Philip Glass – Sesame Street – Geometry of Circles

The wheel of colors by Sesame Street, music by Philip Glass


February 13, 2011 at 09:13 Leave a comment

Laser guide star

from Wikipedia

Laser guide stars are a form of artificial star created for use in astronomical adaptive optics imaging.

Adaptive optics (AO) systems require a wavefront reference source in order to correct atmospheric distortion of light (called “astronomical seeing“). Sufficiently bright stars are not available in all parts of the sky, which greatly limits the usefulness of natural guide star adaptive optics. Instead, one can create an artificial guide star by shining a laser into the atmosphere. This star can be positioned anywhere the telescope desires to point, opening up much greater amounts of the sky to adaptive optics. Because the laser beam is deflected by astronomical seeing on the way up, the laser light moves around in the sky in a random fashion. In order to keep astronomical images steady, a natural star nearby in the sky must be monitored in order that the motion of the laser guide star can be subtracted using a tip-tilt mirror. However, this star can be much fainter than is required for natural guide star adaptive optics, which means many more stars are suitable and a correspondingly larger fraction of the sky is accessible.

There are two main types of laser guide star system, known as sodium and Rayleigh beacon guide stars. Sodium beacons are created by using a laser specially tuned to 589.2 nanometers to energize a layer of sodium atoms which is naturally present in the mesosphere at an altitude of around 90 kilometers. The sodium atoms then re-emit the laser light, producing a glowing artificial star. The same atomic transition of sodium is used to create bright yellow street lights in many cities. Rayleigh beacons rely on the scattering of light by the molecules which make up the lower atmosphere. In contrast to sodium beacons, Rayleigh beacons are a much simpler and less costly technology, but do not provide as good a wavefront reference as the artificial beacon is generated much lower in the atmosphere. The lasers are often pulsed, with measurement of the atmosphere being time-gated (taking place a few microseconds after the pulse has been launched so that scattered light at ground level is ignored and only light which has traveled for several microseconds high up into the atmosphere and back is actually detected).

January 14, 2011 at 21:27 Leave a comment

The Meaning of ‘Hack’

from the Jargon File

“The word hack doesn’t really have 69 different meanings”, according to MIT hacker Phil Agre. “In fact, hack has only one meaning, an extremely subtle and profound one which defies articulation. Which connotation is implied by a given use of the word depends in similarly profound ways on the context. Similar remarks apply to a couple of other hacker words, most notably random.”

Hacking might be characterized as ‘an appropriate application of ingenuity’. Whether the result is a quick-and-dirty patchwork job or a carefully crafted work of art, you have to admire the cleverness that went into it.

An important secondary meaning of hack is ‘a creative practical joke’. This kind of hack is easier to explain to non-hackers than the programming kind. Of course, some hacks have both natures (…)

January 14, 2011 at 02:44 Leave a comment

Tim Hunkin and Rex Garrod’s show, the Secret Life of Machine: THE ELECTRIC LIGHT

January 12, 2011 at 22:03 Leave a comment

The end of the rainbow

On December 26th 2010 I saw my first end of a rainbow, it is hard to see in the picture but it is actually in front of the mountain.


January 12, 2011 at 21:58 Leave a comment

Sweet talking your computer, by Clifford Nass

Originally posted by Clayman Affiliate Clifford Nass in the Wall Street Journal, August 28, 2010.

When BMW introduced one of the most sophisticated navigation and telematics systems into its 5 Series car in Germany a decade ago, it represented the pinnacle of German engineering excellence, with great advances in accuracy and functionality. Yet BMW was forced to recall the product—because the system had a female voice. The service desk had received numerous calls from agitated German men who had the same basic complaint. They couldn’t trust a woman to give them directions.

While this might seem like a story of men’s weird attachment to cars or gender stereotyping run amok, a growing body of research suggests that there is something much deeper at work: People respond to computers and other technologies using the same social rules and expectations that they use when interacting with other people. These responses are not spur-of-the-moment reactions. They run broadly and deeply.

If you were asked how much you liked, say, a plate of lasagna, you would undoubtedly say nicer things to the chef than you would to a person who had no connection to the chef. This would be the polite thing to do. Would you also be overly nice to a computer that tutored you for 30 minutes and then asked how well it taught you?

To find out, I ran an experiment at Stanford University. After being tutored by a computer, half of the participants were asked about the computer’s performance by the computer itself and the other half were asked by an identical computer across the room. Remarkably, the participants gave significantly more positive responses to the computer that asked about itself than they did to the computer across the room. These weren’t overly sensitive people: They were graduate students in computer science and electrical engineering, all of whom insisted that they would never be polite to a computer.


September 14, 2010 at 04:08 Leave a comment

Recommendations for colored lights, 1967 and 1956

“Colored lights should be chosen using available data to have good recognizability and to cause the least amount of confusion. Table 6.5 recommends colors and describes their effect on color recognition of small-point light sources near the threshold of visibility (Dreyfuss, 1967). Table 6.6 shows 10 colored-light choices that were shown to reduce confusion error; that is, these 10 wavelengths had a less than 2% misidentification error in experimental studies (Chapanis and Halsey, 1956). Use of those values increases the number of color choices available to device designers that are more easily recognizable and can reduce misidentification.”

Source: ANSI/AAMI HE75, 2009 Human factors engineering – Design of medical devices

September 6, 2010 at 08:17 Leave a comment

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