Estimation of the generalized covariance function: II. A response surface approach     

Thomas H. Starks  Allen R. Sparks 《Mathematical Geology》1987,19(8):769-783

A procedure is proposed that employs first-moment estimation (kriging), cross-validation, and response surface analysis to estimate parameters of a generalized covariance function. Results from application of this procedure to two data sets are given.  相似文献   

Results from the Wide-Angle Search for Planets prototype (WASP0) – I. Analysis of the Pegasus field     

Stephen R. Kane  rew Collier Cameron  Keith Horne  David James  Tim A. Lister  Don L. Pollacco  Rachel A. Street  Yiannis Tsapras 《Monthly notices of the Royal Astronomical Society》2004,353(2):689-696

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Regions and Restructuring in New Zealand: Issues And Questions in the 1980s     

Stephen Britton  Richard Le  Heron 《New Zealand geographer》1987,43(3):129-139

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Squeezing the fossil record: unravelling the evolution of stalked crinoids in the Caribbean     

Cornelis J Veltkamp  Stephen K Donovan† 《Geology Today》2002,18(3):107-110

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Stellar populations in early-type Coma cluster galaxies – I. The data     

Stephen A. W. Moore  John R. Lucey  Harald Kuntschner  Matthew Colless 《Monthly notices of the Royal Astronomical Society》2002,336(2):382-408

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Far-Infrared/Submillimeter Astronomical Interferometry with Spaceborne Tether Formations     

Enrico Lorenzini  Claudio Bombardelli  Mario Cosmo  Martin Harwit  David Leisawitz  Rodger Farley  Stephen Rinehart  David Quinn  David Miller 《Astrophysics and Space Science》2006,302(1-4):225-239

Through the continuing development of improved detectors and detector arrays, far-infrared/submillimeter astronomical space missions have had enormous successes in recent years. Despite these advances, the diffraction-limited angular resolving power has remained virtually constant. The advent of telescopes with apertures of several meters will improve this capability, but will still leave image resolution many orders of magnitude poorer than in most other spectral ranges. Here we point out that the only foreseeable way to improve image quality to rival that of modern optical telescopes will be with interferometers whose light collectors are connected by tethers. After making the scientific case for high spatial resolution far-infrared/submillimeter imaging and the use of interferometry as the most immediate way of producing results, we discuss recent advances in dynamic analysis and control of tethered formations, and argue that the further development and testing of tethers in space is a first step toward providing improved far-infrared/submillimeter angular resolution and astronomical image quality.  相似文献   

Estimation of areal specific yield in sands using the central limit theorem     

Stephen B. K. Tan  E. B. Shuy  Lloyd H. C. Chua  Ngonidzashe Mzila 《水文研究》2006,20(18):3975-3987

A new approach is demonstrated that permits a reliable estimate of specific yield using published values of the van Genuchten water retention parameters and effective grain sizes and the measured effective grain sizes of soil samples. The specific yield distribution of the soil texture was computed using the published values of the van Genuchten parameters. The specific yield values and the published values of effective grain sizes were then used to construct a specific yield–effective grain size curve, which estimates the ‘point’ specific yield of the soil samples. Applying the central limit theorem, the point specific yields could be transformed into an ‘areal’ specific yield for a study area. Compared with other commonly used approaches, the present procedure requires relatively low computational efforts and readily obtainable data. It is cost effective and does not depend on soil texture classification. More importantly, it incorporates the depth to water table and the variations in grain sizes inherent in natural soil conditions in the estimation. The approach developed was applied for estimating the specific yield of an unconfined sandy aquifer created by land reclamation in the equatorial region. The values obtained were compared with field measurements and the typical ranges of specific yield from the literature. Instead of a single estimate of the specific yield, the method yields a confidence interval with a high confidence level of 95% and with a narrower range than the typical ranges from the literature. In addition, the estimated values are close to the field measurements; hence, the procedure provides a cost‐effective alternative to field measurement. The applicability of the present approach could be extended to sites with heterogeneity in the horizontal direction. Nevertheless, the applicability of the present approach for layered soil profiles requires further evaluations. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Gemini/GMOS spectra of globular clusters in the Virgo giant elliptical NGC 4649     

Michael Pierce  Terry Bridges  Duncan A. Forbes  Robert Proctor  Michael A. Beasley  Karl Gebhardt  Favio Raul Faifer  Juan Carlos Forte  Stephen E. Zepf  Ray Sharples  David A. Hanes 《Monthly notices of the Royal Astronomical Society》2006,368(1):325-334

NGC 4649 (M60) is one of a handful of giant Virgo ellipticals. We have obtained Gemini/GMOS (Gemini North Multi-Object Spectrograph) spectra for 38 globular clusters (GCs) associated with this galaxy. Applying the multi-index  χ²  minimization technique of Proctor and Sansom with the single stellar population models of Thomas, Maraston and Korn, we derive ages, metallicities and α-element abundance ratios. We find several young (2–3 Gyr old) supersolar metallicity GCs, while the majority are old (>10 Gyr), spanning a range of metallicities from solar to  [Z/H]=−2  . At least two of these young GCs are at large projected radii of 17–20 kpc. The galaxy itself shows no obvious signs of a recent starburst, interaction or merger. A trend of decreasing α-element ratio with increasing metallicity is found.  相似文献   

Three-dimensional smoothed particle hydrodynamics simulations of radiation-driven warped accretion discs     

Stephen B. Foulkes  Carole A. Haswell  James R. Murray 《Monthly notices of the Royal Astronomical Society》2006,366(4):1399-1409

We present three-dimensional smoothed particle hydrodynamics calculations of warped accretion discs in X-ray binary systems. Geometrically thin, optically thick accretion discs are illuminated by a central radiation source. This illumination exerts a non-axisymmetric radiation pressure on the surface of the disc, resulting in a torque that acts on the disc to induce a twist or warp. Initially planar discs are unstable to warping driven by the radiation torque and, in general, the warps also precess in a retrograde direction relative to the orbital flow. We simulate a number of X-ray binary systems which have different mass ratios, using a number of different luminosities for each. Radiation-driven warping occurs for all systems simulated. For mass ratios   q ∼ 0.1  a moderate warp occurs in the inner disc while the outer disc remains in the orbital plane (cf. X 1916−053). For less extreme mass ratios, the entire disc tilts out of the orbital plane (cf. Her X–1). For discs that are tilted out of the orbital plane in which the outer edge material of the disc is precessing in a prograde direction, we obtain both positive and negative superhumps simultaneously in the dissipation light curve (cf. V603 Aql).  相似文献   

Neutrino Geophysics Conference Introduction     

John G. Learned  Stephen T. Dye  Sandip Pakvasa 《Earth, Moon, and Planets》2006,99(1-4):1-15

Long distance detection of electron anti-neutrinos from reactors at distances of order 200 km has been achieved with the 1000 ton liquid scintillator-based KamLAND instrument in Japan. In summer 2005 the KamLAND group reported the first detection of anti-neutrinos from the natural radioactivity of the earth. These measurements are due to uranium and thorium decays dominantly from the nearby crust in Japan, and are expected to have only a small contribution from the earth’s mantle (and core). Several new detectors are under consideration around the world for measurements which when taken together can reveal the location of these heavy elements, which are expected to contribute a major share of the internal earth’s heating via their radioactivity. This heating is of course associated with providing the power to drive the geomagnetic field and plate tectonics. Geologists have only indirect evidence about the deep earth, mostly from seismic wave velocity and inferences from a few meteorites. Anti-neutrino detection, on the other hand, yields direct information about earth’s interior. The location and magnitude of the earth’s uranium and thorium are crucial to understanding the origin and evolution of the earth and present day activity. Lead Article in Proceedings of Neutrino Sciences 2005  相似文献