Transverse Excitations Research Articles

Experimental observation of gapped shear waves and liquid-like to gas-like dynamical crossover in active granular matter

Unlike crystalline solids, liquids lack long-range order, resulting in diffusive shear fluctuations rather than propagating waves. Simulations predict that liquids exhibit a k-gap in wave-vector space, where solid-like transverse waves reappear above this gap. Experimental evidence in classical liquids has been limited, observed only in 2D dusty plasmas. Here, we investigate this phenomenon using active Brownian vibrators and uncover distinct gas-like and liquid-like phases depending on the packing fraction. We measure key properties, including pair correlation functions, mean square displacements, velocity auto-correlation functions, and vibrational density of states. In the liquid-like phase, we confirm the k-gap in transverse excitations, whose size grows as the packing fraction decreases and eventually disappears in the gas phase. Our findings extend the concept of the k-gap to active granular systems and reveal striking parallels with supercritical fluids.

Combined molecular and spin dynamics simulation of BCC iron with vacancy defects.

Utilizing an atomistic computational model, which handles both translational and spin degrees of freedom, combined molecular and spin dynamics simulations have been performed to investigate the effect of vacancy defects on spin wave excitations in ferromagnetic iron. Fourier transforms of space- and time-displaced correlation functions yield the dynamic structure factor, providing characteristic frequencies and lifetimes of the spin wave modes. A comparison of the system with a 5% vacancy concentration with pure lattice data shows a decrease in frequency and a decrease in lifetime for all transverse spin wave excitations observed. In addition, the clearly defined transverse spin wave excitations are distorted with the introduction of vacancy defects, and we observe reduced excitation lifetimes due to increased magnon-magnon scattering. We observe further evidence of increased magnon-magnon scattering, as the peaks in the longitudinal spin wave spectrum become less distinct. Similar impacts are observed in the vibrational subsystem, with a decrease in characteristic phonon frequency and flattening of lattice excitation signals due to vacancy defects.

Mechanical manipulation of electromechanical fields in multi-tunnel piezoelectric semiconductor thin film devices by creating localized transverse mechanical field excitations

Mechanical manipulation of electromechanical fields in multi-tunnel piezoelectric semiconductor thin film devices by creating localized transverse mechanical field excitations

Entanglement entropy of a color flux tube in (2+1)D Yang-Mills theory

We construct a novel flux tube entanglement entropy (FTE2), defined as the excess entanglement entropy relative to the vacuum of a region of color flux stretching between a heavy quark-anti-quark pair in pure gauge Yang-Mills theory. We show that FTE2 can be expressed in terms of correlators of Polyakov loops, is manifestly gauge-invariant, and therefore free of the ambiguities in computations of the entanglement entropy in gauge theories related to the choice of the center algebra. Employing the replica trick, we compute FTE2 for SU(2) Yang-Mills theory in (2+1)D and demonstrate that it is finite in the continuum limit. We explore the properties of FTE2 for a half-slab geometry, which allows us to vary the width and location of the slab, and the extent to which the slab cross-cuts the color flux tube. Following the intuition provided by computations of FTE2 in (1+1)D, and in a thin string model, we examine the extent to which our FTE2 results can be interpreted as the sum of an internal color entropy and a vibrational entropy corresponding to the transverse excitations of the string.

Propagation gap for shear waves in binary liquids: Analytical and simulation study.

Transverse collective excitations in 50-50 and 80-20 Lennard-Jones binary liquid mixtures are studied for different mass ratio of components R at fixed numerical densities. Increasing the mass ratio results in a growing difference between frequencies of shear waves and transverse optic modes. We report an increase in the propagation gap width for shear waves with mass ratio of components and compare it to the gap width expression, known from the transverse dynamics of simple liquids. A four-variable dynamic model of transverse dynamics in binary liquids with an account of cross correlations between total-mass and mass-concentration transverse current fluctuations is solved analytically in the long-wavelength region. An equation for the propagation gap of shear waves for binary liquids is reported and analyzed.

Nonlinear combined resonance of magneto-electro-elastic plates

Nonlinear combined resonance of magneto-electro-elastic plates

Coupled axial and transverse currents method for finite element modelling of periodic superconductors

In this paper, we propose the Coupled Axial and Transverse currents (I) (CATI) method, as an efficient and accurate finite element approach for modelling the electric and magnetic behavior of periodic composite superconducting conductors. The method consists of a pair of two-dimensional models coupled via circuit equations to account for the conductor geometrical periodicity. This allows to capture three-dimensional effects with two-dimensional models and leads to a significant reduction in computational time compared to conventional three-dimensional models. After presenting the method in detail, we verify it by comparison with reference finite element models, focussing on its application to twisted multifilamentary superconducting strands. In particular, we show that the CATI method captures the transition from uncoupled to coupled filaments, with accurate calculation of the interfilament coupling time constant. We then illustrate the capabilities of the method by generating detailed loss maps and magnetization curves of given strand types for a range of external transverse magnetic field excitations, with and without transport current.

Carroll strings with an extended symmetry algebra

Starting from the Polyakov action we consider two distinct Carroll limits in target space, keeping the string worldsheet relativistic. The resulting magnetic and chiral Carroll string models exhibit different symmetries and dynamics. Both models have an infinite dimensional symmetry algebra with Carroll symmetry included in a finite dimensional subalgebra. For the magnetic model, this is the so-called string Carroll algebra. The chiral model realises an extended version of the string Carroll algebra. The magnetic model does not have any transverse string excitations. The chiral model is less restrictive and includes arbitrary left-moving modes that carry transverse momentum but do not contribute to the energy in target space.

System Identification and Dynamic Analysis of the Propulsion Shaft Systems Using Response Surface Optimization Technique

Marine vessels rely heavily on propeller shaft systems to adjust the engine torque and propeller thrust. However, these systems are subjected to various dynamic excitations during operation, such as transverse, longitudinal, and torsional excitations. These excitations can arise from factors like non-uniform stern flow fields, misaligned components, and the whirling motion of the shafts, which can affect the integrity and reliability of the vehicle. To analyze the dynamic response of the propulsion shaft system and ensure its reliability, numerical/analytical models are currently in practice. The finite element method (FEM) is a popular choice, but uncertainties in bearings and connectors stiffness lead to inaccuracies in the Finite Element model, resulting in significant differences between the experimental and theoretical models. This paper proposes the response surface optimization (RSO) technique to estimate unknown bearing stiffness in the propulsion shaft system. The experimental model of the propeller shaft system is constructed using steady-state response with step sine excitation. The RSO technique is then used to update the natural frequencies and vibration amplitude of the FE (Finite Element) model. The updated model shows less than a 10% difference in natural frequencies and vibration amplitude compared to the experimental model, demonstrating that the proposed technique is an efficient tool for marine shaft dynamic analysis.

Experimental investigation of seismic performance of segmental tunnel with secondary lining under strong earthquake

Experimental investigation of seismic performance of segmental tunnel with secondary lining under strong earthquake

The effect of bandwidth on the noise-induced chaos of shape memory alloy webs under mixed transverse and parametric excitations: an analytic approach

The effect of bandwidth on the noise-induced chaos of shape memory alloy webs under mixed transverse and parametric excitations: an analytic approach

Investigation on the 1:2:3 internal resonance of high dimensional nonlinear dynamic system for FGGP reinforced rotating pre-twisted blade under the aerodynamic forces

Investigation on the 1:2:3 internal resonance of high dimensional nonlinear dynamic system for FGGP reinforced rotating pre-twisted blade under the aerodynamic forces

Nonlinear vibrations of FG-GRLCC rectangular variable cross-section plate subjected to transverse and parametric excitations in thermal environment

Nonlinear vibrations of FG-GRLCC rectangular variable cross-section plate subjected to transverse and parametric excitations in thermal environment

Three-dimensional nonlinear vibrations of slightly curved cantilevered pipes conveying fluid

Three-dimensional nonlinear vibrations of slightly curved cantilevered pipes conveying fluid

Seismic assessment and strengthening of a historical masonry bridge considering soil-structure interaction

A holistic methodology for developing the digital twins and conducting seismic vulnerability assessments of masonry arch bridges is proposed and applied to a historical stone masonry bridge. In this light, digital cameras, drones, and 3D laser scanners were utilized for 3D geometric documentation of the bridge. 3D finite element (FE) models were constructed and calibrated based on the operational modal analysis results derived from the accelerometer sensors. The fragility curves for different limit states were derived by performing a multi-stripe analysis (MSA). The effect of soil-structure interaction (SSI) on the calibration results and seismic response of the bridge was evaluated. The results of the visual inspection, model calibration, and seismic analysis revealed that the central pier and the arches are the most susceptible parts of the bridge. Therefore, three strengthening techniques were proposed, and corresponding numerical models were developed. The first model was developed by enhancing the mechanical properties of the vulnerable parts of the bridge, and the two other models were built by covering the central pier’s outer surface with polyparaphenylene benzobisoxazole (PBO) and carbon fiber-reinforced concrete mortar (FRCM) layers. Results revealed that the strengthening techniques improved the seismic response of the bridge when subjected to transverse seismic excitations. Negligible differences in the displacement response and crack width of the strengthened models were observed from the nonlinear dynamic analysis.

Role of the single-particle dynamics in the transverse current autocorrelation function of a liquid metal.

A recent simulation study of the transverse current autocorrelation of the Lennard-Jones fluid [Guarini et al., Phys. Rev. E 107, 014139 (2023)] revealed that this function can be perfectly described within the exponential expansion theory [Barocchi et al., Phys. Rev. E 85, 022102 (2012)]. However, above a certain wavevector Q, not only transverse collective excitations were found to propagate in the fluid, but a second oscillatory component of unclear origin (therefore called X) must be considered to fully account for the time dependence of the correlation function. Here, we present an extended investigation of the transverse current autocorrelation of liquid Au as obtained by abinitio molecular dynamics in the very wide range of wavevectors 5.7 ≤ Q ≤ 32.8 nm-1 in order to also follow the behavior of the X component, if present, at large Q values. A joint analysis of the transverse current spectrum and its self-portion indicates that the second oscillatory component arises from the longitudinal dynamics, as suggested by its close resemblance with the previously determined component accounting for the longitudinal part of the density of states. We conclude that such a mode, albeit featuring a merely transverse property, fingerprints the effect of longitudinal collective excitations on single-particle dynamics, rather than arising from a possible coupling between transverse and longitudinal acoustic waves.

Commensurate and spiral magnetic order in the doped two-dimensional Hubbard model: Dynamical mean-field theory analysis

We develop a dynamical mean-field theory approach for the spiral magnetic order, changing to a local coordinate frame with preferable spin alignment along the $z$-axis, which can be considered with the impurity solvers treating the spin diagonal local Green's function. We furthermore solve the Bethe-Salpeter equations for nonuniform dynamic magnetic susceptibilities in the local coordinate frame. We apply this approach to describe the evolution of magnetic order with doping in the $t-t'$ Hubbard model with $t'=0.15$, which is appropriate for the description of the doped La$_2$CuO$_4$ high-temperature superconductor. We find that with doping the antiferromagnetic order changes to the $(Q,\pi)$ incommensurate one, and then to the paramagnetic phase. The spectral weight at the Fermi level is suppressed near half filling and continuously increases with doping. The dispersion of holes in the antiferromagnetic phase shows qualitative agreement with the results of the $t$-$J$ model consideration. In the incommensurate phase we find two branches of hole dispersions, one of which crosses the Fermi level. The resulting Fermi surface forms hole pockets. We also consider the dispersion of the magnetic excitations, obtained from the non-local dynamic magnetic susceptibilities. The transverse spin excitations are gapless, fulfilling the Goldstone theorem; in contrast to the mean-field approach the obtained magnetic state is found to be stable. The longitudinal excitations are characterized by a small gap, showing the rigidity of the spin excitations. For realistic hopping and interaction parameters we reproduce the experimentally measured spin-wave dispersion of La$_2$CuO$_4$.

Nonlinear analysis of a rotating pre-twisted composite blade reinforced with functionally graded graphene platelets under axial and transverse excitations

Nonlinear analysis of a rotating pre-twisted composite blade reinforced with functionally graded graphene platelets under axial and transverse excitations

An Axially Compressed Moving Nanobeam Based on the Nonlocal Couple Stress Theory and the Thermoelastic DPL Model

This article introduces a new model that can be used to describe elastic thermal vibrations caused by changes in temperature in elastic nanobeams in response to transverse external excitations. Using the idea of nonlocal elasticity and the dual-phase lagging thermoelastic model (DPL), the coupled equations of motion and heat transfer were derived to explain small-scale effects. Additionally, modified couple stress theory (MCST) and Euler–Bernoulli (EB) beam assumptions were considered. The proposed theory was verified by considering the thermodynamic response of nanobeams moving horizontally at a constant speed while one end is subjected to a periodic thermal load. The system of governing equations has been solved numerically with the help of Laplace transforms and one of the tested evolutionary algorithms. The effects of changing the nonlocal modulus, the magnitude of the external force, and the length scale parameter on the system fields were investigated. It is also shown how the behavior of the thermal nanobeam changes depending on the phase delay factors in addition to the horizontal velocity of the beam. To determine this model’s accuracy, its results were compared with the results of the classical continuity model and thermoelastic concepts. The numerical results show that when the nanobeam moves, the length scale can change the studied thermal and mechanical vibration wave patterns and physical fields. Additionally, during thermally stimulated vibrations, thermodynamic effects that have implications for the dynamic design and performance improvement of nanostructures must be considered.

Simulation study of the collective excitations in liquid sodium under high pressure

The dynamic structure of liquid sodium is investigated using classical molecular dynamics simulations over a wide range of densities (from 739 to 4177 kg m−3). The interactions are described using screened pseudopotential formalism with Fiolhais model of electron-ion interaction. The effective pair potentials obtained are validated by comparing the predicted static structure, coordination number, self-diffusion coefficients and spectral density of the velocity autocorrelation function with results from ab initio simulations at the same state points. Both longitudinal and transverse collective excitations are computed from the corresponding structure functions and their evolution with density is investigated. The frequency of the longitudinal excitations increases with density, as well as the sound speed, which is extracted from their dispersion curves. The frequency of the transverse excitations also increases with density, but they cannot propagate over macroscopic distances and the propagation gap clearly appears. The values of the viscosity, which are extracted from these transverse functions are in good agreement with available results computed from stress autocorrelation functions.