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Sticky explanation

Most of us have had the experience of the food we’re cooking sticking to a non-stick frying pan, even if we’ve used oil to slick things up. What’s with that?

Apparently keen cooks, scientists at the Czech Academy of Sciences have investigated the fluid properties of oil on a flat surface, such as a frying pan. Their work, reported in the journal Physics of Fluids, shows convection may be to blame for stuck-on food.

When a pan is heated from below, a temperature gradient is established in the oil film. For common liquids, such as the sunflower oil used in the experiment, the surface tension decreases when temperature increases. A surface tension gradient is established, directed away from the pan’s centre where the temperature is higher and towards its edges.

This gradient sets up a type of convection known as thermocapillary convection, which moves oil outward. When the oil film in the middle becomes thinner than a critical value, the film ruptures.

“To avoid unwanted dry spots, the following set of measures should be applied: increasing the oil film thickness, moderate heating, completely wetting the surface of the pan with oil, using a pan with a thick bottom, or stirring food regularly during cooking,” says author Alexander Fedorchenko.

Good to know: the research may have wider application in understanding how electronic components overheat. 

Native nuisance?

Kangaroos are considered a pest on Australian farmlands – where they compete with introduced livestock for resources – but they usually aren’t seen as a problem in conservation areas. They’re native animals, after all.

But a new collaborative study led by UNSW Sydney found that conservation reserves are showing signs that intensive grazing by kangaroos is having a negative impact on the health and biodiversity of the land.

Surprisingly, the ’roos’ grazing impacts appeared to be more damaging to the land than rabbits – widely considered among the worst of species introduced to Australia.

The findings, published late last year in Global Ecology and Conservation, are based on fieldwork in four conservation reserves in semi-arid parts of Australia during the drought in 2018. 

“The kangaroos had severe impacts on soils and vegetation that were symptomatic of overgrazing,” says UNSW Sydney’s Michael Letnic, senior author of the paper. “Not only did the areas grazed by overabundant kangaroos have fewer species of plants, but the soils were depleted in nutrients and were compacted – which means that less water can be absorbed by the soil when it rains.”

Study lead author Charlotte Mills, a visiting fellow at UNSW Science, says she hopes that the work paves the way for future research into how threatened species might be affected by kangaroo overgrazing.

“There isn’t a lot of research about how kangaroos differentially affect different parts of the ecosystem,” she says. “A lot of past research has focused on rabbits.”

The study found that rabbits still had negative impacts on the land but not to the same degree as kangaroos.

“Rabbits and other introduced herbivores like goats are often considered the main contributor to overgrazing in Australia,” says Mills. “But we found kangaroos had a greater impact on the land – and on the grass in particular.”

Power hiking

Hikers and schoolkids take heart: researchers have developed a prototype backpack that not only makes loads feel about 20% lighter, but also harvests energy from human movements to power small electronics.

As reported in ACS Nano, the new bag could be especially useful for athletes, explorers and disaster rescuers who work in remote areas without electricity, the researchers say.

While they’re brilliant for hands-free load carrying, heavy backpacks can cause walkers or runners back and neck pain. Wilderness walkers (or anyone lacking access to a power source) would find useful a bag that harvests the mechanical energy of walking to small electronic devices.

A prototype backpack harvests energy from walking to power small electronics, and it makes loads feel lighter. Credit: adapted from ACS Nano 2021, DOI: 10.1021/acsnano.0c07498

Earlier energy-harvesting backpacks had relatively low power outputs and didn’t offer load lightening or shock absorption. The research team wanted to design a prototype that overcame these limitations.

The new backpack has two built-in elastomers that stretch and shrink to save effort, absorb shock and keep the bag steady when it’s in use; this yields about a 20% reduced force on the wearer. Movement between the backpack’s frame and its load during walking drives a triboelectric nanogenerator (TENG) to convert mechanical energy into electricity, with 14% efficiency.

The researchers showed that the bag could power LEDs, an electric watch and fluorescent tubes. Once its energy-conversion efficiency is improved, the backpack has promise as a power source for small-scale wearable and portable electronics, such as GPSs and health-care sensors, the researchers say.

Marmoset judgement

Captive marmosets that listened in on recorded vocal interactions between other monkeys appeared to understand what they overheard, a new study suggests.

The findings, published in Science Advances, point to the eavesdropping monkeys perceiving these vocalisations as “conversations” rather than isolated elements, and indicate that, on the whole, they prefer to interact with cooperative rather than uncooperative individuals.

Behavioural studies have increasingly offered glimpses into primates’ social lives, but they tend to lack reliable measurements of the inner workings of an animal’s mind.

To delve into the heads of snooping marmosets, Rahel Brügger and colleagues presented 21 captive-born adult marmosets with recordings of an opposite-sex adult making either food-offering calls or aggressive chatter calls in response to begging infants. As controls, the researchers also played back each call individually.

They then assessed changes in the marmosets’ nasal temperatures, which correspond with the autonomous nervous-system changes that accompany shifting emotional states. The marmosets showed different temperature changes in response to the holistic encounters than to their individual components; Brügger’s team concluded that the monkeys perceived them as conversations. 

Next, the researchers tested whether the monkeys preferred the cooperative, food-sharing individuals or the noncooperative ones by opening both testing compartment doors from which the recordings had been played.

Overall, marmosets were less likely to enter the compartment from which they had heard the negative interaction, suggesting that they tend to prefer cooperative individuals.

Windy cartography

American wind-energy scientists have released a new global “wind atlas” – to help engineers select the turbines in any given region and accelerate the development of sustainable energy.

The atlas is the first publicly available, uniform and location-explicit description of extreme wind speeds, according to the research, published in Nature Energy.

“This kind of information will ensure the correct selection of wind turbines for specific deployment,” says study author Sara C Pryor, from Cornell University. She adds that the work will “help ensure cost-efficient and dependable electricity generation from those turbines.”

Before this study and the resulting atlas, in many locations around the globe extreme wind-load estimates on projects were uncertain due to limited on-site measurements. The atlas provides accessible, evidence-based data on which to base the expansion of wind turbine electricity.

By the end of 2019, total global wind turbine installed capacity was generating over 1,700 terawatt hours of electricity per year, or about 7.5% of the global electricity supply, Pryor says.

Pryor and her colleague Rebecca J Barthelmie report that the US carries 17% of the world’s current installed wind-energy capacity; Europe (with 31%) and China (36%) carry more. Wind turbines generating carbon-free electricity in more than 90 countries, Pryor says.

You are what you eat (for life)

Eating too much fat and sugar as a child can alter your microbiome for life, even if you later learn to eat a healthier diet, a new study in mice suggests.

“We studied mice, but the effect we observed is equivalent to kids having a Western diet, high in fat and sugar and their gut microbiome still being affected up to six years after puberty,” explains evolutionary physiologist Theodore Garland, from the University of California Riverside (UCR).

A paper resulting from the study has been published in the Journal of Experimental Biology.

The UCR researchers found that early-life Western diet had more long-lasting effects on the microbiome than did early-life exercise.

Shock finding: Airbnb makes a difference

US researchers have confirmed what anyone living in a tourist-destination town will tell you: Airbnb does have an impact on housing prices and rents.

The impact is stronger in areas with fewer owner-occupiers, such as popular holiday towns, where it contributes to increased supply of short-term rentals, and decreased supply of long-term rentals.

In areas with a higher share of owner-occupancy, Airbnb had somewhat less of an impact on property prices and rents.

The study used data from all US properties listed on the Airbnb website between 2012 and the end of 2016. The research is published in the journal Marketing Science,