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71.
Xiao-Bing?Li Dongfang?Wang Qing-Chang?Lu Zhong-Ren?PengEmail author Qingyan?Fu Xiao-Ming?Hu Juntao?Huo Guangli?Xiu Bai?Li Chao?Li Dong-Sheng?Wang Hanyu?Wang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(5):1189-1203
A lightweight unmanned aerial vehicle (UAV) and a tethered balloon platform were jointly used to investigate three-dimensional distributions of ozone and PM2.5 concentrations within the lower troposphere (1000 m) at a localized coastal area in Shanghai, China. Eight tethered balloon soundings and three UAV flights were conducted on May 25, 2016. Generalized additive models (GAMs) were used to quantitatively describe the relationships between air pollutants and other obtained parameters. Field observations showed that large variations were captured both in the vertical and horizontal distributions of ozone and PM2.5 concentrations. Significant stratified layers of ozone and PM2.5 concentrations as well as wind directions were observed throughout the day. Estimated bulk Richardson numbers indicate that the vertical mixing of air masses within the lower troposphere were heavily suppressed throughout the day, leading to much higher concentrations of ozone and PM2.5 in the planetary boundary layer (PBL). The NO and NO2 concentrations in the experimental field were much lower than that in the urban area of Shanghai and demonstrated totally different vertical distribution patterns from that of ozone and PM2.5. This indicates that aged air masses of different sources were transported to the experimental field at different heights. Results derived from the GAMs showed that the aggregate impact of the selected variables for the vertical variations can explain 94.3% of the variance in ozone and 94.5% in PM2.5. Air temperature, relative humidity and atmospheric pressure had the strongest effects on the variations of ozone and PM2.5. As for the horizontal variations, the GAMs can explain 56.3% of the variance in ozone and 57.6% in PM2.5. The strongest effect on ozone was related to air temperature, while PM2.5 was related to relative humidity. The output of GAMs also implied that fine aerosol particles were in the stage of growth in the experimental field, which is different from ozone (aged air parcels of ozone). Geographical parameters influenced the horizontal variations of ozone and PM2.5 concentrations by changing underlying surface types. The differences of thermodynamic properties between land and sea resulted in quick changes of PBL height, air temperature and dew point over the coastal area, which was linked to the extent of vertical mixing at different locations. The results of GAMs can be used to analyze the sources and formation mechanisms of ozone and PM2.5 pollutions at a localized area. 相似文献
72.
We report 7 mammalian and 16 pollen species from the top of the Shimagou Formation in Kumkol Basin of northern Qinghai-Xizang Plateau, whose age is latest Middle Miocene(about 12.5 Ma). We erect a new species of fossil rodent,Spermophilinus kumkolensis sp. nov. The micromammalian fauna from the Kumkol Basin shares high similarities with contemporary faunas from Europe and northern China, indicating the existence of active zoogeographic exchange between Europe and northern Asia. Trees are dominant in pollen fossils, and herbs and shrubs are minorities. Broadleaved Quercus and Fagus predominate in tree pollens. The flora reconstructed by pollens displays a mixture of evergreen broadleaved forest and dry and warm steppe landscape. Compared to the modern vegetation in Yunnan region, the latest Middle Miocene flora in the Kumkol Basin represents a distinct vertical distribution. The ecotypes of the latest Middle Miocene fauna and flora in the Kumkol Basin,as a whole, are markedly different from those of modern animals and vegetation, the past climate being more suitable than today. 相似文献
73.
G. P. Chernov V. V. Fomichev Y. Yan B. Tan Ch. Tan Q. Fu 《Geomagnetism and Aeronomy》2017,57(6):738-751
The reason for the occurrence of different elements of the fine structure of solar radio bursts in the decimeter and centimeter wavelength ranges has been determined based on all available data from terrestrial and satellite observations. In some phenomena, fast pulsations, a zebra structre, fiber bursts, and spikes have been observed almost simultaneously. Two phenomena have been selected to show that the pulsations of radio emission are caused by particles accelerated in the magnetic reconnection region and that the zebra structure is excited in a source, such as a magnetic trap for fast particles. The complex combination of unusual fiber bursts, zebra structure, and spikes in the phenomenon on December 1, 2004, is associated with a single source, a magnetic island formed after a coronal mass ejection. 相似文献
74.
Investigation of highly efficient algorithms for solving linear equations in the discontinuous deformation analysis method 下载免费PDF全文
Large‐scale engineering computing using the discontinuous deformation analysis (DDA) method is time‐consuming, which hinders the application of the DDA method. The simulation result of a typical numerical example indicates that the linear equation solver is a key factor that affects the efficiency of the DDA method. In this paper, highly efficient algorithms for solving linear equations are investigated, and two modifications of the DDA programme are presented. The first modification is a linear equation solver with high efficiency. The block Jacobi (BJ) iterative method and the block conjugate gradient with Jacobi pre‐processing (Jacobi‐PCG) iterative method are introduced, and the key operations are detailed, including the matrix‐vector product and the diagonal matrix inversion. Another modification consists of a parallel linear equation solver, which is separately constructed based on the multi‐thread and CPU‐GPU heterogeneous platforms with OpenMP and CUDA, respectively. The simulation results from several numerical examples using the modified DDA programme demonstrate that the Jacobi‐PCG is a better iterative method for large‐scale engineering computing and that adoptive parallel strategies can greatly enhance computational efficiency. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
75.
Selection of sand models and identification of parameters using an enhanced genetic algorithm 下载免费PDF全文
Numerous constitutive models of granular soils have been developed during the last few decades. As a consequence, how to select an appropriate model with the necessary features based on conventional tests and with an easy way of identifying parameters for geotechnical applications has become a major issue. This paper aims to discuss the selection of sand models and parameters identification by using genetic algorithm. A real‐coded genetic algorithm is enhanced for the optimization with high efficiency. Models with gradually varying features (elastic‐perfectly plastic modelling, nonlinear stress–strain hardening, critical state concept and two‐surface concept) are selected from numerous sand models as examples for optimization. Conventional triaxial tests on Hostun sand are selected as the objectives in the optimization. Four key points are then discussed in turn: (i) which features are necessary to be accounted for in constitutive modelling of sand; (ii) which type of tests (drained and/or undrained) should be selected for an optimal identification of parameters; (iii) what is the minimum number of tests that should be selected for parameter identification; and (iv) what is the suitable and least strain level of objective tests to obtain reliable and reasonable parameters. Finally, a useful guide, based on all comparisons, is provided at the end of the discussion. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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77.
Collision between the Indian and the Eurasian plates since the early Cenozoic produces one of the world’s most remarkable continental escarpments between the Tibetan Plateau and the adjacent Sichuan Basin. Yet Tertiary sediments are rare in the Sichuan Basin; the oldest preserved Late Cenozoic deposits called Dayi conglomerates directly overlie the Cretaceous or Jurassic red beds. Using cosmogenic 10Be and 26Al burial dating, we obtain deposition ages of ~2.0 Ma and catchment erosion rates of ~400 mm/ka for the Dayi conglomerates. Zircon U–Pb age distributions suggest derivation of these conglomerates from the Songpan-Ganzi flysch, the Pengguan complex and Late Permian and Triassic granite plutons in the headwater regions of the Min Jiang (Jiang, a Chinese term, means river). The formation of the poorly-sorted, sub-angular to sub-rounded and tens-centimeter-sized deposits in the western margin of the Sichuan Basin, after long distance transportation, is best explained by glacial activity ~2.0 Ma ago in east Tibet. 相似文献
78.
Fabric evolution within shear bands of granular materials and its relation to critical state theory 总被引:2,自引:0,他引:2
In an effort to study the relation of fabrics to the critical states of granular aggregates, the discrete element method (DEM) is used to investigate the evolution of fabrics of virtual granular materials consisting of 2D elongated particles. Specimens with a great variety of initial fabrics in terms of void ratios, preferred particle orientations, and intensities of fabric anisotropy were fabricated and tested with direct shear and biaxial compression tests. During loading of a typical specimen, deformation naturally localizes within shear bands while the remaining of the sample stops deforming. Thus, studying the evolution of fabric requires performing continuous local fabric measurements inside these bands, a suitable task for the proposed DEM methodology. It is found that a common ultimate/critical state is eventually reached by all specimens regardless of their initial states. The ultimate/critical state is characterized by a critical void ratio e which depends on the mean stress p, while the other critical state fabric variables related to particle orientations are largely independent of p. These findings confirm the uniqueness of the critical state line in the e ? p space, and show that the critical state itself is necessarily anisotropic. Additional findings include the following: (1) shear bands are highly heterogeneous and critical states exist only in a statistical sense; (2) critical states can only be reached at very large local shear deformations, which are not always obtained by biaxial compression tests (both physical and numerical); (3) the fabric evolution processes are very complex and highly dependent on the initial fabrics. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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