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Search Results: 1 - 10 of 462389 matches for " Jarbas J. R;Raimundo Jr "
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Gran method for end point anticipation in monosegmented flow titration
Aquino Emerson V,Pasquini Celio,Rohwedder Jarbas J. R,Raimundo Jr Ivo M
Journal of the Brazilian Chemical Society , 2004,
Abstract: An automatic potentiometric monosegmented flow titration procedure based on Gran linearisation approach has been developed. The controlling program can estimate the end point of the titration after the addition of three or four aliquots of titrant. Alternatively, the end point can be determined by the second derivative procedure. In this case, additional volumes of titrant are added until the vicinity of the end point and three points before and after the stoichiometric point are used for end point calculation. The performance of the system was assessed by the determination of chloride in isotonic beverages and parenteral solutions. The system employs a tubular Ag2S/AgCl indicator electrode. A typical titration, performed according to the IUPAC definition, requires only 60 mL of sample and about the same volume of titrant (AgNO3) solution. A complete titration can be carried out in 1 - 5 min. The accuracy and precision (relative standard deviation of ten replicates) are 2% and 1% for the Gran and 1% and 0.5% for the Gran/derivative end point determination procedures, respectively. The proposed system reduces the time to perform a titration, ensuring low sample and reagent consumption, and full automatic sampling and titrant addition in a calibration-free titration protocol.
Design and development of a multichannel potentiometer for monitoring an electrode array and its application in flow analysis
Jarbas J. R. Rohwedder,Celio Pasquini,Ivo M. Raimundo, Jr.,M. Concei ao,B. S. M. Montenegro,Alberto N. Araújo,Cristina M. C. M. Couto
Journal of Analytical Methods in Chemistry , 2002, DOI: 10.1155/s1463924602000147
Abstract: A versatile potentiometer that works with electrode arrays in flow injection and/or monosegmented flow systems is described. The potentiometer is controlled by a microcomputer that allows individual, sequential multiplexed or random accesses to eight electrodes while employing only one reference electrode. The instrument was demonstrated by monitoring an array of seven flow-through ion-selective electrodes for Ag
Gran method for end point anticipation in monosegmented flow titration
Aquino, Emerson V;Pasquini, Celio;Rohwedder, Jarbas J. R;Raimundo Jr, Ivo M;Montenegro, M. Concei??o B. S. M;Araújo, Alberto N;
Journal of the Brazilian Chemical Society , 2004, DOI: 10.1590/S0103-50532004000100017
Abstract: an automatic potentiometric monosegmented flow titration procedure based on gran linearisation approach has been developed. the controlling program can estimate the end point of the titration after the addition of three or four aliquots of titrant. alternatively, the end point can be determined by the second derivative procedure. in this case, additional volumes of titrant are added until the vicinity of the end point and three points before and after the stoichiometric point are used for end point calculation. the performance of the system was assessed by the determination of chloride in isotonic beverages and parenteral solutions. the system employs a tubular ag2s/agcl indicator electrode. a typical titration, performed according to the iupac definition, requires only 60 ml of sample and about the same volume of titrant (agno3) solution. a complete titration can be carried out in 1 - 5 min. the accuracy and precision (relative standard deviation of ten replicates) are 2% and 1% for the gran and 1% and 0.5% for the gran/derivative end point determination procedures, respectively. the proposed system reduces the time to perform a titration, ensuring low sample and reagent consumption, and full automatic sampling and titrant addition in a calibration-free titration protocol.
A pH optode based on thymol blue: application to determination of CO2 using flow injection analysis system
Sotomayor, M.D.P.T.;Raimundo Jr, I.M.;Rohwedder, J.J. R.;Oliveira Neto, G.;
Eclética Química , 2010, DOI: 10.1590/S0100-46702010000200004
Abstract: an optode based on thymol blue (tb), an acid-based indicator, has been constructed and evaluated as a detector in fia system for co2 determination. the dye was chemically immobilised on the surface of a bifurcated glass optical fibre bundle, using silanisation in organic media. in fia system, hydrogen carbonate or carbonate samples are injected in a buffer carrier solution, and then are mixed with phosphoric acid solution to generate co2, which diffuses through a ptfe membrane, in order to be collected in an acceptor carrier fluid, pumped towards to detection cell, in which the optode was adapted. the proposed system presents two linear response ranges, from 1.0 x 10-3 to 1.0 x 10-2 mol l-1, and from 2.0 x 10-2 to 0.10 mol l-1. the sampling frequency was 11 sample h-1, with good repeatability (r.s.d < 4 %, n = 10). in flow conditions the optode lifetime was 170 h. the system was applied in the analysis of commercial mineral water and the results obtained in the hydrogen carbonate determination did not differ significantly from those obtained by potentiometry, at a confidence level of 95 %.
Flow system for pre-concentration and spectrophotometric determination of reactive mercury
Yonehara, Fernando S.;Pasquini, Celio;Rohwedder, Jarbas J. R.;
Journal of the Brazilian Chemical Society , 2005, DOI: 10.1590/S0103-50532005000600007
Abstract: a new flow system to pre-concentrate and determine reactive mercury in effluents by photometry is presented. the system is based on the reduction of the reactive mercury present in a 500 ml sample with a sn(ii) solution. the reduced mercury is swept out by an argon stream and carried to a straight glass tube (60 cm long, 3 mm i.d.) inclined in an angle of 15o. the inner surface of this tube has been previously covered by a renewable liquid layer of an oxidant solution containing h2o2 (12%, m/v) and hno3 (3.0 mol l-1) produced after introduction and passage of a liquid monosegment containing those reagents. the swept hg0 undergoes an oxidative process and the hg(ii) formed is retained in the layer. after a 10 min sweep time interval the argon flow is stopped and a reagent monosegment (350 μl) containing par [4-(2-pyridylazo)resorcinol], 1.0 x 10-3 mol l-1, in an ammonia/ ammonium chloride buffer (4.0 mol l-1; ph 9.0) is introduced and passes through the glass tube. a strongly coloured complex between par and hg(ii) is formed and carried to the detection system composed of a light emitting diode (led, lmax = 525 nm) and a photodiode detector. sample processing time is about 12 min. the system is washed and a fresh liquid layer is formed, preparing the system for a new determination. this method concentrates the sample by a factor of 148 and achieves a detection limit of 0.16 μg l-1.
Relationship between Fracture Toughness and Fracture Surface Fractal Dimension in AISI 4340 Steel  [PDF]
Luis R. Carney, John J. Mecholsky Jr.
Materials Sciences and Applications (MSA) , 2013, DOI: 10.4236/msa.2013.44032
Abstract:

This study analyzes the relationship between fracture toughness and the fracture surface fractal dimension for a set of twenty-four CT-type AISI 4340 steel specimens heat treated to a variety of tensile strengths. Specimens were tested in accordance with ASTM E 399. Their respective fracture surfaces were plated, polished, photographed under an SEM in BSE mode and measured according to the Richardson method to obtain fractal dimensions. For brittle materials the limited results are consistent with previous literature: increasing fractal dimension with increasing toughness. For partially or fully ductile materials the results indicate a decrease in fractal dimension with an increase in fracture toughness. The data are modeled using a variation of the function applied to ceramics. Fracture in a ductile mode is characterized by the formation of dimples which exhibit fractal characteristics. The results are discussed in terms of the micromechanisms of fracture.

Two-phase non-equilibrium models: the challenge of improving phase change heat transfer prediction
Barbosa, Jr, J. R.;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2005, DOI: 10.1590/S1678-58782005000100003
Abstract: this lecture addresses some recent developments in modelling of macroscopic thermodynamic and hydrodynamic non-equilibrium phenomena in convective phase change (boiling and condensation) of pure fluids and mixtures. proper accounting of such phenomena may hold the key to explain and predict deviations from the classical (equilibrium) phase change convective heat transfer behaviour reported in the literature and yet not fully understood. in the first part of the paper, a detailed qualitative description of the classical heat transfer coefficient behaviour is presented together with two examples of departure from macroscopic equilibrium largely supported by experimental evidence. the second part of the paper reviews successful attempts to model the non-equilibrium phase change phenomena taking place in the two situations. the first example is a thermodynamic non-equilibrium slug flow model (one in which saturated taylor bubbles become separated by slugs of subcooled liquid) that predicts the peaks in heat transfer coefficient at near-zero thermodynamic quality observed in forced convective boiling of some pure liquids. the occurrence of such peaks is typical of low latent heat, low thermal conductivity systems and of systems in which the vapour volume formation rate for a given heat flux is large. the second example is a comprehensive annular flow calculation methodology that predicts the decrease in the heat transfer coefficient with increasing quality observed in convective boiling of binary and multicomponent mixtures. in this case, as will be seen, coupled mass transfer resistance and hydrodynamic non-equilibrium effects generate concentration gradients between the liquid film and entrained droplets that are responsible for the heat transfer deterioration. in addition, it will be shown that for condensation of mixtures the methodology predicts a heat transfer intensification which has been subsequently confirmed by independent experimental results.
Constru??o e otimiza??o de um sistema para produ??o e aplica??o de oz?nio em escala de laboratório
Kunz, Airton;Freire, Renato S.;Rohwedder, Jarbas J. R.;Duran, Nelson;Mansilla, Hector;Rodriguez, Jaime;
Química Nova , 1999, DOI: 10.1590/S0100-40421999000300022
Abstract: this paper shows the assembly of an ozonization system to be used in laboratory scale, mainly to study effluent treatability. the system is simple, practical and provides easy acquisition of data when interfaced to a microcomputer. the performance of ozone generation and kla values are also described.
Constru o e otimiza o de um sistema para produ o e aplica o de oz nio em escala de laboratório
Kunz Airton,Freire Renato S.,Rohwedder Jarbas J. R.,Duran Nelson
Química Nova , 1999,
Abstract: This paper shows the assembly of an ozonization system to be used in laboratory scale, mainly to study effluent treatability. The system is simple, practical and provides easy acquisition of data when interfaced to a microcomputer. The performance of ozone generation and K La values are also described.
Inquéritos nacionais de saúde National health surveys
Jarbas Barbosa da Silva Jr
Revista Brasileira de Epidemiologia , 2011, DOI: 10.1590/s1415-790x2011000500001
Abstract:
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