Aurelia Butler

Solar cells have come a long way, but inexpensive, thin film solar cells are still far behind more expensive, crystalline solar cells in efficiency. Now, a team of researchers suggests that using two thin films of different materials may be the way to go to create affordable, thin film cells with about 34% efficiency.
“Ten years ago I knew very little about solar cells, but it became clear to me they were very important,” said Akhlesh Lakhtakia, Evan Pugh University Professor and Charles Godfrey Binder Professor of Engineering Science and Mechanics, Penn State.
Investigating the field, he found that researchers approached solar cells from two sides, the optical side — looking on how the sun’s light is collected — and the electrical side — looking at how the collected sunlight is converted into electricity. Optical researchers strive to optimize light capture, while electrical researchers strive to optimize conversion to electricity, both sides simplifying the other.
“I decided to create a model in which both electrical and optical aspects will be treated equally,” said Lakhtakia. “We needed to increase actual efficiency, because if the efficiency of a cell is less than 30% it isn’t going to make a difference.” The researchers report their results in a recent issue of Applied Physics Letters.
Lakhtakia is a theoretician. He does not make thin films in a laboratory, but creates mathematical models to test the possibilities of configurations and materials so that others can test the results. The problem, he said, was that the mathematical structure of optimizing the optical and the electrical are very different.
Solar cells appear to be simple devices, he explained. A clear top layer allows sunlight to fall on an energy conversion layer. The material chosen to convert the energy, absorbs the light and produces streams of negatively charged electrons and positively charged holes moving in opposite directions. The differently charged particles get transferred to a top contact layer and a bottom contact layer that channel the electricity out of the cell for use. The amount of energy a cell can produce depends on the amount of sunlight collected and the ability of the conversion layer. Different materials react to and convert different wavelengths of light.
“I realized that to increase efficiency we had to absorb more light,” said Lakhtakia. “To do that we had to make the absorbent layer nonhomogeneous in a special way.”
That special way was to use two different absorbent materials in two different thin films. The researchers chose commercially available CIGS — copper indium gallium diselenide — and CZTSSe — copper zinc tin sulfur selenide — for the layers. By itself, CIGS’s efficiency is about 20% and CZTSSe’s is about 11%.
These two materials work in a solar cell because the structure of both materials is the same. They have roughly the same lattice structure, so they can be grown one on top of the other, and they absorb different frequencies of the spectrum so they should increase efficiency, according to Lakhtakia.
“It was amazing,” said Lakhtakia. “Together they produced a solar cell with 34% efficiency. This creates a new solar cell architecture — layer upon layer. Others who can actually make solar cells can find other formulations of layers and perhaps do better.”
According to the researchers, the next step is to create these experimentally and see what the options are to get the final, best answers.

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Materials provided by Penn State. Original written by A’ndrea Elyse Messer. Note: Content may be edited for style and length. More

Army research has extended the state-of-the-art in autonomy by providing a more complete picture of how actions and nonverbal signals contribute to promoting cooperation. Researchers suggested guidelines for designing autonomous machines such as robots, self-driving cars, drones and personal assistants that will effectively collaborate with Soldiers.
Dr. Celso de Melo, computer scientist with the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory at CCDC ARL West in Playa Vista, California, in collaboration with Dr. Kazunori Teradafrom Gifu University in Japan, recently published a paper in Scientific Reports where they show that emotion expressions can shape cooperation.
Autonomous machines that act on people’s behalf are poised to become pervasive in society, de Melo said; however, for these machines to succeed and be adopted, it is essential that people are able to trust and cooperate with them.
“Human cooperation is paradoxical,” de Melo said. “An individual is better off being a free rider, while everyone else cooperates; however, if everyone thought like that, cooperation would never happen. Yet, humans often cooperate. This research aims to understand the mechanisms that promote cooperation with a particular focus on the influence of strategy and signaling.”
Strategy defines how individuals act in one-shot or repeated interaction. For instance, tit-for-tat is a simple strategy that specifies that the individual should act as his/her counterpart acted in the previous interaction.
Signaling refers to communication that may occur between individuals, which could be verbal (e.g., natural language conversation) and nonverbal (e.g., emotion expressions).

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This research effort, which supports the Next Generation Combat Vehicle Army Modernization Priority and the Army Priority Research Area for Autonomy, aims to apply this insight in the development of intelligent autonomous systems that promote cooperation with Soldiers and successfully operate in hybrid teams to accomplish a mission.
“We show that emotion expressions can shape cooperation,” de Melo said. “For instance, smiling after mutual cooperation encourages more cooperation; however, smiling after exploiting others — which is the most profitable outcome for the self — hinders cooperation.”
The effect of emotion expressions is moderated by strategy, he said. People will only process and be influenced by emotion expressions if the counterpart’s actions are insufficient to reveal the counterpart’s intentions.
For example, when the counterpart acts very competitively, people simply ignore-and even mistrust-the counterpart’s emotion displays.
“Our research provides novel insight into the combined effects of strategy and emotion expressions on cooperation,” de Melo said. “It has important practical application for the design of autonomous systems, suggesting that a proper combination of action and emotion displays can maximize cooperation from Soldiers. Emotion expression in these systems could be implemented in a variety of ways, including via text, voice, and nonverbally through (virtual or robotic) bodies.”
According to de Melo, the team is very optimistic that future Soldiers will benefit from research such as this as it sheds light on the mechanisms of cooperation.
“This insight will be critical for the development of socially intelligent autonomous machines, capable of acting and communicating nonverbally with the Soldier,” he said. “As an Army researcher, I am excited to contribute to this research as I believe it has the potential to greatly enhance human-agent teaming in the Army of the future.”
The next steps for this research include pursuing further understanding of the role of nonverbal signaling and strategy in promoting cooperation and identifying creative ways to apply this insight on a variety of autonomous systems that have different affordances for acting and communicating with the Soldier. More

Four-hundred fifty light-years from Earth, a young star is glowing at the center of a system of concentric rings made from gas and dust, and it is producing planets, one for each gap in the ring.
Its discovery has shaken solar system origin theories to their core. Mayer Humi, a scientist from the Worcester Polytechnic Institute, believes it provides an apt study target for theories about protoplanetary rings around stars. The research is published in the Journal of Mathematical Physics, by AIP Publishing.
The star, HL Tauri, is located in the constellation Taurus and awakened interest in Pierre-Simon Laplace’s 1796 conjecture that celestial clouds of gas and dust around new stars condense to form rings and then planets. An exciting image of HL Tauri captured in 2014 by the Atacama Large Millimeter Array is the first time planetary rings have been photographed in such crisp detail, an observational confirmation of Laplace’s conjecture.
“We can observe many gas clouds in the universe that can evolve into a solar system,” Humi said. “Recent observational data shows solar systems are abundant in the universe, and some of them might harbor different types of life.”
Humi, alongside some of the greatest astronomers throughout history, wondered about the creation of solar systems and their evolution in the universe. How do they form and what trajectory will they follow in the future?
“The basic issue was and is how a primordial cloud of gas can evolve under its own gravitation to create a solar system,” Humi said.
Humi uses the Euler-Poisson equations, which describe the evolution of gas clouds, and reduces them from six to three model equations to apply to axi-symmetric rotating gas clouds.
In the paper, Humi considers the fluid in the primordial gas cloud to be an incompressible, stratified fluid flow and derives time dependent solutions to study the evolution of density patterns and oscillations in the cloud.
Humi’s work shows that, with the right set of circumstances, rings could form from the cloud of dust and gas, and it lends credence to Laplace’s 1796 hypothesis that our solar system formed from a similar dust and gas cloud around the sun.
“I was able to present three analytical solutions that demonstrate rings can form, insight that cannot be obtained from the original system of equations,” Humi said. “The real challenge is to show that the rings can evolve further to create the planets.”

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How do you turn on and off an ultra-small component in advanced technologies? You need an actuator, a device that transmits an input such as electricity into physical motion. However, actuators in small-scale technologies to date have critical limitations. For example, if it’s difficult to integrate the actuator into semiconductor electronics, real-world applications of the technology will be limited. An actuator design that operates quickly, has precise on/off control, and is compatible with modern electronics would be immensely useful.
In a study recently published in Nano Letters, a team including researchers from Osaka University has developed such an actuator. Its sensitivity, fast on/off response, and nanometer-scale precision are unparalleled.
The researchers’ actuator is based on vanadium oxide crystals. Many current technologies use a property of vanadium oxide known as the phase transition to cause out-of-plane bending motions within small-scale devices. For example, such actuators are useful in ultra-small mirrors. Using the phase transition to cause in-plane bending is far more difficult, but would be useful, for example, in ultra-small grippers in medicine.
“At 68°C, vanadium oxide undergoes a sharp monoclinic to rutile phase transition that’s useful in microscale technologies,” explains co-author Teruo Kanki. “We used a chevron-type (sawtooth) device geometry to amplify in-plane bending of the crystal, and open up new applications.”
Using a two-step protocol, the researchers fabricated a fifteen-micrometer-long vanadium oxide crystal attached by a series of ten-micrometer arms to a fixed frame. By means of a phase transition caused by a readily attainable stimulus — a 10°C temperature change — the crystal moves 225 nanometers in-plane. The expansion behavior is highly reproducible, over thousands of cycles and several months.
“We also moved the actuator in-plane in response to a laser beam,” says Nicola Manca and Luca Pelligrino, co-authors. “The on/off response time was a fraction of a millisecond near the phase transition temperature, with little change at other temperatures, which makes our actuators the most advanced in the world.”
Small-scale technologies such as advanced implanted drug delivery devices wouldn’t work without the ability to rapidly turn them on and off. The underlying principle of the researchers’ actuator — a reversible phase transition for on/off, in-plane motion — will dramatically expand the utility of many modern technologies. The researchers expect that the accuracy and speed of their actuator will be especially useful to micro-robotics.

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For many people who are struggling to conceive, in-vitro fertilization (IVF) can offer a life-changing solution. But the average success rate for IVF is only about 30 percent.
Investigators from Brigham and Women’s Hospital and Massachusetts General Hospital are developing an artificial intelligence system with the goal of improving IVF success by helping embryologists objectively select embryos most likely to result in a healthy birth. Using thousands of embryo image examples and deep-learning artificial intelligence (AI), the team developed a system that was able to differentiate and identify embryos with the highest potential for success significantly better than 15 experienced embryologists from five different fertility centers across the United States.
Results of their study are published in eLife.
“We believe that these systems will benefit clinical embryologists and patients,” said corresponding author Hadi Shafiee, PhD, of the Division of Engineering in Medicine at the Brigham. “A major challenge in the field is deciding on the embryos that need to be transferred during IVF. Our system has tremendous potential to improve clinical decision making and access to care.”
Currently, the tools available to embryologists are limited and expensive, and most embryologists must rely on their observational skills and expertise. Shafiee and colleagues are developing an assistive tool that can evaluate images captured using microscopes traditionally available at fertility centers.
“There is so much at stake for our patients with each IVF cycle. Embryologists make dozens of critical decisions that impact the success of a patient cycle. With assistance from our AI system, embryologists will be able to select the embryo that will result in a successful pregnancy better than ever before,” said co-lead author Charles Bormann, PhD, MGH IVF Laboratory director.
The team trained the AI system using images of embryos captured at 113 hours post-insemination. Among 742 embryos, the AI system was 90 percent accurate in choosing the most high-quality embryos. The investigators further assessed the AI system’s ability to distinguish among high-quality embryos with the normal number of human chromosomes and compared the system’s performance to that of trained embryologists. The system performed with an accuracy of approximately 75 percent while the embryologists performed with an average accuracy of 67 percent.
The authors note that in its current stage, this system is intended to act only as an assistive tool for embryologists to make judgments during embryo selection.
“Our approach has shown the potential of AI systems to be used in aiding embryologists to select the embryo with the highest implantation potential, especially amongst high-quality embryos,” said Manoj Kumar Kanakasabapathy, one of the co-lead authors.
Funding for this work was provided by Brigham and Women’s Hospital and Partners Healthcare (Precision Medicine Developmental Grant and Innovation Discovery Grant), and National Institutes of Health (R01AI138800).

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Quantum technology holds great promise: Just a few years from now, quantum computers are expected to revolutionize database searches, AI systems, and computational simulations. Today already, quantum cryptography can guarantee absolutely secure data transfer, albeit with limitations. The greatest possible compatibility with our current silicon-based electronics will be a key advantage. And that is precisely where physicists from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and TU Dresden have made remarkable progress: The team has designed a silicon-based light source to generate single photons that propagate well in glass fibers.
Quantum technology relies on the ability to control the behavior of quantum particles as precisely as possible, for example by locking individual atoms in magnetic traps or by sending individual light particles — called photons — through glass fibers. The latter is the basis of quantum cryptography, a communication method that is, in principle, tap-proof: Any would-be data thief intercepting the photons unavoidably destroys their quantum properties. The senders and receivers of the message will notice that and can stop the compromised transmission in time.
This requires light sources that deliver single photons. Such systems already exist, especially based on diamonds, but they have one flaw: “These diamond sources can only generate photons at frequencies that are not suitable for fiber optic transmission,” explains HZDR physicist Dr. Georgy Astakhov. “Which is a significant limitation for practical use.” So Astakhov and his team decided to use a different material — the tried and tested electronic base material silicon.
100,000 single photons per second
To make the material generate the infrared photons required for fiber optic communication, the experts subjected it to a special treatment, selectively shooting carbon into the silicon with an accelerator at the HZDR Ion Beam Center. This created what is called G-centers in the material — two adjacent carbon atoms coupled to a silicon atom forming a sort of artificial atom.
When radiated with red laser light, this artificial atom emits the desired infrared photons at a wavelength of 1.3 micrometers, a frequency excellently suited for fiber optic transmission. “Our prototype can produce 100,000 single photons per second,” Astakhov reports. “And it is stable. Even after several days of continuous operation, we haven’t observed any deterioration.” However, the system only works in extremely cold conditions — the physicists use liquid helium to cool it down to a temperature of minus 268 degrees Celsius.
“We were able to show for the first time that a silicon-based single-photon source is possible,” Astakhov’s colleague Dr. Yonder Berencén is happy to report. “This basically makes it possible to integrate such sources with other optical components on a chip.” Among other things, it would be of interest to couple the new light source with a resonator to solve the problem that infrared photons largely emerge from the source randomly. For use in quantum communication, however, it would be necessary to generate photons on demand.
Light source on a chip
This resonator could be tuned to exactly hit the wavelength of the light source, which would make it possible to increase the number of generated photons to the point that they are available at any given time. “It has already been proven that such resonators can be built in silicon,” reports Berencén. “The missing link was a silicon-based source for single photons. And that’s exactly what we’ve now been able to create.”
But before they can consider practical applications, the HZDR researchers still have to solve some problems — such as a more systematic production of the new telecom single-photon sources. “We will try to implant the carbon into silicon with greater precision,” explains Georgy Astakhov. “HZDR with its Ion Beam Center provides an ideal infrastructure for realizing ideas like this.”

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Researchers at CRANN and the School of Physics at Trinity College Dublin have discovered that a new material can act as a super-fast magnetic switch. When struck by successive ultra-short laser pulses it exhibits “toggle switching” that could increase the capacity of the global fibre optic cable network by an order of magnitude.
Expanding the capacity of the internet
Switching between two states — 0 and 1 — is the basis of digital technology and the backbone of the internet. The vast majority of all the data we download is stored magnetically in huge data centres across the world, linked by a network of optical fibres.
Obstacles to further progress with the internet are three-fold, specifically the speed and energy consumption of the semiconducting or magnetic switches that process and store our data and the capacity of the fibre optic network to handle it.
The new discovery of ultra-fast toggle switching using laser light on mirror-like films of an alloy of manganese, ruthenium and gallium known as MRG could help with all three problems.
Not only does light offer a great advantage when it comes to speed but magnetic switches need no power to maintain their state. More importantly, they now offer the prospect of rapid time-domain multiplexing of the existing fibre network, which could enable it to handle ten times as much data.

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The science behind magnetic switching
Working in the photonics laboratory at CRANN, Trinity’s nanoscience research centre, Dr Chandrima Banerjee and Dr Jean Besbas used ultra-fast laser pulses lasting just a hundred femtoseconds (one ten thousand billionth of a second) to switch the magnetisation of thin films of MRG back and forth. The direction of magnetisation can point either in or out of the film.
With every successive laser pulse, it abruptly flips its direction. Each pulse is thought to momentarily heat the electrons in MRG by about 1,000 degrees, which leads to a flip of its magnetisation. The discovery of ultra-fast toggle switching of MRG has just been published in leading international journal, Nature Communications.
Dr Karsten Rode, Senior Research Fellow in the ‘Magnetism and Spin Electronics Group’ in Trinity’s School of Physics, suggests that the discovery just marks the beginning of an exciting new research direction. Dr Rode said:
“We have a lot of work to do to fully understand the behaviour of the atoms and electrons in a solid that is far from equilibrium on a femtosecond timescale. In particular, how can magnetism change so quickly while obeying the fundamental law of physics that says that angular momentum must be conserved?
“In the spirit of our spintronics team, we will now gather data from new pulsed-laser experiments on MRG, and other materials, to better understand these dynamics and link the ultra-fast optical response with electronic transport. We plan experiments with ultra-fast electronic pulses to test the hypothesis that the origin of the toggle switching is purely thermal.”
Next year Chandrima will continue her work at the University of Haifa, Israel, with a group who can generate even shorter laser pulses. The Trinity researchers, led by Karsten, plan a new joint project with collaborators in the Netherlands, France, Norway and Switzerland, aimed at proving the concept of ultra-fast, time-domain multiplexing of fibre-optic channels.

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As the COVID-19 pandemic has swept the world, researchers have published hundreds of papers each week reporting their findings — many of which have not undergone a thorough peer review process to gauge their reliability.
In some cases, poorly validated research has massively influenced public policy, as when a French team reported COVID patients were cured by a combination of hydroxychloroquine and azithromycin. The claim was widely publicized, and soon U.S. patients were prescribed these drugs under an emergency use authorization. Further research involving larger numbers of patients has cast serious doubts on these claims, however.
With so much COVID-related information being released each week, how can researchers, clinicians and policymakers keep up?
In a commentary published this week in Nature Biotechnology, University of New Mexico scientist Tudor Oprea, MD, PhD, and his colleagues, many of whom work at artificial intelligence (AI) companies, make the case that AI and machine learning have the potential to help researchers separate the wheat from the chaff.
Oprea, professor of Medicine and Pharmaceutical Sciences and chief of the UNM Division of Translational Informatics, notes that the sense of urgency to develop a vaccine and devise effective treatments for the coronavirus has led many scientists to bypass the traditional peer review process by publishing “preprints” — preliminary versions of their work — online.
While that enables rapid dissemination of new findings, “The problem comes when claims about certain drugs that have not been experimentally validated appear in the preprint world,” Oprea says. Among other things, bad information may lead scientists and clinicians to waste time and money chasing blind leads.
AI and machine learning can harness massive computing power to check many of the claims that are being made in a research paper, the suggest the authors, a group of public and private-sector researchers from the U.S., Sweden, Denmark, Israel, France, the United Kingdom, Hong Kong, Italy and China led by Jeremy Levin, chair of the Biotechnology Innovation Organization, and Alex Zhavoronkov, CEO of InSilico Medicine.
“I think there is tremendous potential there,” Oprea says. “I think we are on the cusp of developing tools that will assist with the peer review process.”
Although the tools are not fully developed, “We’re getting really, really close to enabling automated systems to digest tons of publications and look for discrepancies,” he says. “I am not aware of any such system that is currently in place, but we’re suggesting with adequate funding this can become available.”
Text mining, in which a computer combs through millions of pages of text looking for specified patterns, has already been “tremendously helpful,” Oprea says. “We’re making progress in that.”
Since the COVID epidemic took hold, Oprea himself has used advanced computational methods to help identify existing drugs with potential antiviral activity, culled from a library of thousands of candidates.
“We’re not saying we have a cure for peer review deficiency, but we are saying that that a cure is within reach, and we can improve the way the system is currently implemented,” he says. “As soon as next year we may be able to process a lot of these data and serve as additional resources to support the peer review process.” More