832 research outputs found
A global overview of isotopic heterogeneities in the oceanic mantle
No full textStudies on modern oceanic lithosphere and ophiolites have revealed high degrees of chemical and isotopic heterogeneity in the mantle, as well as isotopic contrasts between mantle and crust. These features cannot be explained just by simple extraction of partial melt, but require considerably more complex petrogenetic processes. Here we present an overview of the present knowledge on isotopic heterogeneities of Sr, Nd, Hf and Os in oceanic peridotites (by reviewing data on modern abyssal peridotites and the Alpine–Apennine ophiolites), and discuss their significance in terms of i) length scale and extent of isotopic heterogeneities in the upper mantle and ii) isotopic mantle–crust relations at oceanic settings. Overall results show that mantle peridotites record significant isotopic heterogeneity, detectable on awide range of length scales,much larger than observed in associated MORB. In addition, abyssal peridotites are on averagemore depleted than MORB. The high degree of isotopic heterogeneity is clear evidence for the inefficiency ofmantle convection in homogenizing mantle rocks. It may be caused by i) variably old depletion events (unrelated to recentMORB production), ii) pyroxenite components in the mantle source, iii) recent pre- and/or post melting metasomatism. Some abyssal peridotites have extremely depleted isotopic compositions, not seen in MORBs, and these have been interpreted as the evidence for old (1 to 2 Ga) refractory domains in the asthenospheric mantle or, alternatively, as evidence for recent incorporation of (also old) subcontinental lithospheric mantle, potentially through delamination during continental breakup. The first hypothesis has been corroborated by finding, in a few ridge segments (e.g. Gakkel Ridge) of correlations between chemical fertility indexes and isotopic (Os, Hf) ratios, indicative of recycling of old residual oceanic lithospheric mantle into the MORB source. However, no general consensus exists yet on the two proposed models. The difference in average isotopic depletion between peridotites and basalts has been also ascribed to the presence of pyroxenites, which have “enriched” isotopic signature relative to the peridotite component. The origin and composition of such small-scale lithological heterogeneities remain however still controversial and poorly constrained, due to the difficulty to link petrologic and geochemical studies with direct field observations, and to the scarcity of chemical and isotopic data on pyroxenites in ophiolitic and abyssal peridotites, i.e. the closest available “proxies” of the MORB mantle. Larger isotopic homogeneity observed in MORB relative to peridotites in single ridge segments clearly reflect their origin as aggregated melts which inevitably “smooth” and averagemantle source heterogeneities. Overall, the questions about the origin and spatial distribution of chemical and isotopic heterogeneities are not resolved, and this calls for detailed field-based studies in spatially-controlled settings to shed light on the issue of small-scale mantle heterogeneities and the role of enriched (e.g. pyroxenites) and highly depleted domains in MORB melting
Albrecht Dürer’s and Cranach’s art at the artistic court of Albrecht Hohenzollern in the capital Königsberg
No full textArtykuł prezentuje wpływy sztuki Albrechta Dürera i warsztatu Cranachów na sztukę Prus Książęcych oraz szczególnie na ich udział w tworzeniu artystycznego oblicza dworu Albrechta Hohenzollerna. Początkowo autor omawia przykłady oddziaływania grafik Martina Schongauera oraz Albrechta Dürera na malarstwo w Prusach Królewskich w okresie przedreformacyjnym. Przywołano tu przykłady z Fromborka i Elbląga oraz jeden z Prus Książęcych, czyli z kościoła w Rychnowie. Następnie przedstawiono kolejne przykłady obecności dzieł sztuki obydwu artystów na dworze Albrechta Hohenzollerna, oddziaływania Wittenbergi i Norymbergi na tworzony przez księcia nowożytny dwór w Królewcu. Tu przedstawiono zarówno działania w zakresie kształcenia miejscowych artystów, jak i pracy wielu wykwalifikowanych rzemieślników na rzecz Albrechta. Wszystkie te działania, jak wykazano, pozwoliły stworzyć bogaty w dzieła sztuki nowożytny dwór renesansowego władcy.This article presents the influence of Albrecht Dürer’s art and the Cranach’s workshop on the art of Ducal Prussia and particularly on their participation in the creation of objects of art on the court of Albrecht Hohenzollern. Initially, the author discusses the impact of Martin Schongauer’s and Albrecht Dürer’s graphic art on the paintings in the Royal Prussia during before Reformation. The two examples comes from Frombork and Elbląg (Royal Prussia)
and one of one from the church in Rychnowo (Ducal Prussia). Next the paper shows other examples of the presence of works of art by both artists at the court of Albrecht Hohenzollern, the influence of Wittenberg and Nuremberg on the early modern royal court created by Prince Albrecht. The paper presents the artistic education of local artists and objects of art made by many skilled craftsmen for Albrecht. All these activities, as shown, have created a modern manor house/court of renaissance ruler
GREGOR - optical design considerations
No full textAfter many years of successful work the Gregory Coude Telescope (GCT) is going to be replaced by GREGOR. This new 1.5 m telescope is the result of design considerations which to a wide extent are based on new technologies. Special aspects of the design are presented, including measures to compensate for optical aberrations caused by instrumental and atmospheric effects (Adaptive Optics). First light is expected for the end of 2004
GREGOR, a 1.5 m Gregory-type telescope for solar observation
No full textGREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an adaptive optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar atmosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the 30 years old Gregory Coude Telescope at the Observatorio del Teide on Tenerife. We describe the optical design and the focal plane instrumentation. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and of the underlying processes. GREGOR will also serve as a test bed for next-generation solar telescopes
Fotogrametria, polityka i przedsiębiorczość a inwentaryzacja zabytków. Albrecht Meydenbauer w Poznańskiem w roku 1885 i 1887
No full textA standard belief as regards the conservation of architectural monuments in the 19thcentury is that the very idea of conservation was commonly accepted, while the monuments of the past were used to promote national identity. On the other hand, photography is also commonly considered a technology that was naturally predisposed to popularize those monuments and/or appropriate them as symbols. For those reasons, the photogrammetric documentation of some buildings from the region of Poznań, made by Albrecht Meydenbauer commissioned to do it by the Prussian government, could be classified as combination of conservation and nationalism, “typical” of the late 19thcentury. However, the author proposes another interpretation and claims that such events were not necessarily “realizations” of “widespread” ideas of identity building. Referring to the generative model of identity building developed by Friedrik Barth, she analyzes how specific situations and meanings were gradually generated through the interaction of actors who attempted to reach their goals and values by available means. The introduction and popularization of Meydenbauer’s invention is presented in the paper with reference to Bruno Latour’s research on the development and implementation of innovations in science. In such a context, photogrammetry turns out to have been a result of seeking support by business, i.e. the mobilization of resources, while the national discourse was used for that purpose as one of the available means
An academic in the face of the Th ird Reich. Hans-Albrecht Fischer – Professor of Roman and German civil law at the University of Wrocław
No full textHans-Albrecht Fischer was a professor of philosophy, Roman law, and German civil law. He had the luck and opportunity to meet the most eminent academics of his days on the path of his life. Some, including Karl Larenz and Julius Binder, destroyed their reputation after 1933 as partisans of the new system. Fischer did not follow that road, nor did he emigrate after 1933, thus choosing the most difficult of the potential roads, that of the socalled internal exile, like one of the most eminent writers of the time, Ernst Wichert. The years of the Third Reich were the time of avoiding and generalising. Ever more intensely suspected by the Nazis, Hans-Albrecht Fischer kept his employment for quite a simple reason, namely, all experts in the field left Germany in the beginning of the Third Reich, and there was no one to lecture civil law (as Roman had been stricken from the curriculum). Fischer made history with his short Contribution to the knowledge of the impossible, in which, being a master wordsmith, he proved the difference between ‘inability’ and ‘impossibility’ to the readers. The two works he wrote in the Third Reich provided the grounds to portray his heroic fight against censorship, which finally haunted the author to the point of contributing to his premature death.Hans-Albrecht Fischer był profesorem filozofii, prawa rzymskiego i niemieckiego prawa cywilnego. Miał szczęście spotkać na swej drodze życia najwybitniejszych uczonych epoki. Niektórzy po 1933 roku jak Karl Larenz, czy Julius Binder zniszczyli swoją reputację jako zwolennicy nowego ustroju. Tą drogą Fischer nie podążył, nie udał się też po 1933 roku na emigrację, wybierając najtrudniejszą z możliwych dróg, tzw. emigracji wewnętrznej, jak jeden z najwybitniejszych pisarzy epoki Ernst Wichert. Lata Trzeciej Rzeszy to lata uników, ogólników, w których coraz bardziej podejrzany dla nazistów Hans-Albrecht Fischer był zatrudniany z prozaicznego powodu, wszyscy specjaliści opuścili Niemcy w początkach Trzeciej Rzeszy i nie było nikogo, kto mógłby wykładać prawo cywilne (rzymskie usunięto z programu studiów). Fischer przeszedł do historii swych krótkim dziełem Przyczynek do nauki o niemożliwości, w którym jako mistrz słowa pokazał czytelnikom, czym różnią się od siebie „niemożliwość” i „niemożność”. Dwie prace napisane w okresie Trzeciej Rzeszy dają podstawę do ukazania heroicznej walki z cenzurą, która ostatecznie zamęczyła Autora i przyczyniła się do jego nagłej śmierci
Making continental crust through slab melting: Constraints from niobium-tantalum fractionation in UHP metamorphic rutile
No full textThe formation of the continental crust (CC) is one of the most important processes in the evolution of the silicate Earth. Exactly how the CC formed is the subject of ongoing debate that focuses on its subchondritic Nb/Ta ratio. Nb and Ta are "geochemical identical twins," so they usually do not fractionate from each other. Here, we show that rutile grains from hydrous rutile-bearing eclogitic layers recovered from drillcores in the Dabie-Sulu ultrahigh pressure terrain have highly variable Nb/Ta values (ranging from 5.4 to 29.1, with an average of 9.8 +/- 0.6), indicating major fractionation of Nb and Ta most likely occurred during blueschist to amphibole-eclogite transformation in the absence of rutile. It is suggested that the released fluids with subchondritic Nb/Ta were transported to, and retained by, hydrous rutile-bearing eclogite in colder regions, resulting in suprachondritic Nb/Ta ratios for drier eclogite in hotter regions. Further dehydration of hydrous rutile-bearing eclogites cannot transfer the fractionated Nb/Ta values to the CC due to the low solubility of Nb and Ta in fluids in the presence of rutile, while dehydration-melting results in a major component of the CC, the tonalite-trondhjemite-granodiorite (TTG) component, which is responsible for the low Nb/Ta of the CC. Consequently, residual eclogites have variable but overall suprachondritic Nb/Ta. (c) 2006 Elsevier Inc. All rights reserved
Post-focus instrumentation for GREGOR
No full textGREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coude Telescope at the Observatorio del Teide on Tenerife. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying physical processes. GREGOR will also serve as a test bed for next generation solar telescopes. We discuss briefly the postfocus instrumentation of GREGOR
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