Tech

Nanochannels have important applications in biomedicine, sensing, and many other fields. Though engineers working in the field of nanotechnology have been fabricating these tiny, tube-like structures for years, much remains unknown about their properties and behavior.

Now, University of Maryland mechanical engineering associate professor Siddhartha Das and a group of his Ph.D. students have published surprising new findings in the journal ACS Nano. Using atomic-level simulations, Das and his team were able to demonstrate that charge properties as well as charge-induced fluid flow within a functionalized nanochannel does not always behave as expected.

"We've discovered a new context for nanochannels functionalized by grafting their inner walls with charged polymer molecules (also known as polyelectrolytes or PEs)," Das said, referring to the process of grafting polymers or other substances onto the nanochannel in order to cause it to function in a certain way. "The functionalization of nanochannels is not new. But we've come up with a paradigm shift in terms of understanding the behavior and properties of such systems in the context of their charge properties and their ability to regulate fluid flow.

"For example," Das said, "we've discovered a new type of flow behavior in such functionalized nanochannels; by increasing the magnitude of the electric field applied to a nanochannel, the direction of this electric-field-driven flow (often known as electroosmotic flow) can be reversed."

The paper by Das and his students details three specific discoveries. Firstly, they showed that, when polyelectrolytes (PEs) are grafted in the form of a layer on the inner wall of the nanochannel, this PE layer will, under certain conditions, undergo a surprising reversal of electrical charge. Normally, if negative PE molecules have been attached to the nanochannel, the PE layer nearby should have a net negative charge. Das and his students, however, identified situations in which the charge becomes inverted and the net charge within the layer is positive due to the attraction of more number of positive ions (than needed to screen the charge of the PE layer) within the layer--this phenomenon is known as "overscreening."

The team then investigated how this overscreening affects the external electric field driven flow (known as the electroosmotic or EOS flow) within the nanochannel. They found, surprisingly, that in such situations the flow is driven by ions having the same charge as the Pes grafted onto the channel walls; thus, a negatively charged polymer creates a net positive field in its vicinity, but the flow is driven by the negative ions.

"We call this 'co-ion driven electro-osmosis,' and our paper marks the first time this phenomenon has been identified," Das said.

Finally, the team demonstrated the unexpected results of ramping up the magnitude of the electric field: the PE molecules attached to the nanochannel become deformed, and the ions that caused the instance of overscreening start to escape from the PE layer. This causes the overscreening to stop, and also reverses the direction of flow in the channel: if it was moving left to right, for instance, it switches to right-left. "No one predicted this," Das said.

The findings are significant, Das said, because much of the interest in nanochannels relates from their ability to transport molecules. "Since flow is so important, a new discovery in this area allows us to build on our understanding of how nanochannels work and what we can do with them," Das said. "There are other methods of reversing flow, but until now it was not known that we can accomplish this by increasing field strength."

Radiation at terahertz frequencies (wavelengths between 0.03 and 0.3 mm) can be used successfully to analyze the structural dynamics of water and biomolecules. But applying the technique to aqueous solutions and tissues remains challenging, since terahertz (THz) radiation is strongly absorbed by water. While this absorption enables certain analyses, such as the structure of water and its interactions with biological solutes, it limits the thickness of samples that can be analyzed, and it drowns out weaker signals from biomolecules of interest. Strong absorption of THz radiation in water has presented a bottleneck preventing THz radiation from revealing biophysical and biochemical processes deep within tissues.

To overcome these limitations, a research team led by Zhen Tian and Jiao Li at Tianjin University recently developed a method for analyzing water-rich samples via time-domain THz optoacoustics. As reported in Advanced Photonics, the novel system enables time-domain THz optoacoustic detection of water-rich samples, such as aqueous solutions and tissues. The optoacoustic signal of water can be dampened by altering temperature to enable the sensitive detection of other molecules of interest.

Water detection and dampening based on THz optoacoustics

The time-domain THz optoacoustics demonstrated is a breakthrough that enables precise and nondestructive detection of optoacoustic signals in water-rich samples over a 104-fold thickness, ranging from microns to centimeters (102-fold larger than traditional THz detection methods such as THz time-domain spectroscopy). The team successfully obtained the time-domain THz optoacoustic signals from water in different samples of agar-in-water phantoms, bio-tissues, and aqueous solutions with different solutes.

By adjusting the temperature to alter the THz optoacoustic signal of water, they improved the sensitivity with which it can be analyzed. Conversely, the signal of water can be reduced or even silenced.

The biomedical advantages are clear. According to the authors, "By manipulating THz optoacoustic signals of an aqueous background, we can achieve uniquely enhanced sensitivity for label-free quantification of ions, in concentrations reaching the levels in the human body." The reported method achieves an order of magnitude greater sensitivity than commercially available THz spectroscopy systems.

Powerful tool for spectroscopy

The authors note that this new THz optoacoustic method can be extended to the study of other biological molecules and tissues, such as sugars, proteins, DNA, and RNA. Additional temperature and concentration parameters related to both THz absorption and ultrasonic propagation can be provided by time-domain THz optoacoustics, potentially contributing to studies of biological and chemical properties, such as the hydration number of ion solutions.

A powerful new tool for spectroscopy, THz optoacoustics opens up possibilities for imaging aqueous solutions and tissues to investigate molecular interactions and biochemical processes. Zhen Tian says, "We aim to inspire long-term research in THz spectroscopy and imaging in order to harness the biophysical, structural, and functional insights that cannot be obtained using radiation of other frequencies."

Read the open access research article by Jiao Li et al., "Time-domain terahertz optoacoustics: manipulable water sensing and dampening," Adv. Photon. 3(2), 026003 (2021), doi 10.1117/1.AP.3.2.026003.

Metals are one of the most widely used materials in the world - they are used in cookware, tools, electric appliances, electric wires, computer chips, jewelry and so on. With the growing demand for metal products, it is crucial to promote sustainable and environmentally-friendly methods of recycling metal waste to help reduce the environmental impact of using metals in the economy.

The conventional approaches for recycling metal waste are energy intensive and some of these methods also generate environmentally harmful by-products, such as ammonia and methane during aluminium recycling.

To address this challenge, a team of researchers from the National University of Singapore (NUS) has demonstrated a new eco-friendly technique to convert aluminium and magnesium waste into high-value, multi-functional aerogels. This upcycling method could be applied to all types of metal waste in power form, such as metal chips and electronic waste.

"Our approach is cheaper, does not produce any hazardous waste, consumes less energy and is more environmentally-friendly than conventional recycling methods for metal waste. The metal-based aerogels created using our unique fabrication technique have high thermal and mechanical stability. Hence, they are promising candidates for heat and sound insulation in harsh environments with high temperature or high mechanical impact. We are also exploring new uses for such aerogels, such as biomedical applications," explained research team leader Associate Professor Duong Hai-Minh, who is from the NUS Department of Mechanical Engineering.

This latest technological breakthrough achieved by Assoc Prof Duong and his team builds upon their earlier successes in developing aerogels using different types of waste such as plastics, textiles, paper, pineapple leaves and other types of food and agricultural waste.

Simple, low-cost fabrication process

The NUS team has developed a simple fabrication process to create metal-based aerogels. Metal waste is first ground into powder and mixed with chemical crosslinkers. The mixture is heated in the oven, frozen and then freeze-dried to create the aerogel. The process may vary slightly depending on the metal waste involved. On average, it takes about one to three days to transform powdered metal waste into aerogels, compared to three to seven days using conventional methods of producing aerogels.

The simple process also means that metal-based aerogels can be produced at a much lower cost. Using the technique developed by the NUS team, a piece of metal-based aerogel that is 1 sqm in size and 1 cm thick costs less than S$10.50 (US$7.90) to produce, half the price of commercially available silica aerogel.

Metal-based aerogels as versatile construction materials

Aerogels are highly absorbent, extremely light, and they have excellent thermal and sound insulation capabilities. In their earlier work, Assoc Prof Duong and his team had shown that the properties of aerogels can be altered by coating them with chemicals - for instance, they can become water repellent or fire resistant.

In their latest work, the NUS team has identified new exciting applications for metal-based aerogels. One promising application is to be used as light-weight construction materials.

"Our aluminium aerogel is 30 times lighter and insulates heat 21 times better than conventional concrete. When optical fibres are added during the mixing stage, we can create translucent aluminium aerogels which, as building materials, can improve natural lighting, reduce energy consumption for lighting and illuminate dark or windowless areas. Translucent concrete can also be used to construct sidewalks and speed bumps that light up at night to improve safety for pedestrians and road traffic," Assoc Prof Duong added.

The translucent aluminium aerogels created by the NUS team is six times lighter, six times better in thermal insulation and 120 times cheaper compared to commercial translucent concrete (LiTraCon).

When coated with a chemical called methyltriethoxysilane (MTEOS), aluminium aerogels can repel water and becomes a self-cleaning construction material which allows dirt or debris to be easily washed away when it comes into contact with water.

Metal-based aerogels are also suitable as fire retardant boards, thermal insulation materials in buildings and piping systems, for absorption of airborne contaminants for indoor environments, and oil-spill cleaning.

Metal-based aerogels for cell cultivation

The NUS team is also looking at using aerogels for biomedical applications.

"We are currently working with a commercial partner to test our aluminium aerogels as microcarriers for cell cultivation. Microcarriers are micro-size beads for cells to anchor and grow. Our first trials were performed on stem cells, using a cell line commonly used for testing of drugs as well as cosmetics, and the results are very encouraging," explained Assoc Prof Duong.

To be used as microcarriers, aluminium aerogels are ground into powder and added to the mixture of cells and growth media (including nutrients, antibiotics and growth supplements). The cells are cultivated at 37 degree Celsius in an incubator for 12 days. The microcarriers are then removed and the cells are harvested for various uses.

"After 12 days of incubation, our experiments obtained a yield of 70%. This is the first successful demonstration of growing cells using aerogels. We need to conduct more studies to optimise the culture conditions and address biocompatibility requirements. This is an exciting development that could open doors to a wider use of aerogels for non-conventional applications such as testing drugs and cosmetics, vaccine development and tissue engineering," Assoc Prof Duong explained.

The NUS team has recently published its work on creating aerogels using aluminium waste in the Journal of Material Cycles and Waste Management on 22 February 2021. Assoc Prof Duong and his team are also in discussion with industry partners to commercialise the technology for fabricating metal-based aerogels.

In the next phase of their research, the NUS team is also looking at developing metal-based aerogels for applications that require extremely high temperature tolerance, such as for military applications.

With inherent orthogonality, both SAMs and OAMs of light have been utilized to expand the dimensions of optical communications and signal processing, wherein unambiguous SAM and OAM identification is one of the significant topics. Conventional sorting approaches suffer from complicated optical setups, multiple bulky devices, repeated projection measurements, and cannot simultaneously distinguish SAM and OAM.

In a new paper published in Light Science & Application, a team of scientists, led by Professor Xiangang Luo from State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics Chinese Academy of Sciences, and co-workers have showed that a single spin-decoupled metasurface that merges the geometric phase and dynamic phase could perform simultaneous SAM and OAM mode discrimination via momentum transformation, where vortex beams of different spins were transformed into focusing patterns on two separated halves of the screen on a transverse focal plane with topological charge-dependent azimuthal rotations. Further experimental investigations have proven that the single spin-decoupled metasurface possesses the ability to detect cylindrical vortex vector beams with simultaneous phase and polarization singularities. Spin-decoupled PMTs were experimentally demonstrated at several different wavelengths in the visible band. Finally, they showed that the proposed approach could be extended to sorting of superimposed OAMs with a proper mode interval. These results reported here may have many important applications in momentum measurement of both the spin and angular momentum and singularity detection of both phase and polarization singularities.

The results of coral beaching are obvious -- stark underwater forests of white coral skeletons -- yet the physiological processes of bleaching are not well understood. Now, KAUST researchers show that, long before signs of bleaching appear, prolonged spells of warm water cause heat stress that disrupts the nutrient cycling of the coral and its symbiotic algae.

Coral reefs occur in warm low-nutrient waters. Stony corals include the coral animal, which is a cnidarian host that lives in symbiosis with Symbiodiniaceae, single-celled algae that photosynthesize to help "feed" the coral in exchange for the protection of the coral tissue. During a bleaching event, the algae are expelled by the coral, which may lead to the coral's starvation and death. Current thinking, explains Nils Rädecker, a former Ph.D. student at KAUST and now at the École Polytechnique Fédérale de Lausanne (EPFL), "was that this starvation was the result of the corals losing the algae as their main source of energy." However, a few signals suggested that it is not as simple as that.

To investigate, the research team transported five colonies of a cauliflower coral (Stylophora pistillata) from Abu Shosha reef in the Red Sea to KAUST's aquarium tanks, which were set up to closely mimic reef conditions. Once acclimatized, the corals were subjected to heat stress conditions that matched local maximum summer temperatures in 2017.

The research team showed that the stable coral-algal symbiosis relies on the algae remaining nitrogen-limited as it "ensures the algae transfer photosynthetic carbon as sugars to the coral host instead of investing it in their own growth," explains Rädecker. "However, during heat stress the corals consume their own energy reserves (amino acids) and release waste ammonium that, in turn, stimulates algal symbiont growth."

This sets up a new cycle. "This metabolic imbalance destabilizes the symbiotic nutrient cycling: as the algal symbionts grow, they translocate less carbon to their coral host," says Rädecker. "Then, because the coral host receives less carbon from its algae, it releases ammonium, thereby stimulating algal growth." The expulsion of the algae during bleaching is not the cause of coral stress, says Nils, but rather "bleaching is a symptom of a disturbed symbiosis, in which the algae no longer provide food to their coral host," he says.

Current management strategies focus on quantifying the severity of bleaching, but these new results suggest an alternative focus. "Regular monitoring of the nutritional status of corals could help to detect long-term trends in the response of corals to changing environmental conditions and to anticipate problems before reefs are bleaching," explains Rädecker.

These findings also emphasize broad benefits "from identifying reefs that are vulnerable to bleaching and implementing appropriate countermeasures, rather than having to 'rescue' them once bleached," says Christian Voolstra, formerly of KAUST and now at the University of Konstanz in Germany. "Our study shows that controlling the water quality, such as nitrate levels, in the environment could help repress destabilizing the metabolic feedback loop when reef water temperatures go up."

OSAKA, Japan. Look at any piece of machinery and you will see a complex network of moving parts, or actuators, each with its own function, all working together for a common goal. From this perspective, the way most machines differ is in the way their actuators are powered: excavators rely on compressed liquid (hydraulic), the brake system in a car uses compressed air (pneumatic), and a printer has electricity.

What if the moving parts of a machine could be powered by light? A machine made up of photoactuators would not need direct contact with the power source to move. Among its many possible functions, it could be accurately manipulated within places machines with electrical wiring or circuitry cannot - for example, the capillaries of the human body.

"The problem has been manipulating a material with light at the speed and size appropriate for photomechanical devices", says graduate student Masato Tamaoki. He was part of a research group, led by Professor Seiya Kobatake of the Graduate School of Engineering, Osaka City University that, using UV light on crystals made of a compound called diarylethene, peeled off crystals the size of 2 - 4 micrometers at the speed of 260 microseconds, making it the world's fastest exfoliation of a photomechanical material. Their results were published online in Crystal Growth & Design of the American Chemical Society on April 19, 2021.

"My lab has been exploring the photomechanical properties of diarylethene for many years now", says Professor Kobatake. They found that under UV light, the molecules of the compound demonstrated behaviors such as expansion/contraction, bending, twisting and peeling. "There were only two examples of the peeling behavior, making it a very rare motion," states Mr. Tamaoki, "we focused on this issue by experimenting with crystal size and photoirradiation conditions".

They found that under the strain of UV light penetrating relatively all the diarylethene, it would change to a blue color and crack. However, if the light was focused on a vicinity of the crystal, peeling of the exposed section occurred at a surprising 260 microseconds. Comparing this to previously recorded measurements of 10s of seconds to 10s of minutes, "we are very pleased to have discovered the world's fastest, photoreversible exfoliation behavior, which is expected to become a new manufacturing method for photoactuator materials," states Mr. Tamaoki.

MIAMI--The Galápagos Islands have played a historic role since Charles Darwin's visit onboard the HMS Beagle in 1835. Today, a team of scientists, including from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, studied a large eruption in the archipelago to get new insights into how volcanoes behave and could help forecast future events.

The study gives the first detailed description of a volcanic eruption from Sierra Negra found on Isla Isabela - the largest of the Galápagos Islands and home to nearly 2,000 people.

The findings, published in Nature Communications, reveal how the volcano inflated and fractured before it erupted and captures a new level of detail for any eruption from a volcano on the islands.

Networks of ground-based seismic and GPS monitoring stations, and satellites, captured data for 13 years before Sierra Negra's eruption, in June 2018.

The surface of the volcano rose during this time, indicating a gradual accumulation of molten rock - known as magma - found in a reservoir under the volcano. The signals were among the largest ever recorded at a volcano of this type, experts say.

The Galápagos Islands' remote location, in the Pacific Ocean, about 1000 kilometers off the Ecuadorian coast, means there were big gaps in scientists' understanding of the volcanic processes that formed them and control their activity.

This eruption provided a rare opportunity to fill some of the gaps, researchers say. An international team integrated geophysical data with analysis of the chemical composition of the erupted lava. They were supported in doing so by the Parque Nacional Galápagos.

"The run-up to the eruption was very exciting," said Falk Amelung, a professor of marine geosciences at the UM Rosenstiel School and a coauthor of the study. "Half-a-year earlier we saw from our satellite data that the caldera floor was uplifting at a rate of 10 centimeters a month. Such high inflation rates are rarely seen at active volcanoes."

Sierra Negra's eruption continued for nearly two months, spurting out lava flows which extended 10 miles to the island's coast. Fresh earthquakes accompanied the eruption and emptying of the magma reservoir.

After the eruption, the hills within a six-mile wide hollow at the summit of the volcano - known as a caldera - were nearly two meters higher. This phenomenon, known as caldera resurgence, is important for understanding when and where eruptions happen, scientists say. However, it is rare and has never been observed to this extent before.

The team also discovered that the ascending magma permanently uplifted what they call a 'trapdoor' in the floor of the caldera. This raised its surface and, in a complex interplay, triggered large earthquakes that led to the eruption.

The 2018 eruption was a stark reminder of the potential threat to life, livelihoods, and the iconic wildlife of the Galápagos - including the slow-moving giant tortoise and land iguana - the researchers said.

This new understanding of volcano behavior will allow local scientists to track the evolution of volcanic unrest before future eruptions and communicate warnings to local authorities and the public.

"The 2018 eruption of Sierra Negra was a really spectacular volcanic event, occurring in the 'living laboratory' of the Galápagos Islands," said Andrew Bell from the University of Edinburgh's School of GeoSciences who led the research.

"Great teamwork, and a bit of luck, allowed us to capture this unique dataset that provide us with important new understanding as to how these volcanoes behave, and how we might be able to better forecast future eruptions."

The Galápagos' Isla Isabela is also the destination of the UM Rosenstiel School's UGalapagos Study Abroad program, which Sierra Negra volcano being one of several geological field trips where students got an opportunity to see first-hand a volcano showing signs of significant unrest.

MIAMI--A new study led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science provides evidence that humans are influencing wind and weather patterns across the eastern United States and western Europe by releasing CO2 and other pollutants into Earth's atmosphere.

In the new paper, published in the journal npj Climate and Atmospheric Science, the research team found that changes in the last 50 years to an important weather phenomenon in the North Atlantic--known as the North Atlantic Oscillation--can be traced back to human activities that impact the climate system.

"Scientists have long understood that human actions are warming the planet," said the study's lead author Jeremy Klavans, a UM Rosenstiel School alumnus. "However, this human-induced signal on weather patterns is much harder to identify."

"In this study, we show that humans are influencing patterns of weather and climate over the Atlantic and that we may be able to use this information predict changes in weather and climate up to a decade in advance," said Klavans.

The North Atlantic Oscillation, the result of fluctuations in air pressure across the Atlantic, affects weather by influencing the intensity and location of the jet stream. This oscillation has a strong effect on winter weather in Europe, Greenland, the northeastern U.S. and North Africa and the quality of crop yields and productivity of fisheries in the North Atlantic.

The researchers used multiple large climate model ensembles, compiled by researchers at the National Center for Atmospheric Research, to predict the North Atlantic Oscillation. The analysis consisted of 269 model runs, which is over 14,000 simulated model years.

The study, titled "NAO Predictability from External Forcing in the Late Twentieth Century," was published on March 25 in the journal npj Climate and Atmospheric Science. The study's authors include: Klavans, Amy Clement and Lisa Murphy from the UM Rosenstiel School, and Mark Cane from Columbia University's Lamont-Doherty Earth Observatory.

The study was supported by the National Science Foundation (NSF) Climate and Large-Scale Dynamics program (grant # AGS 1735245 and AGS 1650209), NSF Paleo Perspectives on Climate Change program (grant # AGS 1703076) and NOAA's Climate Variability and Predictability Program.

Researchers within the Biomedicine Discovery Institute at Monash University have made a breakthrough in understanding the role played by high-risk immune genes associated with the development of rheumatoid arthritis (RA).

The findings, published in Science Immunology, were the result of a seven-year collaboration led by Monash University, involving Janssen Biotech, Inc., Janssen Cilag Pty Ltd., Janssen Research & Development, LLC and the Karolinska Institute, Sweden.

Certain immune system genes, called Human Leukocyte antigen (HLA)-DR4, cause an increased susceptibility to RA. In this study, using mice genetically modified to express the human HLA-DR4 molecule, the team examined, at the molecular and cellular levels, how T cells recognise these HLA-DR4 molecules. The team also showed that highly similar T cell receptors, likely with similar recognition characteristics, are also present in “RA-susceptible” humans expressing these HLA molecules.

“This suggests that there may be an immune signature of RA development, providing a potential avenue for diagnostic development or a window of opportunity for therapeutic development,” says Dr Hugh Reid, who co-led the study with Professor Jamie Rossjohn and Professor Nicole La Gruta at Monash University.

With the assistance of the Australian Synchrotron, the researchers were able to determine the structure of the molecular complexes that form during the interaction between T cell receptors and altered joint proteins bound to HLA-DR4. Armed with this information, they were able to work out what was important in this deleterious T cell response.

“This research is an excellent example of how collaborative efforts between major academic and industrial partners can lead to breakthroughs in basic science that in turn provide avenues for the development of better therapeutics for common diseases,” says Dr Reid.

Rheumatoid arthritis is an autoimmune disease affecting about one per cent of the world's population. It is characterised by swollen, painful, stiff joints, and consequently, restricted mobility in sufferers. By working out how T cells recognise altered joint proteins in complex with ‘susceptibility’ HLA molecules, Monash scientists have advanced our understanding of how these HLA molecules may predispose individuals to the development of disease. The insight provided may greatly assist in achieving the long-term goal of producing personalised medicines and/or preclinical interventions to treat RA.

One of the most comprehensive statistical analyses of drivers of food insecurity across 65 countries has concluded that household income consistently explains more discrepancy in food security than any other factor, including agricultural land resources and production. The Thayer School of Engineering at Dartmouth study, "Cross-national analysis of food security drivers: comparing results based on the Food Insecurity Experience Scale and Global Food Security Index," was recently published by the peer-reviewed journal Food Security.

Given the persistent issue of food insecurity--one of the United Nation's sustainable development goals is to achieve zero hunger--the study's results are vital in determining how best to tackle the complex problem.

"We're trying to inform international development efforts. There's a long history of rich countries launching initiatives to help the developing world which aren't very effective," said co-author Lee Lynd, the Paul E. and Joan H. Queneau Distinguished Professor of Engineering at Dartmouth. "If the real reason people are food insecure is that they're poor, the best thing you may be able to do for them is to give them a job."

"When we took a data-driven look at this, we found that the amount of money that households were actually spending on goods and services was by far the most important determinant of food security amongst the countries that we studied," said first author Andrew Allee, Dartmouth Engineering PhD candidate.

At the cross-national level, the study concludes quantity and quality of a nation's agricultural land were not predictive of national food security, and instead, the most effective strategies to improve food security will include measures to increase citizens' capacity for consumption. The researchers are quick to point out that no single metric can capture all dimensions of food security, but the models consistently showed that household spending, measured as per-capita household final consumption expenditure, was the single best predictor of food security, meaning an increase in income usually drives an increase in food security.

Allee and Lynd worked with Vikrant Vaze, the Stata Family Career Development Associate Professor of Engineering at Dartmouth, on linear regression models which used country characteristics to predict food security from the Food Insecurity Experience Scale and the Global Food Security Index, two well-known indicators of food insecurity. The 65 countries studied represent 56 percent of the global population.

Faced with the tragic loss of the Arecibo observatory in Puerto Rico and the often prohibitive cost of satellite missions, astronomers are searching for savvy alternatives to continue answering fundamental questions in physics.

At a press conference during the 2021 APS April Meeting, they will reveal new tactics across both hemispheres for illuminating gravitational waves and dark matter.

Shining the oldest light in the universe on dark matter

At the South Pole, a powerful set of telescopes could add a new function: studying the nature of dark matter and the history of stars.

Only satellites can carry out surveys of the full sky, while Earth-based telescopes are able to spend years accumulating a lot of data on small patches. The BICEP/Keck array was designed as the world's most sensitive detector of the polarization of medium-to-large sky features. From Antarctica, the array searches small areas of the Big Bang's afterglow for primordial gravitational waves.

Cyndia Yu, a graduate student at Stanford University, and the BICEP/Keck team are exploring the possibility that the very same telescopes could increase the length of their scans--and thus capture much larger areas.

"We are appreciating more and more the promise of moving away from detecting extremely faint signals on a small area, to looking for features on a larger sky patch," said Yu.

The unconventional approach has yielded promising early results. Yu will share the initial performance of trial scans and forecast how sensitive the telescopes will be to targets including axion-like dark matter candidates and WIMP annihilations.

"Satellite missions are very rare and expensive, so any chance we get to make more measurements from ground-based programs is very exciting," she said.

Catching the wake of supermassive black holes

In the northern hemisphere, galaxy-sized detectors are hunting for gravitational waves of very low frequency from the largest black holes in the universe.

"In some ways, these arrays are like the LIGO detector," said Megan DeCesar, Senior Research Scientist at George Mason University, referring to the observatory that first detected gravitational waves from other types of smaller black holes.

"While LIGO uses lasers on Earth, pulsar timing arrays use steady pulses of radio waves from small, dense, rapidly rotating stars called pulsars that are located thousands of light years from Earth," she said.

DeCesar and the North American Nanohertz Observatory for Gravitational Waves collaboration analyzed more than a dozen years of pulsar data.

They recently reported a signal that may be the first hint of a gravitational wave background, and which was stronger than expected based on previous data. If confirmed to be a gravitational wave signal, it would mean the discovery of gravitational waves produced from many double-black-hole systems, each of which will eventually merge to form even larger single black holes.

Arecibo played a crucial role in NANOGrav observations. Its collapse in December dealt a blow to the collaboration, but thanks to increased observations at Green Bank and other facilities, NANOGrav is still on track to detect gravitational waves with several more years of data. DeCesar will discuss how current telescopes in West Virginia, New Mexico, and British Columbia, and future sensitive radio arrays, will allow NANOGrav to meet its gravitational-wave science goals.

FEATURED TALKS

CMB E-mode Science With the BICEP/Keck Program (S09.8)
2:54 p.m. - 3:06 p.m. CDT, Monday, April 19, 2021
Cyndia Yu, cyndiayu@stanford.edu
Livestream: Access here
Abstract: http://meetings.aps.org/Meeting/APR21/Session/S09.8

The Search for Gravitational Waves With the NANOGrav Pulsar Timing Array (B01.1)
10:45 a.m. - 11:21 a.m. CDT, Saturday, April 17, 2021
Megan DeCesar, megan.decesar@nanograv.org
Livestream: Access here
Abstract: http://meetings.aps.org/Meeting/APR21/Session/B01.1

PRESS CONFERENCE

Register for the press conference, to be held on Zoom at 12:00 p.m. CDT, Saturday, April 17, 2021.

Speakers:

Cyndia Yu (Stanford)

Megan DeCesar (George Mason)

AMES, Iowa - A lot is riding on the continued advancement of plant sciences.

Take the food supply, for starters. Climate change and population growth will continue to pose challenges in the future, and crop production will require innovation and progress by plant scientists in order to keep pace. It isn't an overstatement to say that populations around the world will go hungry if plant science stagnates, said Gustavo MacIntosh, a professor in the Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology at Iowa State University.

"At the end of the day, either you eat plants or you eat food that ate plants," MacIntosh said. "Plants are the basis for the food we have."

MacIntosh predicts plant science will play an increasingly important role in society, but he said many people lack an understanding of plants, both their biology and their critical place in the functioning of human society. He worries that plant scientists aren't doing enough to raise awareness of the discipline among the general population, which could slow the rate of progress in the future.

So MacIntosh worked with around 30 other scientists over the course of more than two years to put together a comprehensive guide to help plant scientists communicate their work to the world. This guide takes the form of a 28-page white paper published this week in the academic journal Plant Direct. The guide identifies challenges to communicating the importance of plant science to a wide audience and provides some strategies to help plant scientists get the word out. The document stresses the importance of diversity throughout the text, offering scientists and educators a roadmap for introducing plant sciences to a wide variety of audiences.

"We want people to be convinced that we need more outreach efforts, and we want this guide to make sure those outreach efforts are effective," MacIntosh said.

The guide grew out of a National Science Foundation-funded symposium and workshop held in Davis, California, in November of 2018. Plant scientists collaborated over the course of the three-day event to create a new vision for scientific outreach in their discipline. They formed teams and made a plan to put together a document that could act as a roadmap for the future. The document produced by the effort covers case studies and a number of strategies to communicate important plant science topics to the world at large. The document includes ideas for classroom activities as well as tips for how to plan museum exhibits and booths at farmers markets and similar events.

It also stresses the importance of humanizing plant science to make it accessible to a wide range of audiences. MacIntosh said scientists and nonscientists seem to be growing farther apart for various reasons, but he said everyone benefits when more diverse voices enter the conversation.

To that end, MacIntosh led efforts to make diversity and inclusion central tenets of the new outreach guide. He said the plant sciences will benefit by removing historical barriers related to ethnicity and gender. The white paper also calls for more involvement from undergraduates and early career scientists as well as a more dynamic mix of private and public sector collaboration.

"Good outreach is diverse outreach, in every sense," he said.

The lack of basic plant science literacy could make a huge difference in the future, MacIntosh said. He pointed to studies showing that the number of students earning doctorates in plant-related disciplines is not growing fast enough to keep up with job trends in agriculture and plant-related industries in recent decades.

MacIntosh's own research focuses on the study of plant cellular functions as well as how soybeans resist insect pests. He said his involvement with the outreach guide dovetails with his soybean research, which also requires extension and outreach efforts to get scientific advancements into the hands of farmers. He said the land-grant model at the heart of Iowa State's mission, which stresses the importance of teaching and outreach alongside research, springs from the same motivations that produced the new white paper.

LOS ALAMOS, N.M., April 16, 2021 -- Large-scale supercomputer simulations at the atomic level show that the dominant G form variant of the COVID-19-causing virus is more infectious partly because of its greater ability to readily bind to its target host receptor in the body, compared to other variants. These research results from a Los Alamos National Laboratory-led team illuminate the mechanism of both infection by the G form and antibody resistance against it, which could help in future vaccine development.

"We found that the interactions among the basic building blocks of the Spike protein become more symmetrical in the G form, and that gives it more opportunities to bind to the receptors in the host -- in us," said Gnana Gnanakaran, corresponding author of the paper published today in Science Advances. "But at the same time, that means antibodies can more easily neutralize it. In essence, the variant puts its head up to bind to the receptor, which gives antibodies the chance to attack it."

Researchers knew that the variant, also known as D614G, was more infectious and could be neutralized by antibodies, but they didn't know how. Simulating more than a million individual atoms and requiring about 24 million CPU hours of supercomputer time, the new work provides molecular-level detail about the behavior of this variant's Spike.

Current vaccines for SARS-CoV-2, the virus that causes COVID-19, are based on the original D614 form of the virus. This new understanding of the G variant -- the most extensive supercomputer simulations of the G form at the atomic level -- could mean it offers a backbone for future vaccines.

The team discovered the D614G variant in early 2020, as the COVID-19 pandemic caused by the SARS-CoV-2 virus was ramping up. These findings were published in Cell. Scientists had observed a mutation in the Spike protein. (In all variants, it is the Spike protein that gives the virus its characteristic corona.) This D614G mutation, named for the amino acid at position 614 on the SARS-CoV-2 genome that underwent a substitution from aspartic acid, prevailed globally within a matter of weeks.

The Spike proteins bind to a specific receptor found in many of our cells through the Spike's receptor binding domain, ultimately leading to infection. That binding requires the receptor binding domain to transition structurally from a closed conformation, which cannot bind, to an open conformation, which can.

The simulations in this new research demonstrate that interactions among the building blocks of the Spike are more symmetrical in the new G-form variant than those in the original D-form strain. That symmetry leads to more viral Spikes in the open conformation, so it can more readily infect a person.

A team of postdoctoral fellows from Los Alamos -- Rachael A. Mansbach (now assistant professor of Physics at Concordia University), Srirupa Chakraborty, and Kien Nguyen -- led the study by running multiple microsecond-scale simulations of the two variants in both conformations of the receptor binding domain to illuminate how the Spike protein interacts with both the host receptor and with the neutralizing antibodies that can help protect the host from infection. The members of the research team also included Bette Korber of Los Alamos National Laboratory, and David C. Montefiori, of Duke Human Vaccine Institute.

Encoding information into light, and transmitting it through optical fibers lies at the core of optical communications. With an incredibly low loss of 0.2 dB/km, optical fibers made from silica have laid the foundations of today's global telecommunication networks and our information society.

Such ultralow optical loss is equally essential for integrated photonics, which enable the synthesis, processing and detection of optical signals using on-chip waveguides. Today, a number of innovative technologies are based on integrated photonics, including semiconductor lasers, modulators, and photodetectors, and are used extensively in data centers, communications, sensing and computing.

Integrated photonic chips are usually made from silicon that is abundant and has good optical properties. But silicon can't do everything we need in integrated photonics, so new material platforms have emerged. One of these is silicon nitride (Si3N4), whose exceptionally low optical loss (orders of magnitude lower than that of silicon), has made it the material of choice for applications for which low loss is critical, such as narrow-linewidth lasers, photonic delay lines, and nonlinear photonics.

Now, scientists in the group of Professor Tobias J. Kippenberg at EPFL's School of Basic Sciences have developed a new technology for building silicon nitride integrated photonic circuits with record low optical losses and small footprints. The work is published in Nature Communications.

Combining nanofabrication and material science, the technology is based on the photonic Damascene process developed at EPFL. Using this process, the team made integrated circuits of optical losses of only 1 dB/m, a record value for any nonlinear integrated photonic material. Such low loss significantly reduces the power budget for building chip-scale optical frequency combs ("microcombs"), used in applications like coherent optical transceivers, low-noise microwave synthesizers, LiDAR, neuromorphic computing, and even optical atomic clocks. The team used the new technology to develop meter-long waveguides on 5x5 mm2 chips and high-quality-factor microresonators. They also report high fabrication yield, which is essential for scaling up to industrial production.

"These chip devices have already been used for parametric optical amplifiers, narrow-linewidth lasers and chip-scale frequency combs", says Dr. Junqiu Liu who led the fabrication at EPFL's Center of MicroNanoTechnology (CMi). "We are also looking forward to seeing our technology being used for emerging applications such as coherent LiDAR, photonic neural networks, and quantum computing."

Researchers at Aalto University have developed a new device for spintronics. The results have been published in the journal Nature Communications, and mark a step towards the goal of using spintronics to make computer chips and devices for data processing and communication technology that are small and powerful.

Traditional electronics uses electrical charge to carry out computations that power most of our day-to-day technology. However, engineers are unable to make electronics do calculations faster, as moving charge creates heat, and we're at the limits of how small and fast chips can get before overheating. Because electronics can't be made smaller, there are concerns that computers won't be able to get more powerful and cheaper at the same rate they have been for the past 7 decades. This is where spintronics comes in.

"Spin" is a property of particles like electrons in the same way that "charge" is. Researchers are excited about using spin to carry out computations because it avoids the heating issues of current computer chips. 'If you use spin waves, it's transfer of spin, you don't move charge, so you don't create heating,' says Professor Sebastiaan van Dijken, who leads the group that wrote the paper.

Nanoscale magnetic materials

The device the team made is a Fabry-Pérot resonator, a well known tool in optics for creating beams of light with a tightly controlled wavelength. The spin-wave version made by the researchers in this work allows them to control and filter waves of spin in devices that are only a few hundreds of nanometres across.

The devices were made by sandwiching very thin layers of materials with exotic magnetic properties on top of eachother. This created a device where the spin waves in the material would be trapped and cancelled out if they weren't of the desired frequency. 'The concept is new, but easy to implement,' explains Dr Huajun Qin, the first author of the paper, 'the trick is to make good quality materials, which we have here at Aalto. The fact that it is not challenging to make these devices means we have lots of opportunities for new exciting work.'

Wireless data processing and analogue computing

The issues with speeding up electronics goes beyond overheating, they also cause complications in wireless transmission, as wireless signals need to be converted from their higher frequencies down to frequencies that electronic circuits can manage. This conversion slows the process down, and requires energy. Spin wave chips are able to operate at the microwave frequencies used in mobile phone and wifi signals, which means that there is a lot of potential for them to be used in even faster and more reliable wireless communication technologies in the future.

Furthermore, spin waves can be used to do computing in ways that are faster that electronic computing at specific tasks 'Electronic computing uses "Boolean" or Binary logic to do calculations,' explains Professor van Dijken, 'with spin waves, the information is carried in the amplitude of the wave, which allows for more analogue style computing. This means that it could be very useful for specific tasks like image processing, or pattern recognition. The great thing about our system is that the size structure of it means that it should be easy to integrate into existing technology'

Now that the team has the resonator to filter and control the spin waves, the next steps are to make a complete circuit for them. "To build a magnetic circuit, we need to be able to guide the spin waves towards functional components, like the way conducting electrical channels do on electronic microchips. We are looking at making similar structures to steer spin waves" explains Dr Qin.