We study the sources of intense ultra-high-frequency (UHF) radiation (in the frequency range 1–6 GHz) arising during the development of high-voltage atmospheric discharges. The discharges were initiated in a long discharge gap by applying an approximately 1-MV pulse with positive or negative polarity. By employing a radio registration system based on ultrawideband antennas, we managed to localize the UHF radiation sources in the discharge with centimeter accuracy and investigate their temporal and spatial correlation with the discharge structures. The vast majority of the localized sources turned out to be concentrated in the near-electrode regions. It is found that the generation mechanism of intense UHF radiation in a laboratory discharge cannot be unambiguously associated with such basic processes as the head-on collision of opposite-polarity streamers or the interaction of single streamers with the near-electrode plasma at the surface of metal electrodes. We discovered that the observed UHF emission appears basically as a precursor of the intense plasma development in a certain discharge region, whereinto a bright counterstreamer comes a bit later. The findings were confirmed by the statistical observations and results of imaging the dynamics of the discharge structures with a nanosecond temporal resolution.

A bipartite spin system is proposed for which a fast transfer from one defined state into another exists. For sufficient coupling between the spins, this implements a bit-flipping mechanism, which is much faster than that induced by tunneling. The states correspond in the semiclassical limit to equilibrium points with a stability transition from elliptic-elliptic stability to complex instability for increased coupling. The fast transfer is due to the spiraling characteristics of the complex unstable dynamics. Based on the classical system we find an approximate scaling relation for the transfer time, which even applies in the deep quantum regime. By investigating a simple model system, we show that the classical stability transition is reflected in a fundamental change in the structure of the eigenfunctions.

In this study, we study noise-induced bistability in a simple bivariate mutual inhibition system with slow fluctuating responses to external signals. We give a general condition that the marginal stationary probability density of one of the two variables experiences a transition from a unimodal shape to a bimodal one. We show that the transition occurs even when the stationary probability density of the response to external signals is monotone. The mechanism for the transition is investigated in terms of the calculation of the mean first passage time. We also discuss the genericity of the transition mechanism.

The different variants of two-stage random sequential adsorption (RSA) models for packing of disks and discorectangles on a two-dimensional (2D) surface were investigated. In the SD (sticks+disks) model, the discorectangles were first deposited and then the disks were added. In the DS (disks+sticks) model, the disks were first deposited and then discorectangles were added. At the first stage the particles were deposited up to the selected concentration and at the final (second) stage the particles were deposited up to the saturated (jamming) state. The main parameters of the models were the concentration of particles deposited at the first stage, aspect ratio of the discorectangles $\varepsilon$ (length to diameter of ratio $\varepsilon =l/d$) and disk diameter $D$. All distances were measured using the value of $d$ as a unit of measurement of linear dimensions, the disk diameter was varied in the interval $D\in [1-10]$, and the aspect ratio value was varied in the interval $\varepsilon \in [1-50]$. The dependencies of the jamming coverage of particles deposited at the second stage versus the parameters of the models were analyzed. The presence of first deposited particles for both models regulated the maximum possible disk diameter $D_{\max }$ (SD model) or the maximum aspect ratio ${\varepsilon }_{\max }$ (DS model). This behavior was explained by the deposition of particles in the second stage into triangular (SD model) or elongated (DS model) pores formed by particles deposited at the first stage. The percolation connectivity of disks (SD model) and discorectangles (DS model) for the particles with a hard core and a soft shell structure was analyzed. The disconnectedness was ensured by overlapping of soft shells. The dependencies of connectivity versus the parameters of SD and DS models were also analyzed.

We analytically calculate the cumulant generating function of energy and particle transport in an open one-dimensional Kitaev chain at finite temperature by utilizing the Keldysh technique. The joint distribution of particle and energy currents satisfies different fluctuation relations in different regions of the parameter space as a result of U(1) symmetry breaking and energy conservation. Furthermore, we investigate the linear response behavior of the Kitaev chain within the framework of three-terminal systems, deriving the expressions for the Seebeck coefficient and thermal conductance. Notably, we observe a pronounced peak in the thermal conductance near the phase transition point, in agreement with previous predictions. Additionally, we prove that the peak value saturates at half of the thermal conductance quantum for finite-length chains at the zero temperature limit.

When studying social dilemma games, a crucial question arises regarding the impact of general heterogeneity on cooperation, which has been shown to have positive effects in numerous studies. Here, we demonstrate that heterogeneity in the contribution value for the focal public goods game can jeopardize cooperation. We show that there is an optimal contribution value in the homogeneous case that most benefits cooperation depending on the lattice. In a heterogeneous scenario, where strategy and contribution coevolve, cooperators making contributions higher than the optimal value end up harming those who contribute less. This effect is notably detrimental to cooperation in the square lattice with von Neumann neighborhood, while it can have no impact in other lattices. Furthermore, in parameter regions where a higher-contributing cooperator cannot normally survive alone, the exploitation of lower-value contribution cooperators allows their survival, resembling a parasitic behavior. To obtain these results, we examined the effect of various distributions for the contribution values in the initial condition and we conducted Monte Carlo simulations.

A heat conduction equation on a lattice composed of nodes and bonds is formulated assuming the Fourier law and the energy conservation law. Based on this equation, we propose a higher-order topological heat conduction model on the breathing kagome lattice. We show that the temperature measurement at a corner node can detect the corner state which causes rapid heat conduction toward the heat bath, and that several-nodes measurement can determine the precise energy of the corner states.

Recently, the learning by confusion (LbC) approach has been proposed as a machine learning tool to determine the critical temperature $T_c$ of phase transitions without any prior knowledge of its even approximate value. The method has been proven effective, but it has been used only for continuous phase transitions, where the confusion results only from deliberate incorrect labeling of the data. However, in the case of a discontinuous phase transition, additional confusion can result from the coexistence of different phases. To verify whether the confusion scheme can also be used for discontinuous phase transitions, we apply the LbC method to three microscopic models, the Blume-Capel, the $q$–state Potts, and the Falicov-Kimball models, which undergo continuous or discontinuous phase transitions depending on model parameters. With the help of a simple model, we predict that the phase coexistence present in discontinuous phase transitions can indeed make the neural network more confused and thus decrease its performance. However, numerical calculations performed for the models mentioned above indicate that other aspects of this kind of phase transition are more important and can render the LbC method even less effective. Nevertheless, we demonstrate that in some cases the same aspects allow us to use the LbC method to identify the order of a phase transition.

We give compelling evidence that diversity, represented by a quenched disorder, can produce a resonant collective transition between two unsteady states in a network of coupled oscillators. The stability of a metastable state is optimized and the mean first-passage time maximized at an intermediate value of diversity. This finding shows that a system can benefit from inherent heterogeneity by allowing it to maximize the transition time from one state to another at the appropriate degree of heterogeneity.

The phenomenon of synchronization in self-sustained systems has been successfully illuminated in many fields, ranging from biology to electrical engineering. To date, the majority of theoretical studies on synchronization focus on isolated self-sustained systems, leaving the effects of surrounding environments less touched due to the lack of appropriate descriptions. Here we derive a generalized Langevin equation that governs the dynamics of open classical Van der Pol (VdP) oscillators immersed in a common thermal bath with arbitrary memory time and subsumes an existing equation for memoryless bath as a special limit. The so-obtained Langevin equation reveals that the bath can induce a dissipative coupling between VdP oscillators, besides the usual damping and thermal noise terms connected by the fluctuation-dissipation theorem. To demonstrate the utility of the approach, we investigate a model system consisting of two open VdP oscillators coupled to a thermal bath with an Ohmic or a Lorentzian-shape spectrum. Unlike the isolated setup where the stable synchronization can be either in-phase or antiphase when varying initial conditions, we find that the bath always favors a single type of synchronization in the long-time limit regardless of initial conditions and the synchronization type can be switched by tuning the temperature. Moreover, we show that the bath-induced dissipative coupling can trigger a synchronization of open VdP oscillators that is otherwise absent between isolated counterparts. Our results complement and extend previous findings for open VdP oscillators.

The presence of large-scale real-world networks with various architectures has motivated active research towards a unified understanding of diverse topologies of networks. Such studies have revealed that many networks with scale-free and fractal properties exhibit the structural multifractality, some of which are actually bifractal. Bifractality is a particular case of the multifractal property, where only two local fractal dimensions $d_{\text{f}}^{\text{min}}$ and $d_{\text{f}}^{\text{max}}(>d_{\text{f}}^{\text{min}})$ suffice to explain the structural inhomogeneity of a network. In this work we investigate analytically and numerically the multifractal property of a wide range of fractal scale-free networks (FSFNs) including deterministic hierarchical, stochastic hierarchical, nonhierarchical, and real-world FSFNs. Then we demonstrate how commonly FSFNs exhibit the bifractal property. The results show that all these networks possess the bifractal nature. We conjecture from our findings that any FSFN is bifractal. Furthermore, we find that in the thermodynamic limit the lower local fractal dimension $d_{\text{f}}^{\text{min}}$ describes substructures around infinitely high-degree hub nodes and finite-degree nodes at finite distances from these hub nodes, whereas $d_{\text{f}}^{\text{max}}$ characterizes local fractality around finite-degree nodes infinitely far from the infinite-degree hub nodes. Since the bifractal nature of FSFNs may strongly influence time-dependent phenomena on FSFNs, our results will be useful for understanding dynamics such as information diffusion and synchronization on FSFNs from a unified perspective.

We analyze the changes in the vicinal acidity (pH) at a spherical amphiphilic membrane. The membrane is assumed to contain solvent accessible, embedded, dissociable, charge-regulated moieties. Basing our approach on the linear Debye-Hückel approximation, as well as on the nonlinear Poisson-Boltzmann theory, together with the general Frumkin-Fowler-Guggenheim adsorption isotherm model of the charge-regulation process, we analyze and review the dependence of the local pH on the position, as well as bulk electrolyte concentration, bulk pH, and curvature of the amphiphilic single membrane vesicle. With appropriately chosen adsorption parameters of the charge-regulation model, we find a good agreement with the available experimental data.

The binary collision of water drops in the air is studied by two-dimensional numerical simulation utilizing smoothed particle hydrodynamics with adaptive spatial resolution. The numerical method is validated by comparing the simulation with experiment. Three basic modes of equal-size drop collision are observed in numerical simulations at Weber number $3\le \mathrm{We}\le 120$ and impact parameter $0\le x\le 0.8$, namely, reflexive separation, stretching separation, and coalescence collision. Based on the numerical results of different collision modes, the specific phenomena, evolution patterns, and physical principles are discussed. In particular, the detailed processes of the necking phenomenon and the propagation of surface wave in separation collision are obtained, corroborating the “end-pinching” theory proposed in the literature. At higher Weber numbers, the recoalescence of satellite drops is observed. The collision of unequal-size drops is also investigated. The effects of three dimensionless parameters, namely, drop diameter ratio, Weber number, and impact parameter are discussed. The physical mechanisms of some special phenomena are expressed in detail.

In this work, a simplified wetting boundary scheme in the phase-field lattice Boltzmann model is developed for wetting phenomena on curved boundaries. The proposed scheme combines the advantages of the fluid-solid interaction scheme and geometric scheme—easy to implement (no need to interpolate the values of parameters exactly on solid boundaries and find proper characteristic vectors), the value of contact angle can be directly prescribed, and no unphysical spurious mass layer—and avoids mass leakage. Different from previous works, the values of the order parameter gradient on fluid boundary nodes are directly determined according to the geometric formulation rather than indirectly regulated through the order parameters on ghost solid nodes (i.e., ghost contact-line region). For this purpose, two numerical approaches to evaluate the order parameter gradient on fluid boundary nodes are utilized, one with the prevalent isotropic central scheme and the other with a local gradient scheme that utilizes the distribution functions. The simplified wetting boundary schemes with both numerical approaches are validated and compared through several numerical simulations. The results demonstrate that the proposed model has good ability and satisfactory accuracy to simulate wetting phenomena on curved boundaries under large density ratios.

In this paper a phase-field based lattice Boltzmann equation (LBE) is developed to simulate wettable particles fluid dynamics together with the smoothed-profile method (SPM). In this model the evolution of a fluid-fluid interface is captured by the conservative Allen-Cahn equation (CACE) LBE, and the flow field is solved by a classical incompressible LBE. The solid particle is represent by SPM, and the fluid-solid interaction force is calculated by direct force method. Some benchmark tests including a single wettable particle trapped at the fluid-fluid interface without gravity, capillary interactions between two wettable particles under gravity, and sinking of a horizontal cylinder through an air-water interface are carried out to validate present CACE LBE for fluid-fluid-solid flows. Raft sinking of multiple horizontal cylinders (up to five cylinders) through an air-water interface is further investigated with the present CACE LBE, and a nontrivial dynamics with an unusual nonmonotonic motion of the multiple cylinders is observed in the vertical plane. Numerical results show that the predictions by the present LBE are in good agreement with theoretical solutions and experimental data.

The growth of correlation lengths in equilibrium glass-forming liquids near the glass transition is considered a critical finding in the quest to understand the physics of glass formation. These understandings helped us understand various dynamical phenomena observed in supercooled liquids. It is known that at least two different length scales exist; one is of thermodynamic origin, while the other is dynamical in nature. Recent observations of glassy dynamics in biological and synthetic systems where the external or internal driving source controls the dynamics, apart from the usual thermal noise, lead to the emergence of the field of active glassy matter. A question of whether the physics of glass formation in these active systems is also accompanied by growing dynamic and static lengths is indeed timely. In this article, we probe the growth of dynamic and static lengths in a model active glass system using rod-like elongated probe particles, an experimentally viable method. We show that the dynamic and static lengths in these nonequilibrium systems grow much more rapidly than their passive counterparts. We then offer an understanding of the violation of the Stokes-Einstein relation and Stokes-Einstein-Debye relation using these lengths via a scaling theory.

The quantum size and shape effects are often considered difficult to distinguish from each other because of their coexistence. Essentially, it is possible to separate them and focus solely on the shape effect by considering a size-invariant shape transformation, which changes the discrete energy spectra of strongly confined systems and causes the quantum shape effects. The size-invariant shape transformation is a geometric technique of transforming shapes by preserving the boundary curvature, topology, and the Lebesgue measure of a bounded domain. The quantum shape effect is a quite different phenomenon from quantum size effects, as it can have the opposite influence on the physical properties of nanoscale systems. While quantum size effects can usually be obtained via bounded continuum approximation, the quantum shape effect is a direct consequence of the energy quantization in specifically designed confined geometries. Here, we explore the origin of the quantum shape effect by theoretically investigating the simplest system that can produce the same physics: quantum particles in a one-dimensional box separated by a moving partition. The partition moves quasistatically from one end of the box to the other, allowing the system to remain in equilibrium with a reservoir throughout the process. The partition and the boundaries are impenetrable by particles, forming two effectively interconnected regions. The position of the partition becomes the shape variable. We investigate the quantum shape effect on the thermodynamic properties of confined particles considering their discrete spectrum. In addition, we applied an analytical model based on dimensional transitions to predict thermodynamic properties under the quantum shape effect accurately. A fundamental understanding of quantum shape effects could pave the way for employing them to engineer physical properties and design better materials at the nanoscale.

Human society is believed to be becoming increasingly polarized, yet it remains unclear how role polarization influences the evolution of fairness. In addition, little is known about role adaptation, despite the fact that altering the roles of players can often change the outcome of the ultimatum game. Unlike earlier static, random, symmetric role assignment, here I suggest a succeed-reinforce–fail-slacken role adaptation rule that encourages successful proposers in the present round to propose again in the next round and vice versa. The results demonstrate that this simple rule can tip the scales in favor of fair strategies when it comes to the proposer advantage, and therein lies the key to promoting fairness. Depending on its pace, notably, role adaptation can direct the system to equilibrium states that bear variable degrees of role polarization, with two consequences incidentally. Not only does it favor fairness, it also fosters empathy. Noise associated with role adaptation often reduces role polarization and thus has a negative impact on fairness and empathy. The comparison of experiments with various networks validates the substantial resilience of role polarization to structural changes. These findings add to the evidence for role polarization and highlight the centrality of role adaptation in the evolution of fairness.

We study phase space properties of critical, parity symmetric, $N$-qudit systems undergoing a quantum phase transition (QPT) in the thermodynamic $N\to \infty$ limit. The $D=3$ level (qutrit) Lipkin-Meshkov-Glick model is eventually examined as a particular example. For this purpose, we consider $\mathrm{U}\left(D\right)$-spin coherent states (DSCS), generalizing the standard $D=2$ atomic coherent states, to define the coherent state representation $Q_{\psi }$ (Husimi function) of a symmetric $N$-qudit state $|\psi \rangle$ in the phase space $\mathbb{C}{P}^{D-1}$ (complex projective manifold). DSCS are good variational approximations to the ground state of an $N$-qudit system, especially in the $N\to \infty$ limit, where the discrete parity symmetry ${\mathbb{Z}}_2^{D-1}$ is spontaneously broken. For finite $N$, parity can be restored by projecting DSCS onto $2^{D-1}$ different parity invariant subspaces, which define generalized “Schrödinger cat states” reproducing quite faithfully low-lying Hamiltonian eigenstates obtained by numerical diagonalization. Precursors of the QPT are then visualized for finite $N$ by plotting the Husimi function of these parity projected DSCS in phase space, together with their Husimi moments and Wehrl entropy, in the neighborhood of the critical points. These are good localization measures and markers of the QPT.

Quantum synchronization has been a central topic in quantum nonlinear dynamics. Despite the rapid development in this field, very few have studied how to efficiently boost synchronization. Homodyne measurement emerges as one of the successful candidates for this task but preferably in the semiclassical regime. In our work, we focus on the phase synchronization of a harmonic-driven quantum Stuart–Landau oscillator and show that the enhancement induced by homodyne measurement persists into the quantum regime. Interestingly, optimal two-photon damping rates exist when the oscillator and driving are at resonance and with a small single-photon damping rate. We also report noise-induced enhancement in quantum synchronization when the single-photon damping rate is sufficiently large. Apart from these results, we discover that adding a squeezing Hamiltonian can further boost synchronization, especially in the semiclassical regime. Furthermore, the addition of squeezing causes the optimal two-photon pumping rates to shift and converge.