1,299 research outputs found

    Faraday Rotation, Band Splitting, and One-Way Propagation of Plasmon Waves on a Nanoparticle Chain

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    We calculate the dispersion relations of plasmonic waves propagating along a chain of semiconducting or metallic nanoparticles in the presence of both a static magnetic field B{\bf B} and a liquid crystalline host. The dispersion relations are obtained using the quasistatic approximation and a dipole-dipole approximation to treat the interaction between surface plasmons on different nanoparticles. For a plasmons propagating along a particle chain in a nematic liquid crystalline host with both B{\bf B} and the director parallel to the chain, we find a small, but finite, Faraday rotation angle. For B{\bf B} perpendicular to the chain, but director still parallel to the chain, the field couples the longitudinal and one of the two transverse plasmonic branches. This coupling is shown to split the two branches at the zero field crossing by an amount proportional to ∣B∣|{\bf B}|. In a cholesteric liquid crystal host and an applied magnetic field parallel to the chain, the dispersion relations for left- and right-moving waves are found to be different. For some frequencies, the plasmonic wave propagates only in one of the two directions.Comment: 6 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:1502.0496

    Tight-Binding Model for Adatoms on Graphene: Analytical Density of States, Spectral Function, and Induced Magnetic Moment

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    In the limit of low adatom concentration, we obtain exact analytic expressions for the local and total density of states (LDOS, TDOS) for a tight-binding model of adatoms on graphene. The model is not limited to nearest-neighbor hopping but can include hopping between carbon atoms at any separation. We also find an analytical expression for the spectral function A(k,E)A({\bf k}, E) of an electron of Bloch vector k{\bf k} and energy E on the graphene lattice, to first order in the adatom concentration. We treat the electron-electron interaction by including a Hubbard term on the adatom, which we solve within a mean-field approximation. For finite Hubbard UU, we find the spin-polarized LDOS, TDOS, and spectral function self-consistently. For any choice of parameters of the tight-binding model within mean field theory, we find a critical value of UU above which a moment develops on the adatom. For most choices of parameters, we find a substantial charge transfer from the adatom to the graphene host.Comment: 11 Pages, 6 figures, 1 tabl

    The road to the structure of the mitochondrial respiratory chain supercomplex

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    The four complexes of the mitochondrial respiratory chain are critical for ATP production in most eukaryotic cells. Structural characterisation of these complexes has been critical for understanding the mechanisms underpinning their function. The three proton-pumping complexes, Complexes I, III and IV associate to form stable supercomplexes or respirasomes, the most abundant form containing 80 subunits in mammals. Multiple functions have been proposed for the supercomplexes, including enhancing the diffusion of electron carriers, providing stability for the complexes and protection against reactive oxygen species. Although high-resolution structures for Complexes III and IV were determined by X-ray crystallography in the 1990s, the size of Complex I and the supercomplexes necessitated advances in sample preparation and the development of cryo-electron microscopy techniques. We now enjoy structures for these beautiful complexes isolated from multiple organisms and in multiple states and together they provide important insights into respiratory chain function and the role of the supercomplex. While we as non-structural biologists use these structures for interpreting our own functional data, we need to remind ourselves that they stand on the shoulders of a large body of previous structural studies, many of which are still appropriate for use in understanding our results. In this mini-review, we discuss the history of respiratory chain structural biology studies leading to the structures of the mammalian supercomplexes and beyond

    Development of the text of the Ramsar Convention: 1965–1971

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    The ‘Ramsar’ Convention on Wetlands was the first of the modern era global biodiversity conventions and remains the only multilateral environmental agreement focused on a single group of ecosystem types. At the time of initial discussions within the wetland conservation science community in the late 1960s, its ambition was unprecedented, with no successful models to draw upon, especially with regard to novel concepts such as the modus for an ‘internationally protected site’. Drawing on previously unpublished draft texts, we track the Convention’s textual development to its ultimate agreement in 1971. During this period its geographic scope changed from an initial European to global focus, whereas core obligations related to the designation of internationally important wetlands and the provision of secretariat coordination functions were substantively developed. We present (as supplementary material) all draft texts, from 1965 to 1971, previously unavailable online

    QTL mapping in salad tomatoes

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    Single-Particle Density of States of a Superconductor with a Spatially Varying Gap and Phase Fluctuations

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    Recent experiments have shown that the superconducting energy gap in some cuprates is spatially inhomogeneous. Motivated by these experiments, and using exact diagonalization of a model d-wave Hamiltonian, combined with Monte Carlo simulations of a Ginzburg-Landau free energy functional, we have calculated the single-particle density of states LDOS(ω,r)(\omega,r) of a model high-Tc_c superconductor as a function of temperature. Our calculations include both quenched disorder in the pairing potential and thermal fluctuations in both phase and amplitude of the superconducting gap. Most of our calculations assume two types of superconducting regions: α\alpha, with a small gap and large superfluid density, and β\beta, with the opposite. If the β\beta regions are randomly embedded in an α\alpha host, the LDOS on the α\alpha sites still has a sharp coherence peak at T=0T = 0, but the β\beta component does not, in agreement with experiment. An ordered arrangement of β\beta regions leads to oscillations in the LDOS as a function of energy. The model leads to a superconducting transition temperature TcT_c well below the pseudogap temperature Tc0T_{c0}, and has a spatially varying gap at very low TT, both consistent with experiments in underdoped Bi2212. Our calculated LDOS(ω,r)(\omega,r) shows coherence peaks for TTcT T_c, in agreement with previous work considering phase but not amplitude fluctuations in a homogeneous superconductor. Well above TcT_c, the gap in the LDOS disappears.Comment: 37 pages, 12 figures. Accepted by Phys. Rev. B. Scheduled Issue: 01 Nov 200
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