Models of OH Maser Variations in U Her

Arecibo spectra of the mainline OH maser emission from U Her over more than a decade show variations of the OH emission over these time scales. These observations are combined with high spatial resolution VLBA maps to investigate the causes of the variations in the velocities of the maser components. Global properties of the dust shell, such as accelerations, variations in the pump and shell-wide magnetic field changes are examined as possibilities, and eliminated. A possible solution to the problem involving plasma turbulence and the local magnetic field is introduced, and the relevant time scales of the turbulence are calculated. The turbulent velocity field yields time scales of the turbulence are calculated. The turbulent velocity field yields time scales that are too long (of order centuries), while the turbulent magnetic field produces variations on appropriate time scales of a few years. A line-of-sight model of the turbulence is developed and investigated. The complete exploration of this solution requires extensive theoretical and observational work. Possible avenues of investigation of the plasma turbulence model are presented.Comment: 23 pages, 17 figures, ApJ: accepted Sept, 199

Dust Grains and the Luminosity of Circumnuclear Water Masers in Active Galaxies

In previous calculations for the luminosities of 22 GHz water masers, the pumping is reduced and ultimately quenched with increasing depth into the gas because of trapping of the infrared (approximately equals 30-150 micrometers), spectral line radiation of the water molecule. When the absorption (and reemission) of infrared radiation by dust grains is included, we demonstrate that the pumping is no longer quenched but remains constant with increasing optical depth. A temperature difference between the grains and the gas is required. Such conditions are expected to occur, for example, in the circumnuclear masing environments created by X-rays in active galaxies. Here, the calculated 22 GHz maser luminosities are increased by more than an order of magnitude. Application to the well-studied, circumnuclear masing disk in the galaxy NGC 4258 yields a maser luminosity near that inferred from observations if the observed X-ray flux is assumed to be incident onto only the inner surface of the disk

Interactions of Organic Fluorophores with Plasmonic Surface Lattice Resonances

It is common knowledge that metals, alloys and pure elements alike, are lustrous and reflective, the more so when a metal surface is flat, polished, and free from oxidation and surface fouling. However, some metals reflect visible light, in the 380 nm to 740 nm range of wavelengths, much more strongly than others. In particular, some metals reflect wavelengths in certain portions of the ultraviolet (UV), visible, and near-infrared (NIR) regime, let us say 200 nm to 2000 nm, while absorbing light strongly in other segments of this range. There are several factors that account for this difference between various metals. For a particular metal, its absorbance and reflectance (and, for thin films, transmittance) at various wavelengths are a function of the metal electronic band structure. Metals that have both an abundance of mobile (“free”) valence electrons and an abundance of vacant states in the valence band are able to support propagating oscillations in the free-electron density, much like sound waves in air, which are referred to as plasma oscillations, which are essentially pressure waves in the “plasma” or gas of free electrons in the solid metal. When described as quasiparticles in a manner analogous to phonons (lattice vibrations, propagating oscillations in the positions of atomic nuclei), these electron-density oscillations are referred to as plasmons, specifically volume or bulk plasmons when they exist and propagate in a continuous three-dimensional metal space. In principle, all metals have free electrons and partially occupied valence bands, so all metals ought to support plasmons to some extent, but the strength of the oscillations is greater in some metals (metals with large valence band occupancy and a high density of states at the Fermi level) than in others, and the metals with the strongest plasma oscillations are known as “plasmonic” metals. In terms of pure elements, the most plasmonic metals are, canonically, copper, silver, and gold. But there are several others that are known to be plasmonic, namely aluminum, gallium, and indium, as well as the alkali metals, magnesium, and nickel. Depending on the definition of plasmonic that one chooses, other metals would also qualify, but these listed metals are broadly considered “plasmonic”, and are accordingly known to strongly reflect visible light (barring surface oxidation, of course). The plasmonicity of these metals contributes to the high reflectivity of their bulk surfaces and films, which explains, in part, the fiery glint of gold-plated statues in sunlight, the faithful image reflection from silvered-glass mirrors, the use of a burnished speculum (roughly 70% copper, 30 % tin, by weight) alloy plate in the first reflecting telescope, and the use today of aluminum films in electric lamps, including car headlights, where reflecting the light out with minimal light loss due to absorption is key to their function. Of course, in all of these cases, the resistance to surface oxidation (especially for gold) or, for silver, the discovery that it could be deposited onto glass chemically, also contribute to their visible luster and to their historical use in mirrors and reflectors. But the plasmonicity of these metals can have very different effects when they are not shaped into smooth surfaces. In particular, when nanoparticles roughly 5 nm to 200 nm wide are made from plasmonic metals, they exhibit intense light scattering and absorption in the ultraviolet-visible-near-infrared regime. These intense optical effects are due, at least in large part, to the localized surface plasmon resonances (LSPRs) of the particles, and in particles in the 5 nm to 200 nm width range, the dipolar LSPRs, in which incident light excites an oscillating electric dipole within the particle, is often the fundamental mode that gives rise to their light scattering and absorbing properties, although higher order LSPRs (quadrupole, sextupole, octupole, etc.) may also play a significant role, especially for larger particles. Nanoparticles supporting LSPRs have many applications in colloidal suspension and in amorphous films and solids, in which they can act as a powerful pigment, as light-to-heat converters, as anti-reflection coatings, and as optical tags for biomolecules. This dissertation is not primarily concerned with the LSPRs of colloids and disordered films of plasmonic particles. Rather, this dissertation focusses on a different kind of plasmonic resonance that requires plasmonic particles to be arranged in an ordered one-dimensional or two-dimensional lattice, and embedded in a transparent dielectric (electrically insulating or semiconducting) medium. This new plasmonic mode, formed by the mutual radiative coupling of the dipolar LSPRs of the individual plasmonic nanoparticles constituting the lattice, is known as a surface lattice resonance (SLR), sometimes described as a plasmonic SLR to distinguish it from lattice resonances supported by lattices of Mie-scattering dielectric particles or excitonic nanoparticles. SLRs are another plasmonic mode, in addition to surface plasmons polaritons and LSPRs, through which visible light can be absorbed or scattered. In addition, SLRs in combination with various excitonic materials have been used to support a variety of exotic phenomena, including Bose-Einstein condensation of exciton-SLR-polaritons1–3, directional fluorescence4,5 and lasing from thin films (~200 nm thick) of dye-doped polymer in the direction normal to the plane of the lattice and the film6–8, and enhanced light absorption in thin-film amorphous silicon solar cells, which was shown to improve the photonic efficiency and overall performance of a solar cell based on a 100-nm-thick amorphous silicon active layer at the angles-of-incidence and wavelengths that were resonant with the SLR9,10. This last report is significant, in that it represents one system in which an SLR-supporting lattice was used to increase the photonic efficiency (portion of the incident light absorbed) in a solar cell. Meanwhile, a variety of reports demonstrates how the mobility and transferability of excitons can be increased by coupling the excitons to nanostructure-based plasmonic and photonic modes. These developments motivated the research presented in this dissertation. Specifically, the original research detailed in this dissertation consists of a series of experiments with SLRs and Frenkel-exciton supporting materials (organic dye-doped polymers) that were done to investigate whether SLRs might be able to increase the quantum efficiency of excitonic solar cells, in addition to increasing their photonic efficiency. Organic and excitonic solar cells are limited by the short exciton diffusion lengths (typically \u3c 10 nm for disordered organic semiconductors) and short charge carrier diffusion lengths (typically \u3c 10 nm for electrons or holes, depending on the material) and numerous practical and theoretical reports11 indicating that increasing the diffusion length or exciton-energy-transferability in the active layers of excitonic solar cells will increase their quantum efficiency by allowing more photogenerated excitons to reach an electrode, p-n junction, or another type of interface where they can be separated into charge carriers. Therefore, using photonic and plasmonic modes, such as the resonant photon modes in optical microcavities, to increase the mobility of these excitons, or to increase the rate at which their energy can be transferred over a distance, is a plausible means by which one could improve excitonic solar cells. While increased exciton diffusion lengths and increased energy transfer rates have been observed for excitons coupled to optical microcavities and various other modes, and while there are certainly reports indicating similar effects for SLR-coupled excitons (e. g. SLR-coupled excitons exhibit spatially coherent fluorescence over several microns at least) a clear report of enhanced energy transfer, or a quantitively defined increase in the energy transfer radius or diffusion length of excitons in an SLR-coupled dye film still has not been reported. It was with the aim of investigating whether excitons can indeed be made more mobile or transferable by coupling them to and SLR that the research presented here was undertaken. Accordingly, experiments were done to fabricate and characterize SLR-supporting lattices, and to correlate the structure and composition of the lattices to the optical properties and dispersions of the SLRs they support. These include the fabrication methods and angle-resolved transmission, reflection, and fluorescence spectra reported in Chapter 1 for lattices made of Au and Al nanoparticles, and also in Chapter 2 for dimeric Al nanoparticles, and Chapter 3 for Ag nanoparticle lattices. The spectra and other data presented in Chapter 1 demonstrate that the lattices that were fabricated did indeed support SLRs across the visible range, and that these SLRs could be successfully coupled to the excitons of a small molecule laser dye when a film of a transparent polymer, poly(methyl methacrylate), doped with the laser dye was coated onto the SLR-supporting nanoparticle lattice. The lingering ambiguity of the true nature of this coupling, despite the ample literature on this topic, is discussed in light of these original results in Chapter 1. In Chapter 2, the effects of exciton-SLR coupling on the transferability of the dye excitons was examined by measuring the effect of the SLRs on the efficiently of Förster resonance energy transfer (FRET) between two different small molecule laser dyes. The results did not show any increase in the FRET efficiency due to coupling of the donor dye exciton to the SLRs in the aluminum nanoparticle lattices. However, it did show a significant increase in the fluorescent emission of the donor dye, such that SLRs at a certain wavelength effectively outcoupled the donor dyes emission from the film and appeared increase the rate at which the donor dye excitons decayed radiatively, likely due to the increase in the local density of optical states that the SLRs furnished, which would increase the radiative decay rate of the donor dye exciton per Fermi’s golden rule. Therefore, while this result did not clearly corroborate or negate our hypothesis that exciton-SLR coupling can increase exciton diffusion length and FRET radius, it did provide interesting example of how SLR-enhanced fluorescence can decrease FRET efficiency, not by changing the FRET rate, but by increasing the radiative decay rate of the donor to make it the primary channel by which the donor dye exciton decays in films in which FRET to the acceptor is the primary channel for donor dye exciton decay without SLR-coupling. Chapter 3 explores the potential for SLRs to enhance and direct the emission from single-photon emitters, specifically fluorescent atomic lattice defects in few-atomic-later films of hexagonal boron nitride (hBN), a two-dimensional material and inorganic, insulator/wide-bandgap semiconductor. The results indicate that the SLRs hosted by the plasmonic lattice of Ag nanocylinders does indeed spatially filter (direct) the hBN defect fluorescence, such that the hBN fluorescent emission follows the wavelength-angle of emission relationship dictated by the SLR dispersion. Thus, the defects in hBN couple to the lattice in manner similar to organic dyes in a transparent polymer. Furthermore, the SLRs lattices supporting SLRs of certainly wavelengths (e. g. around 500 nm) increased by a factor of 6 the intensity of the hBN defect emission, and increased the emission from defects located both direction on the Ag nanocylinders, and defects in the film between the Ag nanocylinders, indicating that SLRs can activate defects by optical field effects, in addition to the mechanical strain induced in the hBN by the Ag pillars, which is known to increase the emissivity of the defects based on a previous study with hBN draped over non-plasmonic SiO2 nanopillars12,13. (1) Hakala, T. K.; Moilanen, A. J.; Väkeväinen, A. I.; Guo, R.; Martikainen, J.-P.; Daskalakis, K. S.; Rekola, H. T.; Julku, A.; Törmä, P. Bose-Einstein Condensation in a Plasmonic Lattice. 2017. https://doi.org/10.1038/s41567-018-0109-9. (2) Väkeväinen, A. I. Lasing and Bose-Einstein Condensation in Plasmonic Lattices at Weak and Strong Coupling Regimes; Aalto University, 2019. (3) De Giorgi, M.; Ramezani, M.; Todisco, F.; Halpin, A.; Caputo, D.; Fieramosca, A.; Gomez-Rivas, J.; Sanvitto, D. Interaction and Coherence of a Plasmon–Exciton Polariton Condensate. ACS Photonics 2018, 5 (9), 3666–3672. https://doi.org/10.1021/acsphotonics.8b00662. (4) Zakharko, Y.; Held, M.; Graf, A.; Rödlmeier, T.; Eckstein, R.; Hernandez-Sosa, G.; Hähnlein, B.; Pezoldt, J.; Zaumseil, J. Surface Lattice Resonances for Enhanced and Directional Electroluminescence at High Current Densities. ACS Photonics 2016, 3 (12), 2225–2230. https://doi.org/10.1021/acsphotonics.6b00491. (5) Vecchi, G.; Giannini, V.; Gómez Rivas, J. Shaping the Fluorescent Emission by Lattice Resonances in Plasmonic Crystals of Nanoantennas. Phys. Rev. Lett. 2009, 102 (14), 146807. https://doi.org/10.1103/PhysRevLett.102.146807. (6) Hoang, T. B.; Akselrod, G. M.; Yang, A.; Odom, T. W.; Mikkelsen, M. H. Millimeter-Scale Spatial Coherence from a Plasmon Laser. Nano Lett. 2017, 17 (11), 6690–6695. https://doi.org/10.1021/acs.nanolett.7b02677. (7) Knudson, M. P.; Li, R.; Wang, D.; Wang, W.; Schaller, R. D.; Odom, T. W. Polarization-Dependent Lasing Behavior from Low-Symmetry Nanocavity Arrays. ACS Nano 2019, 13 (7), 7435–7441. https://doi.org/10.1021/acsnano.9b01142. (8) Zhou, W.; Dridi, M.; Suh, J. Y.; Kim, C. H.; Co, D. T.; Wasielewski, M. R.; Schatz, G. C.; Odom, T. W. Lasing Action in Strongly Coupled Plasmonic Nanocavity Arrays. Nat. Nanotechnol. 2013, 8 (7), 506–511. https://doi.org/10.1038/nnano.2013.99. (9) Ferry, V. E.; Verschuuren, M. A.; Li, H. B. T.; Verhagen, E.; Walters, R. J.; Schropp, R. E. I.; Atwater, H. A.; Polman, A. Light Trapping in Ultrathin Plasmonic Solar Cells. Opt. Express 2010, 18 (102), A237–A245. https://doi.org/10.1364/OE.18.00A237. (10) Ferry, V. E.; Verschuuren, M. A.; Li, H. B. T.; Schropp, R. E. I.; Atwater, H. A.; Polman, A. Improved Red-Response in Thin Film a-Si:H Solar Cells with Soft-Imprinted Plasmonic Back Reflectors. Appl. Phys. Lett. 2009, 95 (18), 183503. https://doi.org/10.1063/1.3256187. (11) Kozyreff, G.; Urbanek, D. C.; Vuong, L. T.; Nieto-Silleras, O.; Martorell, J. Microcavity Effects on the Generation, Fluorescence, and Diffusion of Excitons in Organic Solar Cells. Opt. Express 2013, 21 (S3), A336. https://doi.org/10.1364/OE.21.00A336. (12) Proscia, N. V.; Proscia, N. V.; Proscia, N. V.; Shoton, Z.; Jayakumar, H.; Reddy, P.; Dollar, M.; Doherty, M.; Alkauskas, A.; Meriles, C. A.; Meriles, C. A.; Menon, V. M.; Menon, V. M. Formation of Quantum Emitter Arrays in Hexagonal Boron Nitride at Room Temperature. In Conference on Lasers and Electro-Optics (2018), paper FTu4H.1; Optical Society of America, 2018; p FTu4H.1. https://doi.org/10.1364/CLEO_QELS.2018.FTu4H.1. (13) Proscia, N. V.; Shotan, Z.; Jayakumar, H.; Reddy, P.; Cohen, C.; Dollar, M.; Alkauskas, A.; Doherty, M.; Meriles, C. A.; Menon, V. M. Near-Deterministic Activation of Room-Temperature Quantum Emitters in Hexagonal Boron Nitride. Optica 2018, 5 (9), 1128–1134. https://doi.org/10.1364/OPTICA.5.001128

Single versus two-stent strategies for coronary bifurcation lesions: a systematic review and meta-analysis of randomized trials with long-term follow-up

Background: The majority of coronary bifurcation lesions are treated with a provisional single‐stent strategy rather than an up‐front 2‐stent strategy. This approach is supported by multiple randomized controlled clinical trials with short‐ to medium‐term follow‐up; however, long‐term follow‐up data is evolving from many data sets. Methods and Results: Meta‐analysis of randomized controlled trials evaluating long‐term outcomes (≥1 year) according to treatment strategy for coronary bifurcation lesions. Nine randomized controlled trials with 3265 patients reported long‐term clinical outcomes at mean weighted follow‐up of 3.1±1.8 years. Provisional single stenting was associated with lower all‐cause mortality (2.94% versus 4.23%; risk ratio: 0.69; 95% confidence interval, 0.48–1.00; P=0.049; I2=0). There was no difference in major adverse cardiac events (15.8% versus 15.4%; P=0.79), myocardial infarction (4.8% versus 5.5%; P=0.51), target lesion revascularization (9.3% versus 7.6%; P=0.19), or stent thrombosis (1.8% versus 1.6%; P=0.28) between the groups. Prespecified sensitivity analysis of long‐term mortality at a mean of 4.7 years of follow‐up showed that the provisional single‐stent strategy was associated with reduced all‐cause mortality (3.9% versus 6.2%; risk ratio: 0.63; 95% confidence interval, 0.42–0.97; P=0.036; I2=0). Conclusions: Coronary bifurcation percutaneous coronary intervention using a provisional single‐stent strategy is associated with a reduction in all‐cause mortality at long‐term follow‐up

How should we turn data into decisions in AgriFood?

The AgriFood supply chain is under significant pressures related to food security, climate change, and consumer demands for affordable and higher quality food. Various technologies are already deployed producing a large amount of data, which can be utilised to guide decision-making to improve productivity, reduce wastage, and increase traceability across the AgriFood supply chain. Several examples of the use of data are given, including improving efficiency in livestock production, supporting automation and use of robotics in crop production, increasing food safety and evidencing its provenance. The opportunities and ways forward were discussed at a workshop in November 2017, run by the Society of Chemical Industry and the Knowledge Transfer Network in the UK. This paper presents a summary of the key messages from the presentations and focus-group discussions during this event, as interpreted by the authors. A number of challenges in digitalisation of the AgriFood supply chain are discussed, such as low inter-operability of different data sets, silo mentality, low willingness to share data and a significant skills gap. Various approaches are presented that could help to unlock the benefits of using data, from practical support to producers and addressing skills gaps, to industrial leadership and the role of government departments and regulatory bodies in leading by example. Looking forward, data are already revolutionising the AgriFood supply chain, however, the benefits will remain piecemeal until the leaders of today are able to bring together the disparate groups into a cohesive whole

Legal determinants of external finance revisited : the inverse relationship between investor protection and societal well-being

This paper investigates relationships between corporate governance traditions and quality of life as measured by a number of widely reported indicators. It provides an empirical analysis of indicators of societal health in developed economies using a classification based on legal traditions. Arguably the most widely cited work in the corporate governance literature has been the collection of papers by La Porta et al. which has shown, inter alia, statistically significant relationships between legal traditions and various proxies for investor protection. We show statistically significant relationships between legal traditions and various proxies for societal health. Our comparative evidence suggests that the interests of investors may not be congruent with the interests of wider society, and that the criteria for judging the effectiveness of approaches to corporate governance should not be restricted to financial metrics