24,971 research outputs found
ratios in relativistic heavy-ion collisions
We study ratios as a function of centrality (participant nucleon
number), transverse mass (), and rapidity, in heavy-ion collisions at beam
energies between 1A and 2A GeV. We use the relativistic transport model that
includes expicitly the strangeness degrees of freedom and consider two
scenarios for kaon properties in dense matter, one with and one without medium
modifications of their properties. In both scenarios, The ratio does
not change very much with the centrality, while the and
ratios increase with increasing centrality. Significant differences are
predicted, both in magnitudes and shapes, for the spectra and rapidity
distributions of ratio. Experimental measurement of these ratios,
currently under investigation by the FOPI, KaoS, E866, and E895 collaborations,
will be useful in revealing the kaon in-medium properties.Comment: RevTex, 10 pages, including 17 postscript figures, submitted to Phys.
Rev.
Difficulties in probing density dependent symmetry potential with the HBT interferometry
Based on the updated UrQMD transport model, the effect of the symmetry
potential energy on the two-nucleon HBT correlation is investigated with the
help of the coalescence program for constructing clusters, and the CRAB
analyzing program of the two-particle HBT correlation. An obvious non-linear
dependence of the neutron-proton (or neutron-neutron) HBT correlation function
() at small relative momenta on the stiffness factor of the
symmetry potential energy is found: when , the
increases rapidly with increasing , while it starts to saturate if
. It is also found that both the symmetry potential energy
at low densities and the conditions of constructing clusters at the late stage
of the whole process influence the two-nucleon HBT correlation with the same
power.Comment: 11 pages, 4 figure
Enhancement of low-mass dileptons in SPS heavy-ion collisions: possible evidence for dropping rho meson mass in medium
Dilepton production in proton- and nucleus-induced reactions at SPS energies
is studied in the relativistic transport model using initial conditions
determined by the string dynamics from RQMD. It is found that both the CERES
and HELIOS-3 data for dilepton spectra in proton-nucleus reactions can be well
described by the conventional mechanism of Dalitz decay and direct vector meson
decay. However, to provide a quantitative explanation of the observed dilepton
spectra in central S+Au and S+W collisions requires contributions other than
these direct decays. Introducing a decrease of vector meson masses in hot dense
medium, we find that these heavy-ion data can also be satisfactorily explained.
We also give predictions for Pb+Au collisions at 160 GeV/nucleon using current
CERES mass resolution and acceptance.Comment: 8 pages, LaTeX, figures available from [email protected],
contribution to QM'96, to appear in the proceeding
Mechanism of cellular uptake of genotoxic silica nanoparticles.
Mechanisms for cellular uptake of nanoparticles have important implications for nanoparticulate drug delivery and toxicity. We have explored the mechanism of uptake of amorphous silica nanoparticles of 14 nm diameter, which agglomerate in culture medium to hydrodynamic diameters around 500 nm. In HT29, HaCat and A549 cells, cytotoxicity was observed at nanoparticle concentrations ≥ 1 μg/ml, but DNA damage was evident at 0.1 μg/ml and above. Transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy confirmed entry of the silica particles into A549 cells exposed to 10 μg/ml of nanoparticles. The particles were observed in the cytoplasm but not within membrane bound vesicles or in the nucleus. TEM of cells exposed to nanoparticles at 4°C for 30 minutes showed particles enter cells when activity is low, suggesting a passive mode of entry. Plasma lipid membrane models identified physical interactions between the membrane and the silica NPs. Quartz crystal microbalance experiments on tethered bilayer lipid membrane systems show that the nanoparticles strongly bind to lipid membranes, forming an adherent monolayer on the membrane. Leakage assays on large unilamellar vesicles (400 nm diameter) indicate that binding of the silica NPs transiently disrupts the vesicles which rapidly self-seal. We suggest that an adhesive interaction between silica nanoparticles and lipid membranes could cause passive cellular uptake of the particles
Medium Dependence of the Vector-Meson Mass: Dynamical and/or Brown-Rho Scaling?
We discuss the similarities and differences for the theories of Rapp, Wambach
and collaborators (called R/W in short) and those based on Brown-Rho scaling
(called B/R), as applied to reproduce the dileptons measured by the CERES
collaboration in the CERN experiments. In both theories the large number of
dileptons at invariant masses ~ are shown to be chiefly
produced by a density-dependent -meson mass. In R/W the medium dependence
is dynamically calculated using hadronic variables defined in the matter-free
vacuum. In B/R scaling it follows from movement towards chiral symmetry
restoration due to medium-induced vacuum change, and is described in terms of
constituent (or quasiparticle) quarks. We argue that the R/W description should
be reliable up to densities somewhat beyond nuclear density, where hadrons are
the effective variables. At higher density there should be a crossover to
constituent quarks as effective variables scaling according to B/R. In the
crossover region, the two descriptions must be ``dual''.Comment: 13 pages LaTeX, incl. 5 eps-figures and appb.sty; Talk given at the
Workshop on 'The Structure of Mesons, Baryons and Nuclei', Cracow, May 1998,
in honor of J. Speth's 60th birthday, to be published in Acta Physica
Polonica
A model comparison of resonance lifetime modifications, a soft equation of state and non-Gaussian effects on correlations at FAIR/AGS energies
HBT correlations of pairs at FAIR/AGS energies are investigated
by using the UrQMD transport model and the CRAB analyzing program. Three
different possible sources (treatment of resonance lifetimes, a soft equation
of state and non-Gaussian effects) to understand the HBT puzzle are
investigated. Firstly, we find that different treatments of the resonance decay
time can not resolve the HBT time-related puzzle, however it can modify the HBT
radii at low transverse momenta to some extent to explain the data slightly.
Secondly, with a soft equation of state with momentum dependence, the measured
transverse momentum dependent HBT radii and ratio can be described
fairly well. Thirdly, non-Gaussian effects are visible in the calculated
correlation function. Using the Edgeworth expansion, one finds that the
non-Gaussian effect is strongest in the longitudinal direction and weakest in
the sideward direction.Comment: 18 pages, 6 figures. To be published in J.Phys.
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