46,356 research outputs found
The relation between velocity dispersions and chemical abundances in RAVE giants
We developed a Bayesian framework to determine in a robust way the relation
between velocity dispersions and chemical abundances in a sample of stars. Our
modelling takes into account the uncertainties in the chemical and kinematic
properties. We make use of RAVE DR5 radial velocities and abundances together
with Gaia DR1 proper motions and parallaxes (when possible, otherwise UCAC4
data is used). We found that, in general, the velocity dispersions increase
with decreasing [Fe/H] and increasing [Mg/Fe]. A possible decrease in velocity
dispersion for stars with high [Mg/Fe] is a property of a negligible fraction
of stars and hardly a robust result. At low [Fe/H] and high [Mg/Fe] the sample
is incomplete, affected by biases, and likely not representative of the
underlying stellar population.Comment: 2 pages, to appear in Proceedings of the IAU Symposium 330,
"Astrometry and Astrophysics in the Gaia Sky", held in April 2017, Nice,
Franc
A generalization of convergence actions
Let a group act properly discontinuously and cocompactly on a locally
compact space . A Hausdorff compact space that contains as an open
subspace has the perspectivity property if the action
extends to an action , by homeomorphisms, such that for
every compact and every element of the unique uniform
structure compatible with the topology of , the set has
finitely many non -small sets. We describe a correspondence between the
compact spaces with the perspectivity property with respect to (and the
fixed action of on it) and the compact spaces with the perspectivity
property with respect to (and the left multiplication on itself). This
generalizes a similar result for convergence group actions.Comment: 57 page
Strangeness production in STAR
We present a summary of strangeness enhancement results comparing data from
Cu+Cu and Au+Au collisions at sqrt(SNN) = 200GeV measured by the STAR
experiment. Relative yields in central Cu+Cu data seem to be higher than the
equivalent sized peripheral Au+Au collision. In addition, strange particle
production from these two systems is compared in terms of a statistical model,
applying a Grand-Canonical ensemble and also applying a canonical correlation
volume for the strange particles. Thermal fit results from the Grand-Canonical
formalism shows little dependence on the system size but, when considering a
strange canonical ensemble, strangeness enhancement shows a strong dependency
on the correlation volume.Comment: proceedings to 24th Winter Workshop on Nuclear Dynamics, South Padre
Island, Texas, April 200
Eigensequences for Multiuser Communication over the Real Adder Channel
Shape-invariant signals under the Discrete Fourier Transform are
investigated, leading to a class of eigenfunctions for the unitary discrete
Fourier operator. Such invariant sequences (eigensequences) are suggested as
user signatures over the real adder channel (t-RAC) and a multiuser
communication system over the t-RAC is presented.Comment: 6 pages, 1 figure, 1 table. VI International Telecommunications
Symposium (ITS2006
Orthogonal Multilevel Spreading Sequence Design
Finite field transforms are offered as a new tool of spreading sequence
design. This approach exploits orthogonality properties of synchronous
non-binary sequences defined over a complex finite field. It is promising for
channels supporting a high signal-to-noise ratio. New digital multiplex schemes
based on such sequences have also been introduced, which are multilevel Code
Division Multiplex. These schemes termed Galois-field Division Multiplex (GDM)
are based on transforms for which there exists fast algorithms. They are also
convenient from the hardware viewpoint since they can be implemented by a
Digital Signal Processor. A new Efficient-bandwidth
code-division-multiple-access (CDMA) is introduced, which is based on
multilevel spread spectrum sequences over a Galois field. The primary advantage
of such schemes regarding classical multiple access digital schemes is their
better spectral efficiency. Galois-Fourier transforms contain some redundancy
and only cyclotomic coefficients are needed to be transmitted yielding compact
spectrum requirements.Comment: 9 pages, 5 figures. In: Coding, Communication and Broadcasting.1
ed.Hertfordshire: Reseach Studies Press (RSP), 2000. ISBN 0-86380-259-
Symplectic Integrator Mercury: Bug Report
We report on a problem found in MERCURY, a hybrid symplectic integrator used
for dynamical problems in Astronomy. The variable that keeps track of bodies'
statuses is uninitialised, which can result in bodies disappearing from
simulations in a non-physical manner. Some FORTRAN compilers implicitly
initialise variables, preventing simulations from having this problem. With
other compilers, simulations with a suitably large maximum number of bodies
parameter value are also unaffected. Otherwise, the problem manifests at the
first event after the integrator is started, whether from scratch or continuing
a previously stopped simulation. Although the problem does not manifest in some
conditions, explicitly initialising the variable solves the problem in a
permanent and unconditional manner.Comment: 4 pages, 2 figures, 1 tabl
Dynamics of a Mathematical Hematopoietic Stem-Cell Population Model
We explore the bifurcations and dynamics of a scalar differential equation
with a single constant delay which models the population of human hematopoietic
stem cells in the bone marrow. One parameter continuation reveals that with a
delay of just a few days, stable periodic dynamics can be generated of all
periods from about one week up to one decade! The long period orbits seem to be
generated by several mechanisms, one of which is a canard explosion, for which
we approximate the dynamics near the slow manifold. Two-parameter continuation
reveals parameter regions with even more exotic dynamics including
quasi-periodic and phase-locked tori, and chaotic solutions. The panoply of
dynamics that we find in the model demonstrates that instability in the stem
cell dynamics could be sufficient to generate the rich behaviour seen in
dynamic hematological diseases
Introducing an Analysis in Finite Fields
Looking forward to introducing an analysis in Galois Fields, discrete
functions are considered (such as transcendental ones) and MacLaurin series are
derived by Lagrange's Interpolation. A new derivative over finite fields is
defined which is based on the Hasse Derivative and is referred to as negacyclic
Hasse derivative. Finite field Taylor series and alpha-adic expansions over
GF(p), p prime, are then considered. Applications to exponential and
trigonometric functions are presented. Theses tools can be useful in areas such
as coding theory and digital signal processing.Comment: 6 pages, 1 figure. Conference: XVII Simposio Brasileiro de
Telecomunicacoes, 1999, Vila Velha, ES, Brazil. (pp.472-477
A Factorization Scheme for Some Discrete Hartley Transform Matrices
Discrete transforms such as the discrete Fourier transform (DFT) and the
discrete Hartley transform (DHT) are important tools in numerical analysis. The
successful application of transform techniques relies on the existence of
efficient fast transforms. In this paper some fast algorithms are derived. The
theoretical lower bound on the multiplicative complexity for the DFT/DHT are
achieved. The approach is based on the factorization of DHT matrices.
Algorithms for short blocklengths such as are
presented.Comment: 10 pages, 4 figures, 2 tables, International Conference on System
Engineering, Communications and Information Technologies, 2001, Punta Arenas.
ICSECIT 2001 Proceedings. Punta Arenas: Universidad de Magallanes, 200
Multilayer Hadamard Decomposition of Discrete Hartley Transforms
Discrete transforms such as the discrete Fourier transform (DFT) or the
discrete Hartley transform (DHT) furnish an indispensable tool in signal
processing. The successful application of transform techniques relies on the
existence of the so-called fast transforms. In this paper some fast algorithms
are derived which meet the lower bound on the multiplicative complexity of the
DFT/DHT. The approach is based on a decomposition of the DHT into layers of
Walsh-Hadamard transforms. In particular, fast algorithms for short block
lengths such as are presented.Comment: Fixed several typos. 7 pages, 5 figures, XVIII Simp\'osio Brasileiro
de Telecomunica\c{c}\~oes, 2000, Gramado, RS, Brazi
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