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81.
利用MCNP程序对450kV X光机建立模型,计算各参考辐射质下的原级谱、平均光子能量。对ISO4037-1中已有范围的管电压与附加过滤片厚度关系曲线进行二次拟合,确定模拟厚度范围。利用MCNP计算各附加过滤组合下的平均光子能量值,并与外推法得出的平均光子能量值进行对比,将相对偏差最小时的附加过滤作为最终确定值。从部分能量点的模拟与测量结果的对比可看出,模拟得出的平均光子能量在2%以内与PTB及中国计量院测量结果保持一致,附加过滤最大相对偏差为18%。 相似文献
82.
83.
本文分析了1981年4月27日的一个特大高能爆发。它在硬X射线(HXR)、γ射线和微波(MW)记录上显示一一对应的多脉冲结构。文中讨论了这些脉冲的寿命、时延与HXR的能量、MW的波长之间的关系,发现时延量与湍动加速所预期的值相符合。提出了各脉冲期间的谱呈软→硬→软的演化,可能是由高能电子受到加速的看法。还对产生HXR的高能电子的谱指数、电子总数和MW源区的磁场也作了估计。 相似文献
84.
Eijiro Hiei 《Space Science Reviews》1994,70(1-2):189-192
X-ray emission from solar coronal loops changes on two different timescales: a) flare loops and transient active region brightenings show a rapid variability, b) quiet region loops are quasi-steady and change only slowly with time. This different time behavior has been analyzed on the basis of Yohkoh SXT observations and we report here on the results from our analysis, mainly focussing on quiet loop variability. 相似文献
85.
Dale P. Cruikshank 《Space Science Reviews》2005,116(1-2):421-439
The diverse populations of icy bodies of the outer Solar System (OSS) give critical information on the composition and structure
of the solar nebula and the early phases of planet formation. The two principal repositories of icy bodies are the Kuiper
belt or disk, and the Oort Cloud, both of which are the source regions of the comets. Nearly 1000 individual Kuiper belt objects
have been discovered; their dynamical distribution is a clue to the early outward migration and gravitational scattering power
of Neptune. Pluto is perhaps the largest Kuiper belt object. Pluto is distinguished by its large satellite, a variable atmosphere,
and a surface composed of several ices and probable organic solid materials that give it color. Triton is probably a former
member of the Kuiper belt population, suggested by its retrograde orbit as a satellite of Neptune. Like Pluto, Triton has
a variable atmosphere, compositionally diverse icy surface, and an organic atmospheric haze. Centaur objects appear to come
from the Kuiper belt and occupy temporary orbits in the planetary zone; the compositional similarity of one well studied Centaur
(5145 Pholus) to comets is notable. New discoveries continue apace, as observational surveys reveal new objects and refined
observing techniques yield more physical information about specific bodies. 相似文献
86.
Dario Lorenzetti 《Space Science Reviews》2005,119(1-4):181-199
Observations of pre-main sequence objects (T Tauri, Herbig Ae/Be and FU Orionis stars) obtained with the instrumentation on
board the Infrared Space Observatory (ISO) are reviewed. All the observations have been mainly carried out by using the two
spectrographs SWS and LWS, adopting their low resolution modes and such data have been used both for lines detection and to
reconstruct the spectral energy distributions. Line emission and photometric behaviour of pre-main sequence objects have been
analyzed in the framework of the current models, discussing the agreement (or disagreement) with them and trying to derive
the questions which should be answered by the forthcoming FIR instrumentation.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
87.
Alain Abergel Laurent Verstraete Christine Joblin René Laureijs Marc-Antoine Miville-Deschênes 《Space Science Reviews》2005,119(1-4):247-271
Infrared spectroscopy and photometry with ISO covering most of the emission range of the interstellar medium has led to important
progress in the understanding of the physics and chemistry of the gas, the nature and evolution of the dust grains and also
the coupling between the gas and the grains. We review here the ISO results on the cool and low-excitation regions of the
interstellar medium, where T
gas≲ 500 K, n
H∼ 100–105 cm−3 and the electron density is a few 10−4.
JEL codes: D24, L60, 047
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
88.
89.
Eugene M. Trunkovsky 《Space Science Reviews》1995,74(3-4):485-488
Photoelectric WBVR observations of Be star HDE 245770=V 725 Tau, the optical counterpart of the transient X-ray pulsar A0535+26, having a pulse period of about 104 s, were conducted for more than 10 years. An irregular long-term optical variability of the star with amplitudes of the order of a few tenths of magnitude was found to be a usual phenomenon. In some cases rapid changes of the star's optical luminosity with a characteristic period of a few tens of minutes or a few hours, and an amplitude of several hundredths of magnitude in all the spectral bands used, which have practically coincided or correlated with the X-ray pulsar outbursts detected by X-ray satellites, were observed.Photoelectric recording of the optical flux from HDE 245770 were made in 1981–1982 with a time resolution of 1 second and 10 s, respectively, in theR spectral band (0 7000 Å) and in the narrowH
-emission-line band (1/2 75 Å) using a 48-cm reflector of High-Mountain Tien-Shan observatory of the Sternberg Astronomical Institute near Alma-Ata. An analysis of autocorrelation functions of the flux changes from object under study and a comparison with the star BD+26° 876 indicated the variability of luminosity of V 725 Tau in theR spectral band on a time scale of a few tens of second; this variability resembles shot noise with a characteristic time of stochastic bursts of about 15–20 s and their amplitudes of about a few tenths of a percent. InH
-emission-line radiation autocorrelation functions and power spectra show quasiperiodic variability of luminosity of HDE 245770 with a characteristic period of about 100–150 s and an amplitude in the neighbour-hood of 0.5%. The latter result is not quite reliable because of not quite fine weather conditions during the observations; independent observations and check-up are required. 相似文献
90.
Knowledge of the observable properties of orbital debris is necessary to validate debris models for both the low Earth orbit (LEO) and the geosynchronous Earth orbit (GEO). Current methods determine the size and mass of orbital debris based on knowledge or assumption of the material type of the piece. Improvement in the knowledge of material is the goal of the research described herein. The process of using spectral absorption features to determine the material type is explored. A review of the optical measurements of orbital debris as well as current research in the area is discussed. Reflectances of common spacecraft materials are compared. The need for, and advances made possible by obtaining real data are explored. The prospects of the venture are investigated. 相似文献