Computers Math

When stretched or deformed, shape memory polymers return to their original shapes after heat or light is applied. These materials show great promise for soft robotics, smart biomedical devices and deployable space structures, but until now they haven’t been able to store enough energy. Now, researchers reporting in ACS Central Science have developed a shape memory polymer that stores almost six times more energy than previous versions.
Shape memory polymers alternate between an original, undeformed state and a secondary, deformed state. The deformed state is created by stretching the polymer and is held in place by molecular changes, such as dynamic bonding networks or strain-induced crystallization, that are reversed with heat or light. The polymer then returns to its original state through the release of stored entropic energy. But it’s been challenging for scientists to make these polymers perform energy-intensive tasks. Zhenan Bao and colleagues wanted to develop a new type of shape memory polymer that stretches into a stable, highly elongated state, allowing it to release large amounts of energy when returning to its original state.
The researchers incorporated 4-,4′-methylene bisphenylurea units into a poly(propylene glycol) polymer backbone. In the polymer’s original state, polymer chains were tangled and disordered. Stretching caused the chains to align and form hydrogen bonds between urea groups, creating supermolecular structures that stabilized the highly elongated state. Heating caused the bonds to break and the polymer to contract to its initial, disordered state.
In tests, the polymer could be stretched up to five times its original length and store up to 17.9 J/g energy — almost six times more energy than previous shape memory polymers. The team demonstrated that the stretched material could use this energy to lift objects 5,000 times its own weight upon heating. They also made an artificial muscle by attaching the pre-stretched polymer to the upper and lower arm of a wooden mannequin. When heated, the material contracted, causing the mannequin to bend its arm at the elbow. In addition to its record-high energy density, the shape memory polymer is also inexpensive (raw materials cost about $11 per lb) and easy to make, the researchers say.
Story Source:
Materials provided by American Chemical Society. Note: Content may be edited for style and length. More

Elastomers, or elastic polymers, materials with high elasticity, are widely used for applications in industries, such as automotive, manufacturing, and oil and gas. The degree of elasticity in these materials, denoted by a parameter known as “Young’s modulus,” depends on the extent of cross-linking between the constituent polymer layers such that higher cross-linking leads to higher rigidity, and, in turn, implies a large Young’s modulus.
Different applications require elastomers of different stiffness. For instance, the desirable Young’s modulus for tires is different from that for pipes and hoses. So far, for conventional elastomers, once the cross-linking of polymer chains takes place, their properties cannot be changed, requiring industries to manufacture different elastomers for different applications. But what if we could prepare a single elastomer with versatile properties for a range of applications?
In a new study published in Polymer, Dr. Mikihiro Hayashi from Nagoya Institute of Technology, Japan, and his colleagues have now done just that. The team has successfully synthesized an elastomer film whose elongation can be controlled by post-preparation photo reaction to suit the desired application, thus, saving time, cost and human resources.
To develop this elastomer, the scientists equipped a polyester (polymer having ester group) with thermoreactive and photoreactive groups, which react to heat and light, respectively. They then followed a two-step process in which the thermoreactive groups first underwent thermal cross-linking and then the photoreactive group formed cross-links in presence of UV light. The scientists observed that the material obtained after thermal cross-linking was soft and flexible, but when further treated with UV light, the material increased in stiffness depending on the time of exposure. In fact, when exposed for 30 minutes, the material’s Young’s Modulus increased by two orders of magnitude!
This unprecedented finding excited the scientists. Dr. Hayashi states, “By developing this elastomer using the dual thermal and photo cross-linking, we proved that post-preparation tuning of tensile strength in materials is possible. We were intrigued to further explore the benefits of this material.”
Accordingly, they designed elastomer films with inhomogeneous patterning of Young’s modulus through selective UV illumination. The scientists accomplished this using horizontal and vertical photomasking slits, creating patterns of soft and rigid sections. On testing the horizontal patterned films under stress, the rigid sections hardly showed any deformation, whereas the soft sections showed 5 times elongation. Surprisingly, however, the vertically patterned films showed excellent toughness and delayed the propagation of cracks. While a crack on a fully rigid film propagates instantly, a crack on the inhomogeneous film stopped on reaching the soft section. The more the number of patterns, the slower was the growth of the crack.
“Our findings can provide useful insights for developing new methodologies for controlling the fracture behavior of elastomers,” comments Dr. Hayashi, speaking of the practical ramifications of their study. “In addition, our technique could help save excess chemical consumption, and solve problems associated with depletion of petroleum resources,” he adds.
These versatile films are sure to find applications in a diverse range of fields and pave the way to sustainable societies!
Story Source:
Materials provided by Nagoya Institute of Technology. Note: Content may be edited for style and length. More

For millions of people with epilepsy and movement disorders such as Parkinson’s disease, electrical stimulation of the brain already is widening treatment possibilities. In the future, electrical stimulation may help people with psychiatric illness and direct brain injuries, such as stroke.
However, studying how brain networks interact with each other is complicated. Brain networks can be explored by delivering brief pulses of electrical current in one area of a patient’s brain while measuring voltage responses in other areas. In principle, one should be able to infer the structure of brain networks from these data. However, with real-world data, the problem is difficult because the recorded signals are complex, and a limited amount of measurements can be made.
To make the problem manageable, Mayo Clinic researchers developed a set of paradigms, or viewpoints, that simplify comparisons between effects of electrical stimulation on the brain. Because a mathematical technique to characterize how assemblies of inputs converge in human brain regions did not exist in the scientific literature, the Mayo team collaborated with an international expert in artificial intelligence (AI) algorithms to develop a new type of algorithm called “basis profile curve identification.”
In a study published in PLOS Computational Biology, a patient with a brain tumor underwent placement of an electrocorticographic electrode array to locate seizures and map brain function before a tumor was removed. Every electrode interaction resulted in hundreds to thousands of time points to be studied using the new algorithm.
“Our findings show that this new type of algorithm may help us understand which brain regions directly interact with one another, which in turn may help guide placement of electrodes for stimulating devices to treat network brain diseases,” says Kai Miller, M.D., Ph.D., a Mayo Clinic neurosurgeon and first author of the study. “As new technology emerges, this type of algorithm may help us to better treat patients with epilepsy, movement disorders like Parkinson’s disease, and psychiatric illnesses like obsessive compulsive disorder and depression.”
“Neurologic data to date is perhaps the most challenging and exciting data to model for AI researchers,” says Klaus-Robert Mueller, Ph.D., study co-author and member of the Google Research Brain Team. Dr. Mueller is co-director of the Berlin Institute for the Foundations of Learning and Data and director of the Machine Learning Group — both at Technical University of Berlin.
In the study, the authors provide a downloadable code package so others may explore the technique. “Sharing the developed code is a core part of our efforts to help reproducibility of research,” says Dora Hermes, Ph.D., a Mayo Clinic biomedical engineer and senior author.
This research was supported by National Institutes of Health’s National Center for Advancing Translational Science Clinical and Translational Science Award, National Institute of Mental Health Collaborative Research in Computational Neuroscience, and the Federal Ministry of Education and Research.
Story Source:
Materials provided by Mayo Clinic. Original written by Susan Barber Lindquist. Note: Content may be edited for style and length. More

Quantum computers are advancing at a rapid pace and are already starting to push the limits of the world’s largest supercomputers. Yet, these devices are extremely sensitive to external influences and thus prone to errors which can change the result of the computation. This is particularly challenging for quantum computations that are beyond the reach of our trusted classical computers, where we can no longer independently verify the results through simulation. “In order to take full advantage of future quantum computers for critical calculations we need a way to ensure the output is correct, even if we cannot perform the calculation in question by other means,” says Chiara Greganti from the University of Vienna.
Let the quantum computers check each other
To address this challenge, the team developed and implemented a new cross-check procedure that allows the results of a calculation performed on one device to be verified through a related but fundamentally different calculation on another device. “We ask different quantum computers to perform different random-looking computations,” explains Martin Ringbauer from the University of Innsbruck. “What the quantum computers don’t know is that there is a hidden connection between the computations they are doing.” Using an alternative model of quantum computing that is built on graph structures, the team is able to generate many different computations from a common source. “While the results may appear random and the computations are different, there are certain outputs that must agree if the devices are working correctly.”
A simple and efficient technique
The team implemented their method on 5 current quantum computers using 4 distinct hardware technologies: superconducting circuits, trapped ions, photonics, and nuclear magnetic resonance. This goes to show that the method works on current hardware without any special requirements. The team also demonstrated that the technique could be used to check a single device against itself. Since the two computations are so different, the two results will only agree if they are also correct. Another key advantage of the new approach is that the researchers do not have to look at the full result of the computation, which can be very time consuming. “It is enough to check how often the different devices agree for the cases where they should, which can be done even for very large quantum computers,” says Tommaso Demarie from Entropica Labs in Singapore. With more and more quantum computers becoming available, this technique may be key to making sure they are doing what is advertised
Academia and industry joining forces to make quantum computers trustworthy
The research aiming to make quantum computers trustworthy is a joint effort of university researchers and quantum computing industry experts from multiple companies. “This close collaboration of academia and industry is what makes this paper unique from a sociological perspective,” shares Joe Fitzsimons from Horizon Quantum Computing in Singapore. “While there’s a progressive shift with some researchers moving to companies, they keep contributing to the common effort making quantum computing reliable and useful.”
Story Source:
Materials provided by University of Vienna. Note: Content may be edited for style and length. More

Researchers at Case Western Reserve University have developed an online tool to help medical staff quickly determine which COVID-19 patients will need help breathing with a ventilator.
The tool, developed through analysis of CT scans from nearly 900 COVID-19 patients diagnosed in 2020, was able to predict ventilator need with 84% accuracy.
“That could be important for physicians as they plan how to care for a patient — and, of course, for the patient and their family to know,” said Anant Madabhushi, the Donnell Institute Professor of Biomedical Engineering at Case Western Reserve and head of the Center for Computational Imaging and Personalized Diagnostics (CCIPD). “It could also be important for hospitals as they determine how many ventilators they’ll need.”
Next, Madabhushi said he hopes to use those results to try out the computational tool in real time at University Hospitals and Louis Stokes Cleveland VA Medical Center with COVID-19 patients.
If successful, he said medical staff at the two hospitals could upload a digitized image of the chest scan to a cloud-based application, where the AI at Case Western Reserve would analyze it and predict whether that patient would likely need a ventilator.
Dire need for ventilators
Among the more common symptoms of severe COVID-19 cases is the need for patients to be placed on ventilators to ensure they will be able to continue to take in enough oxygen as they breathe. More

A new analysis suggests that, in order to boost freedoms and protect against overwhelming new waves of COVID-19, the pace at which restrictions to reduce spread are lifted must be directly tied to the pace of vaccination. Simon Bauer, Viola Priesemann, and colleagues of the Max Planck Institute for Dynamics and Self-Organization, Germany, present these findings in the open-access journal PLOS Computational Biology.
More than a year after the COVID-19 pandemic began, vaccination programs now hold promise to ease many burdens caused by the disease — including necessary restrictions that have had negative social and economic consequences. Much research has focused on vaccine allocation and prioritization, and optimal ways to control spread. However, how to execute a smooth transition between an unprotected population to eventual population immunity remained an open question.
To address that question, Bauer and colleagues applied mathematical modeling to epidemiological and vaccination data from Germany, France, the U.K., and other European countries. Specifically, they quantified the pace at which restrictions could be lifted during vaccine rollout in order to mitigate the risk of rebound COVID-19 waves that overwhelm intensive care units.
After considering various plausible scenarios, the researchers concluded that further severe waves can only be avoided if restrictions are lifted no faster than the pace dictated by vaccination progress, and that there is basically no gain in freedom if one eases restrictions too quickly. The findings suggest that, even after 80 percent of the adult population has been vaccinated, novel, more infectious variants could trigger a new wave and overwhelm intensive care units if lifting all restrictions.
“In such an event, restrictions would quickly have to be reinstated, thus quickly vanishing the mirage of freedom,” Priesemann says. “Furthermore, an early lift would have high morbidity and mortality costs. Meanwhile, relaxing restrictions at the pace of vaccination shows almost the same progress in ‘freedom’ while maintaining low incidence.”
The researchers say their findings suggest that, despite public pressure, policymakers should not rush relaxation of restrictions, and a high vaccination rate — especially among high-risk populations — is necessary. Further research will be needed to design optimal scenarios from a global perspective.
Story Source:
Materials provided by PLOS. Note: Content may be edited for style and length. More

While studying the behavior of electrons in iron-based superconducting materials, researchers at the University of Tokyo observed a strange signal relating to the way electrons are arranged. The signal implies a new arrangement of electrons the researchers call a nematicity wave, and they hope to collaborate with theoretical physicists to better understand it. The nematicity wave could help researchers understand the way electrons interact with each other in superconductors.
A long-standing dream of solid state physicists is to fully understand the phenomenon of superconductivity — essentially electronic conduction without the resistance that creates heat and drains power. It would usher in a whole new world of incredibly efficient or powerful devices and is already being used on Japan’s experimental magnetic levitation bullet train. But there is much to explore in this complex topic, and it often surprises researchers with unexpected results and observations.
Professor Shik Shin from the Institute for Solid State Physics at the University of Tokyo and his team study the way electrons behave in iron-based superconducting materials, or IBSCs. These materials show a lot of promise as they could work at higher temperatures than some other superconducting materials which is an important concern. They also use less exotic material components so can be easier and cheaper to work with. To activate a sample’s superconducting ability, the material needs to be cooled down to several hundreds of degrees below zero. And interesting things happen during this cooling process.
“As IBSCs cool down to a certain level, they express a state we call electronic nematicity,” said Shin. “This is where the crystal lattice of the material and the electrons within it appear to be arranged differently depending on the angle you look at them, otherwise known as anisotropy. We expect the way electrons are arranged to be tightly coupled to the way the surrounding crystal lattice is arranged. But our recent observation shows something very different and actually quite surprising.”
Shin and his team used a special technique developed by their group called laser-PEEM (photoemission electron microscopy) to visualize their IBSC sample on the microscopic scale. They expected to see a familiar pattern that repeats every few nanometers (billionths of a meter). And sure enough the crystal lattice did show this pattern. But to their surprise, the team found that the pattern of electrons was repeating every few hundred nanometers instead.
This disparity between the electron nematicity wave and the crystalline structure of the IBSC was unexpected, so its implications are still under investigation. But the result could open the door to theoretical and experimental explorations into something fundamental to the phenomenon of superconductivity, and that is the way that electrons form pairs at low temperatures. Knowledge of this process could be crucial to the development of high-temperature superconductivity. So if nematicity waves are related, it is important to know how.
“Next, I hope we can work with theoretical physicists to further our understanding of nematicity waves,” said Shin. “We also wish to use laser-PEEM to study other related materials such as metal oxides like copper oxide. It may not always be obvious where the applications lie, but working on problems of fundamental physics really fascinates me.”
Story Source:
Materials provided by University of Tokyo. Note: Content may be edited for style and length. More

New experiments using trapped one-dimensional gases — atoms cooled to the coldest temperatures in the universe and confined so that they can only move in a line — fit with the predictions of the recently developed theory of “generalized hydrodynamics.” Quantum mechanics is necessary to describe the novel properties of these gases. Achieving a better understanding of how such systems with many particles evolve in time is a frontier of quantum physics. The result could greatly simplify the study of quantum systems that have been excited out of equilibrium. Besides its fundamental importance, it could eventually inform the development of quantum-based technologies, which include quantum computers and simulators, quantum communication, and quantum sensors. A paper describing the experiments by a team led by Penn State physicists appears September 2, 2021 in the journal Science.
Even within classical physics, where the additional complexities of quantum mechanics can be ignored, it is impossible to simulate the motion of all the atoms in a moving fluid. To approximate these systems of particles, physicists use hydrodynamics descriptions.
“The basic idea behind hydrodynamics is to forget about the atoms and consider the fluid as a continuum,” said Marcos Rigol, professor of physics at Penn State and one of the leaders of the research team. “To simulate the fluid, one ends up writing coupled equations that result from imposing a few constraints, such as the conservation of mass and energy. These are the same types of equations solved, for example, to simulate how air flows when you open windows to improve ventilation in a room.”
Matter becomes more complicated if quantum mechanics is involved, as is the case when one wants to simulate quantum many-body systems that are out of equilibrium.
“Quantum many body systems — which are composed of many interacting particles, such as atoms — are at the heart of atomic, nuclear, and particle physics,” said David Weiss, Distinguished Professor of Physics at Penn State and one of the leaders of the research team. “It used to be that except in extreme limits you couldn’t do a calculation to describe out-of-equilibrium quantum many-body systems. That recently changed.”
The change was motivated by the development of a theoretical framework known as generalized hydrodynamics.
“The problem with those quantum many-body systems in one dimension is that they have so many constraints on their motion that regular hydrodynamics descriptions cannot be used,” said Rigol. “Generalized hydrodynamics was developed to keep track of all those constraints.”
Until now, generalized hydrodynamics had only previously been experimentally tested under conditions where the strength of interactions among particles was weak.
“We set out to test the theory further, by looking at the dynamics of one dimensional gases with a wide range of interaction strengths,” said Weiss. “The experiments are extremely well controlled, so the results can be precisely compared to the predictions of this theory.
The research team uses one dimensional gases of interacting atoms that are initially confined in a very shallow trap in equilibrium. They then very suddenly increase the depth of the trap by 100 times, which forces the particles to collapse into the center of the trap, causing their collective properties to change. Throughout the collapse, the team precisely measures their properties, which they can then compare to the predictions of generalized hydrodynamics.
“Our measurements matched the prediction of theory across dozens of trap oscillations,” said Weiss. “There currently aren’t other ways to study out-of-equilibrium quantum systems for long periods of time with reasonable accuracy, especially with a lot of particles. Generalized hydrodynamics allow us to do this for some systems like the one we tested, but how generally applicable it is still needs to be determined.”
Story Source:
Materials provided by Penn State. Original written by Sam Sholtis. Note: Content may be edited for style and length. More