VariosArtículos de revista, ponencias, capítulos de libro y otroshttp://sedici.unlp.edu.ar:80/handle/10915/242014-11-26T05:55:24Z2014-11-26T05:55:24ZInfluencia de la superficie en la biocatalisis de la oxidacion de sulfuros metalicosDonati, EdgardoPorro, SilviaPogliani, CristinaCurutchet, GustavoTedesco, Pascual Héctorhttp://sedici.unlp.edu.ar:80/handle/10915/407012014-10-02T02:02:29Z1990-01-01T00:00:00ZArticulo
Effect of the surface on biocatalysis of metal sulfide oxidation
Revista de Metalurgia (Madrid); Volume 26, Issue 6
La biolixiviación de sulfuros metálicos, proceso en el cual los microorganismos actúan como catalizadores de la oxidación de sulfuros insolubles, convirtiéndolos en componentes solubles, ha sido estudiada en relación al papel desempeñado por la superficie, tanto del material atacado como de otros sólidos inertes presentes en cl medio. Los resultados obtenidos permitieron apreciar: a) la importancia de la adherencia de las bacterias a las superficies en los mecanismos propuestos para explicar la biocatálisis de la oxidación de los sulfuros; y b) el efecto prácticamente nulo que la adherencia a sólidos inertes tiene sobre el proceso de biolixiviación.; Bioleaching of metal sulfides, in which microorganisms behave as catalysts of the oxidation of insoluble sulfides, promoting their conversion in soluble compounds, is studied, paying attention to the role of the surface of the attacked solid and other solids present in the medium. This study shows the importance of the attachment of bacteria to the surface to explain the biocatalysis and the practically null effect of the bacterial adherence to other solids on the bioleaching process.
1990-01-01T00:00:00ZLa biolixiviación de sulfuros metálicos, proceso en el cual los microorganismos actúan como catalizadores de la oxidación de sulfuros insolubles, convirtiéndolos en componentes solubles, ha sido estudiada en relación al papel desempeñado por la superficie, tanto del material atacado como de otros sólidos inertes presentes en cl medio. Los resultados obtenidos permitieron apreciar: a) la importancia de la adherencia de las bacterias a las superficies en los mecanismos propuestos para explicar la biocatálisis de la oxidación de los sulfuros; y b) el efecto prácticamente nulo que la adherencia a sólidos inertes tiene sobre el proceso de biolixiviación.
Bioleaching of metal sulfides, in which microorganisms behave as catalysts of the oxidation of insoluble sulfides, promoting their conversion in soluble compounds, is studied, paying attention to the role of the surface of the attacked solid and other solids present in the medium. This study shows the importance of the attachment of bacteria to the surface to explain the biocatalysis and the practically null effect of the bacterial adherence to other solids on the bioleaching process.Active-set strategy in Powell's method for optimization without derivativesArouxét, María BelénEchebest, Nélida E.Pilotta, Elvio A.http://sedici.unlp.edu.ar:80/handle/10915/401732014-09-20T02:02:26Z2011-01-01T00:00:00ZArticulo
Computational and Applied Mathematics; vol. 30, no. 1
In this article we present an algorithm for solving bound constrained optimization problems without derivatives based on Powell's method [38] for derivative-free optimization. First we consider the unconstrained optimization problem. At each iteration a quadratic interpolation model of the objective function is constructed around the current iterate and this model is minimized to obtain a new trial point. The whole process is embedded within a trust-region framework. Our algorithm uses infinity norm instead of the Euclidean norm and we solve a box constrained quadratic subproblem using an active-set strategy to explore faces of the box. Therefore, a bound constrained optimization algorithm is easily extended. We compare our implementation with NEWUOA and BOBYQA, Powell's algorithms for unconstrained and bound constrained derivative free optimization respectively. Numerical experiments show that, in general, our algorithm require less functional evaluations than Powell's algorithms. Mathematical subject classification: Primary: 06B10; Secondary: 06D05.
2011-01-01T00:00:00ZIn this article we present an algorithm for solving bound constrained optimization problems without derivatives based on Powell's method [38] for derivative-free optimization. First we consider the unconstrained optimization problem. At each iteration a quadratic interpolation model of the objective function is constructed around the current iterate and this model is minimized to obtain a new trial point. The whole process is embedded within a trust-region framework. Our algorithm uses infinity norm instead of the Euclidean norm and we solve a box constrained quadratic subproblem using an active-set strategy to explore faces of the box. Therefore, a bound constrained optimization algorithm is easily extended. We compare our implementation with NEWUOA and BOBYQA, Powell's algorithms for unconstrained and bound constrained derivative free optimization respectively. Numerical experiments show that, in general, our algorithm require less functional evaluations than Powell's algorithms. Mathematical subject classification: Primary: 06B10; Secondary: 06D05.Two derivative-free methods for solving underdetermined nonlinear systems of equationsEchebest, Nélida E.Schuverdt, M. L.Vignau, R. P.http://sedici.unlp.edu.ar:80/handle/10915/401722014-09-20T02:02:27Z2011-01-01T00:00:00ZArticulo
Computational and Applied Mathematics; vol. 30, no. 1
In this paper, two different approaches to solve underdetermined nonlinear system of equations are proposed. In one of them, the derivative-free method defined by La Cruz, Martínez and Raydan for solving square nonlinear systems is modified and extended to cope with the underdetermined case. The other approach is a Quasi-Newton method that uses the Broyden update formula and the globalized line search that combines the strategy of Grippo, Lampariello and Lucidi with the Li and Fukushima one. Global convergence results for both methods are proved and numerical experiments are presented.
2011-01-01T00:00:00ZIn this paper, two different approaches to solve underdetermined nonlinear system of equations are proposed. In one of them, the derivative-free method defined by La Cruz, Martínez and Raydan for solving square nonlinear systems is modified and extended to cope with the underdetermined case. The other approach is a Quasi-Newton method that uses the Broyden update formula and the globalized line search that combines the strategy of Grippo, Lampariello and Lucidi with the Li and Fukushima one. Global convergence results for both methods are proved and numerical experiments are presented.Chemoselective preparation of 1,1-diacetates from aldehydes, mediated by a Keggin heteropolyacid under solvent free conditions at room temperatureRomanelli, Gustavo P.Dimitroff, P.Vázquez, PatriciaAutino, Juan Carloshttp://sedici.unlp.edu.ar:80/handle/10915/401642014-09-20T02:02:27Z2007-01-01T00:00:00ZArticulo
E-Journal of Chemistry; vol. 4, no. 1
A simple, general and efficient method has been developed for the conversion of aldehydes to 1,1-diacetates using acetic anhydride, a catalytic amount of non commercial Keggin heteropolyacid (H<SUB>6</SUB> PalMo<SUB>11</SUB>O<SUB>40</SUB>) (1% mol) in solvent free conditions at room temperature. Aromatic and aliphatic, simple and conjugated aldehydes were protected with excellent yields.
2007-01-01T00:00:00ZA simple, general and efficient method has been developed for the conversion of aldehydes to 1,1-diacetates using acetic anhydride, a catalytic amount of non commercial Keggin heteropolyacid (H<SUB>6</SUB> PalMo<SUB>11</SUB>O<SUB>40</SUB>) (1% mol) in solvent free conditions at room temperature. Aromatic and aliphatic, simple and conjugated aldehydes were protected with excellent yields.A simple and mild acylation of alcohols, phenols, amines, and thiols with a reusable heteropoly acid catalyst (H<SUB>6</SUB>P<SUB>2</SUB>W<SUB>18</SUB>O<SUB>62</SUB>·24 H<SUB>2</SUB>O)Romanelli, Gustavo P.Bennardi, Daniel OscarAutino, Juan CarlosBaronetti, G.Thomas, Horacio J.http://sedici.unlp.edu.ar:80/handle/10915/401112014-09-19T02:02:35Z2008-01-01T00:00:00ZArticulo
E-Journal of Chemistry; vol. 5, no. 3
The acylation of alcohols, phenols, thiols, and amines with varied substitution using acid anhydrides is efficiently catalyzed by Wells-Dawson heteropoly acid (H<SUB>6</SUB>P<SUB>2</SUB>W<SUB>18</SUB>O<SUB>62</SUB>·24 H<SUB>2</SUB>O). Reactions proceed with very good to excellent yield in air at room temperature, using toluene as solvent (40 examples). The bulk catalyst was easily reused without appreciable loss of its activity.
2008-01-01T00:00:00ZThe acylation of alcohols, phenols, thiols, and amines with varied substitution using acid anhydrides is efficiently catalyzed by Wells-Dawson heteropoly acid (H<SUB>6</SUB>P<SUB>2</SUB>W<SUB>18</SUB>O<SUB>62</SUB>·24 H<SUB>2</SUB>O). Reactions proceed with very good to excellent yield in air at room temperature, using toluene as solvent (40 examples). The bulk catalyst was easily reused without appreciable loss of its activity.Generalized complexity and classical-quantum transitionKowalski, AndrésPlastino, Ángel LuisCasas, Montserrathttp://sedici.unlp.edu.ar:80/handle/10915/401092014-09-19T02:02:35Z2009-03-01T00:00:00ZArticulo
Entropy; vol. 11, no. 1
We investigate the classical limit of the dynamics of a semiclassical system that represents the interaction between matter and a given field. On using as a quantifier the <i>q</i>-Complexity, we find that it describes appropriately the quantum-classical transition, detecting the most salient details of the changeover. Additionally the <i>q</i>-Complexity results a better quantifier of the problem than the <i>q</i>-entropy, in the sense that the <i>q</i>-range is enlarged, describing the <i>q</i>-Complexity, the most important characteristics of the transition for all <i>q</i>-value.
2009-03-01T00:00:00ZWe investigate the classical limit of the dynamics of a semiclassical system that represents the interaction between matter and a given field. On using as a quantifier the <i>q</i>-Complexity, we find that it describes appropriately the quantum-classical transition, detecting the most salient details of the changeover. Additionally the <i>q</i>-Complexity results a better quantifier of the problem than the <i>q</i>-entropy, in the sense that the <i>q</i>-range is enlarged, describing the <i>q</i>-Complexity, the most important characteristics of the transition for all <i>q</i>-value.The quantum-classical transition as an information flowKowalski, AndrésMartín, María TeresaZunino, Luciano JoséPlastino, Ángel LuisCasas, Montserrathttp://sedici.unlp.edu.ar:80/handle/10915/401052014-09-19T02:02:35Z2010-01-01T00:00:00ZArticulo
Entropy; vol. 12, no. 1
We investigate the classical limit of the semiclassical evolution with reference to a well-known model that represents the interaction between matter and a given field. This is done by recourse to a special statistical quantifier called the "symbolic transfer entropy". We encounter that the quantum-classical transition gets thereby described as the sign-reversal of the dominating direction of the information flow between classical and quantal variables.
2010-01-01T00:00:00ZWe investigate the classical limit of the semiclassical evolution with reference to a well-known model that represents the interaction between matter and a given field. This is done by recourse to a special statistical quantifier called the "symbolic transfer entropy". We encounter that the quantum-classical transition gets thereby described as the sign-reversal of the dominating direction of the information flow between classical and quantal variables.Spectral Properties and Stability in the Two-Dimensional Lattice-Hubbard ModelLamas, Carlos Albertohttp://sedici.unlp.edu.ar:80/handle/10915/389722014-08-23T02:02:29Z2009-01-13T00:00:00ZPreprint
Journal of the Physical Society of Japan; vol. 78, no. 1
The two-dimensional Hubbard model on the square lattice is studied in the presence of lattice distortions in the adiabatic approximation. The self energy is computed within perturbation theory up to second order, which provides a way for studying the quasiparticle dispersion. We compute numerically the second order contribution to the self-energy using a standard fast Fourier transform algorithm for finite sizes system. The stability of the lattice distortions is investigated and a schematic phase diagram is drawn. The Fermi surface is analyzed for densities close to half filling, the presence of lattice distortions changes some spectral properties of the model and gives an anisotropic interacting Fermi surface. The spectral function is calculated along several lines in momentum space and the renormalized quasiparticle dispersion is obtained. The behavior of the density of states is shown for different values of the intrasite repulsion U in the different phases.
2009-01-13T00:00:00ZThe two-dimensional Hubbard model on the square lattice is studied in the presence of lattice distortions in the adiabatic approximation. The self energy is computed within perturbation theory up to second order, which provides a way for studying the quasiparticle dispersion. We compute numerically the second order contribution to the self-energy using a standard fast Fourier transform algorithm for finite sizes system. The stability of the lattice distortions is investigated and a schematic phase diagram is drawn. The Fermi surface is analyzed for densities close to half filling, the presence of lattice distortions changes some spectral properties of the model and gives an anisotropic interacting Fermi surface. The spectral function is calculated along several lines in momentum space and the renormalized quasiparticle dispersion is obtained. The behavior of the density of states is shown for different values of the intrasite repulsion U in the different phases.Combined analytical and numerical approach to study magnetization plateaux in doped quasi-one-dimensional antiferromagnetsLamas, Carlos AlbertoCapponi, S.Pujol, Pierrehttp://sedici.unlp.edu.ar:80/handle/10915/389122014-08-22T02:02:29Z2011-09-21T00:00:00ZPreprint
Physical Review B; vol. 84
We investigate the magnetic properties of quasi-one-dimensional quantum spin-S antiferromagnets. We use a combination of analytical and numerical techniques to study the presence of plateaux in the magnetization curve. The analytical technique consists in a path integral formulation in terms of coherent states. This technique can be extended to the presence of doping and has the advantage of a much better control for large spins than the usual bosonization technique. We discuss the appearance of doping-dependent plateaux in the magnetization curves for spin-S chains and ladders. The analytical results are complemented by a density matrix renormalization group (DMRG) study for a trimerized spin-1/2 and anisotropic spin-3/2 doped chains.
2011-09-21T00:00:00ZWe investigate the magnetic properties of quasi-one-dimensional quantum spin-S antiferromagnets. We use a combination of analytical and numerical techniques to study the presence of plateaux in the magnetization curve. The analytical technique consists in a path integral formulation in terms of coherent states. This technique can be extended to the presence of doping and has the advantage of a much better control for large spins than the usual bosonization technique. We discuss the appearance of doping-dependent plateaux in the magnetization curves for spin-S chains and ladders. The analytical results are complemented by a density matrix renormalization group (DMRG) study for a trimerized spin-1/2 and anisotropic spin-3/2 doped chains.Crystallographic and theoretical studies on a coupled chain of AF binuclear Cu(II)-fluoraspirinate complexesLamas, Carlos AlbertoPiro, Oscar E.Castellano, Eduardo E.Rustoy, E. M.Quinzani, O. V.http://sedici.unlp.edu.ar:80/handle/10915/388262014-08-21T02:02:24Z2008-01-01T00:00:00ZObjeto de conferencia
IV Reunión de la Asociación Argentina de Cristalografía (Bahía Blanca, Argentina, 2008)
We present here the low temperature (116K) crystal and molecular structure of
poly-[μ-pyrazine{tetrakis-fluoraspirinate-dicopper(II)}]diacetonitrile, for short [Cu(Fasp)<SUB>4</SUB>Cu(pyz)]<SUB>n</SUB>, a 5-halogenated derivative of pharmacologically relevant copper aspirinates. We also discuss the theoretically expected magnetic and thermodynamic behavior of this interesting system for molecular magnetism.
2008-01-01T00:00:00ZWe present here the low temperature (116K) crystal and molecular structure of
poly-[μ-pyrazine{tetrakis-fluoraspirinate-dicopper(II)}]diacetonitrile, for short [Cu(Fasp)<SUB>4</SUB>Cu(pyz)]<SUB>n</SUB>, a 5-halogenated derivative of pharmacologically relevant copper aspirinates. We also discuss the theoretically expected magnetic and thermodynamic behavior of this interesting system for molecular magnetism.Exotic disordered phases in the quantum J1-J2 model on the honeycomb latticeLamas, Carlos AlbertoZhang, Haohttp://sedici.unlp.edu.ar:80/handle/10915/386912014-08-15T02:02:22Z2013-01-22T00:00:00ZPreprint
Physical Review B; vol. 87
We study the ground-state phase diagram of the frustrated quantum J1-J2 Heisenberg antiferromagnet on the honeycomb lattice using a mean-field approach in terms of the Schwinger boson representation of the spin operators. We present results for the ground-state energy, local magnetization, energy gap, and spin-spin correlations. The system shows magnetic long-range order for 0⩽J2/J1≲0.2075 (Néel) and 0.398≲J2/J1⩽0.5 (spiral). In the intermediate region, we find two magnetically disordered phases: a gapped spin liquid phase, which shows short-range Néel correlations (0.2075≲J2/J1≲0.3732), and a lattice nematic phase (0.3732≲J2/J1≲0.398), which is magnetically disordered but breaks lattice rotational symmetry. The errors in the values of the phase boundaries, which are implicit in the number of significant figures quoted, correspond purely to the error in the extrapolation of our finite-size results to the thermodynamic limit.
2013-01-22T00:00:00ZWe study the ground-state phase diagram of the frustrated quantum J1-J2 Heisenberg antiferromagnet on the honeycomb lattice using a mean-field approach in terms of the Schwinger boson representation of the spin operators. We present results for the ground-state energy, local magnetization, energy gap, and spin-spin correlations. The system shows magnetic long-range order for 0⩽J2/J1≲0.2075 (Néel) and 0.398≲J2/J1⩽0.5 (spiral). In the intermediate region, we find two magnetically disordered phases: a gapped spin liquid phase, which shows short-range Néel correlations (0.2075≲J2/J1≲0.3732), and a lattice nematic phase (0.3732≲J2/J1≲0.398), which is magnetically disordered but breaks lattice rotational symmetry. The errors in the values of the phase boundaries, which are implicit in the number of significant figures quoted, correspond purely to the error in the extrapolation of our finite-size results to the thermodynamic limit.Quantum phases in the frustrated Heisenberg model on the bilayer honeycomb latticeLamas, Carlos AlbertoArlego, MarceloZhang, Haohttp://sedici.unlp.edu.ar:80/handle/10915/386872014-08-15T02:02:23Z2014-01-06T00:00:00ZPreprint
Physical Review B; vol. 89
We use a combination of analytical and numerical techniques to study the phase diagram of the frustrated Heisenberg model on the bilayer honeycomb lattice. Using the Schwinger-boson description of the spin operators followed by a mean-field decoupling, the magnetic phase diagram is studied as a function of the frustration coupling J2 and the interlayer coupling J⊥. The presence of both magnetically ordered and disordered phases is investigated by means of the evaluation of ground-state energy, spin gap, local magnetization, and spin-spin correlations. We observe a phase with a spin gap and short-range Néel correlations that survives for nonzero next-nearest-neighbor interaction and interlayer coupling. Furthermore, we detect signatures of a reentrant behavior in the melting of the Néel phase and symmetry restoring when the system undergoes a transition from an on-layer nematic valence-bond crystal phase to an interlayer valence-bond crystal phase. We complement our work with exact diagonalization on small clusters and dimer-series expansion calculations, together with a linear spin-wave approach to study the phase diagram as a function of the spin S, the frustration, and the interlayer couplings.
2014-01-06T00:00:00ZWe use a combination of analytical and numerical techniques to study the phase diagram of the frustrated Heisenberg model on the bilayer honeycomb lattice. Using the Schwinger-boson description of the spin operators followed by a mean-field decoupling, the magnetic phase diagram is studied as a function of the frustration coupling J2 and the interlayer coupling J⊥. The presence of both magnetically ordered and disordered phases is investigated by means of the evaluation of ground-state energy, spin gap, local magnetization, and spin-spin correlations. We observe a phase with a spin gap and short-range Néel correlations that survives for nonzero next-nearest-neighbor interaction and interlayer coupling. Furthermore, we detect signatures of a reentrant behavior in the melting of the Néel phase and symmetry restoring when the system undergoes a transition from an on-layer nematic valence-bond crystal phase to an interlayer valence-bond crystal phase. We complement our work with exact diagonalization on small clusters and dimer-series expansion calculations, together with a linear spin-wave approach to study the phase diagram as a function of the spin S, the frustration, and the interlayer couplings.Phase diagram study of a dimerized spin-S zig-zag ladderLamas, Carlos AlbertoMatera, Juan Mauriciohttp://sedici.unlp.edu.ar:80/handle/10915/386832014-08-15T02:02:23Z2014-07-23T00:00:00ZPreprint
Journal of Physics: Condensed Matter; vol. 26, no. 32
The phase diagram of a frustrated spin-S zig-zag ladder is studied through different numerical and analytical methods. We show that for arbitrary S, there is a family of Hamiltonians for which a fully-dimerized state is an exact ground state, being the Majumdar-Ghosh point a particular member of the family. We show that the system presents a transition between a dimerized phase to a N ́eel-like phase for S = 1/2, and spiral phases can appear for large S. The phase diagram is characterized by means of a generalization of the usual Mean Field Approximation (MFA). The novelty in the present implementation is to consider the strongest coupled sites as the unit cell. The gap and the excitation spectrum is analyzed through the Random Phase Approximation (RPA). Also, a perturbative treatment to obtain the critical points is discussed. Comparisons of the results with numerical methods like DMRG are also presented.
2014-07-23T00:00:00ZThe phase diagram of a frustrated spin-S zig-zag ladder is studied through different numerical and analytical methods. We show that for arbitrary S, there is a family of Hamiltonians for which a fully-dimerized state is an exact ground state, being the Majumdar-Ghosh point a particular member of the family. We show that the system presents a transition between a dimerized phase to a N ́eel-like phase for S = 1/2, and spiral phases can appear for large S. The phase diagram is characterized by means of a generalization of the usual Mean Field Approximation (MFA). The novelty in the present implementation is to consider the strongest coupled sites as the unit cell. The gap and the excitation spectrum is analyzed through the Random Phase Approximation (RPA). Also, a perturbative treatment to obtain the critical points is discussed. Comparisons of the results with numerical methods like DMRG are also presented.Information, deformed <i>κ</i>-Wehrl entropies and semiclassical delocalizationPennini, FlaviaPlastino, Ángel LuisFerri, Gustavo L.Olivares, FelipeCasas, Montserrathttp://sedici.unlp.edu.ar:80/handle/10915/384072014-08-09T02:02:21Z2009-03-01T00:00:00ZArticulo
Entropy; vol. 11, no. 1
Semiclassical delocalization in phase space constitutes a manifestation of the Uncertainty Principle, one indispensable part of the present understanding of Nature and the Wehrl entropy is widely regarded as the foremost localization-indicator. We readdress the matter here within the framework of the celebrated semiclassical Husimi distributions and their associatedWehrl entropies, suitably κ-deformed. We are able to show that it is possible to significantly improve on the extant phase-space classical-localization power.
2009-03-01T00:00:00ZSemiclassical delocalization in phase space constitutes a manifestation of the Uncertainty Principle, one indispensable part of the present understanding of Nature and the Wehrl entropy is widely regarded as the foremost localization-indicator. We readdress the matter here within the framework of the celebrated semiclassical Husimi distributions and their associatedWehrl entropies, suitably κ-deformed. We are able to show that it is possible to significantly improve on the extant phase-space classical-localization power.Estudio de la distribución de los tiempos de residencia en un reactor tubular para la hidrólisis de lecitina de soja con fosfolipasa A<SUB>2</SUB> inmovilizadaMaroto, Beatriz G.Camusso, C.Zaritzky, Noemí E.http://sedici.unlp.edu.ar:80/handle/10915/384062014-08-09T02:02:21Z2001-01-01T00:00:00ZArticulo
Study of residence times distribution in a tubular reactor for the hydrolisis of soybean lecithin using immobilized A<SUB>2</SUB> phospholipase
Grasas y Aceites; vol. 52, no. 5
The hydrolisis of soybean lecithin can be carried out by means of the use of immobilized A<SUB>2</SUB> phospholipase which releases a fatty acid of C-2 position of the phospholipids so that an enriched product in lysolecithins is obtained. The enzymatic reaction follows a first order kinetics when the substrate concentrations are in the range: 6.34•10<SUP>-3</SUP> M to 19.0•10<SUP>-3</SUP> M. The value of the rate constant: k= 9.88•10<SUP>-2</SUP> min<SUP>-1</SUP> corresponds to the one obtained for the immobilized enzyme on alumina. A reactor was constructed and alumina was the selected support because of its good mechanic properties and fundamentally because of its low cost. The flow behaviour in the reactor and how it departs from the ideal model of plug-flow was analyzed by injecting a NaCl solution of a well-known concentration (tracer) and then, passing it through the reactor. According to the experiences carried out, the conductivity measures proved adequate for the determination of the residence times. The system showed lineal behaviour. The residence times in the experimentally built reactor for different load arrangements (particle support + inert load) was analyzed by using three different flows. The nonconverted fractions for the reactor were calculated and differences in the output were observed, in comparison to the plug-flow reactor, precisely because of channelizations and shut-offs that are generated inside the column. Maximal conversion in the experiences carried out both with higher substrate concentrations and for a minor feed flow were achieved. The dispersion module resulted quite higher than the limit that introduces a gaussian curve, for the one for which the degree of supposition of high dispersion was correct. The reactor showed a behaviour similar to that of a reactor of complete mixture and it was concluded that the degree of back-mixing, the formation of whirls and zones of redistribution of material are important.
2001-01-01T00:00:00ZThe hydrolisis of soybean lecithin can be carried out by means of the use of immobilized A<SUB>2</SUB> phospholipase which releases a fatty acid of C-2 position of the phospholipids so that an enriched product in lysolecithins is obtained. The enzymatic reaction follows a first order kinetics when the substrate concentrations are in the range: 6.34•10<SUP>-3</SUP> M to 19.0•10<SUP>-3</SUP> M. The value of the rate constant: k= 9.88•10<SUP>-2</SUP> min<SUP>-1</SUP> corresponds to the one obtained for the immobilized enzyme on alumina. A reactor was constructed and alumina was the selected support because of its good mechanic properties and fundamentally because of its low cost. The flow behaviour in the reactor and how it departs from the ideal model of plug-flow was analyzed by injecting a NaCl solution of a well-known concentration (tracer) and then, passing it through the reactor. According to the experiences carried out, the conductivity measures proved adequate for the determination of the residence times. The system showed lineal behaviour. The residence times in the experimentally built reactor for different load arrangements (particle support + inert load) was analyzed by using three different flows. The nonconverted fractions for the reactor were calculated and differences in the output were observed, in comparison to the plug-flow reactor, precisely because of channelizations and shut-offs that are generated inside the column. Maximal conversion in the experiences carried out both with higher substrate concentrations and for a minor feed flow were achieved. The dispersion module resulted quite higher than the limit that introduces a gaussian curve, for the one for which the degree of supposition of high dispersion was correct. The reactor showed a behaviour similar to that of a reactor of complete mixture and it was concluded that the degree of back-mixing, the formation of whirls and zones of redistribution of material are important.Estudio cinético de la reacción de hidrólisis de lecitina de soja pura en polvo con fosfolipasa A<SUB>2</SUB> inmovilizadaMaroto, Beatriz G.Camusso, C.Zaritzky, Noemí E.http://sedici.unlp.edu.ar:80/handle/10915/383292014-08-06T02:02:25Z2001-01-01T00:00:00ZArticulo
Kinetic study of soybean pure powder lecithin hydrolysis using immobilized phospholipase A<SUB>2</SUB>
Grasas y Aceites; vol. 52, no. 1
La enzima fosfolipasa A<SUB>2</SUB> inmovilizada promueve la reacción hidrolítica de lecitina de soja pura en polvo liberando un mol de ácido graso de la posición C-2. El principal propósito de este trabajo fue determinar los parámetros cinéticos de la reacción cuando la enzima fue adsorbida sobre alúmina o sobre DEAE-sephadex.
Las mejores condiciones para la reacción son: temperatura 45-48ºC: concentración de iones Ca 6mM y pH 8,65.
Las concentraciones de sustrato ensayadas fueron 6,3; 12,7; 19 y 25 mM trabajando en un reactor tipo batch y con la enzima inmovilizada. El tiempo de incubación no modificó la actividad enzimática.
La actividad hidrolítica de fosfolipasa A<SUB>2</SUB> adsorbida sobre alúmina o sobre sephadex fue menor que la de la enzima soluble porque las propiedades intrínsecas de la enzima se modificaron con la inmovilización. Para concentraciones de sustrato entre 6 y 19 mM las constantes de velocidad para cinética de 1er orden fueron k = 9,88.10<SUP>-2</SUP> min<SUP>-1</SUP> para enzima inmovilizada sobre alúmina y k = 1,766.10<SUP>-1</SUP> min<SUP>-1</SUP> para enzima inmovilizada sobre DEAEsephadex.
Para los mismos soportes, pero a mayores concentraciones de sustrato (25mM) las constantes de velocidad para cinética de orden cero fueron k = 1,62.10<SUP>-3</SUP> mol.l<SUP>-1</SUP>min<SUP>-1</SUP> (alúmina) y k = 3,58. 10<SUP>-3</SUP> mol.l<SUP>-1</SUP> min<SUP>-1</SUP> (DEAE-sephadex).; Immobilized A<SUB>2</SUB> phospholipase enzyme promotes the hydrolytic reaction of pure powder soybean lecithin releasing a mole of fatty acid from C-2 position. The main purpose of this paper was to determine the kinetic parameters of this reaction when the enzyme was adsorbed on alumina or DEAE-sephadex. The best conditions for the reaction were: temperature: 45-48°C, Ca ions concentration: 6mM, pH: 8,65. Tested conditions for substrate concentration were: 6,3; 12,7; 19 and 25 mM working in a batch type reactor and with the immobilized enzyme. The incubating time did not change the enzymatic activity.
The hydrolytic activity of alumina or DEAE-sephadex adsorbed A<SUB>2</SUB> phospholipase enzyme was lower than of the soluble enzyme because the intrinsic properties are modified by immobilization. For substrate concentrations ranging between 6 and 19 mM first order kinetic velocity constants were k = 9, 88. 10<SUP>-2</SUP> min<SUP>-1</SUP> and k = 1,766. 10<SUP>-1</SUP> min<SUP>-1</SUP> for alumina and DEAEsephadex respectively. For the same supports but at higher substrate concentration (25mM) the zero order kinetic velocity constants were k= 1,62. 10<SUP>-3</SUP> mol.l<SUP>-1</SUP>. min<SUP>-1</SUP> (alumina) and k = 3,58. 10<SUP>-3</SUP> mol.l<SUP>–1</SUP>.min<SUP>-1</SUP> (DEAE-sephadex).
2001-01-01T00:00:00ZLa enzima fosfolipasa A<SUB>2</SUB> inmovilizada promueve la reacción hidrolítica de lecitina de soja pura en polvo liberando un mol de ácido graso de la posición C-2. El principal propósito de este trabajo fue determinar los parámetros cinéticos de la reacción cuando la enzima fue adsorbida sobre alúmina o sobre DEAE-sephadex.
Las mejores condiciones para la reacción son: temperatura 45-48ºC: concentración de iones Ca 6mM y pH 8,65.
Las concentraciones de sustrato ensayadas fueron 6,3; 12,7; 19 y 25 mM trabajando en un reactor tipo batch y con la enzima inmovilizada. El tiempo de incubación no modificó la actividad enzimática.
La actividad hidrolítica de fosfolipasa A<SUB>2</SUB> adsorbida sobre alúmina o sobre sephadex fue menor que la de la enzima soluble porque las propiedades intrínsecas de la enzima se modificaron con la inmovilización. Para concentraciones de sustrato entre 6 y 19 mM las constantes de velocidad para cinética de 1er orden fueron k = 9,88.10<SUP>-2</SUP> min<SUP>-1</SUP> para enzima inmovilizada sobre alúmina y k = 1,766.10<SUP>-1</SUP> min<SUP>-1</SUP> para enzima inmovilizada sobre DEAEsephadex.
Para los mismos soportes, pero a mayores concentraciones de sustrato (25mM) las constantes de velocidad para cinética de orden cero fueron k = 1,62.10<SUP>-3</SUP> mol.l<SUP>-1</SUP>min<SUP>-1</SUP> (alúmina) y k = 3,58. 10<SUP>-3</SUP> mol.l<SUP>-1</SUP> min<SUP>-1</SUP> (DEAE-sephadex).
Immobilized A<SUB>2</SUB> phospholipase enzyme promotes the hydrolytic reaction of pure powder soybean lecithin releasing a mole of fatty acid from C-2 position. The main purpose of this paper was to determine the kinetic parameters of this reaction when the enzyme was adsorbed on alumina or DEAE-sephadex. The best conditions for the reaction were: temperature: 45-48°C, Ca ions concentration: 6mM, pH: 8,65. Tested conditions for substrate concentration were: 6,3; 12,7; 19 and 25 mM working in a batch type reactor and with the immobilized enzyme. The incubating time did not change the enzymatic activity.
The hydrolytic activity of alumina or DEAE-sephadex adsorbed A<SUB>2</SUB> phospholipase enzyme was lower than of the soluble enzyme because the intrinsic properties are modified by immobilization. For substrate concentrations ranging between 6 and 19 mM first order kinetic velocity constants were k = 9, 88. 10<SUP>-2</SUP> min<SUP>-1</SUP> and k = 1,766. 10<SUP>-1</SUP> min<SUP>-1</SUP> for alumina and DEAEsephadex respectively. For the same supports but at higher substrate concentration (25mM) the zero order kinetic velocity constants were k= 1,62. 10<SUP>-3</SUP> mol.l<SUP>-1</SUP>. min<SUP>-1</SUP> (alumina) and k = 3,58. 10<SUP>-3</SUP> mol.l<SUP>–1</SUP>.min<SUP>-1</SUP> (DEAE-sephadex).Evaluación de efectos difusionales sobre la cinética de hidrólisis de lecitina de soja con fosfolipasa A<SUB>2</SUB>Maroto, Beatriz G.Camusso, Jorge P. C.Zaritzky, Noemí E.http://sedici.unlp.edu.ar:80/handle/10915/383212014-08-06T02:02:25Z2004-01-01T00:00:00ZArticulo
Evaluation of diffusional effects on kinetics of soybean lecithin hydrolysis using A<SUB>2</SUB> phospholipase
Grasas y Aceites; vol. 55, no. 2
La Fosfolipasa A<SUB>2</SUB>, soluble o inmovilizada, libera un mol de ácido graso de la posición C-2 de los fosfolípidos de la lecitina de soja para producir lisolecitinas. Cuando se utiliza la enzima en su forma inmovilizada, la actividad enzimática decrece debido al fenómeno de transporte de sustrato y de producto. Se evaluaron los efectos de difusión comparando los parámetros cinéticos de la reacción de hidrólisis de lecitina de soja catalizada por fosfolipasa A<SUB>2</SUB> inmovilizada sobre alúmina o sobre DEAE-Sephadex, frente a los de enzima soluble. La disminución de la velocidad de reacción fue cuantificada en presencia de efectos difusionales y se calcularon los factores de eficiencia. Se determinaron los parámetros de Michaelis-Menten: <i>K</i><SUB>M</SUB> = 8.2.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> y 5.36.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> y V<SUB>max</SUB> = 7.7.10<SUP>-5</SUP> mol.l<SUB>-1</SUB>.min<SUP>-1</SUP> y 9.5.10<SUP>-5</SUP> mol.l<SUP>-1</SUP>.min<SUP>-1</SUP> para la enzima inmovilizada sobre alúmina y sobre DEAE-Sephadex, respectivamente. El factor de eficiencia fue 0.277 para alúmina y 0.376 para DEAE-Sephadex.; Soluble or immobilized A<SUB>2</SUB> phospholipase liberates one mole of fatty acid of the C-2 position in soybean lecithin phospholipids to product lysolecithins. When using the enzyme in its immobilized form the enzymatic activity decreases due to substrate and product transport phenomenon. By comparison of the kinetic parameters of the hydrolysis reaction catalized by A<SUB>2</SUB> phospholipase immobilized on alumina or on DEAE-Sephadex against those of the soluble enzyme, for soybean lecithin hydrolysis reaction, the diffusive effects were evaluated. The decrease of the reaction rate was quantified in presence of diffusive effects and the effectiveness factors were calculated. The Michaelis-Menten kinetic parameters were determined: <i>K</i><SUB>M</SUB> = 8,2.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> and 5.36.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> and V<SUB>max</SUB> = 7, 7.10<SUP>-5</SUP> mol.l<SUP>-1</SUP>.min<SUP>-1</SUP> and 9,5.10<SUP>-5</SUP> mol.l<SUP>-1</SUP>min<SUP>-1</SUP> for the enzyme immobilized on alumina and on DEAE-Sephadex, respectively. The effectiveness factors were 0,277 for alumina and 0,376 for DEAE-Sephadex.
2004-01-01T00:00:00ZLa Fosfolipasa A<SUB>2</SUB>, soluble o inmovilizada, libera un mol de ácido graso de la posición C-2 de los fosfolípidos de la lecitina de soja para producir lisolecitinas. Cuando se utiliza la enzima en su forma inmovilizada, la actividad enzimática decrece debido al fenómeno de transporte de sustrato y de producto. Se evaluaron los efectos de difusión comparando los parámetros cinéticos de la reacción de hidrólisis de lecitina de soja catalizada por fosfolipasa A<SUB>2</SUB> inmovilizada sobre alúmina o sobre DEAE-Sephadex, frente a los de enzima soluble. La disminución de la velocidad de reacción fue cuantificada en presencia de efectos difusionales y se calcularon los factores de eficiencia. Se determinaron los parámetros de Michaelis-Menten: <i>K</i><SUB>M</SUB> = 8.2.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> y 5.36.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> y V<SUB>max</SUB> = 7.7.10<SUP>-5</SUP> mol.l<SUB>-1</SUB>.min<SUP>-1</SUP> y 9.5.10<SUP>-5</SUP> mol.l<SUP>-1</SUP>.min<SUP>-1</SUP> para la enzima inmovilizada sobre alúmina y sobre DEAE-Sephadex, respectivamente. El factor de eficiencia fue 0.277 para alúmina y 0.376 para DEAE-Sephadex.
Soluble or immobilized A<SUB>2</SUB> phospholipase liberates one mole of fatty acid of the C-2 position in soybean lecithin phospholipids to product lysolecithins. When using the enzyme in its immobilized form the enzymatic activity decreases due to substrate and product transport phenomenon. By comparison of the kinetic parameters of the hydrolysis reaction catalized by A<SUB>2</SUB> phospholipase immobilized on alumina or on DEAE-Sephadex against those of the soluble enzyme, for soybean lecithin hydrolysis reaction, the diffusive effects were evaluated. The decrease of the reaction rate was quantified in presence of diffusive effects and the effectiveness factors were calculated. The Michaelis-Menten kinetic parameters were determined: <i>K</i><SUB>M</SUB> = 8,2.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> and 5.36.10<SUP>-2</SUP> mol.l<SUP>-1</SUP> and V<SUB>max</SUB> = 7, 7.10<SUP>-5</SUP> mol.l<SUP>-1</SUP>.min<SUP>-1</SUP> and 9,5.10<SUP>-5</SUP> mol.l<SUP>-1</SUP>min<SUP>-1</SUP> for the enzyme immobilized on alumina and on DEAE-Sephadex, respectively. The effectiveness factors were 0,277 for alumina and 0,376 for DEAE-Sephadex.Magnesium and its alloys as degradable biomaterials: Corrosion studies using potentiodynamic and EIS electrochemical techniquesMüller, Wolf DieterNascimento, Maria LuciaZeddies, MiriamCórsico, MarianaGassa, Liliana MabelFernández Lorenzo de Mele, Mónica Aliciahttp://sedici.unlp.edu.ar:80/handle/10915/383122014-08-06T02:02:25Z2007-01-01T00:00:00ZArticulo
Materials Research; vol. 10, no. 1
Magnesium is potentially useful for orthopaedic and cardiovascular applications. However, the corrosion rate of this metal is so high that its degradation occurs before the end of the healing process. In industrial media the behaviour of several magnesium alloys have been probed to be better than magnesium performance. However, the information related to their corrosion behaviour in biological media is insufficient. The aim of this work is to study the influence of the components of organic fluids on the corrosion behaviour of Mg and AZ31 and LAE442 alloys using potentiodynamic, potentiostatic and EIS techniques. Results showed localized attack in chloride containing media. The breakdown potential decreased when chloride concentration increased. The potential range of the passivation region was extended in the presence of albumin. EIS measurements showed that the corrosion behaviour of the AZ31 was very different from that of LAE442 alloy in chloride solutions.
2007-01-01T00:00:00ZMagnesium is potentially useful for orthopaedic and cardiovascular applications. However, the corrosion rate of this metal is so high that its degradation occurs before the end of the healing process. In industrial media the behaviour of several magnesium alloys have been probed to be better than magnesium performance. However, the information related to their corrosion behaviour in biological media is insufficient. The aim of this work is to study the influence of the components of organic fluids on the corrosion behaviour of Mg and AZ31 and LAE442 alloys using potentiodynamic, potentiostatic and EIS techniques. Results showed localized attack in chloride containing media. The breakdown potential decreased when chloride concentration increased. The potential range of the passivation region was extended in the presence of albumin. EIS measurements showed that the corrosion behaviour of the AZ31 was very different from that of LAE442 alloy in chloride solutions.Emulsiones tipo crema preparadas a base de leche de soja 3: efecto de ciclos de temperaturaMárquez, Andrés L.Palazolo, Gonzalo GastónWagner, Jorgehttp://sedici.unlp.edu.ar:80/handle/10915/382582014-08-05T02:02:18Z2005-01-01T00:00:00ZArticulo
Cream-like emulsions prepared with soy milk 3: effect of temperature cycling
Grasas y Aceites; vol. 56, no. 3
En este trabajo se analizó el efecto de ciclos calentamientoenfriamiento sobre cremas preparadas a 60ºC con leche de soja en polvo reconstituida, aceite de girasol y grasa láctea y almacenadas posteriormente a 4ºC durante 3 horas. Los ciclos consistieron en un calentamiento a 40ºC o 50ºC (30 min) seguido de un enfriamiento a 4ºC (2 horas). En los ensayos realizados sobre cremas formuladas con 40% de fase lipídica se observó un aumento de los valores de G’ y G’’ después del ciclo 40ºC-4ºC, a pesar de no haberse observado un aumento en el contenido de grasa sólida. Estos resultados se atribuyen a la formación de agregados de gotas inducida por la fusión parcial, reordenamiento y recristalización de la grasa láctea en las gotas. Estudios de resonancia magnética nuclear de pulsos, calorimetría diferencial de barrido y distribución de tamaño de partícula por difracción de luz permitieron corroborar que el principal mecanismo de formación de agregados es la coalescencia parcial. Frente al mismo ciclo térmico, la crema con 20% de fase lipídica no aumentó su consistencia, dada la ausencia o formación insuficiente de agregados por el bajo número de gotas. Ensayos similares sobre la nata a 40ºC o sobre las cremas de leche de soja a 50ºC, no mostraron cambios reológicos, debido a la fusión casi total de la grasa.; In this work, the effect of temperature cycling on emulsions formulated with reconstituted soy milk, sunflower oil and high melting point milk fat was analysed. The emulsions were prepared at 60°C, stored at 4°C (3 h), warmed at 40°C or 50°C (30 min) and afterwards cooled at 4°C (2h). Although solid fat content of emulsions did not raised after tempering at 40°C, increase of G' and G″ was observed only in those formulated with 40% lipid phase. This phenomenon was attributed to droplet aggregation due to partial melting, recrystallization and reordering of fat crystals in oil droplets. The main droplet destabilization mechanism was the partial coalescence; it was corroborated by nuclear magnetic resonance, differential scanning calorimetry and droplet size distribution studies. On the other hand, the consistency of 20% of lipid phase emulsion did not increased. Low droplet concentration disfavoured the partial coalescence of droplets. Similar assays on cream at 40°C and cream-like soy milk emulsions at 50°C, did not show rheological modifications, due to almost total melting of milk fat during tempering.
2005-01-01T00:00:00ZEn este trabajo se analizó el efecto de ciclos calentamientoenfriamiento sobre cremas preparadas a 60ºC con leche de soja en polvo reconstituida, aceite de girasol y grasa láctea y almacenadas posteriormente a 4ºC durante 3 horas. Los ciclos consistieron en un calentamiento a 40ºC o 50ºC (30 min) seguido de un enfriamiento a 4ºC (2 horas). En los ensayos realizados sobre cremas formuladas con 40% de fase lipídica se observó un aumento de los valores de G’ y G’’ después del ciclo 40ºC-4ºC, a pesar de no haberse observado un aumento en el contenido de grasa sólida. Estos resultados se atribuyen a la formación de agregados de gotas inducida por la fusión parcial, reordenamiento y recristalización de la grasa láctea en las gotas. Estudios de resonancia magnética nuclear de pulsos, calorimetría diferencial de barrido y distribución de tamaño de partícula por difracción de luz permitieron corroborar que el principal mecanismo de formación de agregados es la coalescencia parcial. Frente al mismo ciclo térmico, la crema con 20% de fase lipídica no aumentó su consistencia, dada la ausencia o formación insuficiente de agregados por el bajo número de gotas. Ensayos similares sobre la nata a 40ºC o sobre las cremas de leche de soja a 50ºC, no mostraron cambios reológicos, debido a la fusión casi total de la grasa.
In this work, the effect of temperature cycling on emulsions formulated with reconstituted soy milk, sunflower oil and high melting point milk fat was analysed. The emulsions were prepared at 60°C, stored at 4°C (3 h), warmed at 40°C or 50°C (30 min) and afterwards cooled at 4°C (2h). Although solid fat content of emulsions did not raised after tempering at 40°C, increase of G' and G″ was observed only in those formulated with 40% lipid phase. This phenomenon was attributed to droplet aggregation due to partial melting, recrystallization and reordering of fat crystals in oil droplets. The main droplet destabilization mechanism was the partial coalescence; it was corroborated by nuclear magnetic resonance, differential scanning calorimetry and droplet size distribution studies. On the other hand, the consistency of 20% of lipid phase emulsion did not increased. Low droplet concentration disfavoured the partial coalescence of droplets. Similar assays on cream at 40°C and cream-like soy milk emulsions at 50°C, did not show rheological modifications, due to almost total melting of milk fat during tempering.Cytoplasmic ribonucleoprotein foci in eukaryotes: hotspots of bio(chemical)diversityLayana, CarlaFerrero, Paola VivianaRivera Pomar, Rolando V.http://sedici.unlp.edu.ar:80/handle/10915/382562014-08-05T02:02:18Z2012-01-01T00:00:00ZArticulo
Comparative and Functional Genomics; vol. 2012
The life of an mRNA from transcription to degradation offers multiple control check points that regulate gene expression. Transcription, splicing, and translation have been widely studied for many years; however, in recent years, new layers of posttranscriptional and posttranslational control have been uncovered. They involve the regulation of the metabolism of mRNA in cytoplasmic foci. They are collections of ribonucleoprotein complexes that, in most cases, remain still uncharacterized, except the processing bodies (PBs) and stress granules (SGs), which have been studied (and reviewed) in detail. A challenging prospective is to know how many different classes of foci exist, which functions they support, how are they formed, and how do they relate one to each other. Here, we present an update of the component of the different granules, a possible function, and hypothesis on their <i>in vivo</i> dynamics related to translational control.
2012-01-01T00:00:00ZThe life of an mRNA from transcription to degradation offers multiple control check points that regulate gene expression. Transcription, splicing, and translation have been widely studied for many years; however, in recent years, new layers of posttranscriptional and posttranslational control have been uncovered. They involve the regulation of the metabolism of mRNA in cytoplasmic foci. They are collections of ribonucleoprotein complexes that, in most cases, remain still uncharacterized, except the processing bodies (PBs) and stress granules (SGs), which have been studied (and reviewed) in detail. A challenging prospective is to know how many different classes of foci exist, which functions they support, how are they formed, and how do they relate one to each other. Here, we present an update of the component of the different granules, a possible function, and hypothesis on their <i>in vivo</i> dynamics related to translational control.