Browsing by Author "Silva, Luís M. S."
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- Evaluation of the Resilient Modulus of Hot-Mix Asphalt Made with Recycled Concrete Aggregates from Construction and Demolition WastePublication . Galan, Juan J.; Silva, Luís M. S.; Pasandín, Ana R.; Pérez, IgnacioThis paper reports the influence of the percentage of recycled aggregate (RCA) fromconstruction and demolition waste (C&DW) together with the percentage of binder (L), curing time(t) and temperature (T) of the samples on the stiffness of a hot asphalt mixture. The study was carriedout using the response surface methodology (RSM). The resilient modulus was chosen to estimate thestiffness of the mixture. The percentages of RCA studied were 0% (control), 5%, 10%, 20% and 30%,whilst 3.5%, 4% and 4.5% were those chosen for the binder content. Before compacting the samples,they were left into the oven to cure. Curing time, or pretreatment time, were set at 0 (control), 2 and4 h. The samples were subjected to temperatures of 0, 10 and 20◦C. The natural aggregate is of thehornfels type. All the specimens studied showed high stiffness at low temperatures. According tothis research, temperature proved to be the most influential factor on the decrease in the resilientmodulus and, conversely, the percentage of recycled aggregate is not a significant factor in the rangeof values studied.
- Inventories and concentration profiles of 137Cs in undisturbed soils in the northeast of Buenos Aires Province, ArgentinaPublication . Silva, Luís M. S.; Montes, M. L.; Sá, Christopher; Runco, J.; Taylor, M. A.; Desimoni, J.Inventories and vertical distribution of (137)Cs were determined in La Plata region undisturbed soils, Argentina. A mean inventory value of 891 ± 220 Bq/m(2) was established, which is compatible with the values expected from atmospheric weapon tests fallout. The study was complemented with pH, organic carbon fraction, texture and mineralogical soil analyses. Putting together Southern Hemisphere (137)Cs inventory data, it is possible to correlate these data with the mean annual precipitations. The large differences in (137)Cs concentration profiles were attributed to soil properties, especially the clay content and the pH values. A convection-dispersion model with irreversible retention was used to fit the activity concentration profiles. The obtained effective diffusion coefficient and effective convection velocity parameters values were in the range from 0.2 cm(2)/y to 0.4 cm(2)/y and from 0.23 cm/y to 0.43 cm/y, respectively. These data are in agreement with values reported in literature. In general, with the growth of clay content in the soil, there was an increase in the transfer rate from free to bound state. Finally, the highest transfer rate from free to bound state was obtained for soil pH value equal to 8.
- Kinetic and equilibrium adsorption parameters estimation based on a heterogeneous intraparticle diffusion modelPublication . Silva, Luís M. S.; Muñoz-Peña, Maria J.; Domínguez-Vargas, Joaquín R.; González, Teresa; Cuerda-Correa, Eduardo M.In this work, a commercial resin with a well-developed internal pore structure was chosen to adsorb four parabens used as probe molecules. The main novelty was to propose and validate a phenomenological transient adsorption model based on conservation law in both phases coupled with Langmuir’s equilibrium law and Fick’s mass transfer rate law inside the pores. With such an aim, a heterogeneous three-parameter intraparticle diffusion model, IPDM, was formulated, and its numerical solution was fitted to time-dependent concentration data by minimizing the sum of squared residuals. Equilibrium constants were also predicted by fitting Langmuir isotherm to equilibrium data. A monolayer capacity of 0.81 mmol/g was calculated for the four parabens regardless of the number of carbons in the ester group. With the optimal parameters values from the IPDM fitting process, a system of ODEs comprising local sensitivity coefficients as dependent variables was solved to compute the parameters’ variance-covariance matrix and infer their ranges for a 95% marginal confidence interval. In order to test the validity of the proposed model, an attempt to crosscheck between the parameters obtained by the estimation of the equilibrium related parameter, κ, and the modified capacity parameter, and the ones obtained by fitting the Langmuir’s isotherm to equilibrium data was carried out. As far as equilibrium related parameters concern, there is a relative agreement inside the limits of the confidence range between the estimated values of the amount adsorbed in equilibrium with initial bulk solution concentration, q0, and Langmuir’s equilibrium constant, K, adjusted to kinetic and equilibrium data, independently. Additionally, the order of magnitude of pore diffusivity obtained in this work is in accordance with the one predicted by Wilke-Chang correlation and is inversely proportional to the van der Waals volume raised to the power 0.53 in close agreement with the literature.
- Mass spectrometry parameters optimization for the 46 multiclass pesticides determination in strawberries with gas chromatography ion-trap tandem mass spectrometryPublication . Fernandes, Virgínia C.; Vera, Jose L.; Domingues, Valentina F.; Silva, Luís M. S.; Mateus, Nuno; Delerue-Matos, CristinaMulticlass analysis method was optimized in order to analyze pesticides traces by gas chromatography with ion-trap and tandem mass spectrometry (GC-MS/MS). The influence of some analytical parameters on pesticide signal response was explored. Five ion trap mass spectrometry (IT-MS) operating parameters, including isolation time (IT), excitation voltage (EV), excitation time (ET),maximum excitation energy or “q” value (q), and isolationmass window (IMW) were numerically tested in order to maximize the instrument analytical signal response. For this, multiple linear regression was used in data analysis to evaluate the influence of the five parameters on the analytical response in the ion trap mass spectrometer and to predict its response. The assessment of the five parameters based on the regression equations substantially increased the sensitivity of IT-MS/MS in the MS/MS mode. The results obtained show that for most of the pesticides, these parameters have a strong influence on both signal response and detection limit.Using the optimized method, a multiclass pesticide analysis was performed for 46 pesticides in a strawberry matrix. Levels higher than the limit established for strawberries by the European Union were found in some samples.
- Minerals and fatty acids profile of Northwest Portuguese coast shrimpsPublication . Maia, Maria Luz; Almeida, Agostinho; Soares, Cristina; Silva, Luís M. S.; Delerue-Matos, Cristina; Calhau, Conceição; Domingues, ValentinaTwo shrimp species were sampled in different seasons and locations on Portuguese coast. Their fatty acid content and 28 essential, probably essential and potentially toxic/non-essential elements were quantified. A 100 g serving of shrimp muscle from the Portuguese coast provides 78 % of the recommended daily intake. Both species presented low ω-6/ω-3 ratio, 0.15 for P. serratus and 0.23 for P. varians, respectively. The quality indices presented also good values for shrimp samples, hypocholesterolemic/hypercholesterolemic ratio (HH) was 2.60 for P. serratus and 2.55 for P.varians. The index of thrombogenicity (IT) were 0.24 and 0.25 for P. serratus and P. varians, respectively and index of atherogenicity (IA) was 0.41 and 0.43 for P. serratus and P. varians, respectively. The Mg, Na, K, Ca, I, Cr, Cu and Se in shrimp samples analyzed can provide more than 5 % of the Recommended Dietary Allowance (RDA)/ Adequate Intake (AI). The best nutritional Ca/Mg ratio was found in P. serratus (1.7). Portuguese shrimp has proven to be a good dietary source of EPA, DHA and some essential elements, also Target Hazard Quotient (THQ) and risk-benefit evaluation shown that there is no significant danger associated with the consumption of Portuguese shrimp
- Optimization of the Ion Source-Mass Spectrometry Parameters in Non-Steroidal Anti-Inflammatory and Analgesic Pharmaceuticals Analysis by a Design of Experiments ApproachPublication . Paíga, Paula; Silva, Luís M. S.; Delerue-Matos, CristinaThe flow rates of drying and nebulizing gas, heat block and desolvation line temperatures and interface voltage are potential electrospray ionization parameters as they may enhance sensitivity of the mass spectrometer. The conditions that give higher sensitivity of 13 pharmaceuticals were explored. First, Plackett-Burman design was implemented to screen significant factors, and it was concluded that interface voltage and nebulizing gas flow were the only factors that influence the intensity signal for all pharmaceuticals. This fractionated factorial design was projected to set a full 2(2) factorial design with center points. The lack-of-fit test proved to be significant. Then, a central composite face-centered design was conducted. Finally, a stepwise multiple linear regression and subsequently an optimization problem solving were carried out. Two main drug clusters were found concerning the signal intensities of all runs of the augmented factorial design. p-Aminophenol, salicylic acid, and nimesulide constitute one cluster as a result of showing much higher sensitivity than the remaining drugs. The other cluster is more homogeneous with some sub-clusters comprising one pharmaceutical and its respective metabolite. It was observed that instrumental signal increased when both significant factors increased with maximum signal occurring when both codified factors are set at level +1. It was also found that, for most of the pharmaceuticals, interface voltage influences the intensity of the instrument more than the nebulizing gas flowrate. The only exceptions refer to nimesulide where the relative importance of the factors is reversed and still salicylic acid where both factors equally influence the instrumental signal. Graphical Abstract ᅟ.