The voltage characteristics of a half-wavelength transmission(HWLT)system lack mechanism explanation and systematic summary.In this paper,both the steady-state and fault voltage characteristics are analyzed and explai...The voltage characteristics of a half-wavelength transmission(HWLT)system lack mechanism explanation and systematic summary.In this paper,both the steady-state and fault voltage characteristics are analyzed and explained based on the wave process method.An analysis model is established for HWLT lines and wave propagation equations with different terminal conditions are deduced.For steady-state conditions,voltage profiles along HWLT lines are depicted and partial overvoltage occurs when there is an overload or low-power factor.In addition,fault voltage characteristics are analyzed under load-rejection or short-circuit conditions.The series resonance overvoltage will happen when short-circuit faults occur at certain positions and its peak value is influenced by grid strength or fault type.Furthermore,a refined transmission line model is presented to consider non-ideal factors and simulation results demonstrate that geomorphic conditions and electromagnetic environments influence line voltage characteristics to a certain extent.展开更多
多端直流电网架空线路故障概率高、设备耐受过电流能力有限,无选择性的重合将严重危害一次设备的安全性和电网的稳定性,因此提出了一种基于动态时间规整(dynamic time warping, DTW)的重构序列重合方法,实现重合前故障性质的预判。首先...多端直流电网架空线路故障概率高、设备耐受过电流能力有限,无选择性的重合将严重危害一次设备的安全性和电网的稳定性,因此提出了一种基于动态时间规整(dynamic time warping, DTW)的重构序列重合方法,实现重合前故障性质的预判。首先介绍了直流线路的贝杰龙时域等值建模方法,在此基础上,建立了各关键一次设备的贝杰龙等值模型,分析了瞬时性、永久性故障工况下模型等效时域波过程的差异性。然后以瞬时性故障为基准,对直流断路器注入信号所引发的电气分量暂态成分进行理论计算,并借助DTW重构序列量化整定门槛、进一步消除色散误差,最终以此为指标构造判据实现故障性质的识别。基于PSCAD/EMTDC平台的四端直流电网仿真算例显示,所提出的自适应重合方法仅需要单端量,不依赖通信,能够消除死区,且拥有600Ω的灵敏性。展开更多
内孤立波(internal solitary wave,ISW)的传播扰动声速场,进而引起声场周期起伏。本文利用数值仿真的研究手段,研究了内孤立波在不同类型的初始发射角度声线的多个声线上转折区域中传播时对声场产生的周期性影响,分析了对于声线掠射角...内孤立波(internal solitary wave,ISW)的传播扰动声速场,进而引起声场周期起伏。本文利用数值仿真的研究手段,研究了内孤立波在不同类型的初始发射角度声线的多个声线上转折区域中传播时对声场产生的周期性影响,分析了对于声线掠射角度、声能量到达时间这两个物理量的起伏频率,发现利用声学参数-时间曲线两点间的斜率与差值的偶次平方的乘积(product of the slope and the even square of the difference between two points of the acoustic parameter-time curve,PSD)处理方法更容易从这两种物理量中提取到显著的声场起伏特征。此外,讨论了高阶PSD参数对声场起伏特征提取效果的影响。结果表明,合适的高阶PSD参数可以提高PSD处理方法对声场起伏特征的提取能力。展开更多
The probability distributions of wave characteristics from three groups of sampled ocean data with different significant wave heights have been analyzed using two transformation functions estimated by non-parametric a...The probability distributions of wave characteristics from three groups of sampled ocean data with different significant wave heights have been analyzed using two transformation functions estimated by non-parametric and parametric methods. The marginal wave characteristic distribution and the joint density of wave properties have been calculated using the two transformations, with the results and accuracy of both transformations presented here. The two transformations deviate slightly between each other for the calculation of the crest and trough height marginal wave distributions, as well as the joint densities of wave amplitude with other wave properties. The transformation methods for the calculation of the wave crest and trough height distributions are shown to provide good agreement with real ocean data. Our work will help in the determination of the most appropriate transformation procedure for the prediction of extreme values.展开更多
There is a growing interest in the diagnosis and treatment of patients with dementia and cognitive impairment at an early stage. Recent imaging studies have explored neural mechanisms underlying cognitive dysfunction ...There is a growing interest in the diagnosis and treatment of patients with dementia and cognitive impairment at an early stage. Recent imaging studies have explored neural mechanisms underlying cognitive dysfunction based on brain network architecture and functioning. The dorsal anterior cingulate cortex (dACC) is thought to regulate large-scale intrinsic brain networks, and plays a primary role in cognitive processing with the anterior insular cortex (aIC), thus providing salience functions. Although neural mechanisms have been elucidated at the connectivity level by imaging studies, their understanding at the activity level still remains unclear because of limited time-based resolution of conventional imaging techniques. In this study, we investigated temporal activity of the dACC during word (verb) generation tasks based on our newly developed event-related deep brain activity (ER-DBA) method using occipital electroencephalogram (EEG) alpha-2 powers with a time resolution of a few hundred milliseconds. The dACC exhibited dip-like temporal waveforms indicating deactivation in an initial stage of each trial when appropriate verbs were successfully generated. By contrast, monotonous increase was observed for incorrect responses and a decrease was detected for no responses. The dip depth was correlated with the percentage of success. Additionally, the dip depth linearly increased with increasing slow component of the DBA index at rest across all subjects. These findings suggest that dACC deactivation is essential for cognitive processing, whereas its activation is required for goal-oriented behavioral outputs, such as cued speech. Such dACC functioning, represented by the dip depth, is supported by the activity of the upper brainstem region including monoaminergic neural systems.展开更多
基金supported by the State Grid Corporation of China(No.SGSDDK00KJJS1600149).
文摘The voltage characteristics of a half-wavelength transmission(HWLT)system lack mechanism explanation and systematic summary.In this paper,both the steady-state and fault voltage characteristics are analyzed and explained based on the wave process method.An analysis model is established for HWLT lines and wave propagation equations with different terminal conditions are deduced.For steady-state conditions,voltage profiles along HWLT lines are depicted and partial overvoltage occurs when there is an overload or low-power factor.In addition,fault voltage characteristics are analyzed under load-rejection or short-circuit conditions.The series resonance overvoltage will happen when short-circuit faults occur at certain positions and its peak value is influenced by grid strength or fault type.Furthermore,a refined transmission line model is presented to consider non-ideal factors and simulation results demonstrate that geomorphic conditions and electromagnetic environments influence line voltage characteristics to a certain extent.
文摘多端直流电网架空线路故障概率高、设备耐受过电流能力有限,无选择性的重合将严重危害一次设备的安全性和电网的稳定性,因此提出了一种基于动态时间规整(dynamic time warping, DTW)的重构序列重合方法,实现重合前故障性质的预判。首先介绍了直流线路的贝杰龙时域等值建模方法,在此基础上,建立了各关键一次设备的贝杰龙等值模型,分析了瞬时性、永久性故障工况下模型等效时域波过程的差异性。然后以瞬时性故障为基准,对直流断路器注入信号所引发的电气分量暂态成分进行理论计算,并借助DTW重构序列量化整定门槛、进一步消除色散误差,最终以此为指标构造判据实现故障性质的识别。基于PSCAD/EMTDC平台的四端直流电网仿真算例显示,所提出的自适应重合方法仅需要单端量,不依赖通信,能够消除死区,且拥有600Ω的灵敏性。
文摘内孤立波(internal solitary wave,ISW)的传播扰动声速场,进而引起声场周期起伏。本文利用数值仿真的研究手段,研究了内孤立波在不同类型的初始发射角度声线的多个声线上转折区域中传播时对声场产生的周期性影响,分析了对于声线掠射角度、声能量到达时间这两个物理量的起伏频率,发现利用声学参数-时间曲线两点间的斜率与差值的偶次平方的乘积(product of the slope and the even square of the difference between two points of the acoustic parameter-time curve,PSD)处理方法更容易从这两种物理量中提取到显著的声场起伏特征。此外,讨论了高阶PSD参数对声场起伏特征提取效果的影响。结果表明,合适的高阶PSD参数可以提高PSD处理方法对声场起伏特征的提取能力。
基金Supported by the Marine Engineering Equipment Scientific Research Project of Ministry of Industry and Information Technology of PRCthe National Science and Technology Major Project of China(Grant No.2016ZX05057020)National Natural Science Foundation of China(Grant No.51809067)
文摘The probability distributions of wave characteristics from three groups of sampled ocean data with different significant wave heights have been analyzed using two transformation functions estimated by non-parametric and parametric methods. The marginal wave characteristic distribution and the joint density of wave properties have been calculated using the two transformations, with the results and accuracy of both transformations presented here. The two transformations deviate slightly between each other for the calculation of the crest and trough height marginal wave distributions, as well as the joint densities of wave amplitude with other wave properties. The transformation methods for the calculation of the wave crest and trough height distributions are shown to provide good agreement with real ocean data. Our work will help in the determination of the most appropriate transformation procedure for the prediction of extreme values.
文摘There is a growing interest in the diagnosis and treatment of patients with dementia and cognitive impairment at an early stage. Recent imaging studies have explored neural mechanisms underlying cognitive dysfunction based on brain network architecture and functioning. The dorsal anterior cingulate cortex (dACC) is thought to regulate large-scale intrinsic brain networks, and plays a primary role in cognitive processing with the anterior insular cortex (aIC), thus providing salience functions. Although neural mechanisms have been elucidated at the connectivity level by imaging studies, their understanding at the activity level still remains unclear because of limited time-based resolution of conventional imaging techniques. In this study, we investigated temporal activity of the dACC during word (verb) generation tasks based on our newly developed event-related deep brain activity (ER-DBA) method using occipital electroencephalogram (EEG) alpha-2 powers with a time resolution of a few hundred milliseconds. The dACC exhibited dip-like temporal waveforms indicating deactivation in an initial stage of each trial when appropriate verbs were successfully generated. By contrast, monotonous increase was observed for incorrect responses and a decrease was detected for no responses. The dip depth was correlated with the percentage of success. Additionally, the dip depth linearly increased with increasing slow component of the DBA index at rest across all subjects. These findings suggest that dACC deactivation is essential for cognitive processing, whereas its activation is required for goal-oriented behavioral outputs, such as cued speech. Such dACC functioning, represented by the dip depth, is supported by the activity of the upper brainstem region including monoaminergic neural systems.
