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排序方式： 共有71条查询结果，搜索用时 25 毫秒
1.
Pol Johannes C. Kanning Willem van Beek Vera M. Robbins Bryant A. Jonkman Sebastiaan N. 《Acta Geotechnica》2022,17(10):4555-4576
Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations.
相似文献2.
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Kristen E. K. Coppin Christopher J. Davis & Milena Micono 《Monthly notices of the Royal Astronomical Society》1998,301(1):L10-L14
We discuss the formation of spectral features in the decelerating ejecta of gamma-ray bursts, including the possible effect of inhomogeneities. These should lead to blueshifted and broadened absorption edges and resonant features, especially from H and He. An external neutral ISM could produce detectable H and He, as well as Fe X-ray absorption edges and lines. Hypernova scenarios may be diagnosed by Fe Kα and H Lyα emission lines. 相似文献
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Combining indicator trends to assess ongoing changes in exploited fish communities: diagnostic of communities off the coasts of France 总被引：1，自引：1，他引：1
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M. V. Panchenko T. B. Zhuravleva V. S. Kozlov I. M. Nasrtdinov V. V. Pol’kin S. A. Terpugova D. G. Chernov 《Russian Meteorology and Hydrology》2016,41(2):104-111
The results of numerical simulation of downward solar radiation fluxes for background and smoke-contaminated atmospheric conditions are discussed. Vertical profiles of aerosol characteristics are obtained from the empirical model based on the data of aircraft sounding of profiles of angular scattering coefficients and content of absorbing particles in the lower troposphere. The background model was created using the results of measurements obtained under cloudless and mostly cloudless atmospheric conditions in 1999–2011. Optical parameters of smoke aerosol are determined from the data of aircraft measurements in the period of long-term wildfires in Siberia in the summer 2012. It is demonstrated that deficiency in diurnal values of total solar radiation at the surface level caused by the formation of the optically dense smoke layer as compared to background conditions, is more than 13 MJ/m2. 相似文献
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The reaction of CN? with cyanoacetylene (HC3N), has been studied as a function of the HC3N pressure in a quadrupole tandem mass spectrometer. The mass spectra revealed the fast depletion of the CN? parent ion and formation of larger anions of rapidly growing size. Most of the ions observed were found to belong to two series of products: (HC3N)x·C2p+1N? and (HC3N)x·C2pN? resulting from the sequential additions of HC3N molecules and loss of HCN or HCCN molecules. The mechanism and energetics of the first two reaction steps are briefly discussed. The laboratory data are compared with those from the Cassini CAPS-ELS spectrometer. It is believed that the reactions observed could account for the growth of anions in Titan’s ionosphere. 相似文献
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Hidetoshi HARA Koji WAKITA Jun-ichiro KURODA Toshiyuki KURIHARA Katsumi UENO Yoshihito KAMATA Ken-ichiro HISADA Punya CHARUSIRI Thasinee CHAROENTITIRAT Pol CHAODUMRONG 《地球学报》2009,30(Z1):12-12
The Paleo-Tethys formed a large ocean basin that existed between Laurasia and Gondwana during Late Paleozoic to Early Mesozoic times. It opened in the Early Devonian by the rifting of Gondwanaland and closed at around latest Triassic time by the collision of the Cimmerian continent to Laurasia (Metcalfe, 1999). We reconstructed opening and closing process of the Paleo-Tethys in Northern Thailand. 相似文献
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Summary In microperthitic alkali feldspars from the Haut Boréon anatexites in the Argentera Massif, Maritime Alps, the dominant K-rich phases are devoid of grid twinning but usually show weak uneven extinction. They consist of monoclinic forms characterized by (a) highly ordered Si,Al distributions in theT-sites, (b) weak but systematic residual strain due to coherency with the exsolved Na-rich phase, and (c) not very pure compositions ranging from 0.85 to 0.88 mole fraction KAlSi3O8. Weak triclinic peaks in X-ray powder patterns and the evidence of incipient formation of M-twinning and the diagonal association in single-crystal X-ray photographs indicate that the dominant monoclinic K-rich phases have undergone a partial transformation into triclinic material. The microperthites investigated appear to be the expression of a relatively rapid thermal history which started and terminated at temperatures higher than those experienced by the microperthites from the Mt. Pélago anatexites, which are exposed to the West of the Haut Boréon anatexites.
With 6 Figures 相似文献
Monokline K-Feldspäte mit hohem Ordnungsgrad aus Anatexiten des Haut Boréon, Argentera Massiv Seealpen
Zusammenfassung In den mikroperthitischen Alkalifeldspäten der Anatexite des Haut Boréon im Argentera Massiv (Seealpen) zeigen die vorherrschenden monoklinen Phasen keine Zwillingsgitterung, aber gewöhnlich schwach unregelmäßige Auslöschung. Sie bestehen aus monoklinem Kali-feldspat, der 1, durch eine weitgehend geordnete Si,Al-Verteilung auf denT-Positionen, 2. durch schwache aber systematische Spannungen, welche durch die Kohärenz mit der entmischten Na-reichen Phase verursacht sind, und 3, durch eine nicht sehr scharfe Zusammensetzung, die von 0,85 bis 0,88 Molenbruch KAlSi3O8 schwankt, charakterisiert ist. Schwache trikline Maxima in den Röntgen-Pulverdiagrammen sowie der Hinweis auf beginnende M-Verzwilligung und diagonale Assoziation in Röntgen-Einkristallaufnahmen weisen darauf hin, daß die vorherrschenden monoklinen Phasen partiell in triklines Material umgewandelt wurden. Die untersuchten Mikroperthite scheinen eine relativ rasche thermische Geschichte zu widerspiegeln, die bei höheren Temperaturen begann und endete als jene, welche die westlich des Haut Boréon aufgeschlossenen Anatexite des Mt. Pélago erlitten.
With 6 Figures 相似文献