西藏高原洞穴碎屑沉积的电镜扫描研究     

P.A.Bull  A.W.Magee  M.M.Sweeting  章典  施振斌 《中国岩溶》1990,9(1):76-87

应用电镜扫描石英颗粒结构分析,对西藏高原洞穴碎屑沉积及其相关的地表沉积物进行了研究。其结论是:绝大部分样品的物质来源于附近的火成岩和变质岩基岩,这些沉积物的石英颗粒表面并未显示经受冰川的、河流的或风的搬运作用所造成的变形痕迹,也缺乏成土作用或热带湿热环境的化学变形证据。很明显,目前的环境难于在石英颗粒表面产生物理的或化学的结构形态。   相似文献   

An investigation of the effects of mass distribution on pounding structures     

Gregory Cole  Rajesh Dhakal  Athol Carr  Des Bull 《地震工程与结构动力学》2011,40(6):641-659

The effects of diaphragm mass distribution are investigated for building pounding. Elastic diaphragm‐to‐diaphragm collisions are explained by considering the total momentum over the length of each diaphragm at three critical instants during collision. Expressions for collision force and collision duration are produced, providing additional information about the collision process. Equations for the post collision velocity of each diaphragm are produced and are found to appreciably differ from conventional impact—momentum equations under certain conditions. The change in post collision velocity is found to be dependent on the ratio of the axial periods of free vibration of the two diaphragms and the ratio of their masses. An equivalent lumped mass model is proposed and assessed against simplified distributed mass models with numerical modelling of two two‐storey buildings. Finally, a new parameter is introduced to represent the plasticity of an inelastic collision between the two distributed masses. This paper highlights the significant influence that diaphragm mass distribution may have on the analysis of pounding structures. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Cooling by grains and H2 in collapsing clouds of different metallicities     

S. C. F. Rossi  B. Barbuy  G. Pineau Des Forêts  P. Benevides-Soares 《Astrophysics and Space Science》1994,213(1):113-119

Computations of the cooling by grains and by H₂ molecules are carried out and applied to different stages of cloud collapse during the isothermal phase. Clouds of 10⁶ M of different metallicites are considered, with the purpose of obtaining a relation between metallicity and importance of grain cooling relative to H₂ cooling. Our results show that grain cooling dominates over H₂ cooling for metallicities [M/H] > -4.0, in the absence of external UV field.  相似文献   

Prediction of bioconcentration and related lethal and sublethal effects with aquatic organisms     

Des W. Connell 《Marine pollution bulletin》1995,31(4-12)

It is now well established that the octanol/water partition coefficient (K_0W) can be used to estimate bioconcentration of persistent organic compounds, such as the chlorohydrocarbons as well as PAHs and other hydrophobic substances. However, while these relationships are well established in the laboratory, use in the field often poses a number of problems. In recent studies of contaminants in fish from Australia, bioconcentration has been described using additional information on specimen size, lipid content and fish movement patterns.The use of internal biotic concentration provides an additional new and different perspective on toxicant behaviour as compared to the conventional ambient aqueous concentration-based toxicity measures. The internal lethal concentration for persistent organic compounds approaches a constant value for many compounds, and at these concentrations lethal effects are observed. This constant internal lethal concentration provides a basis for predicting toxicity and its relationship to exposure period. In addition, sublethal effects can be successfully related to the internal biotic concentration.  相似文献   

Optical properties of benthic photosynthetic communities: fiber-optic studies of cyanobacterial mats     

Jorgensen BB  Des Marais DJ 《Limnology and oceanography》1988,33(1):99-113

A fiber-optic microphobe was used to analyze the spectral light gradients in benthic cyanobacterial mats with 50-micrometer depth resolution and 10-nm spectral resolution. Microcoleus chthononplastes mats were collected from hypersaline, coastal ponds at Guerrero Negro, Baja California. Gradients of spectral radiance, L, were measured at different angles through the mats and the spherically integrated scalar irradiance, Eo, was calculated. Maximal spectral light attenuation was found at the absorption peaks for the dominant photosynthetic pigments: chlorophyll a at 430 and 670 nm, carotenoids at 450-500 nm, phycocyanin at 620 nm, and bacteriochlorophyll a at 800-900 nm. Scattered light had a marked spectral effect on the scalar irradiance which near the mat surface reached up to 190% of the incident irradiance. The spherically integrated irradiance thus differed strongly from the incident irradiance both in total intensity and in spectral composition. These basic optical properties are important for the understanding of photosynthesis and light harvesting in benthic and epiphytic communities.  相似文献   

Volcanic influences in a storm‐ and tide‐dominated shallow marine depositional system: The late permian broughton formation,southern Sydney Basin,Kiama, NSW     

Stuart W. Bull  R.A.F. Cas 《Australian Journal of Earth Sciences》2013,60(4):569-584

Shallow marine sediments of the Broughton Formation are dominated by immature volcanic debris of intermediate to basic composition, generated in an adjacent subaerial environment by volcanism responsible for the nine shoshonite units intercalated within sediments of the Kiama region. Sediment was supplied to the offshore environment via periodic storm‐generated, expanded high density turbidity currents. Initial deposition, represented by the Westley Park Sandstone Member, was below storm wave base, during which time the depositional surface was subjected to post‐depositional tractional reworking by northerly directed, tidally influenced bottom currents. The resulting positive‐relief sand bodies on the seafloor contain tractional sedimentary structures (the ‘tractional facies association'). Areas of the substrate between these sand bodies retained their turbidite bedding structure (the ‘rhythmically bedded facies association') but were extensively bioturbated by a diverse deposit‐feeding biomass.

Upon emplacement of the lowest of the nine shoshonite units as a tri‐composite, locally intrusive lava flow, the depositional surface was elevated, transgressing storm wave base. The body of the shoshonite flow also shielded the substrate from the northerly directed tractional currents, allowing the development and preservation of the hummocky cross‐stratified sandstone facies in the Kiama Sandstone Member. Following burial of the shoshonite flow by continued deposition, this local shielding effect was overcome and tractional currents again reworked the entire depositional surface.  相似文献   

Further aspects of the mountain building problem     

A.J. Bull 《Proceedings of the Geologists' Association. Geologists' Association》1929,40(2):105-IN6

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The geology of the Eastbourne—Hastings Coastline: With Special Reference to the Localities visited by the Association in June, 1925     

H.B. Milner  A.J. Bull 《Proceedings of the Geologists' Association. Geologists' Association》1925,36(3):291-IN17

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Some aspects of the mountain building problem: Presidential address     

A.J. Bull 《Proceedings of the Geologists' Association. Geologists' Association》1927,38(2):145-156

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Evidence for cannibalism in the 0004.8–3450 cluster of galaxies     

H. V. Capelato  G. Des Forets  A. Mazure  E. Salvador-Sole 《Astrophysics and Space Science》1985,108(2):363-368

The analysis of the luminosity segregation in the 0004.8–3450 cluster of galaxies is made which reinforces the assumption of merging mechanisms.  相似文献