分类： 生物学 >> 生物物理学 >> 细胞生物学 提交时间： 2016-05-05
Shan, Hong
Yin, Chang-Cheng
Sun, Fei
Wang, Zihao
Zhang, Fa
Wang, Zihao
Zhang, Fa
Wang, Zihao
Sun, Fei
Xiong, Yong
Sun, Fei
摘要： Single particle analysis, which can be regarded as an average of signals from thousands or even millions of particle projections, is an efficient method to study the three-dimensional structures of biological macromolecules. An intrinsic assumption in single particle analysis is that all the analyzed particles must have identical composition and conformation. Thus specimen heterogeneity in either composition or conformation has raised great challenges for high-resolution analysis. For particles with multiple conformations, inaccurate alignments and orientation parameters will yield an averaged map with diminished resolution and smeared density. Besides extensive classification approaches, here based on the assumption that the macromolecular complex is made up of multiple rigid modules whose relative orientations and positions are in slight fluctuation around equilibriums, we propose a new method called as local optimization refinement to address this conformational heterogeneity for an improved resolution. The key idea is to optimize the orientation and shift parameters of each rigid module and then reconstruct their three-dimensional structures individually. Using simulated data of 80S/70S ribosomes with relative fluctuations between the large (60S/50S) and the small (40S/30S) subunits, we tested this algorithm and found that the resolutions of both subunits are significantly improved. Our method provides a proof-of-principle solution for high-resolution single particle analysis of macromolecular complexes with dynamic conformations.
分类： 核科学技术 >> 核科学与技术 分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-20
摘要： With the development of high-performance photon sources which have extremely low emittance,autotuning magnet girders have drawn more and more attention, especially for diffraction-limited storagerings and free-electron lasers. The biggest challenge is to simultaneously obtain high stability and highflexibility. In this paper, an autotuning magnet-girder prototype has been designed and developed.Topological optimization, multipoint supports, and locking systems have been applied for magnet-girderdesign to improve the stability. The modal analysis accords with the vibration test well. The naturalfrequency of the magnet-girder assembly is deduced as high as 45.6 Hz, which demonstrates good stability.Ball-cam movers have been chosen as adjustment mechanisms, and a closed-loop control scheme has beenused to pursue high accuracy. The kinematic resolution is better than 1 m, and the accuracy is better than1 m within the adjusting range of #1;5 mm. Besides, it can eliminate most of the calibration, which cansave much manpower and time. The tests demonstrate that the magnet girder can be used for beam-basedgirder alignment with high stability and high accuracy.
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