Research

Air Tracker

July 22, 2022

Air Tracker

New tool shows air pollution’s path.

On June 13, 2022, Environmental Defense Fund unveiled Air Tracker, a first-of-its-kind web-based tool that allows users to plot the likely path of air pollution. Run on real-time, trusted scientific models and coupled with air pollution and weather data and developed in partnership with the University of Utah and the CREATE Lab at Carnegie Mellon University, Air Tracker helps users learn more about the air they’re breathing, including pollution concentrations and its potential sources.

U professor John Lin, of the Department of Atmospheric Sciences, adapted his research group’s atmospheric model (the Stochastic Time-Inverted Lagrangian Transport model, or STILT) to run as part of Air Tracker.

John Lin

“Air Tracker is designed to trace our potential source regions for pollution. Users can make use of Air Tracker to investigate emission sources with a research-grade atmospheric model at their fingertips.”

 

“Air quality monitors can show us how polluted our air is, but they aren’t equipped to tell us what is causing the pollution,” says Tammy Thompson, Senior Air Quality Scientist and creator of the tool. “With Air Tracker, we’re able to see likely sources of pollution hotspots, which is especially helpful in cities where a variety of emitters contribute to overall air quality.”

Users can click anywhere on maps of Houston, Salt Lake City and Pittsburgh to create a “source area,” which shows the most likely origin of the air they’re breathing at any given time. They can also click on locations of individual air quality sensors to show real-time and historical fine particle (PM2.5) pollution readings, wind speed and direction.

Relying on STILT, Air Tracker incorporates a variety of weather forecasting models to show how particles move through the atmosphere, allowing the tool to map the probability of pollution’s path. Air Tracker goes beyond common source identification models–which are unable to capture fine-scale air pollution variability–to identify pollution sources at the city block level.

In Houston, for example, where a lack of zoning has allowed industrial sources to operate near communities with homes, schools, churches and hospitals, Air Tracker uses both real-time and historical data to show how different sources contribute to poor air quality at different dates and times.

“Breathing dirty air is bad for our health, and these health effects are not distributed equally,” said Sarah Vogel, EDF Senior Vice President, Healthy Communities. “The poorer and more disadvantaged groups disproportionately suffer the greater exposures and health impacts from air pollution. We hope community leaders and individuals will use this pollution data to hold polluters accountable and advocate for clean air policy change.”

In addition to learning more about the sources likely influencing the air they breathe, Air Tracker users can also use the real-time source area identification to help speed mitigation and help spot and control emissions resulting from accidents and unusual events. Through its “Share” feature, users can take screenshots of source areas to send to regulators and local officials.

Air Tracker is part of EDF’s ongoing work to better understand local air pollution, its behavior and its impacts. Air Tracker can be adapted to include additional pollutants and used in other cities around the world, including those that may not yet feature extensive, hyper-local air quality monitoring programs.

Learn more about Air Tracker, EDF’s Global Clean Air efforts and the project partners here.

One of the world’s leading international nonprofit organizations, Environmental Defense Fund creates transformational solutions to the most serious environmental problems. To do so, EDF links science, economics, law, and innovative private-sector partnerships. With more than 3 million members and offices in the United States, China, Mexico, Indonesia and the European Union, EDF’s scientists, economists, attorneys and policy experts are working in 28 countries to turn our solutions into action. Connect with us on Twitter @EnvDefenseFund.

 

by Paul Gabrielsen, first published in @theU. Adapted from a release by the Environmental Defense Fund. 

 

Cellular Crosslinking

July 19, 2022

Cellular Crosslinking

Structural signatures of Escherichia coli chemoreceptor signaling states revealed by cellular crosslinking

Motile bacteria are capable of swimming efficiently toward favorable chemical environments and away from inhospitable ones. This behavior–called “chemotaxis”–is frequently used by unicellular organisms for finding food.

Not surprisingly, such behaviors play important roles in establishing beneficial host symbioses and pathogenic infections. The value of understanding in detail this mechanism of directed cell migration in response to extracellular chemical signals cannot be over-stated, and Escherichia coli, commonly referred to as E. coli, has become the paradigm molecular model.

“Despite their tiny size, bacteria have evolved amazingly sophisticated protein machines for detecting and responding to changes in their environment,” says John “Sandy” Parkinson, principal investigator in the School of Biological Sciences. Caralyn Flack, a research associate in the Parkinson Lab, developed a technique for monitoring the behavior of living bacteria before and after she changed the structure of a critical signaling protein inside the cell.

Flack’s new findings were recently published in Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS). The paper, titled “Structural signatures of Escherichia coli chemoreceptor signaling states revealed by cellular crosslinking,” makes an important advance in elucidating the molecular mechanism(s) of signal propagation through chemoreceptor molecules.

Caralyn Flack

"This new cellular crosslinking approach delivers unprecedented insight into receptor structural properties as the receptors function within cells"

 

“Bacteria are amazing at sensing and responding quickly to changes in their environment,” states Flack. “This makes them a great model for trying to understand transmembrane signaling.” But it turns out that changes that accompany signaling events in chemoreceptors are difficult to follow with traditional structural methods, and those techniques that do work cannot replicate the native cellular environment. To remedy that, the technique Flack developed does three things. First, it assesses behavior. Second, it changes the structure of a protein inside living bacteria, and third, it then watches the signaling behavior change in real-time. The technique, which involves “crosslinking,” she says, has proven to be “really powerful for structure-function analyses of signaling proteins.”

In essence, what Flack did was create receptor proteins with a special amino acid at a position of interest. That amino acid, cysteine, has unique chemical properties that, under the right conditions, allow it to form a covalent bond (to “crosslink”) to a nearby cysteine in the same protein or in another protein. Such crosslinks constrain the structural movements of the proteins and can change its behavior. This is how Flack was able to change the structure, and in consequence, the function of a receptor within a living cell.

The crosslinking reporter sites “enabled us to evaluate receptor output states before and after crosslink formation,” she writes. This new cellular crosslinking approach “delivers unprecedented insight into receptor structural properties as the receptors function within cells” stated one reviewer of the PNAS manuscript. Flack suggests that “similar crosslinking approaches could serve to follow signal transmission in other regions of the chemoreceptor molecule and perhaps in other signaling proteins, as well.”

Work on those topics is ongoing.

Photo: Colorized scanning electron micrograph of Escherichia coli, grown in culture and adhered to a cover slip by NIAID on Flickr

 

by David Pace, first published in biology.utah.edu.

 

Biomimetic Cephalopods

July 11, 2022

Biomimetic Cephalopods

Bringing ancient animals back to life—as robots.

In a university swimming pool, scientists and their underwater cameras watch carefully as a coiled shell is released from a pair of metal tongs. The shell begins to move under its own power, giving the researchers a glimpse into what the oceans might have looked like millions of years ago when they were full of these ubiquitous animals.

This isn’t Jurassic Park, but it is an effort to learn about ancient life by recreating it. In this case, the recreations are 3-D-printed robots designed to replicate the shape and motion of ammonites, marine animals that both preceded and were contemporaneous with the dinosaurs.

 

David Peterman

"Evolution dealt them a very unique mode of locomotion after liberating them from the seafloor with a chambered, gas-filled conch. These animals are essentially rigid-bodied submarines propelled by jets of water."

 

The robotic ammonites allowed the researchers to explore questions about how shell shapes affected swimming ability. They found trade-offs between stability in the water and maneuverability, suggesting that the evolution of ammonite shells explored different designs for different advantages rather than converged toward a single best design.

“These results reiterate that there is no single optimum shell shape,” says David Peterman, a postdoctoral fellow in the University of Utah’s Department of Geology and Geophysics.

The study is published in Scientific Reports and supported by the National Science Foundation.

Bringing ammonites to “life”

For years, Peterman and Kathleen Ritterbush, assistant professor of geology and geophysics, have been exploring the hydrodynamics, or physics of moving through the water, of ancient shelled cephalopods, including ammonites. Cephalopods today include octopuses and squid, with only one group sporting an external shell—the nautiluses.

Before the current era, cephalopods with shells were everywhere. Although their rigid coiled shells would have impacted their free movement through the water, they were phenomenally successful evolution-wise, persisting for hundreds of millions of years and surviving every mass extinction.

“These properties make them excellent tools to study evolutionary biomechanics,” Peterman says, “the story of how benthic (bottom-dwelling) mollusks became among the most complex and mobile group of marine invertebrates. My broader research goal is to provide a better understanding of these enigmatic animals, their ecosystem roles, and the evolutionary processes that have shaped them.”

Peterman and Ritterbush previously built life-sized 3-D weighted models of cone-shaped cephalopod shells and found, through releasing them in pools, that the ancient animals likely lived a vertical life, bobbing up and down through the water column to find food. These models’ movements were governed solely by buoyancy and the hydrodynamics of the shell.

But Peterman has always wanted to build models more similar to living animals.

Diagram of a Biometic Cehalapod.

“I have wanted to build robots ever since I developed the first techniques to replicate hydrostatic properties in physical models, and Kathleen strongly encouraged me as well,” Peterman says. “On-board propulsion enables us to explore new questions regarding the physical constraints on the life habits of these animals.”

Buoyancy became Peterman’s chief challenge. He needed the models to be neutrally buoyant, neither floating nor sinking. He also needed the models to be water-tight, both to protect the electronics inside and to prevent leaking water from changing the delicate buoyancy balance.

But the extra work is worth it. “New questions can be investigated using these techniques,” Peterman says, “including complex jetting dynamics, coasting efficiency, and the 3-D maneuverability of particular shell shapes.”

Three kinds of shells

The researchers tested robotic ammonites with three shell shapes. They’re partially based on the shell of a modern Nautilus and modified to represent the range of ancient ammonites’ shell shapes. The model called a serpenticone had tight whorls and a narrow shell, while the sphaerocone model had few thick whorls and a wide, almost spherical shell. The third model, the oxycone, was somewhere in the middle: thick whorls and a narrow, streamlined shell. You can think of them occupying a triangular diagram, representing “end-members” of different shell characteristics.

“Every planispiral cephalopod to ever exist plots somewhere on this diagram,” Peterman says, allowing the properties for in-between shapes to be estimated.

Once the 3-D-printed models were built, rigged and weighted, it was time to go to the pool. Working first in the pool of Geology and Geophysics professor Brenda Bowen and later in the U’s Crimson Lagoon, Peterman and Ritterbush set up cameras and lights underwater and released the robotic ammonites, tracking their position in 3-D space throughout around a dozen “runs” for each shell type.

No perfect shell shape

By analyzing the data from the pool experiments, the researchers were looking for the pros and cons associated with each shell characteristic.

“We expected there to be various advantages and consequences for any particular shapes,” Peterman says. “Evolution dealt them a very unique mode of locomotion after liberating them from the seafloor with a chambered, gas-filled conch. These animals are essentially rigid-bodied submarines propelled by jets of water.” That shell isn’t great for speed or maneuverability, he says, but coiled-shell cephalopods still managed remarkable diversity through each mass extinction.

“Throughout their evolution, externally shelled cephalopods navigated their physical limitations by endlessly experimenting with variations on the shape of their coiled shells,” Peterman says.

So, which shell shape was the best?

David Peterman

“The idea that one shape is better than another is meaningless without asking the question—‘better at what?’” Peterman says. Narrower shells enjoyed less drag and more stability while traveling in one direction, improving their jetting efficiency. But wider, more spherical shells could more easily change directions, spinning on an axis. This maneuverability may have helped them catch prey or avoid slow predators (like other shelled cephalopods).

Peterman notes that some interpretations consider many ammonite shells as hydrodynamically “inferior” to others, limiting their motion too much.

“Our experiments, along with the work of colleagues in our lab, demonstrate that shell designs traditionally interpreted as hydrodynamically ‘inferior’ may have had some disadvantages but are not immobile drifters,” Peterman says. “For externally shelled cephalopods, speed is certainly not the only metric of performance.” Nearly every variation in shell design iteratively appears at some point in the fossil record, he says, showing that different shapes conferred different advantages.

“Natural selection is a dynamic process, changing through time and involving numerous functional tradeoffs and other constraints,” he says, “Externally-shelled cephalopods are perfect targets to study these complex dynamics because of their enormous temporal range, ecological significance, abundance, and high evolutionary rates.”

Find the full study @ Nature.com.

 

by Paul Gabrielsen, first published in @TheU.

 

Moiré Magic

June 22, 2022

Moiré Magic

Highly tunable composite materials—with a twist.

The above animation shows the patterns created as two circles move across each other. Those patterns, created by two sets of lines offset from each other, are called moiré (pronounced mwar-AY) effects. As optical illusions, moiré patterns create neat simulations of movement. But at the atomic scale, when one sheet of atoms arranged in a lattice is slightly offset from another sheet, these moiré patterns can create some exciting and important physics with interesting and unusual electronic properties.

Mathematicians at the University of Utah have found that they can design a range of composite materials from moiré patterns created by rotating and stretching one lattice relative to another. Their electrical and other physical properties can change—sometimes quite abruptly, depending on whether the resulting moiré patterns are regularly repeating or non-repeating. Their findings are published in Communications Physics.

The mathematics and physics of these twisted lattices applies to a wide variety of material properties, says Kenneth Golden, distinguished professor of mathematics. “The underlying theory also holds for materials on a large range of length scales, from nanometers to kilometers, demonstrating just how broad the scope is for potential technological applications of our findings.”

 

Ken Golden

"We observe a geometry-driven localization transition that has nothing to do with wave scattering or interference effects, which is a surprising and unexpected discovery."

 

With a twist

Before we arrive at these new findings, we’ll need to chart the history of two important concepts: aperiodic geometry and twistronics.

Aperiodic geometry means patterns that don’t repeat. An example is the Penrose tiling pattern of rhombuses. If you draw a box around a part of the pattern and start sliding it in any direction, without rotating it, you’ll never find a part of the pattern that matches it.

Aperiodic patterns designed over 1000 years ago appeared in Girih tilings used in Islamic architecture. More recently, in the early 1980s, materials scientist Dan Shechtman discovered a crystal with an aperiodic atomic structure. This revolutionized crystallography, since the classic definition of a crystal includes only regularly repeating atomic patterns, and earned Shechtman the 2011 Nobel Prize in Chemistry.

Okay, now onto twistronics, a field that also has a Nobel in its lineage. In 2010, Andre Geim and Konstantin Novoselov won the Nobel Prize in Physics for discovering graphene, a material that’s made of a single layer of carbon atoms in a lattice that looks like chicken wire. Graphene itself has its own suite of interesting properties, but in recent years physicists have found that when you stack two layers of graphene and turn one slightly, the resulting material becomes a superconductor that also happens to be extraordinarily strong. This field of study of the electronic properties of twisted bilayer graphene is called “twistronics.”

Two-phase composites

In the new study, Golden and his colleagues imagined something different. It’s like twistronics, but instead of two layers of atoms, the moiré patterns formed from interfering lattices determine how two different material components, such as a good conductor and a bad one, are arranged geometrically into a composite material. They call the new material a “twisted bilayer composite,” since one of the lattices is twisted and/or stretched relative to the other. Exploring the mathematics of such a material, they found that moiré patterns produced some surprising properties.

“As the twist angle and scale parameters vary, these patterns yield myriad microgeometries, with very small changes in the parameters causing very large changes in the material properties,” says Ben Murphy, co-author of the paper and adjunct assistant professor of mathematics.

Twisting one lattice just two degrees, for example, can cause the moiré patterns to go from regularly repeating to non-repeating—and even appear to be randomly disordered, although all the patterns are non-random.  If the pattern is ordered and periodic, the material can conduct electrical current very well or not at all, displaying on/off behavior similar to semiconductors used in computer chips. But for the aperiodic, disordered-looking patterns, the material can be a current-squashing insulator, “similar to the rubber on the handle of a tool that helps to eliminate electrical shock,” says David Morison, lead author of the study who recently finished his Ph.D. in Physics at the University of Utah under Golden’s supervision.

This kind of abrupt transition from electrical conductor to insulator reminded the researchers of yet another Nobel-winning discovery: the Anderson localization transition for quantum conductors. That discovery, which won the 1977 Nobel Prize in Physics, explains how an electron can move freely through a material (a conductor) or get trapped or localized (an insulator), using the mathematics of wave scattering and interference. But Golden says that the quantum wave equations Anderson used don’t work on the scale of these twisted bilayer composites, so there must be something else going on to create this conductor/insulator effect. “We observe a geometry-driven localization transition that has nothing to do with wave scattering or interference effects, which is a surprising and unexpected discovery,” Golden says.

The electromagnetic properties of these new materials vary so much with just tiny changes in the twist angle that engineers may someday use that variation to precisely tune a material’s properties and select, for example, the visible frequencies of light (a.k.a. colors) that the material will allow to pass through and the frequencies it will block.

“Moreover, our mathematical framework applies to tuning other properties of these materials, such as magnetic, diffusive and thermal, as well as optical and electrical,” says professor of mathematics and study co-author Elena Cherkaev, “and points toward the possibility of similar behavior in acoustic and other mechanical analogues.”

Find the full study in Communications Physics.

 

by Paul Gabrielsen, first published in @TheU.

 

Interactive Forest Maps

May 23, 2022

Wildfire, Drought & Insects

Dying forests in the western U.S.

Threats impacting forests are increasing nationwide.

Planting a tree seems like a generally good thing to do for the environment. Trees, after all, take in carbon dioxide, offsetting some of the emissions that contribute to climate change.

But all of that carbon in trees and forests worldwide could be thrown back into the atmosphere again if the trees burn up in a forest fire. Trees also stop scrubbing carbon dioxide from the air if they die due to drought or insect damage.

The likelihood of those threats impacting forests is increasing nationwide, according to new research in Ecology Letters, making relying on forests to soak up carbon emissions a much riskier prospect.

“U.S. forests could look dramatically different by the end of the century,” says William Anderegg, study lead author and associate professor in the University of Utah School of Biological Sciences. “More severe and frequent fires and disturbances have huge impacts on our landscapes. We are likely to lose forests from some areas in the Western U.S. due to these disturbances, but much of this depends on how quickly we tackle climate change.”

 

William Anderegg

"We’ve seen devastating fire seasons with increasing severity in the past several years. Generally, we expect the western U.S. to be hit hardest."

 

The researchers modeled the risk of tree death from fire, climate stress (heat and/or drought) and insect damage for forests throughout the United States, projecting how those risks might increase over the course of the 21st century.

See their findings in an interactive map at carbonplan.org.

By 2099, the models found, that United States forest fire risks may increase by between four and 14 times, depending on different carbon emissions scenarios. The risks of climate stress-related tree death and insect mortality may roughly double over the same time.

But in those same models, human actions to tackle climate change mattered enormously—reducing the severity of climate change dramatically reduced the fire, drought and insect-driven forest die-off.

“Climate change is going to supercharge these three big disturbances in the U.S.,” Anderegg says. “We’ve seen devastating fire seasons with increasing severity in the past several years. Generally, we expect the western U.S. to be hit hardest by all three of these. And they’re somewhat interconnected too. Really hot and dry years, driven by climate change, tend to drive lots of fires, climate-driven tree mortality and insect outbreaks. But we have an opportunity here too. Addressing climate change quickly can help keep our forests and landscapes healthy.”

The study is published in Ecology Letters and was supported by the National Science Foundation, U.S. Department of Agriculture, David and Lucille Packard Foundation and Microsoft’s AI for Earth.

Find the full study at Ecology Letters.

 

by Paul Gabrielsen, first published at @TheU.

 

How Trees Grow

May 16, 2022

How Trees Grow

William Anderegg

What we’re still learning about how trees grow.

What will happen to the world’s forests in a warming world? Will increased atmospheric carbon dioxide help trees grow? Or will extremes in temperature and precipitation hold growth back? That all depends on whether tree growth is more limited by the amount of photosynthesis or by the environmental conditions that affect tree cell growth—a fundamental question in tree biology, and one for which the answer wasn’t well understood, until now.

A study led by University of Utah researchers, with an international team of collaborators, finds that tree growth does not seem to be generally limited by photosynthesis but rather by cell growth. This suggests that we need to rethink the way we forecast forest growth in a changing climate and that forests in the future may not be able to absorb as much carbon from the atmosphere as we thought.

“A tree growing is like a horse and cart system moving forward down the road,” says William Anderegg, an associate professor in the U’s School of Biological Sciences and principal investigator of the study. “But we basically don’t know if photosynthesis is the horse most often or if it’s cell expansion and division. This has been a longstanding and difficult question in the field. And it matters immensely for understanding how trees will respond to climate change.”

The study is published in Science and is funded by the U.S. Department of Agriculture, the David and Lucille Packard Foundation, the National Science Foundation, the U.S. Department of Energy and the Arctic Challenge for Sustainability II.

Growth rings - oldest growth is at the top.

Source vs. sink

We learned the basics in elementary school—trees produce their own food through photosynthesis, taking sunlight, carbon dioxide and water and turning it into leaves and wood.

There’s more to the story, though. Converting carbon gained from photosynthesis into wood requires wood cells to expand and divide.

So trees get carbon from the atmosphere through photosynthesis. This is the trees’ carbon source. They then spend that carbon to build new wood cells—the tree’s carbon sink.

If the trees’ growth is source-limited, then it’s limited only by how much photosynthesis the tree can carry out and tree growth would be relatively easy to predict in a mathematical model. So rising carbon dioxide in the atmosphere should ease that limitation and let trees grow more, right?

But if instead the trees’ growth is sink-limited, then the tree can only grow as fast as its cells can divide. Lots of factors can directly affect both photosynthesis and cell growth rate, including temperature and the availability of water or nutrients. So if trees are sink-limited, simulating their growth has to include the sink response to these factors.

The researchers tested that question by comparing the trees’ source and sink rates at sites in North America, Europe, Japan and Australia. Measuring carbon sink rates was relatively easy—the researchers just collected samples from trees that contained records of growth. “Extracting wood cores from tree stems and measuring the width of each ring on these cores essentially lets us reconstruct past tree growth,” says Antoine Cabon, a postdoctoral scholar in the School of Biological Sciences and lead author of the study.

Measuring carbon sources is tougher, but doable. Source data was measured with 78 eddy covariance towers, 30 feet tall or more, that measure carbon dioxide concentrations and wind speeds in three dimensions at the top of forest canopies, Cabon says. “Based on these measurements and some other calculations,” he says, “we can estimate the total forest photosynthesis of a forest stand.”

Decoupled

The researchers analyzed the data they collected, looking for evidence that tree growth and photosynthesis were processes that are linked, or coupled. They didn’t find it. When photosynthesis increased or decreased, there was not a parallel increase or decrease in tree growth.

“Strong coupling between photosynthesis and tree growth would be expected in the case where tree growth is source limited,” Cabon says. “The fact that we mostly observe a decoupling is our principal argument to conclude that tree growth is not source-limited.”

Surprisingly, the decoupling was seen in environments across the globe. Cabon says they did expect to see some decoupling in some places, but “we did not expect to see such a widespread pattern.”

The strength of coupling or decoupling between two processes can lie on a spectrum, so the researchers were interested in what conditions led to stronger or weaker decoupling. Fruit-bearing and flowering trees, for example, exhibited different source-sink relationships than conifers. More diversity in a forest increased coupling. Dense, covered leaf canopies decreased it.

Finally, coupling between photosynthesis and growth increased in warm and wet conditions, with the opposite also true: that in cold and dry conditions, trees are more limited by cell growth.

Cabon says that this last finding suggests that the source vs. sink issue depends on the tree’s environment and climate. “This means that climate change may reshape the distribution of source and sink limitations of the world forests,” he says.

A new way to look forward

The key takeaway is that vegetation models, which use mathematical equations and plant characteristics to estimate future forest growth, may need to be updated. “Virtually all these models assume that tree growth is source limited,” Cabon says.

For example, he says, current vegetation models predict that forests will thrive with higher atmospheric carbon dioxide. “The fact that tree growth is often sink limited means that for many forests this may not actually happen.”

That has additional implications: forests currently absorb and store about a quarter of our current carbon dioxide emissions. If forest growth slows down, so do forests’ ability to take in carbon, and their ability to slow climate change.

Find the full study @ science.org.

Other authors of the study include Steven A. Kannenberg, University of Utah; Altaf Arain and Shawn McKenzie, McMaster University; Flurin Babst, Soumaya Belmecheri and David J. Moore, University of Arizona; Dennis Baldocchi, University of California, Berkeley; Nicolas Delpierre, Université Paris-Saclay; Rossella Guerrieri, University of Bologna; Justin T. Maxwell, Indiana University Bloomington; Frederick C. Meinzer and David Woodruff, USDA Forest Service, Pacific Northwest Research Station; Christoforos Pappas, Université du Québec à Montréal; Adrian V. Rocha, University of Notre Dame; Paul Szejner, National Autonomous University of Mexico; Masahito Ueyama, Osaka Prefecture University; Danielle Ulrich, Montana State University; Caroline Vincke, Université Catholique de Louvain; Steven L. Voelker, Michigan Technological University and Jingshu Wei, Polish Academy of Sciences.

 

- by Paul Gabrielsen, first published in @theU

 

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Carbon Nanotubes

April 4, 2022

Carbon Nanotubes

Vikram Deshpande

Long carbon nanotubes reveal subtleties of quantum mechanics.

Vikram Deshpande had a hunch that carbon nanotubes held a lot of promise as a building block. He suspected that their unusual electrical and thermal properties and extraordinary strength could be modified for specific purposes by adding nanofabricated structures.

Working with nanotubes more than a micron long, the University of Utah physicist and his team found that the nanotubes held surprises, even without being adorned with those structural bells and whistles. “We started seeing all this richness in the data and had to investigate that before making the experiment more complicated,” Deshpande says. “Because they are only a nanometer or so in diameter, they are excellent playgrounds for studying the quantum mechanics of electrons in one dimension.”

But thin walls also mean little shielding. Impurities on the surface scatter electrons in the nanotube, and that initially prevented Deshpande from getting clean data.

His solution was to both clean the nanotubes and run his experiments in a DRY ICE 1.5K 70 mm cryostat made by ICEoxford. The UK-based company’s cryostat allows him to suspend nanotubes between supports and run a current through them. The nanotubes heat up to several hundred degrees, and the impurities are knocked off the surface.

ICEoxford cryogenic equipment.

The setup is cooled by pumped helium-4 at around 1.5 K, which is important, says Deshpande. “A lot of cryogenic equipment is vacuum-based, but the heat injected into the nanotube has no way out except along the tube, which is very ineffective.” Another boon is the fact that the cryostat is top loading so it’s easy to access. Within 12 hours of installing a new sample, the entire system is cooled and ready for testing.

With a good nanotube in place and thoroughly clean, Deshpande applies voltage to inject electrons and explore their quantum behavior.

A major influence on electron behavior inside the nanotube is the quality of the end contacts. The electrons travel unimpeded within the tube, known as the ballistic regime. But the ease at which they can escape the tube affects their behavior radically.

Using low-conductivity contacts, Deshpande’s team measured the energy required to add individual electrons to the tube. Subtle changes in the energy showed that the electrons were falling into an ordered pattern called a Wigner crystal—effectively a solid made of pure electrons—which occurs only at very low density. “Lower electron density is obtained with longer lengths, which make our experimental signature possible,” Deshpande says. His team reported their results in Physical Review Letters (volume 123, page 197701, 2019).

Last year the team published another paper in Physical Review Letters (volume 126, page 216802, 2021) with results from high-conductance contacts. They found the electrons’ wave-functions spread along the tube, creating quantum interference, analogous to light in an interferometer. There was not only interference similar to the Fabry-Perot effect between electrons bouncing back and forth, but also a more subtle interference caused by slight variations in the nanotubes, such as chirality. “These are exquisite measurements of delicate quantum effects that we can only see because our long nanotubes accumulate measurable phase difference between these modes,” Deshpande says.

He has also made use of the DRY ICE cryostat’s ability to apply magnetic fields up to 9 teslas. “If you thought the data so far were rich, you should see what happens in a magnetic field!” he says.

Phil Dooley is a freelance writer and former laser physicist based in Canberra, Australia.

 

- by Phil Dooley, first published in Physics Today

 

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Galápagos Letters

March 14, 2022

Galápagos Letters

by Nora Clayton, first published @ biology.utah.edu

January 17, 2022

Adventure Awaits

Getting ready for a field expedition is always an adventure. After packing, COVID testing, homework, buying supplies, planning travel, and coordinating a study, we are very ready to be on our way. Read More >

1

January 24, 2022

El Garrapatero

Our first day in the field we went to “El Garrapatero.” Meaning “Tick Eater,” both the site and its namesake, which happens to be a beach, are named after a common bird called an Ani. Read More >

2

January 31, 2022

Philornis Downsi

Philornis downsi is well known because its larvae are harmful to bird nestlings. The larvae suck blood, hence the “vampire” part of their name. Read More >

3

February 7, 2022

Lions, Iguanas, and Birds

People and wildlife share the space, which means you have to be careful not to step on an iguana or sit too close to a sea lion! Read More >

4

February 14, 2022

Field Observations

Readers should note that biologists, grad students, and intrigued 13-year-olds may stop frequently to observe things. Read More >

5

February 21, 2022

Galápagos Portraits

If it’s true that a picture paints a thousand words, you will have several thousand to read today! Read More >

6

February 28, 2022

Plumber’s Camera

We’re beginning to look inside the nests with a camera, taking notes on the contents of each. Read More >

7

March 7 2022

It’s a Small World

Every day, walking around town, to the beach, the station, or on our patio outside, our group constantly points out ants, carpenter bees, geckos, millipedes, katydids and grasshoppers. Read More >

8

March 14, 2022

Galápagos Penguins

We woke up early to get ready, and catch a bus to the dock on the other side of the island. The drive went through the highlands, where it was beginning to rain. Read More >

9

March 14, 2022

Old Town Quito

The city, full of people, is so different from Puerto Ayora. The streets are packed with shops and each big hill is covered in bright colorful buildings. Read More >

10

Originally published @ biology.utah.edu

Extraordinary Black Hole

January 31, 2022

A Different Kind of Black Hole

Astronomers discovered a black hole unlike any other. At one hundred thousand solar masses, it is smaller than the black holes we have found at the centers of galaxies but bigger than the black holes that are born when stars explode. This makes it one of the only confirmed intermediate-mass black holes, an object that has long been sought by astronomers.

Anil Seth

“We have very good detections of the biggest, stellar-mass black holes up to 100 times the size of our sun, and supermassive black holes at the centers of galaxies that are millions of times the size of our sun, but there aren’t any measurements of black between these. That’s a large gap,” said senior author Anil Seth, associate professor of astronomy at the University of Utah and co-author of the study. “This discovery fills the gap.”

The black hole was hidden within B023-G078, an enormous star cluster in our closest neighboring galaxy Andromeda. Long thought to be a globular star cluster, the researchers argue that B023-G078 is instead a stripped nucleus. Stripped nuclei are remnants of small galaxies that fell into bigger ones and had their outer stars stripped away by gravitational forces. What’s left behind is a tiny, dense nucleus orbiting the bigger galaxy and at the center of that nucleus, a black hole.

“Previously, we’ve found big black holes within massive, stripped nuclei that are much bigger than B023-G078. We knew that there must be smaller black holes in lower mass stripped nuclei, but there’s never been direct evidence,” said lead author Renuka Pechetti of Liverpool John Moores University, who started the research while at the U. “I think this is a pretty clear case that we have finally found one of these objects.”

The study published on Jan. 11, 2022, in The Astrophysical Journal.

A decades-long hunch

B023-G078 was known as a massive globular star cluster—a spherical collection of stars bound tightly by gravity. However, there had only been a single observation of the object that determined its overall mass, about 6.2 million solar masses. For years, Seth had a feeling it was something else.

“I knew that the B023-G078 object was one of the most massive objects in Andromeda and thought it could be a candidate for a stripped nucleus. But we needed data to prove it. We’d been applying to various telescopes to get more observations for many, many years and my proposals always failed,” said Seth. “When we discovered a supermassive black hole within a stripped nucleus in 2014, the Gemini Observatory gave us the chance to explore the idea.”

A wide-field image of M31 with the red box and inset showing the location and image of B023-G78 where the black hole was found.

With their new observational data from the Gemini Observatory and images from the Hubble Space Telescope, Pechetti, Seth and their team calculated how mass was distributed within the object by modeling its light profile. A globular cluster has a signature light profile that has the same shape near the center as it does in the outer regions. B023-G078 is different. The light at the center is round and then gets flatter moving outwards. The chemical makeup of the stars changes too, with more heavy elements in the stars at the center than those near the object’s edge.

“Globular star clusters basically form at the same time. In contrast, these stripped nuclei can have repeated formation episodes, where gas falls into the center of the galaxy, and forms stars. And other star clusters can get dragged into the center by the gravitational forces of the galaxy,” said Seth. “It’s kind of the dumping ground for a bunch of different stuff. So, stars in stripped nuclei will be more complicated than in globular clusters. And that’s what we saw in B023-G078.”

The researchers used the object’s mass distribution to predict how fast the stars should be moving at any given location within the cluster and compared it to their data. The highest velocity stars were orbiting around the center. When they built a model without including a black hole, the stars at the center were too slow compared their observations. When they added the black hole, they got speeds that matched the data. The black hole adds to the evidence that this object is a stripped nucleus.

“The stellar velocities we are getting gives us direct evidence that there’s some kind of dark mass right at the center,” said Pechetti. “It’s very hard for globular clusters to form big black holes. But if it’s in a stripped nucleus, then there must already be a black hole present, left as a remnant from the smaller galaxy that fell into the bigger one.”

The researchers are hoping to observe more stripped nuclei that may hold more intermediate-mass black holes. These are an opportunity to learn more about the black hole population at the centers of low-mass galaxies, and to learn about how galaxies are built up from smaller building blocks.

“We know big galaxies form generally from the merging of smaller galaxies, but these stripped nuclei allow us to decipher the details of those past interactions,” said Seth.

Other authors include Sebastian Kamann of the Liverpool John Moores University; Nelson Caldwell, Harvard-Smithsonian Center for Astrophysics; Jay Strader, Michigan State University; Mark den Brok, Leibniz-Institut für Astrophysik Potsdam; Nora Luetzgendorf, European Space Agency; Nadine Neumayer, Max Planck Institüt für Astronomie; and Karina Voggel, Observatoire astronomique de Strasbourg.

- by Lisa Potter, published in @theU and the Deseret News

 

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Of Mice and Monarchs

January 20, 2022

Of Mice and Monarchs

Sara Weinstein, Postdoctoral Researcher

Monarch butterflies possess a potent chemical armor. As caterpillars, they eat plants filled with toxic cardenolides that build up in their bodies and make them unpalatable to most—but not all—predators. In central Mexico, where the largest winter monarch aggregations occur, scientists observed that rodents attack monarchs that fall to the ground. In particular, the black-eared mouse (Peromyscus melanotis) specializes in these bitter-tasting insects, eating as many as 40 per night.

In a new study, University of Utah biologists found that mice at California monarch overwintering sites can also consume monarch butterflies. Working at one of the largest monarch aggregations outside of Mexico, Pismo State Beach Monarch Butterfly Grove, the researchers discovered that the western harvest mouse (Reithrodontomys megalotis) also ate the grounded monarchs. However, with the precipitous decline in western monarch populations, this butterfly buffet may be in jeopardy.

A harvest mouse munching on a monarch.

The authors do not think that rodents are contributing to the western monarch decline, nor that the monarchs are the only thing that mice can eat. Rather, documenting this new feeding behavior is a reminder of how little we know about the interactions that may be lost as insect populations decline.

“We are in an insect apocalypse right now. There are estimates that 40% of studied invertebrate species are threatened and that over 70% of flying insect biomass is already gone. This is devastating on its own and is also going to have enormous impacts on the other organisms that feed on insects,” said Sara Weinstein, the postdoctoral researcher who led the study.

“Western monarchs and other western butterflies need conservation attention and part of that awareness-raising is illuminating the many ways these animals are interconnected to other insects, birds, mammals, as well as our human communities. This study helps us appreciate more deeply how fewer butterflies means less food for other native animals” said Emma Pelton, senior conservation biologist at the Xerces Society.

Weinstein with a lab-reared monarch.

The study published in the journal Ecology on Dec. 12, 2021.

To study mouse-monarch interactions, the researchers first trapped rodents in the grove in February 2020. The rodents were released, but their feces were kept to screen for monarch DNA—which they found in one sample. This first survey occurred in late winter as monarchs were leaving the aggregation and few remained for mice to munch. Weinstein and colleagues intended to return the following fall during peak monarch season. However, after years of decline, the western monarch population crashed.

“At a site where 100,000 butterflies used to roost, in 2020 there where were fewer than 200 monarchs. So, we had to change tactics,” Weinstein said. “We tested whether rodents would feed on the butterflies using captive-reared monarchs.”

Weinstein set up lab-reared monarch carcasses under camera traps and captured footage of wild harvest mice eating butterflies. She also caught a half dozen mice and offered them monarchs. The mice ate monarchs, typically favoring the abdomen or thorax, high-calorie parts with fewer toxins.

“Many rodent species are likely to have some resistance to cardenolides in monarchs, due to genetic changes at the site where these toxins bind,” said Weinstein. “The Pismo Grove is one of hundreds of western monarch aggregation sites, and it seems likely that, at least in the past, rodents throughout the western monarch range may have supplemented their winter diets with monarchs. If you can handle the cardenolides in a monarch, their bodies are full of fat and offer a pretty good meal.”

Animation of mouse eating a butterfly.

Mouse eating an entire monarch butterfly.

This meal will be a lot harder to find, as over 90% of western monarchs have disappeared in the last 40 years. The missing beauties will surely impact the ecosystem that depends on them for food.

Denise Dearing, Distinguished Professor at the U, was senior author of the study. Photos and animations by Sara Weinstein.

Find the study, “Harvest mice (Reithrodontomys megalotis) consume monarch butterflies (Danaus plexippus), in the journal Ecology: https://doi.org/10.1002/ecy.3607

 

by Lisa Potter, first published in @theU

 

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