9,443 research outputs found

    Chemically Ordered Ptā€“Coā€“Cu/C as Excellent Electrochemical Catalyst for Oxygen Reduction Reaction

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    This paper reveals the ordered structure and composition effect to electrochemical catalytic activity towards oxygen reduction reaction (ORR) of ternary metallic Ptā€“Coā€“Cu/C catalysts. Bimetallic Pt-Co alloy nanoparticles (NPs) represent an emerging class of electrocatalysts for ORR, but practical applications, e.g. in fuel cells, have been hindered by low catalytic performances owning to crystal phase and atomic composition. Cu is introduced into Pt-Co/C lattices to form PtCoxCu1āˆ’x/C (x = 0.25, 0.5 and 0.75) ternary-face-centered tetragonal (fct) ordered ternary metallic NPs. The chemically ordered Ptā€“Coā€“Cu/C catalysts exhibit excellent performance of 1.31 A mgāˆ’1 Pt in mass activity and 0.59 A cmāˆ’2 Pt in specific activity which are significantly higher than Pt-Co/C and commercial Johnson Matthey (JM) Pt/C catalysts, because of the ordered crystal phase and composition control modified the Pt-Pt atoms distance and the surface electronic properties. The presence of Cu improves the surface electronic structure, as well as enhances the stability of catalysts

    Cosmological investigation of multi-frequency VLBI observations of ultra-compact structure in zāˆ¼3z\sim 3 radio quasars

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    In this paper, we use multi-frequency angular size measurements of 58 intermediate-luminosity quasars reaching the redshifts zāˆ¼3z\sim 3 and demonstrate that they can be used as standard rulers for cosmological inference. Our results indicate that, for the majority of radio-sources in our sample their angular sizes are inversely proportional to the observing frequency. From the physical point of view it means that opacity of the jet is governed by pure synchrotron self-absorption, i.e. external absorption does not play any significant role in the observed angular sizes at least up to 43 GHz. Therefore, we use the value of the intrinsic metric size of compact milliarcsecond radio quasars derived in a cosmology independent manner from survey conducted at 2 GHz and rescale it properly according to predictions of the conical jet model. This approach turns out to work well and produce quite stringent constraints on the matter density parameter Ī©m\Omega_m in the flat Ī›\LambdaCDM model and Dvali-Gabadadze-Porrati braneworld model. The results presented in this paper pave the way for the follow up engaging multi-frequency VLBI observations of more compact radio quasars with higher sensitivity and angular resolution.Comment: 10 pages, 5 figures, 2 table, accepted for publication in European Physical Journal

    Interaction of a symmetrical Ī±,Ī±',Ī“,Ī“'-Tetramethyl-cucurbit[6]uril with LnĀ³āŗ : potential applications for isolation of lanthanides

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    The interaction of a symmetrical Ī±,Ī±ā€²,Ī“,Ī“ā€²-tetramethyl-cucurbit[6]uril (TMeQ[6]) with a series of lanthanide cations (LnĀ³āŗ) was investigated in neutral water and in acidic solution. Analysis by single crystal X-ray diffraction revealed that different isomorphous families formed under different synthetic conditions. Such differences in the interaction between TMeQ[6] and LnĀ³āŗ could potentially be used for isolating heavier LnĀ³āŗ from their lighter counterparts in neutral solution, and lighter lanthanide cations from their heavier counterparts in acidic solution

    Promotion of Myelopoiesis in Myelosuppressed Mice by Ganoderma lucidum Polysaccharides

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    Our previous studies demonstrated that Ganoderma lucidum polysaccharides (Gl-PS) exhibit potent immunomodulating effects. Immunomodulation plays an important role in hematopoiesis. To investigate the possible mechanism by which Gl-PS promote myelopoiesis during myelosuppression induced by cyclophosphamide, mice were injected intraperitoneally (i.p.) once daily with 2.5ā€‰mg/kg of Gl-PS for 10ā€‰days and were treated i.p. once daily with cyclophosphamide (100ā€‰mg/kg) on days 2 through 4. In the present study in vivo and in vitro, we find that Gl-PS selectively bind to bone marrow stromal cells, stimulate the secretion of hematopoietic growth factors, and enhance the clonogenic activities of hematopoietic and stromal cells to promote hematopoiesis in myelosuppressed mice

    Magnetic Borophenes from an Evolutionary Search

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    A computational methodology based on ab initio evolutionary algorithms and spin-polarized density functional theory was developed to predict two-dimensional magnetic materials. Its application to a model system borophene reveals an unexpected rich magnetism and polymorphism. A metastable borophene with nonzero thickness is an antiferromagnetic semiconductor from first-principles calculations, and can be further tuned into a half-metal by finite electron doping. In this borophene, the buckling and coupling among three atomic layers are not only responsible for magnetism, but also result in an out-of-plane negative Poisson\u27s ratio under uniaxial tension, making it the first elemental material possessing auxetic and magnetic properties simultaneously
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