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611.
T. Blöcker H. Holweger B. Freytag F. Herwig H.-G. Ludwig M. Steffen 《Space Science Reviews》1998,85(1-2):105-112
Based on radiation hydrodynamics modeling of stellar convection zones, a diffusion scheme has been devised describing the
downward penetration of convective motions beyond the Schwarzschild boundary (overshoot) into the radiative interior. This
scheme of exponential diffusive overshoot has already been successfully applied to AGB stars. Here we present an application
to the Sun in order to determine the time scale and depth extent of this additional mixing, i.e. diffusive overshoot at the
base of the convective envelope. We calculated the associated destruction of lithium during the evolution towards and on the
main-sequence. We found that the slow-mixing processes induced by the diffusive overshoot may lead to a substantial depletion
of lithium during the Sun's main-sequence evolution.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
612.
The Radarsat Earth-observation satellite was launched on November 4, 1995 aboard a Delta 2 rocket. Equipped with a sophisticated synthetic aperture radar (SAR), Radarsat can produce images of extraordinary clarity even through clouds, smog, haze, smoke, and darkness. The SAR has a variety of operating modes. It can be adjusted to produce swathes between 35 and 500 km in width, with ground resolutions from 100 m to as low as eight. In addition, the beam can be steered at angles up to 49° from the satellite's nadir vector, giving it the unique ability to image areas it is not directly overflying. In exchange for the launch, CSA agreed to provide NASA with access to the SAR data, and to execute a 180° yaw-around of Radarsat twice during its lifetime to map the Antarctic continent. Preliminary results from the first of these Antarctic Mapping Missions, dubbed AMM-1, are presented 相似文献
613.
Ch. I. Chaban R. T. Ripetskyj E. L. Kordyum N. A. Kit 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(12):2011-2016
Under gravistimulation, dark-grown protonemata of Pottia intermedia revealed negative gravitropism with a growth rate of approximately 28 μm·h−1 at room temperature (20 °C). In 7 days, the protonema formed a bundle of vertically oriented filaments. At an elevated temperature (30 °C), bundles of vertically growing filaments were also formed. However, both filament growth rate and amplitude of the gravicurvature were reduced. Red light (RL) irradiation induced a positive phototropism of most apical protonemal cells at 20 °C. In a following period of darkness, approximately two-thirds of such cells began to grow upward again, recovering their negative gravitropism. RL irradiation at the elevated temperature caused a partial increase in the number of protonemal cells with negative phototropism, but the protonemata did not exhibit negative gravitropism after transfer to darkness. The negative gravitropic reaction was renewed only when protonemata were placed at 20 °C. A dramatic decrease in starch amount in protonemal apical cells, which are sensitive to both gravity and light, occurred at the higher temperature. Such a decrease may be one of the reasons for the inhibition of the protonemal gravireaction at the higher temperature. The observation has a bearing on the starch-statolith theory. 相似文献
614.
Jao J.K. Lee C.F. Ayasli S. Haywiser E.J. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(6):5-9
In July and October 1995, a large-scale airborne SAR experiment was conducted in the Yuma Proving Ground, Yuma, Arizona, to investigate ground penetration radar phenomenology and buried target detection. This paper describes the Yuma experiment and measurement results for many tactical, utility, and environmental targets deployed in the test 相似文献
615.
E. N. Parker 《Space Science Reviews》1962,1(1):62-99
This paper is intended as a critical review of current ideas concerning the mechanisms responsible for the geomagnetic storm.The dynamical theory of the geomagnetic storm phenomenon is formulated as a problem in elasticity. The observed variations in the field are the strains produced by particle stresses exerted by gases in interplanetary space, by gases enmeshed in the field, and by the gases in the ionosphere. The stresses exerted by interplanetary gases are principally inward, resulting in the initial phase increase of the horizontal component. The stresses exerted by gases enmeshed in the field are principally outward, resulting in the main phase decrease of the horizontal component. The transient sudden commencement is a hydromagnetic wave phenomenon.The main phase is most simply explained by the shock heating of the ions to kev energies at 3 – 5 R
E
during the active phase of the storm. The recovery follows then from charge exchange with the ambient neutral hydrogen. The predicted more rapid recovery at sunspot minimum has been verified observationally.This work was supported by the National Aeronautics and Space Administration under grant NASA-NsG-96-60. 相似文献
616.
Active Spacecraft Potential Control Investigation 总被引:1,自引:0,他引:1
K. Torkar R. Nakamura M. Tajmar C. Scharlemann H. Jeszenszky G. Laky G. Fremuth C. P. Escoubet K. Svenes 《Space Science Reviews》2016,199(1-4):515-544
617.
Functional analysis is a methodology for analyzing the mission and performance requirements of a system, and translating them into discrete activities or tasks which must be performed by the system. Determination of the system's functionality is the first step in obtaining a conceptual view of a system that is to be designed. The methodology for conducting functional analysis is developed, some of the tools used to support the activity are described, including examples to help solidify the concepts presented 相似文献
618.
619.
N S Pechurkin A V Brilkov V V Ganusov T V Kargatova E E Maksimova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(3):335-341
The possibility of introducing genetically engineered microorganisms (GEM) into simple biotic cycles of laboratory water microcosms was investigated. The survival of the recombinant strain Escherichia coli Z905 (Apr, Lux+) in microcosms depends on the type of model ecosystems. During the absence of algae blooming in the model ecosystem, the part of plasmid-containing cells E. coli decreased fast, and the structure of the plasmid was also modified. In conditions of algae blooming (Ankistrodesmus sp.) an almost total maintenance of plasmid-containing cells was observed in E. coli population. A mathematics model of GEM's behavior in water ecosystems with different level of complexity has been formulated. Mechanisms causing the difference in luminescent exhibition of different species are discussed, and attempts are made to forecast the GEM's behavior in water ecosystems. 相似文献
620.