4,434 research outputs found
Bringing Hidden Organizations Out of the Shadows: Introduction to the Special Issue
No full textThis introduction to the special issue describes hidden organizations, offers several reasons for the lack of research on these collectives, and explains how this collection of articles helps move us forward in efforts to empirically study hidden organizations. After providing background information on the history of this special issue, the five articles published here are described in terms of the type of collective examined, the theories and methods used, and the key research questions addressed. Three observations about the published pieces are made: being hidden requires communicative effort; hiddenness is usefully understood in terms of identity management; and any discussion of hidden organizations raises ethical considerations. The piece closes with acknowledgements and a call for continued conceptual/theoretical and empirical research into hidden organizations.This is an introduction to a special issue on Hidden Organizations edited by the author. Published online before print: July 19, 2015
Super-Stretched and Countable Cohen-Macaulay Type
No full textThis dissertation defines what it means for a Cohen-Macaulay ring to to be super-stretched. In particular, a super-stretched Cohen-Macaulay ring of positive dimension has h-vector (1), (1,n), or (1,n,1). It is shown that Cohen-Macaulay rings of graded countable Cohen-Macaulay type are super-stretched. Further, one dimensional standard graded Gorenstein rings of graded countable type are shown to be hypersurfaces; this result is not known in higher dimensions. In Chapter 1, some background material is given along with some preliminary definitions. This chapter defines what it means to be stretched and super-stretched. The chapter ends by showing a couple of scenarios when these two notions coincide. Chapter 2 deals with super-stretched rings that are standard graded. We begin the chapter by exploring the graded category and defining what it means to be graded countable Cohen-Macaulay type. Equivalent characterizations of super-stretched are discovered and it is shown that rings of graded countable Cohen-Macaulay type are super-stretched. The chapter ends by analyzing standard graded rings that are super-stretched with minimal multiplicity. In Chapter 3, we examine what it means for a local ring to be super-stretched. Finally, Chapter 4 uses the previous results to give a partial answer to the following question: Let R be a standard graded Cohen-Macaulay ring of graded countable Cohen-Macaulay representation type, and assume that R has an isolated singularity. Is R then necessarily of graded finite Cohen-Macaulay representation type? In particular, it is shown there is a positive answer when the ring is not Gorenstein. Throughout the chapter, many different cases of graded countable Cohen-Macaulay type are classified. Further, the Gorenstein case is studied is shown to be helpful in giving support to the following folklore conjecture: a Gorenstein ring of countable Cohen-Macaulay representation type is a hypersurface. It is shown that the conjecture holds for one dimensional standard graded Cohen-Macaulay rings of graded countable Cohen-Macaulay type
Two theorems about maximal Cohen–Macaulay modules
No full textThis paper contains two theorems concerning the theory of maximal Cohen-Macaulay modules. The first theorem proves that certain Ext groups between maximal Cohen-Macaulay modules M and N must have finite length, provided only finitely many isomorphism classes of maximal Cohen-Macaulay modules exist having ranks up to the sum of the ranks of M and N. This has several corollaries. In particular it proves that a Cohen-Macaulay local ring of finite Cohen-Macaulay type has an isolated singularity. A well-known theorem of Auslander gives the same conclusion but requires that the ring be Henselian. Other corollaries of our result include statements concerning when a ring is Gorenstein or a complete intersection on the punctured spectrum, and the recent theorem of Leuschke and Wiegand that the completion of an excellent Cohen-Macaulay local ring of finite Cohen-Macaulay type is again of finite Cohen-Macaulay type. The second theorem proves that a complete local Gorenstein domain of positive characteristic p and dimension d is F-rational if and only if the number of copies of R splitting out of R1/p^e divided by pde has a positive limit. This result generalizes work of Smith and Van den Bergh. We call this limit the F-signature of the ring and give some of its properties
Intersection of HIV and Reproductive Health
No full textCopyright © 2013 Craig R. Cohen et al.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. TheHIV epidemic is integrally linked to reproductive health. Indeed HIV itself, which is predominantly a sexually trans-mitted infection, is a key reproductive health issue. Inwomen, HIV can have adverse impact on pregnancy, childbirth, and breastfeeding. HIV status also affects conception and par-enting choices. Both HIV and poor reproductive health share common drivers, including poverty, gender inequality, and social marginalization of vulnerable populations [1]. Responses to both health issues should therefore be closely linked and mutually reinforcing. The 2006 Political Decla-ration on HIV/AIDS that called for greater linkage between HIV/AIDS and reproductive health as an additional approach to curb the epidemic [2]
Craig interpolation for semilinear substructural logics
No full textThe Craig interpolation property is investigated for substructural logics whose algebraic semantics are varieties of semilinear (subdirect products of linearly ordered) pointed commutative residuated lattices. It is shown that Craig interpolation fails for certain classes of these logics with weakening if the corresponding algebras are not idempotent. A complete characterization is then given of axiomatic extensions of the >R-mingle with unit> logic (corresponding to varieties of Sugihara monoids) that have the Craig interpolation property. This latter characterization is obtained using a model-theoretic quantifier elimination strategy to determine the varieties of Sugihara monoids admitting the amalgamation property. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.The first author was supported by the Spanish projects TASSAT (TIN2010-20967-C04-01) and Agree-
ment Technologies (CONSOLIDER CSD2007-0022, INGENIO 2010), the Generalitat de Catalunya grant 2009-SGR-1434, and the Marie Curie IRSES Project (FP7-PEOPLE-2009). The second author was supported by Swiss National Science Foundation grant 20002 129507 and Marie Curie Reintegration Grant PIRG06-GA-2009-256492.Peer Reviewe
Frobenius test exponents for parameter ideals in generalized Cohen-Macaulay local rings
No full textThis paper studies Frobenius powers of parameter ideals in a commutative Noetherian local ring R of prime characteristic p. For a given ideal a of R, there is a power Q of p, depending on a, such that the Qth Frobenius power of the Frobenius closure of a is equal to the Qth Frobenius power of a. The paper addresses the question as to whether there exists a uniform Q(0) which 'works' in this context for all parameter ideals of R simultaneously.
In a recent paper, Katzman and Sharp proved that there does exists such a uniform Q(0) when R is Cohen-Macaulay. The purpose of this paper is to show that such a uniform Q(0) exists when R is a generalized Cohen-Macaulay local ring. A variety of concepts and techniques from commutative algebra are used, including unconditioned strong d-sequences, cohomological annihilators, modules of generalized fractions, and the Hartshome-Speiser-Lyubeznik Theorem employed by Katzman and Sharp in the Cohen-Macaulay case. (c) 2006 Elsevier Inc. All rights reserved
A Note on the Multiplicity of Cohen-Macaulay Algebras with Pure Resolutions
No full textLet R = k[X1, …, Xn] with k a field, and let I ⊂ R be a homogeneous ideal. The algebra R/I is said to have a pure resolution if its homogeneous minimal resolution has the formSome of the known examples of pure resolutions include the coordinate rings of: the tangent cone of a minimally elliptic singularity or a rational surface singularity [15], a variety defined by generic maximal Pfaffians [2], a variety defined by maximal minors of a generic matrix [3], a variety defined by the submaximal minors of a generic square matrix [6], and certain of the Segre-Veronese varieties [1].If I is in addition Cohen-Macaulay, then Herzog and Kühl have shown that the betti numbers bi are completely determined by the twists di.
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Jacobian ideals, resolutions, and the relation types of parameters
No full textGiven a d-dimensional complete noetherian local ring R of equicharacteristic and a finitely generated R-module M, C. Huneke has conjectured a relation between the Jacobian ideal of R and the Fitting ideals in an arbitrary free resolution of M. In Chapter 1, we show that the conjecture holds if R is a Cohen-Macaulay ring of characteristic 0. By using the work of Seheja and Storch on universal finite differential modules, we obtain a similar result for non-Cohen-Macaulay rings. Moreover, we generate some results of Dieterich, Popescu and Roczen about annihilator ideal of the functor Ext, namely, J\sp{k}Ext\sbsp{R}{d+1}(,) = 0 for some where J is the Jacobian ideal of R. In case R is a Cohen-Macaulay ring, k can be chosen to be 1. In Chapter 2, we study two invariants relation type and postulation number associated with ideals generated by systems of parameters over noetherian local rings. The main result is that for some 2-dimensional rings, both the relation type and the postulation number of parameter ideals are uniformly bounded. The proof also shows that if dim R = 2 and depth R = 1 then the relation type is exactly 2 more than the postulation number for every parameter ideal
Cofiniteness and vanishing of local cohomology modules, and colength of conductor ideals
No full textIn Chapter 1 we prove a special case of a conjecture by Huneke and Lyubeznik about the vanishing of local cohomology modules. In Chapter 2 we prove that, if M is a module over a complete noetherian local ring R and if I is an ideal, then H\sbsp{I}{j}(M) is I-cofinite if R is either equicharacteristic, or Cohen-Macaulay, or if the uniformizing parameter of a coefficeint ring of R is in . In Chapter 3 we give equivalent conditions for a one-dimensional local, reduced, excellent ring R to be such that /R) = a (where a is fixed), t = e 1 and t a. Here t is the Cohen-Macaulay type of R, e is the multiplicity, is the length of R-modules, is the integral closure of R in its total quotient ring, and is the conductor of R in $\overline{R}.
Genomewide association scan of suicidal thoughts and behaviour in major depression
No full textBACKGROUND: Suicidal behaviour can be conceptualised as a continuum from suicidal ideation, to suicidal attempts to completed suicide. In this study we identify genes contributing to suicidal behaviour in the depression study RADIANT. METHODOLOGY/PRINCIPAL FINDINGS: A quantitative suicidality score was composed of two items from the SCAN interview. In addition, the 251 depression cases with a history of serious suicide attempts were classified to form a discrete trait. The quantitative trait was correlated with younger onset of depression and number of episodes of depression, but not with gender. A genome-wide association study of 2,023 depression cases was performed to identify genes that may contribute to suicidal behaviour. Two Munich depression studies were used as replication cohorts to test the most strongly associated SNPs. No SNP was associated at genome-wide significance level. For the quantitative trait, evidence of association was detected at GFRA1, a receptor for the neurotrophin GDRA (p = 2e-06). For the discrete trait of suicide attempt, SNPs in KIAA1244 and RGS18 attained p-values of <5e-6. None of these SNPs showed evidence for replication in the additional cohorts tested. Candidate gene analysis provided some support for a polymorphism in NTRK2, which was previously associated with suicidality. CONCLUSIONS/SIGNIFICANCE: This study provides a genome-wide assessment of possible genetic contribution to suicidal behaviour in depression but indicates a genetic architecture of multiple genes with small effects. Large cohorts will be required to dissect this further.Alexandra Schosser, Amy W. Butler, Marcus Ising, Nader Perroud, Rudolf Uher, Mandy Y. Ng, Sarah Cohen-Woods, Nick Craddock, Michael J. Owen, Ania Korszun, Lisa Jones, Ian Jones, Michael Gill, John P. Rice, Wolfgang Maier, Ole Mors, Marcella Rietschel, Susanne Lucae, Elisabeth B. Binder, Martin Preisig, Julia Perry, Federica Tozzi, Pierandrea Muglia, Katherine J. Aitchison, Gerome Breen, Ian W. Craig, Anne E. Farmer, Bertram Müller-Myhsok, Peter McGuffin and Cathryn M. Lewi
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