A dynamical equivalent to the equilateral libration points of the earth-moon system     

Carles Díez  Àngel Jorba  Carles Simó 《Celestial Mechanics and Dynamical Astronomy》1990,50(1):13-29

Consider the Earth-Moon-particle system as a Restricted Three Body Problem. There are two equilateral libration points. In the actual world system, those points are no longer relative equilibrium points mainly due to the effect of the Sun and to the noncircular motion of the Moon around the Earth. In this paper we present the problem as a perturbation of the RTBP and we look for the dynamical equivalent of L _4,5. It turns out to be a quasiperiodic orbit. It is obtained for a simplified model but the procedure to obtain it is general and can be carried out with an additional computational effort.  相似文献   

Beyond maximum entropy: Fractal pixon-based image reconstruction     

R. C. Puetter  R. K. Piña 《Experimental Astronomy》1994,3(1-4):293-296

We have developed a new Bayesian image reconstruction method that has been shown to be superior to the best implementations of other methods, including Goodnessof-Fit (e.g. Least-Squares and Lucy-Richardson) and Maximum Entropy (ME). Our new method is based on the concept of the pixon, the fundamental, indivisible unit of picture information. Use of the pixon concept provides an improved image model, resulting in an image prior which is superior to that of standard ME.  相似文献   

Single multipurpose reservoir design: a modified optimal control problem by chance-constrained programming     

Miguel A. Mariño  Slobodan P. Simonovic 《Advances in water resources》1981,4(1):43-48

This paper presents a chance-constrained programming model for optimal control of a multipurpose reservoir and its modification to a model for single reservoir design. An algorithm is developed for solving complex stochastic problems of multipurpose reservoir planning and design. The complexity of the problem is resolved by a two-step algorithm: (1) transformation of chance constraints on the state and control variables is performed at the first step; and (2) the choice of optimum control or optimal reservoir storage is carried out in the second step. The method of iterative convolution is chosen for the first step, while linear programming is selected for the second step. The algorithm allows the use of random inflows and random demands together with other deterministic demands. The reservoir design problem is presented as a modified optimal control problem. The procedure is illustrated with an example of a hypothetical reservoir design problem with three different types of downstream releases (hydropower production, municipal water supply, and irrigation).  相似文献   

Early Paleozoic orogeny in southern South America     

F.G. Aceñolaza  H. Miller 《Precambrian Research》1982,17(2):133-146

In northwest Argentina, weakly metamorphic clastic and calcareous sedimentary rocks of latest Precambrian to Lower Cambrian age (Puncoviscana Formation and related units) contain an abundant ichnofauna of both chronostratigraphic and paleoenvironmental value. In the western and central Sierras Pampeanas, metasedimentary and metavolcanic rocks are considered to form part of the same geotectonic unit. This “Pampean orogenic cycle” includes geosynclinal sedimentation of latest Precambrian to Lower Cambrian age, as well as magmatism, metamorphism and deformation of Middle to Upper Cambrian age, documented by an angular unconformity below the Upper Cambrian to Devonian rocks of the “Famatinian orogenic cycle”. In some of the metamorphic rocks of the Pampean Cycle a pre-Ordovician folding is also distinguished from a later tectonic overprinting. Hence, the concept of a Pampean cycle differs from other concepts of late Precambrian orogenic cycles of South America which are only defined by radiometric ages. The Pampean orogenesis may be compared with the Ross orogenesis of the Transantarctic Mts., the Tyennan orogenesis of Australia and some of the deformation phases of the Damara orogen in Namibia.  相似文献   

Spatial statistics for urban analysis: A review of techniques with examples   总被引：8，自引：0，他引：8  

Antonio Páez  Darren M. Scott 《GeoJournal》2004,61(1):53-67

Traditionally, urban analysis has been quick to adopt and benefit from developments in technology (e.g., microcomputer, GIS) and techniques (e.g., statistics, mathematical programming). This has not been the case, however, with newer methods of spatial analysis — in particular, spatial statistics. Only recently has this situation started to change. This paper documents the confluence of spatial statistics and urban analysis by first reviewing developments in spatial statistics, and then presenting examples of recent applications in urban analysis. The developments reviewed fall under the rubric of global and local forms of spatial analysis, and cover three major technical issues: spatial association, spatial heterogeneity and the modifiable areal unit problem. The examples highlight the relevance and usefulness of the techniques reviewed for urban transportation and land-use applications. The paper concludes with conjectures concerning future developments at the intersection of spatial statistics and urban analysis.  相似文献   

A warning model based on temporal changes of coda Q for volcanic activity at Nevado Del Ruiz Volcano, Colombia     

John M. Londoño  Yasuaki Sudo 《Bulletin of Volcanology》2002,64(5):303-315

The coda Q has been calculated for Nevado del Ruiz Volcano, Colombia (NRV) from 1985 to 1999 by using a single scattering model. During this period, the inverse of Q (Q^-1 proportional to attenuation) exhibited a long-term decrease with time, as well as shorter-term variations related to the volcanic activity. Q^-1 increased prior to volcanic crises and decreased afterward. Based on these observations, a seismic warning criterion has been developed. The parameters (frequency band, size of moving average window, and threshold levels) necessary to evidence clear and significant short-term changes in Q^-1 have been investigated and appropriated values are proposed. We suggest a phenomenological model with three stages for the short-term temporal changes in Q^-1 at NRV. Firstly, Q^-1 increases before a volcanic crises because of accumulation of gas and/or liquid, which decreases the aspect ratio of fluid pockets and increases the fractional volume of fluid in the rocks and the pore aspect ratio. Secondly, Q^-1 starts to decrease during the crises by the discharging of fluids such as gas, water, etc. from the volcano. Finally, Q^-1 becomes more stable after the crisis at a lower value because of the degassing and/or increasing of rigidity of the medium because of the long-term crystallization and cooling processes. Q^-1 seems to be a promising monitoring tool at NRV. It is possible that the observed temporal changes of Q^-1, combined with other parameters, may help to predict with greater accuracy a volcanic crisis at NRV.  相似文献   

Response to B. Morse (2001) on "The role of arsenic-bearing rocks in groundwater pollution at Zimapan Valley, Mexico" by Armienta and others, Environmental Geology 40(4/5)     

M. Armienta  L. Ongley  R. Rodríguez  G. Villaseñor  H. Mango 《Environmental Geology》2002,42(4):433-438

  相似文献   

Geostatistical study of the feldspar content and quality of a granite deposit     

J. Taboada  A. Vaamonde  A. Saavedra  C. Ordez 《Engineering Geology》2002,65(4):285-292

In order to characterise the saleable feldspar in a granite deposit, a methodology was developed in accordance with the exploitation process. This consisted of mechanically extracting the surface layer of the batholith and separating the feldspar from the quartz using the granulometric separation method, given that the size of the grains of the feldspar is greater than that of quartz.

Following washing, grinding and magnetic separation of the feldspar in order to eliminate the ferromagnesium minerals, the saleable feldspar was characterised in terms of the factors that determine its market value, namely, its content in Al₂O₃, SiO₂, Na₂O and K₂O.

Following the opening of prospecting pits in the granite massif, samples were analysed in the laboratory using three different granulometric cuts and by reproducing the treatment process. The values for the quality variables of saleable feldspar were obtained, and the results were interpolated to the entire deposit using the kriging method.

In order to summarise the information from the above-mentioned variables, a quality index was constructed using multivariate statistics and by employing market criteria, and subsequently, the values of the index were interpolated to the entire deposit using bidimensional kriging.

The map of saleable quality feldspar from the deposit permits both affirmation of the treatment process yield for each granulometric cut and the planning of extraction from the deposit to obtain a homogeneous quality in the saleable feldspar.  相似文献   

Morphometric relationships of penaeid shrimps in a coastal lagoon: Spatio-temporal variability and management implications     

Roberto Pérez-Castañeda  Omar Defeo 《Estuaries and Coasts》2002,25(2):282-287

Spatio-temporal variability in the length-weight relationship of four sympatric shrimp species (Farfantepeneus aztecus, F. brasiliensis, F. duorarum, andF. notialis) was evaluated in the Celestun lagoon, Mexico. Monthly samples were taken throughout 2 yr in three hydrological zones (seaward, middle, and inner) and climatic seasons (Nortes, Dry, and Rainy). Significant intraspecific and interspecific differences in the length-weight relationships were detected among climatic seasons and hydrological zones, reflecting positive allometric growth.F. notialis registered the highest condition (weight at length), followed byF. duorarum, F. aztecus, andF. brasiliensis. The lowest values in condition were consistently registered during Nortes and at the seaward zone. All species showed a pattern consistent with a density-dependent effect on condition, that is a negative correlation between individual mean weight and total relative abundance. The immediate implication for managing this important multispecific coastal artisanal resource that is supported by our study is the restriction of fishing effort in the seaward zone, mainly during the Nortes seasons.  相似文献   

Sedimentological and palaeohydrological responses to tectonics and climate in a small, closed, lacustrine system: Oligocene As Pontes Basin (Spain)   总被引：1，自引：0，他引：1  

A. Sáez  L. Cabrera 《Sedimentology》2002,49(5):1073-1094

ABSTRACT A small, closed, lacustrine system developed during the restraining overstep stages of the Oligocene As Pontes strike‐slip basin (Spain). The increase in basin accommodation and the headward spread of the drainage, which increased the water input, triggered a change from shallow, holomictic to deeper, meromictic conditions. The lower, shallow, lacustrine assemblage consists of mudstone–carbonate cycles recording lacustrine–palustrine ramp deposition in a saline lake. High Sr content in some early diagenetic calcites suggests that aragonite and calcite made up the primary carbonate muds. Early dolomitization took place together with widespread pedogenic activity. The upper, deep, freshwater, lacustrine assemblage includes bundles of carbonate–clay rhythmites and fine‐grained turbidite beds. Primary calcite and diagenetic siderite make up the carbonate laminae. The Mg content of the primary carbonates records variations in Mg/Ca ratios in lacustrine waters. δ¹⁸O and δ¹³C covariance trends in calcite reinforce closed drainage conditions. δ¹⁸O data indicate that the lake system changed rapidly from short‐lived isotopically light periods (i.e. from seasonal to pluriannual) to longer steady‐state periods of heavier δ¹⁸O (i.e. from pluriannual to millennial). The small δ¹³C changes in the covariant trends were caused by dilute inflow, changing the contributions of dissolved organic carbon in the system and/or internal variations in lacustrine organic productivity and recycling. In both shallow and deep carbonate facies, sulphate reduction and methanogenesis may account, respectively, for the larger negative and positive δ¹³C shifts recorded in the early diagenetic carbonates (calcite, dolomite and siderite). The lacustrine system was very susceptible to high‐frequency, climatically forced water balance variations. These climatic oscillations interfered with the low‐frequency tectonic and morphological changes in the basin catchment. This resulted in the superposition of high‐order depositional, mineralogical and geochemical cycles and rhythms on the lower order lacustrine infill sequence.  相似文献