Showing papers by "Federal University of São Carlos published in 1998"
TL;DR: In this article, the authors construct a model of ac impedance response to blocked linear diffusion that has a sloped low frequency region in the impedance plot, which is equivalent to solving Fick's law with a boundary condition that allows us to set an arbitrary impedance response at low frequencies.
377 citations
TL;DR: In this article, the authors studied the entanglement process in terms of reduced density linear entropy for the $N$-atom Jaynes-Cummings model and found a faster increase in decoherence for chaotic initial conditions as compared to regular ones, which have an oscillatory increase.
Abstract: Manifestation of chaotic behavior is found in an intrinsically quantum property. The entanglement process, quantitatively expressed in terms of the reduced density linear entropy, is studied for the $N$-atom Jaynes-Cummings model. For a given energy, initial conditions are prepared as minimum uncertainty wave packets centered at regular and chaotic regions of the classical phase space. We find for short times a faster increase in decoherence for the chaotic initial conditions as compared to regular ones, which have oscillatory increase.
167 citations
TL;DR: In this article, a comparative study of structural and aerodynamic properties of cellular ceramics prepared by two different techniques: the ceramic replication of an organic substrate and the gelcasting of foams.
Abstract: This work presents a comparative study of structural and aerodynamic properties of cellular ceramics prepared by two different techniques: the ceramic replication of an organic substrate and the gelcasting of foams. Permeability constants calculated from Ergun's equation were related to their apparent porosity and pore size. The technique of gelcasting of foams yielded structures as porous as the replication technique does, but with smaller pores and a fully densified strut. This type of structure ensures a higher mechanical strength without a significant decrease in the permeability.
140 citations
TL;DR: Experiments showed that S. fuscus strongly influences the algal community in its territories, keeping it in an early succession stage and preventing dominance by Jania spp.
135 citations
TL;DR: A series of Ru(II)(1,4-bis(diphenylphosphino)butane)(L)2 complexes were synthesized from [RuCl2(dppb) l2 (μ-dPPb) or RuCl2 (dppB)- (PPh3); dppb = Ph2P(CH2)4PPH2, l2 = NH3, pyridine (py), 4-aminopyridine, 4-NH2py), etc..
125 citations
TL;DR: In this article, the eigenvalue problem for the transfer matrix of the classical Covering Hubbard model within the algebraic Bethe ansatz framework is solved. But the fundamental commutation rules exhibit a hidden 6-vertex symmetry which plays a crucial role in the whole algebraic construction.
114 citations
TL;DR: In this article, the phase diagram of the spin-3/2 Blume-Capel model in two dimensions is explored by conventional finite-size scaling, conformal invariance and Monte Carlo simulations.
Abstract: The phase diagram of the spin-3/2 Blume-Capel model in two dimensions is explored by conventional finite-size scaling, conformal invariance and Monte Carlo simulations. The model in its $\tau$-continuum Hamiltonian version is also considered and compared with others spin-3/2 quantum chains. Our results indicate that differently from the standard spin-1 Blume-Capel model there is no multicritical point along the order-disorder transition line. This is in qualitative agreement with mean field prediction but in disagreement with previous approximate renormalization group calculations. We also presented new results for the spin-1 Blume-Capel model.
105 citations
TL;DR: In this article, a straightforward combustion synthesis technique was described to prepare submicron Al2TiO5 powders, using the corresponding metal precursors-urea mixtures, at low temperature and short reaction times.
Abstract: Initial interest in aluminium titanate was due to its low thermal expansion coefficient and high thermal shock resistance, but further research was soon discouraged following the discovery of the expansion anisotropy and the instability of the compound over a specific range of temperatures. The development of a suitable active precursor powder could provide a possible solution to the fabrication difficulties (microcracking and decomposition). The scarce available thermodynamic data for the formation of Al2TiO5from its constituent oxides indicate that the reaction is endothermic and only possible at high temperature because of the titanate being entropy stabilised. The present work describes a straightforward combustion synthesis technique to prepare submicron Al2TiO5 powders, using the corresponding metal precursors-urea mixtures, at low temperature and short reaction times. A thermodynamic interpretation of the reaction is provided and the characteristics of the powder produced, like morphology, specific surface area and grain size, are discussed. The thermal behaviour of the combustion powder is compared with that of Al2TiO5 produced via the conventional ceramic solid state route.
85 citations
TL;DR: In this article, the effect of the crystallization tem- perature (Tcr) on the phase transitions presented by P(VDF/TrFE) copolymers cast from dimethylformamide (DMF) solution with molar ratios 60/40, 70/30, and 80/20 was investigated.
Abstract: A systematic study was carried out on the effect of the crystallization tem- perature (Tcr), on the phase transitions presented by P(VDF/TrFE) copolymers cast from dimethylformamide (DMF) solution with molar ratios 60/40, 70/30, and 80/20. The results obtained by differential scanning calorimetry (DSC) showed that two- phase transitions are observed only when the copolymer crystallizes above a certain temperature To, and that the temperatures at which these transitions occur are reduced slightly with Tcr increase. It also was observed that when Tcr increases, the intensity of the endotherm corresponding to the lowest temperature transition is increased, whereas the one corresponding to the highest temperature transition is reduced. In order to explain these phenomena, the existence of two ferroelectric and two paraelectric phases is suggested. The conformational differences between like phases occur due to the distinct origin of each one: the best organized phase crystallizes directly from solution, whereas the least organized is the result of a solid phase transition. Wide angle x-ray diffusion (WAXD) diffractograms corroborate this hypothesis. Phase diagrams for samples crystallized below and above To have been proposed. q 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 403-414, 1998
83 citations
TL;DR: Seasonal variability in grazing rates and food-processing characters were assessed for three abundant fishes in a tropical rocky shore: the damselfish Stegastes fuscus, the parrotfish Sparisoma atomarium and the surgeonfish Acanthurus bahianus.
Abstract: Seasonal variability in grazing rates and food-processing characters were assessed for three abundant fishes in a tropical rocky shore: the damselfish Stegastes fuscus, the parrotfish Sparisoma atomarium, and the surgeonfish Acanthurus bahianus. Significant differences were found in grazing rates among hour of day and seasons, and in food-processing characters among seasons for the three fishes. Grazing rates for S. atomarium and A. bahianus peaked at 1300 and 1400 hours for S. fuscus. Three main periods of different intensity in bite rates, low, intermediate and intense, were identified for all fishes. As expected, total bite rates, ingestion rates and gut fullness were highest in A. bahianus, the largest species studied, followed by S. atomarium and S. fuscus. S. atomarium with fused jaw teeth, holds the highest bite size and S. fuscus the lowest one. Gut turnover was high for S. fuscus and similar for S. atomarium and A. bahianus. Grazing rates and food-processing characters seem to vary between seasons not only due to changes in temperature, but also affected by other factors. Fishes employ different food-processing mechanisms and bear some differences in food-processing characters to achieve optimal energetic supplies from a poor nutrient food resource.
80 citations
TL;DR: A simple and effective heuristic to solve the problem of packing the maximum number of rectangles of sizes (l,w) and (w,l) into a larger rectangle (L,W) without overlapping is presented.
Abstract: In this paper we present a simple and effective heuristic to solve the problem of packing the maximum number of rectangles of sizesOl; wU andOw; lU into a larger rectangleOL; WU without overlapping. This problem appears in the loading of identical boxes on pallets, namely the manufacturer’s pallet loading (MPL), as well as in package design and truck or rail car loading. Although apparently easy to be optimally solved, the MPL is claimed to be NP-complete and several authors have proposed approximate methods to deal with it. The procedure described in the present paper can be seen as a refinement of Bischoff and Dowsland’s heuristic and can easily be implemented on a microcomputer. Using moderate computational resources, the procedure was able to find the optimal solution of 99.9% of more than 20 000 examples analysed.
TL;DR: The synthetic racemic mixture of methyl 2,6,10‐trimethyltridecanoate, a component of the male produced pheromone of Euschistus heros (F.) (Heteroptera, Pentatomidae), was attractive to pentatomid species in a field test, using homemade phersomone trap designs.
Abstract: .The synthetic racemic mixture of methyl 2,6,10-trimethyltridecanoate, a component of the male produced pheromone of Euschistus heros (F.) (Heteroptera, Pentatomidae), was attractive to pentatomid species in a field test, using homemade pheromone trap designs. The pentatomid Piezodorus guildinii was caught in high numbers in field traps, during two field experiments, indicating a consistent response of this species to the E. heros pheromone. A correlation was found between the range of insects caught in the pheromone-baited traps and a random sampling method. The synthetic stereoisomeric mixture of methyl 2,6,10-trimethyldodecanoate, a minor component of E. heros pheromone, was also field tested and caught no pentatomids. Egg parasitoids were caught in traps baited with E. heros pheromone, indicating that this pheromone can be exploited as a kairomone. A synchrony in the periodicity of trap catch, between the egg parasitoids and their host, was also recorded.
TL;DR: In this article, the authors studied the dynamical squeezing of the photon-added coherent state (PACS) due to a time dependence of the frequency of the electromagnetic field oscillator in a cavity or a vibrational frequency of an ion inside an electromagnetic trap.
Abstract: We study the dynamical squeezing of the photon-added coherent state ~PACS! due to a time dependence of the frequency of the electromagnetic field oscillator in a cavity or a vibrational frequency of an ion inside an electromagnetic trap. Explicit expressions for the time dependence of various functions characterizing the quantum state, such as the photon distribution, the Wigner function, the mean values and variances of the quadrature components and of the photon number, show that the dynamically squeezed PACS possesses a larger squeezing coefficient than the usual squeezed states. The dynamical squeezing is accompanied by a change of the sub-Poissonian photon statistics to the super-Poissonian one. @S1050-2947~98!07410-1#
TL;DR: A rapid, precise and low cost spectrophotometric method is proposed for the determination of methyldopa and dopamine in pharmaceutical formulations and the results obtained are in close agreement with those obtained using a Pharmacopoeia procedure and also with the label values.
TL;DR: In this article, an integrable loop model and its connection with a supersymmetric spin chain were investigated and the Bethe ansatz solution allowed us to study some properties of the ground state.
Abstract: In this paper, we investigate an integrable loop model and its connection with a supersymmetric spin chain. The Bethe ansatz solution allows us to study some properties of the ground state. When the loop fugacity $q$ lies in the physical regime, we conjecture that the central charge is $c\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}q\ensuremath{-}1$ for $q$ integer $l2$. Low-lying excitations are examined, supporting a superdiffusive behavior for $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$. We argue that these systems are interesting examples of integrable lattice models realizing $c\ensuremath{\le}0$ conformal field theories.
TL;DR: Neotropical fishes present a high chromosome diversity showing a wide diploid number variation range, including different levels of ploidies, sex chromosomes, chromosome supernumeraries, and several cases of polymorphisms, related particularly to heterochromatin and NOR sites.
Abstract: Neotropical fishes present a high chromosome diversity showing a wide diploid number variation range, including different levels of ploidies, sex chromosomes, chromosome supernumeraries, and several cases of polymorphisms, related particularly to heterochromatin and NOR sites. Two main general trends of chromosome diversification can be observed among neotropical fishes. First, several fish groups show a chromosome evolution relatively divergent from the point of view of the karyotypic macrostructure. Sister species show conspicuous differences in karyotype structure and most often also in the number of chromosomes. On the other hand, there are fish groups in which chromosome evolution has been shown to be less divergent, and in this case whole families or even groups of families may share a common karyotype structure and equal number of chromosomes. Several fish groups appear conservative also with respect to the NOR bearing chromosomes. In this case, NOR chromosome location is invariable among ...
TL;DR: In this article, the ground state of N-state quantum chains with free boundary conditions or with non-diagonal boundary terms at one or both ends is obtained using matrix product ansatz.
Abstract: Stationary probability distributions for stochastic processes on linear chains with closed or open ends are obtained using the matrix product ansatz. The matrices are representations of some quadratic algebras. The algebras and the types of representations considered depend on the boundary conditions. In the language of quantum chains we obtain the ground state of N-state quantum chains with free boundary conditions or with non-diagonal boundary terms at one or both ends. In contrast to problems involving the Bethe ansatz, we do not have a general framework for arbitrary N, which when specialized, gives the known results for N = 2; in fact, the N = 2 and N>2 cases appear to be very different.
TL;DR: In this article, the effect of 2-mercaptobenzothiazole (MBT) on the corrosion of copper in ethanol-water mixture with 0.01 mol dm −3 HClO 4 was investigated by linear sweep voltammetry and surface enhanced Raman scattering spectroscopy.
TL;DR: In this article, the authors analyzed the possibility of creating photons from a vacuum due to the dynamical Casimir effect in a nondegenerate cavity with vibrating boundaries, taking into account losses and detuning from the exact resonance.
Abstract: We analyze the possibility of creating photons from a vacuum due to the dynamical Casimir effect in a nondegenerate cavity with vibrating boundaries, taking into account losses and detuning from the exact resonance. Explicit analytical solutions of the equations for the quadrature variances of an equivalent field oscillator with a time-dependent frequency show that photon generation is possible provided the relative detuning and inverse quality factor do not exceed a critical value of the order of ${10}^{\ensuremath{-}8}.$ Under this condition, the field goes finally to a highly squeezed quantum state.
TL;DR: The phase morphology of PC/ABS blends can be significantly affected by its processing conditions as mentioned in this paper, and the phase morphology changes from a well-dispersed PC phase surrounded by the ABS matrix phase to a cocontinuous morphology with increase in the mixing time.
Abstract: The phase morphology of PC/ABS blends can be significantly affected by its processing conditions. Blends prepared in a mixing chamber at different conditions show a strong influence of mixing time and temperature on its morphology. The blend morphology changes from a well-dispersed PC phase surrounded by the ABS matrix phase to a cocontinuous morphology with increase in the mixing time. Higher blending temperatures promote changes in the PC/ABS morphology, probably due to thermal degradation. The rotor speed has not shown much influence on the blend phase morphology. The cocontinuous phase morphology of the PC/ABS blends obtained after mixing for 10 min was shown to be unstable as detected by the heat treatment. A melt annealing for a few minutes showed a significant change in the morphology. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1605–1613, 1998
TL;DR: The behaviour of the sex trivalent leading to a fully paired structure, taken together with the close frequencies of the two spermatocyte types at metaphase II, suggests a normal pattern for male H. malabaricus meiosis, representing a stabilized multiple sex chromosome system in this species.
Abstract: The neotropical fish Hoplias malabaricus shows diversified cytotypes and may represent a group of distinct species. One of these cytotypes is characterized by 2n = 40 and 2n = 39 chromosomes in females and males, respectively, with a multiple sex chromosome system of the X1X1X2X2/X1X2Y type. The Y, representing a large chromosome in male karyotype, is derived from a translocation event between two biarmed chromosomes: one of them similar to X1 chromosome (no. 6) and another one similar to X2 chromosome (probably no. 20). Meiotic data (standard and synaptonemal complexes analyses) show 18 bivalents and one characteristic trivalent in pachytene and metaphase I spermatocytes, as well as two kinds of metaphase II cells with 19 and 20 chromosomes. The trivalent is formed by the Y, X1 and X2 chromosomes and usually presents a complete pairing in pachytene. However, trivalents with partially or fully asynapsed segments are also observed. These segments are assumed to be non-homologous regions of the X1 and X2 chromosomes without correspondence with the Y chromosome, which can heterosynapse. This behaviour of the sex trivalent leading to a fully paired structure, taken together with the close frequencies of the two spermatocyte types at metaphase II, suggests a normal pattern for male H. malabaricus meiosis, representing a stabilized multiple sex chromosome system in this species.
TL;DR: In this paper, the influence of the FeS and (NH 4 ) 2 CO 3 additives on the Ni-Fe battery negative plate was studied through galvanostatic and potentiostatic discharges.
TL;DR: In this paper, the results of flow visualization and residence time distribution experiments in a Taylor-Poiseuille vortex flow apparatus are presented, showing that the vortex drift velocities are less than one, and decrease continuously with increasing rotations, until a full stop.
TL;DR: A particular two-phase column generation procedure is described for the cutting stock formulation of the hardboard industry and is modeled as an integer program and solved by two alternative methods: the first is based on dynamic programming and the second is a simple extension of the implicit enumeration procedure proposed in Gilmore and Gomory.
TL;DR: In this paper, the role of nitric oxide incorporation into the reaction feed for the partial oxidation of methane to C2-hydrocarbons and C 2-oxygenates is evaluated.
Abstract: The role of nitric oxide incorporation into the reaction feed for the partial oxidation of methane to C2-hydrocarbons and C2-oxygenates is evaluated. The addition of NO increases the conversion of methane under all the experimental conditions studied and has a strong effect on the product distribution. At low NO concentration the catalysts yield mainly C2Hn hydrocarbons, but at higher NO concentrations, carbon oxides dominate. Amongst the C1-oxygenates produced, methanol is the major compound observed and its proportion increases with increasing NO concentration. The highest C1-oxygenates yield was 7% at atmospheric pressure.
TL;DR: In this article, an intricate net of factors assigns adolescent pregnancy a very high degree of risk for both mother and child, mainly for those from lower income classes, and serious consequences of premature pregnancy are felt in morbidity/mortality rates among mothers and babies as much as in the economic, educational and social outcomes.
Abstract: An intricate net of factors assigns adolescent pregnancy a very high degree of risk for both mother and child, mainly for those from lower income classes. Serious consequences of premature pregnancy are felt in morbidity/mortality rates among mothers and babies as much as in the economic, educational and social outcomes. Educational action is one manner of facing the problem. Nonetheless, educational actions which emphasize solely the biological approach to family planning have proved uneffective as we consider statistics relative to the reproductive health of girls. In order to have education bringing about effective contribution to the decrease of this particular type of pregnancy, all dimensons of the problem need to be taken into consideration, in special the social-cultural dimension, which establishes the determinants of undesired pregnancies. To approach this latter dimension mainly, from an educational perspective means to open room, inside and outside schools, for the debate about women's identity within a process that encompasses their thoroughness as human beings.
TL;DR: The randomly amplified polymorphic DNA (RAPD) technique was used to distinguish nucellar and zygotic seedlings resulting from crosses between the Montenegrina and King tangerines to develop tangerine varieties with a reduced number of seeds and organoleptic characteristics similar to the latter.
Abstract: The randomly amplified polymorphic DNA (RAPD) technique was used to distinguish nucellar and zygotic seedlings resulting from crosses between the Montenegrina (Citrus deliciosa Tenore) and King (C. nobilis Loureiro) tangerines. The aim of the present study was to develop tangerine varieties with a reduced number of seeds and organoleptic characteristics similar to the Montenegrina tangerine. Embryos were isolated from seeds, cultivated in vitro, and acclimated in a greenhouse. Four random primers were used to identify 54 plants of sexual origin from a total of 202 individuals. The degree of polymorphism of each primer was reflected in the number of zygotic plants obtained per primer. Cluster analysis of parents and progeny separated the individuals into distinct groups with a maximum genetic dissimilarity of 20%.
TL;DR: An improved FIA-spectrophotometric method is proposed for the determination of ascorbic acid in pharmaceutical formulations by exploiting the reproducibility and stability of a solid-phase reactor containing copper(II) phosphate immobilized in a polymeric matrix of polyester resin this paper.
TL;DR: Polyaniline (Pani) films were grown potentiodynamically on Pt electrodes in 0.1 M aniline/0.5 M acid (H2SO4 or HClO4), or in a 0.2 M salt containing an alkaline cation, between −0.25 and 0.69 V vs SCE as mentioned in this paper.
TL;DR: The available data indicate that the differentiation of this sex chromosome system may have occurred by a pericentric inversion, followed by length reduction in an ancestral chromosome similar to the Z one, originating a W chromosome like that now observed in the female karyotype of this fish species.
Abstract: Ten specimens of Hypostomus sp. from the Araguaia basin (Barra do Garcas, MT, Brazil) were cytogenetically studied, with characterization of the constitutive heterochromatin and positive segments for the fluorochrome Mithramycin. It was detected a chromosomal heteromorphism related to sex, of the ZZ/ZW type, not observed yet in Hypostomus catfish. Thus, in male karyotype can be found one pair of subtelo-acrocentric Z chromosomes, represented by a unique component in female karyotype. However, this latter has an exclusive metacentric the W chromosome. The available data indicate that the differentiation of this sex chromosome system may have occurred by a pericentric inversion, followed by length reduction in an ancestral chromosome similar to the Z one, originating a W chromosome like that now observed in the female karyotype of this fish species.