Search

Photonic spin‐orbit interactions describe the interactions between spin angular momentum and orbital angular momentum of photons, which play essential roles in subwavelength optics. However, the influence of frequency dispersion on photonic angular‐momentum coupling is rarely studied. Here, by elaborately designing the contribution of the geometric phase and waveguide propagation phase, the dispersion‐enabled symmetry switching of photonic angular‐momentum coupling is experimentally demonstrated. This notion may induce many exotic phenomena and be found in enormous applications, such as the spin‐Hall effect, optical calculation, and wavelength division multiplexing systems. As a proof‐of‐concept demonstration, two metadevices, a multi‐channel vectorial vortex beam generator and a phase‐only hologram, are applied to experimentally display optical double convolution, which may offer additional degrees of freedom to accelerate computing and a miniaturization configuration for optical convolution without collimation operation. These results may provide a new opportunity for complex vector optical field manipulation and calculation, optical information coding, light‐matter interaction manipulation, and optical communication. [ABSTRACT FROM AUTHOR]

Flat arrays consisting of panels of finite thickness are widely used in aerospace applications such as solar panels and reflectarray antennas. Packaging them into compact bundles without any voids and then deploying them bi-directionally to flat, continuous and accurate surfaces with a single degree of freedom (DoF) has challenged engineers for decades. Here, we present a solution based on origami of thick panels. In modular construction, we first created two deployable unit arrays, each of which comprises four eight-panel elements where panels in regular shapes are connected by simple but robust rotational joints. We prove that these units have only a single DoF, and they can be folded from a flat array to compact bundles without any voids. We then show that the units can be tessellated to form larger flat arrays where a single-DoF deployment and compact packaging properties are intact. A parametric study is carried out, which provides a precise design range that prevents the panels from physical interference during deployment. Physical models were constructed that have successfully validated the concepts. Our work is directly applicable to the design of future flat arrays that can be controlled with ease. [ABSTRACT FROM AUTHOR]

Beyond the scope of Hermitian physics, non-Hermiticity fundamentally changes the topological band theory, leading to interesting phenomena, e.g., non-Hermitian skin effect, as confirmed in one-dimensional systems. However, in higher dimensions, these effects remain elusive. Here, we demonstrate the spin-polarized, higher-order non-Hermitian skin effect in two-dimensional acoustic higher-order topological insulators. We find that non-Hermiticity drives wave localizations toward opposite edges upon different spin polarizations. More interestingly, for finite systems with both edges and corners, the higher-order non-Hermitian skin effect leads to wave localizations toward two opposite corners for all the bulk, edge and corner states in a spin-dependent manner. We further show that such a skin effect enables rich wave manipulation by configuring the non-Hermiticity. Our study reveals the intriguing interplay between higher-order topology and non-Hermiticity, which is further enriched by the pseudospin degree of freedom, unveiling a horizon in the study of non-Hermitian physics. Though non-Hermitian physics has contributed toward the advance of research in quantum, electronic and classical systems, previous work focused on zero- or one-dimensional systems. Here, the authors report higher-order non-Hermitian skin effects in a 2D acoustic higher-order topological insulator. [ABSTRACT FROM AUTHOR]

Summary: Multi‐particle dampers (M‐PD) can be potentially applied in civil engineering because of their good damping effect and wide frequency band. However, because of their complex nonlinear mechanical properties and the lack of a reasonable mechanical model, their development and application in practical engineering are limited. Therefore, without considering the accumulation of particles, an equivalent inertia single‐particle mechanical model (EISM) is proposed by introducing an inerter to consider the effect of particle rolling on the damping mechanism and performance. Dynamic analyses of the EISM single degree of freedom system in the non‐collision stage and the periodic motion after collision are performed based on the analytical solution. The influence of inertance on the frequency response curve of dynamic amplification factors in the no‐collision stage and the analytical solution for the symmetric two‐impacts‐per‐cycle motion are discussed in detail. Numerical simulations and experimental verification are conducted to verify the rationality of the above theoretical analysis. The results show that EISM can further clarify the nonlinear characteristics of M‐PD. The inertance has a significant influence on the frequency response curve of the dynamic amplification factors as well as the boundary conditions and stability of the analytical solution of the symmetric two‐impacts‐per‐cycle motion. The proposed EISM and the corresponding theoretical analysis in this study can theoretically support further analysis of the vibration reduction mechanism and design of M‐PDs. [ABSTRACT FROM AUTHOR]

The dangling‐bond‐free surfaces of 2D materials enable them to possess various degrees of freedom to form heterostructures with non‐2D materials. This allows for the combination of the advantages of different dimensional materials to fabricate van der Waals (vdW) heterostructures, thereby improving device performance and even bringing diversity and novelty. Herein, a mixed‐dimensional vdW heterostructure photodiode comprising a 1D tellurium (Te) nanowire and a 2D molybdenum ditelluride (MoTe2) flake is demonstrated. Forward rectifying and backward rectifying characteristics are realized by applying different gate voltage. The device displays a broad spectral response from visible to near‐infrared and exhibits ultrahigh external quantum efficiency of 7.16 × 103% for photogating effect. Moreover, the response time can be improved by controlling gate voltage and a rapid response time of 4.8 ms is achieved. These mixed‐dimensional vdW heterojunctions, which take advantages of both 1D and 2D semiconductors, will facilitate the development of next‐generation electronics and optoelectronics. [ABSTRACT FROM AUTHOR]

• A new method to design origami cubes with rigid foldability, flat foldability and one DOF. • Four cases of crease patterns that enable origami cubes with distinct folding performances have been proposed. • The folding process has been analysed with kinematics of spherical linkage loops. • Flat folding of cubes are achieved with one DOF. Rigid origami is a branch of origami with great potential in engineering applications to deal with rigid-panel folding. One of the challenges is to compactly fold flat a polyhedron made from rigid facets with a single degree of freedom. In this paper, we present a new method to design origami cubes with three fundamental characteristics: rigid foldability, flat foldability and one degree of freedom (DOF). A total of four cases of crease patterns that enable origami cubes with distinct folding performances have been proposed, which covers all possible layouts of the diagonal creases on the square facets of origami cubes. The folding utilises spherical linkages formed by intersecting creases, and based on the kinematic equivalence between the rigid origami and the spherical linkages, the corresponding spherical linkage loops are introduced and analysed to reveal the motion properties of the origami cubes. The newly found method can be readily utilized to design deployable structures for various engineering applications including cube-shaped cartons, small satellites, containers, etc. [ABSTRACT FROM AUTHOR]

Polyhedral transformation enables large volumetric change amongst Platonic and Archimedean solids. It has great potential in applications where transportability and protection of payload are critical design features, e.g., small or micro satellites, space habitats or planetary rovers. However, existing designs introduce many degrees of freedoms, making the control of transformation process extremely difficult and cumbersome, and thus the practical applicability of the mechanisms is restricted. This paper develops a kinematic method to enable polyhedral transformation with a single degree of freedom. The approach has been implemented for the transformation between truncated octahedron and cube. Motion analysis indicates that transformation path is unique without singularity, which is further demonstrated with physical validation models. We envisage that our method could be suitable for extension to other paired polyhedron sets. [ABSTRACT FROM AUTHOR]

Polyhedrons have great potentials in various engineering fields due to their superior capability of folding in 3D to achieve a large volumetric ratio of packaging. However, their practical applications are limited by the lack of effective folding schemes with minimum degrees of freedom. Here in the paper we created a transformation between a tetrahedron and a truncated tetrahedron with one degree of freedom by properly setting a movable joint at each vertex. Two schemes of joint arrangement were proposed, and their kinematic behaviours were respectively studied analytically and numerically, where mobility calculations are both based on the truss transformation. Finally, the transformation process using the first scheme was demonstrated through a cardboard prototype fabricated with the origami technique. [ABSTRACT FROM AUTHOR]

• The triangular Resch pattern is programmed to achieve surfaces with various curvatures. • The finite particle method is used to simulate the free unfolding of the origami pattern. • The neutral angle is critical in determining the final stable shape of a pattern. • The symmetry of the triangular Resch pattern is broken by adjusting neutral angle. • Specific constraints are applied to create stable unfolding surfaces with various curvatures. The multi-degree of freedom Resch pattern forms most of its surfaces by tuning the folding angles of its creases. In this research, we program the triangular Resch pattern to naturally achieve surfaces with various curvatures by predefining the neutral angle and stiffness of the creases for the whole pattern. We simulate the free unfolding of tessellations by combining a "bar-and-hinge" model with an explicit meshless method, namely, the finite particle method. The effects of the damping factor, crease stiffness, and neutral angle on the unfolding process are investigated. The neutral angle of the creases plays a critical role in determining the final stable shape of the pattern. Then, we break the natural symmetry of the tessellations by changing the neutral angle and applying specific constraints to active creases to create stable unfolding surfaces with various curvatures. This study provides a foundation for the development of programmed curvatures of metamaterials that can be folded into origami patterns with multiple degrees of freedom. [Display omitted] [ABSTRACT FROM AUTHOR]

• Constitutive model for metallic glass within the framework of irreversible nonequilibrium thermodynamics is developed by extending classical STZ theory. • Deformations of metallic glass under different ambient temperatures and applied strain rates are well predicted. • Mechanisms of deformation mode evolution and shear band formation are reasonably explained. We develop a new finite deformation constitutive model for metallic glass within the framework of irreversible nonequilibrium thermodynamics. To consider the intrinsically out-of-equilibrium characteristics of metallic glass, its total internal energy is divided into two weakly coupled configurational and kinetic subsystems, and configurational temperature coupling with configurational degrees of freedom is introduced as a thermodynamic state variable to characterize the evolution of the disordered structure. Furthermore, the classical shear transformation zone theory is extended by reasonably considering the reverse shear transformation as a form of the relaxation of the strain field, which is stored in the elastic matrix and produced by the constraint of the matrix on shear transformation. With the help of the finite element implementation for the new model, the effectiveness of the proposed model is validated by comparing the modeling stress–strain responses of the macroscopic deformations under different temperatures and strain rates with the experimental results, and the utility of the model for predicting the shear banding behavior of metallic glasses is examined as well. The results therefore show that the constructed constitutive model can not only effectively predict the deformations of metallic glass under different ambient temperatures and applied strain rates, but also reasonably explain the mechanisms of deformation mode evolution and shear band formation. [ABSTRACT FROM AUTHOR]

Abstract: By using the dual vortex method (DVM), we develop systematically a simple and effective scheme to use the vortex degree of freedoms on dual lattices to characterize the symmetry breaking patterns of the boson insulating states in the direct lattices. Then we apply our scheme to study quantum phases and phase transitions in an extended boson Hubbard model slightly away from 1/3 (2/3) filling on frustrated lattices such as triangular and Kagome lattice. In a triangular lattice at 1/3, we find a X-CDW, a stripe CDW phase which was found previously by a density operator formalism (DOF). Most importantly, we also find a new CDW-VB phase which has both local CDW and local VB orders, in sharp contrast to a bubble CDW phase found previously by the DOF. In the Kagome lattice at 1/3, we find a VBS phase and a 6-fold CDW phase. Most importantly, we also identify a CDW-VB phase which has both local CDW and local VB orders which was found in previous QMC simulations. We also study several other phases which are not found by the DVM. By analyzing carefully the saddle point structures of the dual gauge fields in the translational symmetry breaking sides and pushing the effective actions slightly away from the commensurate filling , we classified all the possible types of supersolids and analyze their stability conditions. In a triangular lattice, there are X-CDW supersolid, stripe CDW supersolid, but absence of any valence bond supersolid (VB-SS). There are also a new kind of supersolid: CDW-VB supersolid. In a Kagome lattice, there are 6-fold CDW supersolid, stripe CDW supersolid, but absence of any valence bond supersolid (VB-SS). There are also a new kind of supersolid: CDW-VB supersolid. We show that independent of the types of the SS, the quantum phase transitions from solids to supersolids driven by a chemical potential are in the same universality class as that from a Mott insulator to a superfluid, therefore have exact exponents , , (with logarithmic corrections). Excitation spectra of all these insulating phases and supersolid phases are also studied. Implications on QMC simulations with both nearest neighbor and next nearest neighbor interactions in both lattices are given. Some possible intrinsic problems of the DOF in identifying the insulating phases are also pointed out. [Copyright &y& Elsevier]

A duality transformation in quantum field theory is usually established first through partition functions. It is always important to explore the dual relations between various correlation functions in the transformation. Here, we explore such a dual relation to study quantum phases and phase transitions in an extended boson Hubbard model at 1/3 (2/3) filling on a triangular lattice. We develop systematically a simple and effective way to use the vortex degrees of freedom on dual lattices to characterize both the density wave and valence bond symmetry breaking patterns of the boson insulating states in the direct lattices. In addition to a checkerboard charge density wave (X-CDW) and a stripe CDW, we find a novel CDW-VBS phase which has both local CDW and local valence bond solid (VBS) orders. Implications for Quantum Monte Carlo simulations are addressed. The possible experimental realizations of cold atoms loaded on optical lattices are discussed. [ABSTRACT FROM PUBLISHER]

• A novel parabolic cylindrical antenna based on thick-panel origami is proposed. • Two joint-removing techniques based on kinematic equivalence are constructed. • The influencing factors of the deployed/folded ratio are fully studied. This paper proposes a novel parabolic cylindrical antenna with great folding efficiency based on two symmetrically arranged Miura-ori thick-panel origami patterns and the removal of partial material from each panel. A design rule for the transition from the given parabolic equation to the geometric parameters of the thick-panel origami is defined. To ensure that the deployable structure has one degree of freedom (DOF), specific connectors between the two thick-panel origami patterns are designed from spherical 4 R linkages and Bennett linkages, which are verified by kinematic analysis based on the assembly of linkages corresponding to the thick-panel origami pattern. Two joint-removing techniques based on the kinematic equivalence of linkages are constructed to obtain the continuous and smooth parabolic cylindrical surface and maintain the one-DOF property. The deployed/folded ratio influencing factors are fully studied, finding that a small panel thickness and a large origami pattern sector angle are necessary to obtain a high deployed/folded ratio. Finally, a prototype of the deployable structure is manufactured to verify and demonstrate its excellent performance. [ABSTRACT FROM AUTHOR]

The Miura-ori pattern possesses intriguing mechanical features, namely, the one Degree Of Freedom mobility, auxetic in-plane behavior and energy absorption capability, for applications such as core to sandwich structure, shock absorber, airless tire, etc. To realize the folding mechanism of Miura-ori, in this paper a Miura-ori patterned sheet was made from copolymer Elvaloy by compression molding, and then its deformation behavior was investigated experimentally and by using finite element analysis. The intrinsic mechanical properties of Elvaloy were obtained by tensile and four-point-bending tests, respectively, and subsequently used in the finite element (FE) simulation. For utilizing the sheet in all the principal directions, three types of tests were conducted: out-of-plane compression, three-point-bending and in-plane compressions. FE simulations using Abaqus/Explicit were carried out to analyze the deformations of the patterned sheet under the same loading as that in the tests. The simulation results were then compared with the tests, which show good agreements. Based on the simulation results, the deformation patterns of the patterned sheet under different loading conditions were examined, as well as the energy absorption capacity. [ABSTRACT FROM AUTHOR]

• An novel nonlinear beam-column element for PFRP space frame structures is proposed. • The detailed element formulations and element tangent stiffness matrix were derived. • The connection system for PFRP profileswas incorporated into the element formula. • The finally obtained hybrid beam-column element shows significant advantages. In order to achieve accurate structural calculation of pultruded fiber reinforced polymer (PFRP) space frame structures by "a single element per member", an imperfect nonlinear beam-column element considering the hybrid effects of component stiffness is proposed. Based on the unique characteristics of PFRP profiles, the equilibrium differential equations considering transverse shear effect and initial deflection were established. Afterwards, the stability functions, bending functions, force versus deformation equations and element tangent stiffness matrix were further derived. With the consideration of common connection system for PFRP profiles, the effect of joint stiffness, rigid arm and reinforcement segment were incorporated into the element formula without increasing the external degrees of freedom: The effect of joint stiffness is considered by the static condensation procedure; The rigid arm effect is considered based on the relationship between end points of the rigid vector; The effect of reinforcement segment is considered based on the idea of equivalence. Besides, a novel 3D co-rotational procedure allowing for large load step was proposed to update the local-global transformation matrix. The finally obtained hybrid beam-column element was used for calculation of several PFRP structure verification cases, which showed the advantages of easy structural modelling, good accuracy and high computational efficiency. [ABSTRACT FROM AUTHOR]

• Mobile assembly is constructed with two Bennett linkages. • Transformation between a cuboctahedron to an octahedron is realised. • Directions of R -joints in the assembly are obtained by geometric analysis. • Kinematic analysis shows the polyhedral transformation is one-DOF without bifurcation. • A prototype, made with rigid metal faces and revolute joints, validates the results. The Bennett linkage has been proposed as a building block of deployable structures as it can generate desirable spatial motions with the least number of links. However, these deployable structures are based on the tiling of Bennett linkages. No spatial assembly of Bennett linkages has been developed to form any transformation between regular and semi-regular polyhedrons. In this paper, we propose a new type of mobile assembly consisting of a pair of Bennett linkages connected by four spherical joints. We show that this particular assembly can be used to construct transformable polyhedrons. Using an alternative form of such assembly, a polyhedral transformation between cuboctahedron and octahedron with one degree of freedom is realised. The axes of the revolute joints within the Bennett linkages are determined by the geometrical relationship between the deployed geometry and the folded one. The transformation between two polyhedral shapes has no bifurcation which is proven through kinematic analysis and demonstrated by a physical model. This transformable polyhedron has great potential for the aerospace applications where transportability and protection of payload are critical design features. [ABSTRACT FROM AUTHOR]

• A deployable structure with rectangular facets is designed from Miura-ori pattern. • A hinge-replacing method is proposed based on kinematic equivalence of linkages. • A double-layer Miura-ori pattern is used to design a compatible back frame. With the requirements for improvement of earth observation range and accuracy, large-scale two-dimensional deployable antennas are urgently needed. In this paper, a deployable structure for a planar antenna with one degree of freedom and a flat reflection surface that can realize two-dimensional deployment with a compatible back frame is proposed based on a double-layer Miura-ori pattern. First, an antenna folding scheme with rectangular facets is proposed with the Miura-ori pattern. Through the method for hinge removal and replacement, a deployable antenna mechanism with a flat reflection surface is accomplished. Then, a kinematic model of the deployable structure is established to analyze its kinematic characteristics and prove the equivalence of motion before and after changing the hinges. By converting the rotating pairs between the two layers of origami into cylindrical pairs, a thick-panel form of double-layer origami is constructed. On this basis, a compatible back frame for the planar antenna mechanism is designed and a corresponding prototype is fabricated. The work paves the way to design deployable structures. [Display omitted] [ABSTRACT FROM AUTHOR]

• To propose two schemes to construct one-DOF Resch patterns with thick panels. • These structures are constructed with TS-, PS-Bricard, and spherical 6 R linkages. • Analytical kinematics has been derived by considering kinematic compatibilities. • The physical models for two schemes have been made to validate the results. • Kinematic studies reveal the ranges for parameters to realize the complete folding. As a series of tessellation origami patterns consisting of more than one type of polygons, Resch patterns are generally rigid foldable but with a large number of degrees of freedom (DOFs). The patterns are not flat foldable, instead the fully folded configuration is a sandwich style in flat profile. In order to achieve one-DOF forms of triangular Resch pattern units, the thick-panel technique is employed at vertices to replace spherical linkages with spatial linkages. The compatibility among all the vertices is studied by a systematic kinematic analysis of the thick-panel Resch pattern. Finally, two design schemes are obtained to form a one-DOF origami structure between the initial planar structure and the fully folded 3D sandwich structure with dome-curved intermediate folded configurations. The one-DOF Resch pattern structure can be used to generate reliable shape transformation. [ABSTRACT FROM AUTHOR]