Let X be a smooth projective curve of genus g 2 over an algebraically closed field k of characteristic p>0,and F:X→X(1)the relative Frobenius morphism.Let M s X(r,d)(resp.M ss X(r,d))be the moduli space of(resp.semi-)stable vector bundles of rank r and degree d on X.We show that the set-theoretic map S ss Frob:M ss X(r,d)→M ss X(1)(rp,d+r(p-1)(g-1))induced by[E]→[F(E)]is a proper morphism.Moreover,the induced morphism S s Frob:M s X(r,d)→M s X(1)(rp,d+r(p-1)(g-1))is a closed immersion.As an application,we obtain that the locus of moduli space M s X(1)(p,d)consisting of stable vector bundles whose Frobenius pull backs have maximal Harder-Narasimhan polygons is isomorphic to the Jacobian variety Jac X of X.
We provide some exact formulas for the projective dimension and regularity of edge ideals associated to some vertex-weighted oriented cyclic graphs with a common vertex or edge.These formulas axe functions in the weight of the vertices,and the numbers of edges and cycles.Some examples show that these formulas are related to direction selection and the assumption that w(x)≥2 for any vertex x cannot be dropped.
Hong WangGuangjun ZhuLi XuJiaqi ZhangZhongming Tang
Let R be a Noetherian ring, M an Artinian R-module, and p ∈ CosRM. Thencograden. Homn（Rp, M） =-inf{i ｜πi（p, M） 〉 0} and πi（p, M） 〉 0 =〉 cogradeRpHomR（Rp, M） ≤ i ≤ fdRpHomR（Rp, M）,where πi （p,M） is the i-th dual Bass number of M with respect to p, cogradeRpHomR （Rp ,M） is the common length of any maxima[ HomR（Rp, M）-quasi co-regular sequence contained in pRp, and fdRp HomR（Rp, M） is the flat dimension of the Rp-module HomR（Rp, M）. We also study the relations among cograde, co-dimension and flat dimension of co-localization modules.
