對於同一類型的反應堆核電站福島第一製藥東京電力公司，1981年 - 1982年美國的研究機構，進行了模擬的一切權力丟失，向美國核管理委員會（NRC）提交找到了。暴露的計算燃料，氫發電，融化的燃料的情況相似，當然，這一事件。雖然使用NRC的安全規例，如日本，沒想到，如早期恢復和電源線。
此模擬是仿照核火箭Brownsferry，進行由美國橡樹嶺國家實驗室。輸出約 110萬千瓦，福島第一製藥核電站 - 通用電氣的第5號（GE）的水煮沸的標誌“I”是火候。
Artificial Leaf Could Be More Efficient Than the Real Thing
By Mark Brown, Wired UK
Speaking at the National Meeting of the American Chemical Society in California, MIT professor Daniel Nocera claims to have created an artificial leaf made from stable and inexpensive materials that mimics nature’s photosynthesis process.
The device is an advanced solar cell, no bigger than a typical playing card, which is left floating in a pool of water. Then, much like a natural leaf, it uses sunlight to split the water into its two core components, oxygen and hydrogen, which are stored in a fuel cell to be used when producing electricity.
Nocera’s leaf is stable — operating continuously for at least 45 hours without a drop in activity in preliminary tests — and made of widely available, inexpensive materials — like silicon, electronics and chemical catalysts. It’s also powerful, as much as 10 times more efficient at carrying out photosynthesis than a natural leaf.
With a single gallon of water, Nocera says, the chip could produce enough electricity to power a house in a developing country for an entire day. Provide every house on the planet with an artificial leaf and we could satisfy our 14-terrawatt need with just one gallon of water a day.
Those are impressive claims, but they’re also not just pie-in-the-sky, conceptual thoughts. Nocera has already signed a contract with a global megafirm to commercialize his groundbreaking idea. The mammoth Indian conglomerate, Tata Group has forged a deal with the MIT professor to build a small power plant, the size of a refrigerator, in about a year and a half.
This isn’t the first ever artificial leaf, of course. The concept of emulating nature’s energy-generating process has been around for decades and many scientists have tried to create leaves in that time. The first, built more than 10 years ago by John Turner of the U.S. National Renewable Energy Laboratory, was efficient at faking photosynthesis but was made of rare and hugely expensive materials. It was also highly unstable, and had a lifespan of barely one day.
For now, Nocera is setting his sights on developing countries. “Our goal is to make each home its own power station,” he said. “One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology.”
Image: sahmeepee/FlickrOriginal story from Wired.co.uk
福岛核灾难让所有的人都受到惊吓。既使行动迟缓的欧盟这次也迅速做出反应，要求欧盟各国对其核电站的安全性做所谓的应力检验。独立的专家小组将对欧 洲143个核电站应对地震、洪水及恐怖袭击的能力进行评估。现在已经有人提出批评说，当初对银行的应力检验就在粉饰太平，而对核电站的应力检验很可能成为 应景的做法。因为这一检验是在自愿的基础上，并且主要通过计算机模拟。环境保护专家对这种检验方法提出了强烈的批评。Bildunterschrift: Großansicht des Bildes mit der Bildunterschrift: 德国Hamm-Uentrop的核电站
Nuclear Rules in Japan Relied on Old Science
By NORIMITSU ONISHI and JAMES GLANZ
Published: March 26, 2011
TOKYO — In the country that gave the world the word tsunami, the Japanese nuclear establishment largely disregarded the potentially destructive force of the walls of water. The word did not even appear in government guidelines until 2006, decades after plants — including the Fukushima Daiichi facility that firefighters are still struggling to get under control — began dotting the Japanese coastline.
Tokyo Electric Power Co., via Kyodo News, via Associated Press
U.N.’s Nuclear Chief Says Japan Is ‘Far From the End’ (March 27, 2011)
Week in Review: Radiation’s Enduring Afterglow (March 27, 2011)
Tokyo Electric Power Company, via European Pressphoto Agency
The lack of attention may help explain how, on an island nation surrounded by clashing tectonic plates that commonly produce tsunamis, the protections were so tragically minuscule compared with the nearly 46-foot tsunami that overwhelmed the Fukushima plant on March 11. Offshore breakwaters, designed to guard against typhoons but not tsunamis, succumbed quickly as a first line of defense. The wave grew three times as tall as the bluff on which the plant had been built.
Japanese government and utility officials have repeatedly said that engineers could never have anticipated the magnitude 9.0 earthquake — by far the largest in Japanese history — that caused the sea bottom to shudder and generated the huge tsunami. Even so, seismologists and tsunami experts say that according to readily available data, an earthquake with a magnitude as low as 7.5 — almost garden variety around the Pacific Rim — could have created a tsunami large enough to top the bluff at Fukushima.
After an advisory group issued nonbinding recommendations in 2002, Tokyo Electric Power Company, the plant owner and Japan’s biggest utility, raised its maximum projected tsunami at Fukushima Daiichi to between 17.7 and 18.7 feet — considerably higher than the 13-foot-high bluff. Yet the company appeared to respond only by raising the level of an electric pump near the coast by 8 inches, presumably to protect it from high water, regulators said.
“We can only work on precedent, and there was no precedent,” said Tsuneo Futami, a former Tokyo Electric nuclear engineer who was the director of Fukushima Daiichi in the late 1990s. “When I headed the plant, the thought of a tsunami never crossed my mind.”
The intensity with which the earthquake shook the ground at Fukushima also exceeded the criteria used in the plant’s design, though by a less significant factor than the tsunami, according to data Tokyo Electric has given the Japan Atomic Industrial Forum, a professional group. Based on what is known now, the tsunami set off the nuclear crisis by flooding the backup generators needed to power the reactor cooling system.
Japan is known for its technical expertise. For decades, though, Japanese officialdom and even parts of its engineering establishment clung to older scientific precepts for protecting nuclear plants, relying heavily on records of earthquakes and tsunamis, and failing to make use of advances in seismology and risk assessment since the 1970s.
For some experts, the underestimate of the tsunami threat at Fukushima is frustratingly reminiscent of the earthquake — this time with no tsunami — in July 2007 that struck Kashiwazaki, a Tokyo Electric nuclear plant on Japan’s western coast.. The ground at Kashiwazaki shook as much as two and a half times the maximum intensity envisioned in the plant’s design, prompting upgrades at the plant.
“They had years to prepare at that point, after Kashiwazaki, and I am seeing the same thing at Fukushima,” said Peter Yanev, an expert in seismic risk assessment based in California, who has studied Fukushima for the United States Nuclear Regulatory Commission and the Energy Department.
There is no doubt that when Fukushima was designed, seismology and its intersection with the structural engineering of nuclear power plants was in its infancy, said Hiroyuki Aoyama, 78, an expert on the quake resistance of nuclear plants who has served on Japanese government panels. Engineers employed a lot of guesswork, adopting a standard that structures inside nuclear plants should have three times the quake resistance of general buildings.
“There was no basis in deciding on three times,” said Mr. Aoyama, an emeritus professor of structural engineering at the University of Tokyo. “They were shooting from the hip,” he added, making a sign of a pistol with his right thumb and index finger. “There was a vague target.”
Evolution of Designs
When Japanese engineers began designing their first nuclear power plants more than four decades ago, they turned to the past for clues on how to protect their investment in the energy of the future. Official archives, some centuries old, contained information on how tsunamis had flooded coastal villages, allowing engineers to surmise their height.
So seawalls were erected higher than the highest tsunamis on record. At Fukushima Daiichi, Japan’s fourth oldest nuclear plant, officials at Tokyo Electric used a contemporary tsunami — a 10.5-foot-high wave caused by a 9.5-magnitude earthquake in Chile in 1960 — as a reference point. The 13-foot-high cliff on which the plant was built would serve as a natural seawall, according to Masaru Kobayashi, an expert on quake resistance at the Nuclear and Industrial Safety Agency, Japan’s nuclear regulator.
Eighteen-foot-high offshore breakwaters were built as part of the company’s anti-tsunami strategy, said Jun Oshima, a spokesman for Tokyo Electric. But regulators said the breakwaters — mainly intended to shelter boats — offered some resistance against typhoons, but not tsunamis, Mr. Kobayashi said.
Over the decades, preparedness against tsunamis never became a priority for Japan’s power companies or nuclear regulators. They were perhaps lulled, experts said, by the fact that no tsunami had struck a nuclear plant until two weeks ago. Even though tsunami simulations offered new ways to assess the risks of tsunamis, plant operators made few changes at their aging facilities, and nuclear regulators did not press them.
Engineers took a similar approach with earthquakes. When it came to designing the Fukushima plant, official records dating from 1600 showed that the strongest earthquakes off the coast of present-day Fukushima Prefecture had registered between magnitude 7.0 and 8.0, Mr. Kobayashi said.
“We left it to the experts,” said Masatoshi Toyoda, a retired Tokyo Electric vice president who oversaw the construction of the plant. He added, “they researched old documents for information on how many tombstones had toppled over and such.”
Eventually, experts on government committees started pushing for tougher building codes, and by 1981, guidelines included references to earthquakes but not to tsunamis, according to the Nuclear and Industrial Safety Agency. That pressure grew exponentially after the devastating Kobe earthquake in 1995, said Kenji Sumita, who was deputy chairman of the government’s Nuclear Safety Commission of Japan in the late 1990s.
Mr. Sumita said power companies, which were focused on completing the construction of a dozen reactors, resisted adopting tougher standards, and did not send representatives to meetings on the subject at the Nuclear Safety Commission.
“Others sent people immediately,” Mr. Sumita said, referring to academics and construction industry experts. “But the power companies engaged in foot-dragging and didn’t come.”
Meanwhile, the sciences of seismology and risk assessment advanced around the world. Although the United States Nuclear Regulatory Commission has come under severe criticism for not taking the adoption of those new techniques far enough, the agency did use many of them in new, plant-by-plant reviews, said Greg S. Hardy, a structural engineer at Simpson Gumpertz & Heger who specializes in nuclear plant design and seismic risk.
For whatever reasons — whether cultural, historical or simply financial — Japanese engineers working on nuclear plants continued to predict what they believed were maximum earthquakes based on records.
Those methods, however, did not take into account serious uncertainties like faults that had not been discovered or earthquakes that were gigantic but rare, said Mr. Hardy, who visited Kashiwazaki after the 2007 quake as part of a study sponsored by the Electric Power Research Institute.
“The Japanese fell behind,” Mr. Hardy said. “Once they made the proclamation that this was the maximum earthquake, they had a hard time re-evaluating that as new data came in.”
The Japanese approach, referred to in the field as “deterministic” — as opposed to “probabilistic,” or taking unknowns into account — somehow stuck, said Noboru Nakao, a consultant who was a nuclear engineer at Hitachi for 40 years and was president of Japan’s training center for operators of boiling-water reactors.
“Japanese safety rules generally are deterministic because probabilistic methods are too difficult,” Mr. Nakao said, adding that “the U.S. has a lot more risk assessment methods.”
The science of tsunamis also advanced, with far better measurements of their size, vastly expanded statistics as more occurred, and computer calculations that help predict what kinds of tsunamis are produced by earthquakes of various sizes. Two independent draft research papers by leading tsunami experts — Eric Geist of the United States Geological Survey and Costas Synolakis, a professor of civil engineering at the University of Southern California — indicate that earthquakes of a magnitude down to about 7.5 can create tsunamis large enough to go over the 13-foot bluff protecting the Fukushima plant.
Mr. Synolakis called Japan’s underestimation of the tsunami risk a “cascade of stupid errors that led to the disaster” and said that relevant data was virtually impossible to overlook by anyone in the field.
The first clear reference to tsunamis appeared in new standards for Japan’s nuclear plants issued in 2006.
“The 2006 guidelines referred to tsunamis as an accompanying phenomenon of earthquakes, and urged the power companies to think about that,” said Mr. Aoyama, the structural engineering expert.
The risk had received some attention in 2002, when a government advisory group, the Japan Society of Civil Engineers, published recommended tsunami guidelines for nuclear operators.
A study group at the society, including professors and representatives from utilities like Tokyo Electric, scrutinized data from past tsunamis, as well as fresh research on fault lines and local geography, to come up with the guidelines, according to a member of the study group who spoke on condition of anonymity, citing the sensitivity of the situation.
The same group had recently been discussing revisions to those standards, according to the member. At the group’s last meeting, held just over a week before the recent tsunami, researchers debated the usefulness of three-dimensional simulations to predict the potential damage of tsunamis on nuclear plants, according to minutes from those meetings. “We took into account more than past data,” the member said. “We tried to predict. Our objective was to reduce uncertainties.”
Perhaps the saddest observation by scientists outside Japan is that, even through the narrow lens of recorded tsunamis, the potential for easily overtopping the anti-tsunami safeguards at Fukushima should have been recognized. In 1993 a magnitude 7.8 quake produced tsunamis with heights greater than 30 feet off Japan’s western coast, spreading wide devastation, according to scientific studies and reports at the time.
On the hard-hit island of Okushiri, “most of the populated areas worst hit by the tsunami were bounded by tsunami walls” as high as 15 feet, according to a report written by Mr. Yanev. That made the walls a foot or two higher than Fukushima’s bluff.
But in a harbinger of what would happen 18 years later, the walls on Okushiri, Mr. Yanev, the expert in seismic risk assessment, wrote, “may have moderated the overall tsunami effects but were ineffective for higher waves.”
And even the distant past was yielding new information that could have served as fresh warnings.
Two decades after Fukushima Daiichi came online, researchers poring through old records estimated that a quake known as Jogan had actually produced a tsunami that reached nearly one mile inland in an area just north of the plant. That tsunami struck in 869.
Norimitsu Onishi reported from Tokyo, and James Glanz from New York. Ken Belson and Hiroko Tabuchi contributed reporting from Tokyo.
A daily tracker of the damage at the two imperiled nuclear plants.
Sexual Nature exhibition at the Natural History Museum in London
A Natural History Museum employee poses during the press view of the 'Sexual Nature' exhibition at the museum in London.The exhibition features videos, photos, taxidermy and interactive exhibits, showing sexual behaviour in the animal kingdom. It runs from February 11 to October 2, 2011.
Explore the Museum's fantastic natural history artworks in our new permanent gallery, Images of Nature. Free
21 Jan 2011 - 31 Jul 2012
Sexual Nature is the Museum's first exhibition dedicated entirely to the sex lives of animals and plants.
11 Feb 2011 - 02 Oct 2011
Join us as we speak to a seismologist about what caused the earthquake in Japan and the subsequent tsunami.
23 Mar 2011, 14:30
A genetic study of African hunter-gatherers suggests modern humans evolved in southern Africa rather than in the east.More news
Find out about our exciting spring 2011 programme of events, workshops and hands-on activities for school groups.
This science and slavery teaching resource supports a KS3 lesson on diet and nutrition, set in the historical context of the transatlantic slave trade.
Discover the incredible story or our own origins, with interactive skulls, ancient humans in augmented reality and much more.
Text HEART to 70007 to donate £3 and support the Unlock our treasures appeal. Find out more
Get to go to exhibition previews, special talks and events, and receive the quarterly magazine Evolve when you become a Museum Member.
【明 報專訊】從來沒做過推銷的人，但也深知一個道理﹕sex sells。所以英國自然歷史博物館（Natural History Museum）推出以性為主題的展覽Sexual Nature，注定暢銷。不過展覽不純粹是為了大賣而定下這題目﹕性不單是本能，更是物種存亡和進化的重要環節。展覽探討以下範圍﹕性是什麼？為什麼要分 兩性？在雌性生物卵子數目有限、因此有權揀擇的情况下，雄性要如何扭盡六壬獲得佳偶？雄性「得手」後，用什麼手段令其他雄性遠離自己的配偶，確保延續的是 自己的基因？人又如何把性，變成比傳宗接代更複雜的事情？你可以透過展覽，認識交配後獻上自己首級的雄性螳螂，看Isabella Rossellini拍攝有關深海琵琶魚（angler fish）奇特的交配習慣短片等，有噱頭之餘，也能讓人增進生物知識。
地點﹕Natural History Museum,
London SW7 5BD
電話﹕+44（0）20 7942 5000
The type of containment vessel used in the stricken reactors in Japan has long been thought susceptible to failure in an emergency.
Published: March 15, 2011
The warnings were stark and issued repeatedly as far back as 1972: If the cooling systems ever failed at a Mark 1 nuclear reactor, the primary containment vessel surrounding the reactor would probably burst as the fuel rods inside overheated. Dangerous radiation would spew into the environment.
Green Blog: Questions on the Nuclear Crisis in Japan (March 15, 2011)
Related in Opinion
Room For Debate
Traditional forms of disaster relief may only hinder recovery efforts. What will work instead?
Now, with one Mark 1 containment vessel damaged at the embattled Fukushima Daiichi nuclear plant in Japan and other vessels there under severe strain, the weaknesses of the design — developed in the 1960s by General Electric — could be contributing to the unfolding catastrophe.
When the ability to cool a reactor is compromised, the containment vessel is the last line of defense. Typically made of steel and concrete, it is designed to prevent — for a time — melting fuel rods from spewing radiation into the environment if cooling efforts completely fail.
In some reactors, known as pressurized water reactors, the system is sealed inside a thick steel and cement tomb. Most nuclear reactors around the world are of this type.
But the type of containment vessel and pressure suppression system used in the failing reactors at Japan’s Fukushima Daiichi plant — and in 23 reactors at 16 American plants — is physically less robust, and has long been thought to be more susceptible to failure in an emergency than competing designs.
G.E. began making the Mark 1 boiling-water reactors in the 1960s, marketing them as cheaper and easier to build — in part because they used a comparatively smaller and less expensive containment structure.
American regulators began identifying weaknesses very early on.
In 1972, Stephen H. Hanauer, then a safety official with the Atomic Energy Commission, recommended in a memo that the sort of “pressure suppression” system used in G.E.’s Mark 1 plants presented unacceptable safety risks and that it should be discontinued. Among his concerns were that the smaller containment design was more susceptible to explosion and rupture from a buildup in hydrogen — a situation that may have unfolded at the Fukushima Daiichi plant.
“What are the safety advantages of pressure suppression, apart from the cost saving?” Mr. Hanauer asked in the 1972 memo. (The regulatory functions of the Atomic Energy Commission were later transferred to the Nuclear Regulatory Commission.)
A written response came later that same year from Joseph Hendrie, who would later become chairman of the N.R.C. He called the idea of a ban on such systems “attractive” because alternative containment systems have the “notable advantage of brute simplicity in dealing with a primary blowdown.”
But he added that the technology had been so widely accepted by the industry and regulatory officials that “reversal of this hallowed policy, particularly at this time, could well be the end of nuclear power.”
In an e-mail on Tuesday, David Lochbaum, director of the nuclear safety program at the Union of Concerned Scientists, said those words seemed ironic now, given the potential global ripples on the nuclear industry from the Japanese accident.
“Not banning them might be the end of nuclear power,” said Mr. Lochbaum, a nuclear engineer who spent 17 years working in nuclear facilities, including three that used the G.E. design.
Questions about the G.E. reactor design escalated in the mid-1980s, when Harold Denton, an official with the N.R.C., asserted that Mark 1 reactors had a 90 percent probability of bursting should the fuel rods overheat and melt in an accident. A follow-up report from a study group convened by the commission concluded that “Mark 1 failure within the first few hours following core melt would appear rather likely.”
In an extreme accident, that analysis held, the containment could fail in as little as 40 minutes.
Industry officials disputed that assessment, saying the chance of failure was only about 10 percent.
Michael Tetuan, a spokesman for G.E.’s water and power division, staunchly defended the technology this week, calling it “the industry’s workhorse, with a proven track record of safety and reliability for more than 40 years.”
Mr. Tetuan said there were currently 32 Mark 1 boiling-water reactors operating safely around the globe. “There has never been a breach of a Mark 1 containment system,” he said.
Several utilities and plant operators also threatened to sue G.E. in the late 1980s after the disclosure of internal company documents dating back to 1975 suggesting that the containment vessel designs were either insufficiently tested or had flaws that could compromise safety.
Paul Gunter, director of the Reactor Oversight Project with Beyond Nuclear, an organization opposed to nuclear power, said regulators and utilities began raising concerns about the containment design as far back as the 1970s.
“The key concern has always been that the containment structure was undersized, and that a potential accident could overwhelm and rupture it,” Mr. Gunter said.
The Mark 1 reactors in the United States have undergone a variety of modifications since these initial concerns were raised. Among these, according to Mr. Lochbaum, were changes to the doughnut-shaped torus — a water-filled vessel encircling the primary containment vessel that is used to reduce pressure in the reactor. In early iterations, steam rushing from the primary vessel into the torus under high pressure could cause the vessel to literally jump off the floor.
In the late 1980s, all Mark 1 reactors in the United States were also ordered to be retrofitted with venting systems to help reduce pressure in an overheating situation, rather than allow it to build up in a containment system that regulators were concerned could not take it.
It is not clear precisely what modifications were made to the Japanese boiling-water reactors now failing, but James Klapproth, the chief nuclear engineer for General Electric Hitachi, said a venting system was in place at the Fukushima plants to help relieve pressure.
With electrical power cut off in the aftermath of the earthquake and backup sources of power either failing or exhausted, workers have been struggling to inject seawater into the reactor to maintain control, but they have had some trouble venting the resulting steam.
Mr. Gunter argued that in any event, such venting amounts to a circumvention of the whole notion of containment in the first place. “They essentially have to defeat containment to save it,” he said.
What role the specifics of the G.E. design is playing in the rapid deterioration of control at the Fukushima plant is likely to be a matter of debate, and it is possible that any reactor design could succumb to the one-two punch of an earthquake and tsunami like those that unfolded last week in Japan.
Although G.E.’s liability would seem limited in Japan — largely because the regulatory system in that country places most liability on the plant operator -- the company’s share price was down more than 2 percent at midday Tuesday as the situation at the Fukushima plant deteriorated.
Still, Mr. Lochbaum said it was important to emphasize that the design specifications for containment and cooling on any reactor are a matter of balance. The primary alternate reactor design, the pressurized water reactor, calls for a thicker and bigger containment structure, for example. A boiling-water reactor design like the one at Fukushima does allow for scaling back on the size of the containment system while ostensibly maintaining the requisite safety margins.
In that sense, Mr. Lochbaum said, G.E.’s boiling-water reactors should be no better or worse in weathering accidents than any other design.
Should the ability to cool the reactor completely fail, however, Mr. Lochbaum said, “I’d certainly rather have a bigger, thicker containment structure.”
New View of How Humans Moved Away From Apes
Published: March 10, 2011
Anthropologists studying living hunter-gatherers have radically revised their view of how early human societies were structured, a shift that yields new insights into how humans evolved away from apes.
Early human groups, according to the new view, would have been more cooperative and willing to learn from one another than the chimpanzees from which human ancestors split about five million years ago. The advantages of cooperation and social learning then propelled the incipient human groups along a different evolutionary path.
Anthropologists have assumed until now that hunter-gatherer bands consist of people fairly closely related to one another, much as chimpanzee groups do, and that kinship is a main motive for cooperation within the group. Natural selection, which usually promotes only selfish behavior, can reward this kind of cooperative behavior, called kin selection, because relatives contain many of the same genes.
A team of anthropologists led by Kim S. Hill of Arizona State University and Robert S. Walker of the University of Missouri analyzed data from 32 living hunter-gatherer peoples and found that the members of a band are not highly related. Fewer than 10 percent of people in a typical band are close relatives, meaning parents, children or siblings, they report in Friday’s issue of Science.
Michael Tomasello, a psychologist at the Max Planck Institute for Evolutionary Anthropology in Germany, said the survey provided a strong foundation for the view that cooperative behavior, as distinct from the fierce aggression between chimp groups, was the turning point that shaped human evolution. If kin selection was much weaker than thought, Dr. Tomasello said, “then other factors like reciprocity and safeguarding one’s reputation have to be stronger to make cooperation work.”
The finding corroborates an influential new view of early human origins advanced by Bernard Chapais, a primatologist at the University of Montreal, in his book “Primeval Kinship” (2008). Dr. Chapais showed how a simple development, the emergence of a pair bond between male and female, would have allowed people to recognize their relatives, something chimps can do only to a limited extent. When family members dispersed to other bands, they would be recognized and neighboring bands would cooperate instead of fighting to the death as chimp groups do.
In chimpanzee societies, males stay where they are born and females disperse at puberty to neighboring groups, thus avoiding incest. The males, with many male relatives in their group, have a strong interest in cooperating within the group because they are defending both their own children and those of their brothers and other relatives.
Human hunter-gatherer societies have been assumed to follow much the same pattern, with female dispersal being the general, though not universal, rule and with members of bands therefore being closely related to one another. But Dr. Hill and Dr. Walker find that though it is the daughters who move in many hunter-gatherer societies, the sons leave the home community in many others. In fact, the human pattern of residency is so variable that it counts as a pattern in itself, one that the researchers say is not known for any species of ape or monkey. Dr. Chapais calls this social pattern “bilocality.”
Modern humans have lived as hunter-gatherers for more than 90 percent of their existence as a species. If living hunter-gatherers are typical of ancient ones, the new data about their social pattern has considerable bearing on early human evolution.
On a genetic level, the finding that members of a band are not highly interrelated means that “inclusive fitness cannot explain extensive cooperation in hunter-gatherer bands,” the researchers write. Some evolutionary biologists believe that natural selection can favor groups of people, not just individuals, but the idea is hotly disputed.
Dr. Hill said group selection, too, could not operate on hunter-gatherer bands because individuals move too often between them, which undoes any selective effect. But hunter-gatherers probably lived as tribes split into many small bands of 30 or so people. Group selection could possibly act at the level of the tribe, Dr. Hill said, meaning that tribes with highly cooperative members would prevail over those that were less cohesive, thus promoting genes for cooperation.
The new data on early human social structure furnishes the context in which two distinctive human behaviors emerged, those of cooperation and social learning, Dr. Hill said. A male chimp may know in his lifetime just 12 other males, all from his own group. But a hunter-gatherer, because of cooperation between bands, may interact with a thousand individuals in his tribe. Because humans are unusually adept at social learning, including copying useful activities from others, a large social network is particularly effective at spreading and accumulating knowledge.
Knowledge can in fact be lost by hunter-gatherers if a social network gets too small. One group of the Ache people of Paraguay, cut off from its home territory, had lost use of fire when first contacted. Tasmanians apparently forgot various fishing techniques after rising sea levels broke their contact with the Australian mainland 10,000 years ago.
Dr. Chapais said that the new findings “validate and enrich” the model of human social evolution proposed in his book. “If you take the promiscuity that is the main feature of chimp society, and replace it with pair bonding, you get many of the most important features of human society,” he said.
Recognition of relatives promoted cooperation between neighboring bands, in his view, allowing people to move freely from one to another. Both sons and daughters could disperse from the home group, unlike chimp society, where only females can disperse. But this cooperation did not mean that everything was peaceful. The bands were just components of tribes, between which warfare may have been intense. “Males could remain as competitive and xenophobic as before at the between-tribe level,” Dr. Chapais writes.
Celluloid is the name of a class of compounds created from nitrocellulose and camphor, plus dyes and other agents. Generally regarded to be the first thermoplastic, it was first created as Parkesine in 1862 and as Xylonite in 1869, before being registered as Celluloid in 1870. Celluloid is easily molded and shaped, and it was first widely used as an ivory replacement. Celluloid is highly flammable and also easily decomposes, and is no longer widely used. Its most common uses today are in table tennis balls and guitar picks.
この他の化学遺産は、「日本の板硝子（ガラス）工業の発祥を示す資料」▽「日本最初の化学講義録 朋百舎密書（ポンペせいみしょ）」▽「化学新書」など 「日本学士院蔵 川本幸民化学関係資料」、の３件。２６日には神奈川大横浜キャンパスで関連の市民公開講座を開く。問い合わせは日本化学会（０３・ ３２９２・６１６１）へ。（竹石涼子）
The Reinvention of Silk
Published: March 7, 2011
As some silk researchers see it, if spiders were gregarious vegetarians, the world might be a different place.
For spiders are nature’s master silk makers, and over millions of years of evolution have developed silks that could be useful to people — from sticky toothpastelike mush to strong and stretchy draglines.
“There’s not just one kind of material we’re talking about,” said Cheryl Hayashi, who studies the evolutionary genetics of spider silk at the University of California, Riverside. “You can look in nature, and there are a lot of solutions already made. You want a glue? There’s a silk that’s already a glue.”
For years there has been talk of the bright promise of spider silk: that it might one day be used to make cables that are stronger than those of steel, for example, or bulletproof vests that are more effective than those made of Kevlar.
There has been a big fly in the ointment, however: spiders cannot spin enough of the stuff. Although a typical spider can produce five types of silk, it does not make much of any of them. Obtaining commercial quantities is a practical impossibility — spiders are loners and require a diet of live insects; some are cannibals. In other words, spider ranching is out of the question.
Researchers have worked to overcome this fundamental limitation by trying to unlock the secrets of the spider’s silk-making abilities so silk could be made in the laboratory, or by genetically transferring those abilities to other organisms that could produce silk in quantity. But so far the materials produced lack the full strength, elasticity and other qualities of the real thing.
Some scientists are making an end run around the spider problem and working on reinventing the one silk that is plentiful — that of silkworms. They are reconstituting it to make materials that have the potential to go far beyond the dream of bulletproof vests.
Among these researchers are David Kaplan and others at Tufts University, whose creations have potential applications in medicine and other fields. “Here’s a material that’s been around for 5,000 years and used in sutures for about that long,” Dr. Kaplan said. “Yet there’s this untapped territory.”
Dr. Kaplan’s group and colleagues at the University of Illinois and University of Pennsylvania have recently produced electrode arrays, for example, that are printed on flexible, degradable films of silk. The arrays — so thin they can conform to the nooks and crannies of the surface of the brain — may one day be used to treat epilepsy or other conditions without producing the scarring that larger implanted electrodes do.
For centuries, beginning in China, commercial silk has been produced by cultivating silkworms — the larvae of a moth, Bombyx mori — which, unlike spiders, are content to loll about cheek by jowl, munching on mulberry leaves, spinning the material in quantities large enough to be harvested.
“The advantage of silkworms is that they’re easy to grow,” Dr. Hayashi said. “They’re vegetarians. And they produce silk conveniently in this cocoon.”
“But if you look at a silkworm, it only has one kind of spinneret,” she added. “Only one kind of fiber can come out of it. Spiders have this whole toolbox.”
Efforts to make analogues of spider silks, however, have resulted in materials that are not much different from other polymers, said David Porter, a scientist at the University of Sheffield in England who works with a group at Oxford that studies the biology of silk making.
“The consensus is that almost anybody can make a reasonable silk,” Dr. Porter said. “But you really can’t differentiate it from a good nylon.”
“To differentiate the natural product, really you’ve got to get the advantages that nature builds in,” he added.
Silk is a fibrous protein, produced in glands within the spider or silkworm and some insects. What these creatures do is something no laboratory has been able to achieve: control the chemistry so exquisitely that the silk, which is a liquid inside the organism, becomes a solid upon leaving it.
Chief among the advantages of natural silk is the way the proteins are organized. They are folded in complex ways that help give each silk its unique properties. Scientists have not been able to replicate that intricate folding.
“We’re still not getting at the complexity of what’s going on in inside an individual spider,” Dr. Hayashi said. “There’s no lab anywhere in the world where somebody has an artificial silk gland.”
Producing spider-silk proteins in other organisms — bacteria, goats, plants and, most recently, silkworms themselves are among those that have been genetically engineered — has limitations because the process of reconstituting the proteins ruins any folding pattern. “As soon as you extract the silk, you basically randomize the protein structure,” Dr. Porter said. “You destroy all the capacity of that material to do what it wants.”
At Tufts, Dr. Kaplan thinks that eventually, genetically modified plants will produce useful spider-based silk that could be harvested like cotton. Until then, however, he is working with reconstituted silkworm silk, making novel films and other materials.
Dr. Kaplan has been researching silk for 21 years — “sad but true,” he joked — and spent much of the first decade learning about the fundamental mechanisms by which silk assembles.
“We learned how important water is,” he said. “It may sound trivial, but the entire process has been built around controlling water content.”
Over the past decade, Dr. Kaplan’s group has focused on biomedical applications in fields like tissue engineering. In 2005, a postdoctoral researcher in his laboratory developed a water annealing process, reconstituting the silks slowly in a humid environment. “We got these films that were crystal-clear,” Dr. Kaplan said. “No one had ever seen this before with silk.”
That led to thoughts about how to make an artificial cornea from silk. But a cornea has to be permeable, so Dr. Kaplan got the idea to involve a laser scientist down the hall, Fiorenzo Omenetto.
“I said, ‘Take it down to Fio and have him poke some holes in it,’ ” Dr. Kaplan recalled. “That led to a whole optical platform based on silk.”
It also led to a long collaboration with Dr. Omenetto, who has developed ways to pattern silk films, making diffraction gratings and other structures. The grating can act as a substrate for other proteins or compounds, raising the possibility that silk films could be used for implantable biosensors or in drug delivery, with the silk dissolving in the body at a controlled rate to release the drug.
One advantage with silk, Dr. Omenetto said, is that the process of making films or other structures is “green” — water-based and at low temperatures. “You can make incredibly sophisticated diffraction gratings out of glass or plastic,” he said. “But those are made at high temperatures or in a very harsh chemical environment,” conditions that would make it difficult to incorporate drugs or other compounds.
Researchers elsewhere have further developed the idea of using silk films for medical applications. At the Georgia Institute of Technology, Eugenia Kharlampieva experimented with depositing silver nanoparticles on films of silk as a way of strengthening them.
“Silk is a wonderful material because it’s biocompatible,” said Dr. Kharlampieva, who is continuing her research at the University of Alabama, Birmingham. “The main drawback is it’s soft. If you want to use it for optical applications, you need to reinforce it.”
The films she uses are extremely thin, and she layers them. “We make this nanocomposite which is flexible, still soft, but mechanically stronger.”
Because the films remain flexible, Dr. Kharlampieva is experimenting with fashioning them into tiny capsules that could contain minute quantities of drugs. Potentially as small as blood cells, they could be used to deliver drugs through the bloodstream.
At Tufts, Dr. Omenetto’s work on patterning silk has led to even more exotic potential applications. Among the latest, developed with colleagues at Boston University, is the idea of using silk as the basis for metamaterials, which can manipulate light or other electromagnetic radiation in ways that nature ordinarily cannot. By producing intricate structures in the films and depositing metal on them, metamaterial antennas may be produced that could be used inside the body as a means of monitoring health — the signal from the antenna changing as conditions inside the body change.
Such applications may be far off, Dr. Omenetto said, but the potential is vast — a fact he realized when he was first asked to poke holes in silk. “It looked like a cool optical material,” he said. “And I haven’t been sleeping that much ever since.”
This article has been revised to reflect the following correction:
Correction: March 7, 2011
An earlier version of this article misstated the academic affiliation of David Porter. He is with the University of Sheffield, not Suffield University.
An earlier version of this article misstated the academic affiliation of David Porter. He is with the University of Sheffield, not Suffield University.