Forced Response Research Articles

The eyes have it! Functional field of view differences between visual search behavior and body-worn camera during a use of force response in active-duty police officers

ABSTRACT Although officer body-worn cameras (BWCs) have improved transparency of police interactions within the community, BWCs have a limited field of view, are subject to bias, and do not account for the factors that influence rapid decision-making by officers, including their visual attentional control and perceptual processes. The purpose of this study was to investigate the camera perspective of six critical incidents and position data from BWC compared to eye tracking and head movement data in a use-of-force scenario from 44 active-duty police officers. The analysis of gyroscope and accelerometer data demonstrated low correlations between eye cameras and BWC position data. Officers attended 80.5% of all critical incidents, whereas BWC view captured only 66.2%, especially missing key events (<48%). BWC footage did not account for the visual information and the behaviors of the suspect, potential threats, and bystanders who influence the officers' decision-making during the use of force encounters.

A Stylistic Study of Resentment in Al-Zahraa’s Sermon of Fadak

In its active form, resentment can be a forceful response to acts that have created unjustified suffering. In relation to Al-Zahraa’s sermon, she feels injustice when her earth and right has been taken after her father death. As such, she goes to the mosque where Abu Baker and others found and delivers her speech. Stylistically, Al-Zahraa uses certain devices or deviations as a way to deliver her message effectively to the audience. Consequently, the study tries to find answers to the following questions: (1) how is resentment manifested in Al-Zahraa’s sermon? (2) what are the stylistic devices that are utilized in Al-Zahraa’s sermon? (3) Does Al-Zahraa succeed in expressing her resentment effectively? And (4) To who her resentment is directed? Due to these problems, the following aims are set: (1) showing out how resentment is manifested in Al-Zahraa’s sermon, (2) identifying the stylistic devices that are used in Al-Zahraa’s sermon, (3) clarifying whether Al-Zahraa succeeds in expressing her resentment effectively or not, and (4) Identifying the addressee that Al-Zahraa wants to deliver her resentment to. In the light of these aims, the paper hypothesizes the following: (1) resentment is manifested through using certain strategies and devices, (2) there are some stylistic devices that are heavily used in Al-Zahraa’s sermon, and (3) Al-Zahraa succeeds in expressing her resentment effectively, and (4) All of Al-Zahraa resentment speech is directed to an individual. After presenting a background knowledge about resentment and some stylistic devices with analysing some extracts taken from Al-Zahraa’s sermon, some conclusions are reached.

Assessing the Efficiency of the Air Isolation System Based on the Mathematical Models

Two calculation methods of the lumped parameter model (LPM) and mass flow ratio (MFR) used to establish dynamics models of air isolation system (AIS) in vehicles are widely applied. However, the efficiency and application range of the LPM and MFR for the AIS of the vehicles have not been explained in detail. To clarify this issue, the numerical simulation and experiment of the AIS performed under the harmonic excitation are given to evaluate the accuracy of the LPM and MFR. The two-axle automobiles and multi-axle heavy trucks equipped with the AIS are also simulated to evaluate the efficiency of the AIS with the LPM and MFR in improving ride comfort and road friendliness. The study shows that with the single model of the AIS, measured and simulated result in AIS's force response, force-deformation characteristic, and dynamics stiffness-frequency characteristic with LPM and MFR are similar. Therefore, both methods could be applied to establish the dynamic model of the AIS. However, by applying the AIS on the two-axle and multi-axle vehicles, the MFR improves road-friendliness and comfort in two-axle automobiles better than the LPM, conversely, the LPM improves road-friendliness and comfort in multi-axle trucks better than that the MFR. Therefore, to more accurately assess the isolation efficiency of the AIS in improving road-friendliness and comfort in vehicle, the MFR should be applied to the AIS using the pipe designed by the parallel pipes or long pipes of two-axle vehicles whereas the LPM should be applied to the AIS using the pipe designed by the complex pipes of multi-axle vehicles.

Damage Mechanics Challenge: Predictions based on the phase field fracture model

In this work, we describe our contribution to the Purdue-SANDIA-LLNL Damage Mechanics Challenge. The phase field fracture model is adopted to blindly estimate the failure characteristics of the challenge test, an unconventional three-point bending experiment on an additively manufactured rock resembling a type of gypsum. The model is formulated in a variationally consistent fashion, incorporating a volumetric–deviatoric strain energy decomposition, and the numerical implementation adopts a monolithic unconditionally stable solution scheme. Our focus is on providing an efficient and simple yet rigorous approach capable of delivering accurate predictions based solely on physical parameters. Model inputs are Young’s modulus E, Poisson’s ratio ν, toughness Gc and strength σc (as determined by the choice of phase field length scale ℓ). We show that a single mode I three-point bending test is sufficient to calibrate the model, and that the calibrated model can then reliably predict the force versus displacement responses, crack paths and surface crack morphologies of more intricate three-point bending experiments that are inherently mixed-mode. Importantly, our peak load, crack trajectory and crack surface morphology predictions for the challenge test, submitted before the experimental data was released, show a remarkable agreement with experiments. The characteristics of the challenge, and how changes in these can impact the predictive abilities of phase field fracture models, are also discussed.

Shear and shear-induced normal responses of origami cylinders relate to their structural asymmetries

Origami cylinders have been studied extensively under compression, however, their normal force response under shear deformation is still ill-understood. We experimentally studied the shear-induced normal force of these systems and provided a simple model to predict this response in Yoshimura and Kresling origami cylinders in the range of small deformations. Besides that, the effect of disorder is little understood in those origami patterns. Therefore, we investigate the disorder effect and show it can lead to diverse normal responses perpendicular to shear deformation in crumpled Yoshimura, with slopes of the force perpendicular to torsion that can be positive, zero, or negative depending on the disordered pattern of folds. The disorder leads to an asymmetry concerning the shearing direction, which we quantified via an asymmetry index from the 2D Fast Fourier transform spectrum of the crease pattern images. This asymmetry index is found to be linearly related to the slope of the normal force-torsion relationship.

Novel methodology for characterization of thermoelectric modules and materials

The document presents an innovative methodology that combines forced response and natural response theories in thermoelectric materials and devices. It stands out for expressing the thermoelectric figure of merit in terms of the ratio of two temperatures ZT푇̅=∆T′/∆T, enabling comprehensive testing and precise characterization of thermoelectric modules and materials, including measurements of thermal conductance, electrical resistance, Seebeck coefficient, and figure of merit. Additionally, it addresses the determination of thermal resistances and thermal capacitances related to thermal contacts, as well as the derivation of characteristic time constants and angular frequencies. This approach, applicable to both modular devices and individual samples, allows for the simultaneous measurement of all parameters on a single sample. The experiments considered non-ideal contacts and non-adiabatic conditions at room temperature T= 300K, enhancing the feasibility of in-situ characterization and positioning this methodology as a key tool in thermoelectric research.

Predictive dynamic modeling and analysis of blisks through digital representations constructed upon precise geometry measurements

Blade geometric variations generally have a significant impact on the structural dynamics of integrally bladed disks widely used in the advanced aero-engines. This paper presents a holistic research in regard to the predictive dynamic modeling, analysis and experimental verification for a blisk by taking advantage of the advanced 3D optical geometry measurement technology. Geometrically mistuned models (GMMs) are semi-automatically constructed upon the precisely measured blisk geometry by an efficient FE mesh updating strategy. They provide explicit, high-fidelity digital representations of the geometric variations within the integrally manufactured blisk. A ‘Sector Mode Assembling Reduction Technique’ is developed and specifically tailored for efficient dynamic analysis of the large-sized GMMs at a relatively low computational cost and memory requirement. Intensive test campaigns, including forced response tests in the stationary/spinning rig under well-controlled laboratory conditions, are carried out for a full assessment of the GMMs’ dynamic prediction capability. Experimental verification results show that the GMM is able to capture the modal dynamics and resonant vibration of the stationary/rotating blisk with satisfactory accuracy. The physical-reality-based GMM converted directly from the precise geometry measurement data can be considered as a viable and valuable tool for predictive vibration evaluation of blisks. However, its model accuracy exhibits a mode-related dependence on the mesh density. The tradeoff between model accuracy and prohibitive computational cost proved to be the bottleneck of this promising blisk modeling approach.

Proper generalized decomposition-based iterative enrichment process combined with shooting method for steady-state forced response analysis of nonlinear dynamical systems

This paper presents a novel framework combining proper generalized decomposition (PGD) with the shooting method to determine the steady-state response of nonlinear dynamical systems upon a general periodic input. The proposed PGD approximates the response as a low-rank separated representation of the spatial and temporal dimensions. The Galerkin projection is employed to formulate the subproblem for each dimension, then the fixed-point iteration is applied. The subproblem for the spatial vector can be regarded as computing a set of reduced-order basis vectors, and the shooting problem projected onto the subspace spanned by these basis vectors is defined to obtain the temporal coefficients. From this procedure, the proposed framework replaces the complex nonlinear time integration of the full-order model with the series of solving simple iterative subproblems. The proposed framework is validated through two descriptive numerical examples considering the conventional linear normal mode method for comparison. The results show that the proposed shooting method based on PGD can accurately capture nonlinear characteristics within 10 modes, whereas linear modes cannot easily approximate these behaviors. In terms of computational efficiency, the proposed method enables CPU time savings of about one order of magnitude compared with the conventional shooting methods.

Experimental study on the piezo-based energy harvester utilizing the ambient vibrations for smart applications

The proposed energy harvester has novel construction, its performance evaluated through frequency response, force response and power harvested under an optimum load, is presented. This harvester is more suitable for low power applications like IoT devices, Wireless sensor nodes and biomedical implants. The suggested harvester has two sections namely truncated cone and rectangular beam section (TCRB). The analytical model is formulated and natural frequencies are obtained using FEA tool. Simulations for natural frequencies and associated comprehensive parameters are done along with distribution of stress across the piezo patch. The tapered radius ratio of the truncated cone is analysed to obtain the optimal value. The simulated model is fabricated and verified experimentally. The result is compared with uniform cantilever beam harvester. The voltage produced by a TCRB harvester is 56.76 % higher than the harvester with a homogeneous rectangular cantilever beam. The rectangular harvester has a resonant frequency of 52.8 Hz, while the TCRB harvester has 39.4 Hz. Also, the TCRB type piezoelectric vibration energy harvester with optimum taper radius ratio provides greater power, than uniform and trapezoidal cantilever beams. The obtained experimental results match the simulation results, ascertains the validity of the proposed harvester.

Control of vortex shedding and acoustic resonance of a circular cylinder in cross-flow

This study experimentally investigates the effectiveness of a control rod in suppressing self-excited acoustic resonance within a range of Reynolds numbers (Re) spanning from 2.1 × 104 to 1.6 × 105. The investigation focuses on specific parameters, including diameter ratio (d/D) values of 0.1, 0.2, and 0.3; gap ratio (G/D) values of 0.05, 0.1, and 0.2; and angular positions (θ) ranging from 0 to 180 degrees. Comparative analyses are conducted between cases featuring the control rod and a reference case (base case) without it. The near-wake flow field is characterized using Particle Image Velocimetry (PIV), and aeroacoustic response measurements are employed to quantify the aeroacoustic noise emission, particularly during self-excited acoustic resonance. Simultaneous measurements of fluctuating lift force and aeroacoustic response measurements, facilitate the quantification of energy transfer from the flow field to the acoustic field during self-excited acoustic resonance. The results reveal that the control rod’s placement significantly impacts the Strouhal periodicity, with outcomes heavily dependent on the rod’s angular orientation. At certain angular positions, the control rod reduces the sound pressure level (SPL) generated during acoustic resonance excitation. However, at different angular positions, the rod exacerbates resonance excitation. This variability is attributed to the control rod’s profound influence on the vortex core formation and the energy transfer mechanism during acoustic resonance.

Surface-phonon-polariton-enhanced photoinduced dipole force for nanoscale infrared imaging.

The photoinduced dipole force (PiDF) is an attractive force arising from the Coulombic interaction between the light-induced dipoles on the illuminated tip and the sample. It shows extreme sample-tip distance and refractive index dependence, which is promising for nanoscale infrared (IR) imaging of ultrathin samples. However, the existence of PiDF in the mid-IR region has not been experimentally demonstrated due to the coexistence of photoinduced thermal force (PiTF), typically one to two orders of magnitude higher than PiDF. In this study, we demonstrate that, with the assistance of surface phonon polaritons, the PiDF of c-quartz can be enhanced to surpass its PiTF, enabling a clear observation of PiDF spectra reflecting the properties of the real part of permittivity. Leveraging the detection of the PiDF of phonon polaritonic substrate, we propose a strategy to enhance the sensitivity and contrast of photoinduced force responses in transmission images, facilitating the precise differentiation of the heterogeneous distribution of ultrathin samples.

Auxetic honeycomb core layer effect on vibrations of annular plates based on shear deformation theory

Light composite materials such as auxetic honeycomb structures offer a unique combination of strength, lightweight, and durability, making them ideal for a wide range of industrial and structural applications. Consequently, it is crucial to study the effect of these materials on the dynamic behavior of structures. In this study, an analytical solution based on the multiple-scale method has been proposed to solve equations of motion of a multilayer axisymmetric annular plate. The plate includes two top and bottom isotropic layers and one auxetic honeycomb core layer. By considering both radial and transverse deflections, the governing equations are derived based on the first-order shear deformation theory. The radial and transverse frequencies of the plate are determined from the order zero of equations and a correction coefficient for each frequency has been extracted from the order one and solvability conditions. The response of the plate under harmonic transverse excitation has been determined analytically and by conducting a parametric study, the effect of different geometrical and mechanical parameters on the free and forced vibration responses has been studied. It is observed that employing a honeycomb core in the multilayer plate allows us to significantly decrease the plate weight while the dynamic response and the frequencies remain nearly the same or vary slightly. The results are validated by comparing them with the finite element method and some other references.

Multimodal Resonance Response of Incompressible Hyperelastic Moderately Thick Cylindrical Shells

Based on the modified third-order shear deformation theory, the harmonic balance method, and the pseudo-arclength continuation method with two-point prediction, the nonlinear forced vibration response of incompressible hyperelastic moderately thick cylindrical shells subjected to a concentrated harmonic load at mid-span and simply supported boundary conditions at both ends is investigated. The algorithmic procedure for solving steady-state periodic solutions of strongly nonlinear systems of differential equations is presented. The structural response characteristics of shells under different excitation amplitudes and structural parameters are analyzed. The numerical results indicate that the aspect ratio of moderately thick hyperelastic cylindrical shells has a significant effect on the natural frequency ratio. Different frequency ratios lead to varying nonlinear mode coupling effects. The coupling effects among modes result in complex nonlinear behavior in the vibration response of each mode, leading to abundant multi-valued phenomena in the response curve.

Control of buckling behavior in origami-based auxetic structures by functionally graded thickness

Negative Poisson’s ratio in auxetic structures plays a crucial role in energy absorption and impact mitigation. Origami-based lattices within the realm of auxetic structures offer the advantage of facile fabrication and design. Nevertheless, the utilization of periodic lattices in origami-based auxetic structures constrains the available design space for achieving diverse mechanical properties. Addressing this limitation, our study introduces origami-based auxetic structures with functionally graded thickness, utilizing origami-based lattices known as Tachi–Miura polyhedra. We investigated the impact of functionally graded thickness on buckling behavior and force responses through dynamic loading experiments employing 3D-printed test pieces. The experimental results indicate that functionally graded thickness induces partial auxetic deformation in lattices, and the resulting nonsymmetric deformation prevents global buckling, thereby averting bounded forces observed in structures with uniform thickness. These findings extend the applicability of auxetic structures, spanning from energy absorption to the design of cushioning structures.

Responsive Microgels through RAFT-HDA Dynamic Covalent Bonding Chemistry.

This paper developed a method for preparing ultrasound-responsive microgels based on reversible addition fragmentation chain transfer-hetero Diels-Alder (RAFT-HAD) dynamic covalent bonding. First, a styrene cross-linked network was successfully prepared by a Diels-Alder (DA) reaction between phosphoryl dithioester and furan using double-ended diethoxyphosphoryl dithiocarbonate (BDEPDF) for RAFT reagent-mediated styrene (St) polymerization, with a double-ended dienophile linker and copolymer of furfuryl methacrylate (FMA) and St as the dienophile. Subsequently, the microgel system was constructed by the HDA reaction between phosphoryl disulfide and furan groups using the copolymer of polyethylene glycol monomethyl ether acrylate (OEGMA) and FMA as the dienophore building block and hydrophilic segment and the polystyrene pro-dienophile linker as the cross-linker and hydrophobic segment. The number of furans in the dienophile chain and the length of the dienophile linker were regulated by RAFT polymerization to investigate the effects of the single-molecule chain functional group degree, furan/dithioester ratio, and hydrophobic cross-linker length on the microgel system. The prepared microgels can achieve the reversible transformation of materials under force responsiveness, and their preparation steps are simple and adaptive to various potential applications in biomedical materials and adaptive electrical materials.

Dynamic responses of steady-state transition structures under impact loading

Advancements in materials science and mechanical system have spurred widespread investigation into non-traditional structures. In particular, engineers have shown interest in steady-state transition structures with phase transition properties. In this paper, a three-dimensional steady-state transition structure was established using the genetic algorithm and three-dimensional expansion, on which the low-velocity impact tests were carried out. Force response and energy absorption of the steady-state transition structures under impact were studied. From the force response and energy absorption curves, it can be seen that the steady-state transition structures absorb and store portion of impact energy temporarily, gradually releasing it after impact peak. This unique energy behavior results in a steady state transition structure with a long impact response time and a low peak impact force under impact. In addition, investigation into energy transfer within these structures reveals that energy oscillations occur among multilayered bistable surfaces during steady-state transitions, further improving the energy dissipation. Further, the dynamic response and damage modes of the honeycomb structure and the steady state transition structure were compared, showing that the damage mode of the steady state transition structure under the impact is an overall damage, in contrast to the penetration damage of the honeycomb structure. Notably, the steady-state transition structures showcase a higher proportion of elastic strain energy during impacts, effectively delaying structural damage onset, and dispersing impact energy, thus enhancing impact resistance. In light of these findings, the demonstrated behavior of steady-state transition structures in absorbing and dissipating impact energy showcases their potential as promising avenues for the development of more effective impact protection strategies.

Influence of More Mechanistic Representation of Particle Dry Deposition on 1850–2000 Changes in Global Aerosol Burdens and Radiative Forcing

AbstractRobust estimates of historical changes in aerosols are key for accurate constraints on climate sensitivity. Dry deposition is a primary sink of aerosols from the atmosphere. However, most global climate models do not accurately represent observed strong dependencies of dry deposition following turbulent transport on aerosol size. It is unclear whether there is a substantial impact of mischaracterized aerosol deposition velocities on historical aerosol changes. Here we describe improved mechanistic representation of aerosol dry deposition in the NASA Goddard Institute for Space Studies (GISS) global climate model, ModelE, and illustrate the impact on 1850–2000 changes in global aerosol burdens as well as aerosol direct and cloud albedo effects using a set of 1850 and 2000 time slice simulations. We employ two aerosol configurations of ModelE (a “bulk” mass‐based configuration and a configuration that more explicitly represents aerosol size distributions, internal mixing, and microphysics) to explore how model structural differences in aerosol representation alter the response to representation of dry deposition. Both configurations show larger historical increases in the global burdens of non‐dust aerosols with the new dry deposition scheme, by 11% in the simpler mass‐based configuration and 23% in the more complex microphysical configuration. Historical radiative forcing responses, which vary in magnitude from 5% to 12% as well as sign, depend on the aerosol configuration.

Study on the Seismic Performance of High-Speed Railway Extradosed Cable-Stayed Bridge Considering CRTS III Slab Ballastless Track Structure

This paper explores the seismic damping mechanism and performance of CRTS III slab ballastless track on an isolation system extradosed cable-stayed bridge during rare earthquakes. It serves as a guide for designing slab ballastless tracks on high-speed railway extradosed cable-stayed bridges. Using a high-speed railway extradosed cable-stayed bridge as a case study, we established a Midas finite element model to optimize the track plate parameters by adjusting the fastener stiffness and plate joint length. The optimization process and method can be applied as a reference for similar bridge designs. The research findings reveal that, under rare earthquake conditions, the CRTS III slab ballastless track model (with a plate joint length of 90mm and fastener stiffness of 30kN/mm) has a minimal impact on increasing the longitudinal internal force at the pier’s base. It, at most, raises the earthquake internal force response by 5%. The model significantly reduces the overall relative displacement of the bridge pier and girder, with a notable 15.5% reduction in the relative displacement of pier 143# on the side pier. Therefore, when conducting internal force tests for the bridge, it is crucial to consider the influence of track plate restraint.

Identical sequences, different behaviors: Protein diversity captured at the single-molecule level

The classical “one sequence, one structure, one function” paradigm has shaped much of our intuition of how proteins work inside the cell. Partially due to the insight provided by bulk biochemical assays, individual biomolecules are often assumed to behave as identical entities, and their characterization relies on ensemble averages that flatten any conformational diversity into a unique phenotype. While the emergence of single-molecule techniques opened the gates to interrogating individual molecules, technical shortcomings typically limit the duration of these measurements, which precludes a complete characterization of an individual protein and, hence, capturing the heterogeneity among molecular populations. Here, we introduce an ultrastable magnetic tweezers design, which enables us to measure the folding dynamics of a single protein during several uninterrupted days with high temporal and spatial resolution. Thanks to this instrumental development, we fully characterize the nanomechanics of two proteins with a very distinct force response, the talin R3IVVI domain and protein L. Days-long recordings on the same protein individual accumulate thousands of folding transitions with submicrosecond resolution, allowing us to reconstruct their free energy landscapes and describe how they evolve with force. By mapping the nanomechanical identity of many different protein individuals, we directly capture their molecular diversity as a quantifiable dispersion on their force response and folding kinetics. By significantly expanding the measurable timescales, our instrumental development offers a tool for profiling individual molecules, opening the gates to directly characterizing biomolecular heterogeneity.

Conserved mammalian muscle mechanics during eccentric contractions.

Skeletal muscle has a broad range of biomechanical functions, including power generation and energy absorption. These roles are underpinned by the force-velocity relationship, which comprises two distinct components: a concentric and an eccentric force-velocity relationship. The concentric component has been extensively studied across a wide range of muscles with different muscle properties. However, to date, little progress has been made in accurately characterising the eccentric force-velocity relationship in mammalian muscle with varying muscle properties. Consequently, mathematical models of this muscle behaviour are based on a poorly understood phenomenon. Here, we present a comprehensive assessment of the concentric force-velocity and eccentric force-velocity relationships of four mammalian muscles (soleus, extensor digitorum longus, diaphragm and digastric) with varying biomechanical functions, spanning three orders of magnitude in body mass (mouse, rat and rabbits). The force-velocity relationship was characterised using a hyperbolic-linear equation for the concentric component a hyperbolic equation for the eccentric component, at the same time as measuring the rate of force development in the two phases of force development in relation to eccentric lengthening velocity. We demonstrate that, despite differences in the curvature and plateau height of the eccentric force-velocity relationship, the rates of relative force development were consistent for the two phases of the force-time response during isovelocity lengthening ramps, in relation to lengthening velocity, in the four muscles studied. Our data support the hypothesis that this relationship depends on cross-bridge and titin activation. Hill-type musculoskeletal models of the eccentric force-velocity relationship for mammalian muscles should incorporate this biphasic force response. KEY POINTS: The capacity of skeletal muscle to generate mechanical work and absorb energy is underpinned by the force-velocity relationship. Despite identification of the lengthening (eccentric) force-velocity relationship over 80years ago, no comprehensive study has been undertaken to characterise this relationship in skeletal muscle. We show that the biphasic force response seen during active muscle lengthening is conserved over three orders of magnitude of mammalian skeletal muscle mass. Using mice with a small deletion in titin, we show that part of this biphasic force profile in response to muscle lengthening is reliant on normal titin activation. The rate of force development during muscle stretch may be a more reliable way to describe the forces experienced during eccentric muscle contractions compared to the traditional hyperbolic curve fitting, and functions as a novel predictor of force-velocity characteristics that may be used to better inform hill-type musculoskeletal models and assess pathophysiological remodelling.