Dynesys,a pedicle-based dynamic stabilization system,was introduced to overcome some undesirable complications of fusion procedures.Nevertheless,the theoretical advantages of Dynesys over fusion have not been clearly ...Dynesys,a pedicle-based dynamic stabilization system,was introduced to overcome some undesirable complications of fusion procedures.Nevertheless,the theoretical advantages of Dynesys over fusion have not been clearly confirmed.The purpose of this editorial was to compare clinical and radiological outcomes of patients who underwent Dynesys system with those who underwent posterior lumbar fusion according to the existing literature and to see if the application of the Dynesys system is superior to the traditional lumbar fusion surgery.According to published clinical reports,the short-term effects of the Dynesys dynamic stabilization system are similar to that of traditional lumbar fusion surgery.Three comparative studies of Dynesys dynamic stabilization and fusion surgery with medium-term follow-up are encouraging.However,the results from four single-treatment-arm and small-sample studies of case series with long-term follow-up were not encouraging.In the present circumstances,it is not possible to conclude that the Dynesys dynamic stabilization system is superior to fusion surgery for lumbar degenerative diseases.展开更多
BACKGROUND In recent years,the mechanical concept of intervertebral disc regeneration has become more and more popular due to the increasing awareness of the importance of preservation of spine movement.Interestingly,...BACKGROUND In recent years,the mechanical concept of intervertebral disc regeneration has become more and more popular due to the increasing awareness of the importance of preservation of spine movement.Interestingly,there is increasing evidence,however,that dynamic stabilization systems may compensate nonphysiological loads,limit pathological movement,normalize disc height and intradiscal pressure,and provide an adaptive environment for disc regeneration.CASE SUMMARY The patient was a 54-year-old man,who presented with a 10-year history of mechanical back pain,which had become progressively serious and radiated into the left lower limb with numbness 3 mo prior.He had decreased muscle strength(class IV)of the left dorsal extensor and plantar flexor.Magnetic resonance imaging scans showed L3-S1 disc degeneration and L4-L5 disc herniation.Because the patient did not respond to various conservative treatments,he underwent a posterior L4-5 discectomy with fixation of the BioFlex dynamic stabilization system(Bio-Spine,Seoul,Korea).Preoperative symptoms were relieved and lumbar function was markedly improved after the operation.L4-L5 disc rehydration of instrumented segment was noted on magnetic resonance imaging at the 2-year follow-up.CONCLUSION Rehydration of the degenerated disc in our patient indicates that the BioFlex dynamic stabilization system may promote disc regeneration.Further research is needed to provide more evidence to support lumbar disc rehydration in the bridged segment using this system.展开更多
We investigate theoretically the ionization properties of the valence electron for the alkali metal atom Na in an intense pulsed laser field by solving numerically the time-dependent Schrodinger equation with an accur...We investigate theoretically the ionization properties of the valence electron for the alkali metal atom Na in an intense pulsed laser field by solving numerically the time-dependent Schrodinger equation with an accurate l-dependent model potential.By calculating the variations of the ionization probabilities with laser peak intensity for wavelengths ranging from 200 nm to 600 nm,our results present a dynamic stabilization trend for the Na atom initially in its ground state（3 s） and the excited states（3 p and 4 s） exposed to an intense pulsed laser field.Especially a clear ＂window＂ of dynamic stabilization at lower laser intensities and longer wavelengths for the initial state 4 s（the second excited state） is found.By analyzing the time-dependent population distributions of the valence electron in the bound states with the different values of principal quantum number n and orbital quantum number l,we can attribute the dynamic stabilization to the periodic population in the low-excited states since the valence electron oscillates rapidly between the lowly excited states and the continuum states.展开更多
In this paper,we investigate the dynamical stability of transonic shock solutions for the full compressible Euler system in a two dimensional nozzle with a symmetric divergent part.Building upon the existence and uniq...In this paper,we investigate the dynamical stability of transonic shock solutions for the full compressible Euler system in a two dimensional nozzle with a symmetric divergent part.Building upon the existence and uniqueness results for steady symmetric transonic shock solutions to the nonisentropic Euler system established in[Z.P.Xin and H.C.Yin,The transonic shock in a nozzle,2-D and 3-D complete Euler systems,J.Differential Equations 245(2008)],we prove the dynamical stability of the transonic shock solutions under small perturbations.More precisely,if the initial unsteady transonic flow is located in the symmetric divergent part of the nozzle and the flow is a symmetric small perturbation of the steady transonic flow,we use the characteristic method to establish the dynamical stability.展开更多
Background:Many clinical studies over the past decade have indicated positive outcomes for patients treated with Dynesys dynamic stabilization for lumbar degenerative disease.However,long-term outcomes of Dynesys for ...Background:Many clinical studies over the past decade have indicated positive outcomes for patients treated with Dynesys dynamic stabilization for lumbar degenerative disease.However,long-term outcomes of Dynesys for lumbar spinal stenosis are rarely reported.The aim of this study was to analyze the long-term clinical and radiologic outcomes for patients with lumbar spinal stenosis treated with Dynesys stabilization.Methods:Thirty-eight patients with lumbar spinal stenosis were treated with Dynesys stabilization from July 2008 to March 2010.The minimal duration of follow-up was 72 months.The patients were divided into stenosis and spondylolisthesis groups according to degenerative spondylolisthesis.Clinical outcomes were evaluated using the Oswestry Disability Index(ODI)and visual analog scale(VAS).Radiographic evaluations included range of motion(ROM)and the disc heights of stabilized segments and the upper adjacent segments.We also evaluated the occurrence of radiographic and symptomatic adjacent segment degeneration(ASD).Results:There were 23 patients in stenosis group and 15 patients in spondylolisthesis group.The ODl scores were significantly improved at the final follow-up evaluation,as compared to the baseline values(16.1±5.7 vs.57.2±14.2,t=61.4 l,P〈0.01).The VA S scores for back and leg pain were significantly improved from 4.82±0.89 and 4.04±0.82 preoperatively to 0.93±0.61 and 0.54±0.51 postoperatively(t=6.59,P〈0.01,and t=5.91,P〈0.01,respectively).There were no differences between the two groups with respect to VAS and ODI scores.The ROM of stabilized segments decreased significantly from 7.8°±2.4°to 4.5°±1.5°(t=7.18,P〈0.05),while the upper adjacent segments increased significantly from 8.3°±2.4°to 10.4°±2.4°(t=2.87,P=0.01).The change in disc height of stabilized segments was not significant(11.9±2.1 preoperatively vs.12.5±1.5 postoperatively,t=1.43,P=0.15),whereas the decrease in disc height of the upper adjacent segments was significant(12.5±2.0 preopcratively vs.11.0±1.7 postoperatively,t=2.94,P=0.01).The occurrence of radiographic and symptomatic ASD was 16%(6/38)and 3%(1/38),respectively.Conclusions:Decompression and Dynesys stabilization for lumbar stenosis with or without spondylolisthesis showed good long-term clinical and radiographic results.Lumbar stenosis with or without Grade I spondylolisthesis,particularly in patients〈60 years of age with mild-to-moderate lumbar disc degeneration,would be one of the main indications for the Dynesys system.展开更多
Background Dynesys dynamic stabilization system in 2007. Therefore, it was a new technique for Ch about Dynesys in China. The objective of this study degenerative disease in China. was first implanted in patients in 1...Background Dynesys dynamic stabilization system in 2007. Therefore, it was a new technique for Ch about Dynesys in China. The objective of this study degenerative disease in China. was first implanted in patients in 1994, and introduced to China nese orthopedics and hence necessary to collect clinical data was to report the preliminary results of Dynesys for the lumbar Methods Twenty-seven patients were treated with the Dynesys between July 2007 and January 2009. The diagnosis included degenerative spondylolisthesis （12 cases）, degenerative spinal stenosis （nine cases）, and lumbar intervertebral disc herniation （six cases）. Back pain and leg pain were evaluated using 100-mm visual analog scales （VAS）. The Oswestry Disability Index （ODI） was used to evaluate the patients＇ function. The intervertebral disc height and range of motion at the operative level were taken on radiographs. Results All the patients were followed-up, with an average of （22.40±4.23） months （range 15±32 months）. VAS of back pain and leg pain were improved significantly （P 〈0.05） at foUow-up. The ODI scores were reduced from （62.58±12.01）% preoperatively to （15.01±5.71）% at follow-up （P 〈0.05）. The preoperative mean height of the intervertebral disc was （11.21±1.58） mm （range 8.5±13.8 mm） and mean was （10.10±1.78） mm （range 7.0±13.4 mm） at follow-up （P 〈0.05）. The mean range of motion of the implanted segment was （6.00±1.79）° （range 2.5-9.3°） preoperatively and （5.47±1.27）° （range 2.9±7.8°） at follow-up （P=0.11）. Conclusions The preliminary results of Dynesys for the lumbar degenerative disease in China are similar to the published results of other countries. It can significantly improve the clinic symptoms and preserved motion at the level of implantation. However, the long-term follow-up data need to be collected.展开更多
The purpose of this case study is to describe the chiropractic care of a 4-year-old male patient with agenesis of the corpus callosum. Methods: Chiropractic care plan consisted of weekly appointments with the inclusio...The purpose of this case study is to describe the chiropractic care of a 4-year-old male patient with agenesis of the corpus callosum. Methods: Chiropractic care plan consisted of weekly appointments with the inclusion of at-home exercises coupled with academic intervention of physical and occupational therapies and assistive gait devices. Functional changes were monitored via objective clinic findings, independent clinical examination, and parental observation. Results: Agitated flexion contracted non-weight bearing child with gastrointestinal dysfunction and developmentally shunted growth responds to co-managed chiropractic care. Focus on aiding structural balance helped improve the weight bearing movement and mobility, physical calmness and contentment, emotional and verbal communication, as well as gastointestinal function. Discussion: This therapeutic approach decreased aberrant posture and enhanced quality of life. Conclusion: Chiropractic care in combination with academic intervention improved this child’s postural abnormalities, attitude, and cognitive development warranting consideration in subsequent care investigation.展开更多
To predict the occurrence of the collapse disaster in toppling perilous rock under the action of bidirectional earthquakes,the dynamic stability and fuzzy reliability calculation method of toppling perilous rock under...To predict the occurrence of the collapse disaster in toppling perilous rock under the action of bidirectional earthquakes,the dynamic stability and fuzzy reliability calculation method of toppling perilous rock under the action of bidirectional earthquakes is proposed.First,the mass viscoelasticity model is used to simulate two main control surfaces of toppling perilous rock,the seismic dynamic response model and motion equation of toppling perilous rock are established based on the D'Alembert principle,and the Newmark-β method is used to solve the dynamic motion equation.Then,the instability event of toppling perilous rock is considered a fuzzy event,the membership function expression of the stability coefficient of toppling perilous rock is determined based on the fuzzy failure criterion,the calculation equations of the toppling perilous rock dynamic stability coefficient and fuzzy reliability are established,and the fuzzy reliability evaluation method based on the probability distribution of reliability is proposed.Finally,the influence of different superposition modes of seismic excitation on the fuzzy reliability of toppling perilous rock is analyzed.The calculation results of toppling perilous rock in the engineering case show that the fuzzy reliability calculated after considering the fuzzy failure criterion is reduced by 10.73% to 25.66% compared with the classical reliability.Considering the bidirectional seismic excitation,the fuzzy reliability of toppling perilous rock is reduced by 5.46% to 14.89%.Compared with using the acceleration peak time encounter mode to superpose the seismic excitation,the fuzzy reliability of toppling perilous rock is reduced by 3.4% when the maximum action effect time encounter mode is adopted.展开更多
This paper deals with the dynamic output feedback stabilization problem of deterministic finite automata(DFA).The static form of this problem is defined and solved in previous studies via a set of equivalent condition...This paper deals with the dynamic output feedback stabilization problem of deterministic finite automata(DFA).The static form of this problem is defined and solved in previous studies via a set of equivalent conditions.In this paper,the dynamic output feedback(DOF)stabilization of DFAs is defined in which the controller is supposed to be another DFA.The DFA controller will be designed to stabilize the equilibrium point of the main DFA through a set of proposed equivalent conditions.It has been proven that the design problem of DOF stabilization is more feasible than the static output feedback(SOF)stabilization.Three simulation examples are provided to illustrate the results of this paper in more details.The first example considers an instance DFA and develops SOF and DOF controllers for it.The example explains the concepts of the DOF controller and how it will be implemented in the closed-loop DFA.In the second example,a special DFA is provided in which the DOF stabilization is feasible,whereas the SOF stabilization is not.The final example compares the feasibility performance of the SOF and DOF stabilizations through applying them to one hundred random-generated DFAs.The results reveal the superiority of the DOF stabilization.展开更多
The impulsive motion of a dynamically stabilized robot—Gyrover, which is a single-wheel gyroscopically stabilized robot is studied. A method based on the D’Alembert-Lagrange principle is proposed to develop the impu...The impulsive motion of a dynamically stabilized robot—Gyrover, which is a single-wheel gyroscopically stabilized robot is studied. A method based on the D’Alembert-Lagrange principle is proposed to develop the impulsive dynamic model of the single wheel robot. This method that can be used to find ways to investigate a single wheel mobile robot rolling on a rough terrain is tested using the experimental platform Gyrover. The conditions of falling over without actuators are addressed. Simulations that validate the analysis are provided as well.展开更多
BACKGROUND Radiologic adjacent segment degeneration(ASDeg)can occur after spinal surgery.Adjacent segment disease(ASDis)is defined as the development of new clinical symptoms corresponding to radiographic changes adja...BACKGROUND Radiologic adjacent segment degeneration(ASDeg)can occur after spinal surgery.Adjacent segment disease(ASDis)is defined as the development of new clinical symptoms corresponding to radiographic changes adjacent to the level of previous spinal surgery.Greater pre-existing ASDeg is generally considered to result in more severe ASDis;nonetheless,whether the ASDeg status before index surgery influences the postoperative risk of revision surgery due to ASDis warrants investigation.AIM To identify possible risk factors for ASDis and verify the concept that greater preexisting ASDeg leads to more severe ASDis.METHODS Data from 212 patients who underwent posterior decompression with Dynesys stabilization from January 2006 to June 2016 were retrospectively analyzed.Patients who underwent surgery for ASDis were categorized as group A(n=13),whereas those who did not were classified as group B(n=199).Survival analysis and Cox proportional hazards models were used to compare the modified Pfirrmann grade,University of California-Los Angeles grade,body mass index,number of Dynesys-instrumented levels,and age.RESULTS The mean time of reoperation was 7.22(1.65–11.84)years in group A,and the mean follow-up period was 6.09(0.10–12.76)years in group B.No significant difference in reoperation risk was observed:Modified Pfirrmann grade 3 vs 4(P=0.53)or 4 vs 5(P=0.46)for the upper adjacent disc,University of California-Los Angeles grade 2 vs 3 for the upper adjacent segment(P=0.66),age of<60 vs>60 years(P=0.9),body mass index<25 vs>25 kg/m2(P=0.3),and sex(P=0.8).CONCLUSION Greater preexisting upper ASDeg was not associated with a higher rate of reoperation for ASDis after Dynesys surgery.Being overweight tended to increase reoperation risk after Dynesys surgery for ASDis.展开更多
In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin proj...In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin projectile.The platform's reliability is validated by reproducing the characteristic resonance instability of such projectiles.By coupling the solution of the Unsteady Reynolds-Averaged Navier-Stokes equations and the seven-degree-of-freedom RBD equations,the virtual flight simulations of fixed canard dual-spin projectiles at various curvature trajectories are achieved,and the dynamic mechanism of the trajectory following process is analyzed.The instability mechanism of the dynamic instability during trajectory following process of the fixed canard dual-spin projectile is elucidated by simulating the rolling/coning coupled forced motion,and subsequently validated through virtual flight simulations.The findings suggest that an appropriate yaw moment can drive the projectile axis to precession in the tangential direction of the trajectory,thereby enhancing the trajectory following stability.However,the damping of the projectile attains its minimum value when the forward body equilibrium rotational speed(-128 rad/s)is equal to the negative of the fast mode frequency of the projectile.Insufficient damping leads to the fixed canard dual-spin projectile exiting the dynamic stability domain during the trajectory following,resulting in weakly damped instability.Keeping the forward body not rotating or increasing the spin rates to-192 rad/s can enhance the projectile's damping,thereby improving its dynamic stability.展开更多
The equations of motion of an insect with flapping wings are derived and then simplified to that of a flying body using the ＂rigid body＂ assumption. On the basis of the simplified equations of motion, the longitudin...The equations of motion of an insect with flapping wings are derived and then simplified to that of a flying body using the ＂rigid body＂ assumption. On the basis of the simplified equations of motion, the longitudinal dynamic flight stability of four insects （hoverfly, cranefly, dronefly and hawkmoth） in hovering flight is studied （the mass of the insects ranging from 11 to 1,648 mg and wingbeat frequency from 26 to 157Hz）. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are used to solve the equations of motion. The validity of the ＂rigid body＂ assumption is tested and how differences in size and wing kinematics influence the applicability of the ＂rigid body＂ assumption is investigated. The primary findings are： （1） For insects considered in the present study and those with relatively high wingbeat frequency （hoverfly, drone fly and bumblebee）, the ＂rigid body＂ assumption is reasonable, and for those with relatively low wingbeat frequency （cranefly and howkmoth）, the applicability of the ＂rigid body＂ assumption is questionable. （2） The same three natural modes of motion as those reported recently for a bumblebee are identified, i.e., one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. （3） Approximate analytical expressions of the eigenvalues, which give physical insight into the genesis of the natural modes of motion, are derived. The expressions identify the speed derivative Mu （pitching moment produced by unit horizontal speed） as the primary source of the unstable oscillatory mode and the stable fast subsidence mode and Zw （vertical force produced by unit vertical speed） as the primary source of the stable slow subsidence mode.展开更多
Shake table testing was performed to investigate the dynamic stability of a mid-dip bedding rock slope under frequent earthquakes. Then, numerical modelling was established to further study the slope dynamic stability...Shake table testing was performed to investigate the dynamic stability of a mid-dip bedding rock slope under frequent earthquakes. Then, numerical modelling was established to further study the slope dynamic stability under purely microseisms and the influence of five factors, including seismic amplitude, slope height, slope angle, strata inclination and strata thickness, were considered. The experimental results show that the natural frequency of the slope decreases and damping ratio increases as the earthquake loading times increase. The dynamic strength reduction method is adopted for the stability evaluation of the bedding rock slope in numerical simulation, and the slope stability decreases with the increase of seismic amplitude, increase of slope height, reduction of strata thickness and increase of slope angle. The failure mode of a mid-dip bedding rock slope in the shaking table test is integral slipping along the bedding surface with dipping tensile cracks at the slope rear edge going through the bedding surfaces. In the numerical simulation, the long-term stability of a mid-dip bedding slope is worst under frequent microseisms and the slope is at risk of integral sliding instability, whereas the slope rock mass is more broken than shown in the shaking table test. The research results are of practical significance to better understand the formation mechanism of reservoir landslides and prevent future landslide disasters.展开更多
The performance of the vehicle dynamics stability control system（DSC） is dominated by the accurate estimation of tire forces in real-time.The characteristics of tire forces are determined by tire dynamic states and ...The performance of the vehicle dynamics stability control system（DSC） is dominated by the accurate estimation of tire forces in real-time.The characteristics of tire forces are determined by tire dynamic states and parameters,which vary in an obviously large scope along with different working conditions.Currently,there have been many methods based on the nonlinear observer to estimate the tire force and dynamic parameters,but they were only used in off-line analysis because of the computation complexity and the dynamics differences of four tires in the steering maneuver conditions were not considered properly.This paper develops a novel algorithm to observe tire parameters in real-time controller for DSC.The algorithm is based on the sensor-fusion technology with the signals of DSC sensors,and the tire parameters are estimated during a set of maneuver courses.The calibrated tire parameters in the control cycle are treated as the elementary states for vehicle dynamics observation,in which the errors between the calculated and the measured vehicle dynamics are used as the correcting factors for the tire parameter observing process.The test process with a given acceleration following a straight line is used to validate the estimation method of the longitudinal stiffness;while the test process with a given steering angle is used to validate the estimated value of the cornering stiffness.The ground test result shows that the proposed algorithm can estimate the tire stiffness accurately with an acceptable computation cost for real-time controller only using DSC sensor signal.The proposed algorithm can be an efficient algorithm for estimating the tire dynamic parameters in vehicle dynamics stability control system,and can be used to improve the robustness of the DSC controller.展开更多
The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigen...The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. The main results are as following. （i） Three natural modes of motion were identified： one unstable slow divergence mode （mode 1）, one stable slow oscillatory mode （mode 2）, and one stable fast subsidence mode （mode 3）. Modes 1 and 2 mainly consist of a rotation about the horizontal longitudinal axis （x-axis） and a side translation; mode 3 mainly consists of a rotation about the x-axis and a rotation about the vertical axis. （ii） Approximate analytical expressions of the eigenvalues are derived, which give physical insight into the genesis of the natural modes of motion. （iii） For the unstable divergence mode, td, the time for initial disturbances to double, is about 9 times the wingbeat period （the longitudinal motion of the model insect was shown to be also unstable and td of the longitudinal unstable mode is about 14 times the wingbeat period）. Thus, although the flight is not dynamically stable, the instability does not grow very fast and the insect has enough time to control its wing motion to suppress the disturbances.展开更多
A new method （kinetic vector method, KVM） is presented for analyzing the dynamic stability of wedge in rock slope. The dynamic analysis is carried out based on three dimensional distinct element code （3DEC）, and t...A new method （kinetic vector method, KVM） is presented for analyzing the dynamic stability of wedge in rock slope. The dynamic analysis is carried out based on three dimensional distinct element code （3DEC）, and the kinetic inertial force of the wedge under seismic loading can be obtained via calculating the net vectorial nodal force of the finite difference grid. Then, the factor of safety （FOS） of the wedge can be calculated based on limit equilibrium method （LEM） at each dynamic analysis step, therefore time series of the FOS for whole earthquake process can be obtained. For the purpose of evaluating the entire dynamic stability of the wedge, dynamic factor of safety （DFOS） is proposed and defined as a numerical value corresponding with a given rate of probability guarantee based on reliability theory. Consequently, the KVM inherits the merits of the LEM and also has fully nonlinear dynamic analysis capabilities, and the feasibility and correctness of the KVM are tested by an example given by Hoek and Bray （1981）. Finally, a rock slope case in Wenchuan Earthquake regions of China is presented to verify the engineering practicability of the KVM, and the results matched the actual situation well.展开更多
This paper addresses the dynamic stability problem of columns and frames subjected to axially applied periodic loads. Such a structure can become unstable under certain combinations of amplitudes and frequencies of th...This paper addresses the dynamic stability problem of columns and frames subjected to axially applied periodic loads. Such a structure can become unstable under certain combinations of amplitudes and frequencies of the imposed load acting on its columns/beams. These are usually shown in the form of plots which describe regions of instability. The finite element method (FEM) is used in this work to analyse dynamic stability problems of columns. Two-noded beam elements are used for this purpose. The periodic loading is decomposed into various harmonics using Fourier series expansion. Computer codes in C++ using object oriented concepts are developed to determine the stability regions of columns subjected to periodic loading. A number of nu-merical examples are presented to illustrate the working of the program. The direct integration of the equations of motions of the discretised system is carried out using Newmark’s method to verify the results.展开更多
The paper is devoted to mathematical modelling of static and dynamic stability of a simply supported three-layered beam with a metal foam core. Mechanical properties of the core vary along the vertical direction. The ...The paper is devoted to mathematical modelling of static and dynamic stability of a simply supported three-layered beam with a metal foam core. Mechanical properties of the core vary along the vertical direction. The field of displacements is for- mulated using the classical broken line hypothesis and the proposed nonlinear hypothesis that generalizes the classical one. Using both hypotheses, the strains are determined as well as the stresses of each layer. The kinetic energy, the elastic strain energy, and the work of load are also determined. The system of equations of motion is derived using Hamilton＇s principle. Finally, the system of three equations is reduced to one equation of motion, in particular, the Mathieu equation. The Bubnov-Galerkin method is used to solve the system of equations of motion, and the Runge-Kutta method is used to solve the second-order differential equation. Numerical calculations are done for the chosen family of beams. The critical loads, unstable regions, angular frequencies of the beam, and the static and dynamic equilibrium paths are calculated analytically and verified numerically. The results of this study are presented in the forms of figures and tables.展开更多
文摘Dynesys,a pedicle-based dynamic stabilization system,was introduced to overcome some undesirable complications of fusion procedures.Nevertheless,the theoretical advantages of Dynesys over fusion have not been clearly confirmed.The purpose of this editorial was to compare clinical and radiological outcomes of patients who underwent Dynesys system with those who underwent posterior lumbar fusion according to the existing literature and to see if the application of the Dynesys system is superior to the traditional lumbar fusion surgery.According to published clinical reports,the short-term effects of the Dynesys dynamic stabilization system are similar to that of traditional lumbar fusion surgery.Three comparative studies of Dynesys dynamic stabilization and fusion surgery with medium-term follow-up are encouraging.However,the results from four single-treatment-arm and small-sample studies of case series with long-term follow-up were not encouraging.In the present circumstances,it is not possible to conclude that the Dynesys dynamic stabilization system is superior to fusion surgery for lumbar degenerative diseases.
基金Supported by Foundation of Capital Medical Development,Beijing,China,No.2010026.
文摘BACKGROUND In recent years,the mechanical concept of intervertebral disc regeneration has become more and more popular due to the increasing awareness of the importance of preservation of spine movement.Interestingly,there is increasing evidence,however,that dynamic stabilization systems may compensate nonphysiological loads,limit pathological movement,normalize disc height and intradiscal pressure,and provide an adaptive environment for disc regeneration.CASE SUMMARY The patient was a 54-year-old man,who presented with a 10-year history of mechanical back pain,which had become progressively serious and radiated into the left lower limb with numbness 3 mo prior.He had decreased muscle strength(class IV)of the left dorsal extensor and plantar flexor.Magnetic resonance imaging scans showed L3-S1 disc degeneration and L4-L5 disc herniation.Because the patient did not respond to various conservative treatments,he underwent a posterior L4-5 discectomy with fixation of the BioFlex dynamic stabilization system(Bio-Spine,Seoul,Korea).Preoperative symptoms were relieved and lumbar function was markedly improved after the operation.L4-L5 disc rehydration of instrumented segment was noted on magnetic resonance imaging at the 2-year follow-up.CONCLUSION Rehydration of the degenerated disc in our patient indicates that the BioFlex dynamic stabilization system may promote disc regeneration.Further research is needed to provide more evidence to support lumbar disc rehydration in the bridged segment using this system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11465016,11664035,and 11764038)
文摘We investigate theoretically the ionization properties of the valence electron for the alkali metal atom Na in an intense pulsed laser field by solving numerically the time-dependent Schrodinger equation with an accurate l-dependent model potential.By calculating the variations of the ionization probabilities with laser peak intensity for wavelengths ranging from 200 nm to 600 nm,our results present a dynamic stabilization trend for the Na atom initially in its ground state（3 s） and the excited states（3 p and 4 s） exposed to an intense pulsed laser field.Especially a clear ＂window＂ of dynamic stabilization at lower laser intensities and longer wavelengths for the initial state 4 s（the second excited state） is found.By analyzing the time-dependent population distributions of the valence electron in the bound states with the different values of principal quantum number n and orbital quantum number l,we can attribute the dynamic stabilization to the periodic population in the low-excited states since the valence electron oscillates rapidly between the lowly excited states and the continuum states.
基金supported in part by NSFC(Grant Nos.12271205,12171498).
文摘In this paper,we investigate the dynamical stability of transonic shock solutions for the full compressible Euler system in a two dimensional nozzle with a symmetric divergent part.Building upon the existence and uniqueness results for steady symmetric transonic shock solutions to the nonisentropic Euler system established in[Z.P.Xin and H.C.Yin,The transonic shock in a nozzle,2-D and 3-D complete Euler systems,J.Differential Equations 245(2008)],we prove the dynamical stability of the transonic shock solutions under small perturbations.More precisely,if the initial unsteady transonic flow is located in the symmetric divergent part of the nozzle and the flow is a symmetric small perturbation of the steady transonic flow,we use the characteristic method to establish the dynamical stability.
基金supported by a grant from the Youth Project of the“Twelfth Five-year Plan”for Medical Science Development of Chinese People's Liberation Army(No.13QNP010).
文摘Background:Many clinical studies over the past decade have indicated positive outcomes for patients treated with Dynesys dynamic stabilization for lumbar degenerative disease.However,long-term outcomes of Dynesys for lumbar spinal stenosis are rarely reported.The aim of this study was to analyze the long-term clinical and radiologic outcomes for patients with lumbar spinal stenosis treated with Dynesys stabilization.Methods:Thirty-eight patients with lumbar spinal stenosis were treated with Dynesys stabilization from July 2008 to March 2010.The minimal duration of follow-up was 72 months.The patients were divided into stenosis and spondylolisthesis groups according to degenerative spondylolisthesis.Clinical outcomes were evaluated using the Oswestry Disability Index(ODI)and visual analog scale(VAS).Radiographic evaluations included range of motion(ROM)and the disc heights of stabilized segments and the upper adjacent segments.We also evaluated the occurrence of radiographic and symptomatic adjacent segment degeneration(ASD).Results:There were 23 patients in stenosis group and 15 patients in spondylolisthesis group.The ODl scores were significantly improved at the final follow-up evaluation,as compared to the baseline values(16.1±5.7 vs.57.2±14.2,t=61.4 l,P〈0.01).The VA S scores for back and leg pain were significantly improved from 4.82±0.89 and 4.04±0.82 preoperatively to 0.93±0.61 and 0.54±0.51 postoperatively(t=6.59,P〈0.01,and t=5.91,P〈0.01,respectively).There were no differences between the two groups with respect to VAS and ODI scores.The ROM of stabilized segments decreased significantly from 7.8°±2.4°to 4.5°±1.5°(t=7.18,P〈0.05),while the upper adjacent segments increased significantly from 8.3°±2.4°to 10.4°±2.4°(t=2.87,P=0.01).The change in disc height of stabilized segments was not significant(11.9±2.1 preoperatively vs.12.5±1.5 postoperatively,t=1.43,P=0.15),whereas the decrease in disc height of the upper adjacent segments was significant(12.5±2.0 preopcratively vs.11.0±1.7 postoperatively,t=2.94,P=0.01).The occurrence of radiographic and symptomatic ASD was 16%(6/38)and 3%(1/38),respectively.Conclusions:Decompression and Dynesys stabilization for lumbar stenosis with or without spondylolisthesis showed good long-term clinical and radiographic results.Lumbar stenosis with or without Grade I spondylolisthesis,particularly in patients〈60 years of age with mild-to-moderate lumbar disc degeneration,would be one of the main indications for the Dynesys system.
文摘Background Dynesys dynamic stabilization system in 2007. Therefore, it was a new technique for Ch about Dynesys in China. The objective of this study degenerative disease in China. was first implanted in patients in 1994, and introduced to China nese orthopedics and hence necessary to collect clinical data was to report the preliminary results of Dynesys for the lumbar Methods Twenty-seven patients were treated with the Dynesys between July 2007 and January 2009. The diagnosis included degenerative spondylolisthesis （12 cases）, degenerative spinal stenosis （nine cases）, and lumbar intervertebral disc herniation （six cases）. Back pain and leg pain were evaluated using 100-mm visual analog scales （VAS）. The Oswestry Disability Index （ODI） was used to evaluate the patients＇ function. The intervertebral disc height and range of motion at the operative level were taken on radiographs. Results All the patients were followed-up, with an average of （22.40±4.23） months （range 15±32 months）. VAS of back pain and leg pain were improved significantly （P 〈0.05） at foUow-up. The ODI scores were reduced from （62.58±12.01）% preoperatively to （15.01±5.71）% at follow-up （P 〈0.05）. The preoperative mean height of the intervertebral disc was （11.21±1.58） mm （range 8.5±13.8 mm） and mean was （10.10±1.78） mm （range 7.0±13.4 mm） at follow-up （P 〈0.05）. The mean range of motion of the implanted segment was （6.00±1.79）° （range 2.5-9.3°） preoperatively and （5.47±1.27）° （range 2.9±7.8°） at follow-up （P=0.11）. Conclusions The preliminary results of Dynesys for the lumbar degenerative disease in China are similar to the published results of other countries. It can significantly improve the clinic symptoms and preserved motion at the level of implantation. However, the long-term follow-up data need to be collected.
文摘The purpose of this case study is to describe the chiropractic care of a 4-year-old male patient with agenesis of the corpus callosum. Methods: Chiropractic care plan consisted of weekly appointments with the inclusion of at-home exercises coupled with academic intervention of physical and occupational therapies and assistive gait devices. Functional changes were monitored via objective clinic findings, independent clinical examination, and parental observation. Results: Agitated flexion contracted non-weight bearing child with gastrointestinal dysfunction and developmentally shunted growth responds to co-managed chiropractic care. Focus on aiding structural balance helped improve the weight bearing movement and mobility, physical calmness and contentment, emotional and verbal communication, as well as gastointestinal function. Discussion: This therapeutic approach decreased aberrant posture and enhanced quality of life. Conclusion: Chiropractic care in combination with academic intervention improved this child’s postural abnormalities, attitude, and cognitive development warranting consideration in subsequent care investigation.
基金financially supported by the National Key Research and Development Program of China(Nos.2021YFB2600604 and 2021YFB2600600)the General Program of Natural Science Foundation of Chongqing(No.cstc2020jcyj-msxm X0218)the Research and Innovation Program for Graduate Students in Chongqing Jiaotong University(No.2022S0021)。
文摘To predict the occurrence of the collapse disaster in toppling perilous rock under the action of bidirectional earthquakes,the dynamic stability and fuzzy reliability calculation method of toppling perilous rock under the action of bidirectional earthquakes is proposed.First,the mass viscoelasticity model is used to simulate two main control surfaces of toppling perilous rock,the seismic dynamic response model and motion equation of toppling perilous rock are established based on the D'Alembert principle,and the Newmark-β method is used to solve the dynamic motion equation.Then,the instability event of toppling perilous rock is considered a fuzzy event,the membership function expression of the stability coefficient of toppling perilous rock is determined based on the fuzzy failure criterion,the calculation equations of the toppling perilous rock dynamic stability coefficient and fuzzy reliability are established,and the fuzzy reliability evaluation method based on the probability distribution of reliability is proposed.Finally,the influence of different superposition modes of seismic excitation on the fuzzy reliability of toppling perilous rock is analyzed.The calculation results of toppling perilous rock in the engineering case show that the fuzzy reliability calculated after considering the fuzzy failure criterion is reduced by 10.73% to 25.66% compared with the classical reliability.Considering the bidirectional seismic excitation,the fuzzy reliability of toppling perilous rock is reduced by 5.46% to 14.89%.Compared with using the acceleration peak time encounter mode to superpose the seismic excitation,the fuzzy reliability of toppling perilous rock is reduced by 3.4% when the maximum action effect time encounter mode is adopted.
文摘This paper deals with the dynamic output feedback stabilization problem of deterministic finite automata(DFA).The static form of this problem is defined and solved in previous studies via a set of equivalent conditions.In this paper,the dynamic output feedback(DOF)stabilization of DFAs is defined in which the controller is supposed to be another DFA.The DFA controller will be designed to stabilize the equilibrium point of the main DFA through a set of proposed equivalent conditions.It has been proven that the design problem of DOF stabilization is more feasible than the static output feedback(SOF)stabilization.Three simulation examples are provided to illustrate the results of this paper in more details.The first example considers an instance DFA and develops SOF and DOF controllers for it.The example explains the concepts of the DOF controller and how it will be implemented in the closed-loop DFA.In the second example,a special DFA is provided in which the DOF stabilization is feasible,whereas the SOF stabilization is not.The final example compares the feasibility performance of the SOF and DOF stabilizations through applying them to one hundred random-generated DFAs.The results reveal the superiority of the DOF stabilization.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(No.KGCX2-YW-152No.KGCX2-YW-156)+2 种基金Key Laboratory of Robotics and Intelligent System,Guangdong Province(No.2009A060800016)Shenzhen Fundamental Research Program(No.JC200903170431A)China Postdoctoral Science Foundation(No.20090460532)
文摘The impulsive motion of a dynamically stabilized robot—Gyrover, which is a single-wheel gyroscopically stabilized robot is studied. A method based on the D’Alembert-Lagrange principle is proposed to develop the impulsive dynamic model of the single wheel robot. This method that can be used to find ways to investigate a single wheel mobile robot rolling on a rough terrain is tested using the experimental platform Gyrover. The conditions of falling over without actuators are addressed. Simulations that validate the analysis are provided as well.
基金The study was approved by our institutional review board,Research Ethics Committee China Medical University and Hospital,Taichung,Taiwan(Protocol No.:CMUH108-REC2-133).
文摘BACKGROUND Radiologic adjacent segment degeneration(ASDeg)can occur after spinal surgery.Adjacent segment disease(ASDis)is defined as the development of new clinical symptoms corresponding to radiographic changes adjacent to the level of previous spinal surgery.Greater pre-existing ASDeg is generally considered to result in more severe ASDis;nonetheless,whether the ASDeg status before index surgery influences the postoperative risk of revision surgery due to ASDis warrants investigation.AIM To identify possible risk factors for ASDis and verify the concept that greater preexisting ASDeg leads to more severe ASDis.METHODS Data from 212 patients who underwent posterior decompression with Dynesys stabilization from January 2006 to June 2016 were retrospectively analyzed.Patients who underwent surgery for ASDis were categorized as group A(n=13),whereas those who did not were classified as group B(n=199).Survival analysis and Cox proportional hazards models were used to compare the modified Pfirrmann grade,University of California-Los Angeles grade,body mass index,number of Dynesys-instrumented levels,and age.RESULTS The mean time of reoperation was 7.22(1.65–11.84)years in group A,and the mean follow-up period was 6.09(0.10–12.76)years in group B.No significant difference in reoperation risk was observed:Modified Pfirrmann grade 3 vs 4(P=0.53)or 4 vs 5(P=0.46)for the upper adjacent disc,University of California-Los Angeles grade 2 vs 3 for the upper adjacent segment(P=0.66),age of<60 vs>60 years(P=0.9),body mass index<25 vs>25 kg/m2(P=0.3),and sex(P=0.8).CONCLUSION Greater preexisting upper ASDeg was not associated with a higher rate of reoperation for ASDis after Dynesys surgery.Being overweight tended to increase reoperation risk after Dynesys surgery for ASDis.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2141254 and U23B6009)。
文摘In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin projectile.The platform's reliability is validated by reproducing the characteristic resonance instability of such projectiles.By coupling the solution of the Unsteady Reynolds-Averaged Navier-Stokes equations and the seven-degree-of-freedom RBD equations,the virtual flight simulations of fixed canard dual-spin projectiles at various curvature trajectories are achieved,and the dynamic mechanism of the trajectory following process is analyzed.The instability mechanism of the dynamic instability during trajectory following process of the fixed canard dual-spin projectile is elucidated by simulating the rolling/coning coupled forced motion,and subsequently validated through virtual flight simulations.The findings suggest that an appropriate yaw moment can drive the projectile axis to precession in the tangential direction of the trajectory,thereby enhancing the trajectory following stability.However,the damping of the projectile attains its minimum value when the forward body equilibrium rotational speed(-128 rad/s)is equal to the negative of the fast mode frequency of the projectile.Insufficient damping leads to the fixed canard dual-spin projectile exiting the dynamic stability domain during the trajectory following,resulting in weakly damped instability.Keeping the forward body not rotating or increasing the spin rates to-192 rad/s can enhance the projectile's damping,thereby improving its dynamic stability.
基金The project supported by the National Natural Science Foundation of China(10232010 and 10472008)
文摘The equations of motion of an insect with flapping wings are derived and then simplified to that of a flying body using the ＂rigid body＂ assumption. On the basis of the simplified equations of motion, the longitudinal dynamic flight stability of four insects （hoverfly, cranefly, dronefly and hawkmoth） in hovering flight is studied （the mass of the insects ranging from 11 to 1,648 mg and wingbeat frequency from 26 to 157Hz）. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are used to solve the equations of motion. The validity of the ＂rigid body＂ assumption is tested and how differences in size and wing kinematics influence the applicability of the ＂rigid body＂ assumption is investigated. The primary findings are： （1） For insects considered in the present study and those with relatively high wingbeat frequency （hoverfly, drone fly and bumblebee）, the ＂rigid body＂ assumption is reasonable, and for those with relatively low wingbeat frequency （cranefly and howkmoth）, the applicability of the ＂rigid body＂ assumption is questionable. （2） The same three natural modes of motion as those reported recently for a bumblebee are identified, i.e., one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. （3） Approximate analytical expressions of the eigenvalues, which give physical insight into the genesis of the natural modes of motion, are derived. The expressions identify the speed derivative Mu （pitching moment produced by unit horizontal speed） as the primary source of the unstable oscillatory mode and the stable fast subsidence mode and Zw （vertical force produced by unit vertical speed） as the primary source of the stable slow subsidence mode.
基金National Natural Science Foundation of China under Grant No. 41372356the College Cultivation Project of the National Natural Science Foundation of China under Grant No. 2018PY30+1 种基金the Basic Research and Frontier Exploration Project of Chongqing,China under Grant No. cstc2018jcyj A1597the Graduate Scientific Research and Innovation Foundation of Chongqing,China under Grant No. CYS18026。
文摘Shake table testing was performed to investigate the dynamic stability of a mid-dip bedding rock slope under frequent earthquakes. Then, numerical modelling was established to further study the slope dynamic stability under purely microseisms and the influence of five factors, including seismic amplitude, slope height, slope angle, strata inclination and strata thickness, were considered. The experimental results show that the natural frequency of the slope decreases and damping ratio increases as the earthquake loading times increase. The dynamic strength reduction method is adopted for the stability evaluation of the bedding rock slope in numerical simulation, and the slope stability decreases with the increase of seismic amplitude, increase of slope height, reduction of strata thickness and increase of slope angle. The failure mode of a mid-dip bedding rock slope in the shaking table test is integral slipping along the bedding surface with dipping tensile cracks at the slope rear edge going through the bedding surfaces. In the numerical simulation, the long-term stability of a mid-dip bedding slope is worst under frequent microseisms and the slope is at risk of integral sliding instability, whereas the slope rock mass is more broken than shown in the shaking table test. The research results are of practical significance to better understand the formation mechanism of reservoir landslides and prevent future landslide disasters.
基金supported by National Natural Science Foundation of China (Grant No.50905092)
文摘The performance of the vehicle dynamics stability control system（DSC） is dominated by the accurate estimation of tire forces in real-time.The characteristics of tire forces are determined by tire dynamic states and parameters,which vary in an obviously large scope along with different working conditions.Currently,there have been many methods based on the nonlinear observer to estimate the tire force and dynamic parameters,but they were only used in off-line analysis because of the computation complexity and the dynamics differences of four tires in the steering maneuver conditions were not considered properly.This paper develops a novel algorithm to observe tire parameters in real-time controller for DSC.The algorithm is based on the sensor-fusion technology with the signals of DSC sensors,and the tire parameters are estimated during a set of maneuver courses.The calibrated tire parameters in the control cycle are treated as the elementary states for vehicle dynamics observation,in which the errors between the calculated and the measured vehicle dynamics are used as the correcting factors for the tire parameter observing process.The test process with a given acceleration following a straight line is used to validate the estimation method of the longitudinal stiffness;while the test process with a given steering angle is used to validate the estimated value of the cornering stiffness.The ground test result shows that the proposed algorithm can estimate the tire stiffness accurately with an acceptable computation cost for real-time controller only using DSC sensor signal.The proposed algorithm can be an efficient algorithm for estimating the tire dynamic parameters in vehicle dynamics stability control system,and can be used to improve the robustness of the DSC controller.
基金supported by the National Natural Science Foundation of China(10732030)the 111 Project(B07009)
文摘The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. The main results are as following. （i） Three natural modes of motion were identified： one unstable slow divergence mode （mode 1）, one stable slow oscillatory mode （mode 2）, and one stable fast subsidence mode （mode 3）. Modes 1 and 2 mainly consist of a rotation about the horizontal longitudinal axis （x-axis） and a side translation; mode 3 mainly consists of a rotation about the x-axis and a rotation about the vertical axis. （ii） Approximate analytical expressions of the eigenvalues are derived, which give physical insight into the genesis of the natural modes of motion. （iii） For the unstable divergence mode, td, the time for initial disturbances to double, is about 9 times the wingbeat period （the longitudinal motion of the model insect was shown to be also unstable and td of the longitudinal unstable mode is about 14 times the wingbeat period）. Thus, although the flight is not dynamically stable, the instability does not grow very fast and the insect has enough time to control its wing motion to suppress the disturbances.
基金support of the National Basic Research Program of China (No. 2011CB710606)the Geological Survey Program of the China Geological Survey (No. 1212010914036)the National Natural Science Foundation of China (No. 41102195)
文摘A new method （kinetic vector method, KVM） is presented for analyzing the dynamic stability of wedge in rock slope. The dynamic analysis is carried out based on three dimensional distinct element code （3DEC）, and the kinetic inertial force of the wedge under seismic loading can be obtained via calculating the net vectorial nodal force of the finite difference grid. Then, the factor of safety （FOS） of the wedge can be calculated based on limit equilibrium method （LEM） at each dynamic analysis step, therefore time series of the FOS for whole earthquake process can be obtained. For the purpose of evaluating the entire dynamic stability of the wedge, dynamic factor of safety （DFOS） is proposed and defined as a numerical value corresponding with a given rate of probability guarantee based on reliability theory. Consequently, the KVM inherits the merits of the LEM and also has fully nonlinear dynamic analysis capabilities, and the feasibility and correctness of the KVM are tested by an example given by Hoek and Bray （1981）. Finally, a rock slope case in Wenchuan Earthquake regions of China is presented to verify the engineering practicability of the KVM, and the results matched the actual situation well.
文摘This paper addresses the dynamic stability problem of columns and frames subjected to axially applied periodic loads. Such a structure can become unstable under certain combinations of amplitudes and frequencies of the imposed load acting on its columns/beams. These are usually shown in the form of plots which describe regions of instability. The finite element method (FEM) is used in this work to analyse dynamic stability problems of columns. Two-noded beam elements are used for this purpose. The periodic loading is decomposed into various harmonics using Fourier series expansion. Computer codes in C++ using object oriented concepts are developed to determine the stability regions of columns subjected to periodic loading. A number of nu-merical examples are presented to illustrate the working of the program. The direct integration of the equations of motions of the discretised system is carried out using Newmark’s method to verify the results.
基金Project supported by the Ministry of Science and Higher Education of Poland(Nos.04/43/DSPB/0085and 02/21/DSPB/3464)
文摘The paper is devoted to mathematical modelling of static and dynamic stability of a simply supported three-layered beam with a metal foam core. Mechanical properties of the core vary along the vertical direction. The field of displacements is for- mulated using the classical broken line hypothesis and the proposed nonlinear hypothesis that generalizes the classical one. Using both hypotheses, the strains are determined as well as the stresses of each layer. The kinetic energy, the elastic strain energy, and the work of load are also determined. The system of equations of motion is derived using Hamilton＇s principle. Finally, the system of three equations is reduced to one equation of motion, in particular, the Mathieu equation. The Bubnov-Galerkin method is used to solve the system of equations of motion, and the Runge-Kutta method is used to solve the second-order differential equation. Numerical calculations are done for the chosen family of beams. The critical loads, unstable regions, angular frequencies of the beam, and the static and dynamic equilibrium paths are calculated analytically and verified numerically. The results of this study are presented in the forms of figures and tables.
