54,565 research outputs found
Triaxial vs. Spherical Dark Matter Halo Profiles
When analysing dark matter halos forming in cosmological N-body simulations
it is common practice to obtain the density profile utilizing spherical shells.
However, it is also known that the systems under investigation are far from
spherical symmetry and rather follow a triaxial mass distribution. In this
study we present an estimator for the error introduced by spherically averaging
an elliptical mass distribution. We systematically investigate the differences
arising when using a triaxial density profile under the assumption of spherical
symmetry. We show that the variance in the density can be as large as 50% in
the outer parts of dark matter halos for extreme (but still credible) axis
ratios of 0.55:0.67:1. The inner parts are less affected but still show a
scatter at the 16% level for these prolate systems. For more moderate
ellipticities, i.e. axis ratios of 0.73:0.87:1, the error is smaller but still
as large as 10-20% depending on distance. We further provide a simple formula
that allows to estimate this variance as a function of radius for arbitrary
axis ratios. We conclude that highly prolate and/or oblate systems are better
fit by analytical profiles that take into account the triaxial nature of
cosmological objects.Comment: 4 pages. 3 figures, accepted for publication in PAS
Null boundary controllability of a 1-dimensional heat equation with an internal point mass
We consider a linear hybrid system composed by two rods of equal length
connected by a point mass. We show that the system is null controllable with
Dirichlet and Neumann controls. The results are based on a careful spectral
spectral analysis together with the moment method.Comment: 12 pages, typos corrected, added references, matches version to be
submitted to Systems and Control Letter
Inclusive quasielastic electron scattering on He: a probe of the halo structure
We investigate inclusive electron scattering reactions on two-neutron halo
nuclei in the quasielastic region. Expressions for the cross section and
structure functions are given assuming that the halo nucleus can be described
as a three-body system (). The method is applied to He. We
compute cross sections and structure functions, and investigate the kinematic
conditions for which the observables are determined either by -knockout
or by halo neutron-knockout. The optimal kinematical domain to disantangle the
momentum distributions of the various components of the three--body system ( MeV/c and MeV) are explored.Comment: 10 pages, 3 figures. Physics Letters B, in pres
Chain Reduction for Binary and Zero-Suppressed Decision Diagrams
Chain reduction enables reduced ordered binary decision diagrams (BDDs) and
zero-suppressed binary decision diagrams (ZDDs) to each take advantage of the
others' ability to symbolically represent Boolean functions in compact form.
For any Boolean function, its chain-reduced ZDD (CZDD) representation will be
no larger than its ZDD representation, and at most twice the size of its BDD
representation. The chain-reduced BDD (CBDD) of a function will be no larger
than its BDD representation, and at most three times the size of its CZDD
representation. Extensions to the standard algorithms for operating on BDDs and
ZDDs enable them to operate on the chain-reduced versions. Experimental
evaluations on representative benchmarks for encoding word lists, solving
combinatorial problems, and operating on digital circuits indicate that chain
reduction can provide significant benefits in terms of both memory and
execution time
The QCD Critical End Point in the Context of the Polyakov--Nambu--Jona-Lasinio Model
We investigate the phase diagram of the so-called
Polyakov--Nambu--Jona-Lasinio model at finite temperature and nonzero chemical
potential with three quark flavors. Chiral and deconfinement phase transitions
are discussed, and the relevant order-like parameters are analyzed. A special
attention is payed to the critical end point (CEP): the influence of the
strangeness on the location of the CEP is studied; also the strength of the
flavor-mixing interaction alters the CEP location, once when it becomes weaker
the CEP moves to low temperatures and can even disappear.Comment: Prepared for Strangeness in Quark Matter 2011, Sept. 18--24, Cracow,
Polan
Non-linear Poisson-Boltzmann Theory for Swollen Clays
The non-linear Poisson-Boltzmann equation for a circular, uniformly charged
platelet, confined together with co- and counter-ions to a cylindrical cell, is
solved semi-analytically by transforming it into an integral equation and
solving the latter iteratively. This method proves efficient, robust, and can
be readily generalized to other problems based on cell models, treated within
non-linear Poisson-like theory. The solution to the PB equation is computed
over a wide range of physical conditions, and the resulting osmotic equation of
state is shown to be in fair agreement with recent experimental data for
Laponite clay suspensions, in the concentrated gel phase.Comment: 13 pages, 4 postscript figure
Exploring the role of model parameters and regularization procedures in the thermodynamics of the PNJL model
The equation of state and the critical behavior around the critical end point
are studied in the context of the Polyakov--Nambu--Jona--Lasinio model. We
prove that a convenient choice of the model parameters is crucial to get the
correct description of isentropic trajectories. The physical relevance of the
effects of the regularization procedure is insured by the agreement with
general thermodynamic requirements. The results are compared with simple
thermodynamic expectations and lattice data.Comment: Talk given at XIII International Conference on Hadron Spectroscopy
(Hadron 2009), Tallahassee, Florida, USA, 29 Nov - 4 Dec, 200
How parameters and regularization affect the PNJL model phase diagram and thermodynamic quantities
We explore the phase diagram and the critical behavior of QCD thermodynamic
quantities in the context of the so-called Polyakov--Nambu--Jona-Lasinio model.
We show that this improved field theoretical model is a successful candidate
for studying the equation of state and the critical behavior around the
critical end point. We argue that a convenient choice of the model parameters
is crucial to get the correct description of isentropic trajectories. The
effects of the regularization procedure in several thermodynamic quantities is
also analyzed. The results are compared with simple thermodynamic expectations
and lattice data.Comment: 27 pages, 7 figures, 4 tables; PRD versio
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