966 research outputs found
Low Mass Dimuons Produced in Relativistic Nuclear Collisions
The NA60 experiment has measured low-mass muon pair production in In-In
collisions at 158 A GeV with unprecedented precision. We show that this data is
reproduced very well by a dynamical model with parameters scaled from fits to
measurements of hadronic transverse mass spectra and Hanbury-Brown and Twiss
correlations in Pb-Pb and Pb-Au collisions at the same energy. The data is
consistent with in-medium properties of and -mesons at finite
temperature and density as deduced from empirical forward-scattering
amplitudes. Inclusion of the vacuum decay of the -meson after freeze-out
is necessary for an understanding of the mass and transverse momentum spectrum
of dimuons with M \apprle 0.9 {\rm GeV}/c^2.Comment: 4 pages, 3 figures, updated hadronic analysi
Properties of the phi meson at high temperatures and densities
We calculate the spectral density of the phi meson in a hot bath of nucleons
and pions using a general formalism relating self-energy to the forward
scattering amplitude (FSA). In order to describe the low energy FSA, we use
experimental data along with a background term. For the high energy FSA, a
Regge parameterization is employed. We verify the resulting FSA using
dispersion techniques. We find that the position of the peak of the spectral
density is slightly shifted from its vacuum position and that its width is
considerably increased. The width of the spectral density at a temperature of
150 MeV and at normal nuclear density is more than 90 MeV.Comment: 4 pages, 5 figures, Poster presented at Quark Matter 200
Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC
We calculate and compare bremsstrahlung and collisional energy loss of hard
partons traversing a quark-gluon plasma. Our treatment of both processes is
complete at leading order in the coupling and accounts for the probabilistic
nature of the jet energy loss. We find that the nuclear modification factor
for neutral production in heavy ion collisions is sensitive to
the inclusion of collisional and radiative energy loss contributions while the
averaged energy loss only slightly increases if collisional energy loss is
included for parent parton energies . These results are important for
the understanding of jet quenching in Au+Au collisions at at
RHIC. Comparison with data is performed applying the energy loss calculation to
a relativistic ideal (3+1)-dimensional hydrodynamic description of the
thermalized medium formed at RHIC.Comment: 4 pages, 3 figure
Extraction of coherent structures in a rotating turbulent flow experiment
The discrete wavelet packet transform (DWPT) and discrete wavelet transform
(DWT) are used to extract and study the dynamics of coherent structures in a
turbulent rotating fluid. Three-dimensional (3D) turbulence is generated by
strong pumping through tubes at the bottom of a rotating tank (48.4 cm high,
39.4 cm diameter). This flow evolves toward two-dimensional (2D) turbulence
with increasing height in the tank. Particle Image Velocimetry (PIV)
measurements on the quasi-2D flow reveal many long-lived coherent vortices with
a wide range of sizes. The vorticity fields exhibit vortex birth, merger,
scattering, and destruction. We separate the flow into a low-entropy
``coherent'' and a high-entropy ``incoherent'' component by thresholding the
coefficients of the DWPT and DWT of the vorticity fields. Similar thresholdings
using the Fourier transform and JPEG compression together with the Okubo-Weiss
criterion are also tested for comparison. We find that the DWPT and DWT yield
similar results and are much more efficient at representing the total flow than
a Fourier-based method. Only about 3% of the large-amplitude coefficients of
the DWPT and DWT are necessary to represent the coherent component and preserve
the vorticity probability density function, transport properties, and spatial
and temporal correlations. The remaining small amplitude coefficients represent
the incoherent component, which has near Gaussian vorticity PDF, contains no
coherent structures, rapidly loses correlation in time, and does not contribute
significantly to the transport properties of the flow. This suggests that one
can describe and simulate such turbulent flow using a relatively small number
of wavelet or wavelet packet modes.Comment: experimental work aprox 17 pages, 11 figures, accepted to appear in
PRE, last few figures appear at the end. clarifications, added references,
fixed typo
An Adaptive Neuro-Fuzzy Strategy for a Wireless Coded Power Control in Doubly-Fed Induction Aerogenerators
Exploring wind direction and SO2 concentration by circular-linear density estimation
The study of environmental problems usually requires the description of
variables with different nature and the assessment of relations between them.
In this work, an algorithm for flexible estimation of the joint density for a
circular-linear variable is proposed. The method is applied for exploring the
relation between wind direction and SO2 concentration in a monitoring station
close to a power plant located in Galicia (NW-Spain), in order to compare the
effectiveness of precautionary measures for pollutants reduction in two
different years.Comment: 17 pages, 7 figures, 2 table
Accumulation of driver and passenger mutations during tumor progression
Major efforts to sequence cancer genomes are now occurring throughout the
world. Though the emerging data from these studies are illuminating, their
reconciliation with epidemiologic and clinical observations poses a major
challenge. In the current study, we provide a novel mathematical model that
begins to address this challenge. We model tumors as a discrete time branching
process that starts with a single driver mutation and proceeds as each new
driver mutation leads to a slightly increased rate of clonal expansion. Using
the model, we observe tremendous variation in the rate of tumor development -
providing an understanding of the heterogeneity in tumor sizes and development
times that have been observed by epidemiologists and clinicians. Furthermore,
the model provides a simple formula for the number of driver mutations as a
function of the total number of mutations in the tumor. Finally, when applied
to recent experimental data, the model allows us to calculate, for the first
time, the actual selective advantage provided by typical somatic mutations in
human tumors in situ. This selective advantage is surprisingly small, 0.005 +-
0.0005, and has major implications for experimental cancer research
Development of relativistic shock waves in viscous gluon matter
To investigate the formation and the propagation of relativistic shock waves
in viscous gluon matter we solve the relativistic Riemann problem using a
microscopic parton cascade. We demonstrate the transition from ideal to viscous
shock waves by varying the shear viscosity to entropy density ratio .
We show that an ratio larger than 0.2 prevents the development of
well-defined shock waves on time scales typical for ultrarelativistic heavy-ion
collisions. These findings are confirmed by viscous hydrodynamic calculations.Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
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