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31.
Zdenek F. Švestka 《Solar physics》1982,113(1-2):67-86
The talk reviews briefly historical development of the imaging of the Sun, and flare imaging in particular, at different wavelengths. The present state is then critically analyzed, emphasizing and demonstrating problems related to simultaneity of observed data, differences in time resolution, limitations of the imaged field of view, unequal spatial resolution, and alignment of the images. Prospects for the future are briefly sketched, including imaging in very hard X-rays and -rays. 相似文献
32.
Zdenek Sekanina 《Icarus》1975,25(2):218-238
The properties of the icy-grain model, formulated recently for the nearly straight, structureless tails of a number of comets with large perihelion distances, are studied. The approach used is based on the comparison of the orientation and general profile of the tails with a set of synchrones, i.e., theoretical trajectories of particles emitted from the cometary nucleus at particular times. A number of features observed in the distant comets, such as a sharply bounded envelope around the nuclear condensation, jet activity in the coma, a slight curvature of the tail, and the absence of its appreciable broadening with increasing distance from the nucleus, are also explained by the icy-grain model. The model is further confronted with the tail-orientation, spectroscopic, and spectrophotometric data available on comets with perihelia beyond 2.2 AU. It is established that the transition region between 2 and 3 AU, where water snow starts evaporating rapidly, has a profound effect on the dynamics of the icy tails. It is suggested that the icy (or solid-hydrate) grains, constituting the tails of the distant comets, may be carriers of fine meteoric-dust particles, of microns and submicron sizes, which are set free once the grains start disintegrating by evaporation. 相似文献
33.
Z. Weiss Z. Klika P. Čapkova D. Janeba S. Kozubova 《Physics and Chemistry of Minerals》1998,25(7):534-540
A sodium montmorillonite from Ivan?ice (Czech Republic) was treated with solutions containing various molar concentrations of Zn and Cd for the purpose of determining ion exchange equilibria. The sorption isotherms for Zn and Cd exhibit a rather similar shape, which depends on pH; the maxima for Zn and Cd sorbed on Na-montmorillonite are very close to each other (e.g., 0.419?mmol/1?g and 0.440?mmol/1?g, respectively, for pH=5). It is a characteristic of both elements that a high level of sorption is reached at low concentration in solution. The leachability of Zn and Cd in deionized water from fully saturated montmorillonites is very similar, but a different results were observed for Na leached from fully saturated Na-montmorillonite. The total amount of leached Na was 21.7% (after four consecutive leaching runs). However, only 2.1% and 1.6% were found for Cd and Zn, respectively. Different quantities of Cd and Zn exchanged in Na-montmorillonite influence significantly the shape and position of maximum of the 001 XRD profile. Experimental XRD profiles of montmorillonites, fully saturated with Na, Cd and Zn, corrected for instrumental and physical factors exhibit maxima at 12.59, 14.86, and 14.77?Å, respectively. When the d 001 spacing is determined from a corrected profile, it varies systematically with the percentage of exchanged Zn and Cd and the relationships seem to be linear for both elements. For montmorillonites, not fully saturated with one element, the peak shift and peak broadening, characteristic for mixed layered structures with random layer sequences, has been observed. 相似文献
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Claudia?Aparicio Jan?FilipEmail author Henrik?Skogby Zdenek?Marusak Miroslav?Mashlan Radek?Zboril 《Physics and Chemistry of Minerals》2012,39(4):311-318
The thermally induced reductive decomposition of a natural near end-member almandine [VIII(Fe2.85Mg0.11Ca0.05Mn0.02)VI(Al1.99)IV(Si2.99)O12] and possible hydrogen diffusion into its structure have been carried out at temperatures up to 1,200°C, monitored by simultaneous thermogravimetric analysis and differential scanning calorimetry (DSC), infrared and 57Fe Mössbauer spectroscopy and X-ray powder diffraction. Below 1,000°C, evidence for hydrogen diffusion into almandine structure was not observed. At temperatures above 1,000°C, reductive decomposition sets in, as displayed by a sharp endothermic peak at 1,055°C on the DSC curve accompanied by a total mass loss of 3.51%. We observe the following decomposition mechanism: almandine + hydrogen → α-Fe + cristobalite + hercynite + water. At higher temperatures, fayalite and sekaninaite are formed by consecutive reaction of α-Fe with cristobalite and water, and cristobalite with hercynite, respectively. The metallic α-Fe phase forms spherical and isolated particles (~1 μm). 相似文献