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541.
542.
基于接口的协同仿真技术在动态优化设计中的应用 总被引:7,自引:0,他引:7
机械系统进行结构动态优化设计的最终目标大多归结为对其进行几何形状的优化,在应用极小值原理对机械结构进行三维形状优化设计时,通常须要使用复杂数值方法才能求解,并且求解的过程相当困难。将先进的协同仿真技术作为一种有效求解工具应用到极小值原理的动态优化设计中,实现对不同设计变量的目标函数的求解。以行星框架为例,采用基于接口的协同仿真技术为求解工具,以行星轮数目为参变量,应用极小值原理对行星框架的几何形状进行动态优化设计,对行星框架的疲劳损伤寿命提供量化数据,为对其进行结构改进提供科学理论依据。 相似文献
543.
利用电磁波传递能量和信息一直是备受人们关注和重视的研究课题,因为它在通讯、能源、环境、医药等多应用领域中都扮演重要的角色。近年来,随着微纳米制造技术的进步,超材料的出现为解决传统电磁技术的瓶颈问题(如光路体积大、结构复杂、功能单一等问题)提供了新思路和新机会。得益于超强的电磁场调控能力,这些材料不仅能够实现传统光学元件的诸多功能,而且还能实现很多自然界不存在的、奇异的电磁响应和特性。本文将结合作者近年来的研究工作,对超材料的研究进展和发展趋势进行综述,主要思路是根据调控的电磁波自由度对超材料进行分类和阐述。最后作者还将介绍基于相变材料的主动调控超材料。 相似文献
544.
研究了在高温工作环境下Ti/Al/Ni/Au(15nm/220nm/40nm/50nm)四层复合金属层与n-GaN的欧姆接触的高温工作特性.退火后样品在500℃高温下工作仍能显示出良好的欧姆接触特性;接触电阻率随测量温度的增加而增大,且增加幅度与掺杂浓度有密切关系.掺杂浓度越高,其接触电阻率随测量温度的升高而增加越缓慢;重掺杂样品的Ti/Al/Ni/Au-n-GaN欧姆接触具有更佳的高温可靠性;当样品被施加500℃,1h的热应力后,其接触电阻率表现出不可恢复性增加. 相似文献
545.
随着5G移动通信网络走向商业化,围绕新一代移动通信系统(6G)的发展愿景、能力需求与关键技术开展研究正在成为新的热点。首先,该文概括了未来6G可能涉及的星地深度融合、新谱段通信、分布式协作MIMO和智能通信等关键技术方向,重点探讨了基于星地深度融合的天地一体化网络(SGIN);然后,针对可能存在的两种典型网络拓扑架构,分析了星间高速链路、星地馈电链路和星地用户链路的特点和技术要求,综述了3种不同类型传输链路的高速通信进展情况。最后,对未来6G天地互联网络亟需突破的光学相控阵多用户接入、高效能星地激光通信和光电一体化组网等关键技术进行分析与展望,以期为后续相关研究指明方向。 相似文献
546.
近场信源定位是下一代无线通信中的一个重要研究方向,现有的方法大多集中在传统子空间或在格稀疏方法。针对子空间类方法损失阵列孔径和稀疏表示类方法精度受网格划分效应制约的问题,该文提出了一种基于离格稀疏表示的定位方法。首先通过获得一个高阶累积量矩阵建立基于角度参数的离格信号模型,利用交替迭代优化方法实现角度的估计。然后根据角度估计值建立基于距离参数的离格信号模型,并采用交替迭代方法进行求解。仿真结果表明,所提方法不仅具有较高的估计精度,而且可以实现角度和距离参数的正确配对。 相似文献
547.
548.
Tianjin Li Bo Chen Meifang Cao Xinping Ouyang Xueqing Qiu Changzhi Li 《American Institute of Chemical Engineers》2023,69(2):e17877
The efficient utilization of lignin remains a great challenge due to its complex nonrepetitive structure and the lack of efficient catalyst. Herein, a single-atom catalyst Ni@N-C was designed via a facile chelation-anchored strategy. Ni atoms were immobilized on the N-doped carbon carrier by a two-stage pyrolysis of a mixture of d -glucosamine hydrochloride, nickel acetate, and melamine. d -glucosamine hydrochloride as a chelating agent prevented the aggregation of Ni2+, and melamine provided enough N to anchor Ni by forming Ni–N4 structure. Ni@N-C gave a 31.2% yield of aromatic compounds from lignin hydrogenolysis, which was twice higher than that achieved by Ni cluster catalyst. Based on the experimental and density functional theory (DFT) calculation results, the higher activity of Ni@N-C was attributed to its lower H2 dissociation energy and the reduced energy barriers of the transition states. The strategy described opens an efficient green avenue for preparing single-atom catalyst that possesses outstanding activity in lignin depolymerization. 相似文献
549.
Kang Du Changzhi Yin Zhengyu Zou Mingfei Cheng Yiyang Cai Jiaqing Yang Meng Zhang Wenzhong Lu Shengxiang Wang Wen Lei 《Journal of the American Ceramic Society》2023,106(10):5822-5831
Novel BaCa2M3O9 (M = Si, Ge) microwave dielectric ceramics were prepared via solid-state reaction with sintering at 1125°C–1275°C for 5 h. Single-phase BaCa2M3O9 (M = Si, Ge) ceramics were obtained according to stoichiometry. The single-phase BaCa2Ge3O9 ceramic was confirmed through Rietveld refinement and high-resolution transmission electron microscopy/selected area electron diffraction and synthesized for the first time. The BaCa2M3O9 (M = Si, Ge) exhibited a triclinic structure with a P space group and good microwave dielectric properties. The εr, Q × f, and τf values of BaCa2M3O9 (M = Si, Ge) ceramics are mostly dominated by the relative density, ionic polarizability, relative covalence, and bond energy of M–O bond, respectively. A high Q × f value (61 800 GHz at 16.3 GHz) was obtained in BaCa2Ge3O9 ceramic due to its high rc (Ge–O) and low intrinsic dielectric loss. The BaCa2Si3O9 ceramic exhibited small |τf| value (‒36.4 ppm/°C) due to its large ESi-O. Excellent microwave dielectric properties (εr = 8.31, Q × f = 61 800 GHz, and τf = ‒58.7 ppm/°C) were obtained for the BaCa2Ge3O9 ceramic. 相似文献
550.
Kang Du Tailai Wen Mengdie Zhou Zheyu Liu Changzhi Yin Wei Zhu Cai Zhou Bohan Zhang Shengxiang Wang Wen Lei 《Journal of the American Ceramic Society》2023,106(5):2941-2952
The traditional solid-state reaction method was used to prepare Ca2Sn2−xMxAl2O9 (M = Ti, Zr, and Hf) ceramics. Then, the impact of an M4+ substitution of Sn4+ on the phase transition, crystal structural parameter, and microwave dielectric properties of Ca2Sn2−xMxAl2O9 (0 ≤ x ≤ 0.4) ceramics were investigated. Ti4+ could not replace the Sn4+ of Ca2Sn2Al2O9 due to its small ionic radius, and the Al-based second phases of Ca2Sn2−xTixAl2O9 ceramics were confirmed by the X-ray diffractometer and EDS map scanning results. With the Zr4+ and Hf4+ substitutions of Sn4+, the SnO2 and CaSnO3 second phases of Ca2Sn2Al2O9 ceramic were inhibited, and the Ca2Sn2−xMxAl2O9 (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) single-phase ceramics with orthorhombic structure (Pbcn space group) were obtained. New MO2 (M = Zr and Hf) and CaAl2O4 second phases appeared in the Ca2Sn2−xMxAl2O9 (M = Zr and Hf) (0.3 ≤ x ≤ 0.4) ceramics, and their contents increased gradually with the increase in x. The Ca2Sn2−xMxAl2O9 (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) ceramics exhibited high Q × f because of their pure phase compositions, and the Q × f of Ca2Sn2Al2O9 ceramic was improved to 77 800 GHz (12.6 GHz) in the Ca2Sn1.9Zr0.1Al2O9 ceramic. The Q × f values of Ca2Sn2−xMxAl2O9 single-phase ceramics were mainly controlled by rc (Sn/M–O) and rc (Al–O). The τf values of single-phase Ca2Sn2−xMxAl2O9 ceramics were related to octahedral distortions. The Zr4+ and Hf4+ substitution of Sn4+ optimized the phase compositions and microwave dielectric properties of the Ca2Sn2−xMxAl2O9 ceramics, and the Ca2Sn1.9Zr0.1Al2O9 ceramic sintered at optimal temperature exhibited excellent microwave dielectric properties (εr = 8.67, Q × f = 77 800 GHz at 12.6 GHz and τf = −69.8 ppm/°C). 相似文献