9,457 research outputs found
Thermalization through Hagedorn states - the importance of multiparticle collisions
Quick chemical equilibration times of hadrons within a hadron gas are
explained dynamically using Hagedorn states, which drive particles into
equilibrium close to the critical temperature. Within this scheme master
equations are employed for the chemical equilibration of various hadronic
particles like (strange) baryon and antibaryons. A comparison of the Hagedorn
model to recent lattice results is made and it is found that for both Tc =176
MeV and Tc=196 MeV, the hadrons can reach chemical equilibrium almost
immediately, well before the chemical freeze-out temperatures found in thermal
fits for a hadron gas without Hagedorn states.Comment: 8 pages, 3 figures, talk presented at the International Conference on
Strangeness in Quark Matter, Buzios, Rio de Janeiro, Brazil, Sept. 27 - Oct.
2, 200
The Characteristics of Magnetic CVs in the Period Gap
We have observed several magnetic cataclysmic variables located in the range
between 2 and 3 hours, known as the period gap. This work was prompted by the
recent discovery of RX J1554.2+2721. It has 2.54 hours orbital period and shows
almost pure cyclotron continuum in a low luminosity state, similar to
HS1023+3900,
HS0922+1333 and RBS206. These are low accretion rate polars (LARPs) known to
have mass transfer rates of order of a few 10^-13Msun/year.
The aim of the study was to find out, if magnetic systems filling the period
gap are in any way different from their counterparts outside that range of
periods. The only significant difference we encounter, is much higher number of
asynchronous magnetic systems to-wards longer periods than below the gap.Comment: 7 pages, 7 figures, To appear in `Magnetic Cataclysmic Variables',
IAU Col. 190 (Cape Town), eds. M. Cropper & S. Vrielman
Optical tuning of the scattering length of cold alkaline earth atoms
It is possible to tune the scattering length for the collision of ultra-cold
1S0 ground state alkaline-earth atoms using an optical Feshbach resonance. This
is achieved with a laser far detuned from an excited molecular level near the
frequency of the atomic intercombination 1S0--3P1 transition. Simple resonant
scattering theory, illustrated by the example of 40Ca, allows an estimate of
the magnitude of the effect. Unlike alkali metal species, large changes of the
scattering length are possible while atom loss remains small, because of the
very narrow line width of the molecular photoassociation transition. This
raises prospects for control of atomic interactions for a system without
magnetically tunable Feshbach resonance levels
The Discovery of Quasisoft and Supersoft Sources in External Galaxies
We apply a uniform procedure to select very soft sources from point sources
observed by Chandra in 4 galaxies. This sample includes one elliptical galaxy
(NGC 4967), 2 face-on spirals (M101 and M83), and an interacting galaxy (M51).
We have found very soft X-ray sources (VSSs) in every galaxy. Some of these fit
the criteria for canonical supersoft sources (SSSs), while others are somewhat
harder. These latter have characteristic values of kT < 300 eV; we refer to
them as quasisoft sources (QSSs). We found a combined total of 149 VSSs in the
4 galaxies we considered; 77 were SSSs and 72 were QSSs. (See the paper for the
original long abstract)Comment: 20 pages, 6 figures. Accepted for publication in Ap
Time-dependent Hartree-Fock studies of superheavy molecules
The time dependent Hartree-Fock approximation is used to study the dynamical formation of long-lived superheavy nuclear complexes. The effects of long-range Coulomb polarization are treated in terms of a classical quadrupole polarization model. Our calculations show the existence of "resonantlike" structures over a narrow range of bombarding energies near the Coulomb barrier. Calculations of 238U + 238U are presented and the consequences of these results for supercritical positron emission are discussed. NUCLEAR REACTIONS 238U + 238U collisions as a function of bombarding energy, in the time-dependent Hartree-Fock approximation. Superheavy molecules and strongly damped collisions
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