Research Highlights

Our pick of the latest scientific literature

  • Volume 548
  • Issue 7667

Physics

Metal flouts Ohm’s law

Finding could provide new way to spot elusive topological effects.

The intensity of an electric current running through a metal is directly proportional to the voltage applied. This linear relationship, called Ohm’s law, is sometimes taken to be a defining characteristic of metals; the constant ratio of voltage to intensity is the electrical resistance of a given substance.

Jeehoon Kim at Pohang University of Science and Technology in South Korea and his collaborators found that, in a particular type of bismuth antimonide crystal, the electrical resistance is not constant but changes with voltage. This effect is due to a topological quirk in the energy levels of electrons that allows some of these particles to flow without resistance, and the fact that the number of such electrons varies with voltage. 

Similar deviations from Ohm’s law in other materials could be used as easier experimental signatures of such topological effects, which have tended to require expensive synchrotrons to demonstrate. 

Physics

Dark matter without the WIMPS

Theorists propose alternative route to elusive matter.

A favoured explanation for the origin of dark matter posits that the existing amount was determined in the early Universe and comes in the form of weakly interacting massive particles (WIMPs). It suggests that, in the hot, early Universe, pairs of WIMPs collided and annihilated each other, forming other particles. The reverse reaction was also taking place. This theory predicts that WIMPs should be discovered in experiments, but so far they have failed to show up.

Josh Ruderman at New York University in New York City and his colleagues propose that the crucial primordial reaction was not the annihilation, but the collision of two different types of particle. Their theory suggests that dark-matter particles would be lighter than WIMPs are thought to be. These particles would potentially be even harder to detect, but might still be observable in the cosmic microwave background and in collisions between electrons and positrons.

Fish farms, such as this one in Norway, could expand drastically to meet future demand for seafood.

Fish farms, such as this one in Norway, could expand drastically to meet future demand for seafood. Design Pics Inc/NGC

Ecology

Aquaculture has plenty of room to grow

Global analysis charts ocean areas suitable for expansion of fish farming.

The total amount of seafood caught by fishermen could be equalled by farming fish in less than 0.015% of Earth’s oceans, an area smaller than Lake Michigan in the United States.

Aquaculture is increasingly important to the supply of food around the world, and many hope it can be expanded to meet the demands of a growing global population.

Rebecca Gentry at the University of California, Santa Barbara, and her colleagues modelled the ability of the world’s seas to support the farming of fish and bivalves, such as oysters and mussels. They found that both types of farming could be increased around the globe, in both tropical and temperate countries. In total, around 11.4 million square kilometres of ocean are potentially suitable for fish farming, and more than 1.5 million square kilometres for bivalves. If all suitable areas for finfish farming were used, about 15 billion tonnes of fish could be grown a year — more than 100 times current global seafood consumption. 

Small-scale gold mining often uses mercury that is then released to the environment.

Small-scale gold mining often uses mercury that is then released to the environment. Sven Torfinn/Panos

Environmental sciences

Old cooking oil could be used to clean up mercury

Material can pick up pollutant from soils and water.

A type of rubber that can soak up mercury from the environment can be made cheaply from old cooking oil.

Thousands of tonnes of mercury are emitted around the world annually as a result of human activities, and put health and the environment at risk. Justin Chalker at Flinders University in Adelaide, Australia, and his colleagues created a polysulfide rubber from waste products of industrial cooking and petroleum refining. They stirred cooking oil and hot sulfur for 20 minutes at 180 °C to produce a brown solid polymer. Adding sodium chloride produced a porous, sponge-like structure that could capture mercury from water, soil and air. 

The compound can also soak up mercury that is stuck to organic matter or in the form of highly toxic alkyl-mercury compounds. The authors say that the compound could be used to clean up mercury that ends up in soil and waste water after gold mining, for example.

Genomics

Gene editing switches off pig viruses

Technique overcomes barrier to pig–human organ transplants.

The CRISPR–Cas9 gene-editing technology can be used to generate pigs that are free from viruses that could potentially infect humans.

Researchers hope that pigs might one day be able to serve as organ donors when no human organ is available. But there are concerns that viruses embedded in the pig genome could infect humans who have porcine transplants.

Luhan Yang at eGenesis in Cambridge, Massachusetts, and her colleagues injected pig cells with a CRISPR–Cas9 gene-editing system that inactivated all copies of porcine endogenous retroviruses (PERVs) from the cells. They then transferred the nuclei of these cells into pig embryos, which they implanted into sows whose genomes contained PERVs. When piglets were born, the researchers found that 100% of the PERVs in their cells had been inactivated.

The authors say that this PERV-inactivated pig strain can be a resource for researchers developing pigs with human-like organs. 

Careful incisions on remains such as these hare bones and reindeer antlers have now been found on human bone.

Careful incisions on remains such as these hare bones and reindeer antlers have now been found on human bone. Bello et al./PLoS ONE

Archaeology

Ritualistic cannibalism in the Palaeolithic

Zigzag marks on bones found in English cave give insight into ancient traditions.

Zigzag marks on a roughly 15,000-year-old human limb bone may be the result of ritualistic cannibalism in ancient Britain.

Marks on bones found in Gough’s Cave in southwest England have previously shown that humans who lived there practised cannibalism for nutritional purposes. A team led by Silvia Bello at the Natural History Museum in London examined a human arm bone excavated from the cave in 1987. The team found evidence that humans had eaten meat from the bone: it bore incisions, human-tooth marks and damage from being pounded with a stone.

However, the radius also bore unusual zigzag marks, which are unlikely to have been created to extract flesh, the authors say. Similar patterns appear on animal bones from other European sites dated to the same period.

This type of intentional engraving has not been seen before on human bones, and suggests a previously unrecognized cannibalistic funerary practice in the Palaeolithic period.

An example of the new species — seen here on display in Argentina — is currently in a New York museum.

An example of the new species — seen here on display in Argentina — is currently in a New York museum. D. Pol

Palaeontology

Patagonian titan is largest dinosaur ever seen

Excavations at Argentinian ranch find remains of at least six gigantic herbivores.

A bounty of bones belonging to the largest dinosaur yet discovered has revealed a previously unknown group of prehistoric titans.

José Carballido at the Museum of Palaeontology Egidio Feruglio in Trelew, Argentina, and his colleagues analysed more than 150 bones excavated at a ranch in Patagonia. They identified at least six individuals of a new species they name Patagotitan mayorum, part of a diverse group of long-necked herbivores called titanosaurs.

The authors conclude that P. mayorum belonged to a group of particularly large titanosaurs that roamed Patagonia around 100 million years ago. The gigantism of this group probably emerged in favourable conditions created when a warmer climate took hold and the rise of flowering plants provided an abundance of food, the team suggests. P. mayorum reached almost 40 metres long and weighed up to 70 tonnes — roughly the same as 10 male African savannah elephants. 

Climate sciences

Climate patterns drove hotspot of sea-level rise on southeastern US shores

El Niño and North Atlantic Oscillation teamed up to raise coastal water levels.

Working in concert, two climate processes funnelled extra water along the south eastern coast of the United States between 2011 and 2015, exacerbating sea-level rise in the area.

Tide gauges show that, during this period, sea levels south of North Carolina’s Cape Hatteras rose by more than 20 millimetres a year — more than three times the mean global increase. A team led by Arnoldo Valle-Levinson at the University of Florida in Gainesville analysed climate patterns that could be shifting water to the region — including El Niño and the North Atlantic Oscillation.

During El Niño, changes in trade winds push more ocean water westward across the Atlantic and towards the US coast, the scientists found. And changes in the North Atlantic Oscillation, a pattern of variations in atmospheric pressure between Iceland and the Azores, drove that extra water south of Cape Hatteras to the coasts of the Carolinas and Florida. Understanding such localized ‘hotspots’ in sea-level rise could help communities better prepare for flooding.

Many different animals have been modified with CRISPR; ants have now joined their ranks.

Many different animals have been modified with CRISPR; ants have now joined their ranks. Daniel Kronauer/Rockefeller University

Genetics

CRISPR ants lose ability to smell

First gene-edited mutant-ant lines show defects in social behaviour.

Two separate teams have developed the first gene-edited mutant ants, in both cases disrupting the ability to smell, and hence the ability to use pheromones to communicate.

Daniel Kronauer at the Rockefeller University in New York City and his colleagues used CRISPR gene-editing technology on the eggs of Ooceraea biroi ants, exploiting the fact that these animals reproduce through parthenogenesis to spread mutations through a colony.

Separately, Claude Desplan of New York University and his colleagues used CRISPR to modify Harpegnathos saltator eggs, making modified colonies using a feature of this species by which worker ants can become ‘pseudoqueens’ and found their own colonies.

In both cases, the ants were given mutated versions of the orco gene, which is required for odorant-receptor function. As well as showing an impaired sense of smell, both sets of mutant ants had impaired social behaviour. Both also had big reductions in an area of the brain associated with smell sensed through the antennae, suggesting that loss of odorant-receptor function can stop the development of this brain region in these animals. 

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