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361.
Rapp D Naderi F Neugebauer M Sevilla D Sweetnam D Burnett D Wiens R Smith N Clark B McComas D Stansbery E 《Acta Astronautica》1996,39(1-4):229-238
The Suess-Urey (S-U) mission has been proposed as a NASA Discovery mission to return samples of matter from the Sun to the Earth for isotopic and chemical analyses in terrestrial laboratories to provide a major improvement in our knowledge of the average chemical and isotopic composition of the solar system. The S-U spacecraft and sample return capsule will be placed in a halo orbit around the L1 Sun-Earth libration point for two years to collect solar wind ions which implant into large passive collectors made of ultra-pure materials. Constant Spacecraft-Sun-Earth geometries enable simple spin stabilized attitude control, simple passive thermal control, and a fixed medium gain antenna. Low data requirements and the safety of a Sun-pointed spinner, result in extremely low mission operations costs. 相似文献
362.
D. B. Melrose 《Space Science Reviews》1994,68(1-4):159-170
The theory of electron cyclotron maser emission and its application to solar spike bursts are reviewed. By analogy with the Earth's AKR, three sources of free energy are considered: a loss-cone anisotropy, a velocity-space hole, and a trapped distribution. The problem of how the radiation escapes through the second harmonic absorption layer is emphasized. Harmonic emission due to z mode coalescence may operate for some bursts, but the 2–5s delay between hard X-ray bursts and spike bursts suggests that some other mechanisms is required for most spike bursts. A model involving formation of a trapped distribution in low-density regions neighboring the flaring flux tube is considered. 相似文献
363.
The heating of solar coronal loops by the resonant absorption or phase-mixing of incident wave energy is investigated in the framework of 3D nonlinear magnetohydrodynamics (MHD) by means of numerical simulations. 相似文献
364.
Spectral emission lines created in the solar chromosphere — corona transition region show net red-shifts. It has been proposed that this may be the result of the return of spicular material. We simulate a spicule numerically using the rebound shock model and find that the resulting hydrodynamic evolution leads to a perceived up-flow in transition region spectral lines even though the average velocity in the line forming region is directed downward. The explanation for this apparent paradox is found in the correlation between density and velocity in the waves generated by the rebound shock spicule. 相似文献
365.
O Rasmussen R L Bondar C Baggerud 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(8):189-196
During the 8 day IML-1 mission, regeneration of cell walls and cell divisions in rapeseed protoplasts were studied using the Biorack microscope onboard the Space Shuttle "Discovery". Samples from microgravity and 1g protoplast cultures were loaded on microscope slides. Visual microscopic observations were reported by the payload specialist Roberta Bondar, by down-link video transmission and by use of a microscope camera. Protoplasts grown under microgravity conditions do regenerate cell walls but to a lesser extent than under 1g. Cell divisions are delayed under microgravity. Few cell aggregates with maximum 4-6 cells per aggregate are formed under microgravity conditions, indicating that microgravity may have a profound influence on plant cell differentiation. 相似文献
366.
Joel WM. Parker 《Space Science Reviews》1993,66(1-4):55-59
I Present the results of ground-based and Hubble Space Telescope photometry and spectroscopy of the stars in the central region (roughly 7×7 arcmin) of 30 Doradus in the Large Magellanic Cloud (LMC). Using photometric data for over 2400 stars (complete toV18 mag), and spectroscopic observations of over 150 stars in the region, the best estimate of the initial mass function (IMF) yields a slope of =–1.5±0.2 for masses > 12M, where the Salpeter slope is =–1.35. I compare these results to other measurements of the IMF for OB associations in the Magellanic Clouds. 相似文献
367.
The current state of research involving manifestations of nonlinearity in geomagnetic pulsations is reviewed. Traditionally, the attention of researchers was focused on the effects of resonant interaction of geomagnetic pulsations with small groups of energetic particles, which actually means the study of the quasi-linear relaxation of radiation belt ions, the modulation of auroral electron fluxes, etc. The present review concentrates on the problem of the nonlinear effect influence of pulsations on the backgroud (cold) plasma and on the geomagnetic field. This kind of interaction results in a significant modification of the plasma distribution in the magnetosphere. Self-consistent wave structures—solitons and vortices may occur as well. Such nonlinear effects contribute to physics of geomagnetic pulsations and are also of fundamental importance for general physics. Another set of more narrow problems considered in the review, is related to phenomenological modeling of fluctuational and critical phenomena in the magnetosphere. The essence of our approach is to present the magnetosphere as a black box, whose properties should be determined by the statistical characteristics of its output signals. This approach to phenomenology can be a useful supplement to the methods of microscopic modeling aimed at detecting nonlinear manifestations of geomagnetic pulsations. 相似文献
368.
We describe work that has recently been completed on deriving the fundamental parameters of eight WR stars through the photoionization modelling of their surrounding nebulae using non-LTE WR flux distributions. The resulting effective temperatures range from 57 000–71 000 K for the WN4-5 stars and <30 000–42 000 K for the WN6-8 stars. The derived stellar parameters are compared with those obtained from stellar emission line modelling. We find good agreement for the hot early WN stars, indicating that the non-LTE WR flux distributions have essentially the correct shape in the crucial far-UV region. We find lower temperatures for the four cooler late WN stars, particularly for the two WN6 stars. For the nebulae surrounding these stars, we find that the model flux distributions produce too much nebular ionization. We suggest that these discrepancies arise because of the lack of line-blanketing in the WR atmospheres. For the WO1 central star of G2.4+1.4, with strong nebular He II 4686 A emission, we derive a temperature of 105 000 K, somewhat less than previous estimates. The positions of our eight WR stars on the H-R diagram are compared with the evolutionary tracks of Maeder (1990) for solar metallicity. In common with previous workers, we find that our derived luminosities are too low, giving an initial mass range of 25–40 M, below that expected for the majority of WR stars. 相似文献
369.
We analyse the effects of semi-convection and overshooting on the predicted surface abundances after the first and second dredge-ups in 15 and 20 M Pop. I stars. Overshooting is applied either to the core boundary or to the boundaries of all convective zones. It is shown that the surface abundances are sensitive to the mixing scheme adopted in the interior. The models including semi-convection lead to lower12C/13C ratios than the other mixing schemes, while models with overshooting predict higher enhancements of sodium at the surface. 相似文献
370.
J. Smolinski J. L. Climenhaga Y. Huang Sh. Jiang M. Schmidt O. Stahl 《Space Science Reviews》1993,66(1-4):231-236
The profiles of H observed during the 1970–1992 period in the binary hypergiant HR 8752 (G0 Ia) are presented. We distinguish five typical H profiles designated as A, B, C, D and E types according to the number of emission and absorption features. The profiles of H are complex and contain several emission and absorption components, with: –130 km/s in emission or absorption, –84 km/s in absorption, –49 km/s in emission and about +6 km/s in emission. All of them are rather stable in radial velocities except of the main absorption component in the P Cygni profile with –84 km/s. The frequency of appearance and the periods of duration of the occurrence of the components is discussed. The duration times range between about 3 to 10 months for various components. The red emission component E2 is particularly interesting. Possible explanations of its origin are discussed.A long-term acceleration of the absorption component in the P Cygni profile is found; it can be interpreted as monotonous acceleration of the stellar wind. 相似文献