A study published August 17 in the journal Science shows that in fire ant colonies, a small number of workers does most of the digging, leaving the other ants to look somewhat less than industrious. For digging nest tunnels, this less busy approach gets the job done without ant traffic jams – ensuring smooth excavation flow. Researchers found that applying the ant optimization strategy to autonomous robots avoids mechanized clogs and gets the work done with the least amount of energy.

Optimizing the activity of autonomous underground robots could be useful for tasks such as disaster recovery, mining or even digging underground shelters for future planetary explorers. The research was supported by the National Science Foundation’s Physics of Living Systems program, the Army Research Office and the Dunn Family Professorship.

“We noticed that if you have 150 ants in a container, only 10 or 15 of them will actually be digging in the tunnels at any given time,” said Daniel Goldman, a professor in the School of Physics at the Georgia Institute of Technology. “We wanted to know why, and to understand how basic laws of physics might be at work. We found a functional, community benefit to this seeming inequality in the work environment. Without it, digging just doesn’t get done.”

By monitoring the activities of 30 ants that had been painted to identify each individual, Goldman and colleagues, including former postdoctoral fellow Daria Monaenkova and Ph.D. student Bahnisikha Dutta, discovered that just 30 percent of the ants were doing 70 percent of the work – an inequality that seems to keep the work humming right along. However, that is apparently not because the busiest ants are the most qualified. When the researchers removed the five hardest working ants from the nest container, they saw no productivity decline as the remaining 25 continued to dig.

Having a nest is essential to fire ants, and if a colony is displaced – by a flood, for instance – the first thing the ants will do upon reaching dry land is start digging. Their tunnels are narrow, barely wide enough for two ants to pass, a design feature hypothesized to give locomotion advantages in the developing vertical tunnels. Still, the ants know how to avoid creating clogs by retreating from tunnels already occupied by other workers – and sometimes by not doing anything much at all. 

To avoid clogs and maximize digging in the absence of a leader, robots built by Goldman’s master’s degree student Vadim Linevich were programmed to capture aspects of the dawdling and retreating ants. The researchers found that as many as three robots could work effectively in a narrow horizontal tunnel digging 3D printed magnetic plastic balls that simulated sticky soil. If a fourth robot entered the tunnel, however, that produced a clog that stopped the work entirely.

“When we put four robots into a confined environment and tried to get them to dig, they immediately jammed up,” said Goldman, who is the Dunn Family Professor in the School of Physics. “While observing the ants, we were surprised to see that individuals would sometimes go to the tunnel and if they encountered even a small amount of clog, they’d just turn around and retreat. When we put those rules into combinations with the robots, that created a good strategy for digging rapidly with low amounts of energy use per robot.”

Experimentally, the research team tested three potential behaviors for the robots, which they termed “eager,” “reversal” or “lazy.” Using the eager strategy, all four robots plunged into the work – and quickly jammed up. In the reversal behavior, robots gave up and turned around when they encountered delays reaching the work site. In the lazy strategy, dawdling was encouraged.

“Eager is the best strategy if you only have three robots, but if you add a fourth, that behavior tanks because they get in each other’s way,” said Goldman. “Reversal produces relatively sane and sensible digging. It is not the fastest strategy, but there are no jams. If you look at energy consumed, lazy is the best course.” Analysis techniques based on glassy and supercooled fluids, led by former Ph.D. student Jeffrey Aguilar, gave insight into how the different strategies mitigated and prevented clog-forming clusters.

To understand what was going on and experiment with the parameters, Goldman and colleagues – including Will Savoie, a Georgia Tech Ph.D. student, Research Assistant Hui-Shun Kuan and Professor Meredith Betterton from the Department of Physics at the University of Colorado Boulder – used computer modeling known as cellular automata that has similarities to the way in which traffic engineers model the movement of cars and trucks on a highway.

“On highways, too few cars don’t provide much flow, while too many cars create a jam,” Goldman said. “There is an intermediate level where things are best, and that is called the fundamental diagram. From our modeling, we learned that the ants are working right at the peak of the diagram. The right mix of unequal work distributions and reversal behaviors has the benefit of keeping them moving at maximum efficiency without jamming.”

The ability to avoid clumping seems to meet a need that many systems have, Betterton noted. “The ants work in a sweet spot where they can dig quickly without too many clogs. We see the same physics in ant digging, simulation models, and digging by robots, which suggests that for groups of animals that need to excavate, avoiding clogs is crucial.”

The researchers used robots designed and built for the research, but they were no match for the capabilities of the ants. The ants are flexible and robust, able to squeeze past each other in confines that would cause the inflexible robots to jam. In some cases, the robots in Goldman’s lab even damaged each other while jostling into position for digging.

The research findings could be useful for space exploration where tunnels might be needed to quickly shield humans from approaching dust storms or other threats. “If you were a robot swarm on Mars and needed to dig deeply in a hurry to get away from dust storms, this strategy might help provide shelter without having perfect information about what everybody was doing,” Goldman explained. 

Beyond the potential robotics applications, the work provides insights into the complex social skills of ants and adds to the understanding of active matter. 

“Ants that live in complex subterranean environments have to develop sophisticated social rules to avoid the bad things that can happen when you have a lot of individuals in a crowded environment,” Goldman said. “We are also contributing to understanding the physics of task-oriented active matter, putting more experimental knowledge into phenomenon such as swarms.”

In addition to those already mentioned, the research included Michael Goodisman, associate professor in Georgia Tech’s School of Biological Sciences.

This research was supported by the National Science Foundation through grant numbers PoLS-0957659, PHY-1205878 and DMR-1551095 as well as a grant W911NF-13-1-0347 from the Army Research Office, and the National Academies Keck Futures Initiative. 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 or Army Research Office.

CITATION: J. Aguilar, et. al., “Collective clog control: optimizing traffic flow in confined biological and robophysical excavation,” (Science 2018).

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Put more scientifically, a piece of DNA’s movements are often counterintuitive to those of objects in our everyday grasp.  Take a rod of rubber, for example. Bend it until its ends meet, and you can count on the elastic tension to snap it back straight when you let go, said biological physicist Harold Kim.

“That doesn’t always work that way with a piece of DNA. When you bend it into a loop, the elastic energy more often than not wants to bend the chain further in instead of pushing it back out,” said Kim, an associate professor at the Georgia Institute of Technology.

At the School of Physics, Kim is fine-tuning the observation of how biopolymers behave, in particular DNA at short lengths. He published his latest results on “Force distribution in a semiflexible loop” in the journal Physical Review E on April 18, 2016.  The research is funded by National Institutes of Health. Georgia Tech’s James T. Waters coauthored the research paper.

In complex simulations, Kim studied the motions of DNA chains at lengths where they still have springy qualities, in order to understand their mechanochemical properties, or how they work as microscopic objects. In particular, he has illuminated the forces acting upon DNA bound up in short loops.

That’s a common and important shape that keeps DNA from expressing when it shouldn’t and then possibly messing up cell functioning.

Kim’s most significant counterintuitive find could improve understanding of how DNA snaps free from the proteins that bind them into those loops. He has observed that looped DNA, though on average very gentle in its motions, is beset by moments of unusually high force. 

“It would be a little like a chaotic spring drawn up to a loop making pretty even jumbly movements then suddenly whipping out violently,” Kim said.

The range of observed forces on DNA loops breaks the bounds of what thermodynamics predicts. Even though the mean of the force distribution does indeed equal the thermodynamic force, the distribution of forces pushes past the anticipated norm, falling broadly outside a Gaussian distribution on both ends.

That’s a key determination.

It could help scientists in various disciplines predict the lifespans of many DNA loops and understand the frequency and likelihood of their undoing.

The forces contributing to those momentary jerks and snaps work on the whole contrary to one another. While that elastic energy works on DNA pieces in its ways, the forces of entropy push hard in their own ways.

Reflective of the universe overall, in Kim’s observations of springy DNA loops, entropy, here too, wins. Entropic forces slightly outdo the elastic forces.

And they, too, defy intuition.

To understand how, let’s take a look back at that rubber bar. When a short DNA chain is not looped but only bent, it acts more like the rubber bar. The elastic force dominates and mostly wants to push it back straight, while entropy mostly wants to keep it curvy.

Then, as the DNA chain lengthens a bit and loops: That relation starkly turns on its head.

The elastic force then pulls inward with vehemence, and the entropic force then pushes the chain outward with even more vigor.

The length of a DNA loop appears to contribute strongly to how likely these intermittent extreme forces are to destabilize its bond with the protein holding it shut.

That, incidentally, plays right into many scientists’ current discussions on other biopolymers.

“There’s a lot of speculation right now that the kinds of force-peaks we observed actually regulate the length of some biopolymers, so, in an interesting way, our observations and methods may help colleagues explore this idea more closely,” Kim said.

Kim’s group augmented thermodynamic calculations with a novel simulation method, “phase-space sampling.” It not only establishes the positon of molecular components in space but also their momentum at a given time.

This took into account the constant bombardment by water molecules, i.e. the “heat bath.”

This way, Kim was better able to access the fluctuating forces on looped DNA chains – and see more closely how they really wriggle.

The work is funded by the National Institutes of Health, grant number R01GM112882. Any conclusions or opinions are those of the authors and do not necessarily represent the official views of the NIH.

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For the two undergrads, TEDxDouglasville is a means to give back to a town and community that supported them as they began their undergraduate studies at Georgia Tech. Looking ahead to their graduation from Georgia Tech, Barnett and Al-Husseini regard TEDxDouglasville as a way to stay connected to their community of origin even as they might move farther away in search of their individual futures.

Barnett and Al-Husseini have known each other since their freshman days in Douglas County High School. “By the time we graduated, we were best friends and bound for Georgia Tech,” Barnett says. Al-Husseini masterminded the creation of TEDxDouglasville, asking Barnett to join soon after the TED license was approved. Barnett did not hesitate to take the role of co-organizer. “Both of us were deeply affected by a philosophy course we had taken in high school,” he says. “And we were convinced by the power of ideas and the impact of how ideas are conveyed.”

A big surprise of the event last year was how much younger the audience was than the organizers had expected. “A large number of high school students attended,” Barnett says. “This year we have made tickets more accessible to these students, and we’re even holding the event in a school that many of them attend.”

That would be Douglas County High School. When TEDxDouglasville 2016 is held there on April 9, two College of Sciences faculty members will speak:

Brian Hammer, from the School of Biology, will talk about cooperation and conflict in the microbial world. “Microbes are ubiquitous on Earth and interact with one another and their surroundings in diverse associations that maintain the health of our planet and all of its inhabitants,” Hammer says. His research is helping to explain how bacteria cooperate and compete. And he hopes the knowledge “will allow us to monitor and manipulate these behaviors to prevent and treat human diseases and to mitigate perturbations to global ecological systems.”

Laura Cadonati, from the School of Physics, will describe the discovery of gravitational waves. “Gravitational waves are ripples in the fabric of space and time that are produced by cataclysmic astrophysical events,” Cadonati explains. One hundred years  after Albert Einstein predicted their existence,  one such wave was detected for the first time on Sept. 14, 2015; the wave came from the merging of two gigantic black holes 1.3 billion years ago. Cadonati will explain how gravitational waves open a new way to probe the universe.

“Events like TEDxDouglasville speak to Georgia Tech’s and the College of Sciences’ tradition of educating and nurturing the whole person and not just the engineering or the physics aspects,” says College of Sciences Dean Paul M. Goldbart. “They also underscore the College’s commitment to sharing with nonscientists everywhere the excitement and promise of our researchers’ breakthrough discoveries.”  

With an average age of 21, Barnett, Al-Husseini, and the organizing team of TEDxDouglasville are on a steep learning curve to achieve their aspirations for TEDxDouglasville. Following are edited excerpts from a Q&A conducted by e-mail. Responses are from both Barnett and Al-Husseini except where indicated.

Why is Douglasville a good venue for a TEDx program?

It’s hard to resist Douglasville’s southern charm, incredible past, beautiful parks, and strength of community. Douglasville is where history meets modernity. This little, big city rests on the fringes of Atlanta, but remains far enough to stay humble.

This event is a way to engage our community. It would give people a chance to meet and converse with individuals with whom they might never interact otherwise. Diverse interactions is important in the development of a wholesome, interconnected community.

Who are the people you are trying to reach with TEDxDouglasville?

Students, construction workers, teachers, businessmen, janitors, social workers, doctors, lawyers. Anyone with a sense of curiosity. We seek to get people thinking, dreaming, and achieving.

What is your measure of success for TEDxDouglasville?

Exposing our audience to different people and new ideas was one of our goals from the beginning. But we must also consider the impact on the wider community. TEDxDouglasville inspired a new level of civic engagement: It led to a proposal for the Douglas Youth Department and catalyzed the creation of a service organization, Progressive Action Towards the Health of Douglasville, a lasting legacy.

It is also great to have scientists from Georgia Tech speak to a general audience, especially to high school students. TEDxDouglasville not only gives the audience a chance to connect with scientists on a tangible, accessible level, but it also helps to steer youth who are considering majoring in the sciences by providing a realistic snapshot of what scientific research looks like on the collegiate level.

Give us a preview of TEDxDouglasville 2016.

Our theme for this year is “Laying the Tracks,” which is rooted in the city’s origins from a railroad track. TEDxDouglasville 2016 will explore the intricacies of pioneering and building in the sciences, arts, education, and business. The event is laying tracks for ideas worth spreading, in hopes of building something extraordinary.

What happens to TEDxDouglasville when you graduate from Georgia Tech? 

Al-Husseini: We aim to transform TEDxDouglasville from an annual event into a continuous platform for creative thinking and community outreach. The proceeds from this year’s event will be stored in a scholarship fund dedicated to high school students in Douglas County.

I intend to spend four years on active-duty with the US Army, after a spring 2018 Georgia Tech graduation. Upon completing my service contract, I hope to attend graduate school and eventually return to Douglasville.

Barnett: I hope to take an advisory role for a successor who will come to organize the event. With plans to attend graduate school, I must commit more and more time to research and my courses. Meanwhile, we will explore various options.

So far, 666 employees have given $205,113 toward the goal of 1,500 people giving $330,000. The deadline to donate is Friday, Nov. 14.

Michele Green, an administrative professional for the Georgia Tech Research Corporation, knows the power of the campaign firsthand. After a divorce left her in need of furniture and assistance, she found the Atlanta Step-Up Society, a campaign beneficiary that runs a thrift shop and provides services to veterans, the homeless, and those who are rebuilding their lives. Now that she’s able, Green gives back to the organization. 

“I give from my heart,” said Green, who has also served as a Charitable Campaign ambassador for 10 years. “You just never know when you might need assistance.”

Those who donate by Nov. 14 will be entered into a drawing for golf for four at the Currahee Club in Toccoa, Georgia. Faculty and staff can give through payroll deduction, check donations, credit/debit card payment or WebCheck. Giving online through TechWorks is confidential, secure, and simple to use.

For more information, visit charitable.gatech.edu or email charitable@gatech.edu.