Objective To examine whether the selectivity of visual cortical neurons to stimulus spatial frequencies would be affected by aging in cats.Methods In vivo extracellular single-unit recording techniques were employed t...Objective To examine whether the selectivity of visual cortical neurons to stimulus spatial frequencies would be affected by aging in cats.Methods In vivo extracellular single-unit recording techniques were employed to record the tuning responses of V1 neurons to different stimulus spatial frequencies in old and young adult cats.Results Statistical analysis showed that the mean optimal spatial frequency of grating stimuli that evoked the maximal response of V1 neurons in old cats was significantly lower than that in young adult cats.Furthermore,the mean high cut-off spatial frequency of grating stimuli that evoked the half amplitude of the maximal response of V1 neurons in old cats was also significantly lower than that in young adult cats.Conclusion These results are consistent with those reported in the V1 of old monkeys,suggesting that the age-related decline in the selectivity of visual cortical cells to spatial frequency could be generalized to all mammalian species and might contribute to visual acuity reduction in senescent individuals.展开更多
目的采用低频振幅(amplitude of low frequency fluctuation,ALFF)初步探索轻度认知障碍(mild cognitive impairment,MCI)患者言语流畅性下降的脑机制。材料与方法前瞻性纳入20例MCI患者(MCI组)及16例性别、年龄、受教育程度相匹配的健...目的采用低频振幅(amplitude of low frequency fluctuation,ALFF)初步探索轻度认知障碍(mild cognitive impairment,MCI)患者言语流畅性下降的脑机制。材料与方法前瞻性纳入20例MCI患者(MCI组)及16例性别、年龄、受教育程度相匹配的健康人作为对照组(健康对照组),入组前分别采集两组临床资料、神经心理学量表和静息态功能磁共振(resting-state functional magnetic resonance,rs-fMRI)数据。采取ALFF分析方法,比较MCI组与健康对照组静息态脑功能差异,并进一步采用Spearman相关分析分别观察ALFF变化的脑区与言语流畅性测试量表的相关性。结果与健康对照组比较,MCI组患者右侧岛叶/颞上回ALFF降低(高斯随机场校正,voxel P<0.005,cluster P<0.05)。未发现ALFF升高脑区。降低的ALFF值与蒙特利尔认知量表基础版的流畅性测试有显著的正相关性(r_(s)=0.500,P=0.025)。结论MCI存在右侧岛叶/颞上回大脑活动降低,可能是患者言语流畅性下降的原因。展开更多
There is no common accepted way for calculating the valve power loss of modular multilevel converter(MMC).Valve power loss estimation based on analytical calculation is inaccurate to address the switching power loss a...There is no common accepted way for calculating the valve power loss of modular multilevel converter(MMC).Valve power loss estimation based on analytical calculation is inaccurate to address the switching power loss and valve power loss estimation based on detailed electro-magnetic simulation is of low speed.To solve this problem,a method of valve power loss estimation based on the detailed equivalent simulation model of MMC is proposed.Results of valve power loss analysis of 201-level 500MW MMC operating at 50Hz~1000Hz are presented.It is seen that the valve power loss of a MMC increased by 12,40 and 93%under 200Hz,500Hz and 1000Hz operating frequency.The article concludes that in a device with isolated inner AC system,MMC operating at higher frequency will be more competitive than typical 50Hz/60Hz MMC with moderate increase of operating power loss and significant reduction of the size of the AC components.展开更多
基金supported by Natural Science Foundation of Anhui Province(No. 070413138)the Key Research Foundation of Education Department of Anhui Province,China(No. KJ2009A167)
文摘Objective To examine whether the selectivity of visual cortical neurons to stimulus spatial frequencies would be affected by aging in cats.Methods In vivo extracellular single-unit recording techniques were employed to record the tuning responses of V1 neurons to different stimulus spatial frequencies in old and young adult cats.Results Statistical analysis showed that the mean optimal spatial frequency of grating stimuli that evoked the maximal response of V1 neurons in old cats was significantly lower than that in young adult cats.Furthermore,the mean high cut-off spatial frequency of grating stimuli that evoked the half amplitude of the maximal response of V1 neurons in old cats was also significantly lower than that in young adult cats.Conclusion These results are consistent with those reported in the V1 of old monkeys,suggesting that the age-related decline in the selectivity of visual cortical cells to spatial frequency could be generalized to all mammalian species and might contribute to visual acuity reduction in senescent individuals.
文摘目的采用低频振幅(amplitude of low frequency fluctuation,ALFF)初步探索轻度认知障碍(mild cognitive impairment,MCI)患者言语流畅性下降的脑机制。材料与方法前瞻性纳入20例MCI患者(MCI组)及16例性别、年龄、受教育程度相匹配的健康人作为对照组(健康对照组),入组前分别采集两组临床资料、神经心理学量表和静息态功能磁共振(resting-state functional magnetic resonance,rs-fMRI)数据。采取ALFF分析方法,比较MCI组与健康对照组静息态脑功能差异,并进一步采用Spearman相关分析分别观察ALFF变化的脑区与言语流畅性测试量表的相关性。结果与健康对照组比较,MCI组患者右侧岛叶/颞上回ALFF降低(高斯随机场校正,voxel P<0.005,cluster P<0.05)。未发现ALFF升高脑区。降低的ALFF值与蒙特利尔认知量表基础版的流畅性测试有显著的正相关性(r_(s)=0.500,P=0.025)。结论MCI存在右侧岛叶/颞上回大脑活动降低,可能是患者言语流畅性下降的原因。
基金supported by the PowerChina Hubei Electric Engineering Corporation。
文摘There is no common accepted way for calculating the valve power loss of modular multilevel converter(MMC).Valve power loss estimation based on analytical calculation is inaccurate to address the switching power loss and valve power loss estimation based on detailed electro-magnetic simulation is of low speed.To solve this problem,a method of valve power loss estimation based on the detailed equivalent simulation model of MMC is proposed.Results of valve power loss analysis of 201-level 500MW MMC operating at 50Hz~1000Hz are presented.It is seen that the valve power loss of a MMC increased by 12,40 and 93%under 200Hz,500Hz and 1000Hz operating frequency.The article concludes that in a device with isolated inner AC system,MMC operating at higher frequency will be more competitive than typical 50Hz/60Hz MMC with moderate increase of operating power loss and significant reduction of the size of the AC components.
