374 research outputs found
Dynamics of relativistic particle with Lagrangian dependent on acceleration
Models of relativistic particle with Lagrangian , depending on
the curvature of the worldline , are considered. By making use of the
Frenet basis, the equations of motion are reformulated in terms of the
principal curvatures of the worldline. It is shown that for arbitrary
Lagrangian function these equations are completely integrable,
i.e., the principal curvatures are defined by integrals. The constants of
integration are the particle mass and its spin. The developed method is applied
to the study of a model of relativistic particle with maximal proper
acceleration, whose Lagrangian is uniquely determined by a modified form of the
invariant relativistic interval. This model gives us an example of a consistent
relativistic dynamics obeying the principle of a superiorly limited value of
the acceleration, advanced recently.Comment: 15 pages, LATEX, Preprint Salerno University DFT-US-3/9
Strong deflection limit of black hole gravitational lensing with arbitrary source distances
The gravitational field of supermassive black holes is able to strongly bend
light rays emitted by nearby sources. When the deflection angle exceeds ,
gravitational lensing can be analytically approximated by the so-called strong
deflection limit. In this paper we remove the conventional assumption of
sources very far from the black hole, considering the distance of the source as
an additional parameter in the lensing problem to be treated exactly. We find
expressions for critical curves, caustics and all lensing observables valid for
any position of the source up to the horizon. After analyzing the spherically
symmetric case we focus on the Kerr black hole, for which we present an
analytical 3-dimensional description of the higher order caustic tubes.Comment: 20 pages, 8 figures, appendix added. In press on Physical Review
Contribuição da bracatinga (Mimosa scabrella) para a produção de serapilheira em sistema silvipastoril agroecológico.
O presente trabalho teve por objetivo analisar a produção e o conteúdo de nutrientes da serapilheira produzida por árvores de bracatinga em uma área de pastagem agroecológica, localizada no CPRA ? Centro Paranaense de Referência em Agroecologia. As coletas de material foram efetuadas mensalmente, entre fevereiro de 2010 e julho de 2012. Com base na quantidade de matéria seca e dos teores de N, P, K, Ca e Mg foi obtida a estimativa da quantidade destes elementos aportados à pastagem pela serapilheira. A produção média de serapilheira foi de 2.006 kg de matéria seca por hectare por ano, correspondendo a uma incorporação ao solo de 30 kg de N, 0,4 kg de P, 3,8 kg de K, 7,4 kg de Ca e 3,2 kg de Mg
Automatic Classification of Seismic Signals at Mt. Vesuvius Volcano, Italy, Using Neural Networks
We present a new strategy for reliable automatic classification of local seismic signals and volcano-tectonic earthquakes (VT). The method is based on a supervised neural network in which a new approach for feature extraction from short period seismic signals is applied. To reduce the number of records required for the analysis we set up a specialized neural classifier, able to distinguish two classes of signals, for each of the selected stations. The neural network architecture is a multilayer
perceptron (MLP) with a single hidden layer. Spectral features of the signals
and the parameterized attributes of their waveform have been used as input for this
network. Feature extraction is done by using both the linear predictor coding technique for computing the spectrograms, and a function of the amplitude for characterizing waveforms. Compared to strategies that use only spectral signatures, the inclusion of properly normalized amplitude features improves the performance of the classifiers, and allows the network to better generalize. To train the MLP network we compared the performance of the quasi-Newton algorithm with the scaled conjugate gradient method. We found that the scaled conjugate gradient approach is the faster of the two, with quite equally good performance. Our method was tested on a dataset recorded by four selected stations of the Mt. Vesuvius monitoring network, for the discrimination of low magnitude VT events and transient signals caused by either artificial (quarry blasts, underwater explosions) and natural (thunder) sources. In this test application we obtained 100% correct classification for one of the possible pairs of signal types (VT versus quarry blasts). Because this method was developed independently of this particular discrimination task, it can be applied to a broad range of other applications
Electromagnetic shape resonances of a dielectric sphere and radiation of portable telephones
The frequency band used by cellular telephones includes the eigenfrequencies
of a dielectric sphere with physical characteristics close to those of a human
head. Proceeding from the spatial features of the natural modes of such a
sphere we propose an independent and clear evident accuracy test for the
complicated numerical calculations which are conducted when estimating the
potential hazard due to the use of cellular telephones, in particular, for the
check of a proper handling of the electromagnetic shape resonances of a human
head.Comment: 10 pages, 1 figure with 2 eps file
Casimir energy of a dilute dielectric ball in the mode summation method
In the --approximation the Casimir energy of a
dilute dielectric ball is derived using a simple and clear method of the mode
summation. The addition theorem for the Bessel functions enables one to present
in a closed form the sum over the angular momentum before the integration over
the imaginary frequencies. The linear in contribution
into the vacuum energy is removed by an appropriate subtraction. The role of
the contact terms used in other approaches to this problem is elucidated.Comment: 14 pages, REVTeX, no figures, no tables; presentation is made better,
new references are adde
Slott-Agape Project
SLOTT-AGAPE (Systematic Lensing Observation at Toppo Telescope - Andromeda
Gravitational Amplification Pixel Lensing Experiment) is a new collaboration
project among international partners from England, France, Germany, Italy and
Switzerland that intends to perform microlensing observation by using M31 as
target. The MACHOs search is made thanks to the pixel lensing technique.Comment: 4 pages, 2 figures, proceeding of XLIII Congresso della Societa'
Astronomica Italiana, Napoli, 4-8 Maggio, 199
Lower Neutrino Mass Bound from SN1987A Data and Quantum Geometry
A lower bound on the light neutrino mass is derived in the framework
of a geometrical interpretation of quantum mechanics. Using this model and the
time of flight delay data for neutrinos coming from SN1987A, we find that the
neutrino masses are bounded from below by eV, in
agreement with the upper bound
eV currently available. When the model is applied to photons with effective
mass, we obtain a lower limit on the electron density in intergalactic space
that is compatible with recent baryon density measurements.Comment: 22 pages, 3 figure
Minimal vertex covers on finite-connectivity random graphs - a hard-sphere lattice-gas picture
The minimal vertex-cover (or maximal independent-set) problem is studied on
random graphs of finite connectivity. Analytical results are obtained by a
mapping to a lattice gas of hard spheres of (chemical) radius one, and they are
found to be in excellent agreement with numerical simulations. We give a
detailed description of the replica-symmetric phase, including the size and the
entropy of the minimal vertex covers, and the structure of the unfrozen
component which is found to percolate at connectivity . The
replica-symmetric solution breaks down at . We give a simple
one-step replica symmetry broken solution, and discuss the problems in
interpretation and generalization of this solution.Comment: 32 pages, 9 eps figures, to app. in PRE (01 May 2001
Acoustic Response of a Layer of Spherical Inclusions with a Random or Periodic Arrangement
Starting with the classic work of Ying and Truell [1], the scattering of a plane elastic wave by an isolated elastic sphere embedded in an unbounded medium has been studied in great detail. Similarly, the propagation of an effective elastic wave in an elastic matrix containing a random or periodic distribution of inclusions has received considerable attention. By comparison, an intermediate level of microstructure — a single layer of inclusions in an elastic matrix — has received very little attention. Apart from the fact that this problem is worth studying in its own right because of its inherent value as a canonical problem in elastodynamics of materials with a microstructure, it has applications in geophysics and quantitative nondestructive evaluation
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