A review of topic modeling methods

Topic modeling is a popular analytical tool for evaluating data. Numerous methods of topic modeling have been developed which consider many kinds of relationships and restrictions within datasets; however, these methods are not frequently employed. Instead many researchers gravitate to Latent Dirichlet Analysis, which although flexible and adaptive, is not always suited for modeling more complex data relationships. We present different topic modeling approaches capable of dealing with correlation between topics, the changes of topics over time, as well as the ability to handle short texts such as encountered in social media or sparse text data. We also briefly review the algorithms which are used to optimize and infer parameters in topic modeling, which is essential to producing meaningful results regardless of method. We believe this review will encourage more diversity when performing topic modeling and help determine what topic modeling method best suits the user needs.     

Internet中文信息搜索引擎评析

介绍搜索引擎的分类、对比和查询技巧。     

Generation and selection of likely interpretations during plan recognition in task-oriented consultation systems

This paper presents a mechanism which infers a user's plans from his/her utterances by directing the inference process towards the more likely interpretations of a speaker's statements among many possible interpretations. Our mechanism uses Bayesian theory of probability to assess the likelihood of an interpretation, and it complements this assessment by taking into consideration two aspects of an interpretation: its coherence and its information content. The coherence of an interpretation is determined by the relationships between the different statements in the discourse. The information content of an interpretation is a measure of how well defined the interpretation is in terms of the actions to be performed on the basis of this interpretation. This measure is used to guide the inference process towards interpretations with higher information content. The information content of an interpretation depends on the specificity and the certainty of the inferences in it, where the certainty of an inference depends on the knowledge on which the inference is based. Our mechanism has been developed for use in task-oriented consultation systems. The particular domain that we have chosen for exploration is that of travel booking.     

利用先进的结构试验系统进行发动机构件的仿真疲劳试验

本文介绍一套先进的构件实验设备的功能及其在发动机构件疲劳试验方面的具体应用实例．通过对几种受力较复杂构件的受力分析设计出实验方法，使构件在实验室中受力情况与构件实际受力情况相似或相同，这样，得出的试验数据就可为构件的可靠性分析工作提供较好的依据．     

大功率柴油机连杆三维精细分析

连杆作为柴油机的关键零部件，其刚度和强度对于柴油机的性能和功率的提高起到至关重要的作用。采用MSC／MARC程序及三维多体接触的方法，对G32柴油机连杆的应力场和位移场进行了数值模拟。进而为降低机械负荷、改善应力分布和进一步强化奠定基础。     

内燃机节油率计算的探讨

讨论比较了现有内燃机节油率计算方法的优缺点、产生误差的原因，提出了采用曲线拟合的方法求取率的新方法。文中给出了计算公式和计算步骤，通过编制计算机程序，计算了几种典型发动机的节油率指标，并传统的按度试验数据逐点计算方法进行了对比，证明此方法是一种比较客观、科学的节油率指标计算方法。     

低旋流进气直喷燃烧系统在195柴油机上的应用研究

介绍了低旋流进气直喷燃烧系统应用于１９５柴油机的试验结果，着重探讨了燃烧室结构尺寸和供油系统主要参数对柴油机性能和燃烧放热规律的影响。研究表明，这种燃烧系统应用于小缸径直喷柴油机具有良好的推广前景。     

第三代伞状喷雾的分布特性及多片喷雾系统的应用研究

为解决前两代伞状喷雾在高背压下贯穿距不足的问题,借鉴碰撞喷雾方式,提出了第三代伞状喷雾概念。通过高速摄影对喷雾的分布特性进行了研究,结果表明:喷雾具有贯穿距可设定、扩散度高、空间分布均匀等特点。为避免碰撞后二次油束雾线相互干涉,又提出了一种多片喷雾概念,并在单缸四气门135柴油机上对多片喷雾燃烧系统进行了初步的性能试验,结果显示:系统能够有效地促进缸内均质混合气的形成;在供油提前角为19°CA时,全负荷范围内柴油机的油耗和碳烟排放均较低。     

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研究燃料汽车及其氢源系统是当今国内外能源工业与汽车工业的共同课题，而优选制氢能源则是这一课题的关键。章介绍了利用能源、经济、环境(EEE)——生命周期评估(LCA)这一综合评估方法，针对以天然气、煤或石油作为制氢能源的多种燃料电池氢源供应方式以及配套的燃料电池汽车系统，从经济性、能源利用效率和环境影响三个方面进行了生命周期清单分析和EEE综合评价。结果显示：天然气作为发展燃料电池汽车氢源的一次能源，具有氢制取技术路线多样化、经济上竞争力强、能源利用效率高和环境效益好等诸多优势，应为燃料电池汽车的首选制氢能源。对这一评估模型的敏感性分析显示，即使在天然气价格波动较大时，天然气制甲醇--甲醇车载重整车和天然气制氢--纯氢车这两个方案仍然最具优势。     

热膜式气体质量流量计设计

介绍能够测定空气质量流量,且可自动补偿温度及压力变化对空气流量影响,测量精度高的热膜式气体质量流量计的原理、构造和性能。这种流量计可以满足各种发动机进气流量测量,特别是排放测试的需要。