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School of Physics' undergraduate prizes for 2012-2013

Thursday, April 25, 2013

H. Fukuyo Outstanding Physics Undergraduate Award to Benjamin Land and Rita Garrido:
Award of $2,500 given to the most outstanding undergraduate academic student(s) in
the School of Physics.

H. Fukuyo Memorial Scholarship Award in Physics to Alan Pryor and Greg Douthit:
This award consisting of $2,500.

The Joyce M. and Glenn A. Burdick Award to Edward Dannemiller:
Recognizes rising seniors in the School of Physics who demonstrate scholastic
achievement and leadership, and possess characteristics that embody the mission
of Georgia Tech. The award consists of $500.

Summary: 

We are pleased to announce the winners of the School of Physics' undergraduate prizes for 2012-2013. The winners were recently acknowledged at the Student Awards luncheon. Congratulations to all the prize winners!

Intro: 

We are pleased to announce the winners of the School of Physics' undergraduate prizes for 2012-2013. The winners were recently acknowledged at the Student Awards luncheon. Congratulations to all the prize winners!

Alumni: 

Benjamin Land, Undergraduate Student, Award Recipient

Wednesday, April 24, 2013

Current SoP undergraduate student Benjamin Land is a recipient of the Robert A. Pierotti Memorial Scholarship and the H. Fukuyo Outstanding Physics Undergraduate Award. Benjamin Land is a graduating Physics major and works under the supervision of Prof. Michael Chapman. He will be pursuing a Ph.D in Physics at the University of California, Berkeley in the Fall. Join us in wishing him congratulations for this great accomplishment.

 

Summary: 

Congratulations to Benjamin Land recipient of the Robert A. Pierotti Memorial Scholarship and the H. Fukuyo Outstanding Physics Undergraduate Award

Intro: 

Congratulations to Benjamin Land recipient of the Robert A. Pierotti Memorial Scholarship and the H. Fukuyo Outstanding Physics Undergraduate Award

Alumni: 

Sea Turtles and FlipperBot Show How to Walk on Granular Surfaces like Sand

Tuesday, April 23, 2013

For sea turtle hatchlings struggling to reach the ocean, success may depend on having flexible wrists that allow them to move without disturbing too much sand. A similar wrist also helps a robot known as “FlipperBot” move through a test bed, demonstrating how animals and bio-inspired robots can together provide new information on the principles governing locomotion on granular surfaces.

Both the baby turtles and FlipperBot run into trouble under the same conditions: traversing granular media disturbed by previous steps. Information from the robot research helped scientists understand why some of the hatchlings they studied experienced trouble, creating a unique feedback loop from animal to robot – and back to animal.

The research could help robot designers better understand locomotion on complex surfaces and lead biologists to a clearer picture of how sea turtles and other animals like mudskippers use their flippers. The research could also help explain how animals evolved limbs – including flippers – for walking on land.

The research was published April 24 in the journal Bioinspiration & Biomimetics. The work was supported by the National Science Foundation, the U.S. Army Research Laboratory’s Micro Autonomous Systems and Technology (MAST) Program, the U.S. Army Research Office, and the Burroughs Wellcome Fund.

“We are looking at different ways that robots can move about on sand,” said Daniel Goldman, an associate professor in the School of Physics at the Georgia Institute of Technology. “We wanted to make a systematic study of what makes flippers useful or effective. We’ve learned that the flow of the materials plays a large role in the strategy that can be used by either animals or robots.”

The research began in 2010 with a six-week study of hatchling loggerhead sea turtles emerging at night from nests on Jekyll Island, one of Georgia’s coastal islands. The research was done in collaboration with the Georgia Sea Turtle Center.

Nicole Mazouchova, then a graduate student in the Georgia Tech School of Biology, studied the baby turtles using a trackway filled with beach sand and housed in a truck parked near the beach. She recorded kinematic and biomechanical data as the turtles moved in darkness toward an LED light that simulated the moon.

Mazouchova and Goldman studied data from the 25 hatchlings, and were surprised to learn that they managed to maintain their speed regardless of the surface on which they were running.

“On soft sand, the animals move their limbs in such a way that they don’t create a yielding of the material on which they’re walking,” said Goldman. “That means the material doesn’t flow around the limbs and they don’t slip. The surprising thing to us was that the turtles had comparable performance when they were running on hard ground or soft sand.”

The key to maintaining performance seemed to be the ability of the hatchlings to control their wrists, allowing them to change how they used their flippers under different sand conditions.

“On hard ground, their wrists locked in place, and they pivoted about a fixed arm,” Goldman explained. “On soft sand, they put their flippers into the sand and the wrist would bend as they moved forward. We decided to investigate this using a robot model.”

That led to development of FlipperBot, with assistance from Paul Umbanhowar, a research associate professor at Northwestern University. The robot measures about 19 centimeters in length, weighs about 970 grams, and has two flippers driven by servo-motors. Like the turtles, the robot has flexible wrists that allow variations in its movement. To move through a track bed filled with poppy seeds that simulate sand, the robot lifts its flippers up, drops them into the seeds, then moves the flippers backward to propel itself.

Mazouchova, now a Ph.D. student at Temple University, studied many variations of gait and wrist position and found that the free-moving mechanical wrist also provided an advantage to the robot.

“In the robot, the free wrist does provide some advantage,” said Goldman. “For the most part, the wrist confers advantage for moving forward without slipping. The wrist flexibility minimizes material yielding, which disturbs less ground. The flexible wrist also allows both the robot and turtles to maintain a high angle of attack for their bodies, which reduces performance-impeding drag from belly friction.”

The researchers also noted that the robot often failed when limbs encountered material that the same limbs had already disturbed. That led them to re-examine the data collected on the hatchling turtles, some of which had also experienced difficulty walking across the soft sand.

“When we saw the turtles moving poorly, they appeared to be suffering from the same failure mode that we saw in the robot,” Goldman explained. “When they interacted with materials that had been previously disturbed, they tended to lose performance.”

Mazouchova and Goldman then worked with Umbanhowar to model the robot’s performance in an effort to predict how the turtle hatchlings should respond to different conditions. The predictions closely matched what was actually observed, closing the loop between robot and animal.

“The robot study allowed us to test how principles applied to the animals,” Goldman said.

While the results may not directly improve robot designs, what the researchers learned should contribute to a better understanding of the principles governing movement using flippers. That would be useful to the designers of robots that must swim through water and walk on land.

“A multi-modal robot might need to use paddles for swimming in water, but it might also need to walk in an effective way on the beach,” Goldman said. “This work can provide fundamental information on what makes flippers good or bad. This information could give robot designers clues to appendage designs and control techniques for robots moving in these environments.”

The research could ultimately provide clues to how turtles evolved to walk on land with appendages designed for swimming.

“To understand the mechanics of how the first terrestrial animals moved, you have to understand how their flipper-like limbs interacted with complex, yielding substrates like mud flats,” said Goldman. “We don’t have solid results on the evolutionary questions yet, but this certainly points to a way that we could address these issues.”

This research has been supported by the National Science Foundation under grant CMMI-0825480 and the Physics of Living Systems PoLS program, the U.S. Army Research Laboratory’s (ARL) Micro Autonomous Systems and Technology (MAST) Program under cooperative agreement W911NF-08-2-0004, the U.S. Army Research Office (ARO) and the Burroughs Wellcome Fund Career Award. Any conclusions are those of the authors and do not necessarily represent the official views of the NSF, ARL or ARO.

CITATION: Nicole Mazouchova, Paul B. Umbanhowar and Daniel I. Goldman, “Flipper-driven terrestrial locomotion of a sea turtle-inspired robot, (Bioinspiration & Biomimetics, 2013).

Research News
Georgia Institute of Technology
177 North Avenue
Atlanta, Georgia  30332-0181  USA

Media Relations Contact: John Toon (404-894-6986)(jtoon@gatech.edu).

Writer: John Toon

 

Media Contact: 

John Toon

Research News

jtoon@gatech.edu

(404) 894-6986

Summary: 

Based on a study of both hatchling sea turtles and "FlipperBot" -- a robot with flippers -- researchers have learned principles for how both robots and turtles move on granular surfaces such as sand.

Intro: 

Based on a study of both hatchling sea turtles and "FlipperBot" -- a robot with flippers -- researchers have learned principles for how both robots and turtles move on granular surfaces such as sand.

Alumni: 

Rita Garrido and Lorena Magana Zertuche Win Second Prize

Friday, April 19, 2013

Congratulations to Rita and Lorena for winning second prize for their individual posters on numerical relativity and gravitational wave astronomy!

 
Summary: 

Congratulations to Rita and Lorena

Intro: 

Congratulations to Rita and Lorena

Alumni: 

Bose-Einstein Condensates Evaluated for Communicating Among Quantum Computers

Thursday, April 11, 2013

Quantum computers promise to perform certain types of operations much more quickly than conventional digital computers. But many challenges must be addressed before these ultra-fast machines become available, among them, the loss of order in the systems – a problem known as quantum decoherence – which worsens as the number of bits in a quantum computer increases.

One proposed solution is to divide the computing among multiple small quantum computers that would work together much as today’s multi-core supercomputers team up to tackle big digital operations. The individual computers in such a system could communicate quantum information using Bose-Einstein condensates (BECs) – clouds of ultra-cold atoms that all exist in exactly the same quantum state. The approach could address the decoherence problem by reducing the number of bits necessary for a single computer.

Now, a team of physicists at the Georgia Institute of Technology has examined how this Bose-Einstein communication might work. The researchers determined the amount of time needed for quantum information to propagate across their BEC, essentially establishing the top speed at which such quantum computers could communicate.

“What we did in this study was look at how this kind of quantum information would propagate,” said Chandra Raman, an associate professor in Georgia Tech’s School of Physics. “We are interested in the dynamics of this quantum information flow not just for quantum information systems, but also more generally for fundamental problems in physics.”

The research is scheduled to be published in the April 19 online version of the journal Physical Review Letters. The research was funded by the U.S. Department of Energy (DOE) and the National Science Foundation (NSF). The work involved both an experimental physics group headed by Raman and a theoretical physics group headed by associate professor Carlos Sa De Melo, also in the Georgia Tech School of Physics.

The researchers first assembled a gaseous Bose-Einstein condensate that consisted of as many as three million sodium atoms cooled to nearly absolute zero. To begin the experiment, they switched on a magnetic field applied to the BEC that instantly placed the system out of equilibrium. That triggered spin-exchange collisions as the atoms attempted to transition from one ground state to a new one. Atoms near one another became entangled, pairing up with one atom’s spin pointing up, and the other’s pointing down. This pairing of opposite spins created a correlation between pairs of atoms that moved through the entire BEC as it established a new equilibrium.

The researchers, who included graduate student Anshuman Vinit and former postdoctoral fellow Eva Bookjans, measured the correlations as they spread through the cloud of cold atoms. At first, the quantum entanglement was concentrated in space, but over time, it spread outward like drop of dye diffuses through water.

“You can imagine having a drop of dye that is concentrated at one point in space,” Raman said. “Through diffusion, the dye molecules move throughout the water, slowly spreading throughout the entire system.”

The research could help scientists anticipate the operating speed for a quantum computing system composed of many cores communicating through a BEC.

“This propagation takes place on the time scale of ten to a hundred milliseconds,” Raman said. “This is the speed at which quantum information naturally flows through this kind of system. If you were to use this medium for quantum communication, that would be its natural time scale, and that would set the timing for other processes.”

Though relevant to communication of quantum information, the process also showed how a large system undergoing a phase transition does so in localized patches that expand to attempt to incorporate the entire system.

“An extended system doesn’t move from one phase to another in a uniform way,” said Raman. “It does this locally. Things happen locally that are not connected to one another initially, so you see this inhomogeneity.”

Beyond quantum computing, the results may also have implications for quantum sensing – and for the study of other physical systems that undergo phase transitions.

“Phase transitions have universal properties,” Raman noted. “You can take the phase transitions that happen in a variety of systems and find that they are described by the same physics. It is a unifying principle.”

Raman hopes the work will lead to new ways of thinking about quantum computing, regardless of its immediate practical use.

“One paradigm of quantum computing is to build a linear chain of as many trapped ions as possible and to simultaneously engineer away as many challenges as possible,” he said. “But perhaps what may be successful is to build these smaller quantum systems that can communicate with one another. It’s important to try as many things as possible and to keep an open mind. We need to try to understand these systems as well as we can.”

This research was supported by the Department of Energy (DOE) through grant DE-FG-02-03ER15450 and by the National Science Foundation under grant PHY-1100179. The conclusions in this article are those of the principal investigator and do not necessarily represent the official views of the DOE or the NSF.

CITATION: Vinit, Anshuman, et al., “Antiferromagnetic Spatial Ordering in a Quenched One-dimensional Spinor Gas, (Physical Review Letters, 2013).

Research News
Georgia Institute of Technology
177 North Avenue
Atlanta, Georgia  30332-0181

Media Relations Contact:  John Toon (404-894-6986)(jtoon@gatech.edu)

Writer: John Toon

Media Contact: 

John Toon

Research News

jtoon@gatech.edu

(404) 894-6986

Summary: 

Physicists have examined how Bose-Einstein condensates (BEC) might be used to provide communication among the nodes of a distributed quantum computer. The researchers determined the amount of time needed for quantum information to propagate across their BEC.

Intro: 

Physicists have examined how Bose-Einstein condensates (BEC) might be used to provide communication among the nodes of a distributed quantum computer. The researchers determined the amount of time needed for quantum information to propagate across their BEC.

Alumni: 

Prof. Tamara Bogdanovic, Wins Sloan Fellowship

Friday, March 29, 2013

 Awarded annually since 1955, the fellowships are given to early-career scientists and scholars whose achievements and potential identify them as rising stars, the next generation of scientific leaders.

“It is quite an honor to receive one of the Sloan Research Fellowships, which I see not only as a recognition of my research activities, but also as an invitation to do bigger and better things,” said Bogdanovic.

Bogdanovic came to Georgia Tech last August where she works on the astrophysics of supermassive black holes and the physics of the intracluster medium.

With black holes, she said her main objective is to understand how these massive bodies interact with stars and gas in the centers of their host galaxies in order to predict the observational signatures of these interactions, so that they can be recognized in the future.

“I also study the hot, x-ray emitting gas, the intracluster medium, that resides in the clusters of galaxies. This medium is an unmistakable tracer of the massive dark matter potentials of galaxy clusters,” she said.

The Sloan Research Fellowships are awarded in eight scientific fields - chemistry, computer science, economics, mathematics, evolutionary and computational biology, neuroscience, ocean sciences and physics. Candidates must be nominated by their fellow scientists and are selected by an independent panel of senior scholars. This year, 126 scholars from 61 colleges and universities in the U.S. and Canada were awarded these fellowships of $50,000.

“The Sloan Research Fellows are the best of the best among young scientists,” said Paul L. Joskow, president of the Alfred P. Sloan Foundation. “If you want to know were the next big scientific breakthrough will come from look to these extraordinary men and women. The foundation is proud to support them during this pivotal stage of their careers.”

Source: http://www.cos.gatech.edu/news/Tamara-Bogdanovic-Wins-Sloan-Fellowship

 
Summary: 

Tamara Bogdanovic, assistant professor in the School of Physics, was awarded a Sloan Research Fellowship from the Alfred P. Sloan Foundation.

Intro: 

Tamara Bogdanovic, assistant professor in the School of Physics, was awarded a Sloan Research Fellowship from the Alfred P. Sloan Foundation.

Alumni: 

"Terradynamics" Could Help Designers Predict How Legged Robots Will Move on Granular Media

Thursday, March 21, 2013

Using a combination of theory and experiment, researchers have developed a new approach for understanding and predicting how small legged robots – and potentially also animals – move on and interact with complex granular materials such as sand.

The research could help create and advance the field of “terradynamics” – a name the researchers have given to the science of legged animals and vehicles moving on granular and other complex surfaces. Providing equations to describe and predict this type of movement – comparable to what has been done to predict the motion of animals and vehicles through the air or water – could allow designers to optimize legged robots operating in complex environments for search-and-rescue missions, space exploration or other tasks.

“We now have the tools to understand the movement of legged vehicles over loose sand in the same way that scientists and engineers have had tools to understand aerodynamics and hydrodynamics,” said Daniel Goldman, a professor in the School of Physics at the Georgia Institute of Technology. “We are at the beginning of tools that will allow us to do the design and simulation of legged robots to not only predict their performance, but also to optimize designs and allow us to create new concepts.”

The research behind “terradynamics” was described in the March 22 issue of the journal Science. The research was supported by the National Science Foundation Physics of Living Systems program, the Army Research Office, the Army Research Laboratory, the Burroughs Wellcome Fund and the Miller Institute for Basic Research in Science of the University of California, Berkeley.

Robots such as the Mars Rover have depended on wheels for moving in complex environments such as sand and rocky terrain. Robots envisioned for autonomous search-and-rescue missions also rely on wheels, but as the vehicles become smaller, designers may need to examine alternative means of locomotion, Goldman said.

Existing techniques for describing locomotion on surfaces are complex and can’t take into account the intrusion of legs into a granular surface. To improve and simplify the understanding, Goldman and collaborators Chen Li and Tingnan Zhang examined the motion of a small legged robot as it moved on granular media. Using a 3-D printer, they created legs in a variety of shapes and used them to study how different configurations affected the robot’s speed along a track bed. They then measured granular force laws from experiments to predict forces on legs, and created simulation to predict the robot’s motion.

The key insight, according to Goldman, was that the forces applied to independent elements of the robot legs could be simply summed together to provide a reasonably accurate measure of the net force on a robot moving through granular media. That technique, known as linear superposition, worked surprisingly well for legs moving in diverse kinds of granular media.

“We discovered that the force laws affecting this motion are generic in a diversity of granular media, including poppy seeds, glass beads and natural sand,” said Li, who is now a Miller postdoctoral fellow at the University of California at Berkeley. “Based on this generalization, we developed a practical procedure for non-specialists to easily apply terradynamics in their own studies using just a single force measurement made with simple equipment they can buy off the shelf, such as a penetrometer.”

For more complicated granular materials, although the terradynamics approach still worked well, an additional factor – perhaps the degree to which particles resemble a sphere – may be required to describe the forces with equivalent accuracy.

Beyond understanding the basic physics principles involved, the researchers also learned that convex legs made in the shape of the letter “C” worked better than other variations.

“As long as the legs are convex, the robot generates large lift and small body drag, and thus can run fast,” Goldman said. “When the limb shape was changed to flat or concave, the performance dropped. This information is important for optimizing the energy efficiency of legged robots.”

Aerodynamic designers have long used a series of equations known as Navier-Stokes to describe the movement of vehicles through the air. Similarly, these equations also allow hydrodynamics designers to know how submarines and other vehicles move through water.

“Terradynamics” could provide designers with an efficient technique for understanding motion through media that flows around legs of terrestrial animals and robots.

“Using terradynamics, our simulation is not only as accurate as the established discrete element method (DEM) simulation, but also much more computationally efficient,” said Zhang, who is a graduate student in Goldman’s laboratory. “For example, to simulate one second of robot locomotion on a granular bed of five million poppy seeds takes the DEM simulation a month using computers in our lab. Using terradynamics, the simulation takes only 10 seconds.”

The six-legged experimental robot was just 13 centimeters long and weighed about 150 grams. Robots of that size could be used in the future for search-and-rescue missions, or to scout out unknown environments such as the surface of Mars. They could also provide biologists with a better understanding of how animals such as sand lizards run and kangaroo rats hop on granular media.

“From a biological perspective, this opens up a new area,” said Goldman, who has studied a variety of animals to learn how their locomotion may assist robot designers. “These are the kinds of tools that can help understand why lizards have feet and bodies of certain shapes. The problems associated with movement in sandy environments are as important to many animals as they are to robots.”

Beyond optimizing the design of future small robots, the work could also lead to a better understanding of the complex environment through which they will have to move.

“We think that the kind of approach we are taking allows us to ask questions about the physics of granular materials that no one has asked before,” Goldman added. “This may reveal new features of granular materials to help us create more comprehensive models and theories of motion. We are now beginning to get the rules of how vehicles move through these materials.”

This research was supported by the Burroughs Wellcome Fund, the Army Research Laboratory Micro Autonomous Systems and Technology Collaborative Technology Alliance (CTA W911NF-08-2-004), the Army Research Office (W911NF-11-1-0514), the National Science Foundation (NSF) Physics of Living Systems program (PHY-1150760) and the Miller Institute for Basic Research in Science at the University of California, Berkeley. Any conclusions are those of the principal investigators, and do not necessarily represent the official position of the Army Research Laboratory, the Army Research Office or the NSF.

CITATION: Chen Li, Tingnan Zhang, Daniel I. Goldman. “A Terradynamics of Legged Locomotion on Granular Media,” Science (2013): http://dx.doi.org/10.1126/science.1229163.

Research News
Georgia Institute of Technology
177 North Avenue
Atlanta, Georgia  30332-0181

Media Relations Contact: John Toon (404-894-6986)(jtoon@gatech.edu).

Writer: John Toon

Media Contact: 

John Toon

Research News

jtoon@gatech.edu

(404) 894-6986

Summary: 

Using a combination of theory and experiment, researchers have developed a new approach for understanding and predicting how small legged robots – and potentially also animals – move on and interact with complex granular materials such as sand.

Intro: 

Using a combination of theory and experiment, researchers have developed a new approach for understanding and predicting how small legged robots – and potentially also animals – move on and interact with complex granular materials such as sand.

Alumni: 

Dynamics Days US 2014

Thursday, January 2, 2014

Dynamics Days 2014

International Conference on Chaos and Nonlinear Dynamics

Georgia Tech Campus

Clough Undergraduate Learning Commons - Room 152

Host: Roman Grigoriev


Summary: 

Dynamic Days 2014: January 2-5

Intro: 

Dynamic Days 2014: January 2-5

Alumni: 

Fabrication on Patterned Silicon Carbide Produces Bandgap for Graphene-Based Electronics

Sunday, November 18, 2012

By fabricating graphene structures atop nanometer-scale “steps” etched into silicon carbide, researchers have for the first time created a substantial electronic bandgap in the material suitable for room-temperature electronics. Use of nanoscale topography to control the properties of graphene could facilitate fabrication of transistors and other devices, potentially opening the door for developing all-carbon integrated circuits.

Researchers have measured a bandgap of approximately 0.5 electron-volts in 1.4-nanometer bent sections of graphene nanoribbons. The development could provide new direction to the field of graphene electronics, which has struggled with the challenge of creating bandgap necessary for operation of electronic devices.

“This is a new way of thinking about how to make high-speed graphene electronics,” said Edward Conrad, a professor in the School of Physics at the Georgia Institute of Technology. “We can now look seriously at making fast transistors from graphene. And because our process is scalable, if we can make one transistor, we can potentially make millions of them.”

The findings were reported November 18 in the journal Nature Physics. The research, done at the Georgia Institute of Technology in Atlanta and at SOLEIL, the French national synchrotron facility, has been supported by the National Science Foundation Materials Research Science and Engineering Center (MRSEC) at Georgia Tech, the W.M. Keck Foundation and the Partner University Fund from the Embassy of France.

Researchers don’t yet understand why graphene nanoribbons become semiconducting as they bend to enter tiny steps – about 20 nanometers deep – that are cut into the silicon carbide wafers. But the researchers believe that strain induced as the carbon lattice bends, along with the confinement of electrons, may be factors creating the bandgap. The nanoribbons are composed of two layers of graphene.

Production of the semiconducting graphene structures begins with the use of e-beams to cut “trenches” into silicon carbide wafers, which are normally polished to create a flat surface for the growth of epitaxial graphene. Using a high-temperature furnace, tens of thousands of graphene ribbons are then grown across the steps, using photolithography.

During the growth, the sharp edges of trenches become smoother as the material attempts to regain its flat surface. The growth time must therefore be carefully controlled to prevent the narrow silicon carbide features from melting too much.

The graphene fabrication also must be controlled along a specific direction so that the carbon atom lattice grows into the steps along the material’s “armchair” direction. “It’s like trying to bend a length of chain-link fence,” Conrad explained. “It only wants to bend one way.”

The new technique permits not only the creation of a bandgap in the material, but potentially also the fabrication of entire integrated circuits from graphene without the need for interfaces that introduce resistance. On either side of the semiconducting section of the graphene, the nanoribbons retain their metallic properties.

“We can make thousands of these trenches, and we can make them anywhere we want on the wafer,” said Conrad. “This is more than just semiconducting graphene. The material at the bends is semiconducting, and it’s attached to graphene continuously on both sides. It’s basically a Shottky barrier junction.”

By growing the graphene down one edge of the trench and then up the other side, the researchers could in theory produce two connected Shottky barriers – a fundamental component of semiconductor devices. Conrad and his colleagues are now working to fabricate transistors based on their discovery.

Confirmation of the bandgap came from angle-resolved photoemission spectroscopy measurements made at the Synchrotron CNRS in France. There, the researchers fired powerful photon beams into arrays of the graphene nanoribbons and measured the electrons emitted.

“You can measure the energy of the electrons that come out, and you can measure the direction from which they come out,” said Conrad. “From that information, you can work backward to get information about the electronic structure of the nanoribbons.”

Theorists had predicted that bending graphene would create a bandgap in the material. But the bandgap measured by the research team was larger than what had been predicted.

Beyond building transistors and other devices, in future work the researchers will attempt to learn more about what creates the bandgap – and how to control it. The property may be controlled by the angle of the bend in the graphene nanoribbon, which can be controlled by altering the depth of the step.

“If you try to lay a carpet over a small imperfection in the floor, the carpet will go over it and you may not even know the imperfection is there,” Conrad explained. “But if you go over a step, you can tell. There are probably a range of heights in which we can affect the bend.”

He predicts that the discovery will create new activity as other graphene researchers attempt to utilize the results.

“If you can demonstrate a fast device, a lot of people will be interested in this,” Conrad said. “If this works on a large scale, it could launch a niche market for high-speed, high-powered electronic devices.”

In addition to Conrad, the research team included J. Hicks, M.S. Nevius, F. Wang, K. Shepperd, J. Palmer, J. Kunc, W.A. De Heer and C. Berger, all from Georgia Tech; A. Tejeda from the Institut Jean Lamour, CNES – Univ. de Nancy and the Synchrotron SOLEIL; A. Taleb-Ibrahimi from the CNRS/Synchrotron SOLEIL, and F. Bertran and P. Le Fevre from Synchrotron SOLEIL.

This research was supported by the National Science Foundation Materials Research Science and Engineering Center (MRSEC) at Georgia Tech under Grants DMR-0820382 and DMR-1005880, the W.M. Keck Foundation, and the Partner University Fund from the Embassy of France. The content of the article is the responsibility of the authors and does not necessarily represent the views of the National Science Foundation.

CITATION: Hicks, J., A wide-bandgap metal-semiconductor-metal nanostructure made entirely from graphene, Nature Physics (2012). http://dx.doi.org/10.1038/NPHYS2487.

Research News & Publications Office
Georgia Institute of Technology
177 North Avenue
Atlanta, Georgia  30332-0181

Media Relations Contact: John Toon (404-894-6986)(jtoon@gatech.edu)
Writer: John Toon

Media Contact: 

John Toon

Research News & Publications Office

(404) 894-6986

jtoon@gatech.edu

Summary: 

By fabricating graphene structures atop nanometer-scale “steps” etched into silicon carbide, researchers have for the first time created a substantial electronic bandgap in the material suitable for room-temperature electronics. Use of nanoscale topography to control the properties of graphene could facilitate fabrication of transistors and other devices, potentially opening the door for developing all-carbon integrated circuits.

Intro: 

By fabricating graphene structures atop nanometer-scale “steps” etched into silicon carbide, researchers have for the first time created a substantial electronic bandgap in the material suitable for room-temperature electronics. Use of nanoscale topography to control the properties of graphene could facilitate fabrication of transistors and other devices, potentially opening the door for developing all-carbon integrated circuits.

Alumni: 

Study Shows How a Hopping Robot Could Conserve its Energy

Friday, October 26, 2012

A new study shows that jumping can be much more complicated than it might seem. In research that could extend the range of future rescue and exploration robots, scientists have found that hopping robots could dramatically reduce their power demands by adopting a unique two-part “stutter jump.”

Taking a short hop before a big jump could allow spring-based “pogo-stick” robots to reduce their power demands as much as ten-fold. The formula for the two-part jump was discovered by analyzing nearly 20,000 jumps made by a simple laboratory robot under a wide range of conditions.

“If we time things right, the robot can jump with a tenth of the power required to jump to the same height under other conditions,” said Daniel Goldman, an assistant professor in the School of Physics at the Georgia Institute of Technology. “In the stutter jumps, we can move the mass at a lower frequency to get off the ground. We achieve the same takeoff velocity as a conventional jump, but it is developed over a longer period of time with much less power.”

The research was reported October 26 in the journal Physical Review Letters. The work was supported by the Army Research Laboratory’s MAST program, the Army Research Office, the National Science Foundation, the Burroughs Wellcome Fund and the GEM Fellowship.

Jumping is an important means of locomotion for animals, and could be important to future generations of robots. Jumping has been extensively studied in biological organisms, which use stretched tendons to store energy.

The Georgia Tech research into robot jumping began with a goal of learning how hopping robots would interact with complicated surfaces – such as sand, granular materials or debris from a disaster. Goldman quickly realized he’d need to know more about the physics of jumping to separate the surface issues from the factors controlled by the dynamics of jumping.

Inspired by student-directed experiments on the dynamics of hopping in his nonlinear dynamics and chaos class, Goldman asked Jeffrey Aguilar, a graduate student in the George W. Woodruff School of Mechanical Engineering, to construct the simplest jumping robot.

Aguilar built a one-kilogram robot that is composed of a spring beneath a mass capable of moving up and down on a thrust rod. Aguilar used computer controls to vary the starting position of the mass on the rod, the amplitude of the motion, the pattern of movement and the frequency of movement applied by an actuator built into the robot’s mass. A high-speed camera and a contact sensor measured and recorded the height of each jump.

Aguilar and Goldman then collaborated with theorists Professor Kurt Wiesenfeld and Alex Lesov, from the Georgia Tech School of Physics, to explain the results of the experiments.

The researchers expected to find that the optimal jumping frequency would be related to the resonant frequency of the spring and mass system, but that turned out not to be true. Detailed evaluation of the jumps showed that frequencies above and below the resonance provided optimal jumping – and additional analysis revealed what the researchers called the “stutter jump.”

“The preparatory hop allows the robot to time things such that it can use a lower power to get to the same jump height,” Goldman explained. “You really don’t have to move the mass rapidly to get a good jump.”

The amount of energy that can be stored in batteries can limit the range and duration of robotic missions, so the stutter jump could be helpful for small robots that have limited power. Optimizing the efficiency of jumping could therefore allow the robots to complete longer and more complex missions.

But because it requires longer to perform than a simple jump, the two-step jump may not be suitable for all conditions.

“If you’re a small robot and you want to jump over an obstacle, you could use low power by using the stutter jump even though that would take longer,” said Goldman. “But if a hazard is threatening, you may need to generate the additional power to make a quick jump to get out of the way.”

For the future, Goldman and his research team plan to study how complicated surfaces affect jumping. They are currently studying the effects of sand, and will turn to other substrates to develop a better understanding of how exploration or rescue robots can hop through them.

Goldman’s past work has focused on the lessons learned from the locomotion of biological systems, so the team is also interested in what the robot can teach them about how animals jump. “What we have learned here can function as a hypothesis for biological systems, but it may not explain everything,” he said.

The simple jumping robot turned out to be a useful system to study, not only because of the interesting behaviors that turned up, but also because the results were counter to what the researchers had expected.

“In physics, we often study the steady-state solution,” Goldman noted. “If we wait enough time for the transient phenomena to die off, then we can study what’s left. It turns out that in this system, we really care about the transients.”

This research is supported by the Army Research Laboratory under cooperative agreement number W911NF-08-2-004, by the Army Research Office under cooperative agreement W911NF-11-1-0514, and by the National Science Foundation under contract PoLS PHY-1150760. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Army Research Laboratory, the Army Research Office or the National Science Foundation.

CITATION: Aguilar, Jeffrey et al., “Lift-off dynamics in a simple jumping robot,” Physical Review Letters (2012): http://prl.aps.org/abstract/PRL/v109/i17/e174301

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Summary: 

A new study shows that jumping can be much more complicated than it might seem. In research that could extend the range of future rescue and exploration robots, scientists have found that hopping robots could dramatically reduce their power demands by adopting a unique two-part “stutter jump.”

Intro: 

A new study shows that jumping can be much more complicated than it might seem. In research that could extend the range of future rescue and exploration robots, scientists have found that hopping robots could dramatically reduce their power demands by adopting a unique two-part “stutter jump.”

Alumni: 

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