对数平均值的极小积问题

考虑一类含参数对数平均值的极小积问题。利用对数平均值不等式，问题转述为不含对数的参数规划问题。作为它们的应用，如果涉及的函数均为线性齐次、约束集为凸多面体（无论有界或无界），则必存在最优解并且可以在其极点处实现。     

Trends of the precipitation acidity over China during 1992–2006

The trends of the precipitation acidity from 1992 to 2006 were studied, based on the long-term acid rain observations at 74 sites in China. The results show that there was no remarkable change or extension of acid rain area (i.e., with annual mean of precipitation pH<5.6) during the 15 years. The largest and continuous acid rain area exists in the south of the Yangtze River, while the acid rain areas north of the Yangtze River remain separate. The severe acid rain area (i.e., with annual mean of precipitation pH<4.5) exists mainly in the south of the Yangtze River. The overall precipitation acidity for the 74 stations showed different trends before 1999 and after 2000. In the period 1992–1999, the precipitation acidity at most of the sites remained steady or showed a decreasing trend. After 2000, however, an increasing trend of the precipitation acidity was observed at many sites in North China, Central China, East China, and South China. As a result, the pattern of acid rain area changed during 1992–2006. The precipitation over North China, Central China, and South China became more acidified in the 15 years, with more pronounced trends in North China and the north of Central China. A slight decrease in the precipitation acidity was found in Southwest China, an area characterized as severest acid rain area for about two decades after the early 1980s. Consequently, the center of severe acid rain area in the south of the Yangtze River moved eastwards. The non-hydrogen conductivity (NHC), which is defined as the difference between the measured precipitation conductivity and the H+ conductivity calculated from measured pH, was estimated and treated as a proxy of soluble ions in precipitation. The result shows that the overall trend of the NHC before 1999 was pronounced and positive, while the trend after 2000 was inconspicuous or slightly negative. During 2000–2006, the change rate of pH was positively correlated to that of the NHC at 21 sites, implying that the increasing acidities found at these sites may partly be attributed to the decrease in the concentration of airborne particulate matter in recent years.     

Influence of chemical liquids on the fatigue crack growth of the AZ31 magnesium alloy

The fatigue crack growth behavior of an AZ31 magnesium alloy was investigated by comparing the effect of zirconate and phosphate chemical liquids. The morphology, components, and phase compositions of the chemical depositions at the fatigue crack tip were analyzed by employing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), respectively. For samples with and without the chemical liquids, their stress-intensity factor values at the fatigue crack tip were compared by using a stress-strain gauge. The results demonstrated that a zirconate film (Zr_xO_y·Zn_xO_y) and a phosphate film (Zn₃(PO₄)₂·4H₂O and MgZnP₂O₇) could be formed on the fatigue crack-surface at the fatigue crack tip. The stress distribution was changed because of the chemical depositions and the causticity of the chemical liquids. This could decrease the stress-intensity factor value and thus effectively cause fatigue crack closure, which reduces the fatigue crack growth rate. Moreover, it was found that the fatigue crack closure effect of zirconates was more positive than that of phosphates.     

混合信号处理实现2D-DCT的CMOS图像传感器结构

为了减少原有混合信号处理方法实现二维离散余弦变换(2D-DCT)的运算周期,提出了一种新型的CMOS图像传感器(CIS)结构.该结构利用2D-DCT可以行列分离以及变换核对称的原理,对像素阵列进行8×8分块,增添采样电容阵列,通过寄存器控制、选择相应核系数的电容比例、结合模拟累加器完成列变换,通过电容复用和数字域累加完成行变换.对结构进行建模验证,结果表明:此结构能够正确实现2D-DCT,保留15.63%DCT系数压缩时,峰值信噪比(PSNR)达到73.54,dB,运算周期缩短为原有混合信号处理方法的25%.该结构提高了传统CIS的输出效率,适用于无线视频传感网络、生物医疗等低功耗高效率成像系统.     

基于模糊聚类算法的精炼过程真空系统故障诊断

针对大型真空冶金系统(DVMS)的故障点多、故障征兆不明显且要求其故障诊断快速、准确的特点,提出了一种基于模糊聚类算法的智能诊断模型·该模型具有很强的自学习、自组织能力适用于大型复杂真空系统的故障诊断·在介绍了模糊聚类算法的理论同时,给出了模糊故障诊断的步骤·以RH KTB真空冶金系统的智能故障诊断为例给出了模糊诊断的实际过程·通过分析证实了该算法对大型复杂真空冶金系统智能故障诊断的有效性·     

AutoCAD尺寸标注技巧

通过分析几例尺寸标注的技巧,探讨如何使ＡｕｔｏＣＡＤ尺寸标注适合我国制图标准和尺寸公差的标注。     

退火温度对Fe73.5Cu1Nb3Si13.5B9合金磁后效和正电子寿命的影响

测量了制备态和经不同温度（ｔａ ＝ ４５０ ～７５０ ℃） 退火的Ｆｅ７３－５Ｃｕ１Ｎｂ３Ｓｉ１３－５Ｂ９ 合金的室温磁后效和正电子寿命·发现在６００ ℃以下退火,随着退火温度升高,磁后效和正电子寿命都单调下降;在６５０ ℃以上退火,磁后效基本被抑制,正电子寿命出现两个值,它们分别对应自由体积和空位聚集体,且后者显着增大·实验结果表明,磁后效主要由材料中的非晶相所贡献,这是由于非晶相中存在大量自由体积的缘故·     

巴尔虎人5项舌运动类型的人类学研究

对呼伦贝尔市286例(男95,女191)巴尔虎人的卷舌、叠舌、翻舌、尖舌、三叶舌5项舌运动类型进行了调查研究.结果发现:(1)巴尔虎人卷舌、叠舌、翻舌、尖舌、三叶舌出现率分别为80.42%、6.64%、38.81%、79.72%、16.43%;除叠舌外,巴尔虎人的其他4项舌运动类型在性别间的差异均无统计学意义.(2)在我国各族群中,巴尔虎人卷舌、翻舌出现率偏高,叠舌、尖舌出现率中等,三叶舌出现率偏低.(3)聚类分析结果表明,巴尔虎人与蒙古族其他族群(厄鲁特蒙古族、科尔沁蒙古族、锡林郭勒蒙古族、察哈尔蒙古族、布里亚特蒙古族和乌拉特蒙古族)舌运动类型出现率接近.(4)卷舌与翻舌、尖舌、三叶舌,叠舌与尖舌彼此间存在基因互作关系.巴尔虎人5项舌运动类型具有北亚类型族群的基本特征.     

藏医药学实验教学模式改革探讨

通过实验、实习、实践教学使学生认识、了解和熟悉藏医人体三因(隆、赤巴、培根)和各组织器官的形态、结构、功能以及在疾病状态下的改变,使学生在学习的同时能够进行藏药药效物质基础、传统方剂配伍规律和藏药炮制技术等的初步研究。在充分掌握传统藏医药对人体、疾病、治疗三者辩证统一认识的基础上,了解现代医学实验研究的基本思路、原则和方法,逐步培养了学生的创新思维和初步的科学研究能力。根据藏医药学学科实践性强的特点,把藏医药传统"师带徒"临床实习、野外采认药等实践活动与现代医学室内实验相结合,构建起由"实验+实习+实践"所组成的"三实"结合模式,使学生系统地掌握藏医药实验教学的内容。