8,312 research outputs found
Cascade production in heavy-ion collisions at SIS energies
Production of the doubly strange baryon in heavy-ion collisions at
\textrm{SIS} energies is studied in a relativistic transport model that
includes perturbatively the strangeness-exchange reactions and . Taking the cross sections for these
reactions from the predictions of a hadronic model, we find that the
yield is about in central collisions of Ni + Ni at
\textrm{GeV}. The yield is further found to be more sensitive
to the magnitude of the cross sections for strangeness-exchange reactions than
to the medium effects due to modified kaon properties. We have also made
predictions for production in Au+Au collisions at energies from 1 to 2
GeV/nucleon.Comment: 13 pages, 5 figures, typos fixed and discussions added, to appear in
PL
Multistrange baryon production in relativistic heavy ion collisions
Using a multiphase transport model, we study the production of multistrange
baryons from the hadronic matter formed in relativistic heavy ion collisions.
The mechanism we introduce is the strangeness-exchange reactions between
antikaons and hyperons. We find that these reactions contribute significantly
to the production of multistrange baryons in heavy ion collisions at SPS
energies, which has been found to be appreciably enhanced. We have also made
predictions for multistrange baryon production in heavy ion collisions at RHIC
and found a similar enhancement.Comment: 6 pages, RevTex, 8 figs include
Charmonium Absorption in the Meson-exchange Model
We review the meson-exchange model for charmonium absorption by hadrons. This
includes the construction of the interaction Lagrangians, the determination of
the coupling constants, the introduction of form factors, and the predicted
cross sections for absorption by both mesons and nucleons. We further
discuss the effects due to anomalous parity interactions, uncertainties in form
factors, constraints from chiral symmetry, and the change of charmed meson mass
in medium on the cross sections for charmonium absorption in hadronic matter.Comment: 10 pages, 2 figures. Talk given at Quark Matter 2002 (QM 2002),
Nantes, France, 18-24 July 2002. To appear in the proceedings (Nucl. Phys. A
Single Electron Elliptic Flow Measurements in Au+Au Collisions from STAR
Recent measurements of elliptic flow (v_2) and the nuclear modification
factor (R_{CP}) of strange mesons and baryons in the intermediate p_T domain in
Au+Au collisions demonstrate a scaling with the number of constituent-quarks.
This suggests hadron production via quark coalescence from a thermalized parton
system. Measuring the elliptic flow of charmed hadrons, which are believed to
originate rather from fragmentation than from coalescence processes, might
therefore change our view of hadron production in heavy ion collisions.
While direct v_2 measurements of charmed hadrons are currently not available,
single electron v_2 at sufficiently high transverse momenta can serve as a
substitute. At transverse momenta above 2 GeV/c, the production of single
electrons from non-photonic sources is expected to be dominated by the decay of
charmed hadrons. Simulations show a strong correlation between the flow of the
charmed hadrons and the flow of their decay electrons for p_T > 2 GeV/c.
We will present preliminary STAR results from our single electron v_2
measurements from Au+Au collisions at RHIC energies.Comment: 10 pages, 7 figures Proceedings of the Hot Quarks 2004 Conference,
July 18-24 2004, Taos Valley, New Mexico, USA to be published in Journal of
Physics
Discovery of Extremely Embedded X-ray Sources in the R Coronae Australis Star Forming Core
With the XMM-Newton and Chandra observatories, we detected two extremely
embedded X-ray sources in the R Corona Australis (R CrA) star forming core,
near IRS 7. These sources, designated as XB and XA, have X-ray absorption
columns of ~3e23 cm-2 equivalent to AV ~180 mag. They are associated with the
VLA centimeter radio sources 10E and 10W, respectively. XA is the counterpart
of the near-infrared source IRS 7, whereas XB has no K-band counterpart above
19.4 mag. This indicates that XB is younger than typical Class I protostars,
probably a Class 0 protostar or in an intermediate phase between Class 0 and
Class I. The X-ray luminosity of XB varied between 29<log LX <31.2 ergs s-1 on
timescales of 3-30 months. XB also showed a monotonic increase in X-ray
brightness by a factor of two in 30 ksec during an XMM-Newton observation. The
XMM-Newton spectra indicate emission from a hot plasma with kT ~3-4 keV and
also show fluorescent emission from cold iron. Though the X-ray spectrum from
XB is similar to flare spectra from Class I protostars in luminosity and
temperature, the light curve does not resemble the lightcurves of magnetically
generated X-ray flares because the variability timescale of XB is too long and
because variations in X-ray count rate were not accompanied by variations in
spectral hardness. The short-term variation of XB may be caused by the partial
blocking of the X-ray plasma, while the month-long flux enhancement may be
driven by mass accretion.Comment: 26 pages, 8 figures, To be published in ApJ in April 200
Spark ignition of propane-air mixtures near the minimum ignition energy: Part I. An experimental study
Kernel growth from a spark in propane-air mixtures at atmospheric pressure is studied in a constant volume bomb with a high-speed laser schlieren system. The spark current and voltage waveforms of an inductive ignition source are simultaneously recorded with the photographic recordings. The temporal growth of the measured equivalent radii at conditions near the minimum ignition energy shows the existence of a critical radius and the influence of the critical radius on kernel development. In addition, it is shown that the net spark power for ignition can be estimated using data from minimum ignition energy, electrode fall energy losses, and spark calorimetry experiments. These results are used in Part II to develop a model for kernel growth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29535/1/0000623.pd
Intermittent applied mechanical loading induces subchondral bone thickening that may be intensified locally by contiguous articular cartilage lesions
Objectives: Changes in subchondral bone (SCB) and cross-talk with articular cartilage (AC) have been linked to osteoarthritis (OA). Using micro-computed tomography (micro-CT) this study: (1) examines changes in SCB architecture in a non-invasive loading mouse model in which focal AC lesions are induced selectively in the lateral femur, and (2) determines any modifications in the contralateral knee, linked to changes in gait, which might complicate use of this limb as an internal control. Methods: Right knee joints of CBA mice were loaded: once with 2weeks of habitual use (n=7), for 2weeks (n=8) or for 5weeks (n=5). Both left (contralateral) and right (loaded) knees were micro-CT scanned and the SCB and trabecular bone analysed. Gait analysis was also performed. Results: These analyses showed a significant increase in SCB thickness in the lateral compartments in joints loaded for 5weeks, which was most marked in the lateral femur; the contralateral non-loaded knee also showed transient SCB thickening (loaded once and repetitively). Epiphyseal trabecular bone BV/TV and trabecular thickness were also increased in the lateral compartments after 5 weeks of loading, and in all joint compartments in the contralateral knee. Gait analysis showed that applied loading only affected gait in the contralateral himd-limb in all groups of mice from the second week after the first loading episode. Conclusions: These data indicate a spatial link between SCB thickening and AC lesions following mechanical trauma, and the clear limitations associated with the use of contralateral joints as controls in such OA models, and perhaps in OA diagnosis
The Spectrum of Epstein-Barr Virus-Associated Lymphoproliferative Disease in Korea: Incidence of Disease Entities by Age Groups
This study is to identify the spectrum of Epstein-Barr virus (EBV)-positive lymphoproliferative diseases (LPD) and relationships between these diseases in Korea. The EBV status and clinicopathology of 764 patients, including acute EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH), chronic active EBV (CAEBV) infections, B-LPD arising in chronic latent EBV infection, T & natural killer (NK) cell non-Hodgkin's lymphomas (NHL), B-NHLs, and Hodgkin's lymphomas (HD), were analyzed. T or NK cell NHLs were the most common forms of EBV-positive NHLs (107/167, 64%); among these, nasal-type NK/T cell lymphomas were the most common (89/107, 83%). According to the age, Burkitt's lymphoma was the most common in early childhood; in teenagers, chronic (active) EBV infection-associated LPD was the most common type. The incidence of NK/T cell lymphoma began to increase from the twenties and formed the major type of EBV-associated tumor throughout life. Diffuse large B cell lymphoma formed the major type in the sixties and seventies. In conclusion, primary infections in early childhood are complicated by the development of CAEBV infections that are main predisposing factors for EBV-associated T or NK cell malignancies in young adults. In old patients, decreased immunity associated with old age and environmental cofactors may provoke the development of peripheral T cell lymphoma, unspecified, and diffuse large B cell lymphoma
production in reactions at SIS energies
Detailed predictions for dilepton production from reactions at SIS
energies are presented within a semi-classical BUU transport model that
includes the off-shell propagation of vector mesons nonperturbatively and
calculates the width of the vector mesons dynamically. Different scenarios of
in-medium modifications of vector mesons, such as collisional broadening and
dropping vector meson masses, are investigated and the possibilities for an
experimental observation of in-medium effects in reactions at 1--4 GeV
are discussed for a variety of nuclear targets.Comment: 38 pages, LaTeX, including 20 postscript figures, to be published in
Nucl. Phys.
Theory of Luminescence Spectra of High-Density Electron-Hole Systems: Crossover from Excitonic Bose-Einstein Condenstation to Electron-Hole BCS State
We present a unified theory of luminescence spectra for highly excited
semiconductors, which is applicable both to the electron-hole BCS state and to
the exciton Bose-Einstein condensate. The crossover behavior between
electron-hole BCS state and exciton Bose-Einstein condensate clearly manifests
itself in the calculated luminescence spectra. The analysis is based on the
Bethe-Salpeter equation combined with the generalized
random-phase-approximation, which enables us to consider the multiple Coulomb
scattering and the quantum fluctuation associated with the center-of-mass
motion of electron-hole pairs. In the crossover regime, the calculated spectra
are essentially different from results obtained by the BCS-like mean-field
theory and the interacting Boson model. In particular, it is found that the
broad spectrum, arising from the recombination of electron-hole BCS state,
splits into the P- and P_2-luminescence bands with decreasing the particle
density. The dependence of these bands on the carrier density is in good
agreement with experiments for highly excited semiconductors.Comment: 9 pages, 4 figures, To appear in Solid State Communication
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