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61.
正A Dunaliella strain was isolated from Yuncheng Salt Lake,Shanxi,China(111.05°E,35.03°N).Morphological characteristics and molecular data were used to evaluate the relationship of this algal strain to other Dunaliella 相似文献
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Stereo images obtained during the DS1 flyby were analyzed to derive a topographic model for the nucleus of Comet 19P/Borrelly for morphologic and photometric studies. The elongated nucleus has an overall concave shape, resembling a peanut, with the lower end tilted towards the camera. The bimodal character of surface-slopes and curvatures support the idea that the nucleus is a gravitational aggregate, consisting of two fragments in contact. Our photometric modeling suggests that topographic shading effects on Borrelly's surface are very minor (<10%) at the given resolution of the terrain model. Instead, albedo effects are thought to dominate Borrelly's large variations in surface brightness. With 90% of the visible surface having single scattering albedos between 0.008 and 0.024, Borrelly is confirmed to be among the darkest of the known Solar System objects. Photometrically corrected images emphasize that the nucleus has distinct, contiguous terrains covered with either bright or dark, smooth or mottled materials. Also, mapping of the changes in surface brightness with phase angle suggests that terrain roughness at subpixel scale is not uniform over the nucleus. High surface roughness is noted in particular near the transition between the upper and lower end of the nucleus, as well as near the presumed source region of Borrelly's main jets. Borrelly's surface is complex and characterized by distinct types of materials that have different compositional and/or physical properties. 相似文献
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Airborne laser scanning data contain information about surface features, some of which are of subtle form. These features are usually embedded within the terrain, and rarely form distinct shape-transition to their surroundings. While some efforts have been made in extracting linear elements from laser scanning data, attention was mostly turned to dominant elements that are very clear and distinct. We present in this paper a detection model for gullies of various dimensions using airborne laser scanning data. Gullies are regarded as one of the main landform-reshaping agents, having a pejorative effect on the environment and on regional development. They are commonly observed along receding lakes as a common response to water-level drop. The paper demonstrates how a multi-scale approach enables the extraction of various gully forms, from well developed to subtle. It then proposes an optimization driven model for handling fragmentation in the detection. Results show that using the proposed model, gully networks can be reconstructed and ∼30 cm deep features can be identified and separated from their surroundings using moderate point density data. 相似文献
66.
As a type of negative topography in sand land, blowout has always been one of the main research object of aeolian geomorphology. Especially, multi-directions and long-term research has been conducted internationally on basic morphology, development process and dynamic mechanism of coastal sandy blowout. Based on the systematic review of research on coastal sandy blowout, the main progress of research on coastal sandy blowout in morphological evolution, morpho-dynamic process, and research methods was summarized. In consideration of the disadvantages of research on coastal sandy blowout, it was proposed that, at present, the research on coastal sandy blowout in China should strengthen the further research on the evolution mechanism, morphology-material-dynamic process and numerical simulation of different types of blowouts, and attach importance to the influence of blowout on the beach-dune dynamic environment and foredune restoration. 相似文献
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Alan Marcus 《地球表面变化过程与地形》1980,5(4):389-398
First-order drainage basin morphology consists of two complementary regions: a headwater region, the valley head; and a stream region, the channelway (Figure 1). Each subbasin's morphology is represented by a set of principal components factors that include the properties of area, length, slope, relief, elongation, and plan curvature. The channelway region is a highly-integrated morphological unit that is dominated by a size-shape factor, indicative of an organized flow system and the presence of a permanent channel. The valley head region shows little integration of its morphological factor set, and this is reflected by its lack of a permanent channel. The valley head-channelway definition is utilized to classify first-order basins into three morphological groups or types. Basin type is related to basin location within the larger drainage network, and this relation helps to explain variations in subbasin morphology. The channelway's morphologic properties are influenced by the location of the first-order basin's bifurcation or junction within the higher-ordered network; and valley head morphology is related to the location of the basin's divide position within the drainage net. 相似文献
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Terrestrial gastropods, especially those dwelling in dry habitats such as the Mediterranean, are highly susceptible to dehydration. In this study, the use of refuges by Iberus gualtieranus gualtieranus and Sphincterochila candidissima is compared. These two species belong to families with different distribution ranges, but they live in sympatry on a mountain in southern Spain with a dry Mediterranean climate. I. g. gualtieranus used mainly rock crevices as refuges, consistently throughout the year. S. candidissima hibernated beneath humus during autumn and winter (I. g. gualtieranus did not hibernate). In spring, S. candidissima seemed active, while I. g. gualtieranus was already aestivating. In summer, S. candidissima aestivated on vegetation, while I. gualtieranus aestivated deep within crevices. These differences in the use of refuges may be explained on the basis of the need for more protection by I. g. gualtieranus because of its morphology, which is less suited to the dry habitat, but has evolved to enable this species to exploit karstic crevices as refuges more efficiently. These results illustrate that behaviour and morphology interact allowing both species to coexist in sympatry in an arid environment using different adaptive strategies. 相似文献