37,447 research outputs found
Diversity and Adaptation in Large Population Games
We consider a version of large population games whose players compete for
resources using strategies with adaptable preferences. The system efficiency is
measured by the variance of the decisions. In the regime where the system can
be plagued by the maladaptive behavior of the players, we find that diversity
among the players improves the system efficiency, though it slows the
convergence to the steady state. Diversity causes a mild spread of resources at
the transient state, but reduces the uneven distribution of resources in the
steady state.Comment: 8 pages, 3 figure
QT peak prolongation predicts cardiac death following stroke
Cardiac death has been linked in many populations to prolongation of the QT interval (QTe). However, basic science research suggested that the best estimate of the time point when repolarisation begins is near the T-wave peak. We found QT peak (QTp) was longer in hypertensive subjects with LVH. A prolonged “depolarisation” phase, rather than “repolarisation” (T peak to T end) might therefore account for the higher incidence of cardiac death linked to long QT. Hypothesis: We have tested the hypothesis that QT peak (QTp) prolongation predicts cardiac death in stroke survivors. Methods and Results: ECGs were recorded from 296 stroke survivors (152 male), mean age 67.2 (SD 11.6) approximately 1 year after the event. Their mean blood pressure was 152/88 mmHg (SD 29/15mmHg). These ECGs were digitised by one observer who was blinded to patient outcome. The patients were followed up for a median of 3.3 years. The primary endpoint was cardiac death. A prolonged heart rate corrected QT peak (QTpc) of lead I carried the highest relative risk of death from all cause as well as cardiac death, when compared with the other more conventional QT indices. In multivariate analyses, when adjusted for conventional risk factors of atherosclerosis, a prolonged QTpc of lead I was still associated with a 3-fold increased risk of cardiac death. (adjusted relative risk 3.0 [95% CI 1.1 - 8.5], p=0.037). Conclusion: QT peak prolongation in lead I predicts cardiac death after strok
Current-Induced Spin Polarization in Gallium Nitride
Electrically generated spin polarization is probed directly in bulk GaN using
Kerr rotation spectroscopy. A series of n-type GaN epilayers are grown in the
wurtzite phase both by molecular beam epitaxy (MBE) and metalorganic chemical
vapor deposition (MOCVD) with a variety of doping densities chosen to broadly
modulate the transverse spin lifetime, T2*. The spin polarization is
characterized as a function of electrical excitation energy over a range of
temperatures. Despite weak spin-orbit interactions in GaN, a current-induced
spin polarization (CISP) is observed in the material at temperatures of up to
200 K.Comment: 16 pages, 3 figure
Pion Interferometry for Hydrodynamical Expanding Source with a Finite Baryon Density
We calculate the two-pion correlation function for an expanding hadron source
with a finite baryon density. The space-time evolution of the source is
described by relativistic hydrodynamics and the Hanbury-Brown-Twiss (HBT)
radius is extracted after effects of collective expansion and multiple
scattering on the HBT interferometry have been taken into account, using
quantum probability amplitudes in a path-integral formalism. We find that this
radius is substantially smaller than the HBT radius extracted from the
freeze-out configuration.Comment: 4 pages, 2 figure
Universality and Phase Diagram around Half-filled Landau Level
Gated GaAs/AlGaAs heterostructures were used to determine the low-temperature
behavior of the two-dimensional electron gas near filling factor nu=1/2 in the
disorder-magnetic-field plane. We identify a line on which sigma_{xy} is
temperature independent, has value sigma_{xy}=0.5 (e^{2}/h), and a distinct
line on which rho_{xy}=2 (h/e^{2}). The phase boundaries between the Hall
insulator and the principal quantum Hall liquids at nu=1 and 1/3 show
levitation of the delocalized states of the first Landau levels for electrons
and composite fermions. Finally, the data suggest that there is no true
metallic phase around nu=1/2.Comment: 7 pages (Revtex), 5 figure
Human engineering design criteria study Final report
Human engineering design criteria for use in designing earth launch vehicle systems and equipmen
Spectral distortions to the Cosmic Microwave Background from the recombination of hydrogen and helium
The recombination of hydrogen and helium at z~1000-7000 gives unavoidable
distortions to the Cosmic Microwave Background (CMB) spectrum. We present a
detailed calculation of the line intensities arising from the Ly-alpha (2p-1s)
and two-photon (2s-1s) transitions for the recombination of hydrogen, as well
as the corresponding lines from helium. We give an approximate formula for the
strength of the main recombination line distortion on the CMB in different
cosmologies, this peak occurring at about 170 microns. We also find a
previously undescribed long wavelength peak (which we call the
pre-recombination peak) from the lines of the 2p-1s transitions, which are
formed before significant recombination of the corresponding atoms occurred.
Detailed calculations of the two-photon emission line shapes are presented here
for the first time. The frequencies of the photons emitted from the two-photon
transition have a wide spectrum and this causes the location of the peak of the
two-photon line of hydrogen to be located almost at the same wavelength as the
main Ly-alpha peak. The helium lines also give distortions at similar
wavelengths, so that the combined distortion has a complex shape. The detection
of this distortion would provide direct supporting evidence that the Universe
was indeed once a plasma. Moreover, the distortions are a sensitive probe of
physics during the time of recombination. Although the spectral distortion is
overwhelmed by dust emission from the Galaxy, and is maximum at wavelengths
roughly where the cosmic far-infrared background peaks, it may be able to
tailor an experiment to detect its non-trivial shape.Comment: 12 pages, 12 figures; Minor corrections in text and references; MNRAS
in pres
Fluctuations in the Site Disordered Traveling Salesman Problem
We extend a previous statistical mechanical treatment of the traveling
salesman problem by defining a discrete "site disordered'' problem in which
fluctuations about saddle points can be computed. The results clarify the basis
of our original treatment, and illuminate but do not resolve the difficulties
of taking the zero temperature limit to obtain minimal path lengths.Comment: 17 pages, 3 eps figures, revte
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