203 research outputs found
Universality and its Origins at the Amorphous Solidification Transition
Systems undergoing an equilibrium phase transition from a liquid state to an
amorphous solid state exhibit certain universal characteristics. Chief among
these are the fraction of particles that are randomly localized and the scaling
functions that describe the order parameter and (equivalently) the statistical
distribution of localization lengths for these localized particles. The purpose
of this Paper is to discuss the origins and consequences of this universality,
and in doing so, three themes are explored. First, a replica-Landau-type
approach is formulated for the universality class of systems that are composed
of extended objects connected by permanent random constraints and undergo
amorphous solidification at a critical density of constraints. This formulation
generalizes the cases of randomly cross-linked and end-linked macromolecular
systems, discussed previously. The universal replica free energy is
constructed, in terms of the replica order parameter appropriate to amorphous
solidification, the value of the order parameter is obtained in the liquid and
amorphous solid states, and the chief universal characteristics are determined.
Second, the theory is reformulated in terms of the distribution of local static
density fluctuations rather than the replica order parameter. It is shown that
a suitable free energy can be constructed, depending on the distribution of
static density fluctuations, and that this formulation yields precisely the
same conclusions as the replica approach. Third, the universal predictions of
the theory are compared with the results of extensive numerical simulations of
randomly cross-linked macromolecular systems, due to Barsky and Plischke, and
excellent agreement is found.Comment: 10 pages, including 3 figures (REVTEX
One-step replica symmetry breaking solution of the quadrupolar glass model
We consider the quadrupolar glass model with infinite-range random
interaction. Introducing a simple one-step replica symmetry breaking ansatz we
investigate the para-glass continuous (discontinuous) transition which occurs
below (above) a critical value of the quadrupole dimension m*. By using a
mean-field approximation we study the stability of the one-step replica
symmetry breaking solution and show that for m>m* there are two transitions.
The thermodynamic transition is discontinuous but there is no latent heat. At a
higher temperature we find the dynamical or glass transition temperature and
the corresponding discontinuous jump of the order parameter.Comment: 10 pages, 3 figure
Elasticity near the vulcanization transition
Signatures of the vulcanization transition--amorphous solidification induced
by the random crosslinking of macromolecules--include the random localization
of a fraction of the particles and the emergence of a nonzero static shear
modulus. A semi-microscopic statistical-mechanical theory is presented of the
latter signature that accounts for both thermal fluctuations and quenched
disorder. It is found (i) that the shear modulus grows continuously from zero
at the transition, and does so with the classical exponent, i.e., with the
third power of the excess cross-link density and, quite surprisingly, (ii) that
near the transition the external stresses do not spoil the spherical symmetry
of the localization clouds of the particles.Comment: REVTEX, 5 pages. Minor change
Random solids and random solidification: What can be learned by exploring systems obeying permanent random constraints?
In many interesting physical settings, such as the vulcanization of rubber,
the introduction of permanent random constraints between the constituents of a
homogeneous fluid can cause a phase transition to a random solid state. In this
random solid state, particles are permanently but randomly localized in space,
and a rigidity to shear deformations emerges. Owing to the permanence of the
random constraints, this phase transition is an equilibrium transition, which
confers on it a simplicity (at least relative to the conventional glass
transition) in the sense that it is amenable to established techniques of
equilibrium statistical mechanics. In this Paper I shall review recent
developments in the theory of random solidification for systems obeying
permanent random constraints, with the aim of bringing to the fore the
similarities and differences between such systems and those exhibiting the
conventional glass transition. I shall also report new results, obtained in
collaboration with Weiqun Peng, on equilibrium correlations and
susceptibilities that signal the approach of the random solidification
transition, discussing the physical interpretation and values of these
quantities both at the Gaussian level of approximation and, via a
renormalization-group approach, beyond.Comment: Paper presented at the "Unifying Concepts in Glass Physics" workshop,
International Centre for Theoretical Physics, Trieste, Italy (September
15-18, 1999
On the relevance of percolation theory to the vulcanization transition
The relationship between vulcanization and percolation is explored from the
perspective of renormalized local field theory. We show rigorously that the
vulcanization and percolation correlation functions are governed by the same
Gell--Mann-Low renormalization group equation. Hence, all scaling aspects of
the vulcanization transition are reigned by the critical exponents of the
percolation universality class.Comment: 9 pages, 2 figure
Health education for musicians
Context and aims: Many musicians suffer for their art, and health is often compromised during training. The Health Promotion in Schools of Music (HPSM) project has recommended that health education should be included in core curricula, although few such courses have been evaluated to date. The aim of the study was to design, implement and evaluate a compulsory health education course at a UK conservatoire of music.
Methods: The course design was informed by a critical appraisal of the literature on musicians' health problems and their management, existing health education courses for musicians, and the HPSM recommendations. It was delivered by a team of appropriately-qualified tutors over 5 months to 104 first-year undergraduate students, and evaluated by means of questionnaires at the beginning and end of the course. Thirty-three students who had been in their first year the year before the course was introduced served as a control group, completing the questionnaire on one occasion only. Items concerned: hearing and use of hearing protection; primary outcomes including perceived knowledge and importance of the topics taught on the course; and secondary outcomes including physical and psychological health and health-promoting behaviors. The content of the essays written by the first-year students as part of their course assessment served as a guide to the topics they found most interesting and relevant.
Results: Comparatively few respondents reported using hearing protection when practicing alone, although there was some evidence of hearing loss, tinnitus, and hyperacusis. Perceived knowledge of the topics on the course, and awareness of the risks to health associated with performing music, increased, as did self-efficacy; otherwise, there were negative effects on secondary outcomes, and few differences between the intervention and control groups. The topics most frequently covered in students' essays were managing music performance anxiety, and life skills and behavior change techniques.
Conclusion: There is considerable scope for improving music students' physical and psychological health and health-related behaviors through health education, and persuading senior managers, educators and students themselves that health education can contribute to performance enhancement
Connecting the vulcanization transition to percolation
The vulcanization transition is addressed via a minimal
replica-field-theoretic model. The appropriate long-wave-length behavior of the
two- and three-point vertex functions is considered diagrammatically, to all
orders in perturbation theory, and identified with the corresponding quantities
in the Houghton-Reeve-Wallace field-theoretic approach to the percolation
critical phenomenon. Hence, it is shown that percolation theory correctly
captures the critical phenomenology of the vulcanization transition associated
with the liquid and critical states.Comment: 9 pages, 5 figure
Local superfluid densities probed via current-induced superconducting phase gradients
We have developed a superconducting phase gradiometer consisting of two
parallel DNA-templated nanowires connecting two thin-film leads. We have ramped
the cross current flowing perpendicular to the nanowires, and observed
oscillations in the lead-to-lead resistance due to cross-current-induced phase
differences. By using this gradiometer we have measured the temperature and
magnetic field dependence of the superfluid density and observed an
amplification of phase gradients caused by elastic vortex displacements. We
examine our data in light of Miller-Bardeen theory of dirty superconductors and
a microscale version of Campbell's model of field penetration.Comment: 5 pages, 6 figure
Weber blockade theory of magnetoresistance oscillations in superconducting strips
Recent experiments on the conductance of thin, narrow superconducting strips
have found periodic fluctuations, as a function of the perpendicular magnetic
field, with a period corresponding to approximately two flux quanta per strip
area [A. Johansson et al., Phys. Rev. Lett. {\bf 95}, 116805 (2005)]. We argue
that the low-energy degrees of freedom responsible for dissipation correspond
to vortex motion. Using vortex/charge duality, we show that the superconducting
strip behaves as the dual of a quantum dot, with the vortices, magnetic field,
and bias current respectively playing the roles of the electrons, gate voltage
and source-drain voltage. In the bias-current vs. magnetic-field plane, the
strip conductance displays what we term `Weber blockade' diamonds, with vortex
conductance maxima (i.e., electrical resistance maxima) that, at small
bias-currents, correspond to the fields at which strip states of and
vortices have equal energy.Comment: 4+a bit pages, 3 figures, 1 tabl
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