31,889 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
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
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
Strain Effects on Point Defects and Chain-Oxygen Order-Disorder Transition in 123-Structure Cuprate Superconductors
The energetics of Schottky defects in 123 cuprate superconductor series, (where RE = lanthandies) and (AE =
alkali-earths), were found to have unusual relations if one considers only the
volumetric strain. Our calculations reveal the effect of non-uniform changes of
interatomic distances within the RE-123 structures, introduced by doping
homovalent elements, on the Schottky defect formation energy. The energy of
formation of Frenkel Pair defects, which is an elementary disordering event, in
123 compounds can be substantially altered under both stress and chemical
doping. Scaling the oxygen-oxygen short-range repulsive parameter using the
calculated formation energy of Frenkel pair defects, the transition temperature
between orthorhombic and tetragonal phases is computed by quasi-chemical
approximations (QCA). The theoretical results illustrate the same trend as the
experimental measurements in that the larger the ionic radius of RE, the lower
the orthorhombic/tetragonal phase transition temperature. This study provides
strong evidence of the strain effects on order-disorder transition due to
oxygens in the CuO chain sites.Comment: In print Phys Rev B (2004
Relativistic Modification of the Gamow Factor
In processes involving Coulomb-type initial- and final-state interactions,
the Gamow factor has been traditionally used to take into account these
additional interactions. The Gamow factor needs to be modified when the
magnitude of the effective coupling constant increases or when the velocity
increases. For the production of a pair of particles under their mutual
Coulomb-type interaction, we obtain the modification of the Gamow factor in
terms of the overlap of the Feynman amplitude with the relativistic wave
function of the two particles. As a first example, we study the modification of
the Gamow factor for the production of two bosons. The modification is
substantial when the coupling constant is large.Comment: 13 pages, in LaTe
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