Using neural networks for the derivation of Runge-Kutta-Nyström pairs for integration of orbits     

Ch. Tsitouras  I.Th. Famelis 《New Astronomy》2012,17(4):469-473

In this paper we present Runge-Kutta-Nyström (RKN) pairs of orders 4(3) and 6(4). We choose a test orbit from the Kepler problem to integrate for a specific tolerance. Then we train the free parameters of the above RKN4(3) and RKN6(4) families to perform optimally. For that we form a neural network approach and minimize its objective function using a differential evolution optimization technique. Finally we observe that the produced pairs outperform standard pairs from the literature for Pleiades orbits and Kepler problem over a wide range of eccentricities and tolerances.  相似文献   

Long-term groundwater resource observatory for Southwestern Madagascar     

Simon D. Carrière  Thomas Health  Pascale F. M. Rakotomandrindra  Chloé Ollivier  Riva E. Rajaomahefasoa  Heritiana A. Rakoto  Jean Lapègue  Yves E. Rakotoarison  Marie Mangin  Jean Kempf  Théodore Razakamanana  Konstantinos Chalikakis 《水文研究》2021,35(3):e14108

Madagascar has one of the highest poverty rates in the world and consequently the long-term monitoring of groundwater resources is not a priority for the authorities. However, groundwater is often the only sustainable resource that has a satisfactory quality to supply the population. This is especially true in the south-west of the country, which is a semi-arid region and a global change hot spot (intense land use and climate changes). In response to the lack of data, the Groundwater Resource Observatory for Southwestern Madagascar (GROSoM) was established to monitor piezometry and meteorology over the longer term as part of a humanitarian response. The first site was setup in 2014 in a catchment located over a carbonate plateau; in 2018, a second site was installed in an alluvial setting within a crystalline basement catchment and a third site will be installed in 2020 to monitor groundwater dynamics in a coastal setting. The three sites, located between Toliara and Taolagnaro cities, are complementary and representative of various hydrogeological systems in Southwestern Madagascar. Each site includes a weather station and between 3 and 6 piezometric probes. The monitoring data indicate a strong inter-annual variability in precipitation, which induces a strong variability in aquifers recharge. One of the driest years in 2016 seems to be consistent with strong El Niño – Southern Oscillation (ENSO) effects observed at the global scale, while years with higher recharge appear to be related to cyclones such as Fundi in 2015 and Eketsang in 2019. Preliminary results of cross-disciplinary studies demonstrated a link between groundwater and health issues (i.e., admissions to basic health centres). This observatory aims to produce long-term data and has two objectives: (i) strengthening the early warning system for humanitarian crises in Madagascar; (ii) contributing to a better understanding of the effects of climate change on groundwater resources in this semi-arid region.  相似文献   

Mediterranean desertification and land degradation: Mapping related land use change syndromes based on satellite observations   总被引：3，自引：0，他引：3  

J. Hill  M. Stellmes  Th. Udelhoven  A. Rder  S. Sommer 《Global and Planetary Change》2008,64(3-4):146

  相似文献   

Evaluating the Ability of CRCM5 to Simulate Mixed Precipitation     

É. Bresson  R. Laprise  D. Paquin  J.M. Thériault  R. de Elía 《大气与海洋》2017,55(2):79-93

Precipitation episodes in the form of freezing rain and ice pellets represent natural hazards affecting eastern Canada during the cold season. These types of precipitation mainly occur in the St. Lawrence River valley and the Atlantic provinces of Canada. This study aims to evaluate the ability of the fifth-generation Canadian Regional Climate Model (CRCM5), using a 0.11° horizontal grid mesh, to hindcast mixed precipitation when driven by reanalyses produced by the European Centre for Medium-range Weather Forecasts (ERA-Interim) for a 35-year period. In general, the CRCM5 simulation slightly overestimates the occurrence of freezing rain, but the geographical distribution is well reproduced. The duration of freezing rain events and accompanying surface winds in the Montréal region are reproduced by CRCM5. A case study is performed for an especially catastrophic freezing-rain event in January 1998; the model succeeds in simulating the intensity and duration of the episode, as well as the propitious meteorological environment. Overall, the model is also able to reproduce the climatology and a specific event of freezing rain and ice pellets.  相似文献   

Emissions of Volatile Organic Compounds from Sunflower and Beech: Dependence on Temperature and Light Intensity   总被引：11，自引：0，他引：11  

G. Schuh  A. C. Heiden  Th. Hoffmann  J. Kahl  P. Rockel  J. Rudolph  J. Wildt 《Journal of Atmospheric Chemistry》1997,27(3):291-318

Emissions of volatile organic compounds (VOCs) from sunflower (Helianthus annuus L. cv. giganteus) were measured in a continuously stirred tank reactor. The compounds predominantly emitted from sunflower were: isoprene, the monoterpenes -pinene, -pinene, sabinene, 3-carene and limonene, an oxygenated terpene, not positively identified so far and the sesquiterpene -caryophyllene. Emission rates ranged from 0.8 x 10^–16 to 4.3 x 10 ^–15 mol cm^–2 s^–1 at a temperature of 25°C and at a light intensity of 820 µEm^–2 s^–1. A dependence of the emission rates on temperature as well as on light intensity was observed. The emission rates of -pinene, sabinene and thujene from beech (Fagus sylvatica L.) were also affected by temperature as well as by light intensity. Our results suggest that an emission algorithm for all compounds emitted from sunflower and beech has to consider temperature and light intensity simultaneously. The observations strongly indicate that the emissions of VOCs from sunflower and beech are in part closely coupled to the rate of biosynthesis and in part originate from diffusion out of pools. The emission rates can be described by an algorithm that combines the model given by Tingey and coworkers with the algorithm given by Guenther and coworkers after slight modification.  相似文献   

Formation of vivianite in holocene clay sediments     

I. Th. Rosenqvist 《Lithos》1970,3(4):327-334

Concretions of vivianite attaining 0.5 g occur in the upper 4 m of the bottom sediments of the Åsrum lake, Vestfold, S. Norway. The vivianite-bearing zone is of lacustrine origin. Vivianite is absent in the underlying lagunal and marine sediments. Electro-chemical and chemical data are given for the interstitial water and the clay.

Solubility product of vivianite is determined. The equilibrium constant is K = 10⁻⁴⁰ for the reaction 3 Fe⁺⁺ + 2 HPO₄⁻ + 2 OH⁻ = vivianite. The concretions grew by diffusion from a slightly supersaturated interstitial water phase. The degree of supersaturation is calculated. The stability relations of vivianite and hydroxyl apatite are discussed.  相似文献   

Contribution a la tectonique du Bassin houiller de la Sarre: Recherche du tracé au sol de la Faille de la Sarre et de la Faille de la Rosselle (Faille Felsberg)     

N. Théobald 《International Journal of Earth Sciences》1953,41(1):191-200

Zusammenfassung Es werden genauere Angaben gemacht über den Verlauf des Saarsprungs und des Felsbergsprunges an der Erdoberfläche. Der Saarsprung konnte von Bous bis Burbach verfolgt werden. Der Felsbergsprung verfolgt sich nach SE bis in den Rosselsprung.Das Vorkommen von Oberrotliegendem scheint an diese Verwerfungen gebunden zu sein. Es sind Zerrungsspalten, die während der Hauptfaltungsphase (saalische Phase nachStille) des Saar-Nahe-Beckens aufgebrochen sind. Es ist aber anzunehmen, daß sie während des Oberrotliegenden aktiv waren. Sie wurden nach Ablagerung der Trias neu belebt.  相似文献   

Tiergeschichte oder Erdgeschichte?     

Dr. J. Thöne 《International Journal of Earth Sciences》1928,19(4):315-319

Ohne Zusammenfassung  相似文献   

The planet Jupiter     

Thérèse Encrenaz 《Astronomy and Astrophysics Review》1999,9(3-4):171-219

Summary. The exploration of Jupiter, the closest and biggest giant planet, has provided key information about the origin and evolution of the outer Solar system. Our knowledge has strongly benefited from the Voyager and Galileo space missions. We now have a good understanding of Jupiter's thermal structure, chemical composition and magnetospheric environment. There is still debate about the nature of the heating source responsible for the high thermospheric temperatures (precipitating particles and/or gravity waves). The measurement of elemental abundance ratios (C/H, N/H, S/H) gives strong support to the “nucleation” formation model, according to which giant planets formed from the accretion of an initial core and the collapse of the surrounding gaseous protosolar nebula. The D/H and He/He ratios are found to be representative of their protosolar value. The helium abundance, in contrast, appears to be slightly depleted in the outer envelope with respect to the protosolar value; this departure is interpreted as an evolutionary effect, due to the condensation of helium droplets in the liquid hydrogen ocean inside Jupiter's interior. The cloud structure of Jupiter, characterized by the belt-zone system, is globally understood; also present are specific features like regions of strong infrared radiation (“hot spots”), colder regions (“white ovals”) and the Great Red Spot (GRS). Clouds were surprisingly absent at the hot spot corresponding to the Galileo probe entry site, and the water abundance measured there was strongly depleted with respect to the solar O/H value. This probably implies that hot spots are dry, cloud-free regions of subsidence, while “normal” air, rich in condensibles, is transported upward by convective motions. As a result, the Jovian meteorology, still based on Halley-type cells, seems to be much more complex than a simple zone-belt system. The nature of the GRS, a giant anticyclonic storm, colder and higher than its environment, has been confirmed by the Galileo observations, but its internal structure appears to be very complex. Strong winds, probably driven by the Jovian internal source, were measured at deep tropospheric levels. The troposphere might be statically stable at pressures higher than 18 bars, but the extent of this putative radiative layer is still unknown. Received 23 November 1998  相似文献   

A mass ratio limit for primordial black holes     

P. Brosche  F.‐Th. Lentes  L. J. Tassie 《Astronomische Nachrichten》2003,324(6):556-559

We augment our scenario for the formation of astronomical objects from macroscopic superstrings by the assumption that the central matter keeps its identity in the fragmentation. From the condition that the angular momentum per mass squared of this matter should be less than the Kerr limit G/c, we obtain upper limits for the ratio of the mass of central black holes M(BH) to the mass M of the host object. This limit is M(BH)/M ≈ 0.001, and, expressed in observed quantities, approximately M(BH)/M ≈ σ²/(v · c) where σ is the r.m.s. velocity, v the rotational velocity and c the velocity of light. The valuesM(BH) agree with the observed behaviour both in order of magnitude and in the variation with velocity dispersion. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献