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11.
K. Schindler 《Space Science Reviews》1975,17(2-4):589-614
12.
There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this
way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment.
Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their
time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a
single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and
environmental properties. 相似文献
13.
Modern hydrodynamical simulations offer nowadays a powerful means to trace the evolution of the X-ray properties of the intra-cluster
medium (ICM) during the cosmological history of the hierarchical build up of galaxy clusters. In this paper we review the
current status of these simulations and how their predictions fare in reproducing the most recent X-ray observations of clusters.
After briefly discussing the shortcomings of the self-similar model, based on assuming that gravity only drives the evolution
of the ICM, we discuss how the processes of gas cooling and non-gravitational heating are expected to bring model predictions
into better agreement with observational data. We then present results from the hydrodynamical simulations, performed by different
groups, and how they compare with observational data. As terms of comparison, we use X-ray scaling relations between mass,
luminosity, temperature and pressure, as well as the profiles of temperature and entropy. The results of this comparison can
be summarised as follows: (a) simulations, which include gas cooling, star formation and supernova feedback, are generally successful in reproducing the
X-ray properties of the ICM outside the core regions; (b) simulations generally fail in reproducing the observed “cool core” structure, in that they have serious difficulties in
regulating overcooling, thereby producing steep negative central temperature profiles. This discrepancy calls for the need
of introducing other physical processes, such as energy feedback from active galactic nuclei, which should compensate the
radiative losses of the gas with high density, low entropy and short cooling time, which is observed to reside in the innermost
regions of galaxy clusters. 相似文献
14.
C. Ferrari F. Govoni S. Schindler A. M. Bykov Y. Rephaeli 《Space Science Reviews》2008,134(1-4):93-118
We review observations of extended regions of radio emission in clusters; these include diffuse emission in ‘relics’, and
the large central regions commonly referred to as ‘halos’. The spectral observations, as well as Faraday rotation measurements
of background and cluster radio sources, provide the main evidence for large-scale intracluster magnetic fields and significant
densities of relativistic electrons. Implications from these observations on acceleration mechanisms of these electrons are
reviewed, including turbulent and shock acceleration, and also the origin of some of the electrons in collisions of relativistic
protons by ambient protons in the (thermal) gas. Improved knowledge of non-thermal phenomena in clusters requires more extensive
and detailed radio measurements; we briefly review prospects for future observations. 相似文献
15.
边界层吸气对压气机叶栅角区分离损失的控制 总被引:1,自引:0,他引:1
压气机角区的大范围回流通常会引起叶片通道中的三维阻塞现象,并伴随有强烈的掺混流动损失。采用德国航空航天中心(DLR)开发的TRACE程序,在其推进技术研究所的高速压气机叶栅试验台(包含5个NACA65K48直叶片)上,研究了位于端壁上的边界层吸气措施——叶片弦中近尾缘吸气槽(MTE)对该直压气机叶栅通道的角区分离进行控制,减小二次流动损失,进而削弱其对总损失的影响。通过基于定常雷诺平均Navier-Stokes(RANS)方法的数值模拟研究与相应的试验研究对比,端壁边界层吸气能够较好地重新组织角区气流流动,减弱附着于叶片吸力面尾缘的集中脱落涡,使得角区分离涡强度显著降低,由此引起的二次流损失也明显降低,与无吸气状态相比最大降幅可达81.2%;在设计状态下采用吸气流量率为1%的MTE,总压损失有很大程度的降低:在数值计算中,降幅为15.2%;试验测量中为9.7%。 相似文献
16.
J. S. Kaastra A. M. Bykov S. Schindler J. A. M. Bleeker S. Borgani A. Diaferio K. Dolag F. Durret J. Nevalainen T. Ohashi F. B. S. Paerels V. Petrosian Y. Rephaeli P. Richter J. Schaye N. Werner 《Space Science Reviews》2008,134(1-4):1-6
We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together
to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of
galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the
“missing baryon” problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic
medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and
clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and
discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists
wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations. 相似文献
17.
18.
Andrew J. Ball Stephan Ulamec Bernd Dachwald Michael E. Price Riccardo Nadalini Benjamin Luethi Stephen D. Wolters Simon Sheridan Simon F. Green John C. Zarnecki Paolo D’Arrigo Karsten Seiferlin Günter Kargl Nils Goerke 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
We present a concept for a challenging in situ science mission to a primitive, binary near-Earth asteroid. A sub-400-kg spacecraft would use solar electric propulsion to rendezvous with the C-class binary asteroid (175706) 1996 FG3. A campaign of remote observations of both worlds would be followed by landing on the ∼1 km diameter primary to perform in situ measurements. The total available payload mass would be around 34 kg, allowing a wide range of measurement objectives to be addressed. This mission arose during 2004 from the activities of the ad-hoc Small Bodies Group of the DLR-led Planetary Lander Initiative. Although the particular mission scenario proposed here was not studied further per se, the experience was carried over to subsequent European asteroid mission studies, including first LEONARD and now the Marco Polo near-Earth asteroid sample return proposal for ESA’s Cosmic Vision programme. This paper may thus be of interest as much for insight into the life cycle of mission proposals as for the concept itself. 相似文献
19.
N. Werner F. Durret T. Ohashi S. Schindler R. P. C. Wiersma 《Space Science Reviews》2008,134(1-4):337-362
Because of their deep gravitational potential wells, clusters of galaxies retain all the metals produced by the stellar populations
of the member galaxies. Most of these metals reside in the hot plasma which dominates the baryon content of clusters. This
makes them excellent laboratories for the study of the nucleosynthesis and chemical enrichment history of the Universe. Here
we review the history, current possibilities and limitations of the abundance studies, and the present observational status
of X-ray measurements of the chemical composition of the intra-cluster medium. We summarise the latest progress in using the
abundance patterns in clusters to put constraints on theoretical models of supernovae and we show how cluster abundances provide
new insights into the star-formation history of the Universe. 相似文献
20.
Tilman Spohn Karsten Seiferlin Axel Hagermann Jörg Knollenberg Andrew J. Ball Marek Banaszkiewicz Johannes Benkhoff Stanislaw Gadomski Wojciech Gregorczyk Jerzy Grygorczuk Marek Hlond Günter Kargl Ekkehard Kührt Norbert Kömle Jacek Krasowski Wojciech Marczewski John C. Zarnecki 《Space Science Reviews》2007,128(1-4):339-362
MUPUS, the multi purpose sensor package onboard the Rosetta lander Philae, will measure the energy balance and the physical parameters in the near-surface layers – up to about 30 cm depth- of the
nucleus of Rosetta’s target comet Churyumov-Gerasimenko. Moreover it will monitor changes in these parameters over time as
the comet approaches the sun. Among the parameters studied are the density, the porosity, cohesion, the thermal diffusivity
and conductivity, and temperature. The data should increase our knowledge of how comets work, and how the coma gases form.
The data may also be used to constrain the microstructure of the nucleus material. Changes with time of physical properties
will reveal timescales and possibly the nature of processes that modify the material close to the surface. Thereby, the data
will indicate how pristine cometary matter sampled and analysed by other experiments on Philae really is. 相似文献