17,095 research outputs found
Glassy states and microphase separation in cross-linked homopolymer blends
The physical properties of blends of distinct homopolymers, cross-linked
beyond the gelation point, are addressed via a Landau approach involving a pair
of coupled order-parameter fields: one describing vulcanisation, the other
describing local phase separation. Thermal concentration fluctuations, present
at the time of cross-linking, are frozen in by cross-linking, and the structure
of the resulting glassy fluctuations is analysed at the Gaussian level in
various regimes, determined by the relative values of certain physical
length-scales. The enhancement, due to gelation, of the stability of the blend
with respect to demixing is also analysed. Beyond the corresponding stability
limit, gelation prevents complete demixing, replacing it by microphase
separation, which occurs up to a length-scale set by the rigidity of the
network, as a simple variational scheme reveals.Comment: 7 pages, 6 figure
The Cavity Approach to Parallel Dynamics of Ising Spins on a Graph
We use the cavity method to study parallel dynamics of disordered Ising
models on a graph. In particular, we derive a set of recursive equations in
single site probabilities of paths propagating along the edges of the graph.
These equations are analogous to the cavity equations for equilibrium models
and are exact on a tree. On graphs with exclusively directed edges we find an
exact expression for the stationary distribution of the spins. We present the
phase diagrams for an Ising model on an asymmetric Bethe lattice and for a
neural network with Hebbian interactions on an asymmetric scale-free graph. For
graphs with a nonzero fraction of symmetric edges the equations can be solved
for a finite number of time steps. Theoretical predictions are confirmed by
simulation results. Using a heuristic method, the cavity equations are extended
to a set of equations that determine the marginals of the stationary
distribution of Ising models on graphs with a nonzero fraction of symmetric
edges. The results of this method are discussed and compared with simulations
Early-expressed chemokines predict kidney immunopathology in experimental disseminated Candida albicans infections
Available under the Creative Commons Attribution License (CCAL)Peer reviewedPublisher PD
Symplectic quantization, inequivalent quantum theories, and Heisenberg's principle of uncertainty
We analyze the quantum dynamics of the non-relativistic two-dimensional
isotropic harmonic oscillator in Heisenberg's picture. Such a system is taken
as toy model to analyze some of the various quantum theories that can be built
from the application of Dirac's quantization rule to the various symplectic
structures recently reported for this classical system. It is pointed out that
that these quantum theories are inequivalent in the sense that the mean values
for the operators (observables) associated with the same physical classical
observable do not agree with each other. The inequivalence does not arise from
ambiguities in the ordering of operators but from the fact of having several
symplectic structures defined with respect to the same set of coordinates. It
is also shown that the uncertainty relations between the fundamental
observables depend on the particular quantum theory chosen. It is important to
emphasize that these (somehow paradoxical) results emerge from the combination
of two paradigms: Dirac's quantization rule and the usual Copenhagen
interpretation of quantum mechanics.Comment: 8 pages, LaTex file, no figures. Accepted for publication in Phys.
Rev.
Time reparametrization invariance in arbitrary range p-spin models: symmetric versus non-symmetric dynamics
We explore the existence of time reparametrization symmetry in p-spin models.
Using the Martin-Siggia-Rose generating functional, we analytically probe the
long-time dynamics. We perform a renormalization group analysis where we
systematically integrate over short timescale fluctuations. We find three
families of stable fixed points and study the symmetry of those fixed points
with respect to time reparametrizations. One of those families is composed
entirely of symmetric fixed points, which are associated with the low
temperature dynamics. The other two families are composed entirely of
non-symmetric fixed points. One of these two non-symmetric families corresponds
to the high temperature dynamics.
Time reparametrization symmetry is a continuous symmetry that is
spontaneously broken in the glass state and we argue that this gives rise to
the presence of Goldstone modes. We expect the Goldstone modes to determine the
properties of fluctuations in the glass state, in particular predicting the
presence of dynamical heterogeneity.Comment: v2: Extensively modified to discuss both high temperature
(non-symmetric) and low temperature (symmetric) renormalization group fixed
points. Now 16 pages with 1 figure. v1: 13 page
Property differences among the four major Candida albicans strain clades
Peer reviewedPublisher PD
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
Bilateral adrenalectomy for asynchronous metastases of a malignant melanoma
Indexación: Web of Science; Scielo.Clinical case: We report a 70 years old male with a history of an ear lobe melanoma with was excised seven years ago, who had a bronchial relapse and required a right pneumonectomy. During a follow up abdominal CAT scan, a 9 cm tumor in the left adrenal gland was detected. The patient was operated, performing a left adrenalectomy and nephrectomy. The pathologic study confirmed the presence of a fusocellular melanoma. One year later, a right adrenal mass was detected and excised. The pathological study of the piece again confirmed a metastasis of a malignant melanoma. The patient died due to progression of the disease, 10 years after the adrenalectomy.
Key words: Adrenal metastases, laparoscopic adrenalectomy, melanoma.Objetivo: Presentar un caso de metástasis suprarrenal bilateral asincrónica de Melanoma cutáneo tratado con adrenalectomía laparoscópica bilateral. Caso clínico: Paciente de 70 años con antecedente de melanoma del pabellón auricular extirpado 7 años antes de su consulta urológica. Posteriormente, presenta una recidiva bronquial tratada con quimioterapia, radioterapia y neumonectomía derecha. En sus exámenes de seguimiento una Tomografía computada muestra el hallazgo incidental de una lesión tumoral de 9 cm en la glándula suprarrenal izquierda. Se realizó nefrectomía y adrenalectomía izquierda laparoscópica en bloque sin incidencias. El análisis histopatológico confirmó el hallazgo de una metástasis de melanoma fuso-celular. Un año después el paciente presenta un nuevo hallazgo incidental de un tumor de 3 cm en la glándula suprarrenal derecha, la cual fue tratada con adrenalectomía laparoscópica, y cuyo análisis histopatológico demostró metástasis de melanoma maligno. El paciente fallece por progresión de su enfermedad 10 años después de su cirugía suprarrenal. Conclusiones: En los pacientes con metástasis suprarrenal de melanoma, la adrenalectomía incrementa la supervivencia cáncer especifica en relación a los pacientes tratados sin cirugía. El abordaje laparoscópico constituye una alternativa terapéutica con menor morbilidad que la cirugía abierta en cirujanos con experiencia laparoscópica.
Palabras clave: Metástasis suprarrenal, adrenalectomía laparoscópica, melanoma.http://ref.scielo.org/mymgk
Quasiparticle transport and localization in high-T_c superconductors
We present a theory of the effects of impurity scattering in d_{x^2-y^2}
superconductors and their quantum disordered counterparts, based on a
non-linear sigma model formulation. We show the existence, in a
quasi-two-dimensional system, of a novel spin-metal phase with a non-zero spin
diffusion constant at zero temperature. With decreasing inter-layer coupling,
the system undergoes a quantum phase transition (in a new universality class)
to a localized spin-insulator. Experimental implications for spin and thermal
transport in the high-temperature superconductors are discussed.Comment: 4 pages, 1 figur
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