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   

Analysis of condensates formed at the viking 2 lander site: The first winter     

Stephen D. Wall 《Icarus》1981,47(2):173-183

A thin light-colored ground covering appeared on the surface of Mars near the Viking 2 lander from L_s = 230° to L_s = 16°, a total of 249 Mars days, during the lander's first winter on the surface. This paper presents a reduction of applicable lander imagery during the period. Imaging sequences, relative surface albedo, spectral reflectance estimates, and limited photometric data are presented and compared with previous laboratory measurements. Photometric data are best fit by an average Minnaert k = 1.1 (blue), k = 1.0 (green), and k = 0.95 (red). Appearance and disappearance rates, spectral reflectance, and photometric data all tend to confirm an earlier proposal that the covering was a combination of H₂O and CO₂, which fell already condensed onto dust particles brought northward by the season's first major dust storm. Under this assumption, the covering thickness is estimated to be between 0.5 and a few millimeters.  相似文献   

Radar observations of asteroid 25143 Itokawa (1998 SF36)     

Steven J. OSTRO  Lance A. M. BENNER  Michael C. NOLAN  Christopher MAGRI  Jon D. GIORGINI  Daniel J. SCHEERES  Stephen B. BROSCHART  Mikko KAASALAINEN  David VOKROUHLICKÝ  Steven R. CHESLEY  Jean‐Luc MARGOT  Raymond F. JURGENS  Randy ROSE  Donald K. YEOMANS  Shigeru SUZUKI  Eric M. de JONG 《Meteoritics & planetary science》2004,39(3):407-424

Abstract— We observed 25143 Itokawa, the target of Japan's Hayabusa (MUSES‐C) sample‐return mission, during its 2001 close approach at Arecibo on twelve dates during March 18‐April 9 and at Goldstone on nine dates during March 20‐April 2. We obtained delay‐Doppler images with range resolutions of 100 ns (15 m) at Arecibo and 125 ns (19 m) at Goldstone. Itokawa's average circular polarization ratio at 13 cm, 0.26 ± 0.04, is comparable to that of Eros, so its cm‐to‐m surface roughness probably is comparable to that on Eros. Itokawa's radar reflectivity and polarization properties indicate a near‐surface bulk density within 20% of 2.5 g cm^?3. We present a preliminary estimate of Itokawa's shape, reconstructed from images with rather limited rotation‐phase coverage, using the method of Hudson (1993) and assuming the lightcurve‐derived spin period (12.132 hr) and pole direction (ecliptic long., lat. = 355°, ?84°) of Kaasalainen et al. (2003). The model can be described as a slightly asymmetrical, slightly flattened ellipsoid with extents along its principal axes of 548 times 312 times 276 m ± 10%. Itokawa's topography is very subdued compared to that of other asteroids for which spacecraft images or radar reconstructions are available. Similarly, gravitational slopes on our Itokawa model average only 9° and everywhere are less than 27°. The radar‐refined orbit allows accurate identification of Itokawa's close planetary approaches through 2170. If radar ranging planned for Itokawa's 2004 apparition succeeds, then tracking of Hayabusa during its 2005 rendezvous should reveal Yarkovsky perturbation of the asteroid's orbit.  相似文献   

A geometrical interpretation of ideal body problems     

Stephen P. Huestis 《Geophysical Journal International》1982,69(1):253-263

Summary. For linear geophysical inverse problems, the exercise of finding a greatest lower bound on the uniform norms of positive solutions fitting N data, is shown to have a geometrical counterpart in the N- dimensional space of N -tuples of real numbers. By application of the Fenchel Duality Theorem, we demonstrate that the problem is equivalent to the discovery of a particular hyperplane tangent to a convex set in this space. As examples in the case of two data, the new formulation is applied to the problems of recovering density information from planetary mass and moment of inertia, and from two vertical gravity anomalies.  相似文献   

Estimating Effective Porosity in Bedrock Aquifers     

Stephen R.H. Worthington 《Ground water》2022,60(2):169-179

Flow in many bedrock aquifers is through fracture networks. Point to point tracer tests using applied tracers provide a direct measure of time of travel and are most useful for determining effective porosity. Calculated values from these tests are typically between 10⁻⁴ and 10⁻² (0.01% to 1%), with these low values indicating preferential flow through fracture and channel networks. Tracer tests are not commonly used in site investigations, and specific yield is often used as a proxy for effective porosity. The most popular methods have used centrifuge measurements, water table fluctuations, pumping tests, and packer tests. Specific yield varies substantially with the testing method. No method is as reliable as tracer testing for providing estimates of effective porosity, but all methods provide complementary insights on aquifer structure. Temporal and spatial scaling effects suggest that bedrock aquifers have hierarchical structures, with a network of more permeable fractures and channels, which are connected to less permeable fractures and to the matrix. Consequences of the low effective porosities include groundwater velocities that often exceed 100 m/d and more frequent microbial contamination than in aquifers in unconsolidated sediments. The large uncertainty over the magnitude of effective porosity in bedrock aquifers makes it an important parameter to determine in studies where time of travel is of interest.  相似文献   

Focusing effect of bent GaAs crystals for <Emphasis Type="Italic">γ</Emphasis>-ray Laue lenses: Monte Carlo and experimental results     

E. Virgilli  F. Frontera  P. Rosati  E. Bonnini  E. Buffagni  C. Ferrari  J. B. Stephen  E. Caroli  N. Auricchio  A. Basili  S. Silvestri 《Experimental Astronomy》2016,41(1-2):307-326

We report on results of observation of the focusing effect from the planes (220) of Gallium Arsenide (GaAs) crystals. We have compared the experimental results with the Monte Carlo simulations of the focusing capability of GaAs tiles performed with a dedicated ray-tracer. The GaAs tiles were bent using a lapping process developed at the cnr/imem - Parma (Italy) in the framework of the laue project, funded by ASI, dedicated to build a broad band Laue lens prototype for astrophysical applications in the hard X-/soft γ-ray energy range (80-600 keV). We present and discuss the results obtained from their characterization, mainly in terms of focusing capability. Bent crystals will significantly increase the signal to noise ratio of a telescope based on a Laue lens, consequently leading to an unprecedented enhancement of sensitivity with respect to the present non focusing instrumentation.  相似文献   

Tectonics of the incipient continental rifting     

Youqiang Yu  Cory Ree  Kelly Liu  Stephen Gao 《《地质学报》英文版》2018,92(Z1):99-100

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