【每日阅读训练第四期——速度越障2系列】【2-16】科技

CHRISTINE2010

【计时1】

Antiaging protein helps set daily rhythms

Changing levels of sirtuin alter activity patterns in mice



WASHINGTON — A protein famous for slowing aging and increasing life span also acts as a metronome, helping coordinate metabolism and the body’s daily rhythms.


SIRT1, one of a group of proteins called sirtuins, plays roles in many cellular processes, including aging. Researchers hope that activating the protein with drugs such as resveratrol can extend life span and improve health for people, as it does in animal studies.


Now, researchers at MIT have evidence that SIRT1 may not only help determine long-term health and longevity, but it also has a hand in setting the body’s daily or “circadian” clock. The finding, reported May 31 at the Metabolism, Diet and Disease meeting, could be important for understanding how metabolism and life span are linked.


Studies of cells in laboratory dishes had suggested that SIRT1 might work with certain gears of the circadian clock in liver cells. But until now no one has shown that the protein could influence the body’s master clock in the brain, says Raul Mostoslavsky, a molecular biologist at Harvard Medical School.  


In the new study, scientists led by Leonard Guarente of MIT monitored the natural activity patterns of mice. Normally, mice’s circadian clocks run just shy of a 24-hour day, at about 23.5 hours. Mice that lack SIRT1 in their brains have a longer internal day, closer to 24 hours, Guarente said. And mice that made twice as much SIRT1 as normal in their brains had a shorter-than-usual day. Mice making five times as much SIRT1 as normal had even shorter natural days.
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Amounts of SIRT1 in the brain may help the master clock, which is centered in a group of cells known as the suprachiasmatic nucleus, adjust to seasonal changes in daylight, Guarente said. Previously, some of his colleagues had noticed that mice’s circadian clocks tend to move toward 24-hour days as the mice age. The researchers wanted to know if that lengthening day had anything to do with declining SIRT1 levels in the brain’s master clock.


To find out, the team jet-lagged mice by abruptly shifting light and dark conditions in the lab by four hours. Young mice usually take only about two days to reset their circadian clocks to the new “time zone,” but old mice needed as long as eight days to adjust. In the new tests, young mice lacking SIRT1 in their brains needed about four days to adapt, indicating that SIRT1 is at least partially responsible for the ability to adjust. And old mice that make more SIRT1 than usual in their brains seemed to get over jet lag faster. The researchers also showed that levels of SIRT1 in the brain clock are tied to levels of other important clock proteins.


In a separate experiment, the team found that mice that have their circadian clocks set closest to 24-hour days live longer than mice with faster or slower-running clocks. Constantly resetting circadian clocks may cause stress that leads to aging, Guarente said.
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Supervolcanoes evolve superquickly

Huge underground magma chambers appear and erupt within just several hundred years


The biggest eruptions on Earth may happen faster than volcanologists had thought. Giant blobs of magma appear underground and then pour onto the surface within centuries, suggests a new study of a California supereruption.


If the work holds true for other volcanoes, it means the most powerful eruptions don’t have magma chambers beneath them for very long. So if big changes start happening, like the ground rising or new geysers spouting, volcanologists might expect an eruption sooner rather than later. Yellowstone, for one, experienced a supereruption about 2.1 million years ago.


“The fact that at Yellowstone there’s no giant magma body right now doesn’t mean that in hundreds to thousands of years we couldn’t have one,” says Guilherme Gualda, a geologist at Vanderbilt University in Nashville. “By understanding these time scales better, we know better what to expect.”


Gualda and his colleagues report the discovery May 30 in PLoS ONE.


The researchers studied 760,000-year-old rocks from Long Valley in eastern California. These rocks, known as the Bishop Tuff, formed during one of the biggest eruptions known, which spread some 600 cubic kilometers of ash and other debris across the landscape. Earlier studies, which looked at crystals such as zircon, suggested that the Bishop magma had sat underground, chemically evolving and slowly crystallizing for more than 100,000 years before erupting.
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Gualda’s team looked instead at crystals of quartz. Certain properties of the quartz — such as how much the element titanium migrated within it and how glass pieces within it changed shape over time — can indicate how long ago the quartz solidified within the liquid magma. That process would begin almost as soon as the magma body appears, the researchers’ calculations showed. Once quartz forms, gas pressure builds up and eventually forces the magma to erupt.


Quartz would have crystallized less than 10,000 years before the eruption — and usually more like 500 to 3,000 years, the team reports. The other studies that used zircon, and found a much older age, may represent a longer-term history of volcanism across the entire region, Gualda says.


Research at other supervolcanoes has shown how quickly an eruption can happen once magma starts moving toward the surface (SN: 3/10/12, p. 12). “What we’re finding is that it wasn’t there for very long to begin with,” says Gualda.


The discovery supports the idea that magma can accumulate rapidly before supereruptions, says Erik Klemetti, a geologist at Denison University in Granville, Ohio, who has found similar fast changes in zircon crystals from New Zealand eruptions. Still, he says, “this study really doesn’t address a key question — just how do these large magma bodies initially form?”


For now, Gualda is leaving that challenge to others. He is working to apply the new finding to other supervolcanoes to see whether they play by the same rules as Long Valley.
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【计时5】

How a mosquito survives a raindrop hit

Lightweight insects can ride water droplets, as long as they separate in time


A raindrop hitting a mosquito in flight is like a midair collision between a human and a bus. Except that the mosquito survives.


New experiments show how the insect’s light weight works in its favor, says engineer David Hu of the Georgia Institute of Technology in Atlanta. In essence, the (relatively) huge, fast drop doesn’t transfer much of its momentum to a little wisp of an insect. Instead the falling droplet sweeps the insect along on the downward plunge. As Hu puts it, the mosquito “just rides the drop.”


The trick is breaking away from that drop before it and the insect splash into the ground. Mosquitoes that separate themselves in time easily survive a raindrop strike, Hu and his colleagues report online June 4 in the Proceedings of the National Academy of Sciences.


Such studies help reveal how animals evolved to take advantage of flight, says biologist Tyson Hedrick of the University of North Carolina at Chapel Hill. Mosquito tricks may also inspire engineers designing swarms of tiny flying robots, or interest physicists and mathematicians studying complex fluid dynamics at this scale.
Plenty of lab work has investigated how flying animals recover from disturbances, but there’s little work on raindrops because those collisions are very hard to study, Hu says. To mimic raindrop speed of about 9 meters per second, he and his colleagues tried dripping water off the third floor of a building toward ground-level mosquitoes. “It’s the worst game of darts you can imagine,” he says. “You have no hope of hitting them.”
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【自由】

Finally, Hu sprayed streams of water from a pump at caged lab mosquitoes and then refined the process by spraying mosquito-sized beads. His team found that mosquitoes hit with water survived using an insect version of tai chi: Move with the blow instead of resisting it. A raindrop can reach 50 times the mass of a mosquito, and after colliding, “the mosquito becomes a stowaway,” Hu says.


The wild ride comes with danger. Mosquitoes hitchhiking on water experience acceleration 100 to 300 times the force of Earth’s gravity, the researchers found. The previous champs for surviving acceleration had been jumping fleas, at a mere 130 times Earth’s gravity.


Such studies suggest insects are making tradeoffs, Hedrick says. Mosquitoes’ small mass might allow them fly through raindrops but leave them more vulnerable to other menaces, such as wind. Larger and heavier horseflies “should have no problem with wind but might be more disturbed by raindrop impacts,” he says.
Scientists who work in the field know how readily mosquitoes can survive wet weather. “I’ve worked in the field many rainy nights,” says entomologist Nathan Burkett-Cadena of the University of South Florida in Tampa, “and received zero respite from mosquitoes during even heavy rains.”
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【越障】

Physicists Close in On a Rare Particle-Decay Process: Underground Experiment May Unlock Mysteries of the Neutrino

ScienceDaily (June 4, 2012) — In the biggest result of its kind in more than ten years, physicists have made the most sensitive measurements yet in a decades-long hunt for a hypothetical and rare process involving the radioactive decay of atomic nuclei.

[attachimg=300,228]101955[/attachimg]

If discovered, the researchers say, this process could have profound implications for how scientists understand the fundamental laws of physics and help solve some of the universe's biggest mysteries -- including why there is more matter than antimatter and, therefore, why regular matter like planets, stars, and humans exists at all.


The experiment, the Enriched Xenon Observatory 200 (EXO-200), is an international collaboration that includes the California Institute of Technology (Caltech) and is led by Stanford University and the SLAC National Accelerator Laboratory, a U.S. Department of Energy (DOE) National Laboratory.


The EXO-200 experiment has placed the most stringent constraints yet on the nature of a so-called neutrinoless double beta decay. In doing so, physicists have narrowed down the range of possible masses for the neutrino, a tiny uncharged particle that rarely interacts with anything, passing right through rock, people, and entire planets as it zips along at nearly the speed of light.


The collaboration, consisting of 80 researchers, has submitted a paper describing the results to the journal Physical Review Letters.


In a normal double beta decay, which was first observed in 1986, two neutrons in an unstable atomic nucleus turn into two protons; two electrons and two antineutrinos -- the antimatter counterparts of neutrinos -- are emitted in the process.


But physicists have suggested that two neutrons could also decay into two protons by emitting two electrons without producing any antineutrinos. "eople have been looking for this process for a very long time," says Petr Vogel, senior research associate in physics, emeritus, at Caltech and a member of the EXO-200 team. "It would be a very fundamental discovery if someone actually observes it."


A neutrino is inevitably produced in a single beta decay. Therefore, the two neutrinos that are produced in a neutrinoless double beta decay must somehow cancel each other out. For that to happen, physicists say, a neutrino must be its own antiparticle, allowing one of the two neutrinos to act as an antineutrino and annihilate the other neutrino. That a neutrino can be its own antiparticle is not predicted by the Standard Model -- the remarkably successful theory that describes how all elementary particles behave and interact.


If this neutrinoless process does indeed exist, physicists would be forced to revise the Standard Model.


The process also has implications for cosmology and the origin of matter, Vogel says. Right after the Big Bang, the universe had the same amount of matter as antimatter. Somehow, however, that balance was tipped, producing a slight surplus in matter that eventually led to the existence of all of the matter in the universe. The fact that the neutrino can be its own antiparticle might have played a key role in tipping that balance.


In the EXO-200 experiment, physicists monitor a copper cylinder filled with 200 kilograms of liquid xenon-136, an unstable isotope that, theoretically, can undergo neutrinoless double beta decay. Very sensitive detectors line the wall at both ends of the cylinder. To shield it from cosmic rays and other background radiation that may contaminate the signal of such a decay, the apparatus is buried deep underground in the DOE's Waste Isolation Pilot Plant in Carlsbad, New Mexico, where low-level radioactive waste is stored. The physicists then wait to see a signal.


The process, however, is very rare. In a normal double beta decay, half of a given sample would decay after 10²¹ years -- a half-life roughly 100 billion times longer than the time that has elapsed since the Big Bang.


One of the goals of the experiment is to measure the half-life of the neutrinoless process (if it is discovered). In these first results, no signal for a neutrinoless double beta decay was detected in almost seven months' of data -- and that non-detection allowed the researchers to rule out possible values for the half-life of the neutrinoless process. Indeed, seven months of finding nothing means that the half-life cannot be shorter than 1.6 × 10²⁵ years, or a quadrillion times older than the age of the universe. With the value of the half-life pinned down, physicists can calculate the mass of a neutrino -- another longstanding mystery. The new data suggest that a neutrino cannot be more massive than about 0.140 to 0.380 electron volts (eV, a unit of mass commonly used in particle physics); an electron, by contrast, is about 500,000 eV, or about 9 × 10^-31 kilograms.


More than ten years ago, the collaboration behind the Heidelberg-Moscow Double Beta Decay Experiment controversially claimed to have discovered neutrinoless double beta decay using germanium-76 isotopes. But now, the EXO-200 researchers say, their new data makes it highly unlikely that those earlier results were valid.


The EXO-200 experiment, which started taking data last year, will continue its quest for the next several years.


The EXO collaboration involves scientists from SLAC, Stanford, the University of Alabama, Universität Bern, Caltech, Carleton University, Colorado State University, University of Illinois Urbana-Champaign, Indiana University, UC Irvine, Institute for Theoretical and Experimental Physics (Moscow), Laurentian University, the University of Maryland, the University of Massachusetts-Amherst, the University of Seoul, and the Technische Universität München. This research was supported by the DOE and the National Science Foundation in the United States, the Natural Sciences and Engineering Research Council in Canada, the Swiss National Science Foundation, and the Russian Foundation for Basic Research. This research used resources of the National Energy Research Scientific Computing Center (NERSC).
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spencerX

沙发~占christine辛苦了^_^1min17
1min10
59s
1min10
1min17
1min


5min36

jiline

1'36 SIRT1 influences aging, which is expected to improve health for people. No evidence the protein can influence the clock in the brain, but influences the circadian clocks tested on mice
1'42 Test on young and old mice with different SIRT1, the result is that SIRT1 influences the circadian clocks.
1'42 The biggest eruptions on Earth may happen fast. Then introduce the research about it.
1'20 Quartz forming influences the magma to erupt. Research the magma accumulate eruption.
1'40 The raindrop hitting a mosquito is like a collision between a human and a bus. But the mosquito can survive. The researcher tries to find out the reason and apply them in the real life

越障：
看得云里雾里的
5‘46
The physicists hunt the rare process involving the redioactive decay of atomic nuclei which can help solve some universe mysteries.
Two neutrons turn into tow protons are observed in 1986, the exo-200 want to find the process "emitting two electrons without producing any antiniutinos" which is not definied by Standard Model.
The process has implications for origin of matter.
The ex0-200 experiemnt stated the previous finding of the process is not likely valid

小胖宝

1'31, 1'05, 1'18, 1'28, 2'13, 1'20
5'25

teddybearj4

速度：
1'18     1'02     1'08    1'11     1'27
(觉得当科学家真有好处，蚊子会不会被雨打死都能拿来做研究==……analogy一下，估计下次他们就该研究bus hit human，human能不能幸免于难的问题了==！)

越障：5'36(谢谢Christine，这篇越障可读性蛮强的，而且结构挺清楚~怀念物理课~~)
Main idea: The EXO-200 experiment is trying to explode the decaying process of  neutrion.
Since the neutrion is related to the fundation roles of physic, the dection of neutrion is significant and may reveal some univercial mysteries. The experiment presents 2 processes.
Process 1:
*the component of one neutrion(X atomic nucleus , Y protons, Z electrons or antineutrinos)
conclusion: this finding will even challenge the theory of cosmology or Big bang theory?
Process 2:
*it is about a decay experiment.
conclusion:???
The EXO-200 experiment will continue for sometime

Olina加油

先占上，明天做

bet

1'52'
1'31"
1'32"
1'27"
1'51"

越障
6‘30“
The process of beta's decay is used to explore why there is more matter than antimatter and experiment involving other isotopes is introduced.

jolene91

1.37
1.16
1.21
1.31
1.45
5.23越障好多物理专业知识的说。。。好难读，貌似是讲了一个新项目，讲了这个研究的发展历程和研究的几个方面

babybearmm

速度：55''  50''  1'01''  58''  1'10''


越障：6'38''


MI: a new ground-breaking study (EXO)

Normal double-beta decay:        2 Neutron ----> 2 P+, with 2e- and 2 antineutrino
However, researchers found
new double-beta decay:             2 Neutron ----> 2 P+, with 2e- (no 2 antineutrino!!!!)   "antineutrino-less"


We know that single-beta decay produces 2 neutrino, while double-beta decay produces 2 antineutrino. These two can cancel out. So the new finding is ground-breaking: it means that there are "net" neutrinos, which are not canceled out by antineutrinos


This finding has profound implications in cosmology:
At Big Bang, when the universe begins, [matters] = [anti-matters]
However, now we have matters around the world. so that means now [matters] >> [anti-matters]
How come?
Well, this new finding can explain, as this study found that double-beta decay can be antineutrino-less.


In fact, the goal of this longterm project is to measure the half life of antineutrino-less double-beta decay. Using this info, scientists will be able to know the age of our universe since Big Bang. Also, scientists can calculate the mass of neutrino. Right now, they found there's no signal of this decay in the first 7 years. this information provides a limit (on one side) of the estimated mass. As more data are collected, scientists will be able to narrow the estimate.


This project is US-based, a lot of researchers from different institutes (Stanford, ...).
uses an underground apparatus

babybearmm

晕~~没注意"is an international collaboration"，只注意了一堆美国的institutes
我CR也经常犯这种错，不注意单个形容词

对Standard Model理解有点偏差
neutrino can be its own antiparticle