Low fluence.

The question of the appropriate extrapolation to low dose has long been a subject of controversy. A linear no-threshold model is favored by regulatory bodies as the basis of RBE assignments and estimates of radiation hazards to the general population. This model is largely supported by extensive application of the linear-quadratic survival formula "fitted" statistically to a wide variety of experimental data obtained at doses typically exceeding 1 Gy, and then extrapolated to mGy for practical applications, and even to the prediction of hazards from single electrons. Such extrapolations are questionable at best, and may even prove hazardous for risk evaluations. Fluence and geometry rather than dose based data are proposed as a basis for a limiting "threshold" for a "low dose" extrapolation. The proposed threshold is one where the fluence of particles is one per square micron, where on average only 2/3 of the 1 micrometers2 pixels covering an irradiated area are traversed by one or more particles. The corresponding dose threshold is determined by the LET of the bombarding radiation. For relativistic electrons this dose is about 0.032 Gy.     

The influence of gravity on the structure and functions of plant material

Growth process generate plant form and relate to most physiological functions. The Earth's gravity force affects plant growth in both obvious and subtle ways. It is a major environmental influence on morphology and physiology of plants. Gravity is less important as an agent for plant stress than as an environmental signal to guide growth. The plant's bioaccelerometers are remarkably sensitive, especially in hypogravity. Simulation (clinostat) studies and experiments in satellite laboratories are needed to understand the sensing, transduction, and response characteristics of g related mechanisms. By examining how plants alter growth processes to accomplish developmental or physiological “objectives” we may find it pragmatically desirable to ask ourselves how we might design a plant to achieve such responses to environmental influences. Examples of this design engineering approach for gravity related effects are described as an aid to experimentation.     

Lunar habitat concept employing the space shuttle external tank

The space shuttle external tank, which consists of a liquid oxygen tank, an intertank structure, and a liquid hydrogen tank, is an expendable structure used for approximately 8.5 min during each launch. A concept for outfitting the liquid oxygen tank-intertank unit for a 12-person lunar habitat is described. The concept utilizes existing structures and openings for both man and equipment access without compromising the structural integrity of the tank. Living quarters, instrumentation, environmental control and life support, thermal control, and propulsion systems are installed at Space Station Freedom. The unmanned habitat is then transported to low lunar orbit and autonomously soft landed on the lunar surface. Design studies indicate that this concept is feasible by the year 2000 with concurrent development of a space transfer vehicle and manned cargo lander for crew changeover and resupply.     

永磁有限转角力矩电机的仿真与实验

随着多电飞机的快速发展及成附件轻小化、高效能的迫切需求,有限转角力矩电机(Limited Angle Torque Motor,LATM)在飞机引气系统中的应用日益迫切。一方面,有限转角力矩电机可以显著简化高温引气控制阀结构、减小体积;另一方面,可以基于系统需求实现引气压力和温度按需调节,减少燃油代偿损失。针对高温有限转角力矩电机工作特性不易预测的难题,建立了其数学模型、仿真模型,并通过实物试验验证了仿真模型的准确性。研究结果为有限转角力矩电机特性研究提供了参考依据。     

Characterization of an acoustic liner by means of Laser Doppler Velocimetry in a subsonic flow

This paper describes a new experimental approach to acoustic liner characterization in the presence of a grazing flow. The traditional methods of measurement use microphones to determine liner impedance. The in situ method in particular requires the simultaneous use of two microphones. The first is mounted flush with the surface of the liner grazed by the flow and the second is flush-mounted to the rear face of the liner. However, this method is invasive and assumes the reaction of the liner to be independent of the incidence of the waves (locally-reacting liner). The approach suggested here is radically different since Laser Doppler Velocimetry (LDV) is used to measure the acoustic perturbation of velocity, or acoustic velocity. This latter allows us to determine the acoustic displacement, which is the key parameter in Galbrun's linear theory for assessing the perturbation of pressure and the field of active intensity. The wall impedance and the propagation paths of acoustic energy in the presence of the liner may be deduced without any assumption and non-invasively. This approach was applied for characterizing a resistive liner in a test bench specially designed for aeroacoustic measurements, with a 2D LDV system. The flow was turbulent and the measured nominal Mach number was 0.13. The impedance and field of active intensity were then obtained. A comparison was carried out between the new approach and the in situ method using microphones. According to previous theoretical works in the literature and the presented test results, one has to be cautious about the definition of the impedance when performing in-flow acoustic measurements.     

超临界层流翼型优化设计策略

针对超临界层流翼型设计问题,提出一种两轮优化策略。采用γ-Reθt转捩模型耦合剪切应力输运(SST)模式的湍流模型对翼型边界层转捩进行预测。翼型几何参数化建模采用形状分类函数转换(CST)方法,设计变量为描述翼型几何特征的参数。第1轮优化的目的是尽量提高层流区域的比例,气动分析模型为基于Kriging模型的代理模型,优化算法为遗传算法,通过优化获得满足约束要求的层流翼型。第2轮优化目的是对第1轮优化获得的翼型进行微调,进一步提高翼型的升阻比,气动分析直接采用CFD程序,优化算法采用基于梯度的优化算法。算例表明,应用本文提出的两轮优化策略,可将超临界翼型NASA SC(2)0412优化设计成超临界层流翼型,翼型的上下表面层流区比例分别达到了55.5%和47.0%,升阻比提高了38.1%。     

定常对称背涡流态下细长体绕流结构的演变

应用数值计算的方法模拟了细长体截面绕流结构的演变过程.指出随着细长体背涡的发展,导致截面流场的拓扑结构发生变化,会出现一种临界流动状态.并用微分方程的定性理论分析了此时流场中出现的一种高阶奇点.这种高阶奇点的指数为-3/2,它是结构不稳定的,稍有扰动就会产生分叉,使流场的拓扑结构发生变化.得出了定常对称背涡流态下细长体的空间绕流结构图.     

Materials selection for electronic enclosures in space environment considering electromagnetic interference effect

Using low power electronic devices for space applications to reduce the mass and energy consumption has lead to electromagnetic interference (EMI) problem. Electronic enclosures are used to shield electronic devices against EMI. In the past, electromagnetic shielding has been mainly the only criteria considered in electronic enclosure design. However, there are several structural and thermal requirements for selection of shielding materials which should also be taken into account. In this research work, three quantitative materials selection methods, i.e. Digital Logic (DL), Modified Digital Logic (MDL), and Z-transformation, are employed to select the best material from among a list of candidate materials. Composite and metallic electronic enclosures are explored and the best material is selected. Z-transformation method is applicable to both of the considered case studies while DL and MDL can only be used for solving one of them. Z-transformation method ranks aluminum as the first choice among various metallic materials. The wide range of Z-transformation application and its practical results confirm the superiority of Z-transformation method over DL and MDL methods.     

The effects of the solar magnetic polarity and the solar wind velocity on Bz-component of the interplanetary magnetic field

We have studied the effect of both solar magnetic polarity and the solar wind velocity on the Bz-component of the interplanetary magnetic field, IMFBz, for the minimum activity of the solar cycles 21, 22, 23 and 24. We made a statistical study of IMFBz in the first section which is considered as an extension of Lyatsky et al. (2003). They made a statistical study of IMFBz for two periods of minimum solar activity 22 and 23 related to 1985–1987 and 1995–1997 when the solar magnetic field had opposite polarity. Our results seem to be consistent with the results obtained by Lyatsky et al. (2003). We found that there is a dependence of IMFBz on the IMFBx and the solar magnetic polarity for the minimum periods of the selected four solar cycles. In addition, we found that there is a dependence of IMFBz on the solar wind velocity.