卫星导航天线阵的载波联合跟踪算法

测量卫星导航信号在天线阵各阵元上的载波相位之差可用于卫星波达方向解算,但传统的各阵元独立跟踪算法在干扰条件下无法实现高精度跟踪且容易失锁。针对此问题,通过将天线阵各阵元的载波相位分解为公共的平均载波相位和低动态的残余载波相位,提出了一种联合载波跟踪算法。该算法利用平均载波相位为每个阵元共有的特点,通过对全部阵元的联合处理来提高其跟踪精度,同时通过缩小环路噪声带宽来提高残余载波相位跟踪精度。理论分析与仿真结果表明,该算法提高了波达方向解算所需的阵元间载波相位差的测量精度及跟踪灵敏度,四阵元天线阵在典型应用条件下,跟踪灵敏度提高4d B,相同载噪比下载波相位差测量精度提高3倍。     

连续旋转爆震波传播模态试验

通过保持空气流量不变、改变H2/air当量比开展了连续旋转爆震对比试验,发现随当量比的降低出现三种传播模态:在较高的当量比(0.90~1.86)下,连续旋转爆震波以同向传播模态传播;在较低的当量比(≈0.75)下,则以双波对撞模态传播;在中间工况,则以上述混合模态维持传播。分析了不同传播模态下的高频压力特征,并初步分析了传播模态的转换机制:当量比较高时,爆震强度较高,传播过程中的损失和速度亏损相对较小,爆震波以同向传播模态维持传播;当量比较低时,爆震强度较低,传播过程中的损失和速度亏损较大,此时无法维持同向传播模态,而以双波对撞模态传播,这是由于双波对撞模态中的激波对撞产生高温环境,有利于燃烧放热,其可能是连续旋转爆震的极限传播模态。     

一种强干扰环境下的相干弱目标DOA估计算法

提出了一种强干扰环境下相干弱信号的DOA估计算法。该算法通过修正的Toeplitz矩阵实现了对相干弱信号的解相干,然后将强干扰信号对应的特征矢量从信号子空间中剔除,最后利用MUSIC算法对弱信号进行DOA估计。所提算法不需要预知强干扰信号方位信息,对非平稳噪声有较好的抑制性能。此外,相对JJM算法,该算法具有更高的估计精度和正确概率,对强干扰信源具有更好的抑制性能。     

空时频方位关联算法

针对跳频组网通信中不同信号间的时频分隔特点,利用时频重心进行目标方位数据关联,提出了空时频方位关联算法。根据提取的时频特征设计空时频测向的核函数,实现了简化的空时频测向算法。根据时频距离设计代价函数,基于匈牙利算法实现了方位关联结果的最优化二维分配。根据时频距离选择窗函数的类型和长度,有效避免了信号旁瓣泄露对测向精度的影响,显著提高了密集目标条件下的关联正确概率。数值仿真验证了上述观点。     

An assessment of the ‘democratic’ coup theory

The Egyptian military's unconstitutional removal of President Mohamed Morsi has reignited a debate regarding the theory of the ‘democratic coup’. Though coups are almost invariably condemned, many political observers and a few scholars have recently argued that coups can act as catalysts for democratisation. This paper empirically assesses the democratic coup hypothesis for Africa. Multivariate analyses from 1952 to 2012 suggest that coups statistically improve a country's democratisation prospects. Extensions of the model show that coups appear to be likely precursors for democratisation in staunchly authoritarian regimes and have become less likely to end democracy over time, and that their positive influence has strengthened since the end of the Cold War. As of 2012, countries that have experienced a recent coup are expected to be four times more likely to witness a democratic transition than those that have remained coup-free.     

NATO AS AN EXTERNAL DRIVER OF INSTITUTIONAL CHANGE IN POST‐COMMUNIST COUNTRIES

So far, economic analyses of NATO enlargement have been restricted to aspects of regional security while political analyses focused on indirect peace‐building effects on democracy in the first place. Our panel regressions for 25 post‐communist countries for the period from 1996 to 2008 reveal that direct incentives provided by NATO pre‐accession are important for broad‐based institutional development. Results are even more robust than for variables measuring EU pre‐accession or NATO membership effects. This supports the argument that NATO can act as a transformative power and should strengthen its political agenda.     

弹丸飞行时间拟合误差对射击诸元误差的影响

分析了基本射表中弹丸飞行时间拟合误差对射击诸元误差的影响,给出了因时间拟合误差引起的射击误差的解析表达,并利用5条典型航路分析了飞行时间拟合误差对射角、射向误差的影响,得出了不同航捷、航高、斜距、目标速度下拟合误差对射击诸元误差的影响关系,从而为确定弹丸飞行时间拟合精度提供依据.     

Virtual War in the Ice Jungle: ‘We don't know how to do this’

The Cold War at sea expanded in many realms, including the frigid and treacherous waters of the Arctic Ocean. The US Navy pioneered these efforts with the visit of USS Nautilus to the North Pole in 1958. During the latter stages of the Cold War, however, Soviet naval strategists began to conceptualize the polar ice cap as a strategic asset for cloaking the operations of its nuclear missile submarines. As under-ice operations afforded the Soviet submarine fleet advantages of stealth, proximity to target and tighter lines of communications, both navies were forced to try to develop tactics for combat under these extremely complex and arduous conditions.     

运动模糊图像的运动模糊方向鉴别

曝光瞬间造成图像模糊的运动通常作为直线运动近似处理,若能找出模糊图像的运动模糊方向,并将之旋转到水平轴,则二维问题可简化为一维来处理,大大简化由模糊图像估计出运动模糊点扩散函数以及图像恢复的过程,并为图像恢复的并行计算创造有利条件。由于运动模糊降低了运动方向上图像的高频成分,沿着运动方向实施高通滤波(方向微分),可保证微分图像灰度值(绝对值)之和最小。基于此,本文利用双线性插值的方法,固定并适当选取方向微分的微元大小,构造出3×3方向微分乘子,得到了高效高精度的自动鉴别运动模糊方向的新方法,并通过数值实验进行了验证。     

新疆生产建设兵团教师教育的变迁与发展

新疆生产建设兵团成立以来,不仅担负着国家赋予的屯垦戍边职责,也担负着沉重的文化教育使命。回顾兵团教师教育30年的发展历程,兵团教师教育先后历经了初创期、成长期和发展期三个阶段。当前,兵团教师教育在办学指导思想,师资队伍建设、课程设置、人才培养模式上存在一系列问题。根据当前高等教育的发展趋势,今后兵团教师教育应坚持“师范性”与“学术性”并重的原则,走内涵发展之路,加强特色学科和专业建设,优化人才优化培养模式,改革教师教育课程体系,打造教师教育专业团队,推动兵团教师教育事业更好更快地发展。