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241.
The composition of the solar photosphere is believed to be uniform. Indeed a quantity that does not vary with solar surface
location or with a particular solar feature, i.e., no observational evidence is available to indicate that the photospheric
composition near the solar equator is different from the photospheric composition near the solar poles or that the photospheric
composition in quiet regions is different from the composition in active regions. In contrast, the composition of the solar
upper atmosphere is not well defined. Solar composition work in recent decades has brought the recognition that there are
systematic differences between the composition of the corona and the photosphere and revealed evidence for spatial and time
variability in the composition of various coronal features. We review the spectroscopic techniques used and the progress that
was made in recent years in deriving the plasma compositions of various solar upper atmosphere structures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
242.
S. Patsourakos J.-C. Vial J.-R. Gabryl S. Koutchmy U. Schühle 《Space Science Reviews》1999,87(1-2):291-294
Polar coronal holes represent the most convincing site from which the high-speed solar wind originates. Here we report high-accuracy Doppler shifts measured in the O VI (1037.6 Å) line obtained by SUMER on SOHO inside an interplume region within the south polar coronal hole. We infer limits on the outflow velocity and draw hints about the flow geometry. 相似文献
243.
244.
The European Space Agency (ESA) has decided to carry out a fly-by mission to the comet Halley. The spacecraft will be launched by an ARIANE II and intercept the retrograde Halley orbit on 13 March, 1986. One group of experiments is designed to obtain data on size, mass and composition of the dust in the cometary tail. Because of the very high relative velocity during fly-by (69 km/s) laboratory experiments are necessary to develop and calibrate the experiments. These experiments are presently under way in the laboratory of the Lehrstuhl für Raumfahrttechnik of the Technische Universität München. First results have been obtained for both the Dust Impact Detection System (DIDSY) and the P?articulate Impact Analyzer (PIA). These results are compared with the theoretical models for hypervelocity impact craters. The agreement is good at impact velocities around 15 km/s. 相似文献
245.
基于生产成本的作业调度 总被引:1,自引:0,他引:1
提出了一个基于净现值的调度指标,该指标充分考虑到影响调度决策的各项费用.如在制品库存费用、机床工时费、直接工人的工资、工件提前或拖期完工造成的损失等。然后以遗传算法为工具,研究了作业调度问题,设计了一种很实用的算法。该算法采用基于工序的编码方法把调度编码成染色体,并通过遗传操作来搜索最佳染色体。解码算法根据工序在染色体中的次序和最短加工时间一紧迫度规则得到调度。仿真结果表明该方法是可行的。并有一定的优越性。 相似文献
246.
V.V. Mishin V.M. Mishin Z. Pu S.B. Lunyushkin L.A. Sapronova U. Sukhbaatar D.G. Baishev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The magnetic flux of tail lobes Ψ is divided in two parts of comparable values Ψ1 and Ψ02, with the first that appears during substorm and the second, observed before substorm start. The first was named “new magnetic flux”, the second – “old magnetic flux”. The first, Ψ1, is known to play a definitive role in the energy transport from the solar wind into the magnetosphere-ionosphere-atmosphere system, but the role of Ψ02 in this transport is not well known. From the 27 August 2001 substorm data we study the involvement in the above transport process of the old flux Ψ02. This involvement is observed in the polar cap (PC) area, which existed prior to the substorm and is called respectively “the old PC”. In this study, as distinct from earlier works, we use the balance equation of the energy stored in magnetosphere and energy consumed. Activation of the old PC magnetic flux Ψ02 was found to increase the energy input by ∼85% in the event under consideration. 相似文献
247.
W.M. Moslem S. Rezk U.M. Abdelsalam S.K. El-Labany 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(8):2190-2197
This paper introduces an investigation of shocklike soliton or small amplitude Double Layers (DLs) in a collisionless plasma, consisting of positive and negative ions, nonthermal electrons, as well as solar wind streaming protons and electrons. Gardner equation is derived and its shocklike soliton solution is obtained. The model is employed to recognize a possible nonlinear wave at Venus ionosphere. The results indicate that the number densities and velocities of the streaming particles play crucial role to determine the polarity and characteristic features (amplitude and width) of the shocklike soliton waves. An electron streaming speed modifies a negative shocklike wave profile, while an ion streaming speed modulates a positive shocklike wave characteristic. 相似文献
248.
C.J. Rodriguez-Solano U. HugentoblerP. Steigenberger G. Allende-Alba 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
During Sun-Earth eclipse seasons, GPS-IIA satellites perform noon, shadow and post-shadow yaw maneuvers. If the yaw maneuvers are not properly taken into account in the orbit determination process, two problems appear: (1) the observations residuals increase since the modeled position of the satellite’s navigation antenna differs from the true position, and (2) the non-conservative forces like solar radiation pressure or Earth radiation pressure are mismodeled due to the wrong orientation of the satellite’s surfaces in space. 相似文献
249.
The Dawn Framing Camera 总被引:1,自引:0,他引:1
H. Sierks H. U. Keller R. Jaumann H. Michalik T. Behnke F. Bubenhagen I. B��ttner U. Carsenty U. Christensen R. Enge B. Fiethe P. Guti��rrez Marqu��s H. Hartwig H. Kr��ger W. K��hne T. Maue S. Mottola A. Nathues K.-U. Reiche M. L. Richards T. Roatsch S. E. Schr?der I. Szemerey M. Tschentscher 《Space Science Reviews》2011,163(1-4):263-327
The Framing Camera (FC) is the German contribution to the Dawn mission. The camera will map 4 Vesta and 1 Ceres through a clear filter and 7 band-pass filters covering the wavelengths from the visible to the near-IR. The camera will allow the determination of the physical parameters of the asteroids, the reconstruction of their global shape as well as local topography and surface geomorphology, and provide information on composition via surface reflectance characteristics. The camera will also serve for orbit navigation. The resolution of the Framing Camera will be up to 12 m per pixel in low altitude mapping orbit at Vesta (62 m per pixel at Ceres), at an angular resolution of 93.7 ??rad?px?1. The instrument uses a reclosable front door to protect the optical system and a filter-wheel mechanism to select the band-pass for observation. The detector data is read out and processed by a data processing unit. A power converter unit supplies all required power rails for operation and thermal maintenance. For redundancy reasons, two identical cameras were provided, both located side by side on the +Z-deck of the spacecraft. Each camera has a mass of 5.5 kg. 相似文献
250.
P. Jakobsson D. Malesani J. Hjorth J.P.U. Fynbo B. Milvang-Jensen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We describe the current status and recent results from our Swift/VLT legacy survey, a VLT Large Programme aimed at characterizing the host galaxies of a homogeneously selected sub-sample of Swift GRBs. The immediate goals are to determine the host luminosity function, study the effects of reddening, determine the fraction of Lyα emitters in the hosts, and obtain redshifts for targets without a reported one. The main effort so far has been the definition of a very carefully selected sample, obeying strict and well-defined criteria: 68 targets in total. Among the preliminary results is a large optical detection rate, the lack of extremely red objects (only one possible case in the sample) and an update of the Swift GRB redshift distribution with 〈z〉∼2.0. 相似文献