Asymmetries in Mars' Exosphere

Observations and simulations show that Mars' atmosphere has large seasonal variations. Total atmospheric density can have an order of magnitude latitudinal variation at exobase heights. By numerical simulations we show that these latitude variations in exobase parameters induce asymmetries in the hydrogen exosphere that propagate to large distances from the planet. We show that these asymmetries in the exosphere produce asymmetries in the fluxes of energetic neutral atoms (ENAs) and soft X-rays produced by charge exchange between the solar wind and exospheric hydrogen. This could be an explanation for asymmetries that have been observed in ENA and X-ray fluxes at Mars.     

Broad-band spectral properties of accreting X-ray binary pulsars

Broad-band spectra of accreting X-ray binary pulsars can be fitted by a phenomenological model composed of a power law with a high energy rollover above 10 keV, plus a blackbody component with a temperature of few hundred eV. While, at least qualitatively, the hard tail can be explained in terms of (inverse) Compton scattering, the origin of the soft component cannot find a unique explanation. Recently, a qualitative picture able to explain the overall broad-band spectrum of luminous X-ray pulsars was carried out by taking into account the effect of bulk Comptonization in the accretion column. After a review of these recent theoretical developments, I will present a case study of how different modeling of the continuum affect broad features, in particular the cyclotron resonance features in Vela X-1.     

Solar Gamma-Ray Spectroscopy

Interactions of ions accelerated in solar flares produce gamma-ray lines and continuum and neutrons. These emissions contain a rich set of observables that provides information about both the accelerated ions and the environment where the ions are transported and interact. Ion interactions with the various nuclei present in the ambient medium produce gamma-ray lines at unique energies. How abundance information is extracted from the measurements is discussed and results from analyses of a number of solar flares are presented. The analyses indicate that the composition of the ambient gas where the ions interact (typically at chromospheric densities) is different from that of the photosphere and more like the composition of the corona, exhibiting low-FIP elemental enhancements that may vary from flare to flare. Evidence for increased Ne/O and the photospheric ³He abundance is also discussed.     

太阳微波爆发精细结构与硬X射线耀斑的相关

北京天文台在２．８４ＧＨｚ频率上观测到的带短时标精细结构的微波爆发与日本ＹＯＨＫＯＨ卫星上ＨＸＴ在１９９１年１０月－１９９２年１２月观测到的硬Ｘ射线爆发（ＨＸＢ）事件作了比较，发现在２０个微波精细结构爆发事件只有１２个与ＹＯＨＫＯＨ卫星记录的ＨＸＢ有对应关系．本文对１９９２年６月７日典型事件中２．８４ＧＨｚ与ＨＸＢ共同存在的百秒量级的准周期振荡作了分析及源区参数的计算，并作了简要的讨论．     

Spectra and time variability of black-hole binaries in the low/hard state

We propose a jet model for the low/hard state of galactic black-hole X-ray sources which explains the energy spectra from radio to X-rays and a number of timing properties in the X-ray domain such as the time lag spectra, the hardening of the power density spectra and the narrowing of the autocorrelation function with increasing photon energy. The model assumes that (i) there is a magnetic field along the axis of the jet, (ii) the electron density in the jet drops inversely proportional to distance, (iii) the jet is “hotter” near its center than at its periphery, and (iv) the electrons in the jet follow a power-law distribution function. We have performed Monte Carlo simulations of Compton upscattering of soft photons from the accretion disk and have found power-law high-energy spectra with photon-number index in the range 1.5–2 and cutoff at a few hundred keV, power-law time lags versus Fourier frequency with index 0.8, and an increase of the rms amplitude of variability and a narrowing of the autocorrelation function with increasing photon energy as they have been observed in Cygnus X-1. The spectrum at long wavelengths (radio, infrared, optical) is modeled to come from synchrotron radiation of the energetic electrons in the jet. We find flat to inverted radio spectra that extend from the radio up to about the optical band. For magnetic field strengths of the order 10⁵–10⁶ G at the base of the jet, the calculated spectra agree well in slope and flux with the observations.     

The properties of hard X-ray emitting symbiotic stars

Hard X-ray emitting symbiotic stars are candidates for SN Ia progenitors. The importance of Type Ia SNe as standard candles for cosmology makes the study of their progenitor systems particularly important. Additionally, they provide one of the most promising laboratories for the study of astrophysical jets. Typically, the X-ray emission in these systems is modeled with a collisional plasma model, sometimes with an emission measure distribution taken from a cooling flow model. The lack of any coherent periods in both X-rays and optical wave band strongly suggests that the accreting white dwarfs in the hard X-ray symbiotic stars are non-magnetic. Although relatively few have been discovered to date, but we believe that there are very many of them in our galaxy and could be possible candidates for the Galactic Ridge X-ray Emissions (GRXE).     

E10.7指数在软X射线谱段的修正应用

表征EUV辐射通量的E10.7指数在越来越多的研究和应用中被用来代替传统的F10.7指数.X射线对地球D层和E层的电离起着重要作用,但由于D层观测数据的不足和E层电离源的多样性,难以被用来考虑X射线对电离层的影响.火星电离层下层的电离源几乎是单一的软X射线,这为研究X射线对电离层的作用提供了可能性.通过研究火星电离层下层的峰值电子浓度对E10.7的依赖关系,发现即便经过必要的修正,这种关系对不同的观测时段并不具备一致性.通过理论推导和数据分析,得到了一种特别用于描述太阳软X射线辐射通量的新指数,即Xs指数,用来替代E10.7指数.Xs指数在描述火星电离层下层对太阳辐射的依赖关系时,不同的观测时段有很好的一致性,表明Xs指数在表征太阳软X射线辐射强度方面比E10.7指数更加合适.      

头盔硬衬用聚氨酯泡沫塑料的研究

介绍了聚氨酯泡沫塑料的发泡机理，设计了头盔硬衬用半硬质自结皮聚氨酯泡沫塑料配方，筛选出了高活性聚醚／TDI和高活性聚醚／PAPI两种聚氨酯发泡体系，穿透实验和碰撞实验表明，半硬质自结皮聚氨酯泡沫塑料完全可以取代传统的聚苯乙烯泡沫塑料作为头盔硬衬。     

硬态切削表面残余应力分析研究

以轴承钢GCr15为研究对象,根据热-弹塑性有限元理论,建立了热力耦合的二维正交硬态切削模型。根据硬态切削的特点,在硬态切削有限元模型中设置了未预先设置分离线的点面接触并选择了Johnson-Cook材料本构模型,通过有限元分析计算,得到了不同切削参数和刀具几何参数条件下已加工表面残余应力的模拟结果。对结果进行比较分析得出,最大压残余应力出现在工件表面,沿着深度的增加工件内部的残余应力由残余压应力转化为残余拉应力,并逐渐趋向于零。这对于控制和提高硬态切削工件表面质量具有重要的理论指导意义。     

Balloon altitude studies of southern hemisphere hard X-ray sources by the Imperial College-University of Tasmania-INPE collaboration

Hard X-ray balloon altitude measurements with a 1600 cm² phoswich array are described. Data from observations on Sco X-1, GX1+4, GX5−1, Nova Oph. 1977, SMC X-1, SS433, IC 4329A and MR 2251-178 are presented. The role of Comptonisation in X-ray production for Sco X-1 and GX1+4 is discussed.