Low-energy nuclear fusion reactions can potentially provide clean energy. In stars, low-energy fusion reactions during the stages of carbon and oxygen burning are critical to stellar evolution. These reactions also offer valuable insights into the exotic processes occurring in the inner crust of neutron stars as they accumulate matter.

However, scientists do not fully understand the underlying dynamics governing these reactions. The key to unlocking the fusion process is understanding how nucleons move between the two fusing nuclei. As the nuclei draw close enough for the nuclear forces to become effective, neutrons and protons can migrate from one nucleus to another. This movement potentially eases the fusion process.

A recent study has explored the influence on low-energy fusion processes of isospin composition. This is a key nuclear property that differentiates protons from neutrons. The researchers used computational techniques and theoretical modeling to investigate the fusion of different nuclei with varying isospin configurations. The results show that the isospin composition of the nuclei in a fusion reaction plays a crucial role in understanding the reaction. The paper is published in the journal Physical Review C.

In this study, researchers at Fisk University and Vanderbilt University used high-performance computational and theoretical modeling techniques to conduct a detailed many-body method study of how the dynamics of isospin influence nuclear fusion at low energies across a series of isotopes. The study also examined how the shape of the nuclei involved affect these dynamics. In systems where the nuclei are not symmetrical, the dynamics of isospin become particularly important, often leading to a lowered fusion barrier, especially in systems rich in neutrons. This phenomenon can be explored using facilities that specialize in the generation of beams composed of exotic, unstable nuclei.

The findings provide critical knowledge regarding the fundamental nuclear processes governing these reactions, which have broad implications for fields such as nuclear physics, astrophysics, and, perhaps someday, fusion-based energy.

The first crewed flight of Boeing’s Starliner spaceship was dramatically called off just two hours before launch after a new safety issue was identified, officials said Monday, pushing back a high-stakes test mission to the International Space Station.

Astronauts Butch Wilmore and Suni Williams were strapped into their seats preparing for liftoff when the call for a “scrub” came because engineers noticed audible buzzing from a liquid oxygen relief valve on the Atlas V rocket meant to propel the capsule into orbit.

In a late-night press conference, Tory Bruno, president and CEO of United Launch Alliance (ULA) that built the rocket, told reporters the unusual vibrations were a sign the valve parts might be wearing down to the point of failure, but insisted “the crew was never in any danger.”

Engineers will now work through the night to determine the degree of deterioration and decide whether to re-fit the same part on the launchpad, or wheel the rocket back to its assembly building to install a new valve, he added.

ULA, a Boeing-Lockheed Martin joint venture, later said the next launch attempt would be Friday at the earliest.

“The team needs additional time to complete a full assessment, so we are targeting the next launch attempt no earlier than Friday, May 10,” ULA said on social media platform X.

The mission has already faced years of delays and comes at a challenging time for Boeing, as a safety crisis engulfs the century-old manufacturer’s commercial aviation division.

NASA is banking on a successful test for Starliner so it can certify a second commercial vehicle to carry crews to the ISS.

Elon Musk’s SpaceX achieved the feat with its Dragon capsule in 2020, ending a nearly decade-long dependence on Russian rockets following the end of the Space Shuttle program.

History of setbacks

Following the decision to abort the launch, the astronauts, clad in blue spacesuits, were helped out of Starliner then boarded a van back to their quarters.

Wilmore and Williams, both Navy-trained pilots and space program veterans, have each been to the ISS twice, traveling once on a shuttle and then aboard a Russian Soyuz vessel.

Their new mission will see them put Starliner through its paces, piloting the craft manually to test its capabilities.

The gumdrop-shaped capsule with a cabin about as roomy as an SUV is set to rendezvous with the ISS for a weeklong stay, before returning to Earth for a parachute-assisted landing in the western United States.

A successful mission would help dispel the bitter taste left by numerous setbacks in the Starliner program.

In 2019, during a first uncrewed test flight, software defects meant the capsule was not placed on the right trajectory and returned without reaching the ISS. “Ground intervention prevented loss of vehicle,” said NASA in the aftermath, chiding Boeing for inadequate safety checks.

Then in 2021, with the rocket on the launchpad for a new flight, blocked valves forced another postponement.

The vessel finally reached the ISS in May 2022 in a non-crewed launch. But other problems that came to light—including weak parachutes and flammable tape in the cabin that needed to be removed—caused further delays to the crewed test flight, necessary for the capsule to be certified for NASA use on regular ISS missions.

Exclusive club

SpaceX’s Dragon capsule joined that exclusive club four years ago, following the Mercury, Gemini, Apollo and Space Shuttle programs.

In 2014, the agency awarded fixed-price contracts of $4.2 billion to Boeing and $2.6 billion to SpaceX to develop the capsules under its Commercial Crew Program.

This marked a shift in NASA’s approach from owning space flight hardware to instead paying private partners for their services as the primary customer.

Once Starliner is fully operational, NASA hopes to alternate between SpaceX and Boeing vessels to taxi humans to the ISS.

Even though the orbital lab is due to be mothballed in 2030, both Starliner and Dragon could be used for future private space stations that several companies are developing.

© 2024 AFP

Roughly one in four U.S. households have soil exceeding the new U.S. Environmental Protection Agency’s lead screening levels of 200 parts per million (ppm), halved from the previous level of 400 ppm, a new study found. For households with exposure from multiple sources, the EPA lowered the guidance to 100 ppm; nearly 40% of households exceed that level, the study also found.

“I was shocked at how many households were above the new 200 ppm guideline,” said Gabriel Filippelli, a biochemist at Indiana University who led the new study. “I assumed it was going to be a more modest number. And results for the 100 ppm guideline are even worse.”

Remediating the roughly 29 million affected households using traditional “dig and dump” soil removal methods could cost upward of $1 trillion, the study calculated. The study is published in GeoHealth. Filippelli is the former editor-in-chief of GeoHealth.

National lead problem ‘nowhere near over’

Lead is a heavy metal that can accumulate in the human body, with toxic effects. In children, exposure to lead is associated with lower educational outcomes. In the United States, the burden of lead exposure has historically fallen on lower-income communities and communities of color because of redlining and other discriminatory practices. Lead pollution can come from aging water pipes, old paint, and remnant gasoline and industrial pollution, but today, most lead exposure comes from contaminated soils and dust, even after lead-containing infrastructure is removed.

The Centers for Disease Control and Prevention first set a limit on the concentration of lead in blood in 1991 at 10 micrograms per deciliter, and it lowered that limit several times until reaching the current limit of 3.5 micrograms per deciliter. But the EPA’s soil lead screening level remained unchanged for more than 30 years until the January announcement. Some states had established their own lower guidelines; California has the lowest screening level, at 80 ppm.

The lag is likely due to “the immensity and ubiquity of the problem,” the study authors wrote.

“The scale is astounding, and the nation’s lead and remediation efforts just became substantially more complicated.” That’s because once the EPA lowers a screening limit, they need to tell people what to do if their soils exceed it.

When the EPA lowered the screening level, Filippelli and his co-authors decided to make use of the database of 15,595 residential soil samples from the contiguous United States that they’d collected over the years to find out how many exceeded the new guideline.

Household health hazard

About 25% of the residential soil samples, collected from yards, gardens, alleys, and other residential spots, exceeded the new 200 ppm level, the study found. (Only 12% of samples had exceeded the older, 400 ppm level.) Extrapolating across the country, that equates to roughly 29 million households.

The EPA issued separate guidance for households with multiple sources of exposure, such as both lead-contaminated soil and lead pipes, setting the level in those situations at 100 ppm. In practice, that’s most urban households, Filippelli said. Forty percent of households exceed that limit, increasing the number of affected households to nearly 50 million, the study found.

Typically, contaminated soils are remediated with removal—colloquially, “dig and dump.” But the practice is costly and typically only used after an area is placed on the National Priority List for remediation, a process that can take years. To remediate all contaminated households with “dig and dump” would cost between $290 billion and $1.2 trillion, the authors calculated.

A cheaper option is “capping”: burying the contaminated soil with about a foot of soil or mulch. A geotechnical fabric barrier can also be installed. Most lead contamination is in the top 10 to 12 inches of soil, Filippelli said, so this simple method either covers up the problem or dilutes it to an acceptable level.

“Urban gardeners have been doing this forever anyway, with raised beds, because they’re intuitively concerned about the history of land use at their house,” Filippelli said.

And capping is quicker.

“A huge advantage of capping is speed. It immediately reduces exposure,” Filippelli said. “You’re not waiting two years on a list to have your yard remediated while your child is getting poisoned. It’s done in a weekend.”

Capping still requires time and effort; residents must find clean soil, transport it to their home and spread it out. But the health benefits likely outweigh those costs, Filippelli said.

Because capping has been done more informally, there’s still a lot to be learned about its lifespan and sustainability, Filippelli said. That’s where the research will go next.

Despite the “staggering” scale of the problem, “I’m really optimistic,” Filippelli said. “Lead is the most easily solvable problem that we have. We know where it is, and we know how to avoid it. It’s just a matter of taking action.”

Since the rollout of the COVID-19 vaccine in 2021, fake news on social media has been widely blamed for low vaccine uptake in the United States—but research by MIT Sloan School of Management Ph.D. candidate Jennifer Allen and Professor David Rand finds that the blame lies elsewhere.

In a new paper published in Science and co-authored by Duncan J. Watts of the University of Pennsylvania, the researchers introduce a new methodology for measuring social media content’s causal impact at scale. They show that misleading content from mainstream news sources—rather than outright misinformation or “fake news“—was the primary driver of vaccine hesitancy on Facebook.

A new approach to estimating impact

“Misinformation has been correlated with many societal challenges, but there’s not a lot of research showing that exposure to misinformation actually causes harm,” explained Allen.

During the COVID-19 pandemic, for example, the spread of misinformation related to the virus and vaccine received significant public attention. However, existing research has, for the most part, only established correlations between vaccine refusal and factors such as sharing misinformation online—and largely overlooked the role of “vaccine-skeptical” content, which was potentially misleading but not flagged as misinformation by Facebook fact-checkers.

To address that gap, the researchers first asked a key question: What would be necessary for misinformation or any other type of content to have far-reaching impacts?

“To change behavior at scale, content has to not only be persuasive enough to convince people not to get the vaccine, but also widely seen,” Allen said. “Potential harm results from the combination of persuasion and exposure.”

To quantify content’s persuasive ability, the researchers conducted randomized experiments in which they showed thousands of survey participants the headlines from 130 vaccine-related stories—including both mainstream content and known misinformation—and tested how those headlines impacted their intentions to get vaccinated against COVID-19.

Researchers also asked a separate group of respondents to rate the headlines across various attributes, including plausibility and political leaning. One factor reliably predicted impacts on vaccination intentions: the extent to which a headline suggested that the vaccine was harmful to a person’s health.

Using the “wisdom of crowds” and natural language processing AI tools, Allen and her co-authors extrapolated those survey results to predict the persuasive power of all 13,206 vaccine-related URLs that were widely viewed on Facebook in the first three months of the vaccine rollout.

By combining these predictions with data from Facebook showing the number of users who viewed each URL, the researchers could predict each headline’s overall impact—the number of people it might have persuaded not to get the vaccine. The results were surprising.

The underestimated power of exposure

Contrary to popular perceptions, the researchers estimated that vaccine-skeptical content reduced vaccination intentions 46 times more than misinformation flagged by fact-checkers.

The reason? Even though flagged misinformation was more harmful when seen, it had relatively low reach. In total, the vaccine-related headlines in the Facebook data set received 2.7 billion views—but content flagged as misinformation received just 0.3% of those views, and content from domains rated as low-credibility received 5.1%.

“Even though the outright false content reduced vaccination intentions the most when viewed, comparatively few people saw it,” explained Rand. “Essentially, that means there’s this class of gray-area content that is less harmful per exposure but is seen far more often —and thus more impactful overall—that has been largely overlooked by both academics and social media companies.”

Notably, several of the most impactful URLs within the data set were articles from mainstream sources that cast doubt on the vaccine’s safety. For instance, the most-viewed was an article—from a well-regarded mainstream news source—suggesting that a medical doctor died two weeks after receiving the COVID-19 vaccine. This single headline received 54.9 million views—more than six times the combined views of all flagged misinformation.

While the body of this article did acknowledge the uncertainty of the doctor’s cause of death, its “clickbait” headline was highly suggestive and implied that the vaccine was likely responsible. That’s significant since the vast majority of viewers on social media likely never click out to read past the headline.

How journalists and social media platforms can help

According to Rand, one implication of this work is that media outlets need to take more care with their headlines, even if that means they aren’t as attention-grabbing.

“When you are writing a headline, you should not just be asking yourself if it’s false or not,” he said. “You should be asking yourself if the headline is likely to cause inaccurate perceptions.”

For platforms, added Allen, the research also points to the need for more nuanced moderation—across all subjects, not just public health.

“Content moderation focuses on identifying the most egregiously false information—but that may not be an effective way of identifying the most overall harmful content,” she says. “Platforms should also prioritize reviewing content from the people or organizations with the largest numbers of followers while balancing freedom of expression. We need to invest in more research and creative solutions in this space—for example, crowdsourced moderation tools like X’s Community Notes.”

“Content moderation decisions can be really difficult because of the inherent tension between wanting to mitigate harm and allowing people to express themselves,” Rand said. “Our paper introduces a framework to help balance that trade-off by allowing tech companies to actually quantify potential harm.”

And the trade-offs could be large. An exploratory analysis by the authors found that if Facebook users hadn’t been exposed to this vaccine-skeptical content, as many as 3 million more Americans could have been vaccinated.

“We can’t just ignore this gray area-content,” Allen concluded. “Lives could have been saved.”

Active systems display a wide range of complex and fascinating behaviors, many of which are not yet fully understood. Found on scales ranging from microbes and self-propelling particles to large groups of fish, birds, and mammals, they are made up of many individual parts, which each convert energy from their surroundings into motion.

Through new analysis published in The European Physical Journal E, Antonio Romaguera and collaborators at the Rural Federal University of Pernambuco, Brazil, have gained deeper insights into the collective motions of schools of zebrafish: active systems in which multiple fish can collectively move in the same direction. The team’s discoveries could help researchers to better understand the unique properties of active matter, and how complex behaviors emerge and evolve on different scales.

Individually, zebrafish enhance the efficiency of their movements through sporadic bursts of their tails, followed by longer periods of coasting. When swimming in large groups, these fish coordinate their sporadic motions as they communicate with each other, leading to complex and interesting patterns.

Among these patterns are “polarized groups,” which emerge when groups of fish within the school swim in the same direction. Using mathematical relationships named “polarization time series” (PTSs), researchers can describe how these collective motions will evolve over time.

In their study, Romaguera and his collaborators examined this behavior in a group of zebrafish confined in a circular tank. As they observed the fish, they discovered a distinctive pattern in the PTS, which varied depending on how crowded the tank was.

As lower densities of zebrafish, the team found that the PTS became “multifractal”: meaning that polarized groups within the same group of fish exhibited different degrees of complexity structure over different scales. Yet as higher densities, the PTS instead became “monofracta”‘—displaying uniform behavior across different scales.

The team of researchers now hope this discovery could deepen our understanding of how active systems behave across a wider range of scenarios.