Surface plasmon excitations in metal spheres: Direct comparison of light scattering and electron energy-loss spectroscopy by modal decomposition

In previous publications, qualitative agreement between studies of surface plasmon excitations in nanoparticles by near field light scattering and electron energy-loss spectroscopy (EELS) has been found for experiments and simulations. Here, we present a quantitative method for the comparison of light scattering and EELS for surface plasmons in metal spheres. Defining the Fourier transform of the modal component of the scattered electric field along the equivalent electron trajectory enables a direct evaluation of the relative weighting factor for light- and electron-excited surface plasmon modes. This common quantity for light scattering and EELS is examined for size, composition, and trajectory dependencies, facilitating the analysis of key differences between light and electron excitation. A single functional dependence on Drude model plasmon energies is identified to explain the relative modal weighting factors for light scattering and EELS. This method represents an important step toward the complete spectral and spatial reconstruction of EELS maps from near field light scattering calculations.S.M.C. acknowledges the support of a Gates Cambridge Scholarship. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 291522-3DIMAGE. P.A.M. also acknowledges funding from the European Union's Seventh Framework Programme under a contract for an Integrated Infrastructure Initiative (Reference 312483-ESTEEM2)

Coupled ‘storm-flood’ depositional model: application to the Miocene–Modern Baram Delta Province, north-west Borneo

The Miocene to Modern Baram Delta Province is a highly efficient source to sink system that has accumulated 9 to 12 km of coastal-deltaic to shelf sediments over the past 15 Myr. Facies analysis based on ca 1 km of total vertical outcrop stratigraphy, combined with subsurface geology and sedimentary processes in the present-day Baram Delta Province, suggests a ‘storm-flood’ depositional model comprising two distinct periods: (i) fair-weather periods are dominated by alongshore sediment reworking and coastal sand accumulation; and (ii) monsoon-driven storm periods are characterised by increased wave energy and offshore-directed downwelling storm flow that occur simultaneously with peak fluvial discharge caused by storm-precipitation (‘storm-floods’). The modern equivalent environment has the following characteristics: (i) humid-tropical monsoonal climate; (ii) narrow (ca <100 km) and steep (ca 1°), densely vegetated, coastal plain; (iii) deep tropical weathering of a mudstone-dominated hinterland; (iv) multiple independent, small to moderate-sized (102 to 105 km2) drainage basins; (v) predominance of river-mouth bypassing; and (vi) supply-dominated shelf. The ancient, proximal part of this system (the onshore Belait Formation) is dominated by strongly cyclical sandier-upward successions (metre to decametre-scale) comprising (from bottom to top): (i) finely laminated mudstone with millimetre-scale silty laminae; (ii) heterolithic sandstone-mudstone alternations (centimetre to metre-scale); and (iii) sharp-based, swaley cross-stratified sandstone beds and bedsets (metre to decimetre-scale). Gutter casts (decimetre to metre-scale) are widespread, they are filled with swaley cross-stratified sandstone and their long-axes are oriented perpendicular to the palaeo-shoreline. The gutter casts and other associated waning-flow event beds suggest that erosion and deposition was controlled by high-energy, offshore-directed, oscillatory-dominated, sediment-laden combined flows within a shoreface to delta front setting. The presence of multiple river mouths and exceptionally high rates of accommodation creation (characteristic of the Neogene to Recent Baram Delta Province; up to 3000 m/Ma), in a ‘storm-flood’ dominated environment, resulted in a highly efficient and effective offshore-directed sediment transport system

Out of the shadows: A young woman's journey from hiding to celebrating her identity

In April 2019 the UK government reported that little progress had been made to remedy social outcomes inequality between Roma and the wider population, recommending further recognition of Roma, for example in census data, to enable identification of Roma, their needs, and how to meet those needs. In this article we present an account of one Roma woman’s journey from hiding her identity to celebrating it. We expose five critical incidents that challenge and mould her sense of identity and career aspiration, with insights into her hopes and dreams as she reflects upon the barriers she faces and attempts to overcome. The narrative enhances understanding of the intersection of experience and ethnic identity formation, Marcella’s (pseudonym) case study emerges verbatim through quotes; we do not alter or correct her English. In our exploration, we follow the six classical steps recommended in case study analysis (Yin, 2009) and ground some of the key analytical concepts in Goffman’s theories of stigma (1963) and theatrical performances in everyday life. We conclude by identifying key parallels in her experience, relevant regardless of socioeconomic status to further debate on the nature of internalised shame, stigma and class

The effects of peculiar velocities in SN Ia environments on the local H0 measurement

The discrepancy between estimates of the Hubble Constant ($H_{0}$) measured from local ($z \lesssim 0.1$) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities of standard candle distance indicators can systematically affect local $H_{0}$ measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable $z < 0.05$ under-density in the SGC-6dFGS region of $27 \pm 2$ %. However, no strong evidence for a 'Local Void' pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, $\Delta \phi_{+-}$, which acts as a proxy for peculiar velocity ($v_{pec}$) by quantifying density gradients along a line-of-sight. $\Delta \phi_{+-}$ is found to correlate strongly with local $H_{0}$ estimates from Union 2.1 Type Ia SNe ($0.02 < z < 0.04$). Density structures on scales of $\sim 50$ Mpc are found to correlate most strongly with $H_{0}$ estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Interpolating SN Ia $H_{0}$ estimates to their $\Delta \phi_{+-} = 0$ values, we can correct for the effects of density structure on the local $H_{0}$ estimates, even in the presence of biased peculiar velocities. For these particular observational data, we reveal a $< 0.1 \,\rm km\,s^{-1} Mpc^{-1}$ difference in the sample mean estimate compared to the value uncorrected for peculiar velocities. Our best estimate is then $74.9 \,\rm km\,s^{-1} Mpc^{-1}$. Using the mock data, the systematic uncertainty from these peculiar velocity corrections is estimated to be $0.3 \,\rm km\,s^{-1} Mpc^{-1}$. The dominant source of uncertainty in our estimate instead relates to Cepheid-based calibrations of distance moduli ($1.7 \,\rm km\,s^{-1} Mpc^{-1}$) and SN photometry ($0.7 \,\rm km\,s^{-1} Mpc^{-1}$)

Excitation dependent Fano-like interference effects in plasmonic silver nanorods

Surface plasmon resonances in metal nanoparticles are an emerging technology platform for nano-optics applications from sensing to solar energy conversion. The electromagnetic near field associated with these resonances arises from modes determined by the shape, size, and composition of the metal nanoparticle. When coupled in the near field, multiple resonant modes can interact to give rise to interference effects offering fine control of both the spectral response and spatial distribution of fields near the particle. Here, we present an examination of experimental electron energy loss spectroscopy (EELS) of silver nanorod monomer surface plasmon modes and present an explanation of observed spatial amplitude modulation of the Fabry-Pérot resonance modes of these silver nanorods using electrodynamics simulations. For these simulations, we identify differences in spectral peak symmetry in light scattering and electron spectroscopies (EELS and cathodoluminescence) and analyze the distinct near-field responses of silver nanorods to plane-wave light and electron beam excitation in terms of a coupled oscillator model. Effects of properties of the material and the incident field are evaluated, and the spatially resolved EELS signals are shown to provide a signature for assessing Fano-like interference effects in silver nanorods. These findings outline key considerations and challenges for interpreting electron microscopy data on plasmonic nanoparticles for understanding nanoscale optics and for characterization and design of photonic devices.S.M.C. acknowledges support of a Gates Cambridge Scholarship. D.R. acknowledges support from the Royal Society's Newton International Fellowship scheme. We acknowledge the use of computing facilities provided by CamGrid. Parts of this work were also performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council. We thank F.J. de la Peña for helpful discussions on the use of hyperspy. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (Grant No. FP7/2007-2013)/ERC Grant Agreement No. 291522-3DIMAGE. Data on rod “B” were acquired by one of us (D. Rossouw) with support of a NSERC Discovery Grant (G. A. Botton) at the Canadian Centre for Electron Microscopy, a national facility supported by NSERC and McMaster University. We thank G. A. Botton for access to data on rod “B” and for helpful comments on this manuscript. P.A.M. also acknowledges funding from the European Union's Seventh Framework Program under a contract for an Integrated Infrastructure Initiative (Reference No. 312483-ESTEEM2)

Progress and opportunities in EELS and EDS tomography.

Electron tomography using energy loss and X-ray spectroscopy in the electron microscope continues to develop in rapidly evolving and diverse directions, enabling new insight into the three-dimensional chemistry and physics of nanoscale volumes. Progress has been made recently in improving reconstructions from EELS and EDS signals in electron tomography by applying compressed sensing methods, characterizing new detector technologies in detail, deriving improved models of signal generation, and exploring machine learning approaches to signal processing. These disparate threads can be brought together in a cohesive framework in terms of a model-based approach to analytical electron tomography. Models incorporate information on signal generation and detection as well as prior knowledge of structures in the spectrum image data. Many recent examples illustrate the flexibility of this approach and its feasibility for addressing challenges in non-linear or limited signals in EELS and EDS tomography. Further work in combining multiple imaging and spectroscopy modalities, developing synergistic data acquisition, processing, and reconstruction approaches, and improving the precision of quantitative spectroscopic tomography will expand the frontiers of spatial resolution, dose limits, and maximal information recovery.SMC acknowledges support from the EPSRC Cambridge NanoDTC, EP/G037221/1, and Trinity College, Cambridge. SMC and PAM also acknowledge support from the European Research Council under the European Union's Seventh Framework Program (No. FP7/2007–2013)/ERC Grant Agreement No. 291522-3DIMAGE

Eigenmode Tomography of Surface Charge Oscillations of Plasmonic Nanoparticles by Electron Energy Loss Spectroscopy

Plasmonic devices designed in three dimensions enable careful tuning of optical responses for control of complex electromagnetic interactions on the nanoscale. Probing the fundamental characteristics of the constituent nanoparticle building blocks is, however, often constrained by diffraction-limited spatial resolution in optical spectroscopy. Electron microscopy techniques, including electron energy loss spectroscopy (EELS), have recently been developed to image surface plasmon resonances qualitatively at the nanoscale in three dimensions using tomographic reconstruction techniques. Here, we present an experimental realization of a distinct method that uses direct analysis of modal surface charge distributions to reconstruct quantitatively the three-dimensional eigenmodes of a silver right bipyramid on a metal oxide substrate. This eigenmode tomography removes ambiguity in two-dimensional imaging of spatially-localized plasmonic resonances, reveals substrate-induced mode degeneracy breaking in the bipyramid, and enables EELS for the analysis not of a particular electron-induced response but of the underlying geometric modes characteristic of particle surface plasmons.S.M.C. acknowledges support of a Gates Cambridge Scholarship. E.R. acknowledges support from the Royal Society's Newton International Fellowship scheme and a Trinity Hall Research Fellowship. We thank Ben Knappet for assistance with the synthesis of the silver bipyramids. We thank F.J. de la Peña for helpful discussions on the use of HYPERSPY. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (No. FP7/2007-2013)/ERC Grant Agreement No. 291522-3DIMAGE and the European Union's Seventh Framework Program under a contract for an Integrated Infrastructure Initiative (Reference No. 312483-ESTEEM2)This is the final version of the article. It was first available from ACS via http://dx.doi.org/10.1021/acsphotonics.5b0042

Effects of Oxidative Stress on Behavior, Physiology, and the Redox Thiol Proteome of Caenorhabditis elegans

Accumulation of reactive oxygen species has been implicated in various diseases and aging. However, the precise physiological effects of accumulating oxidants are still largely undefined. Here, we applied a short-term peroxide stress treatment to young Caenorhabditis elegans and measured behavioral, physiological, and cellular consequences. We discovered that exposure to peroxide stress causes a number of immediate changes, including loss in mobility, decreased growth rate, and decreased cellular adenosine triphosphate levels. Many of these alterations, which are highly reminiscent of changes in aging animals, are reversible, suggesting the presence of effective antioxidant systems in young C. elegans. One of these antioxidant systems involves the highly abundant protein peroxiredoxin 2 (PRDX-2), whose gene deletion causes phenotypes symptomatic of chronic peroxide stress and shortens lifespan. Applying the quantitative redox proteomic technique OxICAT to oxidatively stressed wild-type and prdx-2 deletion worms, we identified oxidation-sensitive cysteines in 40 different proteins, including proteins involved in mobility and feeding (e.g., MYO-2 and LET-75), protein translation and homeostasis (e.g., elongation factor 1 [EFT-1] and heat shock protein 1), and adenosine triphosphate regeneration (e.g., nucleoside diphosphate kinase). The oxidative modification of some of these redox-sensitive cysteines may contribute to the physiological and behavioral changes observed in oxidatively stressed animals. Antioxid. Redox Signal. 14, 1023-1037.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90439/1/ars-2E2010-2E3203.pd

Supporting Liverpool's Roma community: an illumination via Bourdieu's theory of capital

We discuss our Fair Work research with the Roma of Liverpool, and showcase how Roma communities have developed coping strategies in increasingly precarious labour conditions. We utilise Pierre Bourdieu’s concepts of capitals, in particular social capital, to show how Roma cope with the uncertainties of precarious employment. We share our work of the Liverpool Roma Employability Network (LREN) and, in so doing, we posit that social networks, borne of social capital, not merely contribute to enhancing opportunity for Roma employability but more so, align deeply with Roma’s habitus