关于卷制螺旋滚子结构尺寸的理论分析

卷制螺旋滚子是一种全新理念的滚子,可以有效地识别出螺旋滚子结构尺寸与变形能之间的相互关系,该滚子的周身遍布缝隙,其区别于普通滚子的一个最大特点就是可以吸收冲击能,既解决普通滚子在高速多冲作用下的早期断裂问题,又提高滚子的抗冲击性能。为此,文章主要针对有关于卷制螺旋滚子结构尺寸的理论,进行简单的分析和探讨。     

The existence of sampling designs with preassigned inclusion probabilities

Summary The question of the existence of a sampling design realizing given preassigned inclusion probabilities is treated. The question can be fully answered in the case of inclusion probabilities of first order. If the inclusion probabilities of second order are given it is shown why necessary and sufficient conditions for the existence of a corresponding sampling design can be derived only in very special cases.     

Concentration of competing retail stores

The geographical concentration of stores that sell similar commodities is analyzed using a two-dimensional spatial competition model. A higher concentration of stores attracts more consumers with taste uncertainty and low price expectations (a market-size effect), while it leads to fiercer price competition (a price-cutting effect). Our model is general enough to allow for the coexistence of multiple (possibly) asymmetric clusters of stores. We provide sufficient conditions for the nonemptiness of equilibrium store location choices in pure strategies. Through numerical examples, we illustrate the trade-off between the market-size and price-cutting effects, and provide agglomeration patterns of stores in special cases.     

Class Size,Teacher Hours and Educational Attainment*

We employ a regression‐discontinuity design to identify effects on educational attainment after compulsory school of class size and the number of pupils per weekly teacher hour using administrative rules as instruments. We use Danish administrative panel data. Average class size is 20, about the same as in the US and most European countries. Restricting the sample to observations close to the enrolment discontinuity points where the administrative rules have greatest predictive power, instrumental variables estimates are consistently negative. Estimates from the preferred specification are marginally significant and indicate modest effects in line with earlier studies. Estimates for subgroups are less precise, but they indicate larger effects for pupils from less advantaged backgrounds.     

Saving–investment correlations, capital mobility and crowding out: some further results

This study attempts to reassess the evidence on the degree of capital mobility and crowding out by applying a varying coefficients model to data on 19 OECD countries over the 1971–1999 period. Our period-specific results strongly support the crowding-out effect as well as the low capital mobility argument for this group of countries as a whole. However, the strength of the crowding-out effect appears to weaken and the degree of capital mobility to increase in the 1990s as compared to the 1970s and 1980s. We also classify countries into five groups according to the relative size of the government sector. Our group-specific results indicate that the degree of capital mobility is generally lower and the crowding-out effect generally stronger, in country groups with smaller governments. The differences are especially evident when we compare the group with largest government size with all other groups, those differences between the latter being much more modest. However, significant differences in the country-specific results suggest that it is prudent to be cautious when we draw conclusions about crowding-out and capital mobility for specific countries from the period-wise or group-wise results. This is particularly important in drawing policy implications for specific countries.     

Size (and competition) among organizations: modeling scale‐based selection among automobile producers in four major countries, 1885–1981

Based on previous empirical research, size is perhaps the most powerful explanatory organizational covariate in strategic analysis. We suggest that theoretical arguments about size be examined carefully to specify models with explicit comparison sets and with mechanisms linking size and underlying processes to outcomes. We illustrate the approach here by advancing arguments about scale competition within an organizational population. In this effort, we feature a theoretical model of scale‐based selection, which posits that a firm's chances of survival decrease with its aggregate distance from larger competitors on a transformed size gradient. The model assumes that the appropriate comparison set consists of all contemporaneous similar organizations competing on the basis of scale and operating in a localized geographic setting. We argue that aggregate distance of a focal firm from larger other firms (a specific form of relative position in the size distribution) reflects the extent to which it can capitalize on potential competitive advantages of scale emanating from economic, political, and social processes. Analyzing the mortality rates of large organizations across the entire histories of automobile industries in four major countries provides support for the theory. We discuss the general implications of our findings for strategic and organizational analysis. Copyright © 2003 John Wiley & Sons, Ltd.     

铁路果蔬运输中物流组织模式研究

本文通过对近年来我国果蔬主要运输分布统计分析，运用物流和供应链管理的理念对铁路果蔬运输市场的特点和发展进行研究，探索形成铁路果蔬运输中集散物流组织的基本模式内容。     

Which school systems sort weaker students into smaller classes? International evidence

We examine whether the sorting of high- and low-achieving students into classes of different sizes results in a regressive or compensatory pattern of class sizes for 18 national school systems. Sorting effects are identified by subtracting the causal effect of class size on performance from their total correlation. Our empirical results reveal strongly compensatory patterns of sorting within and especially between schools in many countries. Only the United States, which has a decentralized education finance and considerable residential mobility, exhibits regressive between-school sorting. Between-school sorting is more compensatory in systems with ability tracking. Within-school sorting is more compensatory where administrators rather than teachers assign students to classrooms.     

Do reductions in tick sizes influence liquidity?

On 4 December 1995, the Australian Stock Exchange reduced the minimum tick size for stocks priced below $A0.50 and stocks priced above $A10. We use this natural experiment to examine the impact of tick size reductions on liquidity. The present paper reports that although lower tick sizes generally lead to increased liquidity, this result is not universal. Stocks with larger relative tick sizes experience the greatest improvement in liquidity, while stocks with small relative tick sizes and low trading volume experience reduced liquidity. There is no change in order exposure as a result of the reduced tick sizes.     

Attitudes and consumption values of consumers of imported fruit in Guangzhou,China

Research on how Chinese consumption values influence Chinese consumer behaviour is rare. First, this paper examines consumers’ attitudes towards the physical and intangible attributes of imported fruit. Then, it identifies consumers’ consumption values and the role of these values in purchasing behaviour. Data were collected through point of sale intercept surveys conducted in Guangzhou, China. Latent consumption values of consumers were identified through factor analysis. K‐means clustering revealed four natural groupings of consumers, each group demonstrating different consumption values. The results demonstrated the primary importance of symbolic values and hedonic values in the decision to purchase imported fruit. Such consumption values may derive from the intermingling of Confucian and Western cultural values. Results from this study could help to better understand interrelationships among product attributes, consumption values and cultural values, and could make a significant contribution in developing strategies to market imported fruit in China.