4,522 research outputs found
Particle spectra and HBT radii for simulated central nuclear collisions of C+C, Al+Al, Cu+Cu, Au+Au, and Pb+Pb from Sqrt(s)=62.4-2760 GeV
We study the temperature profile, pion spectra and HBT radii in central
symmetric and boost-invariant nuclear collisions using a super hybrid model for
heavy-ion collisions (SONIC) combining pre-equilibrium flow with viscous
hydrodynamics and late-stage hadronic rescatterings. In particular, we simulate
Pb+Pb collisions at Sqrt(s)=2.76 TeV, Au+Au, Cu+Cu, Al+Al, and C+C collisions
at Sqrt(s)=200 GeV and Au+Au, Cu+Cu collisions at Sqrt(s)=62.4 GeV. We find
that SONIC provides a good match to the pion spectra and HBT radii for all
collision systems and energies, confirming earlier work that a combination of
pre-equilibrium flow, viscosity and QCD equation of state can resolve the
so-called HBT puzzle. For reference, we also show p+p collisions at Sqrt(s)=7
TeV. We make tabulated data for the 2+1 dimensional temperature evolution of
all systems publicly available for the use in future jet energy loss or similar
studies.Comment: 9 pages, 5 figures, 2 tables; v2: fixed typos, updated figures; v3:
minor changes, matches published versio
Clonal Interference, Multiple Mutations, and Adaptation in Large Asexual Populations
Two important problems affect the ability of asexual populations to
accumulate beneficial mutations, and hence to adapt. First, clonal interference
causes some beneficial mutations to be outcompeted by more-fit mutations which
occur in the same genetic background. Second, multiple mutations occur in some
individuals, so even mutations of large effect can be outcompeted unless they
occur in a good genetic background which contains other beneficial mutations.
In this paper, we use a Monte Carlo simulation to study how these two factors
influence the adaptation of asexual populations. We find that the results
depend qualitatively on the shape of the distribution of the effects of
possible beneficial mutations. When this distribution falls off slower than
exponentially, clonal interference alone reasonably describes which mutations
dominate the adaptation, although it gives a misleading picture of the
evolutionary dynamics. When the distribution falls off faster than
exponentially, an analysis based on multiple mutations is more appropriate.
Using our simulations, we are able to explore the limits of validity of both of
these approaches, and we explore the complex dynamics in the regimes where
neither are fully applicable.Comment: 24 pages, 5 figure
Observational and theoretical studies of the evolving structure of baroclinic waves
Dynamical processes involved in comma cloud formation, and passive tracer evolution in a baroclinic wave are discussed. An analytical solution was obtained demonstrating the complex nongeostrophic flow pattern involved in the redistribution of low level constituents in a finite amplitude baroclinic wave, and in the formation of the typical humidity and cloud distributions in such a wave. Observational and theoretical studies of blocking weather patterns in middle latitude flows were studied. The differences in the energy and enstrophy cascades in blocking and nonblocking situations were shown. It was established that pronounced upscale flow of both of these quantities, from intermediate to planetary scales, occurs during blocking episodes. The upscale flux of enstrophy, in particular, suggests that the persistence of blocking periods may be due to reduced dissipation of the large scale circulation and therefore entail some above normal predictability
Studies of heat source driven natural convection
Natural convection energy transport in a horizontal layer of internally heated fluid with a zero heat flux lower boundary, and an isothermal upper boundary, has been studied. Quantitative information on the time-mean temperature distribution and the fluctuating component of temperature about the mean temperature in steady turbulent convection are obtained from a small thermocouple inserted into the layer through the upper bounding plate. Data are also presented on the development of temperature at several vertical positions when the layer is subject to both a sudden increase and to a sudden decrease in power input. For changes of power input from zero to a value corresponding to a Rayleigh number much greater than the critical linear stability theory value, a slight hysteresis in temperature profiles near the upper boundary is observed between the heat-up and cool-down modes
Is Phytophthora cinnamomi a causal agent of oak decline in Southern Ohio?
White oak (Quercus alba L.) plays a vital ecological role and is one of Ohio’s most important hardwood timber species. The decline and death of large numbers of white oaks in several southern Ohio forests during the past five years has therefore concerned foresters and land managers. The apparent
concentration of mortality in low-lying areas or along waterways, and the isolation of Phytophthora cinnamomi Rands from the
rhizospheres of declining oaks, suggest that this pathogen (a well known root disease agent) may be involved. We investigated the
potential role of topography and environmental factors on pathogen activity by monitoring, monthly from July to October 2008, soil moisture, soil temperature, and soil inoculum densities in declining and healthy stands at Scioto Trail State Forest (STSF). We collected one pair of soil samples at each of three elevations along
120m transects in two declining and two healthy stands.
Both soil moisture and total isolation frequencies of P. cinnamomi declined throughout the summer. Inoculum concentrations were highly variable even at small spatial scales, suggesting a patchy distribution of P. cinnamomi, although elevation was not a significant factor. Despite such high heterogeneity in inoculum levels, declining stands had significantly higher P. cinnamomi propagule densities than healthy stands (P=0.021). These preliminary data provide circumstantial evidence that P.
cinnamomi may be a contributor in this decline syndrome. These results will need to be corroborated before rational management strategies can be devised
The biopolitics of victim construction, elision and contestation in Northern Ireland and Lebanon
Peer reviewedPostprin
Phasespace Correlations of Antideuterons in Heavy Ion Collisions
In the framework of the relativistic quantum molecular dynamics approach
({\small RQMD}) we investigate antideuteron () observables in
Au+Au collisions at 10.7~AGeV. The impact parameter dependence of the formation
ratios and is calculated. In central
collisions, the antideuteron formation ratio is predicted to be two orders of
magnitude lower than the deuteron formation ratio. The yield in
central Au+Au collisions is one order of magnitude lower than in Si+Al
collisions. In semicentral collisions different configuration space
distributions of 's and 's lead to a large
``squeeze--out'' effect for antideuterons, which is not predicted for the
's
The Kasteleyn model and a cellular automaton approach to traffic flow
We propose a bridge between the theory of exactly solvable models and the
investigation of traffic flow. By choosing the activities in an apropriate way
the dimer configurations of the Kasteleyn model on a hexagonal lattice can be
interpreted as space-time trajectories of cars. This then allows for a
calculation of the flow-density relationship (fundamental diagram). We further
introduce a closely-related cellular automaton model. This model can be viewed
as a variant of the Nagel-Schreckenberg model in which the cars do not have a
velocity memory. It is also exactly solvable and the fundamental diagram is
calculated.Comment: Latex, 13 pages including 3 ps-figure
A Nuclear Physics Program at the ATLAS Experiment at the CERN Large Hadron Collider
The ATLAS collaboration has significant interest in the physics of
ultra-relativistic heavy ion collisions. We submitted a Letter of Intent to the
United States Department of Energy in March 2002. The following document is a
slightly modified version of that LOI. More details are available at:
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/SM/ionsComment: Letter of Intent submitted to the United States Department of Energy
Nuclear Physics Division in March 2002 (revised version
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