In this paper, we first introduce the concept ＂harmonically convex functions＂ in the second sense and establish several Hermite-Hadamard type inequalities for harmonically convex functions in the second sense. Final...In this paper, we first introduce the concept ＂harmonically convex functions＂ in the second sense and establish several Hermite-Hadamard type inequalities for harmonically convex functions in the second sense. Finally, some applications to special mean are shown.展开更多
We report the generation of passively tunable high peak signal-to-noise ratio harmonic mode-locked （HML） all- normal-dispersion Yb-doped fiber laser with a single birefringent filter in a ring cavity configuration. ...We report the generation of passively tunable high peak signal-to-noise ratio harmonic mode-locked （HML） all- normal-dispersion Yb-doped fiber laser with a single birefringent filter in a ring cavity configuration. The highest fourth harmonic of the fundamental mode-locked frequency at a repetition rate of 88 MHz is obtained. The pulses are compressed to 627fs by using an external grating-pair compressor. For the fourth HML output, the peak signal-to-noise ratio of the rf is 73dB and the average power is as high as 110mW with the pump power of 500mW. Soliton bunches which contain multipulses are also observed in the weak mode-locked regime of the HML, and the separation between interpulses in a dissipative soliton bunch can be controlled by adjustment of the waveplates and spectral filter in the cavity：展开更多
In this work, a mathematical model of an elastic material with cylindrical cavity will be constructed. The governing equations will be taken into the context of the fractional order generalized thermoelasticity theory...In this work, a mathematical model of an elastic material with cylindrical cavity will be constructed. The governing equations will be taken into the context of the fractional order generalized thermoelasticity theory (Youssef 2010). Laplace transform and direct approach will be used to obtain the solution when the boundary of the cavity is exposed to harmonically heat with constant angular frequency of thermal vibration. The inverse of Laplace transforms will be computed numerically using a method based on Fourier expansion techniques. Some comparisons have been shown in figures to present the effect of the fractional order parameter and the angular frequency of thermal vibration on all the studied felids.展开更多
We studied the response of harmonically and stochastically excited strongly nonlinear oscillators with delayed feedback bang-bang control using the stochastic averaging method. First, the time-delayed feedback bang-ba...We studied the response of harmonically and stochastically excited strongly nonlinear oscillators with delayed feedback bang-bang control using the stochastic averaging method. First, the time-delayed feedback bang-bang control force is expressed approximately in terms of the system state variables without time delay. Then the averaged It6 stochastic differential equations for the system are derived using the stochastic averaging method. Finally, the response of the system is obtained by solving the Fokker-Plank-Kolmogorov （FPK） equation associated with the averaged lt6 equations. A Duffing oscillator with time-delayed feedback bang-bang control under combined harmonic and white noise excitations is taken as an example to illus- trate the proposed method. The analytical results are confirmed by digital simulation. We found that the time delay in feedback bang-bang control will deteriorate the control effectiveness and cause bifurcation of stochastic jump of Duffing oscillator.展开更多
Nonlinear behaviors are investigated for a structure coupled with a nonlinear energy sink. The structure is linear and subject to a harmonic excitation, modeled as a forced single-degree-of-freedom oscillator. The non...Nonlinear behaviors are investigated for a structure coupled with a nonlinear energy sink. The structure is linear and subject to a harmonic excitation, modeled as a forced single-degree-of-freedom oscillator. The nonlinear energy sink is modeled as an oscillator consisting of a mass,a nonlinear spring, and a linear damper. Based on the numerical solutions, global bifurcation diagrams are presented to reveal the coexistence of periodic and chaotic motions for varying nonlinear energy sink mass and stiffness. Chaos is numerically identified via phase trajectories, power spectra,and Poincaré maps. Amplitude-frequency response curves are predicted by the method of harmonic balance for periodic steady-state responses. Their stabilities are analyzed.The Hopf bifurcation and the saddle-node bifurcation are determined. The investigation demonstrates that a nonlinear energy sink may create dynamic complexity.展开更多
Taking two identical ions in a Paul trap,we solved the SchrÖdinger equation for one-,two-,and three-dimensional harmonically bound two-body Coulomb models,in which the eigenfunctions are written in a series form ...Taking two identical ions in a Paul trap,we solved the SchrÖdinger equation for one-,two-,and three-dimensional harmonically bound two-body Coulomb models,in which the eigenfunctions are written in a series form and the eigenenergies are obtained from a continued fraction.Numerical calculations are made for specific discussion of two-and three-dimensional case.The comparison with a former one-dimensional approximate work shows that our result is more general and accurate.展开更多
Harmonic mode-locking,realized actively or passively,is an effective technique for increasing the repetition rate of ultrafast lasers.It is critically important to understand how a harmonically mode-locked pulse train...Harmonic mode-locking,realized actively or passively,is an effective technique for increasing the repetition rate of ultrafast lasers.It is critically important to understand how a harmonically mode-locked pulse train responds to external perturbations and noise,so as to make sure that it is stable and resistant to noise.Here,in a series of carefully designed experiments,we elucidate the retiming dynamics of laser pulses generated in a soliton fiber laser harmonically modelocked at GHz frequencies to the acoustic resonance in a photonic crystal fiber(PCF)core.We characterize the selfdriven optomechanical lattice,which is distributed along the PCF and provides the structure that supports harmonic mode-locking,using a homodyne setup.We reveal that,after an abrupt perturbation,each soliton in the lattice undergoes damped oscillatory retiming within its trapping potential,while the retiming is strongly coupled to soliton dissipation.In addition,we show,through statistical analysis of the intra-cavity pulse spacing,how the trapping potentials are effective for suppressing timing jtter.The measurements and the theory developed in this work lay the groundwork for studies of the general stability and noise performance of harmonically mode-locked lasers as well as providing valuable insight into generic multi-pulse phenomena in mode-locked lasers.展开更多
High harmonic generation(HHG)provides an experimental method for producing attosecond pulses and probing electron dynamics.Achieving precise dipole phase measurements is critical for tailoring the harmonic emission ph...High harmonic generation(HHG)provides an experimental method for producing attosecond pulses and probing electron dynamics.Achieving precise dipole phase measurements is critical for tailoring the harmonic emission phase and identifying the HHG mechanism.However,achieving this feature by applying traditional two-beam far-field interferometry to solid materials remains challenging.In this study,we present a novel interferometric approach that utilizes a single laser beam to excite two ZnO microwires(MWs)simultaneously,thereby generating coherent high-harmonic sources that form interference fringes in the far-field region.We leverage the diameter-dependent field-enhancement effect in MWs to measure the intensity-dependent fringe shift,revealing that the intraband current mechanism dominates the below-bandgap harmonic,whereas the interband polarization mechanism dominates the above-bandgap harmonic.This study offers a robust method for measuring the dipole phase of solid-state HHG and inspires intensity-modulated high-harmonic applications in coherent imaging and microdevice design.展开更多
The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payl...The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.展开更多
This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first ...This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first solved via Newton-Raphson iteration through a set of nonlinear equations,and then input-output variables are selected to estimate the linear transfer function of the original NTP system without perturbations.The applications and insights of the proposed algorithm are discussed,particularly in guiding existing frequency scan algorithms,which are restricted by time-domain signal generation or measurement.This improvement is achieved through linear stability analysis of NTP systems with perturbations.展开更多
With their intricate vectorial structures in space,optical skyrmions have significantly expanded the landscape of topological optics and light-matter interactions.We theoretically investigate high harmonic generation ...With their intricate vectorial structures in space,optical skyrmions have significantly expanded the landscape of topological optics and light-matter interactions.We theoretically investigate high harmonic generation in crystals driven by optical skyrmions.We find that although the skyrmion number is not conserved,the resulting high-order harmonics can exhibit a distinctive multi-vortex structure,whose features are shaped by both the topology of the optical skyrmions and the rotational symmetry of the crystal.The position of the vortex centers can be effectively tuned by employing different types of optical skyrmions.To elucidate the underlying physics,we develop a multi-absorption channel model based on the conservation laws of spin and orbital angular momentum.Our work explores the role of optical topology in extreme nonlinear light-matter interactions,offering new opportunities for the formation and manipulation of optical vortices and novel structured light fields in the visible and ultraviolet regimes.展开更多
In order to eliminate the meshing interference between the flexspline and circular spline after the taper deformation of the flexspline,the radial deformation difference method,major and minor axis fitting method,and ...In order to eliminate the meshing interference between the flexspline and circular spline after the taper deformation of the flexspline,the radial deformation difference method,major and minor axis fitting method,and ellipse fitting method are used to modify the tooth thickness of the flexspline and analyze the performance indexes such as the assembly stress,transmission error,and fatigue life.Firstly,the conjugate tooth profile is solved based on the quadruple-circular-arc tooth profile and modified kinematic method.Then,based on the finite element radial deformation of the flexspline,the principle and characteristics of three modification methods are analyzed,and the modification amount of each section of the flexspline tooth is calculated.Finally,the influence of the three modification methods on the performance of the harmonic drive is compared.The results show that the radial deformation difference method can initially determine the modification amount.The minimum static assembly stress is 406.22 MPa by the major and minor axis fitting method.The ellipse fitting method has the best dynamic performance,small transmission error fluctuation,a peak-to-peak value of 3.060",and a maximum fatigue life of 10^(7.558)cycles.展开更多
Harmonic mode-locking(HML)in soliton fiber lasers is crucial for generating high-repetition-rate pulse trains beyond the fundamental cavity frequency,enabling advanced applications in,for example,optical communication...Harmonic mode-locking(HML)in soliton fiber lasers is crucial for generating high-repetition-rate pulse trains beyond the fundamental cavity frequency,enabling advanced applications in,for example,optical communication and precision sensing.However,achieving HML in experiments is challenging,owing to its inherent instability and high sensitivity to laser parameters,resulting in complex and iterative adjustments.In this paper,a novel HML technique utilizing bidirectional adjustment of pump power is proposed,and it is experimentally demonstrated in an all-fiber hybrid mode-locked soliton laser.By first increasing the pump power to generate a soliton bunch with a certain number of pulses and then gradually decreasing it,HML can be achieved at an order corresponding to the number of pulses in the soliton bunch.Experimental results on the evolution of temporal pulse trains during bidirectional adjustment of the pump power enable a relationship to be established between pump power and soliton bunching with increasing pump power,and reveal the collapse of the soliton bunch and subsequent gradual uniform distribution of solitons into an HML state with decreasing pump power.Second-to sixth-order HML is successfully generated using the proposed technique,and an analysis of the results provides a deeper understanding of the observed pulse dynamics.展开更多
Quasi-periodic solutions with multiple base frequencies exhibit the feature of 2π-periodicity with respect to each of the hyper-time variables.However,it remains a challenge work,due to the lack of effective solution...Quasi-periodic solutions with multiple base frequencies exhibit the feature of 2π-periodicity with respect to each of the hyper-time variables.However,it remains a challenge work,due to the lack of effective solution methods,to solve and track the quasi-periodic solutions with multiple base frequencies until now.In this work,a multi-steps variable-coefficient formulation is proposed,which provides a unified framework to enable either harmonic balance method or collocation method or finite difference method to solve quasi-periodic solutions with multiple base frequencies.For this purpose,a method of alternating U and S domain is also developed to efficiently evaluate the nonlinear force terms.Furthermore,a new robust phase condition is presented for all of the three methods to make them track the quasi-periodic solutions with prior unknown multiple base frequencies,while the stability of the quasi-periodic solutions is assessed by mean of Lyapunov exponents.The feasibility of the constructed methods under the above framework is verified by application to three nonlinear systems.展开更多
Integration of renewable energy sources into power systems requires efficient multilevel inverters,capable of producing high-quality output voltage with low total harmonic distortion(THD).Conventional multilevel inver...Integration of renewable energy sources into power systems requires efficient multilevel inverters,capable of producing high-quality output voltage with low total harmonic distortion(THD).Conventional multilevel inverters often suffer from high component count,high switching stress,low voltage gain,and increased cost,limiting their practical application.This paper introduces a high-gain novel topology for multilevel inverters with reduced number of total components per level count,low voltage stress on power conductive devices,and minimizing a cost function,which depends on the number of components,standing voltage on switches and diodes,output voltage levels,and gain.The designed topology,which can be applied in photovoltaic(PV)systems,utilizes only one direct current(DC)input supply and a modular structure with the ability of capacitor’s voltage self-balancing.The high gain property and low THD of the proposed topology are two advantages that provide sine output waveform,with no need to a high DC input voltage source.Moreover,generalized topology,consisting of cascaded basic units,has been proposed.A comprehensive method has been proposed to determining the values of DC supplies in this configuration,aiming to minimize redundant switching modes and maximize the voltage levels count.The comparison with some other multilevel inverters confirms the desired performance of the basic version given inverter.A prototype has been also implemented and the experimental results have been obtained to verify the advantages of the proposed 25-level topology.展开更多
Hybrid MMC(Hy-MMC)has broad application prospects because of the negative level output ability in its bridge arm.A Hy-MMC topology with a high-modulation ratio is designed in this paper.A second-harmonic current injec...Hybrid MMC(Hy-MMC)has broad application prospects because of the negative level output ability in its bridge arm.A Hy-MMC topology with a high-modulation ratio is designed in this paper.A second-harmonic current injection(SHCI)strategy based on Hy-MMC in high-modulation operation is also proposed to improve the power density of Hy-MMC effectively in steady-state operation.The amplitude of SHCI is determined from the perspective of the root mean square(RMS)value of bridge arm current,and the optimal initial phase angle is determined from the multi-objective optimization(capacitor voltage ripple of sub-modules(SMs),power loss,and peak value of bridge arm current).The effectiveness and engineering practicability of the proposed SHCI strategy based on Hy-MMC in high-modulation operation is verified by the electromagnetic transient(EMT)simulation using PSCAD/EMTDC®.The simulation results show that the capacitor voltage ripple of SMs can be effectively decreased by 61.98%or the capacitance can be decreased by 40%.The power loss is also analyzed.In addition,little influence of low capacitance on multi-operation conditions of Hy-MMC is verified by EMT simulation.展开更多
High-precision optical frequency measurement serves as a cornerstone of modern science and technology,enabling advancements in fields ranging from fundamental physics to quantum information technologies.Obtaining prec...High-precision optical frequency measurement serves as a cornerstone of modern science and technology,enabling advancements in fields ranging from fundamental physics to quantum information technologies.Obtaining precise photon frequencies,especially in the ultraviolet or even extreme ultraviolet regimes,is a key goal in both light–matter interaction experiments and engineering applications.High-order harmonic generation(HHG)is an ideal light source for producing such photons.In this work,we propose an optical temporal interference model(OTIM)that establishes an analogy with multi-slit Fraunhofer diffraction(MSFD)to manipulate fine-frequency photon generation by exploiting the temporal coherence of HHG processes.Our model provides a unified physical framework for three distinct non-integer HHG generation schemes:single-pulse,shaped-pulse,and laser pulse train approaches,which correspond to single-MSFD-like,double-MSFD-like,and multi-MSFD-like processes,respectively.Arbitrary non-integer HHG photons can be obtained using our scheme.Our approach provides a new perspective for accurately measuring and controlling photon frequencies in fields such as frequency comb technology,interferometry,and atomic clocks.展开更多
A novel vibration isolation system designed for superior performance in low-frequency environments is proposed in this work.The isolator is based on a unique hexagonal arrangement of linear springs,allowing for an adj...A novel vibration isolation system designed for superior performance in low-frequency environments is proposed in this work.The isolator is based on a unique hexagonal arrangement of linear springs,allowing for an adjustable geometric configuration via the initial inclination angle.Based on the principle of Lagrangian mechanics,the equation of motion governing the structural dynamics is rigorously derived.The system is modeled as a strongly nonlinear single-degree-of-freedom dynamical system,loaded with a normalized payload and subject to harmonic base excitation.To analyze the steady-state response,the harmonic balance method is employed,providing accurate predictions of the payload's vibration amplitude and displacement transmissibility as functions of both the base excitation amplitude and frequency.The analysis reveals a direct relationship between the isolator's geometric and stiffness parameters and its load-bearing capacity,leading to the identification of three distinct operational regimes.Depending on the unloaded initial inclination angle,the equivalent stiffness ratio,and the payload design configuration,the system can exhibit one of three vibration isolation modes:(i)the quasizero stiffness(QZS)isolation mode,(ii)the zero linear stiffness with controllable nonlinear stiffness,and(iii)the full-band perfect zero stiffness.The vibration isolation performance of the proposed structure is thoroughly discussed for all three oscillation modes in terms of frequency response curves,displacement transmissibility,and time-domain responses.The key novel finding is that this structure can operate as a full-band,high-performance vibration isolator when the initial inclination angle is designed to be a right angle,enabling full isolation of the maximum possible payload.Moreover,the analytical results and numerical simulations demonstrate that the isolator's displacement transmissibility T with the unit dB tends to-∞as the air-damping coefficient approaches zero,enabling ideal vibration isolation across the entire excitation frequency range.These analytical insights are validated through comprehensive numerical simulations,which show excellent agreement with the theoretical predictions.展开更多
High-pressure hydrides have emerged as promising superconducting materials,attracting considerable attention in recent years.In this work,by combining the stochastic self-consistent harmonic approximation with first-p...High-pressure hydrides have emerged as promising superconducting materials,attracting considerable attention in recent years.In this work,by combining the stochastic self-consistent harmonic approximation with first-principles calculations,we elucidate crucial corrections to the vibrational and superconducting properties arising from quantum and anharmonic ionic vibrations of SnH4 in P63/mmc phase at 150–240 GPa.Compared with the classical harmonic approximation,inclusion of these effects results in a pronounced softening(over 500 cm^(−1))of hydrogen-derived optical phonon modes,and increases the superconducting critical temperature(Tc)from 65 K to 79 K(μ^(*)=0.1;isotropic Migdal–Eliashberg theory),corresponding to a 22%enhancement.For μ^(*)=0.13,the predicted Tc is approximately 70 K.Analysis of the Eliashberg spectral function confirms that hydrogen vibrational modes constitute the dominant tuning mechanism.These results provide quantitative insights into quantum ionic effects in hydride superconductors.展开更多
Conventional multilevel inverters often suffer from high harmonic distortion and increased design complexity due to the need for numerous power semiconductor components,particularly at elevated voltage levels.Addressi...Conventional multilevel inverters often suffer from high harmonic distortion and increased design complexity due to the need for numerous power semiconductor components,particularly at elevated voltage levels.Addressing these shortcomings,thiswork presents a robust 15-level PackedUCell(PUC)inverter topology designed for renewable energy and grid-connected applications.The proposed systemintegrates a sensor less proportional-resonant(PR)controller with an advanced carrier-based pulse width modulation scheme.This approach efficiently balances capacitor voltage,minimizes steady-state error,and strongly suppresses both zero and third-order harmonics resulting in reduced total harmonic distortion and enhanced voltage regulation.Additionally,a novel switching algorithm simplifies the design and implementation,further lowering voltage stress across switches.Extensive simulation results validate the performance under various resistive and resistive-inductive load conditions,demonstrating compliance with IEEE-519 THD standards and robust operation under dynamic changes.The proposed sensorless PR-controlled 15-PUC inverter thus offers a compelling,cost-effective solution for efficient power conversion in next-generation renewable energy systems.展开更多
基金The Doctoral Programs Foundation(20113401110009)of Education Ministry of ChinaNatural Science Research Project(2012kj11)of Hefei Normal University+1 种基金Universities Natural Science Foundation(KJ2013A220)of Anhui ProvinceResearch Project of Graduates Innovation Fund(2014yjs02)
文摘In this paper, we first introduce the concept ＂harmonically convex functions＂ in the second sense and establish several Hermite-Hadamard type inequalities for harmonically convex functions in the second sense. Finally, some applications to special mean are shown.
基金Supported by the National Key Technology R&D Program of the Ministry of Science and Technology under Grant No2012BAC23B03the National Key Basic Research Program of China under Grant No 2013CB922401the National Natural Science Foundation of China under Grants No 11474002
文摘We report the generation of passively tunable high peak signal-to-noise ratio harmonic mode-locked （HML） all- normal-dispersion Yb-doped fiber laser with a single birefringent filter in a ring cavity configuration. The highest fourth harmonic of the fundamental mode-locked frequency at a repetition rate of 88 MHz is obtained. The pulses are compressed to 627fs by using an external grating-pair compressor. For the fourth HML output, the peak signal-to-noise ratio of the rf is 73dB and the average power is as high as 110mW with the pump power of 500mW. Soliton bunches which contain multipulses are also observed in the weak mode-locked regime of the HML, and the separation between interpulses in a dissipative soliton bunch can be controlled by adjustment of the waveplates and spectral filter in the cavity：
文摘In this work, a mathematical model of an elastic material with cylindrical cavity will be constructed. The governing equations will be taken into the context of the fractional order generalized thermoelasticity theory (Youssef 2010). Laplace transform and direct approach will be used to obtain the solution when the boundary of the cavity is exposed to harmonically heat with constant angular frequency of thermal vibration. The inverse of Laplace transforms will be computed numerically using a method based on Fourier expansion techniques. Some comparisons have been shown in figures to present the effect of the fractional order parameter and the angular frequency of thermal vibration on all the studied felids.
基金Project supported by the National Natural Science Foundation of China(Nos.10772159 and 10802030)the Research Fund for Doctoral Program of Higher Education of China(No.20060335125)
文摘We studied the response of harmonically and stochastically excited strongly nonlinear oscillators with delayed feedback bang-bang control using the stochastic averaging method. First, the time-delayed feedback bang-bang control force is expressed approximately in terms of the system state variables without time delay. Then the averaged It6 stochastic differential equations for the system are derived using the stochastic averaging method. Finally, the response of the system is obtained by solving the Fokker-Plank-Kolmogorov （FPK） equation associated with the averaged lt6 equations. A Duffing oscillator with time-delayed feedback bang-bang control under combined harmonic and white noise excitations is taken as an example to illus- trate the proposed method. The analytical results are confirmed by digital simulation. We found that the time delay in feedback bang-bang control will deteriorate the control effectiveness and cause bifurcation of stochastic jump of Duffing oscillator.
基金supported by the National Natural Science Foundation of China (Grants 11402151 and 11572182)
文摘Nonlinear behaviors are investigated for a structure coupled with a nonlinear energy sink. The structure is linear and subject to a harmonic excitation, modeled as a forced single-degree-of-freedom oscillator. The nonlinear energy sink is modeled as an oscillator consisting of a mass,a nonlinear spring, and a linear damper. Based on the numerical solutions, global bifurcation diagrams are presented to reveal the coexistence of periodic and chaotic motions for varying nonlinear energy sink mass and stiffness. Chaos is numerically identified via phase trajectories, power spectra,and Poincaré maps. Amplitude-frequency response curves are predicted by the method of harmonic balance for periodic steady-state responses. Their stabilities are analyzed.The Hopf bifurcation and the saddle-node bifurcation are determined. The investigation demonstrates that a nonlinear energy sink may create dynamic complexity.
基金Supported by the National Natural Science Foundation of China under Grant No.19404004。
文摘Taking two identical ions in a Paul trap,we solved the SchrÖdinger equation for one-,two-,and three-dimensional harmonically bound two-body Coulomb models,in which the eigenfunctions are written in a series form and the eigenenergies are obtained from a continued fraction.Numerical calculations are made for specific discussion of two-and three-dimensional case.The comparison with a former one-dimensional approximate work shows that our result is more general and accurate.
基金supported by the National Natural Science Foundation of China(Grant No.62375275 and 62275254)by Strategic Priority Research Program of the Chinese Academy of Science(XDB0650000)+1 种基金by Shanghai Science and Technology Plan Project Funding(Grant No.23JC1410100)by Fuyang High-level Talent Group Project.
文摘Harmonic mode-locking,realized actively or passively,is an effective technique for increasing the repetition rate of ultrafast lasers.It is critically important to understand how a harmonically mode-locked pulse train responds to external perturbations and noise,so as to make sure that it is stable and resistant to noise.Here,in a series of carefully designed experiments,we elucidate the retiming dynamics of laser pulses generated in a soliton fiber laser harmonically modelocked at GHz frequencies to the acoustic resonance in a photonic crystal fiber(PCF)core.We characterize the selfdriven optomechanical lattice,which is distributed along the PCF and provides the structure that supports harmonic mode-locking,using a homodyne setup.We reveal that,after an abrupt perturbation,each soliton in the lattice undergoes damped oscillatory retiming within its trapping potential,while the retiming is strongly coupled to soliton dissipation.In addition,we show,through statistical analysis of the intra-cavity pulse spacing,how the trapping potentials are effective for suppressing timing jtter.The measurements and the theory developed in this work lay the groundwork for studies of the general stability and noise performance of harmonically mode-locked lasers as well as providing valuable insight into generic multi-pulse phenomena in mode-locked lasers.
基金supported by the National Key R&D Program of China (Grant Nos.2023YFA1406801 and 2022YFA1604301)the National Natural Science Foundation of China (Grant Nos.12434013,12595343,12404393,and 12174011)。
文摘High harmonic generation(HHG)provides an experimental method for producing attosecond pulses and probing electron dynamics.Achieving precise dipole phase measurements is critical for tailoring the harmonic emission phase and identifying the HHG mechanism.However,achieving this feature by applying traditional two-beam far-field interferometry to solid materials remains challenging.In this study,we present a novel interferometric approach that utilizes a single laser beam to excite two ZnO microwires(MWs)simultaneously,thereby generating coherent high-harmonic sources that form interference fringes in the far-field region.We leverage the diameter-dependent field-enhancement effect in MWs to measure the intensity-dependent fringe shift,revealing that the intraband current mechanism dominates the below-bandgap harmonic,whereas the interband polarization mechanism dominates the above-bandgap harmonic.This study offers a robust method for measuring the dipole phase of solid-state HHG and inspires intensity-modulated high-harmonic applications in coherent imaging and microdevice design.
基金the National Key Research&Development Program of China(Grant No.2022YFC2203901)the State Key Laboratory of Spatial Datum(Grant No.SKLSD2025-KF-03)+1 种基金Fundamental Research Funds for the Central UniversitiesSun Yat-sen University for the support。
文摘The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.
基金supported by China Southern Power Grid Corporation(036000KC23090005(GDKJXM20231027)).
文摘This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first solved via Newton-Raphson iteration through a set of nonlinear equations,and then input-output variables are selected to estimate the linear transfer function of the original NTP system without perturbations.The applications and insights of the proposed algorithm are discussed,particularly in guiding existing frequency scan algorithms,which are restricted by time-domain signal generation or measurement.This improvement is achieved through linear stability analysis of NTP systems with perturbations.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12234002, 92250303, 12474486, 12504301, and 12504396)the National Key Research and Development Program of China (Grant No. 2024YFA1612101)。
文摘With their intricate vectorial structures in space,optical skyrmions have significantly expanded the landscape of topological optics and light-matter interactions.We theoretically investigate high harmonic generation in crystals driven by optical skyrmions.We find that although the skyrmion number is not conserved,the resulting high-order harmonics can exhibit a distinctive multi-vortex structure,whose features are shaped by both the topology of the optical skyrmions and the rotational symmetry of the crystal.The position of the vortex centers can be effectively tuned by employing different types of optical skyrmions.To elucidate the underlying physics,we develop a multi-absorption channel model based on the conservation laws of spin and orbital angular momentum.Our work explores the role of optical topology in extreme nonlinear light-matter interactions,offering new opportunities for the formation and manipulation of optical vortices and novel structured light fields in the visible and ultraviolet regimes.
文摘In order to eliminate the meshing interference between the flexspline and circular spline after the taper deformation of the flexspline,the radial deformation difference method,major and minor axis fitting method,and ellipse fitting method are used to modify the tooth thickness of the flexspline and analyze the performance indexes such as the assembly stress,transmission error,and fatigue life.Firstly,the conjugate tooth profile is solved based on the quadruple-circular-arc tooth profile and modified kinematic method.Then,based on the finite element radial deformation of the flexspline,the principle and characteristics of three modification methods are analyzed,and the modification amount of each section of the flexspline tooth is calculated.Finally,the influence of the three modification methods on the performance of the harmonic drive is compared.The results show that the radial deformation difference method can initially determine the modification amount.The minimum static assembly stress is 406.22 MPa by the major and minor axis fitting method.The ellipse fitting method has the best dynamic performance,small transmission error fluctuation,a peak-to-peak value of 3.060",and a maximum fatigue life of 10^(7.558)cycles.
基金supported by the National Natural Science Foundation of China(Grant No.52475574).
文摘Harmonic mode-locking(HML)in soliton fiber lasers is crucial for generating high-repetition-rate pulse trains beyond the fundamental cavity frequency,enabling advanced applications in,for example,optical communication and precision sensing.However,achieving HML in experiments is challenging,owing to its inherent instability and high sensitivity to laser parameters,resulting in complex and iterative adjustments.In this paper,a novel HML technique utilizing bidirectional adjustment of pump power is proposed,and it is experimentally demonstrated in an all-fiber hybrid mode-locked soliton laser.By first increasing the pump power to generate a soliton bunch with a certain number of pulses and then gradually decreasing it,HML can be achieved at an order corresponding to the number of pulses in the soliton bunch.Experimental results on the evolution of temporal pulse trains during bidirectional adjustment of the pump power enable a relationship to be established between pump power and soliton bunching with increasing pump power,and reveal the collapse of the soliton bunch and subsequent gradual uniform distribution of solitons into an HML state with decreasing pump power.Second-to sixth-order HML is successfully generated using the proposed technique,and an analysis of the results provides a deeper understanding of the observed pulse dynamics.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172267 and 12302014).
文摘Quasi-periodic solutions with multiple base frequencies exhibit the feature of 2π-periodicity with respect to each of the hyper-time variables.However,it remains a challenge work,due to the lack of effective solution methods,to solve and track the quasi-periodic solutions with multiple base frequencies until now.In this work,a multi-steps variable-coefficient formulation is proposed,which provides a unified framework to enable either harmonic balance method or collocation method or finite difference method to solve quasi-periodic solutions with multiple base frequencies.For this purpose,a method of alternating U and S domain is also developed to efficiently evaluate the nonlinear force terms.Furthermore,a new robust phase condition is presented for all of the three methods to make them track the quasi-periodic solutions with prior unknown multiple base frequencies,while the stability of the quasi-periodic solutions is assessed by mean of Lyapunov exponents.The feasibility of the constructed methods under the above framework is verified by application to three nonlinear systems.
文摘Integration of renewable energy sources into power systems requires efficient multilevel inverters,capable of producing high-quality output voltage with low total harmonic distortion(THD).Conventional multilevel inverters often suffer from high component count,high switching stress,low voltage gain,and increased cost,limiting their practical application.This paper introduces a high-gain novel topology for multilevel inverters with reduced number of total components per level count,low voltage stress on power conductive devices,and minimizing a cost function,which depends on the number of components,standing voltage on switches and diodes,output voltage levels,and gain.The designed topology,which can be applied in photovoltaic(PV)systems,utilizes only one direct current(DC)input supply and a modular structure with the ability of capacitor’s voltage self-balancing.The high gain property and low THD of the proposed topology are two advantages that provide sine output waveform,with no need to a high DC input voltage source.Moreover,generalized topology,consisting of cascaded basic units,has been proposed.A comprehensive method has been proposed to determining the values of DC supplies in this configuration,aiming to minimize redundant switching modes and maximize the voltage levels count.The comparison with some other multilevel inverters confirms the desired performance of the basic version given inverter.A prototype has been also implemented and the experimental results have been obtained to verify the advantages of the proposed 25-level topology.
基金supported by National Natural Science Foundation of China(52277094).
文摘Hybrid MMC(Hy-MMC)has broad application prospects because of the negative level output ability in its bridge arm.A Hy-MMC topology with a high-modulation ratio is designed in this paper.A second-harmonic current injection(SHCI)strategy based on Hy-MMC in high-modulation operation is also proposed to improve the power density of Hy-MMC effectively in steady-state operation.The amplitude of SHCI is determined from the perspective of the root mean square(RMS)value of bridge arm current,and the optimal initial phase angle is determined from the multi-objective optimization(capacitor voltage ripple of sub-modules(SMs),power loss,and peak value of bridge arm current).The effectiveness and engineering practicability of the proposed SHCI strategy based on Hy-MMC in high-modulation operation is verified by the electromagnetic transient(EMT)simulation using PSCAD/EMTDC®.The simulation results show that the capacitor voltage ripple of SMs can be effectively decreased by 61.98%or the capacitance can be decreased by 40%.The power loss is also analyzed.In addition,little influence of low capacitance on multi-operation conditions of Hy-MMC is verified by EMT simulation.
基金supported by the National Natural Science Foundation of China(Grant No.12304379)the Natural Science Foundation of Liaoning Province(Grant No.2024BS-269)the Guangdong Basic and Applied Basic Research Foundation(Grant No.025A1515011117)。
文摘High-precision optical frequency measurement serves as a cornerstone of modern science and technology,enabling advancements in fields ranging from fundamental physics to quantum information technologies.Obtaining precise photon frequencies,especially in the ultraviolet or even extreme ultraviolet regimes,is a key goal in both light–matter interaction experiments and engineering applications.High-order harmonic generation(HHG)is an ideal light source for producing such photons.In this work,we propose an optical temporal interference model(OTIM)that establishes an analogy with multi-slit Fraunhofer diffraction(MSFD)to manipulate fine-frequency photon generation by exploiting the temporal coherence of HHG processes.Our model provides a unified physical framework for three distinct non-integer HHG generation schemes:single-pulse,shaped-pulse,and laser pulse train approaches,which correspond to single-MSFD-like,double-MSFD-like,and multi-MSFD-like processes,respectively.Arbitrary non-integer HHG photons can be obtained using our scheme.Our approach provides a new perspective for accurately measuring and controlling photon frequencies in fields such as frequency comb technology,interferometry,and atomic clocks.
基金Project supported by the National Key R&D Program of China(No.2023YFE0125900)。
文摘A novel vibration isolation system designed for superior performance in low-frequency environments is proposed in this work.The isolator is based on a unique hexagonal arrangement of linear springs,allowing for an adjustable geometric configuration via the initial inclination angle.Based on the principle of Lagrangian mechanics,the equation of motion governing the structural dynamics is rigorously derived.The system is modeled as a strongly nonlinear single-degree-of-freedom dynamical system,loaded with a normalized payload and subject to harmonic base excitation.To analyze the steady-state response,the harmonic balance method is employed,providing accurate predictions of the payload's vibration amplitude and displacement transmissibility as functions of both the base excitation amplitude and frequency.The analysis reveals a direct relationship between the isolator's geometric and stiffness parameters and its load-bearing capacity,leading to the identification of three distinct operational regimes.Depending on the unloaded initial inclination angle,the equivalent stiffness ratio,and the payload design configuration,the system can exhibit one of three vibration isolation modes:(i)the quasizero stiffness(QZS)isolation mode,(ii)the zero linear stiffness with controllable nonlinear stiffness,and(iii)the full-band perfect zero stiffness.The vibration isolation performance of the proposed structure is thoroughly discussed for all three oscillation modes in terms of frequency response curves,displacement transmissibility,and time-domain responses.The key novel finding is that this structure can operate as a full-band,high-performance vibration isolator when the initial inclination angle is designed to be a right angle,enabling full isolation of the maximum possible payload.Moreover,the analytical results and numerical simulations demonstrate that the isolator's displacement transmissibility T with the unit dB tends to-∞as the air-damping coefficient approaches zero,enabling ideal vibration isolation across the entire excitation frequency range.These analytical insights are validated through comprehensive numerical simulations,which show excellent agreement with the theoretical predictions.
基金supported by the Scientific Research Program Funded by Shaanxi Provincial Education Department (Grant No.24JP126)the National Natural Science Foundation of China (Grant No.62174136)the Natural Science Basic Research Program of Shaanxi Province (Grant No.2025JC-YBMS-063)。
文摘High-pressure hydrides have emerged as promising superconducting materials,attracting considerable attention in recent years.In this work,by combining the stochastic self-consistent harmonic approximation with first-principles calculations,we elucidate crucial corrections to the vibrational and superconducting properties arising from quantum and anharmonic ionic vibrations of SnH4 in P63/mmc phase at 150–240 GPa.Compared with the classical harmonic approximation,inclusion of these effects results in a pronounced softening(over 500 cm^(−1))of hydrogen-derived optical phonon modes,and increases the superconducting critical temperature(Tc)from 65 K to 79 K(μ^(*)=0.1;isotropic Migdal–Eliashberg theory),corresponding to a 22%enhancement.For μ^(*)=0.13,the predicted Tc is approximately 70 K.Analysis of the Eliashberg spectral function confirms that hydrogen vibrational modes constitute the dominant tuning mechanism.These results provide quantitative insights into quantum ionic effects in hydride superconductors.
文摘Conventional multilevel inverters often suffer from high harmonic distortion and increased design complexity due to the need for numerous power semiconductor components,particularly at elevated voltage levels.Addressing these shortcomings,thiswork presents a robust 15-level PackedUCell(PUC)inverter topology designed for renewable energy and grid-connected applications.The proposed systemintegrates a sensor less proportional-resonant(PR)controller with an advanced carrier-based pulse width modulation scheme.This approach efficiently balances capacitor voltage,minimizes steady-state error,and strongly suppresses both zero and third-order harmonics resulting in reduced total harmonic distortion and enhanced voltage regulation.Additionally,a novel switching algorithm simplifies the design and implementation,further lowering voltage stress across switches.Extensive simulation results validate the performance under various resistive and resistive-inductive load conditions,demonstrating compliance with IEEE-519 THD standards and robust operation under dynamic changes.The proposed sensorless PR-controlled 15-PUC inverter thus offers a compelling,cost-effective solution for efficient power conversion in next-generation renewable energy systems.
