Metamaterials constructed from origami units of different types and behaviors could potentially offer a broader scope of mechanical properties than those formed from identical unit types.However,the geometric design r...Metamaterials constructed from origami units of different types and behaviors could potentially offer a broader scope of mechanical properties than those formed from identical unit types.However,the geometric design rules and property programming methods for such metamaterials have yet to be extensively explored.In this paper,we propose a new kind of origami metasheet by incorporating a family of different square-twist units.The tessellation rule of these metasheets is established to allow compatible mountain-valley crease assignments and geometric parameters among neighboring units.We demonstrate through experiments that the energy,initial peak force,and maximum stiffness of the metasheets can be obtained by a summation of the properties of the constitutional units.Based on this,we are able to program the mechanical properties of the metasheets over a wide range by varying the types and proportions of the units,as well as their geometric and material parameters.Furthermore,for a metasheet with a fixed number of units,all the geometrically compatible tessellations can be folded out of the same pre-creased sheet material by simply changing the mountain-valley assignments,thereby allowing the properties of the metasheet to be re-programmed based on specific requirements.This work could inspire a new class of programmable origami metamaterials for current and future mechanical and other engineering applications.展开更多
Research about asteroids has recently attracted more and more attention, especially focusing on their physical structures, such as their spin axis, rotation period and shape. The long distance between observers on Ear...Research about asteroids has recently attracted more and more attention, especially focusing on their physical structures, such as their spin axis, rotation period and shape. The long distance between observers on Earth and asteroids makes it impossible to directly calculate the shape and other parameters of asteroids, with the exception of Near Earth Asteroids and others that have passed by some spacecrafts. Photometric measurements are still generally the main way to obtain research data on asteroids, i.e. the lightcurves recording the brightness and positions of asteroids. Supposing that the shape of the asteroid is a triaxial ellipsoid with a stable spin, a new method is presented in this article to reconstruct the shape models of asteroids from the lightcurves, together with other physical parameters. By applying a special curvature function, the method calculates the brightness integration on a unit sphere and Lebedev quadrature is employed for the discretization. Finally, the method searches for the optimal solution by the Levenberg-Marquardt algorithm to minimize the residual of the brightness. By adopting this method, not only can related physical parameters of asteroids be obtained at a reasonable accuracy, but also a simple shape model of an ellipsoid can be generated for reconstructing a more sophisticated shape model.展开更多
A definitive diagnosis of paradoxical embolism is ,based on the evidence that a thrombus crosses through the right-to-left shunting. We report a case of impending paradoxical embolism in a patient with pulmonary embol...A definitive diagnosis of paradoxical embolism is ,based on the evidence that a thrombus crosses through the right-to-left shunting. We report a case of impending paradoxical embolism in a patient with pulmonary embolism diagnosed by echocardiography and proved by operation later.展开更多
Origami has recently emerged as a promising building block of mechanical metamaterials because it offers a purely geometric design approach independent of scale and constituent material.The folding mechanics of origam...Origami has recently emerged as a promising building block of mechanical metamaterials because it offers a purely geometric design approach independent of scale and constituent material.The folding mechanics of origami-inspired metamaterials,i.e.,whether the deformation involves only rotation of crease lines(rigid origami)or both crease rotation and facet distortion(nonrigid origami),is critical for fine-tuning their mechanical properties yet very difficult to determine for origami patterns with complex behaviors.Here,we characterize the folding of tubular waterbomb using a combined kinematic and structural analysis.We for the first time uncover that a waterbomb tube can undergo a mixed mode involving both rigid origami motion and nonrigid structural deformation,and the transition between them can lead to a substantial change in the stiffness.Furthermore,we derive theoretically the range of geometric parameters for the transition to occur,which paves the road to program the mechanical properties of the waterbomb pattern.We expect that such analysis and design approach will be applicable to more general origami patterns to create innovative programmable metamaterials,serving for a wide range of applications including aerospace systems,soft robotics,morphing structures,and medical devices.展开更多
基金supported by the National Natural Science Foundation of China(52035008,51825503,52192631,and 51721003)the Tencent Foundation(XPLORER-2020-1035)Zhong You’s involvement was possible due to the financial support of Department of Engineering Science at Oxford University。
文摘Metamaterials constructed from origami units of different types and behaviors could potentially offer a broader scope of mechanical properties than those formed from identical unit types.However,the geometric design rules and property programming methods for such metamaterials have yet to be extensively explored.In this paper,we propose a new kind of origami metasheet by incorporating a family of different square-twist units.The tessellation rule of these metasheets is established to allow compatible mountain-valley crease assignments and geometric parameters among neighboring units.We demonstrate through experiments that the energy,initial peak force,and maximum stiffness of the metasheets can be obtained by a summation of the properties of the constitutional units.Based on this,we are able to program the mechanical properties of the metasheets over a wide range by varying the types and proportions of the units,as well as their geometric and material parameters.Furthermore,for a metasheet with a fixed number of units,all the geometrically compatible tessellations can be folded out of the same pre-creased sheet material by simply changing the mountain-valley assignments,thereby allowing the properties of the metasheet to be re-programmed based on specific requirements.This work could inspire a new class of programmable origami metamaterials for current and future mechanical and other engineering applications.
基金funded by grant No. 019/2010/A2 from the Science and Technology Development Fund, MSARthe support of the National Natural Science Foundation of China (Grant Nos. 10503013, 11078006 and 10933004)the Minor Planet Foundation of Purple Mountain Observatory
文摘Research about asteroids has recently attracted more and more attention, especially focusing on their physical structures, such as their spin axis, rotation period and shape. The long distance between observers on Earth and asteroids makes it impossible to directly calculate the shape and other parameters of asteroids, with the exception of Near Earth Asteroids and others that have passed by some spacecrafts. Photometric measurements are still generally the main way to obtain research data on asteroids, i.e. the lightcurves recording the brightness and positions of asteroids. Supposing that the shape of the asteroid is a triaxial ellipsoid with a stable spin, a new method is presented in this article to reconstruct the shape models of asteroids from the lightcurves, together with other physical parameters. By applying a special curvature function, the method calculates the brightness integration on a unit sphere and Lebedev quadrature is employed for the discretization. Finally, the method searches for the optimal solution by the Levenberg-Marquardt algorithm to minimize the residual of the brightness. By adopting this method, not only can related physical parameters of asteroids be obtained at a reasonable accuracy, but also a simple shape model of an ellipsoid can be generated for reconstructing a more sophisticated shape model.
文摘A definitive diagnosis of paradoxical embolism is ,based on the evidence that a thrombus crosses through the right-to-left shunting. We report a case of impending paradoxical embolism in a patient with pulmonary embolism diagnosed by echocardiography and proved by operation later.
基金This work was supported by the National Natural Science Foundation of China(Projects 51825503,51721003,and 51575377)the Air Force Office of Scientific Research(FA9550-16-1-0339).
文摘Origami has recently emerged as a promising building block of mechanical metamaterials because it offers a purely geometric design approach independent of scale and constituent material.The folding mechanics of origami-inspired metamaterials,i.e.,whether the deformation involves only rotation of crease lines(rigid origami)or both crease rotation and facet distortion(nonrigid origami),is critical for fine-tuning their mechanical properties yet very difficult to determine for origami patterns with complex behaviors.Here,we characterize the folding of tubular waterbomb using a combined kinematic and structural analysis.We for the first time uncover that a waterbomb tube can undergo a mixed mode involving both rigid origami motion and nonrigid structural deformation,and the transition between them can lead to a substantial change in the stiffness.Furthermore,we derive theoretically the range of geometric parameters for the transition to occur,which paves the road to program the mechanical properties of the waterbomb pattern.We expect that such analysis and design approach will be applicable to more general origami patterns to create innovative programmable metamaterials,serving for a wide range of applications including aerospace systems,soft robotics,morphing structures,and medical devices.
