Novel coordination complexes bearing potentially tetradentate phenolateamine ligands and their applications in polymerisation catalysis

This thesis describes the synthesis and characterisation of novel complexes bearing monoanionic phenolateamine ligands and explores their catalytic behaviour in the ring opening polymerisation of lactide and in the polymerisation of ethylene. Chapter 1 introduces and reviews various aspects of the coordination chemistry of phenolateamine ligands and is followed by an introduction to the field of lactide polymerisation. Chapter 2 describes the preparation of several potentially tetradentate proligands via the Mannich reaction. The ligands presented have various combinations of donors, chain length and substituents on the phenyl backbone. The synthesis and characterisation of several novel main group complexes (K, Ca and Al) using these ligands is presented. The calcium bis-chelate complexes are shown to be highly active in the ring opening polymerisation of lactide. Chapter 3 introduces a new family of zinc species stabilised by these ligands. The coordination chemistry of zinc alkyls and alkoxides is shown to be dependent on ligand structure, most notably on the choice of heteroatom donor and phenolate backbone substituent. The zinc alkoxides are efficient initiators in the polymerisation of rac-lactide, with the catalytic activity influenced by the choice of coordinated ligand. The highest activity is observed with ligands containing two neutral oxygen donors in combination with bulky phenolate substituents. After a brief introduction to the field of olefin polymerisation, Chapter 4 describes the synthesis and characterisation of a wide range of transition metal complexes (Ti, V, Cr, Fe, Co and Ni) and discusses their activity as precatalysts in the polymerisation of ethylene. Full experimental details for Chapters 2-4 are presented in Chapter 5

Pulsation-Initiated Mass Loss in Luminous Blue Variables: A Parameter Study

Luminous blue variables (LBVs) are characterized by semi-periodic episodes of enhanced mass-loss, or outburst. The cause of these outbursts has thus far been a mystery. One explanation is that they are initiated by kappa-effect pulsations in the atmosphere caused by an increase in luminosity at temperatures near the so-called ``iron bump'' (T ~ 200,000 K), where the Fe opacity suddenly increases. Due to a lag in the onset of convection, this luminosity can build until it exceeds the Eddington limit locally, seeding pulsations and possibly driving some mass from the star. We present some preliminary results from a parameter study focusing on the conditions necessary to trigger normal S-Dor type (as opposed to extreme eta-Car type) outbursts. We find that as Y increases or Z decreases, the pulsational amplitude decreases and outburst-like behavior, indicated by a large, sudden increase in photospheric velocity, becomes likes likely.Comment: 6 pages, 4 figures, to be published in the Proceedings of Massive Stars as Cosmic Engines, IAU Symp 250, ed. F. Bresolin, P. A. Crowther, & J. Puls (Cambridge Univ. Press

A study of singularities on rational curves via syzygies

Consider a rational projective curve C of degree d over an algebraically closed field k. There are n homogeneous forms g_1,...,g_n of degree d in B=k[x,y] which parameterize C in a birational, base point free, manner. We study the singularities of C by studying a Hilbert-Burch matrix phi for the row vector [g_1,...,g_n]. In the "General Lemma" we use the generalized row ideals of phi to identify the singular points on C, their multiplicities, the number of branches at each singular point, and the multiplicity of each branch. Let p be a singular point on the parameterized planar curve C which corresponds to a generalized zero of phi. In the "Triple Lemma" we give a matrix phi' whose maximal minors parameterize the closure, in projective 2-space, of the blow-up at p of C in a neighborhood of p. We apply the General Lemma to phi' in order to learn about the singularities of C in the first neighborhood of p. If C has even degree d=2c and the multiplicity of C at p is equal to c, then we apply the Triple Lemma again to learn about the singularities of C in the second neighborhood of p. Consider rational plane curves C of even degree d=2c. We classify curves according to the configuration of multiplicity c singularities on or infinitely near C. There are 7 possible configurations of such singularities. We classify the Hilbert-Burch matrix which corresponds to each configuration. The study of multiplicity c singularities on, or infinitely near, a fixed rational plane curve C of degree 2c is equivalent to the study of the scheme of generalized zeros of the fixed balanced Hilbert-Burch matrix phi for a parameterization of C.Comment: Typos corrected and minor changes made. To appear in the Memoirs of the AM

The creep properties of a nickel base alloy

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Higher education science fictions – how fictional narratives can shape AI futures in the academy

AI is poised to reshape many sectors of our society and economy including higher education. However, the character of this future is often imagined from within particular academic silos or through what technologies can do rather than proven need. In this post, Andrew Cox describes how alongside his conventional research, he has used fictional narratives to explore future AI scenarios within the academy and to raise questions that cut across traditional conceptions of what AI can do for higher education