1,107 research outputs found
Energy landscape picture of supercooled liquids: Application of a generalized random energy model
The thermodynamic and kinetic anomalies of supercooled liquids are analyzed
from the perspective of energy landscapes. A mean field model, a generalized
random energy model of liquids is developed, which exhibits a dynamical
transition of the onset of slow dynamics at T_0, alteration of the nature of
motion from the saddle-to-saddle to minimum-to-minimum motion at T_c, and an
ideal glass transition at T_k. If the energy spectrum of the configurations has
a low energy tail, the model also allows a thermodynamic liquid-liquid
transition at T_l. The liquid-liquid transition of the model is correlated to
the kinetic fragile-strong transition accompanied by the anomalous slowing down
of motion. Fragility of the system is classified in terms of features of the
energy landscape such as ruggedness of the potential energy surface, size of
the cooperative motion invoked in a transition from one configuration to
another, and energy needed to deform the local structure in the cooperative
motion. A simple relation is found between diffusion constant, D and the saddle
index of the potential energy surface, f, as , where a depends
on the size of the cooperative motion.Comment: to appear in J. Chem. Phy
The fluctuation spectra around a Gaussian classical solution of a tensor model and the general relativity
Tensor models can be interpreted as theory of dynamical fuzzy spaces. In this
paper, I study numerically the fluctuation spectra around a Gaussian classical
solution of a tensor model, which represents a fuzzy flat space in arbitrary
dimensions. It is found that the momentum distribution of the low-lying
low-momentum spectra is in agreement with that of the metric tensor modulo the
general coordinate transformation in the general relativity at least in the
dimensions studied numerically, i.e. one to four dimensions. This result
suggests that the effective field theory around the solution is described in a
similar manner as the general relativity.Comment: 29 pages, 13 figure
Shear viscosity of a highly excited string and the black hole membrane paradigm
Black hole membrane paradigm states that a certain viscous membrane seems to
be sitting on a stretched horizon of a black hole from the viewpoint of a
distant observer. We show that the shear viscosity of the fictitious membrane
can be reproduced by a highly excited string covering the stretched horizon
except for a numerical coefficient.Comment: 22 pages, no figure, minor correction
The lowest modes around Gaussian solutions of tensor models and the general relativity
In the previous paper, the number distribution of the low-lying spectra
around Gaussian solutions representing various dimensional fuzzy tori of a
tensor model was numerically shown to be in accordance with the general
relativity on tori. In this paper, I perform more detailed numerical analysis
of the properties of the modes for two-dimensional fuzzy tori, and obtain
conclusive evidences for the agreement. Under a proposed correspondence between
the rank-three tensor in tensor models and the metric tensor in the general
relativity, conclusive agreement is obtained between the profiles of the
low-lying modes in a tensor model and the metric modes transverse to the
general coordinate transformation. Moreover, the low-lying modes are shown to
be well on a massless trajectory with quartic momentum dependence in the tensor
model. This is in agreement with that the lowest momentum dependence of metric
fluctuations in the general relativity will come from the R^2-term, since the
R-term is topological in two dimensions. These evidences support the idea that
the low-lying low-momentum dynamics around the Gaussian solutions of tensor
models is described by the general relativity. I also propose a renormalization
procedure for tensor models. A classical application of the procedure makes the
patterns of the low-lying spectra drastically clearer, and suggests also the
existence of massive trajectories.Comment: 31 pages, 8 figures, Added references, minor corrections, a
misleading figure replace
Phonon Dynamics and Multipolar Isomorphic Transition in beta-pyrochlore KOs2O6
We investigate with a microscopic model anharmonic K-cation oscillation
observed by neutron experiments in beta-pyrochlore superconductor KOs2O6, which
also shows a mysterious first-order structural transition at Tp=7.5 K. We have
identified a set of microscopic model parameters that successfully reproduce
the observed temperature dependence and the superconducting transition
temperature. Considering changes in the parameters at Tp, we can explain
puzzling experimental results about electron-phonon coupling and neutron data.
Our analysis demonstrates that the first-order transition is multipolar
transition driven by the octupolar component of K-cation oscillations. The
octupole moment does not change the symmetry and is characteristic to
noncentrosymmetric K-cation potential.Comment: 5 pages, 4 figures, submitted to J. Phys. Soc. Jp
Matrix models and QCD with chemical potential
The Random Matrix Model approach to Quantum Chromodynamics (QCD) with non-vanishing chemical potential is reviewed. The general concept using global symmetries is introduced, as well as its relation to field theory, the so-called epsilon regime of chiral Perturbation Theory (echPT). Two types of Matrix Model results are distinguished: phenomenological applications leading to phase diagrams, and an exact limit of the QCD Dirac operator spectrum matching with echPT. All known analytic results for the spectrum of complex and symplectic Matrix Models with chemical potential are summarised for the symmetry classes of ordinary and adjoint QCD, respectively. These include correlation functions of Dirac operator eigenvalues in the complex plane for real chemical potential, and in the real plane for imaginary isospin chemical potential. Comparisons of these predictions to recent Lattice simulations are also discussed
Physics of the liquid-liquid critical point
Within the inherent structure (IS) thermodynamic formalism introduced by
Stillinger and Weber [F. H. Stillinger and T. A. Weber, Phys. Rev. A {\bf 25},
978 (1982)] we address the basic question of the physics of the liquid-liquid
transition and of density maxima observed in some complex liquids such as water
by identifying, for the first time, the statistical properties of the potential
energy landscape (PEL) responsible for these anomalies.
We also provide evidence of the connection between density anomalies and the
liquid-liquid critical point. Within the simple (and physically transparent)
model discussed, density anomalies do imply the existence of a liquid-liquid
transition.Comment: Physical Review Letters, in publicatio
Swimming depth of migrating silver eels Anguilla japonica released at seamounts of the West Mariana Ridge, their estimated spawning sites
Five hormone-treated female Japanese silver eels Anguilla japonica were tagged with ultrasonic transmitters and released by submersible in the West Pacific at seamounts of the West Mariana Ridge, their supposed spawning grounds. Four eels were tracked for 60 to 423 min in the vicinity of the seamounts. They did not settle at the seamounts but swam at a mean speed of 0.37 m s-1 into open water above deep ground. Their mean swimming depth ranged from 81 to 172 m. Experiments suggest that pre-matured A. japonica migrate to their spawning grounds in temperate warm water and at shallow depths
A Possible Phase Transition in beta-pyrochlore Compounds
We investigate a lattice of interacting anharmonic oscillators by using a
mean field theory and exact diagonalization. We construct an effective
five-state hopping model with intersite repulsions as a model for
beta-pyrochlore AOs_2O_6(A=K, Rb or Cs). We obtain the first order phase
transition line from large to small oscillation amplitude phases as temperature
decreases. We also discuss the possibility of a phase with local electric
polarizations. Our theory can explain the origin of the mysterious first order
transition in KOs_2O_6.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Design Equation: A Novel Approach to Heteropolymer Design
A novel approach to heteropolymer design is proposed. It is based on the
criterion by Kurosky and Deutsch, with which the probability of a target
conformation in a conformation space is maximized at low but finite
temperature. The key feature of the proposed approach is the use of soft spins
(fuzzy monomers) that leads to a design equation, which is an analog of the
Boltzmann machine learning equation in the design problem. We implement an
algorithm based on the design equation for the generalized HP model on the
3x3x3 cubic lattice and check its performance.Comment: 7 pages, 3 tables, 1 figures, uses jpsj.sty, jpsjbs1.sty, epsf.sty,
Submitted to J. Phys. Soc. Jp
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