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Register a new userOn the parallel lines for nondegenerate conics
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Computation of parallel lines (envelopes) to parabolas, ellipses, and hyperbolas is of importance in structure engineering and theory of mechanisms. Homogeneous polynomials that implicitly define parallel lines for the given offset to a conic are found by computing Groebner bases for an elimination ideal of a suitably defined affine variety. Singularity of the lines is discussed and their singular points are explicitly found as functions of the offset and the parameters of the conic. Critical values of the offset are linked to the maximum curvature of each conic. Application to a finite element analysis is shown. Keywords: Affine variety, elimination ideal, Groebner basis, homogeneous polynomial, singularity, family of curves, envelope, pitch curve, undercutting, cam surface
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This is a survey on the Fano schemes of linear spaces, conics, rational curves, and curves of higher genera in smooth projective hypersurfaces, complete intersections, Fano threefolds, etc.
We count the number of conics through two general points in complete intersections when this number is finite and give an application in terms of quasi-lines.
In this paper we investigate special arrangements of lines in multiprojective spaces. In particular, we characterize codimensional two arithmetically Cohen-Macaulay (ACM) varieties in $mathbb P^1timesmathbb P^1timesmathbb P^1$, called varieties of lines. We also describe their ACM property from combinatorial algebra point of view.
We study the arithmetically Cohen-Macaulay (ACM) property for finite sets of points in multiprojective spaces, especially $(mathbb P^1)^n$. A combinatorial characterization, the $(star)$-property, is known in $mathbb P^1 times mathbb P^1$. We propose a combinatorial property, $(star_n)$, that directly generalizes the $(star)$-property to $(mathbb P^1)^n$ for larger $n$. We show that $X$ is ACM if and only if it satisfies the $(star_n)$-property. The main tool for several of our results is an extension to the multiprojective setting of certain liaison methods in projective space.
By way of Ziegler restrictions we study the relation between nearly free plane arrangements and combinatorics and we give a Yoshinaga-type criterion for plus-one generated plane arrangements.
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