Computers Math

Physicists at the University of Bayreuth are among the international pioneers of power functional theory. This new approach makes it possible for the first time to precisely describe the dynamics of many-particle systems over time. The particles can be atoms, molecules or larger particles invisible to humans. The new theory generalizes the classical density functional theory, which only applies to many-particle systems in thermal equilibrium. In the Reviews of Modern Physics, a research team led by Prof. Dr. Matthias Schmidt presents the basic features of the theory, which was significantly developed and elaborated in Bayreuth.
A many-particle system is in thermal equilibrium when the temperature in its interior is balanced and no heat flows take place. This does not necessarily mean that the system is in a rigid state of rest. Some many-particle systems can also be compared to a lottery draw machine, which rotates at a constant speed. The balls have a lot of freedom of movement in it and jump back and forth in a disorderly fashion. In a fluid many-particle system, the particles are packed considerably more densely than in the drum, which is why they constantly collide with each other at short distances and time intervals. Essential properties of such systems can be described completely and precisely with the density functional theory — provided that a thermal equilibrium of the system is given.
In the case of the lottery draw machine, this equilibrium is lost as soon as the uniform rotation gradually slows down and the chamber goes into reverse. Then the balls with the winning numbers roll onto a rail inside the chamber and are finally ejected. In order to record such processes precisely and without gaps, the power functional theory is needed: it translates the luck of the winners into the language of physics.
“The classical density functional theory is a very in-depth and at the same time aesthetically appealing theory. It is able to describe and relate the often very complex processes that take place in a system during thermal equilibrium. These processes include, for example, phase transitions, crystallizations, or phenomena such as hydrophobicity, which occurs when surfaces or particles avoid contact with water. Often, such processes are of great technological or biological relevance. The elegance and power of density functional theory has spurred us in Bayreuth for the past ten years to search for ways to make many-particle systems in thermal disequilibrium accessible to an equally precise and elegant physical description. Research partners at the University of Fribourg in Switzerland have contributed to this search with important studies. For example, our joint efforts have resulted in power functional theory, which extends density functional theory to time-dependent processes,” reports Prof. Dr. Matthias Schmidt, who holds a chair in theoretical physics at the University of Bayreuth.
The presentation of power functional theory (PFT), which has now been published, incorporates research that was primarily located in two focus areas at the University of Bayreuth: Nonlinear Dynamics and Polymer & Colloid Science. The Research Centre for Scientific Computing at the University of Bayreuth has provided substantial support and funding for many of these studies. Here, the power functional theory first proposed in 2013 was tested, further developed and applied to concrete physical problems. Among other things, the studies dealt with active particles that can self-propel, with shear and flow phenomena in colloids and liquids, or with the microscopic structure of liquids. A decisive factor for the successful development of the PFT was that the forces acting in many-body systems and their correlations with observable phenomena could be convincingly derived in this way. Here, methods of computer simulation and applications of statistical mechanics often proved indispensable.
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New research published in Nature Electronics describes topological control capabilities in an integrated acoustic-electronic system at technologically relevant frequencies. This work paves the way for additional research on topological properties in devices that use high-frequency sound waves, with potential applications including 5G communications and quantum information processing. The study was led by Qicheng (Scott) Zhang, a postdoc in the lab of Charlie Johnson at the University of Pennsylvania, in collaboration with the group of Bo Zhen and colleagues from Beijing University of Posts and Telecommunications and the University of Texas at Austin.
This research builds on concepts from the field of topological materials, a theoretical framework developed by Penn’s Charlie Kane and Eugene Mele. One example of this type of material is a topological insulator, which acts as an electrical insulator on the inside but has a surface that conducts electricity. Topological phenomena are hypothesized to occur in a wide range of materials, including those that use light or sound waves instead of electricity.
In this study, Zhang was interested in studying topological phononic crystals, metamaterials that use acoustic waves, or phonons. In these crystals, topological properties are known to exist at low frequencies in the megahertz range, but Zhang wanted to see if topological phenomena might also occur at higher frequencies in the gigahertz range because of the importance of these frequencies for telecommunication applications such as 5G.
To study this complex system, the researchers combined state-of-the-art methodologies and expertise across theory, simulation, nanofabrication, and experimental measurements. First, researchers in the Zhen lab, who have expertise in studying topological properties in light waves, conducted simulations to determine the best types of devices to fabricate. Then, based on the results of the simulations and using high-precision tools at Penn’s Singh Center for Nanotechnology, the researchers etched nanoscale circuits onto aluminum nitride membranes. These devices were then shipped to the lab of Keji Lai at UT Austin for microwave impedance microscopy, a method that captures high-resolution images of the acoustic waves at incredibly small scales. Lai’s approach uses a commercial atomic force microscope with modifications and additional electronics developed by his lab.
“Before this, if people want to see what’s going on in these materials, they usually need to go to a national lab and use X-rays,” Lai says. “It’s very tedious, time consuming, and expensive. But in my lab, it’s just a tabletop setup, and we measure a sample in about 10 minutes, and the sensitivity and resolution are better than before.”
The key finding of this work is the experimental evidence showing that topological phenomena do in fact occur at higher frequency ranges. “This work brings the concept of topology to gigahertz acoustic waves,” says Zhang. “We demonstrated that we can have this interesting physics at a useful range, and now we can build up the platform for more interesting research to come.”
Another important result is that these properties can be built into the atomic structure of the device so that different areas of the material can propagate signals in unique ways, results that were predicted by theorists but were “amazing” to see experimentally, says Johnson. “That also has its own important implications: When you’re conveying a wave along a sharp trail in ordinary systems that don’t have these topological effect, at every sharp turn you’re going to lose something, like power, but in this system you don’t,” he says.
Overall, the researchers say that this work provides a critical starting point for progress in both fundamental physics research as well as for developing new devices and technologies. In the near term, the researchers are interested in modifying their device to make it more user-friendly and improving its performance at higher frequencies, including frequencies that are used for applications such as quantum information processing.
“In terms of technological implications, this is something that could make its way into the toolbox for 5G or beyond,” says Johnson. “The basic technology we’re working on is already in your phone, so the question with topological vibrations is whether we can come up with a way to do something useful at these higher frequency ranges that are characteristic of 5G.”
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Materials provided by University of Pennsylvania. Original written by Erica K. Brockmeier. Note: Content may be edited for style and length. More

The global bio-health research community is making a tremendous effort to generate knowledge relating to COVID-19 and SARS-CoV-2. In practice, this effort means a huge, very rapid production of scientific publications, which makes it difficult to consult and analyse all the information. That is why experts and decision-making bodies need to be provided with information systems to enable them to acquire the knowledge they need.
This is precisely what has been explored in the VIGICOVID researchers project run by the UPV/EHU’s HiTZ Centre, the UNED’s NLP & IR group, and Elhuyar’s Artificial Intelligence and Language Technologies Unit, thanks to Fondo Supera COVID-19 funding awarded by the CRUE. In the study, under the coordination of the UNED research group they have created a prototype to extract information through questions and answers in natural language from an updated set of scientific articles on COVID-19 and SARS-CoV-2 published by the global research community.
“The information search paradigm is changing thanks to artificial intelligence,” said Eneko Agirre, head of the UPV/EHU’s HiTZ Centre. “Until now, when searching for information on the internet, a question is entered, and the answer has to be sought in the documents displayed by the system. However, in line with the new paradigm, systems that provide the answer directly without any need to read the whole document are becoming more and more widespread.”
In this system, “the user does not request information using keywords, but asks a question directly,” explained Elhuyar researcher Xabier Saralegi. The system searches for answers to this question in two steps: “Firstly, it retrieves documents that may contain the answer to the question asked by using a technology that combines keywords with direct questions. That is why we have explored neural architectures,” added Dr Saralegi. Deep neural architectures fed with examples were used: “That means that search models and question answering models are trained by means of deep machine learning.”
Once the set of documents has been extracted, they are reprocessed through a question and answer system in order to obtain specific answers: “We have built the engine that answers the questions; when the engine is given a question and a document, it is able to detect whether or not the answer is in the document, and if it is, it tells us exactly where it is,” explained Dr Agirre.
A readily marketable prototype
The researchers are satisfied with the results of their research: “From the techniques and evaluations we analysed in our experiments, we took those that give the prototype the best results,” said the Elhuyar researcher. A solid technological base has been established, and several scientific papers on the subject have been published. “We have come up with another way of running searches for whenever information is urgently needed, and this facilitates the information use process. On the research level, we have shown that the proposed technology works, and that the system provides good results,” Agirre pointed out.
“Our result is a prototype of a basic research project. It is not a commercial product,” stressed Saralegi. But such prototypes can be modelled easily within a short time, which means they can be marketed and made available to society. These researchers stress that artificial intelligence enables increasingly powerful tools to be made available for working with large document bases. “We are making very rapid progress in this area. And what is more, everything that is investigated can readily reach the market,” concluded the UPV/EHU researcher.
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A POSTECH research team led by Professor Gil-Ho Lee and Gil Young Cho (Department of Physics) has developed a platform that can control the properties of solid materials with light and measure them.
Recognized for developing a platform to control and measure the properties of materials in various ways with light, the findings from the study were published in the top international academic journal Nature on March 15, 2022 (GMT).
The electrical properties of a material are determined by the movement of electrons in the material. For example, a material is defined as a metal if electrons can move freely, otherwise it is an insulator. In order to change the electrical properties of these solids, applying heat or pressure or adding impurities have been generally used. This is because the change in the position of the atoms in the solid changes the movement of electrons accordingly.
In contrast, the Floquet state, in which the original quantum state is replicated when light is irradiated on matters, has been proposed. By adopting such a concept, quantum states of the matters can be easily manipulated with light, which can be effectively used in quantum systems.
In previous experiments, the light intensity for realizing Floquet state in solids was enormous due to the high frequency of light. Also, Floquet states last only for a very short time of 250 femtoseconds (1 femtosecond is one trillionth of a second). Due to their transient nature, more quantitative studies of their characteristics have been limited.
POSTECH research team succeeded in the experimental realization of the steady Floquet state in a graphene Josephson junction (GJJ) and by irradiating continuous microwaves on it. The intensity of the light has been decreased to one trillionth the value of previous experiments, significantly reducing the heat generation and enabling continuously long-lasting Floquet states.
The research team also developed a novel superconducting tunneling spectroscopy to measure the Floquet states with high energy resolution. This is necessary to quantitatively verify the characteristics of the Floquet state that varies depending on the intensity, frequency and polarization of light applied to the device.
“This study is significant in that we have created a platform that can study the Floquet state in detail,” explained professors Gil-Ho Lee and Gil Young Cho who led the study. They added, “We plan to further investigate the correlation between properties of light, such as polarization, and the Floquet states.”
This study was conducted with the support from the Samsung Science and Technology Foundation, National Research Foundation of Korea, Institute for Basic Science, Air Force Office of Scientific Research, and Elemental Strategy Initiative conducted by the MEXT.
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Earthquakes do more than buckle streets and topple buildings. Seismic waves generated by earthquakes pass through the Earth, acting like a giant MRI machine and providing clues to what lies inside the planet.
Seismologists have developed methods to take wave signals from the networks of seismometers at the Earth’s surface and reverse engineer features and characteristics of the medium they pass through, a process known as seismic tomography.
For decades, seismic tomography was based on ray theory, and seismic waves were treated like light rays. This served as a pretty good approximation and led to major discoveries about the Earth’s interior. But to improve the resolution of current seismic tomographic models, seismologists need to take into account the full complexity of wave propagation using numerical simulations, known as full-waveform inversion, says Ebru Bozdag, assistant professor in the Geophysics Department at the Colorado School of Mines.
“We are at a stage where we need to avoid approximations and corrections in our imaging techniques to construct these models of the Earth’s interior,” she said.
Bozdag was the lead author of the first full-waveform inversion model, GLAD-M15 in 2016, based on full 3D wave simulations and 3D data sensitivities at the global scale. The model used the open-source 3D global wave propagation solver SPECFEM3D_GLOBE (freely available from Computational Infrastructure for Geodynamics) and was created in collaboration with researchers from Princeton University, University of Marseille, King Abdullah University of Science and Technology (KAUST) and Oak Ridge National Laboratory (ORNL). The work was lauded in the press. Its successor, GLAD-M25 (Lei et al. 2020), came out in 2020 and brought prominent features like subduction zones, mantle plumes, and hotspots into view for further discussions on mantle dynamics.
“We showed the feasibility of using full 3D wave simulations and data sensitivities to seismic parameters at the global scale in our 2016 and 2020 papers. Now, it’s time to use better parameterization to describe the physics of the Earth’s interior in the inverse problem,” she said. More

Because the comparative metabolomics field lacks sophisticated data analysis tools that are available to genomics and proteomics researchers, metabolomics researchers spend a lot of time hunting for candidate compounds that could be useful as leads for the development of new pharmaceuticals or agrochemicals. To solve this problem, scientists have developed Metaboseek, a free, easy-to-use app that integrates multiple data analysis features for the metabolomics community.
As a postdoctoral research associate in the lab of BTI faculty member Frank Schroeder, Max Helf saw his labmates continually struggle when they were analyzing data. So, he decided to do something about it and developed a free, open-source app called Metaboseek, which is now essential to the lab’s work.
The Schroeder lab studies the roundworm Caenorhabditis elegans, one of the most successful model systems for human biology, to discover new metabolites that govern evolutionarily conserved signaling pathways and could be useful as leads for the development of new pharmaceuticals or agrochemicals. The researchers accomplish this task by comparing the metabolites between two different worm populations — a process called comparative metabolomics.
Given that samples routinely have more than 100,000 compounds in them, computational approaches are essential to perform the analysis.
The team had been relying on software packages that did not offer the required level of flexibility to easily customize analysis parameters. That limitation, and the lack of a suitable graphical user interface, meant Helf’s colleagues faced the cumbersome task of visually inspecting mounds of data — for example, to spot possible false positives — and jumping between several other software tools to confirm and filter out those meaningless results.
“It just seemed very inefficient to me, and I couldn’t get over the shortcomings of other software solutions for this problem,” Helf said. “I thought there had to be an easier way, so I started to write code for my own software.”
Helf developed the initial version of his software in 2017, and continued to improve it over the next two years. “Besides addressing the problems my labmates were already facing, I talked to them about what else held them back — what they wanted to do but weren’t even trying — and built those features in the app,” said Helf, who is now a bioinformatics product manager at proteomics company Biognosys AG. “I wanted this new tool to be user-friendly and accessible to anyone who does chemical biology.” More

Even though robots don’t have eyes with retinas, the key to helping them see and interact with the world more naturally and safely may rest in optical coherence tomography (OCT) machines commonly found in the offices of ophthalmologists.
One of the imaging technologies that many robotics companies are integrating into their sensor packages is Light Detection and Ranging, or LiDAR for short. Currently commanding great attention and investment from self-driving car developers, the approach essentially works like radar, but instead of sending out broad radio waves and looking for reflections, it uses short pulses of light from lasers.
Traditional time-of-flight LiDAR, however, has many drawbacks that make it difficult to use in many 3D vision applications. Because it requires detection of very weak reflected light signals, other LiDAR systems or even ambient sunlight can easily overwhelm the detector. It also has limited depth resolution and can take a dangerously long time to densely scan a large area such as a highway or factory floor. To tackle these challenges, researchers are turning to a form of LiDAR called frequency-modulated continuous wave (FMCW) LiDAR.
“FMCW LiDAR shares the same working principle as OCT, which the biomedical engineering field has been developing since the early 1990s,” said Ruobing Qian, a PhD student working in the laboratory of Joseph Izatt, the Michael J. Fitzpatrick Distinguished Professor of Biomedical Engineering at Duke. “But 30 years ago, nobody knew autonomous cars or robots would be a thing, so the technology focused on tissue imaging. Now, to make it useful for these other emerging fields, we need to trade in its extremely high resolution capabilities for more distance and speed.”
In a paper appearing March 29 in the journal Nature Communications, the Duke team demonstrates how a few tricks learned from their OCT research can improve on previous FMCW LiDAR data-throughput by 25 times while still achieving submillimeter depth accuracy.
OCT is the optical analogue of ultrasound, which works by sending sound waves into objects and measuring how long they take to come back. To time the light waves’ return times, OCT devices measure how much their phase has shifted compared to identical light waves that have travelled the same distance but have not interacted with another object. More

Artificial intelligence (AI) is an effective tool for fracture detection that has potential to aid clinicians in busy emergency departments, according to a study in Radiology.
Missed or delayed diagnosis of fractures on X-ray is a common error with potentially serious implications for the patient. Lack of timely access to expert opinion as the growth in imaging volumes continues to outpace radiologist recruitment only makes the problem worse.
AI may help address this problem by acting as an aid to radiologists, helping to speed and improve fracture diagnosis.
To learn more about the technology’s potential in the fracture setting, a team of researchers in England reviewed 42 existing studies comparing the diagnostic performance in fracture detection between AI and clinicians. Of the 42 studies, 37 used X-ray to identify fractures, and five used CT.
The researchers found no statistically significant differences between clinician and AI performance. AI’s sensitivity for detecting fractures was 91-92%.
“We found that AI performed with a high degree of accuracy, comparable to clinician performance,” said study lead author Rachel Kuo, M.B. B.Chir., from the Botnar Research Centre, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences in Oxford, England. “Importantly, we found this to be the case when AI was validated using independent external datasets, suggesting that the results may be generalizable to the wider population.”
The study results point to several promising educational and clinical applications for AI in fracture detection, Dr. Kuo said. It could reduce the rate of early misdiagnosis in challenging circumstances in the emergency setting, including cases where patients may sustain multiple fractures. It has potential as an educational tool for junior clinicians.
“It could also be helpful as a ‘second reader,’ providing clinicians with either reassurance that they have made the correct diagnosis or prompting them to take another look at the imaging before treating patients,” Dr. Kuo said.
Dr. Kuo cautioned that research into fracture detection by AI remains in a very early, pre-clinical stage. Only a minority of the studies that she and her colleagues looked at evaluated the performance of clinicians with AI assistance, and there was only one example where an AI was evaluated in a prospective study in a clinical environment.
“It remains important for clinicians to continue to exercise their own judgment,” Dr. Kuo said. “AI is not infallible and is subject to bias and error.”
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