Acceptance sampling plan of accelerated life testing for lognormal distribution under time-censoring

Lognormal distribution is commonly used in engineering.It is also a life distribution of important research values.For long-life products follow this distribution,it is necessary to apply accelerated testing techniques to product demonstration.This paper describes the development of accelerated life testing sampling plans(ALSPs)for lognormal distribution under time-censoring conditions.ALSPs take both producer and consumer risks into account,and they can be designed to work whether acceleration factor(AF)is known or unknown.When AF is known,life testing is assumed to be conducted under accelerated conditions with time-censoring.The producer and consumer risks are satisfied,and the size of test sample and the size of acceptance number are optimized.Then sensitivity analyses are conducted.When AF is unknown,two or more predetermined levels of accelerated stress are used.The sample sizes and sample proportion allocated to each stress level are optimized.The acceptance constant that satisfies producer and consumer risk is obtained by minimizing the generalized asymptotic variance of the test statistics.Finally,the properties of the two ALSPs(one for known-AF conditions and one for unknownAF conditions)are investigated to show that the proposed method is correct and usable through numerical examples.     

Cracking and Mechanical Properties of Airport Concrete Pavement with Fiber and Expansive Agent

Polypropylene fiber and expansive agent are used in airport concrete to improve its shrinkage cracking resistance and mechanical properties. The concrete specimens with amount content of polypropylene fiber or expansive agent or both of them are prepared. The morphology of specimens is observed by scanning electron microscope, the time when the first crack occurred is recorded through slap test, and the mechanical properties such as compressive strength and impact energies of concrete are measured. The results show that polypropylene fiber in concrete can reduce the shrinkage and delay the first crack, improve the impact resistance obviously, and improve the compressive strength slightly. Expansive agent can compensate the shrinkage and reduce cracks of concrete pavement markedly, and improve the mechanical properties of concrete pavement slightly. The study provides recommendations for cracking control of airport concrete pavement in the future.     

Analysis of driving efficiency for LRV wheels using forced-slip method

To investigate and improve the mobility of the Lunar Roving Vehicle (LRV), it is necessary to consider the mechanical properties of the interaction between the wheels and the ground. In this paper, a new solution method, the forced-slip solution method, which uses a semi-empirical approach, was presented. That is, given the wheel’s vertical load and drawbar pull or driving torque as known input values, the unknown slip ratio can be resolved. The alternative method involves predicting the mechanics for a given slip ratio. The proposed method correlates better with actual wheel movements, and by studying a single wheel, this solution method can also be used to resolve the mechanical properties of the front and rear wheels in a four-wheel-drive (4WD) LRV configuration. It can also be used to consider the multi-pass effect of the rear wheels on lunar soil. The calculation results show that the 4WD LRV driving efficiency varies with the position of the center of mass. Thus, the LRV driving efficiency can be optimized by adjusting the position of its center of mass.     

Robust adaptive filtering method for SINS/SAR integrated navigation system

This paper presents a new robust adaptive filtering method for SINS/SAR (Strap-down Inertial Navigation System/Synthetic Aperture Radar) integrated navigation system. This method adopts the principle of robust estimation to adaptive filtering of observational data. A robust adaptive filter is developed to adaptively determine the covariance matrix of observation noise, and adaptively adjust the covariance matrix of system state noise according to the adaptive factor constructed based on predicted residuals. Experimental results and comparison analysis demonstrate that the proposed method cannot only effectively resist disturbances due to system state noise and observation noise, but it can also achieve higher accuracy than the adaptive Kalman filtering method.     

A reflectance spectra-based approach to mapping salt fields using PCA-fused Landsat TM data

In this paper a method based on in situ measured reflectance spectra was developed for accurately mapping salt fields in the Taibei Salt Farm in Lianyungang City of East China. After radiometric correction and geometric rectification, six multispectral ETM+ bands were fused with the panchromatic band via principal components analysis (PCA). The fused data were used to map salt fields in the farm. Salt fields were mapped 91.95% correctly in comparison with ground statistics from raw multispectral bands. This accuracy level rose to 96.4% with the use of the panchromatic band (15 m resolution). However, PCA-fused data produced the highest accuracy of 98.8%. At the zone level, coarse resolution data resulted in an accuracy of 98.93% for crystallization ponds, but only 82.68% for condensation ponds. Use of the panchromatic band alone improved the accuracy for condensation ponds but decreased the accuracy for crystallization and evaporation ponds. Results derived from PCA-fused data are highly consistent with the ground statistics at a discrepancy between 0.35% for evaporation zone and 1.80% for condensation zone. It is concluded that a fine spectral resolution is important to separation of ponds of a varying salt content while a fine spatial resolution is important to their mapped area. Ponds of a lower salt content can be mapped more accurately from fused data than from raw spectral bands.     

一种顾及厄特沃思效应的水下重力辅助导航方法

水下相对于水面环境,准确估计厄特沃思效应更为困难,进而影响重力测量精度。由于传统重力匹配算法未考虑水下厄特沃思估计误差对重力辅助导航定位性能的影响,根据不同导航参数对厄特沃思估计误差的影响程度,构建了水下惯导系统/计程仪/重力仪组合导航框架,采用UKF非线性滤波算法,分析了不同导航模式下厄特沃思估计误差特性,并评估了有无厄特沃思估计误差时重力辅助导航性能的差异。半物理仿真结果表明采用DVL的辅助导航方式可有效抑制惯导误差积累,INS/DVL/Gravimeter三者信息融合导航模式定位性能得到了进一步提高,即使在考虑厄特沃思估计误差的情况下,与仅采用DVL作为辅助信息源相比,水平径向误差定位精度依然提升了17.02%。     

含Nd稀土相对高温钛合金低周疲劳裂纹萌生与扩展行为的影响

实验研究了含稀土Ｎｄ高温钛合金中稀土相颗粒与室温及６００℃低周疲劳裂纹萌生与扩展行为的关系。结果表明，疲劳裂纹在距颗粒一定距离的基体中产生，而不在预先开裂或脱粘的颗粒处萌生。裂纹扩展时绕过颗粒并使裂纹扩展路径曲折化。     

复杂机械设备可靠性考核中的模糊综合评价法

本文介绍了从可靠性指标，可靠性考核等方面阐述了评价过程中的模糊因素，从而为亲搁的可靠性高度提供依据。     

VDMOSFET导通电阻的最佳化设计

分析了VDMOSFET导通电阻模型，提出了单胞尺寸是影响导通电阻的最重要因素。单胞尺寸的最佳化选择可使器件的特征导通电阻RonA（单位面积导通电阻）最小，并通过大量理论计算给出击穿电压为50V时的最佳单胞尺寸。