Electrophilic substitution reactions

Imperial Users onl

Gauge properties and convexity of the effective potential

Imperial Users onl

The Thermal Degradation of Some Bromine Containing Copolymers

The recent increasing commercial interest in the flammability properties of polymeric materials brought about by relevant legislation has stimulated renewed research into the nature and quantity of volatiles produced during polymer pyrolysis. By influencing the degradation behaviour of a polymer in either a physical or chemical manner, its burning properties can be drastically altered. The non-flammability properties of halogenated species has stimulated interest in their thermal stability both in the form of chemical additives and as an integral part of the polymer molecules. This work is aimed at increasing our understanding of the mechanisms involved in the thermal degradation of a brominated methacrylate monomer in a number of different copolymer and polymer blend environments. A brief description of the various ways in which a fire-retardant may affect a burning polymer is presented in Chapter 1. This introductory chapter also reviews briefly the relationship between chemical structure and the thermal stability of vinyl polymers. A list of the chemicals used and polymerisation conditions are given in Chapter 2 along with details of the apparatus and experimental techniques employed. Two methods for obtaining compositions of copolymers of 2-bromoethyl methacrylate and methyl acrylate are described and evaluated in Chapter 3. Reactivity ratios for the monomer pair were calculated using a Nuclear Magnetic Resonance spectroscopy method. In Chapter 4 the thermal properties of poly(2-bromo-ethyl methacrylate) homopolymer are found to be consistent with a depropagation mechanism giving monomer in yields greater than 90%, Trace amounts of ester decomposition products are formed at higher temperatures. This chapter also includes a detailed review of the thermal degradation mechanism of poly(methyl acrylate). Chapter 5 presents a qualitative and quantitative study of the various degradation fractions from copolymers of 2-bromoethyl methacrylate and methyl acrylate covering the entire composition range. The presence of compounds such as methyl bromide, 1,2 dibromoethane and acetaldehyde provides evidence for interactions occurring between the two degrading monomer units. A qualitative study on the thermal behaviour of 1:1 (by weight) blends of poly(2-bromoethyl methacrylate) and poly(raethyl acrylate) is given in Chapter 6. This study provides evidence for an intermolecular reaction between the two polymers. The results from Chapters 4, 5 and 6 are discussed in Chapter 7 in terms of possible mechanisms of formation of the various products of degradation in the 2-bromoethyl methacrylate - methyl acrylate copolymer system. Qualitative studies on the thermal degradation of an approximately 1:1 copolymer of 2-bromoethyl methacrylate and styrene are presented in Chapter 8. The nature of the volatile products suggest that depropagation reactions predominate to give the respective monomers but that transfer processes involving hydrogen and bromine atoms on the ester group of a 2-bromoethyl methacrylate unit can also occur. Chapter 9 describes the qualitative aspects of the thermal decomposition of an approximately 1:1 copolymer of 2-bromoethyl methacrylate and acrylonitrile. The methacrylate unit participates in the nitrile oligomerisation reaction with concomitant release of fragments from the ester group giving volatiles such as acetaldehyde and 1,2 dibromoethane. At higher temperatures these cyclic structures break down to give a number of volatile gases. The results from all the copolymer systems are summarised in Chapter 10 which also includes suggestions for future work

Assessing the prevalence of injuries in competitive rowing athletes: the effects of body location, sex, and perceived fatigue

The purpose of this study is to; assess the lifetime prevalence of musculoskeletal injures, based on different anatomical regions, including the perceptions of muscular fatigue as a contributing factor to these injuries in recreational rowing athletes; to assess the relative effect of muscle fatigue on musculoskeletal injury in male and female athletes, respectively; to assess the effect of sex on LBP prevalence and severity in recreational rowing athletes. With this purpose in mind a survey was conducted involving rowing athletes across all ages and sexes. In this survey information on rowing experience, injury history, prevalence of low back pain, subjective level of fatigue at the time of injury, activity at the time of most severe injury, and type of pain with most severe injury. The most severe injury incurred for participants most commonly on a rowing ergometer (n=31), followed by training on the water (sweep n=26, scull n=24), most severe injuries were described as a dull pain (n=77). The most common injury site was the back, which had a significantly higher prevalence than the upper body, lower body and other injury sites. Injury prevalence of the upper body was significantly greater than the lower body and other injury sites, and lower body injury prevalence was significantly greater than the other injury sites. Lastly, Participants perceived that they were significantly more fatigued when a back injury occurred than injuries to any other site. Additionally, Injuries to the lower extremity had a higher perception of fatigue than upper extremity and other injury sites. The current work also suggests that there are no systematic differences in the prevalence of low back pain between male and female rowing athletes, nor in the severity of duration of such pain experienced at the low back or in other more general body regions

Studies on the Biosynthesis of Bis-Lactone Antibiotics

In this research it has been shown by incorporation experiments using synthetic, labelled precursors that the antibiotics ethisolide (1) and canadensolide (2) have closely related biosynthetic origins in the appropriately substituted citric acids derived from condensation of a fatty acid derived moiety with a TCA cycle acid (probably oxaloacetate). The most convincing evidence to date for this pathway comes from the efficient and specific incorporation by P. canaderse of alpha-n-hexylitaconic acid into canadensolide (2) and the related metabolites

Lattice SUSY for the DiSSEP at λ² = 1 (and λ² = −3)

We investigate whether the dynamical lattice supersymmetry discussed for various Hamiltonians, including one-dimensional quantum spin chains, by Fendley et.al. and Hagendorf et.al. might also exist for the Markov matrices of any one-dimensional exclusion processes, since these can be related by conjugation to quantum spin chain Hamiltonians. We find that the DiSSEP (Dissipative Symmetric Simple Exclusion Process), introduced by Crampe et.al. provides one such example for suitably chosen parameters. The DiSSEP Markov matrix admits the supersymmetry in these cases because it is conjugate to spin chain Hamiltonians which also possess the supersymmetry. We note that the length-changing supersymmetry relation for the DiSSEP Markov matrix and the supercharge is reminiscent of a "transfer matrix" symmetry that has been observed in other exclusion processes and discuss the similarity.Comment: 11 page

A Critical Review of the US State Department's 2015 Progress Report on Haiti

This review, published jointly by the Center for Economic and Policy Research and the Haiti Advocacy Working Group, looks at the US State Department's annual reports on US assistance to Haiti mandated under the 2014 Assessing Progress in Haiti Act. The review analyzes the various components of the reports and identifies significant omissions and deficiencies, including incomplete data, a failure to link projects and outcomes, and a failure to adequately identify mistakes and lessons learned.In addition, the review shares feedback from Haitian civil society groups and makes recommendations on how the US Agency for International Development and the State Department can improve future progress reports

Bringing computation into the classroom

The use of computation in the physics classroom has the potential to revolutionise the teaching of many topics in the Physics curriculum. By allowing teachers to move beyond problems that can be solved by hand in the limited time available in a lecture, students can be given a much more authentic experience of the topic. With carefully scaffolded tasks, either in a lecture or in a dedicated computational lab, students can explore a much wider range of problems, in a more meaningful way. We will discuss our experience of using computational physics at Sydney, with emphasis on how to think about introducing it into your own teaching. We will discuss the types of problems that can be tackled, which tools to use, and how to deal with students with different background experience. Participants are asked to install the Anaconda python distribution before the workshop https://www.anaconda.com/products/distribution and bring along suggestions for parts of the curriculum you would be interested in exploring. Intended Audience: University physics educator