305 research outputs found
D-concurrence bounds for pair coherent states
The pair coherent state is a state of a two-mode radiation field which is
known as a state with non-Gaussian wave function. In this paper, the upper and
lower bounds for D-concurrence (a new entanglement measure) have been studied
over this state and calculated.Comment: 11 page
A Hybrid Monte Carlo Method for Surface Growth Simulations
We introduce an algorithm for treating growth on surfaces which combines
important features of continuum methods (such as the level-set method) and
Kinetic Monte Carlo (KMC) simulations. We treat the motion of adatoms in
continuum theory, but attach them to islands one atom at a time. The technique
is borrowed from the Dielectric Breakdown Model. Our method allows us to give a
realistic account of fluctuations in island shape, which is lacking in
deterministic continuum treatments and which is an important physical effect.
Our method should be most important for problems close to equilibrium where KMC
becomes impractically slow.Comment: 4 pages, 5 figure
Asymptotic step profiles from a nonlinear growth equation for vicinal surfaces
We study a recently proposed nonlinear evolution equation describing the
collective step meander on a vicinal surface subject to the Bales-Zangwill
growth instability [O. Pierre-Louis et al., Phys. Rev. Lett. (80), 4221
(1998)]. A careful numerical analysis shows that the dynamically selected step
profile consists of sloped segments, given by an inverse error function and
steepening as sqrt(t), which are matched to pieces of a stationary
(time-independent) solution describing the maxima and minima. The effect of
smoothening by step edge diffusion is included heuristically, and a
one-parameter family of evolution equations is introduced which contains
relaxation by step edge diffusion and by attachment-detachment as special
cases. The question of the persistence of an initially imposed meander
wavelength is investigated in relation to recent experiments.Comment: 4 pages, 5 included figures. Typo in Eq.(5) corrected, section
headlines added and Ref.[12] update
Morphology of ledge patterns during step flow growth of metal surfaces vicinal to fcc(001)
The morphological development of step edge patterns in the presence of
meandering instability during step flow growth is studied by simulations and
numerical integration of a continuum model. It is demonstrated that the kink
Ehrlich-Schwoebel barrier responsible for the instability leads to an invariant
shape of the step profiles. The step morphologies change with increasing
coverage from a somewhat triangular shape to a more flat, invariant steady
state form. The average pattern shape extracted from the simulations is shown
to be in good agreement with that obtained from numerical integration of the
continuum theory.Comment: 4 pages, 4 figures, RevTeX 3, submitted to Phys. Rev.
Competing mechanisms for step meandering in unstable growth
The meander instability of a vicinal surface growing under step flow
conditions is studied within a solid-on-solid model. In the absence of edge
diffusion the selected meander wavelength agrees quantitatively with the
continuum linear stability analysis of Bales and Zangwill [Phys. Rev. B {\bf
41}, 4400 (1990)]. In the presence of edge diffusion a local instability
mechanism related to kink rounding barriers dominates, and the meander
wavelength is set by one-dimensional nucleation. The long-time behavior of the
meander amplitude differs in the two cases, and disagrees with the predictions
of a nonlinear step evolution equation [O. Pierre-Louis et al., Phys. Rev.
Lett. {\bf 80}, 4221 (1998)]. The variation of the meander wavelength with the
deposition flux and with the activation barriers for step adatom detachment and
step crossing (the Ehrlich-Schwoebel barrier) is studied in detail. The
interpretation of recent experiments on surfaces vicinal to Cu(100) [T.
Maroutian et al., Phys. Rev. B {\bf 64}, 165401 (2001)] in the light of our
results yields an estimate for the kink barrier at the close packed steps.Comment: 8 pages, 7 .eps figures. Final version. Some errors in chapter V
correcte
K^+ production in the reaction at incident energies from 1 to 2 AGeV
Semi-inclusive triple differential multiplicity distributions of positively
charged kaons have been measured over a wide range in rapidity and transverse
mass for central collisions of Ni with Ni nuclei. The transverse
mass () spectra have been studied as a function of rapidity at a beam
energy 1.93 AGeV. The distributions of K^+ mesons are well described by a
single Boltzmann-type function. The spectral slopes are similar to that of the
protons indicating that rescattering plays a significant role in the
propagation of the kaon. Multiplicity densities have been obtained as a
function of rapidity by extrapolating the Boltzmann-type fits to the measured
distributions over the remaining phase space. The total K^+ meson yield has
been determined at beam energies of 1.06, 1.45, and 1.93 AGeV, and is presented
in comparison to existing data. The low total yield indicates that the K^+
meson can not be explained within a hadro-chemical equilibrium scenario,
therefore indicating that the yield does remain sensitive to effects related to
its production processes such as the equation of state of nuclear matter and/or
modifications to the K^+ dispersion relation.Comment: 24 pages Latex (elsart) 7 PS figures to be submitted to Nucl. Phys
Heavy Quarks and Heavy Quarkonia as Tests of Thermalization
We present here a brief summary of new results on heavy quarks and heavy
quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma
Thermalization" Workshop in Vienna, Austria in August 2005, directly following
the International Quark Matter Conference in Hungary.Comment: 8 pages, 5 figures, Quark Gluon Plasma Thermalization Workshop
(Vienna August 2005) Proceeding
Single Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s) = 200 GeV
The invariant differential cross section for inclusive electron production in
p+p collisions at sqrt(s) = 200 GeV has been measured by the PHENIX experiment
at the Relativistic Heavy Ion Collider over the transverse momentum range $0.4
<= p_T <= 5.0 GeV/c at midrapidity (eta <= 0.35). The contribution to the
inclusive electron spectrum from semileptonic decays of hadrons carrying heavy
flavor, i.e. charm quarks or, at high p_T, bottom quarks, is determined via
three independent methods. The resulting electron spectrum from heavy flavor
decays is compared to recent leading and next-to-leading order perturbative QCD
calculations. The total cross section of charm quark-antiquark pair production
is determined as sigma_(c c^bar) = 0.92 +/- 0.15 (stat.) +- 0.54 (sys.) mb.Comment: 329 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Nuclear Modification of Electron Spectra and Implications for Heavy Quark Energy Loss in Au+Au Collisions at sqrt(s_NN)=200 GeV
The PHENIX experiment has measured mid-rapidity transverse momentum spectra
(0.4 < p_T < 5.0 GeV/c) of electrons as a function of centrality in Au+Au
collisions at sqrt(s_NN)=200 GeV. Contributions from photon conversions and
from light hadron decays, mainly Dalitz decays of pi^0 and eta mesons, were
removed. The resulting non-photonic electron spectra are primarily due to the
semi-leptonic decays of hadrons carrying heavy quarks. Nuclear modification
factors were determined by comparison to non-photonic electrons in p+p
collisions. A significant suppression of electrons at high p_T is observed in
central Au+Au collisions, indicating substantial energy loss of heavy quarks.Comment: 330 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Measurement of Transverse Single-Spin Asymmetries for Mid-rapidity Production of Neutral Pions and Charged Hadrons in Polarized p+p Collisions at sqrt(s) = 200 GeV
The transverse single-spin asymmetries of neutral pions and non-identified
charged hadrons have been measured at mid-rapidity in polarized proton-proton
collisions at sqrt(s) = 200 GeV. The data cover a transverse momentum (p_T)
range 0.5-5.0 GeV/c for charged hadrons and 1.0-5.0 GeV/c for neutral pions, at
a Feynman-x (x_F) value of approximately zero. The asymmetries seen in this
previously unexplored kinematic region are consistent with zero within
statistical errors of a few percent. In addition, the inclusive charged hadron
cross section at mid-rapidity from 0.5 < p_T < 7.0 GeV/c is presented and
compared to NLO pQCD calculations. Successful description of the unpolarized
cross section above ~2 GeV/c using NLO pQCD suggests that pQCD is applicable in
the interpretation of the asymmetry results in the relevant kinematic range.Comment: 331 authors, 6 pages text, 2 figures, 3 tables. Submitted to Phys.
Rev. Lett. Plain text data tables for the points plotted in figures for this
and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
- …