996 resultados para 2-10


Relevância:

60.00% 60.00%

Publicador:

Resumo:

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Microstratigraphic, sedimentological, and taphonomic features of the Ferraz Shell Bed, from the Upper Permian (Kazanian-Tatarian?) Corumbatai Formation of Rio Claro Region (the Parana Basin, Brazil), indicate that the bed consists of four distinct microstratigraphic units. They include, from bottom to top, a lag concentration (Unit 1), a partly reworked storm deposit (Unit 2), a rapidly deposited sandstone unit with three thin horizons recording episodes of reworking (Unit 3), and a shell-rich horizon generated by reworking/winnowing that was subsequently buried by storm-induced obrution deposit (Unit 4). The bioclasts of the Ferraz Shell Bed represent exclusively bivalve mollusks. Pinzonella illusa and Terraia aequilateralis are the dominant species. Taphonomic analysis indicates that mollusks are heavily time-averaged (except for some parts of Unit 3). Moreover, different species are time-averaged to a different degree (disharmonious time-averaging). The units differ statistically from one another in their taxonomic and ecological composition, in their taphonomic pattern, and in the size-frequency distributions of the two most common species. Other Permian shell beds of the Parana Basin are similar to the Ferraz Shell Bed in their faunal composition (they typically contain similar sets of 5 to 10 bivalve species) and in their taphonomic, sedimentologic, and microstratigraphic characteristics. However, rare shell beds that include 2-3 species only and are dominated by articulated shells preserved in life position also occur. Diversity levels in the Permian benthic associations of the Parana Basin were very low, with the point diversity of 2-3 species and with the within-habitat and basin-wide (alpha and gamma) diversities of 10 species, at most. The Parana Basin benthic communities may have thus been analogous to low-diversity bivalve-dominated associations of the present-day Baltic Sea. The 'Ferraz-type' shell beds of the Parana Basin represent genetically complex and highly heterogeneous sources of paleontological data. They are cumulative records of spectra of benthic ecosystems time-averaged over long periods of time (10(2)-10(4) years judging from actualistic research). Detailed biostratinomic reconstructions of shell beds can not only offer useful insights into their depositional histories, but may also allow paleoecologists to optimize their sampling designs, and consequently, refine paleoecological and paleoenvironmental interpretations.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Aims. We study trajectories of planetesimals whose orbits decay due to gas drag in a primordial solar nebula and are perturbed by the gravity of the secondary body on an eccentric orbit whose mass ratio takes values from mu(2) = 10(-7) to mu(2) = 10(-3) increasing ten times at each step. Each planetesimal ultimately suffers one of the three possible fates: (1) trapping in a mean motion resonance with the secondary body; (2) collision with the secondary body and consequent increase of its mass; or (3) diffusion after crossing the orbit of the secondary body.Methods. We take the Burlirsh-Stoer numerical algorithm in order to integrate the Newtonian equations of the planar, elliptical restricted three-body problem with the secondary body and the planetesimal orbiting the primary. It is assumed that there is no interaction among planetesimals, and also that the gas does not affect the orbit of the secondary body.Results. The results show that the optimal value of the gas drag constant k for the 1: 1 resonance is between 0.9 and 1.25, representing a meter size planetesimal for each AU of orbital radius. In this study, the conditions of the gas drag are such that in theory, L4 no longer exists in the circular case for a critical value of k that defines a limit size of the planetesimal, but for a secondary body with an eccentricity larger than 0.05 when mu(2) = 10(-6), it reappears. The decrease of the cutoff collision radius increase the difusions but does not affect the distribution of trapping. The contribution to the mass accretion of the secondary body is over 40% with a collision radius 0.05R(Hill) and less than 15% with 0.005R(Hill) for mu(2) = 10(-7). The trappings no longer occur when the drag constant k reachs 30. That means that the size limit of planetesimal trapping is 0.2 m per AU of orbital radius. In most cases, this accretion occurs for a weak gas drag and small secondary eccentricity. The diffusions represent most of the simulations showing that gas drag is an efficient process in scattering planetesimals and that the trapping of planetesimals in the 1: 1 resonance is a less probable fate. These results depend on the specific drag force chosen.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Relevância:

60.00% 60.00%

Publicador:

Resumo:

There are several methods for identifying carious dentinal tissue aiming to avoid removal of healthy dentinal tissue. Objectives: The purpose of this study was to test different methods for the detection of carious dentinal tissue regarding the amount of carious tissue removed and the remaining dentin microhardness after caries removal. Material and methods: The dentin surfaces of 20 bovine teeth were exposed and half of the surface was protected with nail polish. Cariogenic challenge was performed by immersion in a demineralizing solution for 14 days. After transverse cross-section of the crown, the specimens were divided into four groups (n=10), according to the method used to identify and remove the carious tissue: "Papacarie", Caries-detector dye, DIAGNOdent and Tactile method. After caries removal, the cross-sectional surface was included in acrylic resin and polished. In a microhardness tester, the removed dentin thickness and the Vickers microhardness of the following regions were evaluated: remaining dentin after caries removal and superficial and deep healthy dentin. Results: ANOVA and Tukey's test (alpha=0.05) were performed, except for DIAGNOdent, which did not detect the presence of caries. Results for removed dentin thickness were: "Papacarie" (424.7 +/- 105.0; a), Caries-detector dye (370.5 +/- 78.3; ab), Tactile method (322.8 +/- 51.5; bc). Results for the remaining dentin microhardness were: "Papacarie" (42.2 +/- 10.5; bc), Caries-detector dye (44.6 +/- 11.8; bc), Tactile method (24.3 +/- 9.0; d). Conclusions: DIAGNOdent did not detect the presence of carious tissue; Tactile method and "Papacarie" resulted in the least and the most dentinal thickness removal, respectively; Tactile method differed significantly from "Papacarie" and Caries-detector dye in terms of the remaining dentin microhardness, and Tactile method was the one which presented the lowest microhardness values.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Statement of problem. Different combinations of Co-Cr alloys bonded to ceramic have been used in dentistry; however, the bond strength of ceramic to metal can vary because of different compositions of these alloys.Purpose. The purpose of this study was to evaluate the shear bond strength of a dental ceramic to 5 commercially available Co-Cr alloys.Material and methods. Five Co-Cr alloys (IPS d.SIGN 20, IPS d.SIGN 30, Remanium 2000, Heranium P, and Wirobond C) were tested and compared to a control group of an Au-Pd alloy (Olympia). Specimen disks, 5 mm high and 4 mm in diameter, were fabricated with the lost-wax technique. Sixty specimens were prepared using opaque and dentin ceramics (VITA Omega 900), veneered, 4 mm high and 4 mm in diameter, over the metal specimens (n = 10). The shear bond strength test was performed in a universal testing machine with a crosshead speed of 0.5 mm/min. After shear bond testing, fracture surfaces were evaluated in a stereomicroscope under x25 magnification. Ultimate shear bond strength (MPa) data were analyzed with 1-way ANOVA and the Tukey HSD test (alpha = .05).Results. The mean (SID) bond strengths (MPa) were: 61.4 (7.8) for Olympia; 94.0 (18.9) for IPS 20; 96.8 (10.2) for I PS 30; 75.1 (12.4) for Remanium; 71.2 (14.3) for Heranium P; and 63.2 (10.9) for Wirobond C. Mean bond strengths for IPS 20 and IPS 30 were not significantly different, but were significantly (P<.001) higher than mean bond strengths for the other 4 alloys, which were not significantly different from each other.Conclusions. Bond strength of a dental ceramic to a Co-Cr alloy is dependent on the alloy composition.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

A unified description of spacelike and timelike hadron form factors within a light-front model was successfully applied to the pion. The model is extended to the nucleon to study the role of qq pair production and of nonvalence components in the nucleon form factors. Preliminary results in the spacelike range 0 <= Q(2) <= 10 (GeV/c)(2) are presented.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

We study the production of charmed mesons (D) and baryons (Lambda(c)) in antiproton- proton ((p) over barp) annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/ meson exchange or by quark/ gluon dynamics. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on (p) over bar -> (Lambda) over bar Lambda and (p) over barp (K) over bar K by connecting the processes via SU(4) flavor symmetry. Our predictions for the (Lambda) over bar (c)Lambda(c) production cross section are in the order of 1 to 7 mb, i. e. a factor of around 10-70 smaller than the corresponding cross sections for (Lambda) over bar Lambda However, they are 100 to 1000 times larger than predictions of other model calculations in the literature. on the other hand, the resulting cross sections for (D) over barD production are found to be in the order of 10(-2) - 10(-1)mu b and they turned out to be comparable to those obtained in other studies.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Ultrasound effects on the release and activity of invertase from Aspergillus niger cultivated in a medium containing sucrose and peptone and in another with sugar-cane molasses and peptone were investigated. Irradiation was conducted for periods of 2 - 10 min. with waves of amplitude 20 and 40 using an ultrasound processor of 20 kHz. Product formation was determined as reducing equivalents formed by time units using 3,5-dinitrosalicylic acid. Total and specific activities of the culture supernatants were compared in the presence and absence of sonication. Both amplitudes promoted a significant increase of total invertase activity in the time periods investigated and the highest values were obtained with an amplitude of 20. Ultrasound irradiation caused cell disruption, thus releasing invertase and, after 4 min, activation of the enzyme also occurred. The best conditions for production, extraction and activation of invertase were in molasses medium containing peptone and irradiation with ultrasound waves at 20 for 8 min. This method showed high efficiency for the extraction and activation of invertase from A. niger as well as a great potential for use in industrial processes.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Uma síntese das espécies de peixes de cabeceiras do rio Tietê é apresentada com base em material de coleções zoológicas e novas coletas realizadas. São referidas para região 56 espécies pertencentes a sete ordens e 16 famílias, aumentando significativamente números anteriores. Os resultados mostram que as cabeceiras do rio Tietê possuem uma composição ictiofaunistica bastante peculiar, distinta daquela encontrada no restante do Alto rio Paraná, mostrando acentuado grau de endemismo e grande similaridade com bacias hidrográficas litorâneas, corroborando a hipótese de captura de rios da região por drenagens costeiras e vice e versa no passado. Dentre as espécies encontradas na região, oito são endêmicas (14,3%), 13 são encontradas nas cabeceiras do rio Tietê e drenagens litorâneas da região sudeste do Brasil (23,2%), dez ocorrem em todo Alto rio Paraná (17,9%), cinco são encontradas no Alto rio Paraná e drenagens litorâneas da região sudeste do Brasil (8,9%), enquanto 13 espécies mostram uma ampla distribuição na América do Sul (23,2%), das quais parte ainda precisa ter a identidade confirmada. A diversidade de espécies é acrescida de pelo menos cinco espécies novas pertencentes aos gêneros Cyphocharax, Characidium, Astyanax, Pareiorhina e Australoheros e quatro novos registros são feitos para Characidium cf. zebra, Scleromystax barbatus, Crenicicla britskii e Synbranchus cf. marmoratus. Pelo menos sete espécies introduzidas estão estabelecidas na região, enquanto outras dez espécies são relacionadas em listas de espécies ameaçadas.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)