On Tracial Operator Representations of Quantum Decoherence Functionals

A general `quantum history theory' can be characterised by the space of histories and by the space of decoherence functionals. In this note we consider the situation where the space of histories is given by the lattice of projection operators on an infinite dimensional Hilbert space $H$. We study operator representations for decoherence functionals on this space of histories. We first give necessary and sufficient conditions for a decoherence functional being representable by a trace class operator on $H \otimes H$, an infinite dimensional analogue of the Isham-Linden-Schreckenberg representation for finite dimensions. Since this excludes many decoherence functionals of physical interest, we then identify the large and physically important class of decoherence functionals which can be represented, canonically, by bounded operators on $H \otimes H$.Comment: 14 pages, LaTeX2

A biosynthetic approach to the discovery of novel bioactive peptides

Peptides represent a source of novel therapeutics for recalcitrant human diseases, but screening for bioactivity from natural or synthetic sources can be uneconomic. In contrast, in vivo expression of peptides from DNA libraries in a heterologous host such as Escherichia coli may combine production with screening. This dissertation aimed to use such an approach to discover novel bioactive peptides in a high throughput and cost-effective manner, with a focus on antimicrobials and antiaggregants as proof-of-principle. Antimicrobial peptides (AMPs) are innate defence effectors that may combat antibiotic-resistant pathogens. An inducible, autocleaving fusion tag was utilised to produce the model murine cathelicidin K2C18, along with a number of variants, which exhibited varying degrees of antimicrobial activity against a panel of microbes. Importantly, K2C18 also exhibited a bacteriostatic effect in vivo when secreted to the periplasm. This allowed for the implementation of an in vivo whole cell screen for novel AMPs, using genomic DNA libraries as an input. One putative hit, the peptide S-H4, showed similar in vivo behaviour to K2C18 and was active when added exogenously to microbial cultures. A second in vivo screen was constructed to search for inhibitors of Aβ42 aggregation, a process implicated in Alzheimer’s disease. The aggregation state of Aβ42 was coupled to the fluorescence of a chromophore fusion partner, and used to screen co-expressed peptides from a random DNA library for putative antiaggregants. Additionally, the system incorporated an internal fluorescent reference to allow ratiometric comparison between samples. Several hits were identified and further validated using flow cytometry, with work ongoing to assess their activity in vitro. Proof-of-principle of these two screens was achieved, indicating that such in vivo approaches to bioactive peptide discovery could lead to the development of new and useful therapeutics.This work was supported by the Cambridge Commonwealth Trust, an Overseas Research Studentship, the C. T. Taylor Studentship, the Searle Scholarship, Emmanuel College, the Cambridge Philosophical Society and the European Research Council

Studies of the composition of milk

Cover title.Bibliography: p. 60

Green Chemistry for Stainless Steel Corrosion Resistance: Life Cycle Assessment (LCA) of Citric Acid versus Nitric Acid Passivation

Corrosion is a significant problem in many industries, and when using stainless steel, passivation is undertaken to improve corrosion resistance. Traditionally, nitric acid is used within the passivation step, however, this has some detrimental environmental and human health impacts during its production and use. Reducing this impact is critical, and because of its toxicity, associated occupational risk and special disposal requirements, end-users of passivated stainless steels are exploring alternative passivation methods. However, it is also critical to understand the impact of any alternatives. Sustainable processing and manufacture embodies many elements, including; waste reduction, resource efficiency measures, energy reduction and the application of ‘green’ or renewable chemicals. In order to ensure the most effective system is utilised the impact, or potential impact of the system must be measured and options compared. The comparative environmental credentials of bio-based chemicals can be assessed using tools such as Life Cycle Assessment (LCA).This paper is the first paper to evaluate the environmental impact of passivation using nitric and citric acid. It uses attributional Life Cycle Assessment (ALCA) to assess the environmental benefits and dis-benefits of using citric acid - produced biologically via fermentation, to replace nitric acid, whilst keeping the same level of corrosion resistance. The work is anticipatory in nature as the process is not yet undertaken on a commercial basis. The results therefore feed into future manufacturing and design. Citric and nitric acids were compared using three different solutions: 4% and 10% citric acid solutions, and a 10% nitric acid solution (the conventional case). The results show that a scenario using a 4% citric acid solution is environmentally preferable to nitric acid across all impact categories assessed. However, a 10% citric acid solution used on low chromium and nickel steel was only environmentally preferable for 50% of the environmental impact categories assessed due to increased electrical energy demand for that scenario.<br/

Green Chemistry for Stainless Steel Corrosion Resistance: Life Cycle Assessment (LCA) of Citric Acid versus Nitric Acid Passivation

Corrosion is a significant problem in many industries, and when using stainless steel, passivation is undertaken to improve corrosion resistance. Traditionally, nitric acid is used within the passivation step, however, this has some detrimental environmental and human health impacts during its production and use. Reducing this impact is critical, and because of its toxicity, associated occupational risk and special disposal requirements, end-users of passivated stainless steels are exploring alternative passivation methods. However, it is also critical to understand the impact of any alternatives. Sustainable processing and manufacture embodies many elements, including; waste reduction, resource efficiency measures, energy reduction and the application of ‘green’ or renewable chemicals. In order to ensure the most effective system is utilised the impact, or potential impact of the system must be measured and options compared. The comparative environmental credentials of bio-based chemicals can be assessed using tools such as Life Cycle Assessment (LCA).This paper is the first paper to evaluate the environmental impact of passivation using nitric and citric acid. It uses attributional Life Cycle Assessment (ALCA) to assess the environmental benefits and dis-benefits of using citric acid - produced biologically via fermentation, to replace nitric acid, whilst keeping the same level of corrosion resistance. The work is anticipatory in nature as the process is not yet undertaken on a commercial basis. The results therefore feed into future manufacturing and design. Citric and nitric acids were compared using three different solutions: 4% and 10% citric acid solutions, and a 10% nitric acid solution (the conventional case). The results show that a scenario using a 4% citric acid solution is environmentally preferable to nitric acid across all impact categories assessed. However, a 10% citric acid solution used on low chromium and nickel steel was only environmentally preferable for 50% of the environmental impact categories assessed due to increased electrical energy demand for that scenario.<br/