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61.
Anita Bernatek-Jakiel Jiří Bruthans Jan Vojtíšek Mateusz Stolarczyk Tomasz Zaleski 《地球表面变化过程与地形》2020,45(13):3185-3201
Soil piping is a widespread land degradation process that may lead to gully formation. However, the processes involved in sediment detachment from soil pipe walls have not been well studied, although their recognition is a crucial step to protect soils from piping erosion. This study aims to recognize the factors affecting cohesion and to identify the mechanisms which are likely to be responsible for the disintegration of soil. The study has been conducted in mid-altitude mountains under a temperate climate (the Bieszczady Mountains, the Carpathians, SE Poland). The research was based on the detailed field and laboratory analyses of morphology, and the physical and chemical properties of soil profiles with and without soil pipes. Moreover, experiments with flooding the undisturbed soil samples using different solutions (deionized water, ammonium oxalate, dithionate citrate, 35% hydrochloric acid and 30% hydrogen peroxide) were conducted in order to check the role of air slaking, the removal of soil organic carbon (SOC), and Fe and Al oxides on sediment detachment. The obtained results have confirmed that soil pipes develop in quite cohesive soils (silt loams), which allow the formation and maintenance of pipes with a diameter up to 30 cm. Soil cohesion, and thus susceptibility to piping, are impacted by the content of major oxides, soil particle size distribution, biological activity and porosity. The tested soils affected by piping erosion have a lower content of Al2O3 and Fe2O3, and free Fe (Fe(DCB)), lower clay content, higher biological activity (more roots and animal burrows), higher porosity, and more and larger pores than the profile without soil pipes. The experiments have indicated that especially SOC along with Fe and Al oxides are an important cohesion source in the study area. This suggests that the removal of SOC, and Fe and Al oxides may weaken and disintegrate aggregates in soil pipes. Further study of soil leaching and tensile strength will broaden understanding of which chemical processes control where pipes will develop in other cohesive piping-prone soils. © 2020 John Wiley & Sons, Ltd. 相似文献
62.
Shear zones in porous sand: Insights from ring-shear experiments and naturally deformed sandstones 总被引:2,自引:1,他引:2
In a high-resolution small-scale seismic experiment we investigated the shallow structure of the Wadi Araba fault (WAF), the principal fault strand of the Dead Sea Transform System between the Gulf of Aqaba/Eilat and the Dead Sea. The experiment consisted of 8 sub-parallel 1 km long seismic lines crossing the WAF. The recording station spacing was 5 m and the source point distance was 20 m. The first break tomography yields insight into the fault structure down to a depth of about 200 m. The velocity structure varies from one section to the other which were 1 to 2 km apart, but destinct velocity variations along the fault are visible between several profiles. The reflection seismic images show positive flower structures and indications for different sedimentary layers at the two sides of the main fault. Often the superficial sedimentary layers are bent upward close to the WAF. Our results indicate that this section of the fault (at shallow depths) is characterized by a transpressional regime. We detected a 100 to 300 m wide heterogeneous zone of deformed and displaced material which, however, is not characterized by low seismic velocities at a larger scale. At greater depth the geophysical images indicate a blocked cross-fault structure. The structure revealed, fault cores not wider than 10 m, are consistent with scaling from wear mechanics and with the low loading to healing ratio anticipated for the fault. 相似文献
63.
We have analyzed the intermediate-term periodicities in soft X-ray flare index (FISXR) during solar cycles 21, 22 and 23. Power-spectral analysis of daily FISXR reveals a significant period of 161 days in cycle 21 which is absent during cycles 22 and 23. We have found that in cycle 22 periodicities of 74 and 83 days are in operation. A 123-day periodicity has been found to be statistically significant during part of the current solar cycle 23. The existence of these periodicities has been discussed in the light of earlier results. 相似文献
64.
Cochran Anita Veverka Joseph Bell James Belton Michael Benkhoff Johannes Benkhoff Andrew Clark Benton Feldman Paul Kissel Jochen Mahaffy Paul Malin Michael Murchie Scott Neimann Hasso Owen Tobias Robinson Mark Schwehm Gerhard Squyres Steve Thomas Peter Whipple Fred Yeomans Donald 《Earth, Moon, and Planets》2000,89(1-4):289-300
In 1997, the COmet Nucleus TOUR (CONTOUR) was selected byNASA for a new start as part of the Discovery line. In this paper, we review the status of the mission, the mission timeline and the instruments to be flown. Detail is given of the science goals and how they are to be accomplished. 相似文献
65.
In this paper we present complete two-dimensional measurements of the observed brightness of the 9th November 1990Hα flare, using a PDS microdensitometer scanner and image processing software MIDAS. The resulting isophotal contour maps, were
used to describe morphological-cum-temporal behaviour of the flare and also the kernels of the flare. Correlation of theHα flare with SXR and MW radiations were also studied. 相似文献
66.
Anita Mohan Bhola N. Dwivedi Enrico Landi 《Journal of Astrophysics and Astronomy》2000,21(3-4):407-411
Using spectra obtained from the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on the spacecraft
SOHO (Solar and Heliospheric Observatory), we investigate the height dependence of electron density, temperature and abundance
anomalies in the solar atmosphere. In particular, we present the behaviour of the solar FIP effect (the abundance enhancement
of elements with first ionization potential < 10 eV in the corona with respect to photospheric values) with height
above an active region observed at the solar limb, with emphasis on the so-called transition region lines. 相似文献
67.
68.
This article presents a novel open source toolbox for street network comparison based on the Sextante geoprocessing framework for the open source Geographic Information System Quantum GIS (QGIS). In the spirit of open science, the toolbox enables researchers worldwide to assess the quality of street networks such as OpenStreetMap (OSM) by calculating key performance indicators commonly used in street network comparison studies. Additionally, we suggest two new performance indicators for turn restriction and one‐way street comparisons specifically aimed at testing street network quality for routing. We demonstrate the use of this toolbox by comparing OSM and the official Austrian reference graph “Graph Integration Platform” (GIP) in the greater Vienna region. 相似文献
69.
The majority of Alpine glaciers are currently receding because of global warming. Their forefields have become interesting sites to study primary microbial colonisation and microbial adaptation. Here, the structure and enzyme activity of microbial communities in exposed rock substrates and their changes in a gradient of temperature and soil moisture conditions within the forefield of the Damma glacier in the Swiss Central Alps are discussed. The temperature at the sites differed in the course of a day and also showed differing mean temperatures over the summer. Distinct bacterial communities inhabit the differing sites at the beginning of the experiment and even after transplantation they stay distinct. But a seasonal shift in the communities could be observed, which followed the same pattern for all the samples. Interestingly, microbial enzyme activity was highest at the site with the smallest temperature shifts. 相似文献
70.
Maser emission from the circumstellar envelopes of four late-type red supergiants has been mapped with milli-arcsecond resolution
using MERLIN1. The wind is driven by radiation pressure on dust and the structure and kinematics of the masing regions reflect
the dust properties. The unbeamed radius of water maser blobs, ∼ 1012 m, has been measured for the first time. The velocity gradient is used to derive the dust absorption coefficient which increases
with radius from ≤ 0.1 to ≤ 1.0 m2 kg−1. Comparison with laboratory studies suggests that small crystalline grains are formed near the star and are annealed into
astronomical silicates at larger distances.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献