11,130 research outputs found
Comparing the drag force on heavy quarks in N=4 super-Yang-Mills theory and QCD
Computations of the drag force on a heavy quark moving through a thermal
state of strongly coupled N=4 super-Yang-Mills theory have appeared recently in
hep-th/0605158, hep-ph/0605199, and hep-th/0605182. I compare the strength of
this effect between N=4 gauge theory and QCD, using the static force between
external quarks to normalize the 't Hooft coupling. Comparing N=4 and QCD at
fixed energy density then leads to a relaxation time of roughly 2 fm/c for
charm quarks moving through a quark-gluon plasma at T=250 MeV. This estimate
should be regarded as preliminary because of the difficulties of comparing two
such different theories.Comment: 16 pages, 1 figure. v2: corrected estimate of eta/s, refs adde
Worldsheet Matter Superfields on Half-Shell
In this paper we discuss some of the effects of using "unidexterous"
worldsheet superfields, which satisfy worldsheet differential constraints and
so are partly on-shell, i.e., on half-shell. Most notably, this results in a
stratification of the field space that reminds of "brane-world" geometries.
Linear dependence on such superfields provides a worldsheet generalization of
the super-Zeeman effect. In turn, non-linear dependence yields additional
left-right asymmetric dynamical constraints on the propagating fields, again in
a stratified fashion.Comment: 15 pages, 2 figures; minor algebraic correction
S-Wave Quarkonia in Potential Models
We discuss S-wave quarkonia correlators and spectral function using the
Wong-potential, and show that these do not agree with the lattice results.Comment: based on talk presented at Strangeness in Quark Matter, UCLA, March
26-31, 200
Mathematical Modeling for Studying Microbial Processes â Some Examples
Mathematical modeling may have different purposes in chemical
and biochemical engineering sciences. One of them is to confirm or to
reject kinetic models for certain processes, or to evaluate the importance of
some transport phenomena on the net chemical or biochemical reaction rate.
In the present paper different microbial processes are considered and modeled
for evaluation of kinetic constants for batch and continuous processes
accomplished by free and immobilized microbial cells. The practical examples
are from the field of wastewater treatment and biosynthesis of products,
like enzymes, lactic acid, gluconic acid, etc.
By the aid of mathematical modeling the kinetics and the type of inhibition
are specified for microbial wastewater denitrification and biodegradation
of halogenated hydrocarbons. The importance of free and immobilized
cells and their separate contribution to the overall microbial process
is also evaluated for some fermentation processes: gluconic acid production,
dichloroethane biodegradation, lactic acid fermentation and monochloroacetic acid biodegradation
Another deep dimming of the classical T Tauri star RW Aur A
Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich
emission line spectrum. In 2014 the star faded by ~ 3 magnitudes in the V band
and went into a long-lasting minimum. In 2010 the star suffered from a similar
fading, although less deep. These events in RW Aur A are very unusual among the
CTTS, and have been attributed to occultations by passing dust clouds. Aims. We
want to find out if any spectral changes took place after the last fading of RW
Aur A with the intention to gather more information on the occulting body and
the cause of the phenomenon. Methods. We collected spectra of the two
components of RW Aur. Photometry was made before and during the minimum.
Results. The overall spectral signatures reflecting emission from accretion
flows from disk to star did not change after the fading. However, blue-shifted
absorption components related to the stellar wind had increased in strength in
certain resonance lines, and the profiles and strengths, but not fluxes, of
forbidden lines had become drastically different. Conclusions. The extinction
through the obscuring cloud is grey indicating the presence of large dust
grains. At the same time, there are no traces of related absorbing gas. The
cloud occults the star and the interior part of the stellar wind, but not the
wind/jet further out. The dimming in 2014 was not accompanied by changes in the
accretion flows at the stellar surface. There is evidence that the structure
and velocity pattern of the stellar wind did change significantly. The dimmings
could be related to passing condensations in a tidally disrupted disk, as
proposed earlier, but we also speculate that large dust grains have been
stirred up from the inclined disk into the line-of-sight through the
interaction with an enhanced wind.Comment: 5 pages, 5 figures, Accepted for publication in A&
Analytical solutions for the dynamics of two trapped interacting ultracold atoms
We discuss exact solutions of the Schroedinger equation for the system of two
ultracold atoms confined in an axially symmetric harmonic potential. We
investigate different geometries of the trapping potential, in particular we
study the properties of eigenenergies and eigenfunctions for quasi-one- and
quasi-two-dimensional traps. We show that the quasi-one- and the
quasi-two-dimensional regimes for two atoms can be already realized in the
traps with moderately large (or small) ratios of the trapping frequencies in
the axial and the transverse directions. Finally, we apply our theory to
Feshbach resonances for trapped atoms. Introducing in our description an
energy-dependent scattering length we calculate analytically the eigenenergies
for two trapped atoms in the presence of a Feshbach resonance.Comment: RevTeX, 15 pages, 15 figure
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