The paper, co-authored by geology professor Ed Keller and colleagues Summer Gray, an assistant professor of environmental studies, Keith Clarke, a professor of geography, and Erica Goto, a postdoctoral scholar who completed her Ph.D. in geography, is published in the International Journal of Disaster Risk Reduction.

The work is part of an ongoing effort to understand and improve how communities prepare for future disasters. “There were a lot of problems because people didn’t know what to do,” said Keller. “We need to learn from that.”

The Montecito debris flows that occurred in January 2018 were the result of a rare confluence of two uncommonly severe events: the Thomas Fire — at that time the largest wildfire in California history — which which for weeks burned through Ventura and Santa Barbara counties; and the intense winter storm that followed, at one point dumping half an inch of rain in a five-minute period on the newly charred mountainside. Add to that combination a topography that is prone to swift floods, as rain-swollen creeks jump their banks, creating new channels.

“All of Montecito was built on these alluvial fans,” Keller said. “The whole place.”

Residents of Montecito were made aware of the possible disaster and given an evacuation order the day before the storm’s arrival, but many chose to stay.

In surveys and interviews with hundreds of respondents, the researchers sought the residents’ reasons for choosing not to evacuate. Lack of knowledge of debris flows seems to have contributed to a false sense of security.

“From the interviews, we learned that they did not know about previous debris flows in Santa Barbara County and in Montecito, and that they didn’t know what a debris flow was,” said Goto, the lead author of the study, which is likely the first paper to dive into the physical systems of and the behaviors surrounding catastrophic debris flows. “And so, they did not understand their risk.”

Unlike wildfires — regular events for Californians — debris flows of the magnitude that occurred in Montecito are exceptionally rare, with an average recurrence interval of about 1,700 years, and a 6% chance of such a catastrophic event occurring in the next 100 years, according to the paper. However, said the researchers, it is important to remember that rare events based on probability do not mean they cannot occur again at shorter time periods. Smaller debris flows are common when rains follow wildfires, Keller pointed out, but they usually don’t make it out of the mountains.

Nevertheless, the researchers said, smaller but hazardous debris flows have flowed beyond the mountain front in recent decades. Also, with climate change bringing more intense wildfire and rainstorms, hazardous debris flows may become more common.

“These big events, such as the one that happened in Montecito in 2018, are a whole different beast,” said Keller, both for the community and for the county, whose job it was to manage the evacuations. “I think (the county) did the best they could — they didn’t understand what they were dealing with, like many people,” he said.

The lack of experience with and knowledge of this type of natural hazard led to a low perception of risk in many of the respondents, who reported that they “felt safe,” and had “no idea about debris flows,” or “did not think I was at risk.” Others, many of whom recently had to leave their homes due to the still-burning Thomas Fire, cited evacuation fatigue and pets as reasons for staying.

The dominant reason for staying given by the respondents was that they were placed in the voluntary evacuation zone in the county’s evacuation map, which at the time of the event was based on Thomas Fire evacuation zones and not on the estimated movement of water, silt and boulders down a hillside. Thus, according to the paper, “many residents were told to evacuate who lived out of the debris flow hazard area, and many residents in the voluntary evacuation zones were in areas subject to debris flows (that is, along a stream corridor close to the channel).”

In the uncertainty before the storm, residents also turned to their social networks to help them decide whether to stay or go, Goto said, something that was “surprising, but also expected since residents did not understand their risk.” Lack of understanding about debris flows is also thought to be a factor behind some last-minute decisions to flee and try to outrun the 30 mile-per-hour flows, which resulted in some residents being swept up in the rush of mud and rocks.

The interviews and surveys also addressed subsequent evacuation notices in March 2018, ahead of heavy storms. The researchers wanted to see whether evacuation compliance would increase significantly after residents had been primed with the experience of the first disaster. Contrary to the research group’s expectations, evacuation compliance between the January and March orders increased slightly, but was not statistically significant, an outcome the study says could be attributed to the relative moderate to high rates of compliance (more than 60% in both cases) — and possibly also loss of confidence in the county after the tragedy of the January debris flows.

Though catastrophic debris flows are uncommon — and precisely because we’re not likely to see another one in the same area in our lifetimes — Goto, Keller and colleagues have been working to glean as much knowledge as possible about the Montecito debris flows from a variety of perspectives, including physical processes, social implications and vulnerability. The memory of the disaster should be kept alive, they say, if only to serve as a warning to present and future residents that the ground under their feet is not as stable as they might think. And with climate change increasing the intensity and frequency of severe events such as wildfires and winter rains, rare events might become more common.

According to Goto, who specializes in the combination of physical and social aspects of disaster risk reduction, residents, particularly those who are new to the area, would benefit from a long-term, onging public awareness program and educations about the risks.

Katie Stack Morgan is the Mars 2020 Deputy Project Scientist and a research scientist at NASA’s Jet Propulsion Laboratory (JPL), and will be providing an update on early results on the Mars 2020 rover mission on Sunday, 10 Oct., at the Geological Society of America’s Connects 2021 annual meeting in Portland, Oregon.

With Perseverance’s high-tech suite of on-board instruments, the scientific team has been analyzing the rocks of the crater floor, interpreted for now as igneous rocks, presumably a volcanic lava flow.

“The idea that this could be a volcanic rock was really appealing to us from a sample return perspective because igneous rocks are great for getting accurate age dates. Jezero was one of the few ancient crater lake sites on Mars that seemed to have both incredible sedimentary deposits as well as volcanic deposits that could help us construct the geologic time scale of Mars,” said Stack Morgan.

The lake system and rivers that drained into Jezero crater were likely active around 3.8-3.6 billion years ago, but the ability to directly date the age of the rocks in laboratories on Earth will provide the first definitive insight into the window of time that Mars may have been a habitable planet.

Using Perseverance’s abrasion tool — which scratches the top surface of the rock to reveal the rock and its textures — the team discovered that the crater floor seems to be composed of coarser-grained igneous minerals, and there are also a variety of salts in the rocks. Observations suggest that water caused extensive weathering and alteration of the crater floor, meaning that the rocks were subjected to water for a significant duration of time.

After using its on-board tools to analyze characteristics of the crater floor, the next phase was for Perseverance to collect a rock sample using its drill feature. However, after Perseverance completed its first attempt at drilling, the core sample tube came up empty.

“We spent a couple of days looking around the rover thinking that the core might have fallen out of the bit. Then we looked back down the drill hole thinking it might never have made it out of the hole. All these searches turned up empty. In the end we concluded that the core was pulverized during drilling,” said Stack Morgan.

The rock likely became so altered and weakened from interactions with water that the vibrations and strength from the Perseverance drill pulverized the sample.

Scientists then targeted another rock that appeared more resistant to weathering, and Perseverance was able to successfully collect two core samples — the first in its sample collection. Perseverance’s cache of samples will be part of a multi-spacecraft handoff, still in development, that will hopefully be returned to Earth in the early 2030s. From there, scientists in laboratories on Earth will date and analyze the rocks to see if there might be any signs of ancient Martian life.

“The rocks of the crater floor were not originally envisioned as the prime astrobiology target of the mission, but Mars always surprises us when we look up close. We are excited to find that even these rocks have experienced sustained interaction with water and could have been habitable for ancient martian microbes,” said Stack Morgan.

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The study utilized topological photonics, an emergent direction in photonics which leverages fundamental ideas of the mathematical field of topology about conserved quantities — topological invariants — that remain constant when altering parts of a geometric object under continuous deformations. One of the simplest examples of such invariants is number of holes, which, for instance, makes donut and mug equivalent from the topological point of view. The topological properties endow photons with helicity, when photons spin as they propagate, leading to unique and unexpected characteristics, such as robustness to defects and unidirectional propagation along interfaces between topologically distinct materials. Thanks to interactions with vibrations in crystals, these helical photons can then be used to channel infrared light along with vibrations.

The implications of this work are broad, in particular allowing researchers to advance Raman spectroscopy, which is used to determine vibrational modes of molecules. The research also holds promise for vibrational spectroscopy — also known as infrared spectroscopy — which measures the interaction of infrared radiation with matter through absorption, emission, or reflection. This can then be utilized to study and identify and characterize chemical substances.

“We coupled helical photons with lattice vibrations in hexagonal boron nitride, creating a new hybrid matter referred to as phonon-polaritons,” said Alexander Khanikaev, lead author and physicist with affiliation in CCNY’s Grove School of Engineering. “It is half light and half vibrations. Since infrared light and lattice vibrations are associated with heat, we created new channels for propagation of light and heat together. Typically, lattice vibrations are very hard to control, and guiding them around defects and sharp corners was impossible before.”

The new methodology can also implement directional radiative heat transfer, a form of energy transfer during which heat is dissipated through electromagnetic waves.

“We can create channels of arbitrary shape for this form of hybrid light and matter excitations to be guided along within a two-dimensional material we created,” added Dr. Sriram Guddala, postdoctoral researcher in Prof. Khanikaev’s group and the first author of the manuscript. “This method also allows us to switch the direction of propagation of vibrations along these channels, forward or backward, simply by switching polarizations handedness of the incident laser beam. Interestingly, as the phonon-polaritons propagate, the vibrations also rotate along with the electric field. This is an entirely novel way of guiding and rotating lattice vibrations, which also makes them helical.”

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A typical transistor is, for most uses, basically a switch. When it’s on, current flows from one side of a semiconductor to the other; switching it off stops the current. Those actions respectively create the binary 1s and 0s of digital information.

Transistor performance critically depends on how reliably a designated amount of current will flow. Defects in the transistor material, such as unwanted “impurity” regions or broken chemical bonds, interrupt and destabilize the flow. These defects can manifest themselves immediately or over a period of time while the device is operating.

Over many years, scientists have found numerous ways to classify and minimize those effects.

But defects become harder to identify as transistor dimensions become almost unimaginably small and switching speeds very high. For some promising semiconductor materials in development — such as silicon carbide (SiC) instead of silicon (Si) alone for novel high-energy, high-temperature devices — there has been no simple and straightforward way to characterize defects in detail.

“The method we developed works with both traditional Si and SiC, allowing us for the first time to identify not only the type of defect but the number of them in a given space with a simple DC measurement,” said NIST’s James Ashton, who conducted the research with colleagues at NIST and Pennsylvania State University. They published their results on October 6 in the Journal of Applied Physics. The research focuses on interactions between the two kinds of electrical charge carriers in a transistor: negatively charged electrons and positively charged “holes,” which are spaces where an electron is missing from the local atomic structure.

When a transistor is functioning correctly, a specific electron current flows along the desired path. (Holes can also form a current. This research explored electron current, the most common arrangement.) If the current encounters a defect, electrons are trapped or displaced, and can then combine with holes to form an electrically neutral area in a process known as recombination.

Each recombination removes an electron from the current. Multiple defects cause current losses that lead to malfunction. The goal is to determine where the defects are, their specific effects, and — ideally — the number of them.

“We wanted to provide manufacturers with a way to identify and quantify defects as they are testing different new materials,” said NIST co-author Jason Ryan. “We did that by creating a physics model of a defect-detection technique that has been widely used but poorly understood until now. We then conducted proof-of-principle experiments that confirmed our model.”

In a classic metal oxide semiconductor design a metal electrode called the gate is placed atop a thin insulating silicon dioxide layer. Below that interface is the bulk body of the semiconductor.

On one side of the gate is an input terminal, called the source; on the other is an output (drain). Scientists investigate the dynamics of current flow by changing the “bias” voltages applied to the gate, source and drain, all of which affect how current moves.

In the new work, the NIST and Penn State researchers concentrated on one particular region that is typically only about 1 billionth of a meter thick and a millionth of a meter long: the boundary, or channel, between the thin oxide layer and the bulk semiconductor body.

“This layer is hugely important because the effect of a voltage on the metal overtop of the oxide of the transistor acts to change how many electrons are within the channel region under the oxide; this region controls the resistance of the device from source to drain,” Ashton said. “The performance of this layer is dependent on how many defects exist. The detection method we investigated was previously unable to determine how many defects were within this layer.”

One sensitive method to detect defects in the channel is called electrically detected magnetic resonance (EDMR), which is similar in principle to medical MRI. Particles such as protons and electrons have a quantum property called spin, which makes them act like tiny bar magnets with two opposite magnetic poles. In EDMR, the transistor is irradiated with microwaves at a frequency about four times higher than a microwave oven. Experimenters apply a magnetic field to the device and gradually vary its strength while measuring the output current.

At exactly the right combination of frequency and field strength, electrons at defects “flip” — reverse their poles. This causes some to lose enough energy that they recombine with holes at defects in the channel, reducing the current. The channel activity can be hard to measure, however, because the high volume of “noise” from recombination in the bulk of the semiconductor.

To focus exclusively on activity in the channel, researchers use a technique called bipolar amplification effect (BAE), which is achieved by arranging the bias voltages applied to the source, gate and drain in a particular configuration. “So because of the biasing we use in BAE and because we measure current levels at the drain,” Ashton said, “we can eliminate interference from other things going on in the transistor. We can select just defects that we care about within the channel.”

The exact mechanism by which BAE operates was not known until the team developed its model. “The only measurement results were qualitative — that is, they could tell the kinds of defects in the channel but not the number,” said co-author Patrick Lenahan, a distinguished professor of engineering science and mechanics at Penn State.

Before the model of BAE, the scheme was used strictly as a resource for applying voltages and controlling currents for EDMR measurements, which is useful for a more qualitative defect identification. The new model enables BAE as a tool to quantitatively measure the number of defects and to do so with just currents and voltages. The parameter of importance is the interface defect density, which is a number that describes how many defects are within some area of the semiconductor-oxide interface. The BAE model gives researchers a mathematical description of how the BAE current is related to the defect density.

The model, which the researchers tested in a set of proof-of-concept experiments on metal oxide semiconductor transistors, makes quantitative measurements possible. “Now we can account for the variation in charge carrier distribution throughout the channel region,” Ashton said. “This opens up the possibilities of what can be measured with a simple electrical measurement.”

“This technique can provide unique insight into the presence of these destabilizing transistor defects and a path to mechanistic understanding of their formation,” said Markus Kuhn, formerly at Intel and now senior director of semiconductor metrology and fellow at Rigaku, who was not involved in the research. “With such knowledge, there would be greater opportunity to control and reduce them in order to improve transistor performance and reliability. This would be an opportunity to further enhance design of the chip circuitry and device performance leading to better performing products.”

University of Arizona engineers have developed a type of wearable they call a “biosymbiotic device,” which has several unprecedented benefits. Not only are the devices custom 3D-printed and based on body scans of wearers, but they can operate continuously using a combination of wireless power transfer and compact energy storage. The team, led by Philipp Gutruf, assistant professor of biomedical engineering and Craig M. Berge Faculty Fellow in the College of Engineering, published its findings today in the journal Science Advances.

“There’s nothing like this out there,” said Gutruf, a member of the university’s BIO5 Institute. “We introduce a completely new concept of tailoring a device directly to a person and using wireless power casting to allow the device to operate 24/7 without ever needing to recharge.”

Custom Fit Enables Precise Monitoring

Current wearable sensors face various limitations. Smartwatches, for example, need to be charged, and they can only gather limited amounts of data due to their placement on the wrist. By using 3D scans of a wearer’s body, which can be gathered via methods including MRIs, CT scans and even carefully combined smartphone images, Gutruf and his team can 3D-print custom-fitted devices that wrap around various body parts. Think a virtually unnoticeable, lightweight, breathable, mesh cuff designed specifically for your bicep, calf or torso. The ability to specialize sensor placement allows researchers to measure physiological parameters they otherwise couldn’t.

“If you want something close to core body temperature continuously, for example, you’d want to place the sensor in the armpit. Or, if you want to measure the way your bicep deforms during exercise, we can place a sensor in the devices that can accomplish that,” said Tucker Stuart, a doctoral student in biomedical engineering and first author on the paper. “Because of the way we fabricate the device and attach it to the body, we’re able to use it to gather data a traditional, wrist-mounted wearable device wouldn’t be able to collect.”

Because these biosymbiotic devices are custom fitted to the wearer, they’re also highly sensitive. Gutruf’s team tested the device’s ability to monitor parameters including temperature and strain while a person jumped, walked on a treadmill and used a rowing machine. In the rowing machine test, subjects wore multiple devices, tracking exercise intensity and the way muscles deformed with fine detail. The devices were accurate enough to detect body temperature changes induced by walking up a single flight of stairs.

Continuous, Wireless and Effortless

Gutruf and his team aren’t the first to adapt wearables to track health and body function. However, current wearables do not have the ability to track metrics continuously, or with enough precision to make medically meaningful conclusions.

Some wearables used by researchers are patches that stick to the skin, but they come off when skin goes through its normal shedding process, or sometimes when a subject sweats. Even highly sophisticated wearables used in clinical settings, such as ECG monitors, face these issues. Also, they aren’t wireless, which severely limits mobility. Patients can’t go about their normal daily routines if they’re tethered to bulky external devices.

The biosymbiotic device that Gutruf’s team has introduced uses no adhesive, and it receives its power from a wireless system with a range of several meters. The device also includes a small energy storage unit, so that it will function even if the wearer goes out of the system’s range, including out of the house.

“These devices are designed to require no interaction with the wearer,” Gutruf said. “It’s as simple as putting the device on. Then you forget about it, and it does its job.”

This research was funded by the Flinn Foundation Translational Bioscience Seed Grants Pilot Program. The team has also been working with Tech Launch Arizona, the commercialization arm of the university, to protect the intellectual property and launch a startup to bring the technology to market.

Video of new wearable sensor: https://www.youtube.com/watch?v=MhSeWGbuVTU