Marco Antonio Silva

Bio: Marco Antonio Silva is an academic researcher from Federal University of Rio de Janeiro. The author has contributed to research in topics: Computer science & Mathematical optimization. The author has an hindex of 4, co-authored 11 publications receiving 41 citations. Previous affiliations of Marco Antonio Silva include University of Avignon.

Mechanical behaviour of coarse, lightweight, recycled and natural aggregates for concrete

Abstract: In this study the application of the single-particle compression test is discussed as an alternative method for the mechanical characterisation of coarse aggregates generally employed in concrete m...

Solving the bifurcated and nonbifurcated robust network loading problem with k-adaptive routing

Abstract: We experiment with an alternative routing scheme for the robust network loading problem with demand uncertainty. Named k‐adaptive, it is based on the fact that the decision‐maker chooses k second‐stage solutions and then commits to one of them only after realization of the uncertainty. This routing scheme, with its corresponding k‐partition of the uncertainty set, is dynamically defined under an iterative method to sequentially improve the solution. The method has an inherent characteristic of multiplying the number of variables and constraints after each iteration, so that additional measures are introduced in the solution strategy in order to control time performance. We compare our k‐adaptive results with the ones obtained through other routing schemes and also verify the effectiveness of the methods utilized using several realistic networks from SNDlib and other sources.

Excited-state acidity of bifunctional compounds. 7. long distance, solvent-assisted excited-state proton transfer in olivacine

Abstract: — By use of fluorescence spectroscopy and time-correlated single photon counting, solvent-assisted excited-state proton transfer (ESPT) has been observed for olivacine in two organic solvents, 1,4-dioxane and methanol. Because of spectral overlap, factor analysis was used to determine the emission spectrum of the proton-transferred (PT) species. The ESPT is not observed in the nonpolar solvent n-hexane. For the first time in a system of this type, the individual excited-state rate constants have been calculated exactly from time-resolved single photon counting results. Because the PT process involves a path of more than 6 A, its individual rate constant is extremely low, approximately 107 s−1.

Investigação 3D da distribuição de fibras de aço em concreto reforçado por microtomografia de raios X

Abstract: The effects of the inclusion of steel fibers in concrete have been widely studied in order to investigate possible changes in mechanical properties, such as the increase in tensile strength, ductility, stiffness, toughness (energy absorption capacity), and durability. An immediate consequence of this addition is the mitigation of concrete's brittle behavior, so that the material meets new quality requirements. In this context, it is important to study the spatial distribution of the entire internal structure of these materials. Three-dimensional computed microtomography is a non-destructive inspection technique used to characterize the internal structures of various materials based on X-ray interaction with the inspected object. Topological and morphological properties can be obtained directly in three dimensions by means of mathematical reconstruction of the radiographs, which allows analyzing, for example, porosity and distribution of objects. In this context, the aim of this study is to investigate the spatial distribution of steel fibers, as well as of porosity in reinforced concrete samples. To this end, we used a microtomography system calibrated to operate at a voltage of 80 kV, electric current of 100 μA and a pixel size equal to 24 µm. The results showed low porosity and that the steel fibers were not uniformly distributed throughout the sample.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Dual fluorescence of ellipticine: excited state proton transfer from solvent versus solvent mediated intramolecular proton transfer.

Abstract: Photophysical properties of a natural plant alkaloid, ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), which comprises both proton donating and accepting sites, have been studied in different solvents using steady state and time-resolved fluorescence techniques primarily to understand the origin of dual fluorescence that this molecule exhibits in some specific alcoholic solvents. Ground and excited state calculations based on density functional theory have also been carried out to help interpretation of the experimental data. It is shown that the long-wavelength emission of the molecule is dependent on the hydrogen bond donating ability of the solvent, and in methanol, this emission band arises solely from an excited state reaction. However, in ethylene glycol, both ground and excited state reactions contribute to the long wavelength emission. The time-resolved fluorescence data of the system in methanol and ethylene glycol indicates the presence of two different hydrogen bonded species of elliptici...

Photophysical and photodynamical study of ellipticine: an anticancer drug molecule in bile salt modulated in vitro created liposome

Abstract: The entrapment of anticancer drug ellipticine in the dipalmitoylphosphocholine (DPPC) liposome and its release by addition of three different bile salts, namely sodium deoxycholate, cholate and taurocholate, have been studied by steady state and time resolved fluorescence spectroscopy. We found that the release of the drug from a liposome depends on the degree of penetration of bile salts. Among the three bile salts, deoxycholate was most effective in releasing the drug from the hydrocarbon core of the liposome because of its high insertion ability owing to its maximum hydrophobicity. The time resolved studies revealed that with addition of bile salt to the liposome solution, ellipticine molecules were removed from the hydrocarbon core and were entrapped in an interfacial region of liposomes by electrostatic interaction. This led to an increase in the shorter lifetime component. On the other hand, the longer lifetime component decreased because bile salts wet the hydrocarbon core of the liposome by carrying hydrogen bonded water. Entrapment of ellipticine in the interfacial region was also supported by an increase in the rotational relaxation time with addition of bile salt.