Showing papers by "Federal University of São Carlos published in 1997"

Photosynthetic capacity and specific leaf mass in twenty woody species of Cerrado vegetation under field conditions

Abstract: Photosynthetic capacity on area (PNmaxa) and mass bases (PNmaxm) and specific leaf mass (SLM) were determined in twenty adult woody species of Cerrado under field conditions. The mean values obtained for PNmaxa [11.4 µmol(CO2) m-2 s-1], PNmaxm [78 µmol(CO2) kg-1 s-1] and SLM (150 g m-2) were compared with mean values found for deciduous and evergreen sclerophyllous species growing also under field conditions. PNmaxm and SLM were statistically different among deciduous, Cerrado and evergreen sclerophyllous species. There was a gradual decrease of PNmaxm and an increase of SLM from deciduous to evergreen sclerophyllous species. Woody species of Cerrado showed mean values of PNmaxm and SLM between deciduous and evergreen species indicating its brevideciduousness. The comparison using mean values of PNmaxm and SLM belonging to deciduous, Cerrado and evergreen sclerophyllous species was suitable to confirm the interdependence among leaf life span, structure and physiological attributes of leaf.

Effect of Bi2O3 addition on the microstructure and electrical properties of the SnO2.CoO.Nb2O5 varistor system

Abstract: Tin dioxide (SnO2) is an n type semiconductor with crystalline structure of rutile type and has low densification rate due to its high surface diffusion at low temperatures and high SnO2 partial pressure at high temperatures [1]. Dense SnO2 based ceramics can be achieved by introducing dopants [2–5] or by hot isostatic pressure processing [6, 7]. Dopants with valence ‡2 can promote densification of SnO2 ceramics due to the formation of solid solution with the creation of oxygen vacancies. In our previous work [8, 9] we have shown that the CoO and Nb2O5 doped SnO2 ceramic is single phase and presents varistor behaviour with AE ˆ 8.0. By adding 0.05 mol % Cr2O3 the system is still a single phase with the non-linear coefficient increasing to AE ˆ 41. The electrical behaviour of varistors is governed by the presence of voltage barriers at the grain boundaries [10, 11]. For a given varistor system each voltage barrier is characterized by a specific value vb. The reference voltage barrier for a varistor is determined by the average number of barriers n in series multiplied by vb, that is: Vr ˆ n:vb (1)

Shear behaviour of fiber reinforced concrete beams

Abstract: This paper presents the results of shear/flexure tests on steel and polypropylene fiber reinforced concrete beams. In addition to analyzing the influence of fibers on the structural performance in situations of different ratios of shear reinforcement, some aspects of the properties of fresh and hardened concrete are introduced. Fourteen square-section beams were tested. The beams were prepared from seven different mix proportions, varying the type and the volume of fiber added. There were two beams for each composite mix: one model with and the other without stirrups. The main alterations resulting from the use of fibers were increased shear strength, stiffness (particularly after first cracking stage) and ductility. Other parameters used in analyzing performance were the properties of the hardened concrete (compressive strength, tensile strength, and modulus of elasticity), and stresses in the stirrups, in the longitudinal reinforcement and in the concrete (at the web and compression zone).

Rotational features of carbon-nitrogen bonds in axially chiral o-tert-butyl anilides and related molecules. Potential substrates for the ‘prochiral auxiliary’ approach to asymmetric synthesis

Abstract: A new strategy for asymmetric induction termed the ‘prochiral auxiliary’ approach is introduced. Reactions of acylating agents with prochiral N -methyl- o - tert -butyl aniline provide anilides that are axially chiral by virtue of restricted rotation about the NAr bond. Rotamer populations about the amide bond (E/Z) were studied by 1 H NMR. Several pairs of enantiomeric o - tert -butyl anilides were separated by chiral chromatography and barriers about the NAr bond were measured by thermal racemization. Related o -(1-(trialkylsilyloxy)-1-methylethyl) anilides were also studied.

The X1X2Y sex chromosome system in the fish Hoplias malabaricus. I. G-, C- and chromosome replication banding

Abstract: Hoplias malabaricus, a widely distributed neotropical fish (Central America to Argentina), may represent a group of distinct species showing diversified cytotypes with respect to chromosome number, morphology and sex systems. One of these karyotypic forms is characterized by an X1X1X2X2/X1X2Y sex chromosome system, with 2n = 40 and 39 chromosomes in females and males respectively. Analyses with G-, C- and chromosome replication banding permitted a better characterization of the sex chromosomes in this cytotype. The Y chromosome, unique in males, resulted from a translocation event between two biarmed chromosomes: one similar to chromosome 6 (X1) and the other one similar to chromosome 20 (X2), the latter corresponding to a probable identification. On the basis of the observed banding patterns, the Y chromosome may represent a stable dicentric, with an inactive centromere interstitially located on its long arm. The results are also related to a specific satellite DNA subfamily, previously characterized in Hoplias malabaricus, which appears to be associated with the X1 chromosome.

A test of the Hrubÿ parameter to estimate glass-forming ability

Abstract: Experimental nucleation and growth rates for some glasses that nucleate in the bulk were used to calculate critical cooling rates for glass formation (Rc) by the TTT method. Resulting critical cooling rates were consistent with laboratory melting and quenching and also with experimental data of critical cooling rates for lithium disilicate glass. Strong correlation between the Hruby parameter of glass stability (Kgl) and the glass-forming ability, evaluated by Rc, was found. Therefore, Kgl can be used to estimate the glass-forming ability for glasses that exhibit volume nucleation.

Metastable phases in lithium disilicate glasses

Abstract: This article deals with crystal nucleation in glass, with special emphasis on new findings about metastable phase formation in lithium disilicate glass (LS2) and its effects on crystallization of the stable LS2 crystal phase. The early crystallization stages of slightly sub-stoichiometric LS2 glasses were probed with SAXS and selected area diffraction (SAD). The second task was accomplished by carefully measuring the crystal nucleation rate (I), growth rate (U), the time evolution of crystallinity and the apparent induction periods (t′) for crystal nucleation and growth at 500°C (Tg ∼ 450°C). Finally, the independently determined kinetic parameters (I and U) were used in a modified form of the JMAK equation, which account for transient nucleation conditions, to test the nucleation mechanism. Depending on the heat treatment, one or more metastable phases precipitate in the early crystallization stages of LS2 glass, however, they do not play a significant role on the crystallization mechanism of the thermodynamically stable phase.

Fish and wildlife resources in the pantanal wetlands of Brazil and potential disturbances from the release of environmental contaminants

Abstract: The Pantanal is one of the world's largest wetland ecosystems, encompassing 140,000 km2. The region is a breeding ground for waterfowl, and enormous rookeries of storks, herons, egrets, and ibises indicate a vast abundance of birds. The Pantanal is also one of the most important refuges for many of Brazil's threatened or endangered species, such as jaguars, giant anteaters, and swamp deer. The productive web of waters supports an important fishery industry. The Pantanal, with its extraordinary diversity and abundance of wildlife, is a threatened region. Deforestation, expanding agriculture, illegal hunting and fishing, unplanned tourism, and pollution with pesticides have caused a progressive deterioration of the natural environment, placing one of Brazil's most important ecosystems at risk. Gold mining is still common in the northern Pantanal. Along the Cuiaba river are 700 functional gold-mining dredges. In the town of Pocone, unregulated gold mines have also contaminated the area with mercury, which is used during the processing of gold. Approximately 50% of the fishes from the Cuiaba River and 35% from the Bento Gomes River have mercury levels higher than 0.5 μg/g, which is beyond the international standard for contamination. Fishes from the Paraguay River have levels below 0.5. Birds like Phalacrocorax olivaceus, Aramus guarauna, and Rosthramus sociabilis were also contaminated. No research has been conducted on the fate of pesticides in the Pantanal. However, because of the huge demand for soybean plantations on the upland areas surrounding Pantanal, the application of toxic agricultural chemicals is very common.

Dinâmica da alimentação natural de Callinectes danae Smith (Decapoda, Portunidae) na Lagoa da Conceição, Florianôpolis, Santa Catarina, Brasil

Abstract: From March/91 to February/92 monthly collcction surveys were carried out to obtain basic information about the dynamics of feeding and trophic spectrum of C. danae Smith, 1869. A total of 456 males and 527 females were caught. The diet of the species was not sex related. The trophic spectrum of C. danae is composed by a high number of items. The 35 items were assembled in 14 categories and the feeding index was applied. Mollusca, Polychaeta and Crustacea were observed to be basic elements in the species diet, Osteichthyes and MOND appear as secondary resource whereas vegetal material were found to be of less importance.

Drying Of Pastes In Spouted Beds Of Inert Particles: Design Criteria And Modeling

Abstract: The drying of pastelike materials can be performed well in spouted beds (SB) of inert particles. In this work the drying performance of pastes in conical pastes in conical spouted beds is analyzed as a function of column dimensions, fluid flow characteristics and paste properties. imulated data on fluid flow together with the experimental results on drying of different pastelike materials are presented and discussed to provide criteria for the design of a conical spouted bed dryer for suspensions.

Diurnal patterns of chlorophyll a fluorescence and stomatal conductance in species of two types of coastal tree vegetation in southeastern Brazil

Abstract: Diurnal measurements of chlorophyll fluorescence parameters and stomatal conductance to water vapour were carried out in five woody species and a bromeliad from two coastal vegetation types in Brazil, the rock outcrop of Pao de Acucar and the sand dunes of Macae. The environmental conditions of both study sites are characterized by high temperatures and light levels. The studied species comprised C3 plants with different degrees of stomatal closure during the day, overall daily stomatal conductance and a plant with a typical CAM pattern. Plants on Pao de Acucar exhibited only a small decline in potential quantum yield throughout the day. The non-photochemical quenching and the approximate photosynthetic electron transport rates were maximal during the peak of irradiance. In Macae, light response curves of fluorescence parameters in the CAM-tree Clusia hilariana showed a clear differentiation between phases III and IV of CAM. In phase III, decarboxylation of organic acids probably maintained high internal CO2 levels and there was only a small decrease in photochemical quenching with saturating light levels. In phase IV, the depletion of the organic acid pool and low stomatal conductances resulted in much lower levels of effective quantum yield and a substantial increase in both 1-qP and non-photochemical quenching with increasing light levels. This behaviour during phase IV in the CAM-tree C. hilariana was comparable to the performance of the C3-ClusiaC. aff parviflora at Pao de Acucar. It is seen that both the C3 species and the CAM tree occurring in the two coastal communities effectively adjust their photochemical efficiency to environmental conditions and especially to diurnal variations of stress.

Crystallization and corrosion resistance of amorphous FeCuNbSiB

Abstract: The influence of metalloid content and thermal treatment on microstructural evolution and corrosion resistance of FeCuNbSiB amorphos alloys with different Si/B ratio was investigated. The crystallization of FeCuNbBSi amorphous alloys is dependent on Si/B content. An increase of the corrosion resistance with the Si content in a 0.1 M H2SO4 solution was observed. The nanocrystallization of alloys, except that with lower Si content, results in an increase of corrosion resistance.

Critical behaviour of mixed heisenberg chains

Abstract: The critical behaviour of anisotropic Heisenberg models with two kinds of antiferromagnetically exchange-coupled centres are studied numerically by using finite-size calculations and conformal invariance. These models exhibit the interesting property of ferrimagnetism instead of antiferromagnetism. Most of our results are centred in the mixed Heisenberg chain where we have at even (odd) sites a spin- SU(2) operator interacting with a XXZ-like interaction (anisotropy ). Our results indicate universal properties for all these chains. The whole phase, , where the models change from ferromagnetic to ferrimagnetic behaviour is critical. Along this phase the critical fluctuations are ruled by a c = 1 conformal field theory of Gaussian type. The conformal dimensions and critical exponents, along this phase, are calculated by studying these models with several boundary conditions.

Manganese(III) porphyrins: catalytic activity and intermediate studies in homogeneous systems

Abstract: We studied how solvent, stirring method, PhIO/MnP molar ratio, presence of water and axial ligand affect the catalytic activities of Mn(TPP)Cl, Mn(MNPP)Cl, Mn(TDCPP)Cl and Mn(TFPP)Cl in the oxidation of cyclohexane by PhIO. A study of the catalytic intermediates in the reaction between Mn(TPP)Cl or Mn(TDCPP)Cl and PhIO was also carried out by UV–Vis and EPR spectroscopies. The reaction of Mn(TPP)Cl with PhIO showed the formation of a mixture of species MnIV(O)P·+ and MnV(O)P as intermediates, which were confirmed by the deconvolution of the UV–Vis spectra. Addition of imidazole as cocatalyst favoured the formation of the intermediate species MnV(O)P, evidenced by the UV–Vis band at 408 nm. The corresponding EPR spectra gave evidence that in the presence of imidazole, MnIV(O)P·+ species are formed only in very low amounts. For Mn(TDCPP)Cl the dominating intermediate species is MnIV(O)P·+. Addition of imidazole to halogen-substituted MnP systems does not result in increase of the C-ol yields because very stable bis-imidazole-MnP complexes are formed. Anchoring of such MnP on imidazole propyl gel (IPG) results in better catalytic activity because in this case, the catalyst is mono-coordinated to the support and imidazole favours the formation of the intermediate species MnV(O)P.

Nitrosyl ruthenium complexes with general formula [RuCl3(NO)(PP)] (PP = {PPh2(CH2)nPPh2}, n = 1–3 and {PPh2-CHPPh2}). X-ray structure of [RuCl3(NO){PPh2(CH2)3PPh2}]

Abstract: Ruthenium(II) complexes with general formula [RuCl3(NO)(PP)] were obtained in the solid state, where PP = PPh2(CH2)nPPh2 (n = 1) and PPh2-Ch = CH-PPh2. The 31P NMR spectra of these compounds measured in CH2Cl2 showed only singlets, consistent with a fac configuration containing two equivalent phosphorus atoms. However the X-ray diffraction data show that the [RuCl3(NO){PPh2(CH2)3PPh2}] complex crystallizes in a mer configuration, where one of the phosphorus atoms is trans to the NO group, in a slightly distorted octahedral geometry.

Amperometric biosensor for the determination of phenols using a crude extract of sweet potato : (Ipomoea batatas (L.) Lam.)

Abstract: An amperometric biosensor for the determination of phenols is proposed using a crude extract of sweet potato (Ipomoea batatas (L.) Lam.) as an enzymatic source of polyphenol oxidase (PPO; tyrosinase; catechol oxidase; EC 1.14.18.1). The biosensor is constructed by the immobilization of sweet potato crude extract with glutaraldehyde and bovine serum albumin onto an oxygen membrane. This biosensor provides a linear response for catechol, pyrogallol, phenol and p-cresol in the concentration ranges of 2.0×10−5-4.3×10−4mol L−1, 2.0×10−5-4.3×10−4 mol L−1, 2.0×10−5-4.5×10−4 mol L−1 and 2.0×10−5-4.5×10−4mol L−1, respectively. The response time was about 3–5 min for the useful response range, and the lifetime of this electrode was excellent for fifteen days (over 220 determinations for each enzymatic membrane). Application of this biosensor for the determination of phenols in industrial wastewaters is presented.

Acetobacter Cellulosic Biofilms Search for New Modulators of Cellulogenesis and Native Membrane Treatments

Abstract: Since natural substances like pseudoxanthins exert a positive effect on the cellulogenic ability of Acetobacter xylinum when producing cellulosic pellicles suitable for skin burn therapy, new defined and complex modulators were sought. Ca2+ and Mg2+ (4 mM) were strongly stimulatory. Na+ had no effect and K+ was inhibitory. Ammonium dihydrogen phosphate (0.12 g/L) ensured the same nitrogen supply as the same concentration of yeast extract as measured by cellomembrane dry wt./yield albeit higher yeast extract supplies produced thicker membranes. Corn steep liquor (CSL) was also progressively beneficial from 0.125 to 0.5 mL/L, and this yield could be further improved by the combination of CSL with a tea infusion (source of caffeine). Uridine (precursor for UDP-Glc, sugar donor in cellulose biosynthesis), guanine, guanosine, and its butirylated derivatives (precursors for the positive modulator of cellulose synthetase, di-cGMP) resulted in only moderate stimulation. Sodium phytate and betaine were also slightly stimulatory. The fibrilar product from a new Acetobacter isolate (Ax-M) was characterized as cellulose by comparison with the solid-state(13)C-NMR of algal cellulose. Its X-ray diffractogram was a confirmatory analysis. After incorporation of tamarind xyloglucan to previously air-dried cellulosic pellicles, diffractometry displayed only slight differences. Mercerized (5M NaOH) fresh cellulosic biofilms underwent drastic size reduction (3.5-fold), turning compact nut still flexible if maintained wet.