46,031 research outputs found
Performance Analysis of a Dual-Hop Cooperative Relay Network with Co-Channel Interference
This paper analyzes the performance of a dual-hop amplify-and-forward (AF) cooperative relay network in the presence of direct link between the source and destination and multiple co-channel interferences (CCIs) at the relay. Specifically, we derive the new analytical expressions for the moment generating function (MGF) of the output signal-to-interference-plus-noise ratio (SINR) and the average symbol error rate (ASER) of the relay network. Computer simulations are given to confirm the validity of the analytical results and show the effects of direct link and interference on the considered AF relay network
Reading the Number of Extra Dimensions in the Spectrum of Hawking Radiation
After a brief review of the production and decay of Schwarzschild-like
(4+n)-dimensional black holes in the framework of theories with Large Extra
Dimensions, we proceed to derive the greybody factors and emission rates for
scalars, fermions and gauge bosons on the brane. We present and discuss
analytic and numerical methods for obtaining the above results, and demonstrate
that both the amount and type of Hawking radiation emitted by the black hole
can help us to determine the number of spacelike dimensions that exist in
nature.Comment: 8 pages, Latex file, 1 figure, to appear in the proceedings of the
String Phenomenology 2003 Conference, Durham, UK, 29th July-4th August, 200
Entanglement enhancement and postselection for two atoms interacting with thermal light
The evolution of entanglement for two identical two-level atoms coupled to a
resonant thermal field is studied for two different families of input states.
Entanglement enhancement is predicted for a well defined region of the
parameter space of one of these families. The most intriguing result is the
possibility of probabilistic production of maximally entangled atomic states
even if the input atomic state is factorized and the corresponding output state
is separable.Comment: accepted for publication in J. Phys.
First Detection of A Sub-kpc Scale Molecular Outflow in the Starburst Galaxy NGC 3628
We successfully detected a molecular outflow with a scale of 370-450 pc in
the central region of the starburst galaxy NGC 3628 through deep CO(1-0)
observations by using the Nobeyama Millimeter Array (NMA). The mass of the
outflowing molecular gas is ~2.8x10^7 M_sun, and the outflow velocity is
~90(+/-10) km s^{-1}. The expansion timescale of the outflow is 3.3-6.8 Myr,
and the molecular gas mass flow rate is 4.1-8.5 M_sun yr^{-1}. It requires
mechanical energy of (1.8-2.8)x10^{54} erg to create this sub-kpc scale
molecular outflow. In order to understand the evolution of the molecular
outflow, we compare the physical properties between the molecular outflow
observed from our NMA CO(1-0) data and the plasma gas from the soft X-ray
emission of the Chandra X-ray Observatory (CXO) archival data. We found that
the distribution between the molecular outflow and the strong plasma outflow
seems to be in a similar region. In this region, the ram pressure and the
thermal pressure of the plasma outflow are 10^{-(8-10)} dyne cm^{-2}, and the
thermal pressure of molecular outflow is 10^{-(11-13)} dyne cm^{-2}. This
implies the molecular outflow is still expanding outward. The molecular gas
consumption timescale is estimated as 17-27 Myr, and the total starburst
timescale is 20-34 Myr. The evolutionary parameter is 0.11-0.25, suggesting
that the starburst activity in NGC 3628 is still in a young stage.Comment: 15 pages, 14 figures, accepted by Ap
Spectrum of low-lying configurations with negative parity
Spectrum of low-lying five-quark configurations with strangeness quantum
number and negative parity is studied in three kinds of constituent
quark models, namely the one gluon exchange, Goldstone Boson exchange, and
instanton-induced hyperfine interaction models, respectively. Our numerical
results show that the lowest energy states in all the three employed models are
lying at 1800 MeV, about 200 MeV lower than predictions of various
quenched three-quark models. In addition, it is very interesting that the state
with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in
the other two models.Comment: Version published in Phys. Rev.
Environment-dependent dissipation in quantum Brownian motion
The dissipative dynamics of a quantum Brownian particle is studied for
different types of environment. We derive analytic results for the time
evolution of the mean energy of the system for Ohmic, sub-Ohmic and super-Ohmic
environments, without performing the Markovian approximation. Our results allow
to establish a direct link between the form of the environmental spectrum and
the thermalization dynamics. This in turn leads to a natural explanation of the
microscopic physical processes ruling the system time evolution both in the
short-time non-Markovian region and in the long-time Markovian one. Our
comparative study of thermalization for different environments sheds light on
the physical contexts in which non-Markovian dissipation effects are dominant.Comment: 10 pages, 6 figures, v2: added new references and paragraph
Microlensing Characterization of Wide-Separation Planets
With their excellent photometric precision and dramatic increase in
monitoring frequency, future microlensing survey experiments are expected to be
sensitive to very short time-scale, isolated events caused by free-floating and
wide-separation planets with mass as low as a few lunar masses. We estimate the
probability of measuring the Einstein radius \theta_E for bound and
free-floating planets. We carry out detailed simulations of the planetary
events expected in next-generation surveys and estimate the resulting
uncertainty in \theta_E for these events. We show that, for main-sequence
sources and Jupiter-mass planets, the caustic structure of wide-separation
planets with projected separations of < 20 AU substantially increases the
probability of measuring the dimensionless source size and thus determining
\theta_E compared to the case of unbound planets. In this limit where the
source is much smaller than the caustic, the effective cross-section to measure
\theta_E to 10% is ~25% larger than the full width of the caustic. Measurement
of the lens parallax is possible for low-mass planetary events by combined
observations from the ground and a satellite located in an L2 orbit; this would
complete the mass measurements for such wide-separation planets. Finally,
short-duration events caused by bound planets can be routinely distinguished
from those caused by free-floating planets for planet-star separations < 20 AU
from either the deviations due to the planetary caustic or (more often) the
low-amplitude bump from the magnification due to the parent star.Comment: 10 pages including 7 figures. ApJ, in pres
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