我国各区域服务业发展水平比较研究

我国各区域服务业发展水平差异较大。从发展规模、增长速度、行业结构、经济效益、对外开放程度等方面对我国服务业区域发展水平进行比较研究,有利于准确判断服务业在各区域的发展差异及其程度,为相关部门制定正确的区域服务业发展政策与战略提供信息支持。     

试述如何提高学生的英语阅读效率

文章根据《大学英语教学大纲》对英语阅读能力所提出的要求 ,针对非英语专业学生英文阅读速度慢 ,正确率低的问题 ,提出了改进公共外语阅读教学 ,提高学生阅读效率的方法     

雷达天线座传动系统转速波动影响因素分析

为了更深入研究齿轮、轴承系统动力学问题,特别是研究其结构和几何参数对其动力学性能的影响,文中结合实际应用需要,基于某机载雷达天线座传动系统,着重考虑齿轮啮合时的时变刚度、齿轮侧隙以及轴承支撑刚度、摩擦等因素,建立了齿轮、轴、轴承动力学模型,运用数值仿真方法,研究了上述因素对其转速波动的影响.根据上述参数改变对转速波动影响的分析可知,当结构参数调整到一定值时,对转速波动的影响就不再有很大的变化,趋于平稳,此时若再继续调整结构参数就会浪费空间尺寸及重量,尤其是重量和空间都较为苛刻的机载产品,这对齿轮、轴承系统优化设计提供一定的理论依据和方法.     

一种抗蛇行减振器控制系统在高速动车组中的仿真应用

为协调车辆横向稳定性与曲线通过性之间的矛盾,提出一种抗蛇行减振器的控制系统,并采用ADAMS Matlab联合仿真的方法在高速动车组中进行了仿真应用。该控制系统以车体两侧高度差为控制变量,该变量可由空气弹簧高度调节阀和压差阀直接提供,不需要额外的传感器。抗蛇行减振器的控制系统可实现对曲线轨道和直线轨道两种情况之间抗蛇行减振器阻尼系数大小的调节。仿真结果表明：抗蛇行半主动控制在不影响动车组横向稳定性的同时,可大大提高车辆曲线通过时的安全性能。     

Modelling extreme wind speeds in regions prone to hurricanes

Extreme wind speeds can arise as the result of a simple pressure differential, or a complex dynamic system such as a tropical storm. When sets of record values comprise a mixture of two or more different types of event, the standard models for extremes based on a single limiting distribution are not applicable. We develop a mixture model for extreme winds arising from two distinct processes. Working with sequences of annual maximum speeds obtained at hurricane prone locations in the USA, we take a Bayesian approach to inference, which allows the incorporation of prior information obtained from other sites. We model the extremal behaviour for the contrasting wind climates of Boston and Key West, and show that the standard models can give misleading results at such locations.     

不确定性在团队授权与新产品开发业绩关系中的作用

一个最新的理论研究表明授权的作用取决于环境中不确定性的程度。在对212个新产品开发项目的定量研究中,发现了团队授权与创新速度之间显著性相关关系。对由技术新颖性和技术动态性这两个不同因素引起的技术不确定性作了区分。结果发现,团队授权和创新速度之间的关系被技术动态性所调节,而技术新颖性则不能。通过进一步的研究发现,在不确定性较低的情况下,无论来源于技术新颖性或技术动态性,团队授权和创新速度均呈U形函数关系。这说明在不确定性较低的情况下,要么完全授权,要么完全不授权或高层介入,都有利于提高创新速度。与之形成对应,在不确定性高的情况下,团队授权和创新速度之间的关系受技术新颖性和技术动态性的影响是不同的。当技术新颖性高时,团队授权和创新速度之间呈线性关系,而当技术动态性高时,二者呈反U形函数关系。对于后者,极高程度的团队授权并不加快创新速度。这些结果说明,应该根据研发项目的不确定性的不同来源与水平选择不同的团队授权策略。这些发现或许也表明,技术动态性比技术新颖性对不确定性有更重要的影响。     

Spatial–temporal model for wind speed in Lithuania

In this paper, we propose a spatial–temporal model for the wind speed (WS). We first estimate the model at the single spatial meteorological station independently on spatial correlations. The temporal model contains seasonality, a higher-order autoregressive component and a variance describing the remaining heteroskedesticity in residuals. We then model spatial dependencies by a Gaussian random field. The model is estimated on daily WS records from 18 meteorological stations in Lithuania. The validation procedure based on out-of-sample observations shows that the proposed model is reliable and can be used for various practical applications.     

Social acceleration and the network effect: a defence of social ‘science fiction’ and network determinism

This essay is a response to Judy Wajcman's essay ‘Life in the fast lane? Towards a sociology of technology and time’ (2008: 59–77). In that article Wajcman argued that recent developments in the sociology of temporal change had been marked by a tendency in social theory towards a form of ‘science fiction’– a sociological theorizing, she maintains, that bears no real relation to actual, empirically provable developments in the field and should therefore be viewed as not contributing to ‘a richer analysis of the relationship between technology and time’ (2008: 61). This reply argues that as Wajcman suggests in her essay, there is indeed an ‘urgent need for increased dialogue to connect social theory with detailed empirical studies’ (2008: 59) but that the most fruitful way to proceed would not be through a constraining of ‘science fiction’ social theorizing but, rather, through its expansion – and more, that ‘science fiction’ should take the lead in the process. This essay suggests that the connection between social theory and empirical studies would be strengthened by a wider understanding of the function of knowledge and research in the context of what is termed ‘true originality’ and ‘routine originality’. The former is the domain of social theory and the latter resides within traditional sociological disciplines. It is argued that both need each other to advance our understanding of society, especially in the context of the fast‐changing processes of technological development. The example of ‘technological determinism’ is discussed as illustrative of how ‘routine originality’ can harden into dogma without the application of ‘true originality’ to continually question (sometimes through ideas that may appear to border on ‘science fiction’) comfortable assumptions that may have become ‘routine’ and shorn of their initial ‘originality’.     

转子临界转速实验与计算的对比分析

在建立转子实验台的基础上,用实验方法测量转子的一阶临界转速,并与理论计算所得值进行对比分析.利用LabVIEW软件对实验台编制数据采集分析软件,可以直接显示随着转速的变化转子振幅和相位的相应变化,当转子振幅和相位发生突变时,所对应转速便是转子临界转速.根据Prohl法(初参数法)计算转子临界转速,利用VB编写程序进行计算.结果显示,实验数据和理论值基本一致,说明采用此实验台可以准确测量转子临界转速,编制的Prohl法VB程序适用于计算临界转速.     

交流传动调速与节能

本文讨论在交流电气传动系统中,应用电力电子技术对交流电动机的转速进行有效控制,以提高功率因数和传动效率,获得节能效果。文中论述了节能的意义,并列举了调速节能的几种主要类型。