930 resultados para derivation
Resumo:
Crystal size measurements have been carried out on tephra fall layers of Miocene to recent age from Sites 998, 999, and 1000 in the western Caribbean Sea. Maximum crystal size is used as a proxy for the grain size characteristics of the layers and an index of atmospheric dispersal from source eruptions. Crystal sizes range from 50 to 650 µm with the majority falling between 200 and 300 µm. All three sites exhibit a coarsening in the grain size of tephra layers with increasing age to the early Miocene that broadly correlates with an increase in the frequency of layers. Analysis of the present lower and upper level atmospheric circulation in the western Caribbean suggests that the layers were derived from source eruptions to the west of the sites somewhere in the Central American region. Minimum distances to these sources are of the order of 700 km. Crystal sizes in tephra layers at these distances are consistent with their derivation from energetic pyroclastic flow-forming eruptions that injected tephra to stratospheric levels by large-scale co-ignimbrite and plinian-style plumes. Coarsening of the layers during the Miocene peak of explosive volcanism cannot be attributed to any major change in paleowind intensity and is taken to represent the occurrence of more energetic eruptions that were able to disperse tephra over larger areas.
Resumo:
Basalts from the base of a small seamount on ~1.5-m.y.-old crust west of the East Pacific Rise (EPR) at 9°N are intermediate in chemical and isotopic composition between light-rare-earth-element-depleted tholeiite (normal midocean ridge basalt (MORB)) and alkali basalt. Like oceanic alkali basalt, these rocks contain significantly more Ba, K, P, Sr, Ti, U, and Zr than normal MORB. Since the absolute abundances of these elements are still well below alkali basalt levels, the label transitional is adopted for these basalts. A series of fractionated MORB also occurs in this area, northwest of the Siqueiros Fracture Zone - Transform Fault. The normal tholeiites are either olivine-plagioclase or plagioclase-clinopyroxene phyric, while the transitional basalts are spinel-olivine phyric. Fractional crystallization quantitatively accounts for the chemical variability of the tholeiitic series but not for the transitional basalts. The tholeiitic series probably evolved in a crustal magma chamber ~4 km below the crest of the East Pacific Rise. 143Nd/144Nd and other chemical data suggest that the large-ion-lithophile-enriched transitional basalts may represent a hybrid of normal MORB and Siqueiros area alkali basalt. Incompatible element plots of K, P, and U indicate possible derivation of the transitional basalts by magma mixing. Magma mixing of unfractionated normal MORB and Siqueiros alkali basalt has been quantified. Derivation of the transitional basalts from a 1:1 mixture is supported by all available chemical data, including Cr, Cu, Nd, Ni, Sm, Sr, U, and V. This magma mixing apparently occurred at ?<~30 km depth within a few tens of kilometers from the EPR axis. These Siqueiros area EPR transitional basalts are compared with Mid-Atlantic Ridge (MAR) transitional basalts from the Iceland and Azores areas. The Siqueiros area basalts reflect a profound chemical and isotopic heterogeneity in the upper mantle, similar to that found along the MAR. Unlike the MAR, the EPR shows no evidence of plumelike bulges and associated large-scale outpourings of nonnormal MORB resulting from these mantle heterogeneities. Siqueiros alkali basalt and MORB, as well as transitional basalt and MORB, were recovered from single dredge hauls. Such close spatial and temporal proximity of the inferred mantle sources places severe constraints on geometric and physicochemical upper mantle models.
Resumo:
Fossil manganese nodules and encrustations from seamount' and basin' localities in the Transdanubian Central Mountains of Hungary are lithologically, mineralogically and chemically similar to some modern marine ferromanganese oxide deposits, and show no evidence of postdepositional changes other than cementation. Five groups of deposits were encountered: Fe/Mn nodules, encrusted shells, pavements, stains, and Fe oxide encrusted intraclasts, the first three of which are specific to the 'seamount' environment and the last to the basins'. Optical and electron microprobe investigation of the samples shows them to exhibit many similarities with modern ferromanganese oxide deposits, and that many of the nodules are surrounded by a halo of dispersed ferromanganese oxides, strongly suggesting that they continued to accrete metals through the pore waters of unlithified sediments for a period after burial. By contrast, pavements which appear to have grown on hardgrounds at the sea floor show little or no evidence of derivation of metals from underlying sediments. Geochemical investigations on the deposits show the seamount' varieties to be closer in composition to most modern nodules and crusts than the basin' varieties, and that the latter are essentially manganese and trace-element-poor ferruginous deposits. Nevertheless, all can be more or less compositionally equated with modern ferromanganese oxide deposits forming in marginal Atlantic environments, which would be in accord with the proposed depositional environment of the Transdanubian Central Mountains based on other evidence.
Resumo:
The derivation of a detailed sea-surface paleotemperature curve for the middle Miocene-Holocene (10-0 Ma) from ODP Site 811 on the Queensland Plateau, northeast Australia, has clarified the role of sea-surface temperature fluctuations as a control on the initiation and development of the extensive carbonate platforms of this region. This curve was derived from isotopic analyses of the planktonic foraminifer Globigerinoides ruber, and converted to temperature using the surface-water paleotemperature equation accounting for variations in global ice volume. The accuracy of these data were confirmed by derivation of paleotemperatures using the water column isotopic gradient (Delta delta18O), corrected for salinity and variations in seafloor water mass temperature. Results indicate that during this period surface-water temperatures were, on average, greater than the minimum required for tropical reef growth (20°C; Veron, 1986), with the exception of the late Miocene and earliest early Pliocene (10-4.9 Ma), when there were repeated intervals of temperatures between 18-20°C. Tropical reef growth on the Queensland Plateau was extensive from the early to early middle Miocene (~21-13 Ma), after which reef development began to decline. A lowstand near 11 Ma probably exposed shallower portions of the plateau; after re-immersion near 7 Ma, the areal extent of reef development was greatly reduced (~ 50%). Paleotemperature data from Site 811 indicate that decreased sea-surface temperatures were likely to have been instrumental in reducing the area of active reef growth on the Queensland Plateau. Reduced reefal growth rates continued until the late Pliocene or Quaternary, despite the increase of average sea-surface paleotemperatures to 22-23°C. Studies on modern corals show that when sea-surface temperatures are below ~24°C, as they were from the late Miocene to the Pleistocene off northeast Australia, corals are stressed and growth rates are greatly reduced. Consequently, when temperatures are in this range, corals have difficulty keeping pace with subsidence and changing environmental factors. In the late Pliocene, sedimentation rates increased due to increases in non-reefal carbonate production and falling sea levels. It was not until the mid-Quaternary (0.6-0.7 Ma) that sea-surface paleotemperatures increased above 24°C as a result of the formation of a western Coral Sea warm water pool. Because of age discrepancies, it is unclear exactly when an effective barrier developed on the central Great Barrier Reef; the formation of the warm water pool was likely to have either assisted the formation of this barrier and/or permitted increased coral growth rates. Fluctuations in sea-surface temperature can account for much of the observed spatial and temporal variations of reef growth and carbonate platform distribution off northeast Australia, and therefore we conclude that paleotemperature variations are a critical control on the development of carbonate platforms, and must be considered an important cause of ancient platform "drowning".
Geometrical attenuation factors for gamma radiation from cylindrical and spherical surface sources /
Resumo:
Issued September 15, 1963.
Resumo:
Reports 2 and 3 by E. Isaacson, J. J. Stoker, and A. Troesch.
Resumo:
A collection of miscellaneous pamphlets on the romance languages.
Resumo:
cont. VI. The application of standard measurements to school administration. [By] D.C. Bliss. VII. A half-year's progress in the achievement of one school system. A. The progress as measured by the Thorndike visual vocabulary test. B. The progress as measured by the Courtis tests, series B. [By] H.G. Childs. VIII. Courtis tests in arithmetic: value to superintendents and teacher. [By] S.A. Courtis. IX. Use of standard tests at Salt Lake City, Utah. [By] E. P. Cubberley. X. Reading. [By] C.H. Judd. XI. Studies by the Bureau of research and efficiency of Kansas City, Mo. [By] George Melcher. XII. The effects of efficiency tests in reading on a city school system. [By] E.E. Oberholtzer. XIII. Investigation of spelling in the schools of Oakland, Cal. [By] J.B. Sears. XIV. Standard tests as aids in the classification and promotion of pupils. [By] Daniel Starch. XV. The use of mental tests in the school. [By] G.M. Whipple.
Resumo:
"DOT-I-84-01."
Resumo:
O objetivo desta tese é compreender, a partir das categorias trabalho e consumo, como se constituem as relações das redes de colaboração da empresa de tendências de consumo Trendwatching. No âmbito acadêmico, literatura recente revela o aparecimento de novos conceitos, como prosumer, co-criação e públicos produtivos para explicar as transformações no mundo do trabalho que envolvem cada vez mais a participação do consumidor para que o valor se realize. Dessa forma, os fundamentos teóricos que embasam esta tese providenciam elementos sobre os conceitos de valor, trabalho imaterial, consumo e suas interrelações. A coleta de dados ocorreu, em sua maior parte, na matriz da empresa em Londres durante o ano de 2015, sendo composta por: (1) realização de 31 entrevistas semi-estruturadas com spotters, funcionários e clientes da empresa; (2) observação em campo durante 3 meses, período este registrado em um diário de campo; (3) dados obtidos por meios virtuais, através do site da Trendwatching. Os dados foram analisados por meio da Análise de Conteúdo, onde, a partir de um processo de derivação, foram encontradas 49 categorias iniciais, 10 intermediárias e 3 finais. Por meio de um processo de derivação, chegou-se em 10 categorias intermediárias: (1) quem é o spotter; (2) busca de informações pelo spotter; (3) motivação e recompensa dos spotters; (4) spotters e a comunidade TW:IN; (5) formação dos spotters; (6) imagem da Trendwatching; (7) Ambiente de trabalho; (8) O que a Trendwatching vende; (9) base de dados; (10) tendências. Com estas categorias intermediárias em mãos, realizou-se novamente um processo de derivação para chegar nas categorias finais, que são: (1) spotters; (2) trabalho; (3) informação. Os resultados da pesquisa permitem mostrar que o spotter – assim chamado o indivíduo que compõe a rede a colaboração da Trendwatching – é o principal produto/serviço vendido pela empresa. A partir das categorias finais, retorna-se à pergunta de pesquisa, de modo a providenciar contribuições da tese para o campo, que são: (a) ampliar a discussão sobre criação de valor em Estudos Organizacionais, identificando diferentes conceitos e novas formas de apropriação do valor pelo capital implicados nas interações e interfaces entre trabalho e consumo; (b) demonstrar como a operacionalização da Análise de Conteúdo pode auxiliar na organização de dados empíricos virtuais (análise do site); (c) estimular que Estudos de Caso sejam, com mais frequência, realizados em organizações cujo trabalho seja imaterial por excelência.
Resumo:
En trabajos anteriores (Romero, 2008a y b, Alabart Lago, L., P. Díaz y G. Herrera, 2012, Alabart Lago, L. y Herrera, G., 2013) se intentó mostrar que el mecanismo interpretativo que propone la TR podría resultar adecuado como uno de los sistemas externos (también interpretativos) postulados por la GG, más precisamente, el sistema llamado CI. La relación que intentamos establecer tendrá en cuenta lo siguiente como marco teórico: a) En TR se afirma que la interpretación de un enunciado se deriva de las estructuras sintácticas, y esta derivación se realiza "en paralelo" con la derivación de estructuras llevada a cabo por las operaciones del componente sintáctico. b) En las últimas propuestas de la GG, extensiones y revisiones del PM propuesto en Chomsky (1995) no solo se dejan de lado los niveles de representación internos SP y ES sino también se considera prescindible la interfaz FL (Chomsky, 2005). Las estructuras generadas se transfieren a los sistemas externos en cuanto rasgos formales de las Categorías Funcionales son valorados. Mantendremos la noción de que el sistema computacional es relativamente irrestricto y que sus operaciones son condicionadas solo por Atracción y las llamadas "condiciones de legibilidad" impuestas por los sistemas externos, fundamentalmente el Principio de Interpretación Completa (PIC). c) Tendremos en cuenta la propuesta de Leonetti y Escandell Vidal (2004), que sostiene que las CCFF de la GG pueden considerarse equivalentes a las Categoría Procedimentales propuestas por la TR. En este sentido consideraremos válida la afirmación de Chomsky (1998) acerca de que las CCFF centrales (C, T, v y D) tienen propiedades semánticas. d) Otro factor que tendremos en cuenta es la noción de fase en la derivación, considerándola correcta en los términos expuestos en Chomsky (2001 y 2005) y Gallego (2007 y 2009), con ciertas modificaciones. Nuestra hipótesis puede resumirse en lo siguiente: Las operaciones de extracción de inferencias propuestas por TR se aplican durante la derivación sintáctica independientemente de que se haya transferido o no una fase. Es más, esperamos poder demostrar que algunos mecanismos inferenciales imponen ciertas condiciones que afectan a la valoración de los rasgos de las CCFF. Pretendemos también intentar mostrar que además de los núcleos de fase reconocidos, C y v, debe considerarse fase a SD, porque contiene rasgos específicos de cuyo cotejo y valoración se desprende el valor que recibirán otros rasgos en el curso de la derivación. Con estos fundamentos esperamos poder elaborar una descripción de cómo interactúan ambos sistemas en la derivación de una oración y la asignación (casi simultánea) de significado
Resumo:
We produce families of irreducible cyclic presentations of the trivial group. These families comprehensively answer questions about such presentations asked by Dunwoody and by Edjvet, Hammond, and Thomas. Our theorems are purely theoretical, but their derivation is based on practical computations. We explain how we chose the computations and how we deduced the theorems.
Resumo:
We provide a derivation of a more accurate version of the stochastic Gross-Pitaevskii equation, as introduced by Gardiner et al (2002 J. Phys. B: At. Mol. Opt. Phys. 35 1555). This derivation does not rely on the concept of local energy and momentum conservation and is based on a quasiclassical Wigner function representation of a 'high temperature' master equation for a Bose gas, which includes only modes below an energy cut-off ER that are sufficiently highly occupied (the condensate band). The modes above this cutoff (the non-condensate band) are treated as being essentially thermalized. The interaction between these two bands, known as growth and scattering processes, provides noise and damping terms in the equation of motion for the condensate band, which we call the stochastic Gross-Pitaevskii equation. This approach is distinguished by the control of the approximations made in its derivation and by the feasibility of its numerical implementation.
Resumo:
We derive gap equations for superconductivity in coexistence with ferromagnetism. We treat singlet and triplet states With either equal spin pairing (ESP) or opposite spin pairing (OSP) states, and study the behaviour of these states as a function of exchange splitting. For the s-wave singlet state we find that our gap equations correctly reproduce the Clogston-Chandrasekhar limiting behaviour and the phase diagram of the Baltensperger-Sarma equation (excluding the FFLO region). The singlet superconducting order parameter is shown to be independent of exchange splitting at zero temperature, as is assumed in the derivation of the Clogston-Chandrasekhar limit. P-wave triplet states of the OSP type behave similarly to the singlet state as a function of exchange splitting. On the other hand, ESP triplet states show a very different behaviour. In particular, there is no Clogston-Chandrasekhar limiting and the superconducting critical temperature, T-C, is actually increased by exchange splitting.
Resumo:
In this paper, we present a technique for equilibria characterization of activated carbon having slit-shaped pores. This method was first developed by Do (Do, D. D. A new method for the characterisation of micro-mesoporous materials. Presented at the International Symposium on New Trends in Colloid and Interface Science, September 24-26, 1998 Chiba, Japan) and applied by his group and other groups for characterization of pore size distribution (PSD) as well as adsorption equilibria determination of a wide range of hydrocarbons. It is refined in this paper and compared with the grand canonical Monte Carlo (GCMG) simulation and density functional theory (DFT). The refined theory results in a good agreement between the pore filling pressure versus pore width and those obtained by GCMG and DFT. Furthermore, our local isotherms are qualitatively in good agreement with those obtained by the GCMC simulations. The main advantage of this method is that it is about 4 orders of magnitude faster than the GCMC simulations, making it suitable for optimization studies and design purposes. Finally, we apply our method and the GCMG in the derivation of the PSD of a commercial activated carbon. It was found that the PSD derived from our method is comparable to that derived from the GCMG simulations.