Structural Degrees Of Freedom Research Articles

Damage Detection of Truss Structures by Reduction of Degrees of Freedom Using the Serep Method

Damage detection of bridge structures during their operating lifetime is essential. In this paper, two approaches, All Degrees of Freedom and Reduction of the Degrees of Freedom methods, are used to detect the damages in structures. The first method considers All Degrees of Freedom of the structure and the second method, Reduction of the Degrees of Freedom. Since the sensors are installed only on a few degrees of freedom, the responses are available for some of them. The Degrees of Freedom must be reduced and System Equivalent Reduction Expansion Process method is one of the most efficient ways to solve the problem. This research aimed to identify the damage of structures using the Modal Strain Energy method by reducing the structural degree of freedom. Two standard examples are used and the results compared to different damage cases to examine the efficiency of the mentioned method. The results illustrated the proper performance of the Reduction of the Degrees of Freedom method to identify the damage in truss structures. By increasing the number of modes, Reduction of the Degrees of Freedom method detects considerably more accurate the damaged elements, especially when the noise is considered. Also, based on the outcomes to identify damaged elements, it is possible to consider more modes instead of more sensors.

Coulomb correlation in noncollinear antiferromagnetic α -Mn

We have investigated the interplay between magnetic and structural degrees of freedom in elemental Mn. The equilibrium volume is shown to depend critically on the magnetic interactions between the Mn atoms. While the standard generalized-gradient-approximation underestimates the equilibrium volume, a more accurate treatment of the effects of electronic localization and magnetism is found to solve this longstanding problem. We capture well the complexity of the large 58 atoms per unit cell $\alpha$-Mn system for the first time, including its charge and spin patterns and the canting of spins with respect to the average magnetization direction.

Superior surface protection governed by optimized interface characteristics in WC/DLC multilayer coating

This paper introduces a highly durable functional multilayer coating (FMCs) with outstanding mechanical properties using comprehensive design principles. Architecting the layers with degrees of freedom in structure and thickness is the core idea to design WC/DLC FMC. This concept seeks to combine advantages of superior properties of single-layer metal, ceramic, and carbon coatings, without compromising with weaknesses. This research creates a pioneering integration platform that combines the current understanding of materials properties across scale and optimization of interfacial characteristics of ultra-thin films through the combination of theoretical and experimental studies. The aim of this study is to introduce a significant improvement for multilayer sustainability of properties and mechanical strength such as ultra-high hardness (>45 GPa) combined with high elasticity (H/E ~0.15), creep deformation recovery and ultra-durability in macro-scale wear (wear rate <10−13) of WC/DLC multi-nanolayer. “Interface engineering” through the methodology of coating-by-design and concept-based heat treatment creates the gradient structural characteristics, which is called hierarchical multilayer coating (FMC) surface protection concept in this study.

Active Reconfigurable Tristable Square‐Twist Origami

AbstractOrigami structures offer valuable applications in many fields, ranging from metamaterials to robotics. The multistable characteristics of origami structures have been pursued for acquiring unique reconfigurable features. For achieving this goal, an unusual polymeric tristable origami structure is demonstrated using a classic square‐twist origami configuration. By manipulating both material properties and geometric parameters of the heteropolymer structures, a design principle for tailoring the multistable configuration in the square‐twist origami is established based on variation of the structural potential energy. Under thermal triggering, the stiffness of the deformable structure is dramatically reduced, which causes an increase in the structural degree of freedom, allowing for self‐deployment via release of the prestored energy in the elastic twisted hinges. Utilizing such unique features and design principles, a prototype of frequency reconfigurable origami antenna of five diverse operating modes and a programmable multiple‐input multiple‐output communication system is subsequently designed and assembled, aiming to substantially promote the channel capacity and communication reliability. The findings and results firmly provide a remarkable design principle and strategy for advancing active origami structures and devices in shape‐morphing systems.

Identification of Structural Matrices of Shear Buildings Using Ambient Vibration Tests with Incomplete Measurements

System identification methods (SIMs) are powerful tools for structural health monitoring. SIMs are used either for identification of modal parameters or for extraction of structural characteristic matrices. The current study aims to identify the real matrices of a structure using structural dynamics theory and stochastic subspace identification based on realization theory. The study focuses on extraction of the condensed mass and stiffness matrices of shear buildings by means of ambient excitation responses for limited structural degrees of freedom. Realization theory states that there are minimal realizations for appropriate identification of the main real-system matrices. The present study shows that, by using values smaller than the minimal realization, condensed structural matrices can be correctly identified. This is accomplished by accurate estimation of the full real-system order. It is shown that successive repetitions of this approach can lead to complete structural matrices. The practical application of this procedure is examined using an experimental model and an analytical six-story shear model. Analysis revealed that, even in the presence of noise, this method can accurately identify structural matrices in all cases with high precision.

Numerical Research on a Three-Dimensional Solid Element Based on Generalized Elasticity Theory

A finite element equation is established based on generalized elasticity theory by applying a virtual work principle. Then, a penalty function term is added to the virtual work equation by imposing rotation and displacement as independent variables. An 8-node element with full integration, an 8-node element with reduced integration, and a 20-node element with full integration are constructed using difference integration schemes and shape functions. The influences of structural degrees of freedom and the penalty parameter on convergence are analyzed via the three elements. It is shown that the 8-node element with reduction integration and the 20-node element with full integration are convergent, whereas the 8-node element with full integration is divergent. The scale effects of a slender beam, a short beam, a thin plate, and a medium-thick plate are numerically analyzed. Lastly, the scale effects of the frequencies that correspond to the bending mode, torsion mode, and tension-compression mode for a pretwisted plate are studied. It is found that the frequencies that correspond to the bending mode and torsion mode exert a scale effect, whereas the frequency that corresponds to the tension-compression mode does not. The essence of the scale effect is that the rotational deformation of the microstructure is amplified.

Optimization of PID controller parameters for active control of single degree of freedom structures

In active control of structures, the parameters of controllers used application must be perfectly tuned. In that case, a good vibration reduction performance can be obtained without a stability problem. During the tuning process, the limit of control force and time delay of controller system must be considered for applicable design. In the study, the optimum parameters of Proportional-Derivative-Integral (PID) type controllers that are proportional gain (K), integral time (Ti) and derivative time (Td) were optimized by using teaching learning-based optimization (TLBO). TLBO is a metaheuristic algorithm imitating the teaching and learning phases of education in classroom. The optimization was done according to the responses of the structure under a directivity pulse of near fault ground motions. In the study, time delay was considered as 20 ms and the optimum parameters of PID controller for a single degree of freedom (SDOF) structural model was found for different control force limits. The performances and feasibility of the method were evaluated by using sets of near fault earthquake records.

Control of structural disorder in spinel ceramics derived from layered double hydroxides

Spinel oxides are versatile and functional materials with physicochemical properties that are significantly influenced by their structural disorder. The transition from layered double hydroxides (LDHs) to mixed metal oxides (MMOs) containing spinel oxides is a powerful approach to create materials with tailored properties suitable for various applications. Herein, we report the control of structural ordering in spinels related to the crystallinity, cationic inversion, and coordination number of constituent atoms by varying the transformation energy. Transformation from LDHs to spinels with higher applied energy leads to higher crystallinity, lower degree of inversion, and lower ratios of low-coordinated atoms to fully coordinated atoms after treatment with acid. We provide a general framework for controlling structural ordering, that can be applied to other spinels and metal oxides. In addition, LDHs and MMOs possess many chemical and structural degrees of freedom, making it possible to create materials that suit the needs of different applications, such as memory, sensors, catalysis, and energy conversion.

Phase transitions in Bi4Ti3O12.

Bi4Ti3O12 is a representative of the Aurivillius family of layered perovskites. These are high-temperature ferroelectric materials with prospects for applications in random-access memory and are characterized by an extremely confused interaction of their structural degrees of freedom. Using group-theoretical methods, structural distortions in the Bi4Ti3O12 high-symmetry phase, caused by rotations of rigid octahedra and their displacements as a single unit, have been investigated, taking into account the connections between them. Within the Landau theory, a stable thermodynamic model of phase transitions with three order parameters has been constructed. It is shown that, according to the phenomenological phase diagram, the transition between the high-temperature tetragonal phase and the low-temperature ferroelectric can occur both directly and through intermediate states, including those observed experimentally. The role of improper ordered parameters and possible domain configurations in the structure formation of the low-temperature ferroelectric phase are discussed.

Multi-holographic metamaterials: The concept, artificially intelligent designs, and new applications in acoustics

Acoustic holographic metamaterials present a powerful new platform for manipulating acoustic wave fields in fluids and solids. Furthering their development, we introduce a new concept of multi-holographic metamaterials (MHM)—complex media storing multiple volumetric holograms. Such media lack any distributed electromechanical components, yet offer dynamic functionality using only a few electronic components. This novel engineering paradigm shifts device fabrication cost from hardware to computation, presenting the designer with an NP-hard problem of resolving the complex relationship between structure and physical properties. Focused on airborne ultrasonic metamaterials, we treat them as a free-form composite of a fluid and solid(s). This unlocks a huge number of structural degrees of freedom, compared to the standard treatment of metamaterials as periodic arrays of geometrically similar unit cells. While analytical methods for finding all optima of an analytical function are scarce and largely impractical (Groebner basis computation being a notable example), we turn to machine learning methodologies to design MHMs efficiently. We show that unsupervised machine learning, a basic form of Artificial Intelligence, can completely replace human input into the design of MHMs. Experimental demonstrations include airborne ultrasonic metamaterials for coherent beamforming, with applications ranging from directive speakers to contactless manipulation of objects.

Multiple ferromagnetic transitions and structural distortion in the van der Waals ferromagnetVI3at ambient and finite pressures

We present a combined study of zero-field $^{51}$V and $^{127}$I NMR at ambient pressure and specific heat and magnetization measurements under pressure up to 2.08 GPa on bulk single crystals of the van-der-Waals ferromagnet VI$_3$. At ambient pressure, our results consistently demonstrate that VI$_3$ undergoes a structural transition at $T_s \approx $78 K, followed by two subsequent ferromagnetic transitions at $T_{FM1} \approx $50 K and $T_{FM2} \approx $36 K upon cooling. At lowest temperature ($T < T_{FM2}$), two magnetically-ordered V sites exist, whereas only one magnetically-ordered V site is observed for $T_{FM1} < T\,< T_{FM2}$. Whereas $T_{FM1}$ is almost unaffected by external pressure, $T_{FM2}$ is highly responsive to pressure and merges with the $T_{FM1}$ line at $p \approx 0.6 $GPa. At even higher pressures ($p \approx $1.25\,GPa), the $T_{FM2}$ line merges with the structural transition at $T_s$ which becomes moderately suppressed with $p$ for $p < 1.25$ GPa. Taken together, our data point towards a complex magnetic structure and an interesting interplay of magnetic and structural degrees of freedom in VI$_3$.

Development of cubic anvil type high pressure apparatus for neutron diffraction

High-pressure neutron diffraction (HPND) experiments in extended pressure and temperature ranges can provide invaluable information for understanding many pressure-induced emergent phenomena, such as unusual phase transitions and quantum critical behavior involving spin, orbital, charge and structural degrees of freedom, in strongly correlated materials. Many apparatuses for different purposes of HPND experiments have been developed in several laboratories. Recently, a clamp-type cubic anvil high pressure cell that can generate pressure over 7 GPa at 3 K was developed for low-temperature HPND measurements. In this paper, characteristics of the clamp-type cubic anvil high pressure cell are presented and its performances are demonstrated by measuring magnetic neutron scattering under pressure on MnP single crystal samples.

Thermally induced and photoinduced phase transitions in rubidium manganese hexacyanoferrate combining charge transfer and structural reorganization

Abstract External stimuli can alter the physical properties of materials during phase transitions in the solid state. Many researchers have investigated the influence of external stimuli on magnetic, electrical, and optical properties. For example, we previously revealed switching phenomena in cyano-bridged metal complexes induced by various external stimuli. Herein, we introduce how the functionalities of rubidium manganese hexacyanoferrate are driven by a thermally induced and photoinduced charge transfer coupled with structural phase transitions. Understanding how photoinduced phenomena and functions emerge is a great challenge of current interest and new ultrafast techniques, sensitive to electronic and/or structural degrees of freedom, open a nice opportunity for understanding and controlling materials at work.

Optimization of drivability control functions with two-stage rate limiters

Load changes in automotive drivelines may cause uncomfortable vibrations. A suitable motor torque control is able to remedy this problem. Often, a two degrees of freedom structure is used in these drivability control functions. In this structure, the desired motor torque is pre-filtered by a multi-stage rate limiter. However, those functions are still parametrized experimentally by laborious test drives or on the test-bench. This paper addresses the model-based optimal parametrization of these rate limiters in automotive drivability functions. For this, a recently published gear specific model is identified and validated for another gear position. In addition, a linear transfer function of multi-stage rate limiters is approximated by the transient input describing function method. The characteristics of this transfer function are used to reduce the number of design variables for the multi-objective optimization of a two-stage rate limiter for drivability control.

Microscopic Geometry Characterizes Structure/Potential-Energy Correspondence in a Thermodynamic System

Potential energy landscape (PEL) is essential to determine phase stability, reaction path, and other important physical as well as chemical properties. Whereas given PEL can reasonably determine the properties in thermodynamically equilibrium state, it is generally unclear whether a set of known property can uniquely and/or stably determines PEL, i.e., understandings of property/PEL correspondence is basically unidirectional in the current statistical mechanics. Here we make significant advance toward bidirectional bridging of this gap for classical discrete systems under many-body interactions. Our idea is to focus on characteristic microscopic geometry in configuration space for an exactly solvable system, resulting in a new, important quantity of "harmonicity in the structural degree of freedom". This quantity reasonablly characterizes which structures in equilibrium state have practically unique and stable correspondence to PEL, without requiring any thermodynamic information such as energy or temperature. The present findings will open a gate to constructing reliable PEL, where its predictive uncertainty can be a priori known. A significant role of microscopic geometry for non-interacting system should be re-emphasized in statistical mechanics.

Interface Engineering and Emergent Phenomena in Oxide Heterostructures.

Complex oxide interfaces have mesmerized the scientific community in the last decade due to the possibility of creating tunable novel multifunctionalities, which are possible owing to the strong interaction among charge, spin, orbital, and structural degrees of freedom. Artificial interfacial modifications, which include defects, formal polarization, structural symmetry breaking, and interlayer interaction, have led to novel properties in various complex oxide heterostructures. These emergent phenomena not only serve as a platform for investigating strong electronic correlations in low-dimensional systems but also provide potentials for exploring next-generation electronic devices with high functionality. Herein, some recently developed strategies in engineering functional oxide interfaces and their emergent properties are reviewed.

Strongly-coupled quantum critical point in an all-in-all-out antiferromagnet

Dimensionality and symmetry play deterministic roles in the laws of Nature. They are important tools to characterize and understand quantum phase transitions, especially in the limit of strong correlations between spin, orbit, charge, and structural degrees of freedom. Here, using newly-developed, high-pressure resonant X-ray magnetic and charge diffraction techniques, we have discovered a quantum critical point in Cd2Os2O7 as the all-in-all-out antiferromagnetic order is continuously suppressed to zero temperature and, concomitantly, the cubic lattice structure continuously changes from space group Fd-3m to F-43m. Surrounded by three phases of different time reversal and spatial inversion symmetries, the quantum critical region anchors two phase lines of opposite curvature, with striking departures from a mean-field form at high pressure. As spin fluctuations, lattice breathing modes, and quasiparticle excitations interact in the quantum critical region, we argue that they present the necessary components for strongly-coupled quantum criticality in this three-dimensional compound.

Rotational Dynamics of Solutes with Multiple Single Bond Axes Studied by Infrared Pump-Probe Spectroscopy.

To investigate the relationship between the structural degrees of freedom around a vibrational probe and the rotational relaxation process of a solute in solution, we studied the anisotropy decays of three different N3-derivatized amino acids in primary alcohol solutions. By performing polarization-controlled IR pump-probe measurements, we reveal that the anisotropy decays of the vibrational probe molecules in 1-alcohol solutions possess two decay components, at subpicosecond and picosecond time scales. On the basis of results showing that the fast relaxation component is insensitive to the vibrational probe molecule, we suggest that the anisotropy decay of the N3 group on a subpicosecond time scale results from a local, small-amplitude fluctuation of the flexible vibrational probe, which does not depend on the details of its molecular structure. However, the slow relaxation component depends on the solute: with longer alkyl chains attached to the N3 group, the anisotropy decay of the slow component is faster. Consequently, we conclude that the slow relaxation component corresponds to the reorientational motion of the N3 group correlated with other intramolecular rotational motions (e.g., rotational motions of the neighboring alkyl chain). Our experimental results provide important insight into understanding the rotational dynamics of solutes with multiple single bond axes in solution.

Fusion dynamics of stable and weakly bound colliding systems

This work systematically analyzed the fusion dynamics of the projectile-target combinations involving stable and loosely bound systems within the view of the energy-dependent Woods–Saxon potential model (EDWSP model) and the coupled channel approach. The different projectiles are bombarded onto series of Sm-isotopes, which possess the dominance of the different kinds of the nuclear structure degrees of freedom and with the increase of the neutron richness, the Sm-isotopes gradually shift from spherical shape to a statically deformed shape. In the fusion of [Formula: see text] reaction, the impacts of vibrational degrees of freedom of the colliding nuclei are dominant while in the case of [Formula: see text] systems, the rotational states of the deformed target isotopes have a strong impression on the below-barrier fusion data. The heavier target isotopes ([Formula: see text] also exhibit the higher order deformation such as [Formula: see text], [Formula: see text]-deformation parameter in its ground state and couplings to such channels must be incorporated in theoretical calculations in order to achieve close agreement with the sub-barrier fusion data. However, in the case of the loosely bound systems, the projectile breakup channel significantly affects the fusion excitation functions in the domain of the Coulomb barrier. To ensure the role of the projectile breakup channel, the fusion of the different loosely bound projectiles ([Formula: see text] and [Formula: see text] with Sm-isotopes are investigated, wherein the above-barrier fusion data of these reactions are suppressed with reference to the coupled channel calculations. This hindrance is the result of the projectile breakup effects that occur as a consequence of the breakup of the projectile before reaching the fusion barrier due to its low binding energy. However, in the EDWSP model calculations the magnitude of the hindrance of the above-barrier fusion data of [Formula: see text] and [Formula: see text] reactions is reduced by a factor varying from 7% to 13% with respect to a value reported in the literature. In contrast to this, the sub-barrier fusion enhancement of [Formula: see text] and [Formula: see text] reactions is the result of the dominance of the nuclear structure degrees of freedom of the colliding systems.

Inversion in Mg1-xNixAl2O4 Spinel: New Insight into Local Structure.

A wide variety of compositions adopt the isometric spinel structure (AB2O4), in which the atomic-scale ordering is conventionally described according to only three structural degrees of freedom. One, the inversion parameter, is traditionally defined as the degree of cation exchange between the A- and B-sites. This exchange, a measure of intrinsic disorder, is fundamental to understanding the variation in the physical properties of different spinel compositions. Based on neutron total scattering experiments, we have determined that the local structure of Mg1-xNixAl2O4 spinel cannot be understood as simply being due to cation disorder. Rather, cation inversion creates a local tetragonal symmetry that extends over sub-nanometer domains. Consequently, the simple spinel structure is more complicated than previously thought, as more than three parameters are needed to fully describe the structure. This new insight provides a framework by which the behavior of spinel can be more accurately modeled under the extreme environments important for many geophysics and energy-related applications, including prediction of deep seismic activity and immobilization of nuclear waste in oxides.