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Search Results: 1 - 10 of 512952 matches for " I. Mejía "
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EDITORIAL
Amanda I. Mejía G
Vitae , 2007,
Abstract:
Variación del módulo de Young en el acero C45E (norma EN 10083) tratado térmicamente
Fonseca, I.,Benito, J. A.,Mejía, I.,Jorba, J.
Revista de Metalurgia , 2002,
Abstract: The parameters hardness, yield strength, ultimate tensile strength, toughness and Young's modulus of carbon steel C45E, EN 10083 (AISI 1045) annealed, quenched and tempered at various temperatures have been determined. Young's modulus has also been measured from ultrasonic techniques and also from the tension test; elastic deformation has been determined by the electric gaugue method. A metallographic study by scanning electron microscopy has also been carried out to confirm the results of the thermal treatment. Hardness, yield strength and ultimate tensile strength increases as it is with the thermal treatment. In addition Young=s modulus increases from 199-200 GPa (quenched) state to 211-212 GPa (tempered 500 °C, 1 h.). The annealed steel presents a Young's modulus of 206-207 GPa. A good agreement between Young's modulus values obtained by ultrasonic measurements and by tension test has been observed. This behaviour has been correlated with the distribution of dislocations in the material under the various states. Se han determinado distintas propiedades mecánicas del acero C45E según norma EN10083 (AISI 1045) reconocido, templado y revenido a distintas temperaturas. Las propiedades mecánicas analizadas han sido: dureza, límite elástico convecional, resistencia a la tracción, resiliencia y módulo de Young. Esta última propiedad se determinó por ultrasonidos y a partir de curvas tensión-deformación midiendo ésta mediante extensometría eléctrica.En todos los casos se ha comprobado la bondad del tratamiento aplicado madiante observaciones metalográficas por microscopía eléctronica de barrido. Los valores de dureza, límite elástico convecional y resistencia a la tracción presentan las variaciones esperadas después de los distintos tratamientos térmicos aplicados. Sorprendentemente, el módulo de Young se incrementa desde valores de 199-200 GPa para el acero templado hasta 211-212 GPa para el acero templado y revenido a 500oC durante una hora; el acero en estado de recocido presenta un valor de módulo de 206-207GPa. Se detectó una muy buena concordancia entre los valores de módulo obtenidos por ultrasonidos y los obtenidos a partir de las curvas tensión-deformación. Se ha correlacionado este comportamiento con la distribución de dislocaciones en el material bajo diferentes estados.
Yersinia Controls Type III Effector Delivery into Host Cells by Modulating Rho Activity
Edison Mejía,James B Bliska,Gloria I Viboud
PLOS Pathogens , 2008, DOI: 10.1371/journal.ppat.0040003
Abstract: Yersinia pseudotuberculosis binds to β1 integrin receptors, and uses the type III secretion proteins YopB and YopD to introduce pores and to translocate Yop effectors directly into host cells. Y. pseudotuberculosis lacking effectors that inhibit Rho GTPases, YopE and YopT, have high pore forming activity. Here, we present evidence that Y. pseudotuberculosis selectively modulates Rho activity to induce cellular changes that control pore formation and effector translocation. Inhibition of actin polymerization decreased pore formation and YopE translocation in HeLa cells infected with Y. pseudotuberculosis. Inactivation of Rho, Rac, and Cdc42 by treatment with Clostridium difficile toxin B inhibited pore formation and YopE translocation in infected HeLa cells. Expression of a dominant negative form of Rac did not reduce the uptake of membrane impermeable dyes in HeLa cells infected with a pore forming strain YopEHJT?. Similarly, the Rac inhibitor NSC23766 did not decrease pore formation or translocation, although it efficiently hindered Rac-dependent bacterial uptake. In contrast, C. botulinum C3 potently reduced pore formation and translocation, implicating Rho A, B, and/or C in the control of the Yop delivery. An invasin mutant (Y. pseudotuberculosis invD911E) that binds to β1 integrins, but inefficiently transduces signals through the receptors, was defective for YopE translocation. Interfering with the β1 integrin signaling pathway, by inhibiting Src kinase activity, negatively affected YopE translocation. Additionally, Y. pseudotuberculosis infection activated Rho by a mechanism that was dependent on YopB and on high affinity bacteria interaction with β1 integrin receptors. We propose that Rho activation, mediated by signals triggered by the YopB/YopD translocon and from engagement of β1 integrin receptors, stimulates actin polymerization and activates the translocation process, and that once the Yops are translocated, the action of YopE or YopT terminate delivery of Yops and prevents pore formation.
High resolution (3+1) REMPI and dissociation of acetone via 3pn Rydberg transitions
Mejía-Ospino, E.;álvarez, I.;Cisneros, C.;
Revista mexicana de física , 2006,
Abstract: measurements of multiphoton ionization and dissociation of acetone are reported in the wavelength range 490.0-510.0 nm at 1 nm intervals. to our knowledge there are no available results of (3+1) rempi on acetone in this region. the experiments were performed using an nd: yag-opo (optical parametric oscillator) laser system coupled to a time-of-flight mass spectrometer. the experimental results show two dissociation channels of the acetone ion, leading to the products (ch3co+) and (ch3+), the channel ch3coch3+ch3co+ + ch3 being the most favored. the acetone and acetyl ions are observed in the entire wavelength range investigated. finally, the three-photon resonance multiphoton spectrum of the acetone 3pn rydberg transition is also reported.
High resolution (3+1) REMPI and dissociation of acetone via 3p n Rydberg transitions
E. Mejía-Ospino,I. Alvarez,C. Cisneros
Revista mexicana de física , 2006,
Abstract: En este trabajo se reportan medidas de ionización y disociación multifotónica de acetona en la región comprendida entre 490.0 y 510 nm a intervalos de 1 nm. Por primera vez se observa el proceso (3+1) REMPI en esta región del espectro para la molécula de acetona. Los experimentos fueron llevados a cabo usando un sistema láser Nd:YAG-OPO acoplado a un espectrómetro de masas de tiempo de vuelo. Los resultados experimentales muestran que el ión acetona se disocia a través de los canales CH3CO+ + CH3 y CH+ 3 + CH3CO, siendo más favorable el primero de estos canales. Finalmente, presentamos el espectro multifot′onico de la transición 3p n Rydberg para la acetona
Interplay of disorder and $\mathcal{PT}$-symmetry
C. Mejía-Cortés,M. I. Molina
Physics , 2014,
Abstract: We examine a one-dimensional $\mathcal{PT}$-symmetric binary lattice in the presence of diagonal disorder. We focus on the wave transport phenomena of localized and extended input beams for this disordered system. In the pure $\mathcal{PT}$-symmetric case, we derive an exact expression for the evolution of light localization in terms of the typical parameters of the system. In this case localization is enhanced as the gain and loss parameter in increased. In the presence of disorder, we observe that the presence of gain and loss inhibits (favors) the transport for localized (extended) excitations.
A practical strategy for controlling flow oscillations in surge tanks
Nunes,G. C.; Rodrigues Coelho,A. A.; Rodrigues Sumar,R.; Goytia Mejía,R. I.;
Latin American applied research , 2007,
Abstract: the use of accumulation vessels -production separators, electrostatic treaters, etc- as filters of feed oscillations has been proposed to optimize the offshore treatment of crude oils. this change in philosophy of control suggests letting the level to oscillate within certain limits -called band- for which existing algorithms require the measurement of the flow rate. an alternative algorithm is presented in this paper that requires only the measurement of the level. the basic concepts of the proposal are presented. it is demonstrated that besides being simpler, this algorithm has a good performance when compared to the traditional pi controller for surge tanks conception in surge tanks.
A practical strategy for controlling flow oscillations in surge tanks
G. C. Nunes,A. A. Rodrigues Coelho,R. Rodrigues Sumar,R. I. Goytia Mejía
Latin American applied research , 2007,
Abstract: The use of accumulation vessels -production separators, electrostatic treaters, etc- as filters of feed oscillations has been proposed to optimize the offshore treatment of crude oils. This change in philosophy of control suggests letting the level to oscillate within certain limits -called band- for which existing algorithms require the measurement of the flow rate. An alternative algorithm is presented in this paper that requires only the measurement of the level. The basic concepts of the proposal are presented. It is demonstrated that besides being simpler, this algorithm has a good performance when compared to the traditional PI controller for surge tanks conception in surge tanks.
UTILIZACIóN DE RESIDUOS DE PLáTANO PARA LA PRODUCCIóN DE METABOLITOS SECUNDARIOS POR FERMENTACIóN EN ESTADO SóLIDO CON EL HONGO Lentinus crinitus
GRANDA R.,Diana M.; MEJíA G.,Amanda I.; JIMéNEZ T.,Gloria A.;
Vitae , 2005,
Abstract: this paper presents the production of secondary metabolites with pharmaceutical and alimentary interest from plantain waste used as substrate in a solid state fermentation process with the white root fungi lentinus crinitus. the production of metabolites is studied during the growth of the microorganism for a period of 21 days, in a system conformed by 7 substrate combinations: stem-fruit, leaves -fruit, leaves -stem, leaves, stem, fruit and leaves-stem-fruit. the best combination for the production of enzymes -lignin peroxidase (lip) and -manganese peroxidase (mnp) is conformed by leaves-stem of plantain musa paradisiaca. it is then important to take advantage of the huge potential that these residues have for the production of peroxidase enzymes, which have many applications. on the other hand, the use for the first time of the fungi lentinus crinitus in such production constitutes a novel biotechnological approach. in the systems where there is enzymatic activity (stem-fruit, leaves-fruit, leaves-stem and leaves-stem-fruit) the aromatic compounds: ferulic acid, vanilla, vanillin acid and eugenol are determined at 11, 16 and 21 days by high performance liquid chromatographic (hplc). for the systems with the best enzymatic activity (leaves-steam), the concentration of aromatic products is low. in the system conformed by leaves-fruit, where only the production of the lip enzyme is important, significant concentrations of ferulic acid, vanilla, vanillin acid and eugenol are found during the sixteenth day.
Concentración y distribución de metales pesados (Pb, Zn, Cu, Cd y Cr) en sedimentos viarios urbanos
Zafra Mejía,Carlos A; Temprano González,Javier; Tejero Monzón,I?aki;
Revista Facultad de Ingeniería Universidad de Antioquia , 2011,
Abstract: this paper displays the obtained results of the collected sediment deposited during 65 days on road surfaces (torrelavega-spain). two types of samples are distinguished: aspired directly and collected after sweeping. for each type of sample it was determined the particle size distribution and heavy metals concentration. the results suggest that the heavy metals concentration tends to increase exponentially form with the decrease in the size fraction. the associated loading of metallic elements exponentially increases with the size fraction.
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