The influence of F doping on the activity of PbO2 film electrodes in oxygen evolution reaction

The PbO₂ and F⁻-doped PbO₂ (F-PbO₂) film electrodes have been prepared by an electrodeposition process onto platinum substrate. The changes of their electrochemical activity for oxygen evolution (OE) reaction with accelerated electrolysis time have been studied. The results show that the activity of the electrodes decreases with increasing electrolysis time. This can be attributed to the conductivity variations, which are caused by the decrease of the oxygen vacancy concentration in PbO₂ films during OE. The mechanism of the decrease of the oxygen vacancies has been investigated. For F-PbO₂ film electrodes, though its electrochemical activity is somewhat lower than that of undoped one, its activity stability is much higher in comparison with that of PbO₂. The influence of F⁻ doping on the activity of PbO₂ film electrodes has been also discussed.     

Poly(l-lactic acid)/SiO2 nanocomposites via in situ melt polycondensation of l-lactic acid in the presence of acidic silica sol: Preparation and characterization

In situ melt polycondensation of l-lactic acid (LLA) in the presence of acidic silica sol (aSS) is proposed for the first time to prepare PLLA/SiO₂ nanocomposites. The SiO₂ nanoparticles were readily dispersed in LLA monomer, which has similar polarity and hydrophilicity to the silica sol medium. During the polycondensation process, both the matrix and the surface of SiO₂ nanoparticles changed from high polarity/hydrophilicity to weak polarity/hydrophobicity due to simultaneous chain growth in the organic phase and chemical grafting on the particle surface. The chemical grafting provided steric stabilization and ensured satisfactory nano-scale dispersion in the final nanocomposites. The introduction of SiO₂ nanoparticles resulted in unchanged yield and better color. The molecular weight kept almost constant at low SiO₂ content (<8 wt%) but decreased at higher SiO₂ content. The method is also characterized by commercially available and cheap starting material and environmentally benign process. It appears to be a promising approach for the preparation of PLLA/SiO₂ nanocomposites.     

Reward-Based Radio Interface Selection of Hybrid 4G UMTS and LTE Communications for Fast Cloud Accesses

For achieving fast accesses the cloud’s big data through mobile smart node, an extreme high data rate for the forwarding link under high-mobility wireless communications is necessary. 3GPP thus specifies LTE/LTE-Advanced specifications as the 4G system to cooperate with the existing UMTS system. To balance loads among different communication interfaces in the hybrid cellular system is one of the most important issues that should be addressed for achieving efficient radio resource allocations. In a shared packet service, the 3GPP UMTS adopts the VSF-OFCDM interface to allocate orthogonal codes of an OVSF code tree in two-dimension spreading of the time and frequency domains. However, UMTS suffers from high packet loss rate and high bandwidth waste rate. In 4G, although the LTE/LTE-Advanced interface offers a high data rate, it suffers from unbalanced loads and moderate reward. This paper thus proposes an adaptive radio interface selection for balancing loads between the UMTS and LTE/LTE-Advanced interfaces according to various interference and mobility environments. Numerical results indicate that the proposed approach outperforms other approaches in fairness, FRL, utilization and call blocking.     

Face Alignment by Explicit Shape Regression

We present a very efficient, highly accurate, “Explicit Shape Regression” approach for face alignment. Unlike previous regression-based approaches, we directly learn a vectorial regression function to infer the whole facial shape (a set of facial landmarks) from the image and explicitly minimize the alignment errors over the training data. The inherent shape constraint is naturally encoded into the regressor in a cascaded learning framework and applied from coarse to fine during the test, without using a fixed parametric shape model as in most previous methods. To make the regression more effective and efficient, we design a two-level boosted regression, shape indexed features and a correlation-based feature selection method. This combination enables us to learn accurate models from large training data in a short time (20 min for 2,000 training images), and run regression extremely fast in test (15 ms for a 87 landmarks shape). Experiments on challenging data show that our approach significantly outperforms the state-of-the-art in terms of both accuracy and efficiency.     

轴向参错密封的流量系数测量技术及数值分析

该文记述了各种密封实验的实验装置和测试方法,并对模拟自动机械中迷宫密封、平面密封作了总体分析.最后选择一轴向参错结构作了密封流场计算,计算结果展示了准定常状态的流态特性,为揭示密封机理提供了参考依据.     

An improved three-dimensional wavelet-based method for solving the first-order Boltzmann transport equation

A new angular discretization scheme based on the Daubechies’ wavelets has been developed in recent studies. A decoupled S_N and wavelet expansion method was proposed. This paper discusses the limitations and improvements of this decoupled scheme. The scaling function, instead of the wavelet function, is applied as the basis function. It significantly improved the efficiency and computational stability. A new series of wavelets on the interval are applied instead of the ‘wrapped wavelets’, which eliminate the edge effect in the angular subdomain scheme. Based on the improvements, a wavelet-based neutron transport code package WAVTRAN is developed and the previous work is extended to the three-dimensional calculation and anisotropic scattering calculation. Numerical results demonstrate that the improvements are effective. Further investigations demonstrate that the wavelet-based angular discretization scheme is more powerful than the traditional ones in some highly anisotropic angular flux problems.     

Thermal hydraulic behaviors during loss of RHR system at mid-loop operation of Chinese 300 MWe PWR NPP

Thermal hydraulic behavior of nuclear power plant (NPP) is analyzed by using mechanistic computer code for loss of residual heat removal (RHR) system during mid-loop operation of Chinese 300 MWe two-loop pressurized water reactor is presented. In the absence of recovery of RHR or other accident management measures, the reactor core will be uncovered for a long term resulting in core heat-up, degradation and relocation to the lower plenum. The effectiveness of available mitigate measures, such as safety injection system, gravity feed from refueling water storage tank (RWST) and steam generator (SG) reflux-condensation, are investigated. Coolant injection is highly effective in halting the accident progression and make the core recovered. The cooling capability of SG reflux-condensation has a relationship with different availabilities of steam generators and decay heat power. 6 days after shutdown, 2SG operation can keep the water level at mid-line of hot leg. 12 days after shutdown, both 2SG operation and 1SG operation can keep the water level at mid-line of hot leg. The analyses also indicate that the cooling mechanism of safety injection system is more effective than gravity feed from RWST and SG reflux-condensation. Through confirming the success criteria of SG reflux-condensation, time windows can be devided. Then, event trees for loss of RHR system under mid-loop operation are built with considering the analysis results and abnormal procedure.     

装配规化中零件装配方向倾斜时拓扑信息的处理

零件的装配方向倾斜时,需要进行空间坐标变换,使零件的装配方向与变换后的坐标方向相同或相反。本文的目的就是给出新旧坐标体系下的变换矩阵,在倾斜的坐标体系下实现对零件间干涉和接触的判断,并对零件的接触类型进行了分类,最后利用软件实现了产品装配网络模型的自动生成。