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Advances in soft sensors coupled with machine learning are enabling increasingly capable wearable systems. Since hand motion in particular can convey useful information for developing intuitive interfaces, glove-based systems can have a significant impact on many application areas. A key remaining challenge for wearables is to capture, process, and analyze data from the high-degree-of-freedom hand in real time. We propose using a commercially available conductive knit to create an unobtrusive network of resistive sensors that spans all hand joints, coupling this with an accelerometer, and deploying machine learning on a low-profile microcontroller to process and classify data. This yields a self-contained wearable device with rich sensing capabilities for hand pose and orientation, low fabrication time, and embedded activity prediction. To demonstrate its capabilities, we use it to detect static poses and dynamic gestures from American Sign Language (ASL). By pre-training a long short-term memory (LSTM) neural network and using tools to deploy it in an embedded context, the glove and an ST microcontroller can classify 12 ASL letters and 12 ASL words in real time. Using a leave-one-experiment-out cross validation methodology, networks successfully classify 96.3% of segmented examples and generate correct rolling predictions during 92.8% of real-time streaming trials. Author

This paper focuses on the control of nonlinear systems with redundant actuation, where the number of actuators is higher than the controllable degrees of freedom. To effectively handle actuation redundancy, we propose a control allocation (CA) approach that combines numerical optimization methods with control Lyapunov and control barrier functions. The inclusion of control Lyapunov functions enhances the CAs ability to minimize performance loss in the presence of unattainable virtual inputs. The integration of barrier functions allows the CA to exploit actuation redundancy to enforce safety constraints. The proposed approach is applied to the control of an over-actuated system, demonstrating superior transient and safety properties when compared to classical CA algorithms.

This article provides a general framework for the use of low-impedance displacement sensors mounted on the links of a serial robot to provide an intuitive physical human–robot interaction. A general formulation is developed to handle the motion guidance problem, i.e., the mapping of the measured motion of the sensors into the required robot joint motions to provide intuitive responsiveness. The formulation is general and can be applied to any architecture of serial robot with any number of displacement sensors each having an arbitrary number of degrees of freedom. Then, the design of a novel three-degree-of-freedom low-impedance displacement sensor is presented as a particularly effective instantiation of the general concept. Partial force balancing is used to reduce the required elastic return action, thereby ensuring the low impedance of the interaction. A prototype of a three-degree-of-freedom displacement sensor is then introduced. Two such sensors are mounted on the links of a custom-built five-degree-of-freedom robot in order to demonstrate the proposed approach. Experimental results are provided and comparisons with other collaborative robots are given. It is shown that the proposed sensors and motion guidance approach yield very intuitive low-impedance interaction involving very low interaction forces.

Beam scanning antenna brings new opportunities to reduce the data collision of multi-node communication in the Internet of Things (IoT). This paper proposes a new type antenna design scheme that can be used for IoT relay communication. A programmable beam scanning antenna without phase shifters operating in the X-band is designed to evaluate the feasibility of this scheme. The integrated design of excitation source and phasemodulated structure greatly reduces the profile of the antenna and improves the integrated degrees of freedom with other equipment. By switching the state of the PIN diode loaded on each element, different radiators can be selected and the direction of current polarization on elements can be adjusted to change the radiation phase. Furthermore, the diode states are encoded by the holographic antenna theory and controlled by the FPGA controller to realize programmable beam scanning. One element, two-element and 1-D array containing 32 elements are fabricated and measured. Experimental results are in good agreement with the simulation data. The operating bandwidth is 7.5% at 10GHz while the beam scanning range of the array is -60∘ 60∘, with a good scanning accuracy and stability. The proposed low-profile beam scanning antenna can provide stable communication services to multiple users and smart devices as a new type of beam scanning array antenna solution for the IoT application, which is beneficial to this field.

In rotor dynamics, blades are normally modelled as a slender beam, in which elastic deformations are coupled with each other. To identify these coupling effects, new rigid-flexible structural model for helicopter rotor system is proposed in this paper. Finite rotations of the whole blade (on flapwise, lagwise, and torsional) are described as three global rigid degrees of freedom. The nonlinear deformation geometrics of the beam is built on geometrically exact beam theory. New expressions for blade strain energy, kinetic energy, and virtual work of various kinds of external forces are derived as functions of finite rotations and elastic deformations. To quantify the coupling characteristics, following the definition of coupling factor in electromagnetics, a new coupling factor between two modal components on each mode is introduced in modal analysis. Simulations show that the new structural model is highly capable of solving static and dynamic problems in rotor dynamic and the maximum deformation that moderate deformation beam theory can predict might be 15% of beam length. After the new coupling factor is applied to study structurally coupled characteristics of rotor blade, it can be concluded that closeness of natural frequencies likely indicates considerable coupling between corresponding DOFs in structure.

Pole-phase modulation based multiphase induction motor (PPMIM) drives possess the capability of providing an extended range of speed-torque for high power traction application with the available additional degrees of freedom in the multiphase machine. As observed in previous open-loop results of PPMIM drives presented in the literature, the transient currents often exceed twice the rated currents. To address this issue, this paper focuses on the modelling and advanced control of the PPMIM drives during all possible pole-phase combinations. The dynamic mathematical modelling of the PPMIM in actual phase variable domain is presented in detail. Since this model involves time-dependent inductances and torque, the machine model equations are transformed into dq domain using transformation matrices. The transformation matrices, modelling equations in the arbitrary reference frame and multiphase inverter are modelled by considering all parameters of possible pole-phase combinations. Based on the proposed modelling equations, an indirect field oriented control (IFOC) is implemented for PPMIM drives for smoother operation in all possible modes of operation. The modelling equations, as well as IFOC of PPMIM drive, are implemented in MATLAB to illustrate the behaviour of machine during transients as well as different load torques. The proposed concepts are also validated on laboratory setup and the hardware results are demonstrating the smoother transition as well as steady state operation of PPMIM drive in pole changeovers as well as both pole-phase combinations.

Soft-bodied robotic manipulators have great potential for use in minimally invasive surgery, owing to their advantages of high flexibility with infinite degrees of freedom (DOF). One of the potential applications is to perform blood suctioning, which is inevitable during the surgery. To attain higher efficiency in suctioning, the robotic tip should remain vertical while moving along on the work surface. Motivated by this application, this paper presents a novel soft robot design and its control scheme to properly configure the tip of a two-segment soft robot while following a planned trajectory on the work surface. Aiming to reduce the incision size and the possibility of infection, a 3D-printed soft-bodied manipulator utilizing the cable-driven mechanism with a diameter of 9 mm was designed and fabricated. An additional DOF was added through a motorized insertion stage. The robot system was modeled using piecewise constant-curvature assumption, and an RGB-D vision was employed to enhance the accuracy of the kinematic-based controller. Performances of the tip positioning and verticalizing were evaluated via simulation, and further verified through experiments. The results confirm that the manipulator is capable of following different trajectories at various velocities while keeping its tip vertical. Compared to other similar works, our results are satisfactory with an RMSE of trajectory tracking within 7 mm, and a maximum angular deviation of 6. Fluid suction experiments were conducted to demonstrate its effectiveness for automated 3D suction. This work offers a new tool to support the surgeons for surgical blood suction.

Continuum and soft robots can leverage complex actuator shapes to take on useful shapes while actuating only a few of their many degrees of freedom. Continuum robots that also grow increase the range of potential shapes that can be actuated and enable easier access to constrained environments. Existing models for describing the complex kinematics involved in general actuation of continuum robots rely on simulation or well-behaved stress-strain relationships, but the non-linear behavior of the thin-walled inflated-beams used in growing robots makes these techniques difficult to apply. Here we derive kinematic models of single, generally routed tendon paths on a soft pneumatic backbone of inextensible but flexible material from geometric relationships alone. This allows for forward modeling of the resulting shapes with only knowledge of the geometry of the system. We show that this model can accurately predict the shape of the whole robot body and how the model changes with actuation type. We also demonstrate the use of this kinematic model for inverse design, where actuator designs are found based on desired final robot shapes. We deploy these designed actuators on soft pneumatic growing robots to show the benefits of simultaneous growth and shape change., 21 pages, 18 figures

The low-order lumped parameter thermal models (LPTMs) are one of the most competitive online approaches to estimate the critical temperatures in electrical machines. Firstly, this paper explores the correlation between the conventional high-order and low-order LPTMs and then presents some critical modelling guidelines of low-order LPTM together with an improved four-order LPTM. Secondly, a simple dynamic quasi-linear model (DQM) is proposed to define convection thermal resistances, which can be used in both conventional high-order and low-order LPTMs. The application of DQM can improve the estimation accuracy by indirectly introducing more degrees of freedom, which is especially beneficial for the magnet temperature estimation in the low-order LPTM due to its highly abstract rotor thermal modelling. Finally, a prototype permanent magnet synchronous machine is used for experimental validation under different operation profiles.

Objective: In this study, a novel hybrid predictive musculoskeletal model is proposed which has both motion prediction and muscular dynamics assessment capabilities. Methods: First, a two-dimensional (2D) skeletal model with 10 degrees of freedom is used to predict a symmetric lifting motion, outputting joint angle profiles, ground reaction forces (GRFs), and center of pressure (COP). These intermediate outputs are input to the scaled musculoskeletal model in OpenSim for muscle activation and joint reaction load analysis. Finally, the experimental validation is carried out. Results: Static Optimization tool is used to estimate the muscle activation data in OpenSim for the predicted lifting motion. Joint reaction forces of the lumbosacral joint (L5-S1) are generated using the OpenSim Joint Reaction analysis tool. The predicted joint angles, muscle activations, and peak joint reaction forces are compared with experimental data and data from literature to validate the hybrid model. Conclusion: The proposed hybrid model combines the skeletal models rapid motion prediction with OpenSims complex muscular dynamics assessment, and it can serve as a new generic tool for motion prediction and injury analysis in ergonomics and biomechanics.

In practice, offshore cranes are effective transportation tools used on ships. Different from land-fixed cranes, offshore cranes work in the noninertial frame, which are usually affected by different disturbances. Therefore, the control problem of offshore cranes is much more difficult . Till now, only few control methods have been proposed for offshore cranes, which are usually designed for planar offshore cranes, while the more practical three-dimensional (3-D) movements are ignored . Considering these facts, in this article, we focus on the control problem of a 5 degrees of freedom (DOF) offshore crane in 3-D space with persistent ship yaw and roll perturbations and propose an effective output feedback control method. Specifically, we first present an elaborate coordinate transformation method to deal with ship perturbations. Then an energy-like function is constructed based on the transformed model, and then by designing some auxiliary signals, an output feedback method is designed with rigorous mathematical analysis to prove the closed-loop asymptotic stability results. As far as we know, the proposed method is the first control method designed for 5-DOF offshore cranes without any linearization, which only uses output signals. Finally, experimental results are included to verify the performance of the proposed method.

The adequate coupling of dissimilar materials and structural element types provides effective engineering designs. Particularly, it enables high stiffness and low weight mechanical components, which are largely desired in numerous applications. Besides, Isogeometric Analysis (IGA) has recently stood out as a robust and accurate approach for the mechanical modelling of complex 3D engineering designs directly from Computer-Aided Design (CAD) tools. In this context, this study presents nonlinear Isogeometric Boundary Element Method (IGABEM) formulations for the effective mechanical modelling of nonhomogeneous 3D structural systems reinforced by embedded fibres. The IGABEM based on NURBS surfaces represents the solid whereas the 1D approach of BEM models the reinforcements, which characterises a 1DBEM/IGABEM coupling technique. The sub-region technique enables the nonhomogeneous system modelling whereas connection 1DBEM elements allow for crossing reinforcements along boundary interfaces without the need for surfaces remeshing. Thus, the CAD model information can be straightforwardly used in the mechanical model. Nonlinear time independent formulations are presented accounting for both elastoplastic and bond-slip behaviours. Besides, linear and nonlinear time dependent formulations are presented herein applying the Kelvin-Voigt and Boltzmann viscoelastic rheological models. Five applications illustrate the accuracy and robustness of the proposed formulations. The IGABEM formulations lead to accurate and stable results, in addition to efficient modelling. Besides, it demonstrates excellent performance considering the computational time consuming and the total number of degrees of freedom in each application.

This paper presents a robust output-feedback control scheme for the stabilization of a class of non-linear underactuated mechanical systems in presence of coupled disturbances. The scheme is based on the so-called coupled sliding-mode control, i.e., no transformation into the normal form is required. The proposed output approach is composed of a Super-Twisting Controller and a High-Order Sliding-Mode Observer that robustly stabilize the origin of the system asymptotically. All of the results are proven by Lyapunov approaches. The proposed approach is validated by means of simulations and experimental results on a 4 degrees of freedom (DOF) underactuated crane.

This paper presents a new active controller technique effect of functionally graded (FG) cylindrical shell structure model within joint harmonic and parametric excitations. The new active controller involves Nonlinear Proportional-Derivative (NPD) plus Negative Cubic Velocity Feedback (NCVF) as a new nonlinear control method (NPDCVF). The motivation of this study is the well-known observation that NPDCVF control method can offer a means to improve the performance of plant systems. The coupled nonlinear differential equations with two modes have been derived applying the von Karman nonlinear theory, Galerkin’s process, and the static condensation technique. Static condensation is the process of decreasing the number of free displacements or degrees of freedom. We have added other three different controller methods over the structure to select the best controller. The three applied controller methods to the considered structure are: Integral Resonant Control (IRC), Positive Position Feedback (PPF), and Nonlinear Integral Positive Position Feedback (NIPPF) which are applied to the considered structure. We establish that the best one for dipping the high vibration amplitudes is the NPDCVF as a new controller. The perturbation technique is useful to solve the present model including quadratic and cubic nonlinearities subjected to mixed harmonic and parametric forces within the simultaneous primary resonance case ( Ω = ω 1 , Ω = ω 2 ) as the worst resonance case of the system. All numerical outcomes have been completed with the help of MATLAB Ra 18.0 program software over the investigated model. The obtained results have proved that this new controller is excellent for improving the structure by reducing the risky vibrations caused during primary resonances. Frequency response equations have helped in observing the stability examination of the obtained numerical solutions. The actions of several factors performed on the controlled model have been examined and described. Some comparisons have also been prepared with the available recent published papers of a similar model.

In this paper, a joint design for cooperative spectrum sharing framework of multiple-input multiple-output (MIMO) radar and MIMO communication system in radar multi-target optimization is proposed. The interesting design Degrees of Freedom (DOFs) include radar transceiver beamforming vector and communication system codebook, whereby the designed problem is a constrained minimization of total radar effective interference power under power limited conditions and communication rate constraint guaranteeing both the two coexistence systems performance. As to the non-convex multi-variables problem, an alternating iteration approach is developed to solve the three suitably transformed subproblems, the closed form solutions are derived, and the convergence of the proposed design is guaranteed. Finally, numerical results show the spectrum sharing performance of the proposed approaches.

This paper presents a current control methodology equipped with a state and disturbance observer (SDO) to address the uncertain disturbance problem existing in an LCL-type single-phase grid-tied inverter system. In this methodology, disturbance feedforward compensation and full-state feedback of the combined proportional-integral (PI) regulator are utilized to provide more degrees of freedom for a robust design of the controller. In order to realize this technology without additional sensors, a reduced-order SDO is designed by decoupling the real inverter plant into a nominal model with lumped uncertainty and disturbance (LUD), making the estimation results more robust adaption for system uncertainty. Furthermore, the upper bound of the LUD is concerned and innovatively used to evaluate the size of the uncertainty region of the LUD estimated by the observer, that may be important to anti-disturbance control. Other system performances, such as grid current distortion suppression and robust stability, are also analyzed. Finally, the effectiveness of the proposed control strategy is fully supported by simulation and experimental results.

Rail corrugation (RC) is one of the most important indicator to evaluate the quality of rail, which is used to describe the irregularity of rail surface, also known as rail's vertical flatness. However, the definition of RC is still an empirical description for low-speed measurement devices. In this paper, the process of RC measurement is divided into two steps, sampling and extraction, which helps the users to understand more clearly. Then a new mathematic model is proposed to make the process of RC's extraction be an executable operation for machine calculation. The model adopts a new concept of flexible virtual ruler to perform sliding filtering on an overall rail and extract the instantaneous RC with a successive approximation algorithm according to user's requirements and national standards. The proposed FVR model can not only be fully compatible with the traditional extraction method of RC, but also provide a new idea for evaluating RC's quality. Comparing with the current popular methods, the proposed model gives a meaningful strategy for rail maintenance with a complete mathematic description having more degrees of freedom. Experiment results demonstrate its validity and reliability for both indoor simulation and actual outdoor experiments.

Mini-unmanned aerial vehicle (UAV)-based bistatic synthetic aperture radar (BiSAR) is widely used due to its flexibility of system topology selection and simplicity. However, the motion compensation (MOCO) of the system is more difficult because the perturbance of mini-UAV platforms is greater and the spatial variance is more complex. In addition, the degrees of freedom of motion error are twice as those of the monostatic SAR. In this article, a novel MOCO algorithm based on a motion sensitivity model is proposed. First, a BiSAR system motion sensitivity model is established to assess the importance of each motion component error. Second, a novel MOCO method is proposed based on the determination of the main motion errors. Third, the proposed algorithm is validated by both simulations and real data sets. The final well-focused image suggests that the variant phase error after compensation with the new algorithm is much smaller than that with the traditional one.

For drag-free satellites, one core technology required to achieve the mission requirements is the capture control of the test mass after release. The purpose of capture control is to avoid collisions between test mass and satellite cavity. Currently, there are few studies concerning the capture control of test mass after release. This paper presented a high-precision capture control method for the test mass release, which covers attitude-orbit modeling with 12 degrees of freedom, RBF neural network adaptive sliding mode controller design, actuation waveforms selection, actuation strategy selection, performance results, and contrast analysis.

Even though multiphase machines have inherent fault tolerant capabilities due to their additional degrees of freedom, fault diagnosis still plays an important role to continuously monitor these machines and thus prevent critical failures. High resistance connections (HRCs) are one of the most common electric faults in electrical machines, being caused by damaged power connections. These faults create a current unbalance, increasing both the machine losses and torque pulsations and can eventually lead to open-phase faults (OPFs). This paper proposes an online fault diagnostic method to detect HRCs and OPFs in six-phase permanent magnet machine drives. The proposed method is intended for application in electric drives controlled by a predictive current control strategy and does not require the installation of extra hardware. Two variants of the fault diagnostic algorithm are presented in this work: one based on the analysis of the secondary components of the reference current errors and another variant based on the prediction current errors. Experimental results demonstrate the effectiveness and sensitivity of the proposed diagnostic method for the detection of these types of fault.

The paper presents a wall-climbing robot featuring self-compliance for variable curvature facades. The high payload and maneuverability make it highly potential in heavy-duty operation of industrial applications. The robot consists of two traction modules and one link module. Each traction module is equipped with magnetic adhesion and crawler traction submodules. The two traction modules are connected by the link module with 4 degrees of freedom (DoF) of passive compliance. Variable curvature facade self-compliance is achieved by the passive compliant link module, which results in the attitude change decoupling of the two traction modules. The attitude can be adjusted under the effect of magnetic adhesion force to comply with the curvature variations. High payloads are achieved by the large contact area between the crawler and the surface. Omni-directional high maneuverability is enabled by the speed difference between the motors of two traction modules. The robot can maneuver in any direction on the surface with a minimum radius of 1 m and carry 36 kg payload on vertical surfaces.

An alternate transmitting mode (ATM) is an important synthetic aperture radar (SAR) imaging mode as it can provide rich waveform design degrees of freedom to improve the system performance, especially to mitigate range ambiguities. However, the azimuth ambiguity issue caused by the differences between the autocorrelation functions of transmitted waveforms is ignored in existing studies. In this article, a deep understanding of the ambiguities in the ATM allows a correct evaluation of the ambiguity-to-signal ratio and the design of quasi-orthogonal nonlinear frequency modulation (NLFM) waveforms optimized for ambiguity suppression. Moreover, a novel azimuth compensation method is developed to remove the azimuth ambiguities caused by waveform diversity. Finally, detailed simulation experiments are carried out to verify the theoretical analysis.

To overcome the “multiplicative fading effect” introduced by passive reconfigurable intelligent surface (RIS), the concept of active RIS has been recently proposed to amplify the radiated signals. However, the existing fully-connected architecture of active RIS consumes high power due to the additionally integrated active components. To address this issue, we propose the sub-connected architecture of active RIS. Different from fully-connected architecture, where each element integrates a dedicated power amplifier, in the sub-connected architecture, multiple elements control their phase shifts independently but share a same power amplifier, which significantly reduces the number of power amplifiers for power saving at the cost of fewer degrees of freedom (DoFs) for beamforming design. Fortunately, our analysis reveals that performance loss introduced by the sub-connected architecture is slight, indicating that it can achieve much higher energy efficiency (EE). Furthermore, we formulate the EE maximization problem in the active RIS-aided system for both architectures and develop a corresponding joint beamforming design. Simulation results verify the proposed sub-connected architecture as an energy-efficient realization of active RIS.

While electromagnetic metasurfaces have been extensively studied for wavefront manipulations, the real three-dimensional manipulation of wavefront remains challenging. In this paper, an advanced strategy of non-interleaved multi-tasked metaplexer for three-dimensional manipulation of dual-helical electromagnetic wavefronts is reported. We first develop a general method to derive the metasurface phase distribution required to form the desired three-dimensional electric field patterns. Then, the spin-decoupled meta-atoms are designed to achieve this goal and further increase the degrees of freedom in electromagnetic manipulation. As a proof of concept, cascaded multi-plane digital images in the propagation direction are employed as the three-dimensional wavefronts, which are encoded into the spin-decoupled meta-atoms array, making the outputting circularly polarized waves carry different image information at different planes. Both the simulations and experiments verify the desirable three-dimensional wavefront manipulation capacities of our strategy for dual-helical states. Besides, this scheme can be further extended to achieve arbitrary energy allocation in three-dimensional space for dual-helical electromagnetic waves. Our strategy paves an alternative route for applications such as multiple-input multiple-output (MIMO) communications, multi-target radar detection, information storage, as well as three-dimensional microwave imaging.

Author(s): Yuan, Bofeng; Ismailoglu, Nilab; Jafar, Syed A | Abstract: Blind Interference Alignment (BIA) schemes create and exploit channel coherence patterns without the knowledge of channel realizations at transmitters, while beamforming schemes rely primarily on channel knowledge available to the transmit- ters without regard to channel coherence patterns. In order to explore the compatibility of these disparate ideas and the possibility of synergistic gains, this work studies the Degrees of Freedom (DoF) of the 2-user (?1 × ?1)(?2 × ?2) Multiple- Input Multiple-Output (MIMO) Interference Channel (IC) where Transmitter 1 is equipped with reconfigurable antennas and has no channel knowledge, while Transmitter 2 has partial channel knowledge but no reconfigurable antennas. Taking a fundamental dimensional analysis perspective, the main question is to identify which antenna configurations allow synergistic DoF gains. The main results of this work are two-fold. The first result identifies antenna configurations where both reconfigurable antennas and partial channel knowledge are individually beneficial, as those where ?1 l ?1 l min(?2,?2). The second result shows that synergistic gains exist in each of these settings, over the best known solutions that rely on either reconfigurable antennas or partial channel knowledge alone. Coding schemes that jointly exploit partial channel knowledge and reconfigurable antennas emerge as a byproduct of the analysis.

Funding Information: L.V.S.D., A.S.B., and M.H.F.B. acknowledge support from the Brazilian agencies Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). L.V.S.D., A.S.B., and M.H.F.B. also acknowledge Prof. Carlos de Carvalho for computational support at LFTC-DFis-UFPR and at LCPAD-UFPR. The authors acknowledge the beam time at the ISA synchrotron, Aarhus University, Denmark. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) CALIPSO under grant agreement n° 312284. P.L.V. acknowledges the Portuguese National Funding Agency (FCT) through research grant CEFITEC (UIDB/00068/2020), as well as his visiting professor position at Federal University of Paraná, Curitiba, Brazil. This contribution is also based upon work from the COST Action CA18212-Molecular Dynamics in the GAS phase (MD-GAS), supported by COST (European Cooperation in Science and Technology). Publisher Copyright: © 2023 The Authors. Published by American Chemical Society. High-resolution photoabsorption cross-sections in the 3.7-10.8 eV energy range are reinvestigated for nitromethane (CH3NO2), while for nitroethane (C2H5NO2), they are reported for the first time. New absorption features are observed for both molecules which have been assigned to vibronic excitations of valence, Rydberg, and mixed valence-Rydberg characters. In comparison with nitromethane, nitroethane shows mainly broad absorption bands with diffuse structures, which can be interpreted as a result of the side-chain effect contributing to an increased number of internal degrees of freedom. New theoretical quantum chemical calculations performed at the time-dependent density functional theory (TD-DFT) level were used to qualitatively help interpret the recorded photoabsorption spectra. From the photoabsorption cross-sections, photolysis lifetimes in the terrestrial atmosphere have been obtained for both compounds. Relevant internal conversion from Rydberg to valence character is noted for both molecules, while the nuclear dynamics of CH3NO2 and C2H5NO2 along the C-N reaction coordinate have been evaluated through potential energy curves at the TD-DFT level of theory, showing that the pre-dissociative character is more prevalent in nitromethane than in nitroethane. publishersversion published

Metasurfaces are 2D planar lattices of nanoparticles that allow the manipulation of incident light properties. Because of that attribute, metasurfaces are promising candidates to replace bulky optical components. Traditionally, metasurfaces are made from a periodic arrangement of identical unit cells. However, more degrees of freedom are accessible if an increasing number of structured unit cells are combined. The present study explores a type of dielectric metasurface with complex supercells composed of Mie-resonant dielectric nanocylinders and nanoscale rings. We numerically and experimentally demonstrate the signature of an optical response that relies on the structures sustaining staggered optically induced magnetic dipole moments. The optical response is associated with an optical antiferromagnetism. The optical antiferromagnetism exploits the presence of pronounced coupling between dissimilar Mie-resonant dielectric nanoparticles. The coupling is manipulated by engineering the geometry and distance between the nanoparticles, which ultimately enhances their effective magnetic response. Our results suggest possible applications in resonant nanophotonics by broadening the modulation capabilities of metasurfaces.

The study presents the results of linear dynamics of laminated glass panels with different curvatures. This is an actual task in the field of mechanical engineering, aviation, shipbuilding, energy, architecture, etc. Such composites are durable, easy to care for and have a wide range of design options. The aim of the work is to study the influence of the curvature parameter on the frequencies and modes of composites. The paper considers the linear characteristics for laminated glass with polyvinyl butyral interlayer. The article considers behavior of the triplex and the propagation of elastic waves in the linear state. The paper performs calculations using the finite element method in the framework of modal analysis in a three-dimensional formulation in the framework of a physical linear-elastic formulation. The study uses hexagonal finite element with 8 nodes with 3 degrees of freedom in each. This work model laminated glass with a curvature parameter ranging from 0 mm to 250 mm. The composite consisted of three layers: two glass layers thickness of each was 3 mm, and a polyvinyl butyral interlayer with 0.38 mm thickness. The size of the plates was 500×500 mm. As a boundary condition, the laminate was fixed on two opposite sides. The article performs mesh size convergence analysis. The results of natural frequencies in accordance with the curvature parameter are derived. The graphs of natural vibration modes are also shown, that give a clear view about the state of composites.

In the past decade, sparse arrays have aroused considerable attention for the ability to provide larger array aperture, more degrees of freedom (DOFs) and better estimation performance compared with the uniform linear array (ULA). In this paper, the problem of sparse array design is investigated for direction of arrival (DOA) estimation of non-circular (NC) signals, where both the difference co-array (DCA) and sum co-array (SCA) of physical array configuration can be utilized. Specifically, we first introduce a sliding array strategy which moves the array along the axis as a whole in order to reduce the co-array redundancy and enhance the consecutive DOFs of the sum-difference co-array (SDCA). Subsequently, we focus on the SCA of the conventional nested array (NA) and propose an approach which increases the DOFs of the SCA by relocating proper sensors. Furthermore, based on the above strategy and approach, we derive an extended sliding nested array (ESNA) with few redundant virtual sensors and an enhanced SCA, which can offer increased consecutive DOFs, enlarged virtual array aperture (VAA) and can thus bring high angle estimation accuracy of NC signals. Finally, analytic solutions and simulation results are given to validate the superiority of the proposed ESNA in terms of DOFs and estimation performance.

A Consistent One-Bay Frame (COBF) simplified model for the efficient estimation of Engineering Demand Parameters (EDPs) in Steel Moment Resisting Frames (SMRFs) with equal and unequal bay lengths is proposed. The geometry of the Substitute One-Bay Frame (SOBF) simplified model has been used, and the elastic and inelastic properties of the beams and columns in this model are determined using an energy consistent approach in a way that the energy balance is established between the members of the original SMRF and the SOBF simplified model. This way, the SOBF simplified model, which originally could only be used for MRFs with equal bay lengths, can now be used for MRFs with any geometric arrangement for bay lengths. Two 9- and 20-story SMRFs with equal bay lengths and two others with unequal bay lengths have been employed as structural models. The concentrated plastic hinges with modified Ibarra-Medina-Krawinkler (IMK) deterioration model have been used to apply strength and stiffness deterioration in numerical models. The accuracy of the proposed simplified model in estimating the EDPs along the height of the structure has been evaluated using Nonlinear Time History Analysis (NLTHA) under 22 pairs of FEMA P-695 earthquake records at the three seismic intensity levels of SLE, DBE, and MCE. The proposed simplified model has been compared with the Consistent Generic (CG) simplified model previously developed for SMRFs. This comparison suggests that the proposed simplified model is more efficient and reliable. Evaluating the seismic performance of the proposed simplified model using the conventional Incremental Dynamic Analysis (IDA) method and the Endurance Time Analysis (ETA) method at all of the seismic intensity levels reveals that using the COBF simplified model along with the ETA simplified method not only reduces the Degrees of Freedom (DOFs) of the original SMRF and the number of the NLTHAs but also leads to a proper estimation of the EDPs of the original SMRF from low seismic intensity level to collapse intensity level. Therefore, it is very helpful to use it for reducing the complexities of the new generation of Performance-Based Earthquake Evaluation.

Aiming at the problems of complex movement posture, many degrees of freedom and flexible movement of the human body’s lower limbs, a dynamic mathematical model of the squat posture was established, and analyzed the dynamic parameters of the hip joint, knee joint and ankle joint during the squatting posture of the wearable lower extremity exoskeleton robot. Based on the MATLAB simulation software, the motion characteristics of the squat posture are simulated and analyzed, and the results show that: in the process of squatting, the theoretical calculation results are quite different from the simulation results, indicating that the process of squatting is unstable. Therefore, based on the Zero Moment Point (ZMP) theory, a stable polygon of the squat posture is established, the instability rate is defined. From a qualitative and quantitative point of view, the effects of the squat posture and the change of the center of gravity (COG) on the motion stability are analyzed. An experimental platform was built and the experiment was performed to verify the COG and ZMP changes in the squatting posture, which verified the correctness of the theoretical calculation conclusions and the influence of COG changes on ZMP.

The success of the shooting of a moving vehicle can be achieved by providing barrel stabilization. In the meantime, it is necessary barrel angle must be positioned is instantaneously calculated accurately. In this paper, the required barrel elevation angle was calculated via artificial neural networks and the shooting success to a fixed target from a moving tank was investigated. For this purpose, a mathematical model of a tank, which has four degrees of freedom, with a barrel mounted on it has been utilized. The barrel is moved using an inverted slider mechanism. The system is driven hydraulically by considering the movement of the piston–cylinder pair in the inverted slider mechanism. The conventional PID control method has been preferred for angular position control of the barrel. Simulations have been performed with the MATLAB package program. System responses have been obtained graphically and the results have been presented in tabular form. It is seen that the pressure, flow, etc. obtained from the results overlap with the physical system. It is observed that the elevation angle of 10 degrees is captured and shot very well when the vehicle is stationary. In the moving state of the vehicle, the 10-degree elevation angle capture as well. In the moving case, there are tiny deviations in the target hit but these values can be considered to be reasonable levels. The deviation amount for the target 4 kilometers away is 16.28 meters.

Photodynamic therapy (PDT) has received increased attention over the past decades with the potential to non-invasively treat cancer via light exposure. Due to the limited light penetration depth (typically less than 1 cm), the PDT optical fiber typically needs to be placed close to the cancerous region to ensure the treatment outcome. In this paper, we present a novel soft robot laparoscope design that enables accurate and safe deployment of PDT optical fiber for pancreatic tumor treatment. To achieve this, the proposed soft robot is able to produce 3 degrees of freedom (DoF) motions: linear translation, in-plane bending, and axial rotation. A micro camera is integrated with the soft robot to provide intraoperative image guidance during the procedure. The robot forward kinematics model was obtained via a generalized calibration method, and the differential kinematics was derived analytically. Benchtop characterization results indicated that the soft robot was able to achieve 1.4 $\pm$ 0.4 mm position and 1.5 $\pm$ 1.1 degrees orientation accuracy, respectively. The robot was experimentally validated in two \textit{in vivo} mice models, and the results indicated that the proposed system successfully reduced the tumor size from 15.3 $mm^3$ and 11.8 $mm^3$ to 12.1 $mm^3$ and 4.4 $mm^3$ respectively.

Correlated with the trend of increasing degrees of freedom in robotic systems is a similar trend of rising interest in Spatio-Temporal systems described by Partial Differential Equations (PDEs) among the robotics and control communities. These systems often exhibit dramatic under-actuation, high dimensionality, bifurcations, and multimodal instabilities. Their control represents many of the current-day challenges facing the robotics and automation communities. Not only are these systems challenging to control, but the design of their actuation is an NP-hard problem on its own. Recent methods either discretize the space before optimization, or apply tools from linear systems theory under restrictive linearity assumptions in order to arrive at a control solution. This manuscript provides a novel sampling-based stochastic optimization framework based entirely in Hilbert spaces suitable for the general class of \textit{semi-linear} SPDEs which describes many systems in robotics and applied physics. This framework is utilized for simultaneous policy optimization and actuator co-design optimization. The resulting algorithm is based on variational optimization, and performs joint episodic optimization of the feedback control law and the actuation design over episodes. We study first and second order systems, and in doing so, extend several results to the case of second order SPDEs. Finally, we demonstrate the efficacy of the proposed approach with several simulated experiments on a variety of SPDEs in robotics and applied physics including an infinite degree-of-freedom soft robotic manipulator., 34 pages, 10 figures. Submitted to Autonomous Robots special issue of RSS 2020. arXiv admin note: text overlap with arXiv:2002.01397

Hydraulic servo shaking table is an essential testing facility to simulate the actual vibration situation in real time. As a parallel mechanism, multiaxis hydraulic servo shaking table shows strong coupling characteristic among different degrees of freedom. When the multiaxis hydraulic shaking table moves to one direction, some unnecessary related motions will appear in other directions, which seriously affect the control performance. An effective approach to decouple motions in command direction and in unnecessary related directions is an urgent need for a higher precision control performance. In this work, the coupling phenomena and reasons of the multiaxis hydraulic servo table are analyzed based on dynamic model of a multiaxis hydraulic servo shaking table. In this regard, multiaxis hydraulic servo shaking table with strong coupling within the physical space is transformed into a set of single-input single-output systems that are independent of each other in the modal space. A decoupling control strategy is proposed in modal space to restrain the coupling motions. Simulation and experimental results show that the proposed control strategy can effectively improve the control performance and the decoupling effect.

For tacking and localizing sources in the mobile wireless sensor network, underdetermined direction of arrival (DOA) estimation with high-accuracy is a crucial issue. In this paper, a novel sparse array configuration is developed for accurate DOA estimation from the perspective of sum-difference coarray (SDCA). As compared with most of the existing sparse array configurations, the proposed array can effectively reduce the overlap between difference coarray (DCA) and sum coarray (SCA) and can achieve more consecutive degrees of freedom (DOF), more sources can be resolved accordingly. Additionally, the proposed array has hole-free DCA and SDCA. Then, the concept of coarray redundancy ratio (CRR) is introduced for evaluating the coarray overlap quantitatively and the closed-form CRR expressions of the proposed array are derived in detail. Based on the good properties of the proposed array, vectorized conjugate augmented MUSIC (VCAM) is adopted for underdetermined DOA estimation. The theoretical propositions and numerical simulations demonstrate the superior performance of the proposed array in terms of CRR, consecutive DOF, and DOA estimation accuracy.

The sparse Multiple-Input–Multiple-Output radar has large array element spacing, which has a great significance for reducing the mutual coupling effects. In this paper, the authors propose a compensation sparse arrays with flexible inter-element spacing (CSA-FIS). Compared with the sparse arrays with flexible inter-element spacing (SA-FIS), the CSA-FIS improves the situation in that the number of virtual sensors significantly decreases when the inter-element spacing of two sub-array is not coprime. Under the guarantee of lower mutual coupling effects, the system degrees of freedom (DOFs) and the number of consecutive virtual sensors are also improved. Meanwhile, a pre-processing DFT-compressed sensing (D-CS) algorithm is proposed, with the purpose to solve the problem that the traditional CS algorithm has a high calculation cost when all non-zero parameters must be estimated. Numerical simulations demonstrate the superiority of the CSA-FIS in terms of DOFs and estimation accuracy when compared with SA-FIS. Moreover, compared with the traditional CS algorithm, the D-CS has lower computational complexity.

Generalized parallel mechanisms with a configurable moving platform have become popular in the research field of parallel mechanism. This type of gripper mechanism can be applied to grasp large or heavy objects in different environments that are dangerous and complex for humans. This study proposes a family of novel (5 + 1) degrees of freedom (three translations and two rotations plus an additional grasping motion) gripper mechanisms based on the generalized parallel mechanisms with a configurable moving platform. First, the configurable moving platform, which is a closed loop, is designed for grasping manipulation. The hybrid topological arrangement is determined to improve the stiffness of the manipulator and realize high load-to-weight ratios. A sufficient rule based on Lie group theory is proposed to synthesize the mechanism. The hybrid limb structure is also enumerated. A family of novel gripper mechanisms can be assembled through the hybrid limbs by satisfying the rule. Two examples of the gripper mechanisms with and without parallelogram pairs are shown in this study. A kinematic analysis of the example mechanism is presented. The workspace shows that the mechanism possesses high rotational capability. In addition, a stiffness analysis is performed.

In this paper, a novel spatial support mechanism for planar deployable antennas is designed based on the motion principle of planar deployable antennas and the spatial mechanism theory. The composition principle of the novel mechanism and its geometric characteristics are analyzed, and its degrees of freedom are calculated based on the constraint topological diagram. Subsequently, kinematic analysis is conducted, and the angular velocity, linear velocity, and linear acceleration of each component in the mechanism are calculated. Then, numerical calculation and simulation are performed to verify the correctness of the theoretical analysis results. The performance analysis of the spatial support mechanism is completed. A prototype of the proposed support mechanism is developed and tested to validate the feasibility of the mechanism principle. The present work can provide reference for the design and engineering application of this type of mechanisms.

We introduce an alternative approach for wireless body area networks (WBANs) that rely on wearable planar magnetoinductive waveguides (MIWs) placed upon the body to reduce loss by 50–60 dB versus the conventional state of the art. Compared to our recently reported MIW WBANs that rely on axial rather than planar electrically small resonant loops, this approach: 1) overcomes the inherent constraints of anatomical geometry; 2) provides uniform WBAN implementations across the entire human body or different human bodies; 3) allows for frequency scalability over a wide frequency range; 4) exhibits more degrees of freedom for design optimization; and 5) provides significantly better performance (28.92 dB loss improvement for an example 5-loop design). In this work, we discuss the operating principle and validate the idea via a theoretical dispersion model. Numerical full-wave simulations are then presented and further validated via in vitro experimental results on a canonical torso model. Design optimization is subsequently performed for performance (loss and bandwidth), accompanied by a reasoning analysis based on the theoretical dispersion model. Specific absorption rate (SAR) studies confirm electromagnetic safety, while frequency scalability and tolerance to anatomical curvature further highlight its potential. Overall, the reported approach significantly advances the state of the art and shows promise for low-loss WBANs of the future.

In this paper, a downlink (DL) precoding scheme is introduced for time-division-duplex (TDD) multi-cell multi-user 3D massive MIMO/full-dimension MIMO (FD-MIMO) systems. A pre-beamformer based on uplink direction-of-arrival (DoA) is incorporated with interference alignment (IA) scheme to provide more degrees of freedom for each cell. We analyze the feasible conditions of applying IA schemes and provide the corresponding precoding schemes for different inter-cell interference scenarios. Simulation results show that the introduced IA-DoA-based multi-cell multi-user precoding and power allocation scheme significantly outperform the existing IA-based precoding strategies for FD-MIMO systems.

The improvement of the angular resolution of radar sensors is one of the crucial goals of current radar research. A promising approach to achieve this goal is inspired by the ears of a fly called Ormia ochracea. The working principle was adapted for antennas, and the so-called biomimetic antenna arrays (BMAAs) aroused the interest of several research groups. In this work, BMAAs are incorporated into multiple-input multiple-output (MIMO) arrays, a very common approach of improving the angular resolution, to gain more degrees of freedom in array design. The MIMO BMAAs are modeled utilizing the effective biomimetic antenna distance, a fundamentally new measure introduced in this article to translate the special biomimetic phase progression into a spatial quantity. We present straightforward antenna configurations but also describe how a genetic algorithm can be utilized to optimize both antenna positions and BMAA parameters. The proposed arrays show various beneficial effects such as a wider angular range for unambiguous angle estimation or a narrower beamwidth. The impact of MIMO BMAAs on the angular resolution is thoroughly analyzed both theoretically and by radar measurements in the range of 77 GHz. The measurements confirm the modeling method very well and show a significant increase in the angular separability., publishedVersion

Time delays, model uncertainties, faults, and disturbances are frequently the main causes of performance degradation and instability in industrial process control. This article presents a fault-tolerant robust model-predictive control design for processes that involve the above effects and process constraints. The uncertainties are modeled into a polytopic affine form based on variations in the system's parameters. A new model based on augmentation of the state variables and tracking error is used that provides increased degrees of freedom for the control design and guarantees tracking performance. A parameter-dependent Lyapunov–Krasovskii functional is used to design a state-feedback control that reduces the conservatism of the conventional approach and ensures robust stability and tracking performance of the closed-loop system. At each sampling instant, a control action is computed by solving an online constrained optimization problem that minimizes the upper bound of the “worst-case” performance index. Finally, the proposed framework is employed for the fault-tolerant control of a continuous stirred tank reactor to demonstrate its effectiveness in mitigating actuator faults and tracking the desired set point.

We developed and validated a multi-segment foot and ankle model for human walking and running. The model has 6-segments, and 7 degrees of freedom; motion between foot segments were constrained with a single oblique axis to enable triplanar motion [Joint Constrained (JC) model]. The accuracy of the JC model and that of a conventional model using a 6 degrees of freedom approach were assessed by comparison to segment motion determined with biplanar videoradiography. Compared to the 6-DoF model, our JC model demonstrated significantly smaller RMS differences [JC: 2.19° (1.43-2.73); 6-DoF: 3.25° (1.37-5.89)] across walking and running. The JC model is thus capable of more accurate musculoskeletal analyses and is also well suited for predictive simulations.

Assistive technologies (ATs) often have a high-dimensionality of possible movements (e.g., assistive robot with several degrees of freedom or a computer), but the users have to control them with low-dimensionality sensors and interfaces (e.g., switches). This paper presents the development of an open-source interface based on a sequence-matching algorithm for the control of ATs. Sequence matching allows the user to input several different commands with low-dimensionality sensors by not only recognizing their output, but also their sequential pattern through time, similarly to Morse code. In this paper, the algorithm is applied to the recognition of hand gestures, inputted using an inertial measurement unit worn by the user. An SVM-based algorithm, that is aimed to be robust, with small training sets (e.g., five examples per class) is developed to recognize gestures in real-time. Finally, the interface is applied to control a computer’s mouse and keyboard. The interface was compared against (and combined with) the head movement-based AssystMouse software. The hand gesture interface showed encouraging results for this application but could also be used with other body parts (e.g., head and feet) and could control various ATs (e.g., assistive robotic arm and prosthesis).