We use wavelet transform to analyze the daily relative sunspot number series over solar cycles 10-23. The characteristics of some of the periods shorter than - 600-day are discussed. The results exhibit not only the v...We use wavelet transform to analyze the daily relative sunspot number series over solar cycles 10-23. The characteristics of some of the periods shorter than - 600-day are discussed. The results exhibit not only the variation of some short periods in the 14 solar cycles but also the characteristics and differences around solar peaks and valley years. The short periodic components with larger amplitude such as ～27, ～ 150 and ～360-day are obvious in some solar cycles, all of them are time-variable, also their lengths and amplitudes are variable and intermittent in time. The variable characteristics of the periods are rather different in different solar cycles.展开更多
An analytical theory for calculating perturbations of the orbital elements of a satellite due to J2 to accuracy up to fourth power in eccentricity is developed. It is observed that there is significant improvement in ...An analytical theory for calculating perturbations of the orbital elements of a satellite due to J2 to accuracy up to fourth power in eccentricity is developed. It is observed that there is significant improvement in all the orbital elements with the present theory over second-order theory. The theory is used for computing the mean orbital elements, which are found to be more accurate than provided by Bhatnagar and taqvi’s theory (up to second power in eccentricity). Mean elements have a large number of practical applications.展开更多
Alpha helix is a common type of secondary structure in the protein structure that consists of repeating helical turns. Patterns in the protein sequences that cause this repetitive pattern in the structure have long be...Alpha helix is a common type of secondary structure in the protein structure that consists of repeating helical turns. Patterns in the protein sequences that cause this repetitive pattern in the structure have long been sought. We used the discrete Fourier transform (DFT) to detect the periodicity signals correlated to the helical structure. We studied the distribution of multiple properties along the protein sequence, and found a property that showed strong periodicity correlated with the helical structure. Using a short-time Fourier transform (STFT) method, we investigated the amplitude of the periodical signals at each amino acid position. The results show that residues in the helix structure tend to display higher amplitudes than residues outside of the helices. This tendency is dramatically strengthen when sequence profiles obtained from multiple alignment were used to detect the periodicity. A simple method that predicted helices based on the amplitude yielded overall true positive rate (TPR) of 63%, 49% sensitivity, 72% specificity, and 0.22 Matthews Correlation Coefficient (MCC). The performance seemed to depend on the length of helices that the proteins had.展开更多
不同海区的近岸海浪浪高具有明显差异性。针对当前大部分时间序列预测模型缺乏对不同地区(多源)浪高预测的适应性难题,提出了一种基于局部加权回归的多周期趋势分解(Seasonal and Trend decomposition using Loess,STL)和两级融合策略...不同海区的近岸海浪浪高具有明显差异性。针对当前大部分时间序列预测模型缺乏对不同地区(多源)浪高预测的适应性难题,提出了一种基于局部加权回归的多周期趋势分解(Seasonal and Trend decomposition using Loess,STL)和两级融合策略的浪高预测模型,简称为MSTL-WH(Multiple STL-Wave Height)。结合多源近岸浪高时间序列的多周期性、非线性和非平稳性的特点,首先利用周期图法提取多源近岸浪高数据集中的4个主要周期,并基于主要周期进行多次STL分解,将复杂的原始浪高序列分解为周期项、趋势项和余项;然后利用长短期记忆网络(Long Short Term Memory,LSTM)并结合两级融合策略,搭建近岸浪高预测网络;最后使用自注意力机制重新调整权重并输出未来12 h的浪高值。通过与当前主流时间序列预测方法对比,验证了所提方法在多源近岸浪高序列预测中具有较好的实用性和更低的预测误差。展开更多
基金Supported by the National Natural Science Foundation of China.
文摘We use wavelet transform to analyze the daily relative sunspot number series over solar cycles 10-23. The characteristics of some of the periods shorter than - 600-day are discussed. The results exhibit not only the variation of some short periods in the 14 solar cycles but also the characteristics and differences around solar peaks and valley years. The short periodic components with larger amplitude such as ～27, ～ 150 and ～360-day are obvious in some solar cycles, all of them are time-variable, also their lengths and amplitudes are variable and intermittent in time. The variable characteristics of the periods are rather different in different solar cycles.
文摘An analytical theory for calculating perturbations of the orbital elements of a satellite due to J2 to accuracy up to fourth power in eccentricity is developed. It is observed that there is significant improvement in all the orbital elements with the present theory over second-order theory. The theory is used for computing the mean orbital elements, which are found to be more accurate than provided by Bhatnagar and taqvi’s theory (up to second power in eccentricity). Mean elements have a large number of practical applications.
文摘Alpha helix is a common type of secondary structure in the protein structure that consists of repeating helical turns. Patterns in the protein sequences that cause this repetitive pattern in the structure have long been sought. We used the discrete Fourier transform (DFT) to detect the periodicity signals correlated to the helical structure. We studied the distribution of multiple properties along the protein sequence, and found a property that showed strong periodicity correlated with the helical structure. Using a short-time Fourier transform (STFT) method, we investigated the amplitude of the periodical signals at each amino acid position. The results show that residues in the helix structure tend to display higher amplitudes than residues outside of the helices. This tendency is dramatically strengthen when sequence profiles obtained from multiple alignment were used to detect the periodicity. A simple method that predicted helices based on the amplitude yielded overall true positive rate (TPR) of 63%, 49% sensitivity, 72% specificity, and 0.22 Matthews Correlation Coefficient (MCC). The performance seemed to depend on the length of helices that the proteins had.
文摘不同海区的近岸海浪浪高具有明显差异性。针对当前大部分时间序列预测模型缺乏对不同地区(多源)浪高预测的适应性难题,提出了一种基于局部加权回归的多周期趋势分解(Seasonal and Trend decomposition using Loess,STL)和两级融合策略的浪高预测模型,简称为MSTL-WH(Multiple STL-Wave Height)。结合多源近岸浪高时间序列的多周期性、非线性和非平稳性的特点,首先利用周期图法提取多源近岸浪高数据集中的4个主要周期,并基于主要周期进行多次STL分解,将复杂的原始浪高序列分解为周期项、趋势项和余项;然后利用长短期记忆网络(Long Short Term Memory,LSTM)并结合两级融合策略,搭建近岸浪高预测网络;最后使用自注意力机制重新调整权重并输出未来12 h的浪高值。通过与当前主流时间序列预测方法对比,验证了所提方法在多源近岸浪高序列预测中具有较好的实用性和更低的预测误差。
