116 research outputs found
Acoustic radiation force on a heated spherical particle in a fluid including scattering and microstreaming from a standing ultrasound wave
Analytical expressions are derived for the time-averaged, quasi-steady,
acoustic radiation force on a heated, spherical, elastic, solid microparticle
suspended in a fluid and located in an axisymmetric incident acoustic wave. The
heating is assumed to be spherically symmetric, and the effects of particle
vibrations, sound scattering, and acoustic microstreaming are included in the
calculations of the acoustic radiation force. It is found that changes in the
speed of sound of the fluid due to temperature gradients can significantly
change the force on the particle, particularly through perturbations to the
microstreaming pattern surrounding the particle. For some fluid-solid
combinations, the effects of particle heating even reverse the direction of the
force on the particle for a temperature increase at the particle surface as
small as 1 K.Comment: 13 pages, 3 pdf figures, RevTex 4.
The acoustic radiation force on a spherical thermoviscous particle in a thermoviscous fluid including scattering and microstreaming
We derive general analytical expressions for the time-averaged acoustic
radiation force on a small spherical particle suspended in a fluid and located
in an axisymmetric incident acoustic wave. We treat the cases of the particle
being either an elastic solid or a fluid particle. The effects of particle
vibrations, acoustic scattering, acoustic microstreaming, heat conduction, and
temperature-dependent fluid viscosity are all included in the theory. Acoustic
streaming inside the particle is also taken into account for the case of a
fluid particle. No restrictions are placed on the widths of the viscous and
thermal boundary layers relative to the particle radius. We compare the
resulting acoustic radiation force with that obtained from previous theories in
the literature, and we identify limits, where the theories agree, and specific
cases of particle and fluid materials, where qualitative or significant
quantitative deviations between the theories arise.Comment: 29 pages, 4 pdf figures, RevTex 4.
Intermediate mass excess of dilepton production in heavy ion collisions at BEVALAC energies
Dielectron mass spectra are examined for various nuclear reactions recently
measured by the DLS collaboration. A detailed description is given of all
dilepton channels included in the transport model UrQMD 1.0, i.e. Dalitz decays
of mesons and of the resonance, direct
decays of vector mesons and bremsstrahlung. The microscopic calculations
reproduce data for light systems fairly well, but tend to underestimate the
data in at high energies and in at low energies. These conventional
sources, however, cannot explain the recently reported enhancement for
nucleus-nucleus collisions in the mass region 0.15 GeV<<0.6 GeV. Chiral
scaling and meson broadening in the medium are investigated as a
source of this mass excess. They also cannot explain the recent DLS data.Comment: 26 pages, 9 figures, references update
Microscopic Models for Ultrarelativistic Heavy Ion Collisions
In this paper, the concepts of microscopic transport theory are introduced
and the features and shortcomings of the most commonly used ansatzes are
discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics
(UrQMD) transport model is described in great detail. Based on the same
principles as QMD and RQMD, it incorporates a vastly extended collision term
with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin
is explicitly treated for all hadrons. The range of applicability stretches
from GeV/nucleon, allowing for
a consistent calculation of excitation functions from the intermediate energy
domain up to ultrarelativistic energies. The main physics topics under
discussion are stopping, particle production and collective flow.Comment: 129 pages, pagestyle changed using US letter (8.5x11 in) format. The
whole paper (13 Mb ps file) could also be obtained from
ftp://ftp.th.physik.uni-frankfurt.de/pub/urqmd/ppnp2.ps.g
Dilepton production by bremsstrahlung of meson fields in nuclear collisions
We study the bremsstrahlung of virtual omega mesons due to the collective
deceleration of nuclei at the initial stage of an ultrarelativistic heavy-ion
collision. It is shown that electromagnetic decays of these mesons may give an
important contribution to the observed yields of dileptons. Mass spectra of
positron-electron and muon pairs produced in central Au+Au collisions are
calculated under some simplifying assumptions on the space-time variation of
the baryonic current in a nuclear collision process. Comparison with the CERES
data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a
noticeable fraction of the observed lepton pairs in the intermediate region of
invariant masses. Sensitivity of the dilepton yield to the in-medium
modification of masses and widths of vector mesons is demonstrated.Comment: 14 page
Exploring Pompeii: discovering hospitality through research synergy
Hospitality research continues to broaden through an ever-increasing dialogue and alignment with a greater number of academic disciplines. This paper demonstrates how an enhanced understanding of hospitality can be achieved through synergy between archaeology, the classics and sociology. It focuses on classical Roman life, in particular Pompeii, to illustrate the potential for research synergy and collaboration, to advance the debate on hospitality research and to encourage divergence in research approaches. It demonstrates evidence of commercial hospitality activities through the excavation hotels, bars and taverns, restaurants and fast food sites. The paper also provides an example of the benefits to be gained from multidisciplinary analysis of hospitality and tourism
Dilepton Production in Nucleon-Nucleon Reactions With and Without Hadronic Inelasticities
We calculate elementary proton-proton and neutron-proton bremsstrahlung and
their contribution to the invariant mass distribution. At 4.9 GeV, the
proton-proton contribution is larger than neutron-proton, but it is small
compared to recent data. We then make a first calculation of bremsstrahlung in
nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the
many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung
by more than an order of magnitude in the low-mass region. When the
bremsstrahlung contributions are summed with Dalitz decay of the ,
radiative decay of the and from two-pion annihilation, the result
matches recent high statistics proton-proton data from the Dilepton
Spectrometer collaboration.Comment: 1+17 pages plus 11 PostScript figures uuencoded and appended,
McGill/93-9, TPI-MINN-93/18-
Inclusive Dielectron Cross Sections in p+p and p+d Interactions at Beam Energies from 1.04 to 4.88 GeV
Measurements of dielectron production in p+p and p+d collisions with beam
kinetic energies from 1.04 to 4.88 GeV are presented. The differential cross
section is presented as a function of invariant pair mass, transverse momentum,
and rapidity. The shapes of the mass spectra and their evolution with beam
energy provide information about the relative importance of the various
dielectron production mechanisms in this energy regime. The p+d to p+p ratio of
the dielectron yield is also presented as a function of invariant pair mass,
transverse momentum, and rapidity. The shapes of the transverse momentum and
rapidity spectra from the p+d and p+p systems are found to be similar to one
another for each of the beam energies studied. The beam energy dependence of
the integrated cross sections is also presented.Comment: 15 pages and 16 figure
A Poincare-Covariant Parton Cascade Model for Ultrarelativistic Heavy-Ion Reactions
We present a new cascade-type microscopic simulation of nucleus-nucleus
collisions at RHIC energies. The basic elements are partons (quarks and gluons)
moving in 8N-dimensional phase space according to Poincare-covariant dynamics.
The parton-parton scattering cross sections used in the model are computed
within perturbative QCD in the tree-level approximation. The Q^2 dependence of
the structure functions is included by an implementation of the DGLAP mechanism
suitable for a cascade, so that the number of partons is not static, but varies
in space and time as the collision of two nuclei evolves. The resulting parton
distributions are presented, and meaningful comparisons with experimental data
are discussed.Comment: 30 pages. 11 figures. Submitted to Phys.Rev.
Hadron and hadron-cluster production in a hydrodynamical model including particle evaporation
We discuss the evolution of the mixed phase at RHIC and SPS within
boostinvariant hydrodynamics. In addition to the hydrodynamical expansion, we
also consider evaporation of particles off the surface of the fluid. The
back-reaction of the evaporation process on the dynamics of the fluid shortens
the lifetime of the mixed phase. In our model this lifetime of the mixed phase
is <12 fm/c in Au+Au at RHIC and <6.5 fm/c in Pb+Pb at SPS, even in the limit
of vanishing transverse expansion velocity. Strangeness separation occurs,
especially in events (or at rapidities) with relatively high initial net baryon
and strangeness number, enhancing the multiplicity of MEMOs (multiply strange
nuclear clusters). If antiquarks and antibaryons reach saturation in the course
of the pure QGP or mixed phase, we find that at RHIC the ratio of antideuterons
to deuterons may exceed 0.3 and even anti-helium to helium>0.1. Due to
fluctuations, at RHIC even negative baryon number at midrapidity is possible in
individual events, so that the antibaryon and antibaryon-cluster yields exceed
those of the corresponding baryons and clusters.Comment: 17 pages, Latex, epsfig stylefil
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