13,703 research outputs found
Optimal Lattice-Reduction Aided Successive Interference Cancellation for MIMO Systems
In this letter, we investigated the optimal minimummean-squared-error (MMSE) based successive interference cancellation (SIC) strategy designed for lattice-reduction aided multiple-input multiple-output (MIMO) detectors. For the sake of generating the MMSE-based MIMO symbol estimate at each SIC detection stage, we model the so-called effective symbols generated with the aid of lattice-reduction as joint Gaussian distributed random variables. However, after lattice-reduction, the effective symbols become correlated and exhibit a non-zero mean. Hence, we derive the optimal MMSE SIC detector, which updates the mean and variance of the effective symbols at each SIC detection stage. As a result, the proposed detector achieves a better performance compared to its counterpart dispensing with updating the mean and variance, and performs close to the maximum likelihood detector. Index Terms—Lattice-reduction, multiple antennas, MIMO, symbol detection, SIC detector
Swift Observations of X-ray supernovae
We present a result of X-ray supernovae (SNe) survey using the Swift
satellite public archive. An automatic searching program was designed to search
X-ray SNe among all of the Swift archival observations between November 2004
and February 2011. Using the C++ program, 24 X-ray detectable supernovae have
been found in the archive and 3 of them were newly-discovered in X-rays which
are SN 1986L, SN 2003lx, and SN 2007od. In addition, SN 2003lx is a Type Ia
supernova which may be the second X-ray detectable Type Ia after SN 2005ke
(Immler et al. 2006). Calibrated data of luminous type Ib/c supernovae was
consistent to the X-ray emission model done by Chevalier & Fransson (1994).
Statistics about the luminosities and hardness ratio have been done to purpose
of getting the X-ray emission features of the X-ray supernovae. The results
from this work help investigating the X-ray evolution of SNe and developing
similar X-ray SNe surveys in various X-rays missions
Effects of motion on jet exhaust noise from aircraft
The various problems involved in the evaluation of the jet noise field prevailing between an observer on the ground and an aircraft in flight in a typical takeoff or landing approach pattern were studied. Areas examined include: (1) literature survey and preliminary investigation, (2) propagation effects, (3) source alteration effects, and (4) investigation of verification techniques. Sixteen problem areas were identified and studied. Six follow-up programs were recommended for further work. The results and the proposed follow-on programs provide a practical general technique for predicting flyover jet noise for conventional jet nozzles
Quintessential Kination and Leptogenesis
Thermal leptogenesis induced by the CP-violating decay of a right-handed
neutrino (RHN) is discussed in the background of quintessential kination, i.e.,
in a cosmological model where the energy density of the early Universe is
assumed to be dominated by the kinetic term of a quintessence field during some
epoch of its evolution. This assumption may lead to very different
observational consequences compared to the case of a standard cosmology where
the energy density of the Universe is dominated by radiation. We show that,
depending on the choice of the temperature T_r above which kination dominates
over radiation, any situation between the strong and the super--weak wash--out
regime are equally viable for leptogenesis, even with the RHN Yukawa coupling
fixed to provide the observed atmospheric neutrino mass scale ~ 0.05 eV. For M<
T_r < M/100, i.e., when kination stops to dominate at a time which is not much
later than when leptogenesis takes place, the efficiency of the process,
defined as the ratio between the produced lepton asymmetry and the amount of CP
violation in the RHN decay, can be larger than in the standard scenario of
radiation domination. This possibility is limited to the case when the neutrino
mass scale is larger than about 0.01 eV. The super--weak wash--out regime is
obtained for T_r << M/100, and includes the case when T_r is close to the
nucleosynthesis temperature ~ 1 MeV. Irrespective of T_r, we always find a
sufficient window above the electroweak temperature T ~ 100 GeV for the
sphaleron transition to thermalize, so that the lepton asymmetry can always be
converted to the observed baryon asymmetry.Comment: 13 pages, 8 figure
A Two Energy Gap Preformed-Pair Scenario For the Cuprates: Implications for Angle-Resolved Photoemission Spectroscopy
We show how, within a preformed pair scenario for the cuprate pseudogap, the
nodal and antinodal responses in angle resolved photoemission spectroscopy
necessarily have very different temperature dependences. We examine the
behavior and the contrasting dependences for a range of temperatures both
below and above . Our calculations are based on a fully microscopic
-matrix approach for addressing pairing correlations in a regime where the
attraction is stronger than BCS and the coherence length is anomalously short.
Previously, the distinct nodal and anti-nodal responses have provided strong
support for the "two-gap scenario" of the cuprates in which the pseudogap
competes with superconductivity. Instead, our theory supports a picture in
which the pseudogap derives from pairing correlations, identifying the two gap
components with non-condensed and condensed pairs. It leads to reasonably good
agreement with a range of different experiments in the moderately underdoped
regime and we emphasize that here there is no explicit curve fitting. Ours is a
microscopic rather than a phenomenological theory. We briefly address the more
heavily underdoped regime in which the behavior is more complex.Comment: 12 pages; 10 figure
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