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排序方式: 共有1182条查询结果,搜索用时 31 毫秒
781.
Tomáš Laburda Josef Krása David Zumr Jan Devátý Michal Vrána Nives Zambon Lisbeth Lolk Johannsen Andreas Klik Peter Strauss Tomáš Dostál 《地球表面变化过程与地形》2021,46(5):1067-1082
An understanding of splash erosion is the basis to describe the impact of rain characteristics on soil disturbance. In typical splash cup experiments, splashed soil is collected, filtered, and weighed. As a way to collect additional data, our experiments have been supplemented by a photogrammetric approach. A total of three soils were tested across three sites, one in the Czech Republic and two in Austria, all equipped with rain gauges and disdrometers to measure rainfall parameters. The structure from motion multiview stereo (SfM-MVS) photogrammetric method was used to measure the raindrops impact on the soil surface. The images were processed using Agisoft PhotoScan, resulting in orthophotos and digital elevation models (DEMs) with a resolution of 0.1 mm/pix. The surface statistics included the mean surface height (whose standard deviation was used as a measure of surface roughness), slope, and other parameters. These parameters were evaluated depending on soil texture and rainfall parameters. The results show a linear correlation between consolidation and splash erosion with a coefficient of determination (R2) of approximately 0.65 for all three soils. When comparing the change in soil volume with rainfall parameters, the best correlation was found with the maximum 30-minintensity (I30), resulting in R2 values of 0.48 (soil A, silt loam, 26% clay), 0.59 (soil B, silt loam, 18% clay), and 0.68 (soil C, loamy sand, 12% clay). The initial increase in the sample volume for the lowest splashed mass corresponds with the increase in the clay content of each of the soils. Soil A swells the most. Soil B swells less. Soil C does not swell at all and consolidates the most. We derived the relationship between the photogrammetrically measured change in surface height and the splash erosion (measured by weight) by accounting for the effect of the clay content. 相似文献
782.
Peter von Ballmoos Jose Alvarez Nicolas Barrière Steve Boggs Andrei Bykov Juan Manuel Del Cura Velayos Filippo Frontera Lorraine Hanlon Margarita Hernanz Emmanuel Hinglais Jordi Isern Pierre Jean Jürgen Kn?dlseder Lucien Kuiper Mark Leising Beno?t Pirard Jean-Pierre Prost Rui M. Curado da Silva Tadayuki Takahashi John Tomsick Roland Walter Andreas Zoglauer 《Experimental Astronomy》2012,34(2):583-622
DUAL will study the origin and evolution of the elements and explores new frontiers of physics: extreme energies that drive powerful stellar explosions and accelerate particles to macroscopic energies; extreme densities that modify the laws of physics around the most compact objects known; and extreme fields that influence matter in a way that is unknown on Earth. The variability of these extreme objects requires continuous all-sky coverage, while detailed study demands an improvement in sensitivity over previous technologies by at least an order of magnitude. The DUAL payload is composed of an All-Sky Compton Imager (ASCI), and two optical modules, the Laue-Lens Optic (LLO) and the Coded-Mask Optic (CMO). The ASCI serves dual roles simultaneously, both as an optimal focal-plane sensor for deep observations with the optical modules and as a sensitive true all-sky telescope in its own right for all-sky surveys and monitoring. While the optical modules are located on the main satellite, the All-Sky Compton Imager is situated on a deployable structure at a distance of 30?m from the satellite. This configuration not only permits to maintain the less massive payload at the focal distance, it also greatly reduces the spacecraft-induced detector background, and, above all it provides ASCI with a continuous all-sky exposure. 相似文献
783.
Vishnu Reddy Lucille Le Corre David P. O’Brien Andreas Nathues Edward A. Cloutis Daniel D. Durda William F. Bottke Megha U. Bhatt David Nesvorny Debra Buczkowski Jennifer E.C. Scully Elizabeth M. Palmer Holger Sierks Paul J. Mann Kris J. Becker Andrew W. Beck David Mittlefehldt Jian-Yang Li David Blewett 《Icarus》2012,221(2):544-559
NASA’s Dawn spacecraft observations of Asteroid (4) Vesta reveal a surface with the highest albedo and color variation of any asteroid we have observed so far. Terrains rich in low albedo dark material (DM) have been identified using Dawn Framing Camera (FC) 0.75 μm filter images in several geologic settings: associated with impact craters (in the ejecta blanket material and/or on the crater walls and rims); as flow-like deposits or rays commonly associated with topographic highs; and as dark spots (likely secondary impacts) nearby impact craters. This DM could be a relic of ancient volcanic activity or exogenic in origin. We report that the majority of the spectra of DM are similar to carbonaceous chondrite meteorites mixed with materials indigenous to Vesta. Using high-resolution seven color images we compared DM color properties (albedo, band depth) with laboratory measurements of possible analog materials. Band depth and albedo of DM are identical to those of carbonaceous chondrite xenolith-rich howardite Mt. Pratt (PRA) 04401. Laboratory mixtures of Murchison CM2 carbonaceous chondrite and basaltic eucrite Millbillillie also show band depth and albedo affinity to DM. Modeling of carbonaceous chondrite abundance in DM (1–6 vol.%) is consistent with howardite meteorites. We find no evidence for large-scale volcanism (exposed dikes/pyroclastic falls) as the source of DM. Our modeling efforts using impact crater scaling laws and numerical models of ejecta reaccretion suggest the delivery and emplacement of this DM on Vesta during the formation of the ~400 km Veneneia basin by a low-velocity (<2 km/s) carbonaceous impactor. This discovery is important because it strengthens the long-held idea that primitive bodies are the source of carbon and probably volatiles in the early Solar System. 相似文献
784.
Andreas Morlok Chiyoe Koike Kazushige Tomeoka Andrew Mason Carey Lisse Mahesh Anand Monica Grady 《Icarus》2012,219(1):48-56
Mid-infrared (5–25 μm) transmission/absorption spectra of differentiated meteorites (achondrites) were measured to permit comparison with astronomical observations of dust in different stages of evolution of young stellar objects. In contrast to primitive chondrites, achondrites underwent heavy metamorphism and/or extensive melting and represent more advanced stages of planetesimal evolution. Spectra were obtained from primitive achondrites (acapulcoite, winonaite, ureilite, and brachinite) and differentiated achondrites (eucrite, diogenite, aubrite, and mesosiderite silicates). The ureilite and brachinite show spectra dominated by olivine features, and the diogenite and aubrite by pyroxene features. The acapulcoite, winonaite, eucrite, and mesosiderite silicates exhibit more complex spectra, reflecting their multi-phase bulk mineralogy.Mixtures of spectra of the primitive achondrites and differentiated achondrites in various proportions show good similarities to the spectra of the few Myr old protoplanetary disks HD104237A and V410 Anon 13. A spectrum of the differentiated mesosiderite silicates is similar to the spectra of the mature debris disks HD172555 and HD165014. A mixture of spectra of the primitive ureilite and brachinite is similar to the spectrum of the debris disk HD113766. The results raise the possibility that materials produced in the early stage of planetesimal differentiation occur in the protoplanetary and debris disks. 相似文献
785.
Conventional methods of palaeoclimate reconstruction provide estimates of climatic parameters using proxy data which have
originated from individual sites. These reconstructions yield information on the local environment but only limited information
on spatial scales that are required for model-data intercomparisons. We present here a new approach that connects these different
scales by an upscaling of the local palaeoinformation together with a dynamically consistent spatial smoothing. A probabilistic
data-based method for local reconstructions is combined with a dynamic constraint on the reconstructed climate parameter which
stabilises the reconstruction on the target scale. The variational analysis leads to climatological fields being optimised
with respect to the proxy data and to the prescribed dynamics in a statistically consistent way. This method allows a probabilistic
approach of quality control of the palaeodata in terms of their spatial consistency and homogeneity and for an estimation
of reconstruction errors. The method was applied to palaeobotanical data to reconstruct near-surface temperature fields constrained
by simple linear dynamics. An approximate approach was used to estimate the magnitude of reconstruction errors in terms of
standard deviations. Reconstructed January and July mean temperature of the early Eemian (∼ 125,000 years bp) have errors with a median value of about 1.8°C in January and about 1.1°C in July. Reconstructions across Europe show positive
temperature anomalies for Scandinavia and near the East coast of the Baltic Sea. In contrast, early Eemian temperatures were
apparently quite similar to those found today in Central Europe, as no drastic differences were reconstructed between the
Eemian and modern (1961–1990) climate. This implies somewhat stronger temperature gradients in the Eemian than are observed
today.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
786.
Eric Lehne Volker Dieckmann Rolando di Primio Andreas Fuhrmann Brian Horsfield 《Organic Geochemistry》2009,40(5):604-616
Asphaltenes extracted from crude oils are proposed to possess structural features of the related source rock kerogen. For the present study micro-scale sealed vessel pyrolysis (MSSV) and combustion isotope ratio mass spectrometry (GC–C–IRMS) were used to compare gas generation from a whole rock (type II-S kerogen) from southern Italy with that from related sulfur rich asphaltenes isolated from a low maturity heavy crude oil. The purpose of was to determine whether experimental pyrolysis of oil asphaltenes can be used to predict the timing and the chemical and isotopic composition of hydrocarbon gases generated from genetically related kerogen in the source rock during burial maturation. The results show that parameters such as (gas to oil ratio) GOR and oil and gas formation timing are very similar for these two sample types, whereas gas composition, product aromaticity and sulfur content are remarkably different. Slight differences in GOR are mainly due to differences in gas formation characteristics at very high levels of thermal alteration. Secondary gas formation from the whole rock covers a much broader temperature range under geological conditions than that from the asphaltene products. However, it is remarkable that both the onset and the maximum temperature are nearly identical under geological conditions. The observed differences in gas generation characteristics are supported by discrepancies in the carbon isotopic characteristics of the gas range compounds and indicate different precursors and/or mechanisms for gas generated from whole rock and asphaltenes. 相似文献
787.
The phenomenon of deficient electron microprobe totals in radiation-damaged and altered zircon 总被引:2,自引:0,他引:2
Lutz Nasdala Andreas Kronz Tamás Váczi Arne Willner 《Geochimica et cosmochimica acta》2009,73(6):1637-1650
The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents often below 95 wt%, is assigned to the analysis of altered, porous minerals. With the example of three zircon populations we show that low totals are related to textural features (i.e., numerous pores of tens to hundreds of nanometers size) as well as to the chemical composition (i.e., water content well within the wt% range, which may affect partial sample degradation under the electron beam). The formation of the spongy texture is explained by the alteration of a previously radiation-damaged and, thus, volume-expanded material in a fluid-driven replacement reaction. The smaller volume of the reaction product (crystalline, non volume-expanded zircon) accounts for the formation of numerous voids and pores, which are perfect candidates for the incorporation of water. The alteration has also resulted in uptake of non-formula elements such as Al, P, Ca, Fe, Y, and REEs whereas Si and Zr are depleted. In one case, strong uptake of non-radiogenic Pb in altered zircon was observed. Because porous, low-total zircon has formed in secondary alteration process, its occurrence can be considered as an indicator of a secondary alteration history of the host rock. Low-total zircon is easily recognized by very low electron back-scatter intensities, which are closely related to the two main causes of the analytical shortfall (i.e., water content and porosity) and often lowered furthermore by the presence of light non-formula elements (especially P and Fe) up to the wt% range. 相似文献
788.
We characterize the lithospheric structure of Isidis Planitia on Mars by analyzing Mars Global Surveyor and Mars Odyssey gravity and topography data using a flexural model of a thin elastic shell including bending and membrane stresses. Isidis Planitia is a circular, relatively flat plain formed near the end of the Early Noachian, at the edge of the highlands-lowlands boundary and the site of a large free-air gravity anomaly, features consistent with modification and filling of an impact basin. Our results suggest that the bulk density of the fill material inside Isidis must be more than 2600 kg m−3 and higher densities are probable. A comparison of the faulting observed at Nili Fossae to the predicted zone of extensional strain northwest of Isidis constrains the thickness of the elastic lithosphere to be 100-180 km thick beneath the basin at the time of loading. We also find that loads outside of the basin play a significant role in the interpretation of the tectonics; simplified models tend to overestimate the lithospheric thickness. We place relatively narrow bounds on the thermal gradient (3.4-6.5 K km−1) and heat flux (13.6-26 mW m−2) at Isidis at the time of loading. 相似文献
789.
Stéphane Kock Peter Huggenberger Frank Preusser Philippe Rentzel Andreas Wetzel 《Swiss Journal of Geoscience》2009,102(2):307-321
The response of fluvial systems to tectonic activity and climate change during the Late Pleistocene influenced sedimentary
processes and hence the conditions of river terraces formation. The northern Alpine foreland is well adapted for such studies
due to the high sediment input and the variety of depositional environments. This study focuses on sediments of a part of
the Rhine River in the area of Basel, at the Border between Switzerland, Germany and France. A detailed evolution of the Lower
Terrace is inferred from sedimentological, geomorphologic and pedological observations as well as historical documents, and
calibrated using different dating methods (optically stimulated luminescence, uranium series disequilibrium, radiocarbon).
The Lower Terrace was deposited during two periods (30–15 ka and 13–11 ka), which correlate with two cold climatic phases,
representing the Last Glaciation of the Alps and the Younger Dryas. These ages underline that main incision of the Lower Terrace
braidplain in the area of Basel is restricted to post Younger Dryas times, as sediments of that age (13–11 ka) are found atop
the highest levels. From then on, a flight of cut-terraces were formed with minor re-accumulation due to Holocene flood events.
These findings demonstrate that the surface of a terrace does not always represent the age of sediment aggradation, and this
should be remembered when using terraces to reconstruct the tectonic history of an area. 相似文献
790.
过去20年中, 北朝鲜在核不扩散问题的外交政策方面一直与西方国家争论不休. 迫于前苏联的压力, 北朝鲜于1985年勉强加入了1968年签订的《核武器不扩散条约》. 但是, 在加入该条约之后, 北朝鲜就停止了必须履行的谈判, 而且也没有令其与国际原子能机构(IAEA)签署的全面安全协议(CSA)生效. 该协议本应于1986年生效, 但直到1992年4月10日它才有了合法约束力. 同年, 国际原子能机构基于其在伊拉克的经验, 在核安全方面实施了新方法. 在原有系统下, 国际原子能机构采用了一种“材料审计”的方法, 该方法只是检查其所申报核材料的存货清单是否正确. 然而, 自1992年开始, 国际原子能机构对接受其检查的国家所申报内容的完备性也开展了评估工作. 相似文献