Modelling water infiltration in cracked paddy field soil     

Chen‐Wuing Liu  Shih‐Kai Chen  Cheng‐Shin Jang 《水文研究》2004,18(13):2503-2513

Periodic paddy field flooding is a major source of groundwater recharge. Many paddy fields thus are used as groundwater recharge ponds after harvesting the first crop of the summer. Following rice harvesting, paddy field surfaces may crack into fissures as a result of drainage and exposure to sunlight. Field observation indicates that applying precipitation to the paddy field can increase the rate of infiltration. To quantitatively evaluate the amount of infiltration in a cracked paddy field, this study sets up a simple soil crack model to simulate the field infiltration process. A three‐dimensional groundwater model FEMWATER is adopted to simulate water movement in the paddy field subjected to various crack conditions. Using the field and laboratory data of irrigation water requirements, soil physical properties, hydraulic conductivities and soil profiles obtained from Ten‐Chung, FEMWATER simulates the water movement in the dry cracked paddy. Simulation results show that if the cracks develop extensively and penetrate the ploughed soil, the infiltration rate may increase significantly. The infiltration fluxes of crack with depths of 80, 60 and 27·5 cm are 18·77, 14·50 and 8·06 times higher than that of 20 cm, respectively. The simulation results of cracks with 80 cm depth correlated closely with field observations. The results of the study elucidate the processes of unsaturated water movement in a dry cracked paddy field. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Solar wind interactions with Comet 19P/Borrelly     

D.T Young  F.J Crary  J.E Nordholt  D Boice  A Eviatar  J.J Hanley  D.J McComas  D Reisenfeld  R.C Wiens 《Icarus》2004,167(1):80-88

The Plasma Experiment for Planetary Exploration (PEPE) made detailed observations of the plasma environment of Comet 19P/Borrelly during the Deep Space 1 (DS1) flyby on September 22, 2001. Several distinct regions and boundaries have been identified on both inbound and outbound trajectories, including an upstream region of decelerated solar wind plasma and cometary ion pickup, the cometary bow shock, a sheath of heated and mixed solar wind and cometary ions, and a collisional inner coma dominated by cometary ions. All of these features were significantly offset to the north of the nucleus-Sun line, suggesting that the coma itself produces this offset, possibly because of well-collimated large dayside jets directed 8°-10° northward from the nucleus as observed by the DS1 MICAS camera. The maximum observed ion density was 1640 ion/cm³ at a distance of 2650 km from the nucleus while the flow speed dropped from 360 km/s in the solar wind to 8 km/s at closest approach. Preliminary analysis of PEPE mass spectra suggest that the ratio of CO⁺/H₂O⁺ is lower than that observed with Giotto at 1P/Halley.  相似文献   

A Relationship Between Transition Region Brightenings,Abundances, and Magnetic Topology     

Fletcher  Lyndsay  López Fuentes  Marcelo C.  Mandrini  Cristina H.  Schmieder  Brigitte  Démoulin  Pascal  Mason  Helen E.  Young  Peter R.  Nitta  Nariaki 《Solar physics》2001,203(2):255-287

We present multi-instrument observations of active region (AR) 8048, made between 3 June and 5 June 1997, as part of the SOHO Joint Observing Program 33. This AR has a sigmoid-like global shape and undergoes transient brightenings in both soft X-rays and transition region (TR) lines. We compute a magneto-hydrostatic model of the AR magnetic field, using as boundary condition the photospheric observations of SOHO/MDI. The computed large-scale magnetic field lines show that the large-scale sigmoid is formed by two sets of coronal loops. Shorter loops, associated with the core of the SXT emission, coincide with the loops observed in the hotter CDS lines. These loops reveal a gradient of temperature, from 2 MK at the top to 1 MK at the ends. The field lines most closely matching these hot loops extend along the quasi-separatrix layers (QSLs) of the computed coronal field. The TR brightenings observed with SOHO/CDS can also be associated with the magnetic field topology, both QSL intersections with the photosphere, and places where separatrices issuing from bald patches (sites where field lines coming from the corona are tangent to the photosphere) intersect the photosphere. There are, furthermore, suggestions that the element abundances measured in the TR may depend on the type of topological structure present. Typically, the TR brightenings associated with QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values. We suggest that this difference is due to the location and manner in which magnetic reconnection occurs in two different topological structures. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013302317042  相似文献   

The hard X-ray spectrum of the Seyfert galaxy IRAS 18325–5926: reflection from an ionized disc and variable iron K emission     

K. Iwasawa  J. C. Lee †  A. J. Young  C. S. Reynolds  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2004,347(2):411-420

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Geostatistical analysis and conditional simulation for estimating the spatial variability of hydraulic conductivity in the Choushui River alluvial fan,Taiwan     

Cheng‐Shin Jang  Chen‐Wuing Liu 《水文研究》2004,18(7):1333-1350

This work evaluated the spatial variability and distribution of heterogeneous hydraulic conductivity (K) in the Choushui River alluvial fan in Taiwan, using ordinary kriging (OK) and mean and individual sequential Gaussian simulations (SGS). A baseline flow model constructed by upscaling parameters was inversely calibrated to determine the pumping and recharge rates. Simulated heads using different K realizations were then compared with historically measured heads. A global/local simulated error between simulated and measured heads was analysed to assess the different spatial variabilities of various estimated K distributions. The results of a MODFLOW simulation indicate that the OK realization had the smallest sum of absolute mean simulation errors (SAMSE) and the SGS realizations preserved the spatial variability of the measured K fields. Moreover, the SAMSE increases as the spatial variability of the K field increases. The OK realization yields small local simulation errors in the measured K field of moderate magnitude, whereas the SGS realizations have small local simulation errors in the measured K fields, with high and low values. The OK realization of K can be applied to perform a deterministic inverse calibration. The mean SGS method is suggested for constructing a K field when the application focuses on extreme values of estimated parameters and small calibration errors, such as in a simulation of contaminant transport in heterogeneous aquifers. The individual SGS realization is useful in stochastically assessing the spatial uncertainty of highly heterogeneous aquifers. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

A deeper search for the progenitor of the Type Ic supernova 2002ap     

R. M. Crockett  S. J. Smartt  J. J. Eldridge  S. Mattila  D. R. Young  A. Pastorello  J. R. Maund  C. R. Benn  I. Skillen 《Monthly notices of the Royal Astronomical Society》2007,381(2):835-850

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Effects of metals and sediment particle size on the species composition of the epifauna of Pinna bicolor near a lead smelter,Spencer Gulf,South Australia     

Trevor J. Ward  Peter C. Young 《Estuarine, Coastal and Shelf Science》1984,18(1):79-95

Pinna bicolor (Mollusca: Pelecypoda) were transplanted between four sites near a lead smelter. The species composition of their epifauna (sessile and mobile) was examined in relation to characteristics of both sediments and seston at the sites. Seventy-two taxa were distinguished in the epifaunal community. Substantial differences were found in the short-term sensitivity of some of the species to concentrations of Cd, Pb and Zn in sediments and to sediment particle size. The short-term sensitivity of many species to metals or sediment particle size explained their long-term distribution pattern. Twenty-three taxa were identified as significantly characterizing the faunal differences. Of these, eleven (four molluscs, four bryozoans, two barnacles and one ascidian) were affected by both sediment metal concentration and particle size, and eight (four molluscs, one bryozoan, one polychaete, one hydroid and one barnacle) were affected by metal contamination but not particle size. Of all fauna examined, the Bryozoa were the most metal-sensitive. Four species, Smittina raigii (Bryozoa), Galeolaria sp. 1 (Polychaeta), Epopella simplex (Cirripedia) and Monia ione (Pelecypoda) were identified by their short- and long-term sensitivity to metal contamination, and absence of sensitivity to sediment particle size, as suitable species for monitoring the effects of metal contamination on the epifauna. The implications of the results for toxicity-testing are discussed.  相似文献   

Gamma-ray emissions from active galaxies     

M. M. Lau  E. C. M. Young  K. N. Yu 《Astrophysics and Space Science》1989,158(1):117-121

Recently, gamma rays (>100 MeV) have been detected from some active galaxies (Young and Yu, 1988). These gamma-ray data together with data in other wavebands give severe constraints to the emission mechanisms of radiations from these objects. The synchrotron self-Compton (SSC) model will be applied to these objects in the present work. It will be seen that the predictions from the SSC model agree excellently with the observations.  相似文献   

The arctic — in need of an international regime     

Elizabeth Young 《Marine Policy》1981,5(2):154-156

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Transmission of CO₂ in the atmosphere of Venus for the spectral region near 7 microns     

Louise Gray Young 《Icarus》1982,51(3):606-609

The transmission in the 7-μm “window” opf Venus was calculated for a 7-layer model atmosphere. The synthetic spectra show that radiation from the layer 20–30 km above the surface would reach the top of the atmosphere between 6.2 and 7.0 μm if there were no absorption besides the isotopic CO₂ bands; for the 7.0- to 8.2-μm region, the radiating level would be located 40–50 km above the surface of Venus. The brightness temperature for the entire region is 430°K; for the above two regions it is 494 and 341°K, respectively.  相似文献