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Piranha-Proof Fish Gives Inspiration for Body Armor Christopher Intagliata | October 23, 2019
Deep in the Amazon lives one of the world's largest freshwater fish: the legendary Arapaima. It tips the scales at hundreds of pounds… making it a coveted catch for extreme anglers, like Jeremy Wade from the show River Monsters. <<River Monsters audio>> After a dramatically scored struggle, he catches one. It takes two guys to hold it up! <<"There it is, look at that for a fish! Look at that massive female Arapaima, about 150 pounds.">>
Speaking of scales, this giant fish has another superlative quality: "It has these very impressive armored scales on its body which prevent penetration by predator's teeth yet still makes the fish quite flexible and nimble in the water."
Robert Ritchie, a materials scientist at UC Berkeley. The predators he's talking about are piranhas. But the mighty Arapaima has them beat with its scales—one of the "toughest flexible biological materials," according to Ritchie's team.
After subjecting the scales to stress tests and electron microscopy in the lab, they figured out the scales' secrets. For one, they have a hard, mineralized layer on the outside.
"You need the hard layer at the surface to prevent the thing from penetrating. But if the whole scale was made of this hard layer, it would just shatter, like if you tried to penetrate a piece of glass."
And so the scale then has a layer of softer, but tougher, collagen on the inside… more resistant to cracking in a piranha's bite. Materials scientists have already figured out this trick - to build materials with a hard layer on the outside and a tough layer on the inside - but the secret of the Arapaima scales is how exquisitely they transition from the hard to the tough.
"We would love to do that in synthetic materials, it's just very hard to make materials like that. Maybe 3D printing in the future can do this. Nature does this rather cleverly because it builds materials from the bottom up, from the atoms and molecules up to the macro scale."
Photos and details are in the journal Matter. [Wen Yang et al, Arapaima Fish Scale: One of the Toughest Flexible Biological Materials]
So, who cares about a fish's scales? Well, the Air Force Office of Scientific Research does… they funded the study. Because Kevlar and other body armors are incredibly heavy. And this piranha-proof fish could be the key to a lighter load.
Source: Scientific American https://www.scientificamerican.com/podcast/episode/piranha-proof-fish-gives-inspiration-for-body-armor/ [Rephrase 1, 03:03]
Quarrying stone for Easter Island statues made soil more fertile for farming Bruce Bower | October 25, 2019
[Time 2] Easter Island’s Polynesian society cultivated crops in soil made especially fertile by the quarrying of rock for massive, humanlike statues, a new study suggests.
Soil analyses indicate that weathering of volcanic sediment created by quarrying enriched the slopes of Easter Island’s major rock quarry with phosphorus and other elements crucial for farming. Microscopic plant remains suggest that food grown in the enriched soil included sweet potatoes, bananas, taro, paper mulberry fruit and probably bottle gourd, say anthropological archaeologist Sarah Sherwood and colleagues.
Starting in roughly 1400, Easter Islanders farmed in this way, even as soil quality deteriorated in many parts of the island, also known as Rapa Nui, due to deforestation and possibly drought, the team reports in the November Journal of Archaeological Science.
The island’s Polynesian society, which got started from around 900 to 1100, is famous for two reasons: for having erected large statues known as moai that were sculpted out of volcanic rock, and for collapsing in the late 1600s after supposedly overusing the land. But previous research has questioned that narrative of societal disintegration. The new study is “one more piece of evidence against the traditional story of Easter Island’s self-inflicted environmental demise,” says Sherwood, of the University of the South in Sewanee, Tenn.
Radiocarbon dating of burned wood and plant fragments found in sediment layers and on two of 21 partially buried statues on the quarry’s slopes identified two main phases of farming at the quarry. During the first phase, visits probably started between 1495 and 1585 and lasted until roughly 1675 to 1710, shortly before Europeans first arrived on the island in 1722. During that time, one of the statues — which has been more intensively studied than the other — was raised, the scientists say.
Cultivation occurred in many parts of Rapa Nui before European contact, says archaeologist Carl Lipo of Binghamton University in New York. Investigators need to determine whether any other sites on the island contained soil as productive as that at the statue quarry, he suggests. [334 words]
[Time 3] Findings from Sherwood’s group help to show how Rapa Nui was transformed from a palm forest into a cultivated terrain that supported islanders for more than 500 years, Lipo says. Quarry cultivation “adds to growing knowledge of how pre-contact people smartly utilized their landscape,” he says. Related research has found that, as palm forests shrank on Rapa Nui, farmers cultivated yams and other crops using clever techniques such as rock gardens that fortified soil quality.
Farming at the quarry by the island’s native population began again in the 1800s and likely lasted into the early 1900s, the researchers found. Other evidence also suggests that Rapa Nui farming continued after European contact.
What’s more, excavations of the two partially buried statues, led by archaeologist and study coauthor Jo Anne Van Tilburg of UCLA, revealed that each had been placed in a carved pit packed with gravel and boulders to hold it upright. Crescent shapes and other figures carved on statues’ backs, and a carved human head found resting against the base of one statue, suggest that these objects were used in ceremonies of some kind, perhaps intended to promote crop growth. Red pigment pieces and coral found near the statues probably also had ritual uses, the team says.
Researchers traditionally have assumed that builders of the island’s partially buried quarry statues had either planned to move them elsewhere on the island or abandoned them. Designs on the roughly 6.6-meter-tall quarry statues display similarities to those on the only other Rapa Nui statue displaying numerous carved images. That carved figure was previously found at a ceremonial site nearly 20 kilometers west of the quarry.
Although the quarry measures only about 800 to 1,000 meters across, the new soil data show that it was a “little productive gold mine” for farming, says archaeologist Christopher Stevenson of Virginia Commonwealth University in Richmond, who did not participate in the study. Reeds growing in a lake at the base of the quarry would have provided additional phosphorus to the soil, he says.
“The area immediately to the east of the quarry was and is one of the most intensively settled parts of the island, and now that makes much more sense,” Stevenson says. [367 words]
Source: Science News https://www.sciencenews.org/article/quarrying-stone-easter-island-statues-made-soil-more-fertile-farming
Bias in a common health care algorithm disproportionately hurts black patients Sujata Gupta | October 24, 2019
[Time 4] A widely used algorithm that helps hospitals identify high-risk patients who could benefit most from access to special health care programs is racially biased, a study finds.
Eliminating racial bias in that algorithm could more than double the percentage of black patients automatically eligible for specialized programs aimed at reducing complications from chronic health problems, such as diabetes, anemia and high blood pressure, researchers report in the Oct. 25 Science.
This research “shows how once you crack open the algorithm and understand the sources of bias and the mechanisms through which it’s working, you can correct for it,” says Stanford University bioethicist David Magnus, who wasn’t involved in the study.
To identify which patients should receive extra care, health care systems in the last decade have come to rely on machine-learning algorithms, which study past examples and identify patterns to learn how to a complete task.
The top 10 health care algorithms on the market — including Impact Pro, the one analyzed in the study — use patients’ past medical costs to predict future costs. Predicted costs are used as a proxy for health care needs, but spending may not be the most accurate metric. Research shows that even when black patients are as sick as or sicker than white patients, they spend less on health care, including doctor visits and prescription drugs. That disparity exists for many reasons, the researchers say, including unequal access to medical services and a historical distrust among black people of health care providers. That distrust stems in part from events such as the Tuskegee experiment, in which hundreds of black men with syphilis were denied treatment for decades. [272 words]
[Time 5] As a result of this faulty metric, “the wrong people are being prioritized for these [health care] programs,” says study coauthor Ziad Obermeyer, a machine-learning and health policy expert at the University of California, Berkeley.
Concerns about bias in machine-learning algorithms — which are now helping diagnose diseases and predict criminal activity, among other tasks — are not new. But isolating sources of bias has proved challenging as researchers seldom have access to data used to train the algorithms.
Obermeyer and colleagues, however, were already working on another project with an academic hospital (which the researchers decline to name) that used Impact Pro and realized that the data used to get that algorithm up and running were available on the hospital’s servers.
So the team analyzed data on patients with primary care doctors at that hospital from 2013 to 2015 and zoomed in on 43,539 patients who self-identified as white and 6,079 who identified as black. The algorithm had given all patients, who were insured through private insurance or Medicare, a risk score based on past health care costs.
Patients with the same risk scores should, in theory, be equally sick. But the researchers found that, in their sample of black and white patients, black patients with the same risk scores as white patients had, on average, more chronic diseases. For risk scores that surpassed the 97th percentile, for example, the point at which patients would be automatically identified for enrollment into specialized programs, black patients had 26.3 percent more chronic illnesses than white patients — or an average of 4.8 chronic illnesses compared with white patients’ 3.8. Less than a fifth of patients above the 97th percentile were black. [277 words]
[Time 6] Obermeyer likens the algorithm’s biased assessment to patients waiting in line to get into specialized programs. Everyone lines up according to their risk score. But “because of the bias,” he says, “healthier white patients get to cut in line ahead of black patients, even though those black patients go on to be sicker.”
When Obermeyer’s team ranked patients by number of chronic illnesses instead of health care spending, black patients went from 17.7 percent of patients above the 97th percentile to 46.5 percent.
Obermeyer’s team is partnering with Optum, the maker of Impact Pro, to improve the algorithm. The company independently replicated the new analysis and compared chronic health problems among black and white patients in a national dataset of almost 3.7 million insured people. Across risk scores, black patients had almost 50,000 more chronic conditions than white patients, evidence of the racial bias. Retraining the algorithm to rely on both past health care costs and other metrics, including preexisting conditions, reduced the disparity in chronic health conditions between black and white patients at each risk score by 84 percent.
Because the infrastructure for specialized programs is already in place, this research demonstrates that fixing health care algorithms could quickly connect the neediest patients to programs, says Suchi Saria, a machine-learning and health care researcher at Johns Hopkins University. “In a short span of time, you can eliminate this disparity.” [230 words]
Source: Science News https://www.sciencenews.org/article/bias-common-health-care-algorithm-hurts-black-patients
Putting the 'bang' in the Big Bang Massachusetts Institute of Technology | October 25, 2019
[Paraphrase 7] As the Big Bang theory goes, somewhere around 13.8 billion years ago the universe exploded into being, as an infinitely small, compact fireball of matter that cooled as it expanded, triggering reactions that cooked up the first stars and galaxies, and all the forms of matter that we see (and are) today.
Just before the Big Bang launched the universe onto its ever-expanding course, physicists believe, there was another, more explosive phase of the early universe at play: cosmic inflation, which lasted less than a trillionth of a second. During this period, matter -- a cold, homogeneous goop -- inflated exponentially quickly before processes of the Big Bang took over to more slowly expand and diversify the infant universe.
Recent observations have independently supported theories for both the Big Bang and cosmic inflation. But the two processes are so radically different from each other that scientists have struggled to conceive of how one followed the other.
Now physicists at MIT, Kenyon College, and elsewhere have simulated in detail an intermediary phase of the early universe that may have bridged cosmic inflation with the Big Bang. This phase, known as "reheating," occurred at the end of cosmic inflation and involved processes that wrestled inflation's cold, uniform matter into the ultrahot, complex soup that was in place at the start of the Big Bang.
"The postinflation reheating period sets up the conditions for the Big Bang, and in some sense puts the 'bang' in the Big Bang," says David Kaiser, the Germeshausen Professor of the History of Science and professor of physics at MIT. "It's this bridge period where all hell breaks loose and matter behaves in anything but a simple way."
Kaiser and his colleagues simulated in detail how multiple forms of matter would have interacted during this chaotic period at the end of inflation. Their simulations show that the extreme energy that drove inflation could have been redistributed just as quickly, within an even smaller fraction of a second, and in a way that produced conditions that would have been required for the start of the Big Bang.
The team found this extreme transformation would have been even faster and more efficient if quantum effects modified the way that matter responded to gravity at very high energies, deviating from the way Einstein's theory of general relativity predicts matter and gravity should interact.
"This enables us to tell an unbroken story, from inflation to the postinflation period, to the Big Bang and beyond," Kaiser says. "We can trace a continuous set of processes, all with known physics, to say this is one plausible way in which the universe came to look the way we see it today."
The team's results appear today in Physical Review Letters. Kaiser's co-authors are lead author Rachel Nguyen, and John T. Giblin, both of Kenyon College, and former MIT graduate student Evangelos Sfakianakis and Jorinde van de Vis, both of Leiden University in the Netherlands.
"In sync with itself"
The theory of cosmic inflation, first proposed in the 1980s by MIT's Alan Guth, the V.F. Weisskopf Professor of Physics, predicts that the universe began as an extremely small speck of matter, possibly about a hundred-billionth the size of a proton. This speck was filled with ultra-high-energy matter, so energetic that the pressures within generated a repulsive gravitational force -- the driving force behind inflation. Like a spark to a fuse, this gravitational force exploded the infant universe outward, at an ever-faster rate, inflating it to nearly an octillion times its original size (that's the number 1 followed by 26 zeroes), in less than a trillionth of a second.
Kaiser and his colleagues attempted to work out what the earliest phases of reheating -- that bridge interval at the end of cosmic inflation and just before the Big Bang -- might have looked like.
"The earliest phases of reheating should be marked by resonances. One form of high-energy matter dominates, and it's shaking back and forth in sync with itself across large expanses of space, leading to explosive production of new particles," Kaiser says. "That behavior won't last forever, and once it starts transferring energy to a second form of matter, its own swings will get more choppy and uneven across space. We wanted to measure how long it would take for that resonant effect to break up, and for the produced particles to scatter off each other and come to some sort of thermal equilibrium, reminiscent of Big Bang conditions."
The team's computer simulations represent a large lattice onto which they mapped multiple forms of matter and tracked how their energy and distribution changed in space and over time as the scientists varied certain conditions. The simulation's initial conditions were based on a particular inflationary model -- a set of predictions for how the early universe's distribution of matter may have behaved during cosmic inflation.
The scientists chose this particular model of inflation over others because its predictions closely match high-precision measurements of the cosmic microwave background -- a remnant glow of radiation emitted just 380,000 years after the Big Bang, which is thought to contain traces of the inflationary period.
A universal tweak
The simulation tracked the behavior of two types of matter that may have been dominant during inflation, very similar to a type of particle, the Higgs boson, that was recently observed in other experiments.
Before running their simulations, the team added a slight "tweak" to the model's description of gravity. While ordinary matter that we see today responds to gravity just as Einstein predicted in his theory of general relativity, matter at much higher energies, such as what's thought to have existed during cosmic inflation, should behave slightly differently, interacting with gravity in ways that are modified by quantum mechanics, or interactions at the atomic scale.
In Einstein's theory of general relativity, the strength of gravity is represented as a constant, with what physicists refer to as a minimal coupling, meaning that, no matter the energy of a particular particle, it will respond to gravitational effects with a strength set by a universal constant.
However, at the very high energies that are predicted in cosmic inflation, matter interacts with gravity in a slightly more complicated way. Quantum-mechanical effects predict that the strength of gravity can vary in space and time when interacting with ultra-high-energy matter -- a phenomenon known as nonminimal coupling.
Kaiser and his colleagues incorporated a nonminimal coupling term to their inflationary model and observed how the distribution of matter and energy changed as they turned this quantum effect up or down.
In the end they found that the stronger the quantum-modified gravitational effect was in affecting matter, the faster the universe transitioned from the cold, homogeneous matter in inflation to the much hotter, diverse forms of matter that are characteristic of the Big Bang.
By tuning this quantum effect, they could make this crucial transition take place over 2 to 3 "e-folds," referring to the amount of time it takes for the universe to (roughly) triple in size. In this case, they managed to simulate the reheating phase within the time it takes for the universe to triple in size two to three times. By comparison, inflation itself took place over about 60 e-folds.
"Reheating was an insane time, when everything went haywire," Kaiser says. "We show that matter was interacting so strongly at that time that it could relax correspondingly quickly as well, beautifully setting the stage for the Big Bang. We didn't know that to be the case, but that's what's emerging from these simulations, all with known physics. That's what's exciting for us." [1267 words]
This research was supported, in part, by the U.S. Department of Energy and the National Science Foundation.
Source: Science Daily https://www.sciencedaily.com/releases/2019/10/191025130414.htm | 
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发表于 2019-10-28 21:29:10
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