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231.
232.
Jan Klimeš Miroslava Benešová Vít Vilímek Petr Bouška Alejo Cochachin Rapre 《Natural Hazards》2014,71(3):1617-1638
In April 2010, an ice/rockfall into Lake 513 triggered a glacial lake outburst flood (GLOF) along the Chucchun River in the Cordillera Blanca of Peru. This paper reconstructs the hydrological characteristics of this as yet undocumented event using a 1D flood model prepared with HEC-RAS. The principle model inputs were obtained during detailed field surveys of surface characteristics and topography within the river and across the adjacent floodplain; a total of 120 cross-sections were surveyed. These inputs were refined further by eyewitness accounts and additional geomorphological observations. The flood modelling has enabled us to constrain the extent of the water surface and its elevation at each cross-section in addition to defining the peak discharge (580 m3 s?1). These modelling results show good agreement with other information about the flood including: flood marks and minimum flood levels; the lake displacement wave height; the extent of the flooded area; and the travel time from Lake 513 to the confluence with the Santa River. This demonstrates that the model offers a reliable reconstruction of the basic hydrological characteristics of the GLOF. It provides important information about the flood intensity and significantly improves our ability to model future flood scenarios along both the studied river and within neighbouring catchments. The flood hazard, defined by the flood depth during peak discharge, shows that the majority of the damaged infrastructure (houses, bridges, and a drinking water treatment plant) was only subjected to low or medium flood intensities (defined by a maximum water depth of less than 2 m). These low flood intensities help to explain why the flooding caused comparatively minor damage despite the significant public attention it attracted. 相似文献
233.
An Elasto-Plastic Constitutive Model for Rock Joints Under Cyclic Loading and Constant Normal Stiffness Conditions 总被引:1,自引:1,他引:0
An elasto-plastic constitutive model is introduced for rock joints under cyclic loading, considering the additional shear resistance generated by the asperity damage in the first forward shear cycle and sliding mechanism for further shearing. A series of cyclic loading direct shear tests was conducted on artificial joints with triangular asperities and replicas of a real rock asperity surface under constant normal stiffness (CNS) conditions. The model was calibrated and then validated using selected data sets from the experimental results. Model simulations were found to be in good agreement with the rock joints behaviour under cyclic loading and CNS conditions both in stress prediction and dilation behaviour. In addition, dynamic stability analysis of an underground structure was carried out, using Universal Distinct Element Code and the proposed constitutive model. 相似文献
234.
235.
Henning A. Bauch Evguenia S. Kandiano Jan Helmke Nils Andersen Antoni Rosell-Mele Helmut Erlenkeuser 《Quaternary Science Reviews》2011,30(15-16):1813-1818
New multiproxy marine data of the Eemian interglacial (MIS5e) from the Norwegian Sea manifest a cold event with near-glacial surface ocean summer temperatures (3–4 °C). This mid-Eemian cooling divided the otherwise relatively warm interglacial climate and was associated with widespread expansions of winter sea-ice and polar water masses due to changes in atmospheric circulation and ocean stability. While the data also verify a late rather than early last interglacial warm peak, which is in general disharmony with northern hemisphere insolation maximum and the regional climatic progression of the early Holocene, the cold event itself was likely instrumental for delaying the last interglacial climate development in the Polar North when compared with regions farther south. Such a ‘climatic decoupling’ of the Polar region may bear profound implications for the employment of Eemian conditions to help evaluate the present and future state of the Arctic cryosphere during a warming interglacial. 相似文献
236.
The Younger Dryas (YD) cold event was discovered in Denmark by Hartz and Mithers in 1904 and the term coined by Hartz in 1912. It was identified as a lacustrine clay bed containing plant macrofossils of an Arctic flora, including Dryas octopetala, and lying between Allerød and Holocene gyttjas containing a warmer flora with birch trees. The YD is unique in the sense that it is the largest and most abrupt climate change on Earth since the Last Glacial Maximum and thus within the reach of radiocarbon dating. Yet, I consider it is part of a regular Dansgaard-Oeschger event. The term has been used for a climate event and for lithostratigraphical, biostratigraphical and several other stratigraphical units. I prefer using it as a geochronological and chronostratigraphical unit, i.e. that the YD represents a specific period of geological time and the rocks and sediments formed during this period. In the type area of southern Scandinavia, the YD chron represents the age and duration of the cold event. 相似文献
237.
北半球平流层臭氧的时空分布特征 总被引:3,自引:0,他引:3
利用1963-1985年北半球的平流层臭氧观测资料,采用自然平交分解方法,初步分析了北半球、特别是东亚地区大气臭氧层的时空分布特征。结果表明:(1)北半球大气臭氧的空分间分布可能与下垫面的性能有关;(2)东亚地区大气臭氧的时间分布主要具有2年和11年变化的周期特征,这与太阳黑子的准2年和准11年变化有一定的对应关系;(3)北美地区的臭氧变化则主要包含4年和7年的周期变经成分。 相似文献
238.
Alexander Deutsch Christian Koeberl Joel D. Blum Bevan M. French Billy P. Glass Richard Grieve Peter Horn Elmar K. Jessberger Gero Kurat Wolf Uwe Reimold Jan Smit Dieter Stöffler Stuart Ross Taylor 《地学学报》1994,6(6):644-650
In a recent article in Terra Nova, Kristan-Tollmann and Tollmann (1994) suggested that the Biblical Flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on Earth at 03.00h (C.E.T.) on 23 September, 9545 yr BP. We demonstrate that all the ‘geological proofs’ that allegedly support their conclusions are not supported by the available data on impact cratering. Their hypothesis is based on insufficient and ambiguous data, selective citation, and incomplete comprehension of previous research. 相似文献
239.
Jan Vrbik 《Celestial Mechanics and Dynamical Astronomy》1997,69(3):283-291
A simple analysis of tadpole and horseshoe orbits is performed using a new perturbation technique. The first-order results
are presented explicitely, extension to any perturbation order is delineated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
240.
An extensive set of molecular hydrogen observations of centers of southern infrared galaxies is presented. Our data are combined with published infrared and radio observations to investigate the relationship between nuclear and circumnuclear activity. We convert the observational data to absolute luminosities, by applying the known distances. The resulting dataset covers several decades in luminosity for the various parameters, which observe fairly tight correlations. The parameters of our (power law) fits are, at the level of accuracy achieved, not dependent on the type of nuclear activity: while the dataset comprises a mixture of alleged Seyfert, Liner & starburst galaxies, single fits match the complete sample well enough. In particular, non-thermal nuclei (AGN) present in some of the galaxies in the current sample, do not stand out in the parameters we investigated. The absence of a significant dependence on the nuclear type is consistent with the idea that the ever present starbursts energetically dominate a possible ‘AGN in a dusty environment’-component in most galaxy nuclei with infrared excesses.The size of the H2 emitting region is found to be proportional to the square root of the 21 cm radio continuum luminosity. The excitation of the circumnuclear H2 is dominated by shocks. If the H2 extent marks the size of an inner cavity in the dense molecular material surrounding a galaxy nucleus and the radio luminosity is proportional to the mechanical luminosity of (circum)nuclear winds. This result then indicates that the cavity size occurs at constant pressure in the sample galaxies, in accordance with the superwind model by Heckman et al. (1990) [ApJS, 74, 833]. Our results, together with those obtained by others, thus suggest that luminosities and size scales of excited gas associated with active nuclei are dominated by the mechanical energy input. Given the difficulties of uniquely establishing the presence of an AGN, we cannot exclude that (a large fraction of the) infrared luminous galaxies procure part of their radiated energy through accretion onto a massive dark object.F. Duccio Macchetto 相似文献