10,679 research outputs found

    Theoretical study of X-ray absorption of three-dimensional topological insulator Bi2Se3\mathrm{Bi}_2\mathrm{Se}_3

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    X-ray absorption edge singularity which is usually relevant for metals is studied for the prototype topological insulator Bi2Se3\mathrm{Bi}_2\mathrm{Se}_3. The generalized integral equation of Nozi\`eres and Dominicis type for X-ray edge singularity is derived and solved. The spin texture of surfaces states causes a component of singularity dependent on the helicity of the spin texture. It also yields another component for which the singularity from excitonic processes is absent.Comment: RevTeX 4.1. 4 pages, no figur

    Similarity of Operators in the Bergman Space Setting

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    We give a necessary and sufficient condition for an n-hypercontraction to be similar to the backward shift operator in a weighted Bergman space. This characterization serves as a generalization of the description given in the Hardy space setting, where the geometry of the eigenvector bundles of the operators is used

    Nanoscale Heat Transfer from Magnetic Nanoparticles and Ferritin in an Alternating Magnetic Field

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    Recent suggestions of nanoscale heat confinement on the surface of synthetic and biogenic magnetic nanoparticles during heating by radio frequency-alternating magnetic fields have generated intense interest because of the potential utility of this phenomenon for noninvasive control of biomolecular and cellular function. However, such confinement would represent a significant departure from the classical heat transfer theory. Here, we report an experimental investigation of nanoscale heat confinement on the surface of several types of iron oxide nanoparticles commonly used in biological research, using an all-optical method devoid of the potential artifacts present in previous studies. By simultaneously measuring the fluorescence of distinct thermochromic dyes attached to the particle surface or dissolved in the surrounding fluid during radio frequency magnetic stimulation, we found no measurable difference between the nanoparticle surface temperature and that of the surrounding fluid for three distinct nanoparticle types. Furthermore, the metalloprotein ferritin produced no temperature increase on the protein surface nor in the surrounding fluid. Experiments mimicking the designs of previous studies revealed potential sources of the artifacts. These findings inform the use of magnetic nanoparticle hyperthermia in engineered cellular and molecular systems

    X-ray edge singularity of bilayer graphene

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    The X-ray edge singularity of bilayer graphene is studied by generalizing the path integral approach based on local action which was employed for monolayer graphene. In sharp contrast to the case of monolayer graphene, the bilayer graphene is found to exhibit the edge singularity even at half-filling and its characteristics are determined by interlayer coupling. At finite bias the singular behaviors sensitively depend on the relative magnitude of fermi energy and applied bias, which is due to the peculiar shape of energy band at finite bias.Comment: RevTeX 4.1, 4 pages. No figur

    Super Weyl Anomalies in the AdS/CFT Correspondence

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    Anomalies of N = (4,4) superconformal field theories coupled to a conformal supergravity background in two dimensions are computed by using the AdS/CFT correspondence. We find that Weyl, axial gauge and super Weyl transformations are anomalous, while general coordinate, local Lorentz, vector gauge and local super transformations are not. The coefficients of the anomalies show that the superconformal field theories have the central charge expected in the AdS/CFT correspondence.Comment: 16 pages, LaTeX, references added and typos correcte

    Limits on the evolution of galaxies from the statistics of gravitational lenses

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    We use gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS) to constrain the evolution of galaxies since redshift z∼1z \sim 1 in the current \LCDM cosmology. This constraint is unique as it is based on a mass-selected lens sample of galaxies. Our method of statistical analysis is the same as in Chae (2003). We parametrise the early-type number density evolution in the form of (1+z)νn(1+z)^{\nu_n} and the velocity dispersion as (1+z)νv(1+z)^{\nu_v}. We find that νn=−0.11−0.89+0.82\nu_n=-0.11^{+0.82}_{-0.89} (1σ1\sigma) if we assume νv=0\nu_v =0, implying that the number density of early-type galaxies is within 50% to 164% of the present-day value at redshift z=1z=1. Allowing the velocity dispersion to evolve, we find that νv=−0.4−0.4+0.5\nu_v=-0.4^{+0.5}_{-0.4} (1σ1\sigma), indicating that the velocity dispersion must be within 57% and 107% of the present-day value at z=1z=1. These results are consistent with the early formation and passive evolution of early-type galaxies. More stringent limits from lensing can be obtained from future large lens surveys and by using very high-redshift quasars (z \ga 5) such as those found from the Sloan Digital Sky Survey.Comment: 10 pages (preprint format), 2 figures, ApJL in press (December 20th issue

    Blandford-Znajek process as a gamma ray burst central engine

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    We investigate the possibility that gamma-ray bursts are powered by a central engine consisting of a black hole with an external magnetic field supported by a surrounding disk or torus. The rotational energy of the black hole can be extracted electromagnetically as a Poynting flux, a mechanism proposed by Blandford and Znajek(1977). Recently observed magnetars indicate that some compact objects have very high magnetic fields, up to 101510^{15} G, which is required to extract the energy within the duration of a GRB, i.e., in 1000 s or less. We demonstrate also that the Poynting flux need not be substantially dominated by the disk.Comment: 7 pages, no figure, paspconf.sty, to appear in Proceedings " Gamma Ray Bursts: The First Three Minutes", Gr\"aft{\aa}vallen, Sweden, Feb. 6 - 11, 199

    Parity-violating nucleon-nucleon interaction from different approaches

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    Two-pion exchange parity-violating nucleon-nucleon interactions from recent effective field theories and earlier fully covariant approaches are investigated. The potentials are compared with the idea to obtain better insight on the role of low-energy constants appearing in the effective field theory approach and the convergence of this one in terms of a perturbative series. The results are illustrated by considering the longitudinal asymmetry of polarized protons scattering off protons, p⃗+p−>p+p\vec{p}+p -> p+p, and the asymmetry of the photon emission in radiative capture of polarized neutrons by protons, n⃗+p−>d+γ\vec{n}+p -> d+\gamma.Comment: 31 page
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