从“权力距离”视角解读大学英语口语教学之现状

大学英语口语教学中的一个难题是学生在口语练习过程中的不参与、不配合。文化维度理论的“权力距离”可从文化差异的角度去解读造成师生关系尴尬的原因,从而为改进大学英语口语教学效果提出一些有效的教学建议。     

超大功率电推进电源处理单元关键技术研究

针对深空探测等空间任务对超大功率(10kW~100kW范围)电推进系统的需求,通过对国内外超大功率电推进技术的调研,提出了一种50kW超大功率霍尔电推进系统电源处理单元（Power Processing Unit,PPU）设计方案,重点对核心的阳极电源关键技术进行研究,提出了四管Buck-Boost变换器和三相LLC谐振变换器级联的设计方案,为我国超大功率PPU的发展提供了技术参考。     

大功率空间核电推进技术研究进展

大功率空间核电推进系统是空间核电源技术和大功率电推进技术的高度融合,具有高能量密度、超高比冲、较大推力的优势,可适用于超大型航天器轨道转移任务、远距离无人深空探测任务、载人火星等大型深空探测任务,能够极大地拓展人类深空探测的能力。本文针对大功率空间核电推进技术,对其工作原理和系统组成进行了介绍,同时开展了关键技术梳理,重点归纳了国内外在技术领域的研究历程和最新进展。     

电源转换模块LTC3780的工作性能仿真分析

为了获得可应用于航天器系统的稳定的供电电源,采用高性能升压-降压开关稳压控制器LTC3780,设计在低压、高压和正常供电时都能实现预期输出电压的电源转换电路;利用LTspice软件对该电源转换电路进行工作性能仿真,主要对不同输入电压时的输出电压和不同负载时的带载能力进行了仿真,通过仿真实现了稳定的电压输出和较强的带载能力。     

数字模拟技术在非线性随机响应分析中的应用

本文将数字模拟方法与NASTRAN软件的非线性瞬态响应模块结合起来，用于求解在随机激励下非线性系统的随机响应问题，同时用该方法对一个典型结构（悬臂矩型板）进行了计算与实验，结果是令人满意的。     

Impact of DORIS ground antennas environment on their radio signal quality

Among the factors which may disrupt the DORIS measurements quality, the ground antennas environment is of high importance. For a set of 15 selected DORIS beacon, the differences between the effective and theoretical power received on-board the satellites (SPOT-5 and Envisat) have been analyzed in terms of spatial direction around the antenna. Such antenna maps have also been established regarding the Doppler residuals of the least-square precise orbit adjustment. Thanks to 360° views from the antennas and aerial views of the sites, the impact of the signal obstructions (trees, roofs, antennas …) on power attenuation and Doppler residuals is discussed. Depending on the nature of the obstructed object, the attenuation level can reach more than 5 dB, and the residual RMS of the orbit adjustment may be doubled from the nominal value, reaching 1 mm/s locally. The nature of the ground at the foot of the antennas has been correlated to DORIS signal quality at high elevation: reflections on flat surfaces (e.g. roofs) affect the signal more significantly than reflections on natural ground (e.g. soil). In particular, a modeling of the multipath phenomenon affecting Fairbanks site has been established and fits remarkably with the observations. Finally, an evaluation of the direct impact of obstructing objects on the orbit has also been performed. The example of a scaffolding at Kauai site displays a few millimeters error in the along-track position of the satellite.     

Optimal deployment schedule of an active twist rotor for performance enhancement and vibration reduction in high-speed flights

The best active twist schedules exploiting various waveform types are sought taking advantage of the global search algorithm for the reduction of hub vibration and/or power required of a rotor in high-speed conditions.The active twist schedules include two non-harmonic inputs formed based on segmented step functions as well as the simple harmonic waveform input.An advanced Particle Swarm assisted Genetic Algorithm (PSGA) is employed for the optimizer.A rotorcraft Computational Structural Dynamics (CSD) code CAMRAD Ⅱ is used to perform the rotor aeromechanics analysis.A Computation Fluid Dynamics (CFD) code is coupled with CSD for verification and some physical insights.The PSGA optimization results are verified against the parameter sweep study performed using the harmonic actuation.The optimum twist schedules according to the performance and/or vibration reduction strategy are obtained and their optimization gains are compared between the actuation cases.A two-phase non-harmonic actuation schedule demonstrates the best outcome in decreasing the power required while a four-phase non-harmonic schedule results in the best vibration reduction as well as the simultaneous reductions in the power required and vibration.The mechanism of reduction to the performance gains is identified illustrating the section airloads,angle-of-attack distribution,and elastic twist deformation predicted by the present approaches.     

FY-2卫星功率合成器低气压放电和微放电预防

阐述了星载无源大功率部件发生微放电和低气压放电的原因.讨论了提高风云二号(FY-2)卫星测控系统中功率合成器低气压放电阈值的方法,并提出增大内部间隙、提高器件内表面洁净度和改进调谐螺钉设计等措施.实验结果表明,功率合成器放电容量由4.5 W提高至9 W,从而大幅改善了其低气压临界工作状态.     

Experimental investigation of flow and distortion mitigation by mechanical vortex generators in a coupled serpentine inlet-turbofan engine system

The performance of compact,aggressive ducts in advanced propulsion systems is limited by the internal flow separation coupled with the formation of secondary counter-rotating vortices that give rise to intensive flow distortions at the duct exit.An experimental investigation was conducted to study the flow field and passive suppression of flow separation and Aerodynamic Interface Plane (AIP) distortion in a serpentine air inlet duct.Tests were performed by a turbofan engine at several Engine Ope...     

一种基于单定向耦合器比较法的8 mm小功率校准系统

介绍了一种基于单定向耦合器比较法组建的8mm小功率校准系统,讨论了校准原理、系统组成、校准不确定度,通过分析和实验证明系统作为8mm小功率座的校准是可行的.