PLC的编程语言与编程注意事项

本文简述了可编程控制器(PLC)的基本特点和发展情况,介绍了PLC的顺序功能图、梯形图、功能模块图、指令表和结构文本等编程语言及其功能特点,阐述了PLC在编程过程中梯形图与指令表语言编程的规则和注意事项等。熟练掌握PLC程序的编程语言、编程方法及编程注意事项,对于PLC编程的快速入门及工程应用具有十分重要的意义。     

Assessment of the effect of the financial crisis on agents’ expectations through symbolic regression

Agents’ perceptions on the state of the economy can be affected during economic crises. Tendency surveys are the main source of agents’ expectations. The main objective of this study is to assess the impact of the 2008 financial crisis on agents’ expectations. With this aim, we evaluate the capacity of survey-based expectations to anticipate economic growth in the United States, Japan, Germany and the United Kingdom. We propose a symbolic regression (SR) via genetic programming approach to derive mathematical functional forms that link survey-based expectations to GDP growth. By combining the main SR-generated indicators, we generate estimates of the evolution of GDP. Finally, we analyse the effect of the crisis on the formation of expectations, and we find an improvement in the capacity of agents’ expectations to anticipate economic growth after the crisis in all countries except Germany.     

乘数理论在土地利用总体规划可行性评价中的应用——以沈阳市为例

在建设和谐社会的大背景下,节约和集约使用土地,充分发挥土地利用总体规划在调控经济结构和转变经济增长方式方面的调控作用具有深远的战略意义。文章提出了建设用地乘数,并把其应用于土地利用总体规划可行性评价工作中,旨在提高科学性和可操作性。     

Sensitivity analysis of efficiency rankings to distributional assumptions: applications to Japanese water utilities

This article examines the robustness of efficiency score rankings across four distributional assumptions for trans-log stochastic production-frontier models, using data from 1221 Japanese water utilities (for 2004 and 2005). One-sided error terms considered include the half-normal, truncated normal, exponential and gamma distributions. Results are compared for homoscedastic and doubly heteroscedastic models, where we also introduce a doubly heteroscedastic variable mean model, and examine the sensitivity of the nested models to a stronger heteroscedasticity correction for the one-sided error component. The results support three conclusions regarding the sensitivity of efficiency rankings to distributional assumptions. When four standard distributional assumptions are applied to a homoscedastic stochastic frontier model, the efficiency rankings are quite consistent. When those assumptions are applied to a doubly heteroscedastic stochastic frontier model, the efficiency rankings are consistent when proper and sufficient arguments for the variance functions are included in the model. When a more general model, like a variable mean model is estimated, efficiency rankings are quite sensitive to heteroscedasticity correction schemes.