Variance estimation for measures of change in probability sampling

Variance estimation of changes requires estimates of variances and covariances that would be relatively straightforward to make if the sample remained the same from one wave to the next, but this is rarely the case in practice as successive waves are usually different overlapping samples. The author proposes a design‐based estimator for covariance matrices that is adapted to this situation. Under certain conditions, he shows that his approach yields non‐negative definite estimates for covariance matrices and therefore positive variance estimates for a large class of measures of change.     

旋转三维紊流流场的数值分析

应用SIMPLEST方法和标准k-ε紊流模型对旋转直通道内的流场进行计算，给出了该旋转流场的速度矢量图及压力场，并将测量截面上的主流和二次流速度分布与实验值作了对比，结果吻合较好，对叶轮机械内的旋转流场的数值模拟有重要意义。     

离心风机旋转叶片表面压力分布实验研究与三元数值分析

本文利用作者自行设计的机械密封式压力传输器，对离心通风机旋转叶片表面静压分布进行测量，并绘制出静压分布曲线，将此曲线与三元流变分有限元程序的计算结果进行比较分析，得出若干结论，可为离心风机的工程设计提供借鉴．     

转轴故障诊断与监测

讨论了转轴系统的故障诊断理论和相应监测系统的设计;介绍了对调相信号的解调和相位调制信号的提取;研究了PLC和微机监测系统的数据监测、系统抗干扰及数据通讯中的一些问题.     

精密车床回转精度测试机构原理误差计算

结合精密仪器误差合成方法和精密机械设计螺纹机构误差分析方法,提出一种精密车床主轴回转精度动态测试机构原理调节误差的计算分析方法,经算例计算,该方法计算简单有效。     

旋转矢量在工程力学教学中的应用

利用学生已熟练掌握的矢量合成及矢量投影定理，提出了用旋转矢量来记忆并理解工程力学课程中非矢量的、难以掌握的、大量的公式和定理。即：利用三角函数的正交性，将公式中的各代数量定义为平面上可绕一点旋转的矢量表示，再根据矢量合成定理及矢量投影定理表达公式的内容。     

旋转设备在线健康监控指数研究

利用小波包分解方法对在线监控中收集到的齿轮箱振动信号进行频域划分,并在其划分后的频段上有选择地进行了信号重构。在其基础上提出齿轮在线健康监控指数,可以用来反映齿轮箱整个寿命期间的健康状态。同时,为了实现对齿轮早期故障的预警,提出了一个用来在线检测的动态阈值。通过3套不同的齿轮箱全寿命振动信号数据进行了健康指数和早期预警的验证。实验结果证明,该健康监控指数及其动态阈值可以准确地检测出齿轮早期故障发生的时刻。     

琵琶训练中的"轮指"技法论略

“轮指”是琵琶最为独特而又极富表现力的演奏技法之一 ,它的好坏直接关系到琵琶演奏的成败。因此应对琵琶“轮指”的演奏方法、训练步骤、学习方法以及学习的思维方式等进行理论上的探讨和总结 ,力求为琵琶学习者提供理性指导。     

柴油发电机组转速与电压控制系统设计

本文针对柴油发电机组的主要运行特点，设计出切实可行的机电混合式调速器以替代传统的机械式调速器，以及发电机电压控制系统。     

Psychophysiological coherence training to moderate air traffic controllers’ fatigue on rotating roster

The nature of the current rotating roster, providing 24-h air traffic services over five irregular shifts, leads to accumulated fatigue which impairs air traffic controllers’ cognitive function and task performance. It is imperative to develop an effective fatigue risk management system to improve aviation safety based upon scientific approaches. Two empirical studies were conducted to address this issue. Study 1 investigated the mixed effect of circadian rhythm disorders and resource depletion on controllers’ accumulated fatigue. Then, study 2 proposed a potential biofeedback solution of quick coherence technique which can mitigate air traffic controllers’ (ATCOs’) fatigue while on controller working position and improve ATCOs’ mental/physical health. The current two-studies demonstrated a scientific approach to fatigue analysis and fatigue risk mitigation in the air traffic services domain. This research offers insights into the fluctuation of ATCO fatigue levels and the influence of a numbers of factors related to circadian rhythm and resource depletion impact on fatigue levels on study 1; and provides psychophysiological coherence training to increase ATCOs’ fatigue resilience to mitigate negative impacts of fatigue on study 2. Based on these two studies, the authors recommended that an extra short break for air traffic controllers to permit practicing the quick coherence breathing technique for 5 min at the sixth working hour could substantially recharge cognitive resources and increase fatigue resilience. Application: Present studies highlight an effective fatigue intervention based on objective biofeedback to moderate controllers’ accumulated fatigue as a result of rotating shift work. Accordingly, air navigation services providers and regulators can develop fatigue risk management systems based on scientific approaches to improve aviation safety and air traffic controller's wellbeing.