Earth’s planetary core is thankfully intact. But in space, similar cores can collide with other objects, causing the crystalline materials of the core to deform rapidly. Some asteroids in our solar system are massive iron objects that scientists suspect are the remnants of planetary cores after catastrophic impacts.

Measuring what happens during the collision of celestial bodies or at the Earth’s core is obviously not very practical. As such, much of our understanding of planetary cores is based on experimental studies of metals at less extreme temperatures and pressures. But researchers at the Department of Energy’s SLAC National Accelerator Laboratory have now observed for the first time how iron’s atomic structure deforms to accommodate the stress from the pressures and temperatures that occur just outside of the inner core.

The results appear in Physical Review Letters, where they have been highlighted as an Editor’s Suggestion.

Coping with stress

Most of the iron you encounter in your everyday life has its atoms arranged in nanoscopic cubes, with an iron atom at each corner and one in the center. If you squeeze these cubes by applying extremely high pressures, they rearrange into hexagonal prisms, which allow the atoms to pack in more tightly.

The group at SLAC wanted to see what would happen if you kept applying pressure to that hexagonal arrangement to mimic what happens to iron at the Earth’s core or during atmospheric reentry from space. “We didn’t quite make inner core conditions,” says co-author Arianna Gleason, a scientist in the High-Energy Density Science (HEDS) Division at SLAC. “But we achieved the conditions of the outer core of the planet, which is really remarkable.”

No one had ever directly observed iron’s response to stress under such high temperatures and pressures before, so the researchers didn’t know how it would respond. “As we continue to push it, the iron doesn’t know what to do with this extra stress,” says Gleason. “And it needs to relieve that stress, so it tries to find the most efficient mechanism to do that.”

The coping mechanism iron uses to deal with that extra stress is called “twinning.” The arrangement of atoms shunts to the side, rotating all the hexagonal prisms by nearly 90 degrees. Twinning is a common pressure response in metals and minerals — quartz, calcite, titanium and zirconium all undergo twinning.

“Twinning allows iron to be incredibly strong — stronger than we first thought — before it starts to flow plastically on much longer time scales,” Gleason said.

A tale of two lasers

Reaching these extreme conditions required two types of lasers. The first was an optical laser, which generated a shock wave that subjected the iron sample to extremely high temperatures and pressures. The second was SLAC’s Linac Coherent Light Source (LCLS) X-ray free-electron laser, which allowed the researchers to observe the iron on an atomic level. “At the time, LCLS was the only facility in the world where you could do that,” says lead author Sébastien Merkel of the University of Lille in France. “It’s been a door opener for other similar facilities in the world.”

The team fired both lasers at a tiny sample of iron about the width of a human hair, hitting the iron with a shock wave of heat and pressure. “The control room is just above the experimental room,” Merkel says. “When you trigger the discharge, you hear a loud pop.”

As the shock wave hit the iron, researchers used the X-ray laser to observe how the shock changed the arrangement of the iron atoms. “We were able to make a measurement in a billionth of a second,” Gleason says. “Freezing the atoms where they are in that nanosecond is really exciting.”

The researchers collected these images and assembled them into a flipbook that showed iron deforming. Before the experiment was complete, they didn’t know if iron would respond too fast for them to measure or too slow for them to ever see. “The fact that the twinning happens on the time scale that we can measure it as an important result in itself,” Merkel says.

The future is bright

This experiment serves as a bookend for understanding the behavior of iron. Scientists had gathered experimental data on the structure of iron at lower temperatures and pressures and used it to model how iron would behave at extremely high temperatures and pressures, but no one had ever experimentally tested those models.

“Now we can give a thumbs up, thumbs down on some of the physics models for really fundamental deformation mechanisms,” Gleason says. “That helps to build up some of the predictive capability we’re lacking for modeling how materials respond at extreme conditions.”

The study provides exciting insights into the structural properties of iron at extremely high temperatures and pressures. But the results are also a promising indicator that these methods could help scientists understand how other materials behave at extreme conditions, too.

“The future is bright now that we’ve developed a way to make these measurements,” Gleason says. “The recent X-ray undulator upgrade as part of the LCLS-II project allows higher X-ray energies — enabling studies on thicker alloys and materials that have lower symmetry and more complex X-ray fingerprints.”

The upgrade will also enable researchers to observe larger samples, which will give them a more comprehensive view of iron’s atomic behavior and improve their statistics. Plus, “we’re going to get more powerful optical lasers with the approval to proceed with a new flagship petawatt laser facility, known as MEC-U,” says Gleason. “That’ll make future work even more exciting because we’ll be able to get to the Earth’s inner core conditions without any problem.”

Researchers at Los Alamos National Laboratory (LANL) contributed to this study. Funding was provided by the University of Lille, an LANL Reines Laboratory Directed Research and Development grant, and the DOE Office of Science, including Gleason’s DOE Early Career Award in Fusion Energy Sciences. LCLS is a DOE Office of Science user facility.

The research consortium genetically mapped thousands of chickpea varieties, and the UQ team then used this information to identify the most valuable gene combinations using artificial intelligence (AI).

Professor Ben Hayes led the UQ component of the project with Professor Kai Voss-Fels and Associate Professor Lee Hickey, to develop a ‘haplotype’ genomic prediction crop breeding strategy, for enhanced performance for seed weight.

“Most crop species only have a few varieties sequenced, so it was a massive undertaking by the international team to analyse more than 3000 cultivated and wild varieties,” Professor Hayes said.

The landmark international study was led by Dr Rajeev Varshney from the International Crops Research Institute for the Semi-Arid Tropics in Hyderabad, India. The study confirmed chickpea’s origin in the Fertile Crescent and provides a complete picture of genetic variation within chickpea.

“We identified 1,582 novel genes and established the pan-genome of chickpea, which will serve as a foundation for breeding superior chickpea varieties with enhanced yield, higher resistance to drought, heat and diseases,” Dr Varshney said.

Professor Hayes said the UQ team used the data to model a chickpea with perfect genetics for seed weight, a trait linked to yield.

“This additional data led to the increase in yield predicted by our model, which is still being fine-tuned,” he said.

“We are using our AI ‘FastStack’ technology platform to design a chickpea with the ultimate genetics for maximum seed weight, and we think this will ultimately be a valuable tool for chickpea breeders.”

FastStack combines AI with genomic prediction technology to identify the combinations of genes most likely to improve crop performance.

Chickpea is the largest pulse crop in Australia after lupin, both in terms of planting area and production.

It ranks second in area and third in production among the pulses worldwide.

UQ plant breeder and crop geneticist, Associate Professor Lee Hickey, said the global demand for protein-rich pulses was increasing.

“Improving the productivity of chickpea for Australia offers opportunities for our farmers to supply local food industries and export markets,” he said.

“Using this AI-generated chickpea model for increased seed weight in the field will be challenging, given the number of generations it will take in cross-breeding for optimal chickpea genetics, and the impact of different environments and management practices on crop growth.

“But we do have tools like speed breeding that can speed this process up and allows us to test and put into practice these theoretical scenarios.”

Dr Hickey said new genomic breeding approaches, including the haplotype model, are expected to redefine chickpea breeding strategies for developing high-yielding and nutritious chickpea varieties.

Chickpea is an important rotation crop in farming systems, as it is self-fertilising for nitrogen, reducing the need fornitrogen fertiliser.

Human sewage can introduce disease-causing pathogens and nitrogen into the ocean, potentially impacting human health as well as coastal ecosystems and the communities that depend on them for such purposes as fishing. However, most research into humans’ impact on coastal ecosystems has focused on agricultural runoff, while investigations on human sewage have been limited.

To better capture the impact of sewage on coastal ecosystems, Tuholske and colleagues conducted a novel analysis in which they estimated and mapped nitrogen and pathogen inputs into the ocean from sewage for about 135,000 watersheds around the world at a resolution of 1 kilometer. The assessment employed newly available, high-resolution data on global human populations and modeled how wastewater plumes entering the ocean would overlap with different ecosystems.

The analysis suggests that wastewater from human sewage introduces 6.2 teragrams of nitrogen into coastal ecosystems per year — for comparison, that is about 40 percent of estimated inputs from agriculture. Sixty-three percent of the nitrogen is from sewage systems, 5 percent from septic systems, and 32 percent from untreated, direct input.

Of the watersheds that appear to release the most nitrogen from sewage, most are located in India, Korea, and China, with the Chang Jiang (Yangtze) River contributing 11 percent of the global total. The researchers also identified hotspots for coral reef exposure to nitrogen in China, Kenya, Haiti, India, and Yemen. Seagrass exposure hotspots were found in Ghana, Kuwait, India, Nigeria, and China. The Chang Jiang and Brahmaputra Rivers have the highest input of pathogens.

Further research will be needed to refine the model and its estimates. Nonetheless, this work provides a new resource that could play a key role in efforts to mitigate harm to ecosystems and human health — such as by highlighting locations where tradeoffs between managing nitrogen and pathogen levels are particularly important to consider.

The authors add: “The sheer scale of how much wastewater is impacting coastal ecosystems worldwide is staggering. But because we map wastewater inputs to the ocean across more than 130,000 watersheds, our results identify target priority areas to help marine conservation groups and public health officials to work together and reduce the impacts of wastewater on coastal waters across the planet.”

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The researchers have created a visual representation of their research, available at: http://www.globalwastewatermodel.com/webmap.html

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About 64,000 people in the U.S. are diagnosed with type 1 diabetes each year, according to the Juvenile Diabetes Research Foundation. There is no cure for the disease, and to manage symptoms, people must measure their blood sugar levels throughout the day and administer insulin through an injection or pump. Although scientists still don’t know exactly what causes the body to turn against itself and attack insulin-secreting cells, people with type 1 diabetes have fewer regulatory T cells (Tregs) — immune cells that suppress the differentiation and activation of other, self-attacking T cells. In a recent study published in ACS’ Nano Letters, Yunfeng Lin and colleagues showed that treating mice with tFNAs could prevent type 1 diabetes, in part by increasing Treg numbers. Originally designed to carry other therapeutic molecules into cells, tFNAs have recently been shown to modulate the immune system on their own. Now, the researchers wanted to find out if these molecules could reverse new-onset type 1 diabetes, before pancreatic β-cells were completely destroyed.

The researchers made tFNAs from four single-stranded DNA segments that self-assembled into pyramid-like shapes, called tetrahedrons. But whereas a pyramid is square at its base, tetrahedrons are triangular. Then, every other day for 4 weeks, they injected the tFNAs into 10 mice with new-onset type 1 diabetes, while 10 other diabetic mice were injected with saline. In the control mice, blood glucose levels continued to rise, and 60% of the mice died during the 12-week follow-up period. In contrast, blood glucose levels in mice treated with tFNAs went down to normal levels, and none of the rodents died. In a further analysis of the tFNA-treated mice, the team found that pancreatic β-cells were protected, and Tregs were restored to normal levels, while auto-reactive T cells decreased in the pancreas. Although the findings still need to be verified in people, tFNAs are one of the most promising candidates for type 1 diabetes immunotherapy, the researchers say.

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