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Papers by Sebastián Flores

√ s = 7 TeV using final states with an electron or a muon and a hadronically decaying τ lepton

This Letter presents the results of a direct search with the ATLAS detector at the LHC for a Stan... more This Letter presents the results of a direct search with the ATLAS detector at the LHC for a Standard Model Higgs boson of mass 110 ≤ m H ≤ 130 GeV produced in association with a W or Z boson and decaying to bb. Three decay channels are considered: ZH → ℓ + ℓ − bb, W H → ℓνbb and ZH → ννbb, where ℓ corresponds to an electron or a muon. No evidence for Higgs boson production is observed in a dataset of 7 TeV pp collisions corresponding to 4.7 fb −1 of integrated luminosity collected by ATLAS in 2011. Exclusion limits on Higgs boson production, at the 95% confidence level, of 2.5 to 5.5 times the Standard Model cross section are obtained in the mass range 110-130 GeV. The expected exclusion limits range between 2.5 and 4.9 for the same mass interval.

Biochemical Engineering Journal, 2010

A mathematical model that describes the heterogeneous reaction-diffusion process involved in a ba... more A mathematical model that describes the heterogeneous reaction-diffusion process involved in a batch reactor with immobilized enzyme is presented. The model is based on equations considering reaction and diffusion components including biocatalyst particle size distribution. The reaction system includes the bulk liquid phase containing the dissolved substrate (and products) and the solid biocatalyst phase represented by spherical porous particles carrying the enzyme. The model developed is illustrated for the case of penicillin G hydrolysis with immobilized penicillin acylase, which is a complex reaction system in which both products of reaction and the substrate itself are inhibitors. Significant differences in batch reactor performance simulation are observed when considering biocatalyst particles of a single radius and particle size distribution. The magnitude of these differences is proportional to the dispersion (standard deviation) considered in that size distribution function.

Applied Biochemistry and Biotechnology

A mathematical model that describes the heterogeneous reaction–diffusion process involved in peni... more A mathematical model that describes the heterogeneous reaction–diffusion process involved in penicillin G hydrolysis in a batch reactor with immobilized penicillin G acylase is presented. The reaction system includes the bulk liquid phase containing the dissolved substrate (and products) and the solid biocatalyst phase represented by glyoxyl-agarose spherical porous particles carrying the enzyme. The equations consider reaction and diffusion components that are presented in dimensionless form. This is a complex reaction system in which both products of reaction and the substrate itself are inhibitors. The simulation of a batch reactor performance with immobilized penicillin G acylase is presented and discussed for the internal diffusional restrictions impact on effectiveness and productivity. Increasing internal diffusional restrictions, through increasing catalyst particle size and enzyme loading, causes impaired catalyst efficiency expressed in a reduction of effectiveness factor and specific productivity. High penicillin G initial concentrations decrease the impact of internal diffusional restrictions by increasing the mass transfer towards porous catalyst until product inhibition becomes significant over approximately 50 mM of initial penicillin G, where a drop in conversion rate and a maximum in specific productivity are then obtained. Results highlight the relevance of considering internal diffusional restrictions, reactor performance, and productivity analysis for proper catalyst and reactor design.

Electrochimica Acta

A mathematical model is presented for the kinetically controlled synthesis of cephalexin that des... more A mathematical model is presented for the kinetically controlled synthesis of cephalexin that describes the heterogeneous reaction-diffusion process involved in a batch reactor with glyoxyl-agarose immobilized penicillin acylase. The model is based on equations considering reaction and diffusion components. Reaction kinetics was considered according to the mechanism proposed by Schroën, while diffusion of the reacting species was described according to Fick's law. Intrinsic kinetic and diffusion parameters were experimentally determined in independent experiments. It was found that from the four kinetic constants, the one corresponding to the acyl-enzyme complex hydrolysis step had the greatest value, as previously reported by other authors. The effective diffusion coefficients of all substances were about 5×10(-10)m(2)/s, being 10% lower than free diffusion coefficients and therefore agreed with the highly porous structure of glyoxyl-agarose particles. Simulations made from the reaction-diffusion model equations were used to evaluate and analyze the impact of internal diffusional restrictions in function of catalyst enzyme loading and particle size. Increasing internal diffusional restrictions decreases the Cex synthesis/hydrolysis ratio, the conversion yield and the specific productivity. A nonlinear relationship between catalyst enzyme loading and specific productivity of Cex was obtained with the implication that an increase in catalyst enzyme loading will not increase the volumetric productivity by the same magnitude as it occurs with the free enzyme. Optimization of catalyst and reactor design should be done considering catalyst enzyme loading and particle size as the most important variables. The approach presented can be extended to other processes catalyzed by immobilized enzymes.

European Journal of Nutrition

Objective To study heme iron bioavailability and the role of dietary protein (animal and vegetabl... more Objective To study heme iron bioavailability and the role of dietary protein (animal and vegetable) on iron uptake using an in vitro model (Caco-2 cell line). Methods Caco-2 cells were seeded in bicameral chambers with different animal (beef, chicken or fish) or vegetable (peas, lentils, and soybeans) proteins or with pure animal (collagen and casein) or vegetable (gliadin, zein, and glutein) protein extracts. The effect of each protein over heme iron absorption was assessed. Results Intact heme uptake was higher than either heme plus albumin or digested heme plus albumin, but lower than digested heme. White meal exerted the highest inhibitory effect on hemin uptake. Heme iron uptake decreased in the presence of all legume extracts, but was not significantly different among them (one-way ANOVA, NS). Pure animal (collagen and casein) and vegetable (zein and glutelin) proteins increased heme iron uptake, except for gliadin. Conclusion Animal and vegetable protein in general decreased heme iron uptake. However, purified animal and vegetable protein induce an increase in heme iron uptake.

Biological Trace Element Research, 2008

It is known that heme iron and inorganic iron are absorbed differently. Heme iron is found in the... more It is known that heme iron and inorganic iron are absorbed differently. Heme iron is found in the diet mainly in the form of hemoglobin and myoglobin. The mechanism of iron absorption remains uncertain. This study focused on the heme iron uptake by Caco-2 cells from a hemoglobin digest and its response to different iron concentrations. We studied the intracellular Fe concentration and the effect of time, K+ depletion, and cytosol acidification on apical uptake and transepithelial transport in cells incubated with different heme Fe concentrations. Cells incubated with hemoglobin-digest showed a lower intracellular Fe concentration than cells grown with inorganic Fe. However, uptake and transepithelial transport of Fe was higher in cells incubated with heme Fe. Heme Fe uptake had a low V max and K m as compared to inorganic Fe uptake and did not compete with non-heme Fe uptake. Heme Fe uptake was inhibited in cells exposed to K+ depletion or cytosol acidification. Heme oxygenase 1 expression increased and DMT1 expression decreased with higher heme Fe concentrations in the media. The uptake of heme iron is a saturable and temperature-dependent process and, therefore, could occur through a mechanism involving both a receptor and the endocytic pathway.

√ s = 7 TeV using final states with an electron or a muon and a hadronically decaying τ lepton

This Letter presents the results of a direct search with the ATLAS detector at the LHC for a Stan... more This Letter presents the results of a direct search with the ATLAS detector at the LHC for a Standard Model Higgs boson of mass 110 ≤ m H ≤ 130 GeV produced in association with a W or Z boson and decaying to bb. Three decay channels are considered: ZH → ℓ + ℓ − bb, W H → ℓνbb and ZH → ννbb, where ℓ corresponds to an electron or a muon. No evidence for Higgs boson production is observed in a dataset of 7 TeV pp collisions corresponding to 4.7 fb −1 of integrated luminosity collected by ATLAS in 2011. Exclusion limits on Higgs boson production, at the 95% confidence level, of 2.5 to 5.5 times the Standard Model cross section are obtained in the mass range 110-130 GeV. The expected exclusion limits range between 2.5 and 4.9 for the same mass interval.

Biochemical Engineering Journal, 2010

A mathematical model that describes the heterogeneous reaction-diffusion process involved in a ba... more A mathematical model that describes the heterogeneous reaction-diffusion process involved in a batch reactor with immobilized enzyme is presented. The model is based on equations considering reaction and diffusion components including biocatalyst particle size distribution. The reaction system includes the bulk liquid phase containing the dissolved substrate (and products) and the solid biocatalyst phase represented by spherical porous particles carrying the enzyme. The model developed is illustrated for the case of penicillin G hydrolysis with immobilized penicillin acylase, which is a complex reaction system in which both products of reaction and the substrate itself are inhibitors. Significant differences in batch reactor performance simulation are observed when considering biocatalyst particles of a single radius and particle size distribution. The magnitude of these differences is proportional to the dispersion (standard deviation) considered in that size distribution function.

Applied Biochemistry and Biotechnology

A mathematical model that describes the heterogeneous reaction–diffusion process involved in peni... more A mathematical model that describes the heterogeneous reaction–diffusion process involved in penicillin G hydrolysis in a batch reactor with immobilized penicillin G acylase is presented. The reaction system includes the bulk liquid phase containing the dissolved substrate (and products) and the solid biocatalyst phase represented by glyoxyl-agarose spherical porous particles carrying the enzyme. The equations consider reaction and diffusion components that are presented in dimensionless form. This is a complex reaction system in which both products of reaction and the substrate itself are inhibitors. The simulation of a batch reactor performance with immobilized penicillin G acylase is presented and discussed for the internal diffusional restrictions impact on effectiveness and productivity. Increasing internal diffusional restrictions, through increasing catalyst particle size and enzyme loading, causes impaired catalyst efficiency expressed in a reduction of effectiveness factor and specific productivity. High penicillin G initial concentrations decrease the impact of internal diffusional restrictions by increasing the mass transfer towards porous catalyst until product inhibition becomes significant over approximately 50 mM of initial penicillin G, where a drop in conversion rate and a maximum in specific productivity are then obtained. Results highlight the relevance of considering internal diffusional restrictions, reactor performance, and productivity analysis for proper catalyst and reactor design.

Electrochimica Acta

A mathematical model is presented for the kinetically controlled synthesis of cephalexin that des... more A mathematical model is presented for the kinetically controlled synthesis of cephalexin that describes the heterogeneous reaction-diffusion process involved in a batch reactor with glyoxyl-agarose immobilized penicillin acylase. The model is based on equations considering reaction and diffusion components. Reaction kinetics was considered according to the mechanism proposed by Schroën, while diffusion of the reacting species was described according to Fick's law. Intrinsic kinetic and diffusion parameters were experimentally determined in independent experiments. It was found that from the four kinetic constants, the one corresponding to the acyl-enzyme complex hydrolysis step had the greatest value, as previously reported by other authors. The effective diffusion coefficients of all substances were about 5×10(-10)m(2)/s, being 10% lower than free diffusion coefficients and therefore agreed with the highly porous structure of glyoxyl-agarose particles. Simulations made from the reaction-diffusion model equations were used to evaluate and analyze the impact of internal diffusional restrictions in function of catalyst enzyme loading and particle size. Increasing internal diffusional restrictions decreases the Cex synthesis/hydrolysis ratio, the conversion yield and the specific productivity. A nonlinear relationship between catalyst enzyme loading and specific productivity of Cex was obtained with the implication that an increase in catalyst enzyme loading will not increase the volumetric productivity by the same magnitude as it occurs with the free enzyme. Optimization of catalyst and reactor design should be done considering catalyst enzyme loading and particle size as the most important variables. The approach presented can be extended to other processes catalyzed by immobilized enzymes.

European Journal of Nutrition

Objective To study heme iron bioavailability and the role of dietary protein (animal and vegetabl... more Objective To study heme iron bioavailability and the role of dietary protein (animal and vegetable) on iron uptake using an in vitro model (Caco-2 cell line). Methods Caco-2 cells were seeded in bicameral chambers with different animal (beef, chicken or fish) or vegetable (peas, lentils, and soybeans) proteins or with pure animal (collagen and casein) or vegetable (gliadin, zein, and glutein) protein extracts. The effect of each protein over heme iron absorption was assessed. Results Intact heme uptake was higher than either heme plus albumin or digested heme plus albumin, but lower than digested heme. White meal exerted the highest inhibitory effect on hemin uptake. Heme iron uptake decreased in the presence of all legume extracts, but was not significantly different among them (one-way ANOVA, NS). Pure animal (collagen and casein) and vegetable (zein and glutelin) proteins increased heme iron uptake, except for gliadin. Conclusion Animal and vegetable protein in general decreased heme iron uptake. However, purified animal and vegetable protein induce an increase in heme iron uptake.

Biological Trace Element Research, 2008

It is known that heme iron and inorganic iron are absorbed differently. Heme iron is found in the... more It is known that heme iron and inorganic iron are absorbed differently. Heme iron is found in the diet mainly in the form of hemoglobin and myoglobin. The mechanism of iron absorption remains uncertain. This study focused on the heme iron uptake by Caco-2 cells from a hemoglobin digest and its response to different iron concentrations. We studied the intracellular Fe concentration and the effect of time, K+ depletion, and cytosol acidification on apical uptake and transepithelial transport in cells incubated with different heme Fe concentrations. Cells incubated with hemoglobin-digest showed a lower intracellular Fe concentration than cells grown with inorganic Fe. However, uptake and transepithelial transport of Fe was higher in cells incubated with heme Fe. Heme Fe uptake had a low V max and K m as compared to inorganic Fe uptake and did not compete with non-heme Fe uptake. Heme Fe uptake was inhibited in cells exposed to K+ depletion or cytosol acidification. Heme oxygenase 1 expression increased and DMT1 expression decreased with higher heme Fe concentrations in the media. The uptake of heme iron is a saturable and temperature-dependent process and, therefore, could occur through a mechanism involving both a receptor and the endocytic pathway.