工业CT半扫描成像技术

工业CT即ICT(Industrial Computed Tomography)采用三代扫描方式对构件进行快速检测.但受探测器长度的限制,三代的扫描视场小,可检构件的尺寸受到限制.为解决较大尺寸构件ICT快速检测问题,讨论了一种工业CT半扫描成像技术,推导了其滤波反投影FBP(Filter Back-Projection)重构算法.该算法首先利用扇束三代CT重排原理,将半扫描形成的扇束投影数据修正为360°内不完备的平行束数据;然后利用平行束对称性,生成180°内完备的平行束数据;最后利用平行束重建算法实施重建.计算机模拟和实验结果证明了该技术的正确性.分析表明,其有效扫描视野比三代提高0.8倍以上.     

缝隙耦合HT对特性的分析

分析了通过窄缝隙耦俣的矩形波导Ｈ面Ｔ形接头对（以下简称ＨＴ对）的电气特性，利用等效原理和切向场连续性建立积分方程组，采用矩量法化积分方程为代数方程进行数值求解，获得散射场和等效散射参数，以Ｘ波段标准矩形波导ＨＴ接头对为例进行具体求解和计算，以及实验验证，得到良好结果。     

开孔泡沫塑料的应力松弛问题

开孔泡沫塑料具有良好的能量吸收和缓冲性能, 在工程中得到了广泛的应用, 对其粘弹性行为进行研究具有重要的意义.基于Lederman模型,应用三参数标准线性固体模型考虑基体的粘弹性性能,对开孔泡沫塑料的应力松弛行为进行了研究,并讨论了所加应变载荷、结构参数和泊松比对应力松弛曲线的影响.结果表明:应力松弛曲线对泊松比是不敏感的,并且,应变载荷的增加和相对密度的提高会使应力松弛变得更加明显,但应力响应的初始值和终值的比却不随应变载荷的提高而变化.     

Utilization of sweet potatoes in controlled ecological life support systems (CELSS).

A number of studies have selected the sweet potato as a potentially important crop for CELSS. Most hydroponic studies of sweet potatoes have been short term (<80 days). Full term (90 to 150 days) studies of sweet potatoes in hydroponic systems were needed to understand the physiology of storage root enlargement and to evaluate sweet potato production potential for CELSS. Early and late maturing sweet potato varieties were crown in hydroponic systems of different types--static with periodic replacement, flowing with and without recirculation, aggregate, and non-aggregate. In a flowing system with recirculation designed at Tuskegee University using the nutrient film technique (NFT), storage root yields as high as 1790 g were produced with an edible growth rate of up to 66 g m-2 d-1 and a harvest index as high as 89% under greenhouse conditions. Preliminary experiments indicated high yields can be obtained in controlled environmental chambers. Significant cultivar differences were found in all systems studied. Nutritive composition of storage roots and foliage were similar to field-grown plants. The results indicate great potential for sweet potato in CELSS.     

Design and analysis of a direct transfer trajectory from a near rectilinear halo orbit to a low lunar orbit

A near rectilinear halo orbit (NRHO) is regarded as a potential orbit for a future deep space station that can effectively support sustainable crewed lunar exploration missions. In this paper, the L₂ southern NRHOs are selected as the research object, and a direct transfer trajectory from an NRHO to a low lunar orbit (LLO) is designed and analyzed. First, based on the circular restricted three-body problem, the characteristics of NRHOs are discussed including geometric behaviour, stability and synodic resonance. Second, optimal direct transfer trajectories are obtained by combining a local gradient optimization with a numerical continuation strategy. A reachable domain calculation model is established. Finally, simulations are carried out to verify the feasibility of the trajectory design method. The relationship between the velocity change and the reachable domain is further analysed through simulation calculations.     

地下矩形洞室应力分布的复变函数解

为了解决矩形洞室稳定性问题,利用复变函数在处理复杂形状边界方面的优势,对矩形洞室问题进行应力分析。计算得出矩形洞室围岩应力集中系数,并对矩形洞室不同高长比条件下应力变化规律,远场不同应力比情况下洞室围岩的应力变化规律进行研究,研究结果表明:随着应力比的增加,与最大主应力方向垂直的顶板和底板的应力集中系数线性增加,与最小远场应力方向垂直的边墙应力集中系数线性减小;随着洞室几何高长比的增大,洞室顶板和底板的应力集中系数线性增加,边墙应力集中系数线性减小。研究对地下工程的稳定性分析及支护设计具有指导意义。     

军用设备电磁发射测试项RE102的实现CSCD

电磁兼容性(EMC)是指设备或系统在电磁环境中符合要求运行并不对其环境中的其它设备产生影响的电磁干扰的能力。因此,EMC包括两个方面的要求:一方面是指设备在正常运行过程中对所在环境产生的电磁干扰不能超过一定的限值,即电磁干扰度(EMI);另一方面是指设备对所在环境中存在的电磁干扰具有一定程度的抗扰度,即电磁敏感度(EMS)。本文描述符合《GJB 152A-97军用设备和分系统电磁发射和敏感度测量》要求的"RE102 10kHz^40GHz电场辐射发射"实现方法。     

CTBN/CE共聚体系形状记忆性能研究

用液体端羧基丁腈(CTBN)和氰酸脂(CE)在一定条件下,经适度共聚,制备出一种新型具有较高玻璃化转变温度(Tg)的氰酸酯树脂形状记忆体系。运用红外,动态力学性能分析,力学性能分析,形状记忆性能分析等方法对该体系进行了研究。结果表明:CTBN适当含量可以使氰酸酯树脂具有优异的形状记忆性能;最低的Tg为138℃,体系的最大形变回复率为100%,最大形变恢复速率0.024 s-1,最大拉伸形变为51%。在120℃/2h+140℃/2h+160℃/2h+180℃/1h的固化工艺下体系基本完全反应。     

Infrared radiation characteristics of a hypersonic vehicle under time-varying angles of attack

Hypersonic vehicles emit strong infrared(IR) radiation signatures that can be treated as a detecting source for object identification and routine diagnosis. This paper is aimed at examining the intrinsic radiation characteristics of a Boost-Glide Vehicle(BGV) under the condition of various Angles of Attack(AOAs). A two-temperature model considering the thermal and chemical nonequilibrium effects is coupled with Navier-Stokes equations solved by the finite volume technique.A gas–solid conjunction heat transfer model is also added into the fluid solver to simulate the surface temperature of the vehicle. The radiative transfer equation is solved with Line of Sight(LOS)algorithm. The computational results for a Hypersonic Technology Vehicle-2(HTV-2) type vehicle show that radiances of the vehicle are strongly dependent on the surface temperature. The presence of AOA results in the significant difference of the surface temperature. Infrared radiation characteristics are also changed in intensity and spectral band due to the AOA. Simulations are performed with two time-varying AOAs. Transient results indicate that the variation of AOA does have a great effect on the infrared radiance and is closely related to observation angle, spectral band, angle size,angular velocity and time history.