Critical time of the lognormal distribution

The critical time is the time point as the failure rate starts to decrease and also as the mean residual lifetime starts to increase. The estimated critical time is useful for determining the duration of a burn-in process. The method for estimating the critical time of the failure rate for lognormal lifetime distribution is discussed. A single time censored data is used as a example for illustration.     

On the hazard rate of the lognormal distribution

It is argued that plots of the hazard rate for the lognormal random variable which have appeared in some recent literature are incorrect and/or misleading; the hazard rate always begins at zero, rises to a maximum, then decreases very slowly to zero. An equation for the location of the maximum of the hazard rate is derived. The maximum lies in a finite interval for all positive values of the standard deviation of the associated normal random variable. Approximations that can be used to compute the hazard rate for parameter values outside of the usual range in the tables associated with the normal (Gaussian) random variable are presented     

配电自动化终端数据质量分析工具应用研究

本文通过在配电主站开发数据质量分析工具分析配电自动化终端三遥信息数据质量问题,通过工具分析配电自动化终端遥控失败,遥信抖动、频发,遥测存在死区设置过小、不合理和不刷新等情况原因,解决配电自动化终端数据质量问题,提高配电主站数据质量.     

SQLite数据库在数据分发服务中的应用

结合数据分发服务中对海量数据查询匹配的应用需求,基于Windows系统平台,阐述了SQLite数据库的架构和特点.给出了基于SQLite的查询匹配实例的设计,成功地实现了海量数据中的动态匹配,并通过实验验证了采用SQLite数据库后的时效性.     

Predictive densities for the lognormal distribution and their applications

Maximum likelihood predictive densities (MLPDs) for a future lognormal observation are obtained and their applications to reliability and life testing are considered. When applied to reliability and failure rate estimations, they give estimators that can be much less biased and less variable than the usual maximum likelihood estimations (MLEs) obtained by replacing the unknown parameters in the density function by their MLEs. When applied to lifetime predictions, they give prediction intervals that are shorter than the usual frequentist intervals. Using the MLPDs, it is also rather convenient to construct the shortest prediction intervals. Extensive simulations are performed for comparisons. A numerical example is given for illustration.     

Some informational properties of the lognormal distribution (Corresp.)

The marginal, joint, and conditional entropy and the trans-information are derived for random variables with lognormal probability distributions, revealing some interesting deviations from its sister distribution, the normal. A maximal entropy property, capacity theorem for the lognormal channel, and implications for some nonlinear transformations are also presented. Potential applications of the measures to psychophysics are mentioned.     

Synthesis of EM geophysical tomographic data

In order to test tomographic inversion schemes under controlled conditions, we have developed a forward electromagnetic model, using the volume current method (VCM). The algorithm can handle thin irregular-shaped bedding planes as well as inclusions or localized anomalies. It is thus ideal for modeling oil trap regions in the earth. Both transmission and reflection images, in magnitude and phase, are presented. Model results are given for a complex lithology as appropriate for an enhanced oil recovery zone. Particular emphasis is placed upon understanding the qualitative effects of bedding layer planes, both continuous and broken, on the electro-magnetic response of an elliptical shaped anomaly. The point is made that resolution of reservoir features in complex lithoiogies, as encountered in enhanced oil recovery applications, requires accurate processing of both amplitude and phase tomographic data.     

A three-parameter Weibull-like fitting function for flip-chip die strength data

Die cracking in the assembly and reliability testing of flip-chip (FC) packages is often a major concern. A widely used die strength test is the so-called the four-point bending (4PB) test. In the 4PB test, the die is under pure bending and the strength of the die is determined by its breaking tensile stress. Although the 4PB test has been widely used, a well-established relation between the 4PB result and the die breaking in FC package has not been reported. This paper discusses the relation from a probabilistic mechanics point of view. The theory considers the following issues in the material strength test and the application loading conditions: (1) the die top in the 4PB test is under uniaxial tensile stress and the die in FC package is under multi-axial stress; (2) the 4PB test only puts part of the die top under tension and the die top in FC plastic package has almost 100% of the die top area under tension; (3) the die stress in the 4PB and in the package has a different distributions which contribute differently to die cracking. Weibull distribution will be used to analysis the 4PB test data. A three-parameter Weibull distribution fitting procedure will be presented. The function form of the cumulative density function of Weibull distribution is specially modified to take the above three issues into consideration and reflect the stress distribution difference between the test and application. The three-parameter Weibull fitting is compared to a two-parameter fitting. It turns out that some systems need three-parameter fitting and some other systems only need the two-parameter fitting. For systems need three-parameter fitting, a two-parameter fitting will be too conservative in design.     

Bounds on the distribution of a sum of independent lognormal randomvariables

The distribution function of a sum of lognormal random variables (RVs) appears in several communication problems. Approximations are usually used for such distribution as no closed form nor bounds exist. Bounds can be very useful in assessing the performance of any given system. In this letter, we derive upper and lower bounds on the distribution function of a sum of independent lognormal RVs. These bounds are given in a closed form and can be used in studying the performance of cellular radio and broadcasting systems     

Reliability sampling plans for lognormal distribution, based onprogressively-censored samples

This paper presents reliability sampling plans for the lognormal distribution based on progressively censored samples. In constructing these sampling plans, large-sample approximations to the best linear unbiased estimators of the location and scale parameters are used. For some selected progressive censoring schemes, reliability sampling plans are tabulated for p_α and p_β to match MIL-STD-105. While in general, variable-sampling plans require smaller sample size when compared with attribute-sampling plans, the ordinary complete and right-censored life test experiments are special cases of the progressively censored experiment. Hence, the progressively censored reliability sampling plans in this paper are widely applicable. General application of the procedure is discussed, and two examples are provided     

A generalized three-parameter (3-P) aperture distribution forantenna applications

A versatile three-parameter (3-P) elliptical aperture distribution, which encompasses many of the existing circular aperture distributions, is presented. Characteristics of the 3-P distributions such as the edge taper, the taper efficiency, the aperture power, the closed-form far fields, the sidelobe levels, the beamwidth and beam efficiency are analyzed. Also derived is an asymptotic form of the far-field, based on which the far-angle features of the 3-P distributions such as the far-field envelope, the decay rate, and the positions of nulls are determined. Examples are presented to illustrate the improvements resulting from the enlarged parameter space for aperture models obtainable from the 3-P distributions. Issues concerning the total power associated with an aperture distribution are studied and the inadequacy of some commonly used approximation is demonstrated     

Distinguishing between lognormal and Weibull distributions[time-to-failure data]

A previous method for deciding if a set of time-to-fail data follows a lognormal distribution or a Weibull distribution is expanded upon. Pearson's s-correlation coefficient is calculated for lognormal and Weibull probability plots of the time-to-fail data. The test statistic is the ratio of the two s-correlation coefficients. When "standardized", the lognormal and Weibull variables map into 1 of 2 gamma distributions with no dependence on the shape or scaling factors, confirming earlier observations. Using a set of Monte Carlo simulations, the test statistic was found to be s-normally distributed to good approximation. Formulas for estimating the mean and standard deviation of the test statistic were derived, allowing for an estimate of the probability of hypothesis test errors. As anticipated, the test capability increases with increasing sample size, but only if a substantial fraction of the parts actually fail. If less than 10% of the parts are stressed to failure, then it is almost impossible to distinguish between lognormal and Weibull distributions. If all parts are stressed to failure, the probability of making a correct choice is fair for sample sizes as small as 10, and becomes quite good if the sample size is at least 50. The statistical technique for distinguishing lognormal from Weibull distributions is presented. Its theoretical foundation is given at a qualitative level, and the range of useful application is explored. An approximate form for the distribution of the test statistic is inferred from Monte Carlo simulation     

三参数Weibull分布下基于BRM的LED照明灯寿命预测

为了在短时间内准确获得LED照明灯的寿命信息,以3组恒定加速应力的试验数据为基础,采用三参数Weibull函数描述其寿命分布,基于双线性回归法(BRM)对试验数据进行处理分析,并利用自行开发的寿命预测软件较为精确地得出LED照明灯在正常工作应力下的寿命。数值结果表明,LED照明灯的寿命服从三参数Weibull分布,其加速模型符合Arrhenius方程,精确预测的LED照明灯寿命为工程技术人员关于产品的可靠性设计提供技术参考。     

时域有限元法在计算电磁问题上的应用及发展

对时域有限元法应用于三维电磁辐射和散射问题的原理和最新进展作了简要介绍.首先给出了时域有限元法的原理和基本公式;然后介绍了时域有限元法遇到过的开域自由空间截断及庞大的计算域等问题及其解决方案;最后,对该领域尚待解决的问题和可能的发展趋势,例如混合方法、hp-自适应技术、正交基函数以及用图像处理单元(GPU)加速有限元算法等进行了评论和展望.     

配网规划中主干配模式的应用分析

本文将对配网中主干配模式的不同特点进行分析,结合当前主干配模式在配网规划中的应用状况,探讨在配网规划中如何推进配网接线模式向主干配模式应用转变。     

电磁逆散射无相位检测的相位复原

利用入射场作为约束条件,用最优化泛函的方法由总场幅度信息重建散射场幅度和相位.分析了散射场自由度和噪声对重建结果的影响.讨论了成功实施相位复原和避免局部极小值的条件.首次用实验结果验证电磁逆散射无相位检测相位复原的可行性,证明了方法的有效性、高度稳定性和较强的抗噪声能力.该方法的计算成本低,实用性较强.研究结果是实施无相位检测电磁逆散射的基础.     

对数正态分布下的无线光通信系统误码率分析

对开关键控(OOK)强度调制直接检测(IM/DD)方式的无线光通信接收发射系统的光电信号进行分析,并使用最大后验概率(MAP)方法确定判决阈值。将对数正态分布作为湍流信道上光强闪烁模型,建立了系统误码率与湍流强度、光源相干参数、激光发射器光功率等系统参数之间的定量关系。采用部分相干光作为信号光能降低光源相干度,有效抑制湍流效应。计算结果表明：在一定条件下,湍流强度改变0.5个量级系统误码率相差6-8个量级,并且最优源相干参数可以通过计算得到,其对应的部分相干光最有利于提高通信系统性能。     

A comprehensive review of the lognormal failure distribution with application to LED reliability

Life-test data for many semiconductor devices obey the lognormal law of failure. In this paper we offer a survey of the key statistical properties of the lognormal distribution which are relevant in device engineering. The statistical developments are illustrated throughout by specific examples drawn from life-test data for GaP red LEDs which show lognormal failure behavior. Additional theoretical justification for accepting the lognormal distribution in the case of these devices is provided by the statistical recasting of the diffusion theory of red LED degradation.The treatment of the fundamental concepts of reliability in terms of cumulative failure function, instantaneous failure rate, mean time for failure (MTTF), etc., although concise, is self-contained. Moreover, the estimation of the two characteristic parameters (median life, standard deviation) of the lognormal distribution from sample data by means of a number of alternative procedures (graphical, least-square, maximum likelihood) is discussed in detail. The efficient determination of the MTTF and failure rate is facilitated by convenient charts developed here which relate these quantities to the parameters median life and standard deviation at 5, 10, 20 and 40 years of device service life. In order to assess the uncertainty associated with the estimates, the confidence limits on the median life and standard deviation of the population as a function of confidence level and sample size are given in novel graphical forms. Finally, error bounds for the MTTF and failure rate of the population are also presented.     

信息挖掘技术在数据业务分析中的应用

介绍了信息挖掘的定义、系统的结构模型及其作用,阐述了信息挖掘技术在彩信业务以及其他数据业务中的应用情况,认为应将信息挖掘技术应用于数据业务的话单及日志分析中,为维护人员分析解决问题提供有效的数据及信息支持,更好地促进数据业务的发展.