EPC Gen 2 RFID tags were designed to enable tracking, have minimal or no security, and are readable from up to 10 meters away. RF-enabled smart cards contain a fully functioning microprocessor and can deliver security such as public-key cryptography, mutual authentication and encrypted communications. They operate over a 10-centimeter range to prevent tracking or eavesdropping.
Smart Card Alliance
Basis of the Bulge
In “A Solar Big Gulp” [News Scan], David Appell refers to an analysis concluding that in billions of years, as the sun loses mass and expands, its rotation rate will slow down, creating a tidal bulge on its surface whose gravity will pull Earth inward. A tidal bulge, however, is not caused by rotation but by differential gravitation from an external body.
David C. Halley
APPELL REPLIES: Halley is right: an external body, not rotation, causes a tidal bulge. But only when the sun’s rotation is very small or nonexistent does its tidal bulge lag behind Earth in orbital motion, pulling Earth back in its orbit, taking energy out of Earth’s orbital motion and causing the planet to spiral inward. Otherwise, with rapid rotation, the bulge is ahead of Earth, which would be pulled forward and spiral outward (as happens to the moon in the Earth-moon system).
Note: This story was originally printed with the title, "Letters".