A comparative study of ionospheric IRIEup and ISP assimilative models during some intense and severe geomagnetic storms

Three-dimensional (3-D) electron density matrices, computed in the Mediterranean area by the IRI climatological model and IRIEup and ISP nowcasting models, during some intense and severe geomagnetic-ionospheric storms, were ingested by the ray tracing software tool IONORT, to synthesize quasi-vertical ionograms. IRIEup model was run in different operational modes: (1) assimilating validated autoscaled electron density profiles only from a limited area which, in our case, is the Mediterranean sector (IRIEup_re(V) mode); (2) assimilating electron density profiles from a larger region including several stations spread across Europe: (a) without taking care of validating the autoscaled data in the assimilation process (IRIEup(NV)); (b) validating carefully the autoscaled electron density profiles before their assimilation (IRIEup(V)).The comparative analysis was carried out comparing IRI, IRIEup_re(V), ISP, IRIEup(NV), and IRIEup(V) foF2 synthesized values, with corresponding foF2 measurements autoscaled by ARTIST, and then validated, at the truth sites of Roquetes (40.80°N, 0.50°E, Spain), San Vito (40.60°N, 17.80°E, Italy), Athens (38.00°N, 23.50°E, Greece), and Nicosia, (35.03°N, 33.16°E, Cyprus). The outcomes demonstrate that: (1) IRIEup_re(V), performs better than ISP in the western Mediterranean (around Roquetes); (2) ISP performs slightly better than IRIEup_re(V) in the central part of Mediterranean (around Athens and San Vito); (3) ISP performance is better than the IRIEup_re(V) one in the eastern Mediterranean (around Nicosia); (4) IRIEup(NV) performance is worse than the IRIEup(V) one; (5) in the central Mediterranean area, IRIEup(V) performance is better than the IRIEup_re(V) one, and it is practically the same for the western and eastern sectors.Concerning the overall performance, nowcasting models proved to be considerably more reliable than the climatological IRI model to represent the ionosphere behaviour during geomagnetic-ionospheric storm conditions; ISP and IRIEup(V) provided the best performance, but neither of them has clearly prevailed over the other one.     

Analysis of the data processing strategies of spherical harmonic expansion model on global ionosphere mapping for moderate solar activity

Spherical harmonic (SH) expansion is widely used to model the global ionosphere map (GIM) of vertical total electron content (VTEC). According to the impact of different data processing methods of the SH expansion model on the VTEC maps, we specifically performed comprehensive analysis in terms of the data sampling rate, the time resolution, the spherical harmonic degree, and the relative constraint. One month of GPS data (January in 2016) from the International GNSS (Global Navigation Satellite System) Service (IGS) network in a moderate ionospheric activity period at the descending phase of Solar Cycle 24 was processed. To improve the computational efficiency of the daily GIM generation, the data sampling rate of 5?min was recommended allowing the GIM precision loss within 0.10 TECU (total electron content unit). The global VTEC map could be better represented in temporal and spatial domains with higher time resolution and higher spherical harmonic degree, especially at low latitude bands and in the southern hemisphere. The GIM precision improvement was about 10.91% for 1-h and about 15.15% for 0.5-h compared with the commonly used 2-h time resolution. The use of spherical harmonic degree 17 or 20 instead of 15 could improve the precision by 3.19% or 6.06%. We also found that an optimal relative constraint had to be found experimentally considering both the GIM precision and the GIM root mean square (RMS) map.     

一种基于虚拟页地址映射的NAND Flash管理算法

本文提出了一种基于虚拟页地址映射的NAND Flash管理算法.该算法通过定义坏块表、对应表等结构，以及设计的坏块替换策略和虚拟页地址到实际物理页地址的转换算法，实现上层软件采用虚拟地址对NAND Flash的无坏块连续页地址访问.该算法是一种高效的地址映射算法，能高效地对数据进行索引，占用SRAM空间较少，使系统达到高性能，并使得闪存使用的更加稳定持久.     

航天测控系统自主运行的关键技术

航天事业发展趋势和未来需求指明,航天测控系统应该向以自主运行能力为代表特征的智能化方向发展。基于此,提出了标准化的支持与服务、映射现实的体系架构、实时响应的运行模式、服务化的基础平台等4项关键技术。通过将测控系统和卫星系统之间的接口、测控系统和用户系统之间的接口标准化,从而在此基础上建立最优化的操作逻辑。通过在计算机中映射现实系统的思想方法,从而产生稳定性和灵活性兼备的、支持自主运行的,并具有良好进化性能的系统架构。通过实时响应的运行模式可以很好满足全时段和突发性等具有挑战性的测控服务需求。通过大数据和云计算技术构建基础计算服务平台实现基础层与业务层分离,有利于整个系统的持续改进,提高服务质量改善的速度,建立竞争力优势。由此说明,在当前技术条件下实现自主运行的航天测控系统是可行的。     

连续体结构拓扑优化方法评述

连续体结构拓扑优化在优化中能产生新的构型,对实现自动化智能结构设计具有重要意义。目前,连续体结构拓扑优化方法主要有：均匀化方法、变厚度法、变密度法、渐进结构优化方法、水平集法、独立连续映射方法。本文首先系统回顾了以上方法的发展历程,介绍了它们的研究现状。其次,通过对比以上拓扑优化方法对若干典型算例的优化结果,表明以上方法都有较好的减重效果。最后,对以上方法进行了总结,列出了它们的优缺点和发展方向。     

机载系统NANDFlash存储技术

为了发挥NANDFlash在机载环境中非易失性、体积小、固态性、重量轻、低功耗、抗震动等特点,介绍了NANDFlash的存储特性,对NANDFlash存储的关键技术进行了改进,提出了基于域机制的地址映射方式和基于阈值的损耗均衡方法,为机载系统能够更加可靠、实时和安全地进行数据存储提供了选择。     

星载相控阵GNSS-R测高系统设计与实验

星载GNSS-R测高系统采用多波束相控阵天线和干涉互相关处理方式,接收北斗导航卫星和GPS导航卫星发射的L波段导航直射信号与海面反射信号,进行海面高度探测。详细介绍GNSS-R测高系统设计与实现、集成和外场试验等,外场试验不仅验证了相控阵GNSS-R测高系统功能,更重要的是验证了核心软件算法的正确性。GNSS-R测高系统适用于中尺度海洋现象的观测,可在时间和空间尺度上扩展雷达高度计的观测能力,并与之相互补充,有利于对复杂海面的中尺度结构进行较高时间分辨率的观测。GNSS-R测高仪为星载高精度海面高度探测提供了新型载荷。     

基于总线式集成框架的本体构建及映射研究

通过本体的构建及相应的本体映射策略,可以很好地解决信息集成过程中出现的语义异构问题。是实现异构数据源语义解析的基础。在已有研究成果总线式信息集成框架的基础上,针对目前本体构建过程存在的不足,提出了基于共享词汇表的全局本体构建技术和基于UML的局部本体构建技术,使所构建的本体元素间关系更加准确完备,具有良好的一致性。提出了基于综合相似度的本体映射策略,大大提高了本体映射的精度。     

Mining Spatial Associations with Limited Sensory Information

Abstract

Human navigation in an unknown environment requires an understanding of the spatial relationships of the terrain. For example, a soldier who is on a reconnaissance mission in a new city needs to “know” the spatial layout of the surroundings with high confidence. Oftentimes, this understanding must be acquired within a very short amount of time and with limited sensory inputs. The soldier would benefit from a digital avatar that draws inferences about the spatial layout of the city based on an initial set of observations and guides the soldier either in further exploring the environment or in making decisions based on these inferences. In this paper, we present and evaluate an inductive approach to learning spatial associations using sensory data that is available from the simulation environment of a computer game, Unreal Tournament. We study two kinds of spatial relationships between nodes on a level of a game map: nodes that are placed near each other to satisfy some spatial requirement and nodes that are placed near each other to satisfy the design preferences of a level architect. We show that we can infer both kinds of relationships using an association rule mining algorithm. Furthermore, we show how to use an ontology to distinguish between these relationships in order to discover different types of spatial arrangements on a specific map. We discuss how the inferred associations can be used to control an avatar that makes recommendations for navigating unexplored areas on a map. We conclude with some thoughts on the applicability of our methods to scenarios in the real world, beyond the simulation environment of a game, and on how the learned associations can be represented and queried by a simple question-answer type system.     

降低PLC系统峰均比的低复杂度改进SLM算法

针对信道慢时变特性及噪声复杂的特点,提出了适用于低压电力线通信的降低峰均比的改进算法.改进算法对原始输入序列中的部分数据进行循环移位来获得一系列不同的新数据序列;在每个新数据序列尾部插入相应的边带信息组成一个输入候选序列;对这一系列不同的输入候选序列分别实施傅里叶反变换,得到不同的输出序列;从中选择峰均比最小的用于传输,达到降低系统峰均比的目的.结果表明:改进算法能够有效地降低系统的峰均比,并且能够获得更好的误码率性能,同时具有比传统选择性映射方法更低的计算复杂度.