Floating photovoltaic systems installed in water bodies such as natural lakes or dams reservoirs, have attracted increased worldwide attention since 2011 and have already been deployed in several countries, including ...Floating photovoltaic systems installed in water bodies such as natural lakes or dams reservoirs, have attracted increased worldwide attention since 2011 and have already been deployed in several countries, including Japan, South Korea and USA. In Brazil, pilot-projects were announced in the reservoirs of hydroelectric power plants of Balbina （State of Amazonas） and Sobradinho （State of Bahia）. Several advantages, not necessarily valid in Brazil, are mentioned for deploying this kind of technology, such as an increase in energy generation, reduction of water losses through evaporation, low environmental impact, no occupation of land etc. In this article, several of these allegations are analyzed preliminarily under the Brazilian point of view, and relevant considerations are presented. It is concluded that the technical and economic advantages of floating photovoltaic systems are not yet clear in Brazil and that pilot projects, such as those under way, should be used to clarify several important aspects related to them.展开更多
When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is t...When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.展开更多
We review and summarize the applications of the Grad-Shafranov(GS) reconstruction technique to space plasma structures in the Earth's magnetosphere and in the interplanetary space. We organize our presentations fo...We review and summarize the applications of the Grad-Shafranov(GS) reconstruction technique to space plasma structures in the Earth's magnetosphere and in the interplanetary space. We organize our presentations following the branches of the "academic family tree" rooted on Prof. Bengt U. ? Sonnerup, the inventor of the GS method. Special attentions are paid to validations of the GS reconstruction results via(1) the direct validation by co-spatial in-situ measurements among multiple spacecraft, and(2) indirect validation by implications and interpretations of the physical connection between the structures reconstructed and other related processes. For the latter, the inter-comparison and interconnection between the large-scale magnetic flux ropes(i.e., Magnetic Clouds) in the solar wind and their solar source properties are presented. In addition, we also summarize various GS-type(or-like) reconstruction and an extension of the GS technique to toroidal geometry. In particular,we point to a possible advancement with added complexity of "helical symmetry" and mixed helicity, in the hope of stimulating interest in future development. We close by offering some thoughts on appreciating the scientific merit of GS reconstruction in general.展开更多
文摘创业公司Nicira有着一个极为大胆的目标:重新设计计算机网络,让各类联网设备更智能、更快速、更便宜。早在2003年,马丁·卡萨多(Martin Casado)就发现,摆在自己面前的是一个不小的挑战:他需要重新发明用来支撑互联网的技术。现行技术已经制定了数十年之久,并在早些时候被证明经受不起这个时代的网络战。卡萨多当时是劳伦斯·利弗莫尔国家实验室(Lawrence Livermore National Laboratory)的一个研究员,一个美国情报机构找到了他,并丢给他一个棘手的问题。
文摘Floating photovoltaic systems installed in water bodies such as natural lakes or dams reservoirs, have attracted increased worldwide attention since 2011 and have already been deployed in several countries, including Japan, South Korea and USA. In Brazil, pilot-projects were announced in the reservoirs of hydroelectric power plants of Balbina （State of Amazonas） and Sobradinho （State of Bahia）. Several advantages, not necessarily valid in Brazil, are mentioned for deploying this kind of technology, such as an increase in energy generation, reduction of water losses through evaporation, low environmental impact, no occupation of land etc. In this article, several of these allegations are analyzed preliminarily under the Brazilian point of view, and relevant considerations are presented. It is concluded that the technical and economic advantages of floating photovoltaic systems are not yet clear in Brazil and that pilot projects, such as those under way, should be used to clarify several important aspects related to them.
基金financially supported by the National Natural Science Foundation of China (No. 51675268)
文摘When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.
基金supported by National Aeronautics and Space Administration (NASA) and National Science Foundation (NSF) (Grants Nos. AGS-1062050, NNG04GF47G, NNG06GD41G, NNX12AF97G, NNX12AH50G, NNH13ZDA001N, and NNX14AF41G)
文摘We review and summarize the applications of the Grad-Shafranov(GS) reconstruction technique to space plasma structures in the Earth's magnetosphere and in the interplanetary space. We organize our presentations following the branches of the "academic family tree" rooted on Prof. Bengt U. ? Sonnerup, the inventor of the GS method. Special attentions are paid to validations of the GS reconstruction results via(1) the direct validation by co-spatial in-situ measurements among multiple spacecraft, and(2) indirect validation by implications and interpretations of the physical connection between the structures reconstructed and other related processes. For the latter, the inter-comparison and interconnection between the large-scale magnetic flux ropes(i.e., Magnetic Clouds) in the solar wind and their solar source properties are presented. In addition, we also summarize various GS-type(or-like) reconstruction and an extension of the GS technique to toroidal geometry. In particular,we point to a possible advancement with added complexity of "helical symmetry" and mixed helicity, in the hope of stimulating interest in future development. We close by offering some thoughts on appreciating the scientific merit of GS reconstruction in general.
