Droplet Initiated Rupture of High Viscosity Jets to Create Uniform Emulsions

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Creating highly monodisperse emulsions of high viscosity fluids has long been a challenging task. Even with the advent of micro-engineered emulsification systems such as membranes and microchannels obtaining a good degree of uniformity is hampered as these systems are very prone to jetting. We present a method of increasing the range at which uniform droplets can be produced by the use of droplet initiated jet rupture. In this method, a third, low viscosity inner phase, is introduced in the dispersed phase forcing the dispersed phase to form a shell around each drop and effectively reverts the system from jetting to dripping. Formulations are chosen so that the resulting core-shell droplets are unstable and soon rupture to form highly monodisperse emulsions. The rate of internal droplet production is found to be the governing parameter in the system and must be below a critical frequency. This frequency is found to be well predicted by Plateau–Rayleigh instability theory of jet rupture, where the perturbations caused by internal drops are at a wavelength larger than the circumference of the would-be jet. This method is easy to implement in conventional microfluidic designs and equipment and greatly facilitates the ability to produce very uniform emulsions of high viscosity

From Single to Core-Shell Drops in Non-Confined Microfluidics

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.For many encapsulation applications such as nutrients, cells and drugs, large core-shell drops are required. Conventional confined microfluidic devices are limited to a rather small sized (< 1mm) droplets because of difficulties associated with phase separation at low flow rates. We report a microfluidic device which can produce such large range of drop sizes (~200 Am- 6 mm) with varying shell thickness (~1 Am- 1 mm) under the maximum influence of buoyancy, which has so far remained unexplored. The existing physical model for single drop formation is extended for the core-shell drop. The facile nature of working with such systems means scale up would be easy

Modeling adaptive dynamics in microbial populations with applications to the evolution of cellular resource allocation trade-offs

Adaptive evolution is the process by which natural selection, acting on variation within a population, promotes the survival of individuals that are more successful at reproducing and contributing to future generations. Evolutionary processes in microbes occur at the intersection of population genetics, natural selection, and underlying mechanistic constraints, to give rise to the repertoire of adaptation observed in nature. Understanding microbial adaptive evolution is of critical importance for human health for example, through the emergence of pathogenicity and antibiotic resistance. Moreover, the stability and function of natural and artificial ecosystems is contingent on the evolving interactions between microbes, and between microbes and the environment. We present a modelling framework, based on the theory of adaptive dynamics, to investigate how cellular resource allocation trade-offs affect the adaptation process. We used resource-consumer theory, which explicitly models the interactions between cells and their environment, together with matrix models of structured populations, to implement phenotype-determined cellular strategies of resource allocation between mutually exclusive processes. We then analyse the outcome of competitions between different phenotypes across environmental and competitive conditions. We applied our methods to the evolution of strategies (phenotypes) for resource allocation between two competing cellular process in microbial populations growing in chemostat-like environments. We calculated the adaptively stable strategies for several models and showed how state-structured population models can be mapped to simpler chemostat models on invariant manifolds. We then extended our analysis to the case where a limiting nutrient may be utilized using two alternative metabolic pathways. We described how the total population fitness of a metabolic strategy can be constructed from the individual decisions of its constituent members. We developed numerical methods to simulate and analyse general models of adaptive dynamics using principles from graph theory and discrete Markov processes. The methods were used to explore the evolution of nutrient use strategies for microbial populations growing on two and three substitutable nutrients. We highlight the importance of the ancestral phenotype in channelling the adaptation process, which, together with the choice of the mutational kernel, influences the adaptively stable strategies and modes of co-existence. In a related finding, we show how some phenotypes are adaptively stable only in the presence of a competitor lineage that modifies the environment in a manner that permits another phenotype to invade. Our methods also reveal instances where historical contingency and chance have an important effect on determining the stable nutrient use strategies. Finally, we demonstrate the existence of adaptively stable periodic solutions whereby, under some conditions, phenotype successions are cyclical. Our work builds on the foundation of adaptive dynamics theory to provide a general framework for analysing models of microbial adaptation. We focused on understanding the implications of underlying constraints and cellular resource allocation trade-offs in the context of adaptive evolution

Electrophoretic manipulation of multiple-emulsion droplets

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this report the electrophoretic manipulation of structured oil-water-oil (O/W)/O core-shell droplets is presented. Water shells have been created that allow the electrophoretic manipulation of oil droplets in an oil environment. It was found that the inner droplet regardless of size and composition does not affect the electrophoretic mobility of the outer water shell, neither before nor after contact with a biased electrode. This method can be used for the manipulation of oil droplets in a continuous oil phase or for the transportation of microbial cells that would otherwise be killed at low electric field strengths

The ethics of knowledge creation: Anthropological perspectives.

A core historical narrative about anthropological knowledge is that it is created in relations with others, with fieldwork seen as ‘a series of apprenticeships’ whose success is determined by the quality of those relations. An ethnographer connects with the conditions of those studied in ‘circulating exchange’; but on leaving the field a degree of closure is needed to formulate and communicate anthropological knowledge. These obligations and requirements in the creation of knowledge entail attachment and detachment, carrying the seeds of betrayal that can compromise that knowledge. Each epistemological enquiry has its own core ethical imperatives, but as long as knowledge posits a knower, ‘the self of the knower will be at epistemological issue’. In discussing the ethics of knowledge creation I consider the following questions, among others: To what extent is the creation of a particular kind of ethical and epistemic person required for knowledge? How can ethnography produce knowledge about others without betraying them? Can relations of knowledge exchange confer or withhold ‘rights to speak’? Is it possible that unethical relations may destroy or hold up the unfolding of knowledge? And are there circumstances in which it is unethical to disclose knowledge

Studies of states in 19Ne about the 18F + p threshold and the 18Ne(α,p) HCNO breakout reaction

The rate of destruction of 18F via the 18F + p reactions is of importance in both novae and X-ray burster explosive scenarios. The rate of the competing destructive reactions, 18F(p,γ)19Ne and 18F(p,α)15O, depend upon the level structure of the compound nucleus 19Ne. The first experiment in this thesis examines the level structure of 19Ne about the 18F + p threshold via elastic 15O(α,α)15O scattering. The experiment was performed at the CRC Louvain-la-Neuve. A radioactive 15O beam bombarded a thick 4He gaseous target with elastically scattered alpha particles detected using segmented silicon detectors. An R-matrix approach was used to analyse the data and extract the resonance parameters Er and Ѓα. Particular emphasis was placed on extracting information regarding the possible 3/2+ doublet, the parameters of which, to date, have been inferred from the mirror nucleus 19F. The nominal values for the doublet taken from the mirror are Er = 8 and 38 keV, with Ѓα = 0.27 and 1.3 keV respectively. Following this new analysis it has been found that the doublet straddles the threshold at Er = -22 and 3 keV, with Ѓα = 0.15 and 3.3 keV respectively. S-factor calculations and interference effects were also examined. The 18Ne(α,p)21Na reactions is believed to be a key process in X-ray bursters. It is thought to be a possible HCNO-breakout reaction; the mechanism responsible for producing energy to drive the X-ray burster. To date the reaction has been studied both directly and indirectly. The results from each previous experiment show su cient discrepancies to warrant a re-examination of the reaction rate. As such, the second experiment presented in this thesis revolves around a new direct measurement of 18Ne(α,p). The experiment was undertaken at the CRC Louvain-la-Neuve, where, a radioactive 18Ne beam impinged upon a thin gaseous 4He target. The beam energy was chosen to provide data points in common with previous experiments at Er = 1.7 and 2.5 MeV. Reaction protons were detected via a segmented silicon detector telescope system. The total cross section calculated at Er = 2.5 MeV is 1.22 0.151 mb. An upper limit for the cross-section of 0.0208 mb was evaluated at Er = 1.7 Me

Predicting metabolic adaptation from networks of mutational paths

The structure and dynamics of microbial communities reflect trade-offs in the ability to use different resources. Here, Josephides and Swain incorporate metabolic trade-offs into an eco-evolutionary model to predict networks of mutational paths and the evolutionary outcomes for microbial communities

Impacts of the global economic crisis on cyprus tourism and policy responses

This study examines the impacts of the global economic crisis on Cyprus tourism and the pertinent policy responses. A qualitative approach was adopted by conducting eight semi-structured interviews with tourism authorities and suppliers/professionals. Findings indicated the main impacts of the crisis on Cypriot tourism: lack of competitiveness, decreased visitation/revenues, inadequate quality and escalated pricing. Furthermore, findings identify three types of policy measures: (i) immediate response measures; (ii) foreign investment in tourism; and (iii) diversification of the tourism product and quality improvement. The study highlights the need for Cyprus to develop a comprehensive tourism planning framework. It is suggested that crisis plans of small island states should be developed upon a holistic framework that leverages their destination capitals

Language attitudes and use in a transplanted setting: Greek Cypriots in London

In this paper we explore language attitudes and use in the Greek Cypriot community in London, England. Our study is based on an earlier survey carried out in Nicosia, Cyprus and we compare attitudes to language and reported language use in the two communities. We thereby highlight the significance of sociolinguistic variables on similar groups of speakers. We further extend our investigation to include codeswitching practices in the London community. \ud Analysis of language attitudes and use within the Greek-Cypriot population of London, and comparisons with findings in Nicosia, reflect symbolic forces operating in the two contexts. Despite obvious differences between the two communities, (most obviously the official languages and distinct cultural backgrounds of the two nations), the Greek Cypriot Dialect continues to play an active role in both. English is however the ‘default choice‘ for young Cypriots in the UK and Standard Modern Greek occupies a much more limited role than in Cyprus. It is argued that differences in language attitudes and use can be interpreted in light of different market forces operating in the nation (i.e. Cyprus) and the Diaspora (i.e. UK)