Duke Research Blog

Following the people and events that make up the research community at Duke.

Category: Physics (Page 1 of 9)

Can Science Explain Everything? An Exploration of Faith

The Veritas Forum, Feb. 1 in Penn Pavilion

I found out about this year’s Veritas Forum an hour before it started — a friend, who two years ago helped me explore Christianity (I grew up non-religious and was curious), mentioned it when we ran into each other at the Brodhead Center.

So, to avoid my academic responsibilities, I instead listened to Duke physics professor Ronen Plesser, a non-practicing Jew, Troy Van Voorhis, a Christian who teaches chemistry at MIT, and moderator Ehsan Samei, a professor of radiology and biomedical engineering at Duke. They discussed the God Hypothesis and how it fit in with their views as hard scientists.

Ehsan Samei

As someone who has relied on the scientific method instead of an omniscient, higher power to understand the natural world, I found it amazing how the speakers used relatable examples to demonstrate their belief that humans cannot explain everything. They started answering the classic question “Why is the sky blue?,” using more and more complex chemistry and physics as answers only led to more questions.

At some point, science-based explanations about how and why molecules move the way they do and where they come from didn’t suffice — at some point, it just seems like something, or someone, is responsible for the unexplainable.

Troy Van Voorhis of MIT

Something that Van Voorhis said particularly stuck in my mind. Reproducibility and objectivity form the “bedrock of science,” but are also it’s “grand limitations.” They are essential to corroborating the results of a scientific study or experiment, but can they really confirm something as scientific truth? When does reproducibility adequately overcome variation in data, and can something be defined as truly objective?

So, I sat there in the audience, thinking about alternatives to explaining morals, ethics, and the feeling of being human since, to paraphrase Plesser, science just doesn’t cut it in these cases. He elaborated on faith after branching off Van Voorhis’ point of view. Plesser’s explanation made the overlap of science and religion become more and more prominent. As someone who also does not practice a religion, I felt that his comparison of faith in science and faith in religion comforting.

Ronan Plesser

Even though I still struggle to fully accept Christ, I was aware of the similarities of the path to scientific and spiritual enlightenment. In science, incessant questioning of our surroundings is necessary to understand the Truths of our world (“otherwise we wouldn’t be publishing papers and we would be out of our jobs!”), as are the calls to God to come down and help people improve themselves. It is impossible, then, to avoid faith entirely since being human inherently involves belief in some sort of system.

I was wowed by the connections that the three men were making between the seemingly divergent areas. I was even more astonished, though, by their emphasis on humility. They exemplified the need for understanding and patience when describing scientific theories and religious ideologies. To be humble is to accept that people have differences and to acknowledge these differences is the only way to reduce conflicts between religion and science.

Post by Stella Wang

Farewell, Electrons: Future Electronics May Ride on New Three-in-One Particle

“Trion” may sound like the name of one of the theoretical particles blamed for mucking up operations aboard the Starship Enterprise.

But believe it or not, trions are real — and they may soon play a key role in electronic devices. Duke researchers have for the first time pinned down some of the behaviors of these one-of-a-kind particles, a first step towards putting them to work in electronics.

A carbon nanotube, shaped like a rod, is wrapped in a helical coating of polymer

Three-in-one particles called trions — carrying charge, energy and spin — zoom through special polymer-wrapped carbon nanotubes at room temperature. Credit: Yusong Bai.

Trions are what scientists call “quasiparticles,” bundles of energy, electric charge and spin that zoom around inside semiconductors.

“Trions display unique properties that you won’t be able to find in conventional particles like electrons, holes (positive charges) and excitons (electron-hole pairs that are formed when light interacts with certain materials),” said Yusong Bai, a postdoctoral scholar in the chemistry department at Duke. “Because of their unique properties, trions could be used in new electronics such as photovoltaics, photodetectors, or in spintronics.”

Usually these properties – energy, charge and spin – are carried by separate particles. For example, excitons carry the light energy that powers solar cells, and electrons or holes carry the electric charge that drives electronic devices. But trions are essentially three-in-one particles, combining these elements together into a single entity – hence the “tri” in trion.

A diagram of how a trion is formed in carbon nanotubes.

A trion is born when a particle called a polaron (top) marries an exciton (middle). Credit: Yusong Bai.

“A trion is this hybrid that involves a charge marrying an exciton to become a uniquely distinct particle,” said Michael Therien, the William R. Kenan, Jr. Professor of Chemistry at Duke. “And the reason why people are excited about trions is because they are a new way to manipulate spin, charge, and the energy of absorbed light, all simultaneously.”

Until recently, scientists hadn’t given trions much attention because they could only be found in semiconductors at extremely low temperatures – around 2 Kelvin, or -271 Celcius. A few years ago, researchers observed trions in carbon nanotubes at room temperature, opening up the potential to use them in real electronic devices.

Bai used a laser probing technique to study how trions behave in carefully engineered and highly uniform carbon nanotubes. He examined basic properties including how they are formed, how fast they move and how long they live.

He was surprised to find that under certain conditions, these unusual particles were actually quite easy to create and control.

“We found these particles are very stable in materials like carbon nanotubes, which can be used in a new generation of electronics,” Bai said. “This study is the first step in understanding how we might take advantage of their unique properties.”

The team published their results Jan. 8 in the Proceedings of the National Academy of Sciences.

Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes,” Yusong Bai, Jean-Hubert Olivier, George Bullard, Chaoren Liu and Michael J. Therien. Proceedings of the National Academy of Sciences, Jan. 8, 2018 (online) DOI: 10.1073/pnas.1712971115

Post by Kara Manke

Glitter and Jell-O Reveal the Science of Oobleck

A black and white image showing a circular disk dropping into a container of oobleck

Mixing black glitter with oobleck allowed researchers to track the movement of individual cornstarch particles after a sudden impact. A computer program locked onto pieces of glitter and illustrated their motion. Credit: Melody Lim.

What do gelatin and glitter have to do with serious science? For some experiments, a lot! Duke alumna Melody Lim used jiggly Jell-O and a just a pinch of glitter to solve a scientific mystery about the curious goo many like to call oobleck.

To the uninitiated, oobleck is almost magic. The simple mixture of cornstarch and water feels solid if you squeeze it, but moments later runs through your fingers like water. You can dance across a bathtub full of oobleck, but stand still for too long and you will be sucked into a goopy mess. Not surprisingly, the stuff is a Youtube favorite.

Oobleck is an example of what scientists call a non-Newtonian fluid, a liquid whose viscosity – how easily it changes shape and flows – depends upon the force that is applied. But exactly how it is that this material switches from solid to liquid and back again has remained a mystery to scientists.

A piece of gelatin being squeezed viewed through a circular polarizer

This blogger mixed up a batch of jello to see the photoelastic effect for herself. When viewed with polarized light – from an iPhone screen and a circular polarizer – the jello changes color when squeezed.

“Water is simple to understand, and so is cornstarch,” said Lim, ’16, who is currently a graduate student at the University of Chicago. “However, a combination of the two produces this ‘liquid’ that ripples and flows, solidifies beneath your feet if you run on it, then turns back into a liquid if you stop running and stand still. I wanted to know why.”

The question beguiling scientists was whether sudden impact causes the cornstarch particles to “jam” into a solid like cement, or whether the suspension remains liquid but simply moves too slowly for its liquid-like properties to be apparent — similar to what happens if you skip a rock off the surface of a lake.

“There are these two opposing pictures,” said Robert Behringer, James B. Duke Professor of Physics at Duke. “Either you squish the material and turn it into cement temporarily, or you simply transmit the stress from the impactor straight to the boundary.”

Lim did two sets of experiments to find out which way oobleck works. In one experiment, she mixed black glitter into a transparent channel filled with oobleck, and then used a high-speed camera to watch how the material responded to the impact. The glitter let her track the motion of individual particles after the disc hit.

A piece of gelatin changes color when you squeeze it.

The photoelastic effect in gelatin.

Her video shows that the particles near the impact site jam and become solid, forming what the researchers call a “mass shock” wave that travels slowly through the suspension.

In a second set of experiments, Lim placed the oobleck in a container lined with gelatin, the main ingredient in Jell-O – besides sugar and food dye, of course. Gelatin is what is called a photoelastic material, which means that applying pressure bends light that travels through it, like a prism.

“Next time you eat Jell-O, get out your sunglasses and get somebody else’s sunglasses and look between them,” Behringer said. “Because if you give it a shake you should see all these stress patterns bouncing around.”

After the metal disc hit the oobleck, the gelatin let Lim see how fast the resulting pressure wave traveled through the material and reached the boundary.

A black and white image showing pressure waves traveling through a transparent material after impact

The researchers poured oobleck into a clear container lined with gelatin, a material that bends light when a pressure is applied to it. They saw that the force of a sudden impact is rapidly transmitted through the oobleck and to the boundary with the gelatin. Credit: Melody Lim.

They found that when the impact is sudden, the pressure wave traveled to the gelatin boundary faster than the “mass shock” wave. This means that the reason oobleck appears solid after a sudden impact is because the force of the collision is quickly transmitted to a solid boundary.

“If you are running across the water, that actually puts you into an impact velocity range where the pressure wave is significantly faster than the mass shock,” Behringer said. “Whereas if you try to walk across it, the impact speeds are slow, and the system actually doesn’t have the ability to transport the momentum quickly through the material and so you just sink in.”

“If you’d told me when I started that I would line a narrow container with Jell-o, add cornstarch, water, and black glitter, drop a piece of metal on it, then publish a paper on the results, I would have laughed at you,” Lim said.

CITATION: “Force and Mass Dynamics in Non-Newtonian Suspensions,” Melody X. Lim, Jonathan Barés, Hu Zheng and Robert P. Behringer. Physical Review Letters, Nov. 3, 2017. DOI: 10.1103/PhysRevLett.119.184501

Post by Kara Manke

Morphogenesis: All Guts and Morning Glories

What is morphogenesis? Morphogenesis examines the development of the living organisms’ forms.

It also is an area of research for Lakshminarayanan Mahadevan, Professor of Applied Mathematics, Organismic and Evolutionary Biology and Physics at Harvard University. On his presentation in the Public Lectures Unveiling Math (PLUM) series here at Duke, he credited the beginnings of morphogenesis to D’Arcy Wentworth Thompson, author of the book On Growth and Form.

Mathematically, morphogenesis focuses on how different rates of growth change the shapes of organisms as they develop. Cell number, cell size, cell shape, and cell position comprise the primary cellular factors of multicellular morphogenesis, which studies larger structures than individual cells and is Mahadevan’s focus.

Effects on tissues appear through changes in sizes, connectivities, and shapes, altering the phenotype, or the outward physical appearance. All these variables change in space and time. Professor Mahadevan presented on morphogenesis studies that have been conducted on plant shoots, guts, and brains.

Research on plant shoots often concentrates on the question, “Why do plant shoots grow in such a wide variety of directions and what determines their shapes?” The picture below shows the different postures appearances of plant shoots from completely straight to leaning to hanging.

Can morphogenesis make sense of these differences? Through mathematical modeling, two stimuli for shoots’ shapes was determined: gravity and itself. Additionally, elasticity as a function of the shoots’ weight plays a role in the mathematical models of plant shoots’ shapes which appear in Mahadevan’s paper co-written with a fellow professor, Raghunath Chelakkot. Mahadevan also explored the formation of flower and leaf shapes with these morphogenesis studies. 

Over twenty feet of guts are coiled up inside you. In order to fit these intestines inside the mammals, they must coil and loop. But what variables determine how these guts loop around? To discover the answer to this question, Mahadevan and other researchers examined chick embryos which increase their gut lengths by a factor greater than twenty over a twelve-day span. They were able to create a physical model using a rubber tube sewn to a sheet that followed the same patterns as the chicks’ guts. Through their observation of not only chicks but also quail and mice, Mahadevan determined that the morphogenesis of the guts has no dependence on genetics or any other microscopic factors.

Mahadevan’s study of how the brain folds occurs through MRI images of human fetal development. Initially, barely any folding exists on fetal brains but eventually the geometry of the surrounding along with local stress forms folds on the brain. By creating a template with gel and treating it to mimic the relationship between the brain’s gray matter and white matter, Mahadevan along with other researchers discovered that they could reproduce the brain’s folds. Because they were able to recreate the folds through only global geometry and local stress, they concluded that morphogenesis evolution does not depend on microscopic factors such as genetics. Further, by examining if folding regions correlate with the activity regions of the brain, questions about the effect of physical form on abilities and the inner functions of the brain.

  

     

Duke’s Researchers Are 1 Percent of the Top 1 Percent

This year’s listing of the world’s most-cited researchers is out from Clarivate Analytics, and Duke has 34 names on the list of 3,400 researchers from 21 fields of science and social science.

Having your publication cited in a paper written by other scientists is a sign that your work is significant and advances the field. The highly-cited list includes the top 1 percent of scientists cited by others in the years 2005 to 2015.

“Citations by other scientists are an acknowledgement that the work our faculty has published is significant to their fields,” said Vice Provost for Research Lawrence Carin. “In research, we often talk about ‘standing on the shoulders of giants,’ as a way to explain how one person’s work builds on another’s. For Duke to have so many of our people in the top 1 percent indicates that they are leading their fields and their work is indeed something upon which others can build.”

In addition to the Durham researchers, Duke-NUS, our medical school in Singapore,  claims another 13 highly cited scientists.

The highly-cited scientists on the Durham campus are:

Barton Haynes

CLINICAL MEDICINE
Robert Califf
Christopher Granger
Kristin Newby
Christopher O’Connor
Erik Magnus Ohman
Manesh Patel
Michael Pencina
Eric Peterson

ECONOMICS AND BUSINESS
Dan Ariely
John Graham
Campbell Harvey

Drew Shindell

ENVIRONMENT/ECOLOGY
John Terborgh
Mark Wiesner

GEOSCIENCES
Drew Shindell

IMMUNOLOGY
Barton Haynes

MATHEMATICS
James Berger

Georgia Tomaras

Georgia Tomaras

MICROBIOLOGY
Bryan Cullen
Barton Haynes
David Montefiori
Georgia Tomaras

PHARMACOLOGY & TOXICOLOGY
Robert Lefkowitz

PHYSICS
David R. Smith

PLANT AND ANIMAL SCIENCE
Philip Benfey

Terrie Moffitt

Terrie Moffitt

PSYCHIATRY & PSYCHOLOGY
Angold, Adrian
Caspi, Avshalom
Copeland, William E
Costello, E J
Dawson, Geraldine
Keefe, Richard SE
McEvoy, Joseph P
Moffitt, Terrie E

SOCIAL SCIENCES (GENERAL)
Deverick Anderson
Kelly Brownell
Michael Pencina

Cheating Time to Watch Liquids do the Slow Dance

Colorful spheres simulating liquid molecules shift around inside a cube shape

The team’s new algorithm is able to simulate molecular configurations of supercooled liquids below the glass transition. The properties of these configurations are helping to solve a 70-year paradox about the entropy of glasses. Credit: Misaki Ozawa and Andrea Ninarello, Université de Montpellier.

If you could put on a pair of swimming goggles, shrink yourself down like a character from The Magic School Bus and take a deep dive inside a liquid, you would see a crowd of molecules all partying like it’s 1999.

All this frenetic wiggling makes it easy for molecules to rearrange themselves and for the liquid as a whole to change shape. But for supercooled liquids — liquids like honey that are cooled below their freezing point without crystallizing – the lower temperature slows down the dancing like Etta James’ “At Last.” Lower the temperature enough, and the slow-down can be so dramatic that it takes centuries or even millennia for the molecules to rearrange and the liquid to move.

Scientists can’t study processes that last longer than their careers. But Duke chemists and their Simons Foundation collaborators have found a way to cheat time, simulating the slow dance of deeply supercooled liquids. Along the way, they have found new physical properties of “aged” supercooled liquids and glasses.

A droplet rises above a surface of water

Credit: Ruben Alexander via Flickr.

To understand just how slow deeply supercooled liquids move, consider the world’s longest-running experiment, the University of Queensland’s Pitch Drop Experiment. A single drop of pitch forms every eight to thirteen years — and this pitch is moving faster than deeply supercooled liquids.

“Experimentally there is a limit to what you can observe, because even if you managed to do it over your entire career, that is still a maximum of 50 years,” said Patrick Charbonneau, an associate professor of chemistry and physics at Duke. “For many people that was considered a hard glass ceiling, beyond which you couldn’t study the behavior of supercooled liquids.”

Charbonneau, who is an expert on numerical simulations, said that using computers to simulate the behavior of supercooled liquids has even steeper time limitations. He estimates that, given the current rate of computer advancement, it would take 50 to 100 years before computers would be powerful enough for simulations to exceed experimental capabilities – and even then the simulations would take months.

To break this glass ceiling, the Charbonneau group collaborated with Ludovic Berthier and his team, who were developing an algorithm to bypass these time constraints. Rather than taking months or years to simulate how each molecule in a supercooled liquids jiggles around until the molecules rearrange, the algorithm picks individual molecules to swap places with each other, creating new molecular configurations.

This allows the team to explore new configurations that could take millennia to form naturally. These “deeply supercooled liquids and ultra-aged glasses” liquids are at a lower energy, and more stable, than any observed before.

“We were cheating time in the sense that we didn’t have to follow the dynamics of the system,” Charbonneau said. “We were able to simulate deeply supercooled liquids well beyond is possible in experiments, and it opened up a lot of possibilities.”

Two columns of blue and red spheres represent simulations of vapor-deposited glasses.

Glasses that are grown one layer at a time have a much different structure than bulk glasses. The team used their new algorithm to study how molecules in these glasses rearrange, and found that at low temperatures (right), only the molecules at the surface are mobile. The results may be used to design better types of glass for drug delivery or protective coatings. Credit: Elijah Flenner.

Last summer, the team used this technique to discover a new phase transition in low-temperature glasses. They recently published two additional studies, one of which sheds light on the “Kauzmann paradox,” a 70-year question about the entropy of supercooled liquids below the glass transition. The second explores the formation of vapor-deposited glasses, which have applications in drug delivery and protective coatings.

“Nature has only one way to equilibrate, by just following the molecular dynamics,” said Sho Yaida, a postdoctoral fellow in Charbonneau’s lab. “But the great thing about numerical simulations is you can tweak the algorithm to accelerate your experiment.”

Configurational entropy measurements in extremely supercooled liquids that break the glass ceiling.” Ludovic Berthier, Patrick Charbonneau, Daniele Coslovich, Andrea Ninarello, Misaki Ozawa and Sho Yaida. PNAS, Oct. 24, 2017. DOI: 10.1073/pnas.1706860114

The origin of ultrastability in vapor-deposited glasses.” Ludovic Berthier, Patrick Charbonneau, Elijah Flenner and Francesco Zamponi. PRL, Nov. 1, 2017. DOI: 10.1103/PhysRevLett.119.188002

Post by Kara Manke

From Solid to Liquid and Back Again

A black and white moving image of a ball being pulled out from under a pile of circular discs

Force chains erupt as an “intruder” is yanked from beneath a pile of circular discs, which are designed to simulate a granular material. The entire process takes less than one second. Credit: Yue Zhang, Duke University.

You can easily walk across the sand on a beach. But step into a ball pit, and chances are you’ll fall right through.

Sand and ball pits are both granular materials, or materials that are made of collections of much smaller particles or grains. Depending on their density and how much force they experience, granular materials sometimes behave like liquids — something you fall right through — and sometimes “jam” into solids, making them something you can stand on.

“In some cases, these little particles have figured out how to actually form solid-like structures,” said Robert P. Behringer, James B. Duke Professor of Physics. “So why don’t they always just go squirting sideways and relax all the stress?”

Physicists do not yet understand exactly when and how jamming occurs, but Behringer’s team at Duke is on the case. The group squishes, stretches, hits, and pulls at granular materials to get a better picture of how and why they behave like they do. The team recently presented a whopping 10 papers at the 2017 Powders and Grains Conference, which occurred from July 3-7, 2017 in Montpellier, France.

Many of these studies use one of the lab’s favorite techniques, which is to create granular materials from small transparent discs that are about half an inch to an inch in diameter. These discs are made of a material which, thanks to the special way it interacts with light, changes color when squished. This effect allows the team to watch how the stress within the material changes as various forces are applied.

A blue and green moving image of spinning discs

As the wheels turn, shear strain between the discs creates a dense web of inter-particle forces. Credit: Yiqiu Zhao, Duke University.

In one experiment, graduate student Yue Zhang used a high-speed camera to catch the stress patterns as a ball on a string is yanked out from a pile of these discs. In the video, the ball first appears to be stuck under the pile, and then suddenly gives way after enough force is applied — not unlike what you might experience pulling a tent stake out of the ground, or opening the lid on a pesky pickle jar.

“The amusing thing is that you start trying to pull, you add more force, you add more force, and then at some point you pull so hard that you hit yourself in the head,” Behringer said.

The team was surprised to find that the stress patterns created by the ball, which Behringer says look “like hair all standing on end,” are almost identical to the stress of impact, only in reverse.

“What you see is even though you are just gradually gradually pulling harder and harder, the final dynamics are in some sense the same dynamics that you get on impact,” Behringer said.

In another experiment, the team examined what happens in granular materials under shear strain, which is similar to the force your fingers exert on one another when you rub them together.

Graduate student Yiqiu Zhao placed hundreds of these discs onto a circular platform made of a series of flat, concentric rings, each of which is controlled by a separate motor. As the rings turn at different speeds, the particles rub against one another, creating a shear stress.

An image of an experimental set up in a lab

Beneath the small transparent discs lie a series of concentric wheels, each attached to its own motor. By turning these platforms at different speeds, Yiqiu Zhao can observe how shear strain affects the discs.

“We have about twenty stepper motors here, so that we can rotate all the rings to apply a shear not only from the outside boundary, but also from everywhere inside the bulk of the material,” Zhao said. This ensures that each particle in the circle experiences a similar amount of shear.

“One of the key intents of this new experiment was to find a way that we could shear until the cows come home,” Behringer said. “And if it takes a hundred times more shear than I could get with older experiments, well we’ll get it.”

As the rings turn, videos of the material show forces snaking out from the inner circle like lightning bolts. They found that by applying enough shear, it is possible to make the material like a solid at much lower densities than had been seen before.

“You can actually turn a granular fluid into a granular solid by shearing it,” Behringer said. “So it is like you don’t put your ice in the refrigerator, you put it in one of these trays and you shear the tray and it turns into ice.”

Kara J. Manke, PhDPost by Kara Manke

3D Virus Cam Catches Germs Red-Handed

A 3D plot of a virus wiggling around

The Duke team used their 3D virus cam to spy on this small lentivirus as it danced through a salt water solution.

Before germs like viruses can make you sick, they first have to make a landing on one of your cells — Mars Rover style — and then punch their way inside.

A team of physical chemists at Duke is building a microscope so powerful that it can spot these minuscule germs in the act of infection.

The team has created a new 3D “virus cam” that can spy on tiny viral germs as they wriggle around in real time. In a video caught by the microscope, you can watch as a lentivirus bounces and jitters through an area a little wider that a human hair.

Next, they hope to develop this technique into a multi-functional “magic camera” that will let them see not only the dancing viruses, but also the much larger cell membranes they are trying breech.

“Really what we are trying to investigate is the very first contacts of the virus with the cell surface — how it calls receptors, and how it sheds its envelope,” said group leader Kevin Welsher, assistant professor of chemistry at Duke. “We want to watch that process in real time, and to do that, we need to be able to lock on to the virus right from the first moment.”

A 3D plot spells out the name "Duke"

To test out the microscope, the team attached a fluorescent bead to a motion controller and tracked its movements as it spelled out a familiar name.

This isn’t the first microscope that can track real-time, 3D motions of individual particles. In fact, as a postdoctoral researcher at Princeton, Welsher built an earlier model and used it to track a bright fluorescent bead as it gets stuck in the membrane of a cell.

But the new virus cam, built by Duke postdoc Shangguo Hou, can track particles that are faster-moving and dimmer compared to earlier microscopes. “We were trying to overcome a speed limit, and we were trying to do so with the fewest number of photons collected possible,” Welsher said.

The ability to spot dimmer particles is particularly important when tracking viruses, Welsher said. These small bundles of proteins and DNA don’t naturally give off any light, so to see them under a microscope, researchers first have to stick something fluorescent on them. But many bright fluorescent particles, such as quantum dots, are pretty big compared to the size of most viruses. Attaching one is kind of like sticking a baseball onto a basketball – there is a good chance it might affect how the virus moves and interacts with cells.

The new microscope can detect the fainter light given off by much smaller fluorescent proteins – which, if the virus is a basketball, are approximately the size of a pea. Fluorescent proteins can also be inserted to the viral genome, which allows them to be incorporated into the virus as it is being assembled.

“That was the big move for us,” Welsher said, “We didn’t need to use a quantum dot, we didn’t need to use an artificial fluorescent bead. As long as the fluorescent protein was somewhere in the virus, we could spot it.” To create their viral video, Welsher’s team enlisted Duke’s Viral Vector Core to insert a yellow fluorescent protein into their lentivirus.

Now that the virus-tracking microscope is up-and-running, the team is busy building a laser scanning microscope that will also be able to map cell surfaces nearby. “So if we know where the particle is, we can also image around it and reconstruct where the particle is going,” Welsher said. “We hope to adapt this to capturing viral infection in real time.”

Robust real-time 3D single-particle tracking using a dynamically moving laser spot,” Shangguo Hou, Xiaoqi Lang and Kevin Welsher. Optics Letters, June 15, 2017. DOI: 10.1364/OL.42.002390

Kara J. Manke, PhDPost by Kara Manke

Cooking Up “Frustrated” Magnets in Search of Superconductivity

Sara Haravifard

A simplified version of Sara Haravifard’s recipe for new superconductors, by the National High Magnetic Field Laboratory

Duke physics professor Sara Haravifard is mixing, cooking, squishing and freezing “frustrated” magnetic crystals in search of the origins of superconductivity.

Superconductivity refers to the ability of electrons to travel endlessly through certain materials, called superconductors, without adding any energy — think of a car that can drive forever with no gas or electricity. And just the way gas-less, charge-less cars would make travel vastly cheaper, superconductivity has the potential to revolutionize electronics and energy industry.

But superconductors are extremely rare, and are usually only superconductive at extremely cold temperatures — too cold for any but a few highly specialized applications. A few “high-temperature” superconductors have been discovered, but scientists are still flummoxed at why and how these superconductors exist.

Haravifard hopes that her magnet experiments will reveal the origins of high-temperature superconductivity so that researchers can design and build new materials with this amazing property. In the process, her team may also discover materials that are useful in quantum computing, or even entirely new states of matter.

Learn more about their journey on this fascinating infographic by The National High Magnetic Field Laboratory.

Infographic describing magnetic crystal research

Infographic courtesy of the National High Magnetic Field Laboratory

Kara J. Manke, PhD

Post by Kara Manke

Trapping Light to Enhance Material Properties

Professor Mikkelsen is the Nortel Networks Assistant Professor of Electrical and Computer Engineering and Assistant Professor of Physics at Duke University.

A version of this article appeared in Pratt’s 2017 DukEngineer magazine.

Professor Maiken H. Mikkelsen uses optics to tailor the properties of materials, making them stronger and lighter than anything found in nature. This distinguished researcher also teaches my ECE 340: Optics and Photonics course, giving me a wonderful opportunity to ask about her research and experience at the Photonics Asia conference held in China in October 2016.

Below is an edited transcript of our interview.

Q: What sparked your interest in optics and photonics?
I was really excited about doing hands-on research where you could actually probe nanoscale and quantum phenomena from optical experiments. I started out looking into condensed matter and quantum information science and currently observe delicately designed nanostructures. Optics is, to some extent, a tool to modify the properties of materials.

Q: What does your lab do and how do students contribute?
During the last few years, my students and I have been structuring materials on the nanoscale to modify the local electromagnetic environment, which makes these materials behave in new ways. Students play a key role in all aspects of the research, from nanofabrication to performing optical experiments and presenting the results to the scientific community at conferences all over the world. The lab uses tiny metal structures to concentrate the incoming electromagnetic field of light to very small volumes — a research area known as plasmonics. Placing other materials in the near field of this modified environment causes the electrons to behave completely differently.

Platform based on metal nanostructures that allows the lab to dramatically enhance the radiative properties of emitters and other materials.

By controlling how these electrons behave and modifying the geometry of the material, we can gain a deeper understanding of the light-matter interactions. Combining these techniques with our optical experiments shows modifications to material properties that are much stronger than has been seen before. It’s been very exciting!

Q: And this research is what you presented at the Photonics Asia conference?
Yes. With this knowledge, we can enhance the properties of materials significantly, which in the future could lead to ultra-fast and much better LEDs, more efficient photodetectors, or more efficient solar cells and sensors. In Beijing, China, I gave an overview of this research at the leading meeting for the photonics and optics industries in Asia, as well as several other conferences and universities. It was very fulfilling to see how the research I do in a dark lab actually gets noticed around the world. It is always deeply inspiring to learn about recent research breakthroughs from other research groups.

Q: What is the main purpose of trying to find these improved materials?
I am motivated by furthering our fundamental understanding, such as how do light and matter interact when we get to really small scales and how this interaction can be leveraged to achieve useful properties. I believe you often achieve the biggest technological breakthroughs when you’re not trying to solve one particular problem, but creating new materials that could lay the groundwork for a wide range of new technologies. For example, semiconductor materials, with a set of properties that are found naturally, are the cornerstone of most modern technologies. But if you imagine that you now have an entirely new set of building blocks with tailored properties instead, we could revolutionize a lot of different technologies down the road.

The Mikkelsen Research Group. Back row, left to right: Qixin Shen, Andrew Traverso, Maiken Mikkelsen, Guoce Yang, Jon Stewart, Andrew Boyce. Front row, left to right: Wade Wilson, Daniela Cruz, Jiani Huang, Tamra Nebabu.

By improving or completely changing the fabrication technique of these light-matter interactions, new properties begin to emerge. Generally, there’s always a big desire to have something that’s lighter, smaller, more efficient and more flexible. One of the applications we’re targeting with this research is ultrafast LEDs. While future devices might not use this exact approach, the underlying physics will be crucial.

About a year ago, Facebook contacted me and was interested in utilizing our research for omnidirectional detectors that could be ultrafast and detect signals from a large range of incidence angles. This has led to a fruitful collaboration and is one example of how fundamental research can have applications in a wide range of areas — some that you may not even have imagined when you started!

 

Q: What would be your advice to young researchers still trying to decide a career path for themselves or those interested in optics and photonics?
What really helped me was starting to do undergraduate research. I listened to talks by different faculty, asked them to do undergraduate research, and worked on a volunteer basis in their labs. I think that’s really a great way to see if you’re interested in research — use the amazing opportunities both at Duke and around the country. Doing research requires a lot of patience, but I think no two days are the same; there’s always a lot of creativity involved while troubleshooting new problems. After all, if it was easy or if we knew how to do it, it would have already been done. But it hasn’t, so we have to figure it out — I think that is a lot of fun. Doing internships in optics and photonics companies is also another option to learn more about research and development in the industry. Get as many experiences as possible and give things a chance!

Professor Mikkelsen is best known for the first demonstration of nondestructive readout of a single electron spin, ultrafast manipulation of a single spin using all-optical techniques, and extreme radiative decay engineering using nanoantennas.

Mikkelsen has received numerous accolades, including the Cottrell Scholar Award, the Maria Goeppert Mayer Award, and a “triple crown” of Young Investigator Awards from the Air Force, Army and Navy. Her work has been published in the journals Science, Nature Photonics, and Nature Physics, to name a few. Professor Mikkelsen enjoys hiking, gardening, playing tennis, and traveling in her free time.

Learn more at mikkelsen.pratt.duke.edu.

Written by Anika Radiya-Dixit

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