原子时具有较高的短期稳定度,基于毫秒脉冲星自转建立的脉冲星时具有较高的长期稳定度,两者融合可构建长短稳优势兼具的时间尺度。本文通过经典加权平均算法,初步构建一个脉冲星与原子钟融合的联合时间尺度(composite time scale,CT)。...原子时具有较高的短期稳定度,基于毫秒脉冲星自转建立的脉冲星时具有较高的长期稳定度,两者融合可构建长短稳优势兼具的时间尺度。本文通过经典加权平均算法,初步构建一个脉冲星与原子钟融合的联合时间尺度(composite time scale,CT)。基于国际权度局(BIPM)公布的TA(NTSC)-TAI原子时数据,并选取国际脉冲星计时阵(IPTA)公布的计时精度最高的4颗脉冲星,通过并列加权法和分类加权法这两种组合方式得到CT。结果表明并列加权法得到的CT相对于各脉冲星时在10年以内的稳定度改善明显,4~10年内稳定度与稳定度较高的脉冲星J0437-4715接近。分类加权法得到的CT对比并列加权的稳定度结果在采样区间两极优势明显,0.26年达到5.1×10^(-15),16.8年达到1.0×10^(-15),其中4颗星相比2颗星得到的CT于5.2年后稳定度有显著提高,且分类加权法得到的CT相对于TAI偏差更小,时间尺度更平稳。综上说明原子钟组的短稳特性可以对脉冲星钟组的短期噪声进行抑制,同时脉冲星时可提高联合时间尺度CT的长期稳定度。展开更多
氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟...氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟的频率驾驭,并对实时信号加以控制.首先分析了国际脉冲星计时阵(International Pulsar Timing Array,IPTA)第二批发布数据中四颗毫秒脉冲星的稳定度随时间的变化,同时采用哈达玛方差分析了中国科学院国家授时中心(National Time Service Center,NTSC)一台氢钟的频率稳定性能,最终给出了利用脉冲星驾驭氢原子钟频率的方法.展开更多
The pulsar timing residuals induced by gravitational waves from non-evolving single binary sources with general elliptical orbits are analyzed.For different orbital eccentricities,the timing residuals present differen...The pulsar timing residuals induced by gravitational waves from non-evolving single binary sources with general elliptical orbits are analyzed.For different orbital eccentricities,the timing residuals present different properties.The standard deviations of the timing residuals induced by a fixed gravitational wave source are calculated for different values of the eccentricity.We also analyze the timing residuals of PSR J0437-4715 induced by one of the best known single gravitational wave sources,the supermassive black hole binary in the blazar OJ287.展开更多
PACS:99.10.−x,04.30.Db,97.60.Gb,95.85.Sz DOI:10.1088/0256-307X/30/11/119901 One regrettable error appeared in Eq.(21)of our article[Chin.Phys.Lett.30(2013)100402].The cor-rect one of the equation is as follows.
A lexicographic image hash method based on space and frequency features was proposed. At first, the image database was constructed, and then color and texture features were extracted from the image blocks including in...A lexicographic image hash method based on space and frequency features was proposed. At first, the image database was constructed, and then color and texture features were extracted from the image blocks including information for every image in the database, which formed feature vectors. The feature vectors were clustered to form dictionary. In hash generation, the image was preproc^ssed and divided into blocks firstly. Then color and texture features vectors were extracted from the blocks. These feature vectors were used to search the dictionary, and the nearest word in dictionary for each block was used to form the space features. At the same time. frequency feature was extracted from each block. The space and frequency features were connected to form the intermediate hash. Lastly, the final hash sequence was obtained by pseudo-randomly permuting the intermediate hash. Experiments show that the method has a very low probability of collision and a good perception of robustness. Compared with other methods, this method has a low collision rate.展开更多
文摘原子时具有较高的短期稳定度,基于毫秒脉冲星自转建立的脉冲星时具有较高的长期稳定度,两者融合可构建长短稳优势兼具的时间尺度。本文通过经典加权平均算法,初步构建一个脉冲星与原子钟融合的联合时间尺度(composite time scale,CT)。基于国际权度局(BIPM)公布的TA(NTSC)-TAI原子时数据,并选取国际脉冲星计时阵(IPTA)公布的计时精度最高的4颗脉冲星,通过并列加权法和分类加权法这两种组合方式得到CT。结果表明并列加权法得到的CT相对于各脉冲星时在10年以内的稳定度改善明显,4~10年内稳定度与稳定度较高的脉冲星J0437-4715接近。分类加权法得到的CT对比并列加权的稳定度结果在采样区间两极优势明显,0.26年达到5.1×10^(-15),16.8年达到1.0×10^(-15),其中4颗星相比2颗星得到的CT于5.2年后稳定度有显著提高,且分类加权法得到的CT相对于TAI偏差更小,时间尺度更平稳。综上说明原子钟组的短稳特性可以对脉冲星钟组的短期噪声进行抑制,同时脉冲星时可提高联合时间尺度CT的长期稳定度。
文摘氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟的频率驾驭,并对实时信号加以控制.首先分析了国际脉冲星计时阵(International Pulsar Timing Array,IPTA)第二批发布数据中四颗毫秒脉冲星的稳定度随时间的变化,同时采用哈达玛方差分析了中国科学院国家授时中心(National Time Service Center,NTSC)一台氢钟的频率稳定性能,最终给出了利用脉冲星驾驭氢原子钟频率的方法.
基金Supported by the National Natural Science Foundation of China under Grant No 11103024 and the Program of the Light in China’s Western Region of CAS。
文摘The pulsar timing residuals induced by gravitational waves from non-evolving single binary sources with general elliptical orbits are analyzed.For different orbital eccentricities,the timing residuals present different properties.The standard deviations of the timing residuals induced by a fixed gravitational wave source are calculated for different values of the eccentricity.We also analyze the timing residuals of PSR J0437-4715 induced by one of the best known single gravitational wave sources,the supermassive black hole binary in the blazar OJ287.
文摘PACS:99.10.−x,04.30.Db,97.60.Gb,95.85.Sz DOI:10.1088/0256-307X/30/11/119901 One regrettable error appeared in Eq.(21)of our article[Chin.Phys.Lett.30(2013)100402].The cor-rect one of the equation is as follows.
基金Natural Science Foundations of Shanghai,China(Nos.15ZR1418500,15ZR1418400)the Training Program of Shanghai University of Electric Power for Academic Backbone Teachers,China
文摘A lexicographic image hash method based on space and frequency features was proposed. At first, the image database was constructed, and then color and texture features were extracted from the image blocks including information for every image in the database, which formed feature vectors. The feature vectors were clustered to form dictionary. In hash generation, the image was preproc^ssed and divided into blocks firstly. Then color and texture features vectors were extracted from the blocks. These feature vectors were used to search the dictionary, and the nearest word in dictionary for each block was used to form the space features. At the same time. frequency feature was extracted from each block. The space and frequency features were connected to form the intermediate hash. Lastly, the final hash sequence was obtained by pseudo-randomly permuting the intermediate hash. Experiments show that the method has a very low probability of collision and a good perception of robustness. Compared with other methods, this method has a low collision rate.
