Ionospheric F2-Layer critical frequency retrieved from COSMIC radio occultation: A statistical comparison with measurements from a meridional ionosonde chain over Southeast Asia

In this paper, we compared the F2-Layer critical frequency (foF2) derived from FORMOSAT-3/COSMIC radio occultation (RO) and ionosondes at Chiang Mai, Chumphon and Kototabang during the years 2008–2015 to evaluate the performance of COSMIC RO over Southeast Asia region. The results show that the time development of foF2 values derived from COSMIC RO generally agrees well with those from ionosonde measurements. However, the differences between the foF2 derived from COSMIC RO and that derived from ionosonde observations display latitudinal dependence. COSMIC RO tends to underestimate foF2 at Chiang Mai and Kototabang, which is near to the north EIA crest and the south one, respectively, while a little overestimate foF2 at Chumphon, which is close to the geomagnetic equator. COSMIC RO agrees best with ionosonde at Chumphon and worst at Chiang Mai. At each ionosonde station, the quality of COSMIC RO data degrades with the increase of solar activity. In addition, at the station Chiang Mai and Kototabang, COSMIC RO performs better in summer than in equinox and winter. Furthermore, the differences in foF2 derived from COSMIC RO and that from ionosonde measurements vary with local time, i.e., the differences in foF2 are generally smaller at night and larger in noontime when equatorial ionization anomaly (EIA) is well developed.     

限带白噪声随机过程的雨流幅值概率密度函数模型

对17种不同带宽系数的限带白噪声随机过程进行了雨流循环计数统计,提出了一个限带白噪声随机过程的雨流幅值概率密度函数(Probability density function,PDF)模型。该模型是Rayleigh分布和Weibull分布的线性组合,其中待定系数均为随机过程谱参数的函数。采用该模型对这17种随机过程的雨流幅值概率密度函数进行了公式拟合,探究了模型中待定参数与随机过程谱参数之间的关系,确定了模型表达式。对照随机过程的雨流计数统计结果,将该模型与Dirlik模型的预测精度进行了比较,结果表明该模型的预测效果优于Dirlik模型。     

椭圆振动切削加工的同步控制研究

利用椭圆振动切削加工的回转体表面微织构是在机床主轴旋转、平台进给和装置椭圆振动的联合运动下得到的,机床主轴转动与装置位移输出如果不能保持完全的实时同步,会造成微织构加工的偏差。为了解决这一问题,提出了一种新的基于转角的同步控制方法,该方法在主轴的对位基准处实现装置正弦信号的复位,以修正转速漂移造成的加工位置误差,并通过判断主轴角度信号实时输出对应幅值电压来实时同步信号输出和机床旋转运动。基于LabVIEW FPGA搭建同步控制模块,经试验验证,利用该方法加工的矩形阵列微织构轴向排列与中轴线平行,与周向排列的夹角和仿真结果的偏差不超过0.1°,织构深度随转角的不同发生预设的变化,因此,同步控制方法具有实时同步控制椭圆振动切削装置的能力。     

绿色技术创新对企业成长绩效的影响——基于研发投入强度的调节作用

随着我国经济的高速发展,生态问题日渐凸显。通过技术创新处理好经济发展和生态效益的关系成为实现绿色发展的内在要求。本文利用94家创业板制造业上市公司2014—2017年的数据,采用广义最小二乘法对绿色技术创新、研发投入强度与企业成长绩效之间的关系进行实证分析,探讨了绿色技术创新对企业成长绩效的直接影响,并对研发投入强度的调节作用进行分析。结果显示:绿色技术创新对企业成长绩效具有显著的正向影响;研发投入强度对绿色技术创新与企业成长绩效的关系产生显著的负向调节作用。     

视觉测振技术在柔性太阳翼模态试验中的应用

针对8 m×5 m的柔性太阳翼在倒立状态下进行模态试验，设计数字摄像视觉测振系统，基于图像特征跟踪法实现了从相机标定、图像采集、信息提取到三维振动数据获取的过程，通过工况模态辨识方法获取了柔性太阳翼模态频率及振型等动力学参数。并考虑空气和重力影响建立太阳翼有限元模型，通过与基于基恩士激光位移传感器的传统模态试验结果及仿真分析结果进行对比，验证了基于视觉测振工况模态试验方法的准确性，为柔性太阳翼在轨模态辨识奠定基础。     

离散型可靠性参数数学关系研究

在航空航天系统中,已有许多可靠性参数来描述产品的可靠性特性,但大多数都是基于连续时间上的 连续型可靠性参数,而在离散时间上有定义的离散型可靠性参数的描述较少,例如离散失效率。为弥补可靠性 理论在在这方面的缺陷,从离散时间这一角度出发,研究离散型可靠性参数的数学关系。推导离散失效概率与 离散失效率的数学转换公式,利用离散失效率推导计算离散可靠度的数学公式,推导平均失效前工作次数与离 散失效概率的数学转换公式,并进行验证。结果表明:推导出的三个数学转换公式合理,可以用于描述离散型 可靠性参数。     

球阀阀座用聚三氟氯乙烯密封环工艺与性能

选用两种不同降温方式探究压制成型工艺对球阀阀座用聚三氟氯乙烯（PCTFE）密封环密封性能的影响。低温试验结果表明,自然降温工艺成型的制品外表面在常温-低温循环工况下出现裂纹,而保压降温得到的制品则不出现上述问题。性能测试与表征分析结果表明,自然降温工艺成型的密封环PCTFE其内部会出现微裂纹等缺陷,导致其在低温测试后出现亚表面裂纹,造成密封失效。降温阶段保压操作可抑制材料成型阶段微裂纹缺陷的产生,避免材料在室温-低温循环工况下因内应力而产生裂纹缺陷。     

Flow separation control on swept wing with nanosecond pulse driven DBD plasma actuators

A 15° swept wing with dielectric barrier discharge plasma actuator is designed.Experimental study of flow separation control with nanosecond pulsed plasma actuation is performed at flow velocity up to 40 m/s. The effects of the actuation frequency and voltage on the aerodynamic performance of the swept wing are evaluated by the balanced force and pressure measurements in the wind tunnel. At last, the performances on separation flow control of the three types of actuators with plane and saw-toothed exposed electrodes are compared. The optimal actuation frequency for the flow separation control on the swept wing is detected, namely the reduced frequency is 0.775, which is different from 2-D airfoil separation control. There exists a threshold voltage for the low swept wing flow control. Before the threshold voltage, as the actuation voltage increases, the control effects become better. The maximum lift is increased by 23.1% with the drag decreased by 22.4% at 14°, compared with the base line. However, the best effects are obtained on actuator with plane exposed electrode in the low-speed experiment and the abilities of saw-toothed actuators are expected to be verified under high-speed conditions.