Repositório RCAAP

It is shown that the usual quantum field theory leads to an ultraviolet divergence in the vacuum energies and an infrared divergence in the two-point functions of the massive and massless vector fields. Using a new method of quantization it is shown that the vacuum energies converge, and the normal ordering procedure is not necessary. Also the propagators are calculated, which are automatically renormalied.

The angiogenic properties of natural rubber were evaluated in this work. We have used the chick chorioallantoic membrane assay (CAM) as a model to investigate the influence of the heating on biological activity in rubber membranes and in non rubber fraction as well. Results showed that natural rubber membranes can induce vascularization. It was observed that angiogenesis activity was maximum when membranes were heated in temperatures between 65ºC and 85ºC, considering a range from 55ºC to 105ºC. The same behavior was observed for non rubber fraction and it indicates that this serum fraction may be responsible for angiogenesis. When infrared spectroscopy was performed in the cast films of non rubber fraction samples, as a function of heating, no structural changes was observed. The results obtained shown that natural rubber latex films produced by casting induce the vessel growth in the CAM and it can be considered as a potential biomaterial.

Based on the generalized uncertainty principle (GUP), in which the quantum gravitational effects are taken in to account, the corrected Beckenstein-Hawking entropy of the higher dimensional Reissner-Nordström black hole, up to the square order of Planck length, is calculated. Using the corrected entropy, the black hole radiation probability is calculated in the tunneling formalism, which is corrected up to the same order of the Planck length and shows a more probable quantum tunneling.

Higher dimensional cosmological implications ofa decay law for the cosmological constant term are analyzed. Three independent cosmological models are explored mainly: 1) - In the first model, the effective cosmological constant was chosen to decay with times like Λeffective = Ca-2 + D(b/a i)² where aiis an arbitrary scale factor characterizing the isotropic epoch which proceeds the graceful exit period. Further, the extra-dimensional scale factor decays classically like b(t) ≈ a x (t),xisareal negative number. 2) - In the second model, we adopt in addition to Λeffective = Ca-2 + D(b/a i)² the phenomenological law b(t) = a(t) exp(-Qt) as we expect that at the origin of time, there is no distinction between the visible and extra dimensions; Qis a real number. 3) -In the third model, we study a Λ-decaying extra-dimensional cosmology with a static traversable wormhole in which the four-dimensional Friedmann-Robertson-Walker spacetime is subject to the conventional perfect fluid while the extra-dimensional part is endowed by an exotic fluid violating strong energy condition and where the cosmological constant in (3+n+1) is assumed to decays like Λ(a) = 3Ca-2. The three models are discussed and explored in some details where many interesting points are revealed.

In this study, electron paramagnetic resonance spectroscopy was used to investigate free radicals formed in gamma irradiated L-glutamine hydrochloride, iminodiacetic acid hydrochloride and N-(2-hyroxyethyl) iminodiacetic acid powders. The free radicals produced in L-glutamine hydrochloride powders were attributed to the CH2CHCOOH radical; and those in iminodiacetic acid hydrochloride and N-(2-hyroxyethyl) iminodiacetic acid powders to the HNCHCH2(COOH)2 and HOCH2CH2NCHCH2(COOH)2, respectively. The g-values of the radicals and the hyperfine structure constants of the free electron with the environmental protons and 14N nucleus were determined. The samples were not displayed before they were not irradiated. The free radicals were found stable at room temperature for more than six months. Some spectroscopic properties and suggestions concerning possible structure of the radicals are discussed in this paper.

The description of quantum dynamics of nanomagnets is a central issue in most applications proposed for those systems. In this paper, we put forward a modified perturbation approach to study the spin dynamics of a molecular magnet in the presence of time-dependent magnetic fields.The non-perturbed Hamiltonian H0, which defines the interaction picture, may be time-dependent proviso it can be diagonalized at all times by the same basis of states. We probe the method using a simple model Hamiltonian, that contains the important anisotropy terms relevant for Fe8 molecular clusters, and solve as an example the case with the smallest non trivial spin value (S=1). Our modified perturbation approach converges rapidly to the exact solution, goes beyond the Kubo linear response theory, and is well defined even at resonance. Temperature effects in the spin dynamics are taken into account in the context of the density matrix.

Large values for the mass-to-light ratio (Ò) in self-gravitating systems is one of the most important evidences of dark matter. We propose a expression for the mass-to-light ratio in spherical systems using MOND. Results for the COMA cluster reveal that a modification of the gravity, as proposed by MOND, can reduce significantly this value.

We use the spin-1 Heisenberg chain with periodic boundary conditions to ilustrate that the systems get stuck in metastable configurations only when the density-matrix renormalization-group algorithm start with small number of states m. We also show that the convergence of the energies have a huge improvement if we start the algorithm with a large number of states m.

A systematic crystallization kinetic study of two smectogens of homologous series of the inter molecular hydrogen bonded between undecyl, dodecyl benzoic acids and hexadecylaniline complexes viz., 16A+11BA and 16A+12BA respectively has been carried out by thermal microscopy, differential scanning calorimetry (DSC) and dielectric studies. FTIR studies indicate the formation of hydrogen bond in these complexes. The crystallization kinetics was studied by two techniques viz., the traditional thermal analysis (DSC) and electrical studies in which capacitance and dielectric loss variation with temperature were recorded and analyzed. The DSC thermograms were run from crystallization temperature to the isotropic melt for different time intervals. The liquid crystalline behaviour together with the rate of crystallization of smectic ordering in newly synthesized inter hydrogen bonded complexes were discussed in relation to the kinetophase (which occurs prior to the crystallization). The molecular mechanism and dimensionality in the crystal growth were computed from the Avrami equation. The characteristic crystallization time (t*) at each crystallization temperature was deduced from the individual plots of log t and gH. Further, it was observed that the data obtained from DSC and dielectric studies were in good agreement with one another. For the first time in the history of crystallization studies, crystallization kinetics data is experimentally elicited from a novel dielectric technique.

We study a dynamical system which describes the overlap of resonances in a global integrable context and we present a new topological scenario for the reconnection of three resonance island chains in the presence of two robust tori. These tori induce this new scenario and they play the role of transport barriers which are relevant for plasma confinement in Tokamaks.

Wedged beam are often used in clinical radiotherapy to compensate missing tissues and dose gradients. In this work, the Fricke Xylenol Gel (FXG) dosimeter was used for 6 MV photons radiation wedge field profiles measurements, allowing to infer the wedge filter physical attenuation coefficient. This dosimeter is a chemical system of a Fe3+-Xylenol complex concentration, that when measured spectrophotometrically, the absorbance is directly proportional to the absorbed dose. From theses results one can infer that the FXG can be used also as an alternative dosimetric system for measurements of wedge filters.

In this paper we present a spatially homogeneous locally rotationally symmetric (LRS) Bianchi type -V perfect fluid model with heat conduction in scalar tensor theory proposed by Saez and Ballester. The field equations are solved with and without heat conduction by using a law of variation for the mean Hubble parameter, which is related to the average scale factor of metric and yields a constant value for the deceleration parameter. The law of variation for the mean Hubble parameter generates two types of cosmologies one is of power -law form and second the exponential form. Using these two forms singular and non -singular solutions are obtained with and without heat conduction. We observe that a constant value of the deceleration parameter is reasonable a description of the different phases of the universe. We arrive to the conclusion that the universe decelerates for positive value of deceleration parameter where as it accelerates for negative one. The physical constraints on the solutions of the field equations, and, in particular, the thermodynamical laws and energy conditions that govern such solutions are discussed in some detail.The behavior of the observationally important parameters like expansion scalar, anisotropy parameter and shear scalar is considered in detail.

Tin doped indium oxide thin films were prepared on glass substrates kept at room temperature, by activated reactive evaporation (ARE). Structural, electrical and optical properties were studied for films having different thickness. The resulting films are polycrystalline and show ˜ 90 % transmission in the visible region. Hall effect measurements at room temperature for a film with a nominal thickness of ˜ 350 nm shows a relatively high carrier concentration ˜ 6.3 × 10(20) cm-3, mobility ˜ 16 cm² V-1s-1, with a low resistivity ˜ 1.01×10-3W cm.

In this paper, a model of Plasma Focus without surrounding cathode containing the radial expansion of the current sheath is presented. This configuration has been increasingly used in recent miniature devices. The model, based on the snowplow approximation, was applied to calculate the voltage along the pinch in a small 300 J device, showing good agreement with the experiments. The results can be useful in the design of x-rays applications of Plasma-Focus devices.

The effects of Ag addition on some physical properties of YBa2Cu3O7-δ superconductor has been studied. The samples were produced by different routes and characterized by scanning electron microscopy, differential thermal analysis, thermogravimetric analysis, X-ray diffraction and nanoindentation. The superconducting properties were studied by dc magnetization and electrical resistivity measurements. The X-ray patterns revealed that all samples were polycrystalline and corresponded to the orthorhombic YBa2Cu3O7-δ phase. However, for some samples, silver appears to be present within the grains. The superconducting properties were not significantly influenced by Ag addition. Hardness and elastic modulus were also obtained by instrumented indentation. Ag addition was found to be effective in improving the mechanical properties, probably by filling the pores in the grain boundaries. Hardness profiles indicated values between 3.1 and 3.4 GPa at deep tip penetration depths. The highest elastic modulus of 146 GPa was attained for samples prepared using Y2O3, BaCO3, CuO and Ag2O as precursors, while the lowest modulus (125 GPa) was obtained for the pure YBa2Cu3O7-δ sample.

The instantonic approach for a Φ4 model potential is reexamined in the asymptotic limit. The path integral of the system is derived in semiclassical approximation expanding the action around the classical background. It is shown that the singularity in the path integral, arising from the zero mode in the quantum fluctuation spectrum, can be tackled only assuming a finite (although large) system size. On the other hand the standard instantonic method assumes the (anti)kink as classical background. But the (anti)kink is the solution of the Euler-Lagrange equation for the infinite size system. This formal contradiction can be consistently overcome by the finite size instantonic theory based on the Jacobi elliptic functions formalism. In terms of the latter I derive in detail the classical background which solves the finite size Euler-Lagrange equation and obtain the general path integral in finite size. Both problem and solution offer an instructive example of fruitful interaction between mathematics and physics.

We study a classical perturbative membrane based on the string-limit model and we discuss the consistency of the theory where the closure of the classical constraints algebra is verified. We paraquantize the model (extended string) both in the covariant and the transverse approaches. From the generalized Poincaré algebra, the so-called Poincaré (para) algebra, we show that the space-time critical dimensions D are related to the order of the paraquantization Q by the relation D = 3+24/Q. The symplectic structure is generalized for the paraquantum case and applied to the parabosonic membrane coupled to a constant 3-form field. This leads to a deformed noncommutative relations at the ends of the membrane (extended string) describing a geometry which might be called a q-noncommutativity.

The region in the vicinity of 132Sn, gathering numerous isotopes of important masses, shows lots of interests for explaining the most interesting phenomena. It offers among others the possibility to extract the N-N empirical interactions so as to test theoretical shell model description of nuclear structure in this region. The researches on the neutron-rich tin isotopes present the anomalies in a systematic variation on various spectroscopic data such as the first 2+ excited state and reduced probabilities B(E2;2+? 0+). In order to improve the OXBASH interactions which are based on the shell model calculations, we have modified some neutron-neutron and proton-proton tow body matrix elements of CW5082 interaction of 132Sn region by adding to them the pairing gap energy. The calculations turn out a new interaction so called CWΔ5082, allowing to determine the excited energies and the reduced probabilities B(E2) of Sn and Te isotopes for A = 134 and 136 masses. The obtained results display a remarkable enhancement in the predictive power of experimental values.

In this work we report on conductivity fluctuation measurements in polycrystalline samples of the Er1-xPr xBa2Cu3O7-δ superconductor (x = 0.00, 0.05 and 0.10). Samples were prepared by a standard solid-state reaction technique. The results were analyzed in terms of the temperature derivative of the resistivity and of the logarithmic temperature derivative of the conductivity that allowed the identification of power-law divergences of the conductivity. The results show that the transition proceeds in two stages: pairing and coherence transition. Also, our results, from the critical exponent analysis, show a two-peak splitting at pairing transition, indicating possibly a phase separation. On approaching the zero resistance state, our results show a power-law behavior that corresponds to a phase transition from paracoherent to a coherent state of the granular array.

In this work we investigate the vortex dynamics in a square mesoscopic superconducting cylinder in the presence of an applied magnetic field parallel to its axis. The rectangular cross-section of the sample is L² and an engineered columnar defect of area d² at the center is taken into account; L = 12ξ(0) for all simulations while d varies discretely from 1ξ(0) to 10ξ(0). We study the magnetization and the vortex configuration, increasing the magnetic field from zero to the normal state field. We found that for d > 7ξ(0) no vortices in the superconductor area are possible. Also, if the size of the defect is reduced, the nucleation fields decrease.