槽道湍流的法向与展向电磁力壁面减阻

法向与展向电磁力可以有效调制湍流近壁流动及减少壁面摩擦阻力.为进一步揭示该方法的减阻机理,利用Fourier-Chebyshev谱方法,通过直接数值模拟(DNS),对槽道湍流的法向与展向电磁力控制和减阻问题进行了研究.结果表明,对于确定的流向波长λx+,存在最佳的电磁力强度St,使阻力降最大,最佳St与λx+成反比.法向与展向电磁力对湍流的控制过程实质上是一种由电磁力诱导的调制波对壁湍流的调制过程.在优化参数控制下,当法向与展向电磁力诱导的流场被用来调制固有的近壁湍流流场时,固有流场和诱导流场同时受到调制.在这种调制波作用下,调制流场逐渐主宰壁面边界层,这导致了壁面阻力的下降,平均减阻率最高可达8％.     

基于CCSDS标准的航天器上行遥控链路 协议体系与可靠性技术

针对航天测控领域中上行遥控业务的协议体系选择与可靠性设计问题,在对我国现行国军标技术指标要求与现有航天测控系统天地基遥控技术特点进行归纳梳理的基础上,基于空间段信息传输无线链路特点与CCSDS(Consultative Committee for Space Data Systems,空间数据系统咨询委员会)标准规范,研究给出了适用于我国航天测控任务的空间段遥控协议体系与可靠性措施,利用梳理统计方法对上行遥控体制进行了数学建模分析,并与CCSDS给出的应用算例进行了对比分析.分析结果表明,所涉及的上行遥控体制与CCSDS标准规范的工作效能基本相当,能够满足我国航天任务上行遥控任务使用需求.     

Modelling of galactic Carbon in an asymmetrical heliosphere: Effects of asymmetrical modulation conditions

Observations of galactic cosmic rays (GCRs) from the two Voyager spacecraft inside the heliosheath indicate significant differences between them, suggesting that in addition to a possible global asymmetry in the north–south dimensions (meridional plane) of the heliosphere, it is also possible that different modulation (turbulence) conditions could exist between the two hemispheres of the heliosphere. We focus on illustrating the effects on GCR Carbon of asymmetrical modulation conditions combined with a heliosheath thickness that has a significant dependence on heliolatitude. To reflect different modulation conditions between the two heliospheric hemispheres in our numerical model, the enhancement of both polar and radial perpendicular diffusion off the ecliptic plane is assumed to differ from heliographic pole to pole. The computed radial GCR intensities at polar angles of 55° (approximating the Voyager 1 direction) and 125° (approximating the Voyager 2 direction) are compared at different energies and for both particle drift cycles. This is done in the context of illustrating how different values of the enhancement of both polar and radial perpendicular diffusion between the two hemispheres contribute to causing differences in radial intensities during solar minimum and moderate maximum conditions. We find that in the A > 0 cycle these differences between 55° and 125° change both quantitatively and qualitatively for the assumed asymmetrical modulation condition as reflected by polar diffusion, while in the A < 0 cycle, minute quantitative differences are obtained. However, when both polar and radial perpendicular diffusion have significant latitude dependences, major differences in radial intensities between the two polar angles are obtained in both polarity cycles. Furthermore, significant differences in radial intensity gradients obtained in the heliosheath at lower energies may suggest that the solar wind turbulence at and beyond the solar wind termination shock must have a larger latitudinal dependence.     

利用平滑约束复原方法处理CCD相机遥感图像

重点研究了频域平滑约束复原方法以及该方法对遥感领域中的实际应用，文章先介绍了平滑约束复原方法的理论基础，然后用该方法对CCD相机的遥感图像进行了复原处理，讨论了遥感器系统调制传递函数（MTF）曲线的拟合，遥感器系统MTF矩阵的构造以及复原参数的选择。可以得出结论，在一定条件下，利用平滑约束复原方法可以有效地改善整个系统的调制传递函数，从而使图像变得清晰。     

Three-dimensional cosmic-ray simulations: Heliographic latitude and current-sheet tilt

We present the results from a study of the variations of the cosmic-ray intensity with time, heliographic latitude, and longitude, and for varying interplanetary conditions, using our three-dimensional, time-dependent computer code for cosmic-ray transport in the heliosphere. Our code also produces a solar-wind and interplanetary magnetic field (IMF) configuration which is compared with observations. Because of the fully threedimensional nature of the model calculations, we are able to model time variations which would be expected to be observed along Ulysses's trajectory as it moves to high latitudes. In particular we can model the approximately 13-and 26-day solar-rotation induced variations in cosmic rays, solar wind and IMF, as a function of increasing heliographic latitude, as one moves poleward of the interplanetary current sheet. Our preliminary model results seem to be in general form quite similar to published data, but depend on the physical parameters used such as cosmic-ray diffusion coefficients, boundary conditions, and the nature of the solar wind and IMF and current sheet.     

发射脉冲载波泄漏抑制研究与实现

对发射端采用双平衡正交调制器产生线性调频造成载波泄漏的原因进行了详细分析,提出了采用直接数字合成(DDS)技术产生发射端线性调频信号的实现方法,从而很好地解决了载波泄漏的问题,并给出了试验结果。     

空间相机像移补偿方法研究

介绍了空间相机拍照时产生像移的机理及国内外目前较常使用的不同像移补偿方法,并对光、机、电等不同实现方法进行分析比较,得出各种方法的优缺点及适用范围。     

航天光学采样成像系统MTF的优化设计与MTFC

简要介绍了成像链、成像系统和遥感系统的概念；对像质和像质差异的表征和度量、成像系统性能的表征等予以说明；重点探讨航天光学采样成像系统MTF的优化设计与MTFC问题，并给出讨论结果。     

细节信息容量与MTF相关分析

文章从信息容量的角度出发,对图像宏观质量做出评价,再通过研究图像的细节信息容量参数,对在宏观上质量相当的图像做出更进一步的评价,挑选出边缘清晰、纹理等细节信息丰富的图像。然后将该评价参数与Ealing仪测得的调制传递函数(MTF)值的变化趋势作曲线回归分析,实验结果表明,细节信息容量与数字成像系统的MTF值的变化有着很好的正相关关系,这对评价数字成像系统MTF变化情况具有较好的实际应用价值。     

刀刃法在轨MTF测量性能分析

文章主要研究采用刀刃法测量在轨遥感器的MTF。刀刃法MTF测量准确程度如何，需要有一个定量的客观的评价，文章用仿真的方法对MTF测量精度进行了检验，对于噪声对MTF的影响进行了研究。