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The accumulation of microplastics in the environment, and within our bodies, is an increasingly worrisome issue. But predicting where these ubiquitous particles will accumulate, and therefore where remediation efforts should be focused, has been difficult because of the many factors that contribute to their dispersal and deposition.

New research from MIT shows that one key factor in determining where microparticles are likely to build up has to do with the presence of biofilms. These thin, sticky biopolymer layers are shed by microorganisms and can accumulate on surfaces, including along sandy riverbeds or seashores. The study found that, all other conditions being equal, microparticles are less likely to accumulate in sediment infused with biofilms, because if they land there, they are more likely to be resuspended by flowing water and carried away.

The open-access findings appear in the journalGeophysical Research Letters, in a paper by MIT postdoc Hyoungchul Park and professor of civil and environmental engineering Heidi Nepf. "Microplastics are definitely in the news a lot," Nepf says, "and we don't fully understand where the hotspots of accumulation are likely to be. This work gives a little bit of guidance" on some of the factors that can cause these particles, and small particles in general, to accumulate in certain locations.

Most experiments looking at the ways microparticles are transported and deposited have been conducted over bare sand, Park says. "But in nature, there are a lot of microorganisms, such as bacteria, fungi, and algae, and when they adhere to the stream bed they generate some sticky things." These substances are known as extracellular polymeric substances, or EPS, and they "can significantly affect the channel bed characteristics," he says. The new research focused on determining exactly how these substances affected the transport of microparticles, including microplastics.

The research involved a flow tank with a bottom lined with fine sand, and sometimes with vertical plastic tubes simulating the presence of mangrove roots. In some experiments the bed consisted of pure sand, and in others the sand was mixed with a biological material to simulate the natural biofilms found in many riverbed and seashore environments.

Water mixed with tiny plastic particles was pumped through the tank for three hours, and then the bed surface was photographed under ultraviolet light that caused the plastic particles to fluoresce, allowing a quantitative measurement of their concentration.

The results revealed two different phenomena that affected how much of the plastic accumulated on the different surfaces. Immediately around the rods that stood in for above-ground roots, turbulence prevented particle deposition. In addition, as the amount of simulated biofilms in the sediment bed increased, the accumulation of particles also decreased.

Nepf and Park concluded that the biofilms filled up the spaces between the sand grains, leaving less room for the microparticles to fit in. The particles were more exposed because they penetrated less deeply in between the sand grains, and as a result they were much more easily resuspended and carried away by the flowing water.

"These biological films fill the pore spaces between the sediment grains," Park explains, "and that makes the deposited particles — the particles that land on the bed — more exposed to the forces generated by the flow, which makes it easier for them to be resuspended. What we found was that in a channel with the same flow conditions and the same vegetation and the same sand bed, if one is without EPS and one is with EPS, then the one without EPS has a much higher deposition rate than the one with EPS."

Nepf adds: "The biofilm is blocking the plastics from accumulating in the bed because they can't go deep into the bed. They just stay right on the surface, and then they get picked up and moved elsewhere. So, if I spilled a large amount of microplastic in two rivers, and one had a sandy or gravel bottom, and one was muddier with more biofilm, I would expect more of the microplastics to be retained in the sandy or gravelly river."

All of this is complicated by other factors, such as the turbulence of the water or the roughness of the bottom surface, she says. But it provides a "nice lens" to provide some suggestions for people who are trying to study the impacts of microplastics in the field. "They're trying to determine what kinds of habitats these plastics are in, and this gives a framework for how you might categorize those habitats," she says. "It gives guidance to where you should go to find more plastics versus less."

As an example, Park suggests, in mangrove ecosystems, microplastics may preferentially accumulate in the outer edges, which tend to be sandy, while the interior zones have sediment with more biofilm. Thus, this work suggests "the sandy outer regions may be potential hotspots for microplastic accumulation," he says, and can make this a priority zone for monitoring and protection.

The work was supported by Shell International Exploration and Production through the MIT Energy Initiative.

Materialsprovided byMassachusetts Institute of Technology. Original written by David L. Chandler.Note: Content may be edited for style and length.

Using advanced single-nuclei RNA sequencing (snRNA-seq) and a widely used preclinical model for Alzheimer's disease, researchers from Mass General Brigham and collaborators at SUNY Upstate Medical University have identified specific brain cell types that responded most to exercise. These findings, which were validated in samples from people, shed light on the connection between exercise and brain health and point to future drug targets. Results are published inNature Neuroscience.

"While we've long known that exercise helps protect the brain, we didn't fully understand which cells were responsible or how it worked at a molecular level," said senior author Christiane D. Wrann, DVM, PhD, a neuroscientist and leader of the Program in Neuroprotection in Exercise at the Mass General Brigham Heart and Vascular Institute and the McCance Center for Brain Health at Massachusetts General Hospital. "Now, we have a detailed map of how exercise impacts each major cell type in the memory center of the brain in Alzheimer's disease."

The study focused on a part of the hippocampus — a critical region for memory and learning that is damaged early in Alzheimer's disease. The research team leveraged single-nuclei RNA sequencing, a relatively new technologies that allow researchers to look at activity at the molecular level in single cells for an in-depth understanding of diseases like Alzheimer's.

The researchers exercised a common mouse model for Alzheimer's disease using running wheels, which improved their memory compared to the sedentary counterparts. They then analyzed gene activity across thousands of individual brain cells, finding that exercise changed activity both in microglia, a disease-associated population of brain cells, and in a specific type of neurovascular-associated astrocyte (NVA), newly discovered by the team, which are cells associated with blood vessels in the brain. Furthermore, the scientist identified the metabolic gene Atpif1 as an important regulator to create new neurons in the brain. "That we were able to modulate newborn neurons using our new target genes set underscores the promise our study," said lead author Joana Da Rocha, PhD, a postdoctoral fellow working in Dr. Wrann's lab.

To ensure the findings were relevant to humans, the team validated their discoveries in a large dataset of human Alzheimer's brain tissue, finding striking similarities.

"This work not only sheds light on how exercise benefits the brain but also uncovers potential cell-specific targets for future Alzheimer's therapies," said Nathan Tucker, a biostatistician at SUNY Upstate Medical University and co-senior of the study. "Our study offers a valuable resource for the scientific community investigating Alzheimer's prevention and treatment."

Authorship: In addition to da Rocha and Wrann, Mass General Brigham authors include Renhao Luo, Pius Schlachter, Luis Moreira, Mohamed Ariff Iqbal, Paula Kuhn, Sophia Valaris, Mohammad R. Islam, Gabriele M. Gassner, Sofia Mazuera, Kaela Healy, Sanjana Shastri, Nathaniel B. Hibbert, Kristen V. Moran-Figueroa, Erin B. Haley, Sema Aygar, and Ksenia V. Kastanenka. Additional authors include Michelle L. Lance, Robert S. Gardner, Ryan D. Pfeiffer, Logan Brase, Oscar Harari, Bruno A. Benitez, and Nathan R. Tucker.

Disclosures: Wrann is an academic co-founder and consultant for Aevum Therapeutics. Wrann has a financial interest in Aevum Therapeutics, a company developing drugs that harness the protective molecular mechanisms of exercise to treat neurodegenerative and neuromuscular disorders. Wrann's interests were reviewed and are managed by Massachusetts General Hospital and Mass General Brigham in accordance with their conflict of interest policies.

Funding: This study was funded in part by the National Institutes of Health (NS117694, AG062904, AG064580, AG072054, HL140187, AG066171, AG057777, AG072464, NS118146, NS127211), Cure Alzheimer's Fund, Alzheimer Association Research Grant, SPARC Award from the McCance Center for Brain Health, Hassenfeld Clinical Scholar Award, Claflin Distinguished Scholar Award, BIDMC 2023 Translational Research Hub Spark Grant Award, Massachusetts General Hospital Fund for Medical Discovery (2024A022508), ADDF-Harrington

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Genetic material shed by tumors can be detected in the bloodstream three years prior to cancer diagnosis, according to a study led by investigators at the Ludwig Center at Johns Hopkins, Johns Hopkins Kimmel Cancer Center, the Johns Hopkins University School of Medicine and the Johns Hopkins Bloomberg School of Public Health.

The study, partly funded by the National Institutes of Health, was published May 22 inCancer Discovery.

Investigators were surprised they could detect cancer-derived mutations in the blood so much earlier, says lead study author Yuxuan Wang, M.D., Ph.D., an assistant professor of oncology at the Johns Hopkins University School of Medicine. "Three years earlier provides time for intervention. The tumors are likely to be much less advanced and more likely to be curable."

To determine how early cancers could be detected prior to clinical signs or symptoms, Wang and colleagues assessed plasma samples that were collected for the Atherosclerosis Risk in Communities (ARIC) study, a large National Institutes of Health-funded study to investigate risk factors for heart attack, stroke, heart failure and other cardiovascular diseases. They used highly accurate and sensitive sequencing techniques to analyze blood samples from 26 participants in the ARIC study who were diagnosed with cancer within six months after sample collection, and 26 from similar participants who were not diagnosed with cancer.

At the time of blood sample collection, eight of these 52 participants scored positively on a multicancer early detection (MCED) laboratory test. All eight were diagnosed within four months following blood collection. For six of the eight individuals, investigators also were able to assess additional blood samples collected 3.1-3.5 years prior to diagnosis, and in four of these cases, tumor-derived mutations could also be identified in samples taken at the earlier timepoint.

"This study shows the promise of MCED tests in detecting cancers very early, and sets the benchmark sensitivities required for their success," says Bert Vogelstein, M.D., Clayton Professor of Oncology, co-director of the Ludwig Center at Johns Hopkins and a senior author on the study.

"Detecting cancers years before their clinical diagnosis could help provide management with a more favorable outcome," adds Nickolas Papadopoulos, Ph.D., professor of oncology, Ludwig Center investigator and senior author of the study. "Of course, we need to determine the appropriate clinical follow-up after a positive test for such cancers."

The study was supported in part by National Institutes of Health grant #s R21NS113016, RA37CA230400, U01CA230691, P30 CA 06973, DRP 80057309, and U01 CA164975. Additional funding was provided by the Virginia and D.K. Ludwig Fund for Cancer Research, the Commonwealth Fund, the Thomas M Hohman Memorial Cancer Research Fund, The Sol Goldman Sequencing Facility at Johns Hopkins, The Conrad R. Hilton Foundation, the Benjamin Baker Endowment, Swim Across America, Burroughs Wellcome Career Award for Medical Scientists, Conquer Cancer — Fred J. Ansfield, MD, Endowed Young Investigator Award, and The V Foundation for Cancer Research. The Atherosclerosis Risk in Communities study has been funded in whole or in part with federal funds from the National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, under contract numbers 75N92022D00001, 75N92022D00002, 75N92022D00003, 75N92022D00004, and 75N92022D00005.

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A new study to be presented at the SLEEP 2025 annual meeting found that teens who get moderate — but not excessive — catch-up sleep on weekends have fewer symptoms of anxiety.

Results show that teens who got up to two more hours of sleep on weekends than on weekdays exhibited fewer anxiety symptoms compared with those who did not sleep longer on weekends. However, longer durations of catch-up sleep on weekends were associated with slightly more internalizing symptoms.

"The results show that both sleeping less on weekends than weekdays and sleeping substantially more on weekends were associated with higher anxiety symptoms," said lead author Sojeong Kim, a doctoral candidate in the department of clinical psychology and psychology graduate advisor at the University of Oregon in Eugene. "In contrast, moderate catch-up sleep — defined as less than two hours — was associated with lower anxiety symptoms, suggesting that some weekend recovery sleep may be beneficial."

The American Academy of Sleep Medicine recommends that teenagers 13 to 18 years of age should sleep 8 to 10 hours on a regular basis to promote optimal health. However, CDC data show that only 23% of high school students get sufficient sleep on an average school night.

"Many teens try to make up for lost sleep by sleeping in on weekends," Kim said.

Consistently getting sufficient sleep is associated with better health outcomes including improved attention, behavior, learning, memory, emotional regulation, quality of life, and mental and physical health. In contrast, insufficient sleep in teenagers is associated with increased risks of problems such as depression and suicidal thoughts.

The study involved 1,877 adolescents with a mean age of 13.5 years. Sleep duration was estimated using Fitbit devices, while internalizing symptoms were assessed using the Child Behavior Checklist survey. Weekend catch-up sleep was calculated as the difference between weekend and weekday sleep duration.

Kim noted that it is important to identify the right amount of catch-up sleep that is beneficial to teens who restrict their sleep during the week.

"Too little or too much sleep variability from weekday to weekend may contribute to the symptoms someone is trying to combat, like physical or mental fatigue and feelings of anxiety," she said.

The research abstract was published recently in an online supplement of the journal Sleep and will be presented Wednesday, June 11, during SLEEP 2025 in Seattle. SLEEP is the annual meeting of the Associated Professional Sleep Societies, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society.

Abstract Title: The Sweet Spot of Weekend Catch-Up Sleep: A Protective Factor Against Depressive Symptoms?

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The forerunners of dinosaurs and crocodiles in the Triassic period were able to migrate across areas of the ancient world deemed completely inhospitable to life, new research suggests.

In a paper published inNature Ecology and Evolutionon June 11, researchers from the University of Birmingham and University of Bristol have used a new method of geographical analysis to infer how these ancestral reptiles, known as archosauromorphs, dispersed following one of the most impactful climate events the Earth has ever seen, the end-Permian mass extinction.

The first archosauromorphs, some resembling modern reptiles and many times smaller than familiar dinosaurs, were previously believed to only survive in certain parts of the globe due to extreme heat across the tropics, viewed by many paleontologists as a dead zone, in the earliest Triassic.

By developing a new modelling technique based on landscape reconstructions and evolutionary trees, the team of researchers have been able to discover clues about how these reptiles moved around the world during the Triassic period, following the mass extinction where more than half of land-based animals and 81% of marine life died.

The archosauromorphs that survived the extinction event rose to prominence in Earth's ecosystems in the Triassic, leading to the evolution of dinosaurs. The team now suggest that their later success was in part due to their ability to migrate up to 10,000 miles across the tropical dead zone to access new ecosystems.

Dr Joseph Flannery-Sutherland from the University of Birmingham and corresponding author of the study said:

"Amid the worst climatic event in Earth's history, where more species died than at any period since, life still survived. We know that archosauromorphs as a group managed to come out of this event and over the Triassic period became one of the main players in shaping life thereafter.

"Gaps in their fossil record have increasingly begun to tell us something about what we weren't seeing when it comes to these reptiles. Using our modelling system, we have been able to build a picture of what was happening to the archosauromorphs in these gaps and how they dispersed across the ancient world. This is what led us to call our method TARDIS, as we were looking at terrains and routes directed in space-time.

"Our results suggest that these reptiles were much hardier to the extreme climate of the Pangaean tropical dead zone, able to endure these hellish conditions to reach the other side of the world. It's likely that this ability to survive the inhospitable tropics may have conferred an advantage that saw them thrive in the Triassic world."

"The evolution of life has been controlled at times by the environment," says Professor Michael Benton from the University of Bristol, senior author of the study, "but it is difficult to integrate our limited and uncertain knowledge about the ancient landscape with our limited and uncertain knowledge about the ecology of extinct organisms. But by combining the fossils with reconstructed maps of the ancient world, in the context of evolutionary trees, we provide a way of overcoming these challenges."

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Your breath is one of a kind. A study published June 12 in the Cell Press journalCurrent Biologydemonstrated that scientists can identify individuals based solely on their breathing patterns with 96.8% accuracy. These nasal respiratory "fingerprints" also offer insights into physical and mental health.

The research stemmed from the lab's interest in olfaction, or the sense of smell. In mammals, the brain processes odor information during inhalation. This link between the brain and breathing led researchers to wonder: since every brain is unique, wouldn't each person's breathing pattern reflect that?

To test the idea, the team developed a lightweight wearable device that tracks nasal airflow continuously for 24 hours using soft tubes placed under the nostrils. Most breathing tests last just one to 20 minutes, focusing on evaluating lung function or diagnosing disease. But those brief snapshots aren't enough to capture subtle patterns.

"You would think that breathing has been measured and analyzed in every way," says author Noam Sobel of the Weizmann Institute of Science, Israel. "Yet we stumbled upon a completely new way to look at respiration. We consider this as a brain readout."

Sobel's team fitted 100 healthy young adults with the device and asked them to go about their daily lives. Using the collected data, the team identified individuals using only their breathing patterns with high accuracy. This high-level accuracy remained consistent across multiple retests conducted over a two-year period, rivaling the precision of some voice recognition technologies.

"I thought it would be really hard to identify someone because everyone is doing different things, like running, studying, or resting," says author Timna Soroka of the Weizmann Institute of Science. "But it turns out their breathing patterns were remarkably distinct."

Moreover, the study found that these respiratory fingerprints correlated with a person's body mass index, sleep-wake cycle, levels of depression and anxiety, and even behavioral traits. For example, participants who scored relatively higher on anxiety questionnaires had shorter inhales and more variability in the pauses between breaths during sleep. Soroka noted that none of the participants met clinical diagnostic criteria for mental or behavioral conditions. The results suggest that long-term nasal airflow monitoring may serve as a window into physical and emotional well-being.

"We intuitively assume that how depressed or anxious you are changes the way you breathe," says Sobel. "But it might be the other way around. Perhaps the way you breathe makes you anxious or depressed. If that's true, we might be able to change the way you breathe to change those conditions."

The current device still faces real-world challenges. A tube that runs under the nose is often associated with illness and may deter adoption. The device also doesn't account for mouth breathing and can slip out of place when sleeping. The team aims to design a more discreet and comfortable version for everyday use.

Soroka and Sobel are already investigating whether people can mimic healthy breathing patterns to improve their mental and emotional states. "We definitely want to go beyond diagnostics to treatment, and we are cautiously optimistic," says Sobel.

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In a compelling Genomic Press Interview published today in Brain Medicine, Sophia Shi, PhD, unveils her pioneering research that fundamentally changes our understanding of brain aging and opens revolutionary therapeutic pathways for Alzheimer's disease and related neurodegenerative conditions.

Uncovering the Brain's Hidden Shield

Dr. Shi's groundbreaking work focuses on the glycocalyx, a complex "forest" of sugar molecules coating blood-brain barrier endothelial cells. Her research, recently published in Nature, demonstrates that this protective layer deteriorates dramatically with age, leading to blood-brain barrier dysfunction and neuroinflammation, key drivers of cognitive decline and neurodegenerative diseases.

"The glycocalyx acts like a protective shield for the brain's blood vessels," Dr. Shi explains. "When we restored these critical sugar molecules in aged mice, we saw remarkable improvements in both barrier integrity and cognitive function." This discovery represents the first time scientists have successfully reversed age-related blood-brain barrier dysfunction through glycocalyx restoration.

From Puzzles to Proteins: A Scientific Journey

Dr. Shi's path to this breakthrough began with childhood fascinations with puzzles and pattern recognition, skills that would later prove invaluable in decoding the complex language of glycosylation. Working under the mentorship of Nobel laureate Carolyn Bertozzi and renowned neurobiologist Tony Wyss-Coray at Stanford, she bridged two distinct fields, glycobiology and neuroscience, to tackle questions others had overlooked.

Her interdisciplinary approach faced significant challenges. How do you study molecules so structurally complex that they've resisted traditional analysis methods? What techniques can capture the dynamic nature of glycosylation in living brain tissue? Dr. Shi's innovative solutions to these problems exemplify the power of cross-disciplinary thinking in modern biomedical research.

Recognition and Research Excellence

The impact of Dr. Shi's work extends far beyond the laboratory. Her research garnered the prestigious David S. Miller Young Scientist Award at the Cerebral Vascular Biology Conference, recognizing her as one of the field's most promising young investigators. Perhaps more remarkably, she is launching her independent laboratory at Harvard's prestigious Rowland Institute directly from doctoral training — a rare achievement that speaks to the transformative potential of her discoveries.

"Post-translational modifications like glycosylation have been understudied for too long," Dr. Shi notes. "These modifications can completely transform protein function, yet we're only beginning to understand their role in brain health and disease." Her work positions glycoscience at the forefront of neurodegeneration research, challenging long-held assumptions about therapeutic targets.

Therapeutic Implications and Future Directions

The therapeutic implications of Dr. Shi's findings are profound. By identifying specific mucin-type O-glycans as critical for blood-brain barrier integrity, her research provides concrete molecular targets for drug development. This precision approach could lead to treatments that address the root causes of neurodegeneration rather than merely managing symptoms.

Intriguing questions emerge from this work: Can glycocalyx restoration prevent or slow Alzheimer's disease progression in humans? How early in the aging process do these protective molecules begin to deteriorate? What environmental or genetic factors influence glycocalyx health throughout the lifespan? These questions will drive the next phase of Dr. Shi's research program at Harvard.

Building an Inclusive Scientific Future

Beyond her scientific contributions, Dr. Shi is committed to fostering diversity in science. "It's easy to feel isolated or like you don't belong in science, especially without early exposure or role models," she reflects. Her dedication to mentoring and creating inclusive research environments promises to amplify her impact by inspiring the next generation of interdisciplinary scientists.

The interview reveals how personal experiences shape scientific pursuits. Dr. Shi's appreciation for hiking and trail running mirrors her approach to research: seeking new perspectives from challenging vantage points. This blend of rigorous science with human experience characterizes the new generation of biomedical researchers.Implications for Brain Medicine

Dr. Shi's discoveries raise fundamental questions about how we approach brain aging and disease. If glycocalyx deterioration is a common pathway in multiple neurodegenerative conditions, could targeting these molecules provide a unified therapeutic strategy? How might lifestyle factors influence glycocalyx health? These considerations could reshape preventive medicine approaches for brain health.

The transition from viewing the blood-brain barrier as a simple wall to understanding it as a dynamic, sugar-coated interface represents a paradigm shift in neuroscience. This new perspective demands innovative research approaches and may explain why previous therapeutic strategies targeting the barrier have shown limited success.

Dr. Sophia Shi's Genomic Press interview is part of a larger series called Innovators & Ideas that highlights the people behind today's most influential scientific breakthroughs. Each interview in the series offers a blend of cutting-edge research and personal reflections, providing readers with a comprehensive view of the scientists shaping the future. By combining a focus on professional achievements with personal insights, this interview style invites a richer narrative that both engages and educates readers. This format provides an ideal starting point for profiles that explore the scientist's impact on the field, while also touching on broader human themes.

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Despite global reductions in mercury emissions, mercury concentrations in Arctic wildlife continue to rise. A new study published inNature Communicationsby researchers from Aarhus University and the University of Copenhagen reveals that ocean currents may be transporting legacy mercury pollution to the Arctic — posing a long-term threat to ecosystems and human health.

"We've monitored mercury in Arctic animals for over 40 years. Despite declining global emissions since the 1970s, we see no corresponding decrease in Arctic concentrations — on the contrary," says Professor Rune Dietz from Aarhus University.

Mercury released into the atmosphere from sources like coal combustion and gold mining can remain airborne for about a year. However, once it enters the ocean, it can persist for over 300 years. This means that even with current emission reductions, the Arctic may continue to experience elevated mercury levels for centuries.

Mercury's Fingerprint in Arctic Wildlife The researchers analyzed over 700 environmental samples — including tissues from polar bears, seals, fish, and peat — from across Greenland collected over the past 40 years. By examining the composition of six common mercury isotopes, they identified distinct regional differences that align with ocean current patterns.

"These isotope signatures act like fingerprints, revealing the sources and transport pathways of mercury," explains Senior Researcher Jens Søndergaard from Aarhus University.

For example, central West Greenland is influenced by Atlantic inflow via the Irminger Current, while other regions are dominated by Arctic Ocean currents.

Implications for Global Mercury Regulation

Mercury is a potent neurotoxin. In Arctic top predators like polar bears and toothed whales, concentrations are now 20-30 times higher than before industrialization. This poses serious health risks not only to wildlife but also to Indigenous communities that rely on marine mammals for food.

"Mercury affects the immune system, reproduction, and possibly sensory functions in animals, which can impact their survival," says Professor Christian Sonne from Aarhus University.

The findings have significant implications for the UN's Minamata Convention on Mercury, which aims to reduce global mercury pollution. The study offers a potential explanation for why mercury levels in Arctic biota remain high despite falling atmospheric emissions.

"Transport of mercury from major sources like China to Greenland via ocean currents can take up to 150 years," says Rune Dietz. "This helps explain the lack of decline in Arctic mercury levels."

The research team is continuing their work on mercury isotopes across the Arctic through the "GreenPath" project, funded by the Independent Research Fund Denmark. The isotopic analyses also contribute to international projects such as WhaleAdapt and ArcSolutions.

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Astronomers using data from NASA's James Webb Space Telescope have identified dozens of small galaxies that played a starring role in a cosmic makeover that transformed the early universe into the one we know today.

"When it comes to producing ultraviolet light, these small galaxies punch well above their weight," said Isak Wold, an assistant research scientist at Catholic University of America in Washington and NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Our analysis of these tiny but mighty galaxies is 10 times more sensitive than previous studies, and shows they existed in sufficient numbers and packed enough ultraviolet power to drive this cosmic renovation."

Wold discussed his findings Wednesday at the 246th meeting of the American Astronomical Society in Anchorage, Alaska. The study took advantage of existing imaging collected by Webb's NIRCam (Near-Infrared Camera) instrument, as well as new observations made with its NIRSpec (Near-Infrared Spectrograph) instrument.

The tiny galaxies were discovered by Wold and his Goddard colleagues, Sangeeta Malhotra and James Rhoads, by sifting through Webb images captured as part of the UNCOVER (Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization) observing program, led by Rachel Bezanson at the University of Pittsburgh in Pennsylvania.

The project mapped a giant galaxy cluster known as Abell 2744, nicknamed Pandora's cluster, located about 4 billion light-years away in the southern constellation Sculptor. The cluster's mass forms a gravitational lens that magnifies distant sources, adding to Webb's already considerable reach.

For much of its first billion years, the universe was immersed in a fog of neutral hydrogen gas. Today, this gas is ionized — stripped of its electrons. Astronomers, who refer to this transformation as reionization, have long wondered which types of objects were most responsible: big galaxies, small galaxies, or supermassive black holes in active galaxies. As one of its main goals, NASA's Webb was specifically designed to address key questions about this major transition in the history of the universe.

Recent studies have shown that small galaxies undergoing vigorous star formation could have played an outsized role. Such galaxies are rare today, making up only about 1% of those around us. But they were abundant when the universe was about 800 million years old, an epoch astronomers refer to as redshift 7, when reionization was well underway.

The team searched for small galaxies of the right cosmic age that showed signs of extreme star formation, called starbursts, in NIRCam images of the cluster.

"Low-mass galaxies gather less neutral hydrogen gas around them, which makes it easier for ionizing ultraviolet light to escape," Rhoads said. "Likewise, starburst episodes not only produce plentiful ultraviolet light — they also carve channels into a galaxy's interstellar matter that helps this light break out."

The astronomers looked for strong sources of a specific wavelength of light that signifies the presence of high-energy processes: a green line emitted by oxygen atoms that have lost two electrons. Originally emitted as visible light in the early cosmos, the green glow from doubly ionized oxygen was stretched into the infrared as it traversed the expanding universe and eventually reached Webb's instruments.

This technique revealed 83 small starburst galaxies as they appear when the universe was 800 million years old, or about 6% of its current age of 13.8 billion years. The team selected 20 of these for deeper inspection using NIRSpec.

"These galaxies are so small that, to build the equivalent stellar mass of our own Milky Way galaxy, you'd need from 2,000 to 200,000 of them," Malhotra said. "But we are able to detect them because of our novel sample selection technique combined with gravitational lensing."

Similar types of galaxies in the present-day universe, such as green peas, release about 25% of their ionizing ultraviolet light into surrounding space. If the low-mass starburst galaxies explored by Wold and his team release a similar amount, they can account for all of the ultraviolet light needed to convert the universe's neutral hydrogen to its ionized form.

The James Webb Space Telescope is the world's premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

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A rare and bewildering intermediate between crystal and glass can be the most stable arrangement for some combinations of atoms, according to a study from the University of Michigan.

The findings come from the first quantum-mechanical simulations of quasicrystals — a type of solid that scientists once thought couldn't exist. While the atoms in quasicrystals are arranged in a lattice, as in a crystal, the pattern of atoms doesn't repeat like it does in conventional crystals. The new simulation method suggests quasicrystals — like crystals — are fundamentally stable materials, despite their similarity to disordered solids like glass that form as a consequence of rapid heating and cooling.

"We need to know how to arrange atoms into specific structures if we want to design materials with desired properties," said Wenhao Sun, the Dow Early Career Assistant Professor of Materials Science and Engineering, and the corresponding author of the paper published today in Nature Physics. "Quasicrystals have forced us to rethink how and why certain materials can form. Until our study, it was unclear to scientists why they existed."

Quasicrystals seemed to defy physics when they were first described by Israeli scientist Daniel Shechtman in 1984. While experimenting with alloys of aluminum and manganese, Shechtman realized that some of the metals' atoms were arranged in an icosahedral structure resembling many 20-sided dice joined at their faces. This shape gave the material five-fold symmetry — identical from five different vantage points.

Scientists at the time thought that the atoms inside crystals could only be arranged in sequences repeating in each direction, but five-fold symmetry precluded such patterns. Shechtman initially faced intense scrutiny for suggesting the impossible, but other labs later produced their own quasicrystals and found them in billion-year-old meteorites.

Shechtman eventually earned the Nobel Prize in Chemistry in 2011 for his discovery, but scientists still couldn't answer fundamental questions on how quasicrystals formed. The roadblock was that density-functional theory — the quantum-mechanical method for calculating a crystal's stability — relies on patterns that infinitely repeat in a sequence, which quasicrystals lack.

"The first step to understanding a material is knowing what makes it stable, but it has been hard to tell how quasicrystals were stabilized," said Woohyeon Baek, a U-M doctoral student in materials science and engineering and the study's first author.

The atoms in any given material usually arrange into crystals so that the chemical bonds achieve the lowest possible energy. Scientists call such structures enthalpy-stabilized crystals. But other materials form because they have high entropy, meaning there are a lot of different ways for its atoms to be arranged or vibrate.

Glass is one example of an entropy-stabilized solid. It forms when melted silica quickly cools, flash-freezing the atoms into a patternless form. But if the cooling rates slow, or a base is added to heated silica, the atoms can arrange into quartz crystals — the preferred, lowest energy state at room temperature. Quasicrystals are a puzzling intermediate between glass and crystal. They have locally ordered atomic arrangements like crystals, but like glass, they do not form long-range, repeating patterns.

To determine if quasicrystals are enthalpy- or entropy-stabilized, the researcher's method scoops out smaller nanoparticles from a larger simulated block of quasicrystal. The researchers then calculate the total energy in each nanoparticle, which doesn't require an infinite sequence because the particle has defined boundaries.

Since the energy in a nanoparticle is related to its volume and surface area, repeating the calculations for nanoparticles of increasing sizes allows the researchers to extrapolate the total energy inside a larger block of quasicrystal. With this method, the researchers discovered that two well-studied quasicrystals are enthalpy-stabilized. One is an alloy of scandium and zinc, the other of ytterbium and cadmium.

The most accurate estimates of quasicrystal energy require the largest particles possible, but scaling up the nanoparticles is difficult with standard algorithms. For nanoparticles with only hundreds of atoms, doubling the atoms increases the computing time eightfold. But the researchers found a solution for the computing bottleneck, too.

"In conventional algorithms, every computer processor needs to communicate with one another, but our algorithm is up to 100 times faster because only the neighboring processors communicate, and we effectively use GPU acceleration in supercomputers," said study co-author Vikram Gavini, a U-M professor of mechanical engineering and materials science and engineering.

"We can now simulate glass and amorphous materials, interfaces between different crystals, as well as crystal defects that can enable quantum computing bits."

The research is funded by the U.S. Department of Energy and relied on computing resources housed at the University of Texas, Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory.

Materialsprovided byUniversity of Michigan.Note: Content may be edited for style and length.