The effect of heating rate on the sintering of agglomerated NaNbO3 powders

The effect of heating rate on the sintering of agglomerated NaNbO3 powders, processed by the polymeric precursors method, was studied. The results showed that the presence of agglomerated powder leads to a heterogeneous microstructure, with bimodal grain size distribution, after sintering. Using a high heating rate, the sintering of agglomerated particles was inhibits, leading to a homogeneous microstructure, with single grain size distribution. (C) 1998 Kluwer Academic Publishers.

Electrochemical impedance spectroscopy characterization of passive film formed on implant Ti-6Al-7Nb alloy in Hank's solution

The influence of potential on electrochemical behavior of Ti-6Al-7Nb alloy under simulate physiological conditions was investigated by electrochemical impedance spectroscopy (EIS). The experimental results were compared with those obtained by potentiodynamic polarization curves. All measurements were carried out in Hank's aerated solution at 25degreesC, at pH 7.8 and at different potentials (corrosion potential, 0 mV(SCE), 1000 mV(SCE), and 2000 mV(SCE)). The EIS spectra exhibited a two-step or a two-time constant system, suggesting the formation of a two-layer oxide film on the metal surface. The high corrosion resistance, displayed by this alloy in electrochemical polarization tests, is due to the dense inner layer, while its osseointegration ability can be ascribed to the presence of the outer porous layer. (C) 2004 Kluwer Academic Publishers.

THE LONG-TERM EVOLUTION OF IMMUNE DEPOSITS IN PASSIVE HEYMANN NEPHRITIS

1. To study the long term course of passive Heymann nephritis (PHN), 42 adult male Wistar rats were injected with rabbit anti-FX1A serum (PHN group) and 42 rats received normal rabbit serum (control group). Two animals from each group were sacrificed 2 weeks after the inoculation and 10 animals each from the control and PHN groups were sacrificed 4, 13, 25 and 53 weeks later.2. The PHN group exhibited a significant elevation in 20-h proteinuria which lasted from the first week (control group, 9.19 +/- 0.87; PHN group, 25.3 +/- 2.66) to the 25th week (control group, 22.6 +/- 2.15; PHN group, 66.7 +/- 10.4) except for week 17. From week 29 to week 53 there was no statistical difference between the 2 groups.3. Light microscopy showed no difference between the kidneys of PHN and control rats. Immunofluorescence microscopy in PHN rats showed granular deposition of autologous and heterologous IgG on the glomerular basement membrane (GBM), whose intensity and pattern did not change during 53 weeks of observation.4. When examined by electron microscopy the glomeruli of PHN rats showed: a) electron-dense deposits which were initially subepithelial and homogeneous and later intramembranous, granular and often surrounded by an electron-transparent halo; b) focal thickening of the GBM at the sites of intramembranous deposits; c) effacement of podocytes located close to the deposits; d) penetration of the podocytes into the GBM associated with the deposits; e) presence of osmiophilic granules in the cytoplasm of the podocyte located inside the GBM similar to the granules of the deposits next to them. The association of the penetration of the podocytes into the GBM with the deposits and the presence of the osmiophilic granules inside the foot process have not been described previously in PHN.5. The results suggest that the podocytes play a role in the clearing of intramembranous deposits in PHN.

Rift to post-rift evolution of a passive continental margin: the Ponta Grossa Arch, SE Brazil

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

Viscoelastic and Thermal Properties of Collagen-Xanthan Gum and Collagen-Maltodextrin Suspensions During Heating and Cooling

The purpose of this work was to investigate the viscoelastic properties of aqueous suspensions of crude collagen powder extracted from bovine hides and nonsubmitted to the hydrolysis reaction that leads to gelatin. The studied variables included the collagen concentration and the addition of xanthan gum or maltodextrin at varied concentrations during heating/cooling of the mixtures. Differential scanning calorimetry thermograms showed that the addition of polysaccharides decreased the endothermic peak areas observed at the denaturation temperature of collagen. The rheological properties of the pure collagen suspensions were highly dependent on concentration: 4% and 6% collagen suspensions presented a great increase in the storage modulus after heating/cooling, whereas for concentrations of 8% and 10% G' decreased during heating and did not recover its original value after heating/cooling. The frequency sweeps showed that the thermal treatment was responsible by the strengthening of the interactions that formed the polymer network. Addition of 0.1% xanthan gum to collagen suspensions increased the gel strength, especially after heating/cooling of the system, whereas increasing gum concentration to 0.3% resulted in a weaker gel, which could indicate thermodynamic incompatibility between the biopolymers. Mixtures of collagen and maltodextrin resulted in more fluid structures than those obtained with pure collagen at the same collagen concentration and the range of temperatures in which these mixtures behaved as a gel decreased with increasing concentrations of both collagen and maltodextrin, suggesting incompatibilities between the biopolymers.

Denudation history of the Bocaina Plateau, Serra do Mar, southeastern Brazil: Relationships to Gondwana breakup and passive margin development

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

Passive Immunity of Progeny from Broiler Breeders Vaccinated with Oil-Emulsion Bacterin Against Salmonella Enteritidis

Young poultry are very susceptible to Salmonella Enteritidis (SE) infections because of the absence of complete intestinal flora colonization and an immature immune system. This study evaluated the role of passive immunity on the resistance of young birds against early infections caused by SE. The progeny of broiler breeders vaccinated with an oil-emulsion bacterin was compared to the progeny of unvaccinated birds. Efficacy was determined by challenging birds at 1 and 14 days of age with SE Nal Spc strain, phage type 4. After challenge at 1 day of age, the progeny of vaccinated birds presented a significantly lower number (log(10)) of SE Nal Spc reisolation (P < 0.05) in liver (2.21), spleen (2.31), and cecal contents (2.85) compared with control groups (2.76, 3.02, and 6.03, respectively). The examination of the internal organs, 3 days after infection, revealed that 28% of the birds (7/25) from vaccinated breeders were positive, whereas 100% (25/25) of the chicks derived from unvaccinated birds were positive. Birds challenged at 14 days of age presented a lower number of positive samples compared with those challenged at 1 day of age, and the progeny of vaccinated birds presented statistically lower numbers (log(10)) of colony-forming units/ml of SE Nal Spc only in the cecal contents compared with nonvaccinated breeder progeny (2.11 vs. 2.94). Age seems to influence the susceptibility of birds to SE infections: in control groups, the number of positive birds at 14 days of age (9/25) was lower when compared with the group infected at 1 day of age (25/25). The number of positive fecal samples of the progeny of vaccinated birds was significantly lower (36) than those of the control group (108) after challenge at 1 day of age. Unchallenged progeny of vaccinated birds presented passive antibodies detectable by enzyme-linked immunosorbent assay (ELISA) up to 21 days of age. on the other hand, antibodies of the control group were detected by ELISA 14 days after challenge. These results show a significant contribution of breeder vaccination by increasing the resistance of the progeny against early SE infections. However, the bacteria were not completely eliminated, suggesting that additional procedures are needed to effectively control SE infections.

Effect of passive pneumoperitoneum on oesophageal pressure, cardiovascular parameters and blood gas analysis in horses

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Passive and active dispersers respond similarly to environmental and spatial processes: an example from metacommunity dynamics of tree hole invertebrates

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Is maximal lactate steady state during intermittent cycling different for active compared with passive recovery?

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

Interaction of equatorial waves through resonance with the diurnal cycle of tropical heating

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

Analysis of aluminum plates under heating in electrical and natural gas furnaces

This paper analyzes the thermal storage characteristics of aluminum plates in furnaces during their heating for lamination under two sources of heat: an electrical resistance bank and a combustion process carried out with natural gas. The set of equations to model the furnace under operation with electrical energy, for air as the fluid, is presented. This supports the theoretical analysis for the system under operation with natural gas combustion products. A numerical procedure, using the software ANSYS, is applied to determine the convection heat transfer coefficients for heating by the air flow. Temperatures measured in a plate inside a real furnace are used as parameters to determine these coefficients. Then convection and radiation heat transfer coefficients are determined for the natural gas combustion products. Results are compared, indicating a possible gain of 5.5 h in relation to a 19.5 h period of conventional electrical heating per plate.

An improved three-dimensional model for growth of oxide films induced by laser heating

In this paper we consider a three-dimensional heat diffusion model to explain the growth of oxide films which takes place when a laser beam is shined on and heats a metallic layer deposited on a glass substrate in a normal atmospheric environment. In particular, we apply this model to the experimental results obtained for the dependence of the oxide layer thickness on the laser density power for growth of TiO2 films grown on Ti-covered glass slides. We show that there is a very good agreement between the experimental results and the theoretical predictions from our proposed three-dimensional model, improving the results obtained with the one-dimensional heat diffusion model previously reported. Our theoretical results also show the occurrence of surface cooling between consecutive laser pulses, and that the oxide track surface profile closely follows the spatial laser profile indicating that heat diffusive effects can be neglected in the growth of oxide films by laser heating. © 2001 Elsevier Science B.V.

One-dimensional analytical model for oxide thin film growth on Ti metal layers during laser heating in air

This paper presents the theoretical and experimental results for oxide thin film growth on titanium films previously deposited over glass substrate. Ti films of thickness 0.1 μm were heated by Nd:YAG laser pulses in air. The oxide tracks were created by moving the samples with a constant speed of 2 mm/s, under the laser action. The micro-topographic analysis of the tracks was performed by a microprofiler. The results taken along a straight line perpendicular to the track axis revealed a Gaussian profile that closely matches the laser's spatial mode profile, indicating the effectiveness of the surface temperature gradient on the film's growth process. The sample's micro-Raman spectra showed two strong bands at 447 and 612 cm -1 associated with the TiO 2 structure. This is a strong indication that thermo-oxidation reactions took place at the Ti film surface that reached an estimated temperature of 1160 K just due to the action of the first pulse. The results obtained from the numerical integration of the analytical equation which describes the oxidation rate (Wagner equation) are in agreement with the experimental data for film thickness in the high laser intensity region. This shows the partial accuracy of the one-dimensional model adopted for describing the film growth rate. © 2001 Elsevier Science B.V.