Modeling liquid-vapor phase change using the lattice Boltzmann (LB) method has attracted significant attention in recent years. In this paper, we propose an improved three-dimensional thermal multiphase LB model for simulating liquid-vapor phase change. The proposed model has the following features. First, it is still within the framework of the thermal LB method using a temperature distribution function and therefore retains the fundamental advantages of the thermal LB method. Second, in the existing thermal LB models for liquid-vapor phase change, the finite-difference computations of the gradient terms $\mathbf{\nabla }·\mathbf{u}$ and $\mathbf{\nabla }T$ usually require special treatment at boundary nodes, while in the proposed thermal LB model these two terms are calculated locally. Moreover, in some of the existing thermal LB models, the error term ${\partial }_{t_0}\left(T\mathbf{u}\right)$ is eliminated by adding local correction terms to the collision process in the moment space, which causes these thermal LB models to be limited to the D2Q9 lattice in two dimensions and the D3Q15 or D3Q19 lattice in three dimensions. Conversely, the proposed model does not suffer from such an error term and therefore the thermal LB equation can be constructed on the D3Q7 lattice, which simplifies the model and improves the computational efficiency. Numerical simulations are carried out to validate the accuracy and efficiency of the proposed thermal multiphase LB model for simulating liquid-vapor phase change.

We numerically study a three-dimensional system of athermal, overdamped, frictionless spheres, using a simplified model for a non-Brownian suspension. We compute the bulk viscosity under both uniaxial and isotropic compression as a means to address the question of whether stress-anisotropic and stress-isotropic jamming are in the same critical universality class. Carrying out a critical scaling analysis of the system pressure $p$, shear stress $\sigma$, and macroscopic friction $\mu =\sigma /p$, as functions of particle packing fraction $\varphi$ and compression rate $\dot{\epsilon }$, we find good agreement for all critical parameters comparing the isotropic and anisotropic cases. In particular, we determine that the bulk viscosity diverges as $p/\dot{\epsilon }\sim {({\varphi }_J-\varphi )}^{-\beta }$, with $\beta =3.36\pm 0.09$, as jamming is approached from below. We further demonstrate that the average contact number per particle $Z$ can also be written in a scaling form as a function of $\varphi$ and $\dot{\epsilon }$. Once again, we find good agreement between the uniaxial and isotropic cases. We compare our results to prior simulations and theoretical predictions.

Powerful rogue ocean waves have been objects of fascination for centuries. Elusive and awe-inspiring, with the potential to inflict catastrophic damage, rogue waves remain unpredictable and imperfectly understood. To gain further insight into their behavior, we analyzed 3 441 188 683 ocean surface waves to determine the statistical height distribution of the largest waves. We found that the distribution of rare events which resolves the St. Petersburg paradox also describes the relative height distribution of the largest waves. This result is expected to contribute to the modeling of ocean surface dynamics and improve the accuracy of marine weather forecasts.

This paper sheds light on the time structure of betatron radiation, emitted by electrons that undergo betatron oscillations as they accelerate under the action of plasma wakefields. It is a common practice to assume that the betatron pulses are as short as the electron bunch length, however we show that this is not a general rule. Indeed, the betatron pulse length is affected by the betatron motion, which stretches and modulates the radiation pulses already at the source level. Propagation in a vacuum, therefore, can greatly lengthen the betatron pulses by orders of magnitude. In the wake of the above, the coherent emission of betatron radiation is studied. Coherent betatron radiation has been found to propagate in an underdense region created by ponderomotive forces, thus not suppressed by the overdense plasma absorption. This could be observed experimentally, revealing information on the acceleration process and on key beam parameters.

Complex plasmas consist of microparticles embedded in a low-temperature plasma and allow investigating various effects by tracing the motion of these microparticles. Dust density waves appear in complex plasmas as self-excited acoustic waves in the microparticle fluid at low neutral gas pressures. Here we show that various properties of these waves depend on the position of the microparticle cloud with respect to the plasma sheath and explain this finding in terms of the underlying ion-drift instability. These results may be helpful in better understanding the propagation of dust density waves in complex plasmas and beyond, for instance, in astrophysical dusty plasmas.

In this letter, we present evidence for a mechanism responsible for the nonclassical nonlinear dynamics observed in many cemented granular materials that are generally classified as mesoscopic nonlinear elastic materials. We demonstrate numerically that force chains are created within the complex grain-pore network of these materials when subjected to dynamic loading. The interface properties between grains along with the sharp and localized increase of the stress occurring at the grain-grain contacts leads to a reversible decrease of the elastic properties at macroscopic scale and peculiar effects on the propagation of elastic waves when grain boundary properties are appropriately considered. These effects are observed for relatively small amplitudes of the elastic waves, i.e., within tens of microstrain, and relatively large wavelengths, i.e., orders of magnitude larger than the material constituents. The mechanics are investigated numerically using the hybrid finite-discrete-element method and match those observed experimentally using nonlinear resonant ultrasound spectroscopy.

We derive universal bounds for the finite-time survival probability of the stochastic work extracted in steady-state heat engines and the stochastic heat dissipated to the environment. We also find estimates for the time-dependent thresholds that these quantities do not surpass with a prescribed probability. At long times, the tightest thresholds are proportional to the large deviation functions of stochastic entropy production. Our results entail an extension of martingale theory for entropy production, for which we derive universal inequalities involving its maximum and minimum statistics that are valid for generic Markovian dynamics in nonequilibrium stationary states. We test our main results with numerical simulations of a stochastic photoelectric device.

Heterogeneous diffusion with a spatially changing diffusion coefficient arises in many experimental systems such as protein dynamics in the cell cytoplasm, mobility of cajal bodies, and confined hard-sphere fluids. Here, we showcase a simple model of heterogeneous diffusion where the diffusion coefficient $D\left(x\right)$ varies in a power-law way, i.e., $D\left(x\right)\sim {\left|x\right|}^{-\alpha }$ with the exponent $\alpha >-1$. This model is known to exhibit anomalous scaling of the mean-squared displacement (MSD) of the form $\sim t^{\frac{2}{2+\alpha }}$ and weak ergodicity breaking in the sense that ensemble averaged and time averaged MSDs do not converge. In this paper, we look at the extreme value statistics of this model and derive, for all $\alpha$, the exact probability distributions of the maximum spatial displacement $M\left(t\right)$ and arg-maximum $t_m\left(t\right)$ (i.e., the time at which this maximum is reached) till duration $t$. In the second part of our paper, we analyze the statistical properties of the residence time $t_r\left(t\right)$ and the last-passage time $t_{\ell }\left(t\right)$ and compute their distributions exactly for all values of $\alpha$. Our study unravels that the heterogeneous version $(\alpha \ne 0)$ displays many rich and contrasting features compared to that of the standard Brownian motion (BM). For example, while for BM $(\alpha =0)$, the distributions of $t_m\left(t\right),t_r\left(t\right)$, and $t_{\ell }\left(t\right)$ are all identical (á la “arcsine laws” due to Lévy), they turn out to be significantly different for nonzero $\alpha$. Another interesting property of $t_r\left(t\right)$ is the existence of a critical $\alpha$ (which we denote by ${\alpha }_c=-0.3182$) such that the distribution exhibits a local maximum at $t_r=t/2$ for $\alpha <{\alpha }_c$ whereas it has minima at $t_r=t/2$ for $\alpha \ge {\alpha }_c$. The underlying reasoning for this difference hints at the very contrasting natures of the process for $\alpha \ge {\alpha }_c$ and $\alpha <{\alpha }_c$ which we thoroughly examine in our paper. All our analytical results are backed by extensive numerical simulations.

An agent-based model for human behavior in the well-known public goods game (PGG) is developed making use of bounded rationality, but without invoking mechanisms of learning. The underlying Markov decision process is driven by a path integral formulation of reward maximization. The parameters of the model can be related to human preferences accessible to measurement. Fitting simulated game trajectories to available experimental data, we demonstrate that our agents are capable of modeling human behavior in PGG quite well, including aspects of cooperation emerging from the game. We find that only two fitting parameters are relevant to account for the variations in playing behavior observed in 16 cities from all over the world. We thereby find that learning is not a necessary ingredient to account for empirical data.

Sampling the collective, dynamical fluctuations that lead to nonequilibrium pattern formation requires probing rare regions of trajectory space. Recent approaches to this problem, based on importance sampling, cloning, and spectral approximations, have yielded significant insight into nonequilibrium systems but tend to scale poorly with the size of the system, especially near dynamical phase transitions. Here we propose a machine learning algorithm that samples rare trajectories and estimates the associated large deviation functions using a many-body control force by leveraging the flexible function representation provided by deep neural networks, importance sampling in trajectory space, and stochastic optimal control theory. We show that this approach scales to hundreds of interacting particles and remains robust at dynamical phase transitions.

In networks of coupled oscillators, it is of interest to understand how interaction topology affects synchronization. Many studies have gained key insights into this question by studying the classic Kuramoto oscillator model on static networks. However, new questions arise when the network structure is time varying or when the oscillator system is multistable, the latter of which can occur when an inertial term is added to the Kuramoto model. While the consequences of evolving topology and multistability on collective behavior have been examined separately, real-world systems such as gene regulatory networks and the brain may exhibit these properties simultaneously. It is thus relevant to ask how time-varying network connectivity impacts synchronization in systems that can exhibit multistability. To address this question, we study how the dynamics of coupled Kuramoto oscillators with inertia are affected when the topology of the underlying network changes in time. We show that hysteretic synchronization behavior in networks of coupled inertial oscillators can be driven by changes in connection topology alone. Moreover, we find that certain fixed-density rewiring schemes induce significant changes to the level of global synchrony that remain even after the network returns to its initial configuration, and we show that these changes are robust to a wide range of network perturbations. Our findings highlight that the specific progression of network topology over time, in addition to its initial or final static structure, can play a considerable role in modulating the collective behavior of systems evolving on complex networks.

Knots can spontaneously form in DNA, proteins, and other polymers and affect their properties. These knots often experience spatial confinement in biological systems and experiments. While confinement dramatically affects the knot behavior, the physical mechanisms underlying the confinement effects are not fully understood. In this work, we provide a simple physical picture of the polymer knots in slit confinement using the tube model. In the tube model, the polymer segments in the knot core are assumed to be confined in a virtual tube due to the topological restriction. We first perform Monte Carlo simulation of a flexible knotted chain confined in a slit. We find that with the decrease of the slit height from $H=+\infty$ (the 3D case) to $H=2a$ (the 2D case), the most probable knot size $L_{\mathrm{knot}}^{*}$ dramatically shrinks from ${\left(L_{\mathrm{knot}}^{*}\right)}_{3\mathrm{D}}\approx 140a$ to ${\left(L_{\mathrm{knot}}^{*}\right)}_{2\mathrm{D}}\approx 26a$, where $a$ is the monomer diameter of the flexible chain. Then we quantitatively explain the confinement-induced knot shrinking and knot deformation using the tube model. Our results for $H=2a$ can be applied to a polymer knot on a surface, which resembles DNA knots measured by atomic force microscopy under the conditions that DNA molecules are weakly absorbed on the surface and reach equilibrium 2D conformations. This work demonstrates the effectiveness of the tube model in understanding polymer knots.

We combine hydrodynamic and field theoretic methods to develop a general theory of phonons as Goldstone bosons in crystals, glasses, and liquids based on nonaffine displacements and the consequent Goldstone phase relaxation. We relate the conservation, or lack thereof, of specific higher-form currents with properties of the underlying deformation field—nonaffinity—which dictates how molecules move under an applied stress or deformation. In particular, the single-valuedness of the deformation field is associated with conservation of higher-form charges that count the number of topological defects. Our formalism predicts, from first principles, the presence of propagating shear waves above a critical wave vector in liquids, thus giving a formal derivation of the phenomenon in terms of fundamental symmetries. The same picture provides also a theoretical explanation of the corresponding “positive sound dispersion” phenomenon for longitudinal sound. Importantly, accordingly to our theory, the main collective relaxation timescale of a liquid or a glass (known as the $\alpha$ relaxation for the latter) is given by the phase relaxation time, which is not necessarily related to the Maxwell time. Finally, we build a nonequilibrium effective action using the in-in formalism defined on the Schwinger-Keldysh contour, that further supports the emerging picture. In summary, our work suggests that the fundamental difference between solids, fluids, and glasses has to be identified with the associated generalized higher-form global symmetries and their topological structure, and that the Burgers vector for the displacement fields serves as a suitable topological order parameter distinguishing the solid (ordered) phase and the amorphous ones (fluids, glasses).

Geometric frustration results from a discrepancy between the locally favored arrangement of the constituents of a system and the geometry of the embedding space. Geometric frustration can be either noncumulative, which implies an extensive energy growth, or cumulative, which implies superextensive energy scaling and highly cooperative ground-state configurations which may depend on the dimensions of the system. Cumulative geometric frustration was identified in a variety of continuous systems including liquid crystals, filament bundles, and molecular crystals. However, a spin-lattice model which clearly demonstrates cumulative geometric frustration was lacking. In this paper we describe a nonlinear variation of the $XY$-spin model on a triangular lattice that displays cumulative geometric frustration. The model is studied numerically and analyzed in three distinct parameter regimes, which are associated with different energy minimizing configurations. We show that, despite the difference in the ground-state structure in the different regimes, in all cases the superextensive power-law growth of the frustration energy for small domains grows with the same universal exponent that is predicted from the structure of the underlying compatibility condition.

We applied an alternative method for measuring characteristic lengths reported recently by one of us [J. M. Kim, J. Stat. Mech. (2021) 033213] to the models in the Manna universality class, i.e., the stochastic Manna sandpile and conserved lattice gas models in various dimensions. The universality of the Manna model has been under long debate particularly in one dimension since the work of M. Basu et al. [Phys. Rev. Lett. 109, 015702 (2012)], who claimed that the Manna model belongs to the directed percolation (DP) universality class and that the independent Manna universality class does not exist. We carried out Monte Carlo simulations for the stochastic Manna sandpile model in one, two, and three dimensions and the conserved lattice gas model in three dimensions, using both the natural initial states (NISs) and uniform initial states (UISs). In two and three dimensions, the results for $R\left(t\right)$, defined by $R\left(t\right)=L{\left[\langle {\rho }_a^2\rangle /{\langle {\rho }_a\rangle }^2-1\right]}^{1/d}, L$ and ${\rho }_a$ being, respectively, the system size and activity density, yielded consistent results for the two initial states. $R\left(t\right)$ is proportional to the correlation length following $R\left(t\right)\sim t^{1/z}$ at the critical point. In one dimension, the data of $R\left(t\right)$ for the Manna model using NISs yielded anomalous behavior, suggesting that NISs require much longer prerun time steps to homogenize the distribution of particles and larger systems to eliminate the finite-size effect than those employed in the literature. On the other hand, data from UISs yielded a power-law behavior, and the estimated critical exponents differed from the values in the DP class.

We demonstrate the feasibility of electrostatic (dc) tapering such that the net average force of the electromagnetic (ac) field is compensated by a dc field, which at resonance may be interpreted as “direct” energy transfer from the dc to the ac field. This combination persists in all three components of the setup—e-gun, resonant zone, and collector, in each one playing a different role. In equilibrium, the two field components field-emit at the cathode a density modulated cylindrical beam which is accelerated along the e-gun by the dc field; the latter also focuses the e-beam. Radiation confinement perpendicular to the e-beam is ensured by an array of dielectric Bragg-mirrors and an array of metallic hollow electrodes impose synchronous bunches and wave. This double periodic structure ensures the coexistence of dc and ac fields in the same volume. Numerical simulations demonstrate the feasibility of generation of order of 1[W] power at 1 THz from a volume on a scale of few ${\mathrm{mm}}^3$ with efficiency of the order of 25%.

The theory developed in an accompanying paper [Déjardin, Phys. Rev. E 105, 024109 (2022)] is used to compute the Kirkwood correlation factor of simple polar fluids of different nature. From this calculation, the theoretical static permittivity is readily obtained, which is compared with experimental values. This is accomplished by fitting only one parameter accounting for induction or dispersion forces and torques, which is necessarily connected with the individual molecular polarizability but not explicitly related to the physical properties due to the nonadditivity of such energies. Excellent agreement between theoretical and experimental static permittivities is obtained over a very broad temperature range for a number of associated and nonassociated liquids. Finally, limitations of the present theory are given.

The theory of the linear static dielectric constant and linear complex permittivity of isotropic polar fluids is formulated starting from the coupled Langevin equations describing the rototranslational dynamics of long-range interacting molecules with thermal agitation and subjected to external forces and torques. To this aim, adequate reduced densities are introduced and equations governing their dynamics derived. In the equilibrium zero frequency limit, integral expressions for the Kirkwood correlation factor $g_{\mathrm{K}}$ are given, transparently showing that the popular method consisting in comparing $g_{\mathrm{K}}$ with 1 in order to deduce pair dipolar ordering has no serious theoretical grounding. In the dynamical situation, the complex permittivity spectrum of a simple liquid is shown to exhibit an infinite discrete set of relaxation times, some of which may have thermally activated behavior. The theory is also shown to contain all previous results derived in the area provided molecular inertial effects are ignored, so restricting the range of validity of the theory to frequencies much below the far-infrared region. Finally, the theory can be adapted without much effort to relaxation of interacting magnetic nanoparticles for which macroscopic magnetic anisotropy arising from the assembly of nanoparticles is neglected.

We study a field-theoretic model for the metastable liquid using a nonlocal free-energy functional with density $\rho \left(\mathbf{x}\right)$ is the order parameter and three-point correlation effects included in the formulation. We assume fragmentation of the free-energy landscape into distinct basins of local minima and evaluate the partition function for the many-particle system through mapping into a composite system of $m$ identical replicas. Static correlations and configurational entropy ${\mathcal{S}}_c$ are calculated in the $m=1$ limit. The Kauzman packing fraction ${\eta }_K$ obtained are in agreement with other works.

We obtain a representation of the free energy of an $XY$ model on a fully connected graph with spins subjected to a random crystal field of strength $D$ and with random orientation $\alpha$. Results are obtained for an arbitrary probability distribution of the disorder using large deviation theory, for any $D$. We show that the critical temperature is insensitive to the nature and strength of the distribution $p\left(\alpha \right)$, for a large family of distributions which includes quadriperiodic distributions, with $p\left(\alpha \right)=p(\alpha +\frac{\pi }{2})$, which includes the uniform and symmetric bimodal distributions. The specific heat vanishes as temperature $T\to 0$ if $D$ is infinite, but approaches a constant if $D$ is finite. We also studied the effect of asymmetry on a bimodal distribution of the orientation of the random crystal field and obtained the phase diagram comprising four phases: a mixed phase (in which spins are canted at angles which depend on the degree of disorder), an $x$-Ising phase, a $y$-Ising phase, and a paramagnetic phase, all of which meet at a tetracritical point. The canted mixed phase is present for all finite $D$, but vanishes when $D\to \infty$.