Phase transitions in leucite: Order parameter behaviour and the Landau potential deduced from Raman spectroscopy and birefringence studies     

David C. Palmer  Ulrich Bismayer  Ekhard K. H. Salje 《Physics and Chemistry of Minerals》1990,17(3):259-265

Hard mode Raman Spectroscopy and optical birefringence studies have been used to evaluate the temperature behaviour of order parameters for the cubictetragonal phase transition in leucite. There is a strong temperature-dependence of Raman line frequencies near 498 cm^–1 and 529 cm^–1, and the optical birefringence decreases towards zero on heating. Above the transition temperature leucite still shows slight birefringence, which correlates with the persistence of the 200 X-ray reflexion at these temperatures, and is not compatible with the ideal cubic symmetry. Quantitative observations of the temperature evolution of Raman line-frequencies and the birefringence are consistent with an order parameter showing T _1g symmetry, and a nearly-tricritical phase transition behaviour. The results of earlier X-ray and DSC studies imply the operation of an additional order parameter, with E _g symmetry; this is observed, but its influence on the transition behaviour is significant only at temperatures close to T _c. The two order parameters are related via linear-quadratic or biquadratic coupling. We develop the form of the Landau Potential for leucite — including both order parameters and their couplings — to discuss the present observations and previous structural data.  相似文献   

Grain boundary wetness of partially molten dunite     

Shangshang Mu  Ulrich H. Faul 《Contributions to Mineralogy and Petrology》2016,171(5):40

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Towards the assimilation of tree-ring-width records using ensemble Kalman filtering techniques     

Walter Acevedo  Sebastian Reich  Ulrich Cubasch 《Climate Dynamics》2016,46(5-6):1909-1920

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The East African Rift System and the impact of orographic changes on regional climate and the resulting aridification     

Anja Sommerfeld  Kerstin Prömmel  Ulrich Cubasch 《International Journal of Earth Sciences》2016,105(6):1779-1794

Several proxy data indicate an aridification of the East African climate during the Neogene, which might be influenced by the orographic changes of the East African Rift System (EARS) induced by tectonic forcing during the last 20 million years. To investigate the impact of the orography and especially of the rifts, the regional climate model CCLM is used, covering the EARS with Lake Victoria in the centre of the model domain. CCLM is driven by the ERA-Interim reanalysis and applied with a double-nesting method resulting in a very high spatial resolution of 7 km. The resolution clearly shows the shoulders and rifts of the western and eastern branch of the EARS and the Rwenzoris within the western branch. To analyse the orographic influence on climate, a new technique of modifying the orography is used in this sensitivity study. The shoulders of the branches are lowered and the rifts are elevated, resulting in a smoothed orography structure with less altitude difference between the shoulders and rifts. The changes in 2 m-temperature are very local and associated with the changes in the orography. The vertically integrated moisture transport is characterised by less vortices, and its zonal component is increased over the branches. The resulting amount of precipitation is mainly decreased west of the western branch and increased in the rift of the western branch. In the eastern branch, however, the changes in the amount of precipitation are not significant. The changes in the precipitation and temperature patterns lead to a shift of biomes towards a vegetation coverage characterised by more humid conditions in the northern part of the model domain and more arid conditions in the South. Thus, the aridification found in the proxy data can be attributed to the orographic changes of the rifts only in the northern model domain.  相似文献   

Über eine scheinbare Anomalie der Temperaturdifferenz Luft-Wasser     

Ulrich Roll 《Ocean Dynamics》1949,2(4):134-137

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Gibt es eine «kritische Windgeschwindigkeit» für Prozesse an der Grenzfläche Wasser-Luft?     

Dr. Hans Ulrich Roll 《Pure and Applied Geophysics》1952,21(1):110-126

Zusammenfassung Eineabsolute «kritische Windgeschwindigkeit» für Prozesse an der Grenzfläche Wasser-Luft scheint nicht zu existieren. Unsere Beobachtungen liefern jedoch Anzeichen für das Vorhandenseinrelativer «kritischer Windgeschwindigkeiten, die vom Ueberströmungsweg, bzw. von der Wellenlaufstrecke abzuhängen scheinen. Diese relativen «kritischen Windgeschwindigkeiten» sind durch folgende-Merkmale gekennzeichnet: Aenderung der Struktur der Meeresoberfläche (glatt-rauh); Umschlag der laminaren Wassergrenzschicht zur Turbulenz; Ueberbrechen der Schwerewellen; Minimum des Widerstandskoeffizienten der Meeresoberfläche.

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Summary It seems that there is no absolute «critical wind speed» for air-sea boundary processes. From our observations it may, however, be referred that there are relative values of the «critical wind speed» which seem to depend on the fetch. These relative values of the «critical wind speed» are characterized by the following marks: The sea surface pattern is changed (smooth-rough);, the boundary layer in water turns from laminar to turbulent flow; the gravity waves break; the resistance coefficient of the sea surface has a minimum.

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Über Größenunterschiede der Meereswellen bei Warm- und Kaltluft     

Hans Ulrich Roll 《Ocean Dynamics》1952,5(2-3):111-114

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Die Matrix der Fische XVI Zweidimensionale papierchromatographische Analyse von Fischschuppenhydrolysaten und Hydrolysaten einiger weiterer Fischorgane     

Ulrich A. Corti  L. Keller 《Aquatic Sciences - Research Across Boundaries》1952,14(2):336-337

Summary The aminoacids in hydrolysates (HCl) of the scales of six different fish-species have been determined by partition paper chromatography (Consden andDent). The scales contain considerable amounts of protein besides hydroxyl apatit and guanin, but none or only minute quantities of carbohydrates. Some of the aminoacids in the liver, air-bladder, kidney and the body muscles of two fish species were investigated.   相似文献   

Die Matrix der Fische XIV. Elektronenmikroskopische Untersuchung von Fischschuppen     

R. Signer  F. v. Beust  Ulrich A. Corti 《Aquatic Sciences - Research Across Boundaries》1951,13(1):31-35

Summary The investigation with an electron-microscope of the scales of the fresh water fish,Leuciscus rutilus L., showed that their ventral “smooth” surface scems to be formed like a corrugated plate with a distance between the ridges of 1–2 μ. The dorsal “rough” side of the scales shows a very fine roughness. It is interrupted by pointed combs of the same structure in a regular distance of 16–27 μ. The thickness of these combs is of about 1 μ at their base, their height of about 5–10 μ. It seems probable that the surface of scales is partially covered with laminas of hyalodentine or guanine.

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13. Mitteilung siehe diese Zeitschrift,13, 29–30 (1951).  相似文献   

La «Matrix» des Poissons VI. Etudes oscillographiques sur la détermination du caractère nocif de différentes eaux usées de provenance industrielle     

Ulrich A. Corti 《Aquatic Sciences - Research Across Boundaries》1951,13(2):358-364

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