Resumo em Inglês:

Chandler wobble excitation and damping, one of the open problems in geophysics, is treated as a consequence in part of the interaction between Earth and a hypothetical oblate ellipsoid made of dark matter. The physical and geometrical parameters of such an ellipsoid and the interacting torque strength is calculated in such a way to reproduce the Chandler wobble component of the polar motion in several epochs, available in the literature. It is also examined the consequences upon the geomagnetic field dynamo and generation of heat in the Earth outer core.

Resumo em Inglês:

Nowadays, wavelet analysis of turbulent flows have become increasingly popular. However, the study of geometric characteristics from wavelet functions is still poorly explored. In this work we compare the performance of two wavelet functions in extracting the coherent structures from solar wind velocity time series. The data series are from years 1996 to 2002 (except 1998 and 1999). The wavelet algorithm decomposes the annual time-series in two components: the coherent part and non-coherent one, using the daubechies-4 and haar wavelet function. The threshold assumed is based on a percentage of maximum variance found in each dyadic scale. After the extracting procedure, we applied the power spectral density on the original time series and coherent time series to obtain spectral indices. The results from spectral indices show higher values for the coherent part obtained by daubechies-4 than those obtained by the haar wavelet function. Using the kurtosis statistical parameter, on coherent and non-coherent time series, it was possible to conjecture that the differences found between two wavelet functions may be associated with their geometric forms.

Resumo em Inglês:

In earlier work [1], we studied an extension of the canonical symplectic structure in the cotangent bundle of an affine space Q = R N, by additional terms implying the Poisson non-commutativity of both configuration and momentum variables. In this article, we claim that such an extension can be done consistently when Q is a Lie group G.

Resumo em Inglês:

This work is devoted to the study of the electrical characteristics of microhollow cathode discharges (MHCD) at moderate to high pressure in argon and air for different geometries. High-pressure glow discharges can be operated in MHCD devices with µm electrode spacing. Experiments have been performed to determine the so-called Paschen curves, i.e. the dependence of the breakdown voltage on the product electrode gap and gas pressure. Current-voltage characteristic curves were obtained as a function of the pressure and hole diameter. MHCD enables stable direct current discharges that could be ignited for pressures ranging from 12 to 800 Torr, in a very wide range of current densities and electrodes materials. Evidence of electron field emission was observed for several ranges of gap spacing.

Resumo em Inglês:

In this study, sedimentary organic matter of oil shale rejects, calschist, shale fine and the so called retorted shale from Irati formation was characterized. EPR was used to analyse the samples regarding loss of signal in g = 2.003 associated to the organic free radical with the calcined samples and washing with hydrogen peroxide. The radical signal was detected in all samples, however, for the calschist and shale fine samples another signal was identified at g = 2.000 which disappeared when the sample was heated at 400 ºC. Hydrogen peroxide washing was also performed and it was noted that after washing the signal appeared around g = 2.000 for all samples, including retorted shale, which might be due to the quartz E1 defect.

Resumo em Inglês:

A Monte Carlo simulation has been used to model steady-state electron transport in SiC and GaN field effect transistor. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible. Simulations of SiC MESFETs of lengths 2, 2.6 and 3.2 µm have been carried out and compared these results with those on GaN MESFETs of the same dimensions. The direct current IV characteristics of the two materials were found to be similar, though the GaN characteristics were on the whole superior, reaching their operating point at higher drain voltages and possessing higher gains. However, oscillations in the drain current caused by changes in drain voltage in the GaN devices were not present to the same degree in the SiC devices. This difference is caused partially by the onset of the negative differential regime in SiC at a higher electric field than in GaN but the primary cause is the longer ballistic transport times in SiC. This suggests that GaN MESFETs may prove to have superior frequency response characteristics than SiC MESFETs.

Resumo em Inglês:

This work presents the results of neutron spectrum measurements at central position of the IPEN/MB-01 reactor core. For this purpose has been used several activation foils (Au, Sc, U, Mg, Ti, Ni, and In Foils) that have been irradiated at central position of the reactor core (standard rectangular configuration 28 × 26 fuel rods) in the maximum power level (100 watts). After this one the foils were counting at HPGe solid state detector (gamma spectrometry). The nuclear reaction rates experimental results (saturated activity per target nucleus) is together with an initial approach to the neutron reactor spectrum (estimated by reactor physics cellular codes) the main data to obtain the most appropriated neutron spectrum at the irradiation position by interactive adjustment process using the unfolding SANDBP code. The results obtained were (5.1312±0.1609).10(9) n/cm².s to the integral neutron flux, (9.8087±0.4974).10(8) n/cm² to the thermal neutron flux, (3.2272 ± 0.4378).10(9) n/cm².s to the intermediate neutron flux and (1.9040 ± 0.6390).10(9) n/cm².s to the fast neutron flux. These results are important and may be used to check and validate reactor physics codes and several nuclear data libraries.

Resumo em Inglês:

In this work, simulation of the singly charged argon ion trajectories for a variable plasma meniscus is studied with and without space charge for the triode extraction system by using SIMION 3D (Simulation of Ion Optics in Three Dimensions) version 7 personal computer program. The influence of acceleration voltage applied to the acceleration electrode of the triode extraction system on the shape of the plasma meniscus has been determined. The plasma electrode is set at +5000 volt and the acceleration voltage applied to the acceleration electrode is varied from -5000 volt to +5000 volt. In the most of the concave and convex plasma shapes, ion beam emittance can be calculated by using separate standard deviations of positions and elevations angles. Ion beam emittance as a function of the curvature of the plasma meniscus for different plasma shapes ( flat, concave and convex ) without space charge at acceleration voltage varied from -5000 volt to +5000 volt applied to the acceleration electrode of the triode extraction system has been investigated. The influence of the extraction gap on ion beam emittance for a plasma concave shape of 3.75 mm without space charge at acceleration voltage, Vacc = -2000 volt applied to the acceleration electrode of the triode extraction system has been determined. Also the influence of space charge on ion beam emittance for variable plasma meniscus at acceleration voltage, Vacc = - 2000 volt applied to the acceleration electrode of the triode extraction system has been studied.

Resumo em Inglês:

We present a hybrid cladding photonic crystal fiber for shaping high nonlinear and flattened dispersion in a wide range of wavelengths. The new structure adopts hybrid cladding with different pitches, air-holes diameters and air-holes arrayed fashions. The full-vector finite element method with perfectly matched layer is used to investigate the characteristics of the hybrid cladding photonic crystal fiber such as nonlinearity and dispersion properties. The influence of the cladding structure parameters on the nonlinear coefficient and geometric dispersion is analyzed. High nonlinear coefficient and the dispersion properties of fibers are tailored by adjusting the cladding structure parameters. A novel hybrid cladding photonic crystal fiber with high nonlinear coefficient and dispersion flattened which is suited for supercontinuum generation is designed.

Resumo em Inglês:

The gamma rays de-exciting the yrast and near yrast states in neutron deficient as well as neutron rich nuclei from fusion-evaporation and deep-inelastic reactions and other emission particles have been recorded using an array of escape suppressed germanium detectors, a BGO ball, a recoil separator, silicon charge particle detectors and an ionization chamber. For each reaction type, we used different combinations of detectors with increasing gamma ay detectors from fusion-evaporation experiments to deep-inelastic experiments to separate different channels. In two experiments related to fusion-evaporation reactions, additional mass and charge particle detectors showed better resolution of spectra with lower statistics and some ambiguities. In the third experiment, which we used only an array of germanium detectors and a BGO ball, the statistics of spectra are relatively good but not sufficient, which means that we must use additional channel separators.

Resumo em Inglês:

The relation between parallel viscosity and the parallel conductivity for tokamak plasma has been derived by combining Ideal MHD equilibrium equations with the concept of universal profiles. It is obtained that the parallel viscosity Π║ and parallel conductivity σ║ in a tokamak are related by Π║σ║-1 = γ (U-U0)I/R, where U is the loop voltage, U0 is attributed to polarization, I is the toroidal current and R is the major radius of the machine. The coefficient γ depends on para- or diamagnetism and on toroidal effects and exhibits a weak dependence on the minor radius.

Resumo em Inglês:

Pilocarpine is a natural substance with potential application in the treatment of several diseases. In this work Fourier Transform (FT)-Raman spectrum and the Fourier Transform infra red (FT-IR) spectrum of pilocarpine hydrochloride C11H17N2O2+.Cl- were investigated at 300 K. Vibrational wavenumber and wave vector have been predicted using density functional theory (B3LYP) calculations with the 6-31 G(d,p) basis set. A comparison with experiment allowed us to assign most of the normal modes of the crystal.

Resumo em Inglês:

We employed the Schwinger multichannel method to compute elastic cross sections for low-energy electron collisions with ethane (C2H6). The calculations were carried out in the static-exchange and static-exchange plus polarization approximations for energies up to 12 eV. Our integral cross section shows good agreement with experimental data and with theoretical results for energies above 5 eV. There are some differences for energies below 5 eV between our results and the available experimental and theoretical results. Our differential cross sections also agree well with the experiment and with theory for energies above 5 eV; below this energy our results agree in shape, but are smaller than the available experimental and theoretical results. We discuss possible reasons for these discrepancies. We found a broad structure in the integral cross section around 8.5 eV and also a Ramsauer-Townsend minimum around 0.2 eV. These results are in agreement with the experimental observations and theoretical results.

Resumo em Inglês:

An approach for the theory of nonlocal magnetorotational and convective instabilities in a rotating plasma is developed, on the basis of the surface wave concept, which allows the derivation of useful analytical results.It is assumed that the rotation frequency has a step-like profile, so that a narrow transition layer separates two regions with different rotation frequencies. The one-fluid magnetohydrodynamic (MHD) model for description of the perturbed plasma dynamics is used. It is shown that in the case of magnetized plasma the main properties of the nonlocal (surface-wave) instabilities are similar to those of the local ones.

Resumo em Inglês:

In this letter, we have considered the universe is filled with the mixture of tachyonic field and scalar or phantom field. If the tachyonic field interacts with scalar or phantom field, the interaction term decays with time and the energy for scalar field is transferred to tachyonic field or the energy for phantom field is transferred to tachyonic field. The tachyonic field and scalar field potentials always decrease, but phantom field potential always increases.

Resumo em Inglês:

We derive general analytical expressions for the evaluation of the intrinsic asymmetry parameter in nonmesonic hypernuclear weak decay, within an independent particle shell model framework. Present formalism is valid for even-even, even-odd and odd-odd core hypernucleus. A standard strangeness-changing weak transition potential with exchange of the complete meson octet (π, η, K, ρ, ω, K*) is assumed. Very simple analytical formulas are obtained within the s-wave approximation when we restrict to the π and π+K exchange models, providing an useful and manageable tool to understand the origin of the discrepancies between theoretical and experimental results. Numerical values for 4ΛHe, 5ΛHe, 11ΛB, 12ΛC, 16ΛO, 17ΛO and 28ΛSi hypernuclei are exhibited. Present formalism could be used to understand why new contributions to the exchange potential allow to obtain good agreement with data, as indicated in very recent works. The necessity of a consistent inclusion of: i) different modifications of the exchange potential (two-pion exchange, a1 meson, ΔT = 3/2 terms coming from vector mesons, etc); ii) final state interactions on primary nucleons inside the residual nucleus and also correlations between the free emitted ones; and iii) configuration mixing in the final system, is remarked.

Resumo em Inglês:

A common of finite-time heat transfer processes between high- and low-temperature sides with a generalized heat transfer law [q ∝ (Δ(Tn ))m] are studied in this paper. The optimal heating and cooling configurations for minimizing lost available work are derived for the fixed initial and final temperatures of the working fluid of the system (low-temperature side). Optimal paths are compared with the common strategies of constant heat flux, constant source (reservoir) temperature and the minimum entropy generation operation by numerical examples. The condition corresponding to the minimum lost available work strategy is that corresponding to a constant rate of lost available work, not only valid for Newton's heat transfer law [q ∝ ΔT] but also valid for the generalized convective heat transfer law [q ∝ (ΔT)m ]. The obtained results are more general and can provide some theoretical guidelines for the designs and operations of practical heat exchangers.

Resumo em Inglês:

We discuss the generic features of the accelerated universe from Arnowitt-Deser-Misner renormalizable group approach applied for gravity models with variable gravitational coupling constant and cosmological constant. The universe undergoes an endless sequence of cosmic eras which starts inflating after a Big Bang and end contracting to a Big Crunch dominated by phantom energy. Presently, the universe found to be presently accelerating in time and is dominated by dark energy. Some important features and numerical results are revealed and discussed in some details.

Resumo em Inglês:

We utilize a kinetic approach to the problem of wave propagation in dusty plasmas, taking into account the variation of the charge of the dust particles due to inelastic collisions with electrons and ions. The components of the dielectric tensor are written in terms of a finite and an infinite series, containing all effects of harmonics and Larmor radius. The formulation is quite general and valid for the whole range of frequencies above the plasma frequency of the dust particles, which are assumed motionless. The formulation is employed to the study of electrostatic waves propagating along the direction of the ambient magnetic field, in the case for which ions and electrons are described by bi-Maxwellian distributions. The results obtained in a numerical analysis corroborate previous analysis, about the important role played by the dust charge variation, particularly on the imaginary part of the dispersion relation, and about the very minor role played in the case of electrostatic waves by some additional terms appearing in the components of the dielectric tensor, which are entirely due to the occurrence of the dust charge variation.