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791.
T. Kohout A. Kallonen J.‐P. Suuronen P. Rochette A. Hutzler J. Gattacceca D. D. Badjukov R. Skála V. Böhmová J. Čuda 《Meteoritics & planetary science》2014,49(7):1157-1170
X‐ray microtomography (XMT), X‐ray diffraction (XRD), and magnetic hysteresis measurements were used to determine micrometeorite internal structure, mineralogy, crystallography, and physical properties at μm resolution. The study samples include unmelted, partially melted (scoriaceous), and completely melted (cosmic spherules) micrometeorites. This variety not only allows comparison of the mineralogy and porosity of these three micrometeorite types but also reveals changes in meteoroid properties during atmospheric entry at various velocities. At low entry velocities, meteoroids do not melt and their physical properties do not change. The porosity of unmelted micrometeorites varies considerably (0–12%) with one friable example having porosity around 50%. At higher velocities, the range of meteoroid porosity narrows, but average porosity increases (to 16–27%) due to volatile evaporation and partial melting (scoriaceous phase). Metal distribution seems to be mostly unaffected at this stage. At even higher entry velocities, complete melting follows the scoriaceous phase. Complete melting is accompanied by metal oxidation and redistribution, loss of porosity (1 ± 1%), and narrowing of the bulk (3.2 ± 0.5 g cm?3) and grain (3.3 ± 0.5 g cm?3) density range. Melted cosmic spherules with a barred olivine structure show an oriented crystallographic structure, whereas other subtypes do not. 相似文献
792.
Zsolt Kővári Katalin Oláh János Bartus Klaus G. Strassmeier Michael Weber Albert Washuettl John B. Rice Szilárd Csizmadia 《Astrophysics and Space Science》2006,304(1-4):375-377
Doppler images are presented for the RS CVn-type binary ζ And. Our upgraded Doppler imaging code TempMapε takes into account the distorted geometry of the primary giant component. On the maps several low latitude spots are restored with a temperature contrast of about 1000 K. Some weak polar features are also found. Cross-correlation of the consecutive Doppler-maps suggests solar-like differential surface rotation. 相似文献
793.
D. Chochol T. Pribulla M. Vaňko P. Mayer M. Wolf P. G. Niarchos K. D. Gazeas V. N. Manimanis L. Brát M. Zejda 《Astrophysics and Space Science》2006,304(1-4):93-96
Orbital period changes of the eclipsing binaries GO Cyg and GW Cep are explained by the light-time effect for the first time. New minima of the eclipsing binary AR Aur improve the predicted light-time orbit. The light-time orbit with the quadratic ephemeris of the binary matches the new observations of V505 Sgr better than the linear one. As the light-time effect fits in corresponding O − C diagrams of all four systems have been reaching extreme values, the observations of minima times in forthcoming years are highly desirable. 相似文献
794.
Michael Friedjung Andrej Dobrotka Alon Retter Ladislav Hric Rudolf Novák 《Astrophysics and Space Science》2006,304(1-4):317-319
Our mainly R band photometry of V1493 Aql (1999) during its outburst, indicates periodic variations with a period of 0.156 days, seen only 5 days after the maximum in V. This period can be orbital. The light curve indicates in addition, the presence of a faint eclipse like feature. We try to explain its extremely low amlitude, as being due to the eclipse of an expanded white dwarf component of the binary below an optically thick wind. We discuss what conditions would be required for such an interpretation to work. 相似文献
795.
Shocks propagating in the interstellar medium (ISM) play an important role in the life of molecular clouds. Through a theoretical study of interaction between clouds and shocks we can understand, for example, the density distribution of observed molecular clouds and the first steps of star formation. The only way to study of interaction in detail is via a numerical hydrodynamical simulation. In this paper we present the first results of a hydrocode which is able to follow the processes after the collision between the cloud and shock front.Our main theoretical result is that the chemical processes (e.g. H2 dissociation) can affect the dynamical processes significantly. Global parameters of the cloud are calculated for the comparision of the simulation and the observations. 相似文献
796.
M. Jurado Vargas P. Merchán Benítez F. Sánchez Bajo A. Astillero Vivas 《Astrophysics and Space Science》2002,279(3):261-269
In order to determine the atmospheric extinction at Physics Department Astronomical Observatory of the University of Extremadura, located at Badajoz (Spain), several stars were observed during some clear nights of atmospheric stability in the period 1998–2000, at optical wavelengths corresponding to the filters of the Kron-Cousins and Strömgren photometric systems. The determination of the extinction coefficients was made by assuming the Bouguer's law, which was shown to be a good approximation for this study. The results exhibited temporal variations and can be considered to be associated with clean atmospheres at locations of low altitude. 相似文献
797.
798.
799.
The SMF algorithms were recently developed by the authors as a multistep generalization of the ScheifeleG-functions one-step method. Like the last, the proposed codes integrate harmonic oscillations without truncation error and the perturbing parameter appears as a factor of that error when integrating perturbed oscillations. Therefore they seemed to be convenient for the accurate integration of orbital problems after the application of linearizing transformations, such as KS or BF. In this paper we present several numerical experiments concerning the propagation of Earth satellite orbits, that illustrate the performance of the the SMF method. In general, it provides greater accuracy than the usual standard algorithms for similar computational cost. 相似文献
800.
F. J. Sánchez-Salcedo 《Astrophysics and Space Science》1997,249(2):223-226
The arguments against the magnetic alternative given by Katz (1994) are discussed. Our conclusion is that the major problem
regarding this alternative to dark matter is the flaring of the disk as suggested by Cuddeford and Binney (1993). We propose
that the study of the equilibrium in the vertical direction should be carried out in dwarf spirals. Magnetic tension could
alter the rotation curve of spiral galaxies but is not able to eliminate the necessity of dark matter.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献