Comparative electrical behavior at low and high current of SnO(2)- and ZnO-based varistors

The complete I-V characteristics of SnO(2)-based varistors, particularly of the Pianaro system SCNCr consisting in 98.9%SnO(2)+1%CoO+0.05%Nb(2)O(5)+0.05%Cr(2)O(3), all in mol%, have been seldom reported in the literature. A comparative study at low and high currents of the nonohmic behavior of SCNCr- and ZnO-based varistors (modified Matsuoka system) is proposed in this work. The SCNCr system showed higher nonlinearity coefficients in the whole range of measured current. The electrical breakdown field (E(b)) was twice as high for the SCNCr system (5400 V/cm) than for the ZnO varistor (2600 V/cm) due to a smaller average grain size of the former (4.5 mu m) with respect to the latter (8.5 mu m). Nevertheless, we consider that another important factor responsible for the high E(b) in the SCNCr system is the great number of electrically active interfaces (85%) as determined with electrostatic force microscopy (EFM). It was also established that the SCNCr system might be produced in disks of smaller dimensions than that of commercial ZnO-based product, with a 5.0 cm(-1) minimal area-volume (A/V) ratio. The SCNCr reached the saturation current in a short time because of the high resistivity of the grains, which is five times higher than that of the grains in ZnO-based varistors.

químicos das folhas de Qualea grandiflora: atribuição dos dados de RMN de dois flavonóides glicosilados acilados diastereoisoméricos

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Imageamento Elétrico 3D em área contaminada por hidrocarbonetono polo industrial de Cubatão - SP

Este trabalho mostra os resultados obtidos com ensaios geofísicos realizados em uma área contaminada por hidrocarboneto no Polo Industrial de Cubatão - São Paulo, com objetivo de caracterizar as anomalias geoelétricas associadas à presença dos hidrocarbonetos, bem como delimitar e cubar tais anomalias. Para tanto, utilizou-se o método da eletrorresistividade, por meio das técnicas de Sondagem Elétrica Vertical (SEV) e Imageamento Elétrico 3D. Os resultados obtidos permitem indicar que a presença de hidrocarboneto está associada a anomalias condutivas devido aos produtos da biodegradação. As anomalias condutivas ocorrem de forma disseminada na área, totalizando um volume de 1365,3 m³; entretanto, este volume corresponde somente à presença de contaminante em fase residual.

Involvement of the Central Nervous System in the Salivary Secretion Induced by Pilocarpine in Rats

The effect in rats of an anteroventral third ventricle (AV3V) electrolytic lesion on salivary secretion induced by intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) injection of a cholinergic agonist (pilocarpine) was investigated. Sham- or AV3V-lesioned rats anesthetized with urethane and with a stainless steel cannula implanted into the lateral ventricle (LV) were used. The amount of salivary secretion was studied over a seven-minute period after i.c.v. or i.p. injection of pilocarpine. In sham-operated rats, i.p. injection of pilocarpine (1 mg/kg b.w.) (after 6 h, 2, 7, and 15 days) produced salivary secretion (486 +/- 21, 778 +/- 85, 630 +/- 50, and 560 +/- 55 mg/7 min, respectively). This effect was reduced 6 h, 2, and 7 days after an AV3V lesion (142 +/- 22, 113 +/- 32, and 290 +/- 62 mg/7 min, respectively), but not 15 days after an AV3V lesion (516 +/- 19 mg/7 min). I.c.v. injection of pilocarpine (120 mug in 1 muL), in sham-operated rats after 6 h, 2, 7, and 15 days also produced salivary secretion (443 +/- 20, 417 +/- 81, 496 +/- 14, and 427 +/- 47 mg/7 min, respectively). The effects of i.c.v. pilocarpine were also reduced 6 h, 2, and 7 days after an AV3V lesion (143 +/- 19, 273 +/- 14, and 322 +/- 17 mg/7 min, respectively), but not after 15 days (450 +/- 28 mg/7 min). The results demonstrate that the central nervous system, and particularly the AV3V region, is important for the effect of pilocarpine on salivary secretion in rats. Moreover, they suggest that activation of central pathways may play an important part in the salivary secretion to peripheral pilocarpine in rats.

Tolerance to copper and zinc of Acidithiobacillus thiooxidans isolated from sewage sludge

The effect of copper and zinc ions on sulphur oxidation by Acidithiobacillus thiooxidans, strain SFR01, isolated from anaerobic sewage sludge was assessed, resulting in tolerance levels up to 20 and 200 mmol l(-1) for copper and zinc, respectively. The tolerance levels obtained were higher than the concentration of copper and zinc usually found in the collected sewage sludge. The tolerance levels obtained indicate no constraints for sludge bioleaching of those metals due to their toxicities to the indigenous A. thiooxidans.

A hydride generation flow system for determination of arsenic and selenium by total reflection X-ray fluorescence spectrometry

In this work, a preconcentration and separation system based on continuous flow hydride generation is proposed to improve the determination of As and Se by total reflection X-ray fluorescence spectrometry. The generated hydrides are continuously separated from the liquid phase and collected in a chamber containing 250 mul of HCI/HNO3 1:1 (v/v) solution. Hydride generation conditions and collection of the hydrides were evaluated. Under optimised conditions, enrichment factors of 55 for As and 82 for Se were attained. Detection limits of 0.3 mug l(-1) for As and Se were obtained when 20 ml of sample was used. Analysis of a natural water standard reference material from National Institute of Standard and Technology (SRM-1640) was in agreement with the certified values at the 95% confidence level. (C) 2004 Elsevier B.V. All rights reserved.

A comparative study of thermal conductivity in ZnO- and SnO2-based varistor systems

We performed a comparative study of electrical and thermal properties of ZnO- and SnO2-based varistor. The electrical properties of commercial ZnO-based varistor are equivalent to that found in SnO2-based varistor system. In spite of this, the SnO2 showed a thermal conductivity higher than commercial samples of ZnO-based varistor, which allied with its simpler microstructure and lower dopant concentration is a remarkable result that point out to the use of this system to compete commercially with ZnO-based varistor devices.

Greenhouse gas balance due to the conversion of sugarcane areas from burned to green harvest in Brazil

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

Electrical Properties of Textured Niobium-Doped Bismuth Titanate Ceramics

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

Low-Temperature Sputtering Deposition of Aligned Polycrystalline CaCu3Ti4O12 Nanorods

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

Structural and Spectroscopic Properties of Luminescent Er3+-Doped SiO2-Ta2O5 Nanocomposites

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

Influence of dietary protein level on the broiler chicken's response to methionine and betaine supplements

Two experiments were conducted to compare broiler chicken responses to methionine and betaine supplements when fed diets with low protein and relatively high metabolizable energy levels (17%, 3.3 kcal/g) or moderate protein and lower metabolizable energy levels (24%, 3.0 kcal/g), resulting in different levels of carcass fat. In Experiment 1, the basal diets were formulated with corn, soybean meal, poultry by-product meal, and poultry oil. In Experiment 2, glucose monohydrate was also added, so that identical amino acid profiles could be maintained in the 17 and 24% protein diets. On average, feeding the 17 vs. 24% protein diet decreased 21-d body weight gain by 20%, increased feed conversion ratio (FCR) by 13%, and increased abdominal fat pad weight by 104%. Methionine and betaine supplements improved the performance of chicks fed the 24% protein diet in both experiments, as indicated by body weight gain and FCR. Only supplementary methionine increased performance of chicks fed 17% protein diets, and then only in Experiment 2. Neither methionine nor betaine decreased abdominal fat pad size in either experiment. Methionine supplementation decreased relative liver size and increased breast muscle protein. Both methionine and betaine increased sample feather weight, but when expressed as a percentage of body weight, no significant differences were detected. It is concluded that increasing carcass fat by manipulating percentage dietary protein level or amino acid balance does not influence betaine's activity as a lipotropic agent.

Behavioral evaluation during dental care in children ages 0 to 3 years

Purpose: Many studies concluded that the behavior of babies complicated dental care because of child immaturity or the difficulty of establishing acceptable communication and comprehension. Methods: The records of 696 babies were randomly selected from the baby clinic of Araçatuba in Brazil. Patient age ranged from 0 to 36 months. They were divided into 6 groups according to age: Group I-0 to 6 months; Group II-7 to 12 months; Group III-13 to 18 months; Group IV-19 to 24 months; Group V-25 to 30 months; Group VI-31 to 36 months. The behavior of the child was evaluated upon entrance in the dental office and during the first 4 clinical appointments with a clinical exam and oral physiotherapy. The baby was classified as collaborator (C) or noncollaborator (NC). Statistical analysis was performed using Pearson's chi-square method (P< .05). Results: The percentage of NC for Groups II, III, IV, and V (66%), was significantly higher than for groups I (30%) and VI (50%). Conclusions: Babies from 0 to 6 months showed a collaborative behavior; babies from 7 to 30 months showed noncollaborative behavior; and babies from 31 to 36 months showed no statistically significant difference between the percentage of C and NC.

Influence of dental care for infants on caries prevalence: A comparative study

Purpose: The influence of early dental care on the prevalence of dental caries was determined in children ages 35 to 40 months divided into 2 groups of 160 children each, with 1 group participating in a dental care program from the first year of life to the time of the study, while the other group did not receive any dental care. Methods: The clinical conditions considered for the evaluation were: sound teeth, enamel caries without cavitation, enamel caries with cavitation, and dentinal caries. The proportion and chi-square tests were used for statistical analysis with the level of significance set at 5%. Results: A significant difference regarding the presence of dental caries, especially in the number of children presenting enamel caries with cavitation (P<.0001), was observed between the 2 groups. The number of children with enamel caries without cavitation and dentinal caries was similar for the 2 groups. Conclusions: Considering the aspect of dental caries prevention, the authors concluded that children in the age range of 3 to 4 years who received early dental care showed better oral conditions.