Measurement of Aureole and Suppression of Internal Stray Light of Aureole Photometer     

Nian-Ping Liu  Yu Liu  Yun-Deng Shen  Xue-Fei Zhang  Wen-Da Cao  Jean Arnaud 《Chinese Astronomy and Astrophysics》2011,35(4):428

A modern aureole photometer (AP) was developed for the site survey inWest China, in preparation for the installation of future large solar equipments. The performance of this new AP was tested in preliminary observations, and a lot of sky brightness data were accumulated at a few sites in Yunnan Province. The result of data analysis shows that the aureole near the noon time on Jiaozi Snow Mountain is as low as a few millionths of the intensity at the solar disk center, indicating the low internal stray light level of our instrument. The internal stray light of the AP comes mainly from two parts: the edge diffraction of the ferrule for fixing the ND4 filter in the front end of the telescope tube, causing the stray light distributed in the inner region of the field of view, and the edge diffractions of the diaphragms placed inside the telescope tube, causing the stray light distributed in the outer region of the field of view. In order to suppress the stray light of the latter part, the experiment to change the aperture size of an additional diaphragm was performed. The result shows that the stray light in the outer region of the field of view can be effectively suppressed by reducing properly the aperture size of the diaphragm.  相似文献   

GGR Biennial Critical Review: Analytical Developments Since 2010     

Michael Wiedenbeck  Roxana Bugoi  M. John M. Duke  Tibor Dunai  Jacinta Enzweiler  Mary Horan  Klaus Peter Jochum  Kathryn Linge  Jan Košler  Silke Merchel  Luiz F.G. Morales  Lutz Nasdala  Roland Stalder  Paul Sylvester  Ulrike Weis  Arnaud Zoubir 《Geostandards and Geoanalytical Research》2012,36(4):337-398

Advances in the chemical and isotopic characterisation of geological and environmental materials can often be ascribed to technological improvements in analytical hardware. Equally, the creation of novel methods of data acquisition and interpretation, including access to better reference materials, can also be crucial components enabling important breakthroughs. This biennial review highlights key advances in either instrumentation or data acquisition and treatment, which have appeared since January 2010. This review is based on the assessments by scientists prominent in each of the given analytical fields; it is not intended as an exhaustive summary, but rather provides insight from experts of the most significant advances and trends in their given field of expertise. In contrast to earlier reviews, this presentation has been formulated into a unified work, providing a single source covering a broad spectrum of geoanalytical techniques. Additionally, some themes that were not previously emphasised, in particular thermal ionisation mass spectrometry, accelerator‐based methods and vibrational spectroscopy, are also presented in detail.  相似文献   

Ab initio investigation into the elasticity of ultrahigh-pressure phases of SiO2     

Arnaud Metsue  Taku Tsuchiya 《Physics and Chemistry of Minerals》2012,39(3):177-187

In this study, we report the elastic properties of three ultrahigh-pressure phases of SiO₂: pyrite, cotunnite and Fe₂P types between 300 and 1,500 GPa calculated by means of the density functional ab initio method. It is generally thought that materials tend to be more compact and isotropic with increasing pressure. These three ultrahigh-pressure phases of silica are mechanically stable in the investigated pressure range according to the Born criteria, while the cotunnite and Fe₂P types are unstable at lower pressure. The elastic azimuthal anisotropy of these ultrahigh-pressure phases of silica shows that all the structures counterintuitively have considerable anisotropies even at multimegabar pressures. Among the three investigated structures, the cotunnite type of SiO₂ is the most elastically anisotropic phase due to a soft compression along the b axis combined with a large distortion of the polyhedrons that make the structure. This might also be related to its thermodynamic unfavorability compared to the Fe₂P type under extreme pressure condition. The bond property analyses clearly show that the Si–O bond remains an ionic-covalent mixed bond even at multimegabar pressures with an invariable ionicity with pressure. This argument can explain the monotonously pressure dependence of the elastic anisotropy in the case of pyrite, while the changes in the velocity distribution patterns out of the thermodynamic instability range largely contribute to those of the cotunnite and Fe₂P types.  相似文献   

Geology and metamorphism of the Ladakh Terrane and Shyok Suture Zone in the Chogo Lungma – Turmik area (northern Pakistan)     

Franco Rolfo  Bruno Lombardo  Roberto Compagnoni  Patrick Le Fort  Yves Lemennicier  Arnaud Pêcher 《Geodinamica Acta》2013,26(5):251-270

Abstract

Metamorphism of the Askore Amphibolite, metabasaltic and metasedimentary medium-grade hornblendebearing schists at the northernmost portion of the Ladakh Terrane and of the Shyok Suture Zone, mainly a low-grade volcano-sedimentary series, has been studied in the area between the Chogo Lungma glacier and the Indus river halfway between Skardu and Rondu.

In the Askore Amphibolite the peak assemblage in the amphibolite facies defines the regional metamorphic foliation, and is overprinted by a later static recrystallization at comparable P-T conditions. In spite of similar peak temperatures (630–650°C), geobarometry based on amphibole composition reveals a marked difference between garnet – epidote – andesine amphibolites exposed just above the Main Mantle Thrust at the head of Turmik valley, which equilibrated at high pressures (about 10 kbar) in late Miocene (Tortonian), and biotite – epidote – oligoclase amphibolites outcropping at the mouth of Turmik valley, which equilibrated at pressures of c. 6 kbar before late Eocene (Priabonian).

The Dasu Ultramafite and other smaller lens-shaped bodies of low- to medium-grade metaperidotite separate the Ladakh Terrane from the Shyok Suture Zone. They are antigorite serpentinites, often with talc and magnesite, in which relict cumulitic structures are locally recognisable. The ultramafites may represent remnants of oceanic lithosphere separating the Ladakh-Kohistan island arc from the Asian plate, or they may be deep crustal rocks stripped from the basement of the arc.

The mostly greenschist-facies Shyok Suture Zone shows the lithology of a calc-alkaline volcano-sedimentary series. It is supposed to be a remnant of a back arc basin of early Cretaceous age, separating the arc from the southern margin of Asia. Chloritoid, kyanite and biotite have been found in individual thrust sheets occurring at different structural levels and totally subordinate in volume to very low- and low-grade rocks. Such sharp differences in mineral paragenesis, together with field evidence of local shear, suggest a complex internal structure for the Shyok Suture Zone. From the head of Chogo Lungma glacier to the Basha valley, close to the contact with the Karakorum Metamorphic Complex, the rocks of the Shyok Suture Zone record a late Miocene metamorphic event at medium pressures and temperatures. Thermobarometric and geochronological evidence suggests that this event can be related to the exhumation and thrusting of the Karakorum metamorphic core over the Shyok Suture Zone.  相似文献   

Comparison of two snowmelt modelling approaches in the Dudh Koshi basin (eastern Himalayas,Nepal)     

Bijay Kumar Pokhrel  Pierre Chevallier  Vazken Andréassian  Adnan Ahmad Tahir  Yves Arnaud  Luc Neppel 《水文科学杂志》2013,58(8):1507-1518

Abstract

The glaciers in the Nepalese Himalayas are retreating due to rising temperatures. Lack of data and information on Nepal’s cryosphere has impeded scientific studies and field investigations in the Nepalese Himalayas. Therefore, IRD France and Ev-K2 CNR Italy have conducted the PAPRIKA (CryosPheric responses to Anthropogenic PRessures in the HIndu Kush-Himalaya regions: impacts on water resources and society adaptation in Nepal) project in Nepal with the financial support of the French and Italian scientific agencies. This project aims to address the current and future evolution of the cryosphere in response to overall environmental changes in South Asia, and its consequences for water resources in Nepal. Thus, two hydrological models, the GR4J lumped precipitation–runoff model and the snowmelt runoff model (SRM), were used in the Dudh Koshi basin. The GR4J model has been successfully applied in different parts of Europe. To obtain better results in such a harsh and rugged topography, modifications needed to be made, particularly in the snow module. The runoff pattern is analysed herein both for past years and, in a sensitivity analysis, for possible future climatic conditions (i.e. precipitation and temperature) using the SRM and GR4J modelling approaches. The results reveal a significant contribution of snow- and glacier-melt to runoff, and the SRM model shows better performance in Nepalese catchments than the GR4J model.