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281.
Vladimír Skalský 《Astrophysics and Space Science》1988,149(2):375-378
The author considers the possibility of transition of the current universe expansion to contraction. The considerations are based on the fact that a homogeneous Universe is structured into non-homogeneous units, the latter expanding as a whole. An analysis of the effects of these wholes on further development shows that in the future contractions may occur only locally; however, the current spatial expansion of the Universe cannot be replaced by a global contraction. 相似文献
282.
Vladimír Skalský 《Astrophysics and Space Science》1988,147(2):267-270
On the basis of the law of conservation of energy, the variations of radiation energy as a result of the variations of the dimensions of the Universe and of the increase in total energy of the hypothetical false vacuum, the author introduces an assumption that the Universe is an actual subsystem of the infinite whole of reality. Analyzing the consequences of introducing this assumption into the standard model of the Universe, he comes to the conclusion that the Universe, with respect to its evolution, represents an ultrastable system consisting of a dynamic system of the de Sitter evolution phase with the Planck values and of a dynamic system of Friedmann's phase of evolution into which the dynamics of its partial subsystems is incorporated. 相似文献
283.
Ladislav Novotný 《Urban geography》2016,37(7):1009-1029
This article contributes to understanding population migration in Central European urban regions and its connection with urban development. This topic has been addressed in other studies, focused mainly on large cities, particularly Prague, Budapest, and Warsaw. Bratislava, the capital of the Slovak Republic, is a relatively small city at the core of one of the most economically developed regions in Central Europe. The region has experienced a transformation of migration trends, from those determined by socialist urbanization to trends resembling those observed in Western Europe. Similar to those of other major Central European cities, recent patterns of migration to and from Bratislava are characterized by a rising intensity of concentration and decentralization, but also reflect several unique historical circumstances. Furthermore, the results indicate that the global economic crisis that erupted in 2007 has eased the intensity of the observed processes, although it has not changed their nature. This effect is similar to that of the economic decline in the 1990s. 相似文献
284.
285.
286.
The inconsistency of records of local earthquakes and synthetic seismograms due to noise contamination of the data and/or to improper Green function because of an inexact structural model often results in high frequency oscillations of the source time function, which prolongs it spuriously. A priori limit on the roughness of the source time function turned out to reduce the spurious oscillations but it keeps its spurious extension unchanged. Thus, it may yield a severe distortion of the seismic moment. However, it reduces the spurious volumetric component of the mechanism resulting from improper modelling of the structure and, thus, may help decide whether the retrieved volumetric component is real or false. The demand for the smoothness is incorporated as a penalty function in the minimization of the least square residuals, which allows us to decide about the degree of the smoothness. The minimization is performed with a simple genetic algorithm, which offers the advantage of a detailed exploration of the model space reducing the danger of being trapped in local minima. 相似文献
287.
Many rocks mapped as felsic metavolcanics in the eastern part of the Lukavice Group are shown to be altered mafic metavolcanics, similar to those in the Noranda and Flin Flon-Snow Lake mining districts, Canada. The relatively fresh rocks of the Lukavice Group are rhyolite, dacite-andesite, and andesite-basalt of calcalka-line character. Assuming no substantial volume change during alteration, Ti, P, La, Ce, Yb, Lu, Th (partly), Sc and V contents remained unchanged. Altered rocks are enriched in (Fe + Mg), K and Si and depleted in Na, Ca and Zr. Some elements show both increased and decreased contents in altered rocks (Mg, Ba, Sm, eu, Tb and Hf). Although hydrothermal alteration in the Lukavice Group is of large extent, it is of the proximal Kuroko style and not of regional Amulet Rhyolite style. Implications for a large hydrothermal system within a volcanic pile are discussed in relation to the Ordovician Lukavice Group and its mineral deposits and to some other parts of the Bohemian Massif with volcanosedimentary sequences of the same age. 相似文献
288.
Marian Karlický 《Solar physics》1993,145(1):137-150
Using a 1-D hybrid model of the electron beam bombardment in a flare loop, it is demonstrated that beam electrons, back-scattered in dense layers of the solar atmosphere, are accelerated in the return-current electric field. This effect is shown in two regimes of the electron beam bombardment: (a) with a monoenergetic quasi-steady beam, and (b) with a sequence of 4 pulse beams. It is suggested that the mirroring of electrons at loop magnetic mirrors can amplify this process. The role of such acceleration for the formation of a collisionless return-current, and thus for a decrease of return-current losses, is discussed. 相似文献
289.
A. Krüger J. Hildebrandt B. Kliem H. Aurass J. Kurths V. V. Fomichev I. M. Chertok L. Křivský 《Solar physics》1991,134(1):171-186
Behind-the-limb flares provide a unique opportunity for the study of vertical source structures of microwave bursts and dynamic flare processes. Based on complex observational data related to the outstanding solar proton event on 16 February, 1984, the development of burst emission at a height z 200000 km above the photosphere has been investigated. A comparison with the associated X-ray emission measured aboard various spacecraft yields a time lag of about 1 min between the onset of the unocculted impulsive HXR-emission and the onsets of the X-ray and microwave emissions occulted by the solar limb. The lag corresponds to a range of speeds of the propagation of the flare volume of about 3000–5000 km s–1. Considering competing transport agents that could account for such expansion of the source volume, a qualitative model of shock-wave activation of loops successively reaching into larger coronal heights is proposed.From a discussion of the possible emission processes involved, conclusions about the magnetic field, electron density, and particle energies have been obtained. 相似文献
290.
Marian Karlický 《Solar physics》1990,130(1-2):347-360