Computers Math

A research team led by Prof. Kei-May LAU of the Department of Electronic and Computer Engineering at Hong Kong University of Science and Technology (HKUST) has recently developed a novel semiconductor deposition scheme and demonstrated high-performance photodetectors (PDs) grown on silicon-on-insulators (SOI) for silicon photonics. These III-V photodetectors are qualified candidates for high-speed data communications in silicon photonics. These results point to a practical solution for the monolithic integration of III-V active devices and Si-based passive devices on the SOI platform in the future.
The ever-growing communication traffic is pushing the conventional electronic interconnection to the limit. Silicon photonics is regarded as an enabling technology to solve this pressing issue with its high-speed and large bandwidth capability, as well as scalable and high-throughput manufacturing. High-performance PDs are crucial optical building blocks in silicon photonic integrated circuits (Si-PICs). In addition to characteristics such as high responsivity, low dark current, large bandwidth, operation over a wide wavelength band, efficient light coupling with Si waveguides and CMOS compatibility are also needed for the PDs.
III-V photodetectors have long been deployed in InP-based photonic integrated circuits (PICs) because of their superior device performance. Recently, interest on III-V PDs grown on Si started to flourish complementing the research on integrating III-V lasers on Si and the eventual goal of having high-performance III-V-photonics integrated on the Si-photonics platform. For the III-V PDs on Si realized by traditional blanket hetero-epitaxy method, the thick buffer layers used for defect reduction make it challenging for light coupling with Si-waveguides and reported 3 dB bandwidths of these PDs often fall in the range of sub-10GHz.
The HKUST team developed the lateral aspect ratio trapping (ART) method to grow III-V materials on SOI without the need of thick buffers. III-V PDs grown on SOI by this method feature an in-plane configuration with the Si-device layer, which allows easy integration of the PDs and Si-waveguides. The team designed and fabricated III-V PDs with a variety of dimensions on a monolithic InP/SOI platform, also developed by the team. The PDs feature a large 3 dB bandwidth exceeding 40 GHz, a high responsivity of 0.3 A/W at 1550 nm and 0.8 A/W at 1310 nm, a wide operation wavelength span over 400 nm, and a low dark current of 0.55 nA. The photocurrents is adjustable for various applications by varying the length of the PDs. Design of interfacing these PDs with Si-waveguides can be flexible and simple.
For the first time, the team demonstrates III-V photodetectors grown on the monolithic InP/SOI platform (paper to appear in Light: Science and Application) to fulfill the stringent criteria for PDs in silicon photonics. “This was made possible by our latest development of a monolithic InP/SOI platform with both sub-micron InP bars and large-dimension InP membranes. Our team’s combined expertise and insights into both device physics and growth mechanisms allow us to accomplish the challenging task of cross-correlated analysis of epitaxial growth, material characteristics and device performance,” says Prof. Lau.
This is a collaborative work with a research team led by Prof. Hon-Ki TSANG of Department of Electronic Engineering at Chinese University of Hong Kong (CUHK).
The device fabrication technology in the work was developed at HKUST’s Nanosystem Fabrication Facility (NFF) on Clear Water Bay campus. The work is supported by Research Grants Council of Hong Kong and Innovation Technology Fund of Hong Kong. This work has recently been published in Optica.
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Quantum dot light-emitting diode (QLED), which employs quantum dots as a light-emitting material, has attracted significant attention as a promising alternative for next-generation display technologies, owing to its outstanding electroluminescence properties. Since it does not require any bulky components such as backlight units, QLED displays can potentially be manufactured into an ultrathin form factor. A joint research team led by KIM Dae-Hyeong (Professor at Seoul National University) and HYEON Taeghwan (Distinguished professor at Seoul National University) from the Center for Nanoparticle Research within the Institute for Basic Science has previously unveiled a prototype QLED back in 2015. The device had a thickness of only 3 micrometers, which is only one-thirtieth of that of human hair. Due to such an extremely reduced thickness, the ultrathin QLED exhibited outstanding mechanical flexibility, which allowed it to be readily applicable in various wearable devices, such as electronic tattoos.
Recently, the team further advanced this technology and developed a foldable variant of the ultrathin QLED, inspired by the ancient art of paper folding known as origami. The IBS researchers reported three-dimensional foldable QLEDs, which can be freely transformed into various user-customized 3D structures, such as butterflies, airplanes, and pyramids. Considering the rising popularity of foldable smartphones, the advancement of foldable display technology is gaining greater importance. It is expected this technology can provide unprecedented opportunities for next-generation electronics with user-customized form factors with complex structures, as well as allowing for dynamic three-dimensional display of visual information.
The researchers endowed foldability to the conventional planar QLED via a new fabrication process that can partially etch the epoxy film deposited on the QLED surface without damaging the underlying QLED. Using a power-controllable carbon dioxide pulsed laser and the silver-aluminum alloy-based etch-stop layers, the etching depth can be precisely controlled. As the laser-etched part of the device is relatively thinner than the surrounding region, it is possible to etch out deformation lines along which the device can be folded like origami paper.
Based on the selective laser-etching technique, researchers were able to precisely control the radius of curvature down to less than 50 micrometers. Under such a small curvature radius, the fold line resembles a sharp edge with no visible curvature. By using mechanical simulation to carefully engineer the device, researchers were able to minimize the strain loaded on the light-emitting components. The entire QLED including the crease region (a fold line) was able to maintain a stable light-emitting performance even when after it was repeatedly folded 500 times. The technology was applied to fabricate 3D foldable QLEDs with various complex shapes such as butterflies, airplanes, and pyramids.
“We were able to build a 3D foldable QLED that can be freely folded just like a paper artwork,” said KIM Dae-Hyeong, the vice-director of the Center for Nanoparticle Research. He also said, “By fabricating the passively driven, 3D foldable QLED arrays composed of 64 individual pixels, we have shown the possibility of developing displays with greater complexity in the future.” HYEON Taeghwan, the director of the Center for Nanoparticle Research, states that “Through the technology reported in this research, paper-like QLEDs that can be folded into various complex structures have been successfully fabricated. Who knows when the day will come when electronic paper with a display unit can replace real paper?”
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While very little is known on the effects of immersive VR on adults, there is next to no knowledge on the impact of such systems on the sensorimotor abilities of young children.
In 2016 at EPFL’s Open House, EPFL graduate Jenifer Miehlbradt was showcasing her virtual reality setup to allow users to pilot drones using their torso. Users from the general public were invited to wear a VR headset, and movements of their torso would allow them to navigate through a series of obstacles in a virtual landscape.
“Adults had no problem using simple torso movements to fly through the virtual obstacles, but I noticed that children just couldn’t do it,” remembers Miehlbradt. “That’s when Silvestro asked me to come to his office.”
Silvestro Micera, Bertarelli Foundation Chair in Translational Neuroengineering, was Miehlbradt’s supervisor at the time. They realized that their virtual reality torso experiment may be revealing something about the way a child’s nervous system develops, and that no study in the literature had assessed the effect of virtual reality headsets on children. They embarked on a study of several years, in collaboration with the Italian Institute of Technology, involving 80 children between the ages of 6 and 10. The results are published today in Scientific Reports.
“This study confirms the potential of technology to understand motor control,” says Micera.
The development of upper body coordination
Healthy adults have no problem disconnecting their head movements from their torso for piloting, like looking elsewhere while riding a bike. This requires complex integration of multiple sensory inputs: vision, from the inner ear for balance, and proprioception, the body’s ability to sense movement, action and location. More

Researchers and data scientists at UT Southwestern Medical Center and MD Anderson Cancer Center have developed an artificial intelligence technique that can identify which cell surface peptides produced by cancer cells called neoantigens are recognized by the immune system.
The pMTnet technique, detailed online in Nature Machine Intelligence, could lead to new ways to predict cancer prognosis and potential responsiveness to immunotherapies.
“Determining which neoantigens bind to T cell receptors and which don’t has seemed like an impossible feat. But with machine learning, we’re making progress,” said senior author Dr. Tao Wang, Ph.D., Assistant Professor of Population and Data Sciences, and with the Harold C. Simmons Comprehensive Cancer Center and the Center for Genetics of Host Defense at UT Southwestern.
Mutations in the genome of cancer cells cause them to display different neoantigens on their surfaces. Some of these neoantigens are recognized by immune T cells that hunt for signs of cancer and foreign invaders, allowing cancer cells to be destroyed by the immune system. However, others seem invisible to T cells, allowing cancers to grow unchecked.
“For the immune system, the presence of neoantigens is one of the biggest differences between normal and tumor cells,” said Tianshi Lu, first co-author with Ze Zhang, doctoral students in the Tao Wang lab, which uses state-of-the-art bioinformatics and biostatistics approaches to study the implications of tumor immunology for tumorigenesis, metastasis, prognosis, and treatment response in a variety of cancers. “If we can figure out which neoantigens stimulate an immune response, then we may be able to use this knowledge in a variety of different ways to fight cancer,” Ms. Lu said.
Being able to predict which neoantigens are recognized by T cells could help researchers develop personalized cancer vaccines, engineer better T cell-based therapies, or predict how well patients might respond to other types of immunotherapies. But there are tens of thousands of different neoantigens, and methods to predict which ones trigger a T cell response have proven to be time-consuming, technically challenging, and costly.
Searching for a better technique with support of grants from the National Institutes of Health (NIH) and Cancer Prevention and Research Institute of Texas (CPRIT), the research team looked to machine learning. They trained a deep learning-based algorithm that they named pMTnet using data from known binding or nonbinding combinations of three different components: neoantigens; proteins called major histocompatibility complexes (MHCs) that present neoantigens on cancer cell surfaces; and the T cell receptors (TCRs) responsible for recognizing the neoantigen-MHC complexes. They then tested the algorithm against a dataset developed from 30 different studies that had experimentally identified binding or nonbinding neoantigen T cell-receptor pairs. This experiment showed that the new algorithms had a high level of accuracy.
The researchers used this new tool to gather insights on neoantigens cataloged in The Cancer Genome Atlas, a public database that holds information from more than 11,000 primary tumors. pMTnet showed that neoantigens generally trigger a stronger immune response compared with tumor-associated antigens. It also predicted which patients had better responses to immune checkpoint blockade therapies and had better overall survival rates.
“As an immunologist, the most significant hurdle currently facing immunotherapy is the ability to determine which antigens are recognized by which T cells in order to leverage these pairings for therapeutic purposes,” said corresponding author Alexandre Reuben, Ph.D., Assistant Professor of Thoracic-Head & Neck Medical Oncology at MD Anderson. “pMTnet outperforms its current alternatives and brings us significantly closer to this objective.”
Other UTSW researchers who contributed to this study include James Zhu, Yunguan Wang, Xue Xiao, and Lin Xu. Other MD Anderson scientists who contributed to this work include Peixin Jiang, Chantale Bernatchez, John V. Heymach, and Don L. Gibbons. Dr. Jun Wang from NYU Langone Health also contributed to this work.
UT Southwestern’s Simmons Cancer Center and MD Anderson Cancer Center are among the exclusive 51 designated comprehensive centers with the National Cancer Institute, which includes a joint effort with the National Human Genome Research Institute to oversee The Cancer Genome Atlas project. The study was supported by the NIH (grants 5P30CA142543/TW and R01CA258584/TW), CPRIT (RP190208/TW), MD Anderson (Lung Cancer Moon Shot), the University Cancer Foundation at MD Anderson, the Waun Ki Hong Lung Cancer Research Fund, Exon 20 Group, and Rexanna’s Foundation for Fighting Lung Cancer. More

The Moon’s polar regions are home to craters and other depressions that never receive sunlight. Today, a group of researchers led by the Max Planck Institute for Solar System Research (MPS) in Germany presents the highest-resolution images to date covering 17 such craters in the journal Nature Communications.
Craters of this type could contain frozen water, making them attractive targets for future lunar missions, and the researchers focused further on relatively small and accessible craters surrounded by gentle slopes. In fact, three of the craters have turned out to lie within the just-announced mission area of NASA’s Volatiles Investigating Polar Exploration Rover (VIPER), which is scheduled to touch down on the Moon in 2023. Imaging the interior of permanently shadowed craters is difficult, and efforts so far have relied on long exposure times resulting in smearing and lower resolution. By taking advantage of reflected sunlight from nearby hills and a novel image processing method, the researchers have now produced images at 1-2 meters per pixel, which is at or very close to the best capability of the cameras.
The Moon is a cold, dry desert. Unlike the Earth, it is not surrounded by a protective atmosphere and water which existed during the Moon’s formation has long since evaporated under the influence of solar radiation and escaped into space. Nevertheless, craters and depressions in the polar regions give some reason to hope for limited water resources. Scientists from MPS, the University of Oxford and the NASA Ames Research Center have now taken a closer look at some of these regions.
“Near the lunar north and south poles, the incident sunlight enters the craters and depressions at a very shallow angle and never reaches some of their floors,” MPS-scientist Dr. Valentin Bickel, first author of the new paper, explains. In this “eternal night,” temperatures in some places are so cold that frozen water is expected to have lasted for millions of years. Impacts from comets or asteroids could have delivered it, or it could have been outgassed by volcanic eruptions, or formed by the interaction of the surface with the solar wind. Measurements of neutron flux and infrared radiation obtained by space probes in recent years indicate the presence of water in these regions. Eventually, NASA’s Lunar Crater Observation and Sensing Satellite (LCROSS) provided direct proof: twelve years ago, the probe fired a projectile into the shadowed south pole crater Cabeus. As later analysis showed, the dust cloud emitted into space contained a considerable amount of water.
However, permanently shadowed regions are not only of scientific interest. If humans are to ever spend extended periods of time on the Moon, naturally occurring water will be a valuable resource — and shadowed craters and depressions will be an important destination. NASA’s uncrewed VIPER rover, for example, will explore the South Pole region in 2023 and enter such craters. In order to get a precise picture of their topography and geology in advance — for mission planning purposes, for example — images from space probes are indispensable. NASA’s Lunar Reconnaissance Orbiter (LRO) has been providing such images since 2009.
However, capturing images within the deep darkness of permanently shadowed regions is exceptionally difficult; after all, the only sources of light are scattered light, such as that reflecting off the Earth and the surrounding topography, and faint starlight. “Because the spacecraft is in motion, the LRO images are completely blurred at long exposure times,” explains Ben Moseley of the University of Oxford, a co-author of the study. At short exposure times, the spatial resolution is much better. However, due to the small amounts of light available, these images are dominated by noise, making it hard to distinguish real geological features.
To address this problem, the researchers have developed a machine learning algorithm called HORUS (Hyper-effective nOise Removal U-net Software) that “cleans up” such noisy images. It uses more than 70,000 LRO calibration images taken on the dark side of the Moon as well as information about camera temperature and the spacecraft’s trajectory to distinguish which structures in the image are artifacts and which are real. This way, the researchers can achieve a resolution of about 1-2 meters per pixel, which is five to ten times higher than the resolution of all previously available images.
Using this method, the researchers have now re-evaluated images of 17 shadowed regions from the lunar south pole region which measure between 0.18 and 54 square kilometers in size. In the resulting images, small geological structures only a few meters across can be discerned much more clearly than before. These structures include boulders or very small craters, which can be found everywhere on the lunar surface. Since the Moon has no atmosphere, very small meteorites repeatedly fall onto its surface and create such mini-craters.
“With the help of the new HORUS images, it is now possible to understand the geology of lunar shadowed regions much better than before,” explains Moseley. For example, the number and shape of the small craters provide information about the age and composition of the surface. It also makes it easier to identify potential obstacles and hazards for rovers or astronauts. In one of the studied craters, located on the Leibnitz Plateau, the researchers discovered a strikingly bright mini-crater. “Its comparatively bright color may indicate that this crater is relatively young,” says Bickel. Because such a fresh scar provides fairly unhindered insight into deeper layers, this site could be an interesting target for future missions, the researchers suggest.
The new images do not provide evidence of frozen water on the surface, such as bright patches. “Some of the regions we’ve targeted might be slightly too warm,” Bickel speculates. It is likely that lunar water does not exist as a clearly visible deposit on the surface at all — instead, it could be intermixed with the regolith and dust, or may be hidden underground.
To address this and other questions, the researchers’ next step is to use HORUS to study as many shadowed regions as possible. “In the current publication, we wanted to show what our algorithm can do. Now we want to apply it as comprehensively as possible,” says Bickel.
This work has been enabled by the Frontier Development Lab (FDL.ai). FDL is a co-operative agreement between NASA, the SETI Institute and Trillium Technologies Inc, in partnership with the Luxembourg Space Agency and Google Cloud. More

Mathematical constructions of the action of SARS-CoV-2 and its multiple spikes, which enable its success at infecting cells, can give vaccine developers and pharmaceutical companies alike a more precise picture of what the virus is doing inside us and help fine tune prevention and treatment, mathematical modelers say.
Mathematical construction enables examination of the activity of individual virus particles including the emergence of new spikes — and more severe infection potential — that can result when a single virus particle infects a human cell, says Dr. Arni S.R. Rao, director of the Laboratory for Theory and Mathematical Modeling in the Section of Infectious Diseases at the Medical College of Georgia.
The number of spikes and the way they are distributed on a virus particle are believed to be key in the spread of the virus, Rao and his colleague Dr. Steven G. Krantz, professor of mathematics at Washington University in St. Louis, Missouri, write in the Journal of Mathematical Analysis and Applications.
Laboratory experiments on virus particles and their bonding, or infection, of cells more typically are done on a group of viruses, they write.
“Right now, we don’t know when a spike bonds with a cell, what happens with that virus particle’s other spikes,” says Rao, the study’s corresponding author. “How many new infected cells are being produced has never been studied for the coronavirus. We need quantification because ultimately the vaccine or pharmaceutical industry needs to target those infected cells,” he says of the additional insight their mathematical methodology, which also enables the study of the growth of the virus’ spikes over time, provides.
Viral load is considered one of the strong predictors of the severity of sickness and risk of death and the number of spikes successfully bonding with cells is an indicator of the viral load, Rao says. PCR, or polymerase chain reaction, which is used for COVID testing, for example, provides viral load by assessing the amount of the virus’ RNA present in a test sample. More

A prescriptive computer program developed by the USC Marshall School of Business and Wharton School of Business of the University of Pennsylvania for Greece to identify asymptomatic, infected travelers may have slowed tCOVID-19’s spread through its borders, a new study in the journal Nature indicates.
“It was a very high-impact artificial intelligence project, and I believe we saved lives by developing a cutting edge, novel system for targeted testing during the pandemic,” said Kimon Drakopoulos, a USC Marshall assistant professor of Data Sciences and Operations and one of the study’s authors.
In July 2020, Greece largely reopened its borders to spare its tourism-dependent economy from the devastating impact of long-term shutdowns amid COVID-19.
Greece collaborated with USC Marshall and Wharton to create “Eva,” an artificial intelligence algorithm that uses real-time data to identify high-risk visitors for testing. Evidence shows the algorithm caught nearly twice as many asymptomatic infected travelers as would have been caught if Greece had relied on only travel restrictions and randomized COVID testing.
“Our work with Eva proves that carefully integrating real-time data, artificial intelligence and lean operations offers huge benefits over conventional, widely used approaches to managing the pandemic,” said Vishal Gupta, a USC Marshall associate professor of data science another of the study’s authors.
The joint study was published Wednesday in the journal Nature. More

We can learn a lot by studying microscopic and macroscopic changes in a material as it crosses from one phase to another, for example from ice to water to steam. A new Australian study examines systems transitioning from ‘normal’ fluid to a quantum state known as a superfluid, which can flow with zero friction, with a view to future, superfluid-based, quantum technologies, such as ultra-low energy electronics.We can learn a lot by studying microscopic and macroscopic changes in a material as it crosses from one phase to another, for example from ice to water to steam.
But while these phase transitions are well understood in the case of water, much less is known about the dynamics when a system goes from being a normal fluid to a superfluid, which can flow with zero friction, ie without losing any energy.
A new Swinburne study observing transition of an atomic gas from normal fluid to superfluid provides new insights into the formation of these remarkable states, with a view to future, superfluid-based, quantum technologies, such as ultra-low energy electronics.
Superfluid formation was seen to involve a number of different timescales, associated with different dynamical processes that take place upon crossing the phase boundary.
UNDERSTANDING DYNAMIC TRANSITIONS, TOWARDS FUTURE TECHNOLOGIES
As a nonequilibrium, dynamic process, phase transitions are challenging to understand from a theoretical perspective, inside these fascinating and potentially useful states of matter. More