They published their results in Advanced Materials.

“People have been developing soft and stretchable conductors for almost a decade, but the conductivity is not usually very high,” said corresponding author Tao Zhou, Penn State assistant professor of engineering science and mechanics and of biomedical engineering in the College of Engineering and of materials science and engineering in the College of Earth and Mineral Sciences. “Researchers realized they could reach high conductivity with liquid metal-based conductors, but the significant limitation of that is that it requires a secondary method to activate the material before it can reach a high conductivity.”

Liquid metal-based stretchable conductors suffer from inherent complexity and challenges posed by the post-fabrication activation process, the researchers said. The secondary activation methods include stretching, compressing, shear friction, mechanical sintering and laser activation, all of which can lead to challenges in fabrication and can cause the liquid metal to leak, resulting in device failure.

“Our method does not require any secondary activation to make the material conductive,” said Zhou, who also has affiliations with the Huck Institutes of the Life Sciences and the Materials Research Institute. “The material can self-assemble to make its bottom surface be very conductive and its top surface self-insulated.”

In the new method, the researchers combine liquid metal, a conductive polymer mixture called PEDOT:PSS and hydrophilic polyurethane that enables the liquid metal to transform into particles. When the composite soft material is printed and heated, the liquid metal particles on its bottom surface self-assemble into a conductive pathway. The particles in the top layer are exposed to an oxygen-rich environment and oxidize, forming an insulated top layer. The conductive layer is critical for conveying information to the sensor — such as muscle activity recordings and strain sensing on the body — while the insulated layer helps prevent signal leakage that could lead to less accurate data collection.

“Our innovation here is a materials one,” Zhou said. “Normally, when liquid metal mixes with polymers, they are not conductive and require secondary activation to achieve conductivity. But these three components allow for the self-assembly that produces the high conductivity of soft and stretchable material without a secondary activation method.”

The material can also be 3D-printed, Zhou said, making it easier to fabricate wearable devices. The researchers are continuing to explore potential applications, with a focus on assistive technology for people with disabilities.

The papers other authors are Salahuddin Ahmed, Marzia Momin and Jiashu Ren, all doctoral students in the Penn State engineering science and mechanics department, and Hyunjin Lee, a doctoral student in the biomedical engineering department at Penn State. This work was supported by the National Taipei University of Technology-Penn State Collaborative Seed Grant Program and by the Department of Engineering Science and Mechanics, the Materials Research Institute and the Huck Institutes of the Life Sciences at Penn State.

The research team, led by scientists from the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR), used an innovative model that allows for higher-resolution simulations of hurricane formation than ever before. This allowed researchers to study the effects of increased regional moisture over Africa, which is the birthplace of weather systems that later produce hurricanes over the Atlantic.

Past research has suggested that warmer ocean water and a moister atmosphere could cause hurricanes to become more intense with greater amounts of rainfall. But how atmospheric moisture, which is predicted to increase in a warming climate, may be impacting hurricane formation itself has not been studied in detail until now.

The researchers found that a moister environment produced weaker and slower-moving African easterly waves, or disturbances which are the primary precursor or “seed” for hurricanes in the Atlantic. The addition of moisture moved the location of thunderstorms within the wave, making it harder for the wave to grow. Increased moisture also slowed the movement of the wave resulting in weaker and delayed hurricane seed formation by the time it reached eastern Atlantic waters.

“Considerable work during the last two decades has emphasized the role of deep moist convection to explain the development of African easterly waves,” said NSF NCAR scientist and lead author Kelly Núñez Ocasio. “But, the precise role of moisture has proven somewhat elusive. With the development of new modeling capabilities, I was able to focus on the role of moisture in cyclogenesis stemming from the hurricane seed.”

The study is funded by NSF NCAR and published in the Journal of Advances in Modeling Earth Systems. Núñez Ocasio pursued the research through the NSF NCAR Advanced Study Program which allows graduate and postdoctoral students to focus on emerging areas of science.

Next-gen modeling

The birth of hurricanes and other tropical cyclones, known as cyclogenesis, is a complex process where small-scale weather events and large-scale atmospherics happen simultaneously. This complexity has made it difficult to study and model the formation of tropical cyclones. Most climate models provide only a grainy picture of what is happening with localized weather, which makes it difficult to learn anything about the role of individual ingredients, like moisture, that mix together to create cyclogenesis.

To address this, the research team turned to the Model for Prediction Across Scales (MPAS). MPAS has the ability to model weather both locally and globally. This capability allowed Núñez Ocasio and her colleagues to zoom out and simulate global moisture and then zoom in to see how that would interact with localized weather events that lead to the formation of tropical cyclones.

The researchers started the experiment by using MPAS to reproduce a moisture-driven African easterly wave that became hurricane Helene in 2006. The team used that base to add or take away moisture and study what happened with those changes.

“When I increased the moisture we saw more convection and thunderstorms, which is to be expected; however, we discovered that the waves struggled to pair with the more intense and deep convection,” said Núñez Ocasio. “With increased moisture, the energy source of tropical cyclone seeds moved north and further away, reducing the kinetic energy available to the African easterly wave, which led to weak, energy-starved tropical cyclone seeds.”

Studying the evolution of tropical cyclones after this initial phase was outside the scope of this study. More research is needed to discover whether these weaker seeds lead to weaker tropical cyclones and hurricanes or if it will just take them longer to form.

The conditions leading to tropical cyclone formation are complex, but researchers hope these newer modeling techniques will lead to better predictions. For instance, Núñez Ocasio is beginning to run simulations where she alters other atmospheric variables key to generating tropical cyclones.

“In addition to moisture, I’m altering other variables in the model to more realistically reproduce a future climate scenario in collaboration with Erin Dougherty, NSF NCAR project scientist,” she said. “So far, I’m seeing similarities to the results of this study even as I alter those other significant pieces.”

Carbonate fragments provide remarkable information

Professor Cees W. Passchier and Dr. Gül Sürmelihindi from Johannes Gutenberg University Mainz (JGU), in collaboration with colleagues from France and Austria, have now unraveled the history of the mill complex using calcium carbonate deposits that are now stored in the Archaeological Museum of Arles. These deposits had formed towards the end of the roughly 100-year operational life of the Barbegal water mills on the sides and base of the wooden supply system that conveyed the water to the wheels. “We show that it is possible to reconstruct to a large extent the history of a water mill on the basis of such carbonate deposits,” stated Passchier, head of the JGU team. First, the researchers had to fit some of the total of 140 stored pieces together like a jigsaw puzzle, then they analyzed the layers using various techniques, including mass spectrometry.

Wooden water wheels and gutters were replaced

The researchers have now published their results in Geoarchaeology. “We were able to show, for example, that wooden water wheels and water channels had to be replaced after three to eight years. In at least one case, an old water wheel was replaced by a larger one,” said Passchier. The researchers drew this conclusion from the unusual shape of the carbonate deposits that had formed in the water channel. While the lower and earlier layers indicate that water levels must have originally been relatively low, upper and later carbonate layers indicate a higher water level. The possibility that there was originally less water flowing through the water channel which was subsequently increased was rejected by the researchers. They established that — for a gently sloping water channel and low water level — the amount of water provided would not have been sufficient to drive a mill wheel. Therefore, the inclination of the water channel must have been altered, from what was at first a steeper angle with a low water level to a shallower slope transporting water at a correspondingly higher level. “The entire structure of this water mill must have been modified,” said Passchier. “If you uplift the water channel alone, the water tends to splatter, losing the power to drive the wheel efficiently. Thus, when you uplift the water channel, you also need a larger water wheel.” In fact, a section of carbonate deposit formed on the water wheel corroborates this conclusion as it does not contain all the carbonate layers but only those of the latter years of operation.

Results of isotope analysis provide evidence of the mill’s service life

Using isotope analysis of the carbonate layers, the researchers were even able to ascertain the operating periods before which parts of the mill required renewal. Carbonate contains oxygen and the relative ratios of oxygen isotopes differ depending on water temperature. Based on the isotope composition in the carbonate layers, the researchers were able to infer water temperatures and thus identify the seasons in which the layers were deposited. They concluded that the carbonate from the samples in the Archaeological Museum in Arles had been deposited in the water channels over a period of seven to eight years. “The uppermost and thus youngest carbonate layer contains mollusk shells and fragments of wood, showing that the mill must have been abandoned by then and was disintegrating. The water continued to flow for a while so that carbonate deposits also continued to form, but maintenance of the water channels ceased,” said Passchier.

The researchers were able to answer yet another question. It was not previously known whether the mills had been run in combination by a single operator or whether the 16 water wheels had been used independently of each other. Judging from the layers of three investigated water channels, which are clearly different from each other, the mills were in operation separately — at least towards the end of their lifetime. Moreover, the western side of the complex was abandoned earlier than the eastern side. Finally, long pieces of carbonate from the water channels were later used as partition screens in a water basin for other industrial purposes after the mills had already been abandoned.