Characterization of inner layer thickness change of a composite circular tube using nonlinear circumferential guided wave:A feasibility study

The feasibility of using the nonlinear effect of primary circumferential guided wave (CGW) propagation for characterizing the change of inner layer thickness of a composite circular tube (CCT) has been investigated. An appropriate mode pair of the fundamental and double-frequency CGWs (DFCGWs) has been selected to enable the second harmonics of primary wave mode in the given CCT to accumulate along the circumferential direction. When changes in the inner layer thickness (described as the equivalent inner layer thickness) take place, the corresponding nonlinear CGW measurements are conducted. It is found that there is a direct correlation between change of equivalent inner layer thickness of the CCT and the relative acoustic nonlinearity parameter (Δβ) measured with CGWs propagating through one full circumference, and that the effect of second-harmonic generation (SHG) is very sensitive to change in the inner layer thickness. The experimental result obtained demonstrates the feasibility for quantitatively assessing the change of equivalent inner layer thickness in CCTs using the effect of SHG by primary CGW propagation.     

How Does van der Waals Confinement Enhance Phonon Transport?

We study the mechanism of van der Waals(vdW)interactions on phonon transport in atomic scale,which would boost developments in heat management and energy conversion.Commonly,the vdW interactions are regarded as a hindrance in phonon transport.Here we propose that the vdW confinement can enhance phonon transport.Through molecular dynamics simulations,it is realized that the vdW confinement is able to make more than two-fold enhancement on thermal conductivity of both polyethylene single chain and graphene nanoribbon.The quantitative analyses of morphology,local vdW potential energy and dynamical properties are carried out to reveal the underlying physical mechanism.It is found that the confined vdW potential barriers reduce the atomic thermal displacement magnitudes,leading to less phonon scattering and facilitating thermal transport.Our study offers a new strategy to modulate the phonon transport.     

用于储罐底板缺陷检测的超声兰姆波模式研究

从超声兰姆波的声场方程出发,得到板材表面离面位移(法向位移)为零的条件,即当超声兰姆波的相速度等于板材介质的纵波声速时,在板材表面的离面位移为零。在给定适当频厚积的条件下,分别数值模拟了仅有切向位移而无离面位移的A1、S1、A2和S2兰姆波模式在有液体负载的单层钢板中的传播情形。结果表明:离面位移为零的S2模式频散较小且对板中缺陷更为敏感。     

Ca2Li2BiV3O12∶Eu3+荧光粉的制备和发光性能

采用高温固相法成功合成了一种可用于白光LED的Ca₂Li₂BiV₃O₁₂∶Eu³⁺新型红色荧光粉,使用X射线衍射仪和荧光分光光度计对合成样品进行了表征,研究了合成温度和Eu³⁺含量对合成样品相组成和发光性能的影响。结果表明,采用高温固相法在650~700 ℃能合成纯度较高、结晶度好的Ca₂Li₂BiV₃O₁₂∶Eu³⁺荧光粉,合成样品激发带覆盖200~400 nm,发射光谱的线状发射峰可归属于Eu³⁺的⁵D₀→⁷F_J(J= 1, 2, 3,4)特征锐线发射,Eu³⁺摩尔分数为14%时荧光粉的发光强度最大。     

A novel superjunction MOSFET with improved ruggedness under unclamped inductive switching

The ruggedness of a superjunction metal–oxide semiconductor field-effect transistor (MOSFET) under unclamped inductive switching conditions is improved by optimizing the avalanche current path. Inserting a P-island with relatively high doping concentration into the P-column, the avalanche breakdown point is localized. In addition, a trench type P+ contact is designed to shorten the current path. As a consequence, the avalanche current path is located away from the N+ source/P-body junction and the activation of the parasitic transistor can be effectively avoided. To verify the proposed structural mechanism, a two-dimensional (2D) numerical simulation is performed to describe its static and on-state avalanche behaviours, and a method of mixed-mode device and circuit simulation is used to predict its performances under realistic unclamped inductive switching. Simulation shows that the proposed structure can endure a remarkably higher avalanche energy compared with a conventional superjunction MOSFET.     

基于半导体泵浦倍频绿光激光器的探究性实验设计

为探究在谐振腔中倍频晶体位置对绿光激光器输出功率的影响，利用半导体泵浦固体激光实验仪设计了腔内和腔外倍频绿光的探究性实验。分析了绿光倍频效率与基频光束的功率密度及光斑半径之间的关系，分别测量了磷酸钛氧钾(KTP)倍频晶体位于谐振腔內部和外部不同位置时，532 nm倍频绿光的输出功率。其中在腔外倍频实验中，分别设计了腔外不加透镜时KTP晶体位于腔外不同位置，以及加上透镜时KTP晶体位于聚焦位置两种实验方案。同时，在实验中引导学生利用谐振腔理论和高斯光束传输理论等激光原理计算1 064 nm基频光在腔内外不同位置的光斑半径，分析了KTP晶体在不同位置时532 nm倍频光输出功率出现差别的原因，以及利用透镜聚焦提高激光功率密度以达到提高倍频效率的方法。     

聚变实验增殖堆FEB-E粒子抽除和抽气系统(英文)

ＦＥＢ－Ｅ的粒子抽除是通过偏滤器进行的。由４８ 个楔形气室模件环形组装而成的ＦＥＢ－Ｅ偏滤器，位于真空室的下部，与抽气系统和冷却系统相连。ＦＥＢ－Ｅ抽气系统有二个子系统：环粗抽系统和环高真空系统。环高真空系统是由一组处于真空室内１６ 个下部舱口内的低温泵和一组处于生物屏蔽层外的附加涡轮分子泵组成的。这些低温泵能提供的名义总抽速为５７６ｍ ３·ｓ－ １。在偏滤器高中性压力（＞ １Ｐａ）情况下，低温泵入口阀节流控制抽气粒子流。由于偏滤器抽气槽路以及偏滤器下侧通至真空室下部舱口的有限的通导能力，这些低温泵在偏滤器幽僻区域有效抽速为１６０ｍ ３·ｓ－ １。这意味着偏滤器幽僻区域的中性压力应在０．５－ １．０Ｐａ 范围内，以得到８０－ １６０Ｐａ·ｍ ３·ｓ－ １（在预期的偏滤器抽气槽路温度为４７３Ｋ时）范围内的抽气流量。低温泵每次在聚变实验增殖堆燃烧１０００ｓ 后受激运行     

SINGULAR INTEGRAL EQUATIONS IN ORLICZ SPACES (Ⅱ)

The singular integral equations with Cauchy kernels have studied in L_p(Γ),p>1,in detail.Here Γ stands for the set of a finite number of closed Liapunoff's curves which have no common points and T denotes the completely continuous operator in the space sunder consideration. In this paper, we consider the equations mentioned above in Orlicz spaces L_M(Γ). It is proved that the Nether theorem and the index formula are hold true in the case of reflexive Orlicz spaces.     

W_2~1空间中的最佳数值原函数

求数值原函数问题,是对离散形式给出的实函数u(x)(即仅给出u(x)在有限多个点上的函数值),求其近似原函数F_n(x),而且当节点无限加密时,F_n(x)收敛于u(x)的原函数F(x).例如微分方程的数值解法,实质上就归结为求数值原函数问题.通常