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61.
62.
Nathalie van Vliet Ole Mertz Andreas Heinimann Tobias Langanke Unai Pascual Birgit Schmook Cristina Adams Dietrich Schmidt-Vogt Peter Messerli Stephen Leisz Jean-Christophe Castella Lars Jørgensen Torben Birch-Thomsen Cornelia Hett Thilde Bech-Bruun Amy Ickowitz Kim Chi Vu Kono Yasuyuki Jefferson Fox Christine Padoch Alan D. Ziegler 《Global Environmental Change》2012,22(2):418-429
This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems. 相似文献
63.
Laboratory experiments, statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep-sea sediments which are in compaction equilibrium with the overburden. A revised and generalized version of Athy's law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles' surfaces. Especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces. The sediments analyzed almost range from systems of »suspended grains« to nearly perfect »colloidal systems«. The methods and equations required to derive the relevant parameters are given for both, downhole porosity/density measurements and laboratory experiments.
Zusammenfassung Die Synthese experimenteller Labordaten, statistischer Analysen von Messungen an Kernen und theoretischer Modellierung der Kompaktion im Gleichgewicht mit der Auflast ermöglicht die Definition von Typ-Kurven für das Kompaktionsverhalten von verschiedenen Tiefsee-Sedimenten. Eine erweiterte und verbesserte Form der Athy'schen Gleichung erlaubt zusammen mit Laborexperimenten, Sedimente entsprechend des Anteils an strukturell gebundenem Porenwasser zu klassifizieren. Anhand von Saugspannungsexperimenten können die Bindungskräfte zwischen Wasser und Partikeloberflächen abgeschätzt werden. Die untersuchten Sedimente reichen von »suspendierten Körnern« bis zu einem »kolloidalen System«. Die notwendigen Methoden und Gleichungen zur Bestimmung der relevanten Parameter aus Bohrlochdaten und Laborexperimenten werden diskutiert.
Résumé A partir d'une synthèse de résultats d'expériences de laboratoires, d'analyses statistiques de données de terrain et d'une modélisation théorique, il est possible d'établir des courbes standard du processus de compaction pour divers types de sédiments de mer profonde, pour lesquels la compaction est en équilibre avec la charge. Une version revue et généralisée de la loi d'Athy permet, en accord avec les résultats expérimentaux, de classer les sédiments selon la quantité d'eau intersticielle liée structuralement à la surface des particules. Les sédiments analysés correspondent à des systèmes qui vont du type à «grains suspendus» à des colloïdes presque parfaits. Les auteurs présentent une discussion détaillée des méthodes et des équations néssaires à l'obtention des paramètres significatifs tant à partir des expériences de laboratoire qu'à partir des mesures de porosité/densité effectuées dans les forages.
, , . Athy , , . . . .相似文献
64.
65.
Andreas J. Kappos 《地震工程与结构动力学》1991,20(2):177-190
An analytical methodology for estimating the values of behaviour factors (q-factors), suggested in a companion paper, is applied to two typical reinforced concrete structures, a frame and a dual system, designed according to current European trends in seismic design. The two case studies clearly indicated the need to consider both local and overall collapse criteria, since either one can be critical for the determination of the behaviour factor, depending on the type of the structure. The calculated values of q-factors were close to, but higher than those specified by modern seismic codes, the larger discrepancy occurring in the case of the dual system. 相似文献
66.
On the influence of the physico-chemical properties of aerosols on the life cycle of radiation fogs 总被引:3,自引:0,他引:3
Andreas Bott 《Boundary-Layer Meteorology》1991,56(1-2):1-31
A one-dimensional model of radiation fog with detailed microphysics is presented. Aerosols and cloud droplets are treated in a joint two-dimensional size distribution. Radiative fluxes are calculated as functions of the radiative properties of the time-dependent particle spectra. The droplet growth equation is solved by considering radiative effects. Turbulence is treated by means of a higher order closure model. The interaction between the atmosphere and the earth's surface is explicitly simulated.Three numerical sensitivity studies are performed to investigate the impact of the different physico-chemical properties of urban, rural and maritime aerosols on fog formation. Numerical results elucidate that depending on the aerosol type used, the resulting fog events are completely different. This is particularly true for the times of fog formation and dissipation as well as for the liquid water content and supersaturations within the fogs. In the activated part of the particle spectra, the aerosol mass is very inhomogeneously distributed. The maxima of the curves do not coincide with the maxima of the corresponding liquid water distributions. 相似文献
67.
Martin Wessels Angela Lenhard Federico Giovanoli Andreas Bollhöfer 《Aquatic Sciences - Research Across Boundaries》1995,57(4):291-304
Sediments in Lake Constance have been dated by radiometric methods and lamination counting. Investigations into the concentrations of lead and zinc in the sediments were carried out to get detailed information about environmental history. Maximum concentrations were found at the beginning of the 1960's. The lead maximum contamination occurred 3 years before the zinc maximum and has an unidentified source. The use of coal, leaded gasoline or the remobilization within the sediment could be excluded to result in the lead maximum. The fluctuations in zinc contamination could be explained with increasing and decreasing pollution (industry, coal burning, building of sewage plants). The greatest fluctuations of both metals occur during periods of great change in the economic history of Germany. 相似文献
68.
Erhard Wielandt Andreas Sigg Axel Plešinger Josef Horálek Reviewer K. Pěč 《Studia Geophysica et Geodaetica》1987,31(1):1-7
Summary Phase velocities of Rayleigh and Love waves have been measured between the broadband seismic stations KHC (Kaperské Hory, South Bohemia) and KSP (Ksi, Lower Silesia), a profile that nearly coincides with the Interactional DSS Profile VII. The data for both wave types were separately inverted into models of shear-wave velocity versus depth. Novotný's model KHKS 82[1] for the DSS Profile VII was used as a start model. While the crustal section of Novotný's model is compatible with both of our data sets, our Rayleigh-wave data require smaller shear-wave velocities, on the average by 0.24 km/s, in the top 180 km of the mantle. The average difference between Novotný's model and our Love-wave model in that depth range is only 0.06 km/s. If our identification of the observed Love waves as the fundamental mode is correct, this result indicates the presence of polarization anisotropy in the uppermost mantle.
u a mu u a ¶rt; unu uuu mauu (an , a u) u S (, ua uu). u - S nuuum mmmm ¶rt;a¶rt; nu VII . a ¶rt; u mun m¶rt; umua ¶rt;u auumu mu nn mu. am mam¶rt;u a unaa ¶rt; S 82 m[1] ¶rt; nu VII . a am ¶rt;u m aua uu aau au ¶rt;a, ¶rt;a au ¶rt;a ¶rt; mm uu m nn — ¶rt; a 0,24 / 180 uma amuu. ¶rt;a aua ¶rt; ¶rt; m u a ¶rt; ¶rt; a m ¶rt;uanau n¶rt;mam 0,06 /. u aa u¶rt;muuau a¶rt;a a a ¶rt;ama ¶rt;a m nau, m mm mam u¶rt;ummm numuu nuau aumnuu amuu.相似文献
69.
70.
Sebastian Hinsken Kamil Ustaszewski Andreas Wetzel 《International Journal of Earth Sciences》2007,96(6):979-1002
Eocene to Early Oligocene syn-rift deposits of the southern Upper Rhine Graben (URG) accumulated in restricted environments.
Sedimentation was controlled by local clastic supply from the graben flanks, as well as by strong intra-basinal variations
in accommodation space due to differential tectonic subsidence, that in turn led to pronounced lateral variations in depositional
environment. Three large-scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards
brackish or freshwater conditions. They form three major base level cycles that can be traced throughout the basin, each of
them representing a stratigraphic sub-unit. A relatively constant amount of horizontal extension (ΔL) in the range of 4–5 km has been estimated for the URG from numerous cross-sections. The width of the rift (L
f
), however, varies between 35 and more than 60 km, resulting in a variable crustal stretching factor between the bounding
masterfaults. Apart from block tilting, tectonic subsidence was, therefore, largely controlled by changes in the initial rift
width (L
0). The along-strike variations of the graben width are responsible for the development of a deep, trough-like evaporite basin
(Potash Basin) in the narrowest part of the southern URG, adjacent to shallow areas in the wider parts of the rift such as
the Colmar Swell in the north and the Rhine Bresse Transfer Zone that delimits the URG to the south. Under a constant amount
of extension, the along-strike variation in rift width is the principal factor controlling depo-centre development in extensional
basins. 相似文献