分类： 管理学 >> 管理工程 提交时间： 2021-07-16
摘要： Most countries of the world have put forward the goal of striving for carbon neutrality. The goal is hard to achieve by only relying on supply side solutions for the world. Most countries should pay more attention to the potential of energy conservation and emission reduction in the field of final demand. We construct an empirical analytic framework to investigate energy demand characteristics as economic growth from the perspective of final demand, and the results show a U-shaped curve relationship between the ratio of energy embodied in consumption to energy embodied in investment (REECEEI) and real gross domestic product per capita. The REECEEIs of major developing and developed countries are very different. Compare to the average baseline curve scenario, there is a notable conservation potential of energy embodied in final demand for major developing and developed countries. In climate negotiation, the demand for energy embodied in investment of developing countries should be guaranteed because it is the foundation of their economic development. To conserve energy and reduce emissions in the field of final demand, developing countries should focus on the field of energy embodied in investment, while developed countries should focus on the field of energy embodied in consumption.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： To achieve a maximum compression of system matrix in positron emission tomography (PET) image reconstruction, we proposed a polygonal image pixel division strategy in accordance with rotationally symmetric PET geometry. Geometrical definition and indexing rule for polygonal pixels were established. Image conversion from polygonal pixel structure to conventional rectangular pixel structure was implemented using a conversion matrix. A set of test images were analytically defined in polygonal pixel structure, converted to conventional rectangular pixel based images, and correctly displayed which verified the correctness of the image definition, conversion description and conversion of polygonal pixel structure. A compressed system matrix for PET image recon was generated by tap model and tested by forward-projecting three different distributions of radioactive sources to the sinogram domain and comparing them with theoretical predictions. On a practical small animal PET scanner, a compress ratio of 12.6:1 of the system matrix size was achieved with the polygonal pixel structure, comparing with the conventional rectangular pixel based tap-mode one. OS-EM iterative image reconstruction algorithms with the polygonal and conventional Cartesian pixel grid were developed. A hot rod phantom was detected and reconstructed based on these two grids with reasonable time cost. Image resolution of reconstructed images was both 1.35 mm. We conclude that it is feasible to reconstruct and display images in a polygonal image pixel structure based on a compressed system matrix in PET image reconstruction.
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