Showing papers by "Federal University of Roraima published in 2000"

Clues to the presence of pathogenic fungi in certain environments.

Abstract: The presence of various pathogenic fungi in rather unsuspected hosts and environments has always attracted the attention of the scientific community. Reports on the putative role of animals in fungal infections of humans bear important consequences on public health as well as on the understanding of fungal ecology. Fungi are ubiquitous in nature and their great capacity for adaptation allows them to survive and indeed, to thrive, in plants, trees and other natural substrata. Nonetheless, we are just beginning to learn the significance that these diverse fungal habitats have on the increasing number of immunosuppressed individuals. The accidental or permanent presence of fungi in animals, plants, soils and watercourses should not be taken too lightly because they constitute the source where potential pathogens will be contracted. If those fungal habitats that carry the largest risks of exposure could be defined, if seasonal variations in the production of infectious propagules could be determined, and if t...

O uso de sílica gel organofuncionalizada como agente sequestrante para metais

Abstract: An overview about the homogeneous and heterogeneous methods of synthesizing silylating agents and applications of the organofunctionalized silica-gel samples was explored. The pendant molecules attached covalently to the inorganic surface displayed important properties to act as sequestrating agents for metals in aqueous and non-aqueous solutions. The large variety of basic centres anchored on organic molecules improve the capacity in adsorbing cations. The increase in adsorption is dependent on the number of basic atoms disposed on the pendant molecules on the surface. The combination of acidic and basicity properties favours the selectivity, such is exemplified by the thiol modified silicas towards mercury (II) cations.

Fruit size, mineral composition and quality of trickle-irrigated tomatoes as affected by potassium rates

Abstract: Para determinar o efeito da fertirrigacao com K sobre o tamanho, a composicao mineral e a qualidade dos frutos do tomateiro, foi conduzido um experimento com aplicacao de seis doses de K, na forma de KCl, correspondendo a 0, 48,4, 118,6, 188,8, 259,0 e 399,4 kg ha-1, com quatro repeticoes, distribuidas no delineamento experimental em blocos casualizados. Foram observadas respostas quadraticas das producoes das classes de frutos graudo 2 (diâmetro > 60 mm), graudo 1 (56 a 60 mm) e graudo (52 a 56 mm) em relacao as doses de K aplicadas na adubacao. As producoes maximas de frutos de cada classe foram obtidas com as doses de K de 116, 190 e 233 kg ha-1, respectivamente. O conteudo de materia seca e os teores de P, S e Mg dos frutos nao foram influenciados pelas doses de K, mas os teores de nitrato e de potassio aumentaram com o aumento das doses. Os teores de vitamina C, solidos soluveis, licopeno e b-caroteno nao foram influenciados pelas doses de K; porem, os incrementos nas doses reduziram o pH e aumentaram o conteudo de acidos nos frutos.

Pollen tube behavior in yellow passion fruit following compatible and incompatible crosses.

Abstract: Pistil squashes were used to examine the growth of Passiflora edulis f. flavicarpa Deg pollen tubes in self-compatible and self-incompatible crosses. Compatible tubes typically showed a uniform layer of callose deposition in the walls and in small plugs spaced at regular intervals within the tube. Two sites of rejection were observed in incompatible crosses: the stigma and on some occasions the style, especially in anomalous crosses. In the style the inhibition of pollen-tube growth occurred in both the upper and middle parts of the transmitting tract. These findings are consistent with the hypothesis that suggests the presence of a gametophytic gene which acts in association with the sporophytic S-gene in P. edulis.

The yeast community and mycocin producers of guava fruit in Rio de Janeiro, Brazil

Abstract: Two hundred and fifty-seven strains be- longing to 28 ascomycetous yeast species were isolat- ed from fallen guava fruit (Psidium guajava) from an Atlantic forest and a rural area in Rio de Janeiro, Brazil. The most frequent species were Kloeckera af- ricana, K. apis, Pichia kluyveri and P membranifa- ciens. Issatchenkia sp A and Issatchenkia sp B, two probable new species were also isolated in a high fre- quency at the forest site. Mycocinogenic yeasts (killer yeasts) with narrow killing spectra were represented by Candida diddensiae-like, C. diversa, C. stellata, I. terricola, K. africana, K. lindneri, P kluyveri, P mem- branifaciens and Torulaspora delbrueckii. The yeasts

Tomato yield and potassium concentrations in soil and in plant petioles as affected by potassium fertirrigation

Abstract: - Tomato (Lycopersicon esculentum Mill.) cv. Santa Clara was grown on a silt clay soilwith 46 mg dm -3 Mehlich 1 extractable K, to evaluate the effects of trickle-applied K rates on fruityield and to establish K critical concentrations in soil and in plant petioles. Six potassium rates (0, 48,119, 189, 259 and 400 kg ha -1 K) were applied in a randomized complete block design with fourreplications. Soil and plant K critical levels were determined at two plant growth stages (at the beginningof the second and fourth cluster flowering). Total, marketable and weighted yields increased with Krates, reaching their maximum of 86.4, 73.4, and 54.9 ton ha -1 at 198, 194, and 125 kg ha K , respectively.At the first soil sampling date K critical concentrations in the soil associated with K rates for maximummarketable and weighted yields were 92 and 68 mg dm -3 , respectively. Potassium critical concentrationsin the dry matter of the petioles sampled by the beginning of the second and fourth cluster floweringtime, associated with maximum weighted yield, were 10.30 and 7.30 dag kg

Delta matter formation in dense asymmetric nuclear medium

Abstract: In the context of a relativistic mean field theory the delta-resonance matter formation in a highly compressed nuclear medium is investigated. For a given set of nucleon–meson coupling constants, the delta-resonance formation is studied by changing the delta-meson coupling constants. The effect on the equation of state and on the delta-resonance population with respect to changes in the delta-resonance coupling constants values is discussed for very asymmetric and quasi-symmetric nuclear matter, as an extension of works restricted to the symmetric nuclear matter treatment.5,6

Mechanically induced structural modifications in metal-doped lamellar silica

Abstract: Lamellar silica samples were synthesized by a neutral amine process and structural modifications were induced by copper nitrate or sulfate addition. The lamellar silica showed three diffraction peaks at 2θ values of 3.8, 7.3 and 11.5 degrees, due to the 0 0 1, 0 0 2 and 0 0 3 diffraction planes. Addition of copper nitrate or sulfate affected the structure of the starting matrices as demonstrated by X-ray diffraction patterns. Both metal-doped lamellar silicas were mechanically induced to react in the solid state with potassium bromide, to give products which exhibited significant structural modifications. The thermal stability of the lamellar silica samples increased by addition of copper salts. Thus, the precursor lamellar silica and the corresponding nitrate and sulfate metal-doped samples started to degrade at 105°C, 130°C and 230°C, respectively. Structural and thermal measurements on these samples exhibited an increased resistance to decomposition, however, the nitrate and sulfate anions caused remarkable structural modifications in the synthesized matrices.

Crescimento relativo e determinação da idade na fase juvenil de Armases angustipes (Dana) (Decapoda, Brachyura, Grapsidae)

Abstract: The relative growth of the male chelipod and female abdomen of Armases angustipes (Dana, 1852) was studied in order to determine the carapace size of puberty. Also, the age of juvenile crabs in laboratory was established. A total of 537 males and 557 females were analysed and the transition point between mature and immature stages was determined for both sexes. Males attain maturity at 1.00 cm carapace width and females at 1.08 cm. The relative growth of female abdomen was more remarkable than that of the male chelipod, although both are positive allometric. It suggests a greater importance of a large abdomen in females than a strong chelipod in males. Juvenile crabs reared from megalopa stage has five developmental stages before reaching sexual differentiation. This occurs in the sixth juvenile stage, when the intermolt stages become longer. The potential equation between carapace width and accumulated duration of juvenile stages is described as CW = 0,047D0,508.

Decrease of interlamellar spacing of silica samples induced by external pressure

Abstract: Lamellar silica and cadmium or mercury derivative-doped samples were synthesized by neutral amine route through the sol‐gel process. These samples showed a decrease of the interlamellar d-space promoted only by an increase of the externally applied pressure on the samples. For a constant external pressure the observed decrease has a linear behavior as a function of time. The undoped lamellar silica, when pressed under 760 mPa for 45 min, exhibited a decrease of the interlamellar distance of 16%. The obtained results suggested that under an increased external pressure, cadmium is forced to change its coordination environment, to adjust to a most stable structure. ” 2000 Elsevier Science B.V. All rights reserved.

The Ion-exchange Capacity of Ti and Zr Lamellar Hydrogenphosphates. TG measurements

Abstract: Thermogravimetric data were used to calculate the number of acidic Bronsted sites in lamellar α-titanium (α-TiP), γ-titanium (γ-TiP), α-zirconium (α-ZrP) and γ-zirconium (γ-ZrP) hydrogenphosphates. The numbers of acidic sites calculated for these lamellar compounds were 7.81, 5.67, 6.33 and 5.56 for α-TiP, γ-TiP, α-ZrP and γ-ZrP, respectively. These values are in good agreement with those found through potentiometric titration. The data obtained prove that thermogravimetric measurements can be used as a reliable analytical tool to follow the ion-exchange capacity of this kind of crystalline lamellar compounds.

Effect of adsorbed polyaniline on the thermal stability of iron and arsenic oxides

Abstract: Iron and arsenic oxide grains are coated with the conducting organic polymer polyaniline. The obtained samples were characterized by infrared spectroscopy, SEM, conducting measurements and thermogravimetry. The thermal stability of both oxides are increased. For As2O3 the sublimation temperature is increased from 165oC in the pure oxide to 206oC in the polymer modified sample. The pure Fe3O4 sample exhibits sublimation at 780oC whereas the polyaniline coated oxide is stable until at least 1000oC.

Estrutura populacional de Armases angustipes (Dana) (Decapoda, Brachyura, Grapsidae) na Ilha do Farol, Matinhos, Paraná

Abstract: Annual fluetuation of densities and population strueture of Armases angustipes (Dana, 1852) from a rocky shore at Farol Island, Matinhos, Parana, Brazil (25o51'S and 48o32'W) were studied. The population strueture was treated in the following aspects: sexual proportion, dial intensity of activities, size composition and its fluetuation, and general condition of the crabs. The collections were made monthly, from January to December 1991. The samples were obtained handly, in the morning and at night, at the supratidal zone during low tides. There were caught 1,139 crabs, among which 34 were juveniles, 544 males, 555 females and 4 ovigerous females. Population density was highest in April (19.56 ind.m"2 ) and in October (23.86 ind.m"2 ). The sexual proportion was 1:1 in eleven months. Although the male crabs were more abundant than the females in May, there was not any statistical significam difference between the sexes. The activity of the population is intenser at night than at morning for both sexes. The recruitment of juveniles oceurs mainly in March, April and July. The condition factor in females is related to the reproduetive period. The population can migrate to the terrestrial habitat near the supratidal zone.

Procurando um arroz c4 mediante exame anatômico foliar

Abstract: A possibilidade de se encontrar genotipos de arroz, graminea C3, com caracteristicas anatomico-foliares semelhantes as gramineas C4 levou ao presente estudo. Genotipos com caracteristicas C4 seriam superiores fotossinteticamente, mais adaptados ao estresse ambiental e mais produtivos. Nesta pesquisa foi observada a anatomia foliar de 483 exemplares de arroz, sendo 477 da especie Oryza sativa L. e seis de outras especies (Oryza glumaepatula, O. glaberrima, O. nivara, O. rufipogon, O. flotante e O. longistaminata). Na pesquisa, observou-se a presenca de cloroplastos nas celulas da bainha vascular da cultivar CNA 6189. Em alguns outros genotipos, foram encontrados apenas vestigios de cloroplastos, e nenhum cloroplasto na maioria dos genotipos, como o IAC 25. Com base nos resultados encontrados, espera-se que por meio de tecnicas de biologia molecular, caracteristicas de plantas C4 venham a ser incorporadas a plantas, como o arroz, melhorando substancialmente as suas potencialidades de adaptacao a ambientes menos favorecidos.

Sobre a aplicabilidade da termogravimetria para a estimativa de parâmetros termoquímicos de compostos de coordenação: os elementos lantanídicos

Abstract: By using thermochemical data reported for a series of chelates of the type [Ln(thd)3], thd = 2, 2, 6, 6 ­ tetramethyl- 3,5-heptanedione and Ln = La, Pr, Nd, Sm, Gd, Tb, Ho, Er, Tm and Yb, empirical correlations were found involving thermochemical parameters (e.g. dissociation enthalpy) and the thermodynamic temperatures of the beginning of thermal degradation of the chelates, ti. It is shown that ti values are of capital importance in the study of this all class of coordination compounds. Among others, the empirical equation is obtained: r3+ = (-0,013.Z + 1,36)/0,005, that relates the lanthanide cation radius (pm) with the atomic number of the element. The remarkable fact is that this equation is achieved by using thermogravimetric and calorimetric parameters. Is also shown that ti values are related with the P(M) function values, which are very close related with the energy difference, DE, between the lowest electronic energy level of the fns2d1 configuration and the lowest energy level of the fn+1s2 configuration in the neutral gaseous atoms.

Circular Cosmic String Loop in Brans-Dicke Theory

Abstract: The gravitational field of a stationary circular cosmic string loop ,externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity(GR) and goes over to the corresponding solution in GR when the Brans-Dicke parameter $\omega $ becomes infinitely large.