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The equations of space curves on a quadric.

Roberta Di Gennaro, Uwe Nagel (2007)

Collectanea Mathematica

The homogeneous ideals of curves in a double plane have been studied by Chiarli, Greco, Nagel. Completing this work we describe the equations of any curve that is contained in some quadric. As a consequence, we classify the Hartshorne-Rao modules of such curves.

The Hilbert Scheme of Buchsbaum space curves

Jan O. Kleppe (2012)

Annales de l’institut Fourier

We consider the Hilbert scheme H ( d , g ) of space curves C with homogeneous ideal I ( C ) : = H * 0 ( C ) and Rao module M : = H * 1 ( C ) . By taking suitable generizations (deformations to a more general curve) C of C , we simplify the minimal free resolution of I ( C ) by e.g making consecutive free summands (ghost-terms) disappear in a free resolution of I ( C ) . Using this for Buchsbaum curves of diameter one ( M v 0 for only one v ), we establish a one-to-one correspondence between the set 𝒮 of irreducible components of H ( d , g ) that contain ( C ) and a set of minimal...

The Hilbert scheme of space curves of small diameter

Jan Oddvar Kleppe (2006)

Annales de l’institut Fourier

This paper studies space curves C of degree d and arithmetic genus g , with homogeneous ideal I and Rao module M = H * 1 ( I ˜ ) , whose main results deal with curves which satisfy 0 Ext R 2 ( M , M ) = 0 (e.g. of diameter, diam M 2 ). For such curves we find necessary and sufficient conditions for unobstructedness, and we compute the dimension of the Hilbert scheme, H ( d , g ) , at ( C ) under the sufficient conditions. In the diameter one case, the necessary and sufficient conditions coincide, and the unobstructedness of C turns out to be equivalent to the...

The irregularity of ruled surfaces in three dimensional projective space.

Luis Giraldo, Ignacio Sols (1998)

Collectanea Mathematica

Let S be a ruled surface in P3 with no multiple generators. Let d and q be nonnegative integers. In this paper we determine which pairs (d,q) correspond to the degree and irregularity of a ruled surface, by considering these surfaces as curves in a smooth quadric hypersurface in P5.

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