复杂环境下基于时延估计的声源定位技术研究简

为了改善在复杂环境下声源定位算法的性能,提出了一种新的时延估计（TDE）方法,即基于传递函数比的统计模型方法（ATFR-SM）。该方法采用统计模型去除噪声对传递函数（ATF）的影响,在计算传递函数时对功率谱密度（PSD）进行平滑和“白化”,以去除混响对传递函数的影响。同时,算法中引入话音激活检测（VAD）去除对求取传递函数无用的噪声段,以提高时延估计的准确性。此外,将所提时延估计方法与线性定位法相结合,构成一套完整的声源定位方法。实验结果表明,在复杂环境下,时延估计方法具有更低的异常点百分比（PAP）和均方根误差（RMSE）,且明显优于传统的参考算法,同时声源定位方法具有更高的定位精度。     

人体通信信道相位特性研究

采用实验统计方法研究人体信道在1~200 MHz频段下的传播延时和相位特性。实验采用13名志愿者分别进行4个传播路径的群延时测量,并将测试频段划分为1~100 MHz和100~200 MHz两个子频段进行研究,探讨4个传播路径和两个子频段下的延时特性。统计分析表明:信号在人体通信信道的传播延时和传播路径无关;100~200 MHz频段内的传播延时均比1~100 MHz内的传播延时大。1~200 MHz频段内相位归一化曲线表明:在20~40 MHz频段信号畸变较大。根据最大似然估计算法(Maximum Likelihood Estimation,MLE)和Akaike信息量准则(Akaike Information Criterion,AIC),信号相位归一化偏差值符合Lognormal分布。     

全球发光二极管应用技术专利分析

由于具有低功耗和环保等特点,发光二极管照明被认为是最具有发展前景的照明技术之一.通过对全球LED照明应用技术领域的专利申请进行分析,揭示了LED照明应用技术的发展潜力巨大,但核心技术主要被美、日、欧等发达国家或地区的企业掌握,我国企业掌握的核心技术较少.基于专利分析,提出了促进我国LED照明应用技术可持续发展的对策.     

Phase I Analysis of Individual Observations with Missing Data

The effect of the methods for handling missing values on the performance of Phase I multivariate control charts has not been investigated. In this paper, we discuss the effect of four imputation methods: mean substitution, regression, stochastic regression and the expectation maximization algorithm. Estimates of mean vector and variance covariance matrix from the treated data set are used to estimate the unknown parameters in the Hotelling's T² chart statistic. Based on a Monte Carlo simulation study, the performance of each of the four methods is investigated in terms of its ability to obtain the nominal in‐control and out‐of‐control overall probability of a signal. We consider three sample sizes, five levels of the percentage of missing values and three types of variable numbers. Our simulation results show that the stochastic regression method has the best overall performance among all the competing methods. Copyright © 2013 John Wiley & Sons, Ltd.     

Functional Process Capability Indices for Circular Profile

Profile is a relation between one response variable and one or more explanatory variables that represent quality of a product or performance of a process. On the other hand, process capability indices are measures to help practitioners in improving the processes to satisfy the customer's expectations. Few researches are done to account for the process capability index in the areas of profile monitoring. All of these researches are focused on process capability index in simple linear profile. In all of these methods, response variables in different levels of explanatory variable are considered, and the relationship in all range of explanatory variable is neglected. In this paper, a functional method is proposed to measure process capability index of circular profiles in all range of explanatory variable. The proposed method follows the traditional definition of process capability indices. The functional method uses reference profile, functional specification limits and functional natural tolerance limits to present a functional form of process capability indices. This functional form results in measuring the process capability in each level of explanatory variable in circular profile as well as a unique value of process capability index for circular profile. The application of the proposed method is illustrated through a real case in automotive industry. Copyright © 2013 John Wiley & Sons, Ltd.     

不可逆恒温热源空气制冷机的炯经济性能优化

文章用有限时间热力学理论和方法,研究了恒温热源条件下不可逆空气制冷机的有限时间炯经济性能,导出了利润率解析式。用数值计算分析了压比、热源温比、热导率分配、压缩机和膨胀机的效率等参数对利润率的影响,并优化了循环压比和换热器的热导率分配。通过价格比,将有限时间炯经济性能目标与制冷率、熵产率及生态学目标建立了联系。所得结果对实际空气制冷设备的设计有一定指导意义。     

Rapid sintering of silicon nitride foams decorated with one-dimensional nanostructures by intense thermal radiation

Silicon nitride foams were prepared by direct foaming and subsequent rapid sintering at 1600 °C. The intense thermal radiation generated under the pressureless spark plasma sintering condition facilitated necking of Si₃N₄ grains. The prepared foams possessed a porosity of ～80 vol% and a compressive strength of ～10 MPa, which required only ～30 min for the entire sintering processes. Rapid growth of one-dimensional SiC nanowires from the cell walls was also observed. Thermodynamic calculations indicated that the vapor–liquid–solid model is applicable to the formation of SiC nanowires under vacuum.     

关于热工教学中的一些教学法尝试和体会

热工基础课程是一门概念多、公式多、且公式表达形式及使用条件多变的课程,为了避免学生死记硬背公式和概念的僵硬学习方法,教师在教学中应采用换位思考的方法,如果自己是学生,在初次学习本门课程时可能会有哪些困难,然后在教学中想方设法帮助学生解决这些困难。将我们在这方面做的一些尝试和体会介绍给大家,希望与各位同行切磋交流。     

Ti6Al4V表面激光熔覆纯Cr粉热力学分析

为研究在激光作用下元素之间的扩散及作用机理,采用激光熔覆方法在Ti6Al4V表面熔覆纯Cr粉,利用热力学相图分析软件Thermo-Calc对Cr-Ti-Al-V四元体系进行平衡相图计算分析,利用DICTRA软件模拟合金体系的元素在Ti6Al4V基体中扩散分布情况。X射线衍射图谱表明熔覆层主要由α-Ti、Laves相Cr2Ti及亚稳态Cr1.97Ti1.07组成;扫描电镜实验结果显示熔覆层主要由片状、树枝状及细小针状组织组成。熔覆层元素体系中主要为Cr、Ti元素在不断相互扩散,Al元素扩散缓慢,V含量基本没有变化,整个体系中主要参与反应的是Cr与Ti元素。     

改性稻杆吸附U(Ⅵ)的行为和机理研究

通过静态吸附实验,研究了改性稻杆对UO2+2的吸附行为,从吸附热力学和吸附动力学方面对改性稻杆吸附UO2+2的过程进行了分析,并采用红外光谱(FT-IR)、扫描电镜(SEM)、X射线能谱(EDS)、X射线衍射(XRD)等分析手段探讨了改性稻杆吸附UO2+2的机理。结果表明:改性稻杆对UO2+2的吸附过程符合Langmuir等温吸附模型,相关系数达到0.98以上,表现为以单层吸附为主;表面吸附是改性稻杆吸附UO2+2动力学控制的主要步骤,吸附动力学过程符合准二级吸附速率模型,相关系数达0.999 2;热力学研究表明,改性稻杆吸附UO2+2是吸热、自发、不可逆的过程;改性稻杆吸附UO2+2前后的表面形态发生了变化,部分晶体结构发生了改变,吸附过程中改性稻杆细胞壁上的—OH、C O、Si O及P—O等活性基团与UO2+2发生络合反应,形成络合物,故改性稻杆吸附U(Ⅵ)的机理为表面络合吸附。