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Search Results: 1 - 10 of 7395 matches for " Parra-Flores "
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Distribution of pteropods (Mollusca: Gastropoda: Thecosomata) in surface waters (0-100 m) of the Western Caribbean Sea (winter, 2007)
Parra-Flores,Ana; Gasca,Rebeca;
Revista de biología marina y oceanografía , 2009, DOI: 10.4067/S0718-19572009000300011
Abstract: the main goal of this survey was to study the vertical and horizontal distribution of the thecosome pteropods in the upper 100 m of the western caribbean sea. zooplankton was collected at 60 stations in january 2007 at stratified depth intervals of 25 m from the surface to 100 m. the community was analyzed for diversity, evenness, species richness, and similarity. we recorded 36 taxa 12 of which are new records for the western caribbean. the most abundant taxa were limacina inflata, l. trochiformis, creseis acicula f. clava, cuvierina columnella atlantica, and hyalocylis striata. in general, these taxa showed a similar pattern, their highest abundances occurred consistently in 0-25 m layer in both night and day samples; abundance decreased with depth. significant day/night differences were found in the composition and abundance of pteropods, differences among depth intervals were non-significant. our results showed that the upper 25 m harbored the highest species richness, diversity, and vertical abundance of pteropods, thus providing unprecedented detail with respect to previous surveys. the local community structure of the pteropods is determined largely by vertical day/night migrations. pteropods tended to be most abundant in the southern and northern sectors of the area, but highest diversity and species richness were recorded in the central sector. overall, the low variability of the hydrographic conditions and the mixed horizontal distribution of the clusters from the similarity analysis suggest that day/night migratory patterns of the most abundant taxa are determinant of the observed variability of the pteropod community.
On the general structure of Ricci collineations for type B warped spacetimes
J. L. Flores,Y. Parra,U. Percoco
Mathematics , 2004, DOI: 10.1063/1.1775875
Abstract: A complete study of the structure of Ricci collineations for type B warped spacetimes is carried out. This study can be used as a method to obtain these symetries in such spacetimes. Special cases as 2+2 reducible spacetimes, and plane and spherical symmetric spacetimes are considered specifically.
Aprendizaje cooperativo en la solución de problemas con fracciones
Parra álvarez, Miguel ángel;Flores Macías, Rosa del Carmen;
Educación matemática , 2008,
Abstract: the analysis of the process of solution of two problems with fractions is presented, as well as the interaction in a cooperative learning situation between two secondary school students with low achievement the results showed some problems regarding the concept of fraction related to the conservation of the integer, and a wrong interpretation of the problem which led them to the use of inadequate algorithms for the solution. three conceptions were identified in the solution process: in a problem with fractions the value of the integer is always one, just an operation is needed to obtain the result and the only quantity mentioned in the problem is equivalent to the integer. the problems were overcome during the interaction between students and tutor.
Modelos determinísticos de inventarios para demanda independiente. Un estudio en Venezuela
Carlos Enrique Bustos Flores,Galia Beatriz Chacón Parra
Contaduría y administración , 2012,
Abstract: El objetivo de este trabajo es analizar los siguientes modelos determinísticos de inventarios para demanda independiente: un solo lote, lote por lote, cantidad económica de pedido (EOQ), algoritmo Silver-Meal (SM), costo unitario mínimo (CUM), balanceo de periodo fragmentado (BPF) y algoritmo de Wagner-Whitin (WW). Estos modelos surgen del supuesto clave de que la demanda conocida con cierto grado de certidumbre de un artículo que se lleva en inventario es independiente de la demanda de cualquier otro artículo que también se lleve en dicho inventario. Con la intención de lograr el objetivo planteado, los modelos mencionados son aplicados para el cálculo de los tama os de lotes óptimos de resmas de papel carta y oficio de acuerdo con los registros de demanda real e independiente suministrados por el departamento de Publicaciones de la Facultad de Ciencias Económicas y Sociales (FACES) en la Universidad de Los Andes (ULA), en Mérida, Venezuela. La principal conclusión que se deriva de los resultados obtenidos es que el método de un solo lote, utilizado por la administración de la FACES, comparado con los modelos de lote por lote, EOQ, SM, CUM, BPF y WW, es el más costoso y, en consecuencia, el menos indicado.
Enantioselective Ring Opening of meso-Cyclohexene Epoxide with Phenyllithium Catalyzed by Chiral Schiff Base Ligands
Norma Aidé Cortez,Lucía Z. Flores López,Miguel Parra Hake,Gerardo Aguirre
Revista de la Sociedad Química de México , 2004,
Abstract: Se ha sintetizado una biblioteca de ligandos quirales tipo base de Schiff a partir de aldehídos aromáticos y aminoalcoholes quirales. Se midió la capacidad catalítica de estos ligandos en la apertura asimétrica del anillo de meso-epóxido de ciclohexeno con fenillitio para dar (1S,2R)-fenilciclohexanol con 9-67% ee.
Asymmetric Synthesis of Naturally Occurring β-Hydroxyamides (R)-Tembamide and (R)-Aegeline
Gerardo Aguirre,Araceli Salgado Rodríguez,Lucía Z. Flores López,Miguel Parra Hake
Revista de la Sociedad Química de México , 2001,
Abstract:
Asymmetric Synthesis of Naturally Occurring b-Hydroxyamides (R)-Tembamide and (R)-Aegeline
Gerardo Aguirre,Araceli Salgado Rodríguez,Lucía Z. Flores López,Miguel Parra Hake
Revista de la Sociedad Química de México , 2001,
Abstract: Se sintetizaron cianohidrinas quirales a partir de anisaldehído y cianuro de trimetilsililo por medio de la reacción catalizada con un complejo de titanio y una base de Schiff quiral. Las cianohidrinas fueron convertidas a las -hydroxyamidas quirales, (R)- Tembamida y (R)-Aegelina.
Proteína S libre en embarazadas normales: comparación entre dos métodos Free protein S (PS) in normal pregnancy: A comparison between two analytical methods
Patricia Fardella B,Mauro Parra C,Guillermo Conte L,Claudio Flores P
Revista médica de Chile , 2005,
Abstract: Background: Pregnancy is a physiological hypercoagulable state with an increased incidence of thromboembolic phenomena. There is an increase in the concentrations of most clotting factors, a decrease in concentration of some of the natural anticoagulants and reduced fibrinolytic activity. Changes in PS levels have also been reported. Aim: To establish referral range values of functional PS and free PS antigen, during the second (2nd T) and third trimester (3rd T) of normal gestation. Patients and methods: Forty one normal pregnant women were included in our study, 20 during the 2nd T (22-24 weeks) and 21 during the 3rd T (29-38 weeks). Functional PS was measured by a clot based test and free PS antigen by ELISA. Results: Free PS Antigen was 65.8±18.3% during the 2nd T and 62.3±16.5% during the 3rd T. The figures for normal controls were 106±6.5%. Functional PS was 43.8±13.3 and 25.9±14.6% during the 2nd T and 3rd T, respectively. The figures for normal controls were 97±24% (p <0.001 compared with pregnant women). Free PS antigen did not change from the 2nd to the 3rd T (p=NS), however functional PS fell significantly from the 2nd to the 3rd T (p <0.001) and was significantly lower than free PS antigen in both trimesters (p <0.001). Conclusions: Pregnancy is associated to a decrease in PS. This abnormality is more pronounced for functional PS than free PS antigen and functional PS falls progressively during pregnancy. These assays should not be used to screen for PS deficiency during pregnancy because they could lead to a misdiagnosis
Transformation processes of cybermedia: challenges for journalistics enterprises
Dr. David Parra,Dra. Concha Edo,Dr. Jesús Flores,Dr. Pedro García-Alonso
Revista Latina de Comunicación Social , 2008,
Abstract: From the corporative point of view, cybermedia have got four main challenges nowadays: to define a new business pattern; to fit to the new standards in the acquisition and transmission of knowledges; to collect the readers that are leaving the convencional media; and to get a new and efficient formal treatment of the product. Also cyberjournalism is facing to the future challenge of new mobile supports in order to accede to its contents, which create two aditional complications: a very fewer size and a very complex interface. All of these items will imply the development of a new generation of typographical families, adapted to this new reality, to push for the flexibility due to the great versatility of mobile cyberjournalism and, finally, to deepen in interactivity, considered like the strategic formule to profit the wide range of services that is supporting this business pattern.
Evaluation of Morphological Changes of Aeromonas caviae Sch3 Biofilm Formation under Optimal Conditions  [PDF]
Erika Beatriz Angeles-Morales, Ricardo Mondragón-Flores, Juan Pedro Luna-Arias, Cinthia Teresa Enríquez-Nieto, Berenice Parra-Ortega, Graciela Castro-Escarpulli
Advances in Microbiology (AiM) , 2012, DOI: 10.4236/aim.2012.24071
Abstract:

Aeromonas is a Gram-negative bacterium that lives in aquatic habitats. It can be infective in humans. One of its remarkable attributes is the ability of biofilm formation. Many factors are involved in the construction of biofilms as has been described for Pseudomonas, Klebsiella, and Vibrio, among others. The aim of this work was to study the bacterial morphology during the establishment of biofilm through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with a modified microtiter plate assay and to determine the best conditions for the establishment of Aeromonas caviae Sch3 biolfilm in vitro. We observed several phenotypic changes, including surface appearance, size, presence of extracellular vesicles from 100 to 250 nm in diameter, and flagella. The best conditions for biofilm formation were to grow cultures at 28℃ at pH 6, as determined by the crystal violet assay. This is, to the best of our knowledge, the first study that describes the cell’s biological events involved in the establishment of biofilm formation of Aeromonas caviae Sch3 in vitro.

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