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61.
Emilio Rodríguez-Caballero José Raúl Román Sonia Chamizo Beatriz Roncero Ramos Yolanda Cantón 《地球表面变化过程与地形》2019,44(14):2771-2779
Biological soil crust, or biocrust communities, are the dominating life form in many extreme habitats, such as arid and semiarid badlands, where water scarcity and highly erodible substrates limit vegetation cover. While climate, soil and biotic factors have been described as environmental filters influencing biocrust distribution in such biomes, little is known about the effect of terrain attributes on creating specific microhabitats that promote or restrict biocrust colonization. This study aimed to identify the main terrain attributes controlling biocrust distribution in the driest badland system in Europe, the Tabernas Badlands (SE Spain). To do this, we analysed the influence of different terrain attributes related to landscape stability and microclimate formation on the spatial distribution of lichen and cyanobacteria, using field measurements and topographical information from a LiDAR survey. Our results showed that the spatial distribution of cyanobacteria-dominated biocrusts, which are physiologically and morphologically adapted to extreme drought and high UVA radiation, was mostly associated with areas of high potential incoming solar radiation. The exception was bare south-aspect hillslopes with very high sediment transport potential, where bare physically crusted soils were the dominant ground cover. Lichen-dominated biocrusts, in contrast, colonized near the top of north-aspect hillslopes, characterized by low potential incoming solar radiation and potential evapotranspiration, and their cover decreased downstream, as conditions became good enough for vascular plants. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. 相似文献
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Slope movements together with intensive river erosion and the following accumulation are the leading processes in the landscape evolution in the area of Machu Picchu village (former Aguas Calientes), which is located close to the Machu Picchu Sanctuary. Debris flows affect not only the bottoms of valleys or canyons, but also debris fans at the termini of the drainage basins, which are heavily inhabited at some places. The most recent event in the Machu Picchu village occurred in April 2004, but several others were documented in a broader area in the last 50 years. The field inspections at Machu Picchu (May and September 2004; June and September 2005) together with oral testimony revealed the nature and behavior of the debris flow. Machu Picchu village can be assessed as a zone with high landslide risk in relation to its urban development. Despite that, the village recorded a rapid growth (threefold population increase) without urban control within the past two decades. Precipitation, which is the main triggering factor of the debris flows, and natural hazard management of the Machu Picchu village are discussed in this paper. 相似文献
65.
Vertical distribution and seasonality of peracarid crustaceans associated with intertidal macroalgae
J.M. Guerra-García E. Baeza-Rojano M.P. Cabezas J.C. García-Gómez 《Journal of Sea Research》2011,65(2):256-264
Spatial patterns and seasonal fluctuations of intertidal peracarids from Tarifa Island, Strait of Gibraltar, were studied over a two-year period (December 2005–December 2007). A total of 25,749 individuals were collected, comprising 46 species. Amphipods were best represented in the total number of species (32) and individuals (89% of numerical abundance) followed by isopods (12 species and 11% abundance) and tanaids (2 species and 1%). The highest number of species was registered in intermediate levels (1–1.5 m) dominated by Corallina elongata, although the highest abundances of peracarids were associated to seaweeds of lower levels (0–1 m) such as Gelidium corneum, Osmundea pinnatifida, Valonia utricularis and a turf of Caulacanthus ustulatus. The most abundant peracarids, Hyale stebbingi, H. schmidti, H. perieri, Stenothoe monoculoides, Caprella penantis, C. grandimana, Dynamene edwardsii and Ischyromene lacazei, were present throughout the whole year during 2006 and 2007. The highest peracarid densities were measured in April–August coinciding with the highest development of seaweeds, just before the maximum values of water temperature measured at the end of summer. Multivariate analyses confirmed a clear zonation of algae and associated peracarids in a vertical gradient, which was maintained stable during the two-year study. Several physical and biological factors may regulate such patterns of peracarid abundance and future experimental studies are necessary to explore the importance of factors such as competition, predation or weather conditions. 相似文献
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Modelling magnetization processes in single-and multi-domain rock samples using the preisach diagram
Summary The paper presents the results of identifying a model of the Preisach type for haematite grains of the single-domain as well as multi-domain size. Due to the phenomenological conception of the model, the relations between the parameters of the model and actual parameters are very complex, however, impressive accuracy and stability of the modified model indicate the need to resume studies of this problem. The model parameters also confirm the adequate properties of the vibrating-sample magnetometr (VSM) used and developed in our laboratories. 相似文献
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Repeat Ground Track Orbits of the Earth Tesseral Problem as Bifurcations of the Equatorial Family of Periodic Orbits 总被引:1,自引:0,他引:1
Martín Lara 《Celestial Mechanics and Dynamical Astronomy》2003,86(2):143-162
Orbits repeating their ground track on the surface of the earth are found to be members of periodic-orbit families (in a synodic frame) of the tesseral problem of the Earth artificial satellite. Families of repeat ground track orbits appear as vertical bifurcations of the equatorial family of periodic orbits, and they evolve from retrograde to direct motion throughout the 180 degrees of inclination. These bifurcations are always close to the resonances of the Earth's rotation rate and the mean motion of the orbiter. 相似文献
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We study the existence of invariant tori in a neighbourhood of the collinear equilibrium points of the planar three-body problem. To this end some properties of the normal form of the Hamiltonian reduced to the 4D central manifold are proved. Using this normal form, we show that the nondegeneracy conditions of KAM theorem are satisfied for all positive masses, including the 2:1 resonance case. The evaluation of the conditions is done numerically. 相似文献
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The paper is a contribution to the study of two-ribbon flares. A variety of observational material, i.e. Hα pictures, radio spectrum in the frequency band of 150–1000 MHz, radio map at 6 cm, fluxes at other frequencies, magnetograms and X-ray flux in a broad energy interval, enabled us to study the development of the 16 May, 1981 flare. The onset of the flare could be described by the model of Van Tend and Kuperus. A diminishing of the magnetic shear during the activation of the filament was observed. From radio and X-ray data it was found that pulsed acceleration took place in the region under the rising filament, the electrons propagating in a limited region both upwards to greater heights and downwards into the footpoints. Internal oscillations of the filament were observed. A manifestation of the primary process of interplanetary shock-wave generation was found. The 6 cm radio sources could be localized in the footpoints of magnetic loops. 相似文献
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