185 research outputs found
The impact of energy conservation in transport models on the multiplicity ratio in heavy-ion collisions and the symmetry energy
The charged pion multiplicity ratio in intermediate energy central heavy-ion
collisions has been proposed as a suitable observable to constrain the high
density dependence of the isovector part of the equation of state, with
contradicting results. Using an upgraded version of the T\"ubingen QMD
transport model, which allows the conservation of energy at a local or global
level by accounting for the potential energy of hadrons in two-body collisions
and leading thus to particle production threshold shifts, we demonstrate that
compatible constraints for the symmetry energy stiffness can be extracted from
pion multiplicity and elliptic flow observables. Nevertheless, pion
multiplicities are proven to be highly sensitive to the yet unknown isovector
part of the in-medium (1232) potential which hinders presently the
extraction of meaningful information on the high density dependence of the
symmetry energy. A solution to this problem together with the inclusion of
contributions presently neglected, such as in-medium pion potentials and
retardation effects, are needed for a final verdict on this topic.Comment: 12 pages, 7 figure
Feasability of constraining the curvature parameter of the symmetry energy using elliptic flow data
A QMD type transport model supplemented by a phase-space coalescence model
fitted to FOPI experimental multiplicities of free nucleons and light clusters
has been used to study the density dependence of the symmetry energy above the
saturation point by a comparison with experimental elliptic flow ratios
measured by the FOPI-LAND and ASYEOS collaborations in Au+Au
collisions at 400 MeV/nucleon impact energy. A previous calculation has proven
that neutron-to-proton and neutron-to-charged particles elliptic flow ratios
probe on average different densities allowing in principle the extraction of
both the slope and curvature parameters of the symmetry energy.
Consequently a Gogny interaction inspired potential has been modified to allow
independent changes of and . Comparing theoretical predictions
with experimental data for neutron-to-proton and neutron-to-charged particles
elliptic flow ratios the following constraints have been extracted:
=8522(exp)20(th)12(sys) MeV and
=96315(exp)170(th)166(sys) MeV. Residual model
dependence is accounted for in the magnitude of the quoted theoretical error.
Systematical uncertainties are generated by the inability of the transport
model to reproduce experimental light-cluster-to-proton multiplicity ratios. A
value for , free of systematical theoretical uncertainties, can be extracted
from the neutron-to-proton elliptic flow ratio alone:
=8430(exp)19(th) MeV. It has also been demonstrated that elliptic
flow ratios reach a maximum sensitivity on the parameter in heavy-ion
collisions of about 250 MeV/nucleon impact energy, allowing a reduction of the
experimental component of uncertainty to about 150 MeV for this parameter.Comment: 22 pages, 13 figure
Dilepton production at HADES: theoretical predictions
Dileptons represent a unique probe for nuclear matter under extreme
conditions reached in heavy-ion collisions. They allow to study meson
properties, like mass and decay width, at various density and temperature
regimes. Present days models allow generally a good description of dilepton
spectra in ultra-relativistic heavy ion collision. For the energy regime of a
few GeV/nucleon, important discrepancies between theory and experiment, known
as the DLS puzzle, have been observed. Various models, including the one
developed by the T\"{u}bingen group, have tried to address this problem, but
have proven only partially successful. High precision spectra of dilepton
emission in heavy-ion reactions at 1 and 2 GeV/nucleon will be released in the
near future by the HADES Collaboration at GSI. Here we present the predictions
for dilepton spectra in C+C reactions at 1 and 2 GeV/nucleon and investigate up
to what degree possible scenarios for the in-medium modification of vector
mesons properties are accessible by the HADES experiment.Comment: 12 pages, 4 figures; submitted to Phys.Lett.
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.
In-medium potential, pion production in heavy-ion collisions and the symmetry energy
Using the dcQMD transport model, the isoscalar and isovector in-medium
potentials of the (1232) baryon are studied and information regarding
their effective strength is obtained from a comparison to experimental pion
production data in heavy-ion collisions below 800 MeV/nucleon impact energy.
The best description is achieved for an isoscalar potential moderately more
attractive than the nucleon optical potential and a rather small isoscalar
relative effective mass m 0.45. For the isovector component
only a constraint between the potential's strength at saturation and the
isovector effective mass difference can be extracted, which depends on
quantities such as the slope of the symmetry energy and the neutron-proton
effective mass difference. These results are incompatible with the usual
assumption, in transport models, that the (1232) and nucleon potentials
are equal. The density dependence of symmetry energy can be studied using the
high transverse momentum tail of pion multiplicity ratio spectra. Results are
however correlated with the value of neutron-proton effective mass difference.
This region of spectra is shown to be affected by uncertain model ingredients
such as the pion potential or in-medium correction to inelastic scattering
cross-sections at levels smaller than 10. Extraction of precise constraints
for the density dependence of symmetry energy above saturation will require
experimental data for pion production in heavy-ion collisions below 800
MeV/nucleon impact energy and experimental values for the high transverse
momentum tail of pion multiplicity ratio spectra accurate to better than 5.Comment: 22 pages, 13 figure
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
The Assessment of the Insolvency Risk at the Companies From the Manufacturing Industry, Listed on the Bucharest Stock Exchange
The paper presents both theoretically and empirically the insolvency risk for 35 companies from the manufacturing industry in Romania, listed on the Bucharest Stock Exchange, at premium and standard categories, during 2007-2016, through four models: Springate, Taffler, Altman, and French Commercial Credit. The results of the research have revealed that during the period 2007- 2016, over 50% of the companies were facing a high insolvency risk, the most risky of them being Cemacon S.A. and Prefab S.A. The less risky companies during the mentioned period of time were Aerostar S.A. and Conted S.A
Genetic Features of mcr-1 Mediated Colistin Resistance in CMY-2-Producing Escherichia coli From Romanian Poultry
© Copyright © 2019 Maciuca, Cummins, Cozma, Rimbu, Guguianu, Panzaru, Licker, Szekely, Flonta, Djordjevic and Timofte. Colistin is a last resort antibiotic used for the treatment of human infections associated with carbapenemase-producing Enterobacteriales. Here, we evaluated the occurrence of mcr-1 and -2 plasmid-mediated colistin resistance in colistin and/or carbapenem resistant human clinical Enterobacteriales and other gram-negative bacteria (n = 543) as well as third generation cephalosporin-resistant (3GCR) Escherichia coli isolates from poultry abattoir workers (n = 15) and poultry fecal samples (n = 92) collected from two geographically separate abattoirs in Romania. which revealed that mcr-1 was present within four sequence types (STs): ST744 (n = 7), ST57 (n = 7), ST156 (n = 2), and ST10 (n = 1). Within STs, serotypes were conserved and, notably, all except one of the mcr-1-positive isolates were found to exhibit fluoroquinolone-resistance (FQR) associated SNPs in both gyrA and parC. While there were variations in genotypes, all isolates belonging to ST744, ST57, and ST156 were rich in resistance determinants, carrying aminoglycoside-modifying enzymes genes, sulfonamide resistance gene blaTEM–1 as well as blaCMY–2 AmpC β-lactamase resistance genes. They also exhibited high similarity in carriage of virulence genes; ST10, however, only carried the mcr-1 gene. Whole genome sequencing (WGS) analysis also revealed that although the mcr-1 gene was identified in a diverse population of E. coli, two STs (ST57 and ST744) predominated and interestingly, were found in isolates across both abattoirs providing evidence for clonal transmission. Also, two main genomic contexts of mcr-1 isolates were revealed with all ST57 isolates harboring the mcr-1 gene between two copies of ISApl1 (or the Tn6330 transposon) whilst a common mcr-1 containing scaffold, highly similar to IncX type mcr-1-bearing plasmids (pWI2-mcr, Accession number: LT838201), was present among mcr-1 isolates of varying phylogenetic backgrounds (ST10, ST744 and ST156). The high prevalence of the mcr-1 gene in poultry E. coli isolates with co-resistance to cephalosporins and quinolones, in a country where antimicrobial use in food production species is poorly regulated, is concerning and the findings from this study should lead to better surveillance of antimicrobial resistance (AMR) in food-production animals in Romania
Search for Bremsstrahlung radiation in quasi-free n p --> n p gamma reactions
Due to the high sensitivity of the N N --> N N gamma reaction to the
nucleon-nucleon potential, Bremsstrahlung radiation is used as a tool to
investigate details of the nucleon-nucleon interaction. Such investigations can
be performed at the cooler synchrotron COSY in the Research Centre Juelich, by
dint of the COSY-11 detection system. The results of the identification of
Bremsstrahlung radiation emitted via the d p --> d p gamma reaction in data
taken with a proton target and a deuteron beam are presented and discussed.Comment: 3 pages; Presented at Meson 2004: 8th International Workshop on Meson
Production, Properties and Interaction, Krakow, Poland, 4-8 June 2004;
Submitted to International Journal of Modern Physics
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