Chin. Phys. B Vol. 21. No. 6 （2012） 066301

[BO4]^-1＋4SIO2 → [BSi4O1o]^-1 ＋ 02, 2BaC03＋SiO2→Ba2SiO4＋2C02. The relatively higher temperature that is suffi-cient to melt the mixture was chosen to be 1100 ℃. 510 ℃ was determined as the annealing temperature to exclude stress and air bubbles.     

Tunable Ba0.5Sr0.5TiO3 film bulk acoustic resonators using SiO2/Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

Hole-drilling method using grating rosette and Moiré interferometry

The hole-drilling method is one of the most wellknown methods for measuring residual stresses. To identify unknown plane stresses in a specimen, a circular hole is first drilled in the infinite plate under plane stress, then the strains resulting from the hole drilling is measured. The strains may be acquired from interpreting the Moire signature around the hole. In crossed grating Moire interferometry, the horizontal and vertical displacement fields （u and v） can be obtained to determinate two strain fields and one shearing strain field. In this paper, by means of Moire interferometry and three directions grating （grating rosette） developed by the authors, three displacement fields （u, v and s） are obtained to acquire three strain fields. As a practical application, the hole-drilling method is adopted to measure the relief strains for aluminum and fiber reinforced composite. It is a step by step method; in each step a single laminate or equivalent depth is drilled to find some relationships between the drilling depth and the residual strains relieved in the fiber reinforced composite materials.     

NaYF4∶Eu3+, Tm3+, Yb3+材料中Stokes和反Stokes发光研究

合成了Eu3+,Tm3+和Yb3+掺杂的NaYF₄材料。360 nm光激发呈蓝色发光,峰值位于452 nm,对应Tm3+的1D₂→3F₄跃迁;395 nm光激发呈橙色发光,峰值位于591 nm,对应Eu3+的5D₀→7F₁跃迁;409 nm光激发呈红色发光,峰值位于613 nm,对应Eu3+的5D₀→7F₂跃迁;980 nm光激发呈蓝色和红色发光,发光峰位于474和646 nm。蓝光来源Tm3+的1G₄ →3H₆跃迁,红光来源Tm3+的1G₄→3F₄跃迁。在双对数曲线中,蓝光474 nm和红光646 nm的斜率分别为2.1和2.4,在980 nm光激发下,蓝光和红光发射都是双光子过程。还研究了材料的吸收光谱,并利用X射线衍射,扫描电镜测试了材料的物相结构和微观形貌。结果表明：NaYF₄∶Eu3+, Tm3+, Yb3+材料具有较规则的六方相结构,结晶良好。     

化学反应对竖直平板边界磁流体动力学微极流体滑流的影响

Heat and mass transfer effects on the unsteady flow of a micropolar fluid through a porous medium bounded by a semi-infinite vertical plate in a slip-flow regime are studied taking into account a homogeneous chemical reaction of the first order. A uniform magnetic field acts perpendicular to the porous surface absorb micropolar fluid with a suction velocity varying with time. The free stream velocity follows an exponentially increasing or decreasing small perturbation law. Using the approximate method, the expressions for the velocity microrotation, temperature, and concentration are obtained. Futher, the results of the skin friction coefficient, the couple stress coefficient, and the rate of heat and mass transfer at the wall are presented with various values of fluid properties and flow conditions.     

煤粉燃烧中NOx和SOx生成的详细反应机理模拟

采用详细化学反应机理与CFD方法耦合的煤粉燃烧数值模拟程序,计算了煤粉燃烧过 程中CO, NOx和SOx等的浓度分布特性. 通过与实验对照,验证了数值模拟方法的 可靠性,并分析了燃烧温度和煤粉细度等因素对于NO生成的影响. 结果表明温度对于NO的 生成影响较大,随着温度的增加,NO的生成浓度明显增加;对于不同煤种,可能存在一个温 度点,这时NO的生成速率将非常快;在计算范围内,温度对SO2的最终生成浓度没有 明显影响,而只影响SO2的释放过程. 煤粉细度对于NO生成有较小的影响.     

变可信度模型管理优化设计方法在气动外形设计中的应用

在信赖域最优化方法的基础上,将梯度搜索方法与近似模型管理结构相结合,结合N-S方程与Euler方程,建立了一种用于气动外形设计的梯度AMF优化设计方法.该方法在气动优化中,通过对采用不同的流体控制方程的计算结果进行组织和管理,从而可以在优化迭代过程中将主要搜索过程集中在低可信度模型的计算上,并利用高可信度模型监控优化过程,使得最终的优化解收敛到高可信度模型上.本文采用梯度AMF气动优化设计方法进行翼型设计,取得了良好的设计效果,实际结果表明本文提出的方法具有可行性和适用性.     

二维双曲型守恒律的一种五阶松弛格式

松弛格式是Jin和Xin提出的无振荡有限差分方法,其主要思想是将守恒律转化为松弛方程组进行求解.本文用逐维五阶WENO重构和显隐式Runge-Kutta方法对松弛方程组的空间和时间进行离散,得到了一种求解二维双曲型守恒律五阶松弛格式.所得格式保持了松弛格式简单的优点,不用求解Riemann问题和计算通量函数的雅可比矩阵.通过二维Burgers方程和二维浅水方程的数值算例验证了格式的有效性.     

水下圆柱壳体固有频率的近似计算分析

水下发射导弹在出、入水以及水下运行过程中,由于流体、水动力以及运动速度的影响,产生附加质量和轴向荷载作用,影响结构振动频率.本文针对水下高速运动结构,给出了流体影响、轴向荷载分别作用以及二者同时作用下,结构频率的固有频率计算方法;并从理论分析、数值模拟和实验研究三个方面对水下的结构的固有频率进行了分析和研究.近似计算表明计算结果具有较好的一致性,而且由于流体和轴向荷载的影响,结构的固有频率有明显下降的趋势,而且对低阶频率影响较大.     

Integrating Factors and Conservation Laws of Generalized Birkhoff System Dynamics in Event Space

In this paper, the conservation laws of generalized Birkhoff system in event space are studied by using the method of integrating factors. Firstly, the generalized Pfaff-Birkhoff principle and the generalized Birkhoff equations are established, and the definition of the integrating factors for the system is given. Secondly, based on the concept of integrating factors, the conservation theorems and their inverse for the generalized Birkhoff system in the event space are presented in detail, and the relation between the conservation laws and the integrating factors of the system is obtained and the generalized Killing equations for the determination of the integrating factors are given. Finally, an example is given to illustrate the application of the results.