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71.
An interpretation of the gravity observations in Switzerland is presented. The gravity anomalies are mainly caused by crustal effects. Taking 0.5 g/cm3 as the average density contrast between crust and upper mantle, the remaining positive residual field of + 50 mGal can be explained as the effect of the so-called “lithospheric root” underneath the Swiss Alps. This “root” must be considered as a relatively cold body with increased density. In order to calculate the thermally induced density distribution in the upper mantle, a kinematic and geothermal model has been constructed simulating the Alpine history for a time span covering the last 40 m.y.At the same time the moving lithospheric body (crustal uplift and subsidence of the lower lithosphere) is analysed from a dynamical point of view in order to test the kinematic conditions. The calculation leads to a mantle subsidence rate of 1 mm/y for the present period. 相似文献
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74.
This paper is concerned with the design of steel frames using friction damped slotted bolted connections (SBCs) in the diagonal braces. A dynamic model is developed to describe the behaviour of a single‐degree‐of‐freedom (SDOF) steel frame that uses bilinear hysteretic behaviour for the damper. This model is generalized to MDOF systems. A novel algorithm for displacement reversal in the transition from slip to stick is presented. It uses numerical noise for its success. A design procedure that attains the stiffness of the individual braces and their elongation at the threshold of activation is then applied to a 10‐storey steel frame. This design process is a two‐phase iterative procedure that converges quite fast. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
75.
First GOCE gravity field models derived by three different approaches 总被引:18,自引:10,他引:18
Roland Pail Sean Bruinsma Federica Migliaccio Christoph F?rste Helmut Goiginger Wolf-Dieter Schuh Eduard H?ck Mirko Reguzzoni Jan Martin Brockmann Oleg Abrikosov Martin Veicherts Thomas Fecher Reinhard Mayrhofer Ina Krasbutter Fernando Sans�� Carl Christian Tscherning 《Journal of Geodesy》2011,85(11):819-843
Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analysed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared with combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITG-Grace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-month GOCE gravity field models of 10?cm in terms of geoid heights, and 3?mGal in terms of gravity anomalies, globally at a resolution of 100?km (degree/order 200). 相似文献
76.
Determining Effects of Area Burned and Fire Severity on Carbon Cycling and Emissions in Siberia 总被引:14,自引:0,他引:14
Susan G. Conard Anatoly I. Sukhinin Brian J. Stocks Donald R. Cahoon Eduard P. Davidenko Galina A. Ivanova 《Climatic change》2002,55(1-2):197-211
The Russian boreal forest contains about 25% of the global terrestrial biomass, and even a higher percentage of the carbon stored in litter and soils. Fire burns large areas annually, much of it in low-severity surface fires – but data on fire area and impacts or extent of varying fire severity are poor. Changes in land use, cover, and disturbance patterns such as those predicted by global climate change models, have the potential to greatly alter current fire regimes in boreal forests and to significantly impact global carbon budgets. The extent and global importance of fires in the boreal zone have often been greatly underestimated. For the 1998 fire season we estimate from remote sensing data that about 13.3 million ha burned in Siberia. This is about 5 times higher than estimates from the Russian Aerial Forest Protection Service (Avialesookhrana) for the same period. We estimate that fires in the Russian boreal forest in 1998 constituted some 14–20% of average annual global carbon emissions from forest fires. Average annual emissions from boreal zone forests may be equivalent to 23–39% of regional fossil fuel emissions in Canada and Russia, respectively. But the lack of accurate data and models introduces large potential errors into these estimates. Improved monitoring and understanding of the landscape extent and severity of fires and effects of fire on carbon storage, air chemistry, vegetation dynamics and structure, and forest health and productivity are essential to provide inputs into global and regional models of carbon cycling and atmospheric chemistry. 相似文献
77.
This article is devoted to studying the dynamical evolution and orbital stability of compact extrasolar three-planetary system GJ 3138.In this system,all semima... 相似文献
78.
The physical properties of young stellar objects are studied as functions of the initial spatial distributions of the gas
surface density Σ and angular velocity Ω in pre-stellar cores using numerical hydrodynamic simulations. Two limiting cases
are considered: spatially homogeneous cores with Σ = const and Ω = const and centrally concentrated cores with radius-dependent
densities Σ ∝ r
−1 and Ω ∝ r
−1. The degree of gravitational instability and protostellar disk fragmentation is mostly determined by the initial core mass
and the ratio of the rotational to the gravitational energy, and depends only weakly on the initial spatial configuration
of pre-stellar cores, except for the earliest stages of evolution, when models with spatially homogeneous cores can be more
gravitationally unstable. The accretion of disk matter onto a protostar also depends weakly on the initial distributions of
Σ and Ω, with matter from the collapsing core falling onto the disk at a rate that is slightly higher in models with spatially
homogeneous cores. An appreciable dependence of the disk mass, disk radius, and the disk-to-protostar mass ratio on the initial
density and angular velocity profiles of the parent core is found only for class 0 young objects; this relationship is not
systematic in the later I and II stages of stellar evolution. The mass of the central protostar depends weakly on the initial
core configuration in all three evolutionary stages. 相似文献
79.
80.
Eduard F. Kostylev Fedor P. Tkachenko Irina P. Tretiak 《Ocean & Coastal Management》2010,53(5-6):203-208
“Zernov’s Phyllophora field” is a unique habitat located in the northwestern Black Sea. At the site, there is a dense stand of agarophytes (red algae) and a high diversity of associated fauna. On November 21 2008, the president of Ukraine (Victor Yuschenko) declared this area a botanical reserve of state-wide importance; it was established to protect and restore a unique natural environment. “Zernov’s Phyllophora field” is the first offshore, fully marine MPA in the Black Sea, and it is the largest. The total area is 402,500 ha, covering 12.5% of the northwestern shelf of the Black Sea. The Ukrainian Scientific Centre for the Ecology of Sea has developed a program for (1) preservation, (2) restoration and (3) further rational use of biological resources at the site. It contains three conforming and interdependent sub-programs that put forward a series of measures for implementing the objectives (preservation, restoration, sustainable resource use).The northwestern Black Sea was heavily impacted by anthropogenic loading in the period 1970–1980, and Zernov’s Phyllophora field was considerably degraded and reduced in area. During recent years the perimeter of the Phyllophora field has slightly extended, and restoration of the benthic phytocoenosis has begun. Assigning this area the status of a marine reserve (Marine Protected Area) will further promote processes of restoring faunal and floristic biodiversity to historically healthy levels. 相似文献