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Physicists find misaligned carbon sheets yield unparalleled properties

A material composed of two one-atom-thick layers of carbon has grabbed the attention of physicists worldwide for its intriguing — and potentially exploitable — conductive properties.

Dr. Fan Zhang, assistant professor of physics in the School of Natural Sciences and Mathematics at The University of Texas at Dallas, and physics doctoral student Qiyue Wang published an article in June with Dr. Fengnian Xia’s group at Yale University in Nature Photonics that describes how the ability of twisted bilayer graphene to conduct electrical current changes in response to mid-infrared light.

From One to Two Layers

Graphene is a single layer of carbon atoms arranged in a flat honeycomb pattern, where each hexagon is formed by six carbon atoms at its vertices. Since graphene’s first isolation in 2004, its unique properties have been intensely studied by scientists for potential use in advanced computers, materials and devices.

If two sheets of graphene are stacked on top of one another, and one layer is rotated so that the layers are slightly out of alignment, the resulting physical configuration, called twisted bilayer graphene, yields electronic properties that differ significantly from those exhibited by a single layer alone or by two aligned layers.

“Graphene has been of interest for about 15 years,” Zhang said. “A single layer is interesting to study, but if we have two layers, their interaction should render much richer and more interesting physics. This is why we want to study bilayer graphene systems.”

A New Field Emerges

When the graphene layers are misaligned, a new periodic design in the mesh emerges, called a moiré pattern. The moiré pattern is also a hexagon, but it can be made up of more than 10,000 carbon atoms.

“The angle at which the two layers of graphene are misaligned — the twist angle — is critically important to the material’s electronic properties,” Wang said. “The smaller the twist angle, the larger the moiré periodicity.”

The unusual effects of specific twist angles on electron behavior were first proposed in a 2011 article by Dr. Allan MacDonald, professor of physics at UT Austin, and Dr. Rafi Bistritzer. Zhang witnessed the birth of this field as a doctoral student in MacDonald’s group.

“At that time, others really paid no attention to the theory, but now it has become arguably the hottest topic in physics,” Zhang said.

In that 2011 research MacDonald and Bistritzer predicted that electrons’ kinetic energy can vanish in a graphene bilayer misaligned by the so-called “magic angle” of 1.1 degrees. In 2018, researchers at the Massachusetts Institute of Technology proved this theory, finding that offsetting two graphene layers by 1.1 degrees produced a two-dimensional superconductor, a material that conducts electrical current with no resistance and no energy loss.

In a 2019 article in Science Advances, Zhang and Wang, together with Dr. Jeanie Lau’s group at The Ohio State University, showed that when offset by 0.93 degrees, twisted bilayer graphene exhibits both superconducting and insulating states, thereby widening the magic angle significantly.

“In our previous work, we saw superconductivity as well as insulation. That’s what’s making the study of twisted bilayer graphene such a hot field — superconductivity. The fact that you can manipulate pure carbon to superconduct is amazing and unprecedented,” Wang said.

New UT Dallas Findings

In his most recent research in Nature Photonics, Zhang and his collaborators at Yale investigated whether and how twisted bilayer graphene interacts with mid-infrared light, which humans can’t see but can detect as heat. “Interactions between light and matter are useful in many devices — for example, converting sunlight into electrical power,” Wang said. “Almost every object emits infrared light, including people, and this light can be detected with devices.”

Zhang is a theoretical physicist, so he and Wang set out to determine how mid-infrared light might affect the conductance of electrons in twisted bilayer graphene. Their work involved calculating the light absorption based on the moiré pattern’s band structure, a concept that determines how electrons move in a material quantum mechanically.

“There are standard ways to calculate the band structure and light absorption in a regular crystal, but this is an artificial crystal, so we had to come up with a new method,” Wang said. Using resources of the Texas Advanced Computing Center, a supercomputer facility on the UT Austin campus, Wang calculated the band structure and showed how the material absorbs light.

The Yale group fabricated devices and ran experiments showing that the mid-infrared photoresponse — the increase in conductance due to the light shining — was unusually strong and largest at the twist angle of 1.8 degrees. The strong photoresponse vanished for a twist angle less than 0.5 degrees.

“Our theoretical results not only matched well with the experimental findings, but also pointed to a mechanism that is fundamentally connected to the period of moiré pattern, which itself is connected to the twist angle between the two graphene layers,” Zhang said.

Next Step

“The twist angle is clearly very important in determining the properties of twisted bilayer graphene,” Zhang added. “The question arises: Can we apply this to tune other two-dimensional materials to get unprecedented features? Also, can we combine the photoresponse and the superconductivity in twisted bilayer graphene? For example, can shining a light induce or somehow modulate superconductivity? That will be very interesting to study.”

“This new breakthrough will potentially enable a new class of infrared detectors based on graphene with high sensitivity,” said Dr. Joe Qiu, program manager for solid-state electronics and electromagnetics at the U.S. Army Research Office (ARO), an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory. “These new detectors will potentially impact applications such as night vision, which is of critical importance for the U.S. Army.”

In addition to the Yale researchers, other authors included scientists from the National Institute for Materials Science in Japan. The ARO, the National Science Foundation and the Office of Naval Research supported the study.

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Researchers present concept for a new technique to study superheavy elements

Superheavy elements are intriguing nuclear and atomic quantum systems that challenge experimental probing as they do not occur in nature and, when synthesized, vanish within seconds. Pushing the forefront atomic physics research to these elements requires breakthrough developments towards fast atomic spectroscopy techniques with extreme sensitivity. A joint effort within the European Union’s Horizon 2020 Research and Innovation program and led by Dr. Mustapha Laatiaoui from Johannes Gutenberg University Mainz (JGU) culminated in an optical spectroscopy proposal: The so-called Laser Resonance Chromatography (LRC) should enable such investigations even at minute production quantities. The proposal has recently been published in two articles in Physical Review Letters and Physical Review A.

Superheavy elements (SHEs) are found at the bottom part of the periodic table of elements. They represent a fertile ground for the development of understanding on how such exotic atoms can exist and work when an overwhelming number of electrons in atomic shells and protons and neutrons in the nucleus come together. Insights into their electronic structure can be obtained from optical spectroscopy experiments unveiling element-specific emission spectra. These spectra are powerful benchmarks for modern atomic-model calculations and could be useful, for example, when it comes to searching for traces of even heavier elements, which might be created in neutron-star merger events.

LRC approach combines different methods

Although SHEs have been discovered decades ago, their investigation by optical spectroscopy tools lack far behind the synthesis. This is because they are produced at extremely low rates at which traditional methods simply do not work. So far, optical spectroscopy ends at nobelium, element 102 in the periodic table. “Current techniques are at the limit of what is feasible,” explained Laatiaoui. From the next heavier element on, the physicochemical properties change abruptly and impede providing samples in suitable atomic states.”

Together with research colleagues, the physicist has therefore developed the new LRC approach in optical spectroscopy. This combines element selectivity and spectral precision of laser spectroscopy with ion-mobility mass spectrometry and merges the benefits of a high sensitivity with the “simplicity” of optical probing as in laser-induced fluorescence spectroscopy. Its key idea is to detect the products of resonant optical excitations not on the basis of fluorescent light as usual, but based on their characteristic drift time to a particle detector.

In their theoretical work, the researchers focused on singly charged lawrencium, element 103, and on its lighter chemical homolog. But the concept offers unparalleled access to laser spectroscopy of many other monoatomic ions across the periodic table, in particular of the transition metals including the high-temperature refractory metals and elements beyond lawrencium. Other ionic species like triply-charged thorium shall be within reach of the LRC approach as well. Moreover, the method enables to optimize signal-to-noise ratios and thus to ease ion mobility spectrometry, state-selected ion chemistry, and other applications.

Dr. Mustapha Laatiaoui came to Johannes Gutenberg University Mainz and the Helmholtz Institute Mainz (HIM) in February 2018. In late 2018, he received an ERC Consolidator Grant from the European Research Council (ERC), one of the European Union’s most valuable funding grants, for his research into the heaviest elements using laser spectroscopy and ion mobility spectroscopy. The current publications also included work that Laatiaoui had previously carried out at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt and at KU Leuven in Belgium.

This work was conducted in cooperation with Alexei A. Buchachenko from the Skolkovo Institute of Science and Technology and the Institute of Problems of Chemical Physics, both in Moscow, Russia, and Larry A. Viehland from Chatham University, Pittsburgh, USA.

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A twist connecting magnetism and electronic-band topology

Dirac matter is an intriguing class of materials with rather peculiar properties: electrons in these materials behave as if they had no mass. The most prominent Dirac material is graphene, but further members have been discovered during the past 15 years or so. Each one of them serves as a rich playground for exploring ‘exotic’ electronic behaviours, some of which hold the promise to enable novel components for electronics. However, even if Dirac matter and other so-called topological materials — in which electrons behave in similarly unexpected ways — are among the currently most intensively studied condensed-matter systems, there are only very few examples where the topology of the electronic bands is connected in a well-defined manner to the magnetic properties of the materials. One material in which such interplay between topological electronic states and magnetism has been observed is CaMnBi2, but the mechanism connecting the two remained unclear. Writing in Physical Review Letters, postdoc Run Yang and PhD student Matteo Corasaniti from the Optical Spectroscopy group of Prof. Leonardo Degiorgi at the Laboratory for Solid State Physics of ETH Zurich, working with colleagues at Brookhaven National Laboratory (US) and the Chinese Academy of Sciences in Beijing, now report a comprehensive study in which they provide clear evidence that it is a slight nudge on the magnetic moments, known as spin canting, that provokes substantial changes in the electronic band structure.

Compass points to the right direction on a bumpy road

CaMnBi2 and the related compound SrMnBi2 have recently attracted attention as they display quantum magnetism — the manganese ions are antiferromagnetically ordered at around room temperature and below — and at the same time they host Dirac electrons. That there is interplay between the two properties has been suspected for some while, not least as at ~50 K there appears an unexpected ‘bump’ in the conduction properties at these materials. But the precise nature of this anomaly was still poorly understood until now.

In earlier work studying optical properties, Corasaniti, Yang and co-workers had established already a link to the electronic properties of the material. They used in particular the fact that the bump-like anomaly in the transport properties can be shifted in temperature by replacing some of the calcium atoms with sodium. To get now to the microscopic origins of the observed behaviour, they studied samples with different sodium dopings by torque magnetometry. In this technique, the torque on a magnetic sample is measured when it is exposed to a suitably strong field, similarly as a compass needle aligns with the Earth magnetic field. And this approach proved to point the team to the origins of the anomaly.

A firm link between magnetic and electronic properties

In their magnetic-torque experiments, the researchers found that at temperatures where no anomaly is observed in the electronic transport measurements, the magnetic behaviour is such as one would expect for an antiferromagnet. This was not the case anymore at temperatures at which the anomaly is present. There, a ferromagnetic component appeared, which can be explained by a projection of magnetic moments onto the plane orthogonal to the easy spin c-axis of the original antiferromagnetic order. This phenomenon is known as spin-canting, induced by a so-called super-exchange mechanism.

These two sets of experiments — optical and torque measurements — were supported by dedicated first-principles calculations. In particular, for the case where spin canting was included in the calculations, a peculiar hybridization between the manganese and bismuth atoms was found to mediate the interlayer magnetic coupling and to govern the electronic properties in the material. Taken together, the study therefore establishes that sought-after direct link between the magnetic properties and changes to the electronic band structure, reflected in the bump anomaly of the transport properties.

With such detailed understanding on board, the door is now open to exploring not only the electronic properties of CaMnBi2 and related compounds, but also the possibilities arising from the connection between magnetic properties and topological states in these intriguing forms of matter.

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Distortion isn’t a drag on fluid-straddling particles

Some intriguing physics can be found at the interfaces between fluids, particularly if they are straddled by particles like proteins or dust grains. When placed between un-mixable fluids such as oil and water, a variety of processes, including inter-molecular interactions, will cause the particles to move around. These motions are characterised by the drag force experienced by the particles, which is itself thought to depend on the extent to which they distort fluid interfaces. So far, however, experiments investigating the intriguing effect haven’t yet fully confirmed the influence of this distortion. In new research published in EPJ E, a team led by Jean-Christophe Loudet at the University of Bordeaux, France, showed that the drag force experienced by fluid-straddling particles is less affected by interface distortion than previously believed.

Since drag forces are ubiquitous in fluids, the team’s discovery could be relevant to the self-assembling properties of a great variety of species which can stick, or ‘adsorb’ to liquid surfaces, including nano- and microparticles, proteins, and other groups of molecules. For the relatively large particles investigated by Loudet and colleagues, interfacial distortions arise from the buoyant weight of straddling particles. This force produces curved menisci in both fluids, similar to the curves found on the surface of water as it touches a glass.

In their study, the researchers approached this problem numerically using techniques for simulating multi-phase flows, capable of accurately describing how the interfacial dynamics were coupled to flows in the bulk of each fluid. This allowed them to explore how drag forces are affected by interface deformations, which depend on factors including the densities of the two fluids and the particle, and the contact angles between the three substances. Loudet’s team revealed that for some values of these parameters, large drag forces don’t necessarily correspond to large interfacial distortions, and that lower drag forces can even be reached through non-flat distortions.

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  1. J. -C. Loudet, M. Qiu, J. Hemauer, J. J. Feng. Drag force on a particle straddling a fluid interface: Influence of interfacial deformations. The European Physical Journal E, 2020; 43 (2) DOI: 10.1140/epje/i2020-11936-1

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M5Stick: Wearable ESP32 System

Some sweet new featured projects, and an intriguing new system, thanks to our friend Moheeb – the M5Stick!

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// https://www.hackster.io/m5stack/products/m5stickc-esp32-pico-mini-iot-development-board
// https://twitter.com/virgilvox

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Scientists ask: How can liquid organelles in cells coexist without merging?

New research may help to explain an intriguing phenomenon inside human cells: how wall-less liquid organelles are able to coexist as separate entities instead of just merging together.

These structures, called membrane-less organelles (MLOs), are liquid droplets made from proteins and RNA, with each droplet holding both materials. The organelles play a crucial role in organizing the internal contents of cells, and can serve as a center of biochemical activity, recruiting molecules needed to carry out essential cellular reactions.

But how different droplets stay apart from each other remains a mystery. Why don’t they always just combine to form bigger droplets?

“These organelles don’t have any membrane, and hence, common intuition would tell you that they are free to mix,” says Priya Banerjee, PhD, assistant professor of physics in the University at Buffalo College of Arts and Sciences.

Banerjee is the lead researcher on the new study, which explores why this doesn’t happen.

Co-authors of the research include first author and physics PhD student Ibraheem Alshareedah; physics PhD student Taranpreet Kaur; undergraduate Jason Ngo; physics and math undergraduate Hannah Seppala; biomedical engineering undergraduate Liz-Audrey Djomnang Kounatse; and physics postdoctoral researchers Wei Wang and Mahdi Moosa. All are from UB.

Droplets won’t mix easily if they take on a gel-like state

The results — published on Aug. 22 in the Journal of the American Chemical Society — point to the chemical structure of protein and RNA molecules within the droplets as one key factor that may prevent MLOs from mixing.

The team found that certain types of RNA and proteins are “stickier” than others, enabling them to form gelatinous droplets that don’t fuse easily with other droplets in the same viscoelastic state. Specifically, droplets are more likely to be gel-like when they contain RNA molecules rich in a building block called purine, and proteins rich in an amino acid called arginine.

The experiments did not take place in cells. Instead, the findings were based on tests done on model systems consisting of RNA and a droplet-forming protein called fused in sarcoma (FUS) floating in a buffer solution.

One reason FUS is of interest to researchers is its potential connection to the neurodegenerative disease amyotrophic lateral sclerosis (ALS). As Banerjee explains, arginine-rich protein molecules are associated with a prevalent form of the disease, known as c9orf72-mediated ALS.

“Our finding points to a special role of arginine-rich proteins in determining the material state — liquid vs. gel — of membrane-less organelles,” Banerjee says. “This study may be important in understanding how ALS-linked arginine-rich proteins may alter the viscoelastic state of RNA-rich MLOs.”

In addition to providing insight into why MLOs resist mixing (due to enhanced viscoelasticity), the study probed the role of RNA in the formation and dissolution of liquid organelles containing FUS. The research found that for the type of droplet being studied, adding low concentrations of RNA to a solution containing the proteins caused droplets to form. But as more RNA was added, the droplets then dissolved.

“There’s usually a very small window where these droplets exist, but the window is significantly wider for arginine-rich proteins,” Banerjee says.

The complicated life of liquid organelles

The new paper is the latest in a series of studies that Banerjee’s group has conducted to explore forces governing the creation, maintenance and dissolution of MLOs.

Though the team uses model systems to examine individual properties of the droplets, it’s likely that many forces work together in a cell to determine the behavior and function of the organelles, he says. There may be multiple other mechanisms, for example, that cause MLOs to take on a gelatinous state or otherwise refuse to mix.

“Cells are enormously complex, with many different molecules undergoing different processes that come together at the same time to influence what goes on inside MLOs,” Banerjee says. “By using model systems, we are able to better understand how one particular variable may impact the formation and dissolution of these organelles. And we do expect to see these same forces at play in nature, inside cells.”

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This Wearable Could Make the Matrix-Style Skill Downloads Possible

The Matrix was a hit, and now a favorite among hackers, for a lot of reasons. One of the most intriguing plot devices in the movie was the characters’ ability to download new skills. For instance, Neo is able to instantaneously learn advanced martial arts techniques — at least within the digital world. While that is purely science fiction, a new type of wearable sleeve developed by Dr. Pedro Lopes at the University of Chicago’s Human Computer Integration Lab could make a simplified version of that possible.

This wearable device consists of a sleeve that covers a user’s forearm. There are a number of electrodes positioned inside of the sleeve that are capable of using electrical stimulation to activate the user’s muscles. By stimulating their muscles in precise ways, the device can cause the user to move their fingers or bend their wrist. This kind of muscle stimulation is already well-proven, and is sometimes used in rehabilitation therapy today. But Dr. Lopes believes the technique can be harnessed to help people learn the muscle movements necessary to perform completely new skills.

Dr. Lopes hopes that future users will be able to scan an RFID tag attached to something like a trombone, and the device will automatically stimulate the muscles necessary to play a tune. It’s almost like turning a user’s biological arm into a robotic arm. Theoretically, users would eventually develop the muscle memory to play it themselves. On a more practical front, the same technique could be used to teach people how to use power tools they’ve never touched before — though that idea seems awfully risky to us. More testing will be needed to find out if it’s even possible for the device to stimulate a human’s muscles in precise enough ways to make this feasible, but it has already been used for simple tasks such as peeling an avocado and operating a spray can.

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James Webb Space Telescope could begin learning about TRAPPIST-1 atmospheres in a year

New research from astronomers at the University of Washington uses the intriguing TRAPPIST-1 planetary system as a kind of laboratory to model not the planets themselves, but how the coming James Webb Space Telescope might detect and study their atmospheres, on the path toward looking for life beyond Earth.

The study, led by Jacob Lustig-Yaeger, a UW doctoral student in astronomy, finds that the James Webb telescope, set to launch in 2021, might be able to learn key information about the atmospheres of the TRAPPIST-1 worlds even in its first year of operation, unless — as an old song goes — clouds get in the way.

“The Webb telescope has been built, and we have an idea how it will operate,” said Lustig-Yaeger. “We used computer modeling to determine the most efficient way to use the telescope to answer the most basic question we’ll want to ask, which is: Are there even atmospheres on these planets, or not?”

His paper, “The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST,” was published online in June in the Astronomical Journal.

The TRAPPIST-1 system, 39 light-years — or about 235 trillion miles — away in the constellation of Aquarius, interests astronomers because of its seven orbiting rocky, or Earth-like, planets. Three of these worlds are in the star’s habitable zone — that swath of space around a star that is just right to allow liquid water on the surface of a rocky planet, thus giving life a chance.

The star, TRAPPIST-1, was much hotter when it formed than it is now, which would have subjected all seven planets to ocean, ice and atmospheric loss in the past.

“There is a big question in the field right now whether these planets even have atmospheres, especially the innermost planets,” Lustig-Yaeger said. “Once we have confirmed that there are atmospheres, then what can we learn about each planet’s atmosphere — the molecules that make it up?”

Given the way he suggests the James Webb Space Telescope might search, it could learn a lot in fairly short time, this paper finds.

Astronomers detect exoplanets when they pass in front of or “transit” their host star, resulting in a measurable dimming of starlight. Planets closer to their star transit more frequently and so are somewhat easier to study. When a planet transits its star, a bit of the star’s light passes through the planet’s atmosphere, with which astronomers can learn about the molecular composition of the atmosphere.

Lustig-Yaeger said astronomers can see tiny differences in the planet’s size when they look in different colors, or wavelengths, of light.

“This happens because the gases in the planet’s atmosphere absorb light only at very specific colors. Since each gas has a unique ‘spectral fingerprint,’ we can identify them and begin to piece together the composition of the exoplanet’s atmosphere.”

Lustig-Yaeger said the team’s modeling indicates that the James Webb telescope, using a versatile onboard tool called the Near-Infrared Spectrograph, could detect the atmospheres of all seven TRAPPIST-1 planets in 10 or fewer transits — if they have cloud-free atmospheres. And of course we don’t know whether or not they have clouds.

If the TRAPPIST-1 planets have thick, globally enshrouding clouds like Venus does, detecting atmospheres might take up to 30 transits.

“But that is still an achievable goal,” he said. “It means that even in the case of realistic high-altitude clouds, the James Webb telescope will still be capable of detecting the presence of atmospheres — which before our paper was not known.”

Many rocky exoplanets have been discovered in recent years, but astronomers have not yet detected their atmospheres. The modeling in this study, Lustig-Yaeger said, “demonstrates that, for this TRAPPIST-1 system, detecting terrestrial exoplanet atmospheres is on the horizon with the James Webb Space Telescope — perhaps well within its primary five-year mission.”

The team found that the Webb telescope may be able to detect signs that the TRAPPIST-1 planets lost large amounts of water in the past, when the star was much hotter. This could leave instances where abiotically produced oxygen — not representative of life — fills an exoplanet atmosphere, which could give a sort of “false positive” for life. If this is the case with TRAPPIST-1 planets, the Webb telescope may be able to detect those as well.

Lustig-Yaeger’s co-authors, both with the UW, are astronomy professor Victoria Meadows, who is also principal investigator for the UW-based Virtual Planetary Laboratory; and astronomy doctoral student Andrew Lincowski. The work follows, in part, on previous work by Lincowski modeling possible climates for the seven TRAPPIST-1 worlds.

“By doing this study, we have looked at: What are the best-case scenarios for the James Webb Space Telescope? What is it going to be capable of doing? Because there are definitely going to be more Earth-sized planets found before it launches in 2021.”

The research was funded by a grant from the NASA Astrobiology Program’s Virtual Planetary Laboratory team, as part of the Nexus for Exoplanet System Science (NExSS) research coordination network.

Lustig-Yaeger added: “It’s hard to conceive in theory of a planetary system better suited for James Webb than TRAPPIST-1.”

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New retroreflective material could be used in nighttime color-changing road signs

A thin film that reflects light in intriguing ways could be used to make road signs that shine brightly and change color at night, according to a study that will be published on Aug. 9 in Science Advances.

The technology could help call attention to important traffic information when it’s dark, with potential benefits for both drivers and pedestrians, researchers say.

The film consists of polymer microspheres laid down on the sticky side of a transparent tape. The material’s physical structure leads to an interesting phenomenon: When white light shines on the film at night, some observers will see a single, stable color reflected back, while others will see changing colors. It all depends on the angle of observation and whether the light source is moving.

The research was led by Limin Wu, PhD, at Fudan University in China, whose group developed the material. Experts on optics at the University at Buffalo made significant contributions to the work, providing insight into potential applications for the film, such as employing it in nighttime road signs.

“You can use this material to make smart traffic signs,” says Qiaoqiang Gan, PhD, an associate professor of electrical engineering in the UB School of Engineering and Applied Sciences and a co-first author of the new study. “If a person is listening to loud music or isn’t paying attention while they’re walking or driving, a color-changing sign can help to better alert them to the traffic situation.”

Testing color-changing road signs at night

In one set of experiments, researchers created a speed limit sign with letters and numbers made from the new film. The scientists placed a white light nearby to illuminate the sign, and when a fast-moving car drove past, the color of the characters on the sign appeared to flicker from the perspective of the driver as the driver’s viewing angle changed.

In other tests, the team applied the new material to a series of markers lining the side of a road, denoting the boundary of the driving lane. As a car approached, the markers lit up in bright colors, reflecting light from the vehicle’s headlights.

From the driver’s perspective, the markers’ color remained stable. But to a pedestrian standing at the side of the road, the color of the markers appeared to flicker as the car and its headlights sped past.

“If the car goes faster, the pedestrian will see the color change more quickly, so the sign tells you a lot about what is going on,” says co-author Haomin Song, PhD, UB assistant professor of research in electrical engineering.

The experiments were performed in China, but Gan, Song and UB PhD graduate Dengxin Ji, all in the Department of Electrical Engineering, helped design the tests. In addition to his position at UB, Gan was a summer visiting professor at the University of Shanghai for Science and Technology during the period of the collaborative work.

The study was funded by the National Key Research and Development Program of China and the National Natural Science Foundation of China.

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