Re对γ′相粗化行为的影响

研究了三种不同Re含量 (wt % )的新型单晶高温合金 (DD6 0Re合金 ,DD6 1Re合金 ,DD6 2Re合金 )在 110 0℃下的γ′粗化动力学。结果表明 ,Re可以有效地阻碍γ′相的粗化 ,提高γ′相的粗化激活能 ,从而可以Re改善单晶高温合金的高温力学性能     

Near 13.5-day periodicity in Muon Detector data during late 2001 and early 2002

In this study we perform a continuous Morlet wavelet transform method in time series of secondary cosmic rays and 1 AU interplanetary medium parameters for the interval from October 2001 to October 2002. The near 13.5-day periodicity was obtained during late 2001, and it was remarkable for muon data. Even though some works have pointed out that the main activations of the 13.5 day recurrence in near-Earth solar wind are related, e.g., with the heliosheet crossings or to the occurrence at 1 AU of two high speed streams approximately 180° apart in solar longitude per solar rotation, we aim to show that the period of about half the solar rotation during the end months of 2001 present in muon time series was apparently due to the occurrence of non-recurrent interplanetary disturbances. The interconnections among successive Forbush decreases, recovery phases and gradual muon depressions (associated with corotating interaction regions) seem to play an important role in such 13.5-day periodicity.     

大型反射面天线温度分布规律及变形影响分析

针对高频段大型反射面天线对电性能的高要求,必须降低太阳热辐射对天线的影响。先计算一天中太阳入射角度的变化规律,再基于I\|DEAS软件仿真,得到一天中各时刻天线反射面上的温度、热应力场、热变形分布,然后针对阴影对天线结构的重要影响,以“分点分段”的形式给出不同时刻温度在反射面上的分布及其影响程度和规律,为工程人员进行天线的温度补偿和结构优化提供了依据。     

基于上升轨迹可达范围的目标拦截发射窗口计算

针对低轨目标拦截任务,提出一种利用上升轨迹可达范围分析的发射窗口计算方法。首先,建立以上升时长和航程为性能指标的上升轨迹和优化模型,确定拦截器上升轨迹可达范围。然后,根据目标星下点与上升轨迹可达范围外包络的穿越关系以及拦截器的上升时长范围,对发射窗口进行初筛,得到准发射窗口。最后,针对每一段筛选出的准发射窗口,通过精确判定目标星下点与每一上升时长可达范围子环的位置关系,得到每段准窗口中能够实现目标拦截的发射窗口,将其取并集得到针对目标拦截的精确发射窗口。仿真表明本文提出的计算方法能够快速准确得到目标拦截的发射窗口。     

An experiment to study solar flare effects on radio-communication signals

The occurrence of radio signal fading events caused by ionospheric absorption plays an important role in the performance of radio-communication systems. It is necessary to know the magnitude and time-scale of such events in order to specify technical parameters of the communication system to be used. Generally, fading events are associated with solar flares, which are characterized by sudden increase in the solar X-ray flux that causes an increase in the ionization in the lower ionosphere. The abrupt increase of ionization causes the absorption of radio waves propagating in the Earth–ionosphere wave-guide and is reported as radio signal fading events. A simple experiment to monitor the behavior of lower ionosphere has been carried out at the Southern Space Observatory-SSO/INPE (29.43°S, 53.8°W), located in southern Brazil. The experiment is basically a computer controlled radio receiver that records the received signal strength of Amplitude Modulated (AM) radio signals in the HF (High Frequencies) range. We analyzed data of the 6 MHz beacon signal that has been transmitted by a broadcasting radio station located about 400 km from the observation site. In this work we present initial results of daily variation of the received signal strength and fading events associated with solar flares observed in the 6 MHz signal monitored by the experiment during 2001. X-ray solar flux data from the GOES-8 satellite were used to identify X-ray solar bursts associated with solar flares. Based on the one-year data collected by the experiment, a statistical summary of fading occurrences and their correlation with solar flares, as well as the distributions of time-scales and magnitudes of such events are presented.     

Understanding strategic decision making in the context of international space activities

This paper argues that a better understanding of strategic decision making processes in different space agencies is relevant to the successful carrying out of international cooperative undertakings in space and that this kind of information should be taken into account when decisions are to be made on engaging in a new partnership. In this context, the paper provides a general framework for the study of strategic decision making in space organisations, with particular emphasis on the influence of culture. Additionally, it offers practical examples of how differences in policy priorities, decision making environments and practices amongst space organisations can affect international cooperative endeavours. A particular concern is with the role of national and corporate cultures in creating and reflecting differences between space agencies. In order to gather information on strategic decision making processes in the space sector, a series of 30 interviews was conducted with top decision makers from NASA, ESA and the space organisations of Brazil, France, Canada, Russia, The Netherlands and the UK.     

Present-day deformation in São Jorge Island,Azores, from episodic GPS measurements (2001–2011)

A network of geodetic markers for high-precision Global Positioning System (GPS) surveying was established in 2001 in the island of São Jorge, at the Azores triple junction, where the North America–Eurasia–Nubia plates meet. The aim was to monitor tectonic, volcanic, and landslide-induced surface deformation in an active tectono-volcanic region. The network consisted of 17 stations, and was occupied in 2001, 2004, and 2010. GPS observations from the three episodic campaigns were analyzed using the latest geophysical models and geodetic procedures to generate a velocity field for São Jorge Island.     

Object-based representations of spatial images

Object based representations of image data enable new content-related functionalities while facilitating management of large image databases. Developing such representations for multi-date and multi-spectral images is one of the objectives of the second phase of the Alexandria Digital Library (ADL) project at UCSB. Image segmentation and image registration are two of the main issues that are to be addressed in creating localized image representations. We present in this paper some of the recent and current work by the ADL's image processing group on robust image segmentation, registration, and the use of image texture for content representation. Built upon these technologies are techniques for managing large repositories of data. A texture thesaurus assists in creating a semantic classification of image regions. An object-based representation is proposed to facilitate data storage, retrieval, analysis, and navigation.