Inhomogeneous Modes Research Articles

Mechanical Response of Mudstone Based on Acoustic Emission Fractal Features

In this study, the effect of the stress amplitude on the mechanical behavior of mudstone was systematically investigated by cyclic loading and unloading experiments and acoustic emission (AE) monitoring. The results show that at low-stress amplitudes, mudstone specimens show better elastic recovery ability, lower damage accumulation and higher structural stability. At high-stress amplitudes, the irreversible damage of the mudstone increases significantly, the internal fractures gradually expand and penetrate through, and the risk of instability increases significantly. This is manifested by the gradual increase in cumulative irreversible strain of mudstone at different stress amplitudes, up to 0.144%. In addition, different stress amplitudes have significant effects on energy evolution characteristics, with low-stress amplitudes mainly showing elastic deformation and a high percentage of recoverable energy, while high-stress amplitudes show a high percentage of dissipated energy. Under the condition of high-stress amplitude, such as the mudstone specimen #4, the percentage of tensile failure is 81.15%. Tensile failure dominates at all stress amplitudes, where the failure mechanism within mudstone is mainly characterized by the extension of tensile-type fractures. Through the multifractal analysis of AE signals, this study reveals the effect of the stress amplitude on the fracture extension mode and failure mechanism of mudstone. As the stress amplitude increases, Δα and Δf show an increasing trend. This indicates that the fracture extension process transforms from a relatively homogeneous and simple mode to a more inhomogeneous and complex mode. This transformation reflects the nonlinear and multiscale fracture characteristics of mudstone under high-stress conditions. The results of this study help to understand the mechanical behavior of mudstone under cyclic loading during coal mining and provide theoretical support for safe coal production.

An insight on local defect resonance based on modal decomposition analysis: A two-dimensional case

The resonance behaviors of defects, specifically local defect resonance (LDR), are useful for defect detection in structures. However, there is a lack of intuitive elucidation regarding the underlying mechanisms governing defect resonance. This study aims to analyze the LDR of a horizontal crack in a plate activated by Lamb waves using the modal decomposition method (MDM). The MDM involves an approximate decomposition of the wavefield into finite constituent Lamb wave modes, including propagating, non-propagating, and inhomogeneous modes. The amplitude of each mode is determined according to the continuous boundary conditions of displacement and stress between the damaged zone and the intact zone. Analytical results reveal specific frequencies at which the damaged zone exhibits significantly stronger vibrations than the intact zone, indicating the emergence of LDR. The corresponding wavefields exhibit various resonance patterns, encompassing both in-plane LDR and out-of-plane LDR types. In contrast to finite element simulations and experimental observations, the MDM unveils the dominant constituents of resonance patterns: out-of-plane LDR results from the combination of reflected and transmitted A0 and A1 modes within the damaged zone, while in-plane LDR is formed by the superposition of reflected and transmitted A0, A1, and S0 modes.

Mode Multiplication of Cylindrical Vector Beam Using Raytracing Control

Abstract Cylindrical vector beams (CVBs) hold significant promise in mode division multiplexing communication owing to their inherent vector mode orthogonality. However, existing studies for facilitating CVB channel processing are confined to mode shift conversions due to their reliance on spin-dependent helical modulations, overlooking the pursuit of mode multiplication conversion. This challenge lies in the multiplicative operation upon inhomogeneous vector mode manipulation, which is expected to advance versatile CVB channel switching and routing. In this study, we tackle this gap by introducing a raytracing control strategy that conformally maps the light rays of CVB from the whole annulus distribution to an annular sector counterpart. Incorporated with the multifold conformal annulus-sector mappings and polarization-insensitive phase modulations, this approach facilitates the parallel transformation of input CVB into multiple complementary components, enabling the mode multiplication conversion with protected vector structure. Serving as a demonstration, we experimentally implemented the multiplicative operation of four CVB modes with the multiplier factors of N = +2 and N = −3, achieving the converted mode purities over 94.24% and 88.37%. Subsequently, 200 Gbit/s quadrature phase shift keying signals were successfully transmitted upon multiplicative switching of four CVB channels, with the bit-error-rate approaching 1×10-6. These results underscore our strategy’s efficacy in CVB mode multiplication, which may open promising prospects for its advanced applications.

Re-evaluating the cosmological redshift: Insights into inhomogeneities and irreversible processes

Understanding the expansion of the Universe remains a profound challenge in fundamental physics. The complexity of solving general relativity equations in the presence of intricate, inhomogeneous flows has compelled cosmological models to rely on perturbation theory in a homogeneous Friedmann-Lemaître-Robertson-Walker background. This approach accounts for a redshift of light encompassing contributions from both the cosmological background expansion along the photon's trajectory and Doppler effects at emission due to peculiar motions. However, this computation of the redshift is not covariant, as it hinges on specific coordinate choices that may distort physical interpretations of the relativity of motion. In this study we show that peculiar motions, when tracing the dynamics along time-like geodesics, must contribute to the redshift of light through a local volume expansion factor, in addition to the background expansion. By employing a covariant approach to redshift calculation, we address the central question of whether the cosmological principle alone guarantees that the averaged local volume expansion factor matches the background expansion. We establish that this holds true only in scenarios characterised by a reversible evolution of the Universe, where inhomogeneous expansion and compression modes compensate for one another. In the presence of irreversible processes, such as the dissipation of large-scale compression modes through matter virialisation and associated entropy production, the averaged expansion factor becomes dominated by expansion in voids that can no longer be compensated for by compression in virialised structures. Furthermore, for a universe in which a substantial portion of its mass has undergone virialisation, adhering to the background evolution on average leads to significant violations of the second law of thermodynamics. Our approach shows that entropy production due to irreversible processes during the formation of structures plays the same role as an effective, time-dependent cosmological constant (i.e. dynamical dark energy) without the need to invoke new unknown physics. Our findings underscore the imperative need to re-evaluate the influence of inhomogeneities and irreversible processes on cosmological models, shedding new light on the intricate dynamics of our Universe.

Double strategies for reproducing multimodal puns in interlinguistic translation: Experimental research

The research is dedicated to exposing the specifics of translating multimodal puns based on the retrospective experiment. A multimodal pun is defined as a creolized/ polycoded formation substantiated by a specific type of ambiguity consisting of two inhomogeneous semiotic modes. The material for our research was provided by verbal-visual puns functioning as separate texts. Each multimodal pun results from intersemiotic translation when the signs of one semiotic system are transformed into the signs of another. For the vast majority of multimodal puns, verbal signs are interpreted into pictures, but the opposite cannot be excluded either. The role of the visual component is twofold. It can be creative when the picture is part of the ambiguity mechanism, or it can be amplifying when the picture accentuates the verbal wordplay, not participating directly in the creation of ambiguity. Hence, our first hypothesis is that multimodal puns with an amplifying visual component are a lesser challenge for translators than those with a creative one due to the absence of the necessity to coordinate verbal and visual modes in the target text. The research aims to identify the strategies of interlinguistic translation of multimodal puns and the factors that determine them, particularly the impact of the visual mode on the translator’s decision-making. Hence, our second hypothesis is that multimodal puns require double strategies that would allow to correlate the reproduction of the elements of two different semiotic systems. The analysis of the subjects’ translations, as well as their reports received in the course of the delayed retrospective experiment, confirmed both hypotheses. Disclosure Statement The authors reported no potential conflicts of interest. * Corresponding author: Oleksandr Rebrii, 0000-0002-4912-7489o.v.rebrii@karazin.ua

Manipulating the monomers supply of interfacial polymerization towards the ultrathin polyamide composite membrane for CO2 capture

Preparing polyamide (PA) composite membranes with high gas separation performance requires rational control for the interfacial polymerization (IP) process. In this study, the monomer supply of piperazine (PIP) and trimesoyl chloride (TMC) in the IP process was precisely manipulated to generate an ultrathin PA film on the polydimethylsiloxane (PDMS) gutter layer for CO2 separation. Concretely, the PIP supply was regulated from the homogeneous, slow, and excess mode to the inhomogeneous, fast, and small mode by constructing a sodium dodecyl sulfate (SDS) array at the phase interface; subsequently, the TMC supply was increased by elevating the TMC concentration. Therefore, the amine-to-acid chloride concentration ratio in the reaction zone was optimized and, as a consequence, the IP reaction rate was significantly increased. As a result, the thickness of the PA film was reduced from ∼92 nm to ∼37 nm through the optimization of SDS and TMC concentrations, and accordingly, the CO2 permeance was increased from 501 GPU to 1498 GPU under 0.1 MPa without sacrificing selectivity. Moreover, the membrane preparation efficiency was greatly improved with an IP reaction time of less than 30 s. The insights provided could promote the industrial application of interfacial polymerization in the scale-up preparation of high-performance CO2 separation membranes.

Multistability of synchronous modes in a multimachine power grid with a common load and their global and non-local stability

The purpose of this work is studying the dynamics of the power grid consisting of an arbitrary number of synchronous generators supplying a common passive linear load. We focus on searching the conditions for the existence and stability of synchronous modes, i.e. the main operating modes of a power grid. The possibility of the existence of non-synchronous (quasi-synchronous and asynchronous) modes is investigated. Methods. To study the dynamics of a power grid we use the effective network model in the form of an ensemble of globally coupled nodes-generators. The state of every node is described by the swing equation. The approach for reducing the effective network to the network with a hub topology (star topology) is proposed. We use numerical methods to construct a partition of the parameter space into areas with different operating modes of the power grid. Results. The conditions for the existence, stability and multistability of synchronous modes are obtained. The main characteristics of these modes are considered, such as the power supplied by generators to the grid and the distribution of currents along transmission lines. We constructed the partition of the power gird parameter space into areas with different dynamics. Conclusion. The power grid consisting of an arbitrary number of synchronous generators supplying a common passive linear load has been studied. We shown the presence of two types of synchronous modes: homogeneous and inhomogeneous. The first is characterized by equal powers and currents flowing through all load supply paths except one. The second provides another additional path, which differs from the others in current and transmitted power. Moreover, the currents flowing along the same path, but in various modes, differ. The presence of high multistability of inhomogeneous synchronous modes has been established. The possibility of coexistence of homogeneous and inhomogeneous synchronous modes, as well as quasi-synchronous and asynchronous modes, is shown. In the power grid parameters space we found areas corresponding both the existence of only synchronous modes and their coexistence with quasi-synchronous and/or asynchronous modes.

Increasing the efficiency of transfer processes when using inhomogeneous fluidization

The processes of dehydration and granulation are associated with the heat transfer to the solid particles from the gas coolant, which acts as a fluidizing agent and causes the stochastic movement of the granular material in the apparatus. To implement the layered structure mechanism of granulation of organic-mineral fertilizers it is necessary to ensure intensive circulation of granular material with intensive gradual passage through the appropriate technological zones of the apparatus. The main problem is the low efficiency of interphase exchange in the gas-liquid-solid system and the formation of agglomerates during granulation with the injection of a liquid heterogeneous solution into the bed of solid granular material.
 In this work the conditions for increasing the efficiency of the transfer processes when using an inhomogeneous jet-pulsating mode of fluidization were determined.
 Analysis of the intensity of renewal of the contact surface of the phases when using inhomogeneous jet-pulsating fluidization in the self-oscillating mode was carried out. It was established that the use of this mode of fluidization allows getting a significant intensification of heat and mass transfer processes due to the activation of diffusion-controlled processes and an increase in the dynamics of interphase contact exchange by 1.9÷2.9 m2/s, which is 27÷41% of the total surface of the material in device.

Interfacial-constraint-induced intragranular deformation inhomogeneity of Ti−Al layered composites

AbstractA multilayered Ti−Al composite was designed and fabricated by hot pressing and hot rolling of alternately stacked Ti and Al foils. In situ electron backscatter diffraction was utilized to characterize the orientation evolution and deformed substructure upon tension. A remarkably inhomogeneous deformation mode was observed within the interior of Ti grains, in a way that the closer to the grain boundary or Ti/Al interfaces, the harder the plastic flow. Such a phenomenon is attributed to the synergetic constraint of phase interface and grain boundary. The present study thus provides a new strategy to tailor the deformation behavior of metallic materials by sufficiently leveraging the interfacial constraint effect for performance optimization.

Frequency demodulation of an inhomogeneous medium multi-longitudinal mode fiber laser and its sensing application.

Dispersion characteristic could be a significant factor, which impacts the beat frequency of Multi-longitudinal mode fiber laser (MMFL). In this paper, the mechanism of beat frequency generation in inhomogeneous medium Multi-longitudinal mode fiber laser is discussed. Compared with cavity length-dependent fiber laser sensing system, the proposed model uses a several-millimeter-Fiber-Bragg-Grating (FBG) as the sensing head, which features both high sensitivity and compact size. We designed an experiment to exhibit possible sensing application based on the proposed theory as well.

Quantum cosmological backreactions. III. Deparametrized quantum cosmological perturbation theory

This is the third paper in a series of four in which we incorporate backreaction among the homogeneous as well as between the homogeneous and inhomogeneous degrees of freedom in quantum cosmological perturbation theory using space adiabatic methods. Here, we consider a gauge-fixed version of cosmological perturbation theory which uses Gaussian dust as a material reference system. The observable matter content is a real-valued scalar field. We explore the sector of that theory which is purely homogeneous and isotropic with respect to the geometry degrees of freedom but which contains inhomogeneous perturbations up to second order of the scalar field. We explore the quantum field theoretical challenges of the space adiabatic framework in a cosmological model of the early universe which is technically still relatively simple. We compute the quantum backreaction effects from the inhomogeneous matter modes on the homogeneous geometry up to second order in the adiabatic parameter. It turns out that these contributions are not negligible.

The Diagnostic Value of Contrast-enhanced Ultrasound and Its Inhomogeneous Enhancement Mode in Sentinel Lymph Node Metastasis of Breast Cancer

The Diagnostic Value of Contrast-enhanced Ultrasound and Its Inhomogeneous Enhancement Mode in Sentinel Lymph Node Metastasis of Breast Cancer

Microstructure and mechanical properties of a continuous carbon-gradient sheet steel

To take advantage of the high strength of high-carbon martensitic steel and simultaneously avoid insufficient plasticity, a novel continuous carbon-gradient sheet steel (CGSS) with a high-carbon surface and medium-carbon core was developed as a gradient material using surface carburizing and warm rolling. An exceptional strength–ductility combination was achieved. On the premise of carbides precipitation in high-carbon martensitic matrix, tempered CGSS at 200 °C exhibits excellent mechanical property with an ultimate tensile strength of 2440 MPa and a total elongation of 4.6%. Enlarged-strain-component in the tensile direction is the primary cause for higher plasticity in the high-carbon surface. Inhomogeneous fracture mode indicates the typical restraint of crack propagation in the core, suggesting greater toughness for the tempered CGSS.

Mode-sensitive magnetoelastic coupling in phononic-crystal magnomechanics

The acoustically driven spin-wave resonance in a phononic-crystal cavity is numerically investigated. The designed cavity enables confinement of gigahertz vibrations in a wavelength-scale point-defect structure and sustains a variety of resonance modes. Inhomogeneous strain distributions in the modes modify the magnetostrictive coupling and the spin-wave excitation susceptible to an external-field orientation. In particular, a monopole-like mode in the cavity having a near-symmetrical pattern shows a subwavelength-scale mode volume and can provide a versatile acoustic excitation scheme independent of the field-angle variation. Thus, the phononic-crystal platform offers an alternative approach to acoustically control the spin-wave dynamics with ultrasmall and inhomogeneous mode structures, which will be a key technology to integrate and operate large-scale magnomechanical circuits.

Storage and retrieval of ultraslow soliton at optical nanofiber interface via electromagnetically induced transparency.

We theoretically investigate the optical memory in a nanofiber system via electromagnetically induced transparency (EIT) in a nonlinear region. Because of the tight transverse confinement, the light-atom interaction is significantly enhanced and thus, the EIT effect is enhanced. The inhomogeneous mode field distribution contributes spatially to the EIT dispersion. We develop a systematic analysis method to study the nonlinearity of the system and prove that the optical soliton is available in the system and can be stored and retrieved with high efficiency and stability. We also study a strategy to optimize the soliton optical memory. The results obtained in this study are promising for practical applications of all-optical information processing.

High-speed imaging of n-heptane ignition in a high-pressure shock tube

Homogeneous and inhomogeneous ignition modes of n-heptane were studied using high-speed imaging in a high-pressure shock tube (HPST). n-Heptane, a fuel with strong negative temperature coefficient (NTC) behavior, was mixed with 4%-21% oxygen in argon or nitrogen and ignited over a wide temperature range (700–1250 K) and at elevated pressures (> 10 atm). Ultraviolet (UV) images of OH* emission were captured through a sapphire shock-tube end wall using a high-speed camera and a UV intensifier. The current study demonstrates the capability to study auto-ignition modes using high-speed imaging in a high-pressure shock tube. Both homogeneous and inhomogeneous auto-ignition events were observed with the latter generally confined to intermediate temperatures and reactive n-heptane mixtures. We also observed that conventional sidewall diagnostic signals are, in many cases, sufficient to identify inhomogeneous ignitions that are not accurately modeled under the assumption of spatially uniform chemistry.

Ethanol ignition in a high-pressure shock tube: Ignition delay time and high-repetition-rate imaging measurements

Ethanol is known to be prone to pre-ignition in internal combustion engines under high-load conditions and its ignition shows large deviations from ideal, spatially, and temporally-homogeneous ignition in shock tubes at moderate temperatures (800–950 K). In this context, the ignition of stoichiometric ethanol/O2 mixtures with various levels of inert gas dilution was investigated in a high-pressure shock tube at ≅20 bar between 800 and 1250 K. Ignition delay times were determined from spatially integral detection of chemiluminescence emission. Additionally, high-repetition-rate color imaging enabled the differentiation of the luminescence in time, space, and spectral range between various ignition modes. In the low-temperature range (800–860 K), different inhomogeneous ignition modes were identified. The addition of small amounts of helium into the undiluted fuel/air mixture was found to be efficient to mitigate pre-ignition, attributed to a variation in heat transfer and thus suppression of the build-up of local temperature inhomogeneities. The experiments in case of spatially homogeneous ignition show very good agreement with the predictions based on three detailed kinetics mechanisms (Zhang et al., CNF 190 (2018) 74, Frassoldati et al., CNF 159 (2012) 2295, and Zhou et al. CNF 197 (2018) 423), inhomogeneities, however, resulted in a shortening of the ignition delay times up to a factor of 2.6.

Non-uniform along thickness spin excitations in magnetic vortex-state nanodots

We summarize our experimental findings in the arrays of Ni80Fe20 circular nanodots with diameter 300 nm and thickness 20 nm ≤ L ≤ 100 nm, probed by broadband ferromagnetic resonance spectroscopy in the absence of external magnetic field. Spin excitation modes related to the vortex core gyrotropic dynamics were observed in the gigahertz frequency range. Micromagnetic simulations revealed that they are flexure oscillations of the vortex core string with n = 0, 1, 2 nodes along the dot thickness. It was found that for L > 70 nm the intensity of more complicated n = 1 vortex gyrotropic mode is unexpectedly higher than the one of the lowest n = 0 gyrotropic mode. This behavior was clarified on the basis of the inhomogeneous vortex mode phase profiles extracted from micromagnetic simulations and calculated analytically. Precise measurements of the dependence of resonance frequency of the vortex n = 0 mode on the dot thickness demonstrated a clear maximum around L = 70 nm, that was theoretically explained by introducing a vortex mass, which is a result of the vortex distortion due to interaction with spin waves having azimuthal indices m = ±1. Finally, several azimuthal spin-wave modes having curled structure at the dot top and bottom faces were found in the spectrum of the dots with thicknesses L ≥ 40 nm.

Hydrogen-assisted fatigue crack-propagation in a Ni-based superalloy 718, revealed via crack-path crystallography and deformation microstructures

Fatigue crack-growth (FCG) of Ni-based superalloy 718 was investigated under gaseous hydrogen environment (external hydrogen) and uniformly pre-charged state (internal hydrogen). Under external hydrogen, intergranular fracture predominated, whereas dislocation slip-band or twin boundary fracture were prevalent under internal hydrogen. This failure mode divergence encompassed unique characteristics of macroscale FCG response, leading to both cycle- and time-dependent cracking. The intergranular cracking was ascribed to short-circuit diffusion of hydrogen along grain boundaries. Meanwhile, the material’s inherently inhomogeneous deformation mode exerts harmfulness when hydrogen was uniformly distributed inside the specimen, causing slip-bands or twin boundaries to become the weakest links for fracture.

A new Rayleigh-like wave in guided propagation of antiplane waves in couple stress materials.

Motivated by the unexpected appearance of shear horizontal Rayleigh surface waves, we investigate the mechanics of antiplane wave reflection and propagation in couple stress (CS) elastic materials. Surface waves arise by mode conversion at a free surface, whereby bulk travelling waves trigger inhomogeneous modes. Indeed, Rayleigh waves are perturbations of the travelling mode and stem from its reflection at grazing incidence. As is well known, they correspond to the real zeros of the Rayleigh function. Interestingly, we show that the same generating mechanism sustains a new inhomogeneous wave, corresponding to a purely imaginary zero of the Rayleigh function. This wave emerges from 'reflection' of a bulk standing mode: This produces a new type of Rayleigh-like wave that travels away from, as opposed to along, the free surface, with a speed lower than that of bulk shear waves. Besides, a third complex zero of the Rayleigh function may exist, which represents waves attenuating/exploding both along and away from the surface. Since none of these zeros correspond to leaky waves, a new classification of the Rayleigh zeros is proposed. Furthermore, we extend to CS elasticity Mindlin's boundary conditions, by which partial waves are identified, whose interference lends Rayleigh-Lamb guided waves. Finally, asymptotic analysis in the thin-plate limit provides equivalent one-dimensional models.