Resumo em Inglês:

The electronic structure of the A15 compounds A3B A=Nb; B=Al,Ga,Ge,Sn and In is studied by means of fully relativistic full-potential linearized augmented-plane wave (FP-LAPW) calculations within the formalism of the density functional theory. Band structures and densities of states are determined for all the studied compounds. From the calculations are obtained the theoretical lattice constants, the Fermi energy E F, the density of states at the Fermi level N(E F) which is used to estimate the electronic specific heat coefficient gamma and the electron-phonon coupling parameter lambda for the Nb3In compound. Generally, a good agreement between results of the calculations and experiments is found.

Resumo em Inglês:

The diffusion of zinc into n-type InP has been studied by four-point probe electrical measurements on homogeneously doped crystals at 750 ºC. The zinc carrier concentration in the diffused layer was approximately 3 x 10(18) cm-3 and its mobility was assumed to be about 40 cm² V-1 s-1. It was observed that the concentration of free carriers throughout the entire diffused region is always less than the number of introduced impurity atoms. Possible reasons are discussed to explain the observed differences. Moreover this non-correlation phenomenon did provide substantial backing to the Hall Effect and C-V measurements that are being carried out to further analyse the Zn-InP diffused layer.

Resumo em Inglês:

In this paper general solutions are found for domain walls in Lyra geometry in the plane symmetric spacetime metric given by Taub. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying displacement field beta. Some physical consequences of the models are also given. Finally, the geodesic equations and acceleration of the test particle are discussed.

Resumo em Inglês:

A detailed study is presented of the counterrotating model (CRM) for electrovacuum stationary axially symmetric relativistic thin disks of infinite extension without radial stress, in the case when the eigenvalues of the energy-momentum tensor of the disk are real quantities, so that there is not heat flow. We find a general constraint over the counterrotating tangential velocities needed to cast the surface energy-momentum tensor of the disk as the superposition of two counterrotating charged dust fluids. We then show that, in some cases, this constraint can be satisfied if we take the two counterrotating tangential velocities as equal and opposite or by taking the two counterrotating streams as circulating along electro-geodesics. However, we show that, in general, it is not possible to take the two counterrotating fluids as circulating along electro-geodesics nor take the two counterrotating tangential velocities as equal and opposite. A simple family of models of counterrotating charged disks based on the Kerr-Newman solution are considered where we obtain some disks with a CRM well behaved. We also show that the disks constructed from the Kerr-Newman solution can be interpreted, for all the values of parameters, as a matter distribution with currents and purely azimuthal pressure without heat flow. The models are constructed using the well-known "displace, cut and reflect" method extended to solutions of vacuum Einstein-Maxwell equations. We obtain, in all the cases, counterrotating Kerr-Newman disks that are in agreement with all the energy conditions.

Resumo em Inglês:

We propose a new scheme of embedding constrained systems based on the Gauge Unfixing formalism. Our aim is to modify directly the original phase space variables of a system in order to be gauge invariant quantities. We apply our procedure in a nontrivial constrained model that is the Abelian Pure Chern Simons Theory where new results are obtained. Among them we can cite the development of a systematic procedure in order to separate the first and the second class constraints, and the obtainment of the same initial Abelian Pure Chern Simons Lagrangian as the gauge invariant Lagrangian. This last result shows that the gauge symmetry of the action is certainly preserved.

Resumo em Inglês:

The Nd16Co76-xRu xC7B system has been investigated to assess the effect of boron-carbon combined addition on the ferromagnetic behavior of these intermetallic compounds. The results indicate that the addition of 1 at.% B favors the formation of the tetragonal magnetic phase 2:14:1 in these alloys. With the increase of the Ru concentration is observed an expansion of the lattice in the basal plane as well as a contraction along the c direction of the tetragonal unit cell. The Curie temperature decreases from 432 K at x = 6 to 421 K for x = 27, whereas the saturation magnetization has a steep decrease. The highest T C value has been verified for the alloy with the largest c parameter, despite its a parameter is the smallest one. In comparison to isotypic borides and pure carbides, a loss of coercivity and remanence is observed.

Resumo em Inglês:

In this work, triply differential cross sections for single electron emission due to electron impact on the He-isoelectronic sequence are calculated by using a Born-C3 model. The influence of the nuclear charge on the angular distributions is analyzed. The validity of a scaling law initially derived in the framework of photo-double-ionization is discussed.

Resumo em Inglês:

We use the theory of coupled Gross-Pitaevskii equations to derive an expression for the current density of the propagating atoms coupled out of the condensate under the influence of gravity. By describing the propagation vector of the atoms and using a theoretical definition of the coherence length, we calculate the coherence lengths of 37K, 141Ce, and 249Fm atom lasers numerically. Our calculation method is verified with the available experimental and theoretical data in the literature. The results showed a very good agreement.

Resumo em Inglês:

We use the logistic growth model to describe the bacterium growth in the presence of a Gaussian colored noise. The effects of multiplicative colored noise on the steady state probability distribution of the bacterium growth were investigated. Our results show that increasing the strength of the multiplicative colored noise may lead to decreasing bacterium number and even bacterium extinction. Our studies also indicate that increasing the correlate time of the noise may facilitate the bacterium growth to some extent.

Resumo em Inglês:

A simple method for measuring the damping of the liquid surface wave (LSW) based on the diffraction method was proposed in this paper. In the experiment, the phenomenon was observed that the intensity distribution of the diffraction patterns from the LSW varies with the position of the incident spot. By theoretical analysis of the relationship between the intensity distribution and the LSW amplitude, the damping constant was obtained. In addition, the viscosity of the liquid can be calculated with this method, too.

Resumo em Inglês:

Donor binding energies in quantum well systems using position dependent effective masses are obtained. Results are provided for GaAs-Ga1- Al xAs and the semimagnetic CdTe-Cd1-x Mn xTe systems. In the latter the barrier height reduces in a magnetic field. Using the available experimental data the variations of the barrier height with magnetic field has been obtained using a simple model. Our results are in good agreement with similar works in the literature in the case of constant effective mass for the donor electron. However, in the case of the semi magnetic system and in the case of the position dependent effective mass, the results obtained are shown to be appreciably different for narrow well dimensions. The validity of the effective mass approximation in the case of applied magnetic field is also critically examined.

Resumo em Inglês:

The Fricke dosimeter is a ferrous sulfate aqueous solution that, when irradiated, oxidizes the Fe2 + ions to Fe3 + . This new concentration, generally determined through spectrophotometry, is directly proportional to the ionizing radiation absorbed energy. The Fricke Xylenol Gel dosimeter (FXG) was developed through the incorporation of swine skin gelatin and xylenol orange. These modifications provided better signal stability and sensitivity for lower absorbed dose measurements, such as those used in radiotherapy. In this work FXG samples were irradiated with absorbed doses of 2 Gy, from 6 MV and 10 MV photons, using small field sizes geometry for dosimetric parameters determination. All the FXG dosimeter readings were accomplished with our specially developed spectrophotometer, using a narrow light beam at the wavelength of 585 nm, where the highest absorbance sensitivity occurs. From our results, we can confirm not only that the FXG dosimetric system (FXG plus a high lateral spatial resolution spectrophotometer) can be used for general dosimetry, but as well for small field size dosimetry of interest in radiosurgery.

Resumo em Inglês:

Resonant dynamics of magnetic molecules with spin 1/2 ground state, such as V15, is theoretically studied. In our model calculation, crystals of this molecular nanomagnet are probed by time-dependent magnetic fields, which continuously invert populations of spin states. If the sample is placed in a resonant cavity, relaxation of excited states, via spin-photon interaction, allows for stimulated emission of radiation in the microwave range at resonance.

Resumo em Inglês:

We report on the application of the Resistively Shunted Junction (RSJ) model to granular high T C superconductors. Some derived predictions of the RSJ model are applied to a set of superconducting granular samples which can be considered as a network of Josephson junctions. The investigated samples belong to both hole-doped Y1-xPr xBa2Cu3O7-delta (x = 0.0, 0.35, and 0.45) and the electron-doped Sm2-xCe xCuO4-delta (x = 0.18) systems which display the so-called double resistive superconducting transition. We have performed several transport measurements in these compounds including temperature and magnetic field dependence of the electrical resistance, R(T,H), and I-V characteristics. Several aspects of the I-V characteristics were quantitatively well described by the RSJ model. The combined results strongly suggest that dissipation in granular superconducting samples is a natural consequence of the normal current flowing in parallel with the supercurrent current.

Resumo em Inglês:

We have measured transport properties at low temperatures for the granular Sm1.82Ce0.18CuO4-delta samples belonging to the family of electron-doped superconductors. The effect of applied electrical current on the resistive behavior is investigated. The experimental data are analyzed using a modified form of the theory for a field-tuned superconductor-insulator transition in 2D superconductors. The results suggest a possible electrical-current driven superconductor-insulator transition.

Resumo em Inglês:

We generalize an existing geometrical approach for multiparticle production in hadronic interactions, in which the overall multiplicity distribution is given by summing contributions coming from each impact parameter b of the incident hadronic system. In the previous work, the process occurring at a fixed impact parameter b was interpreted as due to an elementary collision with formation of an object similar to the one in e- e+ annihilations. Here, we extend the model allowing the possibility of formation of more than just one string. The output seems to be more consistent with data.

Resumo em Inglês:

We describe the high-field (1.0 T) ultra high vacuum (1.6 10- 9 mbar) controllable temperature (8 ºK up to > 350ºK) MCD setup designed and built at LNLS. We show, for nanocrystals of Hematite alpha-Fe2O3, illustrative results obtained at room and at low temperature.

Resumo em Inglês:

We investigate the effect of Pauli non-locality in the heavy-ion optical potential on sub-barrier fusion reactions. The São Paulo potential, which takes into account the Pauli non-locality and has been widely used in analyzing elastic scattering, has also recently been applied to heavy-ion fusion. However, the approximation employed in deriving the São Paulo potential, based on the Perey-Buck semi-classical treatment of neutron induced reactions, must be assessed for charged particles tunneling through a barrier. It is the purpose of this note to look into this question. We consider the widely studied system 16O + 208Pb at energies that span the barrier region from 10 MeV below to 10 MeV above. It seems that the non-locality plays a minor role. We find the São Paulo potential to be quite adequate throughout the region.