8,873 research outputs found
Soft gluon radiation and energy dependence of total hadronic cross-sections
An impact parameter representation for soft gluon radiation is applied to
obtain both the initial decrease of the total cross-section ()
for proton-proton collisions as well as the later rise of with
energy for both and . The non-perturbative soft part of the
eikonal includes only limited low energy gluon emission and leads to the
initial decrease in the proton-proton cross- section. On the other hand, the
rapid rise in the hard, perturbative jet part of the eikonal is tamed into the
experimentally observed mild increase by soft gluon radiation whose maximum
energy rises slowly with energy.Comment: 30 pages, 6 figures. Version accepted for publication in Physical
Review D. Additional section with explanatory material added making the paper
more self contained and two figures changed to have a complete summary of the
available accelerator dat
Laser-Induced Above-Bandgap Transparency in GaAs
We report the observation of large () laser-induced above-bandgap
transparency in GaAs at room temperature. The induced transparency is present
only during the pulse width of the driving midinfrard laser pulses and its
spectral shape is consistent with a laser-induced blue shift of the band edge.
Our simulations based on the dynamic Franz-Keldysh effect reproduce the salient
features of the experimental results, demonstrating in particular that the
amount of the band edge shift is approximately given by the ponderomtive
potential.Comment: 4 pages, 4 figure
Integrability and level crossing manifolds in a quantum Hamiltonian system
We consider a two-spin model, represented classically by a nonlinear
autonomous Hamiltonian system with two degrees of freedom and a nontrivial
integrability condition, and quantum mechanically by a real symmetric
Hamiltonian matrix with blocks of dimensionalities K=l(l+1)/2, l=1,2,... In the
six-dimensional (6D) parameter space of this model, classical integrability is
satisfied on a 5D hypersurface, and level crossings occur on 4D manifolds that
are completely embedded in the integrability hypersurface except for some
lower-D sub-manifolds. Under mild assumptions, the classical integrability
condition can be reconstructed from a purely quantum mechanical study of level
degeneracies in finite-dimensional invariant blocks of the Hamiltonian matrix.
Our conclusions are based on rigorous results for K=3 and on numerical results
for K=6,10.Comment: 8 pages, 3 figure
Evaluation of uroprotective efficacy of amifostine against cyclophosphamide induced hemorrhagic cystitis
The role of amifostine in the prevention of cyclophosphamide-induced hemorrhagic cystitis (HC) was evaluated in the rat model. Urinary bladders from control rats that received no drugs (group I) were compared with those from rats receiving cyclophosphamide alone at a dose of 150 mg/kg (group II), and two other groups receiving amifostine at 100 mg/kg (group III) and 200 mg/kg (group IV), 15 min prior to cyclophosphamide. Bladders were assessed macroscopically and histologically at 24 h and after 7 days. All the animals that received cyclophosphamide alone developed severe HC. On the basis of the scores of macroscopic and histologic changes, animals that received amifostine showed excellent uroprotection. Only 2/6 rats in group III and 1/6 rats in group IV developed mild HC at 24 h. None of the rats in either of these groups showed any evidence of HC at 7 days. It is concluded that amifostine protects the urothelium against cyclophosphamide-induced HC
Classical and quantum chaos in a circular billiard with a straight cut
We study classical and quantum dynamics of a particle in a circular billiard
with a straight cut. This system can be integrable, nonintegrable with soft
chaos, or nonintegrable with hard chaos, as we vary the size of the cut. We use
a quantum web to show differences in the quantum manifestations of classical
chaos for these three different regimes.Comment: LaTeX2e, 8 pages including 3 Postscript figures and 4 GIF figures,
submitted to Phys. Rev.
Scaling of hadronic transverse momenta in a hydrodynamic treatment of relativistic heavy ion collisions
The transverse momenta of hadrons in central nucleus-nucleus collisions are
evaluated in a boost invariant hydrodynamics with transverse expansion. Quark
gluon plasma is assumed to be formed in the initial state which expands and
cools via a first order phase transition to a rich hadronic matter and
ultimately undergoes a freeze-out. The average transverse momentum of pions,
kaons, and protons is estimated for a wide range of multiplicity densities and
transverse sizes of the system. For a given system it is found to scale with
the square-root of the particle rapidity density per unit transverse area, and
consistent with the corresponding values seen in experiments at
1800 GeV, suggesting a universal behaviour. The average transverse momentum
shows only an approximate scaling with multiplicity density per nucleon which
is at variance with the data.Comment: 6 pages including 9 figure
Integrability and action operators in quantum Hamiltonian systems
For a (classically) integrable quantum mechanical system with two degrees of
freedom, the functional dependence of the
Hamiltonian operator on the action operators is analyzed and compared with the
corresponding functional relationship in
the classical limit of that system. The former is shown to converge toward the
latter in some asymptotic regime associated with the classical limit, but the
convergence is, in general, non-uniform. The existence of the function
in the integrable regime of a parametric
quantum system explains empirical results for the dimensionality of manifolds
in parameter space on which at least two levels are degenerate. The comparative
analysis is carried out for an integrable one-parameter two-spin model.
Additional results presented for the (integrable) circular billiard model
illuminate the same conclusions from a different angle.Comment: 9 page
A massive Feynman integral and some reduction relations for Appell functions
New explicit expressions are derived for the one-loop two-point Feynman
integral with arbitrary external momentum and masses and in D
dimensions. The results are given in terms of Appell functions, manifestly
symmetric with respect to the masses . Equating our expressions with
previously known results in terms of Gauss hypergeometric functions yields
reduction relations for the involved Appell functions that are apparently new
mathematical results.Comment: 19 pages. To appear in Journal of Mathematical Physic
Fludarabine and cyclophosphamide based reduced intensity conditioning (RIC) regimens reduce rejection and improve outcome in Indian patients undergoing allogeneic stem cell transplantation for severe aplastic anemia
Thirty-five patients (25 men and 10 women) with a median age of 20 years with severe aplastic anaemia (SAA) underwent HLA identical stem cell transplantation (HSCT) using a combination of fludarabine and cyclophosphamideanti-thymocyte globulin between 2004 and 2006. Cyclosporine and mini methotrexate were used as GVHD prophylaxis. Graft source included peripheral blood stem cells (28) or G-CSF stimulated bone marrow (7). Two patients expired <7 days post-HSCT while 32 (91.5%) patients engrafted with a median neutrophil and platelet engraftment time of 12 days each. Three patients (8.5%) developed veno-occlusive disease while acute GVHD occurred in 29% of evaluable patients, with chronic GVHD in 32%. At a mean follow-up of 22 months, 29 (82.8%) are alive and well. When compared with 26 patients previously transplanted using Cy200/antilymphocyte globulin, there was faster neutrophil engraftment (12 vs 16 days; P=0.002) with significantly lower rejection rates (2.9 vs 30.7%; P=0.003) and a superior event-free (82.8 vs 38.4%; P=0.001) and overall survival (82.8 vs 46.1%; P=0.005). A combination of fludarabine with cyclophosphamideanti-thymocyte globulin reduces rejection and improves overall and event-free survival in Indian patients undergoing HSCT for severe aplastic anaemia
Bounds for Bose-Einstein Correlation Functions
Bounds for the correlation functions of identical bosons are discussed for
the general case of a Gaussian density matrix. In particular, for a purely
chaotic system the two-particle correlation function must always be greater
than one. On the other hand, in the presence of a coherent component the
correlation function may take values below unity. The experimental situation is
briefly discussed.Comment: 7 pages, LaTeX, DMR-THEP-93-5/
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