पहाड़ से मैदान तक कड़ाके की ठंड, दिल्ली में सर्दी-प्रदूषण की डबल मार

दिल्ली में ठंड और कोहरे की मार जारी है. पहले ठंड ने लोगों को मुसीबत में डाला और अब कोहरे...

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Readers ask about positronium, wild bees and more

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Dance of the doomed particles Scientists are puzzled by an unexpectedly large gap in the energy levels of an exotic “atom” called positronium, which consists of an electron and a positron, Emily Conover reported in “ Positronium result baffles physicists ” ( SN: 9/12/20, p. 14 ). Reader Lee Skinner asked why the electron and its antimatter counterpart, the positron, don’t just annihilate each other when they collide. Eventually, the electron and positron do annihilate one another, Conover says. As a result, positronium doesn’t stick around forever. “The two particles do a little orbital dance with each other for a period of time before they meet up and annihilate,” she says. “That’s actually part of how the researchers made the measurement, though I didn’t have the space to include those details in the story.” The team measured how long it took electrons and positrons to annihilate, which depends on the atoms’ energy level. “Timing that annihilation revealed whether the positr...
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How next-gen computer generated maps detect partisan gerrymandering

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In October 2019, a state court determined that North Carolina’s congressional districts had been severely gerrymandered and struck down the state’s map . The court’s ruling was informed, in part, by tens of thousands of alternative maps demonstrating that the district boundaries had very likely been manipulated for political gain, the very definition of gerrymandering. Researchers had generated a slew of alternative, computer-generated maps designed to help identify potential patterns of bias. The approach is increasingly used, alongside other tests, to ferret out alleged gerrymandering. District manipulations can be so subtle that they’re undetectable just by looking at them. “The eyeball test is no good,” says Jonathan Katz, a political scientist and statistician at Caltech. U.S. states redraw their district lines every 10 years to adjust for changing demographics picked up by the national census. The last round a decade ago raised eyebrows, most notably for districts drawn in Mich...
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