Article of the Day is a free service of TheFreeDictionary.com http://www.jiaoayi.cn en-us Farlex, Inc. Sat, 27 Feb 2021 05:00:00 GMT 360 http://www.jiaoayi.cn http://img.tfd.com/modules/thm_aod.png 120 60 Sat, 27 Feb 2021 05:00:00 GMT https://encyclopedia.thefreedictionary.com/jet+pack //encyclopedia.thefreedictionary.com/jet+pack#2021 Jet packs began to appear in science fiction long before science made them a reality. Toward the end of WWII, scientists began working seriously to develop a wearable propulsion device that would enable a single user to fly. Now a reality, jet packs are prohibitively expensive and difficult to control. Because jet pack flights are brief, most do not achieve the minimum altitude necessary to deploy a parachute in the event of a breakdown. What is currently the only practical use for jet packs? Discuss
]]> Fri, 26 Feb 2021 05:00:00 GMT https://encyclopedia.thefreedictionary.com/Very+Large+Telescope //encyclopedia.thefreedictionary.com/Very+Large+Telescope#2021 Set on a remote and inhospitable mountain in Chile's Atacama Desert, the Very Large Telescope (VLT) is actually an array of four large telescopes. The telescopes can be operated together to achieve an angular resolution so precise that the array could theoretically be used to distinguish between the two headlights of a car on the Moon. The VLT captured the first image of a planet outside the solar system. What do the four telescopes' names mean in the local Mapudungun language?
]]> Thu, 25 Feb 2021 05:00:00 GMT https://encyclopedia.thefreedictionary.com/Population+bottleneck //encyclopedia.thefreedictionary.com/Population+bottleneck#2021 Cheetahs are basically all the same. Any two randomly selected cheetahs will be so similar genetically that a skin graft from one will likely provoke no immune response in the other. In the distant past, cheetahs underwent a population bottleneck—an evolutionary event in which a species nearly dies out and is repopulated by a few individuals whose genes are then disproportionately reflected in the ensuing generations. All humans can trace their ancestry back to a single woman. When did she live?
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