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191.
Karel A. Van Der Hucht Peter S. Conti Ingemar Lundström Björn Stenholm 《Space Science Reviews》1981,28(3):227-306
This paper presents the Sixth Catalogue of galactic Wolf-Rayet stars (Pop. I), a short history on the five earlier WR catalogues, improved spectral classification, finding charts, a discussion on related objects, and a review of the current status of Wolf-Rayet star research.The appendix presents a bibliography on most of the Wolf-Rayet literature published since 1867.Visiting astronomer, Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory.Visiting astronomer, European Southern Observatory. 相似文献
192.
The role of convection in the core helium flash is simulated by two-dimensional eddies interacting with the thermonuclear runaway. These eddies are followed by the explicit solution of the 2D conservation laws with a 2D finite difference hydrodynamics code. Thus, no phenomenological theory of convection such as the local mixing length theory is required.Our core helium flash is violent, producing a deflagration wave. This differs from the detonation wave (and subsequent disruption of the entire star) produced in previous spherically symmetric violent core helium flashes as the second dimension provides a degree of relief which allows the expansion wave to decouple itself from the burning front. Our results predict that a considerable amount of helium in the core will be burned before the horizontal branch is reached and that some envelope mass loss is likely. 相似文献
193.
Space exploration is an emblematic domain of space activities where traditionally only established space powers have been active. However, new actors are demonstrating great interest in it, principally for international prestige reasons, with an increasing number making ambitious plans. Complementing national endeavours, international cooperation has become a central element of most countries' exploration strategy, since the costs of doing it alone are so great. Europe's development into a fully fledged actor in space exploration requires a shared assessment of the future challenges, threats and opportunities with which it will be confronted in order to derive the best options for cooperation to lead and anticipate rather than follow and endure change. 相似文献
194.
Christopher J. Mertens James M. Russell III Martin G. Mlynczak Chiao-Yao She Francis J. Schmidlin Richard A. Goldberg Manuel López-Puertas Peter P. Wintersteiner Richard H. Picard Jeremy R. Winick Xiaojing Xu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is one of four instruments on NASA’s Thermosphere–Ionosphere–Energetics and Dynamics (TIMED) satellite. SABER measures broadband infrared limb emission and derives vertical profiles of kinetic temperature (Tk) from the lower stratosphere to approximately 120 km, and vertical profiles of carbon dioxide (CO2) volume mixing ratio (vmr) from approximately 70 km to 120 km. In this paper we report on SABER Tk/CO2 data in the mesosphere and lower thermosphere (MLT) region from the version 1.06 dataset. The continuous SABER measurements provide an excellent dataset to understand the evolution and mechanisms responsible for the global two-level structure of the mesopause altitude. SABER MLT Tk comparisons with ground-based sodium lidar and rocket falling sphere Tk measurements are generally in good agreement. However, SABER CO2 data differs significantly from TIME-GCM model simulations. Indirect CO2 validation through SABER-lidar MLT Tk comparisons and SABER-radiation transfer comparisons of nighttime 4.3 μm limb emission suggest the SABER-derived CO2 data is a better representation of the true atmospheric MLT CO2 abundance compared to model simulations of CO2 vmr. 相似文献
195.
Pierre Delage Foivos Karakostas Amine Dhemaied Malik Belmokhtar Philippe Lognonné Matt Golombek Emmanuel De Laure Ken Hurst Jean-Claude Dupla Sharon Kedar Yu Jun Cui Bruce Banerdt 《Space Science Reviews》2017,211(1-4):191-213
In support of the InSight mission in which two instruments (the SEIS seismometer and the \(\mbox{HP}^{3}\) heat flow probe) will interact directly with the regolith on the surface of Mars, a series of mechanical tests were conducted on three different regolith simulants to better understand the observations of the physical and mechanical parameters that will be derived from InSight. The mechanical data obtained were also compared to data on terrestrial sands. The density of the regolith strongly influences its mechanical properties, as determined from the data on terrestrial sands. The elastoplastic compression volume changes were investigated through oedometer tests that also provided estimates of possible changes in density with depth. The results of direct shear tests provided values of friction angles that were compared with that of a terrestrial sand, and an extrapolation to lower density provided a friction angle compatible with that estimated from previous observations on the surface of Mars. The importance of the contracting/dilating shear volume changes of sands on the dynamic penetration of the mole was determined, with penetration facilitated by the \(\sim1.3~\mbox{Mg/m}^{3}\) density estimated at the landing site. Seismic velocities, measured by means of piezoelectric bender elements in triaxial specimens submitted to various isotropic confining stresses, show the importance of the confining stress, with lesser influence of density changes under compression. A power law relation of velocity as a function of confining stress with an exponent of 0.3 was identified from the tests, allowing an estimate of the surface seismic velocity of 150 m/s. The effect on the seismic velocity of a 10% proportion of rock in the regolith was also studied. These data will be compared with in situ data measured by InSight after landing. 相似文献
196.
White Oran R. Fox Peter A. Meisner Randy Rast Mark P. Yasukawa Eric Koon Darryl Rice Crystal Lin Haosheng Kuhn Jeff Coulter Roy 《Space Science Reviews》2000,94(1-2):75-82
Two Precision Solar Photometric Telescopes (PSPT) designed and built at the U.S. National Solar Observatory (NSO) are in operation in Rome and Hawaii. A third PSPT is now in operation the NSO at Sunspot, NM. The PSPT system records full disk solar images at three wavelengths: K line at 393.3 nm and two continua at 409 nm and 607 nm throughout the observing day. We currently study properties of limb darkening, sunspots, and network in these images with particular emphasis on data taken in July and September 1998. During this period, the number of observations per month was high enough to show directional properties of the radiation field surrounding sunspots. We show examples of our PSPT images and describe our study of bright rings around sunspots. 相似文献
197.
要使碳氢燃油在常规燃烧循环中高效燃烧,需要非常高的温度,化学循环燃烧可以为大型动力装置提供一个可行的方法。在化学循环燃烧中,使用含氧介质分子来传输两个氧化还原反应之间的氧气,含氧介质在一个反应中被氧化,在另一个与燃油的反应中被减少。从燃烧残余物中分离出含氧介质可以借助于不同的物态,如果介质用钠、钾或锌,这是液态化学循环燃烧的显著优点。液态化学循环燃烧的原理是能量和熵的循环,在考虑用于分离氮和二氧化碳零部件效率、结合水燃气交换、以及用空气作为氧气源的情况下,高的热效率(35Pa下约75%)在理论上可以达到。 相似文献
198.
W. Coburn P. Kretschmar I. Kreykenbohm V.A. McBride R.E. Rothschild R. Staubert J. Wilms 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2747-2751
The hard X-ray spectra of small subset of accreting pulsars show absorption-like line features in the range 10–100 keV. These lines, referred to as cyclotron lines or cyclotron resonance scattering features, are due to photons scattered out of the line of sight by electrons trapped in the 1012 G pulsar polar cap magnetic field. In this paper we present a review of observations, from the discovery of a cyclotron line in Hercules X-1 to recent results with RXTE and INTEGRAL. 相似文献
199.
Sandra Verhagen Peter J.G. Teunissen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The evolving BeiDou Navigation Satellite System constellation brings new opportunities for high-precision applications. In this contribution the focus will be on one such application, namely precise and instantaneous relative navigation of a formation of LEO satellites. The aim is to assess the ambiguity resolution performance with the future GPS and BeiDou constellations depending on system choice (GPS, BeiDou, or GPS+BeiDou), single- or dual-frequency observations, receiver noise, and uncertainties in ionosphere modelling. In addition, for the GPS+BeiDou constellation it will be shown how the growing BeiDou constellation in the years to come can already bring an important performance improvement compared to the GPS-only case. The performance will be assessed based on the percentage of time that the required precision can be obtained with a partial ambiguity resolution strategy. 相似文献
200.
Peter Dickin 《航空制造技术》2004,(6):110-111
在航空航天工业领域里,一些大型企业应用五轴加工已有很多年了,但是直到现在,这项技术对较小的供应商及工具制造企业的影响还是相当小的。然而,最近许多新的发展使五轴加工的应用变得又经济又容易了,因此很小的公司也对它表现出越来越浓的兴趣。 一方面,五轴加工设备的价格下降,并且有继续下跌的趋势。以前只 相似文献