9,397 research outputs found
Freeze out in narrow and wide layers
The freeze out of particles from a layer of finite thickness is discussed in
a phenomenological kinetic model. The proposed model, based on the Modified
Boltzman Transport Equation, is Lorentz invariant and can be applied equally
well for the freeze out layers with space-like and time-like normal vectors. It
leads to non-equilibrated post freeze out distributions. The dependence of the
resulting distribution on the thickness of the layer is presented and discussed
for a space-like freeze out scenario.Comment: Minor corrections to improve the presentation. 4 pages, 2 figures, to
appear in the Proceedings of "Quark Matter 2005", August 4-9, 2005, Budapest,
Hungar
Covariant kinetic freeze out description through a finite space-time layer
We develop and analyze a covariant FO probability valid for a finite
space-time layer.Comment: Proceedings of "Quark Matter 2005", 4 pages, 3 figures, with
correction
AGRICULTURAL ECONOMICS STUDENTS AT SOUTHERN LAND GRANT UNIVERSITIES
Teaching/Communication/Extension/Profession,
The 3rd Flow Component as a QGP Signal
Earlier fluid dynamical calculations with QGP show a softening of the
directed flow while with hadronic matter this effect is absent. On the other
hand, we indicated that a third flow component shows up in the reaction plane
as an enhanced emission, which is orthogonal to the directed flow. This is not
shadowed by the deflected projectile and target, and shows up at measurable
rapidities, . To study the formation of this effect initial stages
of relativistic heavy ion collisions are studied. An effective string rope
model is presented for heavy ion collisions at RHIC energies. Our model takes
into account baryon recoil for both target and projectile, arising from the
acceleration of partons in an effective field. The typical field strength
(string tension) for RHIC energies is about 5-12 GeV/fm, what allows us to talk
about "string ropes". The results show that QGP forms a tilted disk, such that
the direction of the largest pressure gradient stays in the reaction plane, but
deviates from both the beam and the usual transverse flow directions. The
produced initial state can be used as an initial condition for further
hydrodynamical calculations. Such initial conditions lead to the creation of
third flow component. Recent measurements are promising that this effect
can be used as a diagnostic tool of the QGP
Frequency analysis of the first-overtone RR Lyrae stars based on the Extended Aperture Photometry from the K2 data
Additional low-amplitude signals are observed in many RR Lyrae stars, beside
the pulsations in radial modes. The most common ones are short-period signals
forming a period ratio of around 0.60--0.65 with the first overtone, or
long-period signals forming a period ratio of around 0.68. The RR Lyrae stars
may also exhibit quasi-periodic modulation of the light curves, known as the
Blazhko effect. We used the extensive sample of the first-overtone RR Lyrae
stars observed by the Kepler telescope during the K2 mission to search for and
characterize these low-amplitude additional signals. K2 data provides
space-based photometry for a statistically significant sample. Hence this data
is excellent to study in detail pulsation properties of RR Lyrae stars. We used
K2 space-based photometry for RR Lyrae candidates from Campaigns 0-19. We
selected RR Lyrae stars pulsating in the first overtone and performed a
frequency analysis for each star to characterize their frequency contents. We
classified 452 stars as first-overtone RR Lyrae. From that sample, we selected
281 RR stars, 67 RR stars, and 68 Blazhko stars. We found
particularly interesting stars which show all of the above phenomena
simultaneously. We detected signals in RR stars that form period
ratios lower than observed for the majority of stars. These signals likely form
a new sequence in the Petersen diagram, around a period ratio of 0.60. In 32
stars we detected additional signals that form a period ratio close to that
expected in RRd stars, but the classification of these stars as RRd is
uncertain. We also report a discovery of additional signals in eight stars that
form a new group in the Petersen diagram around the period ratio of
0.465-0.490. The nature of this periodicity remains unknown.Comment: 29 pages, 29 figures, 4 tables, accepted for publication in A&A, full
tables are available upon request before publicatio
Covariant description of kinetic freeze out through a finite space-like layer
The problem of Freeze Out (FO) in relativistic heavy ion reactions is
addressed. We develop and analyze an idealized one-dimensional model of FO in a
finite layer, based on the covariant FO probability. The resulting post FO
phase-space distributions are discussed for different FO probabilities and
layer thicknesses.Comment: 16 pages, 19 figures, changed content, references adde
R&D results on a CsI-TTGEM based photodetector
The very high momentum particle identification detector proposed for the
ALICE upgrade is a focusing RICH using a C4F10 gaseous radiator. For the
detection of Cherenkov photons, one of the options currently under
investigation is to use a CsI coated Triple-Thick-GEM (CsI-TTGEM) with metallic
or resistive electrodes. We will present results from the laboratory studies as
well as preliminary results of beam tests of a RICH detector prototype
consisting of a CaF2 radiator coupled to a 10x10 cm2 CsI-TTGEM equipped with a
pad readout and GASSIPLEX-based front-end electronics. With such a prototype
the detection of Cherenkov photons simultaneously with minimum ionizing
particles has been achieved for the first time in a stable operation mode
Acoustic phonon scattering in a low density, high mobility AlGaN/GaN field effect transistor
We report on the temperature dependence of the mobility, , of the
two-dimensional electron gas in a variable density AlGaN/GaN field effect
transistor, with carrier densities ranging from 0.4 cm to
3.0 cm and a peak mobility of 80,000 cm/Vs. Between
20 K and 50 K we observe a linear dependence T
indicating that acoustic phonon scattering dominates the temperature dependence
of the mobility, with being a monotonically increasing function of
decreasing 2D electron density. This behavior is contrary to predictions of
scattering in a degenerate electron gas, but consistent with calculations which
account for thermal broadening and the temperature dependence of the electron
screening. Our data imply a deformation potential D = 12-15 eV.Comment: 3 pages, 2 figures, RevTeX. Submitted to Appl Phys Let
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