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111.
The exchage equilibrium
has been used to measure activity-composition relations along the olivine join FeSi0.5O2−MgSi0.5O2 at 1400 K and 1 atm pressure. Equilibrium Fe−Mg partitioning between the two phases was determined by reversing the compositions
of olivine coexisting with oxide and matallic iron over the composition range Fo23 to Fo92. A detailed study of the thermodynamic properties of the oxide phase has recently been made by Srečec et al. and we have
confirmed their results in the composition range of interest. Application of the oxide data to the exchange equilibrium enables
the properties of olivine to be determined. Within experimental uncertainly (Fe, Mg)Si0.5O2 olivine can, at 1400 K, be treated as a symmetric solution with W
Fe-Mg
o1
of 3.7±0.8 kJ/mol. The data permit the presence of only very slight asymmetry in the series. The data do not support recent
assertions that olivine is highly non-ideal (W≈10 kJ/mol) under these conditions. 相似文献
112.
The linear and weakly nonlinear dynamics of long, low frequency, spatially growing baroclinic waves embedded in slowly varying zonal flow on a β-plane channel are examined in a continuous model of the atmosphere. For a basic state jet flow possessing a locally unstable region, the nonlinear solution yields a maximum amplitude that is located near the region of maximum baroclinicity and substantially upstream of the maximum amplitude obtained from linear theory. The difference between the linear and nonlinear solutions is due to the time-averaged wave fluxes becoming large enough in the nonlinear problem to stabilize the flow prior to reaching the location (jet center) where the basic state baroclinicity and locally computed linear growth rate are maximized. 相似文献
113.
The direct precipitation of apatite in seawater is inhibited by Mg ions. The action of various factors on this precipitation is studied: addition of Ca, addition of F, reduction of pH and simultaneous effect of reduction of pH and addition either of F or of Ca. It is established that the reduction of the pH of seawater to 7 allows the precipitation of the apatite with a Ca/Mg ratio in the water of 1.2. The favourable environment for the settlement of natural apatite must then be either neutral or acid. This result is corroborated by the re-study of Gulbrandsen's equation. Such an acid environment with a high phosphorus content may be the result of oxidation of large quantities of organic matter due to previous intense biological activity. The acidity is probably brought about by bubbling of CO2. 相似文献
114.
Methods for detecting regime shifts in large marine ecosystems: a review with approaches applied to North Pacific data 总被引:1,自引:0,他引:1
This note provides a brief review of five analytical methods previously used or promoted for diagnosing regime shifts in marine ecosystems. The methods discussed are: (i) principal components analysis, (ii) compositing average standard deviates, (iii) autoregressive moving average and intervention analysis modeling, (iv) vector autoregressive process modeling, and (v) Fisher information. Assessments of the relative strengths and weaknesses for the different analytical approaches are also offered. Some of these methods are applied to a collection of fishery oceanographic time series for the N. Pacific to illustrate aspects of their relative utility and limitations for diagnosing regime shift behavior. One recommendation for future studies is to analyze biotic and abiotic time series separately in order to identify ecosystem state variables of interest and to better isolate ecosystem behaviors from other influences like environmental change. Methods that allow for quantitative assessments of the statistical significance of hypothesized regime shifts should be favored over those that do not. Analyses of especially large collections of time series may benefit from first using a data compression technique and then applying one of the methods that are more appropriate for just one or a small number of time series. Because of the difficulties in observing and adequately documenting many aspects of marine ecosystem variability, it is crucial that future research attempt to combine empirical studies of large marine ecosystems with theoretical and modeling studies of other systems for which the dynamics and predictability are better understood. With such a comparative approach it should be possible to refine conceptual and simulation models, while also identifying crucial gaps in existing observations. 相似文献
115.
Nathan Hawley 《Geo-Marine Letters》1981,1(1):7-10
Flume observations of the consolidation of mud beds deposited from an unsteady flow show that 10-mm layer undergoes considerable
consolidation during the time of deposition and within the first hour after deposition ceases, but little additional consolidation
during the next 24 hr. A certain minimum thickness, between 3 and 10 mm, is required for any consolidation to occur. The results
support the hypothesis that thick mud layers may form in nearshore subtidal areas as the result of accumulation of thinner
layers deposited during successive tidal cycles, but only if each individual layer is able to withstand erosion during the
subsequent cycle. 相似文献
116.
We used a numerical model forced with three different scenarios to analyze Baffin Bay circulation sensitivity to runoff around Baffin Bay, especially the Greenland runoff, for the past (1970–2010) and future (2010–2099). We observed an overall decrease in transport from the Arctic to the North Atlantic for the volume, heat, and freshwater over the time period as well as an augmentation of the freshwater and heat in Baffin Bay. In the early 1990s, the increase in heat in Baffin Bay was consistent with an increase in the West Greenland Irminger Water (WGIW) inflow at Davis Strait while later West Greenland Shelf Water played an important role in the heat import, sustaining the idea that the West Greenland Current might have an impact on the melt of West Greenland tidewater glaciers. The increase in freshwater and later in heat in Baffin Bay leads to changes in the steric height inside Baffin Bay, which leads to changes in the circulation. After 1978, the WGIW reaches the North Water polynya and recirculates into the Baffin Bay gyre where it accumulates over time. In the future experiment, the dynamic changes in Baffin Bay are mainly related to the accumulation of heat inside the gyre. 相似文献
117.
Nathan Frey 《Urban geography》2017,38(10):1534-1549
This study examines equity issues in access to urban environmental amenities using Washington, D.C. as a case study. The amenities that are the focus of this study, urban trees and urban parks, have a range of social and health benefits for city dwellers, and Washington, D.C. is a major city with a large, diverse population and long-standing geographic divisions by race and class. Using spatial regression techniques, the study examines disparities in access to these amenities by race, ethnicity, and socioeconomic status at citywide and sub-city scales. Mixed evidence is found for disparities in access across amenities and across scales. The results emphasize the need for studies of access to urban environmental amenities to pay closer attention to the differences between amenities and to issues of scale. 相似文献
118.
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120.
正Forecasting convective storms using NWP models is an important goal and a highly active area of ongoing research.Skillful and reliable NWP of convective storms could allow for severe weather warnings with longer lead times,as operational forecasters begin to incorporate convective-scale forecasts into severe weather forecast operations(Stensrud et al.,2009,2013).This would then provide vulnerable individuals and industries with more time to seek shelter and/or mitigate 相似文献