Ph.D. Candidate Department of Mechanical and Aerospace Engineering University of California, San Diego contact : (858) 729 - 8881 EBUII 304 9500 Gilman Drive La Jolla, CA 92093-0411 curriculum vitae:

A bulk of my work has been on the mechanics of bio-locomotion and cell-cell interactions, studying how cells swim, how they can deform one another passively via fluid-structure interactions when in close proximity and how this affects collective motility. Some microorganisms, such as spermatozoa, have been observed to synchronize their flagella when swimming in close proximity. Using a two-dimensional model we showed that phase-locking arises from hydrodynamics forces alone. In a Newtonian fluid there must exist a front-back asymmetry in the geometry of their flagellar waveform. The time-evolution of the phase difference between co-swimming cells depends only on the nature of this geometrical asymmetry, and microorganisms can phase-lock into conformations which minimize or maximize energy dissipation. However in a viscoelastic fluid the presence of polymeric stresses removes the geometrical asymmetry constraint, and therefore even symmetric swimmers synchronize. Such synchronization occurs on asymptotically faster time scales than in a Newtonian fluid, and the swimmers are seen to be driven into a stable in-phase conformation minimizing the energy dissipated in the surrounding fluid.

G.J. Elfring, E. Lauga Hydrodynamic Phase Locking of Swimming Microorganisms, Physical Review Letters 103 (2009) 088101.
G.J. Elfring, O.S. Pak, E. Lauga Two-dimensional Flagellar Synchronization in Viscoelastic Fluids, Journal of Fluid Mechanics 646 (2010) 505-515.
G.J. Elfring, E. Lauga Passive Hydrodynamic Synchronization of Two-Dimensional Swimming Cells, Physics of Fluids 23 (2011) 011902.
G.J. Elfring, E. Lauga, Synchronization of Flexible Sheets Journal of Fluid Mechanics 674 (2011) 163-173.
M. Sauzade, G.J. Elfring, E. Lauga, Taylor's Swimming Sheet: Analysis and Improvement of the Perturbation Series Physica D 240 (2011) 1567-1573.

Capillary phenomenon is so fascinating as it is ubiquitous and the governing equations so simple yet the behavior can be rich and mysterious. My recent work in this area explored the experimentally observed shape instability of squeezed droplets. In particular it was shown that if the droplet is sufficiently compressed at the top by a surface, it will always develop a shape instability at a critical compression. When the top surface is flat, the shape instability occurs precisely when the apparent contact angle of the droplet at the pinned surface is pi, regardless of the contact angle of the upper surface.

G.J. Elfring, E. Lauga, Buckling Instability of Squeezed Droplets, (Submitted)

I also maintain an active interest in modeling energy systems, especially alternative fuel schemes, in efforts to increase understanding and efficiency. In particular I've studied the sorption and permeation of water throughout a Nafion membrane which is essential for the efficient operation of a PEM fuel cell. I've also a conducted 2nd law efficiency analysis on high-bypass turbo fan air engines.

G.J. Elfring, H. Struchtrup Thermodynamic Considerations on the Stability of Water in Nafion, Journal of Membrane Science 297 (2007) 190-198.
G.J. Elfring, H. Struchtrup Thermodynamics of Pore Wetting and Swelling in Nafion, Journal of Membrane Science 315 (2008) 125-132.
H. Struchtrup, G.J. Elfring External Losses in High-Bypass Turbo Fan Air Engines, International Journal of Exergy, Vol.5, No.4 (2008) 400-412.