These diagnostic processes open the door to a better understanding of plasma physics, which could lead to advances in green energy production through methods including fusion, hydrocarbon reforming and hydrogen generation.

Dr. David Staack and Christopher Campbell in the J. Mike Walker ’66 Department of Mechanical Engineering at Texas A&M University are part of the team pioneering this approach to assessing plasma processes. Partners on the project include diagnostics experts from Los Alamos National Laboratories and using the facilities at the Argonne National Laboratory Advanced Photon Source (APS).

The team is working with LTEOIL on patented research into the use of multiphase plasma in carbon-free fuel reforming. The research is supported by the dynamic materials properties campaign (C2) and the advanced diagnostics campaign (C3) at Los Alamos National Laboratories through the Thermonuclear Plasma Physics group (P4) principal investigator, Zhehui (Jeph) Wang.

The research, which was recently published in Physical Review Research, is producing the first-known ultrafast X-ray images of pulsed plasma initiation processes in water. Staack, associate professor and Sallie and Don Davis ’61 Career Development Professor, said these new images provide valuable insight into how plasma behaves in liquid.

“Our lab is working with industry sponsors on patented research into the use of multiphase plasma in carbon-free fuel reforming,” Staack said. “By understanding this plasma physics, we are able to efficiently convert tar and recycled plastics into hydrogen and fuels for automobiles without any greenhouse gas emissions. In the future, these investigations may lead to improvements in inertial confinement fusion energy sources.”

Inertial confinement fusion — in which high temperature, high energy density plasmas are generated — is a specific focus of the project. To better understand the plasma physics involved in this type of fusion, Staack said the team is developing short timescale, high-speed imaging and diagnostic techniques utilizing a simple, low-cost plasma discharge system.

Additionally, they are seeking to better understand the phenomena that occur when plasma is discharged in liquid, causing a rapid release of energy resulting in low-density microfractures in the water that move at over 20 times the speed of sound.

Campbell, a graduate research assistant and Ph.D. candidate, said the team hopes their discoveries can prove to be a valuable contribution to the collective knowledge of their field as researchers seek to develop robust predictive models for how plasma will react in liquid.

“Our goal is to experimentally probe the regions and timescales of interest surrounding this plasma using ultrafast X-ray and visible imaging techniques, thereby contributing new data to the ongoing literature discussion in this area,” said Campbell. “With a complete conceptual model, we could more efficiently learn how to apply these plasmas in new ways and also improve existing applications.”

Although they have made progress, Campbell said current methods are not yet sophisticated enough to collect multiple images of a single plasma event in such a short amount of time — less than 100 nanoseconds.

“Even with the state-of-the-art techniques and fast framerates available at the Advanced Photon Source, we have only been able to image a single frame during the entire event of interest — by the next video frame, most of the fastest plasma processes have concluded,” Campbell said. “This work highlights several resourceful techniques we have developed to make the most of what few images we are able to take of these fastest processes.”

The team is currently working to measure the pressures induced by the rapid phenomena and preparing for a second round of measurements at APS to investigate interacting discharges, discharges in different fluids and processes that may limit confinement of higher energy discharges. They look forward to the opportunity of using even higher-framerate X-ray imaging methods ranging up to 6.7 million frames per second, compared to 271 thousand frames per second in this study.

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Materials provided by Texas A&M University. Original written by Steve Kuhlmann. Note: Content may be edited for style and length.

The findings upend long-held beliefs about the mechanisms underlying the disease, reinforce the importance of prevention efforts and offer a path forward for investigating the origins of other cancer types.

“Cancers result from DNA mutations that allow defective cells to survive and invade other tissues. However, in most cases, the source of these mutations is not clear, which complicates development of therapies and prevention methods,” said Gerd Pfeifer, Ph.D., a VAI professor and the study’s corresponding author. “In melanoma, we’ve now shown that damage from sunlight primes the DNA by creating ‘premutations’ that then give way to full mutations during DNA replication.”

Melanoma is a serious type of skin cancer that begins in pigment-producing skin cells. Although less common than other types of skin cancer, melanoma is more likely to spread and invade other tissues, which significantly reduces patient survival. Previous large-scale sequencing studies have shown that melanoma has the most DNA mutations of any cancer. Like other skin cancers, melanoma is linked to sun exposure, specifically a type of radiation called UVB. Exposure to UVB damages skin cells as well as the DNA within cells.

Most cancers are thought to begin when DNA damage directly causes a mutation that is then copied into subsequent generations of cells during normal cellular replication. In the case of melanoma, however, Pfeifer and his team found a different mechanism that produces disease-causing mutations — the introduction of a chemical base not normally found in DNA that makes it prone to mutation.

DNA comprises four chemical bases that exist in pairs — adenine (A) and thymine (T), and cytosine (C) and guanine (G). Different sequences of these pairs encode all of the instructions for life. In melanoma, the problem occurs when UVB radiation from the sun hits certain sequences of bases — CC, TT, TC and CT — causing them to chemically link together and become unstable. The resulting instability causes a chemical change to cytosine that transforms it into uracil, a chemical base found in the messenger molecule RNA but not in DNA. This change, called a “premutation,” primes the DNA to mutate during normal cell replication, thereby causing alterations that underlie melanoma.

These mutations may not cause disease right away; instead, they may lay dormant for years. They also can accumulate as time goes on and a person’s lifetime exposure to sunlight increases, resulting in a tough-to-treat cancer that evades many therapeutic options.

“Safe sun practices are very important. In our study, 10-15 minutes of exposure to UVB light was equivalent to what a person would experience at high noon, and was sufficient to cause premutations,” Pfeifer said. “While our cells have built-in safeguards to repair DNA damage, this process occasionally lets something slip by. Protecting the skin is generally the best bet when it comes to melanoma prevention.”

The findings were made possible using a method developed by Pfeifer’s lab called Circle Damage Sequencing, which allows scientists to “break” DNA at each point where damage occurs. They then coax the DNA into circles, which are replicated thousands of times using a technology called PCR. Once they have enough DNA, they use next-generation sequencing to identify which DNA bases are present at the breaks. Going forward, Pfeifer and colleagues plan to use this powerful technique to investigate other types of DNA damage in different kinds of cancer.

Other authors include Seung-Gi Jin, Ph.D., Dean Pettinga, Jennifer Johnson and Peipei Li, Ph.D., of VAI.

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Materials provided by Van Andel Research Institute. Note: Content may be edited for style and length.

Faced with new uncertainty, shoppers began stocking up on basic household items — especially toilet paper — to account for the new unknown. This buying frenzy led to shortages, even though, in most cases, there would have been enough to go around if people only purchased what they needed.

According to a study led by UNSW Sydney, reactive behaviour like this isn’t unusual, but a common way to handle unexpected uncertainty.

In fact, unexpected uncertainty is such a powerful motivator for change that it often prompts us to adjust our behaviour — even when it’s not good for us.

“When people experience an unexpected change in their environment, they start looking for ways to lessen that uncertainty,” says lead author of the study Dr Adrian Walker, who completed this research as part of his PhD in psychology at UNSW Science. “They can change their behaviour and decision-making strategies to try and find a way to regain some sense of control.

“Surprisingly, our study found that unexpected uncertainty caused people to change their behaviours even when they would have been better off sticking to an old strategy.”

The behavioural study, recently published in The Journal of Experimental Psychology: Learning, Memory, and Cognition, is the first to show the type of uncertainty we experience — that is, whether it is expected or unexpected — plays a key role in our reaction.

For example, a city worker who knows their morning commute takes anywhere from 30 to 50 minutes wouldn’t be surprised by a 50-minute trip. On the other hand, a country driver would be very surprised if their predictable 30-minute trip suddenly took 50 minutes.

To test how people respond to unexpected change, the researchers tasked study participants with selling a pair of objects to one of two subjects — in this scenario, aliens — in a virtual simulation. Their task was simple: get as many points (or ‘alien dollars’) as possible.

Participants needed to choose which alien to sell a pair of chemicals to, but only one of the chemicals determined how much the alien would pay. They needed to work out which chemical and alien combination would earn them the greatest rewards.

An initial group of 35 participants were familiarised with the task and quickly learnt that one strategy (say, Option A) gave the better offer of 15 points. But midway through the experiment, the reward pattern changed, and Option A now gave a random number between 8 and 22 points.

“As soon as we added an element of uncertainty, the participants started looking for new ways to complete the task,” says Dr Walker. “The kicker is that in all cases, the best thing they could do was use their old strategy.”

Dr Walker says the pandemic — and our different responses to it — is a large-scale example of unexpected uncertainty.

“Everything changed very suddenly at the start of COVID-19,” he says.

“Many of us were suddenly all working from home, changing how we shop, and changing how we socialise. The rules we were living by beforehand no longer applied, and there was — and still is — no clear answer about when or how the pandemic will end.

“Different people tried all sorts of things — like panic shopping — to reduce this new uncertainty and return to ‘normal’. But as we’ve seen, not all of these reactive strategies were good in the long run.”

Boiling frog syndrome

While unexpected uncertainty led to dramatic responses, expected uncertainty had the opposite effect.

During the second phase of the trial, the researchers introduced uncertainty in a gradual way to a different group of 35 participants. Option A’s usual 15 points changed to 14-16 points, then 13-17 points, until the uncertainty rose to 8-22 points.

“The participants’ behaviour didn’t change dramatically, even though the uncertainty eventually reached the same levels as in the first experiment,” says Dr Walker.

“When uncertainty was introduced gradually, people were able to maintain their old strategies.”

While this specific experiment was designed for the original strategy to be the most beneficial, Dr Walker says other research has shown the harm in not changing behaviour when faced with gradual change.

“We can see this pattern in a lot of real-world challenges, like the climate change crisis,” says Dr Walker.

“When change is slow and barely noticeable, there’s no sudden prompt to change our behaviour, and so we hold to old behaviours.

“Trying to get action on climate change is a lot like the boiling frog fable. If you put a frog in a pot and boil the water, it won’t notice the threat because the water is warming gradually. When it finally notices, it is too late to jump out.”

Professor Ben Newell, the Deputy Head of UNSW School of Psychology, was one of the researchers involved in the project. He says an important next step in this research is translating insights about how people react to uncertainty in the lab to engaging people in climate action.

“If we can identify the triggers for exploring new alternatives, then we might overcome the inertia inherent in developing new, sustainable behaviours,” says Prof. Newell.

Being certain about uncertainty

Uncertainty is something humans face every day, whether it’s how bad traffic will be or what questions might be asked in an exam.

But the COVID-19 pandemic has thrown a new layer of uncertainty to major areas of our lives, like career, health, and living circumstances.

“While this study isn’t the whole picture for human behaviour during the pandemic, it can help explain why so many people looked for new ways to add certainty to their lives,” says Dr Walker, who is now a researcher in the School of Psychiatry at UNSW Medicine & Health.

Co-author Dr Tom Beesley, formerly of UNSW and now based at Lancaster University, says “Dr Walker’s work really helps us understand how people develop a representation of the uncertainty they are facing, and how they might cope, or not cope, with that.

“My lab is trying to formalise this relationship in a computational model of behaviour, so that we can make clearer predictions about what we might expect to happen under different conditions of uncertainty.”

While Dr Walker’s research is now focused on psychiatric epidemiology, he is interested to see where future research in this area goes — especially in predicting individual responses to uncertainty.

“Given how many decisions we make under uncertainty in our everyday lives, the more we can understand about how these decisions are made, the more we hope to enable people to make good decisions,” says Dr Walker.

The primary finding is that pairs of electrons and positrons — particles of matter and antimatter — can be created directly by colliding very energetic photons, which are quantum “packets” of light. This conversion of energetic light into matter is a direct consequence of Einstein’s famous E=mc² equation, which states that energy and matter (or mass) are interchangeable. Nuclear reactions in the sun and at nuclear power plants regularly convert matter into energy. Now scientists have converted light energy directly into matter in a single step.

The second result shows that the path of light traveling through a magnetic field in a vacuum bends differently depending on how that light is polarized. Such polarization-dependent deflection (known as birefringence) occurs when light travels through certain materials. (This effect is similar to the way wavelength-dependent deflection splits white light into rainbows.) But this is the first demonstration of polarization-dependent light-bending in a vacuum.

Both results depend on the ability of RHIC’s STAR detector — the Solenoid Tracker at RHIC — to measure the angular distribution of particles produced in glancing collisions of gold ions moving at nearly the speed of light.

Colliding clouds of photons

Such capabilities didn’t exist when physicists Gregory Breit and John A. Wheeler first described the hypothetical possibility of colliding light particles to create pairs of electrons and their antimatter counterparts, known as positrons, in 1934.

“In their paper, Breit and Wheeler already realized this is almost impossible to do,” said Brookhaven Lab physicist Zhangbu Xu, a member of RHIC’s STAR Collaboration. “Lasers didn’t even exist yet! But Breit and Wheeler proposed an alternative: accelerating heavy ions. And their alternative is exactly what we are doing at RHIC.”

An ion is essentially a naked atom, stripped of its electrons. A gold ion, with 79 protons, carries a powerful positive charge. Accelerating such a charged heavy ion to very high speeds generates a powerful magnetic field that spirals around the speeding particle as it travels — like current flowing through a wire.

“If the speed is high enough, the strength of the circular magnetic field can be equal to the strength of the perpendicular electric field,” Xu said. And that arrangement of perpendicular electric and magnetic fields of equal strength is exactly what a photon is — a quantized “particle” of light. “So, when the ions are moving close to the speed of light, there are a bunch of photons surrounding the gold nucleus, traveling with it like a cloud.”

At RHIC, scientists accelerate gold ions to 99.995% of the speed of light in two accelerator rings.

“We have two clouds of photons moving in opposite directions with enough energy and intensity that when the two ions graze past each other without colliding, those photon fields can interact,” Xu said.

STAR physicists tracked the interactions and looked for the predicted electron-positron pairs.

But such particle pairs can be created by a range of processes at RHIC, including through “virtual” photons, a state of photon that exists briefly and carries an effective mass. To be sure the matter-antimatter pairs were coming from real photons, scientists have to demonstrate that the contribution of “virtual” photons does not change the outcome of the experiment.

To do that, the STAR scientists analyzed the angular distribution patterns of each electron relative to its partner positron. These patterns differ for pairs produced by real photon interactions versus virtual photons.

“We also measured all the energy, mass distributions, and quantum numbers of the systems. They are consistent with theory calculations for what would happen with real photons,” said Daniel Brandenburg, a Goldhaber Fellow at Brookhaven Lab, who analyzed the STAR data on this discovery.

Other scientists have tried to create electron-positron pairs from collisions of light using powerful lasers — focused beams of intense light. But the individual photons within those intense beams don’t have enough energy yet, Brandenburg said.

One experiment at the SLAC National Accelerator Laboratory in 1997 succeeded by using a nonlinear process. Scientists there first had to boost the energy of the photons in one laser beam by colliding it with a powerful electron beam. Collisions of the boosted photons with multiple photons simultaneously in an enormous electromagnetic field created by another laser produced matter and antimatter.

“Our results provide clear evidence of direct, one-step creation of matter-antimatter pairs from collisions of light as originally predicted by Breit and Wheeler,” Brandenburg said. “Thanks to RHIC’s high-energy heavy ion beam and the STAR detector’s large acceptance and precision measurements, we are able to analyze all the kinematic distributions with high statistics to determine that the experimental results are indeed consistent with real photon collisions.”

Bending light in a vacuum

STAR’s ability to measure the tiny deflections of electrons and positrons produced almost back-to-back in these events also gave the physicists a way to study how light particles interact with the powerful magnetic fields generated by the accelerated ions.

“The cloud of photons surrounding the gold ions in one of RHIC’s beams is shooting into the strong circular magnetic field produced by the accelerated ions in the other gold beam,” said Chi Yang, a long-time STAR collaborator from Shandong University who spent his entire career studying electron-positron pairs produced from various processes at RHIC. “Looking at the distribution of particles that come out tells us how polarized light interacts with the magnetic field.”

Werner Heisenberg and Hans Heinrich Euler in 1936, and John Toll in the 1950s, predicted that a vacuum of empty space could be polarized by a powerful magnetic field and that such a polarized vacuum should deflect the paths of photons depending on photon polarization. Toll, in his thesis, also detailed how light absorption by a magnetic field depends on polarization and its connection to the refractive index of light in a vacuum. This polarization-dependent deflection, or birefringence, has been observed in many types of crystals. There was also a recent report of the light coming from a neutron star bending this way, presumably because of its interactions with the star’s magnetic field. But no Earth-based experiment has detected birefringence in a vacuum.

At RHIC, the scientists measured how the polarization of the light affected whether the light was “absorbed” by the magnetic field.

This is similar to the way polarized sunglasses block certain rays from passing through if they don’t match the polarization of the lenses, Yang explained. In the case of the sunglasses, in addition to seeing less light get through, you could, in principle, measure an increase in the temperature of the lens material as it absorbs the energy of the blocked light. At RHIC, the absorbed light energy is what creates the electron-positron pairs.

“When we look at the products produced by photon-photon interactions at RHIC, we see that the angular distribution of the products depends on the angle of the polarization of the light. This indicates that the absorption (or passing) of light depends on its polarization,” Yang said.

This is the first Earth-based experimental observation that polarization affects the interactions of light with the magnetic field in the vacuum — the vacuum birefringence predicted in 1936.

“Both of these findings build on predictions made by some of the great physicists in the early 20th century,” said Frank Geurts, a professor at Rice University, whose team built and operated the state-of-the-art “Time-of-Flight” detector components of STAR that were necessary for this measurement. “They are based on fundamental measurements made possible only recently with the technologies and analysis techniques we have developed at RHIC.”