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The pseudo intensity vector (PIV) is often used to analyze the directional properties of spatial room impulse responses. In the early part of the response, it is capable of estimating the directions of individual reflections. However, thus far, its behaviour in the late field is unclear. Specifically, it is unknown whether anisotropy, i.e., a direction-dependent energy distribution, is captured by the directional estimates. In this study, a closed-form expression of the directional distribution of the pressure-normalized pseudo intensity vector contingent on a general stochastical model of anisotropic fields was analytically derived. This paper shows that the probability density function of this PIV is a multivariate Cauchy distribution, which does indeed depend on the energy distribution of the field, yet the directional distribution has very limited degrees of freedom. The derived distribution is compared to the results of Monte Carlo simulations and fields captured with a microphone array in a real room. These results facilitate better understanding of the behaviour of parametric spatial room impulse response methods and may enable improved directional estimators for anisotropic fields. [ABSTRACT FROM AUTHOR]

On-chip phononic circuits tailor the transmission of elastic waves and couple to electronics and photonics to enable new signal manipulation capabilities. Phononic circuits rely on waveguides that transmit elastic waves within desired frequency passbands, which are typically designed based on the Bloch modes of the constitutive unit cell of the waveguide, assuming periodicity. Acoustic microelectromechanical system waveguides composed of coupled drumhead resonators offer megahertz operation frequencies for applications in acoustic switching. Here, we construct a reduced-order model (ROM) to demonstrate the mechanism of transmission switching in coupled drumhead-resonator waveguides. The ROM considers the mechanics of buckling under the effect of temperature variation. Each unit cell has two degrees of freedom: translation to capture the symmetric bending modes and angular motion to capture the asymmetric bending modes of the membranes. We show that thermoelastic buckling induces a phase transition triggered by temperature variation, causing the localization of the first-passband modes, similar to Anderson localization caused by disorders. The proposed ROM is essential to understanding these phenomena since Bloch mode analysis fails for weakly disordered (<5%) finite waveguides due to the disorder amplification caused by the thermoelastic buckling. The illustrated transmission control can be extended to two-dimensional circuits in the future. [ABSTRACT FROM AUTHOR]

To control mechanical waves and structural vibrations, an important method is to design metamaterials with tailored elastic constants, but it is very difficult. In this paper, a simple and universal metamaterial design method is proposed. This orthotropic metamaterial is composed of elements arrayed periodically in space. The element includes two cuboid structures. The first structure is the basic structure of the element, and the second structure is the transformation of the first structure of the element. The first structure of the element is a cuboid structure composed of 24 bars connected by 8 nodes, and the second structure of the element is a cuboid structure composed of 36 bars connected by 14 nodes. This metamaterial has six independent elastic constants, so there is a large degree of freedom in the material design. Therefore, it has great application value in the fields of mechanical metamaterials, elastic wave metamaterials, acoustic metamaterials, and seismic metamaterials, and has also laid the foundation for realizing the dream of controlling mechanical waves and structural vibrations. [ABSTRACT FROM AUTHOR]

Arrangements of acoustic meta-atoms, better known as acoustic metamaterials, are commonly applied in acoustic cloaking, for the attenuation of acoustic fields or for acoustic focusing. A precise design of single meta-atoms is required for these purposes. Understanding the details of their interaction allows improvement of the collective performance of the meta-atoms as a system, for example, in sound attenuation. Destructive interference of their scattered fields, for example, can be mitigated by adjusting the coupling or tuning of individual meta-atoms. Comprehensive numerical studies of various configurations of a resonator pair show that the coupling can lead to degenerate modes at periodic distances between the resonators. We show how the resonators' separation and relative orientation influence the coupling and thereby tunes the sound attenuation. The simulation results are supported by experiments using a two-dimensional parallel-plate waveguide. It is shown that coupling parameters like distance, orientation, detuning, and radiation loss provide additional degrees of freedom for efficient acoustic meta-atom tuning to achieve unprecedented interactions with excellent sound attenuation properties. [ABSTRACT FROM AUTHOR]

A novel free-standing resonant-cavity-enhanced (RCE) Ge thin-film absorber is designed with a bottom distributed Bragg reflector (DBR) for infrared photodetection at 1550 nm wavelength based on a Si substrate. The free-standing structure offers a high degree of freedom in optimizing the number of periods, the layer arrangement, and the thickness of each layer of the DBR. A SiO2/Si DBR that is compatible with Si processing technology is used on the bottom of the Ge thin film to construct the RCE structure. Based on our theoretical study, the SiO2 low-index layer must be placed next to the Ge layer to utilize the large difference in the refractive indices between SiO2 and Ge to achieve high reflectance for the DBR. In this design, the structure can reach an absorbance of 85.90% with a DBR of three periods on the bottom and an antireflective oxide layer on the top surface of the Ge layer. Without the antireflective oxide layer, the absorbance is increased to 99.17%. The design paves the way for high-responsivity Ge infrared photodetectors in Si-based photonic systems. [ABSTRACT FROM AUTHOR]

The auxiliary superfield approach is proposed as a method to obtain statistical predictions of the acoustic response of complex elastic structures. The potential advantage of the method is the full retention of interference and resonance effects associated with the degrees of freedom being averaged over. It is not known whether this approach leads to tractable problems for structural acoustics systems, however. We have applied the method to the idealized case of an infinite, thin plate with attached oscillators to obtain the mean Green's function. The oscillators are assumed to have an uncorrelated, Gaussian distributed mass and stiffness distribution representing a simple form of complex internal structure. Using the auxiliary superfield approach, the mean Green's functions are expressed exactly as a functional integral. For relatively small disorder, the integral may be estimated by a saddle point approximation which leads to coupled integral equations for effective mass and stiffness matrices that can be solved numerically for a given spatial distribution of the disorder. With the solutions for these matrices, one obtains a self-consistently determined, generalized fuzzy structure model. We give analytical solutions for the simple case of a uniform spatial distribution. The results are promising for the application of the method to more challenging geometries. [ABSTRACT FROM AUTHOR]

With complex coupling of multiple degrees of freedom, transition metal oxides (TMOs) provide a promising platform to tune the magnetic property in heterostructures via the magnetic proximity effect. Recent realization of freestanding TMO thin films allows further extension of this technique to novel two-dimensional heterostructures by mechanically stacking with van der Waals materials. Here, we demonstrate the presence of significant magnetic exchange interactions in a heterostructure of 8 nm freestanding LaMnO3 and monolayer WS2. The high magnetization in freestanding LaMnO3 leads to valley degeneracy breaking in WS2, resulting in unbalanced valley polarization in the photoluminescence (PL). Further temperature-dependent PL measurements reveal the same transition behavior as the magnetization in the freestanding LaMnO3 film. Our results unlock new approaches for tuning the magnetism and the valley degree of freedom in ultrathin two-dimensional heterostructures. [ABSTRACT FROM AUTHOR]

The effects of the coating surface orientation of the α-Fe soft magnetic layer on the Sm(Fe0.8Co0.2)12 hard magnetic phase and the volume fraction of α-Fe, VFe, on the maximum energy product, (BH)max of exchange-coupled Sm(Fe0.8Co0.2)12/α-Fe nanocomposite magnet particles were micromagnetics OOMMF package was systematically investigated. The (BH)max of the reference model, Sm(Fe0.8Co0.2)12 particles without Fe layer, was 630 kJ/m3. In contrast, in the nanocomposite magnet particle model with soft magnetic layers on both sides of the hard magnetic phase, (BH)max reached a maximum value of 657 kJ/m3 at VFe = 12% (Fe layer thickness, tFe = 2 nm). In the model with α-Fe coating on the top and bottom surfaces of the hard magnetic phase, (BH)max = 636 kJ/m3 at VFe = 4% (tFe = 2 nm). Furthermore, the coating of the soft magnetic phase on both sides of the hard phase particles reduces the magnitude of the demagnetizing field, Hd of the nanocomposite magnet particles, indicating that the side coating of the soft magnetic phase is effective in increasing (BH)max. These findings allow for a greater degree of freedom in the design of nanocomposite magnets by adjusting not only the VFe volume fraction of the hard/soft phases but also their arrangement. [ABSTRACT FROM AUTHOR]

An approach for the analysis of atomically resolved scanning transmission electron microscopy data with multiple ferroic variants in the presence of imaging non-idealities and chemical variabilities based on a rotationally invariant variational autoencoder (rVAE) is presented. We show that an optimal local descriptor for the analysis is a sub-image centered at specific atomic units, since materials and microscope distortions preclude the use of an ideal lattice as a reference point. The applicability of unsupervised clustering and dimensionality reduction methods is explored and is shown to produce clusters dominated by chemical and microscope effects, with a large number of classes required to establish the presence of rotational variants. Comparatively, the rVAE allows extraction of the angle corresponding to the orientation of ferroic variants explicitly, enabling straightforward identification of the ferroic variants as regions with constant or smoothly changing latent variables and sharp orientational changes. This approach allows further exploration of the chemical variability by separating the rotational degrees of freedom via rVAE and searching for remaining variability in the system. The code used in this article is available at https://github.com/saimani5/ferroelectric_domains_rVAE. [ABSTRACT FROM AUTHOR]

Hermitian Dirac-like cones are proposed for creating acoustic logic gates herein. The predictive phenomenon of creating Dirac-like cones near a bipolar antisymmetric deaf band was found to be useful for acoustic computing of Boolean algebra. Unlike previous approaches, Dirac-like cone creates exclusive opportunity to perform all possible Boolean algebra computation with valid inputs. The phenomenon is demonstrated in two-dimensional phononic crystals (PnCs), consisting of tunable square columns in air media. By predictive tuning of the deaf bands, a triply to doubly degenerated Dirac-like cone is reported to form and is particularly useful for acoustic computing. It is only possible when a bottom band has a negative curvature that is lifted from a nearby doubly degenerated band with positive curvature, which is again degenerated with a deaf band. On the contrary, similar computing possibilities are difficult when the bottom band degenerates with the deaf band and the top band is lifted. Using these phenomena, acoustic logic gates are designed to perform Boolean algebra through AND, NAND, OR, and NOR gate operations. A simple one degree of freedom system and a complex six degrees of freedom system are proposed and demonstrated in which simple rotation of the PnCs activates a specific gate. [ABSTRACT FROM AUTHOR]

This research gauges the capabilities of deep reinforcement learning (DRL) techniques for direct optimal shape design in computational fluid dynamics (CFD) systems. It uses policy based optimization, a single-step DRL algorithm intended for situations where the optimal policy to be learnt by a neural network does not depend on state. The numerical reward fed to the neural network is computed with an in-house stabilized finite elements environment combining variational multi-scale modeling of the governing equations, immerse volume method, and multi-component anisotropic mesh adaptation. Several cases are tackled in two and three dimensions, for which shapes with fixed camber line, angle of attack, and cross-sectional area are generated by varying a chord length and a symmetric thickness distribution (and possibly extruding in the off-body direction). At a zero incidence, the proposed DRL-CFD framework successfully reduces the drag of the equivalent cylinder (i.e., the cylinder of same cross-sectional area) by 48% at a Reynolds numbers in the range of a few hundreds. At an incidence of 30°, it increases the lift to drag ratio of the equivalent ellipse by 13% in two dimensions and 5% in three dimensions at a chord Reynolds numbers in the range of a few thousands. Although the low number of degrees of freedom inevitably constrains the range of attainable shapes, the optimal is systematically found to perform just as well as a conventional airfoil, despite DRL starting from the ground up and having no a priori knowledge of aerodynamic concepts. Such results showcase the potential of the method for black-box shape optimization of practically meaningful CFD systems. Since the resolution process is agnostic to details of the underlying fluid dynamics, they also pave the way for a general evolution of reference shape optimization strategies for fluid mechanics and any other domain where a relevant reward function can be defined. [ABSTRACT FROM AUTHOR]

We investigate the nonlinear behavior of a simple pendulum fixed to an elastic rod, which can only vibrate horizontally. When released without initial angular momentum, the plane of the pendulum rotates, and the bob traces a delicate stationary pattern. We explain this effect as amplitude modulation due to the nonlinear coupling between the two degrees of freedom. We construct a theoretical model and approximately solve the equations of motion analytically (using the method of multiple scales); we also solve these equations numerically. In the analytical solution, the modulation period depends not only on the dynamical parameters but also on the pendulum's initial release position, which is typical of nonlinear systems. Finally, we build a simple apparatus and conduct a quantitative experiment. The approximate analytical solutions exhibit the same trends as the numerical results and experimental data. After adding linear dissipation, the numerical and experimental results match fairly well. This system can serve as an instructive demonstration as well as a nonlinear dynamics research project for undergraduate students. [ABSTRACT FROM AUTHOR]

Planar lattice metamaterials, such as periodic beam networks, are often considered as the micropolar continuum, where each material point has two translational degrees of freedom and one rotational degree of freedom. The joints through which bars are linked to one another are generally approximated as rigid. This study focuses on lattices with complex-structured deformable joints. The deformation field in each joint is obtained by conducting structural analyses. Once the "stiffness matrix" of the joint-centered unit cell is obtained by the finite element method, it can be used as the input for the standard procedure of calculating micropolar elastic moduli that are based on the equivalence of strain energy. As a result, effective moduli can be expressed in a semi-analytical form, meaning that only the cell structural stiffness is given numerically. The present model is validated by comparison to the FEM simulations. Particularly, the auxetic and anisotropic properties are discussed for various lattice metamaterials with deformable joints. We then take the obtained effective moduli as inputs to the in-house micropolar FEM code and obtain results agreeing well with the FEM structural simulations. [ABSTRACT FROM AUTHOR]

Metalens consisting of arrays of subwavelength nanostructures with ultrathin, lightweight, and tailorable characteristics have been in the spotlight to develop next-generation optical elements beyond existing refractive or diffractive optics. However, billions of subwavelength nanostructures of the metalens pose a serious challenge for fabrication, especially for the large-area ones. Herein, we designed and fabricated an unconventional optical sparse aperture (UOSA) metalens that consists of four identical and concentric annular sectors sub-aperture metalens, and it has the larger nonzero domain of modulation transfer function compared with the OSA metalens. The numerical simulation and experiments jointly show that the UOSA metalens has a limited diffraction resolution (0.91 µm) as the conventional full aperture metalens. The UOSA method can not only enlarge the effective aperture of the metalens with lower cost and less processing time but also extend a new degree of freedom for the design of the OSA metalens. [ABSTRACT FROM AUTHOR]

The eigenfunctions of the Laplace-Beltrami operator have widespread applications in a number of disciplines of engineering, computer vision/graphics, machine learning, etc. These eigenfunctions or manifold harmonics (MHs) provide the means to smoothly interpolate data on a manifold and are highly effective, specifically as it relates to geometry representation and editing; MHs form a natural basis for multi-resolution representation (and editing) of complex surfaces and functions defined therein. In this paper, we seek to develop the framework to exploit the benefits of MHs for shape reconstruction. To this end, a highly compressible, multi-resolution shape reconstruction scheme using MHs is developed. The method relies on subdivision basis sets to construct boundary element isogeometric methods for analysis and surface finite elements to construct MHs. This technique is paired with the volumetric source reconstruction method to determine an initial starting point. The examples presented highlight efficacy of the approach in the presence of noisy data, including a significant reduction in the number of degrees of freedom for complex objects, accuracy of reconstruction, and multi-resolution capabilities. [ABSTRACT FROM AUTHOR]

Despite the recent achievements in the stretchability of kirigami metallic glasses, relevant research is still mainly relying on the single-level kirigami structure. In our work, three different hierarchical levels of patterns were developed for kirigami metallic glass structures for both strip and square units. The degree of freedom that reflects the availability for morphing is shown to be a key factor affecting the mechanical response of the hierarchical metallic glasses. It is found that a high hierarchical order with a large degree of freedom leads to the high stretchability of kirigami metallic glasses. Kirigami metallic glasses, designed with square units, with a large degree of freedom show high stretchability compared to those designed with strip units, with a small degree of freedom, at the same hierarchical level. Our study, combining the degree of freedom in the hierarchical construction, highlights the potential for a multilevel architected structure as a programmable block for stretchable mechanical metamaterials. [ABSTRACT FROM AUTHOR]

The spatially-inhomogeneous magnetization dynamics in a cylindrical magnetic nanodot driven by ac spin-torque is analyzed. To this end, the Landau-Lifshitz-Gilbert-Slonczewski equation is reformulated as a system of coupled nonlinear ordinary differential equations which describe the time-evolution of normal modes amplitudes. This approach provides a class of models with reduced number of degrees of freedom and incremental accuracy between macrospin and full micromagnetics. By using this approach, the onset of foldover effect for fundamental and higher-order modes is demonstrated. The results are confirmed by full micromagnetic simulations. [ABSTRACT FROM AUTHOR]

The generic problem of low-frequency acoustic radiation through quiescent air from a circular pipe that is inclined with respect to its exit flange is studied in this work. The exit flange is taken to extend as an infinite plane away from the pipe opening. The analysis implements a hybrid method that combines modal expansions with the boundary element method. The reflection coefficient and pipe end correction for Helmholtz numbers (based on the pipe radius) less than 2.5 are calculated for various inclination angles up to 75°. Calculations are validated using simulations from the finite-element solver of the commercial software package COMSOL. The reflection coefficient and end correction predictions agree closely with the validation simulations yet differ notably from the results available in the literature. The solution obtained from the hybrid method is subsequently used to analyse the acoustic field at the pipe exit and in the downstream space. The key aspects of the governing physics pertaining to practical engineering applications at low frequencies are captured in a low-order approximation, which significantly reduces the degrees of freedom of the problem and provides generally good estimates of the reflection coefficient and end correction, as well as the downstream acoustic field. [ABSTRACT FROM AUTHOR]

The tracking range and pointing performance of the antenna are important indices to measure the antenna system. First, the 3 degree of freedom parallel mechanism is proposed for the supporting mechanism of the antenna. The trajectory tracking principle of the antenna mechanism is analyzed based on the inverse position solution model. Meanwhile, the kinematic model of the antenna mechanism with a specific motion trajectory is derived. In addition, the structural optimization design is demonstrated based on the actuation torques and motion range index. In addition, the trajectory planning research is carried out according to the trajectory tracking requirements. The trajectory planning simulation is carried out in the joint space. Afterward, the antenna motion range is obtained through simulation. The specific trajectory tracking simulation of the antenna is completed. Furthermore, the pitch and azimuth motion performance experiments are carried out based on the developed antenna mechanism prototype. Finally, the pentagram trajectory tracking performance is verified via experiments. This research serves as a reference for designing and engineering application of the antenna. [ABSTRACT FROM AUTHOR]

The classical and quantum description of a free particle moving inside a confocal parabolic billiard is studied. From a classical approach, we derive the characteristic equations for periodic trajectories, discuss the Poincaré maps, and explore interesting geometrical properties of the orbits inside the billiard. From a quantum description, we determine the eigenstates and energy spectrum of the confined particle. The confocal parabolic billiard is an integrable system that exhibits two degrees of freedom and two constants of motion. The way to establish a correspondence between the classical and quantum solutions is by equating the constants of motion for both descriptions. The parabolic billiard provides a well-motivated and relatively straightforward example of the Hamilton–Jacobi theory in a way that is seldom discussed in the undergraduate curriculum. [ABSTRACT FROM AUTHOR]

The hybrid of the frequency diversity array (FDA) radar and multiple-input multiple-output (MIMO) radar, namely, FDA–MIMO radar, provides more degrees of freedom and improves the overall performance of the system. The essence of FDA–MIMO radar transmitting subaperture design is to divide the transmit array into multiple subapertures to improve the interference suppression capability of the radar. Among them, orthogonal waveforms are transmitted between each subaperture, and each element inside the subaperture transmits the same waveform. Aiming at the problem of how the subaperture design of the FDA–MIMO radar affects its interference suppression performance, we analyzed the two aspects of the normalized beampattern and (non-)adaptive beamforming. We conclude that when interference is dominant, setting the number of subapertures to half of the number of transmit array elements can effectively reduce the sidelobe level and increase the output signal-to-interference-plus-noise ratio. A large number of simulation results verify the effectiveness and superiority of this method. [ABSTRACT FROM AUTHOR]

We consider pure square spin ice, that is, square ice, where only nearest neighbors are coupled. The gauge-free duality between the perpendicular and collinear structure leads to a natural description in terms of topological currents and charges as the relevant degrees of freedom. That, in turn, can be expressed via a continuous field theory where the discrete spins are subsumed into entropic interactions among charges and currents. This approach produces structure factors, correlations, and susceptibilities for spins, monopoles, and currents. It also generalizes the height formalism of the disordered ground state to non-zero temperature. The framework can be applied to the zoology of recent experimental results, especially realizations on quantum annealers, and can be expanded to include longer range interactions. [ABSTRACT FROM AUTHOR]

Traditional ultrasonic motors can usually produce either linear or rotational motion. Piezoelectrically driven structures with multiple degrees of freedom require two or more ultrasonic motors, and the manufacturing process is associated with some problems related to their complex structure and difficult control. This study proposes a new structure of a multi-degree-of-freedom piezoelectric crawling robot. Four modes are selected as the working modes, and mode superposition is used to produce the linear and rotational motion of the robot. This structure is designed based on a combination of size and topological optimization to adjust the frequency response consistency of the motor. The performance of the motor was tested on surfaces with different roughnesses. Its performance on the desk surface was the best. Its maximum linear speed is 37 mm/s, and its maximum rotational speed is 6.28 rad/s. The performance tests were performed under different loads. The linear motion speed of the motor reached its maximum value at 29.2 kHz, and the rotational motion speed reached its maximum value at 32.1 kHz. [ABSTRACT FROM AUTHOR]

A three-dimensional coupled vibroacoustic finite element model for physics-based simulations of the sound generation by mallet percussion instruments in the time domain is discussed in the present paper. The mechanical model takes the orthotropic material properties of the wooden sound bars and the nonlinear nature of the interaction force between the mallet head and the sound bar into account while the acoustical model considers radiation into an unbounded domain. A direct coupling of the sound bars, acoustical cavity resonators, and the excitation by a mallet is considered with exploiting the modal basis to reduce the number of degrees of freedom of the system. Both the mechanical and acoustical models are validated by comparing them to measurements performed on an Orff xylophone. A case study shows the capabilities of the coupled model, including the analysis of the energy balance, the effect of tuning the resonator, and the excitation of the torsional modes of the sound bar. [ABSTRACT FROM AUTHOR]

In the metallurgical industry, the hydraulic automatic gauge control (HAGC) system is a kernel system used to assure the thickness precision of a rolling piece. In addition, the HAGC system is a complex nonlinear system with multiple degrees of freedom (DOF). It is difficult to identify the key parameters and obtain an accurate prediction model that can reflect the output performance of the HAGC system. On the basis of theoretical analysis, a vertical vibration model of the HAGC system with two DOF was established. Moreover, based on the swarm intelligence in nature, a novel method for model parameter identification of the HAGC system was explored, and a parameter identification method was proposed based on the chaotic wolf pack optimization algorithm. Furthermore, the proposed method was verified by experiments. The results indicate that the proposed method presents laudable identification ability. The theoretically predicted response of the identification model is consistent with the measured response of the actual system. The error of the response output waveform is small. The proposed method can be used to identify key structural parameters of the HAGC system. [ABSTRACT FROM AUTHOR]

A generalized modal radiation impulse response approach is presented to evaluate the space-time surface velocity field, time-dependent force, instantaneous power, and energy transfer into a fluid resulting from the space-time force distribution of fluid loaded plate, shell, and panel structures. The basic approach utilizes the in vacuo eigenvectors of the structure to determine the in fluid response of the structure. Self-and mutual modal radiation impulse responses that couple the modal velocities of the fluid loaded structures are used to express the modal time-dependent velocities as a set of coupled convolution integral equations. A canonical fluid loaded single degree of freedom vibrator is addressed to illustrate the basic approach. A fluid loaded admittance impulse response is introduced and plays a central role in the analysis to evaluate the normal velocity resulting from a specified external force. A time-dependent energy equation is also introduced to investigate the temporal evolution of the internal energy loss and the energy transfer to the fluid. Numerical results are presented for an impulsive excitation of the fluid loaded single degree of freedom vibrator which serves as a canonical problem for investigating the response of complex structures. [ABSTRACT FROM AUTHOR]

By means of ab initio calculations, we study the effect of charge transfer and symmetry mismatch on the magnetic and electronic properties of CaMnO3 ultrathin films, epitaxially grown on SrTiO3 (001). We find that the interplay of these degrees of freedom, together with the low dimensionality and the strain imposed by the substrate, changes the bulk occupancy of the Mn eg orbitals, which determines the magnetic configuration of the ultrathin CMO films. A transition from an insulating G-type to a metallic A-type antiferromagnetic configuration is stabilized. [ABSTRACT FROM AUTHOR]

An effective multi-element simulation methodology for quantum eigenvalue problems is investigated. The approach is derived from a reduced-order model based on a data-driven learning algorithm, together with the concept of domain decomposition. The approach partitions the simulation domain of a quantum eigenvalue problem into smaller subdomains that, referred to as elements, could be the building blocks for quantum structures of interest. In this quantum element method (QEM), each element is projected onto a functional space represented by a set of basis functions (or modes) that are generated from proper orthogonal decomposition (POD). To construct a POD model for a large domain, these projected elements can be combined together, and the interior penalty discontinuous Galerkin method is applied to achieve the interface continuity and stabilize the numerical solution. The POD is able to optimize the basis functions specifically tailored to the geometry and parametric variations of the problem and can therefore substantially reduce the degree of freedom (DoF) needed to solve the Schrödinger equation. To understand the fundamental issues of the QEM, demonstrations in this study focus on examining the accuracy and DoF of the QEM influenced by the training settings for generation of POD modes, selection of the penalty number, suppression of interface discontinuities, structure size and complexity, etc. It has been shown that the QEM is able to achieve a substantial reduction in the DoF with a high accuracy even beyond the training conditions for the POD modes if the penalty number is selected within an appropriate range. [ABSTRACT FROM AUTHOR]

In this paper, a forced vibration model of composite beams under the action of periodic excitation force considering geometric nonlinearity is proposed. For the strain–displacement relationship, Timoshenko beam theory is used, and the element and system matrices are developed using the differential quadrature finite element method. Each node has 3 degrees of freedom. The incremental harmonic balance method is used to solve the nonlinear forced vibration equation. In order to prove the validity of the proposed model, the solution of the Duffing equation is calculated using the analytical method and the proposed method. Next, linear forced vibration analysis of the beam made of isotropic material is performed and compared with the result of ABAQUS. The results are very close. Based on these comparisons, nonlinear vibration phenomena of composite beams are studied under the action of periodic forces. [ABSTRACT FROM AUTHOR]

In the present study, a bionic flapping mechanism of a spatial six-bar configuration was designed to transform a single rotation of a motor into a three degrees of freedom "flapping–twist–swing" cooperative motion of a flapping wing. The kinematics model of the flapping mechanism movement was constructed. The flapping trajectory of the wing based on the kinematics model was to mimic the motion of a pigeon wing in landing flight. To reduce the manufacturing complexity, the flapping mechanism was simplified with only two degrees of freedom (flapping and twist) retained. Finally, a prototype model with a 0.9 m wing span was built and tested. A comparison among the experimental data, theoretical calculation results, and ADAMS simulation results revealed that the difference in the flapping and the twist amplitude between experimental observations and theoretical calculation results was 12.5% and 2.3%, respectively. This was owing to the elastic deformation of the bar and the mechanism simplification. The comparison results also indicated that the maximum difference in the inertial force was 5.9% in up-stroke and 6.7% in down-stroke, respectively. The experimental results showed that the inertial force of the model with the wing patagium was approximately 2.2 N, and the maximum positive and negative lift was 2.1 N and −1.5 N, respectively. It is hoped that this study can provide guidance for the design of bionic flapping wing mechanisms of a flapping wing aircraft for short landing flight. [ABSTRACT FROM AUTHOR]

Acoustic metamaterials (AM) have emerged as an academic discipline within the last decade. When used for sound insulation, metamaterials can show high transmission loss at low frequencies, despite having low mass per unit area. This paper investigates the possibility of using AMs to increase the sound insulation of finite single leaf walls (SLWs), focusing on the coincidence effect problem. Formulas are derived using a variational technique for the forced sound transmission of finite SLWs with a coupled array of single degree of freedom resonators. An analytical model is presented for this simple case, and the effects of the band gap in sound transmission and radiation are analyzed. Moreover, the influence of each parameter is studied, especially the presence of losses, giving way to an optimized way of designing this type of structure using constrained parameter optimization. Numerical validations are performed and discussed. Finally, some conclusions are drawn regarding the effectiveness of the proposed model, including possible applications. [ABSTRACT FROM AUTHOR]

A hybrid aeroacoustic approach was developed for the efficient numerical computation of human phonation. In the first step, an incompressible flow simulation on a three-dimensional (3 D) computational grid, which is capable of resolving all relevant turbulent scales, is performed using STARCCM+ and finite volume method. In the second step, the acoustic source terms on the flow grid are computed and a conservative interpolation to the acoustic grid is performed. Finally, the perturbed convective wave equation is solved to obtain the acoustic field in 3 D with the finite element solver CFS++. Thereby, the conservative transformation of the acoustic sources from the flow grid to the acoustic grid is a key step to allow coarse acoustic grids without reducing accuracy. For this transformation, two different interpolation strategies are compared and grid convergence is assessed. Overall, 16 simulation setups are compared. The initial (267 000 degrees of freedom) and the optimized (21 265 degrees of freedom) simulation setup were validated by measurements of a synthetic larynx model. To conclude, the total computational time of the acoustic simulation is reduced by 95% compared to the initial simulation setup without a significant reduction of accuracy, being 7%, in the frequency range of interest. [ABSTRACT FROM AUTHOR]

Embedding microfluidic architectures with microneedles enables fluid management capabilities that present new degrees of freedom for transdermal drug delivery. To this end, fabrication schemes that can simultaneously create and integrate complex millimeter/centimeter-long microfluidic structures and micrometer-scale microneedle features are necessary. Accordingly, three-dimensional (3D) printing techniques are suitable candidates because they allow the rapid realization of customizable yet intricate microfluidic and microneedle features. However, previously reported 3D-printing approaches utilized costly instrumentation that lacked the desired versatility to print both features in a single step and the throughput to render components within distinct length-scales. Here, for the first time in literature, we devise a fabrication scheme to create hollow microneedles interfaced with microfluidic structures in a single step. Our method utilizes stereolithography 3D-printing and pushes its boundaries (achieving print resolutions below the full width half maximum laser spot size resolution) to create complex architectures with lower cost and higher print speed and throughput than previously reported methods. To demonstrate a potential application, a microfluidic-enabled microneedle architecture was printed to render hydrodynamic mixing and transdermal drug delivery within a single device. The presented architectures can be adopted in future biomedical devices to facilitate new modes of operations for transdermal drug delivery applications such as combinational therapy for preclinical testing of biologic treatments. [ABSTRACT FROM AUTHOR]

The zero crossings of basilar-membrane (BM) responses to clicks are nearly independent of stimulus intensity. This work explores the constraints that this invariance imposes on one-dimensional nonlinear cochlear models with two degrees of freedom (2DoF). The locations of the poles and zeros of the BM admittance, calculated for a set of linear models in which the strength of the active force is progressively decreased, provides a playground for evaluating the behavior of a corresponding nonlinear model at increasing stimulus levels. Mathematical constraints on the model parameters are derived by requiring that the poles of the admittance move horizontally in the s-plane as the active force is varied. These constraints ensure approximate zero-crossing invariance over a wide stimulus level range in a nonlinear model in which the active force varies as a function of the local instantaneous BM displacement and velocity. Two different 2DoF models are explored, each capable of reproducing the main qualitative characteristics of the BM response to tones (i.e., the tall and broad activity pattern at low stimulus levels, the large gain dynamics, and the partial decoupling between gain and phase). In each model, the motions of the two masses are compared with response data from animal experiments. [ABSTRACT FROM AUTHOR]

In this paper, we propose a hybrid metallo-dielectric core-shell nanorod for the Kerker-type effect at two different frequencies. The effect arises from the interference of the scattering waves of the nanorod, which are generated by the magnetic dipole moment (MD) of the high-index hollow particle and the electric dipole moment (ED) induced in both metallic and dielectric particles. Interestingly, we find that such kind of unidirectional radiation properties, (i.e., zero back scattering occurring at dual frequencies) can be sustained with a single nanorod, which usually being equivalent to a local electric dipole source. The effect of substrate is also considered to investigate the typical experimental realization for the dual-frequency unidirectionalities of the nanoantenna. Furthermore, the unidirectionality can be further improved by the design of one-dimensional array of the hybrid nanoantenna. Our results could provide an additional degree of freedom for light scattering manipulation, and widen the versatile applications in nanoantennas, optical sensor, light emitters, as well as photovoltaic devices. [ABSTRACT FROM AUTHOR]

This paper presents the design, modeling and theoretical analysis of a novel dual-axis hair flow sensor (DHFS) based on the mode localization of weakly coupled resonators (WCRs). A stereoscopic hair post is adopted to interact with external fluid and transmit the air flow velocity signal. Two-stage micro-leverage mechanisms are designed and optimized to amplify the drag force derived from external air flow. As the main sensitive elements, four optimized WCRs are symmetrically distributed around the main frame. A simplified theoretical model of DHFS is established and verified by comprehensive finite element method (FEM) simulations. Unlike the traditional frequency detection method, the presented DHFS detects the air flow velocity by measuring the amplitude ratio shift of two degree of freedom WCRs. The input-output response simulations demonstrate that the presented DHFS exhibits an x-axis sensitivity of 6.5026×10-2/(m/s)2 and a y-axis sensitivity of 6.4527×10-2/(m/s)2. In addition, the simulated relative shift in amplitude ratio (∼65000 ppm/(m/s)2) is three orders of magnitude larger than that in resonance frequency (∼50 ppm/(m/s)2). Meanwhile, the cross-axis sensitivities are 6.4387×10-4/(m/s)2 (x-axis) and 6.4475×10-4/(m/s)2 (y-axis), respectively. In summary, the feasibility of proposed structure architecture and operation principle is verified. [ABSTRACT FROM AUTHOR]

Compared to plasmonic metasurface, all-dielectric metasurface can suppress radiation loss at terahertz (THz) frequencies due to the low intrinsic loss of dielectric. Here, we propose a THz filter based on all-dielectric metasurface composed of Si microdisk (SiMD) array standing on TPX substrate. Numerical simulation results demonstrate that both electric dipole and magnetic dipole resonances are excited in the SiMD, resulting in a high reflection coefficient of 100%. The working frequency of the designed filter can be passively tuned over a wide range from 1.0 THz to 1.5 THz by manipulating the radius of the SiMD. In addition, the proposed filter is robust to the incident polarizations (x-/y-linear polarizations) and the incident angles (ranging from 0° to 25°). Besides, a new degree of freedom is introduced by cutting a split in the SiMD. The filter can work well even with a split in the SiMD since the presence of the split does not induce additional losses. We further demonstrate the resonant modes can also be modified by tuning the width of the splitting gap, resulting in a tunable THz filter with high efficiency. [ABSTRACT FROM AUTHOR]

The periodic arrangement of equimolar two cations in the corundum structure produces the ilmenite-type and LiNbO3-type orderings. The phase (polymorphism) control is one of the important topics in solid-state chemistry. Using a pulsed-laser deposition technique, we examined the formation of MnSnO3 films as a function of oxygen gas pressure. Under the optimal low oxygen gas pressure, c-axis oriented single-crystalline films of the ilmenite-type MnSnO3 were synthesized on Al2O3 (0001). We found that, with an increase of oxygen gas pressure, x-ray diffraction peaks characteristic of the ilmenite-type ordering disappeared and the c-axis length approached that of the LiNbO3-type MnSnO3 while the crystal structure retained basic features of corundum derivatives. The optical bandgap measurement revealed the decrease of bandgap in the LiNbO3-type (or disordered corundum-type) MnSnO3. The thin-film approach can add a new degree of freedom in the control of structural and physical properties in corundum-derivative oxides. [ABSTRACT FROM AUTHOR]

A novel dynamic mode decomposition (DMD) method based on a Kalman filter is proposed. This paper explains the fast algorithm of the proposed Kalman filter DMD (KFDMD) in combination with truncated proper orthogonal decomposition for many-degree-of-freedom problems. Numerical experiments reveal that KFDMD can estimate eigenmodes more precisely compared with standard DMD or total least-squares DMD (tlsDMD) methods for the severe noise condition if the nature of the observation noise is known, though tlsDMD works better than KFDMD in the low and medium noise level. Moreover, KFDMD can track the eigenmodes precisely even when the system matrix varies with time similar to online DMD, and this extension is naturally conducted owing to the characteristics of the Kalman filter. In summary, the KFDMD is a promising tool with strong antinoise characteristics for analyzing sequential datasets. [ABSTRACT FROM AUTHOR]

We derive master equation for a macroscopic dynamics of complex systems driven by time-dependent processes containing both fast and slow degrees of freedom. Presence of fast degrees of freedom can be established through a timescale test and fast dynamics is averaged out by a rigorous coarse time-stepping procedure applicable to many cross-disciplinary areas. [ABSTRACT FROM AUTHOR]

This study attempted to improve the five-degrees-of-freedom sensors of the Northern Digital Incorporated's Wave electromagnetic articulography system by replacing their cables with thinner and more flexible cables to reduce interference in articulation. Measurement errors and data loss rates were compared between the original and the proposed sensors. The proposed sensors showed twofold tracking accuracy and data loss rates compared to the original sensors in an experiment using a crank-rocker mechanism. Data loss rates of the proposed sensors increased in articulatory data collection from four speakers. The proposed sensors have been made available commercially. [ABSTRACT FROM AUTHOR]

We present a new framework to realize topological edge states in elastic shear waves in a two-dimensional (2D) phononic crystal (PC). The PC has a simple structure and is composed of a triangular array of core-shell cylinders embedded in an epoxy background. By tuning the geometrical parameters of the cylinders, band inversion between E1 and E2 eigenstates can be achieved at the Brillouin zone (BZ) center, which signifies a topological phase transition from a trivial PC to a nontrivial PC. An effective Hamiltonian is developed to characterize the topology of the PC around the Γ point, and spin Chern numbers are identified as the appropriate topological invariant. Helical edge states are formed at the interface between topologically distinct PCs, and these edge modes exhibit interesting one-way propagation behaviors with little backscattering. With full-wave simulations, we unambiguously demonstrate the robustness of the edge states against different types of defects, which is due to the nontrivial topology of the system. These unidirectional and robust transport phenomena of elastic shear wave thus offer people a new degree of freedom to control and manipulating elastic waves and are expected to find potential applications in diverse fields. [ABSTRACT FROM AUTHOR]

In this paper, a method for the assembly of multi-domain substructures with general joints is proposed. Modal domain and physical domain substructures can be coupled in a unified framework. Specially, the physical domain substructures are represented using the impulse response functions of substructures. The modal domain substructures are generated using the Craig–Bampton method.With the introduction of general joints, complex connections like hybrid rigid-elastic or nonlinear connections are able to be considered. Meanwhile, only degree of freedoms directly associated with the joints are retained for the synthesis that makes this method quite suitable for local nonlinear structures. The validity of the proposed method is demonstrated by numerical examples. And the application to the dynamics of a practical lunar lander is provided. The results show that the proposed method possesses high precision and is quite efficient with the reduced substructures employed and a few joints degree of freedoms involved. [ABSTRACT FROM AUTHOR]

A simple, low-cost, fully automated polarimeter, which demonstrates fundamental properties of skylight scattering and polarization for undergraduate physics students, is described. The polarimeter includes a microprocessor-based control unit, a Sun tracker, an elevation-azimuth mount with two degrees of freedom, and a polarization sensor unit equipped with a light-dependent resistor for measuring light intensity. Results obtained in the principal plane of the Sun using the polarimeter on a relatively clear day, together with the theoretically expected results for a molecular atmosphere, are presented. A root-mean-square error comparison indicates fairly good agreement between theory and experiment. Construction and experimentation with the polarimeter will provide students with insight into important physical concepts involved in skylight scattering and polarization as well as improve their instrumentation capabilities. [ABSTRACT FROM AUTHOR]

We present a scheme for realizing femtosecond multi-filamentation with designable quantity and locations of filaments, based on the control of multi-focal spots formed by patterned optical fields (POFs) composed of multiple individual optical fields (IOFs). A computer-controlled spatial light modulator is used to engineer the POFs. In particular, we introduce a blazed phase grating in any IOF, which increases a degree of freedom, making the engineering of multi-focal spots becomes more flexible. We achieve experimentally the aim controlling femtosecond multi-filamentation in a K9 glass. Our scheme has great flexibility and convenience in controlling the multi-filamentation in quantity and locations of filaments and strength of interaction between filaments. [ABSTRACT FROM AUTHOR]

H∞ optimum parameters of a dynamic vibration absorber (DVA) using a hysteretic or structural damping element have been derived analytically for suppressing vibration of a single degree-offreedom (SDOF) system excited by harmonic forces or due to ground motions. Although the frequency response function of the traditional DVA (TDVA) with viscous damping may be converted to that of the hysteretic DVA (HDVA) using the equivalent viscous damping coefficient, it is found that the two frequency response functions are not equivalent after the optimization process. Therefore, the optimum parameters of the HDVA are derived using the fixed-points theory rather than converted directly from the TDVA model. The analytical results show that the optimized hysteretic vibration absorber can provide a similar vibration reduction effect as the optimized traditional dynamic vibration absorber at the resonance of a SDOF primary vibrating system. Advantages as well as the limitations of the fixed-points theory for the H∞ optimization of the hysteretic dynamic vibration absorbers using the fixed-points theory are discussed. [ABSTRACT FROM AUTHOR]

An equivalent analog circuit is designed to mimic the coupled ears of the fly Ormia ochracea for sound source localization. This coupled circuit receives two signals with tiny phase difference from a space closed two-microphone array, and produces two signals with obvious intensity difference. The response sensitivity can be adjusted through the coupled circuit parameters. The directional characteristics of the coupled circuit have been demonstrated in the experiment. The miniature microphone array can localize the sound source with low computational burden by using the intensity difference. This system has significant advantages in various applications where the array size is limited. [ABSTRACT FROM AUTHOR]

This article reports a compact wideband piezoelectric vibration energy harvester consisting of three proof masses and an asymmetric M-shaped cantilever. The M-shaped beam comprises a main beam and two folded and dimension varied auxiliary beams interconnected through the proof mass at the end of the main cantilever. Such an arrangement constitutes a three degree-of-freedom vibrating body, which can tune the resonant frequencies of its first three orders close enough to obtain a utility wide bandwidth. The finite element simulation results and the experimental results are well matched. The operation bandwidth comprises three adjacent voltage peaks on account of the frequency interval shortening mechanism. The result shows that the proposed piezoelectric energy harvester could be efficient and adaptive in practical vibration circumstance based on multiple resonant modes. [ABSTRACT FROM AUTHOR]

When signals are recorded on a planar aperture with point emitters/detectors, from either a three-dimensional (3D) scattering potential or from a 3D spatially-incoherent source distribution, an integral equation arises containing the product of two Green's functions in the weak scattering limit (the Born approximation). This fundamental imaging equation for scatterers or sources is derived and solved analytically. [ABSTRACT FROM AUTHOR]

The cochlea is a spiral-shaped, liquid-filled organ in the inner ear that converts sound with high frequency selectivity over a wide pressure range to neurological signals that are eventually interpreted by the brain. The cochlear partition, consisting of the organ of Corti supported below by the basilar membrane and attached above to the tectorial membrane, plays a major role in the frequency analysis. In early fluid-structure interaction models of the cochlea, the mechanics of the cochlear partition were approximated by a series of single-degree-of-freedom systems representing the distributed stiffness and mass of the basilar membrane. Recent experiments suggest that the mechanical properties of the tectorial membrane may also be important for the cochlea frequency response and that separate waves may propagate along the basilar and tectorial membranes. Therefore, a two-dimensional two-compartment finite difference model of the cochlea was developed to investigate the independent coupling of the basilar and tectorial membranes to the surrounding liquid. Responses are presented for models using two- or three-degree-of-freedom stiffness, damping, and mass parameters derived from a physiologically based finite element model of the cochlear partition. Effects of changes in membrane and organ of Corti stiffnesses on the individual membrane responses are investigated. [ABSTRACT FROM AUTHOR]