News this Week

Science  16 May 2008:
Vol. 320, Issue 5878, pp. 858

    Fermilab Sends Energy Department Final Plan to Lay Off 7% of Staff

    1. Adrian Cho

    BATAVIA, ILLINOIS—The uncertainty has been the worst part, says Rick Tesarek, a physicist here at Fermi National Accelerator Laboratory (Fermilab). He and his 1950 fellow employees have been wondering who among them will lose their jobs in layoffs forced by budget cuts late last year (Science, 11 January, p. 142). “This has been hanging over us for so long now that morale around the lab is starting to plummet,” Tesarek says. “We've been waiting since December.”

    The wait is nearly over. On 25 April, officials at the particle physics lab submitted their final plans for the layoffs to the U.S. Department of Energy (DOE) for approval. About 140 scientists, engineers, technicians, and other staff will receive pink slips in a 3-day process that could begin as early as next week. Roughly 60 more employees have accepted retirement or left because their term positions were not renewed. “We have to do what we have to do to ensure the health of the institution,” says Fermilab Director Piermaria Oddone. “I feel terrible about it. … There is no choice.”


    Fermilab's director, Piermaria Oddone, says budget cuts leave the lab “no choice” but to lay off employees.


    Fermilab officials have been hoping for an 11th-hour reprieve from the U.S. Congress. As Science went to press, the Senate version of a bill to fund the war in Iraq also contained $45 million for DOE particle physics that could be spent this year to avert the layoffs. But the House version of the bill provides no money for the lab, and it's not clear what version will finally prevail. Given that uncertainty, Oddone says that he must proceed with the layoffs.

    The cuts were forced when, in December, Congress passed a budget for fiscal year 2008 that slashed the lab's funding from a requested $372 million to $320 million, $22 million less than it had received the year before. The budget cuts specifically targeted funding for research and development on the proposed multibillion-dollar International Linear Collider; research on a superconducting accelerator technology known as SRF; and a proposed neutrino experiment called NOvA, which would have been the lab's biggest experiment once its Tevatron collider shuts down by the end of the decade. The staff cuts, however, will be spread across the lab, Oddone says.

    In addition to the layoffs, in February, Fermilab instituted a rolling furlough that requires salaried employees to take 1 week out of every 2 months as unpaid leave. (Hourly employees take their furloughs a few hours at a time.) The scheme, which will continue until the end of the year, has enabled the lab to keep the Tevatron running. But it has also made work much more difficult, says physicist William Wester. “The furlough is 10% of your time, but efficiency has gone down way more than 10% because you're gone one week and then the next week the person you're working with is gone,” he says.

    Many researchers say they'll be relieved when the cuts are finally done. But Stephen Pordes, a physicist at the lab, warns that those who elude the ax should not underestimate the impact of watching friends and colleagues lose their jobs. “It's going to be painful to be here even if one survives,” he says. Those laid off receive 2 weeks of paid leave with which to start hunting for another job. Those who remain face the task of rebuilding the lab's future.


    Chinese Cancel International Meeting

    1. Constance Holden

    The Chinese government last week canceled a major anthropology meeting scheduled for July in what appears to be a case of pre-Olympics jitters.

    More than 4000 anthropologists had signed up to attend the World Congress of the International Union of Anthropological and Ethnological Sciences (IUAES) in July in the southwestern Chinese city of Kunming. But on 6 May, the Chinese group hosting the conference told organizers it had encountered “complex difficulties” that would necessitate postponing the meeting. The next day, the group issued a letter saying that those difficulties had proven to be “unconquerable.”

    The sudden cancellation was “a huge surprise,” says sociologist Peter Nas of Leiden University in the Netherlands, secretary-general of IUAES. “Nobody expected this. Everything was going very smoothly.” He says that the Chinese officials said that there were “economic reasons” for the decision but would not elaborate. An official at the Chinese Academy of Social Sciences, which is serving as the host, told Science that “we are not well prepared.”

    Nas says he hopes the executive committee will discuss the problem in August at a European anthropology convocation in Slovenia. The union's Web site mentions July 2009 as a possible date.

    The meeting is held every 5 years at a different location. Some scientists have speculated that Chinese officials were worried that planned discussions about minority ethnic groups and issues relating to human rights could spark further unrest over Tibet, especially because there is a Tibetan enclave in Yunnan Province near Kunming. Travel to Tibet has been sharply restricted, and last month new visa rules were tightened. However, two international scientific meetings planned for just before the Olympics—on rangelands and on the solar eclipse—are going ahead as planned.


    The Cost of a Genuine Collaboration

    1. Yudhijit Bhattacharjee

    Most scientists would be thrilled to hear from the U.S. National Academy of Sciences (NAS) that they had just been elected to the prestigious organization. But when geneticist Nancy Jenkins got the call on 29 April, her reaction was more circumspect than jubilant. “What about Neal?” she asked. Chagrined to find that her husband and longtime scientific partner, geneticist Neal Copeland, was not on the list, Jenkins decided to strike a blow for true scientific coupledom and turn down the invitation.

    “The problem for me is that my husband and I run the lab together as a husband-and-wife team,” she explained in a 4 May letter to the academy's home secretary, John Brauman. “It is impossible to separate my contributions from Neal's as we did everything together on an equal basis. … Someday, if both of us have a chance to accept this honor together, it would be the highlight of our scientific careers.”

    Jenkins and Copeland are specialists in developing mouse models of human disease. They have followed identical scientific paths: After meeting 30 years ago as postdocs at Harvard University, they shared a lab at the U.S. National Cancer Institute for 22 years before moving together in 2006 to the Institute of Molecular and Cell Biology in Singapore. The two say that the academy should change its rules to recognize scientific couples and, more generally, research teams, as appropriate. “If somebody has worked their whole career side by side with another person, it doesn't make sense not to honor them together,” says Jenkins.

    Brauman says that the current standard of electing only individuals works well, adding that it is not impossible to separate the achievements of two partners. “Everybody recognizes that [Jenkins and Copeland] have made equally important contributions,” he says. “But they are not clones. They don't do exactly the same thing.” Brauman also says it's extremely difficult to find room in each annual class of 72 to honor scientists from the same field.


    Nancy Jenkins and Neal Copeland take a stand for science couples.


    This year was not the first time the academy has faced this situation. Neurobiologist Lily Jan delayed accepting her 1995 election because her husband and lab partner, Yuh Nung Jan, had not been chosen. “I was told that I [would] have 1 year to make the decision … and that there [was] a good chance that Yuh Nung [would] be elected by then,” says Jan, who is a professor at the University of California, San Francisco. He was, she adds, “and so we both joined NAS that year.”

    Some NAS colleagues counseled Jenkins to take a similar tack. “They said, ‘Oh, don't be silly, Neal will get in, be a good sport,’” she says. But she felt a larger principle was at stake. “The face of science has changed. … There are more women today and more husband-wife teams like us,” she says. “This kind of thing is going to happen more often in the future.”

    More important, Jenkins says, accepting the honor solo would have betrayed a tacit agreement the two struck before they were married and got their first academic jobs at the Jackson Laboratory in Bar Harbor, Maine. “We had to decide: Are we going to have separate labs and compete, or are we going to collaborate?” says Copeland. “We realized that if we competed even the slightest bit, we wouldn't stay married for long.”

    The two decided to become a team, alternating as last author on every one of their more than 750 papers. “It's a constant give and take,” says Jenkins. “We wouldn't have it any other way.”


    Price Is the Main Barrier to Wider Use of Papillomavirus Vaccine

    1. Jocelyn Kaiser
    Anticancer shot.

    Health experts hope that the HPV vaccine, given routinely in the United States, will become affordable for Latin American countries.


    At its debut 2 years ago, a vaccine that prevents cervical cancer was heralded as a public health breakthrough that could potentially save millions of women's lives. Yet although the vaccine is now given routinely to young girls in the United States and Europe, it hasn't been deployed in poorer countries, where it could make a bigger difference. This week at a meeting* in Mexico City, health officials and researchers are launching a campaign to introduce the vaccine in Latin America, the first region in the developing world likely to benefit.

    Many issues are unresolved, including whether health care systems are ready for the vaccine and whether conservative groups will oppose it. The biggest hurdle, however, is cost. Conference organizers hope that with new data on human papillomavirus infection and the vaccine's potential benefits, Latin American health officials can persuade their governments to negotiate with the two companies that manufacture HPV vaccines to lower the price, now $360 for three doses. The meeting will “send a strong message” about demand, says epidemiologist Jon Andrus of the Pan American Health Organization (PAHO) in Washington, D.C., a cosponsor.

    Cervical cancer is associated with HPV, the most common sexually transmitted disease. Clinical trials have shown that two HPV vaccines, made by Merck and GlaxoSmithKline (GSK), are at least 95% effective in preventing persistent HPV infection by the two main types that cause cervical cancer (HPV-16 and HPV-18) (Science, 29 April 2005, p. 618). Because screening—using Pap smears—catches most cervical cancer in industrialized countries, the HPV vaccines won't make much of a dent in cancer cases. But disease is much more common in the developing world, where screening often falls short. About 85% of the 270,000 deaths from cervical cancer each year occur in these countries.

    To prepare for the Mexico meeting, an international team of researchers pooled data from 15 years' worth of studies on HPV in Latin America and the Caribbean. Their meta-analysis of 118 studies, including data on 33,000 healthy women, found that the HPV infection rate averages 19%, with wide variation—from 13% in Mexico to twice that in Costa Rica. (Prevalence is 27% in the United States.) Women with cervical cancer were almost invariably infected with HPV; HPV-16 and HPV-18 accounted for 59% of cases in the region. That means that the Merck and GSK vaccines could prevent 500,000 deaths if given over 10 years to 70% of 12-year-old girls, the researchers found.

    Health officials in the developing world are questioning whether they can afford the price. HPV vaccination would reduce the burden of cancer treatment and cut back on screening—a woman might need to be tested three times in her lifetime, the analysis by the international team notes. Even so, the benefits would be worth the costs only if the vaccine's price comes down. Even at $25 for the three doses, adding HPV vaccine to the standard inoculation regime would cost $290 million over 5 years.

    Health experts expect that the companies will offer a discount, as they did in 2005 when they agreed to bulk sales of a new rotavirus vaccine aimed at preventing childhood diarrhea (Science, 24 September 2004, p. 1890). First, the World Health Organization (WHO) would need to prequalify the vaccines based on information submitted last year by the manufacturers. Then PAHO could begin negotiating.

    If Latin American countries buy the vaccine, they will move on to the challenge of getting it to young girls. This group is older than the one that receives traditional childhood vaccines, so health officials will likely introduce the HPV vaccine in schools. Latin America is up to the challenge, says Ciro de Quadros, executive vice president of the Sabin Vaccine Institute in Washington, D.C., and one of the meeting organizers. He points to the region's success with other vaccines, including nearly eradicating rubella since 1998 by vaccinating people up to 40 years old. “We hope HPV will be the same,” he says.

    It's still unknown whether the HPV vaccine will draw opposition, as it did in the United States. Some U.S. religious groups initially opposed it as condoning sexual activity by girls. But once the vaccine was widely introduced, notes Scott Wittet of the Seattle, Washington-based Program for Appropriate Technology in Health, those opponents had little influence. In a pilot project to explore introducing the HPV vaccine in Vietnam, Uganda, India, and Peru, this form of opposition has not been a problem so far, says Wittet. “Once people understand the issues, it's not a hard sell.”

    WHO will likely issue its decision on prequalifying the two vaccines within a few months, Andrus says. Also later this year, WHO and PAHO advisory councils will discuss guidelines on administering HPV vaccines. Assuming that they issue strong recommendations, Andrus says, price negotiations should soon follow.

    • *Towards Comprehensive Cervical Cancer Prevention and Control, Region of the Americas, 12–13 May 2008, Mexico City, Mexico.

  5. ITALY

    A Plea for 'Transparent' Funding

    1. Laura Margottini*
    1. Laura Margottini is a freelance writer based in London, U.K.

    A furor over political meddling in grants for stem cell research in Italy has erupted into a broad protest about favoritism and the lack of peer review in deciding who receives national science funding. Researchers in fields from astrophysics to oncology have endorsed a petition, written by Italian scientists and published in March in a national newspaper, that asks the government to authorize a new agency to allocate research funds independently and transparently. “In Italy, only a small proportion of the funds for scientific research is assigned according to a peer-review process. … It is high time that an evaluation system which assures science's success is translated into state laws and regulations,” the petition declares.

    A new plea from the petition's authors appeared in the same newspaper on 11 May; over the past few weeks, more than 1500 Italian researchers have signed the appeal, which was addressed to Italy's president, Giorgio Napolitano. He has publicly endorsed their request but has little authority to advance it within the government. The petition may also hit a dead end, as newly elected Prime Minister Silvio Berlusconi barely mentioned science in his campaign.

    The furor started last year when some prominent scientists were outraged to learn that the €3 million for stem cell research budgeted in Italy's 2007 national finance act had already been allocated; an unofficial list of awardees was leaked to the scientific community, although it has yet to be released by the Italian Institute for Health Research, which oversees the funds (Science, 30 November 2007, p. 1359). “We never saw a call for application or any other official, public announcement of the initiative and of how it would be managed,” says stem cell researcher Paolo Bianco of the University of Rome “La Sapienza.”

    Denying that the stem cell money has already been awarded, Italy's minister of health, Livia Turco, has promised that the funds would not be assigned without public competition and peer review. But no calls for grant applications have been announced.

    Disappointment with Italy's distribution of research funds extends beyond stem cell science. Two weeks ago, economist Andrea Ichino of the University of Bologna penned an editorial in the newspaper Il Sole 24 Ore saying that his field of statistical and economic public research suffered from a similar lack of transparency. Jobs and grants, he claimed, are awarded mainly without peer evaluation.

    Some scientists are now concerned that a new law designed to centralize university grants distribution, scheduled to go into force this year, may further increase favoritism and politicians' influence. “I fear this is the way research will be managed from now on,” says stem cell researcher Ranieri Cancedda of the University of Genova.

    Part of the concern about the new law is that Fabio Mussi, the minister of universities and research, has not yet provided rules governing allocations and public competitions for the so-called FIRST fund, which totals €300 million for 2008 and €360 million for 2009. An online document attributed to Italy's Ministry of Research also worries some researchers. It says that 70% of the newly created fund will be for strategic research on topics decided by government officials rather than projects submitted by scientists and chosen through peer review.


    Scientists are petitioning Italian President Giorgio Napolitano (left) and Prime Minister Silvio Berlusconi (right).


    Yet Francesco Beltrame, head of one of the scientific commissions of the Ministry of Research, tells Science that the online document does not reflect how the ministry plans to distribute FIRST funds, which he says will be distributed both by public competitions and “negotiation” between government and research institutions. As Italy waits to see how Berlusconi reshuffles government ministries, the country's scientists say they will continue to demand more transparency in how research money is awarded. “Every time public funds for scientific research are assigned by the national or regional government without a formal and regulated peer-review process,” says Elena Cattaneo of the University of Milan, trust in the system is “undermined.”


    Staggering Toward a Global Strategy on Alcohol Abuse

    1. David Grimm
    Health hazard.

    San people buy alcohol in a Namibian trading store. Harmful drinking is especially dangerous in poorer countries.


    Alcohol is about to get the type of attention usually reserved for AIDS and malaria. Next week, the World Health Organization (WHO) in Geneva, Switzerland, will take steps toward launching the first global assault on the harms associated with drinking. It's a bold move, but it may not be bold enough. Although recent data indicate that alcohol abuse is a major killer worldwide, some experts feel that objections from member states and the involvement of the alcohol industry have weakened a resolution intended to kick-start a WHO-led offensive. Others wonder whether WHO has the resources to make such a strategy effective—or whether the agency should be focusing on other problems.

    “A resolution is all very well, but it still takes a substantial commitment … for this to be translated into a substantial and lasting program of work,” says Robin Room, an alcohol policy expert at the University of Melbourne in Australia and a long-term observer of WHO.

    This isn't the first time WHO has flirted with an alcohol strategy. In 1983, the agency called on member states to strengthen their national alcohol policies—emphasizing a regional rather than global approach to the problem—but the words “fell on stony ground,” says Room. “Alcohol has been a politically touchy thing for WHO to deal with,” Room notes, saying that the United States threatened to withhold funds from WHO in the 1980s if it pursued policies hostile to private enterprise. For a time, alcohol “dropped off WHO's agenda.”

    Global toll.

    As a percentage of all risk factors that cause ill health, alcohol ranks high in many parts of the world, with developing countries bearing much of the burden.


    Then came WHO's World Health Report 2002. Drawing on various studies, including WHO's Global Burden of Disease project, the report concluded that alcohol was the fifth leading cause of death and disability worldwide. It beat out sanitation problems and high cholesterol and ranked just behind malnutrition and unsafe sex. Alcohol was as dangerous as tobacco, the report found—the source of up to 30% of various cancers and neurological disorders, and it had significant secondary dangers as well, leading to high rates of spousal abuse and homicide. Most devastating, however, was the conclusion that alcohol was the top cause of ill health and premature death in several developing countries, such as Brazil and Indonesia, and that—thanks to rising incomes—things were only going to get worse. “It was a significant wake-up call,” says Peter Anderson, a public health expert previously with WHO, who currently advises the European Commission and other agencies on alcohol policy.

    The report was the final straw for Finland. Having reduced liquor taxes to stay competitive with cheap Estonian imports, the country had seen a spike in alcohol-related deaths. In 2005, Finland banded together with other Nordic countries, including Sweden and Norway, and presented a resolution to the World Health Assembly, WHO's governing body, calling for a united effort to reduce alcohol-related health problems. “We wanted to see if a global strategy was possible,” says Bernt Bull, senior adviser at the Ministry of Health and Care Services in Norway and a member of the Norwegian delegation.

    The resolution passed but quickly ran into trouble. The United States favored a voluntary strategy and called for more input from the alcohol industry. Thailand objected that the resolution didn't go far enough and opposed industry involvement. And when WHO reconvened on the issue in May 2007, the drink trade had a new champion: Cuba. “The alcohol industry gives work and contributes to economic growth,” Oscar León Gonzalez of Cuba's foreign affairs department told the Swedish newspaper Svenska Dagbladet at the time. He also said poorer countries had bigger problems: “Many countries cannot understand why [the Nordic countries] push the alcohol question so hard when people lie dying of AIDS, tuberculosis, and malaria.”

    The resolution died, but a few months later two of these poorer countries, Rwanda and Kenya, resurrected it in the form of a similarly worded resolution, effectively deflating León Gonzalez's argument. “Alcohol causes a disproportionate burden of harm in poorer countries,” says Anderson, noting that people in these regions are likely to have more serious health risks and have less access to treatment. At the same time, the potential for harm is on the rise in countries like India as people get a bit more money in their pockets. “They're going to start developing the same [alcohol-related] problems we had 50 years ago,” notes Ralph Hingson of the U.S. National Institute on Alcohol Abuse and Alcoholism in Bethesda, Maryland. Hingson argues that WHO could help prevent a tragic repetition of this experience.

    Buoyed by Africa's involvement, the resolution won wide support from WHO's executive board. Next week, member states are scheduled to vote at the World Health Assembly, and the measure is expected to pass. As written, the resolution directs the WHO director general to formulate a global alcohol strategy within 2 years. WHO's final plan would not be legally binding but could include recommendations such as increasing alcohol taxes and banning certain types of liquor advertisements, as well as helping developed countries implement prevention strategies. A global approach is needed, says Anderson, because the alcohol trade crosses borders and because nations can learn from each other's efforts. “You can't just rely on a single country's response.”


    Despite its new momentum, however, the plan could run aground. Changes to the resolution, introduced recently by Mexico—and supported by Cuba and the United States—compel WHO's director general to collaborate with the alcohol industry in shaping its strategy. And that could produce a “weak and feckless policy,” says Derek Rutherford, chair of the London-based Global Alcohol Policy Alliance. “The industry tries to play down evidence-based factors that reduce alcohol consumption, such as taxes and advertising bans, and instead focuses on education, even though there's no proof that education works,” he says.

    On the contrary, taxes are often ineffective and can even backfire, driving consumers to dangerous home brews, especially in poorer countries, says Phil Lynch of the U.S.-based spirits company Brown-Forman, a member of the Global Alcohol Producers Group, which is consulting with WHO. The industry is not opposed to regulation, he says, it just wants to see a comprehensive approach. “We understand the products better than everyone else, … and we deserve a seat at the table.”

    WHO also must contend with limited resources. “WHO has a lot of irons in the fire,” says Room, noting that WHO's investment in alcohol programs has been “extremely small in comparison with the size of the problems.” And Ramanan Laxminarayan, an expert on global disease priorities at the Washington, D.C.- based think tank Resources for the Future, says it may be hard for WHO—and poorer countries—to justify interventions aimed at curbing dangerous drinking. Such interventions “are not good value for the money,” says Laxminarayan, noting that malaria interventions are up to 100 times more cost effective.

    Laxminarayan agrees with other global disease experts, however, that WHO is doing the right thing. “Developing countries don't always have the foresight to see that alcohol will be a big issue for them,” he says. “WHO can be very influential in this regard.” Hingson says developed countries could benefit as well. He notes, for example, that the U.S. Surgeon General has released more than 30 reports on tobacco but only two on the harms of alcohol. “We may think we're way ahead, but there are a lot of lessons we can learn.”


    A Mosquito Goes Global

    1. Martin Enserink

    The Asian tiger mosquito is on a rampage. Entomologists are impressed, public health officials are nervous, and many of the rest of us are swatting furiously. How did Aedes albopictus become such a scourge?

    The Asian tiger mosquito is on a rampage. Entomologists are impressed, public health officials are nervous, and many of the rest of us are swatting furiously. How did Aedes albopictus become such a scourge?


    When entomologist Paul Reiter made an odd discovery at a leafy old cemetery in Memphis, Tennessee, few people thought it was a big deal. At the graveyard's refuse dump, where he was studying mosquito behavior and ecology, Reiter, then with the U.S. Centers for Disease Control and Prevention, had caught a bug seen only a few times before in the Western Hemisphere: an Asian tiger mosquito (Aedes albopictus). “How the heck did it get here?” was his first thought. When he reported the find to the local health department, the official was nonplussed. “You better not find another one of those, or people may think you put it there!” he joked. Whatever it was, it wasn't cause for alarm.

    The year was 1983, and nobody knew that the Asian tiger mosquito was about to go on a global rampage. Within a few years, it was found in several southeastern states of the United States, in numbers so great that nobody could suspect Reiter—who's now at the Pasteur Institute in Paris—of planting them.

    Twenty-five years later, the mosquito has invaded 36 U.S. states, as well as many countries in South and Central America. It's on the march in Africa and the Middle East, has exploded in Italy, and seems set to conquer large swaths of Europe. Greenhouses in the Netherlands have been its latest and northernmost outpost. A worldwide trade in secondhand tires—which often contain water—has been the key to its wide-scale conquest. Lately, an exotic plant called Lucky bamboo has also given it a free ride.

    An aggressive daytime biter, Ae. albopictus is making life hell for gardeners and ruining picnics and wedding receptions. But the 2005–06 outbreak of an obscure disease called chikungunya in the Indian Ocean as well as a smaller one last summer in Italy have shown that it could also threaten human health—although how much is still fiercely debated among medical entomologists. Some take heart from the fact that although Ae. albopictus can be infected with a dizzying variety of viruses in the lab, so far in the real world it has been a rather wimpy disease vector. But others warn that its rise could confront Europe and the United States with serious outbreaks of diseases now restricted to the tropics.


    The Asian tiger mosquito, so called because of its bright white stripes, hails from East and Southeast Asia, where it originally lived at the edges of forests, breeding in tree holes and other small natural reservoirs. It has adapted easily to human settlements, where pots, vases, and buckets can replace tree holes, provided there's a bit of vegetation nearby. The mosquito is believed to have spread along with humans to Madagascar and the smaller Indian Ocean islands centuries ago.

    But its big break came with the advent of modern shipping. After World War II, when huge amounts of military equipment were sent back to the United States from war zones, inspectors from the U.S. Public Health Service discovered that Ae. albopictus had traveled along as a stowaway in used tires, as had six other exotic mosquito species. Radical control measures helped prevent it from establishing itself. Ae. albopictus was also found in tires reimported from Vietnam in 1972, but again, it didn't gain a foothold.

    In 1985, officials at the Harris County Mosquito Control District in Texas found an Ae. albopictus population near a roadside tire dump in Houston. Reiter, who helped investigate its source, soon became an expert in the thriving international trade in used tires. Millions of tires are shipped each year from countries such as Japan and Germany, which impose strict rules on their wear and on the use of “recaps,” to those that are more lenient, such as the United States; for various reasons, tires are also shipped from the United States to Europe and South America.

    The water the used tires hold is an ideal place for eggs and larvae, Reiter says; and even if it evaporates, the Asian tiger mosquito's eggs are so drought-resistant that they can survive until the tires reach their destination. (Mosquito species like Anopheles gambiae, a malaria vector, could never pull this off.) Meanwhile, the containers in which the tires are shipped ensure a comfy, sheltered journey.

    The mosquitoes imported into the United States probably came from Japan, Reiter and others wrote in a 1987 Science paper. Like their Japanese counterparts, Asian tiger mosquitoes were able to survive cold winters because their eggs respond to shortening days by going into a state of dormancy called diapause. That capacity, which many other tropical mosquitoes lack, is another key to the tiger's successful spread and explains why it can survive even Chicago's harsh winters.

    Its invasion of Latin America lagged behind by a few years, but it proved just as unstoppable. The mosquito was first found in São Paulo, Brazil, in 1986 and soon spread farther in southeastern Brazil. It popped up in Mexico in 1993, in Guatemala, Honduras, and El Salvador in 1995, and in Paraguay, Colombia, and Argentina in 1998. Panama and Nicaragua joined the club in 2002 and 2003, respectively. Good data are lacking for most parts of Africa, but the mosquito has already been found in Nigeria, Cameroon, Equatorial Guinea, and, last year, in Gabon.

    In Europe, Albania was the first to find Ae. albopictus within its borders, in 1979. The country was still an isolated Stalinist stronghold, and the news reached few scientists elsewhere. When Reiter teamed up with Albanian entomologist Jorgji Adhami to document the outbreak in the 1980s, they concluded that the mosquito may have first entered the country in 1975; the most likely source was China, one of Albania's few trading partners at the time.

    By far the hardest hit European country to date is Italy, which blew its chance to quash the nascent invasion, says Romeo Bellini, an entomologist at the Centro Agricoltura Ambiente “Giorgio Nicoli” (CAA) in Baricella. The first few tiger mosquitoes were found in a kindergarten classroom in the port city of Genoa in 1990, and other hot spots soon followed, but the government didn't act quickly or aggressively enough to kill adults and larvae. “They didn't understand what was going on; it wasn't a priority,” says Bellini. Eighteen years later, the mosquito is driving people nuts and chipping away at tourism revenue in towns and cities across northern Italy, where the climate is particularly favorable.

    In many other places, too, the tiger mosquito is a terrible nuisance. “It's really a horrible pest,” says Duane Gubler of the University of Hawaii, Honolulu. That may seem strange, because human blood isn't always its meal of choice. The mosquito is what entomologists call a “catholic,” or general, feeder: It can bite a wide variety of mammals, including cows and rats, as well as birds and reptiles. But what the tiger mosquito lacks in host specificity, it seems to make up for in aggression and its sheer numbers. And when other host species are scarce—as they likely are in many cities—the mosquito may have little choice but to bite humans.

    A health threat?

    The mosquito's impact on health is potentially more serious but also much less clear. In lab studies, researchers have shown that more than two dozen viruses can reproduce in Ae. albopictus. The most prominent is dengue, a viral disease that causes severe muscle and joint pains and can also lead to dengue hemorrhagic fever, a rare and often fatal disease. And now that Ae. albopictus has become so ubiquitous, “widespread … dengue in the continental United States is a real possibility,” Anthony Fauci and David Morens of the U.S. National Institute of Allergy and Infectious Diseases wrote in the Journal of the American Medical Association in January.

    But whether a mosquito actually spreads disease in the real world depends on many factors: its numbers, how often it bites humans, whether it takes blood meals from multiple people, and how effectively the virus makes it from the mosquito's gut to its salivary glands, and from there, to its victim's veins. So far, there's solid evidence for the tiger mosquito's role in the transmission of only two diseases: dengue and chikungunya. The latter is prominent in Africa and Asia, and its symptoms resemble those of dengue. And even for those two, the mosquito isn't historically known to be a very efficient vector, says Gubler.

    Breeding ground.

    An entomologist finds mosquito larvae in a discarded tire.


    The reason appears to be its wide host range. If a mosquito bites a dengue-infected child only to move on to a lizard, the virus goes nowhere because it infects only primates. By contrast, a species called Ae. aegypti—also known as the yellow fever mosquito—dines almost exclusively on humans, which is why it has caused an explosive rise in dengue cases in the tropics the past 2 decades. Dengue outbreaks in places that have only Ae. albopictus tend to be mild, Gubler says; a 2001–02 outbreak in Hawaii infected only 122 people, for instance.

    In fact, Gubler predicts that the spread of Ae. albopictus will actually result in a net gain for public health because in many places, it is pushing out Ae. aegypti populations. (The species' larvae compete for food when they share water containers, and the tiger mosquito appears to win often.) That's why Gubler dismisses gloomy scenarios like that published by Fauci and Morens. “I couldn't believe they wrote that,” he says.

    Didier Fontenille of the Institute of Research for Development in Montpellier, France, says he once agreed with Gubler but no longer does. The massive chikungunya outbreak in the Indian Ocean islands, which sickened more than a third of the population in a few months in La Réunion, was caused by Ae. albopictus. The small outbreak in Italy's Ravenna province last summer sickened more than 200 and killed one older woman. As-yet-unpublished work by Fontenille and his colleagues shows that the mosquito population in La Réunion strongly prefers humans. If that pattern holds true in other countries, the tiger mosquito may be a much more dangerous vector than people assume, he says.


    Two studies have also suggested that the chikungunya virus underwent a single-nucleotide mutation during the Indian Ocean outbreak that made it more able to use Ae. albopictus as a vehicle (Science, 21 December 2007, p. 1860). Nobody can rule out that something similar could happen with dengue, he warns, or with any of the other viruses it was shown to transmit in the lab. Even if Ae. albopictus pushes out its main competitor, “there's no reason to be happy,” says Fontenille.

    Tough fight

    Can the tiger mosquito be stopped? Experience to date suggests that once it's become established, it's almost impossible to get rid of, says Francis Schaffner of the University of Zürich, Switzerland. At that point, the only option is suppressing its numbers—and even that is difficult and costly.

    Eliminating breeding sites, such as flowerpots and vases, is effective, but it requires the public's participation, which is hard to sustain. Even in Italy, where the public has been bombarded with educational materials—including posters, mugs, and screensavers—larval control is falling short, says Bellini. Spraying insecticides is another widely employed tactic, but its effectiveness is probably limited, says Reiter. Hiding in vegetation, the mosquitoes are much harder to reach with aerosol droplets than are Ae. aegypti, which tend to stay inside or close to houses.

    Italy is betting on a new weapon: the so-called sterile insect technology (SIT), which aims to drive down the population by releasing massive numbers of sterile males. SIT has been used successfully to battle agricultural pests (Science, 20 July 2007, p. 312), but its use with mosquitoes is limited. Bellini's group at CAA has a facility to rear some 100,000 male mosquitoes a week and blast them with infertility-inducing gamma rays. It has studied the mosquitoes' viability and attractiveness to wild females, and a field trial to see whether they can reduce a population is slated for the summer.

    Bellini is under no illusion that SIT can eradicate the mosquito from Italy—that would require an immense investment—but it could help drive down populations in an environmentally benign way, he says. But so far, the budget for a rearing facility able to churn out the millions of males that would be needed weekly is still lacking.

    On the march.

    After becoming established in Albania and Italy, the Asian tiger mosquito started spreading to other European countries.


    Countries that have not yet seen the tiger mosquito can hope to prevent it from entering and can hit hard if it does. But again, the options are limited. For its medium-distance travel, the mosquito has been known to hitch a ride in automobiles and trucks—that's how it appears to have spread from Italy to Spain, France, Croatia, Slovenia, Switzerland, and Germany. There's simply no way to stop this type of spread, says Willem Takken of Wageningen University in the Netherlands.

    To prevent long-distance infestations, governments would have to regulate the international tire trade. But so far, few governments have been willing to clamp down on that economic sector to thwart an uncertain public health risk. Besides, there are other routes as well. In the summer of 2005, greenhouse workers in the Netherlands started complaining about aggressive mosquitoes. This time, researchers found, the mosquito had hitched a ride in shipments of Lucky bamboo (Dracaena sanderiana), a popular decorative plant imported from China.

    A major horticultural hub, the Netherlands exports Lucky bamboo widely, which has triggered fears that it might seed new infestations. Horticultural companies have taken steps to reduce the risk, for instance, by treating shipments before they leave China, and no new tiger mosquitoes have been found in the past 6 months—but this may also be due to natural fluctuations, says Ernst-Jan Scholte of the Dutch Plant Protection Service. Wouter van der Weijden of the Centre for Agriculture and Environment, a lobby group, says the Dutch government isn't tough enough and warns that it risks dropping the ball, just like Italy did 18 years ago.

    Whether the mosquito could become established this far north—or indeed, how much farther it can push its worldwide range—is anyone's guess. The European Centre for Disease Control and Prevention in Stockholm has charged a group of European scientists to come up with some predictions. The group's map, published in the 2007 book Emerging Pests and Vector-Borne Diseases in Europe, shows that France, Belgium, and the Netherlands are at risk of being colonized, as well as the United Kingdom, Ireland, and even the coastal areas of Scandinavian countries. Other models have come up with different ranges, but they agree that the end is not in sight.

    Reiter predicts that at best the countries at risk can postpone becoming colonized. Whatever the natural boundaries of its potential habitat are, the tiger mosquito seems determined to reach them.


    Layers Within Layers Hint at a Wobbly Martian Climate

    1. Richard A. Kerr

    Scientists scrutinizing layered rocks on Mars report online this week in Science that the layers formed in sync with changes in the planet's orbit.

    Like Earth, Mars has a layered geology, but the martian version can have a particularly rhythmic regularity; scientists are finally getting a handle on the mechanism driving it

    For decades, planetary scientists assumed that the stunning layering of Mars goes back to the planet's innate unsteadiness. The planet wobbles and wanders in its orbit, changing the climate rhythmically. What else could shape the cyclic-looking layering in everything from icy polar deposits to crater fill? But without a time scale, researchers were long stymied in linking particular layering to any particular orbital variation. That left the door open for nonorbital explanations.

    Now, new studies are tentatively tying layering to orbital variations. Across the polar caps of Mars and in impact craters, within the past few million years and several billion years ago, new observations and analyses are revealing periodic groupings of layers of the sort that orbitally driven climate change could have laid down. Martian layer counting is all the rage now, says planetary scientist Oded Aharonson of the California Institute of Technology (Caltech) in Pasadena. “That's a good sign.”

    Just identifying martian layering as periodic and not a random jumble has been controversial. On Earth, paleoceanographers can do hands-on work on sediment cores, analyzing them from the meter scale down to the atomic scale to date the layers precisely. On Mars, researchers must work from images taken from hundreds of kilometers up. They know that younger layers pile up on top of older ones, but they have no idea how long a given set of layers took to form. In the North Polar Layered Deposits (NPLD), for example, alternating dark and light layers exposed in cliff faces presumably reflect dust-darkened ice versus bright, nearly dust-free ice, but it gets more complicated. Dark stripes can be shadows, not dirty ice; frost can mask truly dark layers; and less-than-vertical outcrops can distort the apparent thickness of layers.

    To avoid at least some of these problems, geophysicists J. Taylor Perron and Peter Huybers of Harvard University combined images and topography returned from 23 strips across the NPLD by the now-defunct Mars Global Surveyor orbiter. Knowing the slope across layers let them correct apparent thickness to true thickness. As they reported at the Lunar and Planetary Science Conference (LPSC) in March in League City, Texas, most of the surveyed terrains did show—within a lot of climatic noise—periodic layering with a layer thickness of roughly 1.6 meters, although the periodicity waxed and waned with time. A layer in such cyclic bedding may have formed as the planet rhythmically nodded over on its side to 45° or even more—pouring more summer sun on the poles and sending polar ice to the equator. Then Mars would have righted itself and returned to its initial climate, forming a contrasting layer, all in one 120,000-year cycle. If so, the researchers calculate, the upper kilometer or so of the NPLD would have formed over tens of millions of years.

    Mars has rhythm.

    Evidence is mounting that variations in the orbit of Mars drive cyclic climate changes that layer the planet.


    But Perron and Huybers are quick to point out that other, nonorbital processes could be modulating martian climate on a roughly periodic schedule, as El Niño does on Earth. To link layering to changes in orbit, they say, researchers must find a section of ice or rock in which layers change steadily if subtly in thickness or color in step with a longer term rhythm. For example, a series of thin layers might decrease in thickness in a rhythmic pattern that makes them stand out as a single packet. Such bundling could reflect the interaction between two orbital variations—for example, planetary tilt and the shape of Mars's orbit. Such an interaction would create a unique ratio of packet thickness to thin-layer thickness.

    Such bundling ratios are starting to show up. As they report online this week in Science (, planetary geophysicist Roger Phillips of the Southwest Research Institute in Boulder, Colorado, and colleagues analyzed data from SHARAD (SHAllow RADar) onboard the Mars Reconnaissance Orbiter. They found periodic layering on two scales within broad reaches of the NPLD. SHARAD bombards the martian surface with high-frequency radio waves that easily penetrate pure ice but reflect back off dirty ice. The radar sounded out 45 to 50 thin layers beneath the ice's surface, divided into four packets by distinctive zones of low reflection.

    So far, the group has two possible interpretations. The low-reflection regions could represent times when Mars's orbit grew rounder and less elliptical, causing storms loading the ice with dust to become less common. Or they could mark times of relatively small axial tilt over many tilt cycles. In either case, the researchers say, the entire NPLD probably formed over roughly the past 5 million years.

    LPSC attendees also heard the first quantitative evidence that orbital variations drove climate and geology much earlier in martian history. Planetary scientists Kevin Lewis of Caltech and Aharonson reported their analysis of layering in the low-latitude Arabia Terra region of Mars. They found rhythmic bedding at several locations, all dating to roughly 4 billion years ago. In Becquerel crater, 3.5-meter layers were bundled into packets that average 36 meters in thickness. Lewis and Aharonson have not publicly linked that 10:1 bedding ratio to any particular orbital variations, but they noted in their LPSC talk that Mars's thin atmosphere and lack of oceans make cyclic climate change driven by internal, El Niño-like processes much less likely there than it is on Earth. Nailing down periodic layering on Mars will no doubt require a lot more layer counting and perhaps a better sense of martian time.


    Click Chemistry Clicks Along

    1. Robert F. Service

    Researchers seeking new ways to forge molecules are saving steps and effort by adapting high-yield reactions to fill a variety of needs.

    Researchers seeking new ways to forge molecules are saving steps and effort by adapting high-yield reactions to fill a variety of needs

    Big impact.

    Products of click chemistry include this bullet-stopping plastic.


    NEW ORLEANS, LOUISIANA—Halfway into a talk at a meeting* here last month, Charles Hoyle, a chemist at the University of Southern Mississippi, Hattiesburg, whipped out a clear plastic disk a few centimeters thick and about the size of a small Frisbee. Lodged in the disk were two bullets—one .22 caliber and one .38—fired by one of his colleagues in the lab.

    The disc, Hoyle explained, is a laminate of two materials, one a rigid plastic, the other a new rubbery, highly efficient, energy-absorbing material. Putting the two materials together allowed the disk to absorb the energy of the speeding bullets and dissipate it without shattering. What's more, the bullet-stopping armor was made of cheap, everyday starting materials. In addition to armor, such laminates may one day find use in impact-resistant windshields for cars and airplanes, Hoyle says. “That was the most exciting thing I've seen in a couple of months,” says K. Barry Sharpless, a Nobel Prize-winning chemist at the Scripps Research Institute in San Diego, California.

    For many of the chemists in Hoyle's audience, the excitement lay as much in the way the new laminate was produced as in its impressive capabilities. It is a product of “click chemistry,” a term Sharpless coined in 2001 for an approach to synthesis that prizes the use of a few key chemical reactions to link together compounds that contain particular chemical groups. The reactions have a strong energetic driving force that ensures that the starting compounds react every time, quickly, efficiently, and without creating unwanted byproducts. Click chemistry, says chemist Craig Hawker of the University of California, Santa Barbara (UCSB), “is a philosophy about not falling in love with complexity.” And, as Hoyle's talk and others at a symposium at the American Chemical Society meeting here revealed, the philosophy is rapidly expanding throughout the world of polymers, materials science, drug delivery, and even biological imaging. “It has just exploded,” Hawker says.

    Sharpless says the goal of click chemistry is to synthesize materials the way nature does: by starting with a small set of building blocks and then linking them with just a handful of different reactions, as living organisms do in linking amino acids together with peptide bonds to forge proteins.

    By contrast, much of modern organic synthesis—such as the medicinal chemistry used to craft many drug molecules—uses a wide variety of less efficient reactions. After going through perhaps dozens of these inefficient reactions, researchers typically wind up with only a minute amount of their desired molecule. Sharpless argues that chemists need to spend more time adapting efficient reactions to suit their needs.

    Sharpless and his colleagues at Scripps kicked off the effort earlier this decade when they improved a well-known chemical reaction called the Huisgen reaction, in which chemical groups with carbon-carbon triple bonds called alkynes are linked with azides, which harbor N3 groups with two nitrogen-nitrogen double bonds. Once the reaction starts, the alkyne and azide building blocks quickly and reliably form ring-containing compounds called 1,2,3-triazoles. But the reaction normally proceeds slowly because a high energy barrier keeps it from getting started. In 2002, Sharpless's team, along with a separate team led by Morten Meldal at the Carlsberg Laboratory in Valby, Denmark, reported that a simple copper salt catalyst dramatically speeds up the reaction. Even better, the catalyst is highly specific, which meant that the alkynes and azides reacted readily with one another but with essentially nothing else, no matter what chemical bath they were stewing in.

    See here.

    Clicked-on fluorescent tags reveal newly synthesized DNA in tissues.


    That selectivity spawned an explosion of click chemistry, as researchers around the globe have attached alkynes and azides to all kinds of materials and used the reaction to click them together. In hundreds of papers in recent years, researchers have described novel ways to make materials with new functions. Popular techniques include tacking sugars or peptides onto polymers to make them more biocompatible and clicking new chemical functional groups onto proteins, nanoparticles, and fluorescent compounds. “This stuff has taken on a life of its own,” Sharpless says.

    As the session at the meeting made clear, the copper-catalyzed alkyne-azide reaction remains the gold standard of click chemistry. Scripps chemist M. G. Finn, for example, reported that his group has recently used the reaction to create metalbinding adhesives twice as strong as any on the market. David Haddleton, a chemist at the University of Warwick in the United Kingdom, also reported using the technique to link azide-containing sugar groups to alkyne-rich polymers to create precisely controlled mimics of glycoproteins that represent a key part of the way the immune system prevents infections from parasites. Down the road, Haddleton says, he hopes that such mimics could offer a new strategy for preventing infection from organisms that cause dysentery, a disease that hits 40 million people a year worldwide.

    The alkyne-azide reaction, however, is not the only game in town. “Click chemistry is no longer about a single reaction,” Hawker says. One new reaction developed recently links compounds with thiol and ene functional groups. Thiols are compounds with a sulfur-hydrogen group, and enes are compounds with double bonds between two carbon atoms. When triggered by the absorption of energy-rich ultraviolet photons or other initiators, the sulfur atom in the thiol group readily attaches to one of those carbons while the thiol's hydrogen atom links up with the ene's other carbon. And the reaction is so fast that vast numbers of thiols and enes can be linked up in just minutes.

    Progress in linking thiols and enes is taking off, Hoyle says, in part because the starting materials are cheap and abundant. They include commodity polymers such as polyethylene, widely used in products such as milk jugs and plastic grocery bags, and polystyrene, found in applications as diverse as CD jewel cases and packing peanuts. This easy availability has already prompted numerous groups to begin using click chemistry to tailor their standard polymers. Hoyle's bullet-stopping plastics are one example, and one he says he has improved considerably, although he is not ready to reveal details. To make that material, Hoyle's team first polymerized two pairs of thiol- and ene-containing compounds. One combo gave them the energy-absorbing material, the other the rigid polymer. They then laminated the two polymers together to help the energy-absorbing material shed the energy of the impact without breaking. Down the road, Hoyle says, expect researchers to click new functional groups onto plastic polyethylene films to improve their use as cheap food packaging, to prevent fresh food from spoiling, for example. Although similar plastic films are already on the market, they are typically made using a more expensive process.

    Thiol-ene progress promises to open new applications as well. For example, Luis Campos, a postdoctoral associate in Hawker's lab, reported at the meeting that the UCSB group has made thiol-ene polymers that serve as tiny molds for patterning photonic crystals: devices that control the movement of photons much as semiconductors control the motion of electrons. When Campos and his colleagues patterned a titanium-nitride-based photonic crystal atop a semiconductor light-emitting diode, it doubled the light emission from the LEDs, cutting their power consumption in half.


    Metal adhesives begin with two compounds, one capped with alkynes, the other with azides (right). Copper ions click them together to form a network.


    Biology offers another emerging set of applications for click chemistry. Cell biologists Adrian Salic and Timothy Mitchison of Harvard Medical School in Boston, for example, reported in the 19 February issue of the Proceedings of the National Academy of Sciences (PNAS) that they had created a specialized alkyne-containing DNA building block. They fed it to mice, whose bodies took up the nucleotide base and used it to make DNA in their growing cells. After the mice were sacrificed, the researchers spiked the tissues with a fluorescently labeled azide and a copper catalyst that reacted with the alkyne-containing nucleotide and lit up newly synthesized DNA in fast-growing tissues in the animals.

    Such an approach wouldn't work well in live animals, because the copper catalyst is highly toxic. But chemist Carolyn Bertozzi of UC Berkeley and colleagues recently developed a novel version of the azide-alkyne reaction that does away with copper. Last October, they reported in PNAS that by tweaking the normally linear alkynes to include eight-membered rings, they produced a strain in the molecules that prompted them to react more readily with an azide. It worked so well that the reaction essentially matched the rate of the copper catalyst. The researchers then used the reaction to click a fluorescent compound to specific sugar groups on live cells, with no apparent toxicity. In the 2 May issue of Science (p. 664), Bertozzi and her colleagues took the work a major step forward by showing that they could click a series of such fluorescent reporters to different biomolecules to visualize key steps in the development of zebrafish embryos. Bertozzi's team is now using the technique to try to watch the molecular dance that takes place as stem cells differentiate into various tissues.

    Click chemistry may soon be making an impact on medicine as well. Hawker says he and his colleagues are clicking radioactive cobalt-64 to the interior of nanoparticles designed to keep the immune system from clearing the cobalt from the body. Peptides designed to bind to proteins found on damaged vessels of the heart are then clicked to the outside of the nanoparticles to steer them to their target. Ultimately, Hawker says, the system could provide doctors with an extremely sensitive way to spot the warning signs of the blood-vessel damage that accompanies atherosclerosis before any potential heart attack. Bertozzi says she is pursuing a related strategy to image cancer cells.

    Clearly, be it in biology, polymers, or materials science, click chemistry is starting to click.

    • *American Chemical Society Spring 2008 National Meeting, 6–10 April.


    The Hot Question: How New Are the New Superconductors?

    1. Adrian Cho

    Do iron-and-arsenic superconductors work the same way as the older, inscrutable copper-and-oxygen compounds? Early evidence points both ways.

    Do iron-and-arsenic superconductors work the same way as the older, inscrutable copper-and-oxygen compounds? Early evidence points both ways

    Twenty-two years ago, the recondite world of condensed matter physics erupted into a frenzy of headline-grabbing discoveries. In June 1986, German experimenter J. Georg Bednorz and Swiss colleague Karl Alexander Müller reported that a compound called lanthanum barium copper oxide carried electricity without resistance at temperatures as high as 35 kelvin. That was closer to absolute zero than to room temperature (300 kelvin), but it was a whopping 12 degrees above the previous record for such “superconductivity.” The discovery sparked a race for other copper-and-oxygen, or cuprate, superconductors with higher “critical temperatures” and bagged a Nobel Prize.

    Plainly similar.

    The old and the new superconductors both contain planes of ions magnetized in opposite directions. In the older ones, electrons hop from copper to copper (arrow).


    History seems to be repeating itself. In the past 5 months, researchers in Japan and China have cranked out a new family of high-temperature superconductors (Science, 25 April, p. 432). In place of copper and oxygen, the new compounds contain iron and arsenic, and the highest critical temperature for them has already reached 55 kelvin. That's far from the current record of 138 kelvin for the cuprates. But even as researchers strive for higher temperatures, they are preoccupied with one question: Do the new materials work the same way as the old ones?

    It's a key issue because, after 2 decades of debate, physicists still do not agree on how the electrons in the cuprates perform their magic at such high temperatures. Many researchers regard high-temperature superconductivity as the single deepest mystery in condensed matter physics, and the new compounds might help to solve it. By comparing and contrasting the old and new superconductors, physicists might tease out commonalities that reveal how both of them work—if they work the same way.

    That's a tricky if, says Hai-Hu Wen, an experimenter at the Institute of Physics (IOP) at the Chinese Academy of Sciences in Beijing. “The [new family of materials] looks very similar to the cuprates,” Wen says. But, he adds, “the mechanism may not be the same.” Peter Hirschfeld, a theorist at the University of Florida, Gainesville, notes that given the uncertainties surrounding the older materials, it may not make sense to ask if the new ones employ the same tricks. “Tell me how the cuprates work,” he quips.

    Still, physicists are pumping out papers on the new superconductors at a prodigious rate, and they have enough data to explain why they might or might not expect the new materials to work the same way as the old ones. Some are already taking sides in the emerging debate.

    The mystery of the cuprates

    Electricity won't flow through an ordinary wire without power from a battery or another source to push it. That's because the electrons flowing through a metal wire lose energy as they ricochet off the jiggling ions in the crystalline material. In a superconductor, however, the electrons avoid such drag by forming pairs. Deflecting an electron then requires breaking a pair, and at low temperatures there isn't enough energy around to do that. So the pairs glide unperturbed, and current flows without power.

    Of course, like-charged electrons repel each other, so something has to hold a pair together. In 1957, American theorists John Bardeen, Leon Cooper, and Robert Schrieffer showed that in conventional superconductors, such as niobium chilled below 9.3 kelvin, vibrations rippling through the material's positively charged ions attract the electrons to one another. When one electron moves, it sets off a vibration that draws the second electron in its wake. But vibrations don't pull hard enough to produce the sky-high critical temperatures in the cuprates.

    A cuprate superconductor is like a multitiered dancehall for electrons. The compound contains planes of copper and oxygen atoms along which the electrons glide like paired dancers. Between the planes lie elements such as lanthanum, strontium, barium, and yttrium. By default, a material has one potentially mobile electron per copper ion, and the electrons repel one another so mightily that they get stuck in a massive traffic jam called a Mott insulator state. To produce superconductivity, researchers “dope” the nonsuperconducting “parent material” with extra oxygen, which nestles between the copper-and-oxygen planes and soaks up a few electrons. The impasse then breaks, and the electrons somehow pair and flow freely.

    Most physicists believe that the pairing originates not from some external factor such as vibrations but rather solely from the interactions of the electrons among themselves. “It's almost like the electrons are gluing themselves together,” says Michael Norman, a theorist at Argonne National Laboratory in Illinois. But physicists still don't agree on how the electrons do that.

    For example, electrons act like little magnets, and in a parent compound, those on neighboring copper ions point in opposite directions to form a static pattern known as antiferromagnetism (see figure). Some physicists argue that waves rippling through that pattern, which becomes fluid as oxygen is doped in, provide the glue for pairing. Others contend that no glue is needed and that pairing evolves, ironically, out of the repulsion between particles alone. Still others have proposed explanations involving tiny loops of current and other mechanisms. No theory quantitatively accounts for the myriad foibles of the complex materials.

    Same tango, different dance floor

    The new iron-arsenide superconductors could help sort through the different possibilities. Hideo Hosono, a materials scientist at the Tokyo Institute of Technology, and colleagues found the first compound, fluorine-doped lanthanum oxygen iron arsenide (LaO1-xFxFeAs), as they reported online 23 February in the Journal of the American Chemical Society. It weighed in with a critical temperature of 26 kelvin.

    Four Chinese groups quickly pushed the critical temperatures higher by replacing the lanthanum with other elements. On 25 March, Xianhui Chen of the University of Science and Technology of China in Hefei reported on the arXiv preprint server ( that samarium oxygen fluorine iron arsenide (SmO1-xFxFeAs) goes superconducting at 43 kelvin. Four days later, Zhong-Xian Zhao of IOP reported on the server that praseodymium oxygen fluorine iron arsenide (PrO1-xFxFeAs) has a critical temperature of 52 kelvin. On 13 April, Zhao's team reported a critical temperature of 55 kelvin for the samarium compound grown under pressure. The compounds all have the same crystal structure, and higher critical temperatures may be possible if researchers can find structures that pack in the planes more tightly, Zhao says.

    The new compounds show striking similarities to the cuprates. Like the cuprates, they are layered materials, with planes of iron and arsenic along which the electrons presumably waltz. As in the older materials, superconductivity sets in only when the “parent material” is doped to change the number of electrons in it. In a cuprate, the extra oxygen absorbs some electrons; in one of the new materials, the fluorine adds electrons to the iron-and-arsenic planes.

    Many researchers point to another observation as potentially key. Pengcheng Dai, an experimenter at the University of Tennessee, Knoxville, and Oak Ridge National Laboratory, and colleagues scattered neutrons off lanthanum oxygen iron arsenide doped with different amounts of fluorine. They found that the nonsuperconducting parent compound exhibits antiferromagnetism with alternating rows of iron ions magnetized in opposite directions. That pattern goes away as the material is doped and superconductivity sets in, the researchers reported 4 April on the arXiv.

    A similar thing happens in the older hightemperature superconductors, notes Steven Kivelson, a theorist at Stanford University in Palo Alto, California. “Some form of antiferromagnetism turns off as superconductivity turns on,” he says. “That's very reminiscent of the cuprates.” Given that and the other similarities between the new compounds and the cuprates, Kivelson says, “it's a good working hypothesis that they're parts of the same bigger thing.”


    Hideo Hosono, a materials scientist at the Tokyo Institute of Technology, cooked the first of the new superconductors that have captivated researchers the world over.


    Not quite a chip off the ol' block

    The similarities between old and new superconductors may mask more important differences, however. For example, the two families of compounds differ chemically in one obvious way. The new compounds contain iron, and in bulk iron, the individual magnetic ions tend to line up in the same direction to make a “ferromagnet,” the sort of thing that will stick to your refrigerator. But ferromagnetism and superconductivity usually mix about as well as vinegar and oil: A superconductor ordinarily expels a magnetic field that's not too strong, but an overwhelming magnetic field will rip apart electron pairs and kill superconductivity. So the very presence of iron hints at new physics, says Hosono, the discoverer of LaO1-xFxFeAs. “This may be the first compound in which ferromagnetic elements and high-temperature superconductivity coexist,” he says.

    Perhaps more important, the undoped parent compounds for the iron-arsenide materials differ from the undoped parent compounds for the cuprates in one key regard, says Philip Anderson, a theorist at Princeton University. The undoped cuprates are exotic Mott insulators with precisely one electron stuck on each copper ion, he notes. In contrast, the undoped iron-arsenide materials are more conventional metals in which the electrons, numbering two per iron ion, flow relatively freely.

    That means superconductivity evolves from very different starting points in the two families of materials, says Anderson, who argues that his “resonating valence bond” theory explains how superconductivity arises in the cuprates, without glue, from the Mott insulator state. “The only way I can make it the same is to invent some improbable chemistry that reduces [the starting point] to one electron” per iron ion, Anderson says. Superconductivity in the iron-and-arsenic materials must be a new beast entirely, he argues.

    Revitalizing the field

    All agree that physicists will need much more information before they can decipher the new compounds. But such information will surely come in a hurry. Thanks to their decades of work on the cuprates, condensed matter physicists have an arsenal of experimental and theoretical tools that they can now turn to the iron-and-arsenic compounds, says Patrick Lee, a theorist at the Massachusetts Institute of Technology in Cambridge. The fact that in the new materials the superconductivity emerges from a more conventional parent compound may also simplify matters, Lee says. “This may be an easier problem to crack,” he says, because “the physics isn't as profound.”

    Even if the new materials prove as inscrutable as the cuprates, their mere appearance has revitalized the field, as many people have wearied of banging their heads against the same problems, says Dai. “My honest assessment is that this will explode because people are so tired of the cuprates,” Dai says. “This will give people a new playground.” First one to the top of the jungle gym—or to figure out how closely the new one resembles the old one—is the winner.

Log in to view full text

Via your Institution

Log in through your institution

Log in through your institution