Researchers at The University of Texas at Austin have discovered techniques to bestow superpowers upon sapphire, a material that most of us think of as just a pretty jewel. But sapphire is seen as a critical material across many different areas, from defense to consumer electronics to next-generation windows because it’s nearly impossible to scratch.

“Sapphire is such a high-value material because of its hardness and many other favorable properties,” said Chih-Hao Chang, associate professor in the Walker Department of Mechanical Engineering and leader of the new research. “But the same properties that make it attractive also make it difficult manufacture at small scales.”

Chang and his team hope to ease this challenge with new sapphire-based nanostructures as documented in Materials Horizons. The nanostructures show the highest aspect ratio yet for this material, which enables its superpowers without completely losing its stiffness and hardness.

While not quite as scratch-resistant as traditional bulk sapphire — the nanostructures are comparable to tungsten or traditional glass in that way — these new sapphire nanostructures repel fog, dust and glare with self-cleaning capabilities.

“This is very exciting since nanostructures are traditionally seen as being fragile, but making them in sapphire can solve this problem,” said Kun-Chieh Chien, a recent Ph.D. graduate from Chang’s lab and one of the lead authors.

Inspired by the moth eye, the tapered profile of the sapphire nanostructures enhance light transmission and reduce glare. The nanostructures’ high surface energy and aspect ratio create a superhydrophilic surface to prevent fog. The structures can also be treated to be a superhydrophobic surface to allow water droplets to roll off the surface, mimicking the lotus leaf effect.

“Our sapphire nanostructures are not only multifunctional but also mechanically robust, making them ideal for applications where durability and performance are critical,” said Mehmet Kepenekci, a graduate student in Chang’s lab and one of the lead authors.

This technology has a wide variety of benefits. For consumers, it could lead to smartphones that are easier to read in challenging lighting conditions, lenses and windows that don’t fog up, cameras that aren’t prone to glare and hardy windshields that don’t get dusty.

As we embark on the next generation of space travel, the anti-dust properties could ensure mission-critical equipment doesn’t get caked in dust during landing missions on other planets, for example. It could lead to the creation of stronger infrared sensors and protective windows in defense applications.

“Our self-cleaning sapphire surfaces can maintain 98.7% dust-free area using gravity alone,” said Andrew Tunell, the student who conducted the dust adhesion experiments. “This is a significant improvement over existing dust-mitigation technologies and is particularly beneficial for applications in space, where water is not readily available for cleaning.”The researchers aim to bring this technology to life, and they’re looking to improve it several ways. They’re scaling up fabrication to apply these nanostructures over larger samples, improving mechanical and chemical properties to enhance its abilities and exploring even more real-world applications.

He was able to grasp, move and drop objects just by imagining himself performing the actions.

The device, known as a brain-computer interface (BCI), worked for a record 7 months without needing to be adjusted. Until now, such devices have only worked for a day or two.

The BCI relies on an AI model that can adjust to the small changes that take place in the brain as a person repeats a movement — or in this case, an imagined movement — and learns to do it in a more refined way.

“This blending of learning between humans and AI is the next phase for these brain-computer interfaces,” said neurologist, Karunesh Ganguly, MD, PhD, a professor of neurology and a member of the UCSF Weill Institute for Neurosciences. “It’s what we need to achieve sophisticated, lifelike function.”

The study, which was funded by the National Institutes of Health, appears March 6 in Cell.

The key was the discovery of how activity shifts in the brain day to day as a study participant repeatedly imagined making specific movements. Once the AI was programmed to account for those shifts, it worked for months at a time.

Location, location, location

Ganguly studied how patterns of brain activity in animals represent specific movements and saw that these representations changed day-to-day as the animal learned. He suspected the same thing was happening in humans, and that was why their BCIs so quickly lost the ability to recognize these patterns.

Ganguly and neurology researcher Nikhilesh Natraj, PhD, worked with a study participant who had been paralyzed by a stroke years earlier. He could not speak or move.

He had tiny sensors implanted on the surface of his brain that could pick up brain activity when he imagined moving.

To see whether his brain patterns changed over time, Ganguly asked the participant to imagine moving different parts of his body, like his hands, feet or head.

Although he couldn’t actually move, the participant’s brain could still produce the signals for a movement when he imagined himself doing it. The BCI recorded the brain’s representations of these movements through the sensors on his brain.

Ganguly’s team found that the shape of representations in the brain stayed the same, but their locations shifted slightly from day to day.

From virtual to reality

Ganguly then asked the participant to imagine himself making simple movements with his fingers, hands or thumbs over the course of two weeks, while the sensors recorded his brain activity to train the AI.

Then, the participant tried to control a robotic arm and hand. But the movements still weren’t very precise.

So, Ganguly had the participant practice on a virtual robot arm that gave him feedback on the accuracy of his visualizations. Eventually, he got the virtual arm to do what he wanted it to do.

Once the participant began practicing with the real robot arm, it only took a few practice sessions for him to transfer his skills to the real world.

He could make the robotic arm pick up blocks, turn them and move them to new locations. He was even able to open a cabinet, take out a cup and hold it up to a water dispenser.

Months later, the participant was still able to control the robotic arm after a 15-minute “tune-up” to adjust for how his movement representations had drifted since he had begun using the device.

Ganguly is now refining the AI models to make the robotic arm move faster and more smoothly, and planning to test the BCI in a home environment.

For people with paralysis, the ability to feed themselves or get a drink of water would be life changing.

Ganguly thinks this is within reach.

“I’m very confident that we’ve learned how to build the system now, and that we can make this work,” he said.

Researchers fed separate groups of young and old rats the high-fat diet for three days or for three months to compare how quickly changes happen in the brain versus the rest of the body when eating an unhealthy diet.

As expected based on previous diabetes and obesity research, eating fatty foods for three months led to metabolic problems, gut inflammation and dramatic shifts in gut bacteria in all rats compared to those that ate normal chow, while just three days of high fat caused no major metabolic or gut changes.

When it came to changes in the brain, however, researchers found that only older rats — whether they were on the high-fat diet for three months or only three days — performed poorly on memory tests and showed negative inflammatory changes in the brain.

The results dispel the idea that diet-related inflammation in the aging brain is driven by obesity, said senior study author Ruth Barrientos, an investigator in the Institute for Behavioral Medicine Research at The Ohio State University. Most research on the effects of fatty and processed foods on the brain has focused on obesity, yet the impact of unhealthy eating, independent of obesity, remains largely unexplored.

“Unhealthy diets and obesity are linked, but they are not inseparable. We’re really looking for the effects of the diet directly on the brain. And we showed that within three days, long before obesity sets in, tremendous neuroinflammatory shifts are occurring,” said Barrientos, also an associate professor of psychiatry and behavioral health and neuroscience in Ohio State’s College of Medicine.

“Changes in the body in all animals are happening more slowly and aren’t actually necessary to cause the memory impairments and changes in the brain. We never would have known that brain inflammation is the primary cause of high-fat diet-induced memory impairments without comparing the two timelines.”

The research was published recently in the journal Immunity & Ageing.

Years of research in Barrientos’ lab has suggested that aging brings on long-term “priming” of the brain’s inflammatory profile coupled with a loss of brain-cell reserve to bounce back, and that an unhealthy diet can make matters worse for the brain in older adults.

Fat constitutes 60% of calories in the high-fat diet used in the study, which could equate to a range of common fast-food options: For example, nutrition data shows that fat makes up about 60% of calories in a McDonald’s double smoky BLT quarter pounder with cheese or a Burger King double whopper with cheese.

After the animals were on high-fat diets for three days or three months, researchers ran tests assessing two types of memory problems common in older people with dementia that are based in separate regions of the brain: contextual memory mediated by the hippocampus (the primary memory center of the brain), and cued-fear memory that originates in the amygdala (the fear and danger center of the brain).

Compared to control animals eating chow and young rats on the high-fat diet, aged rats showed behaviors indicating both types of memory were impaired after only three days of fatty food — and the behaviors persisted as they continued on the high-fat diet for three months.

Researchers also saw changes in levels of a range of proteins called cytokines in the brains of aged rats after three days of fatty food, which signaled a dysregulated inflammatory response. Three months after being on the high-fat diet, some of the cytokine levels had shifted but remained dysregulated, and the cognitive problems persisted in behavior tests.

“A departure from baseline inflammatory markers is a negative response and has been shown to impair learning and memory functions,” Barrientos said.

Compared to rats eating normal chow, young and old animals gained more weight and showed signs of metabolic dysfunction — poor insulin and blood sugar control, inflammatory proteins in fat (adipose) tissue, and gut microbiome alterations — after three months on the high-fat diet. Young rats’ memory and behavior and brain tissue remained unaffected by the fatty food.

“These diets lead to obesity-related changes in both young and old animals, yet young animals appear more resilient to the high-fat diet’s effects on memory. We think it is likely due to their ability to activate compensatory anti-inflammatory responses, which the aged animals lack,” Barrientos said.

“Also, with glucose, insulin and adipose inflammation all increased in both young and old animals, there’s no way to distinguish what is causing memory impairment in only old animals if you look only at what’s happening in the body. It’s what is happening in the brain that’s important for the memory response.”

This work was supported by grants from the National Institute on Aging.

Co-authors include Michael Butler, Stephanie Muscat, Brigitte González Olmo, Sabrina Mackey-Alfonso, Nashali Massa, Bryan Alvarez, Jade Blackwell, Menaz Bettes and James DeMarsh of Ohio State; and Maria Elisa Caetano-Silva, Akriti Shrestha, Robert McCusker and Jacob Allen of the University of Illinois at Urbana-Champaign.

“What we found is that right around the size of Neptune, planets go from being almost always on circular orbits to very often having elliptical orbits,” said UCLA postdoctoral researcher Gregory Gilbert, the lead author of a paper describing the findings published in Proceedings of the National Academy of Sciences.

The researchers used data collected by NASA’s Kepler telescope, which monitored 150,000 stars and measured dips in their brightness caused by transiting planets to discover thousands of exoplanets. The measurements of stellar brightness over time are called light curves. The researchers performed a detailed analysis of the light curve dips to extract information about the shape of the planets’ orbits.

One of the most challenging aspects of this project was ensuring every single one of the 1,600 light curves was modeled with care.

“If stars behaved like boring light bulbs, this project would have been 10 times easier,” said co-author Erik Petigura, a UCLA physics and astronomy professor. “But the fact is that each star and its collection of planets has its own individual quirks, and it was only after we got eyes on each one of these light curves that we trusted our results.”

This is where UCLA undergraduate Paige Entrican came in. Entrican built a custom visualization tool kit and manually inspected each light curve.

“Reviewing the data was a meticulous process that required careful inspection of all data products to ensure the validity of our results. Several times during this project, I identified failure modes that only affected 1% of all our stars. But we needed to update our analysis to be robust to these issues and go back and reprocess the entire data set,” Entrican said.

The eccentricity split coincides with several other iconic features in the exoplanet population, such as the high abundance of small planets over large planets and a tendency for giant planets to form only around stars enriched in heavy elements such as oxygen, carbon and iron. Astronomers call these heavy elements metals.

“Small planets are common; large planets are rare. Large planets need metal-rich stars in order to form; small planets do not. Small planets have low eccentricities, and large planets have large eccentricities,” Gilbert explained.

The coincidence of trends in abundance, metallicity and eccentricity points to two distinct pathways for forming small and large planets.

“To see a transition in the eccentricities of the orbits at this same point tells us there really is something very different about how these giant planets form versus how small planets like Earth form. That’s really the major discovery to come out of this paper,” Gilbert said.

Scientists think that planets form when small space rocks fuse to form bigger rocks until eventually they form a planet that can be about the size of Earth or, if the planetary core is very large, up to 10 times bigger than Earth. At this point, the planet is large enough to hold onto large amounts of hydrogen and helium and becomes a gas giant like Jupiter and Saturn in our solar system. Planets larger than Neptune are somewhat rare because they must undergo runaway accretion, a feedback loop of accumulating hydrogen and helium gas. But this can usually only happen if they also are orbiting a star that contains large quantities of elements heavier than helium.

Larger planets with eccentric orbits also point to a more chaotic period of formation, during which planets interact via gravitational forces to produce noncircular orbits. For example, eccentric giant planets probably stir up their neighbors more frequently, causing giant impacts such as the one that produced Earth’s moon. In exoplanetary systems, these collisions can be much more violent, involving the mergers of two planets much larger than the Earth.

“It’s remarkable what we’ve been able to learn about the orbits of planets around other stars using the Kepler Space Telescope,” Petigura said. “The telescope was named after Johannes Kepler, who, four centuries ago, was the first scientist to appreciate that the planets in our solar system move on slightly elliptical rather than circular orbits. His discovery was an important moment in human history because it showed that the sun, rather than the Earth, was at the center of the solar system. I’m sure Kepler, the man, would be delighted to learn that a telescope named in his honor measured the subtle shapes of orbits of Earth-size planets around other stars.”