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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.
- Physics
Magnetic snap gives ions extra pop
Magnetic fields pump heat into ions when field lines of opposite orientation snap and reconnect.
- Physics
Groovy ’70s sound keeps X rays tight
Cast aside as a way to reproduce music, LP phonograph records reveal another, unsuspected talent that scientists plan to exploit-focusing X rays.
- Math
Whirling to a chaotic finale
A black hole paired with another body can succumb to chaos when they orbit each other, making it more difficult to detect gravitational waves produced by such objects.
- Math
Traffic woes of the single driver
At moderate traffic volumes, a single car moving at randomly fluctuating speeds can cause traffic jams in its wake.
- Math
Spinning to a rolling stop
Air viscosity makes the rolling speed of a spinning, tipping coin go up as its energy goes down until the coin suddenly stops.
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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 […]
- Health & Medicine
A different GI link to colon cancers
Diets rich in sweets and other quickly digested carbohydrates appear to increase an individual's risk of developing colon cancer.
- Health & Medicine
Berry promising anticancer prospects
Cranberry products can retard the growth and spread of breast cancer in rodents.
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Disabled genes dull sense of smell
Mutated genes may explain why humans have a poor sense of smell.
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Genes, genes, and more genes
Scientists have almost finished sequencing the genes of rice and of a man.
