New anti-ablation candidate for carbon/carbon composites: Preparation,composition and ablation behavior of Y2Hf2O7 coating under an oxyacetylene torch

Y₂Hf₂O₇ possesses low thermal conductivity and high melting point, which make it promising for a new anti-ablation material. For evaluating the thermal stability and the potential applications of Y₂Hf₂O₇ on anti-ablation protection of C/C composites, Y₂Hf₂O₇ ceramic powder was synthesized by solution combustion method and Y₂Hf₂O₇ coating was prepared on the surface of SiC coated C/C composites using SAPS. Results shown that the coating exhibits good ablation resistance under the heat flux of 2.4?MW/m² with the linear and mass ablation rates are 0.16?μm?s^?1 and ?0.028?mg?s^?1, respectively, after ablation for 40?s. With the prolonging of the ablation time, the increasing thermal stress causes the increase of cracks. Moreover, the chemical erosion from SiO₂ and the physical volatilization of low temperature molten products aggravate failure of the Y₂Hf₂O₇ coating.     

Performance index based learning controls for the partial non-regular systems using lifting technique

Deficiencies of the performance-based iterative learning control （ILC） for the non-regular systems are investigated in detail, then a faster control input updating and lifting technique is introduced in the design of performance index based ILCs for the partial non-regular systems. Two ldnds of optimal ILCs based on different performance indices are considered. Finally, simulation examples are given to illustrate the feasibility of the proposed learning controls.     

求解上层含约束条件的模糊二层多随从线性规划的结构元方法

讨论了一类上层含约束条件的模糊二层多随从线性规划模型;利用结构元理论,证明了该模型的最优解等价于上层含约束条件的二层多随从线性规划模型最优解;并通过极点搜索法,得到了该模型最优解;最后通过数值算例验证了该方法的可行性。     

A repetitive S-band long-pulse relativistic backward-wave oscillator

This paper presents both numerical and experimental studies of a repetitive S-band long-pulse relativistic backward-wave oscillator. The dispersion relation curve of the main slow-wave structure is given by the numerical calculation. Experimental results show that a 1 GW microwaves with pulse duration of about 100 ns (full width of half magnitude) under 10 Hz repetitive operation mode are obtained. The microwave frequency is 3.6 GHz with the dominant mode of TM(01), and power conversion efficiency is about 20%. The single pulse energy is about 100 J. The experimental results are in good agreement with the simulation ones. By analyzing the experimental phenomenon, we obtain the conclusion that the explosive emission on the surface of the electrodynamics structure in intense radio frequency field mainly leads to the earlier unexpected termination of microwave output.     

CuxS(x=1,2)纳米薄膜的异步脉冲超声喷雾热解法制备

采用改进的异步脉冲超声喷雾热解技术在玻璃衬底上成功地制备了CuxS(x =1,2 )纳米薄膜 .研究发现 ,所制备的CuxS薄膜为多晶态 ;薄膜的晶相结构依赖于CuCl2 ·2H2 O和硫脲的摩尔比及衬底温度 .XRD和XPS分析表明 :样品为纯CuxS(CuS ,Cu2 S) ,拉曼谱研究表明其峰位分别在 472cm- 1 (Cu2 S)和 474cm- 1 (CuS)处 .     

基于最小统计噪声估计的信号子空间语音增强

针对传统子空间方法中，采用语音活动检测（Voice activity detection，VAD）估计噪声的缺陷，提出了一种基于子空间域的最小统计噪声估计算法。噪声估计通过跟踪带噪语音协方差矩阵用每个特征向量上的特征值的最小值来获得，该方法不需要VAD明确区分语音段和噪声段，能够在整个信号期间实现噪声的连续估计和不断更新。实验结果表明，相对于传统的基于VAD的子空间方法，本文提出的算法对语音增强效果有非常显著的提高。     

Image Quality Assessment for Visual and Infrared Multis-pectral Imager of Gaofen-5

Gaofen-5(GF-5) satellite was successfully launched on May 29, 2018. The Visual and Infrared Multispectral Imager(VIMI) developed independently by China is a multi-spectral imager in the range of visible band to long-wave infrared band, which has broad application prospects. The quality assessment of satellite image is not only the verification of whether the remote sensing satellite meets the design criteria, but also the reference for image processing and application. In this paper, the quality assessment for VIMI is provided, which provides reference for the processing and application of the image. Four indicators, named the Signal-to-Noise Ratio (SNR), clarity, information content and radiation heterogeneity, were used for quality assessment, and were compared with Landsat 8 images. The results show that the SNR of the shortwave infrared band (320.44~388.42) is slightly higher than that of the visible near-infrared band(208.24~238.03). The clarity (0.82~0.91) in the near-shortwave infrared band is higher than that in the other bands, especially in the long-wave infrared band (0.01~0.21). The information content of short-wave infrared band (9.01~9.97) is higher than that of medium-long-wave infrared band (5.71~8.31). The radiation heterogeneity of all 12 bands is less than 2%. The results of comparison with Landsat 8 show that ①the clarity of B1~B4 is better than Landsat 8 and this of other bands are close to Landsat 8,②for information content, B1~B10 of VIMI is close to Landsat 8, while this of B11 and B12 is less than Landsat 8 with 5.23 for B11 and 5.61 for B12,(3)for SNR, GF-5 VIMI still needs to be further improved, with 280.41、226.84 and 151.92 less than Landsat 8 for B1,B2 and B6.     

焊接结构承压管道有限元与可靠性分析

针对工业设备上常见的焊接结构承压管道,应用模糊灰关联FTA安全系统工程理论,以水火管锅壳锅炉为例,通过对失效致因和故障模式的研究,建立以焊接结构承压管道失效为顶事件的模糊灰关联FTA模型,利用有限元法建立焊接结构承压管道模型辅助分析对其更深层次的系统性影响,并综合考虑工况环境、外部载荷等多因素耦合作用,确定导致事故的主要潜在风险项,为承压管道设备安全保障活动的经济决策提供依据。研究结果表明,以水火管锅壳锅炉的“焊接结构承压管道”失效故障模式的发生概率约为8.19%,系统的可靠度约为91.81%。     

腈涤毛混纺开清棉工艺要点

确定了棉型腈纶、涤纶和羊毛A／T／W80／10／1018 tex的纺纱工艺流程，分析了影响开清棉工序成卷质量的因素，通过合理配置开清棉工艺，采取可行性措施，解决了A／T／W80／10／1018 tex混纺纱在开清棉工序粘卷、缠绕、堵车、条干不匀的难题。