Aurelia Butler

Liquid crystals could soon be produced more efficiently and in a more environmentally friendly way. A new process has been developed by researchers at Martin Luther University Halle-Wittenberg (MLU) in Germany, Bangalore University in India and Cairo University in Egypt. Compared to conventional methods, it is faster, more energy-efficient and promises a high yield as the team reports in the Journal of Molecular Liquids. Liquid crystals are used in most smartphone, tablet and computer displays.
The production of liquid crystals is a complex process with many intermediate steps. “Often it requires various solvents and expensive catalysts,” says Dr Mohamed Alaasar, a chemist at MLU. The team from Germany, India and Egypt was looking for a way to simplify the process and make it more environmentally friendly. The idea: instead of the chemical reactions taking place one after the other, certain steps could be combined in a so-called multicomponent reaction in which several substances react directly with one another.
The team developed an approach for producing liquid crystals which does not require environmentally harmful solvents and relies on cheaper catalysts. “We were able to achieve a yield of about 90 per cent. This means that most of the chemicals are used in the process and relatively few residues are produced,” explains Alaasar. This saves energy and ultimately also money. At room temperature the newly created liquid crystals are in a nematic phase — a special arrangement of molecules used in most liquid crystal displays or LCDs.
So far, the researchers have only tested their new process in the laboratory. However, Alaasar is confident that it could also be implemented on an industrial scale. “However, manufacturers would have to rebuild parts of their manufacturing. This has not happened in the past with other promising materials,” says the scientist. However, consumers started valuing sustainability and more environmentally friendly products of the last years. That could be an additional argument in favour for the new approach.
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Materials provided by Martin-Luther-Universität Halle-Wittenberg. Note: Content may be edited for style and length. More

A series of experiments using paper airplanes reveals new aerodynamic effects, a team of scientists has discovered. Its findings enhance our understanding of flight stability and could inspire new types of flying robots and small drones.
“The study started with simple curiosity about what makes a good paper airplane and specifically what is needed for smooth gliding,” explains Leif Ristroph, an associate professor at New York University’s Courant Institute of Mathematical Sciences and an author of the study, which appears in the Journal of Fluid Mechanics. “Answering such basic questions ended up being far from child’s play. We discovered that the aerodynamics of how paper airplanes keep level flight is really very different from the stability of conventional airplanes.”
“Birds glide and soar in an effortless way, and paper airplanes, when tuned properly, can also glide for long distances,” adds author Jane Wang, a professor of engineering and physics at Cornell University. “Surprisingly, there has been no good mathematical model for predicting this seemingly simple but subtle gliding flight.”
Since we can make complicated modern airplanes fly, the researchers say, one might think we know all there is to know about the simplest flying machines.
“But paper airplanes, while simple to make, involve surprisingly complex aerodynamics,” notes Ristroph.
The paper’s authors began their study by considering what is needed for a plane to glide smoothly. Since paper airplanes have no engine and rely on gravity and proper design for their movement, they are good candidates for exploring factors behind flight stability. More

Hearing loss is a rapidly growing area of scientific research as the number of baby boomers dealing with hearing loss continues to increase as they age.
To understand how hearing loss impacts people, researchers study people’s ability to recognize speech. It is more difficult for people to recognize human speech if there is reverberation, some hearing impairment, or significant background noise, such as traffic noise or multiple speakers.
As a result, hearing aid algorithms are often used to improve human speech recognition. To evaluate such algorithms, researchers perform experiments that aim to determine the signal-to-noise ratio at which a specific number of words (commonly 50%) are recognized. These tests, however, are time- and cost-intensive.
In The Journal of the Acoustical Society of America, published by the Acoustical Society of America through AIP Publishing, researchers from Germany explore a human speech recognition model based on machine learning and deep neural networks.
“The novelty of our model is that it provides good predictions for hearing-impaired listeners for noise types with very different complexity and shows both low errors and high correlations with the measured data,” said author Jana Roßbach, from Carl Von Ossietzky University.
The researchers calculated how many words per sentence a listener understands using automatic speech recognition (ASR). Most people are familiar with ASR through speech recognition tools like Alexa and Siri.
The study consisted of eight normal-hearing and 20 hearing-impaired listeners who were exposed to a variety of complex noises that mask the speech. The hearing-impaired listeners were categorized into three groups with different levels of age-related hearing loss.
The model allowed the researchers to predict the human speech recognition performance of hearing-impaired listeners with different degrees of hearing loss for a variety of noise maskers with increasing complexity in temporal modulation and similarity to real speech. The possible hearing loss of a person could be considered individually.
“We were most surprised that the predictions worked well for all noise types. We expected the model to have problems when using a single competing talker. However, that was not the case,” said Roßbach.
The model created predictions for single-ear hearing. Going forward, the researchers will develop a binaural model since understanding speech is impacted by two-ear hearing.
In addition to predicting speech intelligibility, the model could also potentially be used to predict listening effort or speech quality as these topics are very related.
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Materials provided by American Institute of Physics. Note: Content may be edited for style and length. More

The development of highly secure but simple and inexpensive encryption technology for the prevention of data leaks and forgeries is decidedly challenging. In the journal Angewandte Chemie, a research team has introduced a “double lock” based on thermoresponsive polymer hydrogels that encrypts information so that it can only be read at a specific window in temperature and time.
In addition to digital encryption methods, physical methods play an important role. Their decoding is typically based on external stimuli such as light or heat. Multiple stimuli offer more security, but make reading the data cumbersome and complex. “Addition of the time domain greatly raises the chance to achieve the unity of security and simpleness,” according to the team led by Zhikun Zheng, Xudong Chen, and Wei Liu, at Sun Yat-sen University (Guangzhou, China). “We were inspired by the baking of bread: delicious bread can only be produced if the baking temperature is not too low or too high and the baking time is not too short or too long.”
For their novel “double encryption system” they use thermoresponsive polymer hydrogels — cross-linked chain molecules with water incorporated into their “gaps.” Above or below a specific temperature, the clear gels become opaque due to partial unmixing. There are LCST and UCST gels, which have lower or upper critical solution temperatures, respectively. The phase retention and critical temperature can be controlled via the content of -CO-NH2 groups in the main chain of the polymer hydrogels. The density of cross-linking determines the rate of the phase transition.
As an example of a locked label, the team used transparent acrylic plates with grooves in the pattern of a QR code. Three different gels were put in defined areas of the pattern; a UCST gel with a phase change around 40 °C, and two LCST gels with a phase change at 33 °C (one with a fast phase transition, and one with a slow phase change). Below 20 °C, the UCST gel is opaque, but highly shrinking. The pattern is deformed and unreadable. Between 20 and 33 °C, it swells and the part of the code formed by this gel becomes readable. The second part of the code, formed by the “fast” LCST gel, still cannot be read. Only heating to over 33 °C makes both LCST gels opaque. Now the timing comes into play; only the pattern of the “fast” LCST gel has the correct second part of the information. At 37 °C, it becomes readable after about half a minute and the complete code can be read. However, a brief three minutes later, the “slow” LCST gel becomes opaque and adds false information that makes the codes unreadable. Above 40 °C, both LCST gels become opaque simultaneously. In addition, the UCST gel becomes transparent and unreadable.
This encryption can only be decoded if the specific temperature and time windows are known. The source of heat for decoding in this example could be an infrared lamp, a water bath, a hair dryer, or even the human body. If sealed to prevent the evaporation of water, these inexpensive labels are theoretically suitable for long-term use.
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Materials provided by Wiley. Note: Content may be edited for style and length. More

A research team probing the properties of a semiconductor combined with a novel thin oxide film have observed a surprising new source of conductivity from oxygen atoms trapped inside.
Scott Chambers, a materials scientist at the Department of Energy’s Pacific Northwest National Laboratory, reported the team’s discovery at the Spring 2022 meeting of the American Physical Society. The research finding is described in detail in the journal Physical Review Materials.
The discovery has broad implications for understanding the role of thin oxide films in future semiconductor design and manufacture. Specifically, semiconductors used in modern electronics come in two basic flavors — n-type and p-type — depending on the electronic impurity added during crystal growth. Modern electronic devices use both n- and p-type silicon-based materials. But there is ongoing interest in developing other types of semiconductors. Chambers and his team were testing germanium in combination with a specialized thin crystalline film of lanthanum-strontium-zirconium-titanium-oxide (LSZTO).
“We are reporting on a powerful tool for probing semiconductor structure and function,” said Chambers. “Hard X-ray photoelectron spectroscopy revealed in this case that atoms of oxygen, an impurity in the germanium, dominate the properties of the material system when germanium is joined to a particular oxide material. This was a big surprise.”
Using the Diamond Light Source on the Harwell Science and Innovation Campus in Oxfordshire, England, the research team discovered they could learn a great deal more about the electronic properties of the germanium/LSZTO system than was possible using the typical methods.
“When we tried to probe the material with conventional techniques, the much higher conductivity of germanium essentially caused a short circuit,” Chambers said. “As a result, we could learn something about the electronic properties of the Ge, which we already know a lot about, but nothing about the properties of the LSZTO film or the interface between the LSZTO film and the germanium — which we suspected might be very interesting and possibly useful for technology.”
A new role for hard X-rays
The so-called “hard” X-rays produced by the Diamond Light Source could penetrate the material and generate information about what was going on at the atomic level.
“Our results were best interpreted in terms of oxygen impurities in the germanium being responsible for a very interesting effect,” Chambers said. “The oxygen atoms near the interface donate electrons to the LSZTO film, creating holes, or the absence of electrons, in the germanium within a few atomic layers of the interface. These specialized holes resulted in behavior that totally eclipsed the semiconducting properties of both n- and p-type germanium in the different samples we prepared. This, too, was a big surprise.”
The interface, where the thin-film oxide and the base semiconductor come together, is where interesting semiconducting properties often emerge. The challenge, according to Chambers, is to learn how to control the fascinating and potentially useful electric fields that forms at these interfaces by modifying the electric field at the surface. Ongoing experiments at PNNL are probing this possibility.
While the samples used in this research do not likely have the immediate potential for commercial use, the techniques and scientific discoveries made are expected to pay dividends in the longer term, Chambers said. The new scientific knowledge will help materials scientists and physicists better understand how to design new semiconductor material systems with useful properties.
PNNL researchers Bethany Matthews, Steven Spurgeon, Mark Bowden, Zihua Zhu and Peter Sushko contributed to the research. The study was supported by the Department of Energy Office of Science. Some experiments and sample preparation were performed at the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science user facility located at PNNL. Electron microscopy was performed in the PNNL Radiochemical Processing Laboratory. Collaborators Tien-Lin Lee and Judith Gabel performed experiments at the Diamond Light Source. Additional collaborators included the University of Texas at Arlington’s Matt Chrysler and Joe Ngai, who prepared the samples.
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Materials provided by DOE/Pacific Northwest National Laboratory. Original written by Karyn Hede. Note: Content may be edited for style and length. More

A new study challenges the conventional approach to designing soft robotics and a class of materials called metamaterials by utilizing the power of computer algorithms. Researchers from the University of Illinois Urbana-Champaign and Technical University of Denmark can now build multimaterial structures without dependence on human intuition or trial-and-error to produce highly efficient actuators and energy absorbers that mimic designs found in nature.
The study, led by Illinois civil and environmental engineering professor Shelly Zhang, uses optimization theory and an algorithm-based design process called topology optimization. Also known as digital synthesis, the design process builds composite structures that can precisely achieve complex prescribed mechanical responses.
The study results are published in the Proceedings of the National Academy of Sciences.
“The complex mechanical responses called for in soft robotics and metamaterials require the use of multiple materials — but building these types of structures can be a challenge,” Zhang said. “There are so many materials to choose from, and determining the optimal combination of materials to fit a specific function presents an overwhelming amount of data for a researcher to process.”
Zhang’s team set its sights on designing macroscale structures with the prescribed properties of swift stiffening, large-scale deformation buckling, multiphase stability and long-lasting force plateaus.
The new digital synthesis process generated structures with optimal geometric characteristics composed of the optimal materials for the prescribed functions. More

Physicists at UC Santa Barbara have become the first to experimentally observe a quirky behavior of the quantum world: a “quantum boomerang” effect that occurs when particles in a disordered system are kicked out of their locations. Instead of landing elsewhere as one might expect, they turn around and come back to where they started and stop there.
“It’s really a fundamentally quantum mechanical effect,” said atomic physicist David Weld, whose lab produced the effect and documented it in a paper published in Physical Review X. “There’s no classical explanation for this phenomenon.”
The boomerang effect has its roots in a phenomenon that physicist Philip Anderson predicted roughly 60 years ago, a disorder-induced behavior called Anderson localization which inhibits transport of electrons. The disorder, according to the paper’s lead author Roshan Sajjad, can be the result of imperfections in a material’s atomic lattice, whether they be impurities, defects, misalignments or other disturbances.
“This type of disorder will keep them from basically dispersing anywhere,” Sajjad said. As a result, the electrons localize instead of zipping along the lattice, turning what would otherwise be a conducting material into an insulator. From this rather sticky quantum condition, the quantum boomerang effect was predicted a few years ago to arise.
Launching disordered electrons away from their localized position and following them to observe their behavior is extremely difficult if not currently impossible, but the Weld Lab had a few tricks up its sleeve. Using a gas of 100,000 ultracold lithium atoms suspended in a standing wave of light and “kicking” them, emulating a so-called quantum kicked rotor (“similar to a periodically kicked pendulum,” both Weld and Sajjad said), the researchers were able to create the lattice and the disorder, and observe the launch and return of the boomerang. They worked in momentum space, a method that evades some experimental difficulties without changing the underlying physics of the boomerang effect.
“In normal, position space, if you’re looking for the boomerang effect, you’d give your electron some finite velocity and then look for whether it came back to the same spot,” Sajjad explained. “Because we’re in momentum space, we start with a system that is at zero average momentum, and we look for some departure followed by a return to zero average momentum.”
Using their quantum kicked rotor they pulsed the lattice a few dozen times, noting an initial shift in average momentum. Over time and despite repeated kicks, however, average momentum returned to zero. More