4,071 research outputs found

    Origin of the Ising Ferrimagnetism and Spin-Charge Coupling in LuFe2O4

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    The spin ordering and spin-charge coupling in LuFe2O4 were investigated on the basis of density functional calculations and Monte Carlo simulations. The 2:1 ferrimagnetism arises from the strong antiferromagnetic intra-sheet Fe3+-Fe3+ and Fe3+ -Fe2+ as well as some substantial antiferromagnetic Fe2+-Fe3+ inter-sheet spin exchange interactions. The giant magnetocapacitance at room temperature and the enhanced electric polarization at 240 K of LuFe2O4 are explained by the strong spin-charge coupling

    Influence of hepatitis G virus infection on liver disease

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    The influence of hepatitis G virus (HGV) infection on disease activity in hepatitis C related and unrelated liver disease was investigated in 254 individuals using an EIA polymerase chain reaction assay for HGV. One hundred patients had chronic hepatitis C, 26 primary biliary cirrhosis, and 30 alcoholic liver cirrhosis. In addition, 51 hepatitis B surface antigen (HBsAg)-positive and 47 anti-hepatitis C virus (HCV)-positive blood donors were screened. Hepatitis G virus was detected in 18% of patients with chronic hepatitis C, 13% of patients with alcoholic liver cirrhosis, 11 % of patients with primary biliary cirrhosis, 10% of anti-HCV-positive blood donors, and 2% of HBsAg-positive blood donors. Virus load and alanine aminotransferase (ALT) levels did not differ significantly in patients with HCV alone versus patients coinfected with HCV and HGV. However, mild liver fibrosis correlated with HGV coinfection. Hepatitis G virus did not influence ALT levels or liver damage in liver disease unrelated to viral infectio

    General Theory for the Ferroelectric Polarization Induced by Spin-Spiral Order

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    The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order, and incorporates known models of magnetic-order-driven ferroelectricity as special cases.Comment: Accepted for publication in Phys. Rev. Let

    Plasma-Induced Frequency Chirp of Intense Femtosecond Lasers and Its Role in Shaping High-Order Harmonic Spectral Lines

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    We investigate the self-phase modulation of intense femtosecond laser pulses propagating in an ionizing gas and its effects on collective properties of high-order harmonics generated in the medium. Plasmas produced in the medium are shown to induce a positive frequency chirp on the leading edge of the propagating laser pulse, which subsequently drives high harmonics to become positively chirped. In certain parameter regimes, the plasma-induced positive chirp can help to generate sharply peaked high harmonics, by compensating for the dynamically-induced negative chirp that is caused by the steep intensity profile of intense short laser pulses.Comment: 5 pages, 5 figure

    Scale Dependent Dimension of Luminous Matter in the Universe

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    We present a geometrical model of the distribution of luminous matter in the universe, derived from a very simple reaction-diffusion model of turbulent phenomena. The apparent dimension of luminous matter, D(l)D(l), depends linearly on the logarithm of the scale ll under which the universe is viewed: D(l)3log(l/l0)/log(ξ/l0)D(l) \sim 3\log(l/l_0)/\log(\xi/l_0), where ξ\xi is a correlation length. Comparison with data from the SARS red-shift catalogue, and the LEDA database provides a good fit with a correlation length ξ300\xi \sim 300 Mpc. The geometrical interpretation is clear: At small distances, the universe is zero-dimensional and point-like. At distances of the order of 1 Mpc the dimension is unity, indicating a filamentary, string-like structure; when viewed at larger scales it gradually becomes 2-dimensional wall-like, and finally, at and beyond the correlation length, it becomes uniform.Comment: 6 pages, 2 figure

    Optics-less smart sensors and a possible mechanism of cutaneous vision in nature

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    Optics-less cutaneous (skin) vision is not rare among living organisms, though its mechanisms and capabilities have not been thoroughly investigated. This paper demonstrates, using methods from statistical parameter estimation theory and numerical simulations, that an array of bare sensors with a natural cosine-law angular sensitivity arranged on a flat or curved surface has the ability to perform imaging tasks without any optics at all. The working principle of this type of optics-less sensor and the model developed here for determining sensor performance may be used to shed light upon possible mechanisms and capabilities of cutaneous vision in nature

    First results of material charging in the space environment

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    A satellite experiment, designed to measure potential charging of typical thermal control materials at near geosynchronous altitude, was flown as part of the SCATHA program. Direct observations of charging of typical satellite materials in a natural charging event ( 5 keV) are presented. The results show some features which differ significantly from previous laboratory simulations of the environment
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