78 research outputs found
Off-shell effects on particle production
We investigate the observable effects of off-shell propagation of nucleons in
heavy-ion collisions at SIS energies. Within a semi-classical BUU transport
model we find a strong enhancement of subthreshold particle production when
off-shell nucleons are propagated.Comment: 11 pages, 3 figure
Pion-Production in Heavy-Ion Collisions at SIS energies
We investigate the production of pions in heavy-ion collisions in the energy
range of - GeV/A. The dynamics of the nucleus-nucleus collisions is
described by a set of coupled transport equations of the
Boltzmann-Uehling-Uhlenbeck type for baryons and mesons. Besides the
and the we also take into account nucleon resonances up to
masses of as well as -, - and -mesons. We study
in detail the influence of the higher baryonic resonances and the
-production channels () on the pion spectra in
comparison to data from collisions at GeV/A and
-data for at 1.0 GeV/A. We, furthermore, present a detailed
comparison of differential pion angular distributions with the BEVALAC data for
Ar + KCl at 1.8 GeV/A. The general agreement obtained indicates that the
overall reactions dynamics is well described by our novel transport approach.Comment: 31 pages, 18 figures (inlcuded), to appear in Z. Phys.
Hadronic observables from SIS to SPS energies - anything strange with strangeness ?
We calculate and (+) rapidity
distributions and compare to experimental data from SIS to SPS energies within
the UrQMD and HSD transport approaches that are both based on string, quark,
diquark () and hadronic degrees of freedom. The
two transport models do not include any explicit phase transition to a
quark-gluon plasma (QGP). It is found that both approaches agree rather well
with each other and with the experimental rapidity distributions for protons,
's, and . Inspite of this apparent agreement both
transport models fail to reproduce the maximum in the excitation function for
the ratio found experimentally between 11 and 40 AGeV. A
comparison to the various experimental data shows that this 'failure' is
dominantly due to an insufficient description of pion rapidity distributions
rather than missing 'strangeness'. The modest differences in the transport
model results -- on the other hand -- can be attributed to different
implementations of string formation and fragmentation, that are not
sufficiently controlled by experimental data for the 'elementary' reactions in
vacuum.Comment: 46 pages, including 15 eps figures, to be published in Phys. Rev.
Molecular Dynamics for Fermions
The time-dependent variational principle for many-body trial states is used
to discuss the relation between the approaches of different molecular dynamics
models to describe indistinguishable fermions. Early attempts to include
effects of the Pauli principle by means of nonlocal potentials as well as more
recent models which work with antisymmetrized many-body states are reviewed
under these premises.
Keywords: Many-body theory; Fermion system; Molecular dynamics; Wave-packet
dynamics; Time-dependent variational principle; Statistical properties;
Canonical ensemble; Ergodicity; Time averagingComment: 97 pages, 13 postscript figures. To be published in July 2000 issue
of Reviews of Modern Physics. More information at http://www-aix.gsi.de/~fmd
First measurement of the atom lifetime
The goal of the DIRAC experiment at CERN (PS212) is to measure the
atom lifetime with 10% precision. Such a measurement would yield a
precision of 5% on the value of the -wave scattering lengths
combination . Based on part of the collected data we present a first
result on the lifetime, s, and
discuss the major systematic errors. This lifetime corresponds to
.Comment: 18 pages, 6 figure
Comparative Molecular Analysis of Gastrointestinal Adenocarcinomas
We analyzed 921 adenocarcinomas of the esophagus, stomach, colon, and rectum to examine shared and distinguishing molecular characteristics of gastrointestinal tract adenocarcinomas (GIACs). Hypermutated tumors were distinct regardless of cancer type and comprised those enriched for insertions/deletions, representing microsatellite instability cases with epigenetic silencing of MLH1 in the context of CpG island methylator phenotype, plus tumors with elevated single-nucleotide variants associated with mutations in POLE. Tumors with chromosomal instability were diverse, with gastroesophageal adenocarcinomas harboring fragmented genomes associated with genomic doubling and distinct mutational signatures. We identified a group of tumors in the colon and rectum lacking hypermutation and aneuploidy termed genome stable and enriched in DNA hypermethylation and mutations in KRAS, SOX9, and PCBP1. Liu et al. analyze 921 gastrointestinal (GI) tract adenocarcinomas and find that hypermutated tumors are enriched for insertions/deletions, upper GI tumors with chromosomal instability harbor fragmented genomes, and a group of genome-stable colorectal tumors are enriched in mutations in SOX9 and PCBP1
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