Simultaneous determination of neutral nitrogen compounds in gasoline and diesel by differential pulse voltammetry

The presence of trace neutral organonitrogen compounds as carbazole and indole in derivative petroleum fuels plays an important role in the car's engine maintenance. In addition, these substances contribute to the environmental contamination and their control is necessary because most of them are potentially carcinogenic and mutagenic. For those reasons, a reliable and sensitive method was proposed for the determination of neutral nitrogen compounds in fuel samples, such as gasoline and diesel using preconcentration with modified silica gel (Merck 70-230 mesh ASTM) followed by differential pulse voltammetry (DPV) technique on a glassy carbon electrode. The electrochemical behavior of carbazole and indole studied by cyclic voltammetry (CV) suggests that their reduction occurs via a reversible electron transfer followed by an irreversible chemical reaction. Very well resolved diffusion controlled voltammetric peaks were obtained in dimethylformamide (DMF) with tetrabutylammonium tetrafluoroborate (TBAF(4) 0.1 mol L-1) for indole (-2.27 V) and carbazole (-2.67 V) versus Ag vertical bar AgCl vertical bar KClsat reference electrode. The proposed DPV method showed a good linear response range from 0.10 to 300 mg L-1 and a limit of detection (L.O.D) of 7.48 and 2.66 mu g L-1 for indole and carbazole, respectively. The results showed that simultaneous determination of indole and carbazole presents in spiked gasoline samples were 15.8 +/- 0.3 and 64.6 +/- 0.9 mg L-1 and in spiked diesel samples were 9.29 +/- 1 and 142 +/- 1 mg L-1, respectively. The recovery was evaluated and the results shown the values of 88.9 +/- 0.4 and 90.2 +/- 0.8% for carbazole and indole in fuel determinations. The proposed method was also compared with UV-vis spectrophotometric measures and the results obtained for the two methods were in good agreement according to the F and t Student's tests. (C) 2007 Elsevier B.V. All rights reserved.

An implicit BEM formulation to model strong discontinuities in solids

A boundary element method (BEM) formulation to predict the behavior of solids exhibiting displacement (strong) discontinuity is presented. In this formulation, the effects of the displacement jump of a discontinuity interface embedded in an internal cell are reproduced by an equivalent strain field over the cell. To compute the stresses, this equivalent strain field is assumed as the inelastic part of the total strain. As a consequence, the non-linear BEM integral equations that result from the proposed approach are similar to those of the implicit BEM based on initial strains. Since discontinuity interfaces can be introduced inside the cell independently on the cell boundaries, the proposed BEM formulation, combined with a tracking scheme to trace the discontinuity path during the analysis, allows for arbitrary discontinuity propagation using a fixed mesh. A simple technique to track the crack path is outlined. This technique is based on the construction of a polygonal line formed by segments inside the cells, in which the assumed failure criterion is reached. Two experimental concrete fracture tests were analyzed to assess the performance of the proposed formulation.

The effect of mold temperature on castability of CPTi and Ti-6Al-4V castings into phosphate bonded investment materials

Objective. The aim of this study was to evaluate the castability of CP titanium and Ti-6Al-4V alloy castings into Rematitan Plus investment at three different mold temperatures.Methods. A nylon mesh pattern (20 mm with 64 squares and wire of 0.7 mm in diameter) was used for the castability testing. Initially, an image of the wax pattern was obtained by means of a digital camera and the total extension of filaments (mm) was then measured, using the Leica Qwin image analysis system. The mesh sprued was placed in the Rematitan Plus investment material and the castings were made in a Discovery Plasma machine at three different mold temperatures: 430 degrees C (control group), 480 degrees C or 530'C. Ten castings were made for each temperature. The images of the castings were analyzed (Leica Qwin) and the castability index determined by the number of the completely cast segments as a percentage of the wax pattern. Data were analyzed by two-way ANOVA and Tukey's multiple comparison test (a = 0.05) using materials and temperatures as discriminating variables.Results. The Ti-6Al-4V alloy (60.86%) presented a better castability index than CP Ti (48.44%) (p < 0.000001). For CP Ti, the temperature of 530 degrees C (23.96%) presented better castability than at other temperatures, 480 degrees C (14.66%) and 430 degrees C (12.54%), with no difference between them (p < 0.001). For Ti-6Al-4V alloy, there was a statistically significant difference among the three temperatures: 530 degrees C (28.36%) > 480 degrees C (19.66%) > 430 degrees C (15.97%) (p < 0.002).Significance. Within the limitations of this study, the increase in the mold temperature of the Rematitan Plus investment resulted in a better castability index for both materials, and Ti-6Al-4V presented a better castability index than CP Ti. (c) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Composition and abundance of marine shrimps (Crustacea, Decapoda, Penaeidea) in Ubatuba bay, Ubatuba (SP), Brazil

This work aims to analyse the composition, abundance and distribution of the Penaeidea species which occur in the Ubatuba Bay (23 degrees 26'S and 45 degrees 02'W). The samples were monthly collected from October/1992 to September/1993. Each collect was composed of two parallel radials: the first (radial ''A'') was carried out in the mid region of the bay and the second one (radial ''B'') in the bay mouth. The trawls took one hour in a boat equipped with one otter-trawl (10 mm of mesh). The registered environmental factors were depth, bottom water temperature, granulometric composition and organic content of the sediment. After the trawls, the shrimp were separated from other marine organisms and counted. Eight species of shrimp were obtained: Xiphopenaeus kroyeri; Artemesia longinaris; Penaeus (L.) schmitti; P. (F.) brasiliensis; Trachypenaeus; constrictus; Sicyonia typica; S. dorsalis and Pleoticus muelleri. The most abundant species were X. kroyeri, A. longinaris, P. muelleri and T. constrictus. It was verified a very strong seasonality among the species. The X. kroyeri species occurred in both radials along the months but its abundance decreased from a November to March. Such fact is attributed to the temperature which reached a minimum value of 20 degrees C during this period. The species A. longinaris and P. muelleri were more frequent in the radial B which was caracterized by 14 +/- 1.3 m of depth, low organic content in the sediment (2.97%) and granulometric composition of medium sand. The distribution and abundance of these shrimps in the bay, beyond the hydrological features can be related to biotic factors as food availability, migration, inter and intra specific relations (competition, predation, etc.).

Linear analysis of building floor structures by a BEM formulation based on Reissner's theory

In this work, the plate bending formulation of the boundary element method (BEM) based on the Reissner's hypothesis is extended to the analysis of zoned plates in order to model a building floor structure. In the proposed formulation each sub-region defines a beam or a slab and depending on the way the sub-regions are represented, one can have two different types of analysis. In the simple bending problem all sub-regions are defined by their middle surface. on the other hand, for the coupled stretching-bending problem all sub-regions are referred to a chosen reference surface, therefore eccentricity effects are taken into account. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composed structure as a single body. The bending and stretching values defined on the interfaces are approximated along the beam width, reducing therefore the number of degrees of freedom. Then, in the proposed model the set of equations is written in terms of the problem values on the beam axis and on the external boundary without beams. Finally some numerical examples are presented to show the accuracy of the proposed model.

Variabilidade espacial do fósforo e das frações granulométricas de um Latossolo Vermelho Amarelo

This study was conducted to study the spatial variability of phosphorus, estimating it through cokriging taking as covariables the size fractions of soil. The study was conducted at the experimental farm INCAPER-ES. The soil was sampled in the canopy projection of culture and depth of 0-0.20 meters in an irregular mesh with 109 points. The data were initially submitted to a descriptive analysis and correlation. Through geostatistics was made the adjustment of the variograms. The P showed significant correlation with the sand and clay fractions indicating that areas with higher concentrations of clay have lower availability of this nutrient. Both fractions have equal performance as co-variable in the estimate of the levels of P in the soil.

INFLUENCE of THE EVAPORATOR POSITION IN STATIC DOMESTIC REFRIGERATORS

The temperature and velocity distributions of the air inside the cabinet of domestic refrigerators affect the quality of food products. If the consumer knows the location of warm and cold zones in the refrigerator, the products can be placed in the right zone. In addition, the knowledge of the thickness of thermal and hydrodynamic boundary layers near the evaporator and the other walls is also important. If the product is too close to the evaporator wall, freezing can occur, and if it is too close to warm walls, the products can be deteriorated. The aim of the present work is to develop a steady state computational fluid dynamics (CFD) model for domestic refrigerators working on natural convection regime. The Finite Volume Methodology is chosen as numerical procedure for discretizing the governing equations. The SIMPLE-Semi-Implicit Method for Pressure-Linked Equations algorithm applied to a staggered mesh was used for solving the pressure-velocity coupling problem. The Power-Law scheme is employed as interpolation function for the convective-diffusive terms, and the TDMA-Tri-Diagonal Matrix Algorithm is used to solve the systems of algebraic equations. The model is applied to a commercial static refrigerator, where the cabinet is considered an empty three-dimensional rectangular cavity with one drawer at the bottom of the cabinet, but without shelves. In order to analyze the velocity and temperature fields of the air flow inside the cabinet the evaporator temperature, Te, was varied from -20 degrees C to 0 degrees C, and nine different evaporator positions are evaluated for evaporator temperature of -15 degrees C. The cooling capacity of the evaporator for the steady state regime is also computed for each case. One can conclude that the vertical positioning of the evaporator inside the cabinet plays an important role on the temperature distribution inside the cabinet.

Anticoccidial effects of coumestans from Eclipta alba for sustainable control of Eimeria tenella parasitosis in poultry production

The aim of this study was to evaluate the anticoccidial efficacy of a product containing coumestans from Eclipta alba. Experimental conditions were set up as to reproduce the environment conditions for husbandry adopted in commercial broiler farms. Broilers were raised in broiler chicken shed provided with feeders, drinkers, illumination and temperature control systems and floor covering to afford an adequate nourishing environment. Male Cobb broilers (240) were assigned to four experimental groups being each experimental group set apart in rice straw-covered shed isolated with wire mesh. One-day-old broilers were reared in a coccidian-free environment with ad libitum supply of filtered water and freely available standard feed, from the 1st to the 35th day of life. The T1 group received standard feed (negative control); T2 was treated with standard feed supplemented with 66 ppm of salinomycin (positive control); groups T3 and T4 had standard feed supplemented with the ethyl acetate fraction from methanolic extract of E. alba aerial parts, which contains the coumestans WL and DWL (120 and 180 ppm, respectively). The chicken broilers were individually infected with 2 x 104 oocysts of Eimeria tenella when they were 14 days old and were monitored weekly to evaluate zootechnical parameters such as weight gain and food conversion ratio. Counting of coccidial oocyst in chiken feces was assessed from random samples, from the 21st to 28th days of life, which corresponded to 7-14 days after the infection. Five chickens selected at random from each experimental group were subsequently euthanized at 21, 28 or 35 days of life to determine the lesion score in the cecal region and to excise a cecum portion for histopathological evaluation. The group treated with coumestans from E. alba presented an average weight gain and food conversion ratio higher than the negative control group and similar to the mean value of the positive control group. Coumestan-treated groups showed a significant decrease in the oocyst counting since the 21th day of life and displayed a reduced number of macroscopic lesions. Histopathological evaluations of cecum fragments showed that both treatments induced the migration of defense cells at the site of infection. A severe destruction of the cecal lining was found in the intestinal tract of broilers fed with a coumestans dose of 180 ppm. Overall, our results validate the use of a phytotherapy containing E. alba coumestans at a dose of 120 ppm as a therapeutic or prophylactic agent against avian coccidiosis. (C) 2010 Elsevier B.V. All rights reserved.

Predição de propagação de fissuras através de modelos constitutivos locais e técnica de construção progressiva da trajetória de descontinuidade

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spatial variability of infiltration and its relationship to some physical properties

Water infiltration into soil is one of the basic factors for estimating irrigation intensity according to the plants' requirements; this is aimed at avoiding problems of surface run-off and degradation. The purpose of the present investigation was to determine the spatial variation of infiltration and its relationship to some physical properties of soil by means of geostatistical techniques in Typic Plinthaquult soils having average texture and flat relief. A 113 point mesh was designned, having a regular distance of 10 m between points, samples being taken from 0 to 0.20 meters depth. Sand, silt and clay content, bulk density, macroporosity, microporosity and total porosity were determined. Infiltration tests were carried out in the field by means of a 15 cm diameter ring. Descriptive statistics and geostatistics were used for analysing the data. Infiltration, silt and microporosity data did not fit a normal distribution curve. Infiltration had high variability, having an average 36.03 mm h(-1). Total porosity was 56.73%, this being the only property that did not show spatial dependency. The smallest ranges were observed for bulk density, macroporosity and microporosity, having values of less than 40 m. The smallest degrees of spatial dependence were observed for infiltration, silt and clay, evidence also being shown of the influence of silt and clay on infiltration rate. Contour maps were constructed; fitting them to the semivariogram models, together with studying the correlations, led to establishing relationships between the properties.

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.

Efeito das técnicas de fusão sobre a fluidez de ligas do sistema cobre-alumínio.

It was evaluated the castability of four copper-aluminium alloy according the melting casting method used. The specimens were made using polyester mesh screen, with 11 x 11 filaments of 0.26 mm thick, fixed along of two adjacent edges in wax bar, with the sprue attached at their junction. The alloys were in an electrical casting machine and a centrifugal casting machine with an air/gas torch. The castability values were obtained by the percentage of completed segments of the resulting cast alloy screen. It was verified that the use of the electrical casting machine produced higher castability values to the copper-aluminium alloys than those produced by a centrifugal casting machine with an air/gas torch.

Estudo comaprativo da resistência da união esmalt/resina/metal. Efeito de resinas de fixação, artifícios retentivos e ligas metálicas.

The purpose of this study was to compare the enamel/resin/metal bond tensile strength by using human canines, in which castings were bonded. These castings were obtained by Co-Cr or Ni-Cr alloys and showed four types of mechanisms of retention: 50 micrograms aluminum oxide abrasive, electrochemical etch, acrylic beads metal mesh. The castings were bonded utilizing Comspan Opaque and Panavia Ex. The specimens were subjected to tensile forces after 24 hours in an Instron machine. The castings subjected to 50 micrograms aluminum oxide abrasive and bonded utilizing Panavia EX showed the biggest bond tensile strength.

Application of a model updating technique for health condition monitoring and damage detection of flexible structures

This paper discusses the application of a damage detection methodology to monitor the location and extent of partial structural damage. The methodology combines, in an iterative way, the model updating technique based on frequency response functions (FRF) with monitoring data aiming at identifying the damage area of the structure. After the updating procedure reaches a good correlation between the models, it compares the parameters of the damage structure with those of the undamaged one to find the deteriorated area. The influence of the FEM mesh size on the evaluation of the extent of the damage has also been discussed. The methodology is applied using real experimental data from a spatial frame structure.

Fourth-order method for solving the Navier-Stokes equations in a constricting channel

A fourth-order numerical method for solving the Navier-Stokes equations in streamfunction/vorticity formulation on a two-dimensional non-uniform orthogonal grid has been tested on the fluid flow in a constricted symmetric channel. The family of grids is generated algebraically using a conformal transformation followed by a non-uniform stretching of the mesh cells in which the shape of the channel boundary can vary from a smooth constriction to one which one possesses a very sharp but smooth corner. The generality of the grids allows the use of long channels upstream and downstream as well as having a refined grid near the sharp corner. Derivatives in the governing equations are replaced by fourth-order central differences and the vorticity is eliminated, either before or after the discretization, to form a wide difference molecule for the streamfunction. Extra boundary conditions, necessary for wide-molecule methods, are supplied by a procedure proposed by Henshaw et al. The ensuing set of non-linear equations is solved using Newton iteration. Results have been obtained for Reynolds numbers up to 250 for three constrictions, the first being smooth, the second having a moderately sharp corner and the third with a very sharp corner. Estimates of the error incurred show that the results are very accurate and substantially better than those of the corresponding second-order method. The observed order of the method has been shown to be close to four, demonstrating that the method is genuinely fourth-order. © 1977 John Wiley & Sons, Ltd.