53,045 research outputs found
Influence of quantum confinement on the ferromagnetism of (Ga,Mn)As diluted magnetic semiconductor
We investigate the effect of quantum confinement on the ferromagnetism of
diluted magnetic semiconductor GaMnAs using a combination of
tight-binding and density functional methods. We observe strong majority-spin
Mn -As hybridization, as well as half metallic behavior, down to sizes
as small as 20 \AA in diameter. Below this critical size, the doped holes are
self-trapped by the Mn-sites, signalling both valence and electronic
transitions. Our results imply that magnetically doped III-V nanoparticles will
provide a medium for manipulating the electronic structure of dilute magnetic
semiconductors while conserving the ferromagnetic properties and even enhancing
it in certain size regime.Comment: 4 pages, 3 figure
Beyond the constraints underlying Kolmogorov-Johnson-Mehl-Avrami theory related to the growth laws
The theory of Kolmogorov-Johnson-Mehl-Avrami (KJMA) for phase transition
kinetics is subjected to severe limitations concerning the functional form of
the growth law. This paper is devoted to side step this drawback through the
use of correlation function approach. Moreover, we put forward an
easy-to-handle formula, written in terms of the experimentally accessible
actual extended volume fraction, which is found to match several types of
growths. Computer simulations have been done for corroborating the theoretical
approach.Comment: 18 pages ;11 figure
Length Scales of Acceleration for Locally Isotropic Turbulence
Length scales are determined that govern the behavior at small separations of
the correlations of fluid-particle acceleration, viscous force, and pressure
gradient. The length scales and an associated universal constant are quantified
on the basis of published data. The length scale governing pressure spectra at
high wave numbers is discussed. Fluid-particle acceleration correlation is
governed by two length scales; one arises from the pressure gradient, the other
from the viscous force.Comment: 2 figures, 4 pages. Physical Review Letters, accepted August 200
Opportunities for use of exact statistical equations
Exact structure function equations are an efficient means of obtaining
asymptotic laws such as inertial range laws, as well as all measurable effects
of inhomogeneity and anisotropy that cause deviations from such laws. "Exact"
means that the equations are obtained from the Navier-Stokes equation or other
hydrodynamic equations without any approximation. A pragmatic definition of
local homogeneity lies within the exact equations because terms that explicitly
depend on the rate of change of measurement location appear within the exact
equations; an analogous statement is true for local stationarity. An exact
definition of averaging operations is required for the exact equations. Careful
derivations of several inertial range laws have appeared in the literature
recently in the form of theorems. These theorems give the relationships of the
energy dissipation rate to the structure function of acceleration increment
multiplied by velocity increment and to both the trace of and the components of
the third-order velocity structure functions. These laws are efficiently
derived from the exact velocity structure function equations. In some respects,
the results obtained herein differ from the previous theorems. The
acceleration-velocity structure function is useful for obtaining the energy
dissipation rate in particle tracking experiments provided that the effects of
inhomogeneity are estimated by means of displacing the measurement location.Comment: accepted by Journal of Turbulenc
Topological Interactions in Warped Extra Dimensions
Topological interactions will be generated in theories with compact extra
dimensions where fermionic chiral zero modes have different localizations. This
is the case in many warped extra dimension models where the right-handed top
quark is typically localized away from the left-handed one. Using
deconstruction techniques, we study the topological interactions in these
models. These interactions appear as trilinear and quadrilinear gauge boson
couplings in low energy effective theories with three or more sites, as well as
in the continuum limit. We derive the form of these interactions for various
cases, including examples of Abelian, non-Abelian and product gauge groups of
phenomenological interest. The topological interactions provide a window into
the more fundamental aspects of these theories and could result in unique
signatures at the Large Hadron Collider, some of which we explore.Comment: 40 pages, 10 figures, 2 tables; modifications in the KK parity
discussion, final version at JHE
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