Resumo em Inglês:

The fusion of heavy nuclei at energies spanning the Coulomb barrier involves the coupling of their relative motion to the internal degrees of freedom of the binary system formed by them. The fusion process is thus a realisation of the fundamental problem of surmounting a potential barrier in an environment of many other degrees of freedom. In the nuclear binary system the number, strength, and nature of the coupling interactions can be widely varied by selecting specific projectile-target combinations. Strong coupling interactions result in a distribution of fusion barriers. These strong couplings can often be clearly identified by extracting representations of this fusion barrier distribution from precision measurements of the excitation function. Alternative representations of the fusion barrier distribution can be obtained from scattering experiments, which generally involve less experimental effort. Since they are not sensitive to the fusion barrier distribution at energies above the average fusion barrier, these alternative representations can only reveal coupling interactions with signatures in the low energy part of the distribution, such as coupling to positive Q-value neutron transfer channels.

Resumo em Inglês:

Phenomenology of gluonic excitations and possibilities for searches of exotic mesons at JLab are discussed.

Resumo em Inglês:

In this paper, we introduce the q-deformed and quon algebras formalism. Some applications of these algebraic structures are considered. A possible connection of the quon algebra with composite particle systems is discussed and perspectives on using such mathematical objects in the Bose-Einstein condensation is presented.

Resumo em Inglês:

A general shell model formalism for the nonmesonic weak decay of the hypernuclei has been developed. It involves a partial wave expansion of the emitted nucleon waves, preserves naturally the antisymmetrization between the escaping particles and the residual core, and contains as a particular case the weak lambda-core coupling formalism. The hypernuclei are grouped having in view their A - 1 cores, that is in those with even-even, even-odd and odd-oddcores. It is shown that in all three cases the nuclear structure manifests itself basically through Pauli Principle, and very simple expressions are derived for the neutron and proton induced decays rates, gamman and gammap, which does not involve the spectroscopic factors. For the strangeness-changing weak lambda N ->N N transition potential we use the One-Meson-Exchange Model (OMEM), which comprises the exchange of the complete pseudoscalar and vector meson octets (pi, <FONT FACE=Symbol>h,</FONT>K<FONT FACE=Symbol>, r</FONT>, omega, K*).We evaluate ³H, 4H, 4lambdaHe, 5lambdaHe, 11B, 12lambdaC, 16lambdaO, 17lambdaO, and 28Si hypernuclei, with commonly used parametrization for the OMEM, and compare the results with the available experimental information. The calculated rates gammaNM = gamman + gammap are consistent with the data, but the measurements of gamman/p = gamman/gammap are not well accounted for by the theory. It is suggested that, unless additional degrees of freedom are incorporated, the OMEM parameters should be radically modified.

Resumo em Inglês:

One of the most striking features of dripline nuclei is their very low binding energy. The proximity to threshold implies that many of the standard reactions should take into account the possibility of the nucleus breaking up into the continuum and rearranging itself within the continuum, throughout the reaction process. Whereas for stable nuclei often structure could be factorized out of the reaction model, it is clear that for exotic nuclei, the specific structure features cannot be desentangled. We review a variety of different cases where the coupling to the continuum and between continuum states was shown to be crucial for the understanding of the physical phenomena. Breakup reactions of 8B, for various energies and on a few targets, are discussed. The effect of the continuum on the elastic cross sections as well as transfer and fusion processes is also presented.

Resumo em Inglês:

This paper gives a brief overview of the technical progress that can be achieved with the newly available segmented HPGe detectors. Gamma-ray tracking detectors are a new generation of HPGe detectors which are currently being developed to improve significantly the efficiency and resolving power of the 4pi germanium detectors arrays for high-precision gamma-ray spectroscopy. They consist of highly segmented HPGe detectors associated with fast digital front-end electronics. Through the pulse-shape analysis of the signals it is possible to extract the energy, timing and spatial information on the few interactions a gamma-ray undergoes in the HPGe detector. The tracks of the gamma-rays in the HPGe detector can then be reconstructed in three dimensions based on the Compton scattering formula. Such a detector has been used for the first time during an in-beam experiment. The gamma-decay of the Coulomb excitation of a 56Fe nucleus was measured with the highly segmented MARS prototype positioned at 135 degree. The energy resolution has been improved by a factor of 3 as compared to standard HPGe detectors due to very precise Doppler correction based on knowledge of the gamma-ray track.

Resumo em Inglês:

The results of the MACRO experiment on atmospheric neutrino oscillations are presented and discussed. The data concern different event topologies with average neutrino energies of ~ 4 and ~50 GeV. The Multiple Coulomb Scattering of muons in the MACRO absorbers was used to estimate the neutrino energy of each event of the higher energy sample. The angular distributions, the absolute fluxes and the L/E distribution strongly favour <FONT FACE=Symbol>n m</FONT> <FONT FACE=Symbol>® n t</FONT> oscillations with maximal mixing and deltam² = 0:0025 eV². Results are presented on the searches for astrophysical sources of high energy muon neutrinos, for bursts of electron antineutrinos from stellar gravitational collapses and on indirect searches for WIMPs from the Earth and from the Sun.

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For charged-particle induced reactions occurring in astrophysical scenarios, projectile energies are usually well below the Coulomb barrier of the reacting system. Hence, extremely small cross section reactions pose a difficult task for laboratory measurements. Most commonly, these energy-dependent cross sections are studied by detecting the emitted prompt gamma rays following the de-excitation of the produced compound nucleus. In this work we propose an alternative way for the measurement of the extremely small cross sections of the 25Mg(p,gamma)26Al resonant reaction, namely the use of the Accelerator Mass Spectrometry (AMS) technique.

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At very high energies, the partons in the nuclear wavefunction form a color glass condensate. Since the occupation number of partons in the color glass condensate is large, classical methods can be used to compute multi-particle production in the initial instants of a high energy heavy ion collision. Non-perturbative expressions are derived relating the distributions of produced partons to those of wee partons in the wavefunctions of the colliding nuclei. The time evolution of components of the stress-energy tensor is studied and the impact parameter dependence of elliptic flow is extracted. We discuss the space-time picture that emerges and interpret the RHIC data within this framework.

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The Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA) provides nuclear data services to scientists on a worldwide scale with particular emphasis on developing countries. More than 100 data libraries are made available cost-free by Internet, CD-ROM and other media. These databases are used for practically all areas of nuclear applications as well as basic research. An overview is given of the most important nuclear reaction and nuclear structure databases, such as EXFOR, CINDA, ENDF, NSR, ENSDF, NUDAT, and of selected special purpose libraries such as FENDL, RIPL, RNAL, the IAEA Photonuclear Data Library, and the IAEA charged-particle cross section database for medical radioisotope production. The NDS also coordinates two international nuclear data centre networks and is involved in data development activities (to create new or improve existing data libraries when the available data are inadequate) and in technology transfer to developing countries, e.g. through the installation and support of the mirror web site of the IAEA Nuclear Data Services at IPEN (operational since March 2000) and by organizing nuclear-data related workshops. By encouraging their participation in IAEA Co-ordinated Research Projects and also by compiling their experimental results in databases such as EXFOR, the NDS helps to make developing countries' contributions to nuclear science visible and conveniently available. The web address of the IAEA Nuclear Data Services is <A HREF="http://www-nds.iaea.org/">http://www-nds.iaea.org</A> and the NDS mirror service at IPEN (Brasil) can be accessed at <A HREF="http://www-nds.ipen.br/">http://www-nds.ipen.br/</A>

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Extensive systematizations of theoretical and experimental nuclear densities and of optical potential strengths extracted from heavy-ion elastic scattering data analyses at low and intermediate energies are presented. The energy-dependence of the nuclear potential is accounted for within a model based on the nonlocal nature of the interaction. The systematics indicates that the heavy-ion nuclear potential can be described in a simple global way through a double-folding shape, which basically depends only on the density of nucleons of the partners in the collision. The possibility of extracting information about the nucleon-nucleon interaction from the heavy-ion potential is investigated.

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We have measured probabilities for proton, neutron and pion beams from accelerators to induce temporary or soft errors in a wide range of modern 16 Mb and 64 Mb DRAM memory chips, typical of those used in aircraft electronics. Relations among the cross sections for these particles are deduced. Measurement of alpha particle yields from pions on aluminum, as a surrogate for silicon, indicate that these reaction products are the proximate cause of the charge deposition resulting in errors.

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An algebraic model is developed to calculate the T = 0 and T = 1 ground-state binding energies of N = Z nuclei in the 28-50 shell which is currently the object of many experimental studies.

Resumo em Inglês:

Symmetry energy coefficients of asymmetric nuclear matter generalized are investigated as the inverse of nuclear matter polarizabilities with two different approaches. Firstly a general calculation shows they may depend on the neutron-proton asymmetry itself. The choice of particular prescriptions for the density fluctuations lead to certain isospin (n-p asymmetry) dependences of the polarizabilities. Secondly, with Skyrme type interactions, the static limit of the dynamical polarizability is investigated corresponding to the inverse symmetry energy coefficient which assumes different values at different asymmetries (and densities and temperatures). The symmetry energy coefficient (in the isovector channel) is found to increase as n-p asymmetries increase. The spin symmetry energy coefficient is also briefly investigated.

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A connection betweend discrete, Cartesian and angular quantum variables is obtained and discussed.

Resumo em Inglês:

The nuclear structure of the unbound 11N nucleus has been investigated by the 14N(³He,6He)11N reaction. The energies and widths of the observed states are compared with other measurements. Angular distributions for the first five states are obtained for the first time for this reaction and DWBA analysis confirms the spin assignments for the lowest levels.

Resumo em Inglês:

A summary of the world status on R&D related to the utilization of Accelerator Driven System (ADS) for energy generation and mainly for transmutation of long lived nuclear waste is presented. A proposal to start a TechnicalWorking Group (TWG) in Brazil to prepare a Road Map having as a final goal an experimental facility to utilize an accelerator in basic and applied research; products and services and R&D in energy generation and transmutation are presented.

Resumo em Inglês:

Computed Tomography (CT) refers to the cross-sectional imaging of an object from both transmission or reflection data collected by illuminating the object from many different directions. CT is an imaging technique that has revolutionized the field of medical diagnostics. There are many others applications for CT images, such as, nondestructive evaluation of industrial products and analysis of biological specimens. A mini computerized tomograph was projected, constructed and tested. It operates with a gamma ray source of 241Am (photons of 60 keV and 100 mCi of intensity) and a NaI(Tl) solid state detector. The system features translation and rotation scanning modes, a 100 mm effective field of view, and 1 mm spatial resolution. The preliminary results indicated a resolution between 5 % to 7 % to detect mass attenuation coefficient variations. The total cost of the Mini Computerized Tomograph of UNISO (MTCU) was about US$ 20.000,00.

Resumo em Inglês:

This paper discusses the chronology of prehistoric settlements of the central-south Brazilian coast. A charcoal sample from a coastal shellmound of Rio de Janeiro State was dated by 14C-AMS to 7; 860§ 80 years BP as part of an interdisciplinary project between physicists and archaeologists. This is an unexpected result that reinforces two similar previous early dates for the same region, which were questioned by Brazilian archaeologists because they implied in pulling back by some two thousand years the antiquity consensually accepted for the settlement of that region.

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This paper presents a one step self-calibration procedure, based on the least squares method, to be used in gamma-ray energy measurements. The obtained equation allows a qualitative interpretation of the information provided by an experiment.

Resumo em Inglês:

A LIXI(Light Intensifier X-ray Image) device has been employed in a real-time neutron radiography system. The LIXI is coupled to a video camera and the real-time images can be observed in a TV monitor, and processed in a computer. In order to get the real-time system operational, the neutron radiography facility installed at the IEA-R1m nuclear research reactor of the IPEN-CNEN/SP has been optimized. The most important improvements were the neutron/gamma ratio, the effective energy of the neutron beam, decrease of the scattered radiation at the irradiation position, and the additional shielding of the video camera. Several one-frame as well as computer processed images are presented. The overall Modulation Transfer Function for the real-time system was obtained from the resolution parameter p = 0:44 ± 0:04mm; the system sensitivity, evaluated for a Perspex step wedge, was determined and the average value is 0:70 ± 0:09mm.

Resumo em Inglês:

In this work, tomographic images of the same object have been taken with 25 keV X-rays and thermal neutrons (E=0.025 eV) aiming to demonstrate that thermal neutron tomography in some cases is a complementary technique to the X-ray tomography, such as in the examination of hydrogen-bearing compounds wrapped in a metallic matrix for instance. The capability of the neutron to pass through metallic materials such as lead, stainless steel and aluminium, allows to inspect encapsulated plastic explosives and visualize their inner structure like density variations, voids and alien materials, which are important features for the quality control of the final product. To obtain the images, a 3rd generation tomographic system with a Position Sensitive Detector has been developed. For X-rays this proportional detector was provided with an 8cm long carbon window, and filled with Ar - CH4 under a pressure of 2 atm. The X-ray beam was supplied by an ampoule with a tungsten anode manufactured by IPRJ/UERJ. For neutron detection the carbon window has been replaced by aluminium, and the filling-gas by ³He enriched helium, acting simultaneously as neutron converter and ionization gas. The Argonauta reactor at the Instituto de Engenharia Nuclear / CNEN was used as neutron source and furnishes a thermal neutron flux of 4.5x10(5) n · cm-2 · s-1 at its main channel outlet, where the tomographic system was installed.

Resumo em Inglês:

A special target chamber for the direct production & recoil implantation of radioactive probes for perturbed angular correlation has been constructed and tested. Feasibility studies were made by reproducing the known quadrupole frequencies at 77Br and 111In probes in metallic zinc. Preliminary results were obtained on the lattice site dependence of Cd hyperfine field in Pd2MnSn Heusler alloy with the PAC technique.

Resumo em Inglês:

The study of the so called exotic nuclei constitutes an important field of research in nuclear physics. The possibility of producing secondary beams of unstable nuclei(RIB) allows the investigation of nuclei at extreme conditions as low binding energies, high angular momentum and isospin. More laboratories are going through the process of re-direction of their experimental effort towards this activity. The nuclear physics community in Brazil has enthusiastically decided to join this endeavor to provide the Pelletron/LINAC complex with two superconducting solenoids which will permit the production of secondary beams of radioactive nuclei. A description of this facility and project RIBRAS follows.

Resumo em Inglês:

In the present work we discuss the effects of the medium polarization on the nuclear pairing, in the context of the relativistic Hartree-Fock-Bogoliubov (HFB) approximation. The medium polarization effects on the scalar and vector masses, as well on the pairing, as a function of Fermi momentum, are shown for several values of the coupling constants scaled by a parameter x. We find have obtained that the nuclear pairing is strongly affected by the medium polarization.

Resumo em Inglês:

The frame dependence of the pair-term contribution to the electromagnetic form factor of the pion is studied within the Light Front approach. A symmetric ansatz for the pion Bethe-Salpeter amplitude with a pseudo scalar coupling of the constituent to the pion field is used. In this model, the pair term vanishes for the Drell-Yan condition, while it is dominant for momentum transfer along the light-front direction.

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The ground state masses and binding energies of the nucleon, lambda0, lambdac<FONT FACE=Symbol>+</FONT> , lambdab0 are studied within a constituent quark QCD-inspired light-front model. The light-front Faddeev equations for the Qqq composite spin 1/2 baryons, are derived and solved numerically. The experimental data for the masses are qualitatively described by a flavor independent effective interaction.

Resumo em Inglês:

Transport equations for composite nucleons and deconfined quarks in quark-nuclear matter (QNM) are derived. QNM is a many-body system containing hadrons and deconfined quarks. The starting point is a microscopic quark-meson coupling (QMC) Hamiltonian with a density-dependent quark-quark interaction. An effective quark-hadron Hamiltonian containing canonical hadron and quark field operators is constructed using a mapping procedure. For high densities, the effective Hamiltonian contains interactions that lead to quark decon- finement. Transport equations of the Ueling-Ullenbeck-Vlasov type for quarks and nucleons are obtained using standard many-body techniques with the effective quark-hadron Hamiltonian.

Resumo em Inglês:

We study the Borel sum rule for the tensor amplitude of the processes J/<FONT FACE=Symbol>y p ®</FONT> <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >D*,<IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif"> D, <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >*D* and <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >D*. We also evaluate the cross sections as a function of <IMG SRC="/img/revistas/bjp/v33n2/a30img02.gif" >. We find that our results are smaller than the J/<FONT FACE=Symbol>y p ®</FONT> charmed mesons cross sections obtained with models based on meson exchange, but are close to those obtained with quark exchange models.

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The effect of breakup in the fusion cross section in terms of suppression versus enhancement, discussed in a conflicting way in the literature, is addressed. Data and theoretical predictions available in the literature are compared. Excitation functions of the sub- and near-barrier fusion cross-sections for a wide variety of light and heavy systems are presented and interpreted. We have measured fusion excitation functions and breakup correlation functions for the medium weight systems 6Li + 59Co and 7Li + 59Co. These measurements help to establish the influence of the projectile breakup on the fusion process at near-barrier energies and contribute to the determination of how the mass of the target affects the breakup role. The results indicate a light fusion enhancement at sub-barrier energies and a geometry dominated cross section at barrier energies.

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We present results of the study of the influence of the break-up process on the fusion, scattering and reaction cross sections, at near barrier energies. Most of the discussed reactions and scattering mechanisms are induced by the stable weakly bound nuclei 6,7Li and 9Be, although comparisons with reactions induced by strongly bound nuclei are also made. We give a picture of the break-up and fusion mechanisms at energies above the Coulomb barrier.

Resumo em Inglês:

Abrasion-ablation models and the empirical EPAX parametrization of projectile fragmentation are described. Their cross section predictions are compared to recent data of the fragmentation of secondary beams of neutron-rich, unstable 19,20,21O isotopes at beam energies near 600 MeV/nucleon as well as data for stable 17,18O beams.

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Using the Wigner-Heisenberg algebra for bosonic systems in connection with oscillators we find a new representation for the Virasoro algebra.

Resumo em Inglês:

In this work a dc discharge with a copper hollow cathode in argon used for deposition applications is investigated using atomic emission spectroscopy. Typical discharge parameters during our investigation are pressures between 80 and 200 Pa and current densities up to 7 mA cm-2. The radial light intensity profiles of some selected copper and argon lines were measured. An analysis of these profiles gives insigths into the excitation rates of the argon filling gas and the sputtered metal atoms as well as into the radial dimension of the negative glow. The different excitation mechanisms lead to a sharp change of the radial light intensity profiles emitted by many copper spectral lines, which indicates the transition region between the cathode fall and the negative glow. The length of the cathode fall was observed to be very insensitive to all the macroscopic discharge parameters. A nearly constant value was found for the cathode fall length, which corresponds to about 22% of the cathode radius.

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Variation after Projection (VAP) calculations in conjunction with Hartree Bogoliubov (HB) ansatz have been carried out for 124-132Ce mass chain. In this framework, the yrast spectra, B(E2) transition probabilities and occupation numbers for various shell model orbits have been obtained. The observed decrease in deformation in going from 124Ce to 132Ce is seen to arise due to a slow decrease in the occupation of 1g7/2 proton orbit and a systematic increase in the occupations of 2d5/2, 1g7/2 and 1h11/2 neutron orbits. Besides this, the experimental low-lying yrast spectra and B(E2) transition probabilities are reproduced with reasonable accuracy by using PQOH interaction.

Resumo em Inglês:

In this paper, the analog of Maxwell electromagnetism for hydrodynamic turbulence, the metafluid dynamics, is extended in order to reformulate the metafluid dynamics as a gauge field theory. That analogy opens up the possibility to investigate this theory as a constrained system. Having this possibility in mind, we propose a Lagrangian to describe this new theory of turbulence and, subsequently, analyze it from the symplectic point of view. From this analysis, a hidden gauge symmetry is revealed, providing a clear interpretation and meaning of the physics behind the metafluid theory. Also, the geometrical interpretation to the gauge symmetries is discussed.

Resumo em Inglês:

We describe a new system for laser cooling and trapping of neutral Calcium atoms employing the ¹S0 -¹ P1 resonant transition at 423 nm. An on-axis magneto-optical trap (MOT) is loaded from a Zeeman decelerated atomic beam. When a single laser is used, in order to avoid perturbation of the trap by the deceleration laser beam, this one has been tightly focused near the MOT center, with a waist size much smaller than the atomic cloud. In order to test the efficiency of this novel technique, we have then employed a second, independent decelerating laser, with a profile mode matched to the atomic beam. For an oven temperature of 580±C this system can load 1.2 (2) x 10(7) atoms in 16 (1) ms. By the spatial extension of the atomic cloud the one dimension rms velocity was estimated to be 136 (12) cm/s, corresponding to a temperature of 9 (2) mK. The variation of the number of trapped atoms as a function of laser detuning and intensity, trap magnetic field gradient and oven temperature is analyzed. Spatial structures of the trapped atoms, like stable rings created by vortex forces, have been observed. This is the first time that these structures, already observed in alkali-metal elements, are reported in MOTs of alkaline-earth elements.

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Electrical networks provide a natural model to study transport processes such us dielectric breakdown and metal insulator transition in disordered inhomogeneous conductors. We present a calculation for current distribution on an infinite hyper-cubic network due to an external applied current. This is used to compute, analytically, the redistribution of current due to variations in the conductance of a finite number of elements of the network.

Resumo em Inglês:

Complex conductance, sigma*(f) = <FONT FACE=Symbol>s¢</FONT>(f)+isigma"(f), measurements of polyaniline/carnauba wax composites were carried out at room temperature in samples containing different amounts of PAni. While sigma"(f) ever grows as a function of the frequency f; <FONT FACE=Symbol>s¢</FONT>(f) was observed to vary as f n(n <FONT FACE=Symbol>»</FONT> 1) in the high frequency domain, and to be frequency-independent for lower frequencies. This is the quasi-universal behavior characteristic of conduction in a disordered medium. Superposed on this, another signal was observed to occur, and the whole impedance response was then analysed in an Argand Diagram, disclosing an electrode process in series with the bulk one. An equivalent conductance expression was used to explain such electrical behavior, in which the bulk properties of the composite were represented through the Random Free Energy Barrier model, while the composite-electrode interface by a simple parallel combination of a capacitor and a resistor. From the theoretical fittings it was concluded that the increase of PAni concentration acts in the sense of increasing not only the sample conductance, but also the bulk capacitance. The separation of the bulk and the interface contributions was then achieved.

Resumo em Inglês:

We have investigated the photovoltaic properties of polymer devices based on a blend of two polymers, (poly(3-(2'-methoxy-5'-octylphenyl) thiophene) (POMeOPT) and poly(2,5,2',5'-tetrahexyloxy-7,8'-dicyanodi- p-phenylenevinylene) (CN-PPV), where photo induced charge transfer takes place at the interfaces formed by the interpenetrating network of the donor and the acceptor. The polymer blend films resulting from the spin coating were phase separated and the photo response of the devices depended on the morphology of the segregation. We have studied different blend ratios by photoluminescence quenching, scanning force microscopy and photovoltaic measurements. External quantum efficiencies of 4.5% at 500nm were achieved for the less segregated polymer blend.

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The Independent Event Model (IEVM) is used to analyze collision processes for systems with three and four electrons, in situations where up to three active electrons are involved and dynamical correlation effects play a major role. The model is applied to single electron loss and loss-ionization processes. All the possible ionization mechanisms for both collision partners in each exit channel are considered, including antiscreening, which, in the IEVM, can be taken into account in a consistent way along all the other ones, keeping unitarity. As a casestudy, the IEVM is applied to the analysis of the single loss of He+, Li+, and Li2+ ions by He atoms with the simultaneous single and double ionization of the target. We present plots of the cross sections of single electron loss accompanied or not by the ionization of the target as functions of the projectile energy. The calculations describe well the experimental energy dependence and the high-velocity absolute values for the cross sections.

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We investigate the electronic characteristics and the absorption spectra of poly(3-octylthiophene), POT, films grown by electrochemical methods onto Au substrates. We discuss the results considering the morphological factor. POT films thickness can be controlled by current density in the electropolymerization process. The film roughness depends on the thickness, being about 12% of film thickness. The samples for electrical measurements were made in sandwich structure, Au/POT/metal (metal: Ni, Al). Analyzing current-voltage data we were able to estimate the positive charge carrier mobility (5 x 10-4 cm² V-1 s-1) and the potential barrier height in the metal/polymer interfaces (0.1 eV for Au/POT and Ni/POT and 0.85 eV for Al/POT).

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To calculate aerothermodynamic characteristics of the Brazilian satellite SARA (Portuguese abbreviation: SAtélite de Reentrada Atmosférica) during its re-entry the Direct Simulation Monte Carlo method is applied. The numerical calculations were carried out in a wide range of the gas rarefaction beginning from the free molecular regime up to the hydrodynamic one for three values of the Mach number equal to 5, 10 and 20. The following numerical data are presented in the paper: drag force of the satellite, distributions of the heat flux, pressure coefficient and skin friction coefficient over the satellite surface, the density and temperature distributions in the front of the satellite and streamlines in the gas around the satellite. To study the influence of the satellite temperature upon these characteristics some calculations were carried out for different values of the satellite temperature.

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We study the electronic properties (density of states, conductivity and thermopower) of some nearly-freeelectron systems: the liquid alkali metals and two liquid alloys, Li-Na and Na-K. The study has been performed within the self-consistent second order Renormalized Propagator Perturbation Expansion (RPE) for the self-energy. The input ionic pseudopotentials and static correlation functions are derived from the neutral pseudoatom method and the modified hypernetted chain theory of liquids, respectively. Reasonable agreement with experiment is found for Na, K, Rb and Na-K, whereas for Li and Cs and Li-Na the agreement is less satisfactory.

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Particle-in-cell (PIC) methods allow the study of plasma behavior by computing the trajectories of finite-size particles under the action of external and self-consistent electric and magnetic fields defined in a grid of points. In this work, the Finite Element Method (FEM) is used in order to obtain the self-consistent fields. An electrostatic PIC-FEM computational code for simulation of one-dimensional (1D) and two-dimensional (2D) plasmas was developed based on two available and independent codes: the first one a 1D PIC code that uses the Finite Difference Method and the other a FEM code developed at the Instituto de Estudos Avancados (IEAv). The Poisson equation is solved and periodic boundary conditions are used. The ion background that neutralizes the total plasma charge is kept fixed and uniformly distributed in the domain of study. The code is tested by studying the fluctuations of the plasma in thermal equilibrium. In thermal equilibrium a plasma sustain fluctuations of various collective modes of electrostatic oscillations, whose spectral distribution can be analytically obtained by using the fluctuation-dissipation theorem and the Kramers-Kronig relation. In both 1D and 2D cases, there are excellent agreement between the spectral distribution curves predicted theoretically and those obtained by simulation for finite size particles and long wavelengths.