On estimating nonnegative definite quadratic forms

It is often required to estimate a quadratic form in survey sampling, especially when one has to estimate the mean squared error of a linear estimator of the population total. In this note we consider the problem of obtaining uniformly nonnegative quadratic unbiased estimators for nonnegative definite quadratic forms. The estimators considered here are necessarily quadratic. Received January 1997     

等比级数在函数展开成幂级数中的应用

函数的幂级数展开是高等数学的教学重点之一,在解决函数的幂级数展开的问题中,等比级数起着重要的作用。文章介绍了利用等比级数将函数展开成幂级数的常见情形,并给出了具体的例子。     

二项式系列题目类解初探

二次函数是中学数学的重要内容之一,和它相关的内容,如:二次方程、二次不等式、二次三项式及二次函数的图像,构成了一个体系,称之为"二次式系列";本文主要在以下三个方面对这些题目的解法进行探讨:(一)求参数的范围;(二)根的存在情况的判别;(三)求最大、最小值;通过以上的讨论,以期提高中学生对此类题目的解题方法和解题技巧。     

柯西不等式的几种证明方法

如果某一知识跟很多学科或者一个学科的很多分支有着密切联系,那么这个知识肯定是很重要的,而二次型、欧式空间内积、詹森不等式都是高等数学中代数、实函、微积分的基本内容。本文运用二次型理论、欧式空间中内积性质和詹森(Jensen)不等式三种方法证明柯西不等式,并简要说明柯西不等式与高等数学之间的联系。     

幂级数的求和方法

本文应用高等数学的知识,介绍了幂级数的几种常见的求和方法及技巧。     

基于ARIMA模型的风电功率预测

风电功率的随机波动被认为是对电网带来不利影响的主要因素。研究风电功率的波动特性,对改善风电预测精度与克服风电接入对电网的不利影响都有重要意义。本文通过对30天的风电数据加总,求得15min级的风电功率数据,提出了基于ARIMA模型的风电功率的预测模型。通过对数据进行单步预测取得较好的预测结果,说明ARIMA(1,1,1)模型能够较好的拟合原始数据。给风电功率的预测提供了新的思路。     

蒋庄煤矿综放工作面供电方案的研究与实践

蒋庄煤矿3下610工作面为矿井首个综放工作面,设备功率大、供电距离远、综机设备均属首次应用,针对供电系统的复杂情况因地制宜地提出了该供电方案,从多个方面入手解决工作面供电系统中的难点,保证了工作面综机设备的正常运转,为下一步的工作面安装供电设计提供了参考和借鉴。     

Autocorrelation and Bias in Short Time Series: An Alternative Estimator

The conventional first-order autocorrelationcoefficient r₁ generates an empiricalbias when it is applied to short time series.The properties of this estimator have beenexamined with a Monte Carlo simulation studyusing the MATLAB program (version5.2). This study also analyzes the functionof the empirical bias with the polynomicregression and derives a polynomic fittingmodel for different sample sizes. In thisway, a new estimator that has been correctedby the absolute value of the fitting model(r_1') is proposed. Having analyzed thestatistical properties of the estimator r_1',it is shown that the empirical bias generatedby r_1' is less in relationship to r₁ andr₁₊. The results of the study make itpossible to verify that the mean squared errorassociated to the estimator r₁ isless than that of r₁. Thus, the coefficient r_1'is recommended to estimate the lag-oneautocorrelation coefficient in samples under 50observations.     

中距离无线短信传输器

本设计以MSP430系统为核心,设计一个中距离无线短信传输器。用MSP430系统,采用中断控制nrf905单片无线收发器、液晶显示模块、键盘等模块,以实现点对点短信的发送与接收、信息的存储、存储与新建联系人、时间的显示与调整、闹钟、输入法的切换、电子书等功能。低功耗是本设计的一大特点。     

Product Heterogeneity,Intangible Barriers and Distance Decay: The Effect of Multiple Dimensions of Distance on Trade across Different Product Categories

Abstract

We empirically examine the heterogeneity in the effects of multiple dimensions of distance on trade across detailed product groups. Using finite mixture modelling on bilateral trade data at the three-digit Standard International Trade Classification level, we endogenously group product categories into an a priori unknown number of segments based on estimated coefficients of multiple dimensions of distance in the gravity equation. We find that institutional distance, belonging to the same trade bloc and especially geographical distance are crucial and distinct factors for classifying commodities into homogeneous product groups.     

建言方式、建言场合、权力距离对管理者采纳建言的影响

随着建言领域研究的深入,研究者不再满足于探讨如何激发员工建言,而是开始关注管理者采纳建言。基于特质激活理论,本文分析了建言方式（当面/微信）、建言场合（公开/私下）、权力距离（高/低）对管理者采纳建言的影响。研究以267名管理人员为被试,采用2×2×2被试间设计,模拟情境实验的结果表明：权力距离的主效应显著,低权力距离的管理者更多采纳建言;建言方式与权力距离交互效应显著,高权力距离的管理者采纳微信建言多于当面建言,低权力距离的管理者采纳当面建言多于微信建言;建言场合与权力距离交互效应显著,高权力距离的管理者采纳私下建言多于公开建言,低权力距离的管理者采纳公开建言多于私下建言。最后,本文提出研究的理论与实践意义,以及未来研究方向。     

On construction of admissible quadratic estimators

A random linear model for spatially located sensors measured intensity of a source of signals in discrete instants of time is considered. A basis of a quadratic subspace useful in quadratic estimation of a function of model parameters is given. Received: December 1999     

An Updated Literature Review of Distance Correlation and Its Applications to Time Series

The concept of distance covariance/correlation was introduced recently to characterise dependence among vectors of random variables. We review some statistical aspects of distance covariance/correlation function, and we demonstrate its applicability to time series analysis. We will see that the auto‐distance covariance/correlation function is able to identify non‐linear relationships and can be employed for testing the i.i.d. hypothesis. Comparisons with other measures of dependence are included.     

论手动后驱变速器的同步器布置形式对同步性能的影响

文章描述后驱手动变速器的换挡过程,分析变速器同步器性能与操纵舒适性之间的关系,进一步阐述同步器的同步性能指标包含同步时间t_E和同步力Pa,探讨t_E和Pa与同步器布置之间的关系。