A convoy of Walmart trucks waited to enter New Orleans on Sept. 1, 2005, after the city was battered by Hurricane Katrina. Government agencies said the massive storm taught them that big-box retailers need to be an integral part of hurricane preparation and relief efforts. Nicholas Kamm/AFP/Getty Images hide caption

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This image shows the above-normal water temperature in the Pacific Ocean during the December 1997 El Nino. Green-blue colors represent normal temperatures; dark red indicates hotter water. NOAA hide caption

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The P-3B NASA research aircraft, seen on the tarmac at Baltimore Washington International Airport on June 28, will gather data as it flies spirals over six ground stations in Maryland. Paul E. Alers/NASA hide caption

itoggle caption Paul E. Alers/NASA

This undated X-ray image from the Cleveland Clinic shows electrodes implanted in a patient's brain. The method, known as deep brain stimulation, has traditionally been used to treat diseases such as Parkinson's, but new research indicates it could be helpful for patients with obsessive-compulsive disorder. AP hide caption

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Dr. Donald Brown, left, gives 14-year-old Kelly Kent a dose of Gardasil, a vaccine for the human papillomavirus in 2006. The group that advises the U.S. government on vaccination recommendations is now starting to take costs for vaccines like Gardasil into consideration as vaccine prices rise. Charles Rex Arbogast/AP hide caption

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Eve offers Adam the fruit in the garden of Eden in Theatrum Biblicum, a drawing by Johann Fischen (circa 1650). Sex lets a species evolve faster to rapidly adapt to a new environment, researchers say. Hulton Archive/Getty Images hide caption

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An image believed to be that of a hole-punch cloud. Scientists say airplanes create these patterns when they fly through certain types of clouds. The water in the clouds can turn to rain or snow and fall to the ground. H. Raab/Vesta/Wikimedia Commons hide caption

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This image from April 27 shows a series of tornadoes forming over Alabama and Mississippi. Captured from a satellite orbiting located at a fixed location above Earth, images like these help track trends in weather patterns. Another set of polar-orbiting satellites are useful for long-term forecast predictions. NASA Earth Observatory hide caption

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This tornado touched down near Chickasha, Okla., on May 24. In addition to being tracked by the existing NEXRAD radar system, this storm was also being monitored by an experimental radar system that provided more precise information about the tornado's behavior and path. Heather Mosher/Courtesy National Weather Service/NOAA hide caption

itoggle caption Heather Mosher/Courtesy National Weather Service/NOAA

Scientists have known for a long time that nicotine decreases appetite among smokers, but they didn't know why. A new study finds that nicotine triggers a response in certain specific brain cells known to regulate appetite. iStockphoto.com hide caption

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An infant and his mother demonstrate electroencephalography, or EEG, technology at Children's Hospital Boston. The technology could help detect the risk of autism in infants. Courtesy of Michael Carroll hide caption

itoggle caption Courtesy of Michael Carroll

A study published in the journal Science last December suggested that a bacterium found in California's Mono Lake was able to substitute arsenic for phosphorous. But that conclusion has many critics. Miss Bliss 55 via Flickr hide caption

itoggle caption Miss Bliss 55 via Flickr

Amy Womack and her daughter, Alexis Nelson, sit on the front steps of her parents' house in Cleveland, Tenn., in late April. Womack says her father urged her and 13 relatives and friends into the basement before a tornado hit; she credits him with saving their lives. Wade Payne/AP hide caption

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