Diagonal Subschemes and Vector Bundles

We study when a smooth variety $X$, embedded diagonally in its Cartesian square, is the zero scheme of a section of a vector bundle of rank $\dim(X)$ on $X\times X$. We call this the diagonal property (D). It was known that it holds for all flag manifolds ${\rm SL}_n/P$. We consider mainly the cases of proper smooth varieties, and the analogous problems for smooth manifolds (the topological case). Our main new observation in the case of proper varieties is a relation between (D) and cohomologically trivial line bundles on $X$, obtained by a variation of Serre's classic argument relating rank 2 vector bundles and codimension 2 subschemes, combined with Serre duality. Based on this, we have several detailed results on surfaces, and some results in higher dimensions. For smooth affine varieties, we observe that for an affine algebraic group over an algebraically closed field, the diagonal is in fact a complete intersection; thus (D) holds, using the trivial bundle. We conjecture the existence of smooth affine complex varieties for which (D) fails; this leads to an interesting question on projective modules. The arguments in the topological case have a different flavour, with arguments from homotopy theory, topological K-theory, index theory etc. There are 3 variants of the diagonal problem, depending on the type of vector bundle we want (arbitrary, oriented or complex). We obtain a homotopy theoretic reformulation of the diagonal property as an extension problem for a certain homotopy class of maps. We also have detailed results in several cases: spheres, odd dimensional complex projective quadric hypersurfaces, and manifolds of even dimension $\leq 6$ with an almost complex structure.Comment: 33 page

EduCycle: Bicycle-based Low Power Lighting Demonstration

This report describes EduCycle, a system for demonstrating the reduced energy requirements of modern lighting in a hands-on manner to elementary school students. EduCycle consists of a bicycle trainer connecting a bicycle to a generator and a bank of incandescent, compact fluorescent (CFL), and light emitting diode (LED) light bulbs. The EduCycle system facilitates experiential learning by allowing the user to physically experience the amount of power required by each type of lighting. EduCycle has been designed from the ground-up to be portable, durable and safe, and was beta tested on 3rd grade elementary school students. Surveys collected from the beta test indicate that the students achieved the intended learning outcomes of the project