Using multi-source reanalysis data,this study examines the relationship between the tropical Pacific-Atlantic SST Dipole Mode(TPA-DM)and summer precipitation in North China(NCSP)on the interannual timescale during the...Using multi-source reanalysis data,this study examines the relationship between the tropical Pacific-Atlantic SST Dipole Mode(TPA-DM)and summer precipitation in North China(NCSP)on the interannual timescale during the period of 1979-2022.The results show that the TPA-DM,the dominant pattern of interannual variability in the tropical Pacific and Atlantic regions,exhibits a significant negative correlation with NCSP.The positive phase of TPA-DM induces subsidence over the Maritime Continent through a zonal circulation pattern,which initiates a Pacific-Japan-like wave train along the East Asian coast.The circulation anomalies lead to moisture deficits and convergence subsidence over North China,leading to below-normal rainfall.Further analysis reveals that cooler SST in the Southern Tropical Atlantic facilitates the persistence of the TPA-DM by stimulating the anomalous Walker circulation associated with wind-evaporation-SST-convection feedback.展开更多
The existence of rolling deformation area in the rolling mill system is the main characteristic which dis- tinguishes the other machinery. In order to analyze the dynamic property of roll system＇s flexural deformatio...The existence of rolling deformation area in the rolling mill system is the main characteristic which dis- tinguishes the other machinery. In order to analyze the dynamic property of roll system＇s flexural deformation, it is necessary to consider the transverse periodic movement of stock in the rolling deformation area which is caused by the flexural deformation movement of roll system simul- taneously. Therefore, the displacement field of roll system and flow of metal in the deformation area is described by kinematic analysis in the dynamic system. Through intro- ducing the lateral displacement function of metal in the deformation area, the dynamic variation of per unit width rolling force can be determined at the same time. Then the coupling law caused by the co-effect of rigid movement and flexural deformation of the system structural elements is determined. Furthermore, a multi-parameter coupling dynamic model of the roll system and stock is established by the principle of virtual work. More explicitly, the cou- pled motion modal analysis was made for the roll system. Meanwhile, the analytical solutions for the flexural defor- mation movement＇s mode shape functions of rolls are discussed. In addition, the dynamic characteristic of the lateral flow of metal in the rolling deformation area has been analyzed at the same time. The establishment ofdynamic lateral displacement function of metal in the deformation area makes the foundation for analyzing the coupling law between roll system and rolling deformation area, and provides a theoretical basis for the realization of the dynamic shape control of steel strip.展开更多
The bearing is described by constrain matrix, and the spindle system of a NCsurface grinding machine is simplified as elastic-coupling beam, then modal synthesis method is usedto establish the dynamic model of beam. M...The bearing is described by constrain matrix, and the spindle system of a NCsurface grinding machine is simplified as elastic-coupling beam, then modal synthesis method is usedto establish the dynamic model of beam. Moreover, the response of the end of rotor is analyzed, andthe natural frequency, principle mode and other dynamic characteristics of the coupling system arestudied, the law of bearing stiffness to coupling frequency and amplitude of rotor is also found.Finally, according to the actual condition, a dynamic absorber is designed. The simulation andexperimental results show that the amplitude of spindle can be declined effectively when the dynamicabsorber is attached.展开更多
As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To...As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To investigate the mechanical behaviour of coral reef limestone under the coupling impact of size and strain rate,the uniaxial compression tests were conducted on reef limestone samples with length-to-diameter(L/D)ratio ranging from 0.5 to 2.0 at strain rate ranging from 10^(−5)·s^(−1)to 10^(−2)·s^(−1).It is revealed that the uniaxial compressive strength(UCS)and residual compressive strength(RCS)of coral reef limestone exhibits a decreasing trend with L/D ratio increasing.The dynamic increase factor(DIF)of UCS is linearly correlated with the logarithm of strain rate,while increasing the L/D ratio further enhances the DIF.The elastic modulus increases with strain rate or L/D ratio increasing,whereas the Poisson’s ratio approximates to a constant value of 0.24.The failure strain increases with strain rate increasing or L/D ratio decreasing,while the increase in L/D ratio will inhibit the enhancing effect of the strain rate.The high porosity and low mineral strength are the primary factors contributing to a high RCS of 16.7%–64.9%of UCS,a lower brittleness index and multiple irregular fracture planes.The failure pattern of coral reef limestone transits from the shear-dominated to the splitting-dominated failure with strain rate increasing or L/D ratio decreasing,which is mainly governed by the constrained zones induced by end friction and the strain rate-dependent crack propagation.Moreover,a predictive formula incorporating coupling effect of size and strain rate for the UCS of reef limestone was established and verified to effectively capture the trend of UCS.展开更多
In this investigation,the coupling losses caused by Fresnel reflection,core misalignment between single mode fiber(SMF)and HC-PCF are analyzed.A novel solution proposed from this research will reduce the coupling loss...In this investigation,the coupling losses caused by Fresnel reflection,core misalignment between single mode fiber(SMF)and HC-PCF are analyzed.A novel solution proposed from this research will reduce the coupling losses by using a T-type tube as a connector.Meanwhile,the theoretically calculated optimized gaps are at 15μm in SMF-HCPCF direction and 25μm in HCPCF-SMF direction.Thus,an experiment has been carried out,and the results of the practical gap in the above mentioned two directions have also been obtained.Furthermore,compared with detection by traditional methods,the proposed new detection method with PCF can remarkably enhance the Raman spectroscopy signal.Finally,the prospect of using the combination of HC-PCF and Raman spectroscopy in gas-cell detection has been demonstrated by using oxygen and nitrogen.展开更多
Due to scale effects,micromechanical resonators offer an excellent platform for investigating the intrinsic mechanisms of nonlinear dynamical phenomena and their potential applications.This review focuses on mode-coup...Due to scale effects,micromechanical resonators offer an excellent platform for investigating the intrinsic mechanisms of nonlinear dynamical phenomena and their potential applications.This review focuses on mode-coupled micromechanical resonators,highlighting the latest advancements in four key areas:internal resonance,synchronization,frequency combs,and mode localization.The origin,development,and potential applications of each of these dynamic phenomena within mode-coupled micromechanical systems are investigated,with the goal of inspiring new ideas and directions for researchers in this field.展开更多
In the discharge of EAST tokamak, it is observed that （2, 1） neoclassical tearing mode （NTM） is triggered by mode coupling with a （1, 1） internal mode. Using singular value decomposition （SVD） method for soft ...In the discharge of EAST tokamak, it is observed that （2, 1） neoclassical tearing mode （NTM） is triggered by mode coupling with a （1, 1） internal mode. Using singular value decomposition （SVD） method for soft X-ray emission and for electron cyclotron emission （ECE）, the coupling spatial structures and coupling process between these two modes are analyzed in detail. The results of SVD for ECE reveal that the phase difference between these two modes equals to zero. This is consistent with the perfect coupling condition. Finally, performing statistical analysis of r1/1, ξ1/1 and w2/1, we find that r1/1 more accurately represents the coupling strength than ξ1/1, and r1/1 is also strongly related to the （2, 1） NTM triggering, where r1/1 is the width of （1, 1） internal mode, ξ1/1 is the perturbed amplitude of （1, 1） internal mode, and w2/1 denotes the magnetic island width of （2, 1） NTM.展开更多
The converging Richtmyer-Meshkov(RM)instability on single-and dual-mode N2/SF6 interfaces is studied by an upwind conservation element and solution element solver.An unperturbed case is first considered,and it is foun...The converging Richtmyer-Meshkov(RM)instability on single-and dual-mode N2/SF6 interfaces is studied by an upwind conservation element and solution element solver.An unperturbed case is first considered,and it is found that the shocked interface undergoes a long-term deceleration after a period of uniform motion.The evolution of single-mode interface at the early stage exhibits an evident nonlinearity,which can be reasonably predicted by the nonlinear model of Wang et al.(Phys Plasmas 22:082702,2015).During the deceleration stage,the perturbation amplitude drops quickly and even becomes a negative(phase inversion)before the reshock due to the Rayleigh-Taylor(RT)stabilization.After the reshock,the interface experiences a phase inversion again or does not,depending on the reshock time.The growth of the second-order harmonic in the deceleration stage clearly reveals the competition between the RT effect and the nonlinearity.For dual-mode interfaces,the growth of the first mode(wavenumber k1)relies heavily on the second mode(wavenumber k2)due to the mode coupling effect.Specifically,for cases where k2 is an even or odd multiple of k1,the growth of the first mode is inhibited or promoted depending on its initial amplitude sign and the phase difference between two basic waves,while for cases where k2 is a non-integer multiple of k1,the second mode has negligible influence on the first mode.Through a systematic study,signs of perturbation amplitudes of the generated k2−k1 and k2+k1 waves are obtained for all possible dual-mode configurations,which are reasonably predicted by a modified Haan model(Phys Fluids B 3:2349-2355,1991).展开更多
This paper investigates the interaction of a small number of modes in the two-fluid Kelvin-Helmholtz instability at the nonlinear regime by using a two-dimensional hydrodynamic code. This interaction is found to be re...This paper investigates the interaction of a small number of modes in the two-fluid Kelvin-Helmholtz instability at the nonlinear regime by using a two-dimensional hydrodynamic code. This interaction is found to be relatively long range in wave-number space and also it acts in both directions, i.e. short wavelengths affect long wavelengths and vice versa. There is no simple equivalent transformation from a band of similar modes to one mode representing their effective amplitude. Three distinct stages of interaction have been identified.展开更多
The low-mode shell asymmetry and high-mode hot spot mixing appear to be the main reasons for the performance degradation of the National Ignition Facility(NIF)implosion experiments.The effects of the mode coupling bet...The low-mode shell asymmetry and high-mode hot spot mixing appear to be the main reasons for the performance degradation of the National Ignition Facility(NIF)implosion experiments.The effects of the mode coupling between low-mode P2 radiation flux asymmetry and intermediate-mode L=24 capsule roughness on the implosion performance of ignition capsule are investigated by two-dimensional radiation hydrodynamic simulations.It is shown that the amplitudes of new modes generated by the mode coupling are in good agreement with the second-order mode coupling equation during the acceleration phase.The later flow field not only shows large areal density P2 asymmetry in the main fuel,but also generates large-amplitude spikes and bubbles.In the deceleration phase,the increasing mode coupling generates more new modes,and the perturbation spectrum on the hot spot boundary is mainly from the strong mode interactions rather than the initial perturbation conditions.The combination of the low-mode and high-mode perturbations breaks up the capsule shell,resulting in a significant reduction of the hot spot temperature and implosion performance.展开更多
Excess loss on the short wavelength side of the Bragg resonant wavelength caused by cladding mode coupling limits wide use of grating in the fiber communication system, especially in densed wavelength division multipl...Excess loss on the short wavelength side of the Bragg resonant wavelength caused by cladding mode coupling limits wide use of grating in the fiber communication system, especially in densed wavelength division multiplexing (DWDM) system. A novel photosensitive fiber design that have depressed cladding and photosensitive inner cladding in the same fiber is proposed, which can suppress cladding mode coupling greatly. Using MCVD method B/Ge codoped fiber with depressed cladding was fabriceted out, which was also doped in boron and germanium and had the photosensitivity. Finally, the transmission spectrum of written grating in this fiber by phase mask method verified its larger photosensitivity and greatly suppression of cladding mode coupling.展开更多
Fabry–Perot(FP)modes are a class of fundamental resonances in photonic crystal(PhC)slabs.Owing to their low quality factors,FP modes are frequently considered as background fields with their resonance nature being ne...Fabry–Perot(FP)modes are a class of fundamental resonances in photonic crystal(PhC)slabs.Owing to their low quality factors,FP modes are frequently considered as background fields with their resonance nature being neglected.Nevertheless,FP modes can play important roles in some phenomena,as exemplified by their coupling with guided resonance(GR)modes to achieve bound states in the continuum(BIC).Here,we further demonstrate the genuine resonance mode capability of FP modes PhC slabs.Firstly,we utilize temporal coupled-mode theory to obtain the transmittance of a PhC slab based on the FP modes.Secondly,we construct exceptional points(EPs)in both momentum and parameter spaces through the coupling of FP and GR modes.Furthermore,we identify a Fermi arc connecting two EPs and discuss the far-field polarization topology.This work elucidates that the widespread FPs in PhC slabs can serve as genuine resonant modes,facilitating the realization of desired functionalities through mode coupling.展开更多
<div style="text-align:justify;"> Currently, coupled mode theory (CMT) is widely used for calculating the coupling coefficient of twin-core fibers (TCFs) that are used in a broad range of important app...<div style="text-align:justify;"> Currently, coupled mode theory (CMT) is widely used for calculating the coupling coefficient of twin-core fibers (TCFs) that are used in a broad range of important applications. This approach is highly accurate for scenarios with weak coupling between the cores but shows significant errors in the strong coupling scenarios, necessitating the use of a more accurate method for coupling coefficient calculations. Therefore, in this work, we calculate the coupling coefficients of TCFs using the supermode theory with finite element method (FEM) that has higher accuracy than CMT, particularly for the strong coupling TCF. To investigate the origin of the differences between the results obtained by these two methods, the modal field distributions of the supermodes of TCF are simulated and analyzed in detail. </div>展开更多
This paper introduces a bond-based peridynamics(BB-PD)algorithm for crack identification,integrating the Delaunay triangulation method to accurately identify the structural characteristics of threedimensional(3D)crack...This paper introduces a bond-based peridynamics(BB-PD)algorithm for crack identification,integrating the Delaunay triangulation method to accurately identify the structural characteristics of threedimensional(3D)cracks in rocks.A bond-based crack quantification standard is proposed to analyze the evolution of cracks of various sizes.A multi-attribute peridynamic model,developed using a multilayer algorithm,was employed to simulate the fracturing process of sandstone disks and semi-disks under varying temperatures,with the model calibrated and validated against experimental results.The simulation results show that temperature induces nonlinear degradation in the tensile strength and fracture toughness of sandstone,with 500℃ identified as the threshold temperature.Thermal cracks exhibit varying degrees of influence on Mode I cracks across different temperature ranges.Thermal damage significantly promotes the initiation and propagation of Mode I cracks in sandstone,thereby reducing its tensile strength and fracture toughness.Under applied loads,crack propagation in sandstone predominantly occurs during the failure stage,characterized by the rapid growth of longer cracks and a slow increase or reduction in shorter cracks.展开更多
The spin-exchange relaxation-free atomic gyroscope,with its exceptionally high theoretical precision,demonstrates immense potential to become the next-generation strategic-grade gyroscope.However,due to technological ...The spin-exchange relaxation-free atomic gyroscope,with its exceptionally high theoretical precision,demonstrates immense potential to become the next-generation strategic-grade gyroscope.However,due to technological noise,there is still a significant gap between its actual precision and theoretical precision.This study identifies the key factor limiting the precision of the SERF gyroscope as coupling noise.By optimizing the detection loop structure,a distinction between the dual-axis signals'response to optical and magnetic fields was achieved-where the optical errors responded similarly,while the response to magnetic noise was opposite.Based on the differences in the optical-magnetic response of the dual-axis signals,empirical mode decomposition was used to decompose the dual-axis gyroscope signals into multiple intrinsic mode functions,and Allan deviation analysis was applied to analyze the noise characteristics of the intrinsic mode functions over various periods.This study successfully reveals that optical errors caused by thermal-optical coupling and long-period magnetic noise induced by thermal-magnetic coupling are the dominant factors limiting the long-term stability of the SERF gyroscope.Based on these analyses,the study concludes that to achieve strategic-grade precision for the SERF gyroscope,it is essential to effectively address the noise issues caused by multi-physical field couplings.展开更多
Nonlinear couplings of various Alfvén modes driven by energetic particles in HL-2 A are addressed by employing the Fourier bicoherence and Lissajous-curve technique. Long-lived modes and high-frequency coherent m...Nonlinear couplings of various Alfvén modes driven by energetic particles in HL-2 A are addressed by employing the Fourier bicoherence and Lissajous-curve technique. Long-lived modes and high-frequency coherent modes are presented. Then the squared bicoherence of three waves establishes the existence of three-wave coupling. Lissajous-curves of those waves manifest that their phases are locked, which again confirms that they are nonlinearly coupled to each other. Moreover, coupled modes triggered by supersonic molecular beam injection are investigated. The phase evolution of them is given by the Lissajous-curve. Further details of phase-flip and phase-slip are presented and discussed.展开更多
We report a theoretical work on the properties of modulational instability and bright type nonlinear localized modes in one-dimensional easy-axis weak ferromagnetic spin lattices involving next-nearest-neighbor coupli...We report a theoretical work on the properties of modulational instability and bright type nonlinear localized modes in one-dimensional easy-axis weak ferromagnetic spin lattices involving next-nearest-neighbor couplings.With a linear stability analysis, we calculate the growth rates of the modulational instability, and plot the instability regions.When the strength of the next-nearest-neighbor coupling is large enough, two new asymmetric modulational instability regions appear near the boundary of the first Brillouin zone.Furthermore, analytical forms of the bright nonlinear localized modes are constructed by means of a quasi-discreteness approach.The influence of the next-nearest-neighbor coupling on the Brillouin zone center mode and boundary mode are discussed.In particular, we discover a reversal phenomenon of the propagation direction of the Brillouin zone boundary mode.展开更多
An optic-fiber sensor system for measuring distributed forces is presented. The sensor system chooses high-birefringent fiber as sensing e-iement. Based on coupling effects of polarization modes in high-birefringent ...An optic-fiber sensor system for measuring distributed forces is presented. The sensor system chooses high-birefringent fiber as sensing e-iement. Based on coupling effects of polarization modes in high-birefringent fiber, the distribution of the force points along the sensing fiber can be measured by detecting mode couplings in the fiber which are caused by external force disturbance. The location and magnitude of the measured forces are determined by a heterodyne interferometry and the technique of optic path scanning. The spatial resolution of the sensor system is better than 0. 15m for a 50m testing fiber.展开更多
Birefringence （polarization-related phase-shift）, polarization dependent gain （PDG） and mode coupling are three factors that may synchronously influence the transmission of single-wavelength polarized light in opt...Birefringence （polarization-related phase-shift）, polarization dependent gain （PDG） and mode coupling are three factors that may synchronously influence the transmission of single-wavelength polarized light in optical fibers. This paper obtains a new Mueller matrix analysis, which can be used under conditions that all these three factors are existing and changing. According to our transmission model, the state of polarization （SOP） changes along an optical mierostructure fiber with co-existence of birefringence-PDG-mode coupling were simulated. The simulated results, which show the phenomena of SOP constringency, are in good agreement with previous theoretical analyses.展开更多
In this paper,a theoretical model to analyze the mode coupling induced by heat,when the fiber amplifier works at high power configuration,is proposed.The model mainly takes into consideration the mode field change due...In this paper,a theoretical model to analyze the mode coupling induced by heat,when the fiber amplifier works at high power configuration,is proposed.The model mainly takes into consideration the mode field change due to the thermally induced refractive index change and the coupling between modes.A method to predict the largest average output power of fiber is also proposed according to the mode coupling theory.The largest average output power of a large pitch fiber with a core diameter of 190 μm and an available pulse energy of 100 mJ is predicted to be 540 W,which is the highest in large mode field fibers.展开更多
基金jointly supported by the Second Tibetan Plateau Scientific Expedition and Research Program[grant number-ber 2019QZKK0103]the National Natural Science Foundation of China[grant number 42293294]the China Meteorological Admin-istration Climate Change Special Program[grant number QBZ202303]。
文摘Using multi-source reanalysis data,this study examines the relationship between the tropical Pacific-Atlantic SST Dipole Mode(TPA-DM)and summer precipitation in North China(NCSP)on the interannual timescale during the period of 1979-2022.The results show that the TPA-DM,the dominant pattern of interannual variability in the tropical Pacific and Atlantic regions,exhibits a significant negative correlation with NCSP.The positive phase of TPA-DM induces subsidence over the Maritime Continent through a zonal circulation pattern,which initiates a Pacific-Japan-like wave train along the East Asian coast.The circulation anomalies lead to moisture deficits and convergence subsidence over North China,leading to below-normal rainfall.Further analysis reveals that cooler SST in the Southern Tropical Atlantic facilitates the persistence of the TPA-DM by stimulating the anomalous Walker circulation associated with wind-evaporation-SST-convection feedback.
基金Supported by National Natural Science Foundation of China(Grant No.51375424)
文摘The existence of rolling deformation area in the rolling mill system is the main characteristic which dis- tinguishes the other machinery. In order to analyze the dynamic property of roll system＇s flexural deformation, it is necessary to consider the transverse periodic movement of stock in the rolling deformation area which is caused by the flexural deformation movement of roll system simul- taneously. Therefore, the displacement field of roll system and flow of metal in the deformation area is described by kinematic analysis in the dynamic system. Through intro- ducing the lateral displacement function of metal in the deformation area, the dynamic variation of per unit width rolling force can be determined at the same time. Then the coupling law caused by the co-effect of rigid movement and flexural deformation of the system structural elements is determined. Furthermore, a multi-parameter coupling dynamic model of the roll system and stock is established by the principle of virtual work. More explicitly, the cou- pled motion modal analysis was made for the roll system. Meanwhile, the analytical solutions for the flexural defor- mation movement＇s mode shape functions of rolls are discussed. In addition, the dynamic characteristic of the lateral flow of metal in the rolling deformation area has been analyzed at the same time. The establishment ofdynamic lateral displacement function of metal in the deformation area makes the foundation for analyzing the coupling law between roll system and rolling deformation area, and provides a theoretical basis for the realization of the dynamic shape control of steel strip.
基金This project is supported by Provincial Natural Science Foundation of hianjin, China (NO.99380261l)
文摘The bearing is described by constrain matrix, and the spindle system of a NCsurface grinding machine is simplified as elastic-coupling beam, then modal synthesis method is usedto establish the dynamic model of beam. Moreover, the response of the end of rotor is analyzed, andthe natural frequency, principle mode and other dynamic characteristics of the coupling system arestudied, the law of bearing stiffness to coupling frequency and amplitude of rotor is also found.Finally, according to the actual condition, a dynamic absorber is designed. The simulation andexperimental results show that the amplitude of spindle can be declined effectively when the dynamicabsorber is attached.
基金supported by the National Natural Science Foundation of China(Nos.52222110,52401354,and 52301353).
文摘As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To investigate the mechanical behaviour of coral reef limestone under the coupling impact of size and strain rate,the uniaxial compression tests were conducted on reef limestone samples with length-to-diameter(L/D)ratio ranging from 0.5 to 2.0 at strain rate ranging from 10^(−5)·s^(−1)to 10^(−2)·s^(−1).It is revealed that the uniaxial compressive strength(UCS)and residual compressive strength(RCS)of coral reef limestone exhibits a decreasing trend with L/D ratio increasing.The dynamic increase factor(DIF)of UCS is linearly correlated with the logarithm of strain rate,while increasing the L/D ratio further enhances the DIF.The elastic modulus increases with strain rate or L/D ratio increasing,whereas the Poisson’s ratio approximates to a constant value of 0.24.The failure strain increases with strain rate increasing or L/D ratio decreasing,while the increase in L/D ratio will inhibit the enhancing effect of the strain rate.The high porosity and low mineral strength are the primary factors contributing to a high RCS of 16.7%–64.9%of UCS,a lower brittleness index and multiple irregular fracture planes.The failure pattern of coral reef limestone transits from the shear-dominated to the splitting-dominated failure with strain rate increasing or L/D ratio decreasing,which is mainly governed by the constrained zones induced by end friction and the strain rate-dependent crack propagation.Moreover,a predictive formula incorporating coupling effect of size and strain rate for the UCS of reef limestone was established and verified to effectively capture the trend of UCS.
基金Supported by National Nature Science Foundation of China(61308066)
文摘In this investigation,the coupling losses caused by Fresnel reflection,core misalignment between single mode fiber(SMF)and HC-PCF are analyzed.A novel solution proposed from this research will reduce the coupling losses by using a T-type tube as a connector.Meanwhile,the theoretically calculated optimized gaps are at 15μm in SMF-HCPCF direction and 25μm in HCPCF-SMF direction.Thus,an experiment has been carried out,and the results of the practical gap in the above mentioned two directions have also been obtained.Furthermore,compared with detection by traditional methods,the proposed new detection method with PCF can remarkably enhance the Raman spectroscopy signal.Finally,the prospect of using the combination of HC-PCF and Raman spectroscopy in gas-cell detection has been demonstrated by using oxygen and nitrogen.
基金supported by the National Key Research and Development Program of China(No.2022YFB3203600)the National Natural Science Foundation of China(Nos.12202355,12132013,and 12172323)the Zhejiang Provincial Natural Science Foundation of China(No.LZ22A020003)。
文摘Due to scale effects,micromechanical resonators offer an excellent platform for investigating the intrinsic mechanisms of nonlinear dynamical phenomena and their potential applications.This review focuses on mode-coupled micromechanical resonators,highlighting the latest advancements in four key areas:internal resonance,synchronization,frequency combs,and mode localization.The origin,development,and potential applications of each of these dynamic phenomena within mode-coupled micromechanical systems are investigated,with the goal of inspiring new ideas and directions for researchers in this field.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2014GB103000,2011GB101000 and2013GB102000)sponsored in part by National Natural Science Foundation of China(Nos.10725523,10990212 and 11205199)
文摘In the discharge of EAST tokamak, it is observed that （2, 1） neoclassical tearing mode （NTM） is triggered by mode coupling with a （1, 1） internal mode. Using singular value decomposition （SVD） method for soft X-ray emission and for electron cyclotron emission （ECE）, the coupling spatial structures and coupling process between these two modes are analyzed in detail. The results of SVD for ECE reveal that the phase difference between these two modes equals to zero. This is consistent with the perfect coupling condition. Finally, performing statistical analysis of r1/1, ξ1/1 and w2/1, we find that r1/1 more accurately represents the coupling strength than ξ1/1, and r1/1 is also strongly related to the （2, 1） NTM triggering, where r1/1 is the width of （1, 1） internal mode, ξ1/1 is the perturbed amplitude of （1, 1） internal mode, and w2/1 denotes the magnetic island width of （2, 1） NTM.
基金the National Natural Science Foundation of China(Grants 11802304 and 11625211)the Science Challenging Project(Grant TZ2016001).
文摘The converging Richtmyer-Meshkov(RM)instability on single-and dual-mode N2/SF6 interfaces is studied by an upwind conservation element and solution element solver.An unperturbed case is first considered,and it is found that the shocked interface undergoes a long-term deceleration after a period of uniform motion.The evolution of single-mode interface at the early stage exhibits an evident nonlinearity,which can be reasonably predicted by the nonlinear model of Wang et al.(Phys Plasmas 22:082702,2015).During the deceleration stage,the perturbation amplitude drops quickly and even becomes a negative(phase inversion)before the reshock due to the Rayleigh-Taylor(RT)stabilization.After the reshock,the interface experiences a phase inversion again or does not,depending on the reshock time.The growth of the second-order harmonic in the deceleration stage clearly reveals the competition between the RT effect and the nonlinearity.For dual-mode interfaces,the growth of the first mode(wavenumber k1)relies heavily on the second mode(wavenumber k2)due to the mode coupling effect.Specifically,for cases where k2 is an even or odd multiple of k1,the growth of the first mode is inhibited or promoted depending on its initial amplitude sign and the phase difference between two basic waves,while for cases where k2 is a non-integer multiple of k1,the second mode has negligible influence on the first mode.Through a systematic study,signs of perturbation amplitudes of the generated k2−k1 and k2+k1 waves are obtained for all possible dual-mode configurations,which are reasonably predicted by a modified Haan model(Phys Fluids B 3:2349-2355,1991).
基金Project supported by the Research Fund for the Doctoral Program of Higher Education of China (Grant No 20070290008)the National Basic Research Program of China (Grant No 2007CB815100)
文摘This paper investigates the interaction of a small number of modes in the two-fluid Kelvin-Helmholtz instability at the nonlinear regime by using a two-dimensional hydrodynamic code. This interaction is found to be relatively long range in wave-number space and also it acts in both directions, i.e. short wavelengths affect long wavelengths and vice versa. There is no simple equivalent transformation from a band of similar modes to one mode representing their effective amplitude. Three distinct stages of interaction have been identified.
基金This work is supported by the National Natural Science Foundation of China under Grant Nos.11575034,11275031,11401033,and 91330205.
文摘The low-mode shell asymmetry and high-mode hot spot mixing appear to be the main reasons for the performance degradation of the National Ignition Facility(NIF)implosion experiments.The effects of the mode coupling between low-mode P2 radiation flux asymmetry and intermediate-mode L=24 capsule roughness on the implosion performance of ignition capsule are investigated by two-dimensional radiation hydrodynamic simulations.It is shown that the amplitudes of new modes generated by the mode coupling are in good agreement with the second-order mode coupling equation during the acceleration phase.The later flow field not only shows large areal density P2 asymmetry in the main fuel,but also generates large-amplitude spikes and bubbles.In the deceleration phase,the increasing mode coupling generates more new modes,and the perturbation spectrum on the hot spot boundary is mainly from the strong mode interactions rather than the initial perturbation conditions.The combination of the low-mode and high-mode perturbations breaks up the capsule shell,resulting in a significant reduction of the hot spot temperature and implosion performance.
文摘Excess loss on the short wavelength side of the Bragg resonant wavelength caused by cladding mode coupling limits wide use of grating in the fiber communication system, especially in densed wavelength division multiplexing (DWDM) system. A novel photosensitive fiber design that have depressed cladding and photosensitive inner cladding in the same fiber is proposed, which can suppress cladding mode coupling greatly. Using MCVD method B/Ge codoped fiber with depressed cladding was fabriceted out, which was also doped in boron and germanium and had the photosensitivity. Finally, the transmission spectrum of written grating in this fiber by phase mask method verified its larger photosensitivity and greatly suppression of cladding mode coupling.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12074049 and 12347101)。
文摘Fabry–Perot(FP)modes are a class of fundamental resonances in photonic crystal(PhC)slabs.Owing to their low quality factors,FP modes are frequently considered as background fields with their resonance nature being neglected.Nevertheless,FP modes can play important roles in some phenomena,as exemplified by their coupling with guided resonance(GR)modes to achieve bound states in the continuum(BIC).Here,we further demonstrate the genuine resonance mode capability of FP modes PhC slabs.Firstly,we utilize temporal coupled-mode theory to obtain the transmittance of a PhC slab based on the FP modes.Secondly,we construct exceptional points(EPs)in both momentum and parameter spaces through the coupling of FP and GR modes.Furthermore,we identify a Fermi arc connecting two EPs and discuss the far-field polarization topology.This work elucidates that the widespread FPs in PhC slabs can serve as genuine resonant modes,facilitating the realization of desired functionalities through mode coupling.
文摘<div style="text-align:justify;"> Currently, coupled mode theory (CMT) is widely used for calculating the coupling coefficient of twin-core fibers (TCFs) that are used in a broad range of important applications. This approach is highly accurate for scenarios with weak coupling between the cores but shows significant errors in the strong coupling scenarios, necessitating the use of a more accurate method for coupling coefficient calculations. Therefore, in this work, we calculate the coupling coefficients of TCFs using the supermode theory with finite element method (FEM) that has higher accuracy than CMT, particularly for the strong coupling TCF. To investigate the origin of the differences between the results obtained by these two methods, the modal field distributions of the supermodes of TCF are simulated and analyzed in detail. </div>
基金financially supported by the National Natural Science Foundation of China(Grant No.42077231).
文摘This paper introduces a bond-based peridynamics(BB-PD)algorithm for crack identification,integrating the Delaunay triangulation method to accurately identify the structural characteristics of threedimensional(3D)cracks in rocks.A bond-based crack quantification standard is proposed to analyze the evolution of cracks of various sizes.A multi-attribute peridynamic model,developed using a multilayer algorithm,was employed to simulate the fracturing process of sandstone disks and semi-disks under varying temperatures,with the model calibrated and validated against experimental results.The simulation results show that temperature induces nonlinear degradation in the tensile strength and fracture toughness of sandstone,with 500℃ identified as the threshold temperature.Thermal cracks exhibit varying degrees of influence on Mode I cracks across different temperature ranges.Thermal damage significantly promotes the initiation and propagation of Mode I cracks in sandstone,thereby reducing its tensile strength and fracture toughness.Under applied loads,crack propagation in sandstone predominantly occurs during the failure stage,characterized by the rapid growth of longer cracks and a slow increase or reduction in shorter cracks.
基金supported by Hefei National Laboratory,Innovation Program for Quantum Science and Technology(2021ZD0300400/2021ZD0300402)the Beijing Natural Science Foundation(3252013)the China Postdoctoral Science Foundation(2024T171116).
文摘The spin-exchange relaxation-free atomic gyroscope,with its exceptionally high theoretical precision,demonstrates immense potential to become the next-generation strategic-grade gyroscope.However,due to technological noise,there is still a significant gap between its actual precision and theoretical precision.This study identifies the key factor limiting the precision of the SERF gyroscope as coupling noise.By optimizing the detection loop structure,a distinction between the dual-axis signals'response to optical and magnetic fields was achieved-where the optical errors responded similarly,while the response to magnetic noise was opposite.Based on the differences in the optical-magnetic response of the dual-axis signals,empirical mode decomposition was used to decompose the dual-axis gyroscope signals into multiple intrinsic mode functions,and Allan deviation analysis was applied to analyze the noise characteristics of the intrinsic mode functions over various periods.This study successfully reveals that optical errors caused by thermal-optical coupling and long-period magnetic noise induced by thermal-magnetic coupling are the dominant factors limiting the long-term stability of the SERF gyroscope.Based on these analyses,the study concludes that to achieve strategic-grade precision for the SERF gyroscope,it is essential to effectively address the noise issues caused by multi-physical field couplings.
基金supported in part by National Natural Science Foundation of China (Nos. 11875021, 11835010, 11875024, 11775072, 11505053, 11475058)by the ITER-CN (Nos. 2017YFE0300501, 2017YFE0300405, 2017YFE0301202 and 2017YFE030168)
文摘Nonlinear couplings of various Alfvén modes driven by energetic particles in HL-2 A are addressed by employing the Fourier bicoherence and Lissajous-curve technique. Long-lived modes and high-frequency coherent modes are presented. Then the squared bicoherence of three waves establishes the existence of three-wave coupling. Lissajous-curves of those waves manifest that their phases are locked, which again confirms that they are nonlinearly coupled to each other. Moreover, coupled modes triggered by supersonic molecular beam injection are investigated. The phase evolution of them is given by the Lissajous-curve. Further details of phase-flip and phase-slip are presented and discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11604121 and 11875126)the Natural Science Fund Project of Hunan Province,China(Grant No.2017JJ3255)+1 种基金the National College Students’ Innovation Entrepreneurship Training Program,China(Grant No.201810531014)the Scientific Research Fund of Hunan Provincial Education Department,China(Grant No.17B212)
文摘We report a theoretical work on the properties of modulational instability and bright type nonlinear localized modes in one-dimensional easy-axis weak ferromagnetic spin lattices involving next-nearest-neighbor couplings.With a linear stability analysis, we calculate the growth rates of the modulational instability, and plot the instability regions.When the strength of the next-nearest-neighbor coupling is large enough, two new asymmetric modulational instability regions appear near the boundary of the first Brillouin zone.Furthermore, analytical forms of the bright nonlinear localized modes are constructed by means of a quasi-discreteness approach.The influence of the next-nearest-neighbor coupling on the Brillouin zone center mode and boundary mode are discussed.In particular, we discover a reversal phenomenon of the propagation direction of the Brillouin zone boundary mode.
文摘An optic-fiber sensor system for measuring distributed forces is presented. The sensor system chooses high-birefringent fiber as sensing e-iement. Based on coupling effects of polarization modes in high-birefringent fiber, the distribution of the force points along the sensing fiber can be measured by detecting mode couplings in the fiber which are caused by external force disturbance. The location and magnitude of the measured forces are determined by a heterodyne interferometry and the technique of optic path scanning. The spatial resolution of the sensor system is better than 0. 15m for a 50m testing fiber.
基金supported by the National Natural Science Foundation of China(Grants Nos.60877057 and 60907027)
文摘Birefringence （polarization-related phase-shift）, polarization dependent gain （PDG） and mode coupling are three factors that may synchronously influence the transmission of single-wavelength polarized light in optical fibers. This paper obtains a new Mueller matrix analysis, which can be used under conditions that all these three factors are existing and changing. According to our transmission model, the state of polarization （SOP） changes along an optical mierostructure fiber with co-existence of birefringence-PDG-mode coupling were simulated. The simulated results, which show the phenomena of SOP constringency, are in good agreement with previous theoretical analyses.
基金supported by the National Natural Science Foundation of China(Grant No.61475081)
文摘In this paper,a theoretical model to analyze the mode coupling induced by heat,when the fiber amplifier works at high power configuration,is proposed.The model mainly takes into consideration the mode field change due to the thermally induced refractive index change and the coupling between modes.A method to predict the largest average output power of fiber is also proposed according to the mode coupling theory.The largest average output power of a large pitch fiber with a core diameter of 190 μm and an available pulse energy of 100 mJ is predicted to be 540 W,which is the highest in large mode field fibers.
