2,312 research outputs found
The jet quenching in high energy nuclear collisions and quark-gluon plasma
e investigate the energy loss of quark and gluon jets in quark-gluon plasma
produced in central Au+Au collisions at RHIC energy. We use the physical
characteristic of initial and mixed phases, which were found in effective
quasiparticle model for SPS and RHIC energy. At investigation of energy loss we
take into account also the production of hot glue at first stage. The energy
loss in expanding plasma is calculated in dominant first order of radiation
intensity with accounting of finite kinematic bounds. We calculate the
suppression of - spectra with moderate high , which is
caused by energy loss of quark and gluon jets. The comparison with suppression
of reported by PHENIX show, that correct quantitative description of
suppression we have only in model of phase transition with decrease of thermal
gluon mass and effective coupling in region of phase transition plasma
into hadrons (at ). However quasiparticle model with increase of
these values at in accordance with perturbative QCD lead to too
great energy loss of gluon and quark jets, which disagrees with data on
suppression of . Thus it is possible with help of hard processes to
investigate the structure of phase transition. We show also, that energy losses
at SPS energy are too small in order to be observable. This is caused in fact
by sufficiently short plasma phase at this energy.Comment: 17 pages, 3 figures, 2 table
Quantitatively measuring the influence of helium in plasma-exposed tungsten
AbstractTungsten samples are exposed to 3He plasma to quantify their helium retention behavior. The retention saturates quickly with helium fluence and increases only slightly from 4.3×1019He/m2 at 773K, to 7.5×1019He/m2 at 973K. The helium content increases dramatically to 6.8×1020He/m2 when fuzz is formed on the surface of a sample exposed at 1173K, but the majority of the retained helium (5.1×1020He/m2) is found to reside below the layer of fuzz tendrils. Additional tungsten samples were exposed to either simultaneous, or sequential, D/He plasma, followed by TDS. Measurements show the majority of the D retained during simultaneous exposures is located in the near surface region of helium nano-bubbles. No deuterium was detected in any of the samples after the heating to 1273K, but 67% of the helium was released from simultaneously exposed samples, and only 23% of the helium was released from the sequentially exposed samples
Universality of the Crossing Probability for the Potts Model for q=1,2,3,4
The universality of the crossing probability of a system to
percolate only in the horizontal direction, was investigated numerically by
using a cluster Monte-Carlo algorithm for the -state Potts model for
and for percolation . We check the percolation through
Fortuin-Kasteleyn clusters near the critical point on the square lattice by
using representation of the Potts model as the correlated site-bond percolation
model. It was shown that probability of a system to percolate only in the
horizontal direction has universal form for
as a function of the scaling variable . Here,
is the probability of a bond to be closed, is the
nonuniversal crossing amplitude, is the nonuniversal metric factor,
is the nonuniversal scaling index, is the correlation
length index.
The universal function . Nonuniversal scaling factors
were found numerically.Comment: 15 pages, 3 figures, revtex4b, (minor errors in text fixed,
journal-ref added
A Brief Introduction to Chiral Perturbation Theory
A brief introduction to the subject of chiral perturbation theory (pt)
is presented, including a discussion of effective field theory and applications
of pt in the arena of purely mesonic interactions as well as in the sector.Comment: 15 pages, talk given at TAPS detector workshop, Rez, Czech Republic,
Sept. 1999, to be published in Czech. J. Phy
Decoherence in Disordered Conductors at Low Temperatures, the effect of Soft Local Excitations
The conduction electrons' dephasing rate, , is expected to
vanish with the temperature. A very intriguing apparent saturation of this
dephasing rate in several systems was recently reported at very low
temperatures. The suggestion that this represents dephasing by zero-point
fluctuations has generated both theoretical and experimental controversies. We
start by proving that the dephasing rate must vanish at the limit,
unless a large ground state degeneracy exists. This thermodynamic proof
includes most systems of relevance and it is valid for any determination of
from {\em linear} transport measurements. In fact, our
experiments demonstrate unequivocally that indeed when strictly linear
transport is used, the apparent low-temperature saturation of is
eliminated. However, the conditions to be in the linear transport regime are
more strict than hitherto expected. Another novel result of the experiments is
that introducing heavy nonmagnetic impurities (gold) in our samples produces,
even in linear transport, a shoulder in the dephasing rate at very low
temperatures. We then show theoretically that low-lying local defects may
produce a relatively large dephasing rate at low temperatures. However, as
expected, this rate in fact vanishes when , in agreement with our
experimental observations.Comment: To appear in the proceedings of the Euresco Conference on Fundamental
Problems of Mesoscopic Physics, Granada, September 2003, Kluwe
Density functional theory and demixing of binary hard rod-polymer mixtures
A density functional theory for a mixture of hard rods and polymers modeled
as chains built of hard tangent spheres is proposed by combining the functional
due to Yu and Wu for the polymer mixtures [J. Chem. Phys. {\bf 117}, 2368
(2002)] with the Schmidt's functional [Phys. Rev. E {\bf 63}, 50201 (2001)] for
rod-sphere mixtures. As a simple application of the functional, the demixing
transition into polymer-rich and rod-rich phases is examined. When the chain
length increases, the phase boundary broadens and the critical packing fraction
decreases. The shift of the critical point of a demixing transition is most
noticeable for short chains.Comment: 4 pages,2 figures, in press, PR
Optical spectroscopy of the radio pulsar PSR B0656+14
We have obtained the spectrum of a middle-aged PSR B0656+14 in the 4300-9000
AA range with the ESO/VLT/FORS2. Preliminary results show that at 4600-7000 AA
the spectrum is almost featureless and flat with a spectral index $\alpha_nu ~
-0.2 that undergoes a change to a positive value at longer wavelengths.
Combining with available multiwavelength data suggests two wide, red and blue,
flux depressions whose frequency ratio is about 2 and which could be the 1st
and 2nd harmonics of electron/positron cyclotron absorption formed at magnetic
fields ~10^8G in upper magnetosphere of the pulsar.Comment: 4 pages, 4 figures, To appear in Astrophysics and Space Science,
Proceedings of "Isolated Neutron Stars: from the Interior to the Surface",
eds. D. Page, R. Turolla and S. Zan
Interferometric detection of a single vortex in a dilute Bose-Einstein condensate
Using two radio frequency pulses separated in time we perform an amplitude
division interference experiment on a rubidium Bose-Einstein condensate. The
presence of a quantized vortex, which is nucleated by stirring the condensate
with a laser beam, is revealed by a dislocation in the fringe pattern.Comment: 4 pages, 4 figure
An assessment of pulse transit time for detecting heavy blood loss during surgical operation
Copyright @ Wang et al.; Licensee Bentham Open.
This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License
(http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the
work is properly cited.The main contribution of this paper is the use of non-invasive measurements such as electrocardiogram (ECG) and photoplethysmographic (PPG) pulse oximetry waveforms to develop a new physiological signal analysis technique for detecting blood loss during surgical operation. Urological surgery cases were considered as the control group due to its generality, and cardiac surgery as experimental group since it involves blood loss and water supply. Results show that the control group has the tendency of a reduction of the pulse transient time (PTT), and this indicates an increment in the blood flow velocity changes from slow to fast. While for the experimental group, the PTT indicates high values during blood loss, and low values during water supply. Statistical analysis shows considerable differences (i.e., P <0.05) between both groups leading to the conclusion that PTT could be a good indicator for monitoring patients' blood loss during a surgical operation.The National Science Council (NSC) of Taiwan and the Centre for Dynamical Biomarkers and Translational Medicine, National Central University, Taiwan
Quantum System under Periodic Perturbation: Effect of Environment
In many physical situations the behavior of a quantum system is affected by
interaction with a larger environment. We develop, using the method of
influence functional, how to deduce the density matrix of the quantum system
incorporating the effect of environment. After introducing characterization of
the environment by spectral weight, we first devise schemes to approximate the
spectral weight, and then a perturbation method in field theory models, in
order to approximately describe the environment. All of these approximate
models may be classified as extended Ohmic models of dissipation whose
differences are in the high frequency part.
The quantum system we deal with in the present work is a general class of
harmonic oscillators with arbitrary time dependent frequency. The late time
behavior of the system is well described by an approximation that employs a
localized friction in the dissipative part of the correlation function
appearing in the influence functional. The density matrix of the quantum system
is then determined in terms of a single classical solution obtained with the
time dependent frequency. With this one can compute the entropy, the energy
distribution function, and other physical quantities of the system in a closed
form.
Specific application is made to the case of periodically varying frequency.
This dynamical system has a remarkable property when the environmental
interaction is switched off: Effect of the parametric resonance gives rise to
an exponential growth of the populated number in higher excitation levels, or
particle production in field theory models. The effect of the environment is
investigated for this dynamical system and it is demonstrated that there existsComment: 55 pages, LATEX file plus 13 PS figures. A few calculational
mistatkes and corresponding figure 1 in field theory model corrected and some
changes made for publication in Phys. Rev.D (in press
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