The shape of hyperbolic Dehn surgery space

In this paper we develop a new theory of infinitesimal harmonic deformations for compact hyperbolic 3-manifolds with ``tubular boundary''. In particular, this applies to complements of tubes of radius at least R_0 = \arctanh(1/\sqrt{3}) \approx 0.65848 around the singular set of hyperbolic cone manifolds, removing the previous restrictions on cone angles. We then apply this to obtain a new quantitative version of Thurston's hyperbolic Dehn surgery theorem, showing that all generalized Dehn surgery coefficients outside a disc of ``uniform'' size yield hyperbolic structures. Here the size of a surgery coefficient is measured using the Euclidean metric on a horospherical cross section to a cusp in the complete hyperbolic metric, rescaled to have area 1. We also obtain good estimates on the change in geometry (e.g. volumes and core geodesic lengths) during hyperbolic Dehn filling. This new harmonic deformation theory has also been used by Bromberg and his coworkers in their proofs of the Bers Density Conjecture for Kleinian groups.Comment: 46 pages, 3 figure

Heterotopia in Networked Learning: Beyond the Shadow Side of Participation in Learning Communities

As it has evolved, networked learning (NL) has come to emphasise the importance of the collaborative learning aspects and possibilities of online learning. The importance assumed for 'collaboration based' forms of participation within NL has almost become ubiquitous and is frequently seen as an unquestionable good aspect - a utopian view of participation which does not acknowledge the 'shadow side' of participation in learning. In the paper we examine some of the darker sides of collaborative participation which in its extreme manifestations can be experienced as normative and, we suggest, a form of tyranny of the dominant and which instead of having a liberating effect, reinforces a form of oppression and control. We argue this is most likely to be the case in the absence of reflexivity and understanding of different ways and approaches to participation. We go on to suggest an alternative and potentially more productive perspective which, after Foucault, is a heterotopian one. A perspective that acknowledges and assumes disruption and which disturbs our customary notion of ourselves. Participation in heterotopian spaces is disturbing and ambiguous, but it offers a space in which to imagine, to desire and act differently

Non-geometric veering triangulations

Recently, Ian Agol introduced a class of "veering" ideal triangulations for mapping tori of pseudo-Anosov homeomorphisms of surfaces punctured along the singular points. These triangulations have very special combinatorial properties, and Agol asked if these are "geometric", i.e. realised in the complete hyperbolic metric with all tetrahedra positively oriented. This paper describes a computer program Veering, building on the program Trains by Toby Hall, for generating these triangulations starting from a description of the homeomorphism as a product of Dehn twists. Using this we obtain the first examples of non-geometric veering triangulations; the smallest example we have found is a triangulation with 13 tetrahedra

Treatment of Abscessed Primary Molars Utilizing Lesion Sterilization and Tissue Repair: Literature Review and Report of Three Cases

Purpose: The purpose of this report was to review an emerging alternative treatment to pulpectomies and extractions for nonvital primary teeth called lesion sterilization and tissue repair (LSTR) and provide the results of three clinical case applications. LSTR is a noninstrumentation endodontic treatment that involves a triantibiotic mixture in a propylene glycol vehicle, which is used to disinfect root canal systems. This concept was developed by the cariology research unit of the School of Dentistry, Niigata University, Niigata, Niigata Prefecture, Japan. This article reviews the development of the technique, clinical procedures required for the technique, three clinical applications and radiographic documentation and follow-up, and a short literature review of the current evidence supporting its application in clinical practice

Pulp Polyp Associated with a Natal Tooth: Case Report

Natal teeth are an infrequent occurrence at birth. Often these teeth are extracted because they are very mobile and pose a risk of aspiration. This is a rare case in which a natal tooth was extracted by the pediatrician with his fingers. A root fragment remained and out of this developed a large pulp polyp. This relationship has not been previously reported

Evidence of late Quaternary environmental change in a continental east Antarctic lake from lacustrine sedimentary pigment distributions

A sediment core from Progress Lake, one of the oldest lacustrine sequences in East Antarctica, contains distinct zones dating from a previous interglacial (most likely Marine Isotope Stage 5e, c. 125-115 kyr BP) and the present interglacial (Marine Isotope Stage 1), separated by a transition zone representing when the lake became sub-glacial. Profiles of fossil pigments, determined using high performance liquid chromatography and liquid chromatography-tandem mass spectrometry, show distinct differences in the photoautotrophic community during these two interglacial periods. The first was dominated by algae and purple phototrophic bacteria, with periods of photic zone euxinia indicated by pigments from anoxygenic phototrophic bacteria. Specific chlorophyll a derivatives reveal periods when grazing pressure impacted significantly on the phytoplankton community. The virtual absence of pigments in the transition zone reflects severe restriction of photoautotrophic activity, consistent with the take having become sub-glacial. Retreat of snow and ice in the late Holocene (3345 C-14 yr Bp) allowed establishment of a less diverse primary producer community, restricted to algae and cyanobacteria. Grazers were severely restricted and oxidative transformation was more important than during the previous interglacial. The pigment data provide a unique and detailed insight in to the evolution of the lake ecology over an interglacial-glacial-interglacial transition and strong evidence that the Marine Isotope Stage 5e interglacial in this region of coastal East Antarctica was several degrees warmer than at present