84 research outputs found
Crystallization of a supercooled liquid and of a glass - Ising model approach
Using Monte Carlo simulations we study crystallization in the
three-dimensional Ising model with four-spin interaction. We monitor the
morphology of crystals which grow after placing crystallization seeds in a
supercooled liquid. Defects in such crystals constitute an intricate and very
stable network which separate various domains by tensionless domain walls. We
also show that the crystallization which occurs during the continuous heating
of the glassy phase takes place at a heating-rate dependent temperature.Comment: 7 page
Rings and rigidity transitions in network glasses
Three elastic phases of covalent networks, (I) floppy, (II) isostatically
rigid and (III) stressed-rigid have now been identified in glasses at specific
degrees of cross-linking (or chemical composition) both in theory and
experiments. Here we use size-increasing cluster combinatorics and constraint
counting algorithms to study analytically possible consequences of
self-organization. In the presence of small rings that can be locally I, II or
III, we obtain two transitions instead of the previously reported single
percolative transition at the mean coordination number , one from a
floppy to an isostatic rigid phase, and a second one from an isostatic to a
stressed rigid phase. The width of the intermediate phase and the
order of the phase transitions depend on the nature of medium range order
(relative ring fractions). We compare the results to the Group IV
chalcogenides, such as Ge-Se and Si-Se, for which evidence of an intermediate
phase has been obtained, and for which estimates of ring fractions can be made
from structures of high T crystalline phases.Comment: 29 pages, revtex, 7 eps figure
Non-Equilibrium Bose-Einstein Condensates, Dynamical Scaling and Symmetric Evolution in large N Phi^4 theory
We analyze the non-equilibrium dynamics of the O(N) Phi^4 model in the large
N limit and for states of large energy density. The dynamics is dramatically
different when the energy density is above the top of the tree level potential
V_0 than when it is below it.When the energy density is below V_0, we find that
non-perturbative particle production through spinodal instabilities provides a
dynamical mechanism for the Maxwell construction. The asymptotic values of the
order parameter only depend on the initial energy density and all values
between the minima of the tree level potential are available, the asymptotic
dynamical `effective potential' is flat between the minima. When the energy
density is larger than V_0, the evolution samples ergodically the broken
symmetry states, as a consequence of non-perturbative particle production via
parametric amplification. Furthermore, we examine the quantum dynamics of phase
ordering into the broken symmetry phase and find novel scaling behavior of the
correlation function. There is a crossover in the dynamical correlation length
at a time scale t_s \sim \ln(1/lambda). For t < t_s the dynamical correlation
length \xi(t) \propto \sqrt{t} and the evolution is dominated by spinodal
instabilities, whereas for t>t_s the evolution is non-linear and dominated by
the onset of non-equilibrium Bose-Einstein condensation of long-wavelength
Goldstone bosons.In this regime a true scaling solution emerges with a non-
perturbative anomalous scaling length dimension z=1/2 and a dynamical
correlation length \xi(t) \propto (t-t_s). The equal time correlation function
in this scaling regime vanishes for r>2(t-t_s) by causality. For t > t_s the
equal time correlation function falls of as 1/r. A semiclassical but stochastic
description emerges for time scales t > t_s.Comment: Minor improvements, to appear in Phys. Rev. D. Latex file, 48 pages,
12 .ps figure
Government-sponsored immigration into South Australia 1872-86
Thesis (M.A.)--University of Adelaide, [1961
Design of brick diaphram walls
SIGLELD:f84/0023 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Interface of inference models with concept and medical record models
Abstract. Medical information systems and standards are increasingly based on principled models of at least three distinct sorts of information – patient data, concepts (terminology), and guidelines (decision support). Well defined interfaces are required between the three types of model to allow development to proceed independently. Two of the major issues to be dealt with in the defining of such interfaces are the interaction between ontological and inferential abstractions – how general notions such as ‘abnormal cardiovascular finding ’ are abstracted from concrete data – and the management of the meaning of information in guidelines in different contexts. This paper explores these two issues and their ramifications. 1
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