UC San Diego Engineering Professor Solves Deep Earthquake Mystery (Geology)

A University of California San Diego engineering professor has solved one of the biggest mysteries in geophysics: What causes deep-focus earthquakes?

These mysterious earthquakes originate between 400 and 700 kilometers below the surface of the Earth and have been recorded with magnitudes up to 8.3 on the Richter scale.

Xanthippi Markenscoff, a distinguished professor in the Department of Mechanical and Aerospace Engineering at the UC San Diego Jacobs School of Engineering, is the person who solved this mystery. Her paper “Volume collapse instabilities in deep earthquakes: a shear source nucleated and driven by pressure” appears in the Journal of the Mechanics and Physics of Solids.

The term deep-focus earthquake refers to the fact that this type of earthquake originates deep within the Earth’s mantle where pressure forces are very high. Since deep-focus earthquakes were first identified in 1929, researchers had been trying to understand what processes cause them. Researchers thought that the high pressures would produce an implosion which would intuitively produce pressure waves. However, they had not been able to connect the dots between the high pressure and the specific kind of seismic waves — called shear (or distortional) seismic waves — produced by deep-focus earthquakes. (You can feel distortional energy if you hold your forearm and then twist it.)

In her new paper, Markenscoff completes her explanation of this mystery that occurs under ultra-high pressures. She unraveled the mystery in a string of papers beginning in 2019. In addition, her solution gives insight into many other phenomena such as planetary impacts and planetary formation that share similar geophysical processes.

“This is a perfect example of how deep mathematical modeling rigorously rooted in mechanics and physics can help us solve mysteries in nature. Professor Markenscoff’s work can have profound impact not only on how we understand deep-focus earthquakes, but also on how we might controllably use dynamic phase transformations in engineering materials to our benefit,” said Huajian Gao, a Distinguished University Professor in Singapore’s Nanyang Technological University and the Editor of the Journal of the Mechanics and Physics of Solids where Markenscoff’s paper appears.

From transforming rock to earthquake

It has been well recognized that the high pressures that exist between 400 and 700 kilometers below the surface of the earth can cause olivine rock to undergo a phase transformation into a denser type of rock called spinel. This is analogous to how coal can transform into diamond, which also happens deep in Earth’s mantle.

Going from olivine to denser spinel leads to reductions in volume of rock as atoms move closer to each other under great pressure. This can be called “volume collapse.” This volume collapse and the associated “transformational faulting” has been considered the predominant cause for deep-focus earthquakes. However, until now, there was no model based on volume collapse that predicted the shear (distortional) seismic waves that actually arrive at the earth’s surface during deep-focus earthquakes. For this reason other models were also considered, and the state of affairs remained stagnant.

Markenscoff has now solved this mystery using fundamental mathematical physics and mechanics by discovering instabilities that occur at very high pressures. One instability concerns the shape of the expanding region of transforming rock and the other instability concerns its growth.

For the expanding regions of this phase transformation from olivine to spinel to grow large, these transforming regions with large densification will assume a flattened “pancake-like” shape that minimizes the energy required for the densified region to propagate in the untransformed medium as it grows large. This is a symmetry breaking mode which can occur under the very high pressures that exist where deep-focus earthquakes originate, and it is this symmetry breaking that creates the shear deformation responsible for the shear waves that reach Earth’s surface. Previously, researchers assumed symmetry-preserving spherical expansion, which would not result in the shear seismic waves. They did not know that symmetry would be allowed to be broken.

“Breaking the spherical symmetry of the shape of the transforming rock minimizes the energy required for the propagating region of phase transformation to grow large,” said Markenscoff. “You do not spend energy to move the surface of a large sphere, but only the perimeter.”

In addition, Markenscoff explained that inside the expanding region of phase transformation of rock, there is no particle motion and no kinetic energy (it is a “lacuna”), and, thus, the energy that radiates out is maximized. This explains why the seismic waves can get to the surface, rather than much of the energy dissipating in the interior of the Earth.

Markenscoff’s analytical model for the deformation fields of the expanding seismic source is based on the dynamic generalization of the seminal Eshelby (1957) inclusion which satisfies the lacuna theorem (Atiya et al, 1970). The energetics of the expanding region of phase transformation are governed by Noether’s (1918) theorem of theoretical physics through which she obtained the instabilities that create a growing and fast moving avalanche of collapsing volume under pressure. This is the second discovered instability (regarding growth): once an arbitrarily small densified flattened region has been triggered, under a critical pressure it will continue to grow without needing further energy. (It just keeps collapsing “like a house of cards”.) Thus, the mystery is resolved: although it is a shear source, what drives deep-focus earthquake propagation is the pressure acting on the change in volume.

When asked to reflect on her discovery that deep-focus earthquakes could be described with the theorems that are the bedrock of mathematical physics, she said, “I feel like I have bonded to nature. I have discovered the beauty of how nature works. It’s the first time in my life. Before it was putting a little step on someone else’s steps. I felt this immense joy.”

Relevant discovery

The deep-focus earthquakes are only one of the phenomena in which these instabilities manifest themselves. They also occur in other phenomena of dynamic phase transformations under high pressures, such as planetary impacts and amorphization. Today, there are new experimental facilities such as the National Ignition Facility (NIF) managed by Lawrence Liver National Laboratory in which researchers are able to study materials under extremely high pressures that were impossible to test before.

The new work from Markenscoff provides an important demonstration and reminder that gaining deeper understanding of the mysteries of nature often requires the insights that can be gained by harnessing the fundamentals of mathematical physics together with experimental research done in extreme conditions.

In fact, Markenscoff co-organized two National Science Foundation (NSF) funded workshops at UC San Diego in 2016 and 2019 which brought together geophysicists and seismologists with mechanicians to ensure that these research communities remain aware of the methodologies and techniques developed in mechanics.

“Our education systems should continue to invest in the teaching of the fundamentals of science as the pillars for the advancement of knowledge, which can be achieved by interdisciplinary convergence of theory, experiments and data science,” said Markenscoff.

She also noted the importance of the research support she has received over the years from the US National Science Foundation (NSF).

“Knowing that my NSF program manager believed that it was possible to solve this ‘mystery’ and funded me, bolstered both my confidence and my determination to persevere”, said Markenscoff. “I point this out as a reminder for all of us. It’s also critical that we give thoughtful and considered encouragement to our students and colleagues. Knowing that people whom you respect believe in you and your work can be very powerful.”

Featured image: Xanthippi Markenscoff is a distinguished professor in the Department of Mechanical and Aerospace Engineering at the University of California San Diego Jacobs School of Engineering. © Xanthippi Markenscoff

Reference: Xanthippi Markenscoff, “Volume collapse” instabilities in deep-focus earthquakes: A shear source nucleated and driven by pressure, Journal of the Mechanics and Physics of Solids, 2021, 104379, ISSN 0022-5096, https://doi.org/10.1016/j.jmps.2021.104379. (https://www.sciencedirect.com/science/article/pii/S0022509621000685)

Provided by University of California San Diego

What Are The Minimum Periods Of Hydrogen Rich Bodies? (Planetary Science)

Orbital periods in systems containing white dwarfs (‘WDs’) can be extremely short, especially if both of the stars are H-exhausted objects. The best examples of this are WD+WD binaries with periods of 7 and 9 minutes. Such systems almost certainly involve one or more phases of mass transfer. But what will be the minimum allowed orbital periods when at least one of the stars is still H-rich? Take BD+WD binaries, for instance (BD- Brown dwarf). Thats what, Rappaport and colleagues answered in their recently published paper on Arxiv.

Figure 1. Mass-radius relation for H-rich bodies spanning masses from Saturn to stars on the ZAMS up to 1 M (red curve). For the region between Saturn’s mass and the end of the brown-dwarf range (at ∼0.074 M) they used equation (9) given in paper with X = 0.7. For stars on the ZAMS they used the simple expression given by equation (15) given in paper. The blue and cyan dots are an empirical sample of planets and main-sequence stars. The green points are their compilation of brown dwarfs. The black curve is an approximation to the red curve which has been smoothly blended near the transition between the ZAMS stars and brown dwarfs. Note how both the red and black curves hug the lower locus of measured objects – as desired. © Rappaport et al.

They have used radius-mass relations, R(M) displayed in fig 1, in conjunction with function:

to derive the minimum allowed orbital period vs. the body’s mass. The results are shown in fig 2 below.

Figure 2. Minimum allowed orbital period of H-rich bodies as a function of their mass. The various closely spaced colored curves (red, orange, … blue, purple) are for different masses of the host star ranging from 0.3 M to 1.4 M, respectively. The dotted red curve is the limit obtained for incompressible fluid bodies. Heavy, filled, colored circles refer to fiducial-mass objects detailed in Table 1. © Rappaport et al.

As we can see, there is a general trend of decreasing minimum orbital periods, Pmin from 620 min (10.3 hr) for Saturn-mass objects (red circle in Fig. 4), to 430 min (7.2 hr) for Jupiters (orange circle), to 104 min (1.7 hr) for objects on the boundary between super-Jupiters and brown dwarfs (blue circle), all the way down to 37 min (0.62 hr) for the coldest and most massive brown dwarfs (purple circle), respectively. These values are summarized in Table 1 below.

Table 1: Minimum Orbital Periods of H-Rich Bodies © Rappaport et al.

Their work also aimed, towards distinguishing brown dwarfs from planets that are found transiting the host white dwarf without recourse to near infrared or radial velocity measurements. For objects with orbital periods ≲ 100 minutes they concluded that we are observing a brown dwarf (or second WD) rather than a gas-giant planet.

Reference: S. Rappaport, A. Vanderburg, J. Schwab, L. Nelson, “Minimum Orbital Periods of H-Rich Bodies”, Arxiv, pp. 1-10, 2021. https://arxiv.org/abs/2104.12083

Note for editors of other websites: To reuse this article partially or fully kindly give credit to author S. Aman or either provide our article on your website.

Harvesting Water From Air With Hydrogels and MOFs (Chemistry)

With the world facing increased water shortages because of climate change, scientists are getting creative with new methods for harvesting water from the atmosphere. Specialized materials play a key role in these processes, and they could also have applications in cooling systems. A new article in Chemical & Engineering News, the weekly newsmagazine of the American Chemical Society, details the ways researchers are transforming how the world stays hydrated.

Over half of the world’s population faces water scarcity at least one month per year, and a warming planet is only making matters worse, writes special correspondent XiaoZhi Lim. In recent years, scientists have explored using metal-organic frameworks (MOFs), which are porous solid materials that can capture and release water in arid conditions. Other researchers have found that hydrogels can hold more water than MOFs but perform better in more humid conditions. By creating a hybrid of these materials, the goal is to optimize water harvesting technologies for any environment.

Experts say that the applications for water harvesting materials are “almost endless,” from self-irrigating soil to air conditioning. Researchers in Singapore have created a new hybrid material that dehumidifies moist air before it is cooled, possibly making air conditioners more energy efficient. The collected condensation from the dehumidifying process could then be used to supply a building with water. The U.S. Defense Advanced Research Projects Agency (DARPA) has invested heavily in these new technologies and is planning to conduct tests in an array of climate conditions. Experts say that any water-harvesting material will need to demonstrate long-term stability and efficiency, but they’re hopeful that these innovations will help combat drought and desertification worldwide.

“The world needs water. These materials take it from the air”
Chemical & Engineering News

Featured image: Members of the Omar Yaghi group stand next to a water-from-air device loaded with MOF-303 (right). Bottles fill with water that the device pulled from the dry air in the Mojave Desert (left). © Yaghi group/University of California, Berkeley

Provided by American Chemical Society

Two Compounds Can Make Chocolate Smell Musty and Moldy (Food)

Chocolate is a beloved treat, but sometimes the cocoa beans that go into bars and other sweets have unpleasant flavors or scents, making the final products taste bad. Surprisingly, only a few compounds associated with these stinky odors are known. Now, researchers reporting in ACS’ Journal of Agricultural and Food Chemistry have identified the two compounds that cause musty, moldy scents in cocoa — work that can help chocolatiers ensure the quality of their products. 

Cocoa beans, when fermented correctly, have a pleasant smell with sweet and floral notes. But they can have an off-putting scent when fermentation goes wrong, or when storage conditions aren’t quite right and microorganisms grow on them. If these beans make their way into the manufacturing process, the final chocolate can smell unpleasant, leading to consumer complaints and recalls. So, sensory professionals smell fermented cocoa beans before they are roasted, detecting any unwanted musty, moldy, smoky or mushroom-like odors. Even with this testing in place, spoiled beans can evade human noses and ruin batches of chocolate, so a more objective assessment is needed for quality control. In previous studies, researchers used molecular techniques to identify the compounds that contribute to undesirable smoky flavors, but a similar method has not clarified other volatile scent compounds. So, Martin Steinhaus and colleagues wanted to determine the principal compounds that cause musty and moldy odors in tainted cocoa beans.

The researchers identified 57 molecules that made up the scent profiles of both normal and musty/moldy smelling cocoa beans using gas chromatography in combination with olfactometry and mass spectrometry. Of these compounds, four had higher concentrations in off-smelling samples. Then, these four compounds were spiked into unscented cocoa butter, and the researchers conducted smell tests with 15-20 participants. By comparing the results of these tests with the molecular content of nine samples of unpleasant fermented cocoa beans and cocoa liquors, the team determined that (–)-geosmin — associated with moldy and beetroot odors — and 3-methyl-1H-indole — associated with fecal and mothball odors — are the primary contributors to the musty and moldy scents of cocoa beans. Finally, they found that (–)-geosmin was mostly in the beans’ shells, which are removed during processing, while 3-methyl-1H-indole was primarily in the bean nib that is manufactured into chocolate. The researchers say that measuring the amount of these compounds within cocoa beans could be an objective way to detect off-putting scents and flavors, keeping future batches of chocolate smelling sweet.

The authors acknowledge funding from the German Ministry of Economic Affairs and Energy via the German Federation of Industrial Research Associations (AiF) and the Industrial Collective Research (IGF).

“Molecular Background of a Moldy-Musty Off-Flavor in Cocoa”
Journal of Agricultural and Food Chemistry

Featured image: Researchers have identified two compounds that can make chocolate smell musty and moldy. Credit: ivan_kislitsin/Shutterstock.com

Provided by American Chemical Society

Reducing Blue Light With A New Type of LED That Won’t Keep You up all Night (Biology)

To be more energy efficient, many people have replaced their incandescent lights with light-emitting diode (LED) bulbs. However, those currently on the market emit a lot of blue light, which has been linked to eye troubles and sleep disturbances. Now, researchers reporting in ACS Applied Materials & Interfaces have developed a prototype LED that reduces — instead of masks — the blue component, while also making colors appear just as they do in natural sunlight.

LED light bulbs are popular because of their low energy consumption, long lifespan and ability to turn on and off quickly. Inside the bulb, an LED chip converts electrical current into high-energy light, including invisible ultraviolet (UV), violet or blue wavelengths. A cap that is placed on the chip contains multiple phosphors — solid luminescent compounds that convert high-energy light into lower-energy visible wavelengths. Each phosphor emits a different color, and these colors combine to produce a broad-spectrum white light. Commercial LED bulbs use blue LEDs and yellow-emitting phosphors, which appear as a cold, bright white light similar to daylight. Continual exposure to these blue-tinted lights has been linked to cataract formation, and turning them on in the evening can disrupt the production of sleep-inducing hormones, such as melatonin, triggering insomnia and fatigue. To create a warmer white LED bulb for nighttime use, previous researchers added red-emitting phosphors, but this only masked the blue hue without getting rid of it. So, Jakoah Brgoch and Shruti Hariyani wanted to develop a phosphor that, when used in a violet LED device, would result in a warm white light while avoiding the problematic wavelength range.  

As a proof of concept, the researchers identified and synthesized a new luminescent crystalline phosphor containing europium ((Na1.92Eu0.04)MgPO4F). In thermal stability tests, the phosphor’s emission color was consistent between room temperature and the higher operating temperature (301 F) of commercial LED-based lighting. In long-term moisture experiments, the compound showed no change in the color or intensity of light produced. To see how the material might work in a light bulb, the researchers fabricated a prototype device with a violet-light LED covered by a silicone cap containing their luminescent blue compound blended with red-emitting and green-emitting phosphors. It produced the desired bright warm white light while minimizing the intensity across blue wavelengths, unlike commercial LED light bulbs. The prototype’s optical properties revealed the color of objects almost as well as natural sunlight, fulfilling the needs of indoor lighting, the researchers say, though they add that more work needs to be done before it is ready for everyday use.

The authors acknowledge funding from the U.S. National Science Foundation and the Welch Foundation.

“Advancing Human-Centric LED Lighting Using Na2MgPO4F:Eu2+
ACS Applied Materials & Interfaces

Featured image: This prototype device creates a warm white light without the blue hues that can cause health problems. Credit: Jakoah Brgoch

Provided by American Chemical Society

How a SARS-CoV-2 Variant Sacrifices Tight Binding for Antibody Evasion? (Medicine)

The highly infectious SARS-CoV-2 variant that recently emerged in South Africa, known as B.1.351, has scientists wondering how existing COVID-19 vaccines and therapies can be improved to ensure strong protection. Now, researchers reporting in ACS’ Journal of Medicinal Chemistry have used computer modeling to reveal that one of the three mutations that make variant B.1.351 different from the original SARS-CoV-2 reduces the virus’ binding  to human cells –– but potentially allows it to escape some antibodies.

Since the original SARS-CoV-2 was first detected in late 2019, several new variants have emerged, including ones from the U.K., South Africa and Brazil. Because the new variants appear to be more highly transmissible, and thus spread rapidly, many people are worried that they could undermine current vaccines, antibody therapies or natural immunity. Variant B.1.351 bears two mutations (N501Y and E484K) that can enhance binding between the receptor binding domain (RBD) of the coronavirus spike protein and the human ACE2 receptor. However, the third mutation (K417N; a lysine to asparagine mutation at position 417) is puzzling because it eradicates a favorable interaction between the RBD and ACE2. Therefore, Binquan Luan and Tien Huynh from IBM Research wanted to investigate potential benefits of the K417N mutation that could have caused the coronavirus to evolve along this path.

The researchers used molecular dynamics simulations to analyze the consequences of the K417N mutation in variant B.1.351. First, they modeled binding between the original SARS-CoV-2 RBD and ACE2, and between the RBD and CB6, which is a SARS-CoV-2-neutralizing antibody isolated from a recovered COVID-19 patient. They found that the original amino acid, a lysine, at position 417 in the RBD interacted more strongly with CB6 than with ACE2, consistent with the antibody’s therapeutic efficacy in animal models. Then, the team modeled binding with the K417N variant, which changes that lysine to an asparagine. Although this mutation reduced the strength of binding between the RBD and ACE2, it decreased the RBD’s binding to CB6 and several other human antibodies to a much greater extent. Thus, variant B.1.351 appears to have sacrificed tight binding to ACE2 at this site for the ability to evade the immune system. This information could prove useful to scientists as they work to enhance the protection of current vaccines and therapies, the researchers say. 

The authors acknowledge funding from their employer, IBM.

Featured image: Computer simulations shed light on how a SARS-CoV-2 variant evades antibodies. Credit: felipe caparros/Shutterstock.com

“Insights into SARS-CoV-2’s Mutations for Evading Human Antibodies: Sacrifice and Survival”
Journal of Medicinal Chemistry

Provided by American Chemical Society

Mayo Clinic Preclinical Discovery Triggers Wound Healing, Skin Regeneration (Medicine)

Difficult-to-treat, chronic wounds in preclinical models healed with normal scar-free skin after treatment with an acellular product discovered at Mayo Clinic. Derived from platelets, the purified exosomal product, known as PEP, was used to deliver healing messages into cells of preclinical animal models of ischemic wounds. The Mayo Clinic research team documented restoration of skin integrity, hair follicles, sweat glands, skin oils and normal hydration.

Ischemic wounds occur when arteries are clogged or blocked, preventing important nutrients and oxygen from reaching the skin to drive repair. This groundbreaking study titled, “TGF-β Donor Exosome Accelerates Ischemic Wound Healing,” is published in Theranostics.

“This paper documents that PEP, an off-the-shelf, room-temperature-stable exosome, is capable of healing wounds that are depleted of adequate blood supply. Wounds healed with only a single application of exosome,” says Steven Moran, M.D., a Mayo Clinic plastic surgeon and senior co-author on the study. “I was surprised that this product regenerated healthy skin with normal biomechanical properties — not scar tissue. As this technology is now scaled and biomanufactured for clinical applications, it creates the potential for huge advancement in medical science and the field of plastic surgery.”

This study has laid the foundation for Food and Drug Administration approval to begin a first-in-class clinical trial to test safety of using the purified exosomal product for wound healing in patients. This research is supported by Mayo Clinic’s Center for Regenerative Medicine, which is a leader in advancing new, validated regenerative procedures from research into practice.

Chronic ischemic wounds are common in people with conditions such as diabetespressure ulcershardening of arteries, traumatic injury or side effects of radiation therapy. Standard treatments for these wounds include wound dressing, topical gels and surgery. Although these measures offer some relief, they often cannot fully close the wound. As a result, approximately 7 million people in the U.S. have wounds that don’t close properly, and efforts to find solutions have grown to a multibillion dollar industry, according to National Institutes of Health-sponsored research. When the condition progresses, nonhealing wounds lead to limb amputation.

The purified exosomal product is an extracellular vesicle that delivers cargo from one cell to another, targeting exact tissues in need of repair. This technology is manufactured under strict quality control measures and formulated as a dry powder to enable long-term storage at room temperature. In the operating room or at the bedside, the powder is mixed with a hydrogel solution on-site and can be applied directly to the wound. Unlike cellular products, it does not have to be sent to an outside laboratory to be cultured and scaled.

“What we see with this technology is not just that the wound is closed, but also that the blood supply to the tissue is restored. Our effort culminating in the development of this exosomal technology was to create a therapy that can be offered to all patients in need through elimination of logistical limitations often seen with more traditional regenerative therapy,” says Atta Behfar, M.D., Ph.D., deputy director of Translation, Mayo Clinic’s Center for Regenerative Medicine and senior author. “Our research hopes to answer whether this can be a new healing solution for patients suffering with nonhealing chronic wounds.” Dr. Behfar is director of the Mayo Clinic Van Cleve Cardiac Regenerative Medicine Program where the purified exosomal product was discovered.

The research

The research team replicated wounds with low blood supply in large animal models. They treated some of the wounds with the purified exosomal product and compared them to wounds that were treated with the hydrogel alone. They found wounds treated with the purified exosomal product were able to heal with skin restored to its normal architecture.

“We found that this exosome therapy has the ability to enhance regeneration of blood vessels in damaged tissues. Without treatment, chronic ischemic wounds grow larger and more problematic,” says Ao Shi, Ph.D., a student in the Regenerative Sciences Training Program in Mayo Clinic Graduate School of Biomedical Sciences and first author.

Dr. Behfar is the co-founder of Rion LLC, which Mayo Clinic has licensed to manufacture the purified exosomal product. Mayo Clinic and Dr. Behfar have a financial interest in the technology referenced in this news release.

Provided by Mayo Clinic

Ludwig Cancer Research Study Shows Pancreatic Cancer Cells Reverse to Advance Malignancy (Medicine)

A Ludwig Cancer Research study has identified a previously unrecognized mechanism by which cancer cells of a relatively benign subtype of pancreatic tumors methodically revert–or “de-differentiate”–to a progenitor, or immature, state of cellular development to spawn highly aggressive tumors that are capable of metastasis to the liver and lymph nodes.

The study, led by Ludwig Lausanne’s Douglas Hanahan and published in Cancer Discovery, a journal of the American Association for Cancer Research, also shows that engagement of the mechanism is associated with poorer outcomes in patients diagnosed with pancreatic neuroendocrine tumors (PanNETs). Further, its findings provide concrete evidence that such cellular de-differentiation, widely observed across cancer types, is a not merely a random consequence of cancer cells’ other aberrations.

“Our study provides a clear example in a single tumor type that de-differentiation is an independently regulated and separable step in multi-step tumorigenesis,” said Hanahan, distinguished scholar at the Ludwig Lausanne Branch. “Moreover, this is not nonspecific de-differentiation, but rather, the result of a precise reversion of a developmental pathway that generated the mature cell type from which the cancer arose.”

PanNET tumors originate from the islet beta-cells of the pancreas, which produce the hormone insulin. Hanahan and his colleagues had previously reported that these tumors can be divided into two subtypes: a relatively benign, ‘well-differentiated’ subtype that maintains many features of insulin producing beta-cells, and a more aggressive and poorly-differentiated subtype that lacks those features.

Using a PanNET mouse model, they showed in the current study that the ‘poorly differentiated’ cancer cells have many characteristics of normal islet progenitor cells, and that the progression from benign to aggressive PanNET tumors requires cancer cells to retrace the pathway of beta cell differentiation and maturation to assume the progenitor state.

The researchers also uncovered a molecular circuit in cancer cells that governs this de-differentiation. They report that tumor cells poised to de-differentiate step up their production of a type of RNA molecule that regulates gene expression known as microRNA18. This ultimately causes the activation of Hmgb3, a protein that controls the expression of a suite of genes that pushes the cells into a progenitor state.

The results of this study provide new insights on de-differentiation as part of the puzzle of cancer and furnish preliminary evidence supporting its inclusion as a distinct and separable step, or perhaps sub-step, in the deadly progression toward malignancy.

This study was supported by Ludwig Cancer Research, the Swiss National Science Foundation and the Human Frontier Science Program Organization.

In addition to his Ludwig post, Douglas Hanahan is a professor emeritus at École Polytechnique Fédérale de Lausanne (EPFL).

Featured image: Ludwig Lausanne’s Douglas Hanahan © Ludwig Cancer Research

Provided by Ludwig Institute for Cancer Research

About Ludwig Cancer Research

Ludwig Cancer Research is an international collaborative network of acclaimed scientists that has pioneered cancer research and landmark discovery for 50 years. Ludwig combines basic science with the ability to translate its discoveries and conduct clinical trials to accelerate the development of new cancer diagnostics and therapies. Since 1971, Ludwig has invested nearly $3 billion in life-changing science through the not-for-profit Ludwig Institute for Cancer Research and the six U.S.-based Ludwig Centers. To learn more, visit www.ludwigcancerresearch.org.

Mapping the Electronic States in an Exotic Superconductor (Material Science)

Scientists characterized how these states depend on local chemical composition, narrowing the search for where to look compositionally to enable quantum computing

Scientists characterized how the electronic states in a compound containing iron, tellurium, and selenium depend on local chemical concentrations. They discovered that superconductivity (conducting electricity without resistance), along with distinct magnetic correlations, appears when the local concentration of iron is sufficiently low; a coexisting electronic state existing only at the surface (topological surface state) arises when the concentration of tellurium is sufficiently high. Reported in Nature Materials, their findings point to the composition range necessary for topological superconductivity. Topological superconductivity could enable more robust quantum computing, which promises to deliver exponential increases in processing power.

“Quantum computing is still in its infancy, and one of the key challenges is reducing the error rate of the computations,” said first author Yangmu Li, a postdoc in the Neutron Scattering Group of the Condensed Matter Physics and Materials Science (CMPMS) Division at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory. “Errors arise as qubits, or quantum information bits, interact with their environment. However, unlike trapped ions or solid-state qubits such as point defects in diamond, topological superconducting qubits are intrinsically protected from part of the noise. Therefore, they could support computation less prone to errors. The question is, where can we find topological superconductivity?

Photo of Yangmu Li
Yangmu Li © BNL

In this study, the scientists narrowed the search in one compound known to host topological surface states and part of the family of iron-based superconductors. In this compound, topological and superconducting states are not distributed uniformly across the surface. Understanding what’s behind these variations in electronic states and how to control them is key to enabling practical applications like topologically protected quantum computing.

From previous research, the team knew modifying the amount of iron could switch the material from a superconducting to nonsuperconducting state. For this study, physicist Gendu Gu of the CMPMS Division grew two types of large single crystals, one with slightly more iron relative to the other. The sample with the higher iron content is nonsuperconducting; the other sample is superconducting.

To understand whether the arrangement of electrons in the bulk of the material varied between the superconducting and nonsuperconducting samples, the team turned to spin-polarized neutron scattering. The Spallation Neutron Source (SNS), located at DOE’s Oak Ridge National Laboratory, is home to a one-of-a-kind instrument for performing this technique.  

“Neutron scattering can tell us the magnetic moments, or spins, of electrons and the atomic structure of a material,” explained corresponding author, Igor Zaliznyak, a physicist in the CMPMS Division Neutron Scattering Group who led the Brookhaven team that helped design and install the instrument with collaborators at Oak Ridge. “In order to single out the magnetic properties of electrons, we polarize the neutrons using a mirror that reflects only one specific spin direction.”

To their surprise, the scientists observed drastically different patterns of electron magnetic moments in the two samples. Therefore, the slight alteration in the amount of iron caused a change in electronic state.

Photo of Igor Zaliznyak
Igor Zaliznyak © BNL

“After seeing this dramatic change, we figured we should look at the distribution of electronic states as a function of local chemical composition,” said Zaliznyak.

At Brookhaven’s Center for Functional Nanomaterials (CFN), Li, with support from CFN staff members Fernando Camino and Gwen Wright, determined the chemical composition across representative smaller pieces of both sample types through energy-dispersive x-ray spectroscopy. In this technique, a sample is bombarded with electrons, and the emitted x-rays characteristic of different elements are detected. They also measured the local electrical resistance—which indicates how coherently electrons can transport charge—with microscale electrical probes. For each crystal, Li defined a small square grid (100 by 100 microns). In total, the team mapped the local composition and resistance at more than 2,000 different locations.

“Through the experiments at the CFN, we characterized the chemistry and overall conduction properties of the electrons,” said Zaliznyak. “But we also need to characterize the microscopic electronic properties, or how electrons propagate in the material, whether in the bulk or on the surface. Superconductivity induced in electrons propagating on the surface can host topological objects called Majorana modes, which are in theory one of the best ways to perform quantum computations. Information on bulk and surface electronic properties can be obtained through photoemission spectroscopy.”

For the photoemission spectroscopy experiments, Zaliznyak and Li reached out to Peter Johnson, leader of the CMPMS Division Electron Spectroscopy Group, and Nader Zaki, a scientific associate in Johnson’s group. By measuring the energy and momentum of electrons ejected from the samples (using the same spatial grid) in response to light, they quantified the strengths of the electronic states propagating on the surface, in the bulk, and forming the superconducting state. They quantitatively fit the photoemission spectra to a model that characterizes the strengths of these states.

Then, the team mapped the electronic state strengths as a function of local composition, essentially building a phase diagram.

“This phase diagram includes the superconducting and topological phase transitions and points to where we could find a useful chemical composition for quantum computation materials,” said Li. “For certain compositions, no coherent electronic states exist to develop topological superconductivity. In previous studies, people thought instrument failure or measurement error were why they weren’t seeing features of topological superconductivity. Here we show that it’s due to the electronic states themselves.”

“When the material is close to the transition between the topological and nontopological state, you can expect fluctuations,” added Zaliznyak. “For topology to arise, the electronic states need to be well-developed and coherent. So, from a technological perspective, we need to synthesize materials away from the transition line.”

Next, the scientists will expand the phase diagram to explore the compositional range in the topological direction, focusing on samples with less selenium and more tellurium. They are also considering applying neutron scattering to understand an unexpected energy gap (an energy range where no electrons are allowed) opening in the topological surface state of the same compound. Johnson’s group recently discovered this gap and hypothesized it was caused by surface magnetism.

This work was supported by the DOE Office of Science. The CFN and SNS are both DOE Office of Science User Facilities.

Featured image: (Left) Through neutron scattering experiments, scientists observed distinct patterns of magnetic correlations in superconducting (“single-stripe magnetism”) and nonsuperconducting (“double-stripe magnetism”) samples of a compound containing iron (Fe), tellurium (Te), and selenium (Se). (Right) A material phase diagram showing where the superconducting state (SC), nonsuperconducting state (NSC), and topological superconducting state (SC + TSS) appear as a function of Fe and Te concentrations. The starred A refers to the nonsuperconducting sample and the starred B to the superconducting sample. Overlaid on the phase diagram are photoemission spectra showing the emergence (left) and absence (right) of the topological state. Topological superconductivity is an electronic state that could be harnessed for more robust quantum computing. © BNL

Related Links

Provided by Brookhaven National Laboratory