4,009 research outputs found
Longitudinal correlation of the triangular flow event plane in a hybrid approach with hadron and parton cascade initial conditions
The longitudinal long-range correlations of the triangular flow event plane
angles are calculated in a Boltzmann + hydrodynamics hybrid approach. The
potential to disentangle different energy deposition scenarios is explored by
utilizing two different transport approaches for the early non-equilibrium
evolution. In the hadronic transport approach the particle production in high
energy heavy ion reactions is mainly governed by string excitation and
fragmentation processes which are absent in the parton cascade approach. We
find that in both approaches the initial state shows a strong longitudinal
correlation of the event plane angles which is diluted but still persists in
the final state momentum space distributions of the produced particles. A
ridge-like structure can also be caused by near-collinear gluon radiation in a
parton cascade approach and does not necessarily prove longitudinal flux tubes
in the initial state.Comment: 5 pages, 6 figures, replaced with new version with correct labels and
added references, conclusions are unchange
Kaon Interferometry: A Sensitive Probe of the QCD Equation of State?
We calculate the kaon HBT radius parameters for high energy heavy ion
collisions, assuming a first order phase transition from a thermalized
Quark-Gluon-Plasma to a gas of hadrons. At high transverse momenta K_T ~ 1
GeV/c direct emission from the phase boundary becomes important, the emission
duration signal, i.e., the R_out/R_side ratio, and its sensitivity to T_c (and
thus to the latent heat of the phase transition) are enlarged. Moreover, the
QGP+hadronic rescattering transport model calculations do not yield unusual
large radii (R_i<9fm). Finite momentum resolution effects have a strong impact
on the extracted HBT parameters (R_i and lambda) as well as on the ratio
R_out/R_side.Comment: 4 pages, 2 figure
Particle Correlations at RHIC - Scrutiny of a Puzzle
We present calculations of two-pion and two-kaon correlation functions in
relativistic heavy ion collisions from a relativistic transport model that
includes explicitly a first-order phase transition from a thermalized
quark-gluon plasma to a hadron gas. We compare the obtained correlation radii
with recent data from RHIC. The predicted R_side radii agree with data while
the R_out and R_long radii are overestimated. We also address the impact of
in-medium modifications, for example, a broadening of the rho-meson, on the
correlation radii. In particular, the longitudinal correlation radius R_long is
reduced, improving the comparison to data.Comment: 4 pages, 3 figure
Kaon interferometry : a sensitive probe of the QCD equation of state?
We calculate the kaon HBT radius parameters for high energy heavy ion collisions, assuming a first order phase transition from a thermalized Quark-Gluon-Plasma to a gas of hadrons. At high transverse momenta K_T ~ 1 GeV/c direct emission from the phase boundary becomes important, the emission duration signal, i.e., the R_out/R_side ratio, and its sensitivity to T_c (and thus to the latent heat of the phase transition) are enlarged. Moreover, the QGP+hadronic rescattering transport model calculations do not yield unusual large radii (R_i<9fm). Finite momentum resolution effects have a strong impact on the extracted HBT parameters (R_i and lambda) as well as on the ratio R_out/R_side
Solving the TTC 2011 Compiler Optimization Task with metatools
The authors' "metatools" are a collection of tools for generic programming.
This includes generating Java sources from mathematically well-founded
specifications, as well as the creation of strictly typed document object
models for XML encoded texts. In this context, almost every computer-internal
structure is treated as a "model", and every computation is a kind of model
transformation.
This concept differs significantly from "classical model transformation"
executed by specialized tools and languages. Therefore it seemed promising to
the organizers of the TTC 2011, as well as to the authors, to apply metatools
to one of the challenges, namely to the "compiler optimization task". This is a
report on the resulting experiences.Comment: In Proceedings TTC 2011, arXiv:1111.440
Assessing the accuracy of δ<sup>18<\sup>O<sub>sw<?sub> estimates from corals: lessons from simple Monte Carlo simulations
EGU2008-A-04391
Paired measurements of δ18O and Sr/Ca in coral aragonite are routinely used for deriving estimates of δ18Osw and, by extension, sea surface salinity variations over the past centuries. However, in practice, the accuracy (or the error) of these estimates is often difficult to assess.
Here, we use simulated proxy data and Monte-Carlo simulations to investigate the accuracy of δ18Osw estimates from paired coral δ18O and Sr/Ca measurements. First, we estimate expected values of coral Sr/Ca and δ18O from instrumental or reanalysis data of sea surface temperature (SST) and sea surface salinity (SSS). We then add the typical analytical errors onto the expected Sr/Ca (δ18O) data as random numbers and compute δ18Osw+error from the noisy proxy data for a 1000 sample Monte Carlo. From this simple Monte Carlo simulation, the range of correlation coefficients between δ18Osw+error and expected δ18Osw is estimated. As expected, we find that this range mainly depends on the magnitude of the actual SSS variations at a given site, as well as on the slope of the δ18Osw-SSS relationship.
A comparison with real coral-based δ18Osw reconstructions from multiple sites indicates that correlations between reconstructed δ18Osw and instrumental SSS fall within the range of correlation coefficients predicted based on our Monte-Carlo simulation. Thus, our simple simulation exercise may help to assess the feasibility of δ18Osw and salinity reconstructions from corals in different climatic settings, provided that (i) some instrumental data of δ18Osw and/or SSS is available, and (ii) the slope of the
δ18Osw-SSS relationship is known
The Changing AGN Population
We investigate how the fraction of broad-line sources in the AGN population
changes with X-ray luminosity and redshift. We first construct the rest-frame
hard-energy (2-8 keV) X-ray luminosity function (HXLF) at z=0.1-1 using Chandra
Lockman Hole-Northwest wide-area data, Chandra Deep Field-North 2 Ms data,
other Chandra deep field data, and the ASCA Large Sky Survey data. We find that
broad-line AGNs dominate above 3e43 ergs/s and have a mean luminosity of 1.3e44
ergs/s. Type II AGNs can only become an important component of the X-ray
population at Seyfert-like X-ray luminosities. We then construct z=0.1-0.5 and
z=0.5-1 HXLFs and compare them with both the local HXLF measured from HEAO-1 A2
survey data and the z=1.5-3 HXLF measured from soft-energy (0.5-2 keV) Chandra
and ROSAT data. We find that the number density of >1e44 ergs/s sources
(quasars) steadily declines with decreasing redshift, while the number density
of 1e43-1e44 ergs/s sources peaks at z=0.5-1. Strikingly, however, the number
density of broad-line AGNs remains roughly constant with redshift while their
average luminosities decline at the lower redshifts, showing another example of
cosmic downsizing.Comment: Accepted by The Astrophysical Journal Letters, 5 page
Stability Properties of Strongly Magnetized Spine Sheath Relativistic Jets
The linearized relativistic magnetohydrodynamic (RMHD) equations describing a
uniform axially magnetized cylindrical relativistic jet spine embedded in a
uniform axially magnetized relativistically moving sheath are derived. The
displacement current is retained in the equations so that effects associated
with Alfven wave propagation near light speed can be studied. A dispersion
relation for the normal modes is obtained. Analytical solutions for the normal
modes in the low and high frequency limits are found and a general stability
condition is determined. A trans-Alfvenic and even a super-Alfvenic
relativistic jet spine can be stable to velocity shear driven Kelvin-Helmholtz
modes. The resonance condition for maximum growth of the normal modes is
obtained in the kinetically and magnetically dominated regimes. Numerical
solution of the dispersion relation verifies the analytical solutions and is
used to study the regime of high sound and Alfven speeds.Comment: 42 pages includes 7 figures, to appear in Ap
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