柱面菲涅耳太阳聚光透镜的光学设计和光学效率

研究了柱面线聚焦菲涅耳太阳聚光透镜的光学设计和光学效率。依据理论分析，对透镜参数进行了优化设计，成功地研制出了柱面线聚焦菲涅耳聚光透镜。还分析了透镜相对孔径（F数）和成型模具等因素对透镜光学效率的影响。     

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.     

Noise in wireless systems from solar radio bursts

Solar radio bursts were first discovered as result of their interference in early defensive radar systems during the Second World War (1942). Such bursts can still affect radar systems, as well as new wireless technologies. We have investigated a forty-year record of solar radio burst data (1960–1999) as well as several individual radio events in the 23rd solar cycle. This paper reviews the results of a portion of this research. Statistically, for frequencies f  1 GHz (near current wireless bands), there can be a burst with amplitudes >10³ solar flux units (SFU; 1 SFU = 10⁻²² W/m²) every few days during solar maximum conditions, and such burst levels can produce problems in contemporary wireless systems.     

Space telescope and cosmology

The status of institutional arrangements and of the hardware development for Space Telescope are highlighted. After a brief summary of instrument characteristics, some examples are given on the possible use of the ST to study objects of interest to cosmology.     

Coronal mass ejection detection using wavelets,curvelets and ridgelets: Applications for space weather monitoring

Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field that can produce adverse space weather at Earth and other locations in the Heliosphere. Due to the intrinsic multiscale nature of features in coronagraph images, wavelet and multiscale image processing techniques are well suited to enhancing the visibility of CMEs and suppressing noise. However, wavelets are better suited to identifying point-like features, such as noise or background stars, than to enhancing the visibility of the curved form of a typical CME front. Higher order multiscale techniques, such as ridgelets and curvelets, were therefore explored to characterise the morphology (width, curvature) and kinematics (position, velocity, acceleration) of CMEs. Curvelets in particular were found to be well suited to characterising CME properties in a self-consistent manner. Curvelets are thus likely to be of benefit to autonomous monitoring of CME properties for space weather applications.     

空间激光通信系统中的信道纠错编码技术

由于空间激光通信系统的信道状态和链路捕获跟踪的不确定性,多种形式的信道纠错编码技术正被广泛发展研究。结合空间激光通信链路中误码性能的主要影响因素,分别选择合适的编码方案进行分析。通过仿真实验可知,对于在大气结构参数为1.5×10~(-14) m~(-2/3)、风速为20 m/s的空地激光链路的环境下,在系统数据速率为2 Gbit/s、要求误码率为10~(-6)时,LDPC码结合交织码相对未编码系统有3 dB的等效编码增益,LT码相对未编码系统有3.8 dB的等效编码增益。提供了一种能快速生成、扩展和校验的编码和交织实现方法,以抵抗大气湍流的快速变化对系统性能产生的影响。     

WSO-UV project

During last three decades, astronomers have enjoyed continuous access to the 100–300 nm ultraviolet (UV) spectral range where the resonance transitions of the most abundant atoms and ions (at temperatures between 3000 and 300 000 K) reside. This UV range is not accessible from ground-based facilities. The successful International Ultraviolet Explorer (IUE) observatory, the Russian ASTRON mission and successor instruments such as the Galaxy Evolution Explorer (GALEX) mission or the COS and STIS spectrographs on-board the Hubble Space Telescope (HST) prove the major impact of observations in the UV wavelength range in modern astronomy. Future access to space-based observatories is expected to be very limited. For the next decade, the post-HST era, the World Space Observatory – Ultraviolet (WSO–UV) will be the only 2-m class UV telescope with capabilities similar to the HST. WSO–UV will be equipped with instruments for imaging and spectroscopy and it will be a facility dedicated, full-time, to UV astronomy. In this article, we briefly outline the current status of the WSO–UV mission and the science management plan.     

Do RadioAstron detections correlate with flaring states? An initial study of seven southern AGN

We examine the state of seven southern radio sources at the time of their RadioAstron AGN Survey observations. Both ATCA flux density monitoring data and Fermi light-curves are considered in determining the relative activity of the source. A simple hypothesis, that sufficiently compact source structure exists for detections on RadioAstron baselines when the source is in a flaring state, is qualitatively tested. We find four instances of RadioAstron detections during flaring radio states and four instances of RadioAstron non-detections during fading or quiescent radio states, in support of the hypothesis. However, we also find three instances of RadioAstron detections during quiescent or fading radio states, and two non-detections during a flaring state, indicating that the situation is (not unexpectedly) more complex. Radio and gamma-ray monitoring such as that described here, together with the full RadioAstron AGN Survey results, will allow a more thorough investigation of the dependencies of detections on baselines of >10 Earth diameters.