9,854 research outputs found
A unification in the theory of linearization of second order nonlinear ordinary differential equations
In this letter, we introduce a new generalized linearizing transformation
(GLT) for second order nonlinear ordinary differential equations (SNODEs). The
well known invertible point (IPT) and non-point transformations (NPT) can be
derived as sub-cases of the GLT. A wider class of nonlinear ODEs that cannot be
linearized through NPT and IPT can be linearized by this GLT. We also
illustrate how to construct GLTs and to identify the form of the linearizable
equations and propose a procedure to derive the general solution from this GLT
for the SNODEs. We demonstrate the theory with two examples which are of
contemporary interest.Comment: 8 page
The role of the nature of the noise in the thermal conductance of mechanical systems
Focussing on a paradigmatic small system consisting of two coupled damped
oscillators, we survey the role of the L\'evy-It\^o nature of the noise in the
thermal conductance. For white noises, we prove that the L\'evy-It\^o
composition (Lebesgue measure) of the noise is irrelevant for the thermal
conductance of a non-equilibrium linearly coupled chain, which signals the
independence between mechanical and thermodynamical properties. On the other
hand, for the non-linearly coupled case, the two types of properties mix and
the explicit definition of the noise plays a central role.Comment: 9 pages, 2 figures. To be published in Physical Review
Bayesian inference with an adaptive proposal density for GARCH models
We perform the Bayesian inference of a GARCH model by the Metropolis-Hastings
algorithm with an adaptive proposal density. The adaptive proposal density is
assumed to be the Student's t-distribution and the distribution parameters are
evaluated by using the data sampled during the simulation. We apply the method
for the QGARCH model which is one of asymmetric GARCH models and make empirical
studies for for Nikkei 225, DAX and Hang indexes. We find that autocorrelation
times from our method are very small, thus the method is very efficient for
generating uncorrelated Monte Carlo data. The results from the QGARCH model
show that all the three indexes show the leverage effect, i.e. the volatility
is high after negative observations
On exact time-averages of a massive Poisson particle
In this work we study, under the Stratonovich definition, the problem of the
damped oscillatory massive particle subject to a heterogeneous Poisson noise
characterised by a rate of events, \lambda (t), and a magnitude, \Phi,
following an exponential distribution. We tackle the problem by performing
exact time-averages over the noise in a similar way to previous works analysing
the problem of the Brownian particle. From this procedure we obtain the
long-term equilibrium distributions of position and velocity as well as
analytical asymptotic expressions for the injection and dissipation of energy
terms. Considerations on the emergence of stochastic resonance in this type of
system are also set forth.Comment: 21 pages, 5 figures. To be published in Journal of Statistical
Mechanics: Theory and Experimen
Ação do fungicida mepronil no controle de Crinipellis perniciosa em cupuaçuzeiros, no campo.
Publicado também: FRAZÃO, D. A. C.; HOMMA, A. K. O; VIÉGAS, I. de J. M. (Ed.). Contribuição ao desenvolvimento da fruticultura na Amazônia. Belém, PA: Embrapa Amazônia Oriental, 2006. p. 453-457
Square lattice site percolation at increasing ranges of neighbor interactions
We report site percolation thresholds for square lattice with neighbor
interactions at various increasing ranges. Using Monte Carlo techniques we
found that nearest neighbors (N), next nearest neighbors (N), next next
nearest neighbors (N) and fifth nearest neighbors (N) yield the same
. At odds, fourth nearest neighbors (N) give .
These results are given an explanation in terms of symmetry arguments. We then
consider combinations of various ranges of interactions with (N+N),
(N+N), (N+N+N) and (N+N). The calculated associated
thresholds are respectively . The
existing Galam--Mauger universal formula for percolation thresholds does not
reproduce the data showing dimension and coordination number are not sufficient
to build a universal law which extends to complex lattices.Comment: 4 pages, revtex
Avaliação físico-química da manta ovina salgada de Tauá.
A manta ovina é um produto típico da região Nordeste, amplamente consumido, sendo processado a partir da desossa, salga e secagem de carcaças inteiras de ovinos ou caprinos, recebendo esta denominação pela aparência final de uma manta ou lençol. O objetivo deste trabalho foi avaliar amostras de manta ovina proveniente de três restaurantes localizados na cidade de Tauá-CE, em relação aos parâmetros físico-químicos de qualidade. A manta de Tauá apresentou valores de composição centesimal semelhante entre os três restaurantes, com elevados valores de umidade (72,35g/100g) e proteínas (23,97g/100g), reduzidos percentuais de lipídios (1,02g/100g), os quais ressaltam a qualidade nutricional da manta, como um produto protéico e baixo teor de gordura. Os percentuais médios de minerais encontrados, isto é, 2,84% (restaurante A), 2,98% (restaurante B) e, 2,71% (restaurante C) comparando-se com os percentuais médios de cloretos 1,63%, 1,80% e 1,48%, apresentam uma coerência entre eles, uma vez que os cloretos estão associados ao conteúdo total de minerais. Os valores médios de pH dos três estabelecimentos, situaram-se próximo da neutralidade (6,19). Paralelamente, os dados de atividade de água não apresentaram variação, estando a mesma bastante elevada (média de 0,97) considerando-se que o processo de salga não foi drástico. Physicalchemical evaluation salt lamb from Tauá. Abstract: The?manta ovina? is a typical product from the Northeast region, largely consumed, produced from the boning, salting and drying of lamb carcasses, received this denomination for the final appearance like blanket. This paper was evaluated lamb meats samples processing from three establishments in Tauá- CE, in the quality physicalchemical parameters. The ?manta? presented centesimal composition same values between the restaurants, with high levels of moisture (72,35g/100g) and proteins (23,97g/100g), low percentages of lipids (1,02g/100g), wich emphasize the nutricional quality of the blanket, like the protein product and low fat levels. The average percentages of minerals found, ie, 2,84% (restaurant A), 2,98% (restaurant B) e 2,71% (restaurant C) compared with the average percentages of chlorides 1,63%, 1,80% e 1,48%, presents a coherent between them, chlorides are associated with minerals total content. The pH average data, located next the neutrality (6,19). Parallel, water activity data not vary, being so high (0,97), considering no drastic the salting process
POTENTIAL OF ILMENITE AS A SOLAR ABSORBER
Titanium is considered the fourth most widely used material in industry worldwide. Titanium minerals are currently being applied in various branches of industry, mainly in the field of pigmentation. Ilmenite (FeTiO3) is an iron and titanium oxide of more common and abundant occurrence, with theoretical composition of Fe (36.8%), Ti (31.6%) and O (31.6%). Having regard to the potential of titanium minerals and the abundance of ilmenite, together with the importance of validating direct applications of this ore, since the processing of titanium is still complex and expensive, it is necessary to study this mineral and the knowledge of its main characteristics. This work brings thermal, chemical and mineralogical characterizations of ilmenite, in order to know the potential of application of this ore as a solar absorbing material. The characterization techniques used were: X-ray diffraction (XRD) and Rietveld refinement for phase quantification, X-ray fluorescence (XRF), optical spectroscopy in the middle infrared region with Fourier Transformation by Transmittance (FTIR) and thermogravimetric thermal analysis (TGA). The analyzed sample obtained X-ray diffractogram, ilmenite (80.6%) and rutile (19.4%) as significant phases, corroborating the FRX results that indicated greater presence of Fe and titanium oxide in the ilmenite chemical composition under study. The TGA, DTA and DSC analyses indicated good thermal stability of the material in medium and high temperatures. The integration of the obtained data shows that the application of this ore as a precursor material of absorber films for selective purposes is considerable
Beyond Nyquist: Efficient Sampling of Sparse Bandlimited Signals
Wideband analog signals push contemporary analog-to-digital conversion
systems to their performance limits. In many applications, however, sampling at
the Nyquist rate is inefficient because the signals of interest contain only a
small number of significant frequencies relative to the bandlimit, although the
locations of the frequencies may not be known a priori. For this type of sparse
signal, other sampling strategies are possible. This paper describes a new type
of data acquisition system, called a random demodulator, that is constructed
from robust, readily available components. Let K denote the total number of
frequencies in the signal, and let W denote its bandlimit in Hz. Simulations
suggest that the random demodulator requires just O(K log(W/K)) samples per
second to stably reconstruct the signal. This sampling rate is exponentially
lower than the Nyquist rate of W Hz. In contrast with Nyquist sampling, one
must use nonlinear methods, such as convex programming, to recover the signal
from the samples taken by the random demodulator. This paper provides a
detailed theoretical analysis of the system's performance that supports the
empirical observations.Comment: 24 pages, 8 figure
Variability in concentrations of potentially toxic elements in urban parks from six European cities
Use of a harmonised sampling regime has allowed comparison of concentrations of copper, chromium, nickel, lead and zinc in six urban parks located in different European cities differing markedly in their climate and industrial history. Wide concentrations ranges were found for copper, lead and zinc at most sites, but for chromium and nickel a wide range was only seen in the Italian park, where levels were also considerably greater than in other soils. As might be expected, the soils from older cities with a legacy of heavy manufacturing industry (Glasgow, Torino) were richest in potentially toxic elements (PTEs); soils from Ljubljana, Sevilla and Uppsala had intermediate metal contents, and soils from the most recently established park, in the least industrialised city (Aveiro), displayed lowest concentrations. When principal component analysis was applied to the data, associations were revealed between pH and organic carbon content; and between all five PTEs. When pH and organic carbon content were excluded from the PCA, a distinction became clear between copper, lead and zinc (the "urban" metals) on the one hand, and chromium and nickel on the other. Similar results were obtained for the surface (0-10 cm depth) and sub-surface (10-20 cm depth) samples. Comparisons with target or limit concentrations were limited by the existence of different legislation in different countries and the fact that few guidelines deal specifically with public-access urban soils intended for recreational use
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