In a paper just published in the journal Advanced Materials, a team of scientists from Northwestern University and the U.S. Department of Energy’s Brookhaven National Laboratory describe the previously hidden sub-nanoscale origins of both the unusual shrinkage and the exceptional thermoelectric properties in this material, silver gallium telluride (AgGaTe₂). The discovery reveals a quantum mechanical twist on what drives the emergence of these properties — and opens up a completely new direction for searching for new high-performance thermoelectrics.

“Thermoelectric materials will be transformational in green and sustainable energy technologies for heat energy harvesting and cooling — but only if their performance can be improved,” said Hongyao Xie, a postdoctoral researcher at Northwestern and first author on the paper. “We want to find the underlying design principles that will allow us to optimize the performance of these materials,” Xie said.

Thermoelectric devices are currently used in limited, niche applications, including NASA’s Mars rover, where heat released by the radioactive decay of plutonium is converted into electricity. Future applications might include materials controlled by voltage to achieve very stable temperatures critical for operation of high-tech optical detectors and lasers.

The main barrier to wider adoption is the need for materials with just the right cocktail of properties, including good electrical conductivity but resistance to the flow of heat.

“The trouble is, these desirable properties tend to compete,” said Mercouri Kanadzidis, the Northwestern professor who initiated this study. “In most materials, electronic conductivity and thermal conductivity are coupled and both are either high or low. Very few materials have the special high-low combination.”

Under certain conditions, silver gallium telluride appears to have just the right stuff — highly mobile conducting electrons and ultra-low thermal conductivity. In fact, its thermal conductivity is significantly lower than theoretical calculations and comparisons with similar materials such as copper gallium telluride would suggest.

The Northwestern scientists turned to colleagues and tools at Brookhaven Lab to find out why.

“It took a meticulous x-ray examination at Brookhaven’s National Synchrotron Light Source II (NSLS-II) to reveal a previously hidden sub-nanoscale distortion in the positions of the silver atoms in this material,” said Brookhaven Lab physicist Emil Bozin, leader of the structural analysis.

Computational modeling revealed how those distortions trigger the one-axis crystal shrinkage — and how that structural shift scatters atomic vibrations, thus blocking the propagation of heat in the material.

But even with that understanding, there was no clear explanation of what was driving the sub-nanoscale distortions. Complementary computational modeling by Christopher Wolverton, a professor at Northwestern, indicated a novel and subtle quantum mechanical origin for the effect.

Together the findings point to a new mechanism for turning down thermal conductivity and a new guiding principle in the search for better thermoelectric materials.

Mapping atomic positions

The team used x-rays at NSLS-II’s Pair Distribution Function (PDF) beamline to map out the “large” scale arrangement of atoms in both copper gallium telluride and silver gallium telluride over a range of temperatures to see if they could discover why these two materials behave differently.

“A stream of hot air heats the sample with degree-by-degree precision,” said Milinda Abeykoon, who is the lead scientist of the PDF beamline. “At each temperature, as the x-rays bounce off the atoms, they produce patterns that can be translated into high spatial resolution measurements of the distances between each atom and its neighbors (each pair). Computers then assemble the measurements into the most likely 3D arrangements of the atoms.”

The team also did additional measurements over a wider range of temperatures but at lower resolution using the light source at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Germany. And they extrapolated their results down to a temperature of absolute zero, the coldest anything can get.

The data show that both materials have a diamond-like tetragonal structure of corner-connected tetrahedra, one with a single copper atom and the other with silver at the center of the 3D object’s tetrahedral cavity. Describing what happened as these diamondlike crystals were heated, Bozin said, “Immediately we saw a big difference between the silver and copper versions of the material.”

The crystal with copper at its core expanded in every direction, but the one containing silver expanded along one axis while shrinking along another.

“This strange behavior turned out to have its origin in the silver atoms in this material having very large amplitude and disorderly vibrations within structural layers,” said Simon Billinge, a professor at Columbia University with a joint appointment as a physicist at Brookhaven. “Those vibrations cause the linked tetrahedra to jiggle and jump with large amplitude,” he said.

This was a clue that the symmetry — the regular arrangement of atoms — might be “broken” or disrupted at a more “local” (smaller) scale.

The team turned to computational modeling to see how various local symmetry distortions of the silver atoms would match with their data.

“The one that worked the best showed that the silver atom goes off center in the tetrahedron in one of four directions, toward the edge of the crystal formed by two of the tellurium atoms,” Bozin said. On average, the random, off-center shifts cancel out, so the overall tetragonal symmetry is retained.

“But we know the larger scale structure changes too, by shrinking in one direction,” he noted. “As it turns out the local and larger scale distortions are linked.”

Twisting tetrahedrons

“The local distortions are not completely random,” Bozin explained. “They are correlated among adjacent silver atoms — those connected to the same tellurium atom. These local distortions cause adjacent tetrahedra to rotate with respect to one another, and that twisting causes the crystal lattice to shrink in one direction.”

As the shifting silver atoms twist the crystal, they also scatter certain wavelike vibrations, called phonons, that allow heat to propagate through the lattice. Scattering AgGaTe₂‘s energy-carrying phonons keeps heat from propagating, dramatically lowering the material’s thermal conductivity.

But why do the silver atoms shift in the first place?

The Brookhaven scientists had seen similar behavior a decade earlier, in a rock-salt like lead-telluride material. In that case, as the material was heated, “lone pairs” of electrons formed, generating tiny areas of split electric charge, called dipoles. Those dipoles pulled centrally located lead atoms off center and scattered phonons.

“But in silver gallium telluride there are no lone pairs. So, there must be something else in this material — and probably other ‘diamondoid’ structures as well,” Bozin said.

Bending bonding behavior

Christopher Wolverton’s calculations at Northwestern revealed that “something else” to be the bonding characteristics of the electrons orbiting the silver atoms.

“Those calculations compared the silver and copper atoms and found that there is a difference in the arrangement of electrons in the orbitals such that silver has a tendency to form weaker bonds than copper,” said Northwestern’s Xie. “Silver wants to bond with fewer neighboring tellurium atoms; it wants a simpler bonding environment.”

So instead of binding equally with all four surrounding tellurium atoms, as copper does, silver tends to preferentially (but randomly) move closer to two of the four. Those bonding electrons are what pull the silver atom off center, triggering the twisting, shrinkage, and vibrational changes that ultimately lower thermal conductivity in AgGaTe_2.

“We’ve stumbled upon a new mechanism by which lattice thermal conductivity can be reduced,” Northwestern’s Mercouri Kanadzidis said. “Perhaps this mechanism can be used to engineer, or look for, other new materials that have this type of behavior for future high-performance thermoelectrics.”

This research was primarily supported by the DOE Office of Science. NSLS-II is a DOE Office of Science user facility.

By studying the tendency of fish to return to their place of birth to reproduce — a concept known as philopatry that is often, and falsely, thought to apply only to salmon species — and pairing such knowledge with catch distribution maps and tagging and genetic sequencing studies, researchers at UBC’s Sea Around Us initiative identified the tentative migration routes of 11 tuna and other large pelagic fish in the Pacific Ocean and determined that certain areas should be considered as of ‘high’ and ‘very high’ priority when it comes to maintaining their populations.

“We applied the concept of philopatry to the movements extracted from tagging studies of species such as the near-threatened Pacific bluefin tuna and the heavily-fished yellowfin tuna, and we also combined this information with the links between populations inferred from genetic studies. This allowed us to identify tentative annual migration cycles,” said Veronica Relano, a doctoral candidate with the Sea Around Us and lead author of thestudy that presents these findings.

“The interesting thing is that when we compared our proposed migration routes and the mapped catch data from 1950 to 2016 available on the Sea Around Us website, we found many coincidences. Clearly, the accuracy of these routes is reinforced by considering philopatry, although they are still tentative,” she said.

After analyzing the seasonal migration paths of each of the 11 fish species individually, the researchers superposed them and noticed that several species and populations of these large pelagic fishes use the same migration routes.

“Those high-traffic areas, two of which are in northeastern and central sections of the Pacific Ocean and two in the southwestern and central sections, should become parts of blue corridors, which are routes where strict fisheries management measures or partial bans of industrial fishing ought to be enforced to allow for increased connectivity of habitats and thus allow populations of marine species to maintain themselves,” said Dr. Daniel Pauly, co-author of the study and the Sea Around Us principal investigator.

“But before setting up any protected area to support the rebuilding of diminished fish populations, it is important to consider the entire body of knowledge available on the migrations and movements of different species. This is what we set out to do with this study. Our findings suggest in which areas such efforts would be more effective, but as stated in our title, the closed migration cycles we propose are tentative, and thus it would be nice if other researchers set out to test their validity,” he said.

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In a paper published today in Science, the researchers report that trade in land-use emissions — which come from a combination of agriculture and land-use change — increased from 5.1 gigatons of carbon dioxide equivalent (when factoring in other greenhouse gas emissions such as nitrous oxide and methane) per year in 2004 to 5.8 gigatons in 2017.

In the paper, the scientists found that land-use change — including clearing of carbon-absorbing forests to create space for farms and pastures — contributed roughly three-quarters of the amount of greenhouse gases driven by the global trade of agricultural goods between 2004 and 2017.

“Roughly a quarter of all human greenhouse gas emissions are from land use,” said co-author Steven Davis, UCI professor of Earth system science. “Our work shows that large shares of these emissions in lower-income countries are related to consumption in more developed countries.”

The top sources of land-use-change emissions during the period studied were Brazil, where the practice of removing natural vegetation such as forests to make room for livestock pastures and farms has caused large transformation of land use in the country, and Indonesia, where ancient, carbon-storing peats have been burned or otherwise eliminated to enable the cultivation of plants to produce palm oil for export to wealthy countries.

About 22 percent of the world’s crop and pastureland — 1 billion hectares — is used to cultivate products destined for overseas consumers, according to the researchers. Commodities such as rice, wheat, corn, soybeans, palm oil and other oil seeds occupy nearly one third of the land used for traded goods and contribute roughly half of traded greenhouse emissions.

The study showed shifts that took place in certain regions between 2004 and 2017: In the early phase, China was a net exporter of agricultural goods, but by 2017, it had become an importer of both goods and land-use emissions, in part from Brazil. At the same time, Brazil’s exports to Europe and the United States, which had been the nation’s largest trading partners in agricultural goods in 2004, declined.

In 2017, the last year the researchers examined, the largest source of export-related emissions was Brazil, followed by Argentina, Indonesia, Thailand, Russia and Australia. The largest net importers of products tied to such emissions were China, the U.S., Japan and Germany, with the U.K., Italy, South Korea and Saudi Arabia following.

In addition to adding greenhouse gases to the atmosphere, human land use practices have caused significant ecosystem disruption, degraded biodiversity, depleted water resources and introduced other types of pollution to local environments.

From an economic standpoint, the exporters producing the highest amounts of land use emissions are also heavily dependent on export agriculture as a contributor to gross domestic product.

Davis said, “We hope this study will raise awareness of the role of international trade in driving land-use emissions. In turn, importers can adopt ‘buy clean’ policies to reduce the most emissions-intensive imports and discourage regions from gaining an environmentally destructive trade advantage. We recognize that several regions, including Europe, the U.S., and China, have seen an increase in efforts taken to improve supply chain transparency in recent years — a good sign indeed.”

The project — funded by the National Science Foundation and U.S. Department of Agriculture, the ClimateWorks Foundation, and the Gordon and Betty Moore Foundation — also included researchers from the University of California, San Diego; the University of California, Davis; Stanford University; China’s Tsinghua University, Beijing Normal University, Peking University, Chinese Academy of Sciences; and Germany’s Ludwig-Maximilian University.

The disease is relatively rare, but affects an estimated 100,000 persons in the United States, and results in 20,000 deaths annually. There is no cure.

In a study published May 4, 2022 in Science Translational Medicine, researchers at the University of California San Diego School of Medicine describe the underlying signaling pathway that results in PAH — and a novel monoclonal antibody therapy that blocks the abnormal blood vessel formation characterizing the disease.

At the cellular level, PAH progresses with proliferation of vascular smooth muscle cells (vSMC) that cause small arteries in the lungs to become narrowed, leading to progressively less oxygen in the blood. A research team, led by senior author Patricia A. Thistlethwaite, MD, PhD, professor of surgery in at UC San Diego School of Medicine and a cardiothoracic surgeon at UC San Diego Health, focused on overexpression of the NOTCH ligand JAGGED-1, a binding protein involved in cell signaling and, in this case, the development of small pulmonary vSMCs.

They found that overexpression of the NOTCH3 ligand, JAGGED-1, spurs vSMC proliferation, but the NOTCH3 ligand DELTA-LIKE 4 inhibits it. The researchers then developed a therapeutic monoclonal antibody that selectively blocks JAGGED-1-induced NOTCH3 signaling, effectively reversing pulmonary hypertension in two rodent models of the disease, without toxic side effects.

“These findings reveal two opposing roles of NOTCH ligands,” said Thistlethwaite. “Importantly, it opens the door to a potentially new, safe treatment for PAH, using a monoclonal antibody that selectively inhibits NOTCH3 activation in the lung vasculature.”

Co-authors include: Yu Zhang, Moises Hernandez, Jonathan Gower, Nolan Winicki, Xena Morataya, Sebastian Alvarez, Jason X.-J. Yuan and John Shyy, all at UC San Diego.

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Notably, the researchers also found that a majority of people rely on credible sources of information, with two-thirds completely avoiding unreliable news sites.

The study, which appears in the journal Science Advances, centered on credibility ratings determined by NewsGuard, a browser extension that rates news and other information sites in order to guide users in assessing the trustworthiness of the content they come across online.

“While it’s encouraging that most of us rely on credible sources of information, there are many who turn to sites of questionable trustworthiness, which raises concerns about misperceptions people may hold,” says Kevin Aslett, a postdoctoral researcher at the Center for Social Media and Politics (CSMaP) and the lead author of the paper. “However, while our study shows that, overall, credibility ratings have no discernible effect on misperceptions or online news consumption behavior of the average user, our findings suggest that the heaviest consumers of misinformation — those who rely on low-credibility sites — may move toward higher-quality sources when presented with news reliability ratings.”

In the study, conducted in May and June 2020, the researchers encouraged a random sample of more than 3,000 online participants to install the NewsGuard browser extension, which embeds source-level indicators of news reliability into users’ search engine results pages, social feeds, and visited URLs. Different “shield” symbols are placed in-feed to provide visual summaries of sources’ quality:

• Green shield = reliable source
• Red shield = unreliable source
• Gray shield = source with user-generated content
• Gold shield = satire

To measure the effect of these source labels, survey data were collected over two time periods (May 28-June 9 and June-19-June 30).

In addition to this panel survey, the researchers also collected anonymized digital trace data to characterize the quality of news consumption of a subset of approximately 1,000 participants. These quality measures made use of the same NewsGuard ratings shown to study participants as they encountered news links in their browsers.

Previous studies have shown that exposure to misinformation and online fake news can increase belief in misperceptions, heighten cynicism toward politics, lower trust in the news media, and increase affective polarization (i.e., disdain for supporters of the other political party). Moreover, prior research also suggests that expert source ratings, when shown alongside a mock news article, can influence the perceived truthfulness of the article’s claim.

With these earlier findings in mind, the researchers tested whether in-feed source reliability labels can counteract these effects by shifting news consumption from unreliable to more reliable sources, increasing trust in mainstream media and reliable sources, and/or mitigating political polarization and cynicism.

In order to measure whether source reliability information affects belief in misinformation as well as in accurate claims, the respondents were asked to judge the veracity of five widely circulated statements about the Black Lives Matter movement and five similarly well-circulated statements about COVID-19 — some true and some false.

Combining panel survey data and individual-level web-visit data, the results showed the following:

• A majority of people have reliable media diets: Most people (65 percent) did not visit any unreliable news sites before the study began, a finding consistent with the authors’ previous research. In fact, only 1.5 percent of respondents relied extensively on unreliable sources for news.
• Source credibility labels had no impact, on average: In-browser credibility labels did not measurably shift online consumption from unreliable to more reliable sources, failed to significantly alter misperceptions of widely circulated inaccurate claims about COVID-19 and the Black Lives Matter movement, and did not alter trust in the media generally.
• However, source labels made a difference for those who consume the most low-quality news: There was a noticeable improvement in the overall credibility of news sources visited by those who began the study with the lowest news diet quality, according to NewsGuard scores.

“In our partisan age, when attitudes about news sources are strongly correlated with partisanship, relatively subtle cues like source credibility labels may not be powerful enough to shift news habits and counteract misperceptions among the general public,” observes Andrew M. Guess, a faculty research affiliate at CSMaP and an assistant professor at Princeton University. “However, a key metric of success for this intervention is how it changes the behavior of those who consume the most low-quality news. The fact that it doesn’t work for the overall population doesn’t mean the tool is ineffective. It means it must be part of a far larger toolkit to combat the spread of online misinformation.”

The paper’s other authors were Joshua A. Tucker and Jonathan Nagler, professors in NYU’s Department of Politics, and Richard Bonneau, a professor in NYU’s Department of Biology and Courant Institute of Mathematical Sciences. Tucker, Nagler, and Bonneau are co-directors of CSMaP.

NewsGuard was not involved in the design or funding of this research.

Compared with the fast weather fluctuations of the atmosphere, the slowly varying ocean exhibits strong persistence, or “memory,” meaning the ocean temperature tomorrow is likely to look a lot like it does today, with only slight changes. As a result, ocean memory is often used for predicting ocean conditions.

Ocean memory decline is found as a collective response across the climate models to human-induced warming. As greenhouse-gas concentrations continue to rise, such memory decline will become increasingly evident.

“We discovered this phenomenon by examining the similarity in ocean surface temperature from one year to the next as a simple metric for ocean memory,” said Hui Shi, lead author and researcher at the Farallon Institute in Petaluma, California. “It’s almost as if the ocean is developing amnesia.”

Ocean memory is found to be related to the thickness of the uppermost layer of the ocean, known as the mixed layer. Deeper mixed layers have greater heat content, which confers more thermal inertia that translates into memory. However, the mixed layer over most oceans will become shallower in response to continued anthropogenic warming, resulting in a decline in ocean memory.

“Other processes, such as changes in ocean currents and changes in the energy exchange between the atmosphere and ocean, also contribute to changes in ocean memory, but the shoaling of the mixed layer depth and resulting memory decline happens in all regions of the globe, and this makes it an important factor to consider for future climate predictions,” said Robert Jnglin Wills, a research scientist at University of Washington in Seattle, Washington, and co-author of the research.

Along with ocean memory decline, the thinning mixed layer is also found to increase the random fluctuations of the sea surface temperature. As a result, although the ocean will not become much more variable from one year to the next in the future, the fraction of helpful signals for prediction largely reduces.

“Reduced ocean memory together with increased random fluctuations suggest intrinsic changes in the system and new challenges in prediction under warming,” said Fei-Fei Jin, an atmospheric sciences professor at the University of Hawai’i at Manoa School of Ocean and Earth Science and Technology, and co-author of the research.

Ocean memory loss doesn’t just impact the prediction of physical variables, but could also influence the way we manage sensitive marine ecosystems.

“Reduced memory means less time in advance for a forecast to be made. This could hinder our ability to predict and prepare for ocean change including marine heatwaves, which are known to have caused sudden and pronounced changes in ocean ecosystems around the world,” said Michael Jacox, a research scientist at NOAA Fisheries’ Southwest Fisheries Science Center in Monterey, California, and co-author of the research.

In fisheries management, the biological parameters used for stock assessment are estimated assuming a stable environment represented by the recent past. Reduced ocean memory might render such estimation inaccurate and calls for new approaches in ecosystem-based fisheries management to include real-time ocean monitoring and other efforts alike. Ocean memory decline also likely exerts impacts on populations of biological resources. Depending on whether the species are adapted to constant or more variable environmental conditions, future changes in their population can be better estimated and predicted by taking ocean memory loss into consideration.

Besides ocean prediction, forecasting land-based impacts on temperature, precipitation as well as extreme events might also be affected by ocean memory decline due to their dependence on the persistence of sea surface temperature as a predictability source. As ocean memory continues to decline, researchers will likely be challenged to search for alternative predictors for skillful predictions.