A white dwarf so massive that it might collapse

Astronomers have discovered the smallest and most massive white dwarf ever seen. The smoldering cinder, which formed when two less massive white dwarfs merged, is about 4,300 kilometers across, or somewhat larger than Earth’s moon.

Though the white dwarf is small, it is heavy, “packing a mass greater than that of our sun into a body about the size of our moon,” says Ilaria Caiazzo, the Sherman Fairchild Postdoctoral Scholar Research Associate in Theoretical Astrophysics at Caltech and lead author of the new study appearing in the July 1 issue of the journal Nature. “It may seem counterintuitive, but smaller white dwarfs happen to be more massive. This is due to the fact that white dwarfs lack the nuclear burning that keep up normal stars against their own self gravity, and their size is instead regulated by quantum mechanics.”

The discovery was made by the Zwicky Transient Facility, or ZTF, which operates at Caltech’s Palomar Observatory; a host of other telescopes helped characterize the dead star, including: the 200-inch Hale Telescope at Palomar, the W. M. Keck Observatory’s Keck I telescope, the European Gaia space observatory, the University of Hawaii’s Pan-STARRS (Panoramic Survey Telescope and Rapid Response System), and NASA’s Neil Gehrels Swift Observatory (which was renamed after Gehrels, a Caltech alumnus, who passed away in 2017). ZTF is funded by the National Science Foundation (NSF) and other collaborators.

White dwarfs are the collapsed remnants of stars that were once about eight times the mass of our sun or lighter. Our sun, for example, after it first puffs up into a red giant in about 5 billion years, will ultimately slough off its outer layers and shrink down into a compact white dwarf. About 97 percent of all stars become white dwarfs.

While our sun is alone in space without a stellar partner, many stars orbit around each other in pairs. The stars grow old together, and if they are both less than eight solar-masses, they will both evolve into white dwarfs.

The new discovery provides an example of what can happen after this phase. The pair of white dwarfs, which spiral around each other, lose energy in the form of gravitational waves and ultimately merge. If the dead stars are massive enough, they explode in what is called a type Ia supernova. But if they are below a certain mass threshold, they combine together into a new white dwarf that is heavier than either progenitor star. This process of merging boosts the magnetic field of that star and speeds up its rotation compared to that of the progenitors.

Astronomers say that the newfound tiny white dwarf, named ZTF J1901+1458, took the latter route of evolution. Because the sum of the masses of its progenitors was just below the mass limit at which a white dwarf would explode, the merger produced a white dwarf 1.35 times the mass of our sun. The white dwarf has an extreme magnetic field almost one billion times stronger than our sun’s and whips around on its axis at a frenzied pace of one revolution every seven minutes. (The zippiest white dwarf known, called EPIC 228939929, rotates every 5.3 minutes).

“We caught this very interesting object that wasn’t quite massive enough to explode,” says Caiazzo. “We are truly probing how massive a white dwarf can be.”

What is more, Caiazzo and her collaborators think that the merged white dwarf may be massive enough to evolve into a neutron-rich dead star, or neutron star, which typically forms when a star much more massive than our sun explodes in a supernova.

“This is highly speculative, but it’s possible that the white dwarf is massive enough to further collapse into a neutron star,” says Caiazzo. “It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed.”

If this neutron star formation hypothesis is correct, it may mean that a significant portion of other neutron stars take shape in this way. The newfound object’s close proximity (about 130 light-years away) and its young age (about 100 million years old or less) indicate that similar objects may occur more commonly in our galaxy.

Magnetic and Fast

The white dwarf ZTF J1901+1458 was first spotted by Caiazzo’s colleague Kevin Burdge, a postdoctoral scholar at Caltech, after searching through all-sky images captured by ZTF. ZTF scans the entire northern sky every two nights looking for objects that blink, erupt, move, or otherwise change in brightness. This particular white dwarf, when analyzed in combination with data from Gaia, stood out for being very massive and having a rapid rotation.

“Fast time-domain surveys like ZTF are powerful tools for studying phenomena on extremely short timescales, such as this object, the most massive white dwarf known, which completes a full rotation every few minutes,” says Burdge. In 2019, Burdge led the team that discovered a pair of white dwarfs zipping around each other every seven minutes. “No one has systematically been able to explore short-timescale astronomical phenomena on this kind of scale until now. The results of these efforts are stunning.”

The team then analyzed the spectrum of the star using Keck I, and that is when Caiazzo was struck by the signatures of a very powerful magnetic field and realized that she and her team had found something “very special,” as she says. The strength of the magnetic field together with the seven-minute rotational speed of the object indicated that it was the result of two smaller white dwarfs coalescing into one.

Data from Swift, which observes ultraviolet light, helped nail down the size and mass of the white dwarf, further painting a picture of a very extreme object. With a diameter of 4,300 kilometers, or 2,670 miles, ZTF J1901+1458 secures the title for the smallest known white dwarf, edging out previous record holders, RE J0317-853 and WD 1832+089, which each have diameters of about 5,000 kilometers, or 3,100 miles.

In the future, Caiazzo hopes to use ZTF to find more white dwarfs like this one, and, in general, to study the population as a whole. “There are so many questions to address, such as what is the rate of white dwarf mergers in the galaxy, and is it enough to explain the number of type Ia supernovae? How is a magnetic field generated in these powerful events, and why is there such diversity in magnetic field strengths among white dwarfs? Finding a large population of white dwarfs born from mergers will help us answer all these questions and more.”

“The discovery of this unique object illustrates the power of ZTF. By making hundreds of observations of the entire northern sky spread over several years, we can continue to identify exotic objects like this one,” says co-author Tom Prince, the Ira S. Bowen Professor of Physics at Caltech.

Caltech’s ZTF is funded by the NSF and an international collaboration of partners. Additional support comes from the Heising–Simons Foundation and from Caltech. ZTF data are processed and archived by IPAC. NASA supports ZTF’s search for near-Earth objects through the Near-Earth Object Observations program.

The study, titled “A highly magnetised and rapidly rotating white dwarf as small as the Moon,” was funded by the Rose Hills Foundation, the Alfred P. Sloan Foundation, NASA, the Heising–Simons Foundation, the A. F. Morrison Fellowship of the Lick Observatory, the NSF, and the Natural Sciences and Engineering Research Council of Canada.

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Producing Clean Energy Can Diminish Earthquake Risk

In the months following the July 5, 2019 magnitude-7.1 earthquake in Ridgecrest, California, seismologists recorded thousands of aftershocks in the region. Surprisingly, none were seen in the Coso geothermal field, an area only about 10 kilometers from the surface ruptures caused by the main shock.

Now, Caltech researchers have discovered that the operations related to geothermal energy production at Coso over the last 30 years have de-stressed the region, making the area less prone to earthquakes. These findings could indicate ways to systematically de-stress high-risk earthquake regions, while simultaneously building clean energy infrastructure.

The research was conducted in the laboratory of Jean-Philippe Avouac, Earle C. Anthony Professor of Geology and Mechanical and Civil Engineering. A paper describing the study appears in the journal Nature on July 1.

Geothermal fields, like the Coso region, are areas where the subsurface temperatures are particularly high, for example, as a result of volcanic or tectonic activity. This heat can be used create clean energy that requires no burning of fossil fuels. To harness this energy, water is pumped down into the ground, where the high temperatures heat up the water; when the water is brought back up to the surface, that heat energy is used to generate electricity.

Importantly, during the development of a geothermal field, many small earthquakes (around magnitude 4) are triggered when the water is pumped in. This is generally seen as source of concern; a number of geothermal projects have been abandoned because of such “induced” seismicity. However, in this new study, the researchers found that these little earthquakes as well as the “silent” or aseismic deformation (occurring without producing an earthquake) caused by the injection of fluid actually relieves stress and thus lowers the risk of a larger earthquake in the region.

“Geothermal energy is clean energy, and we would like to have as much clean energy as possible,” says Avouac. “Induced seismicity—the triggering of many small earthquakes—during the initial development of a geothermal field has been seen as an impediment to building more of this infrastructure. But our study shows that there is actually a benefit to this. You could imagine developing geothermal fields all along the San Andreas Fault, for example, where you would both get clean energy and diminish the risk of a large earthquake.”

Led by Caltech postdoctoral scholar Kyungjae Im, the team sought to model what is happening under the surface of a geothermal field that has been developed for energy production. Using a technique called synthetic aperture radar (SAR) interferometry, geoscientists have measured that the surface of the Coso geothermal field has deformed and sunk by tens of centimeters in the decades since its development. Im built a model of this deformation and determined that the underground was thermally contracting due to the water being pumped in.

Im concluded that this thermal contraction both relieved some tension in the Coso area and allowed the ground to slip “silently”—that is, in a smooth way that does not produce earthquakes. This explains why the Coso area experienced no major aftershocks after the large July 5, 2019 quake: there was less stress underground because it had already been relieved by the geothermal activity.

“Our study shows that by injecting cold water, you can actually suppress seismicity down the road,” says Im. “But it is still not without risk: when you start developing the field, there is a risk that the small induced earthquakes could potentially grow into a large one. But in principle, over time, the risk of large earthquakes in the region is less than if you had not been developing the field. You are accelerating the seismicity for a little while, so the risk that you get the large one is temporarily higher. But if you look at the risk of having a magnitude 7 or 8 over a long period of time, over 15 years or so, it will be much lower. It is part of our research objective to develop methods to quantify this effect precisely. It will never be zero risk, but our study shows that we ought to do more research into this method of reducing the probability of a large earthquake.”

“Both thermal stress release and hydrofracking can release the accumulated stress and therefore reduce future large earthquakes but, at the same time, still have a risk for inducing large earthquakes during the stress release,” explains Im. “The Coso case is the desired example in that the stress release is done without inducing a large earthquake. It could be due to the nature of thermal destressing, which is slow, intense, and localized comparing to hydrofracking. But to confirming this requires further research.”

The paper is titled “Ridgecrest Aftershocks at Coso Suppressed by Thermal Destressing.” Kyungjae Im is the study’s first author. In addition to Im and Avouac, additional co-authors are Caltech postdoctoral scholar Elías Heimisson and Derek Elsworth of Penn State University. Funding was provided by the National Science Foundation via the Industry-University Cooperative Research Center for Geomechanics and Mitigation of Geohazards and the Southern California Earthquake Center.

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Identifying the Neural Link Between Gut Bacteria and Social Behavior in Mice

This diagram illustrates the cascade of changes occurring in the mouse body and brain in the absence of a gut microbiome. Lack of gut microbes leads the adrenal gland to produce more corticosterone, a stress hormone, which then influences a neural circuit controlling social behavior in the brain, making the mouse exhibit antisocial behaviors.

Could the germs that live inside of our bodies be affecting our ability to socialize and make friends? Research conducted in recent decades suggests that the answer—for mice—is yes.

Research has shown that the communities of bacteria that live in a mouse’s gut are essential for the animals to exhibit normal social behavior with other mice. Mice that have been bred to be germ-free, without a gut microbiome, display significant antisocial behaviors, such as avoiding a stranger mouse rather than interacting with it. How do microbes influence an animal’s behavior? In other words, what is the chain of events happening on the molecular and cellular levels, from gut bacteria to the brain to behavioral changes?

Now, a new study has identified a specific circuit of neurons that is directly influenced by the gut microbiome and is subsequently responsible for antisocial behaviors in mice that lack a gut microbiome. Transplants of fecal matter from mice with healthy gut microbiomes into these germ-free mice were sufficient to change the activity of these neurons and thus improve their social behavior. The researchers also identified a specific bacterial species that can increase sociability.

Identifying the interactions between gut microbes, neurons, and whole-organism health effects (like behavioral changes) may be an important line of inquiry into ways to, someday, help improve social deficits, such as those concurrent with depression and autism. Current practices for treating these types of issues include prescribing pharmaceuticals, such as antidepressants and anxiolytic drugs. However, it is difficult to get these drugs into the right brain regions at the right concentrations, and much of the drug ends up throughout the body. Understanding the gut–brain connections adds to evidence that neuropsychiatric disorders can be indirectly improved by treating the gut microbiome, which is much easier to access pharmaceutically than the brain.

The research was conducted primarily in the laboratory of Sarkis Mazmanian, Luis B. and Nelly Soux Professor of Microbiology and Heritage Medical Research Institute Investigator. A paper describing the study appears in the journal Nature on June 30.

It had already been shown that, on a chemical level, germ-free mice have significantly higher levels of the hormone corticosterone (the analog of the so-called stress hormone, cortisol, in humans) than mice with healthy microbiomes. The team of researchers, led by former Mazmanian lab postdoctoral scholar Wei-Li Wu, aimed to identify the neurons that were both affected by corticosterone and played a role in social behaviors.

“By altering the mouse’s microbiome, we were able to change levels of corticosterone: less microbiome means more stress hormone,” says Mazmanian. “There are a lot of neurons in the body that respond to corticosterone—called glucocorticoid receptor-positive neurons—and we wanted to know which cell populations and brain regions were then responsible for the altered social behaviors in germ-free mice?”

After identifying several subsets of neurons in the brain involving stress control, the team used chemical and genetic tools to artificially block corticosterone from activating these neurons in mice without a microbiome. These mice, despite lacking a gut microbiome, were able to exhibit more normal social behavior because their neurons were not responding to the stress hormone.

So, what was it about the gut bacteria—or lack thereof—that was causing increased corticosterone levels in the first place? To address this, the team conducted fecal transplants from wild-type mice with normal gut microbiota into germ-free mice. These mice then showed decreased corticosterone levels and more normal social behavior. The team then systematically identified a species of bacteria that mediated this improvement, namely Enterococcus faecalis. Germ-free mice that were colonized with E. faecalis showed improved social behaviors and lowered corticosterone levels. The mechanisms through which E. faecalis is able to mediate this improvement will be the subject of future research.

“A number of studies have shown that the gut microbiome impacts complex behaviors in mice, such as sociability. The underlying neuronal circuits that mediate the microbiome’s influence on behavior had not been previously discovered. This work strengthens the emerging appreciation of the profound effects of the gut-brain connection,” says Mazmanian. “Conceptually, the findings lay the groundwork for exploring similar effects in humans.”

Wu is now a faculty member at National Cheng Kung University in Taiwan. Future directions for this research include zooming in closer to the host-bacteria relationship, identifying the molecular signals produced by gut microbes, and how these signals influence the host. Mazmanian and Wu plan to continue their collaboration.

“Our study benefited tremendously from a number of collaborations, including critical contributions from the laboratories of Viviana Gradinaru and Rustem Ismagilov at Caltech,” says Mazmanian.

The paper is titled “Microbiota regulate social behavior via stress response neurons in the brain.” Wei-Li Wu is the study’s first author. In addition to Mazmanian, Caltech co-authors are former research technician assistant Mark Adame; graduate student Jacob Barlow; former Mazmanian lab postdoctoral scholar Gil Sharon; former graduate student Catherine Schretter (PhD ’19); postdoctoral scholar Brittany Needham, former undergraduate Madelyn Wang (BS ’19); graduate students Weiyi Tang, James Ousey, and Reem Abdel-Haq; former research associate Keith Beadle; Viviana Gradinaru (BS ’05), professor of neuroscience and biological engineering, Heritage Medical Research Institute Investigator, and director of the Center for Molecular and Cellular Neuroscience at the T&C Chen Institute for Neuroscience; and Rustem Ismagilov, Ethel Wilson Bowles and Robert Bowles Professor of Chemistry and Chemical Engineering, and director of the Jacobs Institute for Molecular Engineering for Medicine. Additional co-authors are Chia-Wei Liou, Tzu-Ting Lai, Yuan-Yuan Lin, and Tzu-Hsuan Yao of National Cheng Kung University in Taiwan. Funding was provided by the Ministry of Science and Technology in Taiwan, Higher Education Sprout Project, Ministry of Education to the Headquarters of University Advancement; a National Institutes of Health (NIH) Biotechnology Leadership Pre-doctoral Training Program (BLP) Fellowship; the National Science Foundation Graduate Research Fellowship Program; the Jacobs Institute for Molecular Engineering for Medicine, the Kenneth Rainin Foundation Innovator Award; and Lynda and Blaine Fetter, Charlie Trimble (BS ’63, MS ’64), the Heritage Medical Research Institute, and the NIH. Sarkis Mazmanian is an affiliated faculty member with the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech.

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New approach could change how we track extreme air pollution events

When extreme and dangerous air pollution events strike and blanket the air with hazardous levels of pollution, it causes a major threat to public health and safety. It’s also exceedingly challenging to monitor. The pollutants move quickly through the atmosphere, and can undergo chemical transformations from one form to another, leaving it difficult to predict the level of human exposure. 

In the United States, the primary sources of outdoor air-quality data are from ground-based, government-regulated air-quality monitoring systems that measure pollutants such as ozone and particulate matter. Due to the high cost of these high-performing systems, the number of monitors measuring air quality across a geographic area is relatively sparse. As a result, these systems are not well-suited for monitoring extreme air-quality events, in which pollutant levels can be exceedingly high and variable over relatively short distances.  

In a new study, researchers in MIT’s Department of Civil and Environmental Engineering (CEE) demonstrate an alternate approach for monitoring extreme air-quality events with the use of low-cost sensor (LCS) networks. The work was carried out in mid-2018 on the Island of Hawaii, when the eruption of the Kilauea volcano filled the air with toxic sulfurous gases and particles (“volcanic smog” or “vog”). In response, the researchers developed and deployed a network of 40 low-cost sensors around the island to monitor the vog in real-time, which provided much higher resolution of localized levels of air pollution than existing air-quality measurements.
   
The paper, published in PNAS (Proceedings of the National Academy of Sciences), demonstrates the power of LCS networks in their ability to map pollution exposure and chemical transformation of air pollutants for air-quality research, public health monitoring, and emergency response. 

“There is a real demand for this kind of data and information about the air people are breathing,” says lead author Ben Crawford, assistant professor in the Department of Geography and Environmental Sciences at the University of Colorado at Denver, who deployed the sensors in Hawaii while a postdoc at MIT. “We need these low-cost sensors and the regulatory air monitoring systems to give us a better understanding of what’s happening in the air we are breathing.”

Built for remote air quality sensing

The custom MIT sensors provided real-time levels of two toxic components of vog: sulfur dioxide gas (SO₂) and airborne particles, also known as particulate matter. The sensors are also solar powered, so they were deployed in remote areas of the island and communicated wirelessly over the cellular network. Because of the small size and low cost of the sensors, the researchers were able to place the sensors at different distances downwind of the volcano, to estimate the full distribution of pollution levels that people were exposed to in all areas around the island. 

“The data showed a wide range of pollutant exposure,” says co-author Jesse Kroll, professor in MIT’s departments of Civil and Environmental Engineering and Chemical Engineering. “Some residents were exposed to clean air the entire time, while people living in different points downwind of the volcano were exposed to different mixes of pollutants. This in itself isn’t surprising, but with the large number of sensors deployed we were able to quantify these exposures with much higher resolution than is normally possible.”

Capturing the pollutant exposure in the atmosphere around the island allowed the researchers to witness how the plume was chemically changing with time. “By having sensors at different distances downwind of the event we were able to estimate the rate at which one pollutant, sulfur dioxide, reacts in the atmosphere and converts into a different one, particulate matter,” adds Kroll. 

Prototypes of the sensors were originally developed as part of the CEE subject 1.091 (Traveling Research Environmental Experiences, or TREX), an annual undergraduate fieldwork project that takes students to Hawaii to conduct research over Independent Activities Period in January. Over the years, the students discovered limitations of LCS, especially their low accuracy relative to more expensive monitors. Prior to deployment, the researchers co-located all sensors with state monitoring stations run by the Hawaii Department of Health, providing an accurate calibration that was used throughout the entire eruption. 

Tracking smog and wildfires

Hawaii’s pristine environment, with its small number of pollutants, simple chemistry, and straightforward meteorology, was the ideal test environment to establish the viability of this approach. But this general approach could also be used for measuring urban smog and wildfires, according to the researchers. The low-cost, compact, solar-powered design of the sensors allows for the technology to be deployed in a number of configurations, allowing it to be linked to other air-quality data sources and technologies. 

People can use the information from sensors, together with other data sources, to make informed decisions about the health and safety of communities. It also provides an entryway into educating and bringing peace of mind to communities that live with the dangers and harmful effects from reoccurring extreme air-quality events.  

“One of the most exciting parts of this research project was using the sensors for both science and community engagement,” says Crawford. “Since we placed sensors at schools, we went into classrooms and talked about air quality and the ‘vog,’ and we had little demo sensors. It was a really fun way to engage with students about a global environmental issue that was relevant to them because they have lived through this eruption.”

Besides schools, the researchers also placed the MIT sensors at health clinics and some private residences. To provide public knowledge of Kilauea’s vog, the data were shared on a local website created by the researchers that continues to measure air quality on the island today. “These types of sensors provide a real opportunity for people and communities to engage in their own air-quality monitoring that’s independent of government monitoring systems,” adds Crawford. 

Poor air quality is one of the largest environmental risk factors for premature mortality, heightened by extreme air-quality events that are becoming annual events in parts of the world. LCS networks provide a way forward for other communities to monitor air quality, especially resource-limited regions where air-quality monitoring systems are even more sparse or nonexistent.

“It’s crucial from a public health perspective to improve our air quality worldwide. A key step in doing that is identifying the sources of the pollution, as well as the exact mix of pollutants that people are exposed to. Networks of low-cost sensors are great tools for providing such data,” says Kroll.  

Additional co-authors of the study include David Hagan, PhD ’20; Professor Colette Heald of MIT’s departments of Civil and Environmental Engineering and Earth, Atmospheric and Planetary Sciences; and collaborators from The Kohala Center, an independent, community-based center for research, conservation, and education.
 
The research study was funded by the U.S. Environmental Protection Agency (EPA), MIT’s Department of Civil and Environmental Engineering, and the Tata Center.

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Sweat-proof “smart skin” takes reliable vitals, even during workouts and spicy meals

MIT engineers and researchers in South Korea have developed a sweat-proof “electronic skin” — a conformable, sensor-embedded sticky patch that monitors a person’s health without malfunctioning or peeling away, even when a wearer is perspiring.

The patch is patterned with artificial sweat ducts, similar to pores in human skin, that the researchers etched through the material’s ultrathin layers. The pores perforate the patch in a kirigami-like pattern, similar to that of the Japanese paper-cutting art. The design ensures that sweat can escape through the patch, preventing skin irritation and damage to embedded sensors.

The kirigami design also helps the patch conform to human skin as it stretches and bends. This flexibility, paired with the material’s ability to withstand sweat, enables it to monitor a person’s health over long periods of time, which has not been possible with previous “e-skin” designs. The results, published today in Science Advances, are a step toward long-lasting smart skins that may track daily vitals or the progression skin cancer and other conditions.  

“With this conformable, breathable skin patch, there won’t be any sweat accumulation, wrong information, or detachment from the skin,” says Jeehwan Kim, associate professor of mechanical engineering at MIT. “We can provide wearable sensors that can do constant long-term monitoring.”

Kim’s co-authors include lead author and MIT postdoc Hanwool Yeon, and researchers in MIT’s departments of Mechanical Engineering and Materials Science and Engineering, and the Research Laboratory of Electronics, along with collaborators from cosmetics conglomerate Amorepacific and other institutions across South Korea.

A sweaty hurdle

Kim’s group specializes in fabricating flexible semiconductor films. The researchers have pioneered a technique called remote epitaxy, which involves growing ultrathin, high-quality semiconductor films on wafers at high temperature and selectively peeling away the films, which they can then combine and stack to form sensors far thinner and more flexible than conventional wafer-based designs.

Recently, their work drew the attention of the cosmetics company Amorepacific, which was interested in developing thin wearable tape to continuously monitor changes in skin. The company struck up a collaboration with Kim to fashion the group’s flexible semiconducting films into something that could be worn over long periods of time.

But the team soon came against a barrier that other e-skin designs have yet to clear: sweat. Most experimental designs embed sensors in sticky, polymer-based materials that are not very breathable. Other designs, made from woven nanofibers, can let air through, but not sweat. If an e-skin were to work over the long-term, Kim realized it would have to be permeable to not just vapor but also sweat.

“Sweat can accumulate between the e-skin and your skin, which could cause skin damage and sensor malfunctioning,” Kim says. “So we tried to address these two problems at the same time, by allowing sweat to permeate through electronic skin.”

Making the cut

For design inspiration, the researchers looked to human sweat pores. They found that the diameter of the average pore measures about 100 microns, and that pores are randomly distributed throughout skin. They ran some initial simulations to see how they might overlay and arrange artificial pores, in a way that would not block actual pores in human skin.

“Our simple idea is, if we provide artificial sweat ducts in electronic skin and make highly-permeable paths for the sweat, we may achieve long-term monitorability,” Yeon explains. 

They started with a periodic pattern of holes, each about the size of an actual sweat pore. They found that if pores were spaced close together, at a distance smaller than an average pore’s diameter, the pattern as a whole would efficiently permeate sweat. But they also found that if this simple hole pattern were etched through a thin film, the film was not very stretchable, and it broke easily when applied to skin.

The researchers found they could increase the strength and flexibility of the hole pattern by cutting thin channels between each hole, creating a pattern of repeating dumbbells, rather than simple holes, that relaxed strain, rather than concentrating it in one place. This pattern, when etched into a material, created a stretchable, kirigami-like effect.

“If you wrap a piece of paper over a ball, it’s not conformable,” Kim says. “But if you cut a kirigami pattern in the paper, it could conform. So we thought, why not connect the holes with a cut, to have kirigami-like conformability on the skin? At the same time we can permeate sweat.”

Following this rationale, the team fabricated an electronic skin from multiple functional layers, each which they etched with dumbbell-patterned pores. The skin’s layers comprise an ultrathin semiconductor-patterned array of sensors to monitor temperature, hydration, ultraviolet exposure, and mechanical strain. This sensor array is sandwiched between two thin protective films, all of which overlays a sticky polymer adhesive.

“The e-skin is like human skin — very stretchable and soft, and sweat can permeate through it,” Yeon says.

The researchers tested the e-skin by sticking it to a volunteer’s wrist and forehead. The volunteer wore the tape continuously over a week. Throughout this period, the new e-skin reliably measured his temperature, hydration levels, UV exposure, and pulse, even during sweat-inducing activities, such as running on a treadmill for 30 minutes and consuming a spicy meal.

The team’s design also conformed to skin, sticking to the volunteer’s forehead as he was asked to frown repeatedly while sweating profusely, compared with other e-skin designs that lacked sweat permeability, and easily detached from the skin.

Kim plans to improve the design’s strength and durability. While the tape is both permeable to sweat and highly conformable, thanks to its kirigami patterning, it’s this same patterning, paired with the tape’s ultrathin form, that makes it quite fragile to friction. As a result, volunteers had to wear a casing around the tape to protect it during activities such as showering.

“Because the e-skin is very soft, it can be physically damaged,” Yeon says. “We aim to improve the resilience of electronic skin.”

This research was supported by Amorepacific.

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NSA, Cybercom Leader Says Efforts Have Expanded

Adversaries have heavily invested in cyberspace operations and capabilities. As such, cyber operations, cybersecurity and information operations are increasingly important to the joint force, said the commander of U.S. Cyber Command, who’s also the director of the National Security Agency.

“The scope of what we need to defend and protect has dramatically expanded,” Army Gen. Paul M. Nakasone said today during a virtual address to the U.S Naval Institute and Armed Forces Communications and Electronics Association’s WEST Conference.

The Defense Department’s information network is composed of 15,000 sub-networks, 3 million users, 4 million computers, 180,000 mobility devices and 605 million website requests a day, he said.

“We used to think about cyberspace as merely the need to protect these computer networks. And while it’s a good place to start, the attack surface is much broader,” Nakasone said.

For example, protecting weapons systems is a related but distinct challenge compared to networks, he said. They require software updates and patches. In the case of the Navy, they’re onboard ships that don’t return to port for months at a time, making it even more challenging to provide timely updates.

Another challenge with weapons systems is ensuring that cybersecurity considerations are implemented in the earliest phases of the acquisition cycle, he said.

 

 

Protecting DOD’s data is also a major challenge, he said.

Understanding how state and non-state adversaries are able to successfully carry out cyberattacks is important, he said. “They learn over time in terms of what they can do. They’re not static in the terms of how they approach cyberspace.”

In about the past 150 days, adversaries have successfully conducted supply chain attacks, particularly ransomware attacks, he said. In the last several years, election cybersecurity has taken on an increasingly important role.

Terrorist groups are also mounting cyberattacks, he said. In response, the department has emphasized close teamwork between the NSA, Cybercom, and other commands — U.S. Special Operations Command, in particular.

 

 

“We learned how to work closely with U.S. Special Operations Command, both to support their efforts against kinetic targets and to leverage their capabilities against virtual ones,” he said.

Nakasone also emphasized the importance of working with industry, academia, interagency partners like the FBI and the Department of Homeland Security, as well as with allies and partners.

Having a skilled and motivated workforce is also critically important, he said. They need to have the right training and career paths and professional development opportunities, and the DOD must be open to their new ideas.

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Some brain disorders exhibit similar circuit malfunctions

Many neurodevelopmental disorders share similar symptoms, such as learning disabilities or attention deficits. A new study from MIT has uncovered a common neural mechanism for a type of cognitive impairment seen in some people with autism and schizophrenia, even though the genetic variations that produce the impairments are different for each condition.

In a study of mice, the researchers found that certain genes that are mutated or missing in some people with those disorders cause similar dysfunctions in a neural circuit in the thalamus. If scientists could develop drugs that target this circuit, they could be used to treat people who have different disorders with common behavioral symptoms, the researchers say.

“This study reveals a new circuit mechanism for cognitive impairment and points to a future direction for developing new therapeutics, by dividing patients into specific groups not by their behavioral profile, but by the underlying neurobiological mechanisms,” says Guoping Feng, the James W. and Patricia T. Poitras Professor in Brain and Cognitive Sciences at MIT, a member of the Broad Institute of Harvard and MIT, the associate director of the McGovern Institute for Brain Research at MIT, and the senior author of the new study.

Dheeraj Roy, a Warren Alpert Distinguished Scholar and a McGovern Fellow at the Broad Institute, and Ying Zhang, a postdoc at the McGovern Institute, are the lead authors of the paper, which appears today in Neuron.

Thalamic connections

The thalamus plays a key role in cognitive tasks such as memory formation and learning. Previous studies have shown that many of the gene variants linked to brain disorders such as autism and schizophrenia are highly expressed in the thalamus, suggesting that it may play a role in those disorders.

One such gene is called Ptchd1, which Feng has studied extensively. In boys, loss of this gene, which is carried on the X chromosome, can lead to attention deficits, hyperactivity, aggression, intellectual disability, and autism spectrum disorders.

In a study published in 2016, Feng and his colleagues showed that Ptchd1 exerts many of its effects in a part of the thalamus called the thalamic reticular nucleus (TRN). When the gene is knocked out in the TRN of mice, the mice show attention deficits and hyperactivity. However, that study did not find any role for the TRN in the learning disabilities also seen in people with mutations in Ptchd1.

In the new study, the researchers decided to look elsewhere in the thalamus to try to figure out how Ptchd1 loss might affect learning and memory. Another area they identified that highly expresses Ptchd1 is called the anterodorsal (AD) thalamus, a tiny region that is involved in spatial learning and communicates closely with the hippocampus.

Using novel techniques that allowed them to trace the connections between the AD thalamus and another brain region called the retrosplenial cortex (RSC), the researchers determined a key function of this circuit. They found that in mice, the AD-to-RSC circuit is essential for encoding fearful memories of a chamber in which they received a mild foot shock. It is also necessary for working memory, such as creating mental maps of physical spaces to help in decision-making.

The researchers found that a nearby part of the thalamus called the anteroventral (AV) thalamus also plays a role in this memory formation process: AV-to-RSC communication regulates the specificity of the encoded memory, which helps us distinguish this memory from others of similar nature.

“These experiments showed that two neighboring subdivisions in the thalamus contribute differentially to memory formation, which is not what we expected,” Roy says.

Circuit malfunction

Once the researchers discovered the roles of the AV and AD thalamic regions in memory formation, they began to investigate how this circuit is affected by loss of Ptchd1. When they knocked down expression of Ptchd1 in neurons of the AD thalamus, they found a striking deficit in memory encoding, for both fearful memories and working memory.

The researchers then did the same experiments with a series of four other genes — one that is linked with autism and three linked with schizophrenia. In all of these mice, they found that knocking down gene expression produced the same memory impairments. They also found that each of these knockdowns produced hyperexcitability in neurons of the AD thalamus.

These results are consistent with existing theories that learning occurs through the strengthening of synapses that occurs as a memory is formed, the researchers say.

“The dominant theory in the field is that when an animal is learning, these neurons have to fire more, and that increase correlates with how well you learn,” Zhang says. “Our simple idea was if a neuron fires too high at baseline, you may lack a learning-induced increase.”

The researchers demonstrated that each of the genes they studied affects different ion channels that influence neurons’ firing rates. The overall effect of each mutation is an increase in neuron excitability, which leads to the same circuit-level dysfunction and behavioral symptoms.

The researchers also showed that they could restore normal cognitive function in mice with these genetic mutations by artificially turning down hyperactivity in neurons of the AD thalamus. The approach they used, chemogenetics, is not yet approved for use in humans. However, it may be possible to target this circuit in other ways, the researchers say.

The findings lend support to the idea that grouping diseases by the circuit malfunctions that underlie them may help to identify potential drug targets that could help many patients, Feng says.

“There are so many genetic factors and environmental factors that can contribute to a particular disease, but in the end, it has to cause some type of neuronal change that affects a circuit or a few circuits involved in this behavior,” he says. “From a therapeutic point of view, in such cases you may not want to go after individual molecules because they may be unique to a very small percentage of patients, but at a higher level, at the cellular or circuit level, patients may have more commonalities.”

The research was funded by the Stanley Center at the Broad Institute, the Hock E. Tan and K. Lisa Yang Center for Autism Research at MIT, the James and Patricia Poitras Center for Psychiatric Disorders Research at MIT, and the National Institutes of Health BRAIN Initiative.

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Space Clock Moves Toward Increased Spacecraft Autonomy

The technology demonstration was designed to improve navigation for robot explorers and operate GPS satellites. It reports on a significant milestone.

To communicate with Earth stations, spacecraft that travel beyond the Moon’s surface rely on ground stations to find out where they are and where their destination is. NASA’s Deep Space Atomic Clock aims to give far-flung explorers greater autonomy in navigation. The mission published a new paper today in Nature. It reports on progress made in improving the accuracy of space-based atomic clocks in measuring time over long periods.

This feature is also known as stability. It also affects the operation of GPS satellites that aid people to navigate on Earth. Therefore, it has the potential of increasing the autonomy of the next-generation GPS spacecraft.

Engineers send signals from a distant spacecraft to Earth in order to calculate its trajectory. To accurately measure the position of a spacecraft, engineers use small, refrigerator-sized atomic clocks to record the timing of these signals. For robots on Mars and other distant destinations, the waiting time for signals can quickly add up to several minutes or even hours.

These spacecraft could use atomic clocks to calculate their own position, and direction. However, the clocks must be extremely stable. To help us reach our destinations on Earth, GPS satellites have atomic clocks. However, these clocks need to be updated several times per day to ensure that they are always in sync. Space-based clocks that are more stable for deep space missions would be required.

The Deep Space Atomic Clock, which is managed by NASA’s Jet Propulsion Laboratory (South California), has been operating aboard General Atomic’s Orbital Test Bed spacecraft from June 2019. According to the new study, the mission team set a new record in space-based atomic clock stability, surpassing current satellite-based clocks.

When Every Second Counts

Every atomic clock has some level of instability. This causes an offset between the clock’s actual time and the clock’s clock. The offset can quickly increase, even though it is small, and spacecraft navigation could make a big difference.

The mission of Deep Space Atomic Clock was designed to determine the clock’s stability over extended periods of time, and to observe how that changes with the passage of time. The team reported in the paper that the clock’s stability was less than four nanoseconds after 20 days of operation.

Eric Burt, an atomic clock scientist for JPL and coauthor of the paper, stated that a time uncertainty of 1 nanosecond corresponds to a distance uncertainty approximately one foot. GPS clocks that are not updated daily must be maintained at this level of stability. This means GPS is dependent on ground communication. This can be extended to up to a week by the Deep Space Atomic Clock, which could give an application such as GPS more autonomy.

The new paper reports stability and time delay that is five times greater than the team report in spring 2020. This is not a significant improvement in the clock, but rather in the team’s measurement and analysis of its stability. It was possible to increase the accuracy of their measurements by using longer operating times and nearly a year’s worth of additional data.

While the Deep Space Atomic Clock mission is ending in August, NASA announced the continued work on this technology: The Deep Space Atomic Clock-2 will fly on the VERITAS mission to Venus. It’s an improved version the timekeeper that NASA has been working on for years. The new space clock, like its predecessor, is a technology demonstration. Its goal is to improve in-space capabilities through the development of instruments, hardware and software. The ultra-precise signal that was generated by this technology, which was built by JPL and funded NASA’s Space Technology Mission Directorate. It could be used to enable autonomous spacecraft navigation as well as enhance radio science observations during future missions.

NASA’s selection for Deep Space Atomic Clock-2 (VERITAS) speaks to the technology’s promise, stated Todd Ely, Deep Space Atomic Clock principal researcher and JPL project manager. We aim to test this new generation space clock on VERITAS and show its potential for deep-space navigation and science.

Learn More about the Mission

General Atomics Electromagnetic Systems, Englewood, Colorado hosts the Deep Space Atomic Clock. It is sponsored by STMD’s Technology Demonstration Missions (STMD) program at NASA’s Marshall Space Flight Center, Huntsville, Alabama and NASA’s Space Communications and Navigation program (SCaN), NASA’s Human Exploration and Operations Mission Directorate. The project is managed by JPL.

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Crispy gene editing in outer space

Researchers have successfully demonstrated a new method to study how cells repair DNA damage in space. Sarah Stahl-Rommel, Genes in Space, and her colleagues will present the new technique in the PLOS One journal on June 30, 2021.

An organism’s DNA may be damaged by normal biological processes, or environmental causes such as ultraviolet light. Damaged DNA can cause cancer in humans and other animals. There are many natural ways cells can repair damaged DNA. Space radiation can cause DNA damage to astronauts who travel outside the Earth’s protective atmosphere. It may be crucial to know which DNA-repair strategies the body uses in space. Research suggests that microgravity conditions could influence this decision, raising concern that repair may not be sufficient. The issue has been largely ignored due to safety and technological obstacles.

Stahl-Rommel, along with colleagues, have created a new way to study DNA repair in yeast cells. This can be done entirely in space. This technique uses CRISPR/Cas9 genome editor technology to cause precise DNA damage. DNA repair mechanisms can then easily be observed in greater detail than with radiation or other causes. This method targets a particular type of DNA damage, known as a double strand break.

Researchers successfully tested the new method on yeast cells aboard the International Space Station. The technique is expected to allow for extensive space research on DNA repair. This is the first space-based CRISPR/Cas9 gene editing experiment. It also marks the first space-based successful transformation of live cells to incorporate genetic material from outside.

Future research may refine the method to mimic complex DNA damage caused ionizing radiation. This technique could be used as a basis for research into many other topics in molecular biology related to space exploration and long-term space exposure.

Sebastian Kraves, senior author, stated that it wasn’t just that the team was able to successfully deploy novel technologies such as CRISPR genome editing and PCR in extreme environments, but that they were also able to integrate them in a functionally complete workflow for biotechnology that can be used to study DNA repair and other fundamental cell processes in microgravity. These new developments give hope to humanity’s renewed desire to explore and live in the vast expanses of space.

Stahl Rommel, first author, says that Genes in Space-6 was a highlight in her career. She witnessed firsthand how much can be achieved when innovative students are supported and encouraged by NASA, industry, academia, and NASA, she said. Because of their expertise, the researchers were able to do complex science that is high-quality and beyond Earth’s borders. This collaboration is a great example for students and senior researchers, she believes.

Sarah Castro-Wallace, co-author, said that it was an honor to support Genes in Space-6. It is still amazing to me how sophisticated the science was when an organism was transformed and its genome edited using CRISPR/Cas9 in order to break down the DNA. Then, it was grown to allow for DNA repair. Finally, its DNA was sequenced in spaceflight onboard the ISS. This is a major step forward in space biology. This is a testament to both the Genes in Space Program and the outstanding students.

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Five minutes to lower blood pressure

A new CU Boulder study shows that a five-minute exercise per day, which is described as “strength training for your breathing muscles,” lowers blood pressure, improves vascular health, and can be done daily.

The Journal of the American Heart Association published the strongest evidence yet to show that the time-efficient High-Resistance Inspiratory Muscle Strength Training, (IMST), could be a key component in protecting aging adults from the nation’s most deadly killer, cardiovascular disease.

Only 65% of Americans over 50 have high blood pressure, which puts them at higher risk for heart attack and stroke. However, less than 40% of Americans meet the recommended aerobic exercise guidelines.

There are many lifestyle strategies that can be used to maintain good cardiovascular health, according to experts. However, these strategies can be time-consuming and expensive, and may not be accessible to everyone, says Daniel Craighead, assistant researcher in the Department of Integrative Physiology. IMST can easily be completed in just five minutes while you are watching TV, he said.

IMST was developed in 1980 to aid patients with severe respiratory diseases. It involves exhaling through a device that provides resistance. Imagine sucking through a tube that pulls back.

Initial recommendations for patients with breathing disorders were to use a 30-minute per-day regimen at low resistance. Craighead and his colleagues have been examining whether a shorter protocol, which involves 30 inhalations per day at high resistance and six days per week, could reap benefits for cardiovascular, cognitive, and athletic performance.

They recruited 36 healthy adults between the ages of 50 and 79 who had normal systolic blood pressure (120mg mercury or more). Half of the participants did High-Resistance IMTST for six weeks, while half followed a placebo protocol where resistance was lower.

Six weeks later, the IMST group saw their systolic (the highest) blood pressure drop nine points. This is a decrease that generally surpasses that achieved by walking 30 mins per day, five days a semaine. This decline is also comparable to some blood pressure-lowering medication regimens.

Six weeks after quitting IMST, most improvement was maintained by the IMST group.

Craighead said they found it to be more efficient than traditional exercise programs and may have longer-lasting benefits.

Also, the treatment group saw a 45% increase in vascular endothelial functions, which is the ability of arteries to expand upon stimulation. There was also a significant rise in levels nitric dioxide, a key molecule for dilation and prevention of plaque buildup. As we age, our levels of nitric oxide naturally decrease.

After IMST, markers of inflammation and oxidative stresses, which can increase heart attack risk, were markedly lower.

Surprisingly, 95% of sessions were completed by those in the IMST Group.

Doug Seals, a Distinguished Professor in Integrative Physiology, said that he had discovered a new form of therapy that lowers blood pressure without using pharmacological compounds. He also claims that it has a higher adherence rate than aerobic exercise. This is noteworthy.

This practice could be especially helpful for women who are postmenopausal.

Seals’ previous research showed that women postmenopausal who don’t take supplemental estrogen do not reap the same benefits from aerobic exercise as men when it comes to vascular function. The new study found that IMST improved it in these women just as much as in men.

Craighead stated that aerobic exercise will not improve postmenopausal women’s cardiovascular health. They need to change their lifestyle to do so. This could be it.

Some preliminary results show that MST may also improve brain function and physical fit. Other studies have also shown that MST can improve sports performance.

Craighead said that marathon runners experience fatigued respiratory muscles, which can cause them to take blood from their skeletal muscles. He uses IMST for his marathon training. The idea is that your legs will not get fatigued if you increase the endurance of your respiratory muscles.

Seals stated that they aren’t sure how a move to strengthen breathing muscles can lower blood pressure. However, they believe it causes the cells in blood vessels to produce more Nitric Ox, which allows them to relax.

Seals was recently awarded $4 million by the National Institutes of Health to conduct a larger follow up study of approximately 100 people. This will compare a 12-week IMST protocol with an aerobic exercise program.

The research group is currently developing a smartphone app that will allow people to perform the protocol at home with already-commercially available devices.

Anyone considering IMST should first consult their doctor. They said that IMST has been remarkably safe so far.

Working out just five minutes daily via a practice described as “strength training for your breathing muscles” lowers blood pressure and improves some measures of vascular health as well as, or even more than, aerobic exercise or medication, new CU Boulder research shows.

The study, published June 29 in the Journal of the American Heart Association, provides the strongest evidence yet that the ultra-time-efficient maneuver known as High-Resistance Inspiratory Muscle Strength Training (IMST) could play a key role in helping aging adults fend off cardiovascular disease – the nation’s leading killer.

In the United States alone, 65% of adults over age 50 have above-normal blood pressure – putting them at greater risk of heart attack or stroke. Yet fewer than 40% meet recommended aerobic exercise guidelines.

Developed in the 1980s as a way to help critically ill respiratory disease patients strengthen their diaphragm and other inspiratory (breathing) muscles, IMST involves inhaling vigorously through a hand-held device which provides resistance. Imagine sucking hard through a tube that sucks back.

Initially, when prescribing it for breathing disorders, doctors recommended a 30-minute-per-day regimen at low resistance. But in recent years, Craighead and colleagues have been testing whether a more time-efficient protocol–30 inhalations per day at high resistance, six days per week–could also reap cardiovascular, cognitive and sports performance improvements.

For the new study, they recruited 36 otherwise healthy adults ages 50 to 79 with above normal systolic blood pressure (120 millimeters of mercury or higher). Half did High-Resistance IMST for six weeks and half did a placebo protocol in which the resistance was much lower.

After six weeks, the IMST group saw their systolic blood pressure (the top number) dip nine points on average, a reduction which generally exceeds that achieved by walking 30 minutes a day five days a week. That decline is also equal to the effects of some blood pressure-lowering drug regimens.

Even six weeks after they quit doing IMST, the IMST group maintained most of that improvement.

“We found that not only is it more time-efficient than traditional exercise programs, the benefits may be longer lasting,” Craighead said.

The treatment group also saw a 45% improvement in vascular endothelial function, or the ability for arteries to expand upon stimulation, and a significant increase in levels of nitric oxide, a molecule key for dilating arteries and preventing plaque buildup. Nitric oxide levels naturally decline with age.

Markers of inflammation and oxidative stress, which can also boost heart attack risk, were significantly lower after people did IMST.

And, remarkably, those in the IMST group completed 95% of the sessions.

“We have identified a novel form of therapy that lowers blood pressure without giving people pharmacological compounds and with much higher adherence than aerobic exercise,” said senior author Doug Seals, a Distinguished Professor of Integrative Physiology. “That’s noteworthy.”

The practice may be particularly helpful for postmenopausal women.

In previous research, Seals’ lab showed that postmenopausal women who are not taking supplemental estrogen don’t reap as much benefit from aerobic exercise programs as men do when it comes to vascular endothelial function. IMST, the new study showed, improved it just as much in these women as in men.

“If aerobic exercise won’t improve this key measure of cardiovascular health for postmenopausal women, they need another lifestyle intervention that will,” said Craighead. “This could be it.”

Preliminary results suggest MST also improved some measures of brain function and physical fitness. And previous studies from other researchers have shown it can be useful for improving sports performance.

“If you’re running a marathon, your respiratory muscles get tired and begin to steal blood from your skeletal muscles,” said Craighead, who uses IMST in his own marathon training. “The idea is that if you build up endurance of those respiratory muscles, that won’t happen and your legs won’t get as fatigued.”

Seals said they’re uncertain exactly how a maneuver to strengthen breathing muscles ends up lowering blood pressure, but they suspect it prompts the cells lining blood vessels to produce more nitric oxide, enabling them to relax.

The National Institutes of Health recently awarded Seals $4 million to launch a larger follow-up study of about 100 people, comparing a 12-week IMST protocol head-to-head with an aerobic exercise program.

Meanwhile, the research group is developing a smartphone app to enable people to do the protocol at home using already commercially available devices.

Those considering IMST should consult with their doctor first. But thus far, IMST has proven remarkably safe, they said.

“It’s easy to do, it doesn’t take long, and we think it has a lot of potential to help a lot of people,” said Craighead.

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Mayan Poop Shows Climate Change Effects

McGill University has found that climate change has had an impact on the size and composition of the Maya population of Itzan, a lowland city in present-day Guatemala. These findings were published in Quaternary Sciences Reviews. They show that both droughts as well as very wet periods lead to significant population declines.

These results were based on a relatively new technique that involves looking at stanols, organic molecules found in human and animal waste. They are taken from the bottom a nearby lake. To estimate population changes and examine the relationship between stanols and other information such as climate variability and changes to vegetation, measurements were made.

The technique allowed the researchers to track major changes in Maya population over a time period that began 3,300 years ago (BP). They also identified shifts in settlement patterns over hundreds of years, which are related to changes in land use.

Furthermore, they discovered that the land was settled much earlier than originally suggested by archaeological evidence.

A new tool gives surprising insight into human presence in the Maya lowlands

Evidence from faecal statols indicates that humans were present at the Itzan escarpment approximately 650 years before archaeological evidence supports it. The evidence also suggests that the Maya occupied the area even though they were smaller after the “collapse” of 800-1000 AD. This was contrary to previous beliefs that all the population had fled the region due to drought or war. Further evidence is provided by historical records of refugees fleeing Spanish attacks on the southern Maya lowlands of the Maya (Nojpeten or modern-day Flores, Guatemala), which indicate a significant population increase.

Ground inspection and excavation have been the best methods to estimate ancient Maya population size. Archaeologists use ground inspection and excavation to reconstruct the population dynamics. They map and count residential buildings and excavate them to determine dates of occupation. They then compare the population trends at the site with those at regional levels. They then use techniques like pollen analysis and indicators soil erosion into lakes to reconstruct any ecological changes that occurred at the same moment.

“This research should assist archaeologists by providing an additional tool to examine changes that may not have been seen in archaeological evidence,” stated Benjamin Keenan (a PhD candidate in McGill’s Department of Earth and Planetary Sciences and first author of the paper. The tropical forest environment makes it difficult to preserve buildings and other records of human activity in the Maya lowlands.

Maya population size is affected by wet and drought periods

Laguna Itzan’s sediment contains faecal substance that confirms that drought caused the Maya population to decline. It happened at three times: between 90-280 AD, 730-900 AD, and the less studied drought between 1350-950 BC. Researchers also discovered that the population fell during a very dry period between 400–210 BC. This is something that has been overlooked until now. Both dry and wet periods showed that population declined in both dry and humid periods.

Peter Douglas, an assistant professor at the Department of Earth and Planetary Sciences and senior author of the paper, stated that “It’s important that society generally knows that civilisations that have been affected by and adapted for climate change” and added that it was not just his work. “By linking climate evidence and population change, we can see a clear connection between precipitation and the capacity of these ancient cities sustain their population.”

Research also suggests that Maya people might have used techniques such as applying human waste (also called night soil) to fertilize crops. This may have helped them adapt to environmental problems such as soil degradation or nutrient loss. The low levels of fecal substances in lake sediments suggests this, at a time when archaeological evidence points to the greatest human population. This could be explained by the fact that human waste was used as fertilizer to soils and the stanols did not get washed into lake.

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Growing ‘Metallic Wood’ to New Heights

This strip of metallic wood, about an inch long and one-third inch wide, is thinner than household aluminum foil but is supporting more than 50 times its own weight without buckling. If the weight were suspended from it, the same strip could support more than six pounds without breaking.

Natural wood remains a ubiquitous building material because of its high strength-to-density ratio; trees are strong enough to grow hundreds of feet tall but remain light enough to float down a river after being logged.

For the past three years, engineers at the University of Pennsylvania’s School of Engineering and Applied Science have been developing a type of material they’ve dubbed “metallic wood.” Their material gets its useful properties and name from a key structural feature of its natural counterpart: porosity. As a lattice of nanoscale nickel struts, metallic wood is full of regularly spaced cell-sized pores that radically decrease its density without sacrificing the material’s strength.

The precise spacing of these gaps not only gives metallic wood the strength of titanium at a fraction of the weight, but unique optical properties. Because the spaces between gaps are the same size as the wavelengths of visible light, the light reflecting off of metallic wood interferes to enhance specific colors. The enhanced color changes are based on the angle that light reflects off of the surface, giving it a dazzling appearance and the potential to be used as a sensor.

Penn Engineers have now solved a major problem preventing metallic wood from being manufactured at meaningful sizes: eliminating the inverted cracks that form as the material is grown from millions of nanoscale particles to metal films big enough to build with. Preventing these defects, which have plagued similar materials for decades, allows strips of metallic wood to be assembled in areas 20,000 times greater than they were before.

James Pikul and Zhimin Jiang

James Pikul, assistant professor in the Department of Mechanical Engineering and Applied Mechanics, and Zhimin Jiang, a graduate student in his lab, have published a study demonstrating this improvement in the journal Nature Materials.

When a crack forms within an everyday material, bonds between its atoms break, eventually cleaving the material apart. An inverted crack, by contrast, is an excess of atoms; in the case of metallic wood, inverted cracks consist of extra nickel that fills in the nanopores critical to its unique properties.

“Inverted cracks have been a problem since the first synthesis of similar materials in the late 1990s,” says Jiang. “Figuring out a simple way of eliminating them has been a long-standing hurdle in the field.”

These inverted cracks stem from the way that metallic wood is made. It starts as a template of nanoscale spheres, stacked on top of one another. When nickel is deposited through the template, it forms metallic wood’s lattice structure around the spheres, which can then be dissolved away to leave its signature pores.

However, if there are any places where the spheres’ regular stacking pattern is disrupted, the nickel will fill those gaps, producing an inverted crack when the template is removed.

Nanoscale pores are the key to metallic wood’s properties, but if there is a crack in the template before nickel is added, it will become an “inverted crack” — a seam of solid nickel — when the template is removed. The researchers’ technique allows for crack-free regions that are 20,000 times larger than previously possible.

“The standard way to build these materials is to start with a nanoparticle solution and evaporate the water until the particles are dry and regularly stacked. The challenge is that the surface forces of water are so strong that they rip the particles apart and form cracks, just like cracks that form in drying sand,” Pikul says. “These cracks are very difficult to prevent in the structures we are trying to build, so we developed a new strategy that allows us to self-assemble the particles while keeping the template wet. This prevents the films from cracking, but because the particles are wet, we have to lock them in place using electrostatic forces so that we can fill them with metal.”

With larger, more consistent strips of metallic wood now possible, the researchers are particularly interested in using these materials to build better devices.

“Our new manufacturing approach allows us to make porous metals that are three times stronger than previous porous metals at similar relative density and 1,000 times larger than other nanolattices,” Pikul says. “We plan to use these materials to make a number of previously impossible devices, which we are already using as membranes to separate biomaterials in cancer diagnostics, protective coatings and flexible sensors.”

This work was partially funded by the pilot grant program from the Center for Innovation & Precision Dentistry at the University of Pennsylvania and by the National Science Foundation under CAREER Grant No. 1943243.

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