We have calculated the Stark effect of CH3F molecules in external electrical fields, the rotational population of supersonic CH3F molecules in different quantum states, and analyse the motion of weak-field-seeking CH3...We have calculated the Stark effect of CH3F molecules in external electrical fields, the rotational population of supersonic CH3F molecules in different quantum states, and analyse the motion of weak-field-seeking CH3F molecules in a st＇ate ｜J = 1, KM = -1） inside the electrical field of a Stark decelerator by using a simple analytical model. Threedimensional Monte Carlo simulation is performed to simulate the dynamical slowing process of molecules through the decelerator, and the results are compared with those obtained from the analytical model, including the phase stability, slowing efficiency as well as the translational temperature of the slowed molecular packet. Our study shows that with a modest dipole moment （-1.85 Debye） and a relatively slight molecular weight （-34.03）, CH3F molecules in a state ｜J= 1, KM = -1） are a good candidate for slowing with electrostatic field. With high voltages of ±10 kV applied on the decelerator, molecules of 370 m/s can be brought to a standstill within 200 slowing stages.展开更多
We demonstrate the production of cold, slow NH_3 molecules from a supersonic NH_3 molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supe...We demonstrate the production of cold, slow NH_3 molecules from a supersonic NH_3 molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supersonic NH_3 molecular beam can be easily decelerated to trappable velocities. Here we present two modes for operating the Stark decelerator to slow the supersonic NH_3 molecules. The first is the normal mode, where all 179 stages are used to decelerate molecules, and it allows decelerating the NH_3 molecular beam from 333 m/s to 18 m/s, with a final temperature of 29.2 mK.The second is the deceleration-bunch mode, which allows us to decelerate the supersonic NH_3 beam from 333 m/s to 24 m/s,with a final temperature of 2.9 m K. It is clear that the second mode promises to produce colder(high-energy-resolution)molecular samples than the normal mode. Three-dimensional Monte Carlo simulations are also performed for the experiments and they show a good agreement with the observed results. The deceleration-bunch operation mode presented here can find applications in the fields of cold collisions, high-resolution spectroscopy, and precision measurements.展开更多
The surging interest in planetary exploration underscores the need for deployable aerodynamic decelerators with a low ballistic coefficient.This study introduces a novel approach to designing and constructing mechanic...The surging interest in planetary exploration underscores the need for deployable aerodynamic decelerators with a low ballistic coefficient.This study introduces a novel approach to designing and constructing mechanically deployable aerodynamic decelerators(MDADs)that utilize an umbrella-like mechanism and proposes a new mechanism of MDADs through this method.The proposed method utilizes plane-symmetric 7R(R:revolute joint)linkages,and the kinematics of these linkages are systematically analyzed using the product of exponentials method.The 7R linkage kinematics are equated to an equivalent joint,the foundation for constructing umbrella-like deployable mechanisms.Three distinct types of mechanisms are synthesized using this methodology.Subsequently,their kinematics are analyzed based on the equivalent joint,and the configurations are experimentally validated through 3D-printed models and kinematic simulations.Trajectory simulations and structural analyses are conducted to assess the performance of the deployable mechanisms and provide valuable insights into their capabilities.This research contributes to advancing deployable aerodynamic decelerator technology and offers a promising avenue for future planetary entry,descent,and landing applications.展开更多
Terahertz(THz) radiation, spanning the frequency range 100 GHz to 10 THz, offers diverse applications in spectroscopy, materials characterization, medical diagnostics and environmental monitoring. Despite its potentia...Terahertz(THz) radiation, spanning the frequency range 100 GHz to 10 THz, offers diverse applications in spectroscopy, materials characterization, medical diagnostics and environmental monitoring. Despite its potential, the generation of high-intensity, tunable THz radiation remains a significant challenge. In this work, we explore a novel approach to the efficient generation of THz radiation based on laser–plasma interactions, utilizing the principles of photon deceleration.When a relativistic CO_(2) laser passes through a pre-ionized plasma, the laser induces a nonlinear wakefield, creating a strong refractive index gradient. This gradient, combined with the lower-density region of the wakefield, slows down the laser, facilitating the accumulation of THz radiation. The resulting THz pulse exhibits extreme collimation, high energy efficiency and tunability. Our work shows that this method can achieve up to 10% conversion efficiency with optimal plasma density near the critical density. This technique presents a promising solution for overcoming current limitations in THz source development and offers potential for diverse applications.展开更多
Variable Cycle Engine(VCE)serves as the core system in achieving future advanced fighters with cross-generational performance and mission versatility.However,the resultant complex configuration and strong coupling of ...Variable Cycle Engine(VCE)serves as the core system in achieving future advanced fighters with cross-generational performance and mission versatility.However,the resultant complex configuration and strong coupling of control parameters present significant challenges in designing acceleration and deceleration control schedules.To thoroughly explore the performance potential of engine,a global integration design method for acceleration and deceleration control schedule based on inner and outer loop optimization is proposed.The outer loop optimization module employs Integrated Surrogate-Assisted Co-Differential Evolutionary(ISACDE)algorithm to optimize the variable geometry adjustment laws based on B-spline curve,and the inner loop optimization module adopts the fixed-state method to design the open-loop fuel–air ratio control schedules,which are aimed at minimizing the acceleration and deceleration time under multiple constraints.Simulation results demonstrate that the proposed global integration design method not only furthest shortens the acceleration and deceleration time,but also effectively safeguards the engine from overlimit.展开更多
Obtaining a reasonable mold flow field for casting slabs with different sections is challenging by solely modifying the nozzle structure and continuous casting process. Research was conducted on small-sectioned (1000 ...Obtaining a reasonable mold flow field for casting slabs with different sections is challenging by solely modifying the nozzle structure and continuous casting process. Research was conducted on small-sectioned (1000 mm × 220 mm) and large-sectioned (3250 mm × 220 mm) slab continuous casting molds with a fixed nozzle form (concave bottom nozzle, side port inclination angle of 0°). A three-dimensional electromagnetic model is established to analyze the current frequency, installation position, and rotation angle under the active deceleration mode and acceleration mode. The results indicate that, regardless of the deceleration mode for small-sectioned slabs or the acceleration mode for large-sectioned slabs, the magnetic flux density in the mold decreases with increasing current frequency. However, the maximum electromagnetic force initially increases and then decreases, suggesting that both electromagnetic modes have the same optimal current frequency (3 Hz). The optimal mechanical design parameters for the deceleration mode of electromagnetic variable flow device (EM-VFD) with the small-sectioned slab are as follows: installation position Z = 115 mm and rotation angle of 15°, ensuring that the maximum electromagnetic force is applied to the nozzle jet area. For the acceleration mode of the large-sectioned slab EM-VFD, the optimal mechanical design parameters are as follows: Z = 115 mm and rotation angle of 10°, ensuring that the maximum electromagnetic force is applied to 1/4 and 3/4 areas of the wide face. These findings indicate that the new electromagnetic variable flow device, which can actively adjust the flow rate and angle of the steel even under given working conditions, provides the possibility for reasonable control of the mold’s flow field.展开更多
As a common transportation facility, speed humps can control the speed of vehicles on special road sections to reduce traffic risks. At the same time, they also cause instantaneous traffic emissions. Based on the clas...As a common transportation facility, speed humps can control the speed of vehicles on special road sections to reduce traffic risks. At the same time, they also cause instantaneous traffic emissions. Based on the classic instantaneous traffic emission model and the limited deceleration capacity microscopic traffic flow model with slow-to-start rules, this paper has investigated the impact of speed humps on traffic flow and the instantaneous emissions of vehicle pollutants in a single lane situation. The numerical simulation results have shown that speed humps have significant effects on traffic flow and traffic emissions. In a free-flow region, the increase of speed humps leads to the continuous rise of CO_(2), NO_(X) and PM emissions. Within some density ranges, one finds that these pollutant emissions can evolve into some higher values under some random seeds. Under other random seeds, they can evolve into some lower values. In a wide moving jam region, the emission values of these pollutants sometimes appear as continuous or intermittent phenomenon. Compared to the refined Na Sch model, the present model has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher volatile organic components(VOC) emissions. Compared to the limited deceleration capacity model without slow-to-start rules, the present model also has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher VOC emissions in a wide moving jam region. These results can also be confirmed or explained by the statistical values of vehicle velocity and acceleration.展开更多
The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo-...The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo- lation preprocessing, the sensitive zones of feedrate variations are processed with acceleration-deceleration control. By using the proposed algorithm, the machining accuracy is guaranteed and the feedrate is adaptively adjusted to he smoothed. The mechanical shock imposed in the servo system is avoided by the first and the second time derivatives of feedrates. A simulation of NURBS interpolation is given to demonstrate the validity and the effectiveness of the algorithm. The proposed interpolator can also be applied to the trajectory planning of the other parametric curves.展开更多
A parachute-payload model with randomize wind gust is developed to study the landing accuracy of the parachute decelerator system,which can be exactly described by the landing site distribution.The research focuses on...A parachute-payload model with randomize wind gust is developed to study the landing accuracy of the parachute decelerator system,which can be exactly described by the landing site distribution.The research focuses on the steady descent phase of the parachute descent process,so the parachute and the payload suspension formulation during the phase are mainly discussed.In addition,since the wind effects have a significant impact on the land site distribution of the passive decelerator system and it is difficult to obtain the exact wind profile in practice,major features of parachute-payload system are studied via the randomized wind gust formulation.As the randomized wind gust formulation is adopted,the wind effect can be considered without the exact wind gust profile and the parachute aerodynamic simulation can be fulfilled with uncertainties.Finally,the model is validated and discussed,and the parachute land site distributions with different wind randomize profiles are presented for comparison.The results show that when parachute is less stable,the land site tends to have a larger variance.展开更多
This study was to investigate the decoloration effects of activated clay, activated carbon, diatomite, Ca group bentonite, kaolin, activated aluminum oxide, magnesium oxide and attapulgite. Ultraviolet-visible spectro...This study was to investigate the decoloration effects of activated clay, activated carbon, diatomite, Ca group bentonite, kaolin, activated aluminum oxide, magnesium oxide and attapulgite. Ultraviolet-visible spectroscopywas adopted to de- tect the absorbanees of the extracts of Schisandra chinensis fruit and rattan stems, the contents of total triterpenoids in S. chinensis fruit and rattan stems were deter- mined, and the decoloration rate and the retention rate of total triterpenoids of S. chi- nensis fruit and rattan stems were calculated. The results indicated that, attapulgite exhibited the best decoloration effect on the extract of S. chinensis fruit, with a de- coloration rate up to 60.47%, activated carbon exhibited a better decoloration effect on the extract of S. chinensis rattan stems, with a decoloration rate up to 69.24%, and they had relatively higher retention rates of total triterpenoids. In the eight de- colorants, attapulgite showed the best decoloration effect on the extract of S. chi- nensis fruit, and activated carbon exhibited the best decoloration effect on the ex- tract of S. chinensisrattan stems.展开更多
A new adaptive cruise control (ACC) method based on the desired safety headway distance is investigated for improving the vehicle traffic safety at high speed by regulating the additional throttle opening and braking ...A new adaptive cruise control (ACC) method based on the desired safety headway distance is investigated for improving the vehicle traffic safety at high speed by regulating the additional throttle opening and braking torque of driving wheels only. The selection of headway distance sensors, the determination of desired safety headway distance and desired deceleration are elaborated. The ACC flowchart and simulation, as well as signal misinformation and its resolutions are described. The simulation proves that the new ACC method is simpler and feasible. The new method is easily integrated ACC with ABS/ASR to form an organic ABS/ASR/ACC system.展开更多
Transient control law ensures that the aeroengine transits to the command operating state rapidly and reliably. Most of the existing approaches for transient control law design have complicated principle and arithmeti...Transient control law ensures that the aeroengine transits to the command operating state rapidly and reliably. Most of the existing approaches for transient control law design have complicated principle and arithmetic. As a result, those approaches are not convenient for application. This paper proposes an extrapolation approach based on the set-point parameters to construct the transient control law, which has a good practicability. In this approach, the transient main fuel control law for acceleration and deceleration process is designed based on the main fuel flow on steady operating state. In order to analyze the designing feature of the extrapolation approach, the simulation results of several different transient control laws designed by the same approach are compared together. The analysis indicates that the aeroengine has a good performance in the transient process and the designing feature of the extrapolation approach conforms to the elements of the turbofan aeroengine.展开更多
To satisfy the need of high speed NC (numerical control) machining, an acceleration and deceleration (acc/dec) control model is proposed, and the speed curve is also constructed by the cubic polynomial. The proposed c...To satisfy the need of high speed NC (numerical control) machining, an acceleration and deceleration (acc/dec) control model is proposed, and the speed curve is also constructed by the cubic polynomial. The proposed control model provides continuity of acceleration, which avoids the intense vibration in high speed NC machining. Based on the discrete characteristic of the data sampling interpolation, the acc/dec control discrete mathematical model is also set up and the discrete expression of the theoretical deceleration length is obtained furthermore. Aiming at the question of hardly predetermining the deceleration point in acc/dec control before interpolation, the adaptive acc/dec control algorithm is deduced from the expressions of the theoretical deceleration length. The experimental result proves that the acc/dec control model has the characteristic of easy implementation, stable movement and low impact. The model has been applied in multi-axes high speed micro fabrication machining successfully.展开更多
Studies show that different geometries of a Variable Cycle Engine(VCE)can be adjusted during the transient stage of the engine operation to improve the engine performance.However,this improvement increases the complex...Studies show that different geometries of a Variable Cycle Engine(VCE)can be adjusted during the transient stage of the engine operation to improve the engine performance.However,this improvement increases the complexity of the acceleration and deceleration control schedule.In order to resolve this problem,the Transient-state Reverse Method(TRM)is established in the present study based on the Steady-state Reverse Method(SRM)and the Virtual Power Extraction Method(VPEM).The state factors in the component-based engine performance models are replaced by variable geometry parameters to establish the TRM for a double bypass VCE.Obtained results are compared with the conventional component-based model from different aspects,including the accuracy and the convergence rate.The TRM is then employed to optimize the control schedule of a VCE.Obtained results show that the accuracy and the convergence rate of the proposed method are consistent with that of the conventional model.On the other hand,it is found that the new-model-optimized control schedules reduce the acceleration and deceleration time by 45%and 54%,respectively.Meanwhile,the surge margin of compressors,fuel–air ratio and the turbine inlet temperature maintained are within the acceptable criteria.It is concluded that the proposed TRM is a powerful method to design the acceleration and deceleration control schedule of the VCE.展开更多
Pressure waves induced by high-speed trains passing through a tunnel have adverse effects on train structures and passenger comfort. These adverse effects can be alleviated when the train passing through the tunnel wi...Pressure waves induced by high-speed trains passing through a tunnel have adverse effects on train structures and passenger comfort. These adverse effects can be alleviated when the train passing through the tunnel with a speed mode of deceleration. Thus, to investigate the effect of speed modes on pressure waves, three-dimensional compressible unsteady Reynolds-averaged Navier-Stokes simulations and the sliding mesh are used to simulate pressure waves on train surfaces and tunnel walls when trains passing through a tunnel with three different speed modes(a constant speed at350 km/h, a uniform deceleration from 350 to 300 km/h, and another uniform deceleration from 350 to 250 km/h).Compared with the constant speed, the peak-to-peak of the train surface pressure under the other two speed modes reaches a maximum difference of 11.0%. The maximum positive pressure difference of the tunnel wall under different speed modes is caused by the different attenuation of the friction effect when the train enters the tunnel, and the maximum difference is 12.8%. The difference of the maximum negative pressure on the tunnel wall is caused by the different speed and pressure wave intensity of the train arriving at the same measuring point in different speed modes,and the maximum difference is 15.8%. Hence, it can be concluded that a speed mode of deceleration for trains passing a tunnel can effectively alleviate the aerodynamic effect in the tunnel, especially for the pressure on the tunnel wall.展开更多
The algorithms for feedrate profile generation,such as linear and S-curve profiles,have been widely used in machinery controllers,and these algorithms can greatly improve the smoothness of motion.However,most of the a...The algorithms for feedrate profile generation,such as linear and S-curve profiles,have been widely used in machinery controllers,and these algorithms can greatly improve the smoothness of motion.However,most of the algorithms lead to the discontinuous acceleration/deceleration and jerk,or high jerk levels,which is very harmful to machine tool or robot in most occasions. This paper presents a smooth S-curve feedrate profiling generation algorithm that produces continuous feedrate,acceleration,and jerk profiles.Smooth jerk is obtained by imposing limits on the first and second time derivatives of acceleration,resulting in trapezoidal jerk profiles along the tool path.The discretization of smooth S-curve feedrate is realized with a novel approach that improves the efficiency without calculating the deceleration point in each sampled time.To ensure that the interpolation time is a multiple of the value of sampled time,the feedrate,acceleration,jerk,and jerk derivative are recalculated.Meantime,to improve the efficiency,the interpolation steps of all regions are computed before interpolation.According to the distance of trajectory,the smooth S-curve acceleration and decelerations are divided into three blocks：normal block,short block type-Ⅰ,and short block type-Ⅱ.Finally feedrate discretization of short block type-Ⅰand type-Ⅱis obtained with considering the efficiency.The proposed generation algorithm is tested in machining a part on a five axis milling machine,which is controlled with the CNC system for newly developed high-speed machine tools.The test result shows that the smooth S-curve approach has the smoother feedrate,acceleration,deceleration,and jerk profiles than S-curve.The proposed algorithm ensures the automated machinery motion smoothness,and improves the quality and efficiency of the automated machinery motion planning.展开更多
Laser-assisted Stark deceleration scheme was proposed to decelerate the high-field-seeking molecule IC1 in its rovibronic ground state. However, the laser intensity of 1.0×10^10W/cm^2 is hard to realize in experi...Laser-assisted Stark deceleration scheme was proposed to decelerate the high-field-seeking molecule IC1 in its rovibronic ground state. However, the laser intensity of 1.0×10^10W/cm^2 is hard to realize in experiment. The time-of-flight signals of HC2n＋1N （n=2, 3 and 4） by three-dimensional Monte-Carlo simulation suggest that deceleration of such molecules is more feasible experimentally as only one-tenth laser intensity is needed.展开更多
This study was to investigate the changes of autonomic nerve function and hemodynamics in patients with vasovagal syncope(VVS) during head-up tilt-table testing(HUT). HUT was performed in 68 patients with unexplained ...This study was to investigate the changes of autonomic nerve function and hemodynamics in patients with vasovagal syncope(VVS) during head-up tilt-table testing(HUT). HUT was performed in 68 patients with unexplained syncope and 18 healthy subjects served as control group. According to whether bradycardia, hypotension or both took place during the onset of syncope, the patients were divided during the test into three subgroups: vasodepressor syncope(VD), cardioinhibitory syncope(CI) and mixed syncope(MX) subgroups. Heart rate, blood pressure, heart rate variability(HRV), and deceleration capacity(DC) were continuously analyzed during HUT. For all the subjects with positive responses, the normalized low frequency(LFn) and the LF/HF ratio markedly decreased whereas normalized high frequency(HFn) increased when syncope occurred. Syncopal period also caused more significant increase in the power of the DC in positive groups. These changes were more exaggerated compared to controls. All the patients were indicative of a sympathetic surge in the presence of withdrawal vagal activity before syncope and a sympathetic inhibition with a vagal predominance at the syncopal stage by the frequency-domain analysis of HRV. With the measurements of DC, a decreased vagal tone before syncope stage and a vagal activation at the syncopal stage were observed. The vagal tone was higher in subjects showing cardioinhibitory responses at the syncopal stage. DC may provide an alternative method to understand the autonomic profile of VVS patients.展开更多
Generally complex 3D contours are divided into a lot of continuous small line blocks by CAD/CAM software. When these small line blocks are used in conventional way,machine tool has to stop at the end of one move befor...Generally complex 3D contours are divided into a lot of continuous small line blocks by CAD/CAM software. When these small line blocks are used in conventional way,machine tool has to stop at the end of one move before continuing on to the next to meet accuracy requirement,which results in inefficiency.Look-ahead is an intelligent function that aims at adjusting the feed rate automatically to achieve maximum productivity while maintaining accuracy.By now most researchers just utilize the simplest linear acceleration(ACC)and deceleration(DEC)to deal with look-ahead intelligence.A generalized ACC/DEC ap- proach and corresponding optimal look-ahead algorithm based on dynamic back tracking along a doubly linked list are proposed.An improved rounding strategy for reducing interpolation errors is also presented.By using the proposed techniques,arbitrary velocity profiles that offer look-ahead feature and have the desired ACC/DEC characteristics for movement of a lot of continuous line blocks can be generated efficiently.Both simulations and experiments showed the productivity was dramatically increased without sacri- fice of accuracy.展开更多
The acceleration saltation of the traditional S-type acceleration model in the speed planning of the NURBS curve will result in the vibration and flexible impact of the machine tool.It will affect the surface quality ...The acceleration saltation of the traditional S-type acceleration model in the speed planning of the NURBS curve will result in the vibration and flexible impact of the machine tool.It will affect the surface quality of the components.The high speed smooth S-type acceleration and deceleration model deals with flexible impact,but the calculation is tedious.Aimed at the above problems,the traditional S-type acceleration and deceleration model is improved to make the jerk change linearly at a certain slope to reduce the flexible impact.Before the speed planning,it is needed to find the arc length and curvature of each point on the NURBS curve with a tiny step,and to determine the speed sensitivity point on the curve accordingly.According to the speed sensitive point,the NURBS curve is segmented.The attribute parameters of each section are determined by adaptive speed planning.Then,the speed planning can be performed on the NURBS curve according to the speed characteristics classification.The simulation results show that the algorithm can effectively reduce the flexible impact,improve the machining precision and efficiency,and simplify the classification of speed characteristics.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10374029,10434060 and 10674047)the National Key Basic Research and Development Program of China (Grant No 2006CB921604)+2 种基金the Basic Key Program of Shanghai Municipality of China (Grant No 07JC14017)the Program for Changjiang Scholar and Innovative Research Teamthe Shanghai Leading Academic Discipline Project of China (Grant No B408)
文摘We have calculated the Stark effect of CH3F molecules in external electrical fields, the rotational population of supersonic CH3F molecules in different quantum states, and analyse the motion of weak-field-seeking CH3F molecules in a st＇ate ｜J = 1, KM = -1） inside the electrical field of a Stark decelerator by using a simple analytical model. Threedimensional Monte Carlo simulation is performed to simulate the dynamical slowing process of molecules through the decelerator, and the results are compared with those obtained from the analytical model, including the phase stability, slowing efficiency as well as the translational temperature of the slowed molecular packet. Our study shows that with a modest dipole moment （-1.85 Debye） and a relatively slight molecular weight （-34.03）, CH3F molecules in a state ｜J= 1, KM = -1） are a good candidate for slowing with electrostatic field. With high voltages of ±10 kV applied on the decelerator, molecules of 370 m/s can be brought to a standstill within 200 slowing stages.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91536218,11034002,11274114,11504112,and 11504318)the National Basic Research Program of China(Grant No.2011CB921602)+1 种基金the Fundamental Research Funds for the Central Universities,China,Shanghai Pujiang Talents Plan,China(Grant No.18PJ1403100)Exploration Funds for the Shanghai Natural Science Foundation,China(Grant No.18ZR1412700)
文摘We demonstrate the production of cold, slow NH_3 molecules from a supersonic NH_3 molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supersonic NH_3 molecular beam can be easily decelerated to trappable velocities. Here we present two modes for operating the Stark decelerator to slow the supersonic NH_3 molecules. The first is the normal mode, where all 179 stages are used to decelerate molecules, and it allows decelerating the NH_3 molecular beam from 333 m/s to 18 m/s, with a final temperature of 29.2 mK.The second is the deceleration-bunch mode, which allows us to decelerate the supersonic NH_3 beam from 333 m/s to 24 m/s,with a final temperature of 2.9 m K. It is clear that the second mode promises to produce colder(high-energy-resolution)molecular samples than the normal mode. Three-dimensional Monte Carlo simulations are also performed for the experiments and they show a good agreement with the observed results. The deceleration-bunch operation mode presented here can find applications in the fields of cold collisions, high-resolution spectroscopy, and precision measurements.
基金supported by the National Natural Science Foundation of China(Grant No.52175010)the Self-Planned Task of the State Key Laboratory of Robotics and Systems,Harbin Institute of Technology,China(Grant No.SKLRS202202B).
文摘The surging interest in planetary exploration underscores the need for deployable aerodynamic decelerators with a low ballistic coefficient.This study introduces a novel approach to designing and constructing mechanically deployable aerodynamic decelerators(MDADs)that utilize an umbrella-like mechanism and proposes a new mechanism of MDADs through this method.The proposed method utilizes plane-symmetric 7R(R:revolute joint)linkages,and the kinematics of these linkages are systematically analyzed using the product of exponentials method.The 7R linkage kinematics are equated to an equivalent joint,the foundation for constructing umbrella-like deployable mechanisms.Three distinct types of mechanisms are synthesized using this methodology.Subsequently,their kinematics are analyzed based on the equivalent joint,and the configurations are experimentally validated through 3D-printed models and kinematic simulations.Trajectory simulations and structural analyses are conducted to assess the performance of the deployable mechanisms and provide valuable insights into their capabilities.This research contributes to advancing deployable aerodynamic decelerator technology and offers a promising avenue for future planetary entry,descent,and landing applications.
基金Project supported by the China Postdoctoral Science Foundation (Grant No. 2024T170021)the Beijing Municipal Science & Technology Commission, Administrative Commission of Zhongguancun Science Park (Grant No. Z231100006023003)+2 种基金the National Natural Science Foundation of China (Grant Nos. 12175058, 12205007, and 11921006)the National Science Fund of Hunan Province for Distinguished Young Scholars (Grant No. 2024JJ2009)The computing was supported by the High-performance Computing Platform of Peking University。
文摘Terahertz(THz) radiation, spanning the frequency range 100 GHz to 10 THz, offers diverse applications in spectroscopy, materials characterization, medical diagnostics and environmental monitoring. Despite its potential, the generation of high-intensity, tunable THz radiation remains a significant challenge. In this work, we explore a novel approach to the efficient generation of THz radiation based on laser–plasma interactions, utilizing the principles of photon deceleration.When a relativistic CO_(2) laser passes through a pre-ionized plasma, the laser induces a nonlinear wakefield, creating a strong refractive index gradient. This gradient, combined with the lower-density region of the wakefield, slows down the laser, facilitating the accumulation of THz radiation. The resulting THz pulse exhibits extreme collimation, high energy efficiency and tunability. Our work shows that this method can achieve up to 10% conversion efficiency with optimal plasma density near the critical density. This technique presents a promising solution for overcoming current limitations in THz source development and offers potential for diverse applications.
基金supported by the Basic Research on Dynamic Real-time Modeling and Onboard Adaptive Modeling of Aero Engine,China(No.QZPY202308)。
文摘Variable Cycle Engine(VCE)serves as the core system in achieving future advanced fighters with cross-generational performance and mission versatility.However,the resultant complex configuration and strong coupling of control parameters present significant challenges in designing acceleration and deceleration control schedules.To thoroughly explore the performance potential of engine,a global integration design method for acceleration and deceleration control schedule based on inner and outer loop optimization is proposed.The outer loop optimization module employs Integrated Surrogate-Assisted Co-Differential Evolutionary(ISACDE)algorithm to optimize the variable geometry adjustment laws based on B-spline curve,and the inner loop optimization module adopts the fixed-state method to design the open-loop fuel–air ratio control schedules,which are aimed at minimizing the acceleration and deceleration time under multiple constraints.Simulation results demonstrate that the proposed global integration design method not only furthest shortens the acceleration and deceleration time,but also effectively safeguards the engine from overlimit.
基金supported by the Science and Technology Talent Support Project of Hunan province in China(Grant No.2023TJ-Z14).
文摘Obtaining a reasonable mold flow field for casting slabs with different sections is challenging by solely modifying the nozzle structure and continuous casting process. Research was conducted on small-sectioned (1000 mm × 220 mm) and large-sectioned (3250 mm × 220 mm) slab continuous casting molds with a fixed nozzle form (concave bottom nozzle, side port inclination angle of 0°). A three-dimensional electromagnetic model is established to analyze the current frequency, installation position, and rotation angle under the active deceleration mode and acceleration mode. The results indicate that, regardless of the deceleration mode for small-sectioned slabs or the acceleration mode for large-sectioned slabs, the magnetic flux density in the mold decreases with increasing current frequency. However, the maximum electromagnetic force initially increases and then decreases, suggesting that both electromagnetic modes have the same optimal current frequency (3 Hz). The optimal mechanical design parameters for the deceleration mode of electromagnetic variable flow device (EM-VFD) with the small-sectioned slab are as follows: installation position Z = 115 mm and rotation angle of 15°, ensuring that the maximum electromagnetic force is applied to the nozzle jet area. For the acceleration mode of the large-sectioned slab EM-VFD, the optimal mechanical design parameters are as follows: Z = 115 mm and rotation angle of 10°, ensuring that the maximum electromagnetic force is applied to 1/4 and 3/4 areas of the wide face. These findings indicate that the new electromagnetic variable flow device, which can actively adjust the flow rate and angle of the steel even under given working conditions, provides the possibility for reasonable control of the mold’s flow field.
基金funded by the National Natural Science Foundation of China (Grant No. 11875031)the key research projects of Natural Science of Anhui Provincial Colleges and Universities (Grant No. 2022AH050252)。
文摘As a common transportation facility, speed humps can control the speed of vehicles on special road sections to reduce traffic risks. At the same time, they also cause instantaneous traffic emissions. Based on the classic instantaneous traffic emission model and the limited deceleration capacity microscopic traffic flow model with slow-to-start rules, this paper has investigated the impact of speed humps on traffic flow and the instantaneous emissions of vehicle pollutants in a single lane situation. The numerical simulation results have shown that speed humps have significant effects on traffic flow and traffic emissions. In a free-flow region, the increase of speed humps leads to the continuous rise of CO_(2), NO_(X) and PM emissions. Within some density ranges, one finds that these pollutant emissions can evolve into some higher values under some random seeds. Under other random seeds, they can evolve into some lower values. In a wide moving jam region, the emission values of these pollutants sometimes appear as continuous or intermittent phenomenon. Compared to the refined Na Sch model, the present model has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher volatile organic components(VOC) emissions. Compared to the limited deceleration capacity model without slow-to-start rules, the present model also has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher VOC emissions in a wide moving jam region. These results can also be confirmed or explained by the statistical values of vehicle velocity and acceleration.
基金Supported by the Natural Science Foundation of Jiangsu Province(BK2003005)~~
文摘The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo- lation preprocessing, the sensitive zones of feedrate variations are processed with acceleration-deceleration control. By using the proposed algorithm, the machining accuracy is guaranteed and the feedrate is adaptively adjusted to he smoothed. The mechanical shock imposed in the servo system is avoided by the first and the second time derivatives of feedrates. A simulation of NURBS interpolation is given to demonstrate the validity and the effectiveness of the algorithm. The proposed interpolator can also be applied to the trajectory planning of the other parametric curves.
基金supported by the National Natural Science Foundation of China(No.11472137)the Educational Commission of Guangdong Province(No.2017KQNCX203)Science and Technology Project of Guangdong Province (No. 2016A010102023,2017A010102017)
文摘A parachute-payload model with randomize wind gust is developed to study the landing accuracy of the parachute decelerator system,which can be exactly described by the landing site distribution.The research focuses on the steady descent phase of the parachute descent process,so the parachute and the payload suspension formulation during the phase are mainly discussed.In addition,since the wind effects have a significant impact on the land site distribution of the passive decelerator system and it is difficult to obtain the exact wind profile in practice,major features of parachute-payload system are studied via the randomized wind gust formulation.As the randomized wind gust formulation is adopted,the wind effect can be considered without the exact wind gust profile and the parachute aerodynamic simulation can be fulfilled with uncertainties.Finally,the model is validated and discussed,and the parachute land site distributions with different wind randomize profiles are presented for comparison.The results show that when parachute is less stable,the land site tends to have a larger variance.
基金Supported by Key Science and Technology Research and Development Program of Jilin Province(20140204068YY,20140204062YY)Special Fund for Pharmaceutical Industry Development of Jilin Province(YYZW201246)~~
文摘This study was to investigate the decoloration effects of activated clay, activated carbon, diatomite, Ca group bentonite, kaolin, activated aluminum oxide, magnesium oxide and attapulgite. Ultraviolet-visible spectroscopywas adopted to de- tect the absorbanees of the extracts of Schisandra chinensis fruit and rattan stems, the contents of total triterpenoids in S. chinensis fruit and rattan stems were deter- mined, and the decoloration rate and the retention rate of total triterpenoids of S. chi- nensis fruit and rattan stems were calculated. The results indicated that, attapulgite exhibited the best decoloration effect on the extract of S. chinensis fruit, with a de- coloration rate up to 60.47%, activated carbon exhibited a better decoloration effect on the extract of S. chinensis rattan stems, with a decoloration rate up to 69.24%, and they had relatively higher retention rates of total triterpenoids. In the eight de- colorants, attapulgite showed the best decoloration effect on the extract of S. chi- nensis fruit, and activated carbon exhibited the best decoloration effect on the ex- tract of S. chinensisrattan stems.
文摘A new adaptive cruise control (ACC) method based on the desired safety headway distance is investigated for improving the vehicle traffic safety at high speed by regulating the additional throttle opening and braking torque of driving wheels only. The selection of headway distance sensors, the determination of desired safety headway distance and desired deceleration are elaborated. The ACC flowchart and simulation, as well as signal misinformation and its resolutions are described. The simulation proves that the new ACC method is simpler and feasible. The new method is easily integrated ACC with ABS/ASR to form an organic ABS/ASR/ACC system.
基金support of Aeronautical Science Foundation of China (2011ZB51019)
文摘Transient control law ensures that the aeroengine transits to the command operating state rapidly and reliably. Most of the existing approaches for transient control law design have complicated principle and arithmetic. As a result, those approaches are not convenient for application. This paper proposes an extrapolation approach based on the set-point parameters to construct the transient control law, which has a good practicability. In this approach, the transient main fuel control law for acceleration and deceleration process is designed based on the main fuel flow on steady operating state. In order to analyze the designing feature of the extrapolation approach, the simulation results of several different transient control laws designed by the same approach are compared together. The analysis indicates that the aeroengine has a good performance in the transient process and the designing feature of the extrapolation approach conforms to the elements of the turbofan aeroengine.
基金the Hi-Tech Research and Development Pro-gram (863) of China (No. 2006AA04Z233)the National NaturalScience Foundation of China (No. 50575205)the Natural ScienceFoundation of Zhejiang Province (Nos. Y104243 and Y105686),China
文摘To satisfy the need of high speed NC (numerical control) machining, an acceleration and deceleration (acc/dec) control model is proposed, and the speed curve is also constructed by the cubic polynomial. The proposed control model provides continuity of acceleration, which avoids the intense vibration in high speed NC machining. Based on the discrete characteristic of the data sampling interpolation, the acc/dec control discrete mathematical model is also set up and the discrete expression of the theoretical deceleration length is obtained furthermore. Aiming at the question of hardly predetermining the deceleration point in acc/dec control before interpolation, the adaptive acc/dec control algorithm is deduced from the expressions of the theoretical deceleration length. The experimental result proves that the acc/dec control model has the characteristic of easy implementation, stable movement and low impact. The model has been applied in multi-axes high speed micro fabrication machining successfully.
基金supported by the Aviation Power Foundation of China(6141B09050382)。
文摘Studies show that different geometries of a Variable Cycle Engine(VCE)can be adjusted during the transient stage of the engine operation to improve the engine performance.However,this improvement increases the complexity of the acceleration and deceleration control schedule.In order to resolve this problem,the Transient-state Reverse Method(TRM)is established in the present study based on the Steady-state Reverse Method(SRM)and the Virtual Power Extraction Method(VPEM).The state factors in the component-based engine performance models are replaced by variable geometry parameters to establish the TRM for a double bypass VCE.Obtained results are compared with the conventional component-based model from different aspects,including the accuracy and the convergence rate.The TRM is then employed to optimize the control schedule of a VCE.Obtained results show that the accuracy and the convergence rate of the proposed method are consistent with that of the conventional model.On the other hand,it is found that the new-model-optimized control schedules reduce the acceleration and deceleration time by 45%and 54%,respectively.Meanwhile,the surge margin of compressors,fuel–air ratio and the turbine inlet temperature maintained are within the acceptable criteria.It is concluded that the proposed TRM is a powerful method to design the acceleration and deceleration control schedule of the VCE.
基金Project(2017J010-B)supported by the Technology Research and Development Program of China Railway CorporationProject(414010033)supported by the National Natural Science Foundation of China+1 种基金Project(CX20210232)supported by Hunan Provincial Innovation Foundation for Postgraduate,ChinaProjects(2021zzts0671,2021zzts0163)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Pressure waves induced by high-speed trains passing through a tunnel have adverse effects on train structures and passenger comfort. These adverse effects can be alleviated when the train passing through the tunnel with a speed mode of deceleration. Thus, to investigate the effect of speed modes on pressure waves, three-dimensional compressible unsteady Reynolds-averaged Navier-Stokes simulations and the sliding mesh are used to simulate pressure waves on train surfaces and tunnel walls when trains passing through a tunnel with three different speed modes(a constant speed at350 km/h, a uniform deceleration from 350 to 300 km/h, and another uniform deceleration from 350 to 250 km/h).Compared with the constant speed, the peak-to-peak of the train surface pressure under the other two speed modes reaches a maximum difference of 11.0%. The maximum positive pressure difference of the tunnel wall under different speed modes is caused by the different attenuation of the friction effect when the train enters the tunnel, and the maximum difference is 12.8%. The difference of the maximum negative pressure on the tunnel wall is caused by the different speed and pressure wave intensity of the train arriving at the same measuring point in different speed modes,and the maximum difference is 15.8%. Hence, it can be concluded that a speed mode of deceleration for trains passing a tunnel can effectively alleviate the aerodynamic effect in the tunnel, especially for the pressure on the tunnel wall.
基金supported by Major National S&T Program of China (Grant No.2009ZX04009-014-02)National Hi-tech Research and Development Program of China(863 Program,Grant No. 2009AA043901)
文摘The algorithms for feedrate profile generation,such as linear and S-curve profiles,have been widely used in machinery controllers,and these algorithms can greatly improve the smoothness of motion.However,most of the algorithms lead to the discontinuous acceleration/deceleration and jerk,or high jerk levels,which is very harmful to machine tool or robot in most occasions. This paper presents a smooth S-curve feedrate profiling generation algorithm that produces continuous feedrate,acceleration,and jerk profiles.Smooth jerk is obtained by imposing limits on the first and second time derivatives of acceleration,resulting in trapezoidal jerk profiles along the tool path.The discretization of smooth S-curve feedrate is realized with a novel approach that improves the efficiency without calculating the deceleration point in each sampled time.To ensure that the interpolation time is a multiple of the value of sampled time,the feedrate,acceleration,jerk,and jerk derivative are recalculated.Meantime,to improve the efficiency,the interpolation steps of all regions are computed before interpolation.According to the distance of trajectory,the smooth S-curve acceleration and decelerations are divided into three blocks：normal block,short block type-Ⅰ,and short block type-Ⅱ.Finally feedrate discretization of short block type-Ⅰand type-Ⅱis obtained with considering the efficiency.The proposed generation algorithm is tested in machining a part on a five axis milling machine,which is controlled with the CNC system for newly developed high-speed machine tools.The test result shows that the smooth S-curve approach has the smoother feedrate,acceleration,deceleration,and jerk profiles than S-curve.The proposed algorithm ensures the automated machinery motion smoothness,and improves the quality and efficiency of the automated machinery motion planning.
基金This work was supported by the National Natural Science Foundation of China （No.20273066）.
文摘Laser-assisted Stark deceleration scheme was proposed to decelerate the high-field-seeking molecule IC1 in its rovibronic ground state. However, the laser intensity of 1.0×10^10W/cm^2 is hard to realize in experiment. The time-of-flight signals of HC2n＋1N （n=2, 3 and 4） by three-dimensional Monte-Carlo simulation suggest that deceleration of such molecules is more feasible experimentally as only one-tenth laser intensity is needed.
基金supported by a grant from the Wuhan Science and Technology Program of China(No.2014060101010032)
文摘This study was to investigate the changes of autonomic nerve function and hemodynamics in patients with vasovagal syncope(VVS) during head-up tilt-table testing(HUT). HUT was performed in 68 patients with unexplained syncope and 18 healthy subjects served as control group. According to whether bradycardia, hypotension or both took place during the onset of syncope, the patients were divided during the test into three subgroups: vasodepressor syncope(VD), cardioinhibitory syncope(CI) and mixed syncope(MX) subgroups. Heart rate, blood pressure, heart rate variability(HRV), and deceleration capacity(DC) were continuously analyzed during HUT. For all the subjects with positive responses, the normalized low frequency(LFn) and the LF/HF ratio markedly decreased whereas normalized high frequency(HFn) increased when syncope occurred. Syncopal period also caused more significant increase in the power of the DC in positive groups. These changes were more exaggerated compared to controls. All the patients were indicative of a sympathetic surge in the presence of withdrawal vagal activity before syncope and a sympathetic inhibition with a vagal predominance at the syncopal stage by the frequency-domain analysis of HRV. With the measurements of DC, a decreased vagal tone before syncope stage and a vagal activation at the syncopal stage were observed. The vagal tone was higher in subjects showing cardioinhibitory responses at the syncopal stage. DC may provide an alternative method to understand the autonomic profile of VVS patients.
文摘Generally complex 3D contours are divided into a lot of continuous small line blocks by CAD/CAM software. When these small line blocks are used in conventional way,machine tool has to stop at the end of one move before continuing on to the next to meet accuracy requirement,which results in inefficiency.Look-ahead is an intelligent function that aims at adjusting the feed rate automatically to achieve maximum productivity while maintaining accuracy.By now most researchers just utilize the simplest linear acceleration(ACC)and deceleration(DEC)to deal with look-ahead intelligence.A generalized ACC/DEC ap- proach and corresponding optimal look-ahead algorithm based on dynamic back tracking along a doubly linked list are proposed.An improved rounding strategy for reducing interpolation errors is also presented.By using the proposed techniques,arbitrary velocity profiles that offer look-ahead feature and have the desired ACC/DEC characteristics for movement of a lot of continuous line blocks can be generated efficiently.Both simulations and experiments showed the productivity was dramatically increased without sacri- fice of accuracy.
基金the National Key Basic Research Program of China(973 Program)(No.2014CB046501)。
文摘The acceleration saltation of the traditional S-type acceleration model in the speed planning of the NURBS curve will result in the vibration and flexible impact of the machine tool.It will affect the surface quality of the components.The high speed smooth S-type acceleration and deceleration model deals with flexible impact,but the calculation is tedious.Aimed at the above problems,the traditional S-type acceleration and deceleration model is improved to make the jerk change linearly at a certain slope to reduce the flexible impact.Before the speed planning,it is needed to find the arc length and curvature of each point on the NURBS curve with a tiny step,and to determine the speed sensitivity point on the curve accordingly.According to the speed sensitive point,the NURBS curve is segmented.The attribute parameters of each section are determined by adaptive speed planning.Then,the speed planning can be performed on the NURBS curve according to the speed characteristics classification.The simulation results show that the algorithm can effectively reduce the flexible impact,improve the machining precision and efficiency,and simplify the classification of speed characteristics.
