Ceres’ spectral link to carbonaceous chondrites—Analysis of the dark background materials          下载免费PDF全文

Michael Schäfer  Tanja Schäfer  Matthew R. M. Izawa  Edward A. Cloutis  Stefan E. Schröder  Thomas Roatsch  Frank Preusker  Katrin Stephan  Klaus‐Dieter Matz  Carol A. Raymond  Christopher T. Russell 《Meteoritics & planetary science》2018,53(9):1925-1945

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes ?1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥?10% μm^?1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres.  相似文献   

Simple integrals for solving of Kepler's equation     

W. Neutsch  E. Schrüfer 《Astrophysics and Space Science》1986,125(1):77-83

In this paper we derive integral representations for the solution of Kepler's equations for elliptic and hyperbolic orbits. The integrands consist merely of rational expressions of the integration variable and its exponential.  相似文献   

A New Lithostratigraphic Framework for the Cretaceous Colorado Group in the Cold Lake Heavy Oil Area,East-Central Alberta,Canada     

Qiang Tu  Claudia J. Schröder-Adams  Jim Craig 《Natural Resources Research》2007,16(1):17-30

The Albian to Santonian Colorado Group in the heavy oil area of Cold Lake, east-central Alberta represents a relatively condensed section of shale-dominated sedimentation within the Western Interior Sea. These shales form the cap rock to the underlying Clearwater and Grand Rapids formations that are exploited for bitumen extraction. Two cores covering the entire Colorado Group provide a unique opportunity for establishment of a stratigraphic reference in an area that has received attention only for its heavy oil-bearing Mannville Group. Based on sedimentology, geochemistry, micropaleontology, nannofossils, and wireline log data, the Colorado Group was subdivided into the Joli Fou, Viking, Westgate, Fish Scales, Belle Fourche, Second White Specks, and Niobrara formations. The Niobrara Formation was subdivided further into the Verger Member, informal Cold Lake member, and First White Specks Member. Because of this region’s small accommodation space and distance to sources of coarse clastic sediment, disconformities are indicated lithologically by bioclastic layers and missing biozones. Foraminiferal subzones revealed two erosional boundaries associated with the Viking Formation. Faunal and floral evidence coupled with wireline log correlations suggest that the Middle to Upper Turonian Carlile Formation, as described from southeastern Alberta, is missing. That extends the Middle Turonian to Coniacian unconformity, as recognized in central Saskatchewan, westwards into Alberta.  相似文献   

On diurnal variations of the solar rotation rate as derived from sunspot tracings     

A. Koch  H. Wöhl  E. H. Schröter 《Solar physics》1981,71(2):395-399

The heliographic positions of more than 100 sunspots were accurately measured several times a day from 1974 until 1979 by means of the computer-controlled tracing method described by Schröter and Wöhl (1975). A striking degree of constancy of the solar rotation rate (about 0.15% or 3 m s^–1) is found, when east-west proper motion components of each individual stable sunspot is considered. However, large differences of the rotation rate are observed (up to 7% or 130 m s^–1) when comparing different sunspots. We found no significant correlation of these fluctuations with characteristics of the sunspots (age, evolution, etc.).Mitteilungen aus dem Kiepenheuer-Institut Nr. 191.  相似文献   

The intensity,velocity and magnetic structure of a sunspot region     

J. M. Beckers  E. H. Schröter 《Solar physics》1969,10(2):357-369

High resolution sunspot photographs in the blue, red and infrared continuum exposed on various days were used to derive the center-to-limb variation of the intensity ratio = I _sp / I _ph. Special care was taken to correct for image blurring, scattered light and the influence of line absorption.The observed increase of specific umbral intensities _u towards the limb leads to an extremely small temperature gradient in the umbra. From geometrical changes of the profiles (Wilson effect), we derived an umbral depression of about 650 km and a density scale height of about 450 km when H ^- is assumed to be the predominant source of absorption. The penumbral depression was found to be 50 km or less. The density scale height of the umbra as computed from the observed temperature distribution is 80 km in the case of hydrostatic equilibrium. We conclude that either magnetic pressure components produce deviations from hydrostatic equilibrium or that another source of absorption, dominating in the outer layers, has to be taken into account.  相似文献   

A statistical analysis of large-scale brightness and velocity fluctuations in the solar atmosphere     

I. Appenzeller  E. H. Schröter 《Solar physics》1968,4(2):131-141

Simultaneous photoelectric recordings of the intensities and the Doppler shifts in 5 Fraunhofer lines (H, Na D₁, Mg b₂, Fe5123, Fe5223) were used to study the structure of local large-scale fluctuations of the intensity and velocity in different layers of the solar atmosphere. We derived the autocorrelation and cross-correlation functions and the powerspectra of the fluctuations. Fluctuation patterns with a characteristic size of 3–4 × 10⁴ km were found in all observed lines. The intensity of the fluctuations decreases sharply from the chromospheric H-core to the weak iron lines. The results are discussed in terms of the solar supergranulation pattern.  相似文献   

Behandlung und Beseitigung des Klärschlamms     

W. Schröder 《Aquatic Sciences - Research Across Boundaries》1964,26(2):668-689

Ohne Zusammenfassung  相似文献   

A variable lacustrine environment in Lake Winnipeg, Manitoba: Evidence from modern thecamoebian distribution   总被引：1，自引：0，他引：1  

Kaori Torigai  Claudia J. Schröder-Adams  Susan M. Burbidge 《Journal of Paleolimnology》2000,23(3):305-318

Thecamoebians (testate protozoan) were examined in 18 surface sediment samples from the North and South basins and the Narrows of Lake Winnipeg, Manitoba. Significantly higher numbers of thecamoebians and tintinnids in the North Basin compared to the Narrows and South Basin are attributed to the effects of urban development around the South Basin of Lake Winnipeg. Human population growth in this area has led to increased nutrient concentration in runoff, causing eutrophication of the southern lake, which in turn allows for increased algal productivity. Cucurbitella tricuspis is found in large abundances in the South Basin, particularly close to the inlet of the Red and Assiniboine rivers. High abundances of this species have been attributed to eutrophic conditions, which this species appears to withstand more successfully than other species. Increases in domestic waste output, that have led to elevated heavy metal concentrations in lake bottom sediments of the South Basin, may have resulted in lower abundances of thecamoebians, further reducing competition.Strong currents in the Narrows cause a slightly coarser substrate and sweep away food sources such as phytoplankton. This results in a lower faunal abundance and slightly lower species richness of thecamoebians. Robust species such as the coarse-grained Difflugia viscidula and species which feed on bacteria such as Centropyxis aculeata show increased abundances.Modern thecamoebian assemblages are comparable to Late Holocene faunal associations in terms of species composition. Individual species abundances, however, have changed. For example, in the North Basin the Late Holocene dominance of Difflugia manicata is replaced by various strains of Difflugia oblonga during recent times. A common species of the South Basin from Late Holocene to recent times is Difflugia globulus. It would appear that faunal differences between basins are the result of differences in algal food sources.  相似文献   

‘I hate sand … it gets everywhere’—Phanerozoic sedimentary recycling from NW Africa     

James Lovell-Kennedy  Emmanuel Roquette  Stefan Schröder  Jonathan Redfern 《Basin Research》2023,35(1):187-213

Over 10,000 published detrital zircon ages have been reprocessed (applying a +10% normal and reverse concordance range) and analysed to understand the evolution of the detrital zircon record of north-west Africa during the Phanerozoic. Using dissimilarity and clustering analysis, shifts in detrital zircon populations allow interpretation of the evolution of source regions and source to sink systems throughout the Phanerozoic within the West Gondwana superfan. Previous thermochronology and field studies conducted across north-west Africa indicate significant and sustained shifts in source regions in Meso-Cenozoic times which are not recorded in the detrital zircon geochronology record. This discrepancy is most notable for Mesozoic to modern source to sink studies focused on the evolution of the Atlasic rift and opening of the Atlantic and Tethyan Oceans to the west and north respectively. Our results indicate a high degree of similarity between samples from Cambrian times onwards due to successive phases of sediment recycling. This highlights the need to integrate detrital zircon analysis with other techniques to provide confident reconstruction of sediment routing systems across Morocco. This systematic review also reveals the ubiquitous occurrence of Mesoproterozoic zircons within Moroccan sediment. No basement of this age is known from north-west Africa—often described as the ‘Mesoproterozoic Gap’, which was thought to be a diagnostic feature of sediment derived from the West African Craton. However, zircons of this age form 7% of all analysed zircons and are present in sediments from at least 700 Ma. The presence of this population is interpreted as strongly diagnostic of provenance from either the Amazonian Craton or the Eastern Gondwana Orogen within Central Africa. Their presence in the Moroccan detrital record from the Neoproterozoic onwards raises questions about the position of the West African Craton in the Proterozoic, and for the spatial extent of Mesoproterozoic orogeny within north Africa.  相似文献   

Assimilation of Earth rotation parameters into a global ocean model: length of day excitation     

Jan Saynisch  Manfred Wenzel  Jens Schröter 《Journal of Geodesy》2011,85(2):67-73

Changes in the oceanic current system and in the oceanic mass distribution alter, together with other processes, the state of the Earth’s rotation. This state is characterized by the length of day (LOD) and the tilt of the pole-to-pole axis. The aim of our study was to derive the respective governing physical mechanisms in the ocean. Therefore, Earth rotation observations were assimilated into a global circulation model of the ocean. Although assimilation is a well-established tool in climate science, the assimilation of Earth rotation observations into a global ocean model was done here for the first time. Prior to the assimilation, the Earth rotation observations were projected onto the angular momentum of the ocean. Non-oceanic contributions were removed. The result of the subsequent assimilation procedure is a time varying ocean model state that reproduces the projected Earth rotation observations well. This solution was studied to understand the oceanic generation of Earth rotation deviations and to identify governing physical mechanisms. This paper focuses on LOD anomalies although polar motion was assimilated simultaneously. Our results indicate that changes in the oceanic LOD excitation are mostly attributed to changes in total ocean mass. Changes in the spatial distribution of ocean mass turned out to have a minor contribution to the LOD deviations. The same applies to changes in the current system.  相似文献