Large Amplitude Research Articles

Scattering of vortices with excited normal modes

We consider head-on collisions at critical coupling of vortices modeled by the Abelian-Higgs model. We investigate the two-vortex scattering, whereby the vortices are excited by the shape mode causing fluctuations in the gauge-invariant quantities. When the vortices are excited with a sufficiently large amplitude the moduli space approximation fails, and we observe an interesting behavior in which the vortices can become trapped in a quasibound state with multiple bounces. We perform a detailed investigation on the behavior of these excited vortices and sample a phase space of solutions. Interestingly, we find a fractal structure dependent on the initial phase of the mode and velocity of the vortices. Published by the American Physical Society 2024

Transitions between Localised Patterns with Different Spatial Symmetries in Non-Local Hyperbolic Models for Self-Organised Biological Aggregations

Pattern formation in biological aggregations is a topic of great interest, due to the complex spatial structure of various aggregations of cells/bacteria/animals that can be observed in nature. While many such aggregations look similar at the macroscopic level, they might differ in their microscopic spatial structure. However, the complexity of the non-linear and sometimes non-local interactions among individuals inside these aggregations makes it difficult to investigate these spatial structures. In this study, we investigate numerically the transitions between different spatial patterns of animal aggregations with various symmetries (even, odd or no symmetry) that characterise the microscopic distribution of individuals inside these aggregations. To this end, we construct a bifurcation diagram starting with perturbations of spatially homogeneous solutions with low, medium, and high amplitudes. For perturbations with low amplitudes, the bifurcating structures show transitions among even-symmetric, odd-symmetric, and non-symmetric solutions. For perturbations with large amplitudes, there are wide parameter regions with non-convergent solutions, characterised by oscillatory transitions between different relatively similar solutions. These numerical results emphasize: (i) the effect of nonlinear and non-local interactions on the microscopically different symmetric/non-symmetric structures of macroscopically similar ecological aggregations; (ii) the difficulty of developing continuation algorithms for this class of non-local models.

Maximal canards in a slow–fast Rosenzweig–MacArthur model with intraspecific competition among predators

Using geometric singular perturbation theory, this paper investigates the canard phenomenon of a slow–fast Rosenzweig–MacArthur model. The model incorporates intraspecific competition among predators, assuming predator reproduction occurs much slower than prey. We demonstrate the occurrence of maximal canards between attracting and repelling slow manifolds as a bifurcation parameter varies. Additionally, we derive an analytic expression to approximate the bifurcation parameter value at which a maximal canard occurs. The method employed for this analysis relies on the blowup method. This involves finding a quasihomogeneous blowup map to desingularize the nonnormally hyperbolic point. Subsequently, charts are utilized to express the blowup in local coordinates, calculate local data, investigate the dynamics of the blown-up vector fields, and establish connections across charts. Furthermore, we provide numerical simulations to illustrate the canard explosion phenomenon in the model. Through parameter variation, we observe that the model transitions from a small amplitude limit cycle to small amplitude canard cycles (canards without a head), then to large amplitude canard cycles (canards with a head), and finally to a large amplitude relaxation cycle.

Elimination of pores and microstructural characterization in Ti-6Al-4V alloy welds using fast-frequency double pulse TIG welding

This study utilizes a fast-frequency double pulse tungsten inert gas (FFDP TIG) process to weld 2 mm thick Ti-6Al-4V alloy, with the objective of investigating the influence of a large fast-frequency current amplitude on porosity, microstructure, and tensile properties of the weld joint. Unlike conventional TIG welding, the FFDP TIG welding process led to a reduction and elimination of porosity, and refined the prior β grain and α phase by 34.3 % and 33.3 %, respectively, while also refining the martensitic α′ structure. Stirring of the molten pool resulted in improved uniformity of grain orientation distribution, accompanied by decreased variant selection of the α phase and reduced texture strength of the α phases. Moreover, three-variant clusters of α/α′ phases with triangular morphology and micro- and nanoscale recrystallized α grains appear in the FFDP TIG weld. Concurrently, the FFDP TIG process significantly enhanced the tensile strength and ductility by 14.5 % and 114 %, respectively, compared to the conventional TIG process.

Utilizing synergy of MLG and MWCNT with optimized mixing protocol to improve the high temperature stability of SBS modified bitumen

High temperature instability is the biggest problem which limits the application of Styrene-Butadiene-Styrene (SBS) modified bitumen in flexible pavements. Addition of multi-layer graphene (MLG) nanomaterial improves the performance of SBS modified bitumen, but deteriorates its thermal stability. The binary additive comprising of MLG and multi-walled carbon nanotubes (MWCNT) can be a way to improve the thermal stability through their synergistic effects, however, mixing protocol needs to be optimized simultaneously. In this present study, MLG, MWCNT and their combination have been dispersed by two different organic solvent dissolution protocols, i.e., wet and dry to prepare the SBS-nano modified binders. Thermal stability analysis and rheological characterization (small & large amplitude oscillatory shear) have been used to optimize the method and to compare the effect of sole and binary additive. Advanced tools such as Raman spectroscopy and Field emission scanning electron microscopy have been used to understand the underlying science at micro-molecular level. The synergistic effects of combined additives are prominently visible only in dry organic dissolution method and with this method, the combination of MLG-MWCNT (0.1phr-1phr) significantly eliminates the thermal instability of SBS modified binder by upto 96 %. This SBS-nano modified bitumen may serve as futuristic binder for the black top pavements.

Experimental Research on Pressure Pulsation and Flow Structures of the Low Specific Speed Centrifugal Pump

The low specific speed centrifugal pump plays a crucial role in industrial applications, and ensuring its efficient and stable operation is extremely important for the safety of the whole system. The pump must operate with an extremely high head, an extremely low flow rate, and a very fast speed. The internal flow structure is complex and there is a strong interaction between dynamic and static components; consequently, the hydraulic excitation force produced becomes a significant factor that triggers abnormal vibrations in the pump. Therefore, this study focuses on a low specific speed centrifugal pump and uses a single-stage model pump to conduct PIV and pressure pulsation tests. The findings reveal that the PIV tests successfully captured the typical jet-wake structure at the outlet of the impeller, as well as the flow separation structure at the leading edge of the guide vanes and the suction surface. On the left side of the discharge pipe, large-scale flow separation and reverse flow happen as a result of the flow-through effect, producing a strong vortex zone. The flow field on the left side of the pressure chamber is relatively uniform, and the low-speed region on the suction surface of the guide vanes is reduced due to the reverse flow. The results of the pressure pulsation test showed that the energy of pressure pulsation in the flow passage of the guide vane occurs at the fBPF and its harmonics, and the interaction between the rotor and stator is significant. Under the same operating condition, the RMS value distribution and amplitude at fBPF of each measurement point are asymmetric in the circumferential direction. The amplitude of fBPF near the discharge pipe is lower, while the RMS value is higher. A complex flow structure is shown by the larger amplitude and RMS value of the fBPF on the left side of the pressure chamber. With the flow rate increasing, the energy at fBPF of each measurement point increases first and then decreases, while the RMS value decreases, indicating a more uniform flow field inside the pump.

Nonlinear dynamics of wing-like structures using a momentum subspace-based Koiter-Newton reduction

Cantilevers find a wide range of applications in the design of scientific equipment and large-scale engineering structures such as aircraft wings. Analysis techniques based on linearization approximations are unable to capture the large amplitude oscillation behaviour of such structures and thus, necessitates development of dedicated nonlinear methods. In this work, the recent developments in the Koiter-Newton model reduction method are utilized to obtain nonlinear reduced order models (ROMs) from full finite element structural models in order to simulate large amplitude dynamics of cantilevers. The method describes a nonlinear system of governing equations comprising quadratic and cubic terms which are obtained as higher order derivatives of the in-plane strain energy. To ensure that the large rotations in cantilevers and the resultant foreshortening effect is also accounted for, a ROM updating algorithm is adopted where the ROM parameters are varied with the structural deflections. Linear eigenmodes of the structure are utilized to form the reduction subspace. To validate the methodology, the ROM solution is compared against experimental results and a convergence study is conducted to identify the number of modes needed to replicate the nonlinear response. Finally, a composite wingbox structure is considered for which time domain simulations are conducted and frequency response curves, obtained through a frequency sweep, are presented.

Hemp Protein Isolate-Based Natural Thermal-Reversible Hydrogel as a Novel Wound Dressing Material.

Hydrogels, due to their excellent microstructure and mechanical strength, have become a novel biomaterial in wound dressing. However, plant proteins have never been considered because of their poor original gelling performances and insufficient rheological properties. Here, we reported the fabrication of a plant protein-based thermal-reversible gel using a reverse micelle-extracted hemp protein isolate (HPI). A systematic study was conducted to fully reveal their microstructure, rheological properties, and anti-inflammatory effect to lay a foundation for this newly developed plant protein hydrogel as a potential natural wound dressing. By modulating protein concentration (4% HPI) and temperature (85 °C), a thermal-reversible HPI gel appeared as a filament structure with the major molecular driving force of hydrophobic interactions and hydrogen bonds. By characterizing the rheological properties, lower gel strength and wider linear viscoelastic regime were determined in the thermal-reversible HPI gel compared with a thermal-irreversible HPI gel. Besides, large amplitude oscillatory shear data identified the thermal-reversible gel as a soft gel which demonstrated intracycle strain stiffening and shear thinning behavior. Moreover, the thermal-reversible HPI gel is nontoxic and has benefits in neutrophil growth with injectability and perfect wound coverage. This study opens a novel means to form a natural thermal-reversible hydrogel that can be a new material source for wound dressing.

Enhanced O/W emulsifying properties of pea proteins via deamidation: Insights into interfacial behavior

This study examines the effects of protein glutaminase modification on the interfacial properties and emulsion stability of pea protein isolates (PPI). Emulsions were prepared using native (NPPI) and deamidated PPI (DPPI) at concentrations from 0.5 wt% to 3.6 wt%. The stability of these emulsions was evaluated by examining droplet size distribution, flocculation index, ζ-potential, and CLSM. DPPI demonstrated superior emulsifying ability and stability, requiring only 2.0 wt% to prevent flocculation compared to NPPI's 3.6 wt%. Interfacial properties, such as protein coverage, composition, thickness, tension, and rheology, were characterized. Large Amplitude Oscillatory Dilatation analysis showed minimal differences between NPPI and DPPI-stabilized interfaces at 1 wt%. However, at 3.6 wt%, NPPI interfaces demonstrated abrupt intra-cycle yielding and viscous behavior, whereas DPPI interfaces exhibited gradual softening and a higher maximum linear strain. Additionally, DPPI showed higher interfacial protein coverage and lower interfacial tension. NPPI formed dense, brittle films prone to rupture under dynamic deformation, leading to poor stability. Deamidation of PPI unfolded the protein structure, exposing hydrophobic groups and increasing carboxyl groups, which reduced aggregation. This resulted in a uniform, extensible, and elastic interfacial film resistant to large deformations. Thus, DPPI-stabilized emulsions demonstrated superior stability, showcasing their potential for industrial applications.

Annular two-phase flow in a small diameter tube: OpenFOAM simulations with turbulence damping vs optical measurements

In this work, numerical simulations are performed to predict two-phase annular flow of refrigerant R245fa inside a 3.4 mm diameter vertical channel. The VOF (Volume of Fluid) method implemented in an OpenFOAM solver is used to accurately track the vapor-liquid interface. A 2D axisymmetric domain is considered and the Adaptive Mesh Refinement (AMR) method is applied to the cells near the liquid/vapor interface. The Reynolds-Averaged Navier Stokes (RANS) equations are solved and the k-ω SST model is adopted for turbulence modelling in both the liquid and vapor phase. Simulations are used to calculate instantaneous and mean values of the liquid film thickness at mass flux G = 100 kg m-2 s-1 and vapor quality ranging between 0.2 and 0.85. Numerical results are compared against measurements of the liquid film thickness taken during vertical annular downflow. Previous works from the literature and the deviations observed between present numerical and experimental results suggest the need for turbulence damping at the vapor-liquid interface by adding a source term in the ω equation. The simulations show that a low value of the turbulence damping parameter (e.g. 1) causes the average liquid film thickness to increase by 25 %–52 % compared to the non-damped scenario. The interface presents large amplitude disturbance waves in the non-damped case, whereas small ripple waves are predicted when turbulence damping is introduced. Furthermore, the difference between the application of a symmetric and asymmetric treatment for the source term is analysed. From the comparison between experimental data and numerical simulations, it emerges that the value of the correct damping source term to be applied is strictly dependent on the vapor quality.

Unveiling the Spectroscopy of Complex Organic Radicals by Exploiting Faraday Rotation at (Sub-)millimeter Wavelengths. Illustration with the Acetonyl Radical.

Radical species constitute the main reactants of numerous chemical reaction networks occurring in diverse environments. Rotationally resolved laboratory data, essential to undertake the detection of these highly reactive species, remain difficult to obtain using conventional high-resolution spectroscopy techniques. In the present work, we exploit a new experimental setup based on the Faraday rotation detection technique which allows us to study the gas phase spectra of relatively large radicals, such as dehydrogenated complex organic molecules (COMs). We recorded 2086 pure rotational transitions of the acetonyl radical (CH3COCH2) in the 150-450 GHz range, for which no rotational information was previously available. The radical exhibits relatively complex couplings of angular momenta, involving the overall rotation angular momentum, the spin of the unpaired electron, and two large amplitude motions. The data set has been fit using a semirigid Hamiltonian and shows the need for the development of specific theoretical models.

Conformational Landscapes of 2,3-, 2,4-, 2,5-, and 2,6-Difluorobenzaldehyde Unveiled by Rotational Spectroscopy.

We report the coexistence of anti-conformers and energetically unfavorable syn-conformers of 2,3-, 2,4-, 2,5-, and 2,6-difluorobenzaldehyde in the gas phase using broadband chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The rotational spectra of monosubstituted 13C isotopologues of the anti-conformers have also been assigned in natural abundance, which were used to derive their vibrationally averaged geometries and semi-experimental equilibrium structures. The energy differences between anti- and syn-conformations are estimated to be 10.9, 11.3, and 12.9 kJ/mol for 2,3-, 2,4-, and 2,5-difluorobenzaldehyde, respectively, at the theoretical level of DLPNO-CCSD(T)/def2-TZVP. Despite the steric repulsion caused by the close proximity between the oxygen atom of the aldehyde group and the ortho-substituted fluorine atom, our experimental results indicate the planarity of the syn-conformations. The frequencies of the large amplitude torsion between the phenyl and aldehyde groups have been estimated by experimental inertial defects, which agree with theoretical calculation results.

A perturbative multi-mode model with finite parallel electric field for fast-ion-driven Alfvén eigenmodes

Abstract Alfvén eigenmodes are of great interest in any fusion device as they can be excited by fast ions in the plasma. If the modes grow to large amplitudes, they can cause transport and redistribution of the fast ions, thus limiting fusion performance. To save computational resources, the resonant kinetic interaction between the fast-particle species and the modes is often modelled by MHD-kinetic hybrid codes. Here, we present such a hybrid model which is applicable to three-dimensional magnetic fields, accounts for a finite parallel electric field and multiple MHD modes present at the same time. The model extends the one previously implemented in the CKA-EUTERPE code allowing for a better estimate of the damping due to the parallel electric field and nonlinear mode-mode interaction. The capabilities of our model are illustrated by applying the code to model nonlinear frequency chirping and fast-ion profile flattening.

M3D‐DPWM strategy for three‐phase four‐leg inverter with higher harmonic suppression capability

AbstractThree‐phase four‐leg inverters are widely used in power systems due to their inherent ability to handle unbalanced loads. However, with conventional 3D space vector pulse width modulation (3D‐SVPWM), high harmonics of large amplitude exist in the output voltage around the switching frequency and its integer multiples leading to noise in the load motor and limiting the application range of the inverter system. The passband amplification of conventional sinusoidal filters and their cutoff frequency vary with the load, so it is particularly important to investigate the regulation strategy with harmonic suppression. In this study, an improved 3D discontinuous pulse width modulation (M3D‐DPWM) strategy is proposed based on 3D‐SVPWM. By reducing the conventional 3D‐SVPWM switching segments and changing the vector synthesis sequence of the last half switching cycle, the output phase voltage period is reduced to half of the original one, which achieves the purpose of suppressing the output voltage at the switching frequency and its odd multiple high harmonics without changing the fundamental characteristics and adding additional circuits. In contrast, the conventional 3D‐SVPWM switching frequency is increased to 20 kHz to achieve similar performance. Finally, the effectiveness of the proposed strategy is verified by simulation and experiment.

Experimental preparation of multiphoton-added coherent states of light

Conditional addition of photons represents a crucial tool for optical quantum state engineering and it forms a fundamental building block of advanced quantum photonic devices. Here we report on experimental implementation of the conditional addition of several photons. We demonstrate the addition of one, two, and three photons to input coherent states with various amplitudes. The resulting highly nonclassical photon-added states are completely characterized with time-domain homodyne tomography, and the nonclassicality of the prepared states is witnessed by the negativity of their Wigner functions. We experimentally demonstrate that the conditional addition of photons realizes approximate noiseless quantum amplification of coherent states with sufficiently large amplitude. We also investigate certification of the stellar rank of the generated multiphoton-added coherent states, which quantifies the non-Gaussian resources required for their preparation. Our results pave the way towards the experimental realization of complex optical quantum operations based on combination of multiple photon additions and subtractions.

Phase nonlinearity–weighted optical flow for enhanced full-field displacement measurement and vibration imaging

In this study, we developed a technique to utilize phase nonlinearity as a quantifiable confidence measure of the reliability of component displacement vectors extracted from multi-scale and multi-direction phases. The proposed approach includes three novel concepts. First, relative confidence values are established based on phase nonlinearity to quantify the reliability of the displacement components across various environmental conditions. Second, by analyzing the distribution of the relative confidence values, adaptive confidence measures are extracted and are used to reject unreliable displacement components; these confidence measures can dynamically adapt to various environmental conditions, such as varying image noise and large amplitudes of motion. Third, phase nonlinearity–weighted motion integration is conducted to ensure accurate estimation of the full displacement vector from the component vectors. By integrating these three approaches, a remarkable enhancement was achieved in full-field displacement measurement in terms of accuracy, robustness, and signal-to-noise ratio, especially in environments with high noise levels. The capability of the proposed technique was evaluated through numerical experiments using artificial patterns that simulate identical motions under varying noise levels. Experimental validation was also performed on an air compressor to substantiate the accuracy and robustness of the proposed technique. The findings verify its improvements over conventional techniques for full-field displacement measurement.

The Influence of Large‐Scale Spatial Warming on Jet Stream Extreme Waviness on an Aquaplanet

AbstractThe effect of modified equator‐to‐pole temperature gradients on the jet stream by low‐level polar warming and upper‐level tropical warming is not fully understood. We perform aquaplanet simulations to quantify the impact of different sea surface temperature distributions on jet stream strength, large wave amplitudes and extreme waviness. The responses to warming in the waviness metrics Sinuosity Index and Local Wave Activity are sensitive to the latitude range over which they are calculated. Therefore, we use a latitude range that accurately represents the position of the jet. The uniform warming scenario strengthens the jet and reduces large wave amplitudes. Reductions in meridional temperature gradients lead to weakened mid‐latitudinal jet strength and show significant decreases in large wave amplitudes and jet stream waviness. These findings contradict the mechanism that weakened jet streams increase wave amplitudes and extreme jet stream waviness. We conclude that weakened jet streams do not necessarily become wavier.

Experimental investigation of three-dimensional Rayleigh–Taylor instability of a gaseous interface

Validating the theoretical work on Rayleigh–Taylor instability (RTI) through experiments with an exceptionally clean and well-characterized initial condition has been a long-standing challenge. Experiments were conducted to study the three-dimensional RTI of an SF $_6$ –air interface at moderate Atwood numbers. A novel soap film technique was developed to create a discontinuous gaseous interface with controllable initial conditions. Spectrum analysis revealed that the initial perturbation of the soap film interface is half the size of an entire single-mode perturbation. The correlation between the initial interface perturbation and Atwood numbers was determined. Due to the steep and highly curved feature of the initial soap film interface, the early-time evolution of RTI exhibits significant nonlinearity. In the quasi-steady regime, various potential flow models accurately predict the late-time bubble velocities by considering the channel width as the perturbation wavelength. Differently, the late-time spike velocities are described by these potential flow models using the wavelength of the entire single-mode perturbation. These findings indicate that the bubble evolution is influenced primarily by the spatial constraint imposed by walls, while the spike evolution is influenced mainly by the initial curvature of the spike tip. Consequently, a recent potential flow model was adopted to describe the time-varying amplitude growth induced by RTI. Furthermore, the self-similar growth factors for bubbles and spikes were determined from experiments and compared with existing studies, revealing that a large amplitude in the initial soap film interface promotes the spike development.

Physics-constrained adaptive kernel interpolation for region-to-region acoustic transfer function: a Bayesian approach

A kernel interpolation method for the acoustic transfer function (ATF) between regions constrained by the physics of sound while being adaptive to the data is proposed. Most ATF interpolation methods aim to model the ATF for fixed source by using techniques that fit the estimation to the measurements while not taking the physics of the problem into consideration. We aim to interpolate the ATF for a region-to-region estimation, meaning we account for variation of both source and receiver positions. By using a very general formulation for the reproducing kernel function, we have created a kernel function that considers both directed and residual fields as two separate kernel functions. The directed field kernel considers a sparse selection of reflective field components with large amplitudes and is formulated as a combination of directional kernels. The residual field is composed of the remaining densely distributed components with lower amplitudes. Its kernel weight is represented by a universal approximator, a neural network, in order to learn patterns from the data freely. These kernel parameters are learned using Bayesian inference both under the assumption of Gaussian priors and by using a Markov chain Monte Carlo simulation method to perform inference in a more directed manner. We compare all established kernel formulations with each other in numerical simulations, showing that the proposed kernel model is capable of properly representing the complexities of the ATF.

Mechanism of sodium alginate synergistically improving foaming properties of pea protein isolate: Air/water interface microstructure and rheological properties

The synergistic effect of polysaccharides plays a crucial role in regulating the foaming properties of protein based aerated foods. In this study, the synergistic improvement mechanism of pea protein isolate (PPI)-sodium alginate (SA) composite on the foaming performance was determined through multi-component interaction, air/water interface adsorption behavior and foam properties. The results of interactions between PPI and SA indicated that SA and PPI could form smaller and more stable soluble composite through hydrogen bonding, hydrophobic interactions, and electrostatic interactions. The α-helix content of PPI significantly decreased, and PPI exhibited a more flexible secondary structure. In depth research on the air/water interfacial behavior and interfacial microstructure through adsorption kinetics, surface dilatational rheology and Lissajous plots indicated that the PPI-SA composite could accelerate the adsorption process, constructing a highly viscoelastic interface mainly based on elasticity. The results of foam properties showed soluble PPI-SA composite could prepare smaller and more dense foam with thicker and smoother interface film, which was beneficial to the foam stability. The results of small amplitude oscillatory shear and large amplitude oscillatory shear suggested that foam prepared by soluble PPI-SA composite showed stronger ability to resist deformation whether in linear or nonlinear viscoelastic region, revealing the good mechanical properties of these foam under extreme processing conditions and feasibility to improve the quality of aerated food. When the mass ratio of PPI/SA was 1:0.3, the foam properties was strongest. When the mass ratio of PPI/SA exceeded 1:0.3, insoluble substances appeared in the composite system, which was disadvantageous to foam properties and deformation resistance. Therefore, the complexation of PPI and SA was an effective way to improve the air/water interface and foaming properties of PPI, providing theoretical guidance for targeted regulation of the foaming properties of protein based aerated foods.