大家好！胖胖翔报到！一如既往的科技文，今天的文章关于气候和生物这两个主题~
Part I：Speed
【Time 1】
Article 1
Mont Blanc growing with help from glaciers
Icy shield prevents mountain from eroding away.
Western Europe’s tallest mountain may be gaining height thanks to its glaciers, which protect the mountain from erosion, a new study suggests.
Straddling the Italian and French Alps, Mont Blanc’s familiar snowy cap has challenged the most skilled climbers — as well as scientists who aim to understand how the mountain is being shaped by its glacial covering.
Typically, glaciers are known to erode surfaces and transport sediment, carving out deep valleys in mountain ranges and wearing down summits as the ice slowly slides downhill. But in the past few years, research has suggested that glaciers have a role in protecting mountaintops located at high latitudes, far from the equator. The same now seems to be true for mid-latitude Mont Blanc, and could apply more generally to mountains in mid-to-low latitudes, says glacial geologist Jean-François Buoncristiani, co-author of a study that appeared late last month in Earth and Planetary Science Letters.
“It’s interesting that the same processes are happening on mountains worldwide,” says Buoncristiani, who is at the University of Burgundy in Dijon, France. Mont Blanc is growing by 1 millimetre per year because of tectonic uplift, but without the protective effect of glaciers that would not be fast enough to outpace erosion.
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【Time 2】
The study team, led by glaciologist Cécile Godon at the University of Savoy in Le Bourget du Lac, France, measured erosion rates beneath one of Mont Blanc’s largest and least-spoiled glaciers, the Bossons Glacier, and compared them with erosion rates in ice-free areas adjacent to the glacier. By identifying distinctive rock types and by dating the mineral zircon in sediment samples taken from along the glacier’s length, they traced eroded sediments back to their sources.
Glacial pace
Near the summit, beneath the coldest ice of the glacier, erosion was at least 16 times less efficient than beneath the temperate ice of the glacier tongue, farther downslope. The most effective erosion was found to take place in the non-glaciated areas, suggesting that the weighty presence of ice — especially when frozen onto the mountain — tempers abrasion of the underlying bedrock.
But the findings do not necessarily mean that glaciers protect all mountains. Mark Brandon, a geophysicist at Yale University in New Haven, Connecticut, says that glaciers with a wet base are very erosive. It remains to be seen how ice is shaping the world’s largest mountains, he says.
Buoncristiani adds that the role of glaciers could change as temperatures rise with global warming. An increase in ice melt would expose mountaintops to erosion, limiting their ability to reach ever greater heights.
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Resource:
http://www.nature.com/news/mont-blanc-growing-with-help-from-glaciers-1.13357
【Time 3】
Article 2
Scientists Grow Human Livers in Mice
TOKYO—A Japanese group has generated functional human livers by creating liver precursor cells in the laboratory and then transplanting them into mice to complete the developmental process. Their ultimate goal is to transplant the precursor cells into humans and let them develop into replacements for diseased or damaged organs.
The achievement represents a new direction in the use of human pluripotent stem cells, which have the potential to develop into any of the tissues of the human body. So-called induced pluripotent stem (iPS) cells, which are derived from adult human tissue, have the added advantage of producing tissues and organs genetically matched to a recipient, avoiding the problem of immune system rejection. But creating fully mature human tissue in a petri dish (in vitro) has proved a daunting challenge, especially when it comes to producing 3D organs.
Rather than do it all in a dish, the group decided to try starting the process in vitro but completing it in an animal (in vivo). They tried hundreds of different recipes; eventually they discovered that if they mixed liver precursor cells (derived from iPS cells) with two other types of standard human cell lines known to be important for embryonic liver development, then the cells would spontaneously form a 4 to 5-millimeter 3D structure called a liver bud. "This worked beyond our expectations, though the mechanism is not entirely clear," says group leader and stem cell scientist Takanori Takebe of Yokohama City University in Japan.
Next, they implanted these buds in mice with disabled immune systems to see if they would engraft, or attach to the blood vessels of the animal, and continue to mature. They did: The transplanted liver buds developed into what Takebe calls "miniature livers." The team then confirmed that these tiny organs produced proteins typically made by human livers, and they properly processed certain drugs that mouse livers cannot handle. This "proof of concept demonstration" provides a promising new approach to regenerative medicine, the team writes in a paper published online by Nature today.
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Resource:
http://news.sciencemag.org/sciencenow/2013/07/scientists-grow-human-livers-in.html?ref=hp
【Time 4】
The experiment shows that precursor cells can develop into functional organs when placed within the body of an adult mammal, says Takebe, who hopes to use the technique to grow organs in nonhuman primates and eventually in humans. He believes it could be applied to other organs, such as kidneys or pancreases, as well.
Stem cell scientist Martin Pera of the University of Melbourne in Australia, calls it an "exciting study" that demonstrates that the environment within an adult body can help immature stem cells develop to an adult stage, something that has proven difficult to do in vitro. The report "provides hope that even primitive tissues made from stem cells will one day restore the function of dead or diseased organs in patients," he adds.
But there are significant hurdles to clear before the technique reaches the clinic. In addition to passing all the safety checks needed to gain approval for human use, there is a practical problem. Takebe says they will need to transplant huge numbers of liver buds, comprising billions or trillions of the human iPS-derived precursor cells to even partially replace a human liver. Producing cells in those numbers will require a breakthrough in automated cell proliferation. Because of that, Takebe says use in humans is at least a decade away.
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【Time 5】
Article 3
Rockets Are Seeding the Skies With Clouds
An unexpected increase in the water content of certain thin, wispy clouds at high altitudes over polar regions in 2011 and 2012 may be the result of more rocket launches, a new study suggests. Polar mesospheric clouds (PMCs) typically form over high latitudes during summer months at altitudes of about 82 kilometers. (They're also known as noctilucent, or "night-shining" clouds, because they're so lofty that they can catch sunlight even when the ground below remains dark, as seen in this image taken from the International Space Station.) Of the hundreds of PMCs spotted in July from 2008 through 2010, satellite data show that only 11 had unnaturally high concentrations of water. But 27 of the PMCs observed in July of 2011 and 2012 were unnaturally moist, the researchers report in Geophysical Research Letters. Moreover, in recent years the densest—and therefore the brightest—PMCs have contained even more water than normal: From 2008 through 2010, the densest PMCs had peak water content of 9 parts per million, whereas in 2011 and 2012 their peak water content often exceeded 12 ppm. Both trends are unexpected, because solar activity—which tends to boost emissions of ultraviolet radiation that heat and dry the upper atmosphere—was much higher in 2011 and 2012 than in the previous 3 years. The researchers suggest that a spate of rocket launches—including commercial rockets as well as Russian Soyuz missions to carry supplies to the International Space Station—may be behind the moister, more frequent clouds: In 2011 and 2012, they estimate exhaust from 17 different summertime rocket launches added more than 700 tons of water into the upper atmosphere. That's enough to explain the observed enhancement in PMCs, which typically form only at high latitudes and altitudes because that's the coldest part of Earth's atmosphere.
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Resource:
http://news.sciencemag.org/sciencenow/2013/07/scienceshot-rockets-are-seeding-.html
Part II： Obstacle
【Time 6】
Article 4
How Should We Respond When Humans and Sharks Collide?
As vacationers head to the beach this holiday weekend, an expert says communities are taking a variety of approaches to keep swimmers safe.
Would you go swimming where there's recently been a shark attack? It's a quandary that shark attack expert Christopher Neff, a doctoral researcher at the University of Sydney, strives to understand.
Neff has studied how the public and governments respond to shark bites in North America, Australia, and Africa. He says that with more and more people using the ocean, the way we talk about shark attacks and the methods governments use to reduce the risk of shark bites have evolved over time.
Following several shark attacks reported in the U.S. last month—off the coasts of Texas, Hawaii, California, and South Carolina—Neff spoke to National Geographic via email about how communities around the world are responding to similar incidents, and what the thousands of Americans heading to a beach this Fourth of July weekend can do to reduce their chances of encountering a shark.
How rare are fatal shark bites? How can people heading to the beach this holiday weekend stay safe?
The International Shark Attack File has noted that, based on their 2000 data, we have a 1 in 11.5 million chance of being bitten by a shark.
My position is not that sharks are cuddly and we should be friends, but that they can be dangerous and a healthy respect for them is important.
I have a "Three What's" rule that I use when I go to the beach because I want to remind myself that I am stepping into a dynamic and wild ecosystem.
First, I ask, "What's the weather?" because swimming while it's overcast or stormy isn't a good idea. Incoming storms can cause the tide to stir up baitfish, and we want to avoid getting in the way of sharks and their prey. It's recommended that bathers stay out of the water for 24 hours after a storm, not just [until] the next morning.
Second, "What's the time of day and the environmental conditions?" We all know to avoid swimming at dawn and dusk and when the water is cloudy. But we also want to be conscious of other marine life and the seasons.
Are there seals in the area? Did a whale migration just come through? Or, is someone fishing off a pier near the beach or pouring the fish guts in the water? In all of these situations the issue is keeping our distance so sharks do not think that we are their competition [for food].
And third, "What am I doing?" Tips that can help reduce risk include not swimming alone or far away from shore. Simply put, swim in a group and stay close in.
The issue is not depth of the water. You could be waist-deep and 500 feet out standing on a reef; that does not count! In fact, the drop-offs from reefs are a great place for sharks to hang out.
Also, people shouldn't enter the water with shiny jewelry or metal because it can look like a curious thing to check out. Lastly, try not to overdo your splashing around. There are a number of stories about the way playing "shark attack" in the water attracted a shark to the area.
Towns near Cape Cod, Massachusetts, are facing an increase in the great white shark population. How should local governments balance spending money to prevent the relatively remote risk of a shark attack with spending money on other important issues in their communities?
Cape Cod is facing a complicated issue and the balance between costs versus fear is an interesting one. I have actually passed on three recommendations to them from my experience. The emphasis here is on individuals looking at their level of risk before they get in the water.
I suggested conveying information to the public—like signs, texts, and radio ads—that explains the ocean is not a pool. Cape Town [in Africa] has been helped a great deal by issuing citywide press releases to tell people to be cautious during the summer season.
Second, encourage people to swim close to shore. If there is an incident, the closeness to shore makes a huge difference in whether the bite is life-threatening.
Finally, information on the weather and shark behavior can help. Some excellent research out of Western Australia and Cape Town suggests that great white sharks come into shore more frequently when the water temperature is between 64ᵒF and 68ᵒF.
In Chatham, Massachusetts, the average water temperature in the summer is about 70ᵒF. So if you know that there are white sharks in the area and that they are most likely to come inshore when the water temp is somewhere near 64 -70ᵒF, then each bather has information they can use in judging their level of risk.
Public education about sharks is not easy and communities around the world are still sorting out the right ways to talk with locals. Everyone uses the beach in a different way and for different reasons, so finding one message is difficult.
How have responses to shark bites changed over the years? What kind of action should a community take after shark bites like those in the U.S. in recent weeks?
Community responses have changed in a number of ways. The problem is that as more people go in the water, stay in for longer, and do more things—like kayak, surf-ski, bodyboard, or kiteboard—the chances of having shark bites increases.
[There can be] a lot of pressure on a local community that has had three, four, seven shark bites to "do something" about it.
The answer for most of these communities is having notice boards to let surfers know there are risks when going into the surf, good on-site treatment and a nearby hospital to assist with any injuries, and outreach to the public and media to tell the full story. In most cases, the outcome is not serious or not life-threatening, so conveying that is important.
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Resource:
http://news.nationalgeographic.com/news/2013/13/130704-shark-attack-prevention-response-ocean-beach-animal-science/?source=hp_dl2_news_shark_attack_prevention_20130709
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发表于 2013-7-9 23:14:46
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