Brownian molecular motors driven by rotation-translation coupling

We investigated three models of Brownian motors which convert rotational diffusion into directed translational motion by switching on and off a potential. In the first model a spatially asymmetric potential generates directed translational motion by rectifying rotational diffusion. It behaves much like a conventional flashing ratchet. The second model utilizes both rotational diffusion and drift to generate translational motion without spatial asymmetry in the potential. This second model can be driven by a combination of a Brownian motor mechanism (diffusion driven) or by powerstroke (drift driven) depending on the chosen parameters. In the third model, elements of both the Brownian motor and powerstroke mechanisms are combined by switching between three distinct states. Relevance of the model to biological motor proteins is discussed.Comment: 11 pages, 8 figure

Numerical simulations of complex fluid-fluid interface dynamics

Interfaces between two fluids are ubiquitous and of special importance for industrial applications, e.g., stabilisation of emulsions. The dynamics of fluid-fluid interfaces is difficult to study because these interfaces are usually deformable and their shapes are not known a priori. Since experiments do not provide access to all observables of interest, computer simulations pose attractive alternatives to gain insight into the physics of interfaces. In the present article, we restrict ourselves to systems with dimensions comparable to the lateral interface extensions. We provide a critical discussion of three numerical schemes coupled to the lattice Boltzmann method as a solver for the hydrodynamics of the problem: (a) the immersed boundary method for the simulation of vesicles and capsules, the Shan-Chen pseudopotential approach for multi-component fluids in combination with (b) an additional advection-diffusion component for surfactant modelling and (c) a molecular dynamics algorithm for the simulation of nanoparticles acting as emulsifiers.Comment: 24 pages, 12 figure

Filtern war gestern: Sortierung von zirkulierenden Tumorzellen in Lab-on-a-Chip Systemen

Die Sortierung von Zellen entsprechend ihrer Eigenschaften ist von grundlegender Bedeutung für Anwendungen in Forschung und Medizin. Durch das schnell wachsende Feld der Mikrofluidik eröffnen sich neue Möglichkeiten, diese Herausforderung zu meistern. Mit non-inertial lift induced cell sorting (NILICS) gelingt es, auf einem nur wenige Millimeter großen Chip, zirkulierende Tumorzellen hocheffizient von umgebenden Blutzellen zu trennen

Filtern war gestern: Sortierung von zirkulierenden Tumorzellen in Lab-on-a-Chip Systemen

Die Sortierung von Zellen entsprechend ihrer Eigenschaften ist von grundlegender Bedeutung für Anwendungen in Forschung und Medizin. Durch das schnell wachsende Feld der Mikrofluidik eröffnen sich neue Möglichkeiten, diese Herausforderung zu meistern. Mit non-inertial lift induced cell sorting (NILICS) gelingt es, auf einem nur wenige Millimeter großen Chip, zirkulierende Tumorzellen hocheffizient von umgebenden Blutzellen zu trennen

Separation of blood cells using hydrodynamic lift

Using size and deformability as intrinsic biomarkers, we separate red blood cells (RBCs) from other blood components based on a repulsive hydrodynamic cell-wall-interaction. We exploit this purely viscous lift effect at low Reynolds numbers to induce a lateral migration of soft objects perpendicular to the streamlines of the fluid, which closely follows theoretical prediction by Olla [J. Phys. II 7, 1533, (1997)]. We study the effects of flow rate and fluid viscosity on the separation efficiency and demonstrate the separation of RBCs, blood platelets, and solid microspheres from each other. The method can be used for continuous and label-free cell classification and sorting in on-chip blood analysis

Mesoscale simulations of fluid-fluid interfaces

Fluid-fluid interfaces appear in numerous systems of academic and industrial interest. Their dynamics is difficult to track since they are usually deformable and of not a priori known shape. Computer simulations pose an attractive way to gain insight into the physics of interfaces. In this report we restrict ourselves to two classes of interfaces and their simulation by means of numerical schemes coupled to the lattice Boltzmann method as a solver for the hydrodynamics of the problem. These are the immersed boundary method for the simulation of vesicles and capsules and the Shan-Chen pseudopotential approach for multi-component fluids in combination with a molecular dynamics algorithm for the simulation of nanoparticle stabilized emulsions. The advantage of these algorithms is their inherent locality allowing to develop highly scalable codes which can be used to harness the computational power of the currently largest available supercomputers