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大家好，胖胖翔来啦！第三和第四篇来自一篇文章，enjoy~ Part I: Speed [Time 1] Article 1 Why Most Snails Coil to the Right
GUELPH, CANADA—When plucking a snail from the beach you'd be lucky to snag a left-coiling shell. That's because only 5% of all snails are "lefties," new research shows. Shell enthusiasts have long marveled at the lack of sinistral (left-coiling) snails among their collections, especially when other shelled mollusks, such as clams and the now-extinct ammonites—nautiluslike creatures that sported dozens of tentacles inside spiraled shells—are just as likely to be left- as right-coiling. Now, in the largest survey of its kind, researchers inspected more than 55,000 snail species—representing two-thirds of all gastropods—to reveal that left-coiling has arisen more than 100 times, and yet few of the species that have made the switch have been particularly successful. In the rare cases where left-coiling took off, it was almost always on land, the team reported here in a presentation last week at the annual meeting of the Canadian Society of Zoologists. The researchers don't know why sinistrality is so rare underwater, but the most likely explanation, they say, is that unlike land snails that tend to hang around where they hatch out, the microscopic young of sea snails are carried on ocean currents that make the chance of meeting and reproducing with another left-coiling nest-mate slim. Without such a meeting, the left-coiling lineage goes extinct. [字数：217]
[Time 2] Article 2 Fungi Provide an Early Warning System for Plants
The deal between plants and soil fungi is well known. The fungus takes soluble carbohydrates such as sugars from the plant's roots, while the plant makes use of extra soil minerals absorbed by the extensive surface area of the fungal mat or mycelium. Now, it appears that the plant gets something extra in the bargain. When a bean plant (Vicia faba) is infested with aphids, it produces a cocktail of chemicals that repels the insects but attracts a natural aphid predator, the wasp (inset). Even bean plants not attacked by aphids produce these chemical defenses—as long as they are connected to the besieged plants via a fungal mat—a team reports online this month in Ecology Letters. The researchers don't know exactly how the danger is communicated but the possibility of aboveground signaling was ruled out: The plants were covered with bags. The most likely mechanism, they say, is chemical communication by means of the fungal network. The roots of many important food crops including wheat, rice, and maize exist cheek by jowl with symbiotic fungi, and this has major implications for green pest control of the aphid (main picture). Strategically placed plants throughout the crop would trigger the chemical response for the benefit of the other plants. Altruistic? Yes, but a few plants sacrificed for the health of the whole field makes economic sense in the war against this agricultural enemy. [字数：233]
[Time 3] Article 3 Pathogen genome tracks Irish potato famine back to its roots
Strain caused more than a million to die of hunger but was less aggressive than modern ones. The great potato famine of the 1840s was a defining event in Ireland’s recent history. An Gorta Mór — the Great Hunger in the Irish language — caused millions to starve or emigrate and helped catalyse the country’s bloody war of independence from Great Britain. Working from 150-year-old dried leaves, two competing teams have now sequenced the genome of the single-celled organism that wreaked havoc on the Irish potato crop. It is the first ancient plant pathogen to have its genome decoded. (In 2011, scientists reported the sequence of the plague-causing bacteria responsible for the Black Death of the 1340s.) Phytophthora infestans, which causes potato late blight, is an oomycete — a type of single-celled organism related to brown algae. Carried by infected potatoes, the disease probably arrived at the port of Antwerp in Belgium in the summer of 1845, before quickly spreading through the Low Countries and much of western Europe. Ireland’s dependence on potatoes was the reason the epidemic exacted a far greater toll there than it did on the rest of the continent. Irish peasants working plots owned by absentee British landlords relied on potatoes for most of their calories, says Detlef Weigel, a plant geneticist at the Max Planck Institute for Developmental Biology in Tübingen, Germany, who co-led a study published today in the journal eLIFE1. “The potato is really an amazing staple crop. If you have a diet of potato and milk, you don’t need anything else.” The disappearance of that staple had devastating consequences, including 1 million deaths and still more emigrations. Ireland’s population of 4.5 million is still less than three-quarters of its pre-famine level. The perception that Britain did little to intervene in the catastrophe helped foment Irish nationalism, eventually resulting in the Irish War of Independence in 1919. [字数：311]
[Time 4]
A blight across the Earth Long before it hit Europe, P. infestans probably circulated in the Toluca Valley in central Mexico, where it infected wild relatives of the potato. Until recently, only a single strain of P. infestans, dubbed US-1, plagued potatoes outside Mexico and South America. So it came as a surprise when, in 2001, scientists suggested that a different strain was responsible for the famine, after analysing a short stretch of P. infestans DNA from herbarium archives2. Weigel’s team went to herbaria in Kew Gardens, outside of London, and at Germany’s Botanische Staatssammlung in Munich and sequenced DNA preserved from the dried leaves of infected plants dating between 1845 and 1896. Mitochondrial genomes from the famine strains showed they were more closely related to the US-1 strain than the earlier research suggested, and that the two strains diverged only in the early 1800s. Weigel says the split probably occurred in the United States, before the strain responsible for the famine was imported to Europe. That strain now appears to be extinct, or perhaps restricted to small pockets of the world. Weigel’s team also found nothing in the nuclear genomes of the famine strains to explain their ferocity. In fact, the strains lack a gene found in modern strains of P. infestans that overcomes the plant’s resistance genes. And, surprisingly, the famine strain seems less lethal than the P. infestansstrains that now cause US$6 billion in crop damage per year. “It seems rather that the potatoes were unusually susceptible,” he says. Meanwhile, a team led by Tom Gilbert and Mike Martin, evolutionary geneticists at the University of Copenhagen, looked more closely at such genes after sequencing the nuclear genomes of five herbarium strains of P. infestans. In unpublished work, the team identified numerous genes that differ between the historical samples and modern strains, including many disease genes that were missing from the famine strains. Their work also suggests that P. infestans may have been exported to Europe more than once during the famine. “What happened was that this pathogen had never seen cultivated potatoes before,” says Bill Fry, a plant pathologist at Cornell University in Ithaca, New York. It spread through potato fields like wildfire in Ireland and other countries where potatoes were grown intensively. “It destroyed the tops, it destroyed the tubers, and there was nothing for this very poor part of the population to eat.” [字数：398]
[Time 5] Article 4 Cold viruses thrive in frosty conditions
Icy temperatures chill the immune response that thwarts the common cold. Scientists have finally confirmed what parents have cautioned for centuries — that catching a chill can bring on the sniffles. A team from Yale University in New Haven, Connecticut, found that cold temperatures dampen natural defenses against a rhinovirus, the leading cause of seasonal colds, in mice and in human airway cells. “What we show here is a temperature-dependent interaction between the host and the virus,” says team leader Ellen Foxman, who presented the data on 19 May at an American Society of Microbiology conference here. Colds are more common in winter, and researchers have known for decades that many rhinoviruses prefer colder temperatures: they replicate better in the upper respiratory tract than they do in in the warmer environment of the lungs. But efforts to link the viruses’ apparent temperature preference and seasonal fluctuations in incidence have produced mixed results. In 2005, for example, researchers at Cardiff University, UK, dunked healthy people’s feet into icy water to show that exposure to cold could usher in an upper-respiratory infection. But they could not explain why that was the case. And many other studies have found no connection between temperature and rates of infection. In an attempt to solve the cold conundrum, Foxman and her colleagues at Yale studied mice susceptible to a mouse-specific rhinovirus. They discovered that at warmer temperatures, animals infected with the rhinovirus produced a burst of antiviral immune signals, which activated natural defenses that fought off the virus. But at cooler temperatures, the mice produced fewer antiviral signals and the infection could persist. Next, the researchers grew human airway cells in the lab under cold and warm conditions and infected them with rhinovirus. They found the warm infected cells were more likely to undergo programmed cell death — cell suicide brought on by immune responses aimed at limiting the spread of infections — than the cold-infected cells. Foxman says the data suggest that these temperature-dependent immune reactions help to explain the virus’s success at cooler temperatures, and why winter is cold season. As temperatures drop outside, humans breathe in colder air that chills their upper airways just enough to allow rhinoviruses to flourish, she says. Infectious disease researcher Marc Lecuit, of the Institut Pasteur in Paris, France, says the finding is interesting for both basic immunology and for personal health. “It’s a common virus,” he says, “all of us have been infected.” But others caution that there are still many unknowns about how cold temperatures could help spread the viruses. Virologist Vincent Racaniello of Columbia University in New York City says that temperature is probably just one of several factors that explain how rhinoviruses spread. “Simple answers like this are never the whole story,” he says. [字数：457]
Part II: Obstacle Article 5 Data Support Theory On Location of Lost Leonardo Da Vinci Painting
Evidence uncovered during research conducted in Florence's Palazzo Vecchio late last year appears to support the theory that a lost Leonardo da Vinci painting existed on the east wall of the Hall of the 500, behind Giorgio Vasari's mural "The Battle of Marciano." The data supporting the theoretical location of the da Vinci painting "The Battle of Anghiari" was obtained through the use of an endoscopic probe that was inserted through the wall on which the Vasari fresco was painted. The probe was fitted with a camera and allowed a team of researchers, led by scientist Maurizio Seracini, to see what was behind the Vasari and gather samples for further testing.
This comprehensive research effort was led by the National Geographic Society and University of California, San Diego's (UCSD) Center of Interdisciplinary Science for Art, Architecture and Archaeology (CISA3), in partnership with the City of Florence. CISA3 is based at the UCSD division of the California Institute for Telecommunications and Information Technology (Calit2). Work conducted in Palazzo Vecchio's Hall of the 500 was completed in collaboration with the Florentine Superintendency for Cultural Heritage and the Opificio delle Pietre Dure, the Italian state art restoration center based in Florence. Using endoscopic technology provided by Olympus and Wolff, researchers were able to view the wall behind the Vasari mural and obtain samples for analysis. The data from chemical analysis, while not conclusive, suggest the possibility that the da Vinci painting, long assumed to have been destroyed in the mid-16th century when the Hall of the 500 was completely remodeled, might exist behind the Vasari. "These data are very encouraging," said National Geographic Fellow Maurizio Seracini, founding director of UCSD CISA3. "Although we are still in the preliminary stages of the research and there is still a lot of work to be done to solve this mystery, the evidence does suggest that we are searching in the right place." Seracini and his team report four lines of evidence supporting the hypothesis that the lost Leonardo painting is located behind the Vasari mural: A sample containing a black material was analyzed with SEM-EDX (scanning electron microscopy with energy dispersive x-ray spectroscopy), which identifies the chemical elements present in a sample. The material found behind the Vasari wall shows a chemical composition similar to black pigment found in brown glazes on Leonardo's "Mona Lisa" and "St. John the Baptist," identified in a recently published scientific paper by the Louvre, which analyzed all the da Vinci paintings in its collection. Flakes of red material were found. Analysis of these samples seems to identify them as organic material, which could be associated with red lake (lacquer). This type of material is unlikely to be present in an ordinary plastered wall. Visual evidence obtained through high-definition endoscopic images suggests that a beige material seen on the original wall could only have been applied by a paint brush. The research team confirmed the existence of an air gap, originally identified through radar scans conducted of the Hall, between the brick wall on which Vasari painted his mural and the wall located behind it. The finding suggests that Vasari may have preserved da Vinci's masterpiece by building a wall in front of it at this location. No other location in the Hall presented this type of air gap. Seracini, an engineer by training and now one of the world's leading experts in the field of art diagnostics, began searching for the mural more than 30 years ago. In the 1970s, he noticed the words "cerca trova" -- "seek and you shall find" -- painted in Vasari's fresco and believed it was a clue to the mystery of the lost Leonardo. Since then, Seracini has conducted laser, thermal and radar scans of the Hall to determine that the likely location of the Leonardo painting is on the selected panel. When presented with the opportunity to conduct an endoscopic investigation through the Vasari wall, Seracini identified 14 areas to be explored. Following ongoing consultation with Opificio delle Pietre Dure officials, six points of entry were ultimately implemented. These entry points were chosen by the restorers of the Opificio delle Peitre Dure in areas free of original Vasari paint, including cracked or previously restored areas, to ensure that drilling would not cause any damage to the original Vasari mural. Opificio delle Pietre Dure officials conducted the drilling, which then allowed Seracini's team to insert the camera, view the wall behind the mural and obtain samples. Testing on those samples was conducted with portable instruments on the scaffolding itself, in the Florence-based Editech lab and in Pontlab, a private analytical lab in Pontedera, Italy. "Given that the points of actual entry were on the periphery of our original area of focus, the results we obtained are particularly encouraging," said Seracini. In 1503, da Vinci was commissioned by Gonfaloniere Piero Soderini to paint the "The Battle of Anghiari" in the Hall of the 500 of the Palazzo Vecchio, the seat of government in Florence. The painting commemorated the 1440 victory of the battle on the plain of Anghiari between Milan and the Italian League led by the Republic of Florence. The Florentines emerged from the conflict as the most important power in central Italy, re-establishing Papal powers and dominating Italian politics for years to come. Da Vinci used the commission as an opportunity to experiment with new mural techniques, which did not meet with the results he had hoped for, but nonetheless, this masterpiece was later called "the school of the world." In the mid-16th century Giorgio Vasari, himself an admirer of da Vinci's work, enlarged and completely remodeled the Hall and painted six new murals over the east and west walls, possibly hiding the Leonardo masterpiece. Original documents confirm eyewitness accounts of viewing "The Fight for the Standard," the portion of "The Battle of Anghiari" that was completed by Leonardo. [字数：976] | 
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发表于 2013-5-21 22:45:29
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