To describe the spatial trajectory of an overdamped Brownian particle, inertial effects can be neglected. Yet, at the energetic level of stochastic thermodynamics, changes in kinetic energy must be considered to accurately predict the heat exchanged with the thermal bath. On the other hand, in the presence of external driving forces, one would expect the effects of kinetic energy fluctuations to be reduced, as thermal noise becomes comparatively less relevant. Here, we investigate the competition between the kinetic energy and the external work contributions to the heat statistics of passive and active overdamped Brownian particles subject to external driving forces. We find that kinetic energy effects cause fluctuations in the exchanged heat to become non-Gaussian. To evaluate the relevance of these effects, we compute the excess kurtosis and the Pearson correlation. For fixed parameter values adapted from previous experiments with silica beads in passive and active baths, we identify a crossover transition from a regime in which the stochastic heat of overdamped particles is dominated by external work, where kinetic energy changes can be safely ignored, to a regime dominated by kinetic energy effects. Our results also provide a quantitative analytical way to assess how deep into a particular regime the system is.

Random sequential adsorption (RSA) is one of the most widely used theoretical models of macromolecule and particle adsorption. Here we consider jammed (saturated) states of the RSA process of aligned, nonoverlapping $k$-mers (linear objects occupying $k$ consecutive lattice sites) in square, triangular, and cubic lattices and show that each $k$-mer in such a state belongs to a percolating cluster. We also discuss several generalizations of our approach, including a hypercubic lattice and models with several different $k$-mer lengths.

Delay-induced amplitude death (AD) has received considerable research interest. Most studies on delay-induced AD investigated the local stability of equilibrium points. The present study examines the global dynamics of delay-induced AD in a pair of identical Stuart-Landau oscillators. Bifurcation diagrams consisting of synchronized periodic orbits and an equilibrium point are used to determine the mechanism of the emergence of delay-induced AD. It is shown that explosive delay-induced AD can occur via a Hopf bifurcation at the equilibrium point and a saddle-node bifurcation of synchronized periodic orbits when the delay time for the connection is continuously varied. The Hopf and saddle-node bifurcation curves in the coupling parameter space clarify the dependence of the coupling parameters on the global dynamics.

Positron creation and acceleration is one of the major challenges for constructing future lepton colliders. On the one hand, conventional technology can provide a solution, but at a prohibitive cost and scale. On the other hand, alternative, reduced-scale ideas for positron beam generation could bring this dream closer to reality. Here we propose a plasma-based positron acceleration method using a powerful laser propagating through a dense and narrow plasma channel. A large amount of electrons are injected within the channel during laser propagation. This electron loading creates static fields in the plasma, enabling positrons to be guided transversely while they directly gain energy from the laser field itself. Within this context, we present a theoretical model to describe how the laser injects the electrons and estimate the beam-loaded effective electron density. We validate our theoretical predictions through quasi-3D Particle-In-Cell (PIC) simulations and demonstrate the robustness of this guiding and direct laser acceleration process for positrons. Our approach could pave the way for testing this positron acceleration scheme at ELI Beamlines, showcasing an unprecedentedly high average energy gain rate of a few GeV/mm. The fireball jet produced contains GeV-level electrons, positrons, and x-rays and thus brings unique opportunities for applications for laboratory astrophysics such as mimicking the propagation of fireball jets from gamma-ray bursts and seeding pair cascades taking place in pulsars with different ratios of electrons and positrons.

Using the initial-value formulation, a dynamic theory for systems evolving according to a generalized Langevin equation is developed, providing conditions on the existence of equilibrium behavior and its fluctuation-dissipation implications. For systems fulfilling the property of local realizability, that for all the practical purposes corresponds to the postulate of the existence of a Markovian embedding, physical constraints, expressed in the form of dissipative stability and stochastic realizability are derived. If these two properties are met, Kubo theory is constructively recovered, while if one of these conditions is violated a thermodynamic equilibrium behavior does not exist (and this occurs also for “well-behaved dissipative systems”), with implications in the linear response theory.

By means of the concepts of dissipative stability and stochastic realizability, the phenomenon of ergodicity breaking observed in Generalized Langevin Equations (GLEs) in the presence of nonvanishing friction factors [Phys. Rev. E 83, 062102 (2011)] can be properly explained: it occurs at the boundary of the region of dissipative stability; in those cases, this region coincides with that of stochastic realizability. This is the case of the Plyukhin model that considers a generalized Debye kernel. In the presence of dissipative kernels characterized by real-valued relaxation rates corresponding to the rheological behavior of viscoelastic fluids, since the domain of stochastic realizability is strictly contained within the region of dissipative stability, this phenomenon cannot be observed if Kubo's theory of fluctuation-dissipation holds. The hydromechanic theory of GLEs also provides a physical interpretation of the ergodicity breaking reported by [Chin. Phys. Lett. 22, 1845 (2005)] that stems from a dissipationless ‘'fluid-inertial” effect, leading to superdiffusion.

We introduce a planted vertex cover problem on regular random graphs and study it by the cavity method of statistical mechanics. Different from conventional Ising models, the equilibrium ferromagnetic phase transition of this binary-spin two-body interaction system is discontinuous, as the paramagnetic phase is separated from the ferromagnetic phase by an extensive free-energy barrier. The free-energy landscape can be distinguished into three different types depending on the two degree parameters of the planted graph. The critical inverse temperatures at which the paramagnetic phase becomes locally unstable towards the ferromagnetic phase $\left({\beta }_{\text{pf}}\right)$ and towards spin glass phases $\left({\beta }_{\text{pg}}\right)$ satisfy ${\beta }_{\text{pf}}>{\beta }_{\text{pg}},{\beta }_{\text{pf}}<{\beta }_{\text{pg}}$, and ${\beta }_{\text{pf}}={\beta }_{\text{pg}}$, respectively, in these three landscapes. A locally stable antiferromagnetic phase emerges in the free-energy landscape if ${\beta }_{\text{pf}}<{\beta }_{\text{pg}}$. When exploring the free-energy landscape by stochastic local search dynamics, we find that in agreement with our theoretical prediction, the first-passage time from the paramagnetic phase to the ferromagnetic phase is nonmonotonic with the inverse temperature. The potential relevance of the planted vertex cover model to supercooled glass-forming liquids is briefly discussed.

We propose and study a conceptual one-dimensional model to explore how the combined interplay between fixed resources with unlimited carrying capacity and particle exchanges between different parts of an extended system can affect the stationary densities in a current-carrying channel connecting different parts of the system. Our model is composed of a totally asymmetric simple exclusion process (TASEP) connecting two particle reservoirs without any internal dynamics, but which can directly exchange particles between each other, ensuring nonvanishing currents in the TASEP lane in the steady states. The total particle number in the system that defines the “resources” available, although held conserved by the model dynamics, can take any value giving unrestricted carrying capacity. We show how the resulting phase diagrams of the model are controlled by relevant parameters, together with the total available resources. These control parameters can be tuned to make the density on the TASEP lane globally uniform or piecewise continuous with localized domain walls, and can also control populations of the two reservoirs. In general, the phase diagrams are quite different from a TASEP with open boundaries. However, in the limit of a large amount of resources, the phase diagrams in the plane of the control parameters become topologically identical to that for an open TASEP along with delocalization of domain walls.

We study the effectiveness of locally controlling the breakage of a significant space-time symmetry by zero-average periodic excitations at inducing and suppressing directed ratchet transport (i.e., that induced without an applied net bias) and chaos in starlike networks of driven damped pendula. While the emergence of chaos mainly depends upon the impulse transmitted by the periodic excitations, directed ratchet transport does upon a subtle balance between energy transmitted through the pendula via excitations' impulse and degree of symmetry breaking, thus defining a physical criticality scenario. Optimal enhancement of directed ratchet transport is found to occur when the waveform of the periodic excitation matches as closely as possible to a universal waveform when all nodes are homogeneously driven. In the case of networks with heterogeneous distributions of the symmetry breaking, the net ratcheting effect of increasing the effective breakage by periodic excitations acting on a number of particular nodes strongly depends upon their number and degree of connectivity as well as the coupling strength, while showing self-organized criticality with respect to the maximum strength of directed ratchet transport.

Depinning dynamics of a two-dimensional (2D) solid dusty plasma modulated by a one-dimensional (1D) vibrational periodic substrate are investigated using Langevin dynamical simulations. As the uniform driving force increases gradually, from the overall drift velocity varying with the driving force, four significant Shapiro steps are discovered. The data analysis results indicate that, when the ratio of the frequency from the drift motion over potential wells to the external frequency from the modulation substrate is close to integers, dynamic mode locking occurs, corresponding to the discovered Shapiro steps. Around both termini of the first and fourth Shapiro steps, the transitions are found to be always continuous, however, the transition between the second and third Shapiro steps is discontinuous, probably due to the different arrangements of particles.

Whereas the power of reservoir computing (RC) in inferring chaotic systems has been well established in the literature, the studies are mostly restricted to monofunctional machines where the training and testing data are acquired from the same attractor. Here, using the strategies of attractor labeling and trajectory separation, we propose a scheme of RC capable of learning multiple attractors generated by entirely different dynamics, namely multifunctional RC. Specifically, we demonstrate that by incorporating a label channel into the standard reservoir computer, a single machine is able to learn from data the dynamics of multiple chaotic attractors, while each attractor can be accurately retrieved by inputting just a scalar in the prediction phase. The dependence of the machine performance on the labeling and separation parameters is investigated, and it is found that the machine performance is optimized when the parameters take intermediate values. The working mechanism of multifunctional RC is analyzed by the method of functional networks in neuroscience, and it is revealed that each attractor is represented by a stable, unique functional network in the reservoir, and the optimal performance arises as a balance between the stability, complexity, and distinguishability of the functional networks.

Numerous indications suggest that subtle changes occurring in the structures of liquids on supercooling are connected to the phenomenon of the glass transition and that detailed understanding of these changes is crucial for the development of new glasses with desired properties. J. D. Bernal in his 1962 Bakerian lecture in particular reported about an observation of approximately linear chains of several particles, referred to as collineations. He found that in the studied hard sphere system, these collineations can contain up to eight particles. Since then the collineations of three particles have been discussed in many papers in the context of the splitting of the second peak in pair density functions of supercooled liquids and glasses. However, it appears that longer collineations involving more that three particles have not been systematically studied. Here we report on our study of such collineations for the Kob-Andersen system of particles on cooling for the parent and inherent structures. Contrary to intuition, our findings reveal that below the potential energy landscape crossover temperature, the number of collineations in the parent structures can exceed that of the corresponding inherent structures. We also introduce a model that connects long collineations with the pair density and angular density distribution functions and demonstrate that this model describes long collineations quite well. We also studied the diffusion of the particles forming collineations and demonstrated that these particles are slightly slower than the randomly chosen average particle. Preliminary investigation of the collineations' lifetimes suggests that there are vibrational and structural relaxation regimes in the decay of the considered correlation function. The second part of the paper explores potential connections between collineations and (1) the disclination lines associated with the geometric frustration approach, (2) low-energy clusters from the topological cluster classification approach, and (3) chainlike cooperative motion of particles in low-temperature supercooled liquids. For the studied system, according to the used methods, no clear connection was found between collineations and these phenomena.

We numerically study two-dimensional active nematics with periodic activity patterning. For stripes of activity, we observe a transition from two-dimensional to one-dimensional active turbulence as the maximum active force and distance between activity stripes increases, followed by a transition to stable vortices ordered antiferromagnetically along the stripes and ferromagnetically transverse to the stripes. By comparing to a triangular lattice of activity circles, we find that transitions to two-dimensional active turbulence emerge from interplays between the active length scale and activity density, independent of the patterning geometry. The vortex ordering, however, is highly sensitive to patterning geometry, which we show by comparing the activity stripes to columns of activity circles, where the vortex ordering is lost. Our results provide a mechanism for inducing nonequilibrium phase transitions in active nematics using activity inhomogeneity, which can be further exploited to create activity patterned ordered phases.

We have investigated the sliding motion of PMMA microspheres elastically driven on a rippled polyvinyl siloxane surface for different values of normal load, scan velocity, and substrate temperature. The spheres were rubbed both parallel and perpendicular to the ripples, and the resulting friction was found to be almost constant and, respectively, to vary in a stick-slip fashion with time. The average friction value was also enhanced in the perpendicular direction, which we attribute to a larger adhesive force established at the end of the slip phase. In both cases, the friction was also found to increase linearly with increasing load, consistently with the predictions of the Persson contact theory, and to increase logarithmically with increasing scan velocity and decrease with increasing temperature according to the Eyring's reaction rate theory. The stability of this simple system suggests its possible implementation as a basic unit for artificial tactile sensors.

A macroscopic hydrodynamic system that couples a particle and a wave has recently renewed interest in the question as to what extent a classical system may reproduce quantum phenomena. Here we investigate single-particle diffraction with a pilot-wave model originally developed to describe the hydrodynamic system. We study single-particle interactions with a barrier and slits of increasing width by focusing on the near field. We find single-particle diffraction arising as wavelike patterns in the particles' position statistics, which we compare to the predictions of quantum mechanics. We provide a mechanism that rationalizes the diffractive behavior in our system.

The study of phase transitions in frustrated magnetic systems with $\text{O}\left(N\right)\times \text{O}\left(2\right)$ symmetry has been the subject of controversy for more than 20 years, with theoretical, numerical, and experimental results in disagreement. Even theoretical studies led to different results, with some predicting a first-order phase transition while others found it to be second-order. Recently, a series of results from both numerical simulations and theoretical analyses, in particular those based on the Conformal Bootstrap, have rekindled interest in this controversy, especially as they are still not in agreement with each other. Studies based on the functional renormalization group have played a major role in this controversy in the past, and we revisit these studies, taking them a step further by adding nontrivial second-order derivative terms to the derivative expansion of the effective action. We confirm the first-order nature of the phase transition for physical values of $N$, i.e., for $N=2$ and $3,$ in agreement with the latest results obtained with the Conformal Bootstrap. We also study another phase of the $\text{O}\left(N\right)\times \text{O}\left(2\right)$ models, called the sinusoidal phase, qualitatively confirming earlier perturbative results.

Information propagation in network interactions is not an instant event but rather it is happening with a delay in real world. The evolution of network structure to reach to a balanced state in order to minimize the overall tensions is commonly considered without any delays but in fact the role of delay might influence when the network converts from the unbalanced to the balanced state. In this study we considered the coevolutionary balance model in which the interaction of both nodes and links in the network is taken into account and we assume that individuals are receiving the latest updated status of their neighbors with a specific delay. We have shown that this delay effect is equal to the appearance of the higher order interactions that are opposing the existing first order interaction in the simple coevolutionary balance without considering delay.

Strongly magnetized plasmas, characterized by having a gyrofrequency larger than the plasma frequency $(\beta ={\omega }_c/{\omega }_p\gg 1)$, are known to exhibit novel transport properties. Previous works studying pure electron plasmas have shown that strong magnetization significantly inhibits energy exchange between parallel and perpendicular directions, leading to a prolonged time for relaxation of a temperature anisotropy. Recent work studying repulsive electron-ion interactions $(e^{-}-{\mathrm{i}}^{-} \text{or} e^{+}-{\mathrm{i}}^{+})$ showed that strong magnetization increases both the parallel and perpendicular temperature relaxation rates of ions, but in differing magnitudes, resulting in the formation of temperature anisotropy during equilibration. This previous study treated electrons as a heat bath and assumed weak magnetization of ions. Here, we broaden this analysis and compute the full temperature and temperature anisotropy evolution over a broad range of magnetic field strengths. It is found that when electrons are strongly magnetized $({\beta }_e\gg 1)$ and ions are weakly magnetized $({\beta }_i\ll 1)$, the magnetic field strongly suppresses the perpendicular energy exchange rate of electrons, whereas the parallel exchange rate slightly increases in magnitude compared to the value at weak magnetization. In contrast, the ion perpendicular and parallel energy exchange rates both increase in magnitude compared to the values at weak magnetization. Consequently, equilibration causes the electron parallel temperature to rapidly align with the ion temperature, while the electron perpendicular temperature changes much more slowly. It is also shown that when both ions and electrons are strongly magnetized $({\beta }_i,{\beta }_e\gg 1)$, the ion-electron perpendicular relaxation rate dramatically decreases with magnetization strength.