In this paper,we introduce a novel hybrid variational model which generalizes the classical total variation method and the wavelet shrinkage method.An alternating minimization direction algorithm is then employed.We a...In this paper,we introduce a novel hybrid variational model which generalizes the classical total variation method and the wavelet shrinkage method.An alternating minimization direction algorithm is then employed.We also prove that it converges strongly to the minimizer of the proposed hybrid model.Finally,some numerical examples illustrate clearly that the new model outperforms the standard total variation method and wavelet shrinkage method as it recovers better image details and avoids the Gibbs oscillations.展开更多
认知功能障碍是脑高级功能的损伤,由神经精神疾病引起的认知功能损害对患者的生活质量和疾病转归造成严重影响。经颅交流电刺激(transcranial alternating current stimulation,tACS)通过调节特定频率的神经振荡、影响5-羟色胺和多巴胺...认知功能障碍是脑高级功能的损伤,由神经精神疾病引起的认知功能损害对患者的生活质量和疾病转归造成严重影响。经颅交流电刺激(transcranial alternating current stimulation,tACS)通过调节特定频率的神经振荡、影响5-羟色胺和多巴胺等神经递质的释放、增强脑网络局部与远端的同步,达到改善认知功能的效果。特定频率的tACS可以改善阿尔茨海默病(Alzheimer disease,AD)、精神分裂症、抑郁障碍引起的认知功能损害,其中以gamma和theta频率tACS对认知功能的影响最为显著。tACS安全性高,操作难度小,对改善神经精神疾病患者的认知功能具有巨大潜力。展开更多
研究了直驱风电场次同步振荡分析的降阶模型,提出了基于交替方向隐式(alternating direction implicit,ADI)的平衡截断方法。首先,根据直驱式永磁同步风电机组的数学表征搭建风电场的数学模型,采用ADI方法迭代求解李亚普诺夫方程,得到...研究了直驱风电场次同步振荡分析的降阶模型,提出了基于交替方向隐式(alternating direction implicit,ADI)的平衡截断方法。首先,根据直驱式永磁同步风电机组的数学表征搭建风电场的数学模型,采用ADI方法迭代求解李亚普诺夫方程,得到可控的格莱姆矩阵与可观的格莱姆矩阵;然后,采用平衡截断的方法得到降阶模型;通过对比全阶模型与降阶模型的时域仿真波形、Bode图、计算耗时以及次同步振荡模式,验证了方法的有效性。仿真结果表明,降阶模型与全阶模型具有很好的一致性,同时计算速度提高,降阶阶数大大降低。展开更多
抑郁症是以情绪低落为主要表现,伴有认知和行为改变的一种常见精神疾病。目前常用的抗抑郁药物起效缓慢、治疗周期长、复发率高,存在明显缺陷。经颅交流电刺激(transcranial alternating current stimulation,tACS)是一种非侵入性脑刺...抑郁症是以情绪低落为主要表现,伴有认知和行为改变的一种常见精神疾病。目前常用的抗抑郁药物起效缓慢、治疗周期长、复发率高,存在明显缺陷。经颅交流电刺激(transcranial alternating current stimulation,tACS)是一种非侵入性脑刺激技术,近年来逐渐应用于抑郁症的治疗中。抑郁症和大脑内源性神经振荡、突触可塑性的异常有关,tACS可以对以上机制产生影响,从而治疗抑郁症。不同频率的tACS刺激可以改善抑郁症状,其中以γ、α频率的刺激最受关注。本文主要对tACS的可能作用机制以及不同频率tACS在抑郁症中的应用进行综述,有助于进一步探讨tACS治疗抑郁症的可行性。展开更多
为研究半波长交流输电的点对网并网特性,通过PSCAD (power system computer-aided design)仿真,分析了并网点两侧电压存在幅值偏差、相角偏差或频率偏差时的并网特性。等值系统能将半波长线路另一端的发电机拉入同步,但并网后的功率振...为研究半波长交流输电的点对网并网特性,通过PSCAD (power system computer-aided design)仿真,分析了并网点两侧电压存在幅值偏差、相角偏差或频率偏差时的并网特性。等值系统能将半波长线路另一端的发电机拉入同步,但并网后的功率振荡持续时间相对较长。通常,串联调谐器要比并联调谐器更适合于阻尼这些功率振荡,因此,仅对串联调谐器的控制策略进行修改。PSCAD仿真结果表明串联调谐器能有效地阻尼这些功率振荡,显著改善半波长交流输电线路的并网性能。展开更多
NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the ...NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the intraseasonal oscillation （ISO; 30-60 days） in the mid-high latitude meridional circulation of the upper troposphere over East Asia. The abrupt transition from drought to flood occurs in early June. The first two recovered fields of the complex empirical orthogonal function show that northward-propagating westerlies from low latitudes converge with southward-propagating westerlies from high latitudes over the mid-low reaches of the Yangtze River （MLRYR） in mid late May. The timing of this convergence corresponds to the flood period in early-mid June. The ISO index is significantly and positively correlated with rainfall over the MLRYR. During the dry phase （before the transition）, the upper troposphere over the MLRYR is characterized by cyclonic flow, easterly winds, and convergence. The regional circulation is dominated by a wave train with a cyclone over east of Lake Baikal, an anticyclone over northern China, and a cyclone over the MLRYR. During the wet phase, the situation is reversed. The configuration of the wave train during the dry phase favors the southward propagation of westerly wind disturbances, while the configuration of the wave train during the wet phase favors the development and maintenance of a pumping effect and sustained ascending motions over the MLRYR.展开更多
基金supported by RGC 203109,RGC 201508the FRGs of Hong Kong Baptist Universitythe PROCORE-France/Hong Kong Joint Research Scheme sponsored by the Research Grant Council of Hong Kong and the Consulate General of France in Hong Kong F-HK05/08T.
文摘In this paper,we introduce a novel hybrid variational model which generalizes the classical total variation method and the wavelet shrinkage method.An alternating minimization direction algorithm is then employed.We also prove that it converges strongly to the minimizer of the proposed hybrid model.Finally,some numerical examples illustrate clearly that the new model outperforms the standard total variation method and wavelet shrinkage method as it recovers better image details and avoids the Gibbs oscillations.
文摘认知功能障碍是脑高级功能的损伤,由神经精神疾病引起的认知功能损害对患者的生活质量和疾病转归造成严重影响。经颅交流电刺激(transcranial alternating current stimulation,tACS)通过调节特定频率的神经振荡、影响5-羟色胺和多巴胺等神经递质的释放、增强脑网络局部与远端的同步,达到改善认知功能的效果。特定频率的tACS可以改善阿尔茨海默病(Alzheimer disease,AD)、精神分裂症、抑郁障碍引起的认知功能损害,其中以gamma和theta频率tACS对认知功能的影响最为显著。tACS安全性高,操作难度小,对改善神经精神疾病患者的认知功能具有巨大潜力。
文摘研究了直驱风电场次同步振荡分析的降阶模型,提出了基于交替方向隐式(alternating direction implicit,ADI)的平衡截断方法。首先,根据直驱式永磁同步风电机组的数学表征搭建风电场的数学模型,采用ADI方法迭代求解李亚普诺夫方程,得到可控的格莱姆矩阵与可观的格莱姆矩阵;然后,采用平衡截断的方法得到降阶模型;通过对比全阶模型与降阶模型的时域仿真波形、Bode图、计算耗时以及次同步振荡模式,验证了方法的有效性。仿真结果表明,降阶模型与全阶模型具有很好的一致性,同时计算速度提高,降阶阶数大大降低。
文摘抑郁症是以情绪低落为主要表现,伴有认知和行为改变的一种常见精神疾病。目前常用的抗抑郁药物起效缓慢、治疗周期长、复发率高,存在明显缺陷。经颅交流电刺激(transcranial alternating current stimulation,tACS)是一种非侵入性脑刺激技术,近年来逐渐应用于抑郁症的治疗中。抑郁症和大脑内源性神经振荡、突触可塑性的异常有关,tACS可以对以上机制产生影响,从而治疗抑郁症。不同频率的tACS刺激可以改善抑郁症状,其中以γ、α频率的刺激最受关注。本文主要对tACS的可能作用机制以及不同频率tACS在抑郁症中的应用进行综述,有助于进一步探讨tACS治疗抑郁症的可行性。
文摘为研究半波长交流输电的点对网并网特性,通过PSCAD (power system computer-aided design)仿真,分析了并网点两侧电压存在幅值偏差、相角偏差或频率偏差时的并网特性。等值系统能将半波长线路另一端的发电机拉入同步,但并网后的功率振荡持续时间相对较长。通常,串联调谐器要比并联调谐器更适合于阻尼这些功率振荡,因此,仅对串联调谐器的控制策略进行修改。PSCAD仿真结果表明串联调谐器能有效地阻尼这些功率振荡,显著改善半波长交流输电线路的并网性能。
基金Supported by the National Natural Science Foundation of China (41221064 and 40875052)China Meteorological Administration Special Public Welfare Research Fund (GYHY200906017 and GYHY201006020)Basic Research Fund of the Chinese Academy of Meteorological Sciences (2010Z003)
文摘NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the intraseasonal oscillation （ISO; 30-60 days） in the mid-high latitude meridional circulation of the upper troposphere over East Asia. The abrupt transition from drought to flood occurs in early June. The first two recovered fields of the complex empirical orthogonal function show that northward-propagating westerlies from low latitudes converge with southward-propagating westerlies from high latitudes over the mid-low reaches of the Yangtze River （MLRYR） in mid late May. The timing of this convergence corresponds to the flood period in early-mid June. The ISO index is significantly and positively correlated with rainfall over the MLRYR. During the dry phase （before the transition）, the upper troposphere over the MLRYR is characterized by cyclonic flow, easterly winds, and convergence. The regional circulation is dominated by a wave train with a cyclone over east of Lake Baikal, an anticyclone over northern China, and a cyclone over the MLRYR. During the wet phase, the situation is reversed. The configuration of the wave train during the dry phase favors the southward propagation of westerly wind disturbances, while the configuration of the wave train during the wet phase favors the development and maintenance of a pumping effect and sustained ascending motions over the MLRYR.
