基于开挖影响线的隧道分部开挖拱顶沉降分析

隧道的开挖从力学上来说也是一种荷载,掌子面移动的过程可以看作是荷载移动的过程。借鉴结构力学中影响线的概念,定义隧道工程的“开挖影响线”为某一考察指标与掌子面位置的关系曲线。相比结构力学简支梁影响线,隧道工程开挖影响线的主要特征表现为影响范围是局部的,且呈非线性,考察指标的最大响应并非掌子面到达考察断面。基于依托工程的隧道拱顶沉降开挖影响线表明⑥部开挖引起的A点沉降最大,约占其总沉降的21.5%。开挖体量约占总开挖量40%的⑨⑩部开挖由于是在二衬的保护之下进行,其引起的A点沉降仅占总沉降的2.1%。从影响线形态可以看出影响A点沉降的开挖范围大部分集中在到达A点前5m和通过后15m,且以掌子面通过考察断面时影响最为剧烈。     

The influence of achievement goals and perceptions of online help on its actual use in an interactive learning environment

This study explored the influence of achievement goals and perceptions of help-seeking on a learner’s actual use of help in an interactive learning environment. After being shown a web site on statistics, 49 psychology students answered a questionnaire on achievement goals and their perceptions of help-seeking. They were then asked to solve statistics problems in an interactive learning environment. In this environment, they were allowed to use instrumental and executive help. The results showed that high mastery goals were related to a high perception of a threat to the learner’s autonomy but not to the use of help. Performance goals were positively related to a perception of threat of not being considered competent and negatively related to the use of help and especially instrumental help. The implications of these results for future research on the help-seeking process in an interactive learning environment are discussed particularly in relation to the Technology Acceptance Model of the use of help.     

XML信息检索中最小子树根节点问题的分层算法

最小子树根节点问题(smallest lowest common ancestor,简称SLCA)是实现XML信息检索研究中关键字查询的一个基本问题,其主旨就是求解所有包含给定关键字的紧致子树的根节点.XU等人给出了3种算法-基于索引的搜索算法(indexed lookup eager,简称ILE)、基于堆栈的算法以及基于扫描的算法(scan eager,简称SE),并通过实验证明ILE算法具有最好的表现.与基于B+树索引结构的ILE算法不同,所给出的新算法,称为LISA(layered intersec