633 resultados para Cambrian Explosion


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Morphological and U-Pb isotope studies on sedimentary zircons reflect the orogenic evolution of their former host rocks. The orogenic history of detrital zircons from the Trinity Peninsula Formation (TPF) defines the former geological surrounding of the sedimentation basin of the TPF. Same few weil rounded, polycyclic zircons of Precambrian age and Cambrian overprint give hints for an old cratonic source rock. Because of their very low frequency compared with euhedral types, the contribution of an cratonic shield area to the bulk of the sedimentary debris is neglectable low. Euhedral zircons of granitoid origin and Carboniferous age indicate a derivation from an area of widespread Carboniferous intrusions. Except for southern South America and unsurveyed regions in the Antarctic Peninsula itself, no region could deliver zircons with a Carboniferous age record. The only acceptable explanation for the origin of these zircons is a position of the Antarctic Peninsula during the sedimentation of the TPF approximately southwest of southern South America.

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High- to very-high-grade migmatitic basement rocks of the Wilson Hills area in northwestern Oates Land (Antarctica) form part of a low-pressure high-temperature belt located at the western inboard side of the Ross-orogenic Wilson Terrane. Zircon, and in part monazite, from four very-high grade migmatites (migmatitic gneisses to diatexites) and zircon from two undeformed granitic dykes from a central granulite-facies zone of the basement complex were dated by the SHRIMP U-Pb method in order to constrain the timing of metamorphic and related igneous processes and to identify possible age inheritance. Monazite from two migmatites yielded within error identical ages of 499 +/- 10 Ma and 493 +/- 9 Ma. Coexisting zircon gave ages of 500 +/- 4 Ma and 484 +/- 5 Ma for a metatexite (two age populations) and 475 +/- 4 Ma for a diatexite. Zircon populations from a migmatitic gneiss and a posttectonic granitic dyke yielded well-defined ages of 488 +/- 6 Ma and 482 +/- 4 Ma, respectively. There is only minor evidence of age inheritance in zircons of these four samples. Zircon from two other samples (metatexite, posttectonic granitic dyke) gave scattered 206Pb-238U ages. While there is a component similar in age and in low Th/U ratio to those of the other samples, inherited components with ages up to c. 3 Ga predominate. In the metatexite, a major detrital contribution from 545 - 680 Ma old source rocks can be identified. The new age data support the model that granulite- to high-amphibolite-facies metamorphism and related igneous processes in basement rocks of northwestern Oates Land were confined to a relatively short period of time of Late Cambrian to early Ordovican age. An age of approximately 500 Ma is estimated for the Ross-orogenic granulite-facies metamorphism from consistent ages of monazite from two migmatites and of the older zircon age population in one metatexite. The variably younger zircon ages are interpreted to reflect mineral formation in the course of the post-granulite-facies metamorphic evolution, which led to a widespread high-amphibolite-facies retrogression and in part late-stage formation of ms+bi assemblages in the basement rocks and which lasted until about 465 Ma. The presence of inherited zircon components of latest Neoproterozoic to Cambrian age indicates that the high- to very-grade migmatitic basement in northwestern Oates Land originated from clastic series of Cambrian age and, therefore, may well represent the deeper-crustal equivalent of lower-grade metasedimentary series of the Wilson Terrane.

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We used a novel system of three continuous wave Doppler radars to successfully record the directivity of i) Strombolian explosions from the active lava lake of Erebus volcano, Antarctica, ii) eruptions at Stromboli volcano, Italy, and iii) a man-made explosion in a quarry. Erebus volcano contains a convecting phonolite lava lake, presumably connected to a magma chamber at depth. It is one of the few open vent volcanoes that allow a direct observation of source processes during explosions. Its lava lake is the source of frequent violent Strombolian explosions, caused by large gas bubbles bursting at the lake surface. The exact mechanism of these bubble bursts is unclear, as is the mechanism of the creation of the infrasound signal accompanying the explosions. We use the Doppler radar data to calculate the directivity of Strombolian eruptions at Erebus. This allows us to derive information about the expected type of infrasound source pattern (i.e. the role of a dipole in addition to the monopole signature) and the physical structure of the volcano. We recorded 10 large explosions simultaneously with three radars, enabling us to calculate time series of 3D directivity vectors (i.e. effectively 4D), which describe the direction of preferred expansion of the gas bubble during an explosion. Such directivity information allows a comparison to dipole infrasound radiation patterns recorded during similar explosions only a few weeks later. Video observations of explosions support our interpretation of the measurements. We conclude that at Erebus, the directivity of explosions is mainly controlled by random processes. Since the geometry of the uppermost conduit is assumed to have a large effect on the directivity of explosions, the results suggest a largely symmetrical uppermost conduit with a vertical axis of symmetry. For infrasound recordings, a significant dipole signature can be expected in addition to the predominant monopole signature.

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National Highway Safety Bureau, Washington, D.C.

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At head of title: Engineering and design.

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Title from caption.

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The Breslau arts scene during the Weimar period was one of the most vibrant in all of Germany, yet it has disappeared from memory and historiography. Breslau was a key center for innovative artistic production during the Weimar Republic; recovery of its history will shed new light on German cultural dynamics in the 1920s. Such a study has art historical significance because of the incredible extent of innovation that occurred in almost every intellectual field, advances that formed the basis for aesthetic modernism internationally and continue to affect the course of visual art and architecture today. Architecture education, just one example in many, is still largely based on a combination of the Bauhaus model from the 1920s and the model developed at the Breslau Academy of Fine and Applied Art. The exploratory attitude encouraged in Weimar era arts endeavors, as opposed to the conformism of academic art, is still a core value promoted in contemporary art and architecture circles. Given the long-lasting influence of Weimar culture on modernism one would expect to find a spate of studies examining every aspect of its cultural production, but this is not the case. Recent scholarship is almost exclusively focused on Berlin and the Dessau Bauhaus. Although both interests are understandable, the creative explosion was not confined to these cities but was part of a larger cultural ethos that extended into many of the smaller regional centers. The Expressionist associations the Blaue Reiter in Munich and Brücke in Dresden are two well-known examples. Equally, innovation was not confined to a few monumental projects like the Stuttgart Weissenhofsiedlung but part of a broader national cultural ethos. The dispersion of modernism occurred partly because of the political history of Germany as a loosely joined confederation of small city states and principalities that had strong individual cultural identities before unification in 1871 but also because of the German propensity to value and take intense pride in the Heimat, understood both as the hometown and the region. Heimatliebe translated into generous support for cultural institutions in outlying cities. Host to a roster of internationally acclaimed artists and architects, major collectors, arts organizations, museums, presses, galleries, and one of the premier German arts academies of the day, Breslau boasted a thriving modern arts scene until 1933 when the Nazis began their assault on so-called "degenerate" art. This book charts the cultural production of Breslau-based artists, architects, art collectors, urban designers, and arts educators, who were especially interesting because they operated in the space between the margins of Weimar-era cultural debates. Rather than accepting the radical position of the German avant-garde or the reactionary position of German conservatives, many Breslauers sought a middle ground. It is the first book in English to address this history and presents the history in a manner unique to any studies currently on the market. 'Beyond the Bauhaus' explores the polyvalent and contradictory nature of cultural production in Breslau in order to expand the cultural and geographic scope of Weimar history; the book asserts a reciprocal dimension to the relationship between regional culture and national culture, between centers like Breslau and the capital Berlin. With major international figures like the painters Otto Mueller and Oskar Moll, architects Hans Scharoun and Adolf Rading, urban planners Max Berg and Ernst May, collectors Ismar Littmann and Max Silberberg, and an art academy that by 1929 was considered the best in Germany, Breslau clearly had significance to narratives of Weimar cultural production. 'Beyond the Bauhaus' contributes the history of German culture during the Weimar Republic. It belongs alongside histories of art, architecture, urban design, exhibition, collecting, and culture; histories of the Bauhaus; histories of arts education more broadly; and German history. The readership would include those interested in German history; German art, architecture, urban design, planning, collecting, and exhibition history; in the avant-garde; the development of arts academies and arts pedagogy; and the history of Breslau and Silesia.

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"Bibliography of the Cambrian and Carboniferous rocks of the Narragansett basin": p. 212-214.

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continued from verso: showing high banded Cambrian sandstone cliffs rising abruptly from Lake Superior along the w. edge of the island

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Title from caption.

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Molecular investigation of the origin of colour vision has discovered five visual pigment (opsin) genes, all of which are expressed in an agnathan (jawless) fish, the lamprey Geotria australis. Lampreys are extant representatives of an ancient group of vertebrates whose origins are thought to date back to at least the early Cambrian, approximately 540 million years ago [1.]. Phylogenetic analysis has identified the visual pigment opsin genes of G. australis as orthologues of the major classes of vertebrate opsin genes. Therefore, multiple opsin genes must have originated very early in vertebrate evolution, prior to the separation of the jawed and jawless vertebrate lineages, and thereby provided the genetic basis for colour vision in all vertebrate species. The southern hemisphere lamprey Geotria australis (Figure 1A,B) possesses a predominantly cone-based visual system designed for photopic (bright light) vision [2. S.P. Collin, I.C. Potter and C.R. Braekevelt, The ocular morphology of the southern hemisphere lamprey Geotria australis Gray, with special reference to optical specializations and the characterisation and phylogeny of photoreceptor types. Brain Behav. Evol. 54 (1999), pp. 96–111.2. and 3.]. Previous work identified multiple cone types suggesting that the potential for colour vision may have been present in the earliest members of this group. In order to trace the molecular evolution and origins of vertebrate colour vision, we have examined the genetic complement of visual pigment opsins in G. australis.

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Carbon nanotubes (CNT) are well-ordered, high aspect ratio allotropes of carbon. The two main variants, single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) both possess a high tensile strength, are ultra-light weight, and have excellent chemical and thermal stability. They also possess semi- and metallic-conductive properties. This startling array of features has led to many proposed applications in the biomedical field, including biosensors, drug and vaccine delivery and the preparation of unique biomaterials such as reinforced and/or conductive polymer nanocomposites. Despite an explosion of research into potential devices and applications, it is only recently that information on toxicity and biocompatibility has become available. This review presents a summary of the performance of existing carbon biomaterials and gives an outline of the emerging field of nanotoxicology, before reviewing the available and often conflicting investigations into the cytotoxicity and biocompatibility of CNT. Finally, future areas of investigation and possible solutions to current problems are proposed. (c) 2005 Elsevier Ltd. All rights reserved.

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From the break up of the New Left into single issue groups at the end of the 1960s came a variety of groups representing the peace movement, environmental movement, student movement, women’s movement, and gay liberation movement. This explosion of new social movement activism has been heralded as the age of new radical politics. Many theorists and activists understand new social movements, as replacing the working class as an agent for progressive social change. Scholars and activists now alike debate the possibilities for revolutionary change in this era of multinational capitalism and new nationalisms. This paper examines some of the above claims in the context of the contemporary Serbian civil society. It explores the relationship between the civil society, activism, and narratives in Serbia. In particular, it examines the anti-Milosevic’ movement Otpor! (Resistance), and its discourse, practice and politics in public spaces, through an analysis of narratives of a set of roughly 20 interviews with Otpor! activists, aged 18-35. In the following discussion, then, I will focus on some of the particular dilemmas of contemporary Serbian popular movements - they are dilemmas to do with the growing complexity of media life in the Serbian spaces. I ground my debate on particular uses of the notion of civil society in the narratives of Otpor! activists, while I focus on the question of how do Otpor! activists relate to Leftist/radical politics and the idea of civil society.