Moiré Magic

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

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

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

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

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

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

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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James Webb Space Telescope

James Webb Space Telescope


In December 2020 the James Webb Space Telescope (JWST) finally launched. The $10 billion observatory is a twenty-year joint effort of NASA, the European Space Agency, and the Canadian Space Agency, and the most powerful telescope ever developed. Its mission—peer 13.5 billion lightyears back in time to the earliest stages of the universe.

Anil Seth

JWST’s launch date was December 25 from Europe’s Spaceport in Kourou, French Guiana. Longtime fans of the telescope are celebrating it as a Christmas miracle. It was the first planned to launch in 2007, but decades of delays and false hope drove the project from its initial budget of $500 million up to its current $10 billion cost.

You can watch recorded launch video and future NASA livestreams at  https://www.nasa.gov/nasalive.

The stakes are high for Anil Seth, associate professor in the Department of Physics & Astronomy. Out of more than 1,000 proposals for observation time on the telescope, Seth’s is one of 266 that were approved. He spoke with AtTheU to talk about this cosmic milestone.

What is the James Webb Space Telescope?

It is the largest and most powerful telescope that we’ve ever sent into space—the primary mirror is about the size of a typical house. It’s really big compared to the Hubble Space Telescope, which has a primary mirror the size of a bedroom. Hubble uses the ultraviolet and visible light to create jaw-dropping images of deep space that fundamentally changed our understanding of the cosmos. JWST will be much, much, much farther away than Hubble, located almost one million miles from Earth. From there, it can detect the faintest traces of infrared light, the wavelength of light emitted by everything that produces heat.

NASA assembly, July 2017

The telescope’s primary power is to detect faint galaxies far, far away. It’ll be able to pick up the infrared light spectrum of planets, newly forming stars, black holes, and other faint objects in ways that we’ve never been able to before. Almost every astronomer is probably going to want to use JWST for something. We saw so much using the Hubble Space Telescope. With JWST, we’ll be able to see more than we can imagine. It’s very exciting.

The launch date has been pushed back several times including once this week. Is the telescope launch tricker then usual?

The size makes it really hard to launch. The telescope has three big segments—a sunshield the size of a tennis court, the house-sized primary mirror, and the secondary mirror, Right now, it’s all packaged up like a Christmas present to fit inside the rocket. After launch, the segments will begin to unfold. It’s a complicated process involving hundreds of steps that have to work perfectly. This has never been done before—one error and the whole project could fail. That’s why people are so stressed out!

Where will JWST orbit in space?

It’s going to orbit the sun almost one million miles away from Earth. It will live at what is called a Lagrange point, a location where gravity from the earth and sun are equal. And will just sit there, orbiting with the Earth around the sun. This ensures that the telescope will always point away from the sun.

Full-scale model, September 2005

Anything warm emits infrared light—stars, humans, every other thing on Earth. To make an infrared-detecting telescope, the equipment needs to be extremely cold, so its heat doesn’t interfere with infrared readings from space. That’s what the sun shield is for. The massive mylar sail will create a shadow that prevents the telescope from absorbing heat. The sunshade will begin to unfurl a week after launch, starting with 107 release mechanisms that have to fire simultaneously. The sun shield will then always be between the telescope and sun, keeping the telescope really cold. If this doesn’t happen right…it’ll be bad.

JWST’s location also provides a wide-open view for observations. The Hubble space telescope orbits the Earth just over 300 miles up, which means the planet sometimes blocks the telescope’s vision as it orbits the earth every 90 minutes. At JWST’s Lagrange position, it’s much easier to keep a single orientation in the sky for a longer time and to make observations constantly. So we’ll end up getting more data each year from JWST than from Hubble.

You will be one of the first astronomers to get observation time on the JWST. Can you tell us about your research?

I study black holes. Every black hole has stuff falling onto it that emits light. It turns out that a lot of that light gets emitted at infrared wavelengths. This telescope is much, much, more sensitive to those wavelengths than any other previous telescope. The problem is that we’ve never seen what a faint black hole looks like at these wavelengths.

The Andromeda Galaxy, approximately 2.5 million light-years from Earth.

I’m leading a project that will look at places where we know black holes exist, because we’ve measured them from the motions of the stars around them, but that are very faint. These are so much fainter than something like a quasar, which is where the black hole is devouring as much material as it can. The black holes I’m interested in are just sipping their material, and they’re much more typical of the average black hole in the universe. We’re basically looking unique signatures in this wavelength spectrum that will tip us off to a black hole is present. One of the objects we’ll focus on is the first one ever photographed.

- by Lisa Potter, first published at @theU

 

NASA J.W.S.T. VIDEO


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Biological Data

The Science of Biological Data


Fred Adler

In an age when cross-disciplinary collaboration has become a buzzterm, especially in academia, Fred Adler puts his mathematical models where his mouth is. Multi-disciplinary work—in which academic silos are breached in the search for truth—is the hallmark of what Adler, who has a joint appointment in mathematics and biology, does.

His is the kind of work that will be supported by the new science building recently announced by the College of Science, dedicated to applied and multi-disciplinary work, and where most STEM students at the U will eventually find themselves for a time.

As Director of the Center for Quantitative Biology, Adler and his team have applied their data-driven tool kit to everything from viruses to animal behavior, and from biodiversity to infectious diseases. Who else can claim a lab’s subject models as varied as aphid-tending ants, hantavirus, and the Southern Right Whale off the coast of Argentina?

Math in Nature

The Adler group’s approach to research is driven by basic questions about how biology works. To bring together several threads of research, the lab began a study of rhinoviruses, the most common cause of the common cold, and how they routinely and rapidly change. The study uses mathematical models based on known interactions in the immune system and genetic sequences. “We hope to build detailed evolutionary models of this rapidly change set of viruses,” Adler reports.

He and his team are now looking at cancer in humans. There are, of course, hypotheses of how cancer takes over cells in the body and grows. But too many of these hypotheses are based on assumptions that cells behave as they do with complete information and clever plans for the future instead of the confusing world of a real tissue.

“However useful some of these [current] models are,” says Adler, “they are not based on a realistic assumption.” In fact, a prime contribution of the mathematical modeler is “to make sense of things from the perspective of what you’re modeling.” What access to information does the cell or organism have, is a central, guiding question.

Muskan Walia and Emerson Arehart

Part of how cancer behaviors may be better scientifically “unpacked” is through game theory but expanded over time and space and placed in a context of incomplete information between constituent parts.

Mathematical models, or more accurately, an ensemble of models later aggregated like political polls or weather models to predict the future, may be the answer. “We usually don’t get a simple smoking gun,” says Adler referring to complicated questions in biology, whether developmental, behavioral-ecological, immuno- or micro-biological. “With nine or ten big mathematical models running all the time you have a [more robust] hypothesis,” he says.

“All thinking is done using modeling,” Adler reminds us, “whether it’s through language or, in my case, mathematics.” The strength of the latter is that when mathematical modeling is added to the classical biologist’s models, it is “perfectly explicit about its assumptions. When you do the math right (and we always do), the logic leading from assumptions to conclusions is airtight ‘true.’”

This is important because a mathematical argument can’t be controverted. “If conclusions in biological research are wrong, it’s the assumptions that are wrong,” and the researcher can then pivot on those assumptions.

Modeling of this kind, of course, has proven helpful, most recently, in the study of Sars-CoV-19, the virus that has propelled the world into a pandemic. The coronavirus does not operate in isolation, but with other components through the human immune system.

This kind of work is animated not just by its predictive character using statistics—as in the case of artificial intelligence or machine learning (“We aren’t all cyborgs, yet,” Adler says)—but, it is predictive in a mechanistic sense in that it cares deeply about the more nuanced and open-ended “how,” the foundation of the scientific method.

Adler started out at Harvard as a pure mathematician, but by the time he arrived at Cornell University as a graduate student, he had discovered that he really enjoyed talking and collaborating with biologists. Stanford-based Deborah Gordon, a renowned expert on ants, which as he puts it, “achieve a lot of stuff fairly robustly through simple rules,” was one of them. He also found himself with David Winkler in upstate New York in a bird blind and observing the breeding and offspring-raising behaviors of tree swallows. The complicated models he built based on that research were never published, but Adler was hooked on life sciences.

Whether it’s modeling the lungs of cystic fibrosis patients looking for a transplant, determining that the changesnin Covid-19 are driven not just by mutations in the virus but adaptations of human immune response, or other “bench to bedside” medical science, Fred Adler has found a home in the mechanistic aspects, the “how,” of basic science.

How to synthesize his research over the past thirty years is the next big question. For now he will continue with modeling biological systems, their signaling networks based on the body’s own network of “trust” between components, and determining how those systems are corrupted… and maybe how to fix them.

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Theory Meets Intuition

Theory Meets Intuition


Will Feldman

Will Feldman, Assistant Professor of Mathematics, joined the Department of Mathematics in 2020. He studies mathematical models of physics and thinks about the things most of us take for granted, for example, fluid flow, water droplets, and flame propagation. These models are often developed by engineers or physicists using basic assumptions, but the resulting equations can be difficult or impossible to solve exactly.

“I’m interested in proving mathematically rigorous results for these models,” said Feldman. In his research, the results sometimes show the limitations of the modeling assumptions used to derive the equations. Other times, they explain the behavior of all the solutions of the equation without relying on special formulae. “And sometimes, the results are used to justify numerical computations, which are meant to approximate solutions of these equations,” he said.

One particular type of problem Feldman has studied is called “homogenization”—the study of the physical properties of complicated heterogeneous materials. The idea is to “average” or “homogenize” the complicated small-scale inhomogeneities in the material to derive simpler effective equations to describe properties at larger scales. For example, the ideas of homogenization theory can be used to study the shapes of water droplets on surfaces that have microscopic roughness, such as a plant leaf, a piece of glass, or a table top.

Water droplet on fabric.

“I like to work out these kinds of questions because I get to use both physical intuition and theoretical mathematical tools,” he said.
Feldman wasn’t always interested in mathematics. As an undergraduate, he thought he wanted to study physics or history. He started taking math classes because math was useful in studying advanced physics. “I had a lot of amazing math professors, and I started to like math a lot,” he said. “Eventually, I realized I could maybe study math and also bring in my interest in applications (especially physics). Basically, that’s how I ended up studying partial differential equations.”

Like many undergrads who study math, Feldman was worried he would need a special talent to succeed at math, but he had supportive and encouraging mentors, so he never got too discouraged. “I hope the experience of having good mentors has taught me to be a good mentor, too, and show my students I believe in them and the many interesting possibilities available in a career in or related to mathematics,” he said.

Before joining the U, Feldman received his Ph.D. from UCLA in 2015 and was an L.E. Dickson Instructor at the University of Chicago from 2015-2019. He was also a member at the Institute for Advanced Study (IAS) from 2019-2020. The IAS is one of the world’s leading centers for curiosity-driven basic research, based in Princeton, NJ.

In 2019, Feldman was awarded the John E. and Marva M. Warnock Presidential Endowed Chair for Mathematics by the University of Utah. He will hold the chair for five years and anticipates the funding will provide new and interesting directions for his research. He hopes to have a positive impact by training, mentoring, and supporting a next generation of mathematicians. “It was a great honor to be offered the Warnock Chair,” said Feldman. “I am obviously very proud to receive the award and grateful to the Warnock family and the university.”

As he moves forward in his research, he’s been thinking about problems involving interfaces in heterogeneous media. He’s also been wondering about transport equations and models of grain boundary motion in polycrystalline materials. He’s looking forward to discussions and collaborations with his colleagues in the Math Department, especially in the applied and probability groups.
Feldman and his wife are in the midst of raising two young children. He enjoys the great hiking in Utah and is looking forward to relearning how to ski and maybe starting new outdoor activities, such as climbing and biking. He enjoys cooking and has become obsessed (during the pandemic) with making a great cup of coffee.

- by Michele Swaner, first published at math.utah.edu

Warnock Presidential Endowed Chair

“A Presidential Endowed Chair at the University of Utah is one of the highest honors that we can bestow on a faculty member.” —Dean Peter Trapa

Presidential Endowed Chairs are crucial for the recruitment and retainment of the most accomplished faculty members. Through these philanthropic gifts, the faculty are able to further support their cutting-edge research and explore new areas in their field.

John E. Warnock, BS’61, MS’64, PhD’69, and Marva M. Warnock created a Presidential Endowed Chair for Faculty Development in Mathematics in 2001 through a gift of Adobe Systems stock.

For more information on a establishing a Presidential Endowed Chair, or other named gift opportunities, please contact the development team at 801-581-6958, or visit science.utah.edu/giving.

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