Research on PIV Algorithm for Matching of Particle Images Based on Affine Transformation

For the problems of distortion and rotation in the matching of particle images of turbulent motion, according to the nature of affine transformation, using log-polar coordinate transformation, the matching is achieved by performing correlation calculations on the image line by line, and developed a matching algorithm (Turbulent Particle Image Matching, abbreviation: TPIM) for particle image pairs with affine transformation and rigid body transformation: by moving the interpretation window, the algorithm is no longer restricted by displacements of particles; by setting the affine lines according to the angle of the image in the log-polar coordinate system and using the affine line as the matching unit, the decoupling of different transformation factors is realized; according to the characteristic of non-uniform sampling in log-polar coordinate transformation, based on the principle of not losing image information, by reasonably setting the image mask and the rate of sampling, establishing the image pyramid and the relative coordinate system, the algorithm complexity is reduced to about 15% of the original. The experimental results of various types of particle images show that the matching accuracy of the TPIM algorithm can reach more than 99%.

Topological characterization of C2 via open algebraic surface theory

We will give a new proof of Ramanujam’s topological characterization of the affine [Formula: see text]-space [Formula: see text] using the Abhyankar–Moh–Suzuki theorem on embeddings of the affine line in [Formula: see text] and some ideas from the theory of open algebraic surfaces.

Examples of adic spaces

This chapter discusses various examples of adic spaces. These examples include the adic closed unit disc; the adic affine line; the closure of the adic closed unit disc in the adic affine line; the open unit disc; the punctured open unit disc; and the constant adic space associated to a profinite set. The chapter focuses on one example: the adic open unit disc over Zp. The adic spectrum Spa Zp consists of two points, a special point and a generic point. The chapter then studies the structure of analytic points. It also clarifies the relations between analytic rings and Tate rings.

Intersections of two Grassmannians in ℙ9

We study the intersection of two copies of {\mathrm{Gr}(2,5)} embedded in {{{\mathbb{P}}}^{9}}, and the intersection of the two projectively dual Grassmannians in the dual projective space. These intersections are deformation equivalent, derived equivalent Calabi–Yau threefolds. We prove that generically they are not birational. As a consequence, we obtain a counterexample to the birational Torelli problem for Calabi–Yau threefolds. We also show that these threefolds give a new pair of varieties whose classes in the Grothendieck ring of varieties are not equal, but whose difference is annihilated by a power of the class of the affine line. Our proof of non-birationality involves a detailed study of the moduli stack of Calabi–Yau threefolds of the above type, which may be of independent interest.

Rigid local systems with monodromy group the Conway group Co2

We first develop some basic facts about hypergeometric sheaves on the multiplicative group [Formula: see text] in characteristic [Formula: see text]. Certain of their Kummer pullbacks extend to irreducible local systems on the affine line in characteristic [Formula: see text]. One of these, of rank [Formula: see text] in characteristic [Formula: see text], turns out to have the Conway group [Formula: see text], in its irreducible orthogonal representation of degree [Formula: see text], as its arithmetic and geometric monodromy groups.