3,602 research outputs found
Formulating Viscous Hydrodynamics for Large Velocity Gradients
Viscous corrections to relativistic hydrodynamics, which are usually
formulated for small velocity g radients, have recently been extended from
Navier-Stokes formulations to a class of treatments based on Israel-Stewart
equations. Israel-Stewart treatments, which treat the spatial components of the
s tress-energy tensor tau_ij as dynamical objects, introduce new parameters,
such as the relaxati on times describing non-equilibrium behavior of the
elements tau_ij. By considering linear resp onse theory and entropy
constraints, we show how the additional parameters are related to fluctuatio ns
of tau_ij. Furthermore, the Israel-Stewart parameters are analyzed for their
ability to prov ide stable and physical solutions for sound waves. Finally, it
is shown how these parameters, which are naturally described by correlation
functions in real time, might be constrained by lattice calcu lations, which
are based on path-integral formulations in imaginary time.Comment: 16 page
Ground-states of spin-1 bosons in asymmetric double-wells
In this work we investigate the different states of a system of spin-1 bosons
in two potential wells connected by tunneling, with spin-dependent interaction.
The model utilizes the well-known Bose-Hubbard Hamiltonian, adding a local
interaction term that depends on the modulus of the total spin in a well,
favoring a high- or low-spin state for different signs of the coupling
constant. We employ the concept of fidelity to detect critical values of
parameters for which the ground state undergoes significant changes. The nature
of the states is investigated through evaluation of average occupation numbers
in the wells and of spin correlations. A more detailed analysis is done for a
two-particle system, but a discussion of the three-particle case and some
results for larger numbers are also presented.Comment: 7 pages, 10 figure
Near-Infrared spectroscopy of the super star cluster in NGC1705
We study the near-infrared properties of the super star cluster NGC1750-1 in
order to constrain its spatial extent, its stellar population and its age. We
use adaptive optics assisted integral field spectroscopy with SINFONI on the
VLT. We estimate the spatial extent of the cluster and extract its K-band
spectrum from which we constrain the age of the dominant stellar population.
Our observations have an angular resolution of about 0.11", providing an upper
limit on the cluster radius of 2.85+/-0.50 pc depending on the assumed
distance. The K-band spectrum is dominated by strong CO absorption bandheads
typical of red supergiants. Its spectral type is equivalent to a K4-5I star.
Using evolutionary tracks from the Geneva and Utrecht groups, we determine an
age of 12+/-6 Myr. The large uncertainty is rooted in the large difference
between the Geneva and Utrecht tracks in the red supergiants regime. The
absence of ionized gas lines in the K-band spectrum is consistent with the
absence of O and/or Wolf-Rayet stars in the cluster, as expected for the
estimated age.Comment: 5 pages, 4 figures. Research Note accepted in Astronomy and
Astrophysic
Heisenberg spin chains based on sl(2|1) symmetry
We find solutions of the Yang-Baxter equation acting on tensor product of
arbitrary representations of the superalgebra sl(2|1). Based on these solutions
we construct the local Hamiltonians for integrable homogeneous periodic chains
and open chains.Comment: 28 pages LATE
Universal R-matrix as integral operator
We derive the integral operator form for the general rational solution of the
Yang-Baxter equation with symmetry. Considering the defining
relations for the kernel of the R-operator as a system of second order
differential equations we observe remarkable reduction to a system of simple
first order equations. The obtained kernel of R-operator has a very simple
structure. To illustrate all this in the simplest situation we treat also the
case.Comment: 26 pages LaTe
Measures of galaxy dust and gas mass with Herschel photometry and prospects for ALMA
(Abridged) Combining the deepest Herschel extragalactic surveys (PEP,
GOODS-H, HerMES), and Monte Carlo mock catalogs, we explore the robustness of
dust mass estimates based on modeling of broad band spectral energy
distributions (SEDs) with two popular approaches: Draine & Li (2007, DL07) and
a modified black body (MBB). As long as the observed SED extends to at least
160-200 micron in the rest frame, M(dust) can be recovered with a >3 sigma
significance and without the occurrence of systematics. An average offset of a
factor ~1.5 exists between DL07- and MBB-based dust masses, based on consistent
dust properties. At the depth of the deepest Herschel surveys (in the GOODS-S
field) it is possible to retrieve dust masses with a S/N>=3 for galaxies on the
main sequence of star formation (MS) down to M(stars)~1e10 [M(sun)] up to z~1.
At higher redshift (z<=2) the same result is achieved only for objects at the
tip of the MS or lying above it. Molecular gas masses, obtained converting
M(dust) through the metallicity-dependent gas-to-dust ratio delta(GDR), are
consistent with those based on the scaling of depletion time, and on CO
spectroscopy. Focusing on CO-detected galaxies at z>1, the delta(GDR)
dependence on metallicity is consistent with the local relation. We combine
far-IR Herschel data and sub-mm ALMA expected fluxes to study the advantages of
a full SED coverage.Comment: Accepted for publication in Astronomy and Astrophysics. Some figures
have degraded quality for filesize reason
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