Geochemistry of carbonate precipitation from the groundwater in a coastal region     

N. Subba Rao  K. V. Srinivasa Rao  P. Surya Rao  Ch. Venkat Rao  K. Arjunudu  P. Madhusudhana Reddy  A. Subrahmanyam 《Journal of the Geological Society of India》2009,73(5):651-656

Groundwater samples were collected from a coastal region of Andhra Pradesh to assess the possible conditions of the formation of carbonates. The area experiences a semi-arid climate and is underlain by khondalites, over which the Quaternary sediments occur. The study of the geochemistry of groundwater indicates that groundwater is mostly of fresh, with alkaline nature. The study further suggest that the breakdown of feldspars as kaolinite during rock-water interaction, releases Ca²⁺. Soils/weathered products contribute high CO₂ under the open system. The Ca²⁺ and CO₂ are added to the groundwater through the infiltrating recharge water. They subsequently precipitate as fine-grained carbonates in the weathering profile due to evapotranspiration under a freshwater environment.  相似文献   

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   

XHIP: An extended hipparcos compilation     

E. Anderson  Ch. Francis 《Astronomy Letters》2012,38(5):331-346

We present the Extended Hipparcos Compilation (XHIP), a database of all stars in the New Reduction of the Hipparcos Catalog extensively cross-referenced with data from a broad survey of presently available sources. The resulting collection uniquely assigns 116 096 spectral classifications, 46 392 radial velocities, and 18 549 homogenized iron abundances [Fe/H] to Hipparcos stars. Stellar classifications from SIMBAD, indications of multiplicity from CCDM or WDS, stellar ages from the Geneva-Copenhagen Survey III, supplemental photometry from 2MASS and SIMBAD, and identifications of exoplanet host stars are also included. Parameters for solar encounters and Galactic orbits are calculated for a kinematically complete subset. Kinetic bias is found to be minimal. Our compilation is available through the Centre de Données astronomiques de Strasbourg as Catalog V/137A.  相似文献   

The propagation of density waves in a Galaxy     

Ch. K. Terzides 《Astrophysics and Space Science》1982,81(1-2):345-355

We examine the behaviour of the solutions of the Lin-Shu dispersion relation in terms of the stability parameterQ and we find that a modification of the critical values of the dispersion speeds does not change drastically this behaviour. On the contrary the solutions of the Lynden Bell-Kalnajs dispersion relation behave in a more complicated way. The use of this dispersion relation imposes a different definition of the critical values of the dispersion speeds which are in general larger than the corresponding values of the Lin-Shu case.  相似文献   

Fast detection of chaotic behavior in galactic potentials     

G.I. Karanis  Ch.L. Vozikis 《Astronomische Nachrichten》2008,329(4):403-412

In the present paper we apply a new method of distinction between ordered and chaotic motion in galactic potentials. The method uses the Fourier Transform of a series of time intervals each one representing the time that elapsed between two successive points on the Poincaré surface of section. Examples of the methods ability to achieve an early and clear detection of an orbit's behavior are provided using two galactic potentials. The new method can also be applied in order to have an early distinction between ordered and sticky orbits. The method is generalized in order to be used in models with more than two dimensions. Finally we have tried to find an one‐number index to give us the nature of the orbit instead of checking by eye the whole spectrum. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Nekhoroshev stability at L₄ or L₅ in the elliptic-restricted three-body problem – application to Trojan asteroids     

Ch. Lhotka  C. Efthymiopoulos  R. Dvorak 《Monthly notices of the Royal Astronomical Society》2008,384(3):1165-1177

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Damages observed in locations of Oaxaca due to the Tehuantepec Mw8.2 earthquake,Mexico     

Pozos-Estrada  Adrián  Chávez  Marcos M.  Jaimes  Miguel Á.  Arnau  Oriol  Guerrero  Héctor 《Natural Hazards》2019,97(2):623-641

On September 7, 2017, at 23:49 h (local time), a Mw8.2 intermediate-depth normal-fault earthquake occurred in the Gulf of Tehuantepec, 133 km away from Pijijiapan, Chiapas, and about 700 km away from Mexico City. This event caused 95 fatalities and severe damage to different types of structures located close to the epicenter. The main objective of this work is to present observed damages caused in the state of Oaxaca by this earthquake, which were mainly concentrated in self-built houses and historical and ancient buildings. The locations visited by the reconnaissance team of the Institute of Engineering from UNAM in Oaxaca included Salina Cruz, Tehuantepec, Ixtaltepec, Juchitán, Huatulco and La Ventosa.

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Professor Emil Philippi-Stiftung     

E. Hoepffner  E. Kayser  G. Linck  G. Steinmann  W. v. Seidlitz 《International Journal of Earth Sciences》1913,4(8):595-595

Ohne Zusammenfassung  相似文献   

Development of solar flares and features of the fine structure of solar radio emission     

G. P. Chernov  V. V. Fomichev  Y. Yan  B. Tan  Ch. Tan  Q. Fu 《Geomagnetism and Aeronomy》2017,57(6):738-751

The reason for the occurrence of different elements of the fine structure of solar radio bursts in the decimeter and centimeter wavelength ranges has been determined based on all available data from terrestrial and satellite observations. In some phenomena, fast pulsations, a zebra structre, fiber bursts, and spikes have been observed almost simultaneously. Two phenomena have been selected to show that the pulsations of radio emission are caused by particles accelerated in the magnetic reconnection region and that the zebra structure is excited in a source, such as a magnetic trap for fast particles. The complex combination of unusual fiber bursts, zebra structure, and spikes in the phenomenon on December 1, 2004, is associated with a single source, a magnetic island formed after a coronal mass ejection.  相似文献   

Data-based modelling approach for variable density flow and solute transport simulation in a coastal aquifer   总被引：1，自引：1，他引：0  

Basant Yadav  Shashi Mathur  Sudheer Ch  Brijesh Kumar Yadav 《水文科学杂志》2018,63(2):210-226

Data-based models, namely artificial neural network (ANN), support vector machine (SVM), genetic programming (GP) and extreme learning machine (ELM), were developed to approximate three-dimensional, density-dependent flow and transport processes in a coastal aquifer. A simulation model, SEAWAT, was used to generate data required for the training and testing of the data-based models. Statistical analysis of the simulation results obtained by the four models show that the data-based models could simulate the complex salt water intrusion process successfully. The selected models were also compared based on their computational ability, and the results show that the ELM is the fastest technique, taking just 0.5 s to simulate the dataset; however, the SVM is the most accurate, with a Nash-Sutcliffe efficiency (NSE) ≥ 0.95 and correlation coefficient R ≥ 0.92 for all the wells. The root mean square error (RMSE) for the SVM is also significantly less, ranging from 12.28 to 77.61 mg/L.  相似文献