Elemental research: Scientists apply boron to tungsten components in fusion facilities hare krishna hare Krishna.

What is the connection between boron, an element in a common household cleaner, and tokamaks, ring-shaped fusion facilities that heat fuel to million-degree temperatures? Scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have conducted research showing that a PPPL-developed powder dropper can successfully drop boron powder into high-temperature plasma within tokamaks that have parts made of a heat-resistant material known as tungsten. Scientists want to confirm they can use this process to apply boron to tungsten parts because bare tungsten walls can hurt plasma performance if the plasma damages the tungsten.

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Because of its high melting point, tungsten is increasingly used in tokamaks to help components withstand the intense heat of the fusion process. Boron partly shields the tungsten from the plasma and prevents the tungsten from leaking into the plasma; it also absorbs any stray elements like oxygen that may be in the plasma from other sources. These unwanted impurities could cool the plasma and quench the fusion reactions.

"We need a way to deposit boron coatings without turning off the tokamaks' magnetic field, and that's what the powder dropper allows us to do," said Grant Bodner, a postdoctoral researcher at PPPL who was the lead author of the research paper reporting the results in Nuclear Fusion. The research was performed using the W Environment in Steady-State Tokamak (WEST), operated by France's Atomic Energy Commission (CEA). "WEST is one of the few full-tungsten environments that can help us test this technology at long pulses," Bodner said.

Another reason the physicists performed their experiments using WEST is that its magnets are made of superconducting material that will feature in magnets inside future fusion devices. This material conducts electricity with little or no resistance and produces little excess heat so the magnets can operate without stopping for long periods of time, as future fusion reactors will have to do. The magnets create the forces that restrain the plasma so it can undergo fusion.

Fusion, the power that drives the sun and stars, combines light elements in the form of plasma—the hot, charged state of matter composed of free electrons and atomic nuclei—that generates massive amounts of energy. Scientists are seeking to replicate fusion on Earth for a virtually inexhaustible supply of power to generate electricity.

Scientists need a way to replenish the boron coatings while the machines are operating because future fusion facilities will not be able to shut down often for re-coating. "Dropping boron into a tokamak while it is operating is like cleaning your apartment while doing all the other things that you usually do in it," said CEA scientist Alberto Gallo, who contributed to the research. "It's very helpful—it means you don't have to take extra time out of your usual activities to do the cleaning," he said..

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The powder dropper device is mounted to the top of the tokamak and uses precise actuators to move powdered material from their reservoirs to the tokamak's vacuum chamber. This mechanism allows researchers to precisely set the rate and duration of the powder drops, which in other fusion facilities can include other performance-boosting materials like lithium. "Because of that flexibility, the dropper has the potential to be really useful in the future," Bodner said.

The researchers were surprised to find that the boron laid down by the dropper did more than condition the inner tungsten surfaces. "We saw that when we dropped in the powder, the plasma confinement increased, meaning that it retains more of its heat, which aids the fusion process," Bodner said.

The increased confinement was especially helpful because it occurred without the plasma entering a state known as H-mode (high-confinement mode), in which the confinement improves but the plasma is more likely to erupt with what are known as edge-localized modes, or ELMs. These ELMs move heat out of the plasma, reducing the efficiency of the fusion reactions and sometimes damaging internal components. "If we can use the dropper to get the good confinement of H-mode without actually entering H-mode and risking ELMs, that would be great for fusion reactors," Bodner said.

In the future, the researchers want to test using the dropper only when necessary to maintain good plasma performance. "Adding any extra impurities, even boron, can reduce how much fusion power you get because the plasma becomes less pure," Bodner said. "Therefore, we have to try to use the smallest amount of boron that can still produce the effects we want."

Upcoming experiments will focus on how much boron is actually coating the tungsten surfaces. "We want to measure these amounts so we can really quantify what we're doing and extend these results in the future," Bodner said.

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Brain bubbles: Researchers describe the dynamics of cavitation in soft porous material Shri Radhe Shri Radhe Shri Radhe....

A tiny bubble popping within a liquid seems more fanciful than traumatic. But millions of popping vapor bubbles can cause significant damage to rigid structures like boat propellers or bridge supports. Can you imagine the damage such bubbles could do to soft human tissues like the brain? During head impacts and concussions, vapor bubbles form and violently collapse, creating damage to human tissue. Purdue University fluid mechanics researchers are now one step closer to understanding these phenomena..

Hare Krishna hare Krishna..

A tiny bubble popping within a liquid seems more fanciful than traumatic. But millions of popping vapor bubbles can cause significant damage to rigid structures like boat propellers or bridge supports. Can you imagine the damage such bubbles could do to soft human tissues like the brain? During head impacts and concussions, vapor bubbles form and violently collapse, creating damage to human tissue. Purdue University fluid mechanics researchers are now one step closer to understanding these phenomena..

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Brain bubbles: Researchers describe the dynamics of cavitation in soft porous material

Schematic of a spherical poroelastic medium filled with liquid water (blue) and water vapor (yellow). An over-pressure ∆p = p∞ − psat is applied on the external boundary producing the collapse of the bubble, which is accompanied by the deformation of the solid skeleton. Credit: PNAS Nexus (2022). DOI: 10.1093/pnasnexus/pgac150

A tiny bubble popping within a liquid seems more fanciful than traumatic. But millions of popping vapor bubbles can cause significant damage to rigid structures like boat propellers or bridge supports. Can you imagine the damage such bubbles could do to soft human tissues like the brain? During head impacts and concussions, vapor bubbles form and violently collapse, creating damage to human tissue. Purdue University fluid mechanics researchers are now one step closer to understanding these phenomena.

"When a bubble collapses inside a liquid, it generates pressure shock waves," said Hector Gomez, professor of mechanical engineering and principal investigator. "The process of forming a vapor cavity and its collapse is what we call cavitation."

"Cavitation has been studied since the 1800s," said Pavlos Vlachos, the St. Vincent Health Professor of Healthcare Engineering and director of the Regenstrief Center for Healthcare Engineering. "It's a very complex field of study because it involves non-equilibrium thermodynamics, continuum mechanics, and many other factors on a scale of micrometers and microseconds. After hundreds of years of research, we are only just now starting to understand these phenomena."

Even less is known about bubbles that collapse in soft porous materials, such as the brain or other body tissues. That's significant, because understanding how those bubbles behave could lead to a better understanding of concussions—or even be used to deliver targeted medications inside the body.

In new research published in the PNAS Nexus, Gomez, Vlachos, and collaborators presented the development of a mathematical model to describe the dynamics of these cavitation bubbles in a deformable porous medium.

Cavitation occurs throughout the human body—for example, cracking your knuckles is the sound of bubbles popping in your joints' synovial fluid. When the fluids inside the body are subjected to pressure waves—such as when football players endure head impacts—bubbles could form in the fluid surrounding the brain. And just like the bubbles that damage boat propellers, bubbles bursting near the brain could damage its soft tissue.

"The human brain is like a water-filled squishy sponge; it has the consistency of gelatin," said Vlachos. "Its material is porous, heterogeneous, and anisotropic, creating a much more complex scenario. Our current knowledge about cavitation doesn't apply straightforwardly when such phenomena occur in the body."

Gomez and collaborators developed a theoretical and a computational model showing that the deformability of a porous material slows the collapse and expansion of cavitation bubbles. This breaks down the classic scaling relation between bubble size and time.

"Our model embeds the bubbles into deformable porous materials," said Yu Leng, the first author of the paper and postdoctoral research associate working with Gomez. "Then we can extend the study of cavitation bubbles in pure liquid to soft tissues such as the human brain."

While complex, this model can also be reduced to an ordinary differential equation. "A hundred years ago, Lord Rayleigh developed the equation that describes the dynamics of a bubble in a fluid," said Gomez. "We were able to augment that equation to describe when the medium is poroelastic. It's pretty amazing that these complex physics still lead to a simple and elegant equation."

Gomez and Vlachos are currently planning experiments to physically validate their results, but they are also looking to the big picture. "One potential application is targeted drug delivery," said Gomez. "Let's say you want to deliver a drug directly into a tumor. You don't want that medication to disperse elsewhere. We've seen encapsulations that keep the drug in isolation until it has reached its target. The encapsulation can be broken by using bubbles. Our research provides a better understanding of how these bubbles collapse in the body and can lead to more effective drug delivery."

"Another example of future possibilities is traumatic brain injury," Leng said. "We can extend this research to study the impact of uncontrolled cavitation collapse on brain tissue, when military personnel and civilians are exposed to blast shock waves."

Gomez and Vlachos say they are thrilled to establish new foundational science for understanding bubble dynamics in soft porous materials. "This opens up all sorts of possibilities for future research," Gomez said, "and we look forward to how we and others will use this knowledge in the future.

Underwater ‘snow’ could be growing on Jupiter’s moon Europa Shri Radhe

 A study of Antarctic ice shelves suggests that the ice shell covering Jupiter’s moon Europa could contain a significant amount of underwater “snow”. This could have important implications for NASA’s upcoming Europa Clipper mission, which aims to use ground penetrating radar to study the ice shell and the ocean beneath.

The research was done by a team in the US led by Natalie Wolfenbarger at the University of Texas at Austin and focused on two processes by which Antarctic ice shelves grow from the bottom. The study also has implications for our understanding of whether life emerged in Europa’s ocean, which is encased in an ice shell some 15–25 km thick.

By examining the dynamic features that appear on the surface of Europa’s ice shell, scientists have found compelling evidence that the ocean beneath is constantly interacting with its ice shell. So far, however, the lower layers of this shell have proven more difficult to study.

Two mechanisms

To learn more about the processes which may be unfolding beneath Europa’s surface, Wolfenbarger and colleagues drew parallels with oceanic ice on our own planet. In Earth’s polar regions, ice shelves grow from the bottom through two possible mechanisms. One is congelation, whereby ice freezes at the interface between the ice and the water directly beneath it. The second mechanism involves the creation of frazil ice, which forms as millimetre-sized, randomly shaped crystals within columns of supercooled water. These columns are prevented from freezing more completely by turbulent currents. Under buoyant forces, these crystals travel upwards to rest on the underside of the ice, where they resemble underwater snow.

The researchers compared the contributions of each mechanism to ice formation by examining a variety of ice cores collected from ice shelves in Antarctica. They say that this environment is a close analogue to the temperature, pressure, and salinity of Europa’s ice sheet. Some of these samples were collected from features like rifts and glacier tongues, where the ice is thinner. Others were gathered from ancient ice shelves, which can reach several kilometres in thickness.

Their analysis revealed that congelation dominated the gradual thickening of older ice. On Europa, this process would be driven by the gradual cooling of the moon’s solid interior. In contrast, frazil ice is most likely to accumulate where the ice thins – either in small-scale rifts and fractures, or in warmer regions, often found at lower latitudes. On Europa, large sections of the ice shell are also warmed and thinned out through tidal heating, which is generated by Jupiter’s gravitational pull.

Low salinity

The team also found that these mechanisms create sea ice with very different salinities. While frazil ice retained just around 0.1% of the salinity of water from which it formed, congelation ice had a salt content of around 10% of the local water. Salinity strongly affects a variety of important properties of sea ice: including its strength, heat conduction, and its mechanical responses to ocean currents beneath..

Shri Radhe

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Want to be highly cited? Work with collaborators across multiple research fields, study finds Shri Radhe

Researchers who repeatedly collaborate with other scientists across multiple research disciplines produce papers that are more highly cited. That’s according to an analysis of more than 3000 scientists who publish in physical-science journals. But scientists who prefer to stick to single research topics tend, on average, to produce more papers than their peers (Proc. Natl Acad. Sci..

Carried out by a team led by Shlomo Havlin, a physicist at Bar-Ilan University in Israel, the study identified 3420 scientists who had published at least 50 papers in American Physical Society (APS) journals. For each of these “focal” scientists, the team picked out collaborators in the APS dataset who had co-authored at least two papers with them..

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Want to be highly cited? Work with collaborators across multiple research fields, study finds

24 Aug 2022

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Getting together: Scientists with high citation rates are more likely to collaborate with peers who have many publications and high citations per paper (Courtesy: iStock/Weekend Images Inc).

Researchers who repeatedly collaborate with other scientists across multiple research disciplines produce papers that are more highly cited. That’s according to an analysis of more than 3000 scientists who publish in physical-science journals. But scientists who prefer to stick to single research topics tend, on average, to produce more papers than their peers (Proc. Natl Acad. Sci. 119 e2207436119).

Carried out by a team led by Shlomo Havlin, a physicist at Bar-Ilan University in Israel, the study identified 3420 scientists who had published at least 50 papers in American Physical Society (APS) journals. For each of these “focal” scientists, the team picked out collaborators in the APS dataset who had co-authored at least two papers with them.

When the researchers examined the topics covered by the collaboration networks, they discovered that scientists work with collaborators on a relatively limited number of different fields. On average, 63% of a scientist’s collaborators work with them on just a single research topic. A quarter of collaborations cover two research topics, while only 12% span three or more topics.

The team also examined how successful scientists work with their collaborators. Two metrics of success were used: productivity (measured by the total number of publications) and impact (average number of citations with two seconds...

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Want to be highly cited? Work with collaborators across multiple research fields, study finds

24 Aug 2022

two people talking at a table

Getting together: Scientists with high citation rates are more likely to collaborate with peers who have many publications and high citations per paper (Courtesy: iStock/Weekend Images Inc).

Researchers who repeatedly collaborate with other scientists across multiple research disciplines produce papers that are more highly cited. That’s according to an analysis of more than 3000 scientists who publish in physical-science journals. But scientists who prefer to stick to single research topics tend, on average, to produce more papers than their peers (Proc. Natl Acad. Sci. 119 e2207436119).

Carried out by a team led by Shlomo Havlin, a physicist at Bar-Ilan University in Israel, the study identified 3420 scientists who had published at least 50 papers in American Physical Society (APS) journals. For each of these “focal” scientists, the team picked out collaborators in the APS dataset who had co-authored at least two papers with them.

When the researchers examined the topics covered by the collaboration networks, they discovered that scientists work with collaborators on a relatively limited number of different fields. On average, 63% of a scientist’s collaborators work with them on just a single research topic. A quarter of collaborations cover two research topics, while only 12% span three or more topics.

The team also examined how successful scientists work with their collaborators. Two metrics of success were used: productivity (measured by the total number of publications) and impact (average number of citations per paper).

It turns out that the most productive scientists have a high proportion of single-topic collaborators, but only an average citation impact. Researchers with the highest impact, on the other hand, have more collaborators who they work with on multiple topics, yet are only as productive as the average scientist.

Keeping a balance

The study’s authors suggest that impactful scientists lean towards collaborators sharing similar research interests, while those who publish more papers select collaborators who specialize in a particular topic. Compared with more productive scientists, those researchers with high citation rates are more likely to collaborate with peers with many publications and high citations per paper.

Underwater ‘snow’ could be growing on Jupiter’s moon Europa Shri Radhe

Chilly worlds: mounds of snow-like frazil ice under the Antarctic ice shelf. According to this latest research, Europa’s ice shell could be made of the same stuff. (Courtesy: copyright Helen Glazer 2015/from the project "Walking in Antarctica".

A study of Antarctic ice shelves suggests that the ice shell covering Jupiter’s moon Europa could contain a significant amount of underwater “snow”. This could have important implications for NASA’s upcoming Europa Clipper mission, which aims to use ground penetrating radar to study the ice shell and the ocean beneath.

The research was done by a team in the US led by Natalie Wolfenbarger at the University of Texas at Austin and focused on two processes by which Antarctic ice shelves grow from the bottom. The study also has implications for our understanding of whether life emerged in Europa’s ocean, which is encased in an ice shell some 15–25 km thick.

By examining the dynamic features that appear on the surface of Europa’s ice shell, scientists have found compelling evidence that the ocean beneath is constantly interacting with its ice shell. So far, however, the lower layers of this shell have proven more difficult to study.

Two mechanisms

To learn more about the processes which may be unfolding beneath Europa’s surface, Wolfenbarger and colleagues drew parallels with oceanic ice on our own planet. In Earth’s polar regions, ice shelves grow from the bottom through two possible mechanisms. One is congelation, whereby ice freezes at the interface between the ice and the water directly beneath it. The second mechanism involves the creation of frazil ice, which forms as millimetre-sized, randomly shaped crystals within columns of supercooled water. These columns are prevented from freezing more completely by turbulent currents. Under buoyant forces, these crystals travel upwards to rest on the underside of the ice, where they resemble underwater snow.

The researchers compared the contributions of each mechanism to ice formation by examining a variety of ice cores collected from ice shelves in Antarctica. They say that this environment is a close analogue to the temperature, pressure, and salinity of Europa’s ice sheet. Some of these samples were collected from features like rifts and glacier tongues, where the ice is thinner. Others were gathered from ancient ice shelves, which can reach several kilometres in thickness.

Their analysis revealed that congelation dominated the gradual thickening of older ice. On Europa, this process would be driven by the gradual cooling of the moon’s solid interior. In contrast, frazil ice is most likely to accumulate where the ice thins – either in small-scale rifts and fractures, or in warmer regions, often found at lower latitudes. On Europa, large sections of the ice shell are also warmed and thinned out through tidal heating, which is generated by Jupiter’s gravitational pull.

Low salinity

The team also found that these mechanisms create sea ice with very different salinities. While frazil ice retained just around 0.1% of the salinity of water from which it formed, congelation ice had a salt content of around 10% of the local water. Salinity strongly affects a variety of important properties of sea ice: including its strength, heat conduction, and its mechanical responses to ocean currents beneath.

Madam President: On Droupadi Murmu’s election as India’s 15th President Shri Radhe Shri Radhe..

The election of Droupadi Murmu as India’s 15th President is rich in symbolism. In the 75th year of the country’s Independence, Ms. Murmu becomes the second woman to occupy the Rashtrapati Bhavan, and the first member of a tribal community to do so. Her membership of the Santhal tribe is in focus. She has risen through the ranks in the Bharatiya Janata Party (BJP), and has shown a mind of her own during her stint as Governor of Jharkhand. Her election to the highest office of the country comes 101 years after two tribespeople were elected to legislative bodies in colonial India. Founding figures of the Republic were acutely cognisant of the disadvantageous position of the tribespeople and made special provisions such as the Fifth and Sixth Schedules of the Constitution. Jaipal Singh Munda, sportsman and tribal leader, was a prominent member of the Constituent Assembly who forcefully articulated the fears and hopes of tribespeople. In 2000, two States, Jharkhand and Chhattisgarh, were formed to give more focused attention to the concentrated tribal population in these regions. The Scheduled Tribes and Other Traditional Forest Dwellers (Recognition of Forest Rights) Act, was passed in 2006. Ms. Murmu’s election is a milestone in the journey of tribal empowerment, though she is by no means limited to her identity. It is a moment of pride for India......

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