779 resultados para rib waveguides
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Se exponen los resultados de la investigación "Procedimiento en la búsqueda de información y en lautilización de las bibliotecas por los investigadores y docentes de la Universidad Nacional de La Plata, hacia una optimización del uso de recursos de información", realizada por un grupo deinvestigadores del Departamento de Bibliotecología de la Universidad Nacional de La Plata (Argentina). Su objetivo era establecer los perfiles de comportamiento de los investigadores de la Facultadde Humanidades y Ciencias de la Educación de dicha universidad, en el uso de los recursos y fuentesde información y, en particular, su relación con la biblioteca de la Facultad. El primer paso del estudiofue la realización de un censo para determinar la cantidad de investigadores que usan o no labiblioteca en sus procedimientos de búsqueda de información, así como las modalidades de uso. Elmismo permitió la identificación de grupos, de los cuales se seleccionaron algunos casos, con el fin de realizar entrevistas en profundidad tendientes a captar la perspectiva de los investigadores en relación con la temática estudiada
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Este trabajo comparó la cobertura de revistas procedentes de América Latina y el Caribe incluidas en SciELO, RedALyC y SCOPUS, por país y por tema. Calculó el porcentaje de revistas en estas fuentes en relación con las registradas en el catálogo de LATINDEX. Estimó el volumen de la producción científica que registra visibilidad en las tres fuentes y su evolución en el período 2005-2009. Los resultados indicaron que las tres fuentes son complementarias. En promedio, el porcentaje de solapamiento de títulos es bajo y desigual la distribución de revistas por países. Ningún país registró en las fuentes estudiadas todas las revistas incluidas en LATINDEX. SCOPUS y SciELO están más equilibradas temáticamente que RedALyC, que mostró un marcado sesgo hacia las ciencias sociales. El volumen de producción científica visible en SCOPUS es muy superior al de SciELO y RedALyC, aunque su distribución por países es muy desigual. Las tres fuentes registran tendencias de crecimiento de la producción en el período analizado
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Se describe y analiza un estado de situación de la aplicación de tecnologías por parte de graduados en Bibliotecología de la Universidad Nacional de La Plata, a cargo de las decisiones en las instituciones donde se desempeñan en la actualidad. Para tal objeto se conformó una muestra con los casos que respondieran al perfil de interés y se procedió al relevamiento de la información mediante una encuesta auto-administrada, que combinaba preguntas cerradas y abiertas. Entre otros puntos de interés, se indagó sobre el estado de situación de los procesos de automatización, la aplicación de tecnologías en los distintos procesos bibliotecarios, la formación de grado obtenida en temas vinculados con el uso de tecnologías, así como también acerca de los cursos y los seminarios seguidos y las perspectivas de desarrollo futuro imaginadas. El análisis de los resultados mostró que el conjunto de graduados estudiados mantiene con la tecnología una relación que los mueve hacia un terreno de cambios ininterrumpidos, aunque con diferencias cualitativas importantes entre ellos. Asimismo, es claro que perciben la tecnología como una potencia creativa positiva de cara al futuro
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El presente artículo realiza un estudio de diversas películas pertenecientes al género de ciencia ficción, focalizando la atención en los escenarios futuros para el libro y las bibliotecas. A partir del concepto "imaginario social", se exploran las representaciones que se construyen desde el presente sobre el devenir de la cultura impresa en el contexto del creciente proceso de transformación tecnológica. Los films seleccionados componen una muestra que incorpora obras de diferentes momentos en la historia del género de ciencia ficción en relación a las problematizaciones sobre los vínculos entre tecnología y sociedad. Los ejes de análisis giran en torno a la desaparición, la transformación y las permanencias del libro y las bibliotecas. Se concluye que desde el imaginario social contemporáneo, materializado en las películas analizadas, se presenta un futuro en el que conviven elementos de la cultura del libro y la lectura con importantes modificaciones originadas por las innovaciones técnicas. Respecto al profesional de la información, si bien no hay indicaciones de cambios radicales en sus funciones, sí existen planteamientos inquietantes sobre el desplazamiento de lo humano por lo virtual
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El presente artículo analiza la adopción y los principales usos de la plataforma Facebook por parte de las bibliotecas de tres universidades en Argentina. Luego de una revisión bibliográfica sobre la temática, se exponen los procedimientos metodológicos empleados para identificar, en primer lugar, las instituciones que cuentan con esta herramienta de comunicación en la actualidad y, en segundo término, los usos que se hace de ella a partir de una serie de variables, entre las que caben consignar: el momento de inicio, los vínculos con otros medios de comunicación administrados por la institución (webs y redes sociales), el número de seguidores, el empleo de las imágenes, la frecuencia y el tipo de posteos y, por último, la cantidad y la calidad de los comentarios. En los resultados se trabaja la información recabada procurando un análisis cuantitativo y otro cualitativo en la construcción de un panorama global. En las conclusiones se destaca la paulatina adopción de la plataforma por parte de las bibliotecas universitarias, aunque con usos limitados respecto de su potencial. Se sugieren otras posibilidades
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Palynological investigation of a 410 cm long core section from Tso Kar (33°10'N, 78°E, 4527 m a.s.l.), an alpine lake situated in the arid Ladakh area of NW India at the limit of the present-day Indian summer monsoon, was performed in order to reconstruct post-glacial regional vegetation and climate dynamics. The area was covered with alpine desert vegetation from ca. 15.2 to 14 kyr BP (1 kyr=1000 cal. years), reflecting dry and cold conditions. High influx values of long-distance transported Pinus sylvestris type pollen suggest prevailing air flow from the west and northwest. The spread of alpine meadow communities and local aquatic vegetation is a weak sign of climate amelioration after ca. 14 kyr BP. Pollen data (e.g. influx values of Pinus roxburghii type and Quercus) suggest that this was due to a strengthening of the summer monsoon and the reduced activity of westerly winds. The further spread of Artemisia and species-rich meadows occurred in response to improved moisture conditions between ca. 12.9 and 12.5 kyr BP. The subsequent change towards drier desert-steppe vegetation likely indicates more frequent westerly disturbances and associated snowfalls, which favoured the persistence of alpine meadows on edaphically moist sites. The spread of Chenopodiaceae-dominated vegetation associated with an extremely weak monsoon occurred at ca. 12.2-11.8 kyr BP during the Younger Dryas interstadial. A major increase in humidity is inferred from the development of Artemisia-dominated steppe and wet alpine meadows with Gentianaceae after the late glacial/early Holocene transition in response to the strengthening of the summer monsoon. Monsoonal influence reached maximum activity in the Tso Kar region between ca. 10.9 and 9.2 kyr BP. The subsequent development of the alpine meadow, steppe and desert-steppe vegetation points to a moderate reduction in the moisture supply, which can be linked to the weaker summer monsoon and the accompanying enhancement of the winter westerly flow from ca. 9.2 to 4.8 kyr BP. The highest water levels of Tso Kar around 8 kyr BP probably reflect combined effect of both monsoonal and westerly influence in the region. An abrupt shift towards aridity in the Tso Kar region occurred after ca. 4.8 kyr BP, as evidenced by an expansion of Chenopodiaceae-dominated desert-steppe. Low pollen influx values registered ca. 2.8-1.3 kyr BP suggest scarce vegetation cover and unfavourable growing conditions likely associated with a further weakening of the Indian Monsoon.
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On the strongly karstified and almost unvegetated surface of the Zugspitzplatt, at an altitude of about 2290 m in the Wettersteingebirge, there is a doline within which over a period of several thousand years a bed of fine loess-like sediment, almost 1m thick, has accumulated. Notwithstanding the situation of this locality far above the present tree-line, this infill contains quantities of pollen and spores sufficient for pollen analysis without use of any enrichment techniques. Despite poor pollen preservation, it was possible to date the basal layers of this profile on the basis of their pollen assemblages. AMS dating (7415 ± 30 BP) has confirmed that the oldest sediments were laid down during the early Atlantic period, the time of the thermal optimum of the Holocene. At least since that time this site has never been overridden by a glacier. The moraine associated with the Löbben Oscillation between 3400 and 3100 BP - here represented by the so-called Platt Stillstand (Plattstand) - did not quite reach the doline. A diagram shows known Holocene glacial limits. The composition of the pollen assemblages from the two oldest levels with high pollen concentrations strongly suggests that the distance between the doline and the forest was much less during the Atlantic than at present.
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AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the siliclastic and organic carbon fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 Cal. kyrs. BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge due to the final stage of mountain deglaciation of the Putoran Massif. Increased supply of Yenisei-derived material indicated by peak magnetic susceptibility values probably occurred in climate-related pulses culminating near 11, 10, and 9 Cal. kyrs. BP. As sea level rose, the main Holocene depocenter migrated southward. Based on hydrogen index values and n-alkanes, the organic matter is predominantly of terrigenous origin. Maximum accumulation rates of 1.5 to more than 6 g/cm2/y occurred in the early Holocene sediments, suggesting more humid climatic conditions with an increased vegetation cover in the source area at that time. In general, high organic carbon accumulation rates characterize the estuaries and the inner Kara Sea as important sink for terrigenous organic carbon. A high-resolution record of Holocene variability of magnetic susceptibility (MS) in an AMS14C-dated sediment core from the northern Yenisei estuary may indicate natural variability of Arctic climate change and river discharge on a centennial to millenial time scale. Short-term maxima in MS probably related to warmer climate, enhanced precipitation, intensified weathering/erosion and increased river discharge, display a frequency of about 300 to 700 years.
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The physicochemical properties of the sea surface microlayer (SML), i.e. the boundary layer between the air and the sea, and its impact on air-sea exchange processes have been investigated for decades. However, a detailed description about these processes remains incomplete. In order to obtain a better chemical characterization of the SML, in a case study three pairs of SML and corresponding bulk water samples were taken in the southern Baltic Sea. The samples were analyzed for dissolved organic carbon and dissolved total nitrogen, as well as for several organic nitrogen containing compounds and carbohydrates, namely aliphatic amines, dissolved free amino acids, dissolved free monosaccharides, sugar alcohols, and monosaccharide anhydrates. Therefore, reasonable analytical procedures with respect to desalting and enrichment were established. All aliphatic amines and the majority of the investigated amino acids (11 out of 18) were found in the samples with average concentrations between 53 ng/l and 1574 ng/l. The concentrations of carbohydrates were slightly higher, averaging 2900 ng/l. Calculation of the enrichment factor (EF) between the sea surface microlayer and the bulk water showed that dissolved total nitrogen was more enriched (EF: 1.1 and 1.2) in the SML than dissolved organic carbon (EF: 1.0 and 1.1). The nitrogen containing organic compounds were generally found to be enriched in the SML (EF: 1.9-9.2), whereas dissolved carbohydrates were not enriched or even depleted (EF: 0.7-1.2). Although the investigated compounds contributed on average only 0.3% to the dissolved organic carbon and 0.4% to the total dissolved nitrogen fraction, these results underline the importance of single compound analysis to determine SML structure, function, and its potential for a transfer of compounds into the atmosphere.
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Patterns of distribution and variations of group and monosaccharide compositions of carbohydrates in suspended matter of the Pacific Ocean were studied. It is shown that carbohydrate content of surface ocean waters depends on reproduction of organic matter by phytoplankton. Water-insoluble polysaccharides (average 77.9% of total) predominate in composition of carbohydrates in suspended matter. Water-soluble polysaccharides and oligosaccharides were detected in considerably smaller quantities (average 12.4 and 7.3% respectively). Free monosaccharides were not detected. The main sugars in all isolated groups of carbohydrates of suspended matter are hexoses, which account for 90.8% in oligosaccharides, 64.9% in water-soluble polysaccharides, and 69.8% in water-insoluble polysaccharides. Determination of monosaccharide composition of carbohydrates in suspension showed that apparently they basically consist of mixture of reserve and structural polysaccharides (or their residues) of phytoplankton organisms.
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Total organic carbon (TOC), dissolved organic carbon (DOC), total hydrolyzable amino acids (THAA), amino sugars (THAS), and carbohydrates (THCHO) were measured in sediments and interstitial waters from Site 681 (ODP Leg 112). TOC concentrations vary between 0.75% and 8.2% by weight of dry sediment and exhibit a general decrease with depth. DOC concentrations range from 6.1 to 49.5 mg/L, but do not correlate with TOC concentrations in the sediment. Amino compounds (AA and AS) and sugars account for 0.5% to 8% and 0.5% to 3% of TOC, respectively, while amino compounds make up between 2% and 27% of total nitrogen. Dissolved hydrolyzable amino acids (free and combined) and amino sugars were found in concentrations from 3.7 to 150 µM and from 0.1 to 3.7 µM, respectively, and together account for an average of 8.5% of DOC. Dissolved hydrolyzable carbohydrates are in the range of 6 to 49 µM. Amino acid spectra are dominated by glycine, alanine, leucine, and phenylalanine; nonproteinaceous amino acids (gamma-amino butyric acid, beta-alanine, and ornithine) are enriched in the deeper part of the section, gamma-amino butyric acid and beta-alanine are thought to be indicators of continued microbial degradation of TOC. Glycine, serine, glutamic acid, alanine, aspartic acid, and ornithine are the dominating amino compounds in the pore waters. Spectra of carbohydrates in sediments are dominated by glucose, galactose, and mannose, while dissolved sugars are dominated by glucose and fructose. In contrast to the lack of correlation between abundances of bulk TOC and DOC in corresponding interstitial waters, amino compounds and sugars do show some correlation between sediments and pore waters: A depth increase of aspartic acid, serine, glycine, and glutamic acid in the pore waters is reflected in a decrease in the sediment, while an enrichment in valine, iso-leucine, leucine, and phenylalanine in the sediment is mirrored by a decrease in the interstitial waters. The distribution of individual hexoseamines appears to be related to zones of bacterial decomposition of organic matter. Low glucoseamine to galactoseamine ratios coincide with zones of sulfate depletion in the interstitial waters.
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Die pollenanalytische Untersuchung des Rotmooses in Verbindung mit C-14 Daten hat ergeben, daß die organogenen Sedimente nachwärmezeitliche Bildungen sind. Ein Gletschervorstoß um 2500 v. Chr. konnte mit Hilfe der C-14 Daten eingegrenzt und mit anderen Fundstellen parallelisiert werden. Weitere pollenanalytisch festgestellte Gletscher und auch Waldgrenzschwankungen konnten festgestellt, müssen aber noch genau datiert und parallelisiert werden.