Collective stochastic resonance behaviors of two coupled harmonic oscillators driven by dichotomous fluctuating frequency

The collective behaviors of two coupled harmonic oscillators with dichotomous fluctuating frequency are investigated,including stability, synchronization, and stochastic resonance(SR). First, the synchronization condition of the system is obtained. When this condition is satisfied, the mean-field behavior is consistent with any single particle behavior in the system. On this basis, the stability condition and the exact steady-state solution of the system are derived. Comparative analysis shows that, the stability condition is stronger than the synchronization condition, that is to say, when the stability condition is satisfied, the system is both synchronous and stable. Simulation analysis indicates that increasing the coupling strength will reduce the synchronization time. In weak coupling region, there is an optimal coupling strength that maximizes the output amplitude gain(OAG), thus the coupling-induced SR behavior occurs. In strong coupling region, the two particles are bounded as a whole, so that the coupling effect gradually disappears.

Impact of the Intermittency of Photovoltaic Power Plants on the Frequency Management: Case of the Senegalese Electricity Grid

This paper investigates the impact of the intermittency of the photovoltaic (PV) power plants on the electric grid frequency management and the consequences that can occur. To meet these purposes, three years data of the Senegalese grid frequency are used, combined with three PV power plants data since their starting-up. Using these data, we analyzed two days of heavily disturbed operation of the Senegalese grid in order to emphasize the real impact of the presence of PV power plants on the electrical grid. Our study has highlighted that how the intermittency of photovoltaic power plants affects frequency management. It obviously appears that the PV production curves follow the irradiation variations. Instantaneous variations of PV production make it difficult to manage the grid frequency leading to more frequent load shedding as we have shown with the data after the commissioning of the PV power plants. We also estimate the power then energy losses during the load shedding induced by the PV integration on the power grid by comparing a period corresponding to one month before (February 2017) and one month after (February 2018) the integration of variable PV production.

Modified constraint-induced movement therapy enhances cortical plasticity in a rat model of traumatic brain injury:a resting-state functional MRI study

Modified constraint-induced movement therapy(mCIMT)has shown beneficial effects on motor function improvement after brain injury,but the exact mechanism remains unclear.In this study,amplitude of low frequency fluctuation(ALFF)metrics measured by resting-state functional magnetic resonance imaging was obtained to investigate the efficacy and mechanism of mCIMT in a control co rtical impact(CCI)rat model simulating traumatic brain injury.At 3 days after control co rtical impact model establishment,we found that the mean ALFF(mALFF)signals were decreased in the left motor cortex,somatosensory co rtex,insula cortex and the right motor co rtex,and were increased in the right corpus callosum.After 3 weeks of an 8-hour daily mClMT treatment,the mALFF values were significantly increased in the bilateral hemispheres compared with those at 3 days postoperatively.The mALFF signal valu es of left corpus callosum,left somatosensory cortex,right medial prefro ntal cortex,right motor co rtex,left postero dorsal hippocampus,left motor cortex,right corpus callosum,and right somatosensory cortex were increased in the mCIMT group compared with the control cortical impact group.Finally,we identified brain regions with significantly decreased mALFF valu es at 3 days postoperatively.Pearson correlation coefficients with the right forelimb sliding score indicated that the improvement in motor function of the affected upper limb was associated with an increase in mALFF values in these brain regions.Our findings suggest that functional co rtical plasticity changes after brain injury,and that mCIMT is an effective method to improve affected upper limb motor function by promoting bilateral hemispheric co rtical remodeling.mALFF values correlate with behavio ral changes and can potentially be used as biomarkers to assess dynamic cortical plasticity after traumatic brain injury.

CFD simulation of pressure fluctuation characteristics in the gas-solid fluidized bed:Comparisons with experiments

A simple hydrodynamic model based on two-fluid theory, taking into account the effect of discrete particles on both the gas- and solid-phase momentum equations, was used to numerically investigate the pressure fluctuation characteristics in a gas-solid fluidized bed with the aid of CFX 4.4, a commercial CFD software package, by adding user-defined Fortran subroutines. Numerical simulations together with typical experimental measurements show that pressure fluctuations originate above the distributor when a gas pulse is injected into the fluidized bed. The pressure above the bubble gradually increases due to the presence of a rising bubble. When the bubble passes through the bed surface, the pressure near the bed surface gradually decreases to a lower value. Moreover, the pressure signals in the bubbling fluidized beds show obviously periodic characteristics. The major frequency of pressure fluctuations at the same vertical position is affected slightly by the operating gas velocity, and the amplitude of pressure fluctuations is related to both the operating gas velocity and the vertical height. In this study, the influence of the operating gas velocity on the pressure wave propagation velocity can be ignored, and only two peak frequencies in the power spectrum of the pressure fluctuations are observed which are associated with the bubble formation above the distributor and its eruption at the bed surface.

亚洲季风区ITCZ对华北雨季异常的可能影响(英文)

Vast convective activities over tropical zones are analyzed for both wet and dry summers in North China. An ITCZ synthesis index is designed using OLR data. The index can demonstrate quite clearly and objectively the seasonal features of deep convection in Asia monsoon areas. The differences of ITCZ activities in Indian as well as East Asian monsoon regions in winter-spring period are significant and so is the time-lagged correlation, which would be able to provide a new way to the long-lead prediction of summer rain in North China. The propagation characters of low frequency fluctuation are also different between wet and dry years. The intensity of low frequency fluctuation is stronger and the area is larger in wet years than that in dry years in both hemispheres, The fluctuation moves from south to north successively in wet years, which may lead to the leap of the subtropical high northwards, while it remains quasi-stationary in the Southern Hemisphere or the equatorial zone in dry years.

针刺治疗屈光参差性弱视:一项随机对照试验及其潜在起效机制

Objective:To evaluate the effect of acupuncture on anisometropic amblyopia(AA)and explore its potential mechanism for children with AA.Methods:Seventy-six children with monocular AA were randomized into a conventional treatment group and a combined treatment group of acupuncture and conventional treatment,with 38 patients in each group.In the conventional treatment group,on the base of patching regimen,the red flashing,grating and visual stimulation were delivered.Each approach lasted for 5 min per session and was given once every two days,three times a week,for 4 consecutive weeks.In the acupuncture-combined treatment group,on the base of the regimen of conventional treatment group,acupuncture was applied to Jingming(BL1),Cuanzhu(BL2),Fengchi(GB20)and Guangming(GB37),with needles retained for 20 min per session,once every two days,three times of intervention a week and for 4 consecutive weeks.Before and after treatment,the best corrected vision acuity(BCVA)was observed to evaluate the clinical effect in the two groups.Before treatment started,15 patients with AA on left side were randomized selected from each group and the resting-state functional magnetic resonance imaging(rs-fMRI)was operated before and after treatment.Simultaneously,eight healthy children with normal visual acuity were recruited to be the normal control group and received one-time rs-fMRI scanning.Based on the activation likelihood estimation(ALE),the visual"what"pathway network was constructed.By analyzing the amplitude of low frequency fluctuation(ALFF)and the regional homogeneity(ReHo),the differences in the regional autonomous function activities in the key brain areas of the"what"pathway were compared among the three groups.Results:(1)Clinical effect:After treatment,BCVA was(0.6[0.5,0.6]),higher than that(0.4[0.3,0.5])before treatment,presenting the statistical difference(P<0.05)in the conventional treatment group.BCVA was(0.6[0.6,0.8]),higher than that(0.4[0.4,0.5])before treatment,presenting the statistical difference(P<0.05)in the acupuncture-combined treatment group.BCVA in the acupuncture-combined treatment group was higher than that of the conventional treatment group(P<0.05)after treatment.The total effective rate was 86.1%in the acupuncture-combined treatment group,higher than that(65.8%)of the conventional treatment group(P<0.05).(2)Mechanism:(1)ALFF:In comparison with the healthy control group,the ALFF in the primary visual cortex of the"what"pathway for AA children was reduced significantly(P<0.05),and ALFF in the right fusiform gyrus and the right inferior temporal gyrus increased significantly when compared with the healthy children(P<0.05).Compared with that before treatment,there was no significant difference in the brain areas of the"what"pathway after treatment in the conventional treatment group(P>0.05).In the acupuncture-combined treatment group,ALFF in the right inferior occipital gyrus and the right fusiform gyrus of the"what"pathway increased after treatment when compared with that before treatment(P<0.05).After treatment,in comparison with the conventional treatment group,there was no significant difference in the brain areas of"what"pathway in the acupuncture-combined treatment group(P>0.05).(2)ReHo:ReHo in the right inferior occipital gyrus,the right fusiform gyrus and the right inferior temporal gyrus in the"what"pathway was elevated significantly in AA children when compared with that in the healthy control group(P<0.05).ReHo of the left inferior occipital gyrus and the left fusiform gyrus increased significantly after treatment when compared with that before treatment in the conventional treatment group(P<0.05).ReHo of the right inferior occipital gyrus,the left and the right fusiform gyrus increased significantly after treatment when compared with that before treatment in the acupuncture-combined treatment group(P<0.05).After treatment,ReHo of the right inferior temporal gyrus in the"what"pathway in the acupuncture-combined treatment group was significantly higher than that of the conventional treatment group(P<0.05).Conclusion:The acupuncture combined with conventional treatment improves BCVA and the total effective rate of AA children.The changes in the regional function activity of the brain areas within the"what"pathway were dominated by the compensatory increase of the autonomous activity in the occipital lobe(inferior occipital gyrus)and the temporal lobe(inferior temporal gyrus)in AA children.Both conventional treatment and acupuncture can enhance the intensity of autonomous function activities in the occipital lobe(inferior occipital gyrus)and the temporal lobe(fusiform gyrus/inferior temporal gyrus)in the"what"pathway so as to relieve visual impairment.ReHo in the inferior temporal gyrus in the acupuncture-combined treatment group was higher than that of the conventional treatment group and it suggests that the inferior temporal gyrus may be the key brain area to the improvement of visual function in the"what"pathway.

Effects of tube system and data correction for fluctuating pressure test in wind tunnel

The accuracy of fluctuating pressure test in wind tunnel is affected by the tube system. By employing contradistinctive experimental method, systematic study was conducted to investigate the effects of the tube system on fluctuating pressure. The analyzed tube system parameters include tube length, inside diameter, curvature, deflection angle, thickness, material, restrictor length,restrictor inside diameter, and restrictor place. It is found that all the tube system parameters mentioned above except tube curvature have non-negligible effects on fluctuating pressure. Based on the research results, test methods were presented for the fluctuating pressure measurement in low-speed wind tunnel, which can obviously improve the data accuracy but not lose test efficiency. The effectiveness of the method is verified by the wind tunnel test.

Functional MRI study of mild Alzheimer＇s disease using amplitude of low frequency fluctuation analysis

Background Previous studies have shown that the functional brain activity in the resting state is impaired in Alzheimer＇s disease （AD） patients. However, most studies focused on the relationship between different brain areas, rather than the amplitude or strength of the regional brain activity. The purpose of this study was to explore the functional brain changes in AD patients by measuring the amplitude of the blood oxygenation level dependent （BOLD） functional MRI （fMRI） signals.

Impact of Simultaneous Activities on Frequency Fluctuations:Comprehensive Analyses Based on Real Measurement Data from the FNET/GridEye

Simultaneous human activities,such as the Super Bowl game,would cause certain impacts on frequency fluctuations in power systems.With the help of FNET/GridEye measurements,this paper aims to give comprehensive analyses on the frequency fluctuations during Super Bowl LIV held on Feb.2,2020,so as to better understand several phenomena caused by simultaneous activities which will help system operations and controls.First,recent developments of the FNET/GridEye are briefly introduced.Second,the frequency fluctuations of the Eastern Interconnection(El),western electricity coordinating council(WECC),and electric reliability council of Texas(ERCOT)power systems during Super Bowl LIV are analyzed.Third,frequency fluctuations of Super Bowl Sunday and ordinary Sundays in 2020 are compared.Finally,the differences of frequency fluctuations among different years during the Super Bowl and their change trends are also given.Furthermore,several possible explanations,including the simultaneity of electricity consumption at the beginning of commercial breaks and the halftime show,the increasing usage of the Internet,and the increasing size of TV screens,are illustrated in detail in this paper.

Experimental study for frequency spectrum of turbulent boundary layer pressure fluctuation

An experimental study on TBL (turbulent boundary layer) pressure fluctuation frequeny spectrum of a revolution body is presented. With the measured results, a relation of convective frequency fo of the models is obtained. Relations of turbuleat wall-pressure fluctuation spectrum in transition region and development region to frequency and speed are obtained also

基于静息态功能磁共振低频振幅比率分析针刺与艾灸功能性消化不良患者足三里穴的脑功能响应差异

Objective:To explore the differences in the central response after acupuncture and moxibusbution at Zusanli(足三里ST36) in treatment of functional dyspepsia(FD) based on the analysis of fractional amplitude of low frequency fluctuation(fALFF) of resting-state functional magnetic resonance imaging(rfMRI).Methods:A total of 60 patients with FD were randomized into an acupuncture group and a moxibustion group,30 cases in each one.In the acupuncture group,acupuncture was applied to bilateral ST36.In the moxibustion group,moxibustion was exerted at bilateral ST36.The treatment was given once a day,5 times a week,totally for 4 weeks in each group,including 20 treatments with acupuncture or moxibustion.Separately,before and at the end of treatment,rfMRI scanning was conducted in two groups.Using data processing assistant for resting-state fMRI(DPARSF) software and MATLAB data platform,rfMRI data were collected for preprocessing and fALFF analysis.Results:Compared with the data before treatment,after treated with acupuncture at ST36 in FD patients,fALFF value was reduced in the right superior frontal gyrus,left superior frontal gyrus,left inferior frontal gyrus,right cuneus,left precuneus,right middle occipital gyrus,left middle occipital gyrus,etc.,and it was increased in the left parahippocampus,right parahippocampus,left cerebellum,etc(all P <0.01).After treated with moxibustion,the remarkable increase of fALFF was not discovered in brain areas,but fALFF decreased significantly in the left superior parietal gyrus(P <0.01).Compared with moxibustion at ST36,after acupuncture at ST36 in FD patients,the increase of fALFF appeared in the right putamen and the decrease of it occurred in the middle occipital gyrus,indicating the statistical significance(both P <0.05).Conclusion:The differences in central function responses are induced in treamtent with acupuncture and moxibustion,which is probably related to the resting-state default network associated with targeted regulation and ventral attention of brain areas in functional dyspepsia.

Does hydrological fluctuation alter impacts of species richness on biomass in wetland plant communities?

Aims The diversity-productivity relationship is one of the most critical questions in ecology and can be altered by environmental factors.Hydrological fluctuation affects growth of wetland plants,and such effects vary with plant species.Therefore,we hypothesized that hydrological fluctuation changes effects of species richness on productivity of wetland plant communities.Methods We constructed wetland plant communities consisting of three or six wetland plant species and subjected them to hydrological fluctuation(i.e.gradually changing water level)of two frequencies and two ranges,with unchanged water level as the control.We measured height,root and shoot dry mass of each plant at harvest.Important Findings Hydrological fluctuation significantly decreased biomass of wetland plant communities,which was due to impacts of fluctuation range,but not those of fluctuation frequency.Community biomass was significantly higher when species richness was higher,and such an effect did not depend on hydrological fluctuation.Therefore,hydrological fluctuation can decrease the productivity of wetland plant communities but may not alter the diversity-productivity relationship.

Runner cone optimization to reduce vortex rope-induced pressure fluctuations in a Francis turbine

Pressure fluctuations induced by a vortex rope are the major causes of hydraulic turbine vibration in partial load operating conditions. Hence, an effective control strategy should be adopted to improve rotating characteristics of the vortex rope and reduce the corresponding pressure fluctuation. In this study, two new types of runner cones(i.e., abnormally shaped and long straight cones) were proposed to optimize the pressure distribution in the draft tube, and unsteady numerical simulations were performed to determine their mechanism of action. Numerical results were validated using flow observation and pressure fluctuation experiments. Detailed analyses were conducted to understand the effects of the helical vortex rope operating conditions. The results indicated that pressure fluctuations in the draft tube at partial load operation result primarily from low frequency fluctuations induced by the rotation of the helical vortex rope, whose amplitudes are related to the rotating radius of the helical vortex rope. Both runner cone types could effectively reduce the pressure-fluctuation amplitude. The long straight type could reduce the amplitude of low-frequency fluctuation induced by vortex rope to a maximum of 74.08% and the abnormalshape type to 38.31%. Thus, the effective optimization of the runner cone can potentially reduce pressure-fluctuation amplitudes.Our research findings were applied to a real hydraulic plant in China.

Dynamic characteristics of bubbling fluidization through recurrence rate analysis of pressure fluctuations

Pressure fluctuations signals of a lab-scale fiuidized bed （15 cm inner diameter and 2 m height） at different superficial gas velocities were measured. Recurrence plot （RP） and recurrence rate （RR）, and the simplest variable of recurrence quantification analysis （RQA） were used to analyze the pressure signals. Different patterns observed in RP reflect different dynamic behavior of the system under study. It was also found that the variance of RR （a2R） Could reveal the peak dominant frequencies （PDF） of different dynamic systems： completely periodic, completely stochastic, Lorenz system, and fluidized bed. The results were compared with power spectral density. Additionally, the diagram of σ^2RR provides a new technique for prediction of transition velocity from bubbling to turbulent fluidization regime.

Fluidization stability and periodic fluctuations in gas–solid separation fluidized bed using Geldart A dense medium

Gas–solid separation fluidized bed is a typical method for coal separation without water utilization.Geldart A particles is also considered as the ideal dense medium to strengthen separation efficiency.Fluidization stability reflects the bed pressure fluctuations and the distribution of bubble and emulsion phases,affecting the separation performance.And the main frequency of pressure fluctuations can directly reflect the degree of pressure fluctuations.Therefore,the detailed fluidization stability is analyzed combined the method of standard deviation of pressure fluctuations,power spectral density,etc.,for Geldart A particles.The results showed that maintaining an appropriate gas velocity resulted in an average bed pressure of around 2000 Pa.The main frequency is mainly concentrated around 1–1.5 Hz.Finally,a prediction model of the main frequency of pressure fluctuations is established,and the error can be controlled within±0.15.The investigation further proved the stable fluidization of Geldart A particles and provides a method for predicting the main frequency of pressure fluctuations in the gas–solid separation fluidized bed.