15,292 research outputs found
Noise Properties of Coherent Perfect Absorbers and Critically-coupled Resonators
The performance of a coherent perfect absorber (time-reversed laser) is
limited by quantum and thermal noise. At zero temperature, the quantum shot
noise dominates the signal for frequencies close to the resonance frequency,
and both vanish exactly at the resonance frequency. We compute the sensitivity
of the absorbing cavity as a background-free detector, limited by finite signal
or detector bandwidth.Comment: 6 pages, 3 figure
Residual proton-neutron interactions and the scheme
We investigate the correlation between integrated proton-neutron interactions
obtained by using the up-to-date experimental data of binding energies and the
, the product of valence proton number and valence neutron
number with respect to the nearest doubly closed nucleus. We make corrections
on a previously suggested formula for the integrated proton-neutron
interaction. Our results demonstrate a nice, nearly linear, correlation between
the integrated p-n interaction and , which provides us
with a firm foundation of the applicability of the scheme
to nuclei far from the stability line.Comment: four pages, three figures, Physical Review C, in pres
Coherent Perfect Absorbers: Time-reversed Lasers
We show that an arbitrary body or aggregate can be made perfectly absorbing
at discrete frequencies if a precise amount of dissipation is added under
specific conditions of coherent monochromatic illumination. This effect arises
from the interaction of optical absorption and wave interference, and
corresponds to moving a zero of the elastic S-matrix onto the real wavevector
axis. It is thus the time-reversed process of lasing at threshold. The effect
is demonstrated in a simple Si slab geometry illuminated in the 500-900 nm
range. Coherent perfect absorbers are novel linear optical elements, absorptive
interferometers, which may be useful for controlled optical energy transfer.Comment: 4 pages, 4 figure
Spin interference and Fano effect in electron transport through a mesoscopic ring side-coupled with a quantum dot
We investigate the electron transport through a mesoscopic ring side-coupled
with a quantum dot(QD) in the presence of Rashba spin-orbit(SO) interaction. It
is shown that both the Fano resonance and the spin interference effects play
important roles in the electron transport properties. As the QD level is around
the Fermi energy, the total conductance shows typical Fano resonance line
shape. By applying an electrical gate voltage to the QD, the total transmission
through the system can be strongly modulated. By threading the mesoscopic ring
with a magnetic flux, the time-reversal symmetry of the system is broken, and a
spin polarized current can be obtained even though the incident current is
unpolarized.Comment: 5 pages, 5 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]
The Fundamental Plane of Gamma-ray Globular Clusters
We have investigated the properties of a group of -ray emitting
globular clusters (GCs) which have recently been uncovered in our Galaxy. By
correlating the observed -ray luminosities with various
cluster properties, we probe the origin of the high energy photons from these
GCs. We report is positively correlated with the encounter rate
and the metalicity which place an
intimate link between the gamma-ray emission and the millisecond pulsar
population. We also find a tendency that increase with the energy
densities of the soft photon at the cluster location. Furthermore, the
two-dimensional regression analysis suggests that , soft photon
densities, and / possibly span fundamental
planes which potentially provide better predictions for the -ray
properties of GCs.Comment: 17 pages, 4 figures, 3 tables, published in Ap
Semi-leptonic and Non-leptonic meson decays to charmed mesons
We study the semi-leptonic and non-leptonic weak decays which are
governed by the transitions. The branching ratios, CP
asymmetries (CPA) and polarization fractions (FA) of non-leptonic decays are
investigated in the factorization approximation. The
form factors are estimated in the Salpeter method. Our estimation on branching
ratios generally agree with the existent experimental data. For CPA and
polarizations, comparisons among the FA results, the perturbative QCD
predictions and experimental data are made.Comment: 8 pages, 1 figures, 5 table
Negative-Index Refraction in a Lamellar Composite with Alternating Single Negative Layers
Negative-index refraction is achieved in a lamellar composite with
epsilon-negative (ENG) and mu-negative (MNG) materials stacked alternatively.
Based on the effective medium approximation, simultaneously negative effective
permittivity and permeability of such a lamellar composite are obtained
theoretically and further proven by full-wave simulations. Consequently, the
famous left-handed metamaterial comprising split ring resonators and wires is
interpreted as an analogy of such an ENG-MNG lamellar composite. In addition,
beyond the effective medium approximation, the propagating field squeezed near
the ENG/MNG interface is demonstrated to be left-handed surface waves with
backward phase velocity.Comment: 18 pages, 6 figure
A NuSTAR Observation of the Gamma-ray Emitting Millisecond Pulsar PSR J1723-2837
We report on the first NuSTAR observation of the gamma-ray emitting
millisecond pulsar binary PSR J1723-2837. X-ray radiation up to 79 keV is
clearly detected and the simultaneous NuSTAR and Swift spectrum is well
described by an absorbed power-law with a photon index of ~1.3. We also find
X-ray modulations in the 3-10 keV, 10-20 keV, 20-79 keV, and 3-79 keV bands at
the 14.8-hr binary orbital period. All these are entirely consistent with
previous X-ray observations below 10 keV. This new hard X-ray observation of
PSR J1723-2837 provides strong evidence that the X-rays are from the
intrabinary shock via an interaction between the pulsar wind and the outflow
from the companion star. We discuss how the NuSTAR observation constrains the
physical parameters of the intrabinary shock model.Comment: Accepted for publication in ApJ. 5 pages, 3 figure
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