13,477 research outputs found
An analysis of the noise reduction of orthotropic cylindrical shells Final report
Statistical energy and classical methods for calculating noise reduction of orthotropic cylindrical shell
Comment on ``Structure of exotic nuclei and superheavy elements in a relativistic shell model''
A recent paper [M. Rashdan, Phys. Rev. C 63, 044303 (2001)] introduces the
new parameterization NL-RA1 of the relativistic mean-field model which is
claimed to give a better description of nuclear properties than earlier ones.
Using this model ^{298}114 is predicted to be a doubly-magic nucleus. As will
be shown in this comment these findings are to be doubted as they are obtained
with an unrealistic parameterization of the pairing interaction and neglecting
ground-state deformation.Comment: 2 pages REVTEX, 3 figures, submitted to comment section of Phys. Rev.
C. shortened and revised versio
Vector Casimir effect for a D-dimensional sphere
The Casimir energy or stress due to modes in a D-dimensional volume subject
to TM (mixed) boundary conditions on a bounding spherical surface is
calculated. Both interior and exterior modes are included. Together with
earlier results found for scalar modes (TE modes), this gives the Casimir
effect for fluctuating ``electromagnetic'' (vector) fields inside and outside a
spherical shell. Known results for three dimensions, first found by Boyer, are
reproduced. Qualitatively, the results for TM modes are similar to those for
scalar modes: Poles occur in the stress at positive even dimensions, and cusps
(logarithmic singularities) occur for integer dimensions . Particular
attention is given the interesting case of D=2.Comment: 20 pages, 1 figure, REVTe
Simulation of granular soil behaviour using the bullet physics library
A physics engine is computer software which provides a simulation of certain physical systems, such as rigid body dynamics, soft body dynamics and fluid dynamics. Physics engines were firstly developed for using in animation and gaming industry ; nevertheless, due to fast calculation speed they are attracting more and more attetion from researchers of the engineering fields. Since physics engines are capable of performing fast calculations on multibody rigid dynamic systems, soil particles can be modeled as distinct rigid bodies. However, up to date, it is not clear to what extent they perform accurately in modeling soil behaviour from a geotechnical viewpoint. To investigate this, examples of pluviation and vibration-induced desification were simulated using the physics engine called Bullet physics library. In order to create soil samples, first, randomly shaped polyhedrons, representing gravels, were generated using the Voronoi tessellation approach. Then, particles were pluviated through a funnel into a cylinder. Once the soil particles settled in a static state, the cylinder was subjected to horizontal sinusoidal vibration for a period of 20 seconds. The same procedure for sample perparation was performed in the laboratory. The results of pluviation and vibration tests weere recorded and compared to those of simulations. A good agreement has been found between the results of simulations and laboratory tests. The findings in this study reinforce the idea that physics engines can be employed as a geotechnical engineering simulation tool
Quasi-Local Formulation of Non-Abelian Finite-Element Gauge Theory
Recently it was shown how to formulate the finite-element equations of motion
of a non-Abelian gauge theory, by gauging the free lattice difference
equations, and simultaneously determining the form of the gauge
transformations. In particular, the gauge-covariant field strength was
explicitly constructed, locally, in terms of a path ordered product of
exponentials (link operators). On the other hand, the Dirac and Yang-Mills
equations were nonlocal, involving sums over the entire prior lattice. Earlier,
Matsuyama had proposed a local Dirac equation constructed from just the
above-mentioned link operators. Here, we show how his scheme, which is closely
related to our earlier one, can be implemented for a non-Abelian gauge theory.
Although both Dirac and Yang-Mills equations are now local, the field strength
is not. The technique is illustrated with a direct calculation of the current
anomalies in two and four space-time dimensions. Unfortunately, unlike the
original finite-element proposal, this scheme is in general nonunitary.Comment: 19 pages, REVTeX, no figure
Cross-Document Pattern Matching
We study a new variant of the string matching problem called cross-document
string matching, which is the problem of indexing a collection of documents to
support an efficient search for a pattern in a selected document, where the
pattern itself is a substring of another document. Several variants of this
problem are considered, and efficient linear-space solutions are proposed with
query time bounds that either do not depend at all on the pattern size or
depend on it in a very limited way (doubly logarithmic). As a side result, we
propose an improved solution to the weighted level ancestor problem
Dismissal protection and worker flows in small establishments
"Based on a large employer-employee matched data set, the paper investigates the effects of variable enforcement of German dismissal protection legislation on the employment dynamics in small establishments. Specifically, using a difference-in-differences approach, we study the effect of changes in the threshold scale exempting small establishments from dismissal protection provisions on worker flows. In contrast to the predictions of the theory, our results indicate that there are no statistically significant effects of the dismissal protection legislation on worker turnover." (Author's abstract, IAB-Doku) ((en))Kleinbetrieb, Kündigungsschutz, IAB-Linked-Employer-Employee-Datensatz, zwischenbetriebliche Mobilität
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