In this paper , the unilaterally constrained motions of a large class of rigid bodiessystems are studied both locally and globally. The main conclusion is that locally,such a system bahaves like a particle in a R...In this paper , the unilaterally constrained motions of a large class of rigid bodiessystems are studied both locally and globally. The main conclusion is that locally,such a system bahaves like a particle in a Riemannian manifold with boundary;globally.under the assumption of energy conservation, the system behaves like a billiards system over a Riemannina manifold with boundary展开更多
A concurrency control mechanism for collaborative work is akey element in a mixed reality environment. However, conventional lockingmechanisms restrict potential tasks or the support of non-owners, thusincreasing the ...A concurrency control mechanism for collaborative work is akey element in a mixed reality environment. However, conventional lockingmechanisms restrict potential tasks or the support of non-owners, thusincreasing the working time because of waiting to avoid conflicts. Herein, wepropose an adaptive concurrency control approach that can reduce conflictsand work time. We classify shared object manipulation in mixed reality intodetailed goals and tasks. Then, we model the relationships among goal,task, and ownership. As the collaborative work progresses, the proposedsystem adapts the different concurrency control mechanisms of shared objectmanipulation according to the modeling of goal–task–ownership. With theproposed concurrency control scheme, users can hold shared objects andmove and rotate together in a mixed reality environment similar to realindustrial sites. Additionally, this system provides MS Hololens and Myosensors to recognize inputs from a user and provides results in a mixed realityenvironment. The proposed method is applied to install an air conditioneras a case study. Experimental results and user studies show that, comparedwith the conventional approach, the proposed method reduced the number ofconflicts, waiting time, and total working time.展开更多
Most computational structural engineers are paying more attention to applying loads rather than to DBCs （Displacement Boundary Conditions） because most static stable mechanical structures are working under already p...Most computational structural engineers are paying more attention to applying loads rather than to DBCs （Displacement Boundary Conditions） because most static stable mechanical structures are working under already prescribed displacement boundary conditions. In all of the computational analysis of solving a system of algebraic equations, such as FEM （Finite Element Method）, three translational and three rotational degrees of freedom （DOF） should be constrained （by applying DBCs） before solving the system of algebraic equation in order to prevent rigid body motions of the analysis results （singular problem）. However, it is very difficult for an inexperienced engineer or designer to apply proper DBCs in the case of thermal stress analysis where no prescribed DBCs or constraints exist, for example in water quenching for heat treatment. Moreover, improper DBCs cause incorrect solutions in thermal stress analysis, such as stress concentration or unreasonable deformation phases. To avoid these problems, we studied a technique which performs the thermal stress analysis without any DBCs; and then removes rigid body motions from the deformation results in a post process step as the need arises. The proposed technique makes it easy to apply DBCs and prevent the error caused by improper DBCs. We proved it was mathematically possible to solve a system of algebraic equations without a step of applying DBCs. We also compared the analysis results with those of a traditional procedure for real castings.展开更多
In order to realize the small error attitude transformation of a free floating space robot,a new method of three degrees of freedom（ DOF） attitude transformation was proposed for the space robot using a bionic joint...In order to realize the small error attitude transformation of a free floating space robot,a new method of three degrees of freedom（ DOF） attitude transformation was proposed for the space robot using a bionic joint. A general kinematic model of the space robot was established based on the law of linear and angular momentum conservation. A combinational joint model was established combined with bionic joint and closed motion. The attitude transformation of planar,two DOF and three DOF is analyzed and simulated by the model,and it is verified that the feasibility of attitude transformation in three DOF space. Finally,the specific scheme of disturbance elimination in attitude transformation is presented and simulation results are obtained.Therefore,the range of application field of the bionic joint model has been expanded.展开更多
A conventional complex variable boundary integral equation （CVBIE） in plane elasticity is provided. After using the Somigliana identity between a particular fundamental stress field and a physical stress field, an a...A conventional complex variable boundary integral equation （CVBIE） in plane elasticity is provided. After using the Somigliana identity between a particular fundamental stress field and a physical stress field, an additional integral equality is obtained. By adding both sides of this integral equality to both sides of the conventional CVBIE, the amended boundary integral equation （BIE） is obtained. The method based on the discretization of the amended BIE is called the amended influence matrix method. With this method, for the Neumann boundary value problem （BVP） of an interior region, a unique solution for the displacement can be obtained. Several numerical examples are provided to prove the efficiency of the suggested method.展开更多
In this paper, the disturbances to a uniformly rotating ideal fluid with a sphere moving steadily along the axis of rotation are analysed by using linearization theory, the equations of disturbance pressure and distur...In this paper, the disturbances to a uniformly rotating ideal fluid with a sphere moving steadily along the axis of rotation are analysed by using linearization theory, the equations of disturbance pressure and disturbance stream function governing the stability of motion are derived based on the assumption that the flow is rotational symmetric. The equation of disturbance stream function is analysed with the method of normal modes, and the constraints on wave number and wave velocity of the nontrivial neutral disturbances are established and the exact expression of the neutral disturbances are obtained. The conclusion is drawn that there are three kinds of possible forms of neutral disturbances.展开更多
Recognizing and reproducing spatiotemporal motions are necessary when analyzing behaviors andmovements during human-robot interaction. Rigid body motion trajectories are proven as compact and informativeclues in chara...Recognizing and reproducing spatiotemporal motions are necessary when analyzing behaviors andmovements during human-robot interaction. Rigid body motion trajectories are proven as compact and informativeclues in characterizing motions. A flexible dual square-root function (DSRF) descriptor for representing rigid bodymotion trajectories, which can offer robustness in the description over raw data, was proposed in our previousstudy. However, this study focuses on exploring the application of the DSRF descriptor for effective backwardmotion reproduction and motion recognition. Specifically, two DSRF-based reproduction methods are initiallyproposed, including the recursive reconstruction and online optimization. New trajectories with novel situationsand contextual information can be reproduced from a single demonstration while preserving the similarities withthe original demonstration. Furthermore, motion recognition based on DSRF descriptor can be achieved byemploying a template matching method. Finally, the experimental results demonstrate the effectiveness of theproposed method for rigid body motion reproduction and recognition.展开更多
The aim of this study was to characterize the obesity effect on children knee and hip joint range of motion. A randomized controlled trial was performed with goniometry evaluation for hip flexion, extension, abduction...The aim of this study was to characterize the obesity effect on children knee and hip joint range of motion. A randomized controlled trial was performed with goniometry evaluation for hip flexion, extension, abduction, adduction, external and internal rotation, and knee flexion in fifty male children (20 obese and 30 non obese), with age ranging from 6 to 12 years old. The obesity effect was found to be non-uniform across the joint range of motion. In the obesity group, a statistically significant reduction in the range of motion of hip flexion and adduction, and knee flexion was observed;and also an increase in external rotation in the hip was observed. Conclusion: Obese and overweight children present alterations in hip and knee joints mobility when compared to eutrophic children. The obesity/overweight associated with factors previously described in the literature, such as joint overload, postural deviation and sedentariness may influence the musculoskeletal development and, consequently, the motor function.展开更多
It is pointed out that the property of a constant energy characteristic for the circular motions of macroscopic bodies in classical mechanics does not hold when the quantum conditions for the motion are applied. This ...It is pointed out that the property of a constant energy characteristic for the circular motions of macroscopic bodies in classical mechanics does not hold when the quantum conditions for the motion are applied. This is so because any macroscopic body—lo-cated in a high-energy quantum state—is in practice forced to change this state to a state having a lower energy. The rate of the energy decrease is usually extremely small which makes its effect uneasy to detect in course of the observations, or experiments. The energy of the harmonic oscillator is thoroughly examined as an example. Here our point is that not only the energy, but also the oscillator amplitude which depends on energy, are changing with time. In result, no constant positions of the turning points of the oscillator can be specified;consequently the well-known variational procedure concerning the calculation of the action function and its properties cannot be applied.展开更多
Flexible hydrogels have shown promise as strain sensors in medical monitoring,human motion detection and intelligent robotics.For a hydrogel strain sensor,certain challenges need to be urgently addressed for practical...Flexible hydrogels have shown promise as strain sensors in medical monitoring,human motion detection and intelligent robotics.For a hydrogel strain sensor,certain challenges need to be urgently addressed for practical applications,such as the damage caused by external effects,leading to equipment failure,and the inability to perceive ambient temperature,resulting in single functionality.Herein,a stretchable,self-healing and dual temperature-strain sensitive hydrogel,with a physically-crosslinked network,is designed by constructing multiple dynamic reversible bonds.Graphene oxide(GO)and iron ions(Fe^(3+))act as dynamic bridges in the cross-linked network and are mediated by the covalent and hydrogen bonding,rendering excellent stretchability to the hydrogel.The reversible features of coordination interactions and hydrogen interactions endow excellent recoverability and self-healing properties.Moreover,the incorporated N-isopropyl acrylamide(NIPAM)provides excellent temperature responsiveness to the hydrogel,facilitating the detection of external temperature changes.Meanwhile,the hydrogels exhibited strain-sensitivity,with a wide working range of 1%-300%,fast response and electrical stability,which can be used as flexible sensors to monitor body motions,e.g.,speaking and the bending of finger,wrist,elbow and knee.Overall,the hydrogel possesses dual sensory capabilities,combining external temperature and strain,for potential applications in wearable multifunctional sensing devices.展开更多
With the rapid development of computing technology, three-dimensional （3D） human body models and their dynamic motions are widely used in the digital entertainment industry. Human performance mainly involves human b...With the rapid development of computing technology, three-dimensional （3D） human body models and their dynamic motions are widely used in the digital entertainment industry. Human performance mainly involves human body shapes and motions. Key research problems in human performance animation include how to capture and analyze static geometric appearance and dynamic movement of human bodies, and how to simulate human body motions with physical effects. In this survey, according to the main research directions of human body performance capture and animation, we summarize recent advances in key research topics, namely human body surface reconstruction, motion capture and synthesis, as well as physics-based motion simulation, and further discuss future research problems and directions. We hope this will be helpful for readers to have a comprehensive understanding of human performance capture and animation.展开更多
Liquid metals(LMs)are potential inorganic materials which could be applied in flexible and deformable electronics owing to their fluidity,low viscosity,high metallic conductivity,and low toxicity.However,recently repo...Liquid metals(LMs)are potential inorganic materials which could be applied in flexible and deformable electronics owing to their fluidity,low viscosity,high metallic conductivity,and low toxicity.However,recently reported sensing devices based on LMs required complex processes with high cost.Herein,a flexible three-dimensional(3 D)conductive network was prepared by coating LM droplets onto an electrospun thermoplastic polyurethane(TPU)fiber film.The LM is suspended between the TPU fibers and self-coalesces into a vertically buckled and laterally mesh-like structure,which provides good biocompatibility,conductivity,and stretchability simultaneously.The LM-TPU composite-filmbased flexible device demonstrates a multitude of desired features,such as a widely workable stretching range(0%-200%),sufficient sensitivity under stretching strain(gauge factor(GF)of 0.2 at 200%strain),and outstanding stability and durability(9000 cycles).In vitro biocompatibility experiments show that the LM-TPU composite film directly attached to the skin has excellent biocompatibility.Such strain sensorbased integrated monitoring systems could monitor human body motions in real time,such as muscle movement and joint motion,revealing application prospects in healthcare and human-machine interfacing.展开更多
文摘In this paper , the unilaterally constrained motions of a large class of rigid bodiessystems are studied both locally and globally. The main conclusion is that locally,such a system bahaves like a particle in a Riemannian manifold with boundary;globally.under the assumption of energy conservation, the system behaves like a billiards system over a Riemannina manifold with boundary
基金supported by“Regional Innovation Strategy (RIS)”through the National Research Foundation of Korea (NRF)funded by the Ministry of Education (MOE) (2021RIS-004).
文摘A concurrency control mechanism for collaborative work is akey element in a mixed reality environment. However, conventional lockingmechanisms restrict potential tasks or the support of non-owners, thusincreasing the working time because of waiting to avoid conflicts. Herein, wepropose an adaptive concurrency control approach that can reduce conflictsand work time. We classify shared object manipulation in mixed reality intodetailed goals and tasks. Then, we model the relationships among goal,task, and ownership. As the collaborative work progresses, the proposedsystem adapts the different concurrency control mechanisms of shared objectmanipulation according to the modeling of goal–task–ownership. With theproposed concurrency control scheme, users can hold shared objects andmove and rotate together in a mixed reality environment similar to realindustrial sites. Additionally, this system provides MS Hololens and Myosensors to recognize inputs from a user and provides results in a mixed realityenvironment. The proposed method is applied to install an air conditioneras a case study. Experimental results and user studies show that, comparedwith the conventional approach, the proposed method reduced the number ofconflicts, waiting time, and total working time.
文摘Most computational structural engineers are paying more attention to applying loads rather than to DBCs （Displacement Boundary Conditions） because most static stable mechanical structures are working under already prescribed displacement boundary conditions. In all of the computational analysis of solving a system of algebraic equations, such as FEM （Finite Element Method）, three translational and three rotational degrees of freedom （DOF） should be constrained （by applying DBCs） before solving the system of algebraic equation in order to prevent rigid body motions of the analysis results （singular problem）. However, it is very difficult for an inexperienced engineer or designer to apply proper DBCs in the case of thermal stress analysis where no prescribed DBCs or constraints exist, for example in water quenching for heat treatment. Moreover, improper DBCs cause incorrect solutions in thermal stress analysis, such as stress concentration or unreasonable deformation phases. To avoid these problems, we studied a technique which performs the thermal stress analysis without any DBCs; and then removes rigid body motions from the deformation results in a post process step as the need arises. The proposed technique makes it easy to apply DBCs and prevent the error caused by improper DBCs. We proved it was mathematically possible to solve a system of algebraic equations without a step of applying DBCs. We also compared the analysis results with those of a traditional procedure for real castings.
文摘In order to realize the small error attitude transformation of a free floating space robot,a new method of three degrees of freedom（ DOF） attitude transformation was proposed for the space robot using a bionic joint. A general kinematic model of the space robot was established based on the law of linear and angular momentum conservation. A combinational joint model was established combined with bionic joint and closed motion. The attitude transformation of planar,two DOF and three DOF is analyzed and simulated by the model,and it is verified that the feasibility of attitude transformation in three DOF space. Finally,the specific scheme of disturbance elimination in attitude transformation is presented and simulation results are obtained.Therefore,the range of application field of the bionic joint model has been expanded.
文摘A conventional complex variable boundary integral equation （CVBIE） in plane elasticity is provided. After using the Somigliana identity between a particular fundamental stress field and a physical stress field, an additional integral equality is obtained. By adding both sides of this integral equality to both sides of the conventional CVBIE, the amended boundary integral equation （BIE） is obtained. The method based on the discretization of the amended BIE is called the amended influence matrix method. With this method, for the Neumann boundary value problem （BVP） of an interior region, a unique solution for the displacement can be obtained. Several numerical examples are provided to prove the efficiency of the suggested method.
文摘In this paper, the disturbances to a uniformly rotating ideal fluid with a sphere moving steadily along the axis of rotation are analysed by using linearization theory, the equations of disturbance pressure and disturbance stream function governing the stability of motion are derived based on the assumption that the flow is rotational symmetric. The equation of disturbance stream function is analysed with the method of normal modes, and the constraints on wave number and wave velocity of the nontrivial neutral disturbances are established and the exact expression of the neutral disturbances are obtained. The conclusion is drawn that there are three kinds of possible forms of neutral disturbances.
基金the Science and Technology Commission of Shanghai Municipality(No.20DZ2220400)the Interdisciplinary Program of Shanghai Jiao Tong University(No.YG2021QN117)。
文摘Recognizing and reproducing spatiotemporal motions are necessary when analyzing behaviors andmovements during human-robot interaction. Rigid body motion trajectories are proven as compact and informativeclues in characterizing motions. A flexible dual square-root function (DSRF) descriptor for representing rigid bodymotion trajectories, which can offer robustness in the description over raw data, was proposed in our previousstudy. However, this study focuses on exploring the application of the DSRF descriptor for effective backwardmotion reproduction and motion recognition. Specifically, two DSRF-based reproduction methods are initiallyproposed, including the recursive reconstruction and online optimization. New trajectories with novel situationsand contextual information can be reproduced from a single demonstration while preserving the similarities withthe original demonstration. Furthermore, motion recognition based on DSRF descriptor can be achieved byemploying a template matching method. Finally, the experimental results demonstrate the effectiveness of theproposed method for rigid body motion reproduction and recognition.
文摘The aim of this study was to characterize the obesity effect on children knee and hip joint range of motion. A randomized controlled trial was performed with goniometry evaluation for hip flexion, extension, abduction, adduction, external and internal rotation, and knee flexion in fifty male children (20 obese and 30 non obese), with age ranging from 6 to 12 years old. The obesity effect was found to be non-uniform across the joint range of motion. In the obesity group, a statistically significant reduction in the range of motion of hip flexion and adduction, and knee flexion was observed;and also an increase in external rotation in the hip was observed. Conclusion: Obese and overweight children present alterations in hip and knee joints mobility when compared to eutrophic children. The obesity/overweight associated with factors previously described in the literature, such as joint overload, postural deviation and sedentariness may influence the musculoskeletal development and, consequently, the motor function.
文摘It is pointed out that the property of a constant energy characteristic for the circular motions of macroscopic bodies in classical mechanics does not hold when the quantum conditions for the motion are applied. This is so because any macroscopic body—lo-cated in a high-energy quantum state—is in practice forced to change this state to a state having a lower energy. The rate of the energy decrease is usually extremely small which makes its effect uneasy to detect in course of the observations, or experiments. The energy of the harmonic oscillator is thoroughly examined as an example. Here our point is that not only the energy, but also the oscillator amplitude which depends on energy, are changing with time. In result, no constant positions of the turning points of the oscillator can be specified;consequently the well-known variational procedure concerning the calculation of the action function and its properties cannot be applied.
基金financially supported by the National Natural Science Foundation of China(No.52173301)International Science and Technology Cooperation Project of Sichuan Province(No.2022YFH0019)Innovative Research Team of Southwest Petroleum University(No.2017CXTD01)。
文摘Flexible hydrogels have shown promise as strain sensors in medical monitoring,human motion detection and intelligent robotics.For a hydrogel strain sensor,certain challenges need to be urgently addressed for practical applications,such as the damage caused by external effects,leading to equipment failure,and the inability to perceive ambient temperature,resulting in single functionality.Herein,a stretchable,self-healing and dual temperature-strain sensitive hydrogel,with a physically-crosslinked network,is designed by constructing multiple dynamic reversible bonds.Graphene oxide(GO)and iron ions(Fe^(3+))act as dynamic bridges in the cross-linked network and are mediated by the covalent and hydrogen bonding,rendering excellent stretchability to the hydrogel.The reversible features of coordination interactions and hydrogen interactions endow excellent recoverability and self-healing properties.Moreover,the incorporated N-isopropyl acrylamide(NIPAM)provides excellent temperature responsiveness to the hydrogel,facilitating the detection of external temperature changes.Meanwhile,the hydrogels exhibited strain-sensitivity,with a wide working range of 1%-300%,fast response and electrical stability,which can be used as flexible sensors to monitor body motions,e.g.,speaking and the bending of finger,wrist,elbow and knee.Overall,the hydrogel possesses dual sensory capabilities,combining external temperature and strain,for potential applications in wearable multifunctional sensing devices.
基金This work was supported by the Knowledge Innovation Program of the Institute of Computing Technology of the Chinese Academy of Sciences under Grant No. ICT20166040, the Science and Technology Service Network Initiative of Chinese Academy of Sciences under Grant No. KFJ-STS-ZDTP-017, the National Natural Science Foundation of China under Grant Nos. 61502453 and 61611130215, the Royal Society-Newton Mobility Grant of UK under Grant No. IE150731, and the CCP （China Computer Federation）-Tencent Open Research Fund of China under Grant No. AGR20160118.
文摘With the rapid development of computing technology, three-dimensional （3D） human body models and their dynamic motions are widely used in the digital entertainment industry. Human performance mainly involves human body shapes and motions. Key research problems in human performance animation include how to capture and analyze static geometric appearance and dynamic movement of human bodies, and how to simulate human body motions with physical effects. In this survey, according to the main research directions of human body performance capture and animation, we summarize recent advances in key research topics, namely human body surface reconstruction, motion capture and synthesis, as well as physics-based motion simulation, and further discuss future research problems and directions. We hope this will be helpful for readers to have a comprehensive understanding of human performance capture and animation.
基金supported by the National Natural Science Foundation of China(61625404,61888102,and 62174152)Foshan Innovative and Entrepreneurial Research Team Program(2018IT100031)。
文摘Liquid metals(LMs)are potential inorganic materials which could be applied in flexible and deformable electronics owing to their fluidity,low viscosity,high metallic conductivity,and low toxicity.However,recently reported sensing devices based on LMs required complex processes with high cost.Herein,a flexible three-dimensional(3 D)conductive network was prepared by coating LM droplets onto an electrospun thermoplastic polyurethane(TPU)fiber film.The LM is suspended between the TPU fibers and self-coalesces into a vertically buckled and laterally mesh-like structure,which provides good biocompatibility,conductivity,and stretchability simultaneously.The LM-TPU composite-filmbased flexible device demonstrates a multitude of desired features,such as a widely workable stretching range(0%-200%),sufficient sensitivity under stretching strain(gauge factor(GF)of 0.2 at 200%strain),and outstanding stability and durability(9000 cycles).In vitro biocompatibility experiments show that the LM-TPU composite film directly attached to the skin has excellent biocompatibility.Such strain sensorbased integrated monitoring systems could monitor human body motions in real time,such as muscle movement and joint motion,revealing application prospects in healthcare and human-machine interfacing.
