In order to obtain a glassy matrix during quenching, Be is often selected as a constituent of the compositions of Ti/Zr-based bulk metallic glass composites（BMGCs）. The in situ formed β phase in Be-bearing BMGCs wa...In order to obtain a glassy matrix during quenching, Be is often selected as a constituent of the compositions of Ti/Zr-based bulk metallic glass composites（BMGCs）. The in situ formed β phase in Be-bearing BMGCs was reported to be Be-free. However, a thorough investigation of the distribution of Be in BMGCs is still missing to date. In this work, the distribution of Be in a Ti_（47.5）Zr_（33）Cu_（5.8）Co_3Be_（12.5）（at.%） BMGC was studied by the secondary ion mass spectrometry（SIMS） and the electron energy loss spectroscopy（EELS）.It is found that Be almost totally dissolves in the glassy matrix, but a very weak intensity of Be in β phase is still detectable by SIMS, and the content of Be in β-Ti is estimated to be about 0.3 at.%. Based on the recently established two-phase quasi-equilibrium of BMGCs, the distinct solubility of Be in the glassy matrix and in β-Ti has been explained.展开更多
Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite （MGC） was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination ...Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite （MGC） was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination of yield strength （-1618MPa）, plasticity （-4.3%） and specific fracture strength （384 × 10^3 N m kg^-1 ） in compression. The maintained yield strength results from the unique microstruc- ture composed of the Ti layer, the solution layer with gradient structure and the MGC layer. Such a multilayer structure effectively inhibits the propagation of shear band, leading to the enhanced plastic- ity. Those extraordinary properities suggest that combining ductile lamella with brittle metallic glass （MG） by such a lay-up method can be an effective way to improve mechanical properties of MG.展开更多
The high-temperature tensile fracture behavior of the Ni, Cr, Al-TaC eutectic superal-loy directionally solidified under high temperature gradient is investigated. The high-temperature tensile fracture of this in situ...The high-temperature tensile fracture behavior of the Ni, Cr, Al-TaC eutectic superal-loy directionally solidified under high temperature gradient is investigated. The high-temperature tensile fracture of this in situ composite has ductile character with lots of ductile nests whose diameters decrease with the increasing solidification rates. The maximum σb and δ are respectively 668.5MPa and 19.6%. There is α TaC whisker in the center of each nest, and the deformation of γ' and TaC is uneven. The high-temperature tensile behavior cannot be explained by the rule of mixtures but is decided by the formation of the plastic deformation band. The crack extension model is given.展开更多
High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost ...High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost alloyed cast iron rolls is poor and the cost of high-quality PM hard alloy rolls is very high. By means of centrifugal casting, HSS rolls having excellent wear resistance have been manufactured. The hardness of the HSS roll is 6.5~67 HRC, the range of variation is smaller than 2 HRC and its impact toughness is 15 J/cm^2. The wear rate of HSS rolls used in the pre-finishing stands of high-speed hot wire-rod rolling mill reaches 2.5×10^(-4)mm per ton steel. Furthermore, the manufacturing cost of HSS rolls is significantly lower than that of PM hard alloy rolls; it is only 30 percent of that of PM hard alloy rolls.展开更多
With its unique and exclusive linear and nonlinear optical characteristics,epsilon-near-zero(ENZ)photonics has drawn a tremendous amount of attention in the recent decade in the fields of nanophotonics,nonlinear optic...With its unique and exclusive linear and nonlinear optical characteristics,epsilon-near-zero(ENZ)photonics has drawn a tremendous amount of attention in the recent decade in the fields of nanophotonics,nonlinear optics,plasmonics,light-matter interactions,material science,applied optical science,etc.The extraordinary optical properties,relatively high tuning flexibility,and CMOS compatibility of ENZ materials make them popular and competitive candidates for nanophotonic devices and on-chip integration in all-optical and electro-optical platforms.With exclusive features and high performance,ENZ photonics can play a big role in optical communications and optical data processing.In this review,we give a focused discussion on recent advances of the theoretical and experimental studies on ENZ photonics,especially in the regime of nonlinear ENZ nanophotonics and its applications.First,we overview the basics of the ENZ concepts,mechanisms,and nonlinear ENZ nanophotonics.Then the new advancements in theoretical and experimental optical physics are reviewed.For nanophotonic applications,the recent decades saw rapid developments in various kinds of different ENZ-based devices and systems,which are discussed and analyzed in detail.Finally,we give our perspectives on where future endeavors can be made.展开更多
The data rate of a visible light communication(VLC) system is basically determined by the electrical-to-optical(E-O) bandwidth of its light-emitting diode(LED) source. In order to break through the intrinsic limitatio...The data rate of a visible light communication(VLC) system is basically determined by the electrical-to-optical(E-O) bandwidth of its light-emitting diode(LED) source. In order to break through the intrinsic limitation of the carrier recombination rate on E-O bandwidth in conventional c-plane LEDs based on In Ga N quantum wells,a blue micro-LED with an active region of nano-structured In Ga N wetting layer is designed, fabricated, and packaged to realize a high-speed VLC system. The E-O bandwidth of the micro-LED can reach up to 1.3 GHz. Based on this high-speed micro-LED, we demonstrated a data rate of 2 Gbps with a bit error rate(BER) of 1.2×10^(-3) with simple on-off keying signal for a 3-m real-time VLC. In addition, a 4-Gbps VLC system using quadrature phase shift keying-orthogonal frequency-division multiplexing with a BER of 3.2×10^(-3) is also achieved for the same scenario. Among all the point-to-point VLC systems based on a single-pixel LED,this work has the highest distance-bandwidth product of 3 GHz·m and the highest distance-rate product of 12 Gbps·m.展开更多
The minimum variance and tangential discontinuity analyses are used to find the normal directions of the magnetopause using 550 crossings from ISEE 1 and 2, AMPTE/IRM, and IMP 8 satellites. Then, the average shape of ...The minimum variance and tangential discontinuity analyses are used to find the normal directions of the magnetopause using 550 crossings from ISEE 1 and 2, AMPTE/IRM, and IMP 8 satellites. Then, the average shape of the magnetopause is studied by using two\|region fit procedure. These studies show: (i) most of the crossings are reasonably characterized as tangential discontinuity; (ii) there does appear to be east\|west and north\|south asymmetry in the shape of the magnetopause; (iii) the magnetopause in the equatorial region is swept back from the vacuum location for both northward and southward IMF, which means that the simple single conic section used in previous fits may not be appropriate to the entire shape of the magnetopause, especially at the nightside.展开更多
Background:Motor adaptation relies on error-based learning for accurate movements in changing environ-ments.However,the neurophysiological mechanisms driving individual differences in performance are unclear.Transcran...Background:Motor adaptation relies on error-based learning for accurate movements in changing environ-ments.However,the neurophysiological mechanisms driving individual differences in performance are unclear.Transcranial magnetic stimulation(TMS)-evoked potential can provide a direct measure of cortical excitability.Objective:To investigate cortical excitability as a predictor of motor learning and motor adaptation in a robot-mediated forcefield.Methods:A group of 15 right-handed healthy participants(mean age 23 years)performed a robot-mediated forcefield perturbation task.There were two conditions:unperturbed non-adaptation and perturbed adapta-tion.TMS was applied in the resting state at baseline and following motor adaptation over the contralateral primary motor cortex(left M1).Electroencephalographic(EEG)activity was continuously recorded,and cortical excitability was measured by TMS-evoked potential(TEP).Motor learning was quantified by the motor learning index.Results:Larger error-related negativity(ERN)in fronto-central regions was associated with improved motor per-formance as measured by a reduction in trajectory errors.Baseline TEP N100 peak amplitude predicted motor learning(P=0.005),which was significantly attenuated relative to baseline(P=0.0018)following motor adap-tation.Conclusions:ERN reflected the formation of a predictive internal model adapted to the forcefield perturbation.Attenuation in TEP N100 amplitude reflected an increase in cortical excitability with motor adaptation reflecting neuroplastic changes in the sensorimotor cortex.TEP N100 is a potential biomarker for predicting the outcome in robot-mediated therapy and a mechanism to investigate psychomotor abnormalities in depression.展开更多
Phenological responses of vegetation to the ongoing warming trend impact current and future primary productivity.However,few studies focus on wood phenology because its observed data are much scarcer,which hinders the...Phenological responses of vegetation to the ongoing warming trend impact current and future primary productivity.However,few studies focus on wood phenology because its observed data are much scarcer,which hinders the estimation and prediction of forest carbon budgets over large regions.Here,we use a physiological process-based tree-ring growth model(Vaganov-Shashkin model)to investigate the spatial and temporal variations of spring xylem phenology(start of the growing season of xylem,SOS_(x))in tree-ring sites of China during 1962-2016 CE.The model is calibrated on measured tree-ring width chronologies(70 tree-ring chronologies)and successfully validated with field observations of xylogenesis.We found that spring xylem phenology significantly advances during 1962-2016 CE period under global warming,with the rate of advance quickly increasing after the 1990s to an average of 0.25 days per year.The preseason daily mean temperature is the main climatic driver for spring xylem phenology as indicated by its significant correlations with SOS_(x)at most sites(71%).Warmer preseason allows heat requirements for tree growth to be reached more quickly,with increase of 1℃in temperature of preseason anticipates SOS_(x)by 6 to 7 days,which will benefit the radial growth of trees in the relatively cold-humid environments.In addition,the significant positive correlation between the simulated spring xylem phenology and remote sensing derived phenology highlights the primary and secondary growth may be governed by the same variable(temperature)and change in the same direction with global warming.This study provides the long-term perspective on the spring xylem phenology variations covering most of China.展开更多
The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and...The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and lower than critical densities with plasmas extending over few micrometers,i.e.multiple wavelengths.The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam.Experiments at the Glass Hybrid OPCPA Scaled Test-bed(GHOST)laser system at University of Texas,Austin using such targets measured non-Maxwellian,peaked electron distribution with large bunch charge and high electron density in the laser propagation direction.These results are reproduced in 2D PIC simulations using the EPOCH code,identifying direct laser acceleration(DLA)[1]as the responsible mechanism.This is the first time that DLA has been observed to produce peaked spectra as opposed to broad,Maxwellian spectra observed in earlier experiments[2].This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.展开更多
The timing of flowering(FL)and leaf unfolding(LU)determine plants’reproduction and vegetative growth.Global warming has substantially advanced FL and LU of temperate and boreal plants,but their responses to warming d...The timing of flowering(FL)and leaf unfolding(LU)determine plants’reproduction and vegetative growth.Global warming has substantially advanced FL and LU of temperate and boreal plants,but their responses to warming differ,which may influence the time interval between FL and LU(ΔLU-FL),thereby impacting plant fitness and intraspecific physiological processes.Based on twigs collected from two flowering-first tree species,Populus tomentosa and Amygdalus triloba,we conducted a manipulative experiment to investigate the effects of winter chilling,spring warming and photoperiod on theΔLU-FL.We found that photoperiod did not affect theΔLU-FL of Amygdalus triloba,but shortenedΔLU-FL by 5.1 d of Populus tomentosa.Interestingly,spring warming and winter chilling oppositely affected theΔLU-FL of both species.Specifically,low chilling accumulation extended theΔLU-FL by 3.8 and 9.4 d for Populus tomentosa and Amygdalus triloba,but spring warming shortened theΔLU-FL by 4.1 and 0.2 d℃^(-1).Our results indicate that climate warming will decrease or increase theΔLU-FL depending on the warming periods,i.e.,spring or winter.The shifted time interval between flowering and leaf unfolding may have ecological effects including affecting pollen transfer efficiency and alter the structure and functioning of terrestrial ecosystem.展开更多
The Earth is experiencing unprecedented climate change.Vegetation phenology has already showed strong response to the global warming,which alters mass and energy fluxes on terrestrial ecosystems.With technology and me...The Earth is experiencing unprecedented climate change.Vegetation phenology has already showed strong response to the global warming,which alters mass and energy fluxes on terrestrial ecosystems.With technology and method developments in remote sensing,computer science and citizen science,many recent phenology-related studies have been focused on macrophenology.In this perspective,we 1)reviewed the responses of vegetation phenology to climate change and its impacts on carbon cycling,and reported that the effect of shifted phenology on the terrestrial carbon fluxes is substantially different between spring and autumn;2)elaborated how vegetation phenology affects ecohydrological processes at different scales,and further listed the key issues for each scale,i.e.,focusing on seasonal effect,local feedbacks and regional vapor transport for individual,watershed and global respectively);3)envisioned the potentials to improve current hydrological models by coupling vegetation phenology-related processes,in combining with machine learning,deep learning and scale transformation methods.We propose that comprehensive understanding of climate-macrophenology-hydrology interactions are essential and urgently needed for enhancing our understanding of the ecosystem response and its role in hydrological cycle under future climate change.展开更多
The effect of Friction stir process(FSP)parameters on the microstructure and mechanical properties of an extruded Mge2.0Nde0.3Zne1.0Zr(wt.%)alloy was investigated in this paper.The alloy was friction stir processed wi...The effect of Friction stir process(FSP)parameters on the microstructure and mechanical properties of an extruded Mge2.0Nde0.3Zne1.0Zr(wt.%)alloy was investigated in this paper.The alloy was friction stir processed with different passes:single-pass,three-pass and five-pass,under a tool rotation rate of 800μm and a traverse speed of 200 mm min^(-1).FSP results in remarkable grain refinement of the extruded alloy(average grain size w3.8 mm as 3 passes)and almost complete dissolution of the Mg_(12)Nd phase in the matrix.With the increase of pass,the average grain size in the stir zone(SZ)is decreased firstly and then increases.The Vikers hardness of SZs in all FSPed samples is higher than that of the parent material(PM).Tensile tests at room-temperature show that the tensile strengths of the stir zones along the FSP advancing direction are slightly lower than those of PM.However,the elongations are remarkably improved from 13.0%for PM to 24.5%for SZ FSPed with three-passes.These improved tensile properties are attributed to the microstructure refinement,dynamic recrystallization and dissolution of the Mg_(12)Nd phase.展开更多
Climate warming has substantially advanced the timing of spring leaf-out of woody species at middle and high latitudes,albeit with large differences.Insights in the spatial variation of this climate warming response m...Climate warming has substantially advanced the timing of spring leaf-out of woody species at middle and high latitudes,albeit with large differences.Insights in the spatial variation of this climate warming response may therefore help to constrain future trends in leaf-out and its impact on energy,water and carbon balances at global scales.In this study,we used in situ phenology observations of 38 species from 2067 study sites,distributed across the northern hemisphere in China,Europe and the United States,to investigate the latitudinal patterns of spring leaf-out and its sensitivity(S T,advance of leaf-out dates per degree of warming)and correlation(R_(T),partial correlation coefficient)to temperature during the period 1980-2016.Across all species and sites,we found that S_(T) decreased significantly by 0.15±0.02 d℃^(-1)°N^(-1),and R_(T) increased by 0.02±0.001°N^(-1)(both at P<0.001).The latitudinal patterns in R_(T) and S_(T) were explained by the differences in requirements of chilling and thermal forcing that evolved to maximize tree fitness under local climate,particularly climate predictability and summed precipitation during the pre-leaf-out season.Our results thus showed complicated spatial differences in leaf-out responses to ongoing climate warming and indicated that spatial differences in the interactions among environmental cues need to be embedded into large-scale phenology models to improve the simulation accuracy.展开更多
基金support from the National Natural Science Foundation of China (Nos. 51434008, U1435204, and 51531005)the China’s Manned Space Station Project (Mission No.: TGJZ800-2-RW024)the Shuangchuang Project of Jiangsu Province, China
文摘In order to obtain a glassy matrix during quenching, Be is often selected as a constituent of the compositions of Ti/Zr-based bulk metallic glass composites（BMGCs）. The in situ formed β phase in Be-bearing BMGCs was reported to be Be-free. However, a thorough investigation of the distribution of Be in BMGCs is still missing to date. In this work, the distribution of Be in a Ti_（47.5）Zr_（33）Cu_（5.8）Co_3Be_（12.5）（at.%） BMGC was studied by the secondary ion mass spectrometry（SIMS） and the electron energy loss spectroscopy（EELS）.It is found that Be almost totally dissolves in the glassy matrix, but a very weak intensity of Be in β phase is still detectable by SIMS, and the content of Be in β-Ti is estimated to be about 0.3 at.%. Based on the recently established two-phase quasi-equilibrium of BMGCs, the distinct solubility of Be in the glassy matrix and in β-Ti has been explained.
基金supported by the National Natural Science Foundation of China (Nos. 51434008 (U1435204) and 51531005)the China’s Manned Space Station Project (No. TGJZ800-2-RW024)+2 种基金Science and Technology Planning Project of Guangdong Province, China (Nos. 2015B090926001 and 2015B010122001)the Youth Innovation Promotion Association CASShuangchuang Project of Jiangsu Province, China
文摘Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite （MGC） was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination of yield strength （-1618MPa）, plasticity （-4.3%） and specific fracture strength （384 × 10^3 N m kg^-1 ） in compression. The maintained yield strength results from the unique microstruc- ture composed of the Ti layer, the solution layer with gradient structure and the MGC layer. Such a multilayer structure effectively inhibits the propagation of shear band, leading to the enhanced plastic- ity. Those extraordinary properities suggest that combining ductile lamella with brittle metallic glass （MG） by such a lay-up method can be an effective way to improve mechanical properties of MG.
基金supported by the National Natural Science Foundation of China(No.50102004)the Aeronautical Science Foundation of China(No.97G53066)the Developing Program for Outstanding Persons in NPU,China.
文摘The high-temperature tensile fracture behavior of the Ni, Cr, Al-TaC eutectic superal-loy directionally solidified under high temperature gradient is investigated. The high-temperature tensile fracture of this in situ composite has ductile character with lots of ductile nests whose diameters decrease with the increasing solidification rates. The maximum σb and δ are respectively 668.5MPa and 19.6%. There is α TaC whisker in the center of each nest, and the deformation of γ' and TaC is uneven. The high-temperature tensile behavior cannot be explained by the rule of mixtures but is decided by the formation of the plastic deformation band. The crack extension model is given.
文摘High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost alloyed cast iron rolls is poor and the cost of high-quality PM hard alloy rolls is very high. By means of centrifugal casting, HSS rolls having excellent wear resistance have been manufactured. The hardness of the HSS roll is 6.5~67 HRC, the range of variation is smaller than 2 HRC and its impact toughness is 15 J/cm^2. The wear rate of HSS rolls used in the pre-finishing stands of high-speed hot wire-rod rolling mill reaches 2.5×10^(-4)mm per ton steel. Furthermore, the manufacturing cost of HSS rolls is significantly lower than that of PM hard alloy rolls; it is only 30 percent of that of PM hard alloy rolls.
基金Shenzhen Science and Technology Innovation Commission(GJHZ2018411185015272)Guangdong Basic and Applied Basic Research Foundation(2021A1515011450,2021A1515012176)Youth Science and Technology Innovation Talent of Guangdong Province(2019TQ05X227)。
文摘With its unique and exclusive linear and nonlinear optical characteristics,epsilon-near-zero(ENZ)photonics has drawn a tremendous amount of attention in the recent decade in the fields of nanophotonics,nonlinear optics,plasmonics,light-matter interactions,material science,applied optical science,etc.The extraordinary optical properties,relatively high tuning flexibility,and CMOS compatibility of ENZ materials make them popular and competitive candidates for nanophotonic devices and on-chip integration in all-optical and electro-optical platforms.With exclusive features and high performance,ENZ photonics can play a big role in optical communications and optical data processing.In this review,we give a focused discussion on recent advances of the theoretical and experimental studies on ENZ photonics,especially in the regime of nonlinear ENZ nanophotonics and its applications.First,we overview the basics of the ENZ concepts,mechanisms,and nonlinear ENZ nanophotonics.Then the new advancements in theoretical and experimental optical physics are reviewed.For nanophotonic applications,the recent decades saw rapid developments in various kinds of different ENZ-based devices and systems,which are discussed and analyzed in detail.Finally,we give our perspectives on where future endeavors can be made.
基金National Key Research and Development Program of China(2016YFB0401803)National Natural Science Foundation of China(61822404,61974080)+3 种基金Shenzhen Science and Technology Innovation Commission(JCYJ20180507183815699)Tsinghua-Berkeley Shenzhen Institute(TBSI)Faculty Start-up FundShenzhen Fundamental Research Project(JCYJ20170817161720819)Overseas Research Cooperation Fund of Tsinghua Shenzhen International Graduate School(HW2018003)。
文摘The data rate of a visible light communication(VLC) system is basically determined by the electrical-to-optical(E-O) bandwidth of its light-emitting diode(LED) source. In order to break through the intrinsic limitation of the carrier recombination rate on E-O bandwidth in conventional c-plane LEDs based on In Ga N quantum wells,a blue micro-LED with an active region of nano-structured In Ga N wetting layer is designed, fabricated, and packaged to realize a high-speed VLC system. The E-O bandwidth of the micro-LED can reach up to 1.3 GHz. Based on this high-speed micro-LED, we demonstrated a data rate of 2 Gbps with a bit error rate(BER) of 1.2×10^(-3) with simple on-off keying signal for a 3-m real-time VLC. In addition, a 4-Gbps VLC system using quadrature phase shift keying-orthogonal frequency-division multiplexing with a BER of 3.2×10^(-3) is also achieved for the same scenario. Among all the point-to-point VLC systems based on a single-pixel LED,this work has the highest distance-bandwidth product of 3 GHz·m and the highest distance-rate product of 12 Gbps·m.
文摘The minimum variance and tangential discontinuity analyses are used to find the normal directions of the magnetopause using 550 crossings from ISEE 1 and 2, AMPTE/IRM, and IMP 8 satellites. Then, the average shape of the magnetopause is studied by using two\|region fit procedure. These studies show: (i) most of the crossings are reasonably characterized as tangential discontinuity; (ii) there does appear to be east\|west and north\|south asymmetry in the shape of the magnetopause; (iii) the magnetopause in the equatorial region is swept back from the vacuum location for both northward and southward IMF, which means that the simple single conic section used in previous fits may not be appropriate to the entire shape of the magnetopause, especially at the nightside.
基金supported by a University of East London Excellence PhD scholarship to MT and in part from a Medical Research Council grant to CF(grant number G0802594).
文摘Background:Motor adaptation relies on error-based learning for accurate movements in changing environ-ments.However,the neurophysiological mechanisms driving individual differences in performance are unclear.Transcranial magnetic stimulation(TMS)-evoked potential can provide a direct measure of cortical excitability.Objective:To investigate cortical excitability as a predictor of motor learning and motor adaptation in a robot-mediated forcefield.Methods:A group of 15 right-handed healthy participants(mean age 23 years)performed a robot-mediated forcefield perturbation task.There were two conditions:unperturbed non-adaptation and perturbed adapta-tion.TMS was applied in the resting state at baseline and following motor adaptation over the contralateral primary motor cortex(left M1).Electroencephalographic(EEG)activity was continuously recorded,and cortical excitability was measured by TMS-evoked potential(TEP).Motor learning was quantified by the motor learning index.Results:Larger error-related negativity(ERN)in fronto-central regions was associated with improved motor per-formance as measured by a reduction in trajectory errors.Baseline TEP N100 peak amplitude predicted motor learning(P=0.005),which was significantly attenuated relative to baseline(P=0.0018)following motor adap-tation.Conclusions:ERN reflected the formation of a predictive internal model adapted to the forcefield perturbation.Attenuation in TEP N100 amplitude reflected an increase in cortical excitability with motor adaptation reflecting neuroplastic changes in the sensorimotor cortex.TEP N100 is a potential biomarker for predicting the outcome in robot-mediated therapy and a mechanism to investigate psychomotor abnormalities in depression.
基金funded by the National Natural Science Foundation of China(Grant Nos.41888101&42077406)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB26020000)+3 种基金the Key Research Program of the Institute of Geology&Geophysics,CAS(Grant No.IGGCAS-201905)funded by the Youth Innovation Promotion Association CASsupported by the Discovery Grants program of the Natural Sciences and Engineering Research Council of Canada(Grant No.RGPIN-2021-03553)by the Canadian Research Chair in dendroecology and dendroclimatology(Grant No.CRC2021-00368)。
文摘Phenological responses of vegetation to the ongoing warming trend impact current and future primary productivity.However,few studies focus on wood phenology because its observed data are much scarcer,which hinders the estimation and prediction of forest carbon budgets over large regions.Here,we use a physiological process-based tree-ring growth model(Vaganov-Shashkin model)to investigate the spatial and temporal variations of spring xylem phenology(start of the growing season of xylem,SOS_(x))in tree-ring sites of China during 1962-2016 CE.The model is calibrated on measured tree-ring width chronologies(70 tree-ring chronologies)and successfully validated with field observations of xylogenesis.We found that spring xylem phenology significantly advances during 1962-2016 CE period under global warming,with the rate of advance quickly increasing after the 1990s to an average of 0.25 days per year.The preseason daily mean temperature is the main climatic driver for spring xylem phenology as indicated by its significant correlations with SOS_(x)at most sites(71%).Warmer preseason allows heat requirements for tree growth to be reached more quickly,with increase of 1℃in temperature of preseason anticipates SOS_(x)by 6 to 7 days,which will benefit the radial growth of trees in the relatively cold-humid environments.In addition,the significant positive correlation between the simulated spring xylem phenology and remote sensing derived phenology highlights the primary and secondary growth may be governed by the same variable(temperature)and change in the same direction with global warming.This study provides the long-term perspective on the spring xylem phenology variations covering most of China.
基金supported by NNSA cooperative agreement DE-NA0002008the Defense Advanced Research Projects Agency's PULSE program(12-63-PULSE-FP014)the Air Force Office of Scientific Research(FA9550-14-1-0045).
文摘The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and lower than critical densities with plasmas extending over few micrometers,i.e.multiple wavelengths.The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam.Experiments at the Glass Hybrid OPCPA Scaled Test-bed(GHOST)laser system at University of Texas,Austin using such targets measured non-Maxwellian,peaked electron distribution with large bunch charge and high electron density in the laser propagation direction.These results are reproduced in 2D PIC simulations using the EPOCH code,identifying direct laser acceleration(DLA)[1]as the responsible mechanism.This is the first time that DLA has been observed to produce peaked spectra as opposed to broad,Maxwellian spectra observed in earlier experiments[2].This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.
基金the National Funds for Distinguished Young Scholar(42025101)the International Cooperation and Exchanges NSFC-FWO(32111530083)the 111 Project(B18006)。
文摘The timing of flowering(FL)and leaf unfolding(LU)determine plants’reproduction and vegetative growth.Global warming has substantially advanced FL and LU of temperate and boreal plants,but their responses to warming differ,which may influence the time interval between FL and LU(ΔLU-FL),thereby impacting plant fitness and intraspecific physiological processes.Based on twigs collected from two flowering-first tree species,Populus tomentosa and Amygdalus triloba,we conducted a manipulative experiment to investigate the effects of winter chilling,spring warming and photoperiod on theΔLU-FL.We found that photoperiod did not affect theΔLU-FL of Amygdalus triloba,but shortenedΔLU-FL by 5.1 d of Populus tomentosa.Interestingly,spring warming and winter chilling oppositely affected theΔLU-FL of both species.Specifically,low chilling accumulation extended theΔLU-FL by 3.8 and 9.4 d for Populus tomentosa and Amygdalus triloba,but spring warming shortened theΔLU-FL by 4.1 and 0.2 d℃^(-1).Our results indicate that climate warming will decrease or increase theΔLU-FL depending on the warming periods,i.e.,spring or winter.The shifted time interval between flowering and leaf unfolding may have ecological effects including affecting pollen transfer efficiency and alter the structure and functioning of terrestrial ecosystem.
基金the National Science Fund for Distinguished Young Scholars(Grant No.42025101)International Cooperation and Exchanges NSFC-STINT(Grant No.42111530181).
文摘The Earth is experiencing unprecedented climate change.Vegetation phenology has already showed strong response to the global warming,which alters mass and energy fluxes on terrestrial ecosystems.With technology and method developments in remote sensing,computer science and citizen science,many recent phenology-related studies have been focused on macrophenology.In this perspective,we 1)reviewed the responses of vegetation phenology to climate change and its impacts on carbon cycling,and reported that the effect of shifted phenology on the terrestrial carbon fluxes is substantially different between spring and autumn;2)elaborated how vegetation phenology affects ecohydrological processes at different scales,and further listed the key issues for each scale,i.e.,focusing on seasonal effect,local feedbacks and regional vapor transport for individual,watershed and global respectively);3)envisioned the potentials to improve current hydrological models by coupling vegetation phenology-related processes,in combining with machine learning,deep learning and scale transformation methods.We propose that comprehensive understanding of climate-macrophenology-hydrology interactions are essential and urgently needed for enhancing our understanding of the ecosystem response and its role in hydrological cycle under future climate change.
基金This work is supported by Shanghai Phospherus Program(Project No.11QH1401200)Program for New Century Excellent Talents in University by Ministry of Education of China(Project No.NCET-11-0329).
文摘The effect of Friction stir process(FSP)parameters on the microstructure and mechanical properties of an extruded Mge2.0Nde0.3Zne1.0Zr(wt.%)alloy was investigated in this paper.The alloy was friction stir processed with different passes:single-pass,three-pass and five-pass,under a tool rotation rate of 800μm and a traverse speed of 200 mm min^(-1).FSP results in remarkable grain refinement of the extruded alloy(average grain size w3.8 mm as 3 passes)and almost complete dissolution of the Mg_(12)Nd phase in the matrix.With the increase of pass,the average grain size in the stir zone(SZ)is decreased firstly and then increases.The Vikers hardness of SZs in all FSPed samples is higher than that of the parent material(PM).Tensile tests at room-temperature show that the tensile strengths of the stir zones along the FSP advancing direction are slightly lower than those of PM.However,the elongations are remarkably improved from 13.0%for PM to 24.5%for SZ FSPed with three-passes.These improved tensile properties are attributed to the microstructure refinement,dynamic recrystallization and dissolution of the Mg_(12)Nd phase.
基金supported by the National Science Fund for Distinguished Young Scholars(Grant No.42025101)the Interna-tional Cooperation and Exchanges NSFC-STINT Project(Grant No.42111530181)+2 种基金the General Program of National Nature Science Foundation of China(Grant No.31770516)the 111 Project(Grant No.B18006)support from the Euro-pean Research Council through Synergy grant ERC-2013-SyG-610028“IMBALANCE-P”.
文摘Climate warming has substantially advanced the timing of spring leaf-out of woody species at middle and high latitudes,albeit with large differences.Insights in the spatial variation of this climate warming response may therefore help to constrain future trends in leaf-out and its impact on energy,water and carbon balances at global scales.In this study,we used in situ phenology observations of 38 species from 2067 study sites,distributed across the northern hemisphere in China,Europe and the United States,to investigate the latitudinal patterns of spring leaf-out and its sensitivity(S T,advance of leaf-out dates per degree of warming)and correlation(R_(T),partial correlation coefficient)to temperature during the period 1980-2016.Across all species and sites,we found that S_(T) decreased significantly by 0.15±0.02 d℃^(-1)°N^(-1),and R_(T) increased by 0.02±0.001°N^(-1)(both at P<0.001).The latitudinal patterns in R_(T) and S_(T) were explained by the differences in requirements of chilling and thermal forcing that evolved to maximize tree fitness under local climate,particularly climate predictability and summed precipitation during the pre-leaf-out season.Our results thus showed complicated spatial differences in leaf-out responses to ongoing climate warming and indicated that spatial differences in the interactions among environmental cues need to be embedded into large-scale phenology models to improve the simulation accuracy.
