A new type of localized oscillatory pattern is presented in a two-layer coupled reaction-diffusion system under conditions in which no Hopf instability can be discerned in either layer.The transitions from stationary ...A new type of localized oscillatory pattern is presented in a two-layer coupled reaction-diffusion system under conditions in which no Hopf instability can be discerned in either layer.The transitions from stationary patterns to asynchronous and synchronous oscillatory patterns are obtained.A novel method based on decomposing coupled systems into two associated subsystems has been proposed to elucidate the mechanism of formation of oscillating patterns.Linear stability analysis of the associated subsystems reveals that the Turing pattern in one layer induces the other layer locally,undergoes a supercritical Hopf bifurcation and gives rise to localized oscillations.It is found that the sizes and positions of oscillations are determined by the spatial distribution of the Turing patterns.When the size is large,localized traveling waves such as spirals and targets emerge.These results may be useful for deeper understanding of pattern formation in complex systems,particularly multilayered systems.展开更多
Differential inequalities generated in an extended Lyapunov framework are employed in the stability and instability analyses of a class of switched continuous-time second-and higher order linear systems with an arbitr...Differential inequalities generated in an extended Lyapunov framework are employed in the stability and instability analyses of a class of switched continuous-time second-and higher order linear systems with an arbitrary number of switching matrices.The exponential stability and instability(ESI)conditions so obtained involve the supremum and infimum of ratios of certain quadratic forms of the matrices,leading to global time-averages of their activity intervals.Further,motivated by linear switching system examples of(i)instability with stable matrices and(ii)stability with unstable matrices(found in the literature primarily for second-order systems),the proposed framework is generalized to establish ESI conditions that include both the activity intervals of the matrices and their switching rates,the latter being governed by a certain logarithmic measure of the normalized magnitudes of discontinuities caused by switching.In effect,(the new,globally averaged)dwell-time is flexibly traded,apparently for the first time,but under specific conditions(related,in part,to the eigenvalues of the matrices),for switching discontinuity-based conditions.Two further novel aspects of the proposed approach are:(i)For second-order matrices,switching lines in phase space can be chosen for periodic switching to stabilize or destabilize the system,and even generate oscillations,depending on the eigenvalues of the system matrices.But for third-(and higher)order matrices,such an analytically tractable(and controlled)periodical switching entails solution of an explicit non-convex multi-parameter optimization problem for which a stochastic optimization algorithm from the literature can be invoked.(ii)Lower and upper bounds on the solutions of the system equations can be quantified to reflect the stability/instability/oscillatory property of the system.Illustrative examples,which demonstrate the novelty of the derived stability and instability conditions,are presented in part 2 which is advisedly to be read along with this part 1 for a coherent merging of theory with practice.展开更多
In this second part of the paper,bearing the same title as above,but with the last hyphenated phrase replaced by part 1(Theory),the exponential stability and instability(ESI)Theorems 1–4 of part 1 are illustrated by ...In this second part of the paper,bearing the same title as above,but with the last hyphenated phrase replaced by part 1(Theory),the exponential stability and instability(ESI)Theorems 1–4 of part 1 are illustrated by applying them to second-andby,say,third-order linear switched systems with different eigenvalue structures to demonstrate the versatility,novelty and superiority(over many of the results found in the literature,especially for second-order switched lined systems)of the new theoretical results.The computational procedure that is employed with reference to the third-order systems is generic,in the sense that it is applicable to higher(i.e.,greater than third-)order linear switched systems.A pseudo-code for a computer implementation of the stability/instability conditions is also presented.With the principal aim of facilitating an independent reading of this part 2 of the paper,some crucial mathematical notations,definitions and results of part 1 have been repeated,thereby making the contents as self-contained as possible.展开更多
The suppression of ablative Rayleigh–Taylor instability(ARTI)by a spatially modulated laser in inertial confinement fusion(ICF)is studied through numerical simulations.The results show that in the acceleration phase ...The suppression of ablative Rayleigh–Taylor instability(ARTI)by a spatially modulated laser in inertial confinement fusion(ICF)is studied through numerical simulations.The results show that in the acceleration phase of ICF implosion,the growth of ARTI can be suppressed by using a short-wavelength spatially modulated laser.The ARTI growth rate decreases as the wavelength of the spatially modulated laser decreases,and ARTI is completely suppressed after a certain wavelength has been reached.A spatially uniform laser is introduced to keep the state of motion of the implosion fluid consistent,and it is found that the proportion of the spatially modulated laser required for complete suppression of ARTI decreases as the wavelength continues to decrease.We also optimize the spatial intensity distribution of the spatially modulated laser.In addition,as the duration of the spatially modulated laser decreases,the proportion required for completely suppressing ARTI increases,but the required energy decreases.When the perturbation wavenumber decreases,the wavelength of the spatially modulated laser required for complete suppression of ARTI becomes longer.In the case of multimode perturbation,ARTI can also be significantly suppressed by a spatially modulated laser,and the perturbation amplitude can be reduced to less than 10% of that without a spatially modulated laser.We believe that the conclusions drawn from our simulations can provide the basis for new approaches to control ARTI in ICF.展开更多
Roof pre-fracture poses a considerable risk during the re-mining of residual coal above abandoned roadways,threatening the safety of the mining faces.This study employs a Winkler foundation beam model for mechanical a...Roof pre-fracture poses a considerable risk during the re-mining of residual coal above abandoned roadways,threatening the safety of the mining faces.This study employs a Winkler foundation beam model for mechanical analysis of roof structures and adopts a multivariate nonlinear analysis approach to explore the synergistic load-bearing effects within the'coal pillar-support-backfill body'system during the fill and re-mining processes above these roadways.The findings demonstrate that backfill mining significantly reduces stress concentrations in coal pillars and reduces excessive bending moments in roofs near abandoned roadways.The roof deflection equation incorporates three critical factors affecting stability during backfill mining:the width of the coal pillar(L_(3)),the working resistance of the support(q_(z)),and the elastic foundation coefficient of the backfill material(kcÞ.Under single-factor conditions,the impact sequence on roof stability in the coal pillar zone is·k_(c)>L_(3)>q_(z).Further,multivariate nonlinear analysis reveals the interactions within the'coal-support-backfill'structure,indicating that in terms of roof control,the interaction terms are ordered as L_(3)·k_(c)>q_(z)·k_(c)>L_(3)q_(z).Therefore,priority should be given to adjusting the coal pillar width and backfill strength,followed by modifications to the support resistance and backfill strength during the recovery of abandoned roadways.An improved understanding of these interactions will help optimize strategies for the recovery of residual coal through abandoned roadways,thereby enhancing the stability and safety of mining operations under complex geological conditions.展开更多
The rapid cycling synchrotron(RCS)at the China spallation neutron source operates as a high-intensity proton accelerator.The coupled bunch instability was observed during RCS beam commissioning,which significantly lim...The rapid cycling synchrotron(RCS)at the China spallation neutron source operates as a high-intensity proton accelerator.The coupled bunch instability was observed during RCS beam commissioning,which significantly limited the beam power.To investigate the dynamics of instability under an increased beam power,a pulsed octupole magnet with a gradient of 900 T/m^(3) was developed.The magnet system integrated an octupole magnet with a pulsed power supply.The field was carefully measured to examine the performance before its installation into the tunnel.After the installation of the magnets,beam measurements were performed to confirm the effectiveness of the instability mitigation on an actual proton beam.The measurement results show that the instability can be suppressed using the pulsed octupole magnet,particularly at the highenergy stage in an acceleration cycle,meeting the requirements for stable operation of the accelerator.Additionally,when the instability is completely suppressed through chromaticity optimization,octupole magnets can significantly enhance the RCS transmission efficiency,which is crucial for controlling beam loss.The pulsed octupole magnet offers significant progress in beam stability in the RCS,providing valuable experience for further beam power enhancement.展开更多
Aiming at the problem of dynamic instability of hard-brittle jointed rock surrounding in deep tunnel/roadway engineering,combining with the support concepts of"coupling rigidity with flexibility"and"ove...Aiming at the problem of dynamic instability of hard-brittle jointed rock surrounding in deep tunnel/roadway engineering,combining with the support concepts of"coupling rigidity with flexibility"and"overcoming rigidity by flexibility",the prevention and control method with"rigid-flexible coupling(R-F-C)"was put forward.Through numerical simulation calculation,the impact damage process,acoustic emission(AE)evolution characteristics,and element stress/displacement evolution characteristics of unsupported surrounding rock structure model,rigid supporting surrounding rock structure model,and"R-F-C"supporting surrounding rock structure model under horizontal bidirectional impact loading were compared and analyzed.Based on the theory of stress wave propagation,the dynamic instability catastrophe mechanism of three kinds of supporting structure models induced by horizontal bidirectional impact loading was revealed.Based on the Mohr-Coulomb strength theory,the stress discrimination methods of dynamic catastrophe of surrounding rock induced by horizontal bidirectional impact loading under three kinds of supporting structures were proposed.Combined with the above numerical simulation study,the explosion impact physical and mechanical test of"R-F-C"surrounding rock supporting plate structure was further designed and carried out.Finally,combined with the"conceptual model of ball-cliff potential energy instability",the energy driving theory and energy transformation mechanism of impact-induced rockburst under three kinds of supporting structures were discussed deeply.The research results provided a scientific basis for further promoting the effective application of"R-F-C"supporting structure in the prevention and control of dynamic instability of deep tunnel/roadway surrounding rock.展开更多
Background:Acute ankle injury causes damage to joint mechanoreceptors and deafferentation and contributes to proprioception deficits in patients with chronic ankle instability(CAI).We aimed to explore whether deficits...Background:Acute ankle injury causes damage to joint mechanoreceptors and deafferentation and contributes to proprioception deficits in patients with chronic ankle instability(CAI).We aimed to explore whether deficits of proprioception,including kinesthesia and joint position sense(JPS),exist in patients with CAI when compared with the uninjured contralateral side and healthy people.We hypothesized that proprioception deficits did exist in patients with CAI and that the deficits varied by test methodologies.Methods:The study was a systematic review and meta-analysis.We identified studies that compared kinesthesia or JPS in patients with CAI with the uninjured contralateral side or with healthy controls.Meta-analyses were conducted for the studies with similar test procedures,and narrative syntheses were undertaken for the rest.Results:A total of 7731 studies were identified,of which 30 were included for review.A total of 21 studies were eligible for meta-analysis.Compared with the contralateral side,patients with CAI had ankle kinesthesia deficits in inversion and plantarflexion,with a standardized mean difference(SMD)of 0.41 and 0.92,respectively,and active and passive JPS deficits in inversion(SMD=0.92 and 0.72,respectively).Compared with healthy people,patients with CAI had ankle kinesthesia deficits in inversion and eversion(SMD=0.64 and 0.76,respectively),and active JPS deficits in inversion and eversion(SMD=1.00 and 4.82,respectively).Proprioception deficits in the knee and shoulder of patients with CAI were not statistically significant.Conclusion:Proprioception,including both kinesthesia and JPS,of the injured ankle of patients with CAI was impaired,compared with the uninjured contralateral limbs and healthy people.Proprioception varied depending on different movement directions and test methodologies.The use of more detailed measurements of proprioception and interventions for restoring the deficits are recommended in the clinical management of CAI.展开更多
Rayleigh-Marangoni-Bénard instability in a system of two-layer fluids is studied nu- merically.The convective instabilities in the system of Silicon Oil(10cSt)and Fluorinert(FC70)liquids have been analyzed.The cr...Rayleigh-Marangoni-Bénard instability in a system of two-layer fluids is studied nu- merically.The convective instabilities in the system of Silicon Oil(10cSt)and Fluorinert(FC70)liquids have been analyzed.The critical parameters at onset of convection are presented in a large range of two-layer depth ratios from 0.2 to 5.0.Numerical results show that the instability of the two-layer system depends strongly on its depth ratio.When the depth ratio increases,the instability mode changes from mechanical coupling to thermal coupling.Between these two typical coupling modes, a time-dependent oscillation is detected.Nevertheless,traveling wave states are found in the case of oscillatory instability.The oscillation mode results from the competition between Rayleigh instability and Marangoni effect.展开更多
The security challenges from room and pillar gobs include land subsidence, spontaneous combustion of coal pillars and mine flood caused by gob water. To explore the instability mechanism of room and pillar gob, we est...The security challenges from room and pillar gobs include land subsidence, spontaneous combustion of coal pillars and mine flood caused by gob water. To explore the instability mechanism of room and pillar gob, we established a mechanical model of elastic plate on elastic foundation in which pillars and hard roofs were considered as continuous Winkler foundations and elastic plates, respectively. The synergetic instability of pillar and roof system was analyzed based on plate bending theory and catastrophe theory. In addition, mechanical conditions and math criterion of roof failure and overall instability of coal pillar and roof system were given. Through analyzing both advantages and disadvantages of some technologies such as induced caving, filling, gob sealing and isolation, we presented a new filling method named box-filling, in view of box foundation theory, to control the disasters of ground collapse, water inrush and mine fire. In a gob's treatment project in Ordos, safety assessment and filling design of a room and pillar gob have been done by the mechanical model. The results show that the gob will collapse when the pillars' average yield band is wider than 0.93 m, and box-filling can control land collapse, mine flood and mine fire economically and efficiently. So it is worth to study further and popularize.展开更多
Traditional procedures to treat vibrations of gyroscopic continua involve direct application of perturbation methods to a system with both a strong gyroscopic term and other weakly coupled terms.In this study,a gyrosc...Traditional procedures to treat vibrations of gyroscopic continua involve direct application of perturbation methods to a system with both a strong gyroscopic term and other weakly coupled terms.In this study,a gyroscopic modes decoupling method is used to obtain an equivalent system with decoupled gyroscopic modes having only weak couplings.Taking the axially moving string as an example,the instability boundaries in the vicinity of parametric resonances are detected using both the traditional coupled gyroscopic system and our system with decoupled gyroscopic modes,and the results are compared to show the advantages and disadvantages of each method.展开更多
A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear s...A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An instability criterion is derived analytically based on the energy principle using a known size of localization band according to gradient dependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.展开更多
BACKGROUND Hemodynamic instability and shock are associated with untoward outcomes in gastrointestinal bleeding.However,there are no studies in the existing literature on the proportion of patients who developed these...BACKGROUND Hemodynamic instability and shock are associated with untoward outcomes in gastrointestinal bleeding.However,there are no studies in the existing literature on the proportion of patients who developed these outcomes after gastrointestinal bleeding.AIM To determine the pooled event rates in the available literature and specify them based on the bleeding source.METHODS The protocol was registered on PROSPERO in advance(CRD42021283258).A systematic search was performed in three databases(PubMed,EMBASE,and CENTRAL)on 14^(th) October 2021.Pooled proportions with 95%CI were calculated with a random-effects model.A subgroup analysis was carried out based on the time of assessment(on admission or during hospital stay).Heterogeneity was assessed by Higgins and Thompson’s I^(2) statistics.The Joanna Briggs Institute Prevalence Critical Appraisal Tool was used for the risk of bias assessment.The Reference Citation Analysis(https://www.referencecitationanalysis.com/)tool was applied to obtain the latest highlight articles.RESULTS We identified 11589 records,of which 220 studies were eligible for data extraction.The overall proportion of shock and hemodynamic instability in general gastrointestinal bleeding patients was 0.25(95%CI:0.17-0.36,I^(2)=100%).In non-variceal bleeding,the proportion was 0.22(95%CI:0.14-0.31,I^(2)=100%),whereas it was 0.25(95%CI:0.19-0.32,I^(2)=100%)in variceal bleeding.The proportion of patients with colonic diverticular bleeding who developed shock or hemodynamic instability was 0.12(95%CI:0.06-0.22,I^(2)=90%).The risk of bias was low,and heterogeneity was high in all analyses.CONCLUSION One in five,one in four,and one in eight patients develops shock or hemodynamic instability on admission or during hospitalization in the case of non-variceal,variceal,and colonic diverticular bleeding,respectively.展开更多
A longitudinal accumulation scheme based on a triple-frequency RF system,in which the static radio frequency(RF)bucket is lengthened to be compatible with the realizable raise time of a fast pulse kicker,is proposed i...A longitudinal accumulation scheme based on a triple-frequency RF system,in which the static radio frequency(RF)bucket is lengthened to be compatible with the realizable raise time of a fast pulse kicker,is proposed in this paper.With this technique,the bunch from a booster can be captured by the longitudinal acceptance without any disturbance to the stored bunch,which remains at the center.This composite RF system consists of three different frequencies,which can be regarded as the conventional bunch lengthening RF system(usually containing fundamental and third harmonic cavities)extended by an additional second harmonic RF cavity.In this paper,we discuss the RF jitter and the transverse mode-coupling instability(TMCI)when using this special RF system.Considering several different bunch profiles,we discuss the beam stability with regard to the RF jitter.However,for the TMCI we assume an ideal bunch profile,where the bunch is exactly lengthened to the maximum extent.While macroparticle simulation is the main method used to study the impact of the RF jitter,numerical analysis and simulations for the TMCI while using a triple-frequency RF system are also presented in this paper.An approximation formula,based on the existing model,is also derived to estimate the impact of the TMCI on the single bunch current threshold when using harmonic cavities.展开更多
BACKGROUND Recently,the use of ligament advanced reinforcement system(LARS)artificial ligament,a new graft which has several unique advantages such as no donor-site morbidity,early recovery and no risk of disease tran...BACKGROUND Recently,the use of ligament advanced reinforcement system(LARS)artificial ligament,a new graft which has several unique advantages such as no donor-site morbidity,early recovery and no risk of disease transmission which has been a significant breakthrough for anatomical ligament reconstruction.Growing studies suggested that the special design of the LARS ligament with open fibers in its intra-articular part was believed to be more resistant to torsional fatigue and wearing.However,the safety and efficacy of LARS artificial ligament for ankle joint lateral collateral ankle ligament reconstruction has not been defined to date.AIM To evaluate the clinical results of all-arthroscopic anatomical reconstruction of ankle joint lateral collateral ligaments with the LARS artificial ligament for chronic ankle instability.METHODS Twenty-two patients with chronic lateral instability underwent anatomical reconstruction of the lateral collateral ligaments of ankle with LARS artificial ligament.The visual analogue score(VAS),American Orthopaedic Foot and Ankle Society score(AOFAS score)and Karlsson score were used to evaluate the clinical results before and after surgery.RESULTS A total of 22 patients(22 ankles)were followed up for a mean of 12 mo.All patients reported significant improvement compared to their preoperative status.The mean AOFAS score improved from 42.3±4.9 preoperatively to 90.4±6.7 postoperatively.The mean Karlsson score improved from 38.5±3.2 preoperatively to 90.1±7.8 postoperatively.The mean VAS score improved from 1.9±2.5 preoperatively to 0.8±1.7 postoperatively.CONCLUSION All-arthroscopic anatomical reconstruction of the lateral collateral ligaments with LARS artificial ligament achieved a satisfactory surgical outcome for chronic ankle instability.展开更多
The vibration instability of the nonlinear dynamic system of the rolls considering the structural clearance was theoretically investigated,which is caused by the roll assembly accuracy deviation in the hot rolling pro...The vibration instability of the nonlinear dynamic system of the rolls considering the structural clearance was theoretically investigated,which is caused by the roll assembly accuracy deviation in the hot rolling process.Firstly,the dynamic rolling force model was established based on the Wekbrod model under the influence of the roll grinding deviation and the stability of the deformation zone.Further,the horizontal and vertical direction coupling dynamic model of the work roll was established considering the structural clearance between the roll and mill frame.Then,the nonlinear dynamic equation was solved by the Runge-Kutta method.The simulation results show that the dynamic system presents the nonlinear vibration characteristics,which shows that the instability of the system is a slowly varying response process with the characteristics of self-excited vibration and forced vibration.Finally,the comparison results show the consistency between the simulation and the test.展开更多
BACKGROUND The medial patellofemoral ligament(MPFL),along with the medial patellotibial ligament(MPTL)and medial patellomeniscal ligament,aid in the stabilization of the patellofemoral joint.Although the MPFL is the p...BACKGROUND The medial patellofemoral ligament(MPFL),along with the medial patellotibial ligament(MPTL)and medial patellomeniscal ligament,aid in the stabilization of the patellofemoral joint.Although the MPFL is the primary stabilizer and the MPTL is a secondary limiter,this ligament is critical in maintaining joint stability.There have been few studies on the combined MPFL and MPTL reconstruction and its benefits.AIM To look into the outcomes of combined MPFL and MPTL reconstruction in frequent patellar instability.METHODS By May 8,2022,four electronic databases were searched:Medline(PubMed),Scopus,Web of Science,and Google Scholar.General keywords such as"patellar instability,""patellar dislocation,""MPFL,""medial patellofemoral ligament,""MPTL,"and"medial patellotibial ligament"were co-searched to increase the sensitivity of the search.RESULTS The pooled effects of combined MPFL and MPTL reconstruction for Kujala score(12-mo followup)and Kujala score(24-mo follow-up)were positive and incremental,according to the findings of this meta-analysis.The mean difference between the Cincinnati scores was also positive,but not statistically significant.The combination of the two surgeries reduces pain.According to cumulative meta-analysis,the trend of pain reduction in various studies is declining over time.CONCLUSION The combined MPFL and MPTL reconstruction has good clinical results in knee function and,in addition to providing good control to maintain patellofemoral joint balance,the patient's pain level decreases over time,making it a valid surgical method for patella stabilization.展开更多
The paper discusses the equilibrium instability problem of the scleronomic nonholonomic systems acted upon by dissipative, conservative, and circulatory forces. The method is based on the existence of solutions to the...The paper discusses the equilibrium instability problem of the scleronomic nonholonomic systems acted upon by dissipative, conservative, and circulatory forces. The method is based on the existence of solutions to the differential equations of the motion which asymptotically tends to the equilibrium state of the system as t tends to negative infinity. It is assumed that the kinetic energy, the Rayleigh dissipation function, and the positional forces in the neighborhood of the equilibrium position are infinitely differentiable functions. The results obtained here are partially generalized the results obtained by Kozlov et al. （Kozlov, V. V. The asymptotic motions of systems with dissi- pation. Journal of Applied Mathematics and Mechanics, 58（5）, 787-792 （1994）. Merkin, D. R. Introduction to the Theory of the Stability of Motion （in Russian）, Nauka, Moscow （1987）. Thomson, W. and Tait, P. Treatise on Natural Philosophy, Part I, Cambridge University Press, Cambridge （1879））. The results are illustrated by an example.展开更多
AIM: To systematically evaluate the evidence-based literature on surgical treatment interventions for elite rugby players with anterior shoulder instability. METHODS: We conducted a systematic review according to the ...AIM: To systematically evaluate the evidence-based literature on surgical treatment interventions for elite rugby players with anterior shoulder instability. METHODS: We conducted a systematic review according to the PRISMA guidelines. A literature search was performed in PubM ed, EMBASE and Google Scholar using the following search terms: "rugby" and "shoulder" in combination with "instability" or "dislocation". All articles published from inception of the included data sources to January 1st 2014 that evaluated surgical treatment of elite rugby players with anterior shoulder instability were examined. RESULTS: Only five studies were found that met the eligibility criteria. A total of 379 shoulders in 376 elite rugby union and league players were included. All the studies were retrospective cohort or case series studies. The mean Coleman Methodological Score for the 5 studies was 47.4(poor). Owing to heterogeneity amongst the studies, quantitative synthesis was not possible, however a detailed qualitative synthesis is reported. The overall recurrence rate of instability after surgery was 8.7%, and the mean return to competitive play, where reported, was 13 mo.CONCLUSION: Arthroscopic stabilization has been performed successfully in acute anterior instability and there is a preference for open Latarjet-type procedures when instability is associated with osseous defects.展开更多
In the present paper, we investigate the instability, adiabaticity, and controlling effects of external fields for a dark state in a homonuclear atom-tetramer conversion that is implemented by a generalized stimulated...In the present paper, we investigate the instability, adiabaticity, and controlling effects of external fields for a dark state in a homonuclear atom-tetramer conversion that is implemented by a generalized stimulated Raman adiabatic passage. We analytically obtain the regions for the appearance of dynamical instability and study the adiabatic evolution by a newly defined adiabatic fidelity. Moreover, the effects of the external field parameters and the spontaneous emissions on the conversion efficiency are also investigated.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12275065,12275064,12475203)the Natural Science Foundation of Hebei Province(Grant Nos.A2021201010 and A2024201020)+3 种基金Interdisciplinary Research Program of Natural Science of Hebei University(Grant No.DXK202108)Hebei Provincial Central Government Guiding Local Science and Technology Development Funds(Grant No.236Z1501G)Scientific Research and Innovation Team Foundation of Hebei University(Grant No.IT2023B03)the Excellent Youth Research Innovation Team of Hebei University(Grant No.QNTD202402)。
文摘A new type of localized oscillatory pattern is presented in a two-layer coupled reaction-diffusion system under conditions in which no Hopf instability can be discerned in either layer.The transitions from stationary patterns to asynchronous and synchronous oscillatory patterns are obtained.A novel method based on decomposing coupled systems into two associated subsystems has been proposed to elucidate the mechanism of formation of oscillating patterns.Linear stability analysis of the associated subsystems reveals that the Turing pattern in one layer induces the other layer locally,undergoes a supercritical Hopf bifurcation and gives rise to localized oscillations.It is found that the sizes and positions of oscillations are determined by the spatial distribution of the Turing patterns.When the size is large,localized traveling waves such as spirals and targets emerge.These results may be useful for deeper understanding of pattern formation in complex systems,particularly multilayered systems.
文摘Differential inequalities generated in an extended Lyapunov framework are employed in the stability and instability analyses of a class of switched continuous-time second-and higher order linear systems with an arbitrary number of switching matrices.The exponential stability and instability(ESI)conditions so obtained involve the supremum and infimum of ratios of certain quadratic forms of the matrices,leading to global time-averages of their activity intervals.Further,motivated by linear switching system examples of(i)instability with stable matrices and(ii)stability with unstable matrices(found in the literature primarily for second-order systems),the proposed framework is generalized to establish ESI conditions that include both the activity intervals of the matrices and their switching rates,the latter being governed by a certain logarithmic measure of the normalized magnitudes of discontinuities caused by switching.In effect,(the new,globally averaged)dwell-time is flexibly traded,apparently for the first time,but under specific conditions(related,in part,to the eigenvalues of the matrices),for switching discontinuity-based conditions.Two further novel aspects of the proposed approach are:(i)For second-order matrices,switching lines in phase space can be chosen for periodic switching to stabilize or destabilize the system,and even generate oscillations,depending on the eigenvalues of the system matrices.But for third-(and higher)order matrices,such an analytically tractable(and controlled)periodical switching entails solution of an explicit non-convex multi-parameter optimization problem for which a stochastic optimization algorithm from the literature can be invoked.(ii)Lower and upper bounds on the solutions of the system equations can be quantified to reflect the stability/instability/oscillatory property of the system.Illustrative examples,which demonstrate the novelty of the derived stability and instability conditions,are presented in part 2 which is advisedly to be read along with this part 1 for a coherent merging of theory with practice.
文摘In this second part of the paper,bearing the same title as above,but with the last hyphenated phrase replaced by part 1(Theory),the exponential stability and instability(ESI)Theorems 1–4 of part 1 are illustrated by applying them to second-andby,say,third-order linear switched systems with different eigenvalue structures to demonstrate the versatility,novelty and superiority(over many of the results found in the literature,especially for second-order switched lined systems)of the new theoretical results.The computational procedure that is employed with reference to the third-order systems is generic,in the sense that it is applicable to higher(i.e.,greater than third-)order linear switched systems.A pseudo-code for a computer implementation of the stability/instability conditions is also presented.With the principal aim of facilitating an independent reading of this part 2 of the paper,some crucial mathematical notations,definitions and results of part 1 have been repeated,thereby making the contents as self-contained as possible.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.12074399,12204500,and 12004403)the Key Projects of Intergovernmental International Scientific and Technological Innovation Cooperation(No.2021YFE0116700)+1 种基金the Shanghai Natural Science Foundation(No.20ZR1464400)the Shanghai Sailing Program(No.22YF1455300).
文摘The suppression of ablative Rayleigh–Taylor instability(ARTI)by a spatially modulated laser in inertial confinement fusion(ICF)is studied through numerical simulations.The results show that in the acceleration phase of ICF implosion,the growth of ARTI can be suppressed by using a short-wavelength spatially modulated laser.The ARTI growth rate decreases as the wavelength of the spatially modulated laser decreases,and ARTI is completely suppressed after a certain wavelength has been reached.A spatially uniform laser is introduced to keep the state of motion of the implosion fluid consistent,and it is found that the proportion of the spatially modulated laser required for complete suppression of ARTI decreases as the wavelength continues to decrease.We also optimize the spatial intensity distribution of the spatially modulated laser.In addition,as the duration of the spatially modulated laser decreases,the proportion required for completely suppressing ARTI increases,but the required energy decreases.When the perturbation wavenumber decreases,the wavelength of the spatially modulated laser required for complete suppression of ARTI becomes longer.In the case of multimode perturbation,ARTI can also be significantly suppressed by a spatially modulated laser,and the perturbation amplitude can be reduced to less than 10% of that without a spatially modulated laser.We believe that the conclusions drawn from our simulations can provide the basis for new approaches to control ARTI in ICF.
基金support from National Natural Science Foundation of China(Grant No.52474142)The National Science Fund for Distinguished Young Scholars(No.51925402),Chinathe China Postdoctoral Science Foundation(Grant No.2021M702049).
文摘Roof pre-fracture poses a considerable risk during the re-mining of residual coal above abandoned roadways,threatening the safety of the mining faces.This study employs a Winkler foundation beam model for mechanical analysis of roof structures and adopts a multivariate nonlinear analysis approach to explore the synergistic load-bearing effects within the'coal pillar-support-backfill body'system during the fill and re-mining processes above these roadways.The findings demonstrate that backfill mining significantly reduces stress concentrations in coal pillars and reduces excessive bending moments in roofs near abandoned roadways.The roof deflection equation incorporates three critical factors affecting stability during backfill mining:the width of the coal pillar(L_(3)),the working resistance of the support(q_(z)),and the elastic foundation coefficient of the backfill material(kcÞ.Under single-factor conditions,the impact sequence on roof stability in the coal pillar zone is·k_(c)>L_(3)>q_(z).Further,multivariate nonlinear analysis reveals the interactions within the'coal-support-backfill'structure,indicating that in terms of roof control,the interaction terms are ordered as L_(3)·k_(c)>q_(z)·k_(c)>L_(3)q_(z).Therefore,priority should be given to adjusting the coal pillar width and backfill strength,followed by modifications to the support resistance and backfill strength during the recovery of abandoned roadways.An improved understanding of these interactions will help optimize strategies for the recovery of residual coal through abandoned roadways,thereby enhancing the stability and safety of mining operations under complex geological conditions.
基金supported by the Guangdong Basic and Applied Basic Research Foundation,China(No.2021B1515140007).
文摘The rapid cycling synchrotron(RCS)at the China spallation neutron source operates as a high-intensity proton accelerator.The coupled bunch instability was observed during RCS beam commissioning,which significantly limited the beam power.To investigate the dynamics of instability under an increased beam power,a pulsed octupole magnet with a gradient of 900 T/m^(3) was developed.The magnet system integrated an octupole magnet with a pulsed power supply.The field was carefully measured to examine the performance before its installation into the tunnel.After the installation of the magnets,beam measurements were performed to confirm the effectiveness of the instability mitigation on an actual proton beam.The measurement results show that the instability can be suppressed using the pulsed octupole magnet,particularly at the highenergy stage in an acceleration cycle,meeting the requirements for stable operation of the accelerator.Additionally,when the instability is completely suppressed through chromaticity optimization,octupole magnets can significantly enhance the RCS transmission efficiency,which is crucial for controlling beam loss.The pulsed octupole magnet offers significant progress in beam stability in the RCS,providing valuable experience for further beam power enhancement.
基金Project(2023AH051167)supported by the Natural Science Research Project of Anhui Educational Committee,ChinaProject(AHBP2024B-04)supported by the Foundation of Anhui Engineering Research Center of New Explosive Materials and Blasting Technology,China+1 种基金Project(GXZDSYS2023103)supported by the Open Fund for Anhui Key Laboratory of Mining Construction Engineering,ChinaProjects(52274071,52404155)supported by the National Natural Science Foundation of China。
文摘Aiming at the problem of dynamic instability of hard-brittle jointed rock surrounding in deep tunnel/roadway engineering,combining with the support concepts of"coupling rigidity with flexibility"and"overcoming rigidity by flexibility",the prevention and control method with"rigid-flexible coupling(R-F-C)"was put forward.Through numerical simulation calculation,the impact damage process,acoustic emission(AE)evolution characteristics,and element stress/displacement evolution characteristics of unsupported surrounding rock structure model,rigid supporting surrounding rock structure model,and"R-F-C"supporting surrounding rock structure model under horizontal bidirectional impact loading were compared and analyzed.Based on the theory of stress wave propagation,the dynamic instability catastrophe mechanism of three kinds of supporting structure models induced by horizontal bidirectional impact loading was revealed.Based on the Mohr-Coulomb strength theory,the stress discrimination methods of dynamic catastrophe of surrounding rock induced by horizontal bidirectional impact loading under three kinds of supporting structures were proposed.Combined with the above numerical simulation study,the explosion impact physical and mechanical test of"R-F-C"surrounding rock supporting plate structure was further designed and carried out.Finally,combined with the"conceptual model of ball-cliff potential energy instability",the energy driving theory and energy transformation mechanism of impact-induced rockburst under three kinds of supporting structures were discussed deeply.The research results provided a scientific basis for further promoting the effective application of"R-F-C"supporting structure in the prevention and control of dynamic instability of deep tunnel/roadway surrounding rock.
基金the National Natural Science Foundation of China(Grant No.81871823).
文摘Background:Acute ankle injury causes damage to joint mechanoreceptors and deafferentation and contributes to proprioception deficits in patients with chronic ankle instability(CAI).We aimed to explore whether deficits of proprioception,including kinesthesia and joint position sense(JPS),exist in patients with CAI when compared with the uninjured contralateral side and healthy people.We hypothesized that proprioception deficits did exist in patients with CAI and that the deficits varied by test methodologies.Methods:The study was a systematic review and meta-analysis.We identified studies that compared kinesthesia or JPS in patients with CAI with the uninjured contralateral side or with healthy controls.Meta-analyses were conducted for the studies with similar test procedures,and narrative syntheses were undertaken for the rest.Results:A total of 7731 studies were identified,of which 30 were included for review.A total of 21 studies were eligible for meta-analysis.Compared with the contralateral side,patients with CAI had ankle kinesthesia deficits in inversion and plantarflexion,with a standardized mean difference(SMD)of 0.41 and 0.92,respectively,and active and passive JPS deficits in inversion(SMD=0.92 and 0.72,respectively).Compared with healthy people,patients with CAI had ankle kinesthesia deficits in inversion and eversion(SMD=0.64 and 0.76,respectively),and active JPS deficits in inversion and eversion(SMD=1.00 and 4.82,respectively).Proprioception deficits in the knee and shoulder of patients with CAI were not statistically significant.Conclusion:Proprioception,including both kinesthesia and JPS,of the injured ankle of patients with CAI was impaired,compared with the uninjured contralateral limbs and healthy people.Proprioception varied depending on different movement directions and test methodologies.The use of more detailed measurements of proprioception and interventions for restoring the deficits are recommended in the clinical management of CAI.
基金The project supported by the National Natural Science Foundation of China (10372105) and the Knowledge Innovation Program of Chinese Academy of Sciences (KJCX2-SW-L05)
文摘Rayleigh-Marangoni-Bénard instability in a system of two-layer fluids is studied nu- merically.The convective instabilities in the system of Silicon Oil(10cSt)and Fluorinert(FC70)liquids have been analyzed.The critical parameters at onset of convection are presented in a large range of two-layer depth ratios from 0.2 to 5.0.Numerical results show that the instability of the two-layer system depends strongly on its depth ratio.When the depth ratio increases,the instability mode changes from mechanical coupling to thermal coupling.Between these two typical coupling modes, a time-dependent oscillation is detected.Nevertheless,traveling wave states are found in the case of oscillatory instability.The oscillation mode results from the competition between Rayleigh instability and Marangoni effect.
基金provided by the National Natural Science Foundation of China (No. 41071273)
文摘The security challenges from room and pillar gobs include land subsidence, spontaneous combustion of coal pillars and mine flood caused by gob water. To explore the instability mechanism of room and pillar gob, we established a mechanical model of elastic plate on elastic foundation in which pillars and hard roofs were considered as continuous Winkler foundations and elastic plates, respectively. The synergetic instability of pillar and roof system was analyzed based on plate bending theory and catastrophe theory. In addition, mechanical conditions and math criterion of roof failure and overall instability of coal pillar and roof system were given. Through analyzing both advantages and disadvantages of some technologies such as induced caving, filling, gob sealing and isolation, we presented a new filling method named box-filling, in view of box foundation theory, to control the disasters of ground collapse, water inrush and mine fire. In a gob's treatment project in Ordos, safety assessment and filling design of a room and pillar gob have been done by the mechanical model. The results show that the gob will collapse when the pillars' average yield band is wider than 0.93 m, and box-filling can control land collapse, mine flood and mine fire economically and efficiently. So it is worth to study further and popularize.
基金the National Natural Science Foundation of China(Grants 11772009,11672007)the Beijing Municipal Natural Science Foundation(Grant 3172003).
文摘Traditional procedures to treat vibrations of gyroscopic continua involve direct application of perturbation methods to a system with both a strong gyroscopic term and other weakly coupled terms.In this study,a gyroscopic modes decoupling method is used to obtain an equivalent system with decoupled gyroscopic modes having only weak couplings.Taking the axially moving string as an example,the instability boundaries in the vicinity of parametric resonances are detected using both the traditional coupled gyroscopic system and our system with decoupled gyroscopic modes,and the results are compared to show the advantages and disadvantages of each method.
文摘A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An instability criterion is derived analytically based on the energy principle using a known size of localization band according to gradient dependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.
基金The Ministry of Innovation and Technology of Hungary from the National Research,Development,and Innovation Fund(ITM-NRDIF),No.TKP2021-EGA-23.
文摘BACKGROUND Hemodynamic instability and shock are associated with untoward outcomes in gastrointestinal bleeding.However,there are no studies in the existing literature on the proportion of patients who developed these outcomes after gastrointestinal bleeding.AIM To determine the pooled event rates in the available literature and specify them based on the bleeding source.METHODS The protocol was registered on PROSPERO in advance(CRD42021283258).A systematic search was performed in three databases(PubMed,EMBASE,and CENTRAL)on 14^(th) October 2021.Pooled proportions with 95%CI were calculated with a random-effects model.A subgroup analysis was carried out based on the time of assessment(on admission or during hospital stay).Heterogeneity was assessed by Higgins and Thompson’s I^(2) statistics.The Joanna Briggs Institute Prevalence Critical Appraisal Tool was used for the risk of bias assessment.The Reference Citation Analysis(https://www.referencecitationanalysis.com/)tool was applied to obtain the latest highlight articles.RESULTS We identified 11589 records,of which 220 studies were eligible for data extraction.The overall proportion of shock and hemodynamic instability in general gastrointestinal bleeding patients was 0.25(95%CI:0.17-0.36,I^(2)=100%).In non-variceal bleeding,the proportion was 0.22(95%CI:0.14-0.31,I^(2)=100%),whereas it was 0.25(95%CI:0.19-0.32,I^(2)=100%)in variceal bleeding.The proportion of patients with colonic diverticular bleeding who developed shock or hemodynamic instability was 0.12(95%CI:0.06-0.22,I^(2)=90%).The risk of bias was low,and heterogeneity was high in all analyses.CONCLUSION One in five,one in four,and one in eight patients develops shock or hemodynamic instability on admission or during hospitalization in the case of non-variceal,variceal,and colonic diverticular bleeding,respectively.
文摘A longitudinal accumulation scheme based on a triple-frequency RF system,in which the static radio frequency(RF)bucket is lengthened to be compatible with the realizable raise time of a fast pulse kicker,is proposed in this paper.With this technique,the bunch from a booster can be captured by the longitudinal acceptance without any disturbance to the stored bunch,which remains at the center.This composite RF system consists of three different frequencies,which can be regarded as the conventional bunch lengthening RF system(usually containing fundamental and third harmonic cavities)extended by an additional second harmonic RF cavity.In this paper,we discuss the RF jitter and the transverse mode-coupling instability(TMCI)when using this special RF system.Considering several different bunch profiles,we discuss the beam stability with regard to the RF jitter.However,for the TMCI we assume an ideal bunch profile,where the bunch is exactly lengthened to the maximum extent.While macroparticle simulation is the main method used to study the impact of the RF jitter,numerical analysis and simulations for the TMCI while using a triple-frequency RF system are also presented in this paper.An approximation formula,based on the existing model,is also derived to estimate the impact of the TMCI on the single bunch current threshold when using harmonic cavities.
文摘BACKGROUND Recently,the use of ligament advanced reinforcement system(LARS)artificial ligament,a new graft which has several unique advantages such as no donor-site morbidity,early recovery and no risk of disease transmission which has been a significant breakthrough for anatomical ligament reconstruction.Growing studies suggested that the special design of the LARS ligament with open fibers in its intra-articular part was believed to be more resistant to torsional fatigue and wearing.However,the safety and efficacy of LARS artificial ligament for ankle joint lateral collateral ankle ligament reconstruction has not been defined to date.AIM To evaluate the clinical results of all-arthroscopic anatomical reconstruction of ankle joint lateral collateral ligaments with the LARS artificial ligament for chronic ankle instability.METHODS Twenty-two patients with chronic lateral instability underwent anatomical reconstruction of the lateral collateral ligaments of ankle with LARS artificial ligament.The visual analogue score(VAS),American Orthopaedic Foot and Ankle Society score(AOFAS score)and Karlsson score were used to evaluate the clinical results before and after surgery.RESULTS A total of 22 patients(22 ankles)were followed up for a mean of 12 mo.All patients reported significant improvement compared to their preoperative status.The mean AOFAS score improved from 42.3±4.9 preoperatively to 90.4±6.7 postoperatively.The mean Karlsson score improved from 38.5±3.2 preoperatively to 90.1±7.8 postoperatively.The mean VAS score improved from 1.9±2.5 preoperatively to 0.8±1.7 postoperatively.CONCLUSION All-arthroscopic anatomical reconstruction of the lateral collateral ligaments with LARS artificial ligament achieved a satisfactory surgical outcome for chronic ankle instability.
基金supported by Regional Joint Development Fund(No.U20A20289)Project of Leading Local Science and Technology Development Fund(No.206Z1601G)+1 种基金Innovation Research Group Project of Hebei Province(No.E2021203011)Innovation Funding Project for Graduate Students in Hebei Province(No.CXZZBS2020054).
文摘The vibration instability of the nonlinear dynamic system of the rolls considering the structural clearance was theoretically investigated,which is caused by the roll assembly accuracy deviation in the hot rolling process.Firstly,the dynamic rolling force model was established based on the Wekbrod model under the influence of the roll grinding deviation and the stability of the deformation zone.Further,the horizontal and vertical direction coupling dynamic model of the work roll was established considering the structural clearance between the roll and mill frame.Then,the nonlinear dynamic equation was solved by the Runge-Kutta method.The simulation results show that the dynamic system presents the nonlinear vibration characteristics,which shows that the instability of the system is a slowly varying response process with the characteristics of self-excited vibration and forced vibration.Finally,the comparison results show the consistency between the simulation and the test.
文摘BACKGROUND The medial patellofemoral ligament(MPFL),along with the medial patellotibial ligament(MPTL)and medial patellomeniscal ligament,aid in the stabilization of the patellofemoral joint.Although the MPFL is the primary stabilizer and the MPTL is a secondary limiter,this ligament is critical in maintaining joint stability.There have been few studies on the combined MPFL and MPTL reconstruction and its benefits.AIM To look into the outcomes of combined MPFL and MPTL reconstruction in frequent patellar instability.METHODS By May 8,2022,four electronic databases were searched:Medline(PubMed),Scopus,Web of Science,and Google Scholar.General keywords such as"patellar instability,""patellar dislocation,""MPFL,""medial patellofemoral ligament,""MPTL,"and"medial patellotibial ligament"were co-searched to increase the sensitivity of the search.RESULTS The pooled effects of combined MPFL and MPTL reconstruction for Kujala score(12-mo followup)and Kujala score(24-mo follow-up)were positive and incremental,according to the findings of this meta-analysis.The mean difference between the Cincinnati scores was also positive,but not statistically significant.The combination of the two surgeries reduces pain.According to cumulative meta-analysis,the trend of pain reduction in various studies is declining over time.CONCLUSION The combined MPFL and MPTL reconstruction has good clinical results in knee function and,in addition to providing good control to maintain patellofemoral joint balance,the patient's pain level decreases over time,making it a valid surgical method for patella stabilization.
基金supported by the Ministry of Science and Technological Development of the Republic of Serbia (Nos.ON174016 and TR35006)
文摘The paper discusses the equilibrium instability problem of the scleronomic nonholonomic systems acted upon by dissipative, conservative, and circulatory forces. The method is based on the existence of solutions to the differential equations of the motion which asymptotically tends to the equilibrium state of the system as t tends to negative infinity. It is assumed that the kinetic energy, the Rayleigh dissipation function, and the positional forces in the neighborhood of the equilibrium position are infinitely differentiable functions. The results obtained here are partially generalized the results obtained by Kozlov et al. （Kozlov, V. V. The asymptotic motions of systems with dissi- pation. Journal of Applied Mathematics and Mechanics, 58（5）, 787-792 （1994）. Merkin, D. R. Introduction to the Theory of the Stability of Motion （in Russian）, Nauka, Moscow （1987）. Thomson, W. and Tait, P. Treatise on Natural Philosophy, Part I, Cambridge University Press, Cambridge （1879））. The results are illustrated by an example.
文摘AIM: To systematically evaluate the evidence-based literature on surgical treatment interventions for elite rugby players with anterior shoulder instability. METHODS: We conducted a systematic review according to the PRISMA guidelines. A literature search was performed in PubM ed, EMBASE and Google Scholar using the following search terms: "rugby" and "shoulder" in combination with "instability" or "dislocation". All articles published from inception of the included data sources to January 1st 2014 that evaluated surgical treatment of elite rugby players with anterior shoulder instability were examined. RESULTS: Only five studies were found that met the eligibility criteria. A total of 379 shoulders in 376 elite rugby union and league players were included. All the studies were retrospective cohort or case series studies. The mean Coleman Methodological Score for the 5 studies was 47.4(poor). Owing to heterogeneity amongst the studies, quantitative synthesis was not possible, however a detailed qualitative synthesis is reported. The overall recurrence rate of instability after surgery was 8.7%, and the mean return to competitive play, where reported, was 13 mo.CONCLUSION: Arthroscopic stabilization has been performed successfully in acute anterior instability and there is a preference for open Latarjet-type procedures when instability is associated with osseous defects.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11005055,11075020,and 11204117)the National Fundamental Research Programme of China(Grant No.2011CB921503)+1 种基金the Ph.D.Programs Foundation of Liaoning Provincial Science and Technology Bureau(GrantNo.201103778)the Higher School Excellent Researcher Award Program from the Educational Department of Liaoning Province of China(GrantNo.LJQ2011005)
文摘In the present paper, we investigate the instability, adiabaticity, and controlling effects of external fields for a dark state in a homonuclear atom-tetramer conversion that is implemented by a generalized stimulated Raman adiabatic passage. We analytically obtain the regions for the appearance of dynamical instability and study the adiabatic evolution by a newly defined adiabatic fidelity. Moreover, the effects of the external field parameters and the spontaneous emissions on the conversion efficiency are also investigated.
