5,110 research outputs found
Noise enhanced spontaneous chaos in semiconductor superlattices at room temperature
Physical systems exhibiting fast spontaneous chaotic oscillations are used to
generate high-quality true random sequences in random number generators. The
concept of using fast practical entropy sources to produce true random
sequences is crucial to make storage and transfer of data more secure at very
high speeds. While the first high-speed devices were chaotic semiconductor
lasers, the discovery of spontaneous chaos in semiconductor superlattices at
room temperature provides a valuable nanotechnology alternative. Spontaneous
chaos was observed in 1996 experiments at temperatures below liquid nitrogen.
Here we show spontaneous chaos at room temperature appears in idealized
superlattices for voltage ranges where sharp transitions between different
oscillation modes occur. Internal and external noises broaden these voltage
ranges and enhance the sensitivity to initial conditions in the superlattice
snail-shaped chaotic attractor thereby rendering spontaneous chaos more robust.Comment: 6 pages, 4 figures, revte
Backward error analysis for multisymplectic discretizations of Hamiltonian PDEs
Several recently developed multisymplectic schemes for Hamiltonian PDEs have
been shown to preserve associated local conservation laws and constraints very
well in long time numerical simulations. Backward error analysis for PDEs, or
the method of modified equations, is a useful technique for studying the
qualitative behavior of a discretization and provides insight into the
preservation properties of the scheme. In this paper we initiate a backward
error analysis for PDE discretizations, in particular of multisymplectic box
schemes for the nonlinear Schrodinger equation. We show that the associated
modified differential equations are also multisymplectic and derive the
modified conservation laws which are satisfied to higher order by the numerical
solution. Higher order preservation of the modified local conservation laws is
verified numerically.Comment: 12 pages, 6 figures, accepted Math. and Comp. Simul., May 200
Gluon structure function for deeply inelastic scattering with nucleus in QCD
In this talk we present the first calculation of the gluon structure function
for nucleus in QCD. We discuss the Glauber formula for the gluon structure
function and the violation of this simple approach that we anticipate in QCD.
(Talk given by E. Levin at QCD and nuclear target session at the Workshop on
Deep Inelastic Scattering and QCD, Paris, April 1995).Comment: 10 pages(latex file),4 fig (eps.files
Spin wave vortex from the scattering on Bloch point solitons
The interaction of a spin wave with a stationary Bloch point is studied. The
topological non-trivial structure of the Bloch point manifests in the
propagation of spin waves endowing them with a gauge potential that resembles
the one associated with the interaction of a magnetic monopole and an electron.
By pursuing this analogy, we are led to the conclusion that the scattering of
spin waves and Bloch points is accompanied by the creation of a magnon vortex.
Interference between such a vortex and a plane wave leads to dislocations in
the interference pattern that can be measurable by means of magnon holography
Effect of debris size on the tribological performance of thermally sprayed coatings
This research aims to assess the effect of the debris particle size on the tribological performance
and lubrication regime parameters of a Ni-based alloy coating. This is a key industrial problem,
and its resolution can contribute to better machine endurance and proper maintenance.
The debris particles are simulated by hard Al2O3 particles of size ranging from nanometers to 45
ÎŒm and dispersed in an oil lubricant. The coating studied is NiCrBSi deposited by flame spraying
technique followed by the Surface Flame Melting (SFM) process. The counterpart disk sample
was fabricated from quenched and tempered F-5220 steel (in line with A681(O1) ASTM). This
pair was tested under linear sliding contact.
Our results show that the addition of alumina particles contributes to a significant increase in
wear, particularly for the largest particles (micrometric size). In the case of micrometric particles,
it is possible to observe the formation of higher surface roughness, numerous microgrooves, and
plastic flow of NiCrBSi coating perpendicular to the sliding direction, resulting in higher loss of
volume.
It was found that the actual surface roughness (obtained as a function of the debris particle size)
allows better identification and prediction of the lubrication regime for wear processes instead of
the traditional approach that uses the initial surface roughness as a parameter
- âŠ