The intrinsic oxygen fugacities of homogeneous, inclusion-free, megacryst ilmenites from the Frank Smith, Excelsior, Sekameng and Mukorob kimberlite pipes in southern Africa, and the alnöitic breccia in the Solomon Islands have been determined. Similar measurements have been made of the type A and B spinel peridotites from San Carlos in Arizona. The type A peridotites are characterised by oxygen fugacities close to the iron-wüstite buffer, similar to those of equivalent peridotite specimens from other continental and island arc environments. In strong contrast, the type B peridotites and all of the ilmenite megacrysts range between the oxygen fugacities defined by the nickelnickel oxide and fayalite-magnetite-quartz buffers. A close relationship between type B peridotites, oxidized metasomatizing fluids in the upper mantle and oxidized, silicaundersaturated magma types is suggested. It is unlikely that a solid elemental carbon phase can be an equilibrium crystallization product of kimberlite magmas if the ilmenite megacrysts represent the redox state of kimberlite melts. The ultimate source of the oxidizing fluids and the development of such a wide dispersion (>4 orders of magnitude) in oxygen fugacities of the upper mantle is not clear, but may involve recycled lithosphere, fluids from the lower mantle or result from the relatively rapid diffusion of H2, compared with other potential volatile species, in the mantle. 相似文献
Carbon and oxygen isotope analysis of ostracods living in the near-constant conditions of spring-fed ponds in southern England allowed accurate determination of the ostracod’s calcite-water 13C/12C and 18O/16O fractionations. The 13C/12C fractionations of two species, Candona candida and Pseudocandona rostrata, correspond to values expected for isotopic equilibrium with the pond’s dissolved inorganic carbon at the measured temperature (11°C) and pH (6.9), whilst those of a third species, Herpetocypris reptans, would represent equilibrium at a slightly higher pH (7.1).The 18O/16O fractionations confirm two previous studies in being larger, by up to 3‰, than those ‘traditionally’ regarded as representing equilibrium. When the measured fractionations are considered in the context of more recent work, however, they can be explained in terms of equilibrium if the process of calcite formation at the ostracod lamella occurs at a relatively low pH (≤7) irrespective of the pH of the surrounding water. The pH of calcite formation, and therefore the calcite-water 18O/16O fractionation, may be species and stage (adult versus juvenile) specific, and related to the rate of calcification. 相似文献
Spherical harmonic expansions form partial sums of fully normalised associated Legendre functions (ALFs). However, when evaluated
increasingly close to the poles, the ultra-high degree and order (e.g. 2700) ALFs range over thousands of orders of magnitude.
This causes existing recursion techniques for computing values of individual ALFs and their derivatives to fail. A common
solution in geodesy is to evaluate these expansions using Clenshaw's method, which does not compute individual ALFs or their
derivatives. Straightforward numerical principles govern the stability of this technique. Elementary algebra is employed to
illustrate how these principles are implemented in Clenshaw's method. It is also demonstrated how existing recursion algorithms
for computing ALFs and their first derivatives are easily modified to incorporate these same numerical principles. These modified
recursions yield scaled ALFs and first derivatives, which can then be combined using Horner's scheme to compute partial sums,
complete to degree and order 2700, for all latitudes (except at the poles for first derivatives). This exceeds any previously
published result. Numerical tests suggest that this new approach is at least as precise and efficient as Clenshaw's method.
However, the principal strength of the new techniques lies in their simplicity of formulation and implementation, since this
quality should simplify the task of extending the approach to other uses, such as spherical harmonic analysis.
Received: 30 June 2000 / Accepted: 12 June 2001 相似文献
Simplified techniques for high-degree spherical harmonic synthesis are extended to include gravitational potential second
derivatives with respect to latitude.
Received: 23 July 2001 / Accepted: 12 April 2002
Acknowledgement. The authors would like to thank Christian Tscherning for recommending Laplace's equation as an accuracy test. Our use of
Legendre's differential equation, as the most direct means for extending our simplified synthesis methods to second-order
derivatives, was a direct result of this suggestion.
Correspondence to: S. A. Holmes 相似文献
The uptake of research in marine fisheries management and policy making depends on how effectively fisheries managers, researchers and scientific advisers communicate the needs for evidence, and the results and policy implications of research. The MariFish network of the major European funders of marine fisheries has therefore undertaken a study of current practices relating to communication of research needs and results, identifying strengths and weaknesses, and consequently how two-way communications, and hence the effectiveness of generating evidence for marine fisheries policy making and management, can be improved. Conclusions and recommendations for ‘good practice’ include the importance of building good relationships and trust between researchers and fisheries managers, the need for fisheries ministries to have sufficient inhouse scientific capacity to act as ‘intelligent customers’, and the key role of interpreters of research whose skills and career paths need to be carefully developed. 相似文献
The southern coastline of South Africa exhibits extensive aeolianites and spectacular barrier dunes; the ages and palaeoenvironmental significance of which have, until recently, received limited attention. We present preliminary results for samples taken from a single 6.5 m section in the seaward barrier dune near to the town of Wilderness. The reliability of these ages has been investigated using a series of dose recovery and pulsed irradiation experiments, as well as through analyses of single aliquot and single grain De distributions. Results indicate that the SAR protocol is providing accurate and precise De determinations and that adequate sensitivity correction is being made. The application of pulsed irradiations does not result in significant changes in the dose–response curves or averaged De's. Single grain De distributions are broad, with significant levels of overdispersion, which may reflect beta dose heterogeneity effects.
Peaks in aeolian activity date to 157–154 and 140–125 ka, with a slower rate of deposition recorded from 115 to 85 ka. Brief phases at 40 and 21 ka are also identified. Some ages, notably those from OIS 3 and OIS 2, are surprising from a geomorphological perspective, given the likely distance of the dune from the shoreline at such times, although they are not inconsistent with evidence from the east coast of South Africa. The results reveal multiple phases of Late Quaternary barrier dune accumulation, and suggest that aeolian activity in this region has been episodic and potentially more complex than previously thought. 相似文献
Global warming due to the enhanced greenhouse effect through human activities has become a major public policy issue in recent years. The present study focuses on the potential economic impact of climate change on recreational trout fishing in the Southern Appalachian Mountains of North Carolina. Significant reductions in trout habitat and/or populations are anticipated under global warming since the study area is on the extreme margins of trout habitat of the eastern U.S. The purpose of this study is to estimate the potential welfare loss of trout anglers due to global warming. A nested multinomial logit model was developed and estimated to describe the angler's fishing choice behavior. The estimated median welfare loss (Compensating Variation) ranged from $5.63 to $53.18 per angler per single occasion under the various diminished trout habitat and/or population scenarios. 相似文献
The distribution, abundance and chemical characteristics of plastic production pellets on beaches of the island of Malta have been determined. Pellets were observed at all locations visited and were generally most abundant (>1000 m−2 at the surface) on the backshores of beaches with a westerly aspect. Most pellets were disc-shaped or flattened cylinders and could be categorised as white, yellow, amber or brown. The polymeric matrix of all pellets analysed by infrared spectroscopy was polyethylene and the degree of yellowing or darkening was associated with an increase in the carbonyl index, hence extent of photo-oxidation or aging. Qualitatively, pellets are similar to those reported for other regions of the Mediterranean in surveys spanning three decades, suggesting that they are a general and persistent characteristic of the region. 相似文献