Resting-state connectivity in the default mode network and insula during experimental low back pain

Functional magnetic resonance imaging studies have shown that the insular cortex has a signif- icant role in pain identification and information integration, while the default mode network is associated with cognitive and memory-related aspects of pain perception. However, changes in the functional connectivity between the defauk mode network and insula during pain remain unclear. This study used 3.0 T functional magnetic resonance imaging scans in 12 healthy sub- jects aged 24.8 ± 3.3 years to compare the differences in the functional activity and connectivity of the insula and default mode network between the baseline and pain condition induced by intramuscular injection of hypertonic saline. Compared with the baseline, the insula was more functionally connected with the medial prefrontal and lateral temporal cortices, whereas there was lower connectivity with the posterior cingulate cortex, precuneus and inferior parietal lobule in the pain condition. In addition, compared with baseline, the anterior cingulate cortex exhibited greater connectivity with the posterior insula, but lower connectivity with the anterior insula, during the pain condition. These data indicate that experimental low back pain led to dysfunction in the connectivity between the insula and default mode network resulting from an impairment of the regions of the brain related to cognition and emotion, suggesting the impor- tance of the interaction between these regions in pain processing.

Influence of the column-to-beam flexural strength ratio on the failure mode of beam-column connections in RC frames

The column-to-beam flexural strength ratio(CBFSR)has been used in many seismic codes to achieve the strong column-weak beam(SCWB)failure mode in reinforced concrete(RC)frames,in which plastic hinges appear earlier in beams than in columns.However,seismic investigations show that the required limit of CBFSR in seismic codes usually cannot achieve the SCWB failure mode under strong earthquakes.This study investigates the failure modes of RC frames with different CBFSRs.Nine typical three-story RC frame models with different CBFSRs are designed in accordance with Chinese seismic codes.The seismic responses and failure modes of the frames are investigated through time-history analyses using 100 ground motion records.The results show that the required limit of the CBFSR that guarantees the SCWB failure mode depends on the beam-column connection type and the seismic intensity,and different types of beam-column connections exhibit different failure modes even though they are designed with the same CBFSR.Recommended CBFSRs are proposed for achieving the designed SCWB failure mode for different types of connections in RC frames under different seismic intensities.These results may provide some reference for further revisions of the SCWB design criterion in Chinese seismic codes.

Comparison the Performances of Three Earthing Systems for Micro-Grid Protection during the Grid Connected Mode

This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the models of all the micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included in the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the connecting mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN system, Touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited value if current limiter is included with the transformer of the main grid which connects MG. For the two others earthing systems (TT and IT), fault current is small and nearly equal to the over load current which make over current protection relay can not differentiate between fault current and overload current. All models of micro sources, earthing systems, inverters, main grid and control schemes are built using Matlab?/Simulink? environment.

Study on the Application of UHVDC Hierarchical Connection Mode to Multi-infeed HVDC System

随着我国特高压交直流技术的广泛应用，多馈入直流集中落入受端负荷中心将是未来我国电网发展所面临的重要问题。为从电网结构上有效解决多馈入直流系统的问题，提出一种特高压直流分层接入交流电网的方式。研究分层接入方式直流多馈入短路比计算方法的适用性，从理论上对比特高压直流不同接入方式下多馈入直流电网的系统特性，证明特高压直流分层接入方式有助于提高多馈入直流系统的电压支撑能力，引导潮流在1000kV与500kV层级间合理分布。结合国家电网规划，仿真验证了特高压直流分层接入方式的优势。

Experimental and Numerical Studies of Failure Modes and Load-Carrying Capacity of Through-Diaphragm Connections

Shear failure in panel zones and plastic hinges in steel beams are the two major failure modes of connections between concrete-filled steel tubular(CFST) columns and steel beams. To investigate the behavior of this type of connection in both modes,two through-diaphragm connections were tested under cyclic and monotonic loadings and the load-carrying capacity,ductility,and strength of degradation of connections were discussed. Using ABAQUS software,we developed nonlinear finite-element models(FEMs) to simulate the load-carrying capacity and failure modes of the connections under monotonic loading. The finite-element(FE) analysis and test results showed reasonable agreement for the through-diaphragm connections,which confirms the accuracy of FEMs in predicting the load-carrying capacity and failure modes of connections. Based on the validated FEM,a parametric study was then conducted to investigate the infl uence of the thicknesses of the tube and diaphragm on the load-carrying capacity and failure modes of these connections. The results indicate that the strength,stiff ness,and load-carrying capacity are infl uenced less by the thickness of the diaphragm,and more by the thickness of the steel tube. According to the FE analysis results,it can be found that the critical condition between the two failure modes is determined by the shear resistance and bending resistance.

Shaking test research on connection modes between block infill wall and frame beam

In order to achieve an optimal anti-seismic behavior,or rather stability,the out-of-plane stability of infill wall in frame has been researched with the shaking test of four sets of two-layer infill wall,in which four different connection modes of filled with inclined bricks on the top,disconnection,flexibility and semi-flexibility were adapted.The acceleration and displacement response of the specimens were analyzed under the seismic load.Also,some feasible connection modes were gained by comparing the response of infill walls.Finally,the calculation of earthquake of infill wall was held.The results showed that seismic responses of the infill walls whose connect with frame in form of flexibility and semi-flexibility modes are weaker than others obviously,and their integrality is better.Thus the conclusion could be drawn that out-of-plane stability of the specimens with connection modes of flexibility and semi-flexibility are better than those with the connection modes of filled with inclined bricks on the top and disconnection.The research results can provide evidence for establishing specifications and directing the construction and therefore help reduce the casualties and property loss caused by earthquake disasters.

Disrupted functional connectivity of default mode network and executive control network in patients with vascular cognitive impairment, no dementia

Objective： To investigate functional connectivity within default mode network （DMN） and ex-ecutive control network （ECN） in vascular cognitive im-pairment, no dementia （VCIND）. Methods： Twenty-eight VCIND patients and sixteen healthy controls were recruit-ed. A seed-based connectivity analysis was performed us-ing data from resting-state functional magnetic resonance imaging （fMRI）. Based on previous fndings, posteriorcingulate cortex （PCC） and dorsolateral prefrontal cortex （DLPFC） were chosen as regions of interest to study these networks.One-sample t-test and two-sample t-test were used for statistical analysis. Results： Compared with thecontrols, the VCIND group exhibited increased functional activity in such DMN regions as the left inferior temporal gyrus, parahippocampal gyrus, and medial frontal gyrus. The VCIND group had decreased functional connectivity of DMN at right superior frontal gyrus, left mid-cingu-late area, the medial part of left superior frontal gyrus, and bilateral medial frontal gyrus. The VCIND group also showed decreased functional connectivity of ECN pri-marilyat left inferior parietal gyrus, right angular gyrus, right middle occipital gyrus, and right middle frontal cor-tex. Conclusions： Increased functional connectivity with-in DMN and decreased functional connectivity within ECN suggested dysfunction of these two networks, which mightbe associated with the cognitive defcitsin patients with VCIND. These fndingsmay help usunderstandthe pathogenesis and clinical characteristics of VCIND.

Influence of Control Modes of Grid-Connected Solar Photovoltaic Generation on Grid Power Flow

Integration of Solar Photovoltaic (PV) generation into an existing distribution system has many impacts on the system, with the power flow being one of the major issues. This impact is not generic for any network, but it may manifest itself either positively or negatively, depending on the grid configuration, interface control modes, operation mode, and load profile. Grid-connected PV systems have three control options of the local voltage controller of the interface DC-AC converter. These control modes are Power Factor control, voltage control, and Droop Voltage control. This paper aims at evaluating and comparing the impacts of those control modes on the grid power flow. A set of evaluation criteria and indices is defined and mathematically formulated. Based on the requirements of the used program (Power Factory Dig Silent V14.1.3), a computation plan (algorithm) has been proposed. The algorithm has been applied to a typical weak network and a wide range of simulations has been carried out. Simulation results have been thoroughly discussed and important findings have been concluded.

MODEM与ISDN两种网络接入方式的对比

对比两种网络接入方式 (MODEM方式和ISDN方式 )技术上的特性及其存在的差异 ,并通过测试说明ISDN方式比MODEM方式更先进 ,更具优越性。

A tour-based analysis of travel mode choice accounting for regional transit service

The aim of this work is to explore the impact of regional transit service on tour-based commuter travel behavior by using the Bayesian hierarchical multinomial logit model, accounting for the spatial heterogeneity of the people living in the same area.With two indicators, accessibility and connectivity measured at the zone level, the regional transit service is captured and then related to the travel mode choice behavior. The sample data are selected from Washington-Baltimore Household Travel Survey in 2007,including all the trips from home to workplace in morning hours in Baltimore city. Traditional multinomial logit model using Bayesian approach is also estimated. A comparison of the two different models shows that ignoring the spatial context can lead to a misspecification of the effects of the regional transit service on travel behavior. The results reveal that improving transit service at regional level can be effective in reducing auto use for commuters after controlling for socio-demographics and travel-related factors.This work provides insights for interpreting tour-based commuter travel behavior by using recently developed methodological approaches. The results of this work will be helpful for engineers, urban planners, and transit operators to decide the needs to improve regional transit service and spatial location efficiently.

Effects of connection types and elevated temperature on the impact behaviour of restrained beam in portal steel frame

Based on the background of structural protection and Disaster Reduction Engineering, the dynamic behaviour and failure mechanism of restrained beams in portal steel frames in localised fire are investigated via experimental measurement and numerical simulation techniques. Comprehensive parametric studies are carried out to discuss the influence of end connection types, temperature, impact velocity,impact mass and span-to-depth ratio(SDR) on the dynamic response of the beams. The characteristics of deformation, internal force and energy distribution about the restrained beams and its joints are investigated. A temperature dependent criterion for evaluating the frame joint performance is proposed to measure the degree of performance degradation and impact resistance of the joint. The dynamic displacement amplification factor in different temperature environments are proposed for the different beam end constraint types and SDRs. Results of the experimental and numerical analysis show that the welded connection(WC) of three typical joint types is the strongest, and the extended endplate connection(EEC) is the weakest in terms of the impact resistance performance. With regard to the failure mode of the joint, the failure positions of the WC and the welded-bolted connection are located in the inner web of the column. Meanwhile, the EEC is located in the connection position between the beam and the endplate. Three different internal force stages and two obvious critical temperature boundaries of the restrained beams emerge with the increase in temperature, and they have significant characteristics in terms of deformation trend, internal force transfer and energy distribution. During the impact, a phenomenon known as “compression arch action” develops into “catenary action” with the increase in deflection in the frame beam mechanism.

Experimental Study of Moso Bamboo to-Steel Connections with Embedded Grouting Materials

Moso bamboos have attracted excessive attention as a renewable green building material to the concept of sustainable development.In this paper,the 20 bolted Moso bamboo connection specimens with embedded steel plates and grouting materials were designed according to connection configurations with different bolt diameters and end distance of bolt holes,and their bearing capacities and failure modes were analyzed by static tension tests.According to the test results of all connectors,the failure modes of the specimens are divided into four categories,and the effects of bolt diameter and bolt hole end distance on the connection bearing capacity and failure mode are analyzed.The test results show that the deformation and failure process can be divided into four stages.The main influence factor of connector bearing capacity is bolt diameter.Connectors can be divided into four failure modes,and brittle failure can be avoided by adopting certain structural measures.Filling with grouting material can improve the bearing capacity of joints.Due to the large variability of bamboo,further experiments are needed.

大规模可再生能源发电友好并网与运行调控技术研究综述

“双碳”目标下大规模可再生能源系统的友好并网与稳定运行问题被广泛关注,但受精确的发电不确定性建模技术与科学的并网调控策略制约.为解决这一问题,从可再生能源发电预测与不确定性建模、可再生能源系统并网运营模式、可再生能源系统并网控制方法三个方面进行梳理和总结,讨论了不同时间尺度下发电不确定性预测技术、针对多场景运行需求的不确定性建模技术;从可再生能源-储能系统、可再生能源集群-独立储能系统、多能源互补系统三个角度分析总结了目前并网运营模式;在此基础上,分析总结了跟网型与构网型两种并网控制策略.最后展望了高比例可再生能源系统在未来电网形态演变中的发展方向,以期为新型电力系统中可再生能源与电网协同发展的研究和技术应用提供借鉴.

部分包覆钢-混凝土组合梁柱节点抗震性能试验研究

为研究不同连接构造的部分包覆钢-混凝土组合梁柱节点(PEC梁柱节点)的抗震性能,对2个PEC梁柱节点试件进行了拟静力加载试验,研究了低周往复荷载作用下PEC梁柱节点试件的破坏现象、滞回曲线、骨架曲线、延性、耗能能力和刚度退化等抗震性能。结果表明:强轴连接PEC梁柱节点的滞回曲线呈梭形和弓形,在达到极限承载力后仍能保持一定的延性和耗能能力;弱轴连接PEC梁柱节点牛腿与梁间的焊缝处发生破坏,未展现出预期的耗能能力,PEC梁仍在弹塑性状态,没有达到极限状态;PEC梁柱节点核心区混凝土替换为加劲肋板后,试件仍具有较好的承载力、延性和耗能能力,刚度退化规律无明显变化,且强轴连接节点与弱轴连接节点刚度变化规律基本一致;PEC柱牛腿设计过短会导致焊缝连接处断裂,试件延性和耗能能力得不到发挥,剩余刚度较大。

高渗透率新能源发电并网变流器跟网/构网混合模式控制综述

随着新能源发电渗透率的不断提升,目前以跟网型控制为主流的并网变流器稳定运行受到严峻挑战,具有主动电网支撑能力且弱电网稳定性强的构网型变流器控制技术受到广泛关注。然而,在高渗透率新能源发电条件下,尤其是末端弱电网中,并网变流器采用单一的跟网或构网模式控制难以兼顾稳定性、经济性和电网支撑性能。为此,国内外学者从2种模式的互补特性出发,提出并研究了跟网/构网混合模式控制策略,以期使并网变流器在弱电网下稳定运行的同时,最大限度地利用新能源,并取得优越的电网支撑性能。文中首先从跟网型与构网型变流器的基本控制结构出发,分析了跟网型和构网型变流器控制性能的互补特性;在此基础上,重点梳理了几种不同技术路线的混合模式控制方案,涉及多种单机混合控制策略和多机的场站级混合控制策略,并详细阐述了各方案的技术研究思路、原理和优缺点;最后,对跟网/构网混合模式控制技术的发展进行了展望。

混合多馈入直流输电系统中LCC分层接入方式下后续换相失败抑制策略

随着直流输电的发展,LCC-HVDC与VSC-HVDC将不可避免的馈入同一区域电网,我国部分地区已经形成了混合多馈入直流输电系统,而受端LCC分层接入方式能够提高混合多馈入直流输电系统的电压支撑能力。受端分层接入方式下特高压直流输电工程在本层阀组发生换相失败时,由于层间耦合关系,可能引发非故障层阀组同时发生换相失败。提出基于MMC快速无功支援与LCC非故障层超前触发角补偿的协调控制策略,根据不同交流电压跌落程度,考虑受端MMC四象限运行能力向受端LCC非故障层提供无功支援,需要的无功支援量在MMC四象限运行范围内时,仅由MMC进行无功支援,利用公共耦合母线的电压跌落值确定MMC无功支援指令值。需要的无功支援量超过MMC四象限运行范围内时,MMC无功支援指令值为四象限运行有功临界值时的无功最大值,同时启动LCC非故障层的超前触发角补偿控制。大量仿真测试表明所提协调控制策略对高低端逆变器同时发生换相失败的抑制效果明显。

跨国公司东道国和母国制度距离对企业创新绩效的影响——基于上市公司数据的实证分析

基于制度理论和行为者能动性视角,研究跨国公司东道国和母国制度距离如何对企业创新绩效产生不对称的影响,并考察企业政治关联和海外进入模式的调节作用。研究发现,正向制度距离对企业创新绩效产生正向影响,而负向制度距离越大,越不利于企业创新绩效提高;与没有政治关联的企业相比,企业具有政治关联则使得正向制度距离与企业创新绩效之间的正相关关系降低,并削弱了负向制度距离对企业创新绩效的负向影响;此外,企业选择跨国并购或绿地新建的进入模式也会调节制度距离方向与企业创新绩效之间的关系。研究结论不仅丰富了制度距离视角下企业创新绩效的研究,而且为政府制定相关政策和企业国际化决策提供了有益的实践启示。

适应并离网模式切换的DFIG电磁暂态仿真建模

目前,常用的商业仿真软件中的双馈式感应发电机(double-fed Induction Generator,DFIG)模型通常不支持离网运行模式,难以实现风力发电系统由离网到并网的全过程电磁暂态仿真,对电力系统仿真分析工作带来极大不便。研究适应并离网模式切换的DFIG电磁暂态仿真建模方法。基于模块化思想分别对风力机、异步电机、变流器以及断路器进行建模,在系统组装形成DFIG风力发电系统电磁暂态仿真模型。提出了适应并离网模式切换的DFIG受控源等效电路模型和离散时间域实现方法,通过设计状态变量矩阵元素的截取和扩充算法实现了模型在并离网模式下的无缝衔接。在MATLAB/Simulink中搭建DFIG发电系统模型对所提方法和模型进行验证,仿真结果表明,所提建模方法能够很好地支持DFIG离网运行模式,实现DFIG由离网到并网的全过程电磁暂态仿真。

考虑站点类型的城市轨道交通接驳方式选择建模与分析

为更精确地揭示出行者对城市轨道交通接驳方式选择的决策机制,将站点类型作为无序多分类变量引入混合Logit模型,以分析出行者接驳方式的选择行为。首先,通过聚类分析获取轨道交通站点类型数据;然后,结合KDTree空间搜索及网络爬虫获得的交通方式特性数据,以及通过RP调查获得的出行者特性数据,建立城市轨道交通接驳方式选择的混合Logit模型;最后,通过敏感性分析探讨不同类型轨道交通站点的接驳特性以及出行者对接驳方式的选择行为。研究结果表明:接驳距离、接驳费用、接驳时长、收入、出行目的、职业、年龄、性别、同行人数、学历以及接驳时间段均与接驳方式的选择显著相关;与中心型城市轨道交通站点相比,出行者在边缘型站点时倾向选择摩托车、公交车、私家车、出租车或网约车接驳,在混合型轨道交通站点倾向选择自行车或公交车接驳,不同站点类型的出行者对接驳方式选择的敏感性存在差异。由此可见,站点类型对站点接驳方式结构具有一定影响,可采取优化中心型站点接驳设施,提高边缘型站点公共交通的可达性,并完善混合型站点非机动接驳方式的基础设施等措施,来满足不同类型站点出行者的需求。

基于分数阶滑模控制的光伏并网模型预测直接功率控制

针对外界扰动情况下的光伏并网模型预测直接功率控制(model predictive direct power control,MPDPC)系统中存在系统抖振、功率跟踪速度慢、并网电流总谐波失真率较高等问题,提出一种改进分数阶滑模电压控制器,该策略在直流侧母线电压外环采用了分数阶微积分理论.首先,构造分数阶非奇异快速终端滑模面函数,削弱系统抖振,提高系统动态性能;然后,构造分数阶双幂次指数趋近律,引入加权积分型增益和饱和函数,有效避免系统在非滑动模态阶段时切换增益的增大,提高系统控制精度;最后,设计新型分数阶电压环控制器并运用于光伏并网系统中.研究结果表明,改进后的分数阶滑模电压控制器能够满足光伏并网MPDPC系统的各项基本需求,抑制系统抖振,提高功率跟踪性能,降低并网电流总谐波失真率,有效解决可再生能源和公共电网电能转化的关键难题,对光伏并网系统高性能控制的理论研究具有重要意义.