Controllably asymmetric beam splitting via gap-induced diffraction channel transition in dual-layer binary metagratings

In this work, we designed and studied a feasible dual-layer binary metagrating, which can realize controllable asymmetric transmission and beam splitting with nearly perfect performance. Owing to ingenious geometry configuration, only one meta-atom is required to design for the metagrating system. By simply controlling air gap between dual-layer metagratings, high-efficiency beam splitting can be well switched from asymmetric transmission to symmetric transmission. The working principle lies on gap-induced diffraction channel transition for incident waves from opposite directions. The asymmetric/symmetric transmission can work in a certain frequency band and a wide incident range. Compared with previous methods using acoustic metasurfaces, our approach has the advantages of simple design and tunable property and shows promise for applications in wavefront manipulation, noise control and one-way propagation.     

温度/应变/扭曲三参量同时测量低成本传感系统

提出了一种利用布喇格光纤光栅反射光作信号源、高频CO2激光脉冲写入的长周期光纤光栅和超周期光纤光栅作传感器实现温度、应变和扭曲同时测量的全光栅型低成本强度解调传感方案.文中利用长周期光纤光栅边缘滤波效应实现了温度、应变和扭曲传感信号的实时解调.实验结果表明,其温度和应变的测量灵敏度分别为－0.211 dB/℃和－0.012 dB/10με;而扭曲率的测量灵敏度为0.4394 dB/(rad·m－1),是该法写入普通LPFG的4倍以上.     

空间雷电探测实时采集定位系统

星载雷电探测定位系统是利用光学探测器探测闪电事件的地理位置和光脉冲波形,系统采用CPLD+DSP的数字图像处理方案,利用了CPLD复杂逻辑可编程特性将系统的部分或全部功能集成在一片CPLD上,减小了系统硬件复杂程度,节省了印制版空间.利用DSP高速数字信号处理特性完成实时处理图像数据的功能.系统用CPLD完成图像信号的采集、编码和存储控制,缩小了星载设备体积,简化了电路结构;用DSP完成大量图像数据处理工作,提高了系统工作的实时性.     

一种基于数字全息技术的盲音频水印算法

提出了一种基于数字全息技术的盲音频水印算法.水印图像经随机相位调制形成物光波,该物光波的傅里叶变换与参考光波发生干涉,形成傅里叶变换全息图.再利用离散余弦变换的能量压缩能力,通过量化算法把降维的水印,即傅里叶变换全息图嵌入音频信号中,在水印提取过程中不需要原始音频信号的参与.仿真实验表明,该算法对低通滤波、噪音干扰特别是剪裁具有一定的稳健性.     

Structural Entropy of the Stochastic Block Models

With the rapid expansion of graphs and networks and the growing magnitude of data from all areas of science, effective treatment and compression schemes of context-dependent data is extremely desirable. A particularly interesting direction is to compress the data while keeping the “structural information” only and ignoring the concrete labelings. Under this direction, Choi and Szpankowski introduced the structures (unlabeled graphs) which allowed them to compute the structural entropy of the Erdős–Rényi random graph model. Moreover, they also provided an asymptotically optimal compression algorithm that (asymptotically) achieves this entropy limit and runs in expectation in linear time. In this paper, we consider the stochastic block models with an arbitrary number of parts. Indeed, we define a partitioned structural entropy for stochastic block models, which generalizes the structural entropy for unlabeled graphs and encodes the partition information as well. We then compute the partitioned structural entropy of the stochastic block models, and provide a compression scheme that asymptotically achieves this entropy limit.     

The kinetics and compartmentalization of seeded emulsion polymerization of styrene with a series of seeds of different size

The Interval II kinetics and compartmentalization effect of emulsion polymerization of styrene with the seeds of five radii (r=40.2, 51.3, 76.5, 99.7 and 252.0 nm) have been studied. The kinetic parameters, i.e., the rate coefficients ρ, K and C which refer, respectively, to the entry of free radicals into latex particles, the exit of free radicals from the particles and the bimolecular termination of free radicals within the particles; n_ss and n_ss(thermal), the average number of free radicals per particle in the steady state and in the thermally induced background polymerization, respectively, are obtained. The propagating rate coefficient k_p, the termination rate coefficient k_t, as far as possible, are calculated in the runs. From this work, it can be concluded that the kinetic behavior, the kinetic parameters and the compartmentalization effect of emulsion polymerization are greatly influenced by the latex particle size.     

以天然椰壳为碳源制备硼碳氮微米线

首次以天然椰壳为碳源,高温下在流动氨气中用氯化铁(FeCl3)对无定型硼粉和椰壳进行退火,大规模合成了硼碳氮(BCN)微纳米结构,即由纳米片包覆竹节状纳米管组装而成的微米线.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶红外光(FTIR)、X射线光电子能谱仪(XPS)以及荧光光谱仪(PL)等手段对所得微米线进行了表征.结果显示,微米线的直径约为200～600 nm,纳米片的平均厚度小于20 nm.纳米片大多是以弯曲和皱折的形态分离的.微米线由B、C、N元素组成,计算出B、C、N的原子比为11.4:1:9.2.提出了汽液固(VLS)和汽固(VS)相结合的生长机理并对B11.4 CN9.2微米线的形成进行了研究.初步讨论了反应温度对微米线的影响.     

Syntheses,crystal structures and properties of Cd(II) and Ag(I) complexes based on 2-p-methylphenyl-5-(2-pyridyl)-1,3,4-thiadiazole

Abstract

Complexes of [CdL₂(NO₃)₂]·1.5H₂O and [Ag₂(μ-L)₂(NO₃)₂] were synthesized by the reactions of 2-p-methylphenyl-5-(2-pyridyl)-1,3,4-thiadiazole (L) with Cd(NO₃)₂·4H₂O and AgNO₃, respectively. Their structures were determined by single crystal X-ray diffraction. The photophysical property and thermal stability were characterized by FT???IR, UV???Vis absorption, fluorescence, and thermogravimetric analysis (TGA). Both complexes belong to the triclinic system with space group p???1. The central metal of [CdL₂(NO₃)₂]·1.5H₂O has a distorted octahedral geometry [CdN₄O₂], while two central Ag(I) atoms of [Ag₂(μ-L)₂(NO₃)₂] exhibit distorted tetrahedral geometries [AgN₃O].     

主动控制压电旋转悬臂梁的参数振动稳定性分析

在工程实际中旋转机械由于制造和加工误差,装配的不均匀性等原因,往往会脉动运行,这将使得机械系统发生参数振动. 当脉动参数满足一定关系时,这种参数振动将会失稳,进而影响机械结构的正常运转. 本文针对这一问题,引入压电材料对 脉动旋转悬臂梁系统的振动进行控制,研究主动控制悬臂梁系统的参数振动优化设计问题,采用 Hamilton 变分原理与一阶 Galerkin 离散相结合的方法,建立了受速度反馈传感器主动控制的压电旋转悬臂梁的一阶近似线性控制方程. 运用多尺度方法,得到了压电旋转悬臂梁系统在发生1/2亚谐波参数共振时稳定性边界的控制方程,并利用直接分析方法验证了解析摄动解的正确性. 将摄动解中临界阻尼比和轮毂角速度脉动幅值的无量纲参数作为评价系统稳定性能的指标. 通过数值算例,分析了轮毂半径、轮毂角速度平均值和脉动幅值、梁长以及速度传感器的反馈增益系数对系统稳定性区域的影响. 研究结果表明,梁长、轮毂半径、脉动幅值会降低系统稳定性,反馈增益系数可以提高系统稳定性,而轮毂角速度平均值与系统稳定性之间有非单调的关系. 为进一步设计压电旋转机械结构提供了理论依据.      

主动射流控制水翼空化的数值模拟与分析

为了改善高速流动工况下水翼吸力面上流场的空化特性,提出了水翼表面主动射流对绕水翼周围流动加以控制的方法.基于密度分域滤波的FBDCM混合湍流模型联合Zwart-Gerber-Belamri空化模型,分析了来流空化数为0.83,来流攻角为8°,射流位置距水翼前缘为x=0.19c时,主动射流对于水翼吸力面上流动的空化特性和水动力特性影响.对回射流的强度进行了量化分析,以探究回射流与流场空化特性的关系.数值分析结果表明,在射流水翼吸力面上的时均空泡体积为原始水翼的1/15,使得流场内空化流动由云空化状态转变为较为稳定的片空化状态,显著地削弱了云空化的发展.此外,射流极大地改善了水翼的水动力性能,使得水翼的升阻比较原始水翼提高了22.9%,空泡的脱落频率减少了26.2%,空泡脱落所引起的振幅减小了9.1%.射流大幅降低了水翼吸力面上低压区面积,水翼吸力面上流体的逆向压力减小,回射流强度降低;同时,射流使水翼吸力面上的边界层减薄,增强了流动的抗逆压梯度能力,一定程度上阻挡了回射流向水翼前缘的流动,这也从机理上分析了主动射流抑制空化的原因.