基于AT89C51单片机的简易频率计的设计

为了解决市场上各种多功能、高精度数字频率计高价格的问题,本文通过综合分析实际工作的要求,选择市场上低价格的常用元件,由单片机产生闸门时间与时钟等基准信号以减少外围电路,从而提出了一种基于单片机(AT89C51)为主控制核心、LCD1602为显示界面的频率计设计方案。本方案可满足简易频率计体积小、成本低、精度高、可测频带宽的市场需求。     

Chameleon effects in homework research: The homework–achievement association depends on the measures used and the level of analysis chosen

Using a data set specifically tailored to homework research, with a sample of 1275 students from 70 classes in Switzerland, the association between homework and achievement in French as a second language was tested at three levels (class level, between-student level, and within-student level). The strength and direction of the homework–achievement association depended on the homework indicator chosen and differed to some degree across analytical levels. At the class level, achievement was higher in classes set frequent homework assignments and in classes where students reported low overall levels of negative emotions when doing homework. At the between-student level, high individual homework effort and low levels of negative homework emotions predicted favorable developments in French achievement, whereas high homework time predicted lower achievement. At the intraindividual level, high homework effort, high homework time, and low levels of negative homework emotions were statistically significantly associated with positive student evaluations of the learning gains from the specific assignment.     

Childhood emotional abuse characteristics moderate associations with adult psychopathology and caregiving

As the consequences of childhood maltreatment for adult adjustment become increasingly established in the literature, investigations of individual differences in these effects must evolve to examine more nuanced components of the maltreatment experience. This is particularly true for studies of childhood emotional abuse (CEA), which represents an umbrella label for numerous qualitatively different experiences. The present study examined the distinct contributions and potential interactive effects of CEA frequency and intensity on adult psychopathology, caregiving behaviors, and caregivers’ representations of the caregiver-child relationship in a diverse sample of 62 female caregivers of 4-year-old children, all of whom had experienced CEA. Frequency and intensity emerged as orthogonal characteristics of CEA with differential effects on adult adaptation. Higher CEA frequency predicted increased adult psychopathology, whereas higher CEA intensity predicted increased boundary dissolution in caregivers’ representations. Further, an interaction between frequency and intensity predicted negativity in caregivers’ representations, such that higher frequency of high intensity, but not low intensity, CEA predicted decreased negativity. Neither frequency nor intensity of CEA predicted observed caregiving behaviors. These results provide evidence that characteristics of CEA signal important differences in its experience, with differential implications for later adjustment. The specific differences in caregiving representations associated with high vs. low intensity CEA suggest that diverging mechanisms by which these experiences eventuate in adult outcomes should also be investigated. Above all, this study suggests that the measurement of CEA, and childhood maltreatment broadly, will benefit from enhanced attention to specific characteristics of individuals' experiences.     

RFID系统及其在图书馆中的应用

介绍了RFID(无线射频识别)系统及其在图书馆自动化中的应用情况，并阐述了深圳图书馆拟采用的RFID系统解决方案和实施过程。     

基于PLC的涂附磨具揉曲机张力模糊控制系统

为了满足涂附磨具揉曲机的工艺要求,本文设计的涂附磨具揉曲机的自动控制系统以可编程控制器为核心,采用模糊控制技术协调卷取的张力,数字变频器和交流异步电动机控制电动机的速度,力矩控制器和力矩电动机控制收卷速度,张力检测装置检测卷取的张力并构成闭环控制系统。该系统具有速度稳定、张力恒定、可靠性高、操作简便的特点。     

变频器应用中的抗干扰问题探析

变频器大多运行于恶劣的电磁环境,易受外界的一些电气干扰,同时其输入侧和输出侧的电压、电流含有丰富的高次谐波,对供电电网中其他电气设备也产生干扰。因此投入运行既要防止外界干扰它,又要防止它干扰外界,本文对变频器应用中的干扰原因和干扰信号传播途径进行了分析,并提出了相应的防治措施。     

英汉逻辑连接词文体对比研究

本文试图将逻辑连接词的研究与文体结合起来考虑并进行探讨,按照文体分类收集了大量的英汉语料,利用语料分析软件对四种不同文体中连接词的出现频率、连接词的逻辑关系等进行量化分析处理,之后对分析结果进行解释和说明,从而加深人们对不同语篇连接词使用特点的了解。     

基于MATLAB的OFDM系统仿真

正交频分复用调制技术（OFDM Orthogonal Frequency Division Multiplexing）是由多载波调制（MCM）发展而来。文章讨论了OFDM的基本原理、建立了正交频分复用系统的数学仿真模型,用MATLAB语言实现了整个系统的计算机仿真并给出了参考设计程序。最后分析了不同的信道条件和调制体制下,系统的误码率特性。     

基于声发射的RT轨道机疲劳加载信号特征提取与分析

本文在不同应力条件下对RT轨道机进行疲劳加载,采集RT轨道机从加载到断裂时的信号,对信号进行时域和频域分析观察信号特征对RT轨道机断裂原因进行探讨。     

多转速下曲轴模态分析对比

在计算曲轴频率和振型过程中,针对曲轴模态分析时一直采用的是自由模态,考虑由旋转产生离心力对曲轴频率和振型的影响,计算出多种转速情况下的频率和振型,并进行比对,充分说明曲轴在实际工作过程中产生的振动情况,结果更加符合实际情况。