Holonomy groups of pseudo-quaternionic-K\"ahlerian manifolds of non-zero scalar curvature

The holonomy group $G$ of a pseudo-quaternionic-K\"ahlerian manifold of signature $(4r,4s)$ with non-zero scalar curvature is contained in \Sp(1)\cdot\Sp(r,s) and it contains \Sp(1). It is proved that either $G$ is irreducible, or $s=r$ and $G$ preserves an isotropic subspace of dimension $4r$, in the last case, there are only two possibilities for the connected component of the identity of such $G$. This gives the classification of possible connected holonomy groups of pseudo-quaternionic-K\"ahlerian manifolds of non-zero scalar curvature.Comment: 7 pages; Dedicated to Dmitri Vladimirovich Alekseevsky at the occasion of his 70th birthda

Toric anti-self-dual Einstein metrics via complex geometry

Using the twistor correspondence, we give a classification of toric anti-self-dual Einstein metrics: each such metric is essentially determined by an odd holomorphic function. This explains how the Einstein metrics fit into the classification of general toric anti-self-dual metrics given in an earlier paper (math.DG/0602423). The results complement the work of Calderbank-Pedersen (math.DG/0105263), who describe where the Einstein metrics appear amongst the Joyce spaces, leading to a different classification. Taking the twistor transform of our result gives a new proof of their theorem.Comment: v2. Published version. Additional references. 14 page

The G_2 sphere over a 4-manifold

We present a construction of a canonical G_2 structure on the unit sphere tangent bundle S_M of any given orientable Riemannian 4-manifold M. Such structure is never geometric or 1-flat, but seems full of other possibilities. We start by the study of the most basic properties of our construction. The structure is co-calibrated if, and only if, M is an Einstein manifold. The fibres are always associative. In fact, the associated 3-form results from a linear combination of three other volume 3-forms, one of which is the volume of the fibres. We also give new examples of co-calibrated structures on well known spaces. We hope this contributes both to the knowledge of special geometries and to the study of 4-manifolds.Comment: 13 page

Screening of Exosomal MicroRNAs From Colorectal Cancer Cells

BACKGROUND: Cells release extracellular membrane vesicles including microvesicles known as exosomes. Exosomes contain microRNAs (miRNAs) however the full range within colorectal cancer cell secreted exosomes is unknown. OBJECTIVE: To identify the full range of exosome encapsulated miRNAs secreted from 2 colorectal cancer cell lines and to investigate engineering of exosomes over-expressing miRNAs. METHODS: Exosomes were isolated from HCT-116 and HT-29 cell lines. RNA was extracted from exosomes and microRNA array performed. Cells were engineered to express miR-379 (HCT-116-379) or a non-targeting control (HCT-116-NTC) and functional effects were determined. Exosomes secreted by engineered cells were transferred to recipient cells and the impact examined. RESULTS: Microvesicles 40-100 nm in size secreted by cell lines were visualised and confirmed to express exosomal protein CD63. HT-29 exosomes contained 409 miRNAs, HCT-116 exosomes contained 393, and 338 were common to exosomes from both cell lines. Selected targets were validated. HCT-116-379 cells showed decreased proliferation (12-15% decrease, p \u3c 0.001) and decreased migration (32-86% decrease, p \u3c 0.001) compared to controls. HCT-116-379 exosomes were enriched for miR-379. Confocal microscopy visualised transfer of HCT-116-379 exosomes to recipient cells. CONCLUSIONS: Colorectal cancer cells secrete a large number of miRNAs within exosomes. miR-379 decreases cell proliferation and migration, and miR-379 enriched exosomes can be engineered

Closed forms and multi-moment maps

We extend the notion of multi-moment map to geometries defined by closed forms of arbitrary degree. We give fundamental existence and uniqueness results and discuss a number of essential examples, including geometries related to special holonomy. For forms of degree four, multi-moment maps are guaranteed to exist and are unique when the symmetry group is (3,4)-trivial, meaning that the group is connected and the third and fourth Lie algebra Betti numbers vanish. We give a structural description of some classes of (3,4)-trivial algebras and provide a number of examples.Comment: 36 page

Towards a Nonequilibrium Quantum Field Theory Approach to Electroweak Baryogenesis

We propose a general method to compute $CP$-violating observables from extensions of the standard model in the context of electroweak baryogenesis. It is alternative to the one recently developed by Huet and Nelson and relies on a nonequilibrium quantum field theory approach. The method is valid for all shapes and sizes of the bubble wall expanding in the thermal bath during a first-order electroweak phase transition. The quantum physics of $CP$-violation and its suppression coming from the incoherent nature of thermal processes are also made explicit.Comment: 19 pages, 1 figure available upon e-mail reques

Irreducible holonomy algebras of Riemannian supermanifolds

Possible irreducible holonomy algebras \g\subset\osp(p,q|2m) of Riemannian supermanifolds under the assumption that \g is a direct sum of simple Lie superalgebras of classical type and possibly of a one-dimensional center are classified. This generalizes the classical result of Marcel Berger about the classification of irreducible holonomy algebras of pseudo-Riemannian manifolds.Comment: 27 pages, the final versio

Superdeformed rotational bands in the Mercury region; A Cranked Skyrme-Hartree-Fock-Bogoliubov study

A study of rotational properties of the ground superdeformed bands in \Hg{0}, \Hg{2}, \Hg{4}, and \Pb{4} is presented. We use the cranked Hartree-Fock-Bogoliubov method with the {\skm} parametrization of the Skyrme force in the particle-hole channel and a seniority interaction in the pairing channel. An approximate particle number projection is performed by means of the Lipkin-Nogami prescription. We analyze the proton and neutron quasiparticle routhians in connection with the present information on about thirty presently observed superdeformed bands in nuclei close neighbours of \Hg{2}.Comment: 26 LaTeX pages, 14 uuencoded postscript figures included, Preprint IPN-TH 93-6