Showing papers by "State University of Campinas published in 1974"

On the Structure of Feasible Computation

Abstract: During the last four years research on the lower level computational complexity has yielded a rich set of interesting results which have revealed deep and unexpected connections between various problems and thus brought new unity to this area of computer science. This work has also yielded new techniques and insights which are likely to have further applications, and it has identified some very central problems in the quantitative theory of computing. The purpose of this paper is to give the reader an overview of these developments, an insight into some of these results and applications, as well as an appreciation of the unity and structure which has emerged in this area of research.

Electron focusing and Fermi surface diameter

Abstract: We perform a simple model calculation of the effects of electron focusing on the transport properties of a semiinfinite metallic slab in the presence of a magnetic field. We consider, in particular, the case in which current is fed into the slab through two superconducting strips, with the field applied parallel to the strips. A thin resistive layer is assumed to exist on the surface of the metal. We treat the cases of short and long mean free paths compared with the separation of the leads. For the latter case we derive an integral equation relating the normally flowing current to the potential at the surface. This equation is used to study the magnetoresistance for three models of the Fermi surface: a free-electron-like surface, a compensated free-electron, free-hole-like surface, and a compensated surface composed of three free-electron-like sheets and one free-hole-like sheet. This latter model is topologically equivalent to the Bi case. The results of the calculation agree qualitatively with the experimental results for fields of the order of and larger than the focusing field.

Light scattering from a fermi liquid

Abstract: Light scattering from a Fermi liquid is considered. The generalized self-consistent field method is introduced to calculate the scattering spectra. The cross-section is related to the fluctuation in the Landau quasi-particle density operator ϱ. In the presence of a constant magnetic field the equation of motion for ϱ ink-space is obtained by introducing an appropriate transformation. The connection with the Boltzmann transport equation is shown. A brief application to the study of Raman scattering by magnetoplasma waves is given.

Multiple Scattering of X-Rays and Neutrons. I. A Recurrence Formula for the Taylor Series Expansion in the Calculation of Intensities

Abstract: This is the first article of a series dealing with experimental and theoretical work on the multiple scattering of X-rays and neutrons with emphasis on their application to the study of crystal defects, which is a rather new use1) of a known phenomenon.2) The exact intensity solution for a crystal plate1) is too complicated when more than 3 beams are simultaneously diffracted by the crystal. Taylor series expansion limited to the first three orders1,3) have been calculated, but the errors due to the approximation were not assessed and the use of higher order terms involves exceedingly complicated expressions. In this paper a general recurrence formula for the succesive terms of the Taylor series is presented. Thus, a rapid calculation of any number of terms is now possible.

Polaron effects in resonant Raman scattering

Abstract: Loudon's resonant Raman scattering theory is reconsidered by including polaron effects in the intermediate electron states. The Frohlich Hamiltonian is used to derive the polaron propagators. Numerical calculations were carried out for CdS which show that polaron effects produce a large enhancement of the scattered intensity, improving the agreement between theoretical and experimental results.

Glioblastoma multiforme of the medulla oblangata.

Abstract: A case of glioblastoma multiforme of themedulla oblongata in a 13-year-old girl is reported. Clinical features included two-month evolution, involvement of cranial nerves, tetraplegia and sudden respiratory arrest. Anatomically, a necrotizing glioblastoma multiforme involving the lower half of the medulla and the neighboring cervical cord was found. 18 examples of primary glioblastoma of theoblongata were collected from the literature, but it is suggested that several others are probably included, though not emphasized, in the numerous published series of brain stem gliomas.

Extended de launay model study of lattice dynamics of alkali metals

Abstract: The original model of de Launay has been extended to consider interionic interactions out to fourth neighbours. The present formalism has been applied to study lattice dynamics of four alkali metals viz sodium, potassium, lithium and rubidium. The phonon dispersion curves along the principal symmetry directions, frequency versus frequency distribution function as well as lattice heat capacities are calculated and compared to experimental results. An excellent agreement has been obtained between the theoretical and experimental results for all the four metals studied here.

Generalized transport equation

Abstract: A transport equation for the density operator of the Landau quasiparticle in the presence of a constant magnetic field is derived using the generalized self-consistent field (GSCF) method. An appropriate matrix representation in $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space is introduced. The resulting transport equation for the Landau one-quasiparticle density matrix is gauge invariant and not restricted to the long-wavelength limit. In the long-wavelength limit the GSCF transport equation becomes Silin's phenomenological transport equation. The role of exchange and correlation is discussed. It is shown that to a good degree of approximation, the quasiparticle velocity can be replaced by the bare particle velocity, and the Lorentz-type term involving the fluctuation of the self-consistent-field potential can be neglected.

Pion inclusive distribution at cosmic-ray energies and comparison with ISR data

Abstract: We present the inclusive spectra for π0-mesons constructed from the data obtained by Brasil-Japan emulsion chamber experiment with Câmara 15 (40 m2), exposed at Mount Chacaltaya, Bolivia (5220 m, 550 g/cm2), in 1969–70 covering the energy range 15 TeV

Multiple Scattering of X-Rays and Neutrons. II. Neutron Multiple Scattering by an Aluminum Single Crystal

Abstract: Some experiences of multiple diffraction of neutrons by an aluminum crystal are described in this paper. The experimental conditions needed to assure that the results are treatable by the analytical methods developed earlier,1,2) are discussed. It was found that the Soller collimators are not adequate in this technique, as they do not limit the vertical divergence of the incident beam; a new type of collimator, described in the text, had a notable result in the peak resolution. It is seen that the simultaneous differential equations2) cease to be valid, as expected, when the crystal approaches perfection, that is, in this context, when the mosaic angular spread η is lower than about 0.01°; then, the problem has to be treated dynamically.

Dynamics of Electrons in Heavily Doped GaAs

Abstract: Spontaneous emission measurements in GaAs junction lasers are interpreted assuming long thermalization and recombination times of electrons injected into the p region of the diode. Experimental results qualitatively agree with calculations based on this model.

Determination of soil properties from standard penetration test complemented by torque measurement (SPT-T)

Abstract: The major problem on geotechnical work is to ensure that no settlements occur during the life cycle of the construction. This involves proper design of foundations and their bearing capacity. The Brazilian standard for design and execution of foundations, ABNT (2010) NBR 6122 imposes the utilization of field tests when designing building foundations. The Standard Penetration Test, SPT, ABNT (2001) NBR 6484, is still the most common in-situ test for those purposes. Ranzini (1988) suggested supplementing the conventional SPT with the measurement of the torque (SPT-T) required to turn the split spoon after driving, in order to provide a 'static' component to a 'dynamic' test. The adhesion between the soil and the sampler, obtained by the torque measurement, could be used to calculate the lateral skin friction of piles. This paper describes the SPT-T procedure including both a supplementary equipment and practical aspects. Also it presents an accurate torque measurement, a prediction method to calculate the bearing capacity of piles used in building foundations using the SPT-T test and a comparison between the estimated bearing capacities of building foundations with instrumented load tests in order to validate the method.

Neuronal ceroid-lipofuscinosis, a type of amaurotic family idiocy: clinical and pathological study of four cases

Abstract: Neuronal ceroid-lipofuscinosis (NCL) is a recent term, proposed for acurate designation of the late-onset types of Amaurotic Family Idiocy (AFI). Histopathology shows ubiquitous intraneuronal accumulation of lipopigments, being the most important factor for characterization of the entity at present time. Biochemical changes and pathogenesis are obscure. NCL is in contrast to the infantile type of AFI (Tay-Sachs disease), in which intraneuronal accumulation of gangliosides (sphingolipids) is due to the well known deficiency of a lysosomal enzyme. The authors report on four cases of NCL, two brothers of the late infantile (Jansky-Bielschowsky) type and a brother and a sister of the juvenile (Spielmeyer-Sjogren) type. One autopsy and three cortical biopsies revealed moderate to severe distention of the neurons by lipopigment, with nerve cell loss, gliosis and cerebral atrophy. Lipopigment was also increased in liver, heart and spleen. The patients were the first in Brazilian literature in whom the storage material was identified as lipopigment by histochemical methods. A brief summary of the clinical features of NCL is presented, and relevant problems are discussed, concerning interpretation of the nature of the storage material, and significance of the disease for gerontological research.

A Comparative study of solidification of Al-Cu alloy under flow of cylindrical radial heat and the unidirectional vertically

Abstract: In spite of technological importance of solidification of metallic alloys under radial heat flow, relatively few studies have been carried out in this area. In this work the solidification of Al 4.5 wt% Cu cylinders against a steel massive mold is analyzed and compared with unidirectional solidification against a cooled mold. Initially temperature variations at different positions in the casting and in the mold were measured during solidification using a data acquisition system. These temperature variations were introduced in a numerical method in order to determine the variation of heat transfer coefficient at metal/mold interface by inverse method. The primary and secondary dendrite arm spacing variations were measured through optical microscopy. Comparisons carried out between experimental and numerical data showed that the numerical method describes well the solidification processes under radial heat flux.