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19147
I am concerned about this article. It addresses the mass of fissile materials needed to “make a bomb,” yet it’s clear that the critical masses given–10 kilograms for plutonium-239, 50 kg for uranium-235, and 60 kg for neptunium-237–are for bare spheres with no neutron moderation, reflection, or other factors contributing to going critical. Consider that […]
- Physics
Neptunium Nukes? Little-studied metal goes critical
Researchers have measured with far greater accuracy than ever before how much neptunium it would take to make a bomb.
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19186
In your article, a spinning coin’s motion is explained by the existence of an air cushion between coin and tabletop. If this is indeed the case, then I would expect coins to do something quite different in a vacuum. What do they do? Richard Chambers Charlotte, N.C. H. Keith Moffatt offers an explanation for the […]
- Ecosystems
Insects, pollen, seeds travel wildlife corridors
Strips of habitat boost insect movement, plant pollination, and seed dispersal among patches of the same ecosystem.
- Paleontology
Trackway site shows dinosaur on the go
Scientists say that a sediment-filled, bathtub-shape depression found at one of North America's most significant dinosaur trackway sites is the first recognized evidence of urination in dinosaurs.
- Paleontology
Curved claws hint at pterosaur habits
A study of the claws of flying reptiles known as pterosaurs suggests that some of the creatures may have walked like present-day herons and used their wing fingers to hold prey.
- Paleontology
Mosasaurs were born at sea, not in safe harbors
Newly discovered fossils of prehistoric aquatic reptiles known as mosasaurs suggest that the creatures gave birth in midocean rather than in near-shore sanctuaries as previously suspected.
- Paleontology
Stegosaur tails packed a punch
A mathematical analysis of a fossil stegosaur's bones leaves little doubt that the creature's spike-studded tail was an effective defense against predators.
- Chemistry
Dipping deeper into acid
New experiments reveal how a molecule of acid dissolves in water.
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19146
Concerning the Apollo rocket’s third stage returning to Earth orbit: How did the researchers determine the source to be Apollo 12, since there were six other Apollo moon missions? Did they use some fancy orbital mechanics along with statistical probability? George RichesonBrenham, Texas Yes, they did, and the orbit matched. Also, the researchers found no […]
- Astronomy
News flash: Earth still has only one moon
An object discovered orbiting Earth in early September isn't a moon but something much more mundane—an upper stage of a rocket that was used in the Apollo 12 mission to the moon.
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19185
In response to this article, I’d like to ask why is it that on our campus, native swamp maples growing within 30 feet of one another display totally different leaf color? While I appreciate them aesthetically, I’d also like to understand why their anthocyanin production is different. Marcia WalshNorth Andover, Mass. According to David Lee […]
