Description Of Motion Research Articles

Deep Learning‐Based Optical Flow in Fine‐Scale Deformation Mapping of Sea Ice Dynamics

AbstractOptical methods deployed for studying motion and deformation of objects often struggle to distinguish small displacements hidden behind observational noise. In geophysical applications, this has limited analysis to lower spatial and temporal resolutions, while reliable extraction of high‐resolution data is required for understanding material deformation and failure. In this work, we propose a novel method for determining deformation for noisy observational data using deep learning‐based optical flow. To enable higher estimate accuracy, we introduce a novel initialization technique considering contextual information. This allows an unprecedentedly high‐resolution description of motion in radar imagery. We use the proposed technique on verification cases to compare with the currently used methodologies and on ship radar observations on sea ice deformation. The outcome of our work is an open‐source end‐to‐end tool for determining full‐field Lagrangian deformation fields for data sets with small pixel displacements and high observational noise.

Temperature Dependence of Electron Viscosity in Superballistic GaAs Point Contacts.

Hydrodynamic description of collective electron motion turns out to be fruitful, since it provides a reliable physical concept that allows engineering the electron-electron interaction. We experimentally study the relation between two fundamental quantities-the electron viscosity and the Fermi quasiparticle lifetime-beyond the applicability limit of the Fermi liquid theory. We use point contact (PC) geometry to study electron transport and observe superballistic PC conductance, which is a signature of the electron viscosity. At high enough temperatures, the viscosity-lifetime relation is shown to diverge from the theoretically predicted one and turns out to be nontrivial. In addition, we study these phenomena in PCs freely suspended over a substrate, i.e., under the unique experimental conditions of enhanced electron-electron interaction. Suspension is found to reduce the electron viscosity in the whole temperature range, which makes the suspended structures a promising test bed for studying hydrodynamic effects in solids.

Investigation of trochoidal paths in physics lessons

Abstract Using the example of trochoids it is shown how Bruner’s cognitive-psychological model of modes of representations is used to introduce the kinematics and its mathematical description of a complex motion in the introductory phase of physics studies. Enactive (experimental), iconic (simulation) and symbolic (equation) representations of the rolling motion of a wheel are combined to address the different types of learning to gradually introduce the formal description of trochoids.

Mechanical description of charged droplet motion in electrowetting-on-dielectric experiment and modelling

Mechanical description of charged droplet motion in electrowetting-on-dielectric experiment and modelling

Generalized Langevin equation for a tagged monomer in a Gaussian semiflexible polymer.

In this study, we present a comprehensive analysis of the motion of a tagged monomer within a Gaussian semiflexible polymer model. We carefully derived the generalized Langevin equation (GLE) that governs the motion of a tagged central monomer. This derivation involves integrating out all the other degrees of freedom within the polymer chain, thereby yielding an effective description of the viscoelastic motion of the tagged monomer. A critical component of our analysis is the memory kernel that appears in the GLE. By examining this kernel, we characterized the impact of bending rigidity on the non-Markovian diffusion dynamics of the tagged monomer. Furthermore, we calculated the mean-squared displacement of the tagged monomer using the derived GLE. Our theoretical findings were corroborated by the Langevin dynamics simulation and scaling theory. Our results not only show remarkable agreement with previously known results in certain limiting cases but also provide dynamic features over the entire timescale.

A co-rotational finite element for nonlinear analysis of hollow section steel frames accounting for local buckling via lumped damage mechanics

To reduce engineering costs, the search for more efficient materials and design concepts leads to slender structures. Consequently, the need for geometrically nonlinear analysis is becoming increasingly important. Besides, the phenomenon of local instability becomes more evident when dealing with structural components with hollow cross-sections composed of slender plates and shells. It is usual to employ elastoplastic shell finite element models for dealing with such problems, which leads to analyses with high computational costs. Therefore, this paper proposes a geometrical nonlinear beam finite element, developed for the nonlinear analysis of hollow section steel frames, accounting for local buckling. The finite element is locally formulated as the traditional linear Euler-Bernoulli beam element. A co-rotational description of motion is then employed to account for large displacements and rotations. The local buckling phenomenon is taken into account by a lumped damage model, which concentrates the effects at inelastic hinges. The inelastic hinge´s yield functions are defined in terms of the co-rotational nodal axial forces and bending moments, as well as in terms of damage variables. The local buckling of the hollow sections is accounted by the adopted damage evolution law. The inelastic rotations are governed by the normality rule and the evolution laws of the internal variables. A predictor-corrector algorithm is employed at element level, whereas the Newton-Raphson method solves the global nonlinear equilibrium equations. To assess the accuracy of the proposed model, the numerical results obtained in this study are compared against available numerical and experimental responses. The numerical results show good accuracy, which corroborates that the proposed model might be used in practical applications.

Truncated Coulomb potential for planar channeling

It is shown that if the atomic screening function is described in the Thomas-Fermi approximation, the corresponding continuous potential for planar channeling to a good accuracy reduces to a truncated Coulomb potential. The sum of two displaced Coulomb potentials also accurately approximates interplanar static continuous potentials for Si, Ge, W crystals in orientation (110), as well as the thermal potential of a Ge crystal in orientation (111), not too close to atomic planes. Such a possibility can be used to facilitate the description of channeled and quasichanneled particle motions. We illustrate this by calculating classical particle channeling periods, quantum energy levels, and the probability of tunneling of a negatively charged particle through a single atomic plane. Simple scaling laws in dependencies of those quantities on the atomic number Z result this case. Published by the American Physical Society 2024

MaskedMimic: Unified Physics-Based Character Control Through Masked Motion Inpainting

Crafting a single, versatile physics-based controller that can breathe life into interactive characters across a wide spectrum of scenarios represents an exciting frontier in character animation. An ideal controller should support diverse control modalities, such as sparse target keyframes, text instructions, and scene information. While previous works have proposed physically simulated, scene-aware control models, these systems have predominantly focused on developing controllers that each specializes in a narrow set of tasks and control modalities. This work presents MaskedMimic, a novel approach that formulates physics-based character control as a general motion inpainting problem. Our key insight is to train a single unified model to synthesize motions from partial (masked) motion descriptions, such as masked keyframes, objects, text descriptions, or any combination thereof. This is achieved by leveraging motion tracking data and designing a scalable training method that can effectively utilize diverse motion descriptions to produce coherent animations. Through this process, our approach learns a physics-based controller that provides an intuitive control interface without requiring tedious reward engineering for all behaviors of interest. The resulting controller supports a wide range of control modalities and enables seamless transitions between disparate tasks. By unifying character control through motion inpainting, MaskedMimic creates versatile virtual characters. These characters can dynamically adapt to complex scenes and compose diverse motions on demand, enabling more interactive and immersive experiences.

Dynamic modeling method for constrained system with singular mass matrices

Dynamic modeling method for constrained system with singular mass matrices

Crowd Density Estimation via Global Crowd Collectiveness Metric

Drone-captured crowd videos have become increasingly prevalent in various applications in recent years, including crowd density estimation via measuring crowd collectiveness. Traditional methods often measure local differences in motion directions among individuals and scarcely handle the challenge brought by the changing illumination of scenarios. They are limited in their generalization. The crowd density estimation needs both macroscopic and microscopic descriptions of collective motion. In this study, we introduce a Global Measuring Crowd Collectiveness (GMCC) metric that incorporates intra-crowd and inter-crowd collectiveness to assess the collective crowd motion. An energy spread process is introduced to explore the related crucial factors. This process measures the intra-crowd collectiveness of individuals within a crowded cluster by incorporating the collectiveness of motion direction and the velocity magnitude derived from the optical flow field. The global metric is adopted to keep the illumination-invariance of optical flow for intra-crowd motion. Then, we measure the motion consistency among various clusters to generate inter-crowd collectiveness, which constitutes the GMCC metric together with intra-collectiveness. Finally, the proposed energy spread process of GMCC is used to merge the inter-crowd collectiveness to estimate the global distribution of dense crowds. Experimental results validate that GMCC significantly improves the performance and efficiency of measuring crowd collectiveness and crowd density estimation on various crowd datasets, demonstrating a wide range of applications for real-time monitoring in public crowd management.

Particle Virtual Element Method (PVEM): an agglomeration technique for mesh optimization in explicit Lagrangian free-surface fluid modelling

Particle Virtual Element Method (PVEM): an agglomeration technique for mesh optimization in explicit Lagrangian free-surface fluid modelling

Automatic Inbetweening for Stroke‐Based Painterly Animation

AbstractPainterly 2D animation, like the paint‐on‐glass technique, is a tedious task performed by skilled artists, primarily using traditional manual methods. Although CG tools can simplify the creation process, previous works often focus on temporal coherence, which typically results in the loss of the handmade look and feel. In contrast to cartoon animation, where regions are typically filled with smooth gradients, stroke‐based stylized 2D animation requires careful consideration of how shapes are filled, as each stroke may be perceived individually. We propose a method to generate intermediate frames using example keyframes and a motion description. This method allows artists to create only one image for every five to 10 output images in the animation, while the automatically generated intermediate frames provide plausible inbetween frames.

Shear-induced migration of rigid spheres in a Couette flow

Concentration inhomogeneities occur in many flows of non-Brownian suspensions. Their modeling necessitates the description of the relative motion of the particle phase and of the fluid phase, as well as the accounting for their interaction, which is the object of the suspension balance model (SBM). We systematically investigate the dynamics and the steady state of shear-induced migration in a wide-gap Couette flow for a wide range of particle volume fraction, and we test the ability of the SBM to account for the observations. We use a model suspension for which macroscopic particle stresses are known. Surprisingly, the observed magnitude of migration is much lower than that predicted by the SBM when the particle stress in the SBM is equated to the macroscopic particle stress. Another noteworthy observation is the quasi-absence of migration for semidilute suspensions. From the steady-state volume fraction profiles, we derive the local particle normal stress responsible for shear-induced migration according to the SBM. However, the observed dynamics of migration is much faster than that predicted by the SBM when using this stress in the model. More generally, we show that it is not possible to build a local friction law consistent with both the magnitude and the dynamics of migration within the standard SBM framework. This suggests that there is a missing term in the usual macroscopic constitutive law for the particle normal stress driving migration. The SBM is indeed capable of accurately predicting both the magnitude and the dynamics of migration when a tentative phenomenological term involving a concentration gradient is added to the particle normal stresses determined in macroscopic experiments.

A general multi-scale description of metastable adaptive motion across fitness valleys

We consider a stochastic individual-based model of adaptive dynamics on a finite trait graph G=(V,E)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$G=(V,E)$$\\end{document}. The evolution is driven by a linear birth rate, a density dependent logistic death rate and the possibility of mutations along the directed edges in E. We study the limit of small mutation rates for a simultaneously diverging population size. Closing the gap between Bovier et al. (Ann Appl Probab 29(6):3541–358, 2019) and Coquille et al. (Electron J Probab 26:1–37, 2021) we give a precise description of transitions between evolutionary stable conditions (ESC), where multiple mutations are needed to cross a valley in the fitness landscape. The system shows a metastable behaviour on several divergent time scales, corresponding to the widths of these fitness valleys. We develop the framework of a meta graph that is constituted of ESCs and possible metastable transitions between them. This allows for a concise description of the multi-scale jump chain arising from concatenating several jumps. Finally, for each of the various time scales, we prove the convergence of the population process to a Markov jump process visiting only ESCs of sufficiently high stability.

State-restricted adaptive control of a multilevel rotating electromagnetic mechanical flexible device using electromagnetic actuators

This work presents the development of a multilevel electromagnetic actuation system that controls the shape of a flexible rotatory robotic structure. An array of electromagnets is used as the set of actuators that regulate the position of permanent magnets within the flexible device. The primary outcome of this study is the design and experimental validation of the multilevel rotating device. In addition, the theoretical description of the system motion under electromagnetic actuation is formulated using Euler-Lagrange and electromagnetic theories. Given the developed model, a theoretical study leads to designing an adaptive control that considers motion restrictions in the flexible device. The controller aims to modify the current applied to the electromagnets, which changes the interaction forces between the electromagnet and the permanent magnets in the robotic flexible structure. A set of numerical simulations confirms the proposed controller's effectiveness compared to the traditional state feedback approach that does not consider the state restrictions, which is implemented in devices that also operate under an electromagnetic approach. Furthermore, an experimental version of the flexible device allows for testing of the developed controller. The experimental results show the suitability of the proposed control to generate non-oscillatory controlled motion during the regulation of the flexible mechanic device shape.

Assessing the Accuracy of Quantum Dynamics Performed in the Time-Dependent Basis Representation.

A full quantum-mechanical (QM) description of large amplitude nuclear motion, associated with chemical reactions or isomerization of high-dimensional molecular systems, is inherently challenging due to the exponential scaling of the QM complexity with system size. To ameliorate the scaling bottleneck in studies of realistic systems, typically modeled in the configuration space, the nuclear wave functions are represented in terms of time-dependent basis functions. Such bases are expected to give an accurate description with a modest number of basis functions employed, by adapting them to the wave function solving the time-dependent Schrödinger equation. It is not, however, straightforward to estimate the accuracy of the resulting solution: in QM the energy conservation, a convenient such measure for a classical trajectory evolving in a time-independent potential, is not a sufficient criterion of the dynamics' accuracy. In this work, we argue that the expectation value of the Hamiltonian's "variance", quantifying the basis completeness, is a suitable practical measure of the quantum dynamics' accuracy. Illustrations are given for several chemistry-relevant test systems, modeled employing time-independent as well as time-dependent bases, including the coupled and variational coherent states methods and the quantum-trajectory guided adaptable Gaussians (QTAG) as the latter basis type. A novel semilocal definition of the QTAG basis time-evolution for placing the basis functions "in the right place at the right time" is also presented.

Theory of particle beams transport over curved plasma-discharge capillaries

We present a new approach that demonstrates the deflection and guiding of relativistic electron beams over curved paths by means of the magnetic field generated in a plasma-discharge capillary. The active bending plasma (ABP) represents a promising solution that has been recently demonstrated with a proof of principle experiment. An ABP device consists of a curved capillary where large discharges (of the order of kA) are propagated in a plasma channel. Unlike conventional bending magnets, in which the field is constant over the bending plane, in the ABP, the azimuthal magnetic field generated by the discharge grows with the distance from the capillary axis. This features makes the device less affected by the beam chromatic dispersion so that it can be used to efficiently guide particle beams with non-negligible energy spreads. The study we present in the following aims to provide a theoretical basis of the main ABP features by presenting an analytical description of a single-particle motion and rms beam dynamics. The retrieved relationships are verified by means of numerical simulations and provide the theoretical matrix formalism needed to completely characterize such a new transport device. Published by the American Physical Society 2024

Description of phase separation motion in gas‒liquid two-phase flow

Description of phase separation motion in gas‒liquid two-phase flow

An Empirical Study of the Teachability and Learnability of L2 “Thinking for Speaking” Patterns

This study examines whether explicit pedagogical instructions of multimodal strategies based on typological contrastive analysis have any facilitative effect on the restructuring of “thinking for speaking” patterns, focusing on motion event construal which has been demonstrated to be notoriously difficult in second language acquisition (Hendriks and Hickmann 2011, Slobin 1996). Eighty adult Chinese intermediate-level EFL learners were recruited for a classroom-based quasi-experimental study with a pretest-posttest design. Teaching TFS instructions with awareness enhancement strategies as an independent variable divided the participants into two groups, the experimental group that received instructions and control group that followed a traditional teaching approach over a period of 4 weeks. Writing data were elicited by means of the <i>Frog Story</i> and was coded on specific measures of accuracy and complexity of the properties of lexicalization patterns: the description of Motion, Path and Ground. The results showed positive instructional effect on learners’ writing performance of motion event expression and confirmed the possibility of restructuring L1 thinking-for-speaking patterns in L2 through pedagogical instructions. The findings provide practical implications for teachers, typological contrastive awareness and explicit pedagogical instructions prove to be significant for learners’ development of L2 thinking for speaking patterns.

Modeling the skeleton-language uncertainty for 3D action recognition

Modeling the skeleton-language uncertainty for 3D action recognition