排序方式: 共有26条查询结果,搜索用时 218 毫秒
21.
Von R. Eshleman David P. Hinson Gunnar F. Lindal G. Leonard Tyler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1987,7(12):29-32
Measurements of radio waves that have propagated through planetary atmospheres have provided exploratory results on atmospheric constituents, structure, dynamics, and ionization for Venus, Mars, Titan, Jupiter, Saturn, and Uranus. Highlights of past results are reviewed in order to define and illustrate the potential of occultation and related radio studies in future planetary missions. 相似文献
22.
R. A. Leske R. A. Mewaldt A. C. Cummings J. R. Cummings E. C. Stone T. T. Von Rosenvinge 《Space Science Reviews》1996,78(1-2):149-154
Measurements of the anomalous cosmic ray (ACR) isotopic composition have been made in three regions of the magnetosphere accessible from the polar Earth orbit of SAMPEX, including the interplanetary medium at high latitudes and geomagnetically trapped ACRs. At those latitudes where ACRs can penetrate the Earth's magnetic field while fully stripped galactic cosmic rays (GCRs) of similar energies are excluded, a pure ACR sample is observed to have the following composition: 15N/N < 0.023, 18O/16O < 0.0034, and 22Ne/20Ne = 0.077(+0.085, –0.023). We compare our values with those found by previous investigators and with those measured in other samples of solar and galactic material. In particular, a comparison of 22Ne/20Ne measurements from various sources implies that GCRs are not simply an accelerated sample of the local interstellar medium. 相似文献
23.
A 14 days ground based primate hypokinesia investigation was conducted to determine what changes, if any, in bone strength may be demonstrated following 2 weeks cast immobilization and at 14 davs after removal from casts. Controlled compressive loads were applied to vertebral bodies excised from control, 2 weeks immobilization and 2 weeks post immobilization Rhesus monkeys. The material properties reported herein are ultimate load, displacement to ultimate load, stiffness and energy to ultimate load. These results show a decrease in bone strength following immobilization and a still further decrease in bone strength after 14 days. 相似文献
24.
The ESA/NASA spacecraft Ulysses is making, for the first time, direct measurements in the solar wind originating from virtually all places where the corona expands. Since the initial two polar passes of Ulysses occur during relatively quiet solar conditions, we discuss here the three main regimes of quasi-stationary solar wind flow: the high speed streams (HSSTs) coming out of the polar coronal holes, the slow solar wind surrounding the HSSTs, and the streamers which occur at B-field reversals. Comparisons between H- maps and data taken by Ulysses demonstrate that as a result of super-radial expansion, the HSSTs occupy a much larger solid angle than that derived from radial projections of coronal holes. Data obtained with SWICS-Ulysses confirm that the strength of the FIP effect is much reduced in the HSSTs. The systematics in the variations of elemental abundances becomes particularly clear, if these are plotted against the time of ionisation (at the solar surface) rather than against the first ionisation potential (FIP). We have used a superposed-epoch method to investigate the changes in solar wind speed and composition measured during the 9-month period in 1992/93 when Ulysses regularly passed into and out of the southern HSST. We find that the patterns in the variations of the Mg/O and O7+/O6+ ratios are virtually identical and that their transition from high to low values is very steep. Since the Mg/O ratio is controlled by the FIP effect and the O7+/O6+ ratio reflects the coronal temperature, this finding points to a connection between chromospheric and coronal conditions. 相似文献
25.
G. H. R. Von Koenigswald 《Space Science Reviews》1964,3(3):433-446
Tektites are bodies of natural glass of limited size and of typical shape and sculpturing. They occur in relatively large numbers in limited strewn-fields, each formed by a single event in the geological past. Three (perhaps four) tektite fields are known, all of different age. Perhaps only the youngest-the indoaustralian strewn-field, reaching from Thailand to Tasmania — in its original extension, the others having suffered from erosion.Many tektites from Indonesia and all from Australia show two periods of melting, which must be regarded as proof of extraterrestrial origin. These secondary forms with rims or flanges, developed by ablation in the earth's atmosphere, probably depend upon a low entry angle and are therefore only represented from certain regions.Tektites consist for about 70–80% of silica, show fluidal texture, no traces of crystallization and a remarkably low water content. From a chemical point of view they resemble certain terrestrial rocks more than true meteorites. Probably they represent molten parts from the moon's surface, which were thrown into space after the impact of large meteorites. 相似文献
26.
Robert F. Wimmer-Schweingruber Rudolf Von Steiger Johannes Geiss George Gloeckler Fred M. Ipavich Berend Wilken 《Space Science Reviews》1998,85(1-2):387-396
Recent observations with UVCS on SOHO of high outflow velocities of O5+ at low coronal heights have spurred much discussion about the dynamics of solar wind acceleration. On the other hand, O6+ is the most abundant oxygen charge state in the solar wind, but is not observed by UVCS or by SUMER because this helium-like
ion has no emission lines falling in the wave lengths observable by these instruments. Therefore, there is considerable interest
in observing O5+ in situ in order to understand the relative importance of O5+ with respect to the much more abundant O6+. High speed streams are the prime candidates for the search for O5+ because all elements exhibit lower freezing-in temperatures in high speed streams than in the slow solar wind. The Ulysses
spacecraft was exposed to long time periods of high speed streams during its passage over the polar regions of the Sun. The
Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is capable of resolving this rare oxygen charge state. We present
the first measurement of O5+ in the solar wind and compare these data with those of the more abundant oxygen species O6+ and O7+. We find that our observations of the oxygen charge states can be fitted with a single coronal electron temperature in the
range of 1.0 to 1.2 MK assuming collisional ionization/recombination equilibrium with an ambient Maxwellian electron gas.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献