19,893 research outputs found
Designing with Ada for satellite simulation: A case study
A FORTRAN oriented and an Ada oriented design for the same system are compared to learn whether an essentially different design was produced using Ada. The designs were produced by an experiment that involves the parallel development of software for a spacecraft dynamics simulator. Design differences are identified in the use of abstractions, system structure, and simulator operations. Although the designs were vastly different, this result may be influenced by some special characteristics discussed
Field-induced structure transformation in electrorheological solids
We have computed the local electric field in a body-centered tetragonal (BCT)
lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to
examine the effects of a structure transformation on the local field strength.
For the ground state of an electrorheological solid of hard spheres, we
identified a novel structure transformation from the BCT to the face-centered
cubic (FCC) lattices by changing the uniaxial lattice constant c under the hard
sphere constraint. In contrast to the previous results, the local field
exhibits a non-monotonic transition from BCT to FCC. As c increases from the
BCT ground state, the local field initially decreases rapidly towards the
isotropic value at the body-centered cubic lattice, decreases further, reaching
a minimum value and increases, passing through the isotropic value again at an
intermediate lattice, reaches a maximum value and finally decreases to the FCC
value. An experimental realization of the structure transformation is
suggested. Moreover, the change in the local field can lead to a generalized
Clausius-Mossotti equation for the BCT lattices.Comment: Submitted to Phys. Rev.
Designing with Ada for satellite simulation: A case study
A FORTRAN-operated and an Ada-oriented design for the same system are compared to learn whether an essentially different design was produced using Ada. The designs were produced by an experiment that involves the parallel development of software for a spacecraft dynamics simulator. Design differences are identified in the use of abstractions, system structure, and simulator operations. Although the designs were significantly different, this result may be influenced by some special characteristics discussed
Similarity transformations approach for a generalized Fokker-Planck equation
By using similarity transformations approach, the exact propagator for a
generalized one-dimensional Fokker-Planck equation, with linear drift force and
space-time dependent diffusion coefficient, is obtained. The method is simple
and enables us to recover and generalize special cases studied through the Lie
algebraic approach and the Green function technique.Comment: 8 pages, no figure
Separately contacted electron-hole double layer in a GaAs/AlxGa1âxAs heterostructure
We describe a method for creating closely spaced parallel two-dimensional electron and hole gases confined in 200 Ă
GaAs wells separated by a 200 Ă
wide AlxGa1âxAs barrier. Low-temperature ohmic contacts are made to both the electrons and holes, whose densities are individually adjustable between 10^(10)/cm^2 to greater than 10^(11)/cm^2
Orbital magnetism in axially deformed sodium clusters: From scissors mode to dia-para magnetic anisotropy
Low-energy orbital magnetic dipole excitations, known as scissors mode (SM),
are studied in alkali metal clusters. Subsequent dynamic and static effects are
explored. The treatment is based on a self-consistent microscopic approach
using the jellium approximation for the ionic background and the Kohn-Sham mean
field for the electrons. The microscopic origin of SM and its main features
(structure of the mode in light and medium clusters, separation into low- and
high-energy plasmons, coupling high-energy M1 scissors and E2 quadrupole
plasmons, contributions of shape isomers, etc) are discussed. The scissors M1
strength acquires large values with increasing cluster size. The mode is
responsible for the van Vleck paramagnetism of spin-saturated clusters. Quantum
shell effects induce a fragile interplay between Langevin diamagnetism and van
Vleck paramagnetism and lead to a remarkable dia-para anisotropy in magnetic
susceptibility of particular light clusters. Finally, several routes for
observing the SM experimentally are discussed.Comment: 21 pages, 7 figure
Concurrence in arbitrary dimensions
We argue that a complete characterisation of quantum correlations in
bipartite systems of many dimensions may require a quantity which, even for
pure states, does not reduce to a single number. Subsequently, we introduce
multi-dimensional generalizations of concurrence and find evidence that they
may provide useful tools for the analysis of quantum correlations in mixed
bipartite states. We also introudce {\it biconcurrence} that leads to a
necessary and sufficient condition for separability.Comment: RevTeX 7 page
Responsible Oversight of Human Stem Cell Research: The California Institute for Regenerative Medicine's Medical and Ethical Standards
California voters recently approved $3 billion over 10 years for public funding of stem cell research through the California Institute for Regenerative Medicine (CIRM). Geoffrey Lomax and colleagues discuss the principles that guided the CIRM regulations
Nonlinear ac response of anisotropic composites
When a suspension consisting of dielectric particles having nonlinear
characteristics is subjected to a sinusoidal (ac) field, the electrical
response will in general consist of ac fields at frequencies of the
higher-order harmonics. These ac responses will also be anisotropic. In this
work, a self-consistent formalism has been employed to compute the induced
dipole moment for suspensions in which the suspended particles have nonlinear
characteristics, in an attempt to investigate the anisotropy in the ac
response. The results showed that the harmonics of the induced dipole moment
and the local electric field are both increased as the anisotropy increases for
the longitudinal field case, while the harmonics are decreased as the
anisotropy increases for the transverse field case. These results are
qualitatively understood with the spectral representation. Thus, by measuring
the ac responses both parallel and perpendicular to the uniaxial anisotropic
axis of the field-induced structures, it is possible to perform a real-time
monitoring of the field-induced aggregation process.Comment: 14 pages and 4 eps figure
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