The impact of sand slugs against beams and plates: Coupled discrete particle/finite element simulations

The impact of a slug of dry sand particles against a metallic sandwich beam or circular sandwich plate is analysed in order to aid the design of sandwich panels for shock mitigation. The sand particles interact via a combined linear-spring-and-dashpot law whereas the face sheets and compressible core of the sandwich beam and plate are treated as rate-sensitive, elastic-plastic solids. The majority of the calculations are performed in two dimensions and entail the transverse impact of end-clamped monolithic and sandwich beams, with plane strain conditions imposed. The sand slug is of rectangular shape and comprises a random loose packing of identical, circular cylindrical particles. These calculations reveal that loading due to the sand is primarily inertial in nature with negligible fluid-structure interaction: the momentum transmitted to the beam is approximately equal to that of the incoming sand slug. For a slug of given incoming momentum, the dynamic deflection of the beam increases with decreasing duration of sand-loading until the impulsive limit is attained. Sandwich beams with thick, strong cores significantly outperform monolithic beams of equal areal mass. This performance enhancement is traced to the "sandwich effect" whereby the sandwich beams have a higher bending strength than that of the monolithic beams. Three-dimensional (3D) calculations are also performed such that the sand slug has the shape of a circular cylindrical column of finite height, and contains spherical sand particles. The 3D slug impacts a circular monolithic plate or sandwich plate and we show that sandwich plates with thick strong cores again outperform monolithic plates of equal areal mass. Finally, we demonstrate that impact by sand particles is equivalent to impact by a crushable foam projectile. The calculations on the equivalent projectile are significantly less intensive computationally, yet give predictions to within 5% of the full discrete particle calculations for the monolithic and sandwich beams and plates. These foam projectile calculations suggest that metallic foam projectiles can be used to simulate the loading by sand particles within a laboratory setting. © 2013 Elsevier Ltd.

Performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator

This study presents the performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and showthe system's steady-state and dynamic performance and grid low-voltage ride- through capability. The medium-speed brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drivetrain for wind turbine applications. © The Institution of Engineering and Technology 2013.

Self-organized InAs quantum wires on GaAs (331)A substrates

Self-organized InAs quantum wires (QWRs) were fabricated on the step edges of the GaAs (331)A surface by molecular beam epitaxy. The lateral size of InAs QWRs was saturated by the terrace width (i.e., 90 nm) while the size along the step lines increased with the increasing thicknesses of the InAs layers, up to 1100 nm. The height of InAs QWRs varied from 7.9 nm to 13 nm. The evolution of the morphology of InAs QWRs was attributed to the diffusion anisotropy of In adatoms.

Fourier transformation study of the Franz-Keldysh Oscillation in SIN+ GaAs structures

Fourier transformation (FT) method has been used in the theoretical lineshape analysis of the Franz-Keldysh Oscillation (FKO) in detail by numerical simulation. The FKO of a set of GaAs SIN+ samples was obtained in photoreflectance measurements. The FT spectra of a part of the samples,including of the real part,imaginary part, and mode of the FT,are well consistent with the theoretical lineshapes. The ratio of the square root of the reduced mass of the light hole (LH) to the heavy hole (HH), root mu(1)/root mu(h), obtained in the analysis was in the range of 0.805 to 0.816 for different samples. In addition,the built-in electric field F-1, and the modulation field delta F = F-1 - F-2 induced by photo-modulation were also obtained in the analysis. However,for a few samples great difference was found in the lineshape of the real part and imaginary part of their FT spectra from the theoretical lineshape. In this case the mode of the FT spectra still can be used to obtain useful information.

Neuro-Stimulus Chip with Photodiodes Array for Sub-retinal Implants

A prototype neuro-stimulus chip for sub-retinal implants in blind patients affected by Age-related Macular Degeneration (AMD) or Retinitis Pigmentosa (RP) is presented in this paper. This retinal prosthetic chip was designed to replace the degenerated photoreceptor cells, and in order to stimulate directly the remaining healthy layers of retinal neurons. The current stimulus circuits are monolithic integrated with photodiodes (PD) array, which can convert the illumination on the eyes into bi-phasic electrical pulses. In addition, a novel charge cancellation circuit is used to discharge the electrodes for medical safty. The prototype chip is designed and fabricated in HJTC 0.18 mu m N-well CMOS 1P6M Mix-signal process, with a +/- 2.5 V dual voltage power supply.

基于加同态公钥密码体制的匿名数字指纹方案

提出了一种基于加同态公钥密码算法的匿名数字指纹方案，并给出了具有匿名功能的公钥和私钥对的具体构造方法，从而使该匿名指纹方案在发现盗版的情况下，销售商不需要第三方的帮助就能鉴别出数字多媒体作品的非法分发者，解决版权纠纷时也不需要购买者参与并提供相关的秘密信息，从而达到实现两方审判的目的．分析结果表明，该方案具有用户匿名及不可关联、销售商的可保证安全性和用户的可保证安全性等特点．

南海北部潮汕坳陷海区海底地震仪调查实验

潮汕坳陷被认为是一个具有良好油气前景的中生代残留沉积坳陷，其中生代地层也被新近的钻井证实。为研究

快速热退火对高应变InGaAs／GaAs量子阱的影响

用固态分子束外延技术生长了高应变．In0．45Ga0.55As／GaAs量子阱材料．研究了快速热退火对高应变InGaAs／GaAs量子阱材料光学性质的影响．本文采用假设InGaAs／GaAs量子阱中的In—Ga原子扩散为误差函数扩散并解任意形状量子阱的薛定谔方程的方法，对不同退火温度下InGaAs／GaAs量子阱室温光致发光峰值波长拟合，得到了In原子在高应变InGaAs／GaAs量子阱中的扩散系数以及扩散激活能（O．88ev）．

SIN~+GaAs结构中的Franz-Keldysh振荡的傅里叶变换研究

利用傅里叶变换(FT)方法，对Franz-Keldysh振荡(FKO)的理论线性作了详细的数值模拟，并用光调制反射谱(PR)测量了一组本征层(I层)厚度不同的表面-本征层n-型重掺杂层(SIN~+)结构的GaAs样品的FKO.PR谱的FT分析表明，一部分样品的FT谱，包括其实部、虚部和模，与理论线性符合得比较好，由此求出轻空空(LH)和重空穴(HH)的约化质量平方根之比μ_1~(1/2)/(μ_h)~(1/2)对不同样品在0.805-0.816之间，同时也可以求出样品中的内建电场强度F_1，和调制光引起的调制电场δF=F_1-F_2。有一些样品的FT谱实部和虚部与理论线性差别很大，用FT的模仍可以给出有用的信息。