Repositório RCAAP

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.

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.

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.

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.

In the present work we investigate one possible variation on the usual electrically neutral pulsars: the inclusion of electric charge through a naive prescription. We study the effect of electric charge in pulsars assuming that the charge distribution is proportional to the energy density. All calculations were performed for equations of state obtained at zero temperature and also for fixed entropies. We then choose one of the models, the Nambu-Jona-Lasinio model for zero temperature quark stars without the inclusion of leptons, what makes them electrically charged, and compare the results with the previous one.

A detailed investigation on the possible role played by the intrinsic arbitrariness of the perturbative evaluation of physical amplitudes and their symmetry relations, initiated in a first work, is continued. Previously announced results are detailed presented. The very general calculational method, concerning the divergences manipulations and calculations, adopted to discuss the questions of ambiguities and symmetry relations, in purely fermionic divergent Green functions, is applied to explicit evaluate three-point functions. Two of such functions, the well known Scalar-Vector-Vector and Axial-Vector-Vector triangle amplitudes are considered in details. Given the fact that within the adopted strategy, all the arbitrariness intrinsic to the problem are maintained in the final results, and that it is possible to map them in to the ones of traditional techniques, clean and sound conclusions can be extracted. In particular, we can map our results in to the Dimensional Regularization ones as well as in to those corresponding to surface's terms evaluation. The first above cited amplitude can be treated within the Dimensional Regularization while the second do not and, consequently, it is usually treated by the surface's terms evaluation strategy. Within the adopted strategy both problems can be equally treated. We show that when we require consistency in the interpretations of the intrinsic indefinitions present in the perturbative amplitudes, which means to treat all physical amplitudes on the same way, no room is left for the ambiguities. As a natural consequence, the physical amplitudes are obtained symmetry preserving, where they must be, and anomalous, where they need to in spite of being non-ambiguous.

This paper aims at showing how analytical techniques can be employed to explain the global emerged behavior of a heterogeneous population of ultimatum game players, over different strategies, by calculating their payoff moments. The ultimatum game is a game, in which two players are offered a gift to be shared. One of the players (the proposer) suggests how to divide the offer while the other player (the responder) can either agree or reject the deal. Computer simulations were performed considering the concept of turns (in every turn each participant plays necessarily only once, which is equivalent to performing matching a graph) in the game. We reproduce by simulations the expected analytical results at the limit of high number of turns. From these results, we are capable of establishing diagrams to say where each strategy is the best (optimal strategy).

The mechanism for low-temperature photoluminescence (PL) emissions in GaAsSb/AlGaAs and GaAsSbN/GaAs strained-layer single quantum wells (SQWs), grown by molecular-beam epitaxy, is studied in detail, using PL spectroscopy as a function of temperature and excitation intensity. In all samples, the PL peak energy as well as the full width at half maximum (FWHM), as a function of temperature, present anomalous behaviors, i.e., the PL peak energy shows a successive red/blue/redshift (S-shaped behavior) and the FWHM shows a successive blue/red/blueshift ("inverted S-shaped curve") with increasing temperature. At sufficiently low excitation intensity and in a narrow temperature interval (50 - 80 K), the nitrogen-containing samples present two clear competitive PL peaks. The low-energy PL mechanism (8 - 80 K) is dominated by localized PL transitions, while the high-energy PL mechanism is dominated by the ground state (e1-hh1) PL transition. Additionally, these PL peaks show different temperature dependence with the low-energy PL peak, showing a stronger redshift than the high-energy PL peak. A competition process between localized and delocalized excitons is used to discuss these PL properties.

We analyse the reflection of a TM electromagnetic field first on a flat dielectric film and second on a Veselago film with negative refractive index, both films being deposited on a metallic substrat acting as a mirror. An incident harmonic plane wave generates inside a conventional dielectric film a refracted propagating wave and an evanescent wave that does not contribute to reflection on the metallic substrat so that part of the information conveyed by the incident field is lost. At the opposite, inside a Veselago film, evanescent waves are changed into outbursting waves reflecting on the metallic substrat and participating to the total reflected field from the metallic film without loss if information.

In this paper an attempt is made to study the occurrence of a large number of high amplitude anisotropic wave train events in cosmic ray intensity during 1981-1994 and to identify a possible correlation with solar activity using the hourly neutron monitor data of Deep River station. The diurnal time of maximum for both HAE as well as for all days is found to significantly shift towards an earlier time as compared to the corotational/azimuthal direction since the year 1991 onward. It is found that diurnal amplitude and 10.7-cm solar radio flux significantly deviates and reaches to its maximum and phase remains in the corotational direction during the years close to solar activity maximum for HAE. The occurrence of high amplitude anisotropic wave train events is dominant during solar activity minimum as well as maximum years. The amplitude as well as phase of the cosmic ray diurnal anisotropy during HAEs is well correlated with solar activity. The amplitude as well as phase of diurnal anisotropy shows very nominal correlation with 10.7-cm solar radio flux (r = 0.48, 0.47). However, the frequency of occurrence of HAEs shows a very weak correlation (r = - 0.36) with 10.7-cm solar radio flux.

In previous works anomalies were observed in binding energies for the island of inversion nuclei centered at Z=11, N=21 by the comparison of theoretical calculations and experiment. An attempt was made in this work using an improved term of shell corrections to observe the evolution of these anomalies. This term was added to the macroscopic part of the previous mass formula and binding energy calculations have been carried out. A distribution of these latter on a (N,Z) chart has indicated that the calculated values increase with the increase of N for all values studied as for those of experiment except the value of Z=10. This result shows the presence of these anomalies only in the line Z=10 and their absence in the lines Z=11 and 12. Although this shell correction includes a term representing an interaction between protons and neutrons of valence shells, but it is insufficient to study this deformed mass region.

We study a model with decay of dark energy and creation of the dark matter particles. We integrate the field equations and find the transition redshift where the evolution process of the universe change from decelerated to an accelerated phase expansion, and briefly discuss the transition epoch and the broken of the strong energy condition. Finally, we examine the growing of the inhomogeneities.

55Co is not only present in abundance in presupernova phase but is also advocated to play a decisive role in the core collapse of massive stars. The spectroscopy of electron capture and emitted neutrinos yields useful information on the physical conditions and stellar core composition. B(GT) values to low-lying states are calculated microscopically using the pn-QRPA theory. Our rates are enhanced compared to the reported shell model rates. The enhancement is attributed partly to the liberty of selecting a huge model space, allowing consideration of many more excited states in our rate calculations. Unlike previous calculations the so-called Brink’s hypothesis is not assumed leading to a more realistic estimate of the rates. The electron and positron capture rates are calculated over a wide temperature (0.01×10(9) - 30×10(9)K) and density (10 - 10(11) gcm-3) grid.

The construction of theta-local superfield Lagrangian BRST quantization in non-Abelian hypergauges for generic gauge theories based on the action principle is examined in the case of reducible local superfield models (LSM) on the basis of embedding a gauge theory into a special theta-local superfield model with antisymplectic constraints and a Grassmann-odd time parameter theta. We examine the problem of establishing a new correspondence between the odd-Lagrangian and odd-Hamiltonian formulations of a local LSM in the case of degeneracy of the Lagrangian description with respect to derivatives over theta of generalized classical superfields A I(theta). We also reveal the role of the nilpotent BRST-BFV charge for a formal dynamical system corresponding to the BV-BFV dual description of an LSM.

In order to popularize the so called Schwinger's method we reconsider the Feynman propagator of two non-relativistic systems: a charged particle in a uniform magnetic field and a charged harmonic oscillator in a uniform magnetic field. Instead of solving the Heisenberg equations for the position and the canonical momentum operators, R and P, we apply this method by solving the Heisenberg equations for the gauge invariant operators R and pi = P-eA, the latter being the mechanical momentum operator. In our procedure we avoid fixing the gauge from the beginning and the result thus obtained shows explicitly the gauge dependence of the Feynman propagator.

Based on density functional theory, the full potential linearized augmented plane wave (FPLAPW) method is applied to study the electronic structure and the magnetic properties of the compound [Mn(4,4<FONT FACE=Symbol>'</FONT>-bipy)(N3)2]n. The density of states, the spin magnetic moment and the electronic band structure are calculated. The results indicate that the compound has ferromagnetic and semiconductor properties. It is found that there is hybridization between the d orbital of the central Mn atom and the p orbital of the N atom, and that there exists a spin delocalization from the Mn atom towards the N atoms of the EE-azide groups. Through the EE-azide bridges, the spin delocalization makes the neighboring Mn atoms having a dominant ferromagnetic interaction. The magnetic moment 5.0 µB per molecule mainly comes from Mn ion with little contribution from the EE-azide groups.

In this work we briefly review the wave packet approach of two generation neutrino oscillation, aiming its description in a progenitor star supernova environment. We begin calculating the wave packet size in many situations: solar and supernova plasma medium, considering nuclear interactions, as well as accelerators and reactors. This quantity is important to calculate the coherence length, which we compare with the oscillation length to verify if neutrino oscillation will or will not occur. Finally, we compare the wave packet treatment of neutrino oscillation with the plane wave formalism in a progenitor star supernova environment.

We introduce a simple dynamic model to investigate the fragmentation of transport networks. The transport properties like as the size of largest connected cluster, the length of the minimum paths and the optimal paths between a pair of nodes of the network were evaluated upon continuously increasing the load on the system. We use two load insertion strategies: an uniform random distribution of loads and a Cohen-like immunization strategy (one node is selected with a uniform probability p and one of its first neighbours, randomly selected, receives the load). Both strategies may be classified as local strategies but the resulting effects are qualitatively different. Evaluating the physical quantities as a function of time we observe that for the random distribution strategy there is a crossover from a fully connected cluster to a non-connected state in the sense that all links become unavailable. On the other hand, following the Cohen-like strategy we found a sudden change in transport properties which is may be interpreted as a percolation-like transition induced by the cumulative process of load.

Co2+x+yMn1-xAl1-y intermetallic compounds have been prepared by arc melting and studied with X-ray diffraction and magnetization measurements to ascertain the effect of deviations of composition from the stoichiometry on the ferromagnetism of this system. Hysteresis loops registered at room temperature show a soft ferromagnetic behavior in excess Co. In off-stoichiometric alloys the saturation magnetization is lower than in Co2MnAl, whereas the Curie temperature T C is higher in all the studied alloys. T C varies substantially with variations in composition and increases with the Mn content. In the source of this behavior a volume effect is inferred which is expected to lead to strengthened ferromagnetic exchanges.

A drying method suitable for the study of the morphological and structural properties of colloidal magnetic systems, including a contrast agent used in Magnetic Resonance Imaging (MRI) is described. We tested three alternative ferrofluid drying methods: drying at 70 70ºCC in nitrogen atmosphere; drying in air at 70 70ºCC; and drying by liophylization using an MRI marker in the form of a colloidal suspension (EndoremTM - Guebert). X-ray diffraction (XRD), and transmission electron microscopy (TEM) were applied to each characterization method. The XRD allowed the observation of the possible physical-chemical changes of the stabilizers and also Fe3O4 present in the system. The morphology and nanoparticles size distribution was analyzed by TEM. Among the drying methods examined in this study, the liophylization has shown to be the more adequate one for the nanoparticles (Fe3O4) morphological study and nanostructural characterization, because the structure of the nanoparticles was maintained the same as in the suspension. The drying procedures performed at 70 70ºCC in the atmospheres of nitrogen and air let to the coalescence and growth of the nanoparticles, as well as some degradation has been noticed in some of the stabilizers.