3,021 research outputs found
Anomalous mass dependence of radiative quark energy loss in a finite-size quark-gluon plasma
We demonstrate that for a finite-size quark-gluon plasma the induced gluon
radiation from heavy quarks is stronger than that for light quarks when the
gluon formation length becomes comparable with (or exceeds) the size of the
plasma. The effect is due to oscillations of the light-cone wave function for
the in-medium transition. The dead cone model by Dokshitzer and
Kharzeev neglecting quantum finite-size effects is not valid in this regime.
The finite-size effects also enhance the photon emission from heavy quarks.Comment: 8 pages, 3 figure
Final state interaction effects in scattering
We present a systematic study of the final-state interaction (FSI) effects in
scattering in the CEBAF energy range with particular emphasis on the
phenomenon of the angular anisotropy of the missing momentum distribution. We
find that FSI effects dominate at missing momentum p_m \gsim 1.5 fm.
FSI effects in the excitation of the -wave state are much stronger than in
the excitation of the -wave.Comment: LATEX, 11 pages, 5 figures available from the authors on request,
KFA-IKP(TH)-1994-3
Final state interactions and correlations: are the latter observable?
Are effects of short range correlations in the ground state of the target
nucleus (initial state correlations ISC) observable in experiments on
quasielastic scattering at large missing momentum ? Will the
missing momentum spectrum observed at CEBAF be overwhelmed by final state
interactions (FSI) of the struck proton? The recent advances in the theory of
FSI and findings of complex interplay and strong quantum-mechanical
interference of FSI and ISC contributions to scattering at p_{m}\gsim
1\,fm are reviewed. We conclude that for p_m \gsim 1 \, fm
quasielastic scattering is dominated by FSI effects and the sensitivity to
details of the nuclear ground state is lost.Comment: Invited Talk given by N.N.Nikolaev at the Conference on Perspectives
in Nuclear Physics at Intermediate Energies (Trieste, Italy, May 1995) 18
pages, uuencoded including all figure
Non-linear effects in hopping conduction of single-crystal La_{2}CuO_{4 + \delta}
The unusual non-linear effects in hopping conduction of single-crystal
La_{2}CuO_{4 + \delta} with excess oxygen has been observed. The resistance is
measured as a function of applied voltage U (10^{-3} V - 25 V) in the
temperature range 5 K 0.1 V) the
conduction of sample investigated corresponds well to Mott's variable-range
hopping (VRH). An unusual conduction behavior is found, however, in low voltage
range (approximately below 0.1 V), where the influence of electric field and
(or) electron heating effect on VRH ought to be neglected. Here we have
observed strong increase in resistance at increasing U at T < 20 K, whereas at
T > 20 K the resistance decreases with increasing U. The magnetoresistance of
the sample below 20 K has been positive at low voltage and negative at high
voltage. The observed non-Ohmic behavior is attributable to inhomogeneity of
the sample, and namely, to the enrichment of sample surface with oxygen during
the course of the heat treatment of the sample in helium and air atmosphere
before measurements. At low enough temperature (below 20 K) the surface layer
with increased oxygen concentration is presumed to consist of disconnected
superconducting regions (with T_{c} about 20 K) in poor-conducting matrix. The
results obtained demonstrate that transport properties of cuprate oxides may be
determined in essential degree by structural or stoichimetric inhomogeneities.
This should be taken into account at evaluation of "quality" of
high-temperature superconductors on the basis of transport properties
measurements.Comment: 12 pages, REVTex, 11 Postscript figures, To be published in Fizika
Nizkikh Temperatur (published by AIP as Low Temperature Physics
Review of analytical instruments for EEG analysis
Since it was first used in 1926, EEG has been one of the most useful
instruments of neuroscience. In order to start using EEG data we need not only
EEG apparatus, but also some analytical tools and skills to understand what our
data mean. This article describes several classical analytical tools and also
new one which appeared only several years ago. We hope it will be useful for
those researchers who have only started working in the field of cognitive EEG
Condensation of classical nonlinear waves
We study the formation of a large-scale coherent structure (a condensate) in
classical wave equations by considering the defocusing nonlinear Schr\"odinger
equation as a representative model. We formulate a thermodynamic description of
the condensation process by using a wave turbulence theory with ultraviolet
cut-off. In 3 dimensions the equilibrium state undergoes a phase transition for
sufficiently low energy density, while no transition occurs in 2 dimensions, in
analogy with standard Bose-Einstein condensation in quantum systems. Numerical
simulations show that the thermodynamic limit is reached for systems with
computational modes and greater. On the basis of a modified wave
turbulence theory, we show that the nonlinear interaction makes the transition
to condensation subcritical. The theory is in quantitative agreement with the
simulations
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