从恒星到黑洞

１７６７年，丹麦天文学家罗麦首次证明了光速是有限的这一事实，为１００多年后预言黑洞的存在创造了条件。否则，人们是无法理解引力场将对光粒子产生影响这一效应的。一般认为，英国的约翰·米歇尔是最早对黑洞的存在做出预言的人。他于１７８３年发表文章指出，一个有足够大质量和密度的恒星，同时也拥有强大的引力场，甚至从恒星表面发出的光线也会被这个引力场吸引回来。１５年后，法国天文学家拉普拉斯也独立地提出了类似的观点：“一个密度如地球，而直径为２５０个太阳的发光恒星，由于引力作用，将不允许它的任何光线到达我们这儿…     

四类中性大气天顶延迟模型特征的比较

研究大气层对ＧＰＳ信号传播的影响，不同的模型会得出不同的结果，本文依据我国的气候条件和国际上流行模型的共性以及一定量的气象资料，选出了四种典型模型进行比较，比较的重点是天顶延迟，比较结果表明：Ｓａａｓｔｍｏｉｎｅｎ模型的结果约高于Ｈｏｐｆｉｅｌｄ模型的结果，两个模型几乎可互换，中国指数模型平均高过前两种模型两分米左右，而国际指数模型平均高过前两种模型几个厘米，且这种模型在春季和冬季的修正量低于前两     

在EEUROCAT—X系统中使用MTM工具分析雷达原始数据信息

一、引言 随着三大区域管制中,OEUROCAT—X系统的建设与投入使用，中国民航在空管自动化领域进入了一个新阶段。与以前的管制中心相比，区管自动化系统在雷达覆盖范围和目标处理的数量上有较大的扩展和提升，但是对于系统维护而言，大数量的异地雷达质量控制还是一个全新的课题。这些异地接入雷达有如下几个特点：传输路由复杂，雷达信号通过地空多个路由传输至区管中心；信号类型多样，有点迹、航迹以及点／航迹混合多种类型：雷达格式有ASTERIX、ALENIA和ALENIAASTERIX多种。     

怎样选择和建立VSAT系统

本文对VSAT小型卫星地面站的建立过程、建立方法和设备选择等方面作了一定的介绍，对欲建立VSAT小型卫星地面站和从事VSAT小型卫星地面站设计有一定的参考价值。     

“阿波罗”计划

作为迄今为止最庞大的月球探测计划,"阿波罗"飞般的任务包括为载人登月飞行做准备和实现载人登月飞行,已于1972年结束.     

NOVEL RADAR SIGNAL SORTING METHOD BASED ON GEOMETRIC COVERING

With the increase of complexity of electromagnetic environment and continuous appearance of advanced system radars, signals received by radar reconnaissance receivers become even more intensive and complex. There- fore, traditional radar sorting methods based on neural network algorithms and support vector machine （SVM） cannot process them effectively. Aiming at solving this problem, a novel radar signal sorting method based on the cloud model theory and the geometric covering algorithm is proposed. By applying the geometric covering algo- rithm to divide input signals into different covering domains based on their distribution characteristics, the method can overcome a typical problem that it is easy for traditional sorting algorithms to fall into the local extrema due to the use of complex nonlinear equation to describe input signals. The method uses the cloud model to describe the membership degree between signals to be sorted and their covering domains, thus it avoids the disadvantage that traditional sorting methods based on hard clustering cannot deinterleave the signal samples with overlapped param- eters. Experimental results show that the presented method can effectively sort advanced system radar signals with overlapped parameters in complex electromagnetic environment.     

沙漠中的“海市蜃楼”

<正>沙漠,对于生活在现代都市的人们来说是个有点陌生、稍许向往、非常的神秘的地方。万里大漠,黄沙飞舞,这样的景象我们只在电视、电影和杂志见过。沙漠到底是一个什么样的地方?其实,沙漠是     

类人生物之源

类人生物的种类繁多，主要不是类人生物偶然突变的结果。可是，各种类型类人生物之间如此悬殊的差异证明，外星人早已对各种类人生物的基因有目的地施加影响。飞碟学家佩雷拉从所掌握的目击报告中严格筛选出31％，这些目击事件是1946年-1969年间发生在24个国家的。对这部分目击事件进行分析和研究后，佩雷拉提出一个推断，实际上，类人生物、生物机器人和机器人的种类及类型，要比前文所述繁杂得多。     

DYNAMIC RESPONSE ANALYSIS OF CARRIER-BASED AIRCRAFT DURING LANDING

In view of the complexity of landing on the deck of aircraft carrier, a systematic model, composed of six- degree-of-freedom mathematic model of carrier-based aircraft, four-degree-of-freedom model of landing gears and six-degree-of-freedom mathematic model of carrier, is established in the Matlab-Simulink environment, with damping function of landing gears and dynamic characteristics of tires being considered. The model, where the car- rier movement is introduced, is applicable for any abnormal landing condition. Moreover, the equations of motion and relevant parameter are also derived. The dynamic response of aircraft is calculated via the variable step-size Runge-Kuta algorithm. The effect of attitude angles of aircraft and carrier movement during the process of landing is illustrated in details. The analytical results can provide some reference for carrier-based aircraft design and main- tenance.