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Tracking melting points above 4000 degrees Celsius

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With a new grant, a UC San Diego engineer is developing a better platform to study new materials that melt above 4000 degrees Celsius

A materials engineer at the University of California San Diego is leading the development of a new research platform for studying high-performance materials, in particular new materials that melt above 4000 degrees Celsius (C). UC San Diego nanoengineering professor Kenneth Vecchio is leading the project, which is funded by a new $800,000 grant from the US Office of Naval Research (ONR), through the Defense University Research Instrumentation Program (DURIP).

The research platform will be built to specifically address the challenges of studying new materials that melt at temperatures higher than 4000C, which is approximately 80 percent of the temperature of the surface of the sun.

This platform will become a national resource for engineers and other researchers who are pushing the limits of materials science. There are many industrial, energy, space and defense applications that would benefit from new solid materials that perform reliably at record-breaking, ultra-high temperatures. Applications include the containment walls for fusion reactors, leading edges of air vehicles that travel five or more times the speed of sound, and new industrial material machining methods. (The tips of cutting tools, for example, can experience temperatures above 3000C at high machining speeds. New cutting tool materials with much higher melting temperatures would enable faster manufacturing.)

Creating and then characterizing materials that don’t melt until exposed to ultra-high temperatures presents multiple challenges. In addition to creating candidate materials, researchers need to be able to characterize these materials to demonstrate performance. One of the key metrics is the temperature at which materials melt.

When working at temperatures around 4000C, nothing is simple. For example, how do you test the melting point of new materials that melt at temperatures higher than any containers you might try to hold them in? How do you heat a sample to temperatures in the 4000C range while precisely controlling the temperature? Or how do you determine exactly when a sample at such extreme conditions actually melts?

These are some of the issues that Vecchio and his team plan to solve via an experimental platform he designed and will build thanks to $800K in new funding from the ONR DURIP grant.

New Materials that melt at temperatures higher than 4000C

How do you increase the melting point of materials that already melt at ultra-high temperatures? For the past five years, Vecchio has led a UC San Diego project funded by the ONR Multidisciplinary University Research Initiatives (MURI) Program to focus on this.

The team is taking a new approach to this difficult task. To make sense of their strategy, you first need to know that there are two physical phenomena that largely determine the temperature at which a solid material melts into a liquid.

The first phenomenon is enthalpy. Enthalpy describes the energy associated with keeping a material in its solid form. The higher the enthalpy, the stronger the bond between the two atoms will be, and the higher you have to heat the material to melt it by breaking those bonds.

The second phenomenon is entropy. Entropy is associated with disorder and describes the energy driving the atoms to separate.  

“Melting in a solid occurs when the entropy becomes high enough to exceed the enthalpy,” said Vecchio.

Ultra-high-temperature materials development is usually focused on enthalpy. But researchers seem to have reached the limits of the enthalpy approach, at least for materials that do not react with oxygen. The roadblock is due to the fact that the enthalpy of bonding between atoms is largely fixed. That means that once you find materials with the highest enthalpy of bonding, there is little room for increasing the melting temperature of that material via enthalpy.  

In their quest for materials that melt at ever higher temperatures, Vecchio and his team at the UC San Diego Jacobs School of Engineering have turned to the other phenomenon controlling melting temperature: entropy.

Most people have a vague sense that entropy has something to do with chaos or disorder. That notion will come in handy for understanding this new approach to developing materials with record-breaking melting temperatures.

“A liquid has a very high level of entropy. Atoms are moving all around in a liquid, that’s entropy. If we can make a solid look like a liquid, in terms of its free energy, then there will be less driving force to change from the solid to the liquid state,” said Vecchio.

Making a solid “look” like a liquid means increasing the inherent entropy of the material when it’s a solid. That’s what Vecchio has set out to do. Their strategy is to increase the disorder in new high-temperature solid materials by mixing large numbers of different atoms together.

“We create disorder through atomic mixing,” said Vecchio.  

By taking this approach, the researchers are making their solid materials structurally appear more similar to the atomic state of that material’s liquid form. This reduces the driving force for the solid to “want” to melt, which can lead to an increase in the temperature at which it melts.

For example, silicon carbide (SiC) is a well-known material with an ultra-high melting point of 2730C. But it would be useful to have related materials that melt at even high temperatures.

Following the entropy-focused approach in previous research, Vecchio and his collaborators replaced the Si atoms with equal amounts of five different metals, which led to new materials with even higher melting temperatures. These new materials, called, high-entropy carbides, or more broadly high-entropy ceramics, are discussed in a research article published in the journal Acta Materialia in 2019.

Vecchio and his team are pursuing another use of entropy as well. More entropy can be added to a solid-material system by adding other molecular and atomic-bonding variations that alone would not increase the melting temperature. But when you add enough of them into the system, the diversity of molecular elements and bonding scenarios further increases entropy, which can increase the temperature at which the solid melts into a liquid.

Researchers must be able to experimentally validate melting temperature and other properties for these kinds of approaches to materials development to lead to new useful materials. That’s where the new platform comes in.

High Temperature-X-ray Diffraction platform

The new High Temperature-X-ray Diffraction platform being funded by the ONR DURIP grant to UC San Diego is designed to enable the heating of a sample region to 4500C, while measuring its temperature very accurately, and detecting the onset of melting.

The system components include: a platform that enables high-speed measurements called a high brightness X-ray diffraction platform; a high power laser to locally heat a small region of a material sample; and a high-tech thermometer (a pyrometer) that records temperatures up to 4500C by measuring the wavelength of light emitted from the heat source.

“The integration of these three tools is a fascinating engineering challenge,” said Vecchio.

In order to overcome the ‘container problem’ in which a container melts before the experimental sample it is supposed to be holding, Vecchio plans to use sample materials as their own containers.

“We will only heat a small circular region in the middle of the sample using the laser,” he said.

The remaining perimeter of the sample that is not exposed to the laser will serve as the container that holds the sample as it melts from solid to liquid.

“I look forward to being able to share this unique platform with researchers across the country,” said Vecchio. “People have been trying to devise systems to measure melting temperatures of these types of materials, but their biggest scientific problem is they have no method to verify what structure the sample has at the perceived onset of melting. My design will solve this problem,” explained Vecchio. “By building our melting system inside an x-ray diffraction platform, we will be able to exactly know the structure and type of material present right at the point of melting, and we will be able to completely verify melting as it has a completely different X-ray diffraction result compared to a solid sample.”

He estimates that the facility will be up and running by the end of 2022.

The funded ONR DURIP proposal is entitled “Thermodynamic Measurements of Entropy-Stabilized Ultra-high Temperature Materials.” University of California San Diego NanoEngineering Professor Kenneth Vecchio is the Principal Investigator (PI) on the grant. (ONR award number: N00014-20-1-2872).

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Source: https://bioengineer.org/tracking-melting-points-above-4000-degrees-celsius/

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USC Stem Cell study identifies molecular ‘switch’ that turns precursors into kidney cells

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Kidney development is a balancing act between the self-renewal of stem and progenitor cells to maintain and expand their numbers, and the differentiation of these cells into more specialized cell types. In a new study in the journal eLife from Andy McMahon’s laboratory in the Department of Stem Cell Biology and Regenerative Medicine at the Keck School of Medicine of USC, former graduate student Alex Quiyu Guo and a team of scientists demonstrate the importance of a molecule called β-catenin in striking this balance.

β-catenin is a key driver at the end of a complex signaling cascade known as the Wnt pathway. Wnt signaling plays critical roles in the embryonic development of multiple organs including the kidneys. By partnering with other Wnt pathway molecules, β-catenin controls the activity of hundreds to thousands of genes within the cell.

The new study builds on the McMahon Lab’s previous discovery that Wnt/β-catenin can initiate progenitor cells to execute a lengthy and highly orchestrated program of forming structures in the kidney called nephrons. A healthy human kidney contains a million nephrons that balance body fluids and remove soluble waste products. Too few nephrons results in kidney disease.

Previous studies from the UT Southwestern Medical Center laboratory of Thomas Carroll, a former postdoctoral trainee in the McMahon Lab, suggested that Wnt/β-catenin signaling plays opposing roles in ensuring the proper number of nephrons: promoting progenitor maintenance and self-renewal, and stimulating progenitor cell differentiation.

“It sounded like Wnt/β-catenin is doing two things–both maintenance and differentiation–that seem to be opposite operations,” said Guo. “Therefore, the hypothesis was that different levels of Wnt/β-catenin can dictate different fates of the nephron progenitors: when it’s low, it works on maintenance; when it’s high, it directs differentiation.”

In 2015, it became more possible to test this hypothesis when Leif Oxburgh, a scientist at the Rogosin Institute in New York and a co-author of the eLife study, developed a system for growing large numbers of nephron progenitor cells, or NPCs, in a Petri dish.

Relying on this game-changing new system, Guo and his collaborators grew NPCs, added different levels of a chemical that activates β-catenin, and saw their hypothesis play out in the Petri dishes.

They observed that high levels of β-catenin triggered a “switch” in part of the Wnt pathway that relies on another family of transcription factors known as TCF/LEF. There are two types of TCF/LEF transcription factors: one type inhibits genes related to differentiation, and the other activates these genes. In response to high levels of β-catenin, the “activating” members of TCF/LEF switched places with the “inhibiting” members, effectively taking charge. This “switch” triggered NPCs to differentiate into more specialized types of kidney cells.

When they looked at low levels of β-catenin, they saw NPCs self-renewing and maintaining their populations, as expected. However, they were surprised to learn that β-catenin was not engaged with any of the known genes related to self-renewal and maintenance.

“β-catenin does something,” said Guo. “That is for sure. But how it does it is kind of mysterious right now.”

After publishing these results in eLife, Guo earned his PhD from USC, and began his postdoctoral training at UCLA. Helena Bugacov, a current PhD student in the McMahon Lab and a co-author of the eLife study, is now taking the lead in continuing the project–which has implications far beyond the kidney field, due to the broad role of Wnt throughout the body.

“Understanding how Wnt regulates these two very distinct cell outcomes of self-renewal and differentiation, which is very important for kidney development, is also important for understanding the development of other organs and adult stem cells, as Wnt signaling plays important roles in almost all developmental systems,” said Bugacov. “There is also a lot of attention from cancer researchers, as this process can go awry in cancer. Many therapeutics are trying to target this process.”

She added, “The more we know about things, the better we can inform work on developing human kidney organoid cultures, which can be more readily used to understand problems in human health, regeneration and development.”

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Additional co-authors of the eLife study include: Albert Kim, Andrew Ransick, Xi Chen, and Nils Lindstrom from USC; Aaron Brown from the Maine Medical Center Research Institute; and Bin Li and Bing Ren from the University of California, San Diego. The research was supported by federal funding from the National Institute of Diabetes and Digestive and Kidney Diseases (grant number R01 DK054364).

https://stemcell.keck.usc.edu/usc-stem-cell-study-identifies-molecular-switch-that-turns-precursors-into-kidney-cells/

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Source: https://bioengineer.org/usc-stem-cell-study-identifies-molecular-switch-that-turns-precursors-into-kidney-cells/

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Evidence of Antarctic glacier’s tipping point confirmed for first time

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Researchers have confirmed for the first time that Pine Island Glacier in West Antarctica could cross tipping points, leading to a rapid and irreversible retreat which would have significant consequences for global sea level

Researchers have confirmed for the first time that Pine Island Glacier in West Antarctica could cross tipping points, leading to a rapid and irreversible retreat which would have significant consequences for global sea level.

Pine Island Glacier is a region of fast-flowing ice draining an area of West Antarctica approximately two thirds the size of the UK. The glacier is a particular cause for concern as it is losing more ice than any other glacier in Antarctica.

Currently, Pine Island Glacier together with its neighbouring Thwaites glacier are responsible for about 10% of the ongoing increase in global sea level.

Scientists have argued for some time that this region of Antarctica could reach a tipping point and undergo an irreversible retreat from which it could not recover. Such a retreat, once started, could lead to the collapse of the entire West Antarctic Ice Sheet, which contains enough ice to raise global sea level by over three metres.

While the general possibility of such a tipping point within ice sheets has been raised before, showing that Pine Island Glacier has the potential to enter unstable retreat is a very different question.

Now, researchers from Northumbria University have shown, for the first time, that this is indeed the case.

Their findings are published in leading journal, The Cryosphere.

Using a state-of-the-art ice flow model developed by Northumbria’s glaciology research group, the team have developed methods that allow tipping points within ice sheets to be identified.

For Pine Island Glacier, their study shows that the glacier has at least three distinct tipping points. The third and final event, triggered by ocean temperatures increasing by 1.2C, leads to an irreversible retreat of the entire glacier.

The researchers say that long-term warming and shoaling trends in Circumpolar Deep Water, in combination with changing wind patterns in the Amundsen Sea, could expose Pine Island Glacier’s ice shelf to warmer waters for longer periods of time, making temperature changes of this magnitude increasingly likely.

The lead author of the study, Dr Sebastian Rosier, is a Vice-Chancellor’s Research Fellow in Northumbria’s Department of Geography and Environmental Sciences. He specialises in the modelling processes controlling ice flow in Antarctica with the goal of understanding how the continent will contribute to future sea level rise.

Dr Rosier is a member of the University’s glaciology research group, led by Professor Hilmar Gudmundsson, which is currently working on a major £4million study to investigate if climate change will drive the Antarctic Ice Sheet towards a tipping point.

Dr Rosier explained: “The potential for this region to cross a tipping point has been raised in the past, but our study is the first to confirm that Pine Island Glacier does indeed cross these critical thresholds.

“Many different computer simulations around the world are attempting to quantify how a changing climate could affect the West Antarctic Ice Sheet but identifying whether a period of retreat in these models is a tipping point is challenging.

“However, it is a crucial question and the methodology we use in this new study makes it much easier to identify potential future tipping points.”

Hilmar Gudmundsson, Professor of Glaciology and Extreme Environments worked with Dr Rosier on the study. He added: “The possibility of Pine Island Glacier entering an unstable retreat has been raised before but this is the first time that this possibility is rigorously established and quantified.

“This is a major forward step in our understanding of the dynamics of this area and I’m thrilled that we have now been able to finally provide firm answers to this important question.

“But the findings of this study also concern me. Should the glacier enter unstable irreversible retreat, the impact on sea level could be measured in metres, and as this study shows, once the retreat starts it might be impossible to halt it.”

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The paper, The tipping points and early warning indicators for Pine island Glacier, West Antarctica, is now available to view in The Cryosphere.

Northumbria is fast becoming the UK’s leading university for research into Antarctic and extreme environments.

As well as the £4m tipping points study, known as TiPPACCs, Northumbria is also the only UK university to play a part in two projects in the £20m International Thwaites Glacier Collaboration – the largest joint project undertaken by the UK and USA in Antarctica for more than 70 years – where Northumbria is leading the PROPHET and GHC projects. This particular study was funded through both TiPPACCs and PROPHET.

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Source: https://bioengineer.org/evidence-of-antarctic-glaciers-tipping-point-confirmed-for-first-time/

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Diversity can prevent failures in large power grids

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Integrated power grids offer benefits, but also pose challenges best addressed by leveraging differences

The recent power outages in Texas brought attention to its power grid being separated from the rest of the country. While it is not immediately clear whether integration with other parts of the national grid would have completely eliminated the need for rolling outages, the state’s inability to import significant amounts of electricity was decisive in the blackout.

A larger power grid has perks, but also has perils that researchers at Northwestern University are hoping to address to expedite integration and improvements to the system.

An obvious challenge in larger grids is that failures can propagate further — in the case of Texas, across state lines. Another is that all power generators need to be kept synchronized to a common frequency in order to transmit energy. The U.S. is served by three “separate” grids: The Eastern interconnection, the Western interconnection and the Texas interconnection, interlinked only by direct-current power lines. Any persistent deviation in frequencies within a region can lead to an outage.

As a result, researchers are searching for ways to stabilize the grid by looking for methods to mitigate deviations in the power generators’ frequencies.

The new Northwestern research shows that counter to assumptions held by some, there are stability benefits to heterogeneity in the power grid. Examining several power grids across the U.S. and Europe, a team led by Northwestern physicist Adilson Motter recently reported that generators operating on different frequencies return to their normal state more quickly when they are damped by “breakers” at different rates than generators around them.

The paper was published March 5 in the journal Nature Communications.

Motter is the Charles E. and Emma H. Morrison Professor in the department of physics and astronomy in the Weinberg College of Arts and Sciences. His research focuses on nonlinear phenomena in complex systems and networks.

Motter compares power grids to a choir: “It’s a little bit like a choir without a conductor. The generators have to listen to others and speak in sync. They react and respond to each other’s frequencies.”

Listen to an out-of-whack frequency, and the result can be a failure. Given the interconnected makeup of the system, a failure can propagate across the network. Historically, these malfunctions have been prevented by using active controllers. However, failures are often caused precisely by control and equipment errors. This points to a need to build additional stability within the design of the system. To achieve that, the team looked into leveraging the natural heterogeneities of the grid.

When the frequencies of the power generators are moved away from the synchronous state, they can swing around for a long time and even become more erratic. To mitigate these fluctuations, they came up with something akin to a door mechanism used to close a door the fastest, but without slamming.

“Mathematically, the problem of damping frequency deviations in a power generator is analogous to the problem of optimally damping a door to get it to close the fastest, which has a known solution in the case of a single door,” Motter said. “But it’s not a single door in this analogy. It’s a network of many doors that are coupled with each other, if you can imagine the doors as power generators.”

When creating an “optimal damping” effect, they discovered that rather than making each damper identical, damping the power generators in a way that is suitably different from each other can further optimize their ability to synchronize to the same frequency as quickly as possible. That is, suitably heterogenous damping across the network can lead to improved stability in the power grids studied by the team.

This discovery could have implications for future grid design as developers work to optimize technology and in considerations to further integrate now separated networks.

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The paper is titled “Asymmetry underlies stability in power grids.” Additional co-authors include former postdoctoral researcher Ferenc Molnar and research professor Takashi Nishikawa.

The study was supported by Northwestern University’s Finite Earth Initiative (supported by Leslie and Mac McQuown) and ARPA-E Award No. DE-AR0000702 and also benefited from logistical support from the Northwestern Institute for Sustainability and Energy.

https://news.northwestern.edu/stories/2021/04/diversity-can-prevent-failures-in-large-power-grids/

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Source: https://bioengineer.org/diversity-can-prevent-failures-in-large-power-grids/

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How Fortnite and Zelda can up your surgical game (no joke!)

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Scalpel? Check. Gaming console? Check. Study finds video games can be a new tool on surgical tray for medical students

Video games offer students obvious respite from the stresses of studies and, now, a study from a University of Ottawa medical student has found they could benefit surgical skills training.

Arnav Gupta carries a heavy course load as a third-year student in the Faculty of Medicine, so winding down with a game of Legend of Zelda always provides relief from the rigorous of study. But Zelda may be helping improve his surgical education, too, as Gupta and a team of researchers from the University of Toronto found in a paper they recently published in the medical journal Surgery.

“Given the limited availability of simulators and the high accessibility of video games, medical students interested in surgical specialties should know that video games may be a valuable adjunct training for enhancing their medical education, especially in surgical specialties where it can be critical,” says Gupta, whose findings were deciphered from a systematic review of 16 studies involving 575 participants.

“Particularly, in robotic surgery, being a video gamer was associated with improvements in time to completion, economy of motion, and overall performance. In laparoscopic surgery, video games-based training was associated with improvement in duration on certain tasks, economy of motion, accuracy, and overall performance,” explains Gupta, who has been a gamer since age 8.

This study builds on past reviews and is the first to focus on a specific medical student population where this style of training could be feasibly implemented. Their timely study found some of the most beneficial games for students of robotic surgery and laparoscopy were: Super Monkey Ball, Half Life, Rocket League and Underground. Underground is purposely designed to assist medical students with their robotic surgery training via a video game console.

“While video games can never replace the value of first-hand experience, they do have merit as an adjunctive tool, especially when attempting to replicate important movements to surgery. For example, first-person shooting games require you to translate three dimensional motions onto a two-dimensional screen, which is like the concept of laparoscopic surgery,” says Gupta, whose studies are focused on surgery in ophthalmology, which makes games like Resident Evil 4 or Trauma Center: New Blood fitted for his own ambitions.

“I’m not joking when I say that games such as Fortnite have the potential to enhance those necessary movements, providing stronger motivational components and in a low stakes environment.”

Reports suggest 55 percent of university students are gamers and enjoy proficiency with video consoles. Yet, many medical students don’t admit to owning and using a gaming console.

“I think there definitely is some ambivalence towards video games in medicine,” says Gupta, who is also a fan of Witcher 3. “Given how accessible games have become and how video game technology is advancing, video games definitely are an easy go-to for the students who do love them in some capacity. The hope is that maybe this study can inspire someone to take advantage of video games’ unique capabilities, reduce the general ambivalence towards it, and develop some fun ways to let students engage with surgical education.”

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https://media.uottawa.ca/news/how-fortnite-and-zelda-can-your-surgical-game-no-joke

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Source: https://bioengineer.org/how-fortnite-and-zelda-can-up-your-surgical-game-no-joke/

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