Stochastic modelling of groundwater flow and solute transport in aquifers     

T.-C. Jim Yeh 《水文研究》1992,6(4):369-395

This paper presents an introductory overview of recently developed stochastic theories for tackling spatial variability problems in predicting groundwater flow and solute transport. Advantages and limitations of the theories are discussed. Lastly, strategies based on the stochastic approaches to predict solute transport in aquifers are recommended.  相似文献   

Old Pulsators: White Dwarfs and Their Immediate Precursors     

M. Sean O'Brien 《Astrophysics and Space Science》2003,284(1):45-52

There are now fully six classes of pulsators among white dwarfsand their immediate precursors among central stars of planetarynebulae and on the extended horizontal branch.In this review, we outline those observational and theoreticalconsiderations that link them together and set them apart fromother kinds of pulsating stars.We summarize some select astrophysical puzzles to which studiesof such pulsators might speak, and we discuss current applicationsin the fields of atomic, nuclear, and neutrino physics.Finally, we suggest how future observing programs might solve somegeneral problems common not only to the white dwarf and pre-whitedwarf pulsators but to many types of variable stars.  相似文献   

Denis Martin Shaw, 1923–2003     

Jim Crocket 《Meteoritics & planetary science》2004,39(1):161-162

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A high resolution,multiproxy Late‐glacial record of climate change and intrasystem responses in northwest England     

Richard T. Jones  Jim D. Marshall  Stephen F. Crowley  Alan Bedford  Nigel Richardson  Jan Bloemendal  Frank Oldfield 《第四纪科学杂志》2002,17(4):329-340

A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Glacier hazards (Topics in Applied Geography): Tufnell,L. London: Longman, 1984. 97 pp. £5.95 paperback     

Jim Hansom 《Applied geography (Sevenoaks, England)》1985,5(2):171

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A high-velocity ionized outflow and XUV photosphere in the narrow emission line quasar PG1211+143   总被引：1，自引：0，他引：1  

K. A. Pounds  J. N. Reeves  A. R. King  K. L. Page  P. T. O'Brien  M. J. L. Turner 《Monthly notices of the Royal Astronomical Society》2003,345(3):705-713

We report on the analysis of a ∼60-ks XMM–Newton observation of the bright, narrow emission line quasar PG1211+143. Absorption lines are seen in both European Photon Imaging Camera and Reflection Grating Spectrometer spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C. The observed line energies indicate an ionized outflow velocity of ∼24 000 km s⁻¹. The highest energy lines require a column density of   N _H∼ 5 × 10²³ cm⁻²  , at an ionization parameter of  log ξ∼ 3.4  . If the origin of this high-velocity outflow lies in matter being driven from the inner disc, then the flow is likely to be optically thick within a radius of ∼130 Schwarzschild radii, providing a natural explanation for the big blue bump (and strong soft X-ray) emission in PG1211+143.  相似文献   

Diurnal photometric conditions at Teide observatory and long-term solar irradiance variations     

B. Andersen  V. Domingo  A. Jiménez  A. Jones  S. Korzennik  P. L. Pallé  F. Pérez Hernández  C. Régulo  T. Roca Cortés  L. L. Tomás 《Solar physics》1988,116(2):391-399

Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a seasonal variation of about 15%, the best atmospheric conditions being in winter and autumn. Moreover, in anyone day the extinction coefficient in the afternoon is always lower than the one in the morning by 7%. A one-year period fluctuation, with an amplitude of 0.035 mag, has been identified in the instrumental magnitudes outside the atmosphere, and is interpreted as the variation produced by the different Sun-Earth distance from winter to summer. Finally, the study made to detect periodic time fluctuations in both, Sun's magnitude and extinction coefficients, has given null results at levels of 0.04 and 1.8%, respectively.  相似文献   

The arsenic source term for an in-pit uranium mine tailings facility and its long-term impact on the regional groundwater     

Brett J. Moldovan  M. Jim Hendry  Glenn A. Harrington 《Applied Geochemistry》2008

Detailed field sampling and analyses and laboratory-based diffusion-cell experiments were used in conjunction with 3-D reactive transport modeling (MODFLOW and MT3D99) to quantify the fate and long-term (10 ka) transport of As in the Rabbit Lake In-pit Tailings Management Facility (RLITMF), northern Saskatchewan, Canada. The RLITMF (300 m × 425 m × 90 m thick) was engineered to ensure solute transport within the RLITMF is dominated by diffusion. Concentrations of As in the tailings pore fluids ranged from 0.24 to 140 mg/L (n = 43). Arsenic speciation analyses indicate 90% of this arsenic exists as As⁵⁺. This observation is supported by pH–Eh measurements of pore fluids (n = 135). Geochemical analyses yielded a strong inverse correlation between the Fe/As molar ratio in the tailings solids and the corresponding concentration of dissolved As, which is attributed to the adsorption of As to secondary 2-line ferrihydrite present in the tailings. Diffusion-cell testing yielded values for the effective diffusion coefficient, sorption coefficient, and effective porosity of As in the tailings of 4.5 × 10⁻¹⁰ m²/s, 2–4 cm³/g and 0.36, respectively. Reactive transport simulations using the field and laboratory data show adsorption of As to the tailings and diffusive transport of dissolved As in the tailings should reduce the source term concentration of As to between 40% and 70% of the initial concentrations over the 10 ka simulation period. Based on these simulations, the As concentrations in the regional groundwater, 50 m down gradient of the tailings facility, should be maintained at background concentrations of 0.001 mg/L over the 10 ka period. These findings suggest the engineered in-pit disposal of U mine tailings can provide long-term protection for the local groundwater regime from As contamination.  相似文献   

Availability of Aerial Photographs     

C. I. M. O'Brien. 《The Photogrammetric Record》1965,5(25):63-64

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Partitioning of polycyclic aromatic hydrocarbons between water and particles compared to bioaccumulation in mussels: a harbour case   总被引：3，自引：0，他引：3  

Hellou J  Steller S  Leonard J  Langille MA  Tremblay D 《Marine environmental research》2005,59(2):101-117

Water and particles from three sites located in Halifax Harbour, near and further away from combined municipal sewage effluents (CMSE) were analysed for parental and alkylated polycyclic aromatic hydrocarbons (par and alkPAH). Bioavailability of PAH was compared for inter-tidal mussels collected at the same sites in April and November. The PAH fingerprint determined over 9 sampling times covering a period of 19 months differed more between phases (water and particles) and seasons, than between sites. In the spring, more alkPAH associated with diesel and gasoline were detected in the soluble phase, along with more bioaccumulation of alkPAH in inter-tidal mussels. A broader number of parPAH were detected in mussels collected in the fall. The mean sum of dissolved alkPAH concentrations was higher in water at the site closer to raw CMSE than at the other two sites and particles of that site. However, lowest bioconcentration factors (BCF) were determined in mussels of this more contaminated site. Similar biota-particle accumulation factors (BPAF) were determined for parPAH in mussels from the three sites, all lower than the BCF of alkPAH. The study indicates that sewage treatment plants will reduce the amount of parPAH especially larger than fluoranthene and pyrene from being deposited in the harbour; that alk naphthalenes and fluorenes present in water will continue to be discharged; that the disturbance of sediments can make particle-bound PAH available to mussels.  相似文献