Heat and work distributions for mixed Gauss-Cauchy process

We analyze energetics of a non-Gaussian process described by a stochastic differential equation of the Langevin type. The process represents a paradigmatic model of a nonequilibrium system subject to thermal fluctuations and additional external noise, with both sources of perturbations considered as additive and statistically independent forcings. We define thermodynamic quantities for trajectories of the process and analyze contributions to mechanical work and heat. As a working example we consider a particle subjected to a drag force and two independent Levy white noises with stability indices $\alpha=2$ and $\alpha=1$. The fluctuations of dissipated energy (heat) and distribution of work performed by the force acting on the system are addressed by examining contributions of Cauchy fluctuations to either bath or external force acting on the system

Ecological Complex Systems

Main aim of this topical issue is to report recent advances in noisy nonequilibrium processes useful to describe the dynamics of ecological systems and to address the mechanisms of spatio-temporal pattern formation in ecology both from the experimental and theoretical points of view. This is in order to understand the dynamical behaviour of ecological complex systems through the interplay between nonlinearity, noise, random and periodic environmental interactions. Discovering the microscopic rules and the local interactions which lead to the emergence of specific global patterns or global dynamical behaviour and the noises role in the nonlinear dynamics is an important, key aspect to understand and then to model ecological complex systems.Comment: 13 pages, Editorial of a topical issue on Ecological Complex System to appear in EPJ B, Vol. 65 (2008

A physical model describing the transport mechanisms of cytoplasmic dynein

Cytoplasmic dynein 1 is crucial for many cellular processes including endocytosis and cell division. Dynein malfunction can lead to neurodevelopmental and neurodegenerative disease, such as intellectual disability, Charcot-Marie-Tooth disease and spinal muscular atrophy with lower extremity predominance. We formulate, based on physical principles, a mechanical model to describe the stepping behaviour of cytoplasmic dynein walking on microtubules. Unlike previous studies on physical models of this nature, we base our formulation on the whole structure of dynein to include the temporal dynamics of the individual components such as the cargo (for example an endosome or bead), two rings of six ATPase domains associated with diverse cellular activities and the microtubule binding domains. This mathematical framework allows us to examine experimental observations across different species of dynein as well as being able to make predictions (not currently experimentally measured) on the temporal behaviour of the individual components of dynein. Initially, we examine a continuous model using plausible force functions to model the ATP force and binding affinity to the microtubule. Our results show hand-over-hand and shuffling stepping patterns in agreement with experimental observations. We are able to move from a hand-overhand to a shuffling stepping pattern by changing a single parameter. We also explore the effects of multiple motors. Next, we explore stochasticity within the model, modelling the binding of ATP as a random event. Our results reflect experimental observations that dynein walks using a predominantly shuffling stepping pattern. Furthermore, we study the effects of mutated dynein and extend the model to include variable step sizes, backward stepping and dwelling. Independent stepping is studied and the results show that coordinated stepping is needed in order to obtain experimental run lengths