The decision, made at the General Conference on Weights and Measures in Versailles, France, which is organised by the International Bureau of Weights and Measures (BIPM), means that all SI units will now be defined in terms of constants that describe the natural world. This will assure the future stability of the SI and open the opportunity for the use of new technologies, including quantum technologies, to implement the definitions.

The changes, which will come into force on 20 May 2019, will bring an end to the use of physical objects to define measurement units.

The definition of the kilogram for more than 130 years, the International Prototype of the Kilogram (IPK), a cylinder of a platinum alloy stored at the BIPM in France, will now be retired. It will be replaced by the Planck constant — the fundamental constant of quantum physics. While the stability of the IPK could only be confirmed by comparisons with identical copies, a difficult and potentially inaccurate process, the Planck constant is ready for use everywhere and always.

“The SI redefinition is a landmark moment in scientific progress,” said Martin Milton, Director, International Bureau of Weights and Measures (BIPM). “Using the fundamental constants we observe in nature as a foundation for important concepts, such as mass and time, means that we have a stable foundation from which to advance our scientific understanding, develop new technologies and address some of society’s greatest challenges.”

“Today marks the culmination of decades of work by measurement scientists around the world, the significance of which is immense,” said Barry Inglis, Director of the International Committee for Weights and Measures. “We will now no longer be bound by the limitations of objects in our measurement of the world, but have universality accessible units that can pave the way to even greater accuracy, and even accelerate scientific advancement.”

The new definitions impact four of the seven base units of the SI: the kilogram, ampere, kelvin and mole; and all units derived from them, such as the volt, ohm and joule.

• The kilogram — will be defined by the Planck constant (h)
• The ampere — will be defined by the elementary electrical charge (e)
• The kelvin — will be defined by the Boltzmann constant (k)
• The mole — will be defined by the Avogadro constant (N_A)

Although the size of these units will not change (a kilogram will still be a kilogram), the four redefined units will join the second, the metre and the candela to ensure that the set of SI base units will continue to be both stable and useful. The revised SI will maintain its relevance by facilitating technical innovations. Just as the redefinition of the second in 1967 provided the basis for technology that has transformed how we communicate across the globe, through GPS and the internet, the new changes will have wide-reaching impact in science, technology, trade, health and the environment, among many other sectors.

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You can find more information on the SI units at: www.bipm.org/en/measurement-units/rev-si/

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By century’s end, climate models project that this lopsided distribution of rain and snow is likely to become even more skewed, with half of annual precipitation falling in 11 days.

These results are published in Geophysical Research Letters, a journal of the American Geophysical Union.

Previous studies have shown that we can expect both an increase in extreme weather events and a smaller increase in average annual precipitation in the future as the climate warms, but researchers are still exploring the relationship between those two trends.

“This study shows how those two pieces fit together,” said Angeline Pendergrass, a scientist at the National Center for Atmospheric Research (NCAR) and the lead author of the new study. “What we found is that the expected increases happen when it’s already the wettest — the rainiest days get rainier.”

The findings, which suggest that flooding and the damage associated with it could also increase, have implications for water managers, urban planners, and emergency responders. The research results are also a concern for agriculture, which is more productive when rainfall is spread more evenly over the growing season.

The research was supported by the U.S. Department of Energy and the National Science Foundation, which is NCAR’s sponsor.

What it means to be extreme

Scientists who study extreme precipitation — and how such events may change in the future — have used a variety of metrics to define what qualifies as “extreme.” Pendergrass noticed that in some cases the definitions were so broad that extreme precipitation events actually included the bulk of all precipitation.

In those instances, “extreme precipitation” and “average precipitation” became essentially the same thing, making it difficult for scientists to understand from existing studies how the two would change independently as the climate warms.

Other research teams have also been grappling with this problem. For example, a recent paper tried to quantify the unevenness of precipitation by adapting the Gini coefficient, a statistical tool often used to quantify income inequality, to instead look at the distribution of rainfall.

Pendergrass wanted to find something even simpler and more intuitive that could be easily understood by both the public and other scientists. In the end, she chose to quantify the number of days it would take for half of a year’s precipitation to fall. The results surprised her.

“I would have guessed the number would be larger — perhaps a month,” she said. “But when we looked at the median, or midpoint, from all the available observation stations, the number was just 12 days.”

For the analysis, Pendergrass worked with Reto Knutti, of the Institute for Atmospheric and Climate Science in Zurich, Switzerland. They used data from 185 ground stations for the 16 years from 1999 through 2014, a period when measurements could be validated against data from the Tropical Rainfall Measuring Mission (TRMM) satellite. While the stations were dispersed globally, the majority were in North America, Eurasia, and Australia.

To look forward, the scientists used simulations from 36 of the world’s leading climate models that had data for daily precipitation. Then they pinpointed what the climate model projections for the last 16 years of this century would translate to for the individual observation stations.

They found that total annual precipitation at the observation stations increased slightly in the model runs, but the additional precipitation did not fall evenly. Instead, half of the extra rain and snow fell over just six days.

This contributed to total precipitation also falling more unevenly than it does today, with half of a year’s total precipitation falling in just 11 days by 2100, compared to 12 in the current climate.

“While climate models generally project just a small increase in rain in general, we find this increase comes as a handful of events with much more rain and, therefore, could result in more negative impacts, including flooding,” Pendergrass said. “We need to take this into account when we think about how to prepare for the future.”

The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in this material do not necessarily reflect the views of the National Science Foundation.

The researchers used a new type of magnetic resonance imaging (MRI) to take brain scans of 16 high school players, ages 15 to 17, before and after a season of football. They found significant changes in the structure of the grey matter in the front and rear of the brain, where impacts are most likely to occur, as well as changes to structures deep inside the brain. All participants wore helmets, and none received head impacts severe enough to constitute a concussion.

The study, which is the cover story of the November issue of Neurobiology of Disease, is one of the first to look at how impact sports affect the brains of children at this critical age. This study was made available online in July 2018 ahead of final publication in print this month.

“It is becoming pretty clear that repetitive impacts to the head, even over a short period of time, can cause changes in the brain,” said study senior author Chunlei Liu, a professor of electrical engineering and computer sciences and a member of the Helen Wills Neuroscience Institute at UC Berkeley. “This is the period when the brain is still developing, when it is not mature yet, so there are many critical biological processes going on, and it is unknown how these changes that we observe can affect how the brain matures and develops.”

Concerning trends

One bonk to the head may be nothing to sweat over. But mounting evidence shows that repeated blows to the cranium — such as those racked up while playing sports like hockey or football, or through blast injuries in military combat — may lead to long-term cognitive decline and increased risk of neurological disorders, even when the blows do not cause concussion.

Over the past decade, researchers have found that an alarming number of retired soldiers and college and professional football players show signs of a newly identified neurodegenerative disease called chronic traumatic encephalopathy (CTE), which is characterized by a buildup of pathogenic tau protein in the brain. Though still not well understood, CTE is believed to cause mood disorders, cognitive decline and eventually motor impairment as a patient ages. Definitive diagnosis of CTE can only be made by examining the brain for tau protein during an autopsy.

These findings have raised concern over whether repeated hits to the head can cause brain damage in youth or high school players, and whether it is possible to detect these changes at an early age.

“There is a lot of emerging evidence that just playing impact sports actually changes the brain, and you can see these changes at the molecular level in the accumulations of different pathogenic proteins associated with neurodegenerative diseases like Parkinson’s and dementia,” Liu said. “We wanted to know when this actually happens — how early does this occur?”

A matter of grey and white

The brain is built of white matter, long neural wires that pass messages back and forth between different brain regions, and grey matter, tight nets of neurons that give the brain its characteristic wrinkles. Recent MRI studies have shown that playing a season or two of high school football can weaken white matter, which is mostly found nestled in the interior of the brain. Liu and his team wanted to know if repetitive blows to the head could also affect the brain’s gray matter.

“Grey matter in the cortex area is located on the outside of the brain, so we would expect this area to be more directly connected to the impact itself,” Liu said.

The researchers used a new type of MRI called diffusion kurtosis imaging to examine the intricate neural tangles that make up gray matter. They found that the organization of the gray matter in players’ brains changed after a season of football, and these changes correlated with the number and position of head impacts measured by accelerometers mounted inside players’ helmets.

The changes were concentrated in the front and rear of the cerebral cortex, which is responsible for higher-order functions like memory, attention and cognition, and in the centrally located thalamus and putamen, which relay sensory information and coordinate movement.

“Although our study did not look into the consequences of the observed changes, there is emerging evidence suggesting that such changes would be harmful over the long term,” Liu said.

Tests revealed that students’ cognitive function did not change over the course of the season, and it is yet unclear whether these changes in the brain are permanent, the researchers say.

“The brain microstructure of younger players is still rapidly developing, and that may counteract the alterations caused by repetitive head impacts,” said first author Nan-Ji Gong, a postdoctoral researcher in the Department of Electrical Engineering and Computer Sciences at UC Berkeley.

However, the researchers still urge caution — and frequent cognitive and brain monitoring — for youth and high schoolers engaged in impact sports.

“I think it would be reasonable to debate at what age it would be most critical for the brain to endure these sorts of consequences, especially given the popularity of youth football and other sports that cause impact to the brain,” Liu said.

Hiroaki Katsuragi, a granular physics expert from Nagoya University, and Jürgen Blum of the Technische Universität Braunschweig have done just that. Blum has constructed a drop tower where microgravity and vacuum conditions are achieved to mimic the environment in space. They fired various kinds of projectiles — plastic, lead, glass — of varying sizes at clumps of dust — which are soft and fragile — as well as at loose, dense clumps of relatively rigid glass beads. The team then carefully analyzed the impact-induced expansion and found evidence for universal energy transfer and dissipation scaling laws. In addition, the team found that the scaling laws are applicable not only to the porous agglomerate clusters but also to the dense glass-bead clusters.

Katsuragi, explains: “The result is useful to deeply understand the planet-formation process. At the same time, we are surprised at the agreement of the expansion dynamics between porous (fragile) clusters and dense (rigid) clusters. Actually, the porous clusters consist of tiny grains of powder clumped together, and these clusters of many sizes are themselves clustered together. We found that this type of hierarchical structure does not affect the impact-induced dynamics.”

This study links the physics of planetary formation and clump formation through the microgravity experiment. The drop tower used in the study is unique in that short-duration impact experiments can readily be repeated at low cost. The interdisciplinary collaboration team is also unique. Hiroaki Katsuragi is a granular physicist and Jürgen Blum is a planetary physicist and both share the common goal of understanding the impact of porous and dense granular matter.

Katsuragi notes finally, “We’re all familiar with clumps of powder: they’re formed whenever we make a cake with flour. Nevertheless, the physics of clumps — of hierarchical granular matter — has not been studied well so far. This study could open up a novel research direction in the physics of granular matter.”

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The research team headed by Dr. Ulf-Peter Apfel, Chair of Inorganic Chemistry I in Bochum, describes the findings together with their colleagues in the journal Chemical Science from 5 November 2018.

CO₂ conversion replaces hydrogen production

“The conversion of CO₂ into valuable source materials for the chemical industry is a promising approach to combatting climate change,” says Ulf-Peter Apfel. “However, we currently don’t know many cheap and readily available catalysts for CO₂ reduction.” Moreover, potentially suitable catalysts primarily facilitate another chemical reaction, i.e. the synthesis of hydrogen — these including pentlandite. Nevertheless, the researchers have successfully converted the mineral to be a CO₂ catalyst.

They generated electrodes from pentlandite and analysed under which conditions production of hydrogen or carbon monoxide took place at their surface. “The decisive factor was water being present at the electrode surface,” summarises Ulf-Peter Apfel. A lot of water shifted the reaction towards hydrogen production, a little water towards carbon monoxide production. By adjusting the water content, the researchers were thus able to generate carbon monoxide and hydrogen mixtures. “Synthetic gas mixtures like this one play a crucial role in the chemical industry,” points out Apfel.

Stabile catalyst

Pentlandite consists of iron, nickel and sulphur and resembles catalytically active enzyme centres that occur in nature, such as hydrogen-producing hydrogenases. “A huge advantage of this mineral is the fact that it remains stable when confronted with other chemical compounds that occur in industrial emissions and are poison to many catalysts,” explains Apfel.

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‘Hunting, epidemics, and climate change all have the potential to reduce the number of individuals in a population to the point where genetic diversity is lost,’ says Professor Dr Joseph Hoffman, head of the Molecular Behavioural Ecology research group at Bielefeld University and sub-project manager in the Transregio Collaborative Research Centre NC³ that is studying animals and their individual niches. ‘These extreme population reductions are known as bottlenecks and can affect a species’ potential to survive’.

‘When a species lacks genetic diversity, it has a lower chance of adapting to changing environmental conditions or protecting itself against parasites or pathogens. You can compare the gene pool with a toolbox: the fewer tools you have, the less well-equipped you are for different situations,’ says Hoffman.

The researchers analysed which seal species passed through bottlenecks due to overhunting. They carried out this research in cooperation with colleagues in ten different countries. ‘This enabled us to collect genetic data on thousands of seals from 30 different species,’ says Martin Stoffel, the lead author of the study and a doctoral student in Joseph Hoffman’s research group. As there are 33 different seal species alive today, this makes the study the most comprehensive work on the genetic diversity of seals. For example, it even used data from a study of the Antarctic fur seal that lives on Bird Island (South Georgia) in the Sub Antarctic. This research on fur seals is part of the work at the Transregio Collaborative Research Centre NC³.

In their analyses, the researchers used computers to simulate how much genetic diversity would be expected in each seal species if that species were hunted to the brink of extinction around a hundred years ago. They compared these computations with the genetic data from animals living today.

The result: seal hunting around a century ago led to the near extinction of almost one-third of the species studied. ‘Most species have recovered and are still genetically quite diverse despite strong population declines’ says Martin Stoffel.

‘However, there are four exceptions: the northern elephant seal, the Mediterranean monk seal, the Hawaiian monk seal, and the Saimaa ringed seal,’ says Stoffel. ‘The genetic material of individual animals within these species is very similar. These four species only have up to 20 per cent of the genetic diversity of those species that have been hardly or not hunted at all. In the northern elephant seal, for example, only few dozen individuals survived hunting to rebuild the current population of over 200,000 animals.’ Stoffel is an expert on the northern elephant seal. To study them for his dissertation, he went on an expedition to the Islas San Benito, an uninhabited group of islands off the Mexican Pacific coast.

Which factors explain why certain species suffered more from being hunted than others? The study confirms that ‘species that bear their young on land declined much more strongly as a result of excessive hunting than species that give birth on ice,’ says Stoffel. ‘This is probably because those giving birth on ice tend to live in remote Arctic and Antarctic areas where they were out of reach of hunters.’ Population bottlenecks can also be found in those species where a single male defends a harem of several dozen females during the breeding season. ‘This is the case with the northern elephant seal and the southern elephant seal just as much as the Antarctic fur seal,’ says Stoffel. ‘Their mating systems result in dense aggregations of breeding animals, making them easier for hunters to kill.’

Whereas at the end of the nineteenth century, millions of seals were still being killed by hunters, the German animal protection society (Tierschutzbund) reports that nowadays, 750,000 seals are killed each year for commercial purposes. Most of these seals are now being hunted in Canada, Greenland, and Namibia.

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