Nature: Japan closed all of its nuclear reactors following the March 2011 Fukushima Daiichi disaster. Reopening them depends on reports from 17 geophysicists working for the nation’s Nuclear Regulation Authority (NRA). Led by Kunihiko Shimazaki, the group has been evaluating fault lines that run near five reactor sites. The country’s nuclear industry claims that all of the plant locations are now adequately prepared for any potential earthquakes and that the faults near them are inactive. However, Shimazaki’s initial reports claim otherwise. Regarding two of the plants—Tsuruga and Oi—the reports claim that the nearby faults show signs of recent activity, a claim that has been questioned not just by the nuclear industry but by seismologists as well. The reports have also been criticized for misidentifying landslides and for lacking the direct input of specialists on rocks and sediments. Whether the reactors can begin operation again will be determined by the NRA after taking into account the reports both from Shimazaki’s group and from the companies running the reactors.
Daily Archives: February 6, 2013
Largest Mersenne prime discovered is 17 million digits long
Ars Technica: Named for the French monk who studied them in the 17th century, Mersenne primes are prime numbers that can be written in the form Mp = 2p−1. The first three Mersenne primes are M2 = 3, M3 = 7, and M5 = 31. The Great Internet Mersenne Prime Search (GIMPS) is a distributed computing project that uses volunteers’ computers to calculate whether a prime number is also a Mersenne prime. On 25 January, after 39 days of calculations, a computer run by Curtis Cooper, a professor at the University of Central Missouri, discovered the 48th known Mersenne prime, 257,885,161−1. The discovery was confirmed independently by three different computers. GIMPS has been responsible for the discovery of 14 Mersenne primes, with the last discovery occurring in 2009. Cooper will be awarded $3000 for his help.
NASA considering its options for using donated satellites
New Scientist: Last year NASA was offered two military spy telescopes by the National Reconnaissance Office. Similar in size and capabilities to the Hubble Space Telescope, the two satellites have been in storage for the last 20 years. Now NASA is trying to determine how to use them. At a two-day conference at the Marshall Space Flight Center in Huntsville, Alabama, agency officials will be discussing 33 proposals, which include using the telescopes to study dark energy, look for exoplanets, and map space debris around Earth. George Fletcher, who is heading the search for ideas, says the one thing the telescopes won’t be used for is to look at Earth—in order to avoid accusations that NASA is engaging in espionage. The conference members will select up to six of the proposals and announce the agency’s plans in May.
Controlling a laser beam’s shape electronically
MIT Technology Review: A laser works by bouncing light back and forth in a lasing cavity. The cavity is filled with a gain medium that is used to amplify a specific wavelength of light, which is then directed out of the cavity as a narrow, coherent beam. How the intensity of the light varies across the beam—the laser’s “shape”—can be controlled by custom optics outside of the cavity. However, they are expensive and require calibration when they are changed. Now Sandile Ngcobo of the University of KwaZulu–Natal in South Africa and his colleagues have found a way to simplify controlling laser beam shapes. To the inside of the lasing cavity they added a spatial light modifier that can be controlled electronically to shape the light while it is being amplified. Because the researchers can control the shaping with a computer, they are calling their device a digital laser. The result is a laser that can be shaped in real time and that has nearly unlimited applications.