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Chao Xue Jian-Ping Liu Qing Li Jun-Fei Wu Shan-Qing Yang Qi Liu Cheng-Gang Shao Liang-Cheng Tu Zhong-Kun Hu Jun Luo 《国家科学评论(英文版)》2020,7(12):1803
The Newtonian gravitational constant G, which is one of the most important fundamental physical constants in nature, plays a significant role in the fields of theoretical physics, geophysics, astrophysics and astronomy. Although G was the first physical constant to be introduced in the history of science, it is considered to be one of the most difficult to measure accurately so far. Over the past two decades, eleven precision measurements of the gravitational constant have been performed, and the latest recommended value for G published by the Committee on Data for Science and Technology (CODATA) is (6.674 08 ± 0.000 31) × 10−11 m3 kg−1 s−2 with a relative uncertainty of 47 parts per million. This uncertainty is the smallest compared with previous CODATA recommended values of G; however, it remains a relatively large uncertainty among other fundamental physical constants. In this paper we briefly review the history of the G measurement, and introduce eleven values of G adopted in CODATA 2014 after 2000 and our latest two values published in 2018 using two independent methods. 相似文献
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王雪 《四川教育学院学报》2014,(8):64-66
《第七天》是余华继《兄弟》七年之后完成的最新一部长篇小说,描绘了主人公死去后所经历的事情以及勾起的回忆,为读者展现了一个平等、和谐的死亡世界。经过分析,作品中的生死问题包括三个方面:作品中的人物对死亡没有痛苦或恐惧,能够理性地看待死亡;生与死的意义被颠倒,死亡世界接近理想中的现实世界,更加引人向往;生与死由“爱”这条纽带联系起来,让人们在冰冷中感受到温情。这部小说暴露了大量的社会现实,引人深思,也备受争议。 相似文献
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Haicheng Li Yinji Ma Ziwei Liang Zhouheng Wang Yu Cao Yuan Xu Hua Zhou Bingwei Lu Ying Chen Zhiyuan Han Shisheng Cai Xue Feng 《国家科学评论(英文版)》2020,7(5):849
According to the statistics of the World Health Organization, an estimated 17.9 million people die from cardiovascular diseases each year, representing 31% of all global deaths. Continuous non-invasive arterial pressure (CNAP) is essential for the management of cardiovascular diseases. However, it is difficult to achieve long-term CNAP monitoring with the daily use of current devices due to irritation of the skin as well as the lack of motion artifacts suppression. Here, we report a high-performance skin-like optoelectronic system integrated with ultra-thin flexible circuits to monitor CNAP. We introduce a theoretical model via the virtual work principle for predicting the precise blood pressure and suppressing motion artifacts, and propose optical difference in the frequency domain for stable optical measurements in terms of skin-like devices. We compare the results with the blood pressure acquired by invasive (intra-arterial) blood pressure monitoring for >1500 min in total on 44 subjects in an intensive care unit. The maximum absolute errors of diastolic and systolic blood pressure were ±7/±10 mm Hg, respectively, in immobilized, and ±10/±14 mm Hg, respectively, in walking scenarios. These strategies provide advanced blood pressure monitoring techniques, which would directly address an unmet clinical need or daily use for a highly vulnerable population. 相似文献
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David Alan George Poh-Ling Tan Jeffrey Frank Clewett 《Environmental Education Research》2016,22(1):62-88
Using a participatory learning approach, we report on the delivery and evaluation of a climate change and risk assessment tool to help manage water risks within the agricultural sector. Post-graduate water-professional students from a range of countries, from both developed and emerging economies were involved in using this tool. Our approach included participative learning tools – group discussion, software, and risk matrices. The materials developed met the needs of the students, allowing these students to incorporate their learning and adapt the package of materials for use in their home countries. Analysis of evaluations show that the tools and materials are particularly useful and emphasizes the need for sound learning materials and tools, funding to deliver training, and policy support to accelerate education and adoption of authentic climate change adaptation practices. The expected benefits for water professionals about climate change will be translated into improved socioeconomic and environmental outcomes if adopted. 相似文献
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To alleviate teachers’ reluctance toward practical work, there has been much discussion on teachers’ pedagogical content knowledge, teaching materials, and failsafe strategies for practical work. Despite these efforts, practical work is still regarded as a challenging task for many elementary science teachers. To understand the complexity of teachers’ conflicts in practical work, this study examines teachers’ ideas about teaching and learning that influence teachers’ decision‐making and action on teaching practical work. More important than knowing technical–rational aspects of practical work is to understand the internal contradictions that teachers have to resolve within themselves regarding their capabilities and beliefs about science teaching and practical work. Using stories and experiences of 38 third‐year university students in a science method course in Korea, we seek to understand the conflicts and negotiations that they experience as they make decisions regarding practical work throughout their course. Reflective writings and group discussions on their lived experiences and concerns were used to probe participants’ ideas on teaching using practical work. From written and verbal data, themes were saturated in terms of the aspects which could (dis)encourage their practice. Results suggest that there are multifactorial challenges in pre‐service teachers’ understandings and concerns in practical work. Besides time, materials, and curriculum, pedagogical assumptions and values also compositely challenge the minds of teachers. As the pre‐service elementary teachers negotiated within themselves the importance of science in classroom and social levels, the question is raised about their identities as pre‐service elementary teachers to appreciate the balance between science teaching and practical work. 相似文献
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农村留守儿童问题研究:现状与前瞻 总被引:7,自引:0,他引:7
近年来,农村留守儿童问题已逐渐成为媒体和学术界关注的焦点。然而,目前的研究无论理论上还是实践中均显不足。本文梳理了不同学科在这一问题上的研究成果,揭示尚待研究的问题域。 相似文献