Probabilistic Methods Applied to Unsaturated Numerical Modeling     

Murray Fredlund  Gilson GitiranaJr 《Geotechnical and Geological Engineering》2011,29(2):217-223

The numerical modeling of unsaturated soil processes is becoming more prevalent worldwide. Although numerical modeling is becoming increasingly accepted in geotechnical engineering practice, care must be exercised and improper modeling techniques and procedures must be avoided. Many issues such as nodal resolution and imperfect convergence can result in inaccurate solutions. Unfortunately, analyses of highly nonlinear unsaturated soil flow and slope stability models can significantly increase the modeling time required. As a result, there is a trend to reduce the number of model runs. Results are often presented to client as single model runs or simplistic sensitivity analysis. This paper presents methodologies for applying probabilistic methods to unsaturated soils seepage and slope stability analysis models. The focus is on the application of the alternative point estimate method to practical problems in such a way as to minimize the number of model runs. The demonstration of a successful application to a waste rock pile is presented.  相似文献   

The density and temperature structure near the exobase of Saturn from Cassini UVIS solar occultations     

T.T. Koskinen  B.R. Sandel  R.V. Yelle  F.J. Capalbo  G.M. Holsclaw  W.E. McClintock  S. Edgington 《Icarus》2013

We analyzed 15 solar occultations observed by the Cassini UVIS instrument to constrain the density and temperature structure near the exobase of Saturn. We retrieved the density of H₂ and thus the temperature at altitudes higher than 1900 km above the 1 bar level by analyzing the ionization continuum of H₂ at wavelengths shorter than 804 Å. We find that the exospheric temperature ranges from 370 K to 540 K, with a typical uncertainty of less than 20 K. According to our data the temperature increases with latitude from the equator to the poles by 100–150 K. At similar latitudes, the temperature varies by 20–50 K at different times with no evidence for any systematic diurnal trend so far. Based on our data, the exobase of Saturn is 2700–3000 km above the 1 bar level and the thermal escape parameter near the exobase ranges from 260 to 340, implying that thermal escape from Saturn is firmly in the Jeans regime. The mixing ratio of H₂ is close to unity at all altitudes below the exobase. We find that the pressure levels in the thermosphere deviate significantly from a simple spheroid predicted by potential theory. This is consistent with significant meridional temperature variations in the lower thermosphere. A global analysis of the temperature structure at different depths in the atmosphere is required to constrain both the shape and the deposition and redistribution of energy in the upper atmosphere further.  相似文献   

Carbon Sequestration and Release from Antarctic Lakes: Lake Vida and West Lake Bonney (McMurdo Dry Valleys)     

G. M. Marion  A. E. Murray  B. Wagner  C. H. Fritsen  F. Kenig  P. T. Doran 《Aquatic Geochemistry》2013,19(2):135-145

Perennial ice covers on many Antarctic lakes have resulted in high lake inorganic carbon contents. The objective of this paper was to evaluate and compare the brine and CO₂ chemistries of Lake Vida (Victoria Valley) and West Lake Bonney (Taylor Valley), two lakes of the McMurdo Dry Valleys (East Antarctica), and their potential consequences during global warming. An existing geochemical model (FREZCHEM-15) was used to convert measured molarity into molality needed for the FREZCHEM model, and this model added a new algorithm that converts measured DIC into carbonate alkalinity needed for the FREZCHEM model. While quite extensive geochemical information exists for ice-covered Taylor Valley lakes, such as West Lake Bonney, only limited information exists for the recently sampled brine of >25 m ice-thick Lake Vida. Lake Vida brine had a model-calculated pCO₂ = 0.60 bars at the field pH (6.20); West Lake Bonney had a model-calculated pCO₂ = 5.23 bars at the field pH (5.46). Despite the high degree of atmospheric CO₂ supersaturation in West Lake Bonney, it remains significantly undersaturated with the gas hydrate, CO₂·6H₂O, unless these gas hydrates are deep in the sediment layer or are metastable having formed under colder temperatures or greater pressures. Because of lower temperatures, Lake Vida could start forming CO₂·6H₂O at lower pCO₂ values than West Lake Bonney; but both lakes are significantly undersaturated with the gas hydrate, CO₂·6H₂O. For both lakes, simulation of global warming from current subzero temperatures (?13.4 °C in Lake Vida and ?4.7 °C in West Lake Bonney) to 10 °C has shown that a major loss of solution-phase carbon as CO₂ gases and carbonate minerals occurred when the temperatures rose above 0 °C and perennial ice covers would disappear. How important these Antarctic CO₂ sources will be for future global warming remains to be seen. But a recent paper has shown that methane increased in atmospheric concentration due to deglaciation about 10,000 years ago. So, CO₂ release from ice lakes might contribute to atmospheric gases in the future.  相似文献   

Comparison of polar mesospheric cloud measurements from the Cloud Imaging and Particle Size experiment and the solar backscatter ultraviolet instrument in 2007     

Susanne Benze  Cora E. Randall  Matthew T. DeLand  Gary E. Thomas  David W. Rusch  Scott M. Bailey  James M. Russell  William McClintock  Aimee W. Merkel  Chris Jeppesen 《Journal of Atmospheric and Solar》2009,71(3-4):365-372

We compare measurements from the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) experiment to the NOAA-17 solar backscatter ultraviolet (SBUV/2) instrument during the 2007 Northern Hemisphere polar mesospheric cloud (PMC) season. Daily average Rayleigh scattering albedos determined from identical footprints from the CIPS nadir camera and SBUV/2 agree to better than ～5% throughout the season. Average PMC brightness values derived from the two instruments agree to within ±10%. PMC occurrence frequencies are on average ～5% to nearly a factor of two higher in CIPS, depending on latitude. Agreement is best at high latitudes where clouds are brighter and more frequent. The comparisons indicate that AIM CIPS data are valid for scientific analyses. They also show that CIPS measurements can be linked to the long time series of SBUV/2 data to investigate long-term variability in PMCs.  相似文献   

Significance of ichnofossils to genetic stratigraphy--Examples from the Cretaceous of Alberta, Canada   总被引：1，自引：0，他引：1  

S. George Pemberton  James A. MacEachern  Murray K. Gingras  ZHANG Jianping 《中国科学D辑(英文版)》2000,43(5)

Trace fossils represent both sedimentological and paleontological entities, representing a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition of various discontinuity types and to assist in their genetic interpretation. Ichnology may be employed to resolve surfaces of stratigraphic significance in two main ways: 1) through the identification of discontinuities using substrate-controlled ichnofacies, and 2) through careful analysis of vertical softground (penecontemporaneous) ichnologic successions (analogous to facies successions). Ichnological analysis is a valuable tool in genetic stratigraphic studies. Integrating the data derived from substrate-controlled ichnofacies with paleoecological data from vertical ichnologic successions greatly enhances the recognition and interpretation of a wide variety of stratigraphic surfaces. When this is coupled with conventional facies analysis and sequence stratigraphy, a powerful approach to the interpretation of the rock record is generated.  相似文献   

Land Cover Change and its Environmental Significance in the Herbert River Catchment,North-east Queensland     

A.K.L. Johnson  S.P. Ebert  A.E. Murray 《The Australian geographer》2000,31(1):75-86

There has been considerable recent concern over the amount of vegetation clearance in the wet tropics of northern Australia. This paper reports on the results of a case study undertaken in the lower Herbert River catchment in north-east Queensland, which utilised remote sensing and Geographic Information Systems (GIS) to assess both spatial and temporal changes in land cover since European settlement in the mid-nineteenth century. We demonstrate that since European settlement there has been a substantial reduction in the area of Melaleuca, rainforest, and eucalyptus-dominated land-cover patterns. We also provide a range of quantitative measures to show that the landscape diversity, integrity and quality of these ecosystems have also declined between the 1860s and 1996. We conclude that reform is required at policy, planning and enterprise levels if the ecological, economic and social values of these systems are to be maintained in the future.  相似文献   

The precession of eccentric discs in close binaries   总被引：1，自引：0，他引：1  

J. R. Murray 《Monthly notices of the Royal Astronomical Society》2000,314(1):L1-L5

If the emission of gamma-ray bursts were as a result of the synchrotron process in the standard internal shock scenario, then the typical observed spectrum should have a slope F _ν ∝ ν ^−1/2, which strongly conflicts with the much harder spectra observed. This directly follows from the cooling time being much shorter than the dynamical time. Particle re-acceleration, deviations from equipartition, quickly changing magnetic fields and adiabatic losses are found to be inadequate to account for this discrepancy. We also find that in the internal shock scenario the relativistic inverse Compton scattering is always as important as the synchrotron process, and faces the same problems. This indicates that the burst emission is not produced by relativistic electrons emitting synchrotron and inverse Compton radiation.  相似文献   

Accumulation of Cu and Zn in discarded antifouling paint particles by the marine gastropod, Littorina littorea     

Melanie Gammon  Andrew Turner  Murray T. Brown 《Estuarine, Coastal and Shelf Science》2009,84(4):447-452

The short-term (5 day) accumulation of Cu and Zn in different tissues of the marine gastropod, Littorina littorea, has been studied in the presence of 10 mg l⁻¹ of antifouling paint particles and pre- or simultaneously contaminated algal food (Ulva lactuca). Accumulation of Cu was observed in the head–foot, digestive gland–gonad complex and gills to extents dependent on how and when food was contaminated and administered. However, retention of Zn was only observed in the gills and only when L. littorea and U. lactuca were simultaneously exposed to paint particles. Relative to the alga, faecal material was highly enriched in Zn, suggesting that the animal is able to rapidly eliminate this metal, most likely through the formation and egestion of insoluble phosphate granules. Thus, L. littorea is a useful biomonitor of marine contamination by antifouling applications in respect of Cu but not Zn.  相似文献   

The effects of beach nourishment on the sandy-beach amphipod Exoediceros fossor: impact and recovery in Botany Bay, New South Wales, Australia     

Alan R. Jones  Anna Murray  Theresa A. Lasiak  & Robin E. Marsh 《Marine Ecology》2008,29(S1):28-36

Beach nourishment is increasingly being implemented to address problems of erosion. However, the ecological consequences of nourishment are poorly understood, especially in Australia. In Botany Bay, sand was piped from an intertidal borrow area at Elephant's Trunk to nourish the nearby eroding beach at Towra Point. The effects on an intertidal exoedicerotid amphipod, Exoediceros fossor (Stimpson, 1856), were examined using a beyond-BACI (Before–After, Control–Impact) sampling design. Sampling was conducted before and after engineering operations at sites within the borrow and nourishment locations and multiple control locations. Hypotheses concerning impact and recovery were tested using asymmetrical ANOVAs and two-tailed F-tests. These examined the effects on abundance and spatial variability, respectively. The impact of the engineering operations on abundance was very large at both borrow and nourishment locations. However, recovery started within several weeks and, using space × time interactions as a criterion, appeared to be complete within a year. This conclusion is made cautiously because of low statistical power and because other criteria for recovery suggest that it was not complete at some sites. As beach erosion is likely to increase in severity with rising sea levels and greater storm surges associated with climate change, management authorities will need a better understanding of the ecological effects of beach nourishment.  相似文献   

Predicting suitable habitat for the cold-water coral Lophelia pertusa (Scleractinia)     

Andrew J. Davies  Max Wisshak  James C. Orr  J. Murray Roberts   《Deep Sea Research Part I: Oceanographic Research Papers》2008,55(8):1048-1062

Ecological-niche factor analysis (ENFA) was applied to the reef framework-forming cold-water coral Lophelia pertusa. The environmental tolerances of this species were assessed using readily available oceanographic data, including physical, chemical, and biological variables. L. pertusa was found at mean depths of 468 and 480 m on the regional and global scales and occupied a niche that included higher than average current speed and productivity, supporting the theory that their limited food supply is locally enhanced by currents. Most records occurred in areas with a salinity of 35, mean temperatures of 6.2–6.7  °C and dissolved oxygen levels of 6.0–6.2 ml l⁻¹. The majority of records were found in areas that were saturated with aragonite but had low concentration of nutrients (silicate, phosphate, and nitrate). Suitable habitat for L. pertusa was predicted using ENFA on a global and a regional scale that incorporated the north-east Atlantic Ocean. Regional prediction was reliable due to numerous presence points throughout the area, whereas global prediction was less reliable due to the paucity of presence data outside of the north-east Atlantic. However, the species niche was supported at each spatial scale. Predicted maps at the global scale reinforced the general consensus that the North Atlantic Ocean is a key region in the worldwide distribution of L. pertusa. Predictive modelling is an approach that can be applied to cold-water coral species to locate areas of suitable habitat for further study. It may also prove a useful tool to assist spatial planning of offshore marine protected areas. However, issues with eco-geographical datasets, including their coarse resolution and limited geographical coverage, currently restrict the scope of this approach.  相似文献