2,476 research outputs found
Anisotropic Flow and Viscous Hydrodynamics
We report part of our recent work on viscous hydrodynamics with consistent
phase space distribution f(x,\p) for freeze out. We develop the gradient
expansion formalism based on kinetic theory, and with the constraints from the
comparison between hydrodynamics and kinetic theory, viscous corrections to
f(x,\p) can be consistently determined order by order. Then with the obtained
f(x,\p), second order viscous hydrodynamical calculations are carried out for
elliptic flow .Comment: 8 pages, 2 figures. Proceedings for the 28th Winter Workshop on
Nuclear Dynamics, Dorado Del Mar, Puerto Rico, United States Of America, 7 -
14 Apr 201
Has saturation physics been observed in deuteron-gold collisions at RHIC?
In the framework of the recently proposed saturation picture, we examine in a
systematic way whether the nuclear modification factor measured for d-Au
collisions at RHIC may be simply explained. The Cronin peak which is obtained
at mid-rapidity around GeV may be reproduced at the proper
height only by boosting the saturation momentum by an additional nuclear
component as already shown in the literature. In this respect, mid-rapidity
RHIC data cannot necessarily be seen as a probe of the saturation picture. The
large rapidity () region allows us to test the shape of the
unintegrated gluon distribution in the nucleus, investigating various
parameterizations inspired by large rapidity solutions (of the BFKL and) of the
Balitsky-Kovchegov (BK) equation. A satisfactory description of at
RHIC is obtained in the BK picture.Comment: 13 pages, 5 figure
Limit Synchronization in Markov Decision Processes
Markov decision processes (MDP) are finite-state systems with both strategic
and probabilistic choices. After fixing a strategy, an MDP produces a sequence
of probability distributions over states. The sequence is eventually
synchronizing if the probability mass accumulates in a single state, possibly
in the limit. Precisely, for 0 <= p <= 1 the sequence is p-synchronizing if a
probability distribution in the sequence assigns probability at least p to some
state, and we distinguish three synchronization modes: (i) sure winning if
there exists a strategy that produces a 1-synchronizing sequence; (ii)
almost-sure winning if there exists a strategy that produces a sequence that
is, for all epsilon > 0, a (1-epsilon)-synchronizing sequence; (iii) limit-sure
winning if for all epsilon > 0, there exists a strategy that produces a
(1-epsilon)-synchronizing sequence.
We consider the problem of deciding whether an MDP is sure, almost-sure,
limit-sure winning, and we establish the decidability and optimal complexity
for all modes, as well as the memory requirements for winning strategies. Our
main contributions are as follows: (a) for each winning modes we present
characterizations that give a PSPACE complexity for the decision problems, and
we establish matching PSPACE lower bounds; (b) we show that for sure winning
strategies, exponential memory is sufficient and may be necessary, and that in
general infinite memory is necessary for almost-sure winning, and unbounded
memory is necessary for limit-sure winning; (c) along with our results, we
establish new complexity results for alternating finite automata over a
one-letter alphabet
QCD motivated approach to soft interactions at high energies: nucleus-nucleus and hadron-nucleus collisions
In this paper we consider nucleus-nucleus and hadron-nucleus reactions in the
kinematic region: g A^{1/3} G_{3\pom} \exp\Lb \Delta Y\Rb \approx 1
G^2_{3\pom} \exp\Lb \Delta Y\Rb \approx 1 , where G_{3\pom} is the triple
Pomeron coupling, is the vertex of Pomeron nucleon interaction, and 1 +
\Delta_{\pom} denotes the Pomeron intercept. We find that in this kinematic
region the traditional Glauber-Gribov eikonal approach is inadequate. We show
that it is necesssary to take into account inelastic Glauber corrections, which
can not be expressed in terms of the nucleon-nucleon scattering amplitudes. In
the wide range of energies where \alpha'_\pom Y
\ll R^2_A,the scattering amplitude for the nucleus-nucleus interaction, does
not depend on the details of the nucleon-nucleon interaction at high energy. In
the formalism we present, the only (correlated) parameters that are required to
describe the data are \Delta_{\pom}, G_{3\pom} and . These parameters
were taken from our description of the nucleon-nucleon data at high energies
\cite{GLMM}.The predicted nucleus modification factor is compared with RHIC
Au-Au data at Estimates for LHC energies are presented and
discusssed.Comment: 18pp. 14 fugure
Relating different approaches to nuclear broadening
Transverse momentum broadening of fast partons propagating through a large
nucleus is proportional to the average color field strength in the nucleus. In
this work, the corresponding coefficient is determined in three different
frameworks, namely in the color dipole approach, in the approach of Baier et
al. and in the higher twist factorization formalism. This result enables one to
use a parametrization of the dipole cross section to estimate the values of the
gluon transport coefficient and of the higher twist matrix element, which is
relevant for nuclear broadening. A considerable energy dependence of these
quantities is found. In addition, numerical calculations are compared to data
for nuclear broadening of Drell-Yan dileptons, J/psi and Upsilon mesons. The
scale dependence of the strong coupling constant leads to measurable
differences between the higher twist approach and the other two formalisms.Comment: 11 pages, 3 figures; v2: some changes in presentation, reference
added, accepted for publication in PL
The state of MIIND
MIIND (Multiple Interacting Instantiations of Neural Dynamics) is a highly modular multi-level C++ framework, that aims to shorten the development time for models in Cognitive Neuroscience (CNS). It offers reusable code modules (libraries of classes and functions) aimed at solving problems that occur repeatedly in modelling, but tries not to impose a specific modelling philosophy or methodology. At the lowest level, it offers support for the implementation of sparse networks. For example, the library SparseImplementationLib supports sparse random networks and the library LayerMappingLib can be used for sparse regular networks of filter-like operators. The library DynamicLib, which builds on top of the library SparseImplementationLib, offers a generic framework for simulating network processes. Presently, several specific network process implementations are provided in MIIND: the WilsonâCowan and OrnsteinâUhlenbeck type, and population density techniques for leaky-integrate-and-fire neurons driven by Poisson input. A design principle of MIIND is to support detailing: the refinement of an originally simple model into a form where more biological detail is included. Another design principle is extensibility: the reuse of an existing model in a larger, more extended one. One of the main uses of MIIND so far has been the instantiation of neural models of visual attention. Recently, we have added a library for implementing biologically-inspired models of artificial vision, such as HMAX and recent successors. In the long run we hope to be able to apply suitably adapted neuronal mechanisms of attention to these artificial models
Computing Quantiles in Markov Reward Models
Probabilistic model checking mainly concentrates on techniques for reasoning
about the probabilities of certain path properties or expected values of
certain random variables. For the quantitative system analysis, however, there
is also another type of interesting performance measure, namely quantiles. A
typical quantile query takes as input a lower probability bound p and a
reachability property. The task is then to compute the minimal reward bound r
such that with probability at least p the target set will be reached before the
accumulated reward exceeds r. Quantiles are well-known from mathematical
statistics, but to the best of our knowledge they have not been addressed by
the model checking community so far.
In this paper, we study the complexity of quantile queries for until
properties in discrete-time finite-state Markov decision processes with
non-negative rewards on states. We show that qualitative quantile queries can
be evaluated in polynomial time and present an exponential algorithm for the
evaluation of quantitative quantile queries. For the special case of Markov
chains, we show that quantitative quantile queries can be evaluated in time
polynomial in the size of the chain and the maximum reward.Comment: 17 pages, 1 figure; typo in example correcte
PrIC3: Property Directed Reachability for MDPs
IC3 has been a leap forward in symbolic model checking. This paper proposes
PrIC3 (pronounced pricy-three), a conservative extension of IC3 to symbolic
model checking of MDPs. Our main focus is to develop the theory underlying
PrIC3. Alongside, we present a first implementation of PrIC3 including the key
ingredients from IC3 such as generalization, repushing, and propagation
The Properties of the Heterogeneous Shakhbazyan Groups of Galaxies in the SDSS
We present a systematic study of the sub-sample of Shakhbazyan groups (SHKs)
covered by the Sloan Digital Sky Survey Data Release--5 (SDSS-5). SHKs probe an
environment with characteristics which are intermediate between those of loose
and very compact groups. Surprisingly, we found that several groups identifying
algorithms (e.g. Berlind et al. 2006, Tago et al. 2008) miss this type of
structures. Using the SDSS-5 spectroscopic data and the photometric redshifts
derived in D'Abrusco et al. 2007, we identified possible group members in
photometric redshift space and derived, for each group, several individual
properties. We also combined pointed and stacked Rosat All Sky Survey data to
investigate the X-ray luminosities of these systems. Our study confirms that
the majority of groups are physical entities with richness in the range 3--13
galaxies, and properties ranging between those of loose and compact groups. We
confirm that SHK groups are richer in early-type galaxies than the surrounding
environment and the field, as expected from the morphology-density relation and
from the selection of groups of red galaxies. Furthermore, our work supports
the existence of two sub-classes of structures, the first one being formed by
compact and isolated groups and the second formed by extended structures. We
suggest that while the first class of objects dwells in less dense regions like
the outer parts of clusters or the field, possibly sharing the properties of
Hickson Compact Groups, the more extended structures represent a mixture of
[core+halo] configurations and cores of rich clusters. X-ray luminosities for
SHKs are generally consistent with these results and with the expectations for
the L_X-sigma_v relation, but also suggest the velocity dispersions reported in
literature are underestimated for some of the richest systems.Comment: 20 pages, 14 figures, 4 tables. Accepted for publication by MNRA
Evaluation of aluminum tolerance in triticale in a soil with high Al+ content.
Proceedings of the IV International Symposium on Plant-Soil Interactions at Low pH, Belo Horizonte, 1996. Abstract P45
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