Showing papers by "Federal University of São Carlos published in 2000"
359 citations
TL;DR: In this article, the authors compared the variability of chemical composition and macroinvertebrate communities in the streams of two catchments (Pisca and Cabras) belonging to the same ecoregion, but having different types of land use.
Abstract: SUMMARY 1. Several studies have shown that land use has a strong influence on river chemistry and its biotic components. Most of these studies focused on nitrogen in temperate American and European catchments. Much less is known about the relationship between stream conditions and land use in tropical areas of developing countries. 2. Besides climate, there are three important differences between attributes of temperate and tropical catchments: non-point sources are the dominant contributor of pollution in USA, whereas point source pollution is the most important in our study; use of fertilizer is much smaller in developing countries, and the type of agriculture and management practices are distinct. 3. We test whether the chemical composition of streams and their macroinvertebrate communities can be related to land use. Accordingly, we compared the variability of chemical composition and macroinvertebrate communities in the streams of two catchments (Pisca and Cabras) belonging to the same ecoregion, but having different types of land use. 4. The main land use in the Pisca catchment in 1993 was sugar cane (62%), followed by pasture (22%) and urban centres (10%). In contrast, the main land use in the Cabras catchment was pasture (60%), followed by annual crops (13%) and forest (10%); urban centres occupied only 2% of the catchment. 5. In the Cabras catchment, most of the parameters correlated with a land use index (LUI) (Fig. 2). However, only conductivity, major cations and major anions (with exception of sulfate) had a statistically significant correlation coefficient. More than 90% of the variance was explained for these parameters. DIC, NO3 and richness of invertebrates (RI) also strongly correlated with LUI (R 2 = 0.75), although these correlation coefficients were not significant. Total suspended solids (TSS) had a significant correlation with LUI (R 2 = 0.98), but, the correlation was inverse. In the Pisca catchment, conductivity, major cations (with exception of potassium), major anions, and DIC, DO, and DOC had a strong and statistically significant correlation with LUI. Correlation coefficients were also high for respiration rate, although the correlation was not statistically significant.
251 citations
TL;DR: In this article, Europium complexes in the +3 oxidation state, with coordination numbers six, seven, eight, nine and ten, were studied by X-ray structural analyses and an attempt was made to correlate the results with the emission spectrum interpretation.
249 citations
TL;DR: In this paper, the authors reviewed some pertinent research aimed at understanding surface nucleation from both qualitative and quantitative points of view, including surface quality, tips, cracks and scratches, foreign particles and surrounding atmosphere.
Abstract: In this paper we review some pertinent research aimed at understanding surface nucleation from both qualitative and quantitative points of view. The majority of quantitative studies discuss the crystal nucleation kinetics of soda-lime-silica glasses and alkali-free silicate (cordierite, anorthite and diopside) glasses. We emphasize the kinetics of surface nucleation and consider the effects of surface quality, tips, cracks and scratches, foreign particles and surrounding atmosphere on crystallization. Related nucleation mechanisms are discussed.
230 citations
TL;DR: Open-cell hydroxyapatite (HA) foams, produced through the novel technique of gelcasting foams with relative porosities ranging from 0.72 to 0.90, were characterized for poresize distribution, surface area, permeability, compressive strength, elastic modulus, and microstructural features as discussed by the authors.
Abstract: Open-cell hydroxyapatite (HA) foams, produced through the novel technique of gelcasting foams with relative porosities ranging from 0.72 to 0.90, were characterized for pore-size distribution, surface area, permeability, compressive strength, elastic modulus, and microstructural features. The porous structure, which is composed of an array of spherical cells interconnected through windows, had a mode pore diameter in the range 17-122 μm, as demonstrated by mercury porosimetry. The BET specific surface area increased from 1.5 to 3.8 m 2 /g as the sample porosity increased. The compressive strength and elastic modulus were in the range 1.6-5.8 MPa and 3.6-21.0 GPa, respectively. The permeability constants, k 1 (Darcian) and k 2 (non-Darcian), were strongly dependent on porosity fraction and varied widely, from 1.22 × 10 -11 to 4.31 × 10 -10 m 2 and from 1.75 × 10 -6 to 8.06 × 10 -5 m, respectively. This combination of properties make the HA foams suitable for a variety of potential applications in the biomedical field, preferentially nonloading, including materials for bone repair, carriers for controlled drug-delivery systems, and matrixes for tissue engineering.
224 citations
TL;DR: In vitro test of biological evaluation revealed that the original purity of the biomedical-grade hydroxyapatite powder was affected neither through processing nor by the employed reagents, indicating strong gelled bodies with up to 90% porosity that can withstand machining in the green state.
Abstract: This study presents the manufacture of highly porous hydroxyapatite by a novel technique that employs the foaming of suspensions prior to the in situ polymerization of organic monomers contained in the compositions. This method produces strong gelled bodies with up to 90% porosity that can withstand machining in the green state. Complex-shaped components can be obtained if the process comprises casting in one of the processing steps. The organic additives are eliminated at temperatures above 300 degrees C, and sintering is carried out for consolidation of the ceramic matrix. Spherical interconnected cells with sizes ranging from 20 to 1000 micrometer characterize the porous structure, depending on the specimen density. Cytotoxicity tests were conducted on extracts from sintered HA foams based on a quantitative method of cell colony formation and the determination of cell death after indirect contact of the porous material with mammalian cells. This in vitro test of biological evaluation revealed that the original purity of the biomedical-grade hydroxyapatite powder was affected neither through processing nor by the employed reagents.
222 citations
TL;DR: In this article, the authors employed molecular-dynamics simulations to study deformations on nickel nanowires subjected to uniaxial strain at 300 K using a recently reported embedded-atom (many body) model potential.
Abstract: Molecular-dynamics simulations were employed to study deformations on nickel nanowires subjected to uniaxial strain at 300 K using a recently reported embedded-atom (many body) model potential. This embedded-atom model can reproduce exactly the experimental second-order and third-order elastic moduli as well as the phase stability, equation of state and phonon frequency spectra are also in good agreement with experiments. Strong influence was observed in the Young modulus and force constant due to surface effects when considering nanowires with different cross sections. Applying strain rates, from 0.05 to $15%{\mathrm{ps}}^{\ensuremath{-}1},$ we found elastic behavior up to 11.5% strain with corresponding stress of 9.4 GPa. At low strain rates $(l0.05%{\mathrm{ps}}^{\ensuremath{-}1})$ the system passes through plastic deformations although keeping the crystalline structure. This ductile process is showed by several snapshots. At this low strain rate regime we observed that the nanowires shows superplasticity. For high strain rates $(g~7%{\mathrm{ps}}^{\ensuremath{-}1})$ the system changes continuously from crystalline to amorphous phase. Although this amorphization occurs with no use of liquid quenching or introduction of chemical or physical disorder, so being a different and interesting process, the amorphous resulted is unstable. We studied this instability monitoring the recrystallization process.
201 citations
TL;DR: In this article, it was shown that the ringed spherulites are formed exclusively by the α phase when crystallization takes place at temperatures below 155°C and the non-ringed sperulites, only formed at crystallization temperatures above 155°c, consist predominantly of the γ phase, crystallized from the melt, with small α phase inclusions.
Abstract: When PVDF is crystallized at temperatures above 155°C it presents a multiform morphology composed of ringed, non ringed and mixed spherulites. Infrared spectroscopy showed that the ringed spherulites are formed exclusively by the α phase when crystallization takes place at temperatures below 155°C. Higher temperatures induce a solid-state α → γ phase transformation in these structures, increasing the amount of γ phase with crystallization time. The rate at which this transformation takes place increases with crystallization temperature. The non ringed spherulites, only formed at crystallization temperatures above 155°C, consist predominantly of the γ phase, crystallized from the melt, with small α phase inclusions. The melt process of the different spherulites, observed by optical microscopy and calorimetric measurements (DSC) showed that the melt temperature of the γ phase, originated from the phase transition, is 8°C higher than that crystallized directly from the melt. Optical micrographs of samples heated up to 186°C and quickly cooled allowed visualization of the ringed spherulite regions which underwent the α → γ phase transformation at different crystallization times and temperatures.
198 citations
TL;DR: The essential oil from the hydrodistillation of Eugenia dysenterica leaves consisted mainly of beta-caryophyllene and alpha-humulene as the major sesquiterpene, while limonene andalpha-thujene were the major monoterpene hydrocarbons.
180 citations
TL;DR: Pressure-induced structural transformation in cubic silicon carbide is studied with the isothermal-isobaric molecular-dynamics method using a new interatomic potential scheme and the calculated volume change at the transition and hysteresis are in good agreement with experimental data.
Abstract: Pressure-induced structural transformation in cubic silicon carbide is studied with the isothermal-isobaric molecular-dynamics method using a new interatomic potential scheme. The reversible transformation between the fourfold coordinated zinc-blende structure and the sixfold coordinated rocksalt structure is successfully reproduced by the interatomic potentials. The calculated volume change at the transition and hysteresis are in good agreement with experimental data. The atomistic mechanisms of the structural transformation involve a cubic-to-monoclinic unit-cell transformation and a relative shift of Si and C sublattices in the 100 direction.
167 citations
TL;DR: The karyotypic data support the view that the nominal taxon H. malabaricus corresponds to a species complex comprising distinct evolutionary units, each with well-established chromosomal differences.
Abstract: Hoplias malabaricus, a widely distributed neotropical freshwater fish, shows a conspicuous karyotypic diversification. An overview of this diversity is presented here comprising several Brazilian populations, and some others from Argentina, Uruguay and Surinam. Seven general cytotypes are clearly identified on the basis of their diploid number (2n=39 to 2n=42), chromosomal morphology and sex chromosome systems, which can be clustered into two major karyotypic groups. This clustering suggests that karyotype structure would be more informative than the diploid number regarding cytotype relationships in this fish group. While some cytotypes show a wide geographical distribution, some others appear to be endemic to specific hydrographic basins. Sympatric cytotypes can occur without detection of hybrid forms; this situation points to a lack of gene flow, a fact that is also reinforced by studies with genomic markers. The karyotypic data support the view that the nominal taxon H. malabaricus corresponds to a species complex comprising distinct evolutionary units, each with well-established chromosomal differences.
TL;DR: In this paper, the complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS), and micro-Raman spectrographs.
Abstract: The complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS) and micro-Raman spectroscopy. Three crystalline phases (merwinite, melilite and larnite) were identified after heat treatment between Tg (742°C) and the DSC crystallization peak (T=1000°C). Merwinite was identified as a metastable phase. A small amount (0.004 wt%) of metallic platinum was found in the glass composition. Particles of Pt3Fe, detected by EDS and SAD–TEM, were the starting points of crystallization acting, therefore, as heterogeneous nucleating sites. Only melilite and larnite precipitated in a glass sample heat-treated at 1000°C for 1 h. The flexural strength of this crystallized sample was less than that of the glass, probably due the allotropic phase transformation of larnite.
TL;DR: In this paper, the exact two-dimensional numerical solution of the London equation is extended analytically to the realistic three dimensional case and the Meissner state with finite London penetration depth is analyzed for platelet samples of rectangular cross section in a perpendicular magnetic field.
Abstract: The Meissner state with finite London penetration depth is analyzed for platelet samples of rectangular cross section in a perpendicular magnetic field. The exact two-dimensional numerical solution of the London equation is extended analytically to the realistic three dimensional case. Data obtained on Nb cylinders and foils, as well as single crystals of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O, are in a good agreement with the model. The results are particularly relevant for magnetic susceptibility, rf, and microwave resonator measurements of the magnetic penetration depth in high-${T}_{c}$ superconductors.
TL;DR: The present results confirm the XX/XY sex chromosome system in the population analyzed as well as a new cytotype in the Hoplias malabaricus group, confirming a polymorphic size condition observed in the X chromosome.
Abstract: Cytogenetic studies were carried out in the fish, Hoplias malabaricus, from the Parque Florestal do Rio Doce (Brazil). This population is characterized by 2n = 42 chromosomes for both males and females and an XX/XY sex chromosome system, confirmed through several banding methods. Females show 24 metacentric, 16 submetacentric and 2 subtelocentric chromosomes. Males show 24 metacentric, 17 submetacentric and 1 subtelocentric chromosomes. While the X chromosome is easily recognized (the only subtelocentric element), the Y chromosome is somewhat difficult to identify but appears to correspond to the smallest submetacentric in the male karyotype. In-situ hybridization with an 18S rDNA probe showed 10 well-labeled chromosomes, including the X chromosome. The 5S rDNA is interstitially located in a single metacentric pair independent of the 18S rDNA sites. The NOR on the X chromosome is always active and occurs adjacent to a heterochromatic distal segment on the long arm. Variations in size of the NORs and/or heterochromatic segment correspond to a polymorphic size condition observed in the X chromosome. The present results confirm the XX/XY sex chromosome system in the population analyzed as well as a new cytotype in the Hoplias malabaricus group.
TL;DR: In this article, the perchlorinated manganese porphyrin ring stabilizes Mn(II) and unfavour the formation of the active species, Mn V O.
Abstract: Manganese(III) 5-(pentafluorophenyl)-10,15,20-tri(2,6-dichlorophenyl)porphyrin, Mn(PFTDCPP), and manganese(II) 2,3,7,8,12,13,17,18-octachloro-5-(pentafluorophenyl)-10,15-20-tri(2,6-dichlorophenyl)porphyrin, Mn(PFTDCCl 8 PP), have been synthesised and used as catalysts in hydrocarbon oxidations by iodosylbenzene and hydrogen peroxide both in solution and covalently bound to aminopropylated silica. The former shows higher efficiency in the epoxidation of alkenes by iodosylbenzene, whereas the perchlorinated manganese porphyrin is more efficient in the hydroxylation of alkanes by this oxidant. The supported manganese(III) porphyrin show the same activity as its homogeneous analogue. With hydrogen peroxide as oxygen donor, Mn(PFTDCPP) is a stable and effective catalyst in the presence of imidazole. The perchlorinated analogue is a poor catalyst with this oxidant. The eight additional chlorine atoms on the porphyrin ring stabilise Mn(II) and unfavour the formation of the active species, Mn V O.
TL;DR: The localization of a repetitive DNA sequence on both B chromosome arms, and synaptonemal complex formation, are analyzed in order to test the functional homology of both arms and provide strong support for the hypothesis that the B chromosome is an isochromosome.
Abstract: Astyanax scabripinnis possesses a widespread polymorphism for metacentric B chromosomes as large as the largest chromosome pair in the A complement. On the basis of C-banding pattern, it was hypothesized that these B chromosomes are isochromosomes that have arisen by means of centromere misdivision and chromatid nondisjunction. In the present paper we test this hypothesis by analysing (i) the localization of a repetitive DNA sequence on both B chromosome arms, and (ii) synaptonemal complex formation, in order to test the functional homology of both arms. Genomic DNA digested with KpnI and analysed by gel electrophoresis showed fragments in a ladder-like pattern typical of tandemly repetitive DNA. These fragments were cloned and their tandem organization in the genome was confirmed. A 51-bp long consensus sequence, which was AT-rich (59%) and contained a variable region and two imperfect reverse sequences, was obtained. Fluorescence in situ hybridization (FISH) localized this repetitive DNA into noncentromeric constitutive heterochromatin which encompasses the terminal region of some acrocentric chromosomes, the NOR region, and interstitial polymorphic heterochromatin in chromosome 24. Most remarkably, tandem repeats were almost symmetrically placed in the two arms of the B chromosome, with the exception of two additional small clusters proximally located on the slightly longer arm. Synaptonemal complex (SC) analysis showed 26 completely paired SCs in males with 1B. The ring configuration of the B univalent persisting until metaphase I suggests that the two arms formed chiasmata. All these data provided strong support for the hypothesis that the B chromosome is an isochromosome.
TL;DR: There appears to exist a strict relationship between both absence of geographic barriers throughout the marine environment and high mobility of these animals, with a rarity of chromosome rearrangement at the macrostructural level.
Abstract: The number of cytogenetic studies of marine fish has increased in recent years. Fish groups, such as Perciformes, which comprises many of the extant marine teleosts of economic importance, show little divergence in chromosome number and most species display a diploid number of 48 acrocentric chromosomes. In the Serranidae, Sparidae, Sciaenidae (Perciformes) and Mugilidae (Mugiliformes) small chromosome variations are restricted to subtle heterochromatin or nucleolar organizer region (NOR) modifications. There appears to exist a strict relationship between both absence of geographic barriers throughout the marine environment and high mobility of these animals (eggs, larvae, or adults), with a rarity of chromosome rearrangement at the macrostructural level. Moreover, a cellular homeostasis might also be important to karyotype maintenance among these fishes, limiting changes in the chromosome complement to cryptic chromosome rearrangements. Other groups, such as Blenniidae, Gobiidae and Scorpaenidae, for instance, show more extensive chromosome diversity, which is probably related to limited mobility. Numerical and structural chromosome polymorphisms and several sexual chromosome systems are recurrent among these fishes. A wide karyotypic diversification also characterizes the Tetraodontiformes, an interesting fish group with peculiar morphological, physiological and ecological characteristics.
TL;DR: The degradation of polypropylene subjected to multiple extrusions was evaluated by following the changes in the molecular weight distribution curves (MWD) obtained by size exclusion chromatography (SEC).
TL;DR: Astyanax scabripinnis specimens from four distinct populations in Brazil were studied with respect to their karyotype macrostructure, nucleolar organizer regions, and 18S and 5S rRNA genes.
Abstract: Astyanax scabripinnis specimens from four distinct populations in Brazil were studied with respect to their karyotype macrostructure, nucleolar organizer regions, and 18S and 5S rRNA genes. The four populations showed a 2n = 50 chromosomes (3 M + 11 SM + 5 ST + 6 A pairs) and 1–2 B chromosomes. No chromosomal differentiations were observed between sexes. Although a karyotypic diversity has been characterized in this fish group, the populations now analyzed presented the same macrokaryotypic pattern. Chromosome mapping of 5S rDNA showed a total of eight sites located in four distinct chromosomal pairs, with no apparent differences among populations. A comparative study on 18S rDNA locations and Ag-NORs showed some secondary NOR sites that are not usually expressed in karyotypes and a probable differential NOR activity among populations. Correlations between these data, environmental conditions and B chromosomes are discussed.
TL;DR: In this article, the viscosities of polyethylene elastomer (PEE) and polypropylene (PP) were analyzed using an Instron capillary rheometer and a Rheometrics Dynamic Stress Rheometer, SR 200.
Abstract: Rheological and morphological studies were performed on polymer blends of ethylene-octene copolymer [polyethylene elastomer (PEE)] and polypropylene (PP). The viscosities of PEE, PP, and PEE/PP blends were analyzed using an Instron capillary rheometer and a Rheometrics Dynamic Stress Rheometer, SR 200. A non-Newtonian flow behavior was observed in all samples in the shear rate range from 27 to 2700 s−1, whereas at shear rates in the range from 0.01 to 0.04 s−1, a Newtonian flow behavior was verified. The scanning electron micrographs showed that dual-phase continuity may occur between 50 and 60 (wt %) of PEE. This result is consistent with the Sperling's model. The mechanical analysis showed that PEE/PP, with 5 wt % of PEE, presented an increase on the mechanical properties and as the PEE content increased, a negative deviation in relation to an empirical equation was observed. Thermal analysis showed that there were no change in the crystallization behavior of the matrix when different elastomer contents were added. Dynamic mechanical thermal analysis showed that samples with low PEE contents presented only one peak, indicating a certain degree of miscibility between the components of these blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 692–704, 2000
TL;DR: The results show that the disintegrin-like domain of alternagin is responsible for its ability to inhibit collagen binding to alpha2beta1 integrin.
TL;DR: The mechanisms involved in the dispersion of heterochromatin and NORs through the karyotypes, as well as the possible events related to the generation of polymorphism of those regions are discussed.
Abstract: Astyanax scabripinnis has been considered a species complex because it presents high karyotypic and morphological variability among its populations. In this work, individuals of two A. scabripinnis populations from different streams in the same hydrographic basin were analyzed through C‐banding and AgNOR. Although they present distinct diploid numbers, they show meta and submetacentric chromosome groups highly conserved (numerically and morphologically). Other chromosomal characteristics are also shared by both populations, as the pattern of constitutive heterochromatin distribution (large blocks in the telomeric regions of subtelocentric and acrocentric chromosomes) and some nucleolar chromosomes. Inter‐individual variations both in the number and size of heterochromatic blocks, and in the number and localization of NORs were verified in the studied populations, characterizing them as polymorphics for these regions. The mechanisms involved in the dispersion of heterochromatin and NORs through the karyotypes, as well as the possible events related to the generation of polymorphism of those regions are discussed. Furthermore, relationships between these populations and within the context of the scabripinnis complex are also approached.
TL;DR: In this paper, three kinds of duplex stainless steel, with different ferrite-to-austenite ratios, were deformed in torsion over the temperature range 900 °C to 1200 °C; the corresponding microstructural evolution was observed and correlated with the deformation conditions.
Abstract: Three kinds of duplex stainless steel, with different ferrite-to-austenite ratios, were deformed in torsion over the temperature range 900 °C to 1200 °C; the corresponding microstructural evolution was observed and correlated with the deformation conditions. The shapes of the high-temperature flow curves depend strongly on the volume fractions of the phases, the characteristics of the ferrite-austenite interface, and the active softening mechanism. At low volume fractions of austenite, the mechanical behavior is determined by the ferrite matrix and the flow curves are typical of materials that soften by continuous dynamic recrystallization. When the volume fraction of austenite is increased, coherent γ particles distributed within the grains and at the grain boundaries hinder the deformation of the softer α matrix, increasing both the yield and the peak stress. These peaked flow curves are characterized by rapid work hardening followed by extensive flow softening; under these conditions, the hard austenite particles become aligned with the deformation direction after large strains. At high volume fractions of austenite (∼50 pct), the material tends to form a duplex structure, with the flow curves displaying extended work-hardening and work-softening regions; however, a drastic decrease is observed in ductility because of the dissimilar plastic behaviors of the two phases.
TL;DR: An organic-phase biosensor based on paraffin/graphite modified with sweet potato (Ipomoea batatas (L.) Lam.
TL;DR: In this paper, the similarity of the local structure of the network-forming cation Si4+ (Qn units and chemical shifts) in glasses and isochemical crystals and the nucleating ability of these glasses were verified.
Abstract: The purpose of this work is to verify the possible existence of a relationship between the similarity of the local structure of the network-forming cation Si4+ (Qn units and chemical shifts) in glasses and isochemical crystals and the nucleating ability of these glasses. Four metasilicate glasses with widely different volume nucleation rates: Na2Ca2Si3O9 and Na4CaSi3O9 (very large), CaSiO3 (intermediate) and CaMgSi2O6 (undetectably small) were chosen. We present magic angle spinning nuclear magnetic resonance spectroscopy (MAS–NMR) data for Na2Ca2Si3O9 and Na4CaSi3O9 glasses and for their respective isochemical crystalline phases for the first time. Additionally, we repeat NMR measurements of glasses and crystals previously studied by other authors (CaSiO3 and CaMgSi2O6) to test the consistency of our experimental techniques and method of analysis. Different central chemical shifts of Q2 resonances in parent glasses and their isochemical crystals were measured, indicating structural differences. The relative amount of Qn groups in each glass was obtained from the deconvolution of the 29Si MAS–NMR spectra. The shape of the Qn distribution for each system was considered as a measure of the similarity of the connectivities of SiO4 tetrahedra in each glass with respect to its isochemical crystal (which has only Q2 groups). A correlation was found between the shape of the Qn distribution and the nucleation tendency of these glasses, indicating that similarities between the tetrahedra connectivities in glass and isochemical crystal has a role in determining the internal nucleation tendency of the metasilicate glasses studied.
TL;DR: In this article, the selective synthesis of glycerol monolaurate from lauric acid and glycerols as starting materials, employing commercial Beta, Y and Mordenite zeolites with different Si/Al ratio as catalysts.
Abstract: The purpose of this work, is to study the selective synthesis of glycerol monolaurate from lauric acid and glycerol as starting materials, employing commercial Beta, Y and Mordenite zeolites with different Si/Al ratio as catalysts. Reaction conditions such as the stirring rate, temperature, glycerol/lauric acid ratio and catalyst mass in the reaction medium were optimized to diminish homogeneous reaction and reaction limitations due to diffusive effects. In the case of zeolite Y, an increase in glycerol monolaurate yield and selectivity for the monoester were verified at high Si/Al ratio. This behavior seems to be related to the presence of stronger acid sites present in the material with low Al content and probably also because of the higher hydrophobicity exhibited by zeolites having higher Si/Al ratio. Mordenite catalyst, on the contrary, presented low activity and selectivity to glycerol monolaurate, which can be attributed to the diffusional limitations imposes by the monodimensional channel system to the organic substrate accessing the inner catalyst sites, restricting the reaction to the sites present at the external particle surface. Zeolite Beta exhibited the best results as catalyst to obtain the mono-derivative, presenting selectivities higher than 60% at 20% yield.
TL;DR: The composition, diversity and similarity of fish communities associated with macrophytes of two oxbow lakes of Mogi-Guaçu River, São Paulo State, Brazil, were evaluated in the wet and dry seasons of 1994–1995.
Abstract: The composition, diversity and similarity of fish communities associated with macrophytes of two oxbow lakes of Mogi-Guacu River, Sao Paulo State, Brazil, were evaluated in the wet and dry seasons of 1994–1995. Fish species composition and relative abundance values were similar for both lakes, despite their difference in connection time to the river and the abundance of macrophytes. The fish communities were predominantly composed by small sized species typical of lentic environments (Characidae), juveniles of large non-migratory species (Erythrinidae and Gymnotidae) and a few juveniles of migratory species (Anostomidae and Curimatidae). These lakes are not characterized as nurseries for the young of migratory species and the zooplankton does not have an important role as food in the ontogenetic development of migratory species of fish.
TL;DR: Brazil is the largest producer of bioethanol, and sugarcane is the main raw material, and the sugar-ethanol market reaches about 7.5 billion US$/yr, accounting for direct and indirect revenues.
Abstract: Brazil is the largest producer of bioethanol, and sugarcane is the main raw material. Bioethanol is produced by both batch and continuous processes, and in some cases, flocculating yeast is used. This article analyzes the Brazilian Ethanol Program. For the 1996-1997 harvest, Brazil produced 14.16 billion L of ethanol and 13.8 million metric t of sugar, from 286 million metric t of sugarcane. These products were produced by 328 industries in activity, with 101 autonomous ethanol plants producing only ethanol, and 227 sugar mills producing sugar and ethanol. The sugar-ethanol market reaches about 7.5 billion US$/yr, accounting for direct and indirect revenues.
TL;DR: In this paper, the size dependence of surface energy has been removed from the analysis of the nucleation theory and instead the authors focus on the temperature dependence of the macroscopic value of the surface energy, decoupling it from the size dependent part.
Abstract: The most basic assumption of the classical nucleation theory (CNT) is to treat nucleus/liquid surface energy, σ , as a macroscopic property having a value equal to that of a planar interface, σ ∞ . Therefore, when the CNT is used to analyze experimental data, the size dependence of surface energy is often neglected. To date, there has been no reliable method to measure the surface energy of the nucleus/liquid interface except by fitting nucleation rate data to the theory. In this case, one obtains the surface energy of critical size nuclei as a function of temperature. However, the fitted σ ( T ) dependence arises from two different factors: the temperature dependence of σ for a planar interface and its size dependence. This paper focuses on the temperature dependence of the macroscopic value of surface energy, decoupling it from the size dependent part. Tolman’s equation was used to eliminate the size dependence of surface energy from published nucleation data for two stoichiometric silicate glasses (Li 2 O · 2SiO 2 and Na 2 O · 2CaO · 3SiO 2 ). It is shown that the Tolman parameter may be chosen so that surface tension decreases with temperature; d σ ∞ /d T σ ∞ /d T obtained in this way is close to theoretical predictions.
TL;DR: In this paper, the electrochemical oxidation of o-aminophenol (OAP) has been studied by cyclic voltammetry on platinum (Pt) and glassy carbon (GC) electrodes.