Resumo em Inglês:

In this article we analyse the long-term probability density function of non-stationary dynamical processes with time varying multiplicative noise exponents which are enclosed inwards the Feller class of processes. The update in the value of the exponent occurs in the same conditions as presented by BECK and COHEN for superstatistics. Moreover, we are able to provide a dynamical scenario for the emergence of a generalisation of the Weibull distribution previously introduced.

Resumo em Inglês:

We study the self-energy of a model with a tri-linear coupling among spinless fields on a manifold with one spatial dimension compactified. The model is considered to be composed by a quantized scalar field interacting with a classical scalar one. In order to improve the compactification we take the quantum field satisfying quasi periodic boundary conditions, which interpolates continuously the periodic and anti-periodic conditions, whilst the background field satisfies periodic boundary conditions. All the calculations are performed in Euclidean coordinates.

Resumo em Inglês:

We use CORSIKA+Herwig simulation code to produce ultra-high energy neutrino interactions in the atmosphere. Our aim is to reproduce extensive air showers originated by extragalactic tau-neutrinos. For charged current tau-neutrino interactions in the atmosphere, beside the air shower originated from the neutrino interaction, it is expected that a tau is created and may decay before reaching the ground. That phenomenon makes possible the generation of two related extensive air showers, the so called Double-Bang event. We make an analysis of the main characteristics of Double-Bang events in the atmosphere for mean values of the parameters involved in such phenomenon, like the inelasticity and tau decay length. We discuss what may happen for the "out of the average" cases and conclude that it may be possible to observe this kind of event in ultra-high energy cosmic ray observatories such as Pierre Auger or Telescope Array.

Resumo em Inglês:

This is a review paper concerned with the global consistency of the quantum dynamics of non-commutative systems. Our point of departure is the theory of constrained systems, since it provides a unified description of the classical and quantum dynamics for the models under investigation. We then elaborate on recently reported results concerned with the sufficient conditions for the existence of the Born series and unitarity and turn, afterwards, into analyzing the functional quantization of non-commutative systems. The compatibility between the operator and the functional approaches is established in full generality. The intricacies arising in connection with the explicit computation of path integrals, for the systems under scrutiny, is illustrated by presenting the detailed calculation of the Feynman kernel for the non-commutative two dimensional harmonic oscillator.

Resumo em Inglês:

We obtain through a Matrix Product Ansatz (MPA) the exact solution of the most general N-state spin chain with U(1)N symmetry and nearest neighbour interaction. In the case N = 6 this model contain as a special case the integrable SO(6) spin chain related to the one loop mixing matrix for anomalous dimensions in N = 4 SYM, dual to type IIB string theory in the generalised Lunin-Maldacena backgrounds. This MPA is construct by a map between scalar fields and abstract operators that satisfy an appropriate associative algebra. We analyses the Yang-Baxter equation in the N = 3 sector and the consistence of the algebraic relations among the matrices defining the MPA and find a new class of exactly integrable model unknown up to now.

Resumo em Inglês:

Information collected in the present high resolution study of 104Pd(d,t)103Pd is interpreted within the systematics of the A ~ 100 region. The paper complements data previously presented by the S.Paulo Group, which were taken with the Pelletron-Enge-Spectrograph facility. A one-to-one correspondence to gamma ray results for 103Pd, collected by the Nuclear Data Sheets (NDS), was achieved and at least four open questions were settled. More reliable spectroscopic strengths were extracted in the present study.

Resumo em Inglês:

We define and study the probability current and the Hamiltonian operator for a fully general set of Dirac matrices in a flat spacetime with affine coordinates, by using the Bargmann-Pauli hermitizing matrix. We find that with some weak conditions on the affine coordinates, the current, as well as the spectrum of the Dirac Hamiltonian, thus all of quantum mechanics, are independent of that set. These results allow us to show that the tensor Dirac theory, which transforms the wave function as a spacetime vector and the set of Dirac matrices as a third-order affine tensor, is physically equivalent to the genuine Dirac theory, based on the spinor transformation. The tensor Dirac equation extends immediately to general coordinate systems, thus to non-inertial (e.g. rotating) coordinate systems.

Resumo em Inglês:

Nd16Co72-xRu xC11B boro-carbides have been prepared by arc melting and studied by X-ray diffraction and magnetization measurements. X-ray diffraction results confirm that all the prepared alloys possess the tetragonal 2:14:1 (P4(2)/mmm) hard magnetic phase. The observed decrease of the magnetization and Curie temperature indicate the development of antiferromagnetic spin correlations with the increase of the Ru content. The combined addition of B and C is favorable to the formation and stabilization of the tetragonal phase in these compounds. At lower Ru contents the Curie temperature is higher than in the corresponding Co-based boride in spite of larger cell volumes.

Resumo em Inglês:

In this paper we have tried to investigate of dense plasma-material interaction in a Filippov type plasma focus (90KJ, 25KV, 288µf) facility. Dense plasma focus discharges are known as a remarkable source of hot plasma bunches and fast streams, fast neutrons, hard and soft X-rays, and energetic particles such as ions and electrons. The Aluminum made targets with 20cm in diameter and thickness 5mm, were placed at the central part of plasma focus cathode. These targets were exposed to perpendicular dense high temperature plasma stream incidence. The working gases for these experiments were Argon, Deuterium +Krypton, Helium, and pure Deuterium. We took advantage of changeable targets surface and used SEM technique for analyzing irradiated samples by various working gases. As it shown from SEM pictures and surface profiles, melt layer erosion by melt motion, surface smoothing, and bubble formation were some of different effects caused by diverse working conditions.

Resumo em Inglês:

At first we introduce an action for the string, which leads to a worldsheet that always is curved. For this action we study the Poincaré symmetry and the associated conserved currents. Then, a generalization of the above action, which contains an arbitrary function of the two-dimensional scalar curvature, will be introduced. An extra scalar field enables us to modify these actions to Weyl invariant models.

Resumo em Inglês:

We study the effect of noise in an avascular tumor growth model. The growth mechanism we consider is the Gompertz model. The steady state probability distributions and average population of tumor cells are analyzed within the Fokker-Planck formalism to investigate the importance of additive and multiplicative noise. We consider the effect of correlation on tumor growth for both the case of nonzero and zero correlation time. It is observed that the Gompertz model, driven by correlated noise exhibits a stochastic resonance and phase transition. This behaviour is attributed to multiplicative noise. In the case of nonzero correlation time, it is found that the correlation strength and correlation time have opposite effects on the steady state probability distribution. The Gompertz model simulations are also shown to be in qualitative agreement with another similiar non-bistable system, the logistic model.

Resumo em Inglês:

We describe the experimental apparatus and the methods to achieve Bose-Einstein condensation in 87Rb atoms. Atoms are first laser cooled in a standard double magneto-optical trap setup and then transferred into a QUIC trap. The system is brought to quantum degeneracy selectively removing the hottest atoms from the trap by radio-frequency radiation. We also present the main theoretical aspects of the Bose-Einstein condensation phenomena in atomic gases.

Resumo em Inglês:

The complementary information provided by combined MRI-PET modalities promises to facilitate metabolic investigations of complex physiological processes. We developed a radio frequency (RF) coil array that can operate in close proximity (2-mm radial distance) to a miniaturized PET camera insert for simultaneous PET-MRI of a rat brain at high magnetic fields (4 Tesla). All ferromagnetic components in the PET instrument were replaced with non-ferromagnetic components to minimize susceptibility artefacts in MRI, and optical fibres were used to connect the electronics of the PET camera to the acquisition system located outside the MRI scanner room. A passive electromagnetic shielding was developed to minimize the interference between the PET-electronics and MRI RF coil array. MR images of water phantoms and "ex-vivo" rat brains were collected in two different conditions: with and without PET acquisition. Similarly, PET data was acquired in two different conditions: with and without MRI pulses (RF and gradients). The MR images showed good uniform sensitivity profiles for all cases and 66% decrease in SNR for the shielded case. The PET and MRI datasets demonstrated that the electromagnetic shielding successfully minimizes the RF interference between the instruments, minimizing MRI artefacts and protecting the delicate components of the PET electronics from MRI RF pulses.