Restriction on the motion of a solid in a gravitational field     

Roland Sergysels 《Celestial Mechanics and Dynamical Astronomy》1988,44(1-2):155-166

As is well known, the orbital and rotational motions of a solid are coupled, and the integrals of energy and angular momentum (in a gravitational field with spherical symmetry) impose restrictions on them. We study the regions allowed to the motion in configurational space. It turns out that even in the crudest model (planar motion of a triple rod) the restrictions on the libration angle and the orbital radius of the center of mass are coupled, so that excessive ellipticity of the orbit excludes stabilization in the neighbourhood of the spoke equilibrium position by gravitational forces only.Chargé de Cours.  相似文献   

Metabolised Tritium and Radiocarbon in Lichens and Their Use as Biomonitors     

Olivier Daillant  David Boilley  Martin Gerzabek  Justin Porstendörfer  Roland Tesch 《Journal of Atmospheric Chemistry》2004,49(1-3):329-341

Lichens are now well known for their potential as bio-indicators of environmental pollution, but less is known about their suitability as quantitative biomonitors for atmospheric emissions of tritium (mainly as tritiated water, HTO) and radiocarbon (as ¹⁴CO₂) from nuclear facilities, although both radionuclides could result in non-trivial individual or collective radiation doses due to their high environmental mobility and their long half-lives. ³H and ¹⁴C are fixed in lichens mainly by the photosynthesis of the algal partner and then stored in the organic molecules of both alga and fungus. They have the advantage of allowing the monitoring of atmospheric water vapour without interference of soil water or soil organic substances as long as soil-inhabiting species are avoided. Lichens were collected in the surroundings of (military and civil) nuclear facilities, in areas away from any direct source of contamination and some were transplanted from a contaminated area to a non-contaminated one. The influence of the nuclear facilities can be clearly traced, sometimes in a spectacular way and the first results of analyses after transplants give a base for estimating the effective half-life of ³H in lichens.  相似文献   

Fixation of manganese and iron in freshwater sediments through electrochemically initiated processes I: Principles and laboratory studies     

Roland?FischerEmail author  Claudia?Wolf  Dietmar?Rahner  Lothar?Paul  Thomas?Deppe  Christian?E.?W.?Steinberg 《Aquatic Sciences - Research Across Boundaries》2004,66(1):95-102

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Anthropogenic inputs of several heavy metals to nearshore basins off Los Angeles     

Chih-an Huh  Bruce P. Finney  Janet K. Stull 《Progress in Oceanography》1992,30(1-4)

Budgets of anthropogenically-derived Cr, Zn and Pb in the Santa Monica-San Pedro Basin and the Palos Verdes Shelf are estimated from profiles of these metals in a large number of sediment cores. Comparisons of inventories in the deep basin with combined emissions from the responsible sewage outfalls indicate that no more than 7% of the Cr, 2% of the Zn and 5% of the Pb derived from the sewage source are buried in the nearshore basin. A similar comparison of metal accumulation on the Palos Verdes Shelf with discharges from the nearby JWPCP outfall indicates that 12% of the Zn and 20% of the Cr and Pb are deposited locally. The annual percentages of sewage-derived Pb retained should be significantly lower, because surface runoff and atmospheric fallout are also important input pathways for anthropogenic Pb. Offshore variations in sediment metal composition suggest that Cr is most strongly attached to sewage particles while Zn and Pb are more labile. We conclude that the majority of anthropogenic metals are exported offshore beyond the inner basin.  相似文献   

Numerical Modeling of Wave-Enhanced Turbulence in the Oceanic Upper Layer     

Le Ngoc Ly  Roland W. Garwood 《Journal of Oceanography》2000,56(4):473-483

A coupled model of air-wave-sea interaction is modified based on a new roughness formulation and the latest data. The model parameters for aerodynamic roughness from below (ARB) and wave-dependent roughness from above (ARA, z _0a ) are assumed equal. The combined roughness is assumed to be a function of friction velocity, gravity, air and seawater densities, and wave age (c _w ). The model is used in a study of wave-enhanced turbulence under breaking waves to predict turbulent dissipation (), ARA, and drag coefficient (C _d ). Both waves and shear production are considered as sources of ocean turbulent energy. The atmospheric part of the model is used only to specify a correct condition at the interface. Numerical experiments are performed to study the -distribution, z _0a and C _d , and to compare with data. The major achievement is model verification using all available data. The first full application of this model is in conjunction with an ocean circulation model in a coupled circulation-wave system. Simulations show that the -distribution is strongly dependent on local wind-forced wave heights. For each wind and wave state there is a particular wave-dependent depth that is verified by data. The comparison shows that the model predicted agrees well with the observed of the z ^–4 law distribution of Gargett (1989). Simulations also show that waves have an important role in causing to differ from the classical wall-layer theory and z _0a , with a value of 0.30 for the empirical constant a _a . The model-predicted , z _0a , C _d and C _gd agree well with data.  相似文献   

A simulation of radiation imagery for ocean color satellite   总被引：2，自引：0，他引：2  

Pan Delu  Roland Doerffer  Mao Tianming  Li Shujing 《海洋学报(英文版)》1997,16(2):171-191

The ocean color satellite is mainly applied to measure the water constituents such as chlorophyll, suspended material and yellow substance. The leaving water radiance is very small part of the total radiance arrival at the sensor about 3%-15%,and depends on the properties of the orbit and sensor. Before the satellite is launched on the orbit, it needs to simulate the radiation imagery in order to evaluate the quality and availability of the satellite data.
If the parameters of satellite orbit, the properties of sensor as well as the characteristics of the atmosphere and water have been known, the radiation scattered by air molecule and aerosol, reflected solar radiation, water leaving and total radiation arriving at the sensor can be simulated by the models of radiation transfer in the atmosphere, air/water and subsurface water. In this paper, the mechanism, models and procedures of the radiation simulation are first discussed and employed to simulate a series of imageries for the Chinese satellites FY-lA, FY-1B, and ROCSAT-1 (Taiwan, China), and American satellite Ses STAR. Their results show that the solar irradiance arrived at water surface and the sun glitter mainly affect the quality and availability of satellite data, which depend on the orbit properties. Finally, some suggestions are proposed to improve the quality and availability of a:ean color satellite data.  相似文献   

Towards a process-based biogeography of reindeer—scaling space,time, and organizational levels of space use     

Roland Pape 《Norsk geografisk tidsskrift. Norwegian journal of geography》2016,70(4):230-246

Due to increasing anthropogenic habitat alteration, fragmentation, and loss, the analysis of how, when, and why animals select particular habitats has become a central issue in ecology and biogeography. Animals adapt to spatiotemporal variability in resources either by tracking these resources or by plasticity in behavior to cover their needs, leading to three important implications: movement, temporal variation, and individual trade-offs leading to intra-species variability, all of which are directly linked to the use of space by animals. Based on GPS-tracking of domesticated reindeer in southern Norway, the authors addressed these issues by analyzing movement patterns and space use simultaneously across different temporal and organizational scales. Emerging information about the space use by reindeer was found explicitly linked to scaling relations, reflecting the matter of scale as having important functional implications rather than solely being a technical question of extent and resolution. Adding movement into the analysis of space use further advances the necessary functional perspective on space use. The authors conclude that scaling not only space but also time and the organizational level, in combination with accounting for different behavioral states, brings biogeography closer to a process-based view, rather than solely pattern-based view.  相似文献   

The Nolans Bore rare-earth element-phosphorus-uranium mineral system: geology,origin and post-depositional modifications     

David L. Huston  Roland Maas  Andrew Cross  Kelvin J. Hussey  Terrence P. Mernagh  Geoff Fraser  David C. Champion 《Mineralium Deposita》2016,51(6):797-822

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Temporal probability analysis of landslides triggered by intense rainfall in the Bamenda Mountain Region,Cameroon     

Roland Ngwatung Afungang  Carlos Valdir Bateira 《Environmental Earth Sciences》2016,75(12):1032

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An embedded fracture modeling framework for simulation of hydraulic fracturing and shear stimulation   总被引：1，自引：0，他引：1  

Jack H. Norbeck  Mark W. McClure  Jonathan W. Lo  Roland N. Horne 《Computational Geosciences》2016,20(1):1-18

A numerical modeling framework is described that is able to calculate the coupled processes of fluid flow, geomechanics, and rock failure for application to general engineering problems related to reservoir stimulation, including hydraulic fracturing and shear stimulation. The numerical formulation employs the use of an embedded fracture modeling approach, which provides several advantages over more traditional methods in terms of computational complexity and efficiency. Specifically, the embedded fracture modeling strategy avoids the usual requirement that the discretization of the fracture domain conforms to the discretization of the rock volume surrounding the fractures. As fluid is exchanged between the two domains, conservation of mass is guaranteed through a coupling term that appears as a simple source term in the governing mass balance equations. In this manner, as new tensile fractures nucleate and propagate subject to mechanical effects, numerical complexities associated with the introduction of new fracture control volumes are largely negated. In addition, the ability to discretize the fractures and surrounding rock volume independently provides the freedom to choose an acceptable level of discretization for each domain separately. Three numerical examples were performed to demonstrate the utility of the embedded fracture model for application to problems involving fluid flow, mechanical deformation, and rock failure. The results of the numerical examples confirm that the embedded fracture model was able to capture accurately the complex and nonlinear evolution of reservoir permeability as new fractures propagate through the reservoir and as fractures fail in shear.  相似文献