Eric Sembrat's Test Bonanza


Course Reform MIT Style: Student Evaluations vs. Scientific Evidence

The evaluation of most course reforms typically rests heavily on teacher and student evaluations; I’ll argue that this is unwise. In contrast, I’ll discuss course reform MIT style: select objectives, adopt metrics, experiment, and evaluate; recycle until objectives are achieved. Tellingly, educators call this “backward design”.

Prof. Andy Zangwill, 2017 Class of 1940 W. Howard Ector Outstanding Teaching Award.

Friday, March 10, 2017
Congratulating to Prof. Andy Zangwill. He has been selected as the recipient of 2017 Class of 1940 W. Howard Ector Outstanding Teaching Award. This is a tremendous honor for Prof. Zangwill! On behalf of the SoP, thank you for your effort and commitment for excellence in teaching, and your work as Associate Chair of our Graduate Program. Special thanks to Prof. Nepomuk and Flavio, for taking the lead with Andy’s nomination.

Congratulations Prof. Zangwill


Prof. Flavio Fenton, 2017 Junior Faculty Outstanding Undergraduate Research Mentor

Friday, March 10, 2017

Congratulations to Prof. Flavio Fenton. He has been selected 2017 Junior Faculty Outstanding Undergraduate Research Mentor. Prof. Fenton was instrumental in the successful mentoring of undergraduate and high school students over the past five years, as well as multiply PURA winners and Petit Scholars.  Our thanks to Prof. Nepomuk Otte for leading Flavio’s nomination. 


Congratulations to Prof. Flaivo Fenton!


Understanding What’s Happening Inside Liquid Droplets

Friday, March 10, 2017

For most people, the drip, drip, drip of a leaking faucet would be an annoyance. But for Georgia Institute of Technology Ph.D. candidate Alexandros Fragkopoulos, what happens inside droplets is the stuff of serious science.

In the laboratory of Alberto Fernandez-Nieves in Georgia Tech’s School of Physics, Fragkopoulos is studying how toroidal droplets – which initially take the shape of a donut – evolve into spherical droplets by collapsing into themselves or breaking up into smaller droplets.

Work with droplets has implications for the life sciences, where biological materials, including cells, undergo shape changes reminiscent of droplet behavior. And the findings could improve industrial processes ranging from fuel injectors to chemical processes that depend on droplet formation. In the work, researchers in the Fernandez-Nieves lab have developed a new understanding of the processes that control the evolution of unstable, donut-shaped droplets, helping them clarify the complex interplay of forces relevant to the problem.

“Surface tension drives the evolution of the droplets,” said Fragkopoulos. “Fluids tend to minimize their surface area for a given volume because that minimizes the energy required to have an interface between different fluids. Spherical shapes minimize that energy, and as a result, toroidal droplets want to evolve to become spherical. We’re studying how that transition occurs.”

Using a sheet of laser light to observe the scattering from polystyrene particles placed into droplets formed within thick silicone oil, the researchers have observed in detail how droplets change shape – and which factors set the droplets on the path to either collapse or breakup. The research, which was supported by the National Science Foundation, was reported March 1 in the journal Proceedings of the National Academy of Sciences.

“The viscous forcing as the torus collapses exerts stress on the interface, which causes it to both have a circulation inside the torus and deform its surface,” said Fragkopoulos. “We need to take into account these stresses to completely understand the evolution of the droplets.”

The impetus for the experimental work was inconsistencies between theoretical predictions and computer simulation of toroidal droplet transitions. What the Georgia Tech researchers found tends to back up the simulation results. “However, the earlier theoretical work was essential in guiding the theory efforts and in illustrating what the problem was in order to correctly describe the experimental results,” said Fernandez-Nieves.

“Parameters such as the aspect ratio – the overall dimension of the torus divided by the dimensions of the tube – determine whether the toroidal droplet can break up, or if it will simply collapse into itself,” said Fragkopoulos. “We found that the toroidal droplet deforms a lot from the donut shape as it collapses. It flattens as it develops, which was initially unexpected. We had expected the torus to be symmetrical and nicely circular, which is not what we found.”

The breakup or collapse of ordinary raindrops is known to involve the formation of a donut-like rim. However, the process is rather uncontrolled and takes place quickly, so quickly that only high-speed cameras could see it. To allow detailed study of the transition and imaging the flow field within the drops, Fragkopoulos dramatically slowed down the evolution by creating droplets within a type of silicone oil that is six times more viscous than honey. Instead of ordinary water, he used distilled water into which polyethylene glycol has been mixed to further slow the dynamics.

The water is introduced into a rotating bath of the silicone oil using a tiny needle injector. By controlling the pumping rate and where the needle inserts the water, the researchers can control the geometrical parameters of the toroidal droplets, specifically the thickness of the ring and the relative size of the hole inside it. The droplets they study range in size up to about a centimeter in diameter. “This simple strategy affords exquisite control,” said Fernandez-Nieves.

Polystyrene beads in the water allow the researchers to use particle image velocimetry (PIV) to see the flow fields within the droplets, showing how the cross section deviates from circular over time.

“We are using the difference in viscosity to generate the torus,” Fragkopoulos explained. “We are using viscous forces to generate the droplets, because it’s important to slow down the dynamics of the torus collapse so we can have enough time and resolution to see the flow fields developing inside it.”

Research into droplet formation has tended to be applications-focused. Now Fragkopoulos and Fernandez-Nieves are using their experimental and theoretical work to address other science problems.

“We are now using the methods for creating toroidal objects made from different materials to study problems in condensed matter and bioengineering,” said Fernandez-Nieves. “We started working on toroidal droplets with the idea of studying how topology and geometry affected how ordered materials are affected by these aspects, and later to address how curvature affects cell behavior. We wanted to make nontrivial geometries so we could study how this affects behavior,” added Fragkopoulos.

The next step in the work is to study electrically-charged droplets, which are widely used industrially. The electrical charges add a new wrinkle to the flow fields and change how the toroidal droplets transform. In addition to those already mentioned, the research included former graduate and undergraduate students in the Fernandez-Nieves lab, Ekapop Pairam and Eric Berger, and Prof. Phil Segre at Oxford College, Georgia.

The research was supported by the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

CITATION: Alexandros A. Fragkopoulos, et al., “The shrinking instability of toroidal droplets,” (Proceedings of the National Academy of Sciences, 2017).

Research News

Georgia Institute of Technology

177 North Avenue

 Atlanta, Georgia  30332-0181  USA

Content Images: 

For most people, the drip, drip, drip of a leaking faucet would be an annoyance. But for Georgia Institute of Technology Ph.D. candidate Alexandros Fragkopoulos, what happens inside droplets is the stuff of serious science.


10 Years of Southern Stargazing: How Star Trek Changed Everything

This public lecture by Glenn Burns, chief meteorologist of WSB-TV, is one of three events to celebrate 10 Years of Southern Stargazing at the Georgia Tech Observatory. 

The destination for the 1960s Apollo missions was the Moon, but the premiere of Star Trek in 1966 got the nation thinking about possibilities  beyond our Solar System. What about other galaxies, alien life, faster-than-light travel?

Glenn Burns, WSB-TV’s chief meteorologist, will discuss how a unique blend of science fact and science fiction inspires generations of astronomers. 

10 Years of Southern Stargazing: Public Night at the Observatory

This Public Night at the Observatory is one of three events to celebrate the 10th anniversary of the Georgia Tech Observatory. 

Weather permitting, Georgia Tech rolls back the roof on the observatory on top of the Howey Physics Building. This event will be hosted by James Sowell, director of the Georgia Tech Observatory.

10 Years of Southern Stargazing: A Magical Universe Tour in a Planetarium at Clough

This planetarium show is one of three events to celebrate 10 Years of Stargazing at the Georgia Tech Observatory.

Stargazers will enter a 20-foot-diameter, high-resolution planetarium installed in the Clough Atrium. Philip Groce, president of Helping Planetariums Succeed, will take you on a tour of the known universe and preview the Great American Solar Eclipse on August 21, 2017.

Animal Attraction: Bio-inspiration and the Digital Life Project

Nature-inspired solutions have spawned such products as potential cancer cures from animal and plants, novel antibiotics, and gecko-inspired adhesives. This “bio-inspired” approach applies integrative methods from anatomy, animal function, evolution, and biomechanics to inspire novel synthetic materials.  Further, new methods for visualizing animals have opened new doors into understanding the diversity of life.  

How Things in the Universe Came About & How They Ended Up Within Us

Tom Abel will take the audience on a journey through the early stages of the universe, using the latest computer animations of how the first stars formed and died and how stars built up the first galaxies.

Collective dynamics in motile cilia: waves in the airways

Motile cilia are cell organelles able to exert a net force onto a liquid; they are highly conserved across eukaryotes, and enable a variety of functions from the motility of single cell organisms to flow that carries nutrients to our brains.  A fascinating process takes place in mammalian airways: a carpet of motile cilia maintains the cell surface free of pathogens and particles by continuously refreshing and clearing a barrier of mucus.


Subscribe to RSS - Eric Sembrat's Test Bonanza