Computers Math

Polymer science has made possible rubber tires, Teflon and Kevlar, plastic water bottles, nylon jackets among many other ubiquitous features of daily life. Elastic polymers, known as elastomers, can be stretched and released repeatedly and are used in applications such as gloves and heart valves, where they need to last a long time without tearing. But a conundrum has long stumped polymer scientists: Elastic polymers can be stiff, or they can be tough, but they can’t be both.
This stiffness-toughness conflict is a challenge for scientists developing polymers that could be used in applications including tissue regeneration, bioadhesives, bioprinting, wearable electronics, and soft robots.
In a paper published today in Science, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have resolved that long-standing conflict and developed an elastomer that is both stiff and tough.
“In addition to developing polymers for emerging applications, scientists are facing an urgent challenge: plastic pollution,” said Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials, the senior author of the study. “The development of biodegradable polymers has once again brought us back to fundamental questions — why are some polymers tough, but others brittle? How do we make polymers resist tearing under repeated stretching?”
Polymer chains are made by linking together monomer building blocks. To make a material elastic , the polymer chains are crosslinked by covalent bonds. The more crosslinks, the shorter the polymer chains and the stiffer the material.
“As your polymer chains become shorter, the energy you can store in the material becomes less and the material becomes brittle,” said Junsoo Kim, a graduate student at SEAS and co-first author of the paper. “If you have only a few crosslinks, the chains are longer, and the material is tough but it’s too squishy to be useful.”
To develop a polymer that is both stiff and tough, the researchers looked to physical, rather than chemical bonds to link the polymer chains. These physical bonds, called entanglements, have been known in the field for almost as long as polymer science has existed, but they’ve been thought to only impact stiffness, not toughness. More

For the first time, researchers have been able capture images providing unprecedented details of how particles behave in a liquid suspension when the phenomenon known as shear thickening takes place. The work allows us to directly understand the processes behind shear thickening, which had previously only been understood based on inference and computational modeling.
Shear thickening is a phenomenon that can occur when particles are suspended in a low-viscosity solution. If the concentration of particles is high enough, then when stress is applied to the solution it becomes very viscous — effectively behaving like a solid. When the stress is removed or dissipates, the suspension returns to its normal fluid-like viscosity. This phenomenon can be seen in popular YouTube videos in which people are able to run across a solution of corn starch suspended in water — but sink into the solution when they stand still.
Shear thickening can be a liability or an advantage, depending on the context.
For example, in industries from food processing to pharmaceutical manufacturing, companies often try to pump liquids with high particle concentrations to make manufacturing processes more efficient and cost-effective. And if those companies don’t properly account for shear thickening, the liquids being pumped can jam or clog — costing them valuable time and potentially damaging their equipment.
On the other hand, the properties of shear thickening can also be used to develop force-absorbing materials for use in applications such as body armor, or as a mechanism for controlling the physical characteristics of soft robotics devices.
For these reasons, researchers have spent years trying to understand precisely how and why shear thickening occurs. However, researchers have been forced to rely on indirect experimentation, because they were unable to capture the precise behavior of the particles in solution as shear thickening takes place. Until now. More

A new study published in one of the world’s leading medical journals has revealed a link between screen time and higher risk and severity of myopia, or short-sightedness, in children and young adults.
The open-access research, published this week in The Lancet Digital Health, was undertaken by researchers and eye health experts from Singapore, Australia, China and the UK, including Professor Rupert Bourne from Anglia Ruskin University (ARU). The authors examined more than 3,000 studies investigating smart device exposure and myopia in children and young adults aged between 3 months old and 33 years old.
After analysing and statistically combining the available studies, the authors revealed that high levels of smart device screen time, such as looking at a mobile phone, is associated with around a 30% higher risk of myopia and, when combined with excessive computer use, that risk rose to around 80%.
The research comes as millions of children around the world have spent substantial time using remote learning methods following the closure of schools due to the COVID-19 pandemic.
Professor Bourne, Professor of Ophthalmology in the Vision and Eye Research Institute at Anglia Ruskin University (ARU), said: “Around half the global population is expected to have myopia by 2050, so it is a health concern that is escalating quickly. Our study is the most comprehensive yet on this issue and shows a potential link between screen time and myopia in young people.
“This research comes at a time when our children have been spending more time than ever looking at screens for long periods, due to school closures, and it is clear that urgent research is needed to further understand how exposure to digital devices can affect our eyes and vision. We also know that people underestimate their own screen time, so future studies should use objective measures to capture this information.”
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A team from the U.S. Department of Energy’s Oak Ridge National Laboratory, Stanford University and Purdue University developed and demonstrated a novel, fully functional quantum local area network, or QLAN, to enable real-time adjustments to information shared with geographically isolated systems at ORNL using entangled photons passing through optical fiber.
This network exemplifies how experts might routinely connect quantum computers and sensors at a practical scale, thereby realizing the full potential of these next-generation technologies on the path toward the highly anticipated quantum internet. The team’s results, which are published in PRX Quantum, mark the culmination of years of related research.
Local area networks that connect classical computing devices are nothing new, and QLANs have been successfully tested in tabletop studies. Quantum key distribution has been the most common example of quantum communications in the field thus far, but this procedure is limited because it only establishes security, not entanglement, between sites.
“We’re trying to lay a foundation upon which we can build a quantum internet by understanding critical functions, such as entanglement distribution bandwidth,” said Nicholas Peters, the Quantum Information Science section head at ORNL. “Our goal is to develop the fundamental tools and building blocks we need to demonstrate quantum networking applications so that they can be deployed in real networks to realize quantum advantages.”
When two photons — particles of light — are paired together, or entangled, they exhibit quantum correlations that are stronger than those possible with any classical method, regardless of the physical distance between them. These interactions enable counterintuitive quantum communications protocols that can only be achieved using quantum resources.
One such protocol, remote state preparation, harnesses entanglement and classical communications to encode information by measuring one half of an entangled photon pair and effectively converting the other half to the preferred quantum state. Peters led the first general experimental realization of remote state preparation in 2005 while earning his doctorate in physics. The team applied this technique across all the paired links in the QLAN — a feat not previously accomplished on a network — and demonstrated the scalability of entanglement-based quantum communications. More

Athletes still have the edge over action video gamers when it comes to dynamic visual skills, a new study from the University of Waterloo shows.
For an athlete, having strong visual skills can be the difference between delivering a peak performance and achieving average results.
“Athletes involved in sports with a high-level of movement — like soccer, football, or baseball — often score higher on dynamic visual acuity tests than non-athletes,” said Dr. Kristine Dalton of Waterloo’s School of Optometry & Vision Science. “Our research team wanted to investigate if action video gamers — who, like e-sport athletes, are regularly immersed in a dynamic, fast-paced 2-D video environment for large periods of time — would also show superior levels of dynamic visual acuity on par with athletes competing in physical sport.”
While visual acuity (clarity or sharpness of vision) is most often measured under static conditions during annual check-ups with an optometrist, research shows that testing dynamic visual acuity is a more effective measure of a person’s ability to see moving objects clearly — a baseline skill necessary for success in physical and e-sports alike.
Using a dynamic visual acuity skills-test designed and validated at the University of Waterloo, researchers discovered that while physical athletes score highly on dynamic visual acuity tests as expected, action video game players tested closer to non-athletes.
“Ultimately, athletes showed a stronger ability to identify smaller moving targets, which suggests visual processing differences exist between them and our video game players,” said Alan Yee, a PhD candidate in vision science. All participants were matched based on their level of static visual acuity and refractive error, distinguishing dynamic visual acuity as the varying factor on their test performance.
These findings are also important for sports vision training centres that have been exploring the idea of developing video game-based training programs to help athletes elevate their performance.
“Our findings show there is still a benefit to training in a 3-D environment,” said Dalton. “For athletes looking to develop stronger visual skills, the broader visual field and depth perception that come with physical training may be crucial to improving their dynamic visual acuity — and ultimately, their sport performance.”
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Scientists develop groundbreaking theory for calculating what’s happening inside a proton travelling at the speed of light.
For more than 2,000 years, scientists thought the atom was the smallest particle possible. Then, they discovered that it has a nucleus made up of protons and neutrons surrounded by electrons. After that, they found that the protons and neutrons themselves have a complex inner world full of quarks and antiquarks held together by a superglue-like force created by gluons.
“Protons along with neutrons constitute over 99 percent of the visible universe, meaning everything from galaxies and stars to us,” said Yong Zhao — a physicist at the U.S. Department of Energy’s (DOE) Argonne National Laboratory. “Yet, there is still much we do not know about the rich inner life of protons or neutrons.”
Zhao has co-authored a paper on an innovative method for calculating the quark and gluon structure of a proton travelling at the speed of light. The name of the team’s creation is large-momentum effective theory, LaMET for short, which works jointly with a theory called lattice quantum chromodynamics (QCD).
The proton is tiny — about 100,000 times smaller than an atom, so physicists often model it as a point with no dimensions. But these new theories can predict what’s happening within the speed-of-light proton as though it were a body of three dimensions.
The concept of momentum is vital to not only LaMET but physics in general. It equals the speed of an object times its mass. More

LEO carves out a new type of locomotion somewhere between walking and flying.
Researchers at Caltech have built a bipedal robot that combines walking with flying to create a new type of locomotion, making it exceptionally nimble and capable of complex movements.
Part walking robot, part flying drone, the newly developed LEONARDO (short for LEgs ONboARD drOne, or LEO for short) can walk a slackline, hop, and even ride a skateboard. Developed by a team at Caltech’s Center for Autonomous Systems and Technologies (CAST), LEO is the first robot that uses multi-joint legs and propeller-based thrusters to achieve a fine degree of control over its balance.
A paper about the LEO robot was published online on October 6 and was featured on the October 2021 cover of Science Robotics.
“We drew inspiration from nature. Think about the way birds are able to flap and hop to navigate telephone lines,” says Soon-Jo Chung, corresponding author and Bren Professor of Aerospace and Control and Dynamical Systems. “A complex yet intriguing behavior happens as birds move between walking and flying. We wanted to understand and learn from that.”
“There is a similarity between how a human wearing a jet suit controls their legs and feet when landing or taking off and how LEO uses synchronized control of distributed propeller-based thrusters and leg joints,” Chung adds. “We wanted to study the interface of walking and flying from the dynamics and control standpoint.”
Bipedal robots are able to tackle complex real-world terrains by using the same sort of movements that humans use, like jumping or running or even climbing stairs, but they are stymied by rough terrain. Flying robots easily navigate tough terrain by simply avoiding the ground, but they face their own set of limitations: high energy consumption during flight and limited payload capacity. “Robots with a multimodal locomotion ability are able to move through challenging environments more efficiently than traditional robots by appropriately switching between their available means of movement. In particular, LEO aims to bridge the gap between the two disparate domains of aerial and bipedal locomotion that are not typically intertwined in existing robotic systems,” says Kyunam Kim, postdoctoral researcher at Caltech and co-lead author of the Science Robotics paper. More

A team of scientists from Germany, Sweden and China has discovered a new physical phenomenon: complex braided structures made of tiny magnetic vortices known as skyrmions. Skyrmions were first detected experimentally a little over a decade ago and have since been the subject of numerous studies, as well as providing a possible basis for innovative concepts in information processing that offer better performance and lower energy consumption. Furthermore, skyrmions influence the magnetoresistive and thermodynamic properties of a material. The discovery therefore has relevance for both applied and basic research.
Strings, threads and braided structures can be seen everywhere in daily life, from shoelaces, to woollen pullovers, from plaits in a child’s hair to the braided steel cables that are used to support countless bridges. These structures are also commonly seen in nature and can, for example, give plant fibres tensile or flexural strength. Physicists at Forschungszentrum Jülich, together with colleagues from Stockholm and Hefei, have discovered that such structures exist on the nanoscale in alloys of iron and the metalloid germanium.
These nanostrings are each made up of several skyrmions that are twisted together to a greater or lesser extent, rather like the strands of a rope. Each skyrmion itself consists of magnetic moments that point in different directions and together take the form of an elongated tiny vortex. An individual skyrmion strand has a diamater of less than one micrometre. The length of the magnetic structures is limited only by the thickness of the sample; they extend from one surface of the sample to the opposite surface.
Earlier studies by other scientists had shown that such filaments are largely linear and almost rod-shaped. However, ultra-high-resolution microscopy investigations undertaken at the Ernst Ruska-Centre in Jülich the theoretical studies at Jülich’s Peter Grünberg Institute have revealed a more varied picture: the threads can in fact twist together to varying degrees. According to the researchers, these complex shapes stabilise the magnetic structures, making them particularly interesting for use in a range of applications.
“Mathematics contains a great variety of these structures. Now we know that this theoretical knowledge can be translated into real physical phenomena,” Jülich physicist Dr. Nikolai Kiselev is pleased to report. “These types of structures inside magnetic solids suggest unique electrical and magnetic properties. However, further research is needed to verify this.”
To explain the discrepancy between these studies and previous ones, the researcher points out that analyses using an ultra-high-resolution electron microscope do not simply provide an image of the sample, as in the case of, for example, an optical microscope. This is because quantum mechanical phenomena come into play when the high energy electrons interact with those in the sample.
“It is quite feasible that other researchers have also seen these structures under the microscope, but have been unable to interpret them. This is because it is not possible to directly determine the distribution of magnetization directions in the sample from the data obtained. Instead, it is necessary to create a theoretical model of the sample and to generate a kind of electron microscope image from it,” explains Kiselev. “If the theoretical and experimental images match, one can conclude that the model is able to represent reality.” In ultra-high-resolution analyses of this kind, Forschungszentrum Jülich with its Ernst Ruska-Centre counts as one of the leading institutions worldwide.
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