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A. Kučinskas 《Astrophysics and Space Science》1997,251(1-2):231-234
We have calculated terminal gas outflow velocities from the circumstellar shells of the AGB stars. Our results confirm that,
in case of the stationary dust driven winds, the dynamics of the outflow is governed essentially by the dust properties and
stellar luminosities, while only marginally by other stellar parameters. Although being far from comprehensive, our calculations
also indicate that the dust driven winds may only occur in cool, luminous, low mass objects.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
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G. Cevolani G. Bortolotti L. Foschini C. Franceschi G. Grassi G. Trivellone A. Hajduk V. Porubčan 《Earth, Moon, and Planets》1995,68(1-3):247-255
Continuous radio-wave monitoring of the Geminid activity in December 1992 and 1993 by using a forward scatter (FS) bistatic radar over the Bologna-Lecce baseline (700 km) in Italy, reveals peculiar structural aspects of the stream in terms of signal amplitude-rate and duration-rate dependence. The observational results of the Geminid display obtained in the two consecutive years with differentiated peak levels of transmitted power, exhibit different time distributions of underdense meteors against the signal received power. Both sets of the data relative to the peak activity in December 12–14, show reflection properties of Geminids which are atypical if compared with echoes from cometary-type showers, with really high echo counts at mid-upper levels of the peak received power. An assymmetric curve of activity of the Geminids complex is evidenced, with the peak flux of smaller particles occurring earlier than that of larger ones. 相似文献
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J. Klačka 《Earth, Moon, and Planets》1994,64(2):125-132
The problem of the action of the solar radiation on the motion of interplanetary dust particle is discussed. Differences between the action of electromagnetic solar radiation and that of the solar wind are explained not only from the point of view of the physical nature of these phenomena but also from the point of view of dust particle's orbital evolution. As for the electromagnetic solar radiation, general equation of motion for the particle is written and the most important consequences are: (i) the process of inspiralling toward the Sun is not the only possible motion - even spiralling from the Sun is also possible, and, (ii) the orbital plane of the particle (its inclination) may change in time. As for the solar wind, the effect corresponding to the fact that solar wind particles spread out from the Sun in nonradial direction causes that the process of inspiralling toward the Sun is in more than 50% less effective than for radial spread out; in the region of the asteroid belt (long period orbits) the process of inspiralling is changed into offspiralling. Also shift in the perihelion of dust particle's orbit exists. 相似文献
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K–Ar dating of illitic minerals is commonly used in studies of diagenetic series applied to oil prospecting. In spite of a great number of specialized papers, some problems remain unresolved. These are mostly due to a misunderstanding of the argon accumulation process during illitization. Criteria for identifying detrital–authigenic mineral mixtures, crystal ripening, fast precipitation or continuous nucleation‐growth processes are discussed using K–Ar data available in the literature. Using different parameters, such as Δage (ageK–Ar ? agestrati), Δcryst (diagenetic ageK–Ar ? agestrati) or Δfrac (ageK–Arfraction ?ageK–Arfinest), it is shown that the K–Ar age significance depends on the illite nucleation–growth processes. A ‘diagenetic age’ is obtained when these processes are rapid (the K2O accumulation period is shorter than 2σ). If lower than this value, the K–Ar ratio depends on the proportions of new and old particles, respectively, which are controlled by the relative rates of nucleation, crystal growth and ripening. 相似文献
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High levels of Cd and Zn in Jamaican soils observed in geochemical surveys are related to the presence of phosphorites of possible Late-Miocene or Pliocene age. The trace element and REE geochemistry of the phosphorites, together with SEM studies, indicate a guano origin for the phosphorites. No specific host minerals for Cd could be identified in the fossiliferous phosphorite which is characterized by uniquely high levels of Cd, Zn, Ag, Be, U and Y. However, in the soil Cd is present in lithiophorite and a complex history of pedological development is preserved in the aluminous–goethite present in the soil. The unique guano signature is preserved in the soil despite the fact that guanos themselves have either not been observed or have been destroyed by continuing karst and soil development. The phosphorite geochemical signature can be traced in the data of a 1988 island-wide soil geochemical survey, identifying areas where the Palaeo-environment that supported bird ‘rookeries’ existed in the Late-Miocene or Pliocene. 相似文献
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