8,064 research outputs found
Pairing and Vortex Lattices for Interacting Fermions in Optical Lattices with a Large Magnetic Field
We study the structure of pairing order parameter for spin-1/2 fermions with
attractive interactions in a square lattice under a uniform magnetic field.
Because the magnetic translation symmetry gives a unique degeneracy in the
single-particle spectrum, the wave function has both zero and finite momentum
components co-existing, and their relative phases are determined by a
self-consistent mean-field theory. We present a microscopic calculation that
can determine the vortex lattice structure in the superfluid phase for
different flux densities. Phase transition from a Hofstadter insulator to a
superfluid phase is also discussed.Comment: 4 pages, 3 figures, one table, published versio
Giant circular dichroism of a molecule in a region of strong plasmon resonances between two neighboring gold nanocrystals
We report on giant circular dichroism (CD) of a molecule inserted into a
plasmonic hot spot. Naturally occurring molecules and biomolecules have
typically CD signals in the UV range, whereas plasmonic nanocrystals exhibit
strong plasmon resonances in the visible spectral interval. Therefore,
excitations of chiral molecules and plasmon resonances are typically
off-resonant. Nevertheless, we demonstrate theoretically that it is possible to
create strongly-enhanced molecular CD utilizing the plasmons. This task is
doubly challenging since it requires both creation and enhancement of the
molecular CD in the visible region. We demonstrate this effect within the model
which incorporates a chiral molecule and a plasmonic dimer. The associated
mechanism of plasmonic CD comes from the Coulomb interaction which is greatly
amplified in a plasmonic hot spot.Comment: Manuscript: 4+pages, 4 figures; Supplemental_Material: 10 pages, 7
figure
Dimensional Crossover in the Effective Second Harmonic Generation of Films of Random Dielectrics
The effective nonlinear response of films of random composites consisting of
a binary composite with nonlinear particles randomly embedded in a linear host
is theoretically and numerically studied. A theoretical expression for the
effective second harmonic generation susceptibility, incorporating the
thickness of the film, is obtained by combining a modified effective-medium
approximation with the general expression for the effective second harmonic
generation susceptibility in a composite. The validity of the thoretical
results is tested against results obtained by numerical simulations on random
resistor networks. Numerical results are found to be well described by our
theory. The result implies that the effective-medium approximation provides a
convenient way for the estimation of the nonlinear response in films of random
dielectrics.Comment: 9 pages, 2 figures; accepted for publication in Phys. Rev.
Dimensionality Reduction in Deep Learning for Chest X-Ray Analysis of Lung Cancer
Efficiency of some dimensionality reduction techniques, like lung
segmentation, bone shadow exclusion, and t-distributed stochastic neighbor
embedding (t-SNE) for exclusion of outliers, is estimated for analysis of chest
X-ray (CXR) 2D images by deep learning approach to help radiologists identify
marks of lung cancer in CXR. Training and validation of the simple
convolutional neural network (CNN) was performed on the open JSRT dataset
(dataset #01), the JSRT after bone shadow exclusion - BSE-JSRT (dataset #02),
JSRT after lung segmentation (dataset #03), BSE-JSRT after lung segmentation
(dataset #04), and segmented BSE-JSRT after exclusion of outliers by t-SNE
method (dataset #05). The results demonstrate that the pre-processed dataset
obtained after lung segmentation, bone shadow exclusion, and filtering out the
outliers by t-SNE (dataset #05) demonstrates the highest training rate and best
accuracy in comparison to the other pre-processed datasets.Comment: 6 pages, 14 figure
The Origin of Gamma-Rays from Globular Clusters
Fermi has detected gamma-ray emission from eight globular clusters. We
suggest that the gamma-ray emission from globular clusters may result from the
inverse Compton scattering between relativistic electrons/positrons in the
pulsar wind of MSPs in the globular clusters and background soft photons
including cosmic microwave/relic photons, background star lights in the
clusters, the galactic infrared photons and the galactic star lights. We show
that the gamma-ray spectrum from 47 Tuc can be explained equally well by upward
scattering of either the relic photons, the galactic infrared photons or the
galactic star lights whereas the gamma-ray spectra from other seven globular
clusters are best fitted by the upward scattering of either the galactic
infrared photons or the galactic star lights. We also find that the observed
gamma-ray luminosity is correlated better with the combined factor of the
encounter rate and the background soft photon energy density. Therefore the
inverse Compton scattering may also contribute to the observed gamma-ray
emission from globular clusters detected by Fermi in addition to the standard
curvature radiation process. Furthermore, we find that the emission region of
high energy photons from globular cluster produced by inverse Compton
scattering is substantially larger than the core of globular cluster with a
radius >10pc. The diffuse radio and X-rays emitted from globular clusters can
also be produced by synchrotron radiation and inverse Compton scattering
respectively. We suggest that future observations including radio, X-rays, and
gamma-rays with energy higher than 10 GeV and better angular resolution can
provide better constraints for the models.Comment: Accepted by ApJ, Comments may send to Prof. K.S. Cheng:
[email protected]
- …