Coarse graining of slow variables in dynamic simulations of soft matter

A new Brownian dynamics model is presented to describe the coarse grain dynamics of particles with long-lived memory. Instead of solving a set of generalized Langevin equations we introduce a set of variables describing the slowly fluctuating thermodynamic state of the ignored degrees of freedom. These variables give rise to additional transient forces on the simulated particles, whose interpretation provides a new way of thinking about memory effects in soft-matter physics. We illustrate the proposed method by simulating shear thinning of synthetic resins.\u

Domain formation and growth in spinodal decomposition of a binary fluid by molecular dynamics simulations

The two initial stages of spinodal decomposition of a symmetric binary Lennard-Jones fluid have been simulated by molecular dynamics simulations, using a hydrodynamics-conserving thermostat. By analyzing the growth of the average domain size R(t) with time, a satisfactory agreement is found with the R(t)t1/3 Lifshitz-Slyozov growth law for the early diffusion-driven stage of domain formation in a quenched homogeneous mixture. In the subsequent stage of viscous-dominated growth, the mean domain size appears to follow the linear growth law predicted by Siggia

Atherosclerosis: from Bench to Bedside and from Pathophysiology to Treatment

Despite continuous advances in therapeutic options, cardiovascular disease is still the leading cause of death worldwide1. The WHO estimated that in 2008 17.3 million people died from cardiovascular disease, accounting for 30% of all deaths world-wide. Of these deaths, approximately 7.3 million were due to coronary heart disease while 6.2 million were due to stroke2. The number of deaths due to cardiovascular disease will increase to 23.3 million by 2030. Coronary heart disease and stroke are the result of atherosclerotic plaque formation. Atherosclerosis, or stiffening of the artery (from the Greek arteria meaning artery and sclerosis meaning stiffening), is an ongoing process which already starts in childhood3-5. A healthy artery consists of three layers

Repeated segregation and energy dissipation in an axially segregated granular bed

Discrete element simulations were used to study the segregation behaviour in a bed of bidisperse granules in a rotating drum. In the final state the large particles ended up in the upper part of the bed near the vertical walls. In order to arrive at this state, the system went through two cycles of structural changes, on top of which fast oscillations were observed between an axially segregated and a somewhat more mixed state. These oscillations were sustained by different angles of repose near the vertical walls and in the middle of the bed. Concomitantly with the structural changes, the system's energy dissipation went through two cycles after which it settled in the state requiring the least work of all traversed states, suggesting that the granular bed strives for minimal dissipation

Kayaking and wagging of liquid crystals under shear: Comparing director and mesogen motions

Rod-like colloids in dense solutions perform collective orientational motions under shear flow. The periodic tumbling motions of the director, i.e. the average orientation of the rods, are commonly characterized as kayaking, wagging and flow-aligning, in order of increasing shear rate. Our event-driven Brownian dynamics simulations of rigid spherocylinders reproduce these three distinct director motions, but also clearly show, for the first time, that the individual mesogens are kayaking at all shear rates. The synchrony of the mesogens's motions gradually decreases with increasing shear rate, which at a critical shear rate causes a transition of the apparent collective motion from kayaking to wagging. The rods's persistent kayaking also explains the continuity of the tumbling period at this transition and the smooth change from wagging to flow-aligning observed at higher shear rates

Molecular dynamics simulation of amphiphilic membrane and wormlike micelles: a multi-scale modelling approach to the design of visco-elastic surfactant solutions

Bilayer membranes and wormlike micelles have been studied using molecular–dynamics simulations. The structure of the worm is analysed in terms of radial density distribution functions, and mechanical properties such as the elastic modulus are calculated. From an analysis of the fluctuation spectra of the tensionless states, we have calculated bending rigidities. Micelles consisting of coarse–grained (CG) model surfactants are studied in order to map the properties of the atomistic micelle. We optimize the CG model with respect to the structure factor S(q) of the atomistic micelle. The mechanical properties thus obtained will be used as input for a mesoscopic model of wormlike micelles where the persistence length is the smallest length–scale