3,393 research outputs found
Dynamics of uniaxial hard ellipsoids
We study the dynamics of monodisperse hard ellipsoids via a new event-driven
molecular dynamics algorithm as a function of volume fraction and aspect
ratio . We evaluate the translational and the rotational
diffusion coefficient and the associated isodiffusivity lines in the
plane. We observe a decoupling of the translational and rotational
dynamics which generates an almost perpendicular crossing of the
and isodiffusivity lines. While the self intermediate scattering
function exhibits stretched relaxation, i.e. glassy dynamics, only for large
and , the second order orientational correlator
shows stretching only for large and small values. We discuss these
findings in the context of a possible pre-nematic order driven glass
transition.Comment: accepted by Phys. Rev. Let
The Double-Lined Spectrum of LBV 1806-20
Despite much theoretical and observational progress, there is no known firm
upper limit to the masses of stars. Our understanding of the interplay between
the immense radiation pressure produced by massive stars in formation and the
opacity of infalling material is subject to theoretical uncertainties, and many
observational claims of ``the most massive star'' have failed the singularity
test. LBV 1806-20 is a particularly luminous object, L~10^6 Lsun, for which
some have claimed very high mass estimates (M_initial>200 Msun), based, in
part, on its similarity to the Pistol Star. We present high-resolution
near-infrared spectroscopy of LBV 1806-20, showing that it is possibly a binary
system with components separated in velocity by ~70 kms. If correct, then this
system is not the most massive star known, yet it is a massive binary system.
We argue that a binary, or merged, system is more consistent with the ages of
nearby stars in the LBV 1806-20 cluster. In addition, we find that the velocity
of V_LSR=36 kms is consistent with a distance of 11.8 kpc, a luminosity of
10^6.3 Lsun, and a system mass of ~130 Msun.Comment: ApJL, accepte
Recent results from lattice calculations
Recent results from lattice QCD calculations relevant to particle physics
phenomenology are reviewed. They include the calculations of strong coupling
constant, quark masses, kaon matrix elements, and D and B meson matrix
elements. Special emphasis is on the recent progress in the simulations
including dynamical quarks.Comment: 13 pages, 8 figures, plenary talk at the 32nd International
Conference on High-Energy Physics (ICHEP 2004), August 16-22, 2004, Beijing,
Chin
Hadron production in heavy relativistic systems
We investigate particle production in heavy-ion collisions at RHIC energies
as function of incident energy, and centrality in a three-sources Relativistic
Diffusion Model. Pseudorapidity distributions of produced charged hadrons in Au
+ Au and Cu + Cu collisions at sqrt(s_NN) = 19.6 GeV, 62.4 GeV, 130 GeV and 200
GeV show an almost equilibrated midrapidity source that tends to increase in
size towards higher incident energy, and more central collisions. It may
indicate quark-gluon plasma formation prior to hadronization.Comment: 8 pages, 3 figure
Metallicity in the Galactic Center: The Arches cluster
We present a quantitative spectral analysis of five very massive stars in the
Arches cluster, located near the Galactic center, to determine stellar
parameters, stellar wind properties and, most importantly, metallicity content.
The analysis uses a new technique, presented here for the first time, and uses
line-blanketed NLTE wind/atmosphere models fit to high-resolution near-infrared
spectra of late-type nitrogen-rich Wolf-Rayet stars and OfI+ stars in the
cluster. It relies on the fact that massive stars reach a maximum nitrogen
abundance that is related to initial metallicity when they are in the WNL
phase. We determine the present-day nitrogen abundance of the WNL stars in the
Arches cluster to be 1.6% (mass fraction) and constrain the stellar metallicity
in the cluster to be solar. This result is invariant to assumptions about the
mass-luminosity relationship, the mass-loss rates, and rotation speeds. In
addition, from this analysis, we find the age of the Arches cluster to be
2-2.5Myr, assuming coeval formation
Properties of the phonon-induced pairing interaction in YBaCuO within the local density approximation
The properties of the phonon-induced interaction between electrons are
studied using the local density approximation (LDA). Restricting the electron
momenta to the Fermi surface we find generally that this interaction has a
pronounced peak for large momentum transfers and that the interband
contributions between bonding and antibonding band are of the same magnitude as
the intraband ones. Results are given for various symmetry averages of this
interaction over the Fermi surface. In particular, we find that the
dimensionless coupling constant in the d-wave channel , relevant for
superconductivity, is only 0.022, i.e., even about ten times smaller than the
small value of the s-wave channel. Similarly, the LDA contribution to the
resistivity is about a factor 10 times smaller than the observed resistivity
suggesting that phonons are not the important low-energy excitations in
high-T oxides.Comment: 6 pages, 7 figure
Beyond the periodic orbit theory
The global constraints on chaotic dynamics induced by the analyticity of
smooth flows are used to dispense with individual periodic orbits and derive
infinite families of exact sum rules for several simple dynamical systems. The
associated Fredholm determinants are of particularly simple polynomial form.
The theory developed suggests an alternative to the conventional periodic orbit
theory approach to determining eigenspectra of transfer operators.Comment: 29 pages Latex2
A new extragalactic distance determination method using the flux-weighted gravity of late B and early A supergiants
Stellar evolution calculations predict the flux-weighted gravity g/Teff^4 and
absolute bolometric magnitude of blue supergiants to be strongly correlated. We
use medium resolution multi-object spectroscopy of late B and early A
supergiants in two spiral galaxies, NGC 300 and NGC 3621, to demonstrate the
existence of such a relationship, which proves to be surprisingly tight. An
analysis of high resolution spectra of blue supergiants in Local Group galaxies
confirms this detection. We discuss the application of the relationship for
extragalactic distance determinations and conservatively conclude that once
properly calibrated it has the potential to allow for measurements of distance
moduli out to 30.5 mag with an accuracy of 0.1 mag or better.Comment: 9 pages, 1 table, 3 figures. Accepted for publication in the
Astrophysical Journal Letter
Current Pathophysiological and Genetic Aspects of Dilated Cardiomyopathy
Dilated cardiomyopathy is the most common form of cardiomyopathy and the second leading cause of left ventricular dysfunction with highly variable clinical presentation and prognosis. The clinical courses vary and are strongly heterogeneous, ranging from asymptomatic patients to those suffering from intractable heart failure or sudden cardiac death due to arrhythmias. Previous studies have reported a 10 years cardiovascular mortality up to 40% in developed countries, due to advanced heart failure or sudden cardiac death. However, the prognosis of dilated cardiomyopathy patients is variable and depends on multiple risk factors. This chapter provides a review of dilated cardiomyopathy with specific focus on the pathophysiological aspects and genetic etiology of the disease
The implementation of the CLaMS Lagrangian transport core into the chemistry climate model EMAC 2.40.1: application on age of air and transport of long-lived trace species
Lagrangian transport schemes have proven to be useful tools for modelling stratospheric trace gas transport since they are less diffusive than classical Eulerian schemes and therefore especially well suited for maintaining steep tracer gradients. Here, we present the implementation of the full-Lagrangian transport core of the Chemical Lagrangian Model of the Stratosphere (CLaMS) into the ECHAM/MESSy Atmospheric Chemistry model (EMAC). We performed a ten-year time-slice simulation to evaluate the coupled model system EMAC/CLaMS. Simulated zonal mean age of air distributions are compared to age of air derived from airborne measurements, showing a good overall representation of the stratospheric circulation. Results from the new Lagrangian transport scheme are compared to tracer distributions calculated with the standard flux-form semi-Lagrangian (FFSL) transport scheme in EMAC. The differences in the resulting tracer distributions are most pronounced in the regions of strong transport barriers. The polar vortices are presented as an example and simulated trace gas distributions are compared to satellite measurements. The analysis of CFC-11, N2O, CH4, and age of air in the polar vortex regions shows that the CLaMS Lagrangian transport scheme produces a stronger, more realistic transport barrier at the edge of the polar vortex than the FFSL transport scheme of EMAC. Differences in simulated age of air range up to one year in the Arctic polar vortex in late winter/early spring. The new coupled model system EMAC/CLaMS thus constitutes a suitable tool for future model studies of stratospheric tracer transport
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