61,262 research outputs found
Fractal Droplets in Two Dimensional Spin Glasses
The two-dimensional Edwards-Anderson model with Gaussian bond distribution is
investigated at T=0 with a numerical method. Droplet excitations are directly
observed. It turns out that the averaged volume of droplets is proportional to
l^D with D = 1.80(2) where l is the spanning length of droplets, revealing
their fractal nature. The exponent characterizing the l dependence of the
droplet excitation energy is estimated to be -0.42(4), clearly different from
the stiffness exponent for domain wall excitations.Comment: 4 pages 4 figure
Stability of Elastic Glass Phases in Random Field XY Magnets and Vortex Lattices in Type II Superconductors
A description of a dislocation-free elastic glass phase in terms of domain
walls is developed and used as the basis of a renormalization group analysis of
the energetics of dislocation loops added to the system. It is found that even
after optimizing over possible paths of large dislocation loops, their energy
is still very likely to be positive when the dislocation core energy is large.
This implies the existence of an equilibrium elastic glass phase in three
dimensional random field X-Y magnets, and a dislocation free,
bond-orientationally ordered ``Bragg glass'' phase of vortices in dirty Type II
superconductors.Comment: 12 pages, Revtex, no figures, submitted to Phys Rev Letter
A survey of quality measures for gray-scale image compression
Although a variety of techniques are available today for gray-scale image compression, a complete evaluation of these techniques cannot be made as there is no single reliable objective criterion for measuring the error in compressed images. The traditional subjective criteria are burdensome, and usually inaccurate or inconsistent. On the other hand, being the most common objective criterion, the mean square error (MSE) does not have a good correlation with the viewer's response. It is now understood that in order to have a reliable quality measure, a representative model of the complex human visual system is required. In this paper, we survey and give a classification of the criteria for the evaluation of monochrome image quality
Graphene integer quantum Hall effect in the ferromagnetic and paramagnetic regimes
Starting from the graphene lattice tight-binding Hamiltonian with an on-site
U and long-range Coulomb repulsion, we derive an interacting continuum Dirac
theory governing the low-energy behavior of graphene in an applied magnetic
field. Initially, we consider a clean graphene system within this effective
theory and explore integer quantum Hall ferromagnetism stabilized by exchange
from the long-range Coulomb repulsion. We study in detail the ground state and
excitations at nu = 0 and nu = \pm 1, taking into account small
symmetry-breaking terms that arise from the lattice-scale interactions, and
also explore the ground states selected at nu = \pm 3, \pm 4, and \pm 5. We
argue that the ferromagnetic regime may not yet be realized in current
experimental samples, which at the above filling factors perhaps remain
paramagnetic due to strong disorder. In an attempt to access the latter regime
where the role of exchange is strongly suppressed by disorder, we apply Hartree
theory to study the effects of interactions. Here, we find that Zeeman
splitting together with symmetry-breaking interactions can in principle produce
integer quantum Hall states in a paramagnetic system at nu = 0, \pm 1 and \pm
4, but not at nu = \pm 3 or \pm 5, consistent with recent experiments in high
magnetic fields. We make predictions for the activation energies in these
quantum Hall states which will be useful for determining their true origin.Comment: 13 pages, 2 figure
The effects of sensory deprivation on sensory, perceptual, motor, cognitive, and physiological functions
Sensory deprivation effects on human sensory, perceptual, and physiological mechanism
Adaptation to visual and nonvisual rearrangement
Role of informational feedback in producing visual adaptation to visual rearrangement and to various head, eye, and arm position
Density of Yang-Lee zeros for the Ising ferromagnet
The densities of Yang-Lee zeros for the Ising ferromagnet on the
square lattice are evaluated from the exact grand partition functions
(). The properties of the density of Yang-Lee zeros are discussed as
a function of temperature and system size . The three different classes
of phase transitions for the Ising ferromagnet, first-order phase transition,
second-order phase transition, and Yang-Lee edge singularity, are clearly
distinguished by estimating the magnetic scaling exponent from the
densities of zeros for finite-size systems. The divergence of the density of
zeros at Yang-Lee edge in high temperatures (Yang-Lee edge singularity), which
has been detected only by the series expansion until now for the square-lattice
Ising ferromagnet, is obtained from the finite-size data. The identification of
the orders of phase transitions in small systems is also discussed using the
density of Yang-Lee zeros.Comment: to appear in Physical Review
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