth mode are found to comply with experiments. The domain
of validity of the model neglecting mixing entropy is analyzed.Comment: 7 pages, REVTeX two-column format, 3 postscript figures available on
request from [email protected] To appear in Phys. Rev. Letter
Electronic structure and total energy of interstitial hydrogen in iron: Tight binding models
An application of the tight binding approximation is presented for the
description of electronic structure and interatomic force in magnetic iron,
both pure and containing hydrogen impurities. We assess the simple canonical
d-band description in comparison to a non orthogonal model including s and d
bands. The transferability of our models is tested against known properties
including the segregation energies of hydrogen to vacancies and to surfaces of
iron. In many cases agreement is remarkably good, opening up the way to quantum
mechanical atomistic simulation of the effects of hydrogen on mechanical
properties
Preliminary catalog of pictures taken on the lunar surface during the Apollo 15 mission
Catalog of all pictures taken from lunar module or lunar surface during Apollo 15 missio
Transverse Double-Spin Asymmetries for Muon Pair Production in pp-Collisions
We calculate the rapidity dependence of the transverse double-spin asymmetry
for the Drell-Yan process to next-to-leading order in the strong coupling.
Input transversity distributions are obtained by saturating the Soffer
inequality at a low hadronic mass scale. Results for the polarized BNL-RHIC
proton-proton collider and the proposed HERA-N fixed-target experiment are
presented, and the influence of the limited muon acceptance of the detectors on
measurements of the asymmetry is studied in detail.Comment: 7 pages including 5 figures; significantly shortened, to be published
in Phys. Rev.
- …