Perturbed Gylden Systems and Time-Dependent Delaunay-Like Transformations     

Luis Floría 《Celestial Mechanics and Dynamical Astronomy》1997,68(1):75-85

We study the possibilities and limitations of the application of generalized Delaunay-like transformations (in the 6-dimensional phase space) and TR-like mappings (in the 8-dimensional, extended phase space) to perturbed two-body problems with a time-varying Keplerian parameter μ(t), that is, to Gylden-type systems. For the sake of theoretical completeness, both negative- and positive-energy motion (with nonstationary coupling parameter) are, in principle, considered. Our developments are intended to introduce canonical variables parallelling the classical ones of Delaunay and the Delaunay-Similar variables of Scheifele. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO   总被引：1，自引：1，他引：0  

Marc H. Taylor  Jorge Tam  Vernica Blaskovic  Pepe Espinoza  R. Michael Balln  Claudia Wosnitza-Mendo  Juan Argüelles  Erich Díaz  Sara Purca  Noemi Ochoa  Patricia Ayn  Elisa Goya  Dimitri Gutirrez  Luis Quipuzcoa  Matthias Wolff 《Progress in Oceanography》2008,79(2-4):366

The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.  相似文献   

Detection of satellite remnants in the Galactic Halo with Gaia– I. The effect of the Galactic background, observational errors and sampling     

Anthony G. A. Brown  Hector M. Velázquez  Luis A. Aguilar 《Monthly notices of the Royal Astronomical Society》2005,359(4):1287-1305

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The "So What?" factor     

Chapman PM  Guerra LM 《Marine pollution bulletin》2005,50(12):529-1458

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Chlorinated hydrocarbons in the seawater and surface sediments of Blanca Bay,Argentina     

JoséLuis Sericano  Adan E. Pucci 《Estuarine, Coastal and Shelf Science》1984,19(1):27-51

In order to characterize our study area and to provide reference values to be used in the future to measure the changes produced by an increase in contamination, the concentrations of chlorinated hydrocarbons have been investigated in fifty-one samples of seawater, taken at four different depths: air-sea interface, surface, one metre and bottom waters, and in twenty-three samples of surface sediments from Blanca Bay, Argentina. Of eleven organochlorine compounds we were looking for (α BHC, lindane, heptachlor, δ BHC. aldrin, heptachlor epoxide, dieldrin, o-p′DDD, p-p′DDD, o-p′DDT and p-p′DDT), seven could be detected in seawater and three in surface sediments with the following mean concentrations: α-BHC=48·2 ng l^?1; lindane=54·2 ng l^?1; heptachlor=45·0 ng l^?1; δ BHC=12·5 ng l^?1; aldrin=61·8 ng l^?1 and ΣDDT=67·0 ng l^?1; and δ BHC=3·2 ng g^?1; lindane=4·2 ng g^?1 and heptachlor=1·0 ng g^?1 for seawater, regarding the surface waters, and sediment samples, respectively.Concentration factors among the different water layers were also studied to see if there was any correlation between chlorinated hydrocarbon contents and the water depths from which the samples were taken. As a mean value, the air-sea interface water contains 18 times more of these compounds than that of the water near the bottom. A comparison of the values corresponding to seawater and surface sediments from our study area with those levels measured in samples from other geographic locations is also presented.With the purpose to detect a relationship between chlorinated hydrocarbon concentrations and the contents of particulate matter (PM) on the one hand, and particulate organic material (POM) on the other hand, four groups of samples containing different amounts of PM and POM, respectively were formed. From a comparison of the results obtained, lindane, heptachlor and δ BHC showed a tendency to lower concentrations in those samples containing little PM whereas α BHC and aldrin remained without important changes. No significant correlation was found between organochlorine levels and contents of POM.  相似文献   

Climate change and the incidence of a forest pest in Mediterranean ecosystems: can the North Atlantic Oscillation be used as a predictor?     

José A. Hódar  Regino Zamora  Luis Cayuela 《Climatic change》2012,113(3-4):699-711

Many forest pest species strongly depend on temperature in their population dynamics, so that rising temperatures worldwide as a consequence of climatic change are leading to increased frequencies and intensities of insect-pest outbreaks. In the Mediterranean area, the climatic conditions are strongly linked to the effects of the North Atlantic Oscillation (NAO). The aim of this work is to analyze the dynamics of the pine processionary moth (Thaumetopoea pityocampa), a severe pest of Pinus species in the Circunmediterranean, throughout a region of southern Spain, in relation to NAO indices. We related the percentage of forest plots with high defoliation by pine processionary moth each year with NAO values for the present and the three previous winters, using generalized linear models with a binomial error distribution. The time series is 16-year long, and we performed analyses for the whole database and for the five main pine species separately. We found a consistent relationship between the response variable and the NAO index. The relationship is stronger with pine species living at medium-high altitudes, such as Aleppo (P. halepensis), black (P. nigra), and Scots (Pinus sylvestris) pine, which show the higher defoliation intensities up to 3?years after a negative NAO phase. The results highlight, for the first time, the usefulness of using global drivers in order to understand the dynamics of pest outbreaks at a regional scale, and they open the window to the development of NAO-based predictive models as an early-warning signal of severe pest outbreaks.  相似文献   

Long memory, seasonality and time trends in the average monthly temperatures in Alaska   总被引：1，自引：0，他引：1  

Luis A. Gil-Alana 《Theoretical and Applied Climatology》2012,108(3-4):385-396

This paper deals with the analysis of monthly temperatures in 19 meteorological stations in Alaska during the last 50?years. For this purpose, we employ a procedure that permits us to examine in a single framework several features observed in climatological time series such as time trends, long-range persistence and seasonality. The results indicate that the highest degrees of persistence are observed in stations located in the southern regions and seasonality appears as a major issue in all cases. Removing the seasonal structure and focussing on the anomalies with respect to the monthly means, the time trend coefficients appear significantly positive in the majority of the cases, implying that temperatures have increased during the last 50?years.  相似文献   

Everyday realities of climate change adaptation in Mozambique     

Luis Artur  Dorothea Hilhorst 《Global Environmental Change》2012,22(2):529-536

This paper analyzes discourses and practices of flood response and adaptation to climate change in Mozambique. It builds on recent publications on climate change adaptation that suggest that the successes and failures of adaptation highly depend on the cultural and political realms of societal perceptions and the sensitivity of institutions. To capture this, the paper adopted a multi-sited ethnographic approach. Acknowledging that there is no central locus of representation that can unveil the working of disaster response in Mozambique, the paper brings together five vignettes of research in different ‘sites’ of concern to the rise in floods in Mozambique. These are the politics of climate change adaptation at the national institutional level, societal responses to increased flooding, local people's responses to floods, the evacuation and resettlement programme following the 2007 flood. The paper finds how adaptation to climate change becomes part of everyday politics, how actors aim to incorporate responses into the continuation of their normal behavior and how elites are better positioned to take advantage of adaptation programmes than the vulnerable people that were targeted. It argues that climate change adaptation must be made consonant with historically grown and ongoing social and institutional processes. It concludes with lessons that the analysis and methodology of the research can provide for the practice of climate change adaptation.  相似文献   

Mesoscale numerical modeling of meteorological events in a strong topographic gradient in the northeastern part of Mexico     

Luis F. Pineda-Martinez  Noel Carbajal 《Climate Dynamics》2009,33(2-3):297-312

A series of numerical experiments were carried out to study the effect of meteorological events such as warm and cold air masses on climatic features and variability of a understudied region with strong topographic gradients in the northeastern part of Mexico. We applied the mesoscale model MM5. We investigated the influence of soil moisture availability in the performance of the model under two representative events for winter and summer. The results showed that a better resolution in land use cover improved the agreement among observed and calculated data. The topography induces atmospheric circulation patterns that determine the spatial distribution of climate and seasonal behavior. The numerical experiments reveal regions favorable to forced convection on the eastern side of the mountain chains Eastern Sierra Madre and Sierra de Alvarez. These processes affect the vertical and horizontal structure of the meteorological variables along the topographic gradient.  相似文献   

Multivariate geostatistical application for climate characterization of Minas Gerais State, Brazil     

Luiz G. de Carvalho  Marcelo de Carvalho Alves  Marcelo S. de Oliveira  Rubens L. Vianello  Gilberto C. Sediyama  Luis M. T. de Carvalho 《Theoretical and Applied Climatology》2010,102(3-4):417-428

The objective of the present study was to assess for Minas Gerais the cokriging methodology, in order to characterize the spatial variability of Thornthwaite annual moisture index, annual rainfall, and average annual air temperature, based on geographical coordinates, altitude, latitude, and longitude. The climatic element data referred to 39 INMET climatic stations located in the state of Minas Gerais and in nearby areas and the covariables altitude, latitude, and longitude to the SRTM digital elevation model. Spatial dependence of data was observed through spherical cross semivariograms and cross covariance models. Box–Cox and log transformation were applied to the positive variables. In these situations, kriged predictions were back-transformed and returned to the same scale as the original data. Trend was removed using global polynomial interpolation. Universal simple cokriging best characterized the climate variables without tendentiousness and with high accuracy and precision when compared to simple cokriging. Considering the satisfactory implementation of universal simple cokriging for the monitoring of climatic elements, this methodology presents enormous potential for the characterization of climate change impact in Minas Gerais state.  相似文献