Antarctica losing six times more ice mass annually now than 40 years ago

Researchers from UCI and NASA JPL recently conducted an assessment of 40 years' worth of ice mass balance in Antarctica, finding accelerating deterioration of its ice cover.

Antarctica experienced a sixfold increase in yearly ice mass loss between 1979 and 2017, according to a study published today in Proceedings of the National Academy of Sciences. Glaciologists from the University of California, Irvine, NASA's Jet Propulsion Laboratory and the Netherlands' Utrecht University additionally found that the accelerated melting caused global sea levels to rise more than half an inch during that time.

"That's just the tip of the iceberg, so to speak," said lead author Eric Rignot, Donald Bren Professor and chair of Earth system science at UCI. "As the Antarctic ice sheet continues to melt away, we expect multi-meter sea level rise from Antarctica in the coming centuries."

For this study, Rignot and his collaborators conducted what he called the longest-ever assessment of remaining Antarctic ice mass. Spanning four decades, the project was also geographically comprehensive; the research team examined 18 regions encompassing 176 basins, as well as surrounding islands.

Techniques used to estimate ice sheet balance included a comparison of snowfall accumulation in interior basins with ice discharge by glaciers at their grounding lines, where ice begins to float in the ocean and detach from the bed. Data was derived from fairly high-resolution aerial photographs taken from a distance of about 350 meters via NASA's Operation IceBridge; satellite radar interferometry from multiple space agencies; and the ongoing Landsat satellite imagery series, begun in the early 1970s.

The team was able to discern that between 1979 and 1990, Antarctica shed an average of 40 gigatons of ice mass annually. (A gigaton is 1 billion tons.) From 2009 to 2017, about 252 gigatons per year were lost.

The pace of melting rose dramatically over the four-decade period. From 1979 to 2001, it was an average of 48 gigatons annually per decade. The rate jumped 280 percent to 134 gigatons for 2001 to 2017.

Rignot said that one of the key findings of the project is the contribution East Antarctica has made to the total ice mass loss picture in recent decades.

"The Wilkes Land sector of East Antarctica has, overall, always been an important participant in the mass loss, even as far back as the 1980s, as our research has shown," he said. "This region is probably more sensitive to climate [change] than has traditionally been assumed, and that's important to know, because it holds even more ice than West Antarctica and the Antarctic Peninsula together."

He added that the sectors losing the most ice mass are adjacent to warm ocean water.

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Scientists identify two new species of fungi in retreating Arctic glacier

Two new species of fungi isolated from sediments and soil in the Canadian Arctic (A)micrographic image of Vishniacozyma ellesmerensis (B) colonies of V. ellesmerensis (C) micrographic image of Mrakia hoshinonis (D) colonies of M. hoshinonis.

Two new species of fungi have made an appearance in a rapidly melting glacier on Ellesmere Island in the Canadian Arctic, just west of Greenland. A collaborative team of researchers from Japan's National Institute of Polar Research, The Graduate University for Advanced Studies in Tokyo, Japan, and Laval University in Québec, Canada made the discovery.

The scientists published their results on DATE in two separate papers, one for each new species, in the International Journal of Systematic and Evolutionary Microbiology.

"The knowledge of fungi inhabiting the Arctic is still fragmentary. We set out to survey the fungal diversity in the Canadian High Arctic," said Masaharu Tsuji, a project researcher at the National Institute of Polar Research in Japan and first author on both papers. "We found two new fungal species in the same investigation on Ellesmere Island."

One species is the 10th to join the genus Mrakia, with the proposed name M. hoshinonis, in honor of Tamotsu Hoshino, a senior researcher at the National Institute of Advanced Science and Technology in Japan. Hoshino has made significant contributions to the study of fungi in polar regions. The other species is the 12th to join the genus Vishniacozyma, with the proposed name V. ellesmerensis as a nod to the island where it was found. Both species are types of yeast that are well-adapted to the cold and can even grow below 0°C.

The samples of fungi were collected from the unofficially named Walker Glacier. The designation comes from Paul T. Walker, who installed the datum pole that measures the glacier's growth and shrinkage, in 1959. At the time of sample collection in 2016, measurements showed that the glacier was receding at a rate two-and-a-half times faster than its retreat over the previous 50 years.

"Climate-related effects have been observed in this region over the last 20 years," Tsuji said. "Soon, some of the glaciers may completely melt and disappear."

Only about five percent of fungi species have been discovered, but their function across ecological climates is well understood -- from the tropics to the Arctic, fungi decompose dead organic material. Each species operates a little differently, but their general role is to reintroduce nutrients from dead plant material back into the ecosystem. If the glaciers melt, the fungi lose their habitat. The results could have catastrophic knock-on effects throughout the ecosystem, according to Tsuji, although more research is needed to understand exactly how the changing climate is influencing fungi beyond destroying their habitat.

Next, Tsuji and his team plan to survey the fungi in Ward Hunt Lake, the northern most lake in the world. It is on Ward Hunt Island, just off the northern coast of Ellesmere Island, and less than 500 miles from the North Pole.

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11,500-year-old animal bones in Jordan suggest early dogs helped humans hunt

Selection of gazelle bones from Space 3 at Shubayqa 6 displaying evidence for having been in the digestive tract of a carnivore.

11,500 years ago in what is now northeast Jordan, people began to live alongside dogs and may also have used them for hunting, a new study from the University of Copenhagen shows. The archaeologists suggest that the introduction of dogs as hunting aids may explain the dramatic increase of hares and other small prey in the archaeological remains at the site.

Dogs were domesticated by humans as early as 14,000 years ago in the Near East, but whether this was accidental or on purpose is so far not clear. New research published in the Journal of Anthropological Archaeology by a team of archaeologists from the University of Copenhagen and University College London may suggest that humans valued the tracking and hunting abilities of early dogs more than previously known.

A study of animal bones from the 11,500 year old settlement Shubayqa 6 in northeast Jordan not only suggests that dogs were present in this region at the start of the Neolithic period, but that humans and dogs likely hunted animals together:

"The study of the large assemblage of animal bones from Shubayqa 6 revealed a large proportion of bones with unmistakable signs of having passed through the digestive tract of another animal; these bones are so large that they cannot have been swallowed by humans, but must have been digested by dogs," explained zooarchaeologist and the study's lead author Lisa Yeomans.

Lisa Yeomans and her colleagues have been able to show that Shubayqa 6 was occupied year round, which suggests that the dogs were living together with the humans rather than visiting the site when there were no inhabitants:

"The dogs were not kept at the fringes of the settlement, but must have been closely integrated into all aspects of day-to-day life and allowed to freely roam around the settlement, feeding on discarded bones and defecating in and around the site."

Can new hunting techniques account for the increase in small prey?

When Yeomans and her co-authors sifted through the analysed data, they also noted a curious increase in the number of hares at the time that dogs appeared at Shubayqa 6. Hares were hunted for their meat, but Shubayqa 6's inhabitants also used the hare bones to make beads. The team think that it is likely that the appearance of dogs and the increase in hares are related.

"The use of dogs for hunting smaller, fast prey such as hares and foxes, perhaps driving them into enclosures, could provide an explanation that is in line with the evidence we have gathered. The long history of dog use, to hunt both small as well as larger prey, in the region is well known, and it would be strange not to consider hunting aided by dogs as a likely explanation for the sudden abundance of smaller prey in the archaeological record," said Lisa Yeomans.

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3,000-year-old eastern North American quinoa discovered in Ontario

The color seed shot shows the crop (left) and the wild/weedy relative (right).

A mass of charred seeds found while clearing a home construction site in Brantford, Ontario, has been identified as ancient, domesticated goosefoot (C. berlandieri spp. jonesianum), a form of quinoa native to Eastern North America. The seeds date back to 900 B.C., and have never previously been found north of Kentucky this early in history, says Professor Gary Crawford of the Department of Anthropology at the University of Toronto Mississauga (UTM), who was brought in by Archaeological Services Inc. (ASI), the archaeological consulting firm that excavated the site.

Archaeological discoveries don't normally shock Crawford but this one comes close. "Finding domesticated seeds that are so old in Ontario is special," Crawford says. "The next time we find a crop in the province is about 500 A.D., and it's corn. All previous research on this species of quinoa, which is now extinct, has taken place in the central United States: Arkansas, Illinois and Kentucky."

The charred seeds, about 140,000 in total, were discovered in Brantford in 2010 during a required archeological assessment conducted by Archaeological Services Inc. prior to site development. The Tutela Heights site, which has since become a housing development, yielded some stone tools, post holes, debris and the chenopod seeds. Jessica Lytle, a co-author of the resulting research paper, was one of the assessors who did the initial seed analysis and brought them to Crawford for further analysis, having studied with him at UTM. Their findings are published in the October 2018 issue of American Antiquity. The analysis took time, especially given the number of seeds and the need to document whether the whole collection was from the same crop.

"This discovery raises more questions than it answers. We had to consider whether the seeds were only traded here or grown locally," says Ron Williamson, PhD, of ASI, another co-author. "We also had to consider whether this was the beginning of agriculture in the province. It appears not, because we don't see any evidence of local cultivation. If it were grown in the region, we would have expected to see seeds of the crop in other pits around the site, but they were confined to this specific pit. We also don't see any sign of agricultural weeds or stone tools that may have been used for cultivation.

Indigenous peoples at the time exchanged certain kinds of minerals and finished stone objects over long distances, but this is the first evidence of a crop circulating in this exchange system. What meaning this plant had for local indigenous people nearly 3000 years ago still is not clear.

Professor Crawford notes "We always wondered if they were also exchanging perishable materials. We're taking the conservative view that these seeds were traded; it would make sense that it wasn't only stone and minerals being moved around. In Kentucky, Illinois and Arkansas, this was a very important foodstuff; its nutrient value was probably similar to that of modern quinoa, which comes from South America."

The researchers also explored how and why the seeds were charred. They speculate that it may have happened accidentally when the local inhabitants were attempting to parch them.

"You can lightly parch seeds so they don't sprout and store them," Crawford says. "It could have been a mistake to have burned them. There was a slight oxidization of the surrounding sediment, so the soil was heated; we think they were burned in place in the pit."

For Crawford, the next step in answering some of the questions will be to review seeds in his lab that were collected at other sites in Ontario to see if there are other charred seeds that may be variations of this subspecies and to examine other Ontario seed collections. Today, there is a weedy version that grows locally and he is curious whether this is a holdover from Indigenous agriculture.

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DNA tool allows you to trace your ancient ancestry

Scientists at the University of Sheffield studying ancient DNA have created a tool allowing them to more accurately identify ancient Eurasian populations, which can be used to test an individual's similarity to ancient people who once roamed the earth.

Currently the study of ancient DNA requires a lot of information to classify a skeleton to a population or find its biogeographical origins.

Now scientists have defined a new concept called Ancient Ancestry Informative Markers (aAIMs) -- a group of mutations that are sufficiently informative to identify and classify ancient populations.

The research, led by Dr Eran Elhaik, from the University of Sheffield's Department of Animal and Plant Sciences, saw the identification of a small group of aAIMs that can be used to classify skeletons to ancient populations.

Dr Elhaik said: "We developed a new method that finds aAIMs efficiently and have proved that it is accurate."

AIMs (Ancestry Informative Markers) have a long history in science and have been employed for the past decade by health and forensic experts.

But Dr Elhaik said that when his team applied traditional AIMs-finding tools to ancient DNA data, they were disappointed with their low accuracy.

"Ancient populations are much more diverse than modern ones," he said. "Their diversity was reduced over the years following events such as the Neolithic revolution and the Black Death.

"Although we have many more people today they are all far more similar to each other than ancient people. In addition, the ancient data themselves are problematic due to the large amount of degraded DNA."

To overcome these challenges, Dr Elhaik developed a specialised tool that identifies aAIMs by combining traditional methodology with a novel one that takes into account a mixture.

"Ancient genomes typically consist of hundreds of thousands and sometimes millions of markers. We demonstrated that only 13,000 markers are needed to make accurate population classifications for ancient genomes and while the field of ancient forensics does not exist yet, these aAIMs can help us get much closer to ancient people."

He added: "Until now you couldn't test people for ancient DNA ancestry because commercial microarrays, such as the ones used for genetic genealogy, don't have a lot of markers relevant for paleogenomics -- people could not study their primeval origins.

"This finding of aAIMs is like finding the fingerprints of ancient people. It allows testing of a small number of markers -- that can be found in a commonly available array -- and you can ask what part of your genome is from Roman Britons or Viking, or Chumash Indians, or ancient Israelites, etc.

"We can ask any question we want about these ancient people as long as someone sequenced these ancient markers. So this paper brings the field of paleogenomics to the public."

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Upper-ocean warming is changing the global wave climate, making waves stronger

Increasing wave energy with climate change means more challenges for coastal risk and adaptation.

Sea level rise puts coastal areas at the forefront of the impacts of climate change, but new research shows they face other climate-related threats as well. In a study published January 14 in Nature Communications, researchers report that the energy of ocean waves has been growing globally, and they found a direct association between ocean warming and the increase in wave energy.

A wide range of long-term trends and projections carry the fingerprint of climate change, including rising sea levels, increasing global temperatures, and declining sea ice. Analyses of the global marine climate thus far have identified increases in wind speeds and wave heights in localized areas of the ocean in the high latitudes of both hemispheres. These increases have been larger for the most extreme values (e.g., winter waves) than for the mean conditions. However, a global signal of change and a correlation between the localized increases in wave heights and global warming had remained undetected.

The new study focused on the energy contained in ocean waves, which is transmitted from the wind and transformed into wave motion. This metric, called wave power, has been increasing in direct association with historical warming of the ocean surface. The upper ocean warming, measured as a rising trend in sea-surface temperatures, has influenced wind patterns globally, and this, in turn, is making ocean waves stronger.

"For the first time, we have identified a global signal of the effect of global warming in wave climate. In fact, wave power has increased globally by 0.4 percent per year since 1948, and this increase is correlated with the increasing sea-surface temperatures, both globally and by ocean regions," said lead author Borja G. Reguero, a researcher in the Institute of Marine Sciences at the University of California, Santa Cruz.

Climate change is modifying the oceans in different ways, including changes in ocean-atmosphere circulation and water warming, according to coauthor Inigo J. Losada, director of research at the Environmental Hydraulics Institute at the University of Cantabria (IHCantabria), where the study was developed.

"This study shows that the global wave power can be a potentially valuable indicator of global warming, similarly to carbon dioxide concentration, the global sea level rise, or the global surface atmospheric temperature," Losada said.

Understanding how the energy of ocean waves responds to oceanic warming has important implications for coastal communities, including anticipating impacts on infrastructure, coastal cities, and small island states. Ocean waves determine where people build infrastructure, such as ports and harbors, or require protection through coastal defenses such as breakwaters and levees. Indeed, wave action is one of the main drivers of coastal change and flooding, and as wave energy increases, its effects can become more profound. Sea level rise will further aggravate these effects by allowing more wave energy to reach shoreward.

While the study reveals a long-term trend of increasing wave energy, the effects of this increase are particularly apparent during the most energetic storm seasons, as occurred during the winter of 2013-14 in the North Atlantic, which impacted the west coast of Europe, or the devastating 2017 hurricane season in the Caribbean, which offered a harsh reminder of the destructive power and economic impacts of coastal storms.

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The orderly chaos of black holes

The dedicated Gamma-ray Burst Polarimetry experiment POLAR on top of China’s TiangGong-2 spacelab launched on September 15, 2016. The glowing green light mimics the scintillating light when a gamma-ray photon hits one of the 1600 specially made scintillation bars. The artwork is based on a picture taken by a camera located several meters behind.

During the formation of a black hole a bright burst of very energetic light in the form of gamma-rays is produced, these events are called gamma-ray bursts. The physics behind this phenomenon includes many of the least understood fields within physics today: general gravity, extreme temperatures and acceleration of particles far beyond the energy of the most powerful particle accelerators on Earth. In order to analyse these gamma-ray bursts, researchers from the University of Geneva (UNIGE), in collaboration with the Paul Scherrer Institute (PSI) of Villigen, Switzerland, the Institute of High Energy Physics in Beijing and the National Center for Nuclear Research of Swierk in Poland, have built the POLAR instrument, sent in 2016 to the Chinese Tiangong-2 space laboratory, to analyze gamma-ray bursts. Contrary to the theories developed, the first results of POLAR reveal that the high energy photons coming from gamma-ray bursts are neither completely chaotic, nor completely organized, but a mixture of the two: within short time slices, the photons are found to oscillate in the same direction, but the oscillation direction changes with time. These unexpected results are reported in a recent issue of the journal Nature Astronomy.

When two neutron stars collide or a super massive star collapses into itself, a black hole is created. This birth is accompanied by a bright burst of gamma-rays -- very energetic light such as that emitted by radioactive sources -- called a gamma-ray burst (GRB).

Is black hole birth environment organized or chaotic?

How and where the gamma-rays are produced is still a mystery, two different schools of thought on their origin exist. The first predicts that photons from GRBs are polarized, meaning the majority of them oscillate in the same direction. If this were the case, the source of the photons would likely be a strong and well organized magnetic field formed during the violent aftermath of the black hole production. A second theory suggests that the photons are not polarized, implying a more chaotic emission environment. But how to check this?

"Our international teams have built together the first powerful and dedicated detector, called POLAR, capable of measuring the polarization of gamma-rays from GRBs. This instrument allows us to learn more about their source," said Xin Wu, professor in the Department of Nuclear and Particle Physics of the Faculty of Sciences of UNIGE. Its operating system is rather simple. It is a square of 50x50 cm2 consisting of 1600 scintillator bars in which the gamma-rays collide with the atoms that make up these bars. When a photon collides in a bar we can measure it, afterwards it can produce a second photon which can cause a second visible collision. "If the photons are polarized, we observe a directional dependency between the impact positions of the photons, continues Nicolas Produit, researcher at the Department of Astronomy of the Faculty of Sciences of UNIGE. On the contrary, if there is no polarization, the second photon resulting from the first collision will leave in a fully random direction."

Order within chaos

In six months, POLAR has detected 55 gamma-ray bursts and scientist analyzed the polarization of gamma-rays from the 5 brightest ones. The results are surprising to say the least. "When we analyse the polarization of a gamma-ray burst as a whole, we see at most a very weak polarization, which seems to clearly favour several theories," says Merlin Kole, a researcher at the Department of Nuclear and Particle Physics of the Faculty of Sciences of UNIGE and one of the main authors of the paper. Faced with this first result, the scientists looked in more detail at a very powerful 9 second long gamma-ray burst and cut it into time slices, each of 2 seconds long. "There, we discovered with surprise that, on the contrary, the photons are polarized in each slice, but the oscillation direction is different in each slice!," Xin Wu enthuses. It is this changing direction which makes the full GRB appear as very chaotic and unpolarized. "The results show that as the explosion takes place, something happens which causes the photons to be emitted with a different polarization direction, what this could be we really don't know," continues Merlin Kole.

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Double star system flips planet-forming disk into pole position

Artist's impression of a view of the double star system and surrounding disc.

New research led by an astronomer at the University of Warwick has found the first confirmed example of a double star system that has flipped its surrounding disc to a position that leaps over the orbital plane of those stars. The international team of astronomers used the Atacama Large Millimeter/sub-millimeter Array (ALMA) to obtain high-resolution images of the Asteroid belt-sized disc.

The overall system presents the unusual sight of a thick hoop of gas and dust circling at right angles to the binary star orbit. Until now this setup only existed in theorists' minds, but the ALMA observation proves that polar discs of this type exist, and may even be relatively common.

The new research is published today (14 January) by Royal Society University Research Fellow Dr Grant M. Kennedy of the University of Warwick's Department of Physics and Centre for Exoplanets and Habitability in Nature Astronomy in a paper entitled "A circumbinary protoplanetary disc in a polar configuration."

Dr Grant M. Kennedy of the University of Warwick said:

"Discs rich in gas and dust are seen around nearly all young stars, and we know that at least a third of the ones orbiting single stars form planets. Some of these planets end up being misaligned with the spin of the star, so we've been wondering whether a similar thing might be possible for circumbinary planets. A quirk of the dynamics means that a so-called polar misalignment should be possible, but until now we had no evidence of misaligned discs in which these planets might form."

Dr Kennedy and his fellow researchers used ALMA to pin down the orientation of the ring of gas and dust in the system. The orbit of the binary was previously known, from observations that quantified how the stars move in relation to each other. By combining these two pieces of information they were able to establish that the dust ring was consistent with a perfectly polar orbit. This means that while the stellar orbits orbit each other in one plane, like two horses going around on a carousel, the disc surrounds these stars at right angles to their orbits, like a giant ferris wheel with the carousel at the centre.

Dr Grant M. Kennedy of the University of Warwick added:

"Perhaps the most exciting thing about this discovery is that the disc shows some of the same signatures that we attribute to dust growth in discs around single stars. We take this to mean planet formation can at least get started in these polar circumbinary discs. If the rest of the planet formation process can happen, there might be a whole population of misaligned circumbinary planets that we have yet to discover, and things like weird seasonal variations to consider."

If there were a planet or planetoid present at the inner edge of the dust ring, the ring itself would appear from the surface as a broad band rising almost perpendicularly from the horizon. The polar configuration means that the stars would appear to move in and out of the disc plane, giving objects two shadows at times. Seasons on planets in such systems would also be different. On Earth they vary throughout the year as we orbit the Sun. A polar circumbinary planet would have seasons that also vary as different latitudes receive more or less illumination throughout the binary orbit.

Co-author Dr Daniel Price of Monash University's Centre for Astrophysics (MoCA) and School of Physics and Astronomy added:

"We used to think other solar systems would form just like ours, with the planets all orbiting in the same direction around a single sun. But with the new images we see a swirling disc of gas and dust orbiting around two stars. It was quite surprising to also find that that disc orbits at right angles to the orbit of the two stars.

"Incredibly, two more stars were seen orbiting that disc. So if planets were born here there would be four suns in the sky!

"ALMA is just a fantastic telescope, it is teaching us so much about how planets in other solar systems are born."

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Technique identifies electricity-producing bacteria

A microfluidic technique quickly sorts bacteria based on their capability to generate electricity.

Living in extreme conditions requires creative adaptations. For certain species of bacteria that exist in oxygen-deprived environments, this means finding a way to breathe that doesn't involve oxygen. These hardy microbes, which can be found deep within mines, at the bottom of lakes, and even in the human gut, have evolved a unique form of breathing that involves excreting and pumping out electrons. In other words, these microbes can actually produce electricity.

Scientists and engineers are exploring ways to harness these microbial power plants to run fuel cells and purify sewage water, among other uses. But pinning down a microbe's electrical properties has been a challenge: The cells are much smaller than mammalian cells and extremely difficult to grow in laboratory conditions.

Now MIT engineers have developed a microfluidic technique that can quickly process small samples of bacteria and gauge a specific property that's highly correlated with bacteria's ability to produce electricity. They say that this property, known as polarizability, can be used to assess a bacteria's electrochemical activity in a safer, more efficient manner compared to current techniques.

"The vision is to pick out those strongest candidates to do the desirable tasks that humans want the cells to do," says Qianru Wang, a postdoc in MIT's Department of Mechanical Engineering.

"There is recent work suggesting there might be a much broader range of bacteria that have [electricity-producing] properties," adds Cullen Buie, associate professor of mechanical engineering at MIT. "Thus, a tool that allows you to probe those organisms could be much more important than we thought. It's not just a small handful of microbes that can do this."

Buie and Wang have published their results today in Science Advances.

Just between frogs

Bacteria that produce electricity do so by generating electrons within their cells, then transferring those electrons across their cell membranes via tiny channels formed by surface proteins, in a process known as extracellular electron transfer, or EET.

Existing techniques for probing bacteria's electrochemical activity involve growing large batches of cells and measuring the activity of EET proteins -- a meticulous, time-consuming process. Other techniques require rupturing a cell in order to purify and probe the proteins. Buie looked for a faster, less destructive method to assess bacteria's electrical function.

For the past 10 years, his group has been building microfluidic chips etched with small channels, through which they flow microliter-samples of bacteria. Each channel is pinched in the middle to form an hourglass configuration. When a voltage is applied across a channel, the pinched section -- about 100 times smaller than the rest of the channel -- puts a squeeze on the electric field, making it 100 times stronger than the surrounding field. The gradient of the electric field creates a phenomenon known as dielectrophoresis, or a force that pushes the cell against its motion induced by the electric field. As a result, dielectrophoresis can repel a particle or stop it in its tracks at different applied voltages, depending on that particle's surface properties.

Researchers including Buie have used dielectrophoresis to quickly sort bacteria according to general properties, such as size and species. This time around, Buie wondered whether the technique could suss out bacteria's electrochemical activity -- a far more subtle property.

"Basically, people were using dielectrophoresis to separate bacteria that were as different as, say, a frog from a bird, whereas we're trying to distinguish between frog siblings -- tinier differences," Wang says.

An electric correlation

In their new study, the researchers used their microfluidic setup to compare various strains of bacteria, each with a different, known electrochemical activity. The strains included a "wild-type" or natural strain of bacteria that actively produces electricity in microbial fuel cells, and several strains that the researchers had genetically engineered. In general, the team aimed to see whether there was a correlation between a bacteria's electrical ability and how it behaves in a microfluidic device under a dielectrophoretic force.

The team flowed very small, microliter samples of each bacterial strain through the hourglass-shaped microfluidic channel and slowly amped up the voltage across the channel, one volt per second, from 0 to 80 volts. Through an imaging technique known as particle image velocimetry, they observed that the resulting electric field propelled bacterial cells through the channel until they approached the pinched section, where the much stronger field acted to push back on the bacteria via dielectrophoresis and trap them in place.

Some bacteria were trapped at lower applied voltages, and others at higher voltages. Wang took note of the "trapping voltage" for each bacterial cell, measured their cell sizes, and then used a computer simulation to calculate a cell's polarizability -- how easy it is for a cell to form electric dipoles in response to an external electric field.

From her calculations, Wang discovered that bacteria that were more electrochemically active tended to have a higher polarizability. She observed this correlation across all species of bacteria that the group tested.

"We have the necessary evidence to see that there's a strong correlation between polarizability and electrochemical activity," Wang says. "In fact, polarizability might be something we could use as a proxy to select microorganisms with high electrochemical activity."

Wang says that, at least for the strains they measured, researchers can gauge their electricity production by measuring their polarizability -- something that the group can easily, efficiently, and nondestructively track using their microfluidic technique.

Collaborators on the team are currently using the method to test new strains of bacteria that have recently been identified as potential electricity producers.

"If the same trend of correlation stands for those newer strains, then this technique can have a broader application, in clean energy generation, bioremediation, and biofuels production," Wang says.

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3D printing 100 times faster with light

Rather than building up plastic filaments layer by layer, a new approach to 3D printing lifts complex shapes from a vat of liquid at up to 100 times faster than conventional 3D printing processes, University of Michigan researchers have shown.

3D printing could change the game for relatively small manufacturing jobs, producing fewer than 10,000 identical items, because it would mean that the objects could be made without the need for a mold costing upwards of $10,000. But the most familiar form of 3D printing, which is sort of like building 3D objects with a series of 1D lines, hasn't been able to fill that gap on typical production timescales of a week or two.

"Using conventional approaches, that's not really attainable unless you have hundreds of machines," said Timothy Scott, U-M associate professor of chemical engineering who co-led the development of the new 3D printing approach with Mark Burns, the T.C. Chang Professor of Engineering at U-M.

Their method solidifies the liquid resin using two lights to control where the resin hardens -- and where it stays fluid. This enables the team to solidify the resin in more sophisticated patterns. They can make a 3D bas-relief in a single shot rather than in a series of 1D lines or 2D cross-sections. Their printing demonstrations include a lattice, a toy boat and a block M.

"It's one of the first true 3D printers ever made," said Burns, professor of chemical engineering and biomedical engineering.

But the true 3D approach is no mere stunt -- it was necessary to overcome the limitations of earlier vat-printing efforts. Namely, the resin tends to solidify on the window that the light shines through, stopping the print job just as it gets started.

By creating a relatively large region where no solidification occurs, thicker resins -- potentially with strengthening powder additives -- can be used to produce more durable objects. The method also bests the structural integrity of filament 3D printing, as those objects have weak points at the interfaces between layers.

"You can get much tougher, much more wear-resistant materials," Scott said.

An earlier solution to the solidification-on-window problem was a window that lets oxygen through. The oxygen penetrates into the resin and halts the solidification near the window, leaving a film of fluid that will allow the newly printed surface to be pulled away.

But because this gap is only about as thick as a piece of transparent tape, the resin must be very runny to flow fast enough into the tiny gap between the newly solidified object and the window as the part is pulled up. This has limited vat printing to small, customized products that will be treated relatively gently, such as dental devices and shoe insoles.

By replacing the oxygen with a second light to halt solidification, the Michigan team can produce a much larger gap between the object and the window -- millimeters thick -- allowing resin to flow in thousands of times faster.

The key to success is the chemistry of the resin. In conventional systems, there is only one reaction. A photoactivator hardens the resin wherever light shines. In the Michigan system, there is also a photoinhibitor, which responds to a different wavelength of light.

Rather than merely controlling solidification in a 2D plane, as current vat-printing techniques do, the Michigan team can pattern the two kinds of light to harden the resin at essentially any 3D place near the illumination window.

U-M has filed three patent applications to protect the multiple inventive aspects of the approach, and Scott is preparing to launch a startup company.

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