Prof Ramin Golestanian

Abstract:

We study the propulsion of two model swimmers at low Reynolds number. Inspired by Purcell's model, we propose a very simple one-dimensional swimmer consisting of three spheres that are connected by two arms whose lengths can change between two values. The proposed swimmer can swim with a special type of motion, which breaks the time-reversal symmetry. We also show that an ellipsoidal membrane with tangential travelling wave on it can also propel itself in the direction preferred by the travelling wave. This system resembles the realistic biological animals like Paramecium. © 2005 IOP Publishing Ltd.

Abstract:

The response of a short DNA segment to bending is studied, taking into account the anisotropy in the bending rigidities. It is shown that due to the helical structure of DNA, the anisotropy in the bending rigidities can lead to the formation of kinks and modulations in the curvature, depending on the values of the elastic constants. The typical wavelength for the modulations, or the distance between the neighbouring kinks, is found to be set by half of the DNA pitch. © 2005 IOP Publishing Ltd.

Abstract:

The microscopic mechanism for thermodiffusion or the Ludwig-Soret effect is investigated for a single charged colloidal particle. For the specific example of a charged permeable membrane, the different forces arising from the interplay between electrostatic interaction and entropy are identified and their magnitudes are calculated in both no-salt and salt-saturated limits. The competition between these forces, which is controlled by the salt density, is shown to decide the direction of motion for the colloids. © 2005 IOP Publishing Ltd.

Abstract:

In a fluctuating medium of quantum, thermal, or non-thermal origin, an interaction is induced between external objects that modify the fluctuations. These interactions can appear in a vast variety of systems, leading to a plethora of interesting phenomena. Notable examples of these include: (1) like-charge attraction in the presence of multivalent counterions, (2) Ludwig-Soret effect in charged colloids, (3) mass renormalization of moving defects in a phononic background and moving metallic objects in EM quantum vacuum, and (4) dissipation due to motion-induced radiation. The fluctuation-induced forces are statistical in nature, and this could make their measurement very difficult, because the actual value of the force might deviate most of the time from the predicted average value. © Indian Academy of Sciences.