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251.
Andréhette Verster Daan de Waal Robert Schall Chris Prins 《Mathematical Geosciences》2012,44(1):91-100
The metallurgical recovery processes in diamond mining may, under certain circumstances, cause an under-recovery of large
diamonds. In order to predict high quantiles or tail probabilities we use a Bayesian approach to fit a truncated Generalized
Pareto Type distribution to the tail of the data consisting of the weights of individual diamonds. Based on the estimated
tail probability, the expected number of diamonds larger than a specified weight can be estimated. The difference between
the expected and observed frequencies of diamond weights above an upper threshold provides an estimate of the number of diamonds
lost during the recovery process. 相似文献
252.
Detlef P. van Vuuren Jason Lowe Elke Stehfest Laila Gohar Andries F. Hof Chris Hope Rachel Warren Malte Meinshausen Gian-Kasper Plattner 《Climatic change》2011,104(2):255-285
Integrated assessment models (IAMs) are regularly used to evaluate different policies of future emissions reductions. Since
the global costs associated with these policies are immense, it is vital that the uncertainties in IAMs are quantified and
understood. We first demonstrate the significant spread in the climate system and carbon cycle components of several contemporary
IAMs. We then examine these components in more detail to understand the causes of differences, comparing the results with
more complex climate models and earth system models (ESMs), where available. Our results show that in most cases the outcomes
of IAMs are within the range of the outcomes of complex models, but differences are large enough to matter for policy advice.
There are areas where IAMs would benefit from improvements (e.g. climate sensitivity, inertia in climate response, carbon
cycle feedbacks). In some cases, additional climate model experiments are needed to be able to tune some of these improvements.
This will require better communication between the IAM and ESM development communities. 相似文献
253.
Sonali Saha Keith Bradley Michael S. Ross Phillip Hughes Thomas Wilmers Pablo L. Ruiz Chris Bergh 《Climatic change》2011,107(1-2):169-184
We investigate the effects of Hurricane Wilma??s storm surge (23?C24 October 2005) on the dominant tree Pinus elliottii var densa (South Florida slash pine) and rare plant species in subtropical pine rocklands of the Lower Florida Keys. We examine the role of elevation on species abundance in 1995 (Hurricane Betsy in 1965), 2005 (Hurricane Georges in 1998), and 2008 (Hurricane Wilma in 2005) to investigate if hurricanes influence abundance by eliminating plants at lower elevation on Big Pine Key, the largest island in the Lower Florida Keys. We compare densities before and after Hurricane Wilma over the 2005?C2008 sampling period and examine the role of elevation on changes in pine and rare species densities three years after Hurricane Wilma. We use elevation to assess the impact of hurricanes because elevation determined whether a location was influenced by storm surge (maximum surge of 2 m) in the Lower Florida Keys, where pine rocklands occur at a maximum elevation of 3 m. In 1995 (30 years after a major storm), elevation did not explain the abundance of South Florida slash pine or Chamaecrista lineata, but explained significant variation in abundance of Chamaesyce deltoidea. The latter two species are rare herbaceous plants restricted to pine rocklands. In 2008, 3 years after Hurricane Wilma, the positive relationship between elevation and abundance was strongest for South Florida slash pine, C. deltoidea, and C. lineata. Effects of Hurricane Wilma were not significant for rare species with wider distribution, occurring in plant communities adjacent to pine rocklands and in disturbed rocklands. Our results suggest that hurricanes drive population dynamics of South Florida slash pine and rare species that occur exclusively in pine rocklands at higher elevations. Rare species restricted to pine rocklands showed dramatic declines after Hurricane Wilma and were eliminated at elevations <0.5 m. Widely distributed rare species did not show significant changes in density after Hurricane Wilma. Abundance increased with elevation for South Florida slash pine and C. lineata after the hurricane. In an environment influenced by sea level rise, concrete plans to conserve pine ecosystems are warranted. Results from this study will help define conservation strategies by strengthening predictive understanding of plant responses to disturbance in the backdrop of sea level rise. 相似文献
254.
Comparative analysis of the energy and carbon balances of wood vs. non-wood products is a complex issue. In this paper we discuss the definition of an appropriate functional unit and the establishment of effective system boundaries in terms of activity, time and space, with an emphasis on the comparison of buildings. The functional unit can be defined at the level of building component, complete building, or services provided by the built environment. Energy use or carbon emissions per unit of mass or volume of material is inadequate as a functional unit because equal masses or volumes of different materials do not fulfil the same function. Activity-based system boundaries include life cycle processes such as material production, product operation, and post-use material management. If the products compared are functionally equivalent, such that the impacts occurring during the operation phase are equal, we suggest that this phase may be dropped from the analysis allowing a focus on material flows. The use of wood co-products as biofuel can be analytically treated through system expansion, and compared to an alternative of providing the same energy service with fossil fuels. The assumed production of electricity used for material processing is another important energy-related issue, and we suggest that using marginal production data is more appropriate than average production. Temporal system boundaries include such aspects of the wood life cycle as the dynamics of forest growth including regeneration and saturation, the availability of residue biofuels at different times, and the duration of carbon storage in products. The establishment of spatial boundaries can be problematic, because using wood-based materials instead of non-wood materials requires more land area to capture solar energy and accumulate biomass. We discuss several possible approaches to meet this challenge, including the intensification of land use to increase the time rate of biomass production. Finally, we discuss issues related to scaling up an analysis of wood substitution from the micro-level to the macro-level of national, regional or global. 相似文献
255.
Fish consumption is known to be beneficial to human health. However since the age of industrialization, the released/disposed chemical pollutants into water systems make fish a source of various environmental toxicants to humans. In oceanic cities with heavy industrial activities, fish products contribute the greatest proportion of exposure to pollutants. In this study, risks and potential effects of dioxins to health of coastal populations in the Pearl River Delta were assessed. Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (PCBs) were measured in common fish species purchased at local markets. Concentrations of total dioxins in fish ranged from 0.481 to 9.05 pg TEQ/g wet weight were similar to the lesser concentrations reported for fish from other countries. The greatest concentrations of dioxins were measured in mandarin fish, a carnivorous freshwater fish. Exposure of murine primary leydig and ovarian cells to 2,3,7,8-tetrachlorinated dibenzo-p-dioxins (2,3,7,8-TCDD) reduced the synthesis of progesterone, testosterone and/or estrogen. The reductions were probably via inhibitory effects on the expression of the steroidogenic enzymes, steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage enzyme (P450scc). Based on these reproductive parameters, the concentrations of dioxins and dioxin-like residues represent a moderate health risk due to consumption of fish. 相似文献
256.
1999年11月29日,北京时间12点10分39秒(04:10:39 UTC)在我国辽宁海城-岫岩地区发生了一次Ms5.4地震.这次地震是继1975年2月4日海城Ms7.3地震之后该地区发生的震级最大的一次地震.区域性的辽宁数字地震台网记录了这一序列的前震、主震与 余震.本文运用该台网的记录资料,用双差法对海城-岫岩地... 相似文献
257.
Chiara Lesti Massimiliano Porreca Guido Giordano Massimo Mattei Raymond A. F. Cas Heather M. N. Wright Chris B. Folkes Josè Viramonte 《Bulletin of Volcanology》2011,73(10):1535-1565
Estimates of pyroclastic flow emplacement temperatures in the Cerro Galán ignimbrite and Toconquis Group ignimbrites were
determined using thermal remanent magnetization of lithic clasts embedded within the deposits. These ignimbrites belong to
the Cerro Galán volcanic system, one of the largest calderas in the world, in the Puna plateau, NW Argentina. Temperature
estimates for the 2.08-Ma Cerro Galán ignimbrite are retrieved from 40 sites in 14 localities (176 measured clasts), distributed
at different distances from the caldera and different stratigraphic heights. Additionally, temperature estimates were obtained
from 27 sample sites (125 measured clasts) from seven ignimbrite units forming the older Toconquis Group (5.60–4.51 Ma), mainly
outcropping along a type section at Rio Las Pitas, Vega Real Grande. The paleomagnetic data obtained by progressive thermal
demagnetization show that the clasts of the Cerro Galán ignimbrite have one single magnetic component, oriented close to the
expected geomagnetic field at the time of emplacement. Results show therefore that most of the clasts acquired a new magnetization
oriented parallel to the magnetic field at the moment of the ignimbrite deposition, suggesting that the clasts were heated
up to or above the highest blocking temperature (T
b) of the magnetic minerals (T
b = 580°C for magnetite; T
b = 600–630°C for hematite). We obtained similar emplacement temperature estimations for six out of the seven volcanic units
belonging to the Toconquis Group, with the exception of one unit (Lower Merihuaca), where we found two distinct magnetic components.
The estimation of emplacement temperatures in this latter case is constrained at 580–610°C, which are lower than the other
ignimbrites. These estimations are also in agreement with the lowest pre-eruptive magma temperatures calculated for the same
unit (i.e., 790°C; hornblende–plagioclase thermometer; Folkes et al. 2011b). We conclude that the Cerro Galán ignimbrite and Toconquis Group ignimbrites were emplaced at temperatures equal to or higher
than 620°C, except for Lower Merihuaca unit emplaced at lower temperatures. The homogeneity of high temperatures from proximal
to distal facies in the Cerro Galán ignimbrite provides constraints for the emplacement model, marked by a relatively low
eruption column, low levels of turbulence, air entrainment, surface–water interaction, and a high level of topographic confinement,
all ensuring minimal heat loss. 相似文献
258.
Nick E. Timms Peter D. Kinny Steven M. Reddy Katy Evans Chris Clark Dave Healy 《Chemical Geology》2011,280(1-2):33-46
A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along deformation-related fast-diffusion pathways, such as dislocations and low-angle (< 5°) boundaries. These results indicate chemical exchange between zircon and the surrounding matrix and show that Ti-in-zircon thermometry and U–Pb geochronology from deformed zircon may not yield information relating to the conditions and timing of primary crystallisation. 相似文献
259.
Progress in some areas of process‐based aeolian sediment transport research is hampered by limited opportunities for data comparison, synthesis, and integration. This is partially due to a lack of reliable comparison methods. Many comparison methods are forms of calibration that are either restrictive (e.g., time‐averages only) or non‐existent (e.g., for field‐based sediment transport thresholds or vertical mass flux profiles). It is believed that the adoption of standard methods for common measurements may improve inter‐study comparison, add value and longevity to data, and advance integrative modeling efforts. Examples of approaches in allied disciplines where standards are used routinely are reviewed and we discuss how the mutual benefits of standardized data could outweigh perceived disadvantages. Overall, the goal of this commentary is to encourage discussion, self‐assessment, and forethought with regard to measurement methods used in process‐based aeolian geomorphology. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
260.
Modeling and observations of high-frequency flow variability and internal waves at a Caribbean reef spawning aggregation site 总被引:2,自引:2,他引:0
The characteristics and forcing mechanisms of high-frequency flow variations (periods of minutes to days) were investigated
near Gladden Spit, a reef promontory off the coast of Belize. Direct field observations and a high-resolution (50-m grid size)
numerical ocean model are used to describe the flow variations that impact the initial dispersion of eggs and larvae from
this site, which serves as a spawning aggregation site for many species of reef fishes. Idealized sensitivity model experiments
isolate the role of various processes, such as internal waves, wind, tides, and large-scale flow variations. The acute horizontal
curvature and steep topography of the reef intensify the flow, create small-scale convergence and divergence zones, and excite
high-frequency oscillations and internal waves. Although the tides in this area are relatively small (∼10-cm amplitude), the
model simulations show that tides can excite significant high-frequency flow variations near the reef, which suggests that
the preference of fish to aggregate and spawn in the days following the time of full moon may not be coincidental. Even small
variations in remote flows (2–5 cm s−1) due to say, meso-scale eddies, are enough to excite near-reef oscillations. Model simulations and the observations further
suggest that the spawning site at the tip of the reef provides initial strong dispersion for eggs, but then the combined influence
of the along-isobath flow and the westward wind will transport the eggs and larvae downstream of Gladden Spit toward less
turbulent region, which may contribute to enhanced larval survival. 相似文献