共查询到20条相似文献，搜索用时 125 毫秒
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将单螺杆水蒸汽压缩机应用于机械蒸汽再压缩热泵(MVR)系统,并对该压缩机的工作过程进行分析;在不同蒸发温度的工况下,对采用闭式和开式循环的MVR系统进行实验研究.实验结果表明,当蒸发温度高于80℃时,压缩机的容积效率超过0.73,绝热内效率大于0.5;系统的实际COP最高达12.5,实际单位能耗蒸发水量最高可达20 kg/(k W·h);充分显示了单螺杆水蒸汽压缩机驱动MVR系统的高效节能特性. 相似文献
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蒸发循环制冷系统的研究是目前直升机上环控系统的一个研究重点.通过对直升机上传统制冷系统冷凝散热风道结构进行分析,发现其存在明显不足,然后在传统方案基础上提出新的优化方案,并进行计算分析对比了两种风道方案对散热的影响,最后通过某型机验证发现新的优化方案能使系统耗电量可减少2kVA以上,重量可减轻超过5kg,使用温度环境可... 相似文献
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本论文对制作的一台新型扩散吸收式制冷机进行了实验研究,研究结果表明,制冷机的制冷效果良好.对热源温度要求降低.当热源温度为72℃时,蒸发温度已达到了50℃,热源温度至78℃时,蒸发温度已至0℃,且来自吸收器的浓溶液和来自发生器的稀溶液的比值的变化对制冷机的制冷效果产生了重要的影响. 相似文献
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在一般情况下氨(R717)单机双级活塞式压缩机无法像氨(R717)双级螺杆式压缩机那样在蒸发温度-50℃工况条件下运行,其正常工作蒸发温度是在-25℃至-45℃之间。本文通过对氨制冷工艺流程的改造,达到提升中间压力、改善高低压级活塞压力差、降低排气温度,使单机双级活塞式压缩机在系统极限蒸发温度低于-50℃超低温工况条件下下仍然能够安全、正常运行。 相似文献
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双源热泵热水机组能有效的将热泵热水器与制冷空调系统相结合,提供生活热水的同时,降低了空调系统的L冷凝温度,极大地提高了机组的实际利用效率,节省能源,同时有利于减少温室气体的排放。 相似文献
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针对混合工质组成及组份的在Lorenz循环中选择多样化的问题,对R290/R600a混合工质的主要物性参数、饱和蒸气压力、滑移温度特性进行了理论研究;通过对换热器最小有用能的分析,基于对数平均温差法针对非共沸混合工质与换热流体的温度匹配关系,建立了非共沸混合工质制冷系统的循环性能的计算方法。并与常规制冷剂制冷系统进行了性能比较。研究结果表明:R290/R600a在R600a质量分数为0. 5时,相对常规制冷剂系统在空调工况下具有一定的节能潜力,而且运行压力较低。随着R600a质量分数的增加,制冷系统的COP先增加,后减小,在R600a质量分数为0. 5时,COP值最大,而且高于其单质的制冷循环性能。该方法可为混合工质在不同工况下成分及组份的选择提供参考,也可为换热器的优化设计及变工况调节提供理论基础。 相似文献
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通过显微组分测定、镜质组反射率测试、元素分析和工业分析、液氮吸附、透射电镜观察和等温吸附/解吸实验等,对沁水盆地南部高煤级变形煤的结构组成和吸附/解吸特征进行系统研究.结果表明,1)高煤级煤随变形程度不同,其宏观、微观孔裂隙特征不同;2)高煤级变形煤的化学结构组成差异明显;3)高煤级变形煤吸附/解吸与煤岩物化结构组成的关系密切. 相似文献
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A research group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol-a chemical found in the skins of red grapes in red wine-can improve the sensitivity of mice to the hormone insulin according to a report in the October issue of Cell Metabolism.…… 《中国科学院院刊(英文版)》2008,22(1):14-15
Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said. 相似文献
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Marjorie Armstrong-Stassen Margaret Landstrom Ramona Lumpkin 《The Information Society》1998,14(2):153-164
This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors. 相似文献
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A joint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology his co-workers from Norway US Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells suggesting that China's projected climate warming could decrease the pest's numbers. The study was published in Proceedings of the National Academy of Sciences on September .…… 《中国科学院院刊(英文版)》2008,22(1):6-7
Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007. 相似文献
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Caroline Haythornthwaite 《The Information Society》2001,17(3):211-226
A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction. 相似文献
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Active biological molecules functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery disease diagnosis therapy new nanodevice construction.…… 《中国科学院院刊(英文版)》2008,22(1):22-22
Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction. 相似文献
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《中国科学院院刊(英文版)》2008,22(1):2-3
CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing. 相似文献
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《中国科学院院刊(英文版)》2008,22(1)
With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants." 相似文献
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Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies. 相似文献
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Leah A. Lievrouw 《The Information Society》2000,16(2):155-159
This essay focuses on universal service and the Internet as means to support social and political participation. The emphasis on access to telecommunications systems in conventional approaches to universal service is contrasted with access to content. A model of the information environment is described that accounts for the roles of content and conduit, both of which are necessary conditions to achieve true access. A method is outlined for employing information indicators to observe or measure the information environment. 相似文献
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Puay Tang 《The Information Society》1998,14(1):19-31
The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means. 相似文献