Aurelia Butler

Both literally and figuratively, light pervades the world. It banishes darkness, conveys telecommunications signals between continents and makes visible the invisible, from faraway galaxies to the smallest bacterium. Light can also help heat the plasma within ring-shaped devices known as tokamaks as scientists worldwide strive to harness the fusion process to generate green electricity.
Now, scientists have made discoveries about light particles known as photons that could aid the quest for fusion energy. By performing a series of mathematical calculations, the researchers found that one of a photon’s basic properties is topological, meaning that it doesn’t change even as the photon moves through different materials and environments.
This property is polarization, the direction — left or right — that electric fields take as they move around a photon. Because of basic physical laws, a photon’s polarization helps determine the direction the photon travels and limits its movement. Therefore, a beam of light made up of only photons with one type of polarization cannot spread into every part of a given space. These findings demonstrate the Princeton Plasma Physics Laboratory’s (PPPL) strengths in theoretical physics and fusion research.
“Having a more accurate understanding of the fundamental nature of photons could lead to scientists designing better light beams for heating and measuring plasma,” said Hong Qin, a principal research physicist at the U.S. Department of Energy’s (DOE) PPPL and co-author of apaper reporting the results in Physical Review D.
Simplifying a complicated problem
Though the researchers were studying individual photons, they were doing so as a way to solve a larger, more difficult problem — how to use beams of intense light to excite long-lasting perturbations in the plasma that could help maintain the high temperatures needed for fusion.
Known as topological waves, these wiggles often occur on the border of two different regions, like plasma and the vacuum in tokamaks at its outer edge. They are not especially exotic — they occur naturally in Earth’s atmosphere, where they help produce El Niño, a gathering of warm water in the Pacific Ocean that affects weather in North and South America. To produce these waves in plasma, scientists must have a greater understanding of light — specifically, the same sort of radio-frequency wave used in microwave ovens — which physicists already use to heat plasma. With greater understanding comes the greater possibility of control.

“We are trying to find similar waves for fusion,” said Qin. “They are not easily stopped, so if we could create them in plasma, we could increase the efficiency of plasma heating and help create the conditions for fusion.” The technique resembles ringing a bell. Just as using a hammer to hit a bell causes the metal to move in such a way that it creates sound, the scientists want to strike plasma with light so it wiggles in a certain way to create sustained heat.
Solving a problem by simplifying it happens throughout science. “If you’re learning to play a song on the piano, you don’t start by trying to play the whole song at full speed,” said Eric Palmerduca, a graduate student in the Princeton Program in Plasma Physics, which is based at PPPL, and lead author of the paper. “You start playing it at a slower tempo; you break it into small parts; maybe you learn each hand separately. We do this all the time in science — breaking a bigger problem up into smaller problems, solving them one or two at a time, and then putting them back together to solve the big problem.”
Turn, turn, turn
In addition to discovering that a photon’s polarization is topological, the scientists found that the spinning motion of photons could not be separated into internal and external components. Think of Earth: It both spins on its axis, producing day and night, and orbits the sun, producing the seasons. These two types of motion typically do not affect each other; for instance, Earth’s rotation around its axis does not depend on its revolution around the sun. In fact, the turning motion of all objects with mass can be separated this way.
But scientists have not been so sure about particles like photons, which do not have mass. “Most experimentalists assume that the angular momentum of light can be split into spin and orbital angular momentum,” said Palmerduca. “However, among theorists, there has been a long debate about the correct way to do this splitting or whether it is even possible to do this splitting. Our work helps settle this debate, showing that the angular momentum of photons cannot be split into spin and orbital components.”
Moreover, Palmerduca and Qin established that the two movement components can’t be split because of a photon’s topological, unchanging properties, like its polarization. This novel finding has implications for the laboratory. “These results mean that we need a better theoretical explanation of what is going on in our experiments,” Palmerduca said.

All of these findings about photons give the researchers a clearer picture of how light behaves. With a greater understanding of light beams, they hope to figure out how to create topological waves that could be helpful for fusion research.
Insights for theoretical physics
Palmerduca notes that the photon findings demonstrate PPPL’s strengths in theoretical physics. The findings relate to a mathematical result known as the Hairy Ball Theorem. “The theorem states that if you have a ball covered with hairs, you can’t comb all the hairs flat without creating a cowlick somewhere on the ball. Physicists thought this implied that you could not have a light source that sends photons in all directions at the same time,” Palmerduca said. He and Qin found, however, that this is not correct because the theorem does not take into account, mathematically, that photon electric fields can rotate.
The findings also amend research by former Princeton University Professor of Physics Eugene Wigner, who Palmerduca described as one of the most important theoretical physicists of the 20th century. Wigner realized that using principles derived from Albert Einstein’s theory of relativity, he could describe all the possible elementary particles in the universe, even those that hadn’t been discovered yet. But while his classification system is accurate for particles with mass, it produces inaccurate results for massless particles, like photons. “Qin and I showed that using topology,” Palmerduca said, “we can modify Wigner’s classification for massless particles, giving a description of photons that works in all directions at the same time.”
A clearer understanding for the future
In future research, Qin and Palmerduca plan to explore how to create beneficial topological waves that heat plasma without making unhelpful varieties that siphon the heat away. “Some deleterious topological waves can be excited unintentionally, and we want to understand them so that they can be removed from the system,” Qin said. “In this sense, topological waves are like new breeds of insects. Some are beneficial for the garden, and some of them are pests.”
Meanwhile, they are excited about the current findings. “We have a clearer theoretical understanding of the photons that could help excite topological waves,” Qin said. “Now it’s time to build something so we can use them in the quest for fusion energy.”
This research was funded by the DOE award DE-AC02-09CH11466.
PPPL is mastering the art of using plasma — the fourth state of matter — to solve some of the world’s toughest science and technology challenges. More

A new material that moves like skin while preserving signal strength in electronics could enable the development of next-generation wearable devices with continuous, consistent wireless and battery-free functionality.
According to a study published in Nature, an international team of researchers from Rice University and Hanyang University developed the material by embedding clusters of highly dielectric ceramic nanoparticles into an elastic polymer. The material was reverse-engineered to not only mimic skin elasticity and motion types, but also to adjust its dielectric properties to counter the disruptive effects of motion on interfacing electronics, minimize energy loss and dissipate heat.
“Our team was able to combine simulations and experiments to understand how to design a material that can seamlessly deform like skin and change the way electrical charges distribute inside it when it is stretched so as to stabilize radio-frequency communication,” said Raudel Avila, assistant professor of mechanical engineering at Rice and a lead author on the study. “In a way, we are carefully engineering an electrical response to a mechanical event.”
Avila, who was responsible for conducting simulations to help identify the right choice of materials and design, explained that electronic devices use radio frequency (RF) elements like antennas to send and receive electromagnetic waves.
“If you have ever been in a place with poor cellular reception or a very spotty Wi-Fi signal, you probably understand the frustration of weak signals,” Avila said. “When we’re trying to communicate information, we work at specific frequencies: Two antennas communicating with each other do so at a given frequency. So we need to ensure that that frequency does not change so that communication remains stable. The challenge of achieving this in systems designed to be mobile and flexible is that any change or transformation in the shape of those RF components causes a frequency shift, which means you’ll experience signal disruption.”
The nanoparticles embedded in the substrate served to counteract these disruptions, with a key design element being the intentional pattern of their distribution. Both the distance between the particles and the shape of their clusters played a critical role in stabilizing the electrical properties and resonant frequency of the RF components.
“The clustering strategy is very important, and it would take a lot longer to figure out how to go about it through experimental observations alone,” Avila said.

Sun Hong Kim, a former research associate from Hanyang and now a postdoctoral researcher at Northwestern University, pointed out that the research team took a creative approach to solving the problem of RF signal stability in stretchable electronics.
“Unlike previous studies that focused on electrode materials or design, we focused on the design of a high-dielectric nanocomposite for the substrate where the wireless device is located,” Kim said, highlighting the importance of collaboration across three different fields of expertise for developing “such a multidimensional solution to a complex problem.”
“We believe that our technology can be applied to various fields such as wearable medical devices, soft robotics and thin and light high-performance antennas,” said Abdul Basir, a former research associate from Hanyang and now a postdoctoral researcher at Tampere University in Finland.
Wearable technologies are having a profound impact on health care, enabling new forms of individual monitoring, diagnosis and care. Smart wear market predictions reflect the transformative potential of these technologies with health and fitness owning the largest share in terms of end use.
“Wireless skin-integrated stretchable electronics play a key role in health emergencies, e-health care and assistive technologies,” Basir added.
To test whether the material could support the development of effective wearable technologies, the researchers built several stretchable wireless devices, including an antenna, a coil and a transmission line, and evaluated their performance both on the substrate they developed and on a standard elastomer without the added ceramic nanoparticles.

“When we put the electronics on the substrate and then we stretch or bend it, we see that the resonant frequency of our system remains stable,” Avila said. “We showed that our system supports stable wireless communication at a distance of up to 30 meters (~98 feet) even under strain. With a standard substrate, the system completely loses connectivity.”
The wireless working distance of the far-field communication system exceeds that of any other similar skin-interfaced system. Moreover, the new material could be used to enhance wireless connectivity performance in a variety of wearable platforms designed to fit various body parts in a wide range of sizes.
For instance, the researchers developed wearable bionic bands to be worn on the head, knee, arm or wrist to monitor health data across the body, including electroencephalogram (EEG) and electromyogram (EMG) activity, knee motion and body temperature. The headband, which was shown could stretch up to 30% when worn on the head of a toddler and up to 50% on the head of an adult, successfully transmitted real-time EEG measurements at a wireless distance of 30 meters.
“Skin-interfaced stretchable RF devices that can seamlessly conform to skin morphology and monitor key physiological signals require critical design of the individual material layouts and the electronic components to yield mechanical and electrical properties and performance that do not disrupt a user’s experience,” Avila said. “As wearables continue to evolve and influence the way society interacts with technology, particularly in the context of medical technology, the design and development of highly efficient stretchable electronics become critical for stable wireless connectivity.” More

We’ve been told, “The eyes are the window to the soul.” Well, windows work two ways. Our eyes are also our windows to the world. What we see and how we see it help determine how we move through the world. In other words, our vision helps guide our actions, including social behaviors. Now, a young Cold Spring Harbor Laboratory (CSHL) scientist has uncovered a major clue into how this works. He did it by building a special AI model of the common fruit fly brain.
CSHL Assistant Professor Benjamin Cowley and his team honed their AI model through a technique they developed called “knockout training.” First, they recorded a male fruit fly’s courtship behavior — chasing and singing to a female. Next, they genetically silenced specific types of visual neurons in the male fly and trained their AI to detect any changes in behavior. By repeating this process with many different visual neuron types, they were able to get the AI to accurately predict how the real fruit fly would act in response to any sight of the female.
“We can actually predict neural activity computationally and ask how specific neurons contribute to behavior,” Cowley says. “This is something we couldn’t do before.”
With their new AI, Cowley’s team discovered that the fruit fly brain uses a “population code” to process visual data. Instead of one neuron type linking each visual feature to one action, as previously assumed, many combinations of neurons were needed to sculpt behavior. A chart of these neural pathways looks like an incredibly complex subway map and will take years to decipher. Still, it gets us where we need to go. It enables Cowley’s AI to predict how a real-life fruit fly will behave when presented with visual stimuli.
Does this mean AI could someday predict human behavior? Not so fast. Fruit fly brains contain about 100,000 neurons. The human brain has almost 100 billion.
“This is what it’s like for the fruit fly. You can imagine what our visual system is like, ” says Cowley, referring to the subway map.
Still, Cowley hopes his AI model will someday help us decode the computations underlying the human visual system.
“This is going to be decades of work. But if we can figure this out, we’re ahead of the game,” says Cowley. “By learning [fly] computations, we can build a better artificial visual system. More importantly, we’re going to understand disorders of the visual system in much better detail.”
How much better? You’ll have to see it to believe it. More

Nearly 100,000 Danes over the age of 65 and more than 55 million people around the world live with dementia-related disorders such as Alzheimer’s and Parkinson’s. These diseases arise when some of the smallest building blocks in the body clump together and destroy vital functions. Why this occurs and how to treat it remains a scientific mystery. Until now, studying the phenomenon has been very challenging and limited due to an absence of the right tools.
Now, researchers from the Hatzakis lab at the University of Copenhagen’s Department of Chemistry have invented a machine learning algorithm that can track clumping under the microscope in real-time. The algorithm can automatically map and track the important characteristics of the clumped-up building blocks that cause Alzheimer’s and other neurodegenerative disorders. Until now, doing so has been impossible.
“In just minutes, our algorithm solves a challenge that would take researchers several weeks. That it will now be easier to study microscopic images of clumping proteins will hopefully contribute to our knowledge, and in the long term, lead to new therapies for neurodegenerative brain disorders,” says PhD Jacob Kæstel-Hansen from the Department of Chemistry, who, alongside Nikos Hatzakis, led the research team behind the algorithm.
Microscopic proteins detected in no time
The coming together and exchange of compounds and signals among proteins and other molecules occurs billions of times within our cells in natural processes that allow our bodies function. But when errors occur, proteins can clump together in ways that interfere with their ability to work as intended. Among other things, this can lead to neurodegenerative disorders in the brain and cancer.
The researchers’ machine learning algorithm can spot protein clumps down to a billionth of a meter in microscopy images. At the same time, the algorithm can count and then group clumps according to their shapes and sizes, all while tracking their development over time. The appearance of clumps can have a major impact on their function and how they behave in the body, for better or worse.
“When studying clumps through a microscope, one quickly sees, for example, that some are rounder, while others have filamentous structures. And, their exact shape can vary depending on the disorder they trigger. But to sit and count them manually many thousands of times takes a very long time, which could be better spent on other things,” says Steen Bender from the Department of Chemistry, the article’s first author.

In the future, the algorithm will make it much easier to learn more about why clumps form so that we can develop new drugs and therapies to combat these disorders.
“The fundamental understanding of these clumps depends on us being able to see, track and quantify them, and describe what they look like over time. No other methods can currently do so automatically and as effectively,” he says.
Tools are freely available to everyone
The Department of Chemistry researchers are in now in full swing using the tool to conduct experiments with insulin molecules. As insulin molecules clump, their ability to regulate our blood sugar weakens.
“We see this undesirable clumping in insulin molecules as well. Our new tool can let us see how these clumps are affected by whatever compounds we add. In this way, the model can help us work towards understanding how to potentially stop or transform them into less dangerous or more stable clumps,” explains Jacob Kæstel-Hansen.
Thus, the researchers see great potential in being able to use the tool to develop new drugs once the microscopic building blocks have been clearly identified. The researchers hope that their work will kickstart the gathering of more comprehensive knowledge about the shapes and functions of proteins and molecules.
“As other researchers around the world begin to deploy the tool, it will help create a large library of molecule and protein structures related to various disorders and biology in general. This will allow us to better understand diseases and try to stop them,” concludes Nikos Hatzakis from the Department of Chemistry.
The algorithm is freely available on the internet as open source and can be used by scientific researchers and anyone else working to understand the clumping of proteins and other molecules.
The research was conducted by: Steen W.B. Bender, Marcus W. Dreisler, Min Zhang, Jacob Kæstel-Hansen and Nikos S. Hatzakis from the Department of Chemistry with support from the Novo Nordisk Foundation Center for Optimised Oligo Escape and Control of Disease. More

I’m not touching you! When another person’s finger hovers over your skin, you may get the sense that they’re touching you, feeling not necessarily contact, but their proximity. Similarly, researchers reporting in ACS Applied Materials & Interfaces have designed a soft, flexible film that senses the presence of nearby objects without physically touching them. The study features the new sensor technology to detect eyelash proximity in blink-tracking glasses.
Noncontact sensors can identify or measure an object without directly touching it. Examples of these devices include infrared thermometers and vehicle proximity notification systems. One type of noncontact sensor relies on static electricity to detect closeness and small motions, and has the potential to enhance smart devices, such as allowing phone screens to recognize more finger gestures. So far, however, they’ve been limited in what types of objects get detected, how long they stay charged and how hard they are to fabricate. So, Xunlin Qiu, Yiming Wang, Fuzhen Xuan and coworkers wanted to create a flexible static electricity-based sensor that overcame these problems.
The researchers began by simply fabricating a three-part system: fluorinated ethylene propylene (FEP) for the top sensing layer, with an electrically conductive film and flexible plastic base for the middle and bottom layers, respectively. FEP is an electret, a type of material that’s electrically charged and produces an external electrostatic field, similar to the way a magnet produces a magnetic field. Then they electrically charged the FEP-based sensor making it ready for use.
As objects approached the FEP surface, their inherent static charge caused an electrical current to flow in the sensor, thereby “feeling” the object without physical contact. The resulting clear and flexible sensor detected objects — made of glass, rubber, aluminum and paper — that were nearly touching it but not quite, from 2 to 20 millimeters (less than an inch) away. The sensor held its charge for over 3,000 different approach-withdraw cycles over almost two hours.
In a demonstration of the new sensing film, the researchers attached it to the inner side of an eyeglass lens. When worn by a person, the glasses noticed the approach of eyelashes and identified when the wearer blinked Morse code for “E C U S T,” the abbreviation for the researchers’ institution. In the future, the researchers say their noncontact sensors could be used to help people who are unable to speak or use sign language communicate or even detect drowsiness when driving.
The authors acknowledge funding from Natural Science Foundation of China Grants, Shanghai Pilot Program for Basic Research, the “Chenguang Program” supported by the Shanghai Education Development Foundation and Shanghai Municipal Education Commission, National Key Research and Development Program of China, Natural Science Foundation of Shanghai, and the Open Project of State Key Laboratory of Chemical Engineering. More

In a study published in Nature Materials, scientists from the University of California, Irvine describe a new method to make very thin crystals of the element bismuth — a process that may aid the manufacturing of cheap flexible electronics an everyday reality.
“Bismuth has fascinated scientists for over a hundred years due to its low melting point and unique electronic properties,” said Javier Sanchez-Yamagishi, assistant professor of physics & astronomy at UC Irvine and a co-author of the study. “We developed a new method to make very thin crystals of materials such as bismuth, and in the process reveal hidden electronic behaviors of the metal’s surfaces.”
The bismuth sheets the team made are only a few nanometers thick. Sanchez-Yamagishi explained how theorists have predicted that bismuth contains special electronic states allowing it to become magnetic when electricity flows through it — something essential for quantum electronic devices based on the magnetic spin of electrons.
One of the hidden behaviors observed by the team is so-called quantum oscillations originating from the surfaces of the crystals. “Quantum oscillations arise from the motion of an electron in a magnetic field,” said Laisi Chen, a Ph.D. candidate in physics & astronomy at UC Irvine and one of the lead authors of the paper. “If the electron can complete a full orbit around a magnetic field, it can exhibit effects that are important for the performance of electronics. Quantum oscillations were first discovered in bismuth in the 1930s, but have never been seen in nanometer-thin bismuth crystals.”
Amy Wu, a Ph.D. candidate in physics in Sanchez-Yamagishi’s lab, likened the team’s new method to a tortilla press. To make the ultra-thin sheets of bismuth, Wu explained, they had to squish bismuth between two hot plates. To make the sheets as flat as they are, they had to use molding plates that are perfectly smooth at the atomic level, meaning there are no microscopic divots or other imperfections on the surface. “We then made a kind of quesadilla or panini where the bismuth is the cheesy filling and the tortillas are the atomically flat surfaces,” said Wu.
“There was this nervous moment where we had spent over a year making these beautiful thin crystals, but we had no idea whether its electrical properties would be something extraordinary,” said Sanchez-Yamagishi. “But when we cooled down the device in our lab, we were amazed to observe quantum oscillations, which have not been previously seen in thin bismuth films.”
“Compression is a very common manufacturing technique used for making common household materials such as aluminum foil, but is not commonly used for making electronic materials like those in your computers,” Sanchez-Yamagishi added. “We believe our method will generalize to other materials, such as tin, selenium, tellurium and related alloys with low melting points, and it could be interesting to explore for future flexible electronic circuits.”
Next, the team wants to explore other ways in which compression and injection molding methods can be used to make the next computer chips for phones or tablets.
“Our new team members bring exciting ideas to this project, and we’re working on new techniques to gain further control over the shape and thickness of the grown bismuth crystals,” said Chen. “This will simplify how we fabricate devices, and take it one step closer for mass production.”
The research team included collaborators from UC Irvine, Los Alamos National Laboratory and the National Institute for Materials Science in Japan. The research was primarily funded by the Air Force Office of Scientific Research, with partial support coming from the UC Irvine Center for Complex and Active Materials Seed Program, a Materials Research Science and Engineering Center under the National Science Foundation. More

Research into new battery materials is aimed at optimizing their performance and lifetime and at reducing costs. Work is also underway to reduce the consumption of rare elements, such as lithium and cobalt, as well as toxicconstituents. Sodium-ion batteries are considered very promising in this respect. They are based on principles similar to those of lithium-ion batteries, but can be produced from raw materials that are widely accessible in Europe. And they are suitable for both stationary and mobile applications. “Layered oxides, such as sodium-nickel-manganese oxides, are highly promising cathode materials,” says Dr. Simon Daubner, Group Leader at the Institute for Applied Materials — Microstructure Modelling and Simulation (IAM-MMS) of KIT and corresponding author of the study. Within the POLiS (stands for Post Lithium Storage) Cluster of Excellence, he investigates sodium-ion technology.
Fast Charging Creates Mechanical Stress
However, cathode materials of this type have a problem. Sodium-nickel-manganese oxides change their crystal structure depending on how much sodium is stored. If the material is charged slowly, everything proceeds in a well-ordered way. “Sodium leaves the material Layer by layer, just like cars leaving a carpark story by story,” Daubner explains. “But when charging is quick, sodium is extracted from all sides.” This results in mechanical stress that may damage the material permanently.
Researchers from the Institute of Nanotechnology (INT) and IAM-MMS of KIT, together with scientists from Ulm University and the Center for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW), recently carried out simulations to clarify the situation. They report in npj Computational Materials, a journal of the Nature portfolio.
Experiments Confirm Simulation Results
“Computer models can describe various length scales, from the arrangement of atoms in electrode materials to their microstructure to the cell as the functional unit of any battery,” Daubner says. To study the NaXNi1/3Mn2/3O2 layered oxide, microstructured models were combined with slow charge and discharge experiments. The material was found to exhibit several degradation mechanisms causing a loss of capacity. For this reason, it is not yet suited for commercial applications. A change in the crystal structure results in an elastic deformation. The crystal shrinks, which may cause cracking and capacity reduction. INT and IAM-MMS simulations show that this mechanical influence decisively determines the time needed for charging the material. Experimental studies at ZSW confirm these results.
The findings of the study can be transferred partly to other layered oxides. “Now, we understand basic processes and can work on the development of battery materials that are long-lastin and can be charged as quickly as possible,” Daubner summarizes. This could lead to the widespread use of sodium-ion batteries in five to ten years’ time. More