39,213 research outputs found
Existence theorems for a nonlinear second-order distributional differential equation
In this work, we are concerned with existence of solutions for a nonlinear
second-order distributional differential equation, which contains measure
differential equations and stochastic differential equations as special cases.
The proof is based on the Leray--Schauder nonlinear alternative and
Kurzweil--Henstock--Stieltjes integrals. Meanwhile, examples are worked out to
demonstrate that the main results are sharp.Comment: This is a preprint of a paper whose final and definite form is with
'Journal of King Saud University - Science', ISSN 1018-3647. Submitted
05-March-2017; revised 24-April-2017; accepted for publication 26-April-201
Signature of Fermi surface anisotropy in point contact conductance in the presence of defects
In a previous paper (Avotina et al.,Phys. Rev. B Vol.71, 115430 (2005)) we
have shown that in principle it is possible to image the defect positions below
a metal surface by means of a scanning tunnelling microscope. The principle
relies on the interference of electron waves scattered on the defects, which
give rise to small but measurable conductance fluctuations. Whereas in that
work the band structure was assumed to be free-electron like, here we
investigate the effects of Fermi surface anisotropy. We demonstrate that the
amplitude and period of the conductance oscillations are determined by the
local geometry of the Fermi surface. The signal results from those points for
which the electron velocity is directed along the vector connecting the point
contact to the defect. For a general Fermi surface geometry the position of the
maximum amplitude of the conductance oscillations is not found for the tip
directly above the defect. We have determined optimal conditions for
determination of defect positions in metals with closed and open Fermi
surfaces.Comment: 23 pages, 8 figure
Magneto-quantum oscillations of the conductance of a tunnel point-contact in the presence of a single defect
The influence of a quantizing magnetic field to the conductance of a
tunnel point contact in the presence of the single defect has been considered.
We demonstrate that the conductance exhibits specific magneto-quantum
oscillations, the amplitude and period of which depend on the distance between
the contact and the defect. We show that a non-monotonic dependence of the
point-contact conductance results from a superposition of two types of
oscillations: A short period oscillation arising from electron focusing by the
field and a long period oscillation of Aharonov-Bohm-type originated from
the magnetic flux passing through the closed trajectories of electrons moving
from the contact to the defect and returning back to the contact.Comment: 13 pages, 3 figure
Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders
In this Letter, we present a theoretical analysis of the acoustic
transmission through two-dimensional arrays of straight rigid cylinders placed
parallelly in the air. Both periodic and completely random arrangements of the
cylinders are considered. The results for the sound attenuation through the
periodic arrays are shown to be in a remarkable agreement with the reported
experimental data. As the arrangement of the cylinders is randomized, the
transmission is significantly reduced for a wider range of frequencies. For the
periodic arrays, the acoustic band structures are computed by the plane-wave
expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure
Broken symmetry, excitons, gapless modes and topological excitations in Trilayer Quantum Hall systems
We study the interlayer coherent incompressible phase in Trilayer Quantum
Hall systems (TLQH) at total filling factor from three
approaches:
Mutual Composite Fermion (MCF), Composite Boson (CB) and wavefunction
approach.
Just like in Bilayer Quantum Hall system, CB approach is superior than
MCF approach in studying TLQH with broken symmetry. The Hall and Hall drag
resistivities are found to be quantized at . Two neutral gapless
modes with linear dispersion relations are identified and the ratio of the two
velocities is close to .
The novel excitation spectra are classified into two classes: Charge neutral
bosonic
2-body bound states and Charge fermionic 3-body bound states.
In general, there are two 2-body Kosterlize-Thouless (KT) transition
temperatures and one 3-body KT transition. The Charge 3-body
fermionic bound states may be the main dissipation source of transport
measurements.
The broken symmetry in terms of algebra is studied. The structure
of excitons and their flowing patterns are given. The coupling between the two
Goldstone modes may lead to the broadening in the zero-bias peak in the
interlayer correlated tunnelings of the TLQH. Several interesting features
unique to TLQH are outlined.
Limitations of the CB approach are also pointed out.Comment: 10 pages, 3 figures, Final version to be published in Phys. Rev.
Extreme non-linear response of ultra-narrow optical transitions in cavity QED for laser stabilization
We explore the potential of direct spectroscopy of ultra-narrow optical
transitions of atoms localized in an optical cavity. In contrast to
stabilization against a reference cavity, which is the approach currently used
for the most highly stabilized lasers, stabilization against an atomic
transition does not suffer from Brownian thermal noise. Spectroscopy of
ultra-narrow optical transitions in a cavity operates in a very highly
saturated regime in which non-linear effects such as bistability play an
important role. From the universal behavior of the Jaynes-Cummings model with
dissipation, we derive the fundamental limits for laser stabilization using
direct spectroscopy of ultra-narrow atomic lines. We find that with current
lattice clock experiments, laser linewidths of about 1 mHz can be achieved in
principle, and the ultimate limitations of this technique are at the 1 Hz
level.Comment: 5 pages, 4 figure
Elastic Superhydrophobic and Photocatalytic Active Films Used as Blood Repellent Dressing
Strong coupling of a mechanical oscillator and a single atom
We propose and analyze a setup to achieve strong coupling between a single
trapped atom and a mechanical oscillator. The interaction between the motion of
the atom and the mechanical oscillator is mediated by a quantized light field
in a laser driven high-finesse cavity. In particular, we show that high
fidelity transfer of quantum states between the atom and the mechanical
oscillator is in reach for existing or near future experimental parameters. Our
setup provides the basic toolbox for coherent manipulation, preparation and
measurement of micro- and nanomechanical oscillators via the tools of atomic
physics.Comment: 4 pages, 2 figures, minro changes, accepted by PR
SDF1 Gene Variation Is Associated with Circulating SDF1 alpha Level and Endothelial Progenitor Cell Number-The Bruneck Study
BACKGROUND: Stromal cell-derived factor-1 (SDF1) and its receptor CXC chemokine receptor 4 (CXCR4) play a critical role in progenitor cell homing, mobilization and differentiation. It would be interesting to assess the predictive value of SDF-1alpha level for EPC number, and to ascertain whether there is a relationship between SDF1 gene variation, plasma SDF-1alpha level, and the number and function of circulating EPCs. We also tested whether EPC number and function was related to CXCR4 gene variation.
METHODOLOGY AND PRINCIPAL FINDINGS: We genotyped a cohort of individuals who participated in the Bruneck Study for single nucleotide polymorphisms (SNPs) in the SDF1 and CXCR4 genes, and measured blood SDF1alpha level as well as EPC number and function. SDF1alpha levels were correlated with age, gender, alcohol consumption, circulating reticulocyte numbers, and concentrations of matrix metalloproteinase-9, C-reactive protein, cystatin C, fibrinogen and homocytein. In blood samples taken in 2005, EPC number was inversely associated with SDF1alpha level (p<0.001). EPC number in 2005 was also inversely associated with SDF1alpha level in 2000 (p = 0.009), suggesting a predictive value of plasma SDF1alpha level for EPC number. There was an association between the SDF1 gene rs2297630 SNP A/A genotype, increased SDF1alpha level (p = 0.002) and lower EPC number (p = 0.006).
CONCLUSIONS: Our data indicate that a SDF1 gene variation (rs2297630) has an influence on SDF1alpha level and circulating EPC number, and that plasma SDF1alpha level is a predictor of EPC number
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