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151.
The spatial restricted rhomboidal five-body problem, or shortly, SRRFBP, is a five body problem in which four positive masses, called the primaries, move two by two in coplanar circular motions with the center of mass fixed at the origin such that their configuration is always a rhombus, the fifth mass being negligible and not influencing the motion of the four primaries. The Hamiltonian function that governs the motion of the fifth mass is derived and has three degrees of freedom depending periodically on time. Using a synodical system of coordinates, we fix the primaries in order to eliminate the time dependence. With the help of the Hamiltonian structure, we characterize the regions of possible motion. The vertical $z$ axis is invariant and we study what we call the rhomboidal Sitnikov problem. Unlike the classical Sitnikov problem, no chaos exists and the behavior of the fifth mass is quite predictable, periodic solutions of arbitrary long periods are shown to exist and we study numerically their linear horizontal stability. 相似文献
152.
The article analyses the stability properties of minimum-control artificial equilibrium points in the planar circular restricted
three-body problem. It is seen that when the masses of the two primaries are of different orders of magnitude, minimum-control
equilibrium is obtained when the spacecraft is almost coorbiting with the second primary as long as their mutual distance
is not too small. In addition, stability is found when the distance from the second primary exceeds a minimum value which
is a simple function of the mass ratio of the two primaries and their separation. Lyapunov stability under non-resonant conditions
is demonstrated using Arnold’s theorem. Among the most promising applications of the concept we find solar-sail-stabilized
observatories coorbiting with the Earth, Mars, and Venus. 相似文献
153.
We present analytical formulas to estimate the variation of achieved deflection for an Earth-impacting asteroid following a continuous tangential low-thrust deflection strategy. Relatively simple analytical expressions are obtained with the aid of asymptotic theory and the use of Peláez orbital elements set, an approach that is particularly suitable to the asteroid deflection problem and is not limited to small eccentricities. The accuracy of the proposed formulas is evaluated numerically showing negligible error for both early and late deflection campaigns. The results will be of aid in planning future low-thrust asteroid deflection missions. 相似文献
154.
AbstractThe potential impacts of future climate change on the evolution of groundwater recharge are examined at a local scale for a 546-km2 watershed in eastern Canada. Recharge is estimated using the infiltration model Hydrologic Evaluation of Landfill Performance (HELP), with inputs derived from five climate runs generated by a regional climate model in combination with the A2 greenhouse gas emissions scenario. The model runs project an increase in annual recharge over the 2041–2070 period. On a seasonal basis, however, a marked decrease in recharge during the summer and a marked increase during the winter are observed. The results suggest that increased evapotranspiration resulting from higher temperatures does not offset the large increase in winter infiltration. In terms of individual water budget components, clear differences are obtained for the different climate change scenarios. Monthly recharge values are also found to be quite variable, even for a given climate scenario. These findings are compared with results from two regional-scale studies.
Editor D. Koutsoyiannis; Associate editor M. Besbes 相似文献
155.
Growing environmental concern is promoting the necessity of additional ceramic tests. The use of unknown materials with potential
contamination conditions requires further studies to demonstrate that the piece encapsulates the pollutant and that during
its firing it does not produce the emission of harmful volatile elements. The objective of this work was to perform both tests
in a ceramic paste made with slip-casting wastes and electro-plating residues. The leaching methods for determining the encapsulation
of potential harmful elements were performed following the TCLP, EP-Tox norm. Having precise chemical analysis of both crude
and fired brick, the problem of emissions losses during the firing can be solved by the gain/loss techniques used in geological
studies. In particular, the Isocon method that permits a quick visualization of the lost elements is useful. Once the volatile
elements were determined, their amount was calculated considering a constant element and the chemical concentrations normalized
by the loss of ignition, or using the crude/fired brick ratio densities. The leaching tests indicate that the ceramic brick
does not produce harmful leachates according to Argentinean specifications. The leachates of B and Ca are high. Ca does not
seem to be a problem while the B content is beyond the permitted limits. During the firing, volatilized elements are Ag, Br,
Cl, F, Hg, S, Se, and H2O. The loss of Ag, Br, and Se are negligible. For F and Cl the potential emission rate is very low (100 mg/kg) while in the
case of S, the 2,600 mg/kg rate is high. However, extrapolated emission rates at the chimney assuming an air-to-brick ratio
of 2.5 N m3/kg, are approximately 1,040 mg/N m3 for S and 40 mg/N m3 for F and Cl, falling inside environmentally acceptable values. The geochemical procedures proved to be useful tools to assess
the element mobilization during firing of ceramic wares and in the analyzed case, the results indicate that the paste is environmentally
acceptable. 相似文献
156.
Diana Salciarini Claudio Tamagnini Pietro Conversini Silvia Rapinesi 《Natural Hazards》2012,61(1):229-245
The evaluation of the combined influence of rainfall patterns (in terms of mean intensity and duration) and the geomorphological
and mechanical characteristics of hillslopes on their stability conditions is a major goal in the assessment of the shallow
landslide triggering processes. Geographic Information Systems (GIS) represent an important tool to develop models that combine
hydrological and geomechanical analyses for the evaluation of slope stability, as they allow to combine information concerning
rainfall characteristics with topographic and mechanical properties of the slopes over wide areas. In this paper, a GIS-based
code is developed to determine physically based intensity/duration rainfall thresholds at the local scale. Given the rainfall
duration and the local geometric, hydrological and mechanical characteristics of the slopes, the code evaluates the spatial
distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given area. The key
feature of the code is the capability of evaluating the time t
p
required to reach the peak pore pressure head on the failure surface and computing the corresponding critical intensity/duration
thresholds based on post-event peak pore pressures. The reliability of the model is tested using a set of one-dimensional
analyses, comparing the physically based thresholds obtained for three different slopes with some empirical rainfall thresholds.
In a log–log scale, the thresholds provided by the model decrease linearly with increased rainfall duration and they are bracketed
by the empirical thresholds considered. Finally, an example of application to a study area of the Umbria region in central
Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios. 相似文献
157.
Victoria González-Carman Natalia Machain Diego Albareda Hermes Mianzan Claudio Campagna 《Marine Policy》2012
This paper explores conservation policy pertinent to three species of marine turtles affected by fisheries, while crossing jurisdictions in their seasonal migrations through the SW Atlantic, particularly the Argentine waters. This case study reviews local legal and institutional frameworks for Argentina and concludes that tools are in place to monitor and mitigate the negative impact of bycatch on the populations. Argentina is signatory of the most relevant international treaties aimed at protecting transboundary species (e.g. Inter-American Convention for the Protection and Conservation of Sea Turtles, Convention on the Conservation of Migratory Species of Wild Animals). Legislation also exists at the federal and provincial levels. Yet, accidental captures continue to occur due to weaknesses in enforcement and the low priority that conservation has in fisheries management decisions. Some urgent practical actions supported by policy are suggested: (a) placement of on-board observers in coastal fishing fleets, (b) application of existing mitigation measures to reduce bycatch, (c) design of a national plan of action for marine turtles in Argentina, and (d) development of a regional plan between Argentina, Brazil and Uruguay. Stakeholder involvement, especially the fishing sector but also the civil society, would be important to energize practical and effective conservation decisions. The example of Argentina is typical for the region and may apply to other countries as well. The conservation community requires investing more in the application of policy, concomitant with perfecting legal tools. 相似文献
158.
159.
An overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks 总被引:1,自引:0,他引:1
Beatriz Quintal Nicola Tisato Erik H. Saenger Claudio Madonna 《Geophysical Prospecting》2014,62(6):1211-1223
Intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability, fluid properties, and saturation. However, in order to use attenuation as an attribute to extract information on rock/fluid properties from seismic data, experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies. An appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method, but technical challenges kept this technique from being widely used. There is a need for the standardization of devices employing this method, and a comparison of existing setups is a step towards it. Here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency‐dependent attenuation in fluid‐saturated and/or dry reservoir rocks under small strains (10?8–10?5). We list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one. We also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far. 相似文献
160.
Claudio Strobbia Alexander Zarkhidze Roger May Fatma Ibrahim 《Geophysical Prospecting》2014,62(5):1143-1161
Coherent noise in land seismic data primarily consists in source‐generated surface‐wave modes. The component that is traditionally considered most relevant is the so‐called ground roll, consisting in surface‐wave modes propagating directly from sources to receivers. In many geological situations, near?surface heterogeneities and discontinuities, as well as topography irregularities, diffract the surface waves and generate secondary events, which can heavily contaminate records. The diffracted and converted surface waves are often called scattered noise and can be a severe problem particularly in areas with shallow or outcropping hard lithological formations. Conventional noise attenuation techniques are not effective with scattering: they can usually address the tails but not the apices of the scattered events. Large source and receiver arrays can attenuate scattering but only in exchange for a compromise to signal fidelity and resolution. We present a model?based technique for the scattering attenuation, based on the estimation of surface‐wave properties and on the prediction of surface waves with a complex path involving diffractions. The properties are estimated first, to produce surface?consistent volumes of the propagation properties. Then, for all gathers to filter, we integrate the contributions of all possible diffractors, building a scattering model. The estimated scattered wavefield is then subtracted from the data. The method can work in different domains and copes with aliased surface waves. The benefits of the method are demonstrated with synthetic and real data. 相似文献