Vorticella Splashing

Miller Institude Research Fellow
Departments of Integrative Biology and
Civil and Environmental Engineering
University of California at Berkeley

Research Interests


Marine larvae in turbulence:

The larvae of many sessile marine organisms are relased in to the ocean flow in order to settle in a new location.  It is essential for species survival that these larvae find and settle in appropriate locations.  Marine larvae are also part of a larger class of organisms that must navigate turbulent flows to move, feed, and reproduce.  However, the locomotion of most organisms has primarily been studied in stationary fluid.  In contrast, for turbulent flows, the velocity at one location varies rapidly in time, and neighboring parcels of fluid move at different velocities, an effect called shear.  Natural marine flows are turbulent, and without understanding the shear flows organisms experience, it is difficult to understand their dispersion, migration, settlement, and community growth.  To elucidate the physics behind this complex biology, I am fitting flows previously measured in the natural environment of the larvae to models of turbulence.  I will then measure the active and passive responses of marine larvae to time-varying shears based on these natural flows by observing both live and cold-killed larvae in controlled shear.  Finally, I will use computational and analytic modeling to determine the forces larvae experience in natural flow fields in order to understand the larval response to time-varying shear.  Multiple species of larvae will be investigated to determine the effect of size and swimming speed. 


Education research:

My postdoctoral education research focused on the research-based transformation of upper-division physics classes and the student misconceptions and difficulties associated with this upper-level material. I worked to elucidate the misconceptions and learning difficulties in junior-level Electricity and Magnetism and sophomore-level Classical Mechanics/Math Methods by observing lecture and homework help sessions, performing student interviews, and analyzing student exams. I also worked to transform these courses to bring them in line with recent physics education research on effective pedagogical strategies. I ran a weekly tutorial session, which centers on small-group problem solving. I also designed and refine the materials used in both the tutorial and the course as a whole. I assessed the efficacy of the tutorial in enhancing learning by designing and administering tutorial pre-tests and post-tests. I am also validated a conceptual post-test to assess conceptual understand of junior-level Electricity and Magnetism and created a conceptual post-test for Classical Mechanics/Math Methods.


Flow around Vorticella:

From www.micrographia.comVorticella is a stalked protozoan which has an extremely fast biological spring, whose contraction is among the fastest biological motions relative to size. Though the Vorticella body is typically only 30 microns across, the contracting spring accelerates it up to speeds of centimeters per second. Vorticella live in an aqueous environment attached to a solid substrate and use their spring to retract their body towards the substrate. The function of the rapid retraction is not known. Many hypothesize that it stirs the surrounding liquid and exposes the Vorticella to fresh nutrients, others suggest that the retraction is used for predator avoidance. I am interested in testing these hypotheses by modeling the Vorticella as a sphere moving normal to a wall, with a stroke that moves towards the wall at high Reynolds number, and away from the wall at low Reynolds number. I approximate the flow during contraction as potential flow, while the flow during re-extension is considered Stokes flow. The analytical results are compared to the flow field obtained with a finite element (Comsol Multiphysics) simulation of the full Navier-Stokes equations. I am working in collaboration with Marcus Roper.



Understanding liquid on solid splashing:

Tuning of a splash with tension
Decreasing the tension in the substrate from solid to 28 N/m suppresses splashing.
The impact of a liquid drop on a solid surface is so common in everyday life that many people don't realize it is not well understood. Since water, as a Newtonian liquid, has no elasticity, naive reasoning would lead one to expect that upon impact a drop would deform into an outwardly expanding disk of liquid on the surface. Indeed, under certain conditions this occurs, but above the splashing threshold, drops are emitted after impact, and perhaps even more surprisingly, these drops move upwards as well as outwards. My research tries to understand why splashing occurs, and what sets the threshold between splashing and spreading. To do this, I have examined the effect of a flexible substrate on the splash threshold and discovered that the splashing stability a set a very early times after impact. I have also investigated the thickness of the liquid sheet, or lamella, which extends outward after impact and discovered an unexpected time dependence. This work was done with Laurent Courbin and Jolet de Ruiter.