Ants learn from experience. This has been demonstrated by a team of evolutionary biologists from the University of Freiburg, led by Dr Volker Nehring, research associate in the Evolutionary Biology and Animal Ecology group, and doctoral student Mélanie Bey. The researchers repeatedly confronted ants with competitors from another nest. The test ants remembered the negative experiences they had during these encounters: when they encountered ants from a nest they had previously experienced as aggressive, they behaved more aggressively towards them than towards ants from nests unknown to them. Ants that encountered members of a nest from which they had previously only encountered passive ants were less aggressive. The biologists published their results in the journal Current Biology.

Ants are aggressive towards their neighbours

Ants use odours to distinguish between members of their own nest and those from other nests. Each nest has its own specific scent. Previous studies have already shown that ants behave aggressively towards their nearest neighbours in particular. They are especially likely to open their mandibles and bite, or spray acid and kill their competitors. They are less likely to carry out such aggressive manoeuvres against nests that are further away from their own. Until now, it was unclear why this is the case. Nehring’s team has now discovered that ants remember the smell of attackers. This is why they are more aggressive when confronted with competitors from nests they are familiar with.

More aggressive behaviour towards competitors from familiar nests

The scientists conducted an experiment in two phases. In the first phase, ants gained various experiences: one group encountered ants from their own nest, the second group encountered aggressive ants from a rival nest A, and the third group encountered aggressive ants from rival nest B. A total of five encounters took place on consecutive days, with each encounter lasting one minute.

In the subsequent test phase, the researchers examined how the ants from the different groups behaved when they encountered competitors from nest A. The ants that had already been confronted with conspecifics from this nest in the first phase behaved significantly more aggressively than those from the other two groups.

To test the extent to which the higher aggression arises from the behaviour of ants from a particular nest, the scientists repeated the experiment in a slightly modified form. In the first phase, they now distinguished between encounters with aggressive and passive ants. They ensured that an ant behaved passively by cutting off its antennae. In phase two of the experiment, the ants that had previously only encountered passive competitors behaved significantly less aggressively.

“We often have the idea that insects function like pre-programmed robots,” says Nehring. “Our study provides new evidence that, on the contrary, ants also learn from their experiences and can hold a grudge.” Next, Nehring and his team will investigate whether and to what extent ants adapt their olfactory receptors to their experiences, thus reflecting what they have learned at this level as well.

• Mélanie Bey conducted her doctorate under Dr. Volker Nehring. Rebecca Endermann, Christina Raudies and Jonas Steinle are former bachelor’s and master’s students in the Evolutionary Biology and Animal Ecology working group.
• The research was funded by the German Research Foundation (project number NE1969/6-1).

The technology could immediately enable low-cost, efficient real-time monitoring in industrial settings, such as tracking the condition of manufacturing robots or detecting gas leaks in refineries, by eliminating the need for power-hungry signal transmitters. The researchers said that with some engineering improvements, the technology could be used for large-scale applications like smart cities and agriculture.

The technology is an advanced version of a device that transmits data in a wireless system, commonly known as a tag. The new tag can support data transmission for a large network of devices using a technique called backscattering. This is where a central reader sends a signal to a sensor tag to gather information, and the tag reflects this ambient signal directly back to the reader. Backscattering is already used in simple systems like smart payment and building entry cards, but until now has only been possible at low frequencies.

The low frequency limit poses a problem when many devices try to communicate at the same time because when more signals are introduced, they are more likely to run into one another and get jumbled up. Conventional backscatter designs also have slow communication speeds, as lower frequency signals have limitations on how much information can travel back and forth at once.

The new tag, developed by researchers at Princeton, Rice University and Brown University, is the first of its kind that can use backscattering in the sub-terahertz range, a high-frequency portion of the radio spectrum. This range can support high-speed data transmission across broad bandwidths. The development means it could be possible to power signal transmission for dense networks of devices using passive tags, saving significant power and infrastructure compared to conventional wireless systems.

“I believe this technology will find applications in many interesting settings,” said Yasaman Ghasempour, assistant professor of electrical and computer engineering at Princeton and the study’s principal investigator. “Despite the conventional wisdom, this paper shows that it is possible to have low-power, scalable communication in the sub-terahertz range.”

The paper was published Oct. 9 in Nature Communications.

Using backscattering at higher frequencies is challenging because the signals are more susceptible to fading as they propagate and must be very precise to travel long distances. “The reader has to form a narrow pencil-shaped beam to shine into the tag’s precise location, and the low-power tag should do the same without consuming any power. That’s the real challenge,” Ghasempour said.

Traditional backscatter tags reflect signals back to their source using simple antennas that typically broadcast the energy in all directions, causing only a portion of the energy to reach back to the reader. While some advanced tags can adjust the direction of their signal, their ability to do so is limited, and they’re restricted to a narrow range of frequencies. Ghasempour said that achieving sub-terahertz backscattering required the team to rethink the entire architecture of the tag. “It wouldn’t work to use the same old hardware design and scale it up,” she said.

To address these limitations, the researchers came up with an entirely new antenna structure. The new antennas allow the direction of the signal to change automatically in response to changes in frequency. By doing this, the tag can steer the signal to enable longer range communication and avoid interference from other signals. In other words, the interference footprint of each tag is limited in spatial and spectral domains.

Ghasempour said she hopes that others will read this paper and find engineering improvements for advanced applications. By implementing a way to amplify signals in the system at low costs, for example, the technology could power sensor networks across cities to monitor air quality or traffic flow.

The tags could be placed on traffic signs to be detected by self-driving cars, as they can use radio waves to convey messages like “stop” or “yield” even when visibility is blocked by fog or snow. In agriculture, the technology could help create expansive networks of soil sensors across fields or forests, providing real-time data on moisture levels or temperature.

Ghasempour said that developing low-power data modulators in these kinds of systems is an active area of research, and that this innovation is a step toward decreasing cost and power consumption for the entire wireless system.

Lithium-ion batteries and other rechargeable batteries based on metal ions provide our portable devices with electricity, power vehicles, and store solar and wind energy. They work well — as long as it is warm. As temperatures drop, the performance of these batteries can decrease sharply — a problem for electric cars, aerospace, and military applications. Countermeasures such as integrated heaters, improved electrolytes, or electrode coatings increase the cost and complexity of battery production or reduce performance.

One of the causes of the cold problem is the slowed diffusion of lithium ions within the electrode material. A team from Donghua University and Fudan University in Shanghai, as well as Inner Mongolia University in Hohhot has proposed a new approach to tackling this issue: electrodes made of electrochemical energy-storage materials with negative thermal expansion (NTE), such as lithium titanium phosphate LiTi₂(PO₄)₃ (LTP). Led by Liming Wu, Chunfu Lin, and Renchao Che, the team used LTP as a model substance to demonstrate that electrode materials with NTE properties can provide good performance at low temperatures.

Analysis of the crystal structure revealed a three-dimensional lattice of TiO₆ octahedra and PO₄ tetrahedra with an open, flexible structure that contains both “cavities” and “channels,” where lithium ions can lodge. When cooled, the structure stretches along one of its crystal axes. By using spectrometric and electron microscopic analyses in conjunction with computer modeling, the team determined that the vibrational modes of the atoms change at low temperature. This increases the occurrence of special transverse vibrations of certain oxygen atoms, increasing their distances from each other and widening the cavities in the lattice. This facilitates storage and transport of the lithium ions. At −10 °C, their diffusion rate is still at 84% of the value obtained at 25 °C. Electrochemical tests on carbon-coated LTP at −10 °C also showed good electrochemical performance with high capacity and a high rate capability, as well as a high retention of capacity over 1000 charge/discharge cycles.

Materials with negative thermal expansion are thus highly promising for use as an electrode material in lithium-ion batteries in cold environments.