A highly active bi-crystalline photocatalyst consisting of TiO2 (B) nanotube and anatase particle for producing H2 gas from neat ethanol

Sodium titanate nanotubes (NaTNTs) are converted into monoclinic TiO₂ (B) nanotubes by rinsing with 0.10 M HCl followed by drying at 573 K. As calcination temperature is increased to 673 K, these TiO₂ (B) nanotubes start to transform into anatase nanoparticles producing a bi-crystalline mixture consisting of TiO₂ (B) nanotubes and anatase nanoparticles. The primary particle size of the anatase particles was estimated to be around 10 nm using Scherrer equation. After being promoted with 1% Pt, this bi-crystalline material becomes a very active photocatalyst producing 20% more H₂ gas than 1% Pt/Degussa P-25 TiO₂ in the photocatalytic dehydrogenation of neat ethanol after 2 h of UV light irradiation.     

Recent advances on kinetic analysis of electromigration enhanced intermetallic growth and damage formation in Pb-free solder joints

A comprehensive kinetic analysis was established to investigate the electromigration (EM) enhanced intermetallic compound (IMC) growth and void formation for Sn-based Pb-free solder joints with Cu under bump metallization (UBM). The kinetic model takes into account Cu-Sn interdiffusion and current stressing. Derivation of the diffusion coefficients and the effective charge numbers for the intermetallic compounds is an essential but challenging task for the study of this multi-phase multi-component intermetallic system. A new approach was developed to simultaneously derive atomic diffusivities and effective charge numbers based on simulated annealing (SA) in conjunction with the kinetic model. A consistent set of parameters were obtained, which provided important insight into the diffusion behaviors driving the IMC growth. The parameters were used in a finite difference model to numerically solve the IMC growth problem and the result accurately correlated with the experiment. EM reliability test revealed that the ultimate failure of the solder joints was caused by extensive void formation and subsequent crack propagation at the intermetallic interface. This damage formation mechanism was analyzed by first considering vacancy transport under current stressing. This was followed by a finite element analysis on the crack driving force induced by void formation. This paper is concluded with a future perspective on applying the kinetic analysis and damage mechanism developed to investigate the structural reliability of the through-Si-via in 3D interconnects.     

Optimal H∞ Output Feedback Control Systems with Time Delay

An H∞ direct output feedback control algorithm through minimizing the entropy, a performance index measuring the tradeoff between H∞ optimality and H2 optimality, is developed in this paper to reduce the earthquake response of structures. To achieve optimal control performance and assure control system stability, the strategy to select both control parameters γ and α is extensively investigated considering the control force execution time delay. It is found that a lower bound of γ and an upper bound of α exist. The selection beyond these values will cause the control system instability. For a damped structure, analytical expressions of direct output feedback gains, controlled frequencies and damping ratios are derived. It can be proved that the conventional LQR control is a special case of the developed H∞ control. In real active control, control force execution time delay cannot be avoided. This paper gives explicit formulas of maximum allowable delay time and critical control parameters for the design of a stable control system. Some solutions are also proposed to lengthen maximum allowable delay times.     

Abaqus/CAE二次开发功能与应用实例

为实现复杂的有限元前后处理功能,介绍基于Abaqus/CAE进行内核脚本和GUI的程序开发,并阐述这两种开发方式的特点和相互关系.用双动拉深杯形件和汽车覆盖件两个实例说明Python和Abaqus GUI Toolkit在Abaqus/CAE二次开发中的应用;通过二次开发实现将CFD计算得到的热边界条件向实体单元网格模...     

一种不一致不完备信息系统的最优选择及规则约简方法研究

在分析不一致不完备信息系统规则提取的基础上,提出了先将不完备信息系统分为一致的和不一致的信息系统后再求其最优选择的方法。然后利用改进的分辨矩阵对所求得的不一致最优选择进行决策规则提取,并给出不确定决策规则的决策精度。最后,通过应用例子证明了本文提出方法的有效性。     

Parametric cumulant based phase estimation of 1-D and 2-Dnonminimum phase systems by allpass filtering

This paper proposes a parametric cumulant-based phase-estimation method for one-dimensional (1-D) and two-dimensional (2-D) linear time-invariant (LTI) systems with only non-Gaussian measurements corrupted by additive Gaussian noise. The given measurements are processed by an optimum allpass filter such that a single Mth-order (M⩾3) cumulant of the allpass filter output is maximum in absolute value. It can be shown that the phase of the unknown system of interest is equal to the negative of the phase of the optimum allpass filter except for a linear phase term (a time delay). For the phase estimation of 1-D LTI systems, an iterative 1-D algorithm is proposed to find the optimum allpass filter modeled either by an autoregressive moving average (ARMA) model or by a Fourier series-based model. For the phase estimation of 2-D LTI systems, an iterative 2-D algorithm is proposed that only uses the Fourier series-based allpass model. A performance analysis is then presented for the proposed cumulant-based 1-D and 2-D phase estimation algorithms followed by some simulation results and experimental results with real speech data to justify their efficacy and the analytic results on their performance. Finally, the paper concludes with a discussion and some conclusions     

Electromigration statistics and damage evolution for Pb-free solder joints with Cu and Ni UBM in plastic flip-chip packages

A series of electromigration (EM) tests were performed as a function of temperature and current density to investigate lifetime statistics and damage evolution for Pb-free solder joints with Cu and Ni under-bump-metallizations (UBMs). The EM lifetime was found to depend on the failure criterion used, so the results were compared based on the first resistance jump and conventional open-failure criterion. Solder joints with Cu UBM had a longer lifetime than Ni UBM based on the open-failure criterion, but the lifetime with Ni UBM became comparable when the first resistance jump criterion was applied. To determine the temperature in solder joints, the Joule heating effect was investigated with experiments and finite element analysis. The temperature of solder joints was determined to be approximately 15°C higher than that at the Si die surface when 1 A of current was applied. With the appropriate temperature correction, the activation energies and the current density exponents were found to be Q = 1.11 eV, n = 3.75 and Q = 0.86 eV, n = 2.1 based on the open-failure criterion for solder joints with Cu and Ni UBM, respectively. Based on the first resistance jump criterion, Q = 1.05 eV, n = 1.45 for Cu UBM and Q = 0.94 eV, n = 2.2 for Ni UBM, respectively. For solder joints with Cu UBM, voids were formed initially at the Cu₆Sn₅/solder interface while the final open failure occurred at the Cu₃Sn/Cu₆Sn₅ interface. For Ni UBM, voids were formed initially at the Ni₃Sn₄/solder interface leading to failure at the same interface. The formation of intermetallic compounds (IMCs) was enhanced under current stressing, which followed linear growth kinetics with time. The IMC growth was accompanied by volume shrinkage, which accelerated damage evolution under EM.