17,593 research outputs found
On the binary codes with parameters of triply-shortened 1-perfect codes
We study properties of binary codes with parameters close to the parameters
of 1-perfect codes. An arbitrary binary code ,
i.e., a code with parameters of a triply-shortened extended Hamming code, is a
cell of an equitable partition of the -cube into six cells. An arbitrary
binary code , i.e., a code with parameters of a
triply-shortened Hamming code, is a cell of an equitable family (but not a
partition) from six cells. As a corollary, the codes and are completely
semiregular; i.e., the weight distribution of such a code depends only on the
minimal and maximal codeword weights and the code parameters. Moreover, if
is self-complementary, then it is completely regular. As an intermediate
result, we prove, in terms of distance distributions, a general criterion for a
partition of the vertices of a graph (from rather general class of graphs,
including the distance-regular graphs) to be equitable. Keywords: 1-perfect
code; triply-shortened 1-perfect code; equitable partition; perfect coloring;
weight distribution; distance distributionComment: 12 page
Characteristics of Cosmic Time
The nature of cosmic time is illuminated using Hamilton-Jacobi theory for
general relativity. For problems of interest to cosmology, one may solve for
the phase of the wavefunctional by using a line integral in superspace. Each
contour of integration corresponds to a particular choice of time hypersurface,
and each yields the same answer. In this way, one can construct a covariant
formalism where all time hypersurfaces are treated on an equal footing. Using
the method of characteristics, explicit solutions for an inflationary epoch
with several scalar fields are given. The theoretical predictions of double
inflation are compared with recent galaxy data and large angle microwave
background anisotropies.Comment: 20 pages, RevTex using Latex 2.09, Submitted to Physical Review D Two
figures included in fil
Reliability prediction in model driven development
Evaluating the implications of an architecture design early in the software development lifecycle is important in order to reduce costs of development. Reliability is an important concern with regard to the correct delivery of software
system service. Recently, the UML Profile for Modeling Quality of Service has defined a set of UML extensions to represent dependability concerns (including reliability) and other non-functional requirements in early stages of the software
development lifecycle. Our research has shown that these extensions are not comprehensive enough to support reliability analysis for model-driven software engineering,
because the description of reliability characteristics in this profile lacks support for certain dynamic aspects that are essential in modeling reliability. In this work, we define a profile for reliability analysis by extending the UML 2.0
specification to support reliability prediction based on scenario specifications. A UML model specified using the profile is translated to a labelled transition system (LTS), which is used for automated reliability prediction and identification of implied
scenarios; the results of this analysis are then fed back to the UML model. The result is a comprehensive framework for addressing software reliability modeling, including analysis and evolution of reliability predictions. We exemplify our approach using the Boiler System used in previous work and demonstrate
how reliability analysis results can be integrated into UML models
Walking and climbing service robots for safety inspection of nuclear reactor pressure vessels
Intelligent legged climbing service robot for remote maintenance applications in hazardous environments
Solving the Hamilton-Jacobi Equation for General Relativity
We demonstrate a systematic method for solving the Hamilton-Jacobi equation
for general relativity with the inclusion of matter fields. The generating
functional is expanded in a series of spatial gradients. Each term is
manifestly invariant under reparameterizations of the spatial coordinates
(``gauge-invariant''). At each order we solve the Hamiltonian constraint using
a conformal transformation of the 3-metric as well as a line integral in
superspace. This gives a recursion relation for the generating functional which
then may be solved to arbitrary order simply by functionally differentiating
previous orders. At fourth order in spatial gradients, we demonstrate solutions
for irrotational dust as well as for a scalar field. We explicitly evolve the
3-metric to the same order. This method can be used to derive the Zel'dovich
approximation for general relativity.Comment: 13 pages, RevTeX, DAMTP-R93/2
Dark energy, antimatter gravity and geometry of the Universe
This article is based on two hypotheses. The first one is the existence of
the gravitational repulsion between particles and antiparticles. Consequently,
virtual particle-antiparticle pairs in the quantum vacuum may be considered as
gravitational dipoles. The second hypothesis is that the Universe has geometry
of a four-dimensional hyper-spherical shell with thickness equal to the Compton
wavelength of a pion, which is a simple generalization of the usual geometry of
a 3-hypersphere. It is striking that these two hypotheses lead to a simple
relation for the gravitational mass density of the vacuum, which is in very
good agreement with the observed dark energy density
The Surface Region of Superfluid He as a Dilute Bose-Condensed Gas
In the low-density surface region of superfluid He, the atoms are far
apart and collisions can be ignored. The only effect of the interactions is
from the long-range attractive Hartree potential produced by the distant
high-density bulk liquid. As a result, at , all the atoms occupy the same
single-particle state in the low-density tail. Striking numerical evidence for
this 100\% surface BEC was given by Pandharipande and coworkers in 1988. We
derive a generalized Gross-Pitaevskii equation for the inhomogeneous condensate
wave function in the low-density region valid at all temperatures.
The overall amplitude of is fixed by the bulk liquid, which ensures
that it vanishes everywhere at the bulk transition temperature.Comment: 6 pages, paper submitted to Low Temperature Conference (LT21),
Prague, Aug., 1996; to appear in proceeding
Tele-operated climbing and mobile service robots for remote inspection and maintenance in nuclear industry
Feshbach resonances in a quasi-2D atomic gas
Strongly confining an ultracold atomic gas in one direction to create a
quasi-2D system alters the scattering properties of this gas. We investigate
the effects of confinement on Feshbach scattering resonances and show that
strong confinement results in a shift in the position of the Feshbach resonance
as a function of the magnetic field. This shift, as well as the change of the
width of the resonance, are computed. We find that the resonance is strongly
damped in the thermal gas, but in the condensate the resonance remains sharp
due to many-body effects. We introduce a 2D model system, suited for the study
of resonant superfluidity, and having the same scattering properties as the
tightly confined real system near a Feshbach resonance. Exact relations are
derived between measurable quantities and the model parameters.Comment: 8 pages, 2 figure
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