热障涂层无损检测技术研究进展

为提高发动机的涡轮前温度和热端部件服役寿命,热障涂层（TBCs）被广泛应用于燃气涡轮发动机。热障涂层具有多相、多界面和非均质特性,且其服役工况恶劣复杂。寻找一种可以表征涂层显微组织、缺陷、热物性、应力等反映涂层质量和剩余寿命的无损检测方法,对发动机的热端部件安全性和可靠性至关重要。文中综述了超声检测技术（UT）、声发射技术（AE）、红外热成像技术（IRT）、阻抗谱技术（IS）和光激发荧光压电光谱技术（PLPS）的原理以及其在热障涂层无损检测中的研究应用,并详细介绍了太赫兹时域光谱（THz-TDS）技术及其在热障涂层中的应用。最后总结了上述无损检测方法的检测能力,并对热障涂层无损检测方法进行展望。     

Analysis of weld pool vibration characteristics in pulsed gas metal arc welding

Using highspeed camera image measuring and processing, the contour of the weld pool was extracted accurately in pulsed metal inert gas (P-MIG) welding. Based on this extraction method, time and frequency domain characteristics at different points along the contour of the weld pool were analyzed for one pulse one droplet and one pulse two droplets, respectively. The results show that, because of the wave super position that was created by the pulsed arc and droplet impacting the weld pool, the oscillation amplitude along the weld pool fluctuated and decreased with an increase in distance from the point to the arc center. The oscillation near the arc center was complex and intense for one pulse two droplets, and the amplitude were relatively small because the oscillation caused by the pulsed arc could be offset by the molten droplet impact. The weld pool oscillation that was caused by the pulsed arc was stronger than that caused by the droplet.     

湿式离合器先导式电液调压阀时频域建模与分析

先导式电液调压阀是大功率湿式离合器换挡系统的核心部件,由于其多个环节存在参数时变和强非线性特征使其频率响应特性发生变化,进而影响换挡过程的油压调节的快速性与稳定性。在剖析先导式电液调压阀工作原理的基础上,考虑阻尼系数、流量系数和增益系数随油温的可变性,建立了先导式电液调压阀在工作过程中的数值模型,并推导了其频域模型。研究了先导式电液调压阀在不同参数下的时域和频域响应特性,得到了参数变化的影响规律。结果表明：增加系统响应的带宽会提高油压响应速度,但会降低阻尼比,使得油压响应的调节时间增加。系统的结构参数、输入信号以及工作油温均会影响其响应特性。基于该方法能够快速的判断先导式电液调压阀在全工作范围内的响应速度和稳定性问题,从而有助于改善先导式电液调压阀的油压动态跟踪性能。     

ASYMPTOTIC INFERENCES FOR AN AR(1) MODEL WITH A CHANGE POINT: STATIONARY AND NEARLY NON‐STATIONARY CASES

This article examines the asymptotic inference for AR(1) models with a possible structural break in the AR parameter β near the unity at an unknown time k₀. Consider the model y_t = β₁y_{t − 1}I{t ≤ k₀} + β₂y_{t − 1}I{t > k₀} + ϵ_t, t = 1,2, … ,T, where I{ ⋅ } denotes the indicator function. We examine two cases: case I | β₁ | < 1,β₂ = β_2T = 1 − c ∕ T; and case II β₁ = β_1T = 1 − c ∕ T, | β₂ | < 1, where c is a fixed constant, and {ϵ_t,t ≥ 1} is a sequence of i.i.d. random variables, which are in the domain of attraction of the normal law with zero means and possibly infinite variances. We derive the limiting distributions of the least squares estimators of β₁ and β₂ and that of the break‐point estimator for shrinking break for the aforementioned cases. Monte Carlo simulations are conducted to demonstrate the finite‐sample properties of the estimators. Our theoretical results are supported by Monte Carlo simulations.     

Construction of Cellulose Binding Domain Fusion FMN-Dependent NADH-Azoreductase and Glucose 1-Dehydrogenase for the Development of Flow Injection Analysis with Fusion Enzymes Immobilized on Cellulose

The cellulose binding domain (CBD) of cellulosome-integrating protein A from Clostridium thermocellum NBRC 103400 was genetically fused to FMN-dependent NADH-azoreductase (AZR) and glucose 1-dehydrogenase (GDH) from Bacillus subtilis. The fusion enzymes, AZR-CBD and CBD-GDH, were expressed in Escherichia coli Rosetta-gami B (DE3). The enzymes were purified from cell-free extracts, and the specific activity of AZR-CBD was 15.1 U/mg and that of CBD-GDH was 22.6 U/mg. AZR-CBD and CBD-GDH bound strongly to 0.5 % swollen cellulose at approximately 95 and 98 % of the initial protein amounts, respectively. After immobilization onto the swollen cellulose, AZR-CBD and CBD-GDH retained their catalytic activity. Both enzymes bound weakly to 0.5 % microcrystalline cellulose, but the addition of a high concentration of microcrystalline cellulose (10 %) improved the binding rate of both enzymes. A reactor for flow injection analysis was filled with microcrystalline cellulose-immobilized AZR-CBD and CBD-GDH. This flow injection analysis system was successfully applied for the determination of glucose, and a linear calibration curve was observed in the range of approximately 0.16–2.5 mM glucose, with a correlation coefficient, r, of 0.998.     

Optimization of a plate with holes

We consider a simply supported plate with constant thickness, defined on an unknown multiply connected domain. We optimize its shape according to some given performance functional. Our method is of fixed domain type, easy to be implemented, based on a fictitious domain approach and the control variational method. The algorithm that we introduce is of gradient type and performs simultaneous topological and boundary variations. Numerical experiments are also included and show its efficiency.     

基于时频域的卷积神经网络运动想象脑电信号识别方法

针对目前运动想象脑电（EEG）信号识别率较低的问题，考虑到脑电信号蕴含着丰富的时频信息，提出一种基于时频域的卷积神经网络（CNN）运动想象脑电信号识别方法。首先，利用短时傅里叶变换（STFT）对脑电信号的相关频带进行预处理，并将多个电极的时频图组合构造出一种二维时频图；然后，针对二维时频图的时频特性，通过一维卷积的方法设计了一种新颖的CNN结构；最后，通过支持向量机（SVM）对CNN提取的特征进行分类。基于BCI数据集的实验结果表明，所提方法的平均识别率为86.5%，优于其他传统运动想象脑电信号识别方法；同时将该方法应用在智能轮椅上，验证了其有效性。     

Improvement of the Characteristics of Steamed Bread by Supplementation of Recombinant alpha-L-arabinofuranosidase Containing xylan-binding domain

Current study investigated the potential to increase the activity of α-L-arabinofuranosidase (TmAra) from Thermotoga marotima on insoluble arabinoxylan (IAX) through fusion to a family 6 xylan-binding domain (CtXBD6) from Clostridium thermocellum. CtXBD6 was fused to the carboxyl terminus of TmAra, and active forms of both TmAra and TmAraCtXBD6 were produced in E. coli and purified to homogeneity for biochemical characterization. TmAraCtXBD6 had similar temperature and pH profiles to TmAra with a decrease in the thermostability and pH stability at pH 7.0–8.2. It exhibited stronger IAX-binding and hydrolytic activity than TmAra. TmAra and TmAraCtXBD6-treated IAX were added to wheat flour to investigate the rheological and textural properties of the finished product. IAX alone had significant increase in dough development time (DDT) and dough stability (DS) and decrease in the softening degree (SD), crumb firmness (CF) and specific volume (SV). On adding TmAra and TmAraCtXBD6 to treat IAX texture, SV and DS improved but decreased DDT, SD, and CF. TmAraCtXBD6 reduced CF and increased SV, and had higher springiness, cohesiveness, and crumb chewiness than TmAra. These results demonstrated that the fusion of CtXBD6 into arabinofuranosidase enables the increase in catalytic performance on insoluble AX substrates, which can be used as more efficient biocatalysts that can improve the quality of AX-rich products.     

某移动TD-SCDMA网络ATU测试FTP掉线问题分析

本文通过对一个ATU数据业务测试的异常事件的分析,介绍了网络总体构架和系统功能,给出了适合的分析方法及具体解决方案,对以后解决类似的问题起到了一定的帮助作用。