CO2激光微加工实验台定位精度预测模型研究

为了提高CO2激光微加工实验台定位精度,提出基于LSSVM的直线电机定位精度误差回归建模和预测方法.采用径向基核函数的LSSVM对不同速度和加速度下的直线电机伺服系统定位误差进行了预测.研究结果表明,采用径向基核函数的LSSVM能提高预测精度,取得较好的预测结果.     

Co-liquefaction behavior of a sub-bituminous coal and sawdust

The co-thermolysis and co-liquefaction properties of Shenhua coal and sawdust were investigated in this study. The synergistic effect between Shenhua coal and sawdust in co-liquefaction was probed. TG/DTG analysis suggests that the sawdust, which has lower pyrolysis temperature, can promote the thermolysis of Shenhua coal, resulting in more volatile matter to be released from coal molecular structure during the co-thermolysis process. This will result in the larger weight losses of their mixture compared to the corresponding weighted mean values of individual pyrolysis. The individual liquefaction of Shenhua coal and sawdust shows that sawdust has higher liquefaction activity compared to Shenhua coal. It gives much higher liquefaction conversion and oil yield than Shenhua coal at the same liquefaction conditions. Co-liquefactions of Shenhua coal and sawdust at different conditions were carried out. The results suggest that there exists an obviously synergistic effect during the co-liquefaction, and this synergistic effect is the function of liquefaction conditions. At high liquefaction temperatures and long reaction times, the synergistic effect decreases because of the increase of liquefaction activity of coal and lack of hydrogen donating ability of the system at the conditions, resulting in the increase of the rate of retrogressive condensed reactions. The largest enhancements in conversion of 16.8% and oil yield of 11.4% comparing with corresponding calculated weighted mean values of the individual liquefaction of Shenhua coal and sawdust were obtained at 400 and 380 °C, respectively in the co-liquefaction with 1/1 blending ratio of coal/sawdust.     

Trimethylamine sensing properties of nano-LaFeO3 prepared using solid-state reaction in the presence of PEG400

LaFeO₃ precursors are prepared using solid-state reaction in the presence of PEG400, and then LaFeO₃ nano-powders are obtained through heating these precursors under different conditions. Eventually, LaFeO₃ thick film sensors are fabricated by using LaFeO₃ nano-materials as sensing materials. The phase composition and morphology of particles in these materials are characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The XRD analysis results reveal that LaFeO₃ can be obtained by heating at 400–900 °C. TEM images manifest that the average particle sizes increase with heating temperature increasing, the particle sizes are in the range of 50–80 nm when heating temperature is increased to 800 °C. Furthermore, the influence of the heating duration and the heating temperature on the gas-sensing properties of the sensors based on LaFeO₃ nano-materials is also investigated in this work. The sensitivities to several organic gases, such as (CH₃)₃N and (CH₃)₂CO are studied. It is found that the sensor based on LaFeO₃ nano-material (800 °C, 2 h) exhibits best performance in all sensors investigated in this work. In detail, the sensitivities of the sensor based on LaFeO₃ nano-material (800 °C, 2 h) to 1000 and 0.001 ppm (CH₃)₃N at 208 °C are as high as 2553 and 1.6, respectively; and the response time and recovery time for 10 ppm trimethylamine are 8 and 50 s, respectively.     

一种新的图像空域公开水印技术

该文提出了一种新的基于图像空域的公开水印技术,算法充分考虑了数字图像的空间局部相关性与人类视觉系统(HVS)特性。首先将原宿主图像转换为一维Hilbert序列,然后利用混沌序列生成的块索引矩阵在图像Hilbert序列中伪随机选取一块,再结合HVS特性,通过不同强度地调整块中选定的水印嵌入位置像素与其所在块均值之间的大小关系,以自适应嵌入水印信号。实验结果表明,该算法在保证有较好的不可知觉性的同时,对一般的信号处理操作和旋转、缩放等有较强的鲁棒性,特别是锐化、对比度增强、边缘增强和直方图均衡等信号增强处理几乎不影响水印的提取。     

变速周向低应力弯曲断裂下料初始工艺参数的确定

针对当前金属棒料下料技术存在下料断面质量差、下料效率低、污染重等问题,提出一种变速周向低应力弯曲断裂下料方法,并论述其下料机理.利用ANSYS软件,对下料机中柱状锤头的初始径向压下量进行数值计算;给出棒料夹持位置参数的合理取值和进给套筒移动速度的计算公式.研究内容为进一步研究低应力弯曲精密下料奠定理论基础.     

中间相沥青高温炭的氧化动力学研究

研究了２种镁碳砖粘结剂高温炭的氧化动力学。结果表明,中间相沥青粘结剂比酚醛树脂粘结剂高温炭具有更好的抗氧化性能,脱除了原生喹啉不溶物后,可提高中间相沥青粘结剂的抗氧化性能。     

Study on the hydrothermal treatment of Shenhua coal

In this paper, the hydrothermal treatment of Shenhua coal was carried out under 0.1 MPa (initial pressure) nitrogen and different temperature. Effects of hydrothermal treatment on the structure and the hydro-liquefaction activity of Shenhua coal were investigated by the ultimate and proximate analyses, the FTIR measurements and TG analyses of hydrothermally treated coals, and the characterizations of extraction and swelling properties, and the batch hydro-liquefaction of treated coal were also carried out. The results indicate that hydrothermal treatment above 200 °C can increase the hydrogen content of treated coal and decrease the yield of volatiles and the content of ash, especially a large amount of CO and CH₄ are found in gas products obtained by the hydrothermal treatment above 250 °C. Hydrothermal treatment disrupts the weak covalent bond such as ether, ester and side-chain substituent by hydrolysis and pyrolysis, and changes the distribution of H-bond in coal. The swelling ratio and the Soxhlet extraction yield of treated coal decrease with the increase of hydrothermal treatment temperature. The conversion of liquefaction and the yield of CS₂/NMP mixed solvent extraction at ambient temperature are enhanced by hydrothermal treatment at 300 °C. Therefore hydrogen donation reactions and the rupture of non-covalent bond and weak covalent bonds present in the process of hydrothermal treatment resulting in the changes of structure and reactivity of Shenhua coal. The results show that the hydro-liquefaction activity of Shenhua coal can be improved by hydrothermal pretreatment between 250 °C and 300 °C.