【每日阅读训练第四期——速度越障14系列】【14-11】科技

2012Michelle

今儿是年初二呢，新年新气象，小分队的同邪们不要放松哦。

这个是周二的作业。^_^

今天的速度是一篇长文分成的五个部分，内容不多。越障稍微长一点，不过挺有意思。2篇文章的标题回复后就能看到了，免得在大家阅读的时候影响你们对文章大意的理解。

加油！


The Arctic
Tequila sunset
Global warming may make the northernmost ocean less productive, not more so

[attachimg=595,457]114172[/attachimg]
【Time1】
ON SEPTEMBER 16th 2012, at the height of the summer melt, the Arctic Ocean’s ice sheet had shrunk to an area of 3.41m square kilometres (1.32m square miles), half what it was in 1979. And its volume had shrunk faster still, to a quarter of what it was in 1979, for the sheet is getting thinner as well as smaller. One culprit is global warming, which is fiercer at the poles than elsewhere. The world’s average temperature in 2012 was nearly 0.5°C above the average for 1951-80. In the Arctic, it was up almost 2°C.

This sudden warming is like the peeling back of a lid to reveal a new ocean underneath. That prospect is spreading alarm (among greens) and excitement (at the natural resources and other economic opportunities that could be unveiled). Though most of the excitement has been about oil and gas, and the opening of sea routes between the Atlantic and the Pacific, some people hope for a fishing bonanza, too, as warmth and light bring ecological renewal to what is now an icy desert. But they may be disappointed.

At the moment, the waters around the Arctic account for a fifth of the world’s catch. There are few fish, however, under the ice itself. A fishing bonanza would require big ecological change. Arctic Frontiers, a conference organised at the University of Tromso in January, looked at how warming will change the ecology, to estimate whether it will bring one about. The consensus was that it won’t—not because the Arctic will change too little, but because it will change too much.
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【Time2】
Change and decay

At first sight, this is counterintuitive. As the ice melts, more light can reach the water, and that means more photosynthesis by marine algae. In the past, algae began to grow under the ice sheet in May and continued to do so until late September. Now, such growth starts in mid-March and continues until October. These ice algae, attached to the sheet itself, account for half the mass of living things in Arctic waters. Much of the rest is unattached algae, known as phytoplankton, and tiny animals, known as zooplankton. Both sorts of plankton support, directly or indirectly, the fish and mammals that live in the Arctic Ocean. And the plankton, too, are flourishing thanks to global warming. The Arctic phytoplankton bloom, which used to run from June to September, now runs from April to September.

The upshot is more plankton, farther north. That attracts more fish. In 2000 Atlantic cod were caught throughout the Barents Sea. By 2012 their distribution was skewed towards the northern part of that sea. Stocks of capelin (a small fish eaten by cod) used to be concentrated south of Svalbard, at latitude 75°N. In 2012 this had moved to 78°N. Some found their way as far up as 80°N.

Which all sounds most promising. But many researchers think it will not continue. First, the central Arctic is too deep for some important species, such as the polar cod (which belongs to a different genus from the Atlantic cod, and can live farther north). Young polar cod (those less than a year old) are pelagic, meaning they live at or near the surface. Those one or more years old are benthic, meaning they live near the bottom. In the Beaufort that bottom is 200 metres down. In the central Arctic it descends to about 4,000 metres, which is too deep for polar cod to survive.
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【Time3】
A second reason why there may be no bonanza is acidification of the ocean. When water absorbs carbon dioxide, it produces carbonic acid. More CO? means oceans everywhere are becoming more acidic, but the phenomenon is particularly marked at high latitudes because cold water absorbs CO? more readily than warm water does. The retreat of the ice also exposes ever more sea to do the absorbing. Cruises by the United States Geological Survey and the University of South Florida over the past three years have found rising carbonic-acid levels north of Alaska. They have also discovered that the shells of many organisms in the area are short of aragonite, a form of calcium carbonate that gives them strength, but whose formation acid discourages. Weaker shells means fewer shelled organisms and less food for fish.

The most important reason, though, for thinking that global warming will not produce an Arctic feeding frenzy is that it may increase ocean stratification. This is the tendency of seawater to separate into layers, because fresh water is lighter than salt and cold water heavier than warm. The more stratified water is, the less nutrients in it move around.
Most free-swimming sea creatures are pelagic. Algae need light, so must live near the surface—as must the zooplankton and other animals that need the phytoplankton. When they die, all these organisms sink to the bottom, where they become food for benthic creatures. Once they have been consumed their component molecules, including nutrients such as nitrates, phosphates and iron, are stuck in Davy Jones’s locker. For the surface to be productive, the locker must be opened and the nutrients lifted back up, so that they can feed the growth of phytoplankton.
【284】

【Time4】

Walking the plankton
[attachimg=290,317]114173[/attachimg]
One of the most important ways this happens is by upwellings of water from the bottom—great churning columns caused by the collision of cold and temperate waters. Two of the most important are in the Arctic: south of Greenland on the Atlantic side and south of the Bering Strait on the Pacific side. Nitrates are abundant at the surface in both places, which is why they are among the world’s richest fishing grounds. There are few upwellings in the tropics, which are thus nutrient-poor.

Stratification threatens this recycling system by suppressing the vertical movement of water. And global warming encourages stratification because it turns the ice into a layer of fresh water that sits on the surface. Imagine the ocean as a Tequila sunrise sitting on a warm bar. The ice cubes at the top are melting away and the orange juice is sinking to the bottom.

At the conference, a paper by Jean-Éric Tremblay and Marcel Babin of Laval University, in Quebec, described the effect by reporting the density difference of water at the surface and at a depth of 100 metres in different oceans. This density difference is an index of ocean stratification.

Parts of the Arctic seem to be getting badly stratified (see chart). In winter, there is almost no density difference in the North Atlantic and the Barents Sea—as you would expect given the upwelling there. But in summer, the northern part of the Barents Sea is even more stratified than the tropical Atlantic and Pacific. And the Beaufort Sea’s stratification is high in both summer and winter. Dr Tremblay concludes that the replenishment of nutrients is already limited by stratification, especially at high latitudes, and that global warming will make things worse.
【292】

【Time5】
For Arctic productivity, the consequences are likely to be dire. Paul Wassmann of the University of Tromso looked at the production of organic matter by algae (“primary production”) in different parts of the European Arctic, and used a climate model to predict the future. The area is divided into five economic zones. By 2050, according to the model, primary production is likely to have fallen in three of them, to be flat in one and to rise only in the Russian zone (the Kara Sea and part of the Barents Sea). Primary production is measured as the weight of carbon fixed by photosynthesis per square metre of the Earth’s surface. At the moment, in the most productive area of the Arctic, the Norwegian Sea, that figure is 142 grams a square metre a year. The model predicts this will fall to 128 grams. And by 2100, according to the model, things will be worse. By then, four of the five zones will have experienced a loss in primary production. Only Russia will benefit.

A warming Arctic will not, in other words, be full of fish. It will simply be an ice-free version of the desert it already is.
【198】

Obstacle

Motor Memory: Light Shed On How We Learn to Move

[attachimg=800,533]114174[/attachimg]

If you give a bioengineer a cookie..."When you grab a cookie and want to break off a piece with a chocolate chip," says Maurice Smith, balancing a crumbly bit between two of his fingers, "your brain must represent that action plan extrinsically, as it is an activity based in the world."

The cookies are on hand to celebrate the bioengineer's birthday in his lab at 60 Oxford Street, a white squat building located on the northernmost edge of the Harvard campus. A half moon of chocolate cake with a line of colored candles still intact also sits nearby.
Gesticulating with the cookie, Smith, Associate Professor of Bioengineering at the Harvard School of Engineering and Applied Sciences (SEAS), further teases out the intricacies of motor memory.

"An intrinsic representation is one that's body-based and procedural. It relates to the complex series of muscle and joint movements your body has to make to complete a task," Smith says.

"When I first had the thought to grab the cookie and rip off a chunk with a chocolate chip, my body responded appropriately," he notes.

Understanding the way the brain represents extrinsic and intrinsic actions, and the relationship between the two, has been of great interest to researchers who seek to understand motor control and motor learning -- or, put simply, how we learn to move.
Just a few months ago, Smith and his colleagues in the Neuromotor Control Lab laid out a generalizable theory about how the brain encodes such motor memories. Writing in the Journal of Neuroscience, they showed that units of motor memory are not so binary after all, but instead a mixture of both the intrinsic and the extrinsic.

"There's no question that our actions are inherently spatial, but the nature of the coordinate frame used in motor memory to represent space for action planning has been hotly debated," explains Smith. "The predominant idea had been that in memory we maintain separate intrinsic and extrinsic representations of action and translate between the two when necessary. But our work shows that memory representations are combinatorial rather than separate."

Individual neurons in several different motor areas of the brain encode multiplicative combinations of intrinsic and extrinsic representations, a property that neurophysiologists have called gain-field encoding. This much was known before, but it was thought that gain-field encoding simply provided a way to translate between intrinsic and extrinsic representations.

"We found that this gain-field encoding, which leads to a combinatorial representation of space, is not simply an intermediary in the transformation between representations, but is in fact the encoding on which motor memories are based," says Smith. "This suggests that the neurons which display gain-field encoding are the same ones that store the motor memories associated with the actions we learn."

The study, seemingly abstract, plays right into Smith's larger game plan. He and his research group at SEAS are trying to figure out the body's motor system the way a mechanic would: that is, well enough to be able to fix or temporarily repair it when it becomes damaged.

A neurodegenerative disorder resulting from a stroke or from a condition like Alzheimer's disease can make the act of picking up a cookie nearly impossible.But how does one go from an abstract theoretical model about encoding motor memory to something an engineer, a person interested in designing and building actual stuff and collecting real-world data about how we move, might more readily recognize?

The answer lies in a simple room slightly bigger than a walk-in closet. Near the entrance to Smith's lab, an alcove space is outfitted with a table, a monitor, an adjustable barber chair, and a digital pen and pad. The simple setup allows Smith and his team to record movements and to train participants to make hand motions based on visual cues.

Smith's lab is one of the few at SEAS that relies on human trials. In the facilities surrounding his, engineers have built tiny robotic insects, lungs-on-a-chip, and an artificial jellyfish made of a rat's heart tissue and silicone. Yet, despite its name, the work at the Neuromotor Control Lab seems far removed from the snap, crackle, and pop of actual neurons, as there are no neural head meshes or electrodes in sight. There are no brains in jars or neural tissue strands in glass petri dishes. Smith, who has an M.D. as well as a Ph.D. from Johns Hopkins, spends considerable time explaining how it all makes sense.

In the case of this new theory about intrinsic and extrinsic action, Smith's motion recording setup provides a simple yet powerful means to collect large amounts of data -- millions of individual movements -- that elucidate the algorithms and neural representations by which we learn to control our actions.

Jordan Brayanov, a graduate student at SEAS, excitedly explains where all of this work is ultimately headed: helping those suffering from brain injury.

"You cannot break real human brains for science, and it is difficult to work with patients who are already exhibiting cognitive deficits, so our lab is set up to mimic these conditions in healthy people -- in our case, a lot of Harvard undergraduates," says Brayanov. "Understanding how our bodies learn to reach and grasp provides us with insights about how the nervous system works. Just as importantly, we can start to see what may be happening when it's not working, when a person has some kind of motor disorder as a result of neurologic disease."

Motor dysfunction remains one of the most debilitating of health problems, and it is often the hidden deal breaker behind the nursing home placement and loss of independence for patients with Alzheimer's, which most people associate with declining mental abilities and deficits in declarative memories rather than motor skills.

"It's actually not so much the declarative memory loss that leads to having to institutionalize someone with Alzheimer's, but the inability to do the most basic motor tasks, like dressing or eating," explains Smith.

Armed with new insights from the lab, Smith and his team can offer guidance to others who are developing new ways to treat motor problems.

They're placing their hope in noninvasive techniques that use magnetic fields or direct current to selectively increase or decrease the neural plasticity of isolated populations of neurons -- no skull drilling required.

"These techniques have shown some promise for potentially boosting selective neural activity to stave off the onset of motor deficits," says Brayanov. "They're relatively crude right now. They can't yet zero in with millimeter accuracy on specific brain areas, but they will get better and better."

Therapeutic success, however, also requires clinicians to know which neurons to stimulate, and when.

In essence, Smith, Brayanov, and their colleagues are trying to write part of the instructional manual that doctors will one day use to help combat neurodegenerative diseases, much in the same way other engineers might provide the schematics for an artificial hand.

"If we can do that, we can potentially provide a boost in quality of life as well as a savings in healthcare expenditure," says Smith. "Even if it only means staving off a motor deficit for six months, in the case of a progressive neurodegenerative disease like Alzheimer's, that's still six months more of independent living."

This work was supported by grants from the McKnight Endowment for Neuroscience, the Alfred P. Sloan Foundation, and the Wallace H. Coulter Foundation.
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xueluanfei

沙发么、、

1.1'53 Because the climate turns warmer, the ice sheet in Arctic is becoming thiner and smaller. People anticipate a fish bonazar, but the bonazar is unlikely to form, because the climate has been changed too much.
2.2'18 By right the raising temperature should lead to increased number of fish. Because planktons can flourish when there are more sun shine. But scientists claim that the ocean is becoming too deep for some of the fish.
3.2'24 Because the raising temperature, the sea water absorb more CO2 and thus become more acid. This is not a friendly envirionment for the shell creatures, which are food of fishes. In addition, the raising temperature will also made the sea water stratified. This will lock the nutrition in different layers and break the circle. This will badly affact the sea creatures.
4.1'53 the stratification of the Artific ocean threaten the ocean environment severely.It prevent the vertific movement of the sea water. Now the oceans near the polar are badly stratified.
5.1'11  a scientist forcast the future of the ocenas. in three of the five zones  which are now full of fish resources, the number of fish will decrease.
obstacle:7'44
今天大脑不转啊。。为什么为什么呢。。。看什么都不走心
The scientist are trying to explain what is the relationship between the intrinsic actions and extrinsic actions. They've found that the intrinsic actions and extrinsic actions are working together. Combination functions of different nurons in the brain account for the intrinsic and extrinsic actions. By strudying how human learn to move, they can help those patients suffered by disease related to body movement. They are trying to come up with some plans...although these plans are not well-established...

铁板神猴

板凳么 哈哈 今天初二啊 大米新年好~~
晚上来读读小分队~人生一大快事 灭哈哈

铁板神猴

1'31''
1'58'' phytoplankton，zooplankton 印象中这个OG里也有提到吧~
1'47''
1'56''
1'05''

7'35''

jijiyangyu

1:29    
1:44
2:05
1:53
0:52
7:30
由一个神经科学的争论话题引出，介绍一个研究和它的展望。

张博文

大谢lz！！！

张博文

1:1'54
2:2'14
3:1'55
4:1'55
5:1'04
第一天做这个，我可以说完全不知所云么

fifiwong

1.(01'49'')the arctic ocean's ice sheet is getting thinner and smaller because of the global warming;there are few fish under the ice
2.(02'20'')plankton are flourishing thanks to global warming, more plankton will attract more fish;reaearchers think it will not continue,first,the central arctic is too deep for some important species
3.(01'34'')A second reason why there may be no bonanza is acidification of the ocean;The most important reason is that it may increase ocean stratification
4.(01'45'')Stratification threatens this recycling system by suppressing the vertical movement of water. And global warming encourages stratification because it turns the ice into a layer of fresh water that sits on the surfacearts of the Arctic seem to be getting badly stratified
5.(00'52'')A warming Arctic will not, in other words, be full of fish. It will simply be an ice-free version of the desert it already is.
obstacle(05'42'')
what is an intrinsic representation;
researchers with great intrest about how we learn to move,Smith and his colleagues showed that units of motor memory are not so binary after all, but instead a mixture of both the intrinsic and the extrinsic;they found that this gain-field encoding is not simply an intermediary in the transformation between representations, but is in fact the encoding on which motor memories are based
Smith and his research group are trying to figure out the body's motor system would be able to fix it when it becomes damaged; his lab, new thoery
they are trying to do.....

hxfnp92

【每日阅读训练第四期——速度越障14系列】【14-11】科技
1'52 Global warming is one of the reason that Arctic Ocean's ice sheet was half of what it was in 1979.And the big change of ecology cause the banaza .

2'27 This passage describes how the banaza occurs : the melt of ice sheet allows more sunshine reach the water.It causes the change of plankton and other creatures' lifestyle.

2'52 Another reason for banaza is acidification of the ocean.Ocean will be stratified and less creatures.

2'10 Upwellings of water from the bottom is abundant with  nitrates which is the favorate thing of fish.But global warming causes stratification that hamper the upwellings of water from the bottom.

1'13 A warming Arctic will not be full of fish in the future.

搞到这个点真是太不应该了，恶性循环啊恶性循环，明天不可以不可以！！

百嗑全输

第一次~