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The soil water retention function is needed for modeling multiphase flow in porous media. Traditional techniques for measuring the soil water retention function, such as the hanging water column or pressure cell methods, yield average water retention data which have to be modeled using inverse procedures to extract relevant point parameters. In this study, we have developed a technique for directly measuring multiple point (pixel-scale) water retention curves for a repacked sand material using 2-D neutron radiography. Neutron radiographic images were obtained under quasi-equilibrium conditions at nine imposed basal matric potentials during monotonic drying of Flint sand at the High Flux Isotope Reactor (HFIR) Cold Guide (CG) 1D beamline at Oak Ridge National Laboratory. All of the images were normalized with respect to an image of the oven dry sand column. Volumetric water contents were computed on a pixel by pixel basis using an empirical calibration equation after taking into account beam hardening and geometric corrections. Corresponding matric potentials were calculated from the imposed basal matric potential and pixel elevations. Volumetric water content and matric potential data pairs corresponding to 120 selected pixels were used to construct 120 point water retention curves. Each curve was fitted to the Brooks and Corey equation using segmented non-linear regression in SAS. A 98.5% convergence rate was achieved resulting in 115 estimates of the four Brooks and Corey parameters. A single Brooks and Corey point water retention function was constructed for Flint sand using the median values of these parameter estimates. This curve corresponded closely with the point Brooks and Corey function inversely extracted from the average water retention data using TrueCell. Forward numerical simulations performed using HYDRUS 1-D showed that the cumulative outflows predicted using the point Brooks and Corey functions from both the direct (neutron radiography) and inverse (TrueCell) methods were in good agreement with independent measurements of cumulative outflow determined with a transducer. Our results indicate that neutron radiography can be used to quantify the point water retention curve of homogeneous mineral particles. Further research will be needed to extend this approach to more heterogeneous porous media. 相似文献
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Using modern astronomical databases, particularly 2MASS All - Sky Data Release Point Source Catalog and USNO-B1.0 catalog, we investigate the properties of about 840 FBS red stars in order to clarifiy their nature. We use and analyse their JHK 2MASS photometry, together with the R-band magnitudes and the proper motions provided by USNO - B1.0. Approximately 70% of all objects appear to be Asymptotic Giant Branch stars, 18% are giants, and close to 12% are objects with detectable proper motions, allowing to consider them as dwarf M-type stars. When plotted in a J - K versus R - K colour-colour diagram, one finds that objects with proper motions are well separated into a narrow belt.__________Published in Astrofizika, Vol. 48, No. 3, pp. 383–392 (August 2005). 相似文献
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The absolute K-band magnitude determined for the object FBS 0137+400 is typical for Asymptotic Giant Branch (AGB) carbon stars. The large J - K color index as well as large amplitude variability (K > 0.4) and the presence of H in the emission indicate also that this star is a mass-losing long-period Carbon Mira variable with thick circumstellar shell. The IRAS LRS spectrum indicates the presence of a dust shell surrounding this object. Monitoring of the K-band magnitude is necessary for the determination of the pulsation period of FBS 0137+400. 相似文献
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Very red optical and IR-color indices indicate the presence of a dense circumstellar shell around object FBS 2213+421. The
estimated total mass-loss rate is typical for dust-enshrouded oxygen-rich Asymptotic Giant Branch (AGB) Long-Period Mira-type
variables. K-band monitoring is necessary to determine the pulsation period, the absolute bolometric luminosity, and the distance
to this object.
Published in Astrofizika, Vol. 49, No. 1, pp. 91–96 (February 2006). 相似文献
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We present the first results of analysis of infrared properties of the faint M and C type stars found on the FBS plates. By cross - correlating the subsample of FBS late - type stars with infrared catalogues, we have shown that several families of objects can be separated. It provides ways to better characterize the properties of these families, their nature and their typical distances. 相似文献
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K. S. Gigoyan H. V. Abrahamyan M. Azzopardi N. Mauron D. Russeil P. Sinamyan 《Astrophysics》2003,46(4):475-488
We present the fourteenth list of faint late M and carbon type stars detected on the plates of the First Byurakan Spectral Sky Survey in the zone +13° +33° covering about 4736 sq. degrees. From 260 stars, 118 are newly detected objects: they are 19 carbon stars, 5 carbon star candidates, and 94 M-type stars. Among 118 detected objects 73( 57 PSC + 16 FSC ) are unclassified IRAS sources. Accurate positions, spectral classes, red magnitudes, color indices, and near-infrared J, H and K photometry are given, using several astronomical databases. Finding charts from DSS are given for the most interesting objects. 相似文献
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Multi‐block finite‐difference method for 3D elastodynamic simulations in anisotropic subhorizontally layered media 
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下载免费PDF全文 Prediction of elastic full wavefields is required for reverse time migration, full waveform inversion, borehole seismology, seismic modelling, etc. We propose a novel algorithm to solve the Navier wave equation, which is based on multi‐block methodology for high‐order finite‐difference schemes on curvilinear grids. In the current implementation, the blocks are subhorizontal layers. Smooth anisotropic heterogeneous media in each layer can have strong discontinuities at the interfaces. A curvilinear adaptive hexahedral grid in blocks is generated by mapping the original 3D physical domain onto a parametric cube with horizontal layers and interfaces. These interfaces correspond to the main curvilinear physical contrast interfaces of a subhorizontally layered formation. The top boundary of the parametric cube handles the land surface with smooth topography. Free‐surface and solid–solid transmission boundary conditions at interfaces are approximated with the second‐order accuracy. Smooth media in the layers are approximated up to sixth‐order spatial schemes. All expected properties of the developed algorithm are demonstrated in numerical tests using corresponding parallel message passing interface code. 相似文献
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《Marine Geology》1999,153(1-4):221-237
The Quaternary climate of southern Europe (south Italy and Greece) is investigated by pollen analysis of the sapropels which were deposited in the deep eastern Mediterranean Sea during the last 1 million year (Ma). The time-scale of core KC01b in the Ionian Sea has been established by tuning its oxygen isotopic record to the ice volume model of Imbrie and Imbrie (1980). For the last 250,000 year (250 ka), the previous pollen studies and astronomical tuning have been confirmed. Sapropels were deposited under a large range of Mediterranean climates: fully interglacial, fully glacial, and intermediary, as revealed mainly by the balance between the respective pollen abundances of oak (Quercus) and sage-brush (Artemisia). The high value of the oak reveals the warm and wet climate of an Interglacial, and the high value of the sage-brush, the dry and cold climate of a Glacial. Whereas the Mediterranean climate is directly related to the variation of the high-latitude ice sheets, the deposition of sapropels is not so. In contrast with the wide climatic range, sapropels were deposited only when summer insolation in the low latitudes reached its highest peaks. However, between 250 ka and 1 Ma, that stable pattern is not yet established. Only six sapropels are observed, many expected ones do not appear, even as ghosts signalled by peaks of barium abundance, that remain after the post-deposition oxidation of organic matter. The pattern of sapropel formation in stable and direct relationship to highest insolation does not seem to apply. For five of those sapropels, neither climate extremes are observed; they mainly formed during intermediary types of Mediterranean climate. In contrast, one sapropel (and one ghost) relates to a relatively low peak of insolation, and its climate is of a unique, composite type not seen later. This might suggest an unsuspected, more complex pattern linking the formation of Mediterranean sapropels to the astronomical configuration. 相似文献
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