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211.
The12C/13C isotope ratio in the interstellar medium and in stellar atmospheres is discussed and compared to the value found in the solar system and especially in comets. The cometary value (100) tends to be slightly above the terrestrial value and is definitively higher than that for interstellar molecular clouds (about 30 to 50).This result implies that comets are not of interstellar origin; that the original isotopic abundances of the primitive solar nebula has been preserved in the cometary material; and that due to an enrichment of the interstellar medium in13C, the12C/13C isotope ratio has decreased by a factor of about 2.5 since the formation of the solar system (i.e., during the past 4.5×109 years) — a result which is roughly in agreement with present theories of the chemical evolution of our Galaxy. The relatively high cometary carbon isotope ratio (as compared to the terrestrial value) indicates that some correction should be applied to the semi-empirical models describing the13C enrichment in the Galaxy.Paper dedicated to Professor Hannes Alfvén, on the occasion of his 70th birthday, 30 May, 1978. 相似文献
212.
Frequency content of stress waves in the nearest zone of a spherical explosive source in gravel sandy soil 总被引:1,自引:0,他引:1
Zusammenfassung Bei Verfolgung der Entstehung und Formierung der durch eine explosive Kugelquelle erregten Druckwellen steht die Frage ihres Frequenzgehalts im Vordergrund. Der Frequenzgehalt dieser Wellen wurde durch die Abhängigkeit ausgedrückt (2), die die Änderungen der relativen Breite des Amplitudenspektrums (1) vom Gewicht und von der Entfernung der Quelle angibt. Aus(2) erfolgt, dass der Frequenzgehalt der Druckwellen mit wachsender Entfernung und Grösse der Ladung exponential sinkt, wobei die Steilheit dieses Abfalls für höhere Grössen der Ladung kleiner ist. Das Herabsetzen des Frequenzgehalts dieser Wellen verursacht, dass die maximate spektral Dichte in grösseren Entfernungen von der Quelle markanter wird. 相似文献
213.
The modulation of galactic cosmic rays, as derived from ground-based neutron monitors over a solar cycle appears to be a good indicator of solar activity. Especially good correlation was found between short-term variations of cosmic ray flux and solar UV emission in the region of 250 nm during one year (1982). 相似文献
214.
We analyze the complex pattern of anticorrelation between the degree of polarization p in the green λ530.3-nm line and its intensity I λ, which was revealed by coronal observations during the total solar eclipse of July 11, 1991. For coronal points located at approximately the same distance from the disk center, the anticorrelation diagram breaks up into two branches with a zone of avoidance between them. High-latitude streamers form the upper branch, while the lower branch belongs to active equatorial regions. The arrangement of large-scale coronal structures in the p-logI λ diagram is considered for a distance of 1.2R ⊙. The change in anticorrelation diagram with distance is analyzed in detail for the giant high-latitude coronal streamers observed on July 11, 1991. Our results contain important information about the scattering of photospheric radiation at line frequencies in the presence of a coronal magnetic field. 相似文献
215.
Using narrow-band H filtergrams, we develop a quantitative non-LTE approach to determine the physical conditions prevailing at the tops of (post)-flare loops observed against the solar disc. At temperatures 10000–15000 K, the tops of flare loops turn to emission at H line center when the gas pressure P
g
reaches 1 dyn cm–2 and should be clearly visible for P
g
3 dyn cm–2, independently of the loop diameter. This situation corresponds to the electron density of the order 1012 cm–3. The contrast of flare-loops (in projection on the disc) at H line center is mainly the function of P
g
, while in the line wings (H ± 1 Å) the loop can be visible in absorption or emission only when rather strong microturbulence is present or for unrealistically high gas pressures. Finally, we briefly discuss our diagnostical results in frame of the latest (post)-flare loop model. 相似文献
216.
Numerical simulations of the helical (m=1) kink instability of an arched, line-tied flux rope demonstrate that the helical deformation enforces reconnection between
the legs of the rope if modes with two helical turns are dominant as a result of high initial twist in the range Φ≳6π. Such a reconnection is complex, involving also the ambient field. In addition to breaking up the original rope, it can form
a new, low-lying, less twisted flux rope. The new flux rope is pushed downward by the reconnection outflow, which typically
forces it to break as well by reconnecting with the ambient field. The top part of the original rope, largely rooted in the
sources of the ambient flux after the break-up, can fully erupt or be halted at low heights, producing a “failed eruption.”
The helical current sheet associated with the instability is squeezed between the approaching legs, temporarily forming a
double current sheet. The leg – leg reconnection proceeds at a high rate, producing sufficiently strong electric fields that
it would be able to accelerate particles. It may also form plasmoids, or plasmoid-like structures, which trap energetic particles
and propagate out of the reconnection region up to the top of the erupting flux rope along the helical current sheet. The
kinking of a highly twisted flux rope involving leg – leg reconnection can explain key features of an eruptive but partially
occulted solar flare on 18 April 2001, which ejected a relatively compact hard X-ray and microwave source and was associated
with a fast coronal mass ejection. 相似文献
217.
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
218.
M. Kopecký 《Solar physics》1984,93(1):181-187
This article presents a survey of studies incorporating methods of evaluation of Greenwich observations. It also describes some extreme sunspot groups (i.e., groups with a very large area, a very long life, and/or in very high heliographic latitudes); data on the total areas of the largest sunspots are given, and a survey of the parameters concerning individual 11-year cycles, resulting from Greenwich Photoheliographic Results, is presented. 相似文献
219.
Miloš Šidlichovský 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):77-86
The twenty most chaotic objects found among first hundred of numbered asteroids are studied. Lyapunov time calculated with
and without inner planets indicates that for eleven of those asteroids the strongest chaotic effect results from the resonances
with Mars. The filtered semimajor axis displays an abrupt variation only when a close approach to Mars takes place. The study
of the behaviour of the critical argument for candidate resonances can reveal which is responsible for the semimajor axis
variation. We have determined these resonances for the asteroids in question. For the asteroids chaotic even without the inner
planets we have determined the most important resonances with Jupiter, or three-body resonances.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
220.
Jaromír Janský 《Studia Geophysica et Geodaetica》1970,14(4):389-394
Zusammenfassung Den Gegenstand der Arbeit bildet die Berechnung der Amplitudenkurve einer Reflexionswelle für ein bestimmtes gegebenes Medium
anhand der Ersetzung dieses Mediums durch ein horizontal geschichtetes Medium mit einem einfachen Geschwindigkeitsgang in
den Schichten. Die Amplitude wird nach der Nulln?herung der Strahlen-Theorie berechnet.
Address: Ke Karlovu 3, Praha 2. 相似文献
Address: Ke Karlovu 3, Praha 2. 相似文献