347 research outputs found
Towards a model-independent constraint of the high-density dependence of the symmetry energy
Neutron-proton elliptic flow difference and ratio have been shown to be
promising observables in the attempt to constrain the density dependence of the
symmetry energy above the saturation point from heavy-ion collision data. Their
dependence on model parameters like microscopic nucleon-nucleon cross-sections,
compressibility of nuclear matter, optical potential, and symmetry energy
parametrization is thoroughly studied. By using a parametrization of the
symmetry energy derived from the momentum dependent Gogny force in conjunction
with the T\"{u}bingen QMD model and comparing with the experimental FOPI/LAND
data for 197Au+197Au collisions at 400 MeV/nucleon, a moderately stiff, x=-1.35
+/- 1.25, symmetry energy is extracted, a result that agrees with that of a
similar study that employed the UrQMD transport model and a momentum
independent power-law parametrization of the symmetry energy. This contrasts
with diverging results extracted from the FOPI ratio
available in the literature.Comment: 18 pages, 3 figures, accepted for publication in Phys. Rev.
Flow probe of symmetry energy in relativistic heavy-ion reactions
Flow observables in heavy-ion reactions at incident energies up to about 1
GeV per nucleon have been shown to be very useful for investigating the
reaction dynamics and for determining the parameters of reaction models based
on transport theory. In particular, the elliptic flow in collisions of
neutron-rich heavy-ion systems emerges as an observable sensitive to the
strength of the symmetry energy at supra-saturation densities. The comparison
of ratios or differences of neutron and proton flows or neutron and hydrogen
flows with predictions of transport models favors an approximately linear
density dependence, consistent with ab-initio nuclear-matter theories.
Extensive parameter searches have shown that the model dependence is comparable
to the uncertainties of existing experimental data. Comprehensive new flow data
of high accuracy, partly also through providing stronger constraints on model
parameters, can thus be expected to improve our knowledge of the equation of
state of asymmetric nuclear matter.Comment: 20 pages, 24 figures, review to appear in EPJA special volume on
nuclear symmetry energ
Free-living amoebae isolated from a hospital water system in South Africa: A potential source of nosocomial and occupational infection
Abstract: This study investigated the occurrence of free-living amoebae (FLA) in a public hospital in South Africa. A total of 97 water and biofilm samples from the municipal water inlet of the hospital, theatres, theatre sterilization service unit, central sterilization service unit, endoscopy/gastroscopy unit, intensive care unit and the renal unit were collected and examined for the presence of FLA using an amoebal co-culture and molecular techniques. Of the 97 samples, 77 (79.4 %), 40 (52%) water and 37 (48.1%) biofilm, contained FLA. The genera Acanthamoeba, Vermamoeba (formerly Hartmanella) and Naegleria were detected by morphology, 18S rRNA PCR and sequence analyses. Further sequence analysis of the five Acanthamoeba positive isolates revealed a close resemblance with the potentially pathogenic T20 genotype. These results show a potential health risk to immuno-compromised patients and health care workers as some of the species detected are pathogenic and may harbour potential intracellular bacteria responsible for nosocomial infections. To date, this is the first report on the detection of potentially pathogenic amoebae from South African hospital water systems
Detection of amoeba-associated Legionella pneumophila in hospital water networks of Johannesburg
Abstract: The prevalence of free-living amoeba and associated Legionella spp. in hospital water systems may pose a risk of Legionnaires’ disease to immuno-compromised patients. This study investigated the occurrence of amoeba-associated Legionella pneumophila in three South African hospital water systems. A total of 98 water and/or biofilm samples were collected from the sterilisation unit, theatres, neonatal ward and intensive care units. Amoebae were isolated from 71 (72.4%) samples. Isolated amoebae were analysed using qPCR and culture methods to test for the presence of Legionella. L. pneumophila did not grow on selective media in any of the samples. A total of 7 out of the 71 (9.9%) amoeba-positive samples showed a positive reaction for L. pneumophila using qPCR. Although relatively few samples were positive for Legionella in this preliminary study, the association with amoeba still presents a potential public health risk to immuno-compromised patients when exposed to contaminated water
Probing resonance matter with virtual photons
In the energy domain of 1-2 GeV per nucleon, HADES has measured rare
penetrating probes (e+e-) in C+C, Ar+KCl, d+p, p+p and p+Nb collisions. For the
first time the electron pairs were reconstructed from quasi-free n+p
sub-reactions by detecting the proton spectator from the deuteron breakup. An
experimentally constrained NN reference spectrum was established. Our results
demonstrate that the gross features of di-electron spectra in C+C collisions
can be explained as a superposition of independent NN collisions. On the other
hand, a direct comparison of the NN reference spectrum with the e+e- invariant
mass distribution measured in the heavier system Ar+KCl at 1.76 GeV/u shows an
excess yield above the reference, which we attribute to radiation from
resonance matter. Moreover, the combined measurement of di-electrons and
strangeness in Ar+KCl collisions has provided further intriguing results which
are also discussed.Comment: 10 pages, 3 figures, proceedings of the International Nuclear Physics
Conference - INPC 2010, Vancouver, Canada, July 4 - 9 201
FIRST experiment: Fragmentation of Ions Relevant for Space and Therapy
Nuclear fragmentation processes are relevant in different fields of basic research and applied physics and are of particular interest for tumor therapy and for space radiation protection applications. The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at SIS accelerator of GSI laboratory in Darmstadt, has been designed for the measurement of different ions fragmentation cross sections at different energies between 100 and 1000 MeV/nucleon. The experiment is performed by an international collaboration made of institutions from Germany, France, Italy and Spain. The experimental apparatus is partly based on an already existing setup made of the ALADIN magnet, the MUSIC IV TPC, the LAND2 neutron detector and the TOFWALL scintillator TOF system, integrated with newly designed detectors in the interaction Region (IR) around the carbon removable target: a scintillator Start Counter, a Beam Monitor drift chamber, a silicon Vertex Detector and a Proton Tagger for detection of light fragments emitted at large angles (KENTROS). The scientific program of the FIRST experiment started on summer 2011 with the study of the 400 MeV/nucleon 12C beam fragmentation on thin (8mm) carbon targe
Global Water, Sanitation, and Hygiene Research Priorities and Learning Challenges under Sustainable Development Goal 6
On the exact conservation laws in thermal models and the analysis of AGS and SIS experimental results
The production of hadrons in relativistic heavy ion collisions is studied
using a statistical ensemble with thermal and chemical equilibrium. Special
attention is given to exact conservation laws, i.e. certain charges are treated
canonically instead of using the usual grand canonical approach. For small
systems, the exact conservation of baryon number, strangeness and electric
charge is to be taken into account. We have derived compact, analytical
expressions for particle abundances in such ensemble. As an application, the
change in ratios in AGS experiments with different interaction system
sizes is well reproduced. The canonical treatment of three charges becomes
impractical very quickly with increasing system size. Thus, we draw our
attention to exact conservation of strangeness, and treat baryon number and
electric charge grand canonically. We present expressions for particle
abundances in such ensemble as well, and apply them to reproduce the large
variety of particle ratios in GSI SIS 2 A GeV Ni-Ni experiments. At the
energies considered here, the exact strangeness conservation fully accounts for
strange particle suppression, and no extra chemical factor is needed.Comment: Talk given at Strangeness in Quark Matter '98, Padova, Italy (1998).
Submitted to J.Phys. G. 5 pages, 2 figure
The PANDA GEM-based TPC Prototype
We report on the development of a GEM-based TPC prototype for the PANDA
experiment. The design and requirements of this device will be illustrated,
with particular emphasis on the properties of the recently tested GEM-detector,
the characterization of the read-out electronics and the development of the
tracking software that allows to evaluate the GEM-TPC data.Comment: submitted to NIMA 4 pages, 6 picture
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