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The environments of both hot and cool stars are the sites of highly dynamic processes involving motion of gas and plasma in winds, flows across shocks, plasma motions in closed magnetic fields, or streams along magnetospheric accretion funnels. X-ray spectroscopy has opened new windows toward the study of these processes. Kinematics are evident in line shifts and line broadening, and also more indirectly through the analysis and interpretation of density-sensitive lines. In hot stellar winds, expanding-wind kinematics are directly seen in broadened lines although the broadening has turned out to often be smaller than anticipated, and some lines are so narrow that coronal models have been revived. Although X-ray spectra of cool stars have shown line shifts and broadening due to the kinematics of the entire corona, e.g., in binary systems, intrinsic mass motions are challenging to observe at the presently available resolution. Much indirect evidence for mass motion in magnetic coronae is nevertheless available. And finally, spectral diagnostics has also led to a new picture of X-ray production in accreting pre-main sequence stars where massive accretion flows collide with the photospheric gas, producing shocks in which gas is heated to high temperatures. We summarize evidence for the above mechanisms based on spectroscopic data from XMM-Newton and Chandra. 相似文献
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R.G. Ezquer L.A. Scidá Y. Migoya Orué B. Nava M.A. Cabrera C. Brunini 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(7):1803-1818
Using vertical total electron content (VTEC) measurements obtained from GPS satellite signals the capability of the NeQuick 2 and IRI Plas models to predict VTEC over the low latitude and South American sector is analyzed. In the present work both models were used to calculate VTEC up to the height of GPS satellites. Also, comparisons between the performance of IRI Plas and IRI 2007 have been done. The data correspond to June solstice and September equinox 1999 (high solar activity) and they were obtained at nine stations. The considered latitude range extends from 18.4°N to ?64.7°N and the longitude ranges from 281.3°E to 295.9°E in the South American sector. The greatest discrepancies among model predictions and the measured VTEC are obtained at low latitudes stations placed in the equatorial anomaly region. Underestimations as strong as 40?TECU [1?TECU?=?1016?m?2] can be observed at BOGT station for September equinox, when NeQuick2 model is used. The obtained results also show that: (a) for June solstice, in general the performance of IRI Plas for low latitude stations is better than that of NeQuick2 and, vice versa, for highest latitudes the performance of NeQuick2 is better than that of IRI Plas. For the stations TUCU and SANT both models have good performance; (b) for September equinox the performances of the models do not follow a clearly defined pattern as in the other season. However, it can be seen that for the region placed between the Northern peak and the valley of the equatorial anomaly, in general, the performance of IRI Plas is better than that of NeQuick2 for hours of maximum ionization. From TUCU to the South, the best TEC predictions are given by NeQuick2.The source of the observed deviations of the models has been explored in terms of CCIR foF2 determination in the available ionosonde stations in the region. Discrepancies can be also related to an unrealistic shape of the vertical electron density profile and or an erroneous prediction of the plasmaspheric contribution to the vertical total electron content. Moreover, the results of this study could be suggesting that in the case of NeQuick, the underestimation trend could be due to the lack of a proper plasmaspheric model in its topside representation. In contrast, the plasmaspheric model included in IRI, leads to clear overestimations of GPS derived TEC. 相似文献
106.
C. S. Arridge N. Andr�� C. L. Bertucci P. Garnier C. M. Jackman Z. N��meth A. M. Rymer N. Sergis K. Szego A. J. Coates F. J. Crary 《Space Science Reviews》2011,162(1-4):25-83
The formation of Titan??s induced magnetosphere is a unique and important example in the solar system of a plasma-moon interaction where the moon has a substantial atmosphere. The field and particle conditions upstream of Titan are important in controlling the interaction and also play a strong role in modulating the chemistry of the ionosphere. In this paper we review Titan??s plasma interaction to identify important upstream parameters and review the physics of Saturn??s magnetosphere near Titan??s orbit to highlight how these upstream parameters may vary. We discuss the conditions upstream of Saturn in the solar wind and the conditions found in Saturn??s magnetosheath. Statistical work on Titan??s upstream magnetospheric fields and particles are discussed. Finally, various classification schemes are presented and combined into a single list of Cassini Titan encounter classes which is also used to highlight differences between these classification schemes. 相似文献
107.
Navigational aids impair spatial memory for experienced environments, but the cognitive mechanisms underlying impairment remain an open question. Recent evidence implicates divided attention, but to date no study has directly manipulated divided attention in navigational aid contexts. The present study addresses this need. Participants navigated virtual towns with aid presence and divided attention factorially crossed in a within-participants design. They then completed spatial memory assessments. Divided attention alone impaired spatial memory. Navigational aid presence impaired spatial memory when attention was undivided, replicating previous findings, but did not to a greater extent when attention was divided. These findings suggest that navigational aids divide attention sufficiently to impair spatial memory. 相似文献
108.
V. M. Gureev E. B. Mats V. N. Ivanova M. V. Gureev D. A. Malyshkin Yu. R. Agalakov 《Russian Aeronautics (Iz VUZ)》2013,56(2):179-184
In this paper, a layout of an electric power plant that uses the gas turbine engine as a source of energy is presented. We give also the numerical analysis of this power plant and show its high efficiency. 相似文献
109.
André Balogh Andrei Bykov Peter Cargill Richard Dendy Thierry Dudok de Wit John Raymond 《Space Science Reviews》2013,178(2-4):77-80
With the maturing of space plasma research in the solar system, a more general approach to plasma physics in general, applied to cosmic plasmas, has become appropriate. There are both similarities and important differences in describing the phenomenology of space plasmas on scales from the Earth’s magnetosphere to galactic and inter-galactic scales. However, there are important aspects in common, related to the microphysics of plasma processes. This introduction to a coordinated collection of papers that address the several aspects of the microphysics of cosmic plasmas that have unifying themes sets out the scope and ambition of the broad sweep of topics covered in the volume, together with an enumeration of the detailed objectives of the coverage. 相似文献
110.
Émilie Hardy Agnès Levy Gilles Métris Manuel Rodrigues Pierre Touboul 《Space Science Reviews》2013,180(1-4):177-191
The MICROSCOPE space mission aims at testing the Equivalence Principle (EP) with an accuracy of 10?15. The test is based on the precise measurement delivered by a differential electrostatic accelerometer on-board a drag-free microsatellite which includes two cylindrical test masses submitted to the same gravitational field and made of different materials. The experiment consists in testing the equality of the electrostatic acceleration applied to the masses to maintain them relatively motionless at a well-known frequency. This high precision experiment is compatible with only very little perturbations. However, aliasing arises from the finite time span of the measurement, and is amplified by measurement losses. These effects perturb the measurement analysis. Numerical simulations have been run to estimate the contribution of a perturbation at any frequency on the EP violation frequency and to test its compatibility with the mission specifications. Moreover, different data analysis procedures have been considered to select the one minimizing these effects taking into account the uncertainty about the frequencies of the implicated signals. 相似文献