12,636 research outputs found
and Spectra for Au+Au Collisions at = 200 GeV from STAR, PHENIX and BRAHMS in Comparison to Core-Corona Model Predictions
Based on results obtained with event generators we have launched the
core-corona model. It describes in a simplified way but quite successfully the
centrality dependence of multiplicity and of identified particles
observed in heavy-ion reaction at beam energies between = 17 GeV and
200 GeV. Also the centrality dependence of the elliptic flow, , for all
charged and identified particles could be explained in this model. Here we
extend this analysis and study the centrality dependence of single particle
spectra of and measured by the PHENIX, STAR and BRAHMS
collaborations. We find that also for these particles the analysis of the
spectra in the core-corona model suffers from differences in the data published
by the different experimental groups, notably for the pp collisions. As for
protons and for each experience the data agree well with the prediction
of the core-corona model but the value of the two necessary parameters depends
on the experiments. We show as well that the average momentum as a function of
the centrality depends in a very sensitive way on the particle species and may
be quite different for particles which have about the same mass. Therefore the
idea to interpret this centrality dependence as a consequence of a collective
expansion of the system, as done in blast way fits may be premature.Comment: Invited talk to the CPOD conference Dubna August 201
Femtosecond formation of collective modes due to meanfield fluctuations
Starting from a quantum kinetic equation including the mean field and a
conserving relaxation-time approximation we derive an analytic formula which
describes the time dependence of the dielectric function in a plasma created by
a short intense laser pulse. This formula reproduces universal features of the
formation of collective modes seen in recent experimental data of femtosecond
spectroscopy. The presented formula offers a tremendous simplification for the
description of the formation of quasiparticle features in interacting systems.
Numerical demanding treatments can now be focused on effects beyond these gross
features found here to be describable analytically.Comment: 4 pages 3 figures, PRB in pres
Using Provenance to support Good Laboratory Practice in Grid Environments
Conducting experiments and documenting results is daily business of
scientists. Good and traceable documentation enables other scientists to
confirm procedures and results for increased credibility. Documentation and
scientific conduct are regulated and termed as "good laboratory practice."
Laboratory notebooks are used to record each step in conducting an experiment
and processing data. Originally, these notebooks were paper based. Due to
computerised research systems, acquired data became more elaborate, thus
increasing the need for electronic notebooks with data storage, computational
features and reliable electronic documentation. As a new approach to this, a
scientific data management system (DataFinder) is enhanced with features for
traceable documentation. Provenance recording is used to meet requirements of
traceability, and this information can later be queried for further analysis.
DataFinder has further important features for scientific documentation: It
employs a heterogeneous and distributed data storage concept. This enables
access to different types of data storage systems (e. g. Grid data
infrastructure, file servers). In this chapter we describe a number of building
blocks that are available or close to finished development. These components
are intended for assembling an electronic laboratory notebook for use in Grid
environments, while retaining maximal flexibility on usage scenarios as well as
maximal compatibility overlap towards each other. Through the usage of such a
system, provenance can successfully be used to trace the scientific workflow of
preparation, execution, evaluation, interpretation and archiving of research
data. The reliability of research results increases and the research process
remains transparent to remote research partners.Comment: Book Chapter for "Data Provenance and Data Management for eScience,"
of Studies in Computational Intelligence series, Springer. 25 pages, 8
figure
Phase diagram and binding energy of interacting Bose gases
From the many-body T-matrix the condition for a medium-dependent bound state
and its binding energy is derived for a homogeneous interacting Bose gas. This
condition provides the critical line in the phase diagram in terms of the
medium-dependent scattering length. Separating the Bose pole from the
distribution function the influence of a Bose condensate is discussed and a
thermal minimum of the critical scattering length is found
Status of the advanced Stirling conversion system project for 25 kW dish Stirling applications
Heat engines were evaluated for terrestrial Solar Distributed Heat Receivers. The Stirling engine was identified as one of the most promising heat engines for terrestrial applications. Technology development is also conducted for Stirling convertors directed toward a dynamic power source for space applications. Space power requirements include high reliability with very long life, low vibration, and high system efficiency. The free-piston Stirling engine has the potential for future high power space conversion systems, either nuclear or solar powered. Although both applications appear to be quite different, their requirements complement each other
Preliminary designs for 25 kWe advanced Stirling conversion systems for dish electric applications
Under the Department of Energy's (DOE) Solar Thermal Technology Program, Sandia National Laboratories is evaluating heat engines for terrestrial Solar Distributed Heat Receivers. The Stirling engine has been identified by Sandia as one of the most promising engines for terrestrial applications. The Stirling engine also has the potential to meet DOE's performance and cost goals. The NASA Lewis Research Center is conducting Stirling engine technology development activities directed toward a dynamic power source for space applications. Space power systems requirements include high reliability, very long life, low vibration and high efficiency. The free-piston Stirling engine has the potential for future high power space conversion systems, either nuclear or solar powered. Although both applications appear to be quite different, their requirements complement each other. Preliminary designs feature a free-piston Stirling engine, a liquid metal heat transport system, and a means to provide nominally 25 kW electric power to a utility grid while meeting DOE's performance and long term cost goals. The Cummins design incorporates a linear alternator to provide the electrical output, while the STC design generates electrical power indirectly through a hydraulic pump/motor coupled to an induction generator. Both designs for the ASCS's will use technology which can reasonably be expected to be available in the early 1990'
Direct measurement of diurnal polar motion by ring laser gyroscopes
We report the first direct measurements of the very small effect of forced
diurnal polar motion, successfully observed on three of our large ring lasers,
which now measure the instantaneous direction of Earth's rotation axis to a
precision of 1 part in 10^8 when averaged over a time interval of several
hours. Ring laser gyroscopes provide a new viable technique for directly and
continuously measuring the position of the instantaneous rotation axis of the
Earth and the amplitudes of the Oppolzer modes. In contrast, the space geodetic
techniques (VLBI, SLR, GPS, etc.) contain no information about the position of
the instantaneous axis of rotation of the Earth, but are sensitive to the
complete transformation matrix between the Earth-fixed and inertial reference
frame. Further improvements of gyroscopes will provide a powerful new tool for
studying the Earth's interior.Comment: 5 pages, 4 figures, agu2001.cl
Comparison of conceptual designs for 25 kWe advanced Stirling conversion systems for dish electric application
The Advanced Stirling Conversion System (ASCS) Project is managed by NASA Lewis Research Center through a cooperative interagency agreement with DOE. Conceptual designs for the ASCS's were completed under parallel contracts in 1987 by Mechanical Technology Inc. (MTI) of Latham, NY, and Stirling Technology Company (STC) of Richland, WA. Each design features a free-piston Stirling engine, a liquid metal heat pipe receiver, and a means to provide about 25 kW of electric power to a utility grid while meeting DOE's long term performance and cost goals. An independent assessment showed that both designs are manufacturable and have the potential to easily meet DOE's long term cost goals
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