19 Nisan 2008 Cumartesi

Racetrack Memory

Racetrack Memory is an experimental non-volatile memory device under development at IBM's Almaden Research Center by a team led by Stuart Parkin, as well as teams at various other locations. In early 2008 a 3-bit version was successfully demonstrated.

IBM's version of racetrack uses spin-coherent electric current to move the magnetic domains along an U-shaped nanoscopic wire. As current is passing through the wire, the domains move over the magnetic read/write heads positioned at the bottom of the U, which alter the domains to record patterns of bits. A memory device is made up of many such wires and read/write elements. In general operational concept, racetrack memory is similar to the earlier twistor memory or bubble memory of the 1960s and 70s, but uses much smaller magnetic domains and dramatic improvements in magnetic detection capabilities to provide far higher areal densities.

One limitation of the early experimental devices was that the magnetic domains could only be pushed slowly through the wires, requiring current pulses on the orders of microseconds to move them successfully. This was unexpected, and led to performance roughly equal to hard drives, as much as 1000 times slower than predicted. Recent research at the University of Hamburg has traced this problem to microscopic imperfections in the crystal structure of the wires which led to the domains becoming "stuck" at these imperfections. Using an x-ray microscope to directly image the boundaries between the domains, their research found that domain walls would be moved by pulses as short as a few nanoseconds when these imperfections were absent. This corresponds to a macroscopic speed of about 110 m/s.

6 Nisan 2008 Pazar

To Kill a Mockingbird

To Kill a Mockingbird is a Pulitzer Prize-winning novel by Harper Lee published in 1960. Upon its release, it was instantly successful and has become a classic of modern American fiction. The novel is loosely based on the author's observations of her family and neighbors, as well as an event that occurred near her hometown in 1936, when she was 10 years old.

The novel is renowned for its warmth and humor, while still dealing with the serious issues of rape and racial inequality. Atticus Finch, the narrator's father, has served as a moral hero for many readers, and a model of integrity for lawyers. One critic explained its impact by writing, "in the twentieth century, To Kill a Mockingbird is probably the most widely read book dealing with race in America, and its protagonist, Atticus Finch, the most enduring fictional image of racial heroism."

As a Southern gothic novel and a bildungsroman, the primary themes of To Kill a Mockingbird involve racial injustice and the destruction of innocence, but scholars have also noted that Lee addresses the issues of class tensions, courage and compassion, and gender roles in the American Deep South. The book is widely taught in schools in English-speaking countries with lessons that emphasize tolerance and decry prejudice. Despite its themes, To Kill a Mockingbird has been the target of various campaigns to have it removed from public classrooms. Often the book is challenged for its use of racial epithets, and writers have noticed that while white readers react favorably to the novel, black readers tend to respond less positively.

Lee's novel was initially reviewed by at least 30 different newspapers and magazines, which varied widely in their assessment of the novel. More recently, it has been ranked by librarians next to the Bible as a book "every adult should read before they die".The book was adapted into an Oscar-winning film by director Robert Mulligan, with a screenplay by Horton Foote, in 1962. In 1990 it was adapted as a play that is performed annually in Harper Lee's hometown of Monroeville, Alabama and has transformed the town into a tourist destination. To date, it is Lee's only published novel, and though she continues to respond to the book's impact, she has refused any personal publicity for herself or the novel since 1964.


Antares is a star in the Milky Way galaxy and the sixteenth brightest star in the nighttime sky (sometimes listed as fifteenth brightest, if the two brighter components of the Capella quadruple star system are counted as one star). Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic. The similarly colored Aldebaran lies almost directly opposite Antares in the Zodiac.

Antares is a class M supergiant star, with a diameter of approximately 700 times that of the sun; if it were placed in the centre of our solar system, its outer surface would lie between the orbits of Mars and Jupiter. Antares is approximately 600 light years from our solar system. Its visual luminosity is about 10,000 times that of the Sun, but because the star radiates a considerable part of its energy in the infrared part of the spectrum, the bolometric luminosity equals roughly 65,000 times that of the Sun. The mass of the star is calculated to be 15 to 18 solar masses. Its large size and relatively small mass give Antares a very low average density.

The best time to view Antares is on or around May 31 of each year, when the star is at "opposition" to the Sun. At this time, Antares rises at dusk and sets at dawn, and is thus in view all night (depending on your position on Earth). For approximately two to three weeks on either side of November 30, Antares is not visible at all, being lost in the Sun's glare; this period of invisibility is longer in the Northern Hemisphere than in the Southern Hemisphere, since the star's declination is significantly south of the celestial equator.