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Excerpt from the June 5, 1971 issue of Science News
50 YEARS AGO
UPDATE: Those projections
recently veered off course. As of April 2020, 331.5 million people lived in the United States, census data show. But from July 2019 to July 2020, the population grew by just 0.35 percent — the lowest annual growth rate in over a century. For most of the last 50 years, the population grew by about 1 percent per year, partly thanks to immigration. While the fertility rate dropped below 2.1 children per woman after 1971 and the birth rate declined by 29 percent between 1970 to 2014, the foreign-born population quadrupled to over 40 million people. But immigration has slowed. In 2020, the fertility rate dropped to a record low of 1.64 children per woman.
4 SCIENCE NEWS | June 5, 2021
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The Milky Way is strewn with yellowballs (circled in this false-color infrared image), regions of ionized gas bubbles where baby stars are born.
Bubble-blowing baby stars form ‘yellowballs’ Scientists have solved the case of mysterious cosmic objects dubbed “yellowballs.” Each of these celestial specks marks the birthplace of many stars with a wide range of masses, rather than a single supermassive star, researchers report in the April 16 Astrophysical Journal.
The stars in these clusters are relatively young, only about 100,000 years old. “I think of these as stars in utero,” says Grace Wolf-Chase, an astronomer at the Planetary Science Institute who is based in Naperville, Ill. For comparison, the massive stars forming in the Orion Nebula are
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THE EVERYDAY EXPLAINED
How physics helps Brazil nuts come out on top A new experiment reveals, in a nutshell, why the largest particles in some mixtures tend to gather at the top. This phenomenon is known as the Brazil nut effect, since jostling mixed nuts tends to bring bulky, oblong Brazil nuts (the largest nuts shown below) to the top of a container. The effect can also be seen in cereal boxes and even among space rocks (SN: 10/4/14, p. 4). Understanding how it works could help manufacturers create more uniform mixtures of ingredients for food processing, or more even distributions of active ingredients in medicine tablets, researchers report April 19 in Scientific Reports. The Brazil nut effect has been tough to crack because it’s difficult to track how individual objects move around in the middle of a mixture, says Parmesh Gajjar, an imaging scientist at the University of Manchester in England. Using X-ray CT scans, Gajjar and colleagues followed the motion of individual peanuts and Brazil nuts in a box as it was shaken back and forth — creating the first 3-D videos of the Brazil nut effect in action. In the videos, the Brazil nuts mostly laid horizontally when they were dumped into the container. But as the box shook, collisions between nuts nudged some of the Brazil nuts to point more vertically. That vertical orientation allowed smaller peanuts higher in the mixture to tumble down and accumulate at the bottom, pushing the Brazil nuts upward. While this finding could satisfy the curiosity of mixed nut aficionados, that’s peanuts compared with the practical use it could have for the pharmaceutical industry. — Maria Temming Watch a video of jostling nuts at bit.ly/SN_BrazilNut
5/19/21 10:11 AM
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A FROM TOP: JPL-CALTECH/NASA; ADAM LAU/BERKELEY ENGINEERING
The United States’ population is growing at a rate of one percent a year, and even with lower fertility rates this trend will probably continue. If the fertility rate dropped to 2.1 children per woman, the population of the country would level off in the year 2037 at 267 million. But, this would require an unlikely 50 percent decrease in the birth rate.
MYSTERY SOLVED
FROM TOP: CHARLES KERTON/IOWA STATE UNIV., SPITZER/NASA; BOBLIN/E+/GETTY IMAGES PLUS
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