3,229 research outputs found

    Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet

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    The specific heat and thermal conductivity of the insulating ferrimagnet Y3_3Fe5_5O12_{12} (Yttrium Iron Garnet, YIG) single crystal were measured down to 50 mK. The ferromagnetic magnon specific heat CCm_m shows a characteristic T1.5T^{1.5} dependence down to 0.77 K. Below 0.77 K, a downward deviation is observed, which is attributed to the magnetic dipole-dipole interaction with typical magnitude of 104^{-4} eV. The ferromagnetic magnon thermal conductivity κm\kappa_m does not show the characteristic T2T^2 dependence below 0.8 K. To fit the κm\kappa_m data, both magnetic defect scattering effect and dipole-dipole interaction are taken into account. These results complete our understanding of the thermodynamic and thermal transport properties of the low-lying ferromagnetic magnons.Comment: 5 pages, 5 figure

    Natural plant polyphenols for alleviating oxidative damage in man: Current status and future perspectives

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    The balance between oxidation and reduction is important for maintaining a healthy biological system. Oxidative stress results from an imbalance between excessive formation of reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) and limited endogenous defense systems, and this imbalance can adversely alter lipids, proteins and DNA, causing a number of human diseases. Thus, exogenous antioxidants that can neutralize the effect of free radicals are needed to diminish the cumulative effects of oxidative damage over human life span. Current research reveals that phenolic compounds in plants possess high antioxidant activity and free radical scavenging capacity and can prevent the body from oxidative damage over human life span. This review focuses on the present understanding of free radicals and antioxidants and their importance in human health and disease. Information about the chemical features of free radicals as well as their deleterious effects on cell structures is reviewed. The chemical structure and anti-oxidative mechanisms of essential polyphenols and their potential health benefits are presented. In addition, the limitation of natural antioxidants and a perspective on likely future trends in this field are also discussed.Keywords: Free radicals, Oxidative stress, Natural antioxidants, Polyphenols, Health benefits, Reactive oxygen species, Reactive nitrogen specie

    Alpha Lipoic Acid Modulated High Glucose-Induced Rat Mesangial Cell Dysfunction via mTOR/p70S6K/4E-BP1 Pathway

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    The aim of this study was to investigate whether alpha lipoic acid (LA) regulates high glucose-induced mesangial cell proliferation and extracellular matrix production via mTOR/p70S6K/4E-BP1 signaling. The effect of LA on high glucose-induced cell proliferation, fibronectin (FN), and collagen type I (collagen-I) expression and its mechanisms were examined in cultured rat mesangial cells by methylthiazol tetrazolium (MTT) assay, flow cytometry, ELISA assay, and western blot, respectively. LA at a relatively low concentration (0.25 mmol/L) acted as a growth factor in rat mesangial cells, promoted entry of cell cycle into S phase, extracellular matrix formation, and phosphorylated AKT, mTOR, p70S6K, and 4E-BP1. These effects disappeared when AKT expression was downregulated with PI3K/AKT inhibitor LY294002. Conversely, LA at a higher concentration (1.0 mmol/L) inhibited high glucose-induced rat mesangial cell proliferation, entry of cell cycle into S phase, and extracellular matrix exertion, as well as phosphorylation of mTOR, p70S6K, and 4E-BP1 but enhanced the activity of AMPK. However, these effects disappeared when AMPK activity was inhibited with CaMKK inhibitor STO-609. These results suggest that LA dose-dependently regulates mesangial cell proliferation and matrix protein secretion by mTOR/p70S6K/4E-BP1 signaling pathway under high glucose conditions

    Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2

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    The in-plane resistivity ρ\rho and thermal conductivity κ\kappa of FeAs-based superconductor KFe2_2As2_2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior ρ(T)T1.5\rho(T) \sim T^{1.5} at Hc2H_{c_2} = 5 T, and the development of a Fermi liquid state with ρ(T)T2\rho(T) \sim T^2 when further increasing field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field Hc2H_{c_2}. In zero field there is a large residual linear term κ0/T\kappa_0/T, and the field dependence of κ0/T\kappa_0/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2_2As2_2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.Comment: 4 pages, 4 figures - replaces arXiv:0909.485
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