We present an experimental method to obtain neutral beam injection （NBI） power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission effi...We present an experimental method to obtain neutral beam injection （NBI） power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission efficiency, the neutralization efficiency and so on. With the empirical scaling laws, the estimating power can be obtained in every shot of experiment on time, therefore the important parameters such as the energy confinement time can be obtained precisely. The simulation results by the tokamak simulation code （TSC） show that the evolution of the plasma parameters is in good agreement with the experimental results by using the NBI power from the empirical scaling law.展开更多
We calculated a self-thinning exponent of 1.05 for tree mass using the 3/2 power equation in 93 Cunninghamia lanceolata plots.According to Weller’s allometric model,the self-thinning exponent for tree mass was calcul...We calculated a self-thinning exponent of 1.05 for tree mass using the 3/2 power equation in 93 Cunninghamia lanceolata plots.According to Weller’s allometric model,the self-thinning exponent for tree mass was calculated as 1.28 from the allometric exponents h and d.The both self-thinning exponents were significantly lower than 3/2.The self-thinning exponent of organs was estimated to be 1.42 for stems,0.93 for branches,0.96 for leaves,1.35 for roots and 1.28 for shoots,respectively.The self-thinning exponent of stem mass was not significantly different from 3/2,whereas thinning exponents of trees,branches,leaves and roots were significantly lower than 3/2.The stand leaf mass and stand branch mass were constant regardless of the stand density.The scaling relations among branch,leaf,stem,root and shoot mass（MB,ML,MS,MR and MA,respectively） showed that MB and ML scaled as the3/4 power of MS,whereas MS or MA scaled isometrically with respect to MR.展开更多
To listen to brain activity as a piece of music,we previously proposed scale-free brainwave music（SFBM）technology,which translated the scalp electroencephalogram（EEG）into musical notes according to the power law o...To listen to brain activity as a piece of music,we previously proposed scale-free brainwave music（SFBM）technology,which translated the scalp electroencephalogram（EEG）into musical notes according to the power law of both the EEG and music.In this study,the methodology was further extended to ensemble music on two channels from the two hemispheres.EEG data from two channels symmetrically located on the left and right hemispheres were translated into MIDI sequences by SFBM,and the EEG parameters modulated the pitch,duration and volume of each note.Then,the two sequences were filtered into an ensemble with two voices：the pentatonic scale（traditional Chinese music）or the heptatonic scale（standard Western music）.We demonstrated differences in harmony between the two scales generated at different sleep stages,with the pentatonic scale being more harmonious.The harmony intervals of this brain ensemble at various sleep stages followed the power law.Compared with the heptatonic scale,it was easier to distinguish the different stages using the pentatonic scale.These results suggested that the hemispheric ensemble can represent brain activity by variations in pitch,tempo and harmony.The ensemble with the pentatonic scale sounds more consonant,and partially reflects the relations of the two hemispheres.This can be used to distinguish the different states of brain activity and provide a new perspective on EEG analysis.展开更多
Electric power infrastructure has recently undergone a comprehensive transformation from electromagnetics to semiconductors. Such a development is attributed to the rapid growth of power electronic converter applicati...Electric power infrastructure has recently undergone a comprehensive transformation from electromagnetics to semiconductors. Such a development is attributed to the rapid growth of power electronic converter applications in the load side to realize energy conservation and on the supply side for renewable generations and power transmissions using high voltage direct current transmission. This transformation has altered the fundamental mechanism of power system dynamics, which demands the establishment of a new theory for power system control and protection. This paper presents thoughts on a theoretical framework for the coming semiconducting power systems.展开更多
Induced loss at 633 nm is tested in Yb3＋∕Al3＋co-doped silica fiber by a core pumped with a 974 nm laser and probed with a 633 nm laser. The fiber is prepared by the modified chemical vapor deposition method combine...Induced loss at 633 nm is tested in Yb3＋∕Al3＋co-doped silica fiber by a core pumped with a 974 nm laser and probed with a 633 nm laser. The fiber is prepared by the modified chemical vapor deposition method combined with solution doping. Different power scales of pump light and probe light are used in the tests. It is found that there is a dynamic equilibrium between photobleaching induced by 633 nm probe light and photodarkening（PD）induced by 974 nm pump light. For the first time to our knowledge, the effect of 633 nm probe laser power on an induced loss test of Yb3＋∕Al3＋co-doped silica fiber is studied quantitatively. It suggests that as long as the633 nm probe light power is less than 0.2 m W, the induced loss is mainly contributed by the PD effect of pumping light, and the deviation of induced loss is less than 5%.展开更多
Transverse mode instability(TMI),induced by nonlinear thermal-optical coupling,poses a primary challenge for the power scaling of fiber lasers.In the fiber oscillator,a sealed resonant cavity,TMI could become particul...Transverse mode instability(TMI),induced by nonlinear thermal-optical coupling,poses a primary challenge for the power scaling of fiber lasers.In the fiber oscillator,a sealed resonant cavity,TMI could become particularly complex due to the mode competition during the laser oscillation.While traditional theories of TMI predominantly address two-mode coupling,this paper explores the TMI phenomena in few-mode fiber oscillators utilizing a holistic approach that includes solving steady-state thermal-optic coupling equations.The simulation shows that there is a non-monotonic correlation between bending loss and the TMI threshold,which is contrary to the monotonic associations suggested by two-mode interaction theory.When one high-order mode experiences net gain,fluctuations of the TMI threshold would occur,leading to the amplification of a new mode within the uncoupled frequency region,thus affecting the gain saturation.By designing the linewidth of a low-reflection grating(LR),the modal power management in the uncoupled frequency domain can be achieved.An excessively broad LR linewidth exacerbates mode coupling within the shared frequency region,thus exacerbating TMI.To validate the theoretical simulation,we carefully fabricated LRs and optimized the fiber coiling to elevate the TMI threshold.Through careful optimization of LR linewidth and bending radii,we achieved a record-breaking laser output of 10.07kW using a monolithic fiber oscillator,with no observable evidence of TMI.Our work demonstrates that modal power redistribution in independent frequency domains offers a novel approach to mitigating TMI in high-power fiber lasers.Additionally,it provides new insights into mode decoupling strategies pertinent to fiber communications.展开更多
An ultrafast fiber laser system comprising two coherently combined amplifier channels is reported.Within this system,each channel incorporates a rod-type fiber power amplifier,with individual operations reaching appro...An ultrafast fiber laser system comprising two coherently combined amplifier channels is reported.Within this system,each channel incorporates a rod-type fiber power amplifier,with individual operations reaching approximately 233 W.The active-locking of these coherently combined channels,followed by compression using gratings,yields an output with a pulse energy of 504μJ and an average power of 403 W.Exceptional stability is maintained,with a 0.3%root mean square(RMS)deviation and a beam quality factor M^(2)<1.2.Notably,precise dispersion management of the front-end seed light effectively compensates for the accumulated high-order dispersion in subsequent amplification stages.This strategic approach results in a significant reduction in the final output pulse duration for the coherently combined laser beam,reducing it from 488 to 260 fs after the gratings compressor,while concurrently enhancing the energy of the primary peak from 65%to 92%.展开更多
This article investigates the significant performances of orthogonal frequency division multiplexing （OFDM）-based dual-hop system in the presence of phase noise （PN）. A scenario with Rayleigh fading statistics on ...This article investigates the significant performances of orthogonal frequency division multiplexing （OFDM）-based dual-hop system in the presence of phase noise （PN）. A scenario with Rayleigh fading statistics on both hops is assumed. Amplification factor for this amplify-and-forward （AF） relay networks system is divided into two conditions, average power scaling （APS） and instantaneous power scaling （IPS）. Before deriving signal-to-noise ratios （SNR） under APS and IPS, the Gaussianity of intercarrier interference （ICI） is proved firstly. The accurate closed-form expressions of end-to-end SNR cumulative distribution functions （CDF） and probability density functions （PDF） for both cases are obtained later. With the help of moment generating functions （MGF）, we have closed-form asymptotic expressions of bit error rate （BER）, which show that the BER of system in the presence of PN cannot exceed a fixed level even when SNR in high regime. Finally, simulations verify accuracy of the results. Conclusion analysis will provide a useful help in future application of the system.展开更多
We analyzed the number of cumulative positive cases of COVID-19 as a function of time in countries around the World.We tracked the increase in cases from the onset of the pandemic in each region for up to 150 days.We ...We analyzed the number of cumulative positive cases of COVID-19 as a function of time in countries around the World.We tracked the increase in cases from the onset of the pandemic in each region for up to 150 days.We found that in 81 out of 146 regions the trajectory was described with a power-law function for up to 30 days.We also detected scale-free properties in the majority of sub-regions in Australia,Canada,China,and the United States(US).We developed an allometric model that was capable of fitting the initial phase of the pandemic and was the best predictor for the propagation of the illness for up to 100 days.We then determined that the power-law COVID-19 exponent correlated with measurements of human mobility.The COVID-19 exponent correlated with the magnitude of air passengers per country.This correlation persisted when we analyzed the number of air passengers per US states,and even per US metropolitan areas.Furthermore,the COVID19 exponent correlated with the number of vehicle miles traveled in the US.Together,air and vehicular travel explained 70%of the variability of the COVID-19 exponent.Taken together,our results suggest that the scale-free propagation of the virus is present at multiple geographical scales and is correlated with human mobility.We conclude that models of disease transmission should integrate scale-free dynamics as part of the modeling strategy and not only as an emergent phenomenological property.展开更多
文摘We present an experimental method to obtain neutral beam injection （NBI） power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission efficiency, the neutralization efficiency and so on. With the empirical scaling laws, the estimating power can be obtained in every shot of experiment on time, therefore the important parameters such as the energy confinement time can be obtained precisely. The simulation results by the tokamak simulation code （TSC） show that the evolution of the plasma parameters is in good agreement with the experimental results by using the NBI power from the empirical scaling law.
基金supported by Foundation of Guangdong Forestry Bureau (Nos.4400-F11031,4400-F11055)
文摘We calculated a self-thinning exponent of 1.05 for tree mass using the 3/2 power equation in 93 Cunninghamia lanceolata plots.According to Weller’s allometric model,the self-thinning exponent for tree mass was calculated as 1.28 from the allometric exponents h and d.The both self-thinning exponents were significantly lower than 3/2.The self-thinning exponent of organs was estimated to be 1.42 for stems,0.93 for branches,0.96 for leaves,1.35 for roots and 1.28 for shoots,respectively.The self-thinning exponent of stem mass was not significantly different from 3/2,whereas thinning exponents of trees,branches,leaves and roots were significantly lower than 3/2.The stand leaf mass and stand branch mass were constant regardless of the stand density.The scaling relations among branch,leaf,stem,root and shoot mass（MB,ML,MS,MR and MA,respectively） showed that MB and ML scaled as the3/4 power of MS,whereas MS or MA scaled isometrically with respect to MR.
基金supported by the National Natural Science Foundation of China(81201159,90820301 and 60835005)the Fundamental Research Funds for the Central Universitiesthe Neuro Information ‘111’ project,China
文摘To listen to brain activity as a piece of music,we previously proposed scale-free brainwave music（SFBM）technology,which translated the scalp electroencephalogram（EEG）into musical notes according to the power law of both the EEG and music.In this study,the methodology was further extended to ensemble music on two channels from the two hemispheres.EEG data from two channels symmetrically located on the left and right hemispheres were translated into MIDI sequences by SFBM,and the EEG parameters modulated the pitch,duration and volume of each note.Then,the two sequences were filtered into an ensemble with two voices：the pentatonic scale（traditional Chinese music）or the heptatonic scale（standard Western music）.We demonstrated differences in harmony between the two scales generated at different sleep stages,with the pentatonic scale being more harmonious.The harmony intervals of this brain ensemble at various sleep stages followed the power law.Compared with the heptatonic scale,it was easier to distinguish the different stages using the pentatonic scale.These results suggested that the hemispheric ensemble can represent brain activity by variations in pitch,tempo and harmony.The ensemble with the pentatonic scale sounds more consonant,and partially reflects the relations of the two hemispheres.This can be used to distinguish the different states of brain activity and provide a new perspective on EEG analysis.
基金This work was supported in part by the National Basic Research Program of China （973 Program） （Grant No. 2012CB215100）, and the Major Program of the National Natural Science Foundation of China （Grant No. 51190104）.
文摘Electric power infrastructure has recently undergone a comprehensive transformation from electromagnetics to semiconductors. Such a development is attributed to the rapid growth of power electronic converter applications in the load side to realize energy conservation and on the supply side for renewable generations and power transmissions using high voltage direct current transmission. This transformation has altered the fundamental mechanism of power system dynamics, which demands the establishment of a new theory for power system control and protection. This paper presents thoughts on a theoretical framework for the coming semiconducting power systems.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(No.61405215)the Youth Innovation Promotion Associationthe Special Program for Advanced Electronic Materials of the Ministry of Science and Technology,China(No.2016YFB0402201)
文摘Induced loss at 633 nm is tested in Yb3＋∕Al3＋co-doped silica fiber by a core pumped with a 974 nm laser and probed with a 633 nm laser. The fiber is prepared by the modified chemical vapor deposition method combined with solution doping. Different power scales of pump light and probe light are used in the tests. It is found that there is a dynamic equilibrium between photobleaching induced by 633 nm probe light and photodarkening（PD）induced by 974 nm pump light. For the first time to our knowledge, the effect of 633 nm probe laser power on an induced loss test of Yb3＋∕Al3＋co-doped silica fiber is studied quantitatively. It suggests that as long as the633 nm probe light power is less than 0.2 m W, the induced loss is mainly contributed by the PD effect of pumping light, and the deviation of induced loss is less than 5%.
基金support from the National Natural Science Foundation of China(NSFC)(62405373,11974427)the Science and Technology Innovation Program of Hunan Province(2021RC4027).
文摘Transverse mode instability(TMI),induced by nonlinear thermal-optical coupling,poses a primary challenge for the power scaling of fiber lasers.In the fiber oscillator,a sealed resonant cavity,TMI could become particularly complex due to the mode competition during the laser oscillation.While traditional theories of TMI predominantly address two-mode coupling,this paper explores the TMI phenomena in few-mode fiber oscillators utilizing a holistic approach that includes solving steady-state thermal-optic coupling equations.The simulation shows that there is a non-monotonic correlation between bending loss and the TMI threshold,which is contrary to the monotonic associations suggested by two-mode interaction theory.When one high-order mode experiences net gain,fluctuations of the TMI threshold would occur,leading to the amplification of a new mode within the uncoupled frequency region,thus affecting the gain saturation.By designing the linewidth of a low-reflection grating(LR),the modal power management in the uncoupled frequency domain can be achieved.An excessively broad LR linewidth exacerbates mode coupling within the shared frequency region,thus exacerbating TMI.To validate the theoretical simulation,we carefully fabricated LRs and optimized the fiber coiling to elevate the TMI threshold.Through careful optimization of LR linewidth and bending radii,we achieved a record-breaking laser output of 10.07kW using a monolithic fiber oscillator,with no observable evidence of TMI.Our work demonstrates that modal power redistribution in independent frequency domains offers a novel approach to mitigating TMI in high-power fiber lasers.Additionally,it provides new insights into mode decoupling strategies pertinent to fiber communications.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.9215010612021004,and 11934006)the Innovation Project of Optics Valley Laboratory(No.OVL2021ZD001),the Major Program(JD)of Hubei Province(No.203BAA015)the Cross Research Support Program of Huazhong University of Science and Technology(No.2023JCYJ041).
文摘An ultrafast fiber laser system comprising two coherently combined amplifier channels is reported.Within this system,each channel incorporates a rod-type fiber power amplifier,with individual operations reaching approximately 233 W.The active-locking of these coherently combined channels,followed by compression using gratings,yields an output with a pulse energy of 504μJ and an average power of 403 W.Exceptional stability is maintained,with a 0.3%root mean square(RMS)deviation and a beam quality factor M^(2)<1.2.Notably,precise dispersion management of the front-end seed light effectively compensates for the accumulated high-order dispersion in subsequent amplification stages.This strategic approach results in a significant reduction in the final output pulse duration for the coherently combined laser beam,reducing it from 488 to 260 fs after the gratings compressor,while concurrently enhancing the energy of the primary peak from 65%to 92%.
基金supported by the Fundamental Research Funds for the Central Universities of China (TD2014-01)
文摘This article investigates the significant performances of orthogonal frequency division multiplexing （OFDM）-based dual-hop system in the presence of phase noise （PN）. A scenario with Rayleigh fading statistics on both hops is assumed. Amplification factor for this amplify-and-forward （AF） relay networks system is divided into two conditions, average power scaling （APS） and instantaneous power scaling （IPS）. Before deriving signal-to-noise ratios （SNR） under APS and IPS, the Gaussianity of intercarrier interference （ICI） is proved firstly. The accurate closed-form expressions of end-to-end SNR cumulative distribution functions （CDF） and probability density functions （PDF） for both cases are obtained later. With the help of moment generating functions （MGF）, we have closed-form asymptotic expressions of bit error rate （BER）, which show that the BER of system in the presence of PN cannot exceed a fixed level even when SNR in high regime. Finally, simulations verify accuracy of the results. Conclusion analysis will provide a useful help in future application of the system.
文摘We analyzed the number of cumulative positive cases of COVID-19 as a function of time in countries around the World.We tracked the increase in cases from the onset of the pandemic in each region for up to 150 days.We found that in 81 out of 146 regions the trajectory was described with a power-law function for up to 30 days.We also detected scale-free properties in the majority of sub-regions in Australia,Canada,China,and the United States(US).We developed an allometric model that was capable of fitting the initial phase of the pandemic and was the best predictor for the propagation of the illness for up to 100 days.We then determined that the power-law COVID-19 exponent correlated with measurements of human mobility.The COVID-19 exponent correlated with the magnitude of air passengers per country.This correlation persisted when we analyzed the number of air passengers per US states,and even per US metropolitan areas.Furthermore,the COVID19 exponent correlated with the number of vehicle miles traveled in the US.Together,air and vehicular travel explained 70%of the variability of the COVID-19 exponent.Taken together,our results suggest that the scale-free propagation of the virus is present at multiple geographical scales and is correlated with human mobility.We conclude that models of disease transmission should integrate scale-free dynamics as part of the modeling strategy and not only as an emergent phenomenological property.
