Showing papers by "Federal University of Rio de Janeiro published in 1987"

Incorporating random constraints in discrete models of choice set generation

Abstract: This paper proposes a behavioral interpretation of the choice set generation process that is useful for structuring and specifying discrete models that incorporate this stage of choice. The key concept is the notion of random constraints, which is operationalized in the form of probabilistic choice set formation models; we thus explicitly recognize our imperfect understanding and possible lack of data about the process. Several such models are presented and discussed with respect to their behavioral plausibility and estimability. A related paper reports on the calibration of one such specification with work mode choice data from Sao Paulo, Brazil.

The dual reciprocity boundary element formulation for diffusion problems

Abstract: This paper presents an extension of the dual reciprocity boundary element method (DRBEM) to deal with nonlinear diffusion problems in which thermal conductivity, specific heat, and density coefficients are all functions of temperature. The DRBEM, recently applied to the solution of problems governed by parabolic and hyperbolic equations, consists in the transformation of the differential equation into an integral equation involving boundary integrals only, the solution of which is achieved by employing a standard boundary element discretization coupled with a two-level finite difference time integration scheme. Contrary to previous formulations for the diffusion equation, the dual reciprocity BEM utilizes the well-known fundamental solution to Laplace's equation, which is space-dependent only. This avoids complex time integrations that normally appear in formulations employing time-dependent fundamental solutions, and permits accurate numerical solutions to be obtained in an efficient way. For nonlinear problems, the integral of conductivity is introduced as a new variable to obtain a linear diffusion equation in the Kirchhoff transform space. This equation involves a modified time variable which is itself a function of position. The problem is solved in an iterative way by using an efficient Newton-Raphson technique which is shown to be rapidly convergent.

Empirical test of a constrained choice discrete model : mode choice in sao paulo, brazil

Abstract: This paper examines the properties and empirically tests a model of discrete choice which incorporates probabilistic choice set generation. Denominated the Parametrized Logit Captivity (PLC) model, it is a generalization of the well-known “dogit” specification. The PLC model is shown to be theoretically and empirically more flexible than the latter. Work mode choice data collected in a 1977 O/D survey in Sao Paulo, Brazil, is used to obtain parameter estimates, as well as to evaluate consumer reaction to a series of perturbations in travel time, travel cost and income, for both the PLC and Multinomial Logit models. Comparisons between the two specifications are made in terms of statistical fit, reasonableness of predictions and differences in predictions across models.

Visual topography of V1 in the Cebus monkey

Abstract: The representation of the visual field in the striate cortex (V1) was mapped with multiunit electrodes in the Cebus monkey. Nine Cebus apella, anesthetized with N2O and immobilized with pancuromium bromide were studied in repeated recording sessions. In each hemisphere, V1 contains a continuous representation of the contralateral visual hemifield. The representation of the vertical meridian (VM) forms the external border of V1 except at the anteriormost portion of the calcarine fissure. The representation of the horizontal meridian (HM) divides the area so that the representation of the lower visual field is located dorsally, and that of the upper field ventrally. The convoluted surface of V1 can be only partially unfolded, and no precise "flattened" map can be obtained without introducing surface discontinuities. The visual topography of V1 is presented in a series of coronal sections and in "flattened" maps. The representation of the central visual field is magnified relative to that of the periphery in V1. The evaluation of the cortical magnification factors measured along isoeccentric and isopolar dimensions in the partially unfolded model of V1 revealed anisotropies in the representation of the visual field with larger magnification along isopolar lines than along isoeccentric lines. Receptive field size increases with increasing eccentricity, whereas point image size decreases with increasing eccentricity.

The Steiner Problem in Graphs

Abstract: Publisher Summary This chapter reviews formulations and some procedures that have been suggested for the solution of the Steiner Problem in graphs. It presents the definition and results associated with the classical Steiner Problem also known as the Euclidean Steiner Problem (ESP). The chapter discusses the Steiner Problem in graphs where the Steiner Problem in an undirected graph (SPUG) and the Steiner Problem in a directed graph (SPDG) are defined. It also discusses the transformation of a SPUG in a SPDG. The chapter provides an overview on the Lawler algorithm for the SPUG. The chaptre presents four integer programming formulations of the Steiner Problem in graphs, compares the linear relaxations of three of these formulations, and describes an application of Benders method to solve one of these formulations illustrated by an example. It also presents solution methods based on these formulations and describes some computational results.

Bursting phenomena in continuous-time adaptive systems with a σ -modification

Abstract: Recently, the introduction of a kind of forgetting factor, called σ-modification, in the adaptation law for continuous-time systems was proposed to improve the adaptive system robustness However, this paper shows that, similarly to the diserete-time case, bursting phenomena may occur solely due to the forgetting factor

Structural features of sulfated glycans from the tunic of Styela plicata (Chordata-Tunicata). A unique occurrence of L-galactose in sulfated polysaccharides.

Abstract: The sulfated polysaccharides in the tunic of Styela plicata occur as three fractions that differ markedly in molecular mass and chemical composition. The high-molecular-mass fraction has a high galactose content and a strong negative optical rotation while the low-molecular-mass fractions have a higher proportion of amino sugars and glucose. The galactose occurs in these polysaccharides entirely in the L-enantiomeric form. Although L-galactose is a constituent of several polysaccharides, this is the first report of sulfated polysaccharides that contain high amounts of L-galactose, and that lack the D enantiomorph of this sugar. Furthermore, the structure of the high-molecular-mass fraction, which is composed mainly of a core of alpha-L-galactopyranose residues, sulfated at position 3, linked glycosidically though position 1----4, and with non-sulfated L-galactopyranose non-reducing end-units, is unique among other previously described sulfated glycans. These data are of considerable interest as they show an unusual example of possible variants of polyanionic glycans with structure function in living tissues.

Regulation of the trehalose-6-phosphate synthase complex in Saccharomyces. I. Interconversion of forms by phosphorylation.

Abstract: Trehalose-6-phosphate synthase is another example of an enzyme of carbohydrate metabolism, in Saccharomyces, which could be regulated by interconversion of forms. Deactivation was mediated both in vivo and in vitro by a cyclic AMP-dependent protein kinase. Reversibility of this process was obtained by a phosphatase treatment leading to an increase in activity. The phosphorylated, less active form of the enzyme proved to be more susceptible to activation by ATP.Mg. Mutants with well defined lesions in the cyclic AMP-dependent protein kinase system were used to corroborate our findings of a possible regulatory mechanism of trehalose-6-phosphate synthase activity by interconversion of forms.

Highly acidic glycans from sea cucumbers. Isolation and fractionation of fucose-rich sulfated polysaccharides from the body wall of Ludwigothurea grisea.

Abstract: The body wall of the sea cucumber contains high amounts of sulfated glycans, which differ in structure from glycosaminoglycans of animal tissues and also from the fucose-rich sulfated polysaccharides isolated from marine algae and from the jelly coat of sea urchin eggs In Ludwigothurea grisea, glycans can be separated into three fractions which differ in molecular mass and chemical composition The fraction containing a high-molecular-mass component has a high proportion of fucose and small amounts of amino sugars, whereas another fraction contains primarily a sulfated fucan The third fraction, which represents the major portion of the sea cucumber polysaccharides, contains besides fucose, approximately equimolar proportions of glucuronic acid and amino sugars, and has a sulfate content higher than that in the other two fractions Both D and L-isomers of fucose are found in these polysaccharides, and the sulfate is linked to the O-3 position of the fucose residues The attachment position of the sulfate groups to the glucuronic acid units and amino sugars is still undetermined It is possible that these compounds are involved in maintaining the integrity of the sea cucumber's body wall, in analogy with the role of other macromolecules in the vertebrate connective tissue

Chromosome studies in Alouatta belzebul.

Abstract: The chromosome constitution of Alouatta belzebul was studied with G-, C-, and silver staining. In ten specimens identified as Alouatta belzebul, the chromosome constitution of males (2n = 49) differed from that of females (2n = 50) owing to a Y-autosome translocation. In another single female specimen, probably Alouatta belzebul nigerrima, the diploid chromosome number was also 50, though its karyotype was drastically different from that of Alouatta belzebul belzebul. Chromosome studies, taken together with phenotypic and field observations, suggest that Alouatta belzebul belzebul is phenotypically variable in respect to pelage coloration. This attribute is therefore unreliable for the precise identification of Alouatta belzebul subspecies. Conversely, relatively minor phenotypic differences, allowing for the characterization of subspecies within a same species, coexist with unparalleled, drastic karyotypic divergence. These findings clearly question gross morphological attributes as discriminative characteristics of Alouatta belzebul subspecies.

Dual control by targets and afferents of developmental neuronal death in the mammalian central nervous system: a study in the parabigeminal nucleus of the rat.

Abstract: Natural and induced cell degeneration were studied in the mesencephalic parabigeminal nucleus of postnatally developing rats. Natural cell death in the normal parabigeminal nucleus had already started at birth, was maximal at 3 days, and proceeded with a declining rate until postnatal days 8–10 in the dorsal, middle, and ventral divisions that compose the nucleus. The number of neurons declined by approximately one-third between birth and postnatal day 15. A unilateral lesion of the superior colliculus made at birth modified this pattern. In the deafferented ipsilateral middle division, the rate of cell death was above normal from day 1 to day 10, and the number of neurons at day 15 was 60% less than in unoperated controls. In the contralateral middle division, in which at least some of the neurons were axotomized by the lesion, the rate of cell death increased at days 1–2 and decreased below normal at days 3–5. Induced changes in the number of neurons were consistent with this pattern, and at day 15 the number was similar to the control value. In the ipsilateral dorsal and ventral divisions, which suffered simultaneous axotmy and deafferentation, the rate of cell death increased in 2 peaks at days 1–2 and 4–6, and the numbers of neurons dropped to negligible values at day 15. The frequency curves of degenerating cells were poor predictors of the absolute changes in neuron numbers, and evidence was found of continued postnatal migration of neurons into the developing parabigeminal nucleus. This study indicated that retrograde and anterograde degeneration cotemporal with natural cell death in the developing parabigeminal nucleus proceed with distinct time courses and interact when induced simultaneously. The nucleus regulates through a reduction in the rate of cell death after an early depletion of neurons caused by axotomy, as long as the tectal input remains intact. The results support the hypothesis that the afferent supply, as well as the integrity of axons, have major roles in the control of neuronal survival in the developing brain.

Effects of prenatal irradiation on the development of cerebral cortex and corpus callosum of the mouse.

Abstract: Defects of the cerebral cortex and corpus callosum of mice subjected prenatally to gamma irradiation were evaluated as a function of dose and of embryonic age at irradiation. Pregnant mice were exposed to a gamma source at 16, 17, and 19 days of gestation (E16, E17, and E19, respectively), with total doses of 2 Gy and 3 Gy, in order to produce brain defects on their progeny. At 60 postnatal days, the brains of the offspring were analyzed qualitatively and quantitatively and compared with those of nonirradiated animals. Mice irradiated at E16 were all acallosal. Those that were exposed to 2 Gy displayed an aberrant longitudinal bundle typical of other acallosals, but this was not the case in those irradiated with 3 Gy. The corpus callosum of animals irradiated at E17 with 3 Gy was pronouncedly hypotrophic, but milder effects were observed in the other groups. Quantitative analysis confirmed a dependence of callosal midsagittal area upon dose and age at irradiation, and, in addition, indicated an interaction between these variables. The neocortex of irradiated animals was hypotrophic: layers II-III were much more affected than layer V, and this was more affected than layer VI. Quantitative analysis indicated that this effect also depended on dose and age at irradiation and that it was due to a loss of cortical neurons. Furthermore, a positive correlation was found between the number of neurons within layers II-III, and V and the midsagittal area of the corpus callosum. Ectopic neurons were found in the white matter and in layer I of animals irradiated at E16 and E17, indicating that fetal exposure to ionizing radiation interfered with the migration of cortical neuroblasts.

Displaced ganglion cells in the retina of the rat

Abstract: The distribution, laterality of projection, and perikaryal sizes of displaced ganglion cells (DGCs) were examined in whole-mounted retinae after massive unilateral injections of horseradish peroxidase along the optic tract in pigmented rats. The DGCs were found predominantly in the lower temporal periphery of the retina. Nearly all DGCs labeled had contralaterally projecting axons. The sizes of the labeled DGCs spanned the range of ordinary ganglion cells, but few middle-sized DGCs were labeled. The results support the hypothesis that displaced ganglion cells are late-developing neurons that do not complete their migration toward the ganglion cell layer during retinal histogenesis.

Activity of some naphthoquinones on blood stream forms of Trypanosoma cruzi.

Abstract: Accidental transmission of Chagas disease to man by blood transfusion is a serious problem in Latin America. This paper describes the testing of several naphthoquinones, some of which were active against blood trypomastigotes in vitro at 4 degrees C and might therefore warrant further study for preventing transmission of Chagas disease by blood transfusion.

Surface charge of resident, elicited, and activated mouse peritoneal macrophages.

Abstract: The surface charge of resident, thioglycollate-elicited, and Trypanosoma cruzl-activated mouse peritonealmacrophages was analyzed using cellelectrophoresls.All macro. phagea had a net negative surface charge. Activated macrophages had a lower zeta potential and a higher isoelectrophoreticpoint than resident and elicited macrophages. The populationsof resident,elicited, and activated macrophages were heterogeneous in terms of surface charge. The analysis of the effect of the pH of the solution In which the macrophages were suspended on their cellular electrophoretic mobility (EPM) mdi. cated that their surface contained both positively and negatively charged dissociating groups. The contribution of alaiic acid residues to the surface charge was determined by analyzing the effect of neuraminidase treatment on the EPM of the cells. Activated macrophages possessed more slalic acid residues exposed on their surface, and sensitive to the neuraminidase from Clostridlum pert ngens, than resident and elicited macrophages. Treatment of the cells with the neuraminidaae from Wbrlo cholerse, however, reduced the surface charge of all macrophages in about the same extent. Macrophages had their mean EPM reduced when incubaled in the presence of Ca�, suggesting that some cell surface anionogenic sites have Ca55-binding capacity.

Enzymes of ornithine-arginine metabolism in trypanosomatids of the genus Phytomonas

Abstract: Trypanosomatids recently isolated from the plants Euphorbia pinea, E. characias, E. hyssopifolia, Manihoi esculenta (cassava) and Lycopersicon sp. (tomato) plus the McGhee-Postell isolate of Phytomonas davidi have been examined for the presence of enzymes of ornithine-arginine metabolism. Arginase (EC 3.5.3.1) was not detected in the flagellates examined whereas arginine deiminase (EC 3.5.3.6) and citrullinehydrolase (EC 3.5.1.20) were present in all organisms. Phytomonas davidi and the isolate from E. hyssopifolia, besides these enzymes, also had ornithine carbamoyltransferase (EC 2.1.3.3). The enzymic constitution of these flagellates is compared from a taxonomic standpoint to that of previously studied trypanosomatids.

Self-excited induction generator/force-commutated rectifier system operating as a DC power supply

Abstract: The paper presents a new DC energy generation system based on a 3-phase self-excited induction generator coupled to a force-commutated rectifier. This rectifier is switched in such a way that its input current fundamental component is advanced with respect to the corresponding voltage, producing a capacitive characteristic on its terminals. This characteristic helps the self-excitation and improves the direct output voltage regulation, with respect to load variation, to the range of 1 to 2%, for some firing angle. Also, this capacitive effect greatly increases the output power limit, and allows the system to supply a constant direct output voltage over a reasonably wide range of rotor speed variation. The steady-state performance of the system is analysed based on a simplified mathematical model, which is validated experimentally. A study on the influence of the smoothing reactor size is presented and it is shown that the system can operate properly even without this reactor, if there is no limit for current ripple in the load.

Adaptive control with discontinuous σ-factor and saturation for improved robustness

Abstract: An adaptive control law is proposed to improve the robustness of the adaptive system with respect to fast unmodelled dynamics represented by a singular perturbation. The new law is based on saturation of the regressor and control parameter vector with inclusion of a discontinuous σ-factor. The analysis of the resulting system is presented and the conclusions are illustrated by simulations. The introduction of a discontinuous σ-factor represents an extension of an earlier work. The advantages of this extension include global stability, with less restrictive assumptions, and better transient behaviour.

Nailfold capillaroscopy in diabetes mellitus: morphological abnormalities and relationship with microangiopathy.

Abstract: The morphology and density of nailfold capillaries were evaluated in patients with Type I and Type II diabetes mellitus and in healthy controls, using videocapillaroscopy. A protocol of well-defined capillary patterns was used. Diabetic patients had more tortuous and enlarged capillaries than controls. Nodular apical elongation was found only in diabetics and was more frequent in patients with a longer history of disease. Type II diabetic patients with chronic clinical complications had a higher frequency of enlarged capillaries and nodular apical elongation. Glycemic control was without influence. Capillary density did not differ among the groups.

Production of β-carotene by aRhodotorula strain

Abstract: The production of β-carotene by the biomass ofRhodotorula strain var.glutinis, during the stationary phase of growth and in non-proliferating conditions was assayed. When the cells were transferred to distilled water, the fraction of β-carotene produced increased from 130 to 630 μg per gram of dried cells.

Production of staphylococcal enterotoxin in mixed cultures.

Abstract: Two Staphylococcus aureus strains were grown in brain-heart infusion (BHI) broth and a meat medium with Bacillus cereus, Streptococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa. Both S. aureus strains grew well and produced enterotoxin in the presence of S. faecalis in BHI broth; however, enterotoxin production was observable in the meat medium only when the S. aureus inoculum was greater than the S. faecalis inoculum. S. aureus FRI-100 grown with B. cereus produced enterotoxin in both media only when the S. aureus inoculum was much higher than the B. cereus inoculum (10 versus 10(4) CFU), whereas S. aureus FRI-196E produced enterotoxin in both media at all inoculum combinations except in the meat medium, when the inocula of the two organisms were the same. S. aureus grown with E. coli in BHI broth produced enterotoxin at all inoculum combinations except when the E. coli inoculum was greater than the S. aureus inoculum; however, in the meat medium, enterotoxin was produced only when the S. aureus inoculum was much greater than the E. coli inoculum (10 versus 10(4) CFU), S. aureus FRI-100 grown with P. aeruginosa in either medium produced enterotoxin only when the S. aureus inoculum was much greater than the P. aeruginosa inoculum (10 versus 10(3) or 10(4) CFU). It can be concluded from these results that enterotoxin production is unlikely in mixed cultures unless the staphylococci outnumber the other contaminating organisms.

Foliation of 3-dimensional space forms by surfaces with constant mean curvature

Abstract: Let Y represent a 3-dimensional complete simply-connected space form We study C2-foliations g of Y by leaves with the same constant mean curvature We prove that if the curvature of Y is positive such foliations can not exist, When Y is the Euclidean space then such a foliation must consist of parallel planes When Y is the hyperbolic space, if we further assume that the mean curvature satisfies H > l, then F must be a foliation by horospheres These results are still true if F is a fol~atlon of an open set U of Y and if we further assume that the leaves are complete and orientable We observe that on hyperbolic space there are examples of nontrlvial foliations of open sets by complete surfaces with the same constant mean curvature 0 < H < I One example can be obtained from the l-parameter family of catenoids studied by do Carmo and Dajczer ~D] and by Gomes ~] To prove the results, we consider a codimension-one foliation of an orientable Riemannian manifold, whose leaves are orientable and have the same constant mean curvature, and first show that its leaves are strongly stable in the sense defined in ~CE] We then apply the classification theorem for complete stable surfaces of a 3-dimensional space form proved in ~CE] and ~]

Effects of neomycin on calcium channel currents in clonal GH3 pituitary cells

Abstract: Membrane Ca currents were recorded from voltage-clamped clonal (GH3) pituitary cells under conditions where currents through Na and K channels were abolished. Two Ca currents, with distinct kinetics and voltage dependence for activation and inactivation, were identified. Neomycin, an aminoglycoside polycation, inhibited both the "transient" (ICa,t) and the "slowly-inactivating" (ICa,s) Ca currents in a dose-dependent manner (100-1,000 microM). The blockade was reversible and ICa,s was more sensitive to neomycin than ICa,t. The inhibition of ICa,s was frequency and time-independent, and was not affected by changes in the holding membrane potential (-35 to -100 mV). Neomycin did not affect the voltage dependence for inactivation of ICa,t. The blockade of both Ca currents by neomycin is ascribed to the general property of aminoglycosides to compete with, and displace Ca ions from membrane binding sites that determine the currents and selectivity of Ca channels. Because comparable concentrations of neomycin were required for blocking the currents conveyed by Ca or, in the absence of external divalent cations, by Na ions through the slowly-inactivating Ca channels, we suggest that the neomycin binding sites are distinct from the high-affinity transition sites within the Ca channel path.