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Search Results: 1 - 10 of 304392 matches for " Norma Angelica-López-Téllez "
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Presence of Infectious Hypodermal and Haematopoietic Necrosis Virus (IHHNV) in Native Shrimps from Southern Mexico  [PDF]
Ariadne Hernández-Pérez, Jesús Alejandro Zamora-Brise?o, Juan Antonio Pérez Vega, Richard Juan de Dios Mena-Loria, Daniel Coronado-Molina, Jorge Hernández-López, Norma Angelica-López-Téllez, Rossanna Rodríguez-Canul
Open Journal of Marine Science (OJMS) , 2017, DOI: 10.4236/ojms.2017.73029
Abstract: A survey for Infectious Hypodermal and Haematopoietic Necrosis Virus (IHHNV) and White Spot Syndrome Virus (WSSV) was performed during two catching seasons of native shrimps in the Yucatan Coast in the Gulf of Mexico. The mtDNA COI barcode identified two endemic species; the southern pink shrimp Penaeus notialis (Pérez Fantante, 1967) and the northern pink shrimp Penaeus brasiliensis (Latreille, 1987) (previously described as Farfantepenaeus brasiliensis). The prevalence of IHHNV was of 18.18% in 2016, and of 8.57% in 2017. All organisms tested negative for WSSV. This is the first identification of wild shrimps in the state of Yucatan Mexico by mtDNA COI barcode as well as the first identification of IHHNV in such species. The presence of IHHNV in wild shrimps populations has a potential of persisting in the coast of Yucatan with putative detrimental effect on local fisheries because once established in natural waters and hosts; such pathogens are almost impossible to eradicate.
Magnetic characteristics and archeointensity determination on Mesoamerican Pre-Columbian Pottery from Quiahuiztlan, Veracruz, Mexico
J. M. López-Téllez,B. Aguilar Reyes,J. Morales,A. Goguitchaichvili
Geofísica internacional , 2008,
Abstract: We report a detailed archeomagnetic investigation on pre-Columbian potteries from Quiahuiztlan, Veracruz, from ~900 AD to 1521 AD. Archeological samples analyzed by modern magnetic techniques carry a stable univectorial thermoremanent magnetization under alternating field treatment. Continuous low-field susceptibility vs. temperature curves performed in air indicates Ti-poor titanomagnetites as magnetization carriers. Few samples, however, show two ferrimagnetic phases with Curie temperatures compatible with both Ti-poor and Ti-rich titanomagnetites. Hysteresis parameter ratios fall essentially in the pseudo-single-domain region, which may indicate a mixture of multi-domain and a significant amount of single domain grains. Early geomagnetic field intensity determinations using the Coe variant of Thellier method were performed on 90 selected samples. Cooling rate corrected intensity values range from 34.0 ± 1.2 to 62.2 ± 0.2 μT. Corresponding virtual axial dipole moments (VADM) range from 5.7 to 10.7 x1022 Am2. Absolute intensity curves for Mesoamerica present limited spatial/temporal resolution. For tentative dating purposes, we used global archeointensity curves reduced to central and eastern Mexico that permit preliminary dating of Quiahuiztlan potteries. Comparison of our data against those reported in ArcheoInt database allow to identify two periods 900- 1000 and 1400-1600 AD as the most probable manufacturing ranges for the potteries studied.
Magnetic characteristics and archeointensity determination on Mesoamerican Pre-Columbian Pottery from Quiahuiztlan, Veracruz, Mexico
López-Téllez, J. M.;Aguilar-Reyes, B;Morales, J;Goguitchaichvili, A;Calvo-Rathert, M;Urrutia-Fucugauchi, J;
Geofísica internacional , 2008,
Abstract: we report a detailed archeomagnetic investigation on pre-columbian potteries from quiahuiztlan, veracruz, from ~900 ad to 1521 ad. archeological samples analyzed by modern magnetic techniques carry a stable univectorial thermoremanent magnetization under alternating field treatment. continuous low-field susceptibility vs. temperature curves performed in air indicates ti-poor titanomagnetites as magnetization carriers. few samples, however, show two ferrimagnetic phases with curie temperatures compatible with both ti-poor and ti-rich titanomagnetites. hysteresis parameter ratios fall essentially in the pseudo-single-domain region, which may indicate a mixture of multi-domain and a significant amount of single domain grains. early geomagnetic field intensity determinations using the coe variant of thellier method were performed on 90 selected samples. cooling rate corrected intensity values range from 34.0 ± 1.2 to 62.2 ± 0.2 μt. corresponding virtual axial dipole moments (vadm) range from 5.7 to 10.7 x1022 am2. absolute intensity curves for mesoamerica present limited spatial/temporal resolution. for tentative dating purposes, we used global archeointensity curves reduced to central and eastern mexico that permit preliminary dating of quiahuiztlan potteries. comparison of our data against those reported in archeoint database allow to identify two periods 900- 1000 and 1400-1600 ad as the most probable manufacturing ranges for the potteries studied.
Facile Solventless Synthesis of a Nylon-6,6/Silver Nanoparticles Composite and Its XPS Study
Raúl A. Morales-Luckie,Víctor Sánchez-Mendieta,Oscar Olea-Mejia,Alfredo R. Vilchis-Nestor,Gustavo López-Téllez,Víctor Varela-Guerrero,L. Huerta,Jesús Arenas-Alatorre
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/235850
Abstract: Silver nanoparticles were synthesized and supported on thin nylon membranes by means of a simple method of impregnation and chemical reduction of Ag ions at ambient conditions. Particles of less than 10?nm were obtained using this methodology, in which the nylon fibers behave as constrained nanoreactors. Pores on nylon fibres along with oxygen and nitrogen from amide moieties in nylon provide effective sites for in situ reduction of silver ions and for the formation and stabilization of Ag nanoparticles. Transmission electron microscopy (TEM) analysis showed that silver nanoparticles are well dispersed throughout the nylon fibers. Furthermore, an interaction between nitrogen of amides moieties of nylon-6,6 and silver nanoparticles has been found by X-ray photoelectron spectroscopy (XPS). 1. Introduction Research on the synthesis of mesoporous materials containing nanoparticles represents a fast-developing area of nanoscience and nanotechnology. This interest is stimulated by several possible application areas of these materials including catalytic [1], magnetic [2], and optoelectronic [3, 4]. Metal nanoparticles dispersed in polymeric matrixes have recently been the subject of intense study aiming to develop nanocomposite films [5–8]. General approaches for the synthesis and support of nanoparticles inside porous materials include impregnation [9] and deposition-precipitation [10]. A drawback of this nanocomposites is the difficulty to disperse nanoparticles in most systems [11]; hence one potential advantage of such metal/polymer systems is that the size and distribution of dispersed metal nanoparticles can be readily controlled based on the properties of the host polymer [12, 13]. Silver particles with a narrow size distribution have been produced upon reversible chemical transformation between metallic and oxide states in a titania matrix [14] and in a mesoporous silica which was grafted with hydrophobic –Si(CH3)3 groups at the pore surface [15]. Nylon is an electron-rich and polar synthetic polymer (polyamide) usually made from the monomers adipoyl chloride and hexamethylene diamine to form a linear molecular chain (Figure 1). Synthetic nylon membranes have a porous structure [16] and are composed of microfibrils that are interconnected forming a three-dimensional network. Such morphological features provide a unique reaction vessel for synthesizing and supporting metal nanoparticles, allowing enhanced access of guest molecules to catalytic centres, compared with nonporous films. Figure 1: Characteristic synthesis of nylon-6,6 fibers. In this work,
Surveillance of nosocomial infections in a Mexican community hospital: how are we doing?
García-García,Lourdes; Jiménez-Corona,María-Eugenia; Ramírez-López,Laura-Elizabeth; Báez-Salda?a,Renata; Ferreyra-Reyes,Leticia; Ferreira-Guerrero,Elizabeth; Cano-Arellano,Bulmaro; Cruz-Hervert,Pablo; Téllez-Vázquez,Norma Araceli; Verduzco-Rodríguez,Leonardo; Jaramillo-Cosme,Yolanda; Luna-Téllez,Eleazar; León-Rosales,Samuel Ponce de;
Salud Pública de México , 2010, DOI: 10.1590/S0036-36342010000600005
Abstract: objective. to compare the nosocomial infection (ni) rate obtained from a retrospective review of clinical charts with that from the routine nosocomial infection surveillance system in a community hospital. material and methods. retrospective review of a randomized sample of clinical charts.results were compared to standard surveillance using crude and adjusted analyses. results. a total of 440 discharges were reviewed, there were 27 episodes of nis among 22 patients. cumulated incidence was 6.13 ni per 100 discharges. diarrhea, pneumonia and peritonitis were the most common infections. predictors of ni by cox regression analysis included pleural catheter (hr 16.38), entry through the emergency ward, hospitalization in the intensive care unit (hr 7.19), and placement of orotracheal tube (hr 5.54). conclusions. frequency of nis in this community hospital was high and underestimated. we identified urgent needs in the areas of training and monitoring.
Variables económicas y un modelo multifactorial para la bolsa mexicana de valores: análisis empírico sobre una muestra de activos
Francisco López Herrera,Francisco Javier Vázquez Téllez
Academia : Revista Latinoamericana de Administración , 2002,
Abstract: Mediante el método de extracción de componentes principales (ACP) se selecciona un subconjunto de variables macroeconómicas que puedan representar el riesgo sistemático de los activos mexicanos. Una vez seleccionadas esas variables, se analiza una muestra de 31 acciones que se cotizan en la Bolsa Mexicana de Valores mediante el ajuste de un modelo EGARCHX( 1,1) que incluye las variables económicas seleccionadas a través del el ACP en la estimación de los parámetros de la ecuación del rendimiento y de la estructura supuesta de los residuales. Se concluye que durante el período analizado dichas variables exhibieron influencia en los rendimientos, por lo que consideramos que la evidencia proporcionada por nuestro estudio sugiere que son explicativas del riesgo sistemático valorado por el mercado mexicano. Se documenta también la existencia de efectos de la volatilidad pasada, shocks no simétricos y la presencia del efecto apalancamiento en la volatilidad de algunos activos de la muestra.
Testimonios de migración. Tianguistenco, Huejotzingo, Puebla
Ludmila Borisovna Biriukova,Ricardo Téllez Girón López
Revista Intercontinental de Psicología y Educación , 2007,
Abstract:
Un modelo de la APT en la selección de portafolios accionarios en el mercado mexicano
Francisco López Herrera,Francisco Javier Vázquez Téllez
Contaduría y administración , 2002,
Abstract: En este trabajo se presentan pruebas iniciales de la capacidad para explicar mediante el riesgo sistemático derivado de varios factores macroeconómicos, como lo propone la APT (Arbitrage Pricing Theory), el rendimiento de 32 acciones que cotizan en la Bolsa Mexicana de Valores y del potencial para orientar la toma de decisiones sobre la formación de portafolios con base en estimaciones del rendimiento esperado de acuerdo con dichos factores de riesgo. Se analizan 1,400 portafolios formados con esos activos, cuyos rendimientos esperados se estiman por el método de máxima verosimilitud mediante un modelo de la varianza residual EGARCH(1,1). Debido a que se detecta un posible problema de especificación, los resultados que aquí se presentan se consideran sólo provisionales y con base en ellos y, por lo tanto, con las debidas reservas, se concluye que la APT ofrece un marco teórico importante para explicar la relación riesgo-rendimiento de los activos negociados en el mercado mexicano, pero su instrumentación como herramienta para la toma de decisiones no es sencilla, por lo que es importante considerar también nuevas perspectivas teóricas y analíticas
Aplicación del análisis de rango reescalado R/S para la predicción de genes en el genoma vegetal
Almanza Pinzón,Martha Isabel; López López,Karina; Téllez Villa,Carlos Eduardo;
Acta Agronómica , 2010,
Abstract: currently gene's prediction problem is one of the main genomic challenges. prediction allows performing experiments with high probability of interesting genes to be found and compare dna regions of agronomic importance among genomes; besides, it helps to restrict the searching spaces into the data bases. a statistical procedure based on the r/s analysis and the hurst coefficient was developed in order to characterize and predict genes and their structural components (exones and intrones) in the whole eukaryotic genomes of arabidopsis thaliana, oriza sativa and mus musculus. python programming language algorithms were developed with the purpose of extract, screen and modeling more than 80% of the registered gene sequences for these genomes in the ncbi gene bank data base. the r/s analysis allows to demonstrate that a structural order do exist in the distribution of the nucleotides which are constituting sequences with the memory or long range dependence phenomena predominance. the memory structure varies according to the sequences type and the species genome. the genes and exones sequences from the analyzed plant genomes showed a persistent behavior whereas those from the intrones had an anti-persistent behavior, in comparison with animal genome in which the three type of sequences showed persistent behavior. according to r/s analysis out coming parameters the genome sequences distribution pattern was replicated in a statistically similar manner in each chromosome belonging to one species, constituting fundamental evidences of invariance by scale change; it means each chromosome by itself is a statistical replication to a minor scale of the whole genome. the parameters constituted compact criteria in order to derivate sequences predictors (classifiers) which reached sensibility and specificity averages higher than 81% and 70% respectively. this procedure could be tried in other genomes and be used as a criterion in order to increasing selection efficiency in plant ge
Aplicación del análisis de rango reescalado R/S para la predicción de genes en el genoma vegetal
Almanza Pinzón Martha Isabel,López López Karina,Téllez Villa Carlos Eduardo
Acta Agronómica , 2010,
Abstract: La predicción de genes es en la actualidad uno de los principales desafíos de la genómica. La predicción permite realizar experimentos con alta probabilidad de encontrar genes de interés y comparar regiones de ADN de importancia agronómica entre genomas; además, ayuda a restringir los espacios de búsqueda en las bases de datos. Un procedimiento estadístico con base en el análisis R/S y el coeficiente de Hurst fue desarrollado para caracterizar y predecir genes y los componentes estructurales de estos (exones e intrones) en los genomas eucariotas completos de Arabidopsis thaliana, Oriza sativa y Mus musculus. Algoritmos en lenguaje de programación Python fueron desarrollados para extraer, filtrar y modelar más del 80% de las secuencias de genes registradas para estos genomas en la base de datos del GeneBank del NCBI. El análisis R/S permitió demostrar que existe un orden estructural en la distribución de los nucleótidos que constituyen las secuencias en las que predominan los fenómenos de memoria o dependencia de largo alcance. La estructura de memoria varía según el tipo de secuencias y el genoma de la especie. Las secuencias de los genes y exones de los genomas vegetales analizados presentaron comportamiento persistente mientras que las de los intrones tuvieron un comportamiento antipersistente, en comparación, al genoma animal en el cual los tres tipos de secuencias presentaron comportamiento persistente. De acuerdo con los parámetros provenientes del análisis R/S, el patrón de distribución de las secuencias del genoma se repitió de manera estadísticamente similar en cada uno de los cromosomas que pertenecen a una especie, constituyéndose en evidencias fundamentales de invarianza por cambio de escala; es decir, cada cromosoma por sí solo es una réplica estadística a menor escala del genoma completo. Los parámetros constituyeron criterios compactos para derivar predictores (clasificadores) de secuencias que alcanzaron promedios de sensibilidad y especificidad mayor del 81% y 70%, respectivamente. Este procedimiento podría ser probado en otros genomas y utilizado como criterio para incrementar la eficiencia de la selección en los programas de mejoramiento genético vegetal.
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