Cleavage of the dimeric cyclopalladated [Pd(N,C-dmba)(mu-X)](2), (dmba = N,N-dimethylbenzylamine; X = SCN and NCO) by diphosphines. Palladium(II) compounds with distinct structures in the solid-state and in solution

The reactions of the pseudohalide-bridged dimer [Pd(N,C-dmba)(mu -SCN)](2) (1) (dmba = N,N-dimethylbenzylamine) with cis-Ph2PCH=CHPPh2 (cis-dppet) (1:1 molar ratio) and of [Pd(N,C-dmba)(mu -NCO)](2) (2) with Ph2PCH2CH2PPh2 (dppe) (1:2 molar ratio) gave mononuclear [Pd(C-dmba)(SCN)(cis-dppet)].H2O (1a) and [Pd(C-dmba)(NCO)(dppe)] (2a), respectively, with the diphosphines acting as chelating ligands. Reaction of (2) with Fe(C5H4PPh2)(2) (dppf) (1:1 molar ratio) yielded [{Pd(N,C-dmba)(NCO)}(2)(mu -dppf)] (2b), a bimetallic species containing two palladium atoms bridged by the diphosphine, whereas reaction in a 1:2 molar ratio gave the mononuclear [Pd(N,C-dmba)(dppf)][NCO]. CH2Cl2 (2c), with the diphosphine acting as a chelating ligand. The compounds have been characterized by elemental analysis, i.r., P-31{H-1}, C-13- and H-1-n.m.r. spectroscopies. Conductivity measurements together with spectroscopic data showed that (1a) and (2a) do not have the same structure in the solid state and in MeCl solution, whereas for compounds (2b) and (2c) no structural changes were observed when the solids were dissolved in MeCl.

Dissolved radioelements in (oil) water wells in Parana basin, Brazil

This paper describes the results of a study on groundwaters from Tubarao Group at the Parana sedimentary basin, São Paulo State, Brazil. The purpose of this study was to integrate chemical and U-isotopes data in order to evaluate the models for quantifying different relative volumes of mixing waters in a resultant water. Despite it was possible to generate a typical triangle involving U-238 and its daughter U-234, the U-isotopes model failed to interpret the major hydrochemical facies observed in the studied localities.

Improvement of the chemical resistance of zirconium fluoride glasses coated with a Tiron (R) modified tin oxide layer prepared by the sol-gel process

In order to improve the chemical resistance of zirconium fluoride glass a protective transparent SnO2 layer was deposited by the solgel dip-coating process in the presence of Tiron (R) as particle surface modifier agent. After water immersion for different periods of time, both coated and non-coated fluoride glasses were analyzed by scanning electron microscopy, mass loss evaluation, infrared spectroscopy and X-ray photoelectron spectroscopy. In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species, the results for the SnO2-coated glass showed that the filling of the film nanopores by dissolved glass material results in a hermetic barrier protecting the glass surface. The selective glass dissolution was confirmed by liquid chromatography measurements of the etching solution after each exposure time. (c) 2006 Elsevier B.V. All rights reserved.

SAXS study of monodispersed silica nanospheres obtained by an amino acid route

Spherical silica nanoparticles were prepared using a basic amino acid catalysis route and the kinetics of the particles growth was investigated by small angle X-ray scattering (SAXS). L-arginine was used in the polar aqueous phase as the basic catalyst whereas the tetraethylorthosilicate (TEOS) was dissolved in the cyclohexane oil phase as the silicate monomer source. The SAXS measurements were taken in the aqueous phase at different reaction times. A high degree of monodispersity was clearly evidenced for the spherical nanoparticles as a result of the pronounced high-order oscillations observed in the SAXS curves. The SAXS data show that the particles number density remains unchanged since both the particle size as well as the volume fraction gradually increase. This process was discussed based on a reaction-controlled addition of monomer species at the surface of the growing particles. Consequently, the monodispersed spherical nanoparticles radius can as such be finely tuned from 7 to 12 nm by varying the reaction time. (C) 2010 Elsevier B.V. All rights reserved.

Quercetin-PVP K25 solid dispersions: Preparation, thermal characterization and antioxidant activity

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Anthropogenic influences on annual flux of cations and anions at meio stream basin, São Paulo State, Brazil

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

Os efeitos da ação antrópica sobre a distribuição de macroinvertebrados no Rio Guareí, São Paulo

In this study, it was examined, during the period from March to December 2006, the effects of human disturbance on themacroinvertebrates that live near macrophytes in Guare River, São Paulo State - Brazil. It was questioned if the high conductivityrecorded in Guare River affected the distribution of the macroinvertebrates and what were the most important variables thataffect macroinvertebrates in a river with a strong nutrient concentration. The objective of this study was to investigate theeffects of environmental variables on densities and composition of the macroinvertebrates. Three stands of aquatic plantswere sampled with with 0.25 mm mesh net on a 0.07 m2 square metal frame. Air and water temperature, depth, pH, electricalconductivity, suspended solids, dissolved oxygen and macrophyte biomass were measured. A canonical correspondence analysis(CCA) was performed using the density of the macroinvertebrates and environmental variables. Chironomidae, Culicidae,Acanthagrion, Coryphaeschna, Erythrodiplax, Miathyria marcella, Micrathyria, Gastropoda, Ostracoda and Hemiptera werethe only taxa that showed significant correlation with the axes. From the results, we can conclude that the high conductivity recordedin Guare River due to the high amount of organic matter released during its course did not significantly affected thedistribution of the macroinvertebrates during the studied period. However, the ACC recorded that oxygen was the most significantenvironmental factor for the density variance of the macroinvertebrates, especially larval Odonata.

The behavior of dissolved uranium in groundwaters of the Morro do Ferro thorium deposit, Brazil

Groundwater samples were collected for several months in boreholes drilled at Morro do Ferro, a thorium and rare earth deposit located on the Poços de Caldas Plateau, Minas Gerais State, Brazil. An aquifer system has developed in the weathered mantle due to in situ intense alteration. The weathered zone includes a thick argillaceous laterite greater than 100 m thick. The U content and 324U/238U activity ratio were measured in the groundwater samples and in spoil samples of a borehole drilled in the ore body. Some possible mechanisms related to the mobilization of uranium are considered such as complexation with humic substances and adsorption by clays. © 1989.

Diversity of fragments in the collapse of brittle solids

An experimental study of fragmentation of brittle solids under the application of repeated impulsive force is made, emphasizing the behavior of the diversity of fragments. Several scaling relations involving diversity and number of fragments are obtained from experiments and the results are compared with computer simulations. © 1998 Elsevier Science B.V. All rights reserved.

Field-free and field-stimulated electron emission from solids

Electron irradiation of solids produces a backemission of secondary electrons (energies between 0 and 50 eV) and reflected primaries (energies between 50 eV and that of the incident beam). For insulators, it is shown that an externally applied positive electric field penetrating into the solid material, energizes electrons generated by the primary irradiation and enables them to travel back to the surface of incidence and be emitted (stimulated secondary emission).

Reduction of dissolved oxygen in water: Hydrazine and its organic substitutes

In industrial processes using aqueous solutions, corrosion of metal surfaces may occur at various locations. Much of the damage to steam generators and boilers is caused by corrosion. Dissolved oxygen in water is one of the most potent corrosion-causing factors, and therefore oxygen should be eliminated from steam-generating systems' feedwater. Chemical reduction, by reagents such as hydrazine or organic compounds, generally is used for the deoxygenation of water. This article reviews the major oxygen scavengers currently available.

Influence of carrageenan and total solids content on the rheological properties of lactic beverage made with yogurt and whey

The purpose of this work was to study the influence of carrageenan level (X 1) and total solids content of yogurt/whey mixture (X 2) on starter culture fermentation time, physicochetnical properties (pH, fat and total solids contents) and rheological characteristics of lactic beverages using response surface methodology. The physicochemical characteristics of the lactic beverages were similar to those of commercial products. All beverages showed non-Newtonian fluid behavior with thixotropy and yield stress. The total solids content of the lactic beverages had a greater influence on the rheological behavior of these products than the carrageenan level. Wide ranges of consistency measurements were observed by varying the stabilizer level and total solids content.

Simultaneous effects of total solids content, milk base, heat treatment temperature and sample temperature on the rheological properties of plain stirred yogurt

Response surface methodology was used to establish a relationship between total solids content, milk base, heat treatment temperature, and sample temperature, and consistency index, flow behaviour index, and apparent viscosity of plain stirred yogurts. Statistical treatments resulted in developments of mathematical models. All samples presented shear thinning fluid behaviour. The increase of the content of total solids (9.3-22.7 %) and milk base heat treatment temperature (81.6-98.4°C) resulted in a significant increase in consistency index and a decrease in flow behaviour index. Increase in the sample temperature (1.6-18.4°C) caused a decrease in consistency index and increase in flow behaviour index. Apparent viscosity was directly related to the content of total solids. Rheological properties of yogurt were highly dependent on the content of total solids in milk.

Anelastic relaxation due to interstitial solutes diffusion in Nb and Nb-1 wt% Zr

Metals and alloys containing solute atoms dissolved interstitially often show anelastic behavior due to a process know as stress-induced ordering. The application of mechanical spectroscopy measurements to diffusion studies in body-centered cubic metals has been extensively used in the last decades. However the kind of preferential occupation of interstitial solutes in body-centered cubic metals is still controversial. The anelastic properties of the Nb and Nb-1 wt% Zr polycrystalline alloys were determined by internal friction and oscillation frequency measurements using a torsion pendulum inverted performed between 300K and 650K, operating in a frequency oscillation in the hertz bandwidth. The interstitial diffusion coefficients of oxygen and nitrogen in Nb and Nb-1 wt% Zr samples were determined at two distinct conditions: (a) for low concentration of oxygen and (b) for high concentration of oxygen.

Discharge pulses of hydroelectric dams and their effects in the downstream limnological conditions: A case study in a large tropical river (SE Brazil)

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24-h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below-dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south-east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso-eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m3 s-1. In contrast, Taquaruçu Reservoir is relatively shallow, oligo-mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m3 s-1. Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above-dam site) zones of the reservoirs, as well as in the downstream river stretches (below-dam site). In both cases, the sampling was carried out at 4-h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below-dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L-1) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high-amplitude/low-frequency variations could negatively affect the downstream river biota. © 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Asia Pty Ltd.