PROCESSING AND CHARACTERIZATION OF LOW-VOLTAGE VARISTORS

ZnO seed particles and Cr2O3 were used in this study to control the microstructure of ZnO varistors. The seed particles were prepared by adding 1.0 mol % BaO to ZnO. The powder was then calcined at 800-degrees-C for 2 h, pressed into pellets and sintered at 1400-degrees-C for 8 h. The sintered ZnO was ground and the BaO eliminated by washing in water. The remaining ZnO powder was classified into a size fraction ranging from 38 to 149 mum. The addition of a small amount (1 weight %) ZnO seed grains produces varistors with low breakdown voltages (7.6 V/mm) and an alpha coefficient of approximately 10. The addition of Cr2O3 stabilizes the spinel phase yielding a more homogeneous microstructure, but degraded electrical behaviour of the ZnO varistor.

Partial purification and some properties of a T2 ribonuclease from Aspergillus flavipes

A ribonuclease was partially purified from the culture medium of Aspergillus flavipes (IZ:1501), after 96 h of cultivation by chromatography on DEAE-cellulose and Sephadex G100 columns. The molecular weight of the RNase was estimated to be 40 kD by gel filtration using Sephadex G100, and the optimum pH and temperature were 4.0 and 50-55 degrees C, respectively. Catalytic activity was inhibited by Zn+2, Fe+3, Hg+2 and Ag+ ions. The enzyme did not show an exact base specificity and produced four kinds of 3'-nucleotides from yeast RNA.

Sintering and characterization of PLZT (9/65/35)

PLZT(9/65/35) obtained by association between the Pechini method (ZT) and partial oxalate (PLZT) was prepared. The stoichiometric phase and monophasic (cubic) PLZT obtained by calcination did not occur after sintering. The sintering process, by using two stages, caused a liquid phase formation due to a PbO excess (5 and 10 wt%). Samples with high density (similar to 8 g/cm(3)) and optical transparency(similar to 12%) were obtained. However, an equilibrium between the excess of PbO of sample/atmosphere PbO leads to a segregated PbO phase on the boundaries of the microstructure. A diffusion of Zr, Ti and La ions from PLZT to PbO phase promoted a stoichiometric deviation of the matrix and modified the optical and dielectric characteristics. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Identification and characterization of Colletotrichum spp. affecting fruit after harvest in Brazil

Colletotrichum spp. cause anthracnose in various fruits post-harvest and are a particularly important problem in tropical and subtropical fruits. The disease in fruits of avocado, guava, papaya, mango and passion fruit has been reported to be caused by C. gloeosporioides, and in banana by C. musae. In subtropical and temperate crops such apple, grape, peach and kiwi, the disease is caused by C. acutatum. The variation in pathogenic, morphological, cultural and molecular characteristics of Brazilian isolates of Colletotrichum acutatum Simmonds and isolates from post-harvest decays of avocado, banana, guava, papaya, mango and passion fruit was evaluated. The fruits were inoculated with mycelium of C. acutatum, Colletotrichum spp. and C. musae on a disc of potato dextrose agar. The morphological, cultural and molecular characteristics studied were conidia morphology, colony growth at different temperatures, colony coloration and PCR with primers CaInt2 and ITS4 for C. acutatum and CgInt and ITS4 for C. gloeosporioides. C. acutatum was pathogenic to avocado, guava, papaya, mango and passion fruit, but it was not pathogenic to banana. The morphological, cultural and molecular studies indicated that the avocado, papaya, mango and passion fruit isolates were C. gloeosporioides. The natural guava isolate was identified as C. acutatum, which had not been found previously to produce anthracnose symptoms on guava in Brazil.

Allergenic extracts from Metarhizium anisopliae: Obtainment and characterization

Metarhizium anisopliae is used as a biopesticide for insects that damage agricultural plantations like sugar cane and forage plants. In a previous study the sensitization to this fungus of asthmatic patients coming from sugar cane areas was showed. The aims of this work were: to compare crude extracts obtained with Tris-HCl and Coca liquid from several growth phases of M. anisopliae concerning the total content of proteins and their electrophoretic analysis profile; to evaluate in vivo allergic sensitization in Balb/c mice and allergic patients from a sugar cane area, and to characterize the allergenic fractions in the sera of patients positive for the prick test by means of Western-blotting. The extract obtained with Coca liquid on the 16(th) day was the one that presented the greatest number of proteic fractions, including all those present in the other extracts. Twelve fractions were verified in this extract with approximate molecular weights from 94 to 14 kDa. The allergenicity of the extract obtained on the 16(th) day was proven by the production of IgE antibodies in Balb/c mice, with titres of 200. Prick tests carried out with the extract of the 16(th) day in 79 atopic individuals (from sugar cane area), 35 atopic individuals (from urban area) and 11 non- atopic individuals showed respective positivity of 29%, 9% and 0%. The allergenic characterization in vitro was performed by means of Western blotting, and the fractions that reacted with the positive individuals' sera were those of approximate molecular weights of 67 kDa (95%); 20 kDa (55%); 94 kDa (36%); 34 and 36 kDa (23%); 43 and 48 kDa (14%): 16 kDa (9%) and 54kDa (5%). It was concluded that the crude allergenic extract, obtained with Coca liquid from the 16(th) day growth of Metarhizium anisopliae, contains allergenic fractions and can be used in diagnostic screening tests.

Purification and biological activity of the thrombin-like substance isolated from Bothrops insularis venom

The venom of Bothrops insidaris snake, known in Brazil as jararaca ilhoa, contains a variety of proteolytic enzymes such as a thrombin-like substance that is responsible for various pharmacological effects. B. insularis venom chromatography profile showed an elution of seven main fractions. The thrombin-like activity was detected in fractions I and 111, the latter being subjected to two other chromatographic procedures, so to say DEAE and Hi Trap Benzamidine. The purity degree of this fraction was confirmed by analytical reverse phase HPLC, which displayed only one main fraction confirmed by SDS-PAGE constituting fraction III. About 5 mu g of fraction III protein potentiated the secretion of insulin induced by 2.8mM of glucose in rats isolated pancreatic beta-cells treated; the increase being around 3-fold higher than its respective control. B. insidaris lectin (BiLec; 10 mu g/mL) was also studied as to its effect on the renal function of isolated perfused rat kidneys with the use of six Wistar rats. BiLec increased perfusion pressure (PP), renal vascular resistence (RVR), urinary flow (UF) and glomerular filtration rate (GFR). Sodium (%TNa+) and chloride tubular reabsorption (%TCl-) decreased at 120 min, without alteration in potassium transport. In conclusion, the thrombin-like substance isolated from B. insularis venom induced an increase in insulin secretion, in vitro, and transiently altered vascular, glomerular and tubular parameters in the isolated rat kidney. (c) 2006 Elsevier Ltd. All rights reserved.

The putative telomerase reverse transcriptase component of Leishmania amazonensis: gene cloning and characterization

The Leishmania amazonensis telomerase gene was cloned by a polymerase chain reaction-based strategy using primers designed from a Leishmania major sequence that shared similarities with conserved telomerase motifs. The genes from three other species were cloned for comparative purposes. A ClustalW multiple-sequence alignment demonstrated that the Leishmania telomerases show greater homology with each other than with the proteins of other kinetoplastids and eukaryotes. Characterization experiments indicated that the putative Leishmania telomerase gene was probably in single copy and located in the largest chromosomes. A single messenger ribonucleic acid transcript was found in promastigotes. Phylogenetic analysis suggested that Leishmania telomerase might represent a liaison between the oldest and the newest branches of telomerases.

Synthesis by the polymeric precursor method and characterization of undoped and Sn, Cr and V-doped ZrTiO4

In this work, zirconium titanate doped with 0. 1, 0.2, and 0.4 mole% of tin, chromium and vanadium was synthesized by the polymeric precursors method and characterized by thermal analysis (TG/DTA), X-ray diffraction (XRD), nitrogen adsorption and scanning electronic microscopy (SEM). The powder presented two mass losses attributed to the exit of water and to the pyrolysis of the organic material. The surface area reduction observed from 500 degrees C indicates the beginning of the sintering process. All the dopants led to changes in the lattice parameters and to the decrease of both crystallite size and particle size. (c) 2005 Elsevier B.V. All rights reserved.

Preparation and characterization of PAni-PMMA dispersions

Blends of polyaniline (PAni) and poly(methyl methacrylate) (PMMA) have been produced using core-shell particle synthesis, which is advantageous because it allows changing surface-related properties of PMMA with relatively small amounts of PAW and without the use of organic solvents. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements indicated that the deposition of pollyaniline seems to alter the regular shape of the primary acrylic latex particles. The coverage of PMMA particles by PAW was confirmed by FTIR measurements, where distinct data were obtained from the transmission and diffuse reflectance modes, since the latter is surface sensitive. The zeta potential, which is also a surface-related property, increased with the contents of PAW, as the shells probably became protonated with PAW in the emeraldine salt form. Coverage with PAW did not affect the thermal bulk properties of the PMMA shells.

Synthesis and characterization of 9.5/65/35 PLZT prepared from the polymeric precursors

The 9.5/65/35 PLZT was prepared from the polymeric precursors (the Pechini and partial oxalate process) and by sintering in two stages in an oxygen atmosphere. After thermal treatment at 400 degreesC, the powders were calcinated and sintered at 1200 degreesC with slow heating and cooling rates. The second stage of sintering consisted of hot pressing at the same temperature in oxygen atmosphere. After calcination of PLZT powders obtained by both methods, as well as after sintering of PLZT obtained by Pechini process, the paraelectric cubic phase was formed. After sintering of PLZT obtained by partial oxalate procedure, small tetragonality of crystal structure was observed. After hot pressing PLZT was pseudocubic. SEM microstructural analyses were carried out of the sintering and hot pressed samples and indicated the small grain size less than 2 mum. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Screening and characterization of mutations in isoniazid-resistant Mycobacterium tuberculosis isolates obtained in Brazil

We investigated mutations in the genes katG, inhA (regulatory and structural regions), and kasA and the oxyR-ahpC intergenic region of 97 isoniazid (INH)-resistant and 60 INH-susceptible Mycobacterium tuberculosis isolates obtained in two states in Brazil: São Paulo and Parana. PCR-single-strand conformational polymorphism (PCR-SSCP) was evaluated for screening mutations in regions of prevalence, including codons 315 and 463 of katG, the regulatory region and codons 16 and 94 of inhA, kasA, and the oxyR-ahpC intergenic region. DNA sequencing of PCR amplicons was performed for all isolates with altered PCR-SSCP profiles. Mutations in katG were found in 83 (85.6%) of the 97 INH-resistant isolates, including mutations in codon 315 that occurred in 60 (61.9%) of the INH-resistant isolates and 23 previously unreported katG mutations. Mutations in the inhA promoter region occurred in 25 (25.8%) of the INH-resistant isolates; 6.2% of the isolates had inhA structural gene mutations, and 10.3% had mutations in the oxyR-ahpC intergenic region (one, nucleotide -48, previously unreported). Polymorphisms in the kasA gene occurred in both INH-resistant and INH-susceptible isolates. The most frequent polymorphism encoded a G(269)A substitution. Although KatG(315) substitutions are predominant, novel mutations also appear to be responsible for INH resistance in the two states in Brazil. Since ca. 90.7% of the INH-resistant isolates had mutations identified by SSCP electrophoresis, this method may be a useful genotypic screen for INH resistance.

Synthesis and characterization of solid molybdenum(VI) complexes with glycolic, mandelic and tartaric acids. Photochemistry behaviour of the glycolate molybdenum complex

The complexes (NH4)(2)[ MoO2( C2H2O3)(2)]center dot H2O, (NH4)(2)[MoO2(C8H6O3)(2)] and (NH4)(2) [MoO3(C4H4O6)]center dot H2O were prepared by reaction of MoO3 with glycolic, mandelic and tartaric acids, respectively. The complexes were characterized by elemental and thermal analysis, IR spectroscopy and X- ray diffraction. Crystals of the glycolate and tartarate complexes are orthorhombic and the mandelate complex is monoclinic. Elemental and thermal analysis data showed that the glycolate and tartarate complexes are monohydrated. Hydration water is not present in the structure of the mandelate complex. IR spectra showed COO- is involved in coordination as well as the oxygen atom of the deprotonated hydroxyl group of the alpha-carbon. The glycolate molybdenum complexes with general formula M-2[MoO2(C2H2O3)(2)]center dot nH(2)O, where M is an alkali metal and n=1 or 1/2, were also prepared and characterized. Aqueous solutions of the glycolate complex become blue and mandelate and tartarate complexes change to yellow or brown when exposed to UV- radiation.