Kenneth Wilson, RIP
23 hours ago
Po´rismPoncelet's porism refers to the first case. So what is Poncelet's porism? Take two conic sections, now if you can draw one n-sided polygon (n>2) such that its sides all touch tangentially one conic section and its vertices all lie on the other one, then you can draw infinitely many. The infinite comes about because you are able to rotate the polygon (not held fixed though) so that its vertices all rotate around the outer curve. Phew. Let's look at some pictures and see if this is understandable:
n. 1. (Geom.) A proposition affirming the possibility of finding such conditions as will render a certain determinate problem indeterminate or capable of innumerable solutions.
2. (Gr. Geom.) A corollary.
There are plenty more of these animations to be found here.
a triangle (sort of) with vertices on a parabola and circumscribing a circle a quadrilateral with vertices on a circle and sides tangent to a parabola the classic triangle and two circles
"For an even-sided polygon, the diagonals are concurrent at the limiting point of the two circles, whereas for an odd-sided polygon, the lines connecting the vertices to the opposite points of tangency are concurrent at the limiting point."If you click on the aforementioned link showing the diagonals and move the pink line about I think you can see even there that it is not clear that the meeting point of the diagonals stays fixed. John demonstrated to us his expertise with both matlab and an excellent program called the Geometer's Sketchpad. Using matlab John took us through several pages of enormous calculations working out the locus of the meeting points of the diagonals and finally reduced the locus down to a sixth-order polynomial! Using the sketchpad John was able to convince us that the meeting point actually travels around a circle looped on top of itself three times.
"The distribution of dark matter bears no relationship to anything you will have read in the literature up to now," explained Professor Gilmore.The BBC article notes that the research findings have yet to be submitted to a journal so hold your horses...a little.
"It comes in a 'magic volume' which happens to correspond to an amount which is 30 million times the mass of the Sun.
"It looks like you cannot ever pack it smaller than about 300 parsecs - 1,000 light-years; this stuff will not let you. That tells you a speed actually - about 9km/s - at which the dark matter particles are moving because they are moving too fast to be compressed into a smaller scale.
"These are the first properties other than existence that we've been able determine."