1,180 research outputs found
Possible Existence of an Extraordinary Phase in the Driven Lattice Gas
We report recent simulation results which might indicate the existence of a
new low-temperature "phase" in an Ising lattice gas, driven into a
non-equilibrium steady state by an external field. It appears that this
"phase", characterized by multiple-strip configurations, is selected when
square systems are used to approach the thermodynamic limit. We propose a
quantitative criterion for the existence of such a "phase". If confirmed, its
observation may resolve a long-standing controversy over the critical
properties of the driven Ising lattice gas.Comment: 10 pages; 4 figure
A continuum description of the energetics and evolution of stepped surfaces in strained nanostructures
As a departure from existing continuum approaches for describing the
stability and evolution of surfaces of crystalline materials, this article
provides a description of surface evolution based on the physics of the main
feature imposed by the discrete nature of the material, namely,
crystallographic surface steps. It is shown that the formation energy of
surface steps depends on the sign of extensional strain of the crystal surface,
and this behavior plays a crucial role in surface evolution. The nature of this
dependence implies that there is no energetic barrier to nucleation of islands
on the growth surface during deposition, and that island faces tend toward
natural orientations which have no counterpart in unstrained materials. This
behavior is expressed in terms of a small number of parameters that can be
estimated through atomistic analysis of stepped surfaces. The continuum
framework developed is then applied to study the time evolution of surface
shape of an epitaxial film being deposited onto a substrate. The kinetic
equation for mass transport is enforced in a weak form by means of a
variational formulation [...].Comment: 25 pages, 7 figs, KEYWORDS=surface diffusion, surface energy,
morphology evolution, semiconductor material, stability and bifurcatio
The Real-rootedness of Eulerian Polynomials via the Hermite–Biehler Theorem
Based on the Hermite–Biehler theorem, we simultaneously prove the real-rootedness of Eulerian polynomials of type and the real-rootedness of affine Eulerian polynomials of type , which were first obtained by Savage and Visontai by using the theory of -Eulerian polynomials. We also confirm Hyatt’s conjectures on the inter-lacing property of half Eulerian polynomials. Borcea and Brändén’s work on the characterization of linear operators preserving Hurwitz stability is critical to this approach
Growth, immunity and ammonia excretion of albino and normal Apostichopus japonicus (Selenka) feeding with various experimental diets
An experiment was conducted to evaluate the effects of six experimental diets on growth performance, ammonia excretion and immunity of albino and normal Apostichopus japonicus. A factorial design was used, the factors being type of diets (six levels) and colour of A. japonicus (two levels). A total of 30 randomly selected albino A. japonicus were housed in each (60 × 50 × 30 cm3) of 18 blue plastic aquaria to form six groups in triplicate, and the same set-up
was used for the normal A. japonicus. Each group of animals was fed with one of the six experimental diets. Apparent dry matter digestibility (ADMD) and apparent crude protein digestibility (ACPD) were analysed using acid-insoluble
ash (AIA) content method. At the end of the experiment, all
A. japonicus were harvested and weighed to calculate growth parameters. After weighing, six individuals from each aquarium were randomly sampled for immune indices.
Results indicated that all growth parameters of A. japonicus increased with decreasing nutrient content in their diets (p < .01), whereas an opposite result was observed in
case of the ammonia-nitrogen production by A. japonicus. Normal A. japonicus grew better (p < .01) and produced lower (p < .01) quantity of ammonia nitrogen compared to the albino A. japonicus. Immunity particularly superoxide dismutase and lysozyme activities was higher (p < .05) in normal compared to albino A. japonicus. Considering
all measured variables, D1 (diet containing crude protein, crude lipid, carbohydrate and crude ash 51.8, 8.7, 231.3, 708.2 g/kg, respectively) was the best diet among all
experimental diets. More research is still needed to optimize nutrients in the diet of A. japonicus, as this study does not provide information about critical threshold level of nutrients in diets. Until then, diet D1 can be recommended for A. japonicus aquaculture
Spinless particle in rapidly fluctuating random magnetic field
We study a two-dimensional spinless particle in a disordered gaussian
magnetic field with short time fluctuations, by means of the evolution equation
for the density matrix ; in this
description the two coordinates are associated with the retarded and advanced
paths respectively. The static part of the vector potential correlator is
assumed to grow with distance with a power ; the case corresponds to
a -correlated magnetic field, and to free massless field. The
value separates two different regimes, diffusion and logarithmic growth
respectively. When the baricentric coordinate diffuses with a coefficient proportional to , where
is the relative coordinate: . As the
correlator of the magnetic field is a power of distance with positive exponent;
then the coefficient scales as .
The density matrix is a function of and ,and its width in
grows for large times proportionally to .Comment: latex2e; 2 figure
Experimental implications of quantum phase fluctuations in layered superconductors
I study the effect of quantum and thermal phase fluctuations on the in-plane
and c-axis superfluid stiffness of layered d-wave superconductors. First, I
show that quantum phase fluctuations in the superconductor can be damped in the
presence of external screening of Coulomb interactions, and suggest an
experiment to test the importance of these fluctuations, by placing a metal in
close proximity to the superconductor to induce such screening. Second, I show
that a combination of quantum phase fluctuations and the linear temperature
dependence of the in-plane superfluid stiffness leads to a linear temperature
dependence of the c-axis penetration depth, below a temperature scale
determined by the magnitude of in-plane dissipation.Comment: 6 pgs, 1 figure, minor changes in comparison with c-axis expt, final
published versio
Anomalous c-axis charge dynamics in copper oxide materials
Within the t-J model, the c-axis charge dynamics of the copper oxide
materials in the underdoped and optimally doped regimes is studied by
considering the incoherent interlayer hopping. It is shown that the c-axis
charge dynamics is mainly governed by the scattering from the in-plane
fluctuation. In the optimally doped regime, the c-axis resistivity is a linear
in temperatures, and shows the metallic-like behavior for all temperatures,
while the c-axis resistivity in the underdoped regime is characterized by a
crossover from the high temperature metallic-like behavior to the low
temperature semiconducting-like behavior, which are consistent with experiments
and numerical simulations.Comment: 6 pages, Latex, Three figures are adde
On the existence of a Bose Metal at T=0
This paper aims to justify, at a microscopic level, the existence of a
two-dimensional Bose metal, i.e. a metallic phase made out of Cooper pairs at
T=0. To this end, we consider the physics of quantum phase fluctuations in
(granular) superconductors in the absence of disorder and emphasise the role of
two order parameters in the problem, viz. phase order and charge order. We
focus on the 2-d Bose Hubbard model in the limit of very large fillings, i.e. a
2-d array of Josephson junctions. We find that the algebra of phase
fluctuations is that of the Euclidean group in this limit, and show
that the model is equivalent to two coupled XY models in (2+1)-d, one
corresponding to the phase degrees of freedom, and the other the charge degrees
of freedom. The Bose metal, then, is the phase in which both these degrees of
freedom are disordered(as a result of quantum frustration). We analyse the
model in terms of its topological excitations and suggest that there is a
strong indication that this state represents a surface of critical points, akin
to the gapless spin liquid states. We find a remarkable consistency of this
scenario with certain low-T_c thin film experiments.Comment: 16 pages, 2 figure
Gauge Theory of Composite Fermions: Particle-Flux Separation in Quantum Hall Systems
Fractionalization phenomenon of electrons in quantum Hall states is studied
in terms of U(1) gauge theory. We focus on the Chern-Simons(CS) fermion
description of the quantum Hall effect(QHE) at the filling factor
, and show that the successful composite-fermions(CF) theory
of Jain acquires a solid theoretical basis, which we call particle-flux
separation(PFS). PFS can be studied efficiently by a gauge theory and
characterized as a deconfinement phenomenon in the corresponding gauge
dynamics. The PFS takes place at low temperatures, , where
each electron or CS fermion splinters off into two quasiparticles, a fermionic
chargeon and a bosonic fluxon. The chargeon is nothing but Jain's CF, and the
fluxon carries units of CS fluxes. At sufficiently low temperatures , fluxons Bose-condense uniformly and (partly)
cancel the external magnetic field, producing the correlation holes. This
partial cancellation validates the mean-field theory in Jain's CF approach.
FQHE takes place at as a joint effect of (i) integer QHE of
chargeons under the residual field and (ii) Bose condensation of
fluxons. We calculate the phase-transition temperature and the CF
mass. PFS is a counterpart of the charge-spin separation in the t-J model of
high- cuprates in which each electron dissociates into holon and
spinon. Quasiexcitations and resistivity in the PFS state are also studied. The
resistivity is just the sum of contributions of chargeons and fluxons, and
changes its behavior at , reflecting the change of
quasiparticles from chargeons and fluxons at to electrons at
.Comment: 18 pages, 7 figure
Black Holes in Type IIA String on Calabi-Yau Threefolds with Affine ADE Geometries and q-Deformed 2d Quiver Gauge Theories
Motivated by studies on 4d black holes and q-deformed 2d Yang Mills theory,
and borrowing ideas from compact geometry of the blowing up of affine ADE
singularities, we build a class of local Calabi-Yau threefolds (CY^{3})
extending the local 2-torus model \mathcal{O}(m)\oplus \mathcal{O}(-m)\to
T^{2\text{}} considered in hep-th/0406058 to test OSV conjecture. We first
study toric realizations of T^{2} and then build a toric representation of
X_{3} using intersections of local Calabi-Yau threefolds \mathcal{O}(m)\oplus
\mathcal{O}(-m-2)\to \mathbb{P}^{1}. We develop the 2d \mathcal{N}=2 linear
\sigma-model for this class of toric CY^{3}s. Then we use these local
backgrounds to study partition function of 4d black holes in type IIA string
theory and the underlying q-deformed 2d quiver gauge theories. We also make
comments on 4d black holes obtained from D-branes wrapping cycles in
\mathcal{O}(\mathbf{m}) \oplus \mathcal{O}(\mathbf{-m-2}%) \to \mathcal{B}_{k}
with \mathbf{m=}(m_{1},...,m_{k}) a k-dim integer vector and \mathcal{B}_{k} a
compact complex one dimension base consisting of the intersection of k
2-spheres S_{i}^{2} with generic intersection matrix I_{ij}. We give as well
the explicit expression of the q-deformed path integral measure of the
partition function of the 2d quiver gauge theory in terms of I_{ij}.Comment: 36 pages, latex, 9 figures. References adde
- …