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从石油钻井和地质钻探两方面阐述了自动垂直钻井技术的原理及优点,按照不同结构及工作原理对自动垂直钻井工具做出分类,并简要分析了各类工具的优缺点。随后在上述分类基础上系统归纳了国内外现有垂直钻井工具及其技术特点,剖析了国内外自动垂直钻井工具之间的技术差距。最后总结出自动垂直钻井工具存在的问题,指出工具今后的发展趋势为小型化、可取心、高精度和长寿命,并对其未来的研究思路与方法提出建议:对执行机构零部件结构和布局进行优化,在减小工具外径的同时增大工具内部空间,使工具在小口径井眼垂直钻进的同时还能进行取心作业;对电控式垂直钻井工具的测控传感器及其密封系统进行优化改进,使工具整体耐温耐压性能得到提高;对机械式垂直钻井工具的偏重平台在井下复杂环境下的响应规律进行研究,并探索相应的误差抑制补偿方法,以提高工具的井斜控制精度。 相似文献
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Group recommender systems suggest items to groups of users that want to utilize those items together. These systems can support several activities that can be performed together with other people and are typically social, like watching TV or going to the restaurant. In this paper we study ephemeral groups, i.e., groups constituted by users who are together for the first time, and for which therefore there is no history of past group activities.Recent works have studied ephemeral group recommendations proposing techniques that learn complex models of users and items. These techniques, however, are not appropriate to recommend items that are new in the system, while we propose a method able to deal with new items too. Specifically, our technique determines the preference of a group for a given item by combining the individual preferences of the group members on the basis of their contextual influence, the contextual influence representing the ability of an individual, in a given situation, to guide the group’s decision. Moreover, while many works on recommendations do not consider the problem of efficiently producing recommendation lists at runtime, in this paper we speed up the recommendation process by applying techniques conceived for the top- query processing problem. Finally, we present extensive experiments, evaluating: (i) the accuracy of the recommendations, using a real TV dataset containing a log of viewings performed by real groups, and (ii) the efficiency of the online recommendation task, exploiting also a bigger partially synthetic dataset. 相似文献
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Christer Thrane 《Journal of Wine Research》2019,30(2):166-177
The micro level behavioral foundation for how quality reviews of experts and word of mouth (WOM) affect demand for experience goods has received scant attention in previous research. Taking an experimental approach, the present study examines how quality reviews and peer recommendations influence consumers’ decisions to buy red wine. Four main findings are presented for a sample of Norwegian wine consumers. First, consumers prefer wines that have obtained very good quality reviews to wines getting OK quality reviews. Second, consumers prefer peer-recommended wines to non-recommended wines. Third, the effect of a very good quality review is greater for non-recommended wines than for peer-recommended wines. Fourth, some of these effects on wine buying decisions are contingent on price level, and there is also some heterogeneity to their magnitude. The results are mainly in concert with the proposed hypotheses. 相似文献
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The influence of data and recommendations from developed countries on nutrition guidance has overshadowed recognition of the key micronutrients and protein contributed by red meat to the global food supply. Relative to the energy it contributes, the impact of red meat on the nutritional quality of the human diet via its contribution of protein and key micronutrients is under-appreciated. The current discussion will review red meat nutrient composition and global consumption rates and discuss the evidence underpinning current dietary recommendations. The beneficial role of red meat in reducing risk factors associated with noncommunicable disease in developed countries and improving the nutritional status of developing nations will also be reviewed. 相似文献
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为适应城市对国防、治安、反恐、消防、金融、通信、旅游等的需求,许多超高层建筑在屋顶设置了直升飞机停机坪,但现行的消防设计规范对超高层建筑屋顶设置直升机停机坪未做强制的规定,各方意见不一。笔者结合实践工作经验,试图以建筑高度为界限对超高层建筑屋顶直升飞机停机坪进行探讨并提出一些直升飞机停机坪设置的建议。 相似文献