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Search Results: 1 - 10 of 14970 matches for " Edgar;Torres-Huerta "
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Morphology and Corrosion Performance of Chromate Conversion Coatings on Different Substrates
Domínguez-Crespo, Miguel Antonio;Onofre-Bustamante, Edgar;Torres-Huerta, Aidé Minerva;Rodríguez-Gómez, Francisco J.;
Journal of the Mexican Chemical Society , 2008,
Abstract: the aqueous corrosion resistances of galvalume (fe-al+zn) and steel galvanized (fe-zn) alloys, passivated by immersion in chromating solution with different immersion times (0, 10, 30 y 60 s) are compared. the electrochemical behaviour of various chromated and non-chromated coatings was investigated in 3 wt-% nacl solution using polarization techniques. for comparison, aisi 1010 carbon steel substrates were also analyzed. the characterization measurements and polarization curves revealed that textural properties of fe alloys influence the growth of the films and both the cathodic and anodic reactions. an optimum anticorrosive protection was obtained at 30 s. cccs treatments inhibited the corrosion of zinc to a significant degree, but less effectively than coatings formed with aluminium-zinc alloys. the difference in the corrosion protection given by the two substrates types was attributed to the structural properties, thickness coating, grain size and roughness observed, which affect oxygen diffusion.
Morphology and Corrosion Performance of Chromate Conversion Coatings on Different Substrates
Miguel Antonio Domínguez-Crespo,Edgar Onofre-Bustamante,Aidé Minerva Torres-Huerta,Francisco J. Rodríguez-Gómez
Revista de la Sociedad Química de México , 2008,
Abstract: En este trabajo se analizó el efecto de la composición superficial de dos aleaciones de hierro (Fe-Al+Zn, Fe-Zn) y su desempe o contra la corrosión al aplicar tratamientos de conversión química con cromo hexavalente y diferentes tiempos de inmersión (0, 10, 30 y 60 s). El desempe o electroquímico de los materiales se evaluó utilizando técnicas de polarización en una solución al 3 % en peso de NaCl. Como referencia se sintetizaron y compararon películas de cromo en muestras de acero al carbono comercial (AISI-1010). Los recubrimientos obtenidos mostraron un crecimiento no uniforme, con poros y grietas superficiales. Los recubrimientos obtenidos en tiempos de 30 s mostraron las propiedades de protección más eficaces para este tipo de sustratos. Las propiedades texturales de las aleaciones evaluadas juegan un papel muy importante en el tipo de crecimiento de las películas de conversión y afectan las propiedades de protección en medios agresivos.
Biología reproductiva de la cornuda común Sphyrna lewini Griffith & Smith (Sphyrnidae) en el Golfo de California
Torres-Huerta, Ana María;Villavicencio-Garayzar, Carlos;Corro-Espinosa, David;
Hidrobiológica , 2008,
Abstract: reproductive biology of scalloped hammerhead shark sphyrna lewini, was investigated in eight shark fishing camps in the gulf of california (mexico) from 1994 to 1996. a total of 1 693 specimens were determined total length (tl), total weight, sex and the gonadal maturity. the total length range was from 41 to 363 cm for females and from 43 to 290 cm for males. the sex proportion of embryos, neonates and juveniles in most of the cases was 1:1; however, this was not the case for adults, where the proportions varied at the sampling sites. sexual maturity was reached at 170 cm for males and 207 cm tl for females. the gestation period was 11 months and the highest fecundity was 32 embryos. the june births were between 41 and 53 cm tl. the presence of neonates, gravid females, and small juveniles in the east coast of the gulf of california and in la paz bay indicates that these areas are used as a nursery for s. lewini. in addition, the presence of male and female adults during the summer in the central and southeastern gulf of california suggests that these two places are important as mating areas.
Biología reproductiva de la cornuda común Sphyrna lewini Griffith & Smith (Sphyrnidae) en el Golfo de California Reproductive Biology of the Scalloped Hammerhead Shark Sphyrna lewini Griffith & Smith (Sphyrnidae) in the Gulf of California
Ana María Torres-Huerta,Carlos Villavicencio-Garayzar,David Corro-Espinosa
Hidrobiológica , 2008,
Abstract: Durante el período de 1994 a 1996 se obtuvieron datos de longitud total (LT), peso total, sexo y madurez gonádica de 1 693 individuos de Sphyrna lewini, capturados en ocho campos pesqueros de tiburón en el Golfo de California. En las hembras la longitud total tuvo un intervalo de 41 a 363 cm, mientras que en los machos fue de 43 a 290 cm. La proporción de sexos en embriones, neonatos y juveniles fue de 1:1, no así en adultos donde las proporciones variaron en las localidades de muestreo. Los machos y hembras alcanzaron la talla de primera madurez a los 170 y 207 cm de LT, respectivamente. El período de gestación tiene una duración aproximada de 11 meses y la fecundidad máxima fue de 32 embriones por hembra. El nacimiento de las crías ocurre en junio, con una talla entre 41 y 53 cm de LT. La presencia de neonatos y hembras grávidas durante el verano en la región central y sureste del Golfo de California sugiere que éstas son dos importantes áreas de nacimiento para la cornuda común en el Golfo de California. Mientras que, la costa este del Golfo de California y la Bahía de La Paz funcionan como área de crianza para los juveniles. Reproductive biology of scalloped hammerhead shark Sphyrna lewini, was investigated in eight shark fishing camps in the Gulf of California (Mexico) from 1994 to 1996. A total of 1 693 specimens were determined total length (TL), total weight, sex and the gonadal maturity. The total length range was from 41 to 363 cm for females and from 43 to 290 cm for males. The sex proportion of embryos, neonates and juveniles in most of the cases was 1:1; however, this was not the case for adults, where the proportions varied at the sampling sites. Sexual maturity was reached at 170 cm for males and 207 cm TL for females. The gestation period was 11 months and the highest fecundity was 32 embryos. The June births were between 41 and 53 cm TL. The presence of neonates, gravid females, and small juveniles in the east coast of the Gulf of California and in La Paz Bay indicates that these areas are used as a nursery for S. lewini. In addition, the presence of male and female adults during the summer in the central and southeastern Gulf of California suggests that these two places are important as mating areas.
Determinación de la Temperatura de Transición de Cerámicos Piezoeléctricos Libres de Plomo, Mediante Impedancia Electroquímica Transition Temperature of Lead-Free Piezoelectric Ceramics by Electrochemical Impedance Spectroscopy
A. M. Torres-Huerta,J. G. González-Reyes,M. E. Villafuerte-Castrejón,F. González
Portugaliae Electrochimica Acta , 2009,
Abstract: Los materiales cerámicos piezoeléctricos con estructura perovskita basados en titanatos zirconato de plomo (PZT), presentan excelentes propiedades eléctricas cerca del límite de la fase morfotrópica (entre las fases romboédrica y tetragonal), lo que permite que sean ampliamente utilizados como actuadores, sensores y en dispositivos microelectrónicos. Sin embargo, la toxicidad del óxido de plomo (PbO) y su alta presión de vapor durante el procesamiento, ha llevado a la búsqueda de materiales libres de plomo. Actualmente, las investigaciones de materiales piezoeléctricos libres de plomo se ha enfocado hacia niobatos alcalinos, titanatos de bismuto (BiT’s) modificados, y sistemas en los que existe un límite de fase morfotrópica. Entre éstos, los niobatos alcalinos (K,Na)NbO3 (KNN) han sido estudiados con renovado interés, debido a que representan una alternativa menos contaminante para sustituir a los cerámicos piezoeléctricos base Plomo y presentan buenas propiedades piezoeléctricas y ferroeléctricas. En este trabajo, se sintetizaron cerámicos piezoeléctricos libres de plomo, basados en niobatos alcalinos, de acuerdo al sistema (K0,5Na0,5)xLi(1-x) Nb yTa(1-y)O3, y se caracterizaron estructural y morfológicamente mediante difracción de rayos X y microscopía electrónica de barrido; para determinar su temperatura de transición, se utilizó espectroscopia de impedancia electroquímica, encontrándose que esta temperatura de transición está alrededor de 420 oC, valor que es deseable para este tipo de materiales. Piezoelectric ceramics with perovskite structure based on lead zirconate titanate (PZT) show excellent electrical properties near the morphotropic phase boundary (MPB) and thus are widely used for actuators, sensors as well as microelectronic devices. However, because of the high toxicity of lead oxide and its high vapour pressure during sintering, the use of lead-based ceramics has caused serious lead pollution and environmental problems; for this reason, the development of lead-free piezoelectric ceramics has been demanded to replace lead-based ceramics. Therefore, it is necessary to develop lead-free piezoelectric ceramics with good properties. Among the lead-free piezoelectric materials, the alkaline niobate-based perovskite compounds and Bi-containing materials, have attracted a large amount of attention because of their superior characteristics. The alkaline niobates (K,Na)NbO3 (KNN)-based material exhibits especially good piezoelectric properties and have been studied as substitutes for PZT piezoelectrics. In this work, alkaline niobate-based piezo
Síntesis y caracterización electroquímica de películas de SiO2 dopadas con Cerio por la técnica de sol-gel en medio básico Synthesis by Sol-gel Route and Characterization of Ceria Doped Silica Coatings on Commercial Carbon Steel
M.A. Domínguez-Crespo,E. Ramírez-Meneses,A. M. Torres-Huerta,A. García-Murillo
Portugaliae Electrochimica Acta , 2009,
Abstract: La síntesis de recubrimientos con base sílice, en el pretratamiento de diversos materiales antes de un acabado estético o final, se ha incrementado de manera importante en los últimos a os. Las ventajas de este tipo de películas son su baja o nula toxicidad, incremento en las propiedades de adherencia y la generación de una barrera de protección capaz de retardar de manera considerable el proceso de corrosión. Una de las técnicas más utilizadas para la síntesis de estos recubrimientos es la técnica sol-gel, mediante la cual se pueden sintetizar películas con características específicas en estructura, textura, composición química y espesor en una amplia variedad de substratos. En este trabajo se presenta el comportamiento electroquímico de recubrimientos de SiO2 dopados con 0.4 % en peso de cerio sobre acero al carbono comercial (1012), las cuales se sintetizaron por la técnica de sol-gel a partir de TEOS (Si(OC2H5)4) en medio alcalino. Las muestras fueron tratadas térmicamente a tres temperaturas: 623, 723 y 873 K durante 3 h, con el fin de evaluar la influencia en las propiedades de protección y adherencia. La evaluación electroquímica de las películas se realizó mediante las técnicas de Tafel y Espectroscopia de Impedancia Electroquímica, mientras que la evaluación estructural y morfológica se realizó mediante Difracción de rayos-X (DRX), Infrarrojo y Microscopía Electrónica de Barrido (MEB). Los resultados obtenidos indican que este tipo de recubrimientos actúa como una barrera de protección contra la corrosión en medios agresivos (NaCl 3.5% en peso) incrementando el tiempo de vida media de esta clase de substratos. The use of silane formulations for the pre-treatment of metallic substrates prior to painting or as topcoat has been increasing during the recent years. The proposed formulations are very attractive because they present environmental friendliness, enhance adhesion properties and provide a barrier layer that delays the corrosion processes. One of the most used techniques to synthesized based-SiO2 coatings is sol-gel. The preparation of sol-gel coatings with specific chemical functions offers potential advantages over traditional methods as it offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. The present work investigates the electrochemical behaviour of commercial carbon steel coated with ceria doped SiO2 by sol-gel process in basic media. To evaluate the influence of temperature on adhesion and protective properties, the coatings were sintered at three different temperatures, 623 K, 7
Síntesis y caracterización electroquímica de películas de SiO2 dopadas con Cerio por la técnica de sol-gel en medio básico
Domínguez-Crespo,M.A.; Ramírez-Meneses,E.; Torres-Huerta,A. M.; García-Murillo,A.; Arce-Estrada,E. M.; Castillo-Hernández,O. G.;
Portugaliae Electrochimica Acta , 2009,
Abstract: the use of silane formulations for the pre-treatment of metallic substrates prior to painting or as topcoat has been increasing during the recent years. the proposed formulations are very attractive because they present environmental friendliness, enhance adhesion properties and provide a barrier layer that delays the corrosion processes. one of the most used techniques to synthesized based-sio2 coatings is sol-gel. the preparation of sol-gel coatings with specific chemical functions offers potential advantages over traditional methods as it offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. the present work investigates the electrochemical behaviour of commercial carbon steel coated with ceria doped sio2 by sol-gel process in basic media. to evaluate the influence of temperature on adhesion and protective properties, the coatings were sintered at three different temperatures, 623 k, 723 k and 873 k, for 3 h. the anticorrosion behaviour, of the films has been characterized in an aggressive medium by electrochemical techniques, while structural characteristics and morphology was followed by x-ray diffraction, fourier transformed infra-red and scanning electron microscopy techniques. the results indicated that the thin films act as a protective barrier against exposure to the corrosive medium (3.5 wt-% nacl solution) and increase the lifetime of the susbtrate.
Determinación de la Temperatura de Transición de Cerámicos Piezoeléctricos Libres de Plomo, Mediante Impedancia Electroquímica
Torres-Huerta,A. M.; González-Reyes,J. G.; Villafuerte-Castrejón,M. E.; González,F.; Ramírez-Meneses,E.; Domínguez-Crespo,M. A.;
Portugaliae Electrochimica Acta , 2009,
Abstract: piezoelectric ceramics with perovskite structure based on lead zirconate titanate (pzt) show excellent electrical properties near the morphotropic phase boundary (mpb) and thus are widely used for actuators, sensors as well as microelectronic devices. however, because of the high toxicity of lead oxide and its high vapour pressure during sintering, the use of lead-based ceramics has caused serious lead pollution and environmental problems; for this reason, the development of lead-free piezoelectric ceramics has been demanded to replace lead-based ceramics. therefore, it is necessary to develop lead-free piezoelectric ceramics with good properties. among the lead-free piezoelectric materials, the alkaline niobate-based perovskite compounds and bi-containing materials, have attracted a large amount of attention because of their superior characteristics. the alkaline niobates (k,na)nbo3 (knn)-based material exhibits especially good piezoelectric properties and have been studied as substitutes for pzt piezoelectrics. in this work, alkaline niobate-based piezoelectric ceramics were sintetized, system (k0.5na0.5)xli(1-x) nbyta(1-y)o3, and were characterized by x-ray diffraction (drx) and scanning electron microscopy (sem). in order to determine their transition temperature, electrochemical impedance spectroscopy (eis) was used, and it was found the transition temperature was about 420 oc, which is a desirable value in this kind of materials.
Partial diallel analysis of agronomic characters in rice (Oryza sativa L.)
Torres, Edgar Alonso;Geraldi, Isaias O.;
Genetics and Molecular Biology , 2007, DOI: 10.1590/S1415-47572007000400018
Abstract: rice (oryza sativa l.) breeding seeking to combine high productivity and cold tolerance for the temperate latin america region is an important challenge. we estimated some useful parameters which can be used to investigate the genetic control of agronomic characters in crosses combining cold tolerance and productivity. a partial diallel design was used in crosses between six tropical indica rice cold susceptible genotypes (group 1) and seven japonica or indica/japonica cold tolerant rice genotypes (group 2). parents and crosses were evaluated for agronomic characters under field conditions in two different experiments in 2005. the results showed significant mid-parent heterosis for all characters (plant height, tiller number, days to 50% flowering, panicle length, grains per panicle, sterility, and one-hundred grain weight). the predominant direction of dominance effects was negative for days to 50% flowering, and positive for all the other characters. general combining ability (gca) and specific combining ability (sca) were significant for all characters, although the gca effects of the two groups were more important than the sca effects.
Assessing two different peroxidases′ potential for application in recalcitrant organic compound bioremediation Evaluación del potencial de dos peróxidas para su aplicación en biorremedación de compuestos orgánicos recalcitrantes
Caicedo Nelson,Gutiérrez Edgar,Torres Rodrigo
Revista Colombiana de Biotecnología , 2001,
Abstract: This work shows the promising future presented by the following enzymes: Chloroperoxidase (CPO) from Caldariomyces fumago and royal palm peroxidase (Roystonea regia, PPR). These peroxidases were obtained from different sources (microbial and vegetable) and used as biocatalysts for applicating them in bioremediation of recalcitrant organic compounds. Each one of the enzymes' peroxidase catalytic activity was evaluated in organic phase systems, using different model compounds such as: PAHs (pyrene and anthracene), organic-nitrogenated compounds (diphenylamine), monoaromatic phenolic molecules (guayacol) and dyes (methyl orange and ABTS). The reaction systems were composed of mono-phase water mixtures and organic miscible solvent (methanol, ethanol, isopropanol, acetonitrile, tetrahydrofuran, dimethyl sulfoxide and dimethyl formamide), on which both peroxidases' catalytic activity was evaluated. The two enzymes' catalytic activity was observed on the evaluated substrates in most of these assays. However, PPR did not show biocatalytic oxidation for methyl orange dye and some PAHs. This enzyme did show the best tolerance to the evaluated solvents. Its catalytic activity was appreciably enhanced when low hydrophobic solvents were used. The kcat was calculated from this experimental data (as kinetic parameter) leading to each enzyme's biocatalytic performance on substrates being compared. El presente trabajo demuestra el promisorio futuro que presentan las enzimas cloroperoxidasa del hongo Caldariomyces fumago (CPO) y la peroxidasa de palma real (Roystonea regia, PPR), dos peroxidasas de diferente fuente (microbiana y vegetal), usadas como biocatalizadores para aplicación en biorremediación de compuestos orgánicos recalcitrantes. Para este estudio, se evaluó la actividad catalítica tipo peroxidasa, en sistemas de fase orgánica, de cada una de las enzimas empleando diferentes compuestos modelos tales como: PAH's (pireno y antraceno), órgano nitrogenados (difenilamina), moléculas monoaromáticas tipo fenólicas (guayacol), y colorantes [(naranja de metilo y ABTS (2.2′ Azinabis (6- acido surfonic-3- etilbenzotinzolina))]. Los sistemas de reacción estuvieron compuestos por mezclas monofásicas de agua: solvente orgánico miscible (metanol, etanol, isopropanol, acetonitrilo, tetrahidrofurano, dimetil sulfóxido, etc.), sobre los cuales se evaluó la actividad catalítica de ambas peroxidasas. En la mayoría de los ensayos se observó actividad catalítica de las dos enzimas sobre los sustratos evaluados. Sin embargo, para el caso del naranja de metilo y algunos PAH's, la PPR
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