Computers Math

In the early 2010s, LightSquared, a multibillion-dollar startup promising to revolutionize cellular communications, declared bankruptcy. The company couldn’t figure out how to prevent its signals from interfering with those of GPS systems.
Now, Penn Engineers have developed a new tool that could prevent such problems from ever happening again: an adjustable filter that can successfully prevent interference, even in higher-frequency bands of the electromagnetic spectrum.
“I hope it will enable the next generation of wireless communications,” says Troy Olsson, Associate Professor in Electrical and Systems Engineering (ESE) at Penn Engineering and the senior author of a new paper in Nature Communications that describes the filter.
The electromagnetic spectrum itself is one of the modern world’s most precious resources; only a tiny fraction of the spectrum, mostly radio waves, representing less than one billionth of one percent of the overall spectrum, is suitable for wireless communication.
The bands of that fraction of the spectrum are carefully controlled by the Federal Communications Commission (FCC), which only recently made available the Frequency Range 3 (FR3) band, including frequencies from about 7 GHz to 24 GHz, for commercial use. (One hertz is equivalent to a single oscillation in an electromagnetic wave passing a point each second; one gigahertz, or GHz, is a billion such oscillations per second.)
To date, wireless communications have mostly used lower-frequency bands. “Right now we work from 600 MHz to 6 GHz,” says Olsson. “That’s 5G, 4G, 3G.” Wireless devices use different filters for different frequencies, with the effect that covering all frequencies or bands requires large numbers of filters that take up substantial space. (The typical smartphone includes upwards of 100 filters, to ensure that signals from different bands don’t interfere with one another.)
“The FR3 band is most likely to roll out for 6G or Next G,” says Olsson, referring to the next generation of cellular networks, “and right now the performance of small-filter and low-loss switch technologies in those bands is highly limited. Having a filter that could be tunable across those bands means not having to put in another 100+ filters in your phone with many different switches. A filter like the one we created is the most viable path to using the FR3 band.”
One complication posed by using higher-frequency bands is that many frequencies have already been reserved for satellites. “Elon Musk’s Starlink works in those bands,” notes Olsson. “The military — they’ve already been crowded out of many lower bands. They’re not going to give up radar frequencies that sit right in those bands, or their satellite communications.”

As a result, Olsson’s lab — in collaboration with colleagues Mark Allen, Alfred Fitler Moore Professor in ESE, and Firooz Aflatouni, Associate Professor in ESE, and their respective groups — designed the filter to be adjustable, so that engineers can use it to selectively filter different frequencies, rather than have to employ separate filters. “Being tunable is going to be really important,” Olsson continues, “because at these higher frequencies you may not always have a dedicated block of spectrum just for commercial use.”
What makes the filter adjustable is a unique material, “yttrium iron garnet” (YIG), a blend of yttrium, a rare earth metal, along with iron and oxygen. “What’s special about YIG is that it propagates a magnetic spin wave,” says Olsson, referring to the type of wave created in magnetic materials when electrons spin in a synchronized fashion.
When exposed to a magnetic field, the magnetic spin wave generated by YIG changes frequency. “By adjusting the magnetic field,” says Xingyu Du, a doctoral student in Olsson’s lab and the first author of the paper, “the YIG filter achieves continuous frequency tuning across an extremely broad frequency band.”
As a result, the new filter can be tuned to any frequency between 3.4 GHz and 11.1 GHz, which covers much of the new territory the FCC has opened up in the FR3 band. “We hope to demonstrate that a single adaptable filter is sufficient for all the frequency bands,” says Du.
In addition to being tunable, the new filter is also tiny — about the same size as a quarter, in contrast to previous generations of YIG filters, which resembled large packs of index cards.
One reason the new filter is so small, and therefore could potentially be inserted into mobile phones in the future, is that it requires very little power. “We pioneered the design of a zero-static-power, magnetic-bias circuit,” says Du, referring to a type of circuit that creates a magnetic field without requiring any energy beyond the occasional pulse to readjust the field.

While YIG was discovered in the 1950s, and YIG filters have existed for decades, the combination of the novel circuit with extremely thin YIG films micromachined in the Singh Center for Nanotechnology dramatically reduced the new filter’s power consumption and size. “Our filter is 10 times smaller than current commercial YIG filters,” says Du.
In June, Olsson and Du will present the new filter at the 2024 Institute of Electrical and Electronics Engineers (IEEE) Microwave Theory and Techniques Society (MTT-S) International Microwave Symposium, in Washington, D.C.
This study was conducted at the University of Pennsylvania School of Engineering and Applied Science. It was supported by a grant from the Defense Advanced Research Projects Agency (FA8650-21-1-7010) and made use of resources sponsored by the National Science Foundation National Nanotechnology Coordinated Infrastructure Program (NNCI-1542153). More

Lighting a gas grill, getting an ultrasound, using an ultrasonic toothbrush — these actions involve the use of materials that can translate an electric voltage into a change in shape and vice versa.
Known as piezoelectricity, the ability to trade between mechanical stress and electric charge can be harnessed widely in capacitors, actuators, transducers and sensors like accelerometers and gyroscopes for next-generation electronics. However, integrating these materials into miniaturized systems has been difficult due to the tendency of electromechanically active materials to — at the submicrometer scale, when the thickness is just a few millionths of an inch — get “clamped” down by the material they are attached to, which significantly dials down their performance.
Rice University researchers and collaborators at the University of California, Berkeley have found that a class of electromechanically active materials called antiferroelectrics may hold the key to overcoming performance limitations due to clamping in miniaturized electromechanical systems. A new study published in Nature Materials reports that a model antiferroelectric system, lead zirconate (PbZrO3), produces an electromechanical response that can be up to five times greater than that of conventional piezoelectric materials even in films that are only 100 nanometers (or 4 millionths of an inch) thick.
“We’ve been using piezoelectric materials for decades,” said Rice materials scientist Lane Martin, who is the corresponding author on the study. “Recently there has been a strong motivation to further integrate these materials into new types of devices that are very small — as you would want to do for, say, a microchip that goes inside your phone or computer. The problem is that these materials are typically just less usable at these small scales.”
According to current industry standards, a material is considered to have very good electromechanical performance if it can undergo a 1% change in shape — or strain — in response to an electric field. For an object that measures 100 inches in length, for instance, getting 1 inch longer or shorter represents 1% strain.
“From a materials science perspective, this is a significant response, since most hard materials can only change by a fraction of a percent,” said Martin, the Robert A. Welch Professor, professor of materials science and nanoengineering and director of the Rice Advanced Materials Institute.
When conventional piezoelectric materials are scaled down to systems less than a micrometer (1,000 nanometers) in size, their performance generally deteriorates significantly due to the interference of the substrate, which dampens their ability to change shape in response to electric field or, conversely, to generate voltage in response to a change in shape.

According to Martin, if electromechanical performance were rated on a scale of 1-10 — where 1 is lowest performance and 10 is the industry standard of 1% strain — then clamping is typically expected to bring conventional piezoelectrics’ electromechanical response down from a 10 to the 1-4 range.
“To understand how clamping impacts motion, first picture being in a middle seat on an airplane with no one on either side of you — you’d be free to adjust your position if you get uncomfortable, overheated, etc.,” Martin said. “Now picture the same scenario, except now you’re seated between two huge offensive linemen from Rice’s football team. You’d be ‘clamped’ between them such that you really couldn’t meaningfully adjust your position in response to a stimulus.”
The researchers wanted to understand how very thin films of antiferroelectrics — a class of materials that remained understudied until recently due to a lack of access to “model” versions of the materials and to their complex structure and properties — changed their shape in response to voltage and whether they were likewise susceptible to clamping.
First, they grew thin films of the model antiferroelectric material PbZrO 3 with very careful control of the material thickness, quality and orientation. Next, they performed an array of electrical and electromechanical measurements to quantify the responses of the thin films to applied electric voltage.
“We found the response was considerably larger in the thin films of antiferroelectric material than what is achieved in similar geometries of traditional materials,” said Hao Pan, a postdoctoral researcher in Martin’s research group and lead author on the study.
Measuring shape change at such small scales was not an easy feat. In fact, optimizing the measurement setup required so much labor the researchers documented the process in a separate publication.

“With the perfected measurement setup, we can get a resolution of two picometers — that’s about a thousandth of a nanometer,” Pan said. “But just showing that a shape change happened doesn’t mean we understand what’s going on, so we had to explain it. This was one of the first studies to reveal the mechanisms behind this high performance.”
With support from their collaborators at the Massachusetts Institute of Technology, the researchers used a state-of-the-art transmission electron microscope to observe the nanoscale material shapeshift with atomic resolution in real time.
“In other words, we watched the electromechanical actuation as it was happening, so we could see the mechanism for the large shape changes,” Martin said. “What we found was that there is an electric voltage-induced change in the crystal structure of the material, which is like the fundamental building unit or single type of Lego block from which the material is built. In this case, that Lego block gets reversibly stretched with applied electric voltage, giving us a big electromechanical response.”
Surprisingly, the researchers found that not only does clamping not interfere with material performance, but it in fact enhances it. Together with collaborators at Lawrence Berkeley National Laboratory and Dartmouth College, they recreated the material computationally in order to get another view of how the clamping affects the actuation under applied electric voltage.
“Our results are the culmination of years of work on related materials, including the development of new techniques to probe them,” Martin said. “By figuring out how to make these thin materials work better, we’re hoping to enable the development of smaller and more powerful electromechanical devices or microelectromechanical systems (MEMS) — and even nanoelectromechanical systems (NEMS) — that use less energy and can do things we never thought possible before.” More

Concierge services built on artificial intelligence have the potential to improve how hotels and other service businesses interact with customers, a new paper suggests.
In the first work to introduce the concept, researchers have outlined the role an AI concierge, a technologically advanced assistant, may play in various areas of the service sector as well as the different forms such a helper might embody.
Their paper envisions a virtual caretaker that, by combining natural language processing, behavioral data and predictive analytics, would anticipate a customer’s needs, suggest certain actions, and automate routine tasks without having to be explicitly commanded to do so.
Though such a skilled assistant is still years away, Stephanie Liu, lead author of the paper and an associate professor of hospitality management at The Ohio State University, and her colleagues drew insight from several contemporary fields, including service management, psychology, human-computer interaction and ethics research, to detail what opportunities and challenges might arise from having an AI concierge manage human encounters.
“The traditional service industry uses concierges for high-end clients, meaning that only a few people have access to them,” Liu said. “Now with the assistance of AI technology, everybody can have access to a concierge providing superior experiences.”
On that premise, the benefits of incorporating AI into customer service are twofold: It would allow companies to offer around-the-clock availability and consistency in their operations as well as improve how individuals engage with professional service organizations, she said.
Moreover, as the younger workforce gravitates to more tech-oriented jobs and global travel becomes more common, generative AI could be an apt solution to deal with the escalating demands of evolving hospitality trends, said Liu.

“The development of AI technology for hotels, restaurants, health care, retail and tourism has a lot of potential,” she said.
The paper was published recently in the Journal of Service Management.
Despite the social and economic benefits associated with implementing such machines, how effective AI concierges may be at completing a task is dependent on both the specific situation and the type of interface consumers use, said Liu.
There are four primary forms a smart aide might take, each with distinctive attributes that would provide consumers with different levels of convenience, according to Liu.
The first type is a dialogue interface that uses only text or speech to communicate, such as ChatGPT, a conversational agent often used to make inquiries and garner real-time assistance. Many of these interactive devices are already used in hotels and medical buildings for contactless booking or to connect consumers with other services and resources.
The second is a virtual avatar that employs a vivid digital appearance and a fully formed persona to foster a deeper emotional connection with the consumer. This method is often utilized for telehealth consultations and online learning programs.

The third iteration is a holographic projection wherein a simulated 3D image is brought into the physical world. According to the paper, this is ideally suited for scenarios where the visual impact is desired, but physical assistance itself is not necessary.
The paper rounds out the list by suggesting an AI concierge that would present as a tangible, or touchable robot. This form would offer the most human-like sensory experiences and would likely be able to execute multiple physical tasks, like transporting heavy luggage.
Some international companies have already developed these cutting-edge tools for use in a limited capacity. One robotic concierge, known as Sam, was designed to aid those in senior living communities by helping them check in, make fall risk assessments and support staff with non-medical tasks. Another deployed at South Korea’s Incheon International Airport helped consumers navigate paths to their destination and offered premier shopping and dining recommendations.
Yet as advanced computing algorithms become more intertwined in our daily lives, industry experts will likely have to consider consumer privacy concerns when deciding when and where to implement these AI systems. One way to deal with these issues would be to create the AI concierge with limited memory or other safewalls to protect stored personal data, such as identity and financial information, said Liu.
“Different companies are at different stages with this technology,” said Liu. “Some have robots that can detect customers’ emotions or take biometric inputs and others have really basic ones. It opens up a totally different level of service that we have to think critically about.”
What’s more, the paper notes that having a diversity of concierge options available for consumers to choose from is also advantageous from a mental health standpoint.
Because AI is viewed as having less agency than their human counterparts, it might help mitigate psychologically uncomfortable service situations that could arise because of how consumers feel they might be perceived by a human concierge. This reduced apprehension regarding the opinion of a machine may encourage heightened comfort levels and result in more favorable responses about the success of the AI concierge, said Liu.
Ultimately, there’s still much multidisciplinary testing to be done to ensure these technologies can be applied in a widespread and equitable manner. Liu adds that future research should seek to determine how certain design elements, such as the perceived gender, ethnicity or voice of these robotic assistants, would impact overall consumer satisfaction. More

Whereas π-stacking systems involving aromatic compounds are quite common, those made from antiaromatic units are rare. In a recent study, researchers from Japan developed modified norcorrole molecules whose side chains favored the formation of columnar π-stacking structures. Using these compounds, they produced liquid crystals with high electrical conductivity and thermotropic properties. Their findings open up new design avenues for materials useful in electronics, sensing, optics, and biomedicine.
In organic chemistry, π-stacking systems are supramolecular structures that arise due to the dispersion force, a type of intermolecular noncovalent interaction. They are a common occurrence in nature; the stabilized structure of DNA is a very prominent example of a π-stacking system, and so are the arrangement of amino acids in certain proteins. Interestingly, π-stacking can be leveraged in the design of materials with useful electronic and optical properties. These include organic semiconductors of various kinds, as well as conjugated polymers for sensing and biomedical applications.
Thus far, a good portion of technologically relevant π-stacking system has been limited to aromatic compounds, which have inherent π-electron clouds. On the other hand, antiaromatic compounds, though promising candidates for developing electric conductors, have been scarcely reported as the building units of π-stacking systems.
Surprisingly, in a recent study, a research team led by Professor Hiromitsu Maeda from Ritsumeikan University, Japan, reported a novel antiaromatic π-stacking system that enabled the formation of a highly conductive liquid crystal. Their findings were published on April 16, 2024, in the journal Chemical Science. Worth noting, this paper was co-authored by Prof. Go Watanabe from Kitasato University, Prof. Shu Seki from Kyoto University, and Prof. Hiroshi Shinokubo from Nagoya University.
The reported compounds in question are NiII-coordinated norcorroles with modified aryl moieties as side chains. Previously, achieving π-stacking in similar norcorroles failed because hydrogen-bonding interactions between the side chains opposed the face-to-face stacking of the planar antiaromatic units. This time, however, the research team had an ingenious idea. “We hypothesized that the introduction of side interacting moieties with less directionality would enhance the stacking between norcorrole units,” explains Prof. Maeda. “Thus, we attempted the simple introduction of aliphatic chains, which induce van der Waals interactions. These interactions can be effective for modulating the stacking structure of a material,” adds Prof. Maeda.
As evidenced through various experiments and molecular dynamics simulations, the proposed strategy worked as intended. The norcorrole units formed columnar structures through the stacking of arrangements known as ‘triple-decker.’ In these arrangements, a planarized molecule is sandwiched between two slightly bowl-shaped molecules.
Using the proposed molecular design, the researchers then synthesized liquid crystals. Thanks to the triple-decker stacking, a liquid crystal exhibited remarkable electricconductivity as well as thermotropicity; that is, an order parameter that depends on temperature. “The control of molecular interactions based on molecular design and synthesis, as demonstrated in our study, will be crucial for future applications,” remarks Prof. Maeda. “Properties such as high electric conductivity in liquid crystals may be used for the fabrication of electronic devices. In addition, stimuli-responsive behaviors in soft materials can be used to modulate relevant properties, like photoluminescence, according to pressure and temperature,” explains Prof. Maeda.
Taken together, the findings of this study bring to light a promising strategy for designing new compounds based on molecular assemblies of antiaromatic units. With any luck, this will open up new avenues for materials design, ultimately leading to better organic electronics, optoelectronics, and sensing devices. More

Across nature, animals from swarming insects to herding mammals can organize into seemingly choreographed motion. Over the last two decades, scientists have discovered that these coordinated movements arise from each animal following simple rules about where their neighbors are located. Now, scientists studying zebrafish have shown that neighbors might also be moving to the same beat. The team revealed that fish swimming in pairs took turns to move; and, they synchronized the timing of these movements in a two-way process known as reciprocity. Then, in virtual reality experiments, the team could confirm that reciprocity was key to driving collective motion: by implementing this rhythmic rule, they could recreate natural schooling behavior in fish and virtual conspecifics. The study published in Nature Communications was led by scientists from the Cluster of Excellence Collective Behaviour at the University of Konstanz and the Max Planck Institute of Animal Behavior in Germany (MPI-AB).
The results provide further mechanistic detail to our understanding of how animals self-organize into moving collectives. “We show that it takes two fish to tango,” says first author Guy Amichay, who conducted the work while a doctoral student at MPI-AB. “Fish are coordinating the timing of their movements with that of their neighbor, and vice versa. This two-way rhythmic coupling is an important, but overlooked, force that binds animals in motion.”
The synchrony of the swarm
Animals moving in synchrony are the most conspicuous examples of collective behavior in nature; yet many natural collectives synchronize not in space, but in time — fireflies synchronize their flashes, neurons synchronize their firing, and humans in concert halls synchronize the rhythm of clapping.
Amichay and the team were interested in the intersection of the two; they were curious to see what rhythmic synchrony might exist in animal movement. “There’s more rhythm to animal movement than you might expect,” says Amichay, who is now a postdoctoral researcher at Northwestern University, USA. “In the real world most fish don’t swim at fixed speeds, they oscillate.”
Using pairs of zebrafish as a study system, Amichay analyzed their swimming to describe the precise pattern of motion. He found that fish, although moving together, did not swim at the same time. Rather they alternated such that one moved, then the other moved, “like two legs walking,” he says.
The team then looked into how fish managed to alternate. They generated a computational model with a simple rule of thumb: double the delay of your neighbor.

The rule of reciprocity
The next step was to test this model computationally, or in silico. They set one agent to beat with fixed movement bouts, like a metronome. The other agent responded to the first by implementing the ‘double the delay’ rhythmic rule. But in this one-way interaction, the agents did not move in the alternating pattern seen in real fish. When both agents responded to each other, however, they reproduced the natural alternation pattern. “This was the first indication that reciprocity was crucial,” says Amichay.
But reproducing natural behavior in a computer was not where the study ended. The team turned to virtual reality to confirm that the principle they uncovered would also work in real fish. “Virtual reality is a revolutionary tool in animal behavior studies because it allows us to circumvent the curse of causality,” says Iain Couzin, a Speaker at the Cluster of Excellence Collective Behaviour at the University of Konstanz and a Director at MPI-AB.
In nature many traits are linked and so it is extremely difficult to pinpoint the cause of an animal’s behavior. But using virtual reality, Couzin says it is possible to “precisely perturb the system” to test the effect of a particular trait on an animal’s behavior.
A single fish was put into a virtual environment with a fish avatar. In some trials the avatar was set to swim like a metronome, ignoring the behavior of the real fish. In these trials the real fish did not swim in the natural alternating pattern with the avatar. But when the avatar was set to respond to the real fish, in a two-way reciprocal relationship, they recovered its natural alternating behavior.
Turn-taking partners
“It’s fascinating to see that reciprocity is driving this turn-taking behavior in swimming fish,” says co-author Máté Nagy, who leads the MTA-ELTE Collective Behavior Research Group at the Hungarian Academy of Sciences, “because it’s not always the case in biological oscillators.” Fireflies, for example, will synchronize even in one-way interactions.

“But for humans, reciprocity comes into play in almost anything we do in pairs, be it dance, or sport, or conversation,” says Nagy.
The team also provided evidence that fish that were coupled in the timing of movements had stronger social bonds. “In other words, if you and I are coupled, we are more attuned to each other,” says Nagy.
The authors say that this finding can drastically change how we understand who influences whom in animal groups. “We used to think that in a busy group, a fish could be influenced by any other member that it can see,” says Couzin. “Now, we see that the most salient bonds could be between partners that choose to rhythmically synchronize.” More

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