For the planning,operation and control of multiterminal voltage source converter(VSC)based high-voltage direct current(HVDC)(VSC-MTDC)systems,an accurate power flow formulation is a key starting point.Conventional pow...For the planning,operation and control of multiterminal voltage source converter(VSC)based high-voltage direct current(HVDC)(VSC-MTDC)systems,an accurate power flow formulation is a key starting point.Conventional power flow formulations assume the constant frequencies for all asynchronous AC systems.Therefore,a new feature about the complex coupling relations between AC frequencies,DC voltages and the exchanged power via VSC stations cannot be characterized if VSC-MTDC systems are required to provide cross-regional frequency responses.To address this issue,this paper proposes a comprehensive frequency-dependent power flow formulation.The proposed approach takes the frequencies of asynchronous AC systems as explicit variables,and investigates the novel bus models of the interlinking buses of VSC stations.The proposed approach accommodates different operation modes and frequency droop strategies of VSC stations,and considers the power losses of VSC stations.The effectiveness and generality of the developed approach are validated by a 6-terminal VSC-HVDC test system.The test system presents the characteristics of the coexistence of numerous VSC operation modes,the absence of slack buses in both AC and DC subsystems,and diversified grid configurations such as point-to-point integration of renewable energy sources and one AC system integrated with multiple VSC stations.展开更多
BACKGROUND Major depression disorder(MDD)constitutes a significant mental health concern.Epidemiological surveys indicate that the lifetime prevalence of depression in adolescents is much higher than that in adults,wi...BACKGROUND Major depression disorder(MDD)constitutes a significant mental health concern.Epidemiological surveys indicate that the lifetime prevalence of depression in adolescents is much higher than that in adults,with a corresponding increased risk of suicide.In studying brain dysfunction associated with MDD in adolescents,research on brain white matter(WM)is sparse.Some researchers even mistakenly regard the signals generated by the WM as noise points.In fact,studies have shown that WM exhibits similar blood oxygen level-dependent signal fluctuations.The alterations in WM signals and their relationship with disease severity in adolescents with MDD remain unclear.AIM To explore potential abnormalities in WM functional signals in adolescents with MDD.METHODS This study involved 48 adolescent patients with MDD and 31 healthy controls(HC).All participants were assessed using the Patient Health Questionnaire-9 Scale and the mini international neuropsychiatric interview(MINI)suicide inventory.In addition,a Siemens Skyra 3.0T magnetic resonance scanner was used to obtain the subjects'image data.The DPABI software was utilized to calculate the WM signal of the fractional amplitude of low frequency fluctuations(fALFF)and regional homogeneity,followed by a two-sample t-test between the MDD and HC groups.Independent component analysis(ICA)was also used to evaluate the WM functional signal.Pearson’s correlation was performed to assess the relationship between statistical test results and clinical scales.RESULTS Compared to HC,individuals with MDD demonstrated a decrease in the fALFF of WM in the corpus callosum body,left posterior limb of the internal capsule,right superior corona radiata,and bilateral posterior corona radiata[P<0.001,family-wise error(FWE)voxel correction].The regional homogeneity of WM increased in the right posterior limb of internal capsule and left superior corona radiata,and decreased in the left superior longitudinal fasciculus(P<0.001,FWE voxel correction).The ICA results of WM overlapped with t展开更多
Although many functional magnetic resonance imaging(f MRI) studies have investigated the neurophysiology of attention deficit hyperactivity disorder(ADHD),the existing studies have not yielded consistent findings.This...Although many functional magnetic resonance imaging(f MRI) studies have investigated the neurophysiology of attention deficit hyperactivity disorder(ADHD),the existing studies have not yielded consistent findings.This may be related to the different properties of different frequency bands. To investigate the frequency-specific regional homogeneity(Re Ho) of spontaneous neural activities in ADHD, the current study used resting-state f MRI to explore the Re Ho properties of five frequency bands, slow-5(0.01–0.027 Hz), slow-4(0.027–0.073 Hz),slow-3(0.073–0.198 Hz), slow-2(0.198–0.25 Hz) and the extra-low frequency(0–0.01 Hz), in 30 drug-naive boys with ADHD and 30 healthy controls. Compared with controls, the ADHD group showed decreased Re Ho in the default mode network(DMN) including the medial prefrontal cortex and precuneus, middle frontal gyrus and angular gyrus. ADHD patients also showed increased Re Ho in the posterior cerebellum. Significant interactions between frequency band and group were observed predominantly in the dorsolateral prefrontal and parietal cortices, orbital frontal cortex, supplementary motor area,inferior occipital gyrus, thalamus and anterior cerebellum.In particular, we found that the between-group difference in the extra-low frequency band(0–0.01 Hz) seemed to be greater than that in the other frequency bands for most brain regions. The findings suggest that ADHD children display widespread abnormalities in regional brain activity,particularly in the DMN and attention network, and these abnormalities show frequency specificity.展开更多
基金supported by the National Key Research and Development Program of China(No.2017YFB0902200)National Natural Science Foundation of China(No.U1766201)State Grid Technology Project(No.SGGSKY00FJJS1600209)。
文摘For the planning,operation and control of multiterminal voltage source converter(VSC)based high-voltage direct current(HVDC)(VSC-MTDC)systems,an accurate power flow formulation is a key starting point.Conventional power flow formulations assume the constant frequencies for all asynchronous AC systems.Therefore,a new feature about the complex coupling relations between AC frequencies,DC voltages and the exchanged power via VSC stations cannot be characterized if VSC-MTDC systems are required to provide cross-regional frequency responses.To address this issue,this paper proposes a comprehensive frequency-dependent power flow formulation.The proposed approach takes the frequencies of asynchronous AC systems as explicit variables,and investigates the novel bus models of the interlinking buses of VSC stations.The proposed approach accommodates different operation modes and frequency droop strategies of VSC stations,and considers the power losses of VSC stations.The effectiveness and generality of the developed approach are validated by a 6-terminal VSC-HVDC test system.The test system presents the characteristics of the coexistence of numerous VSC operation modes,the absence of slack buses in both AC and DC subsystems,and diversified grid configurations such as point-to-point integration of renewable energy sources and one AC system integrated with multiple VSC stations.
基金Supported by the Suzhou Clinical Medical Center for Mood Disorders,No.Szlcyxzx202109Jiangsu Provincial Department of Science and Technology for Social Development-General Project,No.BE2022735.
文摘BACKGROUND Major depression disorder(MDD)constitutes a significant mental health concern.Epidemiological surveys indicate that the lifetime prevalence of depression in adolescents is much higher than that in adults,with a corresponding increased risk of suicide.In studying brain dysfunction associated with MDD in adolescents,research on brain white matter(WM)is sparse.Some researchers even mistakenly regard the signals generated by the WM as noise points.In fact,studies have shown that WM exhibits similar blood oxygen level-dependent signal fluctuations.The alterations in WM signals and their relationship with disease severity in adolescents with MDD remain unclear.AIM To explore potential abnormalities in WM functional signals in adolescents with MDD.METHODS This study involved 48 adolescent patients with MDD and 31 healthy controls(HC).All participants were assessed using the Patient Health Questionnaire-9 Scale and the mini international neuropsychiatric interview(MINI)suicide inventory.In addition,a Siemens Skyra 3.0T magnetic resonance scanner was used to obtain the subjects'image data.The DPABI software was utilized to calculate the WM signal of the fractional amplitude of low frequency fluctuations(fALFF)and regional homogeneity,followed by a two-sample t-test between the MDD and HC groups.Independent component analysis(ICA)was also used to evaluate the WM functional signal.Pearson’s correlation was performed to assess the relationship between statistical test results and clinical scales.RESULTS Compared to HC,individuals with MDD demonstrated a decrease in the fALFF of WM in the corpus callosum body,left posterior limb of the internal capsule,right superior corona radiata,and bilateral posterior corona radiata[P<0.001,family-wise error(FWE)voxel correction].The regional homogeneity of WM increased in the right posterior limb of internal capsule and left superior corona radiata,and decreased in the left superior longitudinal fasciculus(P<0.001,FWE voxel correction).The ICA results of WM overlapped with t
基金supported by the National Basic Research Development Program of China(2014CB846104)the National Natural Science Foundation of China(81371496+3 种基金3097080281101014)the Program for New Century Excellent Talents in University(NCET-11-0013)supported by the‘‘Qian Jiang Distinguished Professor’’Program
文摘Although many functional magnetic resonance imaging(f MRI) studies have investigated the neurophysiology of attention deficit hyperactivity disorder(ADHD),the existing studies have not yielded consistent findings.This may be related to the different properties of different frequency bands. To investigate the frequency-specific regional homogeneity(Re Ho) of spontaneous neural activities in ADHD, the current study used resting-state f MRI to explore the Re Ho properties of five frequency bands, slow-5(0.01–0.027 Hz), slow-4(0.027–0.073 Hz),slow-3(0.073–0.198 Hz), slow-2(0.198–0.25 Hz) and the extra-low frequency(0–0.01 Hz), in 30 drug-naive boys with ADHD and 30 healthy controls. Compared with controls, the ADHD group showed decreased Re Ho in the default mode network(DMN) including the medial prefrontal cortex and precuneus, middle frontal gyrus and angular gyrus. ADHD patients also showed increased Re Ho in the posterior cerebellum. Significant interactions between frequency band and group were observed predominantly in the dorsolateral prefrontal and parietal cortices, orbital frontal cortex, supplementary motor area,inferior occipital gyrus, thalamus and anterior cerebellum.In particular, we found that the between-group difference in the extra-low frequency band(0–0.01 Hz) seemed to be greater than that in the other frequency bands for most brain regions. The findings suggest that ADHD children display widespread abnormalities in regional brain activity,particularly in the DMN and attention network, and these abnormalities show frequency specificity.
