Heroin sold in the U.S., like this dose confiscated in Alabama last fall, is often cut with other drugs. Tamika Moore/AL.com/Landov hide caption

itoggle caption Tamika Moore/AL.com/Landov

Ah, sugar — we love the sweetness, but not the calories. For more than a century, food technologists have been on a quest for the perfect, guilt-free substitute. The latest candidate, allulose, is not available to consumers in a crystal form: It is a syrup only available to manufacturers. Ryan Kellman/NPR hide caption

itoggle caption Ryan Kellman/NPR

An aerial view of Tokyo Electric Power Co.'s tsunami-crippled Fukushima Dai-ichi nuclear power plant, on March 11. Kyodo/Reuters/Landov hide caption

itoggle caption Kyodo/Reuters/Landov

University Medical Center New Orleans on Aug. 1, when the $1 billion facility welcomed its first patients. Brett Duke/The Times-Picayune/Landov hide caption

itoggle caption Brett Duke/The Times-Picayune/Landov

Michael Arnott, of Cambridge, Mass., says he used to have trouble staying awake on long drives. Sleep specialists discovered he has obstructive sleep apnea, though not for the most common reasons — he isn't overweight, and doesn't smoke or take sedatives. M. Scott Brauer for NPR hide caption

itoggle caption M. Scott Brauer for NPR

Frozen sperm straws and embryos are stored in liquid nitrogen, in a process known as cryopreservation. One question confronting the courts: Should embryos such as these be treated as property, or as children subject to custody action? Veronique Burger/Science Source hide caption

itoggle caption Veronique Burger/Science Source

Dwarf planet Ceres is seen in the asteroid belt between Mars and Jupiter, where it resides well away from Earth. NASA is hoping to quell online rumors that a massive near-Earth asteroid is due to hit us next month. NASA/Reuters/Landov hide caption

itoggle caption NASA/Reuters/Landov

United has purchased 15 million gallons of renewable jet fuel made from beef tallow, or fat, by Alt Air Fuels and plans to use the fuel this year for Los Angeles-to-San Francisco flights. Tony Ruppe/United hide caption

itoggle caption Tony Ruppe/United
Katherine Streeter for NPR

Bacillus subtilis may look like pasta under the microscope, but the bacteria are common in the gut of humans. Could the microbes be contributing to our belly fat? Too soon to tell, scientists say. BSIP/UIG via Getty Images hide caption

itoggle caption BSIP/UIG via Getty Images

African forest elephants stampede in the Central African Republic jungle. Courtesy of Cornell Lab or Ornithology hide caption

itoggle caption Courtesy of Cornell Lab or Ornithology