13,921 research outputs found
Hadronic photon interactions at high energies
A simple phenomenological introduction to the physics of multi-pomeron
exchange amplitudes in connection with the Abramovski-Gribov-Kancheli (AGK)
cutting rules is given. The AGK cutting rules are applied to obtain qualitative
and quantitative predictions on multiparticle production at high energies. On
this basis, particle production in hadron-hadron scattering, photoproduction,
and in particular the transition to deep-inelastic scattering is discussed.Comment: LaTeX, 6 pages, 6 ps-figs, sprocl.sty, talk given by R. Engel at
"XXVI International Symposium on Multiparticle Dynamics" held in Faro,
Portugal, September 199
d-Au and p-p collisions at RHIC and the multichain Monte Carlo Dpmjet-III
In this paper we compare systematically the two-component Dual Parton Model
(DPM) event generator Dpmjet-III to d-Au and p-p data from RHIC. In this
process we are able to improve the model. The need for fusion of chains and a
recalibration of the model to obtain collision scaling in h-A and d-A
collisions was found already in previous comparisons. Here, comparing to
transverse momentum distributions of identified charged hadrons we find also
the need to modify the transverse momentum distributions in the decay of
hadronic strings, the basic building blocks of the model on soft hadronic
collisions.Comment: 8 pages, 13 figures, Based on a contribution to a workshop "QCD at
Cosmic Energies, Erice, Italie, Aug.29 to Sept.5 200
Antibaryon to Baryon Production Ratios in Pb-Pb and p-p collision at LHC energies of the DPMJET-III Monte Carlo
A sizable component of stopped baryons is predicted for pp and P bP b
collisions at LHC. Based on an analysis of RHIC data within framework of our
multichain Monte Carlo DPMJET-III the LHC predictions are presented.Comment: Presented at "Heavy Ion Collisions at the LHC: last call for
predictions", Geneva Switzerland, May 14th-June 8t
RHIC data and the multichain Monte Carlo DPMJET-II
Using data from RHIC we are able to systematically improve the two-component
Dual Parton Model (DPM) event generator DPMJET-III. Introducing percolation
parametrized as fusion of chains the model describes multiplicities and
pseudorapidity distributions in nucleus-nucleus collisions at all centralities.
Guided by the d-Au data from RHIC we recalibrate the model to obtain collision
scaling in h-A and d-A collisions.Comment: 8 pages, Based on a poster submitted to the 17th International
Conference on Ultra Relativistic Nucleus Nucleus Collisions, Jan. 11-17,
Oakland,California US
Stellar and Molecular Gas Kinematics of NGC1097: Inflow Driven by a Nuclear Spiral
We present spatially resolved distributions and kinematics of the stars and
molecular gas in the central 320pc of NGC1097. The stellar continuum confirms
the previously reported 3-arm spiral pattern extending into the central 100pc.
The stellar kinematics and the gas distribution imply this is a shadowing
effect due to extinction by gas and dust in the molecular spiral arms. The
molecular gas kinematics show a strong residual (i.e. non-circular) velocity,
which is manifested as a 2-arm kinematic spiral. Linear models indicate that
this is the line-of-sight velocity pattern expected for a density wave in gas
that generates a 3-arm spiral morphology. We estimate the inflow rate along the
arms. Using hydrodynamical models of nuclear spirals, we show that when
deriving the accretion rate into the central region, outflow in the disk plane
between the arms has to be taken into account. For NGC1097, despite the inflow
rate along the arms being ~1.2Msun/yr, the net gas accretion rate to the
central few tens of parsecs is much smaller. The numerical models indicate that
the inflow rate could be as little as ~0.06Msun/yr. This is sufficient to
generate recurring starbursts, similar in scale to that observed, every
20-150Myr. The nuclear spiral represents a mechanism that can feed gas into the
central parsecs of the galaxy, with the gas flow sustainable for timescales of
a Gigayear.Comment: accepted by Ap
Impact of Uncertainties in Hadron Production on Air-Shower Predictions
At high energy, cosmic rays can only be studied by measuring the extensive
air showers they produce in the atmosphere of the Earth. Although the main
features of air showers can be understood within a simple model of successive
interactions, detailed simulations and a realistic description of particle
production are needed to calculate observables relevant to air shower
experiments. Currently hadronic interaction models are the main source of
uncertainty of such simulations. We will study the effect of using different
hadronic models available in CORSIKA and CONEX on extensive air shower
predictions.Comment: 12 pages, 6 figures, to appear in the proceedings of International
Conference on Interconnection between High Energy Physics and Astroparticle
Physics: From Colliders to Cosmic Rays, Prague, Czech Republic, 7-13 Sep 200
Axial charges of octet and decuplet baryons
We present a study of axial charges of baryon ground and resonant states with
relativistic constituent quark models. In particular, the axial charges of
octet and decuplet , , , , , and
baryons are considered. The theoretical predictions are compared to existing
experimental data and results from other approaches, notably from lattice
quantum chromodynamics and chiral perturbation theory. The relevance of axial
charges with regard to -dressing and spontaneous chiral-symmetry breaking
is discussed
Role of interactions in ferrofluid thermal ratchets
Orientational fluctuations of colloidal particles with magnetic moments may
be rectified with the help of external magnetic fields with suitably chosen
time dependence. As a result a noise-driven rotation of particles occurs giving
rise to a macroscopic torque per volume of the carrier liquid. We investigate
the influence of mutual interactions between the particles on this ratchet
effect by studying a model system with mean-field interactions. The stochastic
dynamics may be described by a nonlinear Fokker-Planck equation for the
collective orientation of the particles which we solve approximately by using
the effective field method. We determine an interval for the ratio between
coupling strength and noise intensity for which a self-sustained rectification
of fluctuations becomes possible. The ratchet effect then operates under
conditions for which it were impossible in the absence of interactions.Comment: 18 pages, 10 figure
Effects of scopolamine on matching to sample paradigm and related tests in human subjects
This was a double-blind placebo-controlled study with a cross-over design to examine the effects of scopolamine on cognitive functions in young healthy subjects. Scopolamine hydrobromide was administered subcutaneously to 12 subjects (mean +/- SD age 23.8 +/- 2.2 years) at doses of 0.3 and 0.6 mg in comparison with two placebo conditions. Scopolamine at both doses produced marked sedation as rated by subjects and an observer. In the continuous performance test, vigilance was impaired by both doses of scopolamine. The span of apprehension test showed differing results (only the high dose of scopolamine showed a performance decrement only in the three-character version of the span of apprehension test). Significant impairment by both doses of scopolamine was seen in immediate and delayed free recall, continuous visual recognition, running word recognition and running picture recognition. While scopolamine caused a significant slowing in average reaction times for simultaneous matching as well as for delayed matching, subjects made more errors under scopolamine compared to placebo only in delayed matching, not in simultaneous matching. Also, the main outcome of matching to sample showed significant effects only in delayed matching, not in simultaneous matching. Notable in this study is the incongruity between the simultaneous matching test and the span of apprehension test on the one hand and the other cognitive tests used on the other. These results demonstrated that scopolamine has a greater effect on memory than on attention. Thus, the scopolamine-induced effects in the present study seem to be more relevant to Alzheimer's disease in an advanced phase than to normal aging. Copyright (C) 2003 S. Karger AG, Basel
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