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Hardy transistor material could be game-changer for nuclear reactor safety monitoring
The safety and efficiency of a large, complex nuclear reactor can be enhanced by hardware as simple as a tiny sensor that monitors a cooling system. That’s why researchers at the Department of Energy’s Oak Ridge National Laboratory are working to make those basic sensors more accurate by pairing them with electronics that can withstand the intense radiation inside a reactor.
The ORNL research team recently met with unexpectedly high success using a gallium nitride semiconductor for sensor electronics. A transistor made with the material maintained operations near the core of a nuclear reactor operated by research partner The Ohio State University.
Gallium nitride, a wide-bandgap semiconductor, had previously been tested against the ionizing radiation encountered when rockets hurtle through space. Devices with wide-bandgap semiconductors can operate at much higher frequencies, temperatures and irradiation rates. But gallium nitride had not faced the even more intense radiation of neutron bombardment.
“We are showing it is great for this neutron environment,” said lead researcher Kyle Reed, a member of the Sensors and Electronics group at ORNL.
That could offer a big boost for equipment monitoring in nuclear facilities. The information gathered by sensors provides early warnings about wear and tear on equipment, allowing timely maintenance to avoid broader equipment failures that cause reactor downtime. Currently, this sensing data is processed from a distance, through yards of cable connected to electronics with silicon-based transistors.
“Our work makes measuring the conditions inside an operating nuclear reactor more robust and accurate,” Reed said. “When you have lengthy cables, you end up with a lot of noise, which can interfere with the accuracy of the sensor information. By placing electronics closer to a sensor, you increase its accuracy and precision.” To meet that goal, scientists need to develop electronics that can better tolerate radiation.
Researchers irradiated gallium nitride transistors for three days at temperatures up to 125 degrees Celsius close to the core of The Ohio State University Research Reactor.
“We fully expected to kill the transistors on the third day, and they survived,” Reed said. The team pushed the transistors all the way to the reactor’s safety threshold: seven hours at 90% power.
The gallium nitride transistors were able to handle at least 100 times higher accumulated dose of radiation than a standard silicon device, said researcher Dianne Ezell, leader of ORNL’s Nuclear and Extreme Environment Measurements group and a member of the transistor research team.
She said the transistor material must be capable of surviving at least five years, the normal maintenance window, in the pool of a nuclear reactor. After the research team exposed the gallium nitride device to days of much higher radiation levels within the core itself, they concluded that the transistors would exceed that requirement.
This is an important technical advance as attention turns from the large-scale existing fleet of nuclear energy plants to microreactors that could generate from tens to hundreds of megawatts of power. Although these novel reactor designs are still in the development and licensing stage, their potential portability could allow them to be deployed on the back of a truck to a military or disaster zone.
Advanced reactors are being designed to operate at higher temperatures using different forms of fuel. Because microreactors will be so compact, all the operating components, including the sensors, will have to be able to function in the radiation field, Ezell said. Gallium nitride transistors could be the key.
Ohio State researchers built devices of different designs and sizes to meet specifications set by ORNL, and then the team compared their responses to radiation, finding that larger devices seemed less susceptible to radiation damage. Ohio State is now developing computer models to project how various circuit designs will perform under different temperatures and radiation levels.
Reed said the radiation testing at Ohio State showed that heat seemed to be more harmful to the gallium nitride than radiation, so the research team wants to measure how gallium nitride reacts to heat alone.
“Since the ultimate goal is to design circuits with these materials, once we understand the temperature and radiation effects, we can compensate for them in the circuit design,” Reed said.
Better nuclear monitoring means increased safety and reduced operating costs, Ezell noted. “Hundreds of thousands of dollars are lost every day a reactor is shut down,” she said. “If we’re going to make nuclear economically competitive with other energy industries, we’ve got to keep our costs low.” Plus, reducing the frequency of maintenance reduces human safety risks. “You’re able to avoid putting people in harsh radiation environments or handling radioactive material as often,” Ezell added.
Although gallium nitride has been commercially available for around a decade, it’s not widely used, Reed said.
“We’re opening up different side avenues for using gallium nitride, so we can start to create a more reasonable market demand for investment, research and workforce development for subclasses of electronics beyond consumer-grade,” Reed said.
In the long run, researchers would like to demonstrate that gallium nitride circuits could be used to transmit data from sensors wirelessly. The material is already used for devices that support radio frequency applications, like cell phones, and for power electronics.
ORNL researchers, staff and interns including Nance Ericson, Brett Witherspoon, Craig Gray, Emma Brown, Adam Buchalter, Caleb Damron and former intern Kevin Deng also contributed to the project.
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Hardy transistor material could be game-changer for nuclear reactor safety monitoring (2024, June 24)
retrieved 25 June 2024
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Informal care is difficult to combine with work
Informal care has a huge impact on your working life. Informal caregivers earn less per hour and are less satisfied with their job. This is the conclusion reached by sociologist Klara Raiber, who will defend her Ph.D. dissertation at Radboud University on 2 July. With more people becoming informal caregivers, the researcher says it is high time for structural support to be provided.
In our aging society, many people are informal caregivers—especially as more and more professional care has been replaced by informal care in recent years. “Caring for friends or family with health problems is placing more and more demands on people,” explains researcher Klara Raiber. “This means that informal care is having a bigger impact on other aspects of life, such as work.”
Raiber studied the extent of this impact on work by conducting multi-year surveys among broad sections of the Dutch, British and German populations. The results are clear: a relatively large number of informal caregivers find caretaking obligations difficult to combine with their work.
Some informal caregivers have had to reduce their hours or even stop working altogether to care for a relative or friend. Others have changed jobs or become self-employed in order to have more flexibility in their working hours. In addition, it seems that informal caregivers earn less and are less satisfied with their jobs than their non-care-giving colleagues.
Men benefit
The sociologist was able to compare different types of informal caregivers. For all these groups, providing informal care seemed to have a negative effect on work. “However, we can see that people who have been informal caregivers for many years experience slightly more benefits,” explains Raiber.
“This may be because they learn from providing informal care, for example about time management and empathy. For this group, the pay gap with other colleagues is smaller, probably because they have found a way to combine work and informal care better.”
Using data from Statistics Netherlands, Raiber was able to investigate how providing informal care affects pay. According to the researcher, the fact that informal caregivers earn less may be because employers feel that informal caregivers are less productive. As a result, they are less likely to be promoted. And some informal caregivers take time off work or work less, so their pay doesn’t keep pace.
For one group of men, however, providing informal care was found to be more beneficial. Raiber states, “Men sometimes even get a higher salary during or after a period of caregiving. This could be because men who are informal caregivers become more empathetic and better at managing their time. Those qualities in men are especially valued by employers, while women are already expected to have those skills.”
Aging
More support needs to be offered to informal caregivers, says the researcher, especially in the face of an aging society. “The problems experienced by informal caregivers are sometimes dismissed as being an individual’s problem, but they’re not. More and more people are having to deal with them. There are things like informal care leave, but that doesn’t solve the problem of lower pay.”
Policymakers should also continue to invest in professional care, thinks Raiber. “Informal care can be a great help to caregivers and dependents, but what happens to grandpa if his informal caregiver falls ill? There has to be an alternative.
“Also, professional care doesn’t have to be more expensive than informal care. If you look at how much less time a family caregiver works, it might only be a few minutes on average per week. That may seem little, but if one-third of the population does that, a total of hundreds of thousands of hours less per week is worked. That also costs society money.”
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Informal care is difficult to combine with work (2024, June 25)
retrieved 25 June 2024
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Engineered skin tissue grants robots special properties and abilities
Researchers have found a way to bind engineered skin tissue to the complex forms of humanoid robots. This brings with it potential benefits to robotic platforms such as increased mobility, self-healing abilities, embedded sensing capabilities and an increasingly lifelike appearance.
Taking inspiration from human skin ligaments, the team, led by Professor Shoji Takeuchi of the University of Tokyo, included special perforations in a robot face, which helped a layer of skin take hold. Their research could be useful in the cosmetics industry and to help train plastic surgeons. The work is published in the journal Cell Reports Physical Science.
Takeuchi is a pioneer in the field of biohybrid robotics, where biology and mechanical engineering meet. So far, his lab, the Biohybrid Systems Laboratory, has created mini robots that walk using biological muscle tissue, 3D printed lab-grown meat, engineered skin that can heal, and more. It was during research on the last of these items that Takeuchi felt the need to take the idea of robotic skin further to improve its properties and capabilities.
“During previous research on a finger-shaped robot covered in engineered skin tissue we grew in our lab, I felt the need for better adhesion between the robotic features and the subcutaneous structure of the skin,” said Takeuchi.
“By mimicking human skin-ligament structures and by using specially made V-shaped perforations in solid materials, we found a way to bind skin to complex structures. The natural flexibility of the skin and the strong method of adhesion mean the skin can move with the mechanical components of the robot without tearing or peeling away.”
Previous methods to attach skin tissue to solid surfaces involved things like mini anchors or hooks, but these limited the kinds of surfaces that could receive skin coatings and could cause damage during motion. By carefully engineering small perforations instead, essentially any shape of surface can have skin applied to it.
The trick the team employed was to use a special collagen gel for adhesion, which is naturally viscous so difficult to feed into the minuscule perforations. But using a common technique for plastic adhesion called plasma treatment, they managed to coax the collagen into the fine structures of the perforations while also holding the skin close to the surface in question.
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The new anchoring method allows flexible skin tissue to conform to any shape it’s attached to. In this case, a relatively flat robotic face is made to smile and the skin deforms without constraining the robot, returning to its original shape afterwards. Credit: 2024 Takeuchi et al. CC-BY-ND
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Other methods to bind skin tissue to solid structures come with limitations. This new method can work on complex, curved, and even moving surfaces. Credit: 2024 Takeuchi et al. CC-BY-ND
“Manipulating soft, wet biological tissues during the development process is much harder than people outside the field might think. For instance, if sterility is not maintained, bacteria can enter and the tissue will die,” said Takeuchi.
“However, now that we can do this, living skin can bring a range of new abilities to robots. Self-healing is a big deal—some chemical-based materials can be made to heal themselves, but they require triggers such as heat, pressure or other signals, and they also do not proliferate like cells. Biological skin repairs minor lacerations as ours does, and nerves and other skin organs can be added for use in sensing and so on.”
This research was not just made to prove a point, though. Takeuchi and his lab have a goal in mind for this application that could help in several areas of medical research. The idea of an organ-on-a-chip is not especially new, and finds use in things like drug development, but something like a face-on-a-chip could be useful in research into skin aging, cosmetics, surgical procedures, plastic surgery and more. Also, if sensors can be embedded, robots may be endowed with better environmental awareness and improved interactive capabilities.
“In this study, we managed to replicate human appearance to some extent by creating a face with the same surface material and structure as humans,” said Takeuchi.
“Additionally, through this research, we identified new challenges, such as the necessity for surface wrinkles and a thicker epidermis to achieve a more humanlike appearance. We believe that creating a thicker and more realistic skin can be achieved by incorporating sweat glands, sebaceous glands, pores, blood vessels, fat and nerves.
“Of course, movement is also a crucial factor, not just the material, so another important challenge is creating humanlike expressions by integrating sophisticated actuators, or muscles, inside the robot. Creating robots that can heal themselves, sense their environment more accurately and perform tasks with humanlike dexterity is incredibly motivating.”
More information:
M. Kawai, M. Nie, H. Oda, S. Takeuchi. Perforation-type anchors inspired by skin ligament for robotic face covered with living skin, Cell Reports Physical Science (2024). DOI: 10.1016/j.xcrp.2024.102066. www.cell.com/cell-reports-phys … 2666-3864(24)00335-7
Citation:
Engineered skin tissue grants robots special properties and abilities (2024, June 25)
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How ‘sticky’ is dense nuclear matter?
Colliding heavy atomic nuclei together creates a fluidlike soup of visible matter’s fundamental building blocks, quarks and gluons. This soup has very low viscosity—a measure of its “stickiness,” or resistance to flow.
Theorists have performed the first systematic study of whether and how this viscosity changes over a wide range of collision energies. The work takes into account changes that take place as the colliding nuclei pass through each other. The work is published in the journal Physical Review Letters.
The calculations predict that the fluid’s viscosity increases with net-baryon density—the relative abundance of baryons (particles made of three quarks, like the neutrons and protons that make up the colliding nuclei) over antibaryons (which are produced in the collision).
This analysis determined the best parameters for fitting new simulations to experimental data from collisions of gold nuclei at different energies. It predicted increased viscosity with increasing net-baryon density. This agrees with some but not all theoretical predictions. In the future, scientists will use this same theoretical framework to incorporate additional data from a range of collision energies.
These expanded simulations will not only provide information about viscosities. They will also offer data on the entire phase diagram of nuclear matter, which maps out how nuclear matter varies from a solid, liquid, gas, or plasma as a function of temperature and baryon density.
This work combines state-of-the-art viscous fluid dynamic simulations in all three spatial dimensions with newly developed dynamic models of the collisions’ initial stage to describe heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC), a Department of Energy user facility, over a wide range of collision energies.
Incorporating the evolution of the initial state allows for the continuous generation of fluid nuclear matter as the colliding nuclei pass through each other. This is particularly important at lower beam energies where the assumption of an instantaneous collision is not valid.
In this research, a team of theorists from Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, the University of California Berkeley, and Wayne State University used this versatile model to perform event-by-event calculations that consider fluctuations in the initial geometry of the colliding nuclei and the resulting shape of the produced fireball.
The researchers varied and constrained the parameters of the model, which include the viscosities of the produced matter as well as properties of the initial state, to perform a statistical analysis with input from experimental data collected during RHIC’s Beam Energy Scan (BES).
This data-driven analysis of how viscosities depend on net-baryon density was based on 5 million numerically simulated collision events. Researchers can now compare this analysis to pure theoretical calculations. The same framework can be applied to measurements from BES Phase II at RHIC and at the future Facility for Antiproton and Ion Research (FAIR) in Europe.
More information:
Chun Shen et al, Viscosities of the Baryon-Rich Quark-Gluon Plasma from Beam Energy Scan Data, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.132.072301
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Citation:
How ‘sticky’ is dense nuclear matter? (2024, June 25)
retrieved 25 June 2024
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