Rachel Pepper

I am a biophysicist, and I study questions at the intersection of fluid mechanics and biology.  My lab is a good place for students from both biology and physics backgrounds to grow as scientists.  No particular physics or biology background (besides a willingness to learn) is needed to work on the projects described below.

There are two main areas of research in my lab described below, with several opportunities for student research projects in each area.  To learn more, E-mail me, visit my office (165G), or visit our lab web page

Fluid flow around microscopic organisms:

Many of the essential life tasks of microscopic organisms (e.g. feeding, moving, and reproducing) are dependent on their manipulation of fluid flow.  We can more fully understand the behavior and ecology of these organisms by understanding the fluid flows they create and inhabit.  Simultaneously, we may more fully understand the fundamental physics of fluid flows at a small scale.  The research in my lab focuses on one class of organisms: microscopic sessile suspension feeders. 

Sessile suspension feeders are an important part of aquatic ecosystem; they consume bacteria and small detritus, and are in turn eaten by larger organisms.  As bacteria consumers, these organisms also play an important role in biological wastewater treatment and may also be important in degrading contaminants from human-caused environmental disasters such as oil spills and sewage leaks.  They live anchored to aquatic surfaces and survive by creating a feeding current that draws fluid towards them, and from which they filter their food of interest.  An understanding of the flow generated by suspension feeders may enable not only a better understanding of marine ecology and carbon cycling, but also improved water treatment plant design and improved remediation after environmental disasters. 

In the lab we culture Vorticella convallaria, one species of microscopic sessile suspension feeder, for experiments.  We are also interested in collecting similar species from local bodies of water.  

Splash Cup Plants:

Splash cup plants disperse their seeds with the help of raindrops.  The plants have millimeter-sized conical cups containing seeds.  When a raindrop impacts the cup, the resulting splash launches the seeds up to meter away from the plant.  I’m interested in understanding how this very effective dispersal occurs, both in order to understand how the plants achieve this feat, and to understand how to harness similar processes industrially for effective combustion, inkjet printing, and piezoelectric energy generation.   In the lab we have an apparatus that can drop millimeter-size water droplets with controlled size and velocity, and a fast camera that can record these impacts at up to 1 million frames per second, so that they can be observed in ultra-slow motion (normal TV is filmed at 30 frames per second).   Combined, we can take beautiful videos of splashing, and analyze all of the details.  So far, we’ve been working with 3D printed models of splash cups, but there are two species of liverworts living outside Harned Hall that disperse their gemmae with splash cups, so there is also opportunity to work with the real plants.