We consider two weakly interacting quasi-1D condensates of cold bosonic atoms. It turns out that a time-dependent variation of the tunnel-coupling between those condensates is equivalent to the ...spatial expansion of a one-dimensional toy-Universe, with regard to the dynamics of the relative phase field. The dynamics of this field is governed by the quantum sine-Gordon equation. Thus, this analogy could be used to 'quantum simulate' the dynamics of a scalar, interacting quantum field on an expanding background. We discuss how to observe the 'freezing' of quantum fluctuations during an accelerating expansion in a possible experiment. We also analyze an experimental protocol to study the formation of sine-Gordon breathers in the relative phase field, seeded by quantum fluctuations.
Stochastic processes of interacting particles in systems with varying length are relevant e.g. for several biological applications. We try to explore what kind of new physical effects one can expect ...in such systems. As an example, we extend the exclusive queueing process that can be viewed as a one-dimensional exclusion process with varying length, by introducing Langmuir kinetics. This process can be interpreted as an effective model for a queue that interacts with other queues by allowing incoming and leaving of customers in the bulk. We find surprising indications for breaking of ergodicity in a certain parameter regime, where the asymptotic growth behavior depends on the initial length. We show that a random walk with site-dependent hopping probabilities exhibits qualitatively the same behavior.
•The EQP, a combination of the ASEP and the M/M/1 queueing model, is investigated.•The model can be interpreted as an ASEP on a lattice of dynamically varying length.•Related models have several applications, especially to biological systems.•The inclusion of Langmuir kinetics leads to an effective breaking of ergodicity.•Some samples have diverging length, others converge in a certain parameter region.
The investigation of traffic flow problems has a long tradition and various methods and approaches have been applied. In this review we focus on statistical mechanics and nonequilibrium aspects. It ...is shown that many properties of traffic flow can be modelled successfully by using rather simple cellular automaton models. Analytical methods for the investigation of discrete models are presented in some detail. Apart from highway traffic, also the modelling of city traffic and pedestrian dynamics will be discussed.
We study the optimal performance of Feynman’s ratchet and pawl, a paradigmatic model in nonequilibrium physics, using ecological criterion as the objective function. The analysis is performed by two ...different methods: (i) a two-parameter optimization over internal energy scales; and (ii) a one-parameter optimization of the estimate for the objective function, after averaging over the prior probability distribution (Jeffreys’ prior) for one of the uncertain internal energy scales. We study the model for both engine and refrigerator modes. We derive expressions for the efficiency/coefficient of performance (COP) at maximum ecological function. These expressions from the two methods are found to agree closely with equilibrium situations. Furthermore, the expressions obtained by the second method (with estimation) agree with the expressions obtained in finite-time thermodynamic models.
We investigate the steady state phase diagram of two-component driven open condensates (DOCs) in one dimension. We identify a miscible-immiscible transition which is predominantly driven by gapped ...density fluctuations and occurs upon increasing the inter-component dissipative coupling. Below the transition in the miscible phase, we find the effective long wavelength dynamics to be described by a two-component Kardar-Parisi-Zhang (KPZ) equation that belongs to the nonequilibrium universality class of the one-dimensional single-component KPZ equation at generic choices of parameters. Our results are relevant for different experimental realizations for two-component DOCs in exciton-polariton systems.
We investigate the totally asymmetrical simple exclusion process (TASEP) in the presence of a bottleneck, i.e. a sequence of consecutive defect sites with reduced hopping rate. The influence of such ...a bottleneck on the phase diagram is studied by computer simulations and a novel analytical approach. We find a clear dependence of the current and the properties of the phase diagram not only on the length of the bottleneck, but also on its position. For bottlenecks near the boundaries, this motivates the concept of effective boundary rates. Furthermore the inclusion of a second, smaller bottleneck far from the first one has no influence on the transport capacity. These results will form the basis of an effective description of the disordered TASEP and are relevant for the modelling of protein synthesis or intracellular transport systems where the motion of molecular motors is hindered by immobile blocking molecules.
At the molecular level biology is intrinsically noisy. The forces that regulate the myriad of molecular reactions in the cell are tiny, on the order of piconewtons (10−12 Newtons), yet they proceed ...in concerted action making life possible. Understanding how this is possible is one of the most fundamental questions biophysicists would like to understand. Single molecule experiments offer an opportunity to delve into the fundamental laws that make biological complexity surface in a physical world governed by the second law of thermodynamics. Techniques such as force spectroscopy, fluorescence, microfluidics, molecular sequencing, and computational studies project a view of the biomolecular world ruled by the conspiracy between the disorganizing forces due to thermal motion and the cosmic evolutionary drive. Here we will digress on some of the evidences in support of this view and the role of physical information in biology.
Cellular automata (CA) provide a simple and intuitive approach for modelling interdisciplinary problems. We discuss the basic principles which have lead to the development of realistic CA models for ...the description of highway traffic. Sophisticated models reproduce even the microscopic structure of traffic flow and have shed some light on the relation between the observed traffic phases and the behaviour of the drivers. Due to the simplicity of the models even large networks can be simulated faster than real time and so traffic forecasting has become possible.
We study evacuation processes of pedestrian crowds with differently interacting groups using an extended floor field cellular automaton model. For homogeneous crowds floor field automaton models ...introduce a mutual dynamic floor field and apply an equal set of update rules. We use an extended model with group-specific floor fields inducing attraction and herding behaviour within respective groups only. As another approach we introduce group-related update rules to form couples with one pedestrian leading the other. We use these approaches to model groups with symmetric and asymmetric group interactions and study the impact of such groups on evacuation dynamics.
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