991 resultados para 1:504


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Deep basement penetration during Legs 69 and 70 at Hole 504B in the Panama Basin allowed the recovery of a 561.5-meter sequence of basaltic pillows, thin flows, and breccias interspersed with thick massive flows. The lavas, which are aphyric to moderately plagioclase-olivine-clinopyroxene phyric, are petrologically indistinguishable from typical mid-ocean-ridge basalts (MORB). Some units are distinctive in that they carry accessory chrome-spinel microphenocrysts or emerald green clinopyroxene phenocrysts. Major and trace element analyses were carried out on 67 samples using X-ray fluorescence techniques. The basalts resemble normal MORB in terms of major elements. However, the trace element analyses show that most of the basalts are characterized by very strong depletion in the more incompatible elements compared with, for instance, normal (N type) MORB from the Atlantic at 22°N. Interdigitated with these units are one or two units that have distinctly higher incompatible element concentrations similar to those in basalts of the transitional (T) type from the Reykjanes Ridge (63°N in the Mid-Atlantic Ridge). All the basalts appear to have undergone some high-level crystal fractionation, although this has not proceeded to the extent of yielding ferrobasalts as it has at the adjacent Galapagos Spreading Center or along the East Pacific Rise. The magnetic anomalies are of lower amplitude than in the latter two regions, which suggests that the absence of ferrobasalts may be a general feature of the ocean crust generated at the Costa Rica Rift. The presence of two distinct magma types, one strongly depleted and the other moderately enriched in incompatible elements, suggests that magma chambers at the spreading center are discontinuous rather than continuous and that there is some chemical heterogeneity in the underlying mantle source. Observed variations in incompatible element ratios of basalts from the more depleted group could, however, reflect mixing between these two magma types. In general it would appear that the mantle feeding the Costa Rica Rift is significantly more depleted in incompatible trace elements than that feeding the Mid-Atlantic Ridge.

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Based on a qualitative and quantitative evaluation of Recent sediments samples (top 3 cm of cores as well as Petersen grab samples) from the Drake Passage, between South America and Antarctica, the distribution of planktonic foraminifera and their relation to oceanographic conditions was investigated. The Antarctic Convergence - the northern limit of the cold Antarctic Surface Water - is shown to be of major importance in controlling the distributional pattern of planktonic species as well as their total numbers. South of the convergence, Globigerina pachyderma is usually the only species found in the sediment. It occurs with abundances not greater than 6000 per gram dry sediment, and at most stations less than 100 specimens per gram of dry sediment were recovered. At a number of deep-sea stations below 3700 m depth approx. no planktonic foraminifera were found at all. It is most probable, that at least some of these stations are located below the limit of CaCO3 dissolution. North of the Antarctic Convergence planktonic foraminiferal numbers are much higher and range from 1800 to 120000 per gram of dry sediment. Eight species are the major constituents of the population: Globigerina pachyderma, Globigerina bulloides, Globogerina quinqueloba, Globigerina inflata, Globorotalia truncatolinoides, Globorotalia scitula, Globigerinita glutinata and Globigerinita uvula. The widespread occurrence of Globorotalia truncatulinoides, which in the northern hemisphere is usually a subtropical form, is especially noteworthy. Another Globigerina, morphologically similar to G. pachyderma, has been recognized frequently north of the Antarctic Convergence. Globigerina megastoma which has its type area in the Drake Passage, has been found only rarely. Orbulina universa occurs in samples from the areas of higher water temperature around the South American Continent. Globigerina pachyderma is predominantly sinistrally coiled throughout the area investigated, but a slight increase in the percentage of dextrally coiled specimens may be noticed with increasing water temperature, i.e. from south to north.

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The hearings, paged continuously, as in this issue, were published also in current numbers. The "Report of the committee appointed pursuant to House resolutions 429 and 504 to investigate the concentration of control of money and credit", together with "Views of the minority" by Everis A. Hayes, Frank E. Guernsey and William H. Heald, and "Views of Mr. McMorran", was published as House rept. 1593, 62d Cong., 3d sess. The "Report" without minority views, and the "Minority report of Henry McMorran" were also published separately without document series notes.

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A TÁMOP „Fenntartható fejlődés, élhető régió, élhető települési táj” alprojektje négy tudományterület szakembereit fogta össze. Az eredmény három kötet, és bennük összesen negyvenhárom tanulmány. A Corvinus Egyetem négy karának, a Gazdálkodástudományi, a Közgazdaságtudományi, a Kertészettudományi és a Tájépítészeti Karok munkatársainak három éves kutatómunkáját tükrözik a kötetek, ami nyilván nemcsak a szerzők, hanem azoknak a műhelyeknek a szellemisége is, amelyekben a szerzők dolgoznak. Konferenciákon, műhelyvitákon csiszolódtak a tanulmányok, mégsem állíthatjuk, hogy mindegyikben letisztult, konszenzust jelentő álláspontokat fogalmaztak meg a szerzők. Különösen igaz ez a társadalomtudományi tanulmányokra, de a klímaváltozással foglalkozó határterületi írásokra is, ahol sokszor még a fogalmak jelentését illetően nem jutottak konszenzusra. Vannak szerencsésebb diszciplínák, például a kertészeti tudományok, amelyeknél reprodukálható eredményekről adhatnak számot a kutatók, és vannak tanulmányok, amelyek a művészetek, a táj- és település tervezés területére vezetnek el bennünket, de a művészeteket illetően is felesleges a konszenzust keresni.

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Compressional- and shear-wave velocity logs (Vp and Vs, respectively) that were run to a sub-basement depth of 1013 m (1287.5 m sub-bottom) in Hole 504B suggest the presence of Layer 2A and document the presence of layers 2B and 2C on the Costa Rica Rift. Layer 2A extends from the mudline to 225 m sub-basement and is characterized by compressional-wave velocities of 4.0 km/s or less. Layer 2B extends from 225 to 900 m and may be divided into two intervals: an upper level from 225 to 600 m in which Vp decreases slowly from 5.0 to 4.8 km/s and a lower level from 600 to about 900 m in which Vp increases slowly to 6.0 km/s. In Layer 2C, which was logged for about 100 m to a depth of 1 km, Vp and Vs appear to be constant at 6.0 and 3.2 km/s, respectively. This velocity structure is consistent with, but more detailed than the structure determined by the oblique seismic experiment in the same hole. Since laboratory measurements of the compressional- and shear-wave velocity of samples from Hole 504B at Pconfining = Pdifferential average 6.0 and 3.2 km/s respectively, and show only slight increases with depth, we conclude that the velocity structure of Layer 2 is controlled almost entirely by variations in porosity and that the crack porosity of Layer 2C approaches zero. A comparison between the compressional-wave velocities determined by logging and the formation porosities calculated from the results of the large-scale resistivity experiment using Archie's Law suggest that the velocity- porosity relation derived by Hyndman et al. (1984) for laboratory samples serves as an upper bound for Vp, and the noninteractive relation derived by Toksöz et al. (1976) for cracks with an aspect ratio a = 1/32 serves as a lower bound.

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The composition and abundance of algal pigments provide information on phytoplankton community characteristics such as photoacclimation, overall biomass and taxonomic composition. In particular, pigments play a major role in photoprotection and in the light-driven part of photosynthesis. Most phytoplankton pigments can be measured by high-performance liquid chromatography (HPLC) techniques applied to filtered water samples. This method, as well as other laboratory analyses, is time consuming and therefore limits the number of samples that can be processed in a given time. In order to receive information on phytoplankton pigment composition with a higher temporal and spatial resolution, we have developed a method to assess pigment concentrations from continuous optical measurements. The method applies an empirical orthogonal function (EOF) analysis to remote-sensing reflectance data derived from ship-based hyperspectral underwater radiometry and from multispectral satellite data (using the Medium Resolution Imaging Spectrometer - MERIS - Polymer product developed by Steinmetz et al., 2011, doi:10.1364/OE.19.009783) measured in the Atlantic Ocean. Subsequently we developed multiple linear regression models with measured (collocated) pigment concentrations as the response variable and EOF loadings as predictor variables. The model results show that surface concentrations of a suite of pigments and pigment groups can be well predicted from the ship-based reflectance measurements, even when only a multispectral resolution is chosen (i.e., eight bands, similar to those used by MERIS). Based on the MERIS reflectance data, concentrations of total and monovinyl chlorophyll a and the groups of photoprotective and photosynthetic carotenoids can be predicted with high quality. As a demonstration of the utility of the approach, the fitted model based on satellite reflectance data as input was applied to 1 month of MERIS Polymer data to predict the concentration of those pigment groups for the whole eastern tropical Atlantic area. Bootstrapping explorations of cross-validation error indicate that the method can produce reliable predictions with relatively small data sets (e.g., < 50 collocated values of reflectance and pigment concentration). The method allows for the derivation of time series from continuous reflectance data of various pigment groups at various regions, which can be used to study variability and change of phytoplankton composition and photophysiology.