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The present paper develops a new procedure for finding the most unfavorable long-period excitation for isolated building structures based on the probabilistic critical excitation method. The upper bound of earthquake input energy per unit mass is considered the problem's constraint, and a modified power spectral density (PSD) function is proposed to conform to the new constraint. It is shown that the new constraint can be used as a criterion to estimate the possible range of input energy of similar earthquakes. In addition, the new PSD function can control the excitation's intensity. Finally, three base-isolated shear buildings modeled as multi degree of freedom systems with nonproportional damping are considered, and the critical excitations for each model are found based on the proposed method. To examine the reliability of the results, three actual accelerograms with a considerably high level of total input energy are selected as benchmarks and linear dynamic analyses are conducted using these accelerograms along with the generated critical excitations. The results show that the generated long-period excitations can better estimate the structural behavior (i.e., maximum displacement, drift, and absolute acceleration of stories) than the actual benchmark accelerograms. [ABSTRACT FROM AUTHOR]

AbstractTraditionally, Gaussian assumption, implied by the Wiener process, is widely admitted for modeling degradation processes. However, when degradation data exhibit heavy tails, this assumption is not suitable. To overcome this limitation, this article proposes a novel class of tail-weighted multivariate degradation model, which is built upon Student-t process. The model is able to account for both between-unit variability and process dependency, while allows adjusting the tail heaviness through tuning the parameter of the degree of freedom. For reliability assessment, we derive the system reliability function and present an efficient Monte Carlo method for its evaluation. Further, we introduce an expectation-maximization algorithm for parameter estimation and design a bootstrap method for interval estimation. Comprehensive simulation studies are conducted to validate the effectiveness of the inference method. Finally, the proposed methodology is applied to analyze two real-world degradation datasets. [ABSTRACT FROM AUTHOR]

AbstractModel degrees of freedom ( df ) is a fundamental concept in statistics because it quantifies the flexibility of a fitting procedure and is indispensable in model selection. To investigate the gap between df and the number of independent variables in the fitting procedure, Tibshirani (2015) introduced the search degrees of freedom ( sdf ) concept to account for the search cost during model selection. However, this definition has two limitations: it does not consider fitting procedures in augmented spaces and does not use the same fitting procedure for sdf and df . We propose a modified search degrees of freedom ( msdf ) to directly account for the cost of searching in either original or augmented spaces. We check this definition for various fitting procedures, including classical linear regressions, spline methods, adaptive regressions (the best subset and the lasso), regression trees, and multivariate adaptive regression splines (MARS). In many scenarios when sdf is applicable, msdf reduces to sdf . However, for certain procedures like the lasso, msdf offers a fresh perspective on search costs. For some complex procedures like MARS, the df has been pre-determined during model fitting, but the df of the final fitted procedure might differ from the pre-determined one. To investigate this discrepancy, we introduce the concepts of nominal df and actual df , and define the property of self-consistency, which occurs when there is no gap between these two df ’s. We propose a correction procedure for MARS to align these two df ’s, demonstrating improved fitting performance through extensive simulations and two real data applications. [ABSTRACT FROM AUTHOR]

The present article aims to develop a finite element formulation for FGM plates carrying concentrated and distributed mass. First-order shear deformation theory with consideration of physical neutral surface has been employed. Nine noded isoparametric element with five degrees of freedom at each node is used for this finite element analysis. To understand the effect of grading pattern under overhead mass carrying conditions, three types of FGMs have been analyzed. The effect of non-dimensional parameters such as aspect ratio, thickness ratio, power index, the intensity of mass etc. are extensively studied. It will bring new insights to the field of FGM structures. [ABSTRACT FROM AUTHOR]

High-speed maglev system is a hot research topic nowadays in the field of high-speed ground transportation. Characteristics of the track irregularity of high-speed maglev system is quite different due to its contactless vehicle-rail relationship and segmented track compared with traditional railway. However, research on maglev track irregularity is still insufficient. This paper summarises, for the first time, the track inspection data collected on Shanghai Maglev Demonstration Line (Shanghai Line) since 2006, and describes the main filtering methods and parameters for acceleration and gap signals, taking into account the characteristics of maglev track. Track irregularity is then determined using the inertial measurement principle. The measured track spectrum on Shanghai Line calculated by the Welch method obeys a chi-square distribution with 2 degrees of freedom, indicating that different track qualities can be transformed by probability methods according to the research requirements. Based on the samples obtained over the past 15 years, and referring to the seven-parameter model of the railway system, a high-speed maglev track spectrum is obtained by the fitting method, parameters of which are obtained by applying the damped least squares method. Preliminary vehicle dynamic analysis is conducted utilising the inverted excitations derived from the measured spectrum of the Shanghai Line. [ABSTRACT FROM AUTHOR]

In many European countries, regional planning is an established institutional framework. In recent years we have observed a resurgent research interest in regional planning with a specific focus on governance and institutional design and on the strategic and practical relevance of regional planning in pursuing sustainable development. However, in Sweden, regional planning traditionally has a weak position in practice as well as in research. Yet over the past 15 years, we have seen an increasing political interest in experimenting with different forms and formats of regional planning. In this paper, we explore the emerging logics of non-statutory regional planning, which the majority of Swedish regions have chosen. Drawing upon a qualitative research design we identify, compare and discuss three different logics and their inherent rationales, practices, challenges and prospects. Our analysis shows that our three case regions can do very little non-statutory regional planning unless they are part of properly working multi-level networks, and have well-established regional informal arenas for interaction and political backing. More specifically, we point at a number of tensions caused by the large degree of freedom to design non-statutory regional planning, which foster conflicts, confusion and insecurity. [ABSTRACT FROM AUTHOR]

Mobile manipulators require whole-body inverse kinematics (IK), encompassing both the mobile base and arm, to execute manipulation tasks. One of the challenges associated with whole-body IK is the redundancy of degrees of freedom when combining those of the mobile base and arm, which generates an infinite number of solutions. Therefore, in this study, we focus on the trend in mobile manipulators where the positional precision of the mobile base is lower than that of the manipulator. We propose a definition for the robustness value to base position control error and discuss a methodology to quickly obtain robust whole-body IK solutions. In an assessment utilizing a dataset that simulates domestic environments and a human support robot, which is a research platform for mobile manipulators designed to operate with humans, we validated that the quick acquisition of IK solutions robust to base position control error is achievable. In addition, we integrated the proposed IK approach into motion planning and evaluated its performance. Our results revealed that motion planning integrated with the proposed IK approach was superior to conventional methods in terms of both computation time and robustness for base position control error. [ABSTRACT FROM AUTHOR]

In this paper, a pulse shifting approach with phase-only weighting is proposed for a cosecant-squared radiation pattern time-modulated linear array (TMLA) synthesis. The sidelobe level (SLL) of fundamental signal and maximum sideband levels (SBLs) of harmonic signals is simultaneously reduced. This is achieved by controlling both the phase and the periodic switching time sequence of each element of the TMLA. In pulse shifting, the on–off switching sequence of each radiating element is characterized by a switch-on instant and interval within the modulation period which increases the degrees of freedom. A genetic algorithm (GA) is employed to optimize the switch-on and switch-off instants of each time pulse along with the phase weight for each element in the antenna array. The simulation results reveal that the proposed method can achieve the required patterns with very low SLL and SBLs. [ABSTRACT FROM AUTHOR]

AbstractThe escalating threat posed by space debris necessitates innovative approaches for its removal. This article presents a comprehensive mathematical modeling and dynamic analysis of a flexible tethered satellite system (FTSS) in the post-capture phase, taking into account nonlinear strain effects for the flexible appendages. The FTSS consists of a rigid central body satellite, two identical flexible panels, and a towing mass that manipulates the satellite through a tether. We develop a detailed dynamic model that accurately represents the system’s three-dimensional motion, incorporating the rigid body’s 6 degrees of freedom (DOF), the tether’s 3 DOF motion, and two modal generalized coordinates for each panel. The extended Hamilton method is employed to derive this model, enabling us to investigate the conditions under which nonlinear strain considerations become critical. The findings of this article reveal that nonlinear strain effects can profoundly impact the system’s dynamics under certain geometric and forcing conditions, often overlooked in previous studies. In these scenarios, the panel strains exceed the linear regime, necessitating the use of nonlinear models for accurate representation. This work emphasizes the importance of incorporating nonlinear strain terms in the dynamic analysis of FTSSs, particularly when dealing with large deformations and high-amplitude vibrations encountered in debris removal applications. [ABSTRACT FROM AUTHOR]

The improved absolute nodal coordinate formulation (D-H-ANCF) is proposed for analyzing dynamic behaviors of the variable cross-section beam with large aspect ratio. The higher-order ANCF (H-ANCF) is established by introducing higher-order freedom degrees. Then the reduction factors of each element are proposed by considering the aspect ratio criterion and shear performance criterion. The experiments are studied to verify the correctness of the proposed method. In conclusion, shear locking can be solved by D-H-ANCF. And the deformation and cross-section distortion also can be accurately predicted by D-H-ANCF. Moreover, the computing efficiency of D-H-ANCF can be improved by introducing reduction factors. [ABSTRACT FROM AUTHOR]

The Next-Generation Networks offer a green environment with demanded data rates with ultra-low latency. Future efforts will be oriented in more degrees of freedom and system complexity with incorporating global optimization in terms of non-linearities, cost-effective, and reduced environmental impacts. The multitone upconverted radio over fibre (RoF) link with an optical modulator as phase modulator as desired alternatives with respect to optimization features and quantum photonic integration. In this paper, a framework has been developed to characterise the upconverted phase modulated signal model based on next-generation networks, in which an analytical model is investigated for single-tone upconverted, two-tone upconverted, and three-tone upconverted. Numerical simulations have been carried out to verify the novel outcomes using OptSIM software. The developed analytical models have a major contribution to the implementation of next-generation networks such as 5G, 6G, WiMAX, Quantum Communication, etc. The fundamentals of harmonics and the intermodulation product terms of third and fifth order via optical link are also evaluated for multitone Phase modulated RoF link with upconversion method. As per the finding outcomes, the proposed link is adaptable with frequency upconversion and long fibre distances. [ABSTRACT FROM AUTHOR]

A thermodynamic model developed by our group has been employed to explore the electro-optical properties of the chiral antiferroelectric smectic C (Sm $C_A^*$ C A ∗ ) phase. In the present study, the temperature dependence of tilt angle and spontaneous polarization of binary ferroelectric mixtures represented as W-330-3 and W-331-3 exhibiting ferroelectric Sm C* and antiferroelectric Sm $C_A^*$ C A ∗ phase has been investigated. Within the framework of this model, the free-energy density characterizing the system featuring the Sm $C_A^*$ C A ∗ phase is expressed as a series expansion that incorporates all pertinent degrees of freedom: tensor orientational order ${{\bf{Q}}_{{\bf{ij}}}}$ Q ij , scalar smectic order ψ, polarization vector P, wave vector q of the helix and the resulting coupling terms between these order parameters. The values of Landau coefficients featured in the expansion series are derived from experimental data (tilt angle and spontaneous polarization) of W-330-3 and W-331-3. A substantial agreement between the theoretical predictions and experimental observations has been found. [ABSTRACT FROM AUTHOR]

Spherical piezoelectric motors (SPMs) represent a promising actuator technology applicable to the development of motion control systems with multiple degrees of freedom. However, few SPMs have made it successfully to market, as an effective and systematic rotor orientation analysis and manipulation technique has yet to be developed. This study thus developed a novel triplet-stator SPM design that integrates electrode configuration to excite lateral vibrations and offers two fundamental rotor orientations for each set of piezoelectric plates by changing the contact position between the rotor and stator. To accomplish omnidirectional orientations for the proposed SPM system, we present a systematic orientation analysis based on spherical coordinates. We further apply the concept of vector composition to derive new composite orientations by adjusting the magnitude ratio of the provided torques between three stators. An orientation angle representation accounting for the rotor dynamics is used to validate the correctness of the synthesized orientation vectors both in simulation and experiments. The orientation analysis results in a three-dimensional sphere containing eight vector spaces corresponding to eight stator actuation modes, in which an arbitrary rotor orientation reference command can be generated under the designed actuation modes. Experimental results were well correlated with simulations, thereby verifying the effectiveness of the proposed SPM system design and orientation analysis. [ABSTRACT FROM AUTHOR]

Robot-assisted rehabilitation is a rapidly advancing field whereby robotic devices are used for the treatment of disabilities. Mechanism design and actuation of these devices play important roles in the treatment and the non-ergonomic designs may even increase the cardiorespiratory load and cause discomfort leading to further gait disorders. This article identifies crucial design and actuation aspects of gait rehabilitation robots and presents the first intrinsically compliant gait robot design with three actuated and five passive degrees of freedom, alleviating the prevalent issues. The gait robot joints remain aligned with the human anatomical joints during the swing and the stance phases due to the use of special bushes and dampers. The intrinsically compliant actuators on the new gait robot make it safe to work with human subjects. Increased degrees of freedom allow for natural walking dynamics instead of canceling or constraining them. The robot firmware, including the kinematic modeling, is designed using multiple adaptive neuro-fuzzy inference system to save on the computational time of the robot controller. The new robot design is finally validated for its intended use in gait rehabilitation, by employing a fuzzy logic controller and evaluating the position, velocity, and acceleration profiles of its joints. [ABSTRACT FROM AUTHOR]

In this study, thermomechanical behavior of regular porous materials is studied using analytical, numerical, and experimental approaches. Analytical relationships for octahedral lattice structure have been obtained based on Euler-Bernoulli beam theory. Three types of finite element models, two based on beam elements and one based on volumetric elements, are made. Additive manufacturing technique is also used to fabricate lattice structures with different relative densities. The manufactured samples are heated to a certain temperature in a closed chamber, and the displacements are measured and compared to their analytical and numerical counterparts. Based on the results, the analytical, numerical, and experimental results are in excellent agreement with each other. The methodologies introduced in this study would be beneficial for further studies on porous materials and lattice structure with other topologies and higher degrees of freedom. [ABSTRACT FROM AUTHOR]

This article employs Mindlin's first-order shear deformation theory to analyze the dynamic behavior of laminated composite shells with various geometries, featuring central cutouts and cracked corners that carry concentrated and distributed mass. The formulation considers an isoparametric element with nine nodes and five degrees of freedom per node. Both in-plane and transverse effects of mass are addressed by incorporating lumped mass with rotational inertia in the formulation. The obtained results are compared to previously published data, showing an excellent agreement with a variation of less than ±2.5% for all cases. Following validation, the study examines shell vibration for various geometries carrying concentrated mass, distributed mass, and distributed patch mass. Additionally, the dynamic analysis of shell panels with central cutouts and cracked corners with different cracked dimensions is conducted. Unique boundary conditions are introduced by applying them to both the outer and cutout edges (i.e., SSSS-CCCC, FFFF-CCCC). [ABSTRACT FROM AUTHOR]

Through composite dry separation, effective precipitation and impurity removal can be achieved, improving the quality of raw coal. This paper mainly systematically analyzes the synergistic control mechanisms of airflow velocity, airflow transition layer height and control angle on the upgrading characteristics of moist coal. The results show that Zone I is a high airflow area, and when v = 2.12 m/s, it can effectively destroy the original static stable structure of low-density particles, increase the degree of freedom of particle accumulation volume, and achieve effective precipitation of particles. Zone II is a medium air volume area, and when v = 1.78 m/s, the high-density particle group in this area has the weakest obstruction effect on airflow, which can achieve efficient particle precipitation. Zone III is a low airflow area, where the dispersion of high-density particle groups increases at v = 1.36 m/s. The airflow can effectively act on the particles through the bed layer, reducing their surface water. When the height (H) of the gas transition layer is 49-52 mm and the regulatory perspective is 20–25, the distribution uniformity of the gas flow in the bed is the best. After separation and upgrading, the moist coal concentrate yield is 78.3%, ash content is 10.05%, as well as the possible deviation E value is 0.1 g/cm3. [ABSTRACT FROM AUTHOR]

Piezoelectric Carbon Nanotube Reinforced Functionally Graded (P-CNT-FG) structures have great application potential in aerospace for vibration control. The precise modeling technique for P-CNT-FG plates and shells is a big challenge, especially for moderate thick and thick P-CNT-FG structures. This paper develops a Finite Element (FE) model for P-CNT-FG plates and shells. The FE model is derived by Reddy's third-order shear deformation theory with consideration of various CNT distribution forms, CNT volume fractions, boundary conditions and arbitrary fiber orientations. Eight-node quadrilateral elements are developed for P-CNT-FG structures with seven mechanical degrees of freedom (DOFs) at each node. The mathematical model is first validated by a simply supported square plate, a cross-ply plate with sinusoidally distributed loading and a CNT plate with PZT layers. Afterwards, vibration and dynamic responses of P-CNT-FG plates have been presented, later the effective of parameters on static and dynamic response of P-CNT-FG smart structures are carried out by the present model. [ABSTRACT FROM AUTHOR]

This study presents a warping included mixed finite element formulation for the static and stress analyses of functionally graded (FG) exact curved beams. Another distinctive feature of this study is to present the range of geometric and material parameters where the first-order shear deformation theory lacks necessary precision. The constitutive equations are derived from the 3D elasticity theory of an elastic continuum. The couple effects are considered in addition to the variations of FG material constituents through the transverse/axial directions. The mixed finite element formulation is enhanced by the cross-sectional warping deformations over a displacement-type finite element formulation. The two-noded curved mixed finite elements with 12 degrees of freedom at per node are derived over exact curvature and length. Satisfactory results are obtained for the static responses and stresses of axially FG-sandwich and transversely FG exact curved beams with power-law dependence compared to the 3D behavior of brick finite elements. Finally, the influences of ellipticity, width to thickness ratio, FG material constituents, and material gradient index on the static response of FG exact curved beams are investigated. [ABSTRACT FROM AUTHOR]

The optimal local truncation error method (OLTEM) with unfitted Cartesian meshes recently developed for the scalar wave and heat equations for heterogeneous materials is extended to a more complex case of a system of the elastodynamics PDEs. Compact 9-point stencils (similar to those for linear finite elements) are used for OLTEM. Compared to our previous results, a new approach is used for the calculation of the right-hand side of the stencil equations due to body forces. It significantly simplifies the analytical derivations of OLTEM for time-dependent problems. There are no unknowns on interfaces between different materials; the structure of the global semi-discrete equations for OLTEM is the same for homogeneous and heterogeneous materials. For the first time we have also developed OLTEM with the diagonal mass matrix. In contrast to many known approaches with some ad-hoc calculations of the diagonal mass matrix, OLTEM offers a rigorous approach which is a particular case of OLTEM with the non-diagonal mass matrix. Another novelty of the article is a new post-processing procedure for the accurate calculations of stresses. It includes the same compact 9-point stencils as those in basic computations and uses the accelerations and the displacements at the grid points along with the PDEs for the stress calculations. OLTEM yields accurate numerical results for heterogeneous materials with big contrasts in the material properties of different components. Numerical experiments for elastic heterogeneous materials show: a) at the same number of degrees of freedom (dof), OLTEM with unfitted Cartesian meshes is more accurate than linear finite elements with similar stencils and conformed meshes; at the engineering accuracy of 0.1 % for the displacements, OLTEM reduces the number of dof by more than 20 times; at the engineering accuracy of 0.1 % for the stresses, OLTEM with the new post-processing procedure reduces the number of dof by more than 104 times compared to linear finite elements; b) at the same number of dof, OLTEM with unfitted Cartesian meshes is even more computationally efficient than high-order finite elements with much wider stencils and conformed meshes. This will lead to a huge reduction in the computation time for elastodynamics problems solved by OLTEM and will allow the direct computations of some complex wave propagation and structural dynamics problems for heterogeneous materials without the scale separation. [ABSTRACT FROM AUTHOR]

Considering the importance of correctly understanding the dynamics of microstructure materials for their applications in related technologies, by eliminating the shortcomings and some overlooked physical concepts in the existing asymmetric elastic theories, we have presented an asymmetric elastodynamic model based on a $ U(1) $ U (1) gauge theory with quantum electrodynamics (QED) structure. Accordingly, we have shown that there is a correspondence between an elastic theory, which can explain the behavior of elastic waves within an asymmetric elastic medium and QED. More specific, we have indicated that the corresponding elastic wave equations are somehow analogous to QED ones. In this regard, by adding vibrational degrees of freedom and introducing a gauge property of the waves of displacement for the waves of rotation, we have generalized and modified the related Cosserat theory (CT) for an elastic environment. Thus on macro scales, the elastic waves can possess the QED treatment. This analogy provides a new paradigm of fermions and bosons. Also, from experimental point of view, we have shown that the behavior of elastic waves in a granular medium is equivalent to behavior of light in dispersive media, which can be explained using QED. Hence, contrary to the Cosserat and discrete models, this amended CT has qualitatively been indicated to be consistent with the corresponding empirical observations. [ABSTRACT FROM AUTHOR]

This paper presents a motion sensor-based haptic master controller capable of static and dynamic force presentation by the newly invented Finger Band Soft Actuator (FBSA). The master controller operates a surgical assist robot using the $ 6 $ 6 degrees of freedom position and posture data tracked by an optical motion capture. The haptic force presentation can be realized by the pneumatic pressure of FBSA, which can be highly integrated into the controller mechanism to maintain precise manipulability. The FBSA can present a pressing force of 3.7 N for a small-sized finger and 5.1 N for a large-sized finger at an internal pressure of 60 kPa, and there is a monotonically increasing and decreasing relationship between the air pressure and the pressing force. The effectiveness of haptic force presentation by the FBSA was experimentally evaluated in the master-follower operation of a surgical assist robot. Ten subjects performed the task of pulling a suture thread and controlled the manipulation to achieve the directed tension. The experimental result shows that with the four levels of force presentation scheme by the FBSA, the error between suture tension and target operating force is significantly smaller than without force presentation. [ABSTRACT FROM AUTHOR]

Incremental sheet formation (ISF) is extensively used versatile technique for newer manufacturing processes, such as creating skull prostheses, aerospace equipment, automobile, and so on. The current work describes the techniques, history, and classification of ISF-based on the results of few aspects such as force forming, stress triaxiality, force forming, bending stress, and so on. In addition, the influence of different parameters and their effect on building force, formability, spring-back, failure, surface roughness, rupture, and so on, have been analysed. It has been noticed that an investigation of the two degrees of freedom (DF) robot-manipulators with the ISF and its influences on surface coarseness and formability are greatly suggested. [ABSTRACT FROM AUTHOR]

Many challenges and obstacles prevail in the agricultural fields, such as weed removal, horticulture, and spraying herbicides and fertilizers. Individual robots for all these tasks cost a lot, which ordinary farmers cannot afford. The delta arm has to perform versatile functions like spraying and weed removal with great accuracy and reduced environmental impact. The primary objective of this research is to design a delta arm that can move in all directions efficiently. The driving and driven arm in the delta arm design should be correlated, which helps with the proper positioning of the end effector carrier. Similarly, the moving platform and the fixed platform are designed in a circular form. These measurements give a proper design and make the robotic arm work properly as it can move in all three degrees of freedom in XYZ directions. The NVIDIA jetson orin nano operates as the controlling unit of the delta arm. The study proved that the delta arm had achieved an accuracy rate of 98% at a speed of 107.5 mm/s, making it well-suited for agricultural field operations. In addition, the delta arm exhibits the capability to handle an end effector weighing up to 300 g. Therefore, introducing the delta arm agribot in the row-based agricultural field can make a revolution in the upcoming years as it can perform versatile tasks at a high speed. [ABSTRACT FROM AUTHOR]

This article aims to analyze rectangular functionally graded material plates with rectangular cutouts of diverse sizes, numbers, and positions for free vibration using Mindlin's first-order shear deformation theory (FSDT). Isoparametric plate elements of nine nodes and five degrees of freedom at each node were used for the present finite element formulation. The Poisson ratio is assumed to be constant throughout the plate. At first, results piled up from the present finite element formulation were compared with existing results collected from various previous journals for different isotropic plates and functionally graded material plates. After verification of finite element formulation, some new results (nondimensional fundamental frequency) were obtained considering various shapes, sizes, numbers, positions of cutouts, thickness ratio, aspect ratio, FGM power law index, and different edge conditions. Dynamic analysis of FGM plate with interior support along rectangular cutout edges is an integral part of this study. [ABSTRACT FROM AUTHOR]

The Dynamic Weighting Control Allocator (DWCA) was introduced by Sadien et al. (Control Engineering Practice, 2019) to solve the allocation problem raised by the yaw control of an on-ground aircraft. It handles the classical tradeoff between virtual reference inputs realisation and control power minimisation. But it also offers three specific features. First, the actuators reach saturation almost simultaneously, which allows an efficient recovery in case of failure. Then, several industrial requirements are taken into account, such as implementation ease, low computational cost and compatibility with certification constraints. And finally, the actuators can be prioritised, the last ones being used sparingly (to avoid overheating, fatigue, maintenance cost...) only when the virtual reference inputs cannot be realised by the first ones only. But despite its attractiveness, the DWCA is limited to the 1-dimensional case, which means that only one degree of freedom can be controlled. This is not sufficient to deal with today's challenges in the aeronautical and automotive fields, for example, where certain control problems are inherently multi-dimensional. With the progressive advent of autonomous cars, new concepts of light hybrid or electric vehicles are, for example, emerging, where both hydraulic and electric actuators are mounted on each wheel to improve the combined management of speed and steering. In this context, this paper introduces a non-trivial generalisation of the DWCA, which retains the various characteristics and advantages of the initial version and can be used in the multi-dimensional case. [ABSTRACT FROM AUTHOR]

A weak Galerkin finite element method is applied to singularly perturbed delay reaction-diffusion problems. A robust uniform convergence has been proved both in the energy and balanced norms using higher-order piecewise discontinuous polynomials on Shishkin meshes. The error analysis for singularly perturbed reaction-diffusion problems with negative or positive shift in the balanced norm has appeared for the first time. The proposed method uses piecewise polynomials of order $ k\geq ~1 $ k ≥ 1 on interior of each element and piecewise constant polynomials on the end points of each element. By the Schur complement technique, the interior degrees of foredoom (DOF) can be eliminated from the discrete system resulting from the numerical scheme, and thus the degrees of freedom of the proposed method comparable with the classical finite element methods, and it is remarkably less than that of the discontinuous Galerkin method. Finally, we give various numerical experiments to verify the theoretical findings. [ABSTRACT FROM AUTHOR]

Cholesky decomposition (CD) of the two-electron integrals and the resolution-of-identity (RI) techniques are established inner projection methods to efficiently evaluate two-electron integrals. Both approaches share the notion of an auxiliary basis set as a mean to reduce the scaling. In the past years, the close relationship between the two approaches has fostered developments on how to systematically derive unbiased auxiliary basis sets – atomic CD (aCD) and atomic compact CD (acCD) auxiliary basis sets, different to the precomputed auxiliary basis sets. The accuracy of these approximations in the RI approach can be further improved via an explicit correction of the one-centred two-electron integrals, which is the main object of this research. Correcting the one-centred two-electron integrals directly, which scales linear with system size, is expected to provide a new degree of freedom to the design of auxiliary basis sets. This can either be used to gain faster convergence towards the conventional treatment of the two-electron integrals or as a mean to design lighter auxiliary basis sets while maintaining the same accuracy as of the uncorrected approach. The benchmarks of the one-centre corrections applied to several auxiliary basis set types were investigated in this paper. [ABSTRACT FROM AUTHOR]

Energy-dependent self-adaptive mesh refinement algorithms are developed for a symmetric interior-penalty scheme for a discontinuous Galerkin spatial discretization of the multi-group neutron diffusion equation using NURBS-based isogeometric analysis (IGA). The spatially self-adaptive algorithms employ both mesh (h) and polynomial degree (p) refinement. The discretized system becomes increasingly ill-conditioned for increasingly large penalty parameters; and there is no gain in accuracy for over penalization. Therefore, optimized penalty parameters are rigorously calculated, for general element types, from a coercivity analysis of the bilinear form. Local mesh refinement allows for a better allocation of computational resources; and thus, more accuracy per degree of freedom. Two a posteriori interpolation-based error measures are proposed. The first heuristically minimizes local contributions to the discretization error, which becomes competitive for global quantities of interest (QoIs). However, for localized QoIs, over energy-dependent meshes, certain multi-group components may become under-resolved. The second employs duality arguments to minimize important error contributions, which consistently and reliably reduces the error in the QoI. [ABSTRACT FROM AUTHOR]

This study examined the role of basic (i.e. positive and negative) and complex (i.e. emotional solidarity) emotions in explaining residents' preference for both intimate and casual social encounters (i.e. social distance) with tourists. Considering a burgeoning rural destination in the U.S., known for its natural and cultural amenities, data were collected on-site and online from 511 residents. A two-step sequence of analysis (i.e. confirmatory factor analysis followed by structural equation modelling) was undertaken to test 12 hypotheses within a proposed conceptual model. Eight hypotheses were supported; three of those not supported involved negative emotions as antecedents to emotional solidarity. A high degree of variance was explained in emotional solidarity and social distance. Implications and recommendations are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a dexterity distribution design method for attitude adjustment of multi-joint robotics based on singularity-free workspace decomposition (SWD). The requirement of attitude adjustment for platform is described by time-varying Euler angles, by which the structural prototyping of universal-prismatic-spherical + spherical (UPS + S) parallel robot body can be generated via mechanism concept design. According to Kutzbach-Grubler formula regarding degree of freedom (DOF), the forward kinematics model is built, meanwhile, the reachable posture workspace of the robot can be depicted in 3D space by exploiting tilt-and-torsion method. The Jacobian matrix is extracted to reckon dexterous performance of the mechanism, including condition number, minimum singular value, manipulability and comprehensive evaluation index. The singularity degree within the design domain, from singularity-free to fully singularity, is comparatively ranked in polar coordinates, which constitutes the essence of SWD, the performance spectrum corresponding to the structural parameters can hereby be acquired for larger workspace and smaller singularity. The impedance control errors with parameter perturbation further validate the consistency of the singularity-free attitude from the perspective of dynamics. The physical experiments are carried out to verify the outcomes by virtue of multi-axis pose sensor array. Hence the presented SWD method has important application prospects regarding DOF coupling, especially in medical rehabilitation, industrial robotics, aerospace manufacturing and so forth. [ABSTRACT FROM AUTHOR]

This article attempts an investigation on the free vibration behavior of the laminated composite angle ply shell experimentally and the obtained results are validated by laminated shell model based on modified higher order zigzag theory. The angle ply shell is modeled by placing six layers of 45° glass fiber laminae. The mechanical properties such as Poisson's ratio, Young's modulus and shear modulus are determined experimentally. The experimental procedure is performed using a vibration testing instrument by Bruel and Kjaer. The theoretical laminated shell is modeled by taking thickness coordinate to radius of curvature of shell ratio in the strain displacement relationship with shear-free conditions at free surfaces. For the theoretical computations of natural frequencies, a C0 finite element model with nine-noded quadrilateral shell element with seven degrees of freedom at each node has been chosen. Theoretical findings have been compared with experimental results and also with relevant published results in the existing literature. Moreover, extensive parametric studies have been performed to investigate the effect of geometric configurations and lamination schemes with different boundary properties on free vibration behavior of laminated shells, which will serve as benchmark solutions for future researchers. [ABSTRACT FROM AUTHOR]

Energy-dependent self-adaptive mesh refinement algorithms are developed for a continuous Bubnov-Galerkin spatial discretization of the multi-group neutron diffusion equation using NURBS-based isogeometric analysis (IGA). The spatially self-adaptive algorithms employ both mesh (h) and polynomial degree (p) refinement. Constraint-based equations are established across irregular interfaces with hanging-nodes; they are based upon master-slave relationships and the conservative interpolation between surface meshes. A similar Galerkin projection is employed in the conservative interpolation between volume meshes to evaluate group-to-group source terms over energy-dependent meshes; and to evaluate interpolation-based error measures. Enforcing continuity over an irregular mesh does introduce discretization errors. However, local mesh refinement allows for a better allocation of computational resources; and thus, more accuracy per degree of freedom. Two a posteriori interpolation-based error measures are proposed. The first heuristically minimizes local contributions to the discretization error, which becomes competitive for global quantities of interest (QoIs). However, for localized QoIs, over energy-dependent meshes, certain multi-group components may become under-resolved. The second employs duality arguments to minimize important error contributions, which consistently and reliably reduces the error in the QoI. [ABSTRACT FROM AUTHOR]

Structural breaks represent periods of turmoil that may influence how tourism affects economic growth. Current research on the tourism-led growth hypothesis (TLGH) measures the effect of structural breaks using dummy variables in regression models. However, the drawback of this approach is that there could be multiple structural breaks which result in an overfitting problem and reduce degrees of freedom in small samples. It also becomes difficult to isolate the effect of individual breaks when multiple structural breaks occur within the same year. We thus highlight the role of the Fourier ARDL model in addressing these shortcomings. We use three Pacific Island Countries: Fiji, Tonga, and Vanuatu as case studies to evaluate the efficacy of the Fourier ARDL model. Contrary to earlier research, our results indicate that tourism does not always lead to economic growth. Appropriate modelling of structural breaks also influences the outcome of asymmetric effects. These findings imply that future research should pay close attention to the effects of structural breaks in the TLGH. [ABSTRACT FROM AUTHOR]

A musculoskeletal (MSK) model is a valuable tool for assessing complex biomechanical problems, estimating joint torques during motion, optimizing motion in sports, and designing exoskeletons and prostheses. This study proposes an open-source upper body MSK model that supports biomechanical analysis of human motion. The MSK model of the upper body consists of 8 body segments (torso, head, left/right upper arm, left/right forearm, and left/right hand). The model has 20 degrees of freedom (DoFs) and 40 muscle torque generators (MTGs), which are constructed using experimental data. The model is adjustable for different anthropometric measurements and subject body characteristics: sex, age, body mass, height, dominant side, and physical activity. Joint limits are modeled using experimental dynamometer data within the proposed multi-DoF MTG model. The model equations are verified by simulating the joint range of motion (ROM) and torque; all simulation results have a good agreement with previously published research. [ABSTRACT FROM AUTHOR]

Sustaining large amount of power flow in the wind power plant, series capacitors are incorporated with the transmission line system which can cause subsynchronous control interaction (SSCI) in the doubly-fed induction generator (DFIG). This SSCI effect can lead to system instability. To damp SSCI in DFIG, several traditional controllers are involved but it leads to poor damping response. To solve this issues, a new controller based on the uncertainty and disturbance estimator and two degree of freedom (UDE-2DOF) controller is proposed. The proposed controller gives the controlled output based on the input control signal like reference and actual value of the d-q axis rotor current. With this evaluation, the proposed controller damp out the SSCI in a series-compensated DFIG. Then, the effectiveness of the proposed control scheme is verified in the MATLAB platform. Both eigenvalue analysis and time-domain simulations are carried out for analyzing the system stability and SSCI damping. The results indicate that the proposed method can mitigate the SSCI within 2.5 sec. Furthermore, the variation in wind speed and the level of series compensation plays an important role on the overall system's stability especially at low wind speed (7 m/sec) and high compensation level under 45%. [ABSTRACT FROM AUTHOR]

The paper examines the possibility of using a nonlinear Quasi-Zero-Stiffness (QZS) spring in a vehicle suspension. The response of a Single Degree of Freedom (SDOF) model to harmonic base excitations is obtained which may be unstable and unbounded depending on the excitation level and the damping ratio. This is followed by obtaining the response of the SDOF model to harmonic base excitation with an amplitude that is varying according to a road profile spectrum. Such dependency of the excitation amplitude to the frequency changes the qualitative behaviour of the nonlinear system and the responses would be always bounded. The QZS spring also improves the isolation of the system. Transient responses of a quarter car model with a QZS suspension to a road hump and random road profile are investigated. The maximum acceleration of the vehicle with the QZS suspension passing over the speed hump is considerably lower than a vehicle with a conventional linear suspension. Wb weighted RMS of acceleration (BS 6841-1987) is also lower by as much as 14% for a vehicle with the QZS suspension travelling at 30 km/h on a class E road compared to its linear counterpart. [ABSTRACT FROM AUTHOR]

Time-modulated arrays (TMAs) have a high design degrees of freedom (DoFs) to improve radiation performance, while they are prone to failure due to their hardware characteristics. In this article, we propose a novel technique to diagnose impaired TMAs based on compressed sensing (CS). The TMA diagnosis problem is reformulated as a sparse signal recovery problem at the center frequency and sidebands. Then, a method based on the difference of convex sets theory and sequential convex programming (DCS-SCP) is developed to implement diagnosis for impaired TMAs. Using a small number of far-field measurements at the same position but different frequencies, the joint recovery of the equivalent excitations at the center frequency and sidebands is realized by a mixed $ l_{0} $ l 0 / $ l_{2} $ l 2 -norm minimization method. The numerical simulation and the successful comparison with the state-of-the-art algorithms demonstrate the superiority of the proposed methods in terms of noise robustness and diagnosis accuracy. [ABSTRACT FROM AUTHOR]

The objectives of this study are to: (1) develop an approach for extracting representative information from dam behaviour data and (2) diagnose deformation and crack opening behaviour by integrating techniques in transfer entropy (TE), chaos theory and wavelet transform (WT). First, TE is employed to map the information flow between measuring points to select the representative measuring point. The phase space reconstruction of observation data on dam behaviour is implemented, where lag time τ and embedding dimension m are identified by the statistical C–C method. The non-linear structural dynamical behaviour of the dam is then quantified in the form of the largest Lyapunov exponent representing system chaoticity. In addition, a moving window formula is employed to scan along the observation data to ensure an on-line continuous diagnosis. WT may be employed to assist in detecting the time where significant changes occur. A simple 4 degrees of freedom spring-mass-damper (K-M-C) system is employed to illustrate the performance of the proposed approach. The approach is then applied to an actual dam using monitoring data. From the deformation and crack opening behaviour, it is concluded that the studied dam is performing with no significant changes in behaviour over time. Transfer entropy is applied to map the information flow between measuring points. The representative information on structural behaviour of an actual dam is identified. TE and chaos theory are combined to diagnose the dam behaviour. A moving window is adopted to facilitate online statistical diagnosis. [ABSTRACT FROM AUTHOR]

Emergency drills and drills against terrorism have been held at nuclear facilities. Shortcomings of these drills are that the numbers of emergency scenarios and roles are limited because many workers must participate in them simultaneously. The times during which all employees can participate simultaneously are limited. As a means of solving these problems, augmented reality (AR) training has been increasingly adopted in recent years, but difficulties of creating contents and the inadequate degrees of freedom in the created contents are becoming problematic. For this study, we developed an AR training environment construction system for users to create scenarios easily by simply assembling and placing blocks representing scenario components in a real-world environment. To realize the construction system, we also developed the "Program Block," which enables users to create scenarios in a puzzle-like style. The system can create and simulate various scenarios involving interaction between trainees and a real-world environment. To evaluate the ease of system usage and flexibility for scenario creation, a subjective experiment was conducted at a nuclear facility. Results indicate that users can construct an AR training environment easily. [ABSTRACT FROM AUTHOR]

A four-level rigid trunk mechanism based on 4-SPS/U, with SPS as the driving branch and U pair as the middle constrained driven branch, is innovatively proposed in this paper. Based on the innovative design of this trunk mechanism, it can improve the flexibility of the hexapod mobile robot's posture adjustment and changes in various motion modes such as walking, water propulsion, climbing and rolling. Firstly, the screw theory is adopted to calculate the degree of freedom of the trunk mechanism. Secondly, a combination of closed vector method and the characteristic structure configuration decoupling method has been applied to constructing the inverse kinematics solution, and deriving the velocity and acceleration models as well as analyzing the high posture flexibility in workspace of the trunk mechanism. Thirdly, theoretical simulation data diagram of the movement branch chain displacement, end height, speed and acceleration of the trunk mechanism are calculated through theoretical numerical examples, and the excellent motion characteristics of the 4-SPS/U-based four-level rigid trunk mechanism are analyzed. Finally, a quantitative comparison was made between the theoretical simulation data and the experimental data of the experimental prototype. The error rates of the variation curves of the displacement length, height, velocity and acceleration of the driving branch chain were 0.8%, 0.2%, 0.5% and 0.9%, which verified the correctness and reliability of the theoretical derivation. [ABSTRACT FROM AUTHOR]

A multivariate t-distribution is introduced such that each element of a normal vector is scaled by using a chi-square that is independent of the chi-squares for the remaining elements of the vector with possibly distinct degrees of freedom. The integral and series expressions of the probability density function are given. The absolute values of the covariances/correlations and Mardia's multivariate measure of kurtosis are shown to be smaller than those for the corresponding usual multivariate t with a common chi-square. An extended multivariate t with common and unique chi-squares is also proposed, which takes a form like factor analysis. [ABSTRACT FROM AUTHOR]

In this paper, two-dimensional (2D) structural models are used to analyze thin-walled stiffened structures. A novel approach is presented to model both skins and stiffeners using 2D finite elements (FEs) with enhanced capabilities. The deformation of the stiffeners is accurately described using higher order Lagrange polynomials, and the mechanical continuity between the reinforcements and the skin is automatically ensured in correspondence of the Lagrange points. The 2D FEs are built using the Carrera Unified Formulation (CUF), which allows arbitrary refinement of the stiffener kinematics. In this way, any type of deformation can be described and, if a higher-order model is used, the three-dimensional (3D) stress distribution can be evaluated. The proposed model is tested on a stiffened plate and compared with results obtained using traditional FEA, including 3D and 2D models and a combination of 2D and one-dimensional (1D) models for the stiffeners. The results show and demonstrate the reliability of the proposed method, both in terms of displacements and stresses, when compared to the 3D solution. In addition, the computational cost, evaluated here as the number of degrees of freedom (DOFs), is much lower. Finally, the ability of this model to deal with curved stiffeners is demonstrated with practical examples. [ABSTRACT FROM AUTHOR]

A network interface program for controllers (NICON) for pseudo-dynamic hybrid simulations is presented. The program is implemented as an independent program residing between the simulation model and an actuator controller with various functions necessary for hybrid simulations, such as communication, coordinate transformation, error compensation. These functions are generalized to allow for a generic configuration of actuator setup theoretically with any number of control points and control degrees of freedom. Application examples of NICON to hybrid simulations of civil infrastructures subjected to earthquakes or fire are presented. [ABSTRACT FROM AUTHOR]

Robotic arms with redundant degrees of freedom are known to exhibit characteristics that make them more suitable than their non-redundant counterparts in many manipulation tasks. These redundant degrees of freedom allow for multiple control objectives to be pursued simultaneously leading to increased efficiency, dexterity and versatility. Redundancy however brings about structural complexity, difficulties in tasks specification, challenging kinematics and dynamics and high computational cost. This work tackles kinematic hyper redundancy resolution in the context of posture (shape) control of a modular serial link arm by proposing a new take on formulating and solving the problem. In the proposed formulations, strategic points along the arm (termed control points) are explicitly controlled in such way that their overall motion steers the posture of the arm toward the desired target posture. These control points stem from the modular structure of the arm and are chosen in order to achieve specific control characteristics. Desired target posture outlines are specified intuitively and arbitrarily with continuous spline curves. The proposed method has demonstrated the ability to safely steer the arm towards intermediate postures which reduce the overall posture tracking error. It copes well with singularities and is capable of tracking target postures that are significantly distinct from the arm's initial posture. Numerical simulations on a 40 DOF arm are conducted to assess the validity and performance of the method. [ABSTRACT FROM AUTHOR]

Acid mine drainage was evaluated using a galvanic (GV) electrochemical system, Al–Cu (anode/cathode), based on a 32 factorial design. The factors analyzed were anodic area/volume ratios (A/V) of 0.037, 0.072, and 0.112 cm2/cm3, and treatment time from 0.25–8 h, and analyses were performed in duplicate with 11 degrees of freedom. The response variables were the total dissolved solids and concentrations of As, Cu, Co, Cr, Pb, Fe, Ni, and S O 4 2 − . The pH, electrical conductivity, and temperature were monitored during the process. Significant differences between treatments were determined by analysis of variance with Tukey's test (p < 0.05) using Statgraphics Centurion XVI.I software. The results showed that a greater electrode surface, A/V ratio, and treatment time improved pollutant removal. The spontaneous reactions generated by the galvanic cell, through the current that flows owing to the potential difference between the Al and Cu electrodes, allows the removal of heavy metals, arsenic, and S O 4 2 − by coagulation and precipitation mechanisms. The removal efficiencies achieved were Cu (99.1%), As (76.6%), Ni (80.2%), Pb (83.6%), Cr (100%), Fe (93.71%), and 92.9% for sulfates. The X-ray diffraction and Raman analyses of the solid fraction indicated that cuprite was formed with a purity of 96%, and the recovery of Cu by the GV system may be a viable option for mining companies. [ABSTRACT FROM AUTHOR]

Structural synthesis plays an important role in the conceptual design of mechanisms. Based on the link assortment array, links are divided into binary links and multi-vertex links. From the relation of binary links and multi-vertex links, a new form of the adjacency matrix is introduced to illustrate planar kinematic chain. It enriches the representative form of the adjacency matrix, which can provide a new direction for rigid-chain detection and structural synthesis. Without auxiliary graph models, based on the link-path adjacency matrix, characteristic code, and Sudoku Crosswords, a computer-aided digitization method is proposed to synthesize the whole family of planar non-fractioned kinematic chains. Compared with most existing methods of structural synthesis, isomorphic kinematic chains and some rigid chains are identified and deleted in the generation of link-path adjacency matrix, which can improve the efficiency of structural synthesis. By synthesizing planar non-fractioned kinematic chains with up to 10 links and 5 degrees of freedom, results confirm that the proposed method is available. [ABSTRACT FROM AUTHOR]

Static and dynamic response analysis of sandwich plates having corrugated core under patch loading is presented in this paper. In this work, the problem formulation is made using finite element-based higher shear deformation theory. The influence of various parameters like aspect ratio, corrugated plate thickness, core thickness, corrugation angle, boundary conditions, ratio of face thickness to corrugation plate thickness on transverse deflection, stresses, and dynamic bending responses are revealed. In the present investigation, a MATLAB program is developed with nine nodded seven degrees of freedom per node of element. The obtained results are verified with available results in the literature to check the program's efficiency. It is found that transverse deflection increases with increase in corrugation angle, and maximum rotation about the 'x' and y-axis increases with increase in the area of the plates exposed to patch loading. Edge constraints have a significant effect on transverse deflection and stress. [ABSTRACT FROM AUTHOR]

Two-sample hypothesis testing is a classical problem in statistics. Given i.i.d. samples X1, :::, Xm ~ P and Y1, :::, Yn ~ Q, the two-sample testing is to test whether P is significantly different from Q or not. Among the various statistical tests, the maximum mean discrepancy (MMD) has been proven to have excellent performance compared to traditional methods. In application of MMD, we are confronted with two challenges: (I) For large data set, MMD is computationally demanding with computational cost O((m + n)²); (II) The limiting distribution under the null hypothesis usually contains infinitely many unknown parameters. In this paper, we propose two testing methods that solve (I) and (II) respectively. To address (I), the data are independently and evenly divided into k groups, calculate the MMD on each group and then combine them by empirical likelihood to yield a test statistic Tk: It converges in distribution to the chi-square distribution with degree of freedom one (X1²) under the null hypothesis as k goes to infinity. To address (II), we propose to compute the two-sample jackknife pseudo-values on each group and combine them by empirical likelihood to get a new test statistic Rnm: Under the null hypothesis, Rnm converges in distribution to X1² if k = o(n): The simulation and real data application indicates that the proposed tests performs well. [ABSTRACT FROM AUTHOR]

Early detection and treatment of intraluminal diseases enable minimally invasive surgery and can lead to a high cure rate. Advanced devices with multiple degrees of freedom (DOFs) make narrow intraluminal procedures easier and safer. In a previous study, we developed a multi-DOF compliant endoluminal forceps with a tendon-sheath mechanism. The maximum bending stress of this design was reduced by changing the thickness of a compliant hinge in each segment, and the forceps achieved a wide range of motion. However, its deformed shapes with a non-constant curvature, due to a compliant inhomogeneous-thickness hinge structure, hinder fine manipulation in a narrow lumen. Here, we construct an accurate model of this compliant inhomogeneous-thickness hinge structure using pseudo-rigid-body model. In the proposed method, each compliant hinge is represented by a torsion spring and rotational joint, and the deformed shape is estimated from the bending angle caused by the tensile force. We derive the coefficient of dynamic friction by considering the friction between the wire and compliant joint based on a belt friction model. These novel calculations allow to consider individual differences in material properties and surface roughness. We experimentally confirm the feasibility of constructing a highly accurate model with a lower calculation cost than the finite element method. Our proposal seems suitable for developing dexterous forceps and other endoluminal devices, such as catheters, which mitigate operation errors and help approach lesions in narrow lumens. [ABSTRACT FROM AUTHOR]