48,512 research outputs found
Finite size effects in isobaric ratios
The properties of isobaric ratios, between nuclei produced in the same
reaction, are investigated using the canonical and grand-canonical statistical
ensembles. Although the grand-canonical for- mulae furnish a means to correlate
the ratios with the liquid drop parameters, finite size effects make it
difficult to obtain their actual values from fitting nuclear collision data.Comment: 4 pages, 2 figure
Many-particle correlations and Coulomb effects on temperatures from fragment momentum fluctuations
We investigate correlations in the fragment momentum distribution due to the
propagation of fragments under the influence of their mutual Coulomb field,
after the breakup of an excited nuclear source.The magnitude of the effects on
the nuclear temperatures obtained from such distributions is estimated with the
help of a simple approach in which a charged fragment interacts with a
homogeneous charged sphere. The resuslts are used to correct the temperatures
obtained from the asymptotic momentum distributions of fragments produced by a
Monte-Carlo simulation in which the system's configuration at breakup is
provided by the canonical version of the Statistical Multifragmentation Model.
In a separate calculation, the dynamics of this many-particle charged system is
followed in a molecular dynamics calculation until the fragments are far away
from the breakup volume. The results suggest that, although the magnitude of
the corrections is similar in both models, many-particle correlations present
in the second approach are non-negligible and should be taken into account in
order to minimize ambiguities in such studies.Comment: 7 pages, 4 figure
Low-cost educational robotics applied to physics teaching in Brazil
In this paper we propose strategies and methodologies of teaching topics in
high school physics, through a show of Educational Robotics. The Exhibition was
part of a set of actions promoted by a brazilian government program of
incentive for teaching activities (PIBID) and whose primary focus is the
training of teachers, improvement of teaching in public schools, dissemination
of science and formation of new scientists and researchers. By means of
workshops, banners and prototyping of robotics, we are able to create a
connection between the study areas and their surrounding, making learning
meaningful and accessible for the students involved and contributing to their
cognitive development.Comment: 5 pages and 10 figure
Multipartite Quantum Eraser
We study the dynamical entanglement distribution in a multipartite system.
The initial state is a maximally entangled two level atom with a single photon
field. Next a sequence of atoms are sent, one at the time, and interact with
the field. We show that the which way information initially stored only in the
field is now distributed among the parties of the global system. We obtain the
corresponding complementarity relations in analytical form. We show that this
dynamics may lead to a quantum eraser phenomenon provided that measurements of
the probe atoms are performed in a basis which maximizes the visibility. The
process may be realized in microwave cavities with present technology
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-
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
Schematic models for fragmentation of brittle solids in one and two dimensions
Stochastic models for the development of cracks in 1 and 2 dimensional
objects are presented. In one dimension, we focus on particular scenarios for
interacting and non-interacting fragments during the breakup process. For two
dimensional objects, we consider only non-interacting fragments, but analyze
isotropic and anisotropic development of fissures. Analytical results are given
for many observables. Power-law size distributions are predicted for some of
the fragmentation pictures considered.Comment: 15 pages, 8 figure
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