On global behavior of the system of rational difference equations xn+1=p+xn/yn-k,yn+1=q+yn/xn-k

In this paper, we investigate the boundedness character, the global attractivity and the periodic nature of the svstem of ratiol difference equatious:xn+1=p+yn-k/xn,yn+1=q+xn-k/yn,n=0,1,2..., where p>0, q>0, k∈ of the system of rational difference equations:xn+1=P+yn-k/xn, yn=q+xn-k/yn,n=0,1,2 {1,2,…} and the initial values x1, y1∈(0,∞), i=- k, -k+1,… 0. Some new results are obtained.     

组合式堵漏箱堵漏过程中的水压作用机理

利用动量定理推导了组合式堵漏箱不同结构形式处于不同工况时的动量方程,探讨了堵漏板垂直堵漏、堵漏板斜置堵漏、堵漏箱垂直堵漏、堵漏箱斜置堵漏等四种工况下堵漏作业过程中的水压作用机理,最后通过堵漏试验对理论分析结果进行了验证。结果表明,理论分析结果与试验现象基本吻合,可以用于组合式堵漏箱的水压计算和测试依据。     

Perceived service quality of paratransit in developing countries: A structural equation approach

This paper develops empirical models for evaluating the service quality (SQ) of paratransit. Specifically, several models are developed based on structural equation modeling (SEM) using twenty-four SQ variables. To calibrate those models, a data set of 2008 paratransit users of Dhaka City are utilized, who were interviewed with a structured questionnaire to know their experience, level of satisfaction and opinion about the existing service as well as their expectations. SEM reveals the observed and latent SQ variables and their relationship with the overall SQ of paratransit. Among the different models developed, the best one is selected using statistical parameters and resemblance with real life expectations. Out of twenty-four SQ variables, ‘Punctuality and Reliability’ and ‘Service Features’ are respectively found to be the observed and latent variables having the greatest influence on the paratransit SQ. Moreover, the effect of heterogeneity among users on the performance of the best model is investigated. All the study findings support the data collected from the paratransit users. The research outcomes can be utilized by the city transportation officials of developing countries to improve the overall paratransit performance to attract new users as well as retain the current ones.     

水动力噪声计算方法综述

  目的  根据Lighthill声类比方程及其发展理论,可以将壁面湍流脉动压力的波数-频率谱作为声源项来预报流噪声,且分析湍流脉动压力的波数-频率谱有助于了解湍流结构的时空关联特性。  方法  以NACA 0012翼型为例,采用大涡模拟（LES）方法进行流场仿真计算,然后通过Fourier变换得到壁面湍流脉动压力波数-频率谱的数值解,并与Corcos的平板湍流边界层脉动压力波数-频率谱模型进行比较;在此基础上,将该波数-频率谱作为声源输入,代入Goldstein版本的声类比方程中预报辐射噪声,并与软件计算的流噪声结果以及Brooks试验拟合结果进行比较。  结果  结果发现：小曲率变化的NACA 0012翼型表面的波数-频率谱具有与平板表面相似的一般特性;在中、低频段采用该方法预报的流噪声结果与Brooks试验结果拟合更好。  结论  所得结果表明开展波数-频率谱研究是有必要的,将其作为主要声源项来预报亚声速下产生的流噪声是合理的。     

Structural equation approach to investigate trip-chaining and mode choice relationships in the context of developing countries

This paper investigates empirical relationships between trip chain type and mode class choice for developing countries. To formulate these two sets of decisions, four empirical models are developed using structural equation modeling (SEM). Those models are calibrated using one-month travel diary data collected in Dhaka city. SEM correlates the observed variables and identifies their relationship with trip-chaining type utility and mode class choice utility. The fitted models are selected based on statistical results and similarity with the real-life situation. Direct relationships between trip-chaining and mode choice utilities are found insignificant. However, several socio-demographic factors influence both simultaneously. Consequently, it is essential to consider mode class choice concurrently for modeling trip chains. This study also investigates the influencing factors for work-based and non-work-based trip chains separately and effects of road users’ heterogeneity. The research results can be utilized to perceive trip chain-mode choice patterns for developing countries.     

Inference on mode preferences,vehicle purchases,and the energy paradox using a Bayesian structural choice model

Discrete choice modeling is experiencing a reemergence of research interest in the inclusion of latent variables as explanatory variables of consumer behavior. There are several reasons that motivate the integration of latent attributes, including better-informed modeling of random consumer heterogeneity and treatment of endogeneity. However, current work still is at an early stage and multiple simplifying assumptions are usually imposed. For instance, most previous applications assume all of the following: independence of taste shocks and of latent attributes, exclusion restrictions, linearity of the effect of the latent attributes on the utility function, continuous manifest variables, and an a priori bound for the number of latent constructs. We derive and apply a structural choice model with a multinomial probit kernel and discrete effect indicators to analyze continuous latent segments of travel behavior, including inference on the energy paradox. Our estimator allows for interaction and simultaneity among the latent attributes, residual correlation, nonlinear effects on the utility function, flexible substitution patterns, and temporal correlation within responses of the same individual. Statistical properties of the Bayes estimator that we propose are exact and are not affected by the number of latent attributes.     

Investigating the impacts of weather variability on individual’s daily activity–travel patterns: A comparison between commuters and non-commuters in Sweden

Understanding travel behaviour change under various weather conditions can help analysts and policy makers incorporate the uniqueness of local weather and climate within their policy design, especially given the fact that future climate and weather will become more unpredictable and adverse. Using datasets from the Swedish National Travel Survey and the Swedish Meteorological and Hydrological Institute that spans a period of thirteen years, this study explores the impacts of weather variability on individual activity–travel patterns. In doing so, this study uses an alternative representation of weather from that of directly applying observed weather parameters. Furthermore, this study employs a holistic model structure. The model structure is able to analyse the simultaneous effects of weather on a wide range of interrelated travel behavioural aspects, which has not been investigated in previous weather studies. Structural equation models (SEM) are applied for this purpose. The models for commuters and non-commuters are constructed separately. The analysis results show that the effects of weather can be even more extreme when considering indirect effects from other travel behaviour indicators involved in the decision-making processes. Commuters are shown to be much less sensitive to weather changes than non-commuters. Variation of monthly average temperature is shown to play a more important role in influencing individual travel behaviour than variation of daily temperature relative to its monthly mean, whilst in the short term, individual activity–travel choices are shown to be more sensitive to the daily variation of the relative humidity and wind speed relative to the month mean. Poor visibility and heavy rain are shown to strongly discourage the intention to travel, leading to a reduction in non-work activity duration, travel time and the number of trips on the given day. These findings depict a more comprehensive picture of weather impact compared to previous studies and highlight the importance of considering interdependencies of activity travel indicators when evaluating weather impacts.     

Dynamic analysis of the biped ice-skater robot of passive wheel type

A new passive wheel type of biped ice-skater robot （BISR） subjected to nonholonomic constraints was presented on the basis of ice-skating principle. Its motion principle and construction were discussed. After the model was simplified and the coordinate systems were established, the motion differential equations of the robot were obtained with the generalized Lagrange-Maggi equation when the nonholonomic constraints existed. Actual examples were given and the result was simulated on computer.     

我国高等院校核心竞争力结构解析

随着我国高等教育市场改革进程的加快,我国高等院校之间的竞争将日趋激烈,从而催生了我国高校核心竞争力培育战略的大力实施。有效地进行核心竞争力结构体系解析是高等院校实施核心竞争力培育战略的基础性前提。验证性因子分析可以为结构体系的有效性和现实性提供实证检验。     

基于Forman方程的随机疲劳长裂纹扩展概率模型

为了提高随机疲劳长裂纹扩展率预测精度, 基于Forman方程, 发展了随机疲劳长裂纹扩展概率模型及其参数测定方法, 考虑数据分散性规律和试样数量对概率评价的影响, 得到了包含存活概率曲线、置信度曲线和两者融合曲线在内的长裂纹扩展率关系曲线, 在给定应力强度因子范围内, 裂纹扩展率服从对数正态分布条件下, 采用线性回归和极大似然法测定模型参数。对铁道车辆LZ50车轴钢裂纹扩展数据分析表明, 该模型反映了材料断裂韧度对长裂纹扩展率的影响, 克服了基于Paris-Er-dogan方程的概率模型在高应力强度因子范围预测偏于危险的缺陷, 验证了该模型的合理性。