191 research outputs found
Role of isospin dependent mean field in pion production in heavy ion reactions
The importance of a isospin dependent nuclear mean field (IDMF) in regard to
the pion production mechanism is studied for the reaction at 1
GeV/nucleon using the Quantum Molecular Dynamics (QMD) model. In particular,
the effect of the IDMF on pion spectra and the charged pion ratio are analyzed.
It is found that the inclusion of a IDMF considerably suppresses the low
pions, thus, leading to a better agreement with the data on pion spectra.
Moreover, the rapidity distribution of the charged pion ratio appears to be
sensitive to the isospin dependence of the nuclear mean field.Comment: 16 pages, using RevTex, 6 PS-Figure
Probing nuclear expansion dynamics with -spectra
We study the dynamics of charged pions in the nuclear medium via the ratio of
differential - and -spectra in a coupled-channel BUU (CBUU)
approach. The relative energy shift of the charged pions is found to correlate
with the pion freeze-out time in nucleus-nucleus collisions as well as with the
impact parameter of the heavy-ion reaction. Furthermore, the long-range Coulomb
force provides a 'clock' for the expansion of the hot nuclear system. Detailed
comparisons with experimental data for at 1 GeV/A and at
2.0 GeV/A are presented.Comment: 21 pages, latex, figures include
Charged pions from Ni on Ni collisions between 1 and 2 AGeV
Charged pions from Ni + Ni reactions at 1.05, 1.45 and 1.93 AGeV are measured
with the FOPI detector. The mean multiplicities per mean number of
participants increase with beam energy, in accordance with earlier studies of
the Ar + KCl and La + La systems. The pion kinetic energy spectra have concave
shape and are fitted by the superposition of two Boltzmann distributions with
different temperatures. These apparent temperatures depend only weakly on
bombarding energy. The pion angular distributions show a forward/backward
enhancement at all energies, but not the enhancement which was
observed in case of the Au + Au system. These features also determine the
rapidity distributions which are therefore in disagreement with the hypothesis
of one thermal source. The importance of the Coulomb interaction and of the
pion rescattering by spectator matter in producing these phenomena is
discussed.Comment: 22 pages, Latex using documentstyle[12pt,a4,epsfig], to appear in Z.
Phys.
Proton polarizability contribution to the hydrogen hyperfine splitting
The contribution of the proton polarizability to the hydrogen hyperfine
splitting is evaluated on the basis of modern experimental and theoretical
results on the proton polarized structure functions. The value of this
correction is equal to 1.4 ppm.Comment: 11 pages, LaTeX2.09, 7 figures, uses linedraw.sty, psfig.sty,
epsf.st
Proton polarizability effect in the Lamb shift of the hydrogen atom
The proton polarizability correction to the Lamb shift of electronic and
muonic hydrogen is calculated on the basis of isobar model and experimental
data on the structure functions of deep inelastic lepton-nucleon scattering.
The contributions of the Born terms, vector-meson exchanges and nucleon
resonances are taken into account in the construction of the photoabsorption
cross sections for transversely and longitudinally polarized virtual photons
sigma_{T,L}.Comment: 11 pages, 3 figure
Body Surface Area and Baseline Blood Pressure Predict Subclinical Anthracycline Cardiotoxicity in Women Treated for Early Breast Cancer
Background and Aims: Anthracyclines are highly effective chemotherapeutic agents which may cause long-term cardiac damage (chronic anthracycline cardiotoxicity) and heart failure. The pathogenesis of anthracycline cardiotoxicity remains incompletely understood and individual susceptibility difficult to predict. We sought clinical features which might contribute to improved risk assessment. / Methods: Subjects were women with early breast cancer, free of pre-existing cardiac disease. Left ventricular ejection fraction was measured using cardiovascular magnetic resonance before and >12 months after anthracycline-based chemotherapy (>3 months post-Trastuzumab). Variables associated with subclinical cardiotoxicity (defined as a fall in left ventricular ejection fraction of ≥5%) were identified by logistic regression. / Results: One hundred and sixty-five women (mean age 48.3 years at enrollment) completed the study 21.7 months [IQR 18.0-26.8] after starting chemotherapy. All received anthracyclines (98.8% epirubicin, cumulative dose 400 [300-450] mg/m2); 18% Trastuzumab. Baseline blood pressure was elevated (≥140/90mmHg, mean 147.3/86.1mmHg) in 18 subjects. Thirty-four subjects (20.7%) were identified with subclinical cardiotoxicity, independent predictors of which were the number of anthracycline cycles (odds ratio, OR 1.64 [1.17-2.30] per cycle), blood pressure ≥140/90mmHg (OR 5.36 [1.73-17.61]), body surface area (OR 2.08 [1.36-3.20] per standard deviation (0.16m2) increase), and Trastuzumab therapy (OR 3.35 [1.18-9.51]). The resultant predictive-model had an area under the receiver operating characteristics curve of 0.78 [0.70-0.86]. / Conclusions: We found subclinical cardiotoxicity to be common even within this low risk cohort. Risk of cardiotoxicity was associated with modestly elevated baseline blood pressure – indicating that close attention should be paid to blood pressure in patients considered for anthracycline based chemotherapy. The association with higher body surface area suggests that indexing of anthracycline doses to surface area may not be appropriate for all, and points to the need for additional research in this area
Neutral Pions and Eta Mesons as Probes of the Hadronic Fireball in Nucleus-Nucleus Collisions around 1A GeV
Chemical and thermal freeze-out of the hadronic fireball formed in symmetric
collisions of light, intermediate-mass, and heavy nuclei at beam energies
between 0.8A GeV and 2.0A GeV are discussed in terms of an equilibrated,
isospin-symmetric ideal hadron gas with grand-canonical baryon-number
conservation. For each collision system the baryochemical potential mu_B and
the chemical freeze-out temperature T_c are deduced from the inclusive neutral
pion and eta yields which are augmented by interpolated data on deuteron
production. With increasing beam energy mu_B drops from 800 MeV to 650 MeV,
while T_c rises from 55 MeV to 90 MeV. For given beam energy mu_B grows with
system size, whereas T_c remains constant. The centrality dependence of the
freeze-out parameters is weak as exemplified by the system Au+Au at 0.8A GeV.
For the highest beam energies the fraction of nucleons excited to resonance
states reaches freeze-out values of nearly 15 %, suggesting resonance densities
close to normal nuclear density at maximum compression. In contrast to the
particle yields, which convey the status at chemical freeze-out, the shapes of
the related transverse-mass spectra do reflect thermal freeze-out. The observed
thermal freeze-out temperatures T_th are equal to or slightly lower than T_c,
indicative of nearly simultaneous chemical and thermal freeze-out.Comment: 42 pages, 12 figure
e^+e^- Pair Production from A Reactions
We present a calculation of e^+e^- production in reactions at MAMI
and TJNAF energies within a semi-classical BUU transport model. Dilepton
invariant mass spectra for C, Ca and Pb are calculated
at 0.8, 1.5 and 2.2 GeV. We focus on observable effects of medium modifications
of the and mesons. The in-medium widths of these mesons are
taken into account in a dynamical, consistent way. We discuss the transport
theoretical treatment of broad resonances.Comment: 42 pages including 16 figure
Antikaon production in nucleon-nucleon reactions near threshold
The antikaon production cross section from nucleon-nucleon reactions near
threshold is studied in a meson exchange model. We include both pion and kaon
exchange, but neglect the interference between the amplitudes. In case of pion
exchange the antikaon production cross section can be expressed in terms of the
antikaon production cross section from a pion-nucleon interaction, which we
take from the experimental data if available. Otherwise, a -resonance
exchange model is introduced to relate the different reaction cross sections.
In case of kaon exchange the antikaon production cross section is related to
the elastic and cross sections, which are again taken from
experimental measurements. We find that the one-meson exchange model gives a
satisfactory fit to the available data for the cross section
at high energies. We compare our predictions for the cross section near
threshold with an earlier empirical parameterization and that from phase space
models.Comment: 16 pages, LaTeX, 5 postscript figures included, submitted to Z. Phys.
Subthreshold antiproton production in proton-carbon reactions
Data from KEK on subthreshold antiproton as well as on pi(+-) and K(+-)
production in proton-nucleus reactions are described at projectile energies
between 3.5 and 12.0 GeV. We use a model which considers a hadron-nucleus
reaction as an incoherent sum over collisions of the projectile with a varying
number of target nucleons. It samples complete events and allows thus for the
simultaneous consideration of all particle species measured. The overall
reproduction of the data is quite satisfactory. It is shown that the
contributions from the interaction of the projectile with groups of several
target nucleons are decisive for the description of subthreshold production.
Since the collective features of subthreshold production become especially
significant far below the threshold, the results are extrapolated down to COSY
energies. It is concluded that an antiproton measurement at ANKE-COSY should be
feasible, if the high background of other particles can be efficiently
suppressed.Comment: 15 pages, 5 figures, gzipped tar file, submitted to J. Phys. G v2:
Modification of text due to demands of referee
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