Mission control: Salty diet makes you hungry, not thirsty

Salty snacks. Surprisingly, in the long run, a salty diet causes people to drink less.

Credit: © fotofabrika / Fotolia

New studies show that salty food diminishes thirst while increasing hunger, due to a higher need for energy

We've all heard it: eating salty foods makes you thirstier. But what sounds like good nutritional advice turns out to be not true in the long run. In a study carried out during a simulated mission to Mars, an international group of scientists has found exactly the opposite to be true. 'Cosmonauts' who ate more salt retained more water, weren't as thirsty, and needed more energy.

For some reason, no one had ever carried out a long-term study to determine the relationship between the amount of salt in a person's diet and his drinking habits. Scientists have known that increasing a person's salt intake stimulates the production of more urine -- it has simply been assumed that the extra fluid comes from drinking. Not so fast! say researchers from the German Aerospace Center (DLR), the Max Delbrück Center for Molecular Medicine (MDC), Vanderbilt University and colleagues around the world. Recently they took advantage of a simulated mission to Mars to put the old adage to the test. Their conclusions appear in two papers in the current issue of The Journal of Clinical Investigation.

What does salt have to do with Mars? Nothing, really, except that on a long space voyage conserving every drop of water might be crucial. A connection between salt intake and drinking could affect your calculations -- you wouldn't want an interplanetary traveler to die because he liked an occasional pinch of salt on his food. The real interest in the simulation, however, was that it provided an environment in which every aspect of a person's nutrition, water consumption, and salt intake could be controlled and measured.

The studies were carried out by Natalia Rakova (MD, PhD) of the Charité and MDC and her colleagues. The subjects were two groups of 10 male volunteers sealed into a mock spaceship for two simulated flights to Mars. The first group was examined for 105 days; the second over 205 days. They had identical diets except that over periods lasting several weeks, they were given three different levels of salt in their food.

The results confirmed that eating more salt led to a higher salt content in urine -- no surprise there. Nor was there any surprise in a correlation between amounts of salt and overall quantity of urine. But the increase wasn't due to more drinking -- in fact, a salty diet caused the subjects to drink less. Salt was triggering a mechanism to conserve water in the kidneys.

Before the study, the prevailing hypothesis had been that the charged sodium and chloride ions in salt grabbed onto water molecules and dragged them into the urine. The new results showed something different: salt stayed in the urine, while water moved back into the kidney and body. This was completely puzzling to Prof. Jens Titze, MD of the University of Erlangen and Vanderbilt University Medical Center and his colleagues. "What alternative driving force could make water move back?" Titze asked.

Experiments in mice hinted that urea might be involved. This substance is formed in muscles and the liver as a way of shedding nitrogen. In mice, urea was accumulating in the kidney, where it counteracts the water-drawing force of sodium and chloride. But synthesizing urea takes a lot of energy, which explains why mice on a high-salt diet were eating more. Higher salt didn't increase their thirst, but it did make them hungrier. Also the human "cosmonauts" receiving a salty diet complained about being hungry.

The project revises scientists' view of the function of urea in our bodies. "It's not solely a waste product, as has been assumed," Prof. Friedrich C. Luft, MD of the Charité and MDC says. "Instead, it turns out to be a very important osmolyte -- a compound that binds to water and helps transport it. Its function is to keep water in when our bodies get rid of salt. Nature has apparently found a way to conserve water that would otherwise be carried away into the urine by salt."

The new findings change the way scientists have thought about the process by which the body achieves water homeostasis -- maintaining a proper amount and balance. That must happen whether a body is being sent to Mars or not. "We now have to see this process as a concerted activity of the liver, muscle and kidney," says Jens Titze.

"While we didn't directly address blood pressure and other aspects of the cardiovascular system, it's also clear that their functions are tightly connected to water homeostasis and energy metabolism."

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Policymakers 'flying blind' into the future of work

New kinds of data needed to assess technology's impact on jobs

Will a robot take away my job? Many people ask that question, yet policymakers don't have the kind of information they need to answer it intelligently, say the authors of a new study.

Will a robot take away my job? Many people ask that question, yet policymakers don't have the kind of information they need to answer it intelligently, say the authors of a new study from the National Academies of Sciences, Engineering and Medicine (NASEM).

"Policymakers are flying blind into what has been called the fourth industrial revolution," said Tom M. Mitchell, the E. Fredkin University Professor in the Carnegie Mellon University School of Computer Science, and Erik Brynjolfsson, the Schussel Family Professor in the MIT Sloan School of Management, co-chairs of the NASEM study.

Government agencies need to collect different kinds of labor data to accurately assess and predict how computer and robotic technologies will affect the workplace, Mitchell and Brynjolfsson said. Failure to do so could, at best, result in missed opportunities; at worst, it could be disastrous.

The study, "Information Technology and the U.S. Workforce: Where Are We and Where Do We Go From Here," and a related commentary by Mitchell and Brynjolfsson was published today by the journal Nature.

Information technology, artificial intelligence and robotics will affect almost all occupations, but how that will occur for each is unclear. Many people will be displaced by technology, while the demand for other jobs will increase. New industries will be born and other as-yet-unimagined jobs will be created.

These future effects likely will be larger than have already been seen, the NASEM report says, but it's hard to say definitively if technology will expand or shrink the workforce.

"There is a dramatic shortage of information and data about the exact state of the workforce and automation, so policymakers don't know answers to even basic questions such as 'Which types of technologies are currently having the greatest impacts on jobs?' and 'What new technologies are likely to have the greatest impact in the next few years?'" Mitchell said.

"Our NASEM study report details a number of both positive and negative influences technology has had on the workforce," Mitchell said. "These include replacing some jobs by automation, creating the opportunity for new types of freelance work in companies like Uber and Lyft, and making education and retraining courses available to everyone through the internet. But nobody can judge today the relative impact these different forces have made on the workforce, or their net outcome."

More research is needed to better understand these different influences of technology on the workforce, and how they will add up. Automation is better than humans at some tasks, but not all. Routine information-processing and manual tasks are readily automated, for instance, but people remain more creative and adaptable, and have better interpersonal skills. Some occupations may be reorganized accordingly and some skills that today aren't recognized or directly compensated may grow in value.

The NASEM panel recommended that to prepare students for a constantly changing workforce, schools should focus attention on those uniquely human characteristics that could differentiate people from machines in the workplace, and emphasize training in fields expected to drive the future economy.

The panel said new data sources, methods and infrastructures are necessary to support this research. In their Naturecommentary, Mitchell and Brynjolfsson go further, calling for the government to create an integrated information strategy to combine public and privately held data.

"Governments must learn the lessons that industry has learned over the past decade, about how to take advantage of the exploding volume of online, real-time data to design more attractive products and more effective management policies," Mitchell said.

Similarly, he and Brynjolfsson argue, governments must shift from the current "plan then implement" paradigm for making policy, to a more iterative "sense and respond" paradigm that monitors the impacts of new policies, measures their effectiveness and adapts to optimize those policies based on their observed impacts.

Report: https://www.nap.edu/catalog/24649/information-technology-and-the-us-workforce-where-are-we-and

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Is soda bad for your brain? (And is diet soda worse?)

Matthew Pase is lead author on two studies that link higher consumption of both sugary and artificially sweetened drinks to adverse brain effects.

Credit: Cydney Scott

Both sugary, diet drinks correlated with accelerated brain aging

Excess sugar -- especially the fructose in sugary drinks -- might damage your brain, new research suggests. Researchers found that people who drink sugary beverages frequently are more likely to have poorer memory, smaller overall brain volume, and a significantly smaller hippocampus. A follow-up study found that people who drank diet soda daily were almost three times as likely to develop stroke and dementia when compared to those who did not.

Americans love sugar. Together we consumed nearly 11 million metric tons of it in 2016, according to the US Department of Agriculture, much of it in the form of sugar-sweetened beverages like sports drinks and soda.

Now, new research suggests that excess sugar -- especially the fructose in sugary drinks -- might damage your brain. Researchers using data from the Framingham Heart Study (FHS) found that people who drink sugary beverages frequently are more likely to have poorer memory, smaller overall brain volume, and a significantly smaller hippocampus -- an area of the brain important for learning and memory.

But before you chuck your sweet tea and reach for a diet soda, there's more: a follow-up study found that people who drank diet soda daily were almost three times as likely to develop stroke and dementia when compared to those who did not.

Researchers are quick to point out that these findings, which appear separately in the journals Alzheimer's & Dementia and Stroke, demonstrate correlation but not cause-and-effect. While researchers caution against over-consuming either diet soda or sugary drinks, more research is needed to determine how -- or if -- these drinks actually damage the brain, and how much damage may be caused by underlying vascular disease or diabetes.

"These studies are not the be-all and end-all, but it's strong data and a very strong suggestion," says Sudha Seshadri, a professor of neurology at Boston University School of Medicine (MED) and a faculty member at BU's Alzheimer's Disease Center, who is senior author on both papers. "It looks like there is not very much of an upside to having sugary drinks, and substituting the sugar with artificial sweeteners doesn't seem to help."

"Maybe good old-fashioned water is something we need to get used to," she adds.

Matthew Pase, a fellow in the MED neurology department and an investigator at the FHS who is corresponding author on both papers, says that excess sugar has long been associated with cardiovascular and metabolic diseases like obesity, heart disease, and type 2 diabetes, but little is known about its long-term effects on the human brain. He chose to study sugary drinks as a way of examining overall sugar consumption. "It's difficult to measure overall sugar intake in the diet," he says, "so we used sugary beverages as a proxy."

For the first study, published in Alzheimer's & Dementia on March 5, 2017, researchers examined data, including magnetic resonance imaging (MRI) scans and cognitive testing results, from about 4,000 people enrolled in the Framingham Heart Study's Offspring and Third-Generation cohorts. (These are the children and grandchildren of the original FHS volunteers enrolled in 1948.) The researchers looked at people who consumed more than two sugary drinks a day of any type -- soda, fruit juice, and other soft drinks -- or more than three per week of soda alone. Among that "high intake" group, they found multiple signs of accelerated brain aging, including smaller overall brain volume, poorer episodic memory, and a shrunken hippocampus, all risk factors for early-stage Alzheimer's disease. Researchers also found that higher intake of diet soda -- at least one per day -- was associated with smaller brain volume.

In the second study, published in Stroke on April 20, 2017, the researchers, using data only from the older Offspring cohort, looked specifically at whether participants had suffered a stroke or been diagnosed with dementia due to Alzheimer's disease. After measuring volunteers' beverage intake at three points over seven years, the researchers then monitored the volunteers for 10 years, looking for evidence of stroke in 2,888 people over age 45, and dementia in 1,484 participants over age 60. Here they found, surprisingly, no correlation between sugary beverage intake and stroke or dementia. However, they found that people who drank at least one diet soda per day were almost three times as likely to develop stroke and dementia.

Although the researchers took age, smoking, diet quality, and other factors into account, they could not completely control for preexisting conditions like diabetes, which may have developed over the course of the study and is a known risk factor for dementia. Diabetics, as a group, drink more diet soda on average, as a way to limit their sugar consumption, and some of the correlation between diet soda intake and dementia may be due to diabetes, as well as other vascular risk factors. However, such preexisting conditions cannot wholly explain the new findings.

"It was somewhat surprising that diet soda consumption led to these outcomes," says Pase, noting that while prior studies have linked diet soda intake to stroke risk, the link with dementia was not previously known. He adds that the studies did not differentiate between types of artificial sweeteners and did not account for other possible sources of artificial sweeteners. He says that scientists have put forth various hypotheses about how artificial sweeteners may cause harm, from transforming gut bacteria to altering the brain's perception of "sweet," but "we need more work to figure out the underlying mechanisms."

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Genetics, environment combine to give everyone a unique sense of smell

Genetically identical mice exposed to different smells as they grow up develop different olfactory receptors in their noses.Credit: © Marion Wear / Fotolia

Genetically identical mice develop different smell receptors in response to their environments.

Receptors in the noses of mice exposed to certain smells during life are different to genetically similar mice that lived without those smells, new research shows. The study found it is this combination of genetics and experience that gives each individual a unique sense of smell.

Researchers from the Wellcome Trust Sanger Institute and their collaborators have shown that receptors in the noses of mice exposed to certain smells during life are different to genetically similar mice that lived without those smells. Published today in eLife, the study found it is this combination of genetics and experience that gives each individual a unique sense of smell.

Our sense of smell comes from the olfactory organ in the nose, which is made up of sensory neurons containing receptors that can detect odours. There are about one thousand types of olfactory receptors in the nose, compared with only three types of visual receptors in the eye, and 49 types of taste receptors on the tongue. Of our senses, the olfactory system is the most complex, and combinations of signals from different olfactory receptors allow people to smell an enormously large repertoire of odours. However, how different people vary in their smelling abilities is not well understood.

To investigate the sense of smell the researchers used laboratory mice as a model, comparing the olfactory neurons from genetically identical animals that grew up in different environments. They also compared animals that grew up in the same environment but were genetically different.

The team used RNA sequencing to see which receptor genes were active. The researchers found that genetics controlled which receptors were present in the mice. Crucially however, they found that the environment that the individual had lived in had a significant effect on the number of cells able to identify each smell.

Professor Fabio Papes, an author on the paper from the University of Campinas in Brazil, said: "It became clear that the role of genes, especially those that encode olfactory receptors in the genome, is very important in the construction of nasal tissue, but there was a very remarkable contribution of the environment, something that has not been previously described to this extent. We found the cellular and molecular construction of the olfactory tissue at a given moment is prepared not only by the organism's genes but also by its life history."

Olfactory neurons are formed throughout an individual's lifetime, and the study showed the olfactory system adapted to the environment, leading to more cells capable of detecting scents to which there has been greater exposure. As a consequence, different individuals, even if genetically similar, may have completely different olfactory abilities. This could contribute to the individuality of the sense of smell, even in humans.

The knowledge that an individual's history can affect the structure of olfactory tissue neurons may have implications for personalised medicine as different people's sense organs could be constructed differently and respond in different ways. Studying olfactory neurons can also provide information about how the neurons in the brain are organised and function.

Dr Darren Logan, the lead author on the study from the Wellcome Trust Sanger Institute, said: "The neurons in the olfactory system are highly connected to the neurons in the brain and studying these can help us understand neuronal development. We have shown that each individual has a very different combination of possible olfactory neurons, driven by genetics. In this study we also show that, with experience of different smells, these combinations of neurons change, so both genetics and environment interplay to give every individual a unique sense of smell."

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Macrophages conduct electricity, help heart to beat

The image shows a volumetric reconstruction of a human atrioventricular node. Cardiomyocytes (red) appear densely interspersed with macrophages (green).

Credit: Maarten Hulsmans & Matthias Nahrendorf

Macrophages have a previously unrecognized role in helping the mammalian heart beat in rhythm. Researchers have discovered that macrophages aggregate around central cardiac cells that regulate electrical impulses within the mouse heart, helping the cells conduct electricity. Mice that were genetically engineered to lack macrophages have irregular heartbeats, hinting that these immune cells may also play a role in heart disease.

Macrophages, immune cells known for their PAC-MAN-like ingestion of microbial intruders and biological waste, have a previously unrecognized role in helping the mammalian heart beat in rhythm. Massachusetts General Hospital researchers discovered that macrophages aggregate around central cardiac cells that regulate electrical impulses within the mouse heart, helping the cells conduct electricity. Mice that were genetically engineered to lack macrophages have irregular heartbeats, hinting that these immune cells may also play a role in heart disease. The findings appear April 20 in the journal Cell.

"This work opens up a completely new view on electrophysiology; now, we have a new cell type on the map that is involved in conduction," says senior author Matthias Nahrendorf, a systems biologist at Massachusetts General Hospital, Harvard Medical School. "Macrophages are famous for sensing their environment and changing their phenotype very drastically, so you can think about a situation where there is inflammation in the heart that may alter conduction, and we now need to look at whether these cells are causally involved in conduction abnormalities."

Researchers have known for decades that macrophages are in high abundance around inflamed or diseased hearts, but Nahrendorf's investigation began when he asked what the immune cells were doing in a healthy heart. After sending a mouse model depleted of macrophages for a heart MRI and electrocardiogram, the technician reported back that something was wrong; the mouse's heart was beating too slowly. Tests in a healthy rodent revealed a high density of resident macrophages at the heart's atrioventricular node, which passes electricity from the atria to the ventricles.

Nahrendorf showed the results to his colleagues, David Milan and Patrick Ellinor, both electrophysiologists at Massachusetts General Hospital, who responded by opening the doors to their labs. Together, the teams found that macrophages extend their cell membranes between cardiac cells and create pores, also called gap junctions, for the electrical current to flow through. The macrophages contribute by preparing the conducting heart cells for the next burst of electricity so conducting cells are able to keep up with a fast contraction rhythm.

"When we got the first patch clamp data that showed the macrophages in contact with cardiomyoctes were rhythmically depolarizing, that was the moment I realized they weren't insulating, but actually helping to conduct," Nahrendorf says. "This work was very exciting because it was an example of how team science can help to connect fields that are traditionally separated -- in this case, immunology and electrophysiology."

The group will follow up by looking at whether macrophages are involved in common conduction abnormalities. There are also potential connections between macrophages and anti-inflammatory drugs, which are widely reported to help with heart disease. If macrophages do play a role in disease, the researchers say it can open up a new line of therapeutics, as these immune cells naturally consume foreign molecules in their presence and are easy to target as a result.

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Water is streaming across Antarctica

New survey finds liquid flow more widespread than thought

In the first such continent-wide survey, scientists have found extensive drainages of meltwater flowing over parts of Antarctica's ice during the brief summer.

In the first such continent-wide survey, scientists have found extensive drainages of meltwater flowing over parts of Antarctica's ice during the brief summer. Researchers already knew such features existed, but assumed they were confined mainly to Antarctica's fastest-warming, most northerly reaches. Many of the newly mapped drainages are not new, but the fact they exist at all is significant; they appear to proliferate with small upswings in temperature, so warming projected for this century could quickly magnify their influence on sea level. An accompanying study looks at how such systems might influence the great ice shelves ringing the continent, which some researchers fear could collapse, bringing catastrophic sea-level rises. Both studies appear this week in the leading scientific journal Nature.

Explorers and scientists have documented a few Antarctic melt streams starting in the early 20th century, but no one knew how extensive they were. The authors found out by systematically cataloging images of surface water in photos taken from military aircraft from 1947 onward, and satellite imagery from 1973 on. They found nearly 700 seasonal systems of interconnected ponds, channels and braided streams fringing the continent on all sides. Some run as far as 75 miles, with ponds up to several miles wide. They start as close as 375 miles from the South Pole, and at 4,300 feet above sea level, where liquid water was generally thought to be rare to impossible.

"This is not in the future -- this is widespread now, and has been for decades," said lead author Jonathan Kingslake, a glaciologist at Columbia University's Lamont-Doherty Earth Observatory. "I think most polar scientists have considered water moving across the surface of Antarctica to be extremely rare. But we found a lot of it, over very large areas." The data are too sparse in many locations for the researchers to tell whether the extent or number of drainages have increased over the seven decades covered by the study. "We have no reason to think they have," said Kingslake. "But without further work, we can't tell. Now, looking forward, it will be really important to work out how these systems will change in response to warming, and how this will affect the ice sheets."

Many of the newly mapped drainages start near mountains poking through glaciers, or in areas where powerful winds have scoured snow off underlying bluish ice. These features are darker than the mostly snow-covered ice sheet, and so absorb more solar energy. This causes melting, and on a slope, liquid water then melts a path downhill through overlying snow. If the continent warms this century as projected, this process will occur on a much larger scale, say the authors. "This study tells us there's already a lot more melting going on than we thought," said coauthor Robin Bell, a Lamont-Doherty polar scientist. "When you turn up the temperature, it's only going to increase."

Antarctica is already losing ice, but the direct effects of meltwater, which generally refreezes in winter, are probably negligible for now. The concern among glaciologists is that this could change in the future. Most loss right now is taking place near the edges, where giant, floating shelves of ice attached to the land are being eroded from underneath by warming ocean currents. The shelves, which ring three-quarters of Antarctica, help hold back the land-bound glaciers behind them, and as they lose mass, glaciers appear to be accelerating their march to the sea.

The most dramatic example is the Antarctic Peninsula, which juts far north from the main ice sheet, and where average temperatures have soared 7 degrees Fahrenheit in the last 50 years. In 1995 and 2002, large chunks of the peninsula's Larsen Ice Shelf suddenly disintegrated into the ocean within days. Scientists now suspect that pooling water was at work; liquid tends to burrow down, fracturing the ice with heat or pressure, or both, until a shattering point is reached. Today, another giant piece of the Larsen is cracking, and could come apart at any time.

Further south, temperatures have remained more or less stable, but many of the newly spotted streams there already make their way from the interior out onto ice shelves, or originate on the shelves themselves. That raises the specter that such collapses could happen across much vaster reaches of Antarctica this century, should warming proceed as expected, said Kingslake.

On the other hand, an accompanying study led by Bell found that a longtime drainage on West Antarctica's Nansen Ice Shelf may actually be helping keep the shelf together. The elaborate river-like system on the 30-mile-long shelf was first observed in 1909, by a team from the expedition led by British explorer Ernest Shackleton. Aerial imagery and remote sensing since then shows it has remained remarkably stable, efficiently draining excess meltwater during summer through a series of deep sinkholes and a roaring 400-foot-wide waterfall into the ocean. "It could develop this way in other places, or things could just devolve into giant slush puddles," said Bell. "Ice is dynamic and complex, and we don't have the data yet."

Near the other pole, seasonal melt streams and ponds are far more common on the fast-warming Greenland ice sheet, and their growing influence may hold lessons. In recent years as much as 90 percent of Greenland's ice surface has undergone some degree of seasonal melting. Much of the water probably stays at or near the surface and refreezes in winter. But in some areas, it is plunging through deep holes to underlying rock, lubricating glaciers' slide to the sea. In others, water may be refreezing near the surface into solid sheets that can more easily channel surface melt to the sea in succeeding seasons. Until recently, icebergs discharged from glaciers were Greenland's main contributor to sea-level rise. But between 2011 and 2014, 70 percent of the 269 million tons of Greenland's ice and snow lost to the ocean came directly from meltwater, not icebergs.

Antarctica's visible drainages may be the tip of the proverbial iceberg. Another study by a separate team published in January revealed that East Antarctica's Roi Baudouin Ice Shelf harbors a largely invisible liquid drainage just under the snow. The team, led by Utrecht University polar scientist Jan Lenaerts, detected it using radar images and drilling. They suspect that such features lurk in many places. And unlike surface streams, these ones are insulated, so may stay liquid year-round.

Helen Fricker, a glaciologist at Scripps Institution of Oceanography who was not involved the new studies, said of the continent-wide survey, "We knew there were other [melt] zones, but we didn't know exactly how extensive they are. This is a really nice study, as it does just that." Douglas MacAyeal, a glaciologist at the University of Chicago also not involved in the studies, said that until recently, "nobody's been that interested in melting," because most scientists thought it was relatively rare. Now, he said, "We're working hard to figure out if this stuff is relevant to sea-level predictions."

Video: https://www.youtube.com/watch?v=dAOBbXQys78

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Naked mole-rats 'turn into plants' when oxygen is low

Ignore the whiskers and teeth -- these are plants.

Credit: Thomas Park/UIC

Discovery could lead to treatments for heart attack, stroke

Deprived of oxygen, naked mole-rats can survive by metabolizing fructose just as plants do -- a finding that could lead to treatments for heart attacks and strokes.

Deprived of oxygen, naked mole-rats can survive by metabolizing fructose just as plants do, researchers report this week in the journal Science.

Understanding how the animals do this could lead to treatments for patients suffering crises of oxygen deprivation, as in heart attacks and strokes.

"This is just the latest remarkable discovery about the naked mole-rat -- a cold-blooded mammal that lives decades longer than other rodents, rarely gets cancer, and doesn't feel many types of pain," says Thomas Park, professor of biological sciences at the University of Illinois at Chicago, who led an international team of researchers from UIC, the Max Delbrück Institute in Berlin and the University of Pretoria in South Africa on the study.

In humans, laboratory mice, and all other known mammals, when brain cells are starved of oxygen they run out of energy and begin to die.

But naked mole-rats have a backup: their brain cells start burning fructose, which produces energy anaerobically through a metabolic pathway that is only used by plants -- or so scientists thought.

In the new study, the researchers exposed naked mole-rats to low oxygen conditions in the laboratory and found that they released large amounts of fructose into the bloodstream. The fructose, the scientists found, was transported into brain cells by molecular fructose pumps that in all other mammals are found only on cells of the intestine.

"The naked mole-rat has simply rearranged some basic building-blocks of metabolism to make it super-tolerant to low oxygen conditions," said Park, who has studied the strange species for 18 years.

At oxygen levels low enough to kill a human within minutes, naked mole-rats can survive for at least five hours, Park said. They go into a state of suspended animation, reducing their movement and dramatically slowing their pulse and breathing rate to conserve energy. And they begin using fructose until oxygen is available again.

The naked mole-rat is the only known mammal to use suspended animation to survive oxygen deprivation.

The scientists also showed that naked mole-rats are protected from another deadly aspect of low oxygen -- a buildup of fluid in the lungs called pulmonary edema that afflicts mountain climbers at high altitude.

The scientists think that the naked mole-rats' unusual metabolism is an adaptation for living in their oxygen-poor burrows. Unlike other subterranean mammals, naked mole-rats live in hyper-crowded conditions, packed in with hundreds of colony mates. With so many animals living together in unventilated tunnels, oxygen supplies are quickly depleted.

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Research uses mirrors to make solar energy cost competitive

Concentrating solar power technologies use mirrors to reflect and concentrate sunlight to produce heat, which can then be used to produce electricity, according to ongoing work by mechanical engineers. These technologies present a distinct advantage over photovoltaic (PV) cells in their ability to store the sun’s energy as thermal energy, experts say.

If the current national challenge to make solar energy cost competitive with other forms of energy by the end of this decade is met, Ranga Pitchumani, the John R. Jones III Professor of Mechanical Engineering at Virginia Tech, will have played a significant role in the process.

U.S. Secretary of Energy Steven Chu announced the Department of Energy's SunShot Initiative in February 2011. Its objective was to reduce the installed cost of solar energy systems by about 75 percent in order to allow widespread, large-scale adoption of this renewable clean energy technology.

Following the announcement, Pitchumani was invited to direct the Concentrating Solar Power (CSP) program for the SunShot Initiative towards its ambitious goals.

"The SunShot goal is to get solar energy technologies to achieve cost-parity with other energy generation sources on the grid without subsidy by the year 2020. That's an aggressive mission which calls for several subcomponent innovations and ingenious system designs to drive costs down, while improving efficiencies," said Pitchumani.

"Concentrating solar power technologies use mirrors to reflect and concentrate sunlight to produce heat, which can then be used to produce electricity," Pitchumani explained. These technologies present a distinct advantage over photovoltaic (PV) cells in their ability to store the sun's energy as thermal energy, and represent a subset of the SunShot Initiative. Pitchumani is a leading expert in the field of concentrating solar power. He and his research group at Virginia Tech have developed novel thermal energy storage technologies for concentrating solar power applications that are widely published. He is the overall conference chair for SolarPACES 2013 this year, the foremost international meeting in the area of concentrating solar power systems, and is an editor for Solar Energy.

"Fossil fueled power plants pose a potential risk to the environment through an increased carbon footprint, and my efforts are in supplanting fossil energy with renewable sources including solar energy. Concentrating solar power plants capture the solar energy and store it as heat, which can, in turn, be used to drive a turbine and produce electricity. In fact, studies have shown that CSP with thermal energy storage also facilitates greater incorporation of other renewables such as wind and photovoltaic on the grid. That's a win-win on all fronts," Pitchumani said.

"Due to the intermittent nature of solar energy availability, it is often desirable to store thermal energy from a concentrating solar power plant for use on demand, including at times when solar energy is unavailable such as during cloud cover or overnight. Energy can be stored either as sensible heat (in solid or molten media), latent heat (using phase change materials), or as products of a thermochemical process, of which latent heat and thermochemical storage offer high volumetric energy density and potentially high power cycle efficiency, provided costs can be tamed," he added.

In his role, Pitchumani oversees a team of several program managers, technical, financial and support personnel, who actively manage the awards in the portfolio. During his leadership, the SunShot Concentrating Solar Power Program has launched over $130 million in new funding initiatives since October 2011. Combined with the awards continuing from prior funding opportunities, the program maintains an appropriately balanced portfolio of projects at industry, national laboratories, and universities dedicated to applied scientific research, development and demonstration to advance cutting edge concentrating solar power technologies for the near-, mid- and long-terms.

Concentrating solar power plants could provide for low-cost energy generation and have the potential to become the leading source of renewable energy for future power generation. In the U.S., several large-scale commercial plants (e.g., Ivanpah Solar Electric Generating Station (SEGS), Crescent Dunes Solar Energy Project, and Abengoa Solana Generating Station) are currently under construction, with some getting ready to be commissioned starting in a few months, that would more than triple the total capacity of Concentrating Solar Power-generated electricity to about 1.8 gigawatt and place the U.S. as one of the global leaders in CSP capacity.

On a worldwide scale, studies suggest that concentrating solar power technology systems could provide approximately one-quarter of the global electricity needs by 2050, Pitchumani said.

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Bubble-wrapped sponge creates steam using sunlight

MIT graduate student George Ni holds a bubble-wrapped, sponge-like device that soaks up natural sunlight and heats water to boiling temperatures, generating steam through its pores.

Credit: Jeremy Cho

Date:

August 22, 2016

Source:

Massachusetts Institute of Technology

Bubble-wrapped structure requires no mirrors or lenses to focus the sun's heat

How do you boil water? Eschewing the traditional kettle and flame, engineers have invented a bubble-wrapped, sponge-like device that soaks up natural sunlight and heats water to boiling temperatures, generating steam through its pores. The design, which the researchers call a 'solar vapor generator,' requires no expensive mirrors or lenses to concentrate the sunlight, but instead relies on a combination of relatively low-tech materials to capture ambient sunlight and concentrate it as heat.

The design, which the researchers call a "solar vapor generator," requires no expensive mirrors or lenses to concentrate the sunlight, but instead relies on a combination of relatively low-tech materials to capture ambient sunlight and concentrate it as heat. The heat is then directed toward the pores of the sponge, which draw water up and release it as steam.

From their experiments -- including one in which they simply placed the solar sponge on the roof of MIT's Building 3 -- the researchers found the structure heated water to its boiling temperature of 100 degrees Celsius, even on relatively cool, overcast days. The sponge also converted 20 percent of the incoming sunlight to steam.

The low-tech design may provide inexpensive alternatives for applications ranging from desalination and residential water heating, to wastewater treatment and medical tool sterilization.

The team has published its results today in the journal Nature Energy. The research was led by George Ni, an MIT graduate student; and Gang Chen, the Carl Richard Soderberg Professor in Power Engineering and the head of the Department of Mechanical Engineering; in collaboration with TieJun Zhang and his group members Hongxia Li and Weilin Yang from the Department of Mechanical and Materials Engineering at the Masdar Institute of Science and Technology, in the United Arab Emirates.

Building up the sun

The researchers' current design builds on a solar-absorbing structure they developed in 2014 -- a similar floating, sponge-like material made of graphite and carbon foam, that was able to boil water to 100 C and convert 85 percent of the incoming sunlight to steam.

To generate steam at such efficient levels, the researchers had to expose the structure to simulated sunlight that was 10 times the intensity of sunlight in normal, ambient conditions.

"It was relatively low optical concentration," Chen says. "But I kept asking myself, 'Can we basically boil water on a rooftop, in normal conditions, without optically concentrating the sunlight? That was the basic premise."

In ambient sunlight, the researchers found that, while the black graphite structure absorbed sunlight well, it also tended to radiate heat back out into the environment. To minimize the amount of heat lost, the team looked for materials that would better trap solar energy.

A bubbly solution

In their new design, the researchers settled on a spectrally-selective absorber -- a thin, blue, metallic-like film that is commonly used in solar water heaters and possesses unique absorptive properties. The material absorbs radiation in the visible range of the electromagnetic spectrum, but it does not radiate in the infrared range, meaning that it both absorbs sunlight and traps heat, minimizing heat loss.

The researchers obtained a thin sheet of copper, chosen for its heat-conducting abilities and coated with the spectrally-selective absorber. They then mounted the structure on a thermally-insulating piece of floating foam. However, they found that even though the structure did not radiate much heat back out to the environment, heat was still escaping through convection, in which moving air molecules such as wind would naturally cool the surface.

A solution to this problem came from an unlikely source: Chen's 16-year-old daughter, who at the time was working on a science fair project in which she constructed a makeshift greenhouse from simple materials, including bubble wrap.

"She was able to heat it to 160 degrees Fahrenheit, in winter!" Chen says. "It was very effective."

Chen proposed the packing material to Ni, as a cost-effective way to prevent heat loss by convection. This approach would let sunlight in through the material's transparent wrapping, while trapping air in its insulating bubbles.

"I was very skeptical of the idea at first," Ni recalls. "I thought it was not a high-performance material. But we tried the clearer bubble wrap with bigger bubbles for more air trapping effect, and it turns out, it works. Now because of this bubble wrap, we don't need mirrors to concentrate the sun."

The bubble wrap, combined with the selective absorber, kept heat from escaping the surface of the sponge. Once the heat was trapped, the copper layer conducted the heat toward a single hole, or channel, that the researchers had drilled through the structure. When they placed the sponge in water, they found that water crept up the channel, where it was heated to 100 C, then turned to steam.

Chen and Ni say that solar absorbers based on this general design could be used as large sheets to desalinate small bodies of water, or to treat wastewater. Ni says other solar-based technologies that rely on optical-concentrating technologies typically are designed to last 10 to 20 years, though they require expensive parts and maintenance. This new, low-tech design, he says, could operate for one to two years before needing to be replaced.

"Even so, the cost is pretty competitive," Ni says. "It's kind of a different approach, where before, people were doing high-tech and long-term [solar absorbers]. We're doing low-tech and short-term."

"What fascinates us is the innovative idea behind this inexpensive device, where we have creatively designed this device based on basic understanding of capillarity and solar thermal radiation. Meanwhile, we are excited to continue probing the complicated physics of solar vapor generation and to discover new knowledge for the scientific community," Zhang says.

This research was funded, in part, by a cooperative agreement between the Masdar Institute of Science and Technology; and by the Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center funded by U.S. Department of Energy.

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Device pulls water from dry air, powered only by the sun

This is the water harvester built at MIT with MOFs from UC Berkeley. Using only sunlight, the harvester can pull liters of water from low-humidity air over a 12-hour period.

Credit: MIT photo from laboratory of Evelyn Wang

Metal-organic framework sucks up water from air with humidity as low as 20 percent

While it's easy to condense water from humid air, machines that harvest water from drier air require energy. Researchers have created the first water harvester that uses only ambient sunlight. The key component is an extremely porous material called a metal-organic framework that absorbs 20 percent of its weight in water from low-humidity air. Sunlight heats the MOF, releasing the water vapor, which condenses to produce liters of water per day.

Imagine a future in which every home has an appliance that pulls all the water the household needs out of the air, even in dry or desert climates, using only the power of the sun.

That future may be around the corner, with the demonstration this week of a water harvester that uses only ambient sunlight to pull liters of water out of the air each day in conditions as low as 20 percent humidity, a level common in arid areas.

The solar-powered harvester, reported in the journal Science, was constructed at the Massachusetts Institute of Technology using a special material -- a metal-organic framework, or MOF -- produced at the University of California, Berkeley.

"This is a major breakthrough in the long-standing challenge of harvesting water from the air at low humidity," said Omar Yaghi, one of two senior authors of the paper, who holds the James and Neeltje Tretter chair in chemistry at UC Berkeley and is a faculty scientist at Lawrence Berkeley National Laboratory. "There is no other way to do that right now, except by using extra energy. Your electric dehumidifier at home 'produces' very expensive water."

The prototype, under conditions of 20-30 percent humidity, was able to pull 2.8 liters (3 quarts) of water from the air over a 12-hour period, using one kilogram (2.2 pounds) of MOF. Rooftop tests at MIT confirmed that the device works in real-world conditions.

"One vision for the future is to have water off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household," said Yaghi, who is the founding director of the Berkeley Global Science Institute, a co-director of the Kavli Energy NanoSciences Institute and the California Research Alliance by BASF. "To me, that will be made possible because of this experiment. I call it personalized water."

Yaghi invented metal-organic frameworks more than 20 years ago, combining metals like magnesium or aluminum with organic molecules in a tinker-toy arrangement to create rigid, porous structures ideal for storing gases and liquids. Since then, more than 20,000 different MOFs have been created by researchers worldwide. Some hold chemicals such as hydrogen or methane: the chemical company BASF is testing one of Yaghi's MOFs in natural gas-fueled trucks, since MOF-filled tanks hold three times the methane that can be pumped under pressure into an empty tank.

Other MOFs are able to capture carbon dioxide from flue gases, catalyze the reaction of adsorbed chemicals or separate petrochemicals in processing plants.

In 2014, Yaghi and his UC Berkeley team synthesized a MOF -- a combination of zirconium metal and adipic acid -- that binds water vapor, and he suggested to Evelyn Wang, a mechanical engineer at MIT, that they join forces to turn the MOF into a water-collecting system.

The system Wang and her students designed consisted of more than two pounds of dust-sized MOF crystals compressed between a solar absorber and a condenser plate, placed inside a chamber open to the air. As ambient air diffuses through the porous MOF, water molecules preferentially attach to the interior surfaces. X-ray diffraction studies have shown that the water vapor molecules often gather in groups of eight to form cubes.

Sunlight entering through a window heats up the MOF and drives the bound water toward the condenser, which is at the temperature of the outside air. The vapor condenses as liquid water and drips into a collector.

"This work offers a new way to harvest water from air that does not require high relative humidity conditions and is much more energy efficient than other existing technologies," Wang said.

This proof of concept harvester leaves much room for improvement, Yaghi said. The current MOF can absorb only 20 percent of its weight in water, but other MOF materials could possibly absorb 40 percent or more. The material can also be tweaked to be more effective at higher or lower humidity levels.

"It's not just that we made a passive device that sits there collecting water; we have now laid both the experimental and theoretical foundations so that we can screen other MOFs, thousands of which could be made, to find even better materials," he said. "There is a lot of potential for scaling up the amount of water that is being harvested. It is just a matter of further engineering now."

Yaghi and his team are at work improving their MOFs, while Wang continues to improve the harvesting system to produce more water.

"To have water running all the time, you could design a system that absorbs the humidity during the night and evolves it during the day," he said. "Or design the solar collector to allow for this at a much faster rate, where more air is pushed in. We wanted to demonstrate that if you are cut off somewhere in the desert, you could survive because of this device. A person needs about a Coke can of water per day. That is something one could collect in less than an hour with this system."

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Super sensitive devices work on recycling atoms

Next-generation sensors to be used in fields as diverse as mineral exploration and climate change will be turbo boosted thanks to new research. Theoretical physicists said future precision sensing technology would exploit unusual effects of quantum mechanics.

Theoretical physicist Dr Stuart Szigeti, of UQ's School of Mathematics and Physics, said future precision sensing technology would exploit unusual effects of quantum mechanics.

"Our research showed a way to recycle atoms and reuse them in a device called an atom interferometer," Dr Szigeti said.

"This technique will vastly improve the performance of these devices, leading to improved sensing technology.

"An atom interferometer uses the quantum 'wave-like' nature of atoms in order to make very precise measurements of accelerations, rotations, and gravitational fields"

Dr Szigeti, who works within one of five nodes of the Australian Research Council Centre for Engineered Quantum Systems, said the devices would have applications on land and sea.

"They can be used in mineral exploration, allowing us to more easily locate mineral reserves underground, and in hydrology, allowing us to track the movement of water across the planet as we monitor the effects of climate change," he said.

"They'll also be important in navigation."

Dr Simon Haine, from the University of Sussex, said the development of precise atom interferometers had been hampered by an effect known as quantum noise, which was uncertainty in a quantum system signal.

"Quantum noise can be combatted with a property of quantum mechanics known as 'entanglement'," he said.

"Proof-of-principle experiments have recently shown how to generate entanglement within atom interferometers, and have used this to alleviate the effects of quantum noise.

"However, this comes at a cost, as in the process of creating entanglement, most of the atoms are wasted, which hinders the performance of these devices.

"Our project has found a way to harvest and recycle these atoms to improve the sensitivity of ultra-precise measurement devices."

The research, involving Dr Szigeti, Dr Haine and colleague Dr Robert Lewis-Swan from UQ, has been published in Physical Review Letters.

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