Solving Linear Equations on the Train

From a post by Alexandre Borovik at Mathematics under the Microscope: 

... from a mathematical point of view, solving a (elementary level) Sudoku puzzle is nothing more than solving a triangle system of Boolean equations by back substitution, something very similar to what we do after a Gauss-Jordan elimination in a system of simultaneous linear equations. But has anyone ever seen people on a train solving systems of linear equations from a newspaper?  ...

(As it happens, I have myself solved systems of linear equations on trains.  It was when I took some maths courses with the Open University 10 years ago.  I did most of my studying on the train to and from work.)

Ancient Tracks on the North Yorkshire Moors

About 400 metres west of Hob Hole, a set of tracks descend from Little Hograh Moor to cross Baysdale Beck.  Old tracks can be found all over the North Yorkshire Moors.  Often they form intertwining braids like this, as if the line of a single road has meandered from side to side over many years.  I suppose it is most likely that they were made in mediaeval times by  sheep and cattle being driven to and from moorland farms owned by the many abbeys and priories in the area.  However, I like to think that their origin is much older, dating back to the Bronze Age and the beginnings of agriculture in the area, but this is just speculation on my part.  (Image from Google Maps.)

Pluvialis almost loses her Goshawk

Reading this was the highlight of the week for me.

Leukocyte Extravasation Video

The process by which white blood cells in the blood are attracted to and enter damaged tissues has been the subject of intensive research in the past few years because of its obvious importance in medicine.  Apparently it is now understood well enough at the molecular level for this animation of the whole process to have been made.  The image of the 'boots' of the motor protein walking along the microtubule, dragging the cytoplasmic vesicle behind it, I find both awesome and comical.

(A clearer version, but with music instead of commentary, can be found here.) 

Update on Sun 2008-02-03 by Tristram Brelstaff

PZ Myers has posted some criticism of this video here.  He says that it oversimplifies the movements of the molecules and makes them appear more directed and purposeful than they really are (so playing into the hands of creationists).  In reality there would be a much larger random component to the movements made by the molecules.  In other words, the 'boots' should not be walking, but dancing!

Arcyria Slime Mould

Another wonderful slime mould photo from Kim Fleming (alias myriorama).