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Search Results: 1 - 10 of 208460 matches for " Nelda L.; "
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Variaciones temporales en cantidad de semillas en el suelo y en lluvia de semillas en un gradiente bosque-sabana en la gran sabana, Venezuela
Flores,Saúl; Dezzeo,Nelda;
Interciencia , 2005,
Abstract: seasonal variation in the total soil seed quantity and in seed rain were studied along a forest-savanna gradient consisting of primary forest (1: mature forest), forest slightly affected by fire (2: secondary forest), forest strongly affected by fire (3: matorral), and open savanna (4), at the gran sabana, venezuela. seed soil quantity was determined by collecting 10 samples of the organic surface layer or of the first 10cm of mineral soil with a 20×20cm steel frame in both dry and wet seasons. seed rain through the year was examined by collecting every two weeks the seeds that fell into 10 trays 90×40cm each. during the dry season the soil seed number was lower (p<0.05) in the savanna than in 1, 2 and 3. during the wet season it was higher (p<0.05) in the secondary forest than in the 1, 3 and 4. seed rain in the primary forest was low and variable, with no well defined production peaks. in the secondary forest the seed rain was slightly higher than in the mature forest, showed a clear peak in october and no production between november and january. in the matorral the seed rain was high and showed well defined production peaks in march and may; this can be associated with the presence of pioneer species in this community. in the savanna the seed rain was slightly higher than in the 1 and 2, with a production peak in february. spatial heterogeneity in the soil seed quantity and in seed rain was observed in all vegetation types, which may be associated with the distribution of species within each community, and with differences in the reproductive periods of these species. disturbances seem to accelerate the seed production and the germination processes in the soils of the gran sabana.
Seedlings dynamics in undisturbed and adjacent fire disturbed forest in the Gran Sabana, Southern Venezuela.
Dezzeo,Nelda; Flores,Saúl; Chacón,Noemí;
Interciencia , 2008,
Abstract: in the gran sabana, southern venezuela, the conversion of large forest areas to a mosaic of forest, bush vegetation and savanna ("savannization") is a critical environmental issue associated with forest fires. little is known about the behaviour of the seedling community in undisturbed and fire impacted forests in this region. recruitment, survival and growth of seedlings was followed over a 6 year period in permanent quadrats established in undisturbed and adjacent fire-disturbed (secondary) forest. at the beginning of the study, secondary forest showed lower (p<0.05) values of seedling abundance and tree seedling richness than undisturbed forest. abundance and species richness of tree seedling in both forests changed very little over the study period, which is associated to the partial balance between initial tree seedlings mortality rate (44-66%) and newly recruited tree seedlings survival rate (47-54%). at the end of the study ~80% of the recruited seedlings in undisturbed forest corresponded to tree species, whereas in secondary forest the proportions of tree (47%) and non-tree (53%) seedlings were rather similar. growth in height during the 6 year period was considerably higher in secondary forest than in undisturbed forest (p<0.05). it is concluded that in undisturbed forest the succession process is relatively at a standstill, whereas in secondary forest this process advances very slowly.
Bioprospection of marine microorganisms: biotechnological applications and methods
Dionisi,Hebe M; Lozada,Mariana; Olivera,Nelda L.;
Revista argentina de microbiolog?-a , 2012,
Abstract: environmental microorganisms constitute an almost inexhaustible reserve of genetic and functional diversity, accumulated during millions of years of adaptive evolution to various selective pressures. in particular, the extent of microbial biodiversity in marine habitats seems to grow larger as new techniques emerge to measure it. this has resulted in novel and more complex approaches for the screening of molecules and activities of biotechnological interest in these environments. in this review, we explore the different partially overlapping biotechnological fields that make use of microorganisms and we describe the different marine habitats that are particularly attractive for bioprospection. in addition, we review the methodological approaches currently used for microbial bioprospection, from the traditional cultivation techniques to state of the art metagenomic approaches, with emphasis in the marine environment.
Bioprospection of marine microorganisms: potential and challenges for Argentina Bioprospección de microorganismos marinos: potencialidades y desafíos para Argentina
Hebe M Dionisi,Mariana Lozada,Nelda L Olivera
Revista argentina de microbiolog?-a , 2012,
Abstract: The marine environments of Argentina have a remarkable extension, as well as high biological productivity and biodiversity of both macro- and microorganisms. Despite having a great potential for biotechnological applications, the microorganisms inhabiting these ecosystems remain mostly unexplored and unexploited. In this review, we study the research topics and the interactions among Argentinean laboratories, by analyzing current articles published on biotechnology-related marine microbiology by researchers of this country. In addition, we identify the challenges and opportunities for Argentina to take advantage of the genetic potential of its marine microorganisms. Finally, we suggest possible actions that could improve the development of this research field, as well as the utilization of this knowledge to solve societal needs. El medio ambiente marino de la Argentina tiene una notable extensión, como así también una alta productividad biológica y biodiversidad de macro y microorganismos. A pesar de presentar un gran potencial para aplicaciones biotecnológicas, los microorganismos que habitan estos ecosistemas permanecen mayormente inexplorados y sus propiedades aún no explotadas. En este trabajo de revisión, estudiamos los temas de investigación y las interacciones entre grupos de investigación argentinos, por medio del análisis de los artículos publicados hasta el momento en temáticas relacionadas con la aplicación biotecnológica de microorganismos marinos. Además, identificamos los desafíos y las oportunidades para que la Argentina tome ventaja del potencial genético de sus microorganismos marinos. Por último, sugerimos posibles acciones que podrían mejorar el desarrollo de este campo de estudio, como así también la utilización de este conocimiento para resolver las necesidades de la sociedad.
Estructura y composición florística de bosques secos y sabanas en los Llanos Orientales del Orinoco, Venezuela
Dezzeo,Nelda; Flores,Saúl; Zambrano-Martínez,Sergio; Rodgers,Louise; Ochoa,Elisa;
Interciencia , 2008,
Abstract: in the llanos orientales of venezuela, agricultural activities, forestry and petroleum exploration and exploitation cause negative environmental impacts on the vegetation. in order to minimize such impacts and to justify the importance of preserving representative areas of fragile communities, detailed ecological and floristic information is required regarding the local vegetal communities. in an area located within the influence zone of the bituminous strip of the orinoco, the vegetation was mapped and characterized floristically and structurally. the area is covered by dense (54.8%) and sparse (18.4%) shrub savannas, palm swamp forests or "morichales" (1%), and riparian and deciduous and semideciduous forests (25.8%). the distribution of forests, morichales and savannas appears to be related with the topography and the gradient of soil humidity availability, since forests and morichales are present in the form of continuous and narrow strips along rivers, while the savannas predominate in the higher parts of the relief. forests and morichales showed high floristic and structural heterogeneity, which can be associated with soil characteristics and water availability. savannas showed structural and floristic differences between them, probably due to differences in soil depth and chemical characteristics. few species of each vegetation type presented a high importance value (ivi), which seems to be something common in other neotropical zones. forests and morichales should be given high priority for conservation because of the protection they provide to the soils and waters, the little surface that they occupy, and the high biodiversity these forests contain.
Valores e identidad en los estudiantes de ingeniería del Instituto Politécnico Nacional
Teresita C. Payán Porras,Margarita Guerra álvarez,Nelda Ruth Martínez López,Rosalinda García-Sierra J.
Reencuentro , 2005,
Abstract: En el presente, el Instituto Politécnico Nacional (IPN) está afectado por la crisis en la educación pública mexicana, que adquiere características particulares determinadas por la propia identidad de la institución. La identidad politécnica, conformada por los valores culturales y la representación que tienen los miembros de la comunidad de sí mismos y la que proyectan frente al resto de las instituciones de ense anza superior en México, se ven reflejadas en las actitudes y acciones de los individuos, particularmente en la práctica estudiantil. El estudio y la compresión de estos valores identitarios en este sector constituye la principal preocupación del presente artículo, para mejorar la currícula y los planes de estudio de la institución, con el fin de obtener un mejor desarrollo de la docencia y la investigación, y con ello, elevar el nivel educativo superior. En este primer acercamiento se logró hacer un diagnóstico de dichas actitudes y valores, mismo que es aplicable a otras universidades como es el caso de la Universidad Autónoma Metropolitana.
Isolation, identification and antimicrobial activity of lactic acid bacteria from the Bahía Blanca Estuary
Sica,María G; Olivera,Nelda L; Brugnoni,Lorena I; Marucci,Patricia L; López-Cazorla,Andrea C; Cubitto,María A;
Revista de biología marina y oceanografía , 2010, DOI: 10.4067/S0718-19572010000300003
Abstract: this study analyzed the biodiversity of lactic acid bacteria present in the bahía blanca estuary and their antimicrobial activity against pathogens associated with the cultivation of salmonid. a total of 21 lactic acid bacteria (lab) strains were isolated from superficial sediments and fish of the estuary. the fish species were selected from those that spend most of their life cycle in the estuary. according to 16s rdna analysis, isolates were affiliated with the genera lactobacillus, pediococcus, leuconostoc, enterococcus and weissella. the predominant lab isolates from the fish species belonged to weissella viridescens, which was isolated from three of the four species analyzed. none of the lab species isolated from fish was found in sediments. the agar diffusion method was used for detection of antagonistic activity against listeria monocytogenes, yersinia ruckeri, aeromonas salmonicida subsp. salmonicida and two strains of lactococcus garvieae. all the isolates exhibited some degree of antagonistic activity against l. monocytogenes, y. ruckeri and both strains of lc. garvieae. twelve strains were found to be inhibitory for a. salmonicida. this study is the first report on the diversity of lactic acid bacteria in a coastal marine environment and fish from argentina. the sediments and fish analyzed showed microbial strains with the ability to suppress pathogen growth under in vitro conditions, suggesting their potential as biological control agents for aquaculture and fish processing.
Litterfall and nutrient input in undisturbed and adjacent fire disturbed forests of the Gran Sabana, southern Venezuela
Dezzeo,Nelda; Chacón,Noemí;
Interciencia , 2006,
Abstract: litterfall and nutrient return were studied in a primary forest (tall forest), a slight fire-affected forest (medium forest with low abundance of charred residues) and a strong fire-affected forest (low forest with abundant burned trunks on the forest floor) in the gran sabana, southern venezuela. the purpose was to determine how old fire disturbances that affected the forest structure are affecting the return of organic matter and nutrients from the biomass to the soil surface. the results did not reveal significant differences (p>0.05) in annual litter production between tall forest (5.2mg·ha-1·year-1) and medium forest (5.7mg·ha-1·year-1), indicating that minor perturbations had not affected the canopy productivity. annual litter production in low forest (3.9mg·ha-1·year-1) was significantly lower than in tall and medium forests (p<0.05). the differences in the litter production of low forest compared to tall and medium forests were surprisingly small considering that low forest were largely degraded, with 74 and 79% less stem density, 91 and 90% less basal area, and 97 and 96% less aboveground biomass than tall and medium forests, respectively. this indicates that fire disturbances that considerably affected the structural attributes of the forests are not influencing substantially the canopy productivity. inputs of nutrients were low in all the forest types with low rates of litterfall to the soil surface and low concentrations of nutrients in such litterfall. the annual input of n and p followed the same trend as the annual input of litterfall, while the annual inputs of ca, k and mg were very variable.
Experimental System for Recovery of Enteroviruses from A Water Source
Aida Maria Suarez,Nelda Rosini
Asian Journal of Information Technology , 2012,
Abstract: Knowledge of the degree of viral water pollution is highly important the epidemiology of waterborne infections, especially those caused by Enteroviruses which are present in different water sources. There exist several procedures for virus recovery from water in literature.Our objective was to desing an experimental system to concentrate the virus in water sources through an adsorption-elution method at neutral pH using a glass wool filter and to evaluate the efficiency of this method. The experiment was carried out with 17 samples of 15 l each of laboratory tap water. Each sample was contaminat with previously known concentrations of Poliovirus type 1, Sabin strain; 9 samples were seeded with 10 7 and 8 with 10 4 TCID 50 per ml (50% tissue culture infectious dose). Water samples were passed through the glass wool filter placed in a Sartorius SM 16249 holder.Virus adsorbed to the filter were first eluded at alcaline pH, them reconcentrated by organic flocculation and finally the virus concentrate was recovered in small volumes. Presence of cytophatic effects on Vero cell monolayers was used as virus recovery criterium for qualitative and quantitative assaying respectively. The infectious titres of the poliovirus stock and virus concentrates of the water samples were determined. The 50% end points titers was calculated with the Karber methods and expressed as 50% tissue culture infectious dose TCID 50 per ml. The average yield of the method was 42% (p> 0.05) for the two virus concentrations assayed. The procedure described provides a reproducible and efficient method for Enteroviruses recovery.
Factores de virulencia de cepas de Enterococcus aisladas de quesos ovinos
Marguet,Emilio Rogelio; Vallejo,Marisol; Olivera,Nelda Lila;
Acta bioqu?-mica cl?-nica latinoamericana , 2008,
Abstract: enterococci are used as starter and probiotic cultures in the food industry, and they occur as natural food contaminants. however, the genus enterococcus is of increased significance as a cause of nosocomial infections, exacerbated by the development of antibiotic resistance. in order to study the potential virulence of eight enterococcus faecium strains and two enterococcus faecalis strains isolated from ovine cheese, vancomicine resistance, hemolytic activity and gelatinase activity were investigated. in addition, polymerase chain reaction (pcr) tests were carried out in order to determine the presence of cytolicyn gene cylb, gelatinase gene gele, sex pheromone gene cpd and aggregation protein gene agg. none of the strains showed vancomicine resistance or hemolitic activity. gene cylb could not be identified by pcr amplification in any of the strains studied. the presence of gene gele was found in seven e. faecium strains and in one e. faecalis strain, however in no case was gelatinase activity detected. gene cpd was detected in e. faecium etw7 and e. faecalis etw23, while gene agg was found in e. faecium etw7 and e. faecalis etw27. these results suggest that the introduction of food products or probiotics based on the use of enterococal strains requires careful safety evaluations.
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