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311.
Effect of Processing and Composition on the Structure and Properties of P/M EP741NP Type Alloys 总被引:1,自引:0,他引:1
A study was carried out on the effects of processing and composition on the structure and properties of P/M EP741NP type alloys. The objectives of this study were to understand the role of Hf in a P/M superalloy containing high niobium used in aircraft engines and to determine the effects of extrusion and forging the powders as contrasted to HIPing (hot isostatic pressing) only. Two alloys of the P/M EP741NP composition were atomized: one alloy contained 0.26%Hf and the other was Hf free. After the as-atomized powders from both alloys were characterized, the powders were extruded into billets, forged and heat treated. After each process, the microstructures were characterized by SEM and the phases were extracted and identified by X-ray diffraction. The presence of Hf in the residues was probed by EDS (energy dispersive spectroscopy). The alloys were given the published Russian heat treatment as well as a more conventional heat treatment more typical of western powder alloys. Tensile, creep and stress rupture mechanical property tests were run. Results of the structural behavior of the alloys after each processing step will be presented and discussed. The role of the Hf on the mechanical proper- ties will be discussed. 相似文献
312.
Charles E. Schlemm II Richard D. Starr George C. Ho Kathryn E. Bechtold Sarah A. Hamilton John D. Boldt William V. Boynton Walter Bradley Martin E. Fraeman Robert E. Gold John O. Goldsten John R. Hayes Stephen E. Jaskulek Egidio Rossano Robert A. Rumpf Edward D. Schaefer Kim Strohbehn Richard G. Shelton Raymond E. Thompson Jacob I. Trombka Bruce D. Williams 《Space Science Reviews》2007,131(1-4):393-415
NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission will further the understanding of
the formation of the planets by examining the least studied of the terrestrial planets, Mercury. During the one-year orbital
phase (beginning in 2011) and three earlier flybys (2008 and 2009), the X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft
will measure the surface elemental composition. XRS will measure the characteristic X-ray emissions induced on the surface
of Mercury by the incident solar flux. The Kα lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected. The 12°
field-of-view of the instrument will allow a spatial resolution that ranges from 42 km at periapsis to 3200 km at apoapsis
due to the spacecraft’s highly elliptical orbit. XRS will provide elemental composition measurements covering the majority
of Mercury’s surface, as well as potential high-spatial-resolution measurements of features of interest. This paper summarizes
XRS’s science objectives, technical design, calibration, and mission observation strategy. 相似文献
313.
D. Breitschwerdt R. Egger M. J. Freyberg P. C. Frisch J. V. Vallerga 《Space Science Reviews》1996,78(1-2):173-182
Recently, observations with the rosat PSPC instrument and the spectrometers onboard the euve satellite have given new detailed information on the structure and physical conditions of the Local Bubble. From the early rocket experiments, and in particular from the WISCONSIN Survey, the existence of a diffuse hot gas in the vicinity of the solar system, extending out to about 100 pc, has been inferred in order to explain the emission below 0.3 keV. The higher angular resolution and sensitivity of rosat made it possible to use diffuse neutral clouds as targets for shadowing the soft X-ray background. Thus, in some directions, more than half of the flux in the 0.25 keV band appears to come from outside the Local Bubble. Further, measurements of the diffuse EUV in the LISM, show surprisingly few emission lines. These findings are in conflict with the standard LHB model, which assumes a local hot (T 106
K) plasma in CIE. Model calculations, based on the non-equilibrium cooling of an expanding plasma, show a promising way of reconciling all available observations. Thus the present temperature within the LB may be as low as 4 × 104
K and its number density as large as 2 × 10–2
cm
–3, giving a total pressure that is roughly in agreement with the Local Cloud.Abbreviations CIE
collisional ionization equilibrium
- ISM
Interstellar Medium
- LHB
Local Hot Bubble
- LB
Local Bubble
- LISM
Local ISM
- SB
superbubble
- SXR
soft X-ray
- SXRB
SXR Background
- VLISM
Very Local ISM
Heisenberg Fellow 相似文献
314.
315.
景象匹配辅助导航系统中的精确图象匹配算法研究 总被引:4,自引:0,他引:4
景象匹配辅助导航系统需要在获取飞行器位置偏差的同时获取飞行器相对预定航迹的航向偏差,即获取实测图相对于参考图之间的旋转变换参数。为此,将最小二乘原理引入景象匹配辅助导航系统以获取图象匹配时的旋转变换参数。由于最小二乘原理只能用于一一对应点集的匹配,为此,在给出实时确定图象特征点集一一对应关系方法的基础上引入了最小二乘原理以计算该图象一一对应点集之间的最优相似变换参数,从而构成了应用于景象匹配辅助导航系统的精确图象匹配算法。仿真结果表明,本文研究的精确图象匹配算法在对50个一一对应点对匹配时可以在0.1秒以内完成,且相似参数计算准确,满足了景象匹配辅助导航系统对图象匹配算法准确性和实时性的性能要求。 相似文献
316.
317.
Yu.N. Gnedin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
The theory of polarization effects in radiation from compact X-ray sources is presented. The following four problems are considered: 1) the polarization of X-rays from the magnetized neutron stars; 2) the polarization of X-rays from the accretion disk around a black hole; 3) the optical polarization from X-ray binaries, and 4) the results of X-ray polarimetric observations. 相似文献
318.
Y. Haba Y. Terashima H. Kunieda K. Ohsuga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(1):174-179
We present the results of a systematic study of narrow-line Seyfert 1 galaxies (NLS1s) observed with XMM-Newton. The 2–12 keV X-ray spectra of NLS1s are well represented by a single power law with a photon index Γ ∼ 2. When this hard power law continuum is extrapolated into the low energy band, we found that all objects in our sample show prominent soft excess emission. This excess emission is well parameterized by the thermal emission expected from an optically thick accretion disk, and we found the following three peculiar features: (1) The derived disk temperatures are significantly higher than the expectation from a standard Shakura-Sunyaev accretion disk, if we assume a central mass of a black hole to be 106–8M⊙. (2) The temperatures are distributed within narrow range (ΔkT ∼ 0.08 keV) with an average temperature of 0.18 keV in spite of the range of four orders of magnitude in luminosity (1041–45 erg s−1). (3) We found a peculiar temperature–luminosity relation, where the luminosity seems to be almost saturated in spite of the significant change in temperature, during the observations of the most luminous NLS1 PKS 0558-504. These results strongly suggest that the standard accretion disk picture is no longer appropriate in the nuclei of NLS1s. We discuss a possible origin for the soft excess component, and suggest that a slim disk may be able to explain the observational results, if the photon trapping effect is properly taken into account. 相似文献
319.
S. Hayakawa T. Hirano H. Kunieda F. Nagase 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
HAKUCHO observation of Cyg X-2 over 40 days did not show a correlation between the hardness ratio and the intensity predicted for dwarf X-ray sources. The energy spectrum in the range 0.3 – 20 keV was found to deviate from the thermal bremsstrahlung spectrum below 2 keV. The X-ray spectrum can be accounted for in terms of the comptonization of blackbody radiation emitted from teh neutron star surface and the accretion disk. 相似文献
320.
S. Hayakawa 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
X-ray astronomy satellite TENMA observed that the X-ray pulsation of Vela X-1 suddenly disappeared for tens of minutes. This phenomenon may be interpreted in terms of the eclipse by a planet of HD77581, the optical companion of Vela X-1. 相似文献