I am interested in theoretical soft matter physics and biophysics. Modeling of complex fluids and elastic materials. I am currently a research fellow at the Flatiron Institute division of the Simons Foundation working with Michael Shelley.Email: naomiop_at_gmail.com Membrane rotors: from Euler vorticity dynamics to quasigeostrophic flows We show that the dynamics of rotors embedded in a quasi 2D membrane exhibit a power law transition in their interactions from Euler fluid at small distances (1/r), to quasigeostrophic at large distances (1/r^2). We derive a Hamiltonian for a discrete system of rotors and describe the conserved quantities. We develop a coarsegrained description for a density field of rotors. We work on theory and simulations for both the discrete and the continuous cases. When a sphere moves next to a solid wall it experiences an increased drag, but no normal force. If, however, elasticity is introduced, then coupling between hydrodynamics and elasticity can break the timereversal symmetry of the Stokes equations. We describe (theoretically and experimentally) a case in which a sphere is falling due to gravity next to a suspended elastic sheet. We predict the induced normal force created on the sphere in the lubrication limit and verify the predictions via experiments. The sphere will move away from the sheet with a velocity which is proportional to the square of its translational velocity and inversely proportional to the bending modulus and the tension of the sheet.
Motion of hot sphere in viscous fluids Imagine a sphere falling through a fluid, what will be the connection between the force acting on the sphere and its velocity? For a regular sphere the result is the known Stokes' law. We found the leading order correction in the case of a particle with some heat distribution on it. We show that in the case of a Janus sphere there will be coupling between translation and rotation.
Nondissipative shapable sheet
A sheet of paper that has been crumpled and flattened retains some amount of shapability that a bare, uncrumpled, sheet does not have: when deformed by external forces, it retains the deformed shape after the forces are removed. Using a frustrated two dimensional lattice of springs, we show that such shapability can be attained in a nondissipative system. Numerical investigations suggest an extensive number of bistable energy minima using several variants of this scheme. The numerical sheet can be bent into a nearlyclosed cylinder that holds its shape. We verify that the deformed shape is locally stable and compare its bending modulus in the deformed state with that in the initial flat state. We investigate the threshold for nonelastic deformation using various kinds of forcing.
Why do sleeping nematodes develop a hockeysticklike posture? C. elegans exhibits a sleeplike state during a stage termed lethargus, during which they are commonly observed in a hockeysticklike posture. Biron et. al. showed that this posture is actively maintained. They also see that the animals flip almost exclusively when they have a single bent. We describe a simple biomechanical model using springs to simulate the muscles, and show that it is sufficient for generating rotation about the anteriorposterior body axis
Anomalously fast kinetics of lipid monolayer jerks
A monolayer of lipids is sitting on top of water and compressed on both sides. As the pressure increases the monolayer buckles with the observation of fast "jerks" spanning the entire range of the system. What can account for this fast motion? We survey the folding mechanism, believed to accounts for this motion, and show that even the most generous energy it can supply does not account for the kinetic energy observed in experiments. So what is actually taking place? We do not know, but we offer some alternative possibilities.
Dynamics of heterogeneous membranes
The dynamics of biomembranes and membrane proteins is a key ingredient in a host of vital cellular processes. We model the membrane as a twodimensional fluid surrounded by a threedimensional different fluid (the solution). The mixed dimensionality results in a rich physical behavior. We have focused on three scenarios: (i) a membrane surrounded by an unbounded fluid; (ii) a membrane adjacent to a rigid surface; and (iii) a membrane containing immobile inclusions (such as the ones anchoring the membrane to the cytoskeleton). Each of the three scenarios exhibits different physics, stemming from different implications of the conservation laws for mass and momentum, and from the symmetry of the problem. We have found longrange correlations between the motions of membrane proteins, leading to anomalous concentration affects.
