共查询到20条相似文献，搜索用时 31 毫秒
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《Astronomy& Geophysics》2009,50(4):4.21-4.26
Monica M Grady reviews the astronomy revealed in samples of solar system material that come to Earth as meteorites, in the Harold Jeffreys Lecture 2008. 相似文献
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Vibration isolation of structures from ground-transmitted waves by open trenches in isotropic, linearly elastic or viscoelastic soil with a shear modulus varying continuously with depth is numerically studied. Both an exponential and a linear shear modulus variation with depth are used in this work. Waves produced by the harmonic motion of a rigid surface machine foundation are considered. The problem is solved by the frequency domain boundary element method employing the Green's function of Kausel-Peek-Hull for a thin layered half-space. Thus only the trench perimeter and the soil-foundation interface need essentially to be discretized. The proposed methodology is first tested for accuracy by solving two Rayleigh wave propagation problems in nonhomogeneous soil with known analytical solutions and/or for which experimental results are available. Then the method is applied to vibration isolation problems and the effect of the inhomogeneity on the wave screening effectiveness of trenches is studied. 相似文献
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The sorption capacity of two natural sorbents of different origin and of Wofatit KPS is determined by dynamic laboratory investigations and the influence of a thermal pretreatment of clinoptilolite, of the type and quantity of regenerants and of the presence of other cations is investigated. There are represented results of the ammonia removal from biologically treated municipal wastewater and of the removal of caesium-ions from laundry wastewaters. The capacity of clinoptilolite is lower than that of the ion-exchange resin, but clinoptilolite has the advantage of a considerably higher affinity for ammonium-ions, so that it can be used also in the presence of other salts in water to be treated. The ammonium concentration should not exceed 30 mg/l, in order to avoid too short filter runs. 相似文献
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The interpretation of magnetotelluric (MT) measurements carried out on shallow (several hundred metres deep) basins and on the surrounding highly resistive rock outcrops can be difficult due to different forms of distortion, mainly 3D effects. A good example for study of this problem is the Mór Graben, which is the transition zone between the Bakony and Vértes Mountains (W-Hungary), where more than 20 MT soundings have been made with stations spaced about 2 km apart to determine the structure of a conductivity anomaly at a depth of about 3–4 km.
The statistical treatment of the different distortions due to varying sediment cover (the S-effect or static shift) and to the steep wall of the resistive basement outcrops (edge effect), etc., enabled the estimation of the actual parameters of the conductive formation. The interpretation of the field data is supported by numerical modelling. 相似文献
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R. Meerkötter U. Schumann D. R. Doelling P. Minnis T. Nakajima Y. Tsushima 《Annales Geophysicae》1999,17(8):1080-1094
A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm−2 daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover. 相似文献
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Lagrangian analysis by clustering 总被引：1，自引：1，他引：0
We propose a new method for obtaining average velocities and eddy diffusivities from Lagrangian data. Rather than grouping
the drifter-derived velocities in geographical bins, we group them by nearest-neighbor distance using a clustering algorithm.
This yields sets with approximately the same number of observations, covering unequal areas. A major advantage is that, because
the number of observations is the same for the clusters, the statistical accuracy is more uniform than with geographical bins.
We illustrate the technique using synthetic data from a stochastic model, employing a realistic mean flow. The latter represents
the surface currents in the Nordic Seas and is strongly inhomogeneous in space. We use the clustering algorithm to extract
the mean velocities and diffusivities and compare the results with the corresponding quantities from the stochastic model.
We perform a similar comparison with the means and diffusivities obtained with geographical bins. Clustering is more successful
at capturing the mean flow and improves convergence in the eddy diffusivity estimates. We discuss both the advantages and
shortcomings of the new method. 相似文献
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Delphis F. Levia Kazuki Nanko Hiromasa Amasaki Thomas W. Giambelluca Norifumi Hotta Shin'ichi Iida Ryan G. Mudd Michael A. Nullet Naoki Sakai Yoshinori Shinohara Xinchao Sun Masakazu Suzuki Nobuaki Tanaka Chatchai Tantasirin Kozo Yamada 《水文研究》2019,33(12):1698-1708
Although we know that rainfall interception (the rain caught, stored, and evaporated from aboveground vegetative surfaces and ground litter) is affected by rain and throughfall drop size, what was unknown until now is the relative proportion of each throughfall type (free throughfall, splash throughfall, canopy drip) beneath coniferous and broadleaved trees. Based on a multinational data set of >120 million throughfall drops, we found that the type, number, and volume of throughfall drops are different between coniferous and broadleaved tree species, leaf states, and timing within rain events. Compared with leafed broadleaved trees, conifers had a lower percentage of canopy drip (51% vs. 69% with respect to total throughfall volume) and slightly smaller diameter splash throughfall and canopy drip. Canopy drip from leafless broadleaved trees consisted of fewer and smaller diameter drops (D50_DR, 50th cumulative drop volume percentile for canopy drip, of 2.24 mm) than leafed broadleaved trees (D50_DR of 4.32 mm). Canopy drip was much larger in diameter under woody drip points (D50_DR of 5.92 mm) than leafed broadleaved trees. Based on throughfall volume, the percentage of canopy drip was significantly different between conifers, leafed broadleaved trees, leafless broadleaved trees, and woody surface drip points (p ranged from <0.001 to 0.005). These findings are partly attributable to differences in canopy structure and plant surface characteristics between plant functional types and canopy state (leaf, leafless), among other factors. Hence, our results demonstrating the importance of drop‐size‐dependent partitioning between coniferous and broadleaved tree species could be useful to those requiring more detailed information on throughfall fluxes to the forest floor. 相似文献
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Steady free-surface seepage in a homogeneous porous aquifer is studied by a conformal mapping of the inversed hodograph (angle) onto the domain in the Riesenkampf plane (slanted-face half-strip or trapezium). Seepage from the water table is caused by evaporation uniformly distributed with a horizontal coordinate. This distributed sink forms a regional trough on the phreatic surface with groundwater moving from the flanks to the trough center on the regional scale and from the water table to the soil surface locally. The free surfaces, streamlines of marked particles, travel times, and Darcian velocity are presented. 相似文献
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