914 research outputs found
Porosity Study of Hybrid Silica Mesostructure in Aluminium Oxide Membrane Columnar by Cyclic Voltammetry Method
Silica mesostructure has been grown within with a porous aluminium oxide membrane columnar material (hybrid-AOM). This was prepared using a sol-gel technique with Pluronic P123 triblock copolymer as the structure-directing agent and tetraethyl orthosilicate as the inorganic source. The porosity of the hybrid-AOM after ethanol extraction was calculated from the cyclic voltammetry response of a neutral probe (FcMeOH), using Randles-SevÄik equation
Split Fermions in Extra Dimensions and CP Violation
We discuss CP violation in the quark sector within a novel approach to the
Yukawa puzzle proposed by Arkani-Hamed and Schmaltz, where Yukawa hierarchies
result from localising the Standard Model quark field wave-functions, at
different positions (in the extra dimensions) in a ``fat-brane.'' We show that
at least two extra dimensions are necessary in order to obtain sufficient CP
violation while reproducing the correct quark mass spectrum and mixing angles.Comment: 11 pages, 3 eps figures, references added, results unchange
Phoretic Motion of Spheroidal Particles Due To Self-Generated Solute Gradients
We study theoretically the phoretic motion of a spheroidal particle, which
generates solute gradients in the surrounding unbounded solvent via chemical
reactions active on its surface in a cap-like region centered at one of the
poles of the particle. We derive, within the constraints of the mapping to
classical diffusio-phoresis, an analytical expression for the phoretic velocity
of such an object. This allows us to analyze in detail the dependence of the
velocity on the aspect ratio of the polar and the equatorial diameters of the
particle and on the fraction of the particle surface contributing to the
chemical reaction. The particular cases of a sphere and of an approximation for
a needle-like particle, which are the most common shapes employed in
experimental realizations of such self-propelled objects, are obtained from the
general solution in the limits that the aspect ratio approaches one or becomes
very large, respectively.Comment: 18 pages, 5 figures, to appear in European Physical Journal
Vortex states in binary mixture of Bose-Einstein condensates
The vortex configurations in the Bose-Einstein condensate of the mixture of
two different spin states |F=1,m_f=-1> and |2,1> of ^{87}Rb atoms corresponding
to the recent experiments by Matthews et. al. (Phys. Rev. Lett. 83, 2498
(1999)) are considered in the framework of the Thomas-Fermi approximation as
functions of N_2/N_1, where N_1 is the number of atoms in the state |1,-1> and
N_2 - in the state |2,1>. It is shown that for nonrotating condensates the
configuration with the |1,-1> fluid forming the shell about the |2,1> fluid
(configuration "a") has lower energy than the opposite configuration
(configuration "b") for all values of N_2/N_1. When the |1,-1> fluid has net
angular momentum and forms an equatorial ring around the resting central
condensate |2,1>, the total energy of the system is higher than the ground
energy, but the configuration "a" has lower energy than the configuration "b"
for all N_2/N_1. On the other hand, when the |2> fluid has the net angular
momentum, for the lowest value of the angular momentum \hbar l (l=1) there is
the range of the ratio N_2/N_1 where the configuration "b" has lower energy
than the configuration "a". For higher values of the angular momentum the
configuration "b" is stable for all values of N_2/N_1.Comment: minor changes, references adde
Yang-Mills theory in Landau gauge as a liquid crystal
Using a spin-charge separation of the gluon field in the Landau gauge we show
that the SU(2) Yang-Mills theory in the low-temperature phase can be considered
as a nematic liquid crystal. The ground state of the nematic crystal is
characterized by the A^2 condensate of the gluon field. The liquid crystal
possesses various topological defects (instantons, monopoles and vortices)
which are suggested to play a role in non-perturbative features of the theory.Comment: 9 pages, no figure
Nonergodic Behavior of Interacting Bosons in Harmonic Traps
We study the time evolution of a system of interacting bosons in a harmonic
trap. In the low-energy regime, the quantum system is not ergodic and displays
rather large fluctuations of the ground state occupation number. In the high
energy regime of classical physics we find nonergodic behavior for modest
numbers of trapped particles. We give two conditions that assure the ergodic
behavior of the quantum system even below the condensation temperature.Comment: 11 pages, 3 PS-figures, uses psfig.st
Brane world corrections to Newton's law
We discuss possible variations of the effective gravitational constant with
length scale, predicted by most of alternative theories of gravity and unified
models of physical interactions. After a brief general exposition, we review in
more detail the predicted corrections to Newton's law of gravity in diverse
brane world models. We consider various configurations in 5 dimensions (flat,
de Sitter and AdS branes in Einstein and Einstein-Gauss-Bonnet theories, with
and without induced gravity and possible incomplete graviton localization), 5D
multi-brane systems and some models in higher dimensions. A common feature of
all models considered is the existence of corrections to Newton's law at small
radii comparable with the bulk characteristic length: at such radii, gravity on
the brane becomes effectively multidimensional. Many models contain superlight
perturbation modes, which modify gravity at large scale and may be important
for astrophysics and cosmology.Comment: Brief review, 16 pages, 92 references. Some description and
references adde
Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors
Based on existing theoretical model and by considering our longitudinal
nonlinear response function, we derive a nonliear equation in which the mixed
state Hall resistivity can be expressed as an analytical function of magnetic
field, temperature and applied current. This equation enables one to compare
quantitatively the experimental data with theoretical model. We also find some
new scaling relations of the temperature and field dependency of Hall
resistivity. The comparison between our theoretical curves and experimental
data shows a fair agreement.Comment: 4 pages, 3 figure
Disorder Induced Phase Transition in a Random Quantum Antiferromagnet
A two-dimensional Heisenberg model with random antiferromagnetic
nearest-neighbor exchange is studied using quantum Monte Carlo techniques. As
the strength of the randomness is increased, the system undergoes a transition
from an antiferromagnetically ordered ground state to a gapless disordered
state. The finite-size scaling of the staggered structure factor and
susceptibility is consistent with a dynamic exponent .Comment: Revtex 3.0, 10 pages + 5 postscript figures available upon request,
UCSBTH-94-1
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