摘要:

In this paper we give an example of two composantsXandX,oof the Hilbert scheme of space curves (i.e. components of subschemes with constant cohomology) satisfying the condition of semi-continuity (the cohomology of curves inXis less than the cohomology of curves inX,o) but not the propertyX0⋂[Xbar]≠Ø.

ISSN:0092-7872    

DOI:10.1080/00927870008827201

出版商:Gordon and Breach Science Publishers Ltd.    

年代:2000

数据来源: Taylor

摘要:

The focal locus ∑xof an affine varietyXis roughly speaking the (projective) closure of the set of pointsOfor which there is a smooth point x ∈Xand a circle with centreOpassing through x which osculatesXinx. Algebraic geometry interprets the focal locus as the branching locus of the endpoint map ∈ between the Euclidean normal bundle Nxand the projective ambient space (∈ sends the normal vectorO- x to its endpointO), and in this paper we address two general problems:.

ISSN:0092-7872    

DOI:10.1080/00927870008827202

出版商:Gordon and Breach Science Publishers Ltd.    

年代:2000

数据来源: Taylor

ISSN:0092-7872    

DOI:10.1080/00927870008827203

出版商:Gordon and Breach Science Publishers Ltd.    

年代:2000

数据来源: Taylor

摘要:

We prove that every curve in the biliaison class of an extremal curve in P3can be connected to an extremal curve.

ISSN:0092-7872    

DOI:10.1080/00927870008827204

出版商:Gordon and Breach Science Publishers Ltd.    

年代:2000

数据来源: Taylor

ISSN:0092-7872    

DOI:10.1080/00927870008827170

出版商:Gordon and Breach Science Publishers Ltd.    

年代:2000

数据来源: Taylor