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Now showing items 1 - 11 of 11

  • 6B.02

    Geraldes, V.   Goncalves-Rosa, N.   Tavares, C.   Liu, B.   Paton, J.   Rocha, I.  

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  • Modelling of flow and concentration patterns in spiral wound membrane modules with ladder-type spacers RID A-2753-2009

    Santos, J. L. C.   Geraldes, V.   Velizarov, S.   Crespo, J. G.  

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  • Lead concentration in feces and urine of exposed rats by x-ray fluorescence and electrothermal atomic absorption spectrometry

    Guimaraes, D.   Carvalho, M. L.   Becker, M.   von Bohlen, A.   Geraldes, V.   Rocha, I.   Santos, J. P.  

    Measurements made in feces and urine of Wistar rats exposed to lead acetate (n?=?20) in drinking water since the fetal period were compared with those obtained from a control group (n?=?20) in order to assess the age influence on Pb excretion. The measurements were made in different collections of rats aging between 1 and 11?months. To determine the Pb content of the samples, total reflection X-ray fluorescence (TXRF) and electrothermal atomic absorption spectrometry (ETAAS) were used for the urine samples and energy dispersive X-ray fluorescence (EDXRF) was used for the feces.
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  • Characterization of minocycline powder micronized by a supercritical antisolvent (SAS) process RID G-2052-2010

    Cardoso, M. A. Tavares   Geraldes, V.   Cabral, J. M. S.   Palavra, A. M. F.  

    The effect of the supercritical antisolvent micronization (SAS) process in the minocycline was evaluated in terms of particles morphology and density of the obtained powder. The minocycline was precipitated in a continuous mode from an ethanol solution using supercritical carbon dioxide as antisolvent and particles with a mean diameter around 250 nm were obtained (at 40 degrees C; 130 bar; solution concentration of 10 mg mL(-1); solution flow rate of 1 ml, min(-1) and antisolvent flow rate, measured at room temperature and atmospheric pressure, of 6.56 Lmin(-1)). Moreover, the Scanning Electron Microscopy (SEM) and the X-ray Diffraction (XRD) allowed the comparison between the crystalline initial state and the amorphous particles obtained after the supercritical micronization process. The density of the minocycline was determined by gas picnometry, before and after the micronization process, and the obtained results showed that it passes from an initial density of 1.574 to 2.951 gcm(-3) after the processing. The increase in density of the micronized powder is clearly in contrast with the idea that SAS micronization produces a powder lighter than the starting material. A discussion about the stability and solubility of the precipitated powder, also contributes to highlight the potential of this micronization technique to integrate the pharmaceutical processing and to develop new formulations of this biopharmaceutical. (C) 2008 Elsevier B.V. All rights reserved.
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  • Ultrasonic energy as a tool to overcome some drawbacks in the determination of lead in brain tissue and urine of rats

    Guimaraes, D.   Santos, J. P.   Carvalho, M. L.   Vale, G.   Santos, H. M.   Geraldes, V.   Rocha, I.  

    An ultrasonic assisted solid-liquid extraction method was developed to determine the level of lead in the brain and urine of rats. Lead was determined by electrothermal atomic absorption spectrometry with longitudinal-Zeeman background correction. Several analytical drawbacks were addressed and overcome, namely small brain sample mass and the formation of precipitate in the urine samples. Utrasonication provided by an ultrasonic probe succeeded in extracting lead from brain samples. Furthermore, it was demonstrated that the formation of a precipitate lowered the lead content in the liquid phase of the urine. Lead was back extracted from the precipitate to the liquid phase with the aid of ultrasonic energy and acidifying the urine with 10% v/v nitric acid. A microwave-assisted acid digestion protocol was used to check the completeness of the lead extraction. The within bath and between bath precision was 5% (n = 9) and 7% (n = 3) respectively. The limit of quantification was 1.05 mu g g(-1) for brain samples and 2.1 mu g L-1 for urine samples. A total of 6 samples of urine and 12 samples of brain from control rats and another 6 samples of urine and 12 samples of brain from rats fed with tap water rich in lead acetate were used in this research. Lead levels in brain and urine from exposed rats ranged from 1.9 +/- 0.2 mu g g(-1) to 3.5 +/- 0.2 mu g g(-1) and from 752 +/- 56 mu g L-1 to 60.9 +/- 1.2 mg L-1 respectively. Statistically significant differences of levels of lead in brain and urine were found between exposed and non exposed rats. (C) 2011 Elsevier B.V. All rights reserved.
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  • Computer program for simulation of mass transport in nanofiltration membranes

    Geraldes, V.   Brites Alves, A.M.  

    A computer program, NanoFiltran, was developed to simulate the mass transport of multi-ionic aqueous solutions in charged nanofiltration (NF) membranes, based on the Donnan steric partitioning pore and dielectric exclusion (DSPM&DE) model, with incorporation of the non-ideality of electrolyte solutions and concentration polarization effects in the membrane/feed-solution interface. With this computer program, the extended Nernst-Planck (ENP) equations are discretized inside the membrane, using the finite-difference scheme. The discretized ENP equations together with the other model equations are linearized in order to obtain a system of equations that are solved simultaneously. The linearized system of equations is based on an initial guess for the electrical potential and ions concentrations profiles, which are updated iteratively. A robust method of under-relaxation of the electrical potential and ions concentrations ensures that the convergence is achieved even for NF systems that exhibit a very stiff numerical behaviour. The prediction of observed solute rejection coefficients compare very well with a set of experimental and numerical values reported in the literature, for a multi-ionic NF system [W.R. Bowen, A.W. Mohammad, Diafiltration by nanofiltration: prediction and optimization, AIChE J. 44(8) (1998) 1799]. The numerical stability of the computer program is analyzed for a very stiff NF system of three ions and the predictions of the concentration and potential profiles within the membrane yielded by the NanoFiltran and by the fourth order Runge-Kutta method are compared and discussed. The results show that NanoFiltran is a valuable tool for accurate and robust prediction of the mass transfer in nanofiltration of multi-ionic solutions. The computer program NanoFiltran is available under a free software license. [All rights reserved Elsevier].
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  • Multi-ionic nanofiltration of highly concentrated salt mixtures in the seawater range RID B-7628-2011 RID B-4622-2012

    Silva, V.   Geraldes, V.   Alves, A. M. Brites   Palacio, L.   Pradanos, P.   Hernandez, A.  

    This work presents experimental observations on the permeation of multi-ionic solutions through a commercial DESAL-HL nanofiltration membrane. Two types of mixed-salt solutions have been analysed with a common co-ion (NaCl + Na(2)SO(4)) and with a common counter-ion ((NaCl + MgCl(2))). The NaCl concentrations have been similar to those of seawater with divalent ions with lower concentrations up to a tenth of that of the monovalent salt. In this study. SEDE-VCh model that includes the variation of the charge inside the membrane pores has been used to model the system and structural, electrical and dielectrical membrane parameters for such systems have been obtained. We show that accurate enough predictions can be achieved for the retention of monovalent ions in the presence of counter or co-ion divalent ions from the single NaCl salt results. While correct predictions for the retention of the divalent ions require membrane charges and dielectric constants dependent of the ionic composition of the solutions filtered. (C) 2011 Elsevier B.V. All rights reserved.
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  • Ethics issues experienced in HBM within Portuguese health surveillance and research projects

    Reis, M. Fatima   Segurado, Susana   Brantes, Ana   Simoes, Helena Teresinha   Melim, J. Mauricio   Geraldes, V.   Miguel, J. Pereira  

    Background: In keeping with the fundamental practice of transparency in the discussion and resolution of ethics conflicts raised by research, a summary of ethics issues raised during Portuguese biomonitoring in health surveillance and research is presented and, where applicable, their resolution is described. Methods: Projects underway aim to promote the surveillance of public health related to the presence of solid waste incinerators or to study associations between human exposure to environmental factors and adverse health effects. The methodological approach involves biomonitoring of heavy metals, dioxins and/or other persistent organic pollutants in tissues including blood, human milk and both scalp and pubic hair in groups such as the general population, children, pregnant women or women attempting pregnancy. As such, the projects entail the recruitment of individuals representing different demographic and health conditions, the collection of body tissues and personal data, and the processing of the data and results. Results: The issue of autonomy is raised during the recruitment of participants and during the collection of samples and data. This right is protected by the requirement for prior written, informed consent from the participant or, in the case of children, from their guardian. Recruitment has been successful, among eligible participants, in spite of incentives rarely being offered. The exception has been in obtaining guardians' consent for children's participation, particularly for blood sampling. In an attempt to mitigate the harm-benefit ratio, current research efforts include alternative less invasive biomarkers. Surveys are currently being conducted under contract as independent biomonitoring actions and as such, must be explicitly disclosed as a potential conflict of interests. Communication of results to participants is in general only practised when a health issue is present and corrective action possible. Concerning human milk a careful approach is taken, considering breast-feeding's proven benefits. Conclusion: No national legislation currently accounts for the surveillance component of biomonitoring as distinct from research. Ethics issues arising within the domain of research are resolved according to available regulations. For issues encountered during surveillance, the same principles are used as guidance, completed by the authors' best judgement and relevant ethics committees' findings.
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  • Investigation of flow patterns and mass transfer in membrane module channels filled with flow-aligned spacers using computational fluid dynamics (CFD) RID A-2753-2009

    Santos, J. L. C.   Geraldes, V.   Velizarov, S.   Crespo, J. G.  

    Experimental and numerical (CFD) results, obtained for 12 different flow-aligned spacer structures under different hydrodynamic conditions, were investigated in order to gain insight into the flow and mass transfer profiles inside the channels of membrane modules. The CFD results were analysed in terms of shear stress and mass transfer at the walls. A modified friction factor was introduced to investigate the effect of the hydrodynamic conditions in the channel on the shear stress at the walls. The experimental results showed that the transition between laminar and transitional flow regime could be rigorously determined for the spacers under study. The excellent agreement between the CFD and experimental results suggests that the cyclic inlet and outlet boundary condition can be applied with high confidence. Additionally, it was found that the flow structure is determined for all cases studied mainly by the transverse filaments. The presence of longitudinal filaments in the channel was shown to not significantly affect the flow structure. Finally, mass transfer results demonstrated that the modified friction factor could be used for selecting the best spacer in terms of mass transfer efficiency. (c) 2007 Elsevier B.V. All rights reserved.
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  • CFD analysis of supercritical antisolvent (SAS) micronization of minocycline hydrochloride RID G-2052-2010

    Cardoso, M. A. Tavares   Cabral, J. M. S.   Palavra, A. M. F.   Geraldes, V.  

    A new mathematical model was developed to understand the process of supercritical antisolvent (SAS) micronization of minocycline using ethanol as solvent and carbon dioxide as antisolvent. This model gathered jet hydrodynamics, mass transfer and phase equilibrium data with the buoyancy effect on the fluid dynamics. The solubility of minocycline in binary mixtures of carbon dioxide plus ethanol was determined for the temperature of 313 K, pressure of 13 MPa and for several mixture compositions. These experimental results were used in the model to calculate pseudo-supersaturations. SAS micronization experiments, using a nozzle with 10 cm length, were carried out to evaluate the model in terms of its predictive capacity. The resolution of the model by computer fluid dynamics (CFD) allowed to discuss the effects of the concentration and flow rate of initial solution in the particle size and particle size distribution. Moreover, the model helped in the identification of problems regarding the suitableness of the precipitation vessel geometry to this particular binary system carbon dioxide plus ethanol and showed the importance of the buoyancy effect in the SAS micronization apparatus performance. Although this model was developed specifically to deal with the system carbon dioxide plus ethanol plus minocycline at 13 MPa and 313 K, some of these considerations can also be applied to similar systems and can help to improve the performance of the SAS micronization apparatuses. (C) 2008 Elsevier B.V. All rights reserved.
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  • On the prediction of permeate flux for nanofiltration of concentrated aqueous solutions with thin-film composite polyamide membranes

    Rodrigues, C.   Morao, A. I. Cavaco   de Pinho, M. N.   Geraldes, V.  

    The nanofiltration of binary aqueous solutions of glucose, sucrose and sodium sulfate was investigated using thin-film composite polyamide membranes with different molecular weight cut-off s. The NF experiments, in total recycle mode, were performed in a plate-and-frame module Lab 20 (AlfaLaval), at 22 degrees C and with a flowrate of 8.2L/min, using the membranes NF90, NF200 and NF270 from FilmTec (Dow Chemical), for transmembrane pressures between I and 6 MPa and with aqueous solutions with osmotic pressures of between 0.5 and 3.0 MPa. The permeate flux was predicted by the osmotic pressure model, using the membrane hydraulic resistance and the solution viscosity inside the membrane pores, and computing the concentration polarization with recourse to a mass-transfer correlation specific for the plate-and-frame module used. The flux predictions, using the pure water viscosity, agree reasonably with the experimental data only for low transmembrane pressures and with the most diluted solutions. For higher transmembrane pressures and for higher solute concentration the predicted fluxes can be as far as 2.5, 4.1 and 9.6 times higher than the experimental one, for the aqueous solutions of Na(2)SO(4), glucose and sucrose, respectively. These deviations are strongly reduced when the pure water viscosity is replaced by the solution viscosity adjacent to the membrane. In this case, the maximum deviation between predictions and experiments occurs also for higher transmembrane pressures and for higher solute concentration, but the maximum ratio between predicted values and the experiments were reduced now to 1.8, 2.1 and 2.9, for the aqueous solutions of Na(2)SO(4), glucose and sucrose, respectively. Even using the solution viscosity adjacent to the membrane, and for the systems investigated, the osmotic pressure model must used with caution for design purposes because it may over predict the permeate flux by a factor of about 2 when the solute concentration is high. (C) 2009 Elsevier B.V. All rights reserved.
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