569 research outputs found

    Lasing in localized modes of a slow light photonic crystal waveguide

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    We demonstrate lasing in GaAs photonic crystal waveguides with InAs quantum dots as gain medium. Structural disorder is present due to fabrication imperfection and causes multiple scat- tering of light and localization of light. Lasing modes with varying spatial extend are observed at random locations along the guide. Lasing frequencies are determined by the local structure and occur within a narrow frequency band which coincides with the slow light regime of the waveguide mode. The three-dimensional numerical simulation reveals that the main loss channel for lasing modes located away from the waveguide end is out-of-plane scattering by structural disorder.Comment: 8 pages, 4 figure

    Community occupational therapy for people with dementia and their family carers: A national survey of United Kingdom occupational therapy practice

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    Introduction: A national survey was conducted with United Kingdom (UK) occupational therapists to scope occupational therapy service provision for people with dementia and their family carers in the community. / Method: This was an online questionnaire with topics on occupational therapists’ roles, service provision, referral, assistive technology and assessment tools. Recruitment was through direct invitation, and promotion via occupational therapy networks, websites and newsletters. / Results: A total of 197 responded. Occupational therapy referrals most commonly came from the multidisciplinary team. Over half primarily undertook profession-specific work, with occupational therapy assessments the most common profession-specific task. Two-thirds of referrals for initial assessments were for people with mild-to-moderate dementia. A median of 2.5 hours for assessment/intervention was spent for each person with dementia. Almost two-thirds used the Model of Human Occupation Screening Tool. Most could prescribe personal activities of daily living equipment and Telecare, with few able to prescribe equipment for reminiscence or leisure. / Conclusion: This national survey increases knowledge of UK community occupational therapy practice and service provision for people with dementia and their family carers. It informs occupational therapists about national trends within this practice area, and development of the community occupational therapy intervention (COTiD-UK) as part of the Valuing Active Life in Dementia research programme

    Wetting of Curved Surfaces

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    As a first step towards a microscopic understanding of the effective interaction between colloidal particles suspended in a solvent we study the wetting behavior of one-component fluids at spheres and fibers. We describe these phenomena within density functional theory which keeps track of the microscopic interaction potentials governing these systems. In particular we properly take into account the power-law decay of both the fluid-fluid interaction potentials and the substrate potentials. The thicknesses of the wetting films as a function of temperature and chemical potential as well as the wetting phase diagrams are determined by minimizing an effective interface potential which we obtain by applying a sharp-kink approximation to the density functional. We compare our results with previous approaches to this problem.Comment: 54 pages, 17 figures, accepted for publication in Physica

    Spatial distribution of local currents of massless Dirac fermions in quantum transport through graphene nanoribbons

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    We employ the formalism of bond currents, expressed in terms of the nonequilibrium Green functions, to image the charge flow between two sites of the honeycomb lattice of graphene ribbons of few nanometers width. In sharp contrast to nonrelativistic electrons, current density profiles of quantum transport at energies close to the Dirac point in clean zigzag graphene nanoribbons (ZGNR) differs markedly from the profiles of charge density peaked at the edges due to zero-energy localized edge states. For transport through the lowest propagating mode induced by these edge states, edge vacancies do not affect current density peaked in the center of ZGNR. The long-range potential of a single impurity acts to reduce local current around it while concurrently increasing the current density along the zigzag edge, so that ZGNR conductance remains perfect G=2e2/hG=2e^2/h.Comment: 5 pages, 5 figure

    Improving Human Health by Increasing Access to Natural Areas: Opportunities and Risks

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    Report of the 2013 Berkley Workshop Held at the Pocantico Center of the Rockefeller Brothers Fund, Tarrytown, NY - July 201

    Structural characterization of nanofiber silk produced by embiopterans (webspinners)

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    Embiopterans produce silken galleries and sheets using exceptionally fine silk fibers in which they live and breed. In this study, we use electron microscopy (EM), Fourier-transform infrared (FT-IR) spectroscopy, wide angle X-ray diffraction (WAXD) and solid-state nuclear magnetic resonance (ssNMR) techniques to elucidate the molecular level protein structure of webspinner (embiid) silks. Silks from two species Antipaluria urichi and Aposthonia ceylonica are studied in this work. Electron microscopy images show that the fibers are about 90–100 nm in diameter, making webspinner silks among the finest of all known animal silks. Structural studies reveal that the silk protein core is dominated by β-sheet structures, and that the protein core is coated with a hydrophobic alkane-rich surface coating. FTIR spectra of native embiid silk shows characteristic alkane CH2 stretchings near 2800–2900 cm−1, which decrease approximately 50% after washing the silk with 2 : 1 CHCl3 : MeOH. Furthermore, 13C ssNMR data shows a significant CH2 resonance that is strongly affected by the presence of water, supporting the idea that the silk fibers are coated with a hydrocarbon-rich layer. Such a layer is likely used to protect the colonies from rain. FTIR data also suggests that embiid silks are dominated by β-sheet secondary structures similar to spider and silkworm silk fibers. NMR data confirms the presence of β-sheet nanostructures dominated by serine-rich repetitive regions. A deconvolution of the serine Cβ NMR resonance reveals that approximately 70% of all seryl residues exist in a β-sheet structure. This is consistent with WAXD results that suggest webspinner silks are 70% crystalline, which is the highest crystalline fraction reported for any animal silks. The work presented here provides a molecular level structural picture of silk fibers produced by webspinners

    Development of a novel, windowless, amorphous selenium based photodetector for use in liquid noble detectors

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    Detection of the vacuum ultraviolet (VUV) scintillation light produced by liquid noble elements is a central challenge in order to fully exploit the available timing, topological, and calorimetric information in detectors leveraging these media. In this paper, we characterize a novel, windowless amorphous selenium based photodetector with direct sensitivity to VUV light. We present here the manufacturing and experimental setup used to operate this detector at low transport electric fields (2.7-5.2 V/μ\mum) and across a wide range of temperatures (77K-290K). This work shows that the first proof-of-principle device windowless amorphous selenium is robust under cryogenic conditions, responsive to VUV light at cryogenic temperatures, and preserves argon purity. These findings motivate a continued exploration of amorphous selenium devices for simultaneous detection of scintillation light and ionization charge in noble element detectors
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