Showing papers by "Federal University of São Carlos published in 1993"

Structure of rings in vitreous SiO 2

Abstract: The structure of n-fold rings in vitreous ${\mathrm{SiO}}_{2}$ is investigated using molecular-dynamics configurations. A recently developed interaction potential for ${\mathrm{SiO}}_{2}$ consisting of long-range Coulomb interactions, the effect of electronic polarizability, and three-body covalent forces is used in the molecular-dynamics study of the vitreous state. Results for the statistics of rings and distribution of interatomic distances and bond angles in the rings are presented for the vitreous state. The statistics of rings for the molten state is also discussed.

Distribution of sex chromosome mechanisms in neotropical fish and description of a ZZ/ZW system in Parodon hilarii (Parodontidae)

Abstract: SUMMARYParodon hilarii, a neotropical fish species of the family Parodontidae, presents a well-differentiated ZZ/ZW system, with a W chromosome being the largest in the complement and mostly heterochromatic. A review of the sex chromosome of neotropical fish is presented and some aspects of their differentiation are discussed, with emphasis on the family Parodontidae.

Limnology and management of reservoirs in Brazil

Abstract: In this paper the authors report and discuss limnological information for reservoirs in Brasil including physical, chemical and biological data in order to provide an insight into some basic mechanisms and interrelationships of forcing functions, biological and biogeochemical factors useful for management.

Structural transformation, intermediate-range order, and dynamical behavior of SiO2 glass at high pressures.

Abstract: Pressure-induced structural transformation in ${\mathrm{SiO}}_{2}$ glass is investigated with molecular dynamics. At high densities, the height of the first sharp diffraction peak is considerably diminished, its position changes from 1.6 to 2.2 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$, and a new peak appears at 2.85 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$. At twice the normal density, the Si-O bond length increases, the Si-O coordination changes from 4 to 6, and the O-Si-O band angle changes from 109\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{}. This is a tetrahedral to octahedral transformation, which was reported recently by Meade, Hemley, and Mao [Phys. Rev. Lett. 69, 1387 (1992)]. Results for phonon density of states also reveal significant changes at high pressures.

Langmuir-Blodgett and electrochemical studies of fullerene films

Abstract: Surface pressure-molecular area isotherms of Langmuir films of pure C[sub 60] and C[sub 60]-eicosanoic acid (arachidic acid) mixed films were measured at the air-water interface, and the electrochemical behavior of the Langmuir-Blodgett films on a hydrophobic gold electrode in acetonitrile solutions is described. The formation of highly incompressible monolayer and multilayer films at the air-water interface was reconfirmed and was strongly dependent on the experimental conditions, such as the purity of the fullerene, spreading solvent, and the age and history of the spreading solution. The voltammetric response of Langmuir-Blodgett C[sub 60] films indicates a higher solubility of the reduced species than that observed for thicker films prepared by drop coating. 22 refs., 6 figs.

Dynamic structure factor and vibrational properties of SiO2 glass.

Abstract: Molecular-dynamics simulations are performed to determine dynamic correlations in ${\mathrm{SiO}}_{2}$ glass. The frequency and eigenvectors of vibrational normal modes are obtained by diagonalizing the dynamical matrix. Dynamic structure factors, partial and total vibrational density of states (DOS), and participation ratios are calculated. The neutron-weighted dynamic structure factor, ${\mathit{S}}_{\mathit{n}}$(q,\ensuremath{\omega}), exhibits all the important features observed in the inelastic-neutron-scattering experiments on ${\mathrm{SiO}}_{2}$ glass. As a function of \ensuremath{\omega}, ${\mathit{S}}_{\mathit{n}}$(q,\ensuremath{\omega}) has two regions separated by a gap near 120 meV. The dominant features in ${\mathit{S}}_{\mathit{n}}$(q,\ensuremath{\omega}) are the peaks around 10--20 meV, an almost monotonic decrease between 20 and 100 meV, the gap near 120 meV, and a broad peak between 130 and 160 meV. The dynamic structure factor oscillates with variations in q. The total phonon DOS show two well-delineated bands, a broad band between 5 and 110 meV and a narrow band between 120 and 180 meV. The modes below 100 meV are spatially extended, whereas the high-frequency modes are localized. Calculations of the generalized neutron-weighted effective density of states are compared with neutron-scattering experiments.

Cardio-respiratory responses in two ecologically distinct erythrinids (Hoplias malabaricus and Hoplias lacerdae) exposed to graded environmental hypoxia

Abstract: Ecologically distinct species of Hoplias were studied as to the cardio-respiratory responses to graded hypoxia. Hoplias malabaricus maintained a constant oxygen uptake down to a PiO2 of 20 mmHg. Oxygen uptake declined markedly at lower PiO2 and, concomitantly, cardiac frequency decreased. Concurrent reductions of oxygen uptake and heart rate also occurred in Hoplias lacerdae but at the considerably higher PiO2 of 35 mmHg. These species-specific differences are consistent with the respective habitats: H. malabaricus occurs in stagnant hypoxic water, whereas H. lacerdae inhabits well-oxygenated rivers.

Organization and molecular cytogenetics of a satellite DNA family from Hoplias malabaricus (Pisces, Erythrinidae)

Abstract: The chromosomes of the primitive South American teleost fishHoplias malabaricus have been analyzed by classical cytogenetic (C-, AgNOR-, Hoechst 33258-, and Q-banding) techniques. A highly repetitive DNA family has been cloned and sequenced. It is a tandemly repeated sequence of about 355 bp, yielding an overall base pair composition of 67% AT with long runs of >50% As and 70% Ts. Analysis of sequence variation has allowed the further categorization ofHoplias satellite DNA into two evolutionarily related subfamilies A and B, distinguishable by characteristic insertions and deletions within this 355-bp monomer. Subfamily A satellite is found (in diverged form) at the centromeres of mostH. malabaricus chromosomes. Sequence variants are clustered on specific chromosomal subsets. Subfamily B satellite is highly specific for the paracentromeric heterochromatin on one particular chromosome pair by fluorescencein situ hybridization. These results indicate that theHoplias satellite DNA family has evolved in a concerted manner predominantly via recombination events involving homologous, rather than non-homologous chromosome regions. The clones isolated here may be useful for the molecular, genetic, and cytological analysis of the genusHoplias.

Molecular structure and nucleation in silicate glasses

Abstract: The molecular structures of several silicate glasses which nucleate homogeneously (CaO·SiO2, Na2O·SiO2, Li2O·SiO2, Li2O·2SiO2, BaO·2SiO2 and CaO·Al2O3·2SiO2) as well as those of glasses which only nucleate heterogeneously (PbO·SiO2, Na2O·2SiO2, CaO·MgO·2SiO2, K2O·TiO2·3SiO2 and Na2O·Al2O3·6SiO2) are critically analyzed and compared with the structures of their equilibrium crystalline phases. It is shown that, for the first class of glasses (displaying homogeneous nucleation), both cationic and anionic arrangements in glass and crystal are similar. In some cases, cation coordination requirements lead to the formation of chain segments of high mobility which favor homogeneous nucleation. For the second family of glasses, the structures of glass and crystal differ and only heterogeneous nucleation is observed.

Cultivo em larga escala de organismos planctônicos para alimentação de larvas e alevinos de peixes: I - Algas clorofíceas

Abstract: Three species of chlorophycean algae (Ankistrodesmus gracilis, Scenedesmus bijugus an Chlamydomonas sp.) were cultures at large quantity in both CHU12 nutrient medium and in a less expensive alternative medium, the NPK fertilizer. The results indicated that the growth curve was very similar for all three species when cultured in a CHU12 medium; on the other hand, growing performance at NPK medium fertilizer was very different and A. gracilis and S. bijugus (2.30 and 2.20 x 10(6) cells/ml, respectively) were very similar when using NPK medium fertilizer and different when using CHU nutrient medium (1.40 and 1.15 x 10(6) cells/ml, respectively). Chlamydomonas sp. exhibited a smaller growth response in both CHU12 and NPK nutrient medium.

Dependence on body size of respiratory function in Hoplias malabaricus (Teleostei, Erythrinidae) during graded hypoxia.

Abstract: Oxygen uptake and ventilatory responses to environmental hypoxia were assessed for two groups of Hoplias malabaricus of nearly tenfold different body weights (mean weights, group I = 39 g; group II = 365 g). The main purpose of the study was to evaluate the relationships between body weight and the critical O2 tension (PCO2) for maintenance of normal resting O2 uptake. The smaller specimens had a threefold larger weight-specific O2 uptake compared to that of the larger specimens. Moreover, smaller size coincided with a higher PCO2, i.e., a more limited range for maintenance of O2 uptake during hypoxia. Likewise, at any inspired PO2 the weight-specific gill ventilation was largest for group I. This was most pronounced during severe hypoxia where both tidal volume and respiratory frequency increased markedly. In addition, the oxygen cost of breathing tended to be highest in the smaller individuals. The results open questions as to correlations between development, weight-dependent O2 demands, and tolerance to hypoxia on an intraspecific level.

Fuzzy Reasoning and Fuzzy Petri Nets in Manufacturing Systems Modeling

Abstract: This article presents a net-based structure to model approximate reasoning using fuzzy logic, the fuzzy Petri net model. The knowledge bases to be considered here are assumed to be fuzzy production rules. After a brief introduction of knowledge representation and fuzzy reasoning, we give a new definition of the Fuzzy Petri net model. Next, the basic net structures for complex forms of rules such as rules with conjunction in the antecedent, rules with linguistic quantifiers, and rules with certainty factors are presented. Typical rules sets like parallel rules and conflicting rules are addressed as well. Design techniques to be used when the basic structures are mixed in the context of a large knowledge base are also included. A fuzzy reasoning algorithm is provided. Finally, an application example concerning manufacturing cells modeling is introduced to illustrate the usefulness of the approach proposed.

Preparation of Coprecipitated Ferroelectric Ceramic Powders by Two‐Stage Calcination

Abstract: A coprecipitation method is described for preparing ferroelectric ceramic powders. The process is based on source solution preparation for coprecipitation after previous calcination of the constituent oxides or carbonates. Rhombohedral PZT 53/47 could be obtained by this method after calcination at 850°C. In addition, PLZT 9/65/35 was prepared by the same method.

Monte Carlo simulation of the binary liquid mixture water—methanol

Abstract: Monte Carlo statistical mechanics simulations of water—methanol mixtures were performed in the isothermal—isobaric ensemble (NPT) at T = 298 K and p = 1.0 atm; canonical ensemble (NVT) simulations were performed at this same temperature and experimental densities. Configurational averages were obtained by using Metropolis importance sampling and truncated octahedron box boundary conditions. To calculate the intermolecular energy, the TIP4P and a tree-site model with united atom representation for the methyl group were used for water and methanol molecules respectively. The potential energy surface for water—methanol interaction was calculated using combining rules and the original potential parameters for the pure liquids. Volume contraction and exothermic mixing were obtained in the present calculation, in fair agreement with experimental results. The radial distribution functions obtained show features indicating a large population of hydrogen bonded complexes. The analysis of site—site coordination numbers shows an enhancement of the average number of hydrogen bonded complexes at a methanol composition near 25%. This result agrees with the experimental observation that the water—methanol system has its largest deviation from the ideal mixture behavior at this same composition.

Heat transfer in spouted beds

Abstract: Experiments were carried out in order to analyse the wall-to-bed and fluid-to-particle heat transfer coefficients in spouted Beds. wall-to-bed heat transfer coefficients were determined in cylindrical-conical and conical spouted beds for various gas flow rates, particle sizes and bed heights for spouted beds with and without draft tubes. A new definition for wall-to-bed transfer coefficient was proposed baaed on experimental observations. The heat tranefer area was also studied to ensure that a physically significant fluid-to-particle heat transfer coefficient was achieved.

Impact of Holoshestes heterodon Eigenmann (Pisces: Characidae) on the plankton community of a subtropical reservoir: the importance of predation by Chaoborus larvae

Abstract: We analyzed the effects of planktivorous Holeshestes heterodon Eigenmann (Characidae) predation on the plankton community of a small subtropical reservoir, using four enclosures (volume about 17.5 m3), open to the sediment, established in the littoral zone. Two enclosures were stocked with fish (mean TL 5.7 cm), at a density of about 4–5 fish m−3 (approx. 8 g m−3), whereas two remained fishless. The experiment lasted a little longer than one month. In the fish enclosures, most Crustacea and Chaoborus larvae remained scarce, probably as a result of visually selective fish predation. In both fishless enclosures, Chaoborus larvae became abundant. However, in only one of these did large individuals become relatively numerous; this discrepancy in the demographic structure of the Chaoborus populations between the two fishless enclosures is unexplained. Only in the fishless enclosure without appreciable numbers of large Chaoborus did densities of Crustacea increase greatly. It is suggested that in the enclosure containing large Chaoborus individuals, crustacean populations were prevented from developing due to predation pressure, while the small Chaoborus larvae of the other enclosure could not readily consume these prey. Rotifers were low in abundance in the absence of fish, probably as a consequence of Chaoborus predation. Phytoplankton density increased in all four enclosures, due probably to the lack of water flow. Only in the fishless enclosure with high densities of crustaceans did phytoplankton abundance decrease markedly at the end of the experiment, perhaps because of grazing losses.

Pseudo-diffusion equation and information entropy of squeezed-coherent states

Abstract: As the squeezed-coherent states are labeled by 3-tuple, the momentum, the coordinate and the squeeze parameter, a phase space probability distribution function associated with a generic wavefunction can be introduced. We verify that this probability function is the solution of a partial differential equation, the pseudo-diffusion equation, hence permitting to extend the concept of information entropy, as introduced by Wehrl for the coherent states, to the squeezed-coherent states. It is shown that the entropy functionals can be used as a measure of quantum correlations between the phase space variables, for a given wavefunction; we also present several properties and discuss the use of the entropic inequality as a concept that complements the Heisenberg uncertainty relationship.

The crystal and molecular structure of bis[1,3-bis(diphenylphosphino)propane] dichlororuthenium(II)

Abstract: The title compound, trans-[Ru(dppp)2Cl2], crystallizes in the triclinic space group P 1, with a = 9.529(1), b = 11.071(1), c = 11.936(1) A, α = 71.967(9), β = 72.879(6), σ = 88.703(9)°, V = 1141.1(2) A3 and Z = 1. The structure was solved and refined to a final R = 0.039, for 3126 independently observed reflections with I > 3σ (I). The ruthenium(II) ion is located on a crystallographic centre of symmetry and shows a distorted octahedral coordination with the chloride atoms in an exactly trans configuration.

Proposição de procedimento de detecção sistemática de perturbações oftalmológicas em escolares

Abstract: Proposicao de um procedimento de deteccao sistematica de perturbacoes oftalmologicas em escolares, com participacao do pessoal da escola. A partir de levantamento realizado em escolas estaduais que oferecem ciclo basico, da cidade de Sao Carlos, SP (Brasil), foi proposta a realizacao de teste de acuidade visual. Nove escolas participaram do estudo. Os professores das escolas foram treinados e realizaram os testes de acuidade visual e estrabismo nos seus alunos, de forma padronizada. Das 2.025 criancas testadas, 88,1% apresentaram niveis de acuidade visual maiores que 0,8 e uma prevalencia de estrabismo de 2,17%. Finalizada a aplicacao dos testes, cada escola apresentou propostas para aplicacao sistematica do teste. As propostas tem em comum a realizacao dos testes pelos professores com a supervisao pelos coordenadores do ciclo basico, cabendo a enfermeira assessoria a todos os niveis de atividades do programa.

Situacao epidemiologica da hanseniase e dos seus comunicantes em campinas

Abstract: Leprosy is a highly prevalent, endemic disease in this country. Due to its long evolution, it gives rise to an extremely important social issue. This paper analyses the epidemiologic status of Leprosy in the municipality of Campinas. The epidemiologic framework indicates that control of leprosy communicants in Campinas remains inefficient, showing the need for further studies upon these social actors, important links in the epidemiologic sequence of this disease.