Doughnut-shaped structures called vortex rings are sometimes seen swirling through fluids. Smokers can form them with their mouths, volcanoes can spit them out during eruptions and dolphins can blow them as bubble rings. Now, scientists can create the rings with light.
A standard vortex is an eddy in a liquid or gas, like a whirlpool (SN: 3/5/13). Imagine taking that swirling eddy, stretching it out and bending it into a circle and attaching it end-to-end. That’s a vortex ring. These rings travel through the liquid or gas as they swirl — for example, smoke rings float through the air away from a smoker’s head. In the new vortex rings, described June 2 in Nature Photonics, light behaves similarly: The flow of energy swirls as the ring moves. Optics researcher Qiwen Zhan and colleagues started from a vortex tube, a hurricanelike structure they already knew how to create using laser light. The team used optics techniques to bend the tube into a circular shape, creating a vortex ring.
The light rings aren’t that different from smoke or bubble rings, says Zhan, of the University of Shanghai for Science and Technology. “That’s kind of cool.”
Zhan is interested in seeing whether scientists could create vortex rings out of electric current or a magnetic field. And further study of the light rings might help scientists better understand how topology — the geometry of doughnuts, knots and similar shapes — affects light and how it interacts with matter.
Turns out there is rest for the wicked: Sleepy mosquitoes are more likely to catch up on missed z’s than drink blood, a new study finds.
Most people are familiar with the aftermath of a poor night’s sleep. Insects also suffer; for instance, drowsy honeybees struggle to perform their signature waggle dance, and weary fruit flies show signs of memory loss. In the case of sleep-deprived mosquitoes, they give up valuable time for feeding in favor of sleeping overtime, researchers report June 1 in Journal of Experimental Biology. The preference for dozing over dining is surprising given that “we know that mosquitoes love blood a lot,” says Oluwaseun Ajayi, a disease ecologist at the University of Cincinnati.
Scientists have long been interested in mosquitoes’ circadian rhythms, the internal clock that determines their sleep and awake times (SN: 10/2/17). Knowing when a mosquito is awake — and biting — is important for understanding and limiting disease transmission. For instance, malaria, often transmitted by nocturnal mosquitoes, is kept under control by slinging netting around beds. But new research suggests that mosquitoes that feed during the day may also spread the disease.
It’s challenging to study sleeping bloodsuckers in the lab. That’s partly because awake mosquitoes are aroused by the presence of a meal — the experimenter. And when mosquitoes do fall asleep, they look rather similar to peers that are merely resting to conserve energy.
That’s the tricky — and often species-specific — question: “How can you tell [when] an insect is sleeping?” says Samuel Rund, a mosquito circadian biologist at the University of Notre Dame in Indiana who was not involved in the research.
One way to tell is by tracking the insect’s behavior. So Ajayi and colleagues watched mosquitoes sleep. The team focused on three species known to carry diseases, including malaria: Aedes aegypti, which are active during the day; Culex pipiens, which prefer dusk; and the nocturnal Anopheles stephensi. The mosquitoes were left alone in a room in small enclosures, where the team used cameras and infrared sensors to spy on them.
After about two hours, the mosquitoes appeared to nod off. Their abdomens lowered to the ground and their hind legs drooped, the footage showed. As time went on, C. pipiens and A. aegypti showed a reduced response when the experimenter walked in the room, suggesting a tasty smell was less likely to wake those species when in a deep sleep. Taken together, the change in posture, periods of inactivity and lower arousal were determined to identify a snoozing mosquito.
What started as a relaxing experiment for the mosquitoes quickly changed gears. The insects were placed in clear tubes that received vibration pulses every few minutes, preventing them from falling into deep sleep. After four to 12 hours of this sleep deprivation, the team mimicked the presence of a host with a pad of heated artificial sweat. In another experiment, a plucky human volunteer offered up a leg to be fed on for five minutes by sleep-deprived and well-rested A. aegypti in batches of 10 insects.
In both cases, the mosquitoes that had had a full night’s rest were much more likely to land on the host than those that had been deprived of sleep. And the leg exposed to sleepy mosquitoes fared much better than when it was exposed to the control group: In eight tests, on average 77 percent of the well-rested mosquitoes went for a blood meal, compared with only 23 percent of sleepy mosquitoes.
The findings, Rund says, open avenues for research into controlling mosquito populations and reducing disease using the insects’ circadian rhythms.
The undoing of toxic “forever chemicals” may be found in products in your pantry.
Perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS, can persist in the environment for centuries. While the health impacts of only a fraction of the thousands of different types of PFAS have been studied, research has linked exposure to high levels of some of these widespread, humanmade chemicals to health issues such as cancer and reproductive problems.
Now, a study shows that the combination of ultraviolet light and a couple of common chemicals can break down nearly all the PFAS in a concentrated solution in just hours. The process involves blasting UV radiation at a solution containing PFAS and iodide, which is often added to table salt, and sulfite, a common food preservative, researchers report in the March 15 Environmental Science & Technology. “They show that when [iodide and sulfite] are combined, the system becomes a lot more efficient,” says Garrett McKay, an environmental chemist at Texas A&M University in College Station who was not involved in the study. “It’s a big step forward.”
A PFAS molecule contains a chain of carbon atoms that are bonded to fluorine atoms. The carbon-fluorine bond is one the strongest known chemical bonds. This sticky bond makes PFAS useful for many applications, such as water- and oil-repellant coatings, firefighting foams and cosmetics (SN: 6/4/19; SN: 6/15/21). Owing to their widespread use and longevity, PFAS have been detected in soils, food and even drinking water. The U.S. Environmental Protection Agency sets healthy advisory levels for PFOA and PFOS — two common types of PFAS — at 70 parts per trillion.
Treatment facilities can filter PFAS out of water using technologies such as activated carbon filters or ion exchange resins. But these removal processes concentrate PFAS into a waste that requires a lot of energy and resources to destroy, says study coauthor Jinyong Liu, an environmental chemist at the University of California, Riverside. “If we don’t [destroy this waste], there will be secondary contamination concerns.”
One of the most well-studied ways to degrade PFAS involves mixing them into a solution with sulfite and then blasting the mixture with UV rays. The radiation rips electrons from the sulfite, which then move around, snipping the stubborn carbon-fluorine bonds and thereby breaking down the molecules.
But some PFAS, such as a type known as PFBS, have proven difficult to degrade this way. Liu and his colleagues irradiated a solution containing PFBS and sulfite for an entire day, only to find that less than half of the pollutant in the solution had broken down. Achieving higher levels of degradation required more time and additional sulfite to be poured in at spaced intervals.
The researchers knew that iodide exposed to UV radiation produces more bond-cutting electrons than sulfite. And previous research has demonstrated that UV irradiation paired with iodide alone could be used to degrade PFAS chemicals.
So Liu and his colleagues blasted UV rays at a solution containing PFBS, iodide and sulfite. To the researchers’ surprise, after 24 hours of irradiation, less than 1 percent of the stubborn PFBS remained.
What’s more, the researchers showed that the process destroyed other types of PFAS with similar efficiency and was also effective when PFAS concentrations were 10 times that which UV light and sulfite alone could degrade. And by adding iodide the researchers found that they could speed up the reaction, Liu says, making the process that much more energy efficient.
In the solution, iodide and sulfite worked together to sustain the destruction of PFAS molecules, Liu explains. When UV rays release an electron from iodide, that iodide is converted into a reactive molecule which may then recapture freed electrons. But here sulfite can step in and bond with these reactive molecules and with electron-scavenging oxygen in the solution. This sulfite “trap” helps keep the released electrons free to cut apart PFAS molecules for eight times longer than if sulfite wasn’t there, the researchers report.
It’s surprising that no one had demonstrated the effectiveness of using sulfite with iodide to degrade PFAS before, McKay says.
Liu and his colleagues are now collaborating with an engineering company, using their new process to treat PFAS in a concentrated waste stream. The pilot test will conclude in about two years.
For weeks, I have been watching coronavirus cases drop across the United States. At the same time, cases were heading skyward in many places in Europe, Asia and Oceania. Those surges may have peaked in some places and seem to be on a downward trajectory again, according to Our World in Data.
Much of the rise in cases has been attributed to the omicron variant’s more transmissible sibling BA.2 clawing its way to prominence. But many public health officials have pointed out that the surges coincide with relaxing of COVID-19 mitigation measures.
People around the world are shedding their masks and gathering in public. Immunity from vaccines and prior infections have helped limit deaths in wealthier countries, but the omicron siblings are very good at evading immune defenses, leading to breakthrough infections and reinfections. Even so, at the end of February, the U.S. Centers for Disease Control and Prevention posted new guidelines for masking, more than doubling the number of cases needed per 100,000 people before officials recommended a return to the face coverings (SN: 3/3/22).
Not everyone has ditched their masks. I have observed some regional trends. The majority of people I see at my grocery store and other places in my community in Maryland are still wearing masks. But on road trips to the Midwest and back, even during the height of the omicron surge, most of the faces I saw in public were bare. Meanwhile, I was wearing my N95 mask even when I was the only person doing so. I reasoned that I was protecting myself from infection as best I could. I was also protecting my loved ones and other people around me from me should I have unwittingly contracted the virus.
But I will tell you a secret. I don’t really like wearing masks. They can be hot and uncomfortable. They leave lines on my face. And sometimes masks make it hard to breathe. At the same time, I know that wearing a good quality, well-fitting mask greatly reduces the chance of testing positive for the coronavirus (SN: 2/12/21). In one study, N95 or KN95 masks reduced the chance of testing positive by 83 percent, researchers reported in the February 11 Morbidity and Mortality Weekly Report. And school districts with mask mandates had about a quarter of the number of in-school infections as districts where masks weren’t required (SN: 3/15/22).
With those data in mind, I am not ready to go barefaced. And I’m not alone. Nearly 36 percent of the 1,916 respondents to a Science News Twitter poll said that they still wear masks everywhere in public. Another 28 percent said they mask in indoor crowds, and 23 percent said they mask only where it’s mandatory. Only about 12 percent have ditched masks entirely.
Some poll respondents left comments clarifying their answers, but most people’s reasons for masking aren’t clear. Maybe they live in the parts of the country or world where transmission levels are high and hospitals are at risk of being overrun. Maybe they are parents of children too young for vaccination. Perhaps they or other loved ones are unvaccinated or have weakened immune systems that put them at risk for severe disease. Maybe, like me, they just don’t want to get sick — with anything.
Before the pandemic, I caught several colds a year and had to deal with seasonal allergies. Since I started wearing a mask, I haven’t had a single respiratory illness, though allergies still irritate my eyes and make my nose run. I’ve also got some health conditions that raise my risk of severe illness. I’m fully vaccinated and boosted, so I probably won’t die if I catch the virus that causes COVID-19, but I don’t want to test it (SN: 11/8/21). Right now, I just feel safer wearing a mask when I’m indoors in public places.
I’ve been thinking a lot about what would convince me that it was safe to go maskless. What is the number or metric that will mark the boundary of my comfort zone?
The CDC now recommends using its COVID-19 Community Levels map for determining when mask use is needed. That metric is mostly concerned with keeping hospitals and other health care systems from becoming overwhelmed. By that measure, most of the country has the green light to go maskless. I’m probably more cautious than the average person, but the levels of transmission in that metric that would trigger mask wearing — 200 or more cases per 100,000 population — seem high to me, particularly since CDC’s prior recommendations urged masking at a quarter of that level.
The metric is designed for communities, not individuals. So what numbers should I, as an individual, go by? There’s always the CDC’s COVID-19 Integrated County View that tracks case rates and test positivity rates — the percentage of tests that have a positive result. Cases in my county have been ticking up in the last few days, with 391 people having gotten COVID-19 in the last week — that’s about 37 out of every 100,000 people. That seems like relatively low odds of coming into contact with a contagious person. But those are only the cases we know about officially. There may be many more cases that were never reported as people take rapid antigen tests at home or decide not to test. There’s no way to know exactly how much COVID-19 is out there.
And the proportion of cases caused by BA.2 is on the rise, with the more infectious omicron variant accounting for about 35 percent of cases nationwide in the week ending March 19. In the mid-Atlantic states where I live, about 30 percent of cases are now caused by BA.2. But in some parts of the Northeast, that variant now causes more than half of cases. The increase is unsettling but doesn’t necessarily mean the United States will experience another wave of infections as Europe has. Or maybe we will. That uncertainty makes me uncomfortable removing my mask indoors in public right now.
Maybe in a few weeks, if there’s no new surge in infections, I’ll feel comfortable walking around in public with my nose and mouth exposed. Or maybe I’ll wait until the number of cases in my county is in single digits. I’m pretty sure there will come a day when I won’t feel the need to filter every breath, but for me, it’s not that time yet. And I truthfully can’t tell you what my magic number will be.
Here’s what I do know: Even if I do decide to have an unmasked summer, I will be strapping my mask back on if COVID-19 cases begin to rise again.
Some bacteria carry tiny syringes filled with chemicals that may thin out competitors or incapacitate predators. Now, researchers have gotten up-close views of these syringes, technically known as contractile injection systems, from a type of cyanobacteria and a marine bacterium.
Figuring out how key parts of the molecular syringes work may help scientists devise their own nanomachines. Artificial injection machines could direct antibiotics against troublesome bacteria while leaving friendly microbes untouched.
Genes encoding pieces of the injection machinery are found in many bacterial species. But, “just by looking at the genes, it’s quite hard to predict how these contractile injection systems work,” says Gregor Weiss, a cellular structural biologist at ETH Zurich. So Weiss and colleagues examined bacterial syringes using cryo-electron microscopy, in which cells are flash frozen to capture cellular structures as they typically look in nature (SN: 6/22/17).
Previously, researchers have found syringes anchored in some bacteria’s outer membranes, where the bacteria can shoot their payload into cells they bump into. Other species’ injectors squirt their contents into the environment.
But in a type of cyanobacteria called Anabaena, the syringes are in an unusual place, nestled in the membrane of the internal structure where the bacteria carry out photosynthesis, Weiss and colleagues report in the March Nature Microbiology. Buried inside the cells, “it’s hard to imagine how [the syringes] could get out and interact with the target organism,” Weiss says. Anabaena may use its syringes against itself to trigger programmed cell death when the cyanobacteria come under stress. In the team’s experiments, ultraviolet light or high salt levels in water triggered some syringes to dump their payload. That led to the death of some Anabaena cells in the long chains that the cyanobacteria grow in, forming hollow “ghost cells.”
Ghost cells shed their outer wall and membrane, exposing unfired syringes in the inner membrane to the outside. The ghosts may act like Trojan horses, delivering their deadly payload to predators or competitors, the team hypothesizes. The researchers haven’t yet found which organisms are the probable targets of Anabaena’s syringes.
Inside a type of marine bacteria called Algoriphagus machipongonensis, the story is a bit different. Here, the syringes have a different architecture and float unmoored within the bacterial cell, ETH Zurich’s Charles Ericson and colleagues report in the March Nature Microbiology. The injectors are also found in the liquid in which the bacteria are grown in the laboratory, but how they get out of the cell is a mystery. Perhaps they are released when the bacteria die or get eaten by a predator, Ericson says.
The team also found two proteins loaded inside the Algoriphagus’ syringes, but what those proteins do isn’t known. The researchers tried genetically engineering E. coli to produce one of the proteins, but it kills the bacteria, says study coauthor Jingwei Xu, also at ETH Zurich. Comparing the structures of syringes from various species, the researchers identified certain structures within the machines that are similar, but slightly different from species to species. Learning how those modifications change the way the injectors work may allow researchers to load different cargoes into the tubes or target the syringes against specific bacteria or other organisms. “Now we have the general blueprint,” Ericson says, “can we re-engineer it?”
You can never have too much ice cream, but you can have too much ice in your ice cream. Adding plant-based nanocrystals to the frozen treat could help solve that problem, researchers reported March 20 at the American Chemical Society spring meeting in San Diego.
Ice cream contains tiny ice crystals that grow bigger when natural temperature fluctuations in the freezer cause them to melt and recrystallize. Stabilizers in ice cream — typically guar gum or locust bean gum — help inhibit crystal growth, but don’t completely stop it. And once ice crystals hit 50 micrometers in diameter, ice cream takes on an unpleasant, coarse, grainy texture.
Cellulose nanocrystals, or CNCs, which are derived from wood pulp, have properties similar to the gums, says Tao Wu, a food scientist at the University of Tennessee in Knoxville. They also share similarities with antifreeze proteins, produced by some animals to help them survive subzero temperatures. Antifreeze proteins work by binding to the surface of ice crystals, inhibiting growth more effectively than gums — but they are also extremely expensive. CNCs might work similarly to antifreeze proteins but at a fraction of the cost, Wu and his colleagues thought.
An experiment with a sucrose solution — a simplified ice cream proxy — and CNCs showed that after 24 hours, the ice crystals completely stopped growing. A week later, the ice crystals remained at 25 micrometers, well beneath the threshold of ice crystal crunchiness. In a similar experiment with guar gum, ice crystals grew to 50 micrometers in just three days. “That by itself suggests that nanocrystals are a lot more potent than the gums,” says Richard Hartel, a food engineer at the University of Wisconsin–Madison, who was not involved in the research. If CNCs do function the same way as antifreeze proteins, they’re a promising alternative to current stabilizers, he says. But that still needs to be proven.
Until that happens, you continue to have a good excuse to eat your ice cream quickly: You wouldn’t want large ice crystals to form, after all.