12,618 research outputs found
Production of squeezed state of single mode cavity field by the coupling of squeezed vacuum field reservoir in nonautonomous case
The dissipative and decoherence properties as well as the asymptotic behavior
of the single mode electromagnetic field interacting with the time-dependent
squeezed vacuum field reservoir are investigated in detail by using the
algebraic dynamical method. With the help of the left and right representations
of the relevant algebra, the dynamical symmetry of the nonautonomous
master equation of the system is found to be . The unique equilibrium
steady solution is found to be the squeezed state and any initial state of the
system is proved to approach the unique squeezed state asymptotically. Thus the
squeezed vacuum field reservoir is found to play the role of a squeezing mold
of the cavity field.Comment: 5 pages, no figure, Revtex
The Reionization History in the Lognormal Model
We study the evolution of baryonic gas before the reionization in the
lognormal (LN) model of cosmic clustering. We show that the thermal history of
the universe around the reionization can roughly be divided into three epochs:
1) cold dark age , in which baryon gas is neutral, and opaque to
Ly photons; 2) hot dark age , in which a predominant
part of baryon gas is ionized and hot, but it is still opaque to Ly
photons; 3) bright age , in which the universe is ionized highly
enough to be transparent to Ly photons. In the flat cold dark matter
cosmological models given by WMAP and COBE, the difference of the two redshifts
is found to be as large as with and
. This reionization history naturally yields a high optical depth
to the CMB observed by the TE polarization of the
WMAP, and a low redshift of the appearance of the Ly
Gunn-Peterson trough in QSO's absorption spectra. The
reason why the universe stays long in an ionized, yet Ly opaque, stage
is because the first photo-ionization heats the intergalactic gas effectively
and has balanced the gravitational clustering a long period of time. Therefore,
the result of a high and low is a common feature of all the
models considered. Besides the cosmological parameters, the only free parameter
we used in the calculation is , the mean ionization photons produced
by each baryon in collapsed objects. We take it to be 40 - 80 in the
calculation.Comment: AAS Latex file, 29 pages, 6 figures included, accepted for
publication in Ap
SXP214, an X-ray Pulsar in the Small Magellanic Cloud, Crossing the Circumstellar Disk of the Companion
Located in the Small Magellanic Cloud (SMC), SXP214 is an X-ray pulsar in a
high mass X-ray binary system with a Be-star companion. A recent survey of the
SMC under a Chandra X-ray Visionary program found the source in a transition
when the X-ray flux was on a steady rise. The Lomb-Scargle periodogram revealed
a pulse period of 211.49 +/- 0.42 s, which is significantly (>5sigma) shorter
than the previous measurements with XMM-Newton and RXTE. This implies that the
system has gone through sudden spin-up episodes recently. The pulse profile
shows a sharp eclipse-like feature with a modulation amplitude of >95%. The
linear rise of the observed X-ray luminosity from <~2x to 7x10^35 erg s^-1 is
correlated with steady softening of the X-ray spectrum, which can be described
by the changes in the local absorption from N_H ~ 10^24 to <~10^20 cm^-2 for an
absorbed power-law model. The soft X-ray emission below 2 keV was absent in the
early part of the observation when only the pulsating hard X-ray component was
observed, whereas at later times both soft and hard X-ray components were
observed pulsating. A likely explanation is that the neutron star was initially
hidden in the circumstellar disk of the companion, and later came out of the
disk with the accreted material that continued fueling the observed pulsation.Comment: 8 pages, 4 figures, 1 table, accepted for publication in Ap
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Rotation Dependence of Electric Quadrupole Hyperfine Interaction in the Ground State of Molecular Iodine by High-Resolution Laser Spectroscopy
Doppler-free high-resolution spectroscopy is applied to molecular iodine at 532 nm by Nd:YAG lasers. The main hyperfine components as well as the crossover lines are measured for R(56)32−0 and P(54)32−0 transitions by heterodyne beating of two I2-stabilized lasers. The measured hyperfine splittings including both main and crossover lines are fitted to a four-term Hamiltonian, which includes the electric quadrupole, spin–rotation, tensor spin–spin, and scalar spin–spin interactions, with an average deviation of ∼1 kHz. Absolute values of the electric quadrupole hyperfine constants for both the upper and the lower states are obtained. The rotation dependence of the ground-state (v\u22=0) electric quadrupole constant eQq\u22 is found to be eQq\u22(J)=−2452.556(2)−0.000164(5)J(J+1)−0.000000005(2)J2(J+1)2 MHz
Continuous extremal optimization for Lennard-Jones Clusters
In this paper, we explore a general-purpose heuristic algorithm for finding
high-quality solutions to continuous optimization problems. The method, called
continuous extremal optimization(CEO), can be considered as an extension of
extremal optimization(EO) and is consisted of two components, one is with
responsibility for global searching and the other is with responsibility for
local searching. With only one adjustable parameter, the CEO's performance
proves competitive with more elaborate stochastic optimization procedures. We
demonstrate it on a well known continuous optimization problem: the
Lennerd-Jones clusters optimization problem.Comment: 5 pages and 3 figure
An Empirical Approach to the Bond Additivity Model in Quantitative Interpretation of Sum Frequency Generation Vibrational Spectra
A complete empirical approach from known Raman and IR spectra is used to make
corrections to the bond additivity model for quantitative interpretation of Sum
Frequency generation Vibrational Spectra (SFG-VS) from molecular interfaces.
This empirical correction successfully addresses the failures of the simple
bond additivity model. This empirical approach not only provides new
understandings of the effectiveness and limitations of the bond additivity
model, but also provides a practical roadmap for its application in SFG-VS
studies of molecular interfaces
First construction of infectious clone for newly emerging mutation porcine circovirus type 2 (PCV2) followed by comparison with PCV2a and PCV2b genotypes in biological characteristics in vitro
<p>Abstract</p> <p>Background</p> <p>Porcine circovirus type 2 (PCV2), the causative agent of postweaning multisystemic wasting syndrome (PMWS), is a serious economic problem in the swine industry. Different genotypes (PCV2a, PCV2b and PCV2d) of the virus are present in the clinical cases in China, and it is necessary to elucidate the pathogenic difference among different genotypes of PCV2. In this study, four strains of different genotypes were isolated, two were ordinary strains and another two were mutation strains, which there are one and two amino acids elongation in the capsid protein (Cap) of PCV2, respectively. Representative strains of different genotypes of the virus were constructed by infectious molecular clone and biological characterization of the rescued viruses were identified <it>in vitro</it>.</p> <p>Results</p> <p>Four PCV2 isolates (PCV2a/CL, PCV2b/YJ, PCV2b/JF and PCV2d/BDH) of different genotypes were isolated from the clinical cases of PMWS in China. Four infectious clones of PCV2 were constructed and the rescued viruses were harvested after transfection into PK15 cells. The rescued viruses were verified by nucleotide sequence analysis, morphology of the viruses and immunoperoxidase monolayer assay (IPMA). The rescued viruses propagated stably after consecutive incubation for more than ten passages, and virus propagation reached its peak 72h post infection (PI), and the virus titers were up to 10<sup>5.7 </sup>TCID<sub>50</sub>/ml. By using neutralizing 1D2 monoclonal antibody (mAb) of PCV2, the antigen capture ELISA showed that only the PCV2a/rCL and PCV2b/rJF strains has immunoreactivity with the 1D2 mAb, however, another two rescued strains (PCV2b/rYJ and PCV2d/rBDH) do not, which indicated the antigenic difference among the rescued viruses of different genotypes. In addition, here is the first report of obtaining the newly emerging PCV2 with mutation <it>in vitro </it>by infectious molecular clone technology.</p> <p>Conclusions</p> <p>Conclusions drawn from this study show that PCV2 has prevailing differences in genomic and ORF2 gene length and antigen in swine herds in China. Four representative clones for different genotypes were constructed and rescued, which will facilitate further studies on the pathogenic differences resulting from different subtypes of PCV2.</p
Superallowed Fermi transitions in RPA with a relativistic point-coupling energy functional
The self-consistent random phase approximation (RPA) approach with the
residual interaction derived from a relativistic point-coupling energy
functional is applied to evaluate the isospin symmetry-breaking corrections
{\delta}c for the 0+\to0+ superallowed Fermi transitions. With these {\delta}c
values, together with the available experimental ft values and the improved
radiative corrections, the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM)
matrix is examined. Even with the consideration of uncertainty, the sum of
squared top-row elements has been shown to deviate from the unitarity condition
by 0.1% for all the employed relativistic energy functionals.Comment: 13 pages,2 figure
Variability of Young Stellar Objects in the Perseus Molecular Cloud
We present an analysis of 288 young stellar objects (YSOs) in the Perseus
Molecular Cloud that have well defined and -band lightcurves from the
Zwicky Transient Facility. Of the 288 YSOs, 238 sources (83% of our working
sample) are identified as variables based on the normalized peak-to-peak
variability metric, with variability fraction of 92% for stars with disks and
77% for the diskless populations. These variables are classified into different
categories using the quasiperiodicity () and flux asymmetry () metrics.
Fifty-three variables are classified as strictly periodic objects that are well
phased and can be attributed to spot modulated stellar rotation. We also
identify 22 bursters and 25 dippers, which can be attributed to accretion burst
and variable extinction, respectively. YSOs with disks tend to have asymmetric
and non-repeatable lightcurves, while the YSOs without disks tend to have
(quasi)periodic lightcurves. The periodic variables have the steepest change in
versus , while bursters have much flatter changes than dippers in
versus . Periodic and quasiperiodic variables display the lowest
variability amplitude. Simple models suggest that the variability amplitudes of
periodic variables correspond to changes of the spot coverage of 30% to 40%,
burster variables are attributed to accretion luminosity changes in the range
of , and dippers are due to variable extinction
with changes in the range of mag.Comment: 26 pages, 16 figures, 3 tables, accepted for publication in RA
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