5,362 research outputs found
Elliptic flow in Au+Au collisions at sqrt(s_NN) = 130 GeV
Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented
On Existence and Properties of Approximate Pure Nash Equilibria in Bandwidth Allocation Games
In \emph{bandwidth allocation games} (BAGs), the strategy of a player
consists of various demands on different resources. The player's utility is at
most the sum of these demands, provided they are fully satisfied. Every
resource has a limited capacity and if it is exceeded by the total demand, it
has to be split between the players. Since these games generally do not have
pure Nash equilibria, we consider approximate pure Nash equilibria, in which no
player can improve her utility by more than some fixed factor through
unilateral strategy changes. There is a threshold (where
is a parameter that limits the demand of each player on a specific
resource) such that -approximate pure Nash equilibria always exist for
, but not for . We give both
upper and lower bounds on this threshold and show that the
corresponding decision problem is -hard. We also show that the
-approximate price of anarchy for BAGs is . For a restricted
version of the game, where demands of players only differ slightly from each
other (e.g. symmetric games), we show that approximate Nash equilibria can be
reached (and thus also be computed) in polynomial time using the best-response
dynamic. Finally, we show that a broader class of utility-maximization games
(which includes BAGs) converges quickly towards states whose social welfare is
close to the optimum
Gamma Ray Bursts: recent results and connections to very high energy Cosmic Rays and Neutrinos
Gamma-ray bursts are the most concentrated explosions in the Universe. They
have been detected electromagnetically at energies up to tens of GeV, and it is
suspected that they could be active at least up to TeV energies. It is also
speculated that they could emit cosmic rays and neutrinos at energies reaching
up to the eV range. Here we review the recent developments in
the photon phenomenology in the light of \swift and \fermi satellite
observations, as well as recent IceCube upper limits on their neutrino
luminosity. We discuss some of the theoretical models developed to explain
these observations and their possible contribution to a very high energy cosmic
ray and neutrino background.Comment: 12 pages, 7 figures. Text of a plenary lecture at the PASCOS 12
conference, Merida, Yucatan, Mexico, June 2012; to appear in J.Phys. (Conf.
Series
Directed and Elliptic Flow at RHIC
We present the directed flow measurement () from Au+Au collisions at
\sqrtsNN = 62 GeV. Over the pseudorapidity range we have studied, which
covers from -1.2 to 1.2 and , the magnitude of
for charged particles is found to increase monotonously with pseudorapidity for
all centralities. No `` wiggle'', as predicted by various theoretical
models, is observed at midrapidity. Elliptic flow () from moderate high
particles () at \sqrtsNN = 200 GeV is presented as a
function of impact parameter. It is found that models that are based on {\it
jet quenching} alone appear to underpredict at moderate high , while
the model that incorporates both, recombination and fragmentation, describes
the data better.Comment: 6 pages, 4 figures. Proceeding for Hot Quark 04 conference Changes in
the revision are mostly English fixes. v1 versus eta plot is flipped over to
follow the conventio
Azimuthal Correlations with High-pT Multi-Hadron Cluster Triggers in Au+Au Collisions at sqrt(sNN) = 200 GeV
Di-hadron correlation measurements have been used to probe di-jet production
in collisions at RHIC. A strong suppression of the away-side high-pT yield in
these measurements is direct evidence that high-pT partons lose energy as they
traverse the strongly interacting medium. However, since the momentum of the
trigger particle is not a good measure of the jet energy, azimuthal di-hadron
correlations have limited sensitivity to the shape of the fragmentation
function. We explore the possibility to better constrain the initial parton
energy by using clusters of multiple high-pT hadrons in a narrow cone as the
'trigger particle' in the azimuthal correlation analysis. We present first
results from this analysis of multi-hadron triggered correlated yields in Au+Au
collisions at sqrt(sNN) = 200 GeV from STAR. The results are compared to Pythia
calculations, and the implications for energy loss and jet fragmentation are
discussed.Comment: 5 pages, 4 figures, submitted to the proceedings of the 24th Winter
Workshop on Nuclear Dynamic
Solving -means on High-dimensional Big Data
In recent years, there have been major efforts to develop data stream
algorithms that process inputs in one pass over the data with little memory
requirement. For the -means problem, this has led to the development of
several -approximations (under the assumption that is a
constant), but also to the design of algorithms that are extremely fast in
practice and compute solutions of high accuracy. However, when not only the
length of the stream is high but also the dimensionality of the input points,
then current methods reach their limits.
We propose two algorithms, piecy and piecy-mr that are based on the recently
developed data stream algorithm BICO that can process high dimensional data in
one pass and output a solution of high quality. While piecy is suited for high
dimensional data with a medium number of points, piecy-mr is meant for high
dimensional data that comes in a very long stream. We provide an extensive
experimental study to evaluate piecy and piecy-mr that shows the strength of
the new algorithms.Comment: 23 pages, 9 figures, published at the 14th International Symposium on
Experimental Algorithms - SEA 201
Observing Spontaneous Strong Parity Violation in Heavy-Ion Collisions
We discuss the problem of observing spontaneous parity and CP violation in
collision systems. We discuss and propose observables which may be used in
heavy-ion collisions to observe such violations, as well as event-by-event
methods to analyze the data. Finally, we discuss simple monte-carlo models of
these CP violating effects which we have used to develop our techniques and
from which we derive rough estimates of sensitivities to signals which may be
seen at RHIC
Energy consumption and capacity utilization of galvanizing furnaces
An explicit equation leading to a method for improving furnace efficiency is presented. This equation is dimensionless and can be applied to furnaces of any size and fuel type for the purposes of comparison. The implications for current furnace design are discussed. Currently the technique most commonly used to reduce energy consumption in galvanizing furnaces is to increase burner turndown. This is shown by the analysis presented here actually to worsen the thermal efficiency of the furnace, particularly at low levels of capacity utilization. Galvanizing furnaces are different to many furnaces used within industry, as a quantity of material (in this case zinc) is kept molten within the furnace at all times, even outside production periods. The dimensionless analysis can, however, be applied to furnaces with the same operational function as a galvanizing furnace, such as some furnaces utilized within the glass industry. © IMechE 2004
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