Analysis of Sub-Synchronous Oscillation of Virtual Synchronous Generator and Research on Suppression Strategy in Weak Grid

At present,the direct drive permanent magnet synchronous generator(DD-PMSG)grid connected system based on virtual synchronous generator(VSG)control will experience power oscillation at sub synchronous frequencies.The mechanism and characteristics of this new type of sub-synchronous interaction(SSI)are not yet clear,and the system cannot recover to steady state solely based on the characteristics of VSG itself.Especially when connected to a weak current network,oscillations are more pronounced,affecting the stability of the system.In severe cases,the systemmay trigger shutdown protection and be disconnected from the network.Existing research has only analyzed the oscillation mechanism under this phenomenon and has not proposed corresponding control strategies.This article proposes aVSM control strategy based on the VSG control algorithm,which balances the dq axis component of voltage and current,and improves the voltage and current loop of VSG control to reduce the impact of sub-synchronous oscillation(SSO)on the power grid.In MATLAB/Simulink,a simulation model of the proposed control strategy was built to verify its correctness and effectiveness.

Synaptic remodeling in mouse motor cortex after spinal cord injury

Spinal cord injury dramatically blocks information exchange between the central nervous system and the peripheral nervous system.The resulting fate of synapses in the motor cortex has not been well studied.To explore synaptic reorganization in the motor cortex after spinal cord injury,we established mouse models of T12 spinal cord hemi-section and then monitored the postsynaptic dendritic spines and presynaptic axonal boutons of pyramidal neurons in the hindlimb area of the motor cortex in vivo.Our results showed that spinal cord hemisection led to the remodeling of dendritic spines bilaterally in the motor cortex and the main remodeling regions changed over time.It made previously stable spines unstable and eliminated spines more unlikely to be re-emerged.There was a significant increase in new spines in the contralateral motor cortex.However,the low survival rate of the new spines demonstrated that new spines were still fragile.Observation of presynaptic axonal boutons found no significant change.These results suggest the existence of synapse remodeling in motor cortex after spinal cord hemi-section and that spinal cord hemi-section affected postsynaptic dendritic spines rather than presynaptic axonal boutons.This study was approved by the Ethics Committee of Chinese PLA General Hospital,China(approval No.201504168S)on April 16,2015.

Extreme Value Estimation of Beaufort Sea Ice Dynamics Driven by Global Wind Effects

The purpose of the present study is to investigate the extreme values of the ice drift speed,which are also considered in the light of the magnitude of the simultaneous wind speed.The relationship between wind speed and ice drift speed is studied.The long-term ice drift data is collected by using local subsurface measurements based on acoustic Doppler current profilers(ADCP)in the Beaufort Sea during the period of 2006-2017.Upward-looking sonars(ULS)are deployed in order to observe the ice thickness as well as to identify events that correspond to open water conditions.The relationship between the ice drift speed and the wind speed is also investigated.It is found that the magnitude of the average ice drift speed is approximately 2.5%of the wind speed during the winter season.Estimation of the extreme values of the ice drift speed is studied by application of the average conditional exceedance rate(ACER)method.It is found that the extreme ice drift speed during the ice melt season(i.e.the summer season)is approximately20%-30%higher than that during the ice growth season(i.e.the winter season).The extreme ice drift speed can be effectively estimated based on the 2.5%wind speed.Moreover,the extreme ice drift speed can be obtained based on the extreme values of 2.5%of the wind speed based on multiplying with an amplification factor which varies in the range from 1.7 to 2.0 during the growth season,corresponding to increasing return periods of 10,25,50 and 100years.

压装过盈量对CRH3动车组车轮轮对强度的影响分析

车轴轮座与车轮轮毂孔之间的压装过盈量是动车组轮对压装工艺中的关键工艺参数,它不仅影响着压装力是否满足压装曲线还影响着轮对在承载情况下的强度水平。本文以CRH3动车组的动力轮对为研究对象,针对TB/T2368-2005载荷工况,运用ANSYS分析过盈量对轮对强度的影响。分析结果表明,当过盈量达到0.238 mm时,CRH3动车组车轮轮毂孔内侧边缘达到许用应力,为压装工艺极限过盈量的选取提供了依据。

腹腔镜保留十二指肠胰头切除术后并发症分析

目的分析总结腹腔镜保留十二指肠的胰头切除术(laparoscopic duodenum-preserving pancreatic head resection,LDPPHR)后常见并发症及预防治疗措施。方法回顾性分析沧州市中心医院普外科2018年6月至2021年6月期间完成的32例LDPPHR患者的临床资料。探讨术后并发症发生情况,并针对并发症的预防及处理措施进行分析和总结。结果32例患者均成功实施LDPPHR,术后并发症发生率为21.9%(7/32),其中包括严重并发症3例(1例术后长期胰瘘、1例术后十二指肠乳头狭窄致梗阻性黄疸、1例术后腹腔出血),均行二次手术治愈;轻微并发症4例,均为单纯性胰瘘,延长带管时间治愈。结论LDPPHR治疗胰头部良性病变技术上可行,但手术难度大,风险高,患者远期生存质量有待评价。

Organogelators based on p-alkoxylbenzamide and their self-assembling properties

展示长烷基链的一系列 p-alkoxylbenzamides 被综合了并且是乐意地在许多器官的溶剂形成稳定的胶化。他们的自己组装性质和结构性质关系被扫描电子显微镜学调查， X 光检查衍射， 1 H 原子磁性的回声，和 Fourier 变换红外线的光谱学。形成的胶化对象温度和氟化物阴离子那样的环境刺激多应答。结果显示出那结合的氢的联合， - 叠并且在 p-alkoxylbenzamides 到的聚集的货车 der Waals 相互作用结果形成三尺寸的网络，取决于长烷基链的长度。

Reliability evaluation of the roll motion under the wind and irregular beam waves

This paper intends to study the stochastic response and reliability of the roll motion under the action of wind and wave excitation.The roll motion in random beam seas is described by a four-dimensional(4D)Markov dynamic system whose probabilistic properties are governed by the Fokker-Planck(FP)equation.The 4D path integration(PI)method,an efficient numerical technique based on the Markov property of the 4D system,is applied in order to solve the high dimensional FP equation and then the stochastic statistics of the roll motion are derived.Based on the obtained response statistics,the reliability evaluation of the ship stability is performed and the effect of wind action is studied.The accuracy of the 4D PI method and the reliability evaluation is assessed by the versatile Monte Carlo simulation(MCS)method.

Novel 1,2,3-triazole-based compounds： Iodo effect on their gelation behavior and cation response

Two new series of 1,2,3-triazole derivatives, with and without iodo substitution, were synthesized and their gelation properties were measured. It was found that the iodo substitution at position 5 of triazole ring could greatly enhance the gelation ability. Scanning electron microscopy and X-ray diffraction reveal that the structures of the organogels from iodo and hydrogenous gelators are totally different, lodo gels are selectively responsive to the stimuli of Hg2＋, whereas hydrogenous gels can respond to Hg2＋ and Cu2＋. Moreover, the reversible gel-sol transition of hydrogenous gels can be controlled by redox reaction or tuned with suitable chemicals. The single crystal analysis of reference compound （C2） suggests that there are intermolecular and intramolecular non-classical hydrogen bonding interactions but no π-π interaction in hydrogenous gelator. The great difference between the two series of compounds results from the iodo effect and implies the existence of halogen bonding interaction in the iodo compounds.

Wastewater treatment control method based on a rule adaptive recurrent fuzzy neural network

Purpose-The purpose of this paper is to present an on-line modeling and controlling scheme based on the dynamic recurrent neural network for wastewater treatment system.Design/methodology/approach-A control strategy based on rule adaptive recurrent neural network(RARFNN)is proposed in this paper to control the dissolved oxygen(DO)concentration and nitrate nitrogen(SNo)concentration.The structure of the RARFNN is self-organized by a rule adaptive algorithm,and the rule adaptive algorithm considers the overall information processing ability of neural network.Furthermore,a stability analysis method is given to prove the convergence of the proposed RARFNN.Findings-By application in the control problem of wastewater treatment process(WWTP),results show that the proposed control method achieves better performance compared to other methods.Originality/value-The proposed on-line modeling and controlling method uses the RARFNN to model and control the dynamic WWTP.The RARFNN can adjust its structure and parameters according to the changes of biochemical reactions and pollutant concentrations.And,the rule adaptive mechanism considers the overall information processing ability judgment of the neural network,which can ensure that the neural network contains the information of the biochemical reactions.

Natural nitrogen-doped multiporous carbon from biological cells as sulfur stabilizers for lithium-sulfur batteries

In this context,we firstly synthesized a novel nitrogen-doped multiporous carbon material from renewable biological cells through a facile chemical activation with K;CO;.After sulfur impregnation,the carbon/sulfur composite achieved a sulfur content of about 67 wt%.The C/S composite as the cathode of lithium-sulfur batteries exhibited a discharge capacity of 1410 mAh/g and good capacity retention of912 mAh/g at 0.1C.These outstanding results were attributed to the synergy effect of microporous carbon and natural doping nitrogen atoms.We believe that the facile approach for the synthesis of nitrogen-doped multiporous carbon from the low-cost and sustainable biological resources will not only be applied in lithium-sulfur batteries,but also in other electrode materials.