恶劣环境中北斗卫星信号强度往往低于-133 d BW,针对北斗卫星信号中相干积分的时间受二次编码符号组合的限制问题,提出一种新的串并结合的算法,首先在一个周期的主码上进行串行搜索得到主码相位,而后在整周期二次编码上并行搜索确定二...恶劣环境中北斗卫星信号强度往往低于-133 d BW,针对北斗卫星信号中相干积分的时间受二次编码符号组合的限制问题,提出一种新的串并结合的算法,首先在一个周期的主码上进行串行搜索得到主码相位,而后在整周期二次编码上并行搜索确定二次编码的相位和多普勒频偏,达到延长相干积分时间实现微弱北斗信号捕获的目的,仿真证明在设定捕获阈值4 d B时算法仍能够捕获-150 d Bm的信号。展开更多
One of the long-standing controversial arguments in protein folding is Levinthal＇s paradox. We have recently proposed a new nucleation hypothesis and shown that the nucleation residues are the most conserved sequence...One of the long-standing controversial arguments in protein folding is Levinthal＇s paradox. We have recently proposed a new nucleation hypothesis and shown that the nucleation residues are the most conserved sequences in protein. To avoid the complicated effect of tertiary interactions, we limit our search for structural codes to the nucleation residues. Starting with the hypotheses of secondary structure nucleation and conservation of residues important for folding, we have analysed 762 folds classified as unique by SCOP. Segments of 17 residues around the top 20% conserved amino acids are analysed, resulting in approximately 100 clusters each for the main secondary structure classes of helix, sheet and coil. Helical clusters have the longest correlation range, coils the shortest （four residues）. Strong specific sequence-structure correlation is observed for coil but not for helix and sheet, suggesting a mapping relationship between the sequence and the structure for coil. We propose that the central sequences in these clusters form ＇structural codes＇, a useful basis set for identifying nucleation sites, protein fragments stable in isolation, and secondary structural patterns in proteins （particularly turns and loops）.展开更多
文摘恶劣环境中北斗卫星信号强度往往低于-133 d BW,针对北斗卫星信号中相干积分的时间受二次编码符号组合的限制问题,提出一种新的串并结合的算法,首先在一个周期的主码上进行串行搜索得到主码相位,而后在整周期二次编码上并行搜索确定二次编码的相位和多普勒频偏,达到延长相干积分时间实现微弱北斗信号捕获的目的,仿真证明在设定捕获阈值4 d B时算法仍能够捕获-150 d Bm的信号。
文摘One of the long-standing controversial arguments in protein folding is Levinthal＇s paradox. We have recently proposed a new nucleation hypothesis and shown that the nucleation residues are the most conserved sequences in protein. To avoid the complicated effect of tertiary interactions, we limit our search for structural codes to the nucleation residues. Starting with the hypotheses of secondary structure nucleation and conservation of residues important for folding, we have analysed 762 folds classified as unique by SCOP. Segments of 17 residues around the top 20% conserved amino acids are analysed, resulting in approximately 100 clusters each for the main secondary structure classes of helix, sheet and coil. Helical clusters have the longest correlation range, coils the shortest （four residues）. Strong specific sequence-structure correlation is observed for coil but not for helix and sheet, suggesting a mapping relationship between the sequence and the structure for coil. We propose that the central sequences in these clusters form ＇structural codes＇, a useful basis set for identifying nucleation sites, protein fragments stable in isolation, and secondary structural patterns in proteins （particularly turns and loops）.
