"Moving dunes on the Google Earth" is my paper on arXiv, published 4 January 2013. It shows how using GH time series you can see the motion of dunes. Here an example.
To see a movie, please visit Moving sand dunes ... post
May 9, 2012 — NASA's Mars Reconnaissance Orbiter has revealed that movement in sand dune fields on the Red Planet occurs on a surprisingly large scale, about the same as in dune fields on Earth.
Chords were used extensively in the early development of trigonometry. The first known trigonometric table, compiled by Hipparchus, tabulated the value of the chord function for every 7.5 degrees. In the second century AD, Ptolemy of Alexandria compiled a more extensive table of chords in his book on astronomy, giving the value of the chord for angles ranging from 1/2 degree to 180 degrees by increments of half a degree. The circle was of diameter 120, and the chord lengths are accurate to two base-60 digits after the integer part. The chord function is defined geometrically as in the picture to the left. The chord of anangleis thelengthof the chord between two points on a unit circle separated by that angle. The chord function can be related to the modernsinefunction, by taking one of the points to be (1,0), and the other point to be (cos, sin), and then using thePythagorean theoremto calculate the chord length:
The last step uses the half-angle formula. Much as modern trigonometry is built on the sine function, ancient trigonometry was built on the chord function.
The chord function satisfies many identities analogous to well-known modern ones:
"Today, P J Miranda at the Federal Technological University of Paraná in Brazil and a couple of pals study the social network between characters in Homer’s ancient Greek poem, the Odyssey. Their conclusion is that this social network bears remarkable similarities to Facebook, Twitter and the like and that this may offer an important clue about the origin of this ancient story." The Remarkable Properties of Mythological Social Networks | MIT Technology Review
Le 9 Sinfonie con l’Orchestra Sinfonica Nazionale della RAI e il Coro del Teatro Regio. I Concerti con l’Orchestra Filarmonica di Torino e grandi interpreti.
Tutte le sere, ore 21, Ingresso libero http://www.festivalbeethoven.it/
Immagine con non-photorealistic rendering; vedi A.C. Sparavigna, B Montrucchio,