Interaction Regime Research Articles

Dissipative Dynamics of Quantum Vortices in Fermionic Superfluid.

In a recent article, Kwon etal. [Nature (London) 600, 64 (2021)NATUAS0028-083610.1038/s41586-021-04047-4] revealed nonuniversal dissipative dynamics of quantum vortices in a fermionic superfluid. The enhancement of the dissipative process is pronounced for the Bardeen-Cooper-Schrieffer interaction regime, and it was suggested that the effect is due to the presence of quasiparticles localized inside the vortex core. We test this hypothesis through numerical simulations with time-dependent density-functional theory: a fully microscopic framework with fermionic degrees of freedom. The results of fully microscopic calculations expose the impact of the vortex-bound states on dissipative dynamics in a fermionic superfluid. Their contribution is too weak to explain the experimental measurements, and we identify that thermal effects, giving rise to mutual friction between superfluid and the normal component, dominate the observed dynamics.

Tunable virtual gain in resonantly absorbing media

Virtual gain refers to the simulation of real light amplification using radiation with exponentially decaying amplitude, so that its complex frequency corresponds to the scattering pole. We theoretically study virtual gain in a two-level resonant medium for different regimes of light-matter interaction depending on the radiation intensity. We show that virtual gain at the pole can be most clearly observed for low intensities, when the medium is absorbing, in contrast to the saturated medium at high intensities. The efficiency of virtual gain can be tuned with the light intensity and can be controlled dynamically through the population inversion of the medium. Our results show that resonantly absorbing media paradoxically mimics gain-like response, which admit a number of related phenomena and methods to mold both optical signals and material properties without relying on instability-prone gain media.

IS INTERNATIONAL MONETARY POLICY COORDINATION FEASIBLE FOR THE ASEAN-5 + 3 COUNTRIES?

We examine the feasibility of international monetary policy coordination among the ASEAN-5 + 3 countries using the two-production-factor Dynamic Stochastic General Equilibrium (DGSE) models. It explores three types of interaction regimes among these countries: (1) No Coordination; (2) Bilateral Coordination; and (3)Multilateral Coordination. We find 18 feasible Bilateral Coordination schemes and four feasible Multilateral Coordination schemes for the ASEAN-5 + 3 countries. The best among these schemes is the Multilateral Coordination scheme that involves all the ASEAN-5 + 3 countries. Therefore, we suggest that the ASEAN-5 + 3 countries should adopt this scheme if coordinating monetary policies.

Many-Body Correlations and Exciton Complexes in CsPbBr3 Quantum Dots.

All-inorganic lead-halide perovskite (LHP) (CsPbX3 , X=Cl, Br, I) quantum dots (QDs) have emerged as a competitive platform for classical light-emitting devices (in the weak light-matter interaction regime, e.g., LEDs and laser), as well as for devices exploiting strong light-matter interaction at room temperature. Many-body interactions and quantum correlations among photogenerated exciton complexes play an essential role, for example, by determining the laser threshold, the overall brightness of LEDs, and the single-photon purity in quantum light sources. Here, by combining cryogenic single-QD photoluminescence spectroscopy with configuration-interaction (CI) calculations, the size-dependent trion and biexciton binding energies are addressed. Trion binding energies increase from 7to 17meV for QD sizes decreasing from 30to 9nm, while the biexciton binding energies increase from 15to 30meV, respectively. CI calculations quantitatively corroborate the experimental results and suggest that the effective dielectric constant for biexcitons slightly deviates from the one of the single excitons, potentially as a result of coupling to the lattice in the multiexciton regime. The findings here provide a deep insight into the multiexciton properties in all-inorganic LHP QDs, essential for classical and quantum optoelectronic devices.

Diffusive scattering of energetic electrons by intense whistler-mode waves in an inhomogeneous plasma

Electron resonant interactions with electromagnetic whistler-mode waves play an important role in electron flux dynamics in various space plasma systems: planetary radiation belts, bow shocks, solar wind and magnetic reconnection regions. Two key wave characteristics determining the regime of wave–particle interactions are the wave intensity and the wave coherency. The classical quasi-linear diffusion approach describes well electron diffusion by incoherent and low-amplitude waves, whereas the nonlinear resonant models describe electron phase bunching and trapping by highly coherent intense waves. This study is devoted to the investigation of the regime of electron resonant interactions with incoherent but intense waves. Although this regime is characterized by electron diffusion, we show that diffusion rates scale linearly with the wave amplitude,$D\propto B_w$, in contrast to the quasi-linear diffusion scaling$D_{QL}\propto B_w^2$. Using observed wave amplitude distributions, we demonstrate that the quasi-linear diffusion model significantly overestimates electron scattering by incoherent, but intense whistler-mode waves. We discuss the results obtained in the context of simulations of long-term electron flux dynamics in space plasma systems.

Fire whirls induced by a line fire on a windward slope: a laboratory-scale study

Background Fire whirls are often reported to occur in wildland fires and can induce serious difficulties in firefighting by abruptly modifying fire behaviour, exposing firefighters and even causing casualties. Aims The aim of this study was to examine the formation of fire whirls on a windward slope. Methods Straight and V-shaped heated wires and burners were used to emulate fire spread fronts of various fire intensities. Different slope angles and ambient wind speeds were considered, to observe the formation and behaviour of fire whirls. Key results A fire whirl appeared over a straight-line fire in the presence of wind, and a couple of counter-rotating fire whirls appeared over the two flanks of a V-shaped line fire. Conclusions Two interaction regimes were experimentally observed and theoretically explained for the interaction of two fire whirls. We found that an effective wind speed instead of the local wind speed in sloped terrains can quantify the critical condition for the formation of fire whirls over line fires of different burning intensities. Implication A critical effective wind speed correlation that couples slope angle, burning intensity and radiative fraction of a line fire can predict fire whirl risk in wildland fire fighting.

Особенности рыночных структур с позиции регулярно-динамической теории

The article focuses on the application of the regular-dynamic method in the theory of industry markets. It introduces the Hamilton function and key parameters of portal connections that describe market barrier properties and formulates the fundamental equations of market dynamics. The solutions of these equations determine crucial characteristics of commodity-money exchange at each market link and establish relationships that describe typical regimes of local equilibrium market interaction, including perfect and monopolistic competition, pure monopolies and monopsonies, as well as oligopolies and oligopsonies. The study reveals that the interaction among agents in a perfectly competitive market is influenced by weakly disturbed portal connections, which prevent firms from reaching a profitable level of exchange with an equilibrium price solely determined by technological parameters within the firms. In the case of a monopolistically competitive market, the price demonstrates an inversely proportional dependence on the volume of supply, which is characteristic of small businesses offering differentiated goods based on quality. It is observed that the equilibrium price in monopoly markets exhibits monotonic growth as the production activity of interacting firms increases. This price increase is attributed to an elevation in the seller’s barrier and a reduction in the depth of buyers’ market pits in the case of pure monopoly, while the reverse occurs in pure monopsony with an increase in the depth of the buyer’s pit and a decrease in sellers’ barriers. The article investigates the relationship between the equilibrium price and the parameters of technological processes, as well as the barrier properties of firms acting as sellers and buyers in oligopoly and oligopsony markets. Furthermore, the study highlights that the structure and effectiveness of oligo markets significantly depend on the relative positioning of technological frequencies between market leaders and outsiders. The article proposes an analytical description of the “race for the leader” effect. Lastly, for all the analyzed modes of market interactions, the stability of the processes governing equilibrium price formation is substantiated.

Highly efficient transient stimulated Raman scattering on secondary vibrational mode of BaWO4 crystal due to its constructive interference with self-phase modulation

An exceptionally high stimulated Raman scattering (SRS) conversion efficiency to the first Stokes component associated with the secondary (low-frequency and low intensity) vibrational mode ν2 (∼330 cm-1) was observed in a BaWO4 crystal in a highly transient regime of interaction. The effect takes place in the range of pump pulse energy from ∼0.1 to ∼0.5 µJ with maximum energy conversion efficiency up to 35% at 0.2 µJ. The nature of the observed effects is explained by interference of SRS and self-phase modulation, where the latter is related to a noninstantaneous orientational Kerr nonlinearity in the BaWO4 crystal.

Jezičke forme između linearnog rasporeda emitovanja i striming platformi u kućnom kontekstu

This paper proposes to observe the linguistic forms by which it is possible to translate and interpret the fruition of audiovisual content in the domestic context, between linear broadcast schedule and on-demand streaming portals. In line with Louis Hjelmslev's linguistic theory, the two devices are observed through their syntagmatic and paradigmatic nature, emphasizing how they differently relate the content they convey by generating different forms of audiovisual discursiveness. Through this differentiation it will then be possible to account for the different valorization at play first in the schedule device - which prioritizes the linguistic/positional value - and then in the streaming portal - in which the phenomenological value proposed by A.J. Greimas comes into play. This comparative reading, in addition to returning to a formalization of the modes of viewing across devices, allows us to introduce a reading of the regimes of interaction that come into play at the time of the fruition of differentially conveyed and valorized content.

Electrically tunable dipolar interactions between layer-hybridized excitons.

Transition-metal dichalcogenide bilayers exhibit a rich exciton landscape including layer-hybridized excitons, i.e. excitons which are of partly intra- and interlayer nature. In this work, we study hybrid exciton-exciton interactions in naturally stacked WSe2 homobilayers. In these materials, the exciton landscape is electrically tunable such that the low-energy states can be rendered more or less interlayer-like depending on the strength of the external electric field. Based on a microscopic and material-specific many-particle theory, we reveal two intriguing interaction regimes: a low-dipole regime at small electric fields and a high-dipole regime at larger fields, involving interactions between hybrid excitons with a substantially different intra- and interlayer composition in the two regimes. While the low-dipole regime is characterized by weak inter-excitonic interactions between intralayer-like excitons, the high-dipole regime involves mostly interlayer-like excitons which display a strong dipole-dipole repulsion and give rise to large spectral blue-shifts and a highly anomalous diffusion. Overall, our microscopic study sheds light on the remarkable electrical tunability of hybrid exciton-exciton interactions in atomically thin semiconductors and can guide future experimental studies in this growing field of research.

Method of difference-differential equations for some Bethe-ansatz-solvable models

In studies of one-dimensional Bethe ansatz solvable models, a Fredholm integral equation of the second kind with a difference kernel on a finite interval often appears. This equation does not generally admit a closed-form solution and hence its analysis is quite complicated. Here we study a family of such equations, concentrating on their moments. We find exact relations between the moments in the form of difference-differential equations. The latter results significantly advance the analysis, enabling one to practically determine all the moments from the explicit knowledge of the lowest one. As applications, several examples are considered. First, we study the moments of the quasimomentum distribution in the Lieb-Liniger model and find explicit analytical results. The latter moments determine several basic quantities, e.g., the $N$-body local correlation functions. We prove the equivalence between different expressions found in the literature for the three-body local correlation functions and find an exact result for the four-body local correlation function in terms of the moments of the quasimomentum distributions. We eventually find the analytical results for the three- and four-body correlation functions in the form of asymptotic series in the regimes of weak and strong interactions. Next, we study the exact form of the low-energy spectrum of a magnon (a polaron) excitation in the two-component Bose gas described by the Yang-Gaudin model. We find its explicit form, which depends on the moments of the quasimomentum distributions of the Lieb-Liniger model. Then, we address a seemingly unrelated problem of capacitance of a circular capacitor and express the exact result for the capacitance in the parametric form. In the most interesting case of short plate separations, the parametric form has a single logarithmic term. This should be contrasted with the explicit result that has a complicated structure of logarithms.

Thermodynamics of the inception and interactions of multiple laser-produced cavitation bubbles using the lattice Boltzmann method

Understanding the thermodynamics associated with the inception and interactions of multiple cavitation bubbles is vital in developing deeper insights into the flow field and temperature properties of cavitation bubble clouds. This paper describes a double-distribution-function thermal lattice Boltzmann method for investigating the thermodynamics of multiple-bubble interactions, and proposes a new two-dimensional method for cavitation bubble inception without the initialization of gas nuclei. This approach is validated by simulating the evolution of a laser-produced bubble. The interaction between two vapor bubbles is simulated, and the hydrodynamics and thermodynamics of cavitation bubbles are systematically investigated. Both weak and strong interactions among bubbles of equal size are accurately reproduced. The coalescence mode is further categorized according to differences in the collapse behaviors: the remaining parts collapse away from each other for coalescence in the collapse stage, but collapse toward each other for coalescence in the growth stage. Interactions among bubbles of different sizes are also explored and the different morphologies for various interaction modes are reported. In the case of small distances between bubbles under the weak interaction regime, the smaller bubble is pushed away from the symmetry axis, leading to an initial decrease in collapse intensity and then an increase as the distance between the two bubbles increases. Finally, the thermodynamics of a bubble cluster are investigated. The hydrodynamic and thermodynamic processes in different regions of the cavitation bubble cluster are determined, and the toroidal shape in the final stage is reproduced. The results demonstrate that the proposed model accurately simulates the complex interactions among multiple cavitation bubbles.

Flow-induced vibrations of a cylinder along a circular arc

An elastically mounted circular cylinder, immersed in a cross-current and free to move along a rectilinear path, is subjected to vortex-induced vibrations (VIV). These vibrations develop through a mechanism referred to as lock-in, where body motion and vortex shedding synchronize at a frequency that may deviate both from the oscillator natural frequency and from the vortex shedding frequency past a fixed cylinder. The present numerical study aims at extending the analysis to curved trajectories, by considering that the cylinder is free to translate along a circular path. The Reynolds number based on the body diameter ( $D$ ) and current velocity ( $U$ ) is set to $100$ . A wide range of path radii, from $0.05D$ to $10D$ , and values of the reduced velocity (inverse of the oscillator natural frequency non-dimensionalized by $D$ and $U$ ) up to $30$ are examined, for the concave and convex configurations, i.e. the circular path centre located upstream or downstream of the cylinder. Path curvature results in a major alteration of the flow–body system behaviour compared with rectilinear VIV, with substantially different evolutions in the concave and convex configurations. In addition to the typical lock-in mechanism, two subharmonic forms of synchronization, at half and one third of vortex formation frequency, are uncovered in the convex configuration. They coexist with a desynchronized regime where the body and the flow oscillate at incommensurable frequencies. The four interaction regimes exhibit contrasted trends in terms of structural response, spatiotemporal organization of the wake and associated forces. They particularly differ by their symmetry properties, which are closely linked to the possible reconfiguration of the oscillator due to mean fluid forcing.

Effect of surface roughness of solid particles on the regimes and outcomes of their collisions with liquid droplets

The paper presents the experimental research findings for the characteristics of the collisions of liquid droplets with solid particles (as illustrated by distilled water and metal particles) with a variable average roughness. The average roughness range (0.05–39 µm) corresponded to a group of practical applications: heat exchange, treatment, evaporation, fuel systems, etc. The regimes of droplet-particle collisions, as well as the characteristics of secondary liquid fragments, i.e., child droplets, were determined. Interaction regime maps for droplets and particles were constructed. Mathematical equations to describe the boundaries of droplet-particle interaction regimes were obtained. The findings were compared with the characteristics of collisions of liquid droplets with a flat solid substrate made of the same material as the particles with equivalent average roughness. Guidelines were provided for applying the research findings to the development of the technologies of secondary atomization of liquid droplets in applications.

Hilbert space fragmentation and interaction-induced localization in the extended Fermi-Hubbard model

We study Hilbert space fragmentation in the extended Fermi-Hubbard model with nearest and next-nearest-neighbor interactions. Using a generalized spin/mover picture and saddle point methods, we derive lower bounds for the scaling of the number of frozen states and for the size of the largest block preserved under the dynamics. We find fragmentation for strong nearest- and next-nearest-neighbor repulsions as well as for the combined case. Our results suggest that the involvement of next-nearest-neighbor repulsions leads to an increased tendency for localization. We then model the dynamics for larger systems using Markov simulations to test these findings and unveil in which interaction regimes the dynamics becomes spatially localized. In particular, we show that for strong nearest- and next-nearest-neighbor interactions random initial states will localize provided that the density of initial movers is sufficiently low.

The beam stop as an intensity monitor

Free-electron lasers (FELs) provide unique possibilities in investigating matter down to femtosecond time and nanometer length scales, as well as in the regime of non-linear light-matter interaction. Due to the nature of FEL sources, the produced beam is significantly more unstable than beams produced by 3rd generation synchrotrons. As a result, pulse-resolved normalization of measurement data becomes essential and can be challenging. The intensity monitors permanently installed at a facility might indeed accurately measure the pulse intensities at a certain point of the beamline, but cannot precisely normalize experimental data. For example the impact of pointing instabilities and hence different clipping of the beam downstream on the way to the actual experiment is not reflected in the intensity measurement. Here, we show how the integral intensity of the FEL beam transmitted through the sample can be measured by photodiodes providing a proper normalization of measurement data.

Characterization of Femtosecond Laser and Porcine Crystalline Lens Interactions by Optical Microscopy.

The use of ultrafast laser pulses for eye anterior segment surgery has seen a tremendous growth of interest as the technique has revolutionized the field, from the treatment of myopia, hyperopia, and presbyopia in the cornea to laser-assisted cataract surgery of the crystalline lens. For the latter, a comprehensive understanding of the laser-tissue interaction has yet to be achieved, mainly because of the challenge of observing the interaction zone in situ with sufficient spatial and temporal resolution in the complex and multi-layered tissue of the crystalline lens. We report here on the dedicated characterization results of the laser-tissue interaction zone in the ex vivo porcine lens using three different methods: in situ and real-time microscopy, wide-field optical imaging, and phase-contrast microscopy of the histological cross sections. These complementary approaches together revealed new physical and biological consequences of laser irradiation: a low-energy interaction regime (pulse energy below ~1 µJ) with very limited cavitation effects and a stronger photo-disruption regime (pulse energy above 1 µJ) with a long cavitation duration from seconds to minutes, resulting in elongated spots. These advances in the understanding of the ultrafast laser's interactions with the lens are of the utmost importance for the preparation of the next-generation treatments that will be applied to the lens.

Excitation spectra of one-dimensional spin-1/2 Fermi gas with an attraction

Using an exact Bethe ansatz solution, we rigorously study excitation spectra of the spin-1/2 Fermi gas (called Yang–Gaudin model) with an attractive interaction. Elementary excitations of this model involve particle-hole excitation, hole excitation and adding particles in the Fermi seas of pairs and unpaired fermions. The gapped magnon excitations in the spin sector show a ferromagnetic coupling to the Fermi sea of the single fermions. By numerically and analytically solving the Bethe ansatz equations and the thermodynamic Bethe ansatz equations of this model, we obtain excitation energies for various polarizations in the phase of the Fulde–Ferrell–Larkin–Ovchinnikov-like state. For a small momentum (long-wavelength limit) and in the strong interaction regime, we analytically obtained their linear dispersions with curvature corrections, effective masses as well as velocities in particle-hole excitations of pairs and unpaired fermions. Such a type of particle-hole excitations display a novel separation of collective motions of bosonic modes within paired and unpaired fermions. Finally, we also discuss magnon excitations in the spin sector and the application of Bragg spectroscopy for testing such separated charge excitation modes of pairs and single fermions.

Puffing frequency of interacting buoyant plumes

Buoyant plumes are known to oscillate at a characteristic frequency, but little is known about how this frequency changes when two plumes are in close proximity. In this work, we conduct a series of high-fidelity simulations varying the spacing and width between two-dimensional helium plumes. We find that the global trends are similar to that of interacting reacting plumes, and four distinct regimes of interaction can be identified, most notably a scaling regime when the plumes are at moderate distances apart.

Quantum transport of strongly interacting fermions in one dimension far out of equilibrium

In the study of quantum transport, much has been known about dynamics near thermal equilibrium. However, quantum transport far away from equilibrium is much less well understood---the linear response approximation does not hold for physics far out of equilibrium in general. In this work, motivated by recent cold atom experiments on probing quantum many-body dynamics of a one-dimensional XXZ spin chain, where a transition from ballistic to diffusive dynamics has been established by increasing the interaction strengths, we study the strong interaction limit of the one-dimensional spinless fermion model, which is dual to the XXZ spin chain. We develop a highly efficient computation algorithm for simulating the nonequilibrium dynamics of this system exactly, and examine the nonequilibrium dynamics starting from a density modulation quantum state. We find ballistic transport in this strongly correlated setting and show that a plane-wave description emerges at long-time evolution. We also observe a sharp distinction between transport velocities in short and long times as induced by interaction effects and provide a quantitative interpretation for the long-time transport velocity. We expect our results to shed light on the understanding of the dynamics of the XXZ spin chain in the strong interaction regime.