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661.
Archeops is a balloon-borne instrument dedicated to measuring cosmic microwave background (CMB) temperature anisotropies at high angular resolution (~ 8 arcminutes) over a large fraction (~ 30%) of the sky in the millimetre domain. The general design is based on Planck High Frequency Instrument (HFI) technology. Bolometers cooled to 0.1 K scan the sky in total power mode along large circles at constant elevation. Archeops is designed to observe a complete annulus on the sky covering all right ascensions between about 25 and 55 degrees during the course of a 24-hour Arctic-night balloon flight, in four frequency bands centered at 143, 217, 353 and 545 GHz. We describe the Archeops flights and the data products obtained during the three successful flights from Trapani (Sicily) to Spain in July 1999, and from Kiruna (Sweden) to Russia in January 2001 and February 2002. We discuss present Archeops results and the future use of Archeops data. 相似文献
662.
S. Sindern A. N. Zaitsev A. Demény K. Bell A. R. Chakmouradian U. Kramm J. Moutte A. S. Rukhlov 《Mineralogy and Petrology》2004,80(3-4):215-239
Summary The eastern part of the agpaitic Khibina complex is characterized by the occurrence of dykes of various alkali silicate rocks and carbonatites. Of these, picrite, monchiquite, nephelinite and phonolite have been studied here. Whole rock and mineral geochemical data indicate that monchiquites evolved from a picritic primary magma by olivine+ magnetite fractionation and subsequent steps involving magma mixing at crustal levels. None of these processes or assimilation/magma mixing of wall rocks or other plutonic rocks within the complex can entirely explain the geochemical and Nd–Sr-isotopic characteristics of the monchiquites (i.e. a covariant alignment between (87Sr/86Sr)370=0.70367, (143Nd/144Nd)370=0.51237 and (87Sr/86Sr)370=0.70400, (143Nd/144Nd)370=0.51225 representing the end points of the array). This signature points to isotopic heterogeneities of the mantle source of the dyke-producing magma. The four mantle components (i.e. depleted mantle, lower mantle plume component, EMI-like component and EMII-like component) must occur in different proportions on a small scale in order to explain the isotopic variations of the dyke rocks. The EMII-like component might be incorporated into the source area of the primary magma by carbonatitic fluids involving subducted crustal material. The most likely model to explain the small-scale isotopic heterogeneity is plume activity. The results of this study do not provide any support to a cogenetic origin (e.g. fractionation or liquid immiscibility) for carbonatite and monchiquite or other alkali-silicate dyke rocks occurring in spatial proximity. Instead, we propose that both, carbonatite and picrite/monchiquite, originated by low-degree partial melting of peridotite. Textural observations, mineralogical data, and C and O isotopic compositions suggest incorporation of calcite from carbonatite in monchiquite and the occurrence of late-stage carbothermal fluids.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s00710-003-0016-2 相似文献
663.
664.
William L. Bandy Franois Michaud Jrme Dyment Carlos A. Mortera-Gutirrez Jacques Bourgois Thierry Calmus Marc Sosson Jose Ortega-Ramirez Jean-Yves Royer Bernard Pontoise Bertrand Sichler 《Tectonophysics》2008,454(1-4):70-85
To better understand the recent motion of the Pacific plate relative to the Rivera plate and to better define the limitations of the existing Rivera–Pacific plate motion models for accurately predicting this motion, total-field magnetic data, multibeam bathymetric data and sidescan sonar images were collected during the BART and FAMEX campaigns of the N/O L'Atalante conducted in April and May 2002 in the area surrounding the Moctezuma Spreading Segment of the East Pacific Rise, located offshore of Manzanillo, Mexico, at 106°16′W, between 17.8°N and 18.5°N. Among the main results are: (1) the principle transform displacement zone of the Rivera Transform is narrow and well defined east of 107o15′W and these azimuths should be used preferentially when deriving new plate motion models, and (2) spreading rates along the Moctezuma Spreading Segment should not be used in plate motion studies as either seafloor spreading has been accommodated at more than one location since the initiation of seafloor spreading in the area of the Moctezuma Spreading Segment, or this spreading center is not a Rivera–Pacific plate boundary as has been previously assumed. Comparison of observed transform azimuths with those predicted by the best-fit poles of six previous models of Rivera–Pacific relative motion indicate that, in the study area, a significant systematic bias is present in the predictions of Rivera–Pacific motion. Although the exact source of this bias remains unclear, this bias indicates the need to derive a new Rivera–Pacific relative plate motion model. 相似文献
665.
Eric H. Oelkers Jacques Schott Jean-Marie Gauthier Teresa Herrero-Roncal 《Geochimica et cosmochimica acta》2008,72(20):4948-4961
Steady-state muscovite dissolution rates have been measured at temperatures from 60 to 201 °C and 1 ? pH ? 10.3 as a function of reactive solution K, Si, and Al concentration. The pegmatitic muscovite used in these experiments has a composition consistent with (Na0.09, K0.86)Fe0.05Al2.92Si3.05O10(OH1.95, F0.06). All experiments were performed in titanium mixed-flow reactors. All experiments were performed at far-from-equilibrium conditions with respect to muscovite. All reactive solutions were undersaturated with respect to secondary product phases other than for some experiments which were supersaturated with respect to bohemite and diaspore; steady-state dissolution was stoichiometric for all experiments that were undersaturated with respect to these phases.The variation of rates with reactive solution composition depends on the solution pH. At pH ? 7 rates were found to decrease significantly with increasing reactive fluid Al activity but be independent of aqueous SiO2 activity. pH < 7 rates measured in the present study from 60 to 175 °C are consistent with
666.
Understanding late Holocene extinctions on islands requires accurate chronologies for all relevant events, including multiple colonisations by humans and the introduction of alien species. The most widely held hypothesis on the causes of Holocene island vertebrate extinctions incorporates human impacts, although climatic-related hypotheses cannot be excluded. Both hypotheses have been suggested to account for the extinction of the endemic Lava Mouse, Malpaisomys insularis from the Canary Islands. Here we present the first accelerator mass spectrometer (AMS) 14C ages from collagen of M. insularis bones from ancient owl pellets collected at Fuerteventura (Canary Islands, eastern Atlantic Ocean). These new dates contribute to an understanding of the extinction of this species. We are able to exclude climatic causes, predation by invasive species, and competition with the house mouse, Mus musculus. The arrival of Europeans in the Canary Islands correlates with the extinction of Malpaisomys. The introduction of rats, Rattus spp., together with their parasites and diseases, emerges as the most reasonable hypothesis explaining the extinction of M. insularis. 相似文献
667.
Using multiple portable/wearable devices for enhanced misalignment estimation in portable navigation
Global navigation satellite system (GNSS), such as global positioning system (GPS), has been widely used for vehicular and outdoor navigation. Accuracy is one, among many, of the advantages of using GNSS in the open sky. However, GNSS finds difficulty in achieving similar results in portable navigation, where users spend most of their time indoors or in urban canyons, places where GNSS signals suffer from multipath error or signal blockage. One of the most common solutions for providing location services in such challenging environments is integrating GNSS with inertial sensors, such as accelerometers and gyroscopes. However, the arbitrary orientation of the portable device can present a more difficult challenge when using inertial sensors for portable navigation. In order to obtain a navigation solution using inertial sensors, an accurate heading estimation is required. Resolving the heading misalignment angle between the portable navigation device and the moving platform, such as using the device while walking or in a vehicle while driving, is critical to obtaining an accurate heading estimation. We present a solution for resolving the misalignment between the portable device and the moving platform, which exploits multiple portable devices like smartphones or tablets and/or smart wearable devices such as smart watches, smart glasses, and/or smart fitness and activity trackers/monitors. Several real field test experiments using portable devices were conducted to examine the performance of the proposed method. Results show how a portable navigation solution can be improved by further enhancing misalignment estimation. 相似文献
668.
Cenozoic evolution of the central Myanmar drainage system: insights from sediment provenance in the Minbu Sub‐Basin
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Alexis Licht Laurie Reisberg Christian France‐Lanord Aung Naing Soe Jean‐Jacques Jaeger 《Basin Research》2016,28(2):237-251
Located at the southern edge of the eastern Himalayan syntaxis, the Central Myanmar Basin (CMB) is divided into several Tertiary sub‐basins that have been almost continuously filled since the Indo‐Asia collision. They are currently drained by the Irrawaddy River, which flows down the eastern Tibetan Plateau and the Sino‐Burman Ranges. Tracing sediment provenance from the CMB is thus critical for reconstructing the past denudation of the Himalayan‐Tibetan orogen; it is especially relevant since a popular drainage scenario involves the capture of the Tsangpo drainage system in Tibet by a precursor to the Irrawaddy River. Here, we document the provenance of sediment samples from the Minbu Sub‐Basin at the southern edge of the CMB, which is traversed by the modern stream of the Irrawaddy River. Samples ranging in age from middle Eocene to Pleistocene were investigated using Nd isotopes, trace element geochemistry and sandstone modal compositions. Our data provide no evidence of a dramatic provenance shift; however, sandstone petrography, trace element ratios and isotopic values display long‐term trends indicating a gradual decrease of the volcanic input and its replacement by a dominant supply from the Burmese basement. These trends are interpreted to reflect the progressive denudation of the Andean‐type volcanic arc that extended onto the Burmese margin, along the flank of the modern Sino‐Burman Ranges, where most of the post‐collisional deformation of central Myanmar is located. Though our results do not exclude an ephemeral or diluted contribution from a past Tsangpo‐Irrawaddy connection, sedimentation rates suggest that this hypothesis is unlikely before the development of a stable Tsangpo‐Brahmaputra River in the Miocene. These results thus suggest that the central Myanmar drainage basin has remained restricted to the Sino‐Burman Ranges since the beginning of the India‐Asia collision. 相似文献
669.
670.
Simon Damien Carrière Konstantinos Chalikakis Chloé Ollivier Tom Heath Marie Mangin Jean Kempf Jacques Bablon Randriatsitohaina Marina Gillon Théodore Razakamanana Jean Lapègue 《Environmental Earth Sciences》2018,77(21):734
Southwestern Madagascar is a semi-arid region and a hot-spot of global change. On the Mahafaly plateau, people live with quasi-permanent water stress and groundwater, the only available resource, is difficult to exploit due to a complex hydrogeological environment. A methodology (suitable for humanitarian projects; <?40 k€) was developed in four phases to assess the sustainable exploitation of the water resource: (A) regional scale exploration, (B) village scale exploration, (C) drilling campaign, and (D) hydro-climatic monitoring. This integrated hydrogeophysical approach involves geophysical measurements (262 TEM-fast soundings, 2588 Slingram measurements, 35 electrical soundings), hydrochemical analyses (112 samples), and a piezometric survey (127 measurements). Two groundwater resources were identified, one deep (below 150 m) and one shallow (<?20 m). Hydrochemical results highlighted the vulnerability of both resources: anthropic contamination for the shallower and seawater intrusion for the deeper. Therefore, subsequent geophysical surveys supported the siting of six boreholes and three wells in the shallow aquifer. This methodological approach was successful in this complex geological setting and requires testing at other sites in and outside Madagascar. The study demonstrates that geophysical results should be used in addition to drilling campaigns and to help monitor the water resource. In fact, to prevent over-exploitation, piezometric and meteorological sensors were installed to monitor the water resource. This unique hydro-climatic observatory may help (1) non-governmental organization and local institutions prevent future water shortages and (2) scientists to understand better how global change will affect this region of the world. 相似文献