3,057 research outputs found
Children’s experiences of migration to the United Kingdom and adaptation in British primary schools: An Interpretative Phenomenological Analysis study
The United Kingdom (UK) is a culturally diverse society, which has witnessed an increase in migration over the years. Despite this, not enough is known about migrant children’s experiences from their perspective, particularly those in primary schools. This research explored first-generation migrant children’s experiences of migration to the UK and adaptation in primary schools. This study aimed to gain insight how children make sense of the migration process, and the role school plays in their adaptation. By providing an opportunity for children to tell their stories, the study also aimed to provide a platform for their voices to be heard. Seven migrant children, aged between 6 to 11, were recruited through purposive sampling from primary schools in an inner-London borough. Semi- structured interviews were used to collect data and interpreters were used where necessary. Drawings were incorporated in the interview process as a stimulus for discussion. The data collected was transcribed and analysed using Interpretative Phenomenological Analysis, to provide an in-depth exploration of individual children’s experiences, while also allowing for similarities and differences across their experiences to be explored. Five Group Experiential Themes were identified from participants’ experiences: ‘Migration: The Move, The Journey and Sense- Making’, ‘Life in the UK’, ‘Relationships: Loss, Changes and a Key to Adaptation’, ‘Adjusting to a New Linguistic Context’, ‘School Adaptation: Interconnection of Language, Social Factors and Learning’. Findings are presented then considered within the context of relevant literature and theoretical frameworks. Implications for migrant children and their families, schools and Educational Psychologists are discussed, alongside the study’s limitations and areas for future research
Enhancing the Structural Stability of α-phase Hybrid Perovskite Films through Defect Engineering Approaches under Ambient Conditions
This thesis investigates methods whereby perovskite solar cell power conversion efficiency and material stability
may be improved. Hybrid perovskites have gained increased attention for optoelectronic applications due to
favourable properties such as strong absorption, facile processing, and changeable band-gap. Despite excellent
improvements in power conversion efficiency of devices, perovskite films are unstable, degrading with relative
ease in the presence of moisture, oxygen, light, heat, and electric fields. The focus of this thesis is on ambient
atmosphere stability, concerned with the influence of moisture in particular on perovskite film fabrication,
degradation, and device functionality. In order to shed light on the impact of ambient atmosphere on perovskite
films, experiments are designed to investigate films during fabrication and degradation. The influences firstly of
stoichiometry during ambient fabrication, and then ionic substitution (with caesium and formadinium) upon
moisture-induced degradation are investigated. Finally, films and devices with a novel composition
incorporating Zn are fabricated under ambient conditions to investigate the effect of Zn addition on perovskite
film stability
Systemic Circular Economy Solutions for Fiber Reinforced Composites
This open access book provides an overview of the work undertaken within the FiberEUse project, which developed solutions enhancing the profitability of composite recycling and reuse in value-added products, with a cross-sectorial approach. Glass and carbon fiber reinforced polymers, or composites, are increasingly used as structural materials in many manufacturing sectors like transport, constructions and energy due to their better lightweight and corrosion resistance compared to metals. However, composite recycling is still a challenge since no significant added value in the recycling and reprocessing of composites is demonstrated. FiberEUse developed innovative solutions and business models towards sustainable Circular Economy solutions for post-use composite-made products. Three strategies are presented, namely mechanical recycling of short fibers, thermal recycling of long fibers and modular car parts design for sustainable disassembly and remanufacturing. The validation of the FiberEUse approach within eight industrial demonstrators shows the potentials towards new Circular Economy value-chains for composite materials
Exoteric effects at nanoscopic interfaces - Uncommon negative compressibility of nanoporous materials and unexpected cavitation at liquid/liquid interfaces
This PhD thesis is devoted to the investigation of some peculiar effects happening at nanoscopic interfaces between immiscible liquids or liquids and solids via molecular dynamics simulations. The study of the properties of interfaces at a nanoscopic scale is driven by the promise of many interesting technological applications, including: a novel technology for developing both eco-friendly energy storage devices in the form of mechanical batteries, as well as energy dissipation systems and, in particular, shock absorbers for the automotive market; biomedical applications related to cavitation, such as High-Intensity Focused Ultrasound (HIFU) ablation of cancer tissues and localised drug delivery, and many more. The kinetics of phenomena taking places at these scales is typically determined by large free-energy barriers separating the initial and final states, and even intermediate metastable states, when they are present. Because of such barriers, the phenomena we are interested in are "rare events", i.e. the system attempts the crossing of the barrier(s) many times before finally succeeding when an energy fluctuation makes it possible. At the same time, the magnitude of the barrier is determined by the energetics and dynamics of atoms, which forces us to model the system by taking into account both the femtosecond atomistic timescale and the timescale of the relevant phenomena, typically exceeding the former by several orders of magnitude. These longer timescales are inaccessible to standard molecular dynamics, so, in order to tackle this issue, advanced MD techniques need to be employed.
The thesis is divided into two parts, corresponding to the main lines of research investigated, which are (I) the interfaces between water and complex nanoporous solids, and (II) planar solid-liquid and liquid-liquid interfaces. Anticipating some results, atomistic simulations helped uncovering the microscopic mechanism behind the (incredibly rare!) giant negative compressibility exhibited by the ZIF-8 metal organic framework (MOF) upon water intrusion. Molecular dynamics simulations also supported experimental results showing how it is possible to change the intermediate intrusion-extrusion performance of ZIF-8 by changing its grain morphology and arrangement, from a fine powder to compact monolith. Free-energy MD calculations allowed to explain the exceptional stability of surface nanobubbles in water, at undersaturated conditions, on a surprisingly wide variety of substrates, characterized by disparate hydrophobicities and gas affinities; and yet, how they catastrophically destabilize in organic solvents. Finally, through simulations, some light was shed upon the working mechanism behind the novelly discovered phenomenon of how the interface between two immiscible liquids can act as a nucleation site for cavitation
Developing a novel and versatile approach to study populations of microbes on surfaces
Spatial structure, for example regarding antibiotic gradients, is an important topic
of investigation in microbial ecology and evolution. Experiments investigating pop-
ulation dynamics in spatially-structured environments are often performed on agar
plates. Whilst inexpensive and straightforward, these provide only rudimentary
temporal and spatial control of environmental conditions.
In chemostats and microfluidic devices, for well-mixed and micrometre-scale
environments, respectively, regulating media inflow and outflow enables environ-
mental control. We combine proven use of agar surfaces with such flow-enabled
control in a novel, low-cost fluidic device; the device comprises an elastomer
supporting base with a thin agar sheet on top on which microbes grow. Indented
channels in the base allow flow of media/antibiotics below the agar surface. A
Raspberry-Pi-operated camera allows for time-lapse imaging suitable for quantita-
tive image analysis.
As a proof of principle, we used our device for extended and robust growth
of non-motile E. coli and motile P. aeruginosa maintaining the initial speed with
which colonies propagate over three days, whilst a continual speed decrease
occurred on agar plates. Guided by simulations of flow and diffusion, we then
used the device to create stable antibiotic gradients within the agar. Along these
gradients, we found P. aeruginosa exhibit unique microbial growth patterns with
local adaptations.
Because flow below the agar surface can be controlled spatially and temporally,
the device promises a range of applications for studying microbial ecology and
evolution in spatially continuous environments at a substrate-air interface.Engineering and Physical Sciences Research Council (EPSRC
Performance and degradation studies of IrOx for polymer electrolyte membrane water electrolyser applications
In order to enable the scale-up of the proton exchange membrane (PEM) electrolyser technology to the terawatt level, improvements in anode catalyst utilisation are necessary. State of the art PEM electrolysers typically use IrOx to catalyse the oxygen evolution at the anode; however, further improvements in iridium utilisation need to be made without compromising performance or device lifetime. The research community has only recently started to attempt systematic benchmarking of catalyst stability. Short term electrochemical methods alone are insufficient to predict catalyst degradation; they can both underestimate and overestimate catalyst durability.
In this work, detailed methods to track trends in catalyst stability using conventional techniques such as rotating disk electrode studies are conducted and supported by complementary techniques. These complementary techniques include inductively coupled plasma – mass spectrometry to track performance and stability during accelerated stress testing. These methods were then assessed by testing a series of IrOx nanoparticles both commercially obtained and synthesized via a variant of the Adams Fusion method. Catalysts synthesized via Adams Fusion method demonstrated significant increases in stability with approximately an order of magnitude difference in dissolved Ir observed between those synthesized at 400 oC and 500 oC. This correlates with change between amorphous (400 oC) and crystalline (500 oC, 600 oC) structure with less significant improvements in stability being seen between 500 oC and 600 oC. Increasing annealing temperature also correlated with reduced surface area and reduced activity. The comparison of different lower potential limits during stability testing also demonstrated increased dissolution upon decreasing lower potential limit. Therefore, the observations indicate that electrochemical reduction plays a large role in the heightened dissolution observed from potential cycling.
Several operando techniques are also demonstrated for investigation of the fundamental understanding of activity and stability of IrOx nanoparticle catalysts using electrochemistry mass spectrometry and optical absorption spectroscopy to probe gas phase products and reaction intermediates. The results of these studies show an optically observable species on the nanoparticle catalysts that begins to occur approximately 100 mV less positive than oxygen onset, defined as the initial potential at which evolved oxygen can be directly observed either electrochemically or via the use of in-situ techniques, and tracks into the oxygen evolving region. Additionally, the differences observed between oxygen onset observed from mass spectrometry between amorphous and crystalline catalysts track with results observed from optical signals.Open Acces
Dielectrophoretic nanotweezers for single-particle force spectroscopy
Studying the structural and functional properties of biological molecules using single-molecule techniques has been fundamental in establishing a comprehensive understanding of the mechanisms that govern complex living systems. The aim of this thesis was to develop a dielectrophoretic nanotweezers setup to provide a new approach for applying and measuring dielectrophoretic forces on individual particles in aqueous solution. To achieve this goal, dual-barrel quartz nanopipettes were filled with pyrolytic carbon, forming a pair of nanoelectrodes at their tip. Their size and shape were characterised both through SEM imaging and electrochemical cyclic voltammetry. By applying low AC voltages (< 1 V) between these nanoelectrodes, very strong and highly inhomogeneous electric fields were generated at the nanopipette’s tip to form dielectrophoretic nanotweezers. The frequency of the electric field was tuned so that individual entities were either attracted or repelled depending on their dielectric properties. In this work, experimental measurements of the dielectrophoretic force acting on single polystyrene beads (2 μm) were acquired by single particle tracking on an inverted fluorescence microscope. The spatial coordinates of individual beads were extracted from their trajectories as a function of time under trapping conditions. The force magnitude, measured from their velocity over distance from the nanotweezers tip, was found in the femtonewtons range for a set of applied voltages and frequencies. In addition, the electric field distribution was simulated close to the nanotweezers tip by a finite element model developed for this system. Estimations of the dielectrophoretic force magnitude for different nanotweezers geometries were also performed. Overall, the simple operational mechanism and design of these dielectrophoretic nanotweezers combined with their ability to be controlled in three-dimensions, make them a versatile and promising platform for single-particle manipulation and force probing
A strategic turnaround model for distressed properties
The importance of commercial real estate is clearly shown by the role it plays, worldwide, in the sustainability of economic activities, with a substantial global impact when measured in monetary terms. This study responds to an important gap in the built environment and turnaround literature relating to the likelihood of a successful distressed commercial property financial recovery. The present research effort addressed the absence of empirical evidence by identifying a number of important factors that influence the likelihood of a successful distressed, commercial property financial recovery. Once the important factors that increase the likelihood of recovery have been determined, the results can be used as a basis for turnaround strategies concerning property investors who invest in distressed opportunities. A theoretical turnaround model concerning properties in distress, would be of interest to ‘opportunistic investing’ yield-hungry investors targeting real estate transactions involving ‘turnaround’ potential. Against this background, the main research problem investigated in the present research effort was as follows: Determine the important factors that would increase the likelihood of a successful distressed commercial property financial recovery. A proposed theoretical model was constructed and empirically tested through a questionnaire distributed physically and electronically to a sample of real estate practitioners from across the globe, and who had all been involved, directly or indirectly, with reviving distressed properties. An explanation was provided to respondents of how the questionnaire was developed and how it would be administered. The demographic information pertaining to the 391 respondents was analysed and summarised. The statistical analysis performed to ensure the validity and reliability of the results, was explained to respondents, together with a detailed description of the covariance structural equation modelling method used to verify the proposed theoretical conceptual model. vi The independent variables of the present research effort comprised; Obsolescence Identification, Capital Improvements Feasibility, Tenant Mix, Triple Net Leases, Concessions, Property Management, Contracts, Business Analysis, Debt Renegotiation, Cost-Cutting, Market Analysis, Strategic Planning and Demography, while the dependent variable was The Perceived Likelihood of a Distressed Commercial Property Financial Recovery. After analysis of the findings, a revised model was then proposed and assessed. Both validity and reliability were assessed and resulted in the following factors that potentially influence the dependent variables; Strategy, Concessions, Tenant Mix, Debt Restructuring, Demography, Analyse Alternatives, Capital Improvements Feasibility, Property Management and Net Leases while, after analysis, the dependent variable was replaced by two dependent variables; The Likelihood of a Distressed Property Turnaround and The Likelihood of a Distressed Property Financial Recovery. The results showed that Strategy (comprising of items from Strategic Planning, Business Analysis, Obsolescence Identification and Property Management) and Concessions (comprising of items from Concessions and Triple Net Leases) had a positive influence on both the dependent variables. Property Management (comprising of items from Business Analysis, Property Management, Capital Improvements Feasibility and Tenant Mix) had a positive influence on Financial Turnaround variable while Capital Improvements Feasibility (comprising of items from Capital Improvements Feasibility, Obsolescence Identification and Property Management) had a negative influence on both. Demography (comprising of items only from Demography) had a negative influence on the Financial Recovery variable. The balance of the relationships were depicted as non-significant. The present research effort presents important actions that can be used to influence the turnaround and recovery of distressed real estate. The literature had indicated reasons to recover distressed properties as having wide-ranging economic consequences for the broader communities and the countries in which they reside. The turnaround of distressed properties will not only present financial rewards for opportunistic investors but will have positive effects on the greater community and economy and, thus, social and economic stability. Vii With the emergence of the COVID-19 pandemic crisis, issues with climate change and sustainability, global demographic shifts, changing user requirements, shifts in technology, the threat of obsolescence, urbanisation, globalisation, geo-political tensions, shifting global order, new trends and different generational expectations, it is becoming more apparent that the threat of distressed, abandoned and derelict properties is here to stay, and which will present future opportunities for turnaround, distressed property owners, as well as future worries for urban authorities and municipalities dealing with urban decay. The study concluded with an examination of the perceived limitations of the study as well as presenting a comprehensive range of suggestions for further research.Thesis (PhD) -- Faculty of Engineering, Built Environment and Information Technology, School of the built Environment, 202
Towards bottom-up reconstitution of a functional FtsZ-based cell division machinery
Synthetic biology aims at the understanding of living organisms through an engineering perspective, with the goal of improving or creating new biological systems. The prospect of building a synthetic cell focuses on producing life from basic elements by combining synthetic and/or organic cellular components in a bottom-up manner. To create a synthetic cell, the minimal functions of life are required and cell-free synthetic biology offers a suitable framework for understanding biological processes outside the inherently noisy environment of cells. A synthetic cell is expected to exhibit characteristics of a living cell, such as fundamental metabolism, proliferation, and communication. The bottom-up approach utilizes a wide range of in vitro tools/technologies such as biomimetic membranes, protein reconstitution, cell-free expression reactions, and microfluidics. As tools, they enable the thorough characterization of functional modules such as metabolism, replication, and cell division. The ultimate goal is to integrate these modules to construct a predictable, customizable, and controllable entity.
Among the functional modules of living organisms, cell division stands out as a hallmark feature. The machinery of division has evolved into a highly organized set of proteins with the aim of accurately splitting a mother cell into two daughter cells, while preserving the genetic information and cellular integrity. In the case of bacteria, and more concretely Escherichia coli, cell division is mediated by the divisome, a contractile ring consisting of a multiprotein complex that precisely assembles at midcell. At the center of this machinery is the essential FtsZ protein, which is able to polymerize and form the FtsZ-ring. This ring is key to the process, serving as a scaffold for the divisome and driving the division process. However, the molecular details of how the ring is functionally assembled, stabilized, and positioned are still not well understood. Therefore, the aim of this thesis is to develop and expand the knowledge about the molecular mechanism of the FtsZ-ring assembly and its function as a potential primary component in the minimal division machinery of synthetic cells.
To this end, and following a bottom-up approach, we conducted assays based on the in vitro reconstitution of FtsZ in cellular mimic environments using lipid vesicles. This allows the characterization of FtsZ’s behavior and functionalities in environments that are similar to a potential synthetic cell. Firstly, we designed a microfluidic device to deform lipid vesicles into bacterial rod-shaped compartments to analyze the effect of different geometries and membrane tension on FtsZ. We found that FtsZ filaments align with the shorter axis of the rod-shaped vesicles and reorganize into cone-like structures when the membrane tension is lowered, causing membrane deformations. This suggests that there is a geometry and tension-dependent mechanism in the assembly of FtsZ structures on membranes. Secondly, we designed an in vitro reconstitution assay based on soft lipid tubes pulled from FtsZ-decorated vesicles using optical tweezers. We observed the transformation of lipid tubes into 3D spring-like structures, where the GTPase activity of FtsZ drives spring compression likely through torsional stress. This allowed us to gain mechanistic insights into the molecular dynamics behind the force generated by FtsZ filaments. Thirdly, we studied the spatiotemporal localization of the division ring by co-reconstituting FtsZ inside lipid vesicles with the MinCDE system, which is involved in positioning the divisome in vivo, and FtsA, the natural tether of FtsZ to the membrane. We achieved the assembly, placement, and onset of constriction of a minimal division ring inside lipid vesicles using two different approaches: purified components or cell-free expression of the MinCDE, FtsA, and FtsZ proteins. This represents a significant advance towards the in vitro reconstitution of functional modules in a synthetic cell and expands our understanding of the molecular mechanism underlying the spatiotemporal organization of the FtsZ-ring. Lastly, we employed biochemical studies combined with cryo-ET visualization to characterize the stabilization of the division ring and the crosslinking of FtsZ filaments by ZapD, a protein known as one of the stabilizers of the divisome. We observed the formation of toroidal structures in solution that are assembled by short FtsZ filaments connected by ZapD and have bacterial size. Their characterization in 3D brings valuable structural information about the FtsZ-ring and its functional stabilization, which is important for its further reconstitution in minimal systems.
In conclusion, this thesis provides important insights into the molecular dynamics of the central protein of division in E. coli and most bacteria, addressing its activity on the membrane, mechanism of force constriction, spatiotemporal localization and stabilization of the FtsZ-ring. Furthermore, we demonstrate significant advancements towards the implementation of FtsZ-based division systems in minimal synthetic cells using a bottom-up approach
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