三元函数极值的探索

函数极值的存在性及判别方法是微分的重要应用之一.文章就三元函数给出了判别极值的存在的一个必要条件和充分条件.     

几种防晃电措施在化工企业电气系统中的应用

电网的晃电对连续型管道化企业的正常生产危害极大。文章提出,针对不同情况,可采取分闸线圈线路、延时技术、UPS稳压设备、控制柜分批启动技术、电动机保护器、合理设置参数等措施,有效避免因晃电产生的跳闸停机,提高企业的经济效益。     

The Partial Credit Model and Generalized Partial Credit Model as Constrained Nominal Response Models,With Applications in Mplus

The purpose of this article is to demonstrate constraining the nominal response model in Mplus software to calibrate data under the partial credit model (PCM) and generalized partial credit model (GPCM). Currently, many researchers are uncertain if the PCM and GPCM can be estimated within Mplus. Through model constraint commands in Mplus, we demonstrate that both models can be estimated in recent versions of this software. We present an example of this approach with data from 522 respondents on a subset of items from the Math Self-Efficacy Scale (Betz & Hackett, 1983). It is demonstrated that the presented model code is a viable way of estimating the models in Mplus.     

多元函数在一元微积分中的一些应用

举例说明了如何把多元函数的一些性质应用于解决一元微积分的问题中.如用多元函数的偏导解决一元隐函数的求导问题,用多元函数的拉格朗日乘数法来求一元函数的极值,用二重积分求平面图形的面积,三重积分求旋转体的体积等等.     

社会资本对幸福感影响的实证研究——以佛山市顺德区为例

利用顺德地区居民调查数据探讨了社会资本对幸福感的影响。首先运用因子分析法构建了与社会资本相关四类综合变量．然后采用核估计方法分别对四类变量与幸福感之间的线性性关系进行了回归,在此基础上,建立半参数回归模型估计了社会资本与幸福感之间的关系,最后,构建了变系数分位数回归模型讨论了社会资本对不同幸福感群体的影响。结果表明：政治环境、社会关系及能力发挥对幸福感有显著影响：社会关系及能力发挥对不同幸福感群体均有较显著的影响并且影响强度大。     

An NCME Instructional Module on Polytomous Item Response Theory Models

A polytomous item is one for which the responses are scored according to three or more categories. Given the increasing use of polytomous items in assessment practices, item response theory (IRT) models specialized for polytomous items are becoming increasingly common. The purpose of this ITEMS module is to provide an accessible overview of polytomous IRT models. The module presents commonly encountered polytomous IRT models, describes their properties, and contrasts their defining principles and assumptions. After completing this module, the reader should have a sound understating of what a polytomous IRT model is, the manner in which the equations of the models are generated from the model's underlying step functions, how widely used polytomous IRT models differ with respect to their definitional properties, and how to interpret the parameters of polytomous IRT models.     

Towards the successful integration of e-learning systems in higher education in Iraq: A student perspective

This study aims to analyse the factors that can explain the adoption and effective use of a new e-learning system in Iraq. To achieve this, it uses a selection of factors that are present in the technology acceptance model (TAM) and the unified theory of acceptance and use of technology (UTAUT) model, and it includes three additional factors. The study hypothesises new relationships between the selected factors. Questionnaires were distributed to 300 university students in Iraq. Partial least squares-structural equation modelling (PLS-SEM) was used to analyse the data received. The findings suggest that perceived usefulness (PU), perceived ease of use (PEOU), subjective norms (SNs), information quality (IQ), system quality (SQ), technical support (TS) and self-efficacy (SE) have significant effects on behavioural intention (BI). In turn, BI and TS have significant direct effects on the actual use (AU) of e-learning systems. The factors age, gender and experience significantly moderated some of the relationships in the model. The research has several implications for policy makers, universities and the management of e-learning systems.     

Teaching the partial products algorithm with the concrete representational abstract sequence and the strategic instruction model

Elementary standards include multiplication of single-digit numbers and students advance to solve complex problems and demonstrate procedural fluency in algorithms. The ability to illustrate procedural fluency in algorithms is dependent on the development of understanding and reasoning in multiplication. Development of multiplicative reasoning provides the foundation for advanced mathematics and algebraic reasoning. For students who struggle in mathematics, instruction in multiplication algorithms should ensure conceptual understanding so that students have a foundation for success in advanced mathematics. The concrete representational abstract (CRA) sequence addresses conceptual understanding and the strategic instruction model (SIM) supports procedural knowledge. The current pilot study combined these methods to teach elementary students the partial products algorithm. Twelve students in grades four and five participated in the study, receiving instruction from teachers in their school during an intervention period. Within a pre-experimental design, using pre- and postintervention data, students showed a significant change in performance. The article will describe and show how teachers implemented the CRA-SIM interventions and discuss implications for practice.     

重积分的原函数法

用原函数的方法,建立计算重积分的一种新方法——原函数法。     

一般三维非齐次偏微分方程的可解性条件

给出了一般形式的三维非齐次偏微分方程的可解性条件,据此可省去繁琐的计算过程,直接判断其解的存在性.可将此条件应用于晶体生长过程中的类似模型.