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"It's the worst possible news on the eve of the tournament," said England midfielder Izzy Christiansen to BBC Sport. Spanish football journalist David Menayo called it "a jug of cold water" thrown over his nation.

They were referring to the loss of Alexia Putellas, who suffered a torn ACL on the eve of this the women's Euro 2022 tournament, leaving Spain without their reigning Ballon d'Or winner. The loss of such a superstar was evident, as Spain, a pre-tournament favorite, looked tame in bowing out to England in the quarterfinals.

Just a week later, young France star Marie-Antoinette Katoto suffered a similar fate in the Euro group stage, and a toothless Les Bleus attack fell short in the semifinals to Germany.

Bright young USWNT star Cat Macario, who lit up the Champions League for Lyon en route to winning the title over Putellas's Barcelona, tore her ACL in the early stages of a meaningless Ligue 1 match in early June. Two weeks later, legendary American striker Christen Press tore her ACL during NWSL play with expansion club Angel City FC. Just a month prior, Macario's Lyon teammate Dzsenifer Marozsan suffered the same fate, ruling the German star out of the Champions League final and leaving her sidelined for the Euros.

It doesn't stop there. USWNT defender Tierna Davidson went down in March of 2022 with an ACL injury during a shortened NWSL preseason. The Australian national team lost three players to ACL tears in a year's span, including young superstar Ellie Carpenter, who has already collected a massive 57 caps at just 22 years old, but went down in late May. A similar rising star for the German national team, Giulia Gwinn, suffered the injury in early October of 2021, her second ACL tear at just 23 years old.

As time progresses, the list just continues to grow — NWSL finalists Kansas City Current saw midfield fixture Claire Lavogez fall victim in the 2022 playoff quarterfinals. In the run-up to the 2023 Women's World Cup, stars Beth Mead and Vivianne Miedema both suffered ACL tears that ruled them out of the game's biggest event.

"The amount of ACL injuries in professional women's soccer in the last two years has just been shocking," Christen Press told ESPN in May of 2023. "If this happened on the men's side, we would have immediately seen a reaction of 'how are we going to solve this and figure this out, and make sure that these players are going to be available at the biggest moments of their career?'"

This is not just limited to the top of the game; clubs and college programs across the United States are noticing an increase in serious knee injuries. The Wake Forest women's team, a top ACC Division I program, has suffered six ACL tears in the past year, an increasingly common struggle for NCAA women's soccer coaches to navigate.

ACL tears have always been a danger in both men's and women's football, but as top players across the women's global game began dropping like flies, The Sporting News began asking questions. It turns out, there are scientific reasons to explain the wave of ACL tears that strike women's soccer.

Women soccer players more prone to ACL tears than men?
Over recent years it has become mainstream knowledge that women are, quite simply, more prone to serious knee injuries than men.

Slight anatomical differences between men's and women's bodies, largely concerning variations in hip structures, leave women at a higher risk of ACL tears or other serious knee damage. "These are trends that we've seen in the sports medicine world for years now," said Dr. Howard Luks, Chief of Sports Medicine and Arthroscopy at New York Medical College and a 20-year orthopedic sports surgeon with over a thousand ACL surgeries under his belt.

"Women in general are at higher risk. They have various differences compared to male athletic counterparts."

Research published by the Yale School of Medicine shows that women are two to eight times more likely to suffer ACL tears than men. Due to a wider hip structure, the knees of females are angled slightly differently, putting more pressure on the ACL. The differences are incredibly slight, but the effects can be witnessed over long periods of time.

"The ACL sits within a narrow notch on the inside of the knee joint," Dr. Luks noted. "That notch has more narrow confines in females, which can increase the risk of injuries."

While anatomical differences between sexes are a large contributing factor, there's another significant difference from males to females. There's medical evidence to support that women are significantly more prone to injury during their menstrual cycle. Given the private and personal nature of this information, research has not permeated the athletic community.

"Our ligament tissue changes based on the influence of hormones," Dr. Luks explains. "The best example of this is a woman's pelvis expands significantly due to the influence of hormones, but pelvis ligaments are not the only ones to change during the various cycles that occur."

Even with all the above, an individual's sex is not the only contributing factor in the ACL tears that occur with greater frequency in women's sports. Playing multiple sports, especially at a young age, can help.

"We've seen an increase in ACL tears due to single-sports participation," says Dr. Luks, explaining that repeated pressure in the exact same manner without variation over time can increase the risk of injury.

"The same stress on the same limbs in the same joints on the same ligaments month after month without any rest has an impact."

ACL injury prevention in women's sports
In recent years, women's soccer and other women's sports have sought to acknowledge the differences in injury risk, and to take steps to try and develop methods of prevention to counter the potential causes.

FIFA 11+ program

While there's no silver bullet when it comes to injury prevention, there's one program that stands out from the rest. The FIFA 11+ program was cited by multiple interview subjects for this report, and often without any prompting.

The FIFA 11+ program focuses on forcing athletes to build muscle memory for one key part of athletics, particularly soccer, that athletes often overlook: landing. The program is designed to be implemented as a short 10-minute warm-up performed before training and/or matches to positively reinforce proper landing techniques.

"They look at the way women jump and land on a surface, and what happens in their knees and ankles," says Brian Maddox, head athletic trainer for NWSL club North Carolina Courage. "They find that [women] move with more motion in their knees and hips when they land."

Dr. Luks, a proponent of the FIFA 11+ program, pointed to a superstar of the men's game for inspiration. "Watch Ronaldo when he lands on a header in the box. He lands on a flexed knee, the leg is as straight as possible, and when he lands he cushions the blow by going into a single-legged or a double-legged squat. These are all techniques that are taught [in the program] to diminish ACL ruptures.

"It's drilled into their heads," Dr. Luks explains. The idea being that such a simple action becomes healthy muscle memory. "Let's say you break your ankle, I put you in a cast, I take the cast off — your muscles are all atrophied. Half of that weakness is loss of muscle strength, but the other half of it is the lack of neuromuscular connections — your brain is no longer connected to those muscle fibers."

Dr. Luks' hypothetical metaphor is meant to show that building neuromuscular connections can create what we know as "muscle memory."

Wake Forest women's soccer senior defender Lyndon Wood, who serves as president of the school's Student Athlete Advisory Committee and is conducting her own research on ACL injuries in women's sports, said she brought the FIFA 11+ program to the Demon Deacons. It was quickly given approval by longtime head coach Tony da Luz.

"I felt like something needed to be done; anything we can do to keep one more girl on the field longer we should do," she said. "I brought it to [Wake Forest Sports Medicine program director] Dr. [John] Hubbard and Tony, and they were like 'Yeah, let's do it.'"

U.S. Soccer medical staff confirmed to The Sporting News that FIFA 11+ and other similar models are employed in training programs at all national team levels, although they would not dive into specifics of the programs at the different levels.

The FIFA 11+ program, however, still has yet to catch on everywhere. When Dr. Luks, whose three kids all play youth soccer, brought the FIFA 11+ program to the directors of their youth soccer programs and volunteered his time, they didn't jump at the opportunity.

"We went out to the schools assuming they would love it…no. Nobody wanted it. I can't explain it, and I was never given a good reason."

Special training regimens
The topic of a woman's menstrual cycle and how it affects injury risk in athletics is a sensitive one, and as a result, action has been slow in taking shape.

An assistant coach at a NCAA Division I women's lacrosse program in a Power 5 conference confirmed to the Sporting News that their program has just this season begun to track their athletes' cycles with the backing and participation from the players themselves.

With this information, women experiencing their menstrual cycle conduct separate, lower intensity training to minimize the risk of injury. It's not yet a practice that's widely adopted, and the same coach indicated that the women's soccer team at his school has yet to implement this same practice.

That's not surprising, says Maddox, the head trainer with the NWSL's Courage. "To my knowledge, it is not widely done in the U.S. because it can be a sensitive subject for some." Maddox says that he is aware of one top European club that does track their athletes' cycles, although he's not sure if they have yet to offer separate training based on the information.

It was widely covered following their 2019 Women's World Cup victory that U.S. women's national team players tracked their menstrual cycle throughout the four years leading into the tournament, and national team players publicly stated that there were several off-field programs implemented to complement this with regards to sleep and mental health. However, U.S. Soccer did not confirm whether these methods currently impact training intensity and injury prevention practices.

This may be the next step in the evolution of injury prevention in women's soccer if the USWNT's experience and that of other college programs yields positive results.

An assistant coach at another NCAA Division 1 women's lacrosse program confirmed to the Sporting News that their program suffered five ACL tears in the past year, and all five women were on their period at the time they were injured.

Mental health and injuries
In recent years mental health has gained increased attention throughout the athletics community, and its importance in injury prevention and recovery is being recognized as part of that push.

"Taking care of the athlete holistically…mentally and nutritionally, those resources are available to athletes these days when maybe they weren't as dialed in 15 or 20 years ago," says Maddox, who has prior athletic training experience in the NHL and minor league baseball.

"You can't disregard the mental aspect of it, this day and age every professional team across sports has those resources available to the athletes because it's useful."

When asked what she's learned through the recovery process, USWNT defender Tierna Davidson told The Sporting News, "Just to be patient with myself. It feels cheesy and simple, but I think as athletes we are impatient because we want results and we want to be 100 percent as quick as possible.

"But I think that through this process I have learned how to celebrate where I'm at in each stage, and not getting down on the fact that I suck at heading at the moment or I'm not as fast at the moment, or whatever it is."

A long way still to go
While more information is being gathered, some programs across the globe have been slow to implement change due to social and societal boundaries that are still difficult to breach.

"[ACL injury research] became a really hot topic in the late '90s and early 2000s," says Maddox. "That's when a lot of the research was conducted, specifically with regards to why women tear their ACLs more than men."

Maddox explains that strength training is a key part of injury prevention, but that the culture around women's sports doesn't lend itself to nearly the amount of strength training that is prevalent in men's sports.

"The way women are training from the youth on up…the emphasis in men's sports and boys sports is that you're not an athlete unless you lift weights. That culture is slowly hitting women's athletics, but it's behind the men."

When asked what they've learned in recent years regarding ACL tear prevention, the U.S. Soccer Federation didn't share any specific details or data points, except to confirm that it's top of mind with their programs.

"U.S. Soccer continuously builds loading programs for players. We work diligently with their clubs and/or universities in monitoring the players and develop individualized plans based on multiple factors in building out ACL prevention, but also soft tissue injuries as well. This has been a long-standing pillar for U.S. Soccer’s care of its players."

Why have so many women's soccer stars torn their ACLs?
The ability to pinpoint specific causes of injuries is ultimately an inexact science. When it comes to the human body, there are so many factors and variables that can affect an athlete's propensity or resistance to injury.

U.S. women's national team star Alex Morgan, who tore her ACL way back in high school, told The Sporting News during a USWNT press conference in the fall of 2022 that she thinks it's possible a shortened preseason and extended competition at the domestic level in the United States could be to blame for injuries in her part of the world.

"We look at the [NWSL] Challenge Cup, it was a great preseason tournament to have," Morgan said in early September in reference to the kickoff tournament of the U.S. women's professional season. "But having that bonus set for players to win, having it be a little more competitive than I think players were really ready for, having players playing 90 minutes week-in and week-out…is that the best for players in the first five weeks of the preseason? Probably not."

Dr. Luks says a quick ramp-up to competitive matches early in the season potentially increases the risk for injury. He explained how a proper and full preseason is critically important to avoiding injury during the year. Essentially, nerves that direct muscle movements connect to those muscles via "motor end plates" which degrade over time. Preseason, which features a slow increase in repetitive activity, is required to rebuild those connections.

"If you don't have connections to all the muscle fibers, I don't care how many weights you put on the rack, it's irrelevant, you're only exercising a third of the muscle fibers, because the other two-thirds don't have a connection to your brain, so they're not firing," Dr. Luks explains. "So that's such a critical component of a preseason program."

The Chicago Red Stars' Davidson, who suffered her ACL tear in preseason training in March 2022 before the Challenge Cup, was less convinced there was a common link in the rash of injuries that afflicted the stars of the women's game in 2022, but she acknowledged that an accumulation of minutes could potentially be responsible for her injury.

"I definitely think you can point to the volume and load that a lot of international players take through their club and country, so I'm sure that a bit of fatigue has to do with it. Sometimes it could just be coincidence, I don't know everybody else's schedule, but I do think there could have been some overuse of players."

A look at the numbers does support Davidson's suspicions. From January to November of 2021, the 24-year-old played 3,224 minutes across both club and international duty, including 1,780 minutes after the start of August. Add in three February 2022 national team appearances in the SheBelieves Cup, and with the short preseason ramp-up, she suffered her tear in March.

Many of the top international players injured this spring had similarly heavy loads. The chart below illustrate the range of matches and minutes played by some of the stars who suffered the ACL injuries (statistics via FBref.com).

Work load for soccer stars prior to ACL injury
(Note: Players listed below in alphabetical order.)

Player Date Range Games Minutes
Tierna Davidson Jan 22, 2021 — Nov 30, 2021 41 3,224
Giulia Gwynn Aug 29, 2021 — Oct 2, 2022 43 3,305
Marie-Antoinette Katoto Aug 5, 2020 — Jun 25, 2022 66 5,145
Catarina Macario Jul 1, 2021 — Jun 1, 2022 45 3,021
Dzsenifer Marozsan Jan 15, 2021 — Apr 12, 2022 70 4,893
Christen Press Oct 4, 2020 — Jun 11, 2022 36 2,686
Alexia Putellas Sep 19, 2020 — Jun 25, 2022 36 2,846
The table above shows 30-year-old Marozsan played close to 5,000 minutes across a 15-month period. So did 24-year-old Katoto, who logged 5,145 minutes over two years. Christen Press's numbers don't quite jump off the page, but what stands out is that she had little activity between mid-July 2021 before the Challenge Cup in March 2022.

The schedule congestion is not unique to these players specifically, but many top players across the globe are juggling busy club and international schedules that are increasing in load as the women's game explodes in popularity.

Alex Morgan, who's been a professional since 2011, ultimately labeled the rash of star knee injuries in 2022 an "unlucky run." But what is clear is that there are more variables that impact a women's soccer player's injury chances than in the case of a male player. And there's more research and information sharing that still can be done to investigate each of those factors.

Was it an unlucky run? We'll find out soon enough in the lead-up to the expanded Women's World Cup with 32 teams in July 2023. Given the names forced to sit out due to injury in the summer of 2022, a similar rash of injuries would not go unnoticed ahead of the biggest tournament in the sport.

Though they be but little, they are fierce.

Airborne particles smaller than 50 nanometers across can intensify storms, particularly over relatively pristine regions such as the Amazon rainforest or the oceans, new research suggests. In a simulation, a plume of these tiny particles increased a storm’s intensity by as much as 50 percent.

Called ultrafine aerosols, the particles are found in everything from auto emissions to wildfire smoke to printer toner. These aerosols were thought to be too small to affect cloud formation. But the new work suggests they can play a role in the water cycle of the Amazon Basin — which, in turn, has a profound effect on the planet’s hydrologic cycle, researchers report in the Jan. 26 Science.
“I have studied aerosol interactions with storms for a decade,” says Jiwen Fan, an atmospheric scientist at the Pacific Northwest National Laboratory in Richland, Wash., who led the new study. “This is the first time I’ve seen such a huge impact” from these minute aerosols.

Larger aerosol particles greater than 100 nanometers, such as soot or black carbon, are known to help seed clouds. Water vapor in the atmosphere condenses onto these particles, called cloud condensation nuclei, and forms tiny droplets. But water vapor doesn’t condense easily around the tinier particles. For that to be possible, the air must contain even more water vapor than is usually required to form clouds, reaching a very high state of supersaturation.

Such a state is rare — larger aerosols are usually also present to form water droplets, removing that extra water from the atmosphere, Fan says. But in humid places with relatively low background air pollution levels, such as over the Amazon, supersaturation is common, she says.
From 2014 to 2015, Brazilian and U.S. research agencies collaborated on a field experiment to collect data on weather and pollution conditions in the Amazon Basin. As part of the experiment, several observation sites tracked plumes of air pollution traveling from the city of Manaus out across the rainforest. During the warm, wet season, there is little difference day to day in most meteorological conditions over the rainforest, such as temperature, humidity and wind direction, Fan says. So a passing pollution plume represents a distinct, detectable perturbation to the system.

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The international team examined vertical wind motion, or updrafts, and aerosol concentration data from one of these stations from March to May 2014. When a large plume of aerosols with an abundance of ultrafine particles passed by an observation station, the researchers observed a corresponding, more powerful vertical wind motion and heavier rain. Such updrafts intensify storms, helping to drive stronger circulation.

Next, the researchers conducted simulations of an actual storm that occurred on March 17, 2014, matching its temperature, wind and water vapor conditions, as well as a low level of background aerosols in the atmosphere. Then, the team introduced several pollution scenarios to interact with the storm, including no plume and a typical plume from the Manaus metropolis. The results suggested that the ultrafine aerosol particles, in particular, were not only acting as cloud condensation nuclei over the Amazon Basin, but also that the water droplets the aerosols created significantly strengthened the gathering storm.

If the conditions are right, the sheer abundance of the ultrafine particles in such a plume would rapidly create a very large number of cloud droplets. The formation of those droplets would also suddenly release a lot of latent heat — released from a substance as it changes from a vapor to a liquid — into the atmosphere. The heat would rise, creating updrafts and quickly strengthening the storm.

Aside from the Amazon, Fan notes that such pristine, humid conditions can also exist over large swaths of the oceans. One recent study in Geophysical Research Letters that she points to found a link between well-traveled shipping lanes, which would contain abundant exhaust including ultrafine aerosols, and an increase in lightning strikes. “This mechanism may have been at play there,” she says.

Atmospheric scientist Joel Thornton of the University of Washington in Seattle, who led the study on the shipping exhaust, says it’s possible that ultrafine particles play a role in that scenario. “What this paper does is raise the stakes in needing to develop a deeper, more accurate understanding of the sources and fates of atmospheric ultrafine particles,” Thornton says.

Meteorologist Johannes Quaas of the University of Leipzig in Germany, who was not involved in either study, agrees. “It’s a very interesting hypothesis.”

But the observations described in the new study don’t definitively demonstrate that ultrafine aerosols alone drive updrafts, Quaas adds. The weather conditions may appear highly consistent from day to day, but such systems are still highly chaotic. Everything from wind to temperature to how the land surface interacts with incoming solar radiation may be variable, he notes. “In reality, it’s not just the aerosols that change.”

California’s crops are creating some noxious air.

The Golden State is at the vanguard in the United States in reducing auto emissions of nitrogen oxide gases, which help produce toxic smog and acid rain. But the NOx pollution problem isn’t limited to auto exhaust. California’s vast agricultural lands — particularly soils heavily treated with nitrogen fertilizers — are now responsible for as much as 51 percent of total NOx emissions across the state, researchers report January 31 in Science Advances.
The catchall term “NOx gases” generally refers to two pollution-promoting gases: nitric oxide, or NO, and nitrogen dioxide, or NO2. Those gases react with incoming sunlight to produce ozone in the troposphere, the lowest layer of the atmosphere. At high levels, tropospheric ozone can cause respiratory problems from asthma to emphysema.

Between 2005 and 2008, regulations issued by the California Air Resources Board on transportation exhaust reduced NOx levels in cities such as Los Angeles, San Francisco and Sacramento by 9 percent per year. However, the U.S. Environmental Protection Agency has increasingly recognized nitrogen fertilizer use as a significant source of NOx gases to the atmosphere.

NOx gases are produced in oxygen-poor soils when microbes break apart nitrogen compounds in the fertilizer, a process called denitrification. The release of those gases from fertilized soils increases at high temperatures due to increased microbial activity, says Darrel Jenerette, an ecologist at the University of California, Riverside, who was not involved in the new study.

Jenerette and others have studied local NOx emissions from soils in California, but no statewide assessment existed. So Maya Almaraz, an ecologist at the University of California, Davis, and her colleagues designed a study to examine the question — both from above and below.
Using a plane equipped with scientific instruments including a chemiluminescence analyzer to detect NOx gases in the atmosphere, the researchers measured the concentrations of the gases above the San Joaquin Valley, an area of California’s fertile Central Valley, over six days at the end of July and beginning of August. The team also simulated NOx emissions from soils across the state, using the San Joaquin Valley data to ensure that the simulations gave accurate results. Finally, the researchers compared those data with nitrogen fertilizer inputs, as estimated by crop type and U.S. Department of Agriculture fertilizer consumption data.

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Croplands are contributing 20 to 51 percent of the total NOx in California’s air, Almaraz’s team reports. In the simulations, those soil emissions were particularly sensitive to two factors: climate, especially temperature, and rates of nitrogen input. That findings suggests that regions with greater inputs of nitrogen fertilizer will also see greater soil emissions — and that the emission of NOx gases from the soils will also increase as temperatures rise in the region due to climate change.

Although food demands — and the need for fertilizer for crops — are likely to increase in the future, there are numerous possible ways to limit unwanted nitrogen fertilizer spillover, the researchers note. For example, farmers can use more efficient fertilization strategies such as adjusting how much fertilizer is used depending on specific growing stages, or planting what are called cover crops along with the target crops that enrich soils and consume the excess nitrogen.

Almaraz’s team has produced an important finding, Jenerette says. “The combination of bottom-up soil emission measurements and top-down airborne measurements provide strong evidence for their emission assessments,” he says. The finding that NOx emission rates will increase with warming temperatures also highlights the urgency of taking steps to better manage nitrogen fertilizer use in a warming world, he says.

Female polar bears prowling springtime sea ice have extreme weight swings, some losing more than 10 percent of their body mass in just over a week. And the beginnings of bear video blogging help explain why.

An ambitious study of polar bears (Ursus maritimus) in Alaska has found that their overall metabolic rate is 1.6 times greater than thought, says wildlife biologist Anthony Pagano of the U.S. Geological Survey in Anchorage. With bodies that burn energy fast, polar bears need to eat a blubbery adult ringed seal (or 19 newborn seals) every 10 to 12 days just to maintain weight, Pagano and his colleagues report in the Feb. 2 Science. Camera-collar vlogs, a bear’s-eye view of the carnivores’ diet and lifestyle secrets, show just how well individual bears are doing.
The study puts the firmest numbers yet on basic needs of polar bears, whose lives are tied to the annual spread and shrinkage of Arctic sea ice, Pagano says. As the climate has warmed, the annual ice minimum has grown skimpier by some 14 percent per decade (SN Online: 9/19/16), raising worries about polar bear populations. These bears hunt the fat-rich seals that feed and breed around ice, and as seal habitat shrinks, so do the bears’ prospects.
Pagano and colleagues used helicopters to search for polar bears on ice about off the Alaska coast in the Beaufort Sea. It’s “a lot of grueling hours looking out the window watching tracks and looking at whiteness,” he says.
After tracking down female bears without cubs, the researchers fitted the animals with a camera collar. A full day’s doings of bears on the sea ice have been mostly a matter of speculation, Pagano says. Collar videos showed that 90 percent of seal hunts are ambushes, often by a bear lurking near a hole in the ice until a seal bursts up for a gulp of air. Videos also caught early glimpses of the breeding season and what passes for courtship among polar bears. Males, Pagano says, “pretty much harass the female until she’ll submit.”

The researchers also injected each bear with a dose of water with extra neutrons in both the hydrogen and oxygen atoms. Eight to 11 days later, the team caught the same bear to check what was left of the altered atoms. Lower traces of the special form of oxygen indicated that the bear’s body chemistry had been very active, and that the bear had exhaled lots of carbon dioxide. (The unusual form of hydrogen let scientists correct results for oxygen atoms lost in H2O, for instance when the bear urinated.)

Using CO₂ data from nine females, Pagano and his colleagues calculated the field metabolic rates for polar bears going about their springtime lives. The team found that female bears need to eat a bit more than 12,000 kilocalories (or what human dieters call calories) a day just to stay even. That estimate adds some 4,600 kilocalories a day to the old estimate. But merely maintaining weight isn’t enough for a polar lifestyle. To survive lean times, polar bears typically pack on extra weight in spring.

To get a broader view of the bears’ energy needs, similar metabolic measurements for other seasons would be useful, says physiological ecologist John Whiteman of the University of New Mexico in Albuquerque. That could help resolve whether and how much bear metabolism drops when there’s little food, a response that might protect bears during hard times. Using temperature loggers to estimate metabolic rates, he has seen only a gradual decline in metabolic rates in summer as food gets tougher to find. Winter metabolic rates remain a mystery.

Hunting success and bear activity are only part of the picture of polar bear health, says ecotoxicologist Sabrina Tartu, of the Norwegian Polar Institute, which is based in Tromsø. Tartu coauthored a 2017 paper showing that toxic pollutants such as polychlorinated biphenyls, or PCBs, can build up in bear fat. Such “pollutants could, by direct or indirect pathways, disrupt metabolic rates,” she says. So changing the climate is far from the only way humankind could affect polar bear energy and hunting dynamics.

Like sailors and spelunkers, physicists know the power of a sturdy knot.

Some physicists have tied their hopes for a new generation of data storage to minuscule knotlike structures called skyrmions, which can form in magnetic materials. Incredibly tiny and tough to undo, magnetic skyrmions could help feed humankind’s hunger for ever-smaller electronics.

On traditional hard drives, the magnetic regions that store data are about 10 times as large as the smallest skyrmions. Ranging from a nanometer to hundreds of nanometers in diameter, skyrmions “are probably the smallest magnetic systems … that can be imagined or that can be realized in nature,” says physicist Vincent Cros of Unité Mixte de Physique CNRS/Thales in Palaiseau, France.
What’s more, skyrmions can easily move through a material, pushed along by an electric current. The magnetic knots’ nimble nature suggests that skyrmions storing data in a computer could be shuttled to a sensor that would read off the information as the skyrmions pass by. In contrast, traditional hard drives read and write data by moving a mechanical arm to the appropriate region on a spinning platter (SN: 10/19/13, p. 28). Those moving parts tend to be fragile, and the task slows down data recall. Scientists hope that skyrmions could one day make for more durable, faster, tinier gadgets.

One thing, however, has held skyrmions back: Until recently, they could be created and controlled only in the frigid cold. When solid-state physicist Christian Pfleiderer and colleagues first reported the detection of magnetic skyrmions, in Science in 2009, the knots were impractical to work with, requiring very low temperatures of about 30 kelvins (–243° Celsius). Those are “conditions where you’d say, ‘This is of no use for anybody,’ ” says Pfleiderer of the Technical University of Munich.

Skyrmions have finally come out of the cold, though they are finicky and difficult to control. Now, scientists are on the cusp of working out the kinks to create thawed-out skyrmions with all the desired characteristics. At the same time, researchers are chasing after new kinds of skyrmions, which may be an even better fit for data storage. The skyrmion field, Pfleiderer says, has “started to develop its own life.”
In a magnetic material, such as iron, each atom acts like a tiny bar magnet with its own north and south poles. This magnetization arises from spin, a quantum property of the atom’s electrons. In a ferromagnet, a standard magnet like the one holding up the grocery list on your refrigerator, the atoms’ magnetic poles point in the same direction (SN Online: 5/14/12).

Skyrmions, which dwell within such magnetic habitats, are composed of groups of atoms with their magnetic poles oriented in whorls. Those spirals of magnetization disrupt the otherwise orderly alignment of atoms in the magnet, like a cowlick in freshly combed hair. Within a skyrmion, the direction of the atoms’ poles twists until the magnetization in the center points in the opposite direction of the magnetization outside. That twisting is difficult to undo, like a strong knot (SN Online: 10/31/08). So skyrmions won’t spontaneously disappear — a plus for long-term data storage.

Using knots of various kinds to store information has a long history. Ancient Incas used khipu, a system of knotted cord, to keep records or send messages (SN Online: 5/8/17). In a more modern example, Pfleiderer says, “if you don’t want to forget something then you put a knot in your handkerchief.” Skyrmions could continue that tradition.
On the right track
Skyrmions are a type of “quasiparticle,” a disturbance within a material that behaves like a single particle, despite being a collective of many individual particles. Although skyrmions are made up of atoms, which remain stationary within the material, skyrmions can move around like a true particle, by sliding from one group of atoms to another. “The magnetism just twists around, and thus the skyrmion travels,” says condensed matter physicist Kirsten von Bergmann of the University of Hamburg.

In fact, skyrmions were first proposed in the context of particles. British physicist Tony Skyrme, who lends his name to the knots, suggested about 60 years ago that particles such as neutrons and protons could be thought of as a kind of knot. In the late 1980s, physicists realized the math that supported Skyrme’s idea could also represent knots in the magnetization of solid materials.

Such skyrmions could be used in futuristic data storage schemes, researchers later proposed. A chain of skyrmions could encode bits within a computer, with the presence of a skyrmion representing 1 and the absence representing 0.

In particular, skyrmions might be ideal for what are known as “racetrack” memories, Cros and colleagues proposed in Nature Nanotechnology in 2013. In racetrack devices, information-holding skyrmions would speed along a magnetic nanoribbon, like cars on the Indianapolis Motor Speedway.

Solid-state physicist Stuart Parkin proposed a first version of the racetrack concept years earlier. In a 2008 paper in Science, Parkin and colleagues demonstrated the beginnings of a racetrack memory based not on skyrmions, but on magnetic features called domain walls, which separate regions with different directions of magnetization in a material. Those domain walls could be pushed along the track using electric currents to a sensor that would read out the data encoded within. To maximize the available space, the racetrack could loop straight up and back down (like a wild Mario Kart ride), allowing for 3-D memory that could pack in more data than a flat chip.
“When I first proposed [racetrack memories] many years ago, I think people were very skeptical,” says Parkin, now at the Max Planck Institute of Microstructure Physics in Halle, Germany. Today, the idea — with and without skyrmions — has caught on. Racetrack memories are being tested in laboratories, though the technology is not yet available in computers.

To make such a system work with skyrmions, scientists need to make the knots easier to wrangle at room temperature. For skyrmion-based racetrack memories to compete with current technologies, skyrmions must be small and move quickly and easily through a material. And they should be easy to create and destroy, using something simple like an electric current. Those are lofty demands: A step forward on one requirement sometimes leads to a step backward on the others. But scientists are drawing closer to reining in the magnetic marvels.

Heating up
Those first magnetic skyrmions found by Pfleiderer and colleagues appeared spontaneously in crystals with asymmetric structures that induce a twist between neighboring atoms. Only certain materials have that skyrmion-friendly asymmetric structure, limiting the possibilities for studying the quasiparticles or coaxing them to form under warmer conditions.

Soon, physicists developed a way to artificially create an asymmetric structure by depositing material in thin layers. Interactions between atoms in different layers can induce a twist in the atoms’ orientations. “Now, we can suddenly use ordinary magnetic materials, combine them in a clever way with other materials, and make them work at room temperature,” says materials scientist Axel Hoffmann of Argonne National Laboratory in Illinois.

Scientists produced such thin film skyrmions for the first time in a one-atom-thick layer of iron on top of iridium, but temperatures were still very low. Reported in Nature Physics in 2011, those thin film skyrmions required a chilly 11 kelvins (–262° C). That’s because the thin film of iron loses its magnetic properties above a certain temperature, says von Bergmann, who coauthored the study, along with nanoscientist Roland Wiesendanger of the University of Hamburg and colleagues. But thicker films can stay magnetic at higher temperatures. And so, “one important step was to increase the amount of magnetic material,” von Bergmann says.

To go thicker, scientists began stacking sheets of various magnetic and nonmagnetic materials, like a club sandwich with repeating layers of meat, cheese and bread. Stacking multiple layers of iridium, platinum and cobalt, Cros and colleagues created the first room-temperature skyrmions smaller than 100 nanometers, the researchers reported in May 2016 in Nature Nanotechnology.

By adjusting the types of materials, the number of layers and their thicknesses, scientists can fashion designer skyrmions with desirable properties. When condensed matter physicist Christos Panagopoulos of Nanyang Technological University in Singapore and colleagues fiddled with the composition of layers of iridium, iron, cobalt and platinum, a variety of skyrmions swirled into existence. The resulting knots came in different sizes, and some were more stable than others, the researchers reported in Nature Materials in September 2017.

Although scientists now know how to make room-temperature skyrmions, the heat-tolerant swirls, tens to hundreds of nanometers in diameter, tend to be too big to be very useful. “If we want to compete with current state-of-the-art technology, we have to go for skyrmionic objects [that] are much smaller in size than 100 nanometers,” Wiesendanger says. The aim is to bring warmed-up skyrmions down to a few nanometers.
As some try to shrink room-temp skyrmions down, others are bringing them up to speed, to make for fast reading and writing of data. In a study reported in Nature Materials in 2016, skyrmions at room temperature reached top speeds of 100 meters per second (about 220 miles per hour). Fittingly, that’s right around the fastest speed NASCAR drivers achieve. The result showed that a skyrmion racetrack might actually work, says study coauthor Mathias Kläui, a condensed matter physicist at Johannes Gutenberg University Mainz in Germany. “Fundamentally, it’s feasible at room temperature.” But to compete against domain walls, which can reach speeds of over 700 m/s, skyrmions still need to hit the gas.

Despite progress, there are a few more challenges to work out. One possible issue: A skyrmion’s swirling pattern makes it behave like a rotating object. “When you have a rotating object moving, it may not want to move in a straight line,” Hoffmann says. “If you’re a bad golf player, you know this.” Skyrmions don’t move in the same direction as an electric current, but at an angle to it. On the racetrack, skyrmions might hit a wall instead of staying in their lanes. Now, researchers are seeking new kinds of skyrmions that stay on track.

A new twist
Just as there’s more than one way to tie a knot, there are several different types of skyrmions, formed with various shapes of magnetic twists. The two best known types are Bloch and Néel. Bloch skyrmions are found in the thick, asymmetric crystals in which skyrmions were first detected, and Néel skyrmions tend to show up in thin films.

“The type of skyrmions you get is related to the crystal structure of the materials,” says physical chemist Claudia Felser of the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany. Felser studies Heusler compounds, materials that have unusual properties particularly useful for manipulating magnetism. Felser, Parkin and colleagues detected a new kind of skyrmion, an antiskyrmion, in a thin layer of such a material. They reported the find in August 2017 in Nature.

Antiskyrmions might avoid some of the pitfalls that their relatives face, Parkin says. “Potentially, they can move in straight lines with currents, rather than moving to the side.” Such straight-shooting skyrmions may be better suited for racetrack schemes. And the observed antiskyrmions are stable at a wide range of temperatures, including room temperature. Antiskyrmions also might be able to shrink down smaller than other kinds of skyrmions.

Physicists are now on the hunt for skyrmions within a different realm: antiferromagnetic materials. Unlike in ferromagnetic materials — in which atoms all align their poles — in antiferromagnets, atoms’ poles point in alternating directions. If one atom points up, its neighbor points down. Like antiskyrmions, antiferromagnetic skyrmions wouldn’t zip off at an angle to an electric current, so they should be easier to control. Antiferromagnetic skyrmions might also move faster, Kläui says.

Materials scientists still need to find an antiferromagnetic material with the necessary properties to form skyrmions, Kläui says. “I would expect that this would be realized in the next couple of years.”

Finding the knots’ niche
Once skyrmions behave as desired, creating a racetrack memory with them is an obvious next step. “It is a technology that combines the best of multiple worlds,” Kläui says — stability, easily accessible data and low energy requirements. But Kläui and others acknowledge the hurdles ahead for skyrmion racetrack memories. It will be difficult, these researchers say, to beat traditional magnetic hard drives — not to mention the flash memories available in newer computers — on storage density, speed and cost simultaneously.

“The racetrack idea, I’m skeptical about,” Hoffmann says. Instead, skyrmions might be useful in devices meant for performing calculations. Because only a small electric current is required to move skyrmions around, such devices might be used to create energy-efficient computer processors.

Another idea is to use skyrmions for biologically inspired computers, which attempt to mimic the human brain (SN: 9/6/14, p. 10). Brains consume about as much power as a lightbulb, yet can perform calculations that computers still can’t match, thanks to large interconnected networks of nerve cells. Skyrmions could help scientists achieve this kind of computation in the lab, without sapping much power.
A single skyrmion could behave like a nerve cell , or neuron, electrical engineer Sai Li of Beihang University in Beijing and colleagues suggest. In the human body, a neuron can add up signals from its neighbors, gradually building up a voltage across its membrane. When that voltage reaches a certain threshold, ions begin shifting across the membrane in waves, generating an electric pulse. Skyrmions could imitate this behavior: An electric current would push a skyrmion along a track, with the distance traveled acting as an analog for the neuron’s increasing voltage. A skyrmion reaching a detector at the end would be equivalent to a firing neuron, the researchers proposed in July 2017 in Nanotechnology .
By combining a large number of neuron-imitating skyrmions, the thinking goes, scientists could create a computer that operates something like a brain.

Additional ideas for how to use the magnetic whirls keep cropping up. “It’s still a growing field,” von Bergmann says. “There are several new ideas ahead.”

Whether or not skyrmions end up in future gadgets, the swirls are part of a burgeoning electronics ecosystem. Ever since electricity was discovered, researchers have focused on the motion of electric charges. But physicists are now fashioning a new parallel system called spintronics — of which skyrmions are a part — based on the motion of electron spin, that property that makes atoms magnetic (SN Online: 9/26/17). By studying skyrmions, researchers are expanding their understanding of how spins move through materials.

Like a kindergartner fumbling with shoelaces, studying how to tie spins up in knots is a learning process.

Dying, it turns out, is not like flipping a switch. Genes keep working for a while after a person dies, and scientists have used that activity in the lab to pinpoint time of death to within about nine minutes.

During the first 24 hours after death, genetic changes kick in across various human tissues, creating patterns of activity that can be used to roughly predict when someone died, researchers report February 13 in Nature Communications.
“This is really cool, just from a biological discovery standpoint,” says microbial ecologist Jennifer DeBruyn of the University of Tennessee in Knoxville who was not part of the study. “What do our cells do after we die, and what actually is death?”

What has become clear is that death isn’t the immediate end for genes. Some mouse and zebrafish genes remain active for up to four days after the animals die, scientists reported in 2017 in Open Biology.
In the new work, researchers examined changes in DNA’s chemical cousin, RNA. “There’s been a dogma that RNA is a weak, unstable molecule,” says Tom Gilbert, a geneticist at the Natural History Museum of Denmark in Copenhagen who has studied postmortem genetics. “So people always assumed that DNA might survive after death, but RNA would be gone.”
But recent research has found that RNA can be surprisingly stable, and some genes in our DNA even continue to be transcribed, or written, into RNA after we die, Gilbert says. “It’s not like you need a brain for gene expression,” he says. Molecular processes can continue until the necessary enzymes and chemical components run out.

“It’s no different than if you’re cooking a pasta and it’s boiling — if you turn the cooker off, it’s still going to bubble away, just at a slower and slower rate,” he says.

No one knows exactly how long a human’s molecular pot might keep bubbling, but geneticist and study leader Roderic Guigó of the Centre for Genomic Regulation in Barcelona says his team’s work may help toward figuring that out. “I think it’s an interesting question,” he says. “When does everything stop?”

Tissues from the dead are frequently used in genetic research, and Guigó and his colleagues had initially set out to learn how genetic activity, or gene expression, compares in dead and living tissues.

The researchers analyzed gene activity and degradation in 36 different kinds of human tissue, such as the brain, skin and lungs. Tissue samples were collected from more than 500 donors who had been dead for up to 29 hours. Postmortem gene activity varied in each tissue, the scientists found, and they used a computer to search for patterns in this activity. Just four tissues, taken together, could give a reliable time of death: subcutaneous fat, lung, thyroid and skin exposed to the sun.

Based on those results, the team developed an algorithm that a medical examiner might one day use to determine time of death. Using tissues in the lab, the algorithm could estimate the time of death to within about nine minutes, performing best during the first few hours after death, DeBruyn says.

For medical examiners, real-world conditions might not allow for such accuracy.

Traditionally, medical examiners use body temperature and physical signs such as rigor mortis to determine time of death. But scientists including DeBruyn are also starting to look at timing death using changes in the microbial community during decomposition (SN Online: 7/22/15).

These approaches — tracking microbial communities and gene activity — are “definitely complementary,” DeBruyn says. In the first 24 hours after death, bacteria, unlike genes, haven’t changed much, so a person’s genetic activity may be more useful for zeroing in on how long ago he or she died during that time frame. At longer time scales, microbes may work better.

“The biggest challenge is nailing down variability,” DeBruyn says. Everything from the temperature where a body is found to the deceased’s age could potentially affect how many and which genes are active after death. So scientists will have to do more experiments to account for these factors before the new method can be widely used.

Knocking back an enzyme swept mouse brains clean of protein globs that are a sign of Alzheimer’s disease. Reducing the enzyme is known to keep these nerve-damaging plaques from forming. But the disappearance of existing plaques was unexpected, researchers report online February 14 in the Journal of Experimental Medicine.

The brains of mice engineered to develop Alzheimer’s disease were riddled with these plaques, clumps of amyloid-beta protein fragments, by the time the animals were 10 months old. But the brains of 10-month-old Alzheimer’s mice that had a severely reduced amount of an enzyme called BACE1 were essentially clear of new and old plaques.
Studies rarely demonstrate the removal of existing plaques, says neuroscientist John Cirrito of Washington University in St. Louis who was not involved in the study. “It suggests there is something special about BACE1,” he says, but exactly what that might be remains unclear.

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One theory to how Alzheimer’s develops is called the amyloid cascade hypothesis. Accumulation of globs of A-beta protein bits, the idea goes, drives the nerve cell loss and dementia seen in the disease, which an estimated 5.5 million Americans had in 2017. If the theory is right, then targeting the BACE1 enzyme, which cuts up another protein to make A-beta, may help patients.
BACE1 was discovered about 20 years ago. Initial studies turned off the gene that makes BACE1 in mice for their entire lives, and those animals produced almost no A-beta. In humans, however, any drug that combats Alzheimer’s by going after the enzyme would be given to adults. So Riqiang Yan, one of the discoverers of BACE1 and a neuroscientist at the Cleveland Clinic, and colleagues set out to learn what happens when mice who start life with normal amounts of BACE1 lose much of the enzyme later on.

The researchers studied mice engineered to develop plaques in their brains when the animals are about 10 weeks old. Some of these mice were also engineered so that levels of the BACE1 enzyme, which is mostly found in the brain, gradually tapered off over time. When these mice were 4 months old, the animals had lost about 80 percent of the enzyme.
Alzheimer’s mice with normal BACE1 levels experienced a steady increase in plaques, clearly seen in samples of their brains. In Alzheimer’s mice without BACE1, however, the clumps followed a different trajectory. The number of plaques initially grew, but by the time the mice were around 6 months old, those plaques had mostly disappeared. And by 10 months, “we hardly see any,” Yan says.

Cirrito was surprised that getting rid of BACE1 later in life didn’t just stop plaques from forming, but removed them, too. “It is possible that perhaps a therapeutic agent targeting BACE1 in humans might have a similar effect,” he says.

Drugs that target BACE1 are already in development. But the enzyme has other jobs in the brain, such as potentially affecting the ability of nerve cells to communicate properly. It may be necessary for a drug to inhibit some, but not all, of the enzyme, enough to prevent plaque formation but also preserve normal signaling between nerve cells, Yan says.

Ultrasounds during pregnancy can be lots of fun, offering peeks at the baby-to-be. But ultrasounds aren’t just a way to get Facebook fodder. They are medical procedures that involve sound waves, technology that could, in theory, affect a growing fetus.

With that concern in mind, some researchers have wondered if the rising rates of autism diagnoses could have anything to do with the increasing number of ultrasound scans that women receive during pregnancy.

The answer is no, suggests a study published online February 12 in JAMA Pediatrics. On average, children with autism were exposed to fewer ultrasounds during pregnancy, scientists found. The results should be “very reassuring” to parents, says study coauthor Jodi Abbott, a maternal fetal medicine specialist at Boston Medical Center and Boston University School of Medicine.
To back up: Autism rates have risen sharply over the last several decades (though are possibly plateauing). Against this backdrop, researchers are searching for the causes of autism — and there are probably many. Autism is known to run in families, and scientists have found some of the particular genetic hot spots that may contribute. Other factors, such as older parents and maternal obesity, can also increase the risk of autism.

Scientists suspect that in many cases, autism is caused by many factors, all working together. Could prenatal ultrasounds, which have become more routine and more powerful, be one of those factors? These scans use sound waves that penetrate mothers’ bodies, and then collect the waves that bounce back, forming a picture of fetal tissues. During this process, the waves may be able to heat up the tissue they travel through.

Work on animals has suggested that ultrasounds can in fact interfere with fetal brain development, derailing the normal movements of cells that populate the brain. Mice exposed to 30 or more minutes of ultrasound in utero had abnormal brain development, for instance. But it’s not at all clear whether a similar thing might happen in humans, and if so, whether such effects might contribute to autism.
The new study compared ultrasound exposure among three groups: 107 children diagnosed with autism spectrum disorder, 104 children diagnosed with a developmental delay, and 209 typically developing children. On average, the children with autism were exposed to 5.9 ultrasound scans over the course of pregnancy. Children with developmental delays were exposed to 6.1 scans, and typically developing children were exposed to 6.3 scans, the researchers found. (For all groups, these numbers are way above the one to two scans per low-risk pregnancy recommended by the American College of Obstetricians and Gynecologists.)

For all three groups, the duration of the scans was similar. So was the thermal index, an indication of how much warming might have happened. “In almost every parameter we looked at, ultrasound seemed perfectly safe,” says study coauthor N. Paul Rosman, a pediatric neurologist at Boston Medical Center and Boston University School of Medicine.

One measure was different, the researchers found: During the first trimester, mothers who had children with autism had slightly deeper ultrasounds than women who had typically developing children and children with developmental delays. Ultrasound depth measures the distance from the transducer paddle that emits the waves to the spot that’s being imaged. The measure “has a lot to do with the size of the mother and the distance between her skin, where the ultrasound transducer is, and where the baby is,” Abbott says.

Lots of questions remain about whether — and how — ultrasound depth, or other aspects of the technology, might affect fetuses. “The study certainly wasn’t perfect,” Rosman says. It combed back through medical records of women instead of following women from the beginning. And it didn’t control for certain traits that may influence autism, such as smoking.

The results suggest that on their own, ultrasounds don’t cause autism spectrum disorder, says Sara Jane Webb of Seattle Children’s Research Institute and the University of Washington, who cowrote a JAMA Pediatrics companion piece. “At this time, there is no evidence that ultrasound is a primary contributor to poor developmental outcomes when delivered within medical guidelines,” she says.

While there’s more science to sort out here, the news is reassuring for women who might be worried about getting scanned. Women should follow their doctors’ guidance on ultrasounds, Rosman says. “We don’t think there’s anything in this study to recommend otherwise.”

What a spectacular Easter basket tardigrade eggs would make — at least for those celebrating in miniature.

A new species of the pudgy, eight-legged, water creatures lays pale, spherical microscopic eggs studded with domes crowned in long, trailing streamers.

Eggs of many land-based tardigrades have bumps, spines, filaments and such, presumably to help attach to a surface, says species codiscoverer Kazuharu Arakawa. The combination of a relatively plain surface on the egg itself (no pores, for instance) plus a filament crown helps distinguish this water bear as a new species, now named Macrobiotus shonaicus, he and colleagues report February 28 in PLOS ONE.
With about 20 new species added each year to the existing 1,200 or so known worldwide, tardigrades have become tiny icons of extreme survival (SN Online: 7/14/17).

“I was actually not looking for a new species,” Arakawa says. He happened on it when searching through moss he plucked from the concrete parking lot at his apartment. He routinely samples such stray spots to search for tardigrades, one of his main interests as a genome biologist at Keio University’s Institute for Advanced Biosciences in Tsuruoka City, Japan.
These particular moss-loving creatures managed to grow and reproduce in the lab —“very rare for a tardigrade,” he says. He didn’t realize it was an unknown species until he started deciphering the DNA that makes up some of its genes. The sequences he found didn’t match any in a worldwide database.

His two coauthors, at Jagiellonian University in Krakow, Poland, worked out that he had found a new member of a storied cluster of relatives of the tardigrade M. hufelandi. That species, described in 1834, kept turning up across continents around the world — or so biologists thought for more than a century. Realization eventually dawned that the single species that could live in such varied places was actually a complex of close cousins.

And now M. shonaicus adds yet another cousin to a group of about 30. Who knows where the next one will turn up. “I think there are lots more to be identified,” Arakawa says.

Adult mice and other rodents sprout new nerve cells in memory-related parts of their brains. People, not so much. That’s the surprising conclusion of a series of experiments on human brains of various ages first described at a meeting in November (SN: 12/9/17, p. 10). A more complete description of the finding, published online March 7 in Nature, gives heft to the controversial result, as well as ammo to researchers looking for reasons to be skeptical of the findings.

In contrast to earlier prominent studies, Shawn Sorrells of the University of California, San Francisco and his colleagues failed to find newborn nerve cells in the memory-related hippocampi of adult brains. The team looked for these cells in nonliving brain samples in two ways: molecular markers that tag dividing cells and young nerve cells, and telltale shapes of newborn cells. Using these metrics, the researchers saw signs of newborn nerve cells in fetal brains and brains from the first year of life, but they became rarer in older children. And the brains of adults had none.

There is no surefire way to spot new nerve cells, particularly in live brains; each way comes with caveats. “These findings are certain to stir up controversy,” neuroscientist Jason Snyder of the University of British Columbia writes in an accompanying commentary in the same issue of Nature.