11,146 research outputs found
All-Atom Simulations of Surfactant Systems: Interfacial Tension, Surface Tension, Adsorption Isotherms and Self-Assembly
The primary objective of this thesis is to establish and validate force field-based all-atom (AA) molecular dynamics (MD) simulations capable of accurately replicating and elucidating the physical properties of surfactants in both bulk water and interfacial regions.
AA MD simulations are employed to simulate interfacial tensions (IFT) and surface tensions (ST) of both ionic and non-ionic surfactants. The General AMBER Force Field (GAFF) and variants are examined in terms of their performance in predicting accurate IFT/ST, Îł, values for chosen water models, together with the hydration free energy, âGhyd, and density, Ï, predictions for organic bulk phases. A strong correlation is observed between the quality of Ï and Îł predictions. Based on the results, the GAFF-LIPID force field, which provides improved Ï predictions, is selected for simulating surfactant tail groups. Good Îł predictions are obtained with GAFF/GAFF-LIPID parameters together with the TIP3P water model for IFT simulations at a water-triolein interface, and for GAFF/GAFF-LIPID parameters together with the OPC4 water model for ST simulations at a water-vacuum interface.
A combined molecular dynamics-molecular thermodynamics theory (MD-MTT) framework for non-ionic surfactants is tested using calculated ST values, together with adsorption free energies (âGads) obtained from calculations of the potential of mean force potential (PMF) and experimental critical micelle concentrations (CMC). The methodology provides excellent predictions for the simulated ST at the CMC, and as a function of bulk surfactant concentration for the non-ionic surfactant C12E6. This gives a ÎMAX of 76 C12E6 molecules at a 36 nm2 water-vacuum surface (3.5 Ă 10-10 mol cm-2), which corresponds to a simulated ST of 35 mN m-1. The results compare favourably with an experimental ÎMAX of C12E6 of 3.7 Ă 10-10 mol cm-2 (80 surfactants for a 36 nm2 surface) and experimental ST of C12E6 of 32 mN m-1 at the CMC.
GAFF and GAFF-derived parameters (combined with the TIP3P water model) are employed to simulate surfactant micelles using AA MD. Results show that C12E5 surfactants micelle simulated using GAFF-LIPID showed a similar structure to ones simulated using OPLS-AA. Simulations of SD6BS micelles, together with polyvinyl acetate (PVA) chains and 5-chloro-2-(4-chlorophenoxy)-phenol (Diclosan) molecules reveal that center-of-mass (COM) diffusion coefficients of PVA chains decrease with an increasing number of chains, reflecting the incorporation of PVA chains into micelles. The COM diffusion coefficients of Diclosan molecules show large fluctuations with an increasing number of Diclosan molecules. However, the trend also appears to indicate that diffusion decreases with increasing numbers of Diclosan molecules as surfactant micelles start to swell.
Amended GAFF parameters are employed to explore the adsorption of surfactants and polymer actives on model polyethylene terephthalate (PET) and cellulose surfaces. Results from simulations of SDS suggest that a hemispherical aggregate and a partially deformed micelle aggregate were obtained on a PET surface and a cellulose surface respectively. âGads values (from bulk water to PET surface) for polymer actives were obtained from MM-GBSA and PMF calculation methods. These calculations considered both globular and stretched-out structures representing the hydrophobic blocks of a series of newly synthesised soil-release polymers. All oligomers studied were found to fold in water to produce a globular structure, which was attracted to the PET surface. PER (a 3,5-substituted pyridine analogue of a PET-based oligomer) was found to form the most strongly surface-attached globular oligomer structure, with a value of âGads of -220.98 ± 3.77 kJ mol-1, but PEY (a PET-based oligomer) was the most strongly-attached stretched-out oligomer, with a value of âGads of -406.68 ± 1.18 kJ mol-1
Russian Sophiology and the Philosophers of Will: The Theanthropic Theology of Solovyov and Bulgakov and their Critical Appropriation of German Voluntarism.
This thesis explores potential theological contributions of Russian Sophiology. Its argument is twofold. First, it is argued that the Russian theologiansâ development of the idea of God as eternal, divine-humanity in relation to Sophia enabled them to address both longstanding and contemporary theological problematics in bold and original ways. Second, it is argued that among the vastly diverse sources upon which Russian Sophiology drew, its critical reappropriation of elements of the German voluntarist tradition stands behind some of Sophiologyâs most creative and controversial theological proposals. In order to demonstrate this twofold claim, this work is organized around the major systematic themes that form the Christian narrative of reality: Trinity-Christology, creation, fall, and eschatology. To limit our focus, the thought of Vladimir Solovyov and Sergius Bulgakov will be considered in relation to each of these themes, and the particular issues that attend them. It is argued that the theanthropic theology of divine-humanity is at work not only in their Christocentric redefinition of the Trinity, but also plays a critical role in the other theological loci surveyed. Furthermore, it will be argued that in each of these areas there is a critical appropriation of the voluntarist tradition, not only the sophiological theosophy of Jacob Boehme, but also the 19th century philosophers of Will: Friedrich Schelling, Arthur Schopenhauer, and Eduard von Hartmann. It is argued that the Russian theologians utilize this voluntarist legacy, particularly the metaphysical principle of an unconscious, impersonal, corporeal Will, not only in their development of the idea of Godâs eternal divine-humanity, but also to explore the ultimate origins of matter and becoming, the nature of the fall and its connection to the evolutionary process, and the eschatological spiritualization of matter
Techniques for high-multiplicity scattering amplitudes and applications to precision collider physics
In this thesis, we present state-of-the-art techniques for the computation of scattering amplitudes in Quantum Field Theories. Following an introduction to the topic, we describe a robust framework that enables the calculation of multi-scale two-loop amplitudes directly relevant to modern particle physics phenomenology at the Large Hadron Collider and beyond. We discuss in detail the use of finite fields to bypass the algebraic complexity of such computations, as well as the method of integration-by-parts relations and differential equations. We apply our framework to calculate the two-loop amplitudes contributing to three process: Higgs boson production in association with a bottom-quark pair, W boson production with a photon and a jet, as well as lepton-pair scattering with an off-shell and an on-shell photon. Finally, we draw our conclusions and discuss directions for future progress of amplitude computations
The Effect of Subgrid Physics Models on the Pattern Speed of Bars in Cosmological Simulations
The amount of dark matter in the central region of galaxies is intimately linked to the slowdown of galactic bars. Recent work has revealed a tension between bars that are observed in the local universe and those produced in cosmological hydrodynamical simulations at z = 0. Observed bars are found to be `fast', i.e. to have a small ratio between the corotation radius and bar length, while those in the simulations are `slow', i.e. the corotation radius much larger than the bar length. Recent work has been carried out in an attempt to find the root cause of this discrepancy, and indeed to explore whether fast bars can exist within a CDM universe. The ratio of stars to dark matter, along with other properties such as gas fraction and velocity dispersion, has been linked to the evolution of bars. The resolution of simulations is often cited as the underlying cause of differences between simulations. In this work, I explore the slowdown of bars in two sets of cosmological zoom-in simulations which are identical, apart from their galaxy formation model (i.e. the subgrid physics). I then study how the slowdown of bars in these two models is related to parameters such as the stellar-to-dark matter ratio, the gas fraction and velocity dispersion, all of which are determined by the subgrid physics itself. Using halos from the Auriga suite of zoom-in cosmological simulations, I rerun them with the subgrid physics model from IllustrisTNG. I find that the bars in Auriga are faster than those run with the TNG model, i.e. Auriga have a smaller ratio of the corotation radius to bar length. The bars in TNG are shorter and stronger than in the Auriga model. In terms of global halo properties, Auriga galaxies have a greater stellar mass in their disc, are more baryon dominated at 30kpc, have a greater gas fraction in the disc. They also have a lower stellar velocity dispersion within a disc of radius 6kpc and height 1kpc from the centre. All of these differences lead to the conclusion that the subgrid physics model has a profound effect on the overall properties of a galaxy, include the speed of the bar. We therefore show that the changes in subgrid physics can have a significant effect on the dynamical properties of barred spiral galaxies and, as such, the dynamical properties of bars can be used to constrain models of galaxy formation and evolution
Self-threat and Compensatory Consumption: The Role of Consumersâ Implicit Theory
Research shows that consumers often engage in compensatory consumption to cope with self-threats. This thesis aims to explore the role of consumersâ implicit theory in compensatory consumption. The research objectives are threefold: (1) to identify the impact of consumersâ implicit theory on their tendency to engage in compensatory consumption and its underlying mechanism; (2) to investigate how consumersâ product preferences in compensatory consumption are influenced by the implicit theory they hold; and (3) to examine the consumersâ self-repair resulting from their compensatory consumption as an individual difference influenced by their implicit theory. A product pre-test (n = 90) was conducted on MTurk, and seven main studies (n = 2,173), including two surveys and five experiments, were conducted on Prolific to examine the relationship between implicit theory and compensatory consumption. The findings of this thesis contribute to two literature streams â the compensatory consumption literature and implicit theory literature â by elucidating how self-threats interact with consumersâ implicit theory to affect compensatory consumption. This includes exploring the underlying mechanism, boundary conditions, and downstream consequence of this interaction. The results not only offer theoretical insights, but also have practical implications for marketers and policymakers concerned about consumer well-being. While considering the research limitations, the thesis also discusses potential avenues for future research
Governing ageing in Chile: from neoliberal hegemony to more hopeful demographic futures?
In this thesis, I explore how demographic ageing is regulated in Chile through the governing of older populations, with particularly close attention to how the âactually existingâ neoliberal context in Chile permeates and conditions diverse political projects and strategies implemented by central and local governments. I approach this shaping as a historical and conjunctural process realised through multiple central and local governing projects, as well as a legacy thrown into particularly sharp relief and retrospective political questioning by the unfolding of the COVID-19 pandemic and the anti-neoliberal social uprising of 2019. These intertwined conjunctural moments have unearthed the limitations of neoliberal strategies in addressing the needs of older people. To explore the governing of older populations in Chile, I undertook a hybrid on-site and online ethnography exploring a wide range of national and local policies and governing projects. In investigating local governing projects, I analysed âwith different depthsâ the case of seven contrasting municipalities in the capital city of Santiago, Chile.
With demographic ageing positioned as a risk to economic development, I suggest that the main rationale guiding Chilean policies and programs has been to avert the central stateâs welfare and caregiving responsibilities toward a growing number of potentially dependent populations; economically, physically and cognitively. I argue that governing strategies directed to older populations are deeply neoliberal âsometimes deliberately and sometimes inadvertentlyâ in that they pervasively have been designed to shift and devolve welfare and caregiving responsibilities to different (non-central state) scales such as families and charitable institutions, local governments, communities and older people themselves. In these explorations, I also consider more closely alternative governing projects that have contested, to differing extents, the central state's neoliberal neglect. Unpacking how progressive governing projects at central and local levels have sought to imprint a different common sense on state responsibility, I also consider how these alternative projects have themselves been reshaped by neoliberal ideas and strategies. In this case, I argue that neoliberal ideas and strategies, together with the material effects of Chileâs neoliberal context, are holding back the advances of progressive governing projects. Nonetheless, as hegemony is never final, I also consider how the intertwined moments of the COVID-19 pandemic and the anti-neoliberal social uprising of October 2019 also shed light on how the history of neoliberal policies directed at older populations in Chile continues to be contested.
Scholarly understandings of neoliberalism as a political hegemonic project are central to this thesisâ argument. I draw on Gramsciâs notion of hegemony as a position of âleadershipâ continuously constructed through the intertwined articulation of coercion and consent (Hall 1986, p.15), to unpack how neoliberal ideas and strategies have reached a position of leadership in the governing of demographic ageing amid opposition from alternative governing ideas and projects. Three crosscutting findings emerge from this research: 1) through a marked politics of devolution within Chilean governance, access to welfare and caregiving has been rendered deeply unequal with old age; 2) the hegemonising capacity of neoliberal ideas and strategies is revealed in the persistence of the central stateâs politics of scalar devolution and ways in which would-be progressive local governing projects end up complying with neoliberal aims; 3) though neoliberal hegemony has been secured thus far in this case through multiple strategies, it continues to be subject to contestation. Such findings offer insights for building more hopeful demographic ageing futures
Quantifying the breeding distribution and habitat use of the snow petrel (Pagodroma nivea), the worldâs most southerly breeding vertebrate
Seabirds in the Southern Ocean serve as important ecological indicators of ecosystem status, responding to environmental conditions at both local and regional scales. However, knowledge of the spatial distribution of many polar seabird species is incomplete due to logistical difficulties of accessing remote breeding locations. A prime example is the snow petrel Pagodroma nivea, the most southerly breeding vertebrate in the world, whose breeding distribution has not been assessed in almost three decades. This thesis aims to quantify this speciesâ breeding distribution, characterise breeding habitat, and test whether remote sensing can detect known breeding sites. To do so, records of breeding locations, including population estimates when available, were collected from previously published work. Local scale environmental conditions at breeding sites (lithology, temperature, precipitation and wind speed), distance to the coast and regional sea-ice conditions accessible within defined foraging ranges were characterised. Two large breeding sites were subsequently selected for remote sensing, with image enhancement and unsupervised classification performed. The results provide the first updated version of the circumpolar breeding distribution, in which 456 breeding sites are now known, 158 more than the previous inventory. Most known breeding sites are biased towards the location of research stations, indicating more remote breeding sites remain undiscovered. As a cavity-nesting species, the distribution is partly controlled by cavity availability, and results suggest preferential use of cavities in intrusive igneous and high-grade metamorphic lithologies, with the majority of the known breeding population located on the latter. Breeding snow petrels face a central-place foraging constraint, needing to repeatedly return to their nests, and it has been hypothesised therefore that the breeding distribution is limited by distance to pack-ice, where they forage. Characterising regional sea-ice conditions in areas accessible from breeding sites (foraging habitat) supports this, with a median distance from breeding sites to the November ice edge of 430 km. However, the most remote sites are > 1000 km from this foraging habitat. The lack of accessible foraging habitat, due to the year-round persistence of high concentration sea ice in the Weddell Sea, likely explains the absence of breeding sites on the eastern Antarctic Peninsula. However, other gaps in the breeding distribution remain unexplained. The results of remote sensing indicate that if we are to detect breeding sites remotely, better spectral and spatial resolution imagery will be needed, as well as ground truthing data recorded at breeding sites. As ~70% of known breeding sites were recorded before 2000, more consistent and detailed data on breeding sites and breeding populations are also needed to better understand the distribution. Similarly, more widespread long-term studies of snow petrel populations are needed in order to predict the response of this species to climate change
The Council of Europeâs Framework of Competences for Democratic Culture: Hope for democracy or an allusive Utopia?
Democracies around the world are increasingly polarized along political and cultural lines. To address these challenges, in 2016, the Council of Europe (CoE) produced a model of twenty competences for democratic culture. In 2018, this same model became the basis of the Reference Framework of Competences for Democratic Culture (RFCDC). The RFCDC provides pedagogical instructions to help implement these competences. Together, I call this set of materials âthe Frameworkâ.
This thesis begins with the premise that utopia has long played an important role in the way power is maintained or resisted in democratic education. It questions the assumption that democratic culture can be cultivated instrumentally through policy- based competences without imposing power on subjects and views this assumption to be utopian. It thus excavates the potential utopian ideals at play in the Framework using âhidden utopiasâ as a conceptual lens and method, which draws inspiration from the theories of MichĂšl Foucault, Ernst Bloch and Ruth Levitas.
It investigates how using âhidden utopiasâ as a theoretical lens might facilitate a deeper understanding of the nature and purpose of the Framework, how implicit utopias might be at play, how this could be problematic and how these theories might shed light on the application of the Framework in pedagogical contexts. The contribution of this thesis is to make visible potential utopias at the heart of the Framework. It suggests that making implicit utopias visible in democratic education can help educators and learners engage with these discourses in critical and innovative ways and think beyond them
âShinu Shika Naiâ â âThere is Nothing to Do but to Dieâ: Contextualising the Rising Young Female Suicide Rate in Japan
During the Covid-19 pandemic, the suicide rate for the 18-39 age cohort of Japanese women has been drastically subverting a long period of prior sustained decline. This work is an anthropological study of social conditions contributing to a social zeitgeist in which these young women are taking their
own lives, as told in survivor and advocate testimonies. It seeks to question the ways ideas around what suicide means in the Japanese cultural context to stakeholders in the suicide process. It further elucidates how these ideas exist, and how they have evolved to be meaningful to young women in contemporary Japan
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