Transient Optical Picocavities Within Coupled Plasmonic Nanostructures

Plasmonic nanocavities, such as a nanometre scale gap between a gold nanoparticle and gold mirror (NPoM), confine light beyond the free space diffraction limit. While these enhanced field intensities allow resolvable measurements of vibrational scattering from only a few hundred molecules, ensemble averaging destroys all information on individual molecular local environments. In this thesis, I first investigate the single molecule vibrational scattering from a molecule placed into NPoM using a DNA structure. The DNA complicates the response, which is time variant with transient features suggestive of possible picocavity formation. Picocavities are transient atomic scale features on the metal surfaces which further confine fields (effective volume <1 nm3) with strong field gradients that locally alter the rules for vibrational scattering efficiency. These can alter the spectral response of a single nearby molecule (isolating it spectrally) and were previously noted in NPoM at cryogenic temperatures. I change the gap material to a molecular monolayer to simplify the system and explore room temperature picocavities. I use automated analysis of large experimental datasets to detect and isolate transient vibrational scattering. Picocavity generation is found to depend on the local chemical environment near the gold surface. Picocavities are observed to chemically interact with the molecule being optically probed. This perturbs bond strengths across the molecule with the strength and direction of this perturbation being highly sensitive to the relative picocavity location on a < 0.1Å scale. This single molecule – metal atom system is explored by comparing experimental data to a theoretical Density Function Theory model. Next, I extract the spatial distribution of picocavity formation in the gap by comparing transient scattering at two simultaneous wavelengths of light. Picocavities are found to more likely form at regions of higher optical intensity within the NPoM gap. This suggests that light plays a direct role in the yet undetermined picocavity generation mechanism

Re-thinking ‘Flourishing’ as an Organic Concept of the Good: The Interpretation of Development and the Evaluation of Life

This thesis explores the relation between the normative structures brought to bear on the evaluation of life and the way in which the coming-into-being of living organisms is fundamentally understood. It provides a new analysis and critique of the standard concept of ‘flourishing’ in neo-Aristotelian meta-ethics, by uncovering the underlying interpretation of organismic becoming on which it relies, and showing how the turn to a ‘constructivist’ conception of development in contemporary biological theory both disrupts this underlying metaphysics, and provides resources for re-thinking flourishing on a fundamentally different basis. The central claim is that we should turn from a view in which life is given a form to fulfil, and becoming is the process of its fulfilment, to one in which living is the process of creating a way in the world, as life goes along.ESR

Why Do Gamers Buy 'Virtual Assets'? An Insight in to the Psychology Behind Purchase Behaviour

The present study investigated the phenomenon of buying ‘virtual assets’ for game avatars. Virtual Assets are items that are bought with real-world money for an avatar in-game; weapons, items, pets, mounts and skin customisations the most popular examples. Using Interpretative phenomenological analysis (IPA) six gamers that regularly bought in-game assets were interviewed. IPA was chosen because of its emphasis on lived experience, and each participant had subjective experiences of gaming and purchase behaviour. Of particular focus in this study were the superordinate themes of motivations for purchase behaviour, the resulting psychological impact on the gamer, the social benefits of gaming and virtual asset purchasing, emotional attachment, self-expression through the avatar, impulsivity versus thoughtfulness in purchase intention, and the impact of a transaction machinery on the ‘game experience’. Motivations that were found to be of particular importance were item exclusivity, function, social appeal, and collectability. It was found that virtual items enable the gamer to express themselves, feel real satisfaction, and build lasting friendships. Essentially, virtual assets and gaming mostly had a very positive impact on the participant’s psychological wellbeing. Implications for gamers and games production companies are considered

PrAGMATiC: a Probabilistic and Generative Model of Areas Tiling the Cortex

Much of the human cortex seems to be organized into topographic cortical maps. Yet few quantitative methods exist for characterizing these maps. To address this issue we developed a modeling framework that can reveal group-level cortical maps based on neuroimaging data. PrAGMATiC, a probabilistic and generative model of areas tiling the cortex, is a hierarchical Bayesian generative model of cortical maps. This model assumes that the cortical map in each individual subject is a sample from a single underlying probability distribution. Learning the parameters of this distribution reveals the properties of a cortical map that are common across a group of subjects while avoiding the potentially lossy step of co-registering each subject into a group anatomical space. In this report we give a mathematical description of PrAGMATiC, describe approximations that make it practical to use, show preliminary results from its application to a real dataset, and describe a number of possible future extensions

Locating Single-Atom Optical Picocavities Using Wavelength-Multiplexed Raman Scattering.

Funder: Leverhulme TrustFunder: Trinity College, University of CambridgeFunder: Isaac Newton TrustTransient atomic protrusions in plasmonic nanocavities confine optical fields to sub-1-nm3 picocavities, allowing the optical interrogation of single molecules at room temperature. While picocavity formation is linked to both the local chemical environment and optical irradiation, the role of light in localizing the picocavity formation is unclear. Here, we combine information from thousands of picocavity events and simultaneously compare the transient Raman scattering arising from two incident pump wavelengths. Full analysis of the data set suggests that light suppresses the local effective barrier height for adatom formation and that the initial barrier height is decreased by reduced atomic coordination numbers near facet edges. Modeling the system also resolves the frequency-dependent picocavity field enhancements supported by these atomic scale features.European Research Council (ERC) under Horizon 2020 research and innovation programme PICOFORCE (Grant Agreement No. 883703) and POSEIDON (Grant Agreement No. 861950). We acknowledge funding from the EPSRC (Cambridge NanoDTC EP/L015978/1, EP/L027151/1, EP/S022953/1, EP/P029426/1, and EP/R020965/1

Measuring the health systems impact of disease control programmes: a critical reflection on the WHO building blocks framework.

BACKGROUND: The WHO health systems Building Blocks framework has become ubiquitous in health systems research. However, it was not developed as a research instrument, but rather to facilitate investments of resources in health systems. In this paper, we reflect on the advantages and limitations of using the framework in applied research, as experienced in three empirical vaccine studies we have undertaken. DISCUSSION: We argue that while the Building Blocks framework is valuable because of its simplicity and ability to provide a common language for researchers, it is not suitable for analysing dynamic, complex and inter-linked systems impacts. In our three studies, we found that the mechanical segmentation of effects by the WHO building blocks, without recognition of their interactions, hindered the understanding of impacts on systems as a whole. Other important limitations were the artificial equal weight given to each building block and the challenge in capturing longer term effects and opportunity costs. Another criticism is not of the framework per se, but rather how it is typically used, with a focus on the six building blocks to the neglect of the dynamic process and outcome aspects of health systems.We believe the framework would be improved by making three amendments: integrating the missing "demand" component; incorporating an overarching, holistic health systems viewpoint and including scope for interactions between components. If researchers choose to use the Building Blocks framework, we recommend that it be adapted to the specific study question and context, with formative research and piloting conducted in order to inform this adaptation. SUMMARY: As with frameworks in general, the WHO Building Blocks framework is valuable because it creates a common language and shared understanding. However, for applied research, it falls short of what is needed to holistically evaluate the impact of specific interventions on health systems. We propose that if researchers use the framework, it should be adapted and made context-specific

Temporal Dynamics of Stomatal Behavior: Modeling and Implications for Photosynthesis and Water Use.

An analysis of stomatal behavior reveals the importance of modeling slow stomatal responses and the impacts on photosynthesis under dynamic light environments

Holomorphic Currents and Duality in N=1 Supersymmetric Theories

Twisted supersymmetric theories on a product of two Riemann surfaces possess non-local holomorphic currents in a BRST cohomology. The holomorphic currents act as vector fields on the chiral ring. The OPE's of these currents are invariant under the renormalization group flow up to BRST-exact terms. In the context of electric-magnetic duality, the algebra generated by the holomorphic currents in the electric theory is isomorphic to the one on the magnetic side. For the currents corresponding to global symmetries this isomorphism follows from 't Hooft anomaly matching conditions. The isomorphism between OPE's of the currents corresponding to non-linear transformations of fields of matter imposes non-trivial conditions on the duality map of chiral ring. We consider in detail the $SU(N_c)$ SQCD with matter in fundamental and adjoint representations, and find agreement with the duality map proposed by Kutasov, Schwimmer and Seiberg.Comment: 19 pages, JHEP3 LaTex, typos correcte

Tracking interfacial single-molecule pH and binding dynamics via vibrational spectroscopy.

Understanding single-molecule chemical dynamics of surface ligands is of critical importance to reveal their individual pathways and, hence, roles in catalysis, which ensemble measurements cannot see. Here, we use a cascaded nano-optics approach that provides sufficient enhancement to enable direct tracking of chemical trajectories of single surface-bound molecules via vibrational spectroscopy. Atomic protrusions are laser-induced within plasmonic nanojunctions to concentrate light to atomic length scales, optically isolating individual molecules. By stabilizing these atomic sites, we unveil single-molecule deprotonation and binding dynamics under ambient conditions. High-speed field-enhanced spectroscopy allows us to monitor chemical switching of a single carboxylic group between three discrete states. Combining this with theoretical calculation identifies reversible proton transfer dynamics (yielding effective single-molecule pH) and switching between molecule-metal coordination states, where the exact chemical pathway depends on the intitial protonation state. These findings open new domains to explore interfacial single-molecule mechanisms and optical manipulation of their reaction pathways