Collaborative epistemic discourse in classroom information-seeking tasks

The authors discuss the relationship between information seeking and epistemic beliefs – beliefs about the source, structure, complexity and stability of knowledge – in the context of collaborative information-seeking discourses. They further suggest that both information seeking, and epistemic cognition research agendas, have suffered from a lack of attention to how information seeking as a collaborative activity is mediated by talk between partners – an area they seek to address in this article. A small-scale observational study using sociocultural discourse analysis was conducted with eight 11-year-old pupils who carried out search engine tasks in small groups. Qualitative and quantitative analysis were performed on their discussions using sociocultural discourse analytic techniques. Extracts of the dialogue are reported, informed by concordance analysis and quantitative coding of dialogue duration. The authors find that: (1) discourse which could be characterised as ‘epistemic’ is identifiable in student talk; (2) it is possible to identify talk which is more or less productive; and (3) epistemic talk is associated with positive learning outcomes.     

大功率汽轮机的经济设计点及经济运行特性分析

本文基于宏观通流热力设计的通流面积与通流能力匹配设计,说明大功率汽轮机经济设计点的确定和与设计点相对应的经济运行方式。为电站汽轮机设计条件的正确确定和机组长期经济运行模式提供参考。对全国范围内实现大容量火电机组的节能减排提出一种新思路。     

蒸汽余热发电技术在棒材加热炉上的应用

从节能减排和环境保护的角度出发,论述了棒材加热炉利用蒸汽余热发电的必要性,分析了加热炉余热发电热力循环系统的运行方式,设计了螺杆膨胀发电机组电气控制系统。实际应用表明,加热炉蒸汽余热发电技术提高了热能利用效率,利于环境保护,具有较高的经济和环境效益。     

采用数显仪表和变频器控制蒸汽锅炉水位的方法

针对蒸汽锅炉补水泵普遍采用变频调速和PID调节相结合的控制方法,提出了采用数字显示仪表的上下限输出触点进行变频器频率控制的方法,选择了锅炉水位测量仪表和变频器,给出了相应的主电路和控制电路原理图,设置了变频器的相关参数。实际运行表明,设备运行更可靠,调节更方便。     

橙皮挥发油的提取及成分分析

采用水蒸气蒸馏法提取橙皮中的挥发油,并用气相色谱-质谱联用仪分析挥发油的组成成分。结果表明,橙皮中挥发油橙香味浓郁,其主要成分为柠檬烯,气相色谱中的保留时间为6.72 min ,含量达到80％以上。     

文献搜索引擎检索结果集成方法的研究

本文针对现有的文献搜索引擎检索结果不全面的问题,提出了多关键词组合加权检索及其结果集成方法。通过计算不同文献搜索引擎检索结果和多关键词组合的相关度,综合应用规范分数集成法和加权分数集成法,实现了不同文献搜索引擎检索结果的集成和综合排序。最后,通过实例分析验证了该方法的有效性。