Transformer Oil Passivation and Impact of Corrosive Sulphur

In recent years a significant volume of research has been undertaken in order to understand the recent failures in oil insulated power apparatus due to deposition of copper sulphide on the conductors and in the insulation paper. Dibenzyl Disulfide (DBDS) has been found to be the leading corrosive sulphur compound in the insulation oil [1]. The process of copper sulphide formation and the deposition in the paper is still being investigated, but a recently proposed method seems to be gaining some confidence [1]. This method suggests a two-step process; initially the DBDS and some oil soluble copper complexes are formed. Secondly the copper complexes are absorbed in the paper insulation, where they then decompose into copper sulphide [2]. The most commonly used mitigating technique for corrosive sulphur contaminated oil is passivation, normally using Irgamet 39 or 1, 2, 3-benzotriazole (BTA). The passivator is diluted into the oil to a concentration of around 100ppm, where it then reacts with the copper conductors to form a complex layer around the copper, preventing it from interacting with DBDS compounds and forming copper sulphide. This research project will investigate the electrical properties of HV transformers which have tested positive for corrosive sulphur, and the evolution of those properties as the asset degrades due to sulphur corrosion. Parallel to this the long term properties of transformers with passivated insulation oil will be analysed in order to understand the passivator stability and whether it is necessary to keep adding the passivator to sustain its performance. Condition monitoring techniques under investigation will include dielectric spectroscopy, frequency response analysis, recovery voltage method (aka interfacial polarisation) amongst others. Partial discharge techniques will not be investigated, as the voltage between the coil plates is low and therefore it will not contribute significantly to the overall insulation breakdown, in corrosive oil related faults [3]. The goal of this research is to establish key electrical properties in both passivated and non-passivated power transformers that demonstrate detectable changes as the equipment degrades due to the insulation oil being corrosive

Pathway-Dependent Post-assembly Modification of an Anthracene-Edged MII4L6 Tetrahedron

FeII4L6 tetrahedral cage 1 undergoes post-assembly modification (PAM) via a Diels–Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage 2 possesses an enclosed cavity suitable for encapsulation of the fullerene C60, whereas original cage 1 forms a unique covalent adduct through a Diels–Alder cycloaddition of three of its anthracene ligands with C60. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C60 and TCNE. Modified cage 2 was also able to bind an anionic guest, [Co(C2B9H11)2]−, which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts

Factors Influencing the Green House Gas Footprint of US Dairy Farms

Environmental Economics and Policy, Livestock Production/Industries,

Spodic horizon characteristics of some forest soils in the White Mountains, New Hampshire, Station Bulletin, no.507

The Bulletin is a publication of the New Hampshire Agricultural Experiment Station, College of Life Sciences and Agriculture, University of New Hampshire, Durham, New Hampshire

Dynamical Belyi maps

We study the dynamical properties of a large class of rational maps with exactly three ramification points. By constructing families of such maps, we obtain infinitely many conservative maps of degree $d$; this answers a question of Silverman. Rather precise results on the reduction of these maps yield strong information on the rational dynamics.Comment: 21 page

Life history parameters in acellular extrinsic fiber cementum microstructure

Life-history parameters such as pregnancies, skeletal trauma, and renal disease have previously been identified from hypomineralized growth layers (incremental lines) of acellular extrinsic fiber cementum (AEFC). The precise periodicity of these growth layers remains vaguely approximated, so causal life-history explanations using tooth cementum cannot yet be rigorously calculated or tested. On the other hand, we show how life history parameters in AEFC can be identified by two contrasting elemental detection methods. Based on our results we reject the possibility of accurate estimation of pregnancies and other life history parameters from cementum using scanning electron microscopy alone. Here, we propose a new methodological approach for cementum research, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), to measure degree and distribution of mineralization of cementum growth layers. Our results show that Tof-SIMS can significantly increase our knowledge of cementum composition and is therefore a powerful new tool for life history researchers

Covalent Post-assembly Modification Triggers Multiple Structural Transformations of a Tetrazine-Edged Fe4L6 Tetrahedron

Covalent post-assembly modification (PAM) reactions are useful synthetic tools for functionalizing and stabilizing self-assembled metal-organic complexes. Recently, PAM reactions have also been explored as stimuli for triggering supramolecular structural transformations. Herein we demonstrate the use of inverse electron-demand Diels-Alder (IEDDA) PAM reactions to induce supramolecular structural transformations starting from a tetrazine-edged FeII4L6 tetrahedral precursor. Following PAM, this tetrahedron rearranged to form three different architectures depending on the addition of other stimuli: an electron-rich aniline or a templating anion. By tracing the stimulus-response relationships within the system, we deciphered a network of transformations that mapped different combinations of stimuli onto specific transformation products. Given the many functions being developed for self-assembled three-dimensional architectures, this newly established ability to control the interconversion between structures using combinations of different stimulus types may serve as the basis for switching the functions expressed within a system.D.A.R. acknowledges the Gates Cambridge Trust. B.S.P. acknowledges the Royal Commission for the Exhibition of 1851 Fellowship and Corpus Christi College, Cambridge. This work was supported by the UK Engineering and Physical Sciences Research Council (EP/M01083X/1)