Existing rigorous statistical approaches still cannot quantitatively describe condensation phenomena in real fluids and even model systems with some simplified interaction potential. Here, we present a method to evaluate the unlimited subcritical set of Mayer's reducible cluster integrals (the power coefficients of virial expansions) by using the information on several virial coefficients and empirical value of saturation activity. As to the requirements on the initial number of known virial coefficients, the calculations for the Lennard-Jones model indicate that only the second virial coefficient is sufficient to reproduce gas isotherms (including the flat phase-transition region) with high accuracy at low temperatures. This remarkable feature allows the simplification of the method for real fluids with an unknown interaction potential: In particular, the calculated isotherms of several real substances (including water) are in good agreement with experiments. Additionally, the obtained results indicate the existence of some important universality which needs serious future exploration.

We consider prototype configurations for quasi-one-dimensional stochastic networks that exhibit negative mobility, meaning that current decreases or even reversed as the bias is increased. We then explore the implications of disorder. In particular, we ask whether lower and upper bias thresholds restrict the possibility to witness nonzero current (sliding and antisliding transitions, respectively), and whether a delocalization effect manifests itself (crossover from over-damped to under-damped relaxation). In the latter context detailed analysis of the relaxation spectrum as a function of the bias is provided for both on-chain and off-chain disorder.

We consider the statistical properties of arrival times and balls on first-passage percolation (FPP) two-dimensional square lattices with strong disorder in the link times. A previous work showed a crossover in the weak disorder regime, between Gaussian and Kardar-Parisi-Zhang (KPZ) universality, with the crossover length decreasing as the noise amplitude grows. On the other hand, this work presents a very different behavior in the strong-disorder regime. An alternative crossover length appears below which the model is described by bond-percolation universality class. This characteristic length scale grows with the noise amplitude and diverges at the infinite-disorder limit. We provide a thorough characterization of the bond-percolation phase, reproducing its associated critical exponents through a careful scaling analysis of the balls, which is carried out through a continuous mapping of the FPP passage time into the occupation probability of the bond-percolation problem. Moreover, the crossover length can be explained merely in terms of properties of the link-time distribution. The interplay between the characteristic length and the correlation length intrinsic to bond percolation determines the crossover between the initial percolation-like growth and the asymptotic KPZ scaling.

If a system is at thermodynamic equilibrium, an observer cannot tell whether a film of it is being played forward or in reverse: any transition will occur with the same frequency in the forward as in the reverse direction. However, if expenditure of energy changes the rate of even a single transition to yield a nonequilibrium steady state, such time-reversal symmetry undergoes a widespread breakdown, far beyond the point at which the energy is expended. An explosion of interdependency also arises, with steady-state probabilities of system states depending in a complicated manner on the rate of every transition in the system. Nevertheless, in the midst of this global nonequilibrium complexity, we find that cyclic paths have reversibility properties that remain local, and which can exhibit symmetry, no matter how far the system is from thermodynamic equilibrium. Specifically, given any cycle of reversible transitions, the ratio of the frequencies with which the cycle occurs in one direction versus the other is determined, in the long-time limit, only by the thermodynamic force on the cycle itself, without requiring knowledge of transition rates elsewhere in the system. In particular, if there is no net energy expenditure on the cycle, then, over long times, the cycle occurrence frequencies are the same in either direction.

We consider a generalized Gibbs ensemble of the classical Toda lattice. We establish that the collision rate ansatz follows because (i) the charge-current susceptibility matrix is symmetric and (ii) the stretch current is proportional to the momentum, hence conserved. The method applies also to other integrable many-body systems, either classical or quantum, provided there is a self-conserved current.

When suspended particles are pushed by liquid flow through a constricted channel, they might either pass the bottleneck without trouble or encounter a permanent clog that will stop them forever. However, they may also flow intermittently with great sensitivity to the neck-to-particle size ratio $D/d$. In this Rapid Communication, we experimentally explore the limits of the intermittent regime for a dense suspension through a single bottleneck as a function of this parameter. To this end, we make use of high time- and space-resolution experiments to obtain the distributions of arrest times ($T$) between successive bursts, which display power-law tails ($\propto T^{-\alpha }$) with characteristic exponents. These exponents compare well with the ones found for as disparate situations as the evacuation of pedestrians from a room, the entry of a flock of sheep into a shed, or the discharge of particles from a silo. Nevertheless, the intrinsic properties of our system (i.e., channel geometry, driving and interaction forces, particle size distribution) seem to introduce a sharp transition from a clogged state ($\alpha \le 2$) to a continuous flow, where clogs do not develop at all. This contrasts with the results obtained in other systems where intermittent flow, with power-law exponents above two, were obtained.

We study a set of run-and-tumble particle (RTP) dynamics in two spatial dimensions. In the first case of the orientation $\theta$ of the particle can assume a set of $n$ possible discrete values, while in the second case $\theta$ is a continuous variable. We calculate exactly the marginal position distributions for $n=3,4$ and the continuous case and show that in all cases the RTP shows a crossover from a ballistic to diffusive regime. The ballistic regime is a typical signature of the active nature of the systems and is characterized by nontrivial position distributions which depend on the specific model. We also show that the signature of activity at long times can be found in the atypical fluctuations, which we also characterize by computing the large deviation functions explicitly.

We study the optimal performance of a three-level quantum refrigerator using two different objective functions: cooling power and $\chi$ function. For both cases, we obtain general expressions for the coefficient of performance (COP) and derive its well-known lower and upper bounds for the limiting cases when the ratio of system-bath coupling constants at the hot and cold contacts approaches infinity and zero, respectively. We also show that the cooling power can be maximized with respect to one control frequency, while $\chi$ function can be maximized globally with respect to two control frequencies. Additionally, we show that in the low-temperature regime, our model of refrigerator can be mapped to Feynman's ratchet and pawl model, a classical mesoscopic heat engine. In the parameter regime where both cooling power and $\chi$ function can be maximized, we compare the cooling power of the quantum refrigerator at maximum $\chi$ function with the maximum cooling power.

A theoretical implementation of a localized thermal diode with a rectification factor greater than ${10}^6$ is demonstrated. In reverse thermal bias, extremely low thermal conductivity is achieved through phononic Rayleigh scattering from a finite-depth defect. In forward bias, the diode oscillator escapes the defect and thermal conductivity becomes up to four orders of magnitude higher. The setup provides a minimal model of a localized thermal diode between two identical oscillator chains and opens up a pathway for thermal diode implementations.

The thermodynamic uncertainty relation (TUR) is a universal constraint for nonequilibrium steady states that requires the entropy production rate to be greater than the relative magnitude of current fluctuations. It has potentially important implications for the thermodynamic efficiency of molecular-scale energy conversion in both biological and artificial systems. An alternative multidimensional thermodynamic uncertainty relation (MTUR) has also been proposed. In this paper we apply the TUR and the MTUR to a description of molecular-scale energy conversion that explicitly contains the degrees of freedom exchanging energy via a time-independent multidimensional periodic potential. The TUR and the MTUR are found to be universal lower bounds on the entropy generation rate and provide upper bounds on the thermodynamic efficiency. The TUR is found to provide only a weak bound while the MTUR provides a much tighter constraint by taking into account correlations between degrees of freedom. The MTUR is found to provide a tight bound in the near or far from equilibrium regimes but not in the intermediate force regime. Collectively, these results demonstrate that the MTUR is more appropriate than the TUR for energy conversion processes, but that both diverge from the actual entropy generation in certain regimes.

Numerous pivotal concepts have been introduced to clarify the puzzle of relaxation and/or equilibration in closed quantum systems. All of these concepts rely in some way on specific conditions on Hamiltonians $H$, observables $A$, and initial states $\rho$ or combinations thereof. We numerically demonstrate and analytically argue that there is a multitude of pairs $H,A$ that meet said conditions for equilibration and generate some typical expectation-value dynamics, which means $\langle A\left(t\right)\rangle \propto f\left(t\right)$ approximately holds for the vast majority of all initial states. Remarkably we find that, while restrictions on the $f\left(t\right)$ exist, they do not at all exclude $f\left(t\right)$ that are rather adverse or strange regarding thermal relaxation.

We construct a statistical framework for investigating the physical origins of radiation effects on biological materials and report the fit of an analytical statistical model to rates of simple lesions in DNA. Modeling primary ionization damage as trails of electron vacancies left on the trajectories of fast charged particles, we derive the dependence of rates of spatial clustering on ionization density [linear energy transfer (LET)]; a clustering scale parameter, $r_0$; and number per cluster. Published experimental results on rates of single strand breaks and base lesions in dry DNA over a range of LET are fitted with the derived functions, assuming clusters of 1 or $\ge 1$. The fits yield reasonable goodness of fit and values of $r_0$ that are consistent with expectations. Limitations of the model and future developments are discussed. This framework may ultimately contribute to an improved understanding of the physical origins of biological radiation effects.

By performing single-molecule force spectroscopy with optical tweezers, we have characterized the interaction between the platinum-based compound transplatin and the DNA molecule, establishing a critical comparison with its isomer cisplatin. While transplatin is ineffective against tumor cells, its isomer is one of the most used drugs in current chemotherapies, and a molecular study on this difference performed at the single-molecule level was lacking until the present work. Our experiments show that transplatin binds DNA under low chloride concentrations (a situation usually found inside many cells) with an equilibrium association binding constant about four orders of magnitude lower than cisplatin. In addition, we have found that, at saturation, transplatin binds preferentially forming interstrand cross links and monoadducts, a situation very different from cisplatin, which forms preferentially intrastrand cross links. Such differences explain the ineffectiveness of transplatin in killing tumor cells. From a physical point of view, the present study advances in using the mechanical properties of the DNA molecule as sensors to evaluate the therapeutic efficiency of drugs.

The aggregation of amyloid-$\beta$ ($\mathrm{A}\beta$) and human islet amyloid polypeptide (hIAPP) proteins have attracted considerable attention because of their involvement in protein misfolding diseases. These proteins have mostly been investigated using atomic force microscopy, transmission electron microscopy, and fluorescence microscopy to study the directional growth of fibrils both perpendicular to and along the fibril axis. Here, we demonstrate the real-time monitoring of the directional growth of fibrils in terms of activation energy of proton transfer using an impedance spectroscopy technique. The activation energy is used to quantify the sensitivity of proton conduction to the different stages of protein aggregation. The decrement (increment) in activation energy is related to the fibril growth along (perpendicular to) the fibril axis in intrinsic protein aggregation. The entire aggregation process shows different phases of the directional growth for $\mathrm{A}\beta$ and hIAPP, indicating different pathways for their aggregation. The activation energy for hIAPP is found to be smaller than the activation energy of $\mathrm{A}\beta$ during the aggregation process. The oscillatory behavior of the activation energy of hIAPP reflects a rapid change in the directional growth of the protofilaments of hIAPP. The results indicate higher aggregation propensity of $\mathrm{A}\beta$ than hIAPP. In the presence of resveratrol, hIAPP exhibits slower aggregation compared to $\mathrm{A}\beta$. Methods of this study may in general be used to reveal the modulated aggregation pathway of proteins in the presence of different ligands.

T-cell receptors (TCR) are key proteins of the adaptive immune system, generated randomly in each individual, whose diversity underlies our ability to recognize infections and malignancies. Modeling the distribution of TCR sequences is of key importance for immunology and medical applications. Here, we compare two inference methods trained on high-throughput sequencing data: a knowledge-guided approach, which accounts for the details of sequence generation, supplemented by a physics-inspired model of selection; and a knowledge-free variational autoencoder based on deep artificial neural networks. We show that the knowledge-guided model outperforms the deep network approach at predicting TCR probabilities, while being more interpretable, at a lower computational cost.

We propose a generic model for thin films and shallow drops of a polar active liquid that have a free surface and are in contact with a solid substrate. The model couples evolution equations for the film height and the local polarization in the form of a gradient dynamics supplemented with active stresses and fluxes. A wetting energy for a partially wetting liquid is incorporated allowing for motion of the liquid-solid-gas contact line. This gives a consistent basis for the description of drops of dense bacterial suspensions or compact aggregates of living cells on solid substrates. As example, we analyze the dynamics of two-dimensional active drops (i.e., ridges) and demonstrate how active forces compete with passive surface forces to shape droplets and drive their motion. In our simple two-dimensional scenario we find that defect structures within the polarization profile drastically influence the shape and motility of active droplets. Thus, we can observe a transition from resting to motile droplets via the elimination of defects in the polarization profile. Furthermore, droplet motility is modulated by strong active stresses. Contractile stresses even lead to topological changes, i.e., drop splitting, which is naturally encoded in the evolution equations.

Catastrophic events in nature can be often triggered by small perturbations, with “remote triggering” of earthquakes being an important example. Here we present a mechanism for the giant amplification of small perturbations that is expected to be generic in systems whose dynamics is not derivable from a Hamiltonian. We offer a general discussion of the typical instabilities involved (being oscillatory with an exponential increase of noise) and examine in detail the normal forms that determine the relevant dynamics. The high sensitivity to external perturbations is explained for systems with and without dissipation. Numerical examples are provided using the dynamics of frictional granular matter. Finally, we point out the relationship of the presently discussed phenomenon to the highly topical issue of “exceptional points” in quantum models with non-Hermitian Hamiltonians.

Building on our previously introduced multicell Monte Carlo ${\text{(MC)}}^2$ method for modeling phase coexistence, this paper provides important improvements for efficient determination of phase equilibria in solids. The ${\text{(MC)}}^2$ method uses multiple cells, representing possible phases. Mass transfer between cells is modeled virtually by solving the mass balance equation after the composition of each cell is changed arbitrarily. However, searching for the minimum free energy during this process poses a practical problem. The solution to the mass balance equation is not unique away from equilibrium, and consequently the algorithm is in risk of getting trapped in nonequilibrium solutions. Therefore, a proper stopping condition for ${\text{(MC)}}^2$ is currently lacking. In this work, we introduce a consistency check via a predictor-corrector algorithm to penalize solutions that do not satisfy a necessary condition for equivalence of chemical potentials and steer the system toward finding equilibrium. The most general acceptance criteria for ${\text{(MC)}}^2$ is derived starting from the isothermal-isobaric Gibbs ensemble for mixtures. Using this ensemble, translational MC moves are added to include vibrational excitations as well as volume MC moves to ensure the condition of constant pressure and temperature entirely with a MC approach, without relying on any other method for relaxation of these degrees of freedom. As a proof of concept the method is applied to two binary alloys with miscibility gaps and a model quaternary alloy, using classical interatomic potentials.

The frictional force (stopping power) acting on a test electron moving through an ideal electron gas is calculated by taking into account electron-neutral atom collisions using the linear plasma response formalism. This allows us to elucidate how the effective Coulomb logarithm is affected by electron-neutral collisions. In agreement with a recent investigation by Hagelaar, Donko, and Dyatko [Phys. Rev. Lett. 123, 025004 (2019)], we observe that the effective Coulomb logarithm decreases considerably due to electron-neutral collisions and becomes inversely proportional to the collision frequency in the highly collisional limit.

The time-dependent Ginzburg-Landau (TDGL) mesoscopic method is utilized to simulate the phase separation of the poly($N$-isopropylacrylamide)–clay nanocomposite hydrogel in the three-dimensional case, where the Cahn-Hilliard-Cook equation with a proposed free energy, which consists of the stretching and mixing energy based on Flory's mean theory, is considered. The main features of the presently proposed model include the following: (i) the proposed free energy consists of both the stretching and mixing energy; (ii) the processes of polymer chains detaching from and reattaching on crosslinks are considered in the proposed free energy; (iii) polymer chains have inhomogeneous chain lengths, which are divided into different types. A stabilized semi-implicit difference scheme is used to numerically solve the corresponding Cahn-Hilliard-Cook equation. Numerical results show the process of the phase separation and are consistent with morphology of the nanocomposite hydrogel.