225 research outputs found
Transition from Baryonic to Mesonic Freeze-Out
The recently discovered sharp peak in the K+/pi+ ratio is discussed in the
framework of the statistical model. In this model a rapid change is expected as
the hadronic gas undergoes a transition from a baryon-dominated to a
meson-dominated gas. The transition happens at sqrt{s_{NN}} = 8.16 GeV,
temperature T = 140 MeV and baryon chemical potential mu_B = 410 MeV. The
maximum in the Lambda/pi ratio is well reproduced by the statistical model, but
the change in the K+/pi+ ratio is much less pronounced than the one observed by
the NA49 collaboration. Further experimental tests are proposed to clarify the
nature of the transition. In particular, the maxima expected in the statistical
model for the Xi/pi and Omega/pi ratios occur at slightly higher beam energies
than the maxima for the Lambda/pi and K+/pi+ ratios.Comment: 5 pages, 5 postscript figures, uses elsart.st
Transverse Energy per Charged Particle and Freeze-Out Criteria in Heavy-Ion Collisions
In relativistic nucleus-nucleus collisions the transverse energy per charged
particle, E_T/N_ch, increases rapidly with beam energy and remains
approximately constant at about 800 MeV for beam energies from SPS to RHIC. It
is shown that the hadron resonance gas model describes the energy dependence,
as well as the lack of centrality dependence, qualitatively. The values of
E_T/N_ch are related to the chemical freeze-out criterium E/N about 1 GeV valid
for primordial hadrons.Comment: 8 pages, 5 figure
Collective Flow Distributions and Nuclear Stopping in Heavy-ion Collisions at AGS, SPS and RHIC
We study the production of proton, antiproton and net-proton at \AGS, \SPS
and \RHIC within the framework non-uniform flow model(NUFM) in this paper. It
is found that the system of RHIC has stronger longitudinally non-uniform
feature than AGS and SPS, which means that nuclei at RHIC energy region is much
more transparent. The NUFM model provides a very good description of all proton
rapidity at whole AGS, SPS and RHIC. It is shown that our analysis relates
closely to the study of nuclear stopping and longitudinally non-uniform flow
distribution of experiment. This comparison with AGS and SPS help us to
understand the feature of particle stopping of thermal freeze-out at RHIC
experiment.Comment: 16 pages,7 figure
Violation of energy-per-hadron scaling in a resonance matter
Yields of hadrons, their average masses and energies per hadron at the stage
of chemical freeze-out in (ultra)relativistic heavy-ion collisions are analyzed
within the statistical model. The violation of the scaling / = 1 GeV
observed in Au+Au collisions at = 130 AGeV is linked to the
formation of resonance-rich matter with a considerable fraction of baryons and
antibaryons. The rise of the energy-per-hadron ratio in baryon-dominated matter
is discussed. A violation of the scaling condition is predicted for a very
central zone of heavy-ion collisions at energies around 40 AGeV.Comment: 5 pages incl. 3 figures and 2 tables, to be published in Phys. Rev.
Full and Partial Thermalization of Nucleons in Relativistic Nucleus-Nucleus Collisions
We propose a mechanism of thermalization of nucleons in relativistic
nucleus-nucleus collisions. Our model belongs, to a certain degree, to the
transport ones; we consider the evolution of the system, but we parametrize
this development by the number of collisions of every particle in the system
rather than by the time variable. We based on the assumption that the nucleon
momentum transfer after several nucleon-nucleon (-hadron) collisions becomes a
random quantity driven by a proper distribution.Comment: 5 pages, 2 figures, Talk given at the Conference on Strong and
Electroweak Matter (SEWM08), August 26-29, 2008, Amsterdam, the Netherland
Certifications Offered by Cost Estimating Organizations
There has been an increasing trend in professional and engineering circles to place greater emphasis on official credentials. These credentials commonly come in the form of certificates – documented recognition by a professional body that an engineer or other professional has the qualifications and technical knowledge to be a practitioner in that field. These certificates are somewhat analogous to merit badges in scouting – the certification is evidence that the holder has a certain minimum level of competence in the subject area. This review will help you decide what certifications are applicable to you and the requirements to obtain a certification
Boundary and expansion effects on two-pion correlation functions in relativistic heavy-ion collisions
We examine the effects that a confining boundary together with hydrodynamical
expansion play on two-pion distributions in relativistic heavy-ion collisions.
We show that the effects arise from the introduction of further correlations
due both to collective motion and the system's finite size. As is well known,
the former leads to a reduction in the apparent source radius with increasing
average pair momentum K. However, for small K, the presence of the boundary
leads to a decrease of the apparent source radius with decreasing K. These two
competing effects produce a maximum for the effective source radius as a
function of K.Comment: 6 pages, 5 Eps figures, uses RevTeX and epsfi
Recommended from our members
Beam Dump Design for the Rare Isotope Accelerator Fragmentation Line
Beam dumps for the heavy ion beams of the fragmentation line of the Rare Isotope Accelerator have been designed. The most severe operational case involves a continuous U beam impacting the beam dump with a power of 295 kW and a nominal spot diameter size of 5 cm. The dump mechanically consists of two rotating barrels with a water cooled outer wall of 2 mm thick aluminum. The barrels are 70 cm in diameter and axially long enough to intercept a variety of other beams. The aluminum wall absorbs approximately 15% of the U beam power with the rest absorbed in the water downstream of the wall. The water acts as an absorber of the beam and as a coolant for the 2 mm aluminum wall. The barrel rotates at less than 400 RPM, maximum aluminum temperatures are less than 100 C and maximum thermal fatigue stresses are low at 3.5 x 10{sup 7} Pa (5 ksi). Rotation of the dump results in relatively low radiation damage levels with an operating lifetime of years for most beams
Strangeness Enhancement in p-A Collisions: Consequences for the Interpretation of Strangeness Production in A-A Collisions
Published measurements of semi-inclusive Lambda production in p-Au collisions
at the AGS are used to estimate the yields of singly strange hadrons in
nucleus-nucleus A-A collisions. Results of a described extrapolation technique
are shown and compared to measurements of K+ production in Si-Al, Si-Au, and
Au-Au collisions at the AGS and net Lambda production in Su-Su, S-Ag, Pb-Pb,
and inclusive p-A collisions at the SPS. The extrapolations can account for
more than 75% of the measured strange particle yields in all of the studied
systems except for very central Au-Au collisions at the AGS where RQMD
comparisons suggest large re-scattering contributions.Comment: 9 pages, 4 figure
Cost Estimating Certifications Offered by Professional Societies in the United States and Abroad
Many projects in industry and government go over budget and schedule. In most engineering economics courses, the emphasis is on how to compare alternatives and learn about time value of money and interest and inflation rates. The students are usually given the costs and asked to compare the alternatives. However, this is the easy part of the analysis. The hard part of real project evaluations is developing the cost and investment numbers to do the engineering economics analysis. In most engineering economic textbooks, there is at most one chapter on cost estimation. More and more companies and government organizations are concerned that their engineers don\u27t know how to do accurate cost and schedule estimates. Cost estimation is a critical element to doing engineering economic evaluations. For example, one of the authors has presented short courses on cost estimation and economic evaluation to over 10,000 professionals, mostly engineers and engineering managers who are in industry and government. Most of these engineers have taken engineering economics courses while in college, and they have a good grasp of the fundamentals of engineering economics. However, most practicing engineers lack the fundamentals to do accurate cost and schedule estimates. To keep projects from going over budget and schedule, more and more organizations are requiring their engineers and engineering managers to obtain certifications in cost estimation from professional societies. The purpose of this paper is to discuss the current certifications offered so practicing engineers and engineering educators will know what is available and what is required to earn these certifications. The four major cost estimating certifications offered by professional societies in the United States are discussed. Eligibility and certification requirements along with examination information are presented. In addition, because many engineers are working on international projects, cost estimation certifications offered by professional societies in other countries are also summarized
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