Alien Registration- Baker, Lewis A. (Van Buren, Aroostook County)

https://digitalmaine.com/alien_docs/33303/thumbnail.jp

A Theory of Claim Resolution

We study claim resolution. A claim consists of a global fact and a local fact. The global fact is observed by the principal and the agent. The local fact is observed by the agent alone. The agent resolves the claim; the principal decides whether the agent is more likely wrong or right. The principal and agent can disagree about the weight to accord each fact or the overall evidence threshold. The agent cares whether the principal follows or ignores her advice. We characterize how the equilibrium varies with the nature of disagreement. Despite lacking commitment power, we nd that the principal grants the agent decision-making authority over an interval of global facts

Observing and understanding the ultrafast photochemistry in small molecules: applications to sunscreens

In this review we discuss the importance of biological and artificial photoprotection against overexposure to harmful ultraviolet radiation. Transient electronic and transient vibrational absorption spectroscopies are highlighted as important tools in understanding the energy transfer in small molecules, with a focus on the application to commercial sunscreens with representative examples given. Oxybenzone, a common ingredient in commercial sunscreens and sinapoyl malate, a biological sunscreen in plant leaves are presented as case studies

Observing and understanding the ultrafast photochemistry in small molecules : applications to sunscreens

In this review we discuss the importance of biological and artificial photoprotection against overexposure to harmful ultraviolet radiation. Transient electronic and transient vibrational absorption spectroscopies are highlighted as important tools in understanding the energy transfer in small molecules, with a focus on the application to commercial sunscreens with representative examples given. Oxybenzone, a common ingredient in commercial sunscreens and sinapoyl malate, a biological sunscreen in plant leaves are presented as case studies

Robustness, efficiency, and optimality in the Fenna-Matthews-Olson photosynthetic pigment-protein complex

Pigment-protein complexes (PPCs) play a central role in facilitating excitation energy transfer (EET) from light-harvesting antenna complexes to reaction centres in photosynthetic systems; understanding molecular organisation in these biological networks is key to developing better artificial light-harvesting systems. In this article, we combine quantum-mechanical simulations and a network-based picture of transport to investigate how chromophore organization and protein environment in PPCs impacts on EET efficiency and robustness. In a prototypical PPC model, the Fenna-Matthews-Olson (FMO) complex, we consider the impact on EET efficiency of both disrupting the chromophore network and changing the influence of (local and global) environmental dephasing. Surprisingly, we find a large degree of resilience to changes in both chromophore network and protein environmental dephasing, the extent of which is greater than previously observed; for example, FMO maintains EET when 50% of the constituent chromophores are removed, or when environmental dephasing fluctuations vary over two orders-of-magnitude relative to the in vivo system. We also highlight the fact that the influence of local dephasing can be strongly dependent on the characteristics of the EET network and the initial excitation; for example, initial excitations resulting in rapid coherent decay are generally insensitive to the environment, whereas the incoherent population decay observed following excitation at weakly coupled chromophores demonstrates a more pronounced dependence on dephasing rate as a result of the greater possibility of local exciton trapping. Finally, we show that the FMO electronic Hamiltonian is not particularly optimised for EET; instead, it is just one of many possible chromophore organisations which demonstrate a good level of EET transport efficiency following excitation at different chromophores. Overall, these robustness and efficiency characteristics are attributed to the highly connected nature of the chromophore network and the presence of multiple EET pathways, features which might easily be built into artificial photosynthetic systems

A perspective on the ultrafast photochemistry of solution-phase sunscreen molecules

Sunscreens are one of the most common ways of providing on-demand additional photoprotection to the skin. Ultrafast transient absorption spectroscopy has recently proven to be an invaluable tool in understanding how the components of commercial sunscreen products display efficient photoprotection. Important examples of how this technique has unravelled the photodynamics of common components are given in this Perspective, and some of the remaining unanswered questions are discussed

Understanding electronic energy transport in biologically relevant systems : the photochemistry of sunscreens and the photophysics of photosynthesis

This thesis focusses on two areas. The first is elucidating the ultrafast photoprotective mechanisms exhibited by a number of commercial and natural sunscreening agents, through the use of femtosecond pump-probe transient absorption spectroscopy, coupled with ab initio electronic structure calculations. The second is understanding the electronic energy transport properties of pigment-protein complexes found in photosynthetic organisms, through the use of quantum dynamics simulations. Oxybenzone, titanium dioxide, octocrylene and ethylhexyl triazone are all studied given their prevalence in commercial sunscreen products. We deduce that oxybenzone relaxes through an enol-keto isomerism (~400 fs) followed by back-isomerisation commensurate with vibration energy transfer to the surrounding solvent (~5-8 ps). Titanium dioxide is then considered in multicomponent suspensions with oxybenzone, where we find that the photodynamics exhibited by each component can be considered independent from one another. Octocrylene is shown to undergo the majority of its photodynamics within ~2 ps, displaying remarkable efficiency as an ultraviolet light chromophore, relaxing through nonradiative internal conversion pathways. Studies of ethylhexyl triazone are presented, where results suggest this molecule relaxes through a number of ultrafast processes, ranging from ~400 fs, ~20 ps and ~200 ps, involving a large change in nuclear geometry, which couples excited states to the ground state through a conical intersection. Sinapoyl malate is the predominant sunscreening agent synthesised in arabidopsis thaliana which is deposited into the upper epidermis of its leaves. This molecule, along with its biological precursor sinapic acid, is shown to relax through ultrafast pathways (~10-30 ps), which we suggest is mediated by a trans-cis isomerism, in stark contrast to the recent time-resolved gas-phase measurements indicating the solvent environment alters the photodynamics significantly. Considering the second half of this thesis, we study the Fenna-Matthews-Olson pigment-protein complex found in green sulphur bacteria, and the light-harvesting complex II found in the spinach plant. Employing a simple quantum master equation, the Haken-Strobl model, we highlight a computationally tractable approach for describing these large, complicated systems. To this end, we perform an enormous array of simulations which include a simple description of environmental perturbations and find, for the first time, the full extent of the robustness of these pigment-protein complexes. Most strikingly, for the Fenna-Matthews-Olson complex, we find that up to 50% of the available pigments may be removed, with a small drop of 20% in electronic energy transport, displaying an incredible robustness to network disruption

Ultrafast photophysical studies of a multicomponent sunscreen : oxybenzone - titanium dioxide mixtures

Recent studies of the sunscreen constituent oxybenzone have suggested that the dominant mechanism underlying the efficient photoprotection it offers relies on an initial ultrafast enol -> keto tautomerisation, followed by nonadiabatic transfer to the ground electronic state. Subsequent collisions with the solvent bath then reform the original enol tautomer. Utilising femtosecond transient electronic absorption spectroscopy we explore the dissipation of electronic excitation energy in oxybenzone in the presence of titanium dioxide, a widely used, and complementary sunscreen component. We find the relaxation dynamics of this popular organic filter are unaltered by the presence of this favoured inorganic scatterer and the overall dynamics can be described by the additive contribution of the individual constituents. The combination of the two components provides broadband photoprotective properties justifying the widely used organic filter and inorganic scatterer mixtures in commercial sunscreen products