摘要：尾座式垂直起降(Vertical takeoff/landing,VTOL)无人机(Unmanned aerial vehicle,UAV)稳定性差,与传统起落架的适配性低。针对上述问题,提出了一种采用自由尾翼技术的新型起落架。该起落架采用串联多级结构,在降低机身高度的同时,保证了巡航状态下尾翼力臂的长度,并通过虚拟中心点力分布技术对动态着陆过程进行调控,简化了控制过程,有利于模式转换过程中的无缝轨迹优化。随后基于猫中心点单点数据集,利用神经网络对起落架控制进行训练,有效提高了起落架自适应起落速度和精度。最后,结合无人机不同模式的参数要求,进行多目标优化和相似性转换,有效提高了尾座式垂直起降无人机的着陆适应性和稳定性。

摘要：Shock control bumps are a promising technique in reducing wave drag of civil transport aircraft flying at transonic *** paper investigates the optimization of 3D shock control bumps on a supercritical wing with a sweep angle of 16°at the1/4 chord.A similar supercritical wing with a higher sweep angle of 24.5°at the 1/4 chord has been adopted as a baseline for the *** results show that the drag coefficient of the low sweep wing with the optimized 3D shock control bumps is reduced below that for the high sweep wing,indicating shock control bumps can be used as an effective means to reduce the wave drag caused by reducing the wing sweep *** the point of view of the wing structure design,lower sweep angle will also bring the benefits of weight reduction,resulting in further fuel reduction.

摘要：声束的连续动态扫描在超声成像、水下目标定位和声呐通信等诸多领域发挥关键作用.传统方法通常依赖于发射装置的机械扫描或有源相控阵的波束整形来实时调控声束的空间指向性,存在成本高、尺寸大、主动控制系统复杂而精准操控困难等问题.本文提出并构建了一种基于无源声学超表面的紧凑型静态声呐器件,无需主动控制和机械移动,仅在单一声源的作用下即可实现声束的动态扫描操控.这种新型声呐器件由具有深度亚波长厚度的二值化振幅编码单元组合而成,能够将单一声源发射的梳状频率谱转化为具有相同频率和空间间隔的声焦点阵列,从而引入频率梯度这一新的声波操控自由度,并通过时空声干涉效应产生可连续旋转的动态扫描声束.实验结果验证了所设计超构声呐的高速、宽角度声束扫描性能.此外,通过与传统的相位梯度调控技术结合,该机制还可以对扫描声束的空间形态进行任意的调节.这种基于静态无源超构声呐的声束动态扫描机制为声波的时空调控开辟了新的研究范式,并有望在水下对抗、超声诊疗等重要领域产生实际应用价值.

摘要：The objective of this study was to investigate the mechanical characteristics of implant-abutment interface design in a dental implant system, using nonlinear finite element analysis （FEA） method. This finite element simulation study was applied on three commonly used commercial dental implant systems： model I, the reduced-diameter 3i implant system （West Palm Beach, FL, USA） with a hex and a 12-point double internal hexagonal connection; model II, the Semados implant system （Bego, Bremen, Germany） with combination of a conical （45° taper） and internal hexagonal connection; and model III, the Br,~nemark implant system （Nobel Biocare, Gothenburg, Sweden） with external hexagonal connection. In simulation, a force of 170 N with 45°oblique to the longitudinal axis of the implant was loaded to the top surface of the abutment. It has been found from the strength and stiffness analysis that the 3i implant system has the lowest maximum yon Mises stress, prirlcipal stress and displacement, while the Br^nemark implant system has the highest. It was concluded from our preliminary study using nonlinear FEA that the reduced-diameter 3i implant system with a hex and a 12-point double internal hexagonal connection had a better stress distribution, and produced a smaller displacement than the other two implant systems.

摘要：通过设计特定的时空调制,合成磁性的概念最近被提出以实现对光子和声子等电荷中性粒子的非互易操控,但现有方案存在着隔离度低、信号频率变化等问题.本文设计了一种新型耦合共振腔系统,其中动态耦合的相位作为实现声学合成磁场的新机制并打破了系统的时间反演对称性,最终取得了优异的声波非互易传输.基于旋转波近似方法,作者严格推导出了实现系统强非互易声传输的参数条件.通过优化动态耦合之间的相位差以及耦合强度,实验展示了隔离度达45-dB和正向传输率达0.85的优异单向声传输.此外,这种单向声传输具有始末态频率不变和隔离方向可电控等重要特性.该研究突破了现有声波单向操控机制在效率和隔离度方面的局限,并为实现弗洛奎和非线性声学拓扑绝缘体提供了新途径.

摘要：Heterosis represents one of the most revolutionary advancements in crop *** the genetic dissection of heterosis,NCIII design is one of the most powerful and widely used mating ***,the methodologies for quantitative trait loci (QTL) detection in the design were mostly based on composite interval ***,in this study,our purpose was to develop a statistical method for mapping epistatic QTL associated with heterosis in the RIL-based NCIII ***,we derivated the expectations of two classical linear transformations,Z 1 and Z 2,while a quantitative trait was controlled by two QTL with digenic epistasis and arbitrary linkage under the F ∞ and F 2 metric ***,we constructed an epistatic genetic model that includes all markers on the whole genome simultaneously,and estimated all the parameters in the model by the empirical Bayes ***,a series of Monte Carlo simulation experiments was carried out to confirm the proposed *** results show that:(1) all the augmented genetic parameters for main-effect QTL could be rightly identified with satisfactory statistical power and precision;(2) the statistical powers in the detection of augmented epistatic effects were substantively affected by the signs of pure epistatic effects;(3) it is more difficult to detect epistatic QTL than to detect main-effect QTL;(4) statistical power is higher in the RIL-based NCIII design than in the F 2-based NCIII design,especially in the detection of the augmented epistatic effect that consists of two pure epistatic effects in opposite directions.

摘要：在设计圆柱形模具的纤维丝束铺放轨迹的过程中,有许多问题需要解决,例如机器与模具之间的干涉以及旋转轴在纤维铺丝头上的超程。当汽缸表面上的压力沿某个方向或法线平面内的某个角度倾斜时,旋转轴的运动特性将有所不同。本文分析了凹形圆柱表面对纤维铺放机运动特征的压力角影响,在升降行程不变的情况下,通过倾斜施压的方式扩大了铺放区域,这对于防止干涉和选择后处理算法具有重要意义。

摘要：增加阴离子交换膜(AEMs)亲水段中柔性侧链阳离子的局部聚集度有助于改善膜材料的性能.然而,受结构设计策略和合成方法的限制,亲水链段局部含有四个以上柔性侧链阳离子结构的AEMs还鲜有报道.为有效提高AEMs的离子传导率、碱稳定性和尺寸稳定性,我们报道了一系列亲水链段局部含八个柔性侧链阳离子的聚芳醚砜AEMs.对所制膜材料(PAES-8TMA-x)的结构、离子交换容量(IEC)、吸水率、尺寸溶胀、碱稳定性和氢氧根电导率进行了研究分析,还系统比较了不同类型AEMs的结构与性能之间的关系.IEC值为1.76–2.76 mmol g^-1的AEMs表现出较全面的优良性能,其60℃时的氢氧根电导率在62.7–92.8 m S cm^-1,尺寸溶胀在8.3%–15.8%.代表性的PAES-8TMA-0.35样品,在90℃的2 mol L^-1Na OH中浸泡480 h后,IEC和氢氧根电导率分别可保持初始值的82.9%和79.6%.本研究工作延伸了局部含高密集柔性侧链阳离子结构AEMs的设计和制备方法,并为新型高性能AEMs材料的研制提供了新的策略.

摘要：为有效改善聚合物阴离子交换膜材料(AEMs)的性能,本研究在综合考虑聚合物结构、离子官能团种类及其链接方式对AEMs影响的基础上,设计制备了一系列含有柔性侧链型季鏻阳离子结构的新型聚芳醚腈(PAEN-TPP-x)阴离子交换膜.分别对所制聚芳醚腈阴离子交换膜的合成方法、结构和离子交换容量、吸水率、溶胀率、氢氧化物电导率及碱稳定性进行了系统研究,并与一些其他已报道的AEMs进行了比较研究,以进一步探索其结构与性能之间的关系.研究发现所制备的含有柔性侧链型季鏻阳离子结构的聚芳醚腈阴离子交换膜具有良好的综合性能.在60℃下,它们的吸水率、溶胀率和离子传导率分别为11.6%–22.7%,4.4%–7.8%和28.6–45.8 mS cm^-1.与此同时,该类AEMs还表现出良好的碱性稳定性,其中代表性样品PAEN-TPP-0.35在2 mol L^-1NaOH溶液中、60和90℃下浸泡480 h后的OH-传导率分别保持在其初始值的82.1%和80.6%.本研究可为高性能聚合物阴离子交换膜材料的设计制备和改性提供新的思路和方法.

摘要：为优化设计切纵流联合收割机纵轴流滚筒的长度,该文通过设计脱粒分离长度可变的纵轴流滚筒并进行喂入量为7 kg/s的水稻脱粒分离性能和籽粒分布试验,分析纵轴流滚筒下脱出混合物的分布规律,建立纵轴流滚筒的籽粒分布方程,计算纵轴流滚筒长度;通过计算纵轴流滚筒顶盖导流板的最佳导角对纵轴流滚筒长度进行优化,确定纵轴流滚筒长度的最佳值并进行水稻脱粒分离性能试验。结果表明,在水稻喂入量为7 kg/s,纵轴流滚筒顶盖导流角为7.64°时,优化后的纵轴流滚筒长度最佳值为3 159.77 mm,经优化后的纵轴流滚筒脱粒分离的籽粒夹带损失率约为0.29%。该研究为纵轴流联合收割机的纵轴流滚筒设计提供了参考。