Scipsy

In algebra, the letter ‘x’ is often used to represent an unknown quantity or variable. Similarly, in English, x represents the unknown, as in X-rays, which baffled their discoverer, and Malcolm X, who chose the symbol to represent the forgotten name of his African ancestors. This meaning of the letter x traces back to the Arabic word for “thing,” or šay’. In ancient texts, such as Al-Jabr, a manuscript written in Baghdad in 820 A.D. that established the rules of algebra, mathematical variables were called things. (An equation might read “three things equal 15,” for example — the thing being five.) When Al-Jabr was later translated into Old Spanish, the word šay’ was written as “xei.” This soon came to be abbreviated as x.
Why Is ‘X’ Used to Represent the Unknown? 

Danish or Doughnut

This series of images is a result of a project to automatically fill holes in polygonal meshes. While in simple cases it suffices to create a patch by triangulating the boundary of a hole, in cases where the topology of the final object is uncertain a more complex method is needed. In the figure shown, using our “Atomic Volumes” method, the outer half of the torus can be filled in two topologically different ways. The viewers can decide if they see a Danish or a doughnut. ( Joshua Podolak GS, Department of Computer Science; via Art of Science Competition)

Danish or Doughnut

This series of images is a result of a project to automatically fill holes in polygonal meshes. While in simple cases it suffices to create a patch by triangulating the boundary of a hole, in cases where the topology of the final object is uncertain a more complex method is needed. In the figure shown, using our “Atomic Volumes” method, the outer half of the torus can be filled in two topologically different ways. The viewers can decide if they see a Danish or a doughnut. ( Joshua Podolak GS, Department of Computer Science; via Art of Science Competition)

Resonating spring (via fsas.upm.edu)

Resonating spring (via fsas.upm.edu)

(via Sage)

(via Sage)

An emirp is a prime number that results in a different prime when its digits are reversed. (via Trivium)

13, 17, 31, 37, 71, 73, 79, 97, 107, 113, 149, 157…