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1.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
2.
Joachim Köppen 《Astrophysics and Space Science》2003,284(2):837-840
Representative results from a comparison of the chemical evolution of spherical collapse models without and with a intercloud
medium are presented. The hot metal-rich gas distributes quickly the metals produced in supernovae throughout the galaxy,
thus leading to a more homogeneous chemical evolution and flatter metallicity gradients in the gas and the stars. The stellar
population is somewhat less concentrated towards the centre. The strong outflow results in a substantial loss of metals from
the galaxy to its surroundings, and a lower effective yield in the galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
A constitutive relation is derived for describing the mechanical response of chalk. The approach is based on a phenomenological framework which employs chemo‐plasticity. The properties of the material are assumed to be affected by the physico‐chemical processes that occur through the interaction between the skeleton and the pore fluid. The underlying mechanism is discussed by invoking a micromechanical analysis. The performance of the framework is illustrated by examining the evolution of mechanical characteristics in the presence of different pore fluids. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
The study of the chemical stability of vitreous material in aqueous media is well‐established. There has to date been little consideration of the implications of variations in the chemical durability of tephra in Quaternary tephrochronology. Chemical alteration can take the form of cationic leaching from the matrix, or complete destruction of the silica network, either of which could constrain the ability to chemically identify distal tephra. Here we apply established models of vitreous durability to the published chemical analyses of a large number of Icelandic tephras in order to predict their relative durabilities under equivalent conditions. This suggests that some important tephras have relatively poor chemical stability, and that rhyolitic tephras are, in general, more stable than basaltic. We conclude that tephras should be expected to show predictable differential chemical stability in the post‐depositional environment. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
I INTRODUCTIONWetland has very important effect on retainingwater and against drought, regUlating climate, controlling soil erosion and so on ac. Today men often attachimportance to economic effect of wetland reclamation,but neglect and destroy other functions and effectswhich result in blind wetland development, a lot ofwetland degeneration. The area of freshwater wetland inthe 1950s was 134 x 10'ha, but in the 1970s 70% hadchanged into farmland (MITSCH, 1993). The area ofwetland in d… 相似文献
6.
Olga Hadz̆ija Mladen Jurac̆ić Marija Luić Maja Tonković Biserka Jeric̆ević 《Estuarine, Coastal and Shelf Science》1985,21(5):701-709
The investigation of mineral, granulometric and chemical composition of sediments of the River Krka estuary (Yugoslavia) were performed in order to elucidate the origin of the sediments and the pattern of sedimentation. Estuarine surface sediments were found to be fine-grained with a bimodal distribution. Environmental conditions in estuarine sediments favour conservation of the organic matter (anoxic conditions). The carbohydrates in the sediments were investigated to determine whether they are of terrigenous or authigenous origin. Glucose, galactose, mannose, xylose, rhamnose, glucosamine and glucuronic acid were detected in the sediments. Their mutual relationship indicates a preferentially terrigenous source of sedimented organic material in estuarine sediments. 相似文献
7.
本矿床是我国金红石矿床重要的成因及工业类型,为具有特定化学成分的岩石在特定变质条件下形成的。本文通过对大量数据的处理,查明了化学成分与成矿的关系:高Al2O3、MgO、Fe2O3+FeO、K2O、P2O5、H2O+、MnO,低SiO2、CaO、Na2O、CO2、S等,利于钛富集;高TiO2、MgO、P2O5、S,低SiO2、CaO、K2O、Al2O3、Fe2O3/FeO,利于金红石形成;高Sc、Zr、Ni、Zn及La/Yb,低Y、Nb、Th、Cd、Ba、Be、ΣREE,利于金红石纯度提高。对研究矿床成因及寻找新的同类矿床等有重要意义 相似文献
8.
This study explores garnet coronas around hedenbergite, which were formed by the reaction plagioclase + hedenbergite→garnet + quartz, to derive information about diffusion paths that allowed for material redistribution during reaction progress. Whereas quartz forms disconnected single grains along the garnet/hedenbergite boundaries, garnet forms ~20‐μm‐wide continuous polycrystalline rims along former plagioclase/hedenbergite phase boundaries. Individual garnet crystals are separated by low‐angle grain boundaries, which commonly form a direct link between the reaction interfaces of the plagioclase|garnet|hedenbergite succession. Compositional variations in garnet involve: (i) an overall asymmetric compositional zoning in Ca, Fe2+, Fe3+ and Al across the garnet layer; and (ii) micron‐scale compositional variations in the near‐grain boundary regions and along plagioclase/garnet phase boundaries. These compositional variations formed during garnet rim growth. Thereby, transfer of the chemical components occurred by a combination of fast‐path diffusion along grain boundaries within the garnet rim, slow diffusion through the interior of the garnet grains, and by fast diffusion along the garnet/plagioclase and the garnet/hedenbergite phase boundaries. Numerical simulation indicates that diffusion of Ca, Al and Fe2+ occurred about three to four, four and six to seven orders of magnitude faster along the grain boundaries than through the interior of the garnet grains. Fast‐path diffusion along grain boundaries contributed substantially to the bulk material transfer across the growing garnet rim. Despite the contribution of fast‐path diffusion, bulk diffusion through the garnet rim was too slow to allow for chemical equilibration of the phases involved in garnet rim formation even on a micrometre scale. Based on published garnet volume diffusion data the growth interval of a 20‐μm‐wide garnet rim is estimated at ~103–104 years at the inferred reaction conditions of 760 ± 50 °C at 7.6 kbar. Using the same parameterization of the growth law, 100‐μm‐ and 1‐mm‐thick garnet rims would grow within 105–106 and 106–107 years respectively. 相似文献
9.
Mauro Lo Cascio Yan Liang Nobumichi Shimizu Paul C. Hess 《Contributions to Mineralogy and Petrology》2008,156(1):87-102
The grain-scale processes of peridotite melting were examined at 1,340°C and 1.5 GPa using reaction couples formed by juxtaposing
pre-synthesized clinopyroxenite against pre-synthesized orthopyroxenite or harzburgite in graphite and platinum-lined molybdenum
capsules. Reaction between the clinopyroxene and orthopyroxene-rich aggregates produces a melt-enriched, orthopyroxene-free,
olivine + clinopyroxene reactive boundary layer. Major and trace element abundance in clinopyroxene vary systematically across
the reactive boundary layer with compositional trends similar to the published clinopyroxene core-to-rim compositional variations
in the bulk lherzolite partial melting studies conducted at similar P–T conditions. The growth of the reactive boundary layer takes place at the expense of the orthopyroxenite or harzburgite and
is consistent with grain-scale processes that involve dissolution, precipitation, reprecipitation, and diffusive exchange
between the interstitial melt and surrounding crystals. An important consequence of dissolution–reprecipitation during crystal-melt
interaction is the dramatic decrease in diffusive reequilibration time between coexisting minerals and melt. This effect is
especially important for high charged, slow diffusing cations during peridotite melting and melt-rock reaction. Apparent clinopyroxene-melt
partition coefficients for REE, Sr, Y, Ti, and Zr, measured from reprecipitated clinopyroxene and coexisting melt in the reactive
boundary layer, approach their equilibrium values reported in the literature. Disequilibrium melting models based on volume
diffusion in solid limited mechanism are likely to significantly underestimate the rates at which major and trace elements
in residual minerals reequilibrate with their surrounding melt.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
D. J. Cherniak 《Physics and Chemistry of Minerals》2008,35(4):179-187
Self-diffusion of Si under anhydrous conditions at 1 atm has been measured in natural zircon. The source of diffusant for
experiments was a mixture of ZrO2 and 30Si-enriched SiO2 in 1:1 molar proportions; experiments were run in crimped Pt capsules in 1-atm furnaces. 30Si profiles were measured with both Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis with the resonant
nuclear reaction 30Si(p,γ)31P. For Si diffusion normal to c over the temperature range 1,350–1,550°C, we obtain an Arrhenius relation D = 5.8 exp(−702 ± 54 kJ mol−1/RT) m2 s−1 for the NRA measurements, which agrees within uncertainty with an Arrhenius relation determined from the RBS measurements
[62 exp(−738 ± 61 kJ mol−1/RT) m2 s−1]. Diffusion of Si parallel to c appears slightly faster, but agrees within experimental uncertainty at most temperatures
with diffusivities for Si normal to c. Diffusion of Si in zircon is similar to that of Ti, but about an order of magnitude faster than diffusion of Hf and two
orders of magnitude faster than diffusion of U and Th. Si diffusion is, however, many orders of magnitude slower than oxygen
diffusion under both dry and hydrothermal conditions, with the difference increasing with decreasing temperature because of
the larger activation energy for Si diffusion. If we consider Hf as a proxy for Zr, given its similar charge and size, we
can rank the diffusivities of the major constituents in zircon as follows: D
Zr < D
Si << D
O, dry < D
O, ‘wet’. 相似文献