750 research outputs found
The derived category of a locally complete intersection ring
In this paper, we answer a question of Dwyer, Greenlees, and Iyengar by
proving a local ring is a complete intersection if and only if every
complex of -modules with finitely generated homology is proxy small.
Moreover, we establish that a commutative noetherian ring is locally a
complete intersection if and only if every complex of -modules with finitely
generated homology is virtually small.Comment: 14 page
Health Insurance Exchanges: Organizing Health Insurance Marketplaces to Promote Health Reform Goals
Examines whether and how the proposed health insurance exchange to organize an efficient marketplace would address problems individuals and employers face in buying insurance and thereby increase coverage. Considers lessons learned from earlier efforts
Maternity Care and Consumer-Driven Health Plans
Compares out-of-pocket costs of maternity care under consumer-driven health plans (CDHP) to a traditional health insurance plan. Explores related factors including prenatal care coverage and unpredictability of costs for delivery and hospital stays
The Derived Category of a Locally Complete Intersection Ring
Let R be a commutative noetherian ring. A well-known theorem in commutative algebra states that R is regular if and only if every complex with finitely generated homology is a perfect complex. This homological and derived category characterization of a regular ring yields important ring theoretic information; for example, this characterization solved the well-known ``localization problem for regular local rings. The main result of this thesis is establishing an analogous characterization for when R is locally a complete intersection. Namely, R is locally a complete intersection if and only if each nontrivial complex with finitely generated homology can build a nontrivial perfect complex in the derived category using finitely many cones and retracts. This answers a question of Dwyer, Greenlees and Iyengar posed in 2006 and yields a completely triangulated category characterization of locally complete intersection rings. Moreover, this work gives a new proof that a complete intersection localizes.
Advisors: Luchezar L. Avramov and Mark E. Walke
A partial converse ghost lemma for the derived category of a commutative noetherian ring
In this article a condition is given to detect the containment among thick
subcategories of the bounded derived category of a commutative noetherian ring.
More precisely, for a commutative noetherian ring and complexes of
-modules with finitely generated homology and , we show is in the
thick subcategory generated by if and only if the ghost index of
with respect to is finite for each prime
of . To do so, we establish a "converse coghost lemma" for
the bounded derived category of a non-negatively graded DG algebra with
noetherian homology.Comment: 10 pages, comments welcom
Bounds on cohomological support varieties
Over a local ring , the theory of cohomological support varieties attaches
to any bounded complex of finitely generated -modules an algebraic
variety that encodes homological properties of . We give lower
bounds for the dimension of in terms of classical invariants of .
In particular, when is Cohen-Macaulay and not complete intersection we find
that there are always varieties that cannot be realized as the cohomological
support of any complex. When has finite projective dimension, we also give
an upper bound for in terms of the dimension of the radical of
the homotopy Lie algebra of . This leads to an improvement of a bound due to
Avramov, Buchweitz, Iyengar, and Miller on the Loewy lengths of finite free
complexes. Finally, we completely classify the varieties that can occur as the
cohomological support of a complex over a Golod ring.Comment: 23 pages. Comments welcom
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