2,997 research outputs found
Baryonic contributions to e+e- yields in a hydrodynamic model of Pb+Au collisions at the SPS
We analyze e+e- yields from matter containing baryons in addition to mesons
using a hydrodynamic approach to describe Pb+Au collisions at 158 A GeV/c. We
use two distinctly different e+e- production rates to provide contrast.
Although the presence of baryons leads to significant enhancement of e+e-
emission relative to that from mesons-only matter, the calculated results fall
below the data in the range 400 < M/MeV < 600. The calculated results are,
however, only 1.3-1.5 standard deviations below the data, which may not be
statistically significant.Comment: 4 pages, 4 figures, proceedings of Quark Matter 9
Optical application and measurement of torque on microparticles of isotropic nonabsorbing material
We show how it is possible to controllably rotate or align microscopic
particles of isotropic nonabsorbing material in a TEM00 Gaussian beam trap,
with simultaneous measurement of the applied torque using purely optical means.
This is a simple and general method of rotation, requiring only that the
particle is elongated along one direction. Thus, this method can be used to
rotate or align a wide range of naturally occurring particles. The ability to
measure the applied torque enables the use of this method as a quantitative
tool--the rotational equivalent of optical tweezers based force measurement. As
well as being of particular value for the rotation of biological specimens,
this method is also suitable for the development of optically-driven
micromachines.Comment: 8 pages, 6 figure
Optical microrheology using rotating laser-trapped particles
We demonstrate an optical system that can apply and accurately measure the
torque exerted by the trapping beam on a rotating birefringent probe particle.
This allows the viscosity and surface effects within liquid media to be
measured quantitatively on a micron-size scale using a trapped rotating
spherical probe particle. We use the system to measure the viscosity inside a
prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction
The effects of meson mixing on dilepton spectra
The effect of scalar and vector meson mixing on the dilepton radiation from
hot and dense hadronic matter is estimated in different isospin channels. In
particular, we study the effect of - and mixing and
calculate the corresponding rates. Effects are found to be significant compared
to standard - and - annihilations. While the mixing in
the isoscalar channel mostly gives a contribution in the invariant mass range
between the two-pion threshold and the peak, the isovector channel
mixing induces an additional peak just below that of the .
Experimentally, the dilepton signals from - mixing seem to be more
tractable than those from - mixing.Comment: 10 pages, 9 figure
Theory of Optical Tweezers
We derive a partial-wave (Mie) expansion of the axial force exerted on a
transparent sphere by a laser beam focused through a high numerical aperture
objective. The results hold throughout the range of interest for practical
applications. The ray optics limit is shown to follow from the Mie expansion by
size averaging. Numerical plots show large deviations from ray optics near the
focal region and oscillatory behavior (explained in terms of a simple
interferometer picture) of the force as a function of the size parameter.
Available experimental data favor the present model over previous ones.Comment: 4 pages, 3 figure
Actinide Thermodynamics at Elevated Temperatures
The postclosure chemical environment in the proposed Yucca Mountain repository is expected to experience elevated temperatures. Predicting migration of actinides is possible if sufficient, reliable thermodynamic data on hydrolysis and complexation are available for these temperatures. Data are scarce and scattered for 25 degrees C, and nonexistent for elevated temperatures. This collaborative project between LBNL and PNNL collects thermodynamic data at elevated temperatures on actinide complexes with inorganic ligands that may be present in Yucca Mountain. The ligands include hydroxide, fluoride, sulfate, phosphate and carbonate. Thermodynamic parameters of complexation, including stability constants, enthalpy, entropy and heat capacity of complexation, are measured with a variety of techniques including solvent extraction, potentiometry, spectrophotometry and calorimetr
Design of the Pluto Event Generator
We present the design of the simulation package Pluto, aimed at the study of
hadronic interactions at SIS and FAIR energies. Its main mission is to offer a
modular framework with an object-oriented structure, thereby making additions
such as new particles, decays of resonances, new models up to modules for
entire changes easily applicable. Overall consistency is ensured by a plugin-
and distribution manager. Particular features are the support of a modular
structure for physics process descriptions, and the possibility to access the
particle stream for on-line modifications. Additional configuration and
self-made classes can be attached by the user without re-compiling the package,
which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High
Energy and Nuclear Physic
Design of the Pluto Event Generator
We present the design of the simulation package Pluto, aimed at the study of
hadronic interactions at SIS and FAIR energies. Its main mission is to offer a
modular framework with an object-oriented structure, thereby making additions
such as new particles, decays of resonances, new models up to modules for
entire changes easily applicable. Overall consistency is ensured by a plugin-
and distribution manager. Particular features are the support of a modular
structure for physics process descriptions, and the possibility to access the
particle stream for on-line modifications. Additional configuration and
self-made classes can be attached by the user without re-compiling the package,
which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High
Energy and Nuclear Physic
System-size dependence
The final state in The final state in heavy-ion collisions has a higher
degree of strangeness saturation than the one produced in collisions between
elementary particles like p-p or p-. A systematic analysis of this
phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider
and for collisions at RHIC and at AGS energies. Strangeness saturation
is shown to increase smoothly with the number of participants at AGS, CERN and
RHIC energies.Comment: 5 pages, 5 figures, presented at SQM2003 conferenc
Design of the Pluto Event Generator
We present the design of the simulation package Pluto, aimed at the study of
hadronic interactions at SIS and FAIR energies. Its main mission is to offer a
modular framework with an object-oriented structure, thereby making additions
such as new particles, decays of resonances, new models up to modules for
entire changes easily applicable. Overall consistency is ensured by a plugin-
and distribution manager. Particular features are the support of a modular
structure for physics process descriptions, and the possibility to access the
particle stream for on-line modifications. Additional configuration and
self-made classes can be attached by the user without re-compiling the package,
which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High
Energy and Nuclear Physic
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