Chemical diffusion profiles in molten CaO---Al2O3---SiO2 have been measured over a large range of compositions at 1500°C and l GPa. The diffusion profiles have been inverted for effective binary diffusion coefficients (EBDCs) and for the chemical diffusion matrix. The EBDCs are shown to depend strongly on both composition and direction of diffusion in composition space. The dependence of EBDCs on direction in composition space, which for the system studied here can be as large as a factor of seven, severely limits the applicability of EBDCs to interdiffusion in any direction other than the one used to derive the EBDCs.
The chemical diffusion matrix for molten CaO---Al2O3---SiO2 was determined using diffusion profiles from two or three mutually orthogonal diffusion couples in the ternary composition space. All features of the diffusion profiles shown in this work can be reproduced by representing the chemical fluxes in the three-component system as a linear combination of concentration gradients via a 2 × 2 diffusion matrix. Chemical diffusion in molten CaO---Al2O3---SiO2 shows clear evidence of strong diffusive coupling among the components. This can be seen in the uphill diffusion profiles of components that were initially uniform, in the fact that the apparent rate of diffusion of some components is a strong function of direction in composition space, and most quantitatively in the magnitude of off-diagonal elements of the diffusion matrix relative to the magnitude of the diagonal elements. SiO2 for example, is found to be strongly coupled with CaO in relatively silicic melts, whereas Al2O3 is strongly coupled with CaO in less silicic melts. Furthermore, the coupling of CaO with either Al2O3 or Si02 reverses sign between more and less polymerized compositions. Interdiffusion profiles in natural melts have numerous features that suggest similar coupling between Al2O3 and CaO and between SiO2 and CaO. 相似文献
Several shales and oils ranging in age from 3 million to 2·7 billion years have been investigated for their hydrocarbon content using gas chromatography and mass spectrometry as primary analytical tools. From the Soudan Shale from Minnesota (2·7 × 109yr) the C18, C19, C20 and C21 isoprenoid-alkanes were obtained. The Antrim shale from Michigan (about 265 × 106 yr) yielded the C16, C18, C19, C20 and C21 isoprenoids, as well as a C16iso-alkane and the C18 and C19 cyclohexyl n-alkanes. The San Joaquin Oil (30 × 106 yr) and the Abbott Rock Oil (3 × 106 yr) contained the C16, C18, C19, C20 and the C18, C19, C20 and C21 isoprenoids respectively. In addition, a series of iso-alkanes (C16−C18), anteiso-alkanes (C16−C18) and n-alkylcyclohexanes (C16−C19) as well as a C21 isoprenoid were obtained from the Nonesuch Seep Oil (1 × 109 yr). This analysis provides a comprehensive picture of the types of biogenic hydrocarbons found in oils and shales of widely differing ages, and in particular, the finding of isoprenoid alkanes in the Soudan Shale furnishes evidence for life processes at that period of geological time. 相似文献
Clinopyroxene megacrysts from young melanephelinitic lavas were divided into Cr-rich and Cr-poor suites. Sr, Nd, and Pb isotopic
ratios of leached megacrysts and host lava are indistinguishable from each other and indicate a depleted source. Host lavas
do not display chemical evidence for significant fractional crystallization, which is required to explain the compositional
range of the megacrysts. This rules out a simple cognate genetic relationship between the two, and strictly defines megacrysts
as xenocrysts. The well-defined correlations of trace elements with the Mg-numbers in the megacrysts are interpreted as the
result of extensive fractional/equilibrium crystallization of magma over a large temperature range at near isobaric condition
in the upper mantle. Trace element variations in megacrysts are consistent with fractional crystallization of clinopyroxene
alone for the Cr-rich suite, and clinopyroxene + garnet for the Cr-poor suite from at least two bathes of related melts. Megacrysts
parent magma might represent mantle melts, which were never erupted in their initial composition. 相似文献
In this paper the search for optical identifications in the 5C-radio surveys is continued. Near the positions of 135 radio sources of the 5C3 catalogue all present optical objects up to the plate limit (about B ≈︁ 21) have been measured photometrically in UBVr and astrometrically on plates of the 134/200 cm Schmidt telescope of the Karl Schwarzschild Observatory Tautenburg. A total of 111 candidates for possible optical identifications were found. The number of real identifications will be, of course, much smaller. Among the 111 objects there are: 12 supposed QSO's, 21 galaxies or probable galaxies, 56 stellar objects the greater part of which may be main sequence stars, subdwarfs and white dwarfs, and I object may be the centre of an H II region in the OB-association OB 182. 21 objects near the plate limit could not be classified. A statistical treatment with information on the real rate of identification (it roughly will amount to about 10%) and its reliability will be given in part III. 相似文献
The optical luminosities of extragalactic objects with broad emission lines, i.e. quasi-stellar radio sources, radio quiet quasi-stellar objects and Seyfert galaxies are compared. At high luminosities (M < - 23) we find no difference in the form of the optical luminosity function for radio quiet and radio emitting objects; at low luminosities this function is growing steeply only for radio quiet objects, whereas for objects with higher radio indices it remains nearly constant below M = - 22. This may possibly be interpreted as indicating a division between the optically bright “quasars” and the less luminous objects. The quasars with the highest radio index show only a small scatter in optical luminosities and thus yield a well defined Hubble relation. 相似文献
The reality of the high percentage of variability among Blue Objects which was found in previous investigations was examined on 170 Tautenburg Schmidt plates of two test fields near M 31. The high percentage could not be confirmed. Spurious amplitudes can be explained by the large probable errors of the photometry (especially near the plate limit) and by bad suitability of good-looking plates. Out of 37 Blue Objects examined, only two (van den Bergh 5 and 12) are distinctly variable, but the final examination of Blue Objects which are suspected of variability can only be done by photoelectric photometry. 相似文献
The hygroscopic properties of sub-micrometer aerosol particles were studied in connection with a ground-based cloud experiment at Great Dun Fell, in northern England in 1995. Hygroscopic diameter growth factors were measured with a Tandem Differential Mobility Analyser (TDMA) for dry particle diameters between 35 and 265 nm at one of the sites upwind of the orographic cloud. An external mixture consisting of three groups of particles, each with different hygroscopic properties, was observed. These particle groups were denoted less-hygroscopic, more-hygroscopic and sea spray particles and had average diameter growth factors of 1.11–1.15, 1.38–1.69 and 2.08–2.21 respectively when taken from a dry state to a relative humidity of 90%. Average growth factors increased with dry particle size. A bimodal hygroscopic behaviour was observed for 74–87% of the cases depending on particle size. Parallel measurements of dry sub-micrometer particle number size distributions were performed with a Differential Mobility Particle Sizer (DMPS). The inorganic ion aerosol composition was determined by means of ion chromatography analysis of samples collected with Berner-type low pressure cascade impactors at ambient conditions. The number of ions collected on each impactor stage was predicted from the size distribution and hygroscopic growth data by means of a model of hygroscopic behaviour assuming that only the inorganic substances interacted with the ambient water vapour. The predicted ion number concentration was compared with the actual number of all positive and negative ions collected on the various impactor stages. For the impactor stage which collected particles with aerodynamic diameters between 0.17–0.53 μm at ambient relative humidity, and for which all pertinent data was available for the hygroscopic closure study, the predicted ion concentrations agreed with the measured values within the combined measurement and model uncertainties for all cases but one. For this impactor sampling occasion, the predicted ion concentration was significantly higher than the measured. The air mass in which this sample was taken had undergone extensive photochemical activity which had probably produced hygroscopically active material other than inorganic ions, such as organic oxygenated substances. 相似文献
Planning, design and operation of urban drainage systems is often based on hydraulic sewer modelling. Sewer models are also
increasingly used to quantify pollution loads discharged to aquatic ecosystems (e.g. via combined sewer overflows), which
ultimately allows an estimation of the ecological impact emanating from urban drainage systems. The establishment of such
network models, however, requires detailed and accurate information about the sewer network structure and the connected surface
area. This infrastructure data is often unavailable, confidential or available in ‘paper’ format only. The present paper outlines
a novel approach to develop a hydraulic sewer model constrained by a minimum amount of data. The approach combines the application
of a surface flow accumulation algorithm to a selectively manipulated Digital Elevation Model (DEM) with a routine for hydraulic
network dimensioning to generate a close-to-reality sewer network ready to be implemented in a hydraulic modelling platform.
The method is tested for three real-life catchments of which characteristics vary in scale, topography, state of development
and network complexity. For all cases the generated network is implemented on the EPA-SWMM platform to allow hydrodynamic
simulations. Model performance is assessed by (1) evaluating the spatial match of existing and generated network layout, (2)
comparing the estimated hydraulic dimension with real-life infrastructure data and (3) benchmarking simulated runoff with
measured data for a defined validation period. The analysis shows that the presented method is capable of reproducing the
original network layout, network length and corresponding discharge rates based on little, freely available information. Further
research potential is identified to improve the hydraulic dimensioning and the application to complex systems that include
control structures. The presented approach is useful to estimate the scope of drainage networks including layout and design
(e.g. for preliminary planning in emerging areas) to screen existing networks and to identify critical spots where more precise
information is required. 相似文献
The world over, neoliberal modes of conservation are hybridising with, or even replacing, other forms of conservation. Under the banner of ‘win–win’ policies, planners actively work to commoditize natural resources and the social relations that determine the use and conservation of these resources. While these general processes seem to hold sway globally, it is crucial not to lose sight of the context specific ways in which neo-liberalism influences conservation practice and local outcomes. The paper examines how neo-liberalism’s global pervasiveness becomes manifest across different levels and scales in South Africa and the Philippines. The conclusion suggests that as a result of these neoliberal pressures, emphasis is shifting from local constructions of ‘nature’ by communities to what the environment should mean for communities in terms of commodified resources and growing capitalist markets. 相似文献