8,948 research outputs found
Elliptic flow from a parton cascade
The dependence of elliptic flow at RHIC energies on the effective parton
scattering cross section is calculated using the ZPC parton cascade model. We
show that the v_2 measure of elliptic flow saturates early in the evolution
before the hadronization transition to a rather large value ~0.05-0.15 as
\sigma_g varies from 2-10 mb and thus is a sensitive probe of the dynamics in
the plasma phase.Comment: 13 pages, 4 figure
Can dileptons reveal the in-medium properties of vector mesons?
Dilepton production from both pion-pion and kaon-antikaon annihilation in
heavy-ion collisions is studied using the relativistic transport model. The
formation of a rho meson from pion-pion annihilation and a phi meson from
kaon-antikaon annihilation, their propagation in the medium, and their decay
into dileptons are explicitly treated. Including the medium modifications of
the masses and widths of vector mesons as predicted by the QCD sum-rule
calculations, we study their effects on the dilepton invariant mass spectra
from heavy-ion collisions at SIS/GSI energies.Comment: 22 pages, 11 figures available upon request to [email protected]
Phi Meson Production in Heavy-Ion Collisions at SIS Energies
Phi meson production in heavy-ion collisions at SIS/GSI energies (
GeV/nucleon) is studied in the relativistic transport model. We include
contributions from baryon-baryon, pion-baryon, and kaon-antikaon collisions.
The cross sections for the first two processes are obtained in an
one-boson-exchange model, while that for the last process is taken to be of
Breit-Wigner form through the phi meson resonance. The dominant contribution to
phi meson production in heavy ion collisions at these energies is found to come
from secondary pion-nucleon collisions. Effects due to medium modifications of
kaon masses are also studied and are found to reduce the phi meson yield by
about a factor of two, mainly because of increased phi decay width as a result
of dropping kaon-antikaon masses. In this case, the ratio is about
4%, which is a factor of 2-3 below preliminary experimental data from the FOPI
collaboration at GSI. Including also the reduction of phi meson mass in medium
increases this ratio to about 8%, which is then in reasonable agreement with
the data.Comment: 46 pages, including 21 postscript figure
Excitation Functions of Stopping Power and Flow in Relativistic Heavy-Ion Collisions
Using a relativistic transport (ART) model, we study the stopping power, the
formation of superdense hadronic matter as well as the strength of transverse
and radial flow in central Au+Au collisions at beam momentum from 2 to 12 GeV/c
per nucleon. We find that complete stopping is achieved in the whole beam
momentum range. In particular, the proton rapidity distribution scaled by the
beam rapidity is independent of the beam momentum, and this is in agreement
with the experimental findings. Also, a large volume of superdense hadronic
matter with a local energy density exceeding that expected for the transition
of a hadronic matter to the quark-gluon plasma is formed in collisions at beam
momenta greater than 8 GeV/c per nucleon. Furthermore, it is found that the
transverse flow in these collisions is sensitive to the nuclear equation of
state and decreases with increasing beam momentum. On the other hand, the
radial flow is insensitive to the equation of state, and its strength increases
with beam momentum.Comment: Talk given at NN97, Gatlinburg, Tennessee June 2-6,1997. To appear in
the proc. in Nucl. Phys.
Seeing phi meson through the dilepton spectra in heavy-ion collisions
Dilepton spectra from the decay of phi mesons produced in heavy-ion
collisions at SIS/GSI energies ( GeV/nucleon) are studied in the
relativistic transport model. We include phi mesons produced from
baryon-baryon, pion-baryon, and kaon-antikaon collisions. The cross sections
for the first two processes are obtained from an one-boson-exchange model,
while that for the last process is taken to be the Breit-Wigner form through
the phi meson resonance. For dileptons with invariant mass near the phi meson
peak, we also include contributions from neutron-proton bremsstrahlung,
pion-pion annihilation, and the decay of rho and omega mesons produced in
baryon-baryon and meson-baryon collisions. Effects due to medium modifications
of the kaon and vector (rho, omega and phi) meson properties are investigated.
We find that the kaon medium effects lead to a broadening of the dilepton
spectrum as a result of the increase of phi meson decay width. Furthermore, the
dropping of phi meson mass in nuclear medium leads to a shoulder structure in
the dilepton spectrum besides the main peak at the bare phi meson mass. The
experimental measurement of the dilepton spectra from heavy-ion collisions is
expected to provide useful information about the phi meson properties in dense
matter.Comment: RevTeX, 18 pages, including 13 postscript figures, submitted to
Nuclear Physics
De novo CD5 Positive Diffuse Large B-cell Lymphomas with Bone Marrow Involvement in Korean
In CD5 positive (CD5+) mature B-cell lymphomas, newly recognized CD5+ diffuse large B-cell lymphoma (DLBCL) has been characterized by aggressive features. We studied twenty-five cases with CD5+ lymphomas involving bone marrow. Eleven cases were diagnosed as chronic lymphocytic leukemia, six cases were diagnosed as mantle cell lymphoma (MCL), and three cases with morphologic characteristics of MCL and without both the cyclin D1 expression and IGH/CCND1 rearrangement were unclassifiable. The remaining five cases, showing large to medium-sized lym-phoid cells with prominent nucleoli and a moderate amount of cytoplasm, were diagnosed as DLBCL. Five DLBCL cases were positive for CD5, CD20, surface immuno-globulin, but negative for CD23. Patients with CD5+ DLBCL showed a high age of onset (median, 68 yr) and two patients expired one month after the diagnosis. Since CD5+ DLBCL forms a distinct subgroup of DLBCL, a study of CD5 expression in DLBCL would be helpful to predict prognosis and to determine future therapeutic strategy. To the best of our knowledge, this is the first report on de novo CD5+ DLBCL in Koreans
Strange Mesons as a Probe for Dense Nuclear Matter
The production and propagation of kaons and antikaons has been studied in
symmetric nucleus-nucleus collisions in the SIS energy range. The ratio of the
excitation functions of K^+ production in Au+Au and C+C collisions increases
with decreasing beam energy. This effect was predicted for a soft nuclear
equation-of-state. In noncentral Au+Au collisions, the K^+ mesons are
preferentially emitted perpendicular to the reaction plane. The K^-/K^+ ratio
from A+A collisions at beam energies which are equivalent with respect to the
threshold is found to be about two orders of magnitude larger than the
corresponding ratio from proton-proton collisions. Both effects are considered
to be experimental signatures for a modification of kaon properties in the
dense nuclear medium.Comment: Talk given at the Erice School on Nuclear Physics, Erice, Sicily,
Italy, Sept. 17-25, 199
Transverse Fresnel-Fizeau drag effects in strongly dispersive media
A light beam normally incident upon an uniformly moving dielectric medium is
in general subject to bendings due to a transverse Fresnel-Fizeau light drag
effect. In conventional dielectrics, the magnitude of this bending effect is
very small and hard to detect. Yet, it can be dramatically enhanced in strongly
dispersive media where slow group velocities in the m/s range have been
recently observed taking advantage of the electromagnetically induced
transparency (EIT) effect. In addition to the usual downstream drag that takes
place for positive group velocities, we predict a significant anomalous
upstream drag to occur for small and negative group velocities. Furthermore,
for sufficiently fast speeds of the medium, higher order dispersion terms are
found to play an important role and to be responsible for peculiar effects such
as light propagation along curved paths and the restoration of the spatial
coherence of an incident noisy beam. The physics underlying this new class of
slow-light effects is thoroughly discussed
Molecular basis for passive immunotherapy of Alzheimer's disease
Amyloid aggregates of the amyloid-{beta} (A{beta}) peptide are implicated in the pathology of Alzheimer's disease. Anti-A{beta} monoclonal antibodies (mAbs) have been shown to reduce amyloid plaques in vitro and in animal studies. Consequently, passive immunization is being considered for treating Alzheimer's, and anti-A{beta} mAbs are now in phase II trials. We report the isolation of two mAbs (PFA1 and PFA2) that recognize A{beta} monomers, protofibrils, and fibrils and the structures of their antigen binding fragments (Fabs) in complex with the A{beta}(1–8) peptide DAEFRHDS. The immunodominant EFRHD sequence forms salt bridges, hydrogen bonds, and hydrophobic contacts, including interactions with a striking WWDDD motif of the antigen binding fragments. We also show that a similar sequence (AKFRHD) derived from the human protein GRIP1 is able to cross-react with both PFA1 and PFA2 and, when cocrystallized with PFA1, binds in an identical conformation to A{beta}(1–8). Because such cross-reactivity has implications for potential side effects of immunotherapy, our structures provide a template for designing derivative mAbs that target A{beta} with improved specificity and higher affinity
The tripod-pulley technique for arthroscopic remplissage in engaging Hill-Sachs lesions
Arthroscopic Bankart repair is now a well-established technique for the treatment of shoulder instability. However, failure rates are considerable when significant bony defects are not addressed. Hill-Sachs lesions, present in the vast majority of those with recurrent anterior instability, when of significant dimension and location, may account for some of these failures. The remplissage procedure involves capsulotenodesis of the posterior capsule and the infraspinatus tendon to fill the Hill-Sachs lesion. "Double-pulley" remplissage is a transtendinous technique that has been described elsewhere and that may simplify the procedure. We present a modification of this technique, the "tripod-pulley" technique, which we feel may potentiate healing of the Hills-Sachs lesions of the capsule and infraspinatus by increasing the surface contact area. At the same time, this technique minimizes the risk of potential damage to the infraspinatus as it uses 2.3-mm "all-suture" anchors
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