New evidence for possible impact of solar activity on long-term fluctuation of the earth rotation

The long-term fluctuation of the Schwabe period (LSP) of sunspots number (SSN) has been found to have high correlation with the variation of the length-of-day (LOD) in low frequency by using the data of smoothed monthly mean SSN during 1818–1999 and the method of wavelet transform. Analyses indicate that the maximum correlation coefficient between the series of LSP and LOD during 1892–1997 is about 0.9, with a time lag of about 5 years for the LOD related to the LSP. Though the maximum correlation coefficients between the LSP and the other two LOD series (1818–1997) reduce to about 0.4, they remain over the thresholds of 95% confidence level. This suggests new evidence for possible impact of solar activity on the long-term fluctuation of the earth rotation.     

BL Lac天体OJ 287射电流量的交叉小波分析

将BL Lac天体OJ 287射电4.8,8.0和14.5 GHz波段从1978–2010年的有效观测数据进行整理,获得了其长期光变曲线,用小波功率谱和交叉小波方法分别分析了其主要振荡周期和彼此之间的相关性及其时延.小波功率谱分析结果表明,OJ 287射电4.8,8.0和14.5 GHz流量存在准6个月、8–16个月和16–32个月的主振荡周期,光变周期为0.54?0.04,1.12?0.07,2.49?0.08年,主振荡周期主要出现在1980–1994年和2000–2007年时间段.交叉小波分析发现OJ 287射电波段之间正相关振荡的凝聚性很强,具有强的关联性,在8–16和16–32个月共振周期尺度上的相关性高.射电波段的爆发在16–32个月的振荡周期尺度上几乎是同时性的,在8–16个月的振荡周期尺度上存在20±6天的时间延迟,高频波段领先低频波段.     

小波分析在太阳辐射神经网络预测中的应用研究

通过小波变换将太阳辐射数据序列分解到不同的时频域上，并对每一频域分量建立一个递归BP网络模型；然后用网络模型对各频域分量进行预测，将各预测结果进行代数叠加，从而得到太阳辐射的预测结果。为体现近期预测结果在精度上的相对重要性，在递归BP网络的权闽值修改算法中，引入了折扣系数法。最后，通过对上海太阳日总辐射的预测实例表明，该方法在预测太阳辐射时是可行的。     

Decadal-centennial-scale change in Asian-Pacific summer thermal contrast and solar activity

To study the temporally varying features of summer thermal contrast between the Asian continent and the adjacent ocean on decadal-centennial time scales and the links between thermal contrast and solar irradiance, we used a time series of the reconstructed Asian-Pacific oscillation index and solar irradiance over the past millennium. The results showed that thermal contrast in the Asian monsoon region has quasi-90-year, 10?C13-year, and 3?C7-year periods. On the centennial time scale, thermal contrast showed three abrupt changes, occurring in 1305?C1315, 1420?C1430, and 1625?C1635. There is a significant positive correlation between thermal contrast and solar irradiance, which is particularly strong at 250-year, 120?C160-year, 60?C70-year, and quasi-15-year periods. The three abrupt changes in thermal contrast corresponded to a significantly weakening or strengthening of solar irradiance, lagging 12?C22 years behind the solar irradiance, which possibly reflects an effect of solar irradiance on the abrupt change in Asian monsoon climate on the centennial time scale. On the decadal time scale, the abrupt change in the thermal contrast was not closely associated with solar irradiance, which implies that solar activity may not be a major factor affecting the decadal abrupt change in Asian-Pacific thermal contrast. Relative to thermal contrast, the decadal abrupt change in Northern Hemispheric annual mean surface temperature is more closely associated with solar activity, while its centennial abrupt change has a weaker relationship with solar activity.     

The wavelet analysis of satellite sea surface temperature in the South China Sea and the Pacific Ocean

Using wavelet transform, the sea surface temperature (SST) during the period of 1982–1999 of the South China Sea and the equatorial Pacific, from datasets of NOAA/AVHRR, was analyzed. It is shown that there are 4- and 8-year interannual oscillations in the eastern equatorial Pacific and 8-year interannual oscillation in the western equatorial Pacific. In terms of attractive time-frequency localization and multi-scale properties of wavelet transform, as shown by the Morlet wavelet, it is found that an in-phase coupling oscillation occurs between the SCS and the equatorial Pacific. The SST changes of SCS will have echoed every event of EI Niño (abnormally warm) and La Niño (abnormally cold) in the equatorial Pacific. There is a positive correlation between the SCS and the western equatorial Pacific in the 8-year time-scale. Evidence is presented that the SST anomalies of the equatorial Pacific influence the SST of the SCS.     

黄河流域降水序列变化的小波分析

采用1961—2000年黄河流域97个气象站点的系列资料,在分析黄河流域降水空间变化格局的基础上,采用墨西哥帽小波函数,对黄河流域近40 a来降水的季节变化和年际变化时间序列进行了小波分析,揭示了黄河流域降水变化的多时间尺度的复杂结构,分析了不同时间尺度下降水序列变化的周期和突变点,并确定了各序列中存在的主要周期。结果表明：黄河流域多年平均降水量的地区分布既受天气系统的制约,又受地形等地理环境的影响,造成明显的地区性差异;黄河流域年降水和各季节降水均存在8~12 a左右时间尺度的多少交替,表现出明显的周期特征,其次4~6 a左右时间尺度的周期特征也较明显,夏季降水和年降水变化趋势具有较大相似性,不同时间尺度的周期特征之间有不同程度的吻合,说明夏季降水较大程度地控制着年降水。小波分析的时频局部化特性可展现降水时间序列的精细结构,为分析气候多时间尺度变化特征及短期气候预测等节水关键问题研究提供了一种新途径。     

基于子波变换谱估计的频率步进毫米波雷达目标成像

根据子波变换所具有良好的时间－频率局域性和逼近性,研究基于子波变换谱估计的频率步进毫米波雷达目标成像方法。由于选用了波动性、衰减性和带通性能好的已调高斯函数作为子波基函数构成一组特性较理想的带通滤波器,对信号进行正交处理,其子波变换同时给出了同相和正交分量。通过信号的功率谱估计,从而获得更好的雷达目标一维距离像。仿真结果表明,这种方法是有效的     

FFT复小波及在设备故障信号分析中的应用

提出一种在频域用数字滤波器定义复小波和展缩小波基,用FFT实现复小波变换的算法。该算法可通过控制滤波器的频率截止特性来生成不同特性的小波函数;通过控制滤波器截止频率位置来改变离散小波变换的频率分辨率。     

Effects of sleep deprivation on gamma oscillation of waking human EEG

This study compares and evaluates the effect of sleep deprivation （SD） on human brain cognition by analyzing the recorded EEG data under normal and 24 h sleep deprived states. EEG auditory event-related potentials were collected from 14 healthy volunteers, and the statistical values of wavelet-transformed EEG in gamma band were decomposed by parallel factor analysis （PARAFAC） to identify where the differences appeared in the time, frequency and spatial domains. The results showed that the changes of brain states caused by SD appeared around 40 Hz at about 400 ms after stimulation on prefrontal and frontal lobes. Negative effects of SD on neuronal activity and oscillation were observed. The analysis of the EEG data by the wavelet transform and PARAFAC can be an integrated way to estimate the change of brain states in the three domains.     

用小波变换提取局部放电信号

为了提取局部放电信号,采用二进尺度小波变换的Ｍａｌａｔ算法,应用Ｄａｕｂｅｃｈｉｃｓ小波,设计了低通、带通滤波器。数值仿真研究中,用指数衰减或衰减振荡波来模拟放电信号,研究了小波变换提取信号的效果及有关影响因素。仿真和现场监测数据处理的结果表明,由于小波变换具有多分辨率特性,能快速而有效地从多种窄带干扰中提取出放电信号,适当条件下还可实现较完整波形的提取。由于处理速率较高,适合在线监测时实时使用。     

Phase relationship between the relative sunspot number and solar 10.7 cm flux

A range of analysis approaches,namely continuous wavelet,cross wavelet,and wavelet coherence analyses,are employed to clarify the phase relationship between the smoothed monthly mean sunspot number and solar 10.7 cm flux(F10.7).Analysis shows that there is a region of high spectral power sitting across the Schwabe cycle belt,where the two time series are in phase.However,analysis of the cross-wavelet transform and wavelet coherence unveils asynchronous behavior featured with phase mixing in the high-frequency components of sunspot activity and solar F10.7,which may explain the different activity properties of the photosphere and corona on a short time scale.     

Simulated analysis of summer climate on centennial time scale in eastern China during the last millennium

Using Lanczos filtered simulation results from the ECHO-G coupled ocean-atmosphere model, this study analyzes the spatiotemporal structure of temperature and precipitation on centennial time scale to examine how climate change in eastern China responded to external forcing during the last millennium. The conclusions are (1) eastern China experienced a warm-cold-warm climate transition, and the transition from the warm period to the cold period was slower than the cold to warm transition which followed it. There was more rainfall in the warm periods, and the transitional peak and valley of precipitation lag those of temperature. The effective solar radiation and solar irradiance have significant impacts on the temporal variation of both temperature and precipitation. Volcanic activity plays an important role in the sudden drop of temperature before the Present Warm Period (PWP). There is a positive correlation between precipitation and volcanic activity before 1400 A.D., and a negative relationship between the two thereafter. The concentration of greenhouse gases increases in the PWP, and the temperature and precipitation increase accordingly. (2) The spatial pattern of the first leading empirical orthogonal function (EOF) mode of temperature on centennial time scale is consistent with that on the inter-annual/inter-decadal (IA-ID) time scales; namely, the entirety of eastern China is of the same sign. This pattern has good coherence with effective solar radiation and the concentrations of greenhouse gases. The first leading EOF mode of precipitation on centennial time scale is totally different from that on the IA-ID time scales. The first leading mode of centennial time scale changes consistently over the entirety of eastern China, while the middle and lower reaches of the Yangtze and Yellow Rivers are the opposite to the rest of eastern China is the leading spatial pattern on IA-ID time scale. The distribution of precipitation on centennial time scale is affected by solar irradiance and greenhouse gas concentrations.     

再生式液体发射药火炮燃烧室压力高频振荡研究

利用小波分析技术提取燃烧室压力高频成分，较精确确定压力高频振荡出现的时域范围，从而确定了振荡流共振振型对应的燃烧室形状。推导了燃气振荡流方程，计算了对应不同燃烧室形状下燃气振荡流的共振频率。对提取的燃烧室压力高频成分相对集中部分进行了频谱分析。研究结果表明：活塞的运动对共振频率影响较小，振荡流多阶共振频率受到激励是燃烧室产生压力高频振荡的一个重要原因。     

利用小波变换进行地震数据压缩

根据Ｍ带小波变换理论,结合地震数据的特征,将Ｍ带小波变换应用于地震数据的压缩处理,提出了地震数据的压缩编码算法。实验结果表明,该方法简单,对地震数据压缩行之有效     

A Scheme of image coding with high compression

Ｉｍａｇｅｃｏｍｐｒｅｓｓｉｏｎｔｅｃｈｎｉｑｕｅｓａｒｅｄｉｖｉｄｅｄｉｎｔｏｔｗｏｍａｉｎｃａｔａｌｏｇｕｅｓ：ｔｒａｎｓｆｏｒｍｃｏｄｉｎｇｓ（ＤＣＴ,ＪＰＥＧ,ＦＦＴ,Ｗａｖｅｌｅｔ）ａｎｄｎｏｎｔｒａｎｓｆｏｒｍｃｏｄｉｎｇｓ（ＰＣＭ,ＤＰＣＭ）．ＴｈｅＰＣＭａｎｄＤＰＣＭｍｅｔｈｏｄｓｅｎａｂｌｅｕｓｔｏｃｏｍｐｒｅｓｓｔｈｅｄａｔａｗｉｔｈｏｕｔｔｒａｎｓｆｏｒｍｉｎｇ．Ｔｈｅｙｂａｓｅｄｏｎｔｈｅｓｉｇｎａｌ○ｓｍｏｄｅｌ．Ｃｏｍｐｒｅｓｓｉｏｎｃａｎｂｅａｃｈｉｅｖｅｄｂｙｔｒ…     

短时电压变动的小波变换模极大值奇异性检测方法

针对短时电压变动的特征,探讨了基于小波变换的模极大值奇异性的短时电压变动实时检测方法及其实现过程,并利用MATLAB对线路发生短时电压变动进行了仿真.仿真结果表明,利用小波变换模极大值奇异性法,可以实时、精确、有效检测短时电压变动信号发生时间、结束时间和幅值及瞬时值.     

玉符河流域地下水位与降水量的时滞分析

选取2000～2014年玉符河流域4组孔隙含水层、岩溶含水层水位监测数据及同期济南市降水量数据,采用连续小波变换和交叉小波变换对地下水位与降水量的时滞进行分析。结果表明:相同地段不同含水层的水位变化规律较为一致,降水量和地下水位存在约1年的连续主震荡周期。自上游到下游,地下水位与降水量的时滞逐渐增大,岩溶水位与降水量的时滞为73.22～117.99 d,孔隙水位与降水量的时滞为75.00～127.52 d。对于相同地段不同的含水层,岩溶水位对降水的时滞整体上小于孔隙水位对降水的时滞。     

九寨沟世界遗产地旅游流时间特征分析

引入4种指数和小波分析工具定量探讨九寨沟旅游流的时间特性。以morlet母小波对1994-2006年逐月和2003-2006年逐日两个旅游流时间序列实施小波变换,揭示了九寨沟旅游流多时间尺度的复杂结构,分析了不同尺度下的周期性。结果表明：在年际尺度上,旅游流呈现出三次函数增长方式,其年内分布为明显的三峰型;在月际尺度上,旅游流季节波动特性逐步变小;近13年来,旅游流存在1年左右的变动周期,尤在近4年表现强烈,此外该时段还在50～70天小尺度上存在周期现象。小波分析的时频局部化特性可以展现旅游流时间序列的精细结构,为分析旅游流时间特性提供了一种新途径。     

银纳米粒子的消光光谱与粒子形状的关系

先利用离散偶极子近似(Discrete Dipole Approximation,DDA)的方法,分别计算置于空气中的球形、不同长径比的椭球形和棒形银纳米粒子的消光光谱.计算结果表明:球形纳米粒子仅存在单个等离子体共振尖峰;而椭球状和棒状粒子则存在横向和纵向两个等离子体共振峰;并且横向峰的变化不甚明显,而纵向峰会随粒子长径比的增大而线性地红移.再结合Gans的解析理论,分析等离子体共振的机理,并研究纵向等离子体共振峰随着粒子长径比的增大而红移的现象.     

基于混合优化算法的最大功率点追踪方法

针对部分阴影条件下粒子群优化（PSO）算法追踪最大功率点时间较长与功率波动大的问题,提出一种基于万有引力与粒子群混合优化(GPSHO)算法的最大功率点追踪（MPPT）方法。该方法将万有引力搜索算法引入粒子群算法,在迭代过程中通过调节PSO算法的惯性权重、认知因子和社会因子提高算法的收敛速度,实现追踪全局最大功率点。仿真与实验结果表明:该方法能够在不同光照情况下精准地追踪全局最大功率点,其搜索速度大约比基于自适应惯性权重粒子群(APSO)算法的MPPT方法快１倍,功率振荡亦更小。