The new robot, dubbed ATMO (aerially transforming morphobot), uses four thrusters to fly, but the shrouds that protect them become the system’s wheels in an alternative driving configuration. The whole transformation relies on a single motor to move a central joint that lifts ATMO’s thrusters up into drone mode or down into drive mode.

The researchers describe the robot and the sophisticated control system that drives it in a paper recently published in the journal Communications Engineering.

“We designed and built a new robotic system that is inspired by nature — by the way that animals can use their bodies in different ways to achieve different types of locomotion,” says Ioannis Mandralis (MS ’22), a graduate student in aerospace at Caltech and lead author of the new paper. For example, he says, birds fly and then change their body morphology to slow themselves down and avoid obstacles. “Having the ability to transform in the air unlocks a lot of possibilities for improved autonomy and robustness,” Mandralis says.

But midair transformation also poses challenges. Complex aerodynamic forces come into play both because the robot is close to the ground and because it is changing its shape as it morphs.

“Even though it seems simple when you watch a bird land and then run, in reality this is a problem that the aerospace industry has been struggling to deal with for probably more than 50 years,” says Mory Gharib (PhD ’83), the Hans W. Liepmann Professor of Aeronautics and Medical Engineering, director and Booth-Kresa Leadership Chair of Caltech’s Center for Autonomous Systems and Technologies (CAST), and director of the Graduate Aerospace Laboratories of the California Institute of Technology (GALCIT). All flying vehicles experience complicated forces close to the ground. Think of a helicopter, as an example. As it comes in for a landing, its thrusters push lots of air downward. When that air hits the ground, some portion of it bounces back up; if the helicopter comes in too quickly, it can get sucked into a vortex formed by that reflected air, causing the vehicle to lose its lift.

In ATMO’s case, the level of difficulty is even greater. Not only does the robot have to contend with complex near-ground forces, but it also has four jets that are constantly altering the extent to which they are shooting toward each other, creating additional turbulence and instability.

To better understand these complex aerodynamic forces, the researchers ran tests in CAST’s drone lab. They used what are called load cell experiments to see how changing the robot’s configuration as it came in for landing affected its thrust force. They also conducted smoke visualization experiments to reveal the underlying phenomena that lead to such changes in the dynamics.

The researchers then fed those insights into the algorithm behind a new control system they created for ATMO. The system uses an advanced control method called model predictive control, which works by continuously predicting how the system will behave in the near future and adjusting its actions to stay on course.

“The control algorithm is the biggest innovation in this paper,” Mandralis says. “Quadrotors use particular controllers because of how their thrusters are placed and how they fly. Here we introduce a dynamic system that hasn’t been studied before. As soon as the robot starts morphing, you get different dynamic couplings — different forces interacting with one another. And the control system has to be able to respond quickly to all of that.”

In a study published today (May 28, 2025) in PLOS One, an international team of archaeologists documents how monuments changed as the climate transitioned from a humid environment to, eventually, an arid desert.

Early monuments were built by larger groups at one time. But as people dispersed with the increasingly drier climate, smaller groups began constructing monuments and eventually built many of them in several visits.

“The findings show that monuments are a flexible technology that reflect the resilience of desert pastoralists in the face of a changing climate,” said Joy McCorriston, lead author of the study and professor of anthropology at The Ohio State University.

But the key role that these monuments played in people’s lives remained a constant.

“These monuments are touchstones for human social belonging,” McCorriston said.

“As these groups became smaller and more spread out in the desert, people’s interactions with the monuments consolidates a sense of being part of a larger society.”

The research team analyzed 371 archaeological monuments in the arid Dhofar region of Oman. The earliest monuments studied were created from 7500 to 6200 BP (years Before Present) in the Holocene Humid Period. This period was characterized by higher-than-modern rainfall in southern Arabia.

The most recent monuments studied were created from 1100-750 BP, during the Late Antiquity when the area had become a desert.

While examples of most of the monuments and archaeological sites had previously been studied and classified, that research was generally very time- and place-specific, McCorriston said.

“What we’ve done is take a holistic look and show how all these individual monuments were part of a larger story of how the monuments changed as the lives of the people changed over thousands of years,” she said.

The researchers did this by looking at a standard set of observations for all the monuments and developing a model that could be used in other contexts and places around the world.

For example, the model may be applicable and adaptable to assess social resilience in regions such as Saharan, Mongolian, or the high Andes.

One of the key measurements the researchers made was the volume and size of stones used in construction of the monuments. The earliest-built monuments in the study were Neolithic platforms, which contained larger stones. They were the largest monuments studied and were built at one time.

“The significance of the larger stones is that it takes more people to lift them. We know that it took at least seven strong men to lift the largest stones,” McCorriston said.

“These large monuments that were built in one episode could only be built early on, before the region became arid. This is when large groups of people could still come together at one time.”

Some of these larger monuments could serve large gatherings of people, where they could converge with multiple herds of cattle, and have animal sacrifices and feasts.

As the region became more arid and could no longer support large numbers of people nor their coming together, small groups traveled widely, going to where they could find water and places for their animals to graze.

They still had to build monuments in one episode, such as for burials, but by this time they tended to be smaller and use smaller stones, the researchers found.

What became more common were what are called accretive monuments, which people built over time — sometimes many years — rather than in one episode, like the earlier platform monuments.

One example of such monuments is accretive triliths. The higher number of triliths, along with the smaller stone volumes with few heavy stones, are consistent with monuments built over time by smaller, dispersed groups in an era of hyper-aridity.

These accretive monuments functioned as touchstones, allowing pastoralists to maintain connections and social resilience even as their movements and populations became more dispersed.

“In many cases, they were building a memory. They come to a monument and add their piece, which was a replicated element of the whole. It helped people maintain a community, even with those they may rarely see,” she said.

It is impossible to say what were the precise messages the monuments were meant to convey, according to McCorriston. “What we can say is that the monuments conveyed readable meanings to others who shared the same cultural context.”

It is possible, though, that some monuments were built to assure others in a social network access to important environmental information as they came by later.

“People would need to know, did it rain here last year? Did the goats eat all the grass? Pastoralists used this technology to help absorb the risk of being in an inherently variable and risky environment,” she said. And they would need to depend on social networks for livestock exchanges, marriage partners, and rare materials, like sea shells, carnelian and agate and metal.

“That is one of the key points of what we found. Our model highlights a reliance on monuments to preserve connections and adapt socially in a changing world.”

Other Ohio State co-authors on the study were Lawrence Ball, Ian Hamilton, Matthew Senn and Abigail Buffington. Other co-authors were Michael Harrower of Johns Hopkins University; Sarah Ivory of Penn State University; Tara Steimer-Herbet of the Université de Genève, Geneva, Switzerland; and ‘Ali Ahmad Al-Kathiri and ‘Ali Musalam Al-Mahriof the Ministry of Heritage and Tourism, Salalah, Sultanate of Oman.

The phenomenon is described in a new study that uses on-site field work and airborne imagery to track the health of the reef in Hōnaunau Bay, Hawaii. Overfishing is the main culprit behind the explosion in sea-urchin numbers, said Kelly van Woesik, Ph.D. student in the North Carolina State University Center for Geospatial Analytics and first author of the study.

“Fishing in these areas has greatly reduced the number of fishes that feed on these urchins, and so urchin populations have grown significantly,” van Woesik said. “We are seeing areas where you have about 51 urchins per square meter, which is among the highest population density for sea urchins anywhere in the world.”

Those urchins eat the reef, which is already not growing at a healthy rate, van Woesik said. Water pollution and overheated water created by climate change result in a poor environment for the coral to reproduce and grow, leaving the reef even less able to keep up with the pace of erosion caused by the urchins.

Reef growth is generally measured in terms of net carbonate production, which refers to the amount of calcium carbonate produced in a square meter over a year. Prior research in the 1980s found areas in Hawaii with carbonate production around 15 kilograms per square meter, which would signal a healthy, growing reef, van Woesik said. The reef in Hōnaunau Bay today, however, showed an average net carbonate production of only 0.5 kg per square meter, indicating that the reef is growing very slowly.

By combining data gathered through on-site scuba diving with images taken from the air, van Woesik determined that the reef would need to maintain an average of 26% coral cover to break even with the pace of urchin erosion, and a higher cover in order to grow. The average coral cover across all depths was 28%, she said, but areas in shallow depths with more erosion would still need nearly 40% cover to break even.

For the islands they surround, coral reefs like those in Hōnaunau Bay provide important coastal protection against erosion from waves, absorbing up to 97% of incoming wave energy. They are also often vital to the economies of those areas, which rely on the reefs and the fishes that live there. Van Woesik said the study highlights the need for more robust fisheries management in the area to bolster the populations of carnivorous fishes that eat the urchins.

“The reefs cannot keep up with erosion without the help of those natural predators, and these reefs are essential to protecting the islands they surround,” she said. “Without action taken now, we risk allowing these reefs to erode past the point of no return.”