All Fall Down
October 31, 1998 | Volume 154 | Number 18
Cover: The flutter of falling leaves has intriguedand puzzledgenerations of scientists. Inspired anew by chaos theory, physicists in a recent spate of studies find the hallmarks of chaotic behavior as well as surprising regularities in the tumble of leaflike objects.
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News of the Week:
Adult Human Brains Add New Cells
Scientists presented the first solid evidence that nerve cells in the human brain continue to be born throughout life.
Cancer drug helps paralyzed mice walk
A bacterial toxin enables a mouse's injured spinal cord to heal.
Studies support an accelerating universe
New findings support the notion that the universe will expand forever at an increasing rate.
Time proves not reversible at deepest level
Certain subatomic physical processes, such as the interconversion of complementary particles called kaons and antikaons, appear to take a different course if time runs in reverse.
At peace with itself, an ant triumphs
Argentine ants are succeeding in their march around the globe in part because theyve stopped scrapping among themselves.
Geologists anticipate an oil crisis soon
Several forecasts indicate that the supply of oil will start drying up in the near future.
Blood, semen harbor distinct HIV mutations
Different, drug-resistant populations of HIV can arise in different locations in the same infected man.
Big shocks push volcanoes over the edge
Some of Earths mightiest earthquakes have triggered volcanic explosions.
Blue eyes, big earplugs: Bad hearing?
Light eye color and large ear-canal size may be linked to greater vulnerability to hearing loss.
Cooking up bubbles to make tiny pumps
Swelling and shrinking bubbles may eventually act as tiny pumps to driv e micromachines.
Sound was secret weapon in Civil War
Because Civil War commanders relied on the sounds of battles to make judgments, unexpected acoustical effects may have altered the course of the war.
African dialect uses unexpected sound
A sound that linguists said was absent from human language turns up in a southern African dialect.
Better seal for see-through sound wall
Researchers have arranged rods into a new kind of sound filter that for bids a selected frequency band from passing through from any angle.
A sugar averts some ear infections
A natural sweetener called birch sugar helps to prevent some ear infect ions in preschoolers by thwarting Streptococcus pneumoniae bacteria.
Survival improving in organ recipients
Among organ transplant recipients in the United States, survival rates improved between 1988 and 1994, especially for those receiving liver, lung, and heart-lung transplants.
The Leonids are Coming! The Leonids are Coming!
A memorable light show or just a bracing shower?
This Nov. 17, Earth makes its closest approach in 33 years to Comet 55P/Tempel-Tuttle, but it isn't clear how dramatic the annual light show put on by its trail of dusty debris the Leonid meteoroids will prove to be.
The Puzzle of Flutter and Tumble
Physicists reconsider the fall of leaves
Computer simulations and chaos theory come to the fore in attempts to ex plain the motions of falling leaves and paper sheets.
Letters: A Selection from Letters to the Editor