26,403 research outputs found
Linear force and moment equations for an annular smooth shaft seal perturbed both angularly and laterally
Coefficients are derived for equations expressing the lateral force and pitching moments associated with both planar translation and angular perturbations from a nominally centered rotating shaft with respect to a stationary seal. The coefficients for the lowest order and first derivative terms emerge as being significant and are of approximately the same order of magnitude as the fundamental coefficients derived by means of Black's equations. Second derivative, shear perturbation, and entrance coefficient variation effects are adjudged to be small
About the screening of the charge of a proton migrating in a metal
The amount of screening of a proton in a metal, migrating under the influence
of an applied electric field, is calculated using different theoretical
formulations. First the lowest order screening expression derived by Sham
(1975) is evaluated. In addition 'exact' expressions are evaluated which were
derived according to different approaches. For a proton in a metal modeled as a
jellium the screening appears to be 15 +/- 10 %, which is neither negligible
not reconcilable with the controversial full-screening point of view of
Bosvieux and Friedel (1962). In reconsidering the theory of electromigration, a
new simplified linear-response expression for the driving force is shown to
lead to essentially the same result as found by Sorbello (1985), who has used a
rather complicated technique. The expressions allow for a reduction such that
only the scattering phase shifts of the migrating impurity are required.
Finally it is shown that the starting formula for the driving force of Bosvieux
and Friedel leads exactly to the zero-temperature limit of well-established
linear response descriptions, by which the sting of the controversy has been
removed.Comment: 14 pages, 5 figure
Achievable efficiencies for probabilistically cloning the states
We present an example of quantum computational tasks whose performance is
enhanced if we distribute quantum information using quantum cloning.
Furthermore we give achievable efficiencies for probabilistic cloning the
quantum states used in implemented tasks for which cloning provides some
enhancement in performance.Comment: 9 pages, 8 figure
Hybridising heuristics within an estimation distribution algorithm for examination timetabling
This paper presents a hybrid hyper-heuristic approach based on estimation distribution algorithms. The main motivation is to raise the level of generality for search methodologies. The objective of the hyper-heuristic is to produce solutions of acceptable quality for a number of optimisation problems. In this work, we demonstrate the generality through experimental results for different variants of exam timetabling problems. The hyper-heuristic represents an automated constructive method that searches for heuristic choices from a given set of low-level heuristics based only on non-domain-specific knowledge. The high-level search methodology is based on a simple estimation distribution algorithm. It is capable of guiding the search to select appropriate heuristics in different problem solving situations. The probability distribution of low-level heuristics at different stages of solution construction can be used to measure their effectiveness and possibly help to facilitate more intelligent hyper-heuristic search methods
Towards designing robust coupled networks
Natural and technological interdependent systems have been shown to be highly
vulnerable due to cascading failures and an abrupt collapse of global
connectivity under initial failure. Mitigating the risk by partial
disconnection endangers their functionality. Here we propose a systematic
strategy of selecting a minimum number of autonomous nodes that guarantee a
smooth transition in robustness. Our method which is based on betweenness is
tested on various examples including the famous 2003 electrical blackout of
Italy. We show that, with this strategy, the necessary number of autonomous
nodes can be reduced by a factor of five compared to a random choice. We also
find that the transition to abrupt collapse follows tricritical scaling
characterized by a set of exponents which is independent on the protection
strategy
Resistivity due to low-symmetrical defects in metals
The impurity resistivity, also known as the residual resistivity, is
calculated ab initio using multiple-scattering theory. The mean-free path is
calculated by solving the Boltzmann equation iteratively. The resistivity due
to low-symmetrical defects, such as an impurity-vacancy pair, is calculated for
the FCC host metals Al and Ag and the BCC transition metal V. Commonly, 1/f
noise is attributed to the motion of such defects in a diffusion process.Comment: 24 pages in REVTEX-preprint format, 10 Postscript figures. Phys. Rev.
B, vol. 57 (1998), accepted for publicatio
Iterative maximum-likelihood reconstruction in quantum homodyne tomography
I propose an iterative expectation maximization algorithm for reconstructing
a quantum optical ensemble from a set of balanced homodyne measurements
performed on an optical state. The algorithm applies directly to the acquired
data, bypassing the intermediate step of calculating marginal distributions.
The advantages of the new method are made manifest by comparing it with the
traditional inverse Radon transformation technique
Mass hierarchy, 2-3 mixing and CP-phase with Huge Atmospheric Neutrino Detectors
We explore the physics potential of multi-megaton scale ice or water
Cherenkov detectors with low ( GeV) threshold. Using some proposed
characteristics of the PINGU detector setup we compute the distributions of
events versus neutrino energy and zenith angle , and study
their dependence on yet unknown neutrino parameters. The
regions are identified where the distributions have the highest sensitivity to
the neutrino mass hierarchy, to the deviation of the 2-3 mixing from the
maximal one and to the CP-phase. We evaluate significance of the measurements
of the neutrino parameters and explore dependence of this significance on the
accuracy of reconstruction of the neutrino energy and direction. The effect of
degeneracy of the parameters on the sensitivities is also discussed. We
estimate the characteristics of future detectors (energy and angle resolution,
volume, etc.) required for establishing the neutrino mass hierarchy with high
confidence level. We find that the hierarchy can be identified at --
level (depending on the reconstruction accuracies) after 5 years of
PINGU operation.Comment: 39 pages, 21 figures. Description of Fig.3 correcte
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