6,086 research outputs found
An automatic electrical distribution system
Computer controlled electric power distribution system for aerospace system
We Don’t Want to Talk About It: Communication Strategies for Teaching Less Popular Subjects
Some subjects are the unloved: the required course in academic writing, the required course in public speaking, the course in communication theory, the course in basic mathematics. This paper brings together perspectives from professors in Communication Studies, Mathematics, and Writing to consider the critical connection between communicative practice and learning, applying a networked perspective of interconnections
Strengths and Weaknesses of Parallel Tempering
Parallel tempering, also known as replica exchange Monte Carlo, is studied in
the context of two simple free energy landscapes. The first is a double well
potential defined by two macrostates separated by a barrier. The second is a
`golf course' potential defined by microstates having two possible energies
with exponentially more high energy states than low energy states. The
equilibration time for replica exchange is analyzed for both systems. For the
double well system, parallel tempering with a number of replicas that scales as
the square root of the barrier height yields exponential speedup of the
equilibration time. On the other hand, replica exchange yields only marginal
speed-up for the golf course system. For the double well system, the free
energy difference between the two wells has a large effect on the equilibration
time. Nearly degenerate wells equilibrate much more slowly than strongly
asymmetric wells. It is proposed that this difference in equilibration time may
lead to a bias in measuring overlaps in spin glasses. These examples illustrate
the strengths and weaknesses of replica exchange and may serve as a guide for
understanding and improving the method in various applications.Comment: 18 pages, 4 figures. v2: typos fixed and wording changes to improve
clarit
Oxidation and crystallization of an amorphous Zr60Al15Ni25 alloy
The amorphous ternary metallic alloy Zr60Al15Ni25 was oxidized in dry oxygen in the temperature range 310 ±C to 410 ±C. Rutherford backscattering (RBS) and cross-sectional transmission electron microscopy (TEM) studies suggest that during this treatment an amorphous layer of zirconium-aluminum-oxide is formed at the surface. Nickel was depleted in the oxide and enriched in the amorphous alloy near the interface. The oxide layer thickness grows parabolically with annealing duration, with a transport constant of 2.8 x 10^-5 m^2/s x exp(-1.7 eV/kT). The oxidation rate may be controlled by the diffusion of Ni in the amorphous alloy. At later stages of the oxidation process, precipitates of nanocrystalline ZrO2 appear in the oxide near the interface. Finally, two intermetallic phases nucleate and grow simultaneously in the alloy, one at the interface and one within the alloy. An explanation involving preferential oxidation is proposed
A proposal for a generalized canonical osp(1,2) quantization of dynamical systems with constraints
The aim of this paper is to consider a possibility of constructing for
arbitrary dynamical systems with first-class constraints a generalized
canonical quantization method based on the osp(1,2) supersymmetry principle.
This proposal can be considered as a counterpart to the osp(1,2)-covariant
Lagrangian quantization method introduced recently by Geyer, Lavrov and
M\"ulsch. The gauge dependence of Green's functions is studied. It is shown
that if the parameter m^2 of the osp(1,2) superalgebra is not equal to zero
then the vacuum functional and S-matrix depend on the gauge. In the limit the gauge independence of vacuum functional and S - matrix are restored. The
Ward identities related to the osp(1,2) symmetry are derived.Comment: Revised version. To appear in Mod.Phys.Lett.
Study of the de Almeida-Thouless line using power-law diluted one-dimensional Ising spin glasses
We test for the existence of a spin-glass phase transition, the de
Almeida-Thouless line, in an externally-applied (random) magnetic field by
performing Monte Carlo simulations on a power-law diluted one-dimensional Ising
spin glass for very large system sizes. We find that an Almeida-Thouless line
only occurs in the mean field regime, which corresponds, for a short-range spin
glass, to dimension d larger than 6.Comment: 4 pages, 2 figures, 1 tabl
A Modified Scheme of Triplectic Quantization
A modified version of triplectic quantization, first introduce by Batalin and
Martnelius, is proposed which makes use of two independent master equations,
one for the action and one for the gauge functional such that the initial
classical action also obeys that master equation.Comment: 8 page
Coordinate Singularities in Harmonically-sliced Cosmologies
Harmonic slicing has in recent years become a standard way of prescribing the
lapse function in numerical simulations of general relativity. However, as was
first noticed by Alcubierre (1997), numerical solutions generated using this
slicing condition can show pathological behaviour. In this paper, analytic and
numerical methods are used to examine harmonic slicings of Kasner and Gowdy
cosmological spacetimes. It is shown that in general the slicings are prevented
from covering the whole of the spacetimes by the appearance of coordinate
singularities. As well as limiting the maximum running times of numerical
simulations, the coordinate singularities can lead to features being produced
in numerically evolved solutions which must be distinguished from genuine
physical effects.Comment: 21 pages, REVTeX, 5 figure
Microcanonical versus Canonical Analysis of Protein Folding
The microcanonical analysis is shown to be a powerful tool to characterize
the protein folding transition and to neatly distinguish between good and bad
folders. An off-lattice model with parameter chosen to represent polymers of
these two types is used to illustrate this approach. Both canonical and
microcanonical ensembles are employed. The required calculations were performed
using parallel tempering Monte Carlo simulations. The most revealing features
of the folding transition are related to its first-order-like character,
namely, the S-bend pattern in the caloric curve, which gives rise to negative
microcanonical specific heats, and the bimodality of the energy distribution
function at the transition temperatures. Models for a good folder are shown to
be quite robust against perturbations in the interaction potential parameters.Comment: 4 pages, 4 figure
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