936 resultados para Themistocles, approximately 524 B.C.-approximately 459 B.C.
Resumo:
Las fases necesarias para elaborar un diagrama de Gant son: determinación de las actividades principales; estimación de la duración efectiva de las mismas; enunciación en el diagrama de las actividades principales y de su relación entre si; representación gráfica de su duración; su utilización sus limitaciones, las actividades que se presentan tienen que ser limitadas perfectamente sin excederse en detalles. Tienen a su favor que son fácilmente realizables por personas no especializadas y que su representación sinóptica e intuitiva es muy útil. En definitiva, podemos decir que es un método útil para las programaciones de los docentes y puede contribuir a la mejora de la enseñanza, ya que proporciona un método sencillo de resumir las progresiones efectuadas y anotar la marcha de las actividades es de fácil seguimiento y una clara visión de conjunto lo que contribuirá a una clara coordinación.
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Se analiza el Proyecto de Ciencia integrada para Bachillerato o proyecto C.I.B. Se trata de un intento de renovación didáctica en el área de Ciencias realizado por el departamento de Ciencias Naturales del IEPS. La conclusión principal a que se llegó fue que el Proyecto debería incluir las pautas necesarias para realizar programaciones integradas del currículum para alumnos de Bachillerato, que abarcaran las materias Física, Química, Biología y Geología. En los grupos de trabajo se analizaron datos de la realidad como cuestión previa: hacia dónde va la investigación educativa en relación a la renovación de los currículos a nivel internacional; y las posibilidades de renovación que ofrece y admite nuestra realidad nacional. Por otro lado se señalan los principios básicos del proyecto CIB, que son: principio de activación, principio de realismo, principio de flexibilidad y principio de creatividad. A continuación se pormenorizan los objetivos generales del proyecto CIB, y los materiales necesarios para llevarlo a cabo. Para concluir se estudia el papel de la física y la química en el proyecto CIB, y el material para el estudio integrado de la física y la química.
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Se desarrollan los objetivos del BSCS (Biological Sciences Curriculum Study), que surge para dar solución al problema de la enorme expansión de conocimientos y la limitación de tiempo y capacidad de los estudiantes. Se crea en 1958 en el Instituto Americano de Ciencias Biológicas, y en él se exponen los conocimientos y la experiencia de cientos de profesores y biólogos profesionales, con el fin de lograr un conocimiento más racional y significativo de la Biología.
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Se persigue que los alumnos y alumnas se conviertan en grandes amantes de la actividad f??sica y que aprendan las habilidades que les permitan desarrollar sus capacidades con la mayor transparencia posible. Se presenta una evoluci??n de trabajo para que el alumnado acceda a la siguiente etapa educativa sin que le cueste tanto trabajo realizar las tareas motrices. Se trata de consolidar las habilidades para progresar hacia una mayor complejidad y especificidad.
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Resumen basado en el de la publicaci??n
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The GEFSOC Project developed a system for estimating soil carbon (C) stocks and changes at the national and sub-national scale. As part of the development of the system, the Century ecosystem model was evaluated for its ability to simulate soil organic C (SOC) changes in environmental conditions in the Indo-Gangetic Plains, India (IGP). Two long-term fertilizer trials (LTFT), with all necessary parameters needed to run Century, were used for this purpose: a jute (Corchorus capsularis L.), rice (Oryza sativa L.) and wheat (Triticum aestivum L.) trial at Barrackpore, West Bengal, and a rice-wheat trial at Ludhiana, Punjab. The trials represent two contrasting climates of the IGP, viz. semi-arid, dry with mean annual rainfall (MAR) of < 800 mm and humid with > 1600 turn. Both trials involved several different treatments with different organic and inorganic fertilizer inputs. In general, the model tended to overestimate treatment effects by approximately 15%. At the semi-arid site, modelled data simulated actual data reasonably well for all treatments, with the control and chemical N + farm yard manure showing the best agreement (RMSE = 7). At the humid site, Century performed less well. This could have been due to a range of factors including site history. During the study, Century was calibrated to simulate crop yields for the two sites considered using data from across the Indian IGP. However, further adjustments may improve model performance at these sites and others in the IGP. The availability of more longterm experimental data sets (especially those involving flooded lowland rice and triple cropping systems from the IGP) for testing and validation is critical to the application of the model's predictive capabilities for this area of the Indian sub-continent. (C) 2007 Elsevier B.V. All rights reserved.
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Measures blocking hybridization would prevent or reduce biotic or environmental change caused by gene flow from genetically modified (GM) crops to wild relatives. The efficacy of any such measure depends on hybrid numbers within the legislative region over the life-span of the GM cultivar. We present a national assessment of hybridization between rapeseed (Brassica napus) and B. rapa from a combination of sources, including population surveys, remote sensing, pollen dispersal profiles, herbarium data, local Floras, and other floristic databases. Across the United Kingdom, we estimate that 32,000 hybrids form annually in waterside B. rapa populations, whereas the less abundant weedy populations contain 17,000 hybrids. These findings set targets for strategies to eliminate hybridization and represent the first step toward quantitative risk assessment on a national scale.
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Maculalactones A, B and C from the marine cyanobacterium Kyrtuthrix maculans are amongst the only compounds based on the tribenzylbutyrolactone skeleton known in nature and (+) maculalactone A from the natural source possesses significant biological activity against various marine herbivores and marine settlers. We now report a concise synthesis of racemic maculalactone A in five steps from inexpensive starting materials. Maculalactones B and C were synthesized by a minor modification to this procedure, and the synthetic design also permitted an asymmetric synthesis of maculalactone A to be achieved in around 85% ee. The (+) and (-) enantiomers of maculalactone A were assigned, respectively, to the S and R configurations on the basis of the chiral selectivity expected for catecholborane reduction of an unsymmetrical ketone in the presence of Corey's oxazoborolidine catalyst. Surprisingly, it appeared that natural (+) maculalactone A was biosynthesized in K. maculans in a partially racemic form, comprising ca. 90-95% of the (S) enantiomer and 5-10% of its (R) enantiomer. Coincidentally therefore, the percentage enantiomeric excess of the product obtained from asymmetric synthesis almost exactly matched that found in nature. (C) 2004 Elsevier Ltd. All rights reserved.
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The confined crystallization of poly(ethylene oxide) (PEO) in predominantly spherical microdomains formed by several diblock copolymers was studied and compared. Two polybutadiene-b-poly(ethylene oxide) diblock copolymers were prepared by sequential anionic polymerization (with approximately 90 and 80 wt % polybutadiene (PB)). These were compared to equivalent samples after catalytic hydrogenation that produced double crystalline polyethylene-b-poly(ethylene oxide) diblock copolymers. Both systems are segregated into microdomains as indicated by small-angle X-ray scattering (SAXS) experiments performed in the melt and at lower temperatures. However, the PB-b-PEO systems exhibited a higher degree of order in the melt. A predominantly spherical morphology of PEO in a PB or a PE matrix was observed by both SAXS and transmission electron microscopy, although a possibly mixed morphology (spheres and cylinders) was formed when the PEO composition was close to the cylinder-sphere domain transitional composition as indicated by SAXS. Differential scanning calorimetry experiments showed that a fractionated crystallization process for the PEO occurred in all samples, indicating that the PE cannot nucleate PEO in these diblock copolymers. A novel result was the observation of a subsequent fractionated melting that reflected the crystallization process. Sequential isothermal crystallization experiments allowed us to thermally separate at least three different crystallization and melting peaks for the PEO microdomains. The lowest melting point fraction was the most important in terms of quantity and corresponded to the crystallization of isolated PEO spheres (or cylinders) that were either superficially or homogeneously nucleated. This was confirmed by Avrami index values of approximately 1. The isothermal crystallization results indicate that the PE matrix restricts the crystallization of the covalently bonded PEO to a higher degree compared to PB.
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The solid-phase synthesis of a cyclic peptide containing the 21-residue epitope found in the A-B loop of the Cepsilon3 domain of human immunoglobulin E has been carried out. The key macrocyclization step to form the 65-membered ring is achieved in similar to15% yield via an "on-resin" Sonogashira coupling reaction which concomitantly installs a diphenylacetylene amino acid conformational constraint within the loop.
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1. Apolipoprotein B-48, the transport protein for chylomicrons, is identical with apolipoprotein B-100 for the first 48% of its sequence. No antiserum has yet been reported that can recognize apolipoprotein B-48, but not apolipoprotein B-100. 2. In the present study an antiserum was raised to the C-terminal sequence of apolipoprotein B-48, using specific chemical reactions to ensure that the charged carboxyl group of the C-terminal isoleucine residue was free. In a Western blot the antiserum was shown to bind to a protein band having the characteristics of apolipoprotein B-48, but not to apolipoprotein B-100. 3. In the early evening 11 subjects were given a test meal which contained 40 g of mixed oil and retinyl palmitate. Blood samples were collected over 9 h. Chylomicron-enriched fractions were prepared and analysed for triacylglycerol, retinyl palmitate and apolipoprotein B-48, the latter after separation using SDS/PAGE and visualization by chemiluminescence on a Western blot. Both triacylglycerol and apolipoprotein B-48 showed an early peak at 1 h, which was not seen with retinyl palmitate. All three substances gave a broader peak between 5 and 6 h postprandially. Retinyl palmitate concentrations declined rapidly during the late (6-9 h) postprandial period, but apolipoprotein B-48 concentrations remained elevated. 4. This study has shown that an antiserum has been produced which is specific for apolipoprotein B-48. This has enabled measurement of postprandial concentrations of the protein that revealed features of chylomicron metabolism which have not been reported previously.