Metastability of Liquid Water on Mars     

Michael H. Hecht 《Icarus》2002,156(2):373-386

A simple model of local heat transport on Mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal-incidence insolation. An experiment has been performed to confirm the model of evaporation rate at low pressure. Reduction of radiative cooling due to gully geometry is shown to be important. Since appropriate meteorological, topographic, and optical conditions may occur on slopes nearly anywhere on the planet, hydrological features such as gullies would likely form only where such ice might accumulate, notably in sheltered locations at high latitudes. It is suggested that cold-trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies.  相似文献   

First Results from ISO Spectra of Supernova Remnants Heavily Interacting with the ISM     

E. Oliva  S. Drapatz  D. Lutz  E. Sturm  A.F.M. Moorwood 《Astrophysics and Space Science》1997,255(1-2):211-219

ISO spectra of the supernova remnant RCW103 are presented. This object is the prototype of a SNR shock heavily interacting with dense ISM (probably a molecular cloud). The spectra are dominated by prominent lines and show very little continuum at λ < 40 μm suggesting that the 12 and 25 μm IRAS emission from these types of remnant could be dominated by lines rather than continuum emission from warm dust heated by the shock as generally believed. The ISO data provide for the first time a simple and reliable estimate of the gas phase abundances of Si and Fe which are found to be close to solar relative to non refractory species such as Ne, S and Ar. This indicates that the shock is very effective in destroying the ISM dust and may therefore explain the absence of warm dust behind the shock. Like the optical Nickel lines, [NiII]6.63 μm yields Ni/Fe abundances a factor ≥ 10 above solar which we conclude results from a large underestimation of the computed Ni+ collision strengths. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Improving trajectory estimation using 3D city models and kinematic point clouds     

Lukas Lucks  Lasse Klingbeil  Lutz Plümer  Youness Dehbi 《Transactions in GIS》2021,25(1):238-260

Accurate and robust positioning of vehicles in urban environments is of high importance for autonomous driving or mobile mapping. In mobile mapping systems, a simultaneous mapping of the environment using laser scanning and an accurate positioning using global navigation satellite systems are targeted. This requirement is often not guaranteed in shadowed cities where global navigation satellite system signals are usually disturbed, weak or even unavailable. We propose a novel approach which incorporates prior knowledge (i.e., a 3D city model of the environment) and improves the trajectory. The recorded point cloud is matched with the semantic city model using a point‐to‐plane iterative closest point method. A pre‐classification step enables an informed sampling of appropriate matching points. Random forest is used as classifier to discriminate between facade and remaining points. Local inconsistencies are tackled by a segmentwise partitioning of the point cloud where an interpolation guarantees a seamless transition between the segments. The general applicability of the method implemented is demonstrated on an inner‐city data set recorded with a mobile mapping system.  相似文献   

Mid-infrared spectral decomposition between starbursts and AGNs     

O. Laurent  D. Tran  D. Lutz  R. Genzel  I.F. Mirabel 《Astrophysics and Space Science》2001,277(1):101-101

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Materials embodied in international trade – Global material extraction and consumption between 1995 and 2005     

Martin Bruckner  Stefan Giljum  Christian Lutz  Kirsten Svenja Wiebe 《Global Environmental Change》2012,22(3):568-576

Production and consumption activities in industrialized countries are increasingly dependent on material and energy resources from other world regions and imply significant economic and environmental consequences in other regions around the world. The substitution of domestic material extraction and processing through imports is also shifting environmental burden abroad and thus extends the responsibility for environmental impacts as well as social consequences from the national to the global level. Based on the results of the Global Resource Accounting Model, this paper presents the first trade balances and consumption indicators for embodied materials in a time series from 1995 to 2005. The model includes 53 countries and two world regions. It is based on the 2009 edition of the input–output tables and bilateral trade data published by the Organisation for Economic Co-operation and Development (OECD) and is extended by physical data on global material extraction. The results quantify the global shift of embodied material resources from developing and emerging countries to the industrialized world. In addition to the level of industrialization and wealth, population density is identified as an important factor for the formation of physical trade patterns. Exports of embodied materials of less densely populated countries tend to surpass their imports, and vice versa. We also provide a quantitative comparison between conventionally applied indicators on material consumption based on direct material flows and indicators including embodied material flows. We show that the difference between those two indicators can be as much as 200%, calling for an adjustment of conventional national material flow indicators. Multi-regional input–output models prove to be a useful methodological approach to derive globally consistent and comprehensive data on material embodiments of trade and consumption.  相似文献   

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   

The texture of condensed CO₂ on the martian polar caps     

Michael H. Hecht 《Planetary and Space Science》2008,56(2):246-250

The widespread deposition of CO₂ ice on the martian polar caps in winter is readily visible from Earth and has been extensively studied from orbit. As the surface cools during polar night, CO₂ condenses directly out of the atmosphere at a rate that establishes equilibrium between radiative loss and latent heat of condensation. Since radiative loss is strongly geometry-dependent, the CO₂ frost will grow most rapidly on exposed surfaces and more slowly in depressions. Positive feedback will cause a dramatic enhancement of the relief of the underlying topography and a corresponding reduction in the average bulk density. The resulting surface will be highly textured and riddled with perforations.  相似文献   

Continental climate in the East Siberian Arctic during the last interglacial: Implications from palaeobotanical records   总被引：1，自引：0，他引：1  

Frank Kienast  Pavel Tarasov  Lutz Schirrmeister  Guido Grosse  Andrei A. Andreev   《Global and Planetary Change》2008,60(3-4):535-562

To evaluate the consequences of possible future climate changes and to identify the main climate drivers in high latitudes, the vegetation and climate in the East Siberian Arctic during the last interglacial are reconstructed and compared with Holocene conditions. Plant macrofossils from permafrost deposits on Bol'shoy Lyakhovsky Island, New Siberian Archipelago, in the Russian Arctic revealed the existence of a shrubland dominated by Duschekia fruticosa, Betula nana and Ledum palustre and interspersed with lakes and grasslands during the last interglacial. The reconstructed vegetation differs fundamentally from the high arctic tundra that exists in this region today, but resembles an open variant of subarctic shrub tundra as occurring near the tree line about 350 km southwest of the study site. Such difference in the plant cover implies that, during the last interglacial, the mean summer temperature was considerably higher, the growing season was longer, and soils outside the range of thermokarst depressions were drier than today. Our pollen-based climatic reconstruction suggests a mean temperature of the warmest month (MTWA) range of 9–14.5 °C during the warmest interval of the last interglacial. The reconstruction from plant macrofossils, representing more local environments, reached MTWA values above 12.5 °C in contrast to today's 2.8 °C. We explain this contrast in summer temperature and soil moisture with a combination of summer insolation higher than present and climatic continentality in arctic Yakutia stronger than present as result of a considerably less inundated Laptev Shelf during the last interglacial.  相似文献   

In situ micro‐Raman and X‐ray diffraction study of diamonds and petrology of the new ureilite UAE 001 from the United Arab Emirates     

Dominik C. HEZEL  Leonid DUBROVINSKY  Lutz NASDALA  Jean CAUZID  Alexandre SIMIONOVICI  Marko GELLISSEN  Thorbjörn SCHÖNBECK 《Meteoritics & planetary science》2008,43(7):1127-1136

Abstract— A new olivine‐pigeonite ureilite containing abundant diamonds and graphite was found in the United Arab Emirates. This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo_79.8–81.8) and pyroxene (En_73.9–75.2, Fs_15.5–16.9, Wo_8.8–9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo_96.1–96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro‐Raman and in situ synchrotron X‐ray diffraction. The main diamond Raman band (LO = TO mode at ?1332 cm^?1) is broadened when compared to well‐ordered diamond single crystals. Full widths at half maximum (FWHM) values scatter around 7 cm^?1. These values resemble FWHM values obtained from chemical vapor deposition (CVD) diamond. In situ XRD measurements show that diamonds have large grain sizes, up to >5 μm. Some of the graphite measured is compressed graphite. We explore the possibilities of CVD versus impact shock origin of diamonds and conclude that a shock origin is much more plausible. The broadening of the Raman bands might be explained by prolonged shock pressure resulting in a transitional Raman signal between experimentally shock‐produced and natural diamonds.  相似文献   

Ground ice and slope sediments archiving late Quaternary paleoenvironment and paleoclimate signals at the margins of El'gygytgyn Impact Crater, NE Siberia     

Georg Schwamborn  Hanno Meyer  Lutz Schirrmeister 《Quaternary Research》2006,66(2):259-272

An accumulation terrace close to the El'gygytgyn Impact Crater in northeastern Siberia contains stratigraphic and periglacial evidence of the paleoenvironmental and paleoclimatic history and permafrost dynamics during late Quaternary time. A succession of paleo active-layer deposits that mirror environmental changes records periods favorable for the establishment and growth of ice-wedge polygonal networks and sediment variations. These two elements of the periglacial landscape serve as complementary paleoenvironmental archives that can be traced back to ∼ 14,000 cal yr BP. The slope sediments and the ground ice contained therein have prominent relative maxima and minima in properties (grain size, total organic content, oxygen isotopes). They document a regional early Holocene thermal maximum at about 9000 cal yr BP, followed by a transition to slightly cooler conditions, and a subsequent transition to slightly warmer conditions after about 4000 cal yr BP. Results from sedimentary analysis resemble morphological and geochemical (oxygen and hydrogen isotopes) results from ice wedge studies, in which successive generations of ice-wedge polygonal networks record warmer winters in late Holocene time. Moreover, peaks of light soluble cation contents and quartz-grain surface textures reveal distinct traces of cryogenic weathering. We propose a conclusive sedimentation model illustrating terrace formation in a permafrost terrain.  相似文献