5,191 research outputs found
Noncommutative resolutions of ADE fibered Calabi-Yau threefolds
In this paper we construct noncommutative resolutions of a certain class of Calabi-Yau threefolds studied by F. Cachazo, S. Katz and C. Vafa. The threefolds under consideration are fibered over a complex plane with the fibers being deformed Kleinian singularities. The construction is in terms of a noncommutative algebra introduced by V. Ginzburg, which we call the "N=1 ADE quiver algebra"
Deep Hole States in Medium Mass Nuclei
Supported by the National Science Foundation and Indiana Universit
Degenerate flag varieties: moment graphs and Schr\"oder numbers
We study geometric and combinatorial properties of the degenerate flag
varieties of type A. These varieties are acted upon by the automorphism group
of a certain representation of a type A quiver, containing a maximal torus T.
Using the group action, we describe the moment graphs, encoding the zero- and
one-dimensional T-orbits. We also study the smooth and singular loci of the
degenerate flag varieties. We show that the Euler characteristic of the smooth
locus is equal to the large Schr\"oder number and the Poincar\'e polynomial is
given by a natural statistics counting the number of diagonal steps in a
Schr\"oder path. As an application we obtain a new combinatorial description of
the large and small Schr\"oder numbers and their q-analogues.Comment: 25 page
Sheaves on fibered threefolds and quiver sheaves
This paper classifies a class of holomorphic D-branes, closely related to
framed torsion-free sheaves, on threefolds fibered in resolved ADE surfaces
over a general curve C, in terms of representations with relations of a twisted
Kronheimer--Nakajima-type quiver in the category Coh(C) of coherent sheaves on
C. For the local Calabi--Yau case C\cong\A^1 and special choice of framing, one
recovers the N=1 ADE quiver studied by Cachazo--Katz--Vafa.Comment: 13 pages, 2 figures, minor change
Equivariant volumes of non-compact quotients and instanton counting
Motivated by Nekrasov's instanton counting, we discuss a method for
calculating equivariant volumes of non-compact quotients in symplectic and
hyper-K\"ahler geometry by means of the Jeffrey-Kirwan residue-formula of
non-abelian localization. In order to overcome the non-compactness, we use
varying symplectic cuts to reduce the problem to a compact setting, and study
what happens in the limit that recovers the original problem. We implement this
method for the ADHM construction of the moduli spaces of framed Yang-Mills
instantons on and rederive the formulas for the equivariant volumes
obtained earlier by Nekrasov-Shadchin, expressing these volumes as iterated
residues of a single rational function.Comment: 34 pages, 2 figures; minor typos corrected, to appear in Comm. Math.
Phy
'Reclaiming the criminal' : the role and training of prison officers in England, 1877-1914
This article examines the role and training of prison officers in England, between 1877 and 1914. It is concerned with the changing penal philosophies and practices of this period and how these were implemented in local prisons, and the duties of the prison officer. More broadly, this article argues that the role of the prison officer and their training (from 1896) reflect wider ambiguities in prison policy and practice during this period
Morse theory of the moment map for representations of quivers
The results of this paper concern the Morse theory of the norm-square of the
moment map on the space of representations of a quiver. We show that the
gradient flow of this function converges, and that the Morse stratification
induced by the gradient flow co-incides with the Harder-Narasimhan
stratification from algebraic geometry. Moreover, the limit of the gradient
flow is isomorphic to the graded object of the
Harder-Narasimhan-Jordan-H\"older filtration associated to the initial
conditions for the flow. With a view towards applications to Nakajima quiver
varieties we construct explicit local co-ordinates around the Morse strata and
(under a technical hypothesis on the stability parameter) describe the negative
normal space to the critical sets. Finally, we observe that the usual Kirwan
surjectivity theorems in rational cohomology and integral K-theory carry over
to this non-compact setting, and that these theorems generalize to certain
equivariant contexts.Comment: 48 pages, small revisions from previous version based on referee's
comments. To appear in Geometriae Dedicat
Testing sensory drive speciation in cichlid fish:Linking light conditions to opsin expression, opsin genotype and female mate preference
Ecological speciation is facilitated when divergent adaptation has direct effects on selective mating. Divergent sensory adaptation could generate such direct effects, by mediating both ecological performance and mate selection. In aquatic environments, light attenuation creates distinct photic environments, generating divergent selection on visual systems. Consequently, divergent sensory drive has been implicated in the diversification of several fish species. Here, we experimentally test whether divergent visual adaptation explains the divergence of mate preferences in Haplochromine cichlids. Blue and red Pundamilia co-occur across south-eastern Lake Victoria. They inhabit different photic conditions and have distinct visual system properties. Previously, we documented that rearing fish under different light conditions influences female preference for blue versus red males. Here, we examine to what extent variation in female mate preference can be explained by variation in visual system properties, testing the causal link between visual perception and preference. We find that our experimental light manipulations influence opsin expression, suggesting a potential role for phenotypic plasticity in optimizing visual performance. However, variation in opsin expression does not explain species differences in female preference. Instead, female preference covaries with allelic variation in the long-wavelength-sensitive opsin gene (LWS), when assessed under broad-spectrum light. Taken together, our study presents evidence for environmental plasticity in opsin expression and confirms the important role of colour perception in shaping female mate preferences in Pundamilia. However, it does not constitute unequivocal evidence for the direct effects of visual adaptation on assortative mating.</p
The epigenetic regulators CBP and p300 facilitate leukemogenesis and represent therapeutic targets in acute myeloid leukemia.
Growing evidence links abnormal epigenetic control to the development of hematological malignancies. Accordingly, inhibition of epigenetic regulators is emerging as a promising therapeutic strategy. The acetylation status of lysine residues in histone tails is one of a number of epigenetic post-translational modifications that alter DNA-templated processes, such as transcription, to facilitate malignant transformation. Although histone deacetylases are already being clinically targeted, the role of histone lysine acetyltransferases (KAT) in malignancy is less well characterized. We chose to study this question in the context of acute myeloid leukemia (AML), where, using in vitro and in vivo genetic ablation and knockdown experiments in murine models, we demonstrate a role for the epigenetic regulators CBP and p300 in the induction and maintenance of AML. Furthermore, using selective small molecule inhibitors of their lysine acetyltransferase activity, we validate CBP/p300 as therapeutic targets in vitro across a wide range of human AML subtypes. We proceed to show that growth retardation occurs through the induction of transcriptional changes that induce apoptosis and cell-cycle arrest in leukemia cells and finally demonstrate the efficacy of the KAT inhibitors in decreasing clonogenic growth of primary AML patient samples. Taken together, these data suggest that CBP/p300 are promising therapeutic targets across multiple subtypes in AML.Funding in the Huntly laboratory comes from Cancer Research UK, Leukemia
Lymphoma Research, the Kay Kendal Leukemia Fund, the Leukemia lymphoma
Society of America, the Wellcome Trust, The Medical Research Council and an NIHR
Cambridge Biomedical Research Centre grant. Patient samples were processed in the
Cambridge Blood and Stem Cell Biobank.This is the author accepted manuscript. The final version is available via NPG at http://dx.doi.org/10.1038/onc.2015.9
- âŠ