995 resultados para 7140-220
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This study investigates the landscape evolution and soil development in the loess area near Regensburg between approximately 6000-2000 yr BP (radiocarbon years), Eastern Bavaria. The focus is on the question how man and climate influenced landscape evolution and what their relative significance was. The theoretical background concerning the factors that controlled prehistoric soil erosion in Middle Europe is summarized with respect to rainfall intensity and distribution, pedogenesis, Pleistocene relief, and prehistoric farming. Colluvial deposits , flood loams, and soils were studied at ten different and representative sites that served as archives of their respective palaeoenvironments. Geomorphological, sedimentological, and pedological methods were applied. According to the findings presented here, there was a high asynchronity of landscape evolution in the investigation area, which was due to prehistoric land-use patterns. Prehistoric land use and settlement caused highly difIerenciated phases of morphodynamic activity and stability in time and space. These are documented at the single catenas ofeach site. In general, Pleistocene relief was substantially lowered. At the same time smaller landforms such as dells and minor asymmetric valleys filled up and strongly transformed. However, there were short phases at many sites, forming short lived linear erosion features ('Runsen'), resulting from exceptional rainfalls. These forms are results of single events without showing regional trends. Generally, the onset of the sedimentation of colluvial deposits took place much earlier (usually 3500 yr BP (radiocarbon) and younger) than the formation of flood loams. Thus, the deposition of flood loams in the Kleine Laaber river valley started mainly as a consequence of iron age farming only at around 2500 yr BP (radiocarbon). A cascade system explains the different ages of colluvial deposits and flood loams: as a result of prehistoric land use, dells and other minor Pleistocene landforms were filled with colluvial sediments. After the filling of these primary sediment traps , eroded material was transported into flood plains, thus forming flood loams. But at the moment we cannot quantify the extent ofprehistoric soil erosion in the investigation area. The three factors that controlled the prehistoric Iandscapc evolution in the Ioess area near Regensburg are as follows: 1. The transformation from a natural to a prehistoric cultural landscape was the most important factor: A landscape with stable relief was changed into a highly morphodynamic one with soil erosion as the dominant process of this change. 2. The sediment traps of the pre-anthropogenic relief determined where the material originated from soil erosion was deposited: either sedimentation took place on the slopes or the filled sediment traps of the slopes rendered flood loam formation possible. Climatic influence of any importance can only be documented as the result of land use in connection with singular and/or statistic events of heavy rainfalls. Without human impact, no significant change in the Holocene landscape would have been possible.
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We present observations of radio recombination lines (RRL) from the starburst galaxy Arp 220 at 8.1 GHz (H92 alpha) and 1.4 GHz (H167 alpha and H165 alpha) and at 84 GHz (H42 alpha), 96 GHz (H40 alpha) and 207 GHz (H31 alpha) using the Very Large Array and the IRAM 30 m telescope, respectively. RRLs were detected at all the frequencies except 1.4 GHz, where a sensitive upper limit was obtained. We also present continuum flux measurements at these frequencies as well as at 327 MHz made with the VLA. The continuum spectrum, which has a spectral index alpha similar to -0.6 (S-nu proportional to nu(alpha)) between 5 and 10 GHz, shows a break near 1.5 GHz, a prominent turnover below 500 MHz, and a flatter spectral index above 50 GHz. We show that a model with three components of ionized gas with different densities and area covering factors can consistently explain both RRL and continuum data. The total mass of ionized gas in the three components is 3.2 x 10(7) M., requiring 3 x 10(5) O5 stars with a total Lyman continuum production rate N-Lyc similar to 1.3 x 10(55) photons s(-1). The ratio of the expected to observed Br alpha and Br gamma fluxes implies a dust extinction A(V) similar to 45 mag. The derived Lyman continuum photon production rate implies a continuous star formation rate (SFR) averaged over the lifetime of OB stars of similar to 240 M yr(-1). The Lyman continuum photon Production rate of similar to 3% associated with the high-density H II regions implies a similar SFR at recent epochs (t < 10(5) yr). An alternative model of high-density gas, which cannot be excluded on the basis of the available data, predicts 10 times higher SFR at recent epochs. If confirmed, this model implies that star formation in Arp 220 consists of multiple starbursts of very high SFR (few times 10(3) M. yr(-1)) and short duration (similar to 10(5) yr). The similarity of IR excess, L-IR/L-Ly alpha similar to 24, in Arp 220 to values observed in starburst galaxies shows that most of the high luminosity of Arp 220 is due to the ongoing starburst rather than to a hidden active galactic nucleus (AGN). A comparison of the IR excesses in Arp 220, the Galaxy, and M33 indicates that the starburst in Arp 220 has an initial mass function that is similar to that in normal galaxies and has a duration longer than 107 yr. If there was no infall of gas during this period, then the star formation efficiency (SFE) in Arp 220 is similar to 50%. The high SFR and SFE in Arp 220 is consistent with their known dependences on mass and density of gas in star-forming regions of normal galaxies.
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Contenido: Editorial – Sesenta años después / Mario Enrique Sacchi – Homenaje a Cornelio Fabro : La importancia del padre Fabro en la búsqueda de un tomismo esencial / Mons. Héctor Aguer – Le premesse filosofiche dell’antitotalitarismo e dell’antinihilismo político di Cornelio Fabro / Danilo Castellano – La noción de libertad en el tomismo esencial de Cornelio Fabro / Christian Ferraro, Ive – De la libertad al ser en Cornelio Fabro / Marcelo Sánchez Sorondo -- Artículos : Aristóteles, fuente principal del De principiis naturae / Thomas Rego – La gracia de la medida: Afrodita, salvadora del placer / Beatriz Bossi López – La disolución de las identidades en la cultura contemporánea / Marisa Mosto – Consecuencias normativas de la naturaleza / José Tomás Alvarado Marambio – Acción y sentido en John Dewey / Juan Carlos Pablo Ballesteros – El problema del innatismo en Antonio Rosmini (parte I) / Juan Francisco Franck – Jacques Maritain y la polémica sobre la Teoría de la Relatividad / Oscar H. Beltrán – La cuestión filosófica de la expansión del universo / Mario Enrique Sacchi – Notas y reseñas – Bibliografía -- Resúmenes de los artículos
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O Relator Bernardo Cabral decidiu dar tratamento privilegiado na distribuição de recursos públicos para as regiões Norte, Nordeste e Centro-Oeste. O Deputado Joaci Góes (PMDB-BA) opina que a mais importante das propostas acolhidas é a da regionalização dos orçamentos. A Deputada Sandra Cavalcanti (PFL-RJ) esclarece que os principais avanços foram a permanência da Zona Franca de Manaus e a mudança na maneira de fazer os repasses dos recursos da União, que servirão para o fomento do desenvolvimento das regiões. O Senador Fernando Henrique Cardoso (PMDB-SP) propõe ao Relator da Assembleia Nacional Constituinte (ANC) a divisão da votação em duas partes. O Senador Virgílio Távora (PDS-CE) avalia que não há previsão para o encerramento dos trabalhos. A Bancada Feminina luta não apenas pelo direitos das mulheres, mas também por avanços em outras áreas, como a Reforma Agrária. A Deputada Wilma Maia (PDS-CE) pede título de propriedade da terra para homens ou mulheres, esposas ou companheiras. A Deputada Anna Maria Rattes (PFL-RJ) afirma o engajamento da bancada feminina em todos os pontos polêmicos da Assembleia Nacional Constituinte (ANC). A Deputada Moema São Thiago (PDT-CE) informa que a mulher pode esperar reconhecimento da igualdade entre homens e mulheres. Velado o corpo de Marcos Freire, no Salão Negro do Congresso Nacional , com missa de corpo presente.
Assessment of the structural properties of GaAs/Si epilayers using X-ray (004) and (220) reflections
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We improved the method previously used to determine the lattice constants and misorientation of GaAs/Si by recording the patterns of X-ray (004) and (220) reflections. The (220) reflection was measured from the (110) cross section of a GaAs/Si epilayer. The structural properties of the GaAs/Si epilayers grown by metal-organic chemical-vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were investigated. The rotation angle of GaAs/Si epilayers grown by MOCVD using an a-Si buffer layer is very small and the lattice constants of these GaAs/Si epilayers agree quite well with elastic theory.
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2005
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Torrefaction based co-firing in a pulverized coal boiler has been proposed for large percentage of biomass co-firing. A 220 MWe pulverized coal-power plant is simulated using Aspen Plus for full understanding the impacts of an additional torrefaction unit on the efficiency of the whole power plant, the studied process includes biomass drying, biomass torrefaction, mill systems, biomass/coal devolatilization and combustion, heat exchanges and power generation. Palm kernel shells (PKS) were torrefied at same residence time but 4 different temperatures, to prepare 4 torrefied biomasses with different degrees of torrefaction. During biomass torrefaction processes, the mass loss properties and released gaseous components have been studied. In addition, process simulations at varying torrefaction degrees and biomass co-firing ratios have been carried out to understand the properties of CO2 emission and electricity efficiency in the studied torrefaction based co-firing power plant. According to the experimental results, the mole fractions of CO 2 and CO account for 69-91% and 4-27% in torrefied gases. The predicted results also showed that the electrical efficiency reduced when increasing either torrefaction temperature or substitution ratio of biomass. A deep torrefaction may not be recommended, because the power saved from biomass grinding is less than the heat consumed by the extra torrefaction process, depending on the heat sources.
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