Linkage

Five years after Google conquered and abandoned RSS, the news-reader ecosystem is showing green shoots (G+). I get most of the links I read via RSS using NetNewsWire and am reasonably happy with that combination. The linked post lists several alternatives.

Soma cube architectural blocks. Sculpture by David Umemoto.

Hopper crystals (G+), stepped shapes that look like they need to be designed (or procedurally generated) and then fabricated, but grow naturally as crystals of bismuth or other materials.

Chemists discover that the perceived significance of a paper isn’t the same as its citation count (G+, via). Completely unsurprising, but it’s good to have data anyway.

All votes should use paper backups to prevent undetectable tampering (via). This autoplay video by security expert Alex Halderman clearly explains why.

Do opera omnia have a future? (G+). Gerald L. Alexanderson and Leonard F. Klosinski ask about those multi-volume sets of collected works of famous mathematicians that are apparently still being published.

The chromatic number of the plane is at least 5 (via). Amateur mathematician Aubrey de Gray makes a big breakthrough on the Hadwiger–Nelson problem, later verified by a computer search. Things are still in rapid flux, with an ongoing Polymath project to tighten de Gray’s construction.

Crossing number of sphere of influence graphs . If you take a collection of disks on the Euclidean plane with the property that no disk interior contains the center of another disk, and draw the intersection graph of the disks (in the obvious way by placing a vertex at the center of each disk and a line segment connecting each two disks that touch or overlap each other) then the resulting graph has bounded degeneracy and bounded chromatic number, but can have a quadratical number of crossings.

EU proposal to force all copyrighted material to require fees, even for linking to the material rather than re-using it (G+). This appears to be a major threat to open-access publishing.

A 2011 discussion concluded that the graph below (the smallest cubic graph with no perfect matching) had no good name, and deserved one. I think it should be called the fidget spinner graph (G+; drawing modified from an earlier one I made for Wikipedia).

Accepted papers to SWAT 2018, the Scandinavian Symposium and Workshops on Algorithm Theory, where I am PC chair, and accepted papers to FUN 2018, the 9th International Conference on Fun With Algorithms, two of them mine (G+). You may need to adjust your browser or its settings to make the FUN list visible.

Nice Neighbors. A topological webgame by Chris Staecker: move the vertices of a graph to neighbors of their home location, so that all adjacencies are preserved (or contracted) and at least one home location becomes free. Staecker also has an amusing series of YouTube videos about mechanical calculation devices (via).